1GCC(1)                                GNU                               GCC(1)
2
3
4

NAME

6       gcc - GNU project C and C++ compiler
7

SYNOPSIS

9       gcc [-c|-S|-E] [-std=standard]
10           [-g] [-pg] [-Olevel]
11           [-Wwarn...] [-Wpedantic]
12           [-Idir...] [-Ldir...]
13           [-Dmacro[=defn]...] [-Umacro]
14           [-foption...] [-mmachine-option...]
15           [-o outfile] [@file] infile...
16
17       Only the most useful options are listed here; see below for the
18       remainder.  g++ accepts mostly the same options as gcc.
19

DESCRIPTION

21       When you invoke GCC, it normally does preprocessing, compilation,
22       assembly and linking.  The "overall options" allow you to stop this
23       process at an intermediate stage.  For example, the -c option says not
24       to run the linker.  Then the output consists of object files output by
25       the assembler.
26
27       Other options are passed on to one or more stages of processing.  Some
28       options control the preprocessor and others the compiler itself.  Yet
29       other options control the assembler and linker; most of these are not
30       documented here, since you rarely need to use any of them.
31
32       Most of the command-line options that you can use with GCC are useful
33       for C programs; when an option is only useful with another language
34       (usually C++), the explanation says so explicitly.  If the description
35       for a particular option does not mention a source language, you can use
36       that option with all supported languages.
37
38       The usual way to run GCC is to run the executable called gcc, or
39       machine-gcc when cross-compiling, or machine-gcc-version to run a
40       specific version of GCC.  When you compile C++ programs, you should
41       invoke GCC as g++ instead.
42
43       The gcc program accepts options and file names as operands.  Many
44       options have multi-letter names; therefore multiple single-letter
45       options may not be grouped: -dv is very different from -d -v.
46
47       You can mix options and other arguments.  For the most part, the order
48       you use doesn't matter.  Order does matter when you use several options
49       of the same kind; for example, if you specify -L more than once, the
50       directories are searched in the order specified.  Also, the placement
51       of the -l option is significant.
52
53       Many options have long names starting with -f or with -W---for example,
54       -fmove-loop-invariants, -Wformat and so on.  Most of these have both
55       positive and negative forms; the negative form of -ffoo is -fno-foo.
56       This manual documents only one of these two forms, whichever one is not
57       the default.
58
59       Some options take one or more arguments typically separated either by a
60       space or by the equals sign (=) from the option name.  Unless
61       documented otherwise, an argument can be either numeric or a string.
62       Numeric arguments must typically be small unsigned decimal or
63       hexadecimal integers.  Hexadecimal arguments must begin with the 0x
64       prefix.  Arguments to options that specify a size threshold of some
65       sort may be arbitrarily large decimal or hexadecimal integers followed
66       by a byte size suffix designating a multiple of bytes such as "kB" and
67       "KiB" for kilobyte and kibibyte, respectively, "MB" and "MiB" for
68       megabyte and mebibyte, "GB" and "GiB" for gigabyte and gigibyte, and so
69       on.  Such arguments are designated by byte-size in the following text.
70       Refer to the NIST, IEC, and other relevant national and international
71       standards for the full listing and explanation of the binary and
72       decimal byte size prefixes.
73

OPTIONS

75   Option Summary
76       Here is a summary of all the options, grouped by type.  Explanations
77       are in the following sections.
78
79       Overall Options
80           -c  -S  -E  -o file -dumpbase dumpbase  -dumpbase-ext auxdropsuf
81           -dumpdir dumppfx  -x language -v  -###  --help[=class[,...]]
82           --target-help  --version -pass-exit-codes  -pipe  -specs=file
83           -wrapper @file  -ffile-prefix-map=old=new -fplugin=file
84           -fplugin-arg-name=arg -fdump-ada-spec[-slim]
85           -fada-spec-parent=unit  -fdump-go-spec=file
86
87       C Language Options
88           -ansi  -std=standard  -aux-info filename
89           -fallow-parameterless-variadic-functions  -fno-asm -fno-builtin
90           -fno-builtin-function  -fcond-mismatch -ffreestanding  -fgimple
91           -fgnu-tm  -fgnu89-inline  -fhosted -flax-vector-conversions
92           -fms-extensions -foffload=arg  -foffload-options=arg -fopenacc
93           -fopenacc-dim=geom -fopenmp  -fopenmp-simd
94           -fpermitted-flt-eval-methods=standard -fplan9-extensions
95           -fsigned-bitfields  -funsigned-bitfields -fsigned-char
96           -funsigned-char  -fsso-struct=endianness
97
98       C++ Language Options
99           -fabi-version=n  -fno-access-control -faligned-new=n
100           -fargs-in-order=n  -fchar8_t  -fcheck-new -fconstexpr-depth=n
101           -fconstexpr-cache-depth=n -fconstexpr-loop-limit=n
102           -fconstexpr-ops-limit=n -fno-elide-constructors
103           -fno-enforce-eh-specs -fno-gnu-keywords -fno-implicit-templates
104           -fno-implicit-inline-templates -fno-implement-inlines
105           -fmodule-header[=kind] -fmodule-only -fmodules-ts
106           -fmodule-implicit-inline -fno-module-lazy
107           -fmodule-mapper=specification -fmodule-version-ignore
108           -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching
109           -fno-nonansi-builtins  -fnothrow-opt  -fno-operator-names
110           -fno-optional-diags  -fpermissive -fno-pretty-templates -fno-rtti
111           -fsized-deallocation -ftemplate-backtrace-limit=n
112           -ftemplate-depth=n -fno-threadsafe-statics  -fuse-cxa-atexit
113           -fno-weak  -nostdinc++ -fvisibility-inlines-hidden
114           -fvisibility-ms-compat -fext-numeric-literals
115           -flang-info-include-translate[=header]
116           -flang-info-include-translate-not -flang-info-module-cmi[=module]
117           -stdlib=libstdc++,libc++ -Wabi-tag  -Wcatch-value  -Wcatch-value=n
118           -Wno-class-conversion  -Wclass-memaccess -Wcomma-subscript
119           -Wconditionally-supported -Wno-conversion-null
120           -Wctad-maybe-unsupported -Wctor-dtor-privacy
121           -Wno-delete-incomplete -Wdelete-non-virtual-dtor
122           -Wno-deprecated-array-compare -Wdeprecated-copy
123           -Wdeprecated-copy-dtor -Wno-deprecated-enum-enum-conversion
124           -Wno-deprecated-enum-float-conversion -Weffc++  -Wno-exceptions
125           -Wextra-semi  -Wno-inaccessible-base -Wno-inherited-variadic-ctor
126           -Wno-init-list-lifetime -Winvalid-imported-macros
127           -Wno-invalid-offsetof  -Wno-literal-suffix -Wmismatched-new-delete
128           -Wmismatched-tags -Wmultiple-inheritance  -Wnamespaces  -Wnarrowing
129           -Wnoexcept  -Wnoexcept-type  -Wnon-virtual-dtor -Wpessimizing-move
130           -Wno-placement-new  -Wplacement-new=n -Wrange-loop-construct
131           -Wredundant-move -Wredundant-tags -Wreorder  -Wregister
132           -Wstrict-null-sentinel  -Wno-subobject-linkage  -Wtemplates
133           -Wno-non-template-friend  -Wold-style-cast -Woverloaded-virtual
134           -Wno-pmf-conversions -Wsign-promo -Wsized-deallocation
135           -Wsuggest-final-methods -Wsuggest-final-types  -Wsuggest-override
136           -Wno-terminate  -Wuseless-cast  -Wno-vexing-parse
137           -Wvirtual-inheritance -Wno-virtual-move-assign  -Wvolatile
138           -Wzero-as-null-pointer-constant
139
140       Objective-C and Objective-C++ Language Options
141           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
142           -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors
143           -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck
144           -fobjc-std=objc1 -fno-local-ivars
145           -fivar-visibility=[public|protected|private|package]
146           -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept
147           -Wno-property-assign-default -Wno-protocol -Wobjc-root-class
148           -Wselector -Wstrict-selector-match -Wundeclared-selector
149
150       Diagnostic Message Formatting Options
151           -fmessage-length=n -fdiagnostics-plain-output
152           -fdiagnostics-show-location=[once|every-line]
153           -fdiagnostics-color=[auto|never|always]
154           -fdiagnostics-urls=[auto|never|always]
155           -fdiagnostics-format=[text|json] -fno-diagnostics-show-option
156           -fno-diagnostics-show-caret -fno-diagnostics-show-labels
157           -fno-diagnostics-show-line-numbers -fno-diagnostics-show-cwe
158           -fdiagnostics-minimum-margin-width=width
159           -fdiagnostics-parseable-fixits  -fdiagnostics-generate-patch
160           -fdiagnostics-show-template-tree  -fno-elide-type
161           -fdiagnostics-path-format=[none|separate-events|inline-events]
162           -fdiagnostics-show-path-depths -fno-show-column
163           -fdiagnostics-column-unit=[display|byte]
164           -fdiagnostics-column-origin=origin
165           -fdiagnostics-escape-format=[unicode|bytes]
166
167       Warning Options
168           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
169           -Wextra  -Wall  -Wabi=n -Waddress  -Wno-address-of-packed-member
170           -Waggregate-return -Walloc-size-larger-than=byte-size  -Walloc-zero
171           -Walloca  -Walloca-larger-than=byte-size
172           -Wno-aggressive-loop-optimizations -Warith-conversion
173           -Warray-bounds  -Warray-bounds=n  -Warray-compare -Wno-attributes
174           -Wattribute-alias=n -Wno-attribute-alias -Wno-attribute-warning
175           -Wbidi-chars=[none|unpaired|any|ucn] -Wbool-compare
176           -Wbool-operation -Wno-builtin-declaration-mismatch
177           -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat
178           -Wc11-c2x-compat -Wc++-compat  -Wc++11-compat  -Wc++14-compat
179           -Wc++17-compat -Wc++20-compat -Wno-c++11-extensions
180           -Wno-c++14-extensions -Wno-c++17-extensions -Wno-c++20-extensions
181           -Wno-c++23-extensions -Wcast-align  -Wcast-align=strict
182           -Wcast-function-type  -Wcast-qual -Wchar-subscripts -Wclobbered
183           -Wcomment -Wconversion  -Wno-coverage-mismatch  -Wno-cpp
184           -Wdangling-else  -Wdangling-pointer  -Wdangling-pointer=n
185           -Wdate-time -Wno-deprecated  -Wno-deprecated-declarations
186           -Wno-designated-init -Wdisabled-optimization
187           -Wno-discarded-array-qualifiers  -Wno-discarded-qualifiers
188           -Wno-div-by-zero  -Wdouble-promotion -Wduplicated-branches
189           -Wduplicated-cond -Wempty-body  -Wno-endif-labels  -Wenum-compare
190           -Wenum-conversion -Werror  -Werror=*  -Wexpansion-to-defined
191           -Wfatal-errors -Wfloat-conversion  -Wfloat-equal  -Wformat
192           -Wformat=2 -Wno-format-contains-nul  -Wno-format-extra-args
193           -Wformat-nonliteral  -Wformat-overflow=n -Wformat-security
194           -Wformat-signedness  -Wformat-truncation=n -Wformat-y2k
195           -Wframe-address -Wframe-larger-than=byte-size
196           -Wno-free-nonheap-object -Wno-if-not-aligned
197           -Wno-ignored-attributes -Wignored-qualifiers
198           -Wno-incompatible-pointer-types -Wimplicit  -Wimplicit-fallthrough
199           -Wimplicit-fallthrough=n -Wno-implicit-function-declaration
200           -Wno-implicit-int -Winfinite-recursion -Winit-self  -Winline
201           -Wno-int-conversion  -Wint-in-bool-context -Wno-int-to-pointer-cast
202           -Wno-invalid-memory-model -Winvalid-pch  -Wjump-misses-init
203           -Wlarger-than=byte-size -Wlogical-not-parentheses  -Wlogical-op
204           -Wlong-long -Wno-lto-type-mismatch -Wmain  -Wmaybe-uninitialized
205           -Wmemset-elt-size  -Wmemset-transposed-args
206           -Wmisleading-indentation  -Wmissing-attributes  -Wmissing-braces
207           -Wmissing-field-initializers  -Wmissing-format-attribute
208           -Wmissing-include-dirs  -Wmissing-noreturn  -Wno-missing-profile
209           -Wno-multichar  -Wmultistatement-macros  -Wnonnull
210           -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
211           -Wnull-dereference  -Wno-odr -Wopenacc-parallelism -Wopenmp-simd
212           -Wno-overflow  -Woverlength-strings
213           -Wno-override-init-side-effects -Wpacked
214           -Wno-packed-bitfield-compat  -Wpacked-not-aligned  -Wpadded
215           -Wparentheses  -Wno-pedantic-ms-format -Wpointer-arith
216           -Wno-pointer-compare  -Wno-pointer-to-int-cast -Wno-pragmas
217           -Wno-prio-ctor-dtor  -Wredundant-decls -Wrestrict
218           -Wno-return-local-addr  -Wreturn-type -Wno-scalar-storage-order
219           -Wsequence-point -Wshadow  -Wshadow=global  -Wshadow=local
220           -Wshadow=compatible-local -Wno-shadow-ivar
221           -Wno-shift-count-negative  -Wno-shift-count-overflow
222           -Wshift-negative-value -Wno-shift-overflow  -Wshift-overflow=n
223           -Wsign-compare  -Wsign-conversion -Wno-sizeof-array-argument
224           -Wsizeof-array-div -Wsizeof-pointer-div  -Wsizeof-pointer-memaccess
225           -Wstack-protector  -Wstack-usage=byte-size  -Wstrict-aliasing
226           -Wstrict-aliasing=n  -Wstrict-overflow  -Wstrict-overflow=n
227           -Wstring-compare -Wno-stringop-overflow -Wno-stringop-overread
228           -Wno-stringop-truncation
229           -Wsuggest-attribute=[pure|const|noreturn|format|malloc] -Wswitch
230           -Wno-switch-bool  -Wswitch-default  -Wswitch-enum
231           -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand
232           -Wsystem-headers  -Wtautological-compare  -Wtrampolines
233           -Wtrigraphs -Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef
234           -Wuninitialized  -Wunknown-pragmas -Wunsuffixed-float-constants
235           -Wunused -Wunused-but-set-parameter  -Wunused-but-set-variable
236           -Wunused-const-variable  -Wunused-const-variable=n
237           -Wunused-function  -Wunused-label  -Wunused-local-typedefs
238           -Wunused-macros -Wunused-parameter  -Wno-unused-result
239           -Wunused-value  -Wunused-variable -Wno-varargs  -Wvariadic-macros
240           -Wvector-operation-performance -Wvla  -Wvla-larger-than=byte-size
241           -Wno-vla-larger-than -Wvolatile-register-var  -Wwrite-strings
242           -Wzero-length-bounds
243
244       Static Analyzer Options
245           -fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=name
246           -fno-analyzer-feasibility -fanalyzer-fine-grained
247           -fno-analyzer-state-merge -fno-analyzer-state-purge
248           -fanalyzer-transitivity -fanalyzer-verbose-edges
249           -fanalyzer-verbose-state-changes -fanalyzer-verbosity=level
250           -fdump-analyzer -fdump-analyzer-callgraph
251           -fdump-analyzer-exploded-graph -fdump-analyzer-exploded-nodes
252           -fdump-analyzer-exploded-nodes-2 -fdump-analyzer-exploded-nodes-3
253           -fdump-analyzer-exploded-paths -fdump-analyzer-feasibility
254           -fdump-analyzer-json -fdump-analyzer-state-purge
255           -fdump-analyzer-stderr -fdump-analyzer-supergraph
256           -fdump-analyzer-untracked -Wno-analyzer-double-fclose
257           -Wno-analyzer-double-free
258           -Wno-analyzer-exposure-through-output-file -Wno-analyzer-file-leak
259           -Wno-analyzer-free-of-non-heap -Wno-analyzer-malloc-leak
260           -Wno-analyzer-mismatching-deallocation -Wno-analyzer-null-argument
261           -Wno-analyzer-null-dereference -Wno-analyzer-possible-null-argument
262           -Wno-analyzer-possible-null-dereference
263           -Wno-analyzer-shift-count-negative
264           -Wno-analyzer-shift-count-overflow
265           -Wno-analyzer-stale-setjmp-buffer
266           -Wno-analyzer-tainted-allocation-size
267           -Wno-analyzer-tainted-array-index -Wno-analyzer-tainted-divisor
268           -Wno-analyzer-tainted-offset -Wno-analyzer-tainted-size
269           -Wanalyzer-too-complex
270           -Wno-analyzer-unsafe-call-within-signal-handler
271           -Wno-analyzer-use-after-free
272           -Wno-analyzer-use-of-pointer-in-stale-stack-frame
273           -Wno-analyzer-use-of-uninitialized-value
274           -Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal
275
276       C and Objective-C-only Warning Options
277           -Wbad-function-cast  -Wmissing-declarations
278           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
279           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
280           -Wtraditional  -Wtraditional-conversion
281           -Wdeclaration-after-statement  -Wpointer-sign
282
283       Debugging Options
284           -g  -glevel  -gdwarf  -gdwarf-version -gbtf -gctf  -gctflevel -ggdb
285           -grecord-gcc-switches  -gno-record-gcc-switches -gstabs  -gstabs+
286           -gstrict-dwarf  -gno-strict-dwarf -gas-loc-support
287           -gno-as-loc-support -gas-locview-support  -gno-as-locview-support
288           -gcolumn-info  -gno-column-info  -gdwarf32  -gdwarf64
289           -gstatement-frontiers  -gno-statement-frontiers
290           -gvariable-location-views  -gno-variable-location-views
291           -ginternal-reset-location-views  -gno-internal-reset-location-views
292           -ginline-points  -gno-inline-points -gvms  -gxcoff  -gxcoff+
293           -gz[=type] -gsplit-dwarf  -gdescribe-dies  -gno-describe-dies
294           -fdebug-prefix-map=old=new  -fdebug-types-section
295           -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly
296           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-
297           list] -fno-eliminate-unused-debug-symbols
298           -femit-class-debug-always -fno-merge-debug-strings
299           -fno-dwarf2-cfi-asm -fvar-tracking  -fvar-tracking-assignments
300
301       Optimization Options
302           -faggressive-loop-optimizations -falign-functions[=n[:m:[n2[:m2]]]]
303           -falign-jumps[=n[:m:[n2[:m2]]]] -falign-labels[=n[:m:[n2[:m2]]]]
304           -falign-loops[=n[:m:[n2[:m2]]]] -fno-allocation-dce
305           -fallow-store-data-races -fassociative-math  -fauto-profile
306           -fauto-profile[=path] -fauto-inc-dec  -fbranch-probabilities
307           -fcaller-saves -fcombine-stack-adjustments  -fconserve-stack
308           -fcompare-elim  -fcprop-registers  -fcrossjumping
309           -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
310           -fcx-limited-range -fdata-sections  -fdce  -fdelayed-branch
311           -fdelete-null-pointer-checks  -fdevirtualize
312           -fdevirtualize-speculatively -fdevirtualize-at-ltrans  -fdse
313           -fearly-inlining  -fipa-sra  -fexpensive-optimizations
314           -ffat-lto-objects -ffast-math  -ffinite-math-only  -ffloat-store
315           -fexcess-precision=style -ffinite-loops -fforward-propagate
316           -ffp-contract=style  -ffunction-sections -fgcse
317           -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity
318           -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion -fif-conversion2
319           -findirect-inlining -finline-functions
320           -finline-functions-called-once  -finline-limit=n
321           -finline-small-functions -fipa-modref -fipa-cp  -fipa-cp-clone
322           -fipa-bit-cp  -fipa-vrp  -fipa-pta  -fipa-profile  -fipa-pure-const
323           -fipa-reference  -fipa-reference-addressable -fipa-stack-alignment
324           -fipa-icf  -fira-algorithm=algorithm -flive-patching=level
325           -fira-region=region  -fira-hoist-pressure -fira-loop-pressure
326           -fno-ira-share-save-slots -fno-ira-share-spill-slots
327           -fisolate-erroneous-paths-dereference
328           -fisolate-erroneous-paths-attribute -fivopts
329           -fkeep-inline-functions  -fkeep-static-functions
330           -fkeep-static-consts  -flimit-function-alignment
331           -flive-range-shrinkage -floop-block  -floop-interchange
332           -floop-strip-mine -floop-unroll-and-jam  -floop-nest-optimize
333           -floop-parallelize-all  -flra-remat  -flto  -flto-compression-level
334           -flto-partition=alg  -fmerge-all-constants -fmerge-constants
335           -fmodulo-sched  -fmodulo-sched-allow-regmoves
336           -fmove-loop-invariants  -fmove-loop-stores  -fno-branch-count-reg
337           -fno-defer-pop  -fno-fp-int-builtin-inexact  -fno-function-cse
338           -fno-guess-branch-probability  -fno-inline  -fno-math-errno
339           -fno-peephole -fno-peephole2  -fno-printf-return-value
340           -fno-sched-interblock -fno-sched-spec  -fno-signed-zeros
341           -fno-toplevel-reorder  -fno-trapping-math
342           -fno-zero-initialized-in-bss -fomit-frame-pointer
343           -foptimize-sibling-calls -fpartial-inlining  -fpeel-loops
344           -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction
345           -fprofile-use  -fprofile-use=path -fprofile-partial-training
346           -fprofile-values -fprofile-reorder-functions -freciprocal-math
347           -free  -frename-registers  -freorder-blocks
348           -freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition
349           -freorder-functions -frerun-cse-after-loop
350           -freschedule-modulo-scheduled-loops -frounding-math
351           -fsave-optimization-record -fsched2-use-superblocks
352           -fsched-pressure -fsched-spec-load  -fsched-spec-load-dangerous
353           -fsched-stalled-insns-dep[=n]  -fsched-stalled-insns[=n]
354           -fsched-group-heuristic  -fsched-critical-path-heuristic
355           -fsched-spec-insn-heuristic  -fsched-rank-heuristic
356           -fsched-last-insn-heuristic  -fsched-dep-count-heuristic
357           -fschedule-fusion -fschedule-insns  -fschedule-insns2
358           -fsection-anchors -fselective-scheduling  -fselective-scheduling2
359           -fsel-sched-pipelining  -fsel-sched-pipelining-outer-loops
360           -fsemantic-interposition  -fshrink-wrap  -fshrink-wrap-separate
361           -fsignaling-nans -fsingle-precision-constant
362           -fsplit-ivs-in-unroller  -fsplit-loops -fsplit-paths
363           -fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop
364           -fssa-phiopt -fstdarg-opt  -fstore-merging  -fstrict-aliasing
365           -fipa-strict-aliasing -fthread-jumps  -ftracer  -ftree-bit-ccp
366           -ftree-builtin-call-dce  -ftree-ccp  -ftree-ch -ftree-coalesce-vars
367           -ftree-copy-prop  -ftree-dce  -ftree-dominator-opts -ftree-dse
368           -ftree-forwprop  -ftree-fre  -fcode-hoisting -ftree-loop-if-convert
369           -ftree-loop-im -ftree-phiprop  -ftree-loop-distribution
370           -ftree-loop-distribute-patterns -ftree-loop-ivcanon
371           -ftree-loop-linear  -ftree-loop-optimize -ftree-loop-vectorize
372           -ftree-parallelize-loops=n  -ftree-pre  -ftree-partial-pre
373           -ftree-pta -ftree-reassoc  -ftree-scev-cprop  -ftree-sink
374           -ftree-slsr  -ftree-sra -ftree-switch-conversion  -ftree-tail-merge
375           -ftree-ter  -ftree-vectorize  -ftree-vrp  -ftrivial-auto-var-init
376           -funconstrained-commons -funit-at-a-time  -funroll-all-loops
377           -funroll-loops -funsafe-math-optimizations  -funswitch-loops
378           -fipa-ra  -fvariable-expansion-in-unroller  -fvect-cost-model
379           -fvpt -fweb  -fwhole-program  -fwpa  -fuse-linker-plugin
380           -fzero-call-used-regs --param name=value -O  -O0  -O1  -O2  -O3
381           -Os  -Ofast  -Og  -Oz
382
383       Program Instrumentation Options
384           -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage
385           -fprofile-abs-path -fprofile-dir=path  -fprofile-generate
386           -fprofile-generate=path -fprofile-info-section
387           -fprofile-info-section=name -fprofile-note=path
388           -fprofile-prefix-path=path -fprofile-update=method
389           -fprofile-filter-files=regex -fprofile-exclude-files=regex
390           -fprofile-reproducible=[multithreaded|parallel-runs|serial]
391           -fsanitize=style  -fsanitize-recover  -fsanitize-recover=style
392           -fasan-shadow-offset=number  -fsanitize-sections=s1,s2,...
393           -fsanitize-undefined-trap-on-error  -fbounds-check
394           -fcf-protection=[full|branch|return|none|check] -fharden-compares
395           -fharden-conditional-branches -fstack-protector
396           -fstack-protector-all  -fstack-protector-strong
397           -fstack-protector-explicit  -fstack-check
398           -fstack-limit-register=reg  -fstack-limit-symbol=sym
399           -fno-stack-limit  -fsplit-stack -fvtable-verify=[std|preinit|none]
400           -fvtv-counts  -fvtv-debug -finstrument-functions
401           -finstrument-functions-exclude-function-list=sym,sym,...
402           -finstrument-functions-exclude-file-list=file,file,...
403           -fprofile-prefix-map=old=new
404
405       Preprocessor Options
406           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD
407           -dI  -dM  -dN  -dU -fdebug-cpp  -fdirectives-only
408           -fdollars-in-identifiers -fexec-charset=charset
409           -fextended-identifiers -finput-charset=charset
410           -flarge-source-files -fmacro-prefix-map=old=new
411           -fmax-include-depth=depth -fno-canonical-system-headers  -fpch-deps
412           -fpch-preprocess -fpreprocessed  -ftabstop=width
413           -ftrack-macro-expansion -fwide-exec-charset=charset
414           -fworking-directory -H  -imacros file  -include file -M  -MD  -MF
415           -MG  -MM  -MMD  -MP  -MQ  -MT -Mno-modules -no-integrated-cpp  -P
416           -pthread  -remap -traditional  -traditional-cpp  -trigraphs -Umacro
417           -undef -Wp,option  -Xpreprocessor option
418
419       Assembler Options
420           -Wa,option  -Xassembler option
421
422       Linker Options
423           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles
424           -nodefaultlibs  -nolibc  -nostdlib -e entry  --entry=entry -pie
425           -pthread  -r  -rdynamic -s  -static  -static-pie  -static-libgcc
426           -static-libstdc++ -static-libasan  -static-libtsan  -static-liblsan
427           -static-libubsan -shared  -shared-libgcc  -symbolic -T script
428           -Wl,option  -Xlinker option -u symbol  -z keyword
429
430       Directory Options
431           -Bprefix  -Idir  -I- -idirafter dir -imacros file  -imultilib dir
432           -iplugindir=dir  -iprefix file -iquote dir  -isysroot dir  -isystem
433           dir -iwithprefix dir  -iwithprefixbefore dir -Ldir
434           -no-canonical-prefixes  --no-sysroot-suffix -nostdinc  -nostdinc++
435           --sysroot=dir
436
437       Code Generation Options
438           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
439           -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
440           -fasynchronous-unwind-tables -fno-gnu-unique
441           -finhibit-size-directive  -fcommon  -fno-ident -fpcc-struct-return
442           -fpic  -fPIC  -fpie  -fPIE  -fno-plt -fno-jump-tables
443           -fno-bit-tests -frecord-gcc-switches -freg-struct-return
444           -fshort-enums  -fshort-wchar -fverbose-asm  -fpack-struct[=n]
445           -fleading-underscore  -ftls-model=model -fstack-reuse=reuse_level
446           -ftrampolines  -ftrapv  -fwrapv
447           -fvisibility=[default|internal|hidden|protected]
448           -fstrict-volatile-bitfields  -fsync-libcalls
449
450       Developer Options
451           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion
452           -fcallgraph-info[=su,da] -fchecking  -fchecking=n -fdbg-cnt-list
453           -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
454           -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list
455           -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list
456           -fdump-debug  -fdump-earlydebug -fdump-noaddr  -fdump-unnumbered
457           -fdump-unnumbered-links -fdump-final-insns[=file] -fdump-ipa-all
458           -fdump-ipa-cgraph  -fdump-ipa-inline -fdump-lang-all
459           -fdump-lang-switch -fdump-lang-switch-options
460           -fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass
461           -fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all
462           -fdump-tree-switch -fdump-tree-switch-options
463           -fdump-tree-switch-options=filename -fcompare-debug[=opts]
464           -fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range-
465           list -fira-verbose=n -flto-report  -flto-report-wpa
466           -fmem-report-wpa -fmem-report  -fpre-ipa-mem-report
467           -fpost-ipa-mem-report -fopt-info  -fopt-info-options[=file]
468           -fprofile-report -frandom-seed=string  -fsched-verbose=n
469           -fsel-sched-verbose  -fsel-sched-dump-cfg
470           -fsel-sched-pipelining-verbose -fstats  -fstack-usage
471           -ftime-report  -ftime-report-details
472           -fvar-tracking-assignments-toggle  -gtoggle
473           -print-file-name=library  -print-libgcc-file-name
474           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
475           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
476           -print-sysroot-headers-suffix -save-temps  -save-temps=cwd
477           -save-temps=obj  -time[=file]
478
479       Machine-Dependent Options
480           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian
481           -mgeneral-regs-only -mcmodel=tiny  -mcmodel=small  -mcmodel=large
482           -mstrict-align  -mno-strict-align -momit-leaf-frame-pointer
483           -mtls-dialect=desc  -mtls-dialect=traditional -mtls-size=size
484           -mfix-cortex-a53-835769  -mfix-cortex-a53-843419
485           -mlow-precision-recip-sqrt  -mlow-precision-sqrt
486           -mlow-precision-div -mpc-relative-literal-loads
487           -msign-return-address=scope -mbranch-protection=none|standard|pac-
488           ret[+leaf +b-key]|bti -mharden-sls=opts -march=name  -mcpu=name
489           -mtune=name -moverride=string  -mverbose-cost-dump
490           -mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg
491           -mstack-protector-guard-offset=offset -mtrack-speculation
492           -moutline-atomics
493
494           Adapteva Epiphany Options -mhalf-reg-file  -mprefer-short-insn-regs
495           -mbranch-cost=num  -mcmove  -mnops=num  -msoft-cmpsf -msplit-lohi
496           -mpost-inc  -mpost-modify  -mstack-offset=num -mround-nearest
497           -mlong-calls  -mshort-calls  -msmall16 -mfp-mode=mode
498           -mvect-double  -max-vect-align=num -msplit-vecmove-early
499           -m1reg-reg
500
501           AMD GCN Options -march=gpu -mtune=gpu -mstack-size=bytes
502
503           ARC Options -mbarrel-shifter  -mjli-always -mcpu=cpu  -mA6
504           -mARC600  -mA7  -mARC700 -mdpfp  -mdpfp-compact  -mdpfp-fast
505           -mno-dpfp-lrsr -mea  -mno-mpy  -mmul32x16  -mmul64  -matomic -mnorm
506           -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap
507           -mcrc  -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc
508           -mswape -mtelephony  -mxy  -misize  -mannotate-align  -marclinux
509           -marclinux_prof -mlong-calls  -mmedium-calls  -msdata
510           -mirq-ctrl-saved -mrgf-banked-regs  -mlpc-width=width  -G num
511           -mvolatile-cache  -mtp-regno=regno -malign-call  -mauto-modify-reg
512           -mbbit-peephole  -mno-brcc -mcase-vector-pcrel  -mcompact-casesi
513           -mno-cond-exec  -mearly-cbranchsi -mexpand-adddi  -mindexed-loads
514           -mlra  -mlra-priority-none -mlra-priority-compact
515           -mlra-priority-noncompact  -mmillicode -mmixed-code  -mq-class
516           -mRcq  -mRcw  -msize-level=level -mtune=cpu  -mmultcost=num
517           -mcode-density-frame -munalign-prob-threshold=probability
518           -mmpy-option=multo -mdiv-rem  -mcode-density  -mll64  -mfpu=fpu
519           -mrf16  -mbranch-index
520
521           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
522           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-reentrant
523           -mno-apcs-reentrant -mgeneral-regs-only -msched-prolog
524           -mno-sched-prolog -mlittle-endian  -mbig-endian -mbe8  -mbe32
525           -mfloat-abi=name -mfp16-format=name -mthumb-interwork
526           -mno-thumb-interwork -mcpu=name  -march=name  -mfpu=name
527           -mtune=name  -mprint-tune-info -mstructure-size-boundary=n
528           -mabort-on-noreturn -mlong-calls  -mno-long-calls -msingle-pic-base
529           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
530           -mpoke-function-name -mthumb  -marm  -mflip-thumb -mtpcs-frame
531           -mtpcs-leaf-frame -mcaller-super-interworking
532           -mcallee-super-interworking -mtp=name  -mtls-dialect=dialect
533           -mword-relocations -mfix-cortex-m3-ldrd
534           -mfix-cortex-a57-aes-1742098 -mfix-cortex-a72-aes-1655431
535           -munaligned-access -mneon-for-64bits -mslow-flash-data
536           -masm-syntax-unified -mrestrict-it -mverbose-cost-dump -mpure-code
537           -mcmse -mfix-cmse-cve-2021-35465 -mstack-protector-guard=guard
538           -mstack-protector-guard-offset=offset -mfdpic
539
540           AVR Options -mmcu=mcu  -mabsdata  -maccumulate-args
541           -mbranch-cost=cost -mcall-prologues  -mgas-isr-prologues  -mint8
542           -mdouble=bits -mlong-double=bits -mn_flash=size  -mno-interrupts
543           -mmain-is-OS_task  -mrelax  -mrmw  -mstrict-X  -mtiny-stack
544           -mfract-convert-truncate -mshort-calls  -nodevicelib
545           -nodevicespecs -Waddr-space-convert  -Wmisspelled-isr
546
547           Blackfin Options -mcpu=cpu[-sirevision] -msim
548           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
549           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
550           -mno-csync-anomaly -mlow-64k  -mno-low64k  -mstack-check-l1
551           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
552           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
553           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp
554           -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram -micplb
555
556           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim
557           -msdata=sdata-type
558
559           CRIS Options -mcpu=cpu  -march=cpu -mtune=cpu -mmax-stack-frame=n
560           -metrax4  -metrax100  -mpdebug  -mcc-init  -mno-side-effects
561           -mstack-align  -mdata-align  -mconst-align -m32-bit  -m16-bit
562           -m8-bit  -mno-prologue-epilogue -melf  -maout  -sim  -sim2
563           -mmul-bug-workaround  -mno-mul-bug-workaround
564
565           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops
566           -mdata-model=model
567
568           C-SKY Options -march=arch  -mcpu=cpu -mbig-endian  -EB
569           -mlittle-endian  -EL -mhard-float  -msoft-float  -mfpu=fpu
570           -mdouble-float  -mfdivdu -mfloat-abi=name -melrw  -mistack  -mmp
571           -mcp  -mcache  -msecurity  -mtrust -mdsp  -medsp  -mvdsp -mdiv
572           -msmart  -mhigh-registers  -manchor -mpushpop  -mmultiple-stld
573           -mconstpool  -mstack-size  -mccrt -mbranch-cost=n  -mcse-cc
574           -msched-prolog -msim
575
576           Darwin Options -all_load  -allowable_client  -arch
577           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
578           -bundle_loader -client_name  -compatibility_version
579           -current_version -dead_strip -dependency-file  -dylib_file
580           -dylinker_install_name -dynamic  -dynamiclib
581           -exported_symbols_list -filelist  -flat_namespace
582           -force_cpusubtype_ALL -force_flat_namespace
583           -headerpad_max_install_names -iframework -image_base  -init
584           -install_name  -keep_private_externs -multi_module
585           -multiply_defined  -multiply_defined_unused -noall_load
586           -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs
587           -noprebind  -noseglinkedit -pagezero_size  -prebind
588           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
589           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
590           -sectobjectsymbols  -sectorder -segaddr  -segs_read_only_addr
591           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
592           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
593           -single_module  -static  -sub_library  -sub_umbrella
594           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
595           -weak_reference_mismatches -whatsloaded  -F  -gused  -gfull
596           -mmacosx-version-min=version -mkernel  -mone-byte-bool
597
598           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee
599           -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
600           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
601           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
602           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
603           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time
604
605           eBPF Options -mbig-endian -mlittle-endian -mkernel=version
606           -mframe-limit=bytes -mxbpf -mco-re -mno-co-re -mjmpext -mjmp32
607           -malu32 -mcpu=version
608
609           FR30 Options -msmall-model  -mno-lsim
610
611           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm
612
613           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
614           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
615           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
616           -minline-plt  -mgprel-ro  -multilib-library-pic -mlinked-fp
617           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
618           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
619           -moptimize-membar  -mno-optimize-membar -mscc  -mno-scc
620           -mcond-exec  -mno-cond-exec -mvliw-branch  -mno-vliw-branch
621           -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
622           -mno-nested-cond-exec  -mtomcat-stats -mTLS  -mtls -mcpu=cpu
623
624           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid
625           -tno-android-cc  -tno-android-ld
626
627           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32
628           -malign-300
629
630           HPPA Options -march=architecture-type -mcaller-copies
631           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
632           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
633           -mlinker-opt  -mlong-calls -mlong-load-store  -mno-disable-fpregs
634           -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
635           -mno-jump-in-delay  -mno-long-load-store -mno-portable-runtime
636           -mno-soft-float -mno-space-regs  -msoft-float  -mpa-risc-1-0
637           -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime -mschedule=cpu-
638           type  -mspace-regs  -msio  -mwsio -munix=unix-std  -nolibdld
639           -static  -threads
640
641           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
642           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata
643           -mconstant-gp  -mauto-pic  -mfused-madd
644           -minline-float-divide-min-latency
645           -minline-float-divide-max-throughput -mno-inline-float-divide
646           -minline-int-divide-min-latency -minline-int-divide-max-throughput
647           -mno-inline-int-divide -minline-sqrt-min-latency
648           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
649           -mearly-stop-bits -mfixed-range=register-range  -mtls-size=tls-size
650           -mtune=cpu-type  -milp32  -mlp64 -msched-br-data-spec
651           -msched-ar-data-spec  -msched-control-spec -msched-br-in-data-spec
652           -msched-ar-in-data-spec  -msched-in-control-spec -msched-spec-ldc
653           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
654           -msched-prefer-non-control-spec-insns
655           -msched-stop-bits-after-every-cycle
656           -msched-count-spec-in-critical-path
657           -msel-sched-dont-check-control-spec  -msched-fp-mem-deps-zero-cost
658           -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=max-
659           insns
660
661           LM32 Options -mbarrel-shift-enabled  -mdivide-enabled
662           -mmultiply-enabled -msign-extend-enabled  -muser-enabled
663
664           LoongArch Options -march=cpu-type  -mtune=cpu-type -mabi=base-abi-
665           type -mfpu=fpu-type -msoft-float -msingle-float -mdouble-float
666           -mbranch-cost=n  -mcheck-zero-division -mno-check-zero-division
667           -mcond-move-int  -mno-cond-move-int -mcond-move-float
668           -mno-cond-move-float -memcpy  -mno-memcpy -mstrict-align
669           -mno-strict-align -mmax-inline-memcpy-size=n -mcmodel=code-model
670
671           M32R/D Options -m32r2  -m32rx  -m32r -mdebug -malign-loops
672           -mno-align-loops -missue-rate=number -mbranch-cost=number
673           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
674           -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num
675
676           M32C Options -mcpu=cpu  -msim  -memregs=number
677
678           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
679           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
680           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
681           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
682           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
683           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
684           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
685           -mxgot  -mno-xgot  -mlong-jump-table-offsets
686
687           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
688           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
689           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
690           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
691           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
692           -mstack-increment
693
694           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops
695           -mc=n  -mclip  -mconfig=name  -mcop  -mcop32  -mcop64  -mivc2 -mdc
696           -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm  -mminmax
697           -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim
698           -msimnovec  -mtf -mtiny=n
699
700           MicroBlaze Options -msoft-float  -mhard-float  -msmall-divides
701           -mcpu=cpu -mmemcpy  -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift
702           -mxl-pattern-compare  -mxl-stack-check  -mxl-gp-opt  -mno-clearbss
703           -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
704           -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-app-model
705           -mpic-data-is-text-relative
706
707           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
708           -mips3  -mips4  -mips32  -mips32r2  -mips32r3  -mips32r5 -mips32r6
709           -mips64  -mips64r2  -mips64r3  -mips64r5  -mips64r6 -mips16
710           -mno-mips16  -mflip-mips16 -minterlink-compressed
711           -mno-interlink-compressed -minterlink-mips16  -mno-interlink-mips16
712           -mabi=abi  -mabicalls  -mno-abicalls -mshared  -mno-shared  -mplt
713           -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64
714           -mhard-float  -msoft-float -mno-float  -msingle-float
715           -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode
716           -mnan=encoding -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mmcu
717           -mmno-mcu -meva  -mno-eva -mvirt  -mno-virt -mxpa  -mno-xpa -mcrc
718           -mno-crc -mginv  -mno-ginv -mmicromips  -mno-micromips -mmsa
719           -mno-msa -mloongson-mmi  -mno-loongson-mmi -mloongson-ext
720           -mno-loongson-ext -mloongson-ext2  -mno-loongson-ext2 -mfpu=fpu-
721           type -msmartmips  -mno-smartmips -mpaired-single
722           -mno-paired-single  -mdmx  -mno-mdmx -mips3d  -mno-mips3d  -mmt
723           -mno-mt  -mllsc  -mno-llsc -mlong64  -mlong32  -msym32  -mno-sym32
724           -Gnum  -mlocal-sdata  -mno-local-sdata -mextern-sdata
725           -mno-extern-sdata  -mgpopt  -mno-gopt -membedded-data
726           -mno-embedded-data -muninit-const-in-rodata
727           -mno-uninit-const-in-rodata -mcode-readable=setting
728           -msplit-addresses  -mno-split-addresses -mexplicit-relocs
729           -mno-explicit-relocs -mcheck-zero-division
730           -mno-check-zero-division -mdivide-traps  -mdivide-breaks
731           -mload-store-pairs  -mno-load-store-pairs -munaligned-access
732           -mno-unaligned-access -mmemcpy  -mno-memcpy  -mlong-calls
733           -mno-long-calls -mmad  -mno-mad  -mimadd  -mno-imadd  -mfused-madd
734           -mno-fused-madd  -nocpp -mfix-24k  -mno-fix-24k -mfix-r4000
735           -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400 -mfix-r5900
736           -mno-fix-r5900 -mfix-r10000  -mno-fix-r10000  -mfix-rm7000
737           -mno-fix-rm7000 -mfix-vr4120  -mno-fix-vr4120 -mfix-vr4130
738           -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1 -mflush-func=func
739           -mno-flush-func -mbranch-cost=num  -mbranch-likely
740           -mno-branch-likely -mcompact-branches=policy -mfp-exceptions
741           -mno-fp-exceptions -mvr4130-align  -mno-vr4130-align  -msynci
742           -mno-synci -mlxc1-sxc1  -mno-lxc1-sxc1  -mmadd4  -mno-madd4
743           -mrelax-pic-calls  -mno-relax-pic-calls  -mmcount-ra-address
744           -mframe-header-opt  -mno-frame-header-opt
745
746           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
747           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
748           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
749           -mbase-addresses -mno-base-addresses  -msingle-exit
750           -mno-single-exit
751
752           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33  -mam33
753           -mam33-2  -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0
754           -mrelax  -mliw  -msetlb
755
756           Moxie Options -meb  -mel  -mmul.x  -mno-crt0
757
758           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall
759           -mrelax -mwarn-mcu -mcode-region=  -mdata-region= -msilicon-errata=
760           -msilicon-errata-warn= -mhwmult=  -minrt  -mtiny-printf
761           -mmax-inline-shift=
762
763           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs
764           -mfull-regs -mcmov  -mno-cmov -mext-perf  -mno-ext-perf -mext-perf2
765           -mno-ext-perf2 -mext-string  -mno-ext-string -mv3push  -mno-v3push
766           -m16bit  -mno-16bit -misr-vector-size=num -mcache-block-size=num
767           -march=arch -mcmodel=code-model -mctor-dtor  -mrelax
768
769           Nios II Options -G num  -mgpopt=option  -mgpopt  -mno-gpopt
770           -mgprel-sec=regexp  -mr0rel-sec=regexp -mel  -meb -mno-bypass-cache
771           -mbypass-cache -mno-cache-volatile  -mcache-volatile
772           -mno-fast-sw-div  -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx
773           -mno-hw-mulx  -mno-hw-div  -mhw-div -mcustom-insn=N
774           -mno-custom-insn -mcustom-fpu-cfg=name -mhal  -msmallc
775           -msys-crt0=name  -msys-lib=name -march=arch  -mbmx  -mno-bmx  -mcdx
776           -mno-cdx
777
778           Nvidia PTX Options -m64  -mmainkernel  -moptimize
779
780           OpenRISC Options -mboard=name  -mnewlib  -mhard-mul  -mhard-div
781           -msoft-mul  -msoft-div -msoft-float  -mhard-float  -mdouble-float
782           -munordered-float -mcmov  -mror  -mrori  -msext  -msfimm  -mshftimm
783           -mcmodel=code-model
784
785           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
786           -m10 -mint32  -mno-int16  -mint16  -mno-int32 -msplit  -munix-asm
787           -mdec-asm  -mgnu-asm  -mlra
788
789           picoChip Options -mae=ae_type  -mvliw-lookahead=N
790           -msymbol-as-address  -mno-inefficient-warnings
791
792           PowerPC Options See RS/6000 and PowerPC Options.
793
794           PRU Options -mmcu=mcu  -minrt  -mno-relax  -mloop -mabi=variant
795
796           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt
797           -mabi=ABI-string -mfdiv  -mno-fdiv -mdiv  -mno-div -misa-spec=ISA-
798           spec-string -march=ISA-string -mtune=processor-string
799           -mpreferred-stack-boundary=num -msmall-data-limit=N-bytes
800           -msave-restore  -mno-save-restore -mshorten-memrefs
801           -mno-shorten-memrefs -mstrict-align  -mno-strict-align
802           -mcmodel=medlow  -mcmodel=medany -mexplicit-relocs
803           -mno-explicit-relocs -mrelax  -mno-relax -mriscv-attribute
804           -mmo-riscv-attribute -malign-data=type -mbig-endian
805           -mlittle-endian -mstack-protector-guard=guard
806           -mstack-protector-guard-reg=reg
807           -mstack-protector-guard-offset=offset
808
809           RL78 Options -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs
810           -mcpu=g10  -mcpu=g13  -mcpu=g14  -mg10  -mg13  -mg14
811           -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts
812
813           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type
814           -mcmodel=code-model -mpowerpc64 -maltivec  -mno-altivec
815           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
816           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
817           -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb
818           -mhard-dfp  -mno-hard-dfp -mfull-toc   -mminimal-toc
819           -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32  -mxl-compat
820           -mno-xl-compat  -mpe -malign-power  -malign-natural -msoft-float
821           -mhard-float  -mmultiple  -mno-multiple -mupdate  -mno-update
822           -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
823           -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
824           -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
825           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle
826           -mlittle-endian  -mbig  -mbig-endian -mdynamic-no-pic  -mswdiv
827           -msingle-pic-base -mprioritize-restricted-insns=priority
828           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
829           -mcall-aixdesc  -mcall-eabi  -mcall-freebsd -mcall-linux
830           -mcall-netbsd  -mcall-openbsd -mcall-sysv  -mcall-sysv-eabi
831           -mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return
832           -msvr4-struct-return -mabi=abi-type  -msecure-plt  -mbss-plt
833           -mlongcall  -mno-longcall  -mpltseq  -mno-pltseq
834           -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
835           -mblock-compare-inline-loop-limit=num -mno-block-ops-unaligned-vsx
836           -mstring-compare-inline-limit=num -misel  -mno-isel -mvrsave
837           -mno-vrsave -mmulhw  -mno-mulhw -mdlmzb  -mno-dlmzb -mprototype
838           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
839           -msdata=opt  -mreadonly-in-sdata  -mvxworks  -G num -mrecip
840           -mrecip=opt  -mno-recip  -mrecip-precision -mno-recip-precision
841           -mveclibabi=type  -mfriz  -mno-friz -mpointers-to-nested-functions
842           -mno-pointers-to-nested-functions -msave-toc-indirect
843           -mno-save-toc-indirect -mpower8-fusion  -mno-mpower8-fusion
844           -mpower8-vector  -mno-power8-vector -mcrypto  -mno-crypto  -mhtm
845           -mno-htm -mquad-memory  -mno-quad-memory -mquad-memory-atomic
846           -mno-quad-memory-atomic -mcompat-align-parm  -mno-compat-align-parm
847           -mfloat128  -mno-float128  -mfloat128-hardware
848           -mno-float128-hardware -mgnu-attribute  -mno-gnu-attribute
849           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
850           -mstack-protector-guard-offset=offset -mprefixed -mno-prefixed
851           -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect
852           -mprivileged -mno-privileged
853
854           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
855           -mbig-endian-data  -mlittle-endian-data -msmall-data -msim
856           -mno-sim -mas100-syntax  -mno-as100-syntax -mrelax
857           -mmax-constant-size= -mint-register= -mpid -mallow-string-insns
858           -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
859           -msave-acc-in-interrupts
860
861           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
862           -mhard-float  -msoft-float  -mhard-dfp  -mno-hard-dfp
863           -mlong-double-64  -mlong-double-128 -mbackchain  -mno-backchain
864           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
865           -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
866           -mhtm  -mvx  -mzvector -mtpf-trace  -mno-tpf-trace
867           -mtpf-trace-skip  -mno-tpf-trace-skip -mfused-madd  -mno-fused-madd
868           -mwarn-framesize  -mwarn-dynamicstack  -mstack-size  -mstack-guard
869           -mhotpatch=halfwords,halfwords
870
871           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u
872           -mscore7  -mscore7d
873
874           SH Options -m1  -m2  -m2e -m2a-nofpu  -m2a-single-only  -m2a-single
875           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
876           -m4a-nofpu  -m4a-single-only  -m4a-single  -m4a  -m4al -mb  -ml
877           -mdalign  -mrelax -mbigtable  -mfmovd  -mrenesas  -mno-renesas
878           -mnomacsave -mieee  -mno-ieee  -mbitops  -misize
879           -minline-ic_invalidate  -mpadstruct -mprefergot  -musermode
880           -multcost=number  -mdiv=strategy -mdivsi3_libfunc=name
881           -mfixed-range=register-range -maccumulate-outgoing-args
882           -matomic-model=atomic-model -mbranch-cost=num  -mzdcbranch
883           -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
884           -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra
885           -mpretend-cmove  -mtas
886
887           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text
888           -mno-impure-text -pthreads
889
890           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
891           -mmemory-model=mem-model -m32  -m64  -mapp-regs  -mno-app-regs
892           -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat -mfpu
893           -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
894           -msoft-quad-float -mstack-bias  -mno-stack-bias -mstd-struct-return
895           -mno-std-struct-return -munaligned-doubles  -mno-unaligned-doubles
896           -muser-mode  -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis
897           -mvis2  -mno-vis2  -mvis3  -mno-vis3 -mvis4  -mno-vis4  -mvis4b
898           -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld
899           -mno-fsmuld -mpopc  -mno-popc  -msubxc  -mno-subxc -mfix-at697f
900           -mfix-ut699  -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra
901
902           System V Options -Qy  -Qn  -YP,paths  -Ym,dir
903
904           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian
905           -mlittle-endian -mcmodel=code-model
906
907           TILEPro Options -mcpu=cpu  -m32
908
909           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
910           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
911           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
912           -mno-disable-callt -mv850e2v3  -mv850e2  -mv850e1  -mv850es -mv850e
913           -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
914           -mhard-float -mgcc-abi -mrh850-abi -mbig-switch
915
916           VAX Options -mg  -mgnu  -munix  -mlra
917
918           Visium Options -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float
919           -msoft-float -mcpu=cpu-type  -mtune=cpu-type  -msv-mode
920           -muser-mode
921
922           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64
923           -mpointer-size=size
924
925           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
926           -Xbind-now
927
928           x86 Options -mtune=cpu-type  -march=cpu-type -mtune-ctrl=feature-
929           list  -mdump-tune-features  -mno-default -mfpmath=unit
930           -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387  -m80387
931           -mhard-float  -msoft-float -mno-wide-multiply  -mrtd
932           -malign-double -mpreferred-stack-boundary=num
933           -mincoming-stack-boundary=num -mcld  -mcx16  -msahf  -mmovbe
934           -mcrc32 -mmwait -mrecip  -mrecip=opt -mvzeroupper  -mprefer-avx128
935           -mprefer-vector-width=opt -mmove-max=bits -mstore-max=bits -mmmx
936           -msse  -msse2  -msse3  -mssse3  -msse4.1  -msse4.2  -msse4  -mavx
937           -mavx2  -mavx512f  -mavx512pf  -mavx512er  -mavx512cd  -mavx512vl
938           -mavx512bw  -mavx512dq  -mavx512ifma  -mavx512vbmi  -msha  -maes
939           -mpclmul  -mfsgsbase  -mrdrnd  -mf16c  -mfma  -mpconfig  -mwbnoinvd
940           -mptwrite  -mprefetchwt1  -mclflushopt  -mclwb  -mxsavec  -mxsaves
941           -msse4a  -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4
942           -mxop -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm
943           -mhle  -mlwp -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni  -mvaes
944           -mwaitpkg -mshstk -mmanual-endbr -mforce-indirect-call
945           -mavx512vbmi2 -mavx512bf16 -menqcmd -mvpclmulqdq  -mavx512bitalg
946           -mmovdiri  -mmovdir64b  -mavx512vpopcntdq -mavx5124fmaps
947           -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid -mrdseed  -msgx
948           -mavx512vp2intersect -mserialize -mtsxldtrk -mamx-tile  -mamx-int8
949           -mamx-bf16 -muintr -mhreset -mavxvnni -mavx512fp16 -mcldemote
950           -mms-bitfields  -mno-align-stringops  -minline-all-stringops
951           -minline-stringops-dynamically  -mstringop-strategy=alg -mkl
952           -mwidekl -mmemcpy-strategy=strategy  -mmemset-strategy=strategy
953           -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
954           -m96bit-long-double  -mlong-double-64  -mlong-double-80
955           -mlong-double-128 -mregparm=num  -msseregparm -mveclibabi=type
956           -mvect8-ret-in-mem -mpc32  -mpc64  -mpc80  -mstackrealign
957           -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs
958           -mcmodel=code-model  -mabi=name  -maddress-mode=mode -m32  -m64
959           -mx32  -m16  -miamcu  -mlarge-data-threshold=num -msse2avx
960           -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv
961           -minstrument-return=type -mfentry-name=name -mfentry-section=name
962           -mavx256-split-unaligned-load  -mavx256-split-unaligned-store
963           -malign-data=type  -mstack-protector-guard=guard
964           -mstack-protector-guard-reg=reg
965           -mstack-protector-guard-offset=offset
966           -mstack-protector-guard-symbol=symbol -mgeneral-regs-only
967           -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop
968           -mindirect-branch=choice  -mfunction-return=choice
969           -mindirect-branch-register -mharden-sls=choice
970           -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access
971
972           x86 Windows Options -mconsole  -mcygwin  -mno-cygwin  -mdll
973           -mnop-fun-dllimport  -mthread -municode  -mwin32  -mwindows
974           -fno-set-stack-executable
975
976           Xstormy16 Options -msim
977
978           Xtensa Options -mconst16  -mno-const16 -mfused-madd
979           -mno-fused-madd -mforce-no-pic -mserialize-volatile
980           -mno-serialize-volatile -mtext-section-literals
981           -mno-text-section-literals -mauto-litpools  -mno-auto-litpools
982           -mtarget-align  -mno-target-align -mlongcalls  -mno-longcalls
983           -mabi=abi-type
984
985           zSeries Options See S/390 and zSeries Options.
986
987   Options Controlling the Kind of Output
988       Compilation can involve up to four stages: preprocessing, compilation
989       proper, assembly and linking, always in that order.  GCC is capable of
990       preprocessing and compiling several files either into several assembler
991       input files, or into one assembler input file; then each assembler
992       input file produces an object file, and linking combines all the object
993       files (those newly compiled, and those specified as input) into an
994       executable file.
995
996       For any given input file, the file name suffix determines what kind of
997       compilation is done:
998
999       file.c
1000           C source code that must be preprocessed.
1001
1002       file.i
1003           C source code that should not be preprocessed.
1004
1005       file.ii
1006           C++ source code that should not be preprocessed.
1007
1008       file.m
1009           Objective-C source code.  Note that you must link with the libobjc
1010           library to make an Objective-C program work.
1011
1012       file.mi
1013           Objective-C source code that should not be preprocessed.
1014
1015       file.mm
1016       file.M
1017           Objective-C++ source code.  Note that you must link with the
1018           libobjc library to make an Objective-C++ program work.  Note that
1019           .M refers to a literal capital M.
1020
1021       file.mii
1022           Objective-C++ source code that should not be preprocessed.
1023
1024       file.h
1025           C, C++, Objective-C or Objective-C++ header file to be turned into
1026           a precompiled header (default), or C, C++ header file to be turned
1027           into an Ada spec (via the -fdump-ada-spec switch).
1028
1029       file.cc
1030       file.cp
1031       file.cxx
1032       file.cpp
1033       file.CPP
1034       file.c++
1035       file.C
1036           C++ source code that must be preprocessed.  Note that in .cxx, the
1037           last two letters must both be literally x.  Likewise, .C refers to
1038           a literal capital C.
1039
1040       file.mm
1041       file.M
1042           Objective-C++ source code that must be preprocessed.
1043
1044       file.mii
1045           Objective-C++ source code that should not be preprocessed.
1046
1047       file.hh
1048       file.H
1049       file.hp
1050       file.hxx
1051       file.hpp
1052       file.HPP
1053       file.h++
1054       file.tcc
1055           C++ header file to be turned into a precompiled header or Ada spec.
1056
1057       file.f
1058       file.for
1059       file.ftn
1060           Fixed form Fortran source code that should not be preprocessed.
1061
1062       file.F
1063       file.FOR
1064       file.fpp
1065       file.FPP
1066       file.FTN
1067           Fixed form Fortran source code that must be preprocessed (with the
1068           traditional preprocessor).
1069
1070       file.f90
1071       file.f95
1072       file.f03
1073       file.f08
1074           Free form Fortran source code that should not be preprocessed.
1075
1076       file.F90
1077       file.F95
1078       file.F03
1079       file.F08
1080           Free form Fortran source code that must be preprocessed (with the
1081           traditional preprocessor).
1082
1083       file.go
1084           Go source code.
1085
1086       file.d
1087           D source code.
1088
1089       file.di
1090           D interface file.
1091
1092       file.dd
1093           D documentation code (Ddoc).
1094
1095       file.ads
1096           Ada source code file that contains a library unit declaration (a
1097           declaration of a package, subprogram, or generic, or a generic
1098           instantiation), or a library unit renaming declaration (a package,
1099           generic, or subprogram renaming declaration).  Such files are also
1100           called specs.
1101
1102       file.adb
1103           Ada source code file containing a library unit body (a subprogram
1104           or package body).  Such files are also called bodies.
1105
1106       file.s
1107           Assembler code.
1108
1109       file.S
1110       file.sx
1111           Assembler code that must be preprocessed.
1112
1113       other
1114           An object file to be fed straight into linking.  Any file name with
1115           no recognized suffix is treated this way.
1116
1117       You can specify the input language explicitly with the -x option:
1118
1119       -x language
1120           Specify explicitly the language for the following input files
1121           (rather than letting the compiler choose a default based on the
1122           file name suffix).  This option applies to all following input
1123           files until the next -x option.  Possible values for language are:
1124
1125                   c  c-header  cpp-output
1126                   c++  c++-header  c++-system-header c++-user-header c++-cpp-output
1127                   objective-c  objective-c-header  objective-c-cpp-output
1128                   objective-c++ objective-c++-header objective-c++-cpp-output
1129                   assembler  assembler-with-cpp
1130                   ada
1131                   d
1132                   f77  f77-cpp-input f95  f95-cpp-input
1133                   go
1134
1135       -x none
1136           Turn off any specification of a language, so that subsequent files
1137           are handled according to their file name suffixes (as they are if
1138           -x has not been used at all).
1139
1140       If you only want some of the stages of compilation, you can use -x (or
1141       filename suffixes) to tell gcc where to start, and one of the options
1142       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
1143       (for example, -x cpp-output -E) instruct gcc to do nothing at all.
1144
1145       -c  Compile or assemble the source files, but do not link.  The linking
1146           stage simply is not done.  The ultimate output is in the form of an
1147           object file for each source file.
1148
1149           By default, the object file name for a source file is made by
1150           replacing the suffix .c, .i, .s, etc., with .o.
1151
1152           Unrecognized input files, not requiring compilation or assembly,
1153           are ignored.
1154
1155       -S  Stop after the stage of compilation proper; do not assemble.  The
1156           output is in the form of an assembler code file for each non-
1157           assembler input file specified.
1158
1159           By default, the assembler file name for a source file is made by
1160           replacing the suffix .c, .i, etc., with .s.
1161
1162           Input files that don't require compilation are ignored.
1163
1164       -E  Stop after the preprocessing stage; do not run the compiler proper.
1165           The output is in the form of preprocessed source code, which is
1166           sent to the standard output.
1167
1168           Input files that don't require preprocessing are ignored.
1169
1170       -o file
1171           Place the primary output in file file.  This applies to whatever
1172           sort of output is being produced, whether it be an executable file,
1173           an object file, an assembler file or preprocessed C code.
1174
1175           If -o is not specified, the default is to put an executable file in
1176           a.out, the object file for source.suffix in source.o, its assembler
1177           file in source.s, a precompiled header file in source.suffix.gch,
1178           and all preprocessed C source on standard output.
1179
1180           Though -o names only the primary output, it also affects the naming
1181           of auxiliary and dump outputs.  See the examples below.  Unless
1182           overridden, both auxiliary outputs and dump outputs are placed in
1183           the same directory as the primary output.  In auxiliary outputs,
1184           the suffix of the input file is replaced with that of the auxiliary
1185           output file type; in dump outputs, the suffix of the dump file is
1186           appended to the input file suffix.  In compilation commands, the
1187           base name of both auxiliary and dump outputs is that of the primary
1188           output; in compile and link commands, the primary output name,
1189           minus the executable suffix, is combined with the input file name.
1190           If both share the same base name, disregarding the suffix, the
1191           result of the combination is that base name, otherwise, they are
1192           concatenated, separated by a dash.
1193
1194                   gcc -c foo.c ...
1195
1196           will use foo.o as the primary output, and place aux outputs and
1197           dumps next to it, e.g., aux file foo.dwo for -gsplit-dwarf, and
1198           dump file foo.c.???r.final for -fdump-rtl-final.
1199
1200           If a non-linker output file is explicitly specified, aux and dump
1201           files by default take the same base name:
1202
1203                   gcc -c foo.c -o dir/foobar.o ...
1204
1205           will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*.
1206
1207           A linker output will instead prefix aux and dump outputs:
1208
1209                   gcc foo.c bar.c -o dir/foobar ...
1210
1211           will generally name aux outputs dir/foobar-foo.* and
1212           dir/foobar-bar.*, and dump outputs dir/foobar-foo.c.* and
1213           dir/foobar-bar.c.*.
1214
1215           The one exception to the above is when the executable shares the
1216           base name with the single input:
1217
1218                   gcc foo.c -o dir/foo ...
1219
1220           in which case aux outputs are named dir/foo.* and dump outputs
1221           named dir/foo.c.*.
1222
1223           The location and the names of auxiliary and dump outputs can be
1224           adjusted by the options -dumpbase, -dumpbase-ext, -dumpdir,
1225           -save-temps=cwd, and -save-temps=obj.
1226
1227       -dumpbase dumpbase
1228           This option sets the base name for auxiliary and dump output files.
1229           It does not affect the name of the primary output file.
1230           Intermediate outputs, when preserved, are not regarded as primary
1231           outputs, but as auxiliary outputs:
1232
1233                   gcc -save-temps -S foo.c
1234
1235           saves the (no longer) temporary preprocessed file in foo.i, and
1236           then compiles to the (implied) output file foo.s, whereas:
1237
1238                   gcc -save-temps -dumpbase save-foo -c foo.c
1239
1240           preprocesses to in save-foo.i, compiles to save-foo.s (now an
1241           intermediate, thus auxiliary output), and then assembles to the
1242           (implied) output file foo.o.
1243
1244           Absent this option, dump and aux files take their names from the
1245           input file, or from the (non-linker) output file, if one is
1246           explicitly specified: dump output files (e.g. those requested by
1247           -fdump-* options) with the input name suffix, and aux output files
1248           (those requested by other non-dump options, e.g. "-save-temps",
1249           "-gsplit-dwarf", "-fcallgraph-info") without it.
1250
1251           Similar suffix differentiation of dump and aux outputs can be
1252           attained for explicitly-given -dumpbase basename.suf by also
1253           specifying -dumpbase-ext .suf.
1254
1255           If dumpbase is explicitly specified with any directory component,
1256           any dumppfx specification (e.g. -dumpdir or -save-temps=*) is
1257           ignored, and instead of appending to it, dumpbase fully overrides
1258           it:
1259
1260                   gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
1261                     -dumpdir pfx- -save-temps=cwd ...
1262
1263           creates auxiliary and dump outputs named alt/foo.*, disregarding
1264           dir/ in -o, the ./ prefix implied by -save-temps=cwd, and pfx- in
1265           -dumpdir.
1266
1267           When -dumpbase is specified in a command that compiles multiple
1268           inputs, or that compiles and then links, it may be combined with
1269           dumppfx, as specified under -dumpdir.  Then, each input file is
1270           compiled using the combined dumppfx, and default values for
1271           dumpbase and auxdropsuf are computed for each input file:
1272
1273                   gcc foo.c bar.c -c -dumpbase main ...
1274
1275           creates foo.o and bar.o as primary outputs, and avoids overwriting
1276           the auxiliary and dump outputs by using the dumpbase as a prefix,
1277           creating auxiliary and dump outputs named main-foo.*  and
1278           main-bar.*.
1279
1280           An empty string specified as dumpbase avoids the influence of the
1281           output basename in the naming of auxiliary and dump outputs during
1282           compilation, computing default values :
1283
1284                   gcc -c foo.c -o dir/foobar.o -dumpbase " ...
1285
1286           will name aux outputs dir/foo.* and dump outputs dir/foo.c.*.  Note
1287           how their basenames are taken from the input name, but the
1288           directory still defaults to that of the output.
1289
1290           The empty-string dumpbase does not prevent the use of the output
1291           basename for outputs during linking:
1292
1293                   gcc foo.c bar.c -o dir/foobar -dumpbase " -flto ...
1294
1295           The compilation of the source files will name auxiliary outputs
1296           dir/foo.* and dir/bar.*, and dump outputs dir/foo.c.* and
1297           dir/bar.c.*.  LTO recompilation during linking will use dir/foobar.
1298           as the prefix for dumps and auxiliary files.
1299
1300       -dumpbase-ext auxdropsuf
1301           When forming the name of an auxiliary (but not a dump) output file,
1302           drop trailing auxdropsuf from dumpbase before appending any
1303           suffixes.  If not specified, this option defaults to the suffix of
1304           a default dumpbase, i.e., the suffix of the input file when
1305           -dumpbase is not present in the command line, or dumpbase is
1306           combined with dumppfx.
1307
1308                   gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...
1309
1310           creates dir/foo.o as the main output, and generates auxiliary
1311           outputs in dir/x-foo.*, taking the location of the primary output,
1312           and dropping the .c suffix from the dumpbase.  Dump outputs retain
1313           the suffix: dir/x-foo.c.*.
1314
1315           This option is disregarded if it does not match the suffix of a
1316           specified dumpbase, except as an alternative to the executable
1317           suffix when appending the linker output base name to dumppfx, as
1318           specified below:
1319
1320                   gcc foo.c bar.c -o main.out -dumpbase-ext .out ...
1321
1322           creates main.out as the primary output, and avoids overwriting the
1323           auxiliary and dump outputs by using the executable name minus
1324           auxdropsuf as a prefix, creating auxiliary outputs named main-foo.*
1325           and main-bar.* and dump outputs named main-foo.c.* and
1326           main-bar.c.*.
1327
1328       -dumpdir dumppfx
1329           When forming the name of an auxiliary or dump output file, use
1330           dumppfx as a prefix:
1331
1332                   gcc -dumpdir pfx- -c foo.c ...
1333
1334           creates foo.o as the primary output, and auxiliary outputs named
1335           pfx-foo.*, combining the given dumppfx with the default dumpbase
1336           derived from the default primary output, derived in turn from the
1337           input name.  Dump outputs also take the input name suffix:
1338           pfx-foo.c.*.
1339
1340           If dumppfx is to be used as a directory name, it must end with a
1341           directory separator:
1342
1343                   gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...
1344
1345           creates obj/bar.o as the primary output, and auxiliary outputs
1346           named dir/bar.*, combining the given dumppfx with the default
1347           dumpbase derived from the primary output name.  Dump outputs also
1348           take the input name suffix: dir/bar.c.*.
1349
1350           It defaults to the location of the output file, unless the output
1351           file is a special file like "/dev/null". Options -save-temps=cwd
1352           and -save-temps=obj override this default, just like an explicit
1353           -dumpdir option.  In case multiple such options are given, the last
1354           one prevails:
1355
1356                   gcc -dumpdir pfx- -c foo.c -save-temps=obj ...
1357
1358           outputs foo.o, with auxiliary outputs named foo.* because
1359           -save-temps=* overrides the dumppfx given by the earlier -dumpdir
1360           option.  It does not matter that =obj is the default for
1361           -save-temps, nor that the output directory is implicitly the
1362           current directory.  Dump outputs are named foo.c.*.
1363
1364           When compiling from multiple input files, if -dumpbase is
1365           specified, dumpbase, minus a auxdropsuf suffix, and a dash are
1366           appended to (or override, if containing any directory components)
1367           an explicit or defaulted dumppfx, so that each of the multiple
1368           compilations gets differently-named aux and dump outputs.
1369
1370                   gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...
1371
1372           outputs auxiliary dumps to dir/pfx-main-foo.* and
1373           dir/pfx-main-bar.*, appending dumpbase- to dumppfx.  Dump outputs
1374           retain the input file suffix: dir/pfx-main-foo.c.*  and
1375           dir/pfx-main-bar.c.*, respectively.  Contrast with the single-input
1376           compilation:
1377
1378                   gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...
1379
1380           that, applying -dumpbase to a single source, does not compute and
1381           append a separate dumpbase per input file.  Its auxiliary and dump
1382           outputs go in dir/pfx-main.*.
1383
1384           When compiling and then linking from multiple input files, a
1385           defaulted or explicitly specified dumppfx also undergoes the
1386           dumpbase- transformation above (e.g. the compilation of foo.c and
1387           bar.c above, but without -c).  If neither -dumpdir nor -dumpbase
1388           are given, the linker output base name, minus auxdropsuf, if
1389           specified, or the executable suffix otherwise, plus a dash is
1390           appended to the default dumppfx instead.  Note, however, that
1391           unlike earlier cases of linking:
1392
1393                   gcc foo.c bar.c -dumpdir dir/pfx- -o main ...
1394
1395           does not append the output name main to dumppfx, because -dumpdir
1396           is explicitly specified.  The goal is that the explicitly-specified
1397           dumppfx may contain the specified output name as part of the
1398           prefix, if desired; only an explicitly-specified -dumpbase would be
1399           combined with it, in order to avoid simply discarding a meaningful
1400           option.
1401
1402           When compiling and then linking from a single input file, the
1403           linker output base name will only be appended to the default
1404           dumppfx as above if it does not share the base name with the single
1405           input file name.  This has been covered in single-input linking
1406           cases above, but not with an explicit -dumpdir that inhibits the
1407           combination, even if overridden by -save-temps=*:
1408
1409                   gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...
1410
1411           Auxiliary outputs are named foo.*, and dump outputs foo.c.*, in the
1412           current working directory as ultimately requested by
1413           -save-temps=cwd.
1414
1415           Summing it all up for an intuitive though slightly imprecise data
1416           flow: the primary output name is broken into a directory part and a
1417           basename part; dumppfx is set to the former, unless overridden by
1418           -dumpdir or -save-temps=*, and dumpbase is set to the latter,
1419           unless overriden by -dumpbase.  If there are multiple inputs or
1420           linking, this dumpbase may be combined with dumppfx and taken from
1421           each input file.  Auxiliary output names for each input are formed
1422           by combining dumppfx, dumpbase minus suffix, and the auxiliary
1423           output suffix; dump output names are only different in that the
1424           suffix from dumpbase is retained.
1425
1426           When it comes to auxiliary and dump outputs created during LTO
1427           recompilation, a combination of dumppfx and dumpbase, as given or
1428           as derived from the linker output name but not from inputs, even in
1429           cases in which this combination would not otherwise be used as
1430           such, is passed down with a trailing period replacing the compiler-
1431           added dash, if any, as a -dumpdir option to lto-wrapper; being
1432           involved in linking, this program does not normally get any
1433           -dumpbase and -dumpbase-ext, and it ignores them.
1434
1435           When running sub-compilers, lto-wrapper appends LTO stage names to
1436           the received dumppfx, ensures it contains a directory component so
1437           that it overrides any -dumpdir, and passes that as -dumpbase to
1438           sub-compilers.
1439
1440       -v  Print (on standard error output) the commands executed to run the
1441           stages of compilation.  Also print the version number of the
1442           compiler driver program and of the preprocessor and the compiler
1443           proper.
1444
1445       -###
1446           Like -v except the commands are not executed and arguments are
1447           quoted unless they contain only alphanumeric characters or "./-_".
1448           This is useful for shell scripts to capture the driver-generated
1449           command lines.
1450
1451       --help
1452           Print (on the standard output) a description of the command-line
1453           options understood by gcc.  If the -v option is also specified then
1454           --help is also passed on to the various processes invoked by gcc,
1455           so that they can display the command-line options they accept.  If
1456           the -Wextra option has also been specified (prior to the --help
1457           option), then command-line options that have no documentation
1458           associated with them are also displayed.
1459
1460       --target-help
1461           Print (on the standard output) a description of target-specific
1462           command-line options for each tool.  For some targets extra target-
1463           specific information may also be printed.
1464
1465       --help={class|[^]qualifier}[,...]
1466           Print (on the standard output) a description of the command-line
1467           options understood by the compiler that fit into all specified
1468           classes and qualifiers.  These are the supported classes:
1469
1470           optimizers
1471               Display all of the optimization options supported by the
1472               compiler.
1473
1474           warnings
1475               Display all of the options controlling warning messages
1476               produced by the compiler.
1477
1478           target
1479               Display target-specific options.  Unlike the --target-help
1480               option however, target-specific options of the linker and
1481               assembler are not displayed.  This is because those tools do
1482               not currently support the extended --help= syntax.
1483
1484           params
1485               Display the values recognized by the --param option.
1486
1487           language
1488               Display the options supported for language, where language is
1489               the name of one of the languages supported in this version of
1490               GCC.  If an option is supported by all languages, one needs to
1491               select common class.
1492
1493           common
1494               Display the options that are common to all languages.
1495
1496           These are the supported qualifiers:
1497
1498           undocumented
1499               Display only those options that are undocumented.
1500
1501           joined
1502               Display options taking an argument that appears after an equal
1503               sign in the same continuous piece of text, such as:
1504               --help=target.
1505
1506           separate
1507               Display options taking an argument that appears as a separate
1508               word following the original option, such as: -o output-file.
1509
1510           Thus for example to display all the undocumented target-specific
1511           switches supported by the compiler, use:
1512
1513                   --help=target,undocumented
1514
1515           The sense of a qualifier can be inverted by prefixing it with the ^
1516           character, so for example to display all binary warning options
1517           (i.e., ones that are either on or off and that do not take an
1518           argument) that have a description, use:
1519
1520                   --help=warnings,^joined,^undocumented
1521
1522           The argument to --help= should not consist solely of inverted
1523           qualifiers.
1524
1525           Combining several classes is possible, although this usually
1526           restricts the output so much that there is nothing to display.  One
1527           case where it does work, however, is when one of the classes is
1528           target.  For example, to display all the target-specific
1529           optimization options, use:
1530
1531                   --help=target,optimizers
1532
1533           The --help= option can be repeated on the command line.  Each
1534           successive use displays its requested class of options, skipping
1535           those that have already been displayed.  If --help is also
1536           specified anywhere on the command line then this takes precedence
1537           over any --help= option.
1538
1539           If the -Q option appears on the command line before the --help=
1540           option, then the descriptive text displayed by --help= is changed.
1541           Instead of describing the displayed options, an indication is given
1542           as to whether the option is enabled, disabled or set to a specific
1543           value (assuming that the compiler knows this at the point where the
1544           --help= option is used).
1545
1546           Here is a truncated example from the ARM port of gcc:
1547
1548                     % gcc -Q -mabi=2 --help=target -c
1549                     The following options are target specific:
1550                     -mabi=                                2
1551                     -mabort-on-noreturn                   [disabled]
1552                     -mapcs                                [disabled]
1553
1554           The output is sensitive to the effects of previous command-line
1555           options, so for example it is possible to find out which
1556           optimizations are enabled at -O2 by using:
1557
1558                   -Q -O2 --help=optimizers
1559
1560           Alternatively you can discover which binary optimizations are
1561           enabled by -O3 by using:
1562
1563                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1564                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1565                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1566
1567       --version
1568           Display the version number and copyrights of the invoked GCC.
1569
1570       -pass-exit-codes
1571           Normally the gcc program exits with the code of 1 if any phase of
1572           the compiler returns a non-success return code.  If you specify
1573           -pass-exit-codes, the gcc program instead returns with the
1574           numerically highest error produced by any phase returning an error
1575           indication.  The C, C++, and Fortran front ends return 4 if an
1576           internal compiler error is encountered.
1577
1578       -pipe
1579           Use pipes rather than temporary files for communication between the
1580           various stages of compilation.  This fails to work on some systems
1581           where the assembler is unable to read from a pipe; but the GNU
1582           assembler has no trouble.
1583
1584       -specs=file
1585           Process file after the compiler reads in the standard specs file,
1586           in order to override the defaults which the gcc driver program uses
1587           when determining what switches to pass to cc1, cc1plus, as, ld,
1588           etc.  More than one -specs=file can be specified on the command
1589           line, and they are processed in order, from left to right.
1590
1591       -wrapper
1592           Invoke all subcommands under a wrapper program.  The name of the
1593           wrapper program and its parameters are passed as a comma separated
1594           list.
1595
1596                   gcc -c t.c -wrapper gdb,--args
1597
1598           This invokes all subprograms of gcc under gdb --args, thus the
1599           invocation of cc1 is gdb --args cc1 ....
1600
1601       -ffile-prefix-map=old=new
1602           When compiling files residing in directory old, record any
1603           references to them in the result of the compilation as if the files
1604           resided in directory new instead.  Specifying this option is
1605           equivalent to specifying all the individual -f*-prefix-map options.
1606           This can be used to make reproducible builds that are location
1607           independent.  See also -fmacro-prefix-map, -fdebug-prefix-map and
1608           -fprofile-prefix-map.
1609
1610       -fplugin=name.so
1611           Load the plugin code in file name.so, assumed to be a shared object
1612           to be dlopen'd by the compiler.  The base name of the shared object
1613           file is used to identify the plugin for the purposes of argument
1614           parsing (See -fplugin-arg-name-key=value below).  Each plugin
1615           should define the callback functions specified in the Plugins API.
1616
1617       -fplugin-arg-name-key=value
1618           Define an argument called key with a value of value for the plugin
1619           called name.
1620
1621       -fdump-ada-spec[-slim]
1622           For C and C++ source and include files, generate corresponding Ada
1623           specs.
1624
1625       -fada-spec-parent=unit
1626           In conjunction with -fdump-ada-spec[-slim] above, generate Ada
1627           specs as child units of parent unit.
1628
1629       -fdump-go-spec=file
1630           For input files in any language, generate corresponding Go
1631           declarations in file.  This generates Go "const", "type", "var",
1632           and "func" declarations which may be a useful way to start writing
1633           a Go interface to code written in some other language.
1634
1635       @file
1636           Read command-line options from file.  The options read are inserted
1637           in place of the original @file option.  If file does not exist, or
1638           cannot be read, then the option will be treated literally, and not
1639           removed.
1640
1641           Options in file are separated by whitespace.  A whitespace
1642           character may be included in an option by surrounding the entire
1643           option in either single or double quotes.  Any character (including
1644           a backslash) may be included by prefixing the character to be
1645           included with a backslash.  The file may itself contain additional
1646           @file options; any such options will be processed recursively.
1647
1648   Compiling C++ Programs
1649       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
1650       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
1651       (for shared template code) .tcc; and preprocessed C++ files use the
1652       suffix .ii.  GCC recognizes files with these names and compiles them as
1653       C++ programs even if you call the compiler the same way as for
1654       compiling C programs (usually with the name gcc).
1655
1656       However, the use of gcc does not add the C++ library.  g++ is a program
1657       that calls GCC and automatically specifies linking against the C++
1658       library.  It treats .c, .h and .i files as C++ source files instead of
1659       C source files unless -x is used.  This program is also useful when
1660       precompiling a C header file with a .h extension for use in C++
1661       compilations.  On many systems, g++ is also installed with the name
1662       c++.
1663
1664       When you compile C++ programs, you may specify many of the same
1665       command-line options that you use for compiling programs in any
1666       language; or command-line options meaningful for C and related
1667       languages; or options that are meaningful only for C++ programs.
1668
1669   Options Controlling C Dialect
1670       The following options control the dialect of C (or languages derived
1671       from C, such as C++, Objective-C and Objective-C++) that the compiler
1672       accepts:
1673
1674       -ansi
1675           In C mode, this is equivalent to -std=c90. In C++ mode, it is
1676           equivalent to -std=c++98.
1677
1678           This turns off certain features of GCC that are incompatible with
1679           ISO C90 (when compiling C code), or of standard C++ (when compiling
1680           C++ code), such as the "asm" and "typeof" keywords, and predefined
1681           macros such as "unix" and "vax" that identify the type of system
1682           you are using.  It also enables the undesirable and rarely used ISO
1683           trigraph feature.  For the C compiler, it disables recognition of
1684           C++ style // comments as well as the "inline" keyword.
1685
1686           The alternate keywords "__asm__", "__extension__", "__inline__" and
1687           "__typeof__" continue to work despite -ansi.  You would not want to
1688           use them in an ISO C program, of course, but it is useful to put
1689           them in header files that might be included in compilations done
1690           with -ansi.  Alternate predefined macros such as "__unix__" and
1691           "__vax__" are also available, with or without -ansi.
1692
1693           The -ansi option does not cause non-ISO programs to be rejected
1694           gratuitously.  For that, -Wpedantic is required in addition to
1695           -ansi.
1696
1697           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
1698           used.  Some header files may notice this macro and refrain from
1699           declaring certain functions or defining certain macros that the ISO
1700           standard doesn't call for; this is to avoid interfering with any
1701           programs that might use these names for other things.
1702
1703           Functions that are normally built in but do not have semantics
1704           defined by ISO C (such as "alloca" and "ffs") are not built-in
1705           functions when -ansi is used.
1706
1707       -std=
1708           Determine the language standard.   This option is currently only
1709           supported when compiling C or C++.
1710
1711           The compiler can accept several base standards, such as c90 or
1712           c++98, and GNU dialects of those standards, such as gnu90 or
1713           gnu++98.  When a base standard is specified, the compiler accepts
1714           all programs following that standard plus those using GNU
1715           extensions that do not contradict it.  For example, -std=c90 turns
1716           off certain features of GCC that are incompatible with ISO C90,
1717           such as the "asm" and "typeof" keywords, but not other GNU
1718           extensions that do not have a meaning in ISO C90, such as omitting
1719           the middle term of a "?:" expression. On the other hand, when a GNU
1720           dialect of a standard is specified, all features supported by the
1721           compiler are enabled, even when those features change the meaning
1722           of the base standard.  As a result, some strict-conforming programs
1723           may be rejected.  The particular standard is used by -Wpedantic to
1724           identify which features are GNU extensions given that version of
1725           the standard. For example -std=gnu90 -Wpedantic warns about C++
1726           style // comments, while -std=gnu99 -Wpedantic does not.
1727
1728           A value for this option must be provided; possible values are
1729
1730           c90
1731           c89
1732           iso9899:1990
1733               Support all ISO C90 programs (certain GNU extensions that
1734               conflict with ISO C90 are disabled). Same as -ansi for C code.
1735
1736           iso9899:199409
1737               ISO C90 as modified in amendment 1.
1738
1739           c99
1740           c9x
1741           iso9899:1999
1742           iso9899:199x
1743               ISO C99.  This standard is substantially completely supported,
1744               modulo bugs and floating-point issues (mainly but not entirely
1745               relating to optional C99 features from Annexes F and G).  See
1746               <https://gcc.gnu.org/c99status.html> for more information.  The
1747               names c9x and iso9899:199x are deprecated.
1748
1749           c11
1750           c1x
1751           iso9899:2011
1752               ISO C11, the 2011 revision of the ISO C standard.  This
1753               standard is substantially completely supported, modulo bugs,
1754               floating-point issues (mainly but not entirely relating to
1755               optional C11 features from Annexes F and G) and the optional
1756               Annexes K (Bounds-checking interfaces) and L (Analyzability).
1757               The name c1x is deprecated.
1758
1759           c17
1760           c18
1761           iso9899:2017
1762           iso9899:2018
1763               ISO C17, the 2017 revision of the ISO C standard (published in
1764               2018).  This standard is same as C11 except for corrections of
1765               defects (all of which are also applied with -std=c11) and a new
1766               value of "__STDC_VERSION__", and so is supported to the same
1767               extent as C11.
1768
1769           c2x The next version of the ISO C standard, still under
1770               development.  The support for this version is experimental and
1771               incomplete.
1772
1773           gnu90
1774           gnu89
1775               GNU dialect of ISO C90 (including some C99 features).
1776
1777           gnu99
1778           gnu9x
1779               GNU dialect of ISO C99.  The name gnu9x is deprecated.
1780
1781           gnu11
1782           gnu1x
1783               GNU dialect of ISO C11.  The name gnu1x is deprecated.
1784
1785           gnu17
1786           gnu18
1787               GNU dialect of ISO C17.  This is the default for C code.
1788
1789           gnu2x
1790               The next version of the ISO C standard, still under
1791               development, plus GNU extensions.  The support for this version
1792               is experimental and incomplete.
1793
1794           c++98
1795           c++03
1796               The 1998 ISO C++ standard plus the 2003 technical corrigendum
1797               and some additional defect reports. Same as -ansi for C++ code.
1798
1799           gnu++98
1800           gnu++03
1801               GNU dialect of -std=c++98.
1802
1803           c++11
1804           c++0x
1805               The 2011 ISO C++ standard plus amendments.  The name c++0x is
1806               deprecated.
1807
1808           gnu++11
1809           gnu++0x
1810               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.
1811
1812           c++14
1813           c++1y
1814               The 2014 ISO C++ standard plus amendments.  The name c++1y is
1815               deprecated.
1816
1817           gnu++14
1818           gnu++1y
1819               GNU dialect of -std=c++14.  The name gnu++1y is deprecated.
1820
1821           c++17
1822           c++1z
1823               The 2017 ISO C++ standard plus amendments.  The name c++1z is
1824               deprecated.
1825
1826           gnu++17
1827           gnu++1z
1828               GNU dialect of -std=c++17.  This is the default for C++ code.
1829               The name gnu++1z is deprecated.
1830
1831           c++20
1832           c++2a
1833               The 2020 ISO C++ standard plus amendments.  Support is
1834               experimental, and could change in incompatible ways in future
1835               releases.  The name c++2a is deprecated.
1836
1837           gnu++20
1838           gnu++2a
1839               GNU dialect of -std=c++20.  Support is experimental, and could
1840               change in incompatible ways in future releases.  The name
1841               gnu++2a is deprecated.
1842
1843           c++2b
1844           c++23
1845               The next revision of the ISO C++ standard, planned for 2023.
1846               Support is highly experimental, and will almost certainly
1847               change in incompatible ways in future releases.
1848
1849           gnu++2b
1850           gnu++23
1851               GNU dialect of -std=c++2b.  Support is highly experimental, and
1852               will almost certainly change in incompatible ways in future
1853               releases.
1854
1855       -aux-info filename
1856           Output to the given filename prototyped declarations for all
1857           functions declared and/or defined in a translation unit, including
1858           those in header files.  This option is silently ignored in any
1859           language other than C.
1860
1861           Besides declarations, the file indicates, in comments, the origin
1862           of each declaration (source file and line), whether the declaration
1863           was implicit, prototyped or unprototyped (I, N for new or O for
1864           old, respectively, in the first character after the line number and
1865           the colon), and whether it came from a declaration or a definition
1866           (C or F, respectively, in the following character).  In the case of
1867           function definitions, a K&R-style list of arguments followed by
1868           their declarations is also provided, inside comments, after the
1869           declaration.
1870
1871       -fallow-parameterless-variadic-functions
1872           Accept variadic functions without named parameters.
1873
1874           Although it is possible to define such a function, this is not very
1875           useful as it is not possible to read the arguments.  This is only
1876           supported for C as this construct is allowed by C++.
1877
1878       -fno-asm
1879           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
1880           code can use these words as identifiers.  You can use the keywords
1881           "__asm__", "__inline__" and "__typeof__" instead.  In C, -ansi
1882           implies -fno-asm.
1883
1884           In C++, "inline" is a standard keyword and is not affected by this
1885           switch.  You may want to use the -fno-gnu-keywords flag instead,
1886           which disables "typeof" but not "asm" and "inline".  In C99 mode
1887           (-std=c99 or -std=gnu99), this switch only affects the "asm" and
1888           "typeof" keywords, since "inline" is a standard keyword in ISO C99.
1889
1890       -fno-builtin
1891       -fno-builtin-function
1892           Don't recognize built-in functions that do not begin with
1893           __builtin_ as prefix.
1894
1895           GCC normally generates special code to handle certain built-in
1896           functions more efficiently; for instance, calls to "alloca" may
1897           become single instructions which adjust the stack directly, and
1898           calls to "memcpy" may become inline copy loops.  The resulting code
1899           is often both smaller and faster, but since the function calls no
1900           longer appear as such, you cannot set a breakpoint on those calls,
1901           nor can you change the behavior of the functions by linking with a
1902           different library.  In addition, when a function is recognized as a
1903           built-in function, GCC may use information about that function to
1904           warn about problems with calls to that function, or to generate
1905           more efficient code, even if the resulting code still contains
1906           calls to that function.  For example, warnings are given with
1907           -Wformat for bad calls to "printf" when "printf" is built in and
1908           "strlen" is known not to modify global memory.
1909
1910           With the -fno-builtin-function option only the built-in function
1911           function is disabled.  function must not begin with __builtin_.  If
1912           a function is named that is not built-in in this version of GCC,
1913           this option is ignored.  There is no corresponding
1914           -fbuiltin-function option; if you wish to enable built-in functions
1915           selectively when using -fno-builtin or -ffreestanding, you may
1916           define macros such as:
1917
1918                   #define abs(n)          __builtin_abs ((n))
1919                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))
1920
1921       -fcond-mismatch
1922           Allow conditional expressions with mismatched types in the second
1923           and third arguments.  The value of such an expression is void.
1924           This option is not supported for C++.
1925
1926       -ffreestanding
1927           Assert that compilation targets a freestanding environment.  This
1928           implies -fno-builtin.  A freestanding environment is one in which
1929           the standard library may not exist, and program startup may not
1930           necessarily be at "main".  The most obvious example is an OS
1931           kernel.  This is equivalent to -fno-hosted.
1932
1933       -fgimple
1934           Enable parsing of function definitions marked with "__GIMPLE".
1935           This is an experimental feature that allows unit testing of GIMPLE
1936           passes.
1937
1938       -fgnu-tm
1939           When the option -fgnu-tm is specified, the compiler generates code
1940           for the Linux variant of Intel's current Transactional Memory ABI
1941           specification document (Revision 1.1, May 6 2009).  This is an
1942           experimental feature whose interface may change in future versions
1943           of GCC, as the official specification changes.  Please note that
1944           not all architectures are supported for this feature.
1945
1946           For more information on GCC's support for transactional memory,
1947
1948           Note that the transactional memory feature is not supported with
1949           non-call exceptions (-fnon-call-exceptions).
1950
1951       -fgnu89-inline
1952           The option -fgnu89-inline tells GCC to use the traditional GNU
1953           semantics for "inline" functions when in C99 mode.
1954
1955           Using this option is roughly equivalent to adding the "gnu_inline"
1956           function attribute to all inline functions.
1957
1958           The option -fno-gnu89-inline explicitly tells GCC to use the C99
1959           semantics for "inline" when in C99 or gnu99 mode (i.e., it
1960           specifies the default behavior).  This option is not supported in
1961           -std=c90 or -std=gnu90 mode.
1962
1963           The preprocessor macros "__GNUC_GNU_INLINE__" and
1964           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
1965           effect for "inline" functions.
1966
1967       -fhosted
1968           Assert that compilation targets a hosted environment.  This implies
1969           -fbuiltin.  A hosted environment is one in which the entire
1970           standard library is available, and in which "main" has a return
1971           type of "int".  Examples are nearly everything except a kernel.
1972           This is equivalent to -fno-freestanding.
1973
1974       -flax-vector-conversions
1975           Allow implicit conversions between vectors with differing numbers
1976           of elements and/or incompatible element types.  This option should
1977           not be used for new code.
1978
1979       -fms-extensions
1980           Accept some non-standard constructs used in Microsoft header files.
1981
1982           In C++ code, this allows member names in structures to be similar
1983           to previous types declarations.
1984
1985                   typedef int UOW;
1986                   struct ABC {
1987                     UOW UOW;
1988                   };
1989
1990           Some cases of unnamed fields in structures and unions are only
1991           accepted with this option.
1992
1993           Note that this option is off for all targets except for x86 targets
1994           using ms-abi.
1995
1996       -foffload=disable
1997       -foffload=default
1998       -foffload=target-list
1999           Specify for which OpenMP and OpenACC offload targets code should be
2000           generated.  The default behavior, equivalent to -foffload=default,
2001           is to generate code for all supported offload targets.  The
2002           -foffload=disable form generates code only for the host fallback,
2003           while -foffload=target-list generates code only for the specified
2004           comma-separated list of offload targets.
2005
2006           Offload targets are specified in GCC's internal target-triplet
2007           format. You can run the compiler with -v to show the list of
2008           configured offload targets under "OFFLOAD_TARGET_NAMES".
2009
2010       -foffload-options=options
2011       -foffload-options=target-triplet-list=options
2012           With -foffload-options=options, GCC passes the specified options to
2013           the compilers for all enabled offloading targets.  You can specify
2014           options that apply only to a specific target or targets by using
2015           the -foffload-options=target-list=options form.  The target-list is
2016           a comma-separated list in the same format as for the -foffload=
2017           option.
2018
2019           Typical command lines are
2020
2021                   -foffload-options=-lgfortran -foffload-options=-lm
2022                   -foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic
2023                   -foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm
2024
2025       -fopenacc
2026           Enable handling of OpenACC directives "#pragma acc" in C/C++ and
2027           "!$acc" in Fortran.  When -fopenacc is specified, the compiler
2028           generates accelerated code according to the OpenACC Application
2029           Programming Interface v2.6 <https://www.openacc.org>.  This option
2030           implies -pthread, and thus is only supported on targets that have
2031           support for -pthread.
2032
2033       -fopenacc-dim=geom
2034           Specify default compute dimensions for parallel offload regions
2035           that do not explicitly specify.  The geom value is a triple of
2036           ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A
2037           size can be omitted, to use a target-specific default value.
2038
2039       -fopenmp
2040           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
2041           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
2042           generates parallel code according to the OpenMP Application Program
2043           Interface v4.5 <https://www.openmp.org>.  This option implies
2044           -pthread, and thus is only supported on targets that have support
2045           for -pthread. -fopenmp implies -fopenmp-simd.
2046
2047       -fopenmp-simd
2048           Enable handling of OpenMP's SIMD directives with "#pragma omp" in
2049           C/C++ and "!$omp" in Fortran. Other OpenMP directives are ignored.
2050
2051       -fpermitted-flt-eval-methods=style
2052           ISO/IEC TS 18661-3 defines new permissible values for
2053           "FLT_EVAL_METHOD" that indicate that operations and constants with
2054           a semantic type that is an interchange or extended format should be
2055           evaluated to the precision and range of that type.  These new
2056           values are a superset of those permitted under C99/C11, which does
2057           not specify the meaning of other positive values of
2058           "FLT_EVAL_METHOD".  As such, code conforming to C11 may not have
2059           been written expecting the possibility of the new values.
2060
2061           -fpermitted-flt-eval-methods specifies whether the compiler should
2062           allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or
2063           the extended set of values specified in ISO/IEC TS 18661-3.
2064
2065           style is either "c11" or "ts-18661-3" as appropriate.
2066
2067           The default when in a standards compliant mode (-std=c11 or
2068           similar) is -fpermitted-flt-eval-methods=c11.  The default when in
2069           a GNU dialect (-std=gnu11 or similar) is
2070           -fpermitted-flt-eval-methods=ts-18661-3.
2071
2072       -fplan9-extensions
2073           Accept some non-standard constructs used in Plan 9 code.
2074
2075           This enables -fms-extensions, permits passing pointers to
2076           structures with anonymous fields to functions that expect pointers
2077           to elements of the type of the field, and permits referring to
2078           anonymous fields declared using a typedef.    This is only
2079           supported for C, not C++.
2080
2081       -fsigned-bitfields
2082       -funsigned-bitfields
2083       -fno-signed-bitfields
2084       -fno-unsigned-bitfields
2085           These options control whether a bit-field is signed or unsigned,
2086           when the declaration does not use either "signed" or "unsigned".
2087           By default, such a bit-field is signed, because this is consistent:
2088           the basic integer types such as "int" are signed types.
2089
2090       -fsigned-char
2091           Let the type "char" be signed, like "signed char".
2092
2093           Note that this is equivalent to -fno-unsigned-char, which is the
2094           negative form of -funsigned-char.  Likewise, the option
2095           -fno-signed-char is equivalent to -funsigned-char.
2096
2097       -funsigned-char
2098           Let the type "char" be unsigned, like "unsigned char".
2099
2100           Each kind of machine has a default for what "char" should be.  It
2101           is either like "unsigned char" by default or like "signed char" by
2102           default.
2103
2104           Ideally, a portable program should always use "signed char" or
2105           "unsigned char" when it depends on the signedness of an object.
2106           But many programs have been written to use plain "char" and expect
2107           it to be signed, or expect it to be unsigned, depending on the
2108           machines they were written for.  This option, and its inverse, let
2109           you make such a program work with the opposite default.
2110
2111           The type "char" is always a distinct type from each of "signed
2112           char" or "unsigned char", even though its behavior is always just
2113           like one of those two.
2114
2115       -fsso-struct=endianness
2116           Set the default scalar storage order of structures and unions to
2117           the specified endianness.  The accepted values are big-endian,
2118           little-endian and native for the native endianness of the target
2119           (the default).  This option is not supported for C++.
2120
2121           Warning: the -fsso-struct switch causes GCC to generate code that
2122           is not binary compatible with code generated without it if the
2123           specified endianness is not the native endianness of the target.
2124
2125   Options Controlling C++ Dialect
2126       This section describes the command-line options that are only
2127       meaningful for C++ programs.  You can also use most of the GNU compiler
2128       options regardless of what language your program is in.  For example,
2129       you might compile a file firstClass.C like this:
2130
2131               g++ -g -fstrict-enums -O -c firstClass.C
2132
2133       In this example, only -fstrict-enums is an option meant only for C++
2134       programs; you can use the other options with any language supported by
2135       GCC.
2136
2137       Some options for compiling C programs, such as -std, are also relevant
2138       for C++ programs.
2139
2140       Here is a list of options that are only for compiling C++ programs:
2141
2142       -fabi-version=n
2143           Use version n of the C++ ABI.  The default is version 0.
2144
2145           Version 0 refers to the version conforming most closely to the C++
2146           ABI specification.  Therefore, the ABI obtained using version 0
2147           will change in different versions of G++ as ABI bugs are fixed.
2148
2149           Version 1 is the version of the C++ ABI that first appeared in G++
2150           3.2.
2151
2152           Version 2 is the version of the C++ ABI that first appeared in G++
2153           3.4, and was the default through G++ 4.9.
2154
2155           Version 3 corrects an error in mangling a constant address as a
2156           template argument.
2157
2158           Version 4, which first appeared in G++ 4.5, implements a standard
2159           mangling for vector types.
2160
2161           Version 5, which first appeared in G++ 4.6, corrects the mangling
2162           of attribute const/volatile on function pointer types, decltype of
2163           a plain decl, and use of a function parameter in the declaration of
2164           another parameter.
2165
2166           Version 6, which first appeared in G++ 4.7, corrects the promotion
2167           behavior of C++11 scoped enums and the mangling of template
2168           argument packs, const/static_cast, prefix ++ and --, and a class
2169           scope function used as a template argument.
2170
2171           Version 7, which first appeared in G++ 4.8, that treats nullptr_t
2172           as a builtin type and corrects the mangling of lambdas in default
2173           argument scope.
2174
2175           Version 8, which first appeared in G++ 4.9, corrects the
2176           substitution behavior of function types with function-cv-
2177           qualifiers.
2178
2179           Version 9, which first appeared in G++ 5.2, corrects the alignment
2180           of "nullptr_t".
2181
2182           Version 10, which first appeared in G++ 6.1, adds mangling of
2183           attributes that affect type identity, such as ia32 calling
2184           convention attributes (e.g. stdcall).
2185
2186           Version 11, which first appeared in G++ 7, corrects the mangling of
2187           sizeof... expressions and operator names.  For multiple entities
2188           with the same name within a function, that are declared in
2189           different scopes, the mangling now changes starting with the
2190           twelfth occurrence.  It also implies -fnew-inheriting-ctors.
2191
2192           Version 12, which first appeared in G++ 8, corrects the calling
2193           conventions for empty classes on the x86_64 target and for classes
2194           with only deleted copy/move constructors.  It accidentally changes
2195           the calling convention for classes with a deleted copy constructor
2196           and a trivial move constructor.
2197
2198           Version 13, which first appeared in G++ 8.2, fixes the accidental
2199           change in version 12.
2200
2201           Version 14, which first appeared in G++ 10, corrects the mangling
2202           of the nullptr expression.
2203
2204           Version 15, which first appeared in G++ 11, changes the mangling of
2205           "__alignof__" to be distinct from that of "alignof", and dependent
2206           operator names.
2207
2208           See also -Wabi.
2209
2210       -fabi-compat-version=n
2211           On targets that support strong aliases, G++ works around mangling
2212           changes by creating an alias with the correct mangled name when
2213           defining a symbol with an incorrect mangled name.  This switch
2214           specifies which ABI version to use for the alias.
2215
2216           With -fabi-version=0 (the default), this defaults to 11 (GCC 7
2217           compatibility).  If another ABI version is explicitly selected,
2218           this defaults to 0.  For compatibility with GCC versions 3.2
2219           through 4.9, use -fabi-compat-version=2.
2220
2221           If this option is not provided but -Wabi=n is, that version is used
2222           for compatibility aliases.  If this option is provided along with
2223           -Wabi (without the version), the version from this option is used
2224           for the warning.
2225
2226       -fno-access-control
2227           Turn off all access checking.  This switch is mainly useful for
2228           working around bugs in the access control code.
2229
2230       -faligned-new
2231           Enable support for C++17 "new" of types that require more alignment
2232           than "void* ::operator new(std::size_t)" provides.  A numeric
2233           argument such as "-faligned-new=32" can be used to specify how much
2234           alignment (in bytes) is provided by that function, but few users
2235           will need to override the default of "alignof(std::max_align_t)".
2236
2237           This flag is enabled by default for -std=c++17.
2238
2239       -fchar8_t
2240       -fno-char8_t
2241           Enable support for "char8_t" as adopted for C++20.  This includes
2242           the addition of a new "char8_t" fundamental type, changes to the
2243           types of UTF-8 string and character literals, new signatures for
2244           user-defined literals, associated standard library updates, and new
2245           "__cpp_char8_t" and "__cpp_lib_char8_t" feature test macros.
2246
2247           This option enables functions to be overloaded for ordinary and
2248           UTF-8 strings:
2249
2250                   int f(const char *);    // #1
2251                   int f(const char8_t *); // #2
2252                   int v1 = f("text");     // Calls #1
2253                   int v2 = f(u8"text");   // Calls #2
2254
2255           and introduces new signatures for user-defined literals:
2256
2257                   int operator""_udl1(char8_t);
2258                   int v3 = u8'x'_udl1;
2259                   int operator""_udl2(const char8_t*, std::size_t);
2260                   int v4 = u8"text"_udl2;
2261                   template<typename T, T...> int operator""_udl3();
2262                   int v5 = u8"text"_udl3;
2263
2264           The change to the types of UTF-8 string and character literals
2265           introduces incompatibilities with ISO C++11 and later standards.
2266           For example, the following code is well-formed under ISO C++11, but
2267           is ill-formed when -fchar8_t is specified.
2268
2269                   char ca[] = u8"xx";     // error: char-array initialized from wide
2270                                           //        string
2271                   const char *cp = u8"xx";// error: invalid conversion from
2272                                           //        `const char8_t*' to `const char*'
2273                   int f(const char*);
2274                   auto v = f(u8"xx");     // error: invalid conversion from
2275                                           //        `const char8_t*' to `const char*'
2276                   std::string s{u8"xx"};  // error: no matching function for call to
2277                                           //        `std::basic_string<char>::basic_string()'
2278                   using namespace std::literals;
2279                   s = u8"xx"s;            // error: conversion from
2280                                           //        `basic_string<char8_t>' to non-scalar
2281                                           //        type `basic_string<char>' requested
2282
2283       -fcheck-new
2284           Check that the pointer returned by "operator new" is non-null
2285           before attempting to modify the storage allocated.  This check is
2286           normally unnecessary because the C++ standard specifies that
2287           "operator new" only returns 0 if it is declared "throw()", in which
2288           case the compiler always checks the return value even without this
2289           option.  In all other cases, when "operator new" has a non-empty
2290           exception specification, memory exhaustion is signalled by throwing
2291           "std::bad_alloc".  See also new (nothrow).
2292
2293       -fconcepts
2294       -fconcepts-ts
2295           Below -std=c++20, -fconcepts enables support for the C++ Extensions
2296           for Concepts Technical Specification, ISO 19217 (2015).
2297
2298           With -std=c++20 and above, Concepts are part of the language
2299           standard, so -fconcepts defaults to on.  But the standard
2300           specification of Concepts differs significantly from the TS, so
2301           some constructs that were allowed in the TS but didn't make it into
2302           the standard can still be enabled by -fconcepts-ts.
2303
2304       -fconstexpr-depth=n
2305           Set the maximum nested evaluation depth for C++11 constexpr
2306           functions to n.  A limit is needed to detect endless recursion
2307           during constant expression evaluation.  The minimum specified by
2308           the standard is 512.
2309
2310       -fconstexpr-cache-depth=n
2311           Set the maximum level of nested evaluation depth for C++11
2312           constexpr functions that will be cached to n.  This is a heuristic
2313           that trades off compilation speed (when the cache avoids repeated
2314           calculations) against memory consumption (when the cache grows very
2315           large from highly recursive evaluations).  The default is 8.  Very
2316           few users are likely to want to adjust it, but if your code does
2317           heavy constexpr calculations you might want to experiment to find
2318           which value works best for you.
2319
2320       -fconstexpr-fp-except
2321           Annex F of the C standard specifies that IEC559 floating point
2322           exceptions encountered at compile time should not stop compilation.
2323           C++ compilers have historically not followed this guidance, instead
2324           treating floating point division by zero as non-constant even
2325           though it has a well defined value.  This flag tells the compiler
2326           to give Annex F priority over other rules saying that a particular
2327           operation is undefined.
2328
2329                   constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except
2330
2331       -fconstexpr-loop-limit=n
2332           Set the maximum number of iterations for a loop in C++14 constexpr
2333           functions to n.  A limit is needed to detect infinite loops during
2334           constant expression evaluation.  The default is 262144 (1<<18).
2335
2336       -fconstexpr-ops-limit=n
2337           Set the maximum number of operations during a single constexpr
2338           evaluation.  Even when number of iterations of a single loop is
2339           limited with the above limit, if there are several nested loops and
2340           each of them has many iterations but still smaller than the above
2341           limit, or if in a body of some loop or even outside of a loop too
2342           many expressions need to be evaluated, the resulting constexpr
2343           evaluation might take too long.  The default is 33554432 (1<<25).
2344
2345       -fcoroutines
2346           Enable support for the C++ coroutines extension (experimental).
2347
2348       -fno-elide-constructors
2349           The C++ standard allows an implementation to omit creating a
2350           temporary that is only used to initialize another object of the
2351           same type.  Specifying this option disables that optimization, and
2352           forces G++ to call the copy constructor in all cases.  This option
2353           also causes G++ to call trivial member functions which otherwise
2354           would be expanded inline.
2355
2356           In C++17, the compiler is required to omit these temporaries, but
2357           this option still affects trivial member functions.
2358
2359       -fno-enforce-eh-specs
2360           Don't generate code to check for violation of exception
2361           specifications at run time.  This option violates the C++ standard,
2362           but may be useful for reducing code size in production builds, much
2363           like defining "NDEBUG".  This does not give user code permission to
2364           throw exceptions in violation of the exception specifications; the
2365           compiler still optimizes based on the specifications, so throwing
2366           an unexpected exception results in undefined behavior at run time.
2367
2368       -fextern-tls-init
2369       -fno-extern-tls-init
2370           The C++11 and OpenMP standards allow "thread_local" and
2371           "threadprivate" variables to have dynamic (runtime) initialization.
2372           To support this, any use of such a variable goes through a wrapper
2373           function that performs any necessary initialization.  When the use
2374           and definition of the variable are in the same translation unit,
2375           this overhead can be optimized away, but when the use is in a
2376           different translation unit there is significant overhead even if
2377           the variable doesn't actually need dynamic initialization.  If the
2378           programmer can be sure that no use of the variable in a non-
2379           defining TU needs to trigger dynamic initialization (either because
2380           the variable is statically initialized, or a use of the variable in
2381           the defining TU will be executed before any uses in another TU),
2382           they can avoid this overhead with the -fno-extern-tls-init option.
2383
2384           On targets that support symbol aliases, the default is
2385           -fextern-tls-init.  On targets that do not support symbol aliases,
2386           the default is -fno-extern-tls-init.
2387
2388       -ffold-simple-inlines
2389       -fno-fold-simple-inlines
2390           Permit the C++ frontend to fold calls to "std::move",
2391           "std::forward", "std::addressof" and "std::as_const".  In contrast
2392           to inlining, this means no debug information will be generated for
2393           such calls.  Since these functions are rarely interesting to debug,
2394           this flag is enabled by default unless -fno-inline is active.
2395
2396       -fno-gnu-keywords
2397           Do not recognize "typeof" as a keyword, so that code can use this
2398           word as an identifier.  You can use the keyword "__typeof__"
2399           instead.  This option is implied by the strict ISO C++ dialects:
2400           -ansi, -std=c++98, -std=c++11, etc.
2401
2402       -fimplicit-constexpr
2403           Make inline functions implicitly constexpr, if they satisfy the
2404           requirements for a constexpr function.  This option can be used in
2405           C++14 mode or later.  This can result in initialization changing
2406           from dynamic to static and other optimizations.
2407
2408       -fno-implicit-templates
2409           Never emit code for non-inline templates that are instantiated
2410           implicitly (i.e. by use); only emit code for explicit
2411           instantiations.  If you use this option, you must take care to
2412           structure your code to include all the necessary explicit
2413           instantiations to avoid getting undefined symbols at link time.
2414
2415       -fno-implicit-inline-templates
2416           Don't emit code for implicit instantiations of inline templates,
2417           either.  The default is to handle inlines differently so that
2418           compiles with and without optimization need the same set of
2419           explicit instantiations.
2420
2421       -fno-implement-inlines
2422           To save space, do not emit out-of-line copies of inline functions
2423           controlled by "#pragma implementation".  This causes linker errors
2424           if these functions are not inlined everywhere they are called.
2425
2426       -fmodules-ts
2427       -fno-modules-ts
2428           Enable support for C++20 modules.  The -fno-modules-ts is usually
2429           not needed, as that is the default.  Even though this is a C++20
2430           feature, it is not currently implicitly enabled by selecting that
2431           standard version.
2432
2433       -fmodule-header
2434       -fmodule-header=user
2435       -fmodule-header=system
2436           Compile a header file to create an importable header unit.
2437
2438       -fmodule-implicit-inline
2439           Member functions defined in their class definitions are not
2440           implicitly inline for modular code.  This is different to
2441           traditional C++ behavior, for good reasons.  However, it may result
2442           in a difficulty during code porting.  This option makes such
2443           function definitions implicitly inline.  It does however generate
2444           an ABI incompatibility, so you must use it everywhere or nowhere.
2445           (Such definitions outside of a named module remain implicitly
2446           inline, regardless.)
2447
2448       -fno-module-lazy
2449           Disable lazy module importing and module mapper creation.
2450
2451       -fmodule-mapper=[hostname]:port[?ident]
2452       -fmodule-mapper=|program[?ident] args...
2453       -fmodule-mapper==socket[?ident]
2454       -fmodule-mapper=<>[inout][?ident]
2455       -fmodule-mapper=<in>out[?ident]
2456       -fmodule-mapper=file[?ident]
2457           An oracle to query for module name to filename mappings.  If
2458           unspecified the CXX_MODULE_MAPPER environment variable is used, and
2459           if that is unset, an in-process default is provided.
2460
2461       -fmodule-only
2462           Only emit the Compiled Module Interface, inhibiting any object
2463           file.
2464
2465       -fms-extensions
2466           Disable Wpedantic warnings about constructs used in MFC, such as
2467           implicit int and getting a pointer to member function via non-
2468           standard syntax.
2469
2470       -fnew-inheriting-ctors
2471           Enable the P0136 adjustment to the semantics of C++11 constructor
2472           inheritance.  This is part of C++17 but also considered to be a
2473           Defect Report against C++11 and C++14.  This flag is enabled by
2474           default unless -fabi-version=10 or lower is specified.
2475
2476       -fnew-ttp-matching
2477           Enable the P0522 resolution to Core issue 150, template template
2478           parameters and default arguments: this allows a template with
2479           default template arguments as an argument for a template template
2480           parameter with fewer template parameters.  This flag is enabled by
2481           default for -std=c++17.
2482
2483       -fno-nonansi-builtins
2484           Disable built-in declarations of functions that are not mandated by
2485           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
2486           "bzero", "conjf", and other related functions.
2487
2488       -fnothrow-opt
2489           Treat a "throw()" exception specification as if it were a
2490           "noexcept" specification to reduce or eliminate the text size
2491           overhead relative to a function with no exception specification.
2492           If the function has local variables of types with non-trivial
2493           destructors, the exception specification actually makes the
2494           function smaller because the EH cleanups for those variables can be
2495           optimized away.  The semantic effect is that an exception thrown
2496           out of a function with such an exception specification results in a
2497           call to "terminate" rather than "unexpected".
2498
2499       -fno-operator-names
2500           Do not treat the operator name keywords "and", "bitand", "bitor",
2501           "compl", "not", "or" and "xor" as synonyms as keywords.
2502
2503       -fno-optional-diags
2504           Disable diagnostics that the standard says a compiler does not need
2505           to issue.  Currently, the only such diagnostic issued by G++ is the
2506           one for a name having multiple meanings within a class.
2507
2508       -fpermissive
2509           Downgrade some diagnostics about nonconformant code from errors to
2510           warnings.  Thus, using -fpermissive allows some nonconforming code
2511           to compile.
2512
2513       -fno-pretty-templates
2514           When an error message refers to a specialization of a function
2515           template, the compiler normally prints the signature of the
2516           template followed by the template arguments and any typedefs or
2517           typenames in the signature (e.g. "void f(T) [with T = int]" rather
2518           than "void f(int)") so that it's clear which template is involved.
2519           When an error message refers to a specialization of a class
2520           template, the compiler omits any template arguments that match the
2521           default template arguments for that template.  If either of these
2522           behaviors make it harder to understand the error message rather
2523           than easier, you can use -fno-pretty-templates to disable them.
2524
2525       -fno-rtti
2526           Disable generation of information about every class with virtual
2527           functions for use by the C++ run-time type identification features
2528           ("dynamic_cast" and "typeid").  If you don't use those parts of the
2529           language, you can save some space by using this flag.  Note that
2530           exception handling uses the same information, but G++ generates it
2531           as needed. The "dynamic_cast" operator can still be used for casts
2532           that do not require run-time type information, i.e. casts to "void
2533           *" or to unambiguous base classes.
2534
2535           Mixing code compiled with -frtti with that compiled with -fno-rtti
2536           may not work.  For example, programs may fail to link if a class
2537           compiled with -fno-rtti is used as a base for a class compiled with
2538           -frtti.
2539
2540       -fsized-deallocation
2541           Enable the built-in global declarations
2542
2543                   void operator delete (void *, std::size_t) noexcept;
2544                   void operator delete[] (void *, std::size_t) noexcept;
2545
2546           as introduced in C++14.  This is useful for user-defined
2547           replacement deallocation functions that, for example, use the size
2548           of the object to make deallocation faster.  Enabled by default
2549           under -std=c++14 and above.  The flag -Wsized-deallocation warns
2550           about places that might want to add a definition.
2551
2552       -fstrict-enums
2553           Allow the compiler to optimize using the assumption that a value of
2554           enumerated type can only be one of the values of the enumeration
2555           (as defined in the C++ standard; basically, a value that can be
2556           represented in the minimum number of bits needed to represent all
2557           the enumerators).  This assumption may not be valid if the program
2558           uses a cast to convert an arbitrary integer value to the enumerated
2559           type.
2560
2561       -fstrong-eval-order
2562           Evaluate member access, array subscripting, and shift expressions
2563           in left-to-right order, and evaluate assignment in right-to-left
2564           order, as adopted for C++17.  Enabled by default with -std=c++17.
2565           -fstrong-eval-order=some enables just the ordering of member access
2566           and shift expressions, and is the default without -std=c++17.
2567
2568       -ftemplate-backtrace-limit=n
2569           Set the maximum number of template instantiation notes for a single
2570           warning or error to n.  The default value is 10.
2571
2572       -ftemplate-depth=n
2573           Set the maximum instantiation depth for template classes to n.  A
2574           limit on the template instantiation depth is needed to detect
2575           endless recursions during template class instantiation.  ANSI/ISO
2576           C++ conforming programs must not rely on a maximum depth greater
2577           than 17 (changed to 1024 in C++11).  The default value is 900, as
2578           the compiler can run out of stack space before hitting 1024 in some
2579           situations.
2580
2581       -fno-threadsafe-statics
2582           Do not emit the extra code to use the routines specified in the C++
2583           ABI for thread-safe initialization of local statics.  You can use
2584           this option to reduce code size slightly in code that doesn't need
2585           to be thread-safe.
2586
2587       -fuse-cxa-atexit
2588           Register destructors for objects with static storage duration with
2589           the "__cxa_atexit" function rather than the "atexit" function.
2590           This option is required for fully standards-compliant handling of
2591           static destructors, but only works if your C library supports
2592           "__cxa_atexit".
2593
2594       -fno-use-cxa-get-exception-ptr
2595           Don't use the "__cxa_get_exception_ptr" runtime routine.  This
2596           causes "std::uncaught_exception" to be incorrect, but is necessary
2597           if the runtime routine is not available.
2598
2599       -fvisibility-inlines-hidden
2600           This switch declares that the user does not attempt to compare
2601           pointers to inline functions or methods where the addresses of the
2602           two functions are taken in different shared objects.
2603
2604           The effect of this is that GCC may, effectively, mark inline
2605           methods with "__attribute__ ((visibility ("hidden")))" so that they
2606           do not appear in the export table of a DSO and do not require a PLT
2607           indirection when used within the DSO.  Enabling this option can
2608           have a dramatic effect on load and link times of a DSO as it
2609           massively reduces the size of the dynamic export table when the
2610           library makes heavy use of templates.
2611
2612           The behavior of this switch is not quite the same as marking the
2613           methods as hidden directly, because it does not affect static
2614           variables local to the function or cause the compiler to deduce
2615           that the function is defined in only one shared object.
2616
2617           You may mark a method as having a visibility explicitly to negate
2618           the effect of the switch for that method.  For example, if you do
2619           want to compare pointers to a particular inline method, you might
2620           mark it as having default visibility.  Marking the enclosing class
2621           with explicit visibility has no effect.
2622
2623           Explicitly instantiated inline methods are unaffected by this
2624           option as their linkage might otherwise cross a shared library
2625           boundary.
2626
2627       -fvisibility-ms-compat
2628           This flag attempts to use visibility settings to make GCC's C++
2629           linkage model compatible with that of Microsoft Visual Studio.
2630
2631           The flag makes these changes to GCC's linkage model:
2632
2633           1.  It sets the default visibility to "hidden", like
2634               -fvisibility=hidden.
2635
2636           2.  Types, but not their members, are not hidden by default.
2637
2638           3.  The One Definition Rule is relaxed for types without explicit
2639               visibility specifications that are defined in more than one
2640               shared object: those declarations are permitted if they are
2641               permitted when this option is not used.
2642
2643           In new code it is better to use -fvisibility=hidden and export
2644           those classes that are intended to be externally visible.
2645           Unfortunately it is possible for code to rely, perhaps
2646           accidentally, on the Visual Studio behavior.
2647
2648           Among the consequences of these changes are that static data
2649           members of the same type with the same name but defined in
2650           different shared objects are different, so changing one does not
2651           change the other; and that pointers to function members defined in
2652           different shared objects may not compare equal.  When this flag is
2653           given, it is a violation of the ODR to define types with the same
2654           name differently.
2655
2656       -fno-weak
2657           Do not use weak symbol support, even if it is provided by the
2658           linker.  By default, G++ uses weak symbols if they are available.
2659           This option exists only for testing, and should not be used by end-
2660           users; it results in inferior code and has no benefits.  This
2661           option may be removed in a future release of G++.
2662
2663       -fext-numeric-literals (C++ and Objective-C++ only)
2664           Accept imaginary, fixed-point, or machine-defined literal number
2665           suffixes as GNU extensions.  When this option is turned off these
2666           suffixes are treated as C++11 user-defined literal numeric
2667           suffixes.  This is on by default for all pre-C++11 dialects and all
2668           GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14.
2669           This option is off by default for ISO C++11 onwards (-std=c++11,
2670           ...).
2671
2672       -nostdinc++
2673           Do not search for header files in the standard directories specific
2674           to C++, but do still search the other standard directories.  (This
2675           option is used when building the C++ library.)
2676
2677       -flang-info-include-translate
2678       -flang-info-include-translate-not
2679       -flang-info-include-translate=header
2680           Inform of include translation events.  The first will note accepted
2681           include translations, the second will note declined include
2682           translations.  The header form will inform of include translations
2683           relating to that specific header.  If header is of the form "user"
2684           or "<system>" it will be resolved to a specific user or system
2685           header using the include path.
2686
2687       -flang-info-module-cmi
2688       -flang-info-module-cmi=module
2689           Inform of Compiled Module Interface pathnames.  The first will note
2690           all read CMI pathnames.  The module form will not reading a
2691           specific module's CMI.  module may be a named module or a header-
2692           unit (the latter indicated by either being a pathname containing
2693           directory separators or enclosed in "<>" or "").
2694
2695       -stdlib=libstdc++,libc++
2696           When G++ is configured to support this option, it allows
2697           specification of alternate C++ runtime libraries.  Two options are
2698           available: libstdc++ (the default, native C++ runtime for G++) and
2699           libc++ which is the C++ runtime installed on some operating systems
2700           (e.g. Darwin versions from Darwin11 onwards).  The option switches
2701           G++ to use the headers from the specified library and to emit
2702           "-lstdc++" or "-lc++" respectively, when a C++ runtime is required
2703           for linking.
2704
2705       In addition, these warning options have meanings only for C++ programs:
2706
2707       -Wabi-tag (C++ and Objective-C++ only)
2708           Warn when a type with an ABI tag is used in a context that does not
2709           have that ABI tag.  See C++ Attributes for more information about
2710           ABI tags.
2711
2712       -Wcomma-subscript (C++ and Objective-C++ only)
2713           Warn about uses of a comma expression within a subscripting
2714           expression.  This usage was deprecated in C++20 and is going to be
2715           removed in C++23.  However, a comma expression wrapped in "( )" is
2716           not deprecated.  Example:
2717
2718                   void f(int *a, int b, int c) {
2719                       a[b,c];     // deprecated in C++20, invalid in C++23
2720                       a[(b,c)];   // OK
2721                   }
2722
2723           In C++23 it is valid to have comma separated expressions in a
2724           subscript when an overloaded subscript operator is found and
2725           supports the right number and types of arguments.  G++ will accept
2726           the formerly valid syntax for code that is not valid in C++23 but
2727           used to be valid but deprecated in C++20 with a pedantic warning
2728           that can be disabled with -Wno-comma-subscript.
2729
2730           Enabled by default with -std=c++20 unless -Wno-deprecated, and with
2731           -std=c++23 regardless of -Wno-deprecated.
2732
2733       -Wctad-maybe-unsupported (C++ and Objective-C++ only)
2734           Warn when performing class template argument deduction (CTAD) on a
2735           type with no explicitly written deduction guides.  This warning
2736           will point out cases where CTAD succeeded only because the compiler
2737           synthesized the implicit deduction guides, which might not be what
2738           the programmer intended.  Certain style guides allow CTAD only on
2739           types that specifically "opt-in"; i.e., on types that are designed
2740           to support CTAD.  This warning can be suppressed with the following
2741           pattern:
2742
2743                   struct allow_ctad_t; // any name works
2744                   template <typename T> struct S {
2745                     S(T) { }
2746                   };
2747                   S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered
2748
2749       -Wctor-dtor-privacy (C++ and Objective-C++ only)
2750           Warn when a class seems unusable because all the constructors or
2751           destructors in that class are private, and it has neither friends
2752           nor public static member functions.  Also warn if there are no non-
2753           private methods, and there's at least one private member function
2754           that isn't a constructor or destructor.
2755
2756       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
2757           Warn when "delete" is used to destroy an instance of a class that
2758           has virtual functions and non-virtual destructor. It is unsafe to
2759           delete an instance of a derived class through a pointer to a base
2760           class if the base class does not have a virtual destructor.  This
2761           warning is enabled by -Wall.
2762
2763       -Wdeprecated-copy (C++ and Objective-C++ only)
2764           Warn that the implicit declaration of a copy constructor or copy
2765           assignment operator is deprecated if the class has a user-provided
2766           copy constructor or copy assignment operator, in C++11 and up.
2767           This warning is enabled by -Wextra.  With -Wdeprecated-copy-dtor,
2768           also deprecate if the class has a user-provided destructor.
2769
2770       -Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only)
2771           Disable the warning about the case when the usual arithmetic
2772           conversions are applied on operands where one is of enumeration
2773           type and the other is of a different enumeration type.  This
2774           conversion was deprecated in C++20.  For example:
2775
2776                   enum E1 { e };
2777                   enum E2 { f };
2778                   int k = f - e;
2779
2780           -Wdeprecated-enum-enum-conversion is enabled by default with
2781           -std=c++20.  In pre-C++20 dialects, this warning can be enabled by
2782           -Wenum-conversion.
2783
2784       -Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only)
2785           Disable the warning about the case when the usual arithmetic
2786           conversions are applied on operands where one is of enumeration
2787           type and the other is of a floating-point type.  This conversion
2788           was deprecated in C++20.  For example:
2789
2790                   enum E1 { e };
2791                   enum E2 { f };
2792                   bool b = e <= 3.7;
2793
2794           -Wdeprecated-enum-float-conversion is enabled by default with
2795           -std=c++20.  In pre-C++20 dialects, this warning can be enabled by
2796           -Wenum-conversion.
2797
2798       -Wno-init-list-lifetime (C++ and Objective-C++ only)
2799           Do not warn about uses of "std::initializer_list" that are likely
2800           to result in dangling pointers.  Since the underlying array for an
2801           "initializer_list" is handled like a normal C++ temporary object,
2802           it is easy to inadvertently keep a pointer to the array past the
2803           end of the array's lifetime.  For example:
2804
2805           *   If a function returns a temporary "initializer_list", or a
2806               local "initializer_list" variable, the array's lifetime ends at
2807               the end of the return statement, so the value returned has a
2808               dangling pointer.
2809
2810           *   If a new-expression creates an "initializer_list", the array
2811               only lives until the end of the enclosing full-expression, so
2812               the "initializer_list" in the heap has a dangling pointer.
2813
2814           *   When an "initializer_list" variable is assigned from a brace-
2815               enclosed initializer list, the temporary array created for the
2816               right side of the assignment only lives until the end of the
2817               full-expression, so at the next statement the
2818               "initializer_list" variable has a dangling pointer.
2819
2820                       // li's initial underlying array lives as long as li
2821                       std::initializer_list<int> li = { 1,2,3 };
2822                       // assignment changes li to point to a temporary array
2823                       li = { 4, 5 };
2824                       // now the temporary is gone and li has a dangling pointer
2825                       int i = li.begin()[0] // undefined behavior
2826
2827           *   When a list constructor stores the "begin" pointer from the
2828               "initializer_list" argument, this doesn't extend the lifetime
2829               of the array, so if a class variable is constructed from a
2830               temporary "initializer_list", the pointer is left dangling by
2831               the end of the variable declaration statement.
2832
2833       -Winvalid-imported-macros
2834           Verify all imported macro definitions are valid at the end of
2835           compilation.  This is not enabled by default, as it requires
2836           additional processing to determine.  It may be useful when
2837           preparing sets of header-units to ensure consistent macros.
2838
2839       -Wno-literal-suffix (C++ and Objective-C++ only)
2840           Do not warn when a string or character literal is followed by a ud-
2841           suffix which does not begin with an underscore.  As a conforming
2842           extension, GCC treats such suffixes as separate preprocessing
2843           tokens in order to maintain backwards compatibility with code that
2844           uses formatting macros from "<inttypes.h>".  For example:
2845
2846                   #define __STDC_FORMAT_MACROS
2847                   #include <inttypes.h>
2848                   #include <stdio.h>
2849
2850                   int main() {
2851                     int64_t i64 = 123;
2852                     printf("My int64: %" PRId64"\n", i64);
2853                   }
2854
2855           In this case, "PRId64" is treated as a separate preprocessing
2856           token.
2857
2858           This option also controls warnings when a user-defined literal
2859           operator is declared with a literal suffix identifier that doesn't
2860           begin with an underscore. Literal suffix identifiers that don't
2861           begin with an underscore are reserved for future standardization.
2862
2863           These warnings are enabled by default.
2864
2865       -Wno-narrowing (C++ and Objective-C++ only)
2866           For C++11 and later standards, narrowing conversions are diagnosed
2867           by default, as required by the standard.  A narrowing conversion
2868           from a constant produces an error, and a narrowing conversion from
2869           a non-constant produces a warning, but -Wno-narrowing suppresses
2870           the diagnostic.  Note that this does not affect the meaning of
2871           well-formed code; narrowing conversions are still considered ill-
2872           formed in SFINAE contexts.
2873
2874           With -Wnarrowing in C++98, warn when a narrowing conversion
2875           prohibited by C++11 occurs within { }, e.g.
2876
2877                   int i = { 2.2 }; // error: narrowing from double to int
2878
2879           This flag is included in -Wall and -Wc++11-compat.
2880
2881       -Wnoexcept (C++ and Objective-C++ only)
2882           Warn when a noexcept-expression evaluates to false because of a
2883           call to a function that does not have a non-throwing exception
2884           specification (i.e. "throw()" or "noexcept") but is known by the
2885           compiler to never throw an exception.
2886
2887       -Wnoexcept-type (C++ and Objective-C++ only)
2888           Warn if the C++17 feature making "noexcept" part of a function type
2889           changes the mangled name of a symbol relative to C++14.  Enabled by
2890           -Wabi and -Wc++17-compat.
2891
2892           As an example:
2893
2894                   template <class T> void f(T t) { t(); };
2895                   void g() noexcept;
2896                   void h() { f(g); }
2897
2898           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls
2899           "f<void(*)()noexcept>".
2900
2901       -Wclass-memaccess (C++ and Objective-C++ only)
2902           Warn when the destination of a call to a raw memory function such
2903           as "memset" or "memcpy" is an object of class type, and when
2904           writing into such an object might bypass the class non-trivial or
2905           deleted constructor or copy assignment, violate const-correctness
2906           or encapsulation, or corrupt virtual table pointers.  Modifying the
2907           representation of such objects may violate invariants maintained by
2908           member functions of the class.  For example, the call to "memset"
2909           below is undefined because it modifies a non-trivial class object
2910           and is, therefore, diagnosed.  The safe way to either initialize or
2911           clear the storage of objects of such types is by using the
2912           appropriate constructor or assignment operator, if one is
2913           available.
2914
2915                   std::string str = "abc";
2916                   memset (&str, 0, sizeof str);
2917
2918           The -Wclass-memaccess option is enabled by -Wall.  Explicitly
2919           casting the pointer to the class object to "void *" or to a type
2920           that can be safely accessed by the raw memory function suppresses
2921           the warning.
2922
2923       -Wnon-virtual-dtor (C++ and Objective-C++ only)
2924           Warn when a class has virtual functions and an accessible non-
2925           virtual destructor itself or in an accessible polymorphic base
2926           class, in which case it is possible but unsafe to delete an
2927           instance of a derived class through a pointer to the class itself
2928           or base class.  This warning is automatically enabled if -Weffc++
2929           is specified.
2930
2931       -Wregister (C++ and Objective-C++ only)
2932           Warn on uses of the "register" storage class specifier, except when
2933           it is part of the GNU Explicit Register Variables extension.  The
2934           use of the "register" keyword as storage class specifier has been
2935           deprecated in C++11 and removed in C++17.  Enabled by default with
2936           -std=c++17.
2937
2938       -Wreorder (C++ and Objective-C++ only)
2939           Warn when the order of member initializers given in the code does
2940           not match the order in which they must be executed.  For instance:
2941
2942                   struct A {
2943                     int i;
2944                     int j;
2945                     A(): j (0), i (1) { }
2946                   };
2947
2948           The compiler rearranges the member initializers for "i" and "j" to
2949           match the declaration order of the members, emitting a warning to
2950           that effect.  This warning is enabled by -Wall.
2951
2952       -Wno-pessimizing-move (C++ and Objective-C++ only)
2953           This warning warns when a call to "std::move" prevents copy
2954           elision.  A typical scenario when copy elision can occur is when
2955           returning in a function with a class return type, when the
2956           expression being returned is the name of a non-volatile automatic
2957           object, and is not a function parameter, and has the same type as
2958           the function return type.
2959
2960                   struct T {
2961                   ...
2962                   };
2963                   T fn()
2964                   {
2965                     T t;
2966                     ...
2967                     return std::move (t);
2968                   }
2969
2970           But in this example, the "std::move" call prevents copy elision.
2971
2972           This warning is enabled by -Wall.
2973
2974       -Wno-redundant-move (C++ and Objective-C++ only)
2975           This warning warns about redundant calls to "std::move"; that is,
2976           when a move operation would have been performed even without the
2977           "std::move" call.  This happens because the compiler is forced to
2978           treat the object as if it were an rvalue in certain situations such
2979           as returning a local variable, where copy elision isn't applicable.
2980           Consider:
2981
2982                   struct T {
2983                   ...
2984                   };
2985                   T fn(T t)
2986                   {
2987                     ...
2988                     return std::move (t);
2989                   }
2990
2991           Here, the "std::move" call is redundant.  Because G++ implements
2992           Core Issue 1579, another example is:
2993
2994                   struct T { // convertible to U
2995                   ...
2996                   };
2997                   struct U {
2998                   ...
2999                   };
3000                   U fn()
3001                   {
3002                     T t;
3003                     ...
3004                     return std::move (t);
3005                   }
3006
3007           In this example, copy elision isn't applicable because the type of
3008           the expression being returned and the function return type differ,
3009           yet G++ treats the return value as if it were designated by an
3010           rvalue.
3011
3012           This warning is enabled by -Wextra.
3013
3014       -Wrange-loop-construct (C++ and Objective-C++ only)
3015           This warning warns when a C++ range-based for-loop is creating an
3016           unnecessary copy.  This can happen when the range declaration is
3017           not a reference, but probably should be.  For example:
3018
3019                   struct S { char arr[128]; };
3020                   void fn () {
3021                     S arr[5];
3022                     for (const auto x : arr) { ... }
3023                   }
3024
3025           It does not warn when the type being copied is a trivially-copyable
3026           type whose size is less than 64 bytes.
3027
3028           This warning also warns when a loop variable in a range-based for-
3029           loop is initialized with a value of a different type resulting in a
3030           copy.  For example:
3031
3032                   void fn() {
3033                     int arr[10];
3034                     for (const double &x : arr) { ... }
3035                   }
3036
3037           In the example above, in every iteration of the loop a temporary
3038           value of type "double" is created and destroyed, to which the
3039           reference "const double &" is bound.
3040
3041           This warning is enabled by -Wall.
3042
3043       -Wredundant-tags (C++ and Objective-C++ only)
3044           Warn about redundant class-key and enum-key in references to class
3045           types and enumerated types in contexts where the key can be
3046           eliminated without causing an ambiguity.  For example:
3047
3048                   struct foo;
3049                   struct foo *p;   // warn that keyword struct can be eliminated
3050
3051           On the other hand, in this example there is no warning:
3052
3053                   struct foo;
3054                   void foo ();   // "hides" struct foo
3055                   void bar (struct foo&);  // no warning, keyword struct is necessary
3056
3057       -Wno-subobject-linkage (C++ and Objective-C++ only)
3058           Do not warn if a class type has a base or a field whose type uses
3059           the anonymous namespace or depends on a type with no linkage.  If a
3060           type A depends on a type B with no or internal linkage, defining it
3061           in multiple translation units would be an ODR violation because the
3062           meaning of B is different in each translation unit.  If A only
3063           appears in a single translation unit, the best way to silence the
3064           warning is to give it internal linkage by putting it in an
3065           anonymous namespace as well.  The compiler doesn't give this
3066           warning for types defined in the main .C file, as those are
3067           unlikely to have multiple definitions.  -Wsubobject-linkage is
3068           enabled by default.
3069
3070       -Weffc++ (C++ and Objective-C++ only)
3071           Warn about violations of the following style guidelines from Scott
3072           Meyers' Effective C++ series of books:
3073
3074           *   Define a copy constructor and an assignment operator for
3075               classes with dynamically-allocated memory.
3076
3077           *   Prefer initialization to assignment in constructors.
3078
3079           *   Have "operator=" return a reference to *this.
3080
3081           *   Don't try to return a reference when you must return an object.
3082
3083           *   Distinguish between prefix and postfix forms of increment and
3084               decrement operators.
3085
3086           *   Never overload "&&", "||", or ",".
3087
3088           This option also enables -Wnon-virtual-dtor, which is also one of
3089           the effective C++ recommendations.  However, the check is extended
3090           to warn about the lack of virtual destructor in accessible non-
3091           polymorphic bases classes too.
3092
3093           When selecting this option, be aware that the standard library
3094           headers do not obey all of these guidelines; use grep -v to filter
3095           out those warnings.
3096
3097       -Wno-exceptions (C++ and Objective-C++ only)
3098           Disable the warning about the case when an exception handler is
3099           shadowed by another handler, which can point out a wrong ordering
3100           of exception handlers.
3101
3102       -Wstrict-null-sentinel (C++ and Objective-C++ only)
3103           Warn about the use of an uncasted "NULL" as sentinel.  When
3104           compiling only with GCC this is a valid sentinel, as "NULL" is
3105           defined to "__null".  Although it is a null pointer constant rather
3106           than a null pointer, it is guaranteed to be of the same size as a
3107           pointer.  But this use is not portable across different compilers.
3108
3109       -Wno-non-template-friend (C++ and Objective-C++ only)
3110           Disable warnings when non-template friend functions are declared
3111           within a template.  In very old versions of GCC that predate
3112           implementation of the ISO standard, declarations such as friend int
3113           foo(int), where the name of the friend is an unqualified-id, could
3114           be interpreted as a particular specialization of a template
3115           function; the warning exists to diagnose compatibility problems,
3116           and is enabled by default.
3117
3118       -Wold-style-cast (C++ and Objective-C++ only)
3119           Warn if an old-style (C-style) cast to a non-void type is used
3120           within a C++ program.  The new-style casts ("dynamic_cast",
3121           "static_cast", "reinterpret_cast", and "const_cast") are less
3122           vulnerable to unintended effects and much easier to search for.
3123
3124       -Woverloaded-virtual (C++ and Objective-C++ only)
3125           Warn when a function declaration hides virtual functions from a
3126           base class.  For example, in:
3127
3128                   struct A {
3129                     virtual void f();
3130                   };
3131
3132                   struct B: public A {
3133                     void f(int);
3134                   };
3135
3136           the "A" class version of "f" is hidden in "B", and code like:
3137
3138                   B* b;
3139                   b->f();
3140
3141           fails to compile.
3142
3143       -Wno-pmf-conversions (C++ and Objective-C++ only)
3144           Disable the diagnostic for converting a bound pointer to member
3145           function to a plain pointer.
3146
3147       -Wsign-promo (C++ and Objective-C++ only)
3148           Warn when overload resolution chooses a promotion from unsigned or
3149           enumerated type to a signed type, over a conversion to an unsigned
3150           type of the same size.  Previous versions of G++ tried to preserve
3151           unsignedness, but the standard mandates the current behavior.
3152
3153       -Wtemplates (C++ and Objective-C++ only)
3154           Warn when a primary template declaration is encountered.  Some
3155           coding rules disallow templates, and this may be used to enforce
3156           that rule.  The warning is inactive inside a system header file,
3157           such as the STL, so one can still use the STL.  One may also
3158           instantiate or specialize templates.
3159
3160       -Wmismatched-new-delete (C++ and Objective-C++ only)
3161           Warn for mismatches between calls to "operator new" or "operator
3162           delete" and the corresponding call to the allocation or
3163           deallocation function.  This includes invocations of C++ "operator
3164           delete" with pointers returned from either mismatched forms of
3165           "operator new", or from other functions that allocate objects for
3166           which the "operator delete" isn't a suitable deallocator, as well
3167           as calls to other deallocation functions with pointers returned
3168           from "operator new" for which the deallocation function isn't
3169           suitable.
3170
3171           For example, the "delete" expression in the function below is
3172           diagnosed because it doesn't match the array form of the "new"
3173           expression the pointer argument was returned from.  Similarly, the
3174           call to "free" is also diagnosed.
3175
3176                   void f ()
3177                   {
3178                     int *a = new int[n];
3179                     delete a;   // warning: mismatch in array forms of expressions
3180
3181                     char *p = new char[n];
3182                     free (p);   // warning: mismatch between new and free
3183                   }
3184
3185           The related option -Wmismatched-dealloc diagnoses mismatches
3186           involving allocation and deallocation functions other than
3187           "operator new" and "operator delete".
3188
3189           -Wmismatched-new-delete is included in -Wall.
3190
3191       -Wmismatched-tags (C++ and Objective-C++ only)
3192           Warn for declarations of structs, classes, and class templates and
3193           their specializations with a class-key that does not match either
3194           the definition or the first declaration if no definition is
3195           provided.
3196
3197           For example, the declaration of "struct Object" in the argument
3198           list of "draw" triggers the warning.  To avoid it, either remove
3199           the redundant class-key "struct" or replace it with "class" to
3200           match its definition.
3201
3202                   class Object {
3203                   public:
3204                     virtual ~Object () = 0;
3205                   };
3206                   void draw (struct Object*);
3207
3208           It is not wrong to declare a class with the class-key "struct" as
3209           the example above shows.  The -Wmismatched-tags option is intended
3210           to help achieve a consistent style of class declarations.  In code
3211           that is intended to be portable to Windows-based compilers the
3212           warning helps prevent unresolved references due to the difference
3213           in the mangling of symbols declared with different class-keys.  The
3214           option can be used either on its own or in conjunction with
3215           -Wredundant-tags.
3216
3217       -Wmultiple-inheritance (C++ and Objective-C++ only)
3218           Warn when a class is defined with multiple direct base classes.
3219           Some coding rules disallow multiple inheritance, and this may be
3220           used to enforce that rule.  The warning is inactive inside a system
3221           header file, such as the STL, so one can still use the STL.  One
3222           may also define classes that indirectly use multiple inheritance.
3223
3224       -Wvirtual-inheritance
3225           Warn when a class is defined with a virtual direct base class.
3226           Some coding rules disallow multiple inheritance, and this may be
3227           used to enforce that rule.  The warning is inactive inside a system
3228           header file, such as the STL, so one can still use the STL.  One
3229           may also define classes that indirectly use virtual inheritance.
3230
3231       -Wno-virtual-move-assign
3232           Suppress warnings about inheriting from a virtual base with a non-
3233           trivial C++11 move assignment operator.  This is dangerous because
3234           if the virtual base is reachable along more than one path, it is
3235           moved multiple times, which can mean both objects end up in the
3236           moved-from state.  If the move assignment operator is written to
3237           avoid moving from a moved-from object, this warning can be
3238           disabled.
3239
3240       -Wnamespaces
3241           Warn when a namespace definition is opened.  Some coding rules
3242           disallow namespaces, and this may be used to enforce that rule.
3243           The warning is inactive inside a system header file, such as the
3244           STL, so one can still use the STL.  One may also use using
3245           directives and qualified names.
3246
3247       -Wno-terminate (C++ and Objective-C++ only)
3248           Disable the warning about a throw-expression that will immediately
3249           result in a call to "terminate".
3250
3251       -Wno-vexing-parse (C++ and Objective-C++ only)
3252           Warn about the most vexing parse syntactic ambiguity.  This warns
3253           about the cases when a declaration looks like a variable
3254           definition, but the C++ language requires it to be interpreted as a
3255           function declaration.  For instance:
3256
3257                   void f(double a) {
3258                     int i();        // extern int i (void);
3259                     int n(int(a));  // extern int n (int);
3260                   }
3261
3262           Another example:
3263
3264                   struct S { S(int); };
3265                   void f(double a) {
3266                     S x(int(a));   // extern struct S x (int);
3267                     S y(int());    // extern struct S y (int (*) (void));
3268                     S z();         // extern struct S z (void);
3269                   }
3270
3271           The warning will suggest options how to deal with such an
3272           ambiguity; e.g., it can suggest removing the parentheses or using
3273           braces instead.
3274
3275           This warning is enabled by default.
3276
3277       -Wno-class-conversion (C++ and Objective-C++ only)
3278           Do not warn when a conversion function converts an object to the
3279           same type, to a base class of that type, or to void; such a
3280           conversion function will never be called.
3281
3282       -Wvolatile (C++ and Objective-C++ only)
3283           Warn about deprecated uses of the "volatile" qualifier.  This
3284           includes postfix and prefix "++" and "--" expressions of
3285           "volatile"-qualified types, using simple assignments where the left
3286           operand is a "volatile"-qualified non-class type for their value,
3287           compound assignments where the left operand is a
3288           "volatile"-qualified non-class type, "volatile"-qualified function
3289           return type, "volatile"-qualified parameter type, and structured
3290           bindings of a "volatile"-qualified type.  This usage was deprecated
3291           in C++20.
3292
3293           Enabled by default with -std=c++20.
3294
3295       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
3296           Warn when a literal 0 is used as null pointer constant.  This can
3297           be useful to facilitate the conversion to "nullptr" in C++11.
3298
3299       -Waligned-new
3300           Warn about a new-expression of a type that requires greater
3301           alignment than the "alignof(std::max_align_t)" but uses an
3302           allocation function without an explicit alignment parameter. This
3303           option is enabled by -Wall.
3304
3305           Normally this only warns about global allocation functions, but
3306           -Waligned-new=all also warns about class member allocation
3307           functions.
3308
3309       -Wno-placement-new
3310       -Wplacement-new=n
3311           Warn about placement new expressions with undefined behavior, such
3312           as constructing an object in a buffer that is smaller than the type
3313           of the object.  For example, the placement new expression below is
3314           diagnosed because it attempts to construct an array of 64 integers
3315           in a buffer only 64 bytes large.
3316
3317                   char buf [64];
3318                   new (buf) int[64];
3319
3320           This warning is enabled by default.
3321
3322           -Wplacement-new=1
3323               This is the default warning level of -Wplacement-new.  At this
3324               level the warning is not issued for some strictly undefined
3325               constructs that GCC allows as extensions for compatibility with
3326               legacy code.  For example, the following "new" expression is
3327               not diagnosed at this level even though it has undefined
3328               behavior according to the C++ standard because it writes past
3329               the end of the one-element array.
3330
3331                       struct S { int n, a[1]; };
3332                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
3333                       new (s->a)int [32]();
3334
3335           -Wplacement-new=2
3336               At this level, in addition to diagnosing all the same
3337               constructs as at level 1, a diagnostic is also issued for
3338               placement new expressions that construct an object in the last
3339               member of structure whose type is an array of a single element
3340               and whose size is less than the size of the object being
3341               constructed.  While the previous example would be diagnosed,
3342               the following construct makes use of the flexible member array
3343               extension to avoid the warning at level 2.
3344
3345                       struct S { int n, a[]; };
3346                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
3347                       new (s->a)int [32]();
3348
3349       -Wcatch-value
3350       -Wcatch-value=n (C++ and Objective-C++ only)
3351           Warn about catch handlers that do not catch via reference.  With
3352           -Wcatch-value=1 (or -Wcatch-value for short) warn about polymorphic
3353           class types that are caught by value.  With -Wcatch-value=2 warn
3354           about all class types that are caught by value. With
3355           -Wcatch-value=3 warn about all types that are not caught by
3356           reference. -Wcatch-value is enabled by -Wall.
3357
3358       -Wconditionally-supported (C++ and Objective-C++ only)
3359           Warn for conditionally-supported (C++11 [intro.defs]) constructs.
3360
3361       -Wno-delete-incomplete (C++ and Objective-C++ only)
3362           Do not warn when deleting a pointer to incomplete type, which may
3363           cause undefined behavior at runtime.  This warning is enabled by
3364           default.
3365
3366       -Wextra-semi (C++, Objective-C++ only)
3367           Warn about redundant semicolons after in-class function
3368           definitions.
3369
3370       -Wno-inaccessible-base (C++, Objective-C++ only)
3371           This option controls warnings when a base class is inaccessible in
3372           a class derived from it due to ambiguity.  The warning is enabled
3373           by default.  Note that the warning for ambiguous virtual bases is
3374           enabled by the -Wextra option.
3375
3376                   struct A { int a; };
3377
3378                   struct B : A { };
3379
3380                   struct C : B, A { };
3381
3382       -Wno-inherited-variadic-ctor
3383           Suppress warnings about use of C++11 inheriting constructors when
3384           the base class inherited from has a C variadic constructor; the
3385           warning is on by default because the ellipsis is not inherited.
3386
3387       -Wno-invalid-offsetof (C++ and Objective-C++ only)
3388           Suppress warnings from applying the "offsetof" macro to a non-POD
3389           type.  According to the 2014 ISO C++ standard, applying "offsetof"
3390           to a non-standard-layout type is undefined.  In existing C++
3391           implementations, however, "offsetof" typically gives meaningful
3392           results.  This flag is for users who are aware that they are
3393           writing nonportable code and who have deliberately chosen to ignore
3394           the warning about it.
3395
3396           The restrictions on "offsetof" may be relaxed in a future version
3397           of the C++ standard.
3398
3399       -Wsized-deallocation (C++ and Objective-C++ only)
3400           Warn about a definition of an unsized deallocation function
3401
3402                   void operator delete (void *) noexcept;
3403                   void operator delete[] (void *) noexcept;
3404
3405           without a definition of the corresponding sized deallocation
3406           function
3407
3408                   void operator delete (void *, std::size_t) noexcept;
3409                   void operator delete[] (void *, std::size_t) noexcept;
3410
3411           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.
3412
3413       -Wsuggest-final-types
3414           Warn about types with virtual methods where code quality would be
3415           improved if the type were declared with the C++11 "final"
3416           specifier, or, if possible, declared in an anonymous namespace.
3417           This allows GCC to more aggressively devirtualize the polymorphic
3418           calls. This warning is more effective with link-time optimization,
3419           where the information about the class hierarchy graph is more
3420           complete.
3421
3422       -Wsuggest-final-methods
3423           Warn about virtual methods where code quality would be improved if
3424           the method were declared with the C++11 "final" specifier, or, if
3425           possible, its type were declared in an anonymous namespace or with
3426           the "final" specifier.  This warning is more effective with link-
3427           time optimization, where the information about the class hierarchy
3428           graph is more complete. It is recommended to first consider
3429           suggestions of -Wsuggest-final-types and then rebuild with new
3430           annotations.
3431
3432       -Wsuggest-override
3433           Warn about overriding virtual functions that are not marked with
3434           the "override" keyword.
3435
3436       -Wuse-after-free
3437       -Wuse-after-free=n
3438           Warn about uses of pointers to dynamically allocated objects that
3439           have been rendered indeterminate by a call to a deallocation
3440           function.  The warning is enabled at all optimization levels but
3441           may yield different results with optimization than without.
3442
3443           -Wuse-after-free=1
3444               At level 1 the warning attempts to diagnose only unconditional
3445               uses of pointers made indeterminate by a deallocation call or a
3446               successful call to "realloc", regardless of whether or not the
3447               call resulted in an actual reallocatio of memory.  This
3448               includes double-"free" calls as well as uses in arithmetic and
3449               relational expressions.  Although undefined, uses of
3450               indeterminate pointers in equality (or inequality) expressions
3451               are not diagnosed at this level.
3452
3453           -Wuse-after-free=2
3454               At level 2, in addition to unconditional uses, the warning also
3455               diagnoses conditional uses of pointers made indeterminate by a
3456               deallocation call.  As at level 2, uses in equality (or
3457               inequality) expressions are not diagnosed.  For example, the
3458               second call to "free" in the following function is diagnosed at
3459               this level:
3460
3461                       struct A { int refcount; void *data; };
3462
3463                       void release (struct A *p)
3464                       {
3465                         int refcount = --p->refcount;
3466                         free (p);
3467                         if (refcount == 0)
3468                           free (p->data);   // warning: p may be used after free
3469                       }
3470
3471           -Wuse-after-free=3
3472               At level 3, the warning also diagnoses uses of indeterminate
3473               pointers in equality expressions.  All uses of indeterminate
3474               pointers are undefined but equality tests sometimes appear
3475               after calls to "realloc" as an attempt to determine whether the
3476               call resulted in relocating the object to a different address.
3477               They are diagnosed at a separate level to aid legacy code
3478               gradually transition to safe alternatives.  For example, the
3479               equality test in the function below is diagnosed at this level:
3480
3481                       void adjust_pointers (int**, int);
3482
3483                       void grow (int **p, int n)
3484                       {
3485                         int **q = (int**)realloc (p, n *= 2);
3486                         if (q == p)
3487                           return;
3488                         adjust_pointers ((int**)q, n);
3489                       }
3490
3491               To avoid the warning at this level, store offsets into
3492               allocated memory instead of pointers.  This approach obviates
3493               needing to adjust the stored pointers after reallocation.
3494
3495           -Wuse-after-free=2 is included in -Wall.
3496
3497       -Wuseless-cast (C++ and Objective-C++ only)
3498           Warn when an expression is casted to its own type.
3499
3500       -Wno-conversion-null (C++ and Objective-C++ only)
3501           Do not warn for conversions between "NULL" and non-pointer types.
3502           -Wconversion-null is enabled by default.
3503
3504   Options Controlling Objective-C and Objective-C++ Dialects
3505       (NOTE: This manual does not describe the Objective-C and Objective-C++
3506       languages themselves.
3507
3508       This section describes the command-line options that are only
3509       meaningful for Objective-C and Objective-C++ programs.  You can also
3510       use most of the language-independent GNU compiler options.  For
3511       example, you might compile a file some_class.m like this:
3512
3513               gcc -g -fgnu-runtime -O -c some_class.m
3514
3515       In this example, -fgnu-runtime is an option meant only for Objective-C
3516       and Objective-C++ programs; you can use the other options with any
3517       language supported by GCC.
3518
3519       Note that since Objective-C is an extension of the C language,
3520       Objective-C compilations may also use options specific to the C front-
3521       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
3522       use C++-specific options (e.g., -Wabi).
3523
3524       Here is a list of options that are only for compiling Objective-C and
3525       Objective-C++ programs:
3526
3527       -fconstant-string-class=class-name
3528           Use class-name as the name of the class to instantiate for each
3529           literal string specified with the syntax "@"..."".  The default
3530           class name is "NXConstantString" if the GNU runtime is being used,
3531           and "NSConstantString" if the NeXT runtime is being used (see
3532           below).  The -fconstant-cfstrings option, if also present,
3533           overrides the -fconstant-string-class setting and cause "@"...""
3534           literals to be laid out as constant CoreFoundation strings.
3535
3536       -fgnu-runtime
3537           Generate object code compatible with the standard GNU Objective-C
3538           runtime.  This is the default for most types of systems.
3539
3540       -fnext-runtime
3541           Generate output compatible with the NeXT runtime.  This is the
3542           default for NeXT-based systems, including Darwin and Mac OS X.  The
3543           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
3544           is used.
3545
3546       -fno-nil-receivers
3547           Assume that all Objective-C message dispatches ("[receiver
3548           message:arg]") in this translation unit ensure that the receiver is
3549           not "nil".  This allows for more efficient entry points in the
3550           runtime to be used.  This option is only available in conjunction
3551           with the NeXT runtime and ABI version 0 or 1.
3552
3553       -fobjc-abi-version=n
3554           Use version n of the Objective-C ABI for the selected runtime.
3555           This option is currently supported only for the NeXT runtime.  In
3556           that case, Version 0 is the traditional (32-bit) ABI without
3557           support for properties and other Objective-C 2.0 additions.
3558           Version 1 is the traditional (32-bit) ABI with support for
3559           properties and other Objective-C 2.0 additions.  Version 2 is the
3560           modern (64-bit) ABI.  If nothing is specified, the default is
3561           Version 0 on 32-bit target machines, and Version 2 on 64-bit target
3562           machines.
3563
3564       -fobjc-call-cxx-cdtors
3565           For each Objective-C class, check if any of its instance variables
3566           is a C++ object with a non-trivial default constructor.  If so,
3567           synthesize a special "- (id) .cxx_construct" instance method which
3568           runs non-trivial default constructors on any such instance
3569           variables, in order, and then return "self".  Similarly, check if
3570           any instance variable is a C++ object with a non-trivial
3571           destructor, and if so, synthesize a special "- (void)
3572           .cxx_destruct" method which runs all such default destructors, in
3573           reverse order.
3574
3575           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods
3576           thusly generated only operate on instance variables declared in the
3577           current Objective-C class, and not those inherited from
3578           superclasses.  It is the responsibility of the Objective-C runtime
3579           to invoke all such methods in an object's inheritance hierarchy.
3580           The "- (id) .cxx_construct" methods are invoked by the runtime
3581           immediately after a new object instance is allocated; the "- (void)
3582           .cxx_destruct" methods are invoked immediately before the runtime
3583           deallocates an object instance.
3584
3585           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
3586           later has support for invoking the "- (id) .cxx_construct" and "-
3587           (void) .cxx_destruct" methods.
3588
3589       -fobjc-direct-dispatch
3590           Allow fast jumps to the message dispatcher.  On Darwin this is
3591           accomplished via the comm page.
3592
3593       -fobjc-exceptions
3594           Enable syntactic support for structured exception handling in
3595           Objective-C, similar to what is offered by C++.  This option is
3596           required to use the Objective-C keywords @try, @throw, @catch,
3597           @finally and @synchronized.  This option is available with both the
3598           GNU runtime and the NeXT runtime (but not available in conjunction
3599           with the NeXT runtime on Mac OS X 10.2 and earlier).
3600
3601       -fobjc-gc
3602           Enable garbage collection (GC) in Objective-C and Objective-C++
3603           programs.  This option is only available with the NeXT runtime; the
3604           GNU runtime has a different garbage collection implementation that
3605           does not require special compiler flags.
3606
3607       -fobjc-nilcheck
3608           For the NeXT runtime with version 2 of the ABI, check for a nil
3609           receiver in method invocations before doing the actual method call.
3610           This is the default and can be disabled using -fno-objc-nilcheck.
3611           Class methods and super calls are never checked for nil in this way
3612           no matter what this flag is set to.  Currently this flag does
3613           nothing when the GNU runtime, or an older version of the NeXT
3614           runtime ABI, is used.
3615
3616       -fobjc-std=objc1
3617           Conform to the language syntax of Objective-C 1.0, the language
3618           recognized by GCC 4.0.  This only affects the Objective-C additions
3619           to the C/C++ language; it does not affect conformance to C/C++
3620           standards, which is controlled by the separate C/C++ dialect option
3621           flags.  When this option is used with the Objective-C or
3622           Objective-C++ compiler, any Objective-C syntax that is not
3623           recognized by GCC 4.0 is rejected.  This is useful if you need to
3624           make sure that your Objective-C code can be compiled with older
3625           versions of GCC.
3626
3627       -freplace-objc-classes
3628           Emit a special marker instructing ld(1) not to statically link in
3629           the resulting object file, and allow dyld(1) to load it in at run
3630           time instead.  This is used in conjunction with the Fix-and-
3631           Continue debugging mode, where the object file in question may be
3632           recompiled and dynamically reloaded in the course of program
3633           execution, without the need to restart the program itself.
3634           Currently, Fix-and-Continue functionality is only available in
3635           conjunction with the NeXT runtime on Mac OS X 10.3 and later.
3636
3637       -fzero-link
3638           When compiling for the NeXT runtime, the compiler ordinarily
3639           replaces calls to "objc_getClass("...")" (when the name of the
3640           class is known at compile time) with static class references that
3641           get initialized at load time, which improves run-time performance.
3642           Specifying the -fzero-link flag suppresses this behavior and causes
3643           calls to "objc_getClass("...")"  to be retained.  This is useful in
3644           Zero-Link debugging mode, since it allows for individual class
3645           implementations to be modified during program execution.  The GNU
3646           runtime currently always retains calls to "objc_get_class("...")"
3647           regardless of command-line options.
3648
3649       -fno-local-ivars
3650           By default instance variables in Objective-C can be accessed as if
3651           they were local variables from within the methods of the class
3652           they're declared in.  This can lead to shadowing between instance
3653           variables and other variables declared either locally inside a
3654           class method or globally with the same name.  Specifying the
3655           -fno-local-ivars flag disables this behavior thus avoiding variable
3656           shadowing issues.
3657
3658       -fivar-visibility=[public|protected|private|package]
3659           Set the default instance variable visibility to the specified
3660           option so that instance variables declared outside the scope of any
3661           access modifier directives default to the specified visibility.
3662
3663       -gen-decls
3664           Dump interface declarations for all classes seen in the source file
3665           to a file named sourcename.decl.
3666
3667       -Wassign-intercept (Objective-C and Objective-C++ only)
3668           Warn whenever an Objective-C assignment is being intercepted by the
3669           garbage collector.
3670
3671       -Wno-property-assign-default (Objective-C and Objective-C++ only)
3672           Do not warn if a property for an Objective-C object has no assign
3673           semantics specified.
3674
3675       -Wno-protocol (Objective-C and Objective-C++ only)
3676           If a class is declared to implement a protocol, a warning is issued
3677           for every method in the protocol that is not implemented by the
3678           class.  The default behavior is to issue a warning for every method
3679           not explicitly implemented in the class, even if a method
3680           implementation is inherited from the superclass.  If you use the
3681           -Wno-protocol option, then methods inherited from the superclass
3682           are considered to be implemented, and no warning is issued for
3683           them.
3684
3685       -Wobjc-root-class (Objective-C and Objective-C++ only)
3686           Warn if a class interface lacks a superclass. Most classes will
3687           inherit from "NSObject" (or "Object") for example.  When declaring
3688           classes intended to be root classes, the warning can be suppressed
3689           by marking their interfaces with
3690           "__attribute__((objc_root_class))".
3691
3692       -Wselector (Objective-C and Objective-C++ only)
3693           Warn if multiple methods of different types for the same selector
3694           are found during compilation.  The check is performed on the list
3695           of methods in the final stage of compilation.  Additionally, a
3696           check is performed for each selector appearing in a
3697           "@selector(...)"  expression, and a corresponding method for that
3698           selector has been found during compilation.  Because these checks
3699           scan the method table only at the end of compilation, these
3700           warnings are not produced if the final stage of compilation is not
3701           reached, for example because an error is found during compilation,
3702           or because the -fsyntax-only option is being used.
3703
3704       -Wstrict-selector-match (Objective-C and Objective-C++ only)
3705           Warn if multiple methods with differing argument and/or return
3706           types are found for a given selector when attempting to send a
3707           message using this selector to a receiver of type "id" or "Class".
3708           When this flag is off (which is the default behavior), the compiler
3709           omits such warnings if any differences found are confined to types
3710           that share the same size and alignment.
3711
3712       -Wundeclared-selector (Objective-C and Objective-C++ only)
3713           Warn if a "@selector(...)" expression referring to an undeclared
3714           selector is found.  A selector is considered undeclared if no
3715           method with that name has been declared before the "@selector(...)"
3716           expression, either explicitly in an @interface or @protocol
3717           declaration, or implicitly in an @implementation section.  This
3718           option always performs its checks as soon as a "@selector(...)"
3719           expression is found, while -Wselector only performs its checks in
3720           the final stage of compilation.  This also enforces the coding
3721           style convention that methods and selectors must be declared before
3722           being used.
3723
3724       -print-objc-runtime-info
3725           Generate C header describing the largest structure that is passed
3726           by value, if any.
3727
3728   Options to Control Diagnostic Messages Formatting
3729       Traditionally, diagnostic messages have been formatted irrespective of
3730       the output device's aspect (e.g. its width, ...).  You can use the
3731       options described below to control the formatting algorithm for
3732       diagnostic messages, e.g. how many characters per line, how often
3733       source location information should be reported.  Note that some
3734       language front ends may not honor these options.
3735
3736       -fmessage-length=n
3737           Try to format error messages so that they fit on lines of about n
3738           characters.  If n is zero, then no line-wrapping is done; each
3739           error message appears on a single line.  This is the default for
3740           all front ends.
3741
3742           Note - this option also affects the display of the #error and
3743           #warning pre-processor directives, and the deprecated
3744           function/type/variable attribute.  It does not however affect the
3745           pragma GCC warning and pragma GCC error pragmas.
3746
3747       -fdiagnostics-plain-output
3748           This option requests that diagnostic output look as plain as
3749           possible, which may be useful when running dejagnu or other
3750           utilities that need to parse diagnostics output and prefer that it
3751           remain more stable over time.  -fdiagnostics-plain-output is
3752           currently equivalent to the following options:
3753           -fno-diagnostics-show-caret -fno-diagnostics-show-line-numbers
3754           -fdiagnostics-color=never -fdiagnostics-urls=never
3755           -fdiagnostics-path-format=separate-events In the future, if GCC
3756           changes the default appearance of its diagnostics, the
3757           corresponding option to disable the new behavior will be added to
3758           this list.
3759
3760       -fdiagnostics-show-location=once
3761           Only meaningful in line-wrapping mode.  Instructs the diagnostic
3762           messages reporter to emit source location information once; that
3763           is, in case the message is too long to fit on a single physical
3764           line and has to be wrapped, the source location won't be emitted
3765           (as prefix) again, over and over, in subsequent continuation lines.
3766           This is the default behavior.
3767
3768       -fdiagnostics-show-location=every-line
3769           Only meaningful in line-wrapping mode.  Instructs the diagnostic
3770           messages reporter to emit the same source location information (as
3771           prefix) for physical lines that result from the process of breaking
3772           a message which is too long to fit on a single line.
3773
3774       -fdiagnostics-color[=WHEN]
3775       -fno-diagnostics-color
3776           Use color in diagnostics.  WHEN is never, always, or auto.  The
3777           default depends on how the compiler has been configured, it can be
3778           any of the above WHEN options or also never if GCC_COLORS
3779           environment variable isn't present in the environment, and auto
3780           otherwise.  auto makes GCC use color only when the standard error
3781           is a terminal, and when not executing in an emacs shell.  The forms
3782           -fdiagnostics-color and -fno-diagnostics-color are aliases for
3783           -fdiagnostics-color=always and -fdiagnostics-color=never,
3784           respectively.
3785
3786           The colors are defined by the environment variable GCC_COLORS.  Its
3787           value is a colon-separated list of capabilities and Select Graphic
3788           Rendition (SGR) substrings. SGR commands are interpreted by the
3789           terminal or terminal emulator.  (See the section in the
3790           documentation of your text terminal for permitted values and their
3791           meanings as character attributes.)  These substring values are
3792           integers in decimal representation and can be concatenated with
3793           semicolons.  Common values to concatenate include 1 for bold, 4 for
3794           underline, 5 for blink, 7 for inverse, 39 for default foreground
3795           color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode
3796           foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color
3797           modes foreground colors, 49 for default background color, 40 to 47
3798           for background colors, 100 to 107 for 16-color mode background
3799           colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
3800           background colors.
3801
3802           The default GCC_COLORS is
3803
3804                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
3805                   quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
3806                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
3807                   type-diff=01;32
3808
3809           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
3810           32 is green, 34 is blue, 01 is bold, and 31 is red.  Setting
3811           GCC_COLORS to the empty string disables colors.  Supported
3812           capabilities are as follows.
3813
3814           "error="
3815               SGR substring for error: markers.
3816
3817           "warning="
3818               SGR substring for warning: markers.
3819
3820           "note="
3821               SGR substring for note: markers.
3822
3823           "path="
3824               SGR substring for colorizing paths of control-flow events as
3825               printed via -fdiagnostics-path-format=, such as the identifiers
3826               of individual events and lines indicating interprocedural calls
3827               and returns.
3828
3829           "range1="
3830               SGR substring for first additional range.
3831
3832           "range2="
3833               SGR substring for second additional range.
3834
3835           "locus="
3836               SGR substring for location information, file:line or
3837               file:line:column etc.
3838
3839           "quote="
3840               SGR substring for information printed within quotes.
3841
3842           "fixit-insert="
3843               SGR substring for fix-it hints suggesting text to be inserted
3844               or replaced.
3845
3846           "fixit-delete="
3847               SGR substring for fix-it hints suggesting text to be deleted.
3848
3849           "diff-filename="
3850               SGR substring for filename headers within generated patches.
3851
3852           "diff-hunk="
3853               SGR substring for the starts of hunks within generated patches.
3854
3855           "diff-delete="
3856               SGR substring for deleted lines within generated patches.
3857
3858           "diff-insert="
3859               SGR substring for inserted lines within generated patches.
3860
3861           "type-diff="
3862               SGR substring for highlighting mismatching types within
3863               template arguments in the C++ frontend.
3864
3865       -fdiagnostics-urls[=WHEN]
3866           Use escape sequences to embed URLs in diagnostics.  For example,
3867           when -fdiagnostics-show-option emits text showing the command-line
3868           option controlling a diagnostic, embed a URL for documentation of
3869           that option.
3870
3871           WHEN is never, always, or auto.  auto makes GCC use URL escape
3872           sequences only when the standard error is a terminal, and when not
3873           executing in an emacs shell or any graphical terminal which is
3874           known to be incompatible with this feature, see below.
3875
3876           The default depends on how the compiler has been configured.  It
3877           can be any of the above WHEN options.
3878
3879           GCC can also be configured (via the
3880           --with-diagnostics-urls=auto-if-env configure-time option) so that
3881           the default is affected by environment variables.  Under such a
3882           configuration, GCC defaults to using auto if either GCC_URLS or
3883           TERM_URLS environment variables are present and non-empty in the
3884           environment of the compiler, or never if neither are.
3885
3886           However, even with -fdiagnostics-urls=always the behavior is
3887           dependent on those environment variables: If GCC_URLS is set to
3888           empty or no, do not embed URLs in diagnostics.  If set to st, URLs
3889           use ST escape sequences.  If set to bel, the default, URLs use BEL
3890           escape sequences.  Any other non-empty value enables the feature.
3891           If GCC_URLS is not set, use TERM_URLS as a fallback.  Note: ST is
3892           an ANSI escape sequence, string terminator ESC \, BEL is an ASCII
3893           character, CTRL-G that usually sounds like a beep.
3894
3895           At this time GCC tries to detect also a few terminals that are
3896           known to not implement the URL feature, and have bugs or at least
3897           had bugs in some versions that are still in use, where the URL
3898           escapes are likely to misbehave, i.e. print garbage on the screen.
3899           That list is currently xfce4-terminal, certain known to be buggy
3900           gnome-terminal versions, the linux console, and mingw.  This check
3901           can be skipped with the -fdiagnostics-urls=always.
3902
3903       -fno-diagnostics-show-option
3904           By default, each diagnostic emitted includes text indicating the
3905           command-line option that directly controls the diagnostic (if such
3906           an option is known to the diagnostic machinery).  Specifying the
3907           -fno-diagnostics-show-option flag suppresses that behavior.
3908
3909       -fno-diagnostics-show-caret
3910           By default, each diagnostic emitted includes the original source
3911           line and a caret ^ indicating the column.  This option suppresses
3912           this information.  The source line is truncated to n characters, if
3913           the -fmessage-length=n option is given.  When the output is done to
3914           the terminal, the width is limited to the width given by the
3915           COLUMNS environment variable or, if not set, to the terminal width.
3916
3917       -fno-diagnostics-show-labels
3918           By default, when printing source code (via
3919           -fdiagnostics-show-caret), diagnostics can label ranges of source
3920           code with pertinent information, such as the types of expressions:
3921
3922                       printf ("foo %s bar", long_i + long_j);
3923                                    ~^       ~~~~~~~~~~~~~~~
3924                                     |              |
3925                                     char *         long int
3926
3927           This option suppresses the printing of these labels (in the example
3928           above, the vertical bars and the "char *" and "long int" text).
3929
3930       -fno-diagnostics-show-cwe
3931           Diagnostic messages can optionally have an associated
3932           @url{https://cwe.mitre.org/index.html, CWE} identifier.  GCC itself
3933           only provides such metadata for some of the -fanalyzer diagnostics.
3934           GCC plugins may also provide diagnostics with such metadata.  By
3935           default, if this information is present, it will be printed with
3936           the diagnostic.  This option suppresses the printing of this
3937           metadata.
3938
3939       -fno-diagnostics-show-line-numbers
3940           By default, when printing source code (via
3941           -fdiagnostics-show-caret), a left margin is printed, showing line
3942           numbers.  This option suppresses this left margin.
3943
3944       -fdiagnostics-minimum-margin-width=width
3945           This option controls the minimum width of the left margin printed
3946           by -fdiagnostics-show-line-numbers.  It defaults to 6.
3947
3948       -fdiagnostics-parseable-fixits
3949           Emit fix-it hints in a machine-parseable format, suitable for
3950           consumption by IDEs.  For each fix-it, a line will be printed after
3951           the relevant diagnostic, starting with the string "fix-it:".  For
3952           example:
3953
3954                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"
3955
3956           The location is expressed as a half-open range, expressed as a
3957           count of bytes, starting at byte 1 for the initial column.  In the
3958           above example, bytes 3 through 20 of line 45 of "test.c" are to be
3959           replaced with the given string:
3960
3961                   00000000011111111112222222222
3962                   12345678901234567890123456789
3963                     gtk_widget_showall (dlg);
3964                     ^^^^^^^^^^^^^^^^^^
3965                     gtk_widget_show_all
3966
3967           The filename and replacement string escape backslash as "\\", tab
3968           as "\t", newline as "\n", double quotes as "\"", non-printable
3969           characters as octal (e.g. vertical tab as "\013").
3970
3971           An empty replacement string indicates that the given range is to be
3972           removed.  An empty range (e.g. "45:3-45:3") indicates that the
3973           string is to be inserted at the given position.
3974
3975       -fdiagnostics-generate-patch
3976           Print fix-it hints to stderr in unified diff format, after any
3977           diagnostics are printed.  For example:
3978
3979                   --- test.c
3980                   +++ test.c
3981                   @ -42,5 +42,5 @
3982
3983                    void show_cb(GtkDialog *dlg)
3984                    {
3985                   -  gtk_widget_showall(dlg);
3986                   +  gtk_widget_show_all(dlg);
3987                    }
3988
3989           The diff may or may not be colorized, following the same rules as
3990           for diagnostics (see -fdiagnostics-color).
3991
3992       -fdiagnostics-show-template-tree
3993           In the C++ frontend, when printing diagnostics showing mismatching
3994           template types, such as:
3995
3996                     could not convert 'std::map<int, std::vector<double> >()'
3997                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
3998
3999           the -fdiagnostics-show-template-tree flag enables printing a tree-
4000           like structure showing the common and differing parts of the types,
4001           such as:
4002
4003                     map<
4004                       [...],
4005                       vector<
4006                         [double != float]>>
4007
4008           The parts that differ are highlighted with color ("double" and
4009           "float" in this case).
4010
4011       -fno-elide-type
4012           By default when the C++ frontend prints diagnostics showing
4013           mismatching template types, common parts of the types are printed
4014           as "[...]" to simplify the error message.  For example:
4015
4016                     could not convert 'std::map<int, std::vector<double> >()'
4017                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
4018
4019           Specifying the -fno-elide-type flag suppresses that behavior.  This
4020           flag also affects the output of the
4021           -fdiagnostics-show-template-tree flag.
4022
4023       -fdiagnostics-path-format=KIND
4024           Specify how to print paths of control-flow events for diagnostics
4025           that have such a path associated with them.
4026
4027           KIND is none, separate-events, or inline-events, the default.
4028
4029           none means to not print diagnostic paths.
4030
4031           separate-events means to print a separate "note" diagnostic for
4032           each event within the diagnostic.  For example:
4033
4034                   test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
4035                   test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
4036                   test.c:27:3: note: (2) when 'i < count'
4037                   test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
4038
4039           inline-events means to print the events "inline" within the source
4040           code.  This view attempts to consolidate the events into runs of
4041           sufficiently-close events, printing them as labelled ranges within
4042           the source.
4043
4044           For example, the same events as above might be printed as:
4045
4046                     'test': events 1-3
4047                       |
4048                       |   25 |   list = PyList_New(0);
4049                       |      |          ^~~~~~~~~~~~~
4050                       |      |          |
4051                       |      |          (1) when 'PyList_New' fails, returning NULL
4052                       |   26 |
4053                       |   27 |   for (i = 0; i < count; i++) {
4054                       |      |   ~~~
4055                       |      |   |
4056                       |      |   (2) when 'i < count'
4057                       |   28 |     item = PyLong_FromLong(random());
4058                       |   29 |     PyList_Append(list, item);
4059                       |      |     ~~~~~~~~~~~~~~~~~~~~~~~~~
4060                       |      |     |
4061                       |      |     (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
4062                       |
4063
4064           Interprocedural control flow is shown by grouping the events by
4065           stack frame, and using indentation to show how stack frames are
4066           nested, pushed, and popped.
4067
4068           For example:
4069
4070                     'test': events 1-2
4071                       |
4072                       |  133 | {
4073                       |      | ^
4074                       |      | |
4075                       |      | (1) entering 'test'
4076                       |  134 |   boxed_int *obj = make_boxed_int (i);
4077                       |      |                    ~~~~~~~~~~~~~~~~~~
4078                       |      |                    |
4079                       |      |                    (2) calling 'make_boxed_int'
4080                       |
4081                       +--> 'make_boxed_int': events 3-4
4082                              |
4083                              |  120 | {
4084                              |      | ^
4085                              |      | |
4086                              |      | (3) entering 'make_boxed_int'
4087                              |  121 |   boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
4088                              |      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4089                              |      |                                    |
4090                              |      |                                    (4) calling 'wrapped_malloc'
4091                              |
4092                              +--> 'wrapped_malloc': events 5-6
4093                                     |
4094                                     |    7 | {
4095                                     |      | ^
4096                                     |      | |
4097                                     |      | (5) entering 'wrapped_malloc'
4098                                     |    8 |   return malloc (size);
4099                                     |      |          ~~~~~~~~~~~~~
4100                                     |      |          |
4101                                     |      |          (6) calling 'malloc'
4102                                     |
4103                       <-------------+
4104                       |
4105                    'test': event 7
4106                       |
4107                       |  138 |   free_boxed_int (obj);
4108                       |      |   ^~~~~~~~~~~~~~~~~~~~
4109                       |      |   |
4110                       |      |   (7) calling 'free_boxed_int'
4111                       |
4112                   (etc)
4113
4114       -fdiagnostics-show-path-depths
4115           This option provides additional information when printing control-
4116           flow paths associated with a diagnostic.
4117
4118           If this is option is provided then the stack depth will be printed
4119           for each run of events within
4120           -fdiagnostics-path-format=separate-events.
4121
4122           This is intended for use by GCC developers and plugin developers
4123           when debugging diagnostics that report interprocedural control
4124           flow.
4125
4126       -fno-show-column
4127           Do not print column numbers in diagnostics.  This may be necessary
4128           if diagnostics are being scanned by a program that does not
4129           understand the column numbers, such as dejagnu.
4130
4131       -fdiagnostics-column-unit=UNIT
4132           Select the units for the column number.  This affects traditional
4133           diagnostics (in the absence of -fno-show-column), as well as JSON
4134           format diagnostics if requested.
4135
4136           The default UNIT, display, considers the number of display columns
4137           occupied by each character.  This may be larger than the number of
4138           bytes required to encode the character, in the case of tab
4139           characters, or it may be smaller, in the case of multibyte
4140           characters.  For example, the character "GREEK SMALL LETTER PI
4141           (U+03C0)" occupies one display column, and its UTF-8 encoding
4142           requires two bytes; the character "SLIGHTLY SMILING FACE (U+1F642)"
4143           occupies two display columns, and its UTF-8 encoding requires four
4144           bytes.
4145
4146           Setting UNIT to byte changes the column number to the raw byte
4147           count in all cases, as was traditionally output by GCC prior to
4148           version 11.1.0.
4149
4150       -fdiagnostics-column-origin=ORIGIN
4151           Select the origin for column numbers, i.e. the column number
4152           assigned to the first column.  The default value of 1 corresponds
4153           to traditional GCC behavior and to the GNU style guide.  Some
4154           utilities may perform better with an origin of 0; any non-negative
4155           value may be specified.
4156
4157       -fdiagnostics-escape-format=FORMAT
4158           When GCC prints pertinent source lines for a diagnostic it normally
4159           attempts to print the source bytes directly.  However, some
4160           diagnostics relate to encoding issues in the source file, such as
4161           malformed UTF-8, or issues with Unicode normalization.  These
4162           diagnostics are flagged so that GCC will escape bytes that are not
4163           printable ASCII when printing their pertinent source lines.
4164
4165           This option controls how such bytes should be escaped.
4166
4167           The default FORMAT, unicode displays Unicode characters that are
4168           not printable ASCII in the form <U+XXXX>, and bytes that do not
4169           correspond to a Unicode character validly-encoded in UTF-8-encoded
4170           will be displayed as hexadecimal in the form <XX>.
4171
4172           For example, a source line containing the string before followed by
4173           the Unicode character U+03C0 ("GREEK SMALL LETTER PI", with UTF-8
4174           encoding 0xCF 0x80) followed by the byte 0xBF (a stray UTF-8
4175           trailing byte), followed by the string after will be printed for
4176           such a diagnostic as:
4177
4178                    before<U+03C0><BF>after
4179
4180           Setting FORMAT to bytes will display all non-printable-ASCII bytes
4181           in the form <XX>, thus showing the underlying encoding of non-ASCII
4182           Unicode characters.  For the example above, the following will be
4183           printed:
4184
4185                    before<CF><80><BF>after
4186
4187       -fdiagnostics-format=FORMAT
4188           Select a different format for printing diagnostics.  FORMAT is text
4189           or json.  The default is text.
4190
4191           The json format consists of a top-level JSON array containing JSON
4192           objects representing the diagnostics.
4193
4194           The JSON is emitted as one line, without formatting; the examples
4195           below have been formatted for clarity.
4196
4197           Diagnostics can have child diagnostics.  For example, this error
4198           and note:
4199
4200                   misleading-indentation.c:15:3: warning: this 'if' clause does not
4201                     guard... [-Wmisleading-indentation]
4202                      15 |   if (flag)
4203                         |   ^~
4204                   misleading-indentation.c:17:5: note: ...this statement, but the latter
4205                     is misleadingly indented as if it were guarded by the 'if'
4206                      17 |     y = 2;
4207                         |     ^
4208
4209           might be printed in JSON form (after formatting) like this:
4210
4211                   [
4212                       {
4213                           "kind": "warning",
4214                           "locations": [
4215                               {
4216                                   "caret": {
4217                                       "display-column": 3,
4218                                       "byte-column": 3,
4219                                       "column": 3,
4220                                       "file": "misleading-indentation.c",
4221                                       "line": 15
4222                                   },
4223                                   "finish": {
4224                                       "display-column": 4,
4225                                       "byte-column": 4,
4226                                       "column": 4,
4227                                       "file": "misleading-indentation.c",
4228                                       "line": 15
4229                                   }
4230                               }
4231                           ],
4232                           "message": "this \u2018if\u2019 clause does not guard...",
4233                           "option": "-Wmisleading-indentation",
4234                           "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
4235                           "children": [
4236                               {
4237                                   "kind": "note",
4238                                   "locations": [
4239                                       {
4240                                           "caret": {
4241                                               "display-column": 5,
4242                                               "byte-column": 5,
4243                                               "column": 5,
4244                                               "file": "misleading-indentation.c",
4245                                               "line": 17
4246                                           }
4247                                       }
4248                                   ],
4249                                   "escape-source": false,
4250                                   "message": "...this statement, but the latter is ..."
4251                               }
4252                           ]
4253                           "escape-source": false,
4254                           "column-origin": 1,
4255                       }
4256                   ]
4257
4258           where the "note" is a child of the "warning".
4259
4260           A diagnostic has a "kind".  If this is "warning", then there is an
4261           "option" key describing the command-line option controlling the
4262           warning.
4263
4264           A diagnostic can contain zero or more locations.  Each location has
4265           an optional "label" string and up to three positions within it: a
4266           "caret" position and optional "start" and "finish" positions.  A
4267           position is described by a "file" name, a "line" number, and three
4268           numbers indicating a column position:
4269
4270           *   "display-column" counts display columns, accounting for tabs
4271               and multibyte characters.
4272
4273           *   "byte-column" counts raw bytes.
4274
4275           *   "column" is equal to one of the previous two, as dictated by
4276               the -fdiagnostics-column-unit option.
4277
4278           All three columns are relative to the origin specified by
4279           -fdiagnostics-column-origin, which is typically equal to 1 but may
4280           be set, for instance, to 0 for compatibility with other utilities
4281           that number columns from 0.  The column origin is recorded in the
4282           JSON output in the "column-origin" tag.  In the remaining examples
4283           below, the extra column number outputs have been omitted for
4284           brevity.
4285
4286           For example, this error:
4287
4288                   bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
4289                      'struct s'} and 'T' {aka 'struct t'})
4290                      64 |   return callee_4a () + callee_4b ();
4291                         |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
4292                         |          |              |
4293                         |          |              T {aka struct t}
4294                         |          S {aka struct s}
4295
4296           has three locations.  Its primary location is at the "+" token at
4297           column 23.  It has two secondary locations, describing the left and
4298           right-hand sides of the expression, which have labels.  It might be
4299           printed in JSON form as:
4300
4301                       {
4302                           "children": [],
4303                           "kind": "error",
4304                           "locations": [
4305                               {
4306                                   "caret": {
4307                                       "column": 23, "file": "bad-binary-ops.c", "line": 64
4308                                   }
4309                               },
4310                               {
4311                                   "caret": {
4312                                       "column": 10, "file": "bad-binary-ops.c", "line": 64
4313                                   },
4314                                   "finish": {
4315                                       "column": 21, "file": "bad-binary-ops.c", "line": 64
4316                                   },
4317                                   "label": "S {aka struct s}"
4318                               },
4319                               {
4320                                   "caret": {
4321                                       "column": 25, "file": "bad-binary-ops.c", "line": 64
4322                                   },
4323                                   "finish": {
4324                                       "column": 36, "file": "bad-binary-ops.c", "line": 64
4325                                   },
4326                                   "label": "T {aka struct t}"
4327                               }
4328                           ],
4329                           "escape-source": false,
4330                           "message": "invalid operands to binary + ..."
4331                       }
4332
4333           If a diagnostic contains fix-it hints, it has a "fixits" array,
4334           consisting of half-open intervals, similar to the output of
4335           -fdiagnostics-parseable-fixits.  For example, this diagnostic with
4336           a replacement fix-it hint:
4337
4338                   demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
4339                     mean 'color'?
4340                       8 |   return ptr->colour;
4341                         |               ^~~~~~
4342                         |               color
4343
4344           might be printed in JSON form as:
4345
4346                       {
4347                           "children": [],
4348                           "fixits": [
4349                               {
4350                                   "next": {
4351                                       "column": 21,
4352                                       "file": "demo.c",
4353                                       "line": 8
4354                                   },
4355                                   "start": {
4356                                       "column": 15,
4357                                       "file": "demo.c",
4358                                       "line": 8
4359                                   },
4360                                   "string": "color"
4361                               }
4362                           ],
4363                           "kind": "error",
4364                           "locations": [
4365                               {
4366                                   "caret": {
4367                                       "column": 15,
4368                                       "file": "demo.c",
4369                                       "line": 8
4370                                   },
4371                                   "finish": {
4372                                       "column": 20,
4373                                       "file": "demo.c",
4374                                       "line": 8
4375                                   }
4376                               }
4377                           ],
4378                           "escape-source": false,
4379                           "message": "\u2018struct s\u2019 has no member named ..."
4380                       }
4381
4382           where the fix-it hint suggests replacing the text from "start" up
4383           to but not including "next" with "string"'s value.  Deletions are
4384           expressed via an empty value for "string", insertions by having
4385           "start" equal "next".
4386
4387           If the diagnostic has a path of control-flow events associated with
4388           it, it has a "path" array of objects representing the events.  Each
4389           event object has a "description" string, a "location" object, along
4390           with a "function" string and a "depth" number for representing
4391           interprocedural paths.  The "function" represents the current
4392           function at that event, and the "depth" represents the stack depth
4393           relative to some baseline: the higher, the more frames are within
4394           the stack.
4395
4396           For example, the intraprocedural example shown for
4397           -fdiagnostics-path-format= might have this JSON for its path:
4398
4399                       "path": [
4400                           {
4401                               "depth": 0,
4402                               "description": "when 'PyList_New' fails, returning NULL",
4403                               "function": "test",
4404                               "location": {
4405                                   "column": 10,
4406                                   "file": "test.c",
4407                                   "line": 25
4408                               }
4409                           },
4410                           {
4411                               "depth": 0,
4412                               "description": "when 'i < count'",
4413                               "function": "test",
4414                               "location": {
4415                                   "column": 3,
4416                                   "file": "test.c",
4417                                   "line": 27
4418                               }
4419                           },
4420                           {
4421                               "depth": 0,
4422                               "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
4423                               "function": "test",
4424                               "location": {
4425                                   "column": 5,
4426                                   "file": "test.c",
4427                                   "line": 29
4428                               }
4429                           }
4430                       ]
4431
4432           Diagnostics have a boolean attribute "escape-source", hinting
4433           whether non-ASCII bytes should be escaped when printing the
4434           pertinent lines of source code ("true" for diagnostics involving
4435           source encoding issues).
4436
4437   Options to Request or Suppress Warnings
4438       Warnings are diagnostic messages that report constructions that are not
4439       inherently erroneous but that are risky or suggest there may have been
4440       an error.
4441
4442       The following language-independent options do not enable specific
4443       warnings but control the kinds of diagnostics produced by GCC.
4444
4445       -fsyntax-only
4446           Check the code for syntax errors, but don't do anything beyond
4447           that.
4448
4449       -fmax-errors=n
4450           Limits the maximum number of error messages to n, at which point
4451           GCC bails out rather than attempting to continue processing the
4452           source code.  If n is 0 (the default), there is no limit on the
4453           number of error messages produced.  If -Wfatal-errors is also
4454           specified, then -Wfatal-errors takes precedence over this option.
4455
4456       -w  Inhibit all warning messages.
4457
4458       -Werror
4459           Make all warnings into errors.
4460
4461       -Werror=
4462           Make the specified warning into an error.  The specifier for a
4463           warning is appended; for example -Werror=switch turns the warnings
4464           controlled by -Wswitch into errors.  This switch takes a negative
4465           form, to be used to negate -Werror for specific warnings; for
4466           example -Wno-error=switch makes -Wswitch warnings not be errors,
4467           even when -Werror is in effect.
4468
4469           The warning message for each controllable warning includes the
4470           option that controls the warning.  That option can then be used
4471           with -Werror= and -Wno-error= as described above.  (Printing of the
4472           option in the warning message can be disabled using the
4473           -fno-diagnostics-show-option flag.)
4474
4475           Note that specifying -Werror=foo automatically implies -Wfoo.
4476           However, -Wno-error=foo does not imply anything.
4477
4478       -Wfatal-errors
4479           This option causes the compiler to abort compilation on the first
4480           error occurred rather than trying to keep going and printing
4481           further error messages.
4482
4483       You can request many specific warnings with options beginning with -W,
4484       for example -Wimplicit to request warnings on implicit declarations.
4485       Each of these specific warning options also has a negative form
4486       beginning -Wno- to turn off warnings; for example, -Wno-implicit.  This
4487       manual lists only one of the two forms, whichever is not the default.
4488       For further language-specific options also refer to C++ Dialect Options
4489       and Objective-C and Objective-C++ Dialect Options.  Additional warnings
4490       can be produced by enabling the static analyzer;
4491
4492       Some options, such as -Wall and -Wextra, turn on other options, such as
4493       -Wunused, which may turn on further options, such as -Wunused-value.
4494       The combined effect of positive and negative forms is that more
4495       specific options have priority over less specific ones, independently
4496       of their position in the command-line. For options of the same
4497       specificity, the last one takes effect. Options enabled or disabled via
4498       pragmas take effect as if they appeared at the end of the command-line.
4499
4500       When an unrecognized warning option is requested (e.g.,
4501       -Wunknown-warning), GCC emits a diagnostic stating that the option is
4502       not recognized.  However, if the -Wno- form is used, the behavior is
4503       slightly different: no diagnostic is produced for -Wno-unknown-warning
4504       unless other diagnostics are being produced.  This allows the use of
4505       new -Wno- options with old compilers, but if something goes wrong, the
4506       compiler warns that an unrecognized option is present.
4507
4508       The effectiveness of some warnings depends on optimizations also being
4509       enabled. For example -Wsuggest-final-types is more effective with link-
4510       time optimization and some instances of other warnings may not be
4511       issued at all unless optimization is enabled.  While optimization in
4512       general improves the efficacy of control and data flow sensitive
4513       warnings, in some cases it may also cause false positives.
4514
4515       -Wpedantic
4516       -pedantic
4517           Issue all the warnings demanded by strict ISO C and ISO C++; reject
4518           all programs that use forbidden extensions, and some other programs
4519           that do not follow ISO C and ISO C++.  For ISO C, follows the
4520           version of the ISO C standard specified by any -std option used.
4521
4522           Valid ISO C and ISO C++ programs should compile properly with or
4523           without this option (though a rare few require -ansi or a -std
4524           option specifying the required version of ISO C).  However, without
4525           this option, certain GNU extensions and traditional C and C++
4526           features are supported as well.  With this option, they are
4527           rejected.
4528
4529           -Wpedantic does not cause warning messages for use of the alternate
4530           keywords whose names begin and end with __.  This alternate format
4531           can also be used to disable warnings for non-ISO __intN types, i.e.
4532           __intN__.  Pedantic warnings are also disabled in the expression
4533           that follows "__extension__".  However, only system header files
4534           should use these escape routes; application programs should avoid
4535           them.
4536
4537           Some users try to use -Wpedantic to check programs for strict ISO C
4538           conformance.  They soon find that it does not do quite what they
4539           want: it finds some non-ISO practices, but not all---only those for
4540           which ISO C requires a diagnostic, and some others for which
4541           diagnostics have been added.
4542
4543           A feature to report any failure to conform to ISO C might be useful
4544           in some instances, but would require considerable additional work
4545           and would be quite different from -Wpedantic.  We don't have plans
4546           to support such a feature in the near future.
4547
4548           Where the standard specified with -std represents a GNU extended
4549           dialect of C, such as gnu90 or gnu99, there is a corresponding base
4550           standard, the version of ISO C on which the GNU extended dialect is
4551           based.  Warnings from -Wpedantic are given where they are required
4552           by the base standard.  (It does not make sense for such warnings to
4553           be given only for features not in the specified GNU C dialect,
4554           since by definition the GNU dialects of C include all features the
4555           compiler supports with the given option, and there would be nothing
4556           to warn about.)
4557
4558       -pedantic-errors
4559           Give an error whenever the base standard (see -Wpedantic) requires
4560           a diagnostic, in some cases where there is undefined behavior at
4561           compile-time and in some other cases that do not prevent
4562           compilation of programs that are valid according to the standard.
4563           This is not equivalent to -Werror=pedantic, since there are errors
4564           enabled by this option and not enabled by the latter and vice
4565           versa.
4566
4567       -Wall
4568           This enables all the warnings about constructions that some users
4569           consider questionable, and that are easy to avoid (or modify to
4570           prevent the warning), even in conjunction with macros.  This also
4571           enables some language-specific warnings described in C++ Dialect
4572           Options and Objective-C and Objective-C++ Dialect Options.
4573
4574           -Wall turns on the following warning flags:
4575
4576           -Waddress -Warray-bounds=1 (only with -O2) -Warray-compare
4577           -Warray-parameter=2 (C and Objective-C only) -Wbool-compare
4578           -Wbool-operation -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++
4579           and Objective-C++ only) -Wchar-subscripts -Wcomment
4580           -Wdangling-pointer=2 -Wduplicate-decl-specifier (C and Objective-C
4581           only) -Wenum-compare (in C/ObjC; this is on by default in C++)
4582           -Wformat -Wformat-overflow -Wformat-truncation
4583           -Wint-in-bool-context -Wimplicit (C and Objective-C only)
4584           -Wimplicit-int (C and Objective-C only)
4585           -Wimplicit-function-declaration (C and Objective-C only)
4586           -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only
4587           for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized
4588           -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation
4589           (only for C/C++) -Wmismatched-dealloc -Wmismatched-new-delete (only
4590           for C/C++) -Wmissing-attributes -Wmissing-braces (only for C/ObjC)
4591           -Wmultistatement-macros -Wnarrowing (only for C++) -Wnonnull
4592           -Wnonnull-compare -Wopenmp-simd -Wparentheses -Wpessimizing-move
4593           (only for C++) -Wpointer-sign -Wrange-loop-construct (only for C++)
4594           -Wreorder -Wrestrict -Wreturn-type -Wsequence-point -Wsign-compare
4595           (only in C++) -Wsizeof-array-div -Wsizeof-pointer-div
4596           -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1
4597           -Wswitch -Wtautological-compare -Wtrigraphs -Wuninitialized
4598           -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value
4599           -Wunused-variable -Wuse-after-free=3 -Wvla-parameter (C and
4600           Objective-C only) -Wvolatile-register-var -Wzero-length-bounds
4601
4602           Note that some warning flags are not implied by -Wall.  Some of
4603           them warn about constructions that users generally do not consider
4604           questionable, but which occasionally you might wish to check for;
4605           others warn about constructions that are necessary or hard to avoid
4606           in some cases, and there is no simple way to modify the code to
4607           suppress the warning. Some of them are enabled by -Wextra but many
4608           of them must be enabled individually.
4609
4610       -Wextra
4611           This enables some extra warning flags that are not enabled by
4612           -Wall. (This option used to be called -W.  The older name is still
4613           supported, but the newer name is more descriptive.)
4614
4615           -Wclobbered -Wcast-function-type -Wdeprecated-copy (C++ only)
4616           -Wempty-body -Wenum-conversion (C only) -Wignored-qualifiers
4617           -Wimplicit-fallthrough=3 -Wmissing-field-initializers
4618           -Wmissing-parameter-type (C only) -Wold-style-declaration (C only)
4619           -Woverride-init -Wsign-compare (C only) -Wstring-compare
4620           -Wredundant-move (only for C++) -Wtype-limits -Wuninitialized
4621           -Wshift-negative-value (in C++11 to C++17 and in C99 and newer)
4622           -Wunused-parameter (only with -Wunused or -Wall)
4623           -Wunused-but-set-parameter (only with -Wunused or -Wall)
4624
4625           The option -Wextra also prints warning messages for the following
4626           cases:
4627
4628           *   A pointer is compared against integer zero with "<", "<=", ">",
4629               or ">=".
4630
4631           *   (C++ only) An enumerator and a non-enumerator both appear in a
4632               conditional expression.
4633
4634           *   (C++ only) Ambiguous virtual bases.
4635
4636           *   (C++ only) Subscripting an array that has been declared
4637               "register".
4638
4639           *   (C++ only) Taking the address of a variable that has been
4640               declared "register".
4641
4642           *   (C++ only) A base class is not initialized in the copy
4643               constructor of a derived class.
4644
4645       -Wabi (C, Objective-C, C++ and Objective-C++ only)
4646           Warn about code affected by ABI changes.  This includes code that
4647           may not be compatible with the vendor-neutral C++ ABI as well as
4648           the psABI for the particular target.
4649
4650           Since G++ now defaults to updating the ABI with each major release,
4651           normally -Wabi warns only about C++ ABI compatibility problems if
4652           there is a check added later in a release series for an ABI issue
4653           discovered since the initial release.  -Wabi warns about more
4654           things if an older ABI version is selected (with -fabi-version=n).
4655
4656           -Wabi can also be used with an explicit version number to warn
4657           about C++ ABI compatibility with a particular -fabi-version level,
4658           e.g. -Wabi=2 to warn about changes relative to -fabi-version=2.
4659
4660           If an explicit version number is provided and -fabi-compat-version
4661           is not specified, the version number from this option is used for
4662           compatibility aliases.  If no explicit version number is provided
4663           with this option, but -fabi-compat-version is specified, that
4664           version number is used for C++ ABI warnings.
4665
4666           Although an effort has been made to warn about all such cases,
4667           there are probably some cases that are not warned about, even
4668           though G++ is generating incompatible code.  There may also be
4669           cases where warnings are emitted even though the code that is
4670           generated is compatible.
4671
4672           You should rewrite your code to avoid these warnings if you are
4673           concerned about the fact that code generated by G++ may not be
4674           binary compatible with code generated by other compilers.
4675
4676           Known incompatibilities in -fabi-version=2 (which was the default
4677           from GCC 3.4 to 4.9) include:
4678
4679           *   A template with a non-type template parameter of reference type
4680               was mangled incorrectly:
4681
4682                       extern int N;
4683                       template <int &> struct S {};
4684                       void n (S<N>) {2}
4685
4686               This was fixed in -fabi-version=3.
4687
4688           *   SIMD vector types declared using "__attribute ((vector_size))"
4689               were mangled in a non-standard way that does not allow for
4690               overloading of functions taking vectors of different sizes.
4691
4692               The mangling was changed in -fabi-version=4.
4693
4694           *   "__attribute ((const))" and "noreturn" were mangled as type
4695               qualifiers, and "decltype" of a plain declaration was folded
4696               away.
4697
4698               These mangling issues were fixed in -fabi-version=5.
4699
4700           *   Scoped enumerators passed as arguments to a variadic function
4701               are promoted like unscoped enumerators, causing "va_arg" to
4702               complain.  On most targets this does not actually affect the
4703               parameter passing ABI, as there is no way to pass an argument
4704               smaller than "int".
4705
4706               Also, the ABI changed the mangling of template argument packs,
4707               "const_cast", "static_cast", prefix increment/decrement, and a
4708               class scope function used as a template argument.
4709
4710               These issues were corrected in -fabi-version=6.
4711
4712           *   Lambdas in default argument scope were mangled incorrectly, and
4713               the ABI changed the mangling of "nullptr_t".
4714
4715               These issues were corrected in -fabi-version=7.
4716
4717           *   When mangling a function type with function-cv-qualifiers, the
4718               un-qualified function type was incorrectly treated as a
4719               substitution candidate.
4720
4721               This was fixed in -fabi-version=8, the default for GCC 5.1.
4722
4723           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading
4724               to unaligned accesses.  Note that this did not affect the ABI
4725               of a function with a "nullptr_t" parameter, as parameters have
4726               a minimum alignment.
4727
4728               This was fixed in -fabi-version=9, the default for GCC 5.2.
4729
4730           *   Target-specific attributes that affect the identity of a type,
4731               such as ia32 calling conventions on a function type (stdcall,
4732               regparm, etc.), did not affect the mangled name, leading to
4733               name collisions when function pointers were used as template
4734               arguments.
4735
4736               This was fixed in -fabi-version=10, the default for GCC 6.1.
4737
4738           This option also enables warnings about psABI-related changes.  The
4739           known psABI changes at this point include:
4740
4741           *   For SysV/x86-64, unions with "long double" members are passed
4742               in memory as specified in psABI.  Prior to GCC 4.4, this was
4743               not the case.  For example:
4744
4745                       union U {
4746                         long double ld;
4747                         int i;
4748                       };
4749
4750               "union U" is now always passed in memory.
4751
4752       -Wchar-subscripts
4753           Warn if an array subscript has type "char".  This is a common cause
4754           of error, as programmers often forget that this type is signed on
4755           some machines.  This warning is enabled by -Wall.
4756
4757       -Wno-coverage-mismatch
4758           Warn if feedback profiles do not match when using the -fprofile-use
4759           option.  If a source file is changed between compiling with
4760           -fprofile-generate and with -fprofile-use, the files with the
4761           profile feedback can fail to match the source file and GCC cannot
4762           use the profile feedback information.  By default, this warning is
4763           enabled and is treated as an error.  -Wno-coverage-mismatch can be
4764           used to disable the warning or -Wno-error=coverage-mismatch can be
4765           used to disable the error.  Disabling the error for this warning
4766           can result in poorly optimized code and is useful only in the case
4767           of very minor changes such as bug fixes to an existing code-base.
4768           Completely disabling the warning is not recommended.
4769
4770       -Wno-coverage-invalid-line-number
4771           Warn in case a function ends earlier than it begins due to an
4772           invalid linenum macros.  The warning is emitted only with
4773           --coverage enabled.
4774
4775           By default, this warning is enabled and is treated as an error.
4776           -Wno-coverage-invalid-line-number can be used to disable the
4777           warning or -Wno-error=coverage-invalid-line-number can be used to
4778           disable the error.
4779
4780       -Wno-cpp (C, Objective-C, C++, Objective-C++ and Fortran only)
4781           Suppress warning messages emitted by "#warning" directives.
4782
4783       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
4784           Give a warning when a value of type "float" is implicitly promoted
4785           to "double".  CPUs with a 32-bit "single-precision" floating-point
4786           unit implement "float" in hardware, but emulate "double" in
4787           software.  On such a machine, doing computations using "double"
4788           values is much more expensive because of the overhead required for
4789           software emulation.
4790
4791           It is easy to accidentally do computations with "double" because
4792           floating-point literals are implicitly of type "double".  For
4793           example, in:
4794
4795                   float area(float radius)
4796                   {
4797                      return 3.14159 * radius * radius;
4798                   }
4799
4800           the compiler performs the entire computation with "double" because
4801           the floating-point literal is a "double".
4802
4803       -Wduplicate-decl-specifier (C and Objective-C only)
4804           Warn if a declaration has duplicate "const", "volatile", "restrict"
4805           or "_Atomic" specifier.  This warning is enabled by -Wall.
4806
4807       -Wformat
4808       -Wformat=n
4809           Check calls to "printf" and "scanf", etc., to make sure that the
4810           arguments supplied have types appropriate to the format string
4811           specified, and that the conversions specified in the format string
4812           make sense.  This includes standard functions, and others specified
4813           by format attributes, in the "printf", "scanf", "strftime" and
4814           "strfmon" (an X/Open extension, not in the C standard) families (or
4815           other target-specific families).  Which functions are checked
4816           without format attributes having been specified depends on the
4817           standard version selected, and such checks of functions without the
4818           attribute specified are disabled by -ffreestanding or -fno-builtin.
4819
4820           The formats are checked against the format features supported by
4821           GNU libc version 2.2.  These include all ISO C90 and C99 features,
4822           as well as features from the Single Unix Specification and some BSD
4823           and GNU extensions.  Other library implementations may not support
4824           all these features; GCC does not support warning about features
4825           that go beyond a particular library's limitations.  However, if
4826           -Wpedantic is used with -Wformat, warnings are given about format
4827           features not in the selected standard version (but not for
4828           "strfmon" formats, since those are not in any version of the C
4829           standard).
4830
4831           -Wformat=1
4832           -Wformat
4833               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is
4834               equivalent to -Wformat=0.  Since -Wformat also checks for null
4835               format arguments for several functions, -Wformat also implies
4836               -Wnonnull.  Some aspects of this level of format checking can
4837               be disabled by the options: -Wno-format-contains-nul,
4838               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat
4839               is enabled by -Wall.
4840
4841           -Wformat=2
4842               Enable -Wformat plus additional format checks.  Currently
4843               equivalent to -Wformat -Wformat-nonliteral -Wformat-security
4844               -Wformat-y2k.
4845
4846       -Wno-format-contains-nul
4847           If -Wformat is specified, do not warn about format strings that
4848           contain NUL bytes.
4849
4850       -Wno-format-extra-args
4851           If -Wformat is specified, do not warn about excess arguments to a
4852           "printf" or "scanf" format function.  The C standard specifies that
4853           such arguments are ignored.
4854
4855           Where the unused arguments lie between used arguments that are
4856           specified with $ operand number specifications, normally warnings
4857           are still given, since the implementation could not know what type
4858           to pass to "va_arg" to skip the unused arguments.  However, in the
4859           case of "scanf" formats, this option suppresses the warning if the
4860           unused arguments are all pointers, since the Single Unix
4861           Specification says that such unused arguments are allowed.
4862
4863       -Wformat-overflow
4864       -Wformat-overflow=level
4865           Warn about calls to formatted input/output functions such as
4866           "sprintf" and "vsprintf" that might overflow the destination
4867           buffer.  When the exact number of bytes written by a format
4868           directive cannot be determined at compile-time it is estimated
4869           based on heuristics that depend on the level argument and on
4870           optimization.  While enabling optimization will in most cases
4871           improve the accuracy of the warning, it may also result in false
4872           positives.
4873
4874           -Wformat-overflow
4875           -Wformat-overflow=1
4876               Level 1 of -Wformat-overflow enabled by -Wformat employs a
4877               conservative approach that warns only about calls that most
4878               likely overflow the buffer.  At this level, numeric arguments
4879               to format directives with unknown values are assumed to have
4880               the value of one, and strings of unknown length to be empty.
4881               Numeric arguments that are known to be bounded to a subrange of
4882               their type, or string arguments whose output is bounded either
4883               by their directive's precision or by a finite set of string
4884               literals, are assumed to take on the value within the range
4885               that results in the most bytes on output.  For example, the
4886               call to "sprintf" below is diagnosed because even with both a
4887               and b equal to zero, the terminating NUL character ('\0')
4888               appended by the function to the destination buffer will be
4889               written past its end.  Increasing the size of the buffer by a
4890               single byte is sufficient to avoid the warning, though it may
4891               not be sufficient to avoid the overflow.
4892
4893                       void f (int a, int b)
4894                       {
4895                         char buf [13];
4896                         sprintf (buf, "a = %i, b = %i\n", a, b);
4897                       }
4898
4899           -Wformat-overflow=2
4900               Level 2 warns also about calls that might overflow the
4901               destination buffer given an argument of sufficient length or
4902               magnitude.  At level 2, unknown numeric arguments are assumed
4903               to have the minimum representable value for signed types with a
4904               precision greater than 1, and the maximum representable value
4905               otherwise.  Unknown string arguments whose length cannot be
4906               assumed to be bounded either by the directive's precision, or
4907               by a finite set of string literals they may evaluate to, or the
4908               character array they may point to, are assumed to be 1
4909               character long.
4910
4911               At level 2, the call in the example above is again diagnosed,
4912               but this time because with a equal to a 32-bit "INT_MIN" the
4913               first %i directive will write some of its digits beyond the end
4914               of the destination buffer.  To make the call safe regardless of
4915               the values of the two variables, the size of the destination
4916               buffer must be increased to at least 34 bytes.  GCC includes
4917               the minimum size of the buffer in an informational note
4918               following the warning.
4919
4920               An alternative to increasing the size of the destination buffer
4921               is to constrain the range of formatted values.  The maximum
4922               length of string arguments can be bounded by specifying the
4923               precision in the format directive.  When numeric arguments of
4924               format directives can be assumed to be bounded by less than the
4925               precision of their type, choosing an appropriate length
4926               modifier to the format specifier will reduce the required
4927               buffer size.  For example, if a and b in the example above can
4928               be assumed to be within the precision of the "short int" type
4929               then using either the %hi format directive or casting the
4930               argument to "short" reduces the maximum required size of the
4931               buffer to 24 bytes.
4932
4933                       void f (int a, int b)
4934                       {
4935                         char buf [23];
4936                         sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
4937                       }
4938
4939       -Wno-format-zero-length
4940           If -Wformat is specified, do not warn about zero-length formats.
4941           The C standard specifies that zero-length formats are allowed.
4942
4943       -Wformat-nonliteral
4944           If -Wformat is specified, also warn if the format string is not a
4945           string literal and so cannot be checked, unless the format function
4946           takes its format arguments as a "va_list".
4947
4948       -Wformat-security
4949           If -Wformat is specified, also warn about uses of format functions
4950           that represent possible security problems.  At present, this warns
4951           about calls to "printf" and "scanf" functions where the format
4952           string is not a string literal and there are no format arguments,
4953           as in "printf (foo);".  This may be a security hole if the format
4954           string came from untrusted input and contains %n.  (This is
4955           currently a subset of what -Wformat-nonliteral warns about, but in
4956           future warnings may be added to -Wformat-security that are not
4957           included in -Wformat-nonliteral.)
4958
4959       -Wformat-signedness
4960           If -Wformat is specified, also warn if the format string requires
4961           an unsigned argument and the argument is signed and vice versa.
4962
4963       -Wformat-truncation
4964       -Wformat-truncation=level
4965           Warn about calls to formatted input/output functions such as
4966           "snprintf" and "vsnprintf" that might result in output truncation.
4967           When the exact number of bytes written by a format directive cannot
4968           be determined at compile-time it is estimated based on heuristics
4969           that depend on the level argument and on optimization.  While
4970           enabling optimization will in most cases improve the accuracy of
4971           the warning, it may also result in false positives.  Except as
4972           noted otherwise, the option uses the same logic -Wformat-overflow.
4973
4974           -Wformat-truncation
4975           -Wformat-truncation=1
4976               Level 1 of -Wformat-truncation enabled by -Wformat employs a
4977               conservative approach that warns only about calls to bounded
4978               functions whose return value is unused and that will most
4979               likely result in output truncation.
4980
4981           -Wformat-truncation=2
4982               Level 2 warns also about calls to bounded functions whose
4983               return value is used and that might result in truncation given
4984               an argument of sufficient length or magnitude.
4985
4986       -Wformat-y2k
4987           If -Wformat is specified, also warn about "strftime" formats that
4988           may yield only a two-digit year.
4989
4990       -Wnonnull
4991           Warn about passing a null pointer for arguments marked as requiring
4992           a non-null value by the "nonnull" function attribute.
4993
4994           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
4995           with the -Wno-nonnull option.
4996
4997       -Wnonnull-compare
4998           Warn when comparing an argument marked with the "nonnull" function
4999           attribute against null inside the function.
5000
5001           -Wnonnull-compare is included in -Wall.  It can be disabled with
5002           the -Wno-nonnull-compare option.
5003
5004       -Wnull-dereference
5005           Warn if the compiler detects paths that trigger erroneous or
5006           undefined behavior due to dereferencing a null pointer.  This
5007           option is only active when -fdelete-null-pointer-checks is active,
5008           which is enabled by optimizations in most targets.  The precision
5009           of the warnings depends on the optimization options used.
5010
5011       -Winfinite-recursion
5012           Warn about infinitely recursive calls.  The warning is effective at
5013           all optimization levels but requires optimization in order to
5014           detect infinite recursion in calls between two or more functions.
5015           -Winfinite-recursion is included in -Wall.
5016
5017       -Winit-self (C, C++, Objective-C and Objective-C++ only)
5018           Warn about uninitialized variables that are initialized with
5019           themselves.  Note this option can only be used with the
5020           -Wuninitialized option.
5021
5022           For example, GCC warns about "i" being uninitialized in the
5023           following snippet only when -Winit-self has been specified:
5024
5025                   int f()
5026                   {
5027                     int i = i;
5028                     return i;
5029                   }
5030
5031           This warning is enabled by -Wall in C++.
5032
5033       -Wno-implicit-int (C and Objective-C only)
5034           This option controls warnings when a declaration does not specify a
5035           type.  This warning is enabled by default in C99 and later dialects
5036           of C, and also by -Wall.
5037
5038       -Wno-implicit-function-declaration (C and Objective-C only)
5039           This option controls warnings when a function is used before being
5040           declared.  This warning is enabled by default in C99 and later
5041           dialects of C, and also by -Wall.  The warning is made into an
5042           error by -pedantic-errors.
5043
5044       -Wimplicit (C and Objective-C only)
5045           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
5046           warning is enabled by -Wall.
5047
5048       -Wimplicit-fallthrough
5049           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and
5050           -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0.
5051
5052       -Wimplicit-fallthrough=n
5053           Warn when a switch case falls through.  For example:
5054
5055                   switch (cond)
5056                     {
5057                     case 1:
5058                       a = 1;
5059                       break;
5060                     case 2:
5061                       a = 2;
5062                     case 3:
5063                       a = 3;
5064                       break;
5065                     }
5066
5067           This warning does not warn when the last statement of a case cannot
5068           fall through, e.g. when there is a return statement or a call to
5069           function declared with the noreturn attribute.
5070           -Wimplicit-fallthrough= also takes into account control flow
5071           statements, such as ifs, and only warns when appropriate.  E.g.
5072
5073                   switch (cond)
5074                     {
5075                     case 1:
5076                       if (i > 3) {
5077                         bar (5);
5078                         break;
5079                       } else if (i < 1) {
5080                         bar (0);
5081                       } else
5082                         return;
5083                     default:
5084                       ...
5085                     }
5086
5087           Since there are occasions where a switch case fall through is
5088           desirable, GCC provides an attribute, "__attribute__
5089           ((fallthrough))", that is to be used along with a null statement to
5090           suppress this warning that would normally occur:
5091
5092                   switch (cond)
5093                     {
5094                     case 1:
5095                       bar (0);
5096                       __attribute__ ((fallthrough));
5097                     default:
5098                       ...
5099                     }
5100
5101           C++17 provides a standard way to suppress the
5102           -Wimplicit-fallthrough warning using "[[fallthrough]];" instead of
5103           the GNU attribute.  In C++11 or C++14 users can use
5104           "[[gnu::fallthrough]];", which is a GNU extension.  Instead of
5105           these attributes, it is also possible to add a fallthrough comment
5106           to silence the warning.  The whole body of the C or C++ style
5107           comment should match the given regular expressions listed below.
5108           The option argument n specifies what kind of comments are accepted:
5109
5110           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
5111           *<-Wimplicit-fallthrough=1 matches ".*" regular>
5112               expression, any comment is used as fallthrough comment.
5113
5114           *<-Wimplicit-fallthrough=2 case insensitively matches>
5115               ".*falls?[ \t-]*thr(ough|u).*" regular expression.
5116
5117           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
5118               following regular expressions:
5119
5120               *<"-fallthrough">
5121               *<"@fallthrough@">
5122               *<"lint -fallthrough[ \t]*">
5123               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S |
5124               |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?">
5125               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s |
5126               |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?">
5127               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s |
5128               |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?">
5129           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
5130               following regular expressions:
5131
5132               *<"-fallthrough">
5133               *<"@fallthrough@">
5134               *<"lint -fallthrough[ \t]*">
5135               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
5136           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
5137               fallthrough comments, only attributes disable the warning.
5138
5139           The comment needs to be followed after optional whitespace and
5140           other comments by "case" or "default" keywords or by a user label
5141           that precedes some "case" or "default" label.
5142
5143                   switch (cond)
5144                     {
5145                     case 1:
5146                       bar (0);
5147                       /* FALLTHRU */
5148                     default:
5149                       ...
5150                     }
5151
5152           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.
5153
5154       -Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)
5155           Control if warnings triggered by the "warn_if_not_aligned"
5156           attribute should be issued.  These warnings are enabled by default.
5157
5158       -Wignored-qualifiers (C and C++ only)
5159           Warn if the return type of a function has a type qualifier such as
5160           "const".  For ISO C such a type qualifier has no effect, since the
5161           value returned by a function is not an lvalue.  For C++, the
5162           warning is only emitted for scalar types or "void".  ISO C
5163           prohibits qualified "void" return types on function definitions, so
5164           such return types always receive a warning even without this
5165           option.
5166
5167           This warning is also enabled by -Wextra.
5168
5169       -Wno-ignored-attributes (C and C++ only)
5170           This option controls warnings when an attribute is ignored.  This
5171           is different from the -Wattributes option in that it warns whenever
5172           the compiler decides to drop an attribute, not that the attribute
5173           is either unknown, used in a wrong place, etc.  This warning is
5174           enabled by default.
5175
5176       -Wmain
5177           Warn if the type of "main" is suspicious.  "main" should be a
5178           function with external linkage, returning int, taking either zero
5179           arguments, two, or three arguments of appropriate types.  This
5180           warning is enabled by default in C++ and is enabled by either -Wall
5181           or -Wpedantic.
5182
5183       -Wmisleading-indentation (C and C++ only)
5184           Warn when the indentation of the code does not reflect the block
5185           structure.  Specifically, a warning is issued for "if", "else",
5186           "while", and "for" clauses with a guarded statement that does not
5187           use braces, followed by an unguarded statement with the same
5188           indentation.
5189
5190           In the following example, the call to "bar" is misleadingly
5191           indented as if it were guarded by the "if" conditional.
5192
5193                     if (some_condition ())
5194                       foo ();
5195                       bar ();  /* Gotcha: this is not guarded by the "if".  */
5196
5197           In the case of mixed tabs and spaces, the warning uses the
5198           -ftabstop= option to determine if the statements line up
5199           (defaulting to 8).
5200
5201           The warning is not issued for code involving multiline preprocessor
5202           logic such as the following example.
5203
5204                     if (flagA)
5205                       foo (0);
5206                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
5207                     if (flagB)
5208                   #endif
5209                       foo (1);
5210
5211           The warning is not issued after a "#line" directive, since this
5212           typically indicates autogenerated code, and no assumptions can be
5213           made about the layout of the file that the directive references.
5214
5215           This warning is enabled by -Wall in C and C++.
5216
5217       -Wmissing-attributes
5218           Warn when a declaration of a function is missing one or more
5219           attributes that a related function is declared with and whose
5220           absence may adversely affect the correctness or efficiency of
5221           generated code.  For example, the warning is issued for
5222           declarations of aliases that use attributes to specify less
5223           restrictive requirements than those of their targets.  This
5224           typically represents a potential optimization opportunity.  By
5225           contrast, the -Wattribute-alias=2 option controls warnings issued
5226           when the alias is more restrictive than the target, which could
5227           lead to incorrect code generation.  Attributes considered include
5228           "alloc_align", "alloc_size", "cold", "const", "hot", "leaf",
5229           "malloc", "nonnull", "noreturn", "nothrow", "pure",
5230           "returns_nonnull", and "returns_twice".
5231
5232           In C++, the warning is issued when an explicit specialization of a
5233           primary template declared with attribute "alloc_align",
5234           "alloc_size", "assume_aligned", "format", "format_arg", "malloc",
5235           or "nonnull" is declared without it.  Attributes "deprecated",
5236           "error", and "warning" suppress the warning..
5237
5238           You can use the "copy" attribute to apply the same set of
5239           attributes to a declaration as that on another declaration without
5240           explicitly enumerating the attributes. This attribute can be
5241           applied to declarations of functions, variables, or types.
5242
5243           -Wmissing-attributes is enabled by -Wall.
5244
5245           For example, since the declaration of the primary function template
5246           below makes use of both attribute "malloc" and "alloc_size" the
5247           declaration of the explicit specialization of the template is
5248           diagnosed because it is missing one of the attributes.
5249
5250                   template <class T>
5251                   T* __attribute__ ((malloc, alloc_size (1)))
5252                   allocate (size_t);
5253
5254                   template <>
5255                   void* __attribute__ ((malloc))   // missing alloc_size
5256                   allocate<void> (size_t);
5257
5258       -Wmissing-braces
5259           Warn if an aggregate or union initializer is not fully bracketed.
5260           In the following example, the initializer for "a" is not fully
5261           bracketed, but that for "b" is fully bracketed.
5262
5263                   int a[2][2] = { 0, 1, 2, 3 };
5264                   int b[2][2] = { { 0, 1 }, { 2, 3 } };
5265
5266           This warning is enabled by -Wall.
5267
5268       -Wmissing-include-dirs (C, C++, Objective-C, Objective-C++ and Fortran
5269       only)
5270           Warn if a user-supplied include directory does not exist. This
5271           opions is disabled by default for C, C++, Objective-C and
5272           Objective-C++. For Fortran, it is partially enabled by default by
5273           warning for -I and -J, only.
5274
5275       -Wno-missing-profile
5276           This option controls warnings if feedback profiles are missing when
5277           using the -fprofile-use option.  This option diagnoses those cases
5278           where a new function or a new file is added between compiling with
5279           -fprofile-generate and with -fprofile-use, without regenerating the
5280           profiles.  In these cases, the profile feedback data files do not
5281           contain any profile feedback information for the newly added
5282           function or file respectively.  Also, in the case when profile
5283           count data (.gcda) files are removed, GCC cannot use any profile
5284           feedback information.  In all these cases, warnings are issued to
5285           inform you that a profile generation step is due.  Ignoring the
5286           warning can result in poorly optimized code.  -Wno-missing-profile
5287           can be used to disable the warning, but this is not recommended and
5288           should be done only when non-existent profile data is justified.
5289
5290       -Wmismatched-dealloc
5291           Warn for calls to deallocation functions with pointer arguments
5292           returned from from allocations functions for which the former isn't
5293           a suitable deallocator.  A pair of functions can be associated as
5294           matching allocators and deallocators by use of attribute "malloc".
5295           Unless disabled by the -fno-builtin option the standard functions
5296           "calloc", "malloc", "realloc", and "free", as well as the
5297           corresponding forms of C++ "operator new" and "operator delete" are
5298           implicitly associated as matching allocators and deallocators.  In
5299           the following example "mydealloc" is the deallocator for pointers
5300           returned from "myalloc".
5301
5302                   void mydealloc (void*);
5303
5304                   __attribute__ ((malloc (mydealloc, 1))) void*
5305                   myalloc (size_t);
5306
5307                   void f (void)
5308                   {
5309                     void *p = myalloc (32);
5310                     // ...use p...
5311                     free (p);   // warning: not a matching deallocator for myalloc
5312                     mydealloc (p);   // ok
5313                   }
5314
5315           In C++, the related option -Wmismatched-new-delete diagnoses
5316           mismatches involving either "operator new" or "operator delete".
5317
5318           Option -Wmismatched-dealloc is included in -Wall.
5319
5320       -Wmultistatement-macros
5321           Warn about unsafe multiple statement macros that appear to be
5322           guarded by a clause such as "if", "else", "for", "switch", or
5323           "while", in which only the first statement is actually guarded
5324           after the macro is expanded.
5325
5326           For example:
5327
5328                   #define DOIT x++; y++
5329                   if (c)
5330                     DOIT;
5331
5332           will increment "y" unconditionally, not just when "c" holds.  The
5333           can usually be fixed by wrapping the macro in a do-while loop:
5334
5335                   #define DOIT do { x++; y++; } while (0)
5336                   if (c)
5337                     DOIT;
5338
5339           This warning is enabled by -Wall in C and C++.
5340
5341       -Wparentheses
5342           Warn if parentheses are omitted in certain contexts, such as when
5343           there is an assignment in a context where a truth value is
5344           expected, or when operators are nested whose precedence people
5345           often get confused about.
5346
5347           Also warn if a comparison like "x<=y<=z" appears; this is
5348           equivalent to "(x<=y ? 1 : 0) <= z", which is a different
5349           interpretation from that of ordinary mathematical notation.
5350
5351           Also warn for dangerous uses of the GNU extension to "?:" with
5352           omitted middle operand. When the condition in the "?": operator is
5353           a boolean expression, the omitted value is always 1.  Often
5354           programmers expect it to be a value computed inside the conditional
5355           expression instead.
5356
5357           For C++ this also warns for some cases of unnecessary parentheses
5358           in declarations, which can indicate an attempt at a function call
5359           instead of a declaration:
5360
5361                   {
5362                     // Declares a local variable called mymutex.
5363                     std::unique_lock<std::mutex> (mymutex);
5364                     // User meant std::unique_lock<std::mutex> lock (mymutex);
5365                   }
5366
5367           This warning is enabled by -Wall.
5368
5369       -Wsequence-point
5370           Warn about code that may have undefined semantics because of
5371           violations of sequence point rules in the C and C++ standards.
5372
5373           The C and C++ standards define the order in which expressions in a
5374           C/C++ program are evaluated in terms of sequence points, which
5375           represent a partial ordering between the execution of parts of the
5376           program: those executed before the sequence point, and those
5377           executed after it.  These occur after the evaluation of a full
5378           expression (one which is not part of a larger expression), after
5379           the evaluation of the first operand of a "&&", "||", "? :" or ","
5380           (comma) operator, before a function is called (but after the
5381           evaluation of its arguments and the expression denoting the called
5382           function), and in certain other places.  Other than as expressed by
5383           the sequence point rules, the order of evaluation of subexpressions
5384           of an expression is not specified.  All these rules describe only a
5385           partial order rather than a total order, since, for example, if two
5386           functions are called within one expression with no sequence point
5387           between them, the order in which the functions are called is not
5388           specified.  However, the standards committee have ruled that
5389           function calls do not overlap.
5390
5391           It is not specified when between sequence points modifications to
5392           the values of objects take effect.  Programs whose behavior depends
5393           on this have undefined behavior; the C and C++ standards specify
5394           that "Between the previous and next sequence point an object shall
5395           have its stored value modified at most once by the evaluation of an
5396           expression.  Furthermore, the prior value shall be read only to
5397           determine the value to be stored.".  If a program breaks these
5398           rules, the results on any particular implementation are entirely
5399           unpredictable.
5400
5401           Examples of code with undefined behavior are "a = a++;", "a[n] =
5402           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
5403           diagnosed by this option, and it may give an occasional false
5404           positive result, but in general it has been found fairly effective
5405           at detecting this sort of problem in programs.
5406
5407           The C++17 standard will define the order of evaluation of operands
5408           in more cases: in particular it requires that the right-hand side
5409           of an assignment be evaluated before the left-hand side, so the
5410           above examples are no longer undefined.  But this option will still
5411           warn about them, to help people avoid writing code that is
5412           undefined in C and earlier revisions of C++.
5413
5414           The standard is worded confusingly, therefore there is some debate
5415           over the precise meaning of the sequence point rules in subtle
5416           cases.  Links to discussions of the problem, including proposed
5417           formal definitions, may be found on the GCC readings page, at
5418           <https://gcc.gnu.org/readings.html>.
5419
5420           This warning is enabled by -Wall for C and C++.
5421
5422       -Wno-return-local-addr
5423           Do not warn about returning a pointer (or in C++, a reference) to a
5424           variable that goes out of scope after the function returns.
5425
5426       -Wreturn-type
5427           Warn whenever a function is defined with a return type that
5428           defaults to "int".  Also warn about any "return" statement with no
5429           return value in a function whose return type is not "void" (falling
5430           off the end of the function body is considered returning without a
5431           value).
5432
5433           For C only, warn about a "return" statement with an expression in a
5434           function whose return type is "void", unless the expression type is
5435           also "void".  As a GNU extension, the latter case is accepted
5436           without a warning unless -Wpedantic is used.  Attempting to use the
5437           return value of a non-"void" function other than "main" that flows
5438           off the end by reaching the closing curly brace that terminates the
5439           function is undefined.
5440
5441           Unlike in C, in C++, flowing off the end of a non-"void" function
5442           other than "main" results in undefined behavior even when the value
5443           of the function is not used.
5444
5445           This warning is enabled by default in C++ and by -Wall otherwise.
5446
5447       -Wno-shift-count-negative
5448           Controls warnings if a shift count is negative.  This warning is
5449           enabled by default.
5450
5451       -Wno-shift-count-overflow
5452           Controls warnings if a shift count is greater than or equal to the
5453           bit width of the type.  This warning is enabled by default.
5454
5455       -Wshift-negative-value
5456           Warn if left shifting a negative value.  This warning is enabled by
5457           -Wextra in C99 (and newer) and C++11 to C++17 modes.
5458
5459       -Wno-shift-overflow
5460       -Wshift-overflow=n
5461           These options control warnings about left shift overflows.
5462
5463           -Wshift-overflow=1
5464               This is the warning level of -Wshift-overflow and is enabled by
5465               default in C99 and C++11 modes (and newer).  This warning level
5466               does not warn about left-shifting 1 into the sign bit.
5467               (However, in C, such an overflow is still rejected in contexts
5468               where an integer constant expression is required.)  No warning
5469               is emitted in C++20 mode (and newer), as signed left shifts
5470               always wrap.
5471
5472           -Wshift-overflow=2
5473               This warning level also warns about left-shifting 1 into the
5474               sign bit, unless C++14 mode (or newer) is active.
5475
5476       -Wswitch
5477           Warn whenever a "switch" statement has an index of enumerated type
5478           and lacks a "case" for one or more of the named codes of that
5479           enumeration.  (The presence of a "default" label prevents this
5480           warning.)  "case" labels outside the enumeration range also provoke
5481           warnings when this option is used (even if there is a "default"
5482           label).  This warning is enabled by -Wall.
5483
5484       -Wswitch-default
5485           Warn whenever a "switch" statement does not have a "default" case.
5486
5487       -Wswitch-enum
5488           Warn whenever a "switch" statement has an index of enumerated type
5489           and lacks a "case" for one or more of the named codes of that
5490           enumeration.  "case" labels outside the enumeration range also
5491           provoke warnings when this option is used.  The only difference
5492           between -Wswitch and this option is that this option gives a
5493           warning about an omitted enumeration code even if there is a
5494           "default" label.
5495
5496       -Wno-switch-bool
5497           Do not warn when a "switch" statement has an index of boolean type
5498           and the case values are outside the range of a boolean type.  It is
5499           possible to suppress this warning by casting the controlling
5500           expression to a type other than "bool".  For example:
5501
5502                   switch ((int) (a == 4))
5503                     {
5504                     ...
5505                     }
5506
5507           This warning is enabled by default for C and C++ programs.
5508
5509       -Wno-switch-outside-range
5510           This option controls warnings when a "switch" case has a value that
5511           is outside of its respective type range.  This warning is enabled
5512           by default for C and C++ programs.
5513
5514       -Wno-switch-unreachable
5515           Do not warn when a "switch" statement contains statements between
5516           the controlling expression and the first case label, which will
5517           never be executed.  For example:
5518
5519                   switch (cond)
5520                     {
5521                      i = 15;
5522                     ...
5523                      case 5:
5524                     ...
5525                     }
5526
5527           -Wswitch-unreachable does not warn if the statement between the
5528           controlling expression and the first case label is just a
5529           declaration:
5530
5531                   switch (cond)
5532                     {
5533                      int i;
5534                     ...
5535                      case 5:
5536                      i = 5;
5537                     ...
5538                     }
5539
5540           This warning is enabled by default for C and C++ programs.
5541
5542       -Wsync-nand (C and C++ only)
5543           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
5544           built-in functions are used.  These functions changed semantics in
5545           GCC 4.4.
5546
5547       -Wtrivial-auto-var-init
5548           Warn when "-ftrivial-auto-var-init" cannot initialize the automatic
5549           variable.  A common situation is an automatic variable that is
5550           declared between the controlling expression and the first case
5551           label of a "switch" statement.
5552
5553       -Wunused-but-set-parameter
5554           Warn whenever a function parameter is assigned to, but otherwise
5555           unused (aside from its declaration).
5556
5557           To suppress this warning use the "unused" attribute.
5558
5559           This warning is also enabled by -Wunused together with -Wextra.
5560
5561       -Wunused-but-set-variable
5562           Warn whenever a local variable is assigned to, but otherwise unused
5563           (aside from its declaration).  This warning is enabled by -Wall.
5564
5565           To suppress this warning use the "unused" attribute.
5566
5567           This warning is also enabled by -Wunused, which is enabled by
5568           -Wall.
5569
5570       -Wunused-function
5571           Warn whenever a static function is declared but not defined or a
5572           non-inline static function is unused.  This warning is enabled by
5573           -Wall.
5574
5575       -Wunused-label
5576           Warn whenever a label is declared but not used.  This warning is
5577           enabled by -Wall.
5578
5579           To suppress this warning use the "unused" attribute.
5580
5581       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
5582           Warn when a typedef locally defined in a function is not used.
5583           This warning is enabled by -Wall.
5584
5585       -Wunused-parameter
5586           Warn whenever a function parameter is unused aside from its
5587           declaration.
5588
5589           To suppress this warning use the "unused" attribute.
5590
5591       -Wno-unused-result
5592           Do not warn if a caller of a function marked with attribute
5593           "warn_unused_result" does not use its return value. The default is
5594           -Wunused-result.
5595
5596       -Wunused-variable
5597           Warn whenever a local or static variable is unused aside from its
5598           declaration. This option implies -Wunused-const-variable=1 for C,
5599           but not for C++. This warning is enabled by -Wall.
5600
5601           To suppress this warning use the "unused" attribute.
5602
5603       -Wunused-const-variable
5604       -Wunused-const-variable=n
5605           Warn whenever a constant static variable is unused aside from its
5606           declaration.  -Wunused-const-variable=1 is enabled by
5607           -Wunused-variable for C, but not for C++. In C this declares
5608           variable storage, but in C++ this is not an error since const
5609           variables take the place of "#define"s.
5610
5611           To suppress this warning use the "unused" attribute.
5612
5613           -Wunused-const-variable=1
5614               This is the warning level that is enabled by -Wunused-variable
5615               for C.  It warns only about unused static const variables
5616               defined in the main compilation unit, but not about static
5617               const variables declared in any header included.
5618
5619           -Wunused-const-variable=2
5620               This warning level also warns for unused constant static
5621               variables in headers (excluding system headers).  This is the
5622               warning level of -Wunused-const-variable and must be explicitly
5623               requested since in C++ this isn't an error and in C it might be
5624               harder to clean up all headers included.
5625
5626       -Wunused-value
5627           Warn whenever a statement computes a result that is explicitly not
5628           used. To suppress this warning cast the unused expression to
5629           "void". This includes an expression-statement or the left-hand side
5630           of a comma expression that contains no side effects. For example,
5631           an expression such as "x[i,j]" causes a warning, while
5632           "x[(void)i,j]" does not.
5633
5634           This warning is enabled by -Wall.
5635
5636       -Wunused
5637           All the above -Wunused options combined.
5638
5639           In order to get a warning about an unused function parameter, you
5640           must either specify -Wextra -Wunused (note that -Wall implies
5641           -Wunused), or separately specify -Wunused-parameter.
5642
5643       -Wuninitialized
5644           Warn if an object with automatic or allocated storage duration is
5645           used without having been initialized.  In C++, also warn if a non-
5646           static reference or non-static "const" member appears in a class
5647           without constructors.
5648
5649           In addition, passing a pointer (or in C++, a reference) to an
5650           uninitialized object to a "const"-qualified argument of a built-in
5651           function known to read the object is also diagnosed by this
5652           warning.  (-Wmaybe-uninitialized is issued for ordinary functions.)
5653
5654           If you want to warn about code that uses the uninitialized value of
5655           the variable in its own initializer, use the -Winit-self option.
5656
5657           These warnings occur for individual uninitialized elements of
5658           structure, union or array variables as well as for variables that
5659           are uninitialized as a whole.  They do not occur for variables or
5660           elements declared "volatile".  Because these warnings depend on
5661           optimization, the exact variables or elements for which there are
5662           warnings depend on the precise optimization options and version of
5663           GCC used.
5664
5665           Note that there may be no warning about a variable that is used
5666           only to compute a value that itself is never used, because such
5667           computations may be deleted by data flow analysis before the
5668           warnings are printed.
5669
5670           In C++, this warning also warns about using uninitialized objects
5671           in member-initializer-lists.  For example, GCC warns about "b"
5672           being uninitialized in the following snippet:
5673
5674                   struct A {
5675                     int a;
5676                     int b;
5677                     A() : a(b) { }
5678                   };
5679
5680       -Wno-invalid-memory-model
5681           This option controls warnings for invocations of __atomic Builtins,
5682           __sync Builtins, and the C11 atomic generic functions with a memory
5683           consistency argument that is either invalid for the operation or
5684           outside the range of values of the "memory_order" enumeration.  For
5685           example, since the "__atomic_store" and "__atomic_store_n" built-
5686           ins are only defined for the relaxed, release, and sequentially
5687           consistent memory orders the following code is diagnosed:
5688
5689                   void store (int *i)
5690                   {
5691                     __atomic_store_n (i, 0, memory_order_consume);
5692                   }
5693
5694           -Winvalid-memory-model is enabled by default.
5695
5696       -Wmaybe-uninitialized
5697           For an object with automatic or allocated storage duration, if
5698           there exists a path from the function entry to a use of the object
5699           that is initialized, but there exist some other paths for which the
5700           object is not initialized, the compiler emits a warning if it
5701           cannot prove the uninitialized paths are not executed at run time.
5702
5703           In addition, passing a pointer (or in C++, a reference) to an
5704           uninitialized object to a "const"-qualified function argument is
5705           also diagnosed by this warning.  (-Wuninitialized is issued for
5706           built-in functions known to read the object.)  Annotating the
5707           function with attribute "access (none)" indicates that the argument
5708           isn't used to access the object and avoids the warning.
5709
5710           These warnings are only possible in optimizing compilation, because
5711           otherwise GCC does not keep track of the state of variables.
5712
5713           These warnings are made optional because GCC may not be able to
5714           determine when the code is correct in spite of appearing to have an
5715           error.  Here is one example of how this can happen:
5716
5717                   {
5718                     int x;
5719                     switch (y)
5720                       {
5721                       case 1: x = 1;
5722                         break;
5723                       case 2: x = 4;
5724                         break;
5725                       case 3: x = 5;
5726                       }
5727                     foo (x);
5728                   }
5729
5730           If the value of "y" is always 1, 2 or 3, then "x" is always
5731           initialized, but GCC doesn't know this. To suppress the warning,
5732           you need to provide a default case with assert(0) or similar code.
5733
5734           This option also warns when a non-volatile automatic variable might
5735           be changed by a call to "longjmp".  The compiler sees only the
5736           calls to "setjmp".  It cannot know where "longjmp" will be called;
5737           in fact, a signal handler could call it at any point in the code.
5738           As a result, you may get a warning even when there is in fact no
5739           problem because "longjmp" cannot in fact be called at the place
5740           that would cause a problem.
5741
5742           Some spurious warnings can be avoided if you declare all the
5743           functions you use that never return as "noreturn".
5744
5745           This warning is enabled by -Wall or -Wextra.
5746
5747       -Wunknown-pragmas
5748           Warn when a "#pragma" directive is encountered that is not
5749           understood by GCC.  If this command-line option is used, warnings
5750           are even issued for unknown pragmas in system header files.  This
5751           is not the case if the warnings are only enabled by the -Wall
5752           command-line option.
5753
5754       -Wno-pragmas
5755           Do not warn about misuses of pragmas, such as incorrect parameters,
5756           invalid syntax, or conflicts between pragmas.  See also
5757           -Wunknown-pragmas.
5758
5759       -Wno-prio-ctor-dtor
5760           Do not warn if a priority from 0 to 100 is used for constructor or
5761           destructor.  The use of constructor and destructor attributes allow
5762           you to assign a priority to the constructor/destructor to control
5763           its order of execution before "main" is called or after it returns.
5764           The priority values must be greater than 100 as the compiler
5765           reserves priority values between 0--100 for the implementation.
5766
5767       -Wstrict-aliasing
5768           This option is only active when -fstrict-aliasing is active.  It
5769           warns about code that might break the strict aliasing rules that
5770           the compiler is using for optimization.  The warning does not catch
5771           all cases, but does attempt to catch the more common pitfalls.  It
5772           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3
5773
5774       -Wstrict-aliasing=n
5775           This option is only active when -fstrict-aliasing is active.  It
5776           warns about code that might break the strict aliasing rules that
5777           the compiler is using for optimization.  Higher levels correspond
5778           to higher accuracy (fewer false positives).  Higher levels also
5779           correspond to more effort, similar to the way -O works.
5780           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.
5781
5782           Level 1: Most aggressive, quick, least accurate.  Possibly useful
5783           when higher levels do not warn but -fstrict-aliasing still breaks
5784           the code, as it has very few false negatives.  However, it has many
5785           false positives.  Warns for all pointer conversions between
5786           possibly incompatible types, even if never dereferenced.  Runs in
5787           the front end only.
5788
5789           Level 2: Aggressive, quick, not too precise.  May still have many
5790           false positives (not as many as level 1 though), and few false
5791           negatives (but possibly more than level 1).  Unlike level 1, it
5792           only warns when an address is taken.  Warns about incomplete types.
5793           Runs in the front end only.
5794
5795           Level 3 (default for -Wstrict-aliasing): Should have very few false
5796           positives and few false negatives.  Slightly slower than levels 1
5797           or 2 when optimization is enabled.  Takes care of the common
5798           pun+dereference pattern in the front end: "*(int*)&some_float".  If
5799           optimization is enabled, it also runs in the back end, where it
5800           deals with multiple statement cases using flow-sensitive points-to
5801           information.  Only warns when the converted pointer is
5802           dereferenced.  Does not warn about incomplete types.
5803
5804       -Wstrict-overflow
5805       -Wstrict-overflow=n
5806           This option is only active when signed overflow is undefined.  It
5807           warns about cases where the compiler optimizes based on the
5808           assumption that signed overflow does not occur.  Note that it does
5809           not warn about all cases where the code might overflow: it only
5810           warns about cases where the compiler implements some optimization.
5811           Thus this warning depends on the optimization level.
5812
5813           An optimization that assumes that signed overflow does not occur is
5814           perfectly safe if the values of the variables involved are such
5815           that overflow never does, in fact, occur.  Therefore this warning
5816           can easily give a false positive: a warning about code that is not
5817           actually a problem.  To help focus on important issues, several
5818           warning levels are defined.  No warnings are issued for the use of
5819           undefined signed overflow when estimating how many iterations a
5820           loop requires, in particular when determining whether a loop will
5821           be executed at all.
5822
5823           -Wstrict-overflow=1
5824               Warn about cases that are both questionable and easy to avoid.
5825               For example the compiler simplifies "x + 1 > x" to 1.  This
5826               level of -Wstrict-overflow is enabled by -Wall; higher levels
5827               are not, and must be explicitly requested.
5828
5829           -Wstrict-overflow=2
5830               Also warn about other cases where a comparison is simplified to
5831               a constant.  For example: "abs (x) >= 0".  This can only be
5832               simplified when signed integer overflow is undefined, because
5833               "abs (INT_MIN)" overflows to "INT_MIN", which is less than
5834               zero.  -Wstrict-overflow (with no level) is the same as
5835               -Wstrict-overflow=2.
5836
5837           -Wstrict-overflow=3
5838               Also warn about other cases where a comparison is simplified.
5839               For example: "x + 1 > 1" is simplified to "x > 0".
5840
5841           -Wstrict-overflow=4
5842               Also warn about other simplifications not covered by the above
5843               cases.  For example: "(x * 10) / 5" is simplified to "x * 2".
5844
5845           -Wstrict-overflow=5
5846               Also warn about cases where the compiler reduces the magnitude
5847               of a constant involved in a comparison.  For example: "x + 2 >
5848               y" is simplified to "x + 1 >= y".  This is reported only at the
5849               highest warning level because this simplification applies to
5850               many comparisons, so this warning level gives a very large
5851               number of false positives.
5852
5853       -Wstring-compare
5854           Warn for calls to "strcmp" and "strncmp" whose result is determined
5855           to be either zero or non-zero in tests for such equality owing to
5856           the length of one argument being greater than the size of the array
5857           the other argument is stored in (or the bound in the case of
5858           "strncmp").  Such calls could be mistakes.  For example, the call
5859           to "strcmp" below is diagnosed because its result is necessarily
5860           non-zero irrespective of the contents of the array "a".
5861
5862                   extern char a[4];
5863                   void f (char *d)
5864                   {
5865                     strcpy (d, "string");
5866                     ...
5867                     if (0 == strcmp (a, d))   // cannot be true
5868                       puts ("a and d are the same");
5869                   }
5870
5871           -Wstring-compare is enabled by -Wextra.
5872
5873       -Wno-stringop-overflow
5874       -Wstringop-overflow
5875       -Wstringop-overflow=type
5876           Warn for calls to string manipulation functions such as "memcpy"
5877           and "strcpy" that are determined to overflow the destination
5878           buffer.  The optional argument is one greater than the type of
5879           Object Size Checking to perform to determine the size of the
5880           destination.  The argument is meaningful only for functions that
5881           operate on character arrays but not for raw memory functions like
5882           "memcpy" which always make use of Object Size type-0.  The option
5883           also warns for calls that specify a size in excess of the largest
5884           possible object or at most "SIZE_MAX / 2" bytes.  The option
5885           produces the best results with optimization enabled but can detect
5886           a small subset of simple buffer overflows even without optimization
5887           in calls to the GCC built-in functions like "__builtin_memcpy" that
5888           correspond to the standard functions.  In any case, the option
5889           warns about just a subset of buffer overflows detected by the
5890           corresponding overflow checking built-ins.  For example, the option
5891           issues a warning for the "strcpy" call below because it copies at
5892           least 5 characters (the string "blue" including the terminating
5893           NUL) into the buffer of size 4.
5894
5895                   enum Color { blue, purple, yellow };
5896                   const char* f (enum Color clr)
5897                   {
5898                     static char buf [4];
5899                     const char *str;
5900                     switch (clr)
5901                       {
5902                         case blue: str = "blue"; break;
5903                         case purple: str = "purple"; break;
5904                         case yellow: str = "yellow"; break;
5905                       }
5906
5907                     return strcpy (buf, str);   // warning here
5908                   }
5909
5910           Option -Wstringop-overflow=2 is enabled by default.
5911
5912           -Wstringop-overflow
5913           -Wstringop-overflow=1
5914               The -Wstringop-overflow=1 option uses type-zero Object Size
5915               Checking to determine the sizes of destination objects.  At
5916               this setting the option does not warn for writes past the end
5917               of subobjects of larger objects accessed by pointers unless the
5918               size of the largest surrounding object is known.  When the
5919               destination may be one of several objects it is assumed to be
5920               the largest one of them.  On Linux systems, when optimization
5921               is enabled at this setting the option warns for the same code
5922               as when the "_FORTIFY_SOURCE" macro is defined to a non-zero
5923               value.
5924
5925           -Wstringop-overflow=2
5926               The -Wstringop-overflow=2 option uses type-one Object Size
5927               Checking to determine the sizes of destination objects.  At
5928               this setting the option warns about overflows when writing to
5929               members of the largest complete objects whose exact size is
5930               known.  However, it does not warn for excessive writes to the
5931               same members of unknown objects referenced by pointers since
5932               they may point to arrays containing unknown numbers of
5933               elements.  This is the default setting of the option.
5934
5935           -Wstringop-overflow=3
5936               The -Wstringop-overflow=3 option uses type-two Object Size
5937               Checking to determine the sizes of destination objects.  At
5938               this setting the option warns about overflowing the smallest
5939               object or data member.  This is the most restrictive setting of
5940               the option that may result in warnings for safe code.
5941
5942           -Wstringop-overflow=4
5943               The -Wstringop-overflow=4 option uses type-three Object Size
5944               Checking to determine the sizes of destination objects.  At
5945               this setting the option warns about overflowing any data
5946               members, and when the destination is one of several objects it
5947               uses the size of the largest of them to decide whether to issue
5948               a warning.  Similarly to -Wstringop-overflow=3 this setting of
5949               the option may result in warnings for benign code.
5950
5951       -Wno-stringop-overread
5952           Warn for calls to string manipulation functions such as "memchr",
5953           or "strcpy" that are determined to read past the end of the source
5954           sequence.
5955
5956           Option -Wstringop-overread is enabled by default.
5957
5958       -Wno-stringop-truncation
5959           Do not warn for calls to bounded string manipulation functions such
5960           as "strncat", "strncpy", and "stpncpy" that may either truncate the
5961           copied string or leave the destination unchanged.
5962
5963           In the following example, the call to "strncat" specifies a bound
5964           that is less than the length of the source string.  As a result,
5965           the copy of the source will be truncated and so the call is
5966           diagnosed.  To avoid the warning use "bufsize - strlen (buf) - 1)"
5967           as the bound.
5968
5969                   void append (char *buf, size_t bufsize)
5970                   {
5971                     strncat (buf, ".txt", 3);
5972                   }
5973
5974           As another example, the following call to "strncpy" results in
5975           copying to "d" just the characters preceding the terminating NUL,
5976           without appending the NUL to the end.  Assuming the result of
5977           "strncpy" is necessarily a NUL-terminated string is a common
5978           mistake, and so the call is diagnosed.  To avoid the warning when
5979           the result is not expected to be NUL-terminated, call "memcpy"
5980           instead.
5981
5982                   void copy (char *d, const char *s)
5983                   {
5984                     strncpy (d, s, strlen (s));
5985                   }
5986
5987           In the following example, the call to "strncpy" specifies the size
5988           of the destination buffer as the bound.  If the length of the
5989           source string is equal to or greater than this size the result of
5990           the copy will not be NUL-terminated.  Therefore, the call is also
5991           diagnosed.  To avoid the warning, specify "sizeof buf - 1" as the
5992           bound and set the last element of the buffer to "NUL".
5993
5994                   void copy (const char *s)
5995                   {
5996                     char buf[80];
5997                     strncpy (buf, s, sizeof buf);
5998                     ...
5999                   }
6000
6001           In situations where a character array is intended to store a
6002           sequence of bytes with no terminating "NUL" such an array may be
6003           annotated with attribute "nonstring" to avoid this warning.  Such
6004           arrays, however, are not suitable arguments to functions that
6005           expect "NUL"-terminated strings.  To help detect accidental misuses
6006           of such arrays GCC issues warnings unless it can prove that the use
6007           is safe.
6008
6009       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
6010           Warn for cases where adding an attribute may be beneficial. The
6011           attributes currently supported are listed below.
6012
6013           -Wsuggest-attribute=pure
6014           -Wsuggest-attribute=const
6015           -Wsuggest-attribute=noreturn
6016           -Wmissing-noreturn
6017           -Wsuggest-attribute=malloc
6018               Warn about functions that might be candidates for attributes
6019               "pure", "const" or "noreturn" or "malloc". The compiler only
6020               warns for functions visible in other compilation units or (in
6021               the case of "pure" and "const") if it cannot prove that the
6022               function returns normally. A function returns normally if it
6023               doesn't contain an infinite loop or return abnormally by
6024               throwing, calling "abort" or trapping.  This analysis requires
6025               option -fipa-pure-const, which is enabled by default at -O and
6026               higher.  Higher optimization levels improve the accuracy of the
6027               analysis.
6028
6029           -Wsuggest-attribute=format
6030           -Wmissing-format-attribute
6031               Warn about function pointers that might be candidates for
6032               "format" attributes.  Note these are only possible candidates,
6033               not absolute ones.  GCC guesses that function pointers with
6034               "format" attributes that are used in assignment,
6035               initialization, parameter passing or return statements should
6036               have a corresponding "format" attribute in the resulting type.
6037               I.e. the left-hand side of the assignment or initialization,
6038               the type of the parameter variable, or the return type of the
6039               containing function respectively should also have a "format"
6040               attribute to avoid the warning.
6041
6042               GCC also warns about function definitions that might be
6043               candidates for "format" attributes.  Again, these are only
6044               possible candidates.  GCC guesses that "format" attributes
6045               might be appropriate for any function that calls a function
6046               like "vprintf" or "vscanf", but this might not always be the
6047               case, and some functions for which "format" attributes are
6048               appropriate may not be detected.
6049
6050           -Wsuggest-attribute=cold
6051               Warn about functions that might be candidates for "cold"
6052               attribute.  This is based on static detection and generally
6053               only warns about functions which always leads to a call to
6054               another "cold" function such as wrappers of C++ "throw" or
6055               fatal error reporting functions leading to "abort".
6056
6057       -Walloc-zero
6058           Warn about calls to allocation functions decorated with attribute
6059           "alloc_size" that specify zero bytes, including those to the built-
6060           in forms of the functions "aligned_alloc", "alloca", "calloc",
6061           "malloc", and "realloc".  Because the behavior of these functions
6062           when called with a zero size differs among implementations (and in
6063           the case of "realloc" has been deprecated) relying on it may result
6064           in subtle portability bugs and should be avoided.
6065
6066       -Walloc-size-larger-than=byte-size
6067           Warn about calls to functions decorated with attribute "alloc_size"
6068           that attempt to allocate objects larger than the specified number
6069           of bytes, or where the result of the size computation in an integer
6070           type with infinite precision would exceed the value of PTRDIFF_MAX
6071           on the target.  -Walloc-size-larger-than=PTRDIFF_MAX is enabled by
6072           default.  Warnings controlled by the option can be disabled either
6073           by specifying byte-size of SIZE_MAX or more or by
6074           -Wno-alloc-size-larger-than.
6075
6076       -Wno-alloc-size-larger-than
6077           Disable -Walloc-size-larger-than= warnings.  The option is
6078           equivalent to -Walloc-size-larger-than=SIZE_MAX or larger.
6079
6080       -Walloca
6081           This option warns on all uses of "alloca" in the source.
6082
6083       -Walloca-larger-than=byte-size
6084           This option warns on calls to "alloca" with an integer argument
6085           whose value is either zero, or that is not bounded by a controlling
6086           predicate that limits its value to at most byte-size.  It also
6087           warns for calls to "alloca" where the bound value is unknown.
6088           Arguments of non-integer types are considered unbounded even if
6089           they appear to be constrained to the expected range.
6090
6091           For example, a bounded case of "alloca" could be:
6092
6093                   void func (size_t n)
6094                   {
6095                     void *p;
6096                     if (n <= 1000)
6097                       p = alloca (n);
6098                     else
6099                       p = malloc (n);
6100                     f (p);
6101                   }
6102
6103           In the above example, passing "-Walloca-larger-than=1000" would not
6104           issue a warning because the call to "alloca" is known to be at most
6105           1000 bytes.  However, if "-Walloca-larger-than=500" were passed,
6106           the compiler would emit a warning.
6107
6108           Unbounded uses, on the other hand, are uses of "alloca" with no
6109           controlling predicate constraining its integer argument.  For
6110           example:
6111
6112                   void func ()
6113                   {
6114                     void *p = alloca (n);
6115                     f (p);
6116                   }
6117
6118           If "-Walloca-larger-than=500" were passed, the above would trigger
6119           a warning, but this time because of the lack of bounds checking.
6120
6121           Note, that even seemingly correct code involving signed integers
6122           could cause a warning:
6123
6124                   void func (signed int n)
6125                   {
6126                     if (n < 500)
6127                       {
6128                         p = alloca (n);
6129                         f (p);
6130                       }
6131                   }
6132
6133           In the above example, n could be negative, causing a larger than
6134           expected argument to be implicitly cast into the "alloca" call.
6135
6136           This option also warns when "alloca" is used in a loop.
6137
6138           -Walloca-larger-than=PTRDIFF_MAX is enabled by default but is
6139           usually only effective  when -ftree-vrp is active (default for -O2
6140           and above).
6141
6142           See also -Wvla-larger-than=byte-size.
6143
6144       -Wno-alloca-larger-than
6145           Disable -Walloca-larger-than= warnings.  The option is equivalent
6146           to -Walloca-larger-than=SIZE_MAX or larger.
6147
6148       -Warith-conversion
6149           Do warn about implicit conversions from arithmetic operations even
6150           when conversion of the operands to the same type cannot change
6151           their values.  This affects warnings from -Wconversion,
6152           -Wfloat-conversion, and -Wsign-conversion.
6153
6154                   void f (char c, int i)
6155                   {
6156                     c = c + i; // warns with B<-Wconversion>
6157                     c = c + 1; // only warns with B<-Warith-conversion>
6158                   }
6159
6160       -Warray-bounds
6161       -Warray-bounds=n
6162           Warn about out of bounds subscripts or offsets into arrays.  This
6163           warning is enabled by -Wall.  It is more effective when -ftree-vrp
6164           is active (the default for -O2 and above) but a subset of instances
6165           are issued even without optimization.
6166
6167           -Warray-bounds=1
6168               This is the default warning level of -Warray-bounds and is
6169               enabled by -Wall; higher levels are not, and must be explicitly
6170               requested.
6171
6172           -Warray-bounds=2
6173               This warning level also warns about out of bounds accesses to
6174               trailing struct members of one-element array types and about
6175               the intermediate results of pointer arithmetic that may yield
6176               out of bounds values.  This warning level may give a larger
6177               number of false positives and is deactivated by default.
6178
6179       -Warray-compare
6180           Warn about equality and relational comparisons between two operands
6181           of array type.  This comparison was deprecated in C++20.  For
6182           example:
6183
6184                   int arr1[5];
6185                   int arr2[5];
6186                   bool same = arr1 == arr2;
6187
6188           -Warray-compare is enabled by -Wall.
6189
6190       -Warray-parameter
6191       -Warray-parameter=n
6192           Warn about redeclarations of functions involving arguments of array
6193           or pointer types of inconsistent kinds or forms, and enable the
6194           detection of out-of-bounds accesses to such parameters by warnings
6195           such as -Warray-bounds.
6196
6197           If the first function declaration uses the array form the bound
6198           specified in the array is assumed to be the minimum number of
6199           elements expected to be provided in calls to the function and the
6200           maximum number of elements accessed by it.  Failing to provide
6201           arguments of sufficient size or accessing more than the maximum
6202           number of elements may be diagnosed by warnings such as
6203           -Warray-bounds.  At level 1 the warning diagnoses inconsistencies
6204           involving array parameters declared using the "T[static N]" form.
6205
6206           For example, the warning triggers for the following redeclarations
6207           because the first one allows an array of any size to be passed to
6208           "f" while the second one with the keyword "static" specifies that
6209           the array argument must have at least four elements.
6210
6211                   void f (int[static 4]);
6212                   void f (int[]);           // warning (inconsistent array form)
6213
6214                   void g (void)
6215                   {
6216                     int *p = (int *)malloc (4);
6217                     f (p);                  // warning (array too small)
6218                     ...
6219                   }
6220
6221           At level 2 the warning also triggers for redeclarations involving
6222           any other inconsistency in array or pointer argument forms denoting
6223           array sizes.  Pointers and arrays of unspecified bound are
6224           considered equivalent and do not trigger a warning.
6225
6226                   void g (int*);
6227                   void g (int[]);     // no warning
6228                   void g (int[8]);    // warning (inconsistent array bound)
6229
6230           -Warray-parameter=2 is included in -Wall.  The -Wvla-parameter
6231           option triggers warnings for similar inconsistencies involving
6232           Variable Length Array arguments.
6233
6234       -Wattribute-alias=n
6235       -Wno-attribute-alias
6236           Warn about declarations using the "alias" and similar attributes
6237           whose target is incompatible with the type of the alias.
6238
6239           -Wattribute-alias=1
6240               The default warning level of the -Wattribute-alias option
6241               diagnoses incompatibilities between the type of the alias
6242               declaration and that of its target.  Such incompatibilities are
6243               typically indicative of bugs.
6244
6245           -Wattribute-alias=2
6246               At this level -Wattribute-alias also diagnoses cases where the
6247               attributes of the alias declaration are more restrictive than
6248               the attributes applied to its target.  These mismatches can
6249               potentially result in incorrect code generation.  In other
6250               cases they may be benign and could be resolved simply by adding
6251               the missing attribute to the target.  For comparison, see the
6252               -Wmissing-attributes option, which controls diagnostics when
6253               the alias declaration is less restrictive than the target,
6254               rather than more restrictive.
6255
6256               Attributes considered include "alloc_align", "alloc_size",
6257               "cold", "const", "hot", "leaf", "malloc", "nonnull",
6258               "noreturn", "nothrow", "pure", "returns_nonnull", and
6259               "returns_twice".
6260
6261           -Wattribute-alias is equivalent to -Wattribute-alias=1.  This is
6262           the default.  You can disable these warnings with either
6263           -Wno-attribute-alias or -Wattribute-alias=0.
6264
6265       -Wbidi-chars=[none|unpaired|any|ucn]
6266           Warn about possibly misleading UTF-8 bidirectional control
6267           characters in comments, string literals, character constants, and
6268           identifiers.  Such characters can change left-to-right writing
6269           direction into right-to-left (and vice versa), which can cause
6270           confusion between the logical order and visual order.  This may be
6271           dangerous; for instance, it may seem that a piece of code is not
6272           commented out, whereas it in fact is.
6273
6274           There are three levels of warning supported by GCC.  The default is
6275           -Wbidi-chars=unpaired, which warns about improperly terminated bidi
6276           contexts.  -Wbidi-chars=none turns the warning off.
6277           -Wbidi-chars=any warns about any use of bidirectional control
6278           characters.
6279
6280           By default, this warning does not warn about UCNs.  It is, however,
6281           possible to turn on such checking by using
6282           -Wbidi-chars=unpaired,ucn or -Wbidi-chars=any,ucn.  Using
6283           -Wbidi-chars=ucn is valid, and is equivalent to
6284           -Wbidi-chars=unpaired,ucn, if no previous -Wbidi-chars=any was
6285           specified.
6286
6287       -Wbool-compare
6288           Warn about boolean expression compared with an integer value
6289           different from "true"/"false".  For instance, the following
6290           comparison is always false:
6291
6292                   int n = 5;
6293                   ...
6294                   if ((n > 1) == 2) { ... }
6295
6296           This warning is enabled by -Wall.
6297
6298       -Wbool-operation
6299           Warn about suspicious operations on expressions of a boolean type.
6300           For instance, bitwise negation of a boolean is very likely a bug in
6301           the program.  For C, this warning also warns about incrementing or
6302           decrementing a boolean, which rarely makes sense.  (In C++,
6303           decrementing a boolean is always invalid.  Incrementing a boolean
6304           is invalid in C++17, and deprecated otherwise.)
6305
6306           This warning is enabled by -Wall.
6307
6308       -Wduplicated-branches
6309           Warn when an if-else has identical branches.  This warning detects
6310           cases like
6311
6312                   if (p != NULL)
6313                     return 0;
6314                   else
6315                     return 0;
6316
6317           It doesn't warn when both branches contain just a null statement.
6318           This warning also warn for conditional operators:
6319
6320                     int i = x ? *p : *p;
6321
6322       -Wduplicated-cond
6323           Warn about duplicated conditions in an if-else-if chain.  For
6324           instance, warn for the following code:
6325
6326                   if (p->q != NULL) { ... }
6327                   else if (p->q != NULL) { ... }
6328
6329       -Wframe-address
6330           Warn when the __builtin_frame_address or __builtin_return_address
6331           is called with an argument greater than 0.  Such calls may return
6332           indeterminate values or crash the program.  The warning is included
6333           in -Wall.
6334
6335       -Wno-discarded-qualifiers (C and Objective-C only)
6336           Do not warn if type qualifiers on pointers are being discarded.
6337           Typically, the compiler warns if a "const char *" variable is
6338           passed to a function that takes a "char *" parameter.  This option
6339           can be used to suppress such a warning.
6340
6341       -Wno-discarded-array-qualifiers (C and Objective-C only)
6342           Do not warn if type qualifiers on arrays which are pointer targets
6343           are being discarded.  Typically, the compiler warns if a "const int
6344           (*)[]" variable is passed to a function that takes a "int (*)[]"
6345           parameter.  This option can be used to suppress such a warning.
6346
6347       -Wno-incompatible-pointer-types (C and Objective-C only)
6348           Do not warn when there is a conversion between pointers that have
6349           incompatible types.  This warning is for cases not covered by
6350           -Wno-pointer-sign, which warns for pointer argument passing or
6351           assignment with different signedness.
6352
6353       -Wno-int-conversion (C and Objective-C only)
6354           Do not warn about incompatible integer to pointer and pointer to
6355           integer conversions.  This warning is about implicit conversions;
6356           for explicit conversions the warnings -Wno-int-to-pointer-cast and
6357           -Wno-pointer-to-int-cast may be used.
6358
6359       -Wzero-length-bounds
6360           Warn about accesses to elements of zero-length array members that
6361           might overlap other members of the same object.  Declaring interior
6362           zero-length arrays is discouraged because accesses to them are
6363           undefined.  See
6364
6365           For example, the first two stores in function "bad" are diagnosed
6366           because the array elements overlap the subsequent members "b" and
6367           "c".  The third store is diagnosed by -Warray-bounds because it is
6368           beyond the bounds of the enclosing object.
6369
6370                   struct X { int a[0]; int b, c; };
6371                   struct X x;
6372
6373                   void bad (void)
6374                   {
6375                     x.a[0] = 0;   // -Wzero-length-bounds
6376                     x.a[1] = 1;   // -Wzero-length-bounds
6377                     x.a[2] = 2;   // -Warray-bounds
6378                   }
6379
6380           Option -Wzero-length-bounds is enabled by -Warray-bounds.
6381
6382       -Wno-div-by-zero
6383           Do not warn about compile-time integer division by zero.  Floating-
6384           point division by zero is not warned about, as it can be a
6385           legitimate way of obtaining infinities and NaNs.
6386
6387       -Wsystem-headers
6388           Print warning messages for constructs found in system header files.
6389           Warnings from system headers are normally suppressed, on the
6390           assumption that they usually do not indicate real problems and
6391           would only make the compiler output harder to read.  Using this
6392           command-line option tells GCC to emit warnings from system headers
6393           as if they occurred in user code.  However, note that using -Wall
6394           in conjunction with this option does not warn about unknown pragmas
6395           in system headers---for that, -Wunknown-pragmas must also be used.
6396
6397       -Wtautological-compare
6398           Warn if a self-comparison always evaluates to true or false.  This
6399           warning detects various mistakes such as:
6400
6401                   int i = 1;
6402                   ...
6403                   if (i > i) { ... }
6404
6405           This warning also warns about bitwise comparisons that always
6406           evaluate to true or false, for instance:
6407
6408                   if ((a & 16) == 10) { ... }
6409
6410           will always be false.
6411
6412           This warning is enabled by -Wall.
6413
6414       -Wtrampolines
6415           Warn about trampolines generated for pointers to nested functions.
6416           A trampoline is a small piece of data or code that is created at
6417           run time on the stack when the address of a nested function is
6418           taken, and is used to call the nested function indirectly.  For
6419           some targets, it is made up of data only and thus requires no
6420           special treatment.  But, for most targets, it is made up of code
6421           and thus requires the stack to be made executable in order for the
6422           program to work properly.
6423
6424       -Wfloat-equal
6425           Warn if floating-point values are used in equality comparisons.
6426
6427           The idea behind this is that sometimes it is convenient (for the
6428           programmer) to consider floating-point values as approximations to
6429           infinitely precise real numbers.  If you are doing this, then you
6430           need to compute (by analyzing the code, or in some other way) the
6431           maximum or likely maximum error that the computation introduces,
6432           and allow for it when performing comparisons (and when producing
6433           output, but that's a different problem).  In particular, instead of
6434           testing for equality, you should check to see whether the two
6435           values have ranges that overlap; and this is done with the
6436           relational operators, so equality comparisons are probably
6437           mistaken.
6438
6439       -Wtraditional (C and Objective-C only)
6440           Warn about certain constructs that behave differently in
6441           traditional and ISO C.  Also warn about ISO C constructs that have
6442           no traditional C equivalent, and/or problematic constructs that
6443           should be avoided.
6444
6445           *   Macro parameters that appear within string literals in the
6446               macro body.  In traditional C macro replacement takes place
6447               within string literals, but in ISO C it does not.
6448
6449           *   In traditional C, some preprocessor directives did not exist.
6450               Traditional preprocessors only considered a line to be a
6451               directive if the # appeared in column 1 on the line.  Therefore
6452               -Wtraditional warns about directives that traditional C
6453               understands but ignores because the # does not appear as the
6454               first character on the line.  It also suggests you hide
6455               directives like "#pragma" not understood by traditional C by
6456               indenting them.  Some traditional implementations do not
6457               recognize "#elif", so this option suggests avoiding it
6458               altogether.
6459
6460           *   A function-like macro that appears without arguments.
6461
6462           *   The unary plus operator.
6463
6464           *   The U integer constant suffix, or the F or L floating-point
6465               constant suffixes.  (Traditional C does support the L suffix on
6466               integer constants.)  Note, these suffixes appear in macros
6467               defined in the system headers of most modern systems, e.g. the
6468               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
6469               code might normally lead to spurious warnings, however GCC's
6470               integrated preprocessor has enough context to avoid warning in
6471               these cases.
6472
6473           *   A function declared external in one block and then used after
6474               the end of the block.
6475
6476           *   A "switch" statement has an operand of type "long".
6477
6478           *   A non-"static" function declaration follows a "static" one.
6479               This construct is not accepted by some traditional C compilers.
6480
6481           *   The ISO type of an integer constant has a different width or
6482               signedness from its traditional type.  This warning is only
6483               issued if the base of the constant is ten.  I.e. hexadecimal or
6484               octal values, which typically represent bit patterns, are not
6485               warned about.
6486
6487           *   Usage of ISO string concatenation is detected.
6488
6489           *   Initialization of automatic aggregates.
6490
6491           *   Identifier conflicts with labels.  Traditional C lacks a
6492               separate namespace for labels.
6493
6494           *   Initialization of unions.  If the initializer is zero, the
6495               warning is omitted.  This is done under the assumption that the
6496               zero initializer in user code appears conditioned on e.g.
6497               "__STDC__" to avoid missing initializer warnings and relies on
6498               default initialization to zero in the traditional C case.
6499
6500           *   Conversions by prototypes between fixed/floating-point values
6501               and vice versa.  The absence of these prototypes when compiling
6502               with traditional C causes serious problems.  This is a subset
6503               of the possible conversion warnings; for the full set use
6504               -Wtraditional-conversion.
6505
6506           *   Use of ISO C style function definitions.  This warning
6507               intentionally is not issued for prototype declarations or
6508               variadic functions because these ISO C features appear in your
6509               code when using libiberty's traditional C compatibility macros,
6510               "PARAMS" and "VPARAMS".  This warning is also bypassed for
6511               nested functions because that feature is already a GCC
6512               extension and thus not relevant to traditional C compatibility.
6513
6514       -Wtraditional-conversion (C and Objective-C only)
6515           Warn if a prototype causes a type conversion that is different from
6516           what would happen to the same argument in the absence of a
6517           prototype.  This includes conversions of fixed point to floating
6518           and vice versa, and conversions changing the width or signedness of
6519           a fixed-point argument except when the same as the default
6520           promotion.
6521
6522       -Wdeclaration-after-statement (C and Objective-C only)
6523           Warn when a declaration is found after a statement in a block.
6524           This construct, known from C++, was introduced with ISO C99 and is
6525           by default allowed in GCC.  It is not supported by ISO C90.
6526
6527       -Wshadow
6528           Warn whenever a local variable or type declaration shadows another
6529           variable, parameter, type, class member (in C++), or instance
6530           variable (in Objective-C) or whenever a built-in function is
6531           shadowed.  Note that in C++, the compiler warns if a local variable
6532           shadows an explicit typedef, but not if it shadows a
6533           struct/class/enum.  If this warning is enabled, it includes also
6534           all instances of local shadowing.  This means that
6535           -Wno-shadow=local and -Wno-shadow=compatible-local are ignored when
6536           -Wshadow is used.  Same as -Wshadow=global.
6537
6538       -Wno-shadow-ivar (Objective-C only)
6539           Do not warn whenever a local variable shadows an instance variable
6540           in an Objective-C method.
6541
6542       -Wshadow=global
6543           Warn for any shadowing.  Same as -Wshadow.
6544
6545       -Wshadow=local
6546           Warn when a local variable shadows another local variable or
6547           parameter.
6548
6549       -Wshadow=compatible-local
6550           Warn when a local variable shadows another local variable or
6551           parameter whose type is compatible with that of the shadowing
6552           variable.  In C++, type compatibility here means the type of the
6553           shadowing variable can be converted to that of the shadowed
6554           variable.  The creation of this flag (in addition to
6555           -Wshadow=local) is based on the idea that when a local variable
6556           shadows another one of incompatible type, it is most likely
6557           intentional, not a bug or typo, as shown in the following example:
6558
6559                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
6560                   {
6561                     for (int i = 0; i < N; ++i)
6562                     {
6563                       ...
6564                     }
6565                     ...
6566                   }
6567
6568           Since the two variable "i" in the example above have incompatible
6569           types, enabling only -Wshadow=compatible-local does not emit a
6570           warning.  Because their types are incompatible, if a programmer
6571           accidentally uses one in place of the other, type checking is
6572           expected to catch that and emit an error or warning.  Use of this
6573           flag instead of -Wshadow=local can possibly reduce the number of
6574           warnings triggered by intentional shadowing.  Note that this also
6575           means that shadowing "const char *i" by "char *i" does not emit a
6576           warning.
6577
6578           This warning is also enabled by -Wshadow=local.
6579
6580       -Wlarger-than=byte-size
6581           Warn whenever an object is defined whose size exceeds byte-size.
6582           -Wlarger-than=PTRDIFF_MAX is enabled by default.  Warnings
6583           controlled by the option can be disabled either by specifying byte-
6584           size of SIZE_MAX or more or by -Wno-larger-than.
6585
6586           Also warn for calls to bounded functions such as "memchr" or
6587           "strnlen" that specify a bound greater than the largest possible
6588           object, which is PTRDIFF_MAX bytes by default.  These warnings can
6589           only be disabled by -Wno-larger-than.
6590
6591       -Wno-larger-than
6592           Disable -Wlarger-than= warnings.  The option is equivalent to
6593           -Wlarger-than=SIZE_MAX or larger.
6594
6595       -Wframe-larger-than=byte-size
6596           Warn if the size of a function frame exceeds byte-size.  The
6597           computation done to determine the stack frame size is approximate
6598           and not conservative.  The actual requirements may be somewhat
6599           greater than byte-size even if you do not get a warning.  In
6600           addition, any space allocated via "alloca", variable-length arrays,
6601           or related constructs is not included by the compiler when
6602           determining whether or not to issue a warning.
6603           -Wframe-larger-than=PTRDIFF_MAX is enabled by default.  Warnings
6604           controlled by the option can be disabled either by specifying byte-
6605           size of SIZE_MAX or more or by -Wno-frame-larger-than.
6606
6607       -Wno-frame-larger-than
6608           Disable -Wframe-larger-than= warnings.  The option is equivalent to
6609           -Wframe-larger-than=SIZE_MAX or larger.
6610
6611       -Wfree-nonheap-object
6612           Warn when attempting to deallocate an object that was either not
6613           allocated on the heap, or by using a pointer that was not returned
6614           from a prior call to the corresponding allocation function.  For
6615           example, because the call to "stpcpy" returns a pointer to the
6616           terminating nul character and not to the beginning of the object,
6617           the call to "free" below is diagnosed.
6618
6619                   void f (char *p)
6620                   {
6621                     p = stpcpy (p, "abc");
6622                     // ...
6623                     free (p);   // warning
6624                   }
6625
6626           -Wfree-nonheap-object is included in -Wall.
6627
6628       -Wstack-usage=byte-size
6629           Warn if the stack usage of a function might exceed byte-size.  The
6630           computation done to determine the stack usage is conservative.  Any
6631           space allocated via "alloca", variable-length arrays, or related
6632           constructs is included by the compiler when determining whether or
6633           not to issue a warning.
6634
6635           The message is in keeping with the output of -fstack-usage.
6636
6637           *   If the stack usage is fully static but exceeds the specified
6638               amount, it's:
6639
6640                         warning: stack usage is 1120 bytes
6641
6642           *   If the stack usage is (partly) dynamic but bounded, it's:
6643
6644                         warning: stack usage might be 1648 bytes
6645
6646           *   If the stack usage is (partly) dynamic and not bounded, it's:
6647
6648                         warning: stack usage might be unbounded
6649
6650           -Wstack-usage=PTRDIFF_MAX is enabled by default.  Warnings
6651           controlled by the option can be disabled either by specifying byte-
6652           size of SIZE_MAX or more or by -Wno-stack-usage.
6653
6654       -Wno-stack-usage
6655           Disable -Wstack-usage= warnings.  The option is equivalent to
6656           -Wstack-usage=SIZE_MAX or larger.
6657
6658       -Wunsafe-loop-optimizations
6659           Warn if the loop cannot be optimized because the compiler cannot
6660           assume anything on the bounds of the loop indices.  With
6661           -funsafe-loop-optimizations warn if the compiler makes such
6662           assumptions.
6663
6664       -Wno-pedantic-ms-format (MinGW targets only)
6665           When used in combination with -Wformat and -pedantic without GNU
6666           extensions, this option disables the warnings about non-ISO
6667           "printf" / "scanf" format width specifiers "I32", "I64", and "I"
6668           used on Windows targets, which depend on the MS runtime.
6669
6670       -Wpointer-arith
6671           Warn about anything that depends on the "size of" a function type
6672           or of "void".  GNU C assigns these types a size of 1, for
6673           convenience in calculations with "void *" pointers and pointers to
6674           functions.  In C++, warn also when an arithmetic operation involves
6675           "NULL".  This warning is also enabled by -Wpedantic.
6676
6677       -Wno-pointer-compare
6678           Do not warn if a pointer is compared with a zero character
6679           constant.  This usually means that the pointer was meant to be
6680           dereferenced.  For example:
6681
6682                   const char *p = foo ();
6683                   if (p == '\0')
6684                     return 42;
6685
6686           Note that the code above is invalid in C++11.
6687
6688           This warning is enabled by default.
6689
6690       -Wtsan
6691           Warn about unsupported features in ThreadSanitizer.
6692
6693           ThreadSanitizer does not support "std::atomic_thread_fence" and can
6694           report false positives.
6695
6696           This warning is enabled by default.
6697
6698       -Wtype-limits
6699           Warn if a comparison is always true or always false due to the
6700           limited range of the data type, but do not warn for constant
6701           expressions.  For example, warn if an unsigned variable is compared
6702           against zero with "<" or ">=".  This warning is also enabled by
6703           -Wextra.
6704
6705       -Wabsolute-value (C and Objective-C only)
6706           Warn for calls to standard functions that compute the absolute
6707           value of an argument when a more appropriate standard function is
6708           available.  For example, calling "abs(3.14)" triggers the warning
6709           because the appropriate function to call to compute the absolute
6710           value of a double argument is "fabs".  The option also triggers
6711           warnings when the argument in a call to such a function has an
6712           unsigned type.  This warning can be suppressed with an explicit
6713           type cast and it is also enabled by -Wextra.
6714
6715       -Wcomment
6716       -Wcomments
6717           Warn whenever a comment-start sequence /* appears in a /* comment,
6718           or whenever a backslash-newline appears in a // comment.  This
6719           warning is enabled by -Wall.
6720
6721       -Wtrigraphs
6722           Warn if any trigraphs are encountered that might change the meaning
6723           of the program.  Trigraphs within comments are not warned about,
6724           except those that would form escaped newlines.
6725
6726           This option is implied by -Wall.  If -Wall is not given, this
6727           option is still enabled unless trigraphs are enabled.  To get
6728           trigraph conversion without warnings, but get the other -Wall
6729           warnings, use -trigraphs -Wall -Wno-trigraphs.
6730
6731       -Wundef
6732           Warn if an undefined identifier is evaluated in an "#if" directive.
6733           Such identifiers are replaced with zero.
6734
6735       -Wexpansion-to-defined
6736           Warn whenever defined is encountered in the expansion of a macro
6737           (including the case where the macro is expanded by an #if
6738           directive).  Such usage is not portable.  This warning is also
6739           enabled by -Wpedantic and -Wextra.
6740
6741       -Wunused-macros
6742           Warn about macros defined in the main file that are unused.  A
6743           macro is used if it is expanded or tested for existence at least
6744           once.  The preprocessor also warns if the macro has not been used
6745           at the time it is redefined or undefined.
6746
6747           Built-in macros, macros defined on the command line, and macros
6748           defined in include files are not warned about.
6749
6750           Note: If a macro is actually used, but only used in skipped
6751           conditional blocks, then the preprocessor reports it as unused.  To
6752           avoid the warning in such a case, you might improve the scope of
6753           the macro's definition by, for example, moving it into the first
6754           skipped block.  Alternatively, you could provide a dummy use with
6755           something like:
6756
6757                   #if defined the_macro_causing_the_warning
6758                   #endif
6759
6760       -Wno-endif-labels
6761           Do not warn whenever an "#else" or an "#endif" are followed by
6762           text.  This sometimes happens in older programs with code of the
6763           form
6764
6765                   #if FOO
6766                   ...
6767                   #else FOO
6768                   ...
6769                   #endif FOO
6770
6771           The second and third "FOO" should be in comments.  This warning is
6772           on by default.
6773
6774       -Wbad-function-cast (C and Objective-C only)
6775           Warn when a function call is cast to a non-matching type.  For
6776           example, warn if a call to a function returning an integer type is
6777           cast to a pointer type.
6778
6779       -Wc90-c99-compat (C and Objective-C only)
6780           Warn about features not present in ISO C90, but present in ISO C99.
6781           For instance, warn about use of variable length arrays, "long long"
6782           type, "bool" type, compound literals, designated initializers, and
6783           so on.  This option is independent of the standards mode.  Warnings
6784           are disabled in the expression that follows "__extension__".
6785
6786       -Wc99-c11-compat (C and Objective-C only)
6787           Warn about features not present in ISO C99, but present in ISO C11.
6788           For instance, warn about use of anonymous structures and unions,
6789           "_Atomic" type qualifier, "_Thread_local" storage-class specifier,
6790           "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and
6791           so on.  This option is independent of the standards mode.  Warnings
6792           are disabled in the expression that follows "__extension__".
6793
6794       -Wc11-c2x-compat (C and Objective-C only)
6795           Warn about features not present in ISO C11, but present in ISO C2X.
6796           For instance, warn about omitting the string in "_Static_assert",
6797           use of [[]] syntax for attributes, use of decimal floating-point
6798           types, and so on.  This option is independent of the standards
6799           mode.  Warnings are disabled in the expression that follows
6800           "__extension__".
6801
6802       -Wc++-compat (C and Objective-C only)
6803           Warn about ISO C constructs that are outside of the common subset
6804           of ISO C and ISO C++, e.g. request for implicit conversion from
6805           "void *" to a pointer to non-"void" type.
6806
6807       -Wc++11-compat (C++ and Objective-C++ only)
6808           Warn about C++ constructs whose meaning differs between ISO C++
6809           1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
6810           keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and is
6811           enabled by -Wall.
6812
6813       -Wc++14-compat (C++ and Objective-C++ only)
6814           Warn about C++ constructs whose meaning differs between ISO C++
6815           2011 and ISO C++ 2014.  This warning is enabled by -Wall.
6816
6817       -Wc++17-compat (C++ and Objective-C++ only)
6818           Warn about C++ constructs whose meaning differs between ISO C++
6819           2014 and ISO C++ 2017.  This warning is enabled by -Wall.
6820
6821       -Wc++20-compat (C++ and Objective-C++ only)
6822           Warn about C++ constructs whose meaning differs between ISO C++
6823           2017 and ISO C++ 2020.  This warning is enabled by -Wall.
6824
6825       -Wno-c++11-extensions (C++ and Objective-C++ only)
6826           Do not warn about C++11 constructs in code being compiled using an
6827           older C++ standard.  Even without this option, some C++11
6828           constructs will only be diagnosed if -Wpedantic is used.
6829
6830       -Wno-c++14-extensions (C++ and Objective-C++ only)
6831           Do not warn about C++14 constructs in code being compiled using an
6832           older C++ standard.  Even without this option, some C++14
6833           constructs will only be diagnosed if -Wpedantic is used.
6834
6835       -Wno-c++17-extensions (C++ and Objective-C++ only)
6836           Do not warn about C++17 constructs in code being compiled using an
6837           older C++ standard.  Even without this option, some C++17
6838           constructs will only be diagnosed if -Wpedantic is used.
6839
6840       -Wno-c++20-extensions (C++ and Objective-C++ only)
6841           Do not warn about C++20 constructs in code being compiled using an
6842           older C++ standard.  Even without this option, some C++20
6843           constructs will only be diagnosed if -Wpedantic is used.
6844
6845       -Wno-c++23-extensions (C++ and Objective-C++ only)
6846           Do not warn about C++23 constructs in code being compiled using an
6847           older C++ standard.  Even without this option, some C++23
6848           constructs will only be diagnosed if -Wpedantic is used.
6849
6850       -Wcast-qual
6851           Warn whenever a pointer is cast so as to remove a type qualifier
6852           from the target type.  For example, warn if a "const char *" is
6853           cast to an ordinary "char *".
6854
6855           Also warn when making a cast that introduces a type qualifier in an
6856           unsafe way.  For example, casting "char **" to "const char **" is
6857           unsafe, as in this example:
6858
6859                     /* p is char ** value.  */
6860                     const char **q = (const char **) p;
6861                     /* Assignment of readonly string to const char * is OK.  */
6862                     *q = "string";
6863                     /* Now char** pointer points to read-only memory.  */
6864                     **p = 'b';
6865
6866       -Wcast-align
6867           Warn whenever a pointer is cast such that the required alignment of
6868           the target is increased.  For example, warn if a "char *" is cast
6869           to an "int *" on machines where integers can only be accessed at
6870           two- or four-byte boundaries.
6871
6872       -Wcast-align=strict
6873           Warn whenever a pointer is cast such that the required alignment of
6874           the target is increased.  For example, warn if a "char *" is cast
6875           to an "int *" regardless of the target machine.
6876
6877       -Wcast-function-type
6878           Warn when a function pointer is cast to an incompatible function
6879           pointer.  In a cast involving function types with a variable
6880           argument list only the types of initial arguments that are provided
6881           are considered.  Any parameter of pointer-type matches any other
6882           pointer-type.  Any benign differences in integral types are
6883           ignored, like "int" vs. "long" on ILP32 targets.  Likewise type
6884           qualifiers are ignored.  The function type "void (*) (void)" is
6885           special and matches everything, which can be used to suppress this
6886           warning.  In a cast involving pointer to member types this warning
6887           warns whenever the type cast is changing the pointer to member
6888           type.  This warning is enabled by -Wextra.
6889
6890       -Wwrite-strings
6891           When compiling C, give string constants the type "const
6892           char[length]" so that copying the address of one into a non-"const"
6893           "char *" pointer produces a warning.  These warnings help you find
6894           at compile time code that can try to write into a string constant,
6895           but only if you have been very careful about using "const" in
6896           declarations and prototypes.  Otherwise, it is just a nuisance.
6897           This is why we did not make -Wall request these warnings.
6898
6899           When compiling C++, warn about the deprecated conversion from
6900           string literals to "char *".  This warning is enabled by default
6901           for C++ programs.
6902
6903       -Wclobbered
6904           Warn for variables that might be changed by "longjmp" or "vfork".
6905           This warning is also enabled by -Wextra.
6906
6907       -Wconversion
6908           Warn for implicit conversions that may alter a value. This includes
6909           conversions between real and integer, like "abs (x)" when "x" is
6910           "double"; conversions between signed and unsigned, like "unsigned
6911           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
6912           not warn for explicit casts like "abs ((int) x)" and "ui =
6913           (unsigned) -1", or if the value is not changed by the conversion
6914           like in "abs (2.0)".  Warnings about conversions between signed and
6915           unsigned integers can be disabled by using -Wno-sign-conversion.
6916
6917           For C++, also warn for confusing overload resolution for user-
6918           defined conversions; and conversions that never use a type
6919           conversion operator: conversions to "void", the same type, a base
6920           class or a reference to them. Warnings about conversions between
6921           signed and unsigned integers are disabled by default in C++ unless
6922           -Wsign-conversion is explicitly enabled.
6923
6924           Warnings about conversion from arithmetic on a small type back to
6925           that type are only given with -Warith-conversion.
6926
6927       -Wdangling-else
6928           Warn about constructions where there may be confusion to which "if"
6929           statement an "else" branch belongs.  Here is an example of such a
6930           case:
6931
6932                   {
6933                     if (a)
6934                       if (b)
6935                         foo ();
6936                     else
6937                       bar ();
6938                   }
6939
6940           In C/C++, every "else" branch belongs to the innermost possible
6941           "if" statement, which in this example is "if (b)".  This is often
6942           not what the programmer expected, as illustrated in the above
6943           example by indentation the programmer chose.  When there is the
6944           potential for this confusion, GCC issues a warning when this flag
6945           is specified.  To eliminate the warning, add explicit braces around
6946           the innermost "if" statement so there is no way the "else" can
6947           belong to the enclosing "if".  The resulting code looks like this:
6948
6949                   {
6950                     if (a)
6951                       {
6952                         if (b)
6953                           foo ();
6954                         else
6955                           bar ();
6956                       }
6957                   }
6958
6959           This warning is enabled by -Wparentheses.
6960
6961       -Wdangling-pointer
6962       -Wdangling-pointer=n
6963           Warn about uses of pointers (or C++ references) to objects with
6964           automatic storage duration after their lifetime has ended.  This
6965           includes local variables declared in nested blocks, compound
6966           literals and other unnamed temporary objects.  In addition, warn
6967           about storing the address of such objects in escaped pointers.  The
6968           warning is enabled at all optimization levels but may yield
6969           different results with optimization than without.
6970
6971           -Wdangling-pointer=1
6972               At level 1 the warning diagnoses only unconditional uses of
6973               dangling pointers.  For example
6974
6975                       int f (int c1, int c2, x)
6976                       {
6977                         char *p = strchr ((char[]){ c1, c2 }, c3);
6978                         return p ? *p : 'x';   // warning: dangling pointer to a compound literal
6979                       }
6980
6981               In the following function the store of the address of the local
6982               variable "x" in the escaped pointer *p also triggers the
6983               warning.
6984
6985                       void g (int **p)
6986                       {
6987                         int x = 7;
6988                         *p = &x;   // warning: storing the address of a local variable in *p
6989                       }
6990
6991           -Wdangling-pointer=2
6992               At level 2, in addition to unconditional uses the warning also
6993               diagnoses conditional uses of dangling pointers.
6994
6995               For example, because the array a in the following function is
6996               out of scope when the pointer s that was set to point is used,
6997               the warning triggers at this level.
6998
6999                       void f (char *s)
7000                       {
7001                         if (!s)
7002                           {
7003                             char a[12] = "tmpname";
7004                             s = a;
7005                           }
7006                         strcat (s, ".tmp");   // warning: dangling pointer to a may be used
7007                         ...
7008                       }
7009
7010           -Wdangling-pointer=2 is included in -Wall.
7011
7012       -Wdate-time
7013           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are
7014           encountered as they might prevent bit-wise-identical reproducible
7015           compilations.
7016
7017       -Wempty-body
7018           Warn if an empty body occurs in an "if", "else" or "do while"
7019           statement.  This warning is also enabled by -Wextra.
7020
7021       -Wno-endif-labels
7022           Do not warn about stray tokens after "#else" and "#endif".
7023
7024       -Wenum-compare
7025           Warn about a comparison between values of different enumerated
7026           types.  In C++ enumerated type mismatches in conditional
7027           expressions are also diagnosed and the warning is enabled by
7028           default.  In C this warning is enabled by -Wall.
7029
7030       -Wenum-conversion
7031           Warn when a value of enumerated type is implicitly converted to a
7032           different enumerated type.  This warning is enabled by -Wextra in
7033           C.
7034
7035       -Wjump-misses-init (C, Objective-C only)
7036           Warn if a "goto" statement or a "switch" statement jumps forward
7037           across the initialization of a variable, or jumps backward to a
7038           label after the variable has been initialized.  This only warns
7039           about variables that are initialized when they are declared.  This
7040           warning is only supported for C and Objective-C; in C++ this sort
7041           of branch is an error in any case.
7042
7043           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
7044           with the -Wno-jump-misses-init option.
7045
7046       -Wsign-compare
7047           Warn when a comparison between signed and unsigned values could
7048           produce an incorrect result when the signed value is converted to
7049           unsigned.  In C++, this warning is also enabled by -Wall.  In C, it
7050           is also enabled by -Wextra.
7051
7052       -Wsign-conversion
7053           Warn for implicit conversions that may change the sign of an
7054           integer value, like assigning a signed integer expression to an
7055           unsigned integer variable. An explicit cast silences the warning.
7056           In C, this option is enabled also by -Wconversion.
7057
7058       -Wfloat-conversion
7059           Warn for implicit conversions that reduce the precision of a real
7060           value.  This includes conversions from real to integer, and from
7061           higher precision real to lower precision real values.  This option
7062           is also enabled by -Wconversion.
7063
7064       -Wno-scalar-storage-order
7065           Do not warn on suspicious constructs involving reverse scalar
7066           storage order.
7067
7068       -Wsizeof-array-div
7069           Warn about divisions of two sizeof operators when the first one is
7070           applied to an array and the divisor does not equal the size of the
7071           array element.  In such a case, the computation will not yield the
7072           number of elements in the array, which is likely what the user
7073           intended.  This warning warns e.g. about
7074
7075                   int fn ()
7076                   {
7077                     int arr[10];
7078                     return sizeof (arr) / sizeof (short);
7079                   }
7080
7081           This warning is enabled by -Wall.
7082
7083       -Wsizeof-pointer-div
7084           Warn for suspicious divisions of two sizeof expressions that divide
7085           the pointer size by the element size, which is the usual way to
7086           compute the array size but won't work out correctly with pointers.
7087           This warning warns e.g. about "sizeof (ptr) / sizeof (ptr[0])" if
7088           "ptr" is not an array, but a pointer.  This warning is enabled by
7089           -Wall.
7090
7091       -Wsizeof-pointer-memaccess
7092           Warn for suspicious length parameters to certain string and memory
7093           built-in functions if the argument uses "sizeof".  This warning
7094           triggers for example for "memset (ptr, 0, sizeof (ptr));" if "ptr"
7095           is not an array, but a pointer, and suggests a possible fix, or
7096           about "memcpy (&foo, ptr, sizeof (&foo));".
7097           -Wsizeof-pointer-memaccess also warns about calls to bounded string
7098           copy functions like "strncat" or "strncpy" that specify as the
7099           bound a "sizeof" expression of the source array.  For example, in
7100           the following function the call to "strncat" specifies the size of
7101           the source string as the bound.  That is almost certainly a mistake
7102           and so the call is diagnosed.
7103
7104                   void make_file (const char *name)
7105                   {
7106                     char path[PATH_MAX];
7107                     strncpy (path, name, sizeof path - 1);
7108                     strncat (path, ".text", sizeof ".text");
7109                     ...
7110                   }
7111
7112           The -Wsizeof-pointer-memaccess option is enabled by -Wall.
7113
7114       -Wno-sizeof-array-argument
7115           Do not warn when the "sizeof" operator is applied to a parameter
7116           that is declared as an array in a function definition.  This
7117           warning is enabled by default for C and C++ programs.
7118
7119       -Wmemset-elt-size
7120           Warn for suspicious calls to the "memset" built-in function, if the
7121           first argument references an array, and the third argument is a
7122           number equal to the number of elements, but not equal to the size
7123           of the array in memory.  This indicates that the user has omitted a
7124           multiplication by the element size.  This warning is enabled by
7125           -Wall.
7126
7127       -Wmemset-transposed-args
7128           Warn for suspicious calls to the "memset" built-in function where
7129           the second argument is not zero and the third argument is zero.
7130           For example, the call "memset (buf, sizeof buf, 0)" is diagnosed
7131           because "memset (buf, 0, sizeof buf)" was meant instead.  The
7132           diagnostic is only emitted if the third argument is a literal zero.
7133           Otherwise, if it is an expression that is folded to zero, or a cast
7134           of zero to some type, it is far less likely that the arguments have
7135           been mistakenly transposed and no warning is emitted.  This warning
7136           is enabled by -Wall.
7137
7138       -Waddress
7139           Warn about suspicious uses of address expressions. These include
7140           comparing the address of a function or a declared object to the
7141           null pointer constant such as in
7142
7143                   void f (void);
7144                   void g (void)
7145                   {
7146                     if (!func)   // warning: expression evaluates to false
7147                       abort ();
7148                   }
7149
7150           comparisons of a pointer to a string literal, such as in
7151
7152                   void f (const char *x)
7153                   {
7154                     if (x == "abc")   // warning: expression evaluates to false
7155                       puts ("equal");
7156                   }
7157
7158           and tests of the results of pointer addition or subtraction for
7159           equality to null, such as in
7160
7161                   void f (const int *p, int i)
7162                   {
7163                     return p + i == NULL;
7164                   }
7165
7166           Such uses typically indicate a programmer error: the address of
7167           most functions and objects necessarily evaluates to true (the
7168           exception are weak symbols), so their use in a conditional might
7169           indicate missing parentheses in a function call or a missing
7170           dereference in an array expression.  The subset of the warning for
7171           object pointers can be suppressed by casting the pointer operand to
7172           an integer type such as "inptr_t" or "uinptr_t".  Comparisons
7173           against string literals result in unspecified behavior and are not
7174           portable, and suggest the intent was to call "strcmp".  The warning
7175           is suppressed if the suspicious expression is the result of macro
7176           expansion.  -Waddress warning is enabled by -Wall.
7177
7178       -Wno-address-of-packed-member
7179           Do not warn when the address of packed member of struct or union is
7180           taken, which usually results in an unaligned pointer value.  This
7181           is enabled by default.
7182
7183       -Wlogical-op
7184           Warn about suspicious uses of logical operators in expressions.
7185           This includes using logical operators in contexts where a bit-wise
7186           operator is likely to be expected.  Also warns when the operands of
7187           a logical operator are the same:
7188
7189                   extern int a;
7190                   if (a < 0 && a < 0) { ... }
7191
7192       -Wlogical-not-parentheses
7193           Warn about logical not used on the left hand side operand of a
7194           comparison.  This option does not warn if the right operand is
7195           considered to be a boolean expression.  Its purpose is to detect
7196           suspicious code like the following:
7197
7198                   int a;
7199                   ...
7200                   if (!a > 1) { ... }
7201
7202           It is possible to suppress the warning by wrapping the LHS into
7203           parentheses:
7204
7205                   if ((!a) > 1) { ... }
7206
7207           This warning is enabled by -Wall.
7208
7209       -Waggregate-return
7210           Warn if any functions that return structures or unions are defined
7211           or called.  (In languages where you can return an array, this also
7212           elicits a warning.)
7213
7214       -Wno-aggressive-loop-optimizations
7215           Warn if in a loop with constant number of iterations the compiler
7216           detects undefined behavior in some statement during one or more of
7217           the iterations.
7218
7219       -Wno-attributes
7220           Do not warn if an unexpected "__attribute__" is used, such as
7221           unrecognized attributes, function attributes applied to variables,
7222           etc.  This does not stop errors for incorrect use of supported
7223           attributes.
7224
7225           Additionally, using -Wno-attributes=, it is possible to suppress
7226           warnings about unknown scoped attributes (in C++11 and C2X).  For
7227           example, -Wno-attributes=vendor::attr disables warning about the
7228           following declaration:
7229
7230                   [[vendor::attr]] void f();
7231
7232           It is also possible to disable warning about all attributes in a
7233           namespace using -Wno-attributes=vendor:: which prevents warning
7234           about both of these declarations:
7235
7236                   [[vendor::safe]] void f();
7237                   [[vendor::unsafe]] void f2();
7238
7239           Note that -Wno-attributes= does not imply -Wno-attributes.
7240
7241       -Wno-builtin-declaration-mismatch
7242           Warn if a built-in function is declared with an incompatible
7243           signature or as a non-function, or when a built-in function
7244           declared with a type that does not include a prototype is called
7245           with arguments whose promoted types do not match those expected by
7246           the function.  When -Wextra is specified, also warn when a built-in
7247           function that takes arguments is declared without a prototype.  The
7248           -Wbuiltin-declaration-mismatch warning is enabled by default.  To
7249           avoid the warning include the appropriate header to bring the
7250           prototypes of built-in functions into scope.
7251
7252           For example, the call to "memset" below is diagnosed by the warning
7253           because the function expects a value of type "size_t" as its
7254           argument but the type of 32 is "int".  With -Wextra, the
7255           declaration of the function is diagnosed as well.
7256
7257                   extern void* memset ();
7258                   void f (void *d)
7259                   {
7260                     memset (d, '\0', 32);
7261                   }
7262
7263       -Wno-builtin-macro-redefined
7264           Do not warn if certain built-in macros are redefined.  This
7265           suppresses warnings for redefinition of "__TIMESTAMP__",
7266           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".
7267
7268       -Wstrict-prototypes (C and Objective-C only)
7269           Warn if a function is declared or defined without specifying the
7270           argument types.  (An old-style function definition is permitted
7271           without a warning if preceded by a declaration that specifies the
7272           argument types.)
7273
7274       -Wold-style-declaration (C and Objective-C only)
7275           Warn for obsolescent usages, according to the C Standard, in a
7276           declaration. For example, warn if storage-class specifiers like
7277           "static" are not the first things in a declaration.  This warning
7278           is also enabled by -Wextra.
7279
7280       -Wold-style-definition (C and Objective-C only)
7281           Warn if an old-style function definition is used.  A warning is
7282           given even if there is a previous prototype.  A definition using ()
7283           is not considered an old-style definition in C2X mode, because it
7284           is equivalent to (void) in that case, but is considered an old-
7285           style definition for older standards.
7286
7287       -Wmissing-parameter-type (C and Objective-C only)
7288           A function parameter is declared without a type specifier in
7289           K&R-style functions:
7290
7291                   void foo(bar) { }
7292
7293           This warning is also enabled by -Wextra.
7294
7295       -Wmissing-prototypes (C and Objective-C only)
7296           Warn if a global function is defined without a previous prototype
7297           declaration.  This warning is issued even if the definition itself
7298           provides a prototype.  Use this option to detect global functions
7299           that do not have a matching prototype declaration in a header file.
7300           This option is not valid for C++ because all function declarations
7301           provide prototypes and a non-matching declaration declares an
7302           overload rather than conflict with an earlier declaration.  Use
7303           -Wmissing-declarations to detect missing declarations in C++.
7304
7305       -Wmissing-declarations
7306           Warn if a global function is defined without a previous
7307           declaration.  Do so even if the definition itself provides a
7308           prototype.  Use this option to detect global functions that are not
7309           declared in header files.  In C, no warnings are issued for
7310           functions with previous non-prototype declarations; use
7311           -Wmissing-prototypes to detect missing prototypes.  In C++, no
7312           warnings are issued for function templates, or for inline
7313           functions, or for functions in anonymous namespaces.
7314
7315       -Wmissing-field-initializers
7316           Warn if a structure's initializer has some fields missing.  For
7317           example, the following code causes such a warning, because "x.h" is
7318           implicitly zero:
7319
7320                   struct s { int f, g, h; };
7321                   struct s x = { 3, 4 };
7322
7323           This option does not warn about designated initializers, so the
7324           following modification does not trigger a warning:
7325
7326                   struct s { int f, g, h; };
7327                   struct s x = { .f = 3, .g = 4 };
7328
7329           In C this option does not warn about the universal zero initializer
7330           { 0 }:
7331
7332                   struct s { int f, g, h; };
7333                   struct s x = { 0 };
7334
7335           Likewise, in C++ this option does not warn about the empty { }
7336           initializer, for example:
7337
7338                   struct s { int f, g, h; };
7339                   s x = { };
7340
7341           This warning is included in -Wextra.  To get other -Wextra warnings
7342           without this one, use -Wextra -Wno-missing-field-initializers.
7343
7344       -Wno-missing-requires
7345           By default, the compiler warns about a concept-id appearing as a
7346           C++20 simple-requirement:
7347
7348                   bool satisfied = requires { C<T> };
7349
7350           Here satisfied will be true if C<T> is a valid expression, which it
7351           is for all T.  Presumably the user meant to write
7352
7353                   bool satisfied = requires { requires C<T> };
7354
7355           so satisfied is only true if concept C is satisfied for type T.
7356
7357           This warning can be disabled with -Wno-missing-requires.
7358
7359       -Wno-missing-template-keyword
7360           The member access tokens ., -> and :: must be followed by the
7361           "template" keyword if the parent object is dependent and the member
7362           being named is a template.
7363
7364                   template <class X>
7365                   void DoStuff (X x)
7366                   {
7367                     x.template DoSomeOtherStuff<X>(); // Good.
7368                     x.DoMoreStuff<X>(); // Warning, x is dependent.
7369                   }
7370
7371           In rare cases it is possible to get false positives. To silence
7372           this, wrap the expression in parentheses. For example, the
7373           following is treated as a template, even where m and N are
7374           integers:
7375
7376                   void NotATemplate (my_class t)
7377                   {
7378                     int N = 5;
7379
7380                     bool test = t.m < N > (0); // Treated as a template.
7381                     test = (t.m < N) > (0); // Same meaning, but not treated as a template.
7382                   }
7383
7384           This warning can be disabled with -Wno-missing-template-keyword.
7385
7386       -Wno-multichar
7387           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
7388           they indicate a typo in the user's code, as they have
7389           implementation-defined values, and should not be used in portable
7390           code.
7391
7392       -Wnormalized=[none|id|nfc|nfkc]
7393           In ISO C and ISO C++, two identifiers are different if they are
7394           different sequences of characters.  However, sometimes when
7395           characters outside the basic ASCII character set are used, you can
7396           have two different character sequences that look the same.  To
7397           avoid confusion, the ISO 10646 standard sets out some normalization
7398           rules which when applied ensure that two sequences that look the
7399           same are turned into the same sequence.  GCC can warn you if you
7400           are using identifiers that have not been normalized; this option
7401           controls that warning.
7402
7403           There are four levels of warning supported by GCC.  The default is
7404           -Wnormalized=nfc, which warns about any identifier that is not in
7405           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
7406           form for most uses.  It is equivalent to -Wnormalized.
7407
7408           Unfortunately, there are some characters allowed in identifiers by
7409           ISO C and ISO C++ that, when turned into NFC, are not allowed in
7410           identifiers.  That is, there's no way to use these symbols in
7411           portable ISO C or C++ and have all your identifiers in NFC.
7412           -Wnormalized=id suppresses the warning for these characters.  It is
7413           hoped that future versions of the standards involved will correct
7414           this, which is why this option is not the default.
7415
7416           You can switch the warning off for all characters by writing
7417           -Wnormalized=none or -Wno-normalized.  You should only do this if
7418           you are using some other normalization scheme (like "D"), because
7419           otherwise you can easily create bugs that are literally impossible
7420           to see.
7421
7422           Some characters in ISO 10646 have distinct meanings but look
7423           identical in some fonts or display methodologies, especially once
7424           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
7425           LATIN SMALL LETTER N", displays just like a regular "n" that has
7426           been placed in a superscript.  ISO 10646 defines the NFKC
7427           normalization scheme to convert all these into a standard form as
7428           well, and GCC warns if your code is not in NFKC if you use
7429           -Wnormalized=nfkc.  This warning is comparable to warning about
7430           every identifier that contains the letter O because it might be
7431           confused with the digit 0, and so is not the default, but may be
7432           useful as a local coding convention if the programming environment
7433           cannot be fixed to display these characters distinctly.
7434
7435       -Wno-attribute-warning
7436           Do not warn about usage of functions declared with "warning"
7437           attribute.  By default, this warning is enabled.
7438           -Wno-attribute-warning can be used to disable the warning or
7439           -Wno-error=attribute-warning can be used to disable the error when
7440           compiled with -Werror flag.
7441
7442       -Wno-deprecated
7443           Do not warn about usage of deprecated features.
7444
7445       -Wno-deprecated-declarations
7446           Do not warn about uses of functions, variables, and types marked as
7447           deprecated by using the "deprecated" attribute.
7448
7449       -Wno-overflow
7450           Do not warn about compile-time overflow in constant expressions.
7451
7452       -Wno-odr
7453           Warn about One Definition Rule violations during link-time
7454           optimization.  Enabled by default.
7455
7456       -Wopenacc-parallelism
7457           Warn about potentially suboptimal choices related to OpenACC
7458           parallelism.
7459
7460       -Wopenmp-simd
7461           Warn if the vectorizer cost model overrides the OpenMP simd
7462           directive set by user.  The -fsimd-cost-model=unlimited option can
7463           be used to relax the cost model.
7464
7465       -Woverride-init (C and Objective-C only)
7466           Warn if an initialized field without side effects is overridden
7467           when using designated initializers.
7468
7469           This warning is included in -Wextra.  To get other -Wextra warnings
7470           without this one, use -Wextra -Wno-override-init.
7471
7472       -Wno-override-init-side-effects (C and Objective-C only)
7473           Do not warn if an initialized field with side effects is overridden
7474           when using designated initializers.  This warning is enabled by
7475           default.
7476
7477       -Wpacked
7478           Warn if a structure is given the packed attribute, but the packed
7479           attribute has no effect on the layout or size of the structure.
7480           Such structures may be mis-aligned for little benefit.  For
7481           instance, in this code, the variable "f.x" in "struct bar" is
7482           misaligned even though "struct bar" does not itself have the packed
7483           attribute:
7484
7485                   struct foo {
7486                     int x;
7487                     char a, b, c, d;
7488                   } __attribute__((packed));
7489                   struct bar {
7490                     char z;
7491                     struct foo f;
7492                   };
7493
7494       -Wnopacked-bitfield-compat
7495           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
7496           bit-fields of type "char".  This was fixed in GCC 4.4 but the
7497           change can lead to differences in the structure layout.  GCC
7498           informs you when the offset of such a field has changed in GCC 4.4.
7499           For example there is no longer a 4-bit padding between field "a"
7500           and "b" in this structure:
7501
7502                   struct foo
7503                   {
7504                     char a:4;
7505                     char b:8;
7506                   } __attribute__ ((packed));
7507
7508           This warning is enabled by default.  Use
7509           -Wno-packed-bitfield-compat to disable this warning.
7510
7511       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
7512           Warn if a structure field with explicitly specified alignment in a
7513           packed struct or union is misaligned.  For example, a warning will
7514           be issued on "struct S", like, "warning: alignment 1 of 'struct S'
7515           is less than 8", in this code:
7516
7517                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
7518                   struct __attribute__ ((packed)) S {
7519                     struct S8 s8;
7520                   };
7521
7522           This warning is enabled by -Wall.
7523
7524       -Wpadded
7525           Warn if padding is included in a structure, either to align an
7526           element of the structure or to align the whole structure.
7527           Sometimes when this happens it is possible to rearrange the fields
7528           of the structure to reduce the padding and so make the structure
7529           smaller.
7530
7531       -Wredundant-decls
7532           Warn if anything is declared more than once in the same scope, even
7533           in cases where multiple declaration is valid and changes nothing.
7534
7535       -Wrestrict
7536           Warn when an object referenced by a "restrict"-qualified parameter
7537           (or, in C++, a "__restrict"-qualified parameter) is aliased by
7538           another argument, or when copies between such objects overlap.  For
7539           example, the call to the "strcpy" function below attempts to
7540           truncate the string by replacing its initial characters with the
7541           last four.  However, because the call writes the terminating NUL
7542           into "a[4]", the copies overlap and the call is diagnosed.
7543
7544                   void foo (void)
7545                   {
7546                     char a[] = "abcd1234";
7547                     strcpy (a, a + 4);
7548                     ...
7549                   }
7550
7551           The -Wrestrict option detects some instances of simple overlap even
7552           without optimization but works best at -O2 and above.  It is
7553           included in -Wall.
7554
7555       -Wnested-externs (C and Objective-C only)
7556           Warn if an "extern" declaration is encountered within a function.
7557
7558       -Winline
7559           Warn if a function that is declared as inline cannot be inlined.
7560           Even with this option, the compiler does not warn about failures to
7561           inline functions declared in system headers.
7562
7563           The compiler uses a variety of heuristics to determine whether or
7564           not to inline a function.  For example, the compiler takes into
7565           account the size of the function being inlined and the amount of
7566           inlining that has already been done in the current function.
7567           Therefore, seemingly insignificant changes in the source program
7568           can cause the warnings produced by -Winline to appear or disappear.
7569
7570       -Winterference-size
7571           Warn about use of C++17
7572           "std::hardware_destructive_interference_size" without specifying
7573           its value with --param destructive-interference-size.  Also warn
7574           about questionable values for that option.
7575
7576           This variable is intended to be used for controlling class layout,
7577           to avoid false sharing in concurrent code:
7578
7579                   struct independent_fields {
7580                     alignas(std::hardware_destructive_interference_size) std::atomic<int> one;
7581                     alignas(std::hardware_destructive_interference_size) std::atomic<int> two;
7582                   };
7583
7584           Here one and two are intended to be far enough apart that stores to
7585           one won't require accesses to the other to reload the cache line.
7586
7587           By default, --param destructive-interference-size and --param
7588           constructive-interference-size are set based on the current -mtune
7589           option, typically to the L1 cache line size for the particular
7590           target CPU, sometimes to a range if tuning for a generic target.
7591           So all translation units that depend on ABI compatibility for the
7592           use of these variables must be compiled with the same -mtune (or
7593           -mcpu).
7594
7595           If ABI stability is important, such as if the use is in a header
7596           for a library, you should probably not use the hardware
7597           interference size variables at all.  Alternatively, you can force a
7598           particular value with --param.
7599
7600           If you are confident that your use of the variable does not affect
7601           ABI outside a single build of your project, you can turn off the
7602           warning with -Wno-interference-size.
7603
7604       -Wint-in-bool-context
7605           Warn for suspicious use of integer values where boolean values are
7606           expected, such as conditional expressions (?:) using non-boolean
7607           integer constants in boolean context, like "if (a <= b ? 2 : 3)".
7608           Or left shifting of signed integers in boolean context, like "for
7609           (a = 0; 1 << a; a++);".  Likewise for all kinds of multiplications
7610           regardless of the data type.  This warning is enabled by -Wall.
7611
7612       -Wno-int-to-pointer-cast
7613           Suppress warnings from casts to pointer type of an integer of a
7614           different size. In C++, casting to a pointer type of smaller size
7615           is an error. Wint-to-pointer-cast is enabled by default.
7616
7617       -Wno-pointer-to-int-cast (C and Objective-C only)
7618           Suppress warnings from casts from a pointer to an integer type of a
7619           different size.
7620
7621       -Winvalid-pch
7622           Warn if a precompiled header is found in the search path but cannot
7623           be used.
7624
7625       -Wlong-long
7626           Warn if "long long" type is used.  This is enabled by either
7627           -Wpedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
7628           the warning messages, use -Wno-long-long.
7629
7630       -Wvariadic-macros
7631           Warn if variadic macros are used in ISO C90 mode, or if the GNU
7632           alternate syntax is used in ISO C99 mode.  This is enabled by
7633           either -Wpedantic or -Wtraditional.  To inhibit the warning
7634           messages, use -Wno-variadic-macros.
7635
7636       -Wno-varargs
7637           Do not warn upon questionable usage of the macros used to handle
7638           variable arguments like "va_start".  These warnings are enabled by
7639           default.
7640
7641       -Wvector-operation-performance
7642           Warn if vector operation is not implemented via SIMD capabilities
7643           of the architecture.  Mainly useful for the performance tuning.
7644           Vector operation can be implemented "piecewise", which means that
7645           the scalar operation is performed on every vector element; "in
7646           parallel", which means that the vector operation is implemented
7647           using scalars of wider type, which normally is more performance
7648           efficient; and "as a single scalar", which means that vector fits
7649           into a scalar type.
7650
7651       -Wvla
7652           Warn if a variable-length array is used in the code.  -Wno-vla
7653           prevents the -Wpedantic warning of the variable-length array.
7654
7655       -Wvla-larger-than=byte-size
7656           If this option is used, the compiler warns for declarations of
7657           variable-length arrays whose size is either unbounded, or bounded
7658           by an argument that allows the array size to exceed byte-size
7659           bytes.  This is similar to how -Walloca-larger-than=byte-size
7660           works, but with variable-length arrays.
7661
7662           Note that GCC may optimize small variable-length arrays of a known
7663           value into plain arrays, so this warning may not get triggered for
7664           such arrays.
7665
7666           -Wvla-larger-than=PTRDIFF_MAX is enabled by default but is
7667           typically only effective when -ftree-vrp is active (default for -O2
7668           and above).
7669
7670           See also -Walloca-larger-than=byte-size.
7671
7672       -Wno-vla-larger-than
7673           Disable -Wvla-larger-than= warnings.  The option is equivalent to
7674           -Wvla-larger-than=SIZE_MAX or larger.
7675
7676       -Wvla-parameter
7677           Warn about redeclarations of functions involving arguments of
7678           Variable Length Array types of inconsistent kinds or forms, and
7679           enable the detection of out-of-bounds accesses to such parameters
7680           by warnings such as -Warray-bounds.
7681
7682           If the first function declaration uses the VLA form the bound
7683           specified in the array is assumed to be the minimum number of
7684           elements expected to be provided in calls to the function and the
7685           maximum number of elements accessed by it.  Failing to provide
7686           arguments of sufficient size or accessing more than the maximum
7687           number of elements may be diagnosed.
7688
7689           For example, the warning triggers for the following redeclarations
7690           because the first one allows an array of any size to be passed to
7691           "f" while the second one specifies that the array argument must
7692           have at least "n" elements.  In addition, calling "f" with the
7693           associated VLA bound parameter in excess of the actual VLA bound
7694           triggers a warning as well.
7695
7696                   void f (int n, int[n]);
7697                   void f (int, int[]);     // warning: argument 2 previously declared as a VLA
7698
7699                   void g (int n)
7700                   {
7701                       if (n > 4)
7702                         return;
7703                       int a[n];
7704                       f (sizeof a, a);     // warning: access to a by f may be out of bounds
7705                     ...
7706                   }
7707
7708           -Wvla-parameter is included in -Wall.  The -Warray-parameter option
7709           triggers warnings for similar problems involving ordinary array
7710           arguments.
7711
7712       -Wvolatile-register-var
7713           Warn if a register variable is declared volatile.  The volatile
7714           modifier does not inhibit all optimizations that may eliminate
7715           reads and/or writes to register variables.  This warning is enabled
7716           by -Wall.
7717
7718       -Wdisabled-optimization
7719           Warn if a requested optimization pass is disabled.  This warning
7720           does not generally indicate that there is anything wrong with your
7721           code; it merely indicates that GCC's optimizers are unable to
7722           handle the code effectively.  Often, the problem is that your code
7723           is too big or too complex; GCC refuses to optimize programs when
7724           the optimization itself is likely to take inordinate amounts of
7725           time.
7726
7727       -Wpointer-sign (C and Objective-C only)
7728           Warn for pointer argument passing or assignment with different
7729           signedness.  This option is only supported for C and Objective-C.
7730           It is implied by -Wall and by -Wpedantic, which can be disabled
7731           with -Wno-pointer-sign.
7732
7733       -Wstack-protector
7734           This option is only active when -fstack-protector is active.  It
7735           warns about functions that are not protected against stack
7736           smashing.
7737
7738       -Woverlength-strings
7739           Warn about string constants that are longer than the "minimum
7740           maximum" length specified in the C standard.  Modern compilers
7741           generally allow string constants that are much longer than the
7742           standard's minimum limit, but very portable programs should avoid
7743           using longer strings.
7744
7745           The limit applies after string constant concatenation, and does not
7746           count the trailing NUL.  In C90, the limit was 509 characters; in
7747           C99, it was raised to 4095.  C++98 does not specify a normative
7748           minimum maximum, so we do not diagnose overlength strings in C++.
7749
7750           This option is implied by -Wpedantic, and can be disabled with
7751           -Wno-overlength-strings.
7752
7753       -Wunsuffixed-float-constants (C and Objective-C only)
7754           Issue a warning for any floating constant that does not have a
7755           suffix.  When used together with -Wsystem-headers it warns about
7756           such constants in system header files.  This can be useful when
7757           preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from
7758           the decimal floating-point extension to C99.
7759
7760       -Wno-lto-type-mismatch
7761           During the link-time optimization, do not warn about type
7762           mismatches in global declarations from different compilation units.
7763           Requires -flto to be enabled.  Enabled by default.
7764
7765       -Wno-designated-init (C and Objective-C only)
7766           Suppress warnings when a positional initializer is used to
7767           initialize a structure that has been marked with the
7768           "designated_init" attribute.
7769
7770   Options That Control Static Analysis
7771       -fanalyzer
7772           This option enables an static analysis of program flow which looks
7773           for "interesting" interprocedural paths through the code, and
7774           issues warnings for problems found on them.
7775
7776           This analysis is much more expensive than other GCC warnings.
7777
7778           Enabling this option effectively enables the following warnings:
7779
7780           -Wanalyzer-double-fclose -Wanalyzer-double-free
7781           -Wanalyzer-exposure-through-output-file -Wanalyzer-file-leak
7782           -Wanalyzer-free-of-non-heap -Wanalyzer-malloc-leak
7783           -Wanalyzer-mismatching-deallocation -Wanalyzer-null-argument
7784           -Wanalyzer-null-dereference -Wanalyzer-possible-null-argument
7785           -Wanalyzer-possible-null-dereference
7786           -Wanalyzer-shift-count-negative -Wanalyzer-shift-count-overflow
7787           -Wanalyzer-stale-setjmp-buffer
7788           -Wanalyzer-unsafe-call-within-signal-handler
7789           -Wanalyzer-use-after-free
7790           -Wanalyzer-use-of-pointer-in-stale-stack-frame
7791           -Wanalyzer-use-of-uninitialized-value -Wanalyzer-write-to-const
7792           -Wanalyzer-write-to-string-literal
7793
7794           This option is only available if GCC was configured with analyzer
7795           support enabled.
7796
7797       -Wanalyzer-too-complex
7798           If -fanalyzer is enabled, the analyzer uses various heuristics to
7799           attempt to explore the control flow and data flow in the program,
7800           but these can be defeated by sufficiently complicated code.
7801
7802           By default, the analysis silently stops if the code is too
7803           complicated for the analyzer to fully explore and it reaches an
7804           internal limit.  The -Wanalyzer-too-complex option warns if this
7805           occurs.
7806
7807       -Wno-analyzer-double-fclose
7808           This warning requires -fanalyzer, which enables it; use
7809           -Wno-analyzer-double-fclose to disable it.
7810
7811           This diagnostic warns for paths through the code in which a "FILE
7812           *" can have "fclose" called on it more than once.
7813
7814       -Wno-analyzer-double-free
7815           This warning requires -fanalyzer, which enables it; use
7816           -Wno-analyzer-double-free to disable it.
7817
7818           This diagnostic warns for paths through the code in which a pointer
7819           can have a deallocator called on it more than once, either "free",
7820           or a deallocator referenced by attribute "malloc".
7821
7822       -Wno-analyzer-exposure-through-output-file
7823           This warning requires -fanalyzer, which enables it; use
7824           -Wno-analyzer-exposure-through-output-file to disable it.
7825
7826           This diagnostic warns for paths through the code in which a
7827           security-sensitive value is written to an output file (such as
7828           writing a password to a log file).
7829
7830       -Wno-analyzer-file-leak
7831           This warning requires -fanalyzer, which enables it; use
7832           -Wno-analyzer-file-leak to disable it.
7833
7834           This diagnostic warns for paths through the code in which a
7835           "<stdio.h>" "FILE *" stream object is leaked.
7836
7837       -Wno-analyzer-free-of-non-heap
7838           This warning requires -fanalyzer, which enables it; use
7839           -Wno-analyzer-free-of-non-heap to disable it.
7840
7841           This diagnostic warns for paths through the code in which "free" is
7842           called on a non-heap pointer (e.g. an on-stack buffer, or a
7843           global).
7844
7845       -Wno-analyzer-malloc-leak
7846           This warning requires -fanalyzer, which enables it; use
7847           -Wno-analyzer-malloc-leak to disable it.
7848
7849           This diagnostic warns for paths through the code in which a pointer
7850           allocated via an allocator is leaked: either "malloc", or a
7851           function marked with attribute "malloc".
7852
7853       -Wno-analyzer-mismatching-deallocation
7854           This warning requires -fanalyzer, which enables it; use
7855           -Wno-analyzer-mismatching-deallocation to disable it.
7856
7857           This diagnostic warns for paths through the code in which the wrong
7858           deallocation function is called on a pointer value, based on which
7859           function was used to allocate the pointer value.  The diagnostic
7860           will warn about mismatches between "free", scalar "delete" and
7861           vector "delete[]", and those marked as allocator/deallocator pairs
7862           using attribute "malloc".
7863
7864       -Wno-analyzer-possible-null-argument
7865           This warning requires -fanalyzer, which enables it; use
7866           -Wno-analyzer-possible-null-argument to disable it.
7867
7868           This diagnostic warns for paths through the code in which a
7869           possibly-NULL value is passed to a function argument marked with
7870           "__attribute__((nonnull))" as requiring a non-NULL value.
7871
7872       -Wno-analyzer-possible-null-dereference
7873           This warning requires -fanalyzer, which enables it; use
7874           -Wno-analyzer-possible-null-dereference to disable it.
7875
7876           This diagnostic warns for paths through the code in which a
7877           possibly-NULL value is dereferenced.
7878
7879       -Wno-analyzer-null-argument
7880           This warning requires -fanalyzer, which enables it; use
7881           -Wno-analyzer-null-argument to disable it.
7882
7883           This diagnostic warns for paths through the code in which a value
7884           known to be NULL is passed to a function argument marked with
7885           "__attribute__((nonnull))" as requiring a non-NULL value.
7886
7887       -Wno-analyzer-null-dereference
7888           This warning requires -fanalyzer, which enables it; use
7889           -Wno-analyzer-null-dereference to disable it.
7890
7891           This diagnostic warns for paths through the code in which a value
7892           known to be NULL is dereferenced.
7893
7894       -Wno-analyzer-shift-count-negative
7895           This warning requires -fanalyzer, which enables it; use
7896           -Wno-analyzer-shift-count-negative to disable it.
7897
7898           This diagnostic warns for paths through the code in which a shift
7899           is attempted with a negative count.  It is analogous to the
7900           -Wshift-count-negative diagnostic implemented in the C/C++ front
7901           ends, but is implemented based on analyzing interprocedural paths,
7902           rather than merely parsing the syntax tree.  However, the analyzer
7903           does not prioritize detection of such paths, so false negatives are
7904           more likely relative to other warnings.
7905
7906       -Wno-analyzer-shift-count-overflow
7907           This warning requires -fanalyzer, which enables it; use
7908           -Wno-analyzer-shift-count-overflow to disable it.
7909
7910           This diagnostic warns for paths through the code in which a shift
7911           is attempted with a count greater than or equal to the precision of
7912           the operand's type.  It is analogous to the -Wshift-count-overflow
7913           diagnostic implemented in the C/C++ front ends, but is implemented
7914           based on analyzing interprocedural paths, rather than merely
7915           parsing the syntax tree.  However, the analyzer does not prioritize
7916           detection of such paths, so false negatives are more likely
7917           relative to other warnings.
7918
7919       -Wno-analyzer-stale-setjmp-buffer
7920           This warning requires -fanalyzer, which enables it; use
7921           -Wno-analyzer-stale-setjmp-buffer to disable it.
7922
7923           This diagnostic warns for paths through the code in which "longjmp"
7924           is called to rewind to a "jmp_buf" relating to a "setjmp" call in a
7925           function that has returned.
7926
7927           When "setjmp" is called on a "jmp_buf" to record a rewind location,
7928           it records the stack frame.  The stack frame becomes invalid when
7929           the function containing the "setjmp" call returns.  Attempting to
7930           rewind to it via "longjmp" would reference a stack frame that no
7931           longer exists, and likely lead to a crash (or worse).
7932
7933       -Wno-analyzer-tainted-allocation-size
7934           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7935           to enable it; use -Wno-analyzer-tainted-allocation-size to disable
7936           it.
7937
7938           This diagnostic warns for paths through the code in which a value
7939           that could be under an attacker's control is used as the size of an
7940           allocation without being sanitized, so that an attacker could
7941           inject an excessively large allocation and potentially cause a
7942           denial of service attack.
7943
7944           See @url{https://cwe.mitre.org/data/definitions/789.html, CWE-789:
7945           Memory Allocation with Excessive Size Value}.
7946
7947       -Wno-analyzer-tainted-array-index
7948           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7949           to enable it; use -Wno-analyzer-tainted-array-index to disable it.
7950
7951           This diagnostic warns for paths through the code in which a value
7952           that could be under an attacker's control is used as the index of
7953           an array access without being sanitized, so that an attacker could
7954           inject an out-of-bounds access.
7955
7956           See @url{https://cwe.mitre.org/data/definitions/129.html, CWE-129:
7957           Improper Validation of Array Index}.
7958
7959       -Wno-analyzer-tainted-divisor
7960           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7961           to enable it; use -Wno-analyzer-tainted-divisor to disable it.
7962
7963           This diagnostic warns for paths through the code in which a value
7964           that could be under an attacker's control is used as the divisor in
7965           a division or modulus operation without being sanitized, so that an
7966           attacker could inject a division-by-zero.
7967
7968       -Wno-analyzer-tainted-offset
7969           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7970           to enable it; use -Wno-analyzer-tainted-offset to disable it.
7971
7972           This diagnostic warns for paths through the code in which a value
7973           that could be under an attacker's control is used as a pointer
7974           offset without being sanitized, so that an attacker could inject an
7975           out-of-bounds access.
7976
7977           See @url{https://cwe.mitre.org/data/definitions/823.html, CWE-823:
7978           Use of Out-of-range Pointer Offset}.
7979
7980       -Wno-analyzer-tainted-size
7981           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7982           to enable it; use -Wno-analyzer-tainted-size to disable it.
7983
7984           This diagnostic warns for paths through the code in which a value
7985           that could be under an attacker's control is used as the size of an
7986           operation such as "memset" without being sanitized, so that an
7987           attacker could inject an out-of-bounds access.
7988
7989       -Wno-analyzer-unsafe-call-within-signal-handler
7990           This warning requires -fanalyzer, which enables it; use
7991           -Wno-analyzer-unsafe-call-within-signal-handler to disable it.
7992
7993           This diagnostic warns for paths through the code in which a
7994           function known to be async-signal-unsafe (such as "fprintf") is
7995           called from a signal handler.
7996
7997       -Wno-analyzer-use-after-free
7998           This warning requires -fanalyzer, which enables it; use
7999           -Wno-analyzer-use-after-free to disable it.
8000
8001           This diagnostic warns for paths through the code in which a pointer
8002           is used after a deallocator is called on it: either "free", or a
8003           deallocator referenced by attribute "malloc".
8004
8005       -Wno-analyzer-use-of-pointer-in-stale-stack-frame
8006           This warning requires -fanalyzer, which enables it; use
8007           -Wno-analyzer-use-of-pointer-in-stale-stack-frame to disable it.
8008
8009           This diagnostic warns for paths through the code in which a pointer
8010           is dereferenced that points to a variable in a stale stack frame.
8011
8012       -Wno-analyzer-write-to-const
8013           This warning requires -fanalyzer, which enables it; use
8014           -Wno-analyzer-write-to-const to disable it.
8015
8016           This diagnostic warns for paths through the code in which the
8017           analyzer detects an attempt to write through a pointer to a "const"
8018           object.  However, the analyzer does not prioritize detection of
8019           such paths, so false negatives are more likely relative to other
8020           warnings.
8021
8022       -Wno-analyzer-write-to-string-literal
8023           This warning requires -fanalyzer, which enables it; use
8024           -Wno-analyzer-write-to-string-literal to disable it.
8025
8026           This diagnostic warns for paths through the code in which the
8027           analyzer detects an attempt to write through a pointer to a string
8028           literal.  However, the analyzer does not prioritize detection of
8029           such paths, so false negatives are more likely relative to other
8030           warnings.
8031
8032       -Wno-analyzer-use-of-uninitialized-value
8033           This warning requires -fanalyzer, which enables it; use
8034           -Wno-analyzer-use-of-uninitialized-value to disable it.
8035
8036           This diagnostic warns for paths through the code in which an
8037           uninitialized value is used.
8038
8039       Pertinent parameters for controlling the exploration are: --param
8040       analyzer-bb-explosion-factor=value, --param
8041       analyzer-max-enodes-per-program-point=value, --param
8042       analyzer-max-recursion-depth=value, and --param
8043       analyzer-min-snodes-for-call-summary=value.
8044
8045       The following options control the analyzer.
8046
8047       -fanalyzer-call-summaries
8048           Simplify interprocedural analysis by computing the effect of
8049           certain calls, rather than exploring all paths through the function
8050           from callsite to each possible return.
8051
8052           If enabled, call summaries are only used for functions with more
8053           than one call site, and that are sufficiently complicated (as per
8054           --param analyzer-min-snodes-for-call-summary=value).
8055
8056       -fanalyzer-checker=name
8057           Restrict the analyzer to run just the named checker, and enable it.
8058
8059           Some checkers are disabled by default (even with -fanalyzer), such
8060           as the "taint" checker that implements
8061           -Wanalyzer-tainted-array-index, and this option is required to
8062           enable them.
8063
8064           Note: currently, -fanalyzer-checker=taint disables the following
8065           warnings from -fanalyzer:
8066
8067           -Wanalyzer-double-fclose -Wanalyzer-double-free
8068           -Wanalyzer-exposure-through-output-file -Wanalyzer-file-leak
8069           -Wanalyzer-free-of-non-heap -Wanalyzer-malloc-leak
8070           -Wanalyzer-mismatching-deallocation -Wanalyzer-null-argument
8071           -Wanalyzer-null-dereference -Wanalyzer-possible-null-argument
8072           -Wanalyzer-possible-null-dereference
8073           -Wanalyzer-unsafe-call-within-signal-handler
8074           -Wanalyzer-use-after-free
8075
8076       -fno-analyzer-feasibility
8077           This option is intended for analyzer developers.
8078
8079           By default the analyzer verifies that there is a feasible control
8080           flow path for each diagnostic it emits: that the conditions that
8081           hold are not mutually exclusive.  Diagnostics for which no feasible
8082           path can be found are rejected.  This filtering can be suppressed
8083           with -fno-analyzer-feasibility, for debugging issues in this code.
8084
8085       -fanalyzer-fine-grained
8086           This option is intended for analyzer developers.
8087
8088           Internally the analyzer builds an "exploded graph" that combines
8089           control flow graphs with data flow information.
8090
8091           By default, an edge in this graph can contain the effects of a run
8092           of multiple statements within a basic block.  With
8093           -fanalyzer-fine-grained, each statement gets its own edge.
8094
8095       -fanalyzer-show-duplicate-count
8096           This option is intended for analyzer developers: if multiple
8097           diagnostics have been detected as being duplicates of each other,
8098           it emits a note when reporting the best diagnostic, giving the
8099           number of additional diagnostics that were suppressed by the
8100           deduplication logic.
8101
8102       -fno-analyzer-state-merge
8103           This option is intended for analyzer developers.
8104
8105           By default the analyzer attempts to simplify analysis by merging
8106           sufficiently similar states at each program point as it builds its
8107           "exploded graph".  With -fno-analyzer-state-merge this merging can
8108           be suppressed, for debugging state-handling issues.
8109
8110       -fno-analyzer-state-purge
8111           This option is intended for analyzer developers.
8112
8113           By default the analyzer attempts to simplify analysis by purging
8114           aspects of state at a program point that appear to no longer be
8115           relevant e.g. the values of locals that aren't accessed later in
8116           the function and which aren't relevant to leak analysis.
8117
8118           With -fno-analyzer-state-purge this purging of state can be
8119           suppressed, for debugging state-handling issues.
8120
8121       -fanalyzer-transitivity
8122           This option enables transitivity of constraints within the
8123           analyzer.
8124
8125       -fanalyzer-verbose-edges
8126           This option is intended for analyzer developers.  It enables more
8127           verbose, lower-level detail in the descriptions of control flow
8128           within diagnostic paths.
8129
8130       -fanalyzer-verbose-state-changes
8131           This option is intended for analyzer developers.  It enables more
8132           verbose, lower-level detail in the descriptions of events relating
8133           to state machines within diagnostic paths.
8134
8135       -fanalyzer-verbosity=level
8136           This option controls the complexity of the control flow paths that
8137           are emitted for analyzer diagnostics.
8138
8139           The level can be one of:
8140
8141           0   At this level, interprocedural call and return events are
8142               displayed, along with the most pertinent state-change events
8143               relating to a diagnostic.  For example, for a double-"free"
8144               diagnostic, both calls to "free" will be shown.
8145
8146           1   As per the previous level, but also show events for the entry
8147               to each function.
8148
8149           2   As per the previous level, but also show events relating to
8150               control flow that are significant to triggering the issue (e.g.
8151               "true path taken" at a conditional).
8152
8153               This level is the default.
8154
8155           3   As per the previous level, but show all control flow events,
8156               not just significant ones.
8157
8158           4   This level is intended for analyzer developers; it adds various
8159               other events intended for debugging the analyzer.
8160
8161       -fdump-analyzer
8162           Dump internal details about what the analyzer is doing to
8163           file.analyzer.txt.  This option is overridden by
8164           -fdump-analyzer-stderr.
8165
8166       -fdump-analyzer-stderr
8167           Dump internal details about what the analyzer is doing to stderr.
8168           This option overrides -fdump-analyzer.
8169
8170       -fdump-analyzer-callgraph
8171           Dump a representation of the call graph suitable for viewing with
8172           GraphViz to file.callgraph.dot.
8173
8174       -fdump-analyzer-exploded-graph
8175           Dump a representation of the "exploded graph" suitable for viewing
8176           with GraphViz to file.eg.dot.  Nodes are color-coded based on
8177           state-machine states to emphasize state changes.
8178
8179       -fdump-analyzer-exploded-nodes
8180           Emit diagnostics showing where nodes in the "exploded graph" are in
8181           relation to the program source.
8182
8183       -fdump-analyzer-exploded-nodes-2
8184           Dump a textual representation of the "exploded graph" to
8185           file.eg.txt.
8186
8187       -fdump-analyzer-exploded-nodes-3
8188           Dump a textual representation of the "exploded graph" to one dump
8189           file per node, to file.eg-id.txt.  This is typically a large number
8190           of dump files.
8191
8192       -fdump-analyzer-exploded-paths
8193           Dump a textual representation of the "exploded path" for each
8194           diagnostic to file.idx.kind.epath.txt.
8195
8196       -fdump-analyzer-feasibility
8197           Dump internal details about the analyzer's search for feasible
8198           paths.  The details are written in a form suitable for viewing with
8199           GraphViz to filenames of the form file.*.fg.dot and file.*.tg.dot.
8200
8201       -fdump-analyzer-json
8202           Dump a compressed JSON representation of analyzer internals to
8203           file.analyzer.json.gz.  The precise format is subject to change.
8204
8205       -fdump-analyzer-state-purge
8206           As per -fdump-analyzer-supergraph, dump a representation of the
8207           "supergraph" suitable for viewing with GraphViz, but annotate the
8208           graph with information on what state will be purged at each node.
8209           The graph is written to file.state-purge.dot.
8210
8211       -fdump-analyzer-supergraph
8212           Dump representations of the "supergraph" suitable for viewing with
8213           GraphViz to file.supergraph.dot and to file.supergraph-eg.dot.
8214           These show all of the control flow graphs in the program, with
8215           interprocedural edges for calls and returns.  The second dump
8216           contains annotations showing nodes in the "exploded graph" and
8217           diagnostics associated with them.
8218
8219       -fdump-analyzer-untracked
8220           Emit custom warnings with internal details intended for analyzer
8221           developers.
8222
8223   Options for Debugging Your Program
8224       To tell GCC to emit extra information for use by a debugger, in almost
8225       all cases you need only to add -g to your other options.  Some debug
8226       formats can co-exist (like DWARF with CTF) when each of them is enabled
8227       explicitly by adding the respective command line option to your other
8228       options.
8229
8230       GCC allows you to use -g with -O.  The shortcuts taken by optimized
8231       code may occasionally be surprising: some variables you declared may
8232       not exist at all; flow of control may briefly move where you did not
8233       expect it; some statements may not be executed because they compute
8234       constant results or their values are already at hand; some statements
8235       may execute in different places because they have been moved out of
8236       loops.  Nevertheless it is possible to debug optimized output.  This
8237       makes it reasonable to use the optimizer for programs that might have
8238       bugs.
8239
8240       If you are not using some other optimization option, consider using -Og
8241       with -g.  With no -O option at all, some compiler passes that collect
8242       information useful for debugging do not run at all, so that -Og may
8243       result in a better debugging experience.
8244
8245       -g  Produce debugging information in the operating system's native
8246           format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
8247           debugging information.
8248
8249           On most systems that use stabs format, -g enables use of extra
8250           debugging information that only GDB can use; this extra information
8251           makes debugging work better in GDB but probably makes other
8252           debuggers crash or refuse to read the program.  If you want to
8253           control for certain whether to generate the extra information, use
8254           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
8255
8256       -ggdb
8257           Produce debugging information for use by GDB.  This means to use
8258           the most expressive format available (DWARF, stabs, or the native
8259           format if neither of those are supported), including GDB extensions
8260           if at all possible.
8261
8262       -gdwarf
8263       -gdwarf-version
8264           Produce debugging information in DWARF format (if that is
8265           supported).  The value of version may be either 2, 3, 4 or 5; the
8266           default version for most targets is 5 (with the exception of
8267           VxWorks, TPF and Darwin/Mac OS X, which default to version 2, and
8268           AIX, which defaults to version 4).
8269
8270           Note that with DWARF Version 2, some ports require and always use
8271           some non-conflicting DWARF 3 extensions in the unwind tables.
8272
8273           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
8274           maximum benefit. Version 5 requires GDB 8.0 or higher.
8275
8276           GCC no longer supports DWARF Version 1, which is substantially
8277           different than Version 2 and later.  For historical reasons, some
8278           other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a
8279           reference to DWARF Version 2 in their names, but apply to all
8280           currently-supported versions of DWARF.
8281
8282       -gbtf
8283           Request BTF debug information.  BTF is the default debugging format
8284           for the eBPF target.  On other targets, like x86, BTF debug
8285           information can be generated along with DWARF debug information
8286           when both of the debug formats are enabled explicitly via their
8287           respective command line options.
8288
8289       -gctf
8290       -gctflevel
8291           Request CTF debug information and use level to specify how much CTF
8292           debug information should be produced.  If -gctf is specified
8293           without a value for level, the default level of CTF debug
8294           information is 2.
8295
8296           CTF debug information can be generated along with DWARF debug
8297           information when both of the debug formats are enabled explicitly
8298           via their respective command line options.
8299
8300           Level 0 produces no CTF debug information at all.  Thus, -gctf0
8301           negates -gctf.
8302
8303           Level 1 produces CTF information for tracebacks only.  This
8304           includes callsite information, but does not include type
8305           information.
8306
8307           Level 2 produces type information for entities (functions, data
8308           objects etc.)  at file-scope or global-scope only.
8309
8310       -gstabs
8311           Produce debugging information in stabs format (if that is
8312           supported), without GDB extensions.  This is the format used by DBX
8313           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
8314           this option produces stabs debugging output that is not understood
8315           by DBX.  On System V Release 4 systems this option requires the GNU
8316           assembler.
8317
8318       -gstabs+
8319           Produce debugging information in stabs format (if that is
8320           supported), using GNU extensions understood only by the GNU
8321           debugger (GDB).  The use of these extensions is likely to make
8322           other debuggers crash or refuse to read the program.
8323
8324       -gxcoff
8325           Produce debugging information in XCOFF format (if that is
8326           supported).  This is the format used by the DBX debugger on IBM
8327           RS/6000 systems.
8328
8329       -gxcoff+
8330           Produce debugging information in XCOFF format (if that is
8331           supported), using GNU extensions understood only by the GNU
8332           debugger (GDB).  The use of these extensions is likely to make
8333           other debuggers crash or refuse to read the program, and may cause
8334           assemblers other than the GNU assembler (GAS) to fail with an
8335           error.
8336
8337       -gvms
8338           Produce debugging information in Alpha/VMS debug format (if that is
8339           supported).  This is the format used by DEBUG on Alpha/VMS systems.
8340
8341       -glevel
8342       -ggdblevel
8343       -gstabslevel
8344       -gxcofflevel
8345       -gvmslevel
8346           Request debugging information and also use level to specify how
8347           much information.  The default level is 2.
8348
8349           Level 0 produces no debug information at all.  Thus, -g0 negates
8350           -g.
8351
8352           Level 1 produces minimal information, enough for making backtraces
8353           in parts of the program that you don't plan to debug.  This
8354           includes descriptions of functions and external variables, and line
8355           number tables, but no information about local variables.
8356
8357           Level 3 includes extra information, such as all the macro
8358           definitions present in the program.  Some debuggers support macro
8359           expansion when you use -g3.
8360
8361           If you use multiple -g options, with or without level numbers, the
8362           last such option is the one that is effective.
8363
8364           -gdwarf does not accept a concatenated debug level, to avoid
8365           confusion with -gdwarf-level.  Instead use an additional -glevel
8366           option to change the debug level for DWARF.
8367
8368       -fno-eliminate-unused-debug-symbols
8369           By default, no debug information is produced for symbols that are
8370           not actually used. Use this option if you want debug information
8371           for all symbols.
8372
8373       -femit-class-debug-always
8374           Instead of emitting debugging information for a C++ class in only
8375           one object file, emit it in all object files using the class.  This
8376           option should be used only with debuggers that are unable to handle
8377           the way GCC normally emits debugging information for classes
8378           because using this option increases the size of debugging
8379           information by as much as a factor of two.
8380
8381       -fno-merge-debug-strings
8382           Direct the linker to not merge together strings in the debugging
8383           information that are identical in different object files.  Merging
8384           is not supported by all assemblers or linkers.  Merging decreases
8385           the size of the debug information in the output file at the cost of
8386           increasing link processing time.  Merging is enabled by default.
8387
8388       -fdebug-prefix-map=old=new
8389           When compiling files residing in directory old, record debugging
8390           information describing them as if the files resided in directory
8391           new instead.  This can be used to replace a build-time path with an
8392           install-time path in the debug info.  It can also be used to change
8393           an absolute path to a relative path by using . for new.  This can
8394           give more reproducible builds, which are location independent, but
8395           may require an extra command to tell GDB where to find the source
8396           files. See also -ffile-prefix-map.
8397
8398       -fvar-tracking
8399           Run variable tracking pass.  It computes where variables are stored
8400           at each position in code.  Better debugging information is then
8401           generated (if the debugging information format supports this
8402           information).
8403
8404           It is enabled by default when compiling with optimization (-Os, -O,
8405           -O2, ...), debugging information (-g) and the debug info format
8406           supports it.
8407
8408       -fvar-tracking-assignments
8409           Annotate assignments to user variables early in the compilation and
8410           attempt to carry the annotations over throughout the compilation
8411           all the way to the end, in an attempt to improve debug information
8412           while optimizing.  Use of -gdwarf-4 is recommended along with it.
8413
8414           It can be enabled even if var-tracking is disabled, in which case
8415           annotations are created and maintained, but discarded at the end.
8416           By default, this flag is enabled together with -fvar-tracking,
8417           except when selective scheduling is enabled.
8418
8419       -gsplit-dwarf
8420           If DWARF debugging information is enabled, separate as much
8421           debugging information as possible into a separate output file with
8422           the extension .dwo.  This option allows the build system to avoid
8423           linking files with debug information.  To be useful, this option
8424           requires a debugger capable of reading .dwo files.
8425
8426       -gdwarf32
8427       -gdwarf64
8428           If DWARF debugging information is enabled, the -gdwarf32 selects
8429           the 32-bit DWARF format and the -gdwarf64 selects the 64-bit DWARF
8430           format.  The default is target specific, on most targets it is
8431           -gdwarf32 though.  The 32-bit DWARF format is smaller, but can't
8432           support more than 2GiB of debug information in any of the DWARF
8433           debug information sections.  The 64-bit DWARF format allows larger
8434           debug information and might not be well supported by all consumers
8435           yet.
8436
8437       -gdescribe-dies
8438           Add description attributes to some DWARF DIEs that have no name
8439           attribute, such as artificial variables, external references and
8440           call site parameter DIEs.
8441
8442       -gpubnames
8443           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.
8444
8445       -ggnu-pubnames
8446           Generate ".debug_pubnames" and ".debug_pubtypes" sections in a
8447           format suitable for conversion into a GDB index.  This option is
8448           only useful with a linker that can produce GDB index version 7.
8449
8450       -fdebug-types-section
8451           When using DWARF Version 4 or higher, type DIEs can be put into
8452           their own ".debug_types" section instead of making them part of the
8453           ".debug_info" section.  It is more efficient to put them in a
8454           separate comdat section since the linker can then remove
8455           duplicates.  But not all DWARF consumers support ".debug_types"
8456           sections yet and on some objects ".debug_types" produces larger
8457           instead of smaller debugging information.
8458
8459       -grecord-gcc-switches
8460       -gno-record-gcc-switches
8461           This switch causes the command-line options used to invoke the
8462           compiler that may affect code generation to be appended to the
8463           DW_AT_producer attribute in DWARF debugging information.  The
8464           options are concatenated with spaces separating them from each
8465           other and from the compiler version.  It is enabled by default.
8466           See also -frecord-gcc-switches for another way of storing compiler
8467           options into the object file.
8468
8469       -gstrict-dwarf
8470           Disallow using extensions of later DWARF standard version than
8471           selected with -gdwarf-version.  On most targets using non-
8472           conflicting DWARF extensions from later standard versions is
8473           allowed.
8474
8475       -gno-strict-dwarf
8476           Allow using extensions of later DWARF standard version than
8477           selected with -gdwarf-version.
8478
8479       -gas-loc-support
8480           Inform the compiler that the assembler supports ".loc" directives.
8481           It may then use them for the assembler to generate DWARF2+ line
8482           number tables.
8483
8484           This is generally desirable, because assembler-generated line-
8485           number tables are a lot more compact than those the compiler can
8486           generate itself.
8487
8488           This option will be enabled by default if, at GCC configure time,
8489           the assembler was found to support such directives.
8490
8491       -gno-as-loc-support
8492           Force GCC to generate DWARF2+ line number tables internally, if
8493           DWARF2+ line number tables are to be generated.
8494
8495       -gas-locview-support
8496           Inform the compiler that the assembler supports "view" assignment
8497           and reset assertion checking in ".loc" directives.
8498
8499           This option will be enabled by default if, at GCC configure time,
8500           the assembler was found to support them.
8501
8502       -gno-as-locview-support
8503           Force GCC to assign view numbers internally, if
8504           -gvariable-location-views are explicitly requested.
8505
8506       -gcolumn-info
8507       -gno-column-info
8508           Emit location column information into DWARF debugging information,
8509           rather than just file and line.  This option is enabled by default.
8510
8511       -gstatement-frontiers
8512       -gno-statement-frontiers
8513           This option causes GCC to create markers in the internal
8514           representation at the beginning of statements, and to keep them
8515           roughly in place throughout compilation, using them to guide the
8516           output of "is_stmt" markers in the line number table.  This is
8517           enabled by default when compiling with optimization (-Os, -O1, -O2,
8518           ...), and outputting DWARF 2 debug information at the normal level.
8519
8520       -gvariable-location-views
8521       -gvariable-location-views=incompat5
8522       -gno-variable-location-views
8523           Augment variable location lists with progressive view numbers
8524           implied from the line number table.  This enables debug information
8525           consumers to inspect state at certain points of the program, even
8526           if no instructions associated with the corresponding source
8527           locations are present at that point.  If the assembler lacks
8528           support for view numbers in line number tables, this will cause the
8529           compiler to emit the line number table, which generally makes them
8530           somewhat less compact.  The augmented line number tables and
8531           location lists are fully backward-compatible, so they can be
8532           consumed by debug information consumers that are not aware of these
8533           augmentations, but they won't derive any benefit from them either.
8534
8535           This is enabled by default when outputting DWARF 2 debug
8536           information at the normal level, as long as there is assembler
8537           support, -fvar-tracking-assignments is enabled and -gstrict-dwarf
8538           is not.  When assembler support is not available, this may still be
8539           enabled, but it will force GCC to output internal line number
8540           tables, and if -ginternal-reset-location-views is not enabled, that
8541           will most certainly lead to silently mismatching location views.
8542
8543           There is a proposed representation for view numbers that is not
8544           backward compatible with the location list format introduced in
8545           DWARF 5, that can be enabled with
8546           -gvariable-location-views=incompat5.  This option may be removed in
8547           the future, is only provided as a reference implementation of the
8548           proposed representation.  Debug information consumers are not
8549           expected to support this extended format, and they would be
8550           rendered unable to decode location lists using it.
8551
8552       -ginternal-reset-location-views
8553       -gno-internal-reset-location-views
8554           Attempt to determine location views that can be omitted from
8555           location view lists.  This requires the compiler to have very
8556           accurate insn length estimates, which isn't always the case, and it
8557           may cause incorrect view lists to be generated silently when using
8558           an assembler that does not support location view lists.  The GNU
8559           assembler will flag any such error as a "view number mismatch".
8560           This is only enabled on ports that define a reliable estimation
8561           function.
8562
8563       -ginline-points
8564       -gno-inline-points
8565           Generate extended debug information for inlined functions.
8566           Location view tracking markers are inserted at inlined entry
8567           points, so that address and view numbers can be computed and output
8568           in debug information.  This can be enabled independently of
8569           location views, in which case the view numbers won't be output, but
8570           it can only be enabled along with statement frontiers, and it is
8571           only enabled by default if location views are enabled.
8572
8573       -gz[=type]
8574           Produce compressed debug sections in DWARF format, if that is
8575           supported.  If type is not given, the default type depends on the
8576           capabilities of the assembler and linker used.  type may be one of
8577           none (don't compress debug sections), zlib (use zlib compression in
8578           ELF gABI format), or zlib-gnu (use zlib compression in traditional
8579           GNU format).  If the linker doesn't support writing compressed
8580           debug sections, the option is rejected.  Otherwise, if the
8581           assembler does not support them, -gz is silently ignored when
8582           producing object files.
8583
8584       -femit-struct-debug-baseonly
8585           Emit debug information for struct-like types only when the base
8586           name of the compilation source file matches the base name of file
8587           in which the struct is defined.
8588
8589           This option substantially reduces the size of debugging
8590           information, but at significant potential loss in type information
8591           to the debugger.  See -femit-struct-debug-reduced for a less
8592           aggressive option.  See -femit-struct-debug-detailed for more
8593           detailed control.
8594
8595           This option works only with DWARF debug output.
8596
8597       -femit-struct-debug-reduced
8598           Emit debug information for struct-like types only when the base
8599           name of the compilation source file matches the base name of file
8600           in which the type is defined, unless the struct is a template or
8601           defined in a system header.
8602
8603           This option significantly reduces the size of debugging
8604           information, with some potential loss in type information to the
8605           debugger.  See -femit-struct-debug-baseonly for a more aggressive
8606           option.  See -femit-struct-debug-detailed for more detailed
8607           control.
8608
8609           This option works only with DWARF debug output.
8610
8611       -femit-struct-debug-detailed[=spec-list]
8612           Specify the struct-like types for which the compiler generates
8613           debug information.  The intent is to reduce duplicate struct debug
8614           information between different object files within the same program.
8615
8616           This option is a detailed version of -femit-struct-debug-reduced
8617           and -femit-struct-debug-baseonly, which serves for most needs.
8618
8619           A specification has the
8620           syntax[dir:|ind:][ord:|gen:](any|sys|base|none)
8621
8622           The optional first word limits the specification to structs that
8623           are used directly (dir:) or used indirectly (ind:).  A struct type
8624           is used directly when it is the type of a variable, member.
8625           Indirect uses arise through pointers to structs.  That is, when use
8626           of an incomplete struct is valid, the use is indirect.  An example
8627           is struct one direct; struct two * indirect;.
8628
8629           The optional second word limits the specification to ordinary
8630           structs (ord:) or generic structs (gen:).  Generic structs are a
8631           bit complicated to explain.  For C++, these are non-explicit
8632           specializations of template classes, or non-template classes within
8633           the above.  Other programming languages have generics, but
8634           -femit-struct-debug-detailed does not yet implement them.
8635
8636           The third word specifies the source files for those structs for
8637           which the compiler should emit debug information.  The values none
8638           and any have the normal meaning.  The value base means that the
8639           base of name of the file in which the type declaration appears must
8640           match the base of the name of the main compilation file.  In
8641           practice, this means that when compiling foo.c, debug information
8642           is generated for types declared in that file and foo.h, but not
8643           other header files.  The value sys means those types satisfying
8644           base or declared in system or compiler headers.
8645
8646           You may need to experiment to determine the best settings for your
8647           application.
8648
8649           The default is -femit-struct-debug-detailed=all.
8650
8651           This option works only with DWARF debug output.
8652
8653       -fno-dwarf2-cfi-asm
8654           Emit DWARF unwind info as compiler generated ".eh_frame" section
8655           instead of using GAS ".cfi_*" directives.
8656
8657       -fno-eliminate-unused-debug-types
8658           Normally, when producing DWARF output, GCC avoids producing debug
8659           symbol output for types that are nowhere used in the source file
8660           being compiled.  Sometimes it is useful to have GCC emit debugging
8661           information for all types declared in a compilation unit,
8662           regardless of whether or not they are actually used in that
8663           compilation unit, for example if, in the debugger, you want to cast
8664           a value to a type that is not actually used in your program (but is
8665           declared).  More often, however, this results in a significant
8666           amount of wasted space.
8667
8668   Options That Control Optimization
8669       These options control various sorts of optimizations.
8670
8671       Without any optimization option, the compiler's goal is to reduce the
8672       cost of compilation and to make debugging produce the expected results.
8673       Statements are independent: if you stop the program with a breakpoint
8674       between statements, you can then assign a new value to any variable or
8675       change the program counter to any other statement in the function and
8676       get exactly the results you expect from the source code.
8677
8678       Turning on optimization flags makes the compiler attempt to improve the
8679       performance and/or code size at the expense of compilation time and
8680       possibly the ability to debug the program.
8681
8682       The compiler performs optimization based on the knowledge it has of the
8683       program.  Compiling multiple files at once to a single output file mode
8684       allows the compiler to use information gained from all of the files
8685       when compiling each of them.
8686
8687       Not all optimizations are controlled directly by a flag.  Only
8688       optimizations that have a flag are listed in this section.
8689
8690       Most optimizations are completely disabled at -O0 or if an -O level is
8691       not set on the command line, even if individual optimization flags are
8692       specified.  Similarly, -Og suppresses many optimization passes.
8693
8694       Depending on the target and how GCC was configured, a slightly
8695       different set of optimizations may be enabled at each -O level than
8696       those listed here.  You can invoke GCC with -Q --help=optimizers to
8697       find out the exact set of optimizations that are enabled at each level.
8698
8699       -O
8700       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
8701           lot more memory for a large function.
8702
8703           With -O, the compiler tries to reduce code size and execution time,
8704           without performing any optimizations that take a great deal of
8705           compilation time.
8706
8707           -O turns on the following optimization flags:
8708
8709           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments
8710           -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch
8711           -fdse -fforward-propagate -fguess-branch-probability
8712           -fif-conversion -fif-conversion2 -finline-functions-called-once
8713           -fipa-modref -fipa-profile -fipa-pure-const -fipa-reference
8714           -fipa-reference-addressable -fmerge-constants
8715           -fmove-loop-invariants -fmove-loop-stores -fomit-frame-pointer
8716           -freorder-blocks -fshrink-wrap -fshrink-wrap-separate
8717           -fsplit-wide-types -fssa-backprop -fssa-phiopt -ftree-bit-ccp
8718           -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop
8719           -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop
8720           -ftree-fre -ftree-phiprop -ftree-pta -ftree-scev-cprop -ftree-sink
8721           -ftree-slsr -ftree-sra -ftree-ter -funit-at-a-time
8722
8723       -O2 Optimize even more.  GCC performs nearly all supported
8724           optimizations that do not involve a space-speed tradeoff.  As
8725           compared to -O, this option increases both compilation time and the
8726           performance of the generated code.
8727
8728           -O2 turns on all optimization flags specified by -O1.  It also
8729           turns on the following optimization flags:
8730
8731           -falign-functions  -falign-jumps -falign-labels  -falign-loops
8732           -fcaller-saves -fcode-hoisting -fcrossjumping -fcse-follow-jumps
8733           -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize
8734           -fdevirtualize-speculatively -fexpensive-optimizations
8735           -ffinite-loops -fgcse  -fgcse-lm -fhoist-adjacent-loads
8736           -finline-functions -finline-small-functions -findirect-inlining
8737           -fipa-bit-cp  -fipa-cp  -fipa-icf -fipa-ra  -fipa-sra  -fipa-vrp
8738           -fisolate-erroneous-paths-dereference -flra-remat
8739           -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining
8740           -fpeephole2 -freorder-blocks-algorithm=stc
8741           -freorder-blocks-and-partition  -freorder-functions
8742           -frerun-cse-after-loop -fschedule-insns  -fschedule-insns2
8743           -fsched-interblock  -fsched-spec -fstore-merging -fstrict-aliasing
8744           -fthread-jumps -ftree-builtin-call-dce -ftree-loop-vectorize
8745           -ftree-pre -ftree-slp-vectorize -ftree-switch-conversion
8746           -ftree-tail-merge -ftree-vrp -fvect-cost-model=very-cheap
8747
8748           Please note the warning under -fgcse about invoking -O2 on programs
8749           that use computed gotos.
8750
8751       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
8752           and also turns on the following optimization flags:
8753
8754           -fgcse-after-reload -fipa-cp-clone -floop-interchange
8755           -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning
8756           -fsplit-loops -fsplit-paths -ftree-loop-distribution
8757           -ftree-partial-pre -funswitch-loops -fvect-cost-model=dynamic
8758           -fversion-loops-for-strides
8759
8760       -O0 Reduce compilation time and make debugging produce the expected
8761           results.  This is the default.
8762
8763       -Os Optimize for size.  -Os enables all -O2 optimizations except those
8764           that often increase code size:
8765
8766           -falign-functions  -falign-jumps -falign-labels  -falign-loops
8767           -fprefetch-loop-arrays  -freorder-blocks-algorithm=stc
8768
8769           It also enables -finline-functions, causes the compiler to tune for
8770           code size rather than execution speed, and performs further
8771           optimizations designed to reduce code size.
8772
8773       -Ofast
8774           Disregard strict standards compliance.  -Ofast enables all -O3
8775           optimizations.  It also enables optimizations that are not valid
8776           for all standard-compliant programs.  It turns on -ffast-math,
8777           -fallow-store-data-races and the Fortran-specific -fstack-arrays,
8778           unless -fmax-stack-var-size is specified, and -fno-protect-parens.
8779           It turns off -fsemantic-interposition.
8780
8781       -Og Optimize debugging experience.  -Og should be the optimization
8782           level of choice for the standard edit-compile-debug cycle, offering
8783           a reasonable level of optimization while maintaining fast
8784           compilation and a good debugging experience.  It is a better choice
8785           than -O0 for producing debuggable code because some compiler passes
8786           that collect debug information are disabled at -O0.
8787
8788           Like -O0, -Og completely disables a number of optimization passes
8789           so that individual options controlling them have no effect.
8790           Otherwise -Og enables all -O1 optimization flags except for those
8791           that may interfere with debugging:
8792
8793           -fbranch-count-reg  -fdelayed-branch -fdse  -fif-conversion
8794           -fif-conversion2 -finline-functions-called-once
8795           -fmove-loop-invariants  -fmove-loop-stores  -fssa-phiopt
8796           -ftree-bit-ccp  -ftree-dse  -ftree-pta  -ftree-sra
8797
8798       -Oz Optimize aggressively for size rather than speed.  This may
8799           increase the number of instructions executed if those instructions
8800           require fewer bytes to encode.  -Oz behaves similarly to -Os
8801           including enabling most -O2 optimizations.
8802
8803       If you use multiple -O options, with or without level numbers, the last
8804       such option is the one that is effective.
8805
8806       Options of the form -fflag specify machine-independent flags.  Most
8807       flags have both positive and negative forms; the negative form of -ffoo
8808       is -fno-foo.  In the table below, only one of the forms is listed---the
8809       one you typically use.  You can figure out the other form by either
8810       removing no- or adding it.
8811
8812       The following options control specific optimizations.  They are either
8813       activated by -O options or are related to ones that are.  You can use
8814       the following flags in the rare cases when "fine-tuning" of
8815       optimizations to be performed is desired.
8816
8817       -fno-defer-pop
8818           For machines that must pop arguments after a function call, always
8819           pop the arguments as soon as each function returns.  At levels -O1
8820           and higher, -fdefer-pop is the default; this allows the compiler to
8821           let arguments accumulate on the stack for several function calls
8822           and pop them all at once.
8823
8824       -fforward-propagate
8825           Perform a forward propagation pass on RTL.  The pass tries to
8826           combine two instructions and checks if the result can be
8827           simplified.  If loop unrolling is active, two passes are performed
8828           and the second is scheduled after loop unrolling.
8829
8830           This option is enabled by default at optimization levels -O1, -O2,
8831           -O3, -Os.
8832
8833       -ffp-contract=style
8834           -ffp-contract=off disables floating-point expression contraction.
8835           -ffp-contract=fast enables floating-point expression contraction
8836           such as forming of fused multiply-add operations if the target has
8837           native support for them.  -ffp-contract=on enables floating-point
8838           expression contraction if allowed by the language standard.  This
8839           is currently not implemented and treated equal to
8840           -ffp-contract=off.
8841
8842           The default is -ffp-contract=fast.
8843
8844       -fomit-frame-pointer
8845           Omit the frame pointer in functions that don't need one.  This
8846           avoids the instructions to save, set up and restore the frame
8847           pointer; on many targets it also makes an extra register available.
8848
8849           On some targets this flag has no effect because the standard
8850           calling sequence always uses a frame pointer, so it cannot be
8851           omitted.
8852
8853           Note that -fno-omit-frame-pointer doesn't guarantee the frame
8854           pointer is used in all functions.  Several targets always omit the
8855           frame pointer in leaf functions.
8856
8857           Enabled by default at -O1 and higher.
8858
8859       -foptimize-sibling-calls
8860           Optimize sibling and tail recursive calls.
8861
8862           Enabled at levels -O2, -O3, -Os.
8863
8864       -foptimize-strlen
8865           Optimize various standard C string functions (e.g. "strlen",
8866           "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into
8867           faster alternatives.
8868
8869           Enabled at levels -O2, -O3.
8870
8871       -fno-inline
8872           Do not expand any functions inline apart from those marked with the
8873           "always_inline" attribute.  This is the default when not
8874           optimizing.
8875
8876           Single functions can be exempted from inlining by marking them with
8877           the "noinline" attribute.
8878
8879       -finline-small-functions
8880           Integrate functions into their callers when their body is smaller
8881           than expected function call code (so overall size of program gets
8882           smaller).  The compiler heuristically decides which functions are
8883           simple enough to be worth integrating in this way.  This inlining
8884           applies to all functions, even those not declared inline.
8885
8886           Enabled at levels -O2, -O3, -Os.
8887
8888       -findirect-inlining
8889           Inline also indirect calls that are discovered to be known at
8890           compile time thanks to previous inlining.  This option has any
8891           effect only when inlining itself is turned on by the
8892           -finline-functions or -finline-small-functions options.
8893
8894           Enabled at levels -O2, -O3, -Os.
8895
8896       -finline-functions
8897           Consider all functions for inlining, even if they are not declared
8898           inline.  The compiler heuristically decides which functions are
8899           worth integrating in this way.
8900
8901           If all calls to a given function are integrated, and the function
8902           is declared "static", then the function is normally not output as
8903           assembler code in its own right.
8904
8905           Enabled at levels -O2, -O3, -Os.  Also enabled by -fprofile-use and
8906           -fauto-profile.
8907
8908       -finline-functions-called-once
8909           Consider all "static" functions called once for inlining into their
8910           caller even if they are not marked "inline".  If a call to a given
8911           function is integrated, then the function is not output as
8912           assembler code in its own right.
8913
8914           Enabled at levels -O1, -O2, -O3 and -Os, but not -Og.
8915
8916       -fearly-inlining
8917           Inline functions marked by "always_inline" and functions whose body
8918           seems smaller than the function call overhead early before doing
8919           -fprofile-generate instrumentation and real inlining pass.  Doing
8920           so makes profiling significantly cheaper and usually inlining
8921           faster on programs having large chains of nested wrapper functions.
8922
8923           Enabled by default.
8924
8925       -fipa-sra
8926           Perform interprocedural scalar replacement of aggregates, removal
8927           of unused parameters and replacement of parameters passed by
8928           reference by parameters passed by value.
8929
8930           Enabled at levels -O2, -O3 and -Os.
8931
8932       -finline-limit=n
8933           By default, GCC limits the size of functions that can be inlined.
8934           This flag allows coarse control of this limit.  n is the size of
8935           functions that can be inlined in number of pseudo instructions.
8936
8937           Inlining is actually controlled by a number of parameters, which
8938           may be specified individually by using --param name=value.  The
8939           -finline-limit=n option sets some of these parameters as follows:
8940
8941           max-inline-insns-single
8942               is set to n/2.
8943
8944           max-inline-insns-auto
8945               is set to n/2.
8946
8947           See below for a documentation of the individual parameters
8948           controlling inlining and for the defaults of these parameters.
8949
8950           Note: there may be no value to -finline-limit that results in
8951           default behavior.
8952
8953           Note: pseudo instruction represents, in this particular context, an
8954           abstract measurement of function's size.  In no way does it
8955           represent a count of assembly instructions and as such its exact
8956           meaning might change from one release to an another.
8957
8958       -fno-keep-inline-dllexport
8959           This is a more fine-grained version of -fkeep-inline-functions,
8960           which applies only to functions that are declared using the
8961           "dllexport" attribute or declspec.
8962
8963       -fkeep-inline-functions
8964           In C, emit "static" functions that are declared "inline" into the
8965           object file, even if the function has been inlined into all of its
8966           callers.  This switch does not affect functions using the "extern
8967           inline" extension in GNU C90.  In C++, emit any and all inline
8968           functions into the object file.
8969
8970       -fkeep-static-functions
8971           Emit "static" functions into the object file, even if the function
8972           is never used.
8973
8974       -fkeep-static-consts
8975           Emit variables declared "static const" when optimization isn't
8976           turned on, even if the variables aren't referenced.
8977
8978           GCC enables this option by default.  If you want to force the
8979           compiler to check if a variable is referenced, regardless of
8980           whether or not optimization is turned on, use the
8981           -fno-keep-static-consts option.
8982
8983       -fmerge-constants
8984           Attempt to merge identical constants (string constants and
8985           floating-point constants) across compilation units.
8986
8987           This option is the default for optimized compilation if the
8988           assembler and linker support it.  Use -fno-merge-constants to
8989           inhibit this behavior.
8990
8991           Enabled at levels -O1, -O2, -O3, -Os.
8992
8993       -fmerge-all-constants
8994           Attempt to merge identical constants and identical variables.
8995
8996           This option implies -fmerge-constants.  In addition to
8997           -fmerge-constants this considers e.g. even constant initialized
8998           arrays or initialized constant variables with integral or floating-
8999           point types.  Languages like C or C++ require each variable,
9000           including multiple instances of the same variable in recursive
9001           calls, to have distinct locations, so using this option results in
9002           non-conforming behavior.
9003
9004       -fmodulo-sched
9005           Perform swing modulo scheduling immediately before the first
9006           scheduling pass.  This pass looks at innermost loops and reorders
9007           their instructions by overlapping different iterations.
9008
9009       -fmodulo-sched-allow-regmoves
9010           Perform more aggressive SMS-based modulo scheduling with register
9011           moves allowed.  By setting this flag certain anti-dependences edges
9012           are deleted, which triggers the generation of reg-moves based on
9013           the life-range analysis.  This option is effective only with
9014           -fmodulo-sched enabled.
9015
9016       -fno-branch-count-reg
9017           Disable the optimization pass that scans for opportunities to use
9018           "decrement and branch" instructions on a count register instead of
9019           instruction sequences that decrement a register, compare it against
9020           zero, and then branch based upon the result.  This option is only
9021           meaningful on architectures that support such instructions, which
9022           include x86, PowerPC, IA-64 and S/390.  Note that the
9023           -fno-branch-count-reg option doesn't remove the decrement and
9024           branch instructions from the generated instruction stream
9025           introduced by other optimization passes.
9026
9027           The default is -fbranch-count-reg at -O1 and higher, except for
9028           -Og.
9029
9030       -fno-function-cse
9031           Do not put function addresses in registers; make each instruction
9032           that calls a constant function contain the function's address
9033           explicitly.
9034
9035           This option results in less efficient code, but some strange hacks
9036           that alter the assembler output may be confused by the
9037           optimizations performed when this option is not used.
9038
9039           The default is -ffunction-cse
9040
9041       -fno-zero-initialized-in-bss
9042           If the target supports a BSS section, GCC by default puts variables
9043           that are initialized to zero into BSS.  This can save space in the
9044           resulting code.
9045
9046           This option turns off this behavior because some programs
9047           explicitly rely on variables going to the data section---e.g., so
9048           that the resulting executable can find the beginning of that
9049           section and/or make assumptions based on that.
9050
9051           The default is -fzero-initialized-in-bss.
9052
9053       -fthread-jumps
9054           Perform optimizations that check to see if a jump branches to a
9055           location where another comparison subsumed by the first is found.
9056           If so, the first branch is redirected to either the destination of
9057           the second branch or a point immediately following it, depending on
9058           whether the condition is known to be true or false.
9059
9060           Enabled at levels -O1, -O2, -O3, -Os.
9061
9062       -fsplit-wide-types
9063           When using a type that occupies multiple registers, such as "long
9064           long" on a 32-bit system, split the registers apart and allocate
9065           them independently.  This normally generates better code for those
9066           types, but may make debugging more difficult.
9067
9068           Enabled at levels -O1, -O2, -O3, -Os.
9069
9070       -fsplit-wide-types-early
9071           Fully split wide types early, instead of very late.  This option
9072           has no effect unless -fsplit-wide-types is turned on.
9073
9074           This is the default on some targets.
9075
9076       -fcse-follow-jumps
9077           In common subexpression elimination (CSE), scan through jump
9078           instructions when the target of the jump is not reached by any
9079           other path.  For example, when CSE encounters an "if" statement
9080           with an "else" clause, CSE follows the jump when the condition
9081           tested is false.
9082
9083           Enabled at levels -O2, -O3, -Os.
9084
9085       -fcse-skip-blocks
9086           This is similar to -fcse-follow-jumps, but causes CSE to follow
9087           jumps that conditionally skip over blocks.  When CSE encounters a
9088           simple "if" statement with no else clause, -fcse-skip-blocks causes
9089           CSE to follow the jump around the body of the "if".
9090
9091           Enabled at levels -O2, -O3, -Os.
9092
9093       -frerun-cse-after-loop
9094           Re-run common subexpression elimination after loop optimizations
9095           are performed.
9096
9097           Enabled at levels -O2, -O3, -Os.
9098
9099       -fgcse
9100           Perform a global common subexpression elimination pass.  This pass
9101           also performs global constant and copy propagation.
9102
9103           Note: When compiling a program using computed gotos, a GCC
9104           extension, you may get better run-time performance if you disable
9105           the global common subexpression elimination pass by adding
9106           -fno-gcse to the command line.
9107
9108           Enabled at levels -O2, -O3, -Os.
9109
9110       -fgcse-lm
9111           When -fgcse-lm is enabled, global common subexpression elimination
9112           attempts to move loads that are only killed by stores into
9113           themselves.  This allows a loop containing a load/store sequence to
9114           be changed to a load outside the loop, and a copy/store within the
9115           loop.
9116
9117           Enabled by default when -fgcse is enabled.
9118
9119       -fgcse-sm
9120           When -fgcse-sm is enabled, a store motion pass is run after global
9121           common subexpression elimination.  This pass attempts to move
9122           stores out of loops.  When used in conjunction with -fgcse-lm,
9123           loops containing a load/store sequence can be changed to a load
9124           before the loop and a store after the loop.
9125
9126           Not enabled at any optimization level.
9127
9128       -fgcse-las
9129           When -fgcse-las is enabled, the global common subexpression
9130           elimination pass eliminates redundant loads that come after stores
9131           to the same memory location (both partial and full redundancies).
9132
9133           Not enabled at any optimization level.
9134
9135       -fgcse-after-reload
9136           When -fgcse-after-reload is enabled, a redundant load elimination
9137           pass is performed after reload.  The purpose of this pass is to
9138           clean up redundant spilling.
9139
9140           Enabled by -O3, -fprofile-use and -fauto-profile.
9141
9142       -faggressive-loop-optimizations
9143           This option tells the loop optimizer to use language constraints to
9144           derive bounds for the number of iterations of a loop.  This assumes
9145           that loop code does not invoke undefined behavior by for example
9146           causing signed integer overflows or out-of-bound array accesses.
9147           The bounds for the number of iterations of a loop are used to guide
9148           loop unrolling and peeling and loop exit test optimizations.  This
9149           option is enabled by default.
9150
9151       -funconstrained-commons
9152           This option tells the compiler that variables declared in common
9153           blocks (e.g. Fortran) may later be overridden with longer trailing
9154           arrays. This prevents certain optimizations that depend on knowing
9155           the array bounds.
9156
9157       -fcrossjumping
9158           Perform cross-jumping transformation.  This transformation unifies
9159           equivalent code and saves code size.  The resulting code may or may
9160           not perform better than without cross-jumping.
9161
9162           Enabled at levels -O2, -O3, -Os.
9163
9164       -fauto-inc-dec
9165           Combine increments or decrements of addresses with memory accesses.
9166           This pass is always skipped on architectures that do not have
9167           instructions to support this.  Enabled by default at -O1 and higher
9168           on architectures that support this.
9169
9170       -fdce
9171           Perform dead code elimination (DCE) on RTL.  Enabled by default at
9172           -O1 and higher.
9173
9174       -fdse
9175           Perform dead store elimination (DSE) on RTL.  Enabled by default at
9176           -O1 and higher.
9177
9178       -fif-conversion
9179           Attempt to transform conditional jumps into branch-less
9180           equivalents.  This includes use of conditional moves, min, max, set
9181           flags and abs instructions, and some tricks doable by standard
9182           arithmetics.  The use of conditional execution on chips where it is
9183           available is controlled by -fif-conversion2.
9184
9185           Enabled at levels -O1, -O2, -O3, -Os, but not with -Og.
9186
9187       -fif-conversion2
9188           Use conditional execution (where available) to transform
9189           conditional jumps into branch-less equivalents.
9190
9191           Enabled at levels -O1, -O2, -O3, -Os, but not with -Og.
9192
9193       -fdeclone-ctor-dtor
9194           The C++ ABI requires multiple entry points for constructors and
9195           destructors: one for a base subobject, one for a complete object,
9196           and one for a virtual destructor that calls operator delete
9197           afterwards.  For a hierarchy with virtual bases, the base and
9198           complete variants are clones, which means two copies of the
9199           function.  With this option, the base and complete variants are
9200           changed to be thunks that call a common implementation.
9201
9202           Enabled by -Os.
9203
9204       -fdelete-null-pointer-checks
9205           Assume that programs cannot safely dereference null pointers, and
9206           that no code or data element resides at address zero.  This option
9207           enables simple constant folding optimizations at all optimization
9208           levels.  In addition, other optimization passes in GCC use this
9209           flag to control global dataflow analyses that eliminate useless
9210           checks for null pointers; these assume that a memory access to
9211           address zero always results in a trap, so that if a pointer is
9212           checked after it has already been dereferenced, it cannot be null.
9213
9214           Note however that in some environments this assumption is not true.
9215           Use -fno-delete-null-pointer-checks to disable this optimization
9216           for programs that depend on that behavior.
9217
9218           This option is enabled by default on most targets.  On Nios II ELF,
9219           it defaults to off.  On AVR, CR16, and MSP430, this option is
9220           completely disabled.
9221
9222           Passes that use the dataflow information are enabled independently
9223           at different optimization levels.
9224
9225       -fdevirtualize
9226           Attempt to convert calls to virtual functions to direct calls.
9227           This is done both within a procedure and interprocedurally as part
9228           of indirect inlining (-findirect-inlining) and interprocedural
9229           constant propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.
9230
9231       -fdevirtualize-speculatively
9232           Attempt to convert calls to virtual functions to speculative direct
9233           calls.  Based on the analysis of the type inheritance graph,
9234           determine for a given call the set of likely targets. If the set is
9235           small, preferably of size 1, change the call into a conditional
9236           deciding between direct and indirect calls.  The speculative calls
9237           enable more optimizations, such as inlining.  When they seem
9238           useless after further optimization, they are converted back into
9239           original form.
9240
9241       -fdevirtualize-at-ltrans
9242           Stream extra information needed for aggressive devirtualization
9243           when running the link-time optimizer in local transformation mode.
9244           This option enables more devirtualization but significantly
9245           increases the size of streamed data. For this reason it is disabled
9246           by default.
9247
9248       -fexpensive-optimizations
9249           Perform a number of minor optimizations that are relatively
9250           expensive.
9251
9252           Enabled at levels -O2, -O3, -Os.
9253
9254       -free
9255           Attempt to remove redundant extension instructions.  This is
9256           especially helpful for the x86-64 architecture, which implicitly
9257           zero-extends in 64-bit registers after writing to their lower
9258           32-bit half.
9259
9260           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.
9261
9262       -fno-lifetime-dse
9263           In C++ the value of an object is only affected by changes within
9264           its lifetime: when the constructor begins, the object has an
9265           indeterminate value, and any changes during the lifetime of the
9266           object are dead when the object is destroyed.  Normally dead store
9267           elimination will take advantage of this; if your code relies on the
9268           value of the object storage persisting beyond the lifetime of the
9269           object, you can use this flag to disable this optimization.  To
9270           preserve stores before the constructor starts (e.g. because your
9271           operator new clears the object storage) but still treat the object
9272           as dead after the destructor, you can use -flifetime-dse=1.  The
9273           default behavior can be explicitly selected with -flifetime-dse=2.
9274           -flifetime-dse=0 is equivalent to -fno-lifetime-dse.
9275
9276       -flive-range-shrinkage
9277           Attempt to decrease register pressure through register live range
9278           shrinkage.  This is helpful for fast processors with small or
9279           moderate size register sets.
9280
9281       -fira-algorithm=algorithm
9282           Use the specified coloring algorithm for the integrated register
9283           allocator.  The algorithm argument can be priority, which specifies
9284           Chow's priority coloring, or CB, which specifies Chaitin-Briggs
9285           coloring.  Chaitin-Briggs coloring is not implemented for all
9286           architectures, but for those targets that do support it, it is the
9287           default because it generates better code.
9288
9289       -fira-region=region
9290           Use specified regions for the integrated register allocator.  The
9291           region argument should be one of the following:
9292
9293           all Use all loops as register allocation regions.  This can give
9294               the best results for machines with a small and/or irregular
9295               register set.
9296
9297           mixed
9298               Use all loops except for loops with small register pressure as
9299               the regions.  This value usually gives the best results in most
9300               cases and for most architectures, and is enabled by default
9301               when compiling with optimization for speed (-O, -O2, ...).
9302
9303           one Use all functions as a single region.  This typically results
9304               in the smallest code size, and is enabled by default for -Os or
9305               -O0.
9306
9307       -fira-hoist-pressure
9308           Use IRA to evaluate register pressure in the code hoisting pass for
9309           decisions to hoist expressions.  This option usually results in
9310           smaller code, but it can slow the compiler down.
9311
9312           This option is enabled at level -Os for all targets.
9313
9314       -fira-loop-pressure
9315           Use IRA to evaluate register pressure in loops for decisions to
9316           move loop invariants.  This option usually results in generation of
9317           faster and smaller code on machines with large register files (>=
9318           32 registers), but it can slow the compiler down.
9319
9320           This option is enabled at level -O3 for some targets.
9321
9322       -fno-ira-share-save-slots
9323           Disable sharing of stack slots used for saving call-used hard
9324           registers living through a call.  Each hard register gets a
9325           separate stack slot, and as a result function stack frames are
9326           larger.
9327
9328       -fno-ira-share-spill-slots
9329           Disable sharing of stack slots allocated for pseudo-registers.
9330           Each pseudo-register that does not get a hard register gets a
9331           separate stack slot, and as a result function stack frames are
9332           larger.
9333
9334       -flra-remat
9335           Enable CFG-sensitive rematerialization in LRA.  Instead of loading
9336           values of spilled pseudos, LRA tries to rematerialize (recalculate)
9337           values if it is profitable.
9338
9339           Enabled at levels -O2, -O3, -Os.
9340
9341       -fdelayed-branch
9342           If supported for the target machine, attempt to reorder
9343           instructions to exploit instruction slots available after delayed
9344           branch instructions.
9345
9346           Enabled at levels -O1, -O2, -O3, -Os, but not at -Og.
9347
9348       -fschedule-insns
9349           If supported for the target machine, attempt to reorder
9350           instructions to eliminate execution stalls due to required data
9351           being unavailable.  This helps machines that have slow floating
9352           point or memory load instructions by allowing other instructions to
9353           be issued until the result of the load or floating-point
9354           instruction is required.
9355
9356           Enabled at levels -O2, -O3.
9357
9358       -fschedule-insns2
9359           Similar to -fschedule-insns, but requests an additional pass of
9360           instruction scheduling after register allocation has been done.
9361           This is especially useful on machines with a relatively small
9362           number of registers and where memory load instructions take more
9363           than one cycle.
9364
9365           Enabled at levels -O2, -O3, -Os.
9366
9367       -fno-sched-interblock
9368           Disable instruction scheduling across basic blocks, which is
9369           normally enabled when scheduling before register allocation, i.e.
9370           with -fschedule-insns or at -O2 or higher.
9371
9372       -fno-sched-spec
9373           Disable speculative motion of non-load instructions, which is
9374           normally enabled when scheduling before register allocation, i.e.
9375           with -fschedule-insns or at -O2 or higher.
9376
9377       -fsched-pressure
9378           Enable register pressure sensitive insn scheduling before register
9379           allocation.  This only makes sense when scheduling before register
9380           allocation is enabled, i.e. with -fschedule-insns or at -O2 or
9381           higher.  Usage of this option can improve the generated code and
9382           decrease its size by preventing register pressure increase above
9383           the number of available hard registers and subsequent spills in
9384           register allocation.
9385
9386       -fsched-spec-load
9387           Allow speculative motion of some load instructions.  This only
9388           makes sense when scheduling before register allocation, i.e. with
9389           -fschedule-insns or at -O2 or higher.
9390
9391       -fsched-spec-load-dangerous
9392           Allow speculative motion of more load instructions.  This only
9393           makes sense when scheduling before register allocation, i.e. with
9394           -fschedule-insns or at -O2 or higher.
9395
9396       -fsched-stalled-insns
9397       -fsched-stalled-insns=n
9398           Define how many insns (if any) can be moved prematurely from the
9399           queue of stalled insns into the ready list during the second
9400           scheduling pass.  -fno-sched-stalled-insns means that no insns are
9401           moved prematurely, -fsched-stalled-insns=0 means there is no limit
9402           on how many queued insns can be moved prematurely.
9403           -fsched-stalled-insns without a value is equivalent to
9404           -fsched-stalled-insns=1.
9405
9406       -fsched-stalled-insns-dep
9407       -fsched-stalled-insns-dep=n
9408           Define how many insn groups (cycles) are examined for a dependency
9409           on a stalled insn that is a candidate for premature removal from
9410           the queue of stalled insns.  This has an effect only during the
9411           second scheduling pass, and only if -fsched-stalled-insns is used.
9412           -fno-sched-stalled-insns-dep is equivalent to
9413           -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a
9414           value is equivalent to -fsched-stalled-insns-dep=1.
9415
9416       -fsched2-use-superblocks
9417           When scheduling after register allocation, use superblock
9418           scheduling.  This allows motion across basic block boundaries,
9419           resulting in faster schedules.  This option is experimental, as not
9420           all machine descriptions used by GCC model the CPU closely enough
9421           to avoid unreliable results from the algorithm.
9422
9423           This only makes sense when scheduling after register allocation,
9424           i.e. with -fschedule-insns2 or at -O2 or higher.
9425
9426       -fsched-group-heuristic
9427           Enable the group heuristic in the scheduler.  This heuristic favors
9428           the instruction that belongs to a schedule group.  This is enabled
9429           by default when scheduling is enabled, i.e. with -fschedule-insns
9430           or -fschedule-insns2 or at -O2 or higher.
9431
9432       -fsched-critical-path-heuristic
9433           Enable the critical-path heuristic in the scheduler.  This
9434           heuristic favors instructions on the critical path.  This is
9435           enabled by default when scheduling is enabled, i.e. with
9436           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
9437
9438       -fsched-spec-insn-heuristic
9439           Enable the speculative instruction heuristic in the scheduler.
9440           This heuristic favors speculative instructions with greater
9441           dependency weakness.  This is enabled by default when scheduling is
9442           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
9443           or higher.
9444
9445       -fsched-rank-heuristic
9446           Enable the rank heuristic in the scheduler.  This heuristic favors
9447           the instruction belonging to a basic block with greater size or
9448           frequency.  This is enabled by default when scheduling is enabled,
9449           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
9450           higher.
9451
9452       -fsched-last-insn-heuristic
9453           Enable the last-instruction heuristic in the scheduler.  This
9454           heuristic favors the instruction that is less dependent on the last
9455           instruction scheduled.  This is enabled by default when scheduling
9456           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
9457           -O2 or higher.
9458
9459       -fsched-dep-count-heuristic
9460           Enable the dependent-count heuristic in the scheduler.  This
9461           heuristic favors the instruction that has more instructions
9462           depending on it.  This is enabled by default when scheduling is
9463           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
9464           or higher.
9465
9466       -freschedule-modulo-scheduled-loops
9467           Modulo scheduling is performed before traditional scheduling.  If a
9468           loop is modulo scheduled, later scheduling passes may change its
9469           schedule.  Use this option to control that behavior.
9470
9471       -fselective-scheduling
9472           Schedule instructions using selective scheduling algorithm.
9473           Selective scheduling runs instead of the first scheduler pass.
9474
9475       -fselective-scheduling2
9476           Schedule instructions using selective scheduling algorithm.
9477           Selective scheduling runs instead of the second scheduler pass.
9478
9479       -fsel-sched-pipelining
9480           Enable software pipelining of innermost loops during selective
9481           scheduling.  This option has no effect unless one of
9482           -fselective-scheduling or -fselective-scheduling2 is turned on.
9483
9484       -fsel-sched-pipelining-outer-loops
9485           When pipelining loops during selective scheduling, also pipeline
9486           outer loops.  This option has no effect unless
9487           -fsel-sched-pipelining is turned on.
9488
9489       -fsemantic-interposition
9490           Some object formats, like ELF, allow interposing of symbols by the
9491           dynamic linker.  This means that for symbols exported from the DSO,
9492           the compiler cannot perform interprocedural propagation, inlining
9493           and other optimizations in anticipation that the function or
9494           variable in question may change. While this feature is useful, for
9495           example, to rewrite memory allocation functions by a debugging
9496           implementation, it is expensive in the terms of code quality.  With
9497           -fno-semantic-interposition the compiler assumes that if
9498           interposition happens for functions the overwriting function will
9499           have precisely the same semantics (and side effects).  Similarly if
9500           interposition happens for variables, the constructor of the
9501           variable will be the same. The flag has no effect for functions
9502           explicitly declared inline (where it is never allowed for
9503           interposition to change semantics) and for symbols explicitly
9504           declared weak.
9505
9506       -fshrink-wrap
9507           Emit function prologues only before parts of the function that need
9508           it, rather than at the top of the function.  This flag is enabled
9509           by default at -O and higher.
9510
9511       -fshrink-wrap-separate
9512           Shrink-wrap separate parts of the prologue and epilogue separately,
9513           so that those parts are only executed when needed.  This option is
9514           on by default, but has no effect unless -fshrink-wrap is also
9515           turned on and the target supports this.
9516
9517       -fcaller-saves
9518           Enable allocation of values to registers that are clobbered by
9519           function calls, by emitting extra instructions to save and restore
9520           the registers around such calls.  Such allocation is done only when
9521           it seems to result in better code.
9522
9523           This option is always enabled by default on certain machines,
9524           usually those which have no call-preserved registers to use
9525           instead.
9526
9527           Enabled at levels -O2, -O3, -Os.
9528
9529       -fcombine-stack-adjustments
9530           Tracks stack adjustments (pushes and pops) and stack memory
9531           references and then tries to find ways to combine them.
9532
9533           Enabled by default at -O1 and higher.
9534
9535       -fipa-ra
9536           Use caller save registers for allocation if those registers are not
9537           used by any called function.  In that case it is not necessary to
9538           save and restore them around calls.  This is only possible if
9539           called functions are part of same compilation unit as current
9540           function and they are compiled before it.
9541
9542           Enabled at levels -O2, -O3, -Os, however the option is disabled if
9543           generated code will be instrumented for profiling (-p, or -pg) or
9544           if callee's register usage cannot be known exactly (this happens on
9545           targets that do not expose prologues and epilogues in RTL).
9546
9547       -fconserve-stack
9548           Attempt to minimize stack usage.  The compiler attempts to use less
9549           stack space, even if that makes the program slower.  This option
9550           implies setting the large-stack-frame parameter to 100 and the
9551           large-stack-frame-growth parameter to 400.
9552
9553       -ftree-reassoc
9554           Perform reassociation on trees.  This flag is enabled by default at
9555           -O1 and higher.
9556
9557       -fcode-hoisting
9558           Perform code hoisting.  Code hoisting tries to move the evaluation
9559           of expressions executed on all paths to the function exit as early
9560           as possible.  This is especially useful as a code size
9561           optimization, but it often helps for code speed as well.  This flag
9562           is enabled by default at -O2 and higher.
9563
9564       -ftree-pre
9565           Perform partial redundancy elimination (PRE) on trees.  This flag
9566           is enabled by default at -O2 and -O3.
9567
9568       -ftree-partial-pre
9569           Make partial redundancy elimination (PRE) more aggressive.  This
9570           flag is enabled by default at -O3.
9571
9572       -ftree-forwprop
9573           Perform forward propagation on trees.  This flag is enabled by
9574           default at -O1 and higher.
9575
9576       -ftree-fre
9577           Perform full redundancy elimination (FRE) on trees.  The difference
9578           between FRE and PRE is that FRE only considers expressions that are
9579           computed on all paths leading to the redundant computation.  This
9580           analysis is faster than PRE, though it exposes fewer redundancies.
9581           This flag is enabled by default at -O1 and higher.
9582
9583       -ftree-phiprop
9584           Perform hoisting of loads from conditional pointers on trees.  This
9585           pass is enabled by default at -O1 and higher.
9586
9587       -fhoist-adjacent-loads
9588           Speculatively hoist loads from both branches of an if-then-else if
9589           the loads are from adjacent locations in the same structure and the
9590           target architecture has a conditional move instruction.  This flag
9591           is enabled by default at -O2 and higher.
9592
9593       -ftree-copy-prop
9594           Perform copy propagation on trees.  This pass eliminates
9595           unnecessary copy operations.  This flag is enabled by default at
9596           -O1 and higher.
9597
9598       -fipa-pure-const
9599           Discover which functions are pure or constant.  Enabled by default
9600           at -O1 and higher.
9601
9602       -fipa-reference
9603           Discover which static variables do not escape the compilation unit.
9604           Enabled by default at -O1 and higher.
9605
9606       -fipa-reference-addressable
9607           Discover read-only, write-only and non-addressable static
9608           variables.  Enabled by default at -O1 and higher.
9609
9610       -fipa-stack-alignment
9611           Reduce stack alignment on call sites if possible.  Enabled by
9612           default.
9613
9614       -fipa-pta
9615           Perform interprocedural pointer analysis and interprocedural
9616           modification and reference analysis.  This option can cause
9617           excessive memory and compile-time usage on large compilation units.
9618           It is not enabled by default at any optimization level.
9619
9620       -fipa-profile
9621           Perform interprocedural profile propagation.  The functions called
9622           only from cold functions are marked as cold. Also functions
9623           executed once (such as "cold", "noreturn", static constructors or
9624           destructors) are identified. Cold functions and loop less parts of
9625           functions executed once are then optimized for size.  Enabled by
9626           default at -O1 and higher.
9627
9628       -fipa-modref
9629           Perform interprocedural mod/ref analysis.  This optimization
9630           analyzes the side effects of functions (memory locations that are
9631           modified or referenced) and enables better optimization across the
9632           function call boundary.  This flag is enabled by default at -O1 and
9633           higher.
9634
9635       -fipa-cp
9636           Perform interprocedural constant propagation.  This optimization
9637           analyzes the program to determine when values passed to functions
9638           are constants and then optimizes accordingly.  This optimization
9639           can substantially increase performance if the application has
9640           constants passed to functions.  This flag is enabled by default at
9641           -O2, -Os and -O3.  It is also enabled by -fprofile-use and
9642           -fauto-profile.
9643
9644       -fipa-cp-clone
9645           Perform function cloning to make interprocedural constant
9646           propagation stronger.  When enabled, interprocedural constant
9647           propagation performs function cloning when externally visible
9648           function can be called with constant arguments.  Because this
9649           optimization can create multiple copies of functions, it may
9650           significantly increase code size (see --param
9651           ipa-cp-unit-growth=value).  This flag is enabled by default at -O3.
9652           It is also enabled by -fprofile-use and -fauto-profile.
9653
9654       -fipa-bit-cp
9655           When enabled, perform interprocedural bitwise constant propagation.
9656           This flag is enabled by default at -O2 and by -fprofile-use and
9657           -fauto-profile.  It requires that -fipa-cp is enabled.
9658
9659       -fipa-vrp
9660           When enabled, perform interprocedural propagation of value ranges.
9661           This flag is enabled by default at -O2. It requires that -fipa-cp
9662           is enabled.
9663
9664       -fipa-icf
9665           Perform Identical Code Folding for functions and read-only
9666           variables.  The optimization reduces code size and may disturb
9667           unwind stacks by replacing a function by equivalent one with a
9668           different name. The optimization works more effectively with link-
9669           time optimization enabled.
9670
9671           Although the behavior is similar to the Gold Linker's ICF
9672           optimization, GCC ICF works on different levels and thus the
9673           optimizations are not same - there are equivalences that are found
9674           only by GCC and equivalences found only by Gold.
9675
9676           This flag is enabled by default at -O2 and -Os.
9677
9678       -flive-patching=level
9679           Control GCC's optimizations to produce output suitable for live-
9680           patching.
9681
9682           If the compiler's optimization uses a function's body or
9683           information extracted from its body to optimize/change another
9684           function, the latter is called an impacted function of the former.
9685           If a function is patched, its impacted functions should be patched
9686           too.
9687
9688           The impacted functions are determined by the compiler's
9689           interprocedural optimizations.  For example, a caller is impacted
9690           when inlining a function into its caller, cloning a function and
9691           changing its caller to call this new clone, or extracting a
9692           function's pureness/constness information to optimize its direct or
9693           indirect callers, etc.
9694
9695           Usually, the more IPA optimizations enabled, the larger the number
9696           of impacted functions for each function.  In order to control the
9697           number of impacted functions and more easily compute the list of
9698           impacted function, IPA optimizations can be partially enabled at
9699           two different levels.
9700
9701           The level argument should be one of the following:
9702
9703           inline-clone
9704               Only enable inlining and cloning optimizations, which includes
9705               inlining, cloning, interprocedural scalar replacement of
9706               aggregates and partial inlining.  As a result, when patching a
9707               function, all its callers and its clones' callers are impacted,
9708               therefore need to be patched as well.
9709
9710               -flive-patching=inline-clone disables the following
9711               optimization flags: -fwhole-program  -fipa-pta  -fipa-reference
9712               -fipa-ra -fipa-icf  -fipa-icf-functions  -fipa-icf-variables
9713               -fipa-bit-cp  -fipa-vrp  -fipa-pure-const
9714               -fipa-reference-addressable -fipa-stack-alignment -fipa-modref
9715
9716           inline-only-static
9717               Only enable inlining of static functions.  As a result, when
9718               patching a static function, all its callers are impacted and so
9719               need to be patched as well.
9720
9721               In addition to all the flags that -flive-patching=inline-clone
9722               disables, -flive-patching=inline-only-static disables the
9723               following additional optimization flags: -fipa-cp-clone
9724               -fipa-sra  -fpartial-inlining  -fipa-cp
9725
9726           When -flive-patching is specified without any value, the default
9727           value is inline-clone.
9728
9729           This flag is disabled by default.
9730
9731           Note that -flive-patching is not supported with link-time
9732           optimization (-flto).
9733
9734       -fisolate-erroneous-paths-dereference
9735           Detect paths that trigger erroneous or undefined behavior due to
9736           dereferencing a null pointer.  Isolate those paths from the main
9737           control flow and turn the statement with erroneous or undefined
9738           behavior into a trap.  This flag is enabled by default at -O2 and
9739           higher and depends on -fdelete-null-pointer-checks also being
9740           enabled.
9741
9742       -fisolate-erroneous-paths-attribute
9743           Detect paths that trigger erroneous or undefined behavior due to a
9744           null value being used in a way forbidden by a "returns_nonnull" or
9745           "nonnull" attribute.  Isolate those paths from the main control
9746           flow and turn the statement with erroneous or undefined behavior
9747           into a trap.  This is not currently enabled, but may be enabled by
9748           -O2 in the future.
9749
9750       -ftree-sink
9751           Perform forward store motion on trees.  This flag is enabled by
9752           default at -O1 and higher.
9753
9754       -ftree-bit-ccp
9755           Perform sparse conditional bit constant propagation on trees and
9756           propagate pointer alignment information.  This pass only operates
9757           on local scalar variables and is enabled by default at -O1 and
9758           higher, except for -Og.  It requires that -ftree-ccp is enabled.
9759
9760       -ftree-ccp
9761           Perform sparse conditional constant propagation (CCP) on trees.
9762           This pass only operates on local scalar variables and is enabled by
9763           default at -O1 and higher.
9764
9765       -fssa-backprop
9766           Propagate information about uses of a value up the definition chain
9767           in order to simplify the definitions.  For example, this pass
9768           strips sign operations if the sign of a value never matters.  The
9769           flag is enabled by default at -O1 and higher.
9770
9771       -fssa-phiopt
9772           Perform pattern matching on SSA PHI nodes to optimize conditional
9773           code.  This pass is enabled by default at -O1 and higher, except
9774           for -Og.
9775
9776       -ftree-switch-conversion
9777           Perform conversion of simple initializations in a switch to
9778           initializations from a scalar array.  This flag is enabled by
9779           default at -O2 and higher.
9780
9781       -ftree-tail-merge
9782           Look for identical code sequences.  When found, replace one with a
9783           jump to the other.  This optimization is known as tail merging or
9784           cross jumping.  This flag is enabled by default at -O2 and higher.
9785           The compilation time in this pass can be limited using max-tail-
9786           merge-comparisons parameter and max-tail-merge-iterations
9787           parameter.
9788
9789       -ftree-dce
9790           Perform dead code elimination (DCE) on trees.  This flag is enabled
9791           by default at -O1 and higher.
9792
9793       -ftree-builtin-call-dce
9794           Perform conditional dead code elimination (DCE) for calls to built-
9795           in functions that may set "errno" but are otherwise free of side
9796           effects.  This flag is enabled by default at -O2 and higher if -Os
9797           is not also specified.
9798
9799       -ffinite-loops
9800           Assume that a loop with an exit will eventually take the exit and
9801           not loop indefinitely.  This allows the compiler to remove loops
9802           that otherwise have no side-effects, not considering eventual
9803           endless looping as such.
9804
9805           This option is enabled by default at -O2 for C++ with -std=c++11 or
9806           higher.
9807
9808       -ftree-dominator-opts
9809           Perform a variety of simple scalar cleanups (constant/copy
9810           propagation, redundancy elimination, range propagation and
9811           expression simplification) based on a dominator tree traversal.
9812           This also performs jump threading (to reduce jumps to jumps). This
9813           flag is enabled by default at -O1 and higher.
9814
9815       -ftree-dse
9816           Perform dead store elimination (DSE) on trees.  A dead store is a
9817           store into a memory location that is later overwritten by another
9818           store without any intervening loads.  In this case the earlier
9819           store can be deleted.  This flag is enabled by default at -O1 and
9820           higher.
9821
9822       -ftree-ch
9823           Perform loop header copying on trees.  This is beneficial since it
9824           increases effectiveness of code motion optimizations.  It also
9825           saves one jump.  This flag is enabled by default at -O1 and higher.
9826           It is not enabled for -Os, since it usually increases code size.
9827
9828       -ftree-loop-optimize
9829           Perform loop optimizations on trees.  This flag is enabled by
9830           default at -O1 and higher.
9831
9832       -ftree-loop-linear
9833       -floop-strip-mine
9834       -floop-block
9835           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To
9836           use this code transformation, GCC has to be configured with
9837           --with-isl to enable the Graphite loop transformation
9838           infrastructure.
9839
9840       -fgraphite-identity
9841           Enable the identity transformation for graphite.  For every SCoP we
9842           generate the polyhedral representation and transform it back to
9843           gimple.  Using -fgraphite-identity we can check the costs or
9844           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
9845           minimal optimizations are also performed by the code generator isl,
9846           like index splitting and dead code elimination in loops.
9847
9848       -floop-nest-optimize
9849           Enable the isl based loop nest optimizer.  This is a generic loop
9850           nest optimizer based on the Pluto optimization algorithms.  It
9851           calculates a loop structure optimized for data-locality and
9852           parallelism.  This option is experimental.
9853
9854       -floop-parallelize-all
9855           Use the Graphite data dependence analysis to identify loops that
9856           can be parallelized.  Parallelize all the loops that can be
9857           analyzed to not contain loop carried dependences without checking
9858           that it is profitable to parallelize the loops.
9859
9860       -ftree-coalesce-vars
9861           While transforming the program out of the SSA representation,
9862           attempt to reduce copying by coalescing versions of different user-
9863           defined variables, instead of just compiler temporaries.  This may
9864           severely limit the ability to debug an optimized program compiled
9865           with -fno-var-tracking-assignments.  In the negated form, this flag
9866           prevents SSA coalescing of user variables.  This option is enabled
9867           by default if optimization is enabled, and it does very little
9868           otherwise.
9869
9870       -ftree-loop-if-convert
9871           Attempt to transform conditional jumps in the innermost loops to
9872           branch-less equivalents.  The intent is to remove control-flow from
9873           the innermost loops in order to improve the ability of the
9874           vectorization pass to handle these loops.  This is enabled by
9875           default if vectorization is enabled.
9876
9877       -ftree-loop-distribution
9878           Perform loop distribution.  This flag can improve cache performance
9879           on big loop bodies and allow further loop optimizations, like
9880           parallelization or vectorization, to take place.  For example, the
9881           loop
9882
9883                   DO I = 1, N
9884                     A(I) = B(I) + C
9885                     D(I) = E(I) * F
9886                   ENDDO
9887
9888           is transformed to
9889
9890                   DO I = 1, N
9891                      A(I) = B(I) + C
9892                   ENDDO
9893                   DO I = 1, N
9894                      D(I) = E(I) * F
9895                   ENDDO
9896
9897           This flag is enabled by default at -O3.  It is also enabled by
9898           -fprofile-use and -fauto-profile.
9899
9900       -ftree-loop-distribute-patterns
9901           Perform loop distribution of patterns that can be code generated
9902           with calls to a library.  This flag is enabled by default at -O2
9903           and higher, and by -fprofile-use and -fauto-profile.
9904
9905           This pass distributes the initialization loops and generates a call
9906           to memset zero.  For example, the loop
9907
9908                   DO I = 1, N
9909                     A(I) = 0
9910                     B(I) = A(I) + I
9911                   ENDDO
9912
9913           is transformed to
9914
9915                   DO I = 1, N
9916                      A(I) = 0
9917                   ENDDO
9918                   DO I = 1, N
9919                      B(I) = A(I) + I
9920                   ENDDO
9921
9922           and the initialization loop is transformed into a call to memset
9923           zero.  This flag is enabled by default at -O3.  It is also enabled
9924           by -fprofile-use and -fauto-profile.
9925
9926       -floop-interchange
9927           Perform loop interchange outside of graphite.  This flag can
9928           improve cache performance on loop nest and allow further loop
9929           optimizations, like vectorization, to take place.  For example, the
9930           loop
9931
9932                   for (int i = 0; i < N; i++)
9933                     for (int j = 0; j < N; j++)
9934                       for (int k = 0; k < N; k++)
9935                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
9936
9937           is transformed to
9938
9939                   for (int i = 0; i < N; i++)
9940                     for (int k = 0; k < N; k++)
9941                       for (int j = 0; j < N; j++)
9942                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
9943
9944           This flag is enabled by default at -O3.  It is also enabled by
9945           -fprofile-use and -fauto-profile.
9946
9947       -floop-unroll-and-jam
9948           Apply unroll and jam transformations on feasible loops.  In a loop
9949           nest this unrolls the outer loop by some factor and fuses the
9950           resulting multiple inner loops.  This flag is enabled by default at
9951           -O3.  It is also enabled by -fprofile-use and -fauto-profile.
9952
9953       -ftree-loop-im
9954           Perform loop invariant motion on trees.  This pass moves only
9955           invariants that are hard to handle at RTL level (function calls,
9956           operations that expand to nontrivial sequences of insns).  With
9957           -funswitch-loops it also moves operands of conditions that are
9958           invariant out of the loop, so that we can use just trivial
9959           invariantness analysis in loop unswitching.  The pass also includes
9960           store motion.
9961
9962       -ftree-loop-ivcanon
9963           Create a canonical counter for number of iterations in loops for
9964           which determining number of iterations requires complicated
9965           analysis.  Later optimizations then may determine the number
9966           easily.  Useful especially in connection with unrolling.
9967
9968       -ftree-scev-cprop
9969           Perform final value replacement.  If a variable is modified in a
9970           loop in such a way that its value when exiting the loop can be
9971           determined using only its initial value and the number of loop
9972           iterations, replace uses of the final value by such a computation,
9973           provided it is sufficiently cheap.  This reduces data dependencies
9974           and may allow further simplifications.  Enabled by default at -O1
9975           and higher.
9976
9977       -fivopts
9978           Perform induction variable optimizations (strength reduction,
9979           induction variable merging and induction variable elimination) on
9980           trees.
9981
9982       -ftree-parallelize-loops=n
9983           Parallelize loops, i.e., split their iteration space to run in n
9984           threads.  This is only possible for loops whose iterations are
9985           independent and can be arbitrarily reordered.  The optimization is
9986           only profitable on multiprocessor machines, for loops that are CPU-
9987           intensive, rather than constrained e.g. by memory bandwidth.  This
9988           option implies -pthread, and thus is only supported on targets that
9989           have support for -pthread.
9990
9991       -ftree-pta
9992           Perform function-local points-to analysis on trees.  This flag is
9993           enabled by default at -O1 and higher, except for -Og.
9994
9995       -ftree-sra
9996           Perform scalar replacement of aggregates.  This pass replaces
9997           structure references with scalars to prevent committing structures
9998           to memory too early.  This flag is enabled by default at -O1 and
9999           higher, except for -Og.
10000
10001       -fstore-merging
10002           Perform merging of narrow stores to consecutive memory addresses.
10003           This pass merges contiguous stores of immediate values narrower
10004           than a word into fewer wider stores to reduce the number of
10005           instructions.  This is enabled by default at -O2 and higher as well
10006           as -Os.
10007
10008       -ftree-ter
10009           Perform temporary expression replacement during the SSA->normal
10010           phase.  Single use/single def temporaries are replaced at their use
10011           location with their defining expression.  This results in non-
10012           GIMPLE code, but gives the expanders much more complex trees to
10013           work on resulting in better RTL generation.  This is enabled by
10014           default at -O1 and higher.
10015
10016       -ftree-slsr
10017           Perform straight-line strength reduction on trees.  This recognizes
10018           related expressions involving multiplications and replaces them by
10019           less expensive calculations when possible.  This is enabled by
10020           default at -O1 and higher.
10021
10022       -ftree-vectorize
10023           Perform vectorization on trees. This flag enables
10024           -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly
10025           specified.
10026
10027       -ftree-loop-vectorize
10028           Perform loop vectorization on trees. This flag is enabled by
10029           default at -O2 and by -ftree-vectorize, -fprofile-use, and
10030           -fauto-profile.
10031
10032       -ftree-slp-vectorize
10033           Perform basic block vectorization on trees. This flag is enabled by
10034           default at -O2 and by -ftree-vectorize, -fprofile-use, and
10035           -fauto-profile.
10036
10037       -ftrivial-auto-var-init=choice
10038           Initialize automatic variables with either a pattern or with zeroes
10039           to increase the security and predictability of a program by
10040           preventing uninitialized memory disclosure and use.  GCC still
10041           considers an automatic variable that doesn't have an explicit
10042           initializer as uninitialized, -Wuninitialized and
10043           -Wanalyzer-use-of-uninitialized-value will still report warning
10044           messages on such automatic variables.  With this option, GCC will
10045           also initialize any padding of automatic variables that have
10046           structure or union types to zeroes.  However, the current
10047           implementation cannot initialize automatic variables that are
10048           declared between the controlling expression and the first case of a
10049           "switch" statement.  Using -Wtrivial-auto-var-init to report all
10050           such cases.
10051
10052           The three values of choice are:
10053
10054           *   uninitialized doesn't initialize any automatic variables.  This
10055               is C and C++'s default.
10056
10057           *   pattern Initialize automatic variables with values which will
10058               likely transform logic bugs into crashes down the line, are
10059               easily recognized in a crash dump and without being values that
10060               programmers can rely on for useful program semantics.  The
10061               current value is byte-repeatable pattern with byte "0xFE".  The
10062               values used for pattern initialization might be changed in the
10063               future.
10064
10065           *   zero Initialize automatic variables with zeroes.
10066
10067           The default is uninitialized.
10068
10069           You can control this behavior for a specific variable by using the
10070           variable attribute "uninitialized".
10071
10072       -fvect-cost-model=model
10073           Alter the cost model used for vectorization.  The model argument
10074           should be one of unlimited, dynamic, cheap or very-cheap.  With the
10075           unlimited model the vectorized code-path is assumed to be
10076           profitable while with the dynamic model a runtime check guards the
10077           vectorized code-path to enable it only for iteration counts that
10078           will likely execute faster than when executing the original scalar
10079           loop.  The cheap model disables vectorization of loops where doing
10080           so would be cost prohibitive for example due to required runtime
10081           checks for data dependence or alignment but otherwise is equal to
10082           the dynamic model.  The very-cheap model only allows vectorization
10083           if the vector code would entirely replace the scalar code that is
10084           being vectorized.  For example, if each iteration of a vectorized
10085           loop would only be able to handle exactly four iterations of the
10086           scalar loop, the very-cheap model would only allow vectorization if
10087           the scalar iteration count is known to be a multiple of four.
10088
10089           The default cost model depends on other optimization flags and is
10090           either dynamic or cheap.
10091
10092       -fsimd-cost-model=model
10093           Alter the cost model used for vectorization of loops marked with
10094           the OpenMP simd directive.  The model argument should be one of
10095           unlimited, dynamic, cheap.  All values of model have the same
10096           meaning as described in -fvect-cost-model and by default a cost
10097           model defined with -fvect-cost-model is used.
10098
10099       -ftree-vrp
10100           Perform Value Range Propagation on trees.  This is similar to the
10101           constant propagation pass, but instead of values, ranges of values
10102           are propagated.  This allows the optimizers to remove unnecessary
10103           range checks like array bound checks and null pointer checks.  This
10104           is enabled by default at -O2 and higher.  Null pointer check
10105           elimination is only done if -fdelete-null-pointer-checks is
10106           enabled.
10107
10108       -fsplit-paths
10109           Split paths leading to loop backedges.  This can improve dead code
10110           elimination and common subexpression elimination.  This is enabled
10111           by default at -O3 and above.
10112
10113       -fsplit-ivs-in-unroller
10114           Enables expression of values of induction variables in later
10115           iterations of the unrolled loop using the value in the first
10116           iteration.  This breaks long dependency chains, thus improving
10117           efficiency of the scheduling passes.
10118
10119           A combination of -fweb and CSE is often sufficient to obtain the
10120           same effect.  However, that is not reliable in cases where the loop
10121           body is more complicated than a single basic block.  It also does
10122           not work at all on some architectures due to restrictions in the
10123           CSE pass.
10124
10125           This optimization is enabled by default.
10126
10127       -fvariable-expansion-in-unroller
10128           With this option, the compiler creates multiple copies of some
10129           local variables when unrolling a loop, which can result in superior
10130           code.
10131
10132           This optimization is enabled by default for PowerPC targets, but
10133           disabled by default otherwise.
10134
10135       -fpartial-inlining
10136           Inline parts of functions.  This option has any effect only when
10137           inlining itself is turned on by the -finline-functions or
10138           -finline-small-functions options.
10139
10140           Enabled at levels -O2, -O3, -Os.
10141
10142       -fpredictive-commoning
10143           Perform predictive commoning optimization, i.e., reusing
10144           computations (especially memory loads and stores) performed in
10145           previous iterations of loops.
10146
10147           This option is enabled at level -O3.  It is also enabled by
10148           -fprofile-use and -fauto-profile.
10149
10150       -fprefetch-loop-arrays
10151           If supported by the target machine, generate instructions to
10152           prefetch memory to improve the performance of loops that access
10153           large arrays.
10154
10155           This option may generate better or worse code; results are highly
10156           dependent on the structure of loops within the source code.
10157
10158           Disabled at level -Os.
10159
10160       -fno-printf-return-value
10161           Do not substitute constants for known return value of formatted
10162           output functions such as "sprintf", "snprintf", "vsprintf", and
10163           "vsnprintf" (but not "printf" of "fprintf").  This transformation
10164           allows GCC to optimize or even eliminate branches based on the
10165           known return value of these functions called with arguments that
10166           are either constant, or whose values are known to be in a range
10167           that makes determining the exact return value possible.  For
10168           example, when -fprintf-return-value is in effect, both the branch
10169           and the body of the "if" statement (but not the call to "snprint")
10170           can be optimized away when "i" is a 32-bit or smaller integer
10171           because the return value is guaranteed to be at most 8.
10172
10173                   char buf[9];
10174                   if (snprintf (buf, "%08x", i) >= sizeof buf)
10175                     ...
10176
10177           The -fprintf-return-value option relies on other optimizations and
10178           yields best results with -O2 and above.  It works in tandem with
10179           the -Wformat-overflow and -Wformat-truncation options.  The
10180           -fprintf-return-value option is enabled by default.
10181
10182       -fno-peephole
10183       -fno-peephole2
10184           Disable any machine-specific peephole optimizations.  The
10185           difference between -fno-peephole and -fno-peephole2 is in how they
10186           are implemented in the compiler; some targets use one, some use the
10187           other, a few use both.
10188
10189           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
10190           -O2, -O3, -Os.
10191
10192       -fno-guess-branch-probability
10193           Do not guess branch probabilities using heuristics.
10194
10195           GCC uses heuristics to guess branch probabilities if they are not
10196           provided by profiling feedback (-fprofile-arcs).  These heuristics
10197           are based on the control flow graph.  If some branch probabilities
10198           are specified by "__builtin_expect", then the heuristics are used
10199           to guess branch probabilities for the rest of the control flow
10200           graph, taking the "__builtin_expect" info into account.  The
10201           interactions between the heuristics and "__builtin_expect" can be
10202           complex, and in some cases, it may be useful to disable the
10203           heuristics so that the effects of "__builtin_expect" are easier to
10204           understand.
10205
10206           It is also possible to specify expected probability of the
10207           expression with "__builtin_expect_with_probability" built-in
10208           function.
10209
10210           The default is -fguess-branch-probability at levels -O, -O2, -O3,
10211           -Os.
10212
10213       -freorder-blocks
10214           Reorder basic blocks in the compiled function in order to reduce
10215           number of taken branches and improve code locality.
10216
10217           Enabled at levels -O1, -O2, -O3, -Os.
10218
10219       -freorder-blocks-algorithm=algorithm
10220           Use the specified algorithm for basic block reordering.  The
10221           algorithm argument can be simple, which does not increase code size
10222           (except sometimes due to secondary effects like alignment), or stc,
10223           the "software trace cache" algorithm, which tries to put all often
10224           executed code together, minimizing the number of branches executed
10225           by making extra copies of code.
10226
10227           The default is simple at levels -O1, -Os, and stc at levels -O2,
10228           -O3.
10229
10230       -freorder-blocks-and-partition
10231           In addition to reordering basic blocks in the compiled function, in
10232           order to reduce number of taken branches, partitions hot and cold
10233           basic blocks into separate sections of the assembly and .o files,
10234           to improve paging and cache locality performance.
10235
10236           This optimization is automatically turned off in the presence of
10237           exception handling or unwind tables (on targets using
10238           setjump/longjump or target specific scheme), for linkonce sections,
10239           for functions with a user-defined section attribute and on any
10240           architecture that does not support named sections.  When
10241           -fsplit-stack is used this option is not enabled by default (to
10242           avoid linker errors), but may be enabled explicitly (if using a
10243           working linker).
10244
10245           Enabled for x86 at levels -O2, -O3, -Os.
10246
10247       -freorder-functions
10248           Reorder functions in the object file in order to improve code
10249           locality.  This is implemented by using special subsections
10250           ".text.hot" for most frequently executed functions and
10251           ".text.unlikely" for unlikely executed functions.  Reordering is
10252           done by the linker so object file format must support named
10253           sections and linker must place them in a reasonable way.
10254
10255           This option isn't effective unless you either provide profile
10256           feedback (see -fprofile-arcs for details) or manually annotate
10257           functions with "hot" or "cold" attributes.
10258
10259           Enabled at levels -O2, -O3, -Os.
10260
10261       -fstrict-aliasing
10262           Allow the compiler to assume the strictest aliasing rules
10263           applicable to the language being compiled.  For C (and C++), this
10264           activates optimizations based on the type of expressions.  In
10265           particular, an object of one type is assumed never to reside at the
10266           same address as an object of a different type, unless the types are
10267           almost the same.  For example, an "unsigned int" can alias an
10268           "int", but not a "void*" or a "double".  A character type may alias
10269           any other type.
10270
10271           Pay special attention to code like this:
10272
10273                   union a_union {
10274                     int i;
10275                     double d;
10276                   };
10277
10278                   int f() {
10279                     union a_union t;
10280                     t.d = 3.0;
10281                     return t.i;
10282                   }
10283
10284           The practice of reading from a different union member than the one
10285           most recently written to (called "type-punning") is common.  Even
10286           with -fstrict-aliasing, type-punning is allowed, provided the
10287           memory is accessed through the union type.  So, the code above
10288           works as expected.    However, this code might not:
10289
10290                   int f() {
10291                     union a_union t;
10292                     int* ip;
10293                     t.d = 3.0;
10294                     ip = &t.i;
10295                     return *ip;
10296                   }
10297
10298           Similarly, access by taking the address, casting the resulting
10299           pointer and dereferencing the result has undefined behavior, even
10300           if the cast uses a union type, e.g.:
10301
10302                   int f() {
10303                     double d = 3.0;
10304                     return ((union a_union *) &d)->i;
10305                   }
10306
10307           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
10308
10309       -fipa-strict-aliasing
10310           Controls whether rules of -fstrict-aliasing are applied across
10311           function boundaries.  Note that if multiple functions gets inlined
10312           into a single function the memory accesses are no longer considered
10313           to be crossing a function boundary.
10314
10315           The -fipa-strict-aliasing option is enabled by default and is
10316           effective only in combination with -fstrict-aliasing.
10317
10318       -falign-functions
10319       -falign-functions=n
10320       -falign-functions=n:m
10321       -falign-functions=n:m:n2
10322       -falign-functions=n:m:n2:m2
10323           Align the start of functions to the next power-of-two greater than
10324           or equal to n, skipping up to m-1 bytes.  This ensures that at
10325           least the first m bytes of the function can be fetched by the CPU
10326           without crossing an n-byte alignment boundary.
10327
10328           If m is not specified, it defaults to n.
10329
10330           Examples: -falign-functions=32 aligns functions to the next 32-byte
10331           boundary, -falign-functions=24 aligns to the next 32-byte boundary
10332           only if this can be done by skipping 23 bytes or less,
10333           -falign-functions=32:7 aligns to the next 32-byte boundary only if
10334           this can be done by skipping 6 bytes or less.
10335
10336           The second pair of n2:m2 values allows you to specify a secondary
10337           alignment: -falign-functions=64:7:32:3 aligns to the next 64-byte
10338           boundary if this can be done by skipping 6 bytes or less, otherwise
10339           aligns to the next 32-byte boundary if this can be done by skipping
10340           2 bytes or less.  If m2 is not specified, it defaults to n2.
10341
10342           Some assemblers only support this flag when n is a power of two; in
10343           that case, it is rounded up.
10344
10345           -fno-align-functions and -falign-functions=1 are equivalent and
10346           mean that functions are not aligned.
10347
10348           If n is not specified or is zero, use a machine-dependent default.
10349           The maximum allowed n option value is 65536.
10350
10351           Enabled at levels -O2, -O3.
10352
10353       -flimit-function-alignment
10354           If this option is enabled, the compiler tries to avoid
10355           unnecessarily overaligning functions. It attempts to instruct the
10356           assembler to align by the amount specified by -falign-functions,
10357           but not to skip more bytes than the size of the function.
10358
10359       -falign-labels
10360       -falign-labels=n
10361       -falign-labels=n:m
10362       -falign-labels=n:m:n2
10363       -falign-labels=n:m:n2:m2
10364           Align all branch targets to a power-of-two boundary.
10365
10366           Parameters of this option are analogous to the -falign-functions
10367           option.  -fno-align-labels and -falign-labels=1 are equivalent and
10368           mean that labels are not aligned.
10369
10370           If -falign-loops or -falign-jumps are applicable and are greater
10371           than this value, then their values are used instead.
10372
10373           If n is not specified or is zero, use a machine-dependent default
10374           which is very likely to be 1, meaning no alignment.  The maximum
10375           allowed n option value is 65536.
10376
10377           Enabled at levels -O2, -O3.
10378
10379       -falign-loops
10380       -falign-loops=n
10381       -falign-loops=n:m
10382       -falign-loops=n:m:n2
10383       -falign-loops=n:m:n2:m2
10384           Align loops to a power-of-two boundary.  If the loops are executed
10385           many times, this makes up for any execution of the dummy padding
10386           instructions.
10387
10388           If -falign-labels is greater than this value, then its value is
10389           used instead.
10390
10391           Parameters of this option are analogous to the -falign-functions
10392           option.  -fno-align-loops and -falign-loops=1 are equivalent and
10393           mean that loops are not aligned.  The maximum allowed n option
10394           value is 65536.
10395
10396           If n is not specified or is zero, use a machine-dependent default.
10397
10398           Enabled at levels -O2, -O3.
10399
10400       -falign-jumps
10401       -falign-jumps=n
10402       -falign-jumps=n:m
10403       -falign-jumps=n:m:n2
10404       -falign-jumps=n:m:n2:m2
10405           Align branch targets to a power-of-two boundary, for branch targets
10406           where the targets can only be reached by jumping.  In this case, no
10407           dummy operations need be executed.
10408
10409           If -falign-labels is greater than this value, then its value is
10410           used instead.
10411
10412           Parameters of this option are analogous to the -falign-functions
10413           option.  -fno-align-jumps and -falign-jumps=1 are equivalent and
10414           mean that loops are not aligned.
10415
10416           If n is not specified or is zero, use a machine-dependent default.
10417           The maximum allowed n option value is 65536.
10418
10419           Enabled at levels -O2, -O3.
10420
10421       -fno-allocation-dce
10422           Do not remove unused C++ allocations in dead code elimination.
10423
10424       -fallow-store-data-races
10425           Allow the compiler to perform optimizations that may introduce new
10426           data races on stores, without proving that the variable cannot be
10427           concurrently accessed by other threads.  Does not affect
10428           optimization of local data.  It is safe to use this option if it is
10429           known that global data will not be accessed by multiple threads.
10430
10431           Examples of optimizations enabled by -fallow-store-data-races
10432           include hoisting or if-conversions that may cause a value that was
10433           already in memory to be re-written with that same value.  Such re-
10434           writing is safe in a single threaded context but may be unsafe in a
10435           multi-threaded context.  Note that on some processors, if-
10436           conversions may be required in order to enable vectorization.
10437
10438           Enabled at level -Ofast.
10439
10440       -funit-at-a-time
10441           This option is left for compatibility reasons. -funit-at-a-time has
10442           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
10443           and -fno-section-anchors.
10444
10445           Enabled by default.
10446
10447       -fno-toplevel-reorder
10448           Do not reorder top-level functions, variables, and "asm"
10449           statements.  Output them in the same order that they appear in the
10450           input file.  When this option is used, unreferenced static
10451           variables are not removed.  This option is intended to support
10452           existing code that relies on a particular ordering.  For new code,
10453           it is better to use attributes when possible.
10454
10455           -ftoplevel-reorder is the default at -O1 and higher, and also at
10456           -O0 if -fsection-anchors is explicitly requested.  Additionally
10457           -fno-toplevel-reorder implies -fno-section-anchors.
10458
10459       -fweb
10460           Constructs webs as commonly used for register allocation purposes
10461           and assign each web individual pseudo register.  This allows the
10462           register allocation pass to operate on pseudos directly, but also
10463           strengthens several other optimization passes, such as CSE, loop
10464           optimizer and trivial dead code remover.  It can, however, make
10465           debugging impossible, since variables no longer stay in a "home
10466           register".
10467
10468           Enabled by default with -funroll-loops.
10469
10470       -fwhole-program
10471           Assume that the current compilation unit represents the whole
10472           program being compiled.  All public functions and variables with
10473           the exception of "main" and those merged by attribute
10474           "externally_visible" become static functions and in effect are
10475           optimized more aggressively by interprocedural optimizers.
10476
10477           This option should not be used in combination with -flto.  Instead
10478           relying on a linker plugin should provide safer and more precise
10479           information.
10480
10481       -flto[=n]
10482           This option runs the standard link-time optimizer.  When invoked
10483           with source code, it generates GIMPLE (one of GCC's internal
10484           representations) and writes it to special ELF sections in the
10485           object file.  When the object files are linked together, all the
10486           function bodies are read from these ELF sections and instantiated
10487           as if they had been part of the same translation unit.
10488
10489           To use the link-time optimizer, -flto and optimization options
10490           should be specified at compile time and during the final link.  It
10491           is recommended that you compile all the files participating in the
10492           same link with the same options and also specify those options at
10493           link time.  For example:
10494
10495                   gcc -c -O2 -flto foo.c
10496                   gcc -c -O2 -flto bar.c
10497                   gcc -o myprog -flto -O2 foo.o bar.o
10498
10499           The first two invocations to GCC save a bytecode representation of
10500           GIMPLE into special ELF sections inside foo.o and bar.o.  The final
10501           invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
10502           the two files into a single internal image, and compiles the result
10503           as usual.  Since both foo.o and bar.o are merged into a single
10504           image, this causes all the interprocedural analyses and
10505           optimizations in GCC to work across the two files as if they were a
10506           single one.  This means, for example, that the inliner is able to
10507           inline functions in bar.o into functions in foo.o and vice-versa.
10508
10509           Another (simpler) way to enable link-time optimization is:
10510
10511                   gcc -o myprog -flto -O2 foo.c bar.c
10512
10513           The above generates bytecode for foo.c and bar.c, merges them
10514           together into a single GIMPLE representation and optimizes them as
10515           usual to produce myprog.
10516
10517           The important thing to keep in mind is that to enable link-time
10518           optimizations you need to use the GCC driver to perform the link
10519           step.  GCC automatically performs link-time optimization if any of
10520           the objects involved were compiled with the -flto command-line
10521           option.  You can always override the automatic decision to do link-
10522           time optimization by passing -fno-lto to the link command.
10523
10524           To make whole program optimization effective, it is necessary to
10525           make certain whole program assumptions.  The compiler needs to know
10526           what functions and variables can be accessed by libraries and
10527           runtime outside of the link-time optimized unit.  When supported by
10528           the linker, the linker plugin (see -fuse-linker-plugin) passes
10529           information to the compiler about used and externally visible
10530           symbols.  When the linker plugin is not available, -fwhole-program
10531           should be used to allow the compiler to make these assumptions,
10532           which leads to more aggressive optimization decisions.
10533
10534           When a file is compiled with -flto without -fuse-linker-plugin, the
10535           generated object file is larger than a regular object file because
10536           it contains GIMPLE bytecodes and the usual final code (see
10537           -ffat-lto-objects).  This means that object files with LTO
10538           information can be linked as normal object files; if -fno-lto is
10539           passed to the linker, no interprocedural optimizations are applied.
10540           Note that when -fno-fat-lto-objects is enabled the compile stage is
10541           faster but you cannot perform a regular, non-LTO link on them.
10542
10543           When producing the final binary, GCC only applies link-time
10544           optimizations to those files that contain bytecode.  Therefore, you
10545           can mix and match object files and libraries with GIMPLE bytecodes
10546           and final object code.  GCC automatically selects which files to
10547           optimize in LTO mode and which files to link without further
10548           processing.
10549
10550           Generally, options specified at link time override those specified
10551           at compile time, although in some cases GCC attempts to infer link-
10552           time options from the settings used to compile the input files.
10553
10554           If you do not specify an optimization level option -O at link time,
10555           then GCC uses the highest optimization level used when compiling
10556           the object files.  Note that it is generally ineffective to specify
10557           an optimization level option only at link time and not at compile
10558           time, for two reasons.  First, compiling without optimization
10559           suppresses compiler passes that gather information needed for
10560           effective optimization at link time.  Second, some early
10561           optimization passes can be performed only at compile time and not
10562           at link time.
10563
10564           There are some code generation flags preserved by GCC when
10565           generating bytecodes, as they need to be used during the final
10566           link.  Currently, the following options and their settings are
10567           taken from the first object file that explicitly specifies them:
10568           -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and all the
10569           -m target flags.
10570
10571           The following options -fPIC, -fpic, -fpie and -fPIE are combined
10572           based on the following scheme:
10573
10574                   B<-fPIC> + B<-fpic> = B<-fpic>
10575                   B<-fPIC> + B<-fno-pic> = B<-fno-pic>
10576                   B<-fpic/-fPIC> + (no option) = (no option)
10577                   B<-fPIC> + B<-fPIE> = B<-fPIE>
10578                   B<-fpic> + B<-fPIE> = B<-fpie>
10579                   B<-fPIC/-fpic> + B<-fpie> = B<-fpie>
10580
10581           Certain ABI-changing flags are required to match in all compilation
10582           units, and trying to override this at link time with a conflicting
10583           value is ignored.  This includes options such as
10584           -freg-struct-return and -fpcc-struct-return.
10585
10586           Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv,
10587           -fno-trapv or -fno-strict-aliasing are passed through to the link
10588           stage and merged conservatively for conflicting translation units.
10589           Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take
10590           precedence; and for example -ffp-contract=off takes precedence over
10591           -ffp-contract=fast.  You can override them at link time.
10592
10593           Diagnostic options such as -Wstringop-overflow are passed through
10594           to the link stage and their setting matches that of the compile-
10595           step at function granularity.  Note that this matters only for
10596           diagnostics emitted during optimization.  Note that code transforms
10597           such as inlining can lead to warnings being enabled or disabled for
10598           regions if code not consistent with the setting at compile time.
10599
10600           When you need to pass options to the assembler via -Wa or
10601           -Xassembler make sure to either compile such translation units with
10602           -fno-lto or consistently use the same assembler options on all
10603           translation units.  You can alternatively also specify assembler
10604           options at LTO link time.
10605
10606           To enable debug info generation you need to supply -g at compile
10607           time.  If any of the input files at link time were built with debug
10608           info generation enabled the link will enable debug info generation
10609           as well.  Any elaborate debug info settings like the dwarf level
10610           -gdwarf-5 need to be explicitly repeated at the linker command line
10611           and mixing different settings in different translation units is
10612           discouraged.
10613
10614           If LTO encounters objects with C linkage declared with incompatible
10615           types in separate translation units to be linked together
10616           (undefined behavior according to ISO C99 6.2.7), a non-fatal
10617           diagnostic may be issued.  The behavior is still undefined at run
10618           time.  Similar diagnostics may be raised for other languages.
10619
10620           Another feature of LTO is that it is possible to apply
10621           interprocedural optimizations on files written in different
10622           languages:
10623
10624                   gcc -c -flto foo.c
10625                   g++ -c -flto bar.cc
10626                   gfortran -c -flto baz.f90
10627                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
10628
10629           Notice that the final link is done with g++ to get the C++ runtime
10630           libraries and -lgfortran is added to get the Fortran runtime
10631           libraries.  In general, when mixing languages in LTO mode, you
10632           should use the same link command options as when mixing languages
10633           in a regular (non-LTO) compilation.
10634
10635           If object files containing GIMPLE bytecode are stored in a library
10636           archive, say libfoo.a, it is possible to extract and use them in an
10637           LTO link if you are using a linker with plugin support.  To create
10638           static libraries suitable for LTO, use gcc-ar and gcc-ranlib
10639           instead of ar and ranlib; to show the symbols of object files with
10640           GIMPLE bytecode, use gcc-nm.  Those commands require that ar,
10641           ranlib and nm have been compiled with plugin support.  At link
10642           time, use the flag -fuse-linker-plugin to ensure that the library
10643           participates in the LTO optimization process:
10644
10645                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
10646
10647           With the linker plugin enabled, the linker extracts the needed
10648           GIMPLE files from libfoo.a and passes them on to the running GCC to
10649           make them part of the aggregated GIMPLE image to be optimized.
10650
10651           If you are not using a linker with plugin support and/or do not
10652           enable the linker plugin, then the objects inside libfoo.a are
10653           extracted and linked as usual, but they do not participate in the
10654           LTO optimization process.  In order to make a static library
10655           suitable for both LTO optimization and usual linkage, compile its
10656           object files with -flto -ffat-lto-objects.
10657
10658           Link-time optimizations do not require the presence of the whole
10659           program to operate.  If the program does not require any symbols to
10660           be exported, it is possible to combine -flto and -fwhole-program to
10661           allow the interprocedural optimizers to use more aggressive
10662           assumptions which may lead to improved optimization opportunities.
10663           Use of -fwhole-program is not needed when linker plugin is active
10664           (see -fuse-linker-plugin).
10665
10666           The current implementation of LTO makes no attempt to generate
10667           bytecode that is portable between different types of hosts.  The
10668           bytecode files are versioned and there is a strict version check,
10669           so bytecode files generated in one version of GCC do not work with
10670           an older or newer version of GCC.
10671
10672           Link-time optimization does not work well with generation of
10673           debugging information on systems other than those using a
10674           combination of ELF and DWARF.
10675
10676           If you specify the optional n, the optimization and code generation
10677           done at link time is executed in parallel using n parallel jobs by
10678           utilizing an installed make program.  The environment variable MAKE
10679           may be used to override the program used.
10680
10681           You can also specify -flto=jobserver to use GNU make's job server
10682           mode to determine the number of parallel jobs. This is useful when
10683           the Makefile calling GCC is already executing in parallel.  You
10684           must prepend a + to the command recipe in the parent Makefile for
10685           this to work.  This option likely only works if MAKE is GNU make.
10686           Even without the option value, GCC tries to automatically detect a
10687           running GNU make's job server.
10688
10689           Use -flto=auto to use GNU make's job server, if available, or
10690           otherwise fall back to autodetection of the number of CPU threads
10691           present in your system.
10692
10693       -flto-partition=alg
10694           Specify the partitioning algorithm used by the link-time optimizer.
10695           The value is either 1to1 to specify a partitioning mirroring the
10696           original source files or balanced to specify partitioning into
10697           equally sized chunks (whenever possible) or max to create new
10698           partition for every symbol where possible.  Specifying none as an
10699           algorithm disables partitioning and streaming completely.  The
10700           default value is balanced. While 1to1 can be used as an workaround
10701           for various code ordering issues, the max partitioning is intended
10702           for internal testing only.  The value one specifies that exactly
10703           one partition should be used while the value none bypasses
10704           partitioning and executes the link-time optimization step directly
10705           from the WPA phase.
10706
10707       -flto-compression-level=n
10708           This option specifies the level of compression used for
10709           intermediate language written to LTO object files, and is only
10710           meaningful in conjunction with LTO mode (-flto).  GCC currently
10711           supports two LTO compression algorithms. For zstd, valid values are
10712           0 (no compression) to 19 (maximum compression), while zlib supports
10713           values from 0 to 9.  Values outside this range are clamped to
10714           either minimum or maximum of the supported values.  If the option
10715           is not given, a default balanced compression setting is used.
10716
10717       -fuse-linker-plugin
10718           Enables the use of a linker plugin during link-time optimization.
10719           This option relies on plugin support in the linker, which is
10720           available in gold or in GNU ld 2.21 or newer.
10721
10722           This option enables the extraction of object files with GIMPLE
10723           bytecode out of library archives. This improves the quality of
10724           optimization by exposing more code to the link-time optimizer.
10725           This information specifies what symbols can be accessed externally
10726           (by non-LTO object or during dynamic linking).  Resulting code
10727           quality improvements on binaries (and shared libraries that use
10728           hidden visibility) are similar to -fwhole-program.  See -flto for a
10729           description of the effect of this flag and how to use it.
10730
10731           This option is enabled by default when LTO support in GCC is
10732           enabled and GCC was configured for use with a linker supporting
10733           plugins (GNU ld 2.21 or newer or gold).
10734
10735       -ffat-lto-objects
10736           Fat LTO objects are object files that contain both the intermediate
10737           language and the object code. This makes them usable for both LTO
10738           linking and normal linking. This option is effective only when
10739           compiling with -flto and is ignored at link time.
10740
10741           -fno-fat-lto-objects improves compilation time over plain LTO, but
10742           requires the complete toolchain to be aware of LTO. It requires a
10743           linker with linker plugin support for basic functionality.
10744           Additionally, nm, ar and ranlib need to support linker plugins to
10745           allow a full-featured build environment (capable of building static
10746           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib
10747           wrappers to pass the right options to these tools. With non fat LTO
10748           makefiles need to be modified to use them.
10749
10750           Note that modern binutils provide plugin auto-load mechanism.
10751           Installing the linker plugin into $libdir/bfd-plugins has the same
10752           effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-
10753           ranlib).
10754
10755           The default is -fno-fat-lto-objects on targets with linker plugin
10756           support.
10757
10758       -fcompare-elim
10759           After register allocation and post-register allocation instruction
10760           splitting, identify arithmetic instructions that compute processor
10761           flags similar to a comparison operation based on that arithmetic.
10762           If possible, eliminate the explicit comparison operation.
10763
10764           This pass only applies to certain targets that cannot explicitly
10765           represent the comparison operation before register allocation is
10766           complete.
10767
10768           Enabled at levels -O1, -O2, -O3, -Os.
10769
10770       -fcprop-registers
10771           After register allocation and post-register allocation instruction
10772           splitting, perform a copy-propagation pass to try to reduce
10773           scheduling dependencies and occasionally eliminate the copy.
10774
10775           Enabled at levels -O1, -O2, -O3, -Os.
10776
10777       -fprofile-correction
10778           Profiles collected using an instrumented binary for multi-threaded
10779           programs may be inconsistent due to missed counter updates. When
10780           this option is specified, GCC uses heuristics to correct or smooth
10781           out such inconsistencies. By default, GCC emits an error message
10782           when an inconsistent profile is detected.
10783
10784           This option is enabled by -fauto-profile.
10785
10786       -fprofile-partial-training
10787           With "-fprofile-use" all portions of programs not executed during
10788           train run are optimized agressively for size rather than speed.  In
10789           some cases it is not practical to train all possible hot paths in
10790           the program. (For example, program may contain functions specific
10791           for a given hardware and trianing may not cover all hardware
10792           configurations program is run on.)  With
10793           "-fprofile-partial-training" profile feedback will be ignored for
10794           all functions not executed during the train run leading them to be
10795           optimized as if they were compiled without profile feedback. This
10796           leads to better performance when train run is not representative
10797           but also leads to significantly bigger code.
10798
10799       -fprofile-use
10800       -fprofile-use=path
10801           Enable profile feedback-directed optimizations, and the following
10802           optimizations, many of which are generally profitable only with
10803           profile feedback available:
10804
10805           -fbranch-probabilities  -fprofile-values -funroll-loops
10806           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
10807           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
10808           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
10809           -ftree-slp-vectorize -fvect-cost-model=dynamic
10810           -ftree-loop-distribute-patterns -fprofile-reorder-functions
10811
10812           Before you can use this option, you must first generate profiling
10813           information.
10814
10815           By default, GCC emits an error message if the feedback profiles do
10816           not match the source code.  This error can be turned into a warning
10817           by using -Wno-error=coverage-mismatch.  Note this may result in
10818           poorly optimized code.  Additionally, by default, GCC also emits a
10819           warning message if the feedback profiles do not exist (see
10820           -Wmissing-profile).
10821
10822           If path is specified, GCC looks at the path to find the profile
10823           feedback data files. See -fprofile-dir.
10824
10825       -fauto-profile
10826       -fauto-profile=path
10827           Enable sampling-based feedback-directed optimizations, and the
10828           following optimizations, many of which are generally profitable
10829           only with profile feedback available:
10830
10831           -fbranch-probabilities  -fprofile-values -funroll-loops
10832           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
10833           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
10834           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
10835           -ftree-slp-vectorize -fvect-cost-model=dynamic
10836           -ftree-loop-distribute-patterns -fprofile-correction
10837
10838           path is the name of a file containing AutoFDO profile information.
10839           If omitted, it defaults to fbdata.afdo in the current directory.
10840
10841           Producing an AutoFDO profile data file requires running your
10842           program with the perf utility on a supported GNU/Linux target
10843           system.  For more information, see <https://perf.wiki.kernel.org/>.
10844
10845           E.g.
10846
10847                   perf record -e br_inst_retired:near_taken -b -o perf.data \
10848                       -- your_program
10849
10850           Then use the create_gcov tool to convert the raw profile data to a
10851           format that can be used by GCC.  You must also supply the
10852           unstripped binary for your program to this tool.  See
10853           <https://github.com/google/autofdo>.
10854
10855           E.g.
10856
10857                   create_gcov --binary=your_program.unstripped --profile=perf.data \
10858                       --gcov=profile.afdo
10859
10860       The following options control compiler behavior regarding floating-
10861       point arithmetic.  These options trade off between speed and
10862       correctness.  All must be specifically enabled.
10863
10864       -ffloat-store
10865           Do not store floating-point variables in registers, and inhibit
10866           other options that might change whether a floating-point value is
10867           taken from a register or memory.
10868
10869           This option prevents undesirable excess precision on machines such
10870           as the 68000 where the floating registers (of the 68881) keep more
10871           precision than a "double" is supposed to have.  Similarly for the
10872           x86 architecture.  For most programs, the excess precision does
10873           only good, but a few programs rely on the precise definition of
10874           IEEE floating point.  Use -ffloat-store for such programs, after
10875           modifying them to store all pertinent intermediate computations
10876           into variables.
10877
10878       -fexcess-precision=style
10879           This option allows further control over excess precision on
10880           machines where floating-point operations occur in a format with
10881           more precision or range than the IEEE standard and interchange
10882           floating-point types.  By default, -fexcess-precision=fast is in
10883           effect; this means that operations may be carried out in a wider
10884           precision than the types specified in the source if that would
10885           result in faster code, and it is unpredictable when rounding to the
10886           types specified in the source code takes place.  When compiling C,
10887           if -fexcess-precision=standard is specified then excess precision
10888           follows the rules specified in ISO C99; in particular, both casts
10889           and assignments cause values to be rounded to their semantic types
10890           (whereas -ffloat-store only affects assignments).  This option is
10891           enabled by default for C if a strict conformance option such as
10892           -std=c99 is used.  -ffast-math enables -fexcess-precision=fast by
10893           default regardless of whether a strict conformance option is used.
10894
10895           -fexcess-precision=standard is not implemented for languages other
10896           than C.  On the x86, it has no effect if -mfpmath=sse or
10897           -mfpmath=sse+387 is specified; in the former case, IEEE semantics
10898           apply without excess precision, and in the latter, rounding is
10899           unpredictable.
10900
10901       -ffast-math
10902           Sets the options -fno-math-errno, -funsafe-math-optimizations,
10903           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans,
10904           -fcx-limited-range and -fexcess-precision=fast.
10905
10906           This option causes the preprocessor macro "__FAST_MATH__" to be
10907           defined.
10908
10909           This option is not turned on by any -O option besides -Ofast since
10910           it can result in incorrect output for programs that depend on an
10911           exact implementation of IEEE or ISO rules/specifications for math
10912           functions. It may, however, yield faster code for programs that do
10913           not require the guarantees of these specifications.
10914
10915       -fno-math-errno
10916           Do not set "errno" after calling math functions that are executed
10917           with a single instruction, e.g., "sqrt".  A program that relies on
10918           IEEE exceptions for math error handling may want to use this flag
10919           for speed while maintaining IEEE arithmetic compatibility.
10920
10921           This option is not turned on by any -O option since it can result
10922           in incorrect output for programs that depend on an exact
10923           implementation of IEEE or ISO rules/specifications for math
10924           functions. It may, however, yield faster code for programs that do
10925           not require the guarantees of these specifications.
10926
10927           The default is -fmath-errno.
10928
10929           On Darwin systems, the math library never sets "errno".  There is
10930           therefore no reason for the compiler to consider the possibility
10931           that it might, and -fno-math-errno is the default.
10932
10933       -funsafe-math-optimizations
10934           Allow optimizations for floating-point arithmetic that (a) assume
10935           that arguments and results are valid and (b) may violate IEEE or
10936           ANSI standards.  When used at link time, it may include libraries
10937           or startup files that change the default FPU control word or other
10938           similar optimizations.
10939
10940           This option is not turned on by any -O option since it can result
10941           in incorrect output for programs that depend on an exact
10942           implementation of IEEE or ISO rules/specifications for math
10943           functions. It may, however, yield faster code for programs that do
10944           not require the guarantees of these specifications.  Enables
10945           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
10946           -freciprocal-math.
10947
10948           The default is -fno-unsafe-math-optimizations.
10949
10950       -fassociative-math
10951           Allow re-association of operands in series of floating-point
10952           operations.  This violates the ISO C and C++ language standard by
10953           possibly changing computation result.  NOTE: re-ordering may change
10954           the sign of zero as well as ignore NaNs and inhibit or create
10955           underflow or overflow (and thus cannot be used on code that relies
10956           on rounding behavior like "(x + 2**52) - 2**52".  May also reorder
10957           floating-point comparisons and thus may not be used when ordered
10958           comparisons are required.  This option requires that both
10959           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
10960           it doesn't make much sense with -frounding-math. For Fortran the
10961           option is automatically enabled when both -fno-signed-zeros and
10962           -fno-trapping-math are in effect.
10963
10964           The default is -fno-associative-math.
10965
10966       -freciprocal-math
10967           Allow the reciprocal of a value to be used instead of dividing by
10968           the value if this enables optimizations.  For example "x / y" can
10969           be replaced with "x * (1/y)", which is useful if "(1/y)" is subject
10970           to common subexpression elimination.  Note that this loses
10971           precision and increases the number of flops operating on the value.
10972
10973           The default is -fno-reciprocal-math.
10974
10975       -ffinite-math-only
10976           Allow optimizations for floating-point arithmetic that assume that
10977           arguments and results are not NaNs or +-Infs.
10978
10979           This option is not turned on by any -O option since it can result
10980           in incorrect output for programs that depend on an exact
10981           implementation of IEEE or ISO rules/specifications for math
10982           functions. It may, however, yield faster code for programs that do
10983           not require the guarantees of these specifications.
10984
10985           The default is -fno-finite-math-only.
10986
10987       -fno-signed-zeros
10988           Allow optimizations for floating-point arithmetic that ignore the
10989           signedness of zero.  IEEE arithmetic specifies the behavior of
10990           distinct +0.0 and -0.0 values, which then prohibits simplification
10991           of expressions such as x+0.0 or 0.0*x (even with
10992           -ffinite-math-only).  This option implies that the sign of a zero
10993           result isn't significant.
10994
10995           The default is -fsigned-zeros.
10996
10997       -fno-trapping-math
10998           Compile code assuming that floating-point operations cannot
10999           generate user-visible traps.  These traps include division by zero,
11000           overflow, underflow, inexact result and invalid operation.  This
11001           option requires that -fno-signaling-nans be in effect.  Setting
11002           this option may allow faster code if one relies on "non-stop" IEEE
11003           arithmetic, for example.
11004
11005           This option should never be turned on by any -O option since it can
11006           result in incorrect output for programs that depend on an exact
11007           implementation of IEEE or ISO rules/specifications for math
11008           functions.
11009
11010           The default is -ftrapping-math.
11011
11012       -frounding-math
11013           Disable transformations and optimizations that assume default
11014           floating-point rounding behavior.  This is round-to-zero for all
11015           floating point to integer conversions, and round-to-nearest for all
11016           other arithmetic truncations.  This option should be specified for
11017           programs that change the FP rounding mode dynamically, or that may
11018           be executed with a non-default rounding mode.  This option disables
11019           constant folding of floating-point expressions at compile time
11020           (which may be affected by rounding mode) and arithmetic
11021           transformations that are unsafe in the presence of sign-dependent
11022           rounding modes.
11023
11024           The default is -fno-rounding-math.
11025
11026           This option is experimental and does not currently guarantee to
11027           disable all GCC optimizations that are affected by rounding mode.
11028           Future versions of GCC may provide finer control of this setting
11029           using C99's "FENV_ACCESS" pragma.  This command-line option will be
11030           used to specify the default state for "FENV_ACCESS".
11031
11032       -fsignaling-nans
11033           Compile code assuming that IEEE signaling NaNs may generate user-
11034           visible traps during floating-point operations.  Setting this
11035           option disables optimizations that may change the number of
11036           exceptions visible with signaling NaNs.  This option implies
11037           -ftrapping-math.
11038
11039           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
11040           defined.
11041
11042           The default is -fno-signaling-nans.
11043
11044           This option is experimental and does not currently guarantee to
11045           disable all GCC optimizations that affect signaling NaN behavior.
11046
11047       -fno-fp-int-builtin-inexact
11048           Do not allow the built-in functions "ceil", "floor", "round" and
11049           "trunc", and their "float" and "long double" variants, to generate
11050           code that raises the "inexact" floating-point exception for
11051           noninteger arguments.  ISO C99 and C11 allow these functions to
11052           raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
11053           bindings to IEEE 754-2008, as integrated into ISO C2X, does not
11054           allow these functions to do so.
11055
11056           The default is -ffp-int-builtin-inexact, allowing the exception to
11057           be raised, unless C2X or a later C standard is selected.  This
11058           option does nothing unless -ftrapping-math is in effect.
11059
11060           Even if -fno-fp-int-builtin-inexact is used, if the functions
11061           generate a call to a library function then the "inexact" exception
11062           may be raised if the library implementation does not follow TS
11063           18661.
11064
11065       -fsingle-precision-constant
11066           Treat floating-point constants as single precision instead of
11067           implicitly converting them to double-precision constants.
11068
11069       -fcx-limited-range
11070           When enabled, this option states that a range reduction step is not
11071           needed when performing complex division.  Also, there is no
11072           checking whether the result of a complex multiplication or division
11073           is "NaN + I*NaN", with an attempt to rescue the situation in that
11074           case.  The default is -fno-cx-limited-range, but is enabled by
11075           -ffast-math.
11076
11077           This option controls the default setting of the ISO C99
11078           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
11079           languages.
11080
11081       -fcx-fortran-rules
11082           Complex multiplication and division follow Fortran rules.  Range
11083           reduction is done as part of complex division, but there is no
11084           checking whether the result of a complex multiplication or division
11085           is "NaN + I*NaN", with an attempt to rescue the situation in that
11086           case.
11087
11088           The default is -fno-cx-fortran-rules.
11089
11090       The following options control optimizations that may improve
11091       performance, but are not enabled by any -O options.  This section
11092       includes experimental options that may produce broken code.
11093
11094       -fbranch-probabilities
11095           After running a program compiled with -fprofile-arcs, you can
11096           compile it a second time using -fbranch-probabilities, to improve
11097           optimizations based on the number of times each branch was taken.
11098           When a program compiled with -fprofile-arcs exits, it saves arc
11099           execution counts to a file called sourcename.gcda for each source
11100           file.  The information in this data file is very dependent on the
11101           structure of the generated code, so you must use the same source
11102           code and the same optimization options for both compilations.  See
11103           details about the file naming in -fprofile-arcs.
11104
11105           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
11106           JUMP_INSN and CALL_INSN.  These can be used to improve
11107           optimization.  Currently, they are only used in one place: in
11108           reorg.cc, instead of guessing which path a branch is most likely to
11109           take, the REG_BR_PROB values are used to exactly determine which
11110           path is taken more often.
11111
11112           Enabled by -fprofile-use and -fauto-profile.
11113
11114       -fprofile-values
11115           If combined with -fprofile-arcs, it adds code so that some data
11116           about values of expressions in the program is gathered.
11117
11118           With -fbranch-probabilities, it reads back the data gathered from
11119           profiling values of expressions for usage in optimizations.
11120
11121           Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile.
11122
11123       -fprofile-reorder-functions
11124           Function reordering based on profile instrumentation collects first
11125           time of execution of a function and orders these functions in
11126           ascending order.
11127
11128           Enabled with -fprofile-use.
11129
11130       -fvpt
11131           If combined with -fprofile-arcs, this option instructs the compiler
11132           to add code to gather information about values of expressions.
11133
11134           With -fbranch-probabilities, it reads back the data gathered and
11135           actually performs the optimizations based on them.  Currently the
11136           optimizations include specialization of division operations using
11137           the knowledge about the value of the denominator.
11138
11139           Enabled with -fprofile-use and -fauto-profile.
11140
11141       -frename-registers
11142           Attempt to avoid false dependencies in scheduled code by making use
11143           of registers left over after register allocation.  This
11144           optimization most benefits processors with lots of registers.
11145           Depending on the debug information format adopted by the target,
11146           however, it can make debugging impossible, since variables no
11147           longer stay in a "home register".
11148
11149           Enabled by default with -funroll-loops.
11150
11151       -fschedule-fusion
11152           Performs a target dependent pass over the instruction stream to
11153           schedule instructions of same type together because target machine
11154           can execute them more efficiently if they are adjacent to each
11155           other in the instruction flow.
11156
11157           Enabled at levels -O2, -O3, -Os.
11158
11159       -ftracer
11160           Perform tail duplication to enlarge superblock size.  This
11161           transformation simplifies the control flow of the function allowing
11162           other optimizations to do a better job.
11163
11164           Enabled by -fprofile-use and -fauto-profile.
11165
11166       -funroll-loops
11167           Unroll loops whose number of iterations can be determined at
11168           compile time or upon entry to the loop.  -funroll-loops implies
11169           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
11170           turns on complete loop peeling (i.e. complete removal of loops with
11171           a small constant number of iterations).  This option makes code
11172           larger, and may or may not make it run faster.
11173
11174           Enabled by -fprofile-use and -fauto-profile.
11175
11176       -funroll-all-loops
11177           Unroll all loops, even if their number of iterations is uncertain
11178           when the loop is entered.  This usually makes programs run more
11179           slowly.  -funroll-all-loops implies the same options as
11180           -funroll-loops.
11181
11182       -fpeel-loops
11183           Peels loops for which there is enough information that they do not
11184           roll much (from profile feedback or static analysis).  It also
11185           turns on complete loop peeling (i.e. complete removal of loops with
11186           small constant number of iterations).
11187
11188           Enabled by -O3, -fprofile-use, and -fauto-profile.
11189
11190       -fmove-loop-invariants
11191           Enables the loop invariant motion pass in the RTL loop optimizer.
11192           Enabled at level -O1 and higher, except for -Og.
11193
11194       -fmove-loop-stores
11195           Enables the loop store motion pass in the GIMPLE loop optimizer.
11196           This moves invariant stores to after the end of the loop in
11197           exchange for carrying the stored value in a register across the
11198           iteration.  Note for this option to have an effect -ftree-loop-im
11199           has to be enabled as well.  Enabled at level -O1 and higher, except
11200           for -Og.
11201
11202       -fsplit-loops
11203           Split a loop into two if it contains a condition that's always true
11204           for one side of the iteration space and false for the other.
11205
11206           Enabled by -fprofile-use and -fauto-profile.
11207
11208       -funswitch-loops
11209           Move branches with loop invariant conditions out of the loop, with
11210           duplicates of the loop on both branches (modified according to
11211           result of the condition).
11212
11213           Enabled by -fprofile-use and -fauto-profile.
11214
11215       -fversion-loops-for-strides
11216           If a loop iterates over an array with a variable stride, create
11217           another version of the loop that assumes the stride is always one.
11218           For example:
11219
11220                   for (int i = 0; i < n; ++i)
11221                     x[i * stride] = ...;
11222
11223           becomes:
11224
11225                   if (stride == 1)
11226                     for (int i = 0; i < n; ++i)
11227                       x[i] = ...;
11228                   else
11229                     for (int i = 0; i < n; ++i)
11230                       x[i * stride] = ...;
11231
11232           This is particularly useful for assumed-shape arrays in Fortran
11233           where (for example) it allows better vectorization assuming
11234           contiguous accesses.  This flag is enabled by default at -O3.  It
11235           is also enabled by -fprofile-use and -fauto-profile.
11236
11237       -ffunction-sections
11238       -fdata-sections
11239           Place each function or data item into its own section in the output
11240           file if the target supports arbitrary sections.  The name of the
11241           function or the name of the data item determines the section's name
11242           in the output file.
11243
11244           Use these options on systems where the linker can perform
11245           optimizations to improve locality of reference in the instruction
11246           space.  Most systems using the ELF object format have linkers with
11247           such optimizations.  On AIX, the linker rearranges sections
11248           (CSECTs) based on the call graph.  The performance impact varies.
11249
11250           Together with a linker garbage collection (linker --gc-sections
11251           option) these options may lead to smaller statically-linked
11252           executables (after stripping).
11253
11254           On ELF/DWARF systems these options do not degenerate the quality of
11255           the debug information.  There could be issues with other object
11256           files/debug info formats.
11257
11258           Only use these options when there are significant benefits from
11259           doing so.  When you specify these options, the assembler and linker
11260           create larger object and executable files and are also slower.
11261           These options affect code generation.  They prevent optimizations
11262           by the compiler and assembler using relative locations inside a
11263           translation unit since the locations are unknown until link time.
11264           An example of such an optimization is relaxing calls to short call
11265           instructions.
11266
11267       -fstdarg-opt
11268           Optimize the prologue of variadic argument functions with respect
11269           to usage of those arguments.
11270
11271       -fsection-anchors
11272           Try to reduce the number of symbolic address calculations by using
11273           shared "anchor" symbols to address nearby objects.  This
11274           transformation can help to reduce the number of GOT entries and GOT
11275           accesses on some targets.
11276
11277           For example, the implementation of the following function "foo":
11278
11279                   static int a, b, c;
11280                   int foo (void) { return a + b + c; }
11281
11282           usually calculates the addresses of all three variables, but if you
11283           compile it with -fsection-anchors, it accesses the variables from a
11284           common anchor point instead.  The effect is similar to the
11285           following pseudocode (which isn't valid C):
11286
11287                   int foo (void)
11288                   {
11289                     register int *xr = &x;
11290                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
11291                   }
11292
11293           Not all targets support this option.
11294
11295       -fzero-call-used-regs=choice
11296           Zero call-used registers at function return to increase program
11297           security by either mitigating Return-Oriented Programming (ROP)
11298           attacks or preventing information leakage through registers.
11299
11300           The possible values of choice are the same as for the
11301           "zero_call_used_regs" attribute.  The default is skip.
11302
11303           You can control this behavior for a specific function by using the
11304           function attribute "zero_call_used_regs".
11305
11306       --param name=value
11307           In some places, GCC uses various constants to control the amount of
11308           optimization that is done.  For example, GCC does not inline
11309           functions that contain more than a certain number of instructions.
11310           You can control some of these constants on the command line using
11311           the --param option.
11312
11313           The names of specific parameters, and the meaning of the values,
11314           are tied to the internals of the compiler, and are subject to
11315           change without notice in future releases.
11316
11317           In order to get minimal, maximal and default value of a parameter,
11318           one can use --help=param -Q options.
11319
11320           In each case, the value is an integer.  The following choices of
11321           name are recognized for all targets:
11322
11323           predictable-branch-outcome
11324               When branch is predicted to be taken with probability lower
11325               than this threshold (in percent), then it is considered well
11326               predictable.
11327
11328           max-rtl-if-conversion-insns
11329               RTL if-conversion tries to remove conditional branches around a
11330               block and replace them with conditionally executed
11331               instructions.  This parameter gives the maximum number of
11332               instructions in a block which should be considered for if-
11333               conversion.  The compiler will also use other heuristics to
11334               decide whether if-conversion is likely to be profitable.
11335
11336           max-rtl-if-conversion-predictable-cost
11337               RTL if-conversion will try to remove conditional branches
11338               around a block and replace them with conditionally executed
11339               instructions.  These parameters give the maximum permissible
11340               cost for the sequence that would be generated by if-conversion
11341               depending on whether the branch is statically determined to be
11342               predictable or not.  The units for this parameter are the same
11343               as those for the GCC internal seq_cost metric.  The compiler
11344               will try to provide a reasonable default for this parameter
11345               using the BRANCH_COST target macro.
11346
11347           max-crossjump-edges
11348               The maximum number of incoming edges to consider for cross-
11349               jumping.  The algorithm used by -fcrossjumping is O(N^2) in the
11350               number of edges incoming to each block.  Increasing values mean
11351               more aggressive optimization, making the compilation time
11352               increase with probably small improvement in executable size.
11353
11354           min-crossjump-insns
11355               The minimum number of instructions that must be matched at the
11356               end of two blocks before cross-jumping is performed on them.
11357               This value is ignored in the case where all instructions in the
11358               block being cross-jumped from are matched.
11359
11360           max-grow-copy-bb-insns
11361               The maximum code size expansion factor when copying basic
11362               blocks instead of jumping.  The expansion is relative to a jump
11363               instruction.
11364
11365           max-goto-duplication-insns
11366               The maximum number of instructions to duplicate to a block that
11367               jumps to a computed goto.  To avoid O(N^2) behavior in a number
11368               of passes, GCC factors computed gotos early in the compilation
11369               process, and unfactors them as late as possible.  Only computed
11370               jumps at the end of a basic blocks with no more than max-goto-
11371               duplication-insns are unfactored.
11372
11373           max-delay-slot-insn-search
11374               The maximum number of instructions to consider when looking for
11375               an instruction to fill a delay slot.  If more than this
11376               arbitrary number of instructions are searched, the time savings
11377               from filling the delay slot are minimal, so stop searching.
11378               Increasing values mean more aggressive optimization, making the
11379               compilation time increase with probably small improvement in
11380               execution time.
11381
11382           max-delay-slot-live-search
11383               When trying to fill delay slots, the maximum number of
11384               instructions to consider when searching for a block with valid
11385               live register information.  Increasing this arbitrarily chosen
11386               value means more aggressive optimization, increasing the
11387               compilation time.  This parameter should be removed when the
11388               delay slot code is rewritten to maintain the control-flow
11389               graph.
11390
11391           max-gcse-memory
11392               The approximate maximum amount of memory in "kB" that can be
11393               allocated in order to perform the global common subexpression
11394               elimination optimization.  If more memory than specified is
11395               required, the optimization is not done.
11396
11397           max-gcse-insertion-ratio
11398               If the ratio of expression insertions to deletions is larger
11399               than this value for any expression, then RTL PRE inserts or
11400               removes the expression and thus leaves partially redundant
11401               computations in the instruction stream.
11402
11403           max-pending-list-length
11404               The maximum number of pending dependencies scheduling allows
11405               before flushing the current state and starting over.  Large
11406               functions with few branches or calls can create excessively
11407               large lists which needlessly consume memory and resources.
11408
11409           max-modulo-backtrack-attempts
11410               The maximum number of backtrack attempts the scheduler should
11411               make when modulo scheduling a loop.  Larger values can
11412               exponentially increase compilation time.
11413
11414           max-inline-functions-called-once-loop-depth
11415               Maximal loop depth of a call considered by inline heuristics
11416               that tries to inline all functions called once.
11417
11418           max-inline-functions-called-once-insns
11419               Maximal estimated size of functions produced while inlining
11420               functions called once.
11421
11422           max-inline-insns-single
11423               Several parameters control the tree inliner used in GCC.  This
11424               number sets the maximum number of instructions (counted in
11425               GCC's internal representation) in a single function that the
11426               tree inliner considers for inlining.  This only affects
11427               functions declared inline and methods implemented in a class
11428               declaration (C++).
11429
11430           max-inline-insns-auto
11431               When you use -finline-functions (included in -O3), a lot of
11432               functions that would otherwise not be considered for inlining
11433               by the compiler are investigated.  To those functions, a
11434               different (more restrictive) limit compared to functions
11435               declared inline can be applied (--param max-inline-insns-auto).
11436
11437           max-inline-insns-small
11438               This is bound applied to calls which are considered relevant
11439               with -finline-small-functions.
11440
11441           max-inline-insns-size
11442               This is bound applied to calls which are optimized for size.
11443               Small growth may be desirable to anticipate optimization
11444               oppurtunities exposed by inlining.
11445
11446           uninlined-function-insns
11447               Number of instructions accounted by inliner for function
11448               overhead such as function prologue and epilogue.
11449
11450           uninlined-function-time
11451               Extra time accounted by inliner for function overhead such as
11452               time needed to execute function prologue and epilogue.
11453
11454           inline-heuristics-hint-percent
11455               The scale (in percents) applied to inline-insns-single,
11456               inline-insns-single-O2, inline-insns-auto when inline
11457               heuristics hints that inlining is very profitable (will enable
11458               later optimizations).
11459
11460           uninlined-thunk-insns
11461           uninlined-thunk-time
11462               Same as --param uninlined-function-insns and --param uninlined-
11463               function-time but applied to function thunks.
11464
11465           inline-min-speedup
11466               When estimated performance improvement of caller + callee
11467               runtime exceeds this threshold (in percent), the function can
11468               be inlined regardless of the limit on --param max-inline-insns-
11469               single and --param max-inline-insns-auto.
11470
11471           large-function-insns
11472               The limit specifying really large functions.  For functions
11473               larger than this limit after inlining, inlining is constrained
11474               by --param large-function-growth.  This parameter is useful
11475               primarily to avoid extreme compilation time caused by non-
11476               linear algorithms used by the back end.
11477
11478           large-function-growth
11479               Specifies maximal growth of large function caused by inlining
11480               in percents.  For example, parameter value 100 limits large
11481               function growth to 2.0 times the original size.
11482
11483           large-unit-insns
11484               The limit specifying large translation unit.  Growth caused by
11485               inlining of units larger than this limit is limited by --param
11486               inline-unit-growth.  For small units this might be too tight.
11487               For example, consider a unit consisting of function A that is
11488               inline and B that just calls A three times.  If B is small
11489               relative to A, the growth of unit is 300\% and yet such
11490               inlining is very sane.  For very large units consisting of
11491               small inlineable functions, however, the overall unit growth
11492               limit is needed to avoid exponential explosion of code size.
11493               Thus for smaller units, the size is increased to --param large-
11494               unit-insns before applying --param inline-unit-growth.
11495
11496           lazy-modules
11497               Maximum number of concurrently open C++ module files when lazy
11498               loading.
11499
11500           inline-unit-growth
11501               Specifies maximal overall growth of the compilation unit caused
11502               by inlining.  For example, parameter value 20 limits unit
11503               growth to 1.2 times the original size. Cold functions (either
11504               marked cold via an attribute or by profile feedback) are not
11505               accounted into the unit size.
11506
11507           ipa-cp-unit-growth
11508               Specifies maximal overall growth of the compilation unit caused
11509               by interprocedural constant propagation.  For example,
11510               parameter value 10 limits unit growth to 1.1 times the original
11511               size.
11512
11513           ipa-cp-large-unit-insns
11514               The size of translation unit that IPA-CP pass considers large.
11515
11516           large-stack-frame
11517               The limit specifying large stack frames.  While inlining the
11518               algorithm is trying to not grow past this limit too much.
11519
11520           large-stack-frame-growth
11521               Specifies maximal growth of large stack frames caused by
11522               inlining in percents.  For example, parameter value 1000 limits
11523               large stack frame growth to 11 times the original size.
11524
11525           max-inline-insns-recursive
11526           max-inline-insns-recursive-auto
11527               Specifies the maximum number of instructions an out-of-line
11528               copy of a self-recursive inline function can grow into by
11529               performing recursive inlining.
11530
11531               --param max-inline-insns-recursive applies to functions
11532               declared inline.  For functions not declared inline, recursive
11533               inlining happens only when -finline-functions (included in -O3)
11534               is enabled; --param max-inline-insns-recursive-auto applies
11535               instead.
11536
11537           max-inline-recursive-depth
11538           max-inline-recursive-depth-auto
11539               Specifies the maximum recursion depth used for recursive
11540               inlining.
11541
11542               --param max-inline-recursive-depth applies to functions
11543               declared inline.  For functions not declared inline, recursive
11544               inlining happens only when -finline-functions (included in -O3)
11545               is enabled; --param max-inline-recursive-depth-auto applies
11546               instead.
11547
11548           min-inline-recursive-probability
11549               Recursive inlining is profitable only for function having deep
11550               recursion in average and can hurt for function having little
11551               recursion depth by increasing the prologue size or complexity
11552               of function body to other optimizers.
11553
11554               When profile feedback is available (see -fprofile-generate) the
11555               actual recursion depth can be guessed from the probability that
11556               function recurses via a given call expression.  This parameter
11557               limits inlining only to call expressions whose probability
11558               exceeds the given threshold (in percents).
11559
11560           early-inlining-insns
11561               Specify growth that the early inliner can make.  In effect it
11562               increases the amount of inlining for code having a large
11563               abstraction penalty.
11564
11565           max-early-inliner-iterations
11566               Limit of iterations of the early inliner.  This basically
11567               bounds the number of nested indirect calls the early inliner
11568               can resolve.  Deeper chains are still handled by late inlining.
11569
11570           comdat-sharing-probability
11571               Probability (in percent) that C++ inline function with comdat
11572               visibility are shared across multiple compilation units.
11573
11574           modref-max-bases
11575           modref-max-refs
11576           modref-max-accesses
11577               Specifies the maximal number of base pointers, references and
11578               accesses stored for a single function by mod/ref analysis.
11579
11580           modref-max-tests
11581               Specifies the maxmal number of tests alias oracle can perform
11582               to disambiguate memory locations using the mod/ref information.
11583               This parameter ought to be bigger than --param modref-max-bases
11584               and --param modref-max-refs.
11585
11586           modref-max-depth
11587               Specifies the maximum depth of DFS walk used by modref escape
11588               analysis.  Setting to 0 disables the analysis completely.
11589
11590           modref-max-escape-points
11591               Specifies the maximum number of escape points tracked by modref
11592               per SSA-name.
11593
11594           modref-max-adjustments
11595               Specifies the maximum number the access range is enlarged
11596               during modref dataflow analysis.
11597
11598           profile-func-internal-id
11599               A parameter to control whether to use function internal id in
11600               profile database lookup. If the value is 0, the compiler uses
11601               an id that is based on function assembler name and filename,
11602               which makes old profile data more tolerant to source changes
11603               such as function reordering etc.
11604
11605           min-vect-loop-bound
11606               The minimum number of iterations under which loops are not
11607               vectorized when -ftree-vectorize is used.  The number of
11608               iterations after vectorization needs to be greater than the
11609               value specified by this option to allow vectorization.
11610
11611           gcse-cost-distance-ratio
11612               Scaling factor in calculation of maximum distance an expression
11613               can be moved by GCSE optimizations.  This is currently
11614               supported only in the code hoisting pass.  The bigger the
11615               ratio, the more aggressive code hoisting is with simple
11616               expressions, i.e., the expressions that have cost less than
11617               gcse-unrestricted-cost.  Specifying 0 disables hoisting of
11618               simple expressions.
11619
11620           gcse-unrestricted-cost
11621               Cost, roughly measured as the cost of a single typical machine
11622               instruction, at which GCSE optimizations do not constrain the
11623               distance an expression can travel.  This is currently supported
11624               only in the code hoisting pass.  The lesser the cost, the more
11625               aggressive code hoisting is.  Specifying 0 allows all
11626               expressions to travel unrestricted distances.
11627
11628           max-hoist-depth
11629               The depth of search in the dominator tree for expressions to
11630               hoist.  This is used to avoid quadratic behavior in hoisting
11631               algorithm.  The value of 0 does not limit on the search, but
11632               may slow down compilation of huge functions.
11633
11634           max-tail-merge-comparisons
11635               The maximum amount of similar bbs to compare a bb with.  This
11636               is used to avoid quadratic behavior in tree tail merging.
11637
11638           max-tail-merge-iterations
11639               The maximum amount of iterations of the pass over the function.
11640               This is used to limit compilation time in tree tail merging.
11641
11642           store-merging-allow-unaligned
11643               Allow the store merging pass to introduce unaligned stores if
11644               it is legal to do so.
11645
11646           max-stores-to-merge
11647               The maximum number of stores to attempt to merge into wider
11648               stores in the store merging pass.
11649
11650           max-store-chains-to-track
11651               The maximum number of store chains to track at the same time in
11652               the attempt to merge them into wider stores in the store
11653               merging pass.
11654
11655           max-stores-to-track
11656               The maximum number of stores to track at the same time in the
11657               attemt to to merge them into wider stores in the store merging
11658               pass.
11659
11660           max-unrolled-insns
11661               The maximum number of instructions that a loop may have to be
11662               unrolled.  If a loop is unrolled, this parameter also
11663               determines how many times the loop code is unrolled.
11664
11665           max-average-unrolled-insns
11666               The maximum number of instructions biased by probabilities of
11667               their execution that a loop may have to be unrolled.  If a loop
11668               is unrolled, this parameter also determines how many times the
11669               loop code is unrolled.
11670
11671           max-unroll-times
11672               The maximum number of unrollings of a single loop.
11673
11674           max-peeled-insns
11675               The maximum number of instructions that a loop may have to be
11676               peeled.  If a loop is peeled, this parameter also determines
11677               how many times the loop code is peeled.
11678
11679           max-peel-times
11680               The maximum number of peelings of a single loop.
11681
11682           max-peel-branches
11683               The maximum number of branches on the hot path through the
11684               peeled sequence.
11685
11686           max-completely-peeled-insns
11687               The maximum number of insns of a completely peeled loop.
11688
11689           max-completely-peel-times
11690               The maximum number of iterations of a loop to be suitable for
11691               complete peeling.
11692
11693           max-completely-peel-loop-nest-depth
11694               The maximum depth of a loop nest suitable for complete peeling.
11695
11696           max-unswitch-insns
11697               The maximum number of insns of an unswitched loop.
11698
11699           max-unswitch-level
11700               The maximum number of branches unswitched in a single loop.
11701
11702           lim-expensive
11703               The minimum cost of an expensive expression in the loop
11704               invariant motion.
11705
11706           min-loop-cond-split-prob
11707               When FDO profile information is available, min-loop-cond-split-
11708               prob specifies minimum threshold for probability of semi-
11709               invariant condition statement to trigger loop split.
11710
11711           iv-consider-all-candidates-bound
11712               Bound on number of candidates for induction variables, below
11713               which all candidates are considered for each use in induction
11714               variable optimizations.  If there are more candidates than
11715               this, only the most relevant ones are considered to avoid
11716               quadratic time complexity.
11717
11718           iv-max-considered-uses
11719               The induction variable optimizations give up on loops that
11720               contain more induction variable uses.
11721
11722           iv-always-prune-cand-set-bound
11723               If the number of candidates in the set is smaller than this
11724               value, always try to remove unnecessary ivs from the set when
11725               adding a new one.
11726
11727           avg-loop-niter
11728               Average number of iterations of a loop.
11729
11730           dse-max-object-size
11731               Maximum size (in bytes) of objects tracked bytewise by dead
11732               store elimination.  Larger values may result in larger
11733               compilation times.
11734
11735           dse-max-alias-queries-per-store
11736               Maximum number of queries into the alias oracle per store.
11737               Larger values result in larger compilation times and may result
11738               in more removed dead stores.
11739
11740           scev-max-expr-size
11741               Bound on size of expressions used in the scalar evolutions
11742               analyzer.  Large expressions slow the analyzer.
11743
11744           scev-max-expr-complexity
11745               Bound on the complexity of the expressions in the scalar
11746               evolutions analyzer.  Complex expressions slow the analyzer.
11747
11748           max-tree-if-conversion-phi-args
11749               Maximum number of arguments in a PHI supported by TREE if
11750               conversion unless the loop is marked with simd pragma.
11751
11752           vect-max-version-for-alignment-checks
11753               The maximum number of run-time checks that can be performed
11754               when doing loop versioning for alignment in the vectorizer.
11755
11756           vect-max-version-for-alias-checks
11757               The maximum number of run-time checks that can be performed
11758               when doing loop versioning for alias in the vectorizer.
11759
11760           vect-max-peeling-for-alignment
11761               The maximum number of loop peels to enhance access alignment
11762               for vectorizer. Value -1 means no limit.
11763
11764           max-iterations-to-track
11765               The maximum number of iterations of a loop the brute-force
11766               algorithm for analysis of the number of iterations of the loop
11767               tries to evaluate.
11768
11769           hot-bb-count-fraction
11770               The denominator n of fraction 1/n of the maximal execution
11771               count of a basic block in the entire program that a basic block
11772               needs to at least have in order to be considered hot.  The
11773               default is 10000, which means that a basic block is considered
11774               hot if its execution count is greater than 1/10000 of the
11775               maximal execution count.  0 means that it is never considered
11776               hot.  Used in non-LTO mode.
11777
11778           hot-bb-count-ws-permille
11779               The number of most executed permilles, ranging from 0 to 1000,
11780               of the profiled execution of the entire program to which the
11781               execution count of a basic block must be part of in order to be
11782               considered hot.  The default is 990, which means that a basic
11783               block is considered hot if its execution count contributes to
11784               the upper 990 permilles, or 99.0%, of the profiled execution of
11785               the entire program.  0 means that it is never considered hot.
11786               Used in LTO mode.
11787
11788           hot-bb-frequency-fraction
11789               The denominator n of fraction 1/n of the execution frequency of
11790               the entry block of a function that a basic block of this
11791               function needs to at least have in order to be considered hot.
11792               The default is 1000, which means that a basic block is
11793               considered hot in a function if it is executed more frequently
11794               than 1/1000 of the frequency of the entry block of the
11795               function.  0 means that it is never considered hot.
11796
11797           unlikely-bb-count-fraction
11798               The denominator n of fraction 1/n of the number of profiled
11799               runs of the entire program below which the execution count of a
11800               basic block must be in order for the basic block to be
11801               considered unlikely executed.  The default is 20, which means
11802               that a basic block is considered unlikely executed if it is
11803               executed in fewer than 1/20, or 5%, of the runs of the program.
11804               0 means that it is always considered unlikely executed.
11805
11806           max-predicted-iterations
11807               The maximum number of loop iterations we predict statically.
11808               This is useful in cases where a function contains a single loop
11809               with known bound and another loop with unknown bound.  The
11810               known number of iterations is predicted correctly, while the
11811               unknown number of iterations average to roughly 10.  This means
11812               that the loop without bounds appears artificially cold relative
11813               to the other one.
11814
11815           builtin-expect-probability
11816               Control the probability of the expression having the specified
11817               value. This parameter takes a percentage (i.e. 0 ... 100) as
11818               input.
11819
11820           builtin-string-cmp-inline-length
11821               The maximum length of a constant string for a builtin string
11822               cmp call eligible for inlining.
11823
11824           align-threshold
11825               Select fraction of the maximal frequency of executions of a
11826               basic block in a function to align the basic block.
11827
11828           align-loop-iterations
11829               A loop expected to iterate at least the selected number of
11830               iterations is aligned.
11831
11832           tracer-dynamic-coverage
11833           tracer-dynamic-coverage-feedback
11834               This value is used to limit superblock formation once the given
11835               percentage of executed instructions is covered.  This limits
11836               unnecessary code size expansion.
11837
11838               The tracer-dynamic-coverage-feedback parameter is used only
11839               when profile feedback is available.  The real profiles (as
11840               opposed to statically estimated ones) are much less balanced
11841               allowing the threshold to be larger value.
11842
11843           tracer-max-code-growth
11844               Stop tail duplication once code growth has reached given
11845               percentage.  This is a rather artificial limit, as most of the
11846               duplicates are eliminated later in cross jumping, so it may be
11847               set to much higher values than is the desired code growth.
11848
11849           tracer-min-branch-ratio
11850               Stop reverse growth when the reverse probability of best edge
11851               is less than this threshold (in percent).
11852
11853           tracer-min-branch-probability
11854           tracer-min-branch-probability-feedback
11855               Stop forward growth if the best edge has probability lower than
11856               this threshold.
11857
11858               Similarly to tracer-dynamic-coverage two parameters are
11859               provided.  tracer-min-branch-probability-feedback is used for
11860               compilation with profile feedback and tracer-min-branch-
11861               probability compilation without.  The value for compilation
11862               with profile feedback needs to be more conservative (higher) in
11863               order to make tracer effective.
11864
11865           stack-clash-protection-guard-size
11866               Specify the size of the operating system provided stack guard
11867               as 2 raised to num bytes.  Higher values may reduce the number
11868               of explicit probes, but a value larger than the operating
11869               system provided guard will leave code vulnerable to stack clash
11870               style attacks.
11871
11872           stack-clash-protection-probe-interval
11873               Stack clash protection involves probing stack space as it is
11874               allocated.  This param controls the maximum distance between
11875               probes into the stack as 2 raised to num bytes.  Higher values
11876               may reduce the number of explicit probes, but a value larger
11877               than the operating system provided guard will leave code
11878               vulnerable to stack clash style attacks.
11879
11880           max-cse-path-length
11881               The maximum number of basic blocks on path that CSE considers.
11882
11883           max-cse-insns
11884               The maximum number of instructions CSE processes before
11885               flushing.
11886
11887           ggc-min-expand
11888               GCC uses a garbage collector to manage its own memory
11889               allocation.  This parameter specifies the minimum percentage by
11890               which the garbage collector's heap should be allowed to expand
11891               between collections.  Tuning this may improve compilation
11892               speed; it has no effect on code generation.
11893
11894               The default is 30% + 70% * (RAM/1GB) with an upper bound of
11895               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
11896               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
11897               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
11898               particular platform, the lower bound of 30% is used.  Setting
11899               this parameter and ggc-min-heapsize to zero causes a full
11900               collection to occur at every opportunity.  This is extremely
11901               slow, but can be useful for debugging.
11902
11903           ggc-min-heapsize
11904               Minimum size of the garbage collector's heap before it begins
11905               bothering to collect garbage.  The first collection occurs
11906               after the heap expands by ggc-min-expand% beyond ggc-min-
11907               heapsize.  Again, tuning this may improve compilation speed,
11908               and has no effect on code generation.
11909
11910               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
11911               that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
11912               exceeded, but with a lower bound of 4096 (four megabytes) and
11913               an upper bound of 131072 (128 megabytes).  If GCC is not able
11914               to calculate RAM on a particular platform, the lower bound is
11915               used.  Setting this parameter very large effectively disables
11916               garbage collection.  Setting this parameter and ggc-min-expand
11917               to zero causes a full collection to occur at every opportunity.
11918
11919           max-reload-search-insns
11920               The maximum number of instruction reload should look backward
11921               for equivalent register.  Increasing values mean more
11922               aggressive optimization, making the compilation time increase
11923               with probably slightly better performance.
11924
11925           max-cselib-memory-locations
11926               The maximum number of memory locations cselib should take into
11927               account.  Increasing values mean more aggressive optimization,
11928               making the compilation time increase with probably slightly
11929               better performance.
11930
11931           max-sched-ready-insns
11932               The maximum number of instructions ready to be issued the
11933               scheduler should consider at any given time during the first
11934               scheduling pass.  Increasing values mean more thorough
11935               searches, making the compilation time increase with probably
11936               little benefit.
11937
11938           max-sched-region-blocks
11939               The maximum number of blocks in a region to be considered for
11940               interblock scheduling.
11941
11942           max-pipeline-region-blocks
11943               The maximum number of blocks in a region to be considered for
11944               pipelining in the selective scheduler.
11945
11946           max-sched-region-insns
11947               The maximum number of insns in a region to be considered for
11948               interblock scheduling.
11949
11950           max-pipeline-region-insns
11951               The maximum number of insns in a region to be considered for
11952               pipelining in the selective scheduler.
11953
11954           min-spec-prob
11955               The minimum probability (in percents) of reaching a source
11956               block for interblock speculative scheduling.
11957
11958           max-sched-extend-regions-iters
11959               The maximum number of iterations through CFG to extend regions.
11960               A value of 0 disables region extensions.
11961
11962           max-sched-insn-conflict-delay
11963               The maximum conflict delay for an insn to be considered for
11964               speculative motion.
11965
11966           sched-spec-prob-cutoff
11967               The minimal probability of speculation success (in percents),
11968               so that speculative insns are scheduled.
11969
11970           sched-state-edge-prob-cutoff
11971               The minimum probability an edge must have for the scheduler to
11972               save its state across it.
11973
11974           sched-mem-true-dep-cost
11975               Minimal distance (in CPU cycles) between store and load
11976               targeting same memory locations.
11977
11978           selsched-max-lookahead
11979               The maximum size of the lookahead window of selective
11980               scheduling.  It is a depth of search for available
11981               instructions.
11982
11983           selsched-max-sched-times
11984               The maximum number of times that an instruction is scheduled
11985               during selective scheduling.  This is the limit on the number
11986               of iterations through which the instruction may be pipelined.
11987
11988           selsched-insns-to-rename
11989               The maximum number of best instructions in the ready list that
11990               are considered for renaming in the selective scheduler.
11991
11992           sms-min-sc
11993               The minimum value of stage count that swing modulo scheduler
11994               generates.
11995
11996           max-last-value-rtl
11997               The maximum size measured as number of RTLs that can be
11998               recorded in an expression in combiner for a pseudo register as
11999               last known value of that register.
12000
12001           max-combine-insns
12002               The maximum number of instructions the RTL combiner tries to
12003               combine.
12004
12005           integer-share-limit
12006               Small integer constants can use a shared data structure,
12007               reducing the compiler's memory usage and increasing its speed.
12008               This sets the maximum value of a shared integer constant.
12009
12010           ssp-buffer-size
12011               The minimum size of buffers (i.e. arrays) that receive stack
12012               smashing protection when -fstack-protector is used.
12013
12014           min-size-for-stack-sharing
12015               The minimum size of variables taking part in stack slot sharing
12016               when not optimizing.
12017
12018           max-jump-thread-duplication-stmts
12019               Maximum number of statements allowed in a block that needs to
12020               be duplicated when threading jumps.
12021
12022           max-fields-for-field-sensitive
12023               Maximum number of fields in a structure treated in a field
12024               sensitive manner during pointer analysis.
12025
12026           prefetch-latency
12027               Estimate on average number of instructions that are executed
12028               before prefetch finishes.  The distance prefetched ahead is
12029               proportional to this constant.  Increasing this number may also
12030               lead to less streams being prefetched (see simultaneous-
12031               prefetches).
12032
12033           simultaneous-prefetches
12034               Maximum number of prefetches that can run at the same time.
12035
12036           l1-cache-line-size
12037               The size of cache line in L1 data cache, in bytes.
12038
12039           l1-cache-size
12040               The size of L1 data cache, in kilobytes.
12041
12042           l2-cache-size
12043               The size of L2 data cache, in kilobytes.
12044
12045           prefetch-dynamic-strides
12046               Whether the loop array prefetch pass should issue software
12047               prefetch hints for strides that are non-constant.  In some
12048               cases this may be beneficial, though the fact the stride is
12049               non-constant may make it hard to predict when there is clear
12050               benefit to issuing these hints.
12051
12052               Set to 1 if the prefetch hints should be issued for non-
12053               constant strides.  Set to 0 if prefetch hints should be issued
12054               only for strides that are known to be constant and below
12055               prefetch-minimum-stride.
12056
12057           prefetch-minimum-stride
12058               Minimum constant stride, in bytes, to start using prefetch
12059               hints for.  If the stride is less than this threshold, prefetch
12060               hints will not be issued.
12061
12062               This setting is useful for processors that have hardware
12063               prefetchers, in which case there may be conflicts between the
12064               hardware prefetchers and the software prefetchers.  If the
12065               hardware prefetchers have a maximum stride they can handle, it
12066               should be used here to improve the use of software prefetchers.
12067
12068               A value of -1 means we don't have a threshold and therefore
12069               prefetch hints can be issued for any constant stride.
12070
12071               This setting is only useful for strides that are known and
12072               constant.
12073
12074           destructive-interference-size
12075           constructive-interference-size
12076               The values for the C++17 variables
12077               "std::hardware_destructive_interference_size" and
12078               "std::hardware_constructive_interference_size".  The
12079               destructive interference size is the minimum recommended offset
12080               between two independent concurrently-accessed objects; the
12081               constructive interference size is the maximum recommended size
12082               of contiguous memory accessed together.  Typically both will be
12083               the size of an L1 cache line for the target, in bytes.  For a
12084               generic target covering a range of L1 cache line sizes,
12085               typically the constructive interference size will be the small
12086               end of the range and the destructive size will be the large
12087               end.
12088
12089               The destructive interference size is intended to be used for
12090               layout, and thus has ABI impact.  The default value is not
12091               expected to be stable, and on some targets varies with -mtune,
12092               so use of this variable in a context where ABI stability is
12093               important, such as the public interface of a library, is
12094               strongly discouraged; if it is used in that context, users can
12095               stabilize the value using this option.
12096
12097               The constructive interference size is less sensitive, as it is
12098               typically only used in a static_assert to make sure that a type
12099               fits within a cache line.
12100
12101               See also -Winterference-size.
12102
12103           loop-interchange-max-num-stmts
12104               The maximum number of stmts in a loop to be interchanged.
12105
12106           loop-interchange-stride-ratio
12107               The minimum ratio between stride of two loops for interchange
12108               to be profitable.
12109
12110           min-insn-to-prefetch-ratio
12111               The minimum ratio between the number of instructions and the
12112               number of prefetches to enable prefetching in a loop.
12113
12114           prefetch-min-insn-to-mem-ratio
12115               The minimum ratio between the number of instructions and the
12116               number of memory references to enable prefetching in a loop.
12117
12118           use-canonical-types
12119               Whether the compiler should use the "canonical" type system.
12120               Should always be 1, which uses a more efficient internal
12121               mechanism for comparing types in C++ and Objective-C++.
12122               However, if bugs in the canonical type system are causing
12123               compilation failures, set this value to 0 to disable canonical
12124               types.
12125
12126           switch-conversion-max-branch-ratio
12127               Switch initialization conversion refuses to create arrays that
12128               are bigger than switch-conversion-max-branch-ratio times the
12129               number of branches in the switch.
12130
12131           max-partial-antic-length
12132               Maximum length of the partial antic set computed during the
12133               tree partial redundancy elimination optimization (-ftree-pre)
12134               when optimizing at -O3 and above.  For some sorts of source
12135               code the enhanced partial redundancy elimination optimization
12136               can run away, consuming all of the memory available on the host
12137               machine.  This parameter sets a limit on the length of the sets
12138               that are computed, which prevents the runaway behavior.
12139               Setting a value of 0 for this parameter allows an unlimited set
12140               length.
12141
12142           rpo-vn-max-loop-depth
12143               Maximum loop depth that is value-numbered optimistically.  When
12144               the limit hits the innermost rpo-vn-max-loop-depth loops and
12145               the outermost loop in the loop nest are value-numbered
12146               optimistically and the remaining ones not.
12147
12148           sccvn-max-alias-queries-per-access
12149               Maximum number of alias-oracle queries we perform when looking
12150               for redundancies for loads and stores.  If this limit is hit
12151               the search is aborted and the load or store is not considered
12152               redundant.  The number of queries is algorithmically limited to
12153               the number of stores on all paths from the load to the function
12154               entry.
12155
12156           ira-max-loops-num
12157               IRA uses regional register allocation by default.  If a
12158               function contains more loops than the number given by this
12159               parameter, only at most the given number of the most
12160               frequently-executed loops form regions for regional register
12161               allocation.
12162
12163           ira-max-conflict-table-size
12164               Although IRA uses a sophisticated algorithm to compress the
12165               conflict table, the table can still require excessive amounts
12166               of memory for huge functions.  If the conflict table for a
12167               function could be more than the size in MB given by this
12168               parameter, the register allocator instead uses a faster,
12169               simpler, and lower-quality algorithm that does not require
12170               building a pseudo-register conflict table.
12171
12172           ira-loop-reserved-regs
12173               IRA can be used to evaluate more accurate register pressure in
12174               loops for decisions to move loop invariants (see -O3).  The
12175               number of available registers reserved for some other purposes
12176               is given by this parameter.  Default of the parameter is the
12177               best found from numerous experiments.
12178
12179           ira-consider-dup-in-all-alts
12180               Make IRA to consider matching constraint (duplicated operand
12181               number) heavily in all available alternatives for preferred
12182               register class.  If it is set as zero, it means IRA only
12183               respects the matching constraint when it's in the only
12184               available alternative with an appropriate register class.
12185               Otherwise, it means IRA will check all available alternatives
12186               for preferred register class even if it has found some choice
12187               with an appropriate register class and respect the found
12188               qualified matching constraint.
12189
12190           lra-inheritance-ebb-probability-cutoff
12191               LRA tries to reuse values reloaded in registers in subsequent
12192               insns.  This optimization is called inheritance.  EBB is used
12193               as a region to do this optimization.  The parameter defines a
12194               minimal fall-through edge probability in percentage used to add
12195               BB to inheritance EBB in LRA.  The default value was chosen
12196               from numerous runs of SPEC2000 on x86-64.
12197
12198           loop-invariant-max-bbs-in-loop
12199               Loop invariant motion can be very expensive, both in
12200               compilation time and in amount of needed compile-time memory,
12201               with very large loops.  Loops with more basic blocks than this
12202               parameter won't have loop invariant motion optimization
12203               performed on them.
12204
12205           loop-max-datarefs-for-datadeps
12206               Building data dependencies is expensive for very large loops.
12207               This parameter limits the number of data references in loops
12208               that are considered for data dependence analysis.  These large
12209               loops are no handled by the optimizations using loop data
12210               dependencies.
12211
12212           max-vartrack-size
12213               Sets a maximum number of hash table slots to use during
12214               variable tracking dataflow analysis of any function.  If this
12215               limit is exceeded with variable tracking at assignments
12216               enabled, analysis for that function is retried without it,
12217               after removing all debug insns from the function.  If the limit
12218               is exceeded even without debug insns, var tracking analysis is
12219               completely disabled for the function.  Setting the parameter to
12220               zero makes it unlimited.
12221
12222           max-vartrack-expr-depth
12223               Sets a maximum number of recursion levels when attempting to
12224               map variable names or debug temporaries to value expressions.
12225               This trades compilation time for more complete debug
12226               information.  If this is set too low, value expressions that
12227               are available and could be represented in debug information may
12228               end up not being used; setting this higher may enable the
12229               compiler to find more complex debug expressions, but compile
12230               time and memory use may grow.
12231
12232           max-debug-marker-count
12233               Sets a threshold on the number of debug markers (e.g. begin
12234               stmt markers) to avoid complexity explosion at inlining or
12235               expanding to RTL.  If a function has more such gimple stmts
12236               than the set limit, such stmts will be dropped from the inlined
12237               copy of a function, and from its RTL expansion.
12238
12239           min-nondebug-insn-uid
12240               Use uids starting at this parameter for nondebug insns.  The
12241               range below the parameter is reserved exclusively for debug
12242               insns created by -fvar-tracking-assignments, but debug insns
12243               may get (non-overlapping) uids above it if the reserved range
12244               is exhausted.
12245
12246           ipa-sra-ptr-growth-factor
12247               IPA-SRA replaces a pointer to an aggregate with one or more new
12248               parameters only when their cumulative size is less or equal to
12249               ipa-sra-ptr-growth-factor times the size of the original
12250               pointer parameter.
12251
12252           ipa-sra-max-replacements
12253               Maximum pieces of an aggregate that IPA-SRA tracks.  As a
12254               consequence, it is also the maximum number of replacements of a
12255               formal parameter.
12256
12257           sra-max-scalarization-size-Ospeed
12258           sra-max-scalarization-size-Osize
12259               The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA)
12260               aim to replace scalar parts of aggregates with uses of
12261               independent scalar variables.  These parameters control the
12262               maximum size, in storage units, of aggregate which is
12263               considered for replacement when compiling for speed (sra-max-
12264               scalarization-size-Ospeed) or size (sra-max-scalarization-size-
12265               Osize) respectively.
12266
12267           sra-max-propagations
12268               The maximum number of artificial accesses that Scalar
12269               Replacement of Aggregates (SRA) will track, per one local
12270               variable, in order to facilitate copy propagation.
12271
12272           tm-max-aggregate-size
12273               When making copies of thread-local variables in a transaction,
12274               this parameter specifies the size in bytes after which
12275               variables are saved with the logging functions as opposed to
12276               save/restore code sequence pairs.  This option only applies
12277               when using -fgnu-tm.
12278
12279           graphite-max-nb-scop-params
12280               To avoid exponential effects in the Graphite loop transforms,
12281               the number of parameters in a Static Control Part (SCoP) is
12282               bounded.  A value of zero can be used to lift the bound.  A
12283               variable whose value is unknown at compilation time and defined
12284               outside a SCoP is a parameter of the SCoP.
12285
12286           loop-block-tile-size
12287               Loop blocking or strip mining transforms, enabled with
12288               -floop-block or -floop-strip-mine, strip mine each loop in the
12289               loop nest by a given number of iterations.  The strip length
12290               can be changed using the loop-block-tile-size parameter.
12291
12292           ipa-jump-function-lookups
12293               Specifies number of statements visited during jump function
12294               offset discovery.
12295
12296           ipa-cp-value-list-size
12297               IPA-CP attempts to track all possible values and types passed
12298               to a function's parameter in order to propagate them and
12299               perform devirtualization.  ipa-cp-value-list-size is the
12300               maximum number of values and types it stores per one formal
12301               parameter of a function.
12302
12303           ipa-cp-eval-threshold
12304               IPA-CP calculates its own score of cloning profitability
12305               heuristics and performs those cloning opportunities with scores
12306               that exceed ipa-cp-eval-threshold.
12307
12308           ipa-cp-max-recursive-depth
12309               Maximum depth of recursive cloning for self-recursive function.
12310
12311           ipa-cp-min-recursive-probability
12312               Recursive cloning only when the probability of call being
12313               executed exceeds the parameter.
12314
12315           ipa-cp-profile-count-base
12316               When using -fprofile-use option, IPA-CP will consider the
12317               measured execution count of a call graph edge at this
12318               percentage position in their histogram as the basis for its
12319               heuristics calculation.
12320
12321           ipa-cp-recursive-freq-factor
12322               The number of times interprocedural copy propagation expects
12323               recursive functions to call themselves.
12324
12325           ipa-cp-recursion-penalty
12326               Percentage penalty the recursive functions will receive when
12327               they are evaluated for cloning.
12328
12329           ipa-cp-single-call-penalty
12330               Percentage penalty functions containing a single call to
12331               another function will receive when they are evaluated for
12332               cloning.
12333
12334           ipa-max-agg-items
12335               IPA-CP is also capable to propagate a number of scalar values
12336               passed in an aggregate. ipa-max-agg-items controls the maximum
12337               number of such values per one parameter.
12338
12339           ipa-cp-loop-hint-bonus
12340               When IPA-CP determines that a cloning candidate would make the
12341               number of iterations of a loop known, it adds a bonus of ipa-
12342               cp-loop-hint-bonus to the profitability score of the candidate.
12343
12344           ipa-max-loop-predicates
12345               The maximum number of different predicates IPA will use to
12346               describe when loops in a function have known properties.
12347
12348           ipa-max-aa-steps
12349               During its analysis of function bodies, IPA-CP employs alias
12350               analysis in order to track values pointed to by function
12351               parameters.  In order not spend too much time analyzing huge
12352               functions, it gives up and consider all memory clobbered after
12353               examining ipa-max-aa-steps statements modifying memory.
12354
12355           ipa-max-switch-predicate-bounds
12356               Maximal number of boundary endpoints of case ranges of switch
12357               statement.  For switch exceeding this limit, IPA-CP will not
12358               construct cloning cost predicate, which is used to estimate
12359               cloning benefit, for default case of the switch statement.
12360
12361           ipa-max-param-expr-ops
12362               IPA-CP will analyze conditional statement that references some
12363               function parameter to estimate benefit for cloning upon certain
12364               constant value.  But if number of operations in a parameter
12365               expression exceeds ipa-max-param-expr-ops, the expression is
12366               treated as complicated one, and is not handled by IPA analysis.
12367
12368           lto-partitions
12369               Specify desired number of partitions produced during WHOPR
12370               compilation.  The number of partitions should exceed the number
12371               of CPUs used for compilation.
12372
12373           lto-min-partition
12374               Size of minimal partition for WHOPR (in estimated
12375               instructions).  This prevents expenses of splitting very small
12376               programs into too many partitions.
12377
12378           lto-max-partition
12379               Size of max partition for WHOPR (in estimated instructions).
12380               to provide an upper bound for individual size of partition.
12381               Meant to be used only with balanced partitioning.
12382
12383           lto-max-streaming-parallelism
12384               Maximal number of parallel processes used for LTO streaming.
12385
12386           cxx-max-namespaces-for-diagnostic-help
12387               The maximum number of namespaces to consult for suggestions
12388               when C++ name lookup fails for an identifier.
12389
12390           sink-frequency-threshold
12391               The maximum relative execution frequency (in percents) of the
12392               target block relative to a statement's original block to allow
12393               statement sinking of a statement.  Larger numbers result in
12394               more aggressive statement sinking.  A small positive adjustment
12395               is applied for statements with memory operands as those are
12396               even more profitable so sink.
12397
12398           max-stores-to-sink
12399               The maximum number of conditional store pairs that can be sunk.
12400               Set to 0 if either vectorization (-ftree-vectorize) or if-
12401               conversion (-ftree-loop-if-convert) is disabled.
12402
12403           case-values-threshold
12404               The smallest number of different values for which it is best to
12405               use a jump-table instead of a tree of conditional branches.  If
12406               the value is 0, use the default for the machine.
12407
12408           jump-table-max-growth-ratio-for-size
12409               The maximum code size growth ratio when expanding into a jump
12410               table (in percent).  The parameter is used when optimizing for
12411               size.
12412
12413           jump-table-max-growth-ratio-for-speed
12414               The maximum code size growth ratio when expanding into a jump
12415               table (in percent).  The parameter is used when optimizing for
12416               speed.
12417
12418           tree-reassoc-width
12419               Set the maximum number of instructions executed in parallel in
12420               reassociated tree. This parameter overrides target dependent
12421               heuristics used by default if has non zero value.
12422
12423           sched-pressure-algorithm
12424               Choose between the two available implementations of
12425               -fsched-pressure.  Algorithm 1 is the original implementation
12426               and is the more likely to prevent instructions from being
12427               reordered.  Algorithm 2 was designed to be a compromise between
12428               the relatively conservative approach taken by algorithm 1 and
12429               the rather aggressive approach taken by the default scheduler.
12430               It relies more heavily on having a regular register file and
12431               accurate register pressure classes.  See haifa-sched.cc in the
12432               GCC sources for more details.
12433
12434               The default choice depends on the target.
12435
12436           max-slsr-cand-scan
12437               Set the maximum number of existing candidates that are
12438               considered when seeking a basis for a new straight-line
12439               strength reduction candidate.
12440
12441           asan-globals
12442               Enable buffer overflow detection for global objects.  This kind
12443               of protection is enabled by default if you are using
12444               -fsanitize=address option.  To disable global objects
12445               protection use --param asan-globals=0.
12446
12447           asan-stack
12448               Enable buffer overflow detection for stack objects.  This kind
12449               of protection is enabled by default when using
12450               -fsanitize=address.  To disable stack protection use --param
12451               asan-stack=0 option.
12452
12453           asan-instrument-reads
12454               Enable buffer overflow detection for memory reads.  This kind
12455               of protection is enabled by default when using
12456               -fsanitize=address.  To disable memory reads protection use
12457               --param asan-instrument-reads=0.
12458
12459           asan-instrument-writes
12460               Enable buffer overflow detection for memory writes.  This kind
12461               of protection is enabled by default when using
12462               -fsanitize=address.  To disable memory writes protection use
12463               --param asan-instrument-writes=0 option.
12464
12465           asan-memintrin
12466               Enable detection for built-in functions.  This kind of
12467               protection is enabled by default when using -fsanitize=address.
12468               To disable built-in functions protection use --param
12469               asan-memintrin=0.
12470
12471           asan-use-after-return
12472               Enable detection of use-after-return.  This kind of protection
12473               is enabled by default when using the -fsanitize=address option.
12474               To disable it use --param asan-use-after-return=0.
12475
12476               Note: By default the check is disabled at run time.  To enable
12477               it, add "detect_stack_use_after_return=1" to the environment
12478               variable ASAN_OPTIONS.
12479
12480           asan-instrumentation-with-call-threshold
12481               If number of memory accesses in function being instrumented is
12482               greater or equal to this number, use callbacks instead of
12483               inline checks.  E.g. to disable inline code use --param
12484               asan-instrumentation-with-call-threshold=0.
12485
12486           hwasan-instrument-stack
12487               Enable hwasan instrumentation of statically sized stack-
12488               allocated variables.  This kind of instrumentation is enabled
12489               by default when using -fsanitize=hwaddress and disabled by
12490               default when using -fsanitize=kernel-hwaddress.  To disable
12491               stack instrumentation use --param hwasan-instrument-stack=0,
12492               and to enable it use --param hwasan-instrument-stack=1.
12493
12494           hwasan-random-frame-tag
12495               When using stack instrumentation, decide tags for stack
12496               variables using a deterministic sequence beginning at a random
12497               tag for each frame.  With this parameter unset tags are chosen
12498               using the same sequence but beginning from 1.  This is enabled
12499               by default for -fsanitize=hwaddress and unavailable for
12500               -fsanitize=kernel-hwaddress.  To disable it use --param
12501               hwasan-random-frame-tag=0.
12502
12503           hwasan-instrument-allocas
12504               Enable hwasan instrumentation of dynamically sized stack-
12505               allocated variables.  This kind of instrumentation is enabled
12506               by default when using -fsanitize=hwaddress and disabled by
12507               default when using -fsanitize=kernel-hwaddress.  To disable
12508               instrumentation of such variables use --param
12509               hwasan-instrument-allocas=0, and to enable it use --param
12510               hwasan-instrument-allocas=1.
12511
12512           hwasan-instrument-reads
12513               Enable hwasan checks on memory reads.  Instrumentation of reads
12514               is enabled by default for both -fsanitize=hwaddress and
12515               -fsanitize=kernel-hwaddress.  To disable checking memory reads
12516               use --param hwasan-instrument-reads=0.
12517
12518           hwasan-instrument-writes
12519               Enable hwasan checks on memory writes.  Instrumentation of
12520               writes is enabled by default for both -fsanitize=hwaddress and
12521               -fsanitize=kernel-hwaddress.  To disable checking memory writes
12522               use --param hwasan-instrument-writes=0.
12523
12524           hwasan-instrument-mem-intrinsics
12525               Enable hwasan instrumentation of builtin functions.
12526               Instrumentation of these builtin functions is enabled by
12527               default for both -fsanitize=hwaddress and
12528               -fsanitize=kernel-hwaddress.  To disable instrumentation of
12529               builtin functions use --param
12530               hwasan-instrument-mem-intrinsics=0.
12531
12532           use-after-scope-direct-emission-threshold
12533               If the size of a local variable in bytes is smaller or equal to
12534               this number, directly poison (or unpoison) shadow memory
12535               instead of using run-time callbacks.
12536
12537           tsan-distinguish-volatile
12538               Emit special instrumentation for accesses to volatiles.
12539
12540           tsan-instrument-func-entry-exit
12541               Emit instrumentation calls to __tsan_func_entry() and
12542               __tsan_func_exit().
12543
12544           max-fsm-thread-path-insns
12545               Maximum number of instructions to copy when duplicating blocks
12546               on a finite state automaton jump thread path.
12547
12548           max-fsm-thread-length
12549               Maximum number of basic blocks on a jump thread path.
12550
12551           threader-debug
12552               threader-debug=[none|all] Enables verbose dumping of the
12553               threader solver.
12554
12555           parloops-chunk-size
12556               Chunk size of omp schedule for loops parallelized by parloops.
12557
12558           parloops-schedule
12559               Schedule type of omp schedule for loops parallelized by
12560               parloops (static, dynamic, guided, auto, runtime).
12561
12562           parloops-min-per-thread
12563               The minimum number of iterations per thread of an innermost
12564               parallelized loop for which the parallelized variant is
12565               preferred over the single threaded one.  Note that for a
12566               parallelized loop nest the minimum number of iterations of the
12567               outermost loop per thread is two.
12568
12569           max-ssa-name-query-depth
12570               Maximum depth of recursion when querying properties of SSA
12571               names in things like fold routines.  One level of recursion
12572               corresponds to following a use-def chain.
12573
12574           max-speculative-devirt-maydefs
12575               The maximum number of may-defs we analyze when looking for a
12576               must-def specifying the dynamic type of an object that invokes
12577               a virtual call we may be able to devirtualize speculatively.
12578
12579           max-vrp-switch-assertions
12580               The maximum number of assertions to add along the default edge
12581               of a switch statement during VRP.
12582
12583           evrp-sparse-threshold
12584               Maximum number of basic blocks before EVRP uses a sparse cache.
12585
12586           evrp-mode
12587               Specifies the mode Early VRP should operate in.
12588
12589           vrp1-mode
12590               Specifies the mode VRP pass 1 should operate in.
12591
12592           vrp2-mode
12593               Specifies the mode VRP pass 2 should operate in.
12594
12595           ranger-debug
12596               Specifies the type of debug output to be issued for ranges.
12597
12598           evrp-switch-limit
12599               Specifies the maximum number of switch cases before EVRP
12600               ignores a switch.
12601
12602           unroll-jam-min-percent
12603               The minimum percentage of memory references that must be
12604               optimized away for the unroll-and-jam transformation to be
12605               considered profitable.
12606
12607           unroll-jam-max-unroll
12608               The maximum number of times the outer loop should be unrolled
12609               by the unroll-and-jam transformation.
12610
12611           max-rtl-if-conversion-unpredictable-cost
12612               Maximum permissible cost for the sequence that would be
12613               generated by the RTL if-conversion pass for a branch that is
12614               considered unpredictable.
12615
12616           max-variable-expansions-in-unroller
12617               If -fvariable-expansion-in-unroller is used, the maximum number
12618               of times that an individual variable will be expanded during
12619               loop unrolling.
12620
12621           partial-inlining-entry-probability
12622               Maximum probability of the entry BB of split region (in percent
12623               relative to entry BB of the function) to make partial inlining
12624               happen.
12625
12626           max-tracked-strlens
12627               Maximum number of strings for which strlen optimization pass
12628               will track string lengths.
12629
12630           gcse-after-reload-partial-fraction
12631               The threshold ratio for performing partial redundancy
12632               elimination after reload.
12633
12634           gcse-after-reload-critical-fraction
12635               The threshold ratio of critical edges execution count that
12636               permit performing redundancy elimination after reload.
12637
12638           max-loop-header-insns
12639               The maximum number of insns in loop header duplicated by the
12640               copy loop headers pass.
12641
12642           vect-epilogues-nomask
12643               Enable loop epilogue vectorization using smaller vector size.
12644
12645           vect-partial-vector-usage
12646               Controls when the loop vectorizer considers using partial
12647               vector loads and stores as an alternative to falling back to
12648               scalar code.  0 stops the vectorizer from ever using partial
12649               vector loads and stores.  1 allows partial vector loads and
12650               stores if vectorization removes the need for the code to
12651               iterate.  2 allows partial vector loads and stores in all
12652               loops.  The parameter only has an effect on targets that
12653               support partial vector loads and stores.
12654
12655           vect-inner-loop-cost-factor
12656               The maximum factor which the loop vectorizer applies to the
12657               cost of statements in an inner loop relative to the loop being
12658               vectorized.  The factor applied is the maximum of the estimated
12659               number of iterations of the inner loop and this parameter.  The
12660               default value of this parameter is 50.
12661
12662           vect-induction-float
12663               Enable loop vectorization of floating point inductions.
12664
12665           avoid-fma-max-bits
12666               Maximum number of bits for which we avoid creating FMAs.
12667
12668           sms-loop-average-count-threshold
12669               A threshold on the average loop count considered by the swing
12670               modulo scheduler.
12671
12672           sms-dfa-history
12673               The number of cycles the swing modulo scheduler considers when
12674               checking conflicts using DFA.
12675
12676           graphite-allow-codegen-errors
12677               Whether codegen errors should be ICEs when -fchecking.
12678
12679           sms-max-ii-factor
12680               A factor for tuning the upper bound that swing modulo scheduler
12681               uses for scheduling a loop.
12682
12683           lra-max-considered-reload-pseudos
12684               The max number of reload pseudos which are considered during
12685               spilling a non-reload pseudo.
12686
12687           max-pow-sqrt-depth
12688               Maximum depth of sqrt chains to use when synthesizing
12689               exponentiation by a real constant.
12690
12691           max-dse-active-local-stores
12692               Maximum number of active local stores in RTL dead store
12693               elimination.
12694
12695           asan-instrument-allocas
12696               Enable asan allocas/VLAs protection.
12697
12698           max-iterations-computation-cost
12699               Bound on the cost of an expression to compute the number of
12700               iterations.
12701
12702           max-isl-operations
12703               Maximum number of isl operations, 0 means unlimited.
12704
12705           graphite-max-arrays-per-scop
12706               Maximum number of arrays per scop.
12707
12708           max-vartrack-reverse-op-size
12709               Max. size of loc list for which reverse ops should be added.
12710
12711           fsm-scale-path-stmts
12712               Scale factor to apply to the number of statements in a
12713               threading path when comparing to the number of (scaled) blocks.
12714
12715           uninit-control-dep-attempts
12716               Maximum number of nested calls to search for control
12717               dependencies during uninitialized variable analysis.
12718
12719           fsm-scale-path-blocks
12720               Scale factor to apply to the number of blocks in a threading
12721               path when comparing to the number of (scaled) statements.
12722
12723           sched-autopref-queue-depth
12724               Hardware autoprefetcher scheduler model control flag.  Number
12725               of lookahead cycles the model looks into; at ' ' only enable
12726               instruction sorting heuristic.
12727
12728           loop-versioning-max-inner-insns
12729               The maximum number of instructions that an inner loop can have
12730               before the loop versioning pass considers it too big to copy.
12731
12732           loop-versioning-max-outer-insns
12733               The maximum number of instructions that an outer loop can have
12734               before the loop versioning pass considers it too big to copy,
12735               discounting any instructions in inner loops that directly
12736               benefit from versioning.
12737
12738           ssa-name-def-chain-limit
12739               The maximum number of SSA_NAME assignments to follow in
12740               determining a property of a variable such as its value.  This
12741               limits the number of iterations or recursive calls GCC performs
12742               when optimizing certain statements or when determining their
12743               validity prior to issuing diagnostics.
12744
12745           store-merging-max-size
12746               Maximum size of a single store merging region in bytes.
12747
12748           hash-table-verification-limit
12749               The number of elements for which hash table verification is
12750               done for each searched element.
12751
12752           max-find-base-term-values
12753               Maximum number of VALUEs handled during a single find_base_term
12754               call.
12755
12756           analyzer-max-enodes-per-program-point
12757               The maximum number of exploded nodes per program point within
12758               the analyzer, before terminating analysis of that point.
12759
12760           analyzer-max-constraints
12761               The maximum number of constraints per state.
12762
12763           analyzer-min-snodes-for-call-summary
12764               The minimum number of supernodes within a function for the
12765               analyzer to consider summarizing its effects at call sites.
12766
12767           analyzer-max-enodes-for-full-dump
12768               The maximum depth of exploded nodes that should appear in a dot
12769               dump before switching to a less verbose format.
12770
12771           analyzer-max-recursion-depth
12772               The maximum number of times a callsite can appear in a call
12773               stack within the analyzer, before terminating analysis of a
12774               call that would recurse deeper.
12775
12776           analyzer-max-svalue-depth
12777               The maximum depth of a symbolic value, before approximating the
12778               value as unknown.
12779
12780           analyzer-max-infeasible-edges
12781               The maximum number of infeasible edges to reject before
12782               declaring a diagnostic as infeasible.
12783
12784           gimple-fe-computed-hot-bb-threshold
12785               The number of executions of a basic block which is considered
12786               hot.  The parameter is used only in GIMPLE FE.
12787
12788           analyzer-bb-explosion-factor
12789               The maximum number of 'after supernode' exploded nodes within
12790               the analyzer per supernode, before terminating analysis.
12791
12792           ranger-logical-depth
12793               Maximum depth of logical expression evaluation ranger will look
12794               through when evaluating outgoing edge ranges.
12795
12796           relation-block-limit
12797               Maximum number of relations the oracle will register in a basic
12798               block.
12799
12800           min-pagesize
12801               Minimum page size for warning purposes.
12802
12803           openacc-kernels
12804               Specify mode of OpenACC `kernels' constructs handling.  With
12805               --param=openacc-kernels=decompose, OpenACC `kernels' constructs
12806               are decomposed into parts, a sequence of compute constructs,
12807               each then handled individually.  This is work in progress.
12808               With --param=openacc-kernels=parloops, OpenACC `kernels'
12809               constructs are handled by the parloops pass, en bloc.  This is
12810               the current default.
12811
12812           openacc-privatization
12813               Specify mode of OpenACC privatization diagnostics for
12814               -fopt-info-omp-note and applicable -fdump-tree-*-details.  With
12815               --param=openacc-privatization=quiet, don't diagnose.  This is
12816               the current default.  With --param=openacc-privatization=noisy,
12817               do diagnose.
12818
12819           The following choices of name are available on AArch64 targets:
12820
12821           aarch64-sve-compare-costs
12822               When vectorizing for SVE, consider using "unpacked" vectors for
12823               smaller elements and use the cost model to pick the cheapest
12824               approach.  Also use the cost model to choose between SVE and
12825               Advanced SIMD vectorization.
12826
12827               Using unpacked vectors includes storing smaller elements in
12828               larger containers and accessing elements with extending loads
12829               and truncating stores.
12830
12831           aarch64-float-recp-precision
12832               The number of Newton iterations for calculating the reciprocal
12833               for float type.  The precision of division is proportional to
12834               this param when division approximation is enabled.  The default
12835               value is 1.
12836
12837           aarch64-double-recp-precision
12838               The number of Newton iterations for calculating the reciprocal
12839               for double type.  The precision of division is propotional to
12840               this param when division approximation is enabled.  The default
12841               value is 2.
12842
12843           aarch64-autovec-preference
12844               Force an ISA selection strategy for auto-vectorization.
12845               Accepts values from 0 to 4, inclusive.
12846
12847               0   Use the default heuristics.
12848
12849               1   Use only Advanced SIMD for auto-vectorization.
12850
12851               2   Use only SVE for auto-vectorization.
12852
12853               3   Use both Advanced SIMD and SVE.  Prefer Advanced SIMD when
12854                   the costs are deemed equal.
12855
12856               4   Use both Advanced SIMD and SVE.  Prefer SVE when the costs
12857                   are deemed equal.
12858
12859               The default value is 0.
12860
12861           aarch64-loop-vect-issue-rate-niters
12862               The tuning for some AArch64 CPUs tries to take both latencies
12863               and issue rates into account when deciding whether a loop
12864               should be vectorized using SVE, vectorized using Advanced SIMD,
12865               or not vectorized at all.  If this parameter is set to n, GCC
12866               will not use this heuristic for loops that are known to execute
12867               in fewer than n Advanced SIMD iterations.
12868
12869           aarch64-vect-unroll-limit
12870               The vectorizer will use available tuning information to
12871               determine whether it would be beneficial to unroll the main
12872               vectorized loop and by how much.  This parameter set's the
12873               upper bound of how much the vectorizer will unroll the main
12874               loop.  The default value is four.
12875
12876           The following choices of name are available on i386 and x86_64
12877           targets:
12878
12879           x86-stlf-window-ninsns
12880               Instructions number above which STFL stall penalty can be
12881               compensated.
12882
12883   Program Instrumentation Options
12884       GCC supports a number of command-line options that control adding run-
12885       time instrumentation to the code it normally generates.  For example,
12886       one purpose of instrumentation is collect profiling statistics for use
12887       in finding program hot spots, code coverage analysis, or profile-guided
12888       optimizations.  Another class of program instrumentation is adding run-
12889       time checking to detect programming errors like invalid pointer
12890       dereferences or out-of-bounds array accesses, as well as deliberately
12891       hostile attacks such as stack smashing or C++ vtable hijacking.  There
12892       is also a general hook which can be used to implement other forms of
12893       tracing or function-level instrumentation for debug or program analysis
12894       purposes.
12895
12896       -p
12897       -pg Generate extra code to write profile information suitable for the
12898           analysis program prof (for -p) or gprof (for -pg).  You must use
12899           this option when compiling the source files you want data about,
12900           and you must also use it when linking.
12901
12902           You can use the function attribute "no_instrument_function" to
12903           suppress profiling of individual functions when compiling with
12904           these options.
12905
12906       -fprofile-arcs
12907           Add code so that program flow arcs are instrumented.  During
12908           execution the program records how many times each branch and call
12909           is executed and how many times it is taken or returns.  On targets
12910           that support constructors with priority support, profiling properly
12911           handles constructors, destructors and C++ constructors (and
12912           destructors) of classes which are used as a type of a global
12913           variable.
12914
12915           When the compiled program exits it saves this data to a file called
12916           auxname.gcda for each source file.  The data may be used for
12917           profile-directed optimizations (-fbranch-probabilities), or for
12918           test coverage analysis (-ftest-coverage).  Each object file's
12919           auxname is generated from the name of the output file, if
12920           explicitly specified and it is not the final executable, otherwise
12921           it is the basename of the source file.  In both cases any suffix is
12922           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
12923           for output file specified as -o dir/foo.o).
12924
12925           Note that if a command line directly links source files, the
12926           corresponding .gcda files will be prefixed with the unsuffixed name
12927           of the output file.  E.g. "gcc a.c b.c -o binary" would generate
12928           binary-a.gcda and binary-b.gcda files.
12929
12930       --coverage
12931           This option is used to compile and link code instrumented for
12932           coverage analysis.  The option is a synonym for -fprofile-arcs
12933           -ftest-coverage (when compiling) and -lgcov (when linking).  See
12934           the documentation for those options for more details.
12935
12936           *   Compile the source files with -fprofile-arcs plus optimization
12937               and code generation options.  For test coverage analysis, use
12938               the additional -ftest-coverage option.  You do not need to
12939               profile every source file in a program.
12940
12941           *   Compile the source files additionally with -fprofile-abs-path
12942               to create absolute path names in the .gcno files.  This allows
12943               gcov to find the correct sources in projects where compilations
12944               occur with different working directories.
12945
12946           *   Link your object files with -lgcov or -fprofile-arcs (the
12947               latter implies the former).
12948
12949           *   Run the program on a representative workload to generate the
12950               arc profile information.  This may be repeated any number of
12951               times.  You can run concurrent instances of your program, and
12952               provided that the file system supports locking, the data files
12953               will be correctly updated.  Unless a strict ISO C dialect
12954               option is in effect, "fork" calls are detected and correctly
12955               handled without double counting.
12956
12957               Moreover, an object file can be recompiled multiple times and
12958               the corresponding .gcda file merges as long as the source file
12959               and the compiler options are unchanged.
12960
12961           *   For profile-directed optimizations, compile the source files
12962               again with the same optimization and code generation options
12963               plus -fbranch-probabilities.
12964
12965           *   For test coverage analysis, use gcov to produce human readable
12966               information from the .gcno and .gcda files.  Refer to the gcov
12967               documentation for further information.
12968
12969           With -fprofile-arcs, for each function of your program GCC creates
12970           a program flow graph, then finds a spanning tree for the graph.
12971           Only arcs that are not on the spanning tree have to be
12972           instrumented: the compiler adds code to count the number of times
12973           that these arcs are executed.  When an arc is the only exit or only
12974           entrance to a block, the instrumentation code can be added to the
12975           block; otherwise, a new basic block must be created to hold the
12976           instrumentation code.
12977
12978       -ftest-coverage
12979           Produce a notes file that the gcov code-coverage utility can use to
12980           show program coverage.  Each source file's note file is called
12981           auxname.gcno.  Refer to the -fprofile-arcs option above for a
12982           description of auxname and instructions on how to generate test
12983           coverage data.  Coverage data matches the source files more closely
12984           if you do not optimize.
12985
12986       -fprofile-abs-path
12987           Automatically convert relative source file names to absolute path
12988           names in the .gcno files.  This allows gcov to find the correct
12989           sources in projects where compilations occur with different working
12990           directories.
12991
12992       -fprofile-dir=path
12993           Set the directory to search for the profile data files in to path.
12994           This option affects only the profile data generated by
12995           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
12996           -fprofile-use and -fbranch-probabilities and its related options.
12997           Both absolute and relative paths can be used.  By default, GCC uses
12998           the current directory as path, thus the profile data file appears
12999           in the same directory as the object file.  In order to prevent the
13000           file name clashing, if the object file name is not an absolute
13001           path, we mangle the absolute path of the sourcename.gcda file and
13002           use it as the file name of a .gcda file.  See details about the
13003           file naming in -fprofile-arcs.  See similar option -fprofile-note.
13004
13005           When an executable is run in a massive parallel environment, it is
13006           recommended to save profile to different folders.  That can be done
13007           with variables in path that are exported during run-time:
13008
13009           %p  process ID.
13010
13011           %q{VAR}
13012               value of environment variable VAR
13013
13014       -fprofile-generate
13015       -fprofile-generate=path
13016           Enable options usually used for instrumenting application to
13017           produce profile useful for later recompilation with profile
13018           feedback based optimization.  You must use -fprofile-generate both
13019           when compiling and when linking your program.
13020
13021           The following options are enabled: -fprofile-arcs,
13022           -fprofile-values, -finline-functions, and -fipa-bit-cp.
13023
13024           If path is specified, GCC looks at the path to find the profile
13025           feedback data files. See -fprofile-dir.
13026
13027           To optimize the program based on the collected profile information,
13028           use -fprofile-use.
13029
13030       -fprofile-info-section
13031       -fprofile-info-section=name
13032           Register the profile information in the specified section instead
13033           of using a constructor/destructor.  The section name is name if it
13034           is specified, otherwise the section name defaults to ".gcov_info".
13035           A pointer to the profile information generated by -fprofile-arcs is
13036           placed in the specified section for each translation unit.  This
13037           option disables the profile information registration through a
13038           constructor and it disables the profile information processing
13039           through a destructor.  This option is not intended to be used in
13040           hosted environments such as GNU/Linux.  It targets free-standing
13041           environments (for example embedded systems) with limited resources
13042           which do not support constructors/destructors or the C library file
13043           I/O.
13044
13045           The linker could collect the input sections in a continuous memory
13046           block and define start and end symbols.  A GNU linker script
13047           example which defines a linker output section follows:
13048
13049                     .gcov_info      :
13050                     {
13051                       PROVIDE (__gcov_info_start = .);
13052                       KEEP (*(.gcov_info))
13053                       PROVIDE (__gcov_info_end = .);
13054                     }
13055
13056           The program could dump the profiling information registered in this
13057           linker set for example like this:
13058
13059                   #include <gcov.h>
13060                   #include <stdio.h>
13061                   #include <stdlib.h>
13062
13063                   extern const struct gcov_info *__gcov_info_start[];
13064                   extern const struct gcov_info *__gcov_info_end[];
13065
13066                   static void
13067                   filename (const char *f, void *arg)
13068                   {
13069                     puts (f);
13070                   }
13071
13072                   static void
13073                   dump (const void *d, unsigned n, void *arg)
13074                   {
13075                     const unsigned char *c = d;
13076
13077                     for (unsigned i = 0; i < n; ++i)
13078                       printf ("%02x", c[i]);
13079                   }
13080
13081                   static void *
13082                   allocate (unsigned length, void *arg)
13083                   {
13084                     return malloc (length);
13085                   }
13086
13087                   static void
13088                   dump_gcov_info (void)
13089                   {
13090                     const struct gcov_info **info = __gcov_info_start;
13091                     const struct gcov_info **end = __gcov_info_end;
13092
13093                     /* Obfuscate variable to prevent compiler optimizations.  */
13094                     __asm__ ("" : "+r" (info));
13095
13096                     while (info != end)
13097                     {
13098                       void *arg = NULL;
13099                       __gcov_info_to_gcda (*info, filename, dump, allocate, arg);
13100                       putchar ('\n');
13101                       ++info;
13102                     }
13103                   }
13104
13105                   int
13106                   main()
13107                   {
13108                     dump_gcov_info();
13109                     return 0;
13110                   }
13111
13112       -fprofile-note=path
13113           If path is specified, GCC saves .gcno file into path location.  If
13114           you combine the option with multiple source files, the .gcno file
13115           will be overwritten.
13116
13117       -fprofile-prefix-path=path
13118           This option can be used in combination with
13119           profile-generate=profile_dir and profile-use=profile_dir to inform
13120           GCC where is the base directory of built source tree.  By default
13121           profile_dir will contain files with mangled absolute paths of all
13122           object files in the built project.  This is not desirable when
13123           directory used to build the instrumented binary differs from the
13124           directory used to build the binary optimized with profile feedback
13125           because the profile data will not be found during the optimized
13126           build.  In such setups -fprofile-prefix-path=path with path
13127           pointing to the base directory of the build can be used to strip
13128           the irrelevant part of the path and keep all file names relative to
13129           the main build directory.
13130
13131       -fprofile-prefix-map=old=new
13132           When compiling files residing in directory old, record profiling
13133           information (with --coverage) describing them as if the files
13134           resided in directory new instead.  See also -ffile-prefix-map.
13135
13136       -fprofile-update=method
13137           Alter the update method for an application instrumented for profile
13138           feedback based optimization.  The method argument should be one of
13139           single, atomic or prefer-atomic.  The first one is useful for
13140           single-threaded applications, while the second one prevents profile
13141           corruption by emitting thread-safe code.
13142
13143           Warning: When an application does not properly join all threads (or
13144           creates an detached thread), a profile file can be still corrupted.
13145
13146           Using prefer-atomic would be transformed either to atomic, when
13147           supported by a target, or to single otherwise.  The GCC driver
13148           automatically selects prefer-atomic when -pthread is present in the
13149           command line.
13150
13151       -fprofile-filter-files=regex
13152           Instrument only functions from files whose name matches any of the
13153           regular expressions (separated by semi-colons).
13154
13155           For example, -fprofile-filter-files=main\.c;module.*\.c will
13156           instrument only main.c and all C files starting with 'module'.
13157
13158       -fprofile-exclude-files=regex
13159           Instrument only functions from files whose name does not match any
13160           of the regular expressions (separated by semi-colons).
13161
13162           For example, -fprofile-exclude-files=/usr/.* will prevent
13163           instrumentation of all files that are located in the /usr/ folder.
13164
13165       -fprofile-reproducible=[multithreaded|parallel-runs|serial]
13166           Control level of reproducibility of profile gathered by
13167           "-fprofile-generate".  This makes it possible to rebuild program
13168           with same outcome which is useful, for example, for distribution
13169           packages.
13170
13171           With -fprofile-reproducible=serial the profile gathered by
13172           -fprofile-generate is reproducible provided the trained program
13173           behaves the same at each invocation of the train run, it is not
13174           multi-threaded and profile data streaming is always done in the
13175           same order.  Note that profile streaming happens at the end of
13176           program run but also before "fork" function is invoked.
13177
13178           Note that it is quite common that execution counts of some part of
13179           programs depends, for example, on length of temporary file names or
13180           memory space randomization (that may affect hash-table collision
13181           rate).  Such non-reproducible part of programs may be annotated by
13182           "no_instrument_function" function attribute. gcov-dump with -l can
13183           be used to dump gathered data and verify that they are indeed
13184           reproducible.
13185
13186           With -fprofile-reproducible=parallel-runs collected profile stays
13187           reproducible regardless the order of streaming of the data into
13188           gcda files.  This setting makes it possible to run multiple
13189           instances of instrumented program in parallel (such as with "make
13190           -j"). This reduces quality of gathered data, in particular of
13191           indirect call profiling.
13192
13193       -fsanitize=address
13194           Enable AddressSanitizer, a fast memory error detector.  Memory
13195           access instructions are instrumented to detect out-of-bounds and
13196           use-after-free bugs.  The option enables
13197           -fsanitize-address-use-after-scope.  See
13198           <https://github.com/google/sanitizers/wiki/AddressSanitizer> for
13199           more details.  The run-time behavior can be influenced using the
13200           ASAN_OPTIONS environment variable.  When set to "help=1", the
13201           available options are shown at startup of the instrumented program.
13202           See
13203           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
13204           for a list of supported options.  The option cannot be combined
13205           with -fsanitize=thread or -fsanitize=hwaddress.  Note that the only
13206           target -fsanitize=hwaddress is currently supported on is AArch64.
13207
13208       -fsanitize=kernel-address
13209           Enable AddressSanitizer for Linux kernel.  See
13210           <https://github.com/google/kasan> for more details.
13211
13212       -fsanitize=hwaddress
13213           Enable Hardware-assisted AddressSanitizer, which uses a hardware
13214           ability to ignore the top byte of a pointer to allow the detection
13215           of memory errors with a low memory overhead.  Memory access
13216           instructions are instrumented to detect out-of-bounds and use-
13217           after-free bugs.  The option enables
13218           -fsanitize-address-use-after-scope.  See
13219           <https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html>
13220           for more details.  The run-time behavior can be influenced using
13221           the HWASAN_OPTIONS environment variable.  When set to "help=1", the
13222           available options are shown at startup of the instrumented program.
13223           The option cannot be combined with -fsanitize=thread or
13224           -fsanitize=address, and is currently only available on AArch64.
13225
13226       -fsanitize=kernel-hwaddress
13227           Enable Hardware-assisted AddressSanitizer for compilation of the
13228           Linux kernel.  Similar to -fsanitize=kernel-address but using an
13229           alternate instrumentation method, and similar to
13230           -fsanitize=hwaddress but with instrumentation differences necessary
13231           for compiling the Linux kernel.  These differences are to avoid
13232           hwasan library initialization calls and to account for the stack
13233           pointer having a different value in its top byte.
13234
13235           Note: This option has different defaults to the
13236           -fsanitize=hwaddress.  Instrumenting the stack and alloca calls are
13237           not on by default but are still possible by specifying the command-
13238           line options --param hwasan-instrument-stack=1 and --param
13239           hwasan-instrument-allocas=1 respectively. Using a random frame tag
13240           is not implemented for kernel instrumentation.
13241
13242       -fsanitize=pointer-compare
13243           Instrument comparison operation (<, <=, >, >=) with pointer
13244           operands.  The option must be combined with either
13245           -fsanitize=kernel-address or -fsanitize=address The option cannot
13246           be combined with -fsanitize=thread.  Note: By default the check is
13247           disabled at run time.  To enable it, add
13248           "detect_invalid_pointer_pairs=2" to the environment variable
13249           ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
13250           invalid operation only when both pointers are non-null.
13251
13252       -fsanitize=pointer-subtract
13253           Instrument subtraction with pointer operands.  The option must be
13254           combined with either -fsanitize=kernel-address or
13255           -fsanitize=address The option cannot be combined with
13256           -fsanitize=thread.  Note: By default the check is disabled at run
13257           time.  To enable it, add "detect_invalid_pointer_pairs=2" to the
13258           environment variable ASAN_OPTIONS. Using
13259           "detect_invalid_pointer_pairs=1" detects invalid operation only
13260           when both pointers are non-null.
13261
13262       -fsanitize=shadow-call-stack
13263           Enable ShadowCallStack, a security enhancement mechanism used to
13264           protect programs against return address overwrites (e.g. stack
13265           buffer overflows.)  It works by saving a function's return address
13266           to a separately allocated shadow call stack in the function
13267           prologue and restoring the return address from the shadow call
13268           stack in the function epilogue.  Instrumentation only occurs in
13269           functions that need to save the return address to the stack.
13270
13271           Currently it only supports the aarch64 platform.  It is
13272           specifically designed for linux kernels that enable the
13273           CONFIG_SHADOW_CALL_STACK option.  For the user space programs,
13274           runtime support is not currently provided in libc and libgcc.
13275           Users who want to use this feature in user space need to provide
13276           their own support for the runtime.  It should be noted that this
13277           may cause the ABI rules to be broken.
13278
13279           On aarch64, the instrumentation makes use of the platform register
13280           "x18".  This generally means that any code that may run on the same
13281           thread as code compiled with ShadowCallStack must be compiled with
13282           the flag -ffixed-x18, otherwise functions compiled without
13283           -ffixed-x18 might clobber "x18" and so corrupt the shadow stack
13284           pointer.
13285
13286           Also, because there is no userspace runtime support, code compiled
13287           with ShadowCallStack cannot use exception handling.  Use
13288           -fno-exceptions to turn off exceptions.
13289
13290           See <https://clang.llvm.org/docs/ShadowCallStack.html> for more
13291           details.
13292
13293       -fsanitize=thread
13294           Enable ThreadSanitizer, a fast data race detector.  Memory access
13295           instructions are instrumented to detect data race bugs.  See
13296           <https://github.com/google/sanitizers/wiki#threadsanitizer> for
13297           more details. The run-time behavior can be influenced using the
13298           TSAN_OPTIONS environment variable; see
13299           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
13300           for a list of supported options.  The option cannot be combined
13301           with -fsanitize=address, -fsanitize=leak.
13302
13303           Note that sanitized atomic builtins cannot throw exceptions when
13304           operating on invalid memory addresses with non-call exceptions
13305           (-fnon-call-exceptions).
13306
13307       -fsanitize=leak
13308           Enable LeakSanitizer, a memory leak detector.  This option only
13309           matters for linking of executables and the executable is linked
13310           against a library that overrides "malloc" and other allocator
13311           functions.  See
13312           <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
13313           for more details.  The run-time behavior can be influenced using
13314           the LSAN_OPTIONS environment variable.  The option cannot be
13315           combined with -fsanitize=thread.
13316
13317       -fsanitize=undefined
13318           Enable UndefinedBehaviorSanitizer, a fast undefined behavior
13319           detector.  Various computations are instrumented to detect
13320           undefined behavior at runtime.  See
13321           <https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html> for
13322           more details.   The run-time behavior can be influenced using the
13323           UBSAN_OPTIONS environment variable.  Current suboptions are:
13324
13325           -fsanitize=shift
13326               This option enables checking that the result of a shift
13327               operation is not undefined.  Note that what exactly is
13328               considered undefined differs slightly between C and C++, as
13329               well as between ISO C90 and C99, etc.  This option has two
13330               suboptions, -fsanitize=shift-base and
13331               -fsanitize=shift-exponent.
13332
13333           -fsanitize=shift-exponent
13334               This option enables checking that the second argument of a
13335               shift operation is not negative and is smaller than the
13336               precision of the promoted first argument.
13337
13338           -fsanitize=shift-base
13339               If the second argument of a shift operation is within range,
13340               check that the result of a shift operation is not undefined.
13341               Note that what exactly is considered undefined differs slightly
13342               between C and C++, as well as between ISO C90 and C99, etc.
13343
13344           -fsanitize=integer-divide-by-zero
13345               Detect integer division by zero.
13346
13347           -fsanitize=unreachable
13348               With this option, the compiler turns the
13349               "__builtin_unreachable" call into a diagnostics message call
13350               instead.  When reaching the "__builtin_unreachable" call, the
13351               behavior is undefined.
13352
13353           -fsanitize=vla-bound
13354               This option instructs the compiler to check that the size of a
13355               variable length array is positive.
13356
13357           -fsanitize=null
13358               This option enables pointer checking.  Particularly, the
13359               application built with this option turned on will issue an
13360               error message when it tries to dereference a NULL pointer, or
13361               if a reference (possibly an rvalue reference) is bound to a
13362               NULL pointer, or if a method is invoked on an object pointed by
13363               a NULL pointer.
13364
13365           -fsanitize=return
13366               This option enables return statement checking.  Programs built
13367               with this option turned on will issue an error message when the
13368               end of a non-void function is reached without actually
13369               returning a value.  This option works in C++ only.
13370
13371           -fsanitize=signed-integer-overflow
13372               This option enables signed integer overflow checking.  We check
13373               that the result of "+", "*", and both unary and binary "-" does
13374               not overflow in the signed arithmetics.  This also detects
13375               "INT_MIN / -1" signed division.  Note, integer promotion rules
13376               must be taken into account.  That is, the following is not an
13377               overflow:
13378
13379                       signed char a = SCHAR_MAX;
13380                       a++;
13381
13382           -fsanitize=bounds
13383               This option enables instrumentation of array bounds.  Various
13384               out of bounds accesses are detected.  Flexible array members,
13385               flexible array member-like arrays, and initializers of
13386               variables with static storage are not instrumented.
13387
13388           -fsanitize=bounds-strict
13389               This option enables strict instrumentation of array bounds.
13390               Most out of bounds accesses are detected, including flexible
13391               array members and flexible array member-like arrays.
13392               Initializers of variables with static storage are not
13393               instrumented.
13394
13395           -fsanitize=alignment
13396               This option enables checking of alignment of pointers when they
13397               are dereferenced, or when a reference is bound to
13398               insufficiently aligned target, or when a method or constructor
13399               is invoked on insufficiently aligned object.
13400
13401           -fsanitize=object-size
13402               This option enables instrumentation of memory references using
13403               the "__builtin_object_size" function.  Various out of bounds
13404               pointer accesses are detected.
13405
13406           -fsanitize=float-divide-by-zero
13407               Detect floating-point division by zero.  Unlike other similar
13408               options, -fsanitize=float-divide-by-zero is not enabled by
13409               -fsanitize=undefined, since floating-point division by zero can
13410               be a legitimate way of obtaining infinities and NaNs.
13411
13412           -fsanitize=float-cast-overflow
13413               This option enables floating-point type to integer conversion
13414               checking.  We check that the result of the conversion does not
13415               overflow.  Unlike other similar options,
13416               -fsanitize=float-cast-overflow is not enabled by
13417               -fsanitize=undefined.  This option does not work well with
13418               "FE_INVALID" exceptions enabled.
13419
13420           -fsanitize=nonnull-attribute
13421               This option enables instrumentation of calls, checking whether
13422               null values are not passed to arguments marked as requiring a
13423               non-null value by the "nonnull" function attribute.
13424
13425           -fsanitize=returns-nonnull-attribute
13426               This option enables instrumentation of return statements in
13427               functions marked with "returns_nonnull" function attribute, to
13428               detect returning of null values from such functions.
13429
13430           -fsanitize=bool
13431               This option enables instrumentation of loads from bool.  If a
13432               value other than 0/1 is loaded, a run-time error is issued.
13433
13434           -fsanitize=enum
13435               This option enables instrumentation of loads from an enum type.
13436               If a value outside the range of values for the enum type is
13437               loaded, a run-time error is issued.
13438
13439           -fsanitize=vptr
13440               This option enables instrumentation of C++ member function
13441               calls, member accesses and some conversions between pointers to
13442               base and derived classes, to verify the referenced object has
13443               the correct dynamic type.
13444
13445           -fsanitize=pointer-overflow
13446               This option enables instrumentation of pointer arithmetics.  If
13447               the pointer arithmetics overflows, a run-time error is issued.
13448
13449           -fsanitize=builtin
13450               This option enables instrumentation of arguments to selected
13451               builtin functions.  If an invalid value is passed to such
13452               arguments, a run-time error is issued.  E.g. passing 0 as the
13453               argument to "__builtin_ctz" or "__builtin_clz" invokes
13454               undefined behavior and is diagnosed by this option.
13455
13456           While -ftrapv causes traps for signed overflows to be emitted,
13457           -fsanitize=undefined gives a diagnostic message.  This currently
13458           works only for the C family of languages.
13459
13460       -fno-sanitize=all
13461           This option disables all previously enabled sanitizers.
13462           -fsanitize=all is not allowed, as some sanitizers cannot be used
13463           together.
13464
13465       -fasan-shadow-offset=number
13466           This option forces GCC to use custom shadow offset in
13467           AddressSanitizer checks.  It is useful for experimenting with
13468           different shadow memory layouts in Kernel AddressSanitizer.
13469
13470       -fsanitize-sections=s1,s2,...
13471           Sanitize global variables in selected user-defined sections.  si
13472           may contain wildcards.
13473
13474       -fsanitize-recover[=opts]
13475           -fsanitize-recover= controls error recovery mode for sanitizers
13476           mentioned in comma-separated list of opts.  Enabling this option
13477           for a sanitizer component causes it to attempt to continue running
13478           the program as if no error happened.  This means multiple runtime
13479           errors can be reported in a single program run, and the exit code
13480           of the program may indicate success even when errors have been
13481           reported.  The -fno-sanitize-recover= option can be used to alter
13482           this behavior: only the first detected error is reported and
13483           program then exits with a non-zero exit code.
13484
13485           Currently this feature only works for -fsanitize=undefined (and its
13486           suboptions except for -fsanitize=unreachable and
13487           -fsanitize=return), -fsanitize=float-cast-overflow,
13488           -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict,
13489           -fsanitize=kernel-address and -fsanitize=address.  For these
13490           sanitizers error recovery is turned on by default, except
13491           -fsanitize=address, for which this feature is experimental.
13492           -fsanitize-recover=all and -fno-sanitize-recover=all is also
13493           accepted, the former enables recovery for all sanitizers that
13494           support it, the latter disables recovery for all sanitizers that
13495           support it.
13496
13497           Even if a recovery mode is turned on the compiler side, it needs to
13498           be also enabled on the runtime library side, otherwise the failures
13499           are still fatal.  The runtime library defaults to "halt_on_error=0"
13500           for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
13501           value for AddressSanitizer is "halt_on_error=1". This can be
13502           overridden through setting the "halt_on_error" flag in the
13503           corresponding environment variable.
13504
13505           Syntax without an explicit opts parameter is deprecated.  It is
13506           equivalent to specifying an opts list of:
13507
13508                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
13509
13510       -fsanitize-address-use-after-scope
13511           Enable sanitization of local variables to detect use-after-scope
13512           bugs.  The option sets -fstack-reuse to none.
13513
13514       -fsanitize-undefined-trap-on-error
13515           The -fsanitize-undefined-trap-on-error option instructs the
13516           compiler to report undefined behavior using "__builtin_trap" rather
13517           than a "libubsan" library routine.  The advantage of this is that
13518           the "libubsan" library is not needed and is not linked in, so this
13519           is usable even in freestanding environments.
13520
13521       -fsanitize-coverage=trace-pc
13522           Enable coverage-guided fuzzing code instrumentation.  Inserts a
13523           call to "__sanitizer_cov_trace_pc" into every basic block.
13524
13525       -fsanitize-coverage=trace-cmp
13526           Enable dataflow guided fuzzing code instrumentation.  Inserts a
13527           call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
13528           "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for
13529           integral comparison with both operands variable or
13530           "__sanitizer_cov_trace_const_cmp1",
13531           "__sanitizer_cov_trace_const_cmp2",
13532           "__sanitizer_cov_trace_const_cmp4" or
13533           "__sanitizer_cov_trace_const_cmp8" for integral comparison with one
13534           operand constant, "__sanitizer_cov_trace_cmpf" or
13535           "__sanitizer_cov_trace_cmpd" for float or double comparisons and
13536           "__sanitizer_cov_trace_switch" for switch statements.
13537
13538       -fcf-protection=[full|branch|return|none|check]
13539           Enable code instrumentation of control-flow transfers to increase
13540           program security by checking that target addresses of control-flow
13541           transfer instructions (such as indirect function call, function
13542           return, indirect jump) are valid.  This prevents diverting the flow
13543           of control to an unexpected target.  This is intended to protect
13544           against such threats as Return-oriented Programming (ROP), and
13545           similarly call/jmp-oriented programming (COP/JOP).
13546
13547           The value "branch" tells the compiler to implement checking of
13548           validity of control-flow transfer at the point of indirect branch
13549           instructions, i.e. call/jmp instructions.  The value "return"
13550           implements checking of validity at the point of returning from a
13551           function.  The value "full" is an alias for specifying both
13552           "branch" and "return". The value "none" turns off instrumentation.
13553
13554           The value "check" is used for the final link with link-time
13555           optimization (LTO).  An error is issued if LTO object files are
13556           compiled with different -fcf-protection values.  The value "check"
13557           is ignored at the compile time.
13558
13559           The macro "__CET__" is defined when -fcf-protection is used.  The
13560           first bit of "__CET__" is set to 1 for the value "branch" and the
13561           second bit of "__CET__" is set to 1 for the "return".
13562
13563           You can also use the "nocf_check" attribute to identify which
13564           functions and calls should be skipped from instrumentation.
13565
13566           Currently the x86 GNU/Linux target provides an implementation based
13567           on Intel Control-flow Enforcement Technology (CET) which works for
13568           i686 processor or newer.
13569
13570       -fharden-compares
13571           For every logical test that survives gimple optimizations and is
13572           not the condition in a conditional branch (for example, conditions
13573           tested for conditional moves, or to store in boolean variables),
13574           emit extra code to compute and verify the reversed condition, and
13575           to call "__builtin_trap" if the results do not match.  Use with
13576           -fharden-conditional-branches to cover all conditionals.
13577
13578       -fharden-conditional-branches
13579           For every non-vectorized conditional branch that survives gimple
13580           optimizations, emit extra code to compute and verify the reversed
13581           condition, and to call "__builtin_trap" if the result is
13582           unexpected.  Use with -fharden-compares to cover all conditionals.
13583
13584       -fstack-protector
13585           Emit extra code to check for buffer overflows, such as stack
13586           smashing attacks.  This is done by adding a guard variable to
13587           functions with vulnerable objects.  This includes functions that
13588           call "alloca", and functions with buffers larger than or equal to 8
13589           bytes.  The guards are initialized when a function is entered and
13590           then checked when the function exits.  If a guard check fails, an
13591           error message is printed and the program exits.  Only variables
13592           that are actually allocated on the stack are considered, optimized
13593           away variables or variables allocated in registers don't count.
13594
13595       -fstack-protector-all
13596           Like -fstack-protector except that all functions are protected.
13597
13598       -fstack-protector-strong
13599           Like -fstack-protector but includes additional functions to be
13600           protected --- those that have local array definitions, or have
13601           references to local frame addresses.  Only variables that are
13602           actually allocated on the stack are considered, optimized away
13603           variables or variables allocated in registers don't count.
13604
13605       -fstack-protector-explicit
13606           Like -fstack-protector but only protects those functions which have
13607           the "stack_protect" attribute.
13608
13609       -fstack-check
13610           Generate code to verify that you do not go beyond the boundary of
13611           the stack.  You should specify this flag if you are running in an
13612           environment with multiple threads, but you only rarely need to
13613           specify it in a single-threaded environment since stack overflow is
13614           automatically detected on nearly all systems if there is only one
13615           stack.
13616
13617           Note that this switch does not actually cause checking to be done;
13618           the operating system or the language runtime must do that.  The
13619           switch causes generation of code to ensure that they see the stack
13620           being extended.
13621
13622           You can additionally specify a string parameter: no means no
13623           checking, generic means force the use of old-style checking,
13624           specific means use the best checking method and is equivalent to
13625           bare -fstack-check.
13626
13627           Old-style checking is a generic mechanism that requires no specific
13628           target support in the compiler but comes with the following
13629           drawbacks:
13630
13631           1.  Modified allocation strategy for large objects: they are always
13632               allocated dynamically if their size exceeds a fixed threshold.
13633               Note this may change the semantics of some code.
13634
13635           2.  Fixed limit on the size of the static frame of functions: when
13636               it is topped by a particular function, stack checking is not
13637               reliable and a warning is issued by the compiler.
13638
13639           3.  Inefficiency: because of both the modified allocation strategy
13640               and the generic implementation, code performance is hampered.
13641
13642           Note that old-style stack checking is also the fallback method for
13643           specific if no target support has been added in the compiler.
13644
13645           -fstack-check= is designed for Ada's needs to detect infinite
13646           recursion and stack overflows.  specific is an excellent choice
13647           when compiling Ada code.  It is not generally sufficient to protect
13648           against stack-clash attacks.  To protect against those you want
13649           -fstack-clash-protection.
13650
13651       -fstack-clash-protection
13652           Generate code to prevent stack clash style attacks.  When this
13653           option is enabled, the compiler will only allocate one page of
13654           stack space at a time and each page is accessed immediately after
13655           allocation.  Thus, it prevents allocations from jumping over any
13656           stack guard page provided by the operating system.
13657
13658           Most targets do not fully support stack clash protection.  However,
13659           on those targets -fstack-clash-protection will protect dynamic
13660           stack allocations.  -fstack-clash-protection may also provide
13661           limited protection for static stack allocations if the target
13662           supports -fstack-check=specific.
13663
13664       -fstack-limit-register=reg
13665       -fstack-limit-symbol=sym
13666       -fno-stack-limit
13667           Generate code to ensure that the stack does not grow beyond a
13668           certain value, either the value of a register or the address of a
13669           symbol.  If a larger stack is required, a signal is raised at run
13670           time.  For most targets, the signal is raised before the stack
13671           overruns the boundary, so it is possible to catch the signal
13672           without taking special precautions.
13673
13674           For instance, if the stack starts at absolute address 0x80000000
13675           and grows downwards, you can use the flags
13676           -fstack-limit-symbol=__stack_limit and
13677           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
13678           128KB.  Note that this may only work with the GNU linker.
13679
13680           You can locally override stack limit checking by using the
13681           "no_stack_limit" function attribute.
13682
13683       -fsplit-stack
13684           Generate code to automatically split the stack before it overflows.
13685           The resulting program has a discontiguous stack which can only
13686           overflow if the program is unable to allocate any more memory.
13687           This is most useful when running threaded programs, as it is no
13688           longer necessary to calculate a good stack size to use for each
13689           thread.  This is currently only implemented for the x86 targets
13690           running GNU/Linux.
13691
13692           When code compiled with -fsplit-stack calls code compiled without
13693           -fsplit-stack, there may not be much stack space available for the
13694           latter code to run.  If compiling all code, including library code,
13695           with -fsplit-stack is not an option, then the linker can fix up
13696           these calls so that the code compiled without -fsplit-stack always
13697           has a large stack.  Support for this is implemented in the gold
13698           linker in GNU binutils release 2.21 and later.
13699
13700       -fvtable-verify=[std|preinit|none]
13701           This option is only available when compiling C++ code.  It turns on
13702           (or off, if using -fvtable-verify=none) the security feature that
13703           verifies at run time, for every virtual call, that the vtable
13704           pointer through which the call is made is valid for the type of the
13705           object, and has not been corrupted or overwritten.  If an invalid
13706           vtable pointer is detected at run time, an error is reported and
13707           execution of the program is immediately halted.
13708
13709           This option causes run-time data structures to be built at program
13710           startup, which are used for verifying the vtable pointers.  The
13711           options std and preinit control the timing of when these data
13712           structures are built.  In both cases the data structures are built
13713           before execution reaches "main".  Using -fvtable-verify=std causes
13714           the data structures to be built after shared libraries have been
13715           loaded and initialized.  -fvtable-verify=preinit causes them to be
13716           built before shared libraries have been loaded and initialized.
13717
13718           If this option appears multiple times in the command line with
13719           different values specified, none takes highest priority over both
13720           std and preinit; preinit takes priority over std.
13721
13722       -fvtv-debug
13723           When used in conjunction with -fvtable-verify=std or
13724           -fvtable-verify=preinit, causes debug versions of the runtime
13725           functions for the vtable verification feature to be called.  This
13726           flag also causes the compiler to log information about which vtable
13727           pointers it finds for each class.  This information is written to a
13728           file named vtv_set_ptr_data.log in the directory named by the
13729           environment variable VTV_LOGS_DIR if that is defined or the current
13730           working directory otherwise.
13731
13732           Note:  This feature appends data to the log file. If you want a
13733           fresh log file, be sure to delete any existing one.
13734
13735       -fvtv-counts
13736           This is a debugging flag.  When used in conjunction with
13737           -fvtable-verify=std or -fvtable-verify=preinit, this causes the
13738           compiler to keep track of the total number of virtual calls it
13739           encounters and the number of verifications it inserts.  It also
13740           counts the number of calls to certain run-time library functions
13741           that it inserts and logs this information for each compilation
13742           unit.  The compiler writes this information to a file named
13743           vtv_count_data.log in the directory named by the environment
13744           variable VTV_LOGS_DIR if that is defined or the current working
13745           directory otherwise.  It also counts the size of the vtable pointer
13746           sets for each class, and writes this information to
13747           vtv_class_set_sizes.log in the same directory.
13748
13749           Note:  This feature appends data to the log files.  To get fresh
13750           log files, be sure to delete any existing ones.
13751
13752       -finstrument-functions
13753           Generate instrumentation calls for entry and exit to functions.
13754           Just after function entry and just before function exit, the
13755           following profiling functions are called with the address of the
13756           current function and its call site.  (On some platforms,
13757           "__builtin_return_address" does not work beyond the current
13758           function, so the call site information may not be available to the
13759           profiling functions otherwise.)
13760
13761                   void __cyg_profile_func_enter (void *this_fn,
13762                                                  void *call_site);
13763                   void __cyg_profile_func_exit  (void *this_fn,
13764                                                  void *call_site);
13765
13766           The first argument is the address of the start of the current
13767           function, which may be looked up exactly in the symbol table.
13768
13769           This instrumentation is also done for functions expanded inline in
13770           other functions.  The profiling calls indicate where, conceptually,
13771           the inline function is entered and exited.  This means that
13772           addressable versions of such functions must be available.  If all
13773           your uses of a function are expanded inline, this may mean an
13774           additional expansion of code size.  If you use "extern inline" in
13775           your C code, an addressable version of such functions must be
13776           provided.  (This is normally the case anyway, but if you get lucky
13777           and the optimizer always expands the functions inline, you might
13778           have gotten away without providing static copies.)
13779
13780           A function may be given the attribute "no_instrument_function", in
13781           which case this instrumentation is not done.  This can be used, for
13782           example, for the profiling functions listed above, high-priority
13783           interrupt routines, and any functions from which the profiling
13784           functions cannot safely be called (perhaps signal handlers, if the
13785           profiling routines generate output or allocate memory).
13786
13787       -finstrument-functions-exclude-file-list=file,file,...
13788           Set the list of functions that are excluded from instrumentation
13789           (see the description of -finstrument-functions).  If the file that
13790           contains a function definition matches with one of file, then that
13791           function is not instrumented.  The match is done on substrings: if
13792           the file parameter is a substring of the file name, it is
13793           considered to be a match.
13794
13795           For example:
13796
13797                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys
13798
13799           excludes any inline function defined in files whose pathnames
13800           contain /bits/stl or include/sys.
13801
13802           If, for some reason, you want to include letter , in one of sym,
13803           write ,. For example,
13804           -finstrument-functions-exclude-file-list=',,tmp' (note the single
13805           quote surrounding the option).
13806
13807       -finstrument-functions-exclude-function-list=sym,sym,...
13808           This is similar to -finstrument-functions-exclude-file-list, but
13809           this option sets the list of function names to be excluded from
13810           instrumentation.  The function name to be matched is its user-
13811           visible name, such as "vector<int> blah(const vector<int> &)", not
13812           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
13813           match is done on substrings: if the sym parameter is a substring of
13814           the function name, it is considered to be a match.  For C99 and C++
13815           extended identifiers, the function name must be given in UTF-8, not
13816           using universal character names.
13817
13818       -fpatchable-function-entry=N[,M]
13819           Generate N NOPs right at the beginning of each function, with the
13820           function entry point before the Mth NOP.  If M is omitted, it
13821           defaults to 0 so the function entry points to the address just at
13822           the first NOP.  The NOP instructions reserve extra space which can
13823           be used to patch in any desired instrumentation at run time,
13824           provided that the code segment is writable.  The amount of space is
13825           controllable indirectly via the number of NOPs; the NOP instruction
13826           used corresponds to the instruction emitted by the internal GCC
13827           back-end interface "gen_nop".  This behavior is target-specific and
13828           may also depend on the architecture variant and/or other
13829           compilation options.
13830
13831           For run-time identification, the starting addresses of these areas,
13832           which correspond to their respective function entries minus M, are
13833           additionally collected in the "__patchable_function_entries"
13834           section of the resulting binary.
13835
13836           Note that the value of "__attribute__ ((patchable_function_entry
13837           (N,M)))" takes precedence over command-line option
13838           -fpatchable-function-entry=N,M.  This can be used to increase the
13839           area size or to remove it completely on a single function.  If
13840           "N=0", no pad location is recorded.
13841
13842           The NOP instructions are inserted at---and maybe before, depending
13843           on M---the function entry address, even before the prologue.
13844
13845           The maximum value of N and M is 65535.
13846
13847   Options Controlling the Preprocessor
13848       These options control the C preprocessor, which is run on each C source
13849       file before actual compilation.
13850
13851       If you use the -E option, nothing is done except preprocessing.  Some
13852       of these options make sense only together with -E because they cause
13853       the preprocessor output to be unsuitable for actual compilation.
13854
13855       In addition to the options listed here, there are a number of options
13856       to control search paths for include files documented in Directory
13857       Options.  Options to control preprocessor diagnostics are listed in
13858       Warning Options.
13859
13860       -D name
13861           Predefine name as a macro, with definition 1.
13862
13863       -D name=definition
13864           The contents of definition are tokenized and processed as if they
13865           appeared during translation phase three in a #define directive.  In
13866           particular, the definition is truncated by embedded newline
13867           characters.
13868
13869           If you are invoking the preprocessor from a shell or shell-like
13870           program you may need to use the shell's quoting syntax to protect
13871           characters such as spaces that have a meaning in the shell syntax.
13872
13873           If you wish to define a function-like macro on the command line,
13874           write its argument list with surrounding parentheses before the
13875           equals sign (if any).  Parentheses are meaningful to most shells,
13876           so you should quote the option.  With sh and csh,
13877           -D'name(args...)=definition' works.
13878
13879           -D and -U options are processed in the order they are given on the
13880           command line.  All -imacros file and -include file options are
13881           processed after all -D and -U options.
13882
13883       -U name
13884           Cancel any previous definition of name, either built in or provided
13885           with a -D option.
13886
13887       -include file
13888           Process file as if "#include "file"" appeared as the first line of
13889           the primary source file.  However, the first directory searched for
13890           file is the preprocessor's working directory instead of the
13891           directory containing the main source file.  If not found there, it
13892           is searched for in the remainder of the "#include "..."" search
13893           chain as normal.
13894
13895           If multiple -include options are given, the files are included in
13896           the order they appear on the command line.
13897
13898       -imacros file
13899           Exactly like -include, except that any output produced by scanning
13900           file is thrown away.  Macros it defines remain defined.  This
13901           allows you to acquire all the macros from a header without also
13902           processing its declarations.
13903
13904           All files specified by -imacros are processed before all files
13905           specified by -include.
13906
13907       -undef
13908           Do not predefine any system-specific or GCC-specific macros.  The
13909           standard predefined macros remain defined.
13910
13911       -pthread
13912           Define additional macros required for using the POSIX threads
13913           library.  You should use this option consistently for both
13914           compilation and linking.  This option is supported on GNU/Linux
13915           targets, most other Unix derivatives, and also on x86 Cygwin and
13916           MinGW targets.
13917
13918       -M  Instead of outputting the result of preprocessing, output a rule
13919           suitable for make describing the dependencies of the main source
13920           file.  The preprocessor outputs one make rule containing the object
13921           file name for that source file, a colon, and the names of all the
13922           included files, including those coming from -include or -imacros
13923           command-line options.
13924
13925           Unless specified explicitly (with -MT or -MQ), the object file name
13926           consists of the name of the source file with any suffix replaced
13927           with object file suffix and with any leading directory parts
13928           removed.  If there are many included files then the rule is split
13929           into several lines using \-newline.  The rule has no commands.
13930
13931           This option does not suppress the preprocessor's debug output, such
13932           as -dM.  To avoid mixing such debug output with the dependency
13933           rules you should explicitly specify the dependency output file with
13934           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
13935           Debug output is still sent to the regular output stream as normal.
13936
13937           Passing -M to the driver implies -E, and suppresses warnings with
13938           an implicit -w.
13939
13940       -MM Like -M but do not mention header files that are found in system
13941           header directories, nor header files that are included, directly or
13942           indirectly, from such a header.
13943
13944           This implies that the choice of angle brackets or double quotes in
13945           an #include directive does not in itself determine whether that
13946           header appears in -MM dependency output.
13947
13948       -MF file
13949           When used with -M or -MM, specifies a file to write the
13950           dependencies to.  If no -MF switch is given the preprocessor sends
13951           the rules to the same place it would send preprocessed output.
13952
13953           When used with the driver options -MD or -MMD, -MF overrides the
13954           default dependency output file.
13955
13956           If file is -, then the dependencies are written to stdout.
13957
13958       -MG In conjunction with an option such as -M requesting dependency
13959           generation, -MG assumes missing header files are generated files
13960           and adds them to the dependency list without raising an error.  The
13961           dependency filename is taken directly from the "#include" directive
13962           without prepending any path.  -MG also suppresses preprocessed
13963           output, as a missing header file renders this useless.
13964
13965           This feature is used in automatic updating of makefiles.
13966
13967       -Mno-modules
13968           Disable dependency generation for compiled module interfaces.
13969
13970       -MP This option instructs CPP to add a phony target for each dependency
13971           other than the main file, causing each to depend on nothing.  These
13972           dummy rules work around errors make gives if you remove header
13973           files without updating the Makefile to match.
13974
13975           This is typical output:
13976
13977                   test.o: test.c test.h
13978
13979                   test.h:
13980
13981       -MT target
13982           Change the target of the rule emitted by dependency generation.  By
13983           default CPP takes the name of the main input file, deletes any
13984           directory components and any file suffix such as .c, and appends
13985           the platform's usual object suffix.  The result is the target.
13986
13987           An -MT option sets the target to be exactly the string you specify.
13988           If you want multiple targets, you can specify them as a single
13989           argument to -MT, or use multiple -MT options.
13990
13991           For example, -MT '$(objpfx)foo.o' might give
13992
13993                   $(objpfx)foo.o: foo.c
13994
13995       -MQ target
13996           Same as -MT, but it quotes any characters which are special to
13997           Make.  -MQ '$(objpfx)foo.o' gives
13998
13999                   $$(objpfx)foo.o: foo.c
14000
14001           The default target is automatically quoted, as if it were given
14002           with -MQ.
14003
14004       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
14005           The driver determines file based on whether an -o option is given.
14006           If it is, the driver uses its argument but with a suffix of .d,
14007           otherwise it takes the name of the input file, removes any
14008           directory components and suffix, and applies a .d suffix.
14009
14010           If -MD is used in conjunction with -E, any -o switch is understood
14011           to specify the dependency output file, but if used without -E, each
14012           -o is understood to specify a target object file.
14013
14014           Since -E is not implied, -MD can be used to generate a dependency
14015           output file as a side effect of the compilation process.
14016
14017       -MMD
14018           Like -MD except mention only user header files, not system header
14019           files.
14020
14021       -fpreprocessed
14022           Indicate to the preprocessor that the input file has already been
14023           preprocessed.  This suppresses things like macro expansion,
14024           trigraph conversion, escaped newline splicing, and processing of
14025           most directives.  The preprocessor still recognizes and removes
14026           comments, so that you can pass a file preprocessed with -C to the
14027           compiler without problems.  In this mode the integrated
14028           preprocessor is little more than a tokenizer for the front ends.
14029
14030           -fpreprocessed is implicit if the input file has one of the
14031           extensions .i, .ii or .mi.  These are the extensions that GCC uses
14032           for preprocessed files created by -save-temps.
14033
14034       -fdirectives-only
14035           When preprocessing, handle directives, but do not expand macros.
14036
14037           The option's behavior depends on the -E and -fpreprocessed options.
14038
14039           With -E, preprocessing is limited to the handling of directives
14040           such as "#define", "#ifdef", and "#error".  Other preprocessor
14041           operations, such as macro expansion and trigraph conversion are not
14042           performed.  In addition, the -dD option is implicitly enabled.
14043
14044           With -fpreprocessed, predefinition of command line and most builtin
14045           macros is disabled.  Macros such as "__LINE__", which are
14046           contextually dependent, are handled normally.  This enables
14047           compilation of files previously preprocessed with "-E
14048           -fdirectives-only".
14049
14050           With both -E and -fpreprocessed, the rules for -fpreprocessed take
14051           precedence.  This enables full preprocessing of files previously
14052           preprocessed with "-E -fdirectives-only".
14053
14054       -fdollars-in-identifiers
14055           Accept $ in identifiers.
14056
14057       -fextended-identifiers
14058           Accept universal character names and extended characters in
14059           identifiers.  This option is enabled by default for C99 (and later
14060           C standard versions) and C++.
14061
14062       -fno-canonical-system-headers
14063           When preprocessing, do not shorten system header paths with
14064           canonicalization.
14065
14066       -fmax-include-depth=depth
14067           Set the maximum depth of the nested #include. The default is 200.
14068
14069       -ftabstop=width
14070           Set the distance between tab stops.  This helps the preprocessor
14071           report correct column numbers in warnings or errors, even if tabs
14072           appear on the line.  If the value is less than 1 or greater than
14073           100, the option is ignored.  The default is 8.
14074
14075       -ftrack-macro-expansion[=level]
14076           Track locations of tokens across macro expansions. This allows the
14077           compiler to emit diagnostic about the current macro expansion stack
14078           when a compilation error occurs in a macro expansion. Using this
14079           option makes the preprocessor and the compiler consume more memory.
14080           The level parameter can be used to choose the level of precision of
14081           token location tracking thus decreasing the memory consumption if
14082           necessary. Value 0 of level de-activates this option. Value 1
14083           tracks tokens locations in a degraded mode for the sake of minimal
14084           memory overhead. In this mode all tokens resulting from the
14085           expansion of an argument of a function-like macro have the same
14086           location. Value 2 tracks tokens locations completely. This value is
14087           the most memory hungry.  When this option is given no argument, the
14088           default parameter value is 2.
14089
14090           Note that "-ftrack-macro-expansion=2" is activated by default.
14091
14092       -fmacro-prefix-map=old=new
14093           When preprocessing files residing in directory old, expand the
14094           "__FILE__" and "__BASE_FILE__" macros as if the files resided in
14095           directory new instead.  This can be used to change an absolute path
14096           to a relative path by using . for new which can result in more
14097           reproducible builds that are location independent.  This option
14098           also affects "__builtin_FILE()" during compilation.  See also
14099           -ffile-prefix-map.
14100
14101       -fexec-charset=charset
14102           Set the execution character set, used for string and character
14103           constants.  The default is UTF-8.  charset can be any encoding
14104           supported by the system's "iconv" library routine.
14105
14106       -fwide-exec-charset=charset
14107           Set the wide execution character set, used for wide string and
14108           character constants.  The default is UTF-32 or UTF-16, whichever
14109           corresponds to the width of "wchar_t".  As with -fexec-charset,
14110           charset can be any encoding supported by the system's "iconv"
14111           library routine; however, you will have problems with encodings
14112           that do not fit exactly in "wchar_t".
14113
14114       -finput-charset=charset
14115           Set the input character set, used for translation from the
14116           character set of the input file to the source character set used by
14117           GCC.  If the locale does not specify, or GCC cannot get this
14118           information from the locale, the default is UTF-8.  This can be
14119           overridden by either the locale or this command-line option.
14120           Currently the command-line option takes precedence if there's a
14121           conflict.  charset can be any encoding supported by the system's
14122           "iconv" library routine.
14123
14124       -fpch-deps
14125           When using precompiled headers, this flag causes the dependency-
14126           output flags to also list the files from the precompiled header's
14127           dependencies.  If not specified, only the precompiled header are
14128           listed and not the files that were used to create it, because those
14129           files are not consulted when a precompiled header is used.
14130
14131       -fpch-preprocess
14132           This option allows use of a precompiled header together with -E.
14133           It inserts a special "#pragma", "#pragma GCC pch_preprocess
14134           "filename"" in the output to mark the place where the precompiled
14135           header was found, and its filename.  When -fpreprocessed is in use,
14136           GCC recognizes this "#pragma" and loads the PCH.
14137
14138           This option is off by default, because the resulting preprocessed
14139           output is only really suitable as input to GCC.  It is switched on
14140           by -save-temps.
14141
14142           You should not write this "#pragma" in your own code, but it is
14143           safe to edit the filename if the PCH file is available in a
14144           different location.  The filename may be absolute or it may be
14145           relative to GCC's current directory.
14146
14147       -fworking-directory
14148           Enable generation of linemarkers in the preprocessor output that
14149           let the compiler know the current working directory at the time of
14150           preprocessing.  When this option is enabled, the preprocessor
14151           emits, after the initial linemarker, a second linemarker with the
14152           current working directory followed by two slashes.  GCC uses this
14153           directory, when it's present in the preprocessed input, as the
14154           directory emitted as the current working directory in some
14155           debugging information formats.  This option is implicitly enabled
14156           if debugging information is enabled, but this can be inhibited with
14157           the negated form -fno-working-directory.  If the -P flag is present
14158           in the command line, this option has no effect, since no "#line"
14159           directives are emitted whatsoever.
14160
14161       -A predicate=answer
14162           Make an assertion with the predicate predicate and answer answer.
14163           This form is preferred to the older form -A predicate(answer),
14164           which is still supported, because it does not use shell special
14165           characters.
14166
14167       -A -predicate=answer
14168           Cancel an assertion with the predicate predicate and answer answer.
14169
14170       -C  Do not discard comments.  All comments are passed through to the
14171           output file, except for comments in processed directives, which are
14172           deleted along with the directive.
14173
14174           You should be prepared for side effects when using -C; it causes
14175           the preprocessor to treat comments as tokens in their own right.
14176           For example, comments appearing at the start of what would be a
14177           directive line have the effect of turning that line into an
14178           ordinary source line, since the first token on the line is no
14179           longer a #.
14180
14181       -CC Do not discard comments, including during macro expansion.  This is
14182           like -C, except that comments contained within macros are also
14183           passed through to the output file where the macro is expanded.
14184
14185           In addition to the side effects of the -C option, the -CC option
14186           causes all C++-style comments inside a macro to be converted to
14187           C-style comments.  This is to prevent later use of that macro from
14188           inadvertently commenting out the remainder of the source line.
14189
14190           The -CC option is generally used to support lint comments.
14191
14192       -P  Inhibit generation of linemarkers in the output from the
14193           preprocessor.  This might be useful when running the preprocessor
14194           on something that is not C code, and will be sent to a program
14195           which might be confused by the linemarkers.
14196
14197       -traditional
14198       -traditional-cpp
14199           Try to imitate the behavior of pre-standard C preprocessors, as
14200           opposed to ISO C preprocessors.  See the GNU CPP manual for
14201           details.
14202
14203           Note that GCC does not otherwise attempt to emulate a pre-standard
14204           C compiler, and these options are only supported with the -E
14205           switch, or when invoking CPP explicitly.
14206
14207       -trigraphs
14208           Support ISO C trigraphs.  These are three-character sequences, all
14209           starting with ??, that are defined by ISO C to stand for single
14210           characters.  For example, ??/ stands for \, so '??/n' is a
14211           character constant for a newline.
14212
14213           The nine trigraphs and their replacements are
14214
14215                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
14216                   Replacement:      [    ]    {    }    #    \    ^    |    ~
14217
14218           By default, GCC ignores trigraphs, but in standard-conforming modes
14219           it converts them.  See the -std and -ansi options.
14220
14221       -remap
14222           Enable special code to work around file systems which only permit
14223           very short file names, such as MS-DOS.
14224
14225       -H  Print the name of each header file used, in addition to other
14226           normal activities.  Each name is indented to show how deep in the
14227           #include stack it is.  Precompiled header files are also printed,
14228           even if they are found to be invalid; an invalid precompiled header
14229           file is printed with ...x and a valid one with ...! .
14230
14231       -dletters
14232           Says to make debugging dumps during compilation as specified by
14233           letters.  The flags documented here are those relevant to the
14234           preprocessor.  Other letters are interpreted by the compiler
14235           proper, or reserved for future versions of GCC, and so are silently
14236           ignored.  If you specify letters whose behavior conflicts, the
14237           result is undefined.
14238
14239           -dM Instead of the normal output, generate a list of #define
14240               directives for all the macros defined during the execution of
14241               the preprocessor, including predefined macros.  This gives you
14242               a way of finding out what is predefined in your version of the
14243               preprocessor.  Assuming you have no file foo.h, the command
14244
14245                       touch foo.h; cpp -dM foo.h
14246
14247               shows all the predefined macros.
14248
14249               If you use -dM without the -E option, -dM is interpreted as a
14250               synonym for -fdump-rtl-mach.
14251
14252           -dD Like -dM except in two respects: it does not include the
14253               predefined macros, and it outputs both the #define directives
14254               and the result of preprocessing.  Both kinds of output go to
14255               the standard output file.
14256
14257           -dN Like -dD, but emit only the macro names, not their expansions.
14258
14259           -dI Output #include directives in addition to the result of
14260               preprocessing.
14261
14262           -dU Like -dD except that only macros that are expanded, or whose
14263               definedness is tested in preprocessor directives, are output;
14264               the output is delayed until the use or test of the macro; and
14265               #undef directives are also output for macros tested but
14266               undefined at the time.
14267
14268       -fdebug-cpp
14269           This option is only useful for debugging GCC.  When used from CPP
14270           or with -E, it dumps debugging information about location maps.
14271           Every token in the output is preceded by the dump of the map its
14272           location belongs to.
14273
14274           When used from GCC without -E, this option has no effect.
14275
14276       -Wp,option
14277           You can use -Wp,option to bypass the compiler driver and pass
14278           option directly through to the preprocessor.  If option contains
14279           commas, it is split into multiple options at the commas.  However,
14280           many options are modified, translated or interpreted by the
14281           compiler driver before being passed to the preprocessor, and -Wp
14282           forcibly bypasses this phase.  The preprocessor's direct interface
14283           is undocumented and subject to change, so whenever possible you
14284           should avoid using -Wp and let the driver handle the options
14285           instead.
14286
14287       -Xpreprocessor option
14288           Pass option as an option to the preprocessor.  You can use this to
14289           supply system-specific preprocessor options that GCC does not
14290           recognize.
14291
14292           If you want to pass an option that takes an argument, you must use
14293           -Xpreprocessor twice, once for the option and once for the
14294           argument.
14295
14296       -no-integrated-cpp
14297           Perform preprocessing as a separate pass before compilation.  By
14298           default, GCC performs preprocessing as an integrated part of input
14299           tokenization and parsing.  If this option is provided, the
14300           appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
14301           and Objective-C, respectively) is instead invoked twice, once for
14302           preprocessing only and once for actual compilation of the
14303           preprocessed input.  This option may be useful in conjunction with
14304           the -B or -wrapper options to specify an alternate preprocessor or
14305           perform additional processing of the program source between normal
14306           preprocessing and compilation.
14307
14308       -flarge-source-files
14309           Adjust GCC to expect large source files, at the expense of slower
14310           compilation and higher memory usage.
14311
14312           Specifically, GCC normally tracks both column numbers and line
14313           numbers within source files and it normally prints both of these
14314           numbers in diagnostics.  However, once it has processed a certain
14315           number of source lines, it stops tracking column numbers and only
14316           tracks line numbers.  This means that diagnostics for later lines
14317           do not include column numbers.  It also means that options like
14318           -Wmisleading-indentation cease to work at that point, although the
14319           compiler prints a note if this happens.  Passing
14320           -flarge-source-files significantly increases the number of source
14321           lines that GCC can process before it stops tracking columns.
14322
14323   Passing Options to the Assembler
14324       You can pass options to the assembler.
14325
14326       -Wa,option
14327           Pass option as an option to the assembler.  If option contains
14328           commas, it is split into multiple options at the commas.
14329
14330       -Xassembler option
14331           Pass option as an option to the assembler.  You can use this to
14332           supply system-specific assembler options that GCC does not
14333           recognize.
14334
14335           If you want to pass an option that takes an argument, you must use
14336           -Xassembler twice, once for the option and once for the argument.
14337
14338   Options for Linking
14339       These options come into play when the compiler links object files into
14340       an executable output file.  They are meaningless if the compiler is not
14341       doing a link step.
14342
14343       object-file-name
14344           A file name that does not end in a special recognized suffix is
14345           considered to name an object file or library.  (Object files are
14346           distinguished from libraries by the linker according to the file
14347           contents.)  If linking is done, these object files are used as
14348           input to the linker.
14349
14350       -c
14351       -S
14352       -E  If any of these options is used, then the linker is not run, and
14353           object file names should not be used as arguments.
14354
14355       -flinker-output=type
14356           This option controls code generation of the link-time optimizer.
14357           By default the linker output is automatically determined by the
14358           linker plugin.  For debugging the compiler and if incremental
14359           linking with a non-LTO object file is desired, it may be useful to
14360           control the type manually.
14361
14362           If type is exec, code generation produces a static binary. In this
14363           case -fpic and -fpie are both disabled.
14364
14365           If type is dyn, code generation produces a shared library.  In this
14366           case -fpic or -fPIC is preserved, but not enabled automatically.
14367           This allows to build shared libraries without position-independent
14368           code on architectures where this is possible, i.e. on x86.
14369
14370           If type is pie, code generation produces an -fpie executable. This
14371           results in similar optimizations as exec except that -fpie is not
14372           disabled if specified at compilation time.
14373
14374           If type is rel, the compiler assumes that incremental linking is
14375           done.  The sections containing intermediate code for link-time
14376           optimization are merged, pre-optimized, and output to the resulting
14377           object file. In addition, if -ffat-lto-objects is specified, binary
14378           code is produced for future non-LTO linking. The object file
14379           produced by incremental linking is smaller than a static library
14380           produced from the same object files.  At link time the result of
14381           incremental linking also loads faster than a static library
14382           assuming that the majority of objects in the library are used.
14383
14384           Finally nolto-rel configures the compiler for incremental linking
14385           where code generation is forced, a final binary is produced, and
14386           the intermediate code for later link-time optimization is stripped.
14387           When multiple object files are linked together the resulting code
14388           is better optimized than with link-time optimizations disabled (for
14389           example, cross-module inlining happens), but most of benefits of
14390           whole program optimizations are lost.
14391
14392           During the incremental link (by -r) the linker plugin defaults to
14393           rel. With current interfaces to GNU Binutils it is however not
14394           possible to incrementally link LTO objects and non-LTO objects into
14395           a single mixed object file.  If any of object files in incremental
14396           link cannot be used for link-time optimization, the linker plugin
14397           issues a warning and uses nolto-rel. To maintain whole program
14398           optimization, it is recommended to link such objects into static
14399           library instead. Alternatively it is possible to use H.J. Lu's
14400           binutils with support for mixed objects.
14401
14402       -fuse-ld=bfd
14403           Use the bfd linker instead of the default linker.
14404
14405       -fuse-ld=gold
14406           Use the gold linker instead of the default linker.
14407
14408       -fuse-ld=lld
14409           Use the LLVM lld linker instead of the default linker.
14410
14411       -fuse-ld=mold
14412           Use the Modern Linker (mold) instead of the default linker.
14413
14414       -llibrary
14415       -l library
14416           Search the library named library when linking.  (The second
14417           alternative with the library as a separate argument is only for
14418           POSIX compliance and is not recommended.)
14419
14420           The -l option is passed directly to the linker by GCC.  Refer to
14421           your linker documentation for exact details.  The general
14422           description below applies to the GNU linker.
14423
14424           The linker searches a standard list of directories for the library.
14425           The directories searched include several standard system
14426           directories plus any that you specify with -L.
14427
14428           Static libraries are archives of object files, and have file names
14429           like liblibrary.a.  Some targets also support shared libraries,
14430           which typically have names like liblibrary.so.  If both static and
14431           shared libraries are found, the linker gives preference to linking
14432           with the shared library unless the -static option is used.
14433
14434           It makes a difference where in the command you write this option;
14435           the linker searches and processes libraries and object files in the
14436           order they are specified.  Thus, foo.o -lz bar.o searches library z
14437           after file foo.o but before bar.o.  If bar.o refers to functions in
14438           z, those functions may not be loaded.
14439
14440       -lobjc
14441           You need this special case of the -l option in order to link an
14442           Objective-C or Objective-C++ program.
14443
14444       -nostartfiles
14445           Do not use the standard system startup files when linking.  The
14446           standard system libraries are used normally, unless -nostdlib,
14447           -nolibc, or -nodefaultlibs is used.
14448
14449       -nodefaultlibs
14450           Do not use the standard system libraries when linking.  Only the
14451           libraries you specify are passed to the linker, and options
14452           specifying linkage of the system libraries, such as -static-libgcc
14453           or -shared-libgcc, are ignored.  The standard startup files are
14454           used normally, unless -nostartfiles is used.
14455
14456           The compiler may generate calls to "memcmp", "memset", "memcpy" and
14457           "memmove".  These entries are usually resolved by entries in libc.
14458           These entry points should be supplied through some other mechanism
14459           when this option is specified.
14460
14461       -nolibc
14462           Do not use the C library or system libraries tightly coupled with
14463           it when linking.  Still link with the startup files, libgcc or
14464           toolchain provided language support libraries such as libgnat,
14465           libgfortran or libstdc++ unless options preventing their inclusion
14466           are used as well.  This typically removes -lc from the link command
14467           line, as well as system libraries that normally go with it and
14468           become meaningless when absence of a C library is assumed, for
14469           example -lpthread or -lm in some configurations.  This is intended
14470           for bare-board targets when there is indeed no C library available.
14471
14472       -nostdlib
14473           Do not use the standard system startup files or libraries when
14474           linking.  No startup files and only the libraries you specify are
14475           passed to the linker, and options specifying linkage of the system
14476           libraries, such as -static-libgcc or -shared-libgcc, are ignored.
14477
14478           The compiler may generate calls to "memcmp", "memset", "memcpy" and
14479           "memmove".  These entries are usually resolved by entries in libc.
14480           These entry points should be supplied through some other mechanism
14481           when this option is specified.
14482
14483           One of the standard libraries bypassed by -nostdlib and
14484           -nodefaultlibs is libgcc.a, a library of internal subroutines which
14485           GCC uses to overcome shortcomings of particular machines, or
14486           special needs for some languages.
14487
14488           In most cases, you need libgcc.a even when you want to avoid other
14489           standard libraries.  In other words, when you specify -nostdlib or
14490           -nodefaultlibs you should usually specify -lgcc as well.  This
14491           ensures that you have no unresolved references to internal GCC
14492           library subroutines.  (An example of such an internal subroutine is
14493           "__main", used to ensure C++ constructors are called.)
14494
14495       -e entry
14496       --entry=entry
14497           Specify that the program entry point is entry.  The argument is
14498           interpreted by the linker; the GNU linker accepts either a symbol
14499           name or an address.
14500
14501       -pie
14502           Produce a dynamically linked position independent executable on
14503           targets that support it.  For predictable results, you must also
14504           specify the same set of options used for compilation (-fpie, -fPIE,
14505           or model suboptions) when you specify this linker option.
14506
14507       -no-pie
14508           Don't produce a dynamically linked position independent executable.
14509
14510       -static-pie
14511           Produce a static position independent executable on targets that
14512           support it.  A static position independent executable is similar to
14513           a static executable, but can be loaded at any address without a
14514           dynamic linker.  For predictable results, you must also specify the
14515           same set of options used for compilation (-fpie, -fPIE, or model
14516           suboptions) when you specify this linker option.
14517
14518       -pthread
14519           Link with the POSIX threads library.  This option is supported on
14520           GNU/Linux targets, most other Unix derivatives, and also on x86
14521           Cygwin and MinGW targets.  On some targets this option also sets
14522           flags for the preprocessor, so it should be used consistently for
14523           both compilation and linking.
14524
14525       -r  Produce a relocatable object as output.  This is also known as
14526           partial linking.
14527
14528       -rdynamic
14529           Pass the flag -export-dynamic to the ELF linker, on targets that
14530           support it. This instructs the linker to add all symbols, not only
14531           used ones, to the dynamic symbol table. This option is needed for
14532           some uses of "dlopen" or to allow obtaining backtraces from within
14533           a program.
14534
14535       -s  Remove all symbol table and relocation information from the
14536           executable.
14537
14538       -static
14539           On systems that support dynamic linking, this overrides -pie and
14540           prevents linking with the shared libraries.  On other systems, this
14541           option has no effect.
14542
14543       -shared
14544           Produce a shared object which can then be linked with other objects
14545           to form an executable.  Not all systems support this option.  For
14546           predictable results, you must also specify the same set of options
14547           used for compilation (-fpic, -fPIC, or model suboptions) when you
14548           specify this linker option.[1]
14549
14550       -shared-libgcc
14551       -static-libgcc
14552           On systems that provide libgcc as a shared library, these options
14553           force the use of either the shared or static version, respectively.
14554           If no shared version of libgcc was built when the compiler was
14555           configured, these options have no effect.
14556
14557           There are several situations in which an application should use the
14558           shared libgcc instead of the static version.  The most common of
14559           these is when the application wishes to throw and catch exceptions
14560           across different shared libraries.  In that case, each of the
14561           libraries as well as the application itself should use the shared
14562           libgcc.
14563
14564           Therefore, the G++ driver automatically adds -shared-libgcc
14565           whenever you build a shared library or a main executable, because
14566           C++ programs typically use exceptions, so this is the right thing
14567           to do.
14568
14569           If, instead, you use the GCC driver to create shared libraries, you
14570           may find that they are not always linked with the shared libgcc.
14571           If GCC finds, at its configuration time, that you have a non-GNU
14572           linker or a GNU linker that does not support option --eh-frame-hdr,
14573           it links the shared version of libgcc into shared libraries by
14574           default.  Otherwise, it takes advantage of the linker and optimizes
14575           away the linking with the shared version of libgcc, linking with
14576           the static version of libgcc by default.  This allows exceptions to
14577           propagate through such shared libraries, without incurring
14578           relocation costs at library load time.
14579
14580           However, if a library or main executable is supposed to throw or
14581           catch exceptions, you must link it using the G++ driver, or using
14582           the option -shared-libgcc, such that it is linked with the shared
14583           libgcc.
14584
14585       -static-libasan
14586           When the -fsanitize=address option is used to link a program, the
14587           GCC driver automatically links against libasan.  If libasan is
14588           available as a shared library, and the -static option is not used,
14589           then this links against the shared version of libasan.  The
14590           -static-libasan option directs the GCC driver to link libasan
14591           statically, without necessarily linking other libraries statically.
14592
14593       -static-libtsan
14594           When the -fsanitize=thread option is used to link a program, the
14595           GCC driver automatically links against libtsan.  If libtsan is
14596           available as a shared library, and the -static option is not used,
14597           then this links against the shared version of libtsan.  The
14598           -static-libtsan option directs the GCC driver to link libtsan
14599           statically, without necessarily linking other libraries statically.
14600
14601       -static-liblsan
14602           When the -fsanitize=leak option is used to link a program, the GCC
14603           driver automatically links against liblsan.  If liblsan is
14604           available as a shared library, and the -static option is not used,
14605           then this links against the shared version of liblsan.  The
14606           -static-liblsan option directs the GCC driver to link liblsan
14607           statically, without necessarily linking other libraries statically.
14608
14609       -static-libubsan
14610           When the -fsanitize=undefined option is used to link a program, the
14611           GCC driver automatically links against libubsan.  If libubsan is
14612           available as a shared library, and the -static option is not used,
14613           then this links against the shared version of libubsan.  The
14614           -static-libubsan option directs the GCC driver to link libubsan
14615           statically, without necessarily linking other libraries statically.
14616
14617       -static-libstdc++
14618           When the g++ program is used to link a C++ program, it normally
14619           automatically links against libstdc++.  If libstdc++ is available
14620           as a shared library, and the -static option is not used, then this
14621           links against the shared version of libstdc++.  That is normally
14622           fine.  However, it is sometimes useful to freeze the version of
14623           libstdc++ used by the program without going all the way to a fully
14624           static link.  The -static-libstdc++ option directs the g++ driver
14625           to link libstdc++ statically, without necessarily linking other
14626           libraries statically.
14627
14628       -symbolic
14629           Bind references to global symbols when building a shared object.
14630           Warn about any unresolved references (unless overridden by the link
14631           editor option -Xlinker -z -Xlinker defs).  Only a few systems
14632           support this option.
14633
14634       -T script
14635           Use script as the linker script.  This option is supported by most
14636           systems using the GNU linker.  On some targets, such as bare-board
14637           targets without an operating system, the -T option may be required
14638           when linking to avoid references to undefined symbols.
14639
14640       -Xlinker option
14641           Pass option as an option to the linker.  You can use this to supply
14642           system-specific linker options that GCC does not recognize.
14643
14644           If you want to pass an option that takes a separate argument, you
14645           must use -Xlinker twice, once for the option and once for the
14646           argument.  For example, to pass -assert definitions, you must write
14647           -Xlinker -assert -Xlinker definitions.  It does not work to write
14648           -Xlinker "-assert definitions", because this passes the entire
14649           string as a single argument, which is not what the linker expects.
14650
14651           When using the GNU linker, it is usually more convenient to pass
14652           arguments to linker options using the option=value syntax than as
14653           separate arguments.  For example, you can specify -Xlinker
14654           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
14655           Other linkers may not support this syntax for command-line options.
14656
14657       -Wl,option
14658           Pass option as an option to the linker.  If option contains commas,
14659           it is split into multiple options at the commas.  You can use this
14660           syntax to pass an argument to the option.  For example,
14661           -Wl,-Map,output.map passes -Map output.map to the linker.  When
14662           using the GNU linker, you can also get the same effect with
14663           -Wl,-Map=output.map.
14664
14665       -u symbol
14666           Pretend the symbol symbol is undefined, to force linking of library
14667           modules to define it.  You can use -u multiple times with different
14668           symbols to force loading of additional library modules.
14669
14670       -z keyword
14671           -z is passed directly on to the linker along with the keyword
14672           keyword. See the section in the documentation of your linker for
14673           permitted values and their meanings.
14674
14675   Options for Directory Search
14676       These options specify directories to search for header files, for
14677       libraries and for parts of the compiler:
14678
14679       -I dir
14680       -iquote dir
14681       -isystem dir
14682       -idirafter dir
14683           Add the directory dir to the list of directories to be searched for
14684           header files during preprocessing.  If dir begins with = or
14685           $SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix;
14686           see --sysroot and -isysroot.
14687
14688           Directories specified with -iquote apply only to the quote form of
14689           the directive, "#include "file"".  Directories specified with -I,
14690           -isystem, or -idirafter apply to lookup for both the
14691           "#include "file"" and "#include <file>" directives.
14692
14693           You can specify any number or combination of these options on the
14694           command line to search for header files in several directories.
14695           The lookup order is as follows:
14696
14697           1.  For the quote form of the include directive, the directory of
14698               the current file is searched first.
14699
14700           2.  For the quote form of the include directive, the directories
14701               specified by -iquote options are searched in left-to-right
14702               order, as they appear on the command line.
14703
14704           3.  Directories specified with -I options are scanned in left-to-
14705               right order.
14706
14707           4.  Directories specified with -isystem options are scanned in
14708               left-to-right order.
14709
14710           5.  Standard system directories are scanned.
14711
14712           6.  Directories specified with -idirafter options are scanned in
14713               left-to-right order.
14714
14715           You can use -I to override a system header file, substituting your
14716           own version, since these directories are searched before the
14717           standard system header file directories.  However, you should not
14718           use this option to add directories that contain vendor-supplied
14719           system header files; use -isystem for that.
14720
14721           The -isystem and -idirafter options also mark the directory as a
14722           system directory, so that it gets the same special treatment that
14723           is applied to the standard system directories.
14724
14725           If a standard system include directory, or a directory specified
14726           with -isystem, is also specified with -I, the -I option is ignored.
14727           The directory is still searched but as a system directory at its
14728           normal position in the system include chain.  This is to ensure
14729           that GCC's procedure to fix buggy system headers and the ordering
14730           for the "#include_next" directive are not inadvertently changed.
14731           If you really need to change the search order for system
14732           directories, use the -nostdinc and/or -isystem options.
14733
14734       -I- Split the include path.  This option has been deprecated.  Please
14735           use -iquote instead for -I directories before the -I- and remove
14736           the -I- option.
14737
14738           Any directories specified with -I options before -I- are searched
14739           only for headers requested with "#include "file""; they are not
14740           searched for "#include <file>".  If additional directories are
14741           specified with -I options after the -I-, those directories are
14742           searched for all #include directives.
14743
14744           In addition, -I- inhibits the use of the directory of the current
14745           file directory as the first search directory for "#include "file"".
14746           There is no way to override this effect of -I-.
14747
14748       -iprefix prefix
14749           Specify prefix as the prefix for subsequent -iwithprefix options.
14750           If the prefix represents a directory, you should include the final
14751           /.
14752
14753       -iwithprefix dir
14754       -iwithprefixbefore dir
14755           Append dir to the prefix specified previously with -iprefix, and
14756           add the resulting directory to the include search path.
14757           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
14758           puts it where -idirafter would.
14759
14760       -isysroot dir
14761           This option is like the --sysroot option, but applies only to
14762           header files (except for Darwin targets, where it applies to both
14763           header files and libraries).  See the --sysroot option for more
14764           information.
14765
14766       -imultilib dir
14767           Use dir as a subdirectory of the directory containing target-
14768           specific C++ headers.
14769
14770       -nostdinc
14771           Do not search the standard system directories for header files.
14772           Only the directories explicitly specified with -I, -iquote,
14773           -isystem, and/or -idirafter options (and the directory of the
14774           current file, if appropriate) are searched.
14775
14776       -nostdinc++
14777           Do not search for header files in the C++-specific standard
14778           directories, but do still search the other standard directories.
14779           (This option is used when building the C++ library.)
14780
14781       -iplugindir=dir
14782           Set the directory to search for plugins that are passed by
14783           -fplugin=name instead of -fplugin=path/name.so.  This option is not
14784           meant to be used by the user, but only passed by the driver.
14785
14786       -Ldir
14787           Add directory dir to the list of directories to be searched for -l.
14788
14789       -Bprefix
14790           This option specifies where to find the executables, libraries,
14791           include files, and data files of the compiler itself.
14792
14793           The compiler driver program runs one or more of the subprograms
14794           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
14795           it tries to run, both with and without machine/version/ for the
14796           corresponding target machine and compiler version.
14797
14798           For each subprogram to be run, the compiler driver first tries the
14799           -B prefix, if any.  If that name is not found, or if -B is not
14800           specified, the driver tries two standard prefixes, /usr/lib/gcc/
14801           and /usr/local/lib/gcc/.  If neither of those results in a file
14802           name that is found, the unmodified program name is searched for
14803           using the directories specified in your PATH environment variable.
14804
14805           The compiler checks to see if the path provided by -B refers to a
14806           directory, and if necessary it adds a directory separator character
14807           at the end of the path.
14808
14809           -B prefixes that effectively specify directory names also apply to
14810           libraries in the linker, because the compiler translates these
14811           options into -L options for the linker.  They also apply to include
14812           files in the preprocessor, because the compiler translates these
14813           options into -isystem options for the preprocessor.  In this case,
14814           the compiler appends include to the prefix.
14815
14816           The runtime support file libgcc.a can also be searched for using
14817           the -B prefix, if needed.  If it is not found there, the two
14818           standard prefixes above are tried, and that is all.  The file is
14819           left out of the link if it is not found by those means.
14820
14821           Another way to specify a prefix much like the -B prefix is to use
14822           the environment variable GCC_EXEC_PREFIX.
14823
14824           As a special kludge, if the path provided by -B is [dir/]stageN/,
14825           where N is a number in the range 0 to 9, then it is replaced by
14826           [dir/]include.  This is to help with boot-strapping the compiler.
14827
14828       -no-canonical-prefixes
14829           Do not expand any symbolic links, resolve references to /../ or
14830           /./, or make the path absolute when generating a relative prefix.
14831
14832       --sysroot=dir
14833           Use dir as the logical root directory for headers and libraries.
14834           For example, if the compiler normally searches for headers in
14835           /usr/include and libraries in /usr/lib, it instead searches
14836           dir/usr/include and dir/usr/lib.
14837
14838           If you use both this option and the -isysroot option, then the
14839           --sysroot option applies to libraries, but the -isysroot option
14840           applies to header files.
14841
14842           The GNU linker (beginning with version 2.16) has the necessary
14843           support for this option.  If your linker does not support this
14844           option, the header file aspect of --sysroot still works, but the
14845           library aspect does not.
14846
14847       --no-sysroot-suffix
14848           For some targets, a suffix is added to the root directory specified
14849           with --sysroot, depending on the other options used, so that
14850           headers may for example be found in dir/suffix/usr/include instead
14851           of dir/usr/include.  This option disables the addition of such a
14852           suffix.
14853
14854   Options for Code Generation Conventions
14855       These machine-independent options control the interface conventions
14856       used in code generation.
14857
14858       Most of them have both positive and negative forms; the negative form
14859       of -ffoo is -fno-foo.  In the table below, only one of the forms is
14860       listed---the one that is not the default.  You can figure out the other
14861       form by either removing no- or adding it.
14862
14863       -fstack-reuse=reuse-level
14864           This option controls stack space reuse for user declared local/auto
14865           variables and compiler generated temporaries.  reuse_level can be
14866           all, named_vars, or none. all enables stack reuse for all local
14867           variables and temporaries, named_vars enables the reuse only for
14868           user defined local variables with names, and none disables stack
14869           reuse completely. The default value is all. The option is needed
14870           when the program extends the lifetime of a scoped local variable or
14871           a compiler generated temporary beyond the end point defined by the
14872           language.  When a lifetime of a variable ends, and if the variable
14873           lives in memory, the optimizing compiler has the freedom to reuse
14874           its stack space with other temporaries or scoped local variables
14875           whose live range does not overlap with it. Legacy code extending
14876           local lifetime is likely to break with the stack reuse
14877           optimization.
14878
14879           For example,
14880
14881                      int *p;
14882                      {
14883                        int local1;
14884
14885                        p = &local1;
14886                        local1 = 10;
14887                        ....
14888                      }
14889                      {
14890                         int local2;
14891                         local2 = 20;
14892                         ...
14893                      }
14894
14895                      if (*p == 10)  // out of scope use of local1
14896                        {
14897
14898                        }
14899
14900           Another example:
14901
14902                      struct A
14903                      {
14904                          A(int k) : i(k), j(k) { }
14905                          int i;
14906                          int j;
14907                      };
14908
14909                      A *ap;
14910
14911                      void foo(const A& ar)
14912                      {
14913                         ap = &ar;
14914                      }
14915
14916                      void bar()
14917                      {
14918                         foo(A(10)); // temp object's lifetime ends when foo returns
14919
14920                         {
14921                           A a(20);
14922                           ....
14923                         }
14924                         ap->i+= 10;  // ap references out of scope temp whose space
14925                                      // is reused with a. What is the value of ap->i?
14926                      }
14927
14928           The lifetime of a compiler generated temporary is well defined by
14929           the C++ standard. When a lifetime of a temporary ends, and if the
14930           temporary lives in memory, the optimizing compiler has the freedom
14931           to reuse its stack space with other temporaries or scoped local
14932           variables whose live range does not overlap with it. However some
14933           of the legacy code relies on the behavior of older compilers in
14934           which temporaries' stack space is not reused, the aggressive stack
14935           reuse can lead to runtime errors. This option is used to control
14936           the temporary stack reuse optimization.
14937
14938       -ftrapv
14939           This option generates traps for signed overflow on addition,
14940           subtraction, multiplication operations.  The options -ftrapv and
14941           -fwrapv override each other, so using -ftrapv -fwrapv on the
14942           command-line results in -fwrapv being effective.  Note that only
14943           active options override, so using -ftrapv -fwrapv -fno-wrapv on the
14944           command-line results in -ftrapv being effective.
14945
14946       -fwrapv
14947           This option instructs the compiler to assume that signed arithmetic
14948           overflow of addition, subtraction and multiplication wraps around
14949           using twos-complement representation.  This flag enables some
14950           optimizations and disables others.  The options -ftrapv and -fwrapv
14951           override each other, so using -ftrapv -fwrapv on the command-line
14952           results in -fwrapv being effective.  Note that only active options
14953           override, so using -ftrapv -fwrapv -fno-wrapv on the command-line
14954           results in -ftrapv being effective.
14955
14956       -fwrapv-pointer
14957           This option instructs the compiler to assume that pointer
14958           arithmetic overflow on addition and subtraction wraps around using
14959           twos-complement representation.  This flag disables some
14960           optimizations which assume pointer overflow is invalid.
14961
14962       -fstrict-overflow
14963           This option implies -fno-wrapv -fno-wrapv-pointer and when negated
14964           implies -fwrapv -fwrapv-pointer.
14965
14966       -fexceptions
14967           Enable exception handling.  Generates extra code needed to
14968           propagate exceptions.  For some targets, this implies GCC generates
14969           frame unwind information for all functions, which can produce
14970           significant data size overhead, although it does not affect
14971           execution.  If you do not specify this option, GCC enables it by
14972           default for languages like C++ that normally require exception
14973           handling, and disables it for languages like C that do not normally
14974           require it.  However, you may need to enable this option when
14975           compiling C code that needs to interoperate properly with exception
14976           handlers written in C++.  You may also wish to disable this option
14977           if you are compiling older C++ programs that don't use exception
14978           handling.
14979
14980       -fnon-call-exceptions
14981           Generate code that allows trapping instructions to throw
14982           exceptions.  Note that this requires platform-specific runtime
14983           support that does not exist everywhere.  Moreover, it only allows
14984           trapping instructions to throw exceptions, i.e. memory references
14985           or floating-point instructions.  It does not allow exceptions to be
14986           thrown from arbitrary signal handlers such as "SIGALRM".  This
14987           enables -fexceptions.
14988
14989       -fdelete-dead-exceptions
14990           Consider that instructions that may throw exceptions but don't
14991           otherwise contribute to the execution of the program can be
14992           optimized away.  This does not affect calls to functions except
14993           those with the "pure" or "const" attributes.  This option is
14994           enabled by default for the Ada and C++ compilers, as permitted by
14995           the language specifications.  Optimization passes that cause dead
14996           exceptions to be removed are enabled independently at different
14997           optimization levels.
14998
14999       -funwind-tables
15000           Similar to -fexceptions, except that it just generates any needed
15001           static data, but does not affect the generated code in any other
15002           way.  You normally do not need to enable this option; instead, a
15003           language processor that needs this handling enables it on your
15004           behalf.
15005
15006       -fasynchronous-unwind-tables
15007           Generate unwind table in DWARF format, if supported by target
15008           machine.  The table is exact at each instruction boundary, so it
15009           can be used for stack unwinding from asynchronous events (such as
15010           debugger or garbage collector).
15011
15012       -fno-gnu-unique
15013           On systems with recent GNU assembler and C library, the C++
15014           compiler uses the "STB_GNU_UNIQUE" binding to make sure that
15015           definitions of template static data members and static local
15016           variables in inline functions are unique even in the presence of
15017           "RTLD_LOCAL"; this is necessary to avoid problems with a library
15018           used by two different "RTLD_LOCAL" plugins depending on a
15019           definition in one of them and therefore disagreeing with the other
15020           one about the binding of the symbol.  But this causes "dlclose" to
15021           be ignored for affected DSOs; if your program relies on
15022           reinitialization of a DSO via "dlclose" and "dlopen", you can use
15023           -fno-gnu-unique.
15024
15025       -fpcc-struct-return
15026           Return "short" "struct" and "union" values in memory like longer
15027           ones, rather than in registers.  This convention is less efficient,
15028           but it has the advantage of allowing intercallability between GCC-
15029           compiled files and files compiled with other compilers,
15030           particularly the Portable C Compiler (pcc).
15031
15032           The precise convention for returning structures in memory depends
15033           on the target configuration macros.
15034
15035           Short structures and unions are those whose size and alignment
15036           match that of some integer type.
15037
15038           Warning: code compiled with the -fpcc-struct-return switch is not
15039           binary compatible with code compiled with the -freg-struct-return
15040           switch.  Use it to conform to a non-default application binary
15041           interface.
15042
15043       -freg-struct-return
15044           Return "struct" and "union" values in registers when possible.
15045           This is more efficient for small structures than
15046           -fpcc-struct-return.
15047
15048           If you specify neither -fpcc-struct-return nor -freg-struct-return,
15049           GCC defaults to whichever convention is standard for the target.
15050           If there is no standard convention, GCC defaults to
15051           -fpcc-struct-return, except on targets where GCC is the principal
15052           compiler.  In those cases, we can choose the standard, and we chose
15053           the more efficient register return alternative.
15054
15055           Warning: code compiled with the -freg-struct-return switch is not
15056           binary compatible with code compiled with the -fpcc-struct-return
15057           switch.  Use it to conform to a non-default application binary
15058           interface.
15059
15060       -fshort-enums
15061           Allocate to an "enum" type only as many bytes as it needs for the
15062           declared range of possible values.  Specifically, the "enum" type
15063           is equivalent to the smallest integer type that has enough room.
15064
15065           Warning: the -fshort-enums switch causes GCC to generate code that
15066           is not binary compatible with code generated without that switch.
15067           Use it to conform to a non-default application binary interface.
15068
15069       -fshort-wchar
15070           Override the underlying type for "wchar_t" to be "short unsigned
15071           int" instead of the default for the target.  This option is useful
15072           for building programs to run under WINE.
15073
15074           Warning: the -fshort-wchar switch causes GCC to generate code that
15075           is not binary compatible with code generated without that switch.
15076           Use it to conform to a non-default application binary interface.
15077
15078       -fcommon
15079           In C code, this option controls the placement of global variables
15080           defined without an initializer, known as tentative definitions in
15081           the C standard.  Tentative definitions are distinct from
15082           declarations of a variable with the "extern" keyword, which do not
15083           allocate storage.
15084
15085           The default is -fno-common, which specifies that the compiler
15086           places uninitialized global variables in the BSS section of the
15087           object file.  This inhibits the merging of tentative definitions by
15088           the linker so you get a multiple-definition error if the same
15089           variable is accidentally defined in more than one compilation unit.
15090
15091           The -fcommon places uninitialized global variables in a common
15092           block.  This allows the linker to resolve all tentative definitions
15093           of the same variable in different compilation units to the same
15094           object, or to a non-tentative definition.  This behavior is
15095           inconsistent with C++, and on many targets implies a speed and code
15096           size penalty on global variable references.  It is mainly useful to
15097           enable legacy code to link without errors.
15098
15099       -fno-ident
15100           Ignore the "#ident" directive.
15101
15102       -finhibit-size-directive
15103           Don't output a ".size" assembler directive, or anything else that
15104           would cause trouble if the function is split in the middle, and the
15105           two halves are placed at locations far apart in memory.  This
15106           option is used when compiling crtstuff.c; you should not need to
15107           use it for anything else.
15108
15109       -fverbose-asm
15110           Put extra commentary information in the generated assembly code to
15111           make it more readable.  This option is generally only of use to
15112           those who actually need to read the generated assembly code
15113           (perhaps while debugging the compiler itself).
15114
15115           -fno-verbose-asm, the default, causes the extra information to be
15116           omitted and is useful when comparing two assembler files.
15117
15118           The added comments include:
15119
15120           *   information on the compiler version and command-line options,
15121
15122           *   the source code lines associated with the assembly
15123               instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,
15124
15125           *   hints on which high-level expressions correspond to the various
15126               assembly instruction operands.
15127
15128           For example, given this C source file:
15129
15130                   int test (int n)
15131                   {
15132                     int i;
15133                     int total = 0;
15134
15135                     for (i = 0; i < n; i++)
15136                       total += i * i;
15137
15138                     return total;
15139                   }
15140
15141           compiling to (x86_64) assembly via -S and emitting the result
15142           direct to stdout via -o -
15143
15144                   gcc -S test.c -fverbose-asm -Os -o -
15145
15146           gives output similar to this:
15147
15148                           .file   "test.c"
15149                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
15150                     [...snip...]
15151                   # options passed:
15152                     [...snip...]
15153
15154                           .text
15155                           .globl  test
15156                           .type   test, @function
15157                   test:
15158                   .LFB0:
15159                           .cfi_startproc
15160                   # test.c:4:   int total = 0;
15161                           xorl    %eax, %eax      # <retval>
15162                   # test.c:6:   for (i = 0; i < n; i++)
15163                           xorl    %edx, %edx      # i
15164                   .L2:
15165                   # test.c:6:   for (i = 0; i < n; i++)
15166                           cmpl    %edi, %edx      # n, i
15167                           jge     .L5     #,
15168                   # test.c:7:     total += i * i;
15169                           movl    %edx, %ecx      # i, tmp92
15170                           imull   %edx, %ecx      # i, tmp92
15171                   # test.c:6:   for (i = 0; i < n; i++)
15172                           incl    %edx    # i
15173                   # test.c:7:     total += i * i;
15174                           addl    %ecx, %eax      # tmp92, <retval>
15175                           jmp     .L2     #
15176                   .L5:
15177                   # test.c:10: }
15178                           ret
15179                           .cfi_endproc
15180                   .LFE0:
15181                           .size   test, .-test
15182                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
15183                           .section        .note.GNU-stack,"",@progbits
15184
15185           The comments are intended for humans rather than machines and hence
15186           the precise format of the comments is subject to change.
15187
15188       -frecord-gcc-switches
15189           This switch causes the command line used to invoke the compiler to
15190           be recorded into the object file that is being created.  This
15191           switch is only implemented on some targets and the exact format of
15192           the recording is target and binary file format dependent, but it
15193           usually takes the form of a section containing ASCII text.  This
15194           switch is related to the -fverbose-asm switch, but that switch only
15195           records information in the assembler output file as comments, so it
15196           never reaches the object file.  See also -grecord-gcc-switches for
15197           another way of storing compiler options into the object file.
15198
15199       -fpic
15200           Generate position-independent code (PIC) suitable for use in a
15201           shared library, if supported for the target machine.  Such code
15202           accesses all constant addresses through a global offset table
15203           (GOT).  The dynamic loader resolves the GOT entries when the
15204           program starts (the dynamic loader is not part of GCC; it is part
15205           of the operating system).  If the GOT size for the linked
15206           executable exceeds a machine-specific maximum size, you get an
15207           error message from the linker indicating that -fpic does not work;
15208           in that case, recompile with -fPIC instead.  (These maximums are 8k
15209           on the SPARC, 28k on AArch64 and 32k on the m68k and RS/6000.  The
15210           x86 has no such limit.)
15211
15212           Position-independent code requires special support, and therefore
15213           works only on certain machines.  For the x86, GCC supports PIC for
15214           System V but not for the Sun 386i.  Code generated for the IBM
15215           RS/6000 is always position-independent.
15216
15217           When this flag is set, the macros "__pic__" and "__PIC__" are
15218           defined to 1.
15219
15220       -fPIC
15221           If supported for the target machine, emit position-independent
15222           code, suitable for dynamic linking and avoiding any limit on the
15223           size of the global offset table.  This option makes a difference on
15224           AArch64, m68k, PowerPC and SPARC.
15225
15226           Position-independent code requires special support, and therefore
15227           works only on certain machines.
15228
15229           When this flag is set, the macros "__pic__" and "__PIC__" are
15230           defined to 2.
15231
15232       -fpie
15233       -fPIE
15234           These options are similar to -fpic and -fPIC, but the generated
15235           position-independent code can be only linked into executables.
15236           Usually these options are used to compile code that will be linked
15237           using the -pie GCC option.
15238
15239           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
15240           The macros have the value 1 for -fpie and 2 for -fPIE.
15241
15242       -fno-plt
15243           Do not use the PLT for external function calls in position-
15244           independent code.  Instead, load the callee address at call sites
15245           from the GOT and branch to it.  This leads to more efficient code
15246           by eliminating PLT stubs and exposing GOT loads to optimizations.
15247           On architectures such as 32-bit x86 where PLT stubs expect the GOT
15248           pointer in a specific register, this gives more register allocation
15249           freedom to the compiler.  Lazy binding requires use of the PLT;
15250           with -fno-plt all external symbols are resolved at load time.
15251
15252           Alternatively, the function attribute "noplt" can be used to avoid
15253           calls through the PLT for specific external functions.
15254
15255           In position-dependent code, a few targets also convert calls to
15256           functions that are marked to not use the PLT to use the GOT
15257           instead.
15258
15259       -fno-jump-tables
15260           Do not use jump tables for switch statements even where it would be
15261           more efficient than other code generation strategies.  This option
15262           is of use in conjunction with -fpic or -fPIC for building code that
15263           forms part of a dynamic linker and cannot reference the address of
15264           a jump table.  On some targets, jump tables do not require a GOT
15265           and this option is not needed.
15266
15267       -fno-bit-tests
15268           Do not use bit tests for switch statements even where it would be
15269           more efficient than other code generation strategies.
15270
15271       -ffixed-reg
15272           Treat the register named reg as a fixed register; generated code
15273           should never refer to it (except perhaps as a stack pointer, frame
15274           pointer or in some other fixed role).
15275
15276           reg must be the name of a register.  The register names accepted
15277           are machine-specific and are defined in the "REGISTER_NAMES" macro
15278           in the machine description macro file.
15279
15280           This flag does not have a negative form, because it specifies a
15281           three-way choice.
15282
15283       -fcall-used-reg
15284           Treat the register named reg as an allocable register that is
15285           clobbered by function calls.  It may be allocated for temporaries
15286           or variables that do not live across a call.  Functions compiled
15287           this way do not save and restore the register reg.
15288
15289           It is an error to use this flag with the frame pointer or stack
15290           pointer.  Use of this flag for other registers that have fixed
15291           pervasive roles in the machine's execution model produces
15292           disastrous results.
15293
15294           This flag does not have a negative form, because it specifies a
15295           three-way choice.
15296
15297       -fcall-saved-reg
15298           Treat the register named reg as an allocable register saved by
15299           functions.  It may be allocated even for temporaries or variables
15300           that live across a call.  Functions compiled this way save and
15301           restore the register reg if they use it.
15302
15303           It is an error to use this flag with the frame pointer or stack
15304           pointer.  Use of this flag for other registers that have fixed
15305           pervasive roles in the machine's execution model produces
15306           disastrous results.
15307
15308           A different sort of disaster results from the use of this flag for
15309           a register in which function values may be returned.
15310
15311           This flag does not have a negative form, because it specifies a
15312           three-way choice.
15313
15314       -fpack-struct[=n]
15315           Without a value specified, pack all structure members together
15316           without holes.  When a value is specified (which must be a small
15317           power of two), pack structure members according to this value,
15318           representing the maximum alignment (that is, objects with default
15319           alignment requirements larger than this are output potentially
15320           unaligned at the next fitting location.
15321
15322           Warning: the -fpack-struct switch causes GCC to generate code that
15323           is not binary compatible with code generated without that switch.
15324           Additionally, it makes the code suboptimal.  Use it to conform to a
15325           non-default application binary interface.
15326
15327       -fleading-underscore
15328           This option and its counterpart, -fno-leading-underscore, forcibly
15329           change the way C symbols are represented in the object file.  One
15330           use is to help link with legacy assembly code.
15331
15332           Warning: the -fleading-underscore switch causes GCC to generate
15333           code that is not binary compatible with code generated without that
15334           switch.  Use it to conform to a non-default application binary
15335           interface.  Not all targets provide complete support for this
15336           switch.
15337
15338       -ftls-model=model
15339           Alter the thread-local storage model to be used.  The model
15340           argument should be one of global-dynamic, local-dynamic, initial-
15341           exec or local-exec.  Note that the choice is subject to
15342           optimization: the compiler may use a more efficient model for
15343           symbols not visible outside of the translation unit, or if -fpic is
15344           not given on the command line.
15345
15346           The default without -fpic is initial-exec; with -fpic the default
15347           is global-dynamic.
15348
15349       -ftrampolines
15350           For targets that normally need trampolines for nested functions,
15351           always generate them instead of using descriptors.  Otherwise, for
15352           targets that do not need them, like for example HP-PA or IA-64, do
15353           nothing.
15354
15355           A trampoline is a small piece of code that is created at run time
15356           on the stack when the address of a nested function is taken, and is
15357           used to call the nested function indirectly.  Therefore, it
15358           requires the stack to be made executable in order for the program
15359           to work properly.
15360
15361           -fno-trampolines is enabled by default on a language by language
15362           basis to let the compiler avoid generating them, if it computes
15363           that this is safe, and replace them with descriptors.  Descriptors
15364           are made up of data only, but the generated code must be prepared
15365           to deal with them.  As of this writing, -fno-trampolines is enabled
15366           by default only for Ada.
15367
15368           Moreover, code compiled with -ftrampolines and code compiled with
15369           -fno-trampolines are not binary compatible if nested functions are
15370           present.  This option must therefore be used on a program-wide
15371           basis and be manipulated with extreme care.
15372
15373           For languages other than Ada, the "-ftrampolines" and
15374           "-fno-trampolines" options currently have no effect, and
15375           trampolines are always generated on platforms that need them for
15376           nested functions.
15377
15378       -fvisibility=[default|internal|hidden|protected]
15379           Set the default ELF image symbol visibility to the specified
15380           option---all symbols are marked with this unless overridden within
15381           the code.  Using this feature can very substantially improve
15382           linking and load times of shared object libraries, produce more
15383           optimized code, provide near-perfect API export and prevent symbol
15384           clashes.  It is strongly recommended that you use this in any
15385           shared objects you distribute.
15386
15387           Despite the nomenclature, default always means public; i.e.,
15388           available to be linked against from outside the shared object.
15389           protected and internal are pretty useless in real-world usage so
15390           the only other commonly used option is hidden.  The default if
15391           -fvisibility isn't specified is default, i.e., make every symbol
15392           public.
15393
15394           A good explanation of the benefits offered by ensuring ELF symbols
15395           have the correct visibility is given by "How To Write Shared
15396           Libraries" by Ulrich Drepper (which can be found at
15397           <https://www.akkadia.org/drepper/>)---however a superior solution
15398           made possible by this option to marking things hidden when the
15399           default is public is to make the default hidden and mark things
15400           public.  This is the norm with DLLs on Windows and with
15401           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
15402           instead of "__declspec(dllexport)" you get almost identical
15403           semantics with identical syntax.  This is a great boon to those
15404           working with cross-platform projects.
15405
15406           For those adding visibility support to existing code, you may find
15407           "#pragma GCC visibility" of use.  This works by you enclosing the
15408           declarations you wish to set visibility for with (for example)
15409           "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility
15410           pop".  Bear in mind that symbol visibility should be viewed as part
15411           of the API interface contract and thus all new code should always
15412           specify visibility when it is not the default; i.e., declarations
15413           only for use within the local DSO should always be marked
15414           explicitly as hidden as so to avoid PLT indirection
15415           overheads---making this abundantly clear also aids readability and
15416           self-documentation of the code.  Note that due to ISO C++
15417           specification requirements, "operator new" and "operator delete"
15418           must always be of default visibility.
15419
15420           Be aware that headers from outside your project, in particular
15421           system headers and headers from any other library you use, may not
15422           be expecting to be compiled with visibility other than the default.
15423           You may need to explicitly say "#pragma GCC visibility
15424           push(default)" before including any such headers.
15425
15426           "extern" declarations are not affected by -fvisibility, so a lot of
15427           code can be recompiled with -fvisibility=hidden with no
15428           modifications.  However, this means that calls to "extern"
15429           functions with no explicit visibility use the PLT, so it is more
15430           effective to use "__attribute ((visibility))" and/or "#pragma GCC
15431           visibility" to tell the compiler which "extern" declarations should
15432           be treated as hidden.
15433
15434           Note that -fvisibility does affect C++ vague linkage entities. This
15435           means that, for instance, an exception class that is be thrown
15436           between DSOs must be explicitly marked with default visibility so
15437           that the type_info nodes are unified between the DSOs.
15438
15439           An overview of these techniques, their benefits and how to use them
15440           is at <https://gcc.gnu.org/wiki/Visibility>.
15441
15442       -fstrict-volatile-bitfields
15443           This option should be used if accesses to volatile bit-fields (or
15444           other structure fields, although the compiler usually honors those
15445           types anyway) should use a single access of the width of the
15446           field's type, aligned to a natural alignment if possible.  For
15447           example, targets with memory-mapped peripheral registers might
15448           require all such accesses to be 16 bits wide; with this flag you
15449           can declare all peripheral bit-fields as "unsigned short" (assuming
15450           short is 16 bits on these targets) to force GCC to use 16-bit
15451           accesses instead of, perhaps, a more efficient 32-bit access.
15452
15453           If this option is disabled, the compiler uses the most efficient
15454           instruction.  In the previous example, that might be a 32-bit load
15455           instruction, even though that accesses bytes that do not contain
15456           any portion of the bit-field, or memory-mapped registers unrelated
15457           to the one being updated.
15458
15459           In some cases, such as when the "packed" attribute is applied to a
15460           structure field, it may not be possible to access the field with a
15461           single read or write that is correctly aligned for the target
15462           machine.  In this case GCC falls back to generating multiple
15463           accesses rather than code that will fault or truncate the result at
15464           run time.
15465
15466           Note:  Due to restrictions of the C/C++11 memory model, write
15467           accesses are not allowed to touch non bit-field members.  It is
15468           therefore recommended to define all bits of the field's type as
15469           bit-field members.
15470
15471           The default value of this option is determined by the application
15472           binary interface for the target processor.
15473
15474       -fsync-libcalls
15475           This option controls whether any out-of-line instance of the
15476           "__sync" family of functions may be used to implement the C++11
15477           "__atomic" family of functions.
15478
15479           The default value of this option is enabled, thus the only useful
15480           form of the option is -fno-sync-libcalls.  This option is used in
15481           the implementation of the libatomic runtime library.
15482
15483   GCC Developer Options
15484       This section describes command-line options that are primarily of
15485       interest to GCC developers, including options to support compiler
15486       testing and investigation of compiler bugs and compile-time performance
15487       problems.  This includes options that produce debug dumps at various
15488       points in the compilation; that print statistics such as memory use and
15489       execution time; and that print information about GCC's configuration,
15490       such as where it searches for libraries.  You should rarely need to use
15491       any of these options for ordinary compilation and linking tasks.
15492
15493       Many developer options that cause GCC to dump output to a file take an
15494       optional =filename suffix. You can specify stdout or - to dump to
15495       standard output, and stderr for standard error.
15496
15497       If =filename is omitted, a default dump file name is constructed by
15498       concatenating the base dump file name, a pass number, phase letter, and
15499       pass name.  The base dump file name is the name of output file produced
15500       by the compiler if explicitly specified and not an executable;
15501       otherwise it is the source file name.  The pass number is determined by
15502       the order passes are registered with the compiler's pass manager.  This
15503       is generally the same as the order of execution, but passes registered
15504       by plugins, target-specific passes, or passes that are otherwise
15505       registered late are numbered higher than the pass named final, even if
15506       they are executed earlier.  The phase letter is one of i (inter-
15507       procedural analysis), l (language-specific), r (RTL), or t (tree).  The
15508       files are created in the directory of the output file.
15509
15510       -fcallgraph-info
15511       -fcallgraph-info=MARKERS
15512           Makes the compiler output callgraph information for the program, on
15513           a per-object-file basis.  The information is generated in the
15514           common VCG format.  It can be decorated with additional, per-node
15515           and/or per-edge information, if a list of comma-separated markers
15516           is additionally specified.  When the "su" marker is specified, the
15517           callgraph is decorated with stack usage information; it is
15518           equivalent to -fstack-usage.  When the "da" marker is specified,
15519           the callgraph is decorated with information about dynamically
15520           allocated objects.
15521
15522           When compiling with -flto, no callgraph information is output along
15523           with the object file.  At LTO link time, -fcallgraph-info may
15524           generate multiple callgraph information files next to intermediate
15525           LTO output files.
15526
15527       -dletters
15528       -fdump-rtl-pass
15529       -fdump-rtl-pass=filename
15530           Says to make debugging dumps during compilation at times specified
15531           by letters.  This is used for debugging the RTL-based passes of the
15532           compiler.
15533
15534           Some -dletters switches have different meaning when -E is used for
15535           preprocessing.
15536
15537           Debug dumps can be enabled with a -fdump-rtl switch or some -d
15538           option letters.  Here are the possible letters for use in pass and
15539           letters, and their meanings:
15540
15541           -fdump-rtl-alignments
15542               Dump after branch alignments have been computed.
15543
15544           -fdump-rtl-asmcons
15545               Dump after fixing rtl statements that have unsatisfied in/out
15546               constraints.
15547
15548           -fdump-rtl-auto_inc_dec
15549               Dump after auto-inc-dec discovery.  This pass is only run on
15550               architectures that have auto inc or auto dec instructions.
15551
15552           -fdump-rtl-barriers
15553               Dump after cleaning up the barrier instructions.
15554
15555           -fdump-rtl-bbpart
15556               Dump after partitioning hot and cold basic blocks.
15557
15558           -fdump-rtl-bbro
15559               Dump after block reordering.
15560
15561           -fdump-rtl-btl1
15562           -fdump-rtl-btl2
15563               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
15564               two branch target load optimization passes.
15565
15566           -fdump-rtl-bypass
15567               Dump after jump bypassing and control flow optimizations.
15568
15569           -fdump-rtl-combine
15570               Dump after the RTL instruction combination pass.
15571
15572           -fdump-rtl-compgotos
15573               Dump after duplicating the computed gotos.
15574
15575           -fdump-rtl-ce1
15576           -fdump-rtl-ce2
15577           -fdump-rtl-ce3
15578               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
15579               dumping after the three if conversion passes.
15580
15581           -fdump-rtl-cprop_hardreg
15582               Dump after hard register copy propagation.
15583
15584           -fdump-rtl-csa
15585               Dump after combining stack adjustments.
15586
15587           -fdump-rtl-cse1
15588           -fdump-rtl-cse2
15589               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
15590               two common subexpression elimination passes.
15591
15592           -fdump-rtl-dce
15593               Dump after the standalone dead code elimination passes.
15594
15595           -fdump-rtl-dbr
15596               Dump after delayed branch scheduling.
15597
15598           -fdump-rtl-dce1
15599           -fdump-rtl-dce2
15600               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
15601               two dead store elimination passes.
15602
15603           -fdump-rtl-eh
15604               Dump after finalization of EH handling code.
15605
15606           -fdump-rtl-eh_ranges
15607               Dump after conversion of EH handling range regions.
15608
15609           -fdump-rtl-expand
15610               Dump after RTL generation.
15611
15612           -fdump-rtl-fwprop1
15613           -fdump-rtl-fwprop2
15614               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
15615               the two forward propagation passes.
15616
15617           -fdump-rtl-gcse1
15618           -fdump-rtl-gcse2
15619               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
15620               global common subexpression elimination.
15621
15622           -fdump-rtl-init-regs
15623               Dump after the initialization of the registers.
15624
15625           -fdump-rtl-initvals
15626               Dump after the computation of the initial value sets.
15627
15628           -fdump-rtl-into_cfglayout
15629               Dump after converting to cfglayout mode.
15630
15631           -fdump-rtl-ira
15632               Dump after iterated register allocation.
15633
15634           -fdump-rtl-jump
15635               Dump after the second jump optimization.
15636
15637           -fdump-rtl-loop2
15638               -fdump-rtl-loop2 enables dumping after the rtl loop
15639               optimization passes.
15640
15641           -fdump-rtl-mach
15642               Dump after performing the machine dependent reorganization
15643               pass, if that pass exists.
15644
15645           -fdump-rtl-mode_sw
15646               Dump after removing redundant mode switches.
15647
15648           -fdump-rtl-rnreg
15649               Dump after register renumbering.
15650
15651           -fdump-rtl-outof_cfglayout
15652               Dump after converting from cfglayout mode.
15653
15654           -fdump-rtl-peephole2
15655               Dump after the peephole pass.
15656
15657           -fdump-rtl-postreload
15658               Dump after post-reload optimizations.
15659
15660           -fdump-rtl-pro_and_epilogue
15661               Dump after generating the function prologues and epilogues.
15662
15663           -fdump-rtl-sched1
15664           -fdump-rtl-sched2
15665               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
15666               the basic block scheduling passes.
15667
15668           -fdump-rtl-ree
15669               Dump after sign/zero extension elimination.
15670
15671           -fdump-rtl-seqabstr
15672               Dump after common sequence discovery.
15673
15674           -fdump-rtl-shorten
15675               Dump after shortening branches.
15676
15677           -fdump-rtl-sibling
15678               Dump after sibling call optimizations.
15679
15680           -fdump-rtl-split1
15681           -fdump-rtl-split2
15682           -fdump-rtl-split3
15683           -fdump-rtl-split4
15684           -fdump-rtl-split5
15685               These options enable dumping after five rounds of instruction
15686               splitting.
15687
15688           -fdump-rtl-sms
15689               Dump after modulo scheduling.  This pass is only run on some
15690               architectures.
15691
15692           -fdump-rtl-stack
15693               Dump after conversion from GCC's "flat register file" registers
15694               to the x87's stack-like registers.  This pass is only run on
15695               x86 variants.
15696
15697           -fdump-rtl-subreg1
15698           -fdump-rtl-subreg2
15699               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
15700               the two subreg expansion passes.
15701
15702           -fdump-rtl-unshare
15703               Dump after all rtl has been unshared.
15704
15705           -fdump-rtl-vartrack
15706               Dump after variable tracking.
15707
15708           -fdump-rtl-vregs
15709               Dump after converting virtual registers to hard registers.
15710
15711           -fdump-rtl-web
15712               Dump after live range splitting.
15713
15714           -fdump-rtl-regclass
15715           -fdump-rtl-subregs_of_mode_init
15716           -fdump-rtl-subregs_of_mode_finish
15717           -fdump-rtl-dfinit
15718           -fdump-rtl-dfinish
15719               These dumps are defined but always produce empty files.
15720
15721           -da
15722           -fdump-rtl-all
15723               Produce all the dumps listed above.
15724
15725           -dA Annotate the assembler output with miscellaneous debugging
15726               information.
15727
15728           -dD Dump all macro definitions, at the end of preprocessing, in
15729               addition to normal output.
15730
15731           -dH Produce a core dump whenever an error occurs.
15732
15733           -dp Annotate the assembler output with a comment indicating which
15734               pattern and alternative is used.  The length and cost of each
15735               instruction are also printed.
15736
15737           -dP Dump the RTL in the assembler output as a comment before each
15738               instruction.  Also turns on -dp annotation.
15739
15740           -dx Just generate RTL for a function instead of compiling it.
15741               Usually used with -fdump-rtl-expand.
15742
15743       -fdump-debug
15744           Dump debugging information generated during the debug generation
15745           phase.
15746
15747       -fdump-earlydebug
15748           Dump debugging information generated during the early debug
15749           generation phase.
15750
15751       -fdump-noaddr
15752           When doing debugging dumps, suppress address output.  This makes it
15753           more feasible to use diff on debugging dumps for compiler
15754           invocations with different compiler binaries and/or different text
15755           / bss / data / heap / stack / dso start locations.
15756
15757       -freport-bug
15758           Collect and dump debug information into a temporary file if an
15759           internal compiler error (ICE) occurs.
15760
15761       -fdump-unnumbered
15762           When doing debugging dumps, suppress instruction numbers and
15763           address output.  This makes it more feasible to use diff on
15764           debugging dumps for compiler invocations with different options, in
15765           particular with and without -g.
15766
15767       -fdump-unnumbered-links
15768           When doing debugging dumps (see -d option above), suppress
15769           instruction numbers for the links to the previous and next
15770           instructions in a sequence.
15771
15772       -fdump-ipa-switch
15773       -fdump-ipa-switch-options
15774           Control the dumping at various stages of inter-procedural analysis
15775           language tree to a file.  The file name is generated by appending a
15776           switch specific suffix to the source file name, and the file is
15777           created in the same directory as the output file.  The following
15778           dumps are possible:
15779
15780           all Enables all inter-procedural analysis dumps.
15781
15782           cgraph
15783               Dumps information about call-graph optimization, unused
15784               function removal, and inlining decisions.
15785
15786           inline
15787               Dump after function inlining.
15788
15789           Additionally, the options -optimized, -missed, -note, and -all can
15790           be provided, with the same meaning as for -fopt-info, defaulting to
15791           -optimized.
15792
15793           For example, -fdump-ipa-inline-optimized-missed will emit
15794           information on callsites that were inlined, along with callsites
15795           that were not inlined.
15796
15797           By default, the dump will contain messages about successful
15798           optimizations (equivalent to -optimized) together with low-level
15799           details about the analysis.
15800
15801       -fdump-lang
15802           Dump language-specific information.  The file name is made by
15803           appending .lang to the source file name.
15804
15805       -fdump-lang-all
15806       -fdump-lang-switch
15807       -fdump-lang-switch-options
15808       -fdump-lang-switch-options=filename
15809           Control the dumping of language-specific information.  The options
15810           and filename portions behave as described in the -fdump-tree
15811           option.  The following switch values are accepted:
15812
15813           all Enable all language-specific dumps.
15814
15815           class
15816               Dump class hierarchy information.  Virtual table information is
15817               emitted unless 'slim' is specified.  This option is applicable
15818               to C++ only.
15819
15820           module
15821               Dump module information.  Options lineno (locations), graph
15822               (reachability), blocks (clusters), uid (serialization), alias
15823               (mergeable), asmname (Elrond), eh (mapper) & vops (macros) may
15824               provide additional information.  This option is applicable to
15825               C++ only.
15826
15827           raw Dump the raw internal tree data.  This option is applicable to
15828               C++ only.
15829
15830       -fdump-passes
15831           Print on stderr the list of optimization passes that are turned on
15832           and off by the current command-line options.
15833
15834       -fdump-statistics-option
15835           Enable and control dumping of pass statistics in a separate file.
15836           The file name is generated by appending a suffix ending in
15837           .statistics to the source file name, and the file is created in the
15838           same directory as the output file.  If the -option form is used,
15839           -stats causes counters to be summed over the whole compilation unit
15840           while -details dumps every event as the passes generate them.  The
15841           default with no option is to sum counters for each function
15842           compiled.
15843
15844       -fdump-tree-all
15845       -fdump-tree-switch
15846       -fdump-tree-switch-options
15847       -fdump-tree-switch-options=filename
15848           Control the dumping at various stages of processing the
15849           intermediate language tree to a file.  If the -options form is
15850           used, options is a list of - separated options which control the
15851           details of the dump.  Not all options are applicable to all dumps;
15852           those that are not meaningful are ignored.  The following options
15853           are available
15854
15855           address
15856               Print the address of each node.  Usually this is not meaningful
15857               as it changes according to the environment and source file.
15858               Its primary use is for tying up a dump file with a debug
15859               environment.
15860
15861           asmname
15862               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
15863               that in the dump instead of "DECL_NAME".  Its primary use is
15864               ease of use working backward from mangled names in the assembly
15865               file.
15866
15867           slim
15868               When dumping front-end intermediate representations, inhibit
15869               dumping of members of a scope or body of a function merely
15870               because that scope has been reached.  Only dump such items when
15871               they are directly reachable by some other path.
15872
15873               When dumping pretty-printed trees, this option inhibits dumping
15874               the bodies of control structures.
15875
15876               When dumping RTL, print the RTL in slim (condensed) form
15877               instead of the default LISP-like representation.
15878
15879           raw Print a raw representation of the tree.  By default, trees are
15880               pretty-printed into a C-like representation.
15881
15882           details
15883               Enable more detailed dumps (not honored by every dump option).
15884               Also include information from the optimization passes.
15885
15886           stats
15887               Enable dumping various statistics about the pass (not honored
15888               by every dump option).
15889
15890           blocks
15891               Enable showing basic block boundaries (disabled in raw dumps).
15892
15893           graph
15894               For each of the other indicated dump files (-fdump-rtl-pass),
15895               dump a representation of the control flow graph suitable for
15896               viewing with GraphViz to file.passid.pass.dot.  Each function
15897               in the file is pretty-printed as a subgraph, so that GraphViz
15898               can render them all in a single plot.
15899
15900               This option currently only works for RTL dumps, and the RTL is
15901               always dumped in slim form.
15902
15903           vops
15904               Enable showing virtual operands for every statement.
15905
15906           lineno
15907               Enable showing line numbers for statements.
15908
15909           uid Enable showing the unique ID ("DECL_UID") for each variable.
15910
15911           verbose
15912               Enable showing the tree dump for each statement.
15913
15914           eh  Enable showing the EH region number holding each statement.
15915
15916           scev
15917               Enable showing scalar evolution analysis details.
15918
15919           optimized
15920               Enable showing optimization information (only available in
15921               certain passes).
15922
15923           missed
15924               Enable showing missed optimization information (only available
15925               in certain passes).
15926
15927           note
15928               Enable other detailed optimization information (only available
15929               in certain passes).
15930
15931           all Turn on all options, except raw, slim, verbose and lineno.
15932
15933           optall
15934               Turn on all optimization options, i.e., optimized, missed, and
15935               note.
15936
15937           To determine what tree dumps are available or find the dump for a
15938           pass of interest follow the steps below.
15939
15940           1.  Invoke GCC with -fdump-passes and in the stderr output look for
15941               a code that corresponds to the pass you are interested in.  For
15942               example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2"
15943               correspond to the three Value Range Propagation passes.  The
15944               number at the end distinguishes distinct invocations of the
15945               same pass.
15946
15947           2.  To enable the creation of the dump file, append the pass code
15948               to the -fdump- option prefix and invoke GCC with it.  For
15949               example, to enable the dump from the Early Value Range
15950               Propagation pass, invoke GCC with the -fdump-tree-evrp option.
15951               Optionally, you may specify the name of the dump file.  If you
15952               don't specify one, GCC creates as described below.
15953
15954           3.  Find the pass dump in a file whose name is composed of three
15955               components separated by a period: the name of the source file
15956               GCC was invoked to compile, a numeric suffix indicating the
15957               pass number followed by the letter t for tree passes (and the
15958               letter r for RTL passes), and finally the pass code.  For
15959               example, the Early VRP pass dump might be in a file named
15960               myfile.c.038t.evrp in the current working directory.  Note that
15961               the numeric codes are not stable and may change from one
15962               version of GCC to another.
15963
15964       -fopt-info
15965       -fopt-info-options
15966       -fopt-info-options=filename
15967           Controls optimization dumps from various optimization passes. If
15968           the -options form is used, options is a list of - separated option
15969           keywords to select the dump details and optimizations.
15970
15971           The options can be divided into three groups:
15972
15973           1.  options describing what kinds of messages should be emitted,
15974
15975           2.  options describing the verbosity of the dump, and
15976
15977           3.  options describing which optimizations should be included.
15978
15979           The options from each group can be freely mixed as they are non-
15980           overlapping. However, in case of any conflicts, the later options
15981           override the earlier options on the command line.
15982
15983           The following options control which kinds of messages should be
15984           emitted:
15985
15986           optimized
15987               Print information when an optimization is successfully applied.
15988               It is up to a pass to decide which information is relevant. For
15989               example, the vectorizer passes print the source location of
15990               loops which are successfully vectorized.
15991
15992           missed
15993               Print information about missed optimizations. Individual passes
15994               control which information to include in the output.
15995
15996           note
15997               Print verbose information about optimizations, such as certain
15998               transformations, more detailed messages about decisions etc.
15999
16000           all Print detailed optimization information. This includes
16001               optimized, missed, and note.
16002
16003           The following option controls the dump verbosity:
16004
16005           internals
16006               By default, only "high-level" messages are emitted. This option
16007               enables additional, more detailed, messages, which are likely
16008               to only be of interest to GCC developers.
16009
16010           One or more of the following option keywords can be used to
16011           describe a group of optimizations:
16012
16013           ipa Enable dumps from all interprocedural optimizations.
16014
16015           loop
16016               Enable dumps from all loop optimizations.
16017
16018           inline
16019               Enable dumps from all inlining optimizations.
16020
16021           omp Enable dumps from all OMP (Offloading and Multi Processing)
16022               optimizations.
16023
16024           vec Enable dumps from all vectorization optimizations.
16025
16026           optall
16027               Enable dumps from all optimizations. This is a superset of the
16028               optimization groups listed above.
16029
16030           If options is omitted, it defaults to optimized-optall, which means
16031           to dump messages about successful optimizations from all the
16032           passes, omitting messages that are treated as "internals".
16033
16034           If the filename is provided, then the dumps from all the applicable
16035           optimizations are concatenated into the filename.  Otherwise the
16036           dump is output onto stderr. Though multiple -fopt-info options are
16037           accepted, only one of them can include a filename. If other
16038           filenames are provided then all but the first such option are
16039           ignored.
16040
16041           Note that the output filename is overwritten in case of multiple
16042           translation units. If a combined output from multiple translation
16043           units is desired, stderr should be used instead.
16044
16045           In the following example, the optimization info is output to
16046           stderr:
16047
16048                   gcc -O3 -fopt-info
16049
16050           This example:
16051
16052                   gcc -O3 -fopt-info-missed=missed.all
16053
16054           outputs missed optimization report from all the passes into
16055           missed.all, and this one:
16056
16057                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed
16058
16059           prints information about missed optimization opportunities from
16060           vectorization passes on stderr.  Note that -fopt-info-vec-missed is
16061           equivalent to -fopt-info-missed-vec.  The order of the optimization
16062           group names and message types listed after -fopt-info does not
16063           matter.
16064
16065           As another example,
16066
16067                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
16068
16069           outputs information about missed optimizations as well as optimized
16070           locations from all the inlining passes into inline.txt.
16071
16072           Finally, consider:
16073
16074                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
16075
16076           Here the two output filenames vec.miss and loop.opt are in conflict
16077           since only one output file is allowed. In this case, only the first
16078           option takes effect and the subsequent options are ignored. Thus
16079           only vec.miss is produced which contains dumps from the vectorizer
16080           about missed opportunities.
16081
16082       -fsave-optimization-record
16083           Write a SRCFILE.opt-record.json.gz file detailing what
16084           optimizations were performed, for those optimizations that support
16085           -fopt-info.
16086
16087           This option is experimental and the format of the data within the
16088           compressed JSON file is subject to change.
16089
16090           It is roughly equivalent to a machine-readable version of
16091           -fopt-info-all, as a collection of messages with source file, line
16092           number and column number, with the following additional data for
16093           each message:
16094
16095           *   the execution count of the code being optimized, along with
16096               metadata about whether this was from actual profile data, or
16097               just an estimate, allowing consumers to prioritize messages by
16098               code hotness,
16099
16100           *   the function name of the code being optimized, where
16101               applicable,
16102
16103           *   the "inlining chain" for the code being optimized, so that when
16104               a function is inlined into several different places (which
16105               might themselves be inlined), the reader can distinguish
16106               between the copies,
16107
16108           *   objects identifying those parts of the message that refer to
16109               expressions, statements or symbol-table nodes, which of these
16110               categories they are, and, when available, their source code
16111               location,
16112
16113           *   the GCC pass that emitted the message, and
16114
16115           *   the location in GCC's own code from which the message was
16116               emitted
16117
16118           Additionally, some messages are logically nested within other
16119           messages, reflecting implementation details of the optimization
16120           passes.
16121
16122       -fsched-verbose=n
16123           On targets that use instruction scheduling, this option controls
16124           the amount of debugging output the scheduler prints to the dump
16125           files.
16126
16127           For n greater than zero, -fsched-verbose outputs the same
16128           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
16129           greater than one, it also output basic block probabilities,
16130           detailed ready list information and unit/insn info.  For n greater
16131           than two, it includes RTL at abort point, control-flow and regions
16132           info.  And for n over four, -fsched-verbose also includes
16133           dependence info.
16134
16135       -fenable-kind-pass
16136       -fdisable-kind-pass=range-list
16137           This is a set of options that are used to explicitly disable/enable
16138           optimization passes.  These options are intended for use for
16139           debugging GCC.  Compiler users should use regular options for
16140           enabling/disabling passes instead.
16141
16142           -fdisable-ipa-pass
16143               Disable IPA pass pass. pass is the pass name.  If the same pass
16144               is statically invoked in the compiler multiple times, the pass
16145               name should be appended with a sequential number starting from
16146               1.
16147
16148           -fdisable-rtl-pass
16149           -fdisable-rtl-pass=range-list
16150               Disable RTL pass pass.  pass is the pass name.  If the same
16151               pass is statically invoked in the compiler multiple times, the
16152               pass name should be appended with a sequential number starting
16153               from 1.  range-list is a comma-separated list of function
16154               ranges or assembler names.  Each range is a number pair
16155               separated by a colon.  The range is inclusive in both ends.  If
16156               the range is trivial, the number pair can be simplified as a
16157               single number.  If the function's call graph node's uid falls
16158               within one of the specified ranges, the pass is disabled for
16159               that function.  The uid is shown in the function header of a
16160               dump file, and the pass names can be dumped by using option
16161               -fdump-passes.
16162
16163           -fdisable-tree-pass
16164           -fdisable-tree-pass=range-list
16165               Disable tree pass pass.  See -fdisable-rtl for the description
16166               of option arguments.
16167
16168           -fenable-ipa-pass
16169               Enable IPA pass pass.  pass is the pass name.  If the same pass
16170               is statically invoked in the compiler multiple times, the pass
16171               name should be appended with a sequential number starting from
16172               1.
16173
16174           -fenable-rtl-pass
16175           -fenable-rtl-pass=range-list
16176               Enable RTL pass pass.  See -fdisable-rtl for option argument
16177               description and examples.
16178
16179           -fenable-tree-pass
16180           -fenable-tree-pass=range-list
16181               Enable tree pass pass.  See -fdisable-rtl for the description
16182               of option arguments.
16183
16184           Here are some examples showing uses of these options.
16185
16186                   # disable ccp1 for all functions
16187                      -fdisable-tree-ccp1
16188                   # disable complete unroll for function whose cgraph node uid is 1
16189                      -fenable-tree-cunroll=1
16190                   # disable gcse2 for functions at the following ranges [1,1],
16191                   # [300,400], and [400,1000]
16192                   # disable gcse2 for functions foo and foo2
16193                      -fdisable-rtl-gcse2=foo,foo2
16194                   # disable early inlining
16195                      -fdisable-tree-einline
16196                   # disable ipa inlining
16197                      -fdisable-ipa-inline
16198                   # enable tree full unroll
16199                      -fenable-tree-unroll
16200
16201       -fchecking
16202       -fchecking=n
16203           Enable internal consistency checking.  The default depends on the
16204           compiler configuration.  -fchecking=2 enables further internal
16205           consistency checking that might affect code generation.
16206
16207       -frandom-seed=string
16208           This option provides a seed that GCC uses in place of random
16209           numbers in generating certain symbol names that have to be
16210           different in every compiled file.  It is also used to place unique
16211           stamps in coverage data files and the object files that produce
16212           them.  You can use the -frandom-seed option to produce reproducibly
16213           identical object files.
16214
16215           The string can either be a number (decimal, octal or hex) or an
16216           arbitrary string (in which case it's converted to a number by
16217           computing CRC32).
16218
16219           The string should be different for every file you compile.
16220
16221       -save-temps
16222           Store the usual "temporary" intermediate files permanently; name
16223           them as auxiliary output files, as specified described under
16224           -dumpbase and -dumpdir.
16225
16226           When used in combination with the -x command-line option,
16227           -save-temps is sensible enough to avoid overwriting an input source
16228           file with the same extension as an intermediate file.  The
16229           corresponding intermediate file may be obtained by renaming the
16230           source file before using -save-temps.
16231
16232       -save-temps=cwd
16233           Equivalent to -save-temps -dumpdir ./.
16234
16235       -save-temps=obj
16236           Equivalent to -save-temps -dumpdir outdir/, where outdir/ is the
16237           directory of the output file specified after the -o option,
16238           including any directory separators.  If the -o option is not used,
16239           the -save-temps=obj switch behaves like -save-temps=cwd.
16240
16241       -time[=file]
16242           Report the CPU time taken by each subprocess in the compilation
16243           sequence.  For C source files, this is the compiler proper and
16244           assembler (plus the linker if linking is done).
16245
16246           Without the specification of an output file, the output looks like
16247           this:
16248
16249                   # cc1 0.12 0.01
16250                   # as 0.00 0.01
16251
16252           The first number on each line is the "user time", that is time
16253           spent executing the program itself.  The second number is "system
16254           time", time spent executing operating system routines on behalf of
16255           the program.  Both numbers are in seconds.
16256
16257           With the specification of an output file, the output is appended to
16258           the named file, and it looks like this:
16259
16260                   0.12 0.01 cc1 <options>
16261                   0.00 0.01 as <options>
16262
16263           The "user time" and the "system time" are moved before the program
16264           name, and the options passed to the program are displayed, so that
16265           one can later tell what file was being compiled, and with which
16266           options.
16267
16268       -fdump-final-insns[=file]
16269           Dump the final internal representation (RTL) to file.  If the
16270           optional argument is omitted (or if file is "."), the name of the
16271           dump file is determined by appending ".gkd" to the dump base name,
16272           see -dumpbase.
16273
16274       -fcompare-debug[=opts]
16275           If no error occurs during compilation, run the compiler a second
16276           time, adding opts and -fcompare-debug-second to the arguments
16277           passed to the second compilation.  Dump the final internal
16278           representation in both compilations, and print an error if they
16279           differ.
16280
16281           If the equal sign is omitted, the default -gtoggle is used.
16282
16283           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
16284           and nonzero, implicitly enables -fcompare-debug.  If
16285           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
16286           it is used for opts, otherwise the default -gtoggle is used.
16287
16288           -fcompare-debug=, with the equal sign but without opts, is
16289           equivalent to -fno-compare-debug, which disables the dumping of the
16290           final representation and the second compilation, preventing even
16291           GCC_COMPARE_DEBUG from taking effect.
16292
16293           To verify full coverage during -fcompare-debug testing, set
16294           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
16295           rejects as an invalid option in any actual compilation (rather than
16296           preprocessing, assembly or linking).  To get just a warning,
16297           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
16298           will do.
16299
16300       -fcompare-debug-second
16301           This option is implicitly passed to the compiler for the second
16302           compilation requested by -fcompare-debug, along with options to
16303           silence warnings, and omitting other options that would cause the
16304           compiler to produce output to files or to standard output as a side
16305           effect.  Dump files and preserved temporary files are renamed so as
16306           to contain the ".gk" additional extension during the second
16307           compilation, to avoid overwriting those generated by the first.
16308
16309           When this option is passed to the compiler driver, it causes the
16310           first compilation to be skipped, which makes it useful for little
16311           other than debugging the compiler proper.
16312
16313       -gtoggle
16314           Turn off generation of debug info, if leaving out this option
16315           generates it, or turn it on at level 2 otherwise.  The position of
16316           this argument in the command line does not matter; it takes effect
16317           after all other options are processed, and it does so only once, no
16318           matter how many times it is given.  This is mainly intended to be
16319           used with -fcompare-debug.
16320
16321       -fvar-tracking-assignments-toggle
16322           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
16323           toggles -g.
16324
16325       -Q  Makes the compiler print out each function name as it is compiled,
16326           and print some statistics about each pass when it finishes.
16327
16328       -ftime-report
16329           Makes the compiler print some statistics about the time consumed by
16330           each pass when it finishes.
16331
16332       -ftime-report-details
16333           Record the time consumed by infrastructure parts separately for
16334           each pass.
16335
16336       -fira-verbose=n
16337           Control the verbosity of the dump file for the integrated register
16338           allocator.  The default value is 5.  If the value n is greater or
16339           equal to 10, the dump output is sent to stderr using the same
16340           format as n minus 10.
16341
16342       -flto-report
16343           Prints a report with internal details on the workings of the link-
16344           time optimizer.  The contents of this report vary from version to
16345           version.  It is meant to be useful to GCC developers when
16346           processing object files in LTO mode (via -flto).
16347
16348           Disabled by default.
16349
16350       -flto-report-wpa
16351           Like -flto-report, but only print for the WPA phase of link-time
16352           optimization.
16353
16354       -fmem-report
16355           Makes the compiler print some statistics about permanent memory
16356           allocation when it finishes.
16357
16358       -fmem-report-wpa
16359           Makes the compiler print some statistics about permanent memory
16360           allocation for the WPA phase only.
16361
16362       -fpre-ipa-mem-report
16363       -fpost-ipa-mem-report
16364           Makes the compiler print some statistics about permanent memory
16365           allocation before or after interprocedural optimization.
16366
16367       -fprofile-report
16368           Makes the compiler print some statistics about consistency of the
16369           (estimated) profile and effect of individual passes.
16370
16371       -fstack-usage
16372           Makes the compiler output stack usage information for the program,
16373           on a per-function basis.  The filename for the dump is made by
16374           appending .su to the auxname.  auxname is generated from the name
16375           of the output file, if explicitly specified and it is not an
16376           executable, otherwise it is the basename of the source file.  An
16377           entry is made up of three fields:
16378
16379           *   The name of the function.
16380
16381           *   A number of bytes.
16382
16383           *   One or more qualifiers: "static", "dynamic", "bounded".
16384
16385           The qualifier "static" means that the function manipulates the
16386           stack statically: a fixed number of bytes are allocated for the
16387           frame on function entry and released on function exit; no stack
16388           adjustments are otherwise made in the function.  The second field
16389           is this fixed number of bytes.
16390
16391           The qualifier "dynamic" means that the function manipulates the
16392           stack dynamically: in addition to the static allocation described
16393           above, stack adjustments are made in the body of the function, for
16394           example to push/pop arguments around function calls.  If the
16395           qualifier "bounded" is also present, the amount of these
16396           adjustments is bounded at compile time and the second field is an
16397           upper bound of the total amount of stack used by the function.  If
16398           it is not present, the amount of these adjustments is not bounded
16399           at compile time and the second field only represents the bounded
16400           part.
16401
16402       -fstats
16403           Emit statistics about front-end processing at the end of the
16404           compilation.  This option is supported only by the C++ front end,
16405           and the information is generally only useful to the G++ development
16406           team.
16407
16408       -fdbg-cnt-list
16409           Print the name and the counter upper bound for all debug counters.
16410
16411       -fdbg-cnt=counter-value-list
16412           Set the internal debug counter lower and upper bound.  counter-
16413           value-list is a comma-separated list of
16414           name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...]
16415           tuples which sets the name of the counter and list of closed
16416           intervals.  The lower_bound is optional and is zero initialized if
16417           not set.  For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10,
16418           "dbg_cnt(dce)" returns true only for second, third, fourth, tenth
16419           and eleventh invocation.  For "dbg_cnt(tail_call)" true is returned
16420           for first 10 invocations.
16421
16422       -print-file-name=library
16423           Print the full absolute name of the library file library that would
16424           be used when linking---and don't do anything else.  With this
16425           option, GCC does not compile or link anything; it just prints the
16426           file name.
16427
16428       -print-multi-directory
16429           Print the directory name corresponding to the multilib selected by
16430           any other switches present in the command line.  This directory is
16431           supposed to exist in GCC_EXEC_PREFIX.
16432
16433       -print-multi-lib
16434           Print the mapping from multilib directory names to compiler
16435           switches that enable them.  The directory name is separated from
16436           the switches by ;, and each switch starts with an @ instead of the
16437           -, without spaces between multiple switches.  This is supposed to
16438           ease shell processing.
16439
16440       -print-multi-os-directory
16441           Print the path to OS libraries for the selected multilib, relative
16442           to some lib subdirectory.  If OS libraries are present in the lib
16443           subdirectory and no multilibs are used, this is usually just ., if
16444           OS libraries are present in libsuffix sibling directories this
16445           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
16446           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
16447           or ev6.
16448
16449       -print-multiarch
16450           Print the path to OS libraries for the selected multiarch, relative
16451           to some lib subdirectory.
16452
16453       -print-prog-name=program
16454           Like -print-file-name, but searches for a program such as cpp.
16455
16456       -print-libgcc-file-name
16457           Same as -print-file-name=libgcc.a.
16458
16459           This is useful when you use -nostdlib or -nodefaultlibs but you do
16460           want to link with libgcc.a.  You can do:
16461
16462                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`
16463
16464       -print-search-dirs
16465           Print the name of the configured installation directory and a list
16466           of program and library directories gcc searches---and don't do
16467           anything else.
16468
16469           This is useful when gcc prints the error message installation
16470           problem, cannot exec cpp0: No such file or directory.  To resolve
16471           this you either need to put cpp0 and the other compiler components
16472           where gcc expects to find them, or you can set the environment
16473           variable GCC_EXEC_PREFIX to the directory where you installed them.
16474           Don't forget the trailing /.
16475
16476       -print-sysroot
16477           Print the target sysroot directory that is used during compilation.
16478           This is the target sysroot specified either at configure time or
16479           using the --sysroot option, possibly with an extra suffix that
16480           depends on compilation options.  If no target sysroot is specified,
16481           the option prints nothing.
16482
16483       -print-sysroot-headers-suffix
16484           Print the suffix added to the target sysroot when searching for
16485           headers, or give an error if the compiler is not configured with
16486           such a suffix---and don't do anything else.
16487
16488       -dumpmachine
16489           Print the compiler's target machine (for example,
16490           i686-pc-linux-gnu)---and don't do anything else.
16491
16492       -dumpversion
16493           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and
16494           don't do anything else.  This is the compiler version used in
16495           filesystem paths and specs. Depending on how the compiler has been
16496           configured it can be just a single number (major version), two
16497           numbers separated by a dot (major and minor version) or three
16498           numbers separated by dots (major, minor and patchlevel version).
16499
16500       -dumpfullversion
16501           Print the full compiler version---and don't do anything else. The
16502           output is always three numbers separated by dots, major, minor and
16503           patchlevel version.
16504
16505       -dumpspecs
16506           Print the compiler's built-in specs---and don't do anything else.
16507           (This is used when GCC itself is being built.)
16508
16509   Machine-Dependent Options
16510       Each target machine supported by GCC can have its own options---for
16511       example, to allow you to compile for a particular processor variant or
16512       ABI, or to control optimizations specific to that machine.  By
16513       convention, the names of machine-specific options start with -m.
16514
16515       Some configurations of the compiler also support additional target-
16516       specific options, usually for compatibility with other compilers on the
16517       same platform.
16518
16519       AArch64 Options
16520
16521       These options are defined for AArch64 implementations:
16522
16523       -mabi=name
16524           Generate code for the specified data model.  Permissible values are
16525           ilp32 for SysV-like data model where int, long int and pointers are
16526           32 bits, and lp64 for SysV-like data model where int is 32 bits,
16527           but long int and pointers are 64 bits.
16528
16529           The default depends on the specific target configuration.  Note
16530           that the LP64 and ILP32 ABIs are not link-compatible; you must
16531           compile your entire program with the same ABI, and link with a
16532           compatible set of libraries.
16533
16534       -mbig-endian
16535           Generate big-endian code.  This is the default when GCC is
16536           configured for an aarch64_be-*-* target.
16537
16538       -mgeneral-regs-only
16539           Generate code which uses only the general-purpose registers.  This
16540           will prevent the compiler from using floating-point and Advanced
16541           SIMD registers but will not impose any restrictions on the
16542           assembler.
16543
16544       -mlittle-endian
16545           Generate little-endian code.  This is the default when GCC is
16546           configured for an aarch64-*-* but not an aarch64_be-*-* target.
16547
16548       -mcmodel=tiny
16549           Generate code for the tiny code model.  The program and its
16550           statically defined symbols must be within 1MB of each other.
16551           Programs can be statically or dynamically linked.
16552
16553       -mcmodel=small
16554           Generate code for the small code model.  The program and its
16555           statically defined symbols must be within 4GB of each other.
16556           Programs can be statically or dynamically linked.  This is the
16557           default code model.
16558
16559       -mcmodel=large
16560           Generate code for the large code model.  This makes no assumptions
16561           about addresses and sizes of sections.  Programs can be statically
16562           linked only.  The -mcmodel=large option is incompatible with
16563           -mabi=ilp32, -fpic and -fPIC.
16564
16565       -mstrict-align
16566       -mno-strict-align
16567           Avoid or allow generating memory accesses that may not be aligned
16568           on a natural object boundary as described in the architecture
16569           specification.
16570
16571       -momit-leaf-frame-pointer
16572       -mno-omit-leaf-frame-pointer
16573           Omit or keep the frame pointer in leaf functions.  The former
16574           behavior is the default.
16575
16576       -mstack-protector-guard=guard
16577       -mstack-protector-guard-reg=reg
16578       -mstack-protector-guard-offset=offset
16579           Generate stack protection code using canary at guard.  Supported
16580           locations are global for a global canary or sysreg for a canary in
16581           an appropriate system register.
16582
16583           With the latter choice the options -mstack-protector-guard-reg=reg
16584           and -mstack-protector-guard-offset=offset furthermore specify which
16585           system register to use as base register for reading the canary, and
16586           from what offset from that base register. There is no default
16587           register or offset as this is entirely for use within the Linux
16588           kernel.
16589
16590       -mtls-dialect=desc
16591           Use TLS descriptors as the thread-local storage mechanism for
16592           dynamic accesses of TLS variables.  This is the default.
16593
16594       -mtls-dialect=traditional
16595           Use traditional TLS as the thread-local storage mechanism for
16596           dynamic accesses of TLS variables.
16597
16598       -mtls-size=size
16599           Specify bit size of immediate TLS offsets.  Valid values are 12,
16600           24, 32, 48.  This option requires binutils 2.26 or newer.
16601
16602       -mfix-cortex-a53-835769
16603       -mno-fix-cortex-a53-835769
16604           Enable or disable the workaround for the ARM Cortex-A53 erratum
16605           number 835769.  This involves inserting a NOP instruction between
16606           memory instructions and 64-bit integer multiply-accumulate
16607           instructions.
16608
16609       -mfix-cortex-a53-843419
16610       -mno-fix-cortex-a53-843419
16611           Enable or disable the workaround for the ARM Cortex-A53 erratum
16612           number 843419.  This erratum workaround is made at link time and
16613           this will only pass the corresponding flag to the linker.
16614
16615       -mlow-precision-recip-sqrt
16616       -mno-low-precision-recip-sqrt
16617           Enable or disable the reciprocal square root approximation.  This
16618           option only has an effect if -ffast-math or
16619           -funsafe-math-optimizations is used as well.  Enabling this reduces
16620           precision of reciprocal square root results to about 16 bits for
16621           single precision and to 32 bits for double precision.
16622
16623       -mlow-precision-sqrt
16624       -mno-low-precision-sqrt
16625           Enable or disable the square root approximation.  This option only
16626           has an effect if -ffast-math or -funsafe-math-optimizations is used
16627           as well.  Enabling this reduces precision of square root results to
16628           about 16 bits for single precision and to 32 bits for double
16629           precision.  If enabled, it implies -mlow-precision-recip-sqrt.
16630
16631       -mlow-precision-div
16632       -mno-low-precision-div
16633           Enable or disable the division approximation.  This option only has
16634           an effect if -ffast-math or -funsafe-math-optimizations is used as
16635           well.  Enabling this reduces precision of division results to about
16636           16 bits for single precision and to 32 bits for double precision.
16637
16638       -mtrack-speculation
16639       -mno-track-speculation
16640           Enable or disable generation of additional code to track
16641           speculative execution through conditional branches.  The tracking
16642           state can then be used by the compiler when expanding calls to
16643           "__builtin_speculation_safe_copy" to permit a more efficient code
16644           sequence to be generated.
16645
16646       -moutline-atomics
16647       -mno-outline-atomics
16648           Enable or disable calls to out-of-line helpers to implement atomic
16649           operations.  These helpers will, at runtime, determine if the LSE
16650           instructions from ARMv8.1-A can be used; if not, they will use the
16651           load/store-exclusive instructions that are present in the base
16652           ARMv8.0 ISA.
16653
16654           This option is only applicable when compiling for the base ARMv8.0
16655           instruction set.  If using a later revision, e.g. -march=armv8.1-a
16656           or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be
16657           used directly.  The same applies when using -mcpu= when the
16658           selected cpu supports the lse feature.  This option is on by
16659           default.
16660
16661       -march=name
16662           Specify the name of the target architecture and, optionally, one or
16663           more feature modifiers.  This option has the form
16664           -march=arch{+[no]feature}*.
16665
16666           The table below summarizes the permissible values for arch and the
16667           features that they enable by default:
16668
16669           arch value : Architecture : Includes by default
16670           armv8-a : Armv8-A : +fp, +simd
16671           armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
16672           armv8.2-a : Armv8.2-A : armv8.1-a
16673           armv8.3-a : Armv8.3-A : armv8.2-a, +pauth
16674           armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod
16675           armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres
16676           armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm
16677           armv8.7-a : Armv8.7-A : armv8.6-a, +ls64
16678           armv8.8-a : Armv8.8-a : armv8.7-a, +mops
16679           armv9-a : Armv9-A : armv8.5-a, +sve, +sve2
16680           armv8-r : Armv8-R : armv8-r
16681
16682           The value native is available on native AArch64 GNU/Linux and
16683           causes the compiler to pick the architecture of the host system.
16684           This option has no effect if the compiler is unable to recognize
16685           the architecture of the host system,
16686
16687           The permissible values for feature are listed in the sub-section on
16688           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
16689           Where conflicting feature modifiers are specified, the right-most
16690           feature is used.
16691
16692           GCC uses name to determine what kind of instructions it can emit
16693           when generating assembly code.  If -march is specified without
16694           either of -mtune or -mcpu also being specified, the code is tuned
16695           to perform well across a range of target processors implementing
16696           the target architecture.
16697
16698       -mtune=name
16699           Specify the name of the target processor for which GCC should tune
16700           the performance of the code.  Permissible values for this option
16701           are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
16702           cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae,
16703           cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, cortex-a78,
16704           cortex-a78ae, cortex-a78c, ares, exynos-m1, emag, falkor,
16705           neoverse-512tvb, neoverse-e1, neoverse-n1, neoverse-n2,
16706           neoverse-v1, qdf24xx, saphira, phecda, xgene1, vulcan, octeontx,
16707           octeontx81,  octeontx83, octeontx2, octeontx2t98, octeontx2t96
16708           octeontx2t93, octeontx2f95, octeontx2f95n, octeontx2f95mm, a64fx,
16709           thunderx, thunderxt88, thunderxt88p1, thunderxt81, tsv110,
16710           thunderxt83, thunderx2t99, thunderx3t110, zeus,
16711           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
16712           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
16713           cortex-a75.cortex-a55, cortex-a76.cortex-a55, cortex-r82,
16714           cortex-x1, cortex-x2, cortex-a510, cortex-a710, ampere1, native.
16715
16716           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
16717           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
16718           cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC
16719           should tune for a big.LITTLE system.
16720
16721           The value neoverse-512tvb specifies that GCC should tune for
16722           Neoverse cores that (a) implement SVE and (b) have a total vector
16723           bandwidth of 512 bits per cycle.  In other words, the option tells
16724           GCC to tune for Neoverse cores that can execute 4 128-bit Advanced
16725           SIMD arithmetic instructions a cycle and that can execute an
16726           equivalent number of SVE arithmetic instructions per cycle (2 for
16727           256-bit SVE, 4 for 128-bit SVE).  This is more general than tuning
16728           for a specific core like Neoverse V1 but is more specific than the
16729           default tuning described below.
16730
16731           Additionally on native AArch64 GNU/Linux systems the value native
16732           tunes performance to the host system.  This option has no effect if
16733           the compiler is unable to recognize the processor of the host
16734           system.
16735
16736           Where none of -mtune=, -mcpu= or -march= are specified, the code is
16737           tuned to perform well across a range of target processors.
16738
16739           This option cannot be suffixed by feature modifiers.
16740
16741       -mcpu=name
16742           Specify the name of the target processor, optionally suffixed by
16743           one or more feature modifiers.  This option has the form
16744           -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
16745           the same as those available for -mtune.  The permissible values for
16746           feature are documented in the sub-section on
16747           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
16748           Where conflicting feature modifiers are specified, the right-most
16749           feature is used.
16750
16751           GCC uses name to determine what kind of instructions it can emit
16752           when generating assembly code (as if by -march) and to determine
16753           the target processor for which to tune for performance (as if by
16754           -mtune).  Where this option is used in conjunction with -march or
16755           -mtune, those options take precedence over the appropriate part of
16756           this option.
16757
16758           -mcpu=neoverse-512tvb is special in that it does not refer to a
16759           specific core, but instead refers to all Neoverse cores that (a)
16760           implement SVE and (b) have a total vector bandwidth of 512 bits a
16761           cycle.  Unless overridden by -march, -mcpu=neoverse-512tvb
16762           generates code that can run on a Neoverse V1 core, since Neoverse
16763           V1 is the first Neoverse core with these properties.  Unless
16764           overridden by -mtune, -mcpu=neoverse-512tvb tunes code in the same
16765           way as for -mtune=neoverse-512tvb.
16766
16767       -moverride=string
16768           Override tuning decisions made by the back-end in response to a
16769           -mtune= switch.  The syntax, semantics, and accepted values for
16770           string in this option are not guaranteed to be consistent across
16771           releases.
16772
16773           This option is only intended to be useful when developing GCC.
16774
16775       -mverbose-cost-dump
16776           Enable verbose cost model dumping in the debug dump files.  This
16777           option is provided for use in debugging the compiler.
16778
16779       -mpc-relative-literal-loads
16780       -mno-pc-relative-literal-loads
16781           Enable or disable PC-relative literal loads.  With this option
16782           literal pools are accessed using a single instruction and emitted
16783           after each function.  This limits the maximum size of functions to
16784           1MB.  This is enabled by default for -mcmodel=tiny.
16785
16786       -msign-return-address=scope
16787           Select the function scope on which return address signing will be
16788           applied.  Permissible values are none, which disables return
16789           address signing, non-leaf, which enables pointer signing for
16790           functions which are not leaf functions, and all, which enables
16791           pointer signing for all functions.  The default value is none. This
16792           option has been deprecated by -mbranch-protection.
16793
16794       -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti
16795           Select the branch protection features to use.  none is the default
16796           and turns off all types of branch protection.  standard turns on
16797           all types of branch protection features.  If a feature has
16798           additional tuning options, then standard sets it to its standard
16799           level.  pac-ret[+leaf] turns on return address signing to its
16800           standard level: signing functions that save the return address to
16801           memory (non-leaf functions will practically always do this) using
16802           the a-key.  The optional argument leaf can be used to extend the
16803           signing to include leaf functions.  The optional argument b-key can
16804           be used to sign the functions with the B-key instead of the A-key.
16805           bti turns on branch target identification mechanism.
16806
16807       -mharden-sls=opts
16808           Enable compiler hardening against straight line speculation (SLS).
16809           opts is a comma-separated list of the following options:
16810
16811           retbr
16812           blr
16813
16814           In addition, -mharden-sls=all enables all SLS hardening while
16815           -mharden-sls=none disables all SLS hardening.
16816
16817       -msve-vector-bits=bits
16818           Specify the number of bits in an SVE vector register.  This option
16819           only has an effect when SVE is enabled.
16820
16821           GCC supports two forms of SVE code generation: "vector-length
16822           agnostic" output that works with any size of vector register and
16823           "vector-length specific" output that allows GCC to make assumptions
16824           about the vector length when it is useful for optimization reasons.
16825           The possible values of bits are: scalable, 128, 256, 512, 1024 and
16826           2048.  Specifying scalable selects vector-length agnostic output.
16827           At present -msve-vector-bits=128 also generates vector-length
16828           agnostic output for big-endian targets.  All other values generate
16829           vector-length specific code.  The behavior of these values may
16830           change in future releases and no value except scalable should be
16831           relied on for producing code that is portable across different
16832           hardware SVE vector lengths.
16833
16834           The default is -msve-vector-bits=scalable, which produces vector-
16835           length agnostic code.
16836
16837       -march and -mcpu Feature Modifiers
16838
16839       Feature modifiers used with -march and -mcpu can be any of the
16840       following and their inverses nofeature:
16841
16842       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.
16843
16844       crypto
16845           Enable Crypto extension.  This also enables Advanced SIMD and
16846           floating-point instructions.
16847
16848       fp  Enable floating-point instructions.  This is on by default for all
16849           possible values for options -march and -mcpu.
16850
16851       simd
16852           Enable Advanced SIMD instructions.  This also enables floating-
16853           point instructions.  This is on by default for all possible values
16854           for options -march and -mcpu.
16855
16856       sve Enable Scalable Vector Extension instructions.  This also enables
16857           Advanced SIMD and floating-point instructions.
16858
16859       lse Enable Large System Extension instructions.  This is on by default
16860           for -march=armv8.1-a.
16861
16862       rdma
16863           Enable Round Double Multiply Accumulate instructions.  This is on
16864           by default for -march=armv8.1-a.
16865
16866       fp16
16867           Enable FP16 extension.  This also enables floating-point
16868           instructions.
16869
16870       fp16fml
16871           Enable FP16 fmla extension.  This also enables FP16 extensions and
16872           floating-point instructions. This option is enabled by default for
16873           -march=armv8.4-a. Use of this option with architectures prior to
16874           Armv8.2-A is not supported.
16875
16876       rcpc
16877           Enable the RcPc extension.  This does not change code generation
16878           from GCC, but is passed on to the assembler, enabling inline asm
16879           statements to use instructions from the RcPc extension.
16880
16881       dotprod
16882           Enable the Dot Product extension.  This also enables Advanced SIMD
16883           instructions.
16884
16885       aes Enable the Armv8-a aes and pmull crypto extension.  This also
16886           enables Advanced SIMD instructions.
16887
16888       sha2
16889           Enable the Armv8-a sha2 crypto extension.  This also enables
16890           Advanced SIMD instructions.
16891
16892       sha3
16893           Enable the sha512 and sha3 crypto extension.  This also enables
16894           Advanced SIMD instructions. Use of this option with architectures
16895           prior to Armv8.2-A is not supported.
16896
16897       sm4 Enable the sm3 and sm4 crypto extension.  This also enables
16898           Advanced SIMD instructions.  Use of this option with architectures
16899           prior to Armv8.2-A is not supported.
16900
16901       profile
16902           Enable the Statistical Profiling extension.  This option is only to
16903           enable the extension at the assembler level and does not affect
16904           code generation.
16905
16906       rng Enable the Armv8.5-a Random Number instructions.  This option is
16907           only to enable the extension at the assembler level and does not
16908           affect code generation.
16909
16910       memtag
16911           Enable the Armv8.5-a Memory Tagging Extensions.  Use of this option
16912           with architectures prior to Armv8.5-A is not supported.
16913
16914       sb  Enable the Armv8-a Speculation Barrier instruction.  This option is
16915           only to enable the extension at the assembler level and does not
16916           affect code generation.  This option is enabled by default for
16917           -march=armv8.5-a.
16918
16919       ssbs
16920           Enable the Armv8-a Speculative Store Bypass Safe instruction.  This
16921           option is only to enable the extension at the assembler level and
16922           does not affect code generation.  This option is enabled by default
16923           for -march=armv8.5-a.
16924
16925       predres
16926           Enable the Armv8-a Execution and Data Prediction Restriction
16927           instructions.  This option is only to enable the extension at the
16928           assembler level and does not affect code generation.  This option
16929           is enabled by default for -march=armv8.5-a.
16930
16931       sve2
16932           Enable the Armv8-a Scalable Vector Extension 2.  This also enables
16933           SVE instructions.
16934
16935       sve2-bitperm
16936           Enable SVE2 bitperm instructions.  This also enables SVE2
16937           instructions.
16938
16939       sve2-sm4
16940           Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.
16941
16942       sve2-aes
16943           Enable SVE2 aes instructions.  This also enables SVE2 instructions.
16944
16945       sve2-sha3
16946           Enable SVE2 sha3 instructions.  This also enables SVE2
16947           instructions.
16948
16949       tme Enable the Transactional Memory Extension.
16950
16951       i8mm
16952           Enable 8-bit Integer Matrix Multiply instructions.  This also
16953           enables Advanced SIMD and floating-point instructions.  This option
16954           is enabled by default for -march=armv8.6-a.  Use of this option
16955           with architectures prior to Armv8.2-A is not supported.
16956
16957       f32mm
16958           Enable 32-bit Floating point Matrix Multiply instructions.  This
16959           also enables SVE instructions.  Use of this option with
16960           architectures prior to Armv8.2-A is not supported.
16961
16962       f64mm
16963           Enable 64-bit Floating point Matrix Multiply instructions.  This
16964           also enables SVE instructions.  Use of this option with
16965           architectures prior to Armv8.2-A is not supported.
16966
16967       bf16
16968           Enable brain half-precision floating-point instructions.  This also
16969           enables Advanced SIMD and floating-point instructions.  This option
16970           is enabled by default for -march=armv8.6-a.  Use of this option
16971           with architectures prior to Armv8.2-A is not supported.
16972
16973       ls64
16974           Enable the 64-byte atomic load and store instructions for
16975           accelerators.  This option is enabled by default for
16976           -march=armv8.7-a.
16977
16978       mops
16979           Enable the instructions to accelerate memory operations like
16980           "memcpy", "memmove", "memset".  This option is enabled by default
16981           for -march=armv8.8-a
16982
16983       flagm
16984           Enable the Flag Manipulation instructions Extension.
16985
16986       pauth
16987           Enable the Pointer Authentication Extension.
16988
16989       Feature crypto implies aes, sha2, and simd, which implies fp.
16990       Conversely, nofp implies nosimd, which implies nocrypto, noaes and
16991       nosha2.
16992
16993       Adapteva Epiphany Options
16994
16995       These -m options are defined for Adapteva Epiphany:
16996
16997       -mhalf-reg-file
16998           Don't allocate any register in the range "r32"..."r63".  That
16999           allows code to run on hardware variants that lack these registers.
17000
17001       -mprefer-short-insn-regs
17002           Preferentially allocate registers that allow short instruction
17003           generation.  This can result in increased instruction count, so
17004           this may either reduce or increase overall code size.
17005
17006       -mbranch-cost=num
17007           Set the cost of branches to roughly num "simple" instructions.
17008           This cost is only a heuristic and is not guaranteed to produce
17009           consistent results across releases.
17010
17011       -mcmove
17012           Enable the generation of conditional moves.
17013
17014       -mnops=num
17015           Emit num NOPs before every other generated instruction.
17016
17017       -mno-soft-cmpsf
17018           For single-precision floating-point comparisons, emit an "fsub"
17019           instruction and test the flags.  This is faster than a software
17020           comparison, but can get incorrect results in the presence of NaNs,
17021           or when two different small numbers are compared such that their
17022           difference is calculated as zero.  The default is -msoft-cmpsf,
17023           which uses slower, but IEEE-compliant, software comparisons.
17024
17025       -mstack-offset=num
17026           Set the offset between the top of the stack and the stack pointer.
17027           E.g., a value of 8 means that the eight bytes in the range
17028           "sp+0...sp+7" can be used by leaf functions without stack
17029           allocation.  Values other than 8 or 16 are untested and unlikely to
17030           work.  Note also that this option changes the ABI; compiling a
17031           program with a different stack offset than the libraries have been
17032           compiled with generally does not work.  This option can be useful
17033           if you want to evaluate if a different stack offset would give you
17034           better code, but to actually use a different stack offset to build
17035           working programs, it is recommended to configure the toolchain with
17036           the appropriate --with-stack-offset=num option.
17037
17038       -mno-round-nearest
17039           Make the scheduler assume that the rounding mode has been set to
17040           truncating.  The default is -mround-nearest.
17041
17042       -mlong-calls
17043           If not otherwise specified by an attribute, assume all calls might
17044           be beyond the offset range of the "b" / "bl" instructions, and
17045           therefore load the function address into a register before
17046           performing a (otherwise direct) call.  This is the default.
17047
17048       -mshort-calls
17049           If not otherwise specified by an attribute, assume all direct calls
17050           are in the range of the "b" / "bl" instructions, so use these
17051           instructions for direct calls.  The default is -mlong-calls.
17052
17053       -msmall16
17054           Assume addresses can be loaded as 16-bit unsigned values.  This
17055           does not apply to function addresses for which -mlong-calls
17056           semantics are in effect.
17057
17058       -mfp-mode=mode
17059           Set the prevailing mode of the floating-point unit.  This
17060           determines the floating-point mode that is provided and expected at
17061           function call and return time.  Making this mode match the mode you
17062           predominantly need at function start can make your programs smaller
17063           and faster by avoiding unnecessary mode switches.
17064
17065           mode can be set to one the following values:
17066
17067           caller
17068               Any mode at function entry is valid, and retained or restored
17069               when the function returns, and when it calls other functions.
17070               This mode is useful for compiling libraries or other
17071               compilation units you might want to incorporate into different
17072               programs with different prevailing FPU modes, and the
17073               convenience of being able to use a single object file outweighs
17074               the size and speed overhead for any extra mode switching that
17075               might be needed, compared with what would be needed with a more
17076               specific choice of prevailing FPU mode.
17077
17078           truncate
17079               This is the mode used for floating-point calculations with
17080               truncating (i.e. round towards zero) rounding mode.  That
17081               includes conversion from floating point to integer.
17082
17083           round-nearest
17084               This is the mode used for floating-point calculations with
17085               round-to-nearest-or-even rounding mode.
17086
17087           int This is the mode used to perform integer calculations in the
17088               FPU, e.g.  integer multiply, or integer multiply-and-
17089               accumulate.
17090
17091           The default is -mfp-mode=caller
17092
17093       -mno-split-lohi
17094       -mno-postinc
17095       -mno-postmodify
17096           Code generation tweaks that disable, respectively, splitting of
17097           32-bit loads, generation of post-increment addresses, and
17098           generation of post-modify addresses.  The defaults are msplit-lohi,
17099           -mpost-inc, and -mpost-modify.
17100
17101       -mnovect-double
17102           Change the preferred SIMD mode to SImode.  The default is
17103           -mvect-double, which uses DImode as preferred SIMD mode.
17104
17105       -max-vect-align=num
17106           The maximum alignment for SIMD vector mode types.  num may be 4 or
17107           8.  The default is 8.  Note that this is an ABI change, even though
17108           many library function interfaces are unaffected if they don't use
17109           SIMD vector modes in places that affect size and/or alignment of
17110           relevant types.
17111
17112       -msplit-vecmove-early
17113           Split vector moves into single word moves before reload.  In theory
17114           this can give better register allocation, but so far the reverse
17115           seems to be generally the case.
17116
17117       -m1reg-reg
17118           Specify a register to hold the constant -1, which makes loading
17119           small negative constants and certain bitmasks faster.  Allowable
17120           values for reg are r43 and r63, which specify use of that register
17121           as a fixed register, and none, which means that no register is used
17122           for this purpose.  The default is -m1reg-none.
17123
17124       AMD GCN Options
17125
17126       These options are defined specifically for the AMD GCN port.
17127
17128       -march=gpu
17129       -mtune=gpu
17130           Set architecture type or tuning for gpu. Supported values for gpu
17131           are
17132
17133           fiji
17134               Compile for GCN3 Fiji devices (gfx803).
17135
17136           gfx900
17137               Compile for GCN5 Vega 10 devices (gfx900).
17138
17139           gfx906
17140               Compile for GCN5 Vega 20 devices (gfx906).
17141
17142       -msram-ecc=on
17143       -msram-ecc=off
17144       -msram-ecc=any
17145           Compile binaries suitable for devices with the SRAM-ECC feature
17146           enabled, disabled, or either mode.  This feature can be enabled
17147           per-process on some devices.  The compiled code must match the
17148           device mode. The default is any, for devices that support it.
17149
17150       -mstack-size=bytes
17151           Specify how many bytes of stack space will be requested for each
17152           GPU thread (wave-front).  Beware that there may be many threads and
17153           limited memory available.  The size of the stack allocation may
17154           also have an impact on run-time performance.  The default is 32KB
17155           when using OpenACC or OpenMP, and 1MB otherwise.
17156
17157       -mxnack
17158           Compile binaries suitable for devices with the XNACK feature
17159           enabled.  Some devices always require XNACK and some allow the user
17160           to configure XNACK.  The compiled code must match the device mode.
17161           The default is -mno-xnack.  At present this option is a placeholder
17162           for support that is not yet implemented.
17163
17164       ARC Options
17165
17166       The following options control the architecture variant for which code
17167       is being compiled:
17168
17169       -mbarrel-shifter
17170           Generate instructions supported by barrel shifter.  This is the
17171           default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.
17172
17173       -mjli-always
17174           Force to call a function using jli_s instruction.  This option is
17175           valid only for ARCv2 architecture.
17176
17177       -mcpu=cpu
17178           Set architecture type, register usage, and instruction scheduling
17179           parameters for cpu.  There are also shortcut alias options
17180           available for backward compatibility and convenience.  Supported
17181           values for cpu are
17182
17183           arc600
17184               Compile for ARC600.  Aliases: -mA6, -mARC600.
17185
17186           arc601
17187               Compile for ARC601.  Alias: -mARC601.
17188
17189           arc700
17190               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the
17191               default when configured with --with-cpu=arc700.
17192
17193           arcem
17194               Compile for ARC EM.
17195
17196           archs
17197               Compile for ARC HS.
17198
17199           em  Compile for ARC EM CPU with no hardware extensions.
17200
17201           em4 Compile for ARC EM4 CPU.
17202
17203           em4_dmips
17204               Compile for ARC EM4 DMIPS CPU.
17205
17206           em4_fpus
17207               Compile for ARC EM4 DMIPS CPU with the single-precision
17208               floating-point extension.
17209
17210           em4_fpuda
17211               Compile for ARC EM4 DMIPS CPU with single-precision floating-
17212               point and double assist instructions.
17213
17214           hs  Compile for ARC HS CPU with no hardware extensions except the
17215               atomic instructions.
17216
17217           hs34
17218               Compile for ARC HS34 CPU.
17219
17220           hs38
17221               Compile for ARC HS38 CPU.
17222
17223           hs38_linux
17224               Compile for ARC HS38 CPU with all hardware extensions on.
17225
17226           arc600_norm
17227               Compile for ARC 600 CPU with "norm" instructions enabled.
17228
17229           arc600_mul32x16
17230               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
17231               instructions enabled.
17232
17233           arc600_mul64
17234               Compile for ARC 600 CPU with "norm" and "mul64"-family
17235               instructions enabled.
17236
17237           arc601_norm
17238               Compile for ARC 601 CPU with "norm" instructions enabled.
17239
17240           arc601_mul32x16
17241               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
17242               instructions enabled.
17243
17244           arc601_mul64
17245               Compile for ARC 601 CPU with "norm" and "mul64"-family
17246               instructions enabled.
17247
17248           nps400
17249               Compile for ARC 700 on NPS400 chip.
17250
17251           em_mini
17252               Compile for ARC EM minimalist configuration featuring reduced
17253               register set.
17254
17255       -mdpfp
17256       -mdpfp-compact
17257           Generate double-precision FPX instructions, tuned for the compact
17258           implementation.
17259
17260       -mdpfp-fast
17261           Generate double-precision FPX instructions, tuned for the fast
17262           implementation.
17263
17264       -mno-dpfp-lrsr
17265           Disable "lr" and "sr" instructions from using FPX extension aux
17266           registers.
17267
17268       -mea
17269           Generate extended arithmetic instructions.  Currently only "divaw",
17270           "adds", "subs", and "sat16" are supported.  Only valid for
17271           -mcpu=ARC700.
17272
17273       -mno-mpy
17274           Do not generate "mpy"-family instructions for ARC700.  This option
17275           is deprecated.
17276
17277       -mmul32x16
17278           Generate 32x16-bit multiply and multiply-accumulate instructions.
17279
17280       -mmul64
17281           Generate "mul64" and "mulu64" instructions.  Only valid for
17282           -mcpu=ARC600.
17283
17284       -mnorm
17285           Generate "norm" instructions.  This is the default if -mcpu=ARC700
17286           is in effect.
17287
17288       -mspfp
17289       -mspfp-compact
17290           Generate single-precision FPX instructions, tuned for the compact
17291           implementation.
17292
17293       -mspfp-fast
17294           Generate single-precision FPX instructions, tuned for the fast
17295           implementation.
17296
17297       -msimd
17298           Enable generation of ARC SIMD instructions via target-specific
17299           builtins.  Only valid for -mcpu=ARC700.
17300
17301       -msoft-float
17302           This option ignored; it is provided for compatibility purposes
17303           only.  Software floating-point code is emitted by default, and this
17304           default can overridden by FPX options; -mspfp, -mspfp-compact, or
17305           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
17306           -mdpfp-fast for double precision.
17307
17308       -mswap
17309           Generate "swap" instructions.
17310
17311       -matomic
17312           This enables use of the locked load/store conditional extension to
17313           implement atomic memory built-in functions.  Not available for ARC
17314           6xx or ARC EM cores.
17315
17316       -mdiv-rem
17317           Enable "div" and "rem" instructions for ARCv2 cores.
17318
17319       -mcode-density
17320           Enable code density instructions for ARC EM.  This option is on by
17321           default for ARC HS.
17322
17323       -mll64
17324           Enable double load/store operations for ARC HS cores.
17325
17326       -mtp-regno=regno
17327           Specify thread pointer register number.
17328
17329       -mmpy-option=multo
17330           Compile ARCv2 code with a multiplier design option.  You can
17331           specify the option using either a string or numeric value for
17332           multo.  wlh1 is the default value.  The recognized values are:
17333
17334           0
17335           none
17336               No multiplier available.
17337
17338           1
17339           w   16x16 multiplier, fully pipelined.  The following instructions
17340               are enabled: "mpyw" and "mpyuw".
17341
17342           2
17343           wlh1
17344               32x32 multiplier, fully pipelined (1 stage).  The following
17345               instructions are additionally enabled: "mpy", "mpyu", "mpym",
17346               "mpymu", and "mpy_s".
17347
17348           3
17349           wlh2
17350               32x32 multiplier, fully pipelined (2 stages).  The following
17351               instructions are additionally enabled: "mpy", "mpyu", "mpym",
17352               "mpymu", and "mpy_s".
17353
17354           4
17355           wlh3
17356               Two 16x16 multipliers, blocking, sequential.  The following
17357               instructions are additionally enabled: "mpy", "mpyu", "mpym",
17358               "mpymu", and "mpy_s".
17359
17360           5
17361           wlh4
17362               One 16x16 multiplier, blocking, sequential.  The following
17363               instructions are additionally enabled: "mpy", "mpyu", "mpym",
17364               "mpymu", and "mpy_s".
17365
17366           6
17367           wlh5
17368               One 32x4 multiplier, blocking, sequential.  The following
17369               instructions are additionally enabled: "mpy", "mpyu", "mpym",
17370               "mpymu", and "mpy_s".
17371
17372           7
17373           plus_dmpy
17374               ARC HS SIMD support.
17375
17376           8
17377           plus_macd
17378               ARC HS SIMD support.
17379
17380           9
17381           plus_qmacw
17382               ARC HS SIMD support.
17383
17384           This option is only available for ARCv2 cores.
17385
17386       -mfpu=fpu
17387           Enables support for specific floating-point hardware extensions for
17388           ARCv2 cores.  Supported values for fpu are:
17389
17390           fpus
17391               Enables support for single-precision floating-point hardware
17392               extensions.
17393
17394           fpud
17395               Enables support for double-precision floating-point hardware
17396               extensions.  The single-precision floating-point extension is
17397               also enabled.  Not available for ARC EM.
17398
17399           fpuda
17400               Enables support for double-precision floating-point hardware
17401               extensions using double-precision assist instructions.  The
17402               single-precision floating-point extension is also enabled.
17403               This option is only available for ARC EM.
17404
17405           fpuda_div
17406               Enables support for double-precision floating-point hardware
17407               extensions using double-precision assist instructions.  The
17408               single-precision floating-point, square-root, and divide
17409               extensions are also enabled.  This option is only available for
17410               ARC EM.
17411
17412           fpuda_fma
17413               Enables support for double-precision floating-point hardware
17414               extensions using double-precision assist instructions.  The
17415               single-precision floating-point and fused multiply and add
17416               hardware extensions are also enabled.  This option is only
17417               available for ARC EM.
17418
17419           fpuda_all
17420               Enables support for double-precision floating-point hardware
17421               extensions using double-precision assist instructions.  All
17422               single-precision floating-point hardware extensions are also
17423               enabled.  This option is only available for ARC EM.
17424
17425           fpus_div
17426               Enables support for single-precision floating-point, square-
17427               root and divide hardware extensions.
17428
17429           fpud_div
17430               Enables support for double-precision floating-point, square-
17431               root and divide hardware extensions.  This option includes
17432               option fpus_div. Not available for ARC EM.
17433
17434           fpus_fma
17435               Enables support for single-precision floating-point and fused
17436               multiply and add hardware extensions.
17437
17438           fpud_fma
17439               Enables support for double-precision floating-point and fused
17440               multiply and add hardware extensions.  This option includes
17441               option fpus_fma.  Not available for ARC EM.
17442
17443           fpus_all
17444               Enables support for all single-precision floating-point
17445               hardware extensions.
17446
17447           fpud_all
17448               Enables support for all single- and double-precision floating-
17449               point hardware extensions.  Not available for ARC EM.
17450
17451       -mirq-ctrl-saved=register-range, blink, lp_count
17452           Specifies general-purposes registers that the processor
17453           automatically saves/restores on interrupt entry and exit.
17454           register-range is specified as two registers separated by a dash.
17455           The register range always starts with "r0", the upper limit is "fp"
17456           register.  blink and lp_count are optional.  This option is only
17457           valid for ARC EM and ARC HS cores.
17458
17459       -mrgf-banked-regs=number
17460           Specifies the number of registers replicated in second register
17461           bank on entry to fast interrupt.  Fast interrupts are interrupts
17462           with the highest priority level P0.  These interrupts save only PC
17463           and STATUS32 registers to avoid memory transactions during
17464           interrupt entry and exit sequences.  Use this option when you are
17465           using fast interrupts in an ARC V2 family processor.  Permitted
17466           values are 4, 8, 16, and 32.
17467
17468       -mlpc-width=width
17469           Specify the width of the "lp_count" register.  Valid values for
17470           width are 8, 16, 20, 24, 28 and 32 bits.  The default width is
17471           fixed to 32 bits.  If the width is less than 32, the compiler does
17472           not attempt to transform loops in your program to use the zero-
17473           delay loop mechanism unless it is known that the "lp_count"
17474           register can hold the required loop-counter value.  Depending on
17475           the width specified, the compiler and run-time library might
17476           continue to use the loop mechanism for various needs.  This option
17477           defines macro "__ARC_LPC_WIDTH__" with the value of width.
17478
17479       -mrf16
17480           This option instructs the compiler to generate code for a 16-entry
17481           register file.  This option defines the "__ARC_RF16__" preprocessor
17482           macro.
17483
17484       -mbranch-index
17485           Enable use of "bi" or "bih" instructions to implement jump tables.
17486
17487       The following options are passed through to the assembler, and also
17488       define preprocessor macro symbols.
17489
17490       -mdsp-packa
17491           Passed down to the assembler to enable the DSP Pack A extensions.
17492           Also sets the preprocessor symbol "__Xdsp_packa".  This option is
17493           deprecated.
17494
17495       -mdvbf
17496           Passed down to the assembler to enable the dual Viterbi butterfly
17497           extension.  Also sets the preprocessor symbol "__Xdvbf".  This
17498           option is deprecated.
17499
17500       -mlock
17501           Passed down to the assembler to enable the locked load/store
17502           conditional extension.  Also sets the preprocessor symbol
17503           "__Xlock".
17504
17505       -mmac-d16
17506           Passed down to the assembler.  Also sets the preprocessor symbol
17507           "__Xxmac_d16".  This option is deprecated.
17508
17509       -mmac-24
17510           Passed down to the assembler.  Also sets the preprocessor symbol
17511           "__Xxmac_24".  This option is deprecated.
17512
17513       -mrtsc
17514           Passed down to the assembler to enable the 64-bit time-stamp
17515           counter extension instruction.  Also sets the preprocessor symbol
17516           "__Xrtsc".  This option is deprecated.
17517
17518       -mswape
17519           Passed down to the assembler to enable the swap byte ordering
17520           extension instruction.  Also sets the preprocessor symbol
17521           "__Xswape".
17522
17523       -mtelephony
17524           Passed down to the assembler to enable dual- and single-operand
17525           instructions for telephony.  Also sets the preprocessor symbol
17526           "__Xtelephony".  This option is deprecated.
17527
17528       -mxy
17529           Passed down to the assembler to enable the XY memory extension.
17530           Also sets the preprocessor symbol "__Xxy".
17531
17532       The following options control how the assembly code is annotated:
17533
17534       -misize
17535           Annotate assembler instructions with estimated addresses.
17536
17537       -mannotate-align
17538           Explain what alignment considerations lead to the decision to make
17539           an instruction short or long.
17540
17541       The following options are passed through to the linker:
17542
17543       -marclinux
17544           Passed through to the linker, to specify use of the "arclinux"
17545           emulation.  This option is enabled by default in tool chains built
17546           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
17547           profiling is not requested.
17548
17549       -marclinux_prof
17550           Passed through to the linker, to specify use of the "arclinux_prof"
17551           emulation.  This option is enabled by default in tool chains built
17552           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
17553           profiling is requested.
17554
17555       The following options control the semantics of generated code:
17556
17557       -mlong-calls
17558           Generate calls as register indirect calls, thus providing access to
17559           the full 32-bit address range.
17560
17561       -mmedium-calls
17562           Don't use less than 25-bit addressing range for calls, which is the
17563           offset available for an unconditional branch-and-link instruction.
17564           Conditional execution of function calls is suppressed, to allow use
17565           of the 25-bit range, rather than the 21-bit range with conditional
17566           branch-and-link.  This is the default for tool chains built for
17567           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.
17568
17569       -G num
17570           Put definitions of externally-visible data in a small data section
17571           if that data is no bigger than num bytes.  The default value of num
17572           is 4 for any ARC configuration, or 8 when we have double load/store
17573           operations.
17574
17575       -mno-sdata
17576           Do not generate sdata references.  This is the default for tool
17577           chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
17578           targets.
17579
17580       -mvolatile-cache
17581           Use ordinarily cached memory accesses for volatile references.
17582           This is the default.
17583
17584       -mno-volatile-cache
17585           Enable cache bypass for volatile references.
17586
17587       The following options fine tune code generation:
17588
17589       -malign-call
17590           Does nothing.  Preserved for backward compatibility.
17591
17592       -mauto-modify-reg
17593           Enable the use of pre/post modify with register displacement.
17594
17595       -mbbit-peephole
17596           Enable bbit peephole2.
17597
17598       -mno-brcc
17599           This option disables a target-specific pass in arc_reorg to
17600           generate compare-and-branch ("brcc") instructions.  It has no
17601           effect on generation of these instructions driven by the combiner
17602           pass.
17603
17604       -mcase-vector-pcrel
17605           Use PC-relative switch case tables to enable case table shortening.
17606           This is the default for -Os.
17607
17608       -mcompact-casesi
17609           Enable compact "casesi" pattern.  This is the default for -Os, and
17610           only available for ARCv1 cores.  This option is deprecated.
17611
17612       -mno-cond-exec
17613           Disable the ARCompact-specific pass to generate conditional
17614           execution instructions.
17615
17616           Due to delay slot scheduling and interactions between operand
17617           numbers, literal sizes, instruction lengths, and the support for
17618           conditional execution, the target-independent pass to generate
17619           conditional execution is often lacking, so the ARC port has kept a
17620           special pass around that tries to find more conditional execution
17621           generation opportunities after register allocation, branch
17622           shortening, and delay slot scheduling have been done.  This pass
17623           generally, but not always, improves performance and code size, at
17624           the cost of extra compilation time, which is why there is an option
17625           to switch it off.  If you have a problem with call instructions
17626           exceeding their allowable offset range because they are
17627           conditionalized, you should consider using -mmedium-calls instead.
17628
17629       -mearly-cbranchsi
17630           Enable pre-reload use of the "cbranchsi" pattern.
17631
17632       -mexpand-adddi
17633           Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
17634           "adc" etc.  This option is deprecated.
17635
17636       -mindexed-loads
17637           Enable the use of indexed loads.  This can be problematic because
17638           some optimizers then assume that indexed stores exist, which is not
17639           the case.
17640
17641       -mlra
17642           Enable Local Register Allocation.  This is still experimental for
17643           ARC, so by default the compiler uses standard reload (i.e.
17644           -mno-lra).
17645
17646       -mlra-priority-none
17647           Don't indicate any priority for target registers.
17648
17649       -mlra-priority-compact
17650           Indicate target register priority for r0..r3 / r12..r15.
17651
17652       -mlra-priority-noncompact
17653           Reduce target register priority for r0..r3 / r12..r15.
17654
17655       -mmillicode
17656           When optimizing for size (using -Os), prologues and epilogues that
17657           have to save or restore a large number of registers are often
17658           shortened by using call to a special function in libgcc; this is
17659           referred to as a millicode call.  As these calls can pose
17660           performance issues, and/or cause linking issues when linking in a
17661           nonstandard way, this option is provided to turn on or off
17662           millicode call generation.
17663
17664       -mcode-density-frame
17665           This option enable the compiler to emit "enter" and "leave"
17666           instructions.  These instructions are only valid for CPUs with
17667           code-density feature.
17668
17669       -mmixed-code
17670           Does nothing.  Preserved for backward compatibility.
17671
17672       -mq-class
17673           Ths option is deprecated.  Enable q instruction alternatives.  This
17674           is the default for -Os.
17675
17676       -mRcq
17677           Enable Rcq constraint handling.  Most short code generation depends
17678           on this.  This is the default.
17679
17680       -mRcw
17681           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends
17682           on this.  This is the default.
17683
17684       -msize-level=level
17685           Fine-tune size optimization with regards to instruction lengths and
17686           alignment.  The recognized values for level are:
17687
17688           0   No size optimization.  This level is deprecated and treated
17689               like 1.
17690
17691           1   Short instructions are used opportunistically.
17692
17693           2   In addition, alignment of loops and of code after barriers are
17694               dropped.
17695
17696           3   In addition, optional data alignment is dropped, and the option
17697               Os is enabled.
17698
17699           This defaults to 3 when -Os is in effect.  Otherwise, the behavior
17700           when this is not set is equivalent to level 1.
17701
17702       -mtune=cpu
17703           Set instruction scheduling parameters for cpu, overriding any
17704           implied by -mcpu=.
17705
17706           Supported values for cpu are
17707
17708           ARC600
17709               Tune for ARC600 CPU.
17710
17711           ARC601
17712               Tune for ARC601 CPU.
17713
17714           ARC700
17715               Tune for ARC700 CPU with standard multiplier block.
17716
17717           ARC700-xmac
17718               Tune for ARC700 CPU with XMAC block.
17719
17720           ARC725D
17721               Tune for ARC725D CPU.
17722
17723           ARC750D
17724               Tune for ARC750D CPU.
17725
17726       -mmultcost=num
17727           Cost to assume for a multiply instruction, with 4 being equal to a
17728           normal instruction.
17729
17730       -munalign-prob-threshold=probability
17731           Does nothing.  Preserved for backward compatibility.
17732
17733       The following options are maintained for backward compatibility, but
17734       are now deprecated and will be removed in a future release:
17735
17736       -margonaut
17737           Obsolete FPX.
17738
17739       -mbig-endian
17740       -EB Compile code for big-endian targets.  Use of these options is now
17741           deprecated.  Big-endian code is supported by configuring GCC to
17742           build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
17743           endian is the default.
17744
17745       -mlittle-endian
17746       -EL Compile code for little-endian targets.  Use of these options is
17747           now deprecated.  Little-endian code is supported by configuring GCC
17748           to build "arc-elf32" and "arc-linux-uclibc" targets, for which
17749           little endian is the default.
17750
17751       -mbarrel_shifter
17752           Replaced by -mbarrel-shifter.
17753
17754       -mdpfp_compact
17755           Replaced by -mdpfp-compact.
17756
17757       -mdpfp_fast
17758           Replaced by -mdpfp-fast.
17759
17760       -mdsp_packa
17761           Replaced by -mdsp-packa.
17762
17763       -mEA
17764           Replaced by -mea.
17765
17766       -mmac_24
17767           Replaced by -mmac-24.
17768
17769       -mmac_d16
17770           Replaced by -mmac-d16.
17771
17772       -mspfp_compact
17773           Replaced by -mspfp-compact.
17774
17775       -mspfp_fast
17776           Replaced by -mspfp-fast.
17777
17778       -mtune=cpu
17779           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
17780           by ARC600, ARC601, ARC700 and ARC700-xmac respectively.
17781
17782       -multcost=num
17783           Replaced by -mmultcost.
17784
17785       ARM Options
17786
17787       These -m options are defined for the ARM port:
17788
17789       -mabi=name
17790           Generate code for the specified ABI.  Permissible values are: apcs-
17791           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
17792
17793       -mapcs-frame
17794           Generate a stack frame that is compliant with the ARM Procedure
17795           Call Standard for all functions, even if this is not strictly
17796           necessary for correct execution of the code.  Specifying
17797           -fomit-frame-pointer with this option causes the stack frames not
17798           to be generated for leaf functions.  The default is
17799           -mno-apcs-frame.  This option is deprecated.
17800
17801       -mapcs
17802           This is a synonym for -mapcs-frame and is deprecated.
17803
17804       -mthumb-interwork
17805           Generate code that supports calling between the ARM and Thumb
17806           instruction sets.  Without this option, on pre-v5 architectures,
17807           the two instruction sets cannot be reliably used inside one
17808           program.  The default is -mno-thumb-interwork, since slightly
17809           larger code is generated when -mthumb-interwork is specified.  In
17810           AAPCS configurations this option is meaningless.
17811
17812       -mno-sched-prolog
17813           Prevent the reordering of instructions in the function prologue, or
17814           the merging of those instruction with the instructions in the
17815           function's body.  This means that all functions start with a
17816           recognizable set of instructions (or in fact one of a choice from a
17817           small set of different function prologues), and this information
17818           can be used to locate the start of functions inside an executable
17819           piece of code.  The default is -msched-prolog.
17820
17821       -mfloat-abi=name
17822           Specifies which floating-point ABI to use.  Permissible values are:
17823           soft, softfp and hard.
17824
17825           Specifying soft causes GCC to generate output containing library
17826           calls for floating-point operations.  softfp allows the generation
17827           of code using hardware floating-point instructions, but still uses
17828           the soft-float calling conventions.  hard allows generation of
17829           floating-point instructions and uses FPU-specific calling
17830           conventions.
17831
17832           The default depends on the specific target configuration.  Note
17833           that the hard-float and soft-float ABIs are not link-compatible;
17834           you must compile your entire program with the same ABI, and link
17835           with a compatible set of libraries.
17836
17837       -mgeneral-regs-only
17838           Generate code which uses only the general-purpose registers.  This
17839           will prevent the compiler from using floating-point and Advanced
17840           SIMD registers but will not impose any restrictions on the
17841           assembler.
17842
17843       -mlittle-endian
17844           Generate code for a processor running in little-endian mode.  This
17845           is the default for all standard configurations.
17846
17847       -mbig-endian
17848           Generate code for a processor running in big-endian mode; the
17849           default is to compile code for a little-endian processor.
17850
17851       -mbe8
17852       -mbe32
17853           When linking a big-endian image select between BE8 and BE32
17854           formats.  The option has no effect for little-endian images and is
17855           ignored.  The default is dependent on the selected target
17856           architecture.  For ARMv6 and later architectures the default is
17857           BE8, for older architectures the default is BE32.  BE32 format has
17858           been deprecated by ARM.
17859
17860       -march=name[+extension...]
17861           This specifies the name of the target ARM architecture.  GCC uses
17862           this name to determine what kind of instructions it can emit when
17863           generating assembly code.  This option can be used in conjunction
17864           with or instead of the -mcpu= option.
17865
17866           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
17867           armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
17868           armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
17869           armv8.6-a, armv9-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m,
17870           armv7e-m, armv8-m.base, armv8-m.main, armv8.1-m.main, armv9-a,
17871           iwmmxt and iwmmxt2.
17872
17873           Additionally, the following architectures, which lack support for
17874           the Thumb execution state, are recognized but support is
17875           deprecated: armv4.
17876
17877           Many of the architectures support extensions.  These can be added
17878           by appending +extension to the architecture name.  Extension
17879           options are processed in order and capabilities accumulate.  An
17880           extension will also enable any necessary base extensions upon which
17881           it depends.  For example, the +crypto extension will always enable
17882           the +simd extension.  The exception to the additive construction is
17883           for extensions that are prefixed with +no...: these extensions
17884           disable the specified option and any other extensions that may
17885           depend on the presence of that extension.
17886
17887           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
17888           writing -march=armv7-a+vfpv4 since the +simd option is entirely
17889           disabled by the +nofp option that follows it.
17890
17891           Most extension names are generically named, but have an effect that
17892           is dependent upon the architecture to which it is applied.  For
17893           example, the +simd option can be applied to both armv7-a and
17894           armv8-a architectures, but will enable the original ARMv7-A
17895           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
17896           for armv8-a.
17897
17898           The table below lists the supported extensions for each
17899           architecture.  Architectures not mentioned do not support any
17900           extensions.
17901
17902           armv5te
17903           armv6
17904           armv6j
17905           armv6k
17906           armv6kz
17907           armv6t2
17908           armv6z
17909           armv6zk
17910               +fp The VFPv2 floating-point instructions.  The extension
17911                   +vfpv2 can be used as an alias for this extension.
17912
17913               +nofp
17914                   Disable the floating-point instructions.
17915
17916           armv7
17917               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
17918               architectures.
17919
17920               +fp The VFPv3 floating-point instructions, with 16 double-
17921                   precision registers.  The extension +vfpv3-d16 can be used
17922                   as an alias for this extension.  Note that floating-point
17923                   is not supported by the base ARMv7-M architecture, but is
17924                   compatible with both the ARMv7-A and ARMv7-R architectures.
17925
17926               +nofp
17927                   Disable the floating-point instructions.
17928
17929           armv7-a
17930               +mp The multiprocessing extension.
17931
17932               +sec
17933                   The security extension.
17934
17935               +fp The VFPv3 floating-point instructions, with 16 double-
17936                   precision registers.  The extension +vfpv3-d16 can be used
17937                   as an alias for this extension.
17938
17939               +simd
17940                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17941                   instructions.  The extensions +neon and +neon-vfpv3 can be
17942                   used as aliases for this extension.
17943
17944               +vfpv3
17945                   The VFPv3 floating-point instructions, with 32 double-
17946                   precision registers.
17947
17948               +vfpv3-d16-fp16
17949                   The VFPv3 floating-point instructions, with 16 double-
17950                   precision registers and the half-precision floating-point
17951                   conversion operations.
17952
17953               +vfpv3-fp16
17954                   The VFPv3 floating-point instructions, with 32 double-
17955                   precision registers and the half-precision floating-point
17956                   conversion operations.
17957
17958               +vfpv4-d16
17959                   The VFPv4 floating-point instructions, with 16 double-
17960                   precision registers.
17961
17962               +vfpv4
17963                   The VFPv4 floating-point instructions, with 32 double-
17964                   precision registers.
17965
17966               +neon-fp16
17967                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17968                   instructions, with the half-precision floating-point
17969                   conversion operations.
17970
17971               +neon-vfpv4
17972                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17973                   instructions.
17974
17975               +nosimd
17976                   Disable the Advanced SIMD instructions (does not disable
17977                   floating point).
17978
17979               +nofp
17980                   Disable the floating-point and Advanced SIMD instructions.
17981
17982           armv7ve
17983               The extended version of the ARMv7-A architecture with support
17984               for virtualization.
17985
17986               +fp The VFPv4 floating-point instructions, with 16 double-
17987                   precision registers.  The extension +vfpv4-d16 can be used
17988                   as an alias for this extension.
17989
17990               +simd
17991                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17992                   instructions.  The extension +neon-vfpv4 can be used as an
17993                   alias for this extension.
17994
17995               +vfpv3-d16
17996                   The VFPv3 floating-point instructions, with 16 double-
17997                   precision registers.
17998
17999               +vfpv3
18000                   The VFPv3 floating-point instructions, with 32 double-
18001                   precision registers.
18002
18003               +vfpv3-d16-fp16
18004                   The VFPv3 floating-point instructions, with 16 double-
18005                   precision registers and the half-precision floating-point
18006                   conversion operations.
18007
18008               +vfpv3-fp16
18009                   The VFPv3 floating-point instructions, with 32 double-
18010                   precision registers and the half-precision floating-point
18011                   conversion operations.
18012
18013               +vfpv4-d16
18014                   The VFPv4 floating-point instructions, with 16 double-
18015                   precision registers.
18016
18017               +vfpv4
18018                   The VFPv4 floating-point instructions, with 32 double-
18019                   precision registers.
18020
18021               +neon
18022                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
18023                   instructions.  The extension +neon-vfpv3 can be used as an
18024                   alias for this extension.
18025
18026               +neon-fp16
18027                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
18028                   instructions, with the half-precision floating-point
18029                   conversion operations.
18030
18031               +nosimd
18032                   Disable the Advanced SIMD instructions (does not disable
18033                   floating point).
18034
18035               +nofp
18036                   Disable the floating-point and Advanced SIMD instructions.
18037
18038           armv8-a
18039               +crc
18040                   The Cyclic Redundancy Check (CRC) instructions.
18041
18042               +simd
18043                   The ARMv8-A Advanced SIMD and floating-point instructions.
18044
18045               +crypto
18046                   The cryptographic instructions.
18047
18048               +nocrypto
18049                   Disable the cryptographic instructions.
18050
18051               +nofp
18052                   Disable the floating-point, Advanced SIMD and cryptographic
18053                   instructions.
18054
18055               +sb Speculation Barrier Instruction.
18056
18057               +predres
18058                   Execution and Data Prediction Restriction Instructions.
18059
18060           armv8.1-a
18061               +simd
18062                   The ARMv8.1-A Advanced SIMD and floating-point
18063                   instructions.
18064
18065               +crypto
18066                   The cryptographic instructions.  This also enables the
18067                   Advanced SIMD and floating-point instructions.
18068
18069               +nocrypto
18070                   Disable the cryptographic instructions.
18071
18072               +nofp
18073                   Disable the floating-point, Advanced SIMD and cryptographic
18074                   instructions.
18075
18076               +sb Speculation Barrier Instruction.
18077
18078               +predres
18079                   Execution and Data Prediction Restriction Instructions.
18080
18081           armv8.2-a
18082           armv8.3-a
18083               +fp16
18084                   The half-precision floating-point data processing
18085                   instructions.  This also enables the Advanced SIMD and
18086                   floating-point instructions.
18087
18088               +fp16fml
18089                   The half-precision floating-point fmla extension.  This
18090                   also enables the half-precision floating-point extension
18091                   and Advanced SIMD and floating-point instructions.
18092
18093               +simd
18094                   The ARMv8.1-A Advanced SIMD and floating-point
18095                   instructions.
18096
18097               +crypto
18098                   The cryptographic instructions.  This also enables the
18099                   Advanced SIMD and floating-point instructions.
18100
18101               +dotprod
18102                   Enable the Dot Product extension.  This also enables
18103                   Advanced SIMD instructions.
18104
18105               +nocrypto
18106                   Disable the cryptographic extension.
18107
18108               +nofp
18109                   Disable the floating-point, Advanced SIMD and cryptographic
18110                   instructions.
18111
18112               +sb Speculation Barrier Instruction.
18113
18114               +predres
18115                   Execution and Data Prediction Restriction Instructions.
18116
18117               +i8mm
18118                   8-bit Integer Matrix Multiply instructions.  This also
18119                   enables Advanced SIMD and floating-point instructions.
18120
18121               +bf16
18122                   Brain half-precision floating-point instructions.  This
18123                   also enables Advanced SIMD and floating-point instructions.
18124
18125           armv8.4-a
18126               +fp16
18127                   The half-precision floating-point data processing
18128                   instructions.  This also enables the Advanced SIMD and
18129                   floating-point instructions as well as the Dot Product
18130                   extension and the half-precision floating-point fmla
18131                   extension.
18132
18133               +simd
18134                   The ARMv8.3-A Advanced SIMD and floating-point instructions
18135                   as well as the Dot Product extension.
18136
18137               +crypto
18138                   The cryptographic instructions.  This also enables the
18139                   Advanced SIMD and floating-point instructions as well as
18140                   the Dot Product extension.
18141
18142               +nocrypto
18143                   Disable the cryptographic extension.
18144
18145               +nofp
18146                   Disable the floating-point, Advanced SIMD and cryptographic
18147                   instructions.
18148
18149               +sb Speculation Barrier Instruction.
18150
18151               +predres
18152                   Execution and Data Prediction Restriction Instructions.
18153
18154               +i8mm
18155                   8-bit Integer Matrix Multiply instructions.  This also
18156                   enables Advanced SIMD and floating-point instructions.
18157
18158               +bf16
18159                   Brain half-precision floating-point instructions.  This
18160                   also enables Advanced SIMD and floating-point instructions.
18161
18162           armv8.5-a
18163               +fp16
18164                   The half-precision floating-point data processing
18165                   instructions.  This also enables the Advanced SIMD and
18166                   floating-point instructions as well as the Dot Product
18167                   extension and the half-precision floating-point fmla
18168                   extension.
18169
18170               +simd
18171                   The ARMv8.3-A Advanced SIMD and floating-point instructions
18172                   as well as the Dot Product extension.
18173
18174               +crypto
18175                   The cryptographic instructions.  This also enables the
18176                   Advanced SIMD and floating-point instructions as well as
18177                   the Dot Product extension.
18178
18179               +nocrypto
18180                   Disable the cryptographic extension.
18181
18182               +nofp
18183                   Disable the floating-point, Advanced SIMD and cryptographic
18184                   instructions.
18185
18186               +i8mm
18187                   8-bit Integer Matrix Multiply instructions.  This also
18188                   enables Advanced SIMD and floating-point instructions.
18189
18190               +bf16
18191                   Brain half-precision floating-point instructions.  This
18192                   also enables Advanced SIMD and floating-point instructions.
18193
18194           armv8.6-a
18195               +fp16
18196                   The half-precision floating-point data processing
18197                   instructions.  This also enables the Advanced SIMD and
18198                   floating-point instructions as well as the Dot Product
18199                   extension and the half-precision floating-point fmla
18200                   extension.
18201
18202               +simd
18203                   The ARMv8.3-A Advanced SIMD and floating-point instructions
18204                   as well as the Dot Product extension.
18205
18206               +crypto
18207                   The cryptographic instructions.  This also enables the
18208                   Advanced SIMD and floating-point instructions as well as
18209                   the Dot Product extension.
18210
18211               +nocrypto
18212                   Disable the cryptographic extension.
18213
18214               +nofp
18215                   Disable the floating-point, Advanced SIMD and cryptographic
18216                   instructions.
18217
18218               +i8mm
18219                   8-bit Integer Matrix Multiply instructions.  This also
18220                   enables Advanced SIMD and floating-point instructions.
18221
18222               +bf16
18223                   Brain half-precision floating-point instructions.  This
18224                   also enables Advanced SIMD and floating-point instructions.
18225
18226           armv7-r
18227               +fp.sp
18228                   The single-precision VFPv3 floating-point instructions.
18229                   The extension +vfpv3xd can be used as an alias for this
18230                   extension.
18231
18232               +fp The VFPv3 floating-point instructions with 16 double-
18233                   precision registers.  The extension +vfpv3-d16 can be used
18234                   as an alias for this extension.
18235
18236               +vfpv3xd-d16-fp16
18237                   The single-precision VFPv3 floating-point instructions with
18238                   16 double-precision registers and the half-precision
18239                   floating-point conversion operations.
18240
18241               +vfpv3-d16-fp16
18242                   The VFPv3 floating-point instructions with 16 double-
18243                   precision registers and the half-precision floating-point
18244                   conversion operations.
18245
18246               +nofp
18247                   Disable the floating-point extension.
18248
18249               +idiv
18250                   The ARM-state integer division instructions.
18251
18252               +noidiv
18253                   Disable the ARM-state integer division extension.
18254
18255           armv7e-m
18256               +fp The single-precision VFPv4 floating-point instructions.
18257
18258               +fpv5
18259                   The single-precision FPv5 floating-point instructions.
18260
18261               +fp.dp
18262                   The single- and double-precision FPv5 floating-point
18263                   instructions.
18264
18265               +nofp
18266                   Disable the floating-point extensions.
18267
18268           armv8.1-m.main
18269               +dsp
18270                   The DSP instructions.
18271
18272               +mve
18273                   The M-Profile Vector Extension (MVE) integer instructions.
18274
18275               +mve.fp
18276                   The M-Profile Vector Extension (MVE) integer and single
18277                   precision floating-point instructions.
18278
18279               +fp The single-precision floating-point instructions.
18280
18281               +fp.dp
18282                   The single- and double-precision floating-point
18283                   instructions.
18284
18285               +nofp
18286                   Disable the floating-point extension.
18287
18288               +cdecp0, +cdecp1, ... , +cdecp7
18289                   Enable the Custom Datapath Extension (CDE) on selected
18290                   coprocessors according to the numbers given in the options
18291                   in the range 0 to 7.
18292
18293           armv8-m.main
18294               +dsp
18295                   The DSP instructions.
18296
18297               +nodsp
18298                   Disable the DSP extension.
18299
18300               +fp The single-precision floating-point instructions.
18301
18302               +fp.dp
18303                   The single- and double-precision floating-point
18304                   instructions.
18305
18306               +nofp
18307                   Disable the floating-point extension.
18308
18309               +cdecp0, +cdecp1, ... , +cdecp7
18310                   Enable the Custom Datapath Extension (CDE) on selected
18311                   coprocessors according to the numbers given in the options
18312                   in the range 0 to 7.
18313
18314           armv8-r
18315               +crc
18316                   The Cyclic Redundancy Check (CRC) instructions.
18317
18318               +fp.sp
18319                   The single-precision FPv5 floating-point instructions.
18320
18321               +simd
18322                   The ARMv8-A Advanced SIMD and floating-point instructions.
18323
18324               +crypto
18325                   The cryptographic instructions.
18326
18327               +nocrypto
18328                   Disable the cryptographic instructions.
18329
18330               +nofp
18331                   Disable the floating-point, Advanced SIMD and cryptographic
18332                   instructions.
18333
18334           -march=native causes the compiler to auto-detect the architecture
18335           of the build computer.  At present, this feature is only supported
18336           on GNU/Linux, and not all architectures are recognized.  If the
18337           auto-detect is unsuccessful the option has no effect.
18338
18339       -mtune=name
18340           This option specifies the name of the target ARM processor for
18341           which GCC should tune the performance of the code.  For some ARM
18342           implementations better performance can be obtained by using this
18343           option.  Permissible names are: arm7tdmi, arm7tdmi-s, arm710t,
18344           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
18345           strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t,
18346           arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi,
18347           arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e,
18348           arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s,
18349           arm1156t2f-s, arm1176jz-s, arm1176jzf-s, generic-armv7-a,
18350           cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
18351           cortex-a17, cortex-a32, cortex-a35, cortex-a53, cortex-a55,
18352           cortex-a57, cortex-a72, cortex-a73, cortex-a75, cortex-a76,
18353           cortex-a76ae, cortex-a77, cortex-a78, cortex-a78ae, cortex-a78c,
18354           cortex-a710, ares, cortex-r4, cortex-r4f, cortex-r5, cortex-r7,
18355           cortex-r8, cortex-r52, cortex-r52plus, cortex-m0, cortex-m0plus,
18356           cortex-m1, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33,
18357           cortex-m35p, cortex-m55, cortex-x1, cortex-m1.small-multiply,
18358           cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1,
18359           marvell-pj4, neoverse-n1, neoverse-n2, neoverse-v1, xscale, iwmmxt,
18360           iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te,
18361           xgene1.
18362
18363           Additionally, this option can specify that GCC should tune the
18364           performance of the code for a big.LITTLE system.  Permissible names
18365           are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
18366           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
18367           cortex-a72.cortex-a35, cortex-a73.cortex-a53,
18368           cortex-a75.cortex-a55, cortex-a76.cortex-a55.
18369
18370           -mtune=generic-arch specifies that GCC should tune the performance
18371           for a blend of processors within architecture arch.  The aim is to
18372           generate code that run well on the current most popular processors,
18373           balancing between optimizations that benefit some CPUs in the
18374           range, and avoiding performance pitfalls of other CPUs.  The
18375           effects of this option may change in future GCC versions as CPU
18376           models come and go.
18377
18378           -mtune permits the same extension options as -mcpu, but the
18379           extension options do not affect the tuning of the generated code.
18380
18381           -mtune=native causes the compiler to auto-detect the CPU of the
18382           build computer.  At present, this feature is only supported on
18383           GNU/Linux, and not all architectures are recognized.  If the auto-
18384           detect is unsuccessful the option has no effect.
18385
18386       -mcpu=name[+extension...]
18387           This specifies the name of the target ARM processor.  GCC uses this
18388           name to derive the name of the target ARM architecture (as if
18389           specified by -march) and the ARM processor type for which to tune
18390           for performance (as if specified by -mtune).  Where this option is
18391           used in conjunction with -march or -mtune, those options take
18392           precedence over the appropriate part of this option.
18393
18394           Many of the supported CPUs implement optional architectural
18395           extensions.  Where this is so the architectural extensions are
18396           normally enabled by default.  If implementations that lack the
18397           extension exist, then the extension syntax can be used to disable
18398           those extensions that have been omitted.  For floating-point and
18399           Advanced SIMD (Neon) instructions, the settings of the options
18400           -mfloat-abi and -mfpu must also be considered: floating-point and
18401           Advanced SIMD instructions will only be used if -mfloat-abi is not
18402           set to soft; and any setting of -mfpu other than auto will override
18403           the available floating-point and SIMD extension instructions.
18404
18405           For example, cortex-a9 can be found in three major configurations:
18406           integer only, with just a floating-point unit or with floating-
18407           point and Advanced SIMD.  The default is to enable all the
18408           instructions, but the extensions +nosimd and +nofp can be used to
18409           disable just the SIMD or both the SIMD and floating-point
18410           instructions respectively.
18411
18412           Permissible names for this option are the same as those for -mtune.
18413
18414           The following extension options are common to the listed CPUs:
18415
18416           +nodsp
18417               Disable the DSP instructions on cortex-m33, cortex-m35p.
18418
18419           +nofp
18420               Disables the floating-point instructions on arm9e, arm946e-s,
18421               arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
18422               arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
18423               cortex-m7, cortex-m33 and cortex-m35p.  Disables the floating-
18424               point and SIMD instructions on generic-armv7-a, cortex-a5,
18425               cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
18426               cortex-a17, cortex-a15.cortex-a7, cortex-a17.cortex-a7,
18427               cortex-a32, cortex-a35, cortex-a53 and cortex-a55.
18428
18429           +nofp.dp
18430               Disables the double-precision component of the floating-point
18431               instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52,
18432               cortex-r52plus and cortex-m7.
18433
18434           +nosimd
18435               Disables the SIMD (but not floating-point) instructions on
18436               generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.
18437
18438           +crypto
18439               Enables the cryptographic instructions on cortex-a32,
18440               cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
18441               cortex-a73, cortex-a75, exynos-m1, xgene1,
18442               cortex-a57.cortex-a53, cortex-a72.cortex-a53,
18443               cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
18444               cortex-a75.cortex-a55.
18445
18446           Additionally the generic-armv7-a pseudo target defaults to VFPv3
18447           with 16 double-precision registers.  It supports the following
18448           extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16,
18449           vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
18450           neon-vfpv4.  The meanings are the same as for the extensions to
18451           -march=armv7-a.
18452
18453           -mcpu=generic-arch is also permissible, and is equivalent to
18454           -march=arch -mtune=generic-arch.  See -mtune for more information.
18455
18456           -mcpu=native causes the compiler to auto-detect the CPU of the
18457           build computer.  At present, this feature is only supported on
18458           GNU/Linux, and not all architectures are recognized.  If the auto-
18459           detect is unsuccessful the option has no effect.
18460
18461       -mfpu=name
18462           This specifies what floating-point hardware (or hardware emulation)
18463           is available on the target.  Permissible names are: auto, vfpv2,
18464           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
18465           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
18466           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
18467           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
18468           and vfp is an alias for vfpv2.
18469
18470           The setting auto is the default and is special.  It causes the
18471           compiler to select the floating-point and Advanced SIMD
18472           instructions based on the settings of -mcpu and -march.
18473
18474           If the selected floating-point hardware includes the NEON extension
18475           (e.g. -mfpu=neon), note that floating-point operations are not
18476           generated by GCC's auto-vectorization pass unless
18477           -funsafe-math-optimizations is also specified.  This is because
18478           NEON hardware does not fully implement the IEEE 754 standard for
18479           floating-point arithmetic (in particular denormal values are
18480           treated as zero), so the use of NEON instructions may lead to a
18481           loss of precision.
18482
18483           You can also set the fpu name at function level by using the
18484           "target("fpu=")" function attributes or pragmas.
18485
18486       -mfp16-format=name
18487           Specify the format of the "__fp16" half-precision floating-point
18488           type.  Permissible names are none, ieee, and alternative; the
18489           default is none, in which case the "__fp16" type is not defined.
18490
18491       -mstructure-size-boundary=n
18492           The sizes of all structures and unions are rounded up to a multiple
18493           of the number of bits set by this option.  Permissible values are
18494           8, 32 and 64.  The default value varies for different toolchains.
18495           For the COFF targeted toolchain the default value is 8.  A value of
18496           64 is only allowed if the underlying ABI supports it.
18497
18498           Specifying a larger number can produce faster, more efficient code,
18499           but can also increase the size of the program.  Different values
18500           are potentially incompatible.  Code compiled with one value cannot
18501           necessarily expect to work with code or libraries compiled with
18502           another value, if they exchange information using structures or
18503           unions.
18504
18505           This option is deprecated.
18506
18507       -mabort-on-noreturn
18508           Generate a call to the function "abort" at the end of a "noreturn"
18509           function.  It is executed if the function tries to return.
18510
18511       -mlong-calls
18512       -mno-long-calls
18513           Tells the compiler to perform function calls by first loading the
18514           address of the function into a register and then performing a
18515           subroutine call on this register.  This switch is needed if the
18516           target function lies outside of the 64-megabyte addressing range of
18517           the offset-based version of subroutine call instruction.
18518
18519           Even if this switch is enabled, not all function calls are turned
18520           into long calls.  The heuristic is that static functions, functions
18521           that have the "short_call" attribute, functions that are inside the
18522           scope of a "#pragma no_long_calls" directive, and functions whose
18523           definitions have already been compiled within the current
18524           compilation unit are not turned into long calls.  The exceptions to
18525           this rule are that weak function definitions, functions with the
18526           "long_call" attribute or the "section" attribute, and functions
18527           that are within the scope of a "#pragma long_calls" directive are
18528           always turned into long calls.
18529
18530           This feature is not enabled by default.  Specifying -mno-long-calls
18531           restores the default behavior, as does placing the function calls
18532           within the scope of a "#pragma long_calls_off" directive.  Note
18533           these switches have no effect on how the compiler generates code to
18534           handle function calls via function pointers.
18535
18536       -msingle-pic-base
18537           Treat the register used for PIC addressing as read-only, rather
18538           than loading it in the prologue for each function.  The runtime
18539           system is responsible for initializing this register with an
18540           appropriate value before execution begins.
18541
18542       -mpic-register=reg
18543           Specify the register to be used for PIC addressing.  For standard
18544           PIC base case, the default is any suitable register determined by
18545           compiler.  For single PIC base case, the default is R9 if target is
18546           EABI based or stack-checking is enabled, otherwise the default is
18547           R10.
18548
18549       -mpic-data-is-text-relative
18550           Assume that the displacement between the text and data segments is
18551           fixed at static link time.  This permits using PC-relative
18552           addressing operations to access data known to be in the data
18553           segment.  For non-VxWorks RTP targets, this option is enabled by
18554           default.  When disabled on such targets, it will enable
18555           -msingle-pic-base by default.
18556
18557       -mpoke-function-name
18558           Write the name of each function into the text section, directly
18559           preceding the function prologue.  The generated code is similar to
18560           this:
18561
18562                        t0
18563                            .ascii "arm_poke_function_name", 0
18564                            .align
18565                        t1
18566                            .word 0xff000000 + (t1 - t0)
18567                        arm_poke_function_name
18568                            mov     ip, sp
18569                            stmfd   sp!, {fp, ip, lr, pc}
18570                            sub     fp, ip, #4
18571
18572           When performing a stack backtrace, code can inspect the value of
18573           "pc" stored at "fp + 0".  If the trace function then looks at
18574           location "pc - 12" and the top 8 bits are set, then we know that
18575           there is a function name embedded immediately preceding this
18576           location and has length "((pc[-3]) & 0xff000000)".
18577
18578       -mthumb
18579       -marm
18580           Select between generating code that executes in ARM and Thumb
18581           states.  The default for most configurations is to generate code
18582           that executes in ARM state, but the default can be changed by
18583           configuring GCC with the --with-mode=state configure option.
18584
18585           You can also override the ARM and Thumb mode for each function by
18586           using the "target("thumb")" and "target("arm")" function attributes
18587           or pragmas.
18588
18589       -mflip-thumb
18590           Switch ARM/Thumb modes on alternating functions.  This option is
18591           provided for regression testing of mixed Thumb/ARM code generation,
18592           and is not intended for ordinary use in compiling code.
18593
18594       -mtpcs-frame
18595           Generate a stack frame that is compliant with the Thumb Procedure
18596           Call Standard for all non-leaf functions.  (A leaf function is one
18597           that does not call any other functions.)  The default is
18598           -mno-tpcs-frame.
18599
18600       -mtpcs-leaf-frame
18601           Generate a stack frame that is compliant with the Thumb Procedure
18602           Call Standard for all leaf functions.  (A leaf function is one that
18603           does not call any other functions.)  The default is
18604           -mno-apcs-leaf-frame.
18605
18606       -mcallee-super-interworking
18607           Gives all externally visible functions in the file being compiled
18608           an ARM instruction set header which switches to Thumb mode before
18609           executing the rest of the function.  This allows these functions to
18610           be called from non-interworking code.  This option is not valid in
18611           AAPCS configurations because interworking is enabled by default.
18612
18613       -mcaller-super-interworking
18614           Allows calls via function pointers (including virtual functions) to
18615           execute correctly regardless of whether the target code has been
18616           compiled for interworking or not.  There is a small overhead in the
18617           cost of executing a function pointer if this option is enabled.
18618           This option is not valid in AAPCS configurations because
18619           interworking is enabled by default.
18620
18621       -mtp=name
18622           Specify the access model for the thread local storage pointer.  The
18623           valid models are soft, which generates calls to "__aeabi_read_tp",
18624           cp15, which fetches the thread pointer from "cp15" directly
18625           (supported in the arm6k architecture), and auto, which uses the
18626           best available method for the selected processor.  The default
18627           setting is auto.
18628
18629       -mtls-dialect=dialect
18630           Specify the dialect to use for accessing thread local storage.  Two
18631           dialects are supported---gnu and gnu2.  The gnu dialect selects the
18632           original GNU scheme for supporting local and global dynamic TLS
18633           models.  The gnu2 dialect selects the GNU descriptor scheme, which
18634           provides better performance for shared libraries.  The GNU
18635           descriptor scheme is compatible with the original scheme, but does
18636           require new assembler, linker and library support.  Initial and
18637           local exec TLS models are unaffected by this option and always use
18638           the original scheme.
18639
18640       -mword-relocations
18641           Only generate absolute relocations on word-sized values (i.e.
18642           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
18643           SymbianOS) where the runtime loader imposes this restriction, and
18644           when -fpic or -fPIC is specified. This option conflicts with
18645           -mslow-flash-data.
18646
18647       -mfix-cortex-m3-ldrd
18648           Some Cortex-M3 cores can cause data corruption when "ldrd"
18649           instructions with overlapping destination and base registers are
18650           used.  This option avoids generating these instructions.  This
18651           option is enabled by default when -mcpu=cortex-m3 is specified.
18652
18653       -mfix-cortex-a57-aes-1742098
18654       -mno-fix-cortex-a57-aes-1742098
18655       -mfix-cortex-a72-aes-1655431
18656       -mno-fix-cortex-a72-aes-1655431
18657           Enable (disable) mitigation for an erratum on Cortex-A57 and
18658           Cortex-A72 that affects the AES cryptographic instructions.  This
18659           option is enabled by default when either -mcpu=cortex-a57 or
18660           -mcpu=cortex-a72 is specified.
18661
18662       -munaligned-access
18663       -mno-unaligned-access
18664           Enables (or disables) reading and writing of 16- and 32- bit values
18665           from addresses that are not 16- or 32- bit aligned.  By default
18666           unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
18667           ARMv8-M Baseline architectures, and enabled for all other
18668           architectures.  If unaligned access is not enabled then words in
18669           packed data structures are accessed a byte at a time.
18670
18671           The ARM attribute "Tag_CPU_unaligned_access" is set in the
18672           generated object file to either true or false, depending upon the
18673           setting of this option.  If unaligned access is enabled then the
18674           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.
18675
18676       -mneon-for-64bits
18677           This option is deprecated and has no effect.
18678
18679       -mslow-flash-data
18680           Assume loading data from flash is slower than fetching instruction.
18681           Therefore literal load is minimized for better performance.  This
18682           option is only supported when compiling for ARMv7 M-profile and off
18683           by default. It conflicts with -mword-relocations.
18684
18685       -masm-syntax-unified
18686           Assume inline assembler is using unified asm syntax.  The default
18687           is currently off which implies divided syntax.  This option has no
18688           impact on Thumb2. However, this may change in future releases of
18689           GCC.  Divided syntax should be considered deprecated.
18690
18691       -mrestrict-it
18692           Restricts generation of IT blocks to conform to the rules of
18693           ARMv8-A.  IT blocks can only contain a single 16-bit instruction
18694           from a select set of instructions. This option is on by default for
18695           ARMv8-A Thumb mode.
18696
18697       -mprint-tune-info
18698           Print CPU tuning information as comment in assembler file.  This is
18699           an option used only for regression testing of the compiler and not
18700           intended for ordinary use in compiling code.  This option is
18701           disabled by default.
18702
18703       -mverbose-cost-dump
18704           Enable verbose cost model dumping in the debug dump files.  This
18705           option is provided for use in debugging the compiler.
18706
18707       -mpure-code
18708           Do not allow constant data to be placed in code sections.
18709           Additionally, when compiling for ELF object format give all text
18710           sections the ELF processor-specific section attribute
18711           "SHF_ARM_PURECODE".  This option is only available when generating
18712           non-pic code for M-profile targets.
18713
18714       -mcmse
18715           Generate secure code as per the "ARMv8-M Security Extensions:
18716           Requirements on Development Tools Engineering Specification", which
18717           can be found on
18718           <https://developer.arm.com/documentation/ecm0359818/latest/>.
18719
18720       -mfix-cmse-cve-2021-35465
18721           Mitigate against a potential security issue with the "VLLDM"
18722           instruction in some M-profile devices when using CMSE
18723           (CVE-2021-365465).  This option is enabled by default when the
18724           option -mcpu= is used with "cortex-m33", "cortex-m35p" or
18725           "cortex-m55".  The option -mno-fix-cmse-cve-2021-35465 can be used
18726           to disable the mitigation.
18727
18728       -mstack-protector-guard=guard
18729       -mstack-protector-guard-offset=offset
18730           Generate stack protection code using canary at guard.  Supported
18731           locations are global for a global canary or tls for a canary
18732           accessible via the TLS register. The option
18733           -mstack-protector-guard-offset= is for use with
18734           -fstack-protector-guard=tls and not for use in user-land code.
18735
18736       -mfdpic
18737       -mno-fdpic
18738           Select the FDPIC ABI, which uses 64-bit function descriptors to
18739           represent pointers to functions.  When the compiler is configured
18740           for "arm-*-uclinuxfdpiceabi" targets, this option is on by default
18741           and implies -fPIE if none of the PIC/PIE-related options is
18742           provided.  On other targets, it only enables the FDPIC-specific
18743           code generation features, and the user should explicitly provide
18744           the PIC/PIE-related options as needed.
18745
18746           Note that static linking is not supported because it would still
18747           involve the dynamic linker when the program self-relocates.  If
18748           such behavior is acceptable, use -static and -Wl,-dynamic-linker
18749           options.
18750
18751           The opposite -mno-fdpic option is useful (and required) to build
18752           the Linux kernel using the same ("arm-*-uclinuxfdpiceabi")
18753           toolchain as the one used to build the userland programs.
18754
18755       AVR Options
18756
18757       These options are defined for AVR implementations:
18758
18759       -mmcu=mcu
18760           Specify Atmel AVR instruction set architectures (ISA) or MCU type.
18761
18762           The default for this option is avr2.
18763
18764           GCC supports the following AVR devices and ISAs:
18765
18766           "avr2"
18767               "Classic" devices with up to 8 KiB of program memory.  mcu =
18768               "attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333",
18769               "at90s2343", "at90s4414", "at90s4433", "at90s4434",
18770               "at90c8534", "at90s8515", "at90s8535".
18771
18772           "avr25"
18773               "Classic" devices with up to 8 KiB of program memory and with
18774               the "MOVW" instruction.  mcu = "attiny13", "attiny13a",
18775               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
18776               "attiny2313", "attiny2313a", "attiny43u", "attiny44",
18777               "attiny44a", "attiny45", "attiny48", "attiny441", "attiny461",
18778               "attiny461a", "attiny4313", "attiny84", "attiny84a",
18779               "attiny85", "attiny87", "attiny88", "attiny828", "attiny841",
18780               "attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401".
18781
18782           "avr3"
18783               "Classic" devices with 16 KiB up to 64 KiB of program memory.
18784               mcu = "at76c711", "at43usb355".
18785
18786           "avr31"
18787               "Classic" devices with 128 KiB of program memory.  mcu =
18788               "atmega103", "at43usb320".
18789
18790           "avr35"
18791               "Classic" devices with 16 KiB up to 64 KiB of program memory
18792               and with the "MOVW" instruction.  mcu = "attiny167",
18793               "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2",
18794               "ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162".
18795
18796           "avr4"
18797               "Enhanced" devices with up to 8 KiB of program memory.  mcu =
18798               "atmega48", "atmega48a", "atmega48p", "atmega48pa",
18799               "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88",
18800               "atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
18801               "atmega8515", "atmega8535", "ata6285", "ata6286", "ata6289",
18802               "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3",
18803               "at90pwm3b", "at90pwm81".
18804
18805           "avr5"
18806               "Enhanced" devices with 16 KiB up to 64 KiB of program memory.
18807               mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
18808               "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
18809               "atmega161", "atmega162", "atmega163", "atmega164a",
18810               "atmega164p", "atmega164pa", "atmega165", "atmega165a",
18811               "atmega165p", "atmega165pa", "atmega168", "atmega168a",
18812               "atmega168p", "atmega168pa", "atmega168pb", "atmega169",
18813               "atmega169a", "atmega169p", "atmega169pa", "atmega32",
18814               "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
18815               "atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
18816               "atmega324a", "atmega324p", "atmega324pa", "atmega324pb",
18817               "atmega325", "atmega325a", "atmega325p", "atmega325pa",
18818               "atmega328", "atmega328p", "atmega328pb", "atmega329",
18819               "atmega329a", "atmega329p", "atmega329pa", "atmega3250",
18820               "atmega3250a", "atmega3250p", "atmega3250pa", "atmega3290",
18821               "atmega3290a", "atmega3290p", "atmega3290pa", "atmega406",
18822               "atmega64", "atmega64a", "atmega64c1", "atmega64hve",
18823               "atmega64hve2", "atmega64m1", "atmega64rfr2", "atmega640",
18824               "atmega644", "atmega644a", "atmega644p", "atmega644pa",
18825               "atmega644rfr2", "atmega645", "atmega645a", "atmega645p",
18826               "atmega649", "atmega649a", "atmega649p", "atmega6450",
18827               "atmega6450a", "atmega6450p", "atmega6490", "atmega6490a",
18828               "atmega6490p", "ata5795", "ata5790", "ata5790n", "ata5791",
18829               "ata6613c", "ata6614q", "ata5782", "ata5831", "ata8210",
18830               "ata8510", "ata5702m322", "at90pwm161", "at90pwm216",
18831               "at90pwm316", "at90can32", "at90can64", "at90scr100",
18832               "at90usb646", "at90usb647", "at94k", "m3000".
18833
18834           "avr51"
18835               "Enhanced" devices with 128 KiB of program memory.  mcu =
18836               "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2",
18837               "atmega1280", "atmega1281", "atmega1284", "atmega1284p",
18838               "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".
18839
18840           "avr6"
18841               "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
18842               of program memory.  mcu = "atmega256rfr2", "atmega2560",
18843               "atmega2561", "atmega2564rfr2".
18844
18845           "avrxmega2"
18846               "XMEGA" devices with more than 8 KiB and up to 64 KiB of
18847               program memory.  mcu = "atxmega8e5", "atxmega16a4",
18848               "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5",
18849               "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
18850               "atxmega32d3", "atxmega32d4", "atxmega32e5".
18851
18852           "avrxmega3"
18853               "XMEGA" devices with up to 64 KiB of combined program memory
18854               and RAM, and with program memory visible in the RAM address
18855               space.  mcu = "attiny202", "attiny204", "attiny212",
18856               "attiny214", "attiny402", "attiny404", "attiny406",
18857               "attiny412", "attiny414", "attiny416", "attiny417",
18858               "attiny804", "attiny806", "attiny807", "attiny814",
18859               "attiny816", "attiny817", "attiny1604", "attiny1606",
18860               "attiny1607", "attiny1614", "attiny1616", "attiny1617",
18861               "attiny3214", "attiny3216", "attiny3217", "atmega808",
18862               "atmega809", "atmega1608", "atmega1609", "atmega3208",
18863               "atmega3209", "atmega4808", "atmega4809".
18864
18865           "avrxmega4"
18866               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
18867               program memory.  mcu = "atxmega64a3", "atxmega64a3u",
18868               "atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3",
18869               "atxmega64d3", "atxmega64d4".
18870
18871           "avrxmega5"
18872               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
18873               program memory and more than 64 KiB of RAM.  mcu =
18874               "atxmega64a1", "atxmega64a1u".
18875
18876           "avrxmega6"
18877               "XMEGA" devices with more than 128 KiB of program memory.  mcu
18878               = "atxmega128a3", "atxmega128a3u", "atxmega128b1",
18879               "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
18880               "atxmega192a3", "atxmega192a3u", "atxmega192c3",
18881               "atxmega192d3", "atxmega256a3", "atxmega256a3b",
18882               "atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
18883               "atxmega256d3", "atxmega384c3", "atxmega384d3".
18884
18885           "avrxmega7"
18886               "XMEGA" devices with more than 128 KiB of program memory and
18887               more than 64 KiB of RAM.  mcu = "atxmega128a1",
18888               "atxmega128a1u", "atxmega128a4u".
18889
18890           "avrtiny"
18891               "TINY" Tiny core devices with 512 B up to 4 KiB of program
18892               memory.  mcu = "attiny4", "attiny5", "attiny9", "attiny10",
18893               "attiny20", "attiny40".
18894
18895           "avr1"
18896               This ISA is implemented by the minimal AVR core and supported
18897               for assembler only.  mcu = "attiny11", "attiny12", "attiny15",
18898               "attiny28", "at90s1200".
18899
18900       -mabsdata
18901           Assume that all data in static storage can be accessed by LDS / STS
18902           instructions.  This option has only an effect on reduced Tiny
18903           devices like ATtiny40.  See also the "absdata" AVR Variable
18904           Attributes,variable attribute.
18905
18906       -maccumulate-args
18907           Accumulate outgoing function arguments and acquire/release the
18908           needed stack space for outgoing function arguments once in function
18909           prologue/epilogue.  Without this option, outgoing arguments are
18910           pushed before calling a function and popped afterwards.
18911
18912           Popping the arguments after the function call can be expensive on
18913           AVR so that accumulating the stack space might lead to smaller
18914           executables because arguments need not be removed from the stack
18915           after such a function call.
18916
18917           This option can lead to reduced code size for functions that
18918           perform several calls to functions that get their arguments on the
18919           stack like calls to printf-like functions.
18920
18921       -mbranch-cost=cost
18922           Set the branch costs for conditional branch instructions to cost.
18923           Reasonable values for cost are small, non-negative integers. The
18924           default branch cost is 0.
18925
18926       -mcall-prologues
18927           Functions prologues/epilogues are expanded as calls to appropriate
18928           subroutines.  Code size is smaller.
18929
18930       -mdouble=bits
18931       -mlong-double=bits
18932           Set the size (in bits) of the "double" or "long double" type,
18933           respectively.  Possible values for bits are 32 and 64.  Whether or
18934           not a specific value for bits is allowed depends on the
18935           "--with-double=" and "--with-long-double=" configure options
18936           ("https://gcc.gnu.org/install/configure.html#avr"), and the same
18937           applies for the default values of the options.
18938
18939       -mgas-isr-prologues
18940           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo
18941           instruction supported by GNU Binutils.  If this option is on, the
18942           feature can still be disabled for individual ISRs by means of the
18943           AVR Function Attributes,,"no_gccisr" function attribute.  This
18944           feature is activated per default if optimization is on (but not
18945           with -Og, @pxref{Optimize Options}), and if GNU Binutils support
18946           PR21683 ("https://sourceware.org/PR21683").
18947
18948       -mint8
18949           Assume "int" to be 8-bit integer.  This affects the sizes of all
18950           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
18951           and "long long" is 4 bytes.  Please note that this option does not
18952           conform to the C standards, but it results in smaller code size.
18953
18954       -mmain-is-OS_task
18955           Do not save registers in "main".  The effect is the same like
18956           attaching attribute AVR Function Attributes,,"OS_task" to "main".
18957           It is activated per default if optimization is on.
18958
18959       -mn-flash=num
18960           Assume that the flash memory has a size of num times 64 KiB.
18961
18962       -mno-interrupts
18963           Generated code is not compatible with hardware interrupts.  Code
18964           size is smaller.
18965
18966       -mrelax
18967           Try to replace "CALL" resp. "JMP" instruction by the shorter
18968           "RCALL" resp. "RJMP" instruction if applicable.  Setting -mrelax
18969           just adds the --mlink-relax option to the assembler's command line
18970           and the --relax option to the linker's command line.
18971
18972           Jump relaxing is performed by the linker because jump offsets are
18973           not known before code is located. Therefore, the assembler code
18974           generated by the compiler is the same, but the instructions in the
18975           executable may differ from instructions in the assembler code.
18976
18977           Relaxing must be turned on if linker stubs are needed, see the
18978           section on "EIND" and linker stubs below.
18979
18980       -mrmw
18981           Assume that the device supports the Read-Modify-Write instructions
18982           "XCH", "LAC", "LAS" and "LAT".
18983
18984       -mshort-calls
18985           Assume that "RJMP" and "RCALL" can target the whole program memory.
18986
18987           This option is used internally for multilib selection.  It is not
18988           an optimization option, and you don't need to set it by hand.
18989
18990       -msp8
18991           Treat the stack pointer register as an 8-bit register, i.e. assume
18992           the high byte of the stack pointer is zero.  In general, you don't
18993           need to set this option by hand.
18994
18995           This option is used internally by the compiler to select and build
18996           multilibs for architectures "avr2" and "avr25".  These
18997           architectures mix devices with and without "SPH".  For any setting
18998           other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or
18999           removes this option from the compiler proper's command line,
19000           because the compiler then knows if the device or architecture has
19001           an 8-bit stack pointer and thus no "SPH" register or not.
19002
19003       -mstrict-X
19004           Use address register "X" in a way proposed by the hardware.  This
19005           means that "X" is only used in indirect, post-increment or pre-
19006           decrement addressing.
19007
19008           Without this option, the "X" register may be used in the same way
19009           as "Y" or "Z" which then is emulated by additional instructions.
19010           For example, loading a value with "X+const" addressing with a small
19011           non-negative "const < 64" to a register Rn is performed as
19012
19013                   adiw r26, const   ; X += const
19014                   ld   <Rn>, X        ; <Rn> = *X
19015                   sbiw r26, const   ; X -= const
19016
19017       -mtiny-stack
19018           Only change the lower 8 bits of the stack pointer.
19019
19020       -mfract-convert-truncate
19021           Allow to use truncation instead of rounding towards zero for
19022           fractional fixed-point types.
19023
19024       -nodevicelib
19025           Don't link against AVR-LibC's device specific library "lib<mcu>.a".
19026
19027       -nodevicespecs
19028           Don't add -specs=device-specs/specs-mcu to the compiler driver's
19029           command line.  The user takes responsibility for supplying the sub-
19030           processes like compiler proper, assembler and linker with
19031           appropriate command line options.  This means that the user has to
19032           supply her private device specs file by means of -specs=path-to-
19033           specs-file.  There is no more need for option -mmcu=mcu.
19034
19035           This option can also serve as a replacement for the older way of
19036           specifying custom device-specs files that needed -B some-path to
19037           point to a directory which contains a folder named "device-specs"
19038           which contains a specs file named "specs-mcu", where mcu was
19039           specified by -mmcu=mcu.
19040
19041       -Waddr-space-convert
19042           Warn about conversions between address spaces in the case where the
19043           resulting address space is not contained in the incoming address
19044           space.
19045
19046       -Wmisspelled-isr
19047           Warn if the ISR is misspelled, i.e. without __vector prefix.
19048           Enabled by default.
19049
19050       "EIND" and Devices with More Than 128 Ki Bytes of Flash
19051
19052       Pointers in the implementation are 16 bits wide.  The address of a
19053       function or label is represented as word address so that indirect jumps
19054       and calls can target any code address in the range of 64 Ki words.
19055
19056       In order to facilitate indirect jump on devices with more than 128 Ki
19057       bytes of program memory space, there is a special function register
19058       called "EIND" that serves as most significant part of the target
19059       address when "EICALL" or "EIJMP" instructions are used.
19060
19061       Indirect jumps and calls on these devices are handled as follows by the
19062       compiler and are subject to some limitations:
19063
19064       *   The compiler never sets "EIND".
19065
19066       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
19067           instructions or might read "EIND" directly in order to emulate an
19068           indirect call/jump by means of a "RET" instruction.
19069
19070       *   The compiler assumes that "EIND" never changes during the startup
19071           code or during the application. In particular, "EIND" is not
19072           saved/restored in function or interrupt service routine
19073           prologue/epilogue.
19074
19075       *   For indirect calls to functions and computed goto, the linker
19076           generates stubs. Stubs are jump pads sometimes also called
19077           trampolines. Thus, the indirect call/jump jumps to such a stub.
19078           The stub contains a direct jump to the desired address.
19079
19080       *   Linker relaxation must be turned on so that the linker generates
19081           the stubs correctly in all situations. See the compiler option
19082           -mrelax and the linker option --relax.  There are corner cases
19083           where the linker is supposed to generate stubs but aborts without
19084           relaxation and without a helpful error message.
19085
19086       *   The default linker script is arranged for code with "EIND = 0".  If
19087           code is supposed to work for a setup with "EIND != 0", a custom
19088           linker script has to be used in order to place the sections whose
19089           name start with ".trampolines" into the segment where "EIND" points
19090           to.
19091
19092       *   The startup code from libgcc never sets "EIND".  Notice that
19093           startup code is a blend of code from libgcc and AVR-LibC.  For the
19094           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
19095           ("http://nongnu.org/avr-libc/user-manual/").
19096
19097       *   It is legitimate for user-specific startup code to set up "EIND"
19098           early, for example by means of initialization code located in
19099           section ".init3". Such code runs prior to general startup code that
19100           initializes RAM and calls constructors, but after the bit of
19101           startup code from AVR-LibC that sets "EIND" to the segment where
19102           the vector table is located.
19103
19104                   #include <avr/io.h>
19105
19106                   static void
19107                   __attribute__((section(".init3"),naked,used,no_instrument_function))
19108                   init3_set_eind (void)
19109                   {
19110                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
19111                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
19112                   }
19113
19114           The "__trampolines_start" symbol is defined in the linker script.
19115
19116       *   Stubs are generated automatically by the linker if the following
19117           two conditions are met:
19118
19119           -<The address of a label is taken by means of the "gs" modifier>
19120               (short for generate stubs) like so:
19121
19122                       LDI r24, lo8(gs(<func>))
19123                       LDI r25, hi8(gs(<func>))
19124
19125           -<The final location of that label is in a code segment>
19126               outside the segment where the stubs are located.
19127
19128       *   The compiler emits such "gs" modifiers for code labels in the
19129           following situations:
19130
19131           -<Taking address of a function or code label.>
19132           -<Computed goto.>
19133           -<If prologue-save function is used, see -mcall-prologues>
19134               command-line option.
19135
19136           -<Switch/case dispatch tables. If you do not want such dispatch>
19137               tables you can specify the -fno-jump-tables command-line
19138               option.
19139
19140           -<C and C++ constructors/destructors called during
19141           startup/shutdown.>
19142           -<If the tools hit a "gs()" modifier explained above.>
19143       *   Jumping to non-symbolic addresses like so is not supported:
19144
19145                   int main (void)
19146                   {
19147                       /* Call function at word address 0x2 */
19148                       return ((int(*)(void)) 0x2)();
19149                   }
19150
19151           Instead, a stub has to be set up, i.e. the function has to be
19152           called through a symbol ("func_4" in the example):
19153
19154                   int main (void)
19155                   {
19156                       extern int func_4 (void);
19157
19158                       /* Call function at byte address 0x4 */
19159                       return func_4();
19160                   }
19161
19162           and the application be linked with -Wl,--defsym,func_4=0x4.
19163           Alternatively, "func_4" can be defined in the linker script.
19164
19165       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
19166       Registers
19167
19168       Some AVR devices support memories larger than the 64 KiB range that can
19169       be accessed with 16-bit pointers.  To access memory locations outside
19170       this 64 KiB range, the content of a "RAMP" register is used as high
19171       part of the address: The "X", "Y", "Z" address register is concatenated
19172       with the "RAMPX", "RAMPY", "RAMPZ" special function register,
19173       respectively, to get a wide address. Similarly, "RAMPD" is used
19174       together with direct addressing.
19175
19176       *   The startup code initializes the "RAMP" special function registers
19177           with zero.
19178
19179       *   If a AVR Named Address Spaces,named address space other than
19180           generic or "__flash" is used, then "RAMPZ" is set as needed before
19181           the operation.
19182
19183       *   If the device supports RAM larger than 64 KiB and the compiler
19184           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
19185           reset to zero after the operation.
19186
19187       *   If the device comes with a specific "RAMP" register, the ISR
19188           prologue/epilogue saves/restores that SFR and initializes it with
19189           zero in case the ISR code might (implicitly) use it.
19190
19191       *   RAM larger than 64 KiB is not supported by GCC for AVR targets.  If
19192           you use inline assembler to read from locations outside the 16-bit
19193           address range and change one of the "RAMP" registers, you must
19194           reset it to zero after the access.
19195
19196       AVR Built-in Macros
19197
19198       GCC defines several built-in macros so that the user code can test for
19199       the presence or absence of features.  Almost any of the following
19200       built-in macros are deduced from device capabilities and thus triggered
19201       by the -mmcu= command-line option.
19202
19203       For even more AVR-specific built-in macros see AVR Named Address Spaces
19204       and AVR Built-in Functions.
19205
19206       "__AVR_ARCH__"
19207           Build-in macro that resolves to a decimal number that identifies
19208           the architecture and depends on the -mmcu=mcu option.  Possible
19209           values are:
19210
19211           2, 25, 3, 31, 35, 4, 5, 51, 6
19212
19213           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
19214           "avr51", "avr6",
19215
19216           respectively and
19217
19218           100, 102, 103, 104, 105, 106, 107
19219
19220           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
19221           "avrxmega5", "avrxmega6", "avrxmega7", respectively.  If mcu
19222           specifies a device, this built-in macro is set accordingly. For
19223           example, with -mmcu=atmega8 the macro is defined to 4.
19224
19225       "__AVR_Device__"
19226           Setting -mmcu=device defines this built-in macro which reflects the
19227           device's name. For example, -mmcu=atmega8 defines the built-in
19228           macro "__AVR_ATmega8__", -mmcu=attiny261a defines
19229           "__AVR_ATtiny261A__", etc.
19230
19231           The built-in macros' names follow the scheme "__AVR_Device__" where
19232           Device is the device name as from the AVR user manual. The
19233           difference between Device in the built-in macro and device in
19234           -mmcu=device is that the latter is always lowercase.
19235
19236           If device is not a device but only a core architecture like avr51,
19237           this macro is not defined.
19238
19239       "__AVR_DEVICE_NAME__"
19240           Setting -mmcu=device defines this built-in macro to the device's
19241           name. For example, with -mmcu=atmega8 the macro is defined to
19242           "atmega8".
19243
19244           If device is not a device but only a core architecture like avr51,
19245           this macro is not defined.
19246
19247       "__AVR_XMEGA__"
19248           The device / architecture belongs to the XMEGA family of devices.
19249
19250       "__AVR_HAVE_ELPM__"
19251           The device has the "ELPM" instruction.
19252
19253       "__AVR_HAVE_ELPMX__"
19254           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.
19255
19256       "__AVR_HAVE_MOVW__"
19257           The device has the "MOVW" instruction to perform 16-bit register-
19258           register moves.
19259
19260       "__AVR_HAVE_LPMX__"
19261           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.
19262
19263       "__AVR_HAVE_MUL__"
19264           The device has a hardware multiplier.
19265
19266       "__AVR_HAVE_JMP_CALL__"
19267           The device has the "JMP" and "CALL" instructions.  This is the case
19268           for devices with more than 8 KiB of program memory.
19269
19270       "__AVR_HAVE_EIJMP_EICALL__"
19271       "__AVR_3_BYTE_PC__"
19272           The device has the "EIJMP" and "EICALL" instructions.  This is the
19273           case for devices with more than 128 KiB of program memory.  This
19274           also means that the program counter (PC) is 3 bytes wide.
19275
19276       "__AVR_2_BYTE_PC__"
19277           The program counter (PC) is 2 bytes wide. This is the case for
19278           devices with up to 128 KiB of program memory.
19279
19280       "__AVR_HAVE_8BIT_SP__"
19281       "__AVR_HAVE_16BIT_SP__"
19282           The stack pointer (SP) register is treated as 8-bit respectively
19283           16-bit register by the compiler.  The definition of these macros is
19284           affected by -mtiny-stack.
19285
19286       "__AVR_HAVE_SPH__"
19287       "__AVR_SP8__"
19288           The device has the SPH (high part of stack pointer) special
19289           function register or has an 8-bit stack pointer, respectively.  The
19290           definition of these macros is affected by -mmcu= and in the cases
19291           of -mmcu=avr2 and -mmcu=avr25 also by -msp8.
19292
19293       "__AVR_HAVE_RAMPD__"
19294       "__AVR_HAVE_RAMPX__"
19295       "__AVR_HAVE_RAMPY__"
19296       "__AVR_HAVE_RAMPZ__"
19297           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
19298           function register, respectively.
19299
19300       "__NO_INTERRUPTS__"
19301           This macro reflects the -mno-interrupts command-line option.
19302
19303       "__AVR_ERRATA_SKIP__"
19304       "__AVR_ERRATA_SKIP_JMP_CALL__"
19305           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
19306           instructions because of a hardware erratum.  Skip instructions are
19307           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
19308           only defined if "__AVR_HAVE_JMP_CALL__" is also set.
19309
19310       "__AVR_ISA_RMW__"
19311           The device has Read-Modify-Write instructions (XCH, LAC, LAS and
19312           LAT).
19313
19314       "__AVR_SFR_OFFSET__=offset"
19315           Instructions that can address I/O special function registers
19316           directly like "IN", "OUT", "SBI", etc. may use a different address
19317           as if addressed by an instruction to access RAM like "LD" or "STS".
19318           This offset depends on the device architecture and has to be
19319           subtracted from the RAM address in order to get the respective I/O
19320           address.
19321
19322       "__AVR_SHORT_CALLS__"
19323           The -mshort-calls command line option is set.
19324
19325       "__AVR_PM_BASE_ADDRESS__=addr"
19326           Some devices support reading from flash memory by means of "LD*"
19327           instructions.  The flash memory is seen in the data address space
19328           at an offset of "__AVR_PM_BASE_ADDRESS__".  If this macro is not
19329           defined, this feature is not available.  If defined, the address
19330           space is linear and there is no need to put ".rodata" into RAM.
19331           This is handled by the default linker description file, and is
19332           currently available for "avrtiny" and "avrxmega3".  Even more
19333           convenient, there is no need to use address spaces like "__flash"
19334           or features like attribute "progmem" and "pgm_read_*".
19335
19336       "__WITH_AVRLIBC__"
19337           The compiler is configured to be used together with AVR-Libc.  See
19338           the --with-avrlibc configure option.
19339
19340       "__HAVE_DOUBLE_MULTILIB__"
19341           Defined if -mdouble= acts as a multilib option.
19342
19343       "__HAVE_DOUBLE32__"
19344       "__HAVE_DOUBLE64__"
19345           Defined if the compiler supports 32-bit double resp. 64-bit double.
19346           The actual layout is specified by option -mdouble=.
19347
19348       "__DEFAULT_DOUBLE__"
19349           The size in bits of "double" if -mdouble= is not set.  To test the
19350           layout of "double" in a program, use the built-in macro
19351           "__SIZEOF_DOUBLE__".
19352
19353       "__HAVE_LONG_DOUBLE32__"
19354       "__HAVE_LONG_DOUBLE64__"
19355       "__HAVE_LONG_DOUBLE_MULTILIB__"
19356       "__DEFAULT_LONG_DOUBLE__"
19357           Same as above, but for "long double" instead of "double".
19358
19359       "__WITH_DOUBLE_COMPARISON__"
19360           Reflects the "--with-double-comparison={tristate|bool|libf7}"
19361           configure option ("https://gcc.gnu.org/install/configure.html#avr")
19362           and is defined to 2 or 3.
19363
19364       "__WITH_LIBF7_LIBGCC__"
19365       "__WITH_LIBF7_MATH__"
19366       "__WITH_LIBF7_MATH_SYMBOLS__"
19367           Reflects the "--with-libf7={libgcc|math|math-symbols}"
19368           configure option
19369           ("https://gcc.gnu.org/install/configure.html#avr").
19370
19371       Blackfin Options
19372
19373       -mcpu=cpu[-sirevision]
19374           Specifies the name of the target Blackfin processor.  Currently,
19375           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
19376           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
19377           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
19378           bf547m, bf548m, bf549m, bf561, bf592.
19379
19380           The optional sirevision specifies the silicon revision of the
19381           target Blackfin processor.  Any workarounds available for the
19382           targeted silicon revision are enabled.  If sirevision is none, no
19383           workarounds are enabled.  If sirevision is any, all workarounds for
19384           the targeted processor are enabled.  The "__SILICON_REVISION__"
19385           macro is defined to two hexadecimal digits representing the major
19386           and minor numbers in the silicon revision.  If sirevision is none,
19387           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
19388           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
19389           optional sirevision is not used, GCC assumes the latest known
19390           silicon revision of the targeted Blackfin processor.
19391
19392           GCC defines a preprocessor macro for the specified cpu.  For the
19393           bfin-elf toolchain, this option causes the hardware BSP provided by
19394           libgloss to be linked in if -msim is not given.
19395
19396           Without this option, bf532 is used as the processor by default.
19397
19398           Note that support for bf561 is incomplete.  For bf561, only the
19399           preprocessor macro is defined.
19400
19401       -msim
19402           Specifies that the program will be run on the simulator.  This
19403           causes the simulator BSP provided by libgloss to be linked in.
19404           This option has effect only for bfin-elf toolchain.  Certain other
19405           options, such as -mid-shared-library and -mfdpic, imply -msim.
19406
19407       -momit-leaf-frame-pointer
19408           Don't keep the frame pointer in a register for leaf functions.
19409           This avoids the instructions to save, set up and restore frame
19410           pointers and makes an extra register available in leaf functions.
19411
19412       -mspecld-anomaly
19413           When enabled, the compiler ensures that the generated code does not
19414           contain speculative loads after jump instructions. If this option
19415           is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.
19416
19417       -mno-specld-anomaly
19418           Don't generate extra code to prevent speculative loads from
19419           occurring.
19420
19421       -mcsync-anomaly
19422           When enabled, the compiler ensures that the generated code does not
19423           contain CSYNC or SSYNC instructions too soon after conditional
19424           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
19425           is defined.
19426
19427       -mno-csync-anomaly
19428           Don't generate extra code to prevent CSYNC or SSYNC instructions
19429           from occurring too soon after a conditional branch.
19430
19431       -mlow64k
19432           When enabled, the compiler is free to take advantage of the
19433           knowledge that the entire program fits into the low 64k of memory.
19434
19435       -mno-low64k
19436           Assume that the program is arbitrarily large.  This is the default.
19437
19438       -mstack-check-l1
19439           Do stack checking using information placed into L1 scratchpad
19440           memory by the uClinux kernel.
19441
19442       -mid-shared-library
19443           Generate code that supports shared libraries via the library ID
19444           method.  This allows for execute in place and shared libraries in
19445           an environment without virtual memory management.  This option
19446           implies -fPIC.  With a bfin-elf target, this option implies -msim.
19447
19448       -mno-id-shared-library
19449           Generate code that doesn't assume ID-based shared libraries are
19450           being used.  This is the default.
19451
19452       -mleaf-id-shared-library
19453           Generate code that supports shared libraries via the library ID
19454           method, but assumes that this library or executable won't link
19455           against any other ID shared libraries.  That allows the compiler to
19456           use faster code for jumps and calls.
19457
19458       -mno-leaf-id-shared-library
19459           Do not assume that the code being compiled won't link against any
19460           ID shared libraries.  Slower code is generated for jump and call
19461           insns.
19462
19463       -mshared-library-id=n
19464           Specifies the identification number of the ID-based shared library
19465           being compiled.  Specifying a value of 0 generates more compact
19466           code; specifying other values forces the allocation of that number
19467           to the current library but is no more space- or time-efficient than
19468           omitting this option.
19469
19470       -msep-data
19471           Generate code that allows the data segment to be located in a
19472           different area of memory from the text segment.  This allows for
19473           execute in place in an environment without virtual memory
19474           management by eliminating relocations against the text section.
19475
19476       -mno-sep-data
19477           Generate code that assumes that the data segment follows the text
19478           segment.  This is the default.
19479
19480       -mlong-calls
19481       -mno-long-calls
19482           Tells the compiler to perform function calls by first loading the
19483           address of the function into a register and then performing a
19484           subroutine call on this register.  This switch is needed if the
19485           target function lies outside of the 24-bit addressing range of the
19486           offset-based version of subroutine call instruction.
19487
19488           This feature is not enabled by default.  Specifying -mno-long-calls
19489           restores the default behavior.  Note these switches have no effect
19490           on how the compiler generates code to handle function calls via
19491           function pointers.
19492
19493       -mfast-fp
19494           Link with the fast floating-point library. This library relaxes
19495           some of the IEEE floating-point standard's rules for checking
19496           inputs against Not-a-Number (NAN), in the interest of performance.
19497
19498       -minline-plt
19499           Enable inlining of PLT entries in function calls to functions that
19500           are not known to bind locally.  It has no effect without -mfdpic.
19501
19502       -mmulticore
19503           Build a standalone application for multicore Blackfin processors.
19504           This option causes proper start files and link scripts supporting
19505           multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
19506           can only be used with -mcpu=bf561[-sirevision].
19507
19508           This option can be used with -mcorea or -mcoreb, which selects the
19509           one-application-per-core programming model.  Without -mcorea or
19510           -mcoreb, the single-application/dual-core programming model is
19511           used. In this model, the main function of Core B should be named as
19512           "coreb_main".
19513
19514           If this option is not used, the single-core application programming
19515           model is used.
19516
19517       -mcorea
19518           Build a standalone application for Core A of BF561 when using the
19519           one-application-per-core programming model. Proper start files and
19520           link scripts are used to support Core A, and the macro
19521           "__BFIN_COREA" is defined.  This option can only be used in
19522           conjunction with -mmulticore.
19523
19524       -mcoreb
19525           Build a standalone application for Core B of BF561 when using the
19526           one-application-per-core programming model. Proper start files and
19527           link scripts are used to support Core B, and the macro
19528           "__BFIN_COREB" is defined. When this option is used, "coreb_main"
19529           should be used instead of "main".  This option can only be used in
19530           conjunction with -mmulticore.
19531
19532       -msdram
19533           Build a standalone application for SDRAM. Proper start files and
19534           link scripts are used to put the application into SDRAM, and the
19535           macro "__BFIN_SDRAM" is defined.  The loader should initialize
19536           SDRAM before loading the application.
19537
19538       -micplb
19539           Assume that ICPLBs are enabled at run time.  This has an effect on
19540           certain anomaly workarounds.  For Linux targets, the default is to
19541           assume ICPLBs are enabled; for standalone applications the default
19542           is off.
19543
19544       C6X Options
19545
19546       -march=name
19547           This specifies the name of the target architecture.  GCC uses this
19548           name to determine what kind of instructions it can emit when
19549           generating assembly code.  Permissible names are: c62x, c64x,
19550           c64x+, c67x, c67x+, c674x.
19551
19552       -mbig-endian
19553           Generate code for a big-endian target.
19554
19555       -mlittle-endian
19556           Generate code for a little-endian target.  This is the default.
19557
19558       -msim
19559           Choose startup files and linker script suitable for the simulator.
19560
19561       -msdata=default
19562           Put small global and static data in the ".neardata" section, which
19563           is pointed to by register "B14".  Put small uninitialized global
19564           and static data in the ".bss" section, which is adjacent to the
19565           ".neardata" section.  Put small read-only data into the ".rodata"
19566           section.  The corresponding sections used for large pieces of data
19567           are ".fardata", ".far" and ".const".
19568
19569       -msdata=all
19570           Put all data, not just small objects, into the sections reserved
19571           for small data, and use addressing relative to the "B14" register
19572           to access them.
19573
19574       -msdata=none
19575           Make no use of the sections reserved for small data, and use
19576           absolute addresses to access all data.  Put all initialized global
19577           and static data in the ".fardata" section, and all uninitialized
19578           data in the ".far" section.  Put all constant data into the
19579           ".const" section.
19580
19581       CRIS Options
19582
19583       These options are defined specifically for the CRIS ports.
19584
19585       -march=architecture-type
19586       -mcpu=architecture-type
19587           Generate code for the specified architecture.  The choices for
19588           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
19589           ETRAX 100, and ETRAX 100 LX.  Default is v0.
19590
19591       -mtune=architecture-type
19592           Tune to architecture-type everything applicable about the generated
19593           code, except for the ABI and the set of available instructions.
19594           The choices for architecture-type are the same as for
19595           -march=architecture-type.
19596
19597       -mmax-stack-frame=n
19598           Warn when the stack frame of a function exceeds n bytes.
19599
19600       -metrax4
19601       -metrax100
19602           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
19603           -march=v8 respectively.
19604
19605       -mmul-bug-workaround
19606       -mno-mul-bug-workaround
19607           Work around a bug in the "muls" and "mulu" instructions for CPU
19608           models where it applies.  This option is disabled by default.
19609
19610       -mpdebug
19611           Enable CRIS-specific verbose debug-related information in the
19612           assembly code.  This option also has the effect of turning off the
19613           #NO_APP formatted-code indicator to the assembler at the beginning
19614           of the assembly file.
19615
19616       -mcc-init
19617           Do not use condition-code results from previous instruction; always
19618           emit compare and test instructions before use of condition codes.
19619
19620       -mno-side-effects
19621           Do not emit instructions with side effects in addressing modes
19622           other than post-increment.
19623
19624       -mstack-align
19625       -mno-stack-align
19626       -mdata-align
19627       -mno-data-align
19628       -mconst-align
19629       -mno-const-align
19630           These options (no- options) arrange (eliminate arrangements) for
19631           the stack frame, individual data and constants to be aligned for
19632           the maximum single data access size for the chosen CPU model.  The
19633           default is to arrange for 32-bit alignment.  ABI details such as
19634           structure layout are not affected by these options.
19635
19636       -m32-bit
19637       -m16-bit
19638       -m8-bit
19639           Similar to the stack- data- and const-align options above, these
19640           options arrange for stack frame, writable data and constants to all
19641           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
19642           alignment.
19643
19644       -mno-prologue-epilogue
19645       -mprologue-epilogue
19646           With -mno-prologue-epilogue, the normal function prologue and
19647           epilogue which set up the stack frame are omitted and no return
19648           instructions or return sequences are generated in the code.  Use
19649           this option only together with visual inspection of the compiled
19650           code: no warnings or errors are generated when call-saved registers
19651           must be saved, or storage for local variables needs to be
19652           allocated.
19653
19654       -melf
19655           Legacy no-op option.
19656
19657       -sim
19658           This option arranges to link with input-output functions from a
19659           simulator library.  Code, initialized data and zero-initialized
19660           data are allocated consecutively.
19661
19662       -sim2
19663           Like -sim, but pass linker options to locate initialized data at
19664           0x40000000 and zero-initialized data at 0x80000000.
19665
19666       CR16 Options
19667
19668       These options are defined specifically for the CR16 ports.
19669
19670       -mmac
19671           Enable the use of multiply-accumulate instructions. Disabled by
19672           default.
19673
19674       -mcr16cplus
19675       -mcr16c
19676           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
19677           is default.
19678
19679       -msim
19680           Links the library libsim.a which is in compatible with simulator.
19681           Applicable to ELF compiler only.
19682
19683       -mint32
19684           Choose integer type as 32-bit wide.
19685
19686       -mbit-ops
19687           Generates "sbit"/"cbit" instructions for bit manipulations.
19688
19689       -mdata-model=model
19690           Choose a data model. The choices for model are near, far or medium.
19691           medium is default.  However, far is not valid with -mcr16c, as the
19692           CR16C architecture does not support the far data model.
19693
19694       C-SKY Options
19695
19696       GCC supports these options when compiling for C-SKY V2 processors.
19697
19698       -march=arch
19699           Specify the C-SKY target architecture.  Valid values for arch are:
19700           ck801, ck802, ck803, ck807, and ck810.  The default is ck810.
19701
19702       -mcpu=cpu
19703           Specify the C-SKY target processor.  Valid values for cpu are:
19704           ck801, ck801t, ck802, ck802t, ck802j, ck803, ck803h, ck803t,
19705           ck803ht, ck803f, ck803fh, ck803e, ck803eh, ck803et, ck803eht,
19706           ck803ef, ck803efh, ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1,
19707           ck803tr1, ck803htr1, ck803fr1, ck803fhr1, ck803er1, ck803ehr1,
19708           ck803etr1, ck803ehtr1, ck803efr1, ck803efhr1, ck803ftr1,
19709           ck803eftr1, ck803efhtr1, ck803s, ck803st, ck803se, ck803sf,
19710           ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f, ck810e,
19711           ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t, ck810fv,
19712           ck810tv, ck810ft, and ck810ftv.
19713
19714       -mbig-endian
19715       -EB
19716       -mlittle-endian
19717       -EL Select big- or little-endian code.  The default is little-endian.
19718
19719       -mfloat-abi=name
19720           Specifies which floating-point ABI to use.  Permissible values are:
19721           soft, softfp and hard.
19722
19723           Specifying soft causes GCC to generate output containing library
19724           calls for floating-point operations.  softfp allows the generation
19725           of code using hardware floating-point instructions, but still uses
19726           the soft-float calling conventions.  hard allows generation of
19727           floating-point instructions and uses FPU-specific calling
19728           conventions.
19729
19730           The default depends on the specific target configuration.  Note
19731           that the hard-float and soft-float ABIs are not link-compatible;
19732           you must compile your entire program with the same ABI, and link
19733           with a compatible set of libraries.
19734
19735       -mhard-float
19736       -msoft-float
19737           Select hardware or software floating-point implementations.  The
19738           default is soft float.
19739
19740       -mdouble-float
19741       -mno-double-float
19742           When -mhard-float is in effect, enable generation of double-
19743           precision float instructions.  This is the default except when
19744           compiling for CK803.
19745
19746       -mfdivdu
19747       -mno-fdivdu
19748           When -mhard-float is in effect, enable generation of "frecipd",
19749           "fsqrtd", and "fdivd" instructions.  This is the default except
19750           when compiling for CK803.
19751
19752       -mfpu=fpu
19753           Select the floating-point processor.  This option can only be used
19754           with -mhard-float.  Values for fpu are fpv2_sf (equivalent to
19755           -mno-double-float -mno-fdivdu), fpv2 (-mdouble-float -mno-divdu),
19756           and fpv2_divd (-mdouble-float -mdivdu).
19757
19758       -melrw
19759       -mno-elrw
19760           Enable the extended "lrw" instruction.  This option defaults to on
19761           for CK801 and off otherwise.
19762
19763       -mistack
19764       -mno-istack
19765           Enable interrupt stack instructions; the default is off.
19766
19767           The -mistack option is required to handle the "interrupt" and "isr"
19768           function attributes.
19769
19770       -mmp
19771           Enable multiprocessor instructions; the default is off.
19772
19773       -mcp
19774           Enable coprocessor instructions; the default is off.
19775
19776       -mcache
19777           Enable coprocessor instructions; the default is off.
19778
19779       -msecurity
19780           Enable C-SKY security instructions; the default is off.
19781
19782       -mtrust
19783           Enable C-SKY trust instructions; the default is off.
19784
19785       -mdsp
19786       -medsp
19787       -mvdsp
19788           Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions,
19789           respectively.  All of these options default to off.
19790
19791       -mdiv
19792       -mno-div
19793           Generate divide instructions.  Default is off.
19794
19795       -msmart
19796       -mno-smart
19797           Generate code for Smart Mode, using only registers numbered 0-7 to
19798           allow use of 16-bit instructions.  This option is ignored for CK801
19799           where this is the required behavior, and it defaults to on for
19800           CK802.  For other targets, the default is off.
19801
19802       -mhigh-registers
19803       -mno-high-registers
19804           Generate code using the high registers numbered 16-31.  This option
19805           is not supported on CK801, CK802, or CK803, and is enabled by
19806           default for other processors.
19807
19808       -manchor
19809       -mno-anchor
19810           Generate code using global anchor symbol addresses.
19811
19812       -mpushpop
19813       -mno-pushpop
19814           Generate code using "push" and "pop" instructions.  This option
19815           defaults to on.
19816
19817       -mmultiple-stld
19818       -mstm
19819       -mno-multiple-stld
19820       -mno-stm
19821           Generate code using "stm" and "ldm" instructions.  This option
19822           isn't supported on CK801 but is enabled by default on other
19823           processors.
19824
19825       -mconstpool
19826       -mno-constpool
19827           Create constant pools in the compiler instead of deferring it to
19828           the assembler.  This option is the default and required for correct
19829           code generation on CK801 and CK802, and is optional on other
19830           processors.
19831
19832       -mstack-size
19833       -mno-stack-size
19834           Emit ".stack_size" directives for each function in the assembly
19835           output.  This option defaults to off.
19836
19837       -mccrt
19838       -mno-ccrt
19839           Generate code for the C-SKY compiler runtime instead of libgcc.
19840           This option defaults to off.
19841
19842       -mbranch-cost=n
19843           Set the branch costs to roughly "n" instructions.  The default is
19844           1.
19845
19846       -msched-prolog
19847       -mno-sched-prolog
19848           Permit scheduling of function prologue and epilogue sequences.
19849           Using this option can result in code that is not compliant with the
19850           C-SKY V2 ABI prologue requirements and that cannot be debugged or
19851           backtraced.  It is disabled by default.
19852
19853       -msim
19854           Links the library libsemi.a which is in compatible with simulator.
19855           Applicable to ELF compiler only.
19856
19857       Darwin Options
19858
19859       These options are defined for all architectures running the Darwin
19860       operating system.
19861
19862       FSF GCC on Darwin does not create "fat" object files; it creates an
19863       object file for the single architecture that GCC was built to target.
19864       Apple's GCC on Darwin does create "fat" files if multiple -arch options
19865       are used; it does so by running the compiler or linker multiple times
19866       and joining the results together with lipo.
19867
19868       The subtype of the file created (like ppc7400 or ppc970 or i686) is
19869       determined by the flags that specify the ISA that GCC is targeting,
19870       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
19871       override this.
19872
19873       The Darwin tools vary in their behavior when presented with an ISA
19874       mismatch.  The assembler, as, only permits instructions to be used that
19875       are valid for the subtype of the file it is generating, so you cannot
19876       put 64-bit instructions in a ppc750 object file.  The linker for shared
19877       libraries, /usr/bin/libtool, fails and prints an error if asked to
19878       create a shared library with a less restrictive subtype than its input
19879       files (for instance, trying to put a ppc970 object file in a ppc7400
19880       library).  The linker for executables, ld, quietly gives the executable
19881       the most restrictive subtype of any of its input files.
19882
19883       -Fdir
19884           Add the framework directory dir to the head of the list of
19885           directories to be searched for header files.  These directories are
19886           interleaved with those specified by -I options and are scanned in a
19887           left-to-right order.
19888
19889           A framework directory is a directory with frameworks in it.  A
19890           framework is a directory with a Headers and/or PrivateHeaders
19891           directory contained directly in it that ends in .framework.  The
19892           name of a framework is the name of this directory excluding the
19893           .framework.  Headers associated with the framework are found in one
19894           of those two directories, with Headers being searched first.  A
19895           subframework is a framework directory that is in a framework's
19896           Frameworks directory.  Includes of subframework headers can only
19897           appear in a header of a framework that contains the subframework,
19898           or in a sibling subframework header.  Two subframeworks are
19899           siblings if they occur in the same framework.  A subframework
19900           should not have the same name as a framework; a warning is issued
19901           if this is violated.  Currently a subframework cannot have
19902           subframeworks; in the future, the mechanism may be extended to
19903           support this.  The standard frameworks can be found in
19904           /System/Library/Frameworks and /Library/Frameworks.  An example
19905           include looks like "#include <Framework/header.h>", where Framework
19906           denotes the name of the framework and header.h is found in the
19907           PrivateHeaders or Headers directory.
19908
19909       -iframeworkdir
19910           Like -F except the directory is a treated as a system directory.
19911           The main difference between this -iframework and -F is that with
19912           -iframework the compiler does not warn about constructs contained
19913           within header files found via dir.  This option is valid only for
19914           the C family of languages.
19915
19916       -gused
19917           Emit debugging information for symbols that are used.  For stabs
19918           debugging format, this enables -feliminate-unused-debug-symbols.
19919           This is by default ON.
19920
19921       -gfull
19922           Emit debugging information for all symbols and types.
19923
19924       -mmacosx-version-min=version
19925           The earliest version of MacOS X that this executable will run on is
19926           version.  Typical values of version include 10.1, 10.2, and 10.3.9.
19927
19928           If the compiler was built to use the system's headers by default,
19929           then the default for this option is the system version on which the
19930           compiler is running, otherwise the default is to make choices that
19931           are compatible with as many systems and code bases as possible.
19932
19933       -mkernel
19934           Enable kernel development mode.  The -mkernel option sets -static,
19935           -fno-common, -fno-use-cxa-atexit, -fno-exceptions,
19936           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
19937           where applicable.  This mode also sets -mno-altivec, -msoft-float,
19938           -fno-builtin and -mlong-branch for PowerPC targets.
19939
19940       -mone-byte-bool
19941           Override the defaults for "bool" so that "sizeof(bool)==1".  By
19942           default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1
19943           when compiling for Darwin/x86, so this option has no effect on x86.
19944
19945           Warning: The -mone-byte-bool switch causes GCC to generate code
19946           that is not binary compatible with code generated without that
19947           switch.  Using this switch may require recompiling all other
19948           modules in a program, including system libraries.  Use this switch
19949           to conform to a non-default data model.
19950
19951       -mfix-and-continue
19952       -ffix-and-continue
19953       -findirect-data
19954           Generate code suitable for fast turnaround development, such as to
19955           allow GDB to dynamically load .o files into already-running
19956           programs.  -findirect-data and -ffix-and-continue are provided for
19957           backwards compatibility.
19958
19959       -all_load
19960           Loads all members of static archive libraries.  See man ld(1) for
19961           more information.
19962
19963       -arch_errors_fatal
19964           Cause the errors having to do with files that have the wrong
19965           architecture to be fatal.
19966
19967       -bind_at_load
19968           Causes the output file to be marked such that the dynamic linker
19969           will bind all undefined references when the file is loaded or
19970           launched.
19971
19972       -bundle
19973           Produce a Mach-o bundle format file.  See man ld(1) for more
19974           information.
19975
19976       -bundle_loader executable
19977           This option specifies the executable that will load the build
19978           output file being linked.  See man ld(1) for more information.
19979
19980       -dynamiclib
19981           When passed this option, GCC produces a dynamic library instead of
19982           an executable when linking, using the Darwin libtool command.
19983
19984       -force_cpusubtype_ALL
19985           This causes GCC's output file to have the ALL subtype, instead of
19986           one controlled by the -mcpu or -march option.
19987
19988       -allowable_client  client_name
19989       -client_name
19990       -compatibility_version
19991       -current_version
19992       -dead_strip
19993       -dependency-file
19994       -dylib_file
19995       -dylinker_install_name
19996       -dynamic
19997       -exported_symbols_list
19998       -filelist
19999       -flat_namespace
20000       -force_flat_namespace
20001       -headerpad_max_install_names
20002       -image_base
20003       -init
20004       -install_name
20005       -keep_private_externs
20006       -multi_module
20007       -multiply_defined
20008       -multiply_defined_unused
20009       -noall_load
20010       -no_dead_strip_inits_and_terms
20011       -nofixprebinding
20012       -nomultidefs
20013       -noprebind
20014       -noseglinkedit
20015       -pagezero_size
20016       -prebind
20017       -prebind_all_twolevel_modules
20018       -private_bundle
20019       -read_only_relocs
20020       -sectalign
20021       -sectobjectsymbols
20022       -whyload
20023       -seg1addr
20024       -sectcreate
20025       -sectobjectsymbols
20026       -sectorder
20027       -segaddr
20028       -segs_read_only_addr
20029       -segs_read_write_addr
20030       -seg_addr_table
20031       -seg_addr_table_filename
20032       -seglinkedit
20033       -segprot
20034       -segs_read_only_addr
20035       -segs_read_write_addr
20036       -single_module
20037       -static
20038       -sub_library
20039       -sub_umbrella
20040       -twolevel_namespace
20041       -umbrella
20042       -undefined
20043       -unexported_symbols_list
20044       -weak_reference_mismatches
20045       -whatsloaded
20046           These options are passed to the Darwin linker.  The Darwin linker
20047           man page describes them in detail.
20048
20049       DEC Alpha Options
20050
20051       These -m options are defined for the DEC Alpha implementations:
20052
20053       -mno-soft-float
20054       -msoft-float
20055           Use (do not use) the hardware floating-point instructions for
20056           floating-point operations.  When -msoft-float is specified,
20057           functions in libgcc.a are used to perform floating-point
20058           operations.  Unless they are replaced by routines that emulate the
20059           floating-point operations, or compiled in such a way as to call
20060           such emulations routines, these routines issue floating-point
20061           operations.   If you are compiling for an Alpha without floating-
20062           point operations, you must ensure that the library is built so as
20063           not to call them.
20064
20065           Note that Alpha implementations without floating-point operations
20066           are required to have floating-point registers.
20067
20068       -mfp-reg
20069       -mno-fp-regs
20070           Generate code that uses (does not use) the floating-point register
20071           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
20072           register set is not used, floating-point operands are passed in
20073           integer registers as if they were integers and floating-point
20074           results are passed in $0 instead of $f0.  This is a non-standard
20075           calling sequence, so any function with a floating-point argument or
20076           return value called by code compiled with -mno-fp-regs must also be
20077           compiled with that option.
20078
20079           A typical use of this option is building a kernel that does not
20080           use, and hence need not save and restore, any floating-point
20081           registers.
20082
20083       -mieee
20084           The Alpha architecture implements floating-point hardware optimized
20085           for maximum performance.  It is mostly compliant with the IEEE
20086           floating-point standard.  However, for full compliance, software
20087           assistance is required.  This option generates code fully IEEE-
20088           compliant code except that the inexact-flag is not maintained (see
20089           below).  If this option is turned on, the preprocessor macro
20090           "_IEEE_FP" is defined during compilation.  The resulting code is
20091           less efficient but is able to correctly support denormalized
20092           numbers and exceptional IEEE values such as not-a-number and
20093           plus/minus infinity.  Other Alpha compilers call this option
20094           -ieee_with_no_inexact.
20095
20096       -mieee-with-inexact
20097           This is like -mieee except the generated code also maintains the
20098           IEEE inexact-flag.  Turning on this option causes the generated
20099           code to implement fully-compliant IEEE math.  In addition to
20100           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
20101           On some Alpha implementations the resulting code may execute
20102           significantly slower than the code generated by default.  Since
20103           there is very little code that depends on the inexact-flag, you
20104           should normally not specify this option.  Other Alpha compilers
20105           call this option -ieee_with_inexact.
20106
20107       -mfp-trap-mode=trap-mode
20108           This option controls what floating-point related traps are enabled.
20109           Other Alpha compilers call this option -fptm trap-mode.  The trap
20110           mode can be set to one of four values:
20111
20112           n   This is the default (normal) setting.  The only traps that are
20113               enabled are the ones that cannot be disabled in software (e.g.,
20114               division by zero trap).
20115
20116           u   In addition to the traps enabled by n, underflow traps are
20117               enabled as well.
20118
20119           su  Like u, but the instructions are marked to be safe for software
20120               completion (see Alpha architecture manual for details).
20121
20122           sui Like su, but inexact traps are enabled as well.
20123
20124       -mfp-rounding-mode=rounding-mode
20125           Selects the IEEE rounding mode.  Other Alpha compilers call this
20126           option -fprm rounding-mode.  The rounding-mode can be one of:
20127
20128           n   Normal IEEE rounding mode.  Floating-point numbers are rounded
20129               towards the nearest machine number or towards the even machine
20130               number in case of a tie.
20131
20132           m   Round towards minus infinity.
20133
20134           c   Chopped rounding mode.  Floating-point numbers are rounded
20135               towards zero.
20136
20137           d   Dynamic rounding mode.  A field in the floating-point control
20138               register (fpcr, see Alpha architecture reference manual)
20139               controls the rounding mode in effect.  The C library
20140               initializes this register for rounding towards plus infinity.
20141               Thus, unless your program modifies the fpcr, d corresponds to
20142               round towards plus infinity.
20143
20144       -mtrap-precision=trap-precision
20145           In the Alpha architecture, floating-point traps are imprecise.
20146           This means without software assistance it is impossible to recover
20147           from a floating trap and program execution normally needs to be
20148           terminated.  GCC can generate code that can assist operating system
20149           trap handlers in determining the exact location that caused a
20150           floating-point trap.  Depending on the requirements of an
20151           application, different levels of precisions can be selected:
20152
20153           p   Program precision.  This option is the default and means a trap
20154               handler can only identify which program caused a floating-point
20155               exception.
20156
20157           f   Function precision.  The trap handler can determine the
20158               function that caused a floating-point exception.
20159
20160           i   Instruction precision.  The trap handler can determine the
20161               exact instruction that caused a floating-point exception.
20162
20163           Other Alpha compilers provide the equivalent options called
20164           -scope_safe and -resumption_safe.
20165
20166       -mieee-conformant
20167           This option marks the generated code as IEEE conformant.  You must
20168           not use this option unless you also specify -mtrap-precision=i and
20169           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
20170           to emit the line .eflag 48 in the function prologue of the
20171           generated assembly file.
20172
20173       -mbuild-constants
20174           Normally GCC examines a 32- or 64-bit integer constant to see if it
20175           can construct it from smaller constants in two or three
20176           instructions.  If it cannot, it outputs the constant as a literal
20177           and generates code to load it from the data segment at run time.
20178
20179           Use this option to require GCC to construct all integer constants
20180           using code, even if it takes more instructions (the maximum is
20181           six).
20182
20183           You typically use this option to build a shared library dynamic
20184           loader.  Itself a shared library, it must relocate itself in memory
20185           before it can find the variables and constants in its own data
20186           segment.
20187
20188       -mbwx
20189       -mno-bwx
20190       -mcix
20191       -mno-cix
20192       -mfix
20193       -mno-fix
20194       -mmax
20195       -mno-max
20196           Indicate whether GCC should generate code to use the optional BWX,
20197           CIX, FIX and MAX instruction sets.  The default is to use the
20198           instruction sets supported by the CPU type specified via -mcpu=
20199           option or that of the CPU on which GCC was built if none is
20200           specified.
20201
20202       -mfloat-vax
20203       -mfloat-ieee
20204           Generate code that uses (does not use) VAX F and G floating-point
20205           arithmetic instead of IEEE single and double precision.
20206
20207       -mexplicit-relocs
20208       -mno-explicit-relocs
20209           Older Alpha assemblers provided no way to generate symbol
20210           relocations except via assembler macros.  Use of these macros does
20211           not allow optimal instruction scheduling.  GNU binutils as of
20212           version 2.12 supports a new syntax that allows the compiler to
20213           explicitly mark which relocations should apply to which
20214           instructions.  This option is mostly useful for debugging, as GCC
20215           detects the capabilities of the assembler when it is built and sets
20216           the default accordingly.
20217
20218       -msmall-data
20219       -mlarge-data
20220           When -mexplicit-relocs is in effect, static data is accessed via
20221           gp-relative relocations.  When -msmall-data is used, objects 8
20222           bytes long or smaller are placed in a small data area (the ".sdata"
20223           and ".sbss" sections) and are accessed via 16-bit relocations off
20224           of the $gp register.  This limits the size of the small data area
20225           to 64KB, but allows the variables to be directly accessed via a
20226           single instruction.
20227
20228           The default is -mlarge-data.  With this option the data area is
20229           limited to just below 2GB.  Programs that require more than 2GB of
20230           data must use "malloc" or "mmap" to allocate the data in the heap
20231           instead of in the program's data segment.
20232
20233           When generating code for shared libraries, -fpic implies
20234           -msmall-data and -fPIC implies -mlarge-data.
20235
20236       -msmall-text
20237       -mlarge-text
20238           When -msmall-text is used, the compiler assumes that the code of
20239           the entire program (or shared library) fits in 4MB, and is thus
20240           reachable with a branch instruction.  When -msmall-data is used,
20241           the compiler can assume that all local symbols share the same $gp
20242           value, and thus reduce the number of instructions required for a
20243           function call from 4 to 1.
20244
20245           The default is -mlarge-text.
20246
20247       -mcpu=cpu_type
20248           Set the instruction set and instruction scheduling parameters for
20249           machine type cpu_type.  You can specify either the EV style name or
20250           the corresponding chip number.  GCC supports scheduling parameters
20251           for the EV4, EV5 and EV6 family of processors and chooses the
20252           default values for the instruction set from the processor you
20253           specify.  If you do not specify a processor type, GCC defaults to
20254           the processor on which the compiler was built.
20255
20256           Supported values for cpu_type are
20257
20258           ev4
20259           ev45
20260           21064
20261               Schedules as an EV4 and has no instruction set extensions.
20262
20263           ev5
20264           21164
20265               Schedules as an EV5 and has no instruction set extensions.
20266
20267           ev56
20268           21164a
20269               Schedules as an EV5 and supports the BWX extension.
20270
20271           pca56
20272           21164pc
20273           21164PC
20274               Schedules as an EV5 and supports the BWX and MAX extensions.
20275
20276           ev6
20277           21264
20278               Schedules as an EV6 and supports the BWX, FIX, and MAX
20279               extensions.
20280
20281           ev67
20282           21264a
20283               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
20284               extensions.
20285
20286           Native toolchains also support the value native, which selects the
20287           best architecture option for the host processor.  -mcpu=native has
20288           no effect if GCC does not recognize the processor.
20289
20290       -mtune=cpu_type
20291           Set only the instruction scheduling parameters for machine type
20292           cpu_type.  The instruction set is not changed.
20293
20294           Native toolchains also support the value native, which selects the
20295           best architecture option for the host processor.  -mtune=native has
20296           no effect if GCC does not recognize the processor.
20297
20298       -mmemory-latency=time
20299           Sets the latency the scheduler should assume for typical memory
20300           references as seen by the application.  This number is highly
20301           dependent on the memory access patterns used by the application and
20302           the size of the external cache on the machine.
20303
20304           Valid options for time are
20305
20306           number
20307               A decimal number representing clock cycles.
20308
20309           L1
20310           L2
20311           L3
20312           main
20313               The compiler contains estimates of the number of clock cycles
20314               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
20315               (also called Dcache, Scache, and Bcache), as well as to main
20316               memory.  Note that L3 is only valid for EV5.
20317
20318       eBPF Options
20319
20320       -mframe-limit=bytes
20321           This specifies the hard limit for frame sizes, in bytes.
20322           Currently, the value that can be specified should be less than or
20323           equal to 32767.  Defaults to whatever limit is imposed by the
20324           version of the Linux kernel targeted.
20325
20326       -mkernel=version
20327           This specifies the minimum version of the kernel that will run the
20328           compiled program.  GCC uses this version to determine which
20329           instructions to use, what kernel helpers to allow, etc.  Currently,
20330           version can be one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8,
20331           4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19,
20332           4.20, 5.0, 5.1, 5.2, latest and native.
20333
20334       -mbig-endian
20335           Generate code for a big-endian target.
20336
20337       -mlittle-endian
20338           Generate code for a little-endian target.  This is the default.
20339
20340       -mjmpext
20341           Enable generation of extra conditional-branch instructions.
20342           Enabled for CPU v2 and above.
20343
20344       -mjmp32
20345           Enable 32-bit jump instructions. Enabled for CPU v3 and above.
20346
20347       -malu32
20348           Enable 32-bit ALU instructions. Enabled for CPU v3 and above.
20349
20350       -mcpu=version
20351           This specifies which version of the eBPF ISA to target. Newer
20352           versions may not be supported by all kernels. The default is v3.
20353
20354           Supported values for version are:
20355
20356           v1  The first stable eBPF ISA with no special features or
20357               extensions.
20358
20359           v2  Supports the jump extensions, as in -mjmpext.
20360
20361           v3  All features of v2, plus:
20362
20363               -<32-bit jump operations, as in -mjmp32>
20364               -<32-bit ALU operations, as in -malu32>
20365       -mco-re
20366           Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires
20367           and is implied by -gbtf.
20368
20369       -mno-co-re
20370           Disable BPF Compile Once - Run Everywhere (CO-RE) support. BPF CO-
20371           RE support is enabled by default when generating BTF debug
20372           information for the BPF target.
20373
20374       -mxbpf
20375           Generate code for an expanded version of BPF, which relaxes some of
20376           the restrictions imposed by the BPF architecture:
20377
20378           -<Save and restore callee-saved registers at function entry and>
20379               exit, respectively.
20380
20381       FR30 Options
20382
20383       These options are defined specifically for the FR30 port.
20384
20385       -msmall-model
20386           Use the small address space model.  This can produce smaller code,
20387           but it does assume that all symbolic values and addresses fit into
20388           a 20-bit range.
20389
20390       -mno-lsim
20391           Assume that runtime support has been provided and so there is no
20392           need to include the simulator library (libsim.a) on the linker
20393           command line.
20394
20395       FT32 Options
20396
20397       These options are defined specifically for the FT32 port.
20398
20399       -msim
20400           Specifies that the program will be run on the simulator.  This
20401           causes an alternate runtime startup and library to be linked.  You
20402           must not use this option when generating programs that will run on
20403           real hardware; you must provide your own runtime library for
20404           whatever I/O functions are needed.
20405
20406       -mlra
20407           Enable Local Register Allocation.  This is still experimental for
20408           FT32, so by default the compiler uses standard reload.
20409
20410       -mnodiv
20411           Do not use div and mod instructions.
20412
20413       -mft32b
20414           Enable use of the extended instructions of the FT32B processor.
20415
20416       -mcompress
20417           Compress all code using the Ft32B code compression scheme.
20418
20419       -mnopm
20420           Do not generate code that reads program memory.
20421
20422       FRV Options
20423
20424       -mgpr-32
20425           Only use the first 32 general-purpose registers.
20426
20427       -mgpr-64
20428           Use all 64 general-purpose registers.
20429
20430       -mfpr-32
20431           Use only the first 32 floating-point registers.
20432
20433       -mfpr-64
20434           Use all 64 floating-point registers.
20435
20436       -mhard-float
20437           Use hardware instructions for floating-point operations.
20438
20439       -msoft-float
20440           Use library routines for floating-point operations.
20441
20442       -malloc-cc
20443           Dynamically allocate condition code registers.
20444
20445       -mfixed-cc
20446           Do not try to dynamically allocate condition code registers, only
20447           use "icc0" and "fcc0".
20448
20449       -mdword
20450           Change ABI to use double word insns.
20451
20452       -mno-dword
20453           Do not use double word instructions.
20454
20455       -mdouble
20456           Use floating-point double instructions.
20457
20458       -mno-double
20459           Do not use floating-point double instructions.
20460
20461       -mmedia
20462           Use media instructions.
20463
20464       -mno-media
20465           Do not use media instructions.
20466
20467       -mmuladd
20468           Use multiply and add/subtract instructions.
20469
20470       -mno-muladd
20471           Do not use multiply and add/subtract instructions.
20472
20473       -mfdpic
20474           Select the FDPIC ABI, which uses function descriptors to represent
20475           pointers to functions.  Without any PIC/PIE-related options, it
20476           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
20477           small data are within a 12-bit range from the GOT base address;
20478           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
20479           bfin-elf target, this option implies -msim.
20480
20481       -minline-plt
20482           Enable inlining of PLT entries in function calls to functions that
20483           are not known to bind locally.  It has no effect without -mfdpic.
20484           It's enabled by default if optimizing for speed and compiling for
20485           shared libraries (i.e., -fPIC or -fpic), or when an optimization
20486           option such as -O3 or above is present in the command line.
20487
20488       -mTLS
20489           Assume a large TLS segment when generating thread-local code.
20490
20491       -mtls
20492           Do not assume a large TLS segment when generating thread-local
20493           code.
20494
20495       -mgprel-ro
20496           Enable the use of "GPREL" relocations in the FDPIC ABI for data
20497           that is known to be in read-only sections.  It's enabled by
20498           default, except for -fpic or -fpie: even though it may help make
20499           the global offset table smaller, it trades 1 instruction for 4.
20500           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
20501           may be shared by multiple symbols, and it avoids the need for a GOT
20502           entry for the referenced symbol, so it's more likely to be a win.
20503           If it is not, -mno-gprel-ro can be used to disable it.
20504
20505       -multilib-library-pic
20506           Link with the (library, not FD) pic libraries.  It's implied by
20507           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
20508           should never have to use it explicitly.
20509
20510       -mlinked-fp
20511           Follow the EABI requirement of always creating a frame pointer
20512           whenever a stack frame is allocated.  This option is enabled by
20513           default and can be disabled with -mno-linked-fp.
20514
20515       -mlong-calls
20516           Use indirect addressing to call functions outside the current
20517           compilation unit.  This allows the functions to be placed anywhere
20518           within the 32-bit address space.
20519
20520       -malign-labels
20521           Try to align labels to an 8-byte boundary by inserting NOPs into
20522           the previous packet.  This option only has an effect when VLIW
20523           packing is enabled.  It doesn't create new packets; it merely adds
20524           NOPs to existing ones.
20525
20526       -mlibrary-pic
20527           Generate position-independent EABI code.
20528
20529       -macc-4
20530           Use only the first four media accumulator registers.
20531
20532       -macc-8
20533           Use all eight media accumulator registers.
20534
20535       -mpack
20536           Pack VLIW instructions.
20537
20538       -mno-pack
20539           Do not pack VLIW instructions.
20540
20541       -mno-eflags
20542           Do not mark ABI switches in e_flags.
20543
20544       -mcond-move
20545           Enable the use of conditional-move instructions (default).
20546
20547           This switch is mainly for debugging the compiler and will likely be
20548           removed in a future version.
20549
20550       -mno-cond-move
20551           Disable the use of conditional-move instructions.
20552
20553           This switch is mainly for debugging the compiler and will likely be
20554           removed in a future version.
20555
20556       -mscc
20557           Enable the use of conditional set instructions (default).
20558
20559           This switch is mainly for debugging the compiler and will likely be
20560           removed in a future version.
20561
20562       -mno-scc
20563           Disable the use of conditional set instructions.
20564
20565           This switch is mainly for debugging the compiler and will likely be
20566           removed in a future version.
20567
20568       -mcond-exec
20569           Enable the use of conditional execution (default).
20570
20571           This switch is mainly for debugging the compiler and will likely be
20572           removed in a future version.
20573
20574       -mno-cond-exec
20575           Disable the use of conditional execution.
20576
20577           This switch is mainly for debugging the compiler and will likely be
20578           removed in a future version.
20579
20580       -mvliw-branch
20581           Run a pass to pack branches into VLIW instructions (default).
20582
20583           This switch is mainly for debugging the compiler and will likely be
20584           removed in a future version.
20585
20586       -mno-vliw-branch
20587           Do not run a pass to pack branches into VLIW instructions.
20588
20589           This switch is mainly for debugging the compiler and will likely be
20590           removed in a future version.
20591
20592       -mmulti-cond-exec
20593           Enable optimization of "&&" and "||" in conditional execution
20594           (default).
20595
20596           This switch is mainly for debugging the compiler and will likely be
20597           removed in a future version.
20598
20599       -mno-multi-cond-exec
20600           Disable optimization of "&&" and "||" in conditional execution.
20601
20602           This switch is mainly for debugging the compiler and will likely be
20603           removed in a future version.
20604
20605       -mnested-cond-exec
20606           Enable nested conditional execution optimizations (default).
20607
20608           This switch is mainly for debugging the compiler and will likely be
20609           removed in a future version.
20610
20611       -mno-nested-cond-exec
20612           Disable nested conditional execution optimizations.
20613
20614           This switch is mainly for debugging the compiler and will likely be
20615           removed in a future version.
20616
20617       -moptimize-membar
20618           This switch removes redundant "membar" instructions from the
20619           compiler-generated code.  It is enabled by default.
20620
20621       -mno-optimize-membar
20622           This switch disables the automatic removal of redundant "membar"
20623           instructions from the generated code.
20624
20625       -mtomcat-stats
20626           Cause gas to print out tomcat statistics.
20627
20628       -mcpu=cpu
20629           Select the processor type for which to generate code.  Possible
20630           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
20631           and simple.
20632
20633       GNU/Linux Options
20634
20635       These -m options are defined for GNU/Linux targets:
20636
20637       -mglibc
20638           Use the GNU C library.  This is the default except on
20639           *-*-linux-*uclibc*, *-*-linux-*musl* and *-*-linux-*android*
20640           targets.
20641
20642       -muclibc
20643           Use uClibc C library.  This is the default on *-*-linux-*uclibc*
20644           targets.
20645
20646       -mmusl
20647           Use the musl C library.  This is the default on *-*-linux-*musl*
20648           targets.
20649
20650       -mbionic
20651           Use Bionic C library.  This is the default on *-*-linux-*android*
20652           targets.
20653
20654       -mandroid
20655           Compile code compatible with Android platform.  This is the default
20656           on *-*-linux-*android* targets.
20657
20658           When compiling, this option enables -mbionic, -fPIC,
20659           -fno-exceptions and -fno-rtti by default.  When linking, this
20660           option makes the GCC driver pass Android-specific options to the
20661           linker.  Finally, this option causes the preprocessor macro
20662           "__ANDROID__" to be defined.
20663
20664       -tno-android-cc
20665           Disable compilation effects of -mandroid, i.e., do not enable
20666           -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.
20667
20668       -tno-android-ld
20669           Disable linking effects of -mandroid, i.e., pass standard Linux
20670           linking options to the linker.
20671
20672       H8/300 Options
20673
20674       These -m options are defined for the H8/300 implementations:
20675
20676       -mrelax
20677           Shorten some address references at link time, when possible; uses
20678           the linker option -relax.
20679
20680       -mh Generate code for the H8/300H.
20681
20682       -ms Generate code for the H8S.
20683
20684       -mn Generate code for the H8S and H8/300H in the normal mode.  This
20685           switch must be used either with -mh or -ms.
20686
20687       -ms2600
20688           Generate code for the H8S/2600.  This switch must be used with -ms.
20689
20690       -mexr
20691           Extended registers are stored on stack before execution of function
20692           with monitor attribute. Default option is -mexr.  This option is
20693           valid only for H8S targets.
20694
20695       -mno-exr
20696           Extended registers are not stored on stack before execution of
20697           function with monitor attribute. Default option is -mno-exr.  This
20698           option is valid only for H8S targets.
20699
20700       -mint32
20701           Make "int" data 32 bits by default.
20702
20703       -malign-300
20704           On the H8/300H and H8S, use the same alignment rules as for the
20705           H8/300.  The default for the H8/300H and H8S is to align longs and
20706           floats on 4-byte boundaries.  -malign-300 causes them to be aligned
20707           on 2-byte boundaries.  This option has no effect on the H8/300.
20708
20709       HPPA Options
20710
20711       These -m options are defined for the HPPA family of computers:
20712
20713       -march=architecture-type
20714           Generate code for the specified architecture.  The choices for
20715           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
20716           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
20717           system to determine the proper architecture option for your
20718           machine.  Code compiled for lower numbered architectures runs on
20719           higher numbered architectures, but not the other way around.
20720
20721       -mpa-risc-1-0
20722       -mpa-risc-1-1
20723       -mpa-risc-2-0
20724           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
20725
20726       -mcaller-copies
20727           The caller copies function arguments passed by hidden reference.
20728           This option should be used with care as it is not compatible with
20729           the default 32-bit runtime.  However, only aggregates larger than
20730           eight bytes are passed by hidden reference and the option provides
20731           better compatibility with OpenMP.
20732
20733       -mjump-in-delay
20734           This option is ignored and provided for compatibility purposes
20735           only.
20736
20737       -mdisable-fpregs
20738           Prevent floating-point registers from being used in any manner.
20739           This is necessary for compiling kernels that perform lazy context
20740           switching of floating-point registers.  If you use this option and
20741           attempt to perform floating-point operations, the compiler aborts.
20742
20743       -mdisable-indexing
20744           Prevent the compiler from using indexing address modes.  This
20745           avoids some rather obscure problems when compiling MIG generated
20746           code under MACH.
20747
20748       -mno-space-regs
20749           Generate code that assumes the target has no space registers.  This
20750           allows GCC to generate faster indirect calls and use unscaled index
20751           address modes.
20752
20753           Such code is suitable for level 0 PA systems and kernels.
20754
20755       -mfast-indirect-calls
20756           Generate code that assumes calls never cross space boundaries.
20757           This allows GCC to emit code that performs faster indirect calls.
20758
20759           This option does not work in the presence of shared libraries or
20760           nested functions.
20761
20762       -mfixed-range=register-range
20763           Generate code treating the given register range as fixed registers.
20764           A fixed register is one that the register allocator cannot use.
20765           This is useful when compiling kernel code.  A register range is
20766           specified as two registers separated by a dash.  Multiple register
20767           ranges can be specified separated by a comma.
20768
20769       -mlong-load-store
20770           Generate 3-instruction load and store sequences as sometimes
20771           required by the HP-UX 10 linker.  This is equivalent to the +k
20772           option to the HP compilers.
20773
20774       -mportable-runtime
20775           Use the portable calling conventions proposed by HP for ELF
20776           systems.
20777
20778       -mgas
20779           Enable the use of assembler directives only GAS understands.
20780
20781       -mschedule=cpu-type
20782           Schedule code according to the constraints for the machine type
20783           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
20784           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
20785           to determine the proper scheduling option for your machine.  The
20786           default scheduling is 8000.
20787
20788       -mlinker-opt
20789           Enable the optimization pass in the HP-UX linker.  Note this makes
20790           symbolic debugging impossible.  It also triggers a bug in the HP-UX
20791           8 and HP-UX 9 linkers in which they give bogus error messages when
20792           linking some programs.
20793
20794       -msoft-float
20795           Generate output containing library calls for floating point.
20796           Warning: the requisite libraries are not available for all HPPA
20797           targets.  Normally the facilities of the machine's usual C compiler
20798           are used, but this cannot be done directly in cross-compilation.
20799           You must make your own arrangements to provide suitable library
20800           functions for cross-compilation.
20801
20802           -msoft-float changes the calling convention in the output file;
20803           therefore, it is only useful if you compile all of a program with
20804           this option.  In particular, you need to compile libgcc.a, the
20805           library that comes with GCC, with -msoft-float in order for this to
20806           work.
20807
20808       -msio
20809           Generate the predefine, "_SIO", for server IO.  The default is
20810           -mwsio.  This generates the predefines, "__hp9000s700",
20811           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
20812           are available under HP-UX and HI-UX.
20813
20814       -mgnu-ld
20815           Use options specific to GNU ld.  This passes -shared to ld when
20816           building a shared library.  It is the default when GCC is
20817           configured, explicitly or implicitly, with the GNU linker.  This
20818           option does not affect which ld is called; it only changes what
20819           parameters are passed to that ld.  The ld that is called is
20820           determined by the --with-ld configure option, GCC's program search
20821           path, and finally by the user's PATH.  The linker used by GCC can
20822           be printed using which `gcc -print-prog-name=ld`.  This option is
20823           only available on the 64-bit HP-UX GCC, i.e. configured with
20824           hppa*64*-*-hpux*.
20825
20826       -mhp-ld
20827           Use options specific to HP ld.  This passes -b to ld when building
20828           a shared library and passes +Accept TypeMismatch to ld on all
20829           links.  It is the default when GCC is configured, explicitly or
20830           implicitly, with the HP linker.  This option does not affect which
20831           ld is called; it only changes what parameters are passed to that
20832           ld.  The ld that is called is determined by the --with-ld configure
20833           option, GCC's program search path, and finally by the user's PATH.
20834           The linker used by GCC can be printed using which `gcc
20835           -print-prog-name=ld`.  This option is only available on the 64-bit
20836           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.
20837
20838       -mlong-calls
20839           Generate code that uses long call sequences.  This ensures that a
20840           call is always able to reach linker generated stubs.  The default
20841           is to generate long calls only when the distance from the call site
20842           to the beginning of the function or translation unit, as the case
20843           may be, exceeds a predefined limit set by the branch type being
20844           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
20845           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
20846           always limited at 240,000 bytes.
20847
20848           Distances are measured from the beginning of functions when using
20849           the -ffunction-sections option, or when using the -mgas and
20850           -mno-portable-runtime options together under HP-UX with the SOM
20851           linker.
20852
20853           It is normally not desirable to use this option as it degrades
20854           performance.  However, it may be useful in large applications,
20855           particularly when partial linking is used to build the application.
20856
20857           The types of long calls used depends on the capabilities of the
20858           assembler and linker, and the type of code being generated.  The
20859           impact on systems that support long absolute calls, and long pic
20860           symbol-difference or pc-relative calls should be relatively small.
20861           However, an indirect call is used on 32-bit ELF systems in pic code
20862           and it is quite long.
20863
20864       -munix=unix-std
20865           Generate compiler predefines and select a startfile for the
20866           specified UNIX standard.  The choices for unix-std are 93, 95 and
20867           98.  93 is supported on all HP-UX versions.  95 is available on HP-
20868           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
20869           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
20870           11.00, and 98 for HP-UX 11.11 and later.
20871
20872           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
20873           -munix=95 provides additional predefines for "XOPEN_UNIX" and
20874           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
20875           provides additional predefines for "_XOPEN_UNIX",
20876           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
20877           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.
20878
20879           It is important to note that this option changes the interfaces for
20880           various library routines.  It also affects the operational behavior
20881           of the C library.  Thus, extreme care is needed in using this
20882           option.
20883
20884           Library code that is intended to operate with more than one UNIX
20885           standard must test, set and restore the variable
20886           "__xpg4_extended_mask" as appropriate.  Most GNU software doesn't
20887           provide this capability.
20888
20889       -nolibdld
20890           Suppress the generation of link options to search libdld.sl when
20891           the -static option is specified on HP-UX 10 and later.
20892
20893       -static
20894           The HP-UX implementation of setlocale in libc has a dependency on
20895           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
20896           when the -static option is specified, special link options are
20897           needed to resolve this dependency.
20898
20899           On HP-UX 10 and later, the GCC driver adds the necessary options to
20900           link with libdld.sl when the -static option is specified.  This
20901           causes the resulting binary to be dynamic.  On the 64-bit port, the
20902           linkers generate dynamic binaries by default in any case.  The
20903           -nolibdld option can be used to prevent the GCC driver from adding
20904           these link options.
20905
20906       -threads
20907           Add support for multithreading with the dce thread library under
20908           HP-UX.  This option sets flags for both the preprocessor and
20909           linker.
20910
20911       IA-64 Options
20912
20913       These are the -m options defined for the Intel IA-64 architecture.
20914
20915       -mbig-endian
20916           Generate code for a big-endian target.  This is the default for HP-
20917           UX.
20918
20919       -mlittle-endian
20920           Generate code for a little-endian target.  This is the default for
20921           AIX5 and GNU/Linux.
20922
20923       -mgnu-as
20924       -mno-gnu-as
20925           Generate (or don't) code for the GNU assembler.  This is the
20926           default.
20927
20928       -mgnu-ld
20929       -mno-gnu-ld
20930           Generate (or don't) code for the GNU linker.  This is the default.
20931
20932       -mno-pic
20933           Generate code that does not use a global pointer register.  The
20934           result is not position independent code, and violates the IA-64
20935           ABI.
20936
20937       -mvolatile-asm-stop
20938       -mno-volatile-asm-stop
20939           Generate (or don't) a stop bit immediately before and after
20940           volatile asm statements.
20941
20942       -mregister-names
20943       -mno-register-names
20944           Generate (or don't) in, loc, and out register names for the stacked
20945           registers.  This may make assembler output more readable.
20946
20947       -mno-sdata
20948       -msdata
20949           Disable (or enable) optimizations that use the small data section.
20950           This may be useful for working around optimizer bugs.
20951
20952       -mconstant-gp
20953           Generate code that uses a single constant global pointer value.
20954           This is useful when compiling kernel code.
20955
20956       -mauto-pic
20957           Generate code that is self-relocatable.  This implies
20958           -mconstant-gp.  This is useful when compiling firmware code.
20959
20960       -minline-float-divide-min-latency
20961           Generate code for inline divides of floating-point values using the
20962           minimum latency algorithm.
20963
20964       -minline-float-divide-max-throughput
20965           Generate code for inline divides of floating-point values using the
20966           maximum throughput algorithm.
20967
20968       -mno-inline-float-divide
20969           Do not generate inline code for divides of floating-point values.
20970
20971       -minline-int-divide-min-latency
20972           Generate code for inline divides of integer values using the
20973           minimum latency algorithm.
20974
20975       -minline-int-divide-max-throughput
20976           Generate code for inline divides of integer values using the
20977           maximum throughput algorithm.
20978
20979       -mno-inline-int-divide
20980           Do not generate inline code for divides of integer values.
20981
20982       -minline-sqrt-min-latency
20983           Generate code for inline square roots using the minimum latency
20984           algorithm.
20985
20986       -minline-sqrt-max-throughput
20987           Generate code for inline square roots using the maximum throughput
20988           algorithm.
20989
20990       -mno-inline-sqrt
20991           Do not generate inline code for "sqrt".
20992
20993       -mfused-madd
20994       -mno-fused-madd
20995           Do (don't) generate code that uses the fused multiply/add or
20996           multiply/subtract instructions.  The default is to use these
20997           instructions.
20998
20999       -mno-dwarf2-asm
21000       -mdwarf2-asm
21001           Don't (or do) generate assembler code for the DWARF line number
21002           debugging info.  This may be useful when not using the GNU
21003           assembler.
21004
21005       -mearly-stop-bits
21006       -mno-early-stop-bits
21007           Allow stop bits to be placed earlier than immediately preceding the
21008           instruction that triggered the stop bit.  This can improve
21009           instruction scheduling, but does not always do so.
21010
21011       -mfixed-range=register-range
21012           Generate code treating the given register range as fixed registers.
21013           A fixed register is one that the register allocator cannot use.
21014           This is useful when compiling kernel code.  A register range is
21015           specified as two registers separated by a dash.  Multiple register
21016           ranges can be specified separated by a comma.
21017
21018       -mtls-size=tls-size
21019           Specify bit size of immediate TLS offsets.  Valid values are 14,
21020           22, and 64.
21021
21022       -mtune=cpu-type
21023           Tune the instruction scheduling for a particular CPU, Valid values
21024           are itanium, itanium1, merced, itanium2, and mckinley.
21025
21026       -milp32
21027       -mlp64
21028           Generate code for a 32-bit or 64-bit environment.  The 32-bit
21029           environment sets int, long and pointer to 32 bits.  The 64-bit
21030           environment sets int to 32 bits and long and pointer to 64 bits.
21031           These are HP-UX specific flags.
21032
21033       -mno-sched-br-data-spec
21034       -msched-br-data-spec
21035           (Dis/En)able data speculative scheduling before reload.  This
21036           results in generation of "ld.a" instructions and the corresponding
21037           check instructions ("ld.c" / "chk.a").  The default setting is
21038           disabled.
21039
21040       -msched-ar-data-spec
21041       -mno-sched-ar-data-spec
21042           (En/Dis)able data speculative scheduling after reload.  This
21043           results in generation of "ld.a" instructions and the corresponding
21044           check instructions ("ld.c" / "chk.a").  The default setting is
21045           enabled.
21046
21047       -mno-sched-control-spec
21048       -msched-control-spec
21049           (Dis/En)able control speculative scheduling.  This feature is
21050           available only during region scheduling (i.e. before reload).  This
21051           results in generation of the "ld.s" instructions and the
21052           corresponding check instructions "chk.s".  The default setting is
21053           disabled.
21054
21055       -msched-br-in-data-spec
21056       -mno-sched-br-in-data-spec
21057           (En/Dis)able speculative scheduling of the instructions that are
21058           dependent on the data speculative loads before reload.  This is
21059           effective only with -msched-br-data-spec enabled.  The default
21060           setting is enabled.
21061
21062       -msched-ar-in-data-spec
21063       -mno-sched-ar-in-data-spec
21064           (En/Dis)able speculative scheduling of the instructions that are
21065           dependent on the data speculative loads after reload.  This is
21066           effective only with -msched-ar-data-spec enabled.  The default
21067           setting is enabled.
21068
21069       -msched-in-control-spec
21070       -mno-sched-in-control-spec
21071           (En/Dis)able speculative scheduling of the instructions that are
21072           dependent on the control speculative loads.  This is effective only
21073           with -msched-control-spec enabled.  The default setting is enabled.
21074
21075       -mno-sched-prefer-non-data-spec-insns
21076       -msched-prefer-non-data-spec-insns
21077           If enabled, data-speculative instructions are chosen for schedule
21078           only if there are no other choices at the moment.  This makes the
21079           use of the data speculation much more conservative.  The default
21080           setting is disabled.
21081
21082       -mno-sched-prefer-non-control-spec-insns
21083       -msched-prefer-non-control-spec-insns
21084           If enabled, control-speculative instructions are chosen for
21085           schedule only if there are no other choices at the moment.  This
21086           makes the use of the control speculation much more conservative.
21087           The default setting is disabled.
21088
21089       -mno-sched-count-spec-in-critical-path
21090       -msched-count-spec-in-critical-path
21091           If enabled, speculative dependencies are considered during
21092           computation of the instructions priorities.  This makes the use of
21093           the speculation a bit more conservative.  The default setting is
21094           disabled.
21095
21096       -msched-spec-ldc
21097           Use a simple data speculation check.  This option is on by default.
21098
21099       -msched-control-spec-ldc
21100           Use a simple check for control speculation.  This option is on by
21101           default.
21102
21103       -msched-stop-bits-after-every-cycle
21104           Place a stop bit after every cycle when scheduling.  This option is
21105           on by default.
21106
21107       -msched-fp-mem-deps-zero-cost
21108           Assume that floating-point stores and loads are not likely to cause
21109           a conflict when placed into the same instruction group.  This
21110           option is disabled by default.
21111
21112       -msel-sched-dont-check-control-spec
21113           Generate checks for control speculation in selective scheduling.
21114           This flag is disabled by default.
21115
21116       -msched-max-memory-insns=max-insns
21117           Limit on the number of memory insns per instruction group, giving
21118           lower priority to subsequent memory insns attempting to schedule in
21119           the same instruction group. Frequently useful to prevent cache bank
21120           conflicts.  The default value is 1.
21121
21122       -msched-max-memory-insns-hard-limit
21123           Makes the limit specified by msched-max-memory-insns a hard limit,
21124           disallowing more than that number in an instruction group.
21125           Otherwise, the limit is "soft", meaning that non-memory operations
21126           are preferred when the limit is reached, but memory operations may
21127           still be scheduled.
21128
21129       LM32 Options
21130
21131       These -m options are defined for the LatticeMico32 architecture:
21132
21133       -mbarrel-shift-enabled
21134           Enable barrel-shift instructions.
21135
21136       -mdivide-enabled
21137           Enable divide and modulus instructions.
21138
21139       -mmultiply-enabled
21140           Enable multiply instructions.
21141
21142       -msign-extend-enabled
21143           Enable sign extend instructions.
21144
21145       -muser-enabled
21146           Enable user-defined instructions.
21147
21148       LoongArch Options
21149
21150       These command-line options are defined for LoongArch targets:
21151
21152       -march=cpu-type
21153           Generate instructions for the machine type cpu-type.  In contrast
21154           to -mtune=cpu-type, which merely tunes the generated code for the
21155           specified cpu-type, -march=cpu-type allows GCC to generate code
21156           that may not run at all on processors other than the one indicated.
21157           Specifying -march=cpu-type implies -mtune=cpu-type, except where
21158           noted otherwise.
21159
21160           The choices for cpu-type are:
21161
21162           native
21163               This selects the CPU to generate code for at compilation time
21164               by determining the processor type of the compiling machine.
21165               Using -march=native enables all instruction subsets supported
21166               by the local machine (hence the result might not run on
21167               different machines).  Using -mtune=native produces code
21168               optimized for the local machine under the constraints of the
21169               selected instruction set.
21170
21171           loongarch64
21172               A generic CPU with 64-bit extensions.
21173
21174           la464
21175               LoongArch LA464 CPU with LBT, LSX, LASX, LVZ.
21176
21177       -mtune=cpu-type
21178           Optimize the output for the given processor, specified by
21179           microarchitecture name.
21180
21181       -mabi=base-abi-type
21182           Generate code for the specified calling convention.  base-abi-type
21183           can be one of:
21184
21185           lp64d
21186               Uses 64-bit general purpose registers and 32/64-bit floating-
21187               point registers for parameter passing.  Data model is LP64,
21188               where int is 32 bits, while long int and pointers are 64 bits.
21189
21190           lp64f
21191               Uses 64-bit general purpose registers and 32-bit floating-point
21192               registers for parameter passing.  Data model is LP64, where int
21193               is 32 bits, while long int and pointers are 64 bits.
21194
21195           lp64s
21196               Uses 64-bit general purpose registers and no floating-point
21197               registers for parameter passing.  Data model is LP64, where int
21198               is 32 bits, while long int and pointers are 64 bits.
21199
21200       -mfpu=fpu-type
21201           Generate code for the specified FPU type, which can be one of:
21202
21203           64  Allow the use of hardware floating-point instructions for
21204               32-bit and 64-bit operations.
21205
21206           32  Allow the use of hardware floating-point instructions for
21207               32-bit operations.
21208
21209           none
21210           0   Prevent the use of hardware floating-point instructions.
21211
21212       -msoft-float
21213           Force -mfpu=none and prevents the use of floating-point registers
21214           for parameter passing.  This option may change the target ABI.
21215
21216       -msingle-float
21217           Force -mfpu=32 and allow the use of 32-bit floating-point registers
21218           for parameter passing.  This option may change the target ABI.
21219
21220       -mdouble-float
21221           Force -mfpu=64 and allow the use of 32/64-bit floating-point
21222           registers for parameter passing.  This option may change the target
21223           ABI.
21224
21225       -mbranch-cost=n
21226           Set the cost of branches to roughly n instructions.
21227
21228       -mcheck-zero-division
21229       -mno-check-zero-divison
21230           Trap (do not trap) on integer division by zero.  The default is
21231           -mcheck-zero-division.
21232
21233       -mcond-move-int
21234       -mno-cond-move-int
21235           Conditional moves for integral data in general-purpose registers
21236           are enabled (disabled).  The default is -mcond-move-int.
21237
21238       -mcond-move-float
21239       -mno-cond-move-float
21240           Conditional moves for floating-point registers are enabled
21241           (disabled).  The default is -mcond-move-float.
21242
21243       -mmemcpy
21244       -mno-memcpy
21245           Force (do not force) the use of "memcpy" for non-trivial block
21246           moves.  The default is -mno-memcpy, which allows GCC to inline most
21247           constant-sized copies.  Setting optimization level to -Os also
21248           forces the use of "memcpy", but -mno-memcpy may override this
21249           behavior if explicitly specified, regardless of the order these
21250           options on the command line.
21251
21252       -mstrict-align
21253       -mno-strict-align
21254           Avoid or allow generating memory accesses that may not be aligned
21255           on a natural object boundary as described in the architecture
21256           specification. The default is -mno-strict-align.
21257
21258       -msmall-data-limit=number
21259           Put global and static data smaller than number bytes into a special
21260           section (on some targets).  The default value is 0.
21261
21262       -mmax-inline-memcpy-size=n
21263           Inline all block moves (such as calls to "memcpy" or structure
21264           copies) less than or equal to n bytes.  The default value of n is
21265           1024.
21266
21267       -mcmodel=code-model
21268           Set the code model to one of:
21269
21270           tiny-static
21271               *   local symbol and global strong symbol: The data section
21272                   must be within +/-2MiB addressing space.  The text section
21273                   must be within +/-128MiB addressing space.
21274
21275               *   global weak symbol: The got table must be within +/-2GiB
21276                   addressing space.
21277
21278           tiny
21279               *   local symbol: The data section must be within +/-2MiB
21280                   addressing space.  The text section must be within
21281                   +/-128MiB addressing space.
21282
21283               *   global symbol: The got table must be within +/-2GiB
21284                   addressing space.
21285
21286           normal
21287               *   local symbol: The data section must be within +/-2GiB
21288                   addressing space.  The text section must be within
21289                   +/-128MiB addressing space.
21290
21291               *   global symbol: The got table must be within +/-2GiB
21292                   addressing space.
21293
21294           large
21295               *   local symbol: The data section must be within +/-2GiB
21296                   addressing space.  The text section must be within
21297                   +/-128GiB addressing space.
21298
21299               *   global symbol: The got table must be within +/-2GiB
21300                   addressing space.
21301
21302           extreme(Not implemented yet)
21303               *   local symbol: The data and text section must be within
21304                   +/-8EiB addressing space.
21305
21306               *   global symbol: The data got table must be within +/-8EiB
21307                   addressing space.
21308
21309           The default code model is "normal".
21310
21311       M32C Options
21312
21313       -mcpu=name
21314           Select the CPU for which code is generated.  name may be one of r8c
21315           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
21316           m32cm for the M16C/80 series, or m32c for the M32C/80 series.
21317
21318       -msim
21319           Specifies that the program will be run on the simulator.  This
21320           causes an alternate runtime library to be linked in which supports,
21321           for example, file I/O.  You must not use this option when
21322           generating programs that will run on real hardware; you must
21323           provide your own runtime library for whatever I/O functions are
21324           needed.
21325
21326       -memregs=number
21327           Specifies the number of memory-based pseudo-registers GCC uses
21328           during code generation.  These pseudo-registers are used like real
21329           registers, so there is a tradeoff between GCC's ability to fit the
21330           code into available registers, and the performance penalty of using
21331           memory instead of registers.  Note that all modules in a program
21332           must be compiled with the same value for this option.  Because of
21333           that, you must not use this option with GCC's default runtime
21334           libraries.
21335
21336       M32R/D Options
21337
21338       These -m options are defined for Renesas M32R/D architectures:
21339
21340       -m32r2
21341           Generate code for the M32R/2.
21342
21343       -m32rx
21344           Generate code for the M32R/X.
21345
21346       -m32r
21347           Generate code for the M32R.  This is the default.
21348
21349       -mmodel=small
21350           Assume all objects live in the lower 16MB of memory (so that their
21351           addresses can be loaded with the "ld24" instruction), and assume
21352           all subroutines are reachable with the "bl" instruction.  This is
21353           the default.
21354
21355           The addressability of a particular object can be set with the
21356           "model" attribute.
21357
21358       -mmodel=medium
21359           Assume objects may be anywhere in the 32-bit address space (the
21360           compiler generates "seth/add3" instructions to load their
21361           addresses), and assume all subroutines are reachable with the "bl"
21362           instruction.
21363
21364       -mmodel=large
21365           Assume objects may be anywhere in the 32-bit address space (the
21366           compiler generates "seth/add3" instructions to load their
21367           addresses), and assume subroutines may not be reachable with the
21368           "bl" instruction (the compiler generates the much slower
21369           "seth/add3/jl" instruction sequence).
21370
21371       -msdata=none
21372           Disable use of the small data area.  Variables are put into one of
21373           ".data", ".bss", or ".rodata" (unless the "section" attribute has
21374           been specified).  This is the default.
21375
21376           The small data area consists of sections ".sdata" and ".sbss".
21377           Objects may be explicitly put in the small data area with the
21378           "section" attribute using one of these sections.
21379
21380       -msdata=sdata
21381           Put small global and static data in the small data area, but do not
21382           generate special code to reference them.
21383
21384       -msdata=use
21385           Put small global and static data in the small data area, and
21386           generate special instructions to reference them.
21387
21388       -G num
21389           Put global and static objects less than or equal to num bytes into
21390           the small data or BSS sections instead of the normal data or BSS
21391           sections.  The default value of num is 8.  The -msdata option must
21392           be set to one of sdata or use for this option to have any effect.
21393
21394           All modules should be compiled with the same -G num value.
21395           Compiling with different values of num may or may not work; if it
21396           doesn't the linker gives an error message---incorrect code is not
21397           generated.
21398
21399       -mdebug
21400           Makes the M32R-specific code in the compiler display some
21401           statistics that might help in debugging programs.
21402
21403       -malign-loops
21404           Align all loops to a 32-byte boundary.
21405
21406       -mno-align-loops
21407           Do not enforce a 32-byte alignment for loops.  This is the default.
21408
21409       -missue-rate=number
21410           Issue number instructions per cycle.  number can only be 1 or 2.
21411
21412       -mbranch-cost=number
21413           number can only be 1 or 2.  If it is 1 then branches are preferred
21414           over conditional code, if it is 2, then the opposite applies.
21415
21416       -mflush-trap=number
21417           Specifies the trap number to use to flush the cache.  The default
21418           is 12.  Valid numbers are between 0 and 15 inclusive.
21419
21420       -mno-flush-trap
21421           Specifies that the cache cannot be flushed by using a trap.
21422
21423       -mflush-func=name
21424           Specifies the name of the operating system function to call to
21425           flush the cache.  The default is _flush_cache, but a function call
21426           is only used if a trap is not available.
21427
21428       -mno-flush-func
21429           Indicates that there is no OS function for flushing the cache.
21430
21431       M680x0 Options
21432
21433       These are the -m options defined for M680x0 and ColdFire processors.
21434       The default settings depend on which architecture was selected when the
21435       compiler was configured; the defaults for the most common choices are
21436       given below.
21437
21438       -march=arch
21439           Generate code for a specific M680x0 or ColdFire instruction set
21440           architecture.  Permissible values of arch for M680x0 architectures
21441           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
21442           architectures are selected according to Freescale's ISA
21443           classification and the permissible values are: isaa, isaaplus, isab
21444           and isac.
21445
21446           GCC defines a macro "__mcfarch__" whenever it is generating code
21447           for a ColdFire target.  The arch in this macro is one of the -march
21448           arguments given above.
21449
21450           When used together, -march and -mtune select code that runs on a
21451           family of similar processors but that is optimized for a particular
21452           microarchitecture.
21453
21454       -mcpu=cpu
21455           Generate code for a specific M680x0 or ColdFire processor.  The
21456           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
21457           68332 and cpu32.  The ColdFire cpus are given by the table below,
21458           which also classifies the CPUs into families:
21459
21460           Family : -mcpu arguments
21461           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
21462           5206 : 5202 5204 5206
21463           5206e : 5206e
21464           5208 : 5207 5208
21465           5211a : 5210a 5211a
21466           5213 : 5211 5212 5213
21467           5216 : 5214 5216
21468           52235 : 52230 52231 52232 52233 52234 52235
21469           5225 : 5224 5225
21470           52259 : 52252 52254 52255 52256 52258 52259
21471           5235 : 5232 5233 5234 5235 523x
21472           5249 : 5249
21473           5250 : 5250
21474           5271 : 5270 5271
21475           5272 : 5272
21476           5275 : 5274 5275
21477           5282 : 5280 5281 5282 528x
21478           53017 : 53011 53012 53013 53014 53015 53016 53017
21479           5307 : 5307
21480           5329 : 5327 5328 5329 532x
21481           5373 : 5372 5373 537x
21482           5407 : 5407
21483           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
21484           5485
21485
21486           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
21487           Other combinations of -mcpu and -march are rejected.
21488
21489           GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is
21490           selected.  It also defines "__mcf_family_family", where the value
21491           of family is given by the table above.
21492
21493       -mtune=tune
21494           Tune the code for a particular microarchitecture within the
21495           constraints set by -march and -mcpu.  The M680x0 microarchitectures
21496           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
21497           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
21498
21499           You can also use -mtune=68020-40 for code that needs to run
21500           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
21501           is similar but includes 68060 targets as well.  These two options
21502           select the same tuning decisions as -m68020-40 and -m68020-60
21503           respectively.
21504
21505           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for
21506           680x0 architecture arch.  It also defines "mcarch" unless either
21507           -ansi or a non-GNU -std option is used.  If GCC is tuning for a
21508           range of architectures, as selected by -mtune=68020-40 or
21509           -mtune=68020-60, it defines the macros for every architecture in
21510           the range.
21511
21512           GCC also defines the macro "__muarch__" when tuning for ColdFire
21513           microarchitecture uarch, where uarch is one of the arguments given
21514           above.
21515
21516       -m68000
21517       -mc68000
21518           Generate output for a 68000.  This is the default when the compiler
21519           is configured for 68000-based systems.  It is equivalent to
21520           -march=68000.
21521
21522           Use this option for microcontrollers with a 68000 or EC000 core,
21523           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
21524
21525       -m68010
21526           Generate output for a 68010.  This is the default when the compiler
21527           is configured for 68010-based systems.  It is equivalent to
21528           -march=68010.
21529
21530       -m68020
21531       -mc68020
21532           Generate output for a 68020.  This is the default when the compiler
21533           is configured for 68020-based systems.  It is equivalent to
21534           -march=68020.
21535
21536       -m68030
21537           Generate output for a 68030.  This is the default when the compiler
21538           is configured for 68030-based systems.  It is equivalent to
21539           -march=68030.
21540
21541       -m68040
21542           Generate output for a 68040.  This is the default when the compiler
21543           is configured for 68040-based systems.  It is equivalent to
21544           -march=68040.
21545
21546           This option inhibits the use of 68881/68882 instructions that have
21547           to be emulated by software on the 68040.  Use this option if your
21548           68040 does not have code to emulate those instructions.
21549
21550       -m68060
21551           Generate output for a 68060.  This is the default when the compiler
21552           is configured for 68060-based systems.  It is equivalent to
21553           -march=68060.
21554
21555           This option inhibits the use of 68020 and 68881/68882 instructions
21556           that have to be emulated by software on the 68060.  Use this option
21557           if your 68060 does not have code to emulate those instructions.
21558
21559       -mcpu32
21560           Generate output for a CPU32.  This is the default when the compiler
21561           is configured for CPU32-based systems.  It is equivalent to
21562           -march=cpu32.
21563
21564           Use this option for microcontrollers with a CPU32 or CPU32+ core,
21565           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
21566           68341, 68349 and 68360.
21567
21568       -m5200
21569           Generate output for a 520X ColdFire CPU.  This is the default when
21570           the compiler is configured for 520X-based systems.  It is
21571           equivalent to -mcpu=5206, and is now deprecated in favor of that
21572           option.
21573
21574           Use this option for microcontroller with a 5200 core, including the
21575           MCF5202, MCF5203, MCF5204 and MCF5206.
21576
21577       -m5206e
21578           Generate output for a 5206e ColdFire CPU.  The option is now
21579           deprecated in favor of the equivalent -mcpu=5206e.
21580
21581       -m528x
21582           Generate output for a member of the ColdFire 528X family.  The
21583           option is now deprecated in favor of the equivalent -mcpu=528x.
21584
21585       -m5307
21586           Generate output for a ColdFire 5307 CPU.  The option is now
21587           deprecated in favor of the equivalent -mcpu=5307.
21588
21589       -m5407
21590           Generate output for a ColdFire 5407 CPU.  The option is now
21591           deprecated in favor of the equivalent -mcpu=5407.
21592
21593       -mcfv4e
21594           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
21595           This includes use of hardware floating-point instructions.  The
21596           option is equivalent to -mcpu=547x, and is now deprecated in favor
21597           of that option.
21598
21599       -m68020-40
21600           Generate output for a 68040, without using any of the new
21601           instructions.  This results in code that can run relatively
21602           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
21603           generated code does use the 68881 instructions that are emulated on
21604           the 68040.
21605
21606           The option is equivalent to -march=68020 -mtune=68020-40.
21607
21608       -m68020-60
21609           Generate output for a 68060, without using any of the new
21610           instructions.  This results in code that can run relatively
21611           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
21612           generated code does use the 68881 instructions that are emulated on
21613           the 68060.
21614
21615           The option is equivalent to -march=68020 -mtune=68020-60.
21616
21617       -mhard-float
21618       -m68881
21619           Generate floating-point instructions.  This is the default for
21620           68020 and above, and for ColdFire devices that have an FPU.  It
21621           defines the macro "__HAVE_68881__" on M680x0 targets and
21622           "__mcffpu__" on ColdFire targets.
21623
21624       -msoft-float
21625           Do not generate floating-point instructions; use library calls
21626           instead.  This is the default for 68000, 68010, and 68832 targets.
21627           It is also the default for ColdFire devices that have no FPU.
21628
21629       -mdiv
21630       -mno-div
21631           Generate (do not generate) ColdFire hardware divide and remainder
21632           instructions.  If -march is used without -mcpu, the default is "on"
21633           for ColdFire architectures and "off" for M680x0 architectures.
21634           Otherwise, the default is taken from the target CPU (either the
21635           default CPU, or the one specified by -mcpu).  For example, the
21636           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.
21637
21638           GCC defines the macro "__mcfhwdiv__" when this option is enabled.
21639
21640       -mshort
21641           Consider type "int" to be 16 bits wide, like "short int".
21642           Additionally, parameters passed on the stack are also aligned to a
21643           16-bit boundary even on targets whose API mandates promotion to
21644           32-bit.
21645
21646       -mno-short
21647           Do not consider type "int" to be 16 bits wide.  This is the
21648           default.
21649
21650       -mnobitfield
21651       -mno-bitfield
21652           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
21653           -m5200 options imply -mnobitfield.
21654
21655       -mbitfield
21656           Do use the bit-field instructions.  The -m68020 option implies
21657           -mbitfield.  This is the default if you use a configuration
21658           designed for a 68020.
21659
21660       -mrtd
21661           Use a different function-calling convention, in which functions
21662           that take a fixed number of arguments return with the "rtd"
21663           instruction, which pops their arguments while returning.  This
21664           saves one instruction in the caller since there is no need to pop
21665           the arguments there.
21666
21667           This calling convention is incompatible with the one normally used
21668           on Unix, so you cannot use it if you need to call libraries
21669           compiled with the Unix compiler.
21670
21671           Also, you must provide function prototypes for all functions that
21672           take variable numbers of arguments (including "printf"); otherwise
21673           incorrect code is generated for calls to those functions.
21674
21675           In addition, seriously incorrect code results if you call a
21676           function with too many arguments.  (Normally, extra arguments are
21677           harmlessly ignored.)
21678
21679           The "rtd" instruction is supported by the 68010, 68020, 68030,
21680           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
21681
21682           The default is -mno-rtd.
21683
21684       -malign-int
21685       -mno-align-int
21686           Control whether GCC aligns "int", "long", "long long", "float",
21687           "double", and "long double" variables on a 32-bit boundary
21688           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
21689           variables on 32-bit boundaries produces code that runs somewhat
21690           faster on processors with 32-bit busses at the expense of more
21691           memory.
21692
21693           Warning: if you use the -malign-int switch, GCC aligns structures
21694           containing the above types differently than most published
21695           application binary interface specifications for the m68k.
21696
21697           Use the pc-relative addressing mode of the 68000 directly, instead
21698           of using a global offset table.  At present, this option implies
21699           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
21700           -fPIC is not presently supported with -mpcrel, though this could be
21701           supported for 68020 and higher processors.
21702
21703       -mno-strict-align
21704       -mstrict-align
21705           Do not (do) assume that unaligned memory references are handled by
21706           the system.
21707
21708       -msep-data
21709           Generate code that allows the data segment to be located in a
21710           different area of memory from the text segment.  This allows for
21711           execute-in-place in an environment without virtual memory
21712           management.  This option implies -fPIC.
21713
21714       -mno-sep-data
21715           Generate code that assumes that the data segment follows the text
21716           segment.  This is the default.
21717
21718       -mid-shared-library
21719           Generate code that supports shared libraries via the library ID
21720           method.  This allows for execute-in-place and shared libraries in
21721           an environment without virtual memory management.  This option
21722           implies -fPIC.
21723
21724       -mno-id-shared-library
21725           Generate code that doesn't assume ID-based shared libraries are
21726           being used.  This is the default.
21727
21728       -mshared-library-id=n
21729           Specifies the identification number of the ID-based shared library
21730           being compiled.  Specifying a value of 0 generates more compact
21731           code; specifying other values forces the allocation of that number
21732           to the current library, but is no more space- or time-efficient
21733           than omitting this option.
21734
21735       -mxgot
21736       -mno-xgot
21737           When generating position-independent code for ColdFire, generate
21738           code that works if the GOT has more than 8192 entries.  This code
21739           is larger and slower than code generated without this option.  On
21740           M680x0 processors, this option is not needed; -fPIC suffices.
21741
21742           GCC normally uses a single instruction to load values from the GOT.
21743           While this is relatively efficient, it only works if the GOT is
21744           smaller than about 64k.  Anything larger causes the linker to
21745           report an error such as:
21746
21747                   relocation truncated to fit: R_68K_GOT16O foobar
21748
21749           If this happens, you should recompile your code with -mxgot.  It
21750           should then work with very large GOTs.  However, code generated
21751           with -mxgot is less efficient, since it takes 4 instructions to
21752           fetch the value of a global symbol.
21753
21754           Note that some linkers, including newer versions of the GNU linker,
21755           can create multiple GOTs and sort GOT entries.  If you have such a
21756           linker, you should only need to use -mxgot when compiling a single
21757           object file that accesses more than 8192 GOT entries.  Very few do.
21758
21759           These options have no effect unless GCC is generating position-
21760           independent code.
21761
21762       -mlong-jump-table-offsets
21763           Use 32-bit offsets in "switch" tables.  The default is to use
21764           16-bit offsets.
21765
21766       MCore Options
21767
21768       These are the -m options defined for the Motorola M*Core processors.
21769
21770       -mhardlit
21771       -mno-hardlit
21772           Inline constants into the code stream if it can be done in two
21773           instructions or less.
21774
21775       -mdiv
21776       -mno-div
21777           Use the divide instruction.  (Enabled by default).
21778
21779       -mrelax-immediate
21780       -mno-relax-immediate
21781           Allow arbitrary-sized immediates in bit operations.
21782
21783       -mwide-bitfields
21784       -mno-wide-bitfields
21785           Always treat bit-fields as "int"-sized.
21786
21787       -m4byte-functions
21788       -mno-4byte-functions
21789           Force all functions to be aligned to a 4-byte boundary.
21790
21791       -mcallgraph-data
21792       -mno-callgraph-data
21793           Emit callgraph information.
21794
21795       -mslow-bytes
21796       -mno-slow-bytes
21797           Prefer word access when reading byte quantities.
21798
21799       -mlittle-endian
21800       -mbig-endian
21801           Generate code for a little-endian target.
21802
21803       -m210
21804       -m340
21805           Generate code for the 210 processor.
21806
21807       -mno-lsim
21808           Assume that runtime support has been provided and so omit the
21809           simulator library (libsim.a) from the linker command line.
21810
21811       -mstack-increment=size
21812           Set the maximum amount for a single stack increment operation.
21813           Large values can increase the speed of programs that contain
21814           functions that need a large amount of stack space, but they can
21815           also trigger a segmentation fault if the stack is extended too
21816           much.  The default value is 0x1000.
21817
21818       MeP Options
21819
21820       -mabsdiff
21821           Enables the "abs" instruction, which is the absolute difference
21822           between two registers.
21823
21824       -mall-opts
21825           Enables all the optional instructions---average, multiply, divide,
21826           bit operations, leading zero, absolute difference, min/max, clip,
21827           and saturation.
21828
21829       -maverage
21830           Enables the "ave" instruction, which computes the average of two
21831           registers.
21832
21833       -mbased=n
21834           Variables of size n bytes or smaller are placed in the ".based"
21835           section by default.  Based variables use the $tp register as a base
21836           register, and there is a 128-byte limit to the ".based" section.
21837
21838       -mbitops
21839           Enables the bit operation instructions---bit test ("btstm"), set
21840           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
21841           ("tas").
21842
21843       -mc=name
21844           Selects which section constant data is placed in.  name may be
21845           tiny, near, or far.
21846
21847       -mclip
21848           Enables the "clip" instruction.  Note that -mclip is not useful
21849           unless you also provide -mminmax.
21850
21851       -mconfig=name
21852           Selects one of the built-in core configurations.  Each MeP chip has
21853           one or more modules in it; each module has a core CPU and a variety
21854           of coprocessors, optional instructions, and peripherals.  The
21855           "MeP-Integrator" tool, not part of GCC, provides these
21856           configurations through this option; using this option is the same
21857           as using all the corresponding command-line options.  The default
21858           configuration is default.
21859
21860       -mcop
21861           Enables the coprocessor instructions.  By default, this is a 32-bit
21862           coprocessor.  Note that the coprocessor is normally enabled via the
21863           -mconfig= option.
21864
21865       -mcop32
21866           Enables the 32-bit coprocessor's instructions.
21867
21868       -mcop64
21869           Enables the 64-bit coprocessor's instructions.
21870
21871       -mivc2
21872           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
21873
21874       -mdc
21875           Causes constant variables to be placed in the ".near" section.
21876
21877       -mdiv
21878           Enables the "div" and "divu" instructions.
21879
21880       -meb
21881           Generate big-endian code.
21882
21883       -mel
21884           Generate little-endian code.
21885
21886       -mio-volatile
21887           Tells the compiler that any variable marked with the "io" attribute
21888           is to be considered volatile.
21889
21890       -ml Causes variables to be assigned to the ".far" section by default.
21891
21892       -mleadz
21893           Enables the "leadz" (leading zero) instruction.
21894
21895       -mm Causes variables to be assigned to the ".near" section by default.
21896
21897       -mminmax
21898           Enables the "min" and "max" instructions.
21899
21900       -mmult
21901           Enables the multiplication and multiply-accumulate instructions.
21902
21903       -mno-opts
21904           Disables all the optional instructions enabled by -mall-opts.
21905
21906       -mrepeat
21907           Enables the "repeat" and "erepeat" instructions, used for low-
21908           overhead looping.
21909
21910       -ms Causes all variables to default to the ".tiny" section.  Note that
21911           there is a 65536-byte limit to this section.  Accesses to these
21912           variables use the %gp base register.
21913
21914       -msatur
21915           Enables the saturation instructions.  Note that the compiler does
21916           not currently generate these itself, but this option is included
21917           for compatibility with other tools, like "as".
21918
21919       -msdram
21920           Link the SDRAM-based runtime instead of the default ROM-based
21921           runtime.
21922
21923       -msim
21924           Link the simulator run-time libraries.
21925
21926       -msimnovec
21927           Link the simulator runtime libraries, excluding built-in support
21928           for reset and exception vectors and tables.
21929
21930       -mtf
21931           Causes all functions to default to the ".far" section.  Without
21932           this option, functions default to the ".near" section.
21933
21934       -mtiny=n
21935           Variables that are n bytes or smaller are allocated to the ".tiny"
21936           section.  These variables use the $gp base register.  The default
21937           for this option is 4, but note that there's a 65536-byte limit to
21938           the ".tiny" section.
21939
21940       MicroBlaze Options
21941
21942       -msoft-float
21943           Use software emulation for floating point (default).
21944
21945       -mhard-float
21946           Use hardware floating-point instructions.
21947
21948       -mmemcpy
21949           Do not optimize block moves, use "memcpy".
21950
21951       -mno-clearbss
21952           This option is deprecated.  Use -fno-zero-initialized-in-bss
21953           instead.
21954
21955       -mcpu=cpu-type
21956           Use features of, and schedule code for, the given CPU.  Supported
21957           values are in the format vX.YY.Z, where X is a major version, YY is
21958           the minor version, and Z is compatibility code.  Example values are
21959           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.
21960
21961       -mxl-soft-mul
21962           Use software multiply emulation (default).
21963
21964       -mxl-soft-div
21965           Use software emulation for divides (default).
21966
21967       -mxl-barrel-shift
21968           Use the hardware barrel shifter.
21969
21970       -mxl-pattern-compare
21971           Use pattern compare instructions.
21972
21973       -msmall-divides
21974           Use table lookup optimization for small signed integer divisions.
21975
21976       -mxl-stack-check
21977           This option is deprecated.  Use -fstack-check instead.
21978
21979       -mxl-gp-opt
21980           Use GP-relative ".sdata"/".sbss" sections.
21981
21982       -mxl-multiply-high
21983           Use multiply high instructions for high part of 32x32 multiply.
21984
21985       -mxl-float-convert
21986           Use hardware floating-point conversion instructions.
21987
21988       -mxl-float-sqrt
21989           Use hardware floating-point square root instruction.
21990
21991       -mbig-endian
21992           Generate code for a big-endian target.
21993
21994       -mlittle-endian
21995           Generate code for a little-endian target.
21996
21997       -mxl-reorder
21998           Use reorder instructions (swap and byte reversed load/store).
21999
22000       -mxl-mode-app-model
22001           Select application model app-model.  Valid models are
22002
22003           executable
22004               normal executable (default), uses startup code crt0.o.
22005
22006           xmdstub
22007               for use with Xilinx Microprocessor Debugger (XMD) based
22008               software intrusive debug agent called xmdstub. This uses
22009               startup file crt1.o and sets the start address of the program
22010               to 0x800.
22011
22012           bootstrap
22013               for applications that are loaded using a bootloader.  This
22014               model uses startup file crt2.o which does not contain a
22015               processor reset vector handler. This is suitable for
22016               transferring control on a processor reset to the bootloader
22017               rather than the application.
22018
22019           novectors
22020               for applications that do not require any of the MicroBlaze
22021               vectors. This option may be useful for applications running
22022               within a monitoring application. This model uses crt3.o as a
22023               startup file.
22024
22025           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-
22026           model.
22027
22028       -mpic-data-is-text-relative
22029           Assume that the displacement between the text and data segments is
22030           fixed at static link time.  This allows data to be referenced by
22031           offset from start of text address instead of GOT since PC-relative
22032           addressing is not supported.
22033
22034       MIPS Options
22035
22036       -EB Generate big-endian code.
22037
22038       -EL Generate little-endian code.  This is the default for mips*el-*-*
22039           configurations.
22040
22041       -march=arch
22042           Generate code that runs on arch, which can be the name of a generic
22043           MIPS ISA, or the name of a particular processor.  The ISA names
22044           are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3,
22045           mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and
22046           mips64r6.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
22047           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
22048           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1,
22049           74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400, i6500,
22050           interaptiv, loongson2e, loongson2f, loongson3a, gs464, gs464e,
22051           gs264e, m4k, m14k, m14kc, m14ke, m14kec, m5100, m5101, octeon,
22052           octeon+, octeon2, octeon3, orion, p5600, p6600, r2000, r3000,
22053           r3900, r4000, r4400, r4600, r4650, r4700, r5900, r6000, r8000,
22054           rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000,
22055           vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr
22056           and xlp.  The special value from-abi selects the most compatible
22057           architecture for the selected ABI (that is, mips1 for 32-bit ABIs
22058           and mips3 for 64-bit ABIs).
22059
22060           The native Linux/GNU toolchain also supports the value native,
22061           which selects the best architecture option for the host processor.
22062           -march=native has no effect if GCC does not recognize the
22063           processor.
22064
22065           In processor names, a final 000 can be abbreviated as k (for
22066           example, -march=r2k).  Prefixes are optional, and vr may be written
22067           r.
22068
22069           Names of the form nf2_1 refer to processors with FPUs clocked at
22070           half the rate of the core, names of the form nf1_1 refer to
22071           processors with FPUs clocked at the same rate as the core, and
22072           names of the form nf3_2 refer to processors with FPUs clocked a
22073           ratio of 3:2 with respect to the core.  For compatibility reasons,
22074           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
22075           as synonyms for nf1_1.
22076
22077           GCC defines two macros based on the value of this option.  The
22078           first is "_MIPS_ARCH", which gives the name of target architecture,
22079           as a string.  The second has the form "_MIPS_ARCH_foo", where foo
22080           is the capitalized value of "_MIPS_ARCH".  For example,
22081           -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro
22082           "_MIPS_ARCH_R2000".
22083
22084           Note that the "_MIPS_ARCH" macro uses the processor names given
22085           above.  In other words, it has the full prefix and does not
22086           abbreviate 000 as k.  In the case of from-abi, the macro names the
22087           resolved architecture (either "mips1" or "mips3").  It names the
22088           default architecture when no -march option is given.
22089
22090       -mtune=arch
22091           Optimize for arch.  Among other things, this option controls the
22092           way instructions are scheduled, and the perceived cost of
22093           arithmetic operations.  The list of arch values is the same as for
22094           -march.
22095
22096           When this option is not used, GCC optimizes for the processor
22097           specified by -march.  By using -march and -mtune together, it is
22098           possible to generate code that runs on a family of processors, but
22099           optimize the code for one particular member of that family.
22100
22101           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which
22102           work in the same way as the -march ones described above.
22103
22104       -mips1
22105           Equivalent to -march=mips1.
22106
22107       -mips2
22108           Equivalent to -march=mips2.
22109
22110       -mips3
22111           Equivalent to -march=mips3.
22112
22113       -mips4
22114           Equivalent to -march=mips4.
22115
22116       -mips32
22117           Equivalent to -march=mips32.
22118
22119       -mips32r3
22120           Equivalent to -march=mips32r3.
22121
22122       -mips32r5
22123           Equivalent to -march=mips32r5.
22124
22125       -mips32r6
22126           Equivalent to -march=mips32r6.
22127
22128       -mips64
22129           Equivalent to -march=mips64.
22130
22131       -mips64r2
22132           Equivalent to -march=mips64r2.
22133
22134       -mips64r3
22135           Equivalent to -march=mips64r3.
22136
22137       -mips64r5
22138           Equivalent to -march=mips64r5.
22139
22140       -mips64r6
22141           Equivalent to -march=mips64r6.
22142
22143       -mips16
22144       -mno-mips16
22145           Generate (do not generate) MIPS16 code.  If GCC is targeting a
22146           MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.
22147
22148           MIPS16 code generation can also be controlled on a per-function
22149           basis by means of "mips16" and "nomips16" attributes.
22150
22151       -mflip-mips16
22152           Generate MIPS16 code on alternating functions.  This option is
22153           provided for regression testing of mixed MIPS16/non-MIPS16 code
22154           generation, and is not intended for ordinary use in compiling user
22155           code.
22156
22157       -minterlink-compressed
22158       -mno-interlink-compressed
22159           Require (do not require) that code using the standard
22160           (uncompressed) MIPS ISA be link-compatible with MIPS16 and
22161           microMIPS code, and vice versa.
22162
22163           For example, code using the standard ISA encoding cannot jump
22164           directly to MIPS16 or microMIPS code; it must either use a call or
22165           an indirect jump.  -minterlink-compressed therefore disables direct
22166           jumps unless GCC knows that the target of the jump is not
22167           compressed.
22168
22169       -minterlink-mips16
22170       -mno-interlink-mips16
22171           Aliases of -minterlink-compressed and -mno-interlink-compressed.
22172           These options predate the microMIPS ASE and are retained for
22173           backwards compatibility.
22174
22175       -mabi=32
22176       -mabi=o64
22177       -mabi=n32
22178       -mabi=64
22179       -mabi=eabi
22180           Generate code for the given ABI.
22181
22182           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
22183           generates 64-bit code when you select a 64-bit architecture, but
22184           you can use -mgp32 to get 32-bit code instead.
22185
22186           For information about the O64 ABI, see
22187           <https://gcc.gnu.org/projects/mipso64-abi.html>.
22188
22189           GCC supports a variant of the o32 ABI in which floating-point
22190           registers are 64 rather than 32 bits wide.  You can select this
22191           combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1"
22192           and "mfhc1" instructions and is therefore only supported for
22193           MIPS32R2, MIPS32R3 and MIPS32R5 processors.
22194
22195           The register assignments for arguments and return values remain the
22196           same, but each scalar value is passed in a single 64-bit register
22197           rather than a pair of 32-bit registers.  For example, scalar
22198           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
22199           The set of call-saved registers also remains the same in that the
22200           even-numbered double-precision registers are saved.
22201
22202           Two additional variants of the o32 ABI are supported to enable a
22203           transition from 32-bit to 64-bit registers.  These are FPXX
22204           (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).  The FPXX extension
22205           mandates that all code must execute correctly when run using 32-bit
22206           or 64-bit registers.  The code can be interlinked with either FP32
22207           or FP64, but not both.  The FP64A extension is similar to the FP64
22208           extension but forbids the use of odd-numbered single-precision
22209           registers.  This can be used in conjunction with the "FRE" mode of
22210           FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to
22211           interlink and run in the same process without changing FPU modes.
22212
22213       -mabicalls
22214       -mno-abicalls
22215           Generate (do not generate) code that is suitable for SVR4-style
22216           dynamic objects.  -mabicalls is the default for SVR4-based systems.
22217
22218       -mshared
22219       -mno-shared
22220           Generate (do not generate) code that is fully position-independent,
22221           and that can therefore be linked into shared libraries.  This
22222           option only affects -mabicalls.
22223
22224           All -mabicalls code has traditionally been position-independent,
22225           regardless of options like -fPIC and -fpic.  However, as an
22226           extension, the GNU toolchain allows executables to use absolute
22227           accesses for locally-binding symbols.  It can also use shorter GP
22228           initialization sequences and generate direct calls to locally-
22229           defined functions.  This mode is selected by -mno-shared.
22230
22231           -mno-shared depends on binutils 2.16 or higher and generates
22232           objects that can only be linked by the GNU linker.  However, the
22233           option does not affect the ABI of the final executable; it only
22234           affects the ABI of relocatable objects.  Using -mno-shared
22235           generally makes executables both smaller and quicker.
22236
22237           -mshared is the default.
22238
22239       -mplt
22240       -mno-plt
22241           Assume (do not assume) that the static and dynamic linkers support
22242           PLTs and copy relocations.  This option only affects -mno-shared
22243           -mabicalls.  For the n64 ABI, this option has no effect without
22244           -msym32.
22245
22246           You can make -mplt the default by configuring GCC with
22247           --with-mips-plt.  The default is -mno-plt otherwise.
22248
22249       -mxgot
22250       -mno-xgot
22251           Lift (do not lift) the usual restrictions on the size of the global
22252           offset table.
22253
22254           GCC normally uses a single instruction to load values from the GOT.
22255           While this is relatively efficient, it only works if the GOT is
22256           smaller than about 64k.  Anything larger causes the linker to
22257           report an error such as:
22258
22259                   relocation truncated to fit: R_MIPS_GOT16 foobar
22260
22261           If this happens, you should recompile your code with -mxgot.  This
22262           works with very large GOTs, although the code is also less
22263           efficient, since it takes three instructions to fetch the value of
22264           a global symbol.
22265
22266           Note that some linkers can create multiple GOTs.  If you have such
22267           a linker, you should only need to use -mxgot when a single object
22268           file accesses more than 64k's worth of GOT entries.  Very few do.
22269
22270           These options have no effect unless GCC is generating position
22271           independent code.
22272
22273       -mgp32
22274           Assume that general-purpose registers are 32 bits wide.
22275
22276       -mgp64
22277           Assume that general-purpose registers are 64 bits wide.
22278
22279       -mfp32
22280           Assume that floating-point registers are 32 bits wide.
22281
22282       -mfp64
22283           Assume that floating-point registers are 64 bits wide.
22284
22285       -mfpxx
22286           Do not assume the width of floating-point registers.
22287
22288       -mhard-float
22289           Use floating-point coprocessor instructions.
22290
22291       -msoft-float
22292           Do not use floating-point coprocessor instructions.  Implement
22293           floating-point calculations using library calls instead.
22294
22295       -mno-float
22296           Equivalent to -msoft-float, but additionally asserts that the
22297           program being compiled does not perform any floating-point
22298           operations.  This option is presently supported only by some bare-
22299           metal MIPS configurations, where it may select a special set of
22300           libraries that lack all floating-point support (including, for
22301           example, the floating-point "printf" formats).  If code compiled
22302           with -mno-float accidentally contains floating-point operations, it
22303           is likely to suffer a link-time or run-time failure.
22304
22305       -msingle-float
22306           Assume that the floating-point coprocessor only supports single-
22307           precision operations.
22308
22309       -mdouble-float
22310           Assume that the floating-point coprocessor supports double-
22311           precision operations.  This is the default.
22312
22313       -modd-spreg
22314       -mno-odd-spreg
22315           Enable the use of odd-numbered single-precision floating-point
22316           registers for the o32 ABI.  This is the default for processors that
22317           are known to support these registers.  When using the o32 FPXX ABI,
22318           -mno-odd-spreg is set by default.
22319
22320       -mabs=2008
22321       -mabs=legacy
22322           These options control the treatment of the special not-a-number
22323           (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt"
22324           machine instructions.
22325
22326           By default or when -mabs=legacy is used the legacy treatment is
22327           selected.  In this case these instructions are considered
22328           arithmetic and avoided where correct operation is required and the
22329           input operand might be a NaN.  A longer sequence of instructions
22330           that manipulate the sign bit of floating-point datum manually is
22331           used instead unless the -ffinite-math-only option has also been
22332           specified.
22333
22334           The -mabs=2008 option selects the IEEE 754-2008 treatment.  In this
22335           case these instructions are considered non-arithmetic and therefore
22336           operating correctly in all cases, including in particular where the
22337           input operand is a NaN.  These instructions are therefore always
22338           used for the respective operations.
22339
22340       -mnan=2008
22341       -mnan=legacy
22342           These options control the encoding of the special not-a-number
22343           (NaN) IEEE 754 floating-point data.
22344
22345           The -mnan=legacy option selects the legacy encoding.  In this case
22346           quiet NaNs (qNaNs) are denoted by the first bit of their trailing
22347           significand field being 0, whereas signaling NaNs (sNaNs) are
22348           denoted by the first bit of their trailing significand field being
22349           1.
22350
22351           The -mnan=2008 option selects the IEEE 754-2008 encoding.  In this
22352           case qNaNs are denoted by the first bit of their trailing
22353           significand field being 1, whereas sNaNs are denoted by the first
22354           bit of their trailing significand field being 0.
22355
22356           The default is -mnan=legacy unless GCC has been configured with
22357           --with-nan=2008.
22358
22359       -mllsc
22360       -mno-llsc
22361           Use (do not use) ll, sc, and sync instructions to implement atomic
22362           memory built-in functions.  When neither option is specified, GCC
22363           uses the instructions if the target architecture supports them.
22364
22365           -mllsc is useful if the runtime environment can emulate the
22366           instructions and -mno-llsc can be useful when compiling for
22367           nonstandard ISAs.  You can make either option the default by
22368           configuring GCC with --with-llsc and --without-llsc respectively.
22369           --with-llsc is the default for some configurations; see the
22370           installation documentation for details.
22371
22372       -mdsp
22373       -mno-dsp
22374           Use (do not use) revision 1 of the MIPS DSP ASE.
22375             This option defines the preprocessor macro "__mips_dsp".  It also
22376           defines "__mips_dsp_rev" to 1.
22377
22378       -mdspr2
22379       -mno-dspr2
22380           Use (do not use) revision 2 of the MIPS DSP ASE.
22381             This option defines the preprocessor macros "__mips_dsp" and
22382           "__mips_dspr2".  It also defines "__mips_dsp_rev" to 2.
22383
22384       -msmartmips
22385       -mno-smartmips
22386           Use (do not use) the MIPS SmartMIPS ASE.
22387
22388       -mpaired-single
22389       -mno-paired-single
22390           Use (do not use) paired-single floating-point instructions.
22391             This option requires hardware floating-point support to be
22392           enabled.
22393
22394       -mdmx
22395       -mno-mdmx
22396           Use (do not use) MIPS Digital Media Extension instructions.  This
22397           option can only be used when generating 64-bit code and requires
22398           hardware floating-point support to be enabled.
22399
22400       -mips3d
22401       -mno-mips3d
22402           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
22403           -mpaired-single.
22404
22405       -mmicromips
22406       -mno-micromips
22407           Generate (do not generate) microMIPS code.
22408
22409           MicroMIPS code generation can also be controlled on a per-function
22410           basis by means of "micromips" and "nomicromips" attributes.
22411
22412       -mmt
22413       -mno-mt
22414           Use (do not use) MT Multithreading instructions.
22415
22416       -mmcu
22417       -mno-mcu
22418           Use (do not use) the MIPS MCU ASE instructions.
22419
22420       -meva
22421       -mno-eva
22422           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
22423
22424       -mvirt
22425       -mno-virt
22426           Use (do not use) the MIPS Virtualization (VZ) instructions.
22427
22428       -mxpa
22429       -mno-xpa
22430           Use (do not use) the MIPS eXtended Physical Address (XPA)
22431           instructions.
22432
22433       -mcrc
22434       -mno-crc
22435           Use (do not use) the MIPS Cyclic Redundancy Check (CRC)
22436           instructions.
22437
22438       -mginv
22439       -mno-ginv
22440           Use (do not use) the MIPS Global INValidate (GINV) instructions.
22441
22442       -mloongson-mmi
22443       -mno-loongson-mmi
22444           Use (do not use) the MIPS Loongson MultiMedia extensions
22445           Instructions (MMI).
22446
22447       -mloongson-ext
22448       -mno-loongson-ext
22449           Use (do not use) the MIPS Loongson EXTensions (EXT) instructions.
22450
22451       -mloongson-ext2
22452       -mno-loongson-ext2
22453           Use (do not use) the MIPS Loongson EXTensions r2 (EXT2)
22454           instructions.
22455
22456       -mlong64
22457           Force "long" types to be 64 bits wide.  See -mlong32 for an
22458           explanation of the default and the way that the pointer size is
22459           determined.
22460
22461       -mlong32
22462           Force "long", "int", and pointer types to be 32 bits wide.
22463
22464           The default size of "int"s, "long"s and pointers depends on the
22465           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
22466           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
22467           "long"s.  Pointers are the same size as "long"s, or the same size
22468           as integer registers, whichever is smaller.
22469
22470       -msym32
22471       -mno-sym32
22472           Assume (do not assume) that all symbols have 32-bit values,
22473           regardless of the selected ABI.  This option is useful in
22474           combination with -mabi=64 and -mno-abicalls because it allows GCC
22475           to generate shorter and faster references to symbolic addresses.
22476
22477       -G num
22478           Put definitions of externally-visible data in a small data section
22479           if that data is no bigger than num bytes.  GCC can then generate
22480           more efficient accesses to the data; see -mgpopt for details.
22481
22482           The default -G option depends on the configuration.
22483
22484       -mlocal-sdata
22485       -mno-local-sdata
22486           Extend (do not extend) the -G behavior to local data too, such as
22487           to static variables in C.  -mlocal-sdata is the default for all
22488           configurations.
22489
22490           If the linker complains that an application is using too much small
22491           data, you might want to try rebuilding the less performance-
22492           critical parts with -mno-local-sdata.  You might also want to build
22493           large libraries with -mno-local-sdata, so that the libraries leave
22494           more room for the main program.
22495
22496       -mextern-sdata
22497       -mno-extern-sdata
22498           Assume (do not assume) that externally-defined data is in a small
22499           data section if the size of that data is within the -G limit.
22500           -mextern-sdata is the default for all configurations.
22501
22502           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
22503           Mod references a variable Var that is no bigger than num bytes, you
22504           must make sure that Var is placed in a small data section.  If Var
22505           is defined by another module, you must either compile that module
22506           with a high-enough -G setting or attach a "section" attribute to
22507           Var's definition.  If Var is common, you must link the application
22508           with a high-enough -G setting.
22509
22510           The easiest way of satisfying these restrictions is to compile and
22511           link every module with the same -G option.  However, you may wish
22512           to build a library that supports several different small data
22513           limits.  You can do this by compiling the library with the highest
22514           supported -G setting and additionally using -mno-extern-sdata to
22515           stop the library from making assumptions about externally-defined
22516           data.
22517
22518       -mgpopt
22519       -mno-gpopt
22520           Use (do not use) GP-relative accesses for symbols that are known to
22521           be in a small data section; see -G, -mlocal-sdata and
22522           -mextern-sdata.  -mgpopt is the default for all configurations.
22523
22524           -mno-gpopt is useful for cases where the $gp register might not
22525           hold the value of "_gp".  For example, if the code is part of a
22526           library that might be used in a boot monitor, programs that call
22527           boot monitor routines pass an unknown value in $gp.  (In such
22528           situations, the boot monitor itself is usually compiled with -G0.)
22529
22530           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
22531
22532       -membedded-data
22533       -mno-embedded-data
22534           Allocate variables to the read-only data section first if possible,
22535           then next in the small data section if possible, otherwise in data.
22536           This gives slightly slower code than the default, but reduces the
22537           amount of RAM required when executing, and thus may be preferred
22538           for some embedded systems.
22539
22540       -muninit-const-in-rodata
22541       -mno-uninit-const-in-rodata
22542           Put uninitialized "const" variables in the read-only data section.
22543           This option is only meaningful in conjunction with -membedded-data.
22544
22545       -mcode-readable=setting
22546           Specify whether GCC may generate code that reads from executable
22547           sections.  There are three possible settings:
22548
22549           -mcode-readable=yes
22550               Instructions may freely access executable sections.  This is
22551               the default setting.
22552
22553           -mcode-readable=pcrel
22554               MIPS16 PC-relative load instructions can access executable
22555               sections, but other instructions must not do so.  This option
22556               is useful on 4KSc and 4KSd processors when the code TLBs have
22557               the Read Inhibit bit set.  It is also useful on processors that
22558               can be configured to have a dual instruction/data SRAM
22559               interface and that, like the M4K, automatically redirect PC-
22560               relative loads to the instruction RAM.
22561
22562           -mcode-readable=no
22563               Instructions must not access executable sections.  This option
22564               can be useful on targets that are configured to have a dual
22565               instruction/data SRAM interface but that (unlike the M4K) do
22566               not automatically redirect PC-relative loads to the instruction
22567               RAM.
22568
22569       -msplit-addresses
22570       -mno-split-addresses
22571           Enable (disable) use of the "%hi()" and "%lo()" assembler
22572           relocation operators.  This option has been superseded by
22573           -mexplicit-relocs but is retained for backwards compatibility.
22574
22575       -mexplicit-relocs
22576       -mno-explicit-relocs
22577           Use (do not use) assembler relocation operators when dealing with
22578           symbolic addresses.  The alternative, selected by
22579           -mno-explicit-relocs, is to use assembler macros instead.
22580
22581           -mexplicit-relocs is the default if GCC was configured to use an
22582           assembler that supports relocation operators.
22583
22584       -mcheck-zero-division
22585       -mno-check-zero-division
22586           Trap (do not trap) on integer division by zero.
22587
22588           The default is -mcheck-zero-division.
22589
22590       -mdivide-traps
22591       -mdivide-breaks
22592           MIPS systems check for division by zero by generating either a
22593           conditional trap or a break instruction.  Using traps results in
22594           smaller code, but is only supported on MIPS II and later.  Also,
22595           some versions of the Linux kernel have a bug that prevents trap
22596           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
22597           to allow conditional traps on architectures that support them and
22598           -mdivide-breaks to force the use of breaks.
22599
22600           The default is usually -mdivide-traps, but this can be overridden
22601           at configure time using --with-divide=breaks.  Divide-by-zero
22602           checks can be completely disabled using -mno-check-zero-division.
22603
22604       -mload-store-pairs
22605       -mno-load-store-pairs
22606           Enable (disable) an optimization that pairs consecutive load or
22607           store instructions to enable load/store bonding.  This option is
22608           enabled by default but only takes effect when the selected
22609           architecture is known to support bonding.
22610
22611       -munaligned-access
22612       -mno-unaligned-access
22613           Enable (disable) direct unaligned access for MIPS Release 6.
22614           MIPSr6 requires load/store unaligned-access support, by hardware or
22615           trap&emulate.  So -mno-unaligned-access may be needed by kernel.
22616
22617       -mmemcpy
22618       -mno-memcpy
22619           Force (do not force) the use of "memcpy" for non-trivial block
22620           moves.  The default is -mno-memcpy, which allows GCC to inline most
22621           constant-sized copies.
22622
22623       -mlong-calls
22624       -mno-long-calls
22625           Disable (do not disable) use of the "jal" instruction.  Calling
22626           functions using "jal" is more efficient but requires the caller and
22627           callee to be in the same 256 megabyte segment.
22628
22629           This option has no effect on abicalls code.  The default is
22630           -mno-long-calls.
22631
22632       -mmad
22633       -mno-mad
22634           Enable (disable) use of the "mad", "madu" and "mul" instructions,
22635           as provided by the R4650 ISA.
22636
22637       -mimadd
22638       -mno-imadd
22639           Enable (disable) use of the "madd" and "msub" integer instructions.
22640           The default is -mimadd on architectures that support "madd" and
22641           "msub" except for the 74k architecture where it was found to
22642           generate slower code.
22643
22644       -mfused-madd
22645       -mno-fused-madd
22646           Enable (disable) use of the floating-point multiply-accumulate
22647           instructions, when they are available.  The default is
22648           -mfused-madd.
22649
22650           On the R8000 CPU when multiply-accumulate instructions are used,
22651           the intermediate product is calculated to infinite precision and is
22652           not subject to the FCSR Flush to Zero bit.  This may be undesirable
22653           in some circumstances.  On other processors the result is
22654           numerically identical to the equivalent computation using separate
22655           multiply, add, subtract and negate instructions.
22656
22657       -nocpp
22658           Tell the MIPS assembler to not run its preprocessor over user
22659           assembler files (with a .s suffix) when assembling them.
22660
22661       -mfix-24k
22662       -mno-fix-24k
22663           Work around the 24K E48 (lost data on stores during refill) errata.
22664           The workarounds are implemented by the assembler rather than by
22665           GCC.
22666
22667       -mfix-r4000
22668       -mno-fix-r4000
22669           Work around certain R4000 CPU errata:
22670
22671           -   A double-word or a variable shift may give an incorrect result
22672               if executed immediately after starting an integer division.
22673
22674           -   A double-word or a variable shift may give an incorrect result
22675               if executed while an integer multiplication is in progress.
22676
22677           -   An integer division may give an incorrect result if started in
22678               a delay slot of a taken branch or a jump.
22679
22680       -mfix-r4400
22681       -mno-fix-r4400
22682           Work around certain R4400 CPU errata:
22683
22684           -   A double-word or a variable shift may give an incorrect result
22685               if executed immediately after starting an integer division.
22686
22687       -mfix-r10000
22688       -mno-fix-r10000
22689           Work around certain R10000 errata:
22690
22691           -   "ll"/"sc" sequences may not behave atomically on revisions
22692               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.
22693
22694           This option can only be used if the target architecture supports
22695           branch-likely instructions.  -mfix-r10000 is the default when
22696           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
22697
22698       -mfix-r5900
22699       -mno-fix-r5900
22700           Do not attempt to schedule the preceding instruction into the delay
22701           slot of a branch instruction placed at the end of a short loop of
22702           six instructions or fewer and always schedule a "nop" instruction
22703           there instead.  The short loop bug under certain conditions causes
22704           loops to execute only once or twice, due to a hardware bug in the
22705           R5900 chip.  The workaround is implemented by the assembler rather
22706           than by GCC.
22707
22708       -mfix-rm7000
22709       -mno-fix-rm7000
22710           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds
22711           are implemented by the assembler rather than by GCC.
22712
22713       -mfix-vr4120
22714       -mno-fix-vr4120
22715           Work around certain VR4120 errata:
22716
22717           -   "dmultu" does not always produce the correct result.
22718
22719           -   "div" and "ddiv" do not always produce the correct result if
22720               one of the operands is negative.
22721
22722           The workarounds for the division errata rely on special functions
22723           in libgcc.a.  At present, these functions are only provided by the
22724           "mips64vr*-elf" configurations.
22725
22726           Other VR4120 errata require a NOP to be inserted between certain
22727           pairs of instructions.  These errata are handled by the assembler,
22728           not by GCC itself.
22729
22730       -mfix-vr4130
22731           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
22732           implemented by the assembler rather than by GCC, although GCC
22733           avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
22734           "dmacc" and "dmacchi" instructions are available instead.
22735
22736       -mfix-sb1
22737       -mno-fix-sb1
22738           Work around certain SB-1 CPU core errata.  (This flag currently
22739           works around the SB-1 revision 2 "F1" and "F2" floating-point
22740           errata.)
22741
22742       -mr10k-cache-barrier=setting
22743           Specify whether GCC should insert cache barriers to avoid the side
22744           effects of speculation on R10K processors.
22745
22746           In common with many processors, the R10K tries to predict the
22747           outcome of a conditional branch and speculatively executes
22748           instructions from the "taken" branch.  It later aborts these
22749           instructions if the predicted outcome is wrong.  However, on the
22750           R10K, even aborted instructions can have side effects.
22751
22752           This problem only affects kernel stores and, depending on the
22753           system, kernel loads.  As an example, a speculatively-executed
22754           store may load the target memory into cache and mark the cache line
22755           as dirty, even if the store itself is later aborted.  If a DMA
22756           operation writes to the same area of memory before the "dirty" line
22757           is flushed, the cached data overwrites the DMA-ed data.  See the
22758           R10K processor manual for a full description, including other
22759           potential problems.
22760
22761           One workaround is to insert cache barrier instructions before every
22762           memory access that might be speculatively executed and that might
22763           have side effects even if aborted.  -mr10k-cache-barrier=setting
22764           controls GCC's implementation of this workaround.  It assumes that
22765           aborted accesses to any byte in the following regions does not have
22766           side effects:
22767
22768           1.  the memory occupied by the current function's stack frame;
22769
22770           2.  the memory occupied by an incoming stack argument;
22771
22772           3.  the memory occupied by an object with a link-time-constant
22773               address.
22774
22775           It is the kernel's responsibility to ensure that speculative
22776           accesses to these regions are indeed safe.
22777
22778           If the input program contains a function declaration such as:
22779
22780                   void foo (void);
22781
22782           then the implementation of "foo" must allow "j foo" and "jal foo"
22783           to be executed speculatively.  GCC honors this restriction for
22784           functions it compiles itself.  It expects non-GCC functions (such
22785           as hand-written assembly code) to do the same.
22786
22787           The option has three forms:
22788
22789           -mr10k-cache-barrier=load-store
22790               Insert a cache barrier before a load or store that might be
22791               speculatively executed and that might have side effects even if
22792               aborted.
22793
22794           -mr10k-cache-barrier=store
22795               Insert a cache barrier before a store that might be
22796               speculatively executed and that might have side effects even if
22797               aborted.
22798
22799           -mr10k-cache-barrier=none
22800               Disable the insertion of cache barriers.  This is the default
22801               setting.
22802
22803       -mflush-func=func
22804       -mno-flush-func
22805           Specifies the function to call to flush the I and D caches, or to
22806           not call any such function.  If called, the function must take the
22807           same arguments as the common "_flush_func", that is, the address of
22808           the memory range for which the cache is being flushed, the size of
22809           the memory range, and the number 3 (to flush both caches).  The
22810           default depends on the target GCC was configured for, but commonly
22811           is either "_flush_func" or "__cpu_flush".
22812
22813       mbranch-cost=num
22814           Set the cost of branches to roughly num "simple" instructions.
22815           This cost is only a heuristic and is not guaranteed to produce
22816           consistent results across releases.  A zero cost redundantly
22817           selects the default, which is based on the -mtune setting.
22818
22819       -mbranch-likely
22820       -mno-branch-likely
22821           Enable or disable use of Branch Likely instructions, regardless of
22822           the default for the selected architecture.  By default, Branch
22823           Likely instructions may be generated if they are supported by the
22824           selected architecture.  An exception is for the MIPS32 and MIPS64
22825           architectures and processors that implement those architectures;
22826           for those, Branch Likely instructions are not be generated by
22827           default because the MIPS32 and MIPS64 architectures specifically
22828           deprecate their use.
22829
22830       -mcompact-branches=never
22831       -mcompact-branches=optimal
22832       -mcompact-branches=always
22833           These options control which form of branches will be generated.
22834           The default is -mcompact-branches=optimal.
22835
22836           The -mcompact-branches=never option ensures that compact branch
22837           instructions will never be generated.
22838
22839           The -mcompact-branches=always option ensures that a compact branch
22840           instruction will be generated if available.  If a compact branch
22841           instruction is not available, a delay slot form of the branch will
22842           be used instead.
22843
22844           This option is supported from MIPS Release 6 onwards.
22845
22846           The -mcompact-branches=optimal option will cause a delay slot
22847           branch to be used if one is available in the current ISA and the
22848           delay slot is successfully filled.  If the delay slot is not
22849           filled, a compact branch will be chosen if one is available.
22850
22851       -mfp-exceptions
22852       -mno-fp-exceptions
22853           Specifies whether FP exceptions are enabled.  This affects how FP
22854           instructions are scheduled for some processors.  The default is
22855           that FP exceptions are enabled.
22856
22857           For instance, on the SB-1, if FP exceptions are disabled, and we
22858           are emitting 64-bit code, then we can use both FP pipes.
22859           Otherwise, we can only use one FP pipe.
22860
22861       -mvr4130-align
22862       -mno-vr4130-align
22863           The VR4130 pipeline is two-way superscalar, but can only issue two
22864           instructions together if the first one is 8-byte aligned.  When
22865           this option is enabled, GCC aligns pairs of instructions that it
22866           thinks should execute in parallel.
22867
22868           This option only has an effect when optimizing for the VR4130.  It
22869           normally makes code faster, but at the expense of making it bigger.
22870           It is enabled by default at optimization level -O3.
22871
22872       -msynci
22873       -mno-synci
22874           Enable (disable) generation of "synci" instructions on
22875           architectures that support it.  The "synci" instructions (if
22876           enabled) are generated when "__builtin___clear_cache" is compiled.
22877
22878           This option defaults to -mno-synci, but the default can be
22879           overridden by configuring GCC with --with-synci.
22880
22881           When compiling code for single processor systems, it is generally
22882           safe to use "synci".  However, on many multi-core (SMP) systems, it
22883           does not invalidate the instruction caches on all cores and may
22884           lead to undefined behavior.
22885
22886       -mrelax-pic-calls
22887       -mno-relax-pic-calls
22888           Try to turn PIC calls that are normally dispatched via register $25
22889           into direct calls.  This is only possible if the linker can resolve
22890           the destination at link time and if the destination is within range
22891           for a direct call.
22892
22893           -mrelax-pic-calls is the default if GCC was configured to use an
22894           assembler and a linker that support the ".reloc" assembly directive
22895           and -mexplicit-relocs is in effect.  With -mno-explicit-relocs,
22896           this optimization can be performed by the assembler and the linker
22897           alone without help from the compiler.
22898
22899       -mmcount-ra-address
22900       -mno-mcount-ra-address
22901           Emit (do not emit) code that allows "_mcount" to modify the calling
22902           function's return address.  When enabled, this option extends the
22903           usual "_mcount" interface with a new ra-address parameter, which
22904           has type "intptr_t *" and is passed in register $12.  "_mcount" can
22905           then modify the return address by doing both of the following:
22906
22907           *   Returning the new address in register $31.
22908
22909           *   Storing the new address in "*ra-address", if ra-address is
22910               nonnull.
22911
22912           The default is -mno-mcount-ra-address.
22913
22914       -mframe-header-opt
22915       -mno-frame-header-opt
22916           Enable (disable) frame header optimization in the o32 ABI.  When
22917           using the o32 ABI, calling functions will allocate 16 bytes on the
22918           stack for the called function to write out register arguments.
22919           When enabled, this optimization will suppress the allocation of the
22920           frame header if it can be determined that it is unused.
22921
22922           This optimization is off by default at all optimization levels.
22923
22924       -mlxc1-sxc1
22925       -mno-lxc1-sxc1
22926           When applicable, enable (disable) the generation of "lwxc1",
22927           "swxc1", "ldxc1", "sdxc1" instructions.  Enabled by default.
22928
22929       -mmadd4
22930       -mno-madd4
22931           When applicable, enable (disable) the generation of 4-operand
22932           "madd.s", "madd.d" and related instructions.  Enabled by default.
22933
22934       MMIX Options
22935
22936       These options are defined for the MMIX:
22937
22938       -mlibfuncs
22939       -mno-libfuncs
22940           Specify that intrinsic library functions are being compiled,
22941           passing all values in registers, no matter the size.
22942
22943       -mepsilon
22944       -mno-epsilon
22945           Generate floating-point comparison instructions that compare with
22946           respect to the "rE" epsilon register.
22947
22948       -mabi=mmixware
22949       -mabi=gnu
22950           Generate code that passes function parameters and return values
22951           that (in the called function) are seen as registers $0 and up, as
22952           opposed to the GNU ABI which uses global registers $231 and up.
22953
22954       -mzero-extend
22955       -mno-zero-extend
22956           When reading data from memory in sizes shorter than 64 bits, use
22957           (do not use) zero-extending load instructions by default, rather
22958           than sign-extending ones.
22959
22960       -mknuthdiv
22961       -mno-knuthdiv
22962           Make the result of a division yielding a remainder have the same
22963           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
22964           the remainder follows the sign of the dividend.  Both methods are
22965           arithmetically valid, the latter being almost exclusively used.
22966
22967       -mtoplevel-symbols
22968       -mno-toplevel-symbols
22969           Prepend (do not prepend) a : to all global symbols, so the assembly
22970           code can be used with the "PREFIX" assembly directive.
22971
22972       -melf
22973           Generate an executable in the ELF format, rather than the default
22974           mmo format used by the mmix simulator.
22975
22976       -mbranch-predict
22977       -mno-branch-predict
22978           Use (do not use) the probable-branch instructions, when static
22979           branch prediction indicates a probable branch.
22980
22981       -mbase-addresses
22982       -mno-base-addresses
22983           Generate (do not generate) code that uses base addresses.  Using a
22984           base address automatically generates a request (handled by the
22985           assembler and the linker) for a constant to be set up in a global
22986           register.  The register is used for one or more base address
22987           requests within the range 0 to 255 from the value held in the
22988           register.  The generally leads to short and fast code, but the
22989           number of different data items that can be addressed is limited.
22990           This means that a program that uses lots of static data may require
22991           -mno-base-addresses.
22992
22993       -msingle-exit
22994       -mno-single-exit
22995           Force (do not force) generated code to have a single exit point in
22996           each function.
22997
22998       MN10300 Options
22999
23000       These -m options are defined for Matsushita MN10300 architectures:
23001
23002       -mmult-bug
23003           Generate code to avoid bugs in the multiply instructions for the
23004           MN10300 processors.  This is the default.
23005
23006       -mno-mult-bug
23007           Do not generate code to avoid bugs in the multiply instructions for
23008           the MN10300 processors.
23009
23010       -mam33
23011           Generate code using features specific to the AM33 processor.
23012
23013       -mno-am33
23014           Do not generate code using features specific to the AM33 processor.
23015           This is the default.
23016
23017       -mam33-2
23018           Generate code using features specific to the AM33/2.0 processor.
23019
23020       -mam34
23021           Generate code using features specific to the AM34 processor.
23022
23023       -mtune=cpu-type
23024           Use the timing characteristics of the indicated CPU type when
23025           scheduling instructions.  This does not change the targeted
23026           processor type.  The CPU type must be one of mn10300, am33, am33-2
23027           or am34.
23028
23029       -mreturn-pointer-on-d0
23030           When generating a function that returns a pointer, return the
23031           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
23032           only in "a0", and attempts to call such functions without a
23033           prototype result in errors.  Note that this option is on by
23034           default; use -mno-return-pointer-on-d0 to disable it.
23035
23036       -mno-crt0
23037           Do not link in the C run-time initialization object file.
23038
23039       -mrelax
23040           Indicate to the linker that it should perform a relaxation
23041           optimization pass to shorten branches, calls and absolute memory
23042           addresses.  This option only has an effect when used on the command
23043           line for the final link step.
23044
23045           This option makes symbolic debugging impossible.
23046
23047       -mliw
23048           Allow the compiler to generate Long Instruction Word instructions
23049           if the target is the AM33 or later.  This is the default.  This
23050           option defines the preprocessor macro "__LIW__".
23051
23052       -mno-liw
23053           Do not allow the compiler to generate Long Instruction Word
23054           instructions.  This option defines the preprocessor macro
23055           "__NO_LIW__".
23056
23057       -msetlb
23058           Allow the compiler to generate the SETLB and Lcc instructions if
23059           the target is the AM33 or later.  This is the default.  This option
23060           defines the preprocessor macro "__SETLB__".
23061
23062       -mno-setlb
23063           Do not allow the compiler to generate SETLB or Lcc instructions.
23064           This option defines the preprocessor macro "__NO_SETLB__".
23065
23066       Moxie Options
23067
23068       -meb
23069           Generate big-endian code.  This is the default for moxie-*-*
23070           configurations.
23071
23072       -mel
23073           Generate little-endian code.
23074
23075       -mmul.x
23076           Generate mul.x and umul.x instructions.  This is the default for
23077           moxiebox-*-* configurations.
23078
23079       -mno-crt0
23080           Do not link in the C run-time initialization object file.
23081
23082       MSP430 Options
23083
23084       These options are defined for the MSP430:
23085
23086       -masm-hex
23087           Force assembly output to always use hex constants.  Normally such
23088           constants are signed decimals, but this option is available for
23089           testsuite and/or aesthetic purposes.
23090
23091       -mmcu=
23092           Select the MCU to target.  This is used to create a C preprocessor
23093           symbol based upon the MCU name, converted to upper case and pre-
23094           and post-fixed with __.  This in turn is used by the msp430.h
23095           header file to select an MCU-specific supplementary header file.
23096
23097           The option also sets the ISA to use.  If the MCU name is one that
23098           is known to only support the 430 ISA then that is selected,
23099           otherwise the 430X ISA is selected.  A generic MCU name of msp430
23100           can also be used to select the 430 ISA.  Similarly the generic
23101           msp430x MCU name selects the 430X ISA.
23102
23103           In addition an MCU-specific linker script is added to the linker
23104           command line.  The script's name is the name of the MCU with .ld
23105           appended.  Thus specifying -mmcu=xxx on the gcc command line
23106           defines the C preprocessor symbol "__XXX__" and cause the linker to
23107           search for a script called xxx.ld.
23108
23109           The ISA and hardware multiply supported for the different MCUs is
23110           hard-coded into GCC.  However, an external devices.csv file can be
23111           used to extend device support beyond those that have been hard-
23112           coded.
23113
23114           GCC searches for the devices.csv file using the following methods
23115           in the given precedence order, where the first method takes
23116           precendence over the second which takes precedence over the third.
23117
23118           Include path specified with "-I" and "-L"
23119               devices.csv will be searched for in each of the directories
23120               specified by include paths and linker library search paths.
23121
23122           Path specified by the environment variable MSP430_GCC_INCLUDE_DIR
23123               Define the value of the global environment variable
23124               MSP430_GCC_INCLUDE_DIR to the full path to the directory
23125               containing devices.csv, and GCC will search this directory for
23126               devices.csv.  If devices.csv is found, this directory will also
23127               be registered as an include path, and linker library path.
23128               Header files and linker scripts in this directory can therefore
23129               be used without manually specifying "-I" and "-L" on the
23130               command line.
23131
23132           The msp430-elf{,bare}/include/devices directory
23133               Finally, GCC will examine msp430-elf{,bare}/include/devices
23134               from the toolchain root directory.  This directory does not
23135               exist in a default installation, but if the user has created it
23136               and copied devices.csv there, then the MCU data will be read.
23137               As above, this directory will also be registered as an include
23138               path, and linker library path.
23139
23140           If none of the above search methods find devices.csv, then the
23141           hard-coded MCU data is used.
23142
23143       -mwarn-mcu
23144       -mno-warn-mcu
23145           This option enables or disables warnings about conflicts between
23146           the MCU name specified by the -mmcu option and the ISA set by the
23147           -mcpu option and/or the hardware multiply support set by the
23148           -mhwmult option.  It also toggles warnings about unrecognized MCU
23149           names.  This option is on by default.
23150
23151       -mcpu=
23152           Specifies the ISA to use.  Accepted values are msp430, msp430x and
23153           msp430xv2.  This option is deprecated.  The -mmcu= option should be
23154           used to select the ISA.
23155
23156       -msim
23157           Link to the simulator runtime libraries and linker script.
23158           Overrides any scripts that would be selected by the -mmcu= option.
23159
23160       -mlarge
23161           Use large-model addressing (20-bit pointers, 20-bit "size_t").
23162
23163       -msmall
23164           Use small-model addressing (16-bit pointers, 16-bit "size_t").
23165
23166       -mrelax
23167           This option is passed to the assembler and linker, and allows the
23168           linker to perform certain optimizations that cannot be done until
23169           the final link.
23170
23171       mhwmult=
23172           Describes the type of hardware multiply supported by the target.
23173           Accepted values are none for no hardware multiply, 16bit for the
23174           original 16-bit-only multiply supported by early MCUs.  32bit for
23175           the 16/32-bit multiply supported by later MCUs and f5series for the
23176           16/32-bit multiply supported by F5-series MCUs.  A value of auto
23177           can also be given.  This tells GCC to deduce the hardware multiply
23178           support based upon the MCU name provided by the -mmcu option.  If
23179           no -mmcu option is specified or if the MCU name is not recognized
23180           then no hardware multiply support is assumed.  "auto" is the
23181           default setting.
23182
23183           Hardware multiplies are normally performed by calling a library
23184           routine.  This saves space in the generated code.  When compiling
23185           at -O3 or higher however the hardware multiplier is invoked inline.
23186           This makes for bigger, but faster code.
23187
23188           The hardware multiply routines disable interrupts whilst running
23189           and restore the previous interrupt state when they finish.  This
23190           makes them safe to use inside interrupt handlers as well as in
23191           normal code.
23192
23193       -minrt
23194           Enable the use of a minimum runtime environment - no static
23195           initializers or constructors.  This is intended for memory-
23196           constrained devices.  The compiler includes special symbols in some
23197           objects that tell the linker and runtime which code fragments are
23198           required.
23199
23200       -mtiny-printf
23201           Enable reduced code size "printf" and "puts" library functions.
23202           The tiny implementations of these functions are not reentrant, so
23203           must be used with caution in multi-threaded applications.
23204
23205           Support for streams has been removed and the string to be printed
23206           will always be sent to stdout via the "write" syscall.  The string
23207           is not buffered before it is sent to write.
23208
23209           This option requires Newlib Nano IO, so GCC must be configured with
23210           --enable-newlib-nano-formatted-io.
23211
23212       -mmax-inline-shift=
23213           This option takes an integer between 0 and 64 inclusive, and sets
23214           the maximum number of inline shift instructions which should be
23215           emitted to perform a shift operation by a constant amount.  When
23216           this value needs to be exceeded, an mspabi helper function is used
23217           instead.  The default value is 4.
23218
23219           This only affects cases where a shift by multiple positions cannot
23220           be completed with a single instruction (e.g. all shifts >1 on the
23221           430 ISA).
23222
23223           Shifts of a 32-bit value are at least twice as costly, so the value
23224           passed for this option is divided by 2 and the resulting value used
23225           instead.
23226
23227       -mcode-region=
23228       -mdata-region=
23229           These options tell the compiler where to place functions and data
23230           that do not have one of the "lower", "upper", "either" or "section"
23231           attributes.  Possible values are "lower", "upper", "either" or
23232           "any".  The first three behave like the corresponding attribute.
23233           The fourth possible value - "any" - is the default.  It leaves
23234           placement entirely up to the linker script and how it assigns the
23235           standard sections (".text", ".data", etc) to the memory regions.
23236
23237       -msilicon-errata=
23238           This option passes on a request to assembler to enable the fixes
23239           for the named silicon errata.
23240
23241       -msilicon-errata-warn=
23242           This option passes on a request to the assembler to enable warning
23243           messages when a silicon errata might need to be applied.
23244
23245       -mwarn-devices-csv
23246       -mno-warn-devices-csv
23247           Warn if devices.csv is not found or there are problem parsing it
23248           (default: on).
23249
23250       NDS32 Options
23251
23252       These options are defined for NDS32 implementations:
23253
23254       -mbig-endian
23255           Generate code in big-endian mode.
23256
23257       -mlittle-endian
23258           Generate code in little-endian mode.
23259
23260       -mreduced-regs
23261           Use reduced-set registers for register allocation.
23262
23263       -mfull-regs
23264           Use full-set registers for register allocation.
23265
23266       -mcmov
23267           Generate conditional move instructions.
23268
23269       -mno-cmov
23270           Do not generate conditional move instructions.
23271
23272       -mext-perf
23273           Generate performance extension instructions.
23274
23275       -mno-ext-perf
23276           Do not generate performance extension instructions.
23277
23278       -mext-perf2
23279           Generate performance extension 2 instructions.
23280
23281       -mno-ext-perf2
23282           Do not generate performance extension 2 instructions.
23283
23284       -mext-string
23285           Generate string extension instructions.
23286
23287       -mno-ext-string
23288           Do not generate string extension instructions.
23289
23290       -mv3push
23291           Generate v3 push25/pop25 instructions.
23292
23293       -mno-v3push
23294           Do not generate v3 push25/pop25 instructions.
23295
23296       -m16-bit
23297           Generate 16-bit instructions.
23298
23299       -mno-16-bit
23300           Do not generate 16-bit instructions.
23301
23302       -misr-vector-size=num
23303           Specify the size of each interrupt vector, which must be 4 or 16.
23304
23305       -mcache-block-size=num
23306           Specify the size of each cache block, which must be a power of 2
23307           between 4 and 512.
23308
23309       -march=arch
23310           Specify the name of the target architecture.
23311
23312       -mcmodel=code-model
23313           Set the code model to one of
23314
23315           small
23316               All the data and read-only data segments must be within 512KB
23317               addressing space.  The text segment must be within 16MB
23318               addressing space.
23319
23320           medium
23321               The data segment must be within 512KB while the read-only data
23322               segment can be within 4GB addressing space.  The text segment
23323               should be still within 16MB addressing space.
23324
23325           large
23326               All the text and data segments can be within 4GB addressing
23327               space.
23328
23329       -mctor-dtor
23330           Enable constructor/destructor feature.
23331
23332       -mrelax
23333           Guide linker to relax instructions.
23334
23335       Nios II Options
23336
23337       These are the options defined for the Altera Nios II processor.
23338
23339       -G num
23340           Put global and static objects less than or equal to num bytes into
23341           the small data or BSS sections instead of the normal data or BSS
23342           sections.  The default value of num is 8.
23343
23344       -mgpopt=option
23345       -mgpopt
23346       -mno-gpopt
23347           Generate (do not generate) GP-relative accesses.  The following
23348           option names are recognized:
23349
23350           none
23351               Do not generate GP-relative accesses.
23352
23353           local
23354               Generate GP-relative accesses for small data objects that are
23355               not external, weak, or uninitialized common symbols.  Also use
23356               GP-relative addressing for objects that have been explicitly
23357               placed in a small data section via a "section" attribute.
23358
23359           global
23360               As for local, but also generate GP-relative accesses for small
23361               data objects that are external, weak, or common.  If you use
23362               this option, you must ensure that all parts of your program
23363               (including libraries) are compiled with the same -G setting.
23364
23365           data
23366               Generate GP-relative accesses for all data objects in the
23367               program.  If you use this option, the entire data and BSS
23368               segments of your program must fit in 64K of memory and you must
23369               use an appropriate linker script to allocate them within the
23370               addressable range of the global pointer.
23371
23372           all Generate GP-relative addresses for function pointers as well as
23373               data pointers.  If you use this option, the entire text, data,
23374               and BSS segments of your program must fit in 64K of memory and
23375               you must use an appropriate linker script to allocate them
23376               within the addressable range of the global pointer.
23377
23378           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is
23379           equivalent to -mgpopt=none.
23380
23381           The default is -mgpopt except when -fpic or -fPIC is specified to
23382           generate position-independent code.  Note that the Nios II ABI does
23383           not permit GP-relative accesses from shared libraries.
23384
23385           You may need to specify -mno-gpopt explicitly when building
23386           programs that include large amounts of small data, including large
23387           GOT data sections.  In this case, the 16-bit offset for GP-relative
23388           addressing may not be large enough to allow access to the entire
23389           small data section.
23390
23391       -mgprel-sec=regexp
23392           This option specifies additional section names that can be accessed
23393           via GP-relative addressing.  It is most useful in conjunction with
23394           "section" attributes on variable declarations and a custom linker
23395           script.  The regexp is a POSIX Extended Regular Expression.
23396
23397           This option does not affect the behavior of the -G option, and the
23398           specified sections are in addition to the standard ".sdata" and
23399           ".sbss" small-data sections that are recognized by -mgpopt.
23400
23401       -mr0rel-sec=regexp
23402           This option specifies names of sections that can be accessed via a
23403           16-bit offset from "r0"; that is, in the low 32K or high 32K of the
23404           32-bit address space.  It is most useful in conjunction with
23405           "section" attributes on variable declarations and a custom linker
23406           script.  The regexp is a POSIX Extended Regular Expression.
23407
23408           In contrast to the use of GP-relative addressing for small data,
23409           zero-based addressing is never generated by default and there are
23410           no conventional section names used in standard linker scripts for
23411           sections in the low or high areas of memory.
23412
23413       -mel
23414       -meb
23415           Generate little-endian (default) or big-endian (experimental) code,
23416           respectively.
23417
23418       -march=arch
23419           This specifies the name of the target Nios II architecture.  GCC
23420           uses this name to determine what kind of instructions it can emit
23421           when generating assembly code.  Permissible names are: r1, r2.
23422
23423           The preprocessor macro "__nios2_arch__" is available to programs,
23424           with value 1 or 2, indicating the targeted ISA level.
23425
23426       -mbypass-cache
23427       -mno-bypass-cache
23428           Force all load and store instructions to always bypass cache by
23429           using I/O variants of the instructions. The default is not to
23430           bypass the cache.
23431
23432       -mno-cache-volatile
23433       -mcache-volatile
23434           Volatile memory access bypass the cache using the I/O variants of
23435           the load and store instructions. The default is not to bypass the
23436           cache.
23437
23438       -mno-fast-sw-div
23439       -mfast-sw-div
23440           Do not use table-based fast divide for small numbers. The default
23441           is to use the fast divide at -O3 and above.
23442
23443       -mno-hw-mul
23444       -mhw-mul
23445       -mno-hw-mulx
23446       -mhw-mulx
23447       -mno-hw-div
23448       -mhw-div
23449           Enable or disable emitting "mul", "mulx" and "div" family of
23450           instructions by the compiler. The default is to emit "mul" and not
23451           emit "div" and "mulx".
23452
23453       -mbmx
23454       -mno-bmx
23455       -mcdx
23456       -mno-cdx
23457           Enable or disable generation of Nios II R2 BMX (bit manipulation)
23458           and CDX (code density) instructions.  Enabling these instructions
23459           also requires -march=r2.  Since these instructions are optional
23460           extensions to the R2 architecture, the default is not to emit them.
23461
23462       -mcustom-insn=N
23463       -mno-custom-insn
23464           Each -mcustom-insn=N option enables use of a custom instruction
23465           with encoding N when generating code that uses insn.  For example,
23466           -mcustom-fadds=253 generates custom instruction 253 for single-
23467           precision floating-point add operations instead of the default
23468           behavior of using a library call.
23469
23470           The following values of insn are supported.  Except as otherwise
23471           noted, floating-point operations are expected to be implemented
23472           with normal IEEE 754 semantics and correspond directly to the C
23473           operators or the equivalent GCC built-in functions.
23474
23475           Single-precision floating point:
23476
23477           fadds, fsubs, fdivs, fmuls
23478               Binary arithmetic operations.
23479
23480           fnegs
23481               Unary negation.
23482
23483           fabss
23484               Unary absolute value.
23485
23486           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
23487               Comparison operations.
23488
23489           fmins, fmaxs
23490               Floating-point minimum and maximum.  These instructions are
23491               only generated if -ffinite-math-only is specified.
23492
23493           fsqrts
23494               Unary square root operation.
23495
23496           fcoss, fsins, ftans, fatans, fexps, flogs
23497               Floating-point trigonometric and exponential functions.  These
23498               instructions are only generated if -funsafe-math-optimizations
23499               is also specified.
23500
23501           Double-precision floating point:
23502
23503           faddd, fsubd, fdivd, fmuld
23504               Binary arithmetic operations.
23505
23506           fnegd
23507               Unary negation.
23508
23509           fabsd
23510               Unary absolute value.
23511
23512           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
23513               Comparison operations.
23514
23515           fmind, fmaxd
23516               Double-precision minimum and maximum.  These instructions are
23517               only generated if -ffinite-math-only is specified.
23518
23519           fsqrtd
23520               Unary square root operation.
23521
23522           fcosd, fsind, ftand, fatand, fexpd, flogd
23523               Double-precision trigonometric and exponential functions.
23524               These instructions are only generated if
23525               -funsafe-math-optimizations is also specified.
23526
23527           Conversions:
23528
23529           fextsd
23530               Conversion from single precision to double precision.
23531
23532           ftruncds
23533               Conversion from double precision to single precision.
23534
23535           fixsi, fixsu, fixdi, fixdu
23536               Conversion from floating point to signed or unsigned integer
23537               types, with truncation towards zero.
23538
23539           round
23540               Conversion from single-precision floating point to signed
23541               integer, rounding to the nearest integer and ties away from
23542               zero.  This corresponds to the "__builtin_lroundf" function
23543               when -fno-math-errno is used.
23544
23545           floatis, floatus, floatid, floatud
23546               Conversion from signed or unsigned integer types to floating-
23547               point types.
23548
23549           In addition, all of the following transfer instructions for
23550           internal registers X and Y must be provided to use any of the
23551           double-precision floating-point instructions.  Custom instructions
23552           taking two double-precision source operands expect the first
23553           operand in the 64-bit register X.  The other operand (or only
23554           operand of a unary operation) is given to the custom arithmetic
23555           instruction with the least significant half in source register src1
23556           and the most significant half in src2.  A custom instruction that
23557           returns a double-precision result returns the most significant 32
23558           bits in the destination register and the other half in 32-bit
23559           register Y.  GCC automatically generates the necessary code
23560           sequences to write register X and/or read register Y when double-
23561           precision floating-point instructions are used.
23562
23563           fwrx
23564               Write src1 into the least significant half of X and src2 into
23565               the most significant half of X.
23566
23567           fwry
23568               Write src1 into Y.
23569
23570           frdxhi, frdxlo
23571               Read the most or least (respectively) significant half of X and
23572               store it in dest.
23573
23574           frdy
23575               Read the value of Y and store it into dest.
23576
23577           Note that you can gain more local control over generation of Nios
23578           II custom instructions by using the "target("custom-insn=N")" and
23579           "target("no-custom-insn")" function attributes or pragmas.
23580
23581       -mcustom-fpu-cfg=name
23582           This option enables a predefined, named set of custom instruction
23583           encodings (see -mcustom-insn above).  Currently, the following sets
23584           are defined:
23585
23586           -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252
23587           -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant
23588
23589           -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252
23590           -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255
23591           -fsingle-precision-constant
23592
23593           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243
23594           -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246
23595           -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251
23596           -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254
23597           -mcustom-fdivs=255 -fsingle-precision-constant
23598
23599           -mcustom-fpu-cfg=fph2 is equivalent to: -mcustom-fabss=224
23600           -mcustom-fnegs=225 -mcustom-fcmpnes=226 -mcustom-fcmpeqs=227
23601           -mcustom-fcmpges=228 -mcustom-fcmpgts=229 -mcustom-fcmples=230
23602           -mcustom-fcmplts=231 -mcustom-fmaxs=232 -mcustom-fmins=233
23603           -mcustom-round=248 -mcustom-fixsi=249 -mcustom-floatis=250
23604           -mcustom-fsqrts=251 -mcustom-fmuls=252 -mcustom-fadds=253
23605           -mcustom-fsubs=254 -mcustom-fdivs=255
23606
23607           Custom instruction assignments given by individual -mcustom-insn=
23608           options override those given by -mcustom-fpu-cfg=, regardless of
23609           the order of the options on the command line.
23610
23611           Note that you can gain more local control over selection of a FPU
23612           configuration by using the "target("custom-fpu-cfg=name")" function
23613           attribute or pragma.
23614
23615           The name fph2 is an abbreviation for Nios II Floating Point
23616           Hardware 2 Component.  Please note that the custom instructions
23617           enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are only
23618           generated if -ffinite-math-only is specified.  The custom
23619           instruction enabled by -mcustom-round=248 is only generated if
23620           -fno-math-errno is specified.  In contrast to the other
23621           configurations, -fsingle-precision-constant is not set.
23622
23623       These additional -m options are available for the Altera Nios II ELF
23624       (bare-metal) target:
23625
23626       -mhal
23627           Link with HAL BSP.  This suppresses linking with the GCC-provided C
23628           runtime startup and termination code, and is typically used in
23629           conjunction with -msys-crt0= to specify the location of the
23630           alternate startup code provided by the HAL BSP.
23631
23632       -msmallc
23633           Link with a limited version of the C library, -lsmallc, rather than
23634           Newlib.
23635
23636       -msys-crt0=startfile
23637           startfile is the file name of the startfile (crt0) to use when
23638           linking.  This option is only useful in conjunction with -mhal.
23639
23640       -msys-lib=systemlib
23641           systemlib is the library name of the library that provides low-
23642           level system calls required by the C library, e.g. "read" and
23643           "write".  This option is typically used to link with a library
23644           provided by a HAL BSP.
23645
23646       Nvidia PTX Options
23647
23648       These options are defined for Nvidia PTX:
23649
23650       -m64
23651           Ignored, but preserved for backward compatibility.  Only 64-bit ABI
23652           is supported.
23653
23654       -march=architecture-string
23655           Generate code for the specified PTX ISA target architecture (e.g.
23656           sm_35).  Valid architecture strings are sm_30, sm_35, sm_53, sm_70,
23657           sm_75 and sm_80.  The default target architecture is sm_30.
23658
23659           This option sets the value of the preprocessor macro "__PTX_SM__";
23660           for instance, for sm_35, it has the value 350.
23661
23662       -misa=architecture-string
23663           Alias of -march=.
23664
23665       -march-map=architecture-string
23666           Select the closest available -march= value that is not more
23667           capable.  For instance, for -march-map=sm_50 select -march=sm_35,
23668           and for -march-map=sm_53 select -march=sm_53.
23669
23670       -mptx=version-string
23671           Generate code for the specified PTX ISA version (e.g. 7.0).  Valid
23672           version strings include 3.1, 6.0, 6.3, and 7.0.  The default PTX
23673           ISA version is 6.0, unless a higher version is required for
23674           specified PTX ISA target architecture via option -march=.
23675
23676           This option sets the values of the preprocessor macros
23677           "__PTX_ISA_VERSION_MAJOR__" and "__PTX_ISA_VERSION_MINOR__"; for
23678           instance, for 3.1 the macros have the values 3 and 1, respectively.
23679
23680       -mmainkernel
23681           Link in code for a __main kernel.  This is for stand-alone instead
23682           of offloading execution.
23683
23684       -moptimize
23685           Apply partitioned execution optimizations.  This is the default
23686           when any level of optimization is selected.
23687
23688       -msoft-stack
23689           Generate code that does not use ".local" memory directly for stack
23690           storage. Instead, a per-warp stack pointer is maintained
23691           explicitly. This enables variable-length stack allocation (with
23692           variable-length arrays or "alloca"), and when global memory is used
23693           for underlying storage, makes it possible to access automatic
23694           variables from other threads, or with atomic instructions. This
23695           code generation variant is used for OpenMP offloading, but the
23696           option is exposed on its own for the purpose of testing the
23697           compiler; to generate code suitable for linking into programs using
23698           OpenMP offloading, use option -mgomp.
23699
23700       -muniform-simt
23701           Switch to code generation variant that allows to execute all
23702           threads in each warp, while maintaining memory state and side
23703           effects as if only one thread in each warp was active outside of
23704           OpenMP SIMD regions.  All atomic operations and calls to runtime
23705           (malloc, free, vprintf) are conditionally executed (iff current
23706           lane index equals the master lane index), and the register being
23707           assigned is copied via a shuffle instruction from the master lane.
23708           Outside of SIMD regions lane 0 is the master; inside, each thread
23709           sees itself as the master.  Shared memory array "int __nvptx_uni[]"
23710           stores all-zeros or all-ones bitmasks for each warp, indicating
23711           current mode (0 outside of SIMD regions).  Each thread can bitwise-
23712           and the bitmask at position "tid.y" with current lane index to
23713           compute the master lane index.
23714
23715       -mgomp
23716           Generate code for use in OpenMP offloading: enables -msoft-stack
23717           and -muniform-simt options, and selects corresponding multilib
23718           variant.
23719
23720       OpenRISC Options
23721
23722       These options are defined for OpenRISC:
23723
23724       -mboard=name
23725           Configure a board specific runtime.  This will be passed to the
23726           linker for newlib board library linking.  The default is "or1ksim".
23727
23728       -mnewlib
23729           This option is ignored; it is for compatibility purposes only.
23730           This used to select linker and preprocessor options for use with
23731           newlib.
23732
23733       -msoft-div
23734       -mhard-div
23735           Select software or hardware divide ("l.div", "l.divu")
23736           instructions.  This default is hardware divide.
23737
23738       -msoft-mul
23739       -mhard-mul
23740           Select software or hardware multiply ("l.mul", "l.muli")
23741           instructions.  This default is hardware multiply.
23742
23743       -msoft-float
23744       -mhard-float
23745           Select software or hardware for floating point operations.  The
23746           default is software.
23747
23748       -mdouble-float
23749           When -mhard-float is selected, enables generation of double-
23750           precision floating point instructions.  By default functions from
23751           libgcc are used to perform double-precision floating point
23752           operations.
23753
23754       -munordered-float
23755           When -mhard-float is selected, enables generation of unordered
23756           floating point compare and set flag ("lf.sfun*") instructions.  By
23757           default functions from libgcc are used to perform unordered
23758           floating point compare and set flag operations.
23759
23760       -mcmov
23761           Enable generation of conditional move ("l.cmov") instructions.  By
23762           default the equivalent will be generated using set and branch.
23763
23764       -mror
23765           Enable generation of rotate right ("l.ror") instructions.  By
23766           default functions from libgcc are used to perform rotate right
23767           operations.
23768
23769       -mrori
23770           Enable generation of rotate right with immediate ("l.rori")
23771           instructions.  By default functions from libgcc are used to perform
23772           rotate right with immediate operations.
23773
23774       -msext
23775           Enable generation of sign extension ("l.ext*") instructions.  By
23776           default memory loads are used to perform sign extension.
23777
23778       -msfimm
23779           Enable generation of compare and set flag with immediate ("l.sf*i")
23780           instructions.  By default extra instructions will be generated to
23781           store the immediate to a register first.
23782
23783       -mshftimm
23784           Enable generation of shift with immediate ("l.srai", "l.srli",
23785           "l.slli") instructions.  By default extra instructions will be
23786           generated to store the immediate to a register first.
23787
23788       -mcmodel=small
23789           Generate OpenRISC code for the small model: The GOT is limited to
23790           64k. This is the default model.
23791
23792       -mcmodel=large
23793           Generate OpenRISC code for the large model: The GOT may grow up to
23794           4G in size.
23795
23796       PDP-11 Options
23797
23798       These options are defined for the PDP-11:
23799
23800       -mfpu
23801           Use hardware FPP floating point.  This is the default.  (FIS
23802           floating point on the PDP-11/40 is not supported.)  Implies -m45.
23803
23804       -msoft-float
23805           Do not use hardware floating point.
23806
23807       -mac0
23808           Return floating-point results in ac0 (fr0 in Unix assembler
23809           syntax).
23810
23811       -mno-ac0
23812           Return floating-point results in memory.  This is the default.
23813
23814       -m40
23815           Generate code for a PDP-11/40.  Implies -msoft-float -mno-split.
23816
23817       -m45
23818           Generate code for a PDP-11/45.  This is the default.
23819
23820       -m10
23821           Generate code for a PDP-11/10.  Implies -msoft-float -mno-split.
23822
23823       -mint16
23824       -mno-int32
23825           Use 16-bit "int".  This is the default.
23826
23827       -mint32
23828       -mno-int16
23829           Use 32-bit "int".
23830
23831       -msplit
23832           Target has split instruction and data space.  Implies -m45.
23833
23834       -munix-asm
23835           Use Unix assembler syntax.
23836
23837       -mdec-asm
23838           Use DEC assembler syntax.
23839
23840       -mgnu-asm
23841           Use GNU assembler syntax.  This is the default.
23842
23843       -mlra
23844           Use the new LRA register allocator.  By default, the old "reload"
23845           allocator is used.
23846
23847       picoChip Options
23848
23849       These -m options are defined for picoChip implementations:
23850
23851       -mae=ae_type
23852           Set the instruction set, register set, and instruction scheduling
23853           parameters for array element type ae_type.  Supported values for
23854           ae_type are ANY, MUL, and MAC.
23855
23856           -mae=ANY selects a completely generic AE type.  Code generated with
23857           this option runs on any of the other AE types.  The code is not as
23858           efficient as it would be if compiled for a specific AE type, and
23859           some types of operation (e.g., multiplication) do not work properly
23860           on all types of AE.
23861
23862           -mae=MUL selects a MUL AE type.  This is the most useful AE type
23863           for compiled code, and is the default.
23864
23865           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
23866           option may suffer from poor performance of byte (char)
23867           manipulation, since the DSP AE does not provide hardware support
23868           for byte load/stores.
23869
23870       -msymbol-as-address
23871           Enable the compiler to directly use a symbol name as an address in
23872           a load/store instruction, without first loading it into a register.
23873           Typically, the use of this option generates larger programs, which
23874           run faster than when the option isn't used.  However, the results
23875           vary from program to program, so it is left as a user option,
23876           rather than being permanently enabled.
23877
23878       -mno-inefficient-warnings
23879           Disables warnings about the generation of inefficient code.  These
23880           warnings can be generated, for example, when compiling code that
23881           performs byte-level memory operations on the MAC AE type.  The MAC
23882           AE has no hardware support for byte-level memory operations, so all
23883           byte load/stores must be synthesized from word load/store
23884           operations.  This is inefficient and a warning is generated to
23885           indicate that you should rewrite the code to avoid byte operations,
23886           or to target an AE type that has the necessary hardware support.
23887           This option disables these warnings.
23888
23889       PowerPC Options
23890
23891       These are listed under
23892
23893       PRU Options
23894
23895       These command-line options are defined for PRU target:
23896
23897       -minrt
23898           Link with a minimum runtime environment, with no support for static
23899           initializers and constructors.  Using this option can significantly
23900           reduce the size of the final ELF binary.  Beware that the compiler
23901           could still generate code with static initializers and
23902           constructors.  It is up to the programmer to ensure that the source
23903           program will not use those features.
23904
23905       -mmcu=mcu
23906           Specify the PRU MCU variant to use.  Check Newlib for the exact
23907           list of supported MCUs.
23908
23909       -mno-relax
23910           Make GCC pass the --no-relax command-line option to the linker
23911           instead of the --relax option.
23912
23913       -mloop
23914           Allow (or do not allow) GCC to use the LOOP instruction.
23915
23916       -mabi=variant
23917           Specify the ABI variant to output code for.  -mabi=ti selects the
23918           unmodified TI ABI while -mabi=gnu selects a GNU variant that copes
23919           more naturally with certain GCC assumptions.  These are the
23920           differences:
23921
23922           Function Pointer Size
23923               TI ABI specifies that function (code) pointers are 16-bit,
23924               whereas GNU supports only 32-bit data and code pointers.
23925
23926           Optional Return Value Pointer
23927               Function return values larger than 64 bits are passed by using
23928               a hidden pointer as the first argument of the function.  TI
23929               ABI, though, mandates that the pointer can be NULL in case the
23930               caller is not using the returned value.  GNU always passes and
23931               expects a valid return value pointer.
23932
23933           The current -mabi=ti implementation simply raises a compile error
23934           when any of the above code constructs is detected.  As a
23935           consequence the standard C library cannot be built and it is
23936           omitted when linking with -mabi=ti.
23937
23938           Relaxation is a GNU feature and for safety reasons is disabled when
23939           using -mabi=ti.  The TI toolchain does not emit relocations for
23940           QBBx instructions, so the GNU linker cannot adjust them when
23941           shortening adjacent LDI32 pseudo instructions.
23942
23943       RISC-V Options
23944
23945       These command-line options are defined for RISC-V targets:
23946
23947       -mbranch-cost=n
23948           Set the cost of branches to roughly n instructions.
23949
23950       -mplt
23951       -mno-plt
23952           When generating PIC code, do or don't allow the use of PLTs.
23953           Ignored for non-PIC.  The default is -mplt.
23954
23955       -mabi=ABI-string
23956           Specify integer and floating-point calling convention.  ABI-string
23957           contains two parts: the size of integer types and the registers
23958           used for floating-point types.  For example -march=rv64ifd
23959           -mabi=lp64d means that long and pointers are 64-bit (implicitly
23960           defining int to be 32-bit), and that floating-point values up to 64
23961           bits wide are passed in F registers.  Contrast this with
23962           -march=rv64ifd -mabi=lp64f, which still allows the compiler to
23963           generate code that uses the F and D extensions but only allows
23964           floating-point values up to 32 bits long to be passed in registers;
23965           or -march=rv64ifd -mabi=lp64, in which no floating-point arguments
23966           will be passed in registers.
23967
23968           The default for this argument is system dependent, users who want a
23969           specific calling convention should specify one explicitly.  The
23970           valid calling conventions are: ilp32, ilp32f, ilp32d, lp64, lp64f,
23971           and lp64d.  Some calling conventions are impossible to implement on
23972           some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid
23973           because the ABI requires 64-bit values be passed in F registers,
23974           but F registers are only 32 bits wide.  There is also the ilp32e
23975           ABI that can only be used with the rv32e architecture.  This ABI is
23976           not well specified at present, and is subject to change.
23977
23978       -mfdiv
23979       -mno-fdiv
23980           Do or don't use hardware floating-point divide and square root
23981           instructions.  This requires the F or D extensions for floating-
23982           point registers.  The default is to use them if the specified
23983           architecture has these instructions.
23984
23985       -mdiv
23986       -mno-div
23987           Do or don't use hardware instructions for integer division.  This
23988           requires the M extension.  The default is to use them if the
23989           specified architecture has these instructions.
23990
23991       -misa-spec=ISA-spec-string
23992           Specify the version of the RISC-V Unprivileged (formerly User-
23993           Level) ISA specification to produce code conforming to.  The
23994           possibilities for ISA-spec-string are:
23995
23996           2.2 Produce code conforming to version 2.2.
23997
23998           20190608
23999               Produce code conforming to version 20190608.
24000
24001           20191213
24002               Produce code conforming to version 20191213.
24003
24004           The default is -misa-spec=20191213 unless GCC has been configured
24005           with --with-isa-spec= specifying a different default version.
24006
24007       -march=ISA-string
24008           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must
24009           be lower-case.  Examples include rv64i, rv32g, rv32e, and rv32imaf.
24010
24011           When -march= is not specified, use the setting from -mcpu.
24012
24013           If both -march and -mcpu= are not specified, the default for this
24014           argument is system dependent, users who want a specific
24015           architecture extensions should specify one explicitly.
24016
24017       -mcpu=processor-string
24018           Use architecture of and optimize the output for the given
24019           processor, specified by particular CPU name.  Permissible values
24020           for this option are: sifive-e20, sifive-e21, sifive-e24,
24021           sifive-e31, sifive-e34, sifive-e76, sifive-s21, sifive-s51,
24022           sifive-s54, sifive-s76, sifive-u54, and sifive-u74.
24023
24024       -mtune=processor-string
24025           Optimize the output for the given processor, specified by
24026           microarchitecture or particular CPU name.  Permissible values for
24027           this option are: rocket, sifive-3-series, sifive-5-series,
24028           sifive-7-series, size, and all valid options for -mcpu=.
24029
24030           When -mtune= is not specified, use the setting from -mcpu, the
24031           default is rocket if both are not specified.
24032
24033           The size choice is not intended for use by end-users.  This is used
24034           when -Os is specified.  It overrides the instruction cost info
24035           provided by -mtune=, but does not override the pipeline info.  This
24036           helps reduce code size while still giving good performance.
24037
24038       -mpreferred-stack-boundary=num
24039           Attempt to keep the stack boundary aligned to a 2 raised to num
24040           byte boundary.  If -mpreferred-stack-boundary is not specified, the
24041           default is 4 (16 bytes or 128-bits).
24042
24043           Warning: If you use this switch, then you must build all modules
24044           with the same value, including any libraries.  This includes the
24045           system libraries and startup modules.
24046
24047       -msmall-data-limit=n
24048           Put global and static data smaller than n bytes into a special
24049           section (on some targets).
24050
24051       -msave-restore
24052       -mno-save-restore
24053           Do or don't use smaller but slower prologue and epilogue code that
24054           uses library function calls.  The default is to use fast inline
24055           prologues and epilogues.
24056
24057       -mshorten-memrefs
24058       -mno-shorten-memrefs
24059           Do or do not attempt to make more use of compressed load/store
24060           instructions by replacing a load/store of 'base register + large
24061           offset' with a new load/store of 'new base + small offset'.  If the
24062           new base gets stored in a compressed register, then the new
24063           load/store can be compressed.  Currently targets 32-bit integer
24064           load/stores only.
24065
24066       -mstrict-align
24067       -mno-strict-align
24068           Do not or do generate unaligned memory accesses.  The default is
24069           set depending on whether the processor we are optimizing for
24070           supports fast unaligned access or not.
24071
24072       -mcmodel=medlow
24073           Generate code for the medium-low code model. The program and its
24074           statically defined symbols must lie within a single 2 GiB address
24075           range and must lie between absolute addresses -2 GiB and +2 GiB.
24076           Programs can be statically or dynamically linked. This is the
24077           default code model.
24078
24079       -mcmodel=medany
24080           Generate code for the medium-any code model. The program and its
24081           statically defined symbols must be within any single 2 GiB address
24082           range. Programs can be statically or dynamically linked.
24083
24084           The code generated by the medium-any code model is position-
24085           independent, but is not guaranteed to function correctly when
24086           linked into position-independent executables or libraries.
24087
24088       -mexplicit-relocs
24089       -mno-exlicit-relocs
24090           Use or do not use assembler relocation operators when dealing with
24091           symbolic addresses.  The alternative is to use assembler macros
24092           instead, which may limit optimization.
24093
24094       -mrelax
24095       -mno-relax
24096           Take advantage of linker relaxations to reduce the number of
24097           instructions required to materialize symbol addresses. The default
24098           is to take advantage of linker relaxations.
24099
24100       -memit-attribute
24101       -mno-emit-attribute
24102           Emit (do not emit) RISC-V attribute to record extra information
24103           into ELF objects.  This feature requires at least binutils 2.32.
24104
24105       -malign-data=type
24106           Control how GCC aligns variables and constants of array, structure,
24107           or union types.  Supported values for type are xlen which uses x
24108           register width as the alignment value, and natural which uses
24109           natural alignment.  xlen is the default.
24110
24111       -mbig-endian
24112           Generate big-endian code.  This is the default when GCC is
24113           configured for a riscv64be-*-* or riscv32be-*-* target.
24114
24115       -mlittle-endian
24116           Generate little-endian code.  This is the default when GCC is
24117           configured for a riscv64-*-* or riscv32-*-* but not a riscv64be-*-*
24118           or riscv32be-*-* target.
24119
24120       -mstack-protector-guard=guard
24121       -mstack-protector-guard-reg=reg
24122       -mstack-protector-guard-offset=offset
24123           Generate stack protection code using canary at guard.  Supported
24124           locations are global for a global canary or tls for per-thread
24125           canary in the TLS block.
24126
24127           With the latter choice the options -mstack-protector-guard-reg=reg
24128           and -mstack-protector-guard-offset=offset furthermore specify which
24129           register to use as base register for reading the canary, and from
24130           what offset from that base register. There is no default register
24131           or offset as this is entirely for use within the Linux kernel.
24132
24133       RL78 Options
24134
24135       -msim
24136           Links in additional target libraries to support operation within a
24137           simulator.
24138
24139       -mmul=none
24140       -mmul=g10
24141       -mmul=g13
24142       -mmul=g14
24143       -mmul=rl78
24144           Specifies the type of hardware multiplication and division support
24145           to be used.  The simplest is "none", which uses software for both
24146           multiplication and division.  This is the default.  The "g13" value
24147           is for the hardware multiply/divide peripheral found on the
24148           RL78/G13 (S2 core) targets.  The "g14" value selects the use of the
24149           multiplication and division instructions supported by the RL78/G14
24150           (S3 core) parts.  The value "rl78" is an alias for "g14" and the
24151           value "mg10" is an alias for "none".
24152
24153           In addition a C preprocessor macro is defined, based upon the
24154           setting of this option.  Possible values are: "__RL78_MUL_NONE__",
24155           "__RL78_MUL_G13__" or "__RL78_MUL_G14__".
24156
24157       -mcpu=g10
24158       -mcpu=g13
24159       -mcpu=g14
24160       -mcpu=rl78
24161           Specifies the RL78 core to target.  The default is the G14 core,
24162           also known as an S3 core or just RL78.  The G13 or S2 core does not
24163           have multiply or divide instructions, instead it uses a hardware
24164           peripheral for these operations.  The G10 or S1 core does not have
24165           register banks, so it uses a different calling convention.
24166
24167           If this option is set it also selects the type of hardware multiply
24168           support to use, unless this is overridden by an explicit -mmul=none
24169           option on the command line.  Thus specifying -mcpu=g13 enables the
24170           use of the G13 hardware multiply peripheral and specifying
24171           -mcpu=g10 disables the use of hardware multiplications altogether.
24172
24173           Note, although the RL78/G14 core is the default target, specifying
24174           -mcpu=g14 or -mcpu=rl78 on the command line does change the
24175           behavior of the toolchain since it also enables G14 hardware
24176           multiply support.  If these options are not specified on the
24177           command line then software multiplication routines will be used
24178           even though the code targets the RL78 core.  This is for backwards
24179           compatibility with older toolchains which did not have hardware
24180           multiply and divide support.
24181
24182           In addition a C preprocessor macro is defined, based upon the
24183           setting of this option.  Possible values are: "__RL78_G10__",
24184           "__RL78_G13__" or "__RL78_G14__".
24185
24186       -mg10
24187       -mg13
24188       -mg14
24189       -mrl78
24190           These are aliases for the corresponding -mcpu= option.  They are
24191           provided for backwards compatibility.
24192
24193       -mallregs
24194           Allow the compiler to use all of the available registers.  By
24195           default registers "r24..r31" are reserved for use in interrupt
24196           handlers.  With this option enabled these registers can be used in
24197           ordinary functions as well.
24198
24199       -m64bit-doubles
24200       -m32bit-doubles
24201           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
24202           (-m32bit-doubles) in size.  The default is -m32bit-doubles.
24203
24204       -msave-mduc-in-interrupts
24205       -mno-save-mduc-in-interrupts
24206           Specifies that interrupt handler functions should preserve the MDUC
24207           registers.  This is only necessary if normal code might use the
24208           MDUC registers, for example because it performs multiplication and
24209           division operations.  The default is to ignore the MDUC registers
24210           as this makes the interrupt handlers faster.  The target option
24211           -mg13 needs to be passed for this to work as this feature is only
24212           available on the G13 target (S2 core).  The MDUC registers will
24213           only be saved if the interrupt handler performs a multiplication or
24214           division operation or it calls another function.
24215
24216       IBM RS/6000 and PowerPC Options
24217
24218       These -m options are defined for the IBM RS/6000 and PowerPC:
24219
24220       -mpowerpc-gpopt
24221       -mno-powerpc-gpopt
24222       -mpowerpc-gfxopt
24223       -mno-powerpc-gfxopt
24224       -mpowerpc64
24225       -mno-powerpc64
24226       -mmfcrf
24227       -mno-mfcrf
24228       -mpopcntb
24229       -mno-popcntb
24230       -mpopcntd
24231       -mno-popcntd
24232       -mfprnd
24233       -mno-fprnd
24234       -mcmpb
24235       -mno-cmpb
24236       -mhard-dfp
24237       -mno-hard-dfp
24238           You use these options to specify which instructions are available
24239           on the processor you are using.  The default value of these options
24240           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
24241           overrides the specification of these options.  We recommend you use
24242           the -mcpu=cpu_type option rather than the options listed above.
24243
24244           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC
24245           architecture instructions in the General Purpose group, including
24246           floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
24247           to use the optional PowerPC architecture instructions in the
24248           Graphics group, including floating-point select.
24249
24250           The -mmfcrf option allows GCC to generate the move from condition
24251           register field instruction implemented on the POWER4 processor and
24252           other processors that support the PowerPC V2.01 architecture.  The
24253           -mpopcntb option allows GCC to generate the popcount and double-
24254           precision FP reciprocal estimate instruction implemented on the
24255           POWER5 processor and other processors that support the PowerPC
24256           V2.02 architecture.  The -mpopcntd option allows GCC to generate
24257           the popcount instruction implemented on the POWER7 processor and
24258           other processors that support the PowerPC V2.06 architecture.  The
24259           -mfprnd option allows GCC to generate the FP round to integer
24260           instructions implemented on the POWER5+ processor and other
24261           processors that support the PowerPC V2.03 architecture.  The -mcmpb
24262           option allows GCC to generate the compare bytes instruction
24263           implemented on the POWER6 processor and other processors that
24264           support the PowerPC V2.05 architecture.  The -mhard-dfp option
24265           allows GCC to generate the decimal floating-point instructions
24266           implemented on some POWER processors.
24267
24268           The -mpowerpc64 option allows GCC to generate the additional 64-bit
24269           instructions that are found in the full PowerPC64 architecture and
24270           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
24271           -mno-powerpc64.
24272
24273       -mcpu=cpu_type
24274           Set architecture type, register usage, and instruction scheduling
24275           parameters for machine type cpu_type.  Supported values for
24276           cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476,
24277           476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400,
24278           7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3,
24279           e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,
24280           power4, power5, power5+, power6, power6x, power7, power8, power9,
24281           power10, powerpc, powerpc64, powerpc64le, rs64, and native.
24282
24283           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure
24284           32-bit PowerPC (either endian), 64-bit big endian PowerPC and
24285           64-bit little endian PowerPC architecture machine types, with an
24286           appropriate, generic processor model assumed for scheduling
24287           purposes.
24288
24289           Specifying native as cpu type detects and selects the architecture
24290           option that corresponds to the host processor of the system
24291           performing the compilation.  -mcpu=native has no effect if GCC does
24292           not recognize the processor.
24293
24294           The other options specify a specific processor.  Code generated
24295           under those options runs best on that processor, and may not run at
24296           all on others.
24297
24298           The -mcpu options automatically enable or disable the following
24299           options:
24300
24301           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb
24302           -mpopcntd  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt -mmulhw
24303           -mdlmzb  -mmfpgpr  -mvsx -mcrypto  -mhtm  -mpower8-fusion
24304           -mpower8-vector -mquad-memory  -mquad-memory-atomic  -mfloat128
24305           -mfloat128-hardware -mprefixed -mpcrel -mmma -mrop-protect
24306
24307           The particular options set for any particular CPU varies between
24308           compiler versions, depending on what setting seems to produce
24309           optimal code for that CPU; it doesn't necessarily reflect the
24310           actual hardware's capabilities.  If you wish to set an individual
24311           option to a particular value, you may specify it after the -mcpu
24312           option, like -mcpu=970 -mno-altivec.
24313
24314           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
24315           disabled by the -mcpu option at present because AIX does not have
24316           full support for these options.  You may still enable or disable
24317           them individually if you're sure it'll work in your environment.
24318
24319       -mtune=cpu_type
24320           Set the instruction scheduling parameters for machine type
24321           cpu_type, but do not set the architecture type or register usage,
24322           as -mcpu=cpu_type does.  The same values for cpu_type are used for
24323           -mtune as for -mcpu.  If both are specified, the code generated
24324           uses the architecture and registers set by -mcpu, but the
24325           scheduling parameters set by -mtune.
24326
24327       -mcmodel=small
24328           Generate PowerPC64 code for the small model: The TOC is limited to
24329           64k.
24330
24331       -mcmodel=medium
24332           Generate PowerPC64 code for the medium model: The TOC and other
24333           static data may be up to a total of 4G in size.  This is the
24334           default for 64-bit Linux.
24335
24336       -mcmodel=large
24337           Generate PowerPC64 code for the large model: The TOC may be up to
24338           4G in size.  Other data and code is only limited by the 64-bit
24339           address space.
24340
24341       -maltivec
24342       -mno-altivec
24343           Generate code that uses (does not use) AltiVec instructions, and
24344           also enable the use of built-in functions that allow more direct
24345           access to the AltiVec instruction set.  You may also need to set
24346           -mabi=altivec to adjust the current ABI with AltiVec ABI
24347           enhancements.
24348
24349           When -maltivec is used, the element order for AltiVec intrinsics
24350           such as "vec_splat", "vec_extract", and "vec_insert" match array
24351           element order corresponding to the endianness of the target.  That
24352           is, element zero identifies the leftmost element in a vector
24353           register when targeting a big-endian platform, and identifies the
24354           rightmost element in a vector register when targeting a little-
24355           endian platform.
24356
24357       -mvrsave
24358       -mno-vrsave
24359           Generate VRSAVE instructions when generating AltiVec code.
24360
24361       -msecure-plt
24362           Generate code that allows ld and ld.so to build executables and
24363           shared libraries with non-executable ".plt" and ".got" sections.
24364           This is a PowerPC 32-bit SYSV ABI option.
24365
24366       -mbss-plt
24367           Generate code that uses a BSS ".plt" section that ld.so fills in,
24368           and requires ".plt" and ".got" sections that are both writable and
24369           executable.  This is a PowerPC 32-bit SYSV ABI option.
24370
24371       -misel
24372       -mno-isel
24373           This switch enables or disables the generation of ISEL
24374           instructions.
24375
24376       -mvsx
24377       -mno-vsx
24378           Generate code that uses (does not use) vector/scalar (VSX)
24379           instructions, and also enable the use of built-in functions that
24380           allow more direct access to the VSX instruction set.
24381
24382       -mcrypto
24383       -mno-crypto
24384           Enable the use (disable) of the built-in functions that allow
24385           direct access to the cryptographic instructions that were added in
24386           version 2.07 of the PowerPC ISA.
24387
24388       -mhtm
24389       -mno-htm
24390           Enable (disable) the use of the built-in functions that allow
24391           direct access to the Hardware Transactional Memory (HTM)
24392           instructions that were added in version 2.07 of the PowerPC ISA.
24393
24394       -mpower8-fusion
24395       -mno-power8-fusion
24396           Generate code that keeps (does not keeps) some integer operations
24397           adjacent so that the instructions can be fused together on power8
24398           and later processors.
24399
24400       -mpower8-vector
24401       -mno-power8-vector
24402           Generate code that uses (does not use) the vector and scalar
24403           instructions that were added in version 2.07 of the PowerPC ISA.
24404           Also enable the use of built-in functions that allow more direct
24405           access to the vector instructions.
24406
24407       -mquad-memory
24408       -mno-quad-memory
24409           Generate code that uses (does not use) the non-atomic quad word
24410           memory instructions.  The -mquad-memory option requires use of
24411           64-bit mode.
24412
24413       -mquad-memory-atomic
24414       -mno-quad-memory-atomic
24415           Generate code that uses (does not use) the atomic quad word memory
24416           instructions.  The -mquad-memory-atomic option requires use of
24417           64-bit mode.
24418
24419       -mfloat128
24420       -mno-float128
24421           Enable/disable the __float128 keyword for IEEE 128-bit floating
24422           point and use either software emulation for IEEE 128-bit floating
24423           point or hardware instructions.
24424
24425           The VSX instruction set (-mvsx) must be enabled to use the IEEE
24426           128-bit floating point support.  The IEEE 128-bit floating point is
24427           only supported on Linux.
24428
24429           The default for -mfloat128 is enabled on PowerPC Linux systems
24430           using the VSX instruction set, and disabled on other systems.
24431
24432           If you use the ISA 3.0 instruction set (-mpower9-vector or
24433           -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point
24434           support will also enable the generation of ISA 3.0 IEEE 128-bit
24435           floating point instructions.  Otherwise, if you do not specify to
24436           generate ISA 3.0 instructions or you are targeting a 32-bit big
24437           endian system, IEEE 128-bit floating point will be done with
24438           software emulation.
24439
24440       -mfloat128-hardware
24441       -mno-float128-hardware
24442           Enable/disable using ISA 3.0 hardware instructions to support the
24443           __float128 data type.
24444
24445           The default for -mfloat128-hardware is enabled on PowerPC Linux
24446           systems using the ISA 3.0 instruction set, and disabled on other
24447           systems.
24448
24449       -m32
24450       -m64
24451           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
24452           targets (including GNU/Linux).  The 32-bit environment sets int,
24453           long and pointer to 32 bits and generates code that runs on any
24454           PowerPC variant.  The 64-bit environment sets int to 32 bits and
24455           long and pointer to 64 bits, and generates code for PowerPC64, as
24456           for -mpowerpc64.
24457
24458       -mfull-toc
24459       -mno-fp-in-toc
24460       -mno-sum-in-toc
24461       -mminimal-toc
24462           Modify generation of the TOC (Table Of Contents), which is created
24463           for every executable file.  The -mfull-toc option is selected by
24464           default.  In that case, GCC allocates at least one TOC entry for
24465           each unique non-automatic variable reference in your program.  GCC
24466           also places floating-point constants in the TOC.  However, only
24467           16,384 entries are available in the TOC.
24468
24469           If you receive a linker error message that saying you have
24470           overflowed the available TOC space, you can reduce the amount of
24471           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
24472           -mno-fp-in-toc prevents GCC from putting floating-point constants
24473           in the TOC and -mno-sum-in-toc forces GCC to generate code to
24474           calculate the sum of an address and a constant at run time instead
24475           of putting that sum into the TOC.  You may specify one or both of
24476           these options.  Each causes GCC to produce very slightly slower and
24477           larger code at the expense of conserving TOC space.
24478
24479           If you still run out of space in the TOC even when you specify both
24480           of these options, specify -mminimal-toc instead.  This option
24481           causes GCC to make only one TOC entry for every file.  When you
24482           specify this option, GCC produces code that is slower and larger
24483           but which uses extremely little TOC space.  You may wish to use
24484           this option only on files that contain less frequently-executed
24485           code.
24486
24487       -maix64
24488       -maix32
24489           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
24490           64-bit "long" type, and the infrastructure needed to support them.
24491           Specifying -maix64 implies -mpowerpc64, while -maix32 disables the
24492           64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.
24493
24494       -mxl-compat
24495       -mno-xl-compat
24496           Produce code that conforms more closely to IBM XL compiler
24497           semantics when using AIX-compatible ABI.  Pass floating-point
24498           arguments to prototyped functions beyond the register save area
24499           (RSA) on the stack in addition to argument FPRs.  Do not assume
24500           that most significant double in 128-bit long double value is
24501           properly rounded when comparing values and converting to double.
24502           Use XL symbol names for long double support routines.
24503
24504           The AIX calling convention was extended but not initially
24505           documented to handle an obscure K&R C case of calling a function
24506           that takes the address of its arguments with fewer arguments than
24507           declared.  IBM XL compilers access floating-point arguments that do
24508           not fit in the RSA from the stack when a subroutine is compiled
24509           without optimization.  Because always storing floating-point
24510           arguments on the stack is inefficient and rarely needed, this
24511           option is not enabled by default and only is necessary when calling
24512           subroutines compiled by IBM XL compilers without optimization.
24513
24514       -mpe
24515           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
24516           application written to use message passing with special startup
24517           code to enable the application to run.  The system must have PE
24518           installed in the standard location (/usr/lpp/ppe.poe/), or the
24519           specs file must be overridden with the -specs= option to specify
24520           the appropriate directory location.  The Parallel Environment does
24521           not support threads, so the -mpe option and the -pthread option are
24522           incompatible.
24523
24524       -malign-natural
24525       -malign-power
24526           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
24527           -malign-natural overrides the ABI-defined alignment of larger
24528           types, such as floating-point doubles, on their natural size-based
24529           boundary.  The option -malign-power instructs GCC to follow the
24530           ABI-specified alignment rules.  GCC defaults to the standard
24531           alignment defined in the ABI.
24532
24533           On 64-bit Darwin, natural alignment is the default, and
24534           -malign-power is not supported.
24535
24536       -msoft-float
24537       -mhard-float
24538           Generate code that does not use (uses) the floating-point register
24539           set.  Software floating-point emulation is provided if you use the
24540           -msoft-float option, and pass the option to GCC when linking.
24541
24542       -mmultiple
24543       -mno-multiple
24544           Generate code that uses (does not use) the load multiple word
24545           instructions and the store multiple word instructions.  These
24546           instructions are generated by default on POWER systems, and not
24547           generated on PowerPC systems.  Do not use -mmultiple on little-
24548           endian PowerPC systems, since those instructions do not work when
24549           the processor is in little-endian mode.  The exceptions are PPC740
24550           and PPC750 which permit these instructions in little-endian mode.
24551
24552       -mupdate
24553       -mno-update
24554           Generate code that uses (does not use) the load or store
24555           instructions that update the base register to the address of the
24556           calculated memory location.  These instructions are generated by
24557           default.  If you use -mno-update, there is a small window between
24558           the time that the stack pointer is updated and the address of the
24559           previous frame is stored, which means code that walks the stack
24560           frame across interrupts or signals may get corrupted data.
24561
24562       -mavoid-indexed-addresses
24563       -mno-avoid-indexed-addresses
24564           Generate code that tries to avoid (not avoid) the use of indexed
24565           load or store instructions. These instructions can incur a
24566           performance penalty on Power6 processors in certain situations,
24567           such as when stepping through large arrays that cross a 16M
24568           boundary.  This option is enabled by default when targeting Power6
24569           and disabled otherwise.
24570
24571       -mfused-madd
24572       -mno-fused-madd
24573           Generate code that uses (does not use) the floating-point multiply
24574           and accumulate instructions.  These instructions are generated by
24575           default if hardware floating point is used.  The machine-dependent
24576           -mfused-madd option is now mapped to the machine-independent
24577           -ffp-contract=fast option, and -mno-fused-madd is mapped to
24578           -ffp-contract=off.
24579
24580       -mmulhw
24581       -mno-mulhw
24582           Generate code that uses (does not use) the half-word multiply and
24583           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
24584           processors.  These instructions are generated by default when
24585           targeting those processors.
24586
24587       -mdlmzb
24588       -mno-dlmzb
24589           Generate code that uses (does not use) the string-search dlmzb
24590           instruction on the IBM 405, 440, 464 and 476 processors.  This
24591           instruction is generated by default when targeting those
24592           processors.
24593
24594       -mno-bit-align
24595       -mbit-align
24596           On System V.4 and embedded PowerPC systems do not (do) force
24597           structures and unions that contain bit-fields to be aligned to the
24598           base type of the bit-field.
24599
24600           For example, by default a structure containing nothing but 8
24601           "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary
24602           and has a size of 4 bytes.  By using -mno-bit-align, the structure
24603           is aligned to a 1-byte boundary and is 1 byte in size.
24604
24605       -mno-strict-align
24606       -mstrict-align
24607           On System V.4 and embedded PowerPC systems do not (do) assume that
24608           unaligned memory references are handled by the system.
24609
24610       -mrelocatable
24611       -mno-relocatable
24612           Generate code that allows (does not allow) a static executable to
24613           be relocated to a different address at run time.  A simple embedded
24614           PowerPC system loader should relocate the entire contents of
24615           ".got2" and 4-byte locations listed in the ".fixup" section, a
24616           table of 32-bit addresses generated by this option.  For this to
24617           work, all objects linked together must be compiled with
24618           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
24619           stack to an 8-byte boundary.
24620
24621       -mrelocatable-lib
24622       -mno-relocatable-lib
24623           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
24624           to allow static executables to be relocated at run time, but
24625           -mrelocatable-lib does not use the smaller stack alignment of
24626           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
24627           linked with objects compiled with any combination of the
24628           -mrelocatable options.
24629
24630       -mno-toc
24631       -mtoc
24632           On System V.4 and embedded PowerPC systems do not (do) assume that
24633           register 2 contains a pointer to a global area pointing to the
24634           addresses used in the program.
24635
24636       -mlittle
24637       -mlittle-endian
24638           On System V.4 and embedded PowerPC systems compile code for the
24639           processor in little-endian mode.  The -mlittle-endian option is the
24640           same as -mlittle.
24641
24642       -mbig
24643       -mbig-endian
24644           On System V.4 and embedded PowerPC systems compile code for the
24645           processor in big-endian mode.  The -mbig-endian option is the same
24646           as -mbig.
24647
24648       -mdynamic-no-pic
24649           On Darwin and Mac OS X systems, compile code so that it is not
24650           relocatable, but that its external references are relocatable.  The
24651           resulting code is suitable for applications, but not shared
24652           libraries.
24653
24654       -msingle-pic-base
24655           Treat the register used for PIC addressing as read-only, rather
24656           than loading it in the prologue for each function.  The runtime
24657           system is responsible for initializing this register with an
24658           appropriate value before execution begins.
24659
24660       -mprioritize-restricted-insns=priority
24661           This option controls the priority that is assigned to dispatch-slot
24662           restricted instructions during the second scheduling pass.  The
24663           argument priority takes the value 0, 1, or 2 to assign no, highest,
24664           or second-highest (respectively) priority to dispatch-slot
24665           restricted instructions.
24666
24667       -msched-costly-dep=dependence_type
24668           This option controls which dependences are considered costly by the
24669           target during instruction scheduling.  The argument dependence_type
24670           takes one of the following values:
24671
24672           no  No dependence is costly.
24673
24674           all All dependences are costly.
24675
24676           true_store_to_load
24677               A true dependence from store to load is costly.
24678
24679           store_to_load
24680               Any dependence from store to load is costly.
24681
24682           number
24683               Any dependence for which the latency is greater than or equal
24684               to number is costly.
24685
24686       -minsert-sched-nops=scheme
24687           This option controls which NOP insertion scheme is used during the
24688           second scheduling pass.  The argument scheme takes one of the
24689           following values:
24690
24691           no  Don't insert NOPs.
24692
24693           pad Pad with NOPs any dispatch group that has vacant issue slots,
24694               according to the scheduler's grouping.
24695
24696           regroup_exact
24697               Insert NOPs to force costly dependent insns into separate
24698               groups.  Insert exactly as many NOPs as needed to force an insn
24699               to a new group, according to the estimated processor grouping.
24700
24701           number
24702               Insert NOPs to force costly dependent insns into separate
24703               groups.  Insert number NOPs to force an insn to a new group.
24704
24705       -mcall-sysv
24706           On System V.4 and embedded PowerPC systems compile code using
24707           calling conventions that adhere to the March 1995 draft of the
24708           System V Application Binary Interface, PowerPC processor
24709           supplement.  This is the default unless you configured GCC using
24710           powerpc-*-eabiaix.
24711
24712       -mcall-sysv-eabi
24713       -mcall-eabi
24714           Specify both -mcall-sysv and -meabi options.
24715
24716       -mcall-sysv-noeabi
24717           Specify both -mcall-sysv and -mno-eabi options.
24718
24719       -mcall-aixdesc
24720           On System V.4 and embedded PowerPC systems compile code for the AIX
24721           operating system.
24722
24723       -mcall-linux
24724           On System V.4 and embedded PowerPC systems compile code for the
24725           Linux-based GNU system.
24726
24727       -mcall-freebsd
24728           On System V.4 and embedded PowerPC systems compile code for the
24729           FreeBSD operating system.
24730
24731       -mcall-netbsd
24732           On System V.4 and embedded PowerPC systems compile code for the
24733           NetBSD operating system.
24734
24735       -mcall-openbsd
24736           On System V.4 and embedded PowerPC systems compile code for the
24737           OpenBSD operating system.
24738
24739       -mtraceback=traceback_type
24740           Select the type of traceback table. Valid values for traceback_type
24741           are full, part, and no.
24742
24743       -maix-struct-return
24744           Return all structures in memory (as specified by the AIX ABI).
24745
24746       -msvr4-struct-return
24747           Return structures smaller than 8 bytes in registers (as specified
24748           by the SVR4 ABI).
24749
24750       -mabi=abi-type
24751           Extend the current ABI with a particular extension, or remove such
24752           extension.  Valid values are: altivec, no-altivec, ibmlongdouble,
24753           ieeelongdouble, elfv1, elfv2, and for AIX: vec-extabi, vec-default.
24754
24755       -mabi=ibmlongdouble
24756           Change the current ABI to use IBM extended-precision long double.
24757           This is not likely to work if your system defaults to using IEEE
24758           extended-precision long double.  If you change the long double type
24759           from IEEE extended-precision, the compiler will issue a warning
24760           unless you use the -Wno-psabi option.  Requires -mlong-double-128
24761           to be enabled.
24762
24763       -mabi=ieeelongdouble
24764           Change the current ABI to use IEEE extended-precision long double.
24765           This is not likely to work if your system defaults to using IBM
24766           extended-precision long double.  If you change the long double type
24767           from IBM extended-precision, the compiler will issue a warning
24768           unless you use the -Wno-psabi option.  Requires -mlong-double-128
24769           to be enabled.
24770
24771       -mabi=elfv1
24772           Change the current ABI to use the ELFv1 ABI.  This is the default
24773           ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
24774           ABI requires special system support and is likely to fail in
24775           spectacular ways.
24776
24777       -mabi=elfv2
24778           Change the current ABI to use the ELFv2 ABI.  This is the default
24779           ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
24780           ABI requires special system support and is likely to fail in
24781           spectacular ways.
24782
24783       -mgnu-attribute
24784       -mno-gnu-attribute
24785           Emit .gnu_attribute assembly directives to set tag/value pairs in a
24786           .gnu.attributes section that specify ABI variations in function
24787           parameters or return values.
24788
24789       -mprototype
24790       -mno-prototype
24791           On System V.4 and embedded PowerPC systems assume that all calls to
24792           variable argument functions are properly prototyped.  Otherwise,
24793           the compiler must insert an instruction before every non-prototyped
24794           call to set or clear bit 6 of the condition code register ("CR") to
24795           indicate whether floating-point values are passed in the floating-
24796           point registers in case the function takes variable arguments.
24797           With -mprototype, only calls to prototyped variable argument
24798           functions set or clear the bit.
24799
24800       -msim
24801           On embedded PowerPC systems, assume that the startup module is
24802           called sim-crt0.o and that the standard C libraries are libsim.a
24803           and libc.a.  This is the default for powerpc-*-eabisim
24804           configurations.
24805
24806       -mmvme
24807           On embedded PowerPC systems, assume that the startup module is
24808           called crt0.o and the standard C libraries are libmvme.a and
24809           libc.a.
24810
24811       -mads
24812           On embedded PowerPC systems, assume that the startup module is
24813           called crt0.o and the standard C libraries are libads.a and libc.a.
24814
24815       -myellowknife
24816           On embedded PowerPC systems, assume that the startup module is
24817           called crt0.o and the standard C libraries are libyk.a and libc.a.
24818
24819       -mvxworks
24820           On System V.4 and embedded PowerPC systems, specify that you are
24821           compiling for a VxWorks system.
24822
24823       -memb
24824           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags
24825           header to indicate that eabi extended relocations are used.
24826
24827       -meabi
24828       -mno-eabi
24829           On System V.4 and embedded PowerPC systems do (do not) adhere to
24830           the Embedded Applications Binary Interface (EABI), which is a set
24831           of modifications to the System V.4 specifications.  Selecting
24832           -meabi means that the stack is aligned to an 8-byte boundary, a
24833           function "__eabi" is called from "main" to set up the EABI
24834           environment, and the -msdata option can use both "r2" and "r13" to
24835           point to two separate small data areas.  Selecting -mno-eabi means
24836           that the stack is aligned to a 16-byte boundary, no EABI
24837           initialization function is called from "main", and the -msdata
24838           option only uses "r13" to point to a single small data area.  The
24839           -meabi option is on by default if you configured GCC using one of
24840           the powerpc*-*-eabi* options.
24841
24842       -msdata=eabi
24843           On System V.4 and embedded PowerPC systems, put small initialized
24844           "const" global and static data in the ".sdata2" section, which is
24845           pointed to by register "r2".  Put small initialized non-"const"
24846           global and static data in the ".sdata" section, which is pointed to
24847           by register "r13".  Put small uninitialized global and static data
24848           in the ".sbss" section, which is adjacent to the ".sdata" section.
24849           The -msdata=eabi option is incompatible with the -mrelocatable
24850           option.  The -msdata=eabi option also sets the -memb option.
24851
24852       -msdata=sysv
24853           On System V.4 and embedded PowerPC systems, put small global and
24854           static data in the ".sdata" section, which is pointed to by
24855           register "r13".  Put small uninitialized global and static data in
24856           the ".sbss" section, which is adjacent to the ".sdata" section.
24857           The -msdata=sysv option is incompatible with the -mrelocatable
24858           option.
24859
24860       -msdata=default
24861       -msdata
24862           On System V.4 and embedded PowerPC systems, if -meabi is used,
24863           compile code the same as -msdata=eabi, otherwise compile code the
24864           same as -msdata=sysv.
24865
24866       -msdata=data
24867           On System V.4 and embedded PowerPC systems, put small global data
24868           in the ".sdata" section.  Put small uninitialized global data in
24869           the ".sbss" section.  Do not use register "r13" to address small
24870           data however.  This is the default behavior unless other -msdata
24871           options are used.
24872
24873       -msdata=none
24874       -mno-sdata
24875           On embedded PowerPC systems, put all initialized global and static
24876           data in the ".data" section, and all uninitialized data in the
24877           ".bss" section.
24878
24879       -mreadonly-in-sdata
24880           Put read-only objects in the ".sdata" section as well.  This is the
24881           default.
24882
24883       -mblock-move-inline-limit=num
24884           Inline all block moves (such as calls to "memcpy" or structure
24885           copies) less than or equal to num bytes.  The minimum value for num
24886           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
24887           default value is target-specific.
24888
24889       -mblock-compare-inline-limit=num
24890           Generate non-looping inline code for all block compares (such as
24891           calls to "memcmp" or structure compares) less than or equal to num
24892           bytes. If num is 0, all inline expansion (non-loop and loop) of
24893           block compare is disabled. The default value is target-specific.
24894
24895       -mblock-compare-inline-loop-limit=num
24896           Generate an inline expansion using loop code for all block compares
24897           that are less than or equal to num bytes, but greater than the
24898           limit for non-loop inline block compare expansion. If the block
24899           length is not constant, at most num bytes will be compared before
24900           "memcmp" is called to compare the remainder of the block. The
24901           default value is target-specific.
24902
24903       -mstring-compare-inline-limit=num
24904           Compare at most num string bytes with inline code.  If the
24905           difference or end of string is not found at the end of the inline
24906           compare a call to "strcmp" or "strncmp" will take care of the rest
24907           of the comparison. The default is 64 bytes.
24908
24909       -G num
24910           On embedded PowerPC systems, put global and static items less than
24911           or equal to num bytes into the small data or BSS sections instead
24912           of the normal data or BSS section.  By default, num is 8.  The -G
24913           num switch is also passed to the linker.  All modules should be
24914           compiled with the same -G num value.
24915
24916       -mregnames
24917       -mno-regnames
24918           On System V.4 and embedded PowerPC systems do (do not) emit
24919           register names in the assembly language output using symbolic
24920           forms.
24921
24922       -mlongcall
24923       -mno-longcall
24924           By default assume that all calls are far away so that a longer and
24925           more expensive calling sequence is required.  This is required for
24926           calls farther than 32 megabytes (33,554,432 bytes) from the current
24927           location.  A short call is generated if the compiler knows the call
24928           cannot be that far away.  This setting can be overridden by the
24929           "shortcall" function attribute, or by "#pragma longcall(0)".
24930
24931           Some linkers are capable of detecting out-of-range calls and
24932           generating glue code on the fly.  On these systems, long calls are
24933           unnecessary and generate slower code.  As of this writing, the AIX
24934           linker can do this, as can the GNU linker for PowerPC/64.  It is
24935           planned to add this feature to the GNU linker for 32-bit PowerPC
24936           systems as well.
24937
24938           On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU
24939           linkers, GCC can generate long calls using an inline PLT call
24940           sequence (see -mpltseq).  PowerPC with -mbss-plt and PowerPC64
24941           ELFv1 (big-endian) do not support inline PLT calls.
24942
24943           On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee,
24944           L42", plus a branch island (glue code).  The two target addresses
24945           represent the callee and the branch island.  The Darwin/PPC linker
24946           prefers the first address and generates a "bl callee" if the PPC
24947           "bl" instruction reaches the callee directly; otherwise, the linker
24948           generates "bl L42" to call the branch island.  The branch island is
24949           appended to the body of the calling function; it computes the full
24950           32-bit address of the callee and jumps to it.
24951
24952           On Mach-O (Darwin) systems, this option directs the compiler emit
24953           to the glue for every direct call, and the Darwin linker decides
24954           whether to use or discard it.
24955
24956           In the future, GCC may ignore all longcall specifications when the
24957           linker is known to generate glue.
24958
24959       -mpltseq
24960       -mno-pltseq
24961           Implement (do not implement) -fno-plt and long calls using an
24962           inline PLT call sequence that supports lazy linking and long calls
24963           to functions in dlopen'd shared libraries.  Inline PLT calls are
24964           only supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with
24965           newer GNU linkers, and are enabled by default if the support is
24966           detected when configuring GCC, and, in the case of 32-bit PowerPC,
24967           if GCC is configured with --enable-secureplt.  -mpltseq code and
24968           -mbss-plt 32-bit PowerPC relocatable objects may not be linked
24969           together.
24970
24971       -mtls-markers
24972       -mno-tls-markers
24973           Mark (do not mark) calls to "__tls_get_addr" with a relocation
24974           specifying the function argument.  The relocation allows the linker
24975           to reliably associate function call with argument setup
24976           instructions for TLS optimization, which in turn allows GCC to
24977           better schedule the sequence.
24978
24979       -mrecip
24980       -mno-recip
24981           This option enables use of the reciprocal estimate and reciprocal
24982           square root estimate instructions with additional Newton-Raphson
24983           steps to increase precision instead of doing a divide or square
24984           root and divide for floating-point arguments.  You should use the
24985           -ffast-math option when using -mrecip (or at least
24986           -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math
24987           and -fno-trapping-math).  Note that while the throughput of the
24988           sequence is generally higher than the throughput of the non-
24989           reciprocal instruction, the precision of the sequence can be
24990           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
24991           0.99999994) for reciprocal square roots.
24992
24993       -mrecip=opt
24994           This option controls which reciprocal estimate instructions may be
24995           used.  opt is a comma-separated list of options, which may be
24996           preceded by a "!" to invert the option:
24997
24998           all Enable all estimate instructions.
24999
25000           default
25001               Enable the default instructions, equivalent to -mrecip.
25002
25003           none
25004               Disable all estimate instructions, equivalent to -mno-recip.
25005
25006           div Enable the reciprocal approximation instructions for both
25007               single and double precision.
25008
25009           divf
25010               Enable the single-precision reciprocal approximation
25011               instructions.
25012
25013           divd
25014               Enable the double-precision reciprocal approximation
25015               instructions.
25016
25017           rsqrt
25018               Enable the reciprocal square root approximation instructions
25019               for both single and double precision.
25020
25021           rsqrtf
25022               Enable the single-precision reciprocal square root
25023               approximation instructions.
25024
25025           rsqrtd
25026               Enable the double-precision reciprocal square root
25027               approximation instructions.
25028
25029           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
25030           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
25031           "XVRSQRTEDP" instructions which handle the double-precision
25032           reciprocal square root calculations.
25033
25034       -mrecip-precision
25035       -mno-recip-precision
25036           Assume (do not assume) that the reciprocal estimate instructions
25037           provide higher-precision estimates than is mandated by the PowerPC
25038           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
25039           automatically selects -mrecip-precision.  The double-precision
25040           square root estimate instructions are not generated by default on
25041           low-precision machines, since they do not provide an estimate that
25042           converges after three steps.
25043
25044       -mveclibabi=type
25045           Specifies the ABI type to use for vectorizing intrinsics using an
25046           external library.  The only type supported at present is mass,
25047           which specifies to use IBM's Mathematical Acceleration Subsystem
25048           (MASS) libraries for vectorizing intrinsics using external
25049           libraries.  GCC currently emits calls to "acosd2", "acosf4",
25050           "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4",
25051           "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4",
25052           "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2",
25053           "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4",
25054           "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4",
25055           "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4",
25056           "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2",
25057           "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and
25058           "tanhf4" when generating code for power7.  Both -ftree-vectorize
25059           and -funsafe-math-optimizations must also be enabled.  The MASS
25060           libraries must be specified at link time.
25061
25062       -mfriz
25063       -mno-friz
25064           Generate (do not generate) the "friz" instruction when the
25065           -funsafe-math-optimizations option is used to optimize rounding of
25066           floating-point values to 64-bit integer and back to floating point.
25067           The "friz" instruction does not return the same value if the
25068           floating-point number is too large to fit in an integer.
25069
25070       -mpointers-to-nested-functions
25071       -mno-pointers-to-nested-functions
25072           Generate (do not generate) code to load up the static chain
25073           register ("r11") when calling through a pointer on AIX and 64-bit
25074           Linux systems where a function pointer points to a 3-word
25075           descriptor giving the function address, TOC value to be loaded in
25076           register "r2", and static chain value to be loaded in register
25077           "r11".  The -mpointers-to-nested-functions is on by default.  You
25078           cannot call through pointers to nested functions or pointers to
25079           functions compiled in other languages that use the static chain if
25080           you use -mno-pointers-to-nested-functions.
25081
25082       -msave-toc-indirect
25083       -mno-save-toc-indirect
25084           Generate (do not generate) code to save the TOC value in the
25085           reserved stack location in the function prologue if the function
25086           calls through a pointer on AIX and 64-bit Linux systems.  If the
25087           TOC value is not saved in the prologue, it is saved just before the
25088           call through the pointer.  The -mno-save-toc-indirect option is the
25089           default.
25090
25091       -mcompat-align-parm
25092       -mno-compat-align-parm
25093           Generate (do not generate) code to pass structure parameters with a
25094           maximum alignment of 64 bits, for compatibility with older versions
25095           of GCC.
25096
25097           Older versions of GCC (prior to 4.9.0) incorrectly did not align a
25098           structure parameter on a 128-bit boundary when that structure
25099           contained a member requiring 128-bit alignment.  This is corrected
25100           in more recent versions of GCC.  This option may be used to
25101           generate code that is compatible with functions compiled with older
25102           versions of GCC.
25103
25104           The -mno-compat-align-parm option is the default.
25105
25106       -mstack-protector-guard=guard
25107       -mstack-protector-guard-reg=reg
25108       -mstack-protector-guard-offset=offset
25109       -mstack-protector-guard-symbol=symbol
25110           Generate stack protection code using canary at guard.  Supported
25111           locations are global for global canary or tls for per-thread canary
25112           in the TLS block (the default with GNU libc version 2.4 or later).
25113
25114           With the latter choice the options -mstack-protector-guard-reg=reg
25115           and -mstack-protector-guard-offset=offset furthermore specify which
25116           register to use as base register for reading the canary, and from
25117           what offset from that base register. The default for those is as
25118           specified in the relevant ABI.
25119           -mstack-protector-guard-symbol=symbol overrides the offset with a
25120           symbol reference to a canary in the TLS block.
25121
25122       -mpcrel
25123       -mno-pcrel
25124           Generate (do not generate) pc-relative addressing.  The -mpcrel
25125           option requires that the medium code model (-mcmodel=medium) and
25126           prefixed addressing (-mprefixed) options are enabled.
25127
25128       -mprefixed
25129       -mno-prefixed
25130           Generate (do not generate) addressing modes using prefixed load and
25131           store instructions.  The -mprefixed option requires that the option
25132           -mcpu=power10 (or later) is enabled.
25133
25134       -mmma
25135       -mno-mma
25136           Generate (do not generate) the MMA instructions.  The -mma option
25137           requires that the option -mcpu=power10 (or later) is enabled.
25138
25139       -mrop-protect
25140       -mno-rop-protect
25141           Generate (do not generate) ROP protection instructions when the
25142           target processor supports them.  Currently this option disables the
25143           shrink-wrap optimization (-fshrink-wrap).
25144
25145       -mprivileged
25146       -mno-privileged
25147           Generate (do not generate) code that will run in privileged state.
25148
25149       -mblock-ops-unaligned-vsx
25150       -mno-block-ops-unaligned-vsx
25151           Generate (do not generate) unaligned vsx loads and stores for
25152           inline expansion of "memcpy" and "memmove".
25153
25154       RX Options
25155
25156       These command-line options are defined for RX targets:
25157
25158       -m64bit-doubles
25159       -m32bit-doubles
25160           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
25161           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
25162           RX floating-point hardware only works on 32-bit values, which is
25163           why the default is -m32bit-doubles.
25164
25165       -fpu
25166       -nofpu
25167           Enables (-fpu) or disables (-nofpu) the use of RX floating-point
25168           hardware.  The default is enabled for the RX600 series and disabled
25169           for the RX200 series.
25170
25171           Floating-point instructions are only generated for 32-bit floating-
25172           point values, however, so the FPU hardware is not used for doubles
25173           if the -m64bit-doubles option is used.
25174
25175           Note If the -fpu option is enabled then -funsafe-math-optimizations
25176           is also enabled automatically.  This is because the RX FPU
25177           instructions are themselves unsafe.
25178
25179       -mcpu=name
25180           Selects the type of RX CPU to be targeted.  Currently three types
25181           are supported, the generic RX600 and RX200 series hardware and the
25182           specific RX610 CPU.  The default is RX600.
25183
25184           The only difference between RX600 and RX610 is that the RX610 does
25185           not support the "MVTIPL" instruction.
25186
25187           The RX200 series does not have a hardware floating-point unit and
25188           so -nofpu is enabled by default when this type is selected.
25189
25190       -mbig-endian-data
25191       -mlittle-endian-data
25192           Store data (but not code) in the big-endian format.  The default is
25193           -mlittle-endian-data, i.e. to store data in the little-endian
25194           format.
25195
25196       -msmall-data-limit=N
25197           Specifies the maximum size in bytes of global and static variables
25198           which can be placed into the small data area.  Using the small data
25199           area can lead to smaller and faster code, but the size of area is
25200           limited and it is up to the programmer to ensure that the area does
25201           not overflow.  Also when the small data area is used one of the
25202           RX's registers (usually "r13") is reserved for use pointing to this
25203           area, so it is no longer available for use by the compiler.  This
25204           could result in slower and/or larger code if variables are pushed
25205           onto the stack instead of being held in this register.
25206
25207           Note, common variables (variables that have not been initialized)
25208           and constants are not placed into the small data area as they are
25209           assigned to other sections in the output executable.
25210
25211           The default value is zero, which disables this feature.  Note, this
25212           feature is not enabled by default with higher optimization levels
25213           (-O2 etc) because of the potentially detrimental effects of
25214           reserving a register.  It is up to the programmer to experiment and
25215           discover whether this feature is of benefit to their program.  See
25216           the description of the -mpid option for a description of how the
25217           actual register to hold the small data area pointer is chosen.
25218
25219       -msim
25220       -mno-sim
25221           Use the simulator runtime.  The default is to use the libgloss
25222           board-specific runtime.
25223
25224       -mas100-syntax
25225       -mno-as100-syntax
25226           When generating assembler output use a syntax that is compatible
25227           with Renesas's AS100 assembler.  This syntax can also be handled by
25228           the GAS assembler, but it has some restrictions so it is not
25229           generated by default.
25230
25231       -mmax-constant-size=N
25232           Specifies the maximum size, in bytes, of a constant that can be
25233           used as an operand in a RX instruction.  Although the RX
25234           instruction set does allow constants of up to 4 bytes in length to
25235           be used in instructions, a longer value equates to a longer
25236           instruction.  Thus in some circumstances it can be beneficial to
25237           restrict the size of constants that are used in instructions.
25238           Constants that are too big are instead placed into a constant pool
25239           and referenced via register indirection.
25240
25241           The value N can be between 0 and 4.  A value of 0 (the default) or
25242           4 means that constants of any size are allowed.
25243
25244       -mrelax
25245           Enable linker relaxation.  Linker relaxation is a process whereby
25246           the linker attempts to reduce the size of a program by finding
25247           shorter versions of various instructions.  Disabled by default.
25248
25249       -mint-register=N
25250           Specify the number of registers to reserve for fast interrupt
25251           handler functions.  The value N can be between 0 and 4.  A value of
25252           1 means that register "r13" is reserved for the exclusive use of
25253           fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A
25254           value of 3 reserves "r13", "r12" and "r11", and a value of 4
25255           reserves "r13" through "r10".  A value of 0, the default, does not
25256           reserve any registers.
25257
25258       -msave-acc-in-interrupts
25259           Specifies that interrupt handler functions should preserve the
25260           accumulator register.  This is only necessary if normal code might
25261           use the accumulator register, for example because it performs
25262           64-bit multiplications.  The default is to ignore the accumulator
25263           as this makes the interrupt handlers faster.
25264
25265       -mpid
25266       -mno-pid
25267           Enables the generation of position independent data.  When enabled
25268           any access to constant data is done via an offset from a base
25269           address held in a register.  This allows the location of constant
25270           data to be determined at run time without requiring the executable
25271           to be relocated, which is a benefit to embedded applications with
25272           tight memory constraints.  Data that can be modified is not
25273           affected by this option.
25274
25275           Note, using this feature reserves a register, usually "r13", for
25276           the constant data base address.  This can result in slower and/or
25277           larger code, especially in complicated functions.
25278
25279           The actual register chosen to hold the constant data base address
25280           depends upon whether the -msmall-data-limit and/or the
25281           -mint-register command-line options are enabled.  Starting with
25282           register "r13" and proceeding downwards, registers are allocated
25283           first to satisfy the requirements of -mint-register, then -mpid and
25284           finally -msmall-data-limit.  Thus it is possible for the small data
25285           area register to be "r8" if both -mint-register=4 and -mpid are
25286           specified on the command line.
25287
25288           By default this feature is not enabled.  The default can be
25289           restored via the -mno-pid command-line option.
25290
25291       -mno-warn-multiple-fast-interrupts
25292       -mwarn-multiple-fast-interrupts
25293           Prevents GCC from issuing a warning message if it finds more than
25294           one fast interrupt handler when it is compiling a file.  The
25295           default is to issue a warning for each extra fast interrupt handler
25296           found, as the RX only supports one such interrupt.
25297
25298       -mallow-string-insns
25299       -mno-allow-string-insns
25300           Enables or disables the use of the string manipulation instructions
25301           "SMOVF", "SCMPU", "SMOVB", "SMOVU", "SUNTIL" "SWHILE" and also the
25302           "RMPA" instruction.  These instructions may prefetch data, which is
25303           not safe to do if accessing an I/O register.  (See section 12.2.7
25304           of the RX62N Group User's Manual for more information).
25305
25306           The default is to allow these instructions, but it is not possible
25307           for GCC to reliably detect all circumstances where a string
25308           instruction might be used to access an I/O register, so their use
25309           cannot be disabled automatically.  Instead it is reliant upon the
25310           programmer to use the -mno-allow-string-insns option if their
25311           program accesses I/O space.
25312
25313           When the instructions are enabled GCC defines the C preprocessor
25314           symbol "__RX_ALLOW_STRING_INSNS__", otherwise it defines the symbol
25315           "__RX_DISALLOW_STRING_INSNS__".
25316
25317       -mjsr
25318       -mno-jsr
25319           Use only (or not only) "JSR" instructions to access functions.
25320           This option can be used when code size exceeds the range of "BSR"
25321           instructions.  Note that -mno-jsr does not mean to not use "JSR"
25322           but instead means that any type of branch may be used.
25323
25324       Note: The generic GCC command-line option -ffixed-reg has special
25325       significance to the RX port when used with the "interrupt" function
25326       attribute.  This attribute indicates a function intended to process
25327       fast interrupts.  GCC ensures that it only uses the registers "r10",
25328       "r11", "r12" and/or "r13" and only provided that the normal use of the
25329       corresponding registers have been restricted via the -ffixed-reg or
25330       -mint-register command-line options.
25331
25332       S/390 and zSeries Options
25333
25334       These are the -m options defined for the S/390 and zSeries
25335       architecture.
25336
25337       -mhard-float
25338       -msoft-float
25339           Use (do not use) the hardware floating-point instructions and
25340           registers for floating-point operations.  When -msoft-float is
25341           specified, functions in libgcc.a are used to perform floating-point
25342           operations.  When -mhard-float is specified, the compiler generates
25343           IEEE floating-point instructions.  This is the default.
25344
25345       -mhard-dfp
25346       -mno-hard-dfp
25347           Use (do not use) the hardware decimal-floating-point instructions
25348           for decimal-floating-point operations.  When -mno-hard-dfp is
25349           specified, functions in libgcc.a are used to perform decimal-
25350           floating-point operations.  When -mhard-dfp is specified, the
25351           compiler generates decimal-floating-point hardware instructions.
25352           This is the default for -march=z9-ec or higher.
25353
25354       -mlong-double-64
25355       -mlong-double-128
25356           These switches control the size of "long double" type. A size of 64
25357           bits makes the "long double" type equivalent to the "double" type.
25358           This is the default.
25359
25360       -mbackchain
25361       -mno-backchain
25362           Store (do not store) the address of the caller's frame as backchain
25363           pointer into the callee's stack frame.  A backchain may be needed
25364           to allow debugging using tools that do not understand DWARF call
25365           frame information.  When -mno-packed-stack is in effect, the
25366           backchain pointer is stored at the bottom of the stack frame; when
25367           -mpacked-stack is in effect, the backchain is placed into the
25368           topmost word of the 96/160 byte register save area.
25369
25370           In general, code compiled with -mbackchain is call-compatible with
25371           code compiled with -mno-backchain; however, use of the backchain
25372           for debugging purposes usually requires that the whole binary is
25373           built with -mbackchain.  Note that the combination of -mbackchain,
25374           -mpacked-stack and -mhard-float is not supported.  In order to
25375           build a linux kernel use -msoft-float.
25376
25377           The default is to not maintain the backchain.
25378
25379       -mpacked-stack
25380       -mno-packed-stack
25381           Use (do not use) the packed stack layout.  When -mno-packed-stack
25382           is specified, the compiler uses the all fields of the 96/160 byte
25383           register save area only for their default purpose; unused fields
25384           still take up stack space.  When -mpacked-stack is specified,
25385           register save slots are densely packed at the top of the register
25386           save area; unused space is reused for other purposes, allowing for
25387           more efficient use of the available stack space.  However, when
25388           -mbackchain is also in effect, the topmost word of the save area is
25389           always used to store the backchain, and the return address register
25390           is always saved two words below the backchain.
25391
25392           As long as the stack frame backchain is not used, code generated
25393           with -mpacked-stack is call-compatible with code generated with
25394           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
25395           S/390 or zSeries generated code that uses the stack frame backchain
25396           at run time, not just for debugging purposes.  Such code is not
25397           call-compatible with code compiled with -mpacked-stack.  Also, note
25398           that the combination of -mbackchain, -mpacked-stack and
25399           -mhard-float is not supported.  In order to build a linux kernel
25400           use -msoft-float.
25401
25402           The default is to not use the packed stack layout.
25403
25404       -msmall-exec
25405       -mno-small-exec
25406           Generate (or do not generate) code using the "bras" instruction to
25407           do subroutine calls.  This only works reliably if the total
25408           executable size does not exceed 64k.  The default is to use the
25409           "basr" instruction instead, which does not have this limitation.
25410
25411       -m64
25412       -m31
25413           When -m31 is specified, generate code compliant to the GNU/Linux
25414           for S/390 ABI.  When -m64 is specified, generate code compliant to
25415           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
25416           generate 64-bit instructions.  For the s390 targets, the default is
25417           -m31, while the s390x targets default to -m64.
25418
25419       -mzarch
25420       -mesa
25421           When -mzarch is specified, generate code using the instructions
25422           available on z/Architecture.  When -mesa is specified, generate
25423           code using the instructions available on ESA/390.  Note that -mesa
25424           is not possible with -m64.  When generating code compliant to the
25425           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
25426           code compliant to the GNU/Linux for zSeries ABI, the default is
25427           -mzarch.
25428
25429       -mhtm
25430       -mno-htm
25431           The -mhtm option enables a set of builtins making use of
25432           instructions available with the transactional execution facility
25433           introduced with the IBM zEnterprise EC12 machine generation S/390
25434           System z Built-in Functions.  -mhtm is enabled by default when
25435           using -march=zEC12.
25436
25437       -mvx
25438       -mno-vx
25439           When -mvx is specified, generate code using the instructions
25440           available with the vector extension facility introduced with the
25441           IBM z13 machine generation.  This option changes the ABI for some
25442           vector type values with regard to alignment and calling
25443           conventions.  In case vector type values are being used in an ABI-
25444           relevant context a GAS .gnu_attribute command will be added to mark
25445           the resulting binary with the ABI used.  -mvx is enabled by default
25446           when using -march=z13.
25447
25448       -mzvector
25449       -mno-zvector
25450           The -mzvector option enables vector language extensions and
25451           builtins using instructions available with the vector extension
25452           facility introduced with the IBM z13 machine generation.  This
25453           option adds support for vector to be used as a keyword to define
25454           vector type variables and arguments.  vector is only available when
25455           GNU extensions are enabled.  It will not be expanded when
25456           requesting strict standard compliance e.g. with -std=c99.  In
25457           addition to the GCC low-level builtins -mzvector enables a set of
25458           builtins added for compatibility with AltiVec-style implementations
25459           like Power and Cell.  In order to make use of these builtins the
25460           header file vecintrin.h needs to be included.  -mzvector is
25461           disabled by default.
25462
25463       -mmvcle
25464       -mno-mvcle
25465           Generate (or do not generate) code using the "mvcle" instruction to
25466           perform block moves.  When -mno-mvcle is specified, use a "mvc"
25467           loop instead.  This is the default unless optimizing for size.
25468
25469       -mdebug
25470       -mno-debug
25471           Print (or do not print) additional debug information when
25472           compiling.  The default is to not print debug information.
25473
25474       -march=cpu-type
25475           Generate code that runs on cpu-type, which is the name of a system
25476           representing a certain processor type.  Possible values for cpu-
25477           type are z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8,
25478           z196/arch9, zEC12, z13/arch11, z14/arch12, z15/arch13, z16/arch14,
25479           and native.
25480
25481           The default is -march=z900.
25482
25483           Specifying native as cpu type can be used to select the best
25484           architecture option for the host processor.  -march=native has no
25485           effect if GCC does not recognize the processor.
25486
25487       -mtune=cpu-type
25488           Tune to cpu-type everything applicable about the generated code,
25489           except for the ABI and the set of available instructions.  The list
25490           of cpu-type values is the same as for -march.  The default is the
25491           value used for -march.
25492
25493       -mtpf-trace
25494       -mno-tpf-trace
25495           Generate code that adds (does not add) in TPF OS specific branches
25496           to trace routines in the operating system.  This option is off by
25497           default, even when compiling for the TPF OS.
25498
25499       -mtpf-trace-skip
25500       -mno-tpf-trace-skip
25501           Generate code that changes (does not change) the default branch
25502           targets enabled by -mtpf-trace to point to specialized trace
25503           routines providing the ability of selectively skipping function
25504           trace entries for the TPF OS.  This option is off by default, even
25505           when compiling for the TPF OS and specifying -mtpf-trace.
25506
25507       -mfused-madd
25508       -mno-fused-madd
25509           Generate code that uses (does not use) the floating-point multiply
25510           and accumulate instructions.  These instructions are generated by
25511           default if hardware floating point is used.
25512
25513       -mwarn-framesize=framesize
25514           Emit a warning if the current function exceeds the given frame
25515           size.  Because this is a compile-time check it doesn't need to be a
25516           real problem when the program runs.  It is intended to identify
25517           functions that most probably cause a stack overflow.  It is useful
25518           to be used in an environment with limited stack size e.g. the linux
25519           kernel.
25520
25521       -mwarn-dynamicstack
25522           Emit a warning if the function calls "alloca" or uses dynamically-
25523           sized arrays.  This is generally a bad idea with a limited stack
25524           size.
25525
25526       -mstack-guard=stack-guard
25527       -mstack-size=stack-size
25528           If these options are provided the S/390 back end emits additional
25529           instructions in the function prologue that trigger a trap if the
25530           stack size is stack-guard bytes above the stack-size (remember that
25531           the stack on S/390 grows downward).  If the stack-guard option is
25532           omitted the smallest power of 2 larger than the frame size of the
25533           compiled function is chosen.  These options are intended to be used
25534           to help debugging stack overflow problems.  The additionally
25535           emitted code causes only little overhead and hence can also be used
25536           in production-like systems without greater performance degradation.
25537           The given values have to be exact powers of 2 and stack-size has to
25538           be greater than stack-guard without exceeding 64k.  In order to be
25539           efficient the extra code makes the assumption that the stack starts
25540           at an address aligned to the value given by stack-size.  The stack-
25541           guard option can only be used in conjunction with stack-size.
25542
25543       -mhotpatch=pre-halfwords,post-halfwords
25544           If the hotpatch option is enabled, a "hot-patching" function
25545           prologue is generated for all functions in the compilation unit.
25546           The funtion label is prepended with the given number of two-byte
25547           NOP instructions (pre-halfwords, maximum 1000000).  After the
25548           label, 2 * post-halfwords bytes are appended, using the largest NOP
25549           like instructions the architecture allows (maximum 1000000).
25550
25551           If both arguments are zero, hotpatching is disabled.
25552
25553           This option can be overridden for individual functions with the
25554           "hotpatch" attribute.
25555
25556       Score Options
25557
25558       These options are defined for Score implementations:
25559
25560       -meb
25561           Compile code for big-endian mode.  This is the default.
25562
25563       -mel
25564           Compile code for little-endian mode.
25565
25566       -mnhwloop
25567           Disable generation of "bcnz" instructions.
25568
25569       -muls
25570           Enable generation of unaligned load and store instructions.
25571
25572       -mmac
25573           Enable the use of multiply-accumulate instructions. Disabled by
25574           default.
25575
25576       -mscore5
25577           Specify the SCORE5 as the target architecture.
25578
25579       -mscore5u
25580           Specify the SCORE5U of the target architecture.
25581
25582       -mscore7
25583           Specify the SCORE7 as the target architecture. This is the default.
25584
25585       -mscore7d
25586           Specify the SCORE7D as the target architecture.
25587
25588       SH Options
25589
25590       These -m options are defined for the SH implementations:
25591
25592       -m1 Generate code for the SH1.
25593
25594       -m2 Generate code for the SH2.
25595
25596       -m2e
25597           Generate code for the SH2e.
25598
25599       -m2a-nofpu
25600           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
25601           way that the floating-point unit is not used.
25602
25603       -m2a-single-only
25604           Generate code for the SH2a-FPU, in such a way that no double-
25605           precision floating-point operations are used.
25606
25607       -m2a-single
25608           Generate code for the SH2a-FPU assuming the floating-point unit is
25609           in single-precision mode by default.
25610
25611       -m2a
25612           Generate code for the SH2a-FPU assuming the floating-point unit is
25613           in double-precision mode by default.
25614
25615       -m3 Generate code for the SH3.
25616
25617       -m3e
25618           Generate code for the SH3e.
25619
25620       -m4-nofpu
25621           Generate code for the SH4 without a floating-point unit.
25622
25623       -m4-single-only
25624           Generate code for the SH4 with a floating-point unit that only
25625           supports single-precision arithmetic.
25626
25627       -m4-single
25628           Generate code for the SH4 assuming the floating-point unit is in
25629           single-precision mode by default.
25630
25631       -m4 Generate code for the SH4.
25632
25633       -m4-100
25634           Generate code for SH4-100.
25635
25636       -m4-100-nofpu
25637           Generate code for SH4-100 in such a way that the floating-point
25638           unit is not used.
25639
25640       -m4-100-single
25641           Generate code for SH4-100 assuming the floating-point unit is in
25642           single-precision mode by default.
25643
25644       -m4-100-single-only
25645           Generate code for SH4-100 in such a way that no double-precision
25646           floating-point operations are used.
25647
25648       -m4-200
25649           Generate code for SH4-200.
25650
25651       -m4-200-nofpu
25652           Generate code for SH4-200 without in such a way that the floating-
25653           point unit is not used.
25654
25655       -m4-200-single
25656           Generate code for SH4-200 assuming the floating-point unit is in
25657           single-precision mode by default.
25658
25659       -m4-200-single-only
25660           Generate code for SH4-200 in such a way that no double-precision
25661           floating-point operations are used.
25662
25663       -m4-300
25664           Generate code for SH4-300.
25665
25666       -m4-300-nofpu
25667           Generate code for SH4-300 without in such a way that the floating-
25668           point unit is not used.
25669
25670       -m4-300-single
25671           Generate code for SH4-300 in such a way that no double-precision
25672           floating-point operations are used.
25673
25674       -m4-300-single-only
25675           Generate code for SH4-300 in such a way that no double-precision
25676           floating-point operations are used.
25677
25678       -m4-340
25679           Generate code for SH4-340 (no MMU, no FPU).
25680
25681       -m4-500
25682           Generate code for SH4-500 (no FPU).  Passes -isa=sh4-nofpu to the
25683           assembler.
25684
25685       -m4a-nofpu
25686           Generate code for the SH4al-dsp, or for a SH4a in such a way that
25687           the floating-point unit is not used.
25688
25689       -m4a-single-only
25690           Generate code for the SH4a, in such a way that no double-precision
25691           floating-point operations are used.
25692
25693       -m4a-single
25694           Generate code for the SH4a assuming the floating-point unit is in
25695           single-precision mode by default.
25696
25697       -m4a
25698           Generate code for the SH4a.
25699
25700       -m4al
25701           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
25702           assembler.  GCC doesn't generate any DSP instructions at the
25703           moment.
25704
25705       -mb Compile code for the processor in big-endian mode.
25706
25707       -ml Compile code for the processor in little-endian mode.
25708
25709       -mdalign
25710           Align doubles at 64-bit boundaries.  Note that this changes the
25711           calling conventions, and thus some functions from the standard C
25712           library do not work unless you recompile it first with -mdalign.
25713
25714       -mrelax
25715           Shorten some address references at link time, when possible; uses
25716           the linker option -relax.
25717
25718       -mbigtable
25719           Use 32-bit offsets in "switch" tables.  The default is to use
25720           16-bit offsets.
25721
25722       -mbitops
25723           Enable the use of bit manipulation instructions on SH2A.
25724
25725       -mfmovd
25726           Enable the use of the instruction "fmovd".  Check -mdalign for
25727           alignment constraints.
25728
25729       -mrenesas
25730           Comply with the calling conventions defined by Renesas.
25731
25732       -mno-renesas
25733           Comply with the calling conventions defined for GCC before the
25734           Renesas conventions were available.  This option is the default for
25735           all targets of the SH toolchain.
25736
25737       -mnomacsave
25738           Mark the "MAC" register as call-clobbered, even if -mrenesas is
25739           given.
25740
25741       -mieee
25742       -mno-ieee
25743           Control the IEEE compliance of floating-point comparisons, which
25744           affects the handling of cases where the result of a comparison is
25745           unordered.  By default -mieee is implicitly enabled.  If
25746           -ffinite-math-only is enabled -mno-ieee is implicitly set, which
25747           results in faster floating-point greater-equal and less-equal
25748           comparisons.  The implicit settings can be overridden by specifying
25749           either -mieee or -mno-ieee.
25750
25751       -minline-ic_invalidate
25752           Inline code to invalidate instruction cache entries after setting
25753           up nested function trampolines.  This option has no effect if
25754           -musermode is in effect and the selected code generation option
25755           (e.g. -m4) does not allow the use of the "icbi" instruction.  If
25756           the selected code generation option does not allow the use of the
25757           "icbi" instruction, and -musermode is not in effect, the inlined
25758           code manipulates the instruction cache address array directly with
25759           an associative write.  This not only requires privileged mode at
25760           run time, but it also fails if the cache line had been mapped via
25761           the TLB and has become unmapped.
25762
25763       -misize
25764           Dump instruction size and location in the assembly code.
25765
25766       -mpadstruct
25767           This option is deprecated.  It pads structures to multiple of 4
25768           bytes, which is incompatible with the SH ABI.
25769
25770       -matomic-model=model
25771           Sets the model of atomic operations and additional parameters as a
25772           comma separated list.  For details on the atomic built-in functions
25773           see __atomic Builtins.  The following models and parameters are
25774           supported:
25775
25776           none
25777               Disable compiler generated atomic sequences and emit library
25778               calls for atomic operations.  This is the default if the target
25779               is not "sh*-*-linux*".
25780
25781           soft-gusa
25782               Generate GNU/Linux compatible gUSA software atomic sequences
25783               for the atomic built-in functions.  The generated atomic
25784               sequences require additional support from the
25785               interrupt/exception handling code of the system and are only
25786               suitable for SH3* and SH4* single-core systems.  This option is
25787               enabled by default when the target is "sh*-*-linux*" and SH3*
25788               or SH4*.  When the target is SH4A, this option also partially
25789               utilizes the hardware atomic instructions "movli.l" and
25790               "movco.l" to create more efficient code, unless strict is
25791               specified.
25792
25793           soft-tcb
25794               Generate software atomic sequences that use a variable in the
25795               thread control block.  This is a variation of the gUSA
25796               sequences which can also be used on SH1* and SH2* targets.  The
25797               generated atomic sequences require additional support from the
25798               interrupt/exception handling code of the system and are only
25799               suitable for single-core systems.  When using this model, the
25800               gbr-offset= parameter has to be specified as well.
25801
25802           soft-imask
25803               Generate software atomic sequences that temporarily disable
25804               interrupts by setting "SR.IMASK = 1111".  This model works only
25805               when the program runs in privileged mode and is only suitable
25806               for single-core systems.  Additional support from the
25807               interrupt/exception handling code of the system is not
25808               required.  This model is enabled by default when the target is
25809               "sh*-*-linux*" and SH1* or SH2*.
25810
25811           hard-llcs
25812               Generate hardware atomic sequences using the "movli.l" and
25813               "movco.l" instructions only.  This is only available on SH4A
25814               and is suitable for multi-core systems.  Since the hardware
25815               instructions support only 32 bit atomic variables access to 8
25816               or 16 bit variables is emulated with 32 bit accesses.  Code
25817               compiled with this option is also compatible with other
25818               software atomic model interrupt/exception handling systems if
25819               executed on an SH4A system.  Additional support from the
25820               interrupt/exception handling code of the system is not required
25821               for this model.
25822
25823           gbr-offset=
25824               This parameter specifies the offset in bytes of the variable in
25825               the thread control block structure that should be used by the
25826               generated atomic sequences when the soft-tcb model has been
25827               selected.  For other models this parameter is ignored.  The
25828               specified value must be an integer multiple of four and in the
25829               range 0-1020.
25830
25831           strict
25832               This parameter prevents mixed usage of multiple atomic models,
25833               even if they are compatible, and makes the compiler generate
25834               atomic sequences of the specified model only.
25835
25836       -mtas
25837           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice
25838           that depending on the particular hardware and software
25839           configuration this can degrade overall performance due to the
25840           operand cache line flushes that are implied by the "tas.b"
25841           instruction.  On multi-core SH4A processors the "tas.b" instruction
25842           must be used with caution since it can result in data corruption
25843           for certain cache configurations.
25844
25845       -mprefergot
25846           When generating position-independent code, emit function calls
25847           using the Global Offset Table instead of the Procedure Linkage
25848           Table.
25849
25850       -musermode
25851       -mno-usermode
25852           Don't allow (allow) the compiler generating privileged mode code.
25853           Specifying -musermode also implies -mno-inline-ic_invalidate if the
25854           inlined code would not work in user mode.  -musermode is the
25855           default when the target is "sh*-*-linux*".  If the target is SH1*
25856           or SH2* -musermode has no effect, since there is no user mode.
25857
25858       -multcost=number
25859           Set the cost to assume for a multiply insn.
25860
25861       -mdiv=strategy
25862           Set the division strategy to be used for integer division
25863           operations.  strategy can be one of:
25864
25865           call-div1
25866               Calls a library function that uses the single-step division
25867               instruction "div1" to perform the operation.  Division by zero
25868               calculates an unspecified result and does not trap.  This is
25869               the default except for SH4, SH2A and SHcompact.
25870
25871           call-fp
25872               Calls a library function that performs the operation in double
25873               precision floating point.  Division by zero causes a floating-
25874               point exception.  This is the default for SHcompact with FPU.
25875               Specifying this for targets that do not have a double precision
25876               FPU defaults to "call-div1".
25877
25878           call-table
25879               Calls a library function that uses a lookup table for small
25880               divisors and the "div1" instruction with case distinction for
25881               larger divisors.  Division by zero calculates an unspecified
25882               result and does not trap.  This is the default for SH4.
25883               Specifying this for targets that do not have dynamic shift
25884               instructions defaults to "call-div1".
25885
25886           When a division strategy has not been specified the default
25887           strategy is selected based on the current target.  For SH2A the
25888           default strategy is to use the "divs" and "divu" instructions
25889           instead of library function calls.
25890
25891       -maccumulate-outgoing-args
25892           Reserve space once for outgoing arguments in the function prologue
25893           rather than around each call.  Generally beneficial for performance
25894           and size.  Also needed for unwinding to avoid changing the stack
25895           frame around conditional code.
25896
25897       -mdivsi3_libfunc=name
25898           Set the name of the library function used for 32-bit signed
25899           division to name.  This only affects the name used in the call
25900           division strategies, and the compiler still expects the same sets
25901           of input/output/clobbered registers as if this option were not
25902           present.
25903
25904       -mfixed-range=register-range
25905           Generate code treating the given register range as fixed registers.
25906           A fixed register is one that the register allocator cannot use.
25907           This is useful when compiling kernel code.  A register range is
25908           specified as two registers separated by a dash.  Multiple register
25909           ranges can be specified separated by a comma.
25910
25911       -mbranch-cost=num
25912           Assume num to be the cost for a branch instruction.  Higher numbers
25913           make the compiler try to generate more branch-free code if
25914           possible.  If not specified the value is selected depending on the
25915           processor type that is being compiled for.
25916
25917       -mzdcbranch
25918       -mno-zdcbranch
25919           Assume (do not assume) that zero displacement conditional branch
25920           instructions "bt" and "bf" are fast.  If -mzdcbranch is specified,
25921           the compiler prefers zero displacement branch code sequences.  This
25922           is enabled by default when generating code for SH4 and SH4A.  It
25923           can be explicitly disabled by specifying -mno-zdcbranch.
25924
25925       -mcbranch-force-delay-slot
25926           Force the usage of delay slots for conditional branches, which
25927           stuffs the delay slot with a "nop" if a suitable instruction cannot
25928           be found.  By default this option is disabled.  It can be enabled
25929           to work around hardware bugs as found in the original SH7055.
25930
25931       -mfused-madd
25932       -mno-fused-madd
25933           Generate code that uses (does not use) the floating-point multiply
25934           and accumulate instructions.  These instructions are generated by
25935           default if hardware floating point is used.  The machine-dependent
25936           -mfused-madd option is now mapped to the machine-independent
25937           -ffp-contract=fast option, and -mno-fused-madd is mapped to
25938           -ffp-contract=off.
25939
25940       -mfsca
25941       -mno-fsca
25942           Allow or disallow the compiler to emit the "fsca" instruction for
25943           sine and cosine approximations.  The option -mfsca must be used in
25944           combination with -funsafe-math-optimizations.  It is enabled by
25945           default when generating code for SH4A.  Using -mno-fsca disables
25946           sine and cosine approximations even if -funsafe-math-optimizations
25947           is in effect.
25948
25949       -mfsrra
25950       -mno-fsrra
25951           Allow or disallow the compiler to emit the "fsrra" instruction for
25952           reciprocal square root approximations.  The option -mfsrra must be
25953           used in combination with -funsafe-math-optimizations and
25954           -ffinite-math-only.  It is enabled by default when generating code
25955           for SH4A.  Using -mno-fsrra disables reciprocal square root
25956           approximations even if -funsafe-math-optimizations and
25957           -ffinite-math-only are in effect.
25958
25959       -mpretend-cmove
25960           Prefer zero-displacement conditional branches for conditional move
25961           instruction patterns.  This can result in faster code on the SH4
25962           processor.
25963
25964       -mfdpic
25965           Generate code using the FDPIC ABI.
25966
25967       Solaris 2 Options
25968
25969       These -m options are supported on Solaris 2:
25970
25971       -mclear-hwcap
25972           -mclear-hwcap tells the compiler to remove the hardware
25973           capabilities generated by the Solaris assembler.  This is only
25974           necessary when object files use ISA extensions not supported by the
25975           current machine, but check at runtime whether or not to use them.
25976
25977       -mimpure-text
25978           -mimpure-text, used in addition to -shared, tells the compiler to
25979           not pass -z text to the linker when linking a shared object.  Using
25980           this option, you can link position-dependent code into a shared
25981           object.
25982
25983           -mimpure-text suppresses the "relocations remain against
25984           allocatable but non-writable sections" linker error message.
25985           However, the necessary relocations trigger copy-on-write, and the
25986           shared object is not actually shared across processes.  Instead of
25987           using -mimpure-text, you should compile all source code with -fpic
25988           or -fPIC.
25989
25990       These switches are supported in addition to the above on Solaris 2:
25991
25992       -pthreads
25993           This is a synonym for -pthread.
25994
25995       SPARC Options
25996
25997       These -m options are supported on the SPARC:
25998
25999       -mno-app-regs
26000       -mapp-regs
26001           Specify -mapp-regs to generate output using the global registers 2
26002           through 4, which the SPARC SVR4 ABI reserves for applications.
26003           Like the global register 1, each global register 2 through 4 is
26004           then treated as an allocable register that is clobbered by function
26005           calls.  This is the default.
26006
26007           To be fully SVR4 ABI-compliant at the cost of some performance
26008           loss, specify -mno-app-regs.  You should compile libraries and
26009           system software with this option.
26010
26011       -mflat
26012       -mno-flat
26013           With -mflat, the compiler does not generate save/restore
26014           instructions and uses a "flat" or single register window model.
26015           This model is compatible with the regular register window model.
26016           The local registers and the input registers (0--5) are still
26017           treated as "call-saved" registers and are saved on the stack as
26018           needed.
26019
26020           With -mno-flat (the default), the compiler generates save/restore
26021           instructions (except for leaf functions).  This is the normal
26022           operating mode.
26023
26024       -mfpu
26025       -mhard-float
26026           Generate output containing floating-point instructions.  This is
26027           the default.
26028
26029       -mno-fpu
26030       -msoft-float
26031           Generate output containing library calls for floating point.
26032           Warning: the requisite libraries are not available for all SPARC
26033           targets.  Normally the facilities of the machine's usual C compiler
26034           are used, but this cannot be done directly in cross-compilation.
26035           You must make your own arrangements to provide suitable library
26036           functions for cross-compilation.  The embedded targets sparc-*-aout
26037           and sparclite-*-* do provide software floating-point support.
26038
26039           -msoft-float changes the calling convention in the output file;
26040           therefore, it is only useful if you compile all of a program with
26041           this option.  In particular, you need to compile libgcc.a, the
26042           library that comes with GCC, with -msoft-float in order for this to
26043           work.
26044
26045       -mhard-quad-float
26046           Generate output containing quad-word (long double) floating-point
26047           instructions.
26048
26049       -msoft-quad-float
26050           Generate output containing library calls for quad-word (long
26051           double) floating-point instructions.  The functions called are
26052           those specified in the SPARC ABI.  This is the default.
26053
26054           As of this writing, there are no SPARC implementations that have
26055           hardware support for the quad-word floating-point instructions.
26056           They all invoke a trap handler for one of these instructions, and
26057           then the trap handler emulates the effect of the instruction.
26058           Because of the trap handler overhead, this is much slower than
26059           calling the ABI library routines.  Thus the -msoft-quad-float
26060           option is the default.
26061
26062       -mno-unaligned-doubles
26063       -munaligned-doubles
26064           Assume that doubles have 8-byte alignment.  This is the default.
26065
26066           With -munaligned-doubles, GCC assumes that doubles have 8-byte
26067           alignment only if they are contained in another type, or if they
26068           have an absolute address.  Otherwise, it assumes they have 4-byte
26069           alignment.  Specifying this option avoids some rare compatibility
26070           problems with code generated by other compilers.  It is not the
26071           default because it results in a performance loss, especially for
26072           floating-point code.
26073
26074       -muser-mode
26075       -mno-user-mode
26076           Do not generate code that can only run in supervisor mode.  This is
26077           relevant only for the "casa" instruction emitted for the LEON3
26078           processor.  This is the default.
26079
26080       -mfaster-structs
26081       -mno-faster-structs
26082           With -mfaster-structs, the compiler assumes that structures should
26083           have 8-byte alignment.  This enables the use of pairs of "ldd" and
26084           "std" instructions for copies in structure assignment, in place of
26085           twice as many "ld" and "st" pairs.  However, the use of this
26086           changed alignment directly violates the SPARC ABI.  Thus, it's
26087           intended only for use on targets where the developer acknowledges
26088           that their resulting code is not directly in line with the rules of
26089           the ABI.
26090
26091       -mstd-struct-return
26092       -mno-std-struct-return
26093           With -mstd-struct-return, the compiler generates checking code in
26094           functions returning structures or unions to detect size mismatches
26095           between the two sides of function calls, as per the 32-bit ABI.
26096
26097           The default is -mno-std-struct-return.  This option has no effect
26098           in 64-bit mode.
26099
26100       -mlra
26101       -mno-lra
26102           Enable Local Register Allocation.  This is the default for SPARC
26103           since GCC 7 so -mno-lra needs to be passed to get old Reload.
26104
26105       -mcpu=cpu_type
26106           Set the instruction set, register set, and instruction scheduling
26107           parameters for machine type cpu_type.  Supported values for
26108           cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3,
26109           leon3v7, leon5, sparclite, f930, f934, sparclite86x, sparclet,
26110           tsc701, v9, ultrasparc, ultrasparc3, niagara, niagara2, niagara3,
26111           niagara4, niagara7 and m8.
26112
26113           Native Solaris and GNU/Linux toolchains also support the value
26114           native, which selects the best architecture option for the host
26115           processor.  -mcpu=native has no effect if GCC does not recognize
26116           the processor.
26117
26118           Default instruction scheduling parameters are used for values that
26119           select an architecture and not an implementation.  These are v7,
26120           v8, sparclite, sparclet, v9.
26121
26122           Here is a list of each supported architecture and their supported
26123           implementations.
26124
26125           v7  cypress, leon3v7
26126
26127           v8  supersparc, hypersparc, leon, leon3, leon5
26128
26129           sparclite
26130               f930, f934, sparclite86x
26131
26132           sparclet
26133               tsc701
26134
26135           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
26136               niagara7, m8
26137
26138           By default (unless configured otherwise), GCC generates code for
26139           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
26140           compiler additionally optimizes it for the Cypress CY7C602 chip, as
26141           used in the SPARCStation/SPARCServer 3xx series.  This is also
26142           appropriate for the older SPARCStation 1, 2, IPX etc.
26143
26144           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
26145           architecture.  The only difference from V7 code is that the
26146           compiler emits the integer multiply and integer divide instructions
26147           which exist in SPARC-V8 but not in SPARC-V7.  With
26148           -mcpu=supersparc, the compiler additionally optimizes it for the
26149           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
26150           series.
26151
26152           With -mcpu=sparclite, GCC generates code for the SPARClite variant
26153           of the SPARC architecture.  This adds the integer multiply, integer
26154           divide step and scan ("ffs") instructions which exist in SPARClite
26155           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
26156           optimizes it for the Fujitsu MB86930 chip, which is the original
26157           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
26158           optimizes it for the Fujitsu MB86934 chip, which is the more recent
26159           SPARClite with FPU.
26160
26161           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
26162           the SPARC architecture.  This adds the integer multiply,
26163           multiply/accumulate, integer divide step and scan ("ffs")
26164           instructions which exist in SPARClet but not in SPARC-V7.  With
26165           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
26166           SPARClet chip.
26167
26168           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
26169           architecture.  This adds 64-bit integer and floating-point move
26170           instructions, 3 additional floating-point condition code registers
26171           and conditional move instructions.  With -mcpu=ultrasparc, the
26172           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
26173           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
26174           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
26175           -mcpu=niagara, the compiler additionally optimizes it for Sun
26176           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
26177           additionally optimizes it for Sun UltraSPARC T2 chips. With
26178           -mcpu=niagara3, the compiler additionally optimizes it for Sun
26179           UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler
26180           additionally optimizes it for Sun UltraSPARC T4 chips.  With
26181           -mcpu=niagara7, the compiler additionally optimizes it for Oracle
26182           SPARC M7 chips.  With -mcpu=m8, the compiler additionally optimizes
26183           it for Oracle M8 chips.
26184
26185       -mtune=cpu_type
26186           Set the instruction scheduling parameters for machine type
26187           cpu_type, but do not set the instruction set or register set that
26188           the option -mcpu=cpu_type does.
26189
26190           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
26191           but the only useful values are those that select a particular CPU
26192           implementation.  Those are cypress, supersparc, hypersparc, leon,
26193           leon3, leon3v7, leon5, f930, f934, sparclite86x, tsc701,
26194           ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
26195           niagara7 and m8.  With native Solaris and GNU/Linux toolchains,
26196           native can also be used.
26197
26198       -mv8plus
26199       -mno-v8plus
26200           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
26201           difference from the V8 ABI is that the global and out registers are
26202           considered 64 bits wide.  This is enabled by default on Solaris in
26203           32-bit mode for all SPARC-V9 processors.
26204
26205       -mvis
26206       -mno-vis
26207           With -mvis, GCC generates code that takes advantage of the
26208           UltraSPARC Visual Instruction Set extensions.  The default is
26209           -mno-vis.
26210
26211       -mvis2
26212       -mno-vis2
26213           With -mvis2, GCC generates code that takes advantage of version 2.0
26214           of the UltraSPARC Visual Instruction Set extensions.  The default
26215           is -mvis2 when targeting a cpu that supports such instructions,
26216           such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.
26217
26218       -mvis3
26219       -mno-vis3
26220           With -mvis3, GCC generates code that takes advantage of version 3.0
26221           of the UltraSPARC Visual Instruction Set extensions.  The default
26222           is -mvis3 when targeting a cpu that supports such instructions,
26223           such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and
26224           -mvis.
26225
26226       -mvis4
26227       -mno-vis4
26228           With -mvis4, GCC generates code that takes advantage of version 4.0
26229           of the UltraSPARC Visual Instruction Set extensions.  The default
26230           is -mvis4 when targeting a cpu that supports such instructions,
26231           such as niagara-7 and later.  Setting -mvis4 also sets -mvis3,
26232           -mvis2 and -mvis.
26233
26234       -mvis4b
26235       -mno-vis4b
26236           With -mvis4b, GCC generates code that takes advantage of version
26237           4.0 of the UltraSPARC Visual Instruction Set extensions, plus the
26238           additional VIS instructions introduced in the Oracle SPARC
26239           Architecture 2017.  The default is -mvis4b when targeting a cpu
26240           that supports such instructions, such as m8 and later.  Setting
26241           -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis.
26242
26243       -mcbcond
26244       -mno-cbcond
26245           With -mcbcond, GCC generates code that takes advantage of the
26246           UltraSPARC Compare-and-Branch-on-Condition instructions.  The
26247           default is -mcbcond when targeting a CPU that supports such
26248           instructions, such as Niagara-4 and later.
26249
26250       -mfmaf
26251       -mno-fmaf
26252           With -mfmaf, GCC generates code that takes advantage of the
26253           UltraSPARC Fused Multiply-Add Floating-point instructions.  The
26254           default is -mfmaf when targeting a CPU that supports such
26255           instructions, such as Niagara-3 and later.
26256
26257       -mfsmuld
26258       -mno-fsmuld
26259           With -mfsmuld, GCC generates code that takes advantage of the
26260           Floating-point Multiply Single to Double (FsMULd) instruction.  The
26261           default is -mfsmuld when targeting a CPU supporting the
26262           architecture versions V8 or V9 with FPU except -mcpu=leon.
26263
26264       -mpopc
26265       -mno-popc
26266           With -mpopc, GCC generates code that takes advantage of the
26267           UltraSPARC Population Count instruction.  The default is -mpopc
26268           when targeting a CPU that supports such an instruction, such as
26269           Niagara-2 and later.
26270
26271       -msubxc
26272       -mno-subxc
26273           With -msubxc, GCC generates code that takes advantage of the
26274           UltraSPARC Subtract-Extended-with-Carry instruction.  The default
26275           is -msubxc when targeting a CPU that supports such an instruction,
26276           such as Niagara-7 and later.
26277
26278       -mfix-at697f
26279           Enable the documented workaround for the single erratum of the
26280           Atmel AT697F processor (which corresponds to erratum #13 of the
26281           AT697E processor).
26282
26283       -mfix-ut699
26284           Enable the documented workarounds for the floating-point errata and
26285           the data cache nullify errata of the UT699 processor.
26286
26287       -mfix-ut700
26288           Enable the documented workaround for the back-to-back store errata
26289           of the UT699E/UT700 processor.
26290
26291       -mfix-gr712rc
26292           Enable the documented workaround for the back-to-back store errata
26293           of the GR712RC processor.
26294
26295       These -m options are supported in addition to the above on SPARC-V9
26296       processors in 64-bit environments:
26297
26298       -m32
26299       -m64
26300           Generate code for a 32-bit or 64-bit environment.  The 32-bit
26301           environment sets int, long and pointer to 32 bits.  The 64-bit
26302           environment sets int to 32 bits and long and pointer to 64 bits.
26303
26304       -mcmodel=which
26305           Set the code model to one of
26306
26307           medlow
26308               The Medium/Low code model: 64-bit addresses, programs must be
26309               linked in the low 32 bits of memory.  Programs can be
26310               statically or dynamically linked.
26311
26312           medmid
26313               The Medium/Middle code model: 64-bit addresses, programs must
26314               be linked in the low 44 bits of memory, the text and data
26315               segments must be less than 2GB in size and the data segment
26316               must be located within 2GB of the text segment.
26317
26318           medany
26319               The Medium/Anywhere code model: 64-bit addresses, programs may
26320               be linked anywhere in memory, the text and data segments must
26321               be less than 2GB in size and the data segment must be located
26322               within 2GB of the text segment.
26323
26324           embmedany
26325               The Medium/Anywhere code model for embedded systems: 64-bit
26326               addresses, the text and data segments must be less than 2GB in
26327               size, both starting anywhere in memory (determined at link
26328               time).  The global register %g4 points to the base of the data
26329               segment.  Programs are statically linked and PIC is not
26330               supported.
26331
26332       -mmemory-model=mem-model
26333           Set the memory model in force on the processor to one of
26334
26335           default
26336               The default memory model for the processor and operating
26337               system.
26338
26339           rmo Relaxed Memory Order
26340
26341           pso Partial Store Order
26342
26343           tso Total Store Order
26344
26345           sc  Sequential Consistency
26346
26347           These memory models are formally defined in Appendix D of the
26348           SPARC-V9 architecture manual, as set in the processor's "PSTATE.MM"
26349           field.
26350
26351       -mstack-bias
26352       -mno-stack-bias
26353           With -mstack-bias, GCC assumes that the stack pointer, and frame
26354           pointer if present, are offset by -2047 which must be added back
26355           when making stack frame references.  This is the default in 64-bit
26356           mode.  Otherwise, assume no such offset is present.
26357
26358       Options for System V
26359
26360       These additional options are available on System V Release 4 for
26361       compatibility with other compilers on those systems:
26362
26363       -G  Create a shared object.  It is recommended that -symbolic or
26364           -shared be used instead.
26365
26366       -Qy Identify the versions of each tool used by the compiler, in a
26367           ".ident" assembler directive in the output.
26368
26369       -Qn Refrain from adding ".ident" directives to the output file (this is
26370           the default).
26371
26372       -YP,dirs
26373           Search the directories dirs, and no others, for libraries specified
26374           with -l.
26375
26376       -Ym,dir
26377           Look in the directory dir to find the M4 preprocessor.  The
26378           assembler uses this option.
26379
26380       TILE-Gx Options
26381
26382       These -m options are supported on the TILE-Gx:
26383
26384       -mcmodel=small
26385           Generate code for the small model.  The distance for direct calls
26386           is limited to 500M in either direction.  PC-relative addresses are
26387           32 bits.  Absolute addresses support the full address range.
26388
26389       -mcmodel=large
26390           Generate code for the large model.  There is no limitation on call
26391           distance, pc-relative addresses, or absolute addresses.
26392
26393       -mcpu=name
26394           Selects the type of CPU to be targeted.  Currently the only
26395           supported type is tilegx.
26396
26397       -m32
26398       -m64
26399           Generate code for a 32-bit or 64-bit environment.  The 32-bit
26400           environment sets int, long, and pointer to 32 bits.  The 64-bit
26401           environment sets int to 32 bits and long and pointer to 64 bits.
26402
26403       -mbig-endian
26404       -mlittle-endian
26405           Generate code in big/little endian mode, respectively.
26406
26407       TILEPro Options
26408
26409       These -m options are supported on the TILEPro:
26410
26411       -mcpu=name
26412           Selects the type of CPU to be targeted.  Currently the only
26413           supported type is tilepro.
26414
26415       -m32
26416           Generate code for a 32-bit environment, which sets int, long, and
26417           pointer to 32 bits.  This is the only supported behavior so the
26418           flag is essentially ignored.
26419
26420       V850 Options
26421
26422       These -m options are defined for V850 implementations:
26423
26424       -mlong-calls
26425       -mno-long-calls
26426           Treat all calls as being far away (near).  If calls are assumed to
26427           be far away, the compiler always loads the function's address into
26428           a register, and calls indirect through the pointer.
26429
26430       -mno-ep
26431       -mep
26432           Do not optimize (do optimize) basic blocks that use the same index
26433           pointer 4 or more times to copy pointer into the "ep" register, and
26434           use the shorter "sld" and "sst" instructions.  The -mep option is
26435           on by default if you optimize.
26436
26437       -mno-prolog-function
26438       -mprolog-function
26439           Do not use (do use) external functions to save and restore
26440           registers at the prologue and epilogue of a function.  The external
26441           functions are slower, but use less code space if more than one
26442           function saves the same number of registers.  The -mprolog-function
26443           option is on by default if you optimize.
26444
26445       -mspace
26446           Try to make the code as small as possible.  At present, this just
26447           turns on the -mep and -mprolog-function options.
26448
26449       -mtda=n
26450           Put static or global variables whose size is n bytes or less into
26451           the tiny data area that register "ep" points to.  The tiny data
26452           area can hold up to 256 bytes in total (128 bytes for byte
26453           references).
26454
26455       -msda=n
26456           Put static or global variables whose size is n bytes or less into
26457           the small data area that register "gp" points to.  The small data
26458           area can hold up to 64 kilobytes.
26459
26460       -mzda=n
26461           Put static or global variables whose size is n bytes or less into
26462           the first 32 kilobytes of memory.
26463
26464       -mv850
26465           Specify that the target processor is the V850.
26466
26467       -mv850e3v5
26468           Specify that the target processor is the V850E3V5.  The
26469           preprocessor constant "__v850e3v5__" is defined if this option is
26470           used.
26471
26472       -mv850e2v4
26473           Specify that the target processor is the V850E3V5.  This is an
26474           alias for the -mv850e3v5 option.
26475
26476       -mv850e2v3
26477           Specify that the target processor is the V850E2V3.  The
26478           preprocessor constant "__v850e2v3__" is defined if this option is
26479           used.
26480
26481       -mv850e2
26482           Specify that the target processor is the V850E2.  The preprocessor
26483           constant "__v850e2__" is defined if this option is used.
26484
26485       -mv850e1
26486           Specify that the target processor is the V850E1.  The preprocessor
26487           constants "__v850e1__" and "__v850e__" are defined if this option
26488           is used.
26489
26490       -mv850es
26491           Specify that the target processor is the V850ES.  This is an alias
26492           for the -mv850e1 option.
26493
26494       -mv850e
26495           Specify that the target processor is the V850E.  The preprocessor
26496           constant "__v850e__" is defined if this option is used.
26497
26498           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor
26499           -mv850e2v3 nor -mv850e3v5 are defined then a default target
26500           processor is chosen and the relevant __v850*__ preprocessor
26501           constant is defined.
26502
26503           The preprocessor constants "__v850" and "__v851__" are always
26504           defined, regardless of which processor variant is the target.
26505
26506       -mdisable-callt
26507       -mno-disable-callt
26508           This option suppresses generation of the "CALLT" instruction for
26509           the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
26510           v850 architecture.
26511
26512           This option is enabled by default when the RH850 ABI is in use (see
26513           -mrh850-abi), and disabled by default when the GCC ABI is in use.
26514           If "CALLT" instructions are being generated then the C preprocessor
26515           symbol "__V850_CALLT__" is defined.
26516
26517       -mrelax
26518       -mno-relax
26519           Pass on (or do not pass on) the -mrelax command-line option to the
26520           assembler.
26521
26522       -mlong-jumps
26523       -mno-long-jumps
26524           Disable (or re-enable) the generation of PC-relative jump
26525           instructions.
26526
26527       -msoft-float
26528       -mhard-float
26529           Disable (or re-enable) the generation of hardware floating point
26530           instructions.  This option is only significant when the target
26531           architecture is V850E2V3 or higher.  If hardware floating point
26532           instructions are being generated then the C preprocessor symbol
26533           "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is
26534           defined.
26535
26536       -mloop
26537           Enables the use of the e3v5 LOOP instruction.  The use of this
26538           instruction is not enabled by default when the e3v5 architecture is
26539           selected because its use is still experimental.
26540
26541       -mrh850-abi
26542       -mghs
26543           Enables support for the RH850 version of the V850 ABI.  This is the
26544           default.  With this version of the ABI the following rules apply:
26545
26546           *   Integer sized structures and unions are returned via a memory
26547               pointer rather than a register.
26548
26549           *   Large structures and unions (more than 8 bytes in size) are
26550               passed by value.
26551
26552           *   Functions are aligned to 16-bit boundaries.
26553
26554           *   The -m8byte-align command-line option is supported.
26555
26556           *   The -mdisable-callt command-line option is enabled by default.
26557               The -mno-disable-callt command-line option is not supported.
26558
26559           When this version of the ABI is enabled the C preprocessor symbol
26560           "__V850_RH850_ABI__" is defined.
26561
26562       -mgcc-abi
26563           Enables support for the old GCC version of the V850 ABI.  With this
26564           version of the ABI the following rules apply:
26565
26566           *   Integer sized structures and unions are returned in register
26567               "r10".
26568
26569           *   Large structures and unions (more than 8 bytes in size) are
26570               passed by reference.
26571
26572           *   Functions are aligned to 32-bit boundaries, unless optimizing
26573               for size.
26574
26575           *   The -m8byte-align command-line option is not supported.
26576
26577           *   The -mdisable-callt command-line option is supported but not
26578               enabled by default.
26579
26580           When this version of the ABI is enabled the C preprocessor symbol
26581           "__V850_GCC_ABI__" is defined.
26582
26583       -m8byte-align
26584       -mno-8byte-align
26585           Enables support for "double" and "long long" types to be aligned on
26586           8-byte boundaries.  The default is to restrict the alignment of all
26587           objects to at most 4-bytes.  When -m8byte-align is in effect the C
26588           preprocessor symbol "__V850_8BYTE_ALIGN__" is defined.
26589
26590       -mbig-switch
26591           Generate code suitable for big switch tables.  Use this option only
26592           if the assembler/linker complain about out of range branches within
26593           a switch table.
26594
26595       -mapp-regs
26596           This option causes r2 and r5 to be used in the code generated by
26597           the compiler.  This setting is the default.
26598
26599       -mno-app-regs
26600           This option causes r2 and r5 to be treated as fixed registers.
26601
26602       VAX Options
26603
26604       These -m options are defined for the VAX:
26605
26606       -munix
26607           Do not output certain jump instructions ("aobleq" and so on) that
26608           the Unix assembler for the VAX cannot handle across long ranges.
26609
26610       -mgnu
26611           Do output those jump instructions, on the assumption that the GNU
26612           assembler is being used.
26613
26614       -mg Output code for G-format floating-point numbers instead of
26615           D-format.
26616
26617       -mlra
26618       -mno-lra
26619           Enable Local Register Allocation.  This is still experimental for
26620           the VAX, so by default the compiler uses standard reload.
26621
26622       Visium Options
26623
26624       -mdebug
26625           A program which performs file I/O and is destined to run on an MCM
26626           target should be linked with this option.  It causes the libraries
26627           libc.a and libdebug.a to be linked.  The program should be run on
26628           the target under the control of the GDB remote debugging stub.
26629
26630       -msim
26631           A program which performs file I/O and is destined to run on the
26632           simulator should be linked with option.  This causes libraries
26633           libc.a and libsim.a to be linked.
26634
26635       -mfpu
26636       -mhard-float
26637           Generate code containing floating-point instructions.  This is the
26638           default.
26639
26640       -mno-fpu
26641       -msoft-float
26642           Generate code containing library calls for floating-point.
26643
26644           -msoft-float changes the calling convention in the output file;
26645           therefore, it is only useful if you compile all of a program with
26646           this option.  In particular, you need to compile libgcc.a, the
26647           library that comes with GCC, with -msoft-float in order for this to
26648           work.
26649
26650       -mcpu=cpu_type
26651           Set the instruction set, register set, and instruction scheduling
26652           parameters for machine type cpu_type.  Supported values for
26653           cpu_type are mcm, gr5 and gr6.
26654
26655           mcm is a synonym of gr5 present for backward compatibility.
26656
26657           By default (unless configured otherwise), GCC generates code for
26658           the GR5 variant of the Visium architecture.
26659
26660           With -mcpu=gr6, GCC generates code for the GR6 variant of the
26661           Visium architecture.  The only difference from GR5 code is that the
26662           compiler will generate block move instructions.
26663
26664       -mtune=cpu_type
26665           Set the instruction scheduling parameters for machine type
26666           cpu_type, but do not set the instruction set or register set that
26667           the option -mcpu=cpu_type would.
26668
26669       -msv-mode
26670           Generate code for the supervisor mode, where there are no
26671           restrictions on the access to general registers.  This is the
26672           default.
26673
26674       -muser-mode
26675           Generate code for the user mode, where the access to some general
26676           registers is forbidden: on the GR5, registers r24 to r31 cannot be
26677           accessed in this mode; on the GR6, only registers r29 to r31 are
26678           affected.
26679
26680       VMS Options
26681
26682       These -m options are defined for the VMS implementations:
26683
26684       -mvms-return-codes
26685           Return VMS condition codes from "main". The default is to return
26686           POSIX-style condition (e.g. error) codes.
26687
26688       -mdebug-main=prefix
26689           Flag the first routine whose name starts with prefix as the main
26690           routine for the debugger.
26691
26692       -mmalloc64
26693           Default to 64-bit memory allocation routines.
26694
26695       -mpointer-size=size
26696           Set the default size of pointers. Possible options for size are 32
26697           or short for 32 bit pointers, 64 or long for 64 bit pointers, and
26698           no for supporting only 32 bit pointers.  The later option disables
26699           "pragma pointer_size".
26700
26701       VxWorks Options
26702
26703       The options in this section are defined for all VxWorks targets.
26704       Options specific to the target hardware are listed with the other
26705       options for that target.
26706
26707       -mrtp
26708           GCC can generate code for both VxWorks kernels and real time
26709           processes (RTPs).  This option switches from the former to the
26710           latter.  It also defines the preprocessor macro "__RTP__".
26711
26712       -non-static
26713           Link an RTP executable against shared libraries rather than static
26714           libraries.  The options -static and -shared can also be used for
26715           RTPs; -static is the default.
26716
26717       -Bstatic
26718       -Bdynamic
26719           These options are passed down to the linker.  They are defined for
26720           compatibility with Diab.
26721
26722       -Xbind-lazy
26723           Enable lazy binding of function calls.  This option is equivalent
26724           to -Wl,-z,now and is defined for compatibility with Diab.
26725
26726       -Xbind-now
26727           Disable lazy binding of function calls.  This option is the default
26728           and is defined for compatibility with Diab.
26729
26730       x86 Options
26731
26732       These -m options are defined for the x86 family of computers.
26733
26734       -march=cpu-type
26735           Generate instructions for the machine type cpu-type.  In contrast
26736           to -mtune=cpu-type, which merely tunes the generated code for the
26737           specified cpu-type, -march=cpu-type allows GCC to generate code
26738           that may not run at all on processors other than the one indicated.
26739           Specifying -march=cpu-type implies -mtune=cpu-type, except where
26740           noted otherwise.
26741
26742           The choices for cpu-type are:
26743
26744           native
26745               This selects the CPU to generate code for at compilation time
26746               by determining the processor type of the compiling machine.
26747               Using -march=native enables all instruction subsets supported
26748               by the local machine (hence the result might not run on
26749               different machines).  Using -mtune=native produces code
26750               optimized for the local machine under the constraints of the
26751               selected instruction set.
26752
26753           x86-64
26754               A generic CPU with 64-bit extensions.
26755
26756           x86-64-v2
26757           x86-64-v3
26758           x86-64-v4
26759               These choices for cpu-type select the corresponding micro-
26760               architecture level from the x86-64 psABI.  On ABIs other than
26761               the x86-64 psABI they select the same CPU features as the
26762               x86-64 psABI documents for the particular micro-architecture
26763               level.
26764
26765               Since these cpu-type values do not have a corresponding -mtune
26766               setting, using -march with these values enables generic tuning.
26767               Specific tuning can be enabled using the -mtune=other-cpu-type
26768               option with an appropriate other-cpu-type value.
26769
26770           i386
26771               Original Intel i386 CPU.
26772
26773           i486
26774               Intel i486 CPU.  (No scheduling is implemented for this chip.)
26775
26776           i586
26777           pentium
26778               Intel Pentium CPU with no MMX support.
26779
26780           lakemont
26781               Intel Lakemont MCU, based on Intel Pentium CPU.
26782
26783           pentium-mmx
26784               Intel Pentium MMX CPU, based on Pentium core with MMX
26785               instruction set support.
26786
26787           pentiumpro
26788               Intel Pentium Pro CPU.
26789
26790           i686
26791               When used with -march, the Pentium Pro instruction set is used,
26792               so the code runs on all i686 family chips.  When used with
26793               -mtune, it has the same meaning as generic.
26794
26795           pentium2
26796               Intel Pentium II CPU, based on Pentium Pro core with MMX and
26797               FXSR instruction set support.
26798
26799           pentium3
26800           pentium3m
26801               Intel Pentium III CPU, based on Pentium Pro core with MMX, FXSR
26802               and SSE instruction set support.
26803
26804           pentium-m
26805               Intel Pentium M; low-power version of Intel Pentium III CPU
26806               with MMX, SSE, SSE2 and FXSR instruction set support.  Used by
26807               Centrino notebooks.
26808
26809           pentium4
26810           pentium4m
26811               Intel Pentium 4 CPU with MMX, SSE, SSE2 and FXSR instruction
26812               set support.
26813
26814           prescott
26815               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2,
26816               SSE3 and FXSR instruction set support.
26817
26818           nocona
26819               Improved version of Intel Pentium 4 CPU with 64-bit extensions,
26820               MMX, SSE, SSE2, SSE3 and FXSR instruction set support.
26821
26822           core2
26823               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
26824               SSSE3, CX16, SAHF and FXSR instruction set support.
26825
26826           nehalem
26827               Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
26828               SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF and FXSR instruction
26829               set support.
26830
26831           westmere
26832               Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
26833               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR and
26834               PCLMUL instruction set support.
26835
26836           sandybridge
26837               Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
26838               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX,
26839               XSAVE and PCLMUL instruction set support.
26840
26841           ivybridge
26842               Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
26843               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX,
26844               XSAVE, PCLMUL, FSGSBASE, RDRND and F16C instruction set
26845               support.
26846
26847           haswell
26848               Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
26849               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26850               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26851               LZCNT, FMA, MOVBE and HLE instruction set support.
26852
26853           broadwell
26854               Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
26855               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26856               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26857               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX and PREFETCHW instruction
26858               set support.
26859
26860           skylake
26861               Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
26862               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26863               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26864               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26865               CLFLUSHOPT, XSAVEC, XSAVES and SGX instruction set support.
26866
26867           bonnell
26868               Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
26869               SSE2, SSE3 and SSSE3 instruction set support.
26870
26871           silvermont
26872               Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
26873               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26874               PCLMUL, PREFETCHW and RDRND instruction set support.
26875
26876           goldmont
26877               Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE,
26878               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26879               PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC,
26880               XSAVES, XSAVEOPT, CLFLUSHOPT and FSGSBASE instruction set
26881               support.
26882
26883           goldmont-plus
26884               Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX,
26885               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26886               FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE,
26887               XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID
26888               and SGX instruction set support.
26889
26890           tremont
26891               Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE,
26892               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26893               PCLMUL, PREFETCHW, RDRND, AES, SHA, RDSEED, XSAVE, XSAVEC,
26894               XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID, SGX,
26895               CLWB, GFNI-SSE, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG
26896               instruction set support.
26897
26898           knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX,
26899               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26900               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26901               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW,
26902               AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1
26903               instruction set support.
26904
26905           knm Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE,
26906               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26907               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26908               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AVX512PF,
26909               AVX512ER, AVX512F, AVX512CD and PREFETCHWT1, AVX5124VNNIW,
26910               AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support.
26911
26912           skylake-avx512
26913               Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
26914               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26915               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26916               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26917               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
26918               AVX512BW, AVX512DQ and AVX512CD instruction set support.
26919
26920           cannonlake
26921               Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX,
26922               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26923               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26924               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26925               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
26926               AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA and SHA
26927               instruction set support.
26928
26929           icelake-client
26930               Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
26931               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26932               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26933               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26934               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
26935               AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
26936               AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ, AVX512BITALG,
26937               RDPID and AVX512VPOPCNTDQ instruction set support.
26938
26939           icelake-server
26940               Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
26941               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26942               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26943               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26944               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
26945               AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
26946               AVX512VNNI, GFNI, VAES, AVX512VBMI2 , VPCLMULQDQ, AVX512BITALG,
26947               RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD and CLWB instruction
26948               set support.
26949
26950           cascadelake
26951               Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE,
26952               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26953               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26954               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26955               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
26956               AVX512BW, AVX512DQ, AVX512CD and AVX512VNNI instruction set
26957               support.
26958
26959           cooperlake
26960               Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
26961               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26962               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26963               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26964               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL,
26965               AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI and AVX512BF16
26966               instruction set support.
26967
26968           tigerlake
26969               Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
26970               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
26971               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
26972               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26973               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
26974               AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA,
26975               AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG,
26976               RDPID, AVX512VPOPCNTDQ, MOVDIRI, MOVDIR64B, CLWB,
26977               AVX512VP2INTERSECT and KEYLOCKER instruction set support.
26978
26979           sapphirerapids
26980               Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX,
26981               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF,
26982               FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI,
26983               BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
26984               CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW,
26985               AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA,
26986               AVX512VNNI, GFNI, VAES, AVX512VBMI2 VPCLMULQDQ, AVX512BITALG,
26987               RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, MOVDIRI,
26988               MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE, PTWRITE,
26989               WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE,
26990               AMX-INT8, AVX-VNNI, AVX512FP16 and AVX512BF16 instruction set
26991               support.
26992
26993           alderlake
26994               Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
26995               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
26996               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
26997               PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
26998               CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA,
26999               LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL,
27000               WIDEKL and AVX-VNNI instruction set support.
27001
27002           rocketlake
27003               Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
27004               SSE2, SSE3, SSSE3 , SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR,
27005               AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2,
27006               LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES,
27007               CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW,
27008               AVX512DQ, AVX512CD PKU, AVX512VBMI, AVX512IFMA, SHA,
27009               AVX512VNNI, GFNI, VAES, AVX512VBMI2, VPCLMULQDQ, AVX512BITALG,
27010               RDPID and AVX512VPOPCNTDQ instruction set support.
27011
27012           k6  AMD K6 CPU with MMX instruction set support.
27013
27014           k6-2
27015           k6-3
27016               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
27017               set support.
27018
27019           athlon
27020           athlon-tbird
27021               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
27022               prefetch instructions support.
27023
27024           athlon-4
27025           athlon-xp
27026           athlon-mp
27027               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
27028               full SSE instruction set support.
27029
27030           k8
27031           opteron
27032           athlon64
27033           athlon-fx
27034               Processors based on the AMD K8 core with x86-64 instruction set
27035               support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
27036               processors.  (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
27037               3DNow! and 64-bit instruction set extensions.)
27038
27039           k8-sse3
27040           opteron-sse3
27041           athlon64-sse3
27042               Improved versions of AMD K8 cores with SSE3 instruction set
27043               support.
27044
27045           amdfam10
27046           barcelona
27047               CPUs based on AMD Family 10h cores with x86-64 instruction set
27048               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
27049               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
27050
27051           bdver1
27052               CPUs based on AMD Family 15h cores with x86-64 instruction set
27053               support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCLMUL,
27054               CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
27055               and 64-bit instruction set extensions.)
27056
27057           bdver2
27058               AMD Family 15h core based CPUs with x86-64 instruction set
27059               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
27060               LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
27061               SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
27062
27063           bdver3
27064               AMD Family 15h core based CPUs with x86-64 instruction set
27065               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE,
27066               AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
27067               SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
27068               extensions.)
27069
27070           bdver4
27071               AMD Family 15h core based CPUs with x86-64 instruction set
27072               support.  (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
27073               FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE, MMX,
27074               SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit
27075               instruction set extensions.)
27076
27077           znver1
27078               AMD Family 17h core based CPUs with x86-64 instruction set
27079               support.  (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX,
27080               AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16,
27081               MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM,
27082               XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit instruction set
27083               extensions.)
27084
27085           znver2
27086               AMD Family 17h core based CPUs with x86-64 instruction set
27087               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
27088               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
27089               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
27090               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
27091               WBNOINVD, and 64-bit instruction set extensions.)
27092
27093           znver3
27094               AMD Family 19h core based CPUs with x86-64 instruction set
27095               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
27096               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
27097               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
27098               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
27099               WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set
27100               extensions.)
27101
27102           btver1
27103               CPUs based on AMD Family 14h cores with x86-64 instruction set
27104               support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
27105               CX16, ABM and 64-bit instruction set extensions.)
27106
27107           btver2
27108               CPUs based on AMD Family 16h cores with x86-64 instruction set
27109               support. This includes MOVBE, F16C, BMI, AVX, PCLMUL, AES,
27110               SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
27111               and 64-bit instruction set extensions.
27112
27113           winchip-c6
27114               IDT WinChip C6 CPU, dealt in same way as i486 with additional
27115               MMX instruction set support.
27116
27117           winchip2
27118               IDT WinChip 2 CPU, dealt in same way as i486 with additional
27119               MMX and 3DNow!  instruction set support.
27120
27121           c3  VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
27122               scheduling is implemented for this chip.)
27123
27124           c3-2
27125               VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
27126               support.  (No scheduling is implemented for this chip.)
27127
27128           c7  VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
27129               set support.  (No scheduling is implemented for this chip.)
27130
27131           samuel-2
27132               VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
27133               support.  (No scheduling is implemented for this chip.)
27134
27135           nehemiah
27136               VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
27137               (No scheduling is implemented for this chip.)
27138
27139           esther
27140               VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction
27141               set support.  (No scheduling is implemented for this chip.)
27142
27143           eden-x2
27144               VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3
27145               instruction set support.  (No scheduling is implemented for
27146               this chip.)
27147
27148           eden-x4
27149               VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
27150               SSE4.1, SSE4.2, AVX and AVX2 instruction set support.  (No
27151               scheduling is implemented for this chip.)
27152
27153           nano
27154               Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
27155               SSSE3 instruction set support.  (No scheduling is implemented
27156               for this chip.)
27157
27158           nano-1000
27159               VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
27160               instruction set support.  (No scheduling is implemented for
27161               this chip.)
27162
27163           nano-2000
27164               VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
27165               instruction set support.  (No scheduling is implemented for
27166               this chip.)
27167
27168           nano-3000
27169               VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and
27170               SSE4.1 instruction set support.  (No scheduling is implemented
27171               for this chip.)
27172
27173           nano-x2
27174               VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
27175               and SSE4.1 instruction set support.  (No scheduling is
27176               implemented for this chip.)
27177
27178           nano-x4
27179               VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
27180               and SSE4.1 instruction set support.  (No scheduling is
27181               implemented for this chip.)
27182
27183           geode
27184               AMD Geode embedded processor with MMX and 3DNow! instruction
27185               set support.
27186
27187       -mtune=cpu-type
27188           Tune to cpu-type everything applicable about the generated code,
27189           except for the ABI and the set of available instructions.  While
27190           picking a specific cpu-type schedules things appropriately for that
27191           particular chip, the compiler does not generate any code that
27192           cannot run on the default machine type unless you use a -march=cpu-
27193           type option.  For example, if GCC is configured for
27194           i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned
27195           for Pentium 4 but still runs on i686 machines.
27196
27197           The choices for cpu-type are the same as for -march.  In addition,
27198           -mtune supports 2 extra choices for cpu-type:
27199
27200           generic
27201               Produce code optimized for the most common IA32/AMD64/EM64T
27202               processors.  If you know the CPU on which your code will run,
27203               then you should use the corresponding -mtune or -march option
27204               instead of -mtune=generic.  But, if you do not know exactly
27205               what CPU users of your application will have, then you should
27206               use this option.
27207
27208               As new processors are deployed in the marketplace, the behavior
27209               of this option will change.  Therefore, if you upgrade to a
27210               newer version of GCC, code generation controlled by this option
27211               will change to reflect the processors that are most common at
27212               the time that version of GCC is released.
27213
27214               There is no -march=generic option because -march indicates the
27215               instruction set the compiler can use, and there is no generic
27216               instruction set applicable to all processors.  In contrast,
27217               -mtune indicates the processor (or, in this case, collection of
27218               processors) for which the code is optimized.
27219
27220           intel
27221               Produce code optimized for the most current Intel processors,
27222               which are Haswell and Silvermont for this version of GCC.  If
27223               you know the CPU on which your code will run, then you should
27224               use the corresponding -mtune or -march option instead of
27225               -mtune=intel.  But, if you want your application performs
27226               better on both Haswell and Silvermont, then you should use this
27227               option.
27228
27229               As new Intel processors are deployed in the marketplace, the
27230               behavior of this option will change.  Therefore, if you upgrade
27231               to a newer version of GCC, code generation controlled by this
27232               option will change to reflect the most current Intel processors
27233               at the time that version of GCC is released.
27234
27235               There is no -march=intel option because -march indicates the
27236               instruction set the compiler can use, and there is no common
27237               instruction set applicable to all processors.  In contrast,
27238               -mtune indicates the processor (or, in this case, collection of
27239               processors) for which the code is optimized.
27240
27241       -mcpu=cpu-type
27242           A deprecated synonym for -mtune.
27243
27244       -mfpmath=unit
27245           Generate floating-point arithmetic for selected unit unit.  The
27246           choices for unit are:
27247
27248           387 Use the standard 387 floating-point coprocessor present on the
27249               majority of chips and emulated otherwise.  Code compiled with
27250               this option runs almost everywhere.  The temporary results are
27251               computed in 80-bit precision instead of the precision specified
27252               by the type, resulting in slightly different results compared
27253               to most of other chips.  See -ffloat-store for more detailed
27254               description.
27255
27256               This is the default choice for non-Darwin x86-32 targets.
27257
27258           sse Use scalar floating-point instructions present in the SSE
27259               instruction set.  This instruction set is supported by Pentium
27260               III and newer chips, and in the AMD line by Athlon-4, Athlon XP
27261               and Athlon MP chips.  The earlier version of the SSE
27262               instruction set supports only single-precision arithmetic, thus
27263               the double and extended-precision arithmetic are still done
27264               using 387.  A later version, present only in Pentium 4 and AMD
27265               x86-64 chips, supports double-precision arithmetic too.
27266
27267               For the x86-32 compiler, you must use -march=cpu-type, -msse or
27268               -msse2 switches to enable SSE extensions and make this option
27269               effective.  For the x86-64 compiler, these extensions are
27270               enabled by default.
27271
27272               The resulting code should be considerably faster in the
27273               majority of cases and avoid the numerical instability problems
27274               of 387 code, but may break some existing code that expects
27275               temporaries to be 80 bits.
27276
27277               This is the default choice for the x86-64 compiler, Darwin
27278               x86-32 targets, and the default choice for x86-32 targets with
27279               the SSE2 instruction set when -ffast-math is enabled.
27280
27281           sse,387
27282           sse+387
27283           both
27284               Attempt to utilize both instruction sets at once.  This
27285               effectively doubles the amount of available registers, and on
27286               chips with separate execution units for 387 and SSE the
27287               execution resources too.  Use this option with care, as it is
27288               still experimental, because the GCC register allocator does not
27289               model separate functional units well, resulting in unstable
27290               performance.
27291
27292       -masm=dialect
27293           Output assembly instructions using selected dialect.  Also affects
27294           which dialect is used for basic "asm" and extended "asm". Supported
27295           choices (in dialect order) are att or intel. The default is att.
27296           Darwin does not support intel.
27297
27298       -mieee-fp
27299       -mno-ieee-fp
27300           Control whether or not the compiler uses IEEE floating-point
27301           comparisons.  These correctly handle the case where the result of a
27302           comparison is unordered.
27303
27304       -m80387
27305       -mhard-float
27306           Generate output containing 80387 instructions for floating point.
27307
27308       -mno-80387
27309       -msoft-float
27310           Generate output containing library calls for floating point.
27311
27312           Warning: the requisite libraries are not part of GCC.  Normally the
27313           facilities of the machine's usual C compiler are used, but this
27314           cannot be done directly in cross-compilation.  You must make your
27315           own arrangements to provide suitable library functions for cross-
27316           compilation.
27317
27318           On machines where a function returns floating-point results in the
27319           80387 register stack, some floating-point opcodes may be emitted
27320           even if -msoft-float is used.
27321
27322       -mno-fp-ret-in-387
27323           Do not use the FPU registers for return values of functions.
27324
27325           The usual calling convention has functions return values of types
27326           "float" and "double" in an FPU register, even if there is no FPU.
27327           The idea is that the operating system should emulate an FPU.
27328
27329           The option -mno-fp-ret-in-387 causes such values to be returned in
27330           ordinary CPU registers instead.
27331
27332       -mno-fancy-math-387
27333           Some 387 emulators do not support the "sin", "cos" and "sqrt"
27334           instructions for the 387.  Specify this option to avoid generating
27335           those instructions.  This option is overridden when -march
27336           indicates that the target CPU always has an FPU and so the
27337           instruction does not need emulation.  These instructions are not
27338           generated unless you also use the -funsafe-math-optimizations
27339           switch.
27340
27341       -malign-double
27342       -mno-align-double
27343           Control whether GCC aligns "double", "long double", and "long long"
27344           variables on a two-word boundary or a one-word boundary.  Aligning
27345           "double" variables on a two-word boundary produces code that runs
27346           somewhat faster on a Pentium at the expense of more memory.
27347
27348           On x86-64, -malign-double is enabled by default.
27349
27350           Warning: if you use the -malign-double switch, structures
27351           containing the above types are aligned differently than the
27352           published application binary interface specifications for the
27353           x86-32 and are not binary compatible with structures in code
27354           compiled without that switch.
27355
27356       -m96bit-long-double
27357       -m128bit-long-double
27358           These switches control the size of "long double" type.  The x86-32
27359           application binary interface specifies the size to be 96 bits, so
27360           -m96bit-long-double is the default in 32-bit mode.
27361
27362           Modern architectures (Pentium and newer) prefer "long double" to be
27363           aligned to an 8- or 16-byte boundary.  In arrays or structures
27364           conforming to the ABI, this is not possible.  So specifying
27365           -m128bit-long-double aligns "long double" to a 16-byte boundary by
27366           padding the "long double" with an additional 32-bit zero.
27367
27368           In the x86-64 compiler, -m128bit-long-double is the default choice
27369           as its ABI specifies that "long double" is aligned on 16-byte
27370           boundary.
27371
27372           Notice that neither of these options enable any extra precision
27373           over the x87 standard of 80 bits for a "long double".
27374
27375           Warning: if you override the default value for your target ABI,
27376           this changes the size of structures and arrays containing "long
27377           double" variables, as well as modifying the function calling
27378           convention for functions taking "long double".  Hence they are not
27379           binary-compatible with code compiled without that switch.
27380
27381       -mlong-double-64
27382       -mlong-double-80
27383       -mlong-double-128
27384           These switches control the size of "long double" type. A size of 64
27385           bits makes the "long double" type equivalent to the "double" type.
27386           This is the default for 32-bit Bionic C library.  A size of 128
27387           bits makes the "long double" type equivalent to the "__float128"
27388           type. This is the default for 64-bit Bionic C library.
27389
27390           Warning: if you override the default value for your target ABI,
27391           this changes the size of structures and arrays containing "long
27392           double" variables, as well as modifying the function calling
27393           convention for functions taking "long double".  Hence they are not
27394           binary-compatible with code compiled without that switch.
27395
27396       -malign-data=type
27397           Control how GCC aligns variables.  Supported values for type are
27398           compat uses increased alignment value compatible uses GCC 4.8 and
27399           earlier, abi uses alignment value as specified by the psABI, and
27400           cacheline uses increased alignment value to match the cache line
27401           size.  compat is the default.
27402
27403       -mlarge-data-threshold=threshold
27404           When -mcmodel=medium is specified, data objects larger than
27405           threshold are placed in the large data section.  This value must be
27406           the same across all objects linked into the binary, and defaults to
27407           65535.
27408
27409       -mrtd
27410           Use a different function-calling convention, in which functions
27411           that take a fixed number of arguments return with the "ret num"
27412           instruction, which pops their arguments while returning.  This
27413           saves one instruction in the caller since there is no need to pop
27414           the arguments there.
27415
27416           You can specify that an individual function is called with this
27417           calling sequence with the function attribute "stdcall".  You can
27418           also override the -mrtd option by using the function attribute
27419           "cdecl".
27420
27421           Warning: this calling convention is incompatible with the one
27422           normally used on Unix, so you cannot use it if you need to call
27423           libraries compiled with the Unix compiler.
27424
27425           Also, you must provide function prototypes for all functions that
27426           take variable numbers of arguments (including "printf"); otherwise
27427           incorrect code is generated for calls to those functions.
27428
27429           In addition, seriously incorrect code results if you call a
27430           function with too many arguments.  (Normally, extra arguments are
27431           harmlessly ignored.)
27432
27433       -mregparm=num
27434           Control how many registers are used to pass integer arguments.  By
27435           default, no registers are used to pass arguments, and at most 3
27436           registers can be used.  You can control this behavior for a
27437           specific function by using the function attribute "regparm".
27438
27439           Warning: if you use this switch, and num is nonzero, then you must
27440           build all modules with the same value, including any libraries.
27441           This includes the system libraries and startup modules.
27442
27443       -msseregparm
27444           Use SSE register passing conventions for float and double arguments
27445           and return values.  You can control this behavior for a specific
27446           function by using the function attribute "sseregparm".
27447
27448           Warning: if you use this switch then you must build all modules
27449           with the same value, including any libraries.  This includes the
27450           system libraries and startup modules.
27451
27452       -mvect8-ret-in-mem
27453           Return 8-byte vectors in memory instead of MMX registers.  This is
27454           the default on VxWorks to match the ABI of the Sun Studio compilers
27455           until version 12.  Only use this option if you need to remain
27456           compatible with existing code produced by those previous compiler
27457           versions or older versions of GCC.
27458
27459       -mpc32
27460       -mpc64
27461       -mpc80
27462           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
27463           -mpc32 is specified, the significands of results of floating-point
27464           operations are rounded to 24 bits (single precision); -mpc64 rounds
27465           the significands of results of floating-point operations to 53 bits
27466           (double precision) and -mpc80 rounds the significands of results of
27467           floating-point operations to 64 bits (extended double precision),
27468           which is the default.  When this option is used, floating-point
27469           operations in higher precisions are not available to the programmer
27470           without setting the FPU control word explicitly.
27471
27472           Setting the rounding of floating-point operations to less than the
27473           default 80 bits can speed some programs by 2% or more.  Note that
27474           some mathematical libraries assume that extended-precision (80-bit)
27475           floating-point operations are enabled by default; routines in such
27476           libraries could suffer significant loss of accuracy, typically
27477           through so-called "catastrophic cancellation", when this option is
27478           used to set the precision to less than extended precision.
27479
27480       -mstackrealign
27481           Realign the stack at entry.  On the x86, the -mstackrealign option
27482           generates an alternate prologue and epilogue that realigns the run-
27483           time stack if necessary.  This supports mixing legacy codes that
27484           keep 4-byte stack alignment with modern codes that keep 16-byte
27485           stack alignment for SSE compatibility.  See also the attribute
27486           "force_align_arg_pointer", applicable to individual functions.
27487
27488       -mpreferred-stack-boundary=num
27489           Attempt to keep the stack boundary aligned to a 2 raised to num
27490           byte boundary.  If -mpreferred-stack-boundary is not specified, the
27491           default is 4 (16 bytes or 128 bits).
27492
27493           Warning: When generating code for the x86-64 architecture with SSE
27494           extensions disabled, -mpreferred-stack-boundary=3 can be used to
27495           keep the stack boundary aligned to 8 byte boundary.  Since x86-64
27496           ABI require 16 byte stack alignment, this is ABI incompatible and
27497           intended to be used in controlled environment where stack space is
27498           important limitation.  This option leads to wrong code when
27499           functions compiled with 16 byte stack alignment (such as functions
27500           from a standard library) are called with misaligned stack.  In this
27501           case, SSE instructions may lead to misaligned memory access traps.
27502           In addition, variable arguments are handled incorrectly for 16 byte
27503           aligned objects (including x87 long double and __int128), leading
27504           to wrong results.  You must build all modules with
27505           -mpreferred-stack-boundary=3, including any libraries.  This
27506           includes the system libraries and startup modules.
27507
27508       -mincoming-stack-boundary=num
27509           Assume the incoming stack is aligned to a 2 raised to num byte
27510           boundary.  If -mincoming-stack-boundary is not specified, the one
27511           specified by -mpreferred-stack-boundary is used.
27512
27513           On Pentium and Pentium Pro, "double" and "long double" values
27514           should be aligned to an 8-byte boundary (see -malign-double) or
27515           suffer significant run time performance penalties.  On Pentium III,
27516           the Streaming SIMD Extension (SSE) data type "__m128" may not work
27517           properly if it is not 16-byte aligned.
27518
27519           To ensure proper alignment of this values on the stack, the stack
27520           boundary must be as aligned as that required by any value stored on
27521           the stack.  Further, every function must be generated such that it
27522           keeps the stack aligned.  Thus calling a function compiled with a
27523           higher preferred stack boundary from a function compiled with a
27524           lower preferred stack boundary most likely misaligns the stack.  It
27525           is recommended that libraries that use callbacks always use the
27526           default setting.
27527
27528           This extra alignment does consume extra stack space, and generally
27529           increases code size.  Code that is sensitive to stack space usage,
27530           such as embedded systems and operating system kernels, may want to
27531           reduce the preferred alignment to -mpreferred-stack-boundary=2.
27532
27533       -mmmx
27534       -msse
27535       -msse2
27536       -msse3
27537       -mssse3
27538       -msse4
27539       -msse4a
27540       -msse4.1
27541       -msse4.2
27542       -mavx
27543       -mavx2
27544       -mavx512f
27545       -mavx512pf
27546       -mavx512er
27547       -mavx512cd
27548       -mavx512vl
27549       -mavx512bw
27550       -mavx512dq
27551       -mavx512ifma
27552       -mavx512vbmi
27553       -msha
27554       -maes
27555       -mpclmul
27556       -mclflushopt
27557       -mclwb
27558       -mfsgsbase
27559       -mptwrite
27560       -mrdrnd
27561       -mf16c
27562       -mfma
27563       -mpconfig
27564       -mwbnoinvd
27565       -mfma4
27566       -mprfchw
27567       -mrdpid
27568       -mprefetchwt1
27569       -mrdseed
27570       -msgx
27571       -mxop
27572       -mlwp
27573       -m3dnow
27574       -m3dnowa
27575       -mpopcnt
27576       -mabm
27577       -madx
27578       -mbmi
27579       -mbmi2
27580       -mlzcnt
27581       -mfxsr
27582       -mxsave
27583       -mxsaveopt
27584       -mxsavec
27585       -mxsaves
27586       -mrtm
27587       -mhle
27588       -mtbm
27589       -mmwaitx
27590       -mclzero
27591       -mpku
27592       -mavx512vbmi2
27593       -mavx512bf16
27594       -mavx512fp16
27595       -mgfni
27596       -mvaes
27597       -mwaitpkg
27598       -mvpclmulqdq
27599       -mavx512bitalg
27600       -mmovdiri
27601       -mmovdir64b
27602       -menqcmd
27603       -muintr
27604       -mtsxldtrk
27605       -mavx512vpopcntdq
27606       -mavx512vp2intersect
27607       -mavx5124fmaps
27608       -mavx512vnni
27609       -mavxvnni
27610       -mavx5124vnniw
27611       -mcldemote
27612       -mserialize
27613       -mamx-tile
27614       -mamx-int8
27615       -mamx-bf16
27616       -mhreset
27617       -mkl
27618       -mwidekl
27619           These switches enable the use of instructions in the MMX, SSE,
27620           SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F,
27621           AVX512PF, AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ,
27622           AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB,
27623           FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, WBNOINVD, FMA4,
27624           PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, 3DNow!,
27625           enhanced 3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE,
27626           XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU,
27627           AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG,
27628           MOVDIRI, MOVDIR64B, AVX512BF16, ENQCMD, AVX512VPOPCNTDQ,
27629           AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, UINTR, HRESET,
27630           AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI, AVX512FP16 or
27631           CLDEMOTE extended instruction sets. Each has a corresponding -mno-
27632           option to disable use of these instructions.
27633
27634           These extensions are also available as built-in functions: see x86
27635           Built-in Functions, for details of the functions enabled and
27636           disabled by these switches.
27637
27638           To generate SSE/SSE2 instructions automatically from floating-point
27639           code (as opposed to 387 instructions), see -mfpmath=sse.
27640
27641           GCC depresses SSEx instructions when -mavx is used. Instead, it
27642           generates new AVX instructions or AVX equivalence for all SSEx
27643           instructions when needed.
27644
27645           These options enable GCC to use these extended instructions in
27646           generated code, even without -mfpmath=sse.  Applications that
27647           perform run-time CPU detection must compile separate files for each
27648           supported architecture, using the appropriate flags.  In
27649           particular, the file containing the CPU detection code should be
27650           compiled without these options.
27651
27652       -mdump-tune-features
27653           This option instructs GCC to dump the names of the x86 performance
27654           tuning features and default settings. The names can be used in
27655           -mtune-ctrl=feature-list.
27656
27657       -mtune-ctrl=feature-list
27658           This option is used to do fine grain control of x86 code generation
27659           features.  feature-list is a comma separated list of feature names.
27660           See also -mdump-tune-features. When specified, the feature is
27661           turned on if it is not preceded with ^, otherwise, it is turned
27662           off.  -mtune-ctrl=feature-list is intended to be used by GCC
27663           developers. Using it may lead to code paths not covered by testing
27664           and can potentially result in compiler ICEs or runtime errors.
27665
27666       -mno-default
27667           This option instructs GCC to turn off all tunable features. See
27668           also -mtune-ctrl=feature-list and -mdump-tune-features.
27669
27670       -mcld
27671           This option instructs GCC to emit a "cld" instruction in the
27672           prologue of functions that use string instructions.  String
27673           instructions depend on the DF flag to select between autoincrement
27674           or autodecrement mode.  While the ABI specifies the DF flag to be
27675           cleared on function entry, some operating systems violate this
27676           specification by not clearing the DF flag in their exception
27677           dispatchers.  The exception handler can be invoked with the DF flag
27678           set, which leads to wrong direction mode when string instructions
27679           are used.  This option can be enabled by default on 32-bit x86
27680           targets by configuring GCC with the --enable-cld configure option.
27681           Generation of "cld" instructions can be suppressed with the
27682           -mno-cld compiler option in this case.
27683
27684       -mvzeroupper
27685           This option instructs GCC to emit a "vzeroupper" instruction before
27686           a transfer of control flow out of the function to minimize the AVX
27687           to SSE transition penalty as well as remove unnecessary "zeroupper"
27688           intrinsics.
27689
27690       -mprefer-avx128
27691           This option instructs GCC to use 128-bit AVX instructions instead
27692           of 256-bit AVX instructions in the auto-vectorizer.
27693
27694       -mprefer-vector-width=opt
27695           This option instructs GCC to use opt-bit vector width in
27696           instructions instead of default on the selected platform.
27697
27698       -mmove-max=bits
27699           This option instructs GCC to set the maximum number of bits can be
27700           moved from memory to memory efficiently to bits.  The valid bits
27701           are 128, 256 and 512.
27702
27703       -mstore-max=bits
27704           This option instructs GCC to set the maximum number of bits can be
27705           stored to memory efficiently to bits.  The valid bits are 128, 256
27706           and 512.
27707
27708           none
27709               No extra limitations applied to GCC other than defined by the
27710               selected platform.
27711
27712           128 Prefer 128-bit vector width for instructions.
27713
27714           256 Prefer 256-bit vector width for instructions.
27715
27716           512 Prefer 512-bit vector width for instructions.
27717
27718       -mcx16
27719           This option enables GCC to generate "CMPXCHG16B" instructions in
27720           64-bit code to implement compare-and-exchange operations on 16-byte
27721           aligned 128-bit objects.  This is useful for atomic updates of data
27722           structures exceeding one machine word in size.  The compiler uses
27723           this instruction to implement __sync Builtins.  However, for
27724           __atomic Builtins operating on 128-bit integers, a library call is
27725           always used.
27726
27727       -msahf
27728           This option enables generation of "SAHF" instructions in 64-bit
27729           code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
27730           the introduction of Pentium 4 G1 step in December 2005, lacked the
27731           "LAHF" and "SAHF" instructions which are supported by AMD64.  These
27732           are load and store instructions, respectively, for certain status
27733           flags.  In 64-bit mode, the "SAHF" instruction is used to optimize
27734           "fmod", "drem", and "remainder" built-in functions; see Other
27735           Builtins for details.
27736
27737       -mmovbe
27738           This option enables use of the "movbe" instruction to implement
27739           "__builtin_bswap32" and "__builtin_bswap64".
27740
27741       -mshstk
27742           The -mshstk option enables shadow stack built-in functions from x86
27743           Control-flow Enforcement Technology (CET).
27744
27745       -mcrc32
27746           This option enables built-in functions "__builtin_ia32_crc32qi",
27747           "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and
27748           "__builtin_ia32_crc32di" to generate the "crc32" machine
27749           instruction.
27750
27751       -mmwait
27752           This option enables built-in functions "__builtin_ia32_monitor",
27753           and "__builtin_ia32_mwait" to generate the "monitor" and "mwait"
27754           machine instructions.
27755
27756       -mrecip
27757           This option enables use of "RCPSS" and "RSQRTSS" instructions (and
27758           their vectorized variants "RCPPS" and "RSQRTPS") with an additional
27759           Newton-Raphson step to increase precision instead of "DIVSS" and
27760           "SQRTSS" (and their vectorized variants) for single-precision
27761           floating-point arguments.  These instructions are generated only
27762           when -funsafe-math-optimizations is enabled together with
27763           -ffinite-math-only and -fno-trapping-math.  Note that while the
27764           throughput of the sequence is higher than the throughput of the
27765           non-reciprocal instruction, the precision of the sequence can be
27766           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
27767           0.99999994).
27768
27769           Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or
27770           "RSQRTPS") already with -ffast-math (or the above option
27771           combination), and doesn't need -mrecip.
27772
27773           Also note that GCC emits the above sequence with additional Newton-
27774           Raphson step for vectorized single-float division and vectorized
27775           "sqrtf(x)" already with -ffast-math (or the above option
27776           combination), and doesn't need -mrecip.
27777
27778       -mrecip=opt
27779           This option controls which reciprocal estimate instructions may be
27780           used.  opt is a comma-separated list of options, which may be
27781           preceded by a ! to invert the option:
27782
27783           all Enable all estimate instructions.
27784
27785           default
27786               Enable the default instructions, equivalent to -mrecip.
27787
27788           none
27789               Disable all estimate instructions, equivalent to -mno-recip.
27790
27791           div Enable the approximation for scalar division.
27792
27793           vec-div
27794               Enable the approximation for vectorized division.
27795
27796           sqrt
27797               Enable the approximation for scalar square root.
27798
27799           vec-sqrt
27800               Enable the approximation for vectorized square root.
27801
27802           So, for example, -mrecip=all,!sqrt enables all of the reciprocal
27803           approximations, except for square root.
27804
27805       -mveclibabi=type
27806           Specifies the ABI type to use for vectorizing intrinsics using an
27807           external library.  Supported values for type are svml for the Intel
27808           short vector math library and acml for the AMD math core library.
27809           To use this option, both -ftree-vectorize and
27810           -funsafe-math-optimizations have to be enabled, and an SVML or ACML
27811           ABI-compatible library must be specified at link time.
27812
27813           GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102",
27814           "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2",
27815           "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2", "vmldAsin2",
27816           "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4",
27817           "vmlsLn4", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4",
27818           "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4",
27819           "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4"
27820           and "vmlsAcos4" for corresponding function type when
27821           -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos",
27822           "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10",
27823           "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf",
27824           "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the
27825           corresponding function type when -mveclibabi=acml is used.
27826
27827       -mabi=name
27828           Generate code for the specified calling convention.  Permissible
27829           values are sysv for the ABI used on GNU/Linux and other systems,
27830           and ms for the Microsoft ABI.  The default is to use the Microsoft
27831           ABI when targeting Microsoft Windows and the SysV ABI on all other
27832           systems.  You can control this behavior for specific functions by
27833           using the function attributes "ms_abi" and "sysv_abi".
27834
27835       -mforce-indirect-call
27836           Force all calls to functions to be indirect. This is useful when
27837           using Intel Processor Trace where it generates more precise timing
27838           information for function calls.
27839
27840       -mmanual-endbr
27841           Insert ENDBR instruction at function entry only via the "cf_check"
27842           function attribute. This is useful when used with the option
27843           -fcf-protection=branch to control ENDBR insertion at the function
27844           entry.
27845
27846       -mcall-ms2sysv-xlogues
27847           Due to differences in 64-bit ABIs, any Microsoft ABI function that
27848           calls a System V ABI function must consider RSI, RDI and XMM6-15 as
27849           clobbered.  By default, the code for saving and restoring these
27850           registers is emitted inline, resulting in fairly lengthy prologues
27851           and epilogues.  Using -mcall-ms2sysv-xlogues emits prologues and
27852           epilogues that use stubs in the static portion of libgcc to perform
27853           these saves and restores, thus reducing function size at the cost
27854           of a few extra instructions.
27855
27856       -mtls-dialect=type
27857           Generate code to access thread-local storage using the gnu or gnu2
27858           conventions.  gnu is the conservative default; gnu2 is more
27859           efficient, but it may add compile- and run-time requirements that
27860           cannot be satisfied on all systems.
27861
27862       -mpush-args
27863       -mno-push-args
27864           Use PUSH operations to store outgoing parameters.  This method is
27865           shorter and usually equally fast as method using SUB/MOV operations
27866           and is enabled by default.  In some cases disabling it may improve
27867           performance because of improved scheduling and reduced
27868           dependencies.
27869
27870       -maccumulate-outgoing-args
27871           If enabled, the maximum amount of space required for outgoing
27872           arguments is computed in the function prologue.  This is faster on
27873           most modern CPUs because of reduced dependencies, improved
27874           scheduling and reduced stack usage when the preferred stack
27875           boundary is not equal to 2.  The drawback is a notable increase in
27876           code size.  This switch implies -mno-push-args.
27877
27878       -mthreads
27879           Support thread-safe exception handling on MinGW.  Programs that
27880           rely on thread-safe exception handling must compile and link all
27881           code with the -mthreads option.  When compiling, -mthreads defines
27882           -D_MT; when linking, it links in a special thread helper library
27883           -lmingwthrd which cleans up per-thread exception-handling data.
27884
27885       -mms-bitfields
27886       -mno-ms-bitfields
27887           Enable/disable bit-field layout compatible with the native
27888           Microsoft Windows compiler.
27889
27890           If "packed" is used on a structure, or if bit-fields are used, it
27891           may be that the Microsoft ABI lays out the structure differently
27892           than the way GCC normally does.  Particularly when moving packed
27893           data between functions compiled with GCC and the native Microsoft
27894           compiler (either via function call or as data in a file), it may be
27895           necessary to access either format.
27896
27897           This option is enabled by default for Microsoft Windows targets.
27898           This behavior can also be controlled locally by use of variable or
27899           type attributes.  For more information, see x86 Variable Attributes
27900           and x86 Type Attributes.
27901
27902           The Microsoft structure layout algorithm is fairly simple with the
27903           exception of the bit-field packing.  The padding and alignment of
27904           members of structures and whether a bit-field can straddle a
27905           storage-unit boundary are determine by these rules:
27906
27907           1. Structure members are stored sequentially in the order in which
27908           they are
27909               declared: the first member has the lowest memory address and
27910               the last member the highest.
27911
27912           2. Every data object has an alignment requirement.  The alignment
27913           requirement
27914               for all data except structures, unions, and arrays is either
27915               the size of the object or the current packing size (specified
27916               with either the "aligned" attribute or the "pack" pragma),
27917               whichever is less.  For structures, unions, and arrays, the
27918               alignment requirement is the largest alignment requirement of
27919               its members.  Every object is allocated an offset so that:
27920
27921                       offset % alignment_requirement == 0
27922
27923           3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte
27924           allocation
27925               unit if the integral types are the same size and if the next
27926               bit-field fits into the current allocation unit without
27927               crossing the boundary imposed by the common alignment
27928               requirements of the bit-fields.
27929
27930           MSVC interprets zero-length bit-fields in the following ways:
27931
27932           1. If a zero-length bit-field is inserted between two bit-fields
27933           that
27934               are normally coalesced, the bit-fields are not coalesced.
27935
27936               For example:
27937
27938                       struct
27939                        {
27940                          unsigned long bf_1 : 12;
27941                          unsigned long : 0;
27942                          unsigned long bf_2 : 12;
27943                        } t1;
27944
27945               The size of "t1" is 8 bytes with the zero-length bit-field.  If
27946               the zero-length bit-field were removed, "t1"'s size would be 4
27947               bytes.
27948
27949           2. If a zero-length bit-field is inserted after a bit-field, "foo",
27950           and the
27951               alignment of the zero-length bit-field is greater than the
27952               member that follows it, "bar", "bar" is aligned as the type of
27953               the zero-length bit-field.
27954
27955               For example:
27956
27957                       struct
27958                        {
27959                          char foo : 4;
27960                          short : 0;
27961                          char bar;
27962                        } t2;
27963
27964                       struct
27965                        {
27966                          char foo : 4;
27967                          short : 0;
27968                          double bar;
27969                        } t3;
27970
27971               For "t2", "bar" is placed at offset 2, rather than offset 1.
27972               Accordingly, the size of "t2" is 4.  For "t3", the zero-length
27973               bit-field does not affect the alignment of "bar" or, as a
27974               result, the size of the structure.
27975
27976               Taking this into account, it is important to note the
27977               following:
27978
27979               1. If a zero-length bit-field follows a normal bit-field, the
27980               type of the
27981                   zero-length bit-field may affect the alignment of the
27982                   structure as whole. For example, "t2" has a size of 4
27983                   bytes, since the zero-length bit-field follows a normal
27984                   bit-field, and is of type short.
27985
27986               2. Even if a zero-length bit-field is not followed by a normal
27987               bit-field, it may
27988                   still affect the alignment of the structure:
27989
27990                           struct
27991                            {
27992                              char foo : 6;
27993                              long : 0;
27994                            } t4;
27995
27996                   Here, "t4" takes up 4 bytes.
27997
27998           3. Zero-length bit-fields following non-bit-field members are
27999           ignored:
28000                       struct
28001                        {
28002                          char foo;
28003                          long : 0;
28004                          char bar;
28005                        } t5;
28006
28007               Here, "t5" takes up 2 bytes.
28008
28009       -mno-align-stringops
28010           Do not align the destination of inlined string operations.  This
28011           switch reduces code size and improves performance in case the
28012           destination is already aligned, but GCC doesn't know about it.
28013
28014       -minline-all-stringops
28015           By default GCC inlines string operations only when the destination
28016           is known to be aligned to least a 4-byte boundary.  This enables
28017           more inlining and increases code size, but may improve performance
28018           of code that depends on fast "memcpy" and "memset" for short
28019           lengths.  The option enables inline expansion of "strlen" for all
28020           pointer alignments.
28021
28022       -minline-stringops-dynamically
28023           For string operations of unknown size, use run-time checks with
28024           inline code for small blocks and a library call for large blocks.
28025
28026       -mstringop-strategy=alg
28027           Override the internal decision heuristic for the particular
28028           algorithm to use for inlining string operations.  The allowed
28029           values for alg are:
28030
28031           rep_byte
28032           rep_4byte
28033           rep_8byte
28034               Expand using i386 "rep" prefix of the specified size.
28035
28036           byte_loop
28037           loop
28038           unrolled_loop
28039               Expand into an inline loop.
28040
28041           libcall
28042               Always use a library call.
28043
28044       -mmemcpy-strategy=strategy
28045           Override the internal decision heuristic to decide if
28046           "__builtin_memcpy" should be inlined and what inline algorithm to
28047           use when the expected size of the copy operation is known. strategy
28048           is a comma-separated list of alg:max_size:dest_align triplets.  alg
28049           is specified in -mstringop-strategy, max_size specifies the max
28050           byte size with which inline algorithm alg is allowed.  For the last
28051           triplet, the max_size must be "-1". The max_size of the triplets in
28052           the list must be specified in increasing order.  The minimal byte
28053           size for alg is 0 for the first triplet and "max_size + 1" of the
28054           preceding range.
28055
28056       -mmemset-strategy=strategy
28057           The option is similar to -mmemcpy-strategy= except that it is to
28058           control "__builtin_memset" expansion.
28059
28060       -momit-leaf-frame-pointer
28061           Don't keep the frame pointer in a register for leaf functions.
28062           This avoids the instructions to save, set up, and restore frame
28063           pointers and makes an extra register available in leaf functions.
28064           The option -fomit-leaf-frame-pointer removes the frame pointer for
28065           leaf functions, which might make debugging harder.
28066
28067       -mtls-direct-seg-refs
28068       -mno-tls-direct-seg-refs
28069           Controls whether TLS variables may be accessed with offsets from
28070           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
28071           whether the thread base pointer must be added.  Whether or not this
28072           is valid depends on the operating system, and whether it maps the
28073           segment to cover the entire TLS area.
28074
28075           For systems that use the GNU C Library, the default is on.
28076
28077       -msse2avx
28078       -mno-sse2avx
28079           Specify that the assembler should encode SSE instructions with VEX
28080           prefix.  The option -mavx turns this on by default.
28081
28082       -mfentry
28083       -mno-fentry
28084           If profiling is active (-pg), put the profiling counter call before
28085           the prologue.  Note: On x86 architectures the attribute
28086           "ms_hook_prologue" isn't possible at the moment for -mfentry and
28087           -pg.
28088
28089       -mrecord-mcount
28090       -mno-record-mcount
28091           If profiling is active (-pg), generate a __mcount_loc section that
28092           contains pointers to each profiling call. This is useful for
28093           automatically patching and out calls.
28094
28095       -mnop-mcount
28096       -mno-nop-mcount
28097           If profiling is active (-pg), generate the calls to the profiling
28098           functions as NOPs. This is useful when they should be patched in
28099           later dynamically. This is likely only useful together with
28100           -mrecord-mcount.
28101
28102       -minstrument-return=type
28103           Instrument function exit in -pg -mfentry instrumented functions
28104           with call to specified function. This only instruments true returns
28105           ending with ret, but not sibling calls ending with jump. Valid
28106           types are none to not instrument, call to generate a call to
28107           __return__, or nop5 to generate a 5 byte nop.
28108
28109       -mrecord-return
28110       -mno-record-return
28111           Generate a __return_loc section pointing to all return
28112           instrumentation code.
28113
28114       -mfentry-name=name
28115           Set name of __fentry__ symbol called at function entry for -pg
28116           -mfentry functions.
28117
28118       -mfentry-section=name
28119           Set name of section to record -mrecord-mcount calls (default
28120           __mcount_loc).
28121
28122       -mskip-rax-setup
28123       -mno-skip-rax-setup
28124           When generating code for the x86-64 architecture with SSE
28125           extensions disabled, -mskip-rax-setup can be used to skip setting
28126           up RAX register when there are no variable arguments passed in
28127           vector registers.
28128
28129           Warning: Since RAX register is used to avoid unnecessarily saving
28130           vector registers on stack when passing variable arguments, the
28131           impacts of this option are callees may waste some stack space,
28132           misbehave or jump to a random location.  GCC 4.4 or newer don't
28133           have those issues, regardless the RAX register value.
28134
28135       -m8bit-idiv
28136       -mno-8bit-idiv
28137           On some processors, like Intel Atom, 8-bit unsigned integer divide
28138           is much faster than 32-bit/64-bit integer divide.  This option
28139           generates a run-time check.  If both dividend and divisor are
28140           within range of 0 to 255, 8-bit unsigned integer divide is used
28141           instead of 32-bit/64-bit integer divide.
28142
28143       -mavx256-split-unaligned-load
28144       -mavx256-split-unaligned-store
28145           Split 32-byte AVX unaligned load and store.
28146
28147       -mstack-protector-guard=guard
28148       -mstack-protector-guard-reg=reg
28149       -mstack-protector-guard-offset=offset
28150           Generate stack protection code using canary at guard.  Supported
28151           locations are global for global canary or tls for per-thread canary
28152           in the TLS block (the default).  This option has effect only when
28153           -fstack-protector or -fstack-protector-all is specified.
28154
28155           With the latter choice the options -mstack-protector-guard-reg=reg
28156           and -mstack-protector-guard-offset=offset furthermore specify which
28157           segment register (%fs or %gs) to use as base register for reading
28158           the canary, and from what offset from that base register.  The
28159           default for those is as specified in the relevant ABI.
28160
28161       -mgeneral-regs-only
28162           Generate code that uses only the general-purpose registers.  This
28163           prevents the compiler from using floating-point, vector, mask and
28164           bound registers.
28165
28166       -mrelax-cmpxchg-loop
28167           Relax cmpxchg loop by emitting an early load and compare before
28168           cmpxchg, execute pause if load value is not expected. This reduces
28169           excessive cachline bouncing when and works for all atomic logic
28170           fetch builtins that generates compare and swap loop.
28171
28172       -mindirect-branch=choice
28173           Convert indirect call and jump with choice.  The default is keep,
28174           which keeps indirect call and jump unmodified.  thunk converts
28175           indirect call and jump to call and return thunk.  thunk-inline
28176           converts indirect call and jump to inlined call and return thunk.
28177           thunk-extern converts indirect call and jump to external call and
28178           return thunk provided in a separate object file.  You can control
28179           this behavior for a specific function by using the function
28180           attribute "indirect_branch".
28181
28182           Note that -mcmodel=large is incompatible with
28183           -mindirect-branch=thunk and -mindirect-branch=thunk-extern since
28184           the thunk function may not be reachable in the large code model.
28185
28186           Note that -mindirect-branch=thunk-extern is compatible with
28187           -fcf-protection=branch since the external thunk can be made to
28188           enable control-flow check.
28189
28190       -mfunction-return=choice
28191           Convert function return with choice.  The default is keep, which
28192           keeps function return unmodified.  thunk converts function return
28193           to call and return thunk.  thunk-inline converts function return to
28194           inlined call and return thunk.  thunk-extern converts function
28195           return to external call and return thunk provided in a separate
28196           object file.  You can control this behavior for a specific function
28197           by using the function attribute "function_return".
28198
28199           Note that -mindirect-return=thunk-extern is compatible with
28200           -fcf-protection=branch since the external thunk can be made to
28201           enable control-flow check.
28202
28203           Note that -mcmodel=large is incompatible with
28204           -mfunction-return=thunk and -mfunction-return=thunk-extern since
28205           the thunk function may not be reachable in the large code model.
28206
28207       -mindirect-branch-register
28208           Force indirect call and jump via register.
28209
28210       -mharden-sls=choice
28211           Generate code to mitigate against straight line speculation (SLS)
28212           with choice.  The default is none which disables all SLS hardening.
28213           return enables SLS hardening for function returns.  indirect-jmp
28214           enables SLS hardening for indirect jumps.  all enables all SLS
28215           hardening.
28216
28217       -mindirect-branch-cs-prefix
28218           Add CS prefix to call and jmp to indirect thunk with branch target
28219           in r8-r15 registers so that the call and jmp instruction length is
28220           6 bytes to allow them to be replaced with lfence; call *%r8-r15 or
28221           lfence; jmp *%r8-r15 at run-time.
28222
28223       These -m switches are supported in addition to the above on x86-64
28224       processors in 64-bit environments.
28225
28226       -m32
28227       -m64
28228       -mx32
28229       -m16
28230       -miamcu
28231           Generate code for a 16-bit, 32-bit or 64-bit environment.  The -m32
28232           option sets "int", "long", and pointer types to 32 bits, and
28233           generates code that runs on any i386 system.
28234
28235           The -m64 option sets "int" to 32 bits and "long" and pointer types
28236           to 64 bits, and generates code for the x86-64 architecture.  For
28237           Darwin only the -m64 option also turns off the -fno-pic and
28238           -mdynamic-no-pic options.
28239
28240           The -mx32 option sets "int", "long", and pointer types to 32 bits,
28241           and generates code for the x86-64 architecture.
28242
28243           The -m16 option is the same as -m32, except for that it outputs the
28244           ".code16gcc" assembly directive at the beginning of the assembly
28245           output so that the binary can run in 16-bit mode.
28246
28247           The -miamcu option generates code which conforms to Intel MCU
28248           psABI.  It requires the -m32 option to be turned on.
28249
28250       -mno-red-zone
28251           Do not use a so-called "red zone" for x86-64 code.  The red zone is
28252           mandated by the x86-64 ABI; it is a 128-byte area beyond the
28253           location of the stack pointer that is not modified by signal or
28254           interrupt handlers and therefore can be used for temporary data
28255           without adjusting the stack pointer.  The flag -mno-red-zone
28256           disables this red zone.
28257
28258       -mcmodel=small
28259           Generate code for the small code model: the program and its symbols
28260           must be linked in the lower 2 GB of the address space.  Pointers
28261           are 64 bits.  Programs can be statically or dynamically linked.
28262           This is the default code model.
28263
28264       -mcmodel=kernel
28265           Generate code for the kernel code model.  The kernel runs in the
28266           negative 2 GB of the address space.  This model has to be used for
28267           Linux kernel code.
28268
28269       -mcmodel=medium
28270           Generate code for the medium model: the program is linked in the
28271           lower 2 GB of the address space.  Small symbols are also placed
28272           there.  Symbols with sizes larger than -mlarge-data-threshold are
28273           put into large data or BSS sections and can be located above 2GB.
28274           Programs can be statically or dynamically linked.
28275
28276       -mcmodel=large
28277           Generate code for the large model.  This model makes no assumptions
28278           about addresses and sizes of sections.
28279
28280       -maddress-mode=long
28281           Generate code for long address mode.  This is only supported for
28282           64-bit and x32 environments.  It is the default address mode for
28283           64-bit environments.
28284
28285       -maddress-mode=short
28286           Generate code for short address mode.  This is only supported for
28287           32-bit and x32 environments.  It is the default address mode for
28288           32-bit and x32 environments.
28289
28290       -mneeded
28291       -mno-needed
28292           Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to
28293           indicate the micro-architecture ISA level required to execute the
28294           binary.
28295
28296       -mno-direct-extern-access
28297           Without -fpic nor -fPIC, always use the GOT pointer to access
28298           external symbols.  With -fpic or -fPIC, treat access to protected
28299           symbols as local symbols.  The default is -mdirect-extern-access.
28300
28301           Warning: shared libraries compiled with -mno-direct-extern-access
28302           and executable compiled with -mdirect-extern-access may not be
28303           binary compatible if protected symbols are used in shared libraries
28304           and executable.
28305
28306       x86 Windows Options
28307
28308       These additional options are available for Microsoft Windows targets:
28309
28310       -mconsole
28311           This option specifies that a console application is to be
28312           generated, by instructing the linker to set the PE header subsystem
28313           type required for console applications.  This option is available
28314           for Cygwin and MinGW targets and is enabled by default on those
28315           targets.
28316
28317       -mdll
28318           This option is available for Cygwin and MinGW targets.  It
28319           specifies that a DLL---a dynamic link library---is to be generated,
28320           enabling the selection of the required runtime startup object and
28321           entry point.
28322
28323       -mnop-fun-dllimport
28324           This option is available for Cygwin and MinGW targets.  It
28325           specifies that the "dllimport" attribute should be ignored.
28326
28327       -mthreads
28328           This option is available for MinGW targets. It specifies that
28329           MinGW-specific thread support is to be used.
28330
28331       -municode
28332           This option is available for MinGW-w64 targets.  It causes the
28333           "UNICODE" preprocessor macro to be predefined, and chooses Unicode-
28334           capable runtime startup code.
28335
28336       -mwin32
28337           This option is available for Cygwin and MinGW targets.  It
28338           specifies that the typical Microsoft Windows predefined macros are
28339           to be set in the pre-processor, but does not influence the choice
28340           of runtime library/startup code.
28341
28342       -mwindows
28343           This option is available for Cygwin and MinGW targets.  It
28344           specifies that a GUI application is to be generated by instructing
28345           the linker to set the PE header subsystem type appropriately.
28346
28347       -fno-set-stack-executable
28348           This option is available for MinGW targets. It specifies that the
28349           executable flag for the stack used by nested functions isn't set.
28350           This is necessary for binaries running in kernel mode of Microsoft
28351           Windows, as there the User32 API, which is used to set executable
28352           privileges, isn't available.
28353
28354       -fwritable-relocated-rdata
28355           This option is available for MinGW and Cygwin targets.  It
28356           specifies that relocated-data in read-only section is put into the
28357           ".data" section.  This is a necessary for older runtimes not
28358           supporting modification of ".rdata" sections for pseudo-relocation.
28359
28360       -mpe-aligned-commons
28361           This option is available for Cygwin and MinGW targets.  It
28362           specifies that the GNU extension to the PE file format that permits
28363           the correct alignment of COMMON variables should be used when
28364           generating code.  It is enabled by default if GCC detects that the
28365           target assembler found during configuration supports the feature.
28366
28367       See also under x86 Options for standard options.
28368
28369       Xstormy16 Options
28370
28371       These options are defined for Xstormy16:
28372
28373       -msim
28374           Choose startup files and linker script suitable for the simulator.
28375
28376       Xtensa Options
28377
28378       These options are supported for Xtensa targets:
28379
28380       -mconst16
28381       -mno-const16
28382           Enable or disable use of "CONST16" instructions for loading
28383           constant values.  The "CONST16" instruction is currently not a
28384           standard option from Tensilica.  When enabled, "CONST16"
28385           instructions are always used in place of the standard "L32R"
28386           instructions.  The use of "CONST16" is enabled by default only if
28387           the "L32R" instruction is not available.
28388
28389       -mfused-madd
28390       -mno-fused-madd
28391           Enable or disable use of fused multiply/add and multiply/subtract
28392           instructions in the floating-point option.  This has no effect if
28393           the floating-point option is not also enabled.  Disabling fused
28394           multiply/add and multiply/subtract instructions forces the compiler
28395           to use separate instructions for the multiply and add/subtract
28396           operations.  This may be desirable in some cases where strict IEEE
28397           754-compliant results are required: the fused multiply add/subtract
28398           instructions do not round the intermediate result, thereby
28399           producing results with more bits of precision than specified by the
28400           IEEE standard.  Disabling fused multiply add/subtract instructions
28401           also ensures that the program output is not sensitive to the
28402           compiler's ability to combine multiply and add/subtract operations.
28403
28404       -mserialize-volatile
28405       -mno-serialize-volatile
28406           When this option is enabled, GCC inserts "MEMW" instructions before
28407           "volatile" memory references to guarantee sequential consistency.
28408           The default is -mserialize-volatile.  Use -mno-serialize-volatile
28409           to omit the "MEMW" instructions.
28410
28411       -mforce-no-pic
28412           For targets, like GNU/Linux, where all user-mode Xtensa code must
28413           be position-independent code (PIC), this option disables PIC for
28414           compiling kernel code.
28415
28416       -mtext-section-literals
28417       -mno-text-section-literals
28418           These options control the treatment of literal pools.  The default
28419           is -mno-text-section-literals, which places literals in a separate
28420           section in the output file.  This allows the literal pool to be
28421           placed in a data RAM/ROM, and it also allows the linker to combine
28422           literal pools from separate object files to remove redundant
28423           literals and improve code size.  With -mtext-section-literals, the
28424           literals are interspersed in the text section in order to keep them
28425           as close as possible to their references.  This may be necessary
28426           for large assembly files.  Literals for each function are placed
28427           right before that function.
28428
28429       -mauto-litpools
28430       -mno-auto-litpools
28431           These options control the treatment of literal pools.  The default
28432           is -mno-auto-litpools, which places literals in a separate section
28433           in the output file unless -mtext-section-literals is used.  With
28434           -mauto-litpools the literals are interspersed in the text section
28435           by the assembler.  Compiler does not produce explicit ".literal"
28436           directives and loads literals into registers with "MOVI"
28437           instructions instead of "L32R" to let the assembler do relaxation
28438           and place literals as necessary.  This option allows assembler to
28439           create several literal pools per function and assemble very big
28440           functions, which may not be possible with -mtext-section-literals.
28441
28442       -mtarget-align
28443       -mno-target-align
28444           When this option is enabled, GCC instructs the assembler to
28445           automatically align instructions to reduce branch penalties at the
28446           expense of some code density.  The assembler attempts to widen
28447           density instructions to align branch targets and the instructions
28448           following call instructions.  If there are not enough preceding
28449           safe density instructions to align a target, no widening is
28450           performed.  The default is -mtarget-align.  These options do not
28451           affect the treatment of auto-aligned instructions like "LOOP",
28452           which the assembler always aligns, either by widening density
28453           instructions or by inserting NOP instructions.
28454
28455       -mlongcalls
28456       -mno-longcalls
28457           When this option is enabled, GCC instructs the assembler to
28458           translate direct calls to indirect calls unless it can determine
28459           that the target of a direct call is in the range allowed by the
28460           call instruction.  This translation typically occurs for calls to
28461           functions in other source files.  Specifically, the assembler
28462           translates a direct "CALL" instruction into an "L32R" followed by a
28463           "CALLX" instruction.  The default is -mno-longcalls.  This option
28464           should be used in programs where the call target can potentially be
28465           out of range.  This option is implemented in the assembler, not the
28466           compiler, so the assembly code generated by GCC still shows direct
28467           call instructions---look at the disassembled object code to see the
28468           actual instructions.  Note that the assembler uses an indirect call
28469           for every cross-file call, not just those that really are out of
28470           range.
28471
28472       -mabi=name
28473           Generate code for the specified ABI.  Permissible values are:
28474           call0, windowed.  Default ABI is chosen by the Xtensa core
28475           configuration.
28476
28477       -mabi=call0
28478           When this option is enabled function parameters are passed in
28479           registers "a2" through "a7", registers "a12" through "a15" are
28480           caller-saved, and register "a15" may be used as a frame pointer.
28481           When this version of the ABI is enabled the C preprocessor symbol
28482           "__XTENSA_CALL0_ABI__" is defined.
28483
28484       -mabi=windowed
28485           When this option is enabled function parameters are passed in
28486           registers "a10" through "a15", and called function rotates register
28487           window by 8 registers on entry so that its arguments are found in
28488           registers "a2" through "a7".  Register "a7" may be used as a frame
28489           pointer.  Register window is rotated 8 registers back upon return.
28490           When this version of the ABI is enabled the C preprocessor symbol
28491           "__XTENSA_WINDOWED_ABI__" is defined.
28492
28493       zSeries Options
28494
28495       These are listed under
28496

ENVIRONMENT

28498       This section describes several environment variables that affect how
28499       GCC operates.  Some of them work by specifying directories or prefixes
28500       to use when searching for various kinds of files.  Some are used to
28501       specify other aspects of the compilation environment.
28502
28503       Note that you can also specify places to search using options such as
28504       -B, -I and -L.  These take precedence over places specified using
28505       environment variables, which in turn take precedence over those
28506       specified by the configuration of GCC.
28507
28508       LANG
28509       LC_CTYPE
28510       LC_MESSAGES
28511       LC_ALL
28512           These environment variables control the way that GCC uses
28513           localization information which allows GCC to work with different
28514           national conventions.  GCC inspects the locale categories LC_CTYPE
28515           and LC_MESSAGES if it has been configured to do so.  These locale
28516           categories can be set to any value supported by your installation.
28517           A typical value is en_GB.UTF-8 for English in the United Kingdom
28518           encoded in UTF-8.
28519
28520           The LC_CTYPE environment variable specifies character
28521           classification.  GCC uses it to determine the character boundaries
28522           in a string; this is needed for some multibyte encodings that
28523           contain quote and escape characters that are otherwise interpreted
28524           as a string end or escape.
28525
28526           The LC_MESSAGES environment variable specifies the language to use
28527           in diagnostic messages.
28528
28529           If the LC_ALL environment variable is set, it overrides the value
28530           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
28531           default to the value of the LANG environment variable.  If none of
28532           these variables are set, GCC defaults to traditional C English
28533           behavior.
28534
28535       TMPDIR
28536           If TMPDIR is set, it specifies the directory to use for temporary
28537           files.  GCC uses temporary files to hold the output of one stage of
28538           compilation which is to be used as input to the next stage: for
28539           example, the output of the preprocessor, which is the input to the
28540           compiler proper.
28541
28542       GCC_COMPARE_DEBUG
28543           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing
28544           -fcompare-debug to the compiler driver.  See the documentation of
28545           this option for more details.
28546
28547       GCC_EXEC_PREFIX
28548           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
28549           names of the subprograms executed by the compiler.  No slash is
28550           added when this prefix is combined with the name of a subprogram,
28551           but you can specify a prefix that ends with a slash if you wish.
28552
28553           If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an
28554           appropriate prefix to use based on the pathname it is invoked with.
28555
28556           If GCC cannot find the subprogram using the specified prefix, it
28557           tries looking in the usual places for the subprogram.
28558
28559           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
28560           prefix is the prefix to the installed compiler. In many cases
28561           prefix is the value of "prefix" when you ran the configure script.
28562
28563           Other prefixes specified with -B take precedence over this prefix.
28564
28565           This prefix is also used for finding files such as crt0.o that are
28566           used for linking.
28567
28568           In addition, the prefix is used in an unusual way in finding the
28569           directories to search for header files.  For each of the standard
28570           directories whose name normally begins with /usr/local/lib/gcc
28571           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
28572           replacing that beginning with the specified prefix to produce an
28573           alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar
28574           just before it searches the standard directory /usr/local/lib/bar.
28575           If a standard directory begins with the configured prefix then the
28576           value of prefix is replaced by GCC_EXEC_PREFIX when looking for
28577           header files.
28578
28579       COMPILER_PATH
28580           The value of COMPILER_PATH is a colon-separated list of
28581           directories, much like PATH.  GCC tries the directories thus
28582           specified when searching for subprograms, if it cannot find the
28583           subprograms using GCC_EXEC_PREFIX.
28584
28585       LIBRARY_PATH
28586           The value of LIBRARY_PATH is a colon-separated list of directories,
28587           much like PATH.  When configured as a native compiler, GCC tries
28588           the directories thus specified when searching for special linker
28589           files, if it cannot find them using GCC_EXEC_PREFIX.  Linking using
28590           GCC also uses these directories when searching for ordinary
28591           libraries for the -l option (but directories specified with -L come
28592           first).
28593
28594       LANG
28595           This variable is used to pass locale information to the compiler.
28596           One way in which this information is used is to determine the
28597           character set to be used when character literals, string literals
28598           and comments are parsed in C and C++.  When the compiler is
28599           configured to allow multibyte characters, the following values for
28600           LANG are recognized:
28601
28602           C-JIS
28603               Recognize JIS characters.
28604
28605           C-SJIS
28606               Recognize SJIS characters.
28607
28608           C-EUCJP
28609               Recognize EUCJP characters.
28610
28611           If LANG is not defined, or if it has some other value, then the
28612           compiler uses "mblen" and "mbtowc" as defined by the default locale
28613           to recognize and translate multibyte characters.
28614
28615       GCC_EXTRA_DIAGNOSTIC_OUTPUT
28616           If GCC_EXTRA_DIAGNOSTIC_OUTPUT is set to one of the following
28617           values, then additional text will be emitted to stderr when fix-it
28618           hints are emitted.  -fdiagnostics-parseable-fixits and
28619           -fno-diagnostics-parseable-fixits take precedence over this
28620           environment variable.
28621
28622           fixits-v1
28623               Emit parseable fix-it hints, equivalent to
28624               -fdiagnostics-parseable-fixits.  In particular, columns are
28625               expressed as a count of bytes, starting at byte 1 for the
28626               initial column.
28627
28628           fixits-v2
28629               As "fixits-v1", but columns are expressed as display columns,
28630               as per -fdiagnostics-column-unit=display.
28631
28632       Some additional environment variables affect the behavior of the
28633       preprocessor.
28634
28635       CPATH
28636       C_INCLUDE_PATH
28637       CPLUS_INCLUDE_PATH
28638       OBJC_INCLUDE_PATH
28639           Each variable's value is a list of directories separated by a
28640           special character, much like PATH, in which to look for header
28641           files.  The special character, "PATH_SEPARATOR", is target-
28642           dependent and determined at GCC build time.  For Microsoft Windows-
28643           based targets it is a semicolon, and for almost all other targets
28644           it is a colon.
28645
28646           CPATH specifies a list of directories to be searched as if
28647           specified with -I, but after any paths given with -I options on the
28648           command line.  This environment variable is used regardless of
28649           which language is being preprocessed.
28650
28651           The remaining environment variables apply only when preprocessing
28652           the particular language indicated.  Each specifies a list of
28653           directories to be searched as if specified with -isystem, but after
28654           any paths given with -isystem options on the command line.
28655
28656           In all these variables, an empty element instructs the compiler to
28657           search its current working directory.  Empty elements can appear at
28658           the beginning or end of a path.  For instance, if the value of
28659           CPATH is ":/special/include", that has the same effect as
28660           -I. -I/special/include.
28661
28662       DEPENDENCIES_OUTPUT
28663           If this variable is set, its value specifies how to output
28664           dependencies for Make based on the non-system header files
28665           processed by the compiler.  System header files are ignored in the
28666           dependency output.
28667
28668           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
28669           case the Make rules are written to that file, guessing the target
28670           name from the source file name.  Or the value can have the form
28671           file target, in which case the rules are written to file file using
28672           target as the target name.
28673
28674           In other words, this environment variable is equivalent to
28675           combining the options -MM and -MF, with an optional -MT switch too.
28676
28677       SUNPRO_DEPENDENCIES
28678           This variable is the same as DEPENDENCIES_OUTPUT (see above),
28679           except that system header files are not ignored, so it implies -M
28680           rather than -MM.  However, the dependence on the main input file is
28681           omitted.
28682
28683       SOURCE_DATE_EPOCH
28684           If this variable is set, its value specifies a UNIX timestamp to be
28685           used in replacement of the current date and time in the "__DATE__"
28686           and "__TIME__" macros, so that the embedded timestamps become
28687           reproducible.
28688
28689           The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
28690           the number of seconds (excluding leap seconds) since 01 Jan 1970
28691           00:00:00 represented in ASCII; identical to the output of "date
28692           +%s" on GNU/Linux and other systems that support the %s extension
28693           in the "date" command.
28694
28695           The value should be a known timestamp such as the last modification
28696           time of the source or package and it should be set by the build
28697           process.
28698

BUGS

28700       For instructions on reporting bugs, see <https://bugzilla.redhat.com/>.
28701

FOOTNOTES

28703       1.  On some systems, gcc -shared needs to build supplementary stub code
28704           for constructors to work.  On multi-libbed systems, gcc -shared
28705           must select the correct support libraries to link against.  Failing
28706           to supply the correct flags may lead to subtle defects.  Supplying
28707           them in cases where they are not necessary is innocuous.
28708

SEE ALSO

28710       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
28711       dbx(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb.
28712

AUTHOR

28714       See the Info entry for gcc, or
28715       <https://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for
28716       contributors to GCC.
28717
28719       Copyright (c) 1988-2022 Free Software Foundation, Inc.
28720
28721       Permission is granted to copy, distribute and/or modify this document
28722       under the terms of the GNU Free Documentation License, Version 1.3 or
28723       any later version published by the Free Software Foundation; with the
28724       Invariant Sections being "GNU General Public License" and "Funding Free
28725       Software", the Front-Cover texts being (a) (see below), and with the
28726       Back-Cover Texts being (b) (see below).  A copy of the license is
28727       included in the gfdl(7) man page.
28728
28729       (a) The FSF's Front-Cover Text is:
28730
28731            A GNU Manual
28732
28733       (b) The FSF's Back-Cover Text is:
28734
28735            You have freedom to copy and modify this GNU Manual, like GNU
28736            software.  Copies published by the Free Software Foundation raise
28737            funds for GNU development.
28738
28739
28740
28741gcc-12.1.0                        2022-05-06                            GCC(1)
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