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  -fgnu89-inline
89           -fpermitted-flt-eval-methods=standard -aux-info filename
90           -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
91           -fno-builtin-function  -fgimple -fhosted  -ffreestanding -fopenacc
92           -fopenacc-dim=geom -fopenmp  -fopenmp-simd -fms-extensions
93           -fplan9-extensions  -fsso-struct=endianness
94           -fallow-single-precision  -fcond-mismatch  -flax-vector-conversions
95           -fsigned-bitfields  -fsigned-char -funsigned-bitfields
96           -funsigned-char
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  -Wdeprecated-copy
122           -Wdeprecated-copy-dtor -Wno-deprecated-enum-enum-conversion
123           -Wno-deprecated-enum-float-conversion -Weffc++  -Wno-exceptions
124           -Wextra-semi  -Wno-inaccessible-base -Wno-inherited-variadic-ctor
125           -Wno-init-list-lifetime -Winvalid-imported-macros
126           -Wno-invalid-offsetof  -Wno-literal-suffix
127           -Wno-mismatched-new-delete -Wmismatched-tags -Wmultiple-inheritance
128           -Wnamespaces  -Wnarrowing -Wnoexcept  -Wnoexcept-type
129           -Wnon-virtual-dtor -Wpessimizing-move  -Wno-placement-new
130           -Wplacement-new=n -Wrange-loop-construct -Wredundant-move
131           -Wredundant-tags -Wreorder  -Wregister -Wstrict-null-sentinel
132           -Wno-subobject-linkage  -Wtemplates -Wno-non-template-friend
133           -Wold-style-cast -Woverloaded-virtual  -Wno-pmf-conversions
134           -Wsign-promo -Wsized-deallocation  -Wsuggest-final-methods
135           -Wsuggest-final-types  -Wsuggest-override -Wno-terminate
136           -Wuseless-cast  -Wno-vexing-parse -Wvirtual-inheritance
137           -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
166       Warning Options
167           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
168           -Wextra  -Wall  -Wabi=n -Waddress  -Wno-address-of-packed-member
169           -Waggregate-return -Walloc-size-larger-than=byte-size  -Walloc-zero
170           -Walloca  -Walloca-larger-than=byte-size
171           -Wno-aggressive-loop-optimizations -Warith-conversion
172           -Warray-bounds  -Warray-bounds=n -Wno-attributes
173           -Wattribute-alias=n -Wno-attribute-alias -Wno-attribute-warning
174           -Wbool-compare  -Wbool-operation -Wno-builtin-declaration-mismatch
175           -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat
176           -Wc11-c2x-compat -Wc++-compat  -Wc++11-compat  -Wc++14-compat
177           -Wc++17-compat -Wc++20-compat -Wcast-align  -Wcast-align=strict
178           -Wcast-function-type  -Wcast-qual -Wchar-subscripts -Wclobbered
179           -Wcomment -Wconversion  -Wno-coverage-mismatch  -Wno-cpp
180           -Wdangling-else  -Wdate-time -Wno-deprecated
181           -Wno-deprecated-declarations  -Wno-designated-init
182           -Wdisabled-optimization -Wno-discarded-array-qualifiers
183           -Wno-discarded-qualifiers -Wno-div-by-zero  -Wdouble-promotion
184           -Wduplicated-branches  -Wduplicated-cond -Wempty-body
185           -Wno-endif-labels  -Wenum-compare  -Wenum-conversion -Werror
186           -Werror=*  -Wexpansion-to-defined  -Wfatal-errors
187           -Wfloat-conversion  -Wfloat-equal  -Wformat  -Wformat=2
188           -Wno-format-contains-nul  -Wno-format-extra-args
189           -Wformat-nonliteral  -Wformat-overflow=n -Wformat-security
190           -Wformat-signedness  -Wformat-truncation=n -Wformat-y2k
191           -Wframe-address -Wframe-larger-than=byte-size
192           -Wno-free-nonheap-object -Wno-if-not-aligned
193           -Wno-ignored-attributes -Wignored-qualifiers
194           -Wno-incompatible-pointer-types -Wimplicit  -Wimplicit-fallthrough
195           -Wimplicit-fallthrough=n -Wno-implicit-function-declaration
196           -Wno-implicit-int -Winit-self  -Winline  -Wno-int-conversion
197           -Wint-in-bool-context -Wno-int-to-pointer-cast
198           -Wno-invalid-memory-model -Winvalid-pch  -Wjump-misses-init
199           -Wlarger-than=byte-size -Wlogical-not-parentheses  -Wlogical-op
200           -Wlong-long -Wno-lto-type-mismatch -Wmain  -Wmaybe-uninitialized
201           -Wmemset-elt-size  -Wmemset-transposed-args
202           -Wmisleading-indentation  -Wmissing-attributes  -Wmissing-braces
203           -Wmissing-field-initializers  -Wmissing-format-attribute
204           -Wmissing-include-dirs  -Wmissing-noreturn  -Wno-missing-profile
205           -Wno-multichar  -Wmultistatement-macros  -Wnonnull
206           -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
207           -Wnull-dereference  -Wno-odr  -Wopenmp-simd -Wno-overflow
208           -Woverlength-strings  -Wno-override-init-side-effects -Wpacked
209           -Wno-packed-bitfield-compat  -Wpacked-not-aligned  -Wpadded
210           -Wparentheses  -Wno-pedantic-ms-format -Wpointer-arith
211           -Wno-pointer-compare  -Wno-pointer-to-int-cast -Wno-pragmas
212           -Wno-prio-ctor-dtor  -Wredundant-decls -Wrestrict
213           -Wno-return-local-addr  -Wreturn-type -Wno-scalar-storage-order
214           -Wsequence-point -Wshadow  -Wshadow=global  -Wshadow=local
215           -Wshadow=compatible-local -Wno-shadow-ivar
216           -Wno-shift-count-negative  -Wno-shift-count-overflow
217           -Wshift-negative-value -Wno-shift-overflow  -Wshift-overflow=n
218           -Wsign-compare  -Wsign-conversion -Wno-sizeof-array-argument
219           -Wsizeof-array-div -Wsizeof-pointer-div  -Wsizeof-pointer-memaccess
220           -Wstack-protector  -Wstack-usage=byte-size  -Wstrict-aliasing
221           -Wstrict-aliasing=n  -Wstrict-overflow  -Wstrict-overflow=n
222           -Wstring-compare -Wno-stringop-overflow -Wno-stringop-overread
223           -Wno-stringop-truncation
224           -Wsuggest-attribute=[pure|const|noreturn|format|malloc] -Wswitch
225           -Wno-switch-bool  -Wswitch-default  -Wswitch-enum
226           -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand
227           -Wsystem-headers  -Wtautological-compare  -Wtrampolines
228           -Wtrigraphs -Wtsan -Wtype-limits  -Wundef -Wuninitialized
229           -Wunknown-pragmas -Wunsuffixed-float-constants  -Wunused
230           -Wunused-but-set-parameter  -Wunused-but-set-variable
231           -Wunused-const-variable  -Wunused-const-variable=n
232           -Wunused-function  -Wunused-label  -Wunused-local-typedefs
233           -Wunused-macros -Wunused-parameter  -Wno-unused-result
234           -Wunused-value  -Wunused-variable -Wno-varargs  -Wvariadic-macros
235           -Wvector-operation-performance -Wvla  -Wvla-larger-than=byte-size
236           -Wno-vla-larger-than -Wvolatile-register-var  -Wwrite-strings
237           -Wzero-length-bounds
238
239       Static Analyzer Options
240           -fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=name
241           -fno-analyzer-feasibility -fanalyzer-fine-grained
242           -fanalyzer-state-merge -fanalyzer-state-purge
243           -fanalyzer-transitivity -fanalyzer-verbose-edges
244           -fanalyzer-verbose-state-changes -fanalyzer-verbosity=level
245           -fdump-analyzer -fdump-analyzer-stderr -fdump-analyzer-callgraph
246           -fdump-analyzer-exploded-graph -fdump-analyzer-exploded-nodes
247           -fdump-analyzer-exploded-nodes-2 -fdump-analyzer-exploded-nodes-3
248           -fdump-analyzer-feasibility -fdump-analyzer-json
249           -fdump-analyzer-state-purge -fdump-analyzer-supergraph
250           -Wno-analyzer-double-fclose -Wno-analyzer-double-free
251           -Wno-analyzer-exposure-through-output-file -Wno-analyzer-file-leak
252           -Wno-analyzer-free-of-non-heap -Wno-analyzer-malloc-leak
253           -Wno-analyzer-mismatching-deallocation -Wno-analyzer-null-argument
254           -Wno-analyzer-null-dereference -Wno-analyzer-possible-null-argument
255           -Wno-analyzer-possible-null-dereference
256           -Wno-analyzer-shift-count-negative
257           -Wno-analyzer-shift-count-overflow
258           -Wno-analyzer-stale-setjmp-buffer -Wno-analyzer-tainted-array-index
259           -Wanalyzer-too-complex
260           -Wno-analyzer-unsafe-call-within-signal-handler
261           -Wno-analyzer-use-after-free
262           -Wno-analyzer-use-of-pointer-in-stale-stack-frame
263           -Wno-analyzer-use-of-uninitialized-value
264           -Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal
265
266       C and Objective-C-only Warning Options
267           -Wbad-function-cast  -Wmissing-declarations
268           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
269           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
270           -Wtraditional  -Wtraditional-conversion
271           -Wdeclaration-after-statement  -Wpointer-sign
272
273       Debugging Options
274           -g  -glevel  -gdwarf  -gdwarf-version -ggdb  -grecord-gcc-switches
275           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf
276           -gno-strict-dwarf -gas-loc-support  -gno-as-loc-support
277           -gas-locview-support  -gno-as-locview-support -gcolumn-info
278           -gno-column-info  -gdwarf32  -gdwarf64 -gstatement-frontiers
279           -gno-statement-frontiers -gvariable-location-views
280           -gno-variable-location-views -ginternal-reset-location-views
281           -gno-internal-reset-location-views -ginline-points
282           -gno-inline-points -gvms  -gxcoff  -gxcoff+  -gz[=type]
283           -gsplit-dwarf  -gdescribe-dies  -gno-describe-dies
284           -fdebug-prefix-map=old=new  -fdebug-types-section
285           -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly
286           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-
287           list] -fno-eliminate-unused-debug-symbols
288           -femit-class-debug-always -fno-merge-debug-strings
289           -fno-dwarf2-cfi-asm -fvar-tracking  -fvar-tracking-assignments
290
291       Optimization Options
292           -faggressive-loop-optimizations -falign-functions[=n[:m:[n2[:m2]]]]
293           -falign-jumps[=n[:m:[n2[:m2]]]] -falign-labels[=n[:m:[n2[:m2]]]]
294           -falign-loops[=n[:m:[n2[:m2]]]] -fno-allocation-dce
295           -fallow-store-data-races -fassociative-math  -fauto-profile
296           -fauto-profile[=path] -fauto-inc-dec  -fbranch-probabilities
297           -fcaller-saves -fcombine-stack-adjustments  -fconserve-stack
298           -fcompare-elim  -fcprop-registers  -fcrossjumping
299           -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
300           -fcx-limited-range -fdata-sections  -fdce  -fdelayed-branch
301           -fdelete-null-pointer-checks  -fdevirtualize
302           -fdevirtualize-speculatively -fdevirtualize-at-ltrans  -fdse
303           -fearly-inlining  -fipa-sra  -fexpensive-optimizations
304           -ffat-lto-objects -ffast-math  -ffinite-math-only  -ffloat-store
305           -fexcess-precision=style -ffinite-loops -fforward-propagate
306           -ffp-contract=style  -ffunction-sections -fgcse
307           -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity
308           -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion -fif-conversion2
309           -findirect-inlining -finline-functions
310           -finline-functions-called-once  -finline-limit=n
311           -finline-small-functions -fipa-modref -fipa-cp  -fipa-cp-clone
312           -fipa-bit-cp  -fipa-vrp  -fipa-pta  -fipa-profile  -fipa-pure-const
313           -fipa-reference  -fipa-reference-addressable -fipa-stack-alignment
314           -fipa-icf  -fira-algorithm=algorithm -flive-patching=level
315           -fira-region=region  -fira-hoist-pressure -fira-loop-pressure
316           -fno-ira-share-save-slots -fno-ira-share-spill-slots
317           -fisolate-erroneous-paths-dereference
318           -fisolate-erroneous-paths-attribute -fivopts
319           -fkeep-inline-functions  -fkeep-static-functions
320           -fkeep-static-consts  -flimit-function-alignment
321           -flive-range-shrinkage -floop-block  -floop-interchange
322           -floop-strip-mine -floop-unroll-and-jam  -floop-nest-optimize
323           -floop-parallelize-all  -flra-remat  -flto  -flto-compression-level
324           -flto-partition=alg  -fmerge-all-constants -fmerge-constants
325           -fmodulo-sched  -fmodulo-sched-allow-regmoves
326           -fmove-loop-invariants  -fno-branch-count-reg -fno-defer-pop
327           -fno-fp-int-builtin-inexact  -fno-function-cse
328           -fno-guess-branch-probability  -fno-inline  -fno-math-errno
329           -fno-peephole -fno-peephole2  -fno-printf-return-value
330           -fno-sched-interblock -fno-sched-spec  -fno-signed-zeros
331           -fno-toplevel-reorder  -fno-trapping-math
332           -fno-zero-initialized-in-bss -fomit-frame-pointer
333           -foptimize-sibling-calls -fpartial-inlining  -fpeel-loops
334           -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction
335           -fprofile-use  -fprofile-use=path -fprofile-partial-training
336           -fprofile-values -fprofile-reorder-functions -freciprocal-math
337           -free  -frename-registers  -freorder-blocks
338           -freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition
339           -freorder-functions -frerun-cse-after-loop
340           -freschedule-modulo-scheduled-loops -frounding-math
341           -fsave-optimization-record -fsched2-use-superblocks
342           -fsched-pressure -fsched-spec-load  -fsched-spec-load-dangerous
343           -fsched-stalled-insns-dep[=n]  -fsched-stalled-insns[=n]
344           -fsched-group-heuristic  -fsched-critical-path-heuristic
345           -fsched-spec-insn-heuristic  -fsched-rank-heuristic
346           -fsched-last-insn-heuristic  -fsched-dep-count-heuristic
347           -fschedule-fusion -fschedule-insns  -fschedule-insns2
348           -fsection-anchors -fselective-scheduling  -fselective-scheduling2
349           -fsel-sched-pipelining  -fsel-sched-pipelining-outer-loops
350           -fsemantic-interposition  -fshrink-wrap  -fshrink-wrap-separate
351           -fsignaling-nans -fsingle-precision-constant
352           -fsplit-ivs-in-unroller  -fsplit-loops -fsplit-paths
353           -fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop
354           -fssa-phiopt -fstdarg-opt  -fstore-merging  -fstrict-aliasing
355           -fthread-jumps  -ftracer  -ftree-bit-ccp -ftree-builtin-call-dce
356           -ftree-ccp  -ftree-ch -ftree-coalesce-vars  -ftree-copy-prop
357           -ftree-dce  -ftree-dominator-opts -ftree-dse  -ftree-forwprop
358           -ftree-fre  -fcode-hoisting -ftree-loop-if-convert  -ftree-loop-im
359           -ftree-phiprop  -ftree-loop-distribution
360           -ftree-loop-distribute-patterns -ftree-loop-ivcanon
361           -ftree-loop-linear  -ftree-loop-optimize -ftree-loop-vectorize
362           -ftree-parallelize-loops=n  -ftree-pre  -ftree-partial-pre
363           -ftree-pta -ftree-reassoc  -ftree-scev-cprop  -ftree-sink
364           -ftree-slsr  -ftree-sra -ftree-switch-conversion  -ftree-tail-merge
365           -ftree-ter  -ftree-vectorize  -ftree-vrp  -funconstrained-commons
366           -funit-at-a-time  -funroll-all-loops  -funroll-loops
367           -funsafe-math-optimizations  -funswitch-loops -fipa-ra
368           -fvariable-expansion-in-unroller  -fvect-cost-model  -fvpt -fweb
369           -fwhole-program  -fwpa  -fuse-linker-plugin -fzero-call-used-regs
370           --param name=value -O  -O0  -O1  -O2  -O3  -Os  -Ofast  -Og
371
372       Program Instrumentation Options
373           -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage
374           -fprofile-abs-path -fprofile-dir=path  -fprofile-generate
375           -fprofile-generate=path -fprofile-info-section
376           -fprofile-info-section=name -fprofile-note=path
377           -fprofile-prefix-path=path -fprofile-update=method
378           -fprofile-filter-files=regex -fprofile-exclude-files=regex
379           -fprofile-reproducible=[multithreaded|parallel-runs|serial]
380           -fsanitize=style  -fsanitize-recover  -fsanitize-recover=style
381           -fasan-shadow-offset=number  -fsanitize-sections=s1,s2,...
382           -fsanitize-undefined-trap-on-error  -fbounds-check
383           -fcf-protection=[full|branch|return|none|check] -fstack-protector
384           -fstack-protector-all  -fstack-protector-strong
385           -fstack-protector-explicit  -fstack-check
386           -fstack-limit-register=reg  -fstack-limit-symbol=sym
387           -fno-stack-limit  -fsplit-stack -fvtable-verify=[std|preinit|none]
388           -fvtv-counts  -fvtv-debug -finstrument-functions
389           -finstrument-functions-exclude-function-list=sym,sym,...
390           -finstrument-functions-exclude-file-list=file,file,...
391
392       Preprocessor Options
393           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD
394           -dI  -dM  -dN  -dU -fdebug-cpp  -fdirectives-only
395           -fdollars-in-identifiers -fexec-charset=charset
396           -fextended-identifiers -finput-charset=charset
397           -flarge-source-files -fmacro-prefix-map=old=new
398           -fmax-include-depth=depth -fno-canonical-system-headers  -fpch-deps
399           -fpch-preprocess -fpreprocessed  -ftabstop=width
400           -ftrack-macro-expansion -fwide-exec-charset=charset
401           -fworking-directory -H  -imacros file  -include file -M  -MD  -MF
402           -MG  -MM  -MMD  -MP  -MQ  -MT -Mno-modules -no-integrated-cpp  -P
403           -pthread  -remap -traditional  -traditional-cpp  -trigraphs -Umacro
404           -undef -Wp,option  -Xpreprocessor option
405
406       Assembler Options
407           -Wa,option  -Xassembler option
408
409       Linker Options
410           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles
411           -nodefaultlibs  -nolibc  -nostdlib -e entry  --entry=entry -pie
412           -pthread  -r  -rdynamic -s  -static  -static-pie  -static-libgcc
413           -static-libstdc++ -static-libasan  -static-libtsan  -static-liblsan
414           -static-libubsan -shared  -shared-libgcc  -symbolic -T script
415           -Wl,option  -Xlinker option -u symbol  -z keyword
416
417       Directory Options
418           -Bprefix  -Idir  -I- -idirafter dir -imacros file  -imultilib dir
419           -iplugindir=dir  -iprefix file -iquote dir  -isysroot dir  -isystem
420           dir -iwithprefix dir  -iwithprefixbefore dir -Ldir
421           -no-canonical-prefixes  --no-sysroot-suffix -nostdinc  -nostdinc++
422           --sysroot=dir
423
424       Code Generation Options
425           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
426           -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
427           -fasynchronous-unwind-tables -fno-gnu-unique
428           -finhibit-size-directive  -fcommon  -fno-ident -fpcc-struct-return
429           -fpic  -fPIC  -fpie  -fPIE  -fno-plt -fno-jump-tables
430           -fno-bit-tests -frecord-gcc-switches -freg-struct-return
431           -fshort-enums  -fshort-wchar -fverbose-asm  -fpack-struct[=n]
432           -fleading-underscore  -ftls-model=model -fstack-reuse=reuse_level
433           -ftrampolines  -ftrapv  -fwrapv
434           -fvisibility=[default|internal|hidden|protected]
435           -fstrict-volatile-bitfields  -fsync-libcalls
436
437       Developer Options
438           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion
439           -fcallgraph-info[=su,da] -fchecking  -fchecking=n -fdbg-cnt-list
440           -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
441           -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list
442           -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list
443           -fdump-debug  -fdump-earlydebug -fdump-noaddr  -fdump-unnumbered
444           -fdump-unnumbered-links -fdump-final-insns[=file] -fdump-ipa-all
445           -fdump-ipa-cgraph  -fdump-ipa-inline -fdump-lang-all
446           -fdump-lang-switch -fdump-lang-switch-options
447           -fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass
448           -fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all
449           -fdump-tree-switch -fdump-tree-switch-options
450           -fdump-tree-switch-options=filename -fcompare-debug[=opts]
451           -fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range-
452           list -fira-verbose=n -flto-report  -flto-report-wpa
453           -fmem-report-wpa -fmem-report  -fpre-ipa-mem-report
454           -fpost-ipa-mem-report -fopt-info  -fopt-info-options[=file]
455           -fprofile-report -frandom-seed=string  -fsched-verbose=n
456           -fsel-sched-verbose  -fsel-sched-dump-cfg
457           -fsel-sched-pipelining-verbose -fstats  -fstack-usage
458           -ftime-report  -ftime-report-details
459           -fvar-tracking-assignments-toggle  -gtoggle
460           -print-file-name=library  -print-libgcc-file-name
461           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
462           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
463           -print-sysroot-headers-suffix -save-temps  -save-temps=cwd
464           -save-temps=obj  -time[=file]
465
466       Machine-Dependent Options
467           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian
468           -mgeneral-regs-only -mcmodel=tiny  -mcmodel=small  -mcmodel=large
469           -mstrict-align  -mno-strict-align -momit-leaf-frame-pointer
470           -mtls-dialect=desc  -mtls-dialect=traditional -mtls-size=size
471           -mfix-cortex-a53-835769  -mfix-cortex-a53-843419
472           -mlow-precision-recip-sqrt  -mlow-precision-sqrt
473           -mlow-precision-div -mpc-relative-literal-loads
474           -msign-return-address=scope -mbranch-protection=none|standard|pac-
475           ret[+leaf +b-key]|bti -mharden-sls=opts -march=name  -mcpu=name
476           -mtune=name -moverride=string  -mverbose-cost-dump
477           -mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg
478           -mstack-protector-guard-offset=offset -mtrack-speculation
479           -moutline-atomics
480
481           Adapteva Epiphany Options -mhalf-reg-file  -mprefer-short-insn-regs
482           -mbranch-cost=num  -mcmove  -mnops=num  -msoft-cmpsf -msplit-lohi
483           -mpost-inc  -mpost-modify  -mstack-offset=num -mround-nearest
484           -mlong-calls  -mshort-calls  -msmall16 -mfp-mode=mode
485           -mvect-double  -max-vect-align=num -msplit-vecmove-early
486           -m1reg-reg
487
488           AMD GCN Options -march=gpu -mtune=gpu -mstack-size=bytes
489
490           ARC Options -mbarrel-shifter  -mjli-always -mcpu=cpu  -mA6
491           -mARC600  -mA7  -mARC700 -mdpfp  -mdpfp-compact  -mdpfp-fast
492           -mno-dpfp-lrsr -mea  -mno-mpy  -mmul32x16  -mmul64  -matomic -mnorm
493           -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap
494           -mcrc  -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc
495           -mswape -mtelephony  -mxy  -misize  -mannotate-align  -marclinux
496           -marclinux_prof -mlong-calls  -mmedium-calls  -msdata
497           -mirq-ctrl-saved -mrgf-banked-regs  -mlpc-width=width  -G num
498           -mvolatile-cache  -mtp-regno=regno -malign-call  -mauto-modify-reg
499           -mbbit-peephole  -mno-brcc -mcase-vector-pcrel  -mcompact-casesi
500           -mno-cond-exec  -mearly-cbranchsi -mexpand-adddi  -mindexed-loads
501           -mlra  -mlra-priority-none -mlra-priority-compact mlra-priority-
502           noncompact  -mmillicode -mmixed-code  -mq-class  -mRcq  -mRcw
503           -msize-level=level -mtune=cpu  -mmultcost=num  -mcode-density-frame
504           -munalign-prob-threshold=probability  -mmpy-option=multo -mdiv-rem
505           -mcode-density  -mll64  -mfpu=fpu  -mrf16  -mbranch-index
506
507           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
508           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-reentrant
509           -mno-apcs-reentrant -mgeneral-regs-only -msched-prolog
510           -mno-sched-prolog -mlittle-endian  -mbig-endian -mbe8  -mbe32
511           -mfloat-abi=name -mfp16-format=name -mthumb-interwork
512           -mno-thumb-interwork -mcpu=name  -march=name  -mfpu=name
513           -mtune=name  -mprint-tune-info -mstructure-size-boundary=n
514           -mabort-on-noreturn -mlong-calls  -mno-long-calls -msingle-pic-base
515           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
516           -mpoke-function-name -mthumb  -marm  -mflip-thumb -mtpcs-frame
517           -mtpcs-leaf-frame -mcaller-super-interworking
518           -mcallee-super-interworking -mtp=name  -mtls-dialect=dialect
519           -mword-relocations -mfix-cortex-m3-ldrd -munaligned-access
520           -mneon-for-64bits -mslow-flash-data -masm-syntax-unified
521           -mrestrict-it -mverbose-cost-dump -mpure-code -mcmse -mfdpic
522
523           AVR Options -mmcu=mcu  -mabsdata  -maccumulate-args
524           -mbranch-cost=cost -mcall-prologues  -mgas-isr-prologues  -mint8
525           -mdouble=bits -mlong-double=bits -mn_flash=size  -mno-interrupts
526           -mmain-is-OS_task  -mrelax  -mrmw  -mstrict-X  -mtiny-stack
527           -mfract-convert-truncate -mshort-calls  -nodevicelib
528           -nodevicespecs -Waddr-space-convert  -Wmisspelled-isr
529
530           Blackfin Options -mcpu=cpu[-sirevision] -msim
531           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
532           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
533           -mno-csync-anomaly -mlow-64k  -mno-low64k  -mstack-check-l1
534           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
535           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
536           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp
537           -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram -micplb
538
539           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim
540           -msdata=sdata-type
541
542           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
543           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init
544           -mno-side-effects -mstack-align  -mdata-align  -mconst-align
545           -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
546           -melf  -maout  -melinux  -mlinux  -sim  -sim2 -mmul-bug-workaround
547           -mno-mul-bug-workaround
548
549           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops
550           -mdata-model=model
551
552           C-SKY Options -march=arch  -mcpu=cpu -mbig-endian  -EB
553           -mlittle-endian  -EL -mhard-float  -msoft-float  -mfpu=fpu
554           -mdouble-float  -mfdivdu -mfloat-abi=name -melrw  -mistack  -mmp
555           -mcp  -mcache  -msecurity  -mtrust -mdsp  -medsp  -mvdsp -mdiv
556           -msmart  -mhigh-registers  -manchor -mpushpop  -mmultiple-stld
557           -mconstpool  -mstack-size  -mccrt -mbranch-cost=n  -mcse-cc
558           -msched-prolog -msim
559
560           Darwin Options -all_load  -allowable_client  -arch
561           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
562           -bundle_loader -client_name  -compatibility_version
563           -current_version -dead_strip -dependency-file  -dylib_file
564           -dylinker_install_name -dynamic  -dynamiclib
565           -exported_symbols_list -filelist  -flat_namespace
566           -force_cpusubtype_ALL -force_flat_namespace
567           -headerpad_max_install_names -iframework -image_base  -init
568           -install_name  -keep_private_externs -multi_module
569           -multiply_defined  -multiply_defined_unused -noall_load
570           -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs
571           -noprebind  -noseglinkedit -pagezero_size  -prebind
572           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
573           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
574           -sectobjectsymbols  -sectorder -segaddr  -segs_read_only_addr
575           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
576           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
577           -single_module  -static  -sub_library  -sub_umbrella
578           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
579           -weak_reference_mismatches -whatsloaded  -F  -gused  -gfull
580           -mmacosx-version-min=version -mkernel  -mone-byte-bool
581
582           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee
583           -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
584           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
585           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
586           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
587           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time
588
589           eBPF Options -mbig-endian -mlittle-endian -mkernel=version
590           -mframe-limit=bytes -mxbpf
591
592           FR30 Options -msmall-model  -mno-lsim
593
594           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm
595
596           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
597           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
598           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
599           -minline-plt  -mgprel-ro  -multilib-library-pic -mlinked-fp
600           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
601           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
602           -moptimize-membar  -mno-optimize-membar -mscc  -mno-scc
603           -mcond-exec  -mno-cond-exec -mvliw-branch  -mno-vliw-branch
604           -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
605           -mno-nested-cond-exec  -mtomcat-stats -mTLS  -mtls -mcpu=cpu
606
607           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid
608           -tno-android-cc  -tno-android-ld
609
610           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32
611           -malign-300
612
613           HPPA Options -march=architecture-type -mcaller-copies
614           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
615           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
616           -mlinker-opt  -mlong-calls -mlong-load-store  -mno-disable-fpregs
617           -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
618           -mno-jump-in-delay  -mno-long-load-store -mno-portable-runtime
619           -mno-soft-float -mno-space-regs  -msoft-float  -mpa-risc-1-0
620           -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime -mschedule=cpu-
621           type  -mspace-regs  -msio  -mwsio -munix=unix-std  -nolibdld
622           -static  -threads
623
624           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
625           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata
626           -mconstant-gp  -mauto-pic  -mfused-madd
627           -minline-float-divide-min-latency
628           -minline-float-divide-max-throughput -mno-inline-float-divide
629           -minline-int-divide-min-latency -minline-int-divide-max-throughput
630           -mno-inline-int-divide -minline-sqrt-min-latency
631           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
632           -mearly-stop-bits -mfixed-range=register-range  -mtls-size=tls-size
633           -mtune=cpu-type  -milp32  -mlp64 -msched-br-data-spec
634           -msched-ar-data-spec  -msched-control-spec -msched-br-in-data-spec
635           -msched-ar-in-data-spec  -msched-in-control-spec -msched-spec-ldc
636           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
637           -msched-prefer-non-control-spec-insns
638           -msched-stop-bits-after-every-cycle
639           -msched-count-spec-in-critical-path
640           -msel-sched-dont-check-control-spec  -msched-fp-mem-deps-zero-cost
641           -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=max-
642           insns
643
644           LM32 Options -mbarrel-shift-enabled  -mdivide-enabled
645           -mmultiply-enabled -msign-extend-enabled  -muser-enabled
646
647           M32R/D Options -m32r2  -m32rx  -m32r -mdebug -malign-loops
648           -mno-align-loops -missue-rate=number -mbranch-cost=number
649           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
650           -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num
651
652           M32C Options -mcpu=cpu  -msim  -memregs=number
653
654           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
655           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
656           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
657           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
658           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
659           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
660           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
661           -mxgot  -mno-xgot  -mlong-jump-table-offsets
662
663           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
664           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
665           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
666           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
667           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
668           -mstack-increment
669
670           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops
671           -mc=n  -mclip  -mconfig=name  -mcop  -mcop32  -mcop64  -mivc2 -mdc
672           -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm  -mminmax
673           -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim
674           -msimnovec  -mtf -mtiny=n
675
676           MicroBlaze Options -msoft-float  -mhard-float  -msmall-divides
677           -mcpu=cpu -mmemcpy  -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift
678           -mxl-pattern-compare  -mxl-stack-check  -mxl-gp-opt  -mno-clearbss
679           -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
680           -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-app-model
681           -mpic-data-is-text-relative
682
683           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
684           -mips3  -mips4  -mips32  -mips32r2  -mips32r3  -mips32r5 -mips32r6
685           -mips64  -mips64r2  -mips64r3  -mips64r5  -mips64r6 -mips16
686           -mno-mips16  -mflip-mips16 -minterlink-compressed
687           -mno-interlink-compressed -minterlink-mips16  -mno-interlink-mips16
688           -mabi=abi  -mabicalls  -mno-abicalls -mshared  -mno-shared  -mplt
689           -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64
690           -mhard-float  -msoft-float -mno-float  -msingle-float
691           -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode
692           -mnan=encoding -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mmcu
693           -mmno-mcu -meva  -mno-eva -mvirt  -mno-virt -mxpa  -mno-xpa -mcrc
694           -mno-crc -mginv  -mno-ginv -mmicromips  -mno-micromips -mmsa
695           -mno-msa -mloongson-mmi  -mno-loongson-mmi -mloongson-ext
696           -mno-loongson-ext -mloongson-ext2  -mno-loongson-ext2 -mfpu=fpu-
697           type -msmartmips  -mno-smartmips -mpaired-single
698           -mno-paired-single  -mdmx  -mno-mdmx -mips3d  -mno-mips3d  -mmt
699           -mno-mt  -mllsc  -mno-llsc -mlong64  -mlong32  -msym32  -mno-sym32
700           -Gnum  -mlocal-sdata  -mno-local-sdata -mextern-sdata
701           -mno-extern-sdata  -mgpopt  -mno-gopt -membedded-data
702           -mno-embedded-data -muninit-const-in-rodata
703           -mno-uninit-const-in-rodata -mcode-readable=setting
704           -msplit-addresses  -mno-split-addresses -mexplicit-relocs
705           -mno-explicit-relocs -mcheck-zero-division
706           -mno-check-zero-division -mdivide-traps  -mdivide-breaks
707           -mload-store-pairs  -mno-load-store-pairs -mmemcpy  -mno-memcpy
708           -mlong-calls  -mno-long-calls -mmad  -mno-mad  -mimadd  -mno-imadd
709           -mfused-madd  -mno-fused-madd  -nocpp -mfix-24k  -mno-fix-24k
710           -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
711           -mfix-r5900  -mno-fix-r5900 -mfix-r10000  -mno-fix-r10000
712           -mfix-rm7000  -mno-fix-rm7000 -mfix-vr4120  -mno-fix-vr4120
713           -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
714           -mflush-func=func  -mno-flush-func -mbranch-cost=num
715           -mbranch-likely  -mno-branch-likely -mcompact-branches=policy
716           -mfp-exceptions  -mno-fp-exceptions -mvr4130-align
717           -mno-vr4130-align  -msynci  -mno-synci -mlxc1-sxc1  -mno-lxc1-sxc1
718           -mmadd4  -mno-madd4 -mrelax-pic-calls  -mno-relax-pic-calls
719           -mmcount-ra-address -mframe-header-opt  -mno-frame-header-opt
720
721           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
722           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
723           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
724           -mbase-addresses -mno-base-addresses  -msingle-exit
725           -mno-single-exit
726
727           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33  -mam33
728           -mam33-2  -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0
729           -mrelax  -mliw  -msetlb
730
731           Moxie Options -meb  -mel  -mmul.x  -mno-crt0
732
733           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall
734           -mrelax -mwarn-mcu -mcode-region=  -mdata-region= -msilicon-errata=
735           -msilicon-errata-warn= -mhwmult=  -minrt  -mtiny-printf
736           -mmax-inline-shift=
737
738           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs
739           -mfull-regs -mcmov  -mno-cmov -mext-perf  -mno-ext-perf -mext-perf2
740           -mno-ext-perf2 -mext-string  -mno-ext-string -mv3push  -mno-v3push
741           -m16bit  -mno-16bit -misr-vector-size=num -mcache-block-size=num
742           -march=arch -mcmodel=code-model -mctor-dtor  -mrelax
743
744           Nios II Options -G num  -mgpopt=option  -mgpopt  -mno-gpopt
745           -mgprel-sec=regexp  -mr0rel-sec=regexp -mel  -meb -mno-bypass-cache
746           -mbypass-cache -mno-cache-volatile  -mcache-volatile
747           -mno-fast-sw-div  -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx
748           -mno-hw-mulx  -mno-hw-div  -mhw-div -mcustom-insn=N
749           -mno-custom-insn -mcustom-fpu-cfg=name -mhal  -msmallc
750           -msys-crt0=name  -msys-lib=name -march=arch  -mbmx  -mno-bmx  -mcdx
751           -mno-cdx
752
753           Nvidia PTX Options -m64  -mmainkernel  -moptimize
754
755           OpenRISC Options -mboard=name  -mnewlib  -mhard-mul  -mhard-div
756           -msoft-mul  -msoft-div -msoft-float  -mhard-float  -mdouble-float
757           -munordered-float -mcmov  -mror  -mrori  -msext  -msfimm  -mshftimm
758
759           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
760           -m10 -mint32  -mno-int16  -mint16  -mno-int32 -msplit  -munix-asm
761           -mdec-asm  -mgnu-asm  -mlra
762
763           picoChip Options -mae=ae_type  -mvliw-lookahead=N
764           -msymbol-as-address  -mno-inefficient-warnings
765
766           PowerPC Options See RS/6000 and PowerPC Options.
767
768           PRU Options -mmcu=mcu  -minrt  -mno-relax  -mloop -mabi=variant
769
770           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt
771           -mabi=ABI-string -mfdiv  -mno-fdiv -mdiv  -mno-div -march=ISA-
772           string -mtune=processor-string -mpreferred-stack-boundary=num
773           -msmall-data-limit=N-bytes -msave-restore  -mno-save-restore
774           -mshorten-memrefs  -mno-shorten-memrefs -mstrict-align
775           -mno-strict-align -mcmodel=medlow  -mcmodel=medany
776           -mexplicit-relocs  -mno-explicit-relocs -mrelax  -mno-relax
777           -mriscv-attribute  -mmo-riscv-attribute -malign-data=type
778           -mbig-endian  -mlittle-endian +-mstack-protector-guard=guard
779           -mstack-protector-guard-reg=reg
780           +-mstack-protector-guard-offset=offset
781
782           RL78 Options -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs
783           -mcpu=g10  -mcpu=g13  -mcpu=g14  -mg10  -mg13  -mg14
784           -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts
785
786           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type
787           -mcmodel=code-model -mpowerpc64 -maltivec  -mno-altivec
788           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
789           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
790           -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb
791           -mhard-dfp  -mno-hard-dfp -mfull-toc   -mminimal-toc
792           -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32  -mxl-compat
793           -mno-xl-compat  -mpe -malign-power  -malign-natural -msoft-float
794           -mhard-float  -mmultiple  -mno-multiple -mupdate  -mno-update
795           -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
796           -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
797           -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
798           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle
799           -mlittle-endian  -mbig  -mbig-endian -mdynamic-no-pic  -mswdiv
800           -msingle-pic-base -mprioritize-restricted-insns=priority
801           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
802           -mcall-aixdesc  -mcall-eabi  -mcall-freebsd -mcall-linux
803           -mcall-netbsd  -mcall-openbsd -mcall-sysv  -mcall-sysv-eabi
804           -mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return
805           -msvr4-struct-return -mabi=abi-type  -msecure-plt  -mbss-plt
806           -mlongcall  -mno-longcall  -mpltseq  -mno-pltseq
807           -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
808           -mblock-compare-inline-loop-limit=num -mno-block-ops-unaligned-vsx
809           -mstring-compare-inline-limit=num -misel  -mno-isel -mvrsave
810           -mno-vrsave -mmulhw  -mno-mulhw -mdlmzb  -mno-dlmzb -mprototype
811           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
812           -msdata=opt  -mreadonly-in-sdata  -mvxworks  -G num -mrecip
813           -mrecip=opt  -mno-recip  -mrecip-precision -mno-recip-precision
814           -mveclibabi=type  -mfriz  -mno-friz -mpointers-to-nested-functions
815           -mno-pointers-to-nested-functions -msave-toc-indirect
816           -mno-save-toc-indirect -mpower8-fusion  -mno-mpower8-fusion
817           -mpower8-vector  -mno-power8-vector -mcrypto  -mno-crypto  -mhtm
818           -mno-htm -mquad-memory  -mno-quad-memory -mquad-memory-atomic
819           -mno-quad-memory-atomic -mcompat-align-parm  -mno-compat-align-parm
820           -mfloat128  -mno-float128  -mfloat128-hardware
821           -mno-float128-hardware -mgnu-attribute  -mno-gnu-attribute
822           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
823           -mstack-protector-guard-offset=offset -mprefixed -mno-prefixed
824           -mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect
825           -mprivileged -mno-privileged
826
827           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
828           -mbig-endian-data  -mlittle-endian-data -msmall-data -msim
829           -mno-sim -mas100-syntax  -mno-as100-syntax -mrelax
830           -mmax-constant-size= -mint-register= -mpid -mallow-string-insns
831           -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
832           -msave-acc-in-interrupts
833
834           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
835           -mhard-float  -msoft-float  -mhard-dfp  -mno-hard-dfp
836           -mlong-double-64  -mlong-double-128 -mbackchain  -mno-backchain
837           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
838           -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
839           -mhtm  -mvx  -mzvector -mtpf-trace  -mno-tpf-trace
840           -mtpf-trace-skip  -mno-tpf-trace-skip -mfused-madd  -mno-fused-madd
841           -mwarn-framesize  -mwarn-dynamicstack  -mstack-size  -mstack-guard
842           -mhotpatch=halfwords,halfwords
843
844           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u
845           -mscore7  -mscore7d
846
847           SH Options -m1  -m2  -m2e -m2a-nofpu  -m2a-single-only  -m2a-single
848           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
849           -m4a-nofpu  -m4a-single-only  -m4a-single  -m4a  -m4al -mb  -ml
850           -mdalign  -mrelax -mbigtable  -mfmovd  -mrenesas  -mno-renesas
851           -mnomacsave -mieee  -mno-ieee  -mbitops  -misize
852           -minline-ic_invalidate  -mpadstruct -mprefergot  -musermode
853           -multcost=number  -mdiv=strategy -mdivsi3_libfunc=name
854           -mfixed-range=register-range -maccumulate-outgoing-args
855           -matomic-model=atomic-model -mbranch-cost=num  -mzdcbranch
856           -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
857           -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra
858           -mpretend-cmove  -mtas
859
860           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text
861           -mno-impure-text -pthreads
862
863           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
864           -mmemory-model=mem-model -m32  -m64  -mapp-regs  -mno-app-regs
865           -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat -mfpu
866           -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
867           -msoft-quad-float -mstack-bias  -mno-stack-bias -mstd-struct-return
868           -mno-std-struct-return -munaligned-doubles  -mno-unaligned-doubles
869           -muser-mode  -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis
870           -mvis2  -mno-vis2  -mvis3  -mno-vis3 -mvis4  -mno-vis4  -mvis4b
871           -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld
872           -mno-fsmuld -mpopc  -mno-popc  -msubxc  -mno-subxc -mfix-at697f
873           -mfix-ut699  -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra
874
875           System V Options -Qy  -Qn  -YP,paths  -Ym,dir
876
877           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian
878           -mlittle-endian -mcmodel=code-model
879
880           TILEPro Options -mcpu=cpu  -m32
881
882           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
883           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
884           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
885           -mno-disable-callt -mv850e2v3  -mv850e2  -mv850e1  -mv850es -mv850e
886           -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
887           -mhard-float -mgcc-abi -mrh850-abi -mbig-switch
888
889           VAX Options -mg  -mgnu  -munix
890
891           Visium Options -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float
892           -msoft-float -mcpu=cpu-type  -mtune=cpu-type  -msv-mode
893           -muser-mode
894
895           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64
896           -mpointer-size=size
897
898           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
899           -Xbind-now
900
901           x86 Options -mtune=cpu-type  -march=cpu-type -mtune-ctrl=feature-
902           list  -mdump-tune-features  -mno-default -mfpmath=unit
903           -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387  -m80387
904           -mhard-float  -msoft-float -mno-wide-multiply  -mrtd
905           -malign-double -mpreferred-stack-boundary=num
906           -mincoming-stack-boundary=num -mcld  -mcx16  -msahf  -mmovbe
907           -mcrc32 -mrecip  -mrecip=opt -mvzeroupper  -mprefer-avx128
908           -mprefer-vector-width=opt -mmmx  -msse  -msse2  -msse3  -mssse3
909           -msse4.1  -msse4.2  -msse4  -mavx -mavx2  -mavx512f  -mavx512pf
910           -mavx512er  -mavx512cd  -mavx512vl -mavx512bw  -mavx512dq
911           -mavx512ifma  -mavx512vbmi  -msha  -maes -mpclmul  -mfsgsbase
912           -mrdrnd  -mf16c  -mfma  -mpconfig  -mwbnoinvd -mptwrite
913           -mprefetchwt1  -mclflushopt  -mclwb  -mxsavec  -mxsaves -msse4a
914           -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop
915           -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mhle
916           -mlwp -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni  -mvaes
917           -mwaitpkg -mshstk -mmanual-endbr -mforce-indirect-call
918           -mavx512vbmi2 -mavx512bf16 -menqcmd -mvpclmulqdq  -mavx512bitalg
919           -mmovdiri  -mmovdir64b  -mavx512vpopcntdq -mavx5124fmaps
920           -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid -mrdseed  -msgx
921           -mavx512vp2intersect -mserialize -mtsxldtrk -mamx-tile  -mamx-int8
922           -mamx-bf16 -muintr -mhreset -mavxvnni -mcldemote  -mms-bitfields
923           -mno-align-stringops  -minline-all-stringops
924           -minline-stringops-dynamically  -mstringop-strategy=alg -mkl
925           -mwidekl -mmemcpy-strategy=strategy  -mmemset-strategy=strategy
926           -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
927           -m96bit-long-double  -mlong-double-64  -mlong-double-80
928           -mlong-double-128 -mregparm=num  -msseregparm -mveclibabi=type
929           -mvect8-ret-in-mem -mpc32  -mpc64  -mpc80  -mstackrealign
930           -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs
931           -mcmodel=code-model  -mabi=name  -maddress-mode=mode -m32  -m64
932           -mx32  -m16  -miamcu  -mlarge-data-threshold=num -msse2avx
933           -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv
934           -minstrument-return=type -mfentry-name=name -mfentry-section=name
935           -mavx256-split-unaligned-load  -mavx256-split-unaligned-store
936           -malign-data=type  -mstack-protector-guard=guard
937           -mstack-protector-guard-reg=reg
938           -mstack-protector-guard-offset=offset
939           -mstack-protector-guard-symbol=symbol -mgeneral-regs-only
940           -mcall-ms2sysv-xlogues -mindirect-branch=choice
941           -mfunction-return=choice -mindirect-branch-register -mneeded
942
943           x86 Windows Options -mconsole  -mcygwin  -mno-cygwin  -mdll
944           -mnop-fun-dllimport  -mthread -municode  -mwin32  -mwindows
945           -fno-set-stack-executable
946
947           Xstormy16 Options -msim
948
949           Xtensa Options -mconst16  -mno-const16 -mfused-madd
950           -mno-fused-madd -mforce-no-pic -mserialize-volatile
951           -mno-serialize-volatile -mtext-section-literals
952           -mno-text-section-literals -mauto-litpools  -mno-auto-litpools
953           -mtarget-align  -mno-target-align -mlongcalls  -mno-longcalls
954           -mabi=abi-type
955
956           zSeries Options See S/390 and zSeries Options.
957
958   Options Controlling the Kind of Output
959       Compilation can involve up to four stages: preprocessing, compilation
960       proper, assembly and linking, always in that order.  GCC is capable of
961       preprocessing and compiling several files either into several assembler
962       input files, or into one assembler input file; then each assembler
963       input file produces an object file, and linking combines all the object
964       files (those newly compiled, and those specified as input) into an
965       executable file.
966
967       For any given input file, the file name suffix determines what kind of
968       compilation is done:
969
970       file.c
971           C source code that must be preprocessed.
972
973       file.i
974           C source code that should not be preprocessed.
975
976       file.ii
977           C++ source code that should not be preprocessed.
978
979       file.m
980           Objective-C source code.  Note that you must link with the libobjc
981           library to make an Objective-C program work.
982
983       file.mi
984           Objective-C source code that should not be preprocessed.
985
986       file.mm
987       file.M
988           Objective-C++ source code.  Note that you must link with the
989           libobjc library to make an Objective-C++ program work.  Note that
990           .M refers to a literal capital M.
991
992       file.mii
993           Objective-C++ source code that should not be preprocessed.
994
995       file.h
996           C, C++, Objective-C or Objective-C++ header file to be turned into
997           a precompiled header (default), or C, C++ header file to be turned
998           into an Ada spec (via the -fdump-ada-spec switch).
999
1000       file.cc
1001       file.cp
1002       file.cxx
1003       file.cpp
1004       file.CPP
1005       file.c++
1006       file.C
1007           C++ source code that must be preprocessed.  Note that in .cxx, the
1008           last two letters must both be literally x.  Likewise, .C refers to
1009           a literal capital C.
1010
1011       file.mm
1012       file.M
1013           Objective-C++ source code that must be preprocessed.
1014
1015       file.mii
1016           Objective-C++ source code that should not be preprocessed.
1017
1018       file.hh
1019       file.H
1020       file.hp
1021       file.hxx
1022       file.hpp
1023       file.HPP
1024       file.h++
1025       file.tcc
1026           C++ header file to be turned into a precompiled header or Ada spec.
1027
1028       file.f
1029       file.for
1030       file.ftn
1031           Fixed form Fortran source code that should not be preprocessed.
1032
1033       file.F
1034       file.FOR
1035       file.fpp
1036       file.FPP
1037       file.FTN
1038           Fixed form Fortran source code that must be preprocessed (with the
1039           traditional preprocessor).
1040
1041       file.f90
1042       file.f95
1043       file.f03
1044       file.f08
1045           Free form Fortran source code that should not be preprocessed.
1046
1047       file.F90
1048       file.F95
1049       file.F03
1050       file.F08
1051           Free form Fortran source code that must be preprocessed (with the
1052           traditional preprocessor).
1053
1054       file.go
1055           Go source code.
1056
1057       file.brig
1058           BRIG files (binary representation of HSAIL).
1059
1060       file.d
1061           D source code.
1062
1063       file.di
1064           D interface file.
1065
1066       file.dd
1067           D documentation code (Ddoc).
1068
1069       file.ads
1070           Ada source code file that contains a library unit declaration (a
1071           declaration of a package, subprogram, or generic, or a generic
1072           instantiation), or a library unit renaming declaration (a package,
1073           generic, or subprogram renaming declaration).  Such files are also
1074           called specs.
1075
1076       file.adb
1077           Ada source code file containing a library unit body (a subprogram
1078           or package body).  Such files are also called bodies.
1079
1080       file.s
1081           Assembler code.
1082
1083       file.S
1084       file.sx
1085           Assembler code that must be preprocessed.
1086
1087       other
1088           An object file to be fed straight into linking.  Any file name with
1089           no recognized suffix is treated this way.
1090
1091       You can specify the input language explicitly with the -x option:
1092
1093       -x language
1094           Specify explicitly the language for the following input files
1095           (rather than letting the compiler choose a default based on the
1096           file name suffix).  This option applies to all following input
1097           files until the next -x option.  Possible values for language are:
1098
1099                   c  c-header  cpp-output
1100                   c++  c++-header  c++-system-header c++-user-header c++-cpp-output
1101                   objective-c  objective-c-header  objective-c-cpp-output
1102                   objective-c++ objective-c++-header objective-c++-cpp-output
1103                   assembler  assembler-with-cpp
1104                   ada
1105                   d
1106                   f77  f77-cpp-input f95  f95-cpp-input
1107                   go
1108                   brig
1109
1110       -x none
1111           Turn off any specification of a language, so that subsequent files
1112           are handled according to their file name suffixes (as they are if
1113           -x has not been used at all).
1114
1115       If you only want some of the stages of compilation, you can use -x (or
1116       filename suffixes) to tell gcc where to start, and one of the options
1117       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
1118       (for example, -x cpp-output -E) instruct gcc to do nothing at all.
1119
1120       -c  Compile or assemble the source files, but do not link.  The linking
1121           stage simply is not done.  The ultimate output is in the form of an
1122           object file for each source file.
1123
1124           By default, the object file name for a source file is made by
1125           replacing the suffix .c, .i, .s, etc., with .o.
1126
1127           Unrecognized input files, not requiring compilation or assembly,
1128           are ignored.
1129
1130       -S  Stop after the stage of compilation proper; do not assemble.  The
1131           output is in the form of an assembler code file for each non-
1132           assembler input file specified.
1133
1134           By default, the assembler file name for a source file is made by
1135           replacing the suffix .c, .i, etc., with .s.
1136
1137           Input files that don't require compilation are ignored.
1138
1139       -E  Stop after the preprocessing stage; do not run the compiler proper.
1140           The output is in the form of preprocessed source code, which is
1141           sent to the standard output.
1142
1143           Input files that don't require preprocessing are ignored.
1144
1145       -o file
1146           Place the primary output in file file.  This applies to whatever
1147           sort of output is being produced, whether it be an executable file,
1148           an object file, an assembler file or preprocessed C code.
1149
1150           If -o is not specified, the default is to put an executable file in
1151           a.out, the object file for source.suffix in source.o, its assembler
1152           file in source.s, a precompiled header file in source.suffix.gch,
1153           and all preprocessed C source on standard output.
1154
1155           Though -o names only the primary output, it also affects the naming
1156           of auxiliary and dump outputs.  See the examples below.  Unless
1157           overridden, both auxiliary outputs and dump outputs are placed in
1158           the same directory as the primary output.  In auxiliary outputs,
1159           the suffix of the input file is replaced with that of the auxiliary
1160           output file type; in dump outputs, the suffix of the dump file is
1161           appended to the input file suffix.  In compilation commands, the
1162           base name of both auxiliary and dump outputs is that of the primary
1163           output; in compile and link commands, the primary output name,
1164           minus the executable suffix, is combined with the input file name.
1165           If both share the same base name, disregarding the suffix, the
1166           result of the combination is that base name, otherwise, they are
1167           concatenated, separated by a dash.
1168
1169                   gcc -c foo.c ...
1170
1171           will use foo.o as the primary output, and place aux outputs and
1172           dumps next to it, e.g., aux file foo.dwo for -gsplit-dwarf, and
1173           dump file foo.c.???r.final for -fdump-rtl-final.
1174
1175           If a non-linker output file is explicitly specified, aux and dump
1176           files by default take the same base name:
1177
1178                   gcc -c foo.c -o dir/foobar.o ...
1179
1180           will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*.
1181
1182           A linker output will instead prefix aux and dump outputs:
1183
1184                   gcc foo.c bar.c -o dir/foobar ...
1185
1186           will generally name aux outputs dir/foobar-foo.* and
1187           dir/foobar-bar.*, and dump outputs dir/foobar-foo.c.* and
1188           dir/foobar-bar.c.*.
1189
1190           The one exception to the above is when the executable shares the
1191           base name with the single input:
1192
1193                   gcc foo.c -o dir/foo ...
1194
1195           in which case aux outputs are named dir/foo.* and dump outputs
1196           named dir/foo.c.*.
1197
1198           The location and the names of auxiliary and dump outputs can be
1199           adjusted by the options -dumpbase, -dumpbase-ext, -dumpdir,
1200           -save-temps=cwd, and -save-temps=obj.
1201
1202       -dumpbase dumpbase
1203           This option sets the base name for auxiliary and dump output files.
1204           It does not affect the name of the primary output file.
1205           Intermediate outputs, when preserved, are not regarded as primary
1206           outputs, but as auxiliary outputs:
1207
1208                   gcc -save-temps -S foo.c
1209
1210           saves the (no longer) temporary preprocessed file in foo.i, and
1211           then compiles to the (implied) output file foo.s, whereas:
1212
1213                   gcc -save-temps -dumpbase save-foo -c foo.c
1214
1215           preprocesses to in save-foo.i, compiles to save-foo.s (now an
1216           intermediate, thus auxiliary output), and then assembles to the
1217           (implied) output file foo.o.
1218
1219           Absent this option, dump and aux files take their names from the
1220           input file, or from the (non-linker) output file, if one is
1221           explicitly specified: dump output files (e.g. those requested by
1222           -fdump-* options) with the input name suffix, and aux output files
1223           (those requested by other non-dump options, e.g. "-save-temps",
1224           "-gsplit-dwarf", "-fcallgraph-info") without it.
1225
1226           Similar suffix differentiation of dump and aux outputs can be
1227           attained for explicitly-given -dumpbase basename.suf by also
1228           specifying -dumpbase-ext .suf.
1229
1230           If dumpbase is explicitly specified with any directory component,
1231           any dumppfx specification (e.g. -dumpdir or -save-temps=*) is
1232           ignored, and instead of appending to it, dumpbase fully overrides
1233           it:
1234
1235                   gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
1236                     -dumpdir pfx- -save-temps=cwd ...
1237
1238           creates auxiliary and dump outputs named alt/foo.*, disregarding
1239           dir/ in -o, the ./ prefix implied by -save-temps=cwd, and pfx- in
1240           -dumpdir.
1241
1242           When -dumpbase is specified in a command that compiles multiple
1243           inputs, or that compiles and then links, it may be combined with
1244           dumppfx, as specified under -dumpdir.  Then, each input file is
1245           compiled using the combined dumppfx, and default values for
1246           dumpbase and auxdropsuf are computed for each input file:
1247
1248                   gcc foo.c bar.c -c -dumpbase main ...
1249
1250           creates foo.o and bar.o as primary outputs, and avoids overwriting
1251           the auxiliary and dump outputs by using the dumpbase as a prefix,
1252           creating auxiliary and dump outputs named main-foo.*  and
1253           main-bar.*.
1254
1255           An empty string specified as dumpbase avoids the influence of the
1256           output basename in the naming of auxiliary and dump outputs during
1257           compilation, computing default values :
1258
1259                   gcc -c foo.c -o dir/foobar.o -dumpbase " ...
1260
1261           will name aux outputs dir/foo.* and dump outputs dir/foo.c.*.  Note
1262           how their basenames are taken from the input name, but the
1263           directory still defaults to that of the output.
1264
1265           The empty-string dumpbase does not prevent the use of the output
1266           basename for outputs during linking:
1267
1268                   gcc foo.c bar.c -o dir/foobar -dumpbase " -flto ...
1269
1270           The compilation of the source files will name auxiliary outputs
1271           dir/foo.* and dir/bar.*, and dump outputs dir/foo.c.* and
1272           dir/bar.c.*.  LTO recompilation during linking will use dir/foobar.
1273           as the prefix for dumps and auxiliary files.
1274
1275       -dumpbase-ext auxdropsuf
1276           When forming the name of an auxiliary (but not a dump) output file,
1277           drop trailing auxdropsuf from dumpbase before appending any
1278           suffixes.  If not specified, this option defaults to the suffix of
1279           a default dumpbase, i.e., the suffix of the input file when
1280           -dumpbase is not present in the command line, or dumpbase is
1281           combined with dumppfx.
1282
1283                   gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...
1284
1285           creates dir/foo.o as the main output, and generates auxiliary
1286           outputs in dir/x-foo.*, taking the location of the primary output,
1287           and dropping the .c suffix from the dumpbase.  Dump outputs retain
1288           the suffix: dir/x-foo.c.*.
1289
1290           This option is disregarded if it does not match the suffix of a
1291           specified dumpbase, except as an alternative to the executable
1292           suffix when appending the linker output base name to dumppfx, as
1293           specified below:
1294
1295                   gcc foo.c bar.c -o main.out -dumpbase-ext .out ...
1296
1297           creates main.out as the primary output, and avoids overwriting the
1298           auxiliary and dump outputs by using the executable name minus
1299           auxdropsuf as a prefix, creating auxiliary outputs named main-foo.*
1300           and main-bar.* and dump outputs named main-foo.c.* and
1301           main-bar.c.*.
1302
1303       -dumpdir dumppfx
1304           When forming the name of an auxiliary or dump output file, use
1305           dumppfx as a prefix:
1306
1307                   gcc -dumpdir pfx- -c foo.c ...
1308
1309           creates foo.o as the primary output, and auxiliary outputs named
1310           pfx-foo.*, combining the given dumppfx with the default dumpbase
1311           derived from the default primary output, derived in turn from the
1312           input name.  Dump outputs also take the input name suffix:
1313           pfx-foo.c.*.
1314
1315           If dumppfx is to be used as a directory name, it must end with a
1316           directory separator:
1317
1318                   gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...
1319
1320           creates obj/bar.o as the primary output, and auxiliary outputs
1321           named dir/bar.*, combining the given dumppfx with the default
1322           dumpbase derived from the primary output name.  Dump outputs also
1323           take the input name suffix: dir/bar.c.*.
1324
1325           It defaults to the location of the output file; options
1326           -save-temps=cwd and -save-temps=obj override this default, just
1327           like an explicit -dumpdir option.  In case multiple such options
1328           are given, the last one prevails:
1329
1330                   gcc -dumpdir pfx- -c foo.c -save-temps=obj ...
1331
1332           outputs foo.o, with auxiliary outputs named foo.* because
1333           -save-temps=* overrides the dumppfx given by the earlier -dumpdir
1334           option.  It does not matter that =obj is the default for
1335           -save-temps, nor that the output directory is implicitly the
1336           current directory.  Dump outputs are named foo.c.*.
1337
1338           When compiling from multiple input files, if -dumpbase is
1339           specified, dumpbase, minus a auxdropsuf suffix, and a dash are
1340           appended to (or override, if containing any directory components)
1341           an explicit or defaulted dumppfx, so that each of the multiple
1342           compilations gets differently-named aux and dump outputs.
1343
1344                   gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...
1345
1346           outputs auxiliary dumps to dir/pfx-main-foo.* and
1347           dir/pfx-main-bar.*, appending dumpbase- to dumppfx.  Dump outputs
1348           retain the input file suffix: dir/pfx-main-foo.c.*  and
1349           dir/pfx-main-bar.c.*, respectively.  Contrast with the single-input
1350           compilation:
1351
1352                   gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...
1353
1354           that, applying -dumpbase to a single source, does not compute and
1355           append a separate dumpbase per input file.  Its auxiliary and dump
1356           outputs go in dir/pfx-main.*.
1357
1358           When compiling and then linking from multiple input files, a
1359           defaulted or explicitly specified dumppfx also undergoes the
1360           dumpbase- transformation above (e.g. the compilation of foo.c and
1361           bar.c above, but without -c).  If neither -dumpdir nor -dumpbase
1362           are given, the linker output base name, minus auxdropsuf, if
1363           specified, or the executable suffix otherwise, plus a dash is
1364           appended to the default dumppfx instead.  Note, however, that
1365           unlike earlier cases of linking:
1366
1367                   gcc foo.c bar.c -dumpdir dir/pfx- -o main ...
1368
1369           does not append the output name main to dumppfx, because -dumpdir
1370           is explicitly specified.  The goal is that the explicitly-specified
1371           dumppfx may contain the specified output name as part of the
1372           prefix, if desired; only an explicitly-specified -dumpbase would be
1373           combined with it, in order to avoid simply discarding a meaningful
1374           option.
1375
1376           When compiling and then linking from a single input file, the
1377           linker output base name will only be appended to the default
1378           dumppfx as above if it does not share the base name with the single
1379           input file name.  This has been covered in single-input linking
1380           cases above, but not with an explicit -dumpdir that inhibits the
1381           combination, even if overridden by -save-temps=*:
1382
1383                   gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...
1384
1385           Auxiliary outputs are named foo.*, and dump outputs foo.c.*, in the
1386           current working directory as ultimately requested by
1387           -save-temps=cwd.
1388
1389           Summing it all up for an intuitive though slightly imprecise data
1390           flow: the primary output name is broken into a directory part and a
1391           basename part; dumppfx is set to the former, unless overridden by
1392           -dumpdir or -save-temps=*, and dumpbase is set to the latter,
1393           unless overriden by -dumpbase.  If there are multiple inputs or
1394           linking, this dumpbase may be combined with dumppfx and taken from
1395           each input file.  Auxiliary output names for each input are formed
1396           by combining dumppfx, dumpbase minus suffix, and the auxiliary
1397           output suffix; dump output names are only different in that the
1398           suffix from dumpbase is retained.
1399
1400           When it comes to auxiliary and dump outputs created during LTO
1401           recompilation, a combination of dumppfx and dumpbase, as given or
1402           as derived from the linker output name but not from inputs, even in
1403           cases in which this combination would not otherwise be used as
1404           such, is passed down with a trailing period replacing the compiler-
1405           added dash, if any, as a -dumpdir option to lto-wrapper; being
1406           involved in linking, this program does not normally get any
1407           -dumpbase and -dumpbase-ext, and it ignores them.
1408
1409           When running sub-compilers, lto-wrapper appends LTO stage names to
1410           the received dumppfx, ensures it contains a directory component so
1411           that it overrides any -dumpdir, and passes that as -dumpbase to
1412           sub-compilers.
1413
1414       -v  Print (on standard error output) the commands executed to run the
1415           stages of compilation.  Also print the version number of the
1416           compiler driver program and of the preprocessor and the compiler
1417           proper.
1418
1419       -###
1420           Like -v except the commands are not executed and arguments are
1421           quoted unless they contain only alphanumeric characters or "./-_".
1422           This is useful for shell scripts to capture the driver-generated
1423           command lines.
1424
1425       --help
1426           Print (on the standard output) a description of the command-line
1427           options understood by gcc.  If the -v option is also specified then
1428           --help is also passed on to the various processes invoked by gcc,
1429           so that they can display the command-line options they accept.  If
1430           the -Wextra option has also been specified (prior to the --help
1431           option), then command-line options that have no documentation
1432           associated with them are also displayed.
1433
1434       --target-help
1435           Print (on the standard output) a description of target-specific
1436           command-line options for each tool.  For some targets extra target-
1437           specific information may also be printed.
1438
1439       --help={class|[^]qualifier}[,...]
1440           Print (on the standard output) a description of the command-line
1441           options understood by the compiler that fit into all specified
1442           classes and qualifiers.  These are the supported classes:
1443
1444           optimizers
1445               Display all of the optimization options supported by the
1446               compiler.
1447
1448           warnings
1449               Display all of the options controlling warning messages
1450               produced by the compiler.
1451
1452           target
1453               Display target-specific options.  Unlike the --target-help
1454               option however, target-specific options of the linker and
1455               assembler are not displayed.  This is because those tools do
1456               not currently support the extended --help= syntax.
1457
1458           params
1459               Display the values recognized by the --param option.
1460
1461           language
1462               Display the options supported for language, where language is
1463               the name of one of the languages supported in this version of
1464               GCC.  If an option is supported by all languages, one needs to
1465               select common class.
1466
1467           common
1468               Display the options that are common to all languages.
1469
1470           These are the supported qualifiers:
1471
1472           undocumented
1473               Display only those options that are undocumented.
1474
1475           joined
1476               Display options taking an argument that appears after an equal
1477               sign in the same continuous piece of text, such as:
1478               --help=target.
1479
1480           separate
1481               Display options taking an argument that appears as a separate
1482               word following the original option, such as: -o output-file.
1483
1484           Thus for example to display all the undocumented target-specific
1485           switches supported by the compiler, use:
1486
1487                   --help=target,undocumented
1488
1489           The sense of a qualifier can be inverted by prefixing it with the ^
1490           character, so for example to display all binary warning options
1491           (i.e., ones that are either on or off and that do not take an
1492           argument) that have a description, use:
1493
1494                   --help=warnings,^joined,^undocumented
1495
1496           The argument to --help= should not consist solely of inverted
1497           qualifiers.
1498
1499           Combining several classes is possible, although this usually
1500           restricts the output so much that there is nothing to display.  One
1501           case where it does work, however, is when one of the classes is
1502           target.  For example, to display all the target-specific
1503           optimization options, use:
1504
1505                   --help=target,optimizers
1506
1507           The --help= option can be repeated on the command line.  Each
1508           successive use displays its requested class of options, skipping
1509           those that have already been displayed.  If --help is also
1510           specified anywhere on the command line then this takes precedence
1511           over any --help= option.
1512
1513           If the -Q option appears on the command line before the --help=
1514           option, then the descriptive text displayed by --help= is changed.
1515           Instead of describing the displayed options, an indication is given
1516           as to whether the option is enabled, disabled or set to a specific
1517           value (assuming that the compiler knows this at the point where the
1518           --help= option is used).
1519
1520           Here is a truncated example from the ARM port of gcc:
1521
1522                     % gcc -Q -mabi=2 --help=target -c
1523                     The following options are target specific:
1524                     -mabi=                                2
1525                     -mabort-on-noreturn                   [disabled]
1526                     -mapcs                                [disabled]
1527
1528           The output is sensitive to the effects of previous command-line
1529           options, so for example it is possible to find out which
1530           optimizations are enabled at -O2 by using:
1531
1532                   -Q -O2 --help=optimizers
1533
1534           Alternatively you can discover which binary optimizations are
1535           enabled by -O3 by using:
1536
1537                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1538                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1539                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1540
1541       --version
1542           Display the version number and copyrights of the invoked GCC.
1543
1544       -pass-exit-codes
1545           Normally the gcc program exits with the code of 1 if any phase of
1546           the compiler returns a non-success return code.  If you specify
1547           -pass-exit-codes, the gcc program instead returns with the
1548           numerically highest error produced by any phase returning an error
1549           indication.  The C, C++, and Fortran front ends return 4 if an
1550           internal compiler error is encountered.
1551
1552       -pipe
1553           Use pipes rather than temporary files for communication between the
1554           various stages of compilation.  This fails to work on some systems
1555           where the assembler is unable to read from a pipe; but the GNU
1556           assembler has no trouble.
1557
1558       -specs=file
1559           Process file after the compiler reads in the standard specs file,
1560           in order to override the defaults which the gcc driver program uses
1561           when determining what switches to pass to cc1, cc1plus, as, ld,
1562           etc.  More than one -specs=file can be specified on the command
1563           line, and they are processed in order, from left to right.
1564
1565       -wrapper
1566           Invoke all subcommands under a wrapper program.  The name of the
1567           wrapper program and its parameters are passed as a comma separated
1568           list.
1569
1570                   gcc -c t.c -wrapper gdb,--args
1571
1572           This invokes all subprograms of gcc under gdb --args, thus the
1573           invocation of cc1 is gdb --args cc1 ....
1574
1575       -ffile-prefix-map=old=new
1576           When compiling files residing in directory old, record any
1577           references to them in the result of the compilation as if the files
1578           resided in directory new instead.  Specifying this option is
1579           equivalent to specifying all the individual -f*-prefix-map options.
1580           This can be used to make reproducible builds that are location
1581           independent.  See also -fmacro-prefix-map and -fdebug-prefix-map.
1582
1583       -fplugin=name.so
1584           Load the plugin code in file name.so, assumed to be a shared object
1585           to be dlopen'd by the compiler.  The base name of the shared object
1586           file is used to identify the plugin for the purposes of argument
1587           parsing (See -fplugin-arg-name-key=value below).  Each plugin
1588           should define the callback functions specified in the Plugins API.
1589
1590       -fplugin-arg-name-key=value
1591           Define an argument called key with a value of value for the plugin
1592           called name.
1593
1594       -fdump-ada-spec[-slim]
1595           For C and C++ source and include files, generate corresponding Ada
1596           specs.
1597
1598       -fada-spec-parent=unit
1599           In conjunction with -fdump-ada-spec[-slim] above, generate Ada
1600           specs as child units of parent unit.
1601
1602       -fdump-go-spec=file
1603           For input files in any language, generate corresponding Go
1604           declarations in file.  This generates Go "const", "type", "var",
1605           and "func" declarations which may be a useful way to start writing
1606           a Go interface to code written in some other language.
1607
1608       @file
1609           Read command-line options from file.  The options read are inserted
1610           in place of the original @file option.  If file does not exist, or
1611           cannot be read, then the option will be treated literally, and not
1612           removed.
1613
1614           Options in file are separated by whitespace.  A whitespace
1615           character may be included in an option by surrounding the entire
1616           option in either single or double quotes.  Any character (including
1617           a backslash) may be included by prefixing the character to be
1618           included with a backslash.  The file may itself contain additional
1619           @file options; any such options will be processed recursively.
1620
1621   Compiling C++ Programs
1622       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
1623       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
1624       (for shared template code) .tcc; and preprocessed C++ files use the
1625       suffix .ii.  GCC recognizes files with these names and compiles them as
1626       C++ programs even if you call the compiler the same way as for
1627       compiling C programs (usually with the name gcc).
1628
1629       However, the use of gcc does not add the C++ library.  g++ is a program
1630       that calls GCC and automatically specifies linking against the C++
1631       library.  It treats .c, .h and .i files as C++ source files instead of
1632       C source files unless -x is used.  This program is also useful when
1633       precompiling a C header file with a .h extension for use in C++
1634       compilations.  On many systems, g++ is also installed with the name
1635       c++.
1636
1637       When you compile C++ programs, you may specify many of the same
1638       command-line options that you use for compiling programs in any
1639       language; or command-line options meaningful for C and related
1640       languages; or options that are meaningful only for C++ programs.
1641
1642   Options Controlling C Dialect
1643       The following options control the dialect of C (or languages derived
1644       from C, such as C++, Objective-C and Objective-C++) that the compiler
1645       accepts:
1646
1647       -ansi
1648           In C mode, this is equivalent to -std=c90. In C++ mode, it is
1649           equivalent to -std=c++98.
1650
1651           This turns off certain features of GCC that are incompatible with
1652           ISO C90 (when compiling C code), or of standard C++ (when compiling
1653           C++ code), such as the "asm" and "typeof" keywords, and predefined
1654           macros such as "unix" and "vax" that identify the type of system
1655           you are using.  It also enables the undesirable and rarely used ISO
1656           trigraph feature.  For the C compiler, it disables recognition of
1657           C++ style // comments as well as the "inline" keyword.
1658
1659           The alternate keywords "__asm__", "__extension__", "__inline__" and
1660           "__typeof__" continue to work despite -ansi.  You would not want to
1661           use them in an ISO C program, of course, but it is useful to put
1662           them in header files that might be included in compilations done
1663           with -ansi.  Alternate predefined macros such as "__unix__" and
1664           "__vax__" are also available, with or without -ansi.
1665
1666           The -ansi option does not cause non-ISO programs to be rejected
1667           gratuitously.  For that, -Wpedantic is required in addition to
1668           -ansi.
1669
1670           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
1671           used.  Some header files may notice this macro and refrain from
1672           declaring certain functions or defining certain macros that the ISO
1673           standard doesn't call for; this is to avoid interfering with any
1674           programs that might use these names for other things.
1675
1676           Functions that are normally built in but do not have semantics
1677           defined by ISO C (such as "alloca" and "ffs") are not built-in
1678           functions when -ansi is used.
1679
1680       -std=
1681           Determine the language standard.   This option is currently only
1682           supported when compiling C or C++.
1683
1684           The compiler can accept several base standards, such as c90 or
1685           c++98, and GNU dialects of those standards, such as gnu90 or
1686           gnu++98.  When a base standard is specified, the compiler accepts
1687           all programs following that standard plus those using GNU
1688           extensions that do not contradict it.  For example, -std=c90 turns
1689           off certain features of GCC that are incompatible with ISO C90,
1690           such as the "asm" and "typeof" keywords, but not other GNU
1691           extensions that do not have a meaning in ISO C90, such as omitting
1692           the middle term of a "?:" expression. On the other hand, when a GNU
1693           dialect of a standard is specified, all features supported by the
1694           compiler are enabled, even when those features change the meaning
1695           of the base standard.  As a result, some strict-conforming programs
1696           may be rejected.  The particular standard is used by -Wpedantic to
1697           identify which features are GNU extensions given that version of
1698           the standard. For example -std=gnu90 -Wpedantic warns about C++
1699           style // comments, while -std=gnu99 -Wpedantic does not.
1700
1701           A value for this option must be provided; possible values are
1702
1703           c90
1704           c89
1705           iso9899:1990
1706               Support all ISO C90 programs (certain GNU extensions that
1707               conflict with ISO C90 are disabled). Same as -ansi for C code.
1708
1709           iso9899:199409
1710               ISO C90 as modified in amendment 1.
1711
1712           c99
1713           c9x
1714           iso9899:1999
1715           iso9899:199x
1716               ISO C99.  This standard is substantially completely supported,
1717               modulo bugs and floating-point issues (mainly but not entirely
1718               relating to optional C99 features from Annexes F and G).  See
1719               <http://gcc.gnu.org/c99status.html> for more information.  The
1720               names c9x and iso9899:199x are deprecated.
1721
1722           c11
1723           c1x
1724           iso9899:2011
1725               ISO C11, the 2011 revision of the ISO C standard.  This
1726               standard is substantially completely supported, modulo bugs,
1727               floating-point issues (mainly but not entirely relating to
1728               optional C11 features from Annexes F and G) and the optional
1729               Annexes K (Bounds-checking interfaces) and L (Analyzability).
1730               The name c1x is deprecated.
1731
1732           c17
1733           c18
1734           iso9899:2017
1735           iso9899:2018
1736               ISO C17, the 2017 revision of the ISO C standard (published in
1737               2018).  This standard is same as C11 except for corrections of
1738               defects (all of which are also applied with -std=c11) and a new
1739               value of "__STDC_VERSION__", and so is supported to the same
1740               extent as C11.
1741
1742           c2x The next version of the ISO C standard, still under
1743               development.  The support for this version is experimental and
1744               incomplete.
1745
1746           gnu90
1747           gnu89
1748               GNU dialect of ISO C90 (including some C99 features).
1749
1750           gnu99
1751           gnu9x
1752               GNU dialect of ISO C99.  The name gnu9x is deprecated.
1753
1754           gnu11
1755           gnu1x
1756               GNU dialect of ISO C11.  The name gnu1x is deprecated.
1757
1758           gnu17
1759           gnu18
1760               GNU dialect of ISO C17.  This is the default for C code.
1761
1762           gnu2x
1763               The next version of the ISO C standard, still under
1764               development, plus GNU extensions.  The support for this version
1765               is experimental and incomplete.
1766
1767           c++98
1768           c++03
1769               The 1998 ISO C++ standard plus the 2003 technical corrigendum
1770               and some additional defect reports. Same as -ansi for C++ code.
1771
1772           gnu++98
1773           gnu++03
1774               GNU dialect of -std=c++98.
1775
1776           c++11
1777           c++0x
1778               The 2011 ISO C++ standard plus amendments.  The name c++0x is
1779               deprecated.
1780
1781           gnu++11
1782           gnu++0x
1783               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.
1784
1785           c++14
1786           c++1y
1787               The 2014 ISO C++ standard plus amendments.  The name c++1y is
1788               deprecated.
1789
1790           gnu++14
1791           gnu++1y
1792               GNU dialect of -std=c++14.  The name gnu++1y is deprecated.
1793
1794           c++17
1795           c++1z
1796               The 2017 ISO C++ standard plus amendments.  The name c++1z is
1797               deprecated.
1798
1799           gnu++17
1800           gnu++1z
1801               GNU dialect of -std=c++17.  This is the default for C++ code.
1802               The name gnu++1z is deprecated.
1803
1804           c++20
1805           c++2a
1806               The 2020 ISO C++ standard plus amendments.  Support is
1807               experimental, and could change in incompatible ways in future
1808               releases.  The name c++2a is deprecated.
1809
1810           gnu++20
1811           gnu++2a
1812               GNU dialect of -std=c++20.  Support is experimental, and could
1813               change in incompatible ways in future releases.  The name
1814               gnu++2a is deprecated.
1815
1816           c++2b
1817           c++23
1818               The next revision of the ISO C++ standard, planned for 2023.
1819               Support is highly experimental, and will almost certainly
1820               change in incompatible ways in future releases.
1821
1822           gnu++2b
1823           gnu++23
1824               GNU dialect of -std=c++2b.  Support is highly experimental, and
1825               will almost certainly change in incompatible ways in future
1826               releases.
1827
1828       -fgnu89-inline
1829           The option -fgnu89-inline tells GCC to use the traditional GNU
1830           semantics for "inline" functions when in C99 mode.
1831
1832           Using this option is roughly equivalent to adding the "gnu_inline"
1833           function attribute to all inline functions.
1834
1835           The option -fno-gnu89-inline explicitly tells GCC to use the C99
1836           semantics for "inline" when in C99 or gnu99 mode (i.e., it
1837           specifies the default behavior).  This option is not supported in
1838           -std=c90 or -std=gnu90 mode.
1839
1840           The preprocessor macros "__GNUC_GNU_INLINE__" and
1841           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
1842           effect for "inline" functions.
1843
1844       -fpermitted-flt-eval-methods=style
1845           ISO/IEC TS 18661-3 defines new permissible values for
1846           "FLT_EVAL_METHOD" that indicate that operations and constants with
1847           a semantic type that is an interchange or extended format should be
1848           evaluated to the precision and range of that type.  These new
1849           values are a superset of those permitted under C99/C11, which does
1850           not specify the meaning of other positive values of
1851           "FLT_EVAL_METHOD".  As such, code conforming to C11 may not have
1852           been written expecting the possibility of the new values.
1853
1854           -fpermitted-flt-eval-methods specifies whether the compiler should
1855           allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or
1856           the extended set of values specified in ISO/IEC TS 18661-3.
1857
1858           style is either "c11" or "ts-18661-3" as appropriate.
1859
1860           The default when in a standards compliant mode (-std=c11 or
1861           similar) is -fpermitted-flt-eval-methods=c11.  The default when in
1862           a GNU dialect (-std=gnu11 or similar) is
1863           -fpermitted-flt-eval-methods=ts-18661-3.
1864
1865       -aux-info filename
1866           Output to the given filename prototyped declarations for all
1867           functions declared and/or defined in a translation unit, including
1868           those in header files.  This option is silently ignored in any
1869           language other than C.
1870
1871           Besides declarations, the file indicates, in comments, the origin
1872           of each declaration (source file and line), whether the declaration
1873           was implicit, prototyped or unprototyped (I, N for new or O for
1874           old, respectively, in the first character after the line number and
1875           the colon), and whether it came from a declaration or a definition
1876           (C or F, respectively, in the following character).  In the case of
1877           function definitions, a K&R-style list of arguments followed by
1878           their declarations is also provided, inside comments, after the
1879           declaration.
1880
1881       -fallow-parameterless-variadic-functions
1882           Accept variadic functions without named parameters.
1883
1884           Although it is possible to define such a function, this is not very
1885           useful as it is not possible to read the arguments.  This is only
1886           supported for C as this construct is allowed by C++.
1887
1888       -fno-asm
1889           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
1890           code can use these words as identifiers.  You can use the keywords
1891           "__asm__", "__inline__" and "__typeof__" instead.  -ansi implies
1892           -fno-asm.
1893
1894           In C++, this switch only affects the "typeof" keyword, since "asm"
1895           and "inline" are standard keywords.  You may want to use the
1896           -fno-gnu-keywords flag instead, which has the same effect.  In C99
1897           mode (-std=c99 or -std=gnu99), this switch only affects the "asm"
1898           and "typeof" keywords, since "inline" is a standard keyword in ISO
1899           C99.
1900
1901       -fno-builtin
1902       -fno-builtin-function
1903           Don't recognize built-in functions that do not begin with
1904           __builtin_ as prefix.
1905
1906           GCC normally generates special code to handle certain built-in
1907           functions more efficiently; for instance, calls to "alloca" may
1908           become single instructions which adjust the stack directly, and
1909           calls to "memcpy" may become inline copy loops.  The resulting code
1910           is often both smaller and faster, but since the function calls no
1911           longer appear as such, you cannot set a breakpoint on those calls,
1912           nor can you change the behavior of the functions by linking with a
1913           different library.  In addition, when a function is recognized as a
1914           built-in function, GCC may use information about that function to
1915           warn about problems with calls to that function, or to generate
1916           more efficient code, even if the resulting code still contains
1917           calls to that function.  For example, warnings are given with
1918           -Wformat for bad calls to "printf" when "printf" is built in and
1919           "strlen" is known not to modify global memory.
1920
1921           With the -fno-builtin-function option only the built-in function
1922           function is disabled.  function must not begin with __builtin_.  If
1923           a function is named that is not built-in in this version of GCC,
1924           this option is ignored.  There is no corresponding
1925           -fbuiltin-function option; if you wish to enable built-in functions
1926           selectively when using -fno-builtin or -ffreestanding, you may
1927           define macros such as:
1928
1929                   #define abs(n)          __builtin_abs ((n))
1930                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))
1931
1932       -fgimple
1933           Enable parsing of function definitions marked with "__GIMPLE".
1934           This is an experimental feature that allows unit testing of GIMPLE
1935           passes.
1936
1937       -fhosted
1938           Assert that compilation targets a hosted environment.  This implies
1939           -fbuiltin.  A hosted environment is one in which the entire
1940           standard library is available, and in which "main" has a return
1941           type of "int".  Examples are nearly everything except a kernel.
1942           This is equivalent to -fno-freestanding.
1943
1944       -ffreestanding
1945           Assert that compilation targets a freestanding environment.  This
1946           implies -fno-builtin.  A freestanding environment is one in which
1947           the standard library may not exist, and program startup may not
1948           necessarily be at "main".  The most obvious example is an OS
1949           kernel.  This is equivalent to -fno-hosted.
1950
1951       -fopenacc
1952           Enable handling of OpenACC directives "#pragma acc" in C/C++ and
1953           "!$acc" in Fortran.  When -fopenacc is specified, the compiler
1954           generates accelerated code according to the OpenACC Application
1955           Programming Interface v2.6 <https://www.openacc.org>.  This option
1956           implies -pthread, and thus is only supported on targets that have
1957           support for -pthread.
1958
1959       -fopenacc-dim=geom
1960           Specify default compute dimensions for parallel offload regions
1961           that do not explicitly specify.  The geom value is a triple of
1962           ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A
1963           size can be omitted, to use a target-specific default value.
1964
1965       -fopenmp
1966           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
1967           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
1968           generates parallel code according to the OpenMP Application Program
1969           Interface v4.5 <https://www.openmp.org>.  This option implies
1970           -pthread, and thus is only supported on targets that have support
1971           for -pthread. -fopenmp implies -fopenmp-simd.
1972
1973       -fopenmp-simd
1974           Enable handling of OpenMP's SIMD directives with "#pragma omp" in
1975           C/C++ and "!$omp" in Fortran. Other OpenMP directives are ignored.
1976
1977       -fgnu-tm
1978           When the option -fgnu-tm is specified, the compiler generates code
1979           for the Linux variant of Intel's current Transactional Memory ABI
1980           specification document (Revision 1.1, May 6 2009).  This is an
1981           experimental feature whose interface may change in future versions
1982           of GCC, as the official specification changes.  Please note that
1983           not all architectures are supported for this feature.
1984
1985           For more information on GCC's support for transactional memory,
1986
1987           Note that the transactional memory feature is not supported with
1988           non-call exceptions (-fnon-call-exceptions).
1989
1990       -fms-extensions
1991           Accept some non-standard constructs used in Microsoft header files.
1992
1993           In C++ code, this allows member names in structures to be similar
1994           to previous types declarations.
1995
1996                   typedef int UOW;
1997                   struct ABC {
1998                     UOW UOW;
1999                   };
2000
2001           Some cases of unnamed fields in structures and unions are only
2002           accepted with this option.
2003
2004           Note that this option is off for all targets except for x86 targets
2005           using ms-abi.
2006
2007       -fplan9-extensions
2008           Accept some non-standard constructs used in Plan 9 code.
2009
2010           This enables -fms-extensions, permits passing pointers to
2011           structures with anonymous fields to functions that expect pointers
2012           to elements of the type of the field, and permits referring to
2013           anonymous fields declared using a typedef.    This is only
2014           supported for C, not C++.
2015
2016       -fcond-mismatch
2017           Allow conditional expressions with mismatched types in the second
2018           and third arguments.  The value of such an expression is void.
2019           This option is not supported for C++.
2020
2021       -flax-vector-conversions
2022           Allow implicit conversions between vectors with differing numbers
2023           of elements and/or incompatible element types.  This option should
2024           not be used for new code.
2025
2026       -funsigned-char
2027           Let the type "char" be unsigned, like "unsigned char".
2028
2029           Each kind of machine has a default for what "char" should be.  It
2030           is either like "unsigned char" by default or like "signed char" by
2031           default.
2032
2033           Ideally, a portable program should always use "signed char" or
2034           "unsigned char" when it depends on the signedness of an object.
2035           But many programs have been written to use plain "char" and expect
2036           it to be signed, or expect it to be unsigned, depending on the
2037           machines they were written for.  This option, and its inverse, let
2038           you make such a program work with the opposite default.
2039
2040           The type "char" is always a distinct type from each of "signed
2041           char" or "unsigned char", even though its behavior is always just
2042           like one of those two.
2043
2044       -fsigned-char
2045           Let the type "char" be signed, like "signed char".
2046
2047           Note that this is equivalent to -fno-unsigned-char, which is the
2048           negative form of -funsigned-char.  Likewise, the option
2049           -fno-signed-char is equivalent to -funsigned-char.
2050
2051       -fsigned-bitfields
2052       -funsigned-bitfields
2053       -fno-signed-bitfields
2054       -fno-unsigned-bitfields
2055           These options control whether a bit-field is signed or unsigned,
2056           when the declaration does not use either "signed" or "unsigned".
2057           By default, such a bit-field is signed, because this is consistent:
2058           the basic integer types such as "int" are signed types.
2059
2060       -fsso-struct=endianness
2061           Set the default scalar storage order of structures and unions to
2062           the specified endianness.  The accepted values are big-endian,
2063           little-endian and native for the native endianness of the target
2064           (the default).  This option is not supported for C++.
2065
2066           Warning: the -fsso-struct switch causes GCC to generate code that
2067           is not binary compatible with code generated without it if the
2068           specified endianness is not the native endianness of the target.
2069
2070   Options Controlling C++ Dialect
2071       This section describes the command-line options that are only
2072       meaningful for C++ programs.  You can also use most of the GNU compiler
2073       options regardless of what language your program is in.  For example,
2074       you might compile a file firstClass.C like this:
2075
2076               g++ -g -fstrict-enums -O -c firstClass.C
2077
2078       In this example, only -fstrict-enums is an option meant only for C++
2079       programs; you can use the other options with any language supported by
2080       GCC.
2081
2082       Some options for compiling C programs, such as -std, are also relevant
2083       for C++ programs.
2084
2085       Here is a list of options that are only for compiling C++ programs:
2086
2087       -fabi-version=n
2088           Use version n of the C++ ABI.  The default is version 0.
2089
2090           Version 0 refers to the version conforming most closely to the C++
2091           ABI specification.  Therefore, the ABI obtained using version 0
2092           will change in different versions of G++ as ABI bugs are fixed.
2093
2094           Version 1 is the version of the C++ ABI that first appeared in G++
2095           3.2.
2096
2097           Version 2 is the version of the C++ ABI that first appeared in G++
2098           3.4, and was the default through G++ 4.9.
2099
2100           Version 3 corrects an error in mangling a constant address as a
2101           template argument.
2102
2103           Version 4, which first appeared in G++ 4.5, implements a standard
2104           mangling for vector types.
2105
2106           Version 5, which first appeared in G++ 4.6, corrects the mangling
2107           of attribute const/volatile on function pointer types, decltype of
2108           a plain decl, and use of a function parameter in the declaration of
2109           another parameter.
2110
2111           Version 6, which first appeared in G++ 4.7, corrects the promotion
2112           behavior of C++11 scoped enums and the mangling of template
2113           argument packs, const/static_cast, prefix ++ and --, and a class
2114           scope function used as a template argument.
2115
2116           Version 7, which first appeared in G++ 4.8, that treats nullptr_t
2117           as a builtin type and corrects the mangling of lambdas in default
2118           argument scope.
2119
2120           Version 8, which first appeared in G++ 4.9, corrects the
2121           substitution behavior of function types with function-cv-
2122           qualifiers.
2123
2124           Version 9, which first appeared in G++ 5.2, corrects the alignment
2125           of "nullptr_t".
2126
2127           Version 10, which first appeared in G++ 6.1, adds mangling of
2128           attributes that affect type identity, such as ia32 calling
2129           convention attributes (e.g. stdcall).
2130
2131           Version 11, which first appeared in G++ 7, corrects the mangling of
2132           sizeof... expressions and operator names.  For multiple entities
2133           with the same name within a function, that are declared in
2134           different scopes, the mangling now changes starting with the
2135           twelfth occurrence.  It also implies -fnew-inheriting-ctors.
2136
2137           Version 12, which first appeared in G++ 8, corrects the calling
2138           conventions for empty classes on the x86_64 target and for classes
2139           with only deleted copy/move constructors.  It accidentally changes
2140           the calling convention for classes with a deleted copy constructor
2141           and a trivial move constructor.
2142
2143           Version 13, which first appeared in G++ 8.2, fixes the accidental
2144           change in version 12.
2145
2146           Version 14, which first appeared in G++ 10, corrects the mangling
2147           of the nullptr expression.
2148
2149           Version 15, which first appeared in G++ 11, changes the mangling of
2150           "__alignof__" to be distinct from that of "alignof", and dependent
2151           operator names.
2152
2153           See also -Wabi.
2154
2155       -fabi-compat-version=n
2156           On targets that support strong aliases, G++ works around mangling
2157           changes by creating an alias with the correct mangled name when
2158           defining a symbol with an incorrect mangled name.  This switch
2159           specifies which ABI version to use for the alias.
2160
2161           With -fabi-version=0 (the default), this defaults to 11 (GCC 7
2162           compatibility).  If another ABI version is explicitly selected,
2163           this defaults to 0.  For compatibility with GCC versions 3.2
2164           through 4.9, use -fabi-compat-version=2.
2165
2166           If this option is not provided but -Wabi=n is, that version is used
2167           for compatibility aliases.  If this option is provided along with
2168           -Wabi (without the version), the version from this option is used
2169           for the warning.
2170
2171       -fno-access-control
2172           Turn off all access checking.  This switch is mainly useful for
2173           working around bugs in the access control code.
2174
2175       -faligned-new
2176           Enable support for C++17 "new" of types that require more alignment
2177           than "void* ::operator new(std::size_t)" provides.  A numeric
2178           argument such as "-faligned-new=32" can be used to specify how much
2179           alignment (in bytes) is provided by that function, but few users
2180           will need to override the default of "alignof(std::max_align_t)".
2181
2182           This flag is enabled by default for -std=c++17.
2183
2184       -fchar8_t
2185       -fno-char8_t
2186           Enable support for "char8_t" as adopted for C++20.  This includes
2187           the addition of a new "char8_t" fundamental type, changes to the
2188           types of UTF-8 string and character literals, new signatures for
2189           user-defined literals, associated standard library updates, and new
2190           "__cpp_char8_t" and "__cpp_lib_char8_t" feature test macros.
2191
2192           This option enables functions to be overloaded for ordinary and
2193           UTF-8 strings:
2194
2195                   int f(const char *);    // #1
2196                   int f(const char8_t *); // #2
2197                   int v1 = f("text");     // Calls #1
2198                   int v2 = f(u8"text");   // Calls #2
2199
2200           and introduces new signatures for user-defined literals:
2201
2202                   int operator""_udl1(char8_t);
2203                   int v3 = u8'x'_udl1;
2204                   int operator""_udl2(const char8_t*, std::size_t);
2205                   int v4 = u8"text"_udl2;
2206                   template<typename T, T...> int operator""_udl3();
2207                   int v5 = u8"text"_udl3;
2208
2209           The change to the types of UTF-8 string and character literals
2210           introduces incompatibilities with ISO C++11 and later standards.
2211           For example, the following code is well-formed under ISO C++11, but
2212           is ill-formed when -fchar8_t is specified.
2213
2214                   char ca[] = u8"xx";     // error: char-array initialized from wide
2215                                           //        string
2216                   const char *cp = u8"xx";// error: invalid conversion from
2217                                           //        `const char8_t*' to `const char*'
2218                   int f(const char*);
2219                   auto v = f(u8"xx");     // error: invalid conversion from
2220                                           //        `const char8_t*' to `const char*'
2221                   std::string s{u8"xx"};  // error: no matching function for call to
2222                                           //        `std::basic_string<char>::basic_string()'
2223                   using namespace std::literals;
2224                   s = u8"xx"s;            // error: conversion from
2225                                           //        `basic_string<char8_t>' to non-scalar
2226                                           //        type `basic_string<char>' requested
2227
2228       -fcheck-new
2229           Check that the pointer returned by "operator new" is non-null
2230           before attempting to modify the storage allocated.  This check is
2231           normally unnecessary because the C++ standard specifies that
2232           "operator new" only returns 0 if it is declared "throw()", in which
2233           case the compiler always checks the return value even without this
2234           option.  In all other cases, when "operator new" has a non-empty
2235           exception specification, memory exhaustion is signalled by throwing
2236           "std::bad_alloc".  See also new (nothrow).
2237
2238       -fconcepts
2239       -fconcepts-ts
2240           Below -std=c++20, -fconcepts enables support for the C++ Extensions
2241           for Concepts Technical Specification, ISO 19217 (2015).
2242
2243           With -std=c++20 and above, Concepts are part of the language
2244           standard, so -fconcepts defaults to on.  But the standard
2245           specification of Concepts differs significantly from the TS, so
2246           some constructs that were allowed in the TS but didn't make it into
2247           the standard can still be enabled by -fconcepts-ts.
2248
2249       -fconstexpr-depth=n
2250           Set the maximum nested evaluation depth for C++11 constexpr
2251           functions to n.  A limit is needed to detect endless recursion
2252           during constant expression evaluation.  The minimum specified by
2253           the standard is 512.
2254
2255       -fconstexpr-cache-depth=n
2256           Set the maximum level of nested evaluation depth for C++11
2257           constexpr functions that will be cached to n.  This is a heuristic
2258           that trades off compilation speed (when the cache avoids repeated
2259           calculations) against memory consumption (when the cache grows very
2260           large from highly recursive evaluations).  The default is 8.  Very
2261           few users are likely to want to adjust it, but if your code does
2262           heavy constexpr calculations you might want to experiment to find
2263           which value works best for you.
2264
2265       -fconstexpr-loop-limit=n
2266           Set the maximum number of iterations for a loop in C++14 constexpr
2267           functions to n.  A limit is needed to detect infinite loops during
2268           constant expression evaluation.  The default is 262144 (1<<18).
2269
2270       -fconstexpr-ops-limit=n
2271           Set the maximum number of operations during a single constexpr
2272           evaluation.  Even when number of iterations of a single loop is
2273           limited with the above limit, if there are several nested loops and
2274           each of them has many iterations but still smaller than the above
2275           limit, or if in a body of some loop or even outside of a loop too
2276           many expressions need to be evaluated, the resulting constexpr
2277           evaluation might take too long.  The default is 33554432 (1<<25).
2278
2279       -fcoroutines
2280           Enable support for the C++ coroutines extension (experimental).
2281
2282       -fno-elide-constructors
2283           The C++ standard allows an implementation to omit creating a
2284           temporary that is only used to initialize another object of the
2285           same type.  Specifying this option disables that optimization, and
2286           forces G++ to call the copy constructor in all cases.  This option
2287           also causes G++ to call trivial member functions which otherwise
2288           would be expanded inline.
2289
2290           In C++17, the compiler is required to omit these temporaries, but
2291           this option still affects trivial member functions.
2292
2293       -fno-enforce-eh-specs
2294           Don't generate code to check for violation of exception
2295           specifications at run time.  This option violates the C++ standard,
2296           but may be useful for reducing code size in production builds, much
2297           like defining "NDEBUG".  This does not give user code permission to
2298           throw exceptions in violation of the exception specifications; the
2299           compiler still optimizes based on the specifications, so throwing
2300           an unexpected exception results in undefined behavior at run time.
2301
2302       -fextern-tls-init
2303       -fno-extern-tls-init
2304           The C++11 and OpenMP standards allow "thread_local" and
2305           "threadprivate" variables to have dynamic (runtime) initialization.
2306           To support this, any use of such a variable goes through a wrapper
2307           function that performs any necessary initialization.  When the use
2308           and definition of the variable are in the same translation unit,
2309           this overhead can be optimized away, but when the use is in a
2310           different translation unit there is significant overhead even if
2311           the variable doesn't actually need dynamic initialization.  If the
2312           programmer can be sure that no use of the variable in a non-
2313           defining TU needs to trigger dynamic initialization (either because
2314           the variable is statically initialized, or a use of the variable in
2315           the defining TU will be executed before any uses in another TU),
2316           they can avoid this overhead with the -fno-extern-tls-init option.
2317
2318           On targets that support symbol aliases, the default is
2319           -fextern-tls-init.  On targets that do not support symbol aliases,
2320           the default is -fno-extern-tls-init.
2321
2322       -fno-gnu-keywords
2323           Do not recognize "typeof" as a keyword, so that code can use this
2324           word as an identifier.  You can use the keyword "__typeof__"
2325           instead.  This option is implied by the strict ISO C++ dialects:
2326           -ansi, -std=c++98, -std=c++11, etc.
2327
2328       -fno-implicit-templates
2329           Never emit code for non-inline templates that are instantiated
2330           implicitly (i.e. by use); only emit code for explicit
2331           instantiations.  If you use this option, you must take care to
2332           structure your code to include all the necessary explicit
2333           instantiations to avoid getting undefined symbols at link time.
2334
2335       -fno-implicit-inline-templates
2336           Don't emit code for implicit instantiations of inline templates,
2337           either.  The default is to handle inlines differently so that
2338           compiles with and without optimization need the same set of
2339           explicit instantiations.
2340
2341       -fno-implement-inlines
2342           To save space, do not emit out-of-line copies of inline functions
2343           controlled by "#pragma implementation".  This causes linker errors
2344           if these functions are not inlined everywhere they are called.
2345
2346       -fmodules-ts
2347       -fno-modules-ts
2348           Enable support for C++20 modules   The -fno-modules-ts is usually
2349           not needed, as that is the default.  Even though this is a C++20
2350           feature, it is not currently implicitly enabled by selecting that
2351           standard version.
2352
2353       -fmodule-header
2354       -fmodule-header=user
2355       -fmodule-header=system
2356           Compile a header file to create an importable header unit.
2357
2358       -fmodule-implicit-inline
2359           Member functions defined in their class definitions are not
2360           implicitly inline for modular code.  This is different to
2361           traditional C++ behavior, for good reasons.  However, it may result
2362           in a difficulty during code porting.  This option makes such
2363           function definitions implicitly inline.  It does however generate
2364           an ABI incompatibility, so you must use it everywhere or nowhere.
2365           (Such definitions outside of a named module remain implicitly
2366           inline, regardless.)
2367
2368       -fno-module-lazy
2369           Disable lazy module importing and module mapper creation.
2370
2371       -fmodule-mapper=[hostname]:port[?ident]
2372       -fmodule-mapper=|program[?ident] args...
2373       -fmodule-mapper==socket[?ident]
2374       -fmodule-mapper=<>[inout][?ident]
2375       -fmodule-mapper=<in>out[?ident]
2376       -fmodule-mapper=file[?ident]
2377           An oracle to query for module name to filename mappings.  If
2378           unspecified the CXX_MODULE_MAPPER environment variable is used, and
2379           if that is unset, an in-process default is provided.
2380
2381       -fmodule-only
2382           Only emit the Compiled Module Interface, inhibiting any object
2383           file.
2384
2385       -fms-extensions
2386           Disable Wpedantic warnings about constructs used in MFC, such as
2387           implicit int and getting a pointer to member function via non-
2388           standard syntax.
2389
2390       -fnew-inheriting-ctors
2391           Enable the P0136 adjustment to the semantics of C++11 constructor
2392           inheritance.  This is part of C++17 but also considered to be a
2393           Defect Report against C++11 and C++14.  This flag is enabled by
2394           default unless -fabi-version=10 or lower is specified.
2395
2396       -fnew-ttp-matching
2397           Enable the P0522 resolution to Core issue 150, template template
2398           parameters and default arguments: this allows a template with
2399           default template arguments as an argument for a template template
2400           parameter with fewer template parameters.  This flag is enabled by
2401           default for -std=c++17.
2402
2403       -fno-nonansi-builtins
2404           Disable built-in declarations of functions that are not mandated by
2405           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
2406           "bzero", "conjf", and other related functions.
2407
2408       -fnothrow-opt
2409           Treat a "throw()" exception specification as if it were a
2410           "noexcept" specification to reduce or eliminate the text size
2411           overhead relative to a function with no exception specification.
2412           If the function has local variables of types with non-trivial
2413           destructors, the exception specification actually makes the
2414           function smaller because the EH cleanups for those variables can be
2415           optimized away.  The semantic effect is that an exception thrown
2416           out of a function with such an exception specification results in a
2417           call to "terminate" rather than "unexpected".
2418
2419       -fno-operator-names
2420           Do not treat the operator name keywords "and", "bitand", "bitor",
2421           "compl", "not", "or" and "xor" as synonyms as keywords.
2422
2423       -fno-optional-diags
2424           Disable diagnostics that the standard says a compiler does not need
2425           to issue.  Currently, the only such diagnostic issued by G++ is the
2426           one for a name having multiple meanings within a class.
2427
2428       -fpermissive
2429           Downgrade some diagnostics about nonconformant code from errors to
2430           warnings.  Thus, using -fpermissive allows some nonconforming code
2431           to compile.
2432
2433       -fno-pretty-templates
2434           When an error message refers to a specialization of a function
2435           template, the compiler normally prints the signature of the
2436           template followed by the template arguments and any typedefs or
2437           typenames in the signature (e.g. "void f(T) [with T = int]" rather
2438           than "void f(int)") so that it's clear which template is involved.
2439           When an error message refers to a specialization of a class
2440           template, the compiler omits any template arguments that match the
2441           default template arguments for that template.  If either of these
2442           behaviors make it harder to understand the error message rather
2443           than easier, you can use -fno-pretty-templates to disable them.
2444
2445       -fno-rtti
2446           Disable generation of information about every class with virtual
2447           functions for use by the C++ run-time type identification features
2448           ("dynamic_cast" and "typeid").  If you don't use those parts of the
2449           language, you can save some space by using this flag.  Note that
2450           exception handling uses the same information, but G++ generates it
2451           as needed. The "dynamic_cast" operator can still be used for casts
2452           that do not require run-time type information, i.e. casts to "void
2453           *" or to unambiguous base classes.
2454
2455           Mixing code compiled with -frtti with that compiled with -fno-rtti
2456           may not work.  For example, programs may fail to link if a class
2457           compiled with -fno-rtti is used as a base for a class compiled with
2458           -frtti.
2459
2460       -fsized-deallocation
2461           Enable the built-in global declarations
2462
2463                   void operator delete (void *, std::size_t) noexcept;
2464                   void operator delete[] (void *, std::size_t) noexcept;
2465
2466           as introduced in C++14.  This is useful for user-defined
2467           replacement deallocation functions that, for example, use the size
2468           of the object to make deallocation faster.  Enabled by default
2469           under -std=c++14 and above.  The flag -Wsized-deallocation warns
2470           about places that might want to add a definition.
2471
2472       -fstrict-enums
2473           Allow the compiler to optimize using the assumption that a value of
2474           enumerated type can only be one of the values of the enumeration
2475           (as defined in the C++ standard; basically, a value that can be
2476           represented in the minimum number of bits needed to represent all
2477           the enumerators).  This assumption may not be valid if the program
2478           uses a cast to convert an arbitrary integer value to the enumerated
2479           type.
2480
2481       -fstrong-eval-order
2482           Evaluate member access, array subscripting, and shift expressions
2483           in left-to-right order, and evaluate assignment in right-to-left
2484           order, as adopted for C++17.  Enabled by default with -std=c++17.
2485           -fstrong-eval-order=some enables just the ordering of member access
2486           and shift expressions, and is the default without -std=c++17.
2487
2488       -ftemplate-backtrace-limit=n
2489           Set the maximum number of template instantiation notes for a single
2490           warning or error to n.  The default value is 10.
2491
2492       -ftemplate-depth=n
2493           Set the maximum instantiation depth for template classes to n.  A
2494           limit on the template instantiation depth is needed to detect
2495           endless recursions during template class instantiation.  ANSI/ISO
2496           C++ conforming programs must not rely on a maximum depth greater
2497           than 17 (changed to 1024 in C++11).  The default value is 900, as
2498           the compiler can run out of stack space before hitting 1024 in some
2499           situations.
2500
2501       -fno-threadsafe-statics
2502           Do not emit the extra code to use the routines specified in the C++
2503           ABI for thread-safe initialization of local statics.  You can use
2504           this option to reduce code size slightly in code that doesn't need
2505           to be thread-safe.
2506
2507       -fuse-cxa-atexit
2508           Register destructors for objects with static storage duration with
2509           the "__cxa_atexit" function rather than the "atexit" function.
2510           This option is required for fully standards-compliant handling of
2511           static destructors, but only works if your C library supports
2512           "__cxa_atexit".
2513
2514       -fno-use-cxa-get-exception-ptr
2515           Don't use the "__cxa_get_exception_ptr" runtime routine.  This
2516           causes "std::uncaught_exception" to be incorrect, but is necessary
2517           if the runtime routine is not available.
2518
2519       -fvisibility-inlines-hidden
2520           This switch declares that the user does not attempt to compare
2521           pointers to inline functions or methods where the addresses of the
2522           two functions are taken in different shared objects.
2523
2524           The effect of this is that GCC may, effectively, mark inline
2525           methods with "__attribute__ ((visibility ("hidden")))" so that they
2526           do not appear in the export table of a DSO and do not require a PLT
2527           indirection when used within the DSO.  Enabling this option can
2528           have a dramatic effect on load and link times of a DSO as it
2529           massively reduces the size of the dynamic export table when the
2530           library makes heavy use of templates.
2531
2532           The behavior of this switch is not quite the same as marking the
2533           methods as hidden directly, because it does not affect static
2534           variables local to the function or cause the compiler to deduce
2535           that the function is defined in only one shared object.
2536
2537           You may mark a method as having a visibility explicitly to negate
2538           the effect of the switch for that method.  For example, if you do
2539           want to compare pointers to a particular inline method, you might
2540           mark it as having default visibility.  Marking the enclosing class
2541           with explicit visibility has no effect.
2542
2543           Explicitly instantiated inline methods are unaffected by this
2544           option as their linkage might otherwise cross a shared library
2545           boundary.
2546
2547       -fvisibility-ms-compat
2548           This flag attempts to use visibility settings to make GCC's C++
2549           linkage model compatible with that of Microsoft Visual Studio.
2550
2551           The flag makes these changes to GCC's linkage model:
2552
2553           1.  It sets the default visibility to "hidden", like
2554               -fvisibility=hidden.
2555
2556           2.  Types, but not their members, are not hidden by default.
2557
2558           3.  The One Definition Rule is relaxed for types without explicit
2559               visibility specifications that are defined in more than one
2560               shared object: those declarations are permitted if they are
2561               permitted when this option is not used.
2562
2563           In new code it is better to use -fvisibility=hidden and export
2564           those classes that are intended to be externally visible.
2565           Unfortunately it is possible for code to rely, perhaps
2566           accidentally, on the Visual Studio behavior.
2567
2568           Among the consequences of these changes are that static data
2569           members of the same type with the same name but defined in
2570           different shared objects are different, so changing one does not
2571           change the other; and that pointers to function members defined in
2572           different shared objects may not compare equal.  When this flag is
2573           given, it is a violation of the ODR to define types with the same
2574           name differently.
2575
2576       -fno-weak
2577           Do not use weak symbol support, even if it is provided by the
2578           linker.  By default, G++ uses weak symbols if they are available.
2579           This option exists only for testing, and should not be used by end-
2580           users; it results in inferior code and has no benefits.  This
2581           option may be removed in a future release of G++.
2582
2583       -fext-numeric-literals (C++ and Objective-C++ only)
2584           Accept imaginary, fixed-point, or machine-defined literal number
2585           suffixes as GNU extensions.  When this option is turned off these
2586           suffixes are treated as C++11 user-defined literal numeric
2587           suffixes.  This is on by default for all pre-C++11 dialects and all
2588           GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14.
2589           This option is off by default for ISO C++11 onwards (-std=c++11,
2590           ...).
2591
2592       -nostdinc++
2593           Do not search for header files in the standard directories specific
2594           to C++, but do still search the other standard directories.  (This
2595           option is used when building the C++ library.)
2596
2597       -flang-info-include-translate
2598       -flang-info-include-translate-not
2599       -flang-info-include-translate=header
2600           Inform of include translation events.  The first will note accepted
2601           include translations, the second will note declined include
2602           translations.  The header form will inform of include translations
2603           relating to that specific header.  If header is of the form "user"
2604           or "<system>" it will be resolved to a specific user or system
2605           header using the include path.
2606
2607       -flang-info-module-cmi
2608       -flang-info-module-cmi=module
2609           Inform of Compiled Module Interface pathnames.  The first will note
2610           all read CMI pathnames.  The module form will not reading a
2611           specific module's CMI.  module may be a named module or a header-
2612           unit (the latter indicated by either being a pathname containing
2613           directory separators or enclosed in "<>" or "").
2614
2615       -stdlib=libstdc++,libc++
2616           When G++ is configured to support this option, it allows
2617           specification of alternate C++ runtime libraries.  Two options are
2618           available: libstdc++ (the default, native C++ runtime for G++) and
2619           libc++ which is the C++ runtime installed on some operating systems
2620           (e.g. Darwin versions from Darwin11 onwards).  The option switches
2621           G++ to use the headers from the specified library and to emit
2622           "-lstdc++" or "-lc++" respectively, when a C++ runtime is required
2623           for linking.
2624
2625       In addition, these warning options have meanings only for C++ programs:
2626
2627       -Wabi-tag (C++ and Objective-C++ only)
2628           Warn when a type with an ABI tag is used in a context that does not
2629           have that ABI tag.  See C++ Attributes for more information about
2630           ABI tags.
2631
2632       -Wcomma-subscript (C++ and Objective-C++ only)
2633           Warn about uses of a comma expression within a subscripting
2634           expression.  This usage was deprecated in C++20.  However, a comma
2635           expression wrapped in "( )" is not deprecated.  Example:
2636
2637                   void f(int *a, int b, int c) {
2638                       a[b,c];     // deprecated
2639                       a[(b,c)];   // OK
2640                   }
2641
2642           Enabled by default with -std=c++20.
2643
2644       -Wctad-maybe-unsupported (C++ and Objective-C++ only)
2645           Warn when performing class template argument deduction (CTAD) on a
2646           type with no explicitly written deduction guides.  This warning
2647           will point out cases where CTAD succeeded only because the compiler
2648           synthesized the implicit deduction guides, which might not be what
2649           the programmer intended.  Certain style guides allow CTAD only on
2650           types that specifically "opt-in"; i.e., on types that are designed
2651           to support CTAD.  This warning can be suppressed with the following
2652           pattern:
2653
2654                   struct allow_ctad_t; // any name works
2655                   template <typename T> struct S {
2656                     S(T) { }
2657                   };
2658                   S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered
2659
2660       -Wctor-dtor-privacy (C++ and Objective-C++ only)
2661           Warn when a class seems unusable because all the constructors or
2662           destructors in that class are private, and it has neither friends
2663           nor public static member functions.  Also warn if there are no non-
2664           private methods, and there's at least one private member function
2665           that isn't a constructor or destructor.
2666
2667       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
2668           Warn when "delete" is used to destroy an instance of a class that
2669           has virtual functions and non-virtual destructor. It is unsafe to
2670           delete an instance of a derived class through a pointer to a base
2671           class if the base class does not have a virtual destructor.  This
2672           warning is enabled by -Wall.
2673
2674       -Wdeprecated-copy (C++ and Objective-C++ only)
2675           Warn that the implicit declaration of a copy constructor or copy
2676           assignment operator is deprecated if the class has a user-provided
2677           copy constructor or copy assignment operator, in C++11 and up.
2678           This warning is enabled by -Wextra.  With -Wdeprecated-copy-dtor,
2679           also deprecate if the class has a user-provided destructor.
2680
2681       -Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only)
2682           Disable the warning about the case when the usual arithmetic
2683           conversions are applied on operands where one is of enumeration
2684           type and the other is of a different enumeration type.  This
2685           conversion was deprecated in C++20.  For example:
2686
2687                   enum E1 { e };
2688                   enum E2 { f };
2689                   int k = f - e;
2690
2691           -Wdeprecated-enum-enum-conversion is enabled by default with
2692           -std=c++20.  In pre-C++20 dialects, this warning can be enabled by
2693           -Wenum-conversion.
2694
2695       -Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only)
2696           Disable the warning about the case when the usual arithmetic
2697           conversions are applied on operands where one is of enumeration
2698           type and the other is of a floating-point type.  This conversion
2699           was deprecated in C++20.  For example:
2700
2701                   enum E1 { e };
2702                   enum E2 { f };
2703                   bool b = e <= 3.7;
2704
2705           -Wdeprecated-enum-float-conversion is enabled by default with
2706           -std=c++20.  In pre-C++20 dialects, this warning can be enabled by
2707           -Wenum-conversion.
2708
2709       -Wno-init-list-lifetime (C++ and Objective-C++ only)
2710           Do not warn about uses of "std::initializer_list" that are likely
2711           to result in dangling pointers.  Since the underlying array for an
2712           "initializer_list" is handled like a normal C++ temporary object,
2713           it is easy to inadvertently keep a pointer to the array past the
2714           end of the array's lifetime.  For example:
2715
2716           *   If a function returns a temporary "initializer_list", or a
2717               local "initializer_list" variable, the array's lifetime ends at
2718               the end of the return statement, so the value returned has a
2719               dangling pointer.
2720
2721           *   If a new-expression creates an "initializer_list", the array
2722               only lives until the end of the enclosing full-expression, so
2723               the "initializer_list" in the heap has a dangling pointer.
2724
2725           *   When an "initializer_list" variable is assigned from a brace-
2726               enclosed initializer list, the temporary array created for the
2727               right side of the assignment only lives until the end of the
2728               full-expression, so at the next statement the
2729               "initializer_list" variable has a dangling pointer.
2730
2731                       // li's initial underlying array lives as long as li
2732                       std::initializer_list<int> li = { 1,2,3 };
2733                       // assignment changes li to point to a temporary array
2734                       li = { 4, 5 };
2735                       // now the temporary is gone and li has a dangling pointer
2736                       int i = li.begin()[0] // undefined behavior
2737
2738           *   When a list constructor stores the "begin" pointer from the
2739               "initializer_list" argument, this doesn't extend the lifetime
2740               of the array, so if a class variable is constructed from a
2741               temporary "initializer_list", the pointer is left dangling by
2742               the end of the variable declaration statement.
2743
2744       -Winvalid-imported-macros
2745           Verify all imported macro definitions are valid at the end of
2746           compilation.  This is not enabled by default, as it requires
2747           additional processing to determine.  It may be useful when
2748           preparing sets of header-units to ensure consistent macros.
2749
2750       -Wno-literal-suffix (C++ and Objective-C++ only)
2751           Do not warn when a string or character literal is followed by a ud-
2752           suffix which does not begin with an underscore.  As a conforming
2753           extension, GCC treats such suffixes as separate preprocessing
2754           tokens in order to maintain backwards compatibility with code that
2755           uses formatting macros from "<inttypes.h>".  For example:
2756
2757                   #define __STDC_FORMAT_MACROS
2758                   #include <inttypes.h>
2759                   #include <stdio.h>
2760
2761                   int main() {
2762                     int64_t i64 = 123;
2763                     printf("My int64: %" PRId64"\n", i64);
2764                   }
2765
2766           In this case, "PRId64" is treated as a separate preprocessing
2767           token.
2768
2769           This option also controls warnings when a user-defined literal
2770           operator is declared with a literal suffix identifier that doesn't
2771           begin with an underscore. Literal suffix identifiers that don't
2772           begin with an underscore are reserved for future standardization.
2773
2774           These warnings are enabled by default.
2775
2776       -Wno-narrowing (C++ and Objective-C++ only)
2777           For C++11 and later standards, narrowing conversions are diagnosed
2778           by default, as required by the standard.  A narrowing conversion
2779           from a constant produces an error, and a narrowing conversion from
2780           a non-constant produces a warning, but -Wno-narrowing suppresses
2781           the diagnostic.  Note that this does not affect the meaning of
2782           well-formed code; narrowing conversions are still considered ill-
2783           formed in SFINAE contexts.
2784
2785           With -Wnarrowing in C++98, warn when a narrowing conversion
2786           prohibited by C++11 occurs within { }, e.g.
2787
2788                   int i = { 2.2 }; // error: narrowing from double to int
2789
2790           This flag is included in -Wall and -Wc++11-compat.
2791
2792       -Wnoexcept (C++ and Objective-C++ only)
2793           Warn when a noexcept-expression evaluates to false because of a
2794           call to a function that does not have a non-throwing exception
2795           specification (i.e. "throw()" or "noexcept") but is known by the
2796           compiler to never throw an exception.
2797
2798       -Wnoexcept-type (C++ and Objective-C++ only)
2799           Warn if the C++17 feature making "noexcept" part of a function type
2800           changes the mangled name of a symbol relative to C++14.  Enabled by
2801           -Wabi and -Wc++17-compat.
2802
2803           As an example:
2804
2805                   template <class T> void f(T t) { t(); };
2806                   void g() noexcept;
2807                   void h() { f(g); }
2808
2809           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls
2810           "f<void(*)()noexcept>".
2811
2812       -Wclass-memaccess (C++ and Objective-C++ only)
2813           Warn when the destination of a call to a raw memory function such
2814           as "memset" or "memcpy" is an object of class type, and when
2815           writing into such an object might bypass the class non-trivial or
2816           deleted constructor or copy assignment, violate const-correctness
2817           or encapsulation, or corrupt virtual table pointers.  Modifying the
2818           representation of such objects may violate invariants maintained by
2819           member functions of the class.  For example, the call to "memset"
2820           below is undefined because it modifies a non-trivial class object
2821           and is, therefore, diagnosed.  The safe way to either initialize or
2822           clear the storage of objects of such types is by using the
2823           appropriate constructor or assignment operator, if one is
2824           available.
2825
2826                   std::string str = "abc";
2827                   memset (&str, 0, sizeof str);
2828
2829           The -Wclass-memaccess option is enabled by -Wall.  Explicitly
2830           casting the pointer to the class object to "void *" or to a type
2831           that can be safely accessed by the raw memory function suppresses
2832           the warning.
2833
2834       -Wnon-virtual-dtor (C++ and Objective-C++ only)
2835           Warn when a class has virtual functions and an accessible non-
2836           virtual destructor itself or in an accessible polymorphic base
2837           class, in which case it is possible but unsafe to delete an
2838           instance of a derived class through a pointer to the class itself
2839           or base class.  This warning is automatically enabled if -Weffc++
2840           is specified.
2841
2842       -Wregister (C++ and Objective-C++ only)
2843           Warn on uses of the "register" storage class specifier, except when
2844           it is part of the GNU Explicit Register Variables extension.  The
2845           use of the "register" keyword as storage class specifier has been
2846           deprecated in C++11 and removed in C++17.  Enabled by default with
2847           -std=c++17.
2848
2849       -Wreorder (C++ and Objective-C++ only)
2850           Warn when the order of member initializers given in the code does
2851           not match the order in which they must be executed.  For instance:
2852
2853                   struct A {
2854                     int i;
2855                     int j;
2856                     A(): j (0), i (1) { }
2857                   };
2858
2859           The compiler rearranges the member initializers for "i" and "j" to
2860           match the declaration order of the members, emitting a warning to
2861           that effect.  This warning is enabled by -Wall.
2862
2863       -Wno-pessimizing-move (C++ and Objective-C++ only)
2864           This warning warns when a call to "std::move" prevents copy
2865           elision.  A typical scenario when copy elision can occur is when
2866           returning in a function with a class return type, when the
2867           expression being returned is the name of a non-volatile automatic
2868           object, and is not a function parameter, and has the same type as
2869           the function return type.
2870
2871                   struct T {
2872                   ...
2873                   };
2874                   T fn()
2875                   {
2876                     T t;
2877                     ...
2878                     return std::move (t);
2879                   }
2880
2881           But in this example, the "std::move" call prevents copy elision.
2882
2883           This warning is enabled by -Wall.
2884
2885       -Wno-redundant-move (C++ and Objective-C++ only)
2886           This warning warns about redundant calls to "std::move"; that is,
2887           when a move operation would have been performed even without the
2888           "std::move" call.  This happens because the compiler is forced to
2889           treat the object as if it were an rvalue in certain situations such
2890           as returning a local variable, where copy elision isn't applicable.
2891           Consider:
2892
2893                   struct T {
2894                   ...
2895                   };
2896                   T fn(T t)
2897                   {
2898                     ...
2899                     return std::move (t);
2900                   }
2901
2902           Here, the "std::move" call is redundant.  Because G++ implements
2903           Core Issue 1579, another example is:
2904
2905                   struct T { // convertible to U
2906                   ...
2907                   };
2908                   struct U {
2909                   ...
2910                   };
2911                   U fn()
2912                   {
2913                     T t;
2914                     ...
2915                     return std::move (t);
2916                   }
2917
2918           In this example, copy elision isn't applicable because the type of
2919           the expression being returned and the function return type differ,
2920           yet G++ treats the return value as if it were designated by an
2921           rvalue.
2922
2923           This warning is enabled by -Wextra.
2924
2925       -Wrange-loop-construct (C++ and Objective-C++ only)
2926           This warning warns when a C++ range-based for-loop is creating an
2927           unnecessary copy.  This can happen when the range declaration is
2928           not a reference, but probably should be.  For example:
2929
2930                   struct S { char arr[128]; };
2931                   void fn () {
2932                     S arr[5];
2933                     for (const auto x : arr) { ... }
2934                   }
2935
2936           It does not warn when the type being copied is a trivially-copyable
2937           type whose size is less than 64 bytes.
2938
2939           This warning also warns when a loop variable in a range-based for-
2940           loop is initialized with a value of a different type resulting in a
2941           copy.  For example:
2942
2943                   void fn() {
2944                     int arr[10];
2945                     for (const double &x : arr) { ... }
2946                   }
2947
2948           In the example above, in every iteration of the loop a temporary
2949           value of type "double" is created and destroyed, to which the
2950           reference "const double &" is bound.
2951
2952           This warning is enabled by -Wall.
2953
2954       -Wredundant-tags (C++ and Objective-C++ only)
2955           Warn about redundant class-key and enum-key in references to class
2956           types and enumerated types in contexts where the key can be
2957           eliminated without causing an ambiguity.  For example:
2958
2959                   struct foo;
2960                   struct foo *p;   // warn that keyword struct can be eliminated
2961
2962           On the other hand, in this example there is no warning:
2963
2964                   struct foo;
2965                   void foo ();   // "hides" struct foo
2966                   void bar (struct foo&);  // no warning, keyword struct is necessary
2967
2968       -Wno-subobject-linkage (C++ and Objective-C++ only)
2969           Do not warn if a class type has a base or a field whose type uses
2970           the anonymous namespace or depends on a type with no linkage.  If a
2971           type A depends on a type B with no or internal linkage, defining it
2972           in multiple translation units would be an ODR violation because the
2973           meaning of B is different in each translation unit.  If A only
2974           appears in a single translation unit, the best way to silence the
2975           warning is to give it internal linkage by putting it in an
2976           anonymous namespace as well.  The compiler doesn't give this
2977           warning for types defined in the main .C file, as those are
2978           unlikely to have multiple definitions.  -Wsubobject-linkage is
2979           enabled by default.
2980
2981       -Weffc++ (C++ and Objective-C++ only)
2982           Warn about violations of the following style guidelines from Scott
2983           Meyers' Effective C++ series of books:
2984
2985           *   Define a copy constructor and an assignment operator for
2986               classes with dynamically-allocated memory.
2987
2988           *   Prefer initialization to assignment in constructors.
2989
2990           *   Have "operator=" return a reference to *this.
2991
2992           *   Don't try to return a reference when you must return an object.
2993
2994           *   Distinguish between prefix and postfix forms of increment and
2995               decrement operators.
2996
2997           *   Never overload "&&", "||", or ",".
2998
2999           This option also enables -Wnon-virtual-dtor, which is also one of
3000           the effective C++ recommendations.  However, the check is extended
3001           to warn about the lack of virtual destructor in accessible non-
3002           polymorphic bases classes too.
3003
3004           When selecting this option, be aware that the standard library
3005           headers do not obey all of these guidelines; use grep -v to filter
3006           out those warnings.
3007
3008       -Wno-exceptions (C++ and Objective-C++ only)
3009           Disable the warning about the case when an exception handler is
3010           shadowed by another handler, which can point out a wrong ordering
3011           of exception handlers.
3012
3013       -Wstrict-null-sentinel (C++ and Objective-C++ only)
3014           Warn about the use of an uncasted "NULL" as sentinel.  When
3015           compiling only with GCC this is a valid sentinel, as "NULL" is
3016           defined to "__null".  Although it is a null pointer constant rather
3017           than a null pointer, it is guaranteed to be of the same size as a
3018           pointer.  But this use is not portable across different compilers.
3019
3020       -Wno-non-template-friend (C++ and Objective-C++ only)
3021           Disable warnings when non-template friend functions are declared
3022           within a template.  In very old versions of GCC that predate
3023           implementation of the ISO standard, declarations such as friend int
3024           foo(int), where the name of the friend is an unqualified-id, could
3025           be interpreted as a particular specialization of a template
3026           function; the warning exists to diagnose compatibility problems,
3027           and is enabled by default.
3028
3029       -Wold-style-cast (C++ and Objective-C++ only)
3030           Warn if an old-style (C-style) cast to a non-void type is used
3031           within a C++ program.  The new-style casts ("dynamic_cast",
3032           "static_cast", "reinterpret_cast", and "const_cast") are less
3033           vulnerable to unintended effects and much easier to search for.
3034
3035       -Woverloaded-virtual (C++ and Objective-C++ only)
3036           Warn when a function declaration hides virtual functions from a
3037           base class.  For example, in:
3038
3039                   struct A {
3040                     virtual void f();
3041                   };
3042
3043                   struct B: public A {
3044                     void f(int);
3045                   };
3046
3047           the "A" class version of "f" is hidden in "B", and code like:
3048
3049                   B* b;
3050                   b->f();
3051
3052           fails to compile.
3053
3054       -Wno-pmf-conversions (C++ and Objective-C++ only)
3055           Disable the diagnostic for converting a bound pointer to member
3056           function to a plain pointer.
3057
3058       -Wsign-promo (C++ and Objective-C++ only)
3059           Warn when overload resolution chooses a promotion from unsigned or
3060           enumerated type to a signed type, over a conversion to an unsigned
3061           type of the same size.  Previous versions of G++ tried to preserve
3062           unsignedness, but the standard mandates the current behavior.
3063
3064       -Wtemplates (C++ and Objective-C++ only)
3065           Warn when a primary template declaration is encountered.  Some
3066           coding rules disallow templates, and this may be used to enforce
3067           that rule.  The warning is inactive inside a system header file,
3068           such as the STL, so one can still use the STL.  One may also
3069           instantiate or specialize templates.
3070
3071       -Wno-mismatched-new-delete (C++ and Objective-C++ only)
3072           Warn for mismatches between calls to "operator new" or "operator
3073           delete" and the corresponding call to the allocation or
3074           deallocation function.  This includes invocations of C++ "operator
3075           delete" with pointers returned from either mismatched forms of
3076           "operator new", or from other functions that allocate objects for
3077           which the "operator delete" isn't a suitable deallocator, as well
3078           as calls to other deallocation functions with pointers returned
3079           from "operator new" for which the deallocation function isn't
3080           suitable.
3081
3082           For example, the "delete" expression in the function below is
3083           diagnosed because it doesn't match the array form of the "new"
3084           expression the pointer argument was returned from.  Similarly, the
3085           call to "free" is also diagnosed.
3086
3087                   void f ()
3088                   {
3089                     int *a = new int[n];
3090                     delete a;   // warning: mismatch in array forms of expressions
3091
3092                     char *p = new char[n];
3093                     free (p);   // warning: mismatch between new and free
3094                   }
3095
3096           The related option -Wmismatched-dealloc diagnoses mismatches
3097           involving allocation and deallocation functions other than
3098           "operator new" and "operator delete".
3099
3100           -Wmismatched-new-delete is enabled by default.
3101
3102       -Wmismatched-tags (C++ and Objective-C++ only)
3103           Warn for declarations of structs, classes, and class templates and
3104           their specializations with a class-key that does not match either
3105           the definition or the first declaration if no definition is
3106           provided.
3107
3108           For example, the declaration of "struct Object" in the argument
3109           list of "draw" triggers the warning.  To avoid it, either remove
3110           the redundant class-key "struct" or replace it with "class" to
3111           match its definition.
3112
3113                   class Object {
3114                   public:
3115                     virtual ~Object () = 0;
3116                   };
3117                   void draw (struct Object*);
3118
3119           It is not wrong to declare a class with the class-key "struct" as
3120           the example above shows.  The -Wmismatched-tags option is intended
3121           to help achieve a consistent style of class declarations.  In code
3122           that is intended to be portable to Windows-based compilers the
3123           warning helps prevent unresolved references due to the difference
3124           in the mangling of symbols declared with different class-keys.  The
3125           option can be used either on its own or in conjunction with
3126           -Wredundant-tags.
3127
3128       -Wmultiple-inheritance (C++ and Objective-C++ only)
3129           Warn when a class is defined with multiple direct base classes.
3130           Some coding rules disallow multiple inheritance, and this may be
3131           used to enforce that rule.  The warning is inactive inside a system
3132           header file, such as the STL, so one can still use the STL.  One
3133           may also define classes that indirectly use multiple inheritance.
3134
3135       -Wvirtual-inheritance
3136           Warn when a class is defined with a virtual direct base class.
3137           Some coding rules disallow multiple inheritance, and this may be
3138           used to enforce that rule.  The warning is inactive inside a system
3139           header file, such as the STL, so one can still use the STL.  One
3140           may also define classes that indirectly use virtual inheritance.
3141
3142       -Wno-virtual-move-assign
3143           Suppress warnings about inheriting from a virtual base with a non-
3144           trivial C++11 move assignment operator.  This is dangerous because
3145           if the virtual base is reachable along more than one path, it is
3146           moved multiple times, which can mean both objects end up in the
3147           moved-from state.  If the move assignment operator is written to
3148           avoid moving from a moved-from object, this warning can be
3149           disabled.
3150
3151       -Wnamespaces
3152           Warn when a namespace definition is opened.  Some coding rules
3153           disallow namespaces, and this may be used to enforce that rule.
3154           The warning is inactive inside a system header file, such as the
3155           STL, so one can still use the STL.  One may also use using
3156           directives and qualified names.
3157
3158       -Wno-terminate (C++ and Objective-C++ only)
3159           Disable the warning about a throw-expression that will immediately
3160           result in a call to "terminate".
3161
3162       -Wno-vexing-parse (C++ and Objective-C++ only)
3163           Warn about the most vexing parse syntactic ambiguity.  This warns
3164           about the cases when a declaration looks like a variable
3165           definition, but the C++ language requires it to be interpreted as a
3166           function declaration.  For instance:
3167
3168                   void f(double a) {
3169                     int i();        // extern int i (void);
3170                     int n(int(a));  // extern int n (int);
3171                   }
3172
3173           Another example:
3174
3175                   struct S { S(int); };
3176                   void f(double a) {
3177                     S x(int(a));   // extern struct S x (int);
3178                     S y(int());    // extern struct S y (int (*) (void));
3179                     S z();         // extern struct S z (void);
3180                   }
3181
3182           The warning will suggest options how to deal with such an
3183           ambiguity; e.g., it can suggest removing the parentheses or using
3184           braces instead.
3185
3186           This warning is enabled by default.
3187
3188       -Wno-class-conversion (C++ and Objective-C++ only)
3189           Do not warn when a conversion function converts an object to the
3190           same type, to a base class of that type, or to void; such a
3191           conversion function will never be called.
3192
3193       -Wvolatile (C++ and Objective-C++ only)
3194           Warn about deprecated uses of the "volatile" qualifier.  This
3195           includes postfix and prefix "++" and "--" expressions of
3196           "volatile"-qualified types, using simple assignments where the left
3197           operand is a "volatile"-qualified non-class type for their value,
3198           compound assignments where the left operand is a
3199           "volatile"-qualified non-class type, "volatile"-qualified function
3200           return type, "volatile"-qualified parameter type, and structured
3201           bindings of a "volatile"-qualified type.  This usage was deprecated
3202           in C++20.
3203
3204           Enabled by default with -std=c++20.
3205
3206       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
3207           Warn when a literal 0 is used as null pointer constant.  This can
3208           be useful to facilitate the conversion to "nullptr" in C++11.
3209
3210       -Waligned-new
3211           Warn about a new-expression of a type that requires greater
3212           alignment than the "alignof(std::max_align_t)" but uses an
3213           allocation function without an explicit alignment parameter. This
3214           option is enabled by -Wall.
3215
3216           Normally this only warns about global allocation functions, but
3217           -Waligned-new=all also warns about class member allocation
3218           functions.
3219
3220       -Wno-placement-new
3221       -Wplacement-new=n
3222           Warn about placement new expressions with undefined behavior, such
3223           as constructing an object in a buffer that is smaller than the type
3224           of the object.  For example, the placement new expression below is
3225           diagnosed because it attempts to construct an array of 64 integers
3226           in a buffer only 64 bytes large.
3227
3228                   char buf [64];
3229                   new (buf) int[64];
3230
3231           This warning is enabled by default.
3232
3233           -Wplacement-new=1
3234               This is the default warning level of -Wplacement-new.  At this
3235               level the warning is not issued for some strictly undefined
3236               constructs that GCC allows as extensions for compatibility with
3237               legacy code.  For example, the following "new" expression is
3238               not diagnosed at this level even though it has undefined
3239               behavior according to the C++ standard because it writes past
3240               the end of the one-element array.
3241
3242                       struct S { int n, a[1]; };
3243                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
3244                       new (s->a)int [32]();
3245
3246           -Wplacement-new=2
3247               At this level, in addition to diagnosing all the same
3248               constructs as at level 1, a diagnostic is also issued for
3249               placement new expressions that construct an object in the last
3250               member of structure whose type is an array of a single element
3251               and whose size is less than the size of the object being
3252               constructed.  While the previous example would be diagnosed,
3253               the following construct makes use of the flexible member array
3254               extension to avoid the warning at level 2.
3255
3256                       struct S { int n, a[]; };
3257                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
3258                       new (s->a)int [32]();
3259
3260       -Wcatch-value
3261       -Wcatch-value=n (C++ and Objective-C++ only)
3262           Warn about catch handlers that do not catch via reference.  With
3263           -Wcatch-value=1 (or -Wcatch-value for short) warn about polymorphic
3264           class types that are caught by value.  With -Wcatch-value=2 warn
3265           about all class types that are caught by value. With
3266           -Wcatch-value=3 warn about all types that are not caught by
3267           reference. -Wcatch-value is enabled by -Wall.
3268
3269       -Wconditionally-supported (C++ and Objective-C++ only)
3270           Warn for conditionally-supported (C++11 [intro.defs]) constructs.
3271
3272       -Wno-delete-incomplete (C++ and Objective-C++ only)
3273           Do not warn when deleting a pointer to incomplete type, which may
3274           cause undefined behavior at runtime.  This warning is enabled by
3275           default.
3276
3277       -Wextra-semi (C++, Objective-C++ only)
3278           Warn about redundant semicolons after in-class function
3279           definitions.
3280
3281       -Wno-inaccessible-base (C++, Objective-C++ only)
3282           This option controls warnings when a base class is inaccessible in
3283           a class derived from it due to ambiguity.  The warning is enabled
3284           by default.  Note that the warning for ambiguous virtual bases is
3285           enabled by the -Wextra option.
3286
3287                   struct A { int a; };
3288
3289                   struct B : A { };
3290
3291                   struct C : B, A { };
3292
3293       -Wno-inherited-variadic-ctor
3294           Suppress warnings about use of C++11 inheriting constructors when
3295           the base class inherited from has a C variadic constructor; the
3296           warning is on by default because the ellipsis is not inherited.
3297
3298       -Wno-invalid-offsetof (C++ and Objective-C++ only)
3299           Suppress warnings from applying the "offsetof" macro to a non-POD
3300           type.  According to the 2014 ISO C++ standard, applying "offsetof"
3301           to a non-standard-layout type is undefined.  In existing C++
3302           implementations, however, "offsetof" typically gives meaningful
3303           results.  This flag is for users who are aware that they are
3304           writing nonportable code and who have deliberately chosen to ignore
3305           the warning about it.
3306
3307           The restrictions on "offsetof" may be relaxed in a future version
3308           of the C++ standard.
3309
3310       -Wsized-deallocation (C++ and Objective-C++ only)
3311           Warn about a definition of an unsized deallocation function
3312
3313                   void operator delete (void *) noexcept;
3314                   void operator delete[] (void *) noexcept;
3315
3316           without a definition of the corresponding sized deallocation
3317           function
3318
3319                   void operator delete (void *, std::size_t) noexcept;
3320                   void operator delete[] (void *, std::size_t) noexcept;
3321
3322           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.
3323
3324       -Wsuggest-final-types
3325           Warn about types with virtual methods where code quality would be
3326           improved if the type were declared with the C++11 "final"
3327           specifier, or, if possible, declared in an anonymous namespace.
3328           This allows GCC to more aggressively devirtualize the polymorphic
3329           calls. This warning is more effective with link-time optimization,
3330           where the information about the class hierarchy graph is more
3331           complete.
3332
3333       -Wsuggest-final-methods
3334           Warn about virtual methods where code quality would be improved if
3335           the method were declared with the C++11 "final" specifier, or, if
3336           possible, its type were declared in an anonymous namespace or with
3337           the "final" specifier.  This warning is more effective with link-
3338           time optimization, where the information about the class hierarchy
3339           graph is more complete. It is recommended to first consider
3340           suggestions of -Wsuggest-final-types and then rebuild with new
3341           annotations.
3342
3343       -Wsuggest-override
3344           Warn about overriding virtual functions that are not marked with
3345           the "override" keyword.
3346
3347       -Wuseless-cast (C++ and Objective-C++ only)
3348           Warn when an expression is casted to its own type.
3349
3350       -Wno-conversion-null (C++ and Objective-C++ only)
3351           Do not warn for conversions between "NULL" and non-pointer types.
3352           -Wconversion-null is enabled by default.
3353
3354   Options Controlling Objective-C and Objective-C++ Dialects
3355       (NOTE: This manual does not describe the Objective-C and Objective-C++
3356       languages themselves.
3357
3358       This section describes the command-line options that are only
3359       meaningful for Objective-C and Objective-C++ programs.  You can also
3360       use most of the language-independent GNU compiler options.  For
3361       example, you might compile a file some_class.m like this:
3362
3363               gcc -g -fgnu-runtime -O -c some_class.m
3364
3365       In this example, -fgnu-runtime is an option meant only for Objective-C
3366       and Objective-C++ programs; you can use the other options with any
3367       language supported by GCC.
3368
3369       Note that since Objective-C is an extension of the C language,
3370       Objective-C compilations may also use options specific to the C front-
3371       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
3372       use C++-specific options (e.g., -Wabi).
3373
3374       Here is a list of options that are only for compiling Objective-C and
3375       Objective-C++ programs:
3376
3377       -fconstant-string-class=class-name
3378           Use class-name as the name of the class to instantiate for each
3379           literal string specified with the syntax "@"..."".  The default
3380           class name is "NXConstantString" if the GNU runtime is being used,
3381           and "NSConstantString" if the NeXT runtime is being used (see
3382           below).  The -fconstant-cfstrings option, if also present,
3383           overrides the -fconstant-string-class setting and cause "@"...""
3384           literals to be laid out as constant CoreFoundation strings.
3385
3386       -fgnu-runtime
3387           Generate object code compatible with the standard GNU Objective-C
3388           runtime.  This is the default for most types of systems.
3389
3390       -fnext-runtime
3391           Generate output compatible with the NeXT runtime.  This is the
3392           default for NeXT-based systems, including Darwin and Mac OS X.  The
3393           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
3394           is used.
3395
3396       -fno-nil-receivers
3397           Assume that all Objective-C message dispatches ("[receiver
3398           message:arg]") in this translation unit ensure that the receiver is
3399           not "nil".  This allows for more efficient entry points in the
3400           runtime to be used.  This option is only available in conjunction
3401           with the NeXT runtime and ABI version 0 or 1.
3402
3403       -fobjc-abi-version=n
3404           Use version n of the Objective-C ABI for the selected runtime.
3405           This option is currently supported only for the NeXT runtime.  In
3406           that case, Version 0 is the traditional (32-bit) ABI without
3407           support for properties and other Objective-C 2.0 additions.
3408           Version 1 is the traditional (32-bit) ABI with support for
3409           properties and other Objective-C 2.0 additions.  Version 2 is the
3410           modern (64-bit) ABI.  If nothing is specified, the default is
3411           Version 0 on 32-bit target machines, and Version 2 on 64-bit target
3412           machines.
3413
3414       -fobjc-call-cxx-cdtors
3415           For each Objective-C class, check if any of its instance variables
3416           is a C++ object with a non-trivial default constructor.  If so,
3417           synthesize a special "- (id) .cxx_construct" instance method which
3418           runs non-trivial default constructors on any such instance
3419           variables, in order, and then return "self".  Similarly, check if
3420           any instance variable is a C++ object with a non-trivial
3421           destructor, and if so, synthesize a special "- (void)
3422           .cxx_destruct" method which runs all such default destructors, in
3423           reverse order.
3424
3425           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods
3426           thusly generated only operate on instance variables declared in the
3427           current Objective-C class, and not those inherited from
3428           superclasses.  It is the responsibility of the Objective-C runtime
3429           to invoke all such methods in an object's inheritance hierarchy.
3430           The "- (id) .cxx_construct" methods are invoked by the runtime
3431           immediately after a new object instance is allocated; the "- (void)
3432           .cxx_destruct" methods are invoked immediately before the runtime
3433           deallocates an object instance.
3434
3435           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
3436           later has support for invoking the "- (id) .cxx_construct" and "-
3437           (void) .cxx_destruct" methods.
3438
3439       -fobjc-direct-dispatch
3440           Allow fast jumps to the message dispatcher.  On Darwin this is
3441           accomplished via the comm page.
3442
3443       -fobjc-exceptions
3444           Enable syntactic support for structured exception handling in
3445           Objective-C, similar to what is offered by C++.  This option is
3446           required to use the Objective-C keywords @try, @throw, @catch,
3447           @finally and @synchronized.  This option is available with both the
3448           GNU runtime and the NeXT runtime (but not available in conjunction
3449           with the NeXT runtime on Mac OS X 10.2 and earlier).
3450
3451       -fobjc-gc
3452           Enable garbage collection (GC) in Objective-C and Objective-C++
3453           programs.  This option is only available with the NeXT runtime; the
3454           GNU runtime has a different garbage collection implementation that
3455           does not require special compiler flags.
3456
3457       -fobjc-nilcheck
3458           For the NeXT runtime with version 2 of the ABI, check for a nil
3459           receiver in method invocations before doing the actual method call.
3460           This is the default and can be disabled using -fno-objc-nilcheck.
3461           Class methods and super calls are never checked for nil in this way
3462           no matter what this flag is set to.  Currently this flag does
3463           nothing when the GNU runtime, or an older version of the NeXT
3464           runtime ABI, is used.
3465
3466       -fobjc-std=objc1
3467           Conform to the language syntax of Objective-C 1.0, the language
3468           recognized by GCC 4.0.  This only affects the Objective-C additions
3469           to the C/C++ language; it does not affect conformance to C/C++
3470           standards, which is controlled by the separate C/C++ dialect option
3471           flags.  When this option is used with the Objective-C or
3472           Objective-C++ compiler, any Objective-C syntax that is not
3473           recognized by GCC 4.0 is rejected.  This is useful if you need to
3474           make sure that your Objective-C code can be compiled with older
3475           versions of GCC.
3476
3477       -freplace-objc-classes
3478           Emit a special marker instructing ld(1) not to statically link in
3479           the resulting object file, and allow dyld(1) to load it in at run
3480           time instead.  This is used in conjunction with the Fix-and-
3481           Continue debugging mode, where the object file in question may be
3482           recompiled and dynamically reloaded in the course of program
3483           execution, without the need to restart the program itself.
3484           Currently, Fix-and-Continue functionality is only available in
3485           conjunction with the NeXT runtime on Mac OS X 10.3 and later.
3486
3487       -fzero-link
3488           When compiling for the NeXT runtime, the compiler ordinarily
3489           replaces calls to "objc_getClass("...")" (when the name of the
3490           class is known at compile time) with static class references that
3491           get initialized at load time, which improves run-time performance.
3492           Specifying the -fzero-link flag suppresses this behavior and causes
3493           calls to "objc_getClass("...")"  to be retained.  This is useful in
3494           Zero-Link debugging mode, since it allows for individual class
3495           implementations to be modified during program execution.  The GNU
3496           runtime currently always retains calls to "objc_get_class("...")"
3497           regardless of command-line options.
3498
3499       -fno-local-ivars
3500           By default instance variables in Objective-C can be accessed as if
3501           they were local variables from within the methods of the class
3502           they're declared in.  This can lead to shadowing between instance
3503           variables and other variables declared either locally inside a
3504           class method or globally with the same name.  Specifying the
3505           -fno-local-ivars flag disables this behavior thus avoiding variable
3506           shadowing issues.
3507
3508       -fivar-visibility=[public|protected|private|package]
3509           Set the default instance variable visibility to the specified
3510           option so that instance variables declared outside the scope of any
3511           access modifier directives default to the specified visibility.
3512
3513       -gen-decls
3514           Dump interface declarations for all classes seen in the source file
3515           to a file named sourcename.decl.
3516
3517       -Wassign-intercept (Objective-C and Objective-C++ only)
3518           Warn whenever an Objective-C assignment is being intercepted by the
3519           garbage collector.
3520
3521       -Wno-property-assign-default (Objective-C and Objective-C++ only)
3522           Do not warn if a property for an Objective-C object has no assign
3523           semantics specified.
3524
3525       -Wno-protocol (Objective-C and Objective-C++ only)
3526           If a class is declared to implement a protocol, a warning is issued
3527           for every method in the protocol that is not implemented by the
3528           class.  The default behavior is to issue a warning for every method
3529           not explicitly implemented in the class, even if a method
3530           implementation is inherited from the superclass.  If you use the
3531           -Wno-protocol option, then methods inherited from the superclass
3532           are considered to be implemented, and no warning is issued for
3533           them.
3534
3535       -Wobjc-root-class (Objective-C and Objective-C++ only)
3536           Warn if a class interface lacks a superclass. Most classes will
3537           inherit from "NSObject" (or "Object") for example.  When declaring
3538           classes intended to be root classes, the warning can be suppressed
3539           by marking their interfaces with
3540           "__attribute__((objc_root_class))".
3541
3542       -Wselector (Objective-C and Objective-C++ only)
3543           Warn if multiple methods of different types for the same selector
3544           are found during compilation.  The check is performed on the list
3545           of methods in the final stage of compilation.  Additionally, a
3546           check is performed for each selector appearing in a
3547           "@selector(...)"  expression, and a corresponding method for that
3548           selector has been found during compilation.  Because these checks
3549           scan the method table only at the end of compilation, these
3550           warnings are not produced if the final stage of compilation is not
3551           reached, for example because an error is found during compilation,
3552           or because the -fsyntax-only option is being used.
3553
3554       -Wstrict-selector-match (Objective-C and Objective-C++ only)
3555           Warn if multiple methods with differing argument and/or return
3556           types are found for a given selector when attempting to send a
3557           message using this selector to a receiver of type "id" or "Class".
3558           When this flag is off (which is the default behavior), the compiler
3559           omits such warnings if any differences found are confined to types
3560           that share the same size and alignment.
3561
3562       -Wundeclared-selector (Objective-C and Objective-C++ only)
3563           Warn if a "@selector(...)" expression referring to an undeclared
3564           selector is found.  A selector is considered undeclared if no
3565           method with that name has been declared before the "@selector(...)"
3566           expression, either explicitly in an @interface or @protocol
3567           declaration, or implicitly in an @implementation section.  This
3568           option always performs its checks as soon as a "@selector(...)"
3569           expression is found, while -Wselector only performs its checks in
3570           the final stage of compilation.  This also enforces the coding
3571           style convention that methods and selectors must be declared before
3572           being used.
3573
3574       -print-objc-runtime-info
3575           Generate C header describing the largest structure that is passed
3576           by value, if any.
3577
3578   Options to Control Diagnostic Messages Formatting
3579       Traditionally, diagnostic messages have been formatted irrespective of
3580       the output device's aspect (e.g. its width, ...).  You can use the
3581       options described below to control the formatting algorithm for
3582       diagnostic messages, e.g. how many characters per line, how often
3583       source location information should be reported.  Note that some
3584       language front ends may not honor these options.
3585
3586       -fmessage-length=n
3587           Try to format error messages so that they fit on lines of about n
3588           characters.  If n is zero, then no line-wrapping is done; each
3589           error message appears on a single line.  This is the default for
3590           all front ends.
3591
3592           Note - this option also affects the display of the #error and
3593           #warning pre-processor directives, and the deprecated
3594           function/type/variable attribute.  It does not however affect the
3595           pragma GCC warning and pragma GCC error pragmas.
3596
3597       -fdiagnostics-plain-output
3598           This option requests that diagnostic output look as plain as
3599           possible, which may be useful when running dejagnu or other
3600           utilities that need to parse diagnostics output and prefer that it
3601           remain more stable over time.  -fdiagnostics-plain-output is
3602           currently equivalent to the following options:
3603           -fno-diagnostics-show-caret -fno-diagnostics-show-line-numbers
3604           -fdiagnostics-color=never -fdiagnostics-urls=never
3605           -fdiagnostics-path-format=separate-events In the future, if GCC
3606           changes the default appearance of its diagnostics, the
3607           corresponding option to disable the new behavior will be added to
3608           this list.
3609
3610       -fdiagnostics-show-location=once
3611           Only meaningful in line-wrapping mode.  Instructs the diagnostic
3612           messages reporter to emit source location information once; that
3613           is, in case the message is too long to fit on a single physical
3614           line and has to be wrapped, the source location won't be emitted
3615           (as prefix) again, over and over, in subsequent continuation lines.
3616           This is the default behavior.
3617
3618       -fdiagnostics-show-location=every-line
3619           Only meaningful in line-wrapping mode.  Instructs the diagnostic
3620           messages reporter to emit the same source location information (as
3621           prefix) for physical lines that result from the process of breaking
3622           a message which is too long to fit on a single line.
3623
3624       -fdiagnostics-color[=WHEN]
3625       -fno-diagnostics-color
3626           Use color in diagnostics.  WHEN is never, always, or auto.  The
3627           default depends on how the compiler has been configured, it can be
3628           any of the above WHEN options or also never if GCC_COLORS
3629           environment variable isn't present in the environment, and auto
3630           otherwise.  auto makes GCC use color only when the standard error
3631           is a terminal, and when not executing in an emacs shell.  The forms
3632           -fdiagnostics-color and -fno-diagnostics-color are aliases for
3633           -fdiagnostics-color=always and -fdiagnostics-color=never,
3634           respectively.
3635
3636           The colors are defined by the environment variable GCC_COLORS.  Its
3637           value is a colon-separated list of capabilities and Select Graphic
3638           Rendition (SGR) substrings. SGR commands are interpreted by the
3639           terminal or terminal emulator.  (See the section in the
3640           documentation of your text terminal for permitted values and their
3641           meanings as character attributes.)  These substring values are
3642           integers in decimal representation and can be concatenated with
3643           semicolons.  Common values to concatenate include 1 for bold, 4 for
3644           underline, 5 for blink, 7 for inverse, 39 for default foreground
3645           color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode
3646           foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color
3647           modes foreground colors, 49 for default background color, 40 to 47
3648           for background colors, 100 to 107 for 16-color mode background
3649           colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
3650           background colors.
3651
3652           The default GCC_COLORS is
3653
3654                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
3655                   quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
3656                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
3657                   type-diff=01;32
3658
3659           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
3660           32 is green, 34 is blue, 01 is bold, and 31 is red.  Setting
3661           GCC_COLORS to the empty string disables colors.  Supported
3662           capabilities are as follows.
3663
3664           "error="
3665               SGR substring for error: markers.
3666
3667           "warning="
3668               SGR substring for warning: markers.
3669
3670           "note="
3671               SGR substring for note: markers.
3672
3673           "path="
3674               SGR substring for colorizing paths of control-flow events as
3675               printed via -fdiagnostics-path-format=, such as the identifiers
3676               of individual events and lines indicating interprocedural calls
3677               and returns.
3678
3679           "range1="
3680               SGR substring for first additional range.
3681
3682           "range2="
3683               SGR substring for second additional range.
3684
3685           "locus="
3686               SGR substring for location information, file:line or
3687               file:line:column etc.
3688
3689           "quote="
3690               SGR substring for information printed within quotes.
3691
3692           "fixit-insert="
3693               SGR substring for fix-it hints suggesting text to be inserted
3694               or replaced.
3695
3696           "fixit-delete="
3697               SGR substring for fix-it hints suggesting text to be deleted.
3698
3699           "diff-filename="
3700               SGR substring for filename headers within generated patches.
3701
3702           "diff-hunk="
3703               SGR substring for the starts of hunks within generated patches.
3704
3705           "diff-delete="
3706               SGR substring for deleted lines within generated patches.
3707
3708           "diff-insert="
3709               SGR substring for inserted lines within generated patches.
3710
3711           "type-diff="
3712               SGR substring for highlighting mismatching types within
3713               template arguments in the C++ frontend.
3714
3715       -fdiagnostics-urls[=WHEN]
3716           Use escape sequences to embed URLs in diagnostics.  For example,
3717           when -fdiagnostics-show-option emits text showing the command-line
3718           option controlling a diagnostic, embed a URL for documentation of
3719           that option.
3720
3721           WHEN is never, always, or auto.  auto makes GCC use URL escape
3722           sequences only when the standard error is a terminal, and when not
3723           executing in an emacs shell or any graphical terminal which is
3724           known to be incompatible with this feature, see below.
3725
3726           The default depends on how the compiler has been configured.  It
3727           can be any of the above WHEN options.
3728
3729           GCC can also be configured (via the
3730           --with-diagnostics-urls=auto-if-env configure-time option) so that
3731           the default is affected by environment variables.  Under such a
3732           configuration, GCC defaults to using auto if either GCC_URLS or
3733           TERM_URLS environment variables are present and non-empty in the
3734           environment of the compiler, or never if neither are.
3735
3736           However, even with -fdiagnostics-urls=always the behavior is
3737           dependent on those environment variables: If GCC_URLS is set to
3738           empty or no, do not embed URLs in diagnostics.  If set to st, URLs
3739           use ST escape sequences.  If set to bel, the default, URLs use BEL
3740           escape sequences.  Any other non-empty value enables the feature.
3741           If GCC_URLS is not set, use TERM_URLS as a fallback.  Note: ST is
3742           an ANSI escape sequence, string terminator ESC \, BEL is an ASCII
3743           character, CTRL-G that usually sounds like a beep.
3744
3745           At this time GCC tries to detect also a few terminals that are
3746           known to not implement the URL feature, and have bugs or at least
3747           had bugs in some versions that are still in use, where the URL
3748           escapes are likely to misbehave, i.e. print garbage on the screen.
3749           That list is currently xfce4-terminal, certain known to be buggy
3750           gnome-terminal versions, the linux console, and mingw.  This check
3751           can be skipped with the -fdiagnostics-urls=always.
3752
3753       -fno-diagnostics-show-option
3754           By default, each diagnostic emitted includes text indicating the
3755           command-line option that directly controls the diagnostic (if such
3756           an option is known to the diagnostic machinery).  Specifying the
3757           -fno-diagnostics-show-option flag suppresses that behavior.
3758
3759       -fno-diagnostics-show-caret
3760           By default, each diagnostic emitted includes the original source
3761           line and a caret ^ indicating the column.  This option suppresses
3762           this information.  The source line is truncated to n characters, if
3763           the -fmessage-length=n option is given.  When the output is done to
3764           the terminal, the width is limited to the width given by the
3765           COLUMNS environment variable or, if not set, to the terminal width.
3766
3767       -fno-diagnostics-show-labels
3768           By default, when printing source code (via
3769           -fdiagnostics-show-caret), diagnostics can label ranges of source
3770           code with pertinent information, such as the types of expressions:
3771
3772                       printf ("foo %s bar", long_i + long_j);
3773                                    ~^       ~~~~~~~~~~~~~~~
3774                                     |              |
3775                                     char *         long int
3776
3777           This option suppresses the printing of these labels (in the example
3778           above, the vertical bars and the "char *" and "long int" text).
3779
3780       -fno-diagnostics-show-cwe
3781           Diagnostic messages can optionally have an associated
3782           @url{https://cwe.mitre.org/index.html, CWE} identifier.  GCC itself
3783           only provides such metadata for some of the -fanalyzer diagnostics.
3784           GCC plugins may also provide diagnostics with such metadata.  By
3785           default, if this information is present, it will be printed with
3786           the diagnostic.  This option suppresses the printing of this
3787           metadata.
3788
3789       -fno-diagnostics-show-line-numbers
3790           By default, when printing source code (via
3791           -fdiagnostics-show-caret), a left margin is printed, showing line
3792           numbers.  This option suppresses this left margin.
3793
3794       -fdiagnostics-minimum-margin-width=width
3795           This option controls the minimum width of the left margin printed
3796           by -fdiagnostics-show-line-numbers.  It defaults to 6.
3797
3798       -fdiagnostics-parseable-fixits
3799           Emit fix-it hints in a machine-parseable format, suitable for
3800           consumption by IDEs.  For each fix-it, a line will be printed after
3801           the relevant diagnostic, starting with the string "fix-it:".  For
3802           example:
3803
3804                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"
3805
3806           The location is expressed as a half-open range, expressed as a
3807           count of bytes, starting at byte 1 for the initial column.  In the
3808           above example, bytes 3 through 20 of line 45 of "test.c" are to be
3809           replaced with the given string:
3810
3811                   00000000011111111112222222222
3812                   12345678901234567890123456789
3813                     gtk_widget_showall (dlg);
3814                     ^^^^^^^^^^^^^^^^^^
3815                     gtk_widget_show_all
3816
3817           The filename and replacement string escape backslash as "\\", tab
3818           as "\t", newline as "\n", double quotes as "\"", non-printable
3819           characters as octal (e.g. vertical tab as "\013").
3820
3821           An empty replacement string indicates that the given range is to be
3822           removed.  An empty range (e.g. "45:3-45:3") indicates that the
3823           string is to be inserted at the given position.
3824
3825       -fdiagnostics-generate-patch
3826           Print fix-it hints to stderr in unified diff format, after any
3827           diagnostics are printed.  For example:
3828
3829                   --- test.c
3830                   +++ test.c
3831                   @ -42,5 +42,5 @
3832
3833                    void show_cb(GtkDialog *dlg)
3834                    {
3835                   -  gtk_widget_showall(dlg);
3836                   +  gtk_widget_show_all(dlg);
3837                    }
3838
3839           The diff may or may not be colorized, following the same rules as
3840           for diagnostics (see -fdiagnostics-color).
3841
3842       -fdiagnostics-show-template-tree
3843           In the C++ frontend, when printing diagnostics showing mismatching
3844           template types, such as:
3845
3846                     could not convert 'std::map<int, std::vector<double> >()'
3847                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
3848
3849           the -fdiagnostics-show-template-tree flag enables printing a tree-
3850           like structure showing the common and differing parts of the types,
3851           such as:
3852
3853                     map<
3854                       [...],
3855                       vector<
3856                         [double != float]>>
3857
3858           The parts that differ are highlighted with color ("double" and
3859           "float" in this case).
3860
3861       -fno-elide-type
3862           By default when the C++ frontend prints diagnostics showing
3863           mismatching template types, common parts of the types are printed
3864           as "[...]" to simplify the error message.  For example:
3865
3866                     could not convert 'std::map<int, std::vector<double> >()'
3867                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
3868
3869           Specifying the -fno-elide-type flag suppresses that behavior.  This
3870           flag also affects the output of the
3871           -fdiagnostics-show-template-tree flag.
3872
3873       -fdiagnostics-path-format=KIND
3874           Specify how to print paths of control-flow events for diagnostics
3875           that have such a path associated with them.
3876
3877           KIND is none, separate-events, or inline-events, the default.
3878
3879           none means to not print diagnostic paths.
3880
3881           separate-events means to print a separate "note" diagnostic for
3882           each event within the diagnostic.  For example:
3883
3884                   test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
3885                   test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
3886                   test.c:27:3: note: (2) when 'i < count'
3887                   test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
3888
3889           inline-events means to print the events "inline" within the source
3890           code.  This view attempts to consolidate the events into runs of
3891           sufficiently-close events, printing them as labelled ranges within
3892           the source.
3893
3894           For example, the same events as above might be printed as:
3895
3896                     'test': events 1-3
3897                       |
3898                       |   25 |   list = PyList_New(0);
3899                       |      |          ^~~~~~~~~~~~~
3900                       |      |          |
3901                       |      |          (1) when 'PyList_New' fails, returning NULL
3902                       |   26 |
3903                       |   27 |   for (i = 0; i < count; i++) {
3904                       |      |   ~~~
3905                       |      |   |
3906                       |      |   (2) when 'i < count'
3907                       |   28 |     item = PyLong_FromLong(random());
3908                       |   29 |     PyList_Append(list, item);
3909                       |      |     ~~~~~~~~~~~~~~~~~~~~~~~~~
3910                       |      |     |
3911                       |      |     (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
3912                       |
3913
3914           Interprocedural control flow is shown by grouping the events by
3915           stack frame, and using indentation to show how stack frames are
3916           nested, pushed, and popped.
3917
3918           For example:
3919
3920                     'test': events 1-2
3921                       |
3922                       |  133 | {
3923                       |      | ^
3924                       |      | |
3925                       |      | (1) entering 'test'
3926                       |  134 |   boxed_int *obj = make_boxed_int (i);
3927                       |      |                    ~~~~~~~~~~~~~~~~~~
3928                       |      |                    |
3929                       |      |                    (2) calling 'make_boxed_int'
3930                       |
3931                       +--> 'make_boxed_int': events 3-4
3932                              |
3933                              |  120 | {
3934                              |      | ^
3935                              |      | |
3936                              |      | (3) entering 'make_boxed_int'
3937                              |  121 |   boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
3938                              |      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3939                              |      |                                    |
3940                              |      |                                    (4) calling 'wrapped_malloc'
3941                              |
3942                              +--> 'wrapped_malloc': events 5-6
3943                                     |
3944                                     |    7 | {
3945                                     |      | ^
3946                                     |      | |
3947                                     |      | (5) entering 'wrapped_malloc'
3948                                     |    8 |   return malloc (size);
3949                                     |      |          ~~~~~~~~~~~~~
3950                                     |      |          |
3951                                     |      |          (6) calling 'malloc'
3952                                     |
3953                       <-------------+
3954                       |
3955                    'test': event 7
3956                       |
3957                       |  138 |   free_boxed_int (obj);
3958                       |      |   ^~~~~~~~~~~~~~~~~~~~
3959                       |      |   |
3960                       |      |   (7) calling 'free_boxed_int'
3961                       |
3962                   (etc)
3963
3964       -fdiagnostics-show-path-depths
3965           This option provides additional information when printing control-
3966           flow paths associated with a diagnostic.
3967
3968           If this is option is provided then the stack depth will be printed
3969           for each run of events within
3970           -fdiagnostics-path-format=separate-events.
3971
3972           This is intended for use by GCC developers and plugin developers
3973           when debugging diagnostics that report interprocedural control
3974           flow.
3975
3976       -fno-show-column
3977           Do not print column numbers in diagnostics.  This may be necessary
3978           if diagnostics are being scanned by a program that does not
3979           understand the column numbers, such as dejagnu.
3980
3981       -fdiagnostics-column-unit=UNIT
3982           Select the units for the column number.  This affects traditional
3983           diagnostics (in the absence of -fno-show-column), as well as JSON
3984           format diagnostics if requested.
3985
3986           The default UNIT, display, considers the number of display columns
3987           occupied by each character.  This may be larger than the number of
3988           bytes required to encode the character, in the case of tab
3989           characters, or it may be smaller, in the case of multibyte
3990           characters.  For example, the character "GREEK SMALL LETTER PI
3991           (U+03C0)" occupies one display column, and its UTF-8 encoding
3992           requires two bytes; the character "SLIGHTLY SMILING FACE (U+1F642)"
3993           occupies two display columns, and its UTF-8 encoding requires four
3994           bytes.
3995
3996           Setting UNIT to byte changes the column number to the raw byte
3997           count in all cases, as was traditionally output by GCC prior to
3998           version 11.1.0.
3999
4000       -fdiagnostics-column-origin=ORIGIN
4001           Select the origin for column numbers, i.e. the column number
4002           assigned to the first column.  The default value of 1 corresponds
4003           to traditional GCC behavior and to the GNU style guide.  Some
4004           utilities may perform better with an origin of 0; any non-negative
4005           value may be specified.
4006
4007       -fdiagnostics-format=FORMAT
4008           Select a different format for printing diagnostics.  FORMAT is text
4009           or json.  The default is text.
4010
4011           The json format consists of a top-level JSON array containing JSON
4012           objects representing the diagnostics.
4013
4014           The JSON is emitted as one line, without formatting; the examples
4015           below have been formatted for clarity.
4016
4017           Diagnostics can have child diagnostics.  For example, this error
4018           and note:
4019
4020                   misleading-indentation.c:15:3: warning: this 'if' clause does not
4021                     guard... [-Wmisleading-indentation]
4022                      15 |   if (flag)
4023                         |   ^~
4024                   misleading-indentation.c:17:5: note: ...this statement, but the latter
4025                     is misleadingly indented as if it were guarded by the 'if'
4026                      17 |     y = 2;
4027                         |     ^
4028
4029           might be printed in JSON form (after formatting) like this:
4030
4031                   [
4032                       {
4033                           "kind": "warning",
4034                           "locations": [
4035                               {
4036                                   "caret": {
4037                                       "display-column": 3,
4038                                       "byte-column": 3,
4039                                       "column": 3,
4040                                       "file": "misleading-indentation.c",
4041                                       "line": 15
4042                                   },
4043                                   "finish": {
4044                                       "display-column": 4,
4045                                       "byte-column": 4,
4046                                       "column": 4,
4047                                       "file": "misleading-indentation.c",
4048                                       "line": 15
4049                                   }
4050                               }
4051                           ],
4052                           "message": "this \u2018if\u2019 clause does not guard...",
4053                           "option": "-Wmisleading-indentation",
4054                           "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
4055                           "children": [
4056                               {
4057                                   "kind": "note",
4058                                   "locations": [
4059                                       {
4060                                           "caret": {
4061                                               "display-column": 5,
4062                                               "byte-column": 5,
4063                                               "column": 5,
4064                                               "file": "misleading-indentation.c",
4065                                               "line": 17
4066                                           }
4067                                       }
4068                                   ],
4069                                   "message": "...this statement, but the latter is ..."
4070                               }
4071                           ]
4072                           "column-origin": 1,
4073                       },
4074                       ...
4075                   ]
4076
4077           where the "note" is a child of the "warning".
4078
4079           A diagnostic has a "kind".  If this is "warning", then there is an
4080           "option" key describing the command-line option controlling the
4081           warning.
4082
4083           A diagnostic can contain zero or more locations.  Each location has
4084           an optional "label" string and up to three positions within it: a
4085           "caret" position and optional "start" and "finish" positions.  A
4086           position is described by a "file" name, a "line" number, and three
4087           numbers indicating a column position:
4088
4089           *   "display-column" counts display columns, accounting for tabs
4090               and multibyte characters.
4091
4092           *   "byte-column" counts raw bytes.
4093
4094           *   "column" is equal to one of the previous two, as dictated by
4095               the -fdiagnostics-column-unit option.
4096
4097           All three columns are relative to the origin specified by
4098           -fdiagnostics-column-origin, which is typically equal to 1 but may
4099           be set, for instance, to 0 for compatibility with other utilities
4100           that number columns from 0.  The column origin is recorded in the
4101           JSON output in the "column-origin" tag.  In the remaining examples
4102           below, the extra column number outputs have been omitted for
4103           brevity.
4104
4105           For example, this error:
4106
4107                   bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
4108                      'struct s'} and 'T' {aka 'struct t'})
4109                      64 |   return callee_4a () + callee_4b ();
4110                         |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
4111                         |          |              |
4112                         |          |              T {aka struct t}
4113                         |          S {aka struct s}
4114
4115           has three locations.  Its primary location is at the "+" token at
4116           column 23.  It has two secondary locations, describing the left and
4117           right-hand sides of the expression, which have labels.  It might be
4118           printed in JSON form as:
4119
4120                       {
4121                           "children": [],
4122                           "kind": "error",
4123                           "locations": [
4124                               {
4125                                   "caret": {
4126                                       "column": 23, "file": "bad-binary-ops.c", "line": 64
4127                                   }
4128                               },
4129                               {
4130                                   "caret": {
4131                                       "column": 10, "file": "bad-binary-ops.c", "line": 64
4132                                   },
4133                                   "finish": {
4134                                       "column": 21, "file": "bad-binary-ops.c", "line": 64
4135                                   },
4136                                   "label": "S {aka struct s}"
4137                               },
4138                               {
4139                                   "caret": {
4140                                       "column": 25, "file": "bad-binary-ops.c", "line": 64
4141                                   },
4142                                   "finish": {
4143                                       "column": 36, "file": "bad-binary-ops.c", "line": 64
4144                                   },
4145                                   "label": "T {aka struct t}"
4146                               }
4147                           ],
4148                           "message": "invalid operands to binary + ..."
4149                       }
4150
4151           If a diagnostic contains fix-it hints, it has a "fixits" array,
4152           consisting of half-open intervals, similar to the output of
4153           -fdiagnostics-parseable-fixits.  For example, this diagnostic with
4154           a replacement fix-it hint:
4155
4156                   demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
4157                     mean 'color'?
4158                       8 |   return ptr->colour;
4159                         |               ^~~~~~
4160                         |               color
4161
4162           might be printed in JSON form as:
4163
4164                       {
4165                           "children": [],
4166                           "fixits": [
4167                               {
4168                                   "next": {
4169                                       "column": 21,
4170                                       "file": "demo.c",
4171                                       "line": 8
4172                                   },
4173                                   "start": {
4174                                       "column": 15,
4175                                       "file": "demo.c",
4176                                       "line": 8
4177                                   },
4178                                   "string": "color"
4179                               }
4180                           ],
4181                           "kind": "error",
4182                           "locations": [
4183                               {
4184                                   "caret": {
4185                                       "column": 15,
4186                                       "file": "demo.c",
4187                                       "line": 8
4188                                   },
4189                                   "finish": {
4190                                       "column": 20,
4191                                       "file": "demo.c",
4192                                       "line": 8
4193                                   }
4194                               }
4195                           ],
4196                           "message": "\u2018struct s\u2019 has no member named ..."
4197                       }
4198
4199           where the fix-it hint suggests replacing the text from "start" up
4200           to but not including "next" with "string"'s value.  Deletions are
4201           expressed via an empty value for "string", insertions by having
4202           "start" equal "next".
4203
4204           If the diagnostic has a path of control-flow events associated with
4205           it, it has a "path" array of objects representing the events.  Each
4206           event object has a "description" string, a "location" object, along
4207           with a "function" string and a "depth" number for representing
4208           interprocedural paths.  The "function" represents the current
4209           function at that event, and the "depth" represents the stack depth
4210           relative to some baseline: the higher, the more frames are within
4211           the stack.
4212
4213           For example, the intraprocedural example shown for
4214           -fdiagnostics-path-format= might have this JSON for its path:
4215
4216                       "path": [
4217                           {
4218                               "depth": 0,
4219                               "description": "when 'PyList_New' fails, returning NULL",
4220                               "function": "test",
4221                               "location": {
4222                                   "column": 10,
4223                                   "file": "test.c",
4224                                   "line": 25
4225                               }
4226                           },
4227                           {
4228                               "depth": 0,
4229                               "description": "when 'i < count'",
4230                               "function": "test",
4231                               "location": {
4232                                   "column": 3,
4233                                   "file": "test.c",
4234                                   "line": 27
4235                               }
4236                           },
4237                           {
4238                               "depth": 0,
4239                               "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
4240                               "function": "test",
4241                               "location": {
4242                                   "column": 5,
4243                                   "file": "test.c",
4244                                   "line": 29
4245                               }
4246                           }
4247                       ]
4248
4249   Options to Request or Suppress Warnings
4250       Warnings are diagnostic messages that report constructions that are not
4251       inherently erroneous but that are risky or suggest there may have been
4252       an error.
4253
4254       The following language-independent options do not enable specific
4255       warnings but control the kinds of diagnostics produced by GCC.
4256
4257       -fsyntax-only
4258           Check the code for syntax errors, but don't do anything beyond
4259           that.
4260
4261       -fmax-errors=n
4262           Limits the maximum number of error messages to n, at which point
4263           GCC bails out rather than attempting to continue processing the
4264           source code.  If n is 0 (the default), there is no limit on the
4265           number of error messages produced.  If -Wfatal-errors is also
4266           specified, then -Wfatal-errors takes precedence over this option.
4267
4268       -w  Inhibit all warning messages.
4269
4270       -Werror
4271           Make all warnings into errors.
4272
4273       -Werror=
4274           Make the specified warning into an error.  The specifier for a
4275           warning is appended; for example -Werror=switch turns the warnings
4276           controlled by -Wswitch into errors.  This switch takes a negative
4277           form, to be used to negate -Werror for specific warnings; for
4278           example -Wno-error=switch makes -Wswitch warnings not be errors,
4279           even when -Werror is in effect.
4280
4281           The warning message for each controllable warning includes the
4282           option that controls the warning.  That option can then be used
4283           with -Werror= and -Wno-error= as described above.  (Printing of the
4284           option in the warning message can be disabled using the
4285           -fno-diagnostics-show-option flag.)
4286
4287           Note that specifying -Werror=foo automatically implies -Wfoo.
4288           However, -Wno-error=foo does not imply anything.
4289
4290       -Wfatal-errors
4291           This option causes the compiler to abort compilation on the first
4292           error occurred rather than trying to keep going and printing
4293           further error messages.
4294
4295       You can request many specific warnings with options beginning with -W,
4296       for example -Wimplicit to request warnings on implicit declarations.
4297       Each of these specific warning options also has a negative form
4298       beginning -Wno- to turn off warnings; for example, -Wno-implicit.  This
4299       manual lists only one of the two forms, whichever is not the default.
4300       For further language-specific options also refer to C++ Dialect Options
4301       and Objective-C and Objective-C++ Dialect Options.  Additional warnings
4302       can be produced by enabling the static analyzer;
4303
4304       Some options, such as -Wall and -Wextra, turn on other options, such as
4305       -Wunused, which may turn on further options, such as -Wunused-value.
4306       The combined effect of positive and negative forms is that more
4307       specific options have priority over less specific ones, independently
4308       of their position in the command-line. For options of the same
4309       specificity, the last one takes effect. Options enabled or disabled via
4310       pragmas take effect as if they appeared at the end of the command-line.
4311
4312       When an unrecognized warning option is requested (e.g.,
4313       -Wunknown-warning), GCC emits a diagnostic stating that the option is
4314       not recognized.  However, if the -Wno- form is used, the behavior is
4315       slightly different: no diagnostic is produced for -Wno-unknown-warning
4316       unless other diagnostics are being produced.  This allows the use of
4317       new -Wno- options with old compilers, but if something goes wrong, the
4318       compiler warns that an unrecognized option is present.
4319
4320       The effectiveness of some warnings depends on optimizations also being
4321       enabled. For example -Wsuggest-final-types is more effective with link-
4322       time optimization and -Wmaybe-uninitialized does not warn at all unless
4323       optimization is enabled.
4324
4325       -Wpedantic
4326       -pedantic
4327           Issue all the warnings demanded by strict ISO C and ISO C++; reject
4328           all programs that use forbidden extensions, and some other programs
4329           that do not follow ISO C and ISO C++.  For ISO C, follows the
4330           version of the ISO C standard specified by any -std option used.
4331
4332           Valid ISO C and ISO C++ programs should compile properly with or
4333           without this option (though a rare few require -ansi or a -std
4334           option specifying the required version of ISO C).  However, without
4335           this option, certain GNU extensions and traditional C and C++
4336           features are supported as well.  With this option, they are
4337           rejected.
4338
4339           -Wpedantic does not cause warning messages for use of the alternate
4340           keywords whose names begin and end with __.  This alternate format
4341           can also be used to disable warnings for non-ISO __intN types, i.e.
4342           __intN__.  Pedantic warnings are also disabled in the expression
4343           that follows "__extension__".  However, only system header files
4344           should use these escape routes; application programs should avoid
4345           them.
4346
4347           Some users try to use -Wpedantic to check programs for strict ISO C
4348           conformance.  They soon find that it does not do quite what they
4349           want: it finds some non-ISO practices, but not all---only those for
4350           which ISO C requires a diagnostic, and some others for which
4351           diagnostics have been added.
4352
4353           A feature to report any failure to conform to ISO C might be useful
4354           in some instances, but would require considerable additional work
4355           and would be quite different from -Wpedantic.  We don't have plans
4356           to support such a feature in the near future.
4357
4358           Where the standard specified with -std represents a GNU extended
4359           dialect of C, such as gnu90 or gnu99, there is a corresponding base
4360           standard, the version of ISO C on which the GNU extended dialect is
4361           based.  Warnings from -Wpedantic are given where they are required
4362           by the base standard.  (It does not make sense for such warnings to
4363           be given only for features not in the specified GNU C dialect,
4364           since by definition the GNU dialects of C include all features the
4365           compiler supports with the given option, and there would be nothing
4366           to warn about.)
4367
4368       -pedantic-errors
4369           Give an error whenever the base standard (see -Wpedantic) requires
4370           a diagnostic, in some cases where there is undefined behavior at
4371           compile-time and in some other cases that do not prevent
4372           compilation of programs that are valid according to the standard.
4373           This is not equivalent to -Werror=pedantic, since there are errors
4374           enabled by this option and not enabled by the latter and vice
4375           versa.
4376
4377       -Wall
4378           This enables all the warnings about constructions that some users
4379           consider questionable, and that are easy to avoid (or modify to
4380           prevent the warning), even in conjunction with macros.  This also
4381           enables some language-specific warnings described in C++ Dialect
4382           Options and Objective-C and Objective-C++ Dialect Options.
4383
4384           -Wall turns on the following warning flags:
4385
4386           -Waddress -Warray-bounds=1 (only with -O2) -Warray-parameter=2 (C
4387           and Objective-C only) -Wbool-compare -Wbool-operation
4388           -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++ and Objective-C++
4389           only) -Wchar-subscripts -Wcomment -Wduplicate-decl-specifier (C and
4390           Objective-C only) -Wenum-compare (in C/ObjC; this is on by default
4391           in C++) -Wformat -Wformat-overflow -Wformat-truncation
4392           -Wint-in-bool-context -Wimplicit (C and Objective-C only)
4393           -Wimplicit-int (C and Objective-C only)
4394           -Wimplicit-function-declaration (C and Objective-C only)
4395           -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only
4396           for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized
4397           -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation
4398           (only for C/C++) -Wmissing-attributes -Wmissing-braces (only for
4399           C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++)
4400           -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses
4401           -Wpessimizing-move (only for C++) -Wpointer-sign
4402           -Wrange-loop-construct (only for C++) -Wreorder -Wrestrict
4403           -Wreturn-type -Wsequence-point -Wsign-compare (only in C++)
4404           -Wsizeof-array-div -Wsizeof-pointer-div -Wsizeof-pointer-memaccess
4405           -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch
4406           -Wtautological-compare -Wtrigraphs -Wuninitialized
4407           -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value
4408           -Wunused-variable -Wvla-parameter (C and Objective-C only)
4409           -Wvolatile-register-var -Wzero-length-bounds
4410
4411           Note that some warning flags are not implied by -Wall.  Some of
4412           them warn about constructions that users generally do not consider
4413           questionable, but which occasionally you might wish to check for;
4414           others warn about constructions that are necessary or hard to avoid
4415           in some cases, and there is no simple way to modify the code to
4416           suppress the warning. Some of them are enabled by -Wextra but many
4417           of them must be enabled individually.
4418
4419       -Wextra
4420           This enables some extra warning flags that are not enabled by
4421           -Wall. (This option used to be called -W.  The older name is still
4422           supported, but the newer name is more descriptive.)
4423
4424           -Wclobbered -Wcast-function-type -Wdeprecated-copy (C++ only)
4425           -Wempty-body -Wenum-conversion (C only) -Wignored-qualifiers
4426           -Wimplicit-fallthrough=3 -Wmissing-field-initializers
4427           -Wmissing-parameter-type (C only) -Wold-style-declaration (C only)
4428           -Woverride-init -Wsign-compare (C only) -Wstring-compare
4429           -Wredundant-move (only for C++) -Wtype-limits -Wuninitialized
4430           -Wshift-negative-value (in C++03 and in C99 and newer)
4431           -Wunused-parameter (only with -Wunused or -Wall)
4432           -Wunused-but-set-parameter (only with -Wunused or -Wall)
4433
4434           The option -Wextra also prints warning messages for the following
4435           cases:
4436
4437           *   A pointer is compared against integer zero with "<", "<=", ">",
4438               or ">=".
4439
4440           *   (C++ only) An enumerator and a non-enumerator both appear in a
4441               conditional expression.
4442
4443           *   (C++ only) Ambiguous virtual bases.
4444
4445           *   (C++ only) Subscripting an array that has been declared
4446               "register".
4447
4448           *   (C++ only) Taking the address of a variable that has been
4449               declared "register".
4450
4451           *   (C++ only) A base class is not initialized in the copy
4452               constructor of a derived class.
4453
4454       -Wabi (C, Objective-C, C++ and Objective-C++ only)
4455           Warn about code affected by ABI changes.  This includes code that
4456           may not be compatible with the vendor-neutral C++ ABI as well as
4457           the psABI for the particular target.
4458
4459           Since G++ now defaults to updating the ABI with each major release,
4460           normally -Wabi warns only about C++ ABI compatibility problems if
4461           there is a check added later in a release series for an ABI issue
4462           discovered since the initial release.  -Wabi warns about more
4463           things if an older ABI version is selected (with -fabi-version=n).
4464
4465           -Wabi can also be used with an explicit version number to warn
4466           about C++ ABI compatibility with a particular -fabi-version level,
4467           e.g. -Wabi=2 to warn about changes relative to -fabi-version=2.
4468
4469           If an explicit version number is provided and -fabi-compat-version
4470           is not specified, the version number from this option is used for
4471           compatibility aliases.  If no explicit version number is provided
4472           with this option, but -fabi-compat-version is specified, that
4473           version number is used for C++ ABI warnings.
4474
4475           Although an effort has been made to warn about all such cases,
4476           there are probably some cases that are not warned about, even
4477           though G++ is generating incompatible code.  There may also be
4478           cases where warnings are emitted even though the code that is
4479           generated is compatible.
4480
4481           You should rewrite your code to avoid these warnings if you are
4482           concerned about the fact that code generated by G++ may not be
4483           binary compatible with code generated by other compilers.
4484
4485           Known incompatibilities in -fabi-version=2 (which was the default
4486           from GCC 3.4 to 4.9) include:
4487
4488           *   A template with a non-type template parameter of reference type
4489               was mangled incorrectly:
4490
4491                       extern int N;
4492                       template <int &> struct S {};
4493                       void n (S<N>) {2}
4494
4495               This was fixed in -fabi-version=3.
4496
4497           *   SIMD vector types declared using "__attribute ((vector_size))"
4498               were mangled in a non-standard way that does not allow for
4499               overloading of functions taking vectors of different sizes.
4500
4501               The mangling was changed in -fabi-version=4.
4502
4503           *   "__attribute ((const))" and "noreturn" were mangled as type
4504               qualifiers, and "decltype" of a plain declaration was folded
4505               away.
4506
4507               These mangling issues were fixed in -fabi-version=5.
4508
4509           *   Scoped enumerators passed as arguments to a variadic function
4510               are promoted like unscoped enumerators, causing "va_arg" to
4511               complain.  On most targets this does not actually affect the
4512               parameter passing ABI, as there is no way to pass an argument
4513               smaller than "int".
4514
4515               Also, the ABI changed the mangling of template argument packs,
4516               "const_cast", "static_cast", prefix increment/decrement, and a
4517               class scope function used as a template argument.
4518
4519               These issues were corrected in -fabi-version=6.
4520
4521           *   Lambdas in default argument scope were mangled incorrectly, and
4522               the ABI changed the mangling of "nullptr_t".
4523
4524               These issues were corrected in -fabi-version=7.
4525
4526           *   When mangling a function type with function-cv-qualifiers, the
4527               un-qualified function type was incorrectly treated as a
4528               substitution candidate.
4529
4530               This was fixed in -fabi-version=8, the default for GCC 5.1.
4531
4532           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading
4533               to unaligned accesses.  Note that this did not affect the ABI
4534               of a function with a "nullptr_t" parameter, as parameters have
4535               a minimum alignment.
4536
4537               This was fixed in -fabi-version=9, the default for GCC 5.2.
4538
4539           *   Target-specific attributes that affect the identity of a type,
4540               such as ia32 calling conventions on a function type (stdcall,
4541               regparm, etc.), did not affect the mangled name, leading to
4542               name collisions when function pointers were used as template
4543               arguments.
4544
4545               This was fixed in -fabi-version=10, the default for GCC 6.1.
4546
4547           This option also enables warnings about psABI-related changes.  The
4548           known psABI changes at this point include:
4549
4550           *   For SysV/x86-64, unions with "long double" members are passed
4551               in memory as specified in psABI.  Prior to GCC 4.4, this was
4552               not the case.  For example:
4553
4554                       union U {
4555                         long double ld;
4556                         int i;
4557                       };
4558
4559               "union U" is now always passed in memory.
4560
4561       -Wchar-subscripts
4562           Warn if an array subscript has type "char".  This is a common cause
4563           of error, as programmers often forget that this type is signed on
4564           some machines.  This warning is enabled by -Wall.
4565
4566       -Wno-coverage-mismatch
4567           Warn if feedback profiles do not match when using the -fprofile-use
4568           option.  If a source file is changed between compiling with
4569           -fprofile-generate and with -fprofile-use, the files with the
4570           profile feedback can fail to match the source file and GCC cannot
4571           use the profile feedback information.  By default, this warning is
4572           enabled and is treated as an error.  -Wno-coverage-mismatch can be
4573           used to disable the warning or -Wno-error=coverage-mismatch can be
4574           used to disable the error.  Disabling the error for this warning
4575           can result in poorly optimized code and is useful only in the case
4576           of very minor changes such as bug fixes to an existing code-base.
4577           Completely disabling the warning is not recommended.
4578
4579       -Wno-cpp
4580           (C, Objective-C, C++, Objective-C++ and Fortran only) Suppress
4581           warning messages emitted by "#warning" directives.
4582
4583       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
4584           Give a warning when a value of type "float" is implicitly promoted
4585           to "double".  CPUs with a 32-bit "single-precision" floating-point
4586           unit implement "float" in hardware, but emulate "double" in
4587           software.  On such a machine, doing computations using "double"
4588           values is much more expensive because of the overhead required for
4589           software emulation.
4590
4591           It is easy to accidentally do computations with "double" because
4592           floating-point literals are implicitly of type "double".  For
4593           example, in:
4594
4595                   float area(float radius)
4596                   {
4597                      return 3.14159 * radius * radius;
4598                   }
4599
4600           the compiler performs the entire computation with "double" because
4601           the floating-point literal is a "double".
4602
4603       -Wduplicate-decl-specifier (C and Objective-C only)
4604           Warn if a declaration has duplicate "const", "volatile", "restrict"
4605           or "_Atomic" specifier.  This warning is enabled by -Wall.
4606
4607       -Wformat
4608       -Wformat=n
4609           Check calls to "printf" and "scanf", etc., to make sure that the
4610           arguments supplied have types appropriate to the format string
4611           specified, and that the conversions specified in the format string
4612           make sense.  This includes standard functions, and others specified
4613           by format attributes, in the "printf", "scanf", "strftime" and
4614           "strfmon" (an X/Open extension, not in the C standard) families (or
4615           other target-specific families).  Which functions are checked
4616           without format attributes having been specified depends on the
4617           standard version selected, and such checks of functions without the
4618           attribute specified are disabled by -ffreestanding or -fno-builtin.
4619
4620           The formats are checked against the format features supported by
4621           GNU libc version 2.2.  These include all ISO C90 and C99 features,
4622           as well as features from the Single Unix Specification and some BSD
4623           and GNU extensions.  Other library implementations may not support
4624           all these features; GCC does not support warning about features
4625           that go beyond a particular library's limitations.  However, if
4626           -Wpedantic is used with -Wformat, warnings are given about format
4627           features not in the selected standard version (but not for
4628           "strfmon" formats, since those are not in any version of the C
4629           standard).
4630
4631           -Wformat=1
4632           -Wformat
4633               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is
4634               equivalent to -Wformat=0.  Since -Wformat also checks for null
4635               format arguments for several functions, -Wformat also implies
4636               -Wnonnull.  Some aspects of this level of format checking can
4637               be disabled by the options: -Wno-format-contains-nul,
4638               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat
4639               is enabled by -Wall.
4640
4641           -Wformat=2
4642               Enable -Wformat plus additional format checks.  Currently
4643               equivalent to -Wformat -Wformat-nonliteral -Wformat-security
4644               -Wformat-y2k.
4645
4646       -Wno-format-contains-nul
4647           If -Wformat is specified, do not warn about format strings that
4648           contain NUL bytes.
4649
4650       -Wno-format-extra-args
4651           If -Wformat is specified, do not warn about excess arguments to a
4652           "printf" or "scanf" format function.  The C standard specifies that
4653           such arguments are ignored.
4654
4655           Where the unused arguments lie between used arguments that are
4656           specified with $ operand number specifications, normally warnings
4657           are still given, since the implementation could not know what type
4658           to pass to "va_arg" to skip the unused arguments.  However, in the
4659           case of "scanf" formats, this option suppresses the warning if the
4660           unused arguments are all pointers, since the Single Unix
4661           Specification says that such unused arguments are allowed.
4662
4663       -Wformat-overflow
4664       -Wformat-overflow=level
4665           Warn about calls to formatted input/output functions such as
4666           "sprintf" and "vsprintf" that might overflow the destination
4667           buffer.  When the exact number of bytes written by a format
4668           directive cannot be determined at compile-time it is estimated
4669           based on heuristics that depend on the level argument and on
4670           optimization.  While enabling optimization will in most cases
4671           improve the accuracy of the warning, it may also result in false
4672           positives.
4673
4674           -Wformat-overflow
4675           -Wformat-overflow=1
4676               Level 1 of -Wformat-overflow enabled by -Wformat employs a
4677               conservative approach that warns only about calls that most
4678               likely overflow the buffer.  At this level, numeric arguments
4679               to format directives with unknown values are assumed to have
4680               the value of one, and strings of unknown length to be empty.
4681               Numeric arguments that are known to be bounded to a subrange of
4682               their type, or string arguments whose output is bounded either
4683               by their directive's precision or by a finite set of string
4684               literals, are assumed to take on the value within the range
4685               that results in the most bytes on output.  For example, the
4686               call to "sprintf" below is diagnosed because even with both a
4687               and b equal to zero, the terminating NUL character ('\0')
4688               appended by the function to the destination buffer will be
4689               written past its end.  Increasing the size of the buffer by a
4690               single byte is sufficient to avoid the warning, though it may
4691               not be sufficient to avoid the overflow.
4692
4693                       void f (int a, int b)
4694                       {
4695                         char buf [13];
4696                         sprintf (buf, "a = %i, b = %i\n", a, b);
4697                       }
4698
4699           -Wformat-overflow=2
4700               Level 2 warns also about calls that might overflow the
4701               destination buffer given an argument of sufficient length or
4702               magnitude.  At level 2, unknown numeric arguments are assumed
4703               to have the minimum representable value for signed types with a
4704               precision greater than 1, and the maximum representable value
4705               otherwise.  Unknown string arguments whose length cannot be
4706               assumed to be bounded either by the directive's precision, or
4707               by a finite set of string literals they may evaluate to, or the
4708               character array they may point to, are assumed to be 1
4709               character long.
4710
4711               At level 2, the call in the example above is again diagnosed,
4712               but this time because with a equal to a 32-bit "INT_MIN" the
4713               first %i directive will write some of its digits beyond the end
4714               of the destination buffer.  To make the call safe regardless of
4715               the values of the two variables, the size of the destination
4716               buffer must be increased to at least 34 bytes.  GCC includes
4717               the minimum size of the buffer in an informational note
4718               following the warning.
4719
4720               An alternative to increasing the size of the destination buffer
4721               is to constrain the range of formatted values.  The maximum
4722               length of string arguments can be bounded by specifying the
4723               precision in the format directive.  When numeric arguments of
4724               format directives can be assumed to be bounded by less than the
4725               precision of their type, choosing an appropriate length
4726               modifier to the format specifier will reduce the required
4727               buffer size.  For example, if a and b in the example above can
4728               be assumed to be within the precision of the "short int" type
4729               then using either the %hi format directive or casting the
4730               argument to "short" reduces the maximum required size of the
4731               buffer to 24 bytes.
4732
4733                       void f (int a, int b)
4734                       {
4735                         char buf [23];
4736                         sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
4737                       }
4738
4739       -Wno-format-zero-length
4740           If -Wformat is specified, do not warn about zero-length formats.
4741           The C standard specifies that zero-length formats are allowed.
4742
4743       -Wformat-nonliteral
4744           If -Wformat is specified, also warn if the format string is not a
4745           string literal and so cannot be checked, unless the format function
4746           takes its format arguments as a "va_list".
4747
4748       -Wformat-security
4749           If -Wformat is specified, also warn about uses of format functions
4750           that represent possible security problems.  At present, this warns
4751           about calls to "printf" and "scanf" functions where the format
4752           string is not a string literal and there are no format arguments,
4753           as in "printf (foo);".  This may be a security hole if the format
4754           string came from untrusted input and contains %n.  (This is
4755           currently a subset of what -Wformat-nonliteral warns about, but in
4756           future warnings may be added to -Wformat-security that are not
4757           included in -Wformat-nonliteral.)
4758
4759       -Wformat-signedness
4760           If -Wformat is specified, also warn if the format string requires
4761           an unsigned argument and the argument is signed and vice versa.
4762
4763       -Wformat-truncation
4764       -Wformat-truncation=level
4765           Warn about calls to formatted input/output functions such as
4766           "snprintf" and "vsnprintf" that might result in output truncation.
4767           When the exact number of bytes written by a format directive cannot
4768           be determined at compile-time it is estimated based on heuristics
4769           that depend on the level argument and on optimization.  While
4770           enabling optimization will in most cases improve the accuracy of
4771           the warning, it may also result in false positives.  Except as
4772           noted otherwise, the option uses the same logic -Wformat-overflow.
4773
4774           -Wformat-truncation
4775           -Wformat-truncation=1
4776               Level 1 of -Wformat-truncation enabled by -Wformat employs a
4777               conservative approach that warns only about calls to bounded
4778               functions whose return value is unused and that will most
4779               likely result in output truncation.
4780
4781           -Wformat-truncation=2
4782               Level 2 warns also about calls to bounded functions whose
4783               return value is used and that might result in truncation given
4784               an argument of sufficient length or magnitude.
4785
4786       -Wformat-y2k
4787           If -Wformat is specified, also warn about "strftime" formats that
4788           may yield only a two-digit year.
4789
4790       -Wnonnull
4791           Warn about passing a null pointer for arguments marked as requiring
4792           a non-null value by the "nonnull" function attribute.
4793
4794           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
4795           with the -Wno-nonnull option.
4796
4797       -Wnonnull-compare
4798           Warn when comparing an argument marked with the "nonnull" function
4799           attribute against null inside the function.
4800
4801           -Wnonnull-compare is included in -Wall.  It can be disabled with
4802           the -Wno-nonnull-compare option.
4803
4804       -Wnull-dereference
4805           Warn if the compiler detects paths that trigger erroneous or
4806           undefined behavior due to dereferencing a null pointer.  This
4807           option is only active when -fdelete-null-pointer-checks is active,
4808           which is enabled by optimizations in most targets.  The precision
4809           of the warnings depends on the optimization options used.
4810
4811       -Winit-self (C, C++, Objective-C and Objective-C++ only)
4812           Warn about uninitialized variables that are initialized with
4813           themselves.  Note this option can only be used with the
4814           -Wuninitialized option.
4815
4816           For example, GCC warns about "i" being uninitialized in the
4817           following snippet only when -Winit-self has been specified:
4818
4819                   int f()
4820                   {
4821                     int i = i;
4822                     return i;
4823                   }
4824
4825           This warning is enabled by -Wall in C++.
4826
4827       -Wno-implicit-int (C and Objective-C only)
4828           This option controls warnings when a declaration does not specify a
4829           type.  This warning is enabled by default in C99 and later dialects
4830           of C, and also by -Wall.
4831
4832       -Wno-implicit-function-declaration (C and Objective-C only)
4833           This option controls warnings when a function is used before being
4834           declared.  This warning is enabled by default in C99 and later
4835           dialects of C, and also by -Wall.  The warning is made into an
4836           error by -pedantic-errors.
4837
4838       -Wimplicit (C and Objective-C only)
4839           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
4840           warning is enabled by -Wall.
4841
4842       -Wimplicit-fallthrough
4843           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and
4844           -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0.
4845
4846       -Wimplicit-fallthrough=n
4847           Warn when a switch case falls through.  For example:
4848
4849                   switch (cond)
4850                     {
4851                     case 1:
4852                       a = 1;
4853                       break;
4854                     case 2:
4855                       a = 2;
4856                     case 3:
4857                       a = 3;
4858                       break;
4859                     }
4860
4861           This warning does not warn when the last statement of a case cannot
4862           fall through, e.g. when there is a return statement or a call to
4863           function declared with the noreturn attribute.
4864           -Wimplicit-fallthrough= also takes into account control flow
4865           statements, such as ifs, and only warns when appropriate.  E.g.
4866
4867                   switch (cond)
4868                     {
4869                     case 1:
4870                       if (i > 3) {
4871                         bar (5);
4872                         break;
4873                       } else if (i < 1) {
4874                         bar (0);
4875                       } else
4876                         return;
4877                     default:
4878                       ...
4879                     }
4880
4881           Since there are occasions where a switch case fall through is
4882           desirable, GCC provides an attribute, "__attribute__
4883           ((fallthrough))", that is to be used along with a null statement to
4884           suppress this warning that would normally occur:
4885
4886                   switch (cond)
4887                     {
4888                     case 1:
4889                       bar (0);
4890                       __attribute__ ((fallthrough));
4891                     default:
4892                       ...
4893                     }
4894
4895           C++17 provides a standard way to suppress the
4896           -Wimplicit-fallthrough warning using "[[fallthrough]];" instead of
4897           the GNU attribute.  In C++11 or C++14 users can use
4898           "[[gnu::fallthrough]];", which is a GNU extension.  Instead of
4899           these attributes, it is also possible to add a fallthrough comment
4900           to silence the warning.  The whole body of the C or C++ style
4901           comment should match the given regular expressions listed below.
4902           The option argument n specifies what kind of comments are accepted:
4903
4904           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
4905           *<-Wimplicit-fallthrough=1 matches ".*" regular>
4906               expression, any comment is used as fallthrough comment.
4907
4908           *<-Wimplicit-fallthrough=2 case insensitively matches>
4909               ".*falls?[ \t-]*thr(ough|u).*" regular expression.
4910
4911           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
4912               following regular expressions:
4913
4914               *<"-fallthrough">
4915               *<"@fallthrough@">
4916               *<"lint -fallthrough[ \t]*">
4917               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S |
4918               |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?">
4919               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s |
4920               |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?">
4921               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s |
4922               |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?">
4923           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
4924               following regular expressions:
4925
4926               *<"-fallthrough">
4927               *<"@fallthrough@">
4928               *<"lint -fallthrough[ \t]*">
4929               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
4930           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
4931               fallthrough comments, only attributes disable the warning.
4932
4933           The comment needs to be followed after optional whitespace and
4934           other comments by "case" or "default" keywords or by a user label
4935           that precedes some "case" or "default" label.
4936
4937                   switch (cond)
4938                     {
4939                     case 1:
4940                       bar (0);
4941                       /* FALLTHRU */
4942                     default:
4943                       ...
4944                     }
4945
4946           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.
4947
4948       -Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)
4949           Control if warnings triggered by the "warn_if_not_aligned"
4950           attribute should be issued.  These warnings are enabled by default.
4951
4952       -Wignored-qualifiers (C and C++ only)
4953           Warn if the return type of a function has a type qualifier such as
4954           "const".  For ISO C such a type qualifier has no effect, since the
4955           value returned by a function is not an lvalue.  For C++, the
4956           warning is only emitted for scalar types or "void".  ISO C
4957           prohibits qualified "void" return types on function definitions, so
4958           such return types always receive a warning even without this
4959           option.
4960
4961           This warning is also enabled by -Wextra.
4962
4963       -Wno-ignored-attributes (C and C++ only)
4964           This option controls warnings when an attribute is ignored.  This
4965           is different from the -Wattributes option in that it warns whenever
4966           the compiler decides to drop an attribute, not that the attribute
4967           is either unknown, used in a wrong place, etc.  This warning is
4968           enabled by default.
4969
4970       -Wmain
4971           Warn if the type of "main" is suspicious.  "main" should be a
4972           function with external linkage, returning int, taking either zero
4973           arguments, two, or three arguments of appropriate types.  This
4974           warning is enabled by default in C++ and is enabled by either -Wall
4975           or -Wpedantic.
4976
4977       -Wmisleading-indentation (C and C++ only)
4978           Warn when the indentation of the code does not reflect the block
4979           structure.  Specifically, a warning is issued for "if", "else",
4980           "while", and "for" clauses with a guarded statement that does not
4981           use braces, followed by an unguarded statement with the same
4982           indentation.
4983
4984           In the following example, the call to "bar" is misleadingly
4985           indented as if it were guarded by the "if" conditional.
4986
4987                     if (some_condition ())
4988                       foo ();
4989                       bar ();  /* Gotcha: this is not guarded by the "if".  */
4990
4991           In the case of mixed tabs and spaces, the warning uses the
4992           -ftabstop= option to determine if the statements line up
4993           (defaulting to 8).
4994
4995           The warning is not issued for code involving multiline preprocessor
4996           logic such as the following example.
4997
4998                     if (flagA)
4999                       foo (0);
5000                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
5001                     if (flagB)
5002                   #endif
5003                       foo (1);
5004
5005           The warning is not issued after a "#line" directive, since this
5006           typically indicates autogenerated code, and no assumptions can be
5007           made about the layout of the file that the directive references.
5008
5009           This warning is enabled by -Wall in C and C++.
5010
5011       -Wmissing-attributes
5012           Warn when a declaration of a function is missing one or more
5013           attributes that a related function is declared with and whose
5014           absence may adversely affect the correctness or efficiency of
5015           generated code.  For example, the warning is issued for
5016           declarations of aliases that use attributes to specify less
5017           restrictive requirements than those of their targets.  This
5018           typically represents a potential optimization opportunity.  By
5019           contrast, the -Wattribute-alias=2 option controls warnings issued
5020           when the alias is more restrictive than the target, which could
5021           lead to incorrect code generation.  Attributes considered include
5022           "alloc_align", "alloc_size", "cold", "const", "hot", "leaf",
5023           "malloc", "nonnull", "noreturn", "nothrow", "pure",
5024           "returns_nonnull", and "returns_twice".
5025
5026           In C++, the warning is issued when an explicit specialization of a
5027           primary template declared with attribute "alloc_align",
5028           "alloc_size", "assume_aligned", "format", "format_arg", "malloc",
5029           or "nonnull" is declared without it.  Attributes "deprecated",
5030           "error", and "warning" suppress the warning..
5031
5032           You can use the "copy" attribute to apply the same set of
5033           attributes to a declaration as that on another declaration without
5034           explicitly enumerating the attributes. This attribute can be
5035           applied to declarations of functions, variables, or types.
5036
5037           -Wmissing-attributes is enabled by -Wall.
5038
5039           For example, since the declaration of the primary function template
5040           below makes use of both attribute "malloc" and "alloc_size" the
5041           declaration of the explicit specialization of the template is
5042           diagnosed because it is missing one of the attributes.
5043
5044                   template <class T>
5045                   T* __attribute__ ((malloc, alloc_size (1)))
5046                   allocate (size_t);
5047
5048                   template <>
5049                   void* __attribute__ ((malloc))   // missing alloc_size
5050                   allocate<void> (size_t);
5051
5052       -Wmissing-braces
5053           Warn if an aggregate or union initializer is not fully bracketed.
5054           In the following example, the initializer for "a" is not fully
5055           bracketed, but that for "b" is fully bracketed.
5056
5057                   int a[2][2] = { 0, 1, 2, 3 };
5058                   int b[2][2] = { { 0, 1 }, { 2, 3 } };
5059
5060           This warning is enabled by -Wall.
5061
5062       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
5063           Warn if a user-supplied include directory does not exist.
5064
5065       -Wno-missing-profile
5066           This option controls warnings if feedback profiles are missing when
5067           using the -fprofile-use option.  This option diagnoses those cases
5068           where a new function or a new file is added between compiling with
5069           -fprofile-generate and with -fprofile-use, without regenerating the
5070           profiles.  In these cases, the profile feedback data files do not
5071           contain any profile feedback information for the newly added
5072           function or file respectively.  Also, in the case when profile
5073           count data (.gcda) files are removed, GCC cannot use any profile
5074           feedback information.  In all these cases, warnings are issued to
5075           inform you that a profile generation step is due.  Ignoring the
5076           warning can result in poorly optimized code.  -Wno-missing-profile
5077           can be used to disable the warning, but this is not recommended and
5078           should be done only when non-existent profile data is justified.
5079
5080       -Wno-mismatched-dealloc
5081           Warn for calls to deallocation functions with pointer arguments
5082           returned from from allocations functions for which the former isn't
5083           a suitable deallocator.  A pair of functions can be associated as
5084           matching allocators and deallocators by use of attribute "malloc".
5085           Unless disabled by the -fno-builtin option the standard functions
5086           "calloc", "malloc", "realloc", and "free", as well as the
5087           corresponding forms of C++ "operator new" and "operator delete" are
5088           implicitly associated as matching allocators and deallocators.  In
5089           the following example "mydealloc" is the deallocator for pointers
5090           returned from "myalloc".
5091
5092                   void mydealloc (void*);
5093
5094                   __attribute__ ((malloc (mydealloc, 1))) void*
5095                   myalloc (size_t);
5096
5097                   void f (void)
5098                   {
5099                     void *p = myalloc (32);
5100                     // ...use p...
5101                     free (p);   // warning: not a matching deallocator for myalloc
5102                     mydealloc (p);   // ok
5103                   }
5104
5105           In C++, the related option -Wmismatched-new-delete diagnoses
5106           mismatches involving either "operator new" or "operator delete".
5107
5108           Option -Wmismatched-dealloc is enabled by default.
5109
5110       -Wmultistatement-macros
5111           Warn about unsafe multiple statement macros that appear to be
5112           guarded by a clause such as "if", "else", "for", "switch", or
5113           "while", in which only the first statement is actually guarded
5114           after the macro is expanded.
5115
5116           For example:
5117
5118                   #define DOIT x++; y++
5119                   if (c)
5120                     DOIT;
5121
5122           will increment "y" unconditionally, not just when "c" holds.  The
5123           can usually be fixed by wrapping the macro in a do-while loop:
5124
5125                   #define DOIT do { x++; y++; } while (0)
5126                   if (c)
5127                     DOIT;
5128
5129           This warning is enabled by -Wall in C and C++.
5130
5131       -Wparentheses
5132           Warn if parentheses are omitted in certain contexts, such as when
5133           there is an assignment in a context where a truth value is
5134           expected, or when operators are nested whose precedence people
5135           often get confused about.
5136
5137           Also warn if a comparison like "x<=y<=z" appears; this is
5138           equivalent to "(x<=y ? 1 : 0) <= z", which is a different
5139           interpretation from that of ordinary mathematical notation.
5140
5141           Also warn for dangerous uses of the GNU extension to "?:" with
5142           omitted middle operand. When the condition in the "?": operator is
5143           a boolean expression, the omitted value is always 1.  Often
5144           programmers expect it to be a value computed inside the conditional
5145           expression instead.
5146
5147           For C++ this also warns for some cases of unnecessary parentheses
5148           in declarations, which can indicate an attempt at a function call
5149           instead of a declaration:
5150
5151                   {
5152                     // Declares a local variable called mymutex.
5153                     std::unique_lock<std::mutex> (mymutex);
5154                     // User meant std::unique_lock<std::mutex> lock (mymutex);
5155                   }
5156
5157           This warning is enabled by -Wall.
5158
5159       -Wsequence-point
5160           Warn about code that may have undefined semantics because of
5161           violations of sequence point rules in the C and C++ standards.
5162
5163           The C and C++ standards define the order in which expressions in a
5164           C/C++ program are evaluated in terms of sequence points, which
5165           represent a partial ordering between the execution of parts of the
5166           program: those executed before the sequence point, and those
5167           executed after it.  These occur after the evaluation of a full
5168           expression (one which is not part of a larger expression), after
5169           the evaluation of the first operand of a "&&", "||", "? :" or ","
5170           (comma) operator, before a function is called (but after the
5171           evaluation of its arguments and the expression denoting the called
5172           function), and in certain other places.  Other than as expressed by
5173           the sequence point rules, the order of evaluation of subexpressions
5174           of an expression is not specified.  All these rules describe only a
5175           partial order rather than a total order, since, for example, if two
5176           functions are called within one expression with no sequence point
5177           between them, the order in which the functions are called is not
5178           specified.  However, the standards committee have ruled that
5179           function calls do not overlap.
5180
5181           It is not specified when between sequence points modifications to
5182           the values of objects take effect.  Programs whose behavior depends
5183           on this have undefined behavior; the C and C++ standards specify
5184           that "Between the previous and next sequence point an object shall
5185           have its stored value modified at most once by the evaluation of an
5186           expression.  Furthermore, the prior value shall be read only to
5187           determine the value to be stored.".  If a program breaks these
5188           rules, the results on any particular implementation are entirely
5189           unpredictable.
5190
5191           Examples of code with undefined behavior are "a = a++;", "a[n] =
5192           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
5193           diagnosed by this option, and it may give an occasional false
5194           positive result, but in general it has been found fairly effective
5195           at detecting this sort of problem in programs.
5196
5197           The C++17 standard will define the order of evaluation of operands
5198           in more cases: in particular it requires that the right-hand side
5199           of an assignment be evaluated before the left-hand side, so the
5200           above examples are no longer undefined.  But this option will still
5201           warn about them, to help people avoid writing code that is
5202           undefined in C and earlier revisions of C++.
5203
5204           The standard is worded confusingly, therefore there is some debate
5205           over the precise meaning of the sequence point rules in subtle
5206           cases.  Links to discussions of the problem, including proposed
5207           formal definitions, may be found on the GCC readings page, at
5208           <http://gcc.gnu.org/readings.html>.
5209
5210           This warning is enabled by -Wall for C and C++.
5211
5212       -Wno-return-local-addr
5213           Do not warn about returning a pointer (or in C++, a reference) to a
5214           variable that goes out of scope after the function returns.
5215
5216       -Wreturn-type
5217           Warn whenever a function is defined with a return type that
5218           defaults to "int".  Also warn about any "return" statement with no
5219           return value in a function whose return type is not "void" (falling
5220           off the end of the function body is considered returning without a
5221           value).
5222
5223           For C only, warn about a "return" statement with an expression in a
5224           function whose return type is "void", unless the expression type is
5225           also "void".  As a GNU extension, the latter case is accepted
5226           without a warning unless -Wpedantic is used.  Attempting to use the
5227           return value of a non-"void" function other than "main" that flows
5228           off the end by reaching the closing curly brace that terminates the
5229           function is undefined.
5230
5231           Unlike in C, in C++, flowing off the end of a non-"void" function
5232           other than "main" results in undefined behavior even when the value
5233           of the function is not used.
5234
5235           This warning is enabled by default in C++ and by -Wall otherwise.
5236
5237       -Wno-shift-count-negative
5238           Controls warnings if a shift count is negative.  This warning is
5239           enabled by default.
5240
5241       -Wno-shift-count-overflow
5242           Controls warnings if a shift count is greater than or equal to the
5243           bit width of the type.  This warning is enabled by default.
5244
5245       -Wshift-negative-value
5246           Warn if left shifting a negative value.  This warning is enabled by
5247           -Wextra in C99 and C++11 modes (and newer).
5248
5249       -Wno-shift-overflow
5250       -Wshift-overflow=n
5251           These options control warnings about left shift overflows.
5252
5253           -Wshift-overflow=1
5254               This is the warning level of -Wshift-overflow and is enabled by
5255               default in C99 and C++11 modes (and newer).  This warning level
5256               does not warn about left-shifting 1 into the sign bit.
5257               (However, in C, such an overflow is still rejected in contexts
5258               where an integer constant expression is required.)  No warning
5259               is emitted in C++20 mode (and newer), as signed left shifts
5260               always wrap.
5261
5262           -Wshift-overflow=2
5263               This warning level also warns about left-shifting 1 into the
5264               sign bit, unless C++14 mode (or newer) is active.
5265
5266       -Wswitch
5267           Warn whenever a "switch" statement has an index of enumerated type
5268           and lacks a "case" for one or more of the named codes of that
5269           enumeration.  (The presence of a "default" label prevents this
5270           warning.)  "case" labels outside the enumeration range also provoke
5271           warnings when this option is used (even if there is a "default"
5272           label).  This warning is enabled by -Wall.
5273
5274       -Wswitch-default
5275           Warn whenever a "switch" statement does not have a "default" case.
5276
5277       -Wswitch-enum
5278           Warn whenever a "switch" statement has an index of enumerated type
5279           and lacks a "case" for one or more of the named codes of that
5280           enumeration.  "case" labels outside the enumeration range also
5281           provoke warnings when this option is used.  The only difference
5282           between -Wswitch and this option is that this option gives a
5283           warning about an omitted enumeration code even if there is a
5284           "default" label.
5285
5286       -Wno-switch-bool
5287           Do not warn when a "switch" statement has an index of boolean type
5288           and the case values are outside the range of a boolean type.  It is
5289           possible to suppress this warning by casting the controlling
5290           expression to a type other than "bool".  For example:
5291
5292                   switch ((int) (a == 4))
5293                     {
5294                     ...
5295                     }
5296
5297           This warning is enabled by default for C and C++ programs.
5298
5299       -Wno-switch-outside-range
5300           This option controls warnings when a "switch" case has a value that
5301           is outside of its respective type range.  This warning is enabled
5302           by default for C and C++ programs.
5303
5304       -Wno-switch-unreachable
5305           Do not warn when a "switch" statement contains statements between
5306           the controlling expression and the first case label, which will
5307           never be executed.  For example:
5308
5309                   switch (cond)
5310                     {
5311                      i = 15;
5312                     ...
5313                      case 5:
5314                     ...
5315                     }
5316
5317           -Wswitch-unreachable does not warn if the statement between the
5318           controlling expression and the first case label is just a
5319           declaration:
5320
5321                   switch (cond)
5322                     {
5323                      int i;
5324                     ...
5325                      case 5:
5326                      i = 5;
5327                     ...
5328                     }
5329
5330           This warning is enabled by default for C and C++ programs.
5331
5332       -Wsync-nand (C and C++ only)
5333           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
5334           built-in functions are used.  These functions changed semantics in
5335           GCC 4.4.
5336
5337       -Wunused-but-set-parameter
5338           Warn whenever a function parameter is assigned to, but otherwise
5339           unused (aside from its declaration).
5340
5341           To suppress this warning use the "unused" attribute.
5342
5343           This warning is also enabled by -Wunused together with -Wextra.
5344
5345       -Wunused-but-set-variable
5346           Warn whenever a local variable is assigned to, but otherwise unused
5347           (aside from its declaration).  This warning is enabled by -Wall.
5348
5349           To suppress this warning use the "unused" attribute.
5350
5351           This warning is also enabled by -Wunused, which is enabled by
5352           -Wall.
5353
5354       -Wunused-function
5355           Warn whenever a static function is declared but not defined or a
5356           non-inline static function is unused.  This warning is enabled by
5357           -Wall.
5358
5359       -Wunused-label
5360           Warn whenever a label is declared but not used.  This warning is
5361           enabled by -Wall.
5362
5363           To suppress this warning use the "unused" attribute.
5364
5365       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
5366           Warn when a typedef locally defined in a function is not used.
5367           This warning is enabled by -Wall.
5368
5369       -Wunused-parameter
5370           Warn whenever a function parameter is unused aside from its
5371           declaration.
5372
5373           To suppress this warning use the "unused" attribute.
5374
5375       -Wno-unused-result
5376           Do not warn if a caller of a function marked with attribute
5377           "warn_unused_result" does not use its return value. The default is
5378           -Wunused-result.
5379
5380       -Wunused-variable
5381           Warn whenever a local or static variable is unused aside from its
5382           declaration. This option implies -Wunused-const-variable=1 for C,
5383           but not for C++. This warning is enabled by -Wall.
5384
5385           To suppress this warning use the "unused" attribute.
5386
5387       -Wunused-const-variable
5388       -Wunused-const-variable=n
5389           Warn whenever a constant static variable is unused aside from its
5390           declaration.  -Wunused-const-variable=1 is enabled by
5391           -Wunused-variable for C, but not for C++. In C this declares
5392           variable storage, but in C++ this is not an error since const
5393           variables take the place of "#define"s.
5394
5395           To suppress this warning use the "unused" attribute.
5396
5397           -Wunused-const-variable=1
5398               This is the warning level that is enabled by -Wunused-variable
5399               for C.  It warns only about unused static const variables
5400               defined in the main compilation unit, but not about static
5401               const variables declared in any header included.
5402
5403           -Wunused-const-variable=2
5404               This warning level also warns for unused constant static
5405               variables in headers (excluding system headers).  This is the
5406               warning level of -Wunused-const-variable and must be explicitly
5407               requested since in C++ this isn't an error and in C it might be
5408               harder to clean up all headers included.
5409
5410       -Wunused-value
5411           Warn whenever a statement computes a result that is explicitly not
5412           used. To suppress this warning cast the unused expression to
5413           "void". This includes an expression-statement or the left-hand side
5414           of a comma expression that contains no side effects. For example,
5415           an expression such as "x[i,j]" causes a warning, while
5416           "x[(void)i,j]" does not.
5417
5418           This warning is enabled by -Wall.
5419
5420       -Wunused
5421           All the above -Wunused options combined.
5422
5423           In order to get a warning about an unused function parameter, you
5424           must either specify -Wextra -Wunused (note that -Wall implies
5425           -Wunused), or separately specify -Wunused-parameter.
5426
5427       -Wuninitialized
5428           Warn if an object with automatic or allocated storage duration is
5429           used without having been initialized.  In C++, also warn if a non-
5430           static reference or non-static "const" member appears in a class
5431           without constructors.
5432
5433           In addition, passing a pointer (or in C++, a reference) to an
5434           uninitialized object to a "const"-qualified argument of a built-in
5435           function known to read the object is also diagnosed by this
5436           warning.  (-Wmaybe-uninitialized is issued for ordinary functions.)
5437
5438           If you want to warn about code that uses the uninitialized value of
5439           the variable in its own initializer, use the -Winit-self option.
5440
5441           These warnings occur for individual uninitialized elements of
5442           structure, union or array variables as well as for variables that
5443           are uninitialized as a whole.  They do not occur for variables or
5444           elements declared "volatile".  Because these warnings depend on
5445           optimization, the exact variables or elements for which there are
5446           warnings depend on the precise optimization options and version of
5447           GCC used.
5448
5449           Note that there may be no warning about a variable that is used
5450           only to compute a value that itself is never used, because such
5451           computations may be deleted by data flow analysis before the
5452           warnings are printed.
5453
5454       -Wno-invalid-memory-model
5455           This option controls warnings for invocations of __atomic Builtins,
5456           __sync Builtins, and the C11 atomic generic functions with a memory
5457           consistency argument that is either invalid for the operation or
5458           outside the range of values of the "memory_order" enumeration.  For
5459           example, since the "__atomic_store" and "__atomic_store_n" built-
5460           ins are only defined for the relaxed, release, and sequentially
5461           consistent memory orders the following code is diagnosed:
5462
5463                   void store (int *i)
5464                   {
5465                     __atomic_store_n (i, 0, memory_order_consume);
5466                   }
5467
5468           -Winvalid-memory-model is enabled by default.
5469
5470       -Wmaybe-uninitialized
5471           For an object with automatic or allocated storage duration, if
5472           there exists a path from the function entry to a use of the object
5473           that is initialized, but there exist some other paths for which the
5474           object is not initialized, the compiler emits a warning if it
5475           cannot prove the uninitialized paths are not executed at run time.
5476
5477           In addition, passing a pointer (or in C++, a reference) to an
5478           uninitialized object to a "const"-qualified function argument is
5479           also diagnosed by this warning.  (-Wuninitialized is issued for
5480           built-in functions known to read the object.)  Annotating the
5481           function with attribute "access (none)" indicates that the argument
5482           isn't used to access the object and avoids the warning.
5483
5484           These warnings are only possible in optimizing compilation, because
5485           otherwise GCC does not keep track of the state of variables.
5486
5487           These warnings are made optional because GCC may not be able to
5488           determine when the code is correct in spite of appearing to have an
5489           error.  Here is one example of how this can happen:
5490
5491                   {
5492                     int x;
5493                     switch (y)
5494                       {
5495                       case 1: x = 1;
5496                         break;
5497                       case 2: x = 4;
5498                         break;
5499                       case 3: x = 5;
5500                       }
5501                     foo (x);
5502                   }
5503
5504           If the value of "y" is always 1, 2 or 3, then "x" is always
5505           initialized, but GCC doesn't know this. To suppress the warning,
5506           you need to provide a default case with assert(0) or similar code.
5507
5508           This option also warns when a non-volatile automatic variable might
5509           be changed by a call to "longjmp".  The compiler sees only the
5510           calls to "setjmp".  It cannot know where "longjmp" will be called;
5511           in fact, a signal handler could call it at any point in the code.
5512           As a result, you may get a warning even when there is in fact no
5513           problem because "longjmp" cannot in fact be called at the place
5514           that would cause a problem.
5515
5516           Some spurious warnings can be avoided if you declare all the
5517           functions you use that never return as "noreturn".
5518
5519           This warning is enabled by -Wall or -Wextra.
5520
5521       -Wunknown-pragmas
5522           Warn when a "#pragma" directive is encountered that is not
5523           understood by GCC.  If this command-line option is used, warnings
5524           are even issued for unknown pragmas in system header files.  This
5525           is not the case if the warnings are only enabled by the -Wall
5526           command-line option.
5527
5528       -Wno-pragmas
5529           Do not warn about misuses of pragmas, such as incorrect parameters,
5530           invalid syntax, or conflicts between pragmas.  See also
5531           -Wunknown-pragmas.
5532
5533       -Wno-prio-ctor-dtor
5534           Do not warn if a priority from 0 to 100 is used for constructor or
5535           destructor.  The use of constructor and destructor attributes allow
5536           you to assign a priority to the constructor/destructor to control
5537           its order of execution before "main" is called or after it returns.
5538           The priority values must be greater than 100 as the compiler
5539           reserves priority values between 0--100 for the implementation.
5540
5541       -Wstrict-aliasing
5542           This option is only active when -fstrict-aliasing is active.  It
5543           warns about code that might break the strict aliasing rules that
5544           the compiler is using for optimization.  The warning does not catch
5545           all cases, but does attempt to catch the more common pitfalls.  It
5546           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3
5547
5548       -Wstrict-aliasing=n
5549           This option is only active when -fstrict-aliasing is active.  It
5550           warns about code that might break the strict aliasing rules that
5551           the compiler is using for optimization.  Higher levels correspond
5552           to higher accuracy (fewer false positives).  Higher levels also
5553           correspond to more effort, similar to the way -O works.
5554           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.
5555
5556           Level 1: Most aggressive, quick, least accurate.  Possibly useful
5557           when higher levels do not warn but -fstrict-aliasing still breaks
5558           the code, as it has very few false negatives.  However, it has many
5559           false positives.  Warns for all pointer conversions between
5560           possibly incompatible types, even if never dereferenced.  Runs in
5561           the front end only.
5562
5563           Level 2: Aggressive, quick, not too precise.  May still have many
5564           false positives (not as many as level 1 though), and few false
5565           negatives (but possibly more than level 1).  Unlike level 1, it
5566           only warns when an address is taken.  Warns about incomplete types.
5567           Runs in the front end only.
5568
5569           Level 3 (default for -Wstrict-aliasing): Should have very few false
5570           positives and few false negatives.  Slightly slower than levels 1
5571           or 2 when optimization is enabled.  Takes care of the common
5572           pun+dereference pattern in the front end: "*(int*)&some_float".  If
5573           optimization is enabled, it also runs in the back end, where it
5574           deals with multiple statement cases using flow-sensitive points-to
5575           information.  Only warns when the converted pointer is
5576           dereferenced.  Does not warn about incomplete types.
5577
5578       -Wstrict-overflow
5579       -Wstrict-overflow=n
5580           This option is only active when signed overflow is undefined.  It
5581           warns about cases where the compiler optimizes based on the
5582           assumption that signed overflow does not occur.  Note that it does
5583           not warn about all cases where the code might overflow: it only
5584           warns about cases where the compiler implements some optimization.
5585           Thus this warning depends on the optimization level.
5586
5587           An optimization that assumes that signed overflow does not occur is
5588           perfectly safe if the values of the variables involved are such
5589           that overflow never does, in fact, occur.  Therefore this warning
5590           can easily give a false positive: a warning about code that is not
5591           actually a problem.  To help focus on important issues, several
5592           warning levels are defined.  No warnings are issued for the use of
5593           undefined signed overflow when estimating how many iterations a
5594           loop requires, in particular when determining whether a loop will
5595           be executed at all.
5596
5597           -Wstrict-overflow=1
5598               Warn about cases that are both questionable and easy to avoid.
5599               For example the compiler simplifies "x + 1 > x" to 1.  This
5600               level of -Wstrict-overflow is enabled by -Wall; higher levels
5601               are not, and must be explicitly requested.
5602
5603           -Wstrict-overflow=2
5604               Also warn about other cases where a comparison is simplified to
5605               a constant.  For example: "abs (x) >= 0".  This can only be
5606               simplified when signed integer overflow is undefined, because
5607               "abs (INT_MIN)" overflows to "INT_MIN", which is less than
5608               zero.  -Wstrict-overflow (with no level) is the same as
5609               -Wstrict-overflow=2.
5610
5611           -Wstrict-overflow=3
5612               Also warn about other cases where a comparison is simplified.
5613               For example: "x + 1 > 1" is simplified to "x > 0".
5614
5615           -Wstrict-overflow=4
5616               Also warn about other simplifications not covered by the above
5617               cases.  For example: "(x * 10) / 5" is simplified to "x * 2".
5618
5619           -Wstrict-overflow=5
5620               Also warn about cases where the compiler reduces the magnitude
5621               of a constant involved in a comparison.  For example: "x + 2 >
5622               y" is simplified to "x + 1 >= y".  This is reported only at the
5623               highest warning level because this simplification applies to
5624               many comparisons, so this warning level gives a very large
5625               number of false positives.
5626
5627       -Wstring-compare
5628           Warn for calls to "strcmp" and "strncmp" whose result is determined
5629           to be either zero or non-zero in tests for such equality owing to
5630           the length of one argument being greater than the size of the array
5631           the other argument is stored in (or the bound in the case of
5632           "strncmp").  Such calls could be mistakes.  For example, the call
5633           to "strcmp" below is diagnosed because its result is necessarily
5634           non-zero irrespective of the contents of the array "a".
5635
5636                   extern char a[4];
5637                   void f (char *d)
5638                   {
5639                     strcpy (d, "string");
5640                     ...
5641                     if (0 == strcmp (a, d))   // cannot be true
5642                       puts ("a and d are the same");
5643                   }
5644
5645           -Wstring-compare is enabled by -Wextra.
5646
5647       -Wno-stringop-overflow
5648       -Wstringop-overflow
5649       -Wstringop-overflow=type
5650           Warn for calls to string manipulation functions such as "memcpy"
5651           and "strcpy" that are determined to overflow the destination
5652           buffer.  The optional argument is one greater than the type of
5653           Object Size Checking to perform to determine the size of the
5654           destination.  The argument is meaningful only for functions that
5655           operate on character arrays but not for raw memory functions like
5656           "memcpy" which always make use of Object Size type-0.  The option
5657           also warns for calls that specify a size in excess of the largest
5658           possible object or at most "SIZE_MAX / 2" bytes.  The option
5659           produces the best results with optimization enabled but can detect
5660           a small subset of simple buffer overflows even without optimization
5661           in calls to the GCC built-in functions like "__builtin_memcpy" that
5662           correspond to the standard functions.  In any case, the option
5663           warns about just a subset of buffer overflows detected by the
5664           corresponding overflow checking built-ins.  For example, the option
5665           issues a warning for the "strcpy" call below because it copies at
5666           least 5 characters (the string "blue" including the terminating
5667           NUL) into the buffer of size 4.
5668
5669                   enum Color { blue, purple, yellow };
5670                   const char* f (enum Color clr)
5671                   {
5672                     static char buf [4];
5673                     const char *str;
5674                     switch (clr)
5675                       {
5676                         case blue: str = "blue"; break;
5677                         case purple: str = "purple"; break;
5678                         case yellow: str = "yellow"; break;
5679                       }
5680
5681                     return strcpy (buf, str);   // warning here
5682                   }
5683
5684           Option -Wstringop-overflow=2 is enabled by default.
5685
5686           -Wstringop-overflow
5687           -Wstringop-overflow=1
5688               The -Wstringop-overflow=1 option uses type-zero Object Size
5689               Checking to determine the sizes of destination objects.  At
5690               this setting the option does not warn for writes past the end
5691               of subobjects of larger objects accessed by pointers unless the
5692               size of the largest surrounding object is known.  When the
5693               destination may be one of several objects it is assumed to be
5694               the largest one of them.  On Linux systems, when optimization
5695               is enabled at this setting the option warns for the same code
5696               as when the "_FORTIFY_SOURCE" macro is defined to a non-zero
5697               value.
5698
5699           -Wstringop-overflow=2
5700               The -Wstringop-overflow=2 option uses type-one Object Size
5701               Checking to determine the sizes of destination objects.  At
5702               this setting the option warns about overflows when writing to
5703               members of the largest complete objects whose exact size is
5704               known.  However, it does not warn for excessive writes to the
5705               same members of unknown objects referenced by pointers since
5706               they may point to arrays containing unknown numbers of
5707               elements.  This is the default setting of the option.
5708
5709           -Wstringop-overflow=3
5710               The -Wstringop-overflow=3 option uses type-two Object Size
5711               Checking to determine the sizes of destination objects.  At
5712               this setting the option warns about overflowing the smallest
5713               object or data member.  This is the most restrictive setting of
5714               the option that may result in warnings for safe code.
5715
5716           -Wstringop-overflow=4
5717               The -Wstringop-overflow=4 option uses type-three Object Size
5718               Checking to determine the sizes of destination objects.  At
5719               this setting the option warns about overflowing any data
5720               members, and when the destination is one of several objects it
5721               uses the size of the largest of them to decide whether to issue
5722               a warning.  Similarly to -Wstringop-overflow=3 this setting of
5723               the option may result in warnings for benign code.
5724
5725       -Wno-stringop-overread
5726           Warn for calls to string manipulation functions such as "memchr",
5727           or "strcpy" that are determined to read past the end of the source
5728           sequence.
5729
5730           Option -Wstringop-overread is enabled by default.
5731
5732       -Wno-stringop-truncation
5733           Do not warn for calls to bounded string manipulation functions such
5734           as "strncat", "strncpy", and "stpncpy" that may either truncate the
5735           copied string or leave the destination unchanged.
5736
5737           In the following example, the call to "strncat" specifies a bound
5738           that is less than the length of the source string.  As a result,
5739           the copy of the source will be truncated and so the call is
5740           diagnosed.  To avoid the warning use "bufsize - strlen (buf) - 1)"
5741           as the bound.
5742
5743                   void append (char *buf, size_t bufsize)
5744                   {
5745                     strncat (buf, ".txt", 3);
5746                   }
5747
5748           As another example, the following call to "strncpy" results in
5749           copying to "d" just the characters preceding the terminating NUL,
5750           without appending the NUL to the end.  Assuming the result of
5751           "strncpy" is necessarily a NUL-terminated string is a common
5752           mistake, and so the call is diagnosed.  To avoid the warning when
5753           the result is not expected to be NUL-terminated, call "memcpy"
5754           instead.
5755
5756                   void copy (char *d, const char *s)
5757                   {
5758                     strncpy (d, s, strlen (s));
5759                   }
5760
5761           In the following example, the call to "strncpy" specifies the size
5762           of the destination buffer as the bound.  If the length of the
5763           source string is equal to or greater than this size the result of
5764           the copy will not be NUL-terminated.  Therefore, the call is also
5765           diagnosed.  To avoid the warning, specify "sizeof buf - 1" as the
5766           bound and set the last element of the buffer to "NUL".
5767
5768                   void copy (const char *s)
5769                   {
5770                     char buf[80];
5771                     strncpy (buf, s, sizeof buf);
5772                     ...
5773                   }
5774
5775           In situations where a character array is intended to store a
5776           sequence of bytes with no terminating "NUL" such an array may be
5777           annotated with attribute "nonstring" to avoid this warning.  Such
5778           arrays, however, are not suitable arguments to functions that
5779           expect "NUL"-terminated strings.  To help detect accidental misuses
5780           of such arrays GCC issues warnings unless it can prove that the use
5781           is safe.
5782
5783       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
5784           Warn for cases where adding an attribute may be beneficial. The
5785           attributes currently supported are listed below.
5786
5787           -Wsuggest-attribute=pure
5788           -Wsuggest-attribute=const
5789           -Wsuggest-attribute=noreturn
5790           -Wmissing-noreturn
5791           -Wsuggest-attribute=malloc
5792               Warn about functions that might be candidates for attributes
5793               "pure", "const" or "noreturn" or "malloc". The compiler only
5794               warns for functions visible in other compilation units or (in
5795               the case of "pure" and "const") if it cannot prove that the
5796               function returns normally. A function returns normally if it
5797               doesn't contain an infinite loop or return abnormally by
5798               throwing, calling "abort" or trapping.  This analysis requires
5799               option -fipa-pure-const, which is enabled by default at -O and
5800               higher.  Higher optimization levels improve the accuracy of the
5801               analysis.
5802
5803           -Wsuggest-attribute=format
5804           -Wmissing-format-attribute
5805               Warn about function pointers that might be candidates for
5806               "format" attributes.  Note these are only possible candidates,
5807               not absolute ones.  GCC guesses that function pointers with
5808               "format" attributes that are used in assignment,
5809               initialization, parameter passing or return statements should
5810               have a corresponding "format" attribute in the resulting type.
5811               I.e. the left-hand side of the assignment or initialization,
5812               the type of the parameter variable, or the return type of the
5813               containing function respectively should also have a "format"
5814               attribute to avoid the warning.
5815
5816               GCC also warns about function definitions that might be
5817               candidates for "format" attributes.  Again, these are only
5818               possible candidates.  GCC guesses that "format" attributes
5819               might be appropriate for any function that calls a function
5820               like "vprintf" or "vscanf", but this might not always be the
5821               case, and some functions for which "format" attributes are
5822               appropriate may not be detected.
5823
5824           -Wsuggest-attribute=cold
5825               Warn about functions that might be candidates for "cold"
5826               attribute.  This is based on static detection and generally
5827               only warns about functions which always leads to a call to
5828               another "cold" function such as wrappers of C++ "throw" or
5829               fatal error reporting functions leading to "abort".
5830
5831       -Walloc-zero
5832           Warn about calls to allocation functions decorated with attribute
5833           "alloc_size" that specify zero bytes, including those to the built-
5834           in forms of the functions "aligned_alloc", "alloca", "calloc",
5835           "malloc", and "realloc".  Because the behavior of these functions
5836           when called with a zero size differs among implementations (and in
5837           the case of "realloc" has been deprecated) relying on it may result
5838           in subtle portability bugs and should be avoided.
5839
5840       -Walloc-size-larger-than=byte-size
5841           Warn about calls to functions decorated with attribute "alloc_size"
5842           that attempt to allocate objects larger than the specified number
5843           of bytes, or where the result of the size computation in an integer
5844           type with infinite precision would exceed the value of PTRDIFF_MAX
5845           on the target.  -Walloc-size-larger-than=PTRDIFF_MAX is enabled by
5846           default.  Warnings controlled by the option can be disabled either
5847           by specifying byte-size of SIZE_MAX or more or by
5848           -Wno-alloc-size-larger-than.
5849
5850       -Wno-alloc-size-larger-than
5851           Disable -Walloc-size-larger-than= warnings.  The option is
5852           equivalent to -Walloc-size-larger-than=SIZE_MAX or larger.
5853
5854       -Walloca
5855           This option warns on all uses of "alloca" in the source.
5856
5857       -Walloca-larger-than=byte-size
5858           This option warns on calls to "alloca" with an integer argument
5859           whose value is either zero, or that is not bounded by a controlling
5860           predicate that limits its value to at most byte-size.  It also
5861           warns for calls to "alloca" where the bound value is unknown.
5862           Arguments of non-integer types are considered unbounded even if
5863           they appear to be constrained to the expected range.
5864
5865           For example, a bounded case of "alloca" could be:
5866
5867                   void func (size_t n)
5868                   {
5869                     void *p;
5870                     if (n <= 1000)
5871                       p = alloca (n);
5872                     else
5873                       p = malloc (n);
5874                     f (p);
5875                   }
5876
5877           In the above example, passing "-Walloca-larger-than=1000" would not
5878           issue a warning because the call to "alloca" is known to be at most
5879           1000 bytes.  However, if "-Walloca-larger-than=500" were passed,
5880           the compiler would emit a warning.
5881
5882           Unbounded uses, on the other hand, are uses of "alloca" with no
5883           controlling predicate constraining its integer argument.  For
5884           example:
5885
5886                   void func ()
5887                   {
5888                     void *p = alloca (n);
5889                     f (p);
5890                   }
5891
5892           If "-Walloca-larger-than=500" were passed, the above would trigger
5893           a warning, but this time because of the lack of bounds checking.
5894
5895           Note, that even seemingly correct code involving signed integers
5896           could cause a warning:
5897
5898                   void func (signed int n)
5899                   {
5900                     if (n < 500)
5901                       {
5902                         p = alloca (n);
5903                         f (p);
5904                       }
5905                   }
5906
5907           In the above example, n could be negative, causing a larger than
5908           expected argument to be implicitly cast into the "alloca" call.
5909
5910           This option also warns when "alloca" is used in a loop.
5911
5912           -Walloca-larger-than=PTRDIFF_MAX is enabled by default but is
5913           usually only effective  when -ftree-vrp is active (default for -O2
5914           and above).
5915
5916           See also -Wvla-larger-than=byte-size.
5917
5918       -Wno-alloca-larger-than
5919           Disable -Walloca-larger-than= warnings.  The option is equivalent
5920           to -Walloca-larger-than=SIZE_MAX or larger.
5921
5922       -Warith-conversion
5923           Do warn about implicit conversions from arithmetic operations even
5924           when conversion of the operands to the same type cannot change
5925           their values.  This affects warnings from -Wconversion,
5926           -Wfloat-conversion, and -Wsign-conversion.
5927
5928                   void f (char c, int i)
5929                   {
5930                     c = c + i; // warns with B<-Wconversion>
5931                     c = c + 1; // only warns with B<-Warith-conversion>
5932                   }
5933
5934       -Warray-bounds
5935       -Warray-bounds=n
5936           This option is only active when -ftree-vrp is active (default for
5937           -O2 and above). It warns about subscripts to arrays that are always
5938           out of bounds. This warning is enabled by -Wall.
5939
5940           -Warray-bounds=1
5941               This is the warning level of -Warray-bounds and is enabled by
5942               -Wall; higher levels are not, and must be explicitly requested.
5943
5944           -Warray-bounds=2
5945               This warning level also warns about out of bounds access for
5946               arrays at the end of a struct and for arrays accessed through
5947               pointers. This warning level may give a larger number of false
5948               positives and is deactivated by default.
5949
5950       -Warray-parameter
5951       -Warray-parameter=n
5952           Warn about redeclarations of functions involving arguments of array
5953           or pointer types of inconsistent kinds or forms, and enable the
5954           detection of out-of-bounds accesses to such parameters by warnings
5955           such as -Warray-bounds.
5956
5957           If the first function declaration uses the array form the bound
5958           specified in the array is assumed to be the minimum number of
5959           elements expected to be provided in calls to the function and the
5960           maximum number of elements accessed by it.  Failing to provide
5961           arguments of sufficient size or accessing more than the maximum
5962           number of elements may be diagnosed by warnings such as
5963           -Warray-bounds.  At level 1 the warning diagnoses inconsistencies
5964           involving array parameters declared using the "T[static N]" form.
5965
5966           For example, the warning triggers for the following redeclarations
5967           because the first one allows an array of any size to be passed to
5968           "f" while the second one with the keyword "static" specifies that
5969           the array argument must have at least four elements.
5970
5971                   void f (int[static 4]);
5972                   void f (int[]);           // warning (inconsistent array form)
5973
5974                   void g (void)
5975                   {
5976                     int *p = (int *)malloc (4);
5977                     f (p);                  // warning (array too small)
5978                     ...
5979                   }
5980
5981           At level 2 the warning also triggers for redeclarations involving
5982           any other inconsistency in array or pointer argument forms denoting
5983           array sizes.  Pointers and arrays of unspecified bound are
5984           considered equivalent and do not trigger a warning.
5985
5986                   void g (int*);
5987                   void g (int[]);     // no warning
5988                   void g (int[8]);    // warning (inconsistent array bound)
5989
5990           -Warray-parameter=2 is included in -Wall.  The -Wvla-parameter
5991           option triggers warnings for similar inconsistencies involving
5992           Variable Length Array arguments.
5993
5994       -Wattribute-alias=n
5995       -Wno-attribute-alias
5996           Warn about declarations using the "alias" and similar attributes
5997           whose target is incompatible with the type of the alias.
5998
5999           -Wattribute-alias=1
6000               The default warning level of the -Wattribute-alias option
6001               diagnoses incompatibilities between the type of the alias
6002               declaration and that of its target.  Such incompatibilities are
6003               typically indicative of bugs.
6004
6005           -Wattribute-alias=2
6006               At this level -Wattribute-alias also diagnoses cases where the
6007               attributes of the alias declaration are more restrictive than
6008               the attributes applied to its target.  These mismatches can
6009               potentially result in incorrect code generation.  In other
6010               cases they may be benign and could be resolved simply by adding
6011               the missing attribute to the target.  For comparison, see the
6012               -Wmissing-attributes option, which controls diagnostics when
6013               the alias declaration is less restrictive than the target,
6014               rather than more restrictive.
6015
6016               Attributes considered include "alloc_align", "alloc_size",
6017               "cold", "const", "hot", "leaf", "malloc", "nonnull",
6018               "noreturn", "nothrow", "pure", "returns_nonnull", and
6019               "returns_twice".
6020
6021           -Wattribute-alias is equivalent to -Wattribute-alias=1.  This is
6022           the default.  You can disable these warnings with either
6023           -Wno-attribute-alias or -Wattribute-alias=0.
6024
6025       -Wbool-compare
6026           Warn about boolean expression compared with an integer value
6027           different from "true"/"false".  For instance, the following
6028           comparison is always false:
6029
6030                   int n = 5;
6031                   ...
6032                   if ((n > 1) == 2) { ... }
6033
6034           This warning is enabled by -Wall.
6035
6036       -Wbool-operation
6037           Warn about suspicious operations on expressions of a boolean type.
6038           For instance, bitwise negation of a boolean is very likely a bug in
6039           the program.  For C, this warning also warns about incrementing or
6040           decrementing a boolean, which rarely makes sense.  (In C++,
6041           decrementing a boolean is always invalid.  Incrementing a boolean
6042           is invalid in C++17, and deprecated otherwise.)
6043
6044           This warning is enabled by -Wall.
6045
6046       -Wduplicated-branches
6047           Warn when an if-else has identical branches.  This warning detects
6048           cases like
6049
6050                   if (p != NULL)
6051                     return 0;
6052                   else
6053                     return 0;
6054
6055           It doesn't warn when both branches contain just a null statement.
6056           This warning also warn for conditional operators:
6057
6058                     int i = x ? *p : *p;
6059
6060       -Wduplicated-cond
6061           Warn about duplicated conditions in an if-else-if chain.  For
6062           instance, warn for the following code:
6063
6064                   if (p->q != NULL) { ... }
6065                   else if (p->q != NULL) { ... }
6066
6067       -Wframe-address
6068           Warn when the __builtin_frame_address or __builtin_return_address
6069           is called with an argument greater than 0.  Such calls may return
6070           indeterminate values or crash the program.  The warning is included
6071           in -Wall.
6072
6073       -Wno-discarded-qualifiers (C and Objective-C only)
6074           Do not warn if type qualifiers on pointers are being discarded.
6075           Typically, the compiler warns if a "const char *" variable is
6076           passed to a function that takes a "char *" parameter.  This option
6077           can be used to suppress such a warning.
6078
6079       -Wno-discarded-array-qualifiers (C and Objective-C only)
6080           Do not warn if type qualifiers on arrays which are pointer targets
6081           are being discarded.  Typically, the compiler warns if a "const int
6082           (*)[]" variable is passed to a function that takes a "int (*)[]"
6083           parameter.  This option can be used to suppress such a warning.
6084
6085       -Wno-incompatible-pointer-types (C and Objective-C only)
6086           Do not warn when there is a conversion between pointers that have
6087           incompatible types.  This warning is for cases not covered by
6088           -Wno-pointer-sign, which warns for pointer argument passing or
6089           assignment with different signedness.
6090
6091       -Wno-int-conversion (C and Objective-C only)
6092           Do not warn about incompatible integer to pointer and pointer to
6093           integer conversions.  This warning is about implicit conversions;
6094           for explicit conversions the warnings -Wno-int-to-pointer-cast and
6095           -Wno-pointer-to-int-cast may be used.
6096
6097       -Wzero-length-bounds
6098           Warn about accesses to elements of zero-length array members that
6099           might overlap other members of the same object.  Declaring interior
6100           zero-length arrays is discouraged because accesses to them are
6101           undefined.  See
6102
6103           For example, the first two stores in function "bad" are diagnosed
6104           because the array elements overlap the subsequent members "b" and
6105           "c".  The third store is diagnosed by -Warray-bounds because it is
6106           beyond the bounds of the enclosing object.
6107
6108                   struct X { int a[0]; int b, c; };
6109                   struct X x;
6110
6111                   void bad (void)
6112                   {
6113                     x.a[0] = 0;   // -Wzero-length-bounds
6114                     x.a[1] = 1;   // -Wzero-length-bounds
6115                     x.a[2] = 2;   // -Warray-bounds
6116                   }
6117
6118           Option -Wzero-length-bounds is enabled by -Warray-bounds.
6119
6120       -Wno-div-by-zero
6121           Do not warn about compile-time integer division by zero.  Floating-
6122           point division by zero is not warned about, as it can be a
6123           legitimate way of obtaining infinities and NaNs.
6124
6125       -Wsystem-headers
6126           Print warning messages for constructs found in system header files.
6127           Warnings from system headers are normally suppressed, on the
6128           assumption that they usually do not indicate real problems and
6129           would only make the compiler output harder to read.  Using this
6130           command-line option tells GCC to emit warnings from system headers
6131           as if they occurred in user code.  However, note that using -Wall
6132           in conjunction with this option does not warn about unknown pragmas
6133           in system headers---for that, -Wunknown-pragmas must also be used.
6134
6135       -Wtautological-compare
6136           Warn if a self-comparison always evaluates to true or false.  This
6137           warning detects various mistakes such as:
6138
6139                   int i = 1;
6140                   ...
6141                   if (i > i) { ... }
6142
6143           This warning also warns about bitwise comparisons that always
6144           evaluate to true or false, for instance:
6145
6146                   if ((a & 16) == 10) { ... }
6147
6148           will always be false.
6149
6150           This warning is enabled by -Wall.
6151
6152       -Wtrampolines
6153           Warn about trampolines generated for pointers to nested functions.
6154           A trampoline is a small piece of data or code that is created at
6155           run time on the stack when the address of a nested function is
6156           taken, and is used to call the nested function indirectly.  For
6157           some targets, it is made up of data only and thus requires no
6158           special treatment.  But, for most targets, it is made up of code
6159           and thus requires the stack to be made executable in order for the
6160           program to work properly.
6161
6162       -Wfloat-equal
6163           Warn if floating-point values are used in equality comparisons.
6164
6165           The idea behind this is that sometimes it is convenient (for the
6166           programmer) to consider floating-point values as approximations to
6167           infinitely precise real numbers.  If you are doing this, then you
6168           need to compute (by analyzing the code, or in some other way) the
6169           maximum or likely maximum error that the computation introduces,
6170           and allow for it when performing comparisons (and when producing
6171           output, but that's a different problem).  In particular, instead of
6172           testing for equality, you should check to see whether the two
6173           values have ranges that overlap; and this is done with the
6174           relational operators, so equality comparisons are probably
6175           mistaken.
6176
6177       -Wtraditional (C and Objective-C only)
6178           Warn about certain constructs that behave differently in
6179           traditional and ISO C.  Also warn about ISO C constructs that have
6180           no traditional C equivalent, and/or problematic constructs that
6181           should be avoided.
6182
6183           *   Macro parameters that appear within string literals in the
6184               macro body.  In traditional C macro replacement takes place
6185               within string literals, but in ISO C it does not.
6186
6187           *   In traditional C, some preprocessor directives did not exist.
6188               Traditional preprocessors only considered a line to be a
6189               directive if the # appeared in column 1 on the line.  Therefore
6190               -Wtraditional warns about directives that traditional C
6191               understands but ignores because the # does not appear as the
6192               first character on the line.  It also suggests you hide
6193               directives like "#pragma" not understood by traditional C by
6194               indenting them.  Some traditional implementations do not
6195               recognize "#elif", so this option suggests avoiding it
6196               altogether.
6197
6198           *   A function-like macro that appears without arguments.
6199
6200           *   The unary plus operator.
6201
6202           *   The U integer constant suffix, or the F or L floating-point
6203               constant suffixes.  (Traditional C does support the L suffix on
6204               integer constants.)  Note, these suffixes appear in macros
6205               defined in the system headers of most modern systems, e.g. the
6206               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
6207               code might normally lead to spurious warnings, however GCC's
6208               integrated preprocessor has enough context to avoid warning in
6209               these cases.
6210
6211           *   A function declared external in one block and then used after
6212               the end of the block.
6213
6214           *   A "switch" statement has an operand of type "long".
6215
6216           *   A non-"static" function declaration follows a "static" one.
6217               This construct is not accepted by some traditional C compilers.
6218
6219           *   The ISO type of an integer constant has a different width or
6220               signedness from its traditional type.  This warning is only
6221               issued if the base of the constant is ten.  I.e. hexadecimal or
6222               octal values, which typically represent bit patterns, are not
6223               warned about.
6224
6225           *   Usage of ISO string concatenation is detected.
6226
6227           *   Initialization of automatic aggregates.
6228
6229           *   Identifier conflicts with labels.  Traditional C lacks a
6230               separate namespace for labels.
6231
6232           *   Initialization of unions.  If the initializer is zero, the
6233               warning is omitted.  This is done under the assumption that the
6234               zero initializer in user code appears conditioned on e.g.
6235               "__STDC__" to avoid missing initializer warnings and relies on
6236               default initialization to zero in the traditional C case.
6237
6238           *   Conversions by prototypes between fixed/floating-point values
6239               and vice versa.  The absence of these prototypes when compiling
6240               with traditional C causes serious problems.  This is a subset
6241               of the possible conversion warnings; for the full set use
6242               -Wtraditional-conversion.
6243
6244           *   Use of ISO C style function definitions.  This warning
6245               intentionally is not issued for prototype declarations or
6246               variadic functions because these ISO C features appear in your
6247               code when using libiberty's traditional C compatibility macros,
6248               "PARAMS" and "VPARAMS".  This warning is also bypassed for
6249               nested functions because that feature is already a GCC
6250               extension and thus not relevant to traditional C compatibility.
6251
6252       -Wtraditional-conversion (C and Objective-C only)
6253           Warn if a prototype causes a type conversion that is different from
6254           what would happen to the same argument in the absence of a
6255           prototype.  This includes conversions of fixed point to floating
6256           and vice versa, and conversions changing the width or signedness of
6257           a fixed-point argument except when the same as the default
6258           promotion.
6259
6260       -Wdeclaration-after-statement (C and Objective-C only)
6261           Warn when a declaration is found after a statement in a block.
6262           This construct, known from C++, was introduced with ISO C99 and is
6263           by default allowed in GCC.  It is not supported by ISO C90.
6264
6265       -Wshadow
6266           Warn whenever a local variable or type declaration shadows another
6267           variable, parameter, type, class member (in C++), or instance
6268           variable (in Objective-C) or whenever a built-in function is
6269           shadowed.  Note that in C++, the compiler warns if a local variable
6270           shadows an explicit typedef, but not if it shadows a
6271           struct/class/enum.  If this warning is enabled, it includes also
6272           all instances of local shadowing.  This means that
6273           -Wno-shadow=local and -Wno-shadow=compatible-local are ignored when
6274           -Wshadow is used.  Same as -Wshadow=global.
6275
6276       -Wno-shadow-ivar (Objective-C only)
6277           Do not warn whenever a local variable shadows an instance variable
6278           in an Objective-C method.
6279
6280       -Wshadow=global
6281           Warn for any shadowing.  Same as -Wshadow.
6282
6283       -Wshadow=local
6284           Warn when a local variable shadows another local variable or
6285           parameter.
6286
6287       -Wshadow=compatible-local
6288           Warn when a local variable shadows another local variable or
6289           parameter whose type is compatible with that of the shadowing
6290           variable.  In C++, type compatibility here means the type of the
6291           shadowing variable can be converted to that of the shadowed
6292           variable.  The creation of this flag (in addition to
6293           -Wshadow=local) is based on the idea that when a local variable
6294           shadows another one of incompatible type, it is most likely
6295           intentional, not a bug or typo, as shown in the following example:
6296
6297                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
6298                   {
6299                     for (int i = 0; i < N; ++i)
6300                     {
6301                       ...
6302                     }
6303                     ...
6304                   }
6305
6306           Since the two variable "i" in the example above have incompatible
6307           types, enabling only -Wshadow=compatible-local does not emit a
6308           warning.  Because their types are incompatible, if a programmer
6309           accidentally uses one in place of the other, type checking is
6310           expected to catch that and emit an error or warning.  Use of this
6311           flag instead of -Wshadow=local can possibly reduce the number of
6312           warnings triggered by intentional shadowing.  Note that this also
6313           means that shadowing "const char *i" by "char *i" does not emit a
6314           warning.
6315
6316           This warning is also enabled by -Wshadow=local.
6317
6318       -Wlarger-than=byte-size
6319           Warn whenever an object is defined whose size exceeds byte-size.
6320           -Wlarger-than=PTRDIFF_MAX is enabled by default.  Warnings
6321           controlled by the option can be disabled either by specifying byte-
6322           size of SIZE_MAX or more or by -Wno-larger-than.
6323
6324           Also warn for calls to bounded functions such as "memchr" or
6325           "strnlen" that specify a bound greater than the largest possible
6326           object, which is PTRDIFF_MAX bytes by default.  These warnings can
6327           only be disabled by -Wno-larger-than.
6328
6329       -Wno-larger-than
6330           Disable -Wlarger-than= warnings.  The option is equivalent to
6331           -Wlarger-than=SIZE_MAX or larger.
6332
6333       -Wframe-larger-than=byte-size
6334           Warn if the size of a function frame exceeds byte-size.  The
6335           computation done to determine the stack frame size is approximate
6336           and not conservative.  The actual requirements may be somewhat
6337           greater than byte-size even if you do not get a warning.  In
6338           addition, any space allocated via "alloca", variable-length arrays,
6339           or related constructs is not included by the compiler when
6340           determining whether or not to issue a warning.
6341           -Wframe-larger-than=PTRDIFF_MAX is enabled by default.  Warnings
6342           controlled by the option can be disabled either by specifying byte-
6343           size of SIZE_MAX or more or by -Wno-frame-larger-than.
6344
6345       -Wno-frame-larger-than
6346           Disable -Wframe-larger-than= warnings.  The option is equivalent to
6347           -Wframe-larger-than=SIZE_MAX or larger.
6348
6349       -Wno-free-nonheap-object
6350           Warn when attempting to deallocate an object that was either not
6351           allocated on the heap, or by using a pointer that was not returned
6352           from a prior call to the corresponding allocation function.  For
6353           example, because the call to "stpcpy" returns a pointer to the
6354           terminating nul character and not to the begginning of the object,
6355           the call to "free" below is diagnosed.
6356
6357                   void f (char *p)
6358                   {
6359                     p = stpcpy (p, "abc");
6360                     // ...
6361                     free (p);   // warning
6362                   }
6363
6364           -Wfree-nonheap-object is enabled by default.
6365
6366       -Wstack-usage=byte-size
6367           Warn if the stack usage of a function might exceed byte-size.  The
6368           computation done to determine the stack usage is conservative.  Any
6369           space allocated via "alloca", variable-length arrays, or related
6370           constructs is included by the compiler when determining whether or
6371           not to issue a warning.
6372
6373           The message is in keeping with the output of -fstack-usage.
6374
6375           *   If the stack usage is fully static but exceeds the specified
6376               amount, it's:
6377
6378                         warning: stack usage is 1120 bytes
6379
6380           *   If the stack usage is (partly) dynamic but bounded, it's:
6381
6382                         warning: stack usage might be 1648 bytes
6383
6384           *   If the stack usage is (partly) dynamic and not bounded, it's:
6385
6386                         warning: stack usage might be unbounded
6387
6388           -Wstack-usage=PTRDIFF_MAX is enabled by default.  Warnings
6389           controlled by the option can be disabled either by specifying byte-
6390           size of SIZE_MAX or more or by -Wno-stack-usage.
6391
6392       -Wno-stack-usage
6393           Disable -Wstack-usage= warnings.  The option is equivalent to
6394           -Wstack-usage=SIZE_MAX or larger.
6395
6396       -Wunsafe-loop-optimizations
6397           Warn if the loop cannot be optimized because the compiler cannot
6398           assume anything on the bounds of the loop indices.  With
6399           -funsafe-loop-optimizations warn if the compiler makes such
6400           assumptions.
6401
6402       -Wno-pedantic-ms-format (MinGW targets only)
6403           When used in combination with -Wformat and -pedantic without GNU
6404           extensions, this option disables the warnings about non-ISO
6405           "printf" / "scanf" format width specifiers "I32", "I64", and "I"
6406           used on Windows targets, which depend on the MS runtime.
6407
6408       -Wpointer-arith
6409           Warn about anything that depends on the "size of" a function type
6410           or of "void".  GNU C assigns these types a size of 1, for
6411           convenience in calculations with "void *" pointers and pointers to
6412           functions.  In C++, warn also when an arithmetic operation involves
6413           "NULL".  This warning is also enabled by -Wpedantic.
6414
6415       -Wno-pointer-compare
6416           Do not warn if a pointer is compared with a zero character
6417           constant.  This usually means that the pointer was meant to be
6418           dereferenced.  For example:
6419
6420                   const char *p = foo ();
6421                   if (p == '\0')
6422                     return 42;
6423
6424           Note that the code above is invalid in C++11.
6425
6426           This warning is enabled by default.
6427
6428       -Wtsan
6429           Warn about unsupported features in ThreadSanitizer.
6430
6431           ThreadSanitizer does not support "std::atomic_thread_fence" and can
6432           report false positives.
6433
6434           This warning is enabled by default.
6435
6436       -Wtype-limits
6437           Warn if a comparison is always true or always false due to the
6438           limited range of the data type, but do not warn for constant
6439           expressions.  For example, warn if an unsigned variable is compared
6440           against zero with "<" or ">=".  This warning is also enabled by
6441           -Wextra.
6442
6443       -Wabsolute-value (C and Objective-C only)
6444           Warn for calls to standard functions that compute the absolute
6445           value of an argument when a more appropriate standard function is
6446           available.  For example, calling "abs(3.14)" triggers the warning
6447           because the appropriate function to call to compute the absolute
6448           value of a double argument is "fabs".  The option also triggers
6449           warnings when the argument in a call to such a function has an
6450           unsigned type.  This warning can be suppressed with an explicit
6451           type cast and it is also enabled by -Wextra.
6452
6453       -Wcomment
6454       -Wcomments
6455           Warn whenever a comment-start sequence /* appears in a /* comment,
6456           or whenever a backslash-newline appears in a // comment.  This
6457           warning is enabled by -Wall.
6458
6459       -Wtrigraphs
6460           Warn if any trigraphs are encountered that might change the meaning
6461           of the program.  Trigraphs within comments are not warned about,
6462           except those that would form escaped newlines.
6463
6464           This option is implied by -Wall.  If -Wall is not given, this
6465           option is still enabled unless trigraphs are enabled.  To get
6466           trigraph conversion without warnings, but get the other -Wall
6467           warnings, use -trigraphs -Wall -Wno-trigraphs.
6468
6469       -Wundef
6470           Warn if an undefined identifier is evaluated in an "#if" directive.
6471           Such identifiers are replaced with zero.
6472
6473       -Wexpansion-to-defined
6474           Warn whenever defined is encountered in the expansion of a macro
6475           (including the case where the macro is expanded by an #if
6476           directive).  Such usage is not portable.  This warning is also
6477           enabled by -Wpedantic and -Wextra.
6478
6479       -Wunused-macros
6480           Warn about macros defined in the main file that are unused.  A
6481           macro is used if it is expanded or tested for existence at least
6482           once.  The preprocessor also warns if the macro has not been used
6483           at the time it is redefined or undefined.
6484
6485           Built-in macros, macros defined on the command line, and macros
6486           defined in include files are not warned about.
6487
6488           Note: If a macro is actually used, but only used in skipped
6489           conditional blocks, then the preprocessor reports it as unused.  To
6490           avoid the warning in such a case, you might improve the scope of
6491           the macro's definition by, for example, moving it into the first
6492           skipped block.  Alternatively, you could provide a dummy use with
6493           something like:
6494
6495                   #if defined the_macro_causing_the_warning
6496                   #endif
6497
6498       -Wno-endif-labels
6499           Do not warn whenever an "#else" or an "#endif" are followed by
6500           text.  This sometimes happens in older programs with code of the
6501           form
6502
6503                   #if FOO
6504                   ...
6505                   #else FOO
6506                   ...
6507                   #endif FOO
6508
6509           The second and third "FOO" should be in comments.  This warning is
6510           on by default.
6511
6512       -Wbad-function-cast (C and Objective-C only)
6513           Warn when a function call is cast to a non-matching type.  For
6514           example, warn if a call to a function returning an integer type is
6515           cast to a pointer type.
6516
6517       -Wc90-c99-compat (C and Objective-C only)
6518           Warn about features not present in ISO C90, but present in ISO C99.
6519           For instance, warn about use of variable length arrays, "long long"
6520           type, "bool" type, compound literals, designated initializers, and
6521           so on.  This option is independent of the standards mode.  Warnings
6522           are disabled in the expression that follows "__extension__".
6523
6524       -Wc99-c11-compat (C and Objective-C only)
6525           Warn about features not present in ISO C99, but present in ISO C11.
6526           For instance, warn about use of anonymous structures and unions,
6527           "_Atomic" type qualifier, "_Thread_local" storage-class specifier,
6528           "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and
6529           so on.  This option is independent of the standards mode.  Warnings
6530           are disabled in the expression that follows "__extension__".
6531
6532       -Wc11-c2x-compat (C and Objective-C only)
6533           Warn about features not present in ISO C11, but present in ISO C2X.
6534           For instance, warn about omitting the string in "_Static_assert",
6535           use of [[]] syntax for attributes, use of decimal floating-point
6536           types, and so on.  This option is independent of the standards
6537           mode.  Warnings are disabled in the expression that follows
6538           "__extension__".
6539
6540       -Wc++-compat (C and Objective-C only)
6541           Warn about ISO C constructs that are outside of the common subset
6542           of ISO C and ISO C++, e.g. request for implicit conversion from
6543           "void *" to a pointer to non-"void" type.
6544
6545       -Wc++11-compat (C++ and Objective-C++ only)
6546           Warn about C++ constructs whose meaning differs between ISO C++
6547           1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
6548           keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and is
6549           enabled by -Wall.
6550
6551       -Wc++14-compat (C++ and Objective-C++ only)
6552           Warn about C++ constructs whose meaning differs between ISO C++
6553           2011 and ISO C++ 2014.  This warning is enabled by -Wall.
6554
6555       -Wc++17-compat (C++ and Objective-C++ only)
6556           Warn about C++ constructs whose meaning differs between ISO C++
6557           2014 and ISO C++ 2017.  This warning is enabled by -Wall.
6558
6559       -Wc++20-compat (C++ and Objective-C++ only)
6560           Warn about C++ constructs whose meaning differs between ISO C++
6561           2017 and ISO C++ 2020.  This warning is enabled by -Wall.
6562
6563       -Wcast-qual
6564           Warn whenever a pointer is cast so as to remove a type qualifier
6565           from the target type.  For example, warn if a "const char *" is
6566           cast to an ordinary "char *".
6567
6568           Also warn when making a cast that introduces a type qualifier in an
6569           unsafe way.  For example, casting "char **" to "const char **" is
6570           unsafe, as in this example:
6571
6572                     /* p is char ** value.  */
6573                     const char **q = (const char **) p;
6574                     /* Assignment of readonly string to const char * is OK.  */
6575                     *q = "string";
6576                     /* Now char** pointer points to read-only memory.  */
6577                     **p = 'b';
6578
6579       -Wcast-align
6580           Warn whenever a pointer is cast such that the required alignment of
6581           the target is increased.  For example, warn if a "char *" is cast
6582           to an "int *" on machines where integers can only be accessed at
6583           two- or four-byte boundaries.
6584
6585       -Wcast-align=strict
6586           Warn whenever a pointer is cast such that the required alignment of
6587           the target is increased.  For example, warn if a "char *" is cast
6588           to an "int *" regardless of the target machine.
6589
6590       -Wcast-function-type
6591           Warn when a function pointer is cast to an incompatible function
6592           pointer.  In a cast involving function types with a variable
6593           argument list only the types of initial arguments that are provided
6594           are considered.  Any parameter of pointer-type matches any other
6595           pointer-type.  Any benign differences in integral types are
6596           ignored, like "int" vs. "long" on ILP32 targets.  Likewise type
6597           qualifiers are ignored.  The function type "void (*) (void)" is
6598           special and matches everything, which can be used to suppress this
6599           warning.  In a cast involving pointer to member types this warning
6600           warns whenever the type cast is changing the pointer to member
6601           type.  This warning is enabled by -Wextra.
6602
6603       -Wwrite-strings
6604           When compiling C, give string constants the type "const
6605           char[length]" so that copying the address of one into a non-"const"
6606           "char *" pointer produces a warning.  These warnings help you find
6607           at compile time code that can try to write into a string constant,
6608           but only if you have been very careful about using "const" in
6609           declarations and prototypes.  Otherwise, it is just a nuisance.
6610           This is why we did not make -Wall request these warnings.
6611
6612           When compiling C++, warn about the deprecated conversion from
6613           string literals to "char *".  This warning is enabled by default
6614           for C++ programs.
6615
6616       -Wclobbered
6617           Warn for variables that might be changed by "longjmp" or "vfork".
6618           This warning is also enabled by -Wextra.
6619
6620       -Wconversion
6621           Warn for implicit conversions that may alter a value. This includes
6622           conversions between real and integer, like "abs (x)" when "x" is
6623           "double"; conversions between signed and unsigned, like "unsigned
6624           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
6625           not warn for explicit casts like "abs ((int) x)" and "ui =
6626           (unsigned) -1", or if the value is not changed by the conversion
6627           like in "abs (2.0)".  Warnings about conversions between signed and
6628           unsigned integers can be disabled by using -Wno-sign-conversion.
6629
6630           For C++, also warn for confusing overload resolution for user-
6631           defined conversions; and conversions that never use a type
6632           conversion operator: conversions to "void", the same type, a base
6633           class or a reference to them. Warnings about conversions between
6634           signed and unsigned integers are disabled by default in C++ unless
6635           -Wsign-conversion is explicitly enabled.
6636
6637           Warnings about conversion from arithmetic on a small type back to
6638           that type are only given with -Warith-conversion.
6639
6640       -Wdangling-else
6641           Warn about constructions where there may be confusion to which "if"
6642           statement an "else" branch belongs.  Here is an example of such a
6643           case:
6644
6645                   {
6646                     if (a)
6647                       if (b)
6648                         foo ();
6649                     else
6650                       bar ();
6651                   }
6652
6653           In C/C++, every "else" branch belongs to the innermost possible
6654           "if" statement, which in this example is "if (b)".  This is often
6655           not what the programmer expected, as illustrated in the above
6656           example by indentation the programmer chose.  When there is the
6657           potential for this confusion, GCC issues a warning when this flag
6658           is specified.  To eliminate the warning, add explicit braces around
6659           the innermost "if" statement so there is no way the "else" can
6660           belong to the enclosing "if".  The resulting code looks like this:
6661
6662                   {
6663                     if (a)
6664                       {
6665                         if (b)
6666                           foo ();
6667                         else
6668                           bar ();
6669                       }
6670                   }
6671
6672           This warning is enabled by -Wparentheses.
6673
6674       -Wdate-time
6675           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are
6676           encountered as they might prevent bit-wise-identical reproducible
6677           compilations.
6678
6679       -Wempty-body
6680           Warn if an empty body occurs in an "if", "else" or "do while"
6681           statement.  This warning is also enabled by -Wextra.
6682
6683       -Wno-endif-labels
6684           Do not warn about stray tokens after "#else" and "#endif".
6685
6686       -Wenum-compare
6687           Warn about a comparison between values of different enumerated
6688           types.  In C++ enumerated type mismatches in conditional
6689           expressions are also diagnosed and the warning is enabled by
6690           default.  In C this warning is enabled by -Wall.
6691
6692       -Wenum-conversion
6693           Warn when a value of enumerated type is implicitly converted to a
6694           different enumerated type.  This warning is enabled by -Wextra in
6695           C.
6696
6697       -Wjump-misses-init (C, Objective-C only)
6698           Warn if a "goto" statement or a "switch" statement jumps forward
6699           across the initialization of a variable, or jumps backward to a
6700           label after the variable has been initialized.  This only warns
6701           about variables that are initialized when they are declared.  This
6702           warning is only supported for C and Objective-C; in C++ this sort
6703           of branch is an error in any case.
6704
6705           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
6706           with the -Wno-jump-misses-init option.
6707
6708       -Wsign-compare
6709           Warn when a comparison between signed and unsigned values could
6710           produce an incorrect result when the signed value is converted to
6711           unsigned.  In C++, this warning is also enabled by -Wall.  In C, it
6712           is also enabled by -Wextra.
6713
6714       -Wsign-conversion
6715           Warn for implicit conversions that may change the sign of an
6716           integer value, like assigning a signed integer expression to an
6717           unsigned integer variable. An explicit cast silences the warning.
6718           In C, this option is enabled also by -Wconversion.
6719
6720       -Wfloat-conversion
6721           Warn for implicit conversions that reduce the precision of a real
6722           value.  This includes conversions from real to integer, and from
6723           higher precision real to lower precision real values.  This option
6724           is also enabled by -Wconversion.
6725
6726       -Wno-scalar-storage-order
6727           Do not warn on suspicious constructs involving reverse scalar
6728           storage order.
6729
6730       -Wsizeof-array-div
6731           Warn about divisions of two sizeof operators when the first one is
6732           applied to an array and the divisor does not equal the size of the
6733           array element.  In such a case, the computation will not yield the
6734           number of elements in the array, which is likely what the user
6735           intended.  This warning warns e.g. about
6736
6737                   int fn ()
6738                   {
6739                     int arr[10];
6740                     return sizeof (arr) / sizeof (short);
6741                   }
6742
6743           This warning is enabled by -Wall.
6744
6745       -Wsizeof-pointer-div
6746           Warn for suspicious divisions of two sizeof expressions that divide
6747           the pointer size by the element size, which is the usual way to
6748           compute the array size but won't work out correctly with pointers.
6749           This warning warns e.g. about "sizeof (ptr) / sizeof (ptr[0])" if
6750           "ptr" is not an array, but a pointer.  This warning is enabled by
6751           -Wall.
6752
6753       -Wsizeof-pointer-memaccess
6754           Warn for suspicious length parameters to certain string and memory
6755           built-in functions if the argument uses "sizeof".  This warning
6756           triggers for example for "memset (ptr, 0, sizeof (ptr));" if "ptr"
6757           is not an array, but a pointer, and suggests a possible fix, or
6758           about "memcpy (&foo, ptr, sizeof (&foo));".
6759           -Wsizeof-pointer-memaccess also warns about calls to bounded string
6760           copy functions like "strncat" or "strncpy" that specify as the
6761           bound a "sizeof" expression of the source array.  For example, in
6762           the following function the call to "strncat" specifies the size of
6763           the source string as the bound.  That is almost certainly a mistake
6764           and so the call is diagnosed.
6765
6766                   void make_file (const char *name)
6767                   {
6768                     char path[PATH_MAX];
6769                     strncpy (path, name, sizeof path - 1);
6770                     strncat (path, ".text", sizeof ".text");
6771                     ...
6772                   }
6773
6774           The -Wsizeof-pointer-memaccess option is enabled by -Wall.
6775
6776       -Wno-sizeof-array-argument
6777           Do not warn when the "sizeof" operator is applied to a parameter
6778           that is declared as an array in a function definition.  This
6779           warning is enabled by default for C and C++ programs.
6780
6781       -Wmemset-elt-size
6782           Warn for suspicious calls to the "memset" built-in function, if the
6783           first argument references an array, and the third argument is a
6784           number equal to the number of elements, but not equal to the size
6785           of the array in memory.  This indicates that the user has omitted a
6786           multiplication by the element size.  This warning is enabled by
6787           -Wall.
6788
6789       -Wmemset-transposed-args
6790           Warn for suspicious calls to the "memset" built-in function where
6791           the second argument is not zero and the third argument is zero.
6792           For example, the call "memset (buf, sizeof buf, 0)" is diagnosed
6793           because "memset (buf, 0, sizeof buf)" was meant instead.  The
6794           diagnostic is only emitted if the third argument is a literal zero.
6795           Otherwise, if it is an expression that is folded to zero, or a cast
6796           of zero to some type, it is far less likely that the arguments have
6797           been mistakenly transposed and no warning is emitted.  This warning
6798           is enabled by -Wall.
6799
6800       -Waddress
6801           Warn about suspicious uses of memory addresses. These include using
6802           the address of a function in a conditional expression, such as
6803           "void func(void); if (func)", and comparisons against the memory
6804           address of a string literal, such as "if (x == "abc")".  Such uses
6805           typically indicate a programmer error: the address of a function
6806           always evaluates to true, so their use in a conditional usually
6807           indicate that the programmer forgot the parentheses in a function
6808           call; and comparisons against string literals result in unspecified
6809           behavior and are not portable in C, so they usually indicate that
6810           the programmer intended to use "strcmp".  This warning is enabled
6811           by -Wall.
6812
6813       -Wno-address-of-packed-member
6814           Do not warn when the address of packed member of struct or union is
6815           taken, which usually results in an unaligned pointer value.  This
6816           is enabled by default.
6817
6818       -Wlogical-op
6819           Warn about suspicious uses of logical operators in expressions.
6820           This includes using logical operators in contexts where a bit-wise
6821           operator is likely to be expected.  Also warns when the operands of
6822           a logical operator are the same:
6823
6824                   extern int a;
6825                   if (a < 0 && a < 0) { ... }
6826
6827       -Wlogical-not-parentheses
6828           Warn about logical not used on the left hand side operand of a
6829           comparison.  This option does not warn if the right operand is
6830           considered to be a boolean expression.  Its purpose is to detect
6831           suspicious code like the following:
6832
6833                   int a;
6834                   ...
6835                   if (!a > 1) { ... }
6836
6837           It is possible to suppress the warning by wrapping the LHS into
6838           parentheses:
6839
6840                   if ((!a) > 1) { ... }
6841
6842           This warning is enabled by -Wall.
6843
6844       -Waggregate-return
6845           Warn if any functions that return structures or unions are defined
6846           or called.  (In languages where you can return an array, this also
6847           elicits a warning.)
6848
6849       -Wno-aggressive-loop-optimizations
6850           Warn if in a loop with constant number of iterations the compiler
6851           detects undefined behavior in some statement during one or more of
6852           the iterations.
6853
6854       -Wno-attributes
6855           Do not warn if an unexpected "__attribute__" is used, such as
6856           unrecognized attributes, function attributes applied to variables,
6857           etc.  This does not stop errors for incorrect use of supported
6858           attributes.
6859
6860       -Wno-builtin-declaration-mismatch
6861           Warn if a built-in function is declared with an incompatible
6862           signature or as a non-function, or when a built-in function
6863           declared with a type that does not include a prototype is called
6864           with arguments whose promoted types do not match those expected by
6865           the function.  When -Wextra is specified, also warn when a built-in
6866           function that takes arguments is declared without a prototype.  The
6867           -Wbuiltin-declaration-mismatch warning is enabled by default.  To
6868           avoid the warning include the appropriate header to bring the
6869           prototypes of built-in functions into scope.
6870
6871           For example, the call to "memset" below is diagnosed by the warning
6872           because the function expects a value of type "size_t" as its
6873           argument but the type of 32 is "int".  With -Wextra, the
6874           declaration of the function is diagnosed as well.
6875
6876                   extern void* memset ();
6877                   void f (void *d)
6878                   {
6879                     memset (d, '\0', 32);
6880                   }
6881
6882       -Wno-builtin-macro-redefined
6883           Do not warn if certain built-in macros are redefined.  This
6884           suppresses warnings for redefinition of "__TIMESTAMP__",
6885           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".
6886
6887       -Wstrict-prototypes (C and Objective-C only)
6888           Warn if a function is declared or defined without specifying the
6889           argument types.  (An old-style function definition is permitted
6890           without a warning if preceded by a declaration that specifies the
6891           argument types.)
6892
6893       -Wold-style-declaration (C and Objective-C only)
6894           Warn for obsolescent usages, according to the C Standard, in a
6895           declaration. For example, warn if storage-class specifiers like
6896           "static" are not the first things in a declaration.  This warning
6897           is also enabled by -Wextra.
6898
6899       -Wold-style-definition (C and Objective-C only)
6900           Warn if an old-style function definition is used.  A warning is
6901           given even if there is a previous prototype.  A definition using ()
6902           is not considered an old-style definition in C2X mode, because it
6903           is equivalent to (void) in that case, but is considered an old-
6904           style definition for older standards.
6905
6906       -Wmissing-parameter-type (C and Objective-C only)
6907           A function parameter is declared without a type specifier in
6908           K&R-style functions:
6909
6910                   void foo(bar) { }
6911
6912           This warning is also enabled by -Wextra.
6913
6914       -Wmissing-prototypes (C and Objective-C only)
6915           Warn if a global function is defined without a previous prototype
6916           declaration.  This warning is issued even if the definition itself
6917           provides a prototype.  Use this option to detect global functions
6918           that do not have a matching prototype declaration in a header file.
6919           This option is not valid for C++ because all function declarations
6920           provide prototypes and a non-matching declaration declares an
6921           overload rather than conflict with an earlier declaration.  Use
6922           -Wmissing-declarations to detect missing declarations in C++.
6923
6924       -Wmissing-declarations
6925           Warn if a global function is defined without a previous
6926           declaration.  Do so even if the definition itself provides a
6927           prototype.  Use this option to detect global functions that are not
6928           declared in header files.  In C, no warnings are issued for
6929           functions with previous non-prototype declarations; use
6930           -Wmissing-prototypes to detect missing prototypes.  In C++, no
6931           warnings are issued for function templates, or for inline
6932           functions, or for functions in anonymous namespaces.
6933
6934       -Wmissing-field-initializers
6935           Warn if a structure's initializer has some fields missing.  For
6936           example, the following code causes such a warning, because "x.h" is
6937           implicitly zero:
6938
6939                   struct s { int f, g, h; };
6940                   struct s x = { 3, 4 };
6941
6942           This option does not warn about designated initializers, so the
6943           following modification does not trigger a warning:
6944
6945                   struct s { int f, g, h; };
6946                   struct s x = { .f = 3, .g = 4 };
6947
6948           In C this option does not warn about the universal zero initializer
6949           { 0 }:
6950
6951                   struct s { int f, g, h; };
6952                   struct s x = { 0 };
6953
6954           Likewise, in C++ this option does not warn about the empty { }
6955           initializer, for example:
6956
6957                   struct s { int f, g, h; };
6958                   s x = { };
6959
6960           This warning is included in -Wextra.  To get other -Wextra warnings
6961           without this one, use -Wextra -Wno-missing-field-initializers.
6962
6963       -Wno-multichar
6964           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
6965           they indicate a typo in the user's code, as they have
6966           implementation-defined values, and should not be used in portable
6967           code.
6968
6969       -Wnormalized=[none|id|nfc|nfkc]
6970           In ISO C and ISO C++, two identifiers are different if they are
6971           different sequences of characters.  However, sometimes when
6972           characters outside the basic ASCII character set are used, you can
6973           have two different character sequences that look the same.  To
6974           avoid confusion, the ISO 10646 standard sets out some normalization
6975           rules which when applied ensure that two sequences that look the
6976           same are turned into the same sequence.  GCC can warn you if you
6977           are using identifiers that have not been normalized; this option
6978           controls that warning.
6979
6980           There are four levels of warning supported by GCC.  The default is
6981           -Wnormalized=nfc, which warns about any identifier that is not in
6982           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
6983           form for most uses.  It is equivalent to -Wnormalized.
6984
6985           Unfortunately, there are some characters allowed in identifiers by
6986           ISO C and ISO C++ that, when turned into NFC, are not allowed in
6987           identifiers.  That is, there's no way to use these symbols in
6988           portable ISO C or C++ and have all your identifiers in NFC.
6989           -Wnormalized=id suppresses the warning for these characters.  It is
6990           hoped that future versions of the standards involved will correct
6991           this, which is why this option is not the default.
6992
6993           You can switch the warning off for all characters by writing
6994           -Wnormalized=none or -Wno-normalized.  You should only do this if
6995           you are using some other normalization scheme (like "D"), because
6996           otherwise you can easily create bugs that are literally impossible
6997           to see.
6998
6999           Some characters in ISO 10646 have distinct meanings but look
7000           identical in some fonts or display methodologies, especially once
7001           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
7002           LATIN SMALL LETTER N", displays just like a regular "n" that has
7003           been placed in a superscript.  ISO 10646 defines the NFKC
7004           normalization scheme to convert all these into a standard form as
7005           well, and GCC warns if your code is not in NFKC if you use
7006           -Wnormalized=nfkc.  This warning is comparable to warning about
7007           every identifier that contains the letter O because it might be
7008           confused with the digit 0, and so is not the default, but may be
7009           useful as a local coding convention if the programming environment
7010           cannot be fixed to display these characters distinctly.
7011
7012       -Wno-attribute-warning
7013           Do not warn about usage of functions declared with "warning"
7014           attribute.  By default, this warning is enabled.
7015           -Wno-attribute-warning can be used to disable the warning or
7016           -Wno-error=attribute-warning can be used to disable the error when
7017           compiled with -Werror flag.
7018
7019       -Wno-deprecated
7020           Do not warn about usage of deprecated features.
7021
7022       -Wno-deprecated-declarations
7023           Do not warn about uses of functions, variables, and types marked as
7024           deprecated by using the "deprecated" attribute.
7025
7026       -Wno-overflow
7027           Do not warn about compile-time overflow in constant expressions.
7028
7029       -Wno-odr
7030           Warn about One Definition Rule violations during link-time
7031           optimization.  Enabled by default.
7032
7033       -Wopenmp-simd
7034           Warn if the vectorizer cost model overrides the OpenMP simd
7035           directive set by user.  The -fsimd-cost-model=unlimited option can
7036           be used to relax the cost model.
7037
7038       -Woverride-init (C and Objective-C only)
7039           Warn if an initialized field without side effects is overridden
7040           when using designated initializers.
7041
7042           This warning is included in -Wextra.  To get other -Wextra warnings
7043           without this one, use -Wextra -Wno-override-init.
7044
7045       -Wno-override-init-side-effects (C and Objective-C only)
7046           Do not warn if an initialized field with side effects is overridden
7047           when using designated initializers.  This warning is enabled by
7048           default.
7049
7050       -Wpacked
7051           Warn if a structure is given the packed attribute, but the packed
7052           attribute has no effect on the layout or size of the structure.
7053           Such structures may be mis-aligned for little benefit.  For
7054           instance, in this code, the variable "f.x" in "struct bar" is
7055           misaligned even though "struct bar" does not itself have the packed
7056           attribute:
7057
7058                   struct foo {
7059                     int x;
7060                     char a, b, c, d;
7061                   } __attribute__((packed));
7062                   struct bar {
7063                     char z;
7064                     struct foo f;
7065                   };
7066
7067       -Wnopacked-bitfield-compat
7068           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
7069           bit-fields of type "char".  This was fixed in GCC 4.4 but the
7070           change can lead to differences in the structure layout.  GCC
7071           informs you when the offset of such a field has changed in GCC 4.4.
7072           For example there is no longer a 4-bit padding between field "a"
7073           and "b" in this structure:
7074
7075                   struct foo
7076                   {
7077                     char a:4;
7078                     char b:8;
7079                   } __attribute__ ((packed));
7080
7081           This warning is enabled by default.  Use
7082           -Wno-packed-bitfield-compat to disable this warning.
7083
7084       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
7085           Warn if a structure field with explicitly specified alignment in a
7086           packed struct or union is misaligned.  For example, a warning will
7087           be issued on "struct S", like, "warning: alignment 1 of 'struct S'
7088           is less than 8", in this code:
7089
7090                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
7091                   struct __attribute__ ((packed)) S {
7092                     struct S8 s8;
7093                   };
7094
7095           This warning is enabled by -Wall.
7096
7097       -Wpadded
7098           Warn if padding is included in a structure, either to align an
7099           element of the structure or to align the whole structure.
7100           Sometimes when this happens it is possible to rearrange the fields
7101           of the structure to reduce the padding and so make the structure
7102           smaller.
7103
7104       -Wredundant-decls
7105           Warn if anything is declared more than once in the same scope, even
7106           in cases where multiple declaration is valid and changes nothing.
7107
7108       -Wrestrict
7109           Warn when an object referenced by a "restrict"-qualified parameter
7110           (or, in C++, a "__restrict"-qualified parameter) is aliased by
7111           another argument, or when copies between such objects overlap.  For
7112           example, the call to the "strcpy" function below attempts to
7113           truncate the string by replacing its initial characters with the
7114           last four.  However, because the call writes the terminating NUL
7115           into "a[4]", the copies overlap and the call is diagnosed.
7116
7117                   void foo (void)
7118                   {
7119                     char a[] = "abcd1234";
7120                     strcpy (a, a + 4);
7121                     ...
7122                   }
7123
7124           The -Wrestrict option detects some instances of simple overlap even
7125           without optimization but works best at -O2 and above.  It is
7126           included in -Wall.
7127
7128       -Wnested-externs (C and Objective-C only)
7129           Warn if an "extern" declaration is encountered within a function.
7130
7131       -Winline
7132           Warn if a function that is declared as inline cannot be inlined.
7133           Even with this option, the compiler does not warn about failures to
7134           inline functions declared in system headers.
7135
7136           The compiler uses a variety of heuristics to determine whether or
7137           not to inline a function.  For example, the compiler takes into
7138           account the size of the function being inlined and the amount of
7139           inlining that has already been done in the current function.
7140           Therefore, seemingly insignificant changes in the source program
7141           can cause the warnings produced by -Winline to appear or disappear.
7142
7143       -Wint-in-bool-context
7144           Warn for suspicious use of integer values where boolean values are
7145           expected, such as conditional expressions (?:) using non-boolean
7146           integer constants in boolean context, like "if (a <= b ? 2 : 3)".
7147           Or left shifting of signed integers in boolean context, like "for
7148           (a = 0; 1 << a; a++);".  Likewise for all kinds of multiplications
7149           regardless of the data type.  This warning is enabled by -Wall.
7150
7151       -Wno-int-to-pointer-cast
7152           Suppress warnings from casts to pointer type of an integer of a
7153           different size. In C++, casting to a pointer type of smaller size
7154           is an error. Wint-to-pointer-cast is enabled by default.
7155
7156       -Wno-pointer-to-int-cast (C and Objective-C only)
7157           Suppress warnings from casts from a pointer to an integer type of a
7158           different size.
7159
7160       -Winvalid-pch
7161           Warn if a precompiled header is found in the search path but cannot
7162           be used.
7163
7164       -Wlong-long
7165           Warn if "long long" type is used.  This is enabled by either
7166           -Wpedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
7167           the warning messages, use -Wno-long-long.
7168
7169       -Wvariadic-macros
7170           Warn if variadic macros are used in ISO C90 mode, or if the GNU
7171           alternate syntax is used in ISO C99 mode.  This is enabled by
7172           either -Wpedantic or -Wtraditional.  To inhibit the warning
7173           messages, use -Wno-variadic-macros.
7174
7175       -Wno-varargs
7176           Do not warn upon questionable usage of the macros used to handle
7177           variable arguments like "va_start".  These warnings are enabled by
7178           default.
7179
7180       -Wvector-operation-performance
7181           Warn if vector operation is not implemented via SIMD capabilities
7182           of the architecture.  Mainly useful for the performance tuning.
7183           Vector operation can be implemented "piecewise", which means that
7184           the scalar operation is performed on every vector element; "in
7185           parallel", which means that the vector operation is implemented
7186           using scalars of wider type, which normally is more performance
7187           efficient; and "as a single scalar", which means that vector fits
7188           into a scalar type.
7189
7190       -Wvla
7191           Warn if a variable-length array is used in the code.  -Wno-vla
7192           prevents the -Wpedantic warning of the variable-length array.
7193
7194       -Wvla-larger-than=byte-size
7195           If this option is used, the compiler warns for declarations of
7196           variable-length arrays whose size is either unbounded, or bounded
7197           by an argument that allows the array size to exceed byte-size
7198           bytes.  This is similar to how -Walloca-larger-than=byte-size
7199           works, but with variable-length arrays.
7200
7201           Note that GCC may optimize small variable-length arrays of a known
7202           value into plain arrays, so this warning may not get triggered for
7203           such arrays.
7204
7205           -Wvla-larger-than=PTRDIFF_MAX is enabled by default but is
7206           typically only effective when -ftree-vrp is active (default for -O2
7207           and above).
7208
7209           See also -Walloca-larger-than=byte-size.
7210
7211       -Wno-vla-larger-than
7212           Disable -Wvla-larger-than= warnings.  The option is equivalent to
7213           -Wvla-larger-than=SIZE_MAX or larger.
7214
7215       -Wvla-parameter
7216           Warn about redeclarations of functions involving arguments of
7217           Variable Length Array types of inconsistent kinds or forms, and
7218           enable the detection of out-of-bounds accesses to such parameters
7219           by warnings such as -Warray-bounds.
7220
7221           If the first function declaration uses the VLA form the bound
7222           specified in the array is assumed to be the minimum number of
7223           elements expected to be provided in calls to the function and the
7224           maximum number of elements accessed by it.  Failing to provide
7225           arguments of sufficient size or accessing more than the maximum
7226           number of elements may be diagnosed.
7227
7228           For example, the warning triggers for the following redeclarations
7229           because the first one allows an array of any size to be passed to
7230           "f" while the second one specifies that the array argument must
7231           have at least "n" elements.  In addition, calling "f" with the
7232           assotiated VLA bound parameter in excess of the actual VLA bound
7233           triggers a warning as well.
7234
7235                   void f (int n, int[n]);
7236                   void f (int, int[]);     // warning: argument 2 previously declared as a VLA
7237
7238                   void g (int n)
7239                   {
7240                       if (n > 4)
7241                         return;
7242                       int a[n];
7243                       f (sizeof a, a);     // warning: access to a by f may be out of bounds
7244                     ...
7245                   }
7246
7247           -Wvla-parameter is included in -Wall.  The -Warray-parameter option
7248           triggers warnings for similar problems involving ordinary array
7249           arguments.
7250
7251       -Wvolatile-register-var
7252           Warn if a register variable is declared volatile.  The volatile
7253           modifier does not inhibit all optimizations that may eliminate
7254           reads and/or writes to register variables.  This warning is enabled
7255           by -Wall.
7256
7257       -Wdisabled-optimization
7258           Warn if a requested optimization pass is disabled.  This warning
7259           does not generally indicate that there is anything wrong with your
7260           code; it merely indicates that GCC's optimizers are unable to
7261           handle the code effectively.  Often, the problem is that your code
7262           is too big or too complex; GCC refuses to optimize programs when
7263           the optimization itself is likely to take inordinate amounts of
7264           time.
7265
7266       -Wpointer-sign (C and Objective-C only)
7267           Warn for pointer argument passing or assignment with different
7268           signedness.  This option is only supported for C and Objective-C.
7269           It is implied by -Wall and by -Wpedantic, which can be disabled
7270           with -Wno-pointer-sign.
7271
7272       -Wstack-protector
7273           This option is only active when -fstack-protector is active.  It
7274           warns about functions that are not protected against stack
7275           smashing.
7276
7277       -Woverlength-strings
7278           Warn about string constants that are longer than the "minimum
7279           maximum" length specified in the C standard.  Modern compilers
7280           generally allow string constants that are much longer than the
7281           standard's minimum limit, but very portable programs should avoid
7282           using longer strings.
7283
7284           The limit applies after string constant concatenation, and does not
7285           count the trailing NUL.  In C90, the limit was 509 characters; in
7286           C99, it was raised to 4095.  C++98 does not specify a normative
7287           minimum maximum, so we do not diagnose overlength strings in C++.
7288
7289           This option is implied by -Wpedantic, and can be disabled with
7290           -Wno-overlength-strings.
7291
7292       -Wunsuffixed-float-constants (C and Objective-C only)
7293           Issue a warning for any floating constant that does not have a
7294           suffix.  When used together with -Wsystem-headers it warns about
7295           such constants in system header files.  This can be useful when
7296           preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from
7297           the decimal floating-point extension to C99.
7298
7299       -Wno-lto-type-mismatch
7300           During the link-time optimization, do not warn about type
7301           mismatches in global declarations from different compilation units.
7302           Requires -flto to be enabled.  Enabled by default.
7303
7304       -Wno-designated-init (C and Objective-C only)
7305           Suppress warnings when a positional initializer is used to
7306           initialize a structure that has been marked with the
7307           "designated_init" attribute.
7308
7309   Options That Control Static Analysis
7310       -fanalyzer
7311           This option enables an static analysis of program flow which looks
7312           for "interesting" interprocedural paths through the code, and
7313           issues warnings for problems found on them.
7314
7315           This analysis is much more expensive than other GCC warnings.
7316
7317           Enabling this option effectively enables the following warnings:
7318
7319           -Wanalyzer-double-fclose -Wanalyzer-double-free
7320           -Wanalyzer-exposure-through-output-file -Wanalyzer-file-leak
7321           -Wanalyzer-free-of-non-heap -Wanalyzer-malloc-leak
7322           -Wanalyzer-mismatching-deallocation
7323           -Wanalyzer-possible-null-argument
7324           -Wanalyzer-possible-null-dereference -Wanalyzer-null-argument
7325           -Wanalyzer-null-dereference -Wanalyzer-shift-count-negative
7326           -Wanalyzer-shift-count-overflow -Wanalyzer-stale-setjmp-buffer
7327           -Wanalyzer-tainted-array-index
7328           -Wanalyzer-unsafe-call-within-signal-handler
7329           -Wanalyzer-use-after-free
7330           -Wanalyzer-use-of-pointer-in-stale-stack-frame
7331           -Wanalyzer-write-to-const -Wanalyzer-write-to-string-literal
7332
7333           This option is only available if GCC was configured with analyzer
7334           support enabled.
7335
7336       -Wanalyzer-too-complex
7337           If -fanalyzer is enabled, the analyzer uses various heuristics to
7338           attempt to explore the control flow and data flow in the program,
7339           but these can be defeated by sufficiently complicated code.
7340
7341           By default, the analysis silently stops if the code is too
7342           complicated for the analyzer to fully explore and it reaches an
7343           internal limit.  The -Wanalyzer-too-complex option warns if this
7344           occurs.
7345
7346       -Wno-analyzer-double-fclose
7347           This warning requires -fanalyzer, which enables it; use
7348           -Wno-analyzer-double-fclose to disable it.
7349
7350           This diagnostic warns for paths through the code in which a "FILE
7351           *" can have "fclose" called on it more than once.
7352
7353       -Wno-analyzer-double-free
7354           This warning requires -fanalyzer, which enables it; use
7355           -Wno-analyzer-double-free to disable it.
7356
7357           This diagnostic warns for paths through the code in which a pointer
7358           can have a deallocator called on it more than once, either "free",
7359           or a deallocator referenced by attribute "malloc".
7360
7361       -Wno-analyzer-exposure-through-output-file
7362           This warning requires -fanalyzer, which enables it; use
7363           -Wno-analyzer-exposure-through-output-file to disable it.
7364
7365           This diagnostic warns for paths through the code in which a
7366           security-sensitive value is written to an output file (such as
7367           writing a password to a log file).
7368
7369       -Wno-analyzer-file-leak
7370           This warning requires -fanalyzer, which enables it; use
7371           -Wno-analyzer-file-leak to disable it.
7372
7373           This diagnostic warns for paths through the code in which a
7374           "<stdio.h>" "FILE *" stream object is leaked.
7375
7376       -Wno-analyzer-free-of-non-heap
7377           This warning requires -fanalyzer, which enables it; use
7378           -Wno-analyzer-free-of-non-heap to disable it.
7379
7380           This diagnostic warns for paths through the code in which "free" is
7381           called on a non-heap pointer (e.g. an on-stack buffer, or a
7382           global).
7383
7384       -Wno-analyzer-malloc-leak
7385           This warning requires -fanalyzer, which enables it; use
7386           -Wno-analyzer-malloc-leak to disable it.
7387
7388           This diagnostic warns for paths through the code in which a pointer
7389           allocated via an allocator is leaked: either "malloc", or a
7390           function marked with attribute "malloc".
7391
7392       -Wno-analyzer-mismatching-deallocation
7393           This warning requires -fanalyzer, which enables it; use
7394           -Wno-analyzer-mismatching-deallocation to disable it.
7395
7396           This diagnostic warns for paths through the code in which the wrong
7397           deallocation function is called on a pointer value, based on which
7398           function was used to allocate the pointer value.  The diagnostic
7399           will warn about mismatches between "free", scalar "delete" and
7400           vector "delete[]", and those marked as allocator/deallocator pairs
7401           using attribute "malloc".
7402
7403       -Wno-analyzer-possible-null-argument
7404           This warning requires -fanalyzer, which enables it; use
7405           -Wno-analyzer-possible-null-argument to disable it.
7406
7407           This diagnostic warns for paths through the code in which a
7408           possibly-NULL value is passed to a function argument marked with
7409           "__attribute__((nonnull))" as requiring a non-NULL value.
7410
7411       -Wno-analyzer-possible-null-dereference
7412           This warning requires -fanalyzer, which enables it; use
7413           -Wno-analyzer-possible-null-dereference to disable it.
7414
7415           This diagnostic warns for paths through the code in which a
7416           possibly-NULL value is dereferenced.
7417
7418       -Wno-analyzer-null-argument
7419           This warning requires -fanalyzer, which enables it; use
7420           -Wno-analyzer-null-argument to disable it.
7421
7422           This diagnostic warns for paths through the code in which a value
7423           known to be NULL is passed to a function argument marked with
7424           "__attribute__((nonnull))" as requiring a non-NULL value.
7425
7426       -Wno-analyzer-null-dereference
7427           This warning requires -fanalyzer, which enables it; use
7428           -Wno-analyzer-null-dereference to disable it.
7429
7430           This diagnostic warns for paths through the code in which a value
7431           known to be NULL is dereferenced.
7432
7433       -Wno-analyzer-shift-count-negative
7434           This warning requires -fanalyzer, which enables it; use
7435           -Wno-analyzer-shift-count-negative to disable it.
7436
7437           This diagnostic warns for paths through the code in which a shift
7438           is attempted with a negative count.  It is analogous to the
7439           -Wshift-count-negative diagnostic implemented in the C/C++ front
7440           ends, but is implemented based on analyzing interprocedural paths,
7441           rather than merely parsing the syntax tree.  However, the analyzer
7442           does not prioritize detection of such paths, so false negatives are
7443           more likely relative to other warnings.
7444
7445       -Wno-analyzer-shift-count-overflow
7446           This warning requires -fanalyzer, which enables it; use
7447           -Wno-analyzer-shift-count-overflow to disable it.
7448
7449           This diagnostic warns for paths through the code in which a shift
7450           is attempted with a count greater than or equal to the precision of
7451           the operand's type.  It is analogous to the -Wshift-count-overflow
7452           diagnostic implemented in the C/C++ front ends, but is implemented
7453           based on analyzing interprocedural paths, rather than merely
7454           parsing the syntax tree.  However, the analyzer does not prioritize
7455           detection of such paths, so false negatives are more likely
7456           relative to other warnings.
7457
7458       -Wno-analyzer-stale-setjmp-buffer
7459           This warning requires -fanalyzer, which enables it; use
7460           -Wno-analyzer-stale-setjmp-buffer to disable it.
7461
7462           This diagnostic warns for paths through the code in which "longjmp"
7463           is called to rewind to a "jmp_buf" relating to a "setjmp" call in a
7464           function that has returned.
7465
7466           When "setjmp" is called on a "jmp_buf" to record a rewind location,
7467           it records the stack frame.  The stack frame becomes invalid when
7468           the function containing the "setjmp" call returns.  Attempting to
7469           rewind to it via "longjmp" would reference a stack frame that no
7470           longer exists, and likely lead to a crash (or worse).
7471
7472       -Wno-analyzer-tainted-array-index
7473           This warning requires both -fanalyzer and -fanalyzer-checker=taint
7474           to enable it; use -Wno-analyzer-tainted-array-index to disable it.
7475
7476           This diagnostic warns for paths through the code in which a value
7477           that could be under an attacker's control is used as the index of
7478           an array access without being sanitized.
7479
7480       -Wno-analyzer-unsafe-call-within-signal-handler
7481           This warning requires -fanalyzer, which enables it; use
7482           -Wno-analyzer-unsafe-call-within-signal-handler to disable it.
7483
7484           This diagnostic warns for paths through the code in which a
7485           function known to be async-signal-unsafe (such as "fprintf") is
7486           called from a signal handler.
7487
7488       -Wno-analyzer-use-after-free
7489           This warning requires -fanalyzer, which enables it; use
7490           -Wno-analyzer-use-after-free to disable it.
7491
7492           This diagnostic warns for paths through the code in which a pointer
7493           is used after a deallocator is called on it: either "free", or a
7494           deallocator referenced by attribute "malloc".
7495
7496       -Wno-analyzer-use-of-pointer-in-stale-stack-frame
7497           This warning requires -fanalyzer, which enables it; use
7498           -Wno-analyzer-use-of-pointer-in-stale-stack-frame to disable it.
7499
7500           This diagnostic warns for paths through the code in which a pointer
7501           is dereferenced that points to a variable in a stale stack frame.
7502
7503       -Wno-analyzer-write-to-const
7504           This warning requires -fanalyzer, which enables it; use
7505           -Wno-analyzer-write-to-const to disable it.
7506
7507           This diagnostic warns for paths through the code in which the
7508           analyzer detects an attempt to write through a pointer to a "const"
7509           object.  However, the analyzer does not prioritize detection of
7510           such paths, so false negatives are more likely relative to other
7511           warnings.
7512
7513       -Wno-analyzer-write-to-string-literal
7514           This warning requires -fanalyzer, which enables it; use
7515           -Wno-analyzer-write-to-string-literal to disable it.
7516
7517           This diagnostic warns for paths through the code in which the
7518           analyzer detects an attempt to write through a pointer to a string
7519           literal.  However, the analyzer does not prioritize detection of
7520           such paths, so false negatives are more likely relative to other
7521           warnings.
7522
7523       Pertinent parameters for controlling the exploration are: --param
7524       analyzer-bb-explosion-factor=value, --param
7525       analyzer-max-enodes-per-program-point=value, --param
7526       analyzer-max-recursion-depth=value, and --param
7527       analyzer-min-snodes-for-call-summary=value.
7528
7529       The following options control the analyzer.
7530
7531       -fanalyzer-call-summaries
7532           Simplify interprocedural analysis by computing the effect of
7533           certain calls, rather than exploring all paths through the function
7534           from callsite to each possible return.
7535
7536           If enabled, call summaries are only used for functions with more
7537           than one call site, and that are sufficiently complicated (as per
7538           --param analyzer-min-snodes-for-call-summary=value).
7539
7540       -fanalyzer-checker=name
7541           Restrict the analyzer to run just the named checker, and enable it.
7542
7543           Some checkers are disabled by default (even with -fanalyzer), such
7544           as the "taint" checker that implements
7545           -Wanalyzer-tainted-array-index, and this option is required to
7546           enable them.
7547
7548       -fno-analyzer-feasibility
7549           This option is intended for analyzer developers.
7550
7551           By default the analyzer verifies that there is a feasible control
7552           flow path for each diagnostic it emits: that the conditions that
7553           hold are not mutually exclusive.  Diagnostics for which no feasible
7554           path can be found are rejected.  This filtering can be suppressed
7555           with -fno-analyzer-feasibility, for debugging issues in this code.
7556
7557       -fanalyzer-fine-grained
7558           This option is intended for analyzer developers.
7559
7560           Internally the analyzer builds an "exploded graph" that combines
7561           control flow graphs with data flow information.
7562
7563           By default, an edge in this graph can contain the effects of a run
7564           of multiple statements within a basic block.  With
7565           -fanalyzer-fine-grained, each statement gets its own edge.
7566
7567       -fanalyzer-show-duplicate-count
7568           This option is intended for analyzer developers: if multiple
7569           diagnostics have been detected as being duplicates of each other,
7570           it emits a note when reporting the best diagnostic, giving the
7571           number of additional diagnostics that were suppressed by the
7572           deduplication logic.
7573
7574       -fno-analyzer-state-merge
7575           This option is intended for analyzer developers.
7576
7577           By default the analyzer attempts to simplify analysis by merging
7578           sufficiently similar states at each program point as it builds its
7579           "exploded graph".  With -fno-analyzer-state-merge this merging can
7580           be suppressed, for debugging state-handling issues.
7581
7582       -fno-analyzer-state-purge
7583           This option is intended for analyzer developers.
7584
7585           By default the analyzer attempts to simplify analysis by purging
7586           aspects of state at a program point that appear to no longer be
7587           relevant e.g. the values of locals that aren't accessed later in
7588           the function and which aren't relevant to leak analysis.
7589
7590           With -fno-analyzer-state-purge this purging of state can be
7591           suppressed, for debugging state-handling issues.
7592
7593       -fanalyzer-transitivity
7594           This option enables transitivity of constraints within the
7595           analyzer.
7596
7597       -fanalyzer-verbose-edges
7598           This option is intended for analyzer developers.  It enables more
7599           verbose, lower-level detail in the descriptions of control flow
7600           within diagnostic paths.
7601
7602       -fanalyzer-verbose-state-changes
7603           This option is intended for analyzer developers.  It enables more
7604           verbose, lower-level detail in the descriptions of events relating
7605           to state machines within diagnostic paths.
7606
7607       -fanalyzer-verbosity=level
7608           This option controls the complexity of the control flow paths that
7609           are emitted for analyzer diagnostics.
7610
7611           The level can be one of:
7612
7613           0   At this level, interprocedural call and return events are
7614               displayed, along with the most pertinent state-change events
7615               relating to a diagnostic.  For example, for a double-"free"
7616               diagnostic, both calls to "free" will be shown.
7617
7618           1   As per the previous level, but also show events for the entry
7619               to each function.
7620
7621           2   As per the previous level, but also show events relating to
7622               control flow that are significant to triggering the issue (e.g.
7623               "true path taken" at a conditional).
7624
7625               This level is the default.
7626
7627           3   As per the previous level, but show all control flow events,
7628               not just significant ones.
7629
7630           4   This level is intended for analyzer developers; it adds various
7631               other events intended for debugging the analyzer.
7632
7633       -fdump-analyzer
7634           Dump internal details about what the analyzer is doing to
7635           file.analyzer.txt.  This option is overridden by
7636           -fdump-analyzer-stderr.
7637
7638       -fdump-analyzer-stderr
7639           Dump internal details about what the analyzer is doing to stderr.
7640           This option overrides -fdump-analyzer.
7641
7642       -fdump-analyzer-callgraph
7643           Dump a representation of the call graph suitable for viewing with
7644           GraphViz to file.callgraph.dot.
7645
7646       -fdump-analyzer-exploded-graph
7647           Dump a representation of the "exploded graph" suitable for viewing
7648           with GraphViz to file.eg.dot.  Nodes are color-coded based on
7649           state-machine states to emphasize state changes.
7650
7651       -fdump-analyzer-exploded-nodes
7652           Emit diagnostics showing where nodes in the "exploded graph" are in
7653           relation to the program source.
7654
7655       -fdump-analyzer-exploded-nodes-2
7656           Dump a textual representation of the "exploded graph" to
7657           file.eg.txt.
7658
7659       -fdump-analyzer-exploded-nodes-3
7660           Dump a textual representation of the "exploded graph" to one dump
7661           file per node, to file.eg-id.txt.  This is typically a large number
7662           of dump files.
7663
7664       -fdump-analyzer-feasibility
7665           Dump internal details about the analyzer's search for feasible
7666           paths.  The details are written in a form suitable for viewing with
7667           GraphViz to filenames of the form file.*.fg.dot and file.*.tg.dot.
7668
7669       -fdump-analyzer-json
7670           Dump a compressed JSON representation of analyzer internals to
7671           file.analyzer.json.gz.  The precise format is subject to change.
7672
7673       -fdump-analyzer-state-purge
7674           As per -fdump-analyzer-supergraph, dump a representation of the
7675           "supergraph" suitable for viewing with GraphViz, but annotate the
7676           graph with information on what state will be purged at each node.
7677           The graph is written to file.state-purge.dot.
7678
7679       -fdump-analyzer-supergraph
7680           Dump representations of the "supergraph" suitable for viewing with
7681           GraphViz to file.supergraph.dot and to file.supergraph-eg.dot.
7682           These show all of the control flow graphs in the program, with
7683           interprocedural edges for calls and returns.  The second dump
7684           contains annotations showing nodes in the "exploded graph" and
7685           diagnostics associated with them.
7686
7687   Options for Debugging Your Program
7688       To tell GCC to emit extra information for use by a debugger, in almost
7689       all cases you need only to add -g to your other options.
7690
7691       GCC allows you to use -g with -O.  The shortcuts taken by optimized
7692       code may occasionally be surprising: some variables you declared may
7693       not exist at all; flow of control may briefly move where you did not
7694       expect it; some statements may not be executed because they compute
7695       constant results or their values are already at hand; some statements
7696       may execute in different places because they have been moved out of
7697       loops.  Nevertheless it is possible to debug optimized output.  This
7698       makes it reasonable to use the optimizer for programs that might have
7699       bugs.
7700
7701       If you are not using some other optimization option, consider using -Og
7702       with -g.  With no -O option at all, some compiler passes that collect
7703       information useful for debugging do not run at all, so that -Og may
7704       result in a better debugging experience.
7705
7706       -g  Produce debugging information in the operating system's native
7707           format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
7708           debugging information.
7709
7710           On most systems that use stabs format, -g enables use of extra
7711           debugging information that only GDB can use; this extra information
7712           makes debugging work better in GDB but probably makes other
7713           debuggers crash or refuse to read the program.  If you want to
7714           control for certain whether to generate the extra information, use
7715           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
7716
7717       -ggdb
7718           Produce debugging information for use by GDB.  This means to use
7719           the most expressive format available (DWARF, stabs, or the native
7720           format if neither of those are supported), including GDB extensions
7721           if at all possible.
7722
7723       -gdwarf
7724       -gdwarf-version
7725           Produce debugging information in DWARF format (if that is
7726           supported).  The value of version may be either 2, 3, 4 or 5; the
7727           default version for most targets is 5 (with the exception of
7728           VxWorks, TPF and Darwin/Mac OS X, which default to version 2, and
7729           AIX, which defaults to version 4).
7730
7731           Note that with DWARF Version 2, some ports require and always use
7732           some non-conflicting DWARF 3 extensions in the unwind tables.
7733
7734           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
7735           maximum benefit. Version 5 requires GDB 8.0 or higher.
7736
7737           GCC no longer supports DWARF Version 1, which is substantially
7738           different than Version 2 and later.  For historical reasons, some
7739           other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a
7740           reference to DWARF Version 2 in their names, but apply to all
7741           currently-supported versions of DWARF.
7742
7743       -gstabs
7744           Produce debugging information in stabs format (if that is
7745           supported), without GDB extensions.  This is the format used by DBX
7746           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
7747           this option produces stabs debugging output that is not understood
7748           by DBX.  On System V Release 4 systems this option requires the GNU
7749           assembler.
7750
7751       -gstabs+
7752           Produce debugging information in stabs format (if that is
7753           supported), using GNU extensions understood only by the GNU
7754           debugger (GDB).  The use of these extensions is likely to make
7755           other debuggers crash or refuse to read the program.
7756
7757       -gxcoff
7758           Produce debugging information in XCOFF format (if that is
7759           supported).  This is the format used by the DBX debugger on IBM
7760           RS/6000 systems.
7761
7762       -gxcoff+
7763           Produce debugging information in XCOFF format (if that is
7764           supported), using GNU extensions understood only by the GNU
7765           debugger (GDB).  The use of these extensions is likely to make
7766           other debuggers crash or refuse to read the program, and may cause
7767           assemblers other than the GNU assembler (GAS) to fail with an
7768           error.
7769
7770       -gvms
7771           Produce debugging information in Alpha/VMS debug format (if that is
7772           supported).  This is the format used by DEBUG on Alpha/VMS systems.
7773
7774       -glevel
7775       -ggdblevel
7776       -gstabslevel
7777       -gxcofflevel
7778       -gvmslevel
7779           Request debugging information and also use level to specify how
7780           much information.  The default level is 2.
7781
7782           Level 0 produces no debug information at all.  Thus, -g0 negates
7783           -g.
7784
7785           Level 1 produces minimal information, enough for making backtraces
7786           in parts of the program that you don't plan to debug.  This
7787           includes descriptions of functions and external variables, and line
7788           number tables, but no information about local variables.
7789
7790           Level 3 includes extra information, such as all the macro
7791           definitions present in the program.  Some debuggers support macro
7792           expansion when you use -g3.
7793
7794           If you use multiple -g options, with or without level numbers, the
7795           last such option is the one that is effective.
7796
7797           -gdwarf does not accept a concatenated debug level, to avoid
7798           confusion with -gdwarf-level.  Instead use an additional -glevel
7799           option to change the debug level for DWARF.
7800
7801       -fno-eliminate-unused-debug-symbols
7802           By default, no debug information is produced for symbols that are
7803           not actually used. Use this option if you want debug information
7804           for all symbols.
7805
7806       -femit-class-debug-always
7807           Instead of emitting debugging information for a C++ class in only
7808           one object file, emit it in all object files using the class.  This
7809           option should be used only with debuggers that are unable to handle
7810           the way GCC normally emits debugging information for classes
7811           because using this option increases the size of debugging
7812           information by as much as a factor of two.
7813
7814       -fno-merge-debug-strings
7815           Direct the linker to not merge together strings in the debugging
7816           information that are identical in different object files.  Merging
7817           is not supported by all assemblers or linkers.  Merging decreases
7818           the size of the debug information in the output file at the cost of
7819           increasing link processing time.  Merging is enabled by default.
7820
7821       -fdebug-prefix-map=old=new
7822           When compiling files residing in directory old, record debugging
7823           information describing them as if the files resided in directory
7824           new instead.  This can be used to replace a build-time path with an
7825           install-time path in the debug info.  It can also be used to change
7826           an absolute path to a relative path by using . for new.  This can
7827           give more reproducible builds, which are location independent, but
7828           may require an extra command to tell GDB where to find the source
7829           files. See also -ffile-prefix-map.
7830
7831       -fvar-tracking
7832           Run variable tracking pass.  It computes where variables are stored
7833           at each position in code.  Better debugging information is then
7834           generated (if the debugging information format supports this
7835           information).
7836
7837           It is enabled by default when compiling with optimization (-Os, -O,
7838           -O2, ...), debugging information (-g) and the debug info format
7839           supports it.
7840
7841       -fvar-tracking-assignments
7842           Annotate assignments to user variables early in the compilation and
7843           attempt to carry the annotations over throughout the compilation
7844           all the way to the end, in an attempt to improve debug information
7845           while optimizing.  Use of -gdwarf-4 is recommended along with it.
7846
7847           It can be enabled even if var-tracking is disabled, in which case
7848           annotations are created and maintained, but discarded at the end.
7849           By default, this flag is enabled together with -fvar-tracking,
7850           except when selective scheduling is enabled.
7851
7852       -gsplit-dwarf
7853           If DWARF debugging information is enabled, separate as much
7854           debugging information as possible into a separate output file with
7855           the extension .dwo.  This option allows the build system to avoid
7856           linking files with debug information.  To be useful, this option
7857           requires a debugger capable of reading .dwo files.
7858
7859       -gdwarf32
7860       -gdwarf64
7861           If DWARF debugging information is enabled, the -gdwarf32 selects
7862           the 32-bit DWARF format and the -gdwarf64 selects the 64-bit DWARF
7863           format.  The default is target specific, on most targets it is
7864           -gdwarf32 though.  The 32-bit DWARF format is smaller, but can't
7865           support more than 2GiB of debug information in any of the DWARF
7866           debug information sections.  The 64-bit DWARF format allows larger
7867           debug information and might not be well supported by all consumers
7868           yet.
7869
7870       -gdescribe-dies
7871           Add description attributes to some DWARF DIEs that have no name
7872           attribute, such as artificial variables, external references and
7873           call site parameter DIEs.
7874
7875       -gpubnames
7876           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.
7877
7878       -ggnu-pubnames
7879           Generate ".debug_pubnames" and ".debug_pubtypes" sections in a
7880           format suitable for conversion into a GDB index.  This option is
7881           only useful with a linker that can produce GDB index version 7.
7882
7883       -fdebug-types-section
7884           When using DWARF Version 4 or higher, type DIEs can be put into
7885           their own ".debug_types" section instead of making them part of the
7886           ".debug_info" section.  It is more efficient to put them in a
7887           separate comdat section since the linker can then remove
7888           duplicates.  But not all DWARF consumers support ".debug_types"
7889           sections yet and on some objects ".debug_types" produces larger
7890           instead of smaller debugging information.
7891
7892       -grecord-gcc-switches
7893       -gno-record-gcc-switches
7894           This switch causes the command-line options used to invoke the
7895           compiler that may affect code generation to be appended to the
7896           DW_AT_producer attribute in DWARF debugging information.  The
7897           options are concatenated with spaces separating them from each
7898           other and from the compiler version.  It is enabled by default.
7899           See also -frecord-gcc-switches for another way of storing compiler
7900           options into the object file.
7901
7902       -gstrict-dwarf
7903           Disallow using extensions of later DWARF standard version than
7904           selected with -gdwarf-version.  On most targets using non-
7905           conflicting DWARF extensions from later standard versions is
7906           allowed.
7907
7908       -gno-strict-dwarf
7909           Allow using extensions of later DWARF standard version than
7910           selected with -gdwarf-version.
7911
7912       -gas-loc-support
7913           Inform the compiler that the assembler supports ".loc" directives.
7914           It may then use them for the assembler to generate DWARF2+ line
7915           number tables.
7916
7917           This is generally desirable, because assembler-generated line-
7918           number tables are a lot more compact than those the compiler can
7919           generate itself.
7920
7921           This option will be enabled by default if, at GCC configure time,
7922           the assembler was found to support such directives.
7923
7924       -gno-as-loc-support
7925           Force GCC to generate DWARF2+ line number tables internally, if
7926           DWARF2+ line number tables are to be generated.
7927
7928       -gas-locview-support
7929           Inform the compiler that the assembler supports "view" assignment
7930           and reset assertion checking in ".loc" directives.
7931
7932           This option will be enabled by default if, at GCC configure time,
7933           the assembler was found to support them.
7934
7935       -gno-as-locview-support
7936           Force GCC to assign view numbers internally, if
7937           -gvariable-location-views are explicitly requested.
7938
7939       -gcolumn-info
7940       -gno-column-info
7941           Emit location column information into DWARF debugging information,
7942           rather than just file and line.  This option is enabled by default.
7943
7944       -gstatement-frontiers
7945       -gno-statement-frontiers
7946           This option causes GCC to create markers in the internal
7947           representation at the beginning of statements, and to keep them
7948           roughly in place throughout compilation, using them to guide the
7949           output of "is_stmt" markers in the line number table.  This is
7950           enabled by default when compiling with optimization (-Os, -O, -O2,
7951           ...), and outputting DWARF 2 debug information at the normal level.
7952
7953       -gvariable-location-views
7954       -gvariable-location-views=incompat5
7955       -gno-variable-location-views
7956           Augment variable location lists with progressive view numbers
7957           implied from the line number table.  This enables debug information
7958           consumers to inspect state at certain points of the program, even
7959           if no instructions associated with the corresponding source
7960           locations are present at that point.  If the assembler lacks
7961           support for view numbers in line number tables, this will cause the
7962           compiler to emit the line number table, which generally makes them
7963           somewhat less compact.  The augmented line number tables and
7964           location lists are fully backward-compatible, so they can be
7965           consumed by debug information consumers that are not aware of these
7966           augmentations, but they won't derive any benefit from them either.
7967
7968           This is enabled by default when outputting DWARF 2 debug
7969           information at the normal level, as long as there is assembler
7970           support, -fvar-tracking-assignments is enabled and -gstrict-dwarf
7971           is not.  When assembler support is not available, this may still be
7972           enabled, but it will force GCC to output internal line number
7973           tables, and if -ginternal-reset-location-views is not enabled, that
7974           will most certainly lead to silently mismatching location views.
7975
7976           There is a proposed representation for view numbers that is not
7977           backward compatible with the location list format introduced in
7978           DWARF 5, that can be enabled with
7979           -gvariable-location-views=incompat5.  This option may be removed in
7980           the future, is only provided as a reference implementation of the
7981           proposed representation.  Debug information consumers are not
7982           expected to support this extended format, and they would be
7983           rendered unable to decode location lists using it.
7984
7985       -ginternal-reset-location-views
7986       -gno-internal-reset-location-views
7987           Attempt to determine location views that can be omitted from
7988           location view lists.  This requires the compiler to have very
7989           accurate insn length estimates, which isn't always the case, and it
7990           may cause incorrect view lists to be generated silently when using
7991           an assembler that does not support location view lists.  The GNU
7992           assembler will flag any such error as a "view number mismatch".
7993           This is only enabled on ports that define a reliable estimation
7994           function.
7995
7996       -ginline-points
7997       -gno-inline-points
7998           Generate extended debug information for inlined functions.
7999           Location view tracking markers are inserted at inlined entry
8000           points, so that address and view numbers can be computed and output
8001           in debug information.  This can be enabled independently of
8002           location views, in which case the view numbers won't be output, but
8003           it can only be enabled along with statement frontiers, and it is
8004           only enabled by default if location views are enabled.
8005
8006       -gz[=type]
8007           Produce compressed debug sections in DWARF format, if that is
8008           supported.  If type is not given, the default type depends on the
8009           capabilities of the assembler and linker used.  type may be one of
8010           none (don't compress debug sections), zlib (use zlib compression in
8011           ELF gABI format), or zlib-gnu (use zlib compression in traditional
8012           GNU format).  If the linker doesn't support writing compressed
8013           debug sections, the option is rejected.  Otherwise, if the
8014           assembler does not support them, -gz is silently ignored when
8015           producing object files.
8016
8017       -femit-struct-debug-baseonly
8018           Emit debug information for struct-like types only when the base
8019           name of the compilation source file matches the base name of file
8020           in which the struct is defined.
8021
8022           This option substantially reduces the size of debugging
8023           information, but at significant potential loss in type information
8024           to the debugger.  See -femit-struct-debug-reduced for a less
8025           aggressive option.  See -femit-struct-debug-detailed for more
8026           detailed control.
8027
8028           This option works only with DWARF debug output.
8029
8030       -femit-struct-debug-reduced
8031           Emit debug information for struct-like types only when the base
8032           name of the compilation source file matches the base name of file
8033           in which the type is defined, unless the struct is a template or
8034           defined in a system header.
8035
8036           This option significantly reduces the size of debugging
8037           information, with some potential loss in type information to the
8038           debugger.  See -femit-struct-debug-baseonly for a more aggressive
8039           option.  See -femit-struct-debug-detailed for more detailed
8040           control.
8041
8042           This option works only with DWARF debug output.
8043
8044       -femit-struct-debug-detailed[=spec-list]
8045           Specify the struct-like types for which the compiler generates
8046           debug information.  The intent is to reduce duplicate struct debug
8047           information between different object files within the same program.
8048
8049           This option is a detailed version of -femit-struct-debug-reduced
8050           and -femit-struct-debug-baseonly, which serves for most needs.
8051
8052           A specification has the
8053           syntax[dir:|ind:][ord:|gen:](any|sys|base|none)
8054
8055           The optional first word limits the specification to structs that
8056           are used directly (dir:) or used indirectly (ind:).  A struct type
8057           is used directly when it is the type of a variable, member.
8058           Indirect uses arise through pointers to structs.  That is, when use
8059           of an incomplete struct is valid, the use is indirect.  An example
8060           is struct one direct; struct two * indirect;.
8061
8062           The optional second word limits the specification to ordinary
8063           structs (ord:) or generic structs (gen:).  Generic structs are a
8064           bit complicated to explain.  For C++, these are non-explicit
8065           specializations of template classes, or non-template classes within
8066           the above.  Other programming languages have generics, but
8067           -femit-struct-debug-detailed does not yet implement them.
8068
8069           The third word specifies the source files for those structs for
8070           which the compiler should emit debug information.  The values none
8071           and any have the normal meaning.  The value base means that the
8072           base of name of the file in which the type declaration appears must
8073           match the base of the name of the main compilation file.  In
8074           practice, this means that when compiling foo.c, debug information
8075           is generated for types declared in that file and foo.h, but not
8076           other header files.  The value sys means those types satisfying
8077           base or declared in system or compiler headers.
8078
8079           You may need to experiment to determine the best settings for your
8080           application.
8081
8082           The default is -femit-struct-debug-detailed=all.
8083
8084           This option works only with DWARF debug output.
8085
8086       -fno-dwarf2-cfi-asm
8087           Emit DWARF unwind info as compiler generated ".eh_frame" section
8088           instead of using GAS ".cfi_*" directives.
8089
8090       -fno-eliminate-unused-debug-types
8091           Normally, when producing DWARF output, GCC avoids producing debug
8092           symbol output for types that are nowhere used in the source file
8093           being compiled.  Sometimes it is useful to have GCC emit debugging
8094           information for all types declared in a compilation unit,
8095           regardless of whether or not they are actually used in that
8096           compilation unit, for example if, in the debugger, you want to cast
8097           a value to a type that is not actually used in your program (but is
8098           declared).  More often, however, this results in a significant
8099           amount of wasted space.
8100
8101   Options That Control Optimization
8102       These options control various sorts of optimizations.
8103
8104       Without any optimization option, the compiler's goal is to reduce the
8105       cost of compilation and to make debugging produce the expected results.
8106       Statements are independent: if you stop the program with a breakpoint
8107       between statements, you can then assign a new value to any variable or
8108       change the program counter to any other statement in the function and
8109       get exactly the results you expect from the source code.
8110
8111       Turning on optimization flags makes the compiler attempt to improve the
8112       performance and/or code size at the expense of compilation time and
8113       possibly the ability to debug the program.
8114
8115       The compiler performs optimization based on the knowledge it has of the
8116       program.  Compiling multiple files at once to a single output file mode
8117       allows the compiler to use information gained from all of the files
8118       when compiling each of them.
8119
8120       Not all optimizations are controlled directly by a flag.  Only
8121       optimizations that have a flag are listed in this section.
8122
8123       Most optimizations are completely disabled at -O0 or if an -O level is
8124       not set on the command line, even if individual optimization flags are
8125       specified.  Similarly, -Og suppresses many optimization passes.
8126
8127       Depending on the target and how GCC was configured, a slightly
8128       different set of optimizations may be enabled at each -O level than
8129       those listed here.  You can invoke GCC with -Q --help=optimizers to
8130       find out the exact set of optimizations that are enabled at each level.
8131
8132       -O
8133       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
8134           lot more memory for a large function.
8135
8136           With -O, the compiler tries to reduce code size and execution time,
8137           without performing any optimizations that take a great deal of
8138           compilation time.
8139
8140           -O turns on the following optimization flags:
8141
8142           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments
8143           -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch
8144           -fdse -fforward-propagate -fguess-branch-probability
8145           -fif-conversion -fif-conversion2 -finline-functions-called-once
8146           -fipa-modref -fipa-profile -fipa-pure-const -fipa-reference
8147           -fipa-reference-addressable -fmerge-constants
8148           -fmove-loop-invariants -fomit-frame-pointer -freorder-blocks
8149           -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types
8150           -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch
8151           -ftree-coalesce-vars -ftree-copy-prop -ftree-dce
8152           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
8153           -ftree-phiprop -ftree-pta -ftree-scev-cprop -ftree-sink -ftree-slsr
8154           -ftree-sra -ftree-ter -funit-at-a-time
8155
8156       -O2 Optimize even more.  GCC performs nearly all supported
8157           optimizations that do not involve a space-speed tradeoff.  As
8158           compared to -O, this option increases both compilation time and the
8159           performance of the generated code.
8160
8161           -O2 turns on all optimization flags specified by -O.  It also turns
8162           on the following optimization flags:
8163
8164           -falign-functions  -falign-jumps -falign-labels  -falign-loops
8165           -fcaller-saves -fcode-hoisting -fcrossjumping -fcse-follow-jumps
8166           -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize
8167           -fdevirtualize-speculatively -fexpensive-optimizations
8168           -ffinite-loops -fgcse  -fgcse-lm -fhoist-adjacent-loads
8169           -finline-functions -finline-small-functions -findirect-inlining
8170           -fipa-bit-cp  -fipa-cp  -fipa-icf -fipa-ra  -fipa-sra  -fipa-vrp
8171           -fisolate-erroneous-paths-dereference -flra-remat
8172           -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining
8173           -fpeephole2 -freorder-blocks-algorithm=stc
8174           -freorder-blocks-and-partition  -freorder-functions
8175           -frerun-cse-after-loop -fschedule-insns  -fschedule-insns2
8176           -fsched-interblock  -fsched-spec -fstore-merging -fstrict-aliasing
8177           -fthread-jumps -ftree-builtin-call-dce -ftree-pre
8178           -ftree-switch-conversion  -ftree-tail-merge -ftree-vrp
8179
8180           Please note the warning under -fgcse about invoking -O2 on programs
8181           that use computed gotos.
8182
8183       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
8184           and also turns on the following optimization flags:
8185
8186           -fgcse-after-reload -fipa-cp-clone -floop-interchange
8187           -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning
8188           -fsplit-loops -fsplit-paths -ftree-loop-distribution
8189           -ftree-loop-vectorize -ftree-partial-pre -ftree-slp-vectorize
8190           -funswitch-loops -fvect-cost-model -fvect-cost-model=dynamic
8191           -fversion-loops-for-strides
8192
8193       -O0 Reduce compilation time and make debugging produce the expected
8194           results.  This is the default.
8195
8196       -Os Optimize for size.  -Os enables all -O2 optimizations except those
8197           that often increase code size:
8198
8199           -falign-functions  -falign-jumps -falign-labels  -falign-loops
8200           -fprefetch-loop-arrays  -freorder-blocks-algorithm=stc
8201
8202           It also enables -finline-functions, causes the compiler to tune for
8203           code size rather than execution speed, and performs further
8204           optimizations designed to reduce code size.
8205
8206       -Ofast
8207           Disregard strict standards compliance.  -Ofast enables all -O3
8208           optimizations.  It also enables optimizations that are not valid
8209           for all standard-compliant programs.  It turns on -ffast-math,
8210           -fallow-store-data-races and the Fortran-specific -fstack-arrays,
8211           unless -fmax-stack-var-size is specified, and -fno-protect-parens.
8212
8213       -Og Optimize debugging experience.  -Og should be the optimization
8214           level of choice for the standard edit-compile-debug cycle, offering
8215           a reasonable level of optimization while maintaining fast
8216           compilation and a good debugging experience.  It is a better choice
8217           than -O0 for producing debuggable code because some compiler passes
8218           that collect debug information are disabled at -O0.
8219
8220           Like -O0, -Og completely disables a number of optimization passes
8221           so that individual options controlling them have no effect.
8222           Otherwise -Og enables all -O1 optimization flags except for those
8223           that may interfere with debugging:
8224
8225           -fbranch-count-reg  -fdelayed-branch -fdse  -fif-conversion
8226           -fif-conversion2 -finline-functions-called-once
8227           -fmove-loop-invariants  -fssa-phiopt -ftree-bit-ccp  -ftree-dse
8228           -ftree-pta  -ftree-sra
8229
8230       If you use multiple -O options, with or without level numbers, the last
8231       such option is the one that is effective.
8232
8233       Options of the form -fflag specify machine-independent flags.  Most
8234       flags have both positive and negative forms; the negative form of -ffoo
8235       is -fno-foo.  In the table below, only one of the forms is listed---the
8236       one you typically use.  You can figure out the other form by either
8237       removing no- or adding it.
8238
8239       The following options control specific optimizations.  They are either
8240       activated by -O options or are related to ones that are.  You can use
8241       the following flags in the rare cases when "fine-tuning" of
8242       optimizations to be performed is desired.
8243
8244       -fno-defer-pop
8245           For machines that must pop arguments after a function call, always
8246           pop the arguments as soon as each function returns.  At levels -O1
8247           and higher, -fdefer-pop is the default; this allows the compiler to
8248           let arguments accumulate on the stack for several function calls
8249           and pop them all at once.
8250
8251       -fforward-propagate
8252           Perform a forward propagation pass on RTL.  The pass tries to
8253           combine two instructions and checks if the result can be
8254           simplified.  If loop unrolling is active, two passes are performed
8255           and the second is scheduled after loop unrolling.
8256
8257           This option is enabled by default at optimization levels -O, -O2,
8258           -O3, -Os.
8259
8260       -ffp-contract=style
8261           -ffp-contract=off disables floating-point expression contraction.
8262           -ffp-contract=fast enables floating-point expression contraction
8263           such as forming of fused multiply-add operations if the target has
8264           native support for them.  -ffp-contract=on enables floating-point
8265           expression contraction if allowed by the language standard.  This
8266           is currently not implemented and treated equal to
8267           -ffp-contract=off.
8268
8269           The default is -ffp-contract=fast.
8270
8271       -fomit-frame-pointer
8272           Omit the frame pointer in functions that don't need one.  This
8273           avoids the instructions to save, set up and restore the frame
8274           pointer; on many targets it also makes an extra register available.
8275
8276           On some targets this flag has no effect because the standard
8277           calling sequence always uses a frame pointer, so it cannot be
8278           omitted.
8279
8280           Note that -fno-omit-frame-pointer doesn't guarantee the frame
8281           pointer is used in all functions.  Several targets always omit the
8282           frame pointer in leaf functions.
8283
8284           Enabled by default at -O and higher.
8285
8286       -foptimize-sibling-calls
8287           Optimize sibling and tail recursive calls.
8288
8289           Enabled at levels -O2, -O3, -Os.
8290
8291       -foptimize-strlen
8292           Optimize various standard C string functions (e.g. "strlen",
8293           "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into
8294           faster alternatives.
8295
8296           Enabled at levels -O2, -O3.
8297
8298       -fno-inline
8299           Do not expand any functions inline apart from those marked with the
8300           "always_inline" attribute.  This is the default when not
8301           optimizing.
8302
8303           Single functions can be exempted from inlining by marking them with
8304           the "noinline" attribute.
8305
8306       -finline-small-functions
8307           Integrate functions into their callers when their body is smaller
8308           than expected function call code (so overall size of program gets
8309           smaller).  The compiler heuristically decides which functions are
8310           simple enough to be worth integrating in this way.  This inlining
8311           applies to all functions, even those not declared inline.
8312
8313           Enabled at levels -O2, -O3, -Os.
8314
8315       -findirect-inlining
8316           Inline also indirect calls that are discovered to be known at
8317           compile time thanks to previous inlining.  This option has any
8318           effect only when inlining itself is turned on by the
8319           -finline-functions or -finline-small-functions options.
8320
8321           Enabled at levels -O2, -O3, -Os.
8322
8323       -finline-functions
8324           Consider all functions for inlining, even if they are not declared
8325           inline.  The compiler heuristically decides which functions are
8326           worth integrating in this way.
8327
8328           If all calls to a given function are integrated, and the function
8329           is declared "static", then the function is normally not output as
8330           assembler code in its own right.
8331
8332           Enabled at levels -O2, -O3, -Os.  Also enabled by -fprofile-use and
8333           -fauto-profile.
8334
8335       -finline-functions-called-once
8336           Consider all "static" functions called once for inlining into their
8337           caller even if they are not marked "inline".  If a call to a given
8338           function is integrated, then the function is not output as
8339           assembler code in its own right.
8340
8341           Enabled at levels -O1, -O2, -O3 and -Os, but not -Og.
8342
8343       -fearly-inlining
8344           Inline functions marked by "always_inline" and functions whose body
8345           seems smaller than the function call overhead early before doing
8346           -fprofile-generate instrumentation and real inlining pass.  Doing
8347           so makes profiling significantly cheaper and usually inlining
8348           faster on programs having large chains of nested wrapper functions.
8349
8350           Enabled by default.
8351
8352       -fipa-sra
8353           Perform interprocedural scalar replacement of aggregates, removal
8354           of unused parameters and replacement of parameters passed by
8355           reference by parameters passed by value.
8356
8357           Enabled at levels -O2, -O3 and -Os.
8358
8359       -finline-limit=n
8360           By default, GCC limits the size of functions that can be inlined.
8361           This flag allows coarse control of this limit.  n is the size of
8362           functions that can be inlined in number of pseudo instructions.
8363
8364           Inlining is actually controlled by a number of parameters, which
8365           may be specified individually by using --param name=value.  The
8366           -finline-limit=n option sets some of these parameters as follows:
8367
8368           max-inline-insns-single
8369               is set to n/2.
8370
8371           max-inline-insns-auto
8372               is set to n/2.
8373
8374           See below for a documentation of the individual parameters
8375           controlling inlining and for the defaults of these parameters.
8376
8377           Note: there may be no value to -finline-limit that results in
8378           default behavior.
8379
8380           Note: pseudo instruction represents, in this particular context, an
8381           abstract measurement of function's size.  In no way does it
8382           represent a count of assembly instructions and as such its exact
8383           meaning might change from one release to an another.
8384
8385       -fno-keep-inline-dllexport
8386           This is a more fine-grained version of -fkeep-inline-functions,
8387           which applies only to functions that are declared using the
8388           "dllexport" attribute or declspec.
8389
8390       -fkeep-inline-functions
8391           In C, emit "static" functions that are declared "inline" into the
8392           object file, even if the function has been inlined into all of its
8393           callers.  This switch does not affect functions using the "extern
8394           inline" extension in GNU C90.  In C++, emit any and all inline
8395           functions into the object file.
8396
8397       -fkeep-static-functions
8398           Emit "static" functions into the object file, even if the function
8399           is never used.
8400
8401       -fkeep-static-consts
8402           Emit variables declared "static const" when optimization isn't
8403           turned on, even if the variables aren't referenced.
8404
8405           GCC enables this option by default.  If you want to force the
8406           compiler to check if a variable is referenced, regardless of
8407           whether or not optimization is turned on, use the
8408           -fno-keep-static-consts option.
8409
8410       -fmerge-constants
8411           Attempt to merge identical constants (string constants and
8412           floating-point constants) across compilation units.
8413
8414           This option is the default for optimized compilation if the
8415           assembler and linker support it.  Use -fno-merge-constants to
8416           inhibit this behavior.
8417
8418           Enabled at levels -O, -O2, -O3, -Os.
8419
8420       -fmerge-all-constants
8421           Attempt to merge identical constants and identical variables.
8422
8423           This option implies -fmerge-constants.  In addition to
8424           -fmerge-constants this considers e.g. even constant initialized
8425           arrays or initialized constant variables with integral or floating-
8426           point types.  Languages like C or C++ require each variable,
8427           including multiple instances of the same variable in recursive
8428           calls, to have distinct locations, so using this option results in
8429           non-conforming behavior.
8430
8431       -fmodulo-sched
8432           Perform swing modulo scheduling immediately before the first
8433           scheduling pass.  This pass looks at innermost loops and reorders
8434           their instructions by overlapping different iterations.
8435
8436       -fmodulo-sched-allow-regmoves
8437           Perform more aggressive SMS-based modulo scheduling with register
8438           moves allowed.  By setting this flag certain anti-dependences edges
8439           are deleted, which triggers the generation of reg-moves based on
8440           the life-range analysis.  This option is effective only with
8441           -fmodulo-sched enabled.
8442
8443       -fno-branch-count-reg
8444           Disable the optimization pass that scans for opportunities to use
8445           "decrement and branch" instructions on a count register instead of
8446           instruction sequences that decrement a register, compare it against
8447           zero, and then branch based upon the result.  This option is only
8448           meaningful on architectures that support such instructions, which
8449           include x86, PowerPC, IA-64 and S/390.  Note that the
8450           -fno-branch-count-reg option doesn't remove the decrement and
8451           branch instructions from the generated instruction stream
8452           introduced by other optimization passes.
8453
8454           The default is -fbranch-count-reg at -O1 and higher, except for
8455           -Og.
8456
8457       -fno-function-cse
8458           Do not put function addresses in registers; make each instruction
8459           that calls a constant function contain the function's address
8460           explicitly.
8461
8462           This option results in less efficient code, but some strange hacks
8463           that alter the assembler output may be confused by the
8464           optimizations performed when this option is not used.
8465
8466           The default is -ffunction-cse
8467
8468       -fno-zero-initialized-in-bss
8469           If the target supports a BSS section, GCC by default puts variables
8470           that are initialized to zero into BSS.  This can save space in the
8471           resulting code.
8472
8473           This option turns off this behavior because some programs
8474           explicitly rely on variables going to the data section---e.g., so
8475           that the resulting executable can find the beginning of that
8476           section and/or make assumptions based on that.
8477
8478           The default is -fzero-initialized-in-bss.
8479
8480       -fthread-jumps
8481           Perform optimizations that check to see if a jump branches to a
8482           location where another comparison subsumed by the first is found.
8483           If so, the first branch is redirected to either the destination of
8484           the second branch or a point immediately following it, depending on
8485           whether the condition is known to be true or false.
8486
8487           Enabled at levels -O2, -O3, -Os.
8488
8489       -fsplit-wide-types
8490           When using a type that occupies multiple registers, such as "long
8491           long" on a 32-bit system, split the registers apart and allocate
8492           them independently.  This normally generates better code for those
8493           types, but may make debugging more difficult.
8494
8495           Enabled at levels -O, -O2, -O3, -Os.
8496
8497       -fsplit-wide-types-early
8498           Fully split wide types early, instead of very late.  This option
8499           has no effect unless -fsplit-wide-types is turned on.
8500
8501           This is the default on some targets.
8502
8503       -fcse-follow-jumps
8504           In common subexpression elimination (CSE), scan through jump
8505           instructions when the target of the jump is not reached by any
8506           other path.  For example, when CSE encounters an "if" statement
8507           with an "else" clause, CSE follows the jump when the condition
8508           tested is false.
8509
8510           Enabled at levels -O2, -O3, -Os.
8511
8512       -fcse-skip-blocks
8513           This is similar to -fcse-follow-jumps, but causes CSE to follow
8514           jumps that conditionally skip over blocks.  When CSE encounters a
8515           simple "if" statement with no else clause, -fcse-skip-blocks causes
8516           CSE to follow the jump around the body of the "if".
8517
8518           Enabled at levels -O2, -O3, -Os.
8519
8520       -frerun-cse-after-loop
8521           Re-run common subexpression elimination after loop optimizations
8522           are performed.
8523
8524           Enabled at levels -O2, -O3, -Os.
8525
8526       -fgcse
8527           Perform a global common subexpression elimination pass.  This pass
8528           also performs global constant and copy propagation.
8529
8530           Note: When compiling a program using computed gotos, a GCC
8531           extension, you may get better run-time performance if you disable
8532           the global common subexpression elimination pass by adding
8533           -fno-gcse to the command line.
8534
8535           Enabled at levels -O2, -O3, -Os.
8536
8537       -fgcse-lm
8538           When -fgcse-lm is enabled, global common subexpression elimination
8539           attempts to move loads that are only killed by stores into
8540           themselves.  This allows a loop containing a load/store sequence to
8541           be changed to a load outside the loop, and a copy/store within the
8542           loop.
8543
8544           Enabled by default when -fgcse is enabled.
8545
8546       -fgcse-sm
8547           When -fgcse-sm is enabled, a store motion pass is run after global
8548           common subexpression elimination.  This pass attempts to move
8549           stores out of loops.  When used in conjunction with -fgcse-lm,
8550           loops containing a load/store sequence can be changed to a load
8551           before the loop and a store after the loop.
8552
8553           Not enabled at any optimization level.
8554
8555       -fgcse-las
8556           When -fgcse-las is enabled, the global common subexpression
8557           elimination pass eliminates redundant loads that come after stores
8558           to the same memory location (both partial and full redundancies).
8559
8560           Not enabled at any optimization level.
8561
8562       -fgcse-after-reload
8563           When -fgcse-after-reload is enabled, a redundant load elimination
8564           pass is performed after reload.  The purpose of this pass is to
8565           clean up redundant spilling.
8566
8567           Enabled by -fprofile-use and -fauto-profile.
8568
8569       -faggressive-loop-optimizations
8570           This option tells the loop optimizer to use language constraints to
8571           derive bounds for the number of iterations of a loop.  This assumes
8572           that loop code does not invoke undefined behavior by for example
8573           causing signed integer overflows or out-of-bound array accesses.
8574           The bounds for the number of iterations of a loop are used to guide
8575           loop unrolling and peeling and loop exit test optimizations.  This
8576           option is enabled by default.
8577
8578       -funconstrained-commons
8579           This option tells the compiler that variables declared in common
8580           blocks (e.g. Fortran) may later be overridden with longer trailing
8581           arrays. This prevents certain optimizations that depend on knowing
8582           the array bounds.
8583
8584       -fcrossjumping
8585           Perform cross-jumping transformation.  This transformation unifies
8586           equivalent code and saves code size.  The resulting code may or may
8587           not perform better than without cross-jumping.
8588
8589           Enabled at levels -O2, -O3, -Os.
8590
8591       -fauto-inc-dec
8592           Combine increments or decrements of addresses with memory accesses.
8593           This pass is always skipped on architectures that do not have
8594           instructions to support this.  Enabled by default at -O and higher
8595           on architectures that support this.
8596
8597       -fdce
8598           Perform dead code elimination (DCE) on RTL.  Enabled by default at
8599           -O and higher.
8600
8601       -fdse
8602           Perform dead store elimination (DSE) on RTL.  Enabled by default at
8603           -O and higher.
8604
8605       -fif-conversion
8606           Attempt to transform conditional jumps into branch-less
8607           equivalents.  This includes use of conditional moves, min, max, set
8608           flags and abs instructions, and some tricks doable by standard
8609           arithmetics.  The use of conditional execution on chips where it is
8610           available is controlled by -fif-conversion2.
8611
8612           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.
8613
8614       -fif-conversion2
8615           Use conditional execution (where available) to transform
8616           conditional jumps into branch-less equivalents.
8617
8618           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.
8619
8620       -fdeclone-ctor-dtor
8621           The C++ ABI requires multiple entry points for constructors and
8622           destructors: one for a base subobject, one for a complete object,
8623           and one for a virtual destructor that calls operator delete
8624           afterwards.  For a hierarchy with virtual bases, the base and
8625           complete variants are clones, which means two copies of the
8626           function.  With this option, the base and complete variants are
8627           changed to be thunks that call a common implementation.
8628
8629           Enabled by -Os.
8630
8631       -fdelete-null-pointer-checks
8632           Assume that programs cannot safely dereference null pointers, and
8633           that no code or data element resides at address zero.  This option
8634           enables simple constant folding optimizations at all optimization
8635           levels.  In addition, other optimization passes in GCC use this
8636           flag to control global dataflow analyses that eliminate useless
8637           checks for null pointers; these assume that a memory access to
8638           address zero always results in a trap, so that if a pointer is
8639           checked after it has already been dereferenced, it cannot be null.
8640
8641           Note however that in some environments this assumption is not true.
8642           Use -fno-delete-null-pointer-checks to disable this optimization
8643           for programs that depend on that behavior.
8644
8645           This option is enabled by default on most targets.  On Nios II ELF,
8646           it defaults to off.  On AVR, CR16, and MSP430, this option is
8647           completely disabled.
8648
8649           Passes that use the dataflow information are enabled independently
8650           at different optimization levels.
8651
8652       -fdevirtualize
8653           Attempt to convert calls to virtual functions to direct calls.
8654           This is done both within a procedure and interprocedurally as part
8655           of indirect inlining (-findirect-inlining) and interprocedural
8656           constant propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.
8657
8658       -fdevirtualize-speculatively
8659           Attempt to convert calls to virtual functions to speculative direct
8660           calls.  Based on the analysis of the type inheritance graph,
8661           determine for a given call the set of likely targets. If the set is
8662           small, preferably of size 1, change the call into a conditional
8663           deciding between direct and indirect calls.  The speculative calls
8664           enable more optimizations, such as inlining.  When they seem
8665           useless after further optimization, they are converted back into
8666           original form.
8667
8668       -fdevirtualize-at-ltrans
8669           Stream extra information needed for aggressive devirtualization
8670           when running the link-time optimizer in local transformation mode.
8671           This option enables more devirtualization but significantly
8672           increases the size of streamed data. For this reason it is disabled
8673           by default.
8674
8675       -fexpensive-optimizations
8676           Perform a number of minor optimizations that are relatively
8677           expensive.
8678
8679           Enabled at levels -O2, -O3, -Os.
8680
8681       -free
8682           Attempt to remove redundant extension instructions.  This is
8683           especially helpful for the x86-64 architecture, which implicitly
8684           zero-extends in 64-bit registers after writing to their lower
8685           32-bit half.
8686
8687           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.
8688
8689       -fno-lifetime-dse
8690           In C++ the value of an object is only affected by changes within
8691           its lifetime: when the constructor begins, the object has an
8692           indeterminate value, and any changes during the lifetime of the
8693           object are dead when the object is destroyed.  Normally dead store
8694           elimination will take advantage of this; if your code relies on the
8695           value of the object storage persisting beyond the lifetime of the
8696           object, you can use this flag to disable this optimization.  To
8697           preserve stores before the constructor starts (e.g. because your
8698           operator new clears the object storage) but still treat the object
8699           as dead after the destructor, you can use -flifetime-dse=1.  The
8700           default behavior can be explicitly selected with -flifetime-dse=2.
8701           -flifetime-dse=0 is equivalent to -fno-lifetime-dse.
8702
8703       -flive-range-shrinkage
8704           Attempt to decrease register pressure through register live range
8705           shrinkage.  This is helpful for fast processors with small or
8706           moderate size register sets.
8707
8708       -fira-algorithm=algorithm
8709           Use the specified coloring algorithm for the integrated register
8710           allocator.  The algorithm argument can be priority, which specifies
8711           Chow's priority coloring, or CB, which specifies Chaitin-Briggs
8712           coloring.  Chaitin-Briggs coloring is not implemented for all
8713           architectures, but for those targets that do support it, it is the
8714           default because it generates better code.
8715
8716       -fira-region=region
8717           Use specified regions for the integrated register allocator.  The
8718           region argument should be one of the following:
8719
8720           all Use all loops as register allocation regions.  This can give
8721               the best results for machines with a small and/or irregular
8722               register set.
8723
8724           mixed
8725               Use all loops except for loops with small register pressure as
8726               the regions.  This value usually gives the best results in most
8727               cases and for most architectures, and is enabled by default
8728               when compiling with optimization for speed (-O, -O2, ...).
8729
8730           one Use all functions as a single region.  This typically results
8731               in the smallest code size, and is enabled by default for -Os or
8732               -O0.
8733
8734       -fira-hoist-pressure
8735           Use IRA to evaluate register pressure in the code hoisting pass for
8736           decisions to hoist expressions.  This option usually results in
8737           smaller code, but it can slow the compiler down.
8738
8739           This option is enabled at level -Os for all targets.
8740
8741       -fira-loop-pressure
8742           Use IRA to evaluate register pressure in loops for decisions to
8743           move loop invariants.  This option usually results in generation of
8744           faster and smaller code on machines with large register files (>=
8745           32 registers), but it can slow the compiler down.
8746
8747           This option is enabled at level -O3 for some targets.
8748
8749       -fno-ira-share-save-slots
8750           Disable sharing of stack slots used for saving call-used hard
8751           registers living through a call.  Each hard register gets a
8752           separate stack slot, and as a result function stack frames are
8753           larger.
8754
8755       -fno-ira-share-spill-slots
8756           Disable sharing of stack slots allocated for pseudo-registers.
8757           Each pseudo-register that does not get a hard register gets a
8758           separate stack slot, and as a result function stack frames are
8759           larger.
8760
8761       -flra-remat
8762           Enable CFG-sensitive rematerialization in LRA.  Instead of loading
8763           values of spilled pseudos, LRA tries to rematerialize (recalculate)
8764           values if it is profitable.
8765
8766           Enabled at levels -O2, -O3, -Os.
8767
8768       -fdelayed-branch
8769           If supported for the target machine, attempt to reorder
8770           instructions to exploit instruction slots available after delayed
8771           branch instructions.
8772
8773           Enabled at levels -O, -O2, -O3, -Os, but not at -Og.
8774
8775       -fschedule-insns
8776           If supported for the target machine, attempt to reorder
8777           instructions to eliminate execution stalls due to required data
8778           being unavailable.  This helps machines that have slow floating
8779           point or memory load instructions by allowing other instructions to
8780           be issued until the result of the load or floating-point
8781           instruction is required.
8782
8783           Enabled at levels -O2, -O3.
8784
8785       -fschedule-insns2
8786           Similar to -fschedule-insns, but requests an additional pass of
8787           instruction scheduling after register allocation has been done.
8788           This is especially useful on machines with a relatively small
8789           number of registers and where memory load instructions take more
8790           than one cycle.
8791
8792           Enabled at levels -O2, -O3, -Os.
8793
8794       -fno-sched-interblock
8795           Disable instruction scheduling across basic blocks, which is
8796           normally enabled when scheduling before register allocation, i.e.
8797           with -fschedule-insns or at -O2 or higher.
8798
8799       -fno-sched-spec
8800           Disable speculative motion of non-load instructions, which is
8801           normally enabled when scheduling before register allocation, i.e.
8802           with -fschedule-insns or at -O2 or higher.
8803
8804       -fsched-pressure
8805           Enable register pressure sensitive insn scheduling before register
8806           allocation.  This only makes sense when scheduling before register
8807           allocation is enabled, i.e. with -fschedule-insns or at -O2 or
8808           higher.  Usage of this option can improve the generated code and
8809           decrease its size by preventing register pressure increase above
8810           the number of available hard registers and subsequent spills in
8811           register allocation.
8812
8813       -fsched-spec-load
8814           Allow speculative motion of some load instructions.  This only
8815           makes sense when scheduling before register allocation, i.e. with
8816           -fschedule-insns or at -O2 or higher.
8817
8818       -fsched-spec-load-dangerous
8819           Allow speculative motion of more load instructions.  This only
8820           makes sense when scheduling before register allocation, i.e. with
8821           -fschedule-insns or at -O2 or higher.
8822
8823       -fsched-stalled-insns
8824       -fsched-stalled-insns=n
8825           Define how many insns (if any) can be moved prematurely from the
8826           queue of stalled insns into the ready list during the second
8827           scheduling pass.  -fno-sched-stalled-insns means that no insns are
8828           moved prematurely, -fsched-stalled-insns=0 means there is no limit
8829           on how many queued insns can be moved prematurely.
8830           -fsched-stalled-insns without a value is equivalent to
8831           -fsched-stalled-insns=1.
8832
8833       -fsched-stalled-insns-dep
8834       -fsched-stalled-insns-dep=n
8835           Define how many insn groups (cycles) are examined for a dependency
8836           on a stalled insn that is a candidate for premature removal from
8837           the queue of stalled insns.  This has an effect only during the
8838           second scheduling pass, and only if -fsched-stalled-insns is used.
8839           -fno-sched-stalled-insns-dep is equivalent to
8840           -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a
8841           value is equivalent to -fsched-stalled-insns-dep=1.
8842
8843       -fsched2-use-superblocks
8844           When scheduling after register allocation, use superblock
8845           scheduling.  This allows motion across basic block boundaries,
8846           resulting in faster schedules.  This option is experimental, as not
8847           all machine descriptions used by GCC model the CPU closely enough
8848           to avoid unreliable results from the algorithm.
8849
8850           This only makes sense when scheduling after register allocation,
8851           i.e. with -fschedule-insns2 or at -O2 or higher.
8852
8853       -fsched-group-heuristic
8854           Enable the group heuristic in the scheduler.  This heuristic favors
8855           the instruction that belongs to a schedule group.  This is enabled
8856           by default when scheduling is enabled, i.e. with -fschedule-insns
8857           or -fschedule-insns2 or at -O2 or higher.
8858
8859       -fsched-critical-path-heuristic
8860           Enable the critical-path heuristic in the scheduler.  This
8861           heuristic favors instructions on the critical path.  This is
8862           enabled by default when scheduling is enabled, i.e. with
8863           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
8864
8865       -fsched-spec-insn-heuristic
8866           Enable the speculative instruction heuristic in the scheduler.
8867           This heuristic favors speculative instructions with greater
8868           dependency weakness.  This is enabled by default when scheduling is
8869           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
8870           or higher.
8871
8872       -fsched-rank-heuristic
8873           Enable the rank heuristic in the scheduler.  This heuristic favors
8874           the instruction belonging to a basic block with greater size or
8875           frequency.  This is enabled by default when scheduling is enabled,
8876           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
8877           higher.
8878
8879       -fsched-last-insn-heuristic
8880           Enable the last-instruction heuristic in the scheduler.  This
8881           heuristic favors the instruction that is less dependent on the last
8882           instruction scheduled.  This is enabled by default when scheduling
8883           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
8884           -O2 or higher.
8885
8886       -fsched-dep-count-heuristic
8887           Enable the dependent-count heuristic in the scheduler.  This
8888           heuristic favors the instruction that has more instructions
8889           depending on it.  This is enabled by default when scheduling is
8890           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
8891           or higher.
8892
8893       -freschedule-modulo-scheduled-loops
8894           Modulo scheduling is performed before traditional scheduling.  If a
8895           loop is modulo scheduled, later scheduling passes may change its
8896           schedule.  Use this option to control that behavior.
8897
8898       -fselective-scheduling
8899           Schedule instructions using selective scheduling algorithm.
8900           Selective scheduling runs instead of the first scheduler pass.
8901
8902       -fselective-scheduling2
8903           Schedule instructions using selective scheduling algorithm.
8904           Selective scheduling runs instead of the second scheduler pass.
8905
8906       -fsel-sched-pipelining
8907           Enable software pipelining of innermost loops during selective
8908           scheduling.  This option has no effect unless one of
8909           -fselective-scheduling or -fselective-scheduling2 is turned on.
8910
8911       -fsel-sched-pipelining-outer-loops
8912           When pipelining loops during selective scheduling, also pipeline
8913           outer loops.  This option has no effect unless
8914           -fsel-sched-pipelining is turned on.
8915
8916       -fsemantic-interposition
8917           Some object formats, like ELF, allow interposing of symbols by the
8918           dynamic linker.  This means that for symbols exported from the DSO,
8919           the compiler cannot perform interprocedural propagation, inlining
8920           and other optimizations in anticipation that the function or
8921           variable in question may change. While this feature is useful, for
8922           example, to rewrite memory allocation functions by a debugging
8923           implementation, it is expensive in the terms of code quality.  With
8924           -fno-semantic-interposition the compiler assumes that if
8925           interposition happens for functions the overwriting function will
8926           have precisely the same semantics (and side effects).  Similarly if
8927           interposition happens for variables, the constructor of the
8928           variable will be the same. The flag has no effect for functions
8929           explicitly declared inline (where it is never allowed for
8930           interposition to change semantics) and for symbols explicitly
8931           declared weak.
8932
8933       -fshrink-wrap
8934           Emit function prologues only before parts of the function that need
8935           it, rather than at the top of the function.  This flag is enabled
8936           by default at -O and higher.
8937
8938       -fshrink-wrap-separate
8939           Shrink-wrap separate parts of the prologue and epilogue separately,
8940           so that those parts are only executed when needed.  This option is
8941           on by default, but has no effect unless -fshrink-wrap is also
8942           turned on and the target supports this.
8943
8944       -fcaller-saves
8945           Enable allocation of values to registers that are clobbered by
8946           function calls, by emitting extra instructions to save and restore
8947           the registers around such calls.  Such allocation is done only when
8948           it seems to result in better code.
8949
8950           This option is always enabled by default on certain machines,
8951           usually those which have no call-preserved registers to use
8952           instead.
8953
8954           Enabled at levels -O2, -O3, -Os.
8955
8956       -fcombine-stack-adjustments
8957           Tracks stack adjustments (pushes and pops) and stack memory
8958           references and then tries to find ways to combine them.
8959
8960           Enabled by default at -O1 and higher.
8961
8962       -fipa-ra
8963           Use caller save registers for allocation if those registers are not
8964           used by any called function.  In that case it is not necessary to
8965           save and restore them around calls.  This is only possible if
8966           called functions are part of same compilation unit as current
8967           function and they are compiled before it.
8968
8969           Enabled at levels -O2, -O3, -Os, however the option is disabled if
8970           generated code will be instrumented for profiling (-p, or -pg) or
8971           if callee's register usage cannot be known exactly (this happens on
8972           targets that do not expose prologues and epilogues in RTL).
8973
8974       -fconserve-stack
8975           Attempt to minimize stack usage.  The compiler attempts to use less
8976           stack space, even if that makes the program slower.  This option
8977           implies setting the large-stack-frame parameter to 100 and the
8978           large-stack-frame-growth parameter to 400.
8979
8980       -ftree-reassoc
8981           Perform reassociation on trees.  This flag is enabled by default at
8982           -O and higher.
8983
8984       -fcode-hoisting
8985           Perform code hoisting.  Code hoisting tries to move the evaluation
8986           of expressions executed on all paths to the function exit as early
8987           as possible.  This is especially useful as a code size
8988           optimization, but it often helps for code speed as well.  This flag
8989           is enabled by default at -O2 and higher.
8990
8991       -ftree-pre
8992           Perform partial redundancy elimination (PRE) on trees.  This flag
8993           is enabled by default at -O2 and -O3.
8994
8995       -ftree-partial-pre
8996           Make partial redundancy elimination (PRE) more aggressive.  This
8997           flag is enabled by default at -O3.
8998
8999       -ftree-forwprop
9000           Perform forward propagation on trees.  This flag is enabled by
9001           default at -O and higher.
9002
9003       -ftree-fre
9004           Perform full redundancy elimination (FRE) on trees.  The difference
9005           between FRE and PRE is that FRE only considers expressions that are
9006           computed on all paths leading to the redundant computation.  This
9007           analysis is faster than PRE, though it exposes fewer redundancies.
9008           This flag is enabled by default at -O and higher.
9009
9010       -ftree-phiprop
9011           Perform hoisting of loads from conditional pointers on trees.  This
9012           pass is enabled by default at -O and higher.
9013
9014       -fhoist-adjacent-loads
9015           Speculatively hoist loads from both branches of an if-then-else if
9016           the loads are from adjacent locations in the same structure and the
9017           target architecture has a conditional move instruction.  This flag
9018           is enabled by default at -O2 and higher.
9019
9020       -ftree-copy-prop
9021           Perform copy propagation on trees.  This pass eliminates
9022           unnecessary copy operations.  This flag is enabled by default at -O
9023           and higher.
9024
9025       -fipa-pure-const
9026           Discover which functions are pure or constant.  Enabled by default
9027           at -O and higher.
9028
9029       -fipa-reference
9030           Discover which static variables do not escape the compilation unit.
9031           Enabled by default at -O and higher.
9032
9033       -fipa-reference-addressable
9034           Discover read-only, write-only and non-addressable static
9035           variables.  Enabled by default at -O and higher.
9036
9037       -fipa-stack-alignment
9038           Reduce stack alignment on call sites if possible.  Enabled by
9039           default.
9040
9041       -fipa-pta
9042           Perform interprocedural pointer analysis and interprocedural
9043           modification and reference analysis.  This option can cause
9044           excessive memory and compile-time usage on large compilation units.
9045           It is not enabled by default at any optimization level.
9046
9047       -fipa-profile
9048           Perform interprocedural profile propagation.  The functions called
9049           only from cold functions are marked as cold. Also functions
9050           executed once (such as "cold", "noreturn", static constructors or
9051           destructors) are identified. Cold functions and loop less parts of
9052           functions executed once are then optimized for size.  Enabled by
9053           default at -O and higher.
9054
9055       -fipa-modref
9056           Perform interprocedural mod/ref analysis.  This optimization
9057           analyzes the side effects of functions (memory locations that are
9058           modified or referenced) and enables better optimization across the
9059           function call boundary.  This flag is enabled by default at -O and
9060           higher.
9061
9062       -fipa-cp
9063           Perform interprocedural constant propagation.  This optimization
9064           analyzes the program to determine when values passed to functions
9065           are constants and then optimizes accordingly.  This optimization
9066           can substantially increase performance if the application has
9067           constants passed to functions.  This flag is enabled by default at
9068           -O2, -Os and -O3.  It is also enabled by -fprofile-use and
9069           -fauto-profile.
9070
9071       -fipa-cp-clone
9072           Perform function cloning to make interprocedural constant
9073           propagation stronger.  When enabled, interprocedural constant
9074           propagation performs function cloning when externally visible
9075           function can be called with constant arguments.  Because this
9076           optimization can create multiple copies of functions, it may
9077           significantly increase code size (see --param
9078           ipa-cp-unit-growth=value).  This flag is enabled by default at -O3.
9079           It is also enabled by -fprofile-use and -fauto-profile.
9080
9081       -fipa-bit-cp
9082           When enabled, perform interprocedural bitwise constant propagation.
9083           This flag is enabled by default at -O2 and by -fprofile-use and
9084           -fauto-profile.  It requires that -fipa-cp is enabled.
9085
9086       -fipa-vrp
9087           When enabled, perform interprocedural propagation of value ranges.
9088           This flag is enabled by default at -O2. It requires that -fipa-cp
9089           is enabled.
9090
9091       -fipa-icf
9092           Perform Identical Code Folding for functions and read-only
9093           variables.  The optimization reduces code size and may disturb
9094           unwind stacks by replacing a function by equivalent one with a
9095           different name. The optimization works more effectively with link-
9096           time optimization enabled.
9097
9098           Although the behavior is similar to the Gold Linker's ICF
9099           optimization, GCC ICF works on different levels and thus the
9100           optimizations are not same - there are equivalences that are found
9101           only by GCC and equivalences found only by Gold.
9102
9103           This flag is enabled by default at -O2 and -Os.
9104
9105       -flive-patching=level
9106           Control GCC's optimizations to produce output suitable for live-
9107           patching.
9108
9109           If the compiler's optimization uses a function's body or
9110           information extracted from its body to optimize/change another
9111           function, the latter is called an impacted function of the former.
9112           If a function is patched, its impacted functions should be patched
9113           too.
9114
9115           The impacted functions are determined by the compiler's
9116           interprocedural optimizations.  For example, a caller is impacted
9117           when inlining a function into its caller, cloning a function and
9118           changing its caller to call this new clone, or extracting a
9119           function's pureness/constness information to optimize its direct or
9120           indirect callers, etc.
9121
9122           Usually, the more IPA optimizations enabled, the larger the number
9123           of impacted functions for each function.  In order to control the
9124           number of impacted functions and more easily compute the list of
9125           impacted function, IPA optimizations can be partially enabled at
9126           two different levels.
9127
9128           The level argument should be one of the following:
9129
9130           inline-clone
9131               Only enable inlining and cloning optimizations, which includes
9132               inlining, cloning, interprocedural scalar replacement of
9133               aggregates and partial inlining.  As a result, when patching a
9134               function, all its callers and its clones' callers are impacted,
9135               therefore need to be patched as well.
9136
9137               -flive-patching=inline-clone disables the following
9138               optimization flags: -fwhole-program  -fipa-pta  -fipa-reference
9139               -fipa-ra -fipa-icf  -fipa-icf-functions  -fipa-icf-variables
9140               -fipa-bit-cp  -fipa-vrp  -fipa-pure-const
9141               -fipa-reference-addressable -fipa-stack-alignment -fipa-modref
9142
9143           inline-only-static
9144               Only enable inlining of static functions.  As a result, when
9145               patching a static function, all its callers are impacted and so
9146               need to be patched as well.
9147
9148               In addition to all the flags that -flive-patching=inline-clone
9149               disables, -flive-patching=inline-only-static disables the
9150               following additional optimization flags: -fipa-cp-clone
9151               -fipa-sra  -fpartial-inlining  -fipa-cp
9152
9153           When -flive-patching is specified without any value, the default
9154           value is inline-clone.
9155
9156           This flag is disabled by default.
9157
9158           Note that -flive-patching is not supported with link-time
9159           optimization (-flto).
9160
9161       -fisolate-erroneous-paths-dereference
9162           Detect paths that trigger erroneous or undefined behavior due to
9163           dereferencing a null pointer.  Isolate those paths from the main
9164           control flow and turn the statement with erroneous or undefined
9165           behavior into a trap.  This flag is enabled by default at -O2 and
9166           higher and depends on -fdelete-null-pointer-checks also being
9167           enabled.
9168
9169       -fisolate-erroneous-paths-attribute
9170           Detect paths that trigger erroneous or undefined behavior due to a
9171           null value being used in a way forbidden by a "returns_nonnull" or
9172           "nonnull" attribute.  Isolate those paths from the main control
9173           flow and turn the statement with erroneous or undefined behavior
9174           into a trap.  This is not currently enabled, but may be enabled by
9175           -O2 in the future.
9176
9177       -ftree-sink
9178           Perform forward store motion on trees.  This flag is enabled by
9179           default at -O and higher.
9180
9181       -ftree-bit-ccp
9182           Perform sparse conditional bit constant propagation on trees and
9183           propagate pointer alignment information.  This pass only operates
9184           on local scalar variables and is enabled by default at -O1 and
9185           higher, except for -Og.  It requires that -ftree-ccp is enabled.
9186
9187       -ftree-ccp
9188           Perform sparse conditional constant propagation (CCP) on trees.
9189           This pass only operates on local scalar variables and is enabled by
9190           default at -O and higher.
9191
9192       -fssa-backprop
9193           Propagate information about uses of a value up the definition chain
9194           in order to simplify the definitions.  For example, this pass
9195           strips sign operations if the sign of a value never matters.  The
9196           flag is enabled by default at -O and higher.
9197
9198       -fssa-phiopt
9199           Perform pattern matching on SSA PHI nodes to optimize conditional
9200           code.  This pass is enabled by default at -O1 and higher, except
9201           for -Og.
9202
9203       -ftree-switch-conversion
9204           Perform conversion of simple initializations in a switch to
9205           initializations from a scalar array.  This flag is enabled by
9206           default at -O2 and higher.
9207
9208       -ftree-tail-merge
9209           Look for identical code sequences.  When found, replace one with a
9210           jump to the other.  This optimization is known as tail merging or
9211           cross jumping.  This flag is enabled by default at -O2 and higher.
9212           The compilation time in this pass can be limited using max-tail-
9213           merge-comparisons parameter and max-tail-merge-iterations
9214           parameter.
9215
9216       -ftree-dce
9217           Perform dead code elimination (DCE) on trees.  This flag is enabled
9218           by default at -O and higher.
9219
9220       -ftree-builtin-call-dce
9221           Perform conditional dead code elimination (DCE) for calls to built-
9222           in functions that may set "errno" but are otherwise free of side
9223           effects.  This flag is enabled by default at -O2 and higher if -Os
9224           is not also specified.
9225
9226       -ffinite-loops
9227           Assume that a loop with an exit will eventually take the exit and
9228           not loop indefinitely.  This allows the compiler to remove loops
9229           that otherwise have no side-effects, not considering eventual
9230           endless looping as such.
9231
9232           This option is enabled by default at -O2 for C++ with -std=c++11 or
9233           higher.
9234
9235       -ftree-dominator-opts
9236           Perform a variety of simple scalar cleanups (constant/copy
9237           propagation, redundancy elimination, range propagation and
9238           expression simplification) based on a dominator tree traversal.
9239           This also performs jump threading (to reduce jumps to jumps). This
9240           flag is enabled by default at -O and higher.
9241
9242       -ftree-dse
9243           Perform dead store elimination (DSE) on trees.  A dead store is a
9244           store into a memory location that is later overwritten by another
9245           store without any intervening loads.  In this case the earlier
9246           store can be deleted.  This flag is enabled by default at -O and
9247           higher.
9248
9249       -ftree-ch
9250           Perform loop header copying on trees.  This is beneficial since it
9251           increases effectiveness of code motion optimizations.  It also
9252           saves one jump.  This flag is enabled by default at -O and higher.
9253           It is not enabled for -Os, since it usually increases code size.
9254
9255       -ftree-loop-optimize
9256           Perform loop optimizations on trees.  This flag is enabled by
9257           default at -O and higher.
9258
9259       -ftree-loop-linear
9260       -floop-strip-mine
9261       -floop-block
9262           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To
9263           use this code transformation, GCC has to be configured with
9264           --with-isl to enable the Graphite loop transformation
9265           infrastructure.
9266
9267       -fgraphite-identity
9268           Enable the identity transformation for graphite.  For every SCoP we
9269           generate the polyhedral representation and transform it back to
9270           gimple.  Using -fgraphite-identity we can check the costs or
9271           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
9272           minimal optimizations are also performed by the code generator isl,
9273           like index splitting and dead code elimination in loops.
9274
9275       -floop-nest-optimize
9276           Enable the isl based loop nest optimizer.  This is a generic loop
9277           nest optimizer based on the Pluto optimization algorithms.  It
9278           calculates a loop structure optimized for data-locality and
9279           parallelism.  This option is experimental.
9280
9281       -floop-parallelize-all
9282           Use the Graphite data dependence analysis to identify loops that
9283           can be parallelized.  Parallelize all the loops that can be
9284           analyzed to not contain loop carried dependences without checking
9285           that it is profitable to parallelize the loops.
9286
9287       -ftree-coalesce-vars
9288           While transforming the program out of the SSA representation,
9289           attempt to reduce copying by coalescing versions of different user-
9290           defined variables, instead of just compiler temporaries.  This may
9291           severely limit the ability to debug an optimized program compiled
9292           with -fno-var-tracking-assignments.  In the negated form, this flag
9293           prevents SSA coalescing of user variables.  This option is enabled
9294           by default if optimization is enabled, and it does very little
9295           otherwise.
9296
9297       -ftree-loop-if-convert
9298           Attempt to transform conditional jumps in the innermost loops to
9299           branch-less equivalents.  The intent is to remove control-flow from
9300           the innermost loops in order to improve the ability of the
9301           vectorization pass to handle these loops.  This is enabled by
9302           default if vectorization is enabled.
9303
9304       -ftree-loop-distribution
9305           Perform loop distribution.  This flag can improve cache performance
9306           on big loop bodies and allow further loop optimizations, like
9307           parallelization or vectorization, to take place.  For example, the
9308           loop
9309
9310                   DO I = 1, N
9311                     A(I) = B(I) + C
9312                     D(I) = E(I) * F
9313                   ENDDO
9314
9315           is transformed to
9316
9317                   DO I = 1, N
9318                      A(I) = B(I) + C
9319                   ENDDO
9320                   DO I = 1, N
9321                      D(I) = E(I) * F
9322                   ENDDO
9323
9324           This flag is enabled by default at -O3.  It is also enabled by
9325           -fprofile-use and -fauto-profile.
9326
9327       -ftree-loop-distribute-patterns
9328           Perform loop distribution of patterns that can be code generated
9329           with calls to a library.  This flag is enabled by default at -O2
9330           and higher, and by -fprofile-use and -fauto-profile.
9331
9332           This pass distributes the initialization loops and generates a call
9333           to memset zero.  For example, the loop
9334
9335                   DO I = 1, N
9336                     A(I) = 0
9337                     B(I) = A(I) + I
9338                   ENDDO
9339
9340           is transformed to
9341
9342                   DO I = 1, N
9343                      A(I) = 0
9344                   ENDDO
9345                   DO I = 1, N
9346                      B(I) = A(I) + I
9347                   ENDDO
9348
9349           and the initialization loop is transformed into a call to memset
9350           zero.  This flag is enabled by default at -O3.  It is also enabled
9351           by -fprofile-use and -fauto-profile.
9352
9353       -floop-interchange
9354           Perform loop interchange outside of graphite.  This flag can
9355           improve cache performance on loop nest and allow further loop
9356           optimizations, like vectorization, to take place.  For example, the
9357           loop
9358
9359                   for (int i = 0; i < N; i++)
9360                     for (int j = 0; j < N; j++)
9361                       for (int k = 0; k < N; k++)
9362                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
9363
9364           is transformed to
9365
9366                   for (int i = 0; i < N; i++)
9367                     for (int k = 0; k < N; k++)
9368                       for (int j = 0; j < N; j++)
9369                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
9370
9371           This flag is enabled by default at -O3.  It is also enabled by
9372           -fprofile-use and -fauto-profile.
9373
9374       -floop-unroll-and-jam
9375           Apply unroll and jam transformations on feasible loops.  In a loop
9376           nest this unrolls the outer loop by some factor and fuses the
9377           resulting multiple inner loops.  This flag is enabled by default at
9378           -O3.  It is also enabled by -fprofile-use and -fauto-profile.
9379
9380       -ftree-loop-im
9381           Perform loop invariant motion on trees.  This pass moves only
9382           invariants that are hard to handle at RTL level (function calls,
9383           operations that expand to nontrivial sequences of insns).  With
9384           -funswitch-loops it also moves operands of conditions that are
9385           invariant out of the loop, so that we can use just trivial
9386           invariantness analysis in loop unswitching.  The pass also includes
9387           store motion.
9388
9389       -ftree-loop-ivcanon
9390           Create a canonical counter for number of iterations in loops for
9391           which determining number of iterations requires complicated
9392           analysis.  Later optimizations then may determine the number
9393           easily.  Useful especially in connection with unrolling.
9394
9395       -ftree-scev-cprop
9396           Perform final value replacement.  If a variable is modified in a
9397           loop in such a way that its value when exiting the loop can be
9398           determined using only its initial value and the number of loop
9399           iterations, replace uses of the final value by such a computation,
9400           provided it is sufficiently cheap.  This reduces data dependencies
9401           and may allow further simplifications.  Enabled by default at -O
9402           and higher.
9403
9404       -fivopts
9405           Perform induction variable optimizations (strength reduction,
9406           induction variable merging and induction variable elimination) on
9407           trees.
9408
9409       -ftree-parallelize-loops=n
9410           Parallelize loops, i.e., split their iteration space to run in n
9411           threads.  This is only possible for loops whose iterations are
9412           independent and can be arbitrarily reordered.  The optimization is
9413           only profitable on multiprocessor machines, for loops that are CPU-
9414           intensive, rather than constrained e.g. by memory bandwidth.  This
9415           option implies -pthread, and thus is only supported on targets that
9416           have support for -pthread.
9417
9418       -ftree-pta
9419           Perform function-local points-to analysis on trees.  This flag is
9420           enabled by default at -O1 and higher, except for -Og.
9421
9422       -ftree-sra
9423           Perform scalar replacement of aggregates.  This pass replaces
9424           structure references with scalars to prevent committing structures
9425           to memory too early.  This flag is enabled by default at -O1 and
9426           higher, except for -Og.
9427
9428       -fstore-merging
9429           Perform merging of narrow stores to consecutive memory addresses.
9430           This pass merges contiguous stores of immediate values narrower
9431           than a word into fewer wider stores to reduce the number of
9432           instructions.  This is enabled by default at -O2 and higher as well
9433           as -Os.
9434
9435       -ftree-ter
9436           Perform temporary expression replacement during the SSA->normal
9437           phase.  Single use/single def temporaries are replaced at their use
9438           location with their defining expression.  This results in non-
9439           GIMPLE code, but gives the expanders much more complex trees to
9440           work on resulting in better RTL generation.  This is enabled by
9441           default at -O and higher.
9442
9443       -ftree-slsr
9444           Perform straight-line strength reduction on trees.  This recognizes
9445           related expressions involving multiplications and replaces them by
9446           less expensive calculations when possible.  This is enabled by
9447           default at -O and higher.
9448
9449       -ftree-vectorize
9450           Perform vectorization on trees. This flag enables
9451           -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly
9452           specified.
9453
9454       -ftree-loop-vectorize
9455           Perform loop vectorization on trees. This flag is enabled by
9456           default at -O3 and by -ftree-vectorize, -fprofile-use, and
9457           -fauto-profile.
9458
9459       -ftree-slp-vectorize
9460           Perform basic block vectorization on trees. This flag is enabled by
9461           default at -O3 and by -ftree-vectorize, -fprofile-use, and
9462           -fauto-profile.
9463
9464       -fvect-cost-model=model
9465           Alter the cost model used for vectorization.  The model argument
9466           should be one of unlimited, dynamic, cheap or very-cheap.  With the
9467           unlimited model the vectorized code-path is assumed to be
9468           profitable while with the dynamic model a runtime check guards the
9469           vectorized code-path to enable it only for iteration counts that
9470           will likely execute faster than when executing the original scalar
9471           loop.  The cheap model disables vectorization of loops where doing
9472           so would be cost prohibitive for example due to required runtime
9473           checks for data dependence or alignment but otherwise is equal to
9474           the dynamic model.  The very-cheap model only allows vectorization
9475           if the vector code would entirely replace the scalar code that is
9476           being vectorized.  For example, if each iteration of a vectorized
9477           loop would only be able to handle exactly four iterations of the
9478           scalar loop, the very-cheap model would only allow vectorization if
9479           the scalar iteration count is known to be a multiple of four.
9480
9481           The default cost model depends on other optimization flags and is
9482           either dynamic or cheap.
9483
9484       -fsimd-cost-model=model
9485           Alter the cost model used for vectorization of loops marked with
9486           the OpenMP simd directive.  The model argument should be one of
9487           unlimited, dynamic, cheap.  All values of model have the same
9488           meaning as described in -fvect-cost-model and by default a cost
9489           model defined with -fvect-cost-model is used.
9490
9491       -ftree-vrp
9492           Perform Value Range Propagation on trees.  This is similar to the
9493           constant propagation pass, but instead of values, ranges of values
9494           are propagated.  This allows the optimizers to remove unnecessary
9495           range checks like array bound checks and null pointer checks.  This
9496           is enabled by default at -O2 and higher.  Null pointer check
9497           elimination is only done if -fdelete-null-pointer-checks is
9498           enabled.
9499
9500       -fsplit-paths
9501           Split paths leading to loop backedges.  This can improve dead code
9502           elimination and common subexpression elimination.  This is enabled
9503           by default at -O3 and above.
9504
9505       -fsplit-ivs-in-unroller
9506           Enables expression of values of induction variables in later
9507           iterations of the unrolled loop using the value in the first
9508           iteration.  This breaks long dependency chains, thus improving
9509           efficiency of the scheduling passes.
9510
9511           A combination of -fweb and CSE is often sufficient to obtain the
9512           same effect.  However, that is not reliable in cases where the loop
9513           body is more complicated than a single basic block.  It also does
9514           not work at all on some architectures due to restrictions in the
9515           CSE pass.
9516
9517           This optimization is enabled by default.
9518
9519       -fvariable-expansion-in-unroller
9520           With this option, the compiler creates multiple copies of some
9521           local variables when unrolling a loop, which can result in superior
9522           code.
9523
9524           This optimization is enabled by default for PowerPC targets, but
9525           disabled by default otherwise.
9526
9527       -fpartial-inlining
9528           Inline parts of functions.  This option has any effect only when
9529           inlining itself is turned on by the -finline-functions or
9530           -finline-small-functions options.
9531
9532           Enabled at levels -O2, -O3, -Os.
9533
9534       -fpredictive-commoning
9535           Perform predictive commoning optimization, i.e., reusing
9536           computations (especially memory loads and stores) performed in
9537           previous iterations of loops.
9538
9539           This option is enabled at level -O3.  It is also enabled by
9540           -fprofile-use and -fauto-profile.
9541
9542       -fprefetch-loop-arrays
9543           If supported by the target machine, generate instructions to
9544           prefetch memory to improve the performance of loops that access
9545           large arrays.
9546
9547           This option may generate better or worse code; results are highly
9548           dependent on the structure of loops within the source code.
9549
9550           Disabled at level -Os.
9551
9552       -fno-printf-return-value
9553           Do not substitute constants for known return value of formatted
9554           output functions such as "sprintf", "snprintf", "vsprintf", and
9555           "vsnprintf" (but not "printf" of "fprintf").  This transformation
9556           allows GCC to optimize or even eliminate branches based on the
9557           known return value of these functions called with arguments that
9558           are either constant, or whose values are known to be in a range
9559           that makes determining the exact return value possible.  For
9560           example, when -fprintf-return-value is in effect, both the branch
9561           and the body of the "if" statement (but not the call to "snprint")
9562           can be optimized away when "i" is a 32-bit or smaller integer
9563           because the return value is guaranteed to be at most 8.
9564
9565                   char buf[9];
9566                   if (snprintf (buf, "%08x", i) >= sizeof buf)
9567                     ...
9568
9569           The -fprintf-return-value option relies on other optimizations and
9570           yields best results with -O2 and above.  It works in tandem with
9571           the -Wformat-overflow and -Wformat-truncation options.  The
9572           -fprintf-return-value option is enabled by default.
9573
9574       -fno-peephole
9575       -fno-peephole2
9576           Disable any machine-specific peephole optimizations.  The
9577           difference between -fno-peephole and -fno-peephole2 is in how they
9578           are implemented in the compiler; some targets use one, some use the
9579           other, a few use both.
9580
9581           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
9582           -O2, -O3, -Os.
9583
9584       -fno-guess-branch-probability
9585           Do not guess branch probabilities using heuristics.
9586
9587           GCC uses heuristics to guess branch probabilities if they are not
9588           provided by profiling feedback (-fprofile-arcs).  These heuristics
9589           are based on the control flow graph.  If some branch probabilities
9590           are specified by "__builtin_expect", then the heuristics are used
9591           to guess branch probabilities for the rest of the control flow
9592           graph, taking the "__builtin_expect" info into account.  The
9593           interactions between the heuristics and "__builtin_expect" can be
9594           complex, and in some cases, it may be useful to disable the
9595           heuristics so that the effects of "__builtin_expect" are easier to
9596           understand.
9597
9598           It is also possible to specify expected probability of the
9599           expression with "__builtin_expect_with_probability" built-in
9600           function.
9601
9602           The default is -fguess-branch-probability at levels -O, -O2, -O3,
9603           -Os.
9604
9605       -freorder-blocks
9606           Reorder basic blocks in the compiled function in order to reduce
9607           number of taken branches and improve code locality.
9608
9609           Enabled at levels -O, -O2, -O3, -Os.
9610
9611       -freorder-blocks-algorithm=algorithm
9612           Use the specified algorithm for basic block reordering.  The
9613           algorithm argument can be simple, which does not increase code size
9614           (except sometimes due to secondary effects like alignment), or stc,
9615           the "software trace cache" algorithm, which tries to put all often
9616           executed code together, minimizing the number of branches executed
9617           by making extra copies of code.
9618
9619           The default is simple at levels -O, -Os, and stc at levels -O2,
9620           -O3.
9621
9622       -freorder-blocks-and-partition
9623           In addition to reordering basic blocks in the compiled function, in
9624           order to reduce number of taken branches, partitions hot and cold
9625           basic blocks into separate sections of the assembly and .o files,
9626           to improve paging and cache locality performance.
9627
9628           This optimization is automatically turned off in the presence of
9629           exception handling or unwind tables (on targets using
9630           setjump/longjump or target specific scheme), for linkonce sections,
9631           for functions with a user-defined section attribute and on any
9632           architecture that does not support named sections.  When
9633           -fsplit-stack is used this option is not enabled by default (to
9634           avoid linker errors), but may be enabled explicitly (if using a
9635           working linker).
9636
9637           Enabled for x86 at levels -O2, -O3, -Os.
9638
9639       -freorder-functions
9640           Reorder functions in the object file in order to improve code
9641           locality.  This is implemented by using special subsections
9642           ".text.hot" for most frequently executed functions and
9643           ".text.unlikely" for unlikely executed functions.  Reordering is
9644           done by the linker so object file format must support named
9645           sections and linker must place them in a reasonable way.
9646
9647           This option isn't effective unless you either provide profile
9648           feedback (see -fprofile-arcs for details) or manually annotate
9649           functions with "hot" or "cold" attributes.
9650
9651           Enabled at levels -O2, -O3, -Os.
9652
9653       -fstrict-aliasing
9654           Allow the compiler to assume the strictest aliasing rules
9655           applicable to the language being compiled.  For C (and C++), this
9656           activates optimizations based on the type of expressions.  In
9657           particular, an object of one type is assumed never to reside at the
9658           same address as an object of a different type, unless the types are
9659           almost the same.  For example, an "unsigned int" can alias an
9660           "int", but not a "void*" or a "double".  A character type may alias
9661           any other type.
9662
9663           Pay special attention to code like this:
9664
9665                   union a_union {
9666                     int i;
9667                     double d;
9668                   };
9669
9670                   int f() {
9671                     union a_union t;
9672                     t.d = 3.0;
9673                     return t.i;
9674                   }
9675
9676           The practice of reading from a different union member than the one
9677           most recently written to (called "type-punning") is common.  Even
9678           with -fstrict-aliasing, type-punning is allowed, provided the
9679           memory is accessed through the union type.  So, the code above
9680           works as expected.    However, this code might not:
9681
9682                   int f() {
9683                     union a_union t;
9684                     int* ip;
9685                     t.d = 3.0;
9686                     ip = &t.i;
9687                     return *ip;
9688                   }
9689
9690           Similarly, access by taking the address, casting the resulting
9691           pointer and dereferencing the result has undefined behavior, even
9692           if the cast uses a union type, e.g.:
9693
9694                   int f() {
9695                     double d = 3.0;
9696                     return ((union a_union *) &d)->i;
9697                   }
9698
9699           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
9700
9701       -falign-functions
9702       -falign-functions=n
9703       -falign-functions=n:m
9704       -falign-functions=n:m:n2
9705       -falign-functions=n:m:n2:m2
9706           Align the start of functions to the next power-of-two greater than
9707           or equal to n, skipping up to m-1 bytes.  This ensures that at
9708           least the first m bytes of the function can be fetched by the CPU
9709           without crossing an n-byte alignment boundary.
9710
9711           If m is not specified, it defaults to n.
9712
9713           Examples: -falign-functions=32 aligns functions to the next 32-byte
9714           boundary, -falign-functions=24 aligns to the next 32-byte boundary
9715           only if this can be done by skipping 23 bytes or less,
9716           -falign-functions=32:7 aligns to the next 32-byte boundary only if
9717           this can be done by skipping 6 bytes or less.
9718
9719           The second pair of n2:m2 values allows you to specify a secondary
9720           alignment: -falign-functions=64:7:32:3 aligns to the next 64-byte
9721           boundary if this can be done by skipping 6 bytes or less, otherwise
9722           aligns to the next 32-byte boundary if this can be done by skipping
9723           2 bytes or less.  If m2 is not specified, it defaults to n2.
9724
9725           Some assemblers only support this flag when n is a power of two; in
9726           that case, it is rounded up.
9727
9728           -fno-align-functions and -falign-functions=1 are equivalent and
9729           mean that functions are not aligned.
9730
9731           If n is not specified or is zero, use a machine-dependent default.
9732           The maximum allowed n option value is 65536.
9733
9734           Enabled at levels -O2, -O3.
9735
9736       -flimit-function-alignment
9737           If this option is enabled, the compiler tries to avoid
9738           unnecessarily overaligning functions. It attempts to instruct the
9739           assembler to align by the amount specified by -falign-functions,
9740           but not to skip more bytes than the size of the function.
9741
9742       -falign-labels
9743       -falign-labels=n
9744       -falign-labels=n:m
9745       -falign-labels=n:m:n2
9746       -falign-labels=n:m:n2:m2
9747           Align all branch targets to a power-of-two boundary.
9748
9749           Parameters of this option are analogous to the -falign-functions
9750           option.  -fno-align-labels and -falign-labels=1 are equivalent and
9751           mean that labels are not aligned.
9752
9753           If -falign-loops or -falign-jumps are applicable and are greater
9754           than this value, then their values are used instead.
9755
9756           If n is not specified or is zero, use a machine-dependent default
9757           which is very likely to be 1, meaning no alignment.  The maximum
9758           allowed n option value is 65536.
9759
9760           Enabled at levels -O2, -O3.
9761
9762       -falign-loops
9763       -falign-loops=n
9764       -falign-loops=n:m
9765       -falign-loops=n:m:n2
9766       -falign-loops=n:m:n2:m2
9767           Align loops to a power-of-two boundary.  If the loops are executed
9768           many times, this makes up for any execution of the dummy padding
9769           instructions.
9770
9771           If -falign-labels is greater than this value, then its value is
9772           used instead.
9773
9774           Parameters of this option are analogous to the -falign-functions
9775           option.  -fno-align-loops and -falign-loops=1 are equivalent and
9776           mean that loops are not aligned.  The maximum allowed n option
9777           value is 65536.
9778
9779           If n is not specified or is zero, use a machine-dependent default.
9780
9781           Enabled at levels -O2, -O3.
9782
9783       -falign-jumps
9784       -falign-jumps=n
9785       -falign-jumps=n:m
9786       -falign-jumps=n:m:n2
9787       -falign-jumps=n:m:n2:m2
9788           Align branch targets to a power-of-two boundary, for branch targets
9789           where the targets can only be reached by jumping.  In this case, no
9790           dummy operations need be executed.
9791
9792           If -falign-labels is greater than this value, then its value is
9793           used instead.
9794
9795           Parameters of this option are analogous to the -falign-functions
9796           option.  -fno-align-jumps and -falign-jumps=1 are equivalent and
9797           mean that loops are not aligned.
9798
9799           If n is not specified or is zero, use a machine-dependent default.
9800           The maximum allowed n option value is 65536.
9801
9802           Enabled at levels -O2, -O3.
9803
9804       -fno-allocation-dce
9805           Do not remove unused C++ allocations in dead code elimination.
9806
9807       -fallow-store-data-races
9808           Allow the compiler to perform optimizations that may introduce new
9809           data races on stores, without proving that the variable cannot be
9810           concurrently accessed by other threads.  Does not affect
9811           optimization of local data.  It is safe to use this option if it is
9812           known that global data will not be accessed by multiple threads.
9813
9814           Examples of optimizations enabled by -fallow-store-data-races
9815           include hoisting or if-conversions that may cause a value that was
9816           already in memory to be re-written with that same value.  Such re-
9817           writing is safe in a single threaded context but may be unsafe in a
9818           multi-threaded context.  Note that on some processors, if-
9819           conversions may be required in order to enable vectorization.
9820
9821           Enabled at level -Ofast.
9822
9823       -funit-at-a-time
9824           This option is left for compatibility reasons. -funit-at-a-time has
9825           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
9826           and -fno-section-anchors.
9827
9828           Enabled by default.
9829
9830       -fno-toplevel-reorder
9831           Do not reorder top-level functions, variables, and "asm"
9832           statements.  Output them in the same order that they appear in the
9833           input file.  When this option is used, unreferenced static
9834           variables are not removed.  This option is intended to support
9835           existing code that relies on a particular ordering.  For new code,
9836           it is better to use attributes when possible.
9837
9838           -ftoplevel-reorder is the default at -O1 and higher, and also at
9839           -O0 if -fsection-anchors is explicitly requested.  Additionally
9840           -fno-toplevel-reorder implies -fno-section-anchors.
9841
9842       -fweb
9843           Constructs webs as commonly used for register allocation purposes
9844           and assign each web individual pseudo register.  This allows the
9845           register allocation pass to operate on pseudos directly, but also
9846           strengthens several other optimization passes, such as CSE, loop
9847           optimizer and trivial dead code remover.  It can, however, make
9848           debugging impossible, since variables no longer stay in a "home
9849           register".
9850
9851           Enabled by default with -funroll-loops.
9852
9853       -fwhole-program
9854           Assume that the current compilation unit represents the whole
9855           program being compiled.  All public functions and variables with
9856           the exception of "main" and those merged by attribute
9857           "externally_visible" become static functions and in effect are
9858           optimized more aggressively by interprocedural optimizers.
9859
9860           This option should not be used in combination with -flto.  Instead
9861           relying on a linker plugin should provide safer and more precise
9862           information.
9863
9864       -flto[=n]
9865           This option runs the standard link-time optimizer.  When invoked
9866           with source code, it generates GIMPLE (one of GCC's internal
9867           representations) and writes it to special ELF sections in the
9868           object file.  When the object files are linked together, all the
9869           function bodies are read from these ELF sections and instantiated
9870           as if they had been part of the same translation unit.
9871
9872           To use the link-time optimizer, -flto and optimization options
9873           should be specified at compile time and during the final link.  It
9874           is recommended that you compile all the files participating in the
9875           same link with the same options and also specify those options at
9876           link time.  For example:
9877
9878                   gcc -c -O2 -flto foo.c
9879                   gcc -c -O2 -flto bar.c
9880                   gcc -o myprog -flto -O2 foo.o bar.o
9881
9882           The first two invocations to GCC save a bytecode representation of
9883           GIMPLE into special ELF sections inside foo.o and bar.o.  The final
9884           invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
9885           the two files into a single internal image, and compiles the result
9886           as usual.  Since both foo.o and bar.o are merged into a single
9887           image, this causes all the interprocedural analyses and
9888           optimizations in GCC to work across the two files as if they were a
9889           single one.  This means, for example, that the inliner is able to
9890           inline functions in bar.o into functions in foo.o and vice-versa.
9891
9892           Another (simpler) way to enable link-time optimization is:
9893
9894                   gcc -o myprog -flto -O2 foo.c bar.c
9895
9896           The above generates bytecode for foo.c and bar.c, merges them
9897           together into a single GIMPLE representation and optimizes them as
9898           usual to produce myprog.
9899
9900           The important thing to keep in mind is that to enable link-time
9901           optimizations you need to use the GCC driver to perform the link
9902           step.  GCC automatically performs link-time optimization if any of
9903           the objects involved were compiled with the -flto command-line
9904           option.  You can always override the automatic decision to do link-
9905           time optimization by passing -fno-lto to the link command.
9906
9907           To make whole program optimization effective, it is necessary to
9908           make certain whole program assumptions.  The compiler needs to know
9909           what functions and variables can be accessed by libraries and
9910           runtime outside of the link-time optimized unit.  When supported by
9911           the linker, the linker plugin (see -fuse-linker-plugin) passes
9912           information to the compiler about used and externally visible
9913           symbols.  When the linker plugin is not available, -fwhole-program
9914           should be used to allow the compiler to make these assumptions,
9915           which leads to more aggressive optimization decisions.
9916
9917           When a file is compiled with -flto without -fuse-linker-plugin, the
9918           generated object file is larger than a regular object file because
9919           it contains GIMPLE bytecodes and the usual final code (see
9920           -ffat-lto-objects).  This means that object files with LTO
9921           information can be linked as normal object files; if -fno-lto is
9922           passed to the linker, no interprocedural optimizations are applied.
9923           Note that when -fno-fat-lto-objects is enabled the compile stage is
9924           faster but you cannot perform a regular, non-LTO link on them.
9925
9926           When producing the final binary, GCC only applies link-time
9927           optimizations to those files that contain bytecode.  Therefore, you
9928           can mix and match object files and libraries with GIMPLE bytecodes
9929           and final object code.  GCC automatically selects which files to
9930           optimize in LTO mode and which files to link without further
9931           processing.
9932
9933           Generally, options specified at link time override those specified
9934           at compile time, although in some cases GCC attempts to infer link-
9935           time options from the settings used to compile the input files.
9936
9937           If you do not specify an optimization level option -O at link time,
9938           then GCC uses the highest optimization level used when compiling
9939           the object files.  Note that it is generally ineffective to specify
9940           an optimization level option only at link time and not at compile
9941           time, for two reasons.  First, compiling without optimization
9942           suppresses compiler passes that gather information needed for
9943           effective optimization at link time.  Second, some early
9944           optimization passes can be performed only at compile time and not
9945           at link time.
9946
9947           There are some code generation flags preserved by GCC when
9948           generating bytecodes, as they need to be used during the final
9949           link.  Currently, the following options and their settings are
9950           taken from the first object file that explicitly specifies them:
9951           -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and all the
9952           -m target flags.
9953
9954           The following options -fPIC, -fpic, -fpie and -fPIE are combined
9955           based on the following scheme:
9956
9957                   B<-fPIC> + B<-fpic> = B<-fpic>
9958                   B<-fPIC> + B<-fno-pic> = B<-fno-pic>
9959                   B<-fpic/-fPIC> + (no option) = (no option)
9960                   B<-fPIC> + B<-fPIE> = B<-fPIE>
9961                   B<-fpic> + B<-fPIE> = B<-fpie>
9962                   B<-fPIC/-fpic> + B<-fpie> = B<-fpie>
9963
9964           Certain ABI-changing flags are required to match in all compilation
9965           units, and trying to override this at link time with a conflicting
9966           value is ignored.  This includes options such as
9967           -freg-struct-return and -fpcc-struct-return.
9968
9969           Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv,
9970           -fno-trapv or -fno-strict-aliasing are passed through to the link
9971           stage and merged conservatively for conflicting translation units.
9972           Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take
9973           precedence; and for example -ffp-contract=off takes precedence over
9974           -ffp-contract=fast.  You can override them at link time.
9975
9976           Diagnostic options such as -Wstringop-overflow are passed through
9977           to the link stage and their setting matches that of the compile-
9978           step at function granularity.  Note that this matters only for
9979           diagnostics emitted during optimization.  Note that code transforms
9980           such as inlining can lead to warnings being enabled or disabled for
9981           regions if code not consistent with the setting at compile time.
9982
9983           When you need to pass options to the assembler via -Wa or
9984           -Xassembler make sure to either compile such translation units with
9985           -fno-lto or consistently use the same assembler options on all
9986           translation units.  You can alternatively also specify assembler
9987           options at LTO link time.
9988
9989           To enable debug info generation you need to supply -g at compile
9990           time.  If any of the input files at link time were built with debug
9991           info generation enabled the link will enable debug info generation
9992           as well.  Any elaborate debug info settings like the dwarf level
9993           -gdwarf-5 need to be explicitly repeated at the linker command line
9994           and mixing different settings in different translation units is
9995           discouraged.
9996
9997           If LTO encounters objects with C linkage declared with incompatible
9998           types in separate translation units to be linked together
9999           (undefined behavior according to ISO C99 6.2.7), a non-fatal
10000           diagnostic may be issued.  The behavior is still undefined at run
10001           time.  Similar diagnostics may be raised for other languages.
10002
10003           Another feature of LTO is that it is possible to apply
10004           interprocedural optimizations on files written in different
10005           languages:
10006
10007                   gcc -c -flto foo.c
10008                   g++ -c -flto bar.cc
10009                   gfortran -c -flto baz.f90
10010                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
10011
10012           Notice that the final link is done with g++ to get the C++ runtime
10013           libraries and -lgfortran is added to get the Fortran runtime
10014           libraries.  In general, when mixing languages in LTO mode, you
10015           should use the same link command options as when mixing languages
10016           in a regular (non-LTO) compilation.
10017
10018           If object files containing GIMPLE bytecode are stored in a library
10019           archive, say libfoo.a, it is possible to extract and use them in an
10020           LTO link if you are using a linker with plugin support.  To create
10021           static libraries suitable for LTO, use gcc-ar and gcc-ranlib
10022           instead of ar and ranlib; to show the symbols of object files with
10023           GIMPLE bytecode, use gcc-nm.  Those commands require that ar,
10024           ranlib and nm have been compiled with plugin support.  At link
10025           time, use the flag -fuse-linker-plugin to ensure that the library
10026           participates in the LTO optimization process:
10027
10028                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
10029
10030           With the linker plugin enabled, the linker extracts the needed
10031           GIMPLE files from libfoo.a and passes them on to the running GCC to
10032           make them part of the aggregated GIMPLE image to be optimized.
10033
10034           If you are not using a linker with plugin support and/or do not
10035           enable the linker plugin, then the objects inside libfoo.a are
10036           extracted and linked as usual, but they do not participate in the
10037           LTO optimization process.  In order to make a static library
10038           suitable for both LTO optimization and usual linkage, compile its
10039           object files with -flto -ffat-lto-objects.
10040
10041           Link-time optimizations do not require the presence of the whole
10042           program to operate.  If the program does not require any symbols to
10043           be exported, it is possible to combine -flto and -fwhole-program to
10044           allow the interprocedural optimizers to use more aggressive
10045           assumptions which may lead to improved optimization opportunities.
10046           Use of -fwhole-program is not needed when linker plugin is active
10047           (see -fuse-linker-plugin).
10048
10049           The current implementation of LTO makes no attempt to generate
10050           bytecode that is portable between different types of hosts.  The
10051           bytecode files are versioned and there is a strict version check,
10052           so bytecode files generated in one version of GCC do not work with
10053           an older or newer version of GCC.
10054
10055           Link-time optimization does not work well with generation of
10056           debugging information on systems other than those using a
10057           combination of ELF and DWARF.
10058
10059           If you specify the optional n, the optimization and code generation
10060           done at link time is executed in parallel using n parallel jobs by
10061           utilizing an installed make program.  The environment variable MAKE
10062           may be used to override the program used.
10063
10064           You can also specify -flto=jobserver to use GNU make's job server
10065           mode to determine the number of parallel jobs. This is useful when
10066           the Makefile calling GCC is already executing in parallel.  You
10067           must prepend a + to the command recipe in the parent Makefile for
10068           this to work.  This option likely only works if MAKE is GNU make.
10069           Even without the option value, GCC tries to automatically detect a
10070           running GNU make's job server.
10071
10072           Use -flto=auto to use GNU make's job server, if available, or
10073           otherwise fall back to autodetection of the number of CPU threads
10074           present in your system.
10075
10076       -flto-partition=alg
10077           Specify the partitioning algorithm used by the link-time optimizer.
10078           The value is either 1to1 to specify a partitioning mirroring the
10079           original source files or balanced to specify partitioning into
10080           equally sized chunks (whenever possible) or max to create new
10081           partition for every symbol where possible.  Specifying none as an
10082           algorithm disables partitioning and streaming completely.  The
10083           default value is balanced. While 1to1 can be used as an workaround
10084           for various code ordering issues, the max partitioning is intended
10085           for internal testing only.  The value one specifies that exactly
10086           one partition should be used while the value none bypasses
10087           partitioning and executes the link-time optimization step directly
10088           from the WPA phase.
10089
10090       -flto-compression-level=n
10091           This option specifies the level of compression used for
10092           intermediate language written to LTO object files, and is only
10093           meaningful in conjunction with LTO mode (-flto).  GCC currently
10094           supports two LTO compression algorithms. For zstd, valid values are
10095           0 (no compression) to 19 (maximum compression), while zlib supports
10096           values from 0 to 9.  Values outside this range are clamped to
10097           either minimum or maximum of the supported values.  If the option
10098           is not given, a default balanced compression setting is used.
10099
10100       -fuse-linker-plugin
10101           Enables the use of a linker plugin during link-time optimization.
10102           This option relies on plugin support in the linker, which is
10103           available in gold or in GNU ld 2.21 or newer.
10104
10105           This option enables the extraction of object files with GIMPLE
10106           bytecode out of library archives. This improves the quality of
10107           optimization by exposing more code to the link-time optimizer.
10108           This information specifies what symbols can be accessed externally
10109           (by non-LTO object or during dynamic linking).  Resulting code
10110           quality improvements on binaries (and shared libraries that use
10111           hidden visibility) are similar to -fwhole-program.  See -flto for a
10112           description of the effect of this flag and how to use it.
10113
10114           This option is enabled by default when LTO support in GCC is
10115           enabled and GCC was configured for use with a linker supporting
10116           plugins (GNU ld 2.21 or newer or gold).
10117
10118       -ffat-lto-objects
10119           Fat LTO objects are object files that contain both the intermediate
10120           language and the object code. This makes them usable for both LTO
10121           linking and normal linking. This option is effective only when
10122           compiling with -flto and is ignored at link time.
10123
10124           -fno-fat-lto-objects improves compilation time over plain LTO, but
10125           requires the complete toolchain to be aware of LTO. It requires a
10126           linker with linker plugin support for basic functionality.
10127           Additionally, nm, ar and ranlib need to support linker plugins to
10128           allow a full-featured build environment (capable of building static
10129           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib
10130           wrappers to pass the right options to these tools. With non fat LTO
10131           makefiles need to be modified to use them.
10132
10133           Note that modern binutils provide plugin auto-load mechanism.
10134           Installing the linker plugin into $libdir/bfd-plugins has the same
10135           effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-
10136           ranlib).
10137
10138           The default is -fno-fat-lto-objects on targets with linker plugin
10139           support.
10140
10141       -fcompare-elim
10142           After register allocation and post-register allocation instruction
10143           splitting, identify arithmetic instructions that compute processor
10144           flags similar to a comparison operation based on that arithmetic.
10145           If possible, eliminate the explicit comparison operation.
10146
10147           This pass only applies to certain targets that cannot explicitly
10148           represent the comparison operation before register allocation is
10149           complete.
10150
10151           Enabled at levels -O, -O2, -O3, -Os.
10152
10153       -fcprop-registers
10154           After register allocation and post-register allocation instruction
10155           splitting, perform a copy-propagation pass to try to reduce
10156           scheduling dependencies and occasionally eliminate the copy.
10157
10158           Enabled at levels -O, -O2, -O3, -Os.
10159
10160       -fprofile-correction
10161           Profiles collected using an instrumented binary for multi-threaded
10162           programs may be inconsistent due to missed counter updates. When
10163           this option is specified, GCC uses heuristics to correct or smooth
10164           out such inconsistencies. By default, GCC emits an error message
10165           when an inconsistent profile is detected.
10166
10167           This option is enabled by -fauto-profile.
10168
10169       -fprofile-partial-training
10170           With "-fprofile-use" all portions of programs not executed during
10171           train run are optimized agressively for size rather than speed.  In
10172           some cases it is not practical to train all possible hot paths in
10173           the program. (For example, program may contain functions specific
10174           for a given hardware and trianing may not cover all hardware
10175           configurations program is run on.)  With
10176           "-fprofile-partial-training" profile feedback will be ignored for
10177           all functions not executed during the train run leading them to be
10178           optimized as if they were compiled without profile feedback. This
10179           leads to better performance when train run is not representative
10180           but also leads to significantly bigger code.
10181
10182       -fprofile-use
10183       -fprofile-use=path
10184           Enable profile feedback-directed optimizations, and the following
10185           optimizations, many of which are generally profitable only with
10186           profile feedback available:
10187
10188           -fbranch-probabilities  -fprofile-values -funroll-loops
10189           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
10190           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
10191           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
10192           -ftree-slp-vectorize -fvect-cost-model=dynamic
10193           -ftree-loop-distribute-patterns -fprofile-reorder-functions
10194
10195           Before you can use this option, you must first generate profiling
10196           information.
10197
10198           By default, GCC emits an error message if the feedback profiles do
10199           not match the source code.  This error can be turned into a warning
10200           by using -Wno-error=coverage-mismatch.  Note this may result in
10201           poorly optimized code.  Additionally, by default, GCC also emits a
10202           warning message if the feedback profiles do not exist (see
10203           -Wmissing-profile).
10204
10205           If path is specified, GCC looks at the path to find the profile
10206           feedback data files. See -fprofile-dir.
10207
10208       -fauto-profile
10209       -fauto-profile=path
10210           Enable sampling-based feedback-directed optimizations, and the
10211           following optimizations, many of which are generally profitable
10212           only with profile feedback available:
10213
10214           -fbranch-probabilities  -fprofile-values -funroll-loops
10215           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
10216           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
10217           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
10218           -ftree-slp-vectorize -fvect-cost-model=dynamic
10219           -ftree-loop-distribute-patterns -fprofile-correction
10220
10221           path is the name of a file containing AutoFDO profile information.
10222           If omitted, it defaults to fbdata.afdo in the current directory.
10223
10224           Producing an AutoFDO profile data file requires running your
10225           program with the perf utility on a supported GNU/Linux target
10226           system.  For more information, see <https://perf.wiki.kernel.org/>.
10227
10228           E.g.
10229
10230                   perf record -e br_inst_retired:near_taken -b -o perf.data \
10231                       -- your_program
10232
10233           Then use the create_gcov tool to convert the raw profile data to a
10234           format that can be used by GCC.  You must also supply the
10235           unstripped binary for your program to this tool.  See
10236           <https://github.com/google/autofdo>.
10237
10238           E.g.
10239
10240                   create_gcov --binary=your_program.unstripped --profile=perf.data \
10241                       --gcov=profile.afdo
10242
10243       The following options control compiler behavior regarding floating-
10244       point arithmetic.  These options trade off between speed and
10245       correctness.  All must be specifically enabled.
10246
10247       -ffloat-store
10248           Do not store floating-point variables in registers, and inhibit
10249           other options that might change whether a floating-point value is
10250           taken from a register or memory.
10251
10252           This option prevents undesirable excess precision on machines such
10253           as the 68000 where the floating registers (of the 68881) keep more
10254           precision than a "double" is supposed to have.  Similarly for the
10255           x86 architecture.  For most programs, the excess precision does
10256           only good, but a few programs rely on the precise definition of
10257           IEEE floating point.  Use -ffloat-store for such programs, after
10258           modifying them to store all pertinent intermediate computations
10259           into variables.
10260
10261       -fexcess-precision=style
10262           This option allows further control over excess precision on
10263           machines where floating-point operations occur in a format with
10264           more precision or range than the IEEE standard and interchange
10265           floating-point types.  By default, -fexcess-precision=fast is in
10266           effect; this means that operations may be carried out in a wider
10267           precision than the types specified in the source if that would
10268           result in faster code, and it is unpredictable when rounding to the
10269           types specified in the source code takes place.  When compiling C,
10270           if -fexcess-precision=standard is specified then excess precision
10271           follows the rules specified in ISO C99; in particular, both casts
10272           and assignments cause values to be rounded to their semantic types
10273           (whereas -ffloat-store only affects assignments).  This option is
10274           enabled by default for C if a strict conformance option such as
10275           -std=c99 is used.  -ffast-math enables -fexcess-precision=fast by
10276           default regardless of whether a strict conformance option is used.
10277
10278           -fexcess-precision=standard is not implemented for languages other
10279           than C.  On the x86, it has no effect if -mfpmath=sse or
10280           -mfpmath=sse+387 is specified; in the former case, IEEE semantics
10281           apply without excess precision, and in the latter, rounding is
10282           unpredictable.
10283
10284       -ffast-math
10285           Sets the options -fno-math-errno, -funsafe-math-optimizations,
10286           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans,
10287           -fcx-limited-range and -fexcess-precision=fast.
10288
10289           This option causes the preprocessor macro "__FAST_MATH__" to be
10290           defined.
10291
10292           This option is not turned on by any -O option besides -Ofast since
10293           it can result in incorrect output for programs that depend on an
10294           exact implementation of IEEE or ISO rules/specifications for math
10295           functions. It may, however, yield faster code for programs that do
10296           not require the guarantees of these specifications.
10297
10298       -fno-math-errno
10299           Do not set "errno" after calling math functions that are executed
10300           with a single instruction, e.g., "sqrt".  A program that relies on
10301           IEEE exceptions for math error handling may want to use this flag
10302           for speed while maintaining IEEE arithmetic compatibility.
10303
10304           This option is not turned on by any -O option since it can result
10305           in incorrect output for programs that depend on an exact
10306           implementation of IEEE or ISO rules/specifications for math
10307           functions. It may, however, yield faster code for programs that do
10308           not require the guarantees of these specifications.
10309
10310           The default is -fmath-errno.
10311
10312           On Darwin systems, the math library never sets "errno".  There is
10313           therefore no reason for the compiler to consider the possibility
10314           that it might, and -fno-math-errno is the default.
10315
10316       -funsafe-math-optimizations
10317           Allow optimizations for floating-point arithmetic that (a) assume
10318           that arguments and results are valid and (b) may violate IEEE or
10319           ANSI standards.  When used at link time, it may include libraries
10320           or startup files that change the default FPU control word or other
10321           similar optimizations.
10322
10323           This option is not turned on by any -O option since it can result
10324           in incorrect output for programs that depend on an exact
10325           implementation of IEEE or ISO rules/specifications for math
10326           functions. It may, however, yield faster code for programs that do
10327           not require the guarantees of these specifications.  Enables
10328           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
10329           -freciprocal-math.
10330
10331           The default is -fno-unsafe-math-optimizations.
10332
10333       -fassociative-math
10334           Allow re-association of operands in series of floating-point
10335           operations.  This violates the ISO C and C++ language standard by
10336           possibly changing computation result.  NOTE: re-ordering may change
10337           the sign of zero as well as ignore NaNs and inhibit or create
10338           underflow or overflow (and thus cannot be used on code that relies
10339           on rounding behavior like "(x + 2**52) - 2**52".  May also reorder
10340           floating-point comparisons and thus may not be used when ordered
10341           comparisons are required.  This option requires that both
10342           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
10343           it doesn't make much sense with -frounding-math. For Fortran the
10344           option is automatically enabled when both -fno-signed-zeros and
10345           -fno-trapping-math are in effect.
10346
10347           The default is -fno-associative-math.
10348
10349       -freciprocal-math
10350           Allow the reciprocal of a value to be used instead of dividing by
10351           the value if this enables optimizations.  For example "x / y" can
10352           be replaced with "x * (1/y)", which is useful if "(1/y)" is subject
10353           to common subexpression elimination.  Note that this loses
10354           precision and increases the number of flops operating on the value.
10355
10356           The default is -fno-reciprocal-math.
10357
10358       -ffinite-math-only
10359           Allow optimizations for floating-point arithmetic that assume that
10360           arguments and results are not NaNs or +-Infs.
10361
10362           This option is not turned on by any -O option since it can result
10363           in incorrect output for programs that depend on an exact
10364           implementation of IEEE or ISO rules/specifications for math
10365           functions. It may, however, yield faster code for programs that do
10366           not require the guarantees of these specifications.
10367
10368           The default is -fno-finite-math-only.
10369
10370       -fno-signed-zeros
10371           Allow optimizations for floating-point arithmetic that ignore the
10372           signedness of zero.  IEEE arithmetic specifies the behavior of
10373           distinct +0.0 and -0.0 values, which then prohibits simplification
10374           of expressions such as x+0.0 or 0.0*x (even with
10375           -ffinite-math-only).  This option implies that the sign of a zero
10376           result isn't significant.
10377
10378           The default is -fsigned-zeros.
10379
10380       -fno-trapping-math
10381           Compile code assuming that floating-point operations cannot
10382           generate user-visible traps.  These traps include division by zero,
10383           overflow, underflow, inexact result and invalid operation.  This
10384           option requires that -fno-signaling-nans be in effect.  Setting
10385           this option may allow faster code if one relies on "non-stop" IEEE
10386           arithmetic, for example.
10387
10388           This option should never be turned on by any -O option since it can
10389           result in incorrect output for programs that depend on an exact
10390           implementation of IEEE or ISO rules/specifications for math
10391           functions.
10392
10393           The default is -ftrapping-math.
10394
10395       -frounding-math
10396           Disable transformations and optimizations that assume default
10397           floating-point rounding behavior.  This is round-to-zero for all
10398           floating point to integer conversions, and round-to-nearest for all
10399           other arithmetic truncations.  This option should be specified for
10400           programs that change the FP rounding mode dynamically, or that may
10401           be executed with a non-default rounding mode.  This option disables
10402           constant folding of floating-point expressions at compile time
10403           (which may be affected by rounding mode) and arithmetic
10404           transformations that are unsafe in the presence of sign-dependent
10405           rounding modes.
10406
10407           The default is -fno-rounding-math.
10408
10409           This option is experimental and does not currently guarantee to
10410           disable all GCC optimizations that are affected by rounding mode.
10411           Future versions of GCC may provide finer control of this setting
10412           using C99's "FENV_ACCESS" pragma.  This command-line option will be
10413           used to specify the default state for "FENV_ACCESS".
10414
10415       -fsignaling-nans
10416           Compile code assuming that IEEE signaling NaNs may generate user-
10417           visible traps during floating-point operations.  Setting this
10418           option disables optimizations that may change the number of
10419           exceptions visible with signaling NaNs.  This option implies
10420           -ftrapping-math.
10421
10422           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
10423           defined.
10424
10425           The default is -fno-signaling-nans.
10426
10427           This option is experimental and does not currently guarantee to
10428           disable all GCC optimizations that affect signaling NaN behavior.
10429
10430       -fno-fp-int-builtin-inexact
10431           Do not allow the built-in functions "ceil", "floor", "round" and
10432           "trunc", and their "float" and "long double" variants, to generate
10433           code that raises the "inexact" floating-point exception for
10434           noninteger arguments.  ISO C99 and C11 allow these functions to
10435           raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
10436           bindings to IEEE 754-2008, as integrated into ISO C2X, does not
10437           allow these functions to do so.
10438
10439           The default is -ffp-int-builtin-inexact, allowing the exception to
10440           be raised, unless C2X or a later C standard is selected.  This
10441           option does nothing unless -ftrapping-math is in effect.
10442
10443           Even if -fno-fp-int-builtin-inexact is used, if the functions
10444           generate a call to a library function then the "inexact" exception
10445           may be raised if the library implementation does not follow TS
10446           18661.
10447
10448       -fsingle-precision-constant
10449           Treat floating-point constants as single precision instead of
10450           implicitly converting them to double-precision constants.
10451
10452       -fcx-limited-range
10453           When enabled, this option states that a range reduction step is not
10454           needed when performing complex division.  Also, there is no
10455           checking whether the result of a complex multiplication or division
10456           is "NaN + I*NaN", with an attempt to rescue the situation in that
10457           case.  The default is -fno-cx-limited-range, but is enabled by
10458           -ffast-math.
10459
10460           This option controls the default setting of the ISO C99
10461           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
10462           languages.
10463
10464       -fcx-fortran-rules
10465           Complex multiplication and division follow Fortran rules.  Range
10466           reduction is done as part of complex division, but there is no
10467           checking whether the result of a complex multiplication or division
10468           is "NaN + I*NaN", with an attempt to rescue the situation in that
10469           case.
10470
10471           The default is -fno-cx-fortran-rules.
10472
10473       The following options control optimizations that may improve
10474       performance, but are not enabled by any -O options.  This section
10475       includes experimental options that may produce broken code.
10476
10477       -fbranch-probabilities
10478           After running a program compiled with -fprofile-arcs, you can
10479           compile it a second time using -fbranch-probabilities, to improve
10480           optimizations based on the number of times each branch was taken.
10481           When a program compiled with -fprofile-arcs exits, it saves arc
10482           execution counts to a file called sourcename.gcda for each source
10483           file.  The information in this data file is very dependent on the
10484           structure of the generated code, so you must use the same source
10485           code and the same optimization options for both compilations.
10486
10487           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
10488           JUMP_INSN and CALL_INSN.  These can be used to improve
10489           optimization.  Currently, they are only used in one place: in
10490           reorg.c, instead of guessing which path a branch is most likely to
10491           take, the REG_BR_PROB values are used to exactly determine which
10492           path is taken more often.
10493
10494           Enabled by -fprofile-use and -fauto-profile.
10495
10496       -fprofile-values
10497           If combined with -fprofile-arcs, it adds code so that some data
10498           about values of expressions in the program is gathered.
10499
10500           With -fbranch-probabilities, it reads back the data gathered from
10501           profiling values of expressions for usage in optimizations.
10502
10503           Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile.
10504
10505       -fprofile-reorder-functions
10506           Function reordering based on profile instrumentation collects first
10507           time of execution of a function and orders these functions in
10508           ascending order.
10509
10510           Enabled with -fprofile-use.
10511
10512       -fvpt
10513           If combined with -fprofile-arcs, this option instructs the compiler
10514           to add code to gather information about values of expressions.
10515
10516           With -fbranch-probabilities, it reads back the data gathered and
10517           actually performs the optimizations based on them.  Currently the
10518           optimizations include specialization of division operations using
10519           the knowledge about the value of the denominator.
10520
10521           Enabled with -fprofile-use and -fauto-profile.
10522
10523       -frename-registers
10524           Attempt to avoid false dependencies in scheduled code by making use
10525           of registers left over after register allocation.  This
10526           optimization most benefits processors with lots of registers.
10527           Depending on the debug information format adopted by the target,
10528           however, it can make debugging impossible, since variables no
10529           longer stay in a "home register".
10530
10531           Enabled by default with -funroll-loops.
10532
10533       -fschedule-fusion
10534           Performs a target dependent pass over the instruction stream to
10535           schedule instructions of same type together because target machine
10536           can execute them more efficiently if they are adjacent to each
10537           other in the instruction flow.
10538
10539           Enabled at levels -O2, -O3, -Os.
10540
10541       -ftracer
10542           Perform tail duplication to enlarge superblock size.  This
10543           transformation simplifies the control flow of the function allowing
10544           other optimizations to do a better job.
10545
10546           Enabled by -fprofile-use and -fauto-profile.
10547
10548       -funroll-loops
10549           Unroll loops whose number of iterations can be determined at
10550           compile time or upon entry to the loop.  -funroll-loops implies
10551           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
10552           turns on complete loop peeling (i.e. complete removal of loops with
10553           a small constant number of iterations).  This option makes code
10554           larger, and may or may not make it run faster.
10555
10556           Enabled by -fprofile-use and -fauto-profile.
10557
10558       -funroll-all-loops
10559           Unroll all loops, even if their number of iterations is uncertain
10560           when the loop is entered.  This usually makes programs run more
10561           slowly.  -funroll-all-loops implies the same options as
10562           -funroll-loops.
10563
10564       -fpeel-loops
10565           Peels loops for which there is enough information that they do not
10566           roll much (from profile feedback or static analysis).  It also
10567           turns on complete loop peeling (i.e. complete removal of loops with
10568           small constant number of iterations).
10569
10570           Enabled by -O3, -fprofile-use, and -fauto-profile.
10571
10572       -fmove-loop-invariants
10573           Enables the loop invariant motion pass in the RTL loop optimizer.
10574           Enabled at level -O1 and higher, except for -Og.
10575
10576       -fsplit-loops
10577           Split a loop into two if it contains a condition that's always true
10578           for one side of the iteration space and false for the other.
10579
10580           Enabled by -fprofile-use and -fauto-profile.
10581
10582       -funswitch-loops
10583           Move branches with loop invariant conditions out of the loop, with
10584           duplicates of the loop on both branches (modified according to
10585           result of the condition).
10586
10587           Enabled by -fprofile-use and -fauto-profile.
10588
10589       -fversion-loops-for-strides
10590           If a loop iterates over an array with a variable stride, create
10591           another version of the loop that assumes the stride is always one.
10592           For example:
10593
10594                   for (int i = 0; i < n; ++i)
10595                     x[i * stride] = ...;
10596
10597           becomes:
10598
10599                   if (stride == 1)
10600                     for (int i = 0; i < n; ++i)
10601                       x[i] = ...;
10602                   else
10603                     for (int i = 0; i < n; ++i)
10604                       x[i * stride] = ...;
10605
10606           This is particularly useful for assumed-shape arrays in Fortran
10607           where (for example) it allows better vectorization assuming
10608           contiguous accesses.  This flag is enabled by default at -O3.  It
10609           is also enabled by -fprofile-use and -fauto-profile.
10610
10611       -ffunction-sections
10612       -fdata-sections
10613           Place each function or data item into its own section in the output
10614           file if the target supports arbitrary sections.  The name of the
10615           function or the name of the data item determines the section's name
10616           in the output file.
10617
10618           Use these options on systems where the linker can perform
10619           optimizations to improve locality of reference in the instruction
10620           space.  Most systems using the ELF object format have linkers with
10621           such optimizations.  On AIX, the linker rearranges sections
10622           (CSECTs) based on the call graph.  The performance impact varies.
10623
10624           Together with a linker garbage collection (linker --gc-sections
10625           option) these options may lead to smaller statically-linked
10626           executables (after stripping).
10627
10628           On ELF/DWARF systems these options do not degenerate the quality of
10629           the debug information.  There could be issues with other object
10630           files/debug info formats.
10631
10632           Only use these options when there are significant benefits from
10633           doing so.  When you specify these options, the assembler and linker
10634           create larger object and executable files and are also slower.
10635           These options affect code generation.  They prevent optimizations
10636           by the compiler and assembler using relative locations inside a
10637           translation unit since the locations are unknown until link time.
10638           An example of such an optimization is relaxing calls to short call
10639           instructions.
10640
10641       -fstdarg-opt
10642           Optimize the prologue of variadic argument functions with respect
10643           to usage of those arguments.
10644
10645       -fsection-anchors
10646           Try to reduce the number of symbolic address calculations by using
10647           shared "anchor" symbols to address nearby objects.  This
10648           transformation can help to reduce the number of GOT entries and GOT
10649           accesses on some targets.
10650
10651           For example, the implementation of the following function "foo":
10652
10653                   static int a, b, c;
10654                   int foo (void) { return a + b + c; }
10655
10656           usually calculates the addresses of all three variables, but if you
10657           compile it with -fsection-anchors, it accesses the variables from a
10658           common anchor point instead.  The effect is similar to the
10659           following pseudocode (which isn't valid C):
10660
10661                   int foo (void)
10662                   {
10663                     register int *xr = &x;
10664                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
10665                   }
10666
10667           Not all targets support this option.
10668
10669       -fzero-call-used-regs=choice
10670           Zero call-used registers at function return to increase program
10671           security by either mitigating Return-Oriented Programming (ROP)
10672           attacks or preventing information leakage through registers.
10673
10674           The possible values of choice are the same as for the
10675           "zero_call_used_regs" attribute.  The default is skip.
10676
10677           You can control this behavior for a specific function by using the
10678           function attribute "zero_call_used_regs".
10679
10680       --param name=value
10681           In some places, GCC uses various constants to control the amount of
10682           optimization that is done.  For example, GCC does not inline
10683           functions that contain more than a certain number of instructions.
10684           You can control some of these constants on the command line using
10685           the --param option.
10686
10687           The names of specific parameters, and the meaning of the values,
10688           are tied to the internals of the compiler, and are subject to
10689           change without notice in future releases.
10690
10691           In order to get minimal, maximal and default value of a parameter,
10692           one can use --help=param -Q options.
10693
10694           In each case, the value is an integer.  The following choices of
10695           name are recognized for all targets:
10696
10697           predictable-branch-outcome
10698               When branch is predicted to be taken with probability lower
10699               than this threshold (in percent), then it is considered well
10700               predictable.
10701
10702           max-rtl-if-conversion-insns
10703               RTL if-conversion tries to remove conditional branches around a
10704               block and replace them with conditionally executed
10705               instructions.  This parameter gives the maximum number of
10706               instructions in a block which should be considered for if-
10707               conversion.  The compiler will also use other heuristics to
10708               decide whether if-conversion is likely to be profitable.
10709
10710           max-rtl-if-conversion-predictable-cost
10711               RTL if-conversion will try to remove conditional branches
10712               around a block and replace them with conditionally executed
10713               instructions.  These parameters give the maximum permissible
10714               cost for the sequence that would be generated by if-conversion
10715               depending on whether the branch is statically determined to be
10716               predictable or not.  The units for this parameter are the same
10717               as those for the GCC internal seq_cost metric.  The compiler
10718               will try to provide a reasonable default for this parameter
10719               using the BRANCH_COST target macro.
10720
10721           max-crossjump-edges
10722               The maximum number of incoming edges to consider for cross-
10723               jumping.  The algorithm used by -fcrossjumping is O(N^2) in the
10724               number of edges incoming to each block.  Increasing values mean
10725               more aggressive optimization, making the compilation time
10726               increase with probably small improvement in executable size.
10727
10728           min-crossjump-insns
10729               The minimum number of instructions that must be matched at the
10730               end of two blocks before cross-jumping is performed on them.
10731               This value is ignored in the case where all instructions in the
10732               block being cross-jumped from are matched.
10733
10734           max-grow-copy-bb-insns
10735               The maximum code size expansion factor when copying basic
10736               blocks instead of jumping.  The expansion is relative to a jump
10737               instruction.
10738
10739           max-goto-duplication-insns
10740               The maximum number of instructions to duplicate to a block that
10741               jumps to a computed goto.  To avoid O(N^2) behavior in a number
10742               of passes, GCC factors computed gotos early in the compilation
10743               process, and unfactors them as late as possible.  Only computed
10744               jumps at the end of a basic blocks with no more than max-goto-
10745               duplication-insns are unfactored.
10746
10747           max-delay-slot-insn-search
10748               The maximum number of instructions to consider when looking for
10749               an instruction to fill a delay slot.  If more than this
10750               arbitrary number of instructions are searched, the time savings
10751               from filling the delay slot are minimal, so stop searching.
10752               Increasing values mean more aggressive optimization, making the
10753               compilation time increase with probably small improvement in
10754               execution time.
10755
10756           max-delay-slot-live-search
10757               When trying to fill delay slots, the maximum number of
10758               instructions to consider when searching for a block with valid
10759               live register information.  Increasing this arbitrarily chosen
10760               value means more aggressive optimization, increasing the
10761               compilation time.  This parameter should be removed when the
10762               delay slot code is rewritten to maintain the control-flow
10763               graph.
10764
10765           max-gcse-memory
10766               The approximate maximum amount of memory in "kB" that can be
10767               allocated in order to perform the global common subexpression
10768               elimination optimization.  If more memory than specified is
10769               required, the optimization is not done.
10770
10771           max-gcse-insertion-ratio
10772               If the ratio of expression insertions to deletions is larger
10773               than this value for any expression, then RTL PRE inserts or
10774               removes the expression and thus leaves partially redundant
10775               computations in the instruction stream.
10776
10777           max-pending-list-length
10778               The maximum number of pending dependencies scheduling allows
10779               before flushing the current state and starting over.  Large
10780               functions with few branches or calls can create excessively
10781               large lists which needlessly consume memory and resources.
10782
10783           max-modulo-backtrack-attempts
10784               The maximum number of backtrack attempts the scheduler should
10785               make when modulo scheduling a loop.  Larger values can
10786               exponentially increase compilation time.
10787
10788           max-inline-insns-single
10789               Several parameters control the tree inliner used in GCC.  This
10790               number sets the maximum number of instructions (counted in
10791               GCC's internal representation) in a single function that the
10792               tree inliner considers for inlining.  This only affects
10793               functions declared inline and methods implemented in a class
10794               declaration (C++).
10795
10796           max-inline-insns-auto
10797               When you use -finline-functions (included in -O3), a lot of
10798               functions that would otherwise not be considered for inlining
10799               by the compiler are investigated.  To those functions, a
10800               different (more restrictive) limit compared to functions
10801               declared inline can be applied (--param max-inline-insns-auto).
10802
10803           max-inline-insns-small
10804               This is bound applied to calls which are considered relevant
10805               with -finline-small-functions.
10806
10807           max-inline-insns-size
10808               This is bound applied to calls which are optimized for size.
10809               Small growth may be desirable to anticipate optimization
10810               oppurtunities exposed by inlining.
10811
10812           uninlined-function-insns
10813               Number of instructions accounted by inliner for function
10814               overhead such as function prologue and epilogue.
10815
10816           uninlined-function-time
10817               Extra time accounted by inliner for function overhead such as
10818               time needed to execute function prologue and epilogue
10819
10820           inline-heuristics-hint-percent
10821               The scale (in percents) applied to inline-insns-single,
10822               inline-insns-single-O2, inline-insns-auto when inline
10823               heuristics hints that inlining is very profitable (will enable
10824               later optimizations).
10825
10826           uninlined-thunk-insns
10827           uninlined-thunk-time
10828               Same as --param uninlined-function-insns and --param uninlined-
10829               function-time but applied to function thunks
10830
10831           inline-min-speedup
10832               When estimated performance improvement of caller + callee
10833               runtime exceeds this threshold (in percent), the function can
10834               be inlined regardless of the limit on --param max-inline-insns-
10835               single and --param max-inline-insns-auto.
10836
10837           large-function-insns
10838               The limit specifying really large functions.  For functions
10839               larger than this limit after inlining, inlining is constrained
10840               by --param large-function-growth.  This parameter is useful
10841               primarily to avoid extreme compilation time caused by non-
10842               linear algorithms used by the back end.
10843
10844           large-function-growth
10845               Specifies maximal growth of large function caused by inlining
10846               in percents.  For example, parameter value 100 limits large
10847               function growth to 2.0 times the original size.
10848
10849           large-unit-insns
10850               The limit specifying large translation unit.  Growth caused by
10851               inlining of units larger than this limit is limited by --param
10852               inline-unit-growth.  For small units this might be too tight.
10853               For example, consider a unit consisting of function A that is
10854               inline and B that just calls A three times.  If B is small
10855               relative to A, the growth of unit is 300\% and yet such
10856               inlining is very sane.  For very large units consisting of
10857               small inlineable functions, however, the overall unit growth
10858               limit is needed to avoid exponential explosion of code size.
10859               Thus for smaller units, the size is increased to --param large-
10860               unit-insns before applying --param inline-unit-growth.
10861
10862           lazy-modules
10863               Maximum number of concurrently open C++ module files when lazy
10864               loading.
10865
10866           inline-unit-growth
10867               Specifies maximal overall growth of the compilation unit caused
10868               by inlining.  For example, parameter value 20 limits unit
10869               growth to 1.2 times the original size. Cold functions (either
10870               marked cold via an attribute or by profile feedback) are not
10871               accounted into the unit size.
10872
10873           ipa-cp-unit-growth
10874               Specifies maximal overall growth of the compilation unit caused
10875               by interprocedural constant propagation.  For example,
10876               parameter value 10 limits unit growth to 1.1 times the original
10877               size.
10878
10879           ipa-cp-large-unit-insns
10880               The size of translation unit that IPA-CP pass considers large.
10881
10882           large-stack-frame
10883               The limit specifying large stack frames.  While inlining the
10884               algorithm is trying to not grow past this limit too much.
10885
10886           large-stack-frame-growth
10887               Specifies maximal growth of large stack frames caused by
10888               inlining in percents.  For example, parameter value 1000 limits
10889               large stack frame growth to 11 times the original size.
10890
10891           max-inline-insns-recursive
10892           max-inline-insns-recursive-auto
10893               Specifies the maximum number of instructions an out-of-line
10894               copy of a self-recursive inline function can grow into by
10895               performing recursive inlining.
10896
10897               --param max-inline-insns-recursive applies to functions
10898               declared inline.  For functions not declared inline, recursive
10899               inlining happens only when -finline-functions (included in -O3)
10900               is enabled; --param max-inline-insns-recursive-auto applies
10901               instead.
10902
10903           max-inline-recursive-depth
10904           max-inline-recursive-depth-auto
10905               Specifies the maximum recursion depth used for recursive
10906               inlining.
10907
10908               --param max-inline-recursive-depth applies to functions
10909               declared inline.  For functions not declared inline, recursive
10910               inlining happens only when -finline-functions (included in -O3)
10911               is enabled; --param max-inline-recursive-depth-auto applies
10912               instead.
10913
10914           min-inline-recursive-probability
10915               Recursive inlining is profitable only for function having deep
10916               recursion in average and can hurt for function having little
10917               recursion depth by increasing the prologue size or complexity
10918               of function body to other optimizers.
10919
10920               When profile feedback is available (see -fprofile-generate) the
10921               actual recursion depth can be guessed from the probability that
10922               function recurses via a given call expression.  This parameter
10923               limits inlining only to call expressions whose probability
10924               exceeds the given threshold (in percents).
10925
10926           early-inlining-insns
10927               Specify growth that the early inliner can make.  In effect it
10928               increases the amount of inlining for code having a large
10929               abstraction penalty.
10930
10931           max-early-inliner-iterations
10932               Limit of iterations of the early inliner.  This basically
10933               bounds the number of nested indirect calls the early inliner
10934               can resolve.  Deeper chains are still handled by late inlining.
10935
10936           comdat-sharing-probability
10937               Probability (in percent) that C++ inline function with comdat
10938               visibility are shared across multiple compilation units.
10939
10940           modref-max-bases
10941           modref-max-refs
10942           modref-max-accesses
10943               Specifies the maximal number of base pointers, references and
10944               accesses stored for a single function by mod/ref analysis.
10945
10946           modref-max-tests
10947               Specifies the maxmal number of tests alias oracle can perform
10948               to disambiguate memory locations using the mod/ref information.
10949               This parameter ought to be bigger than --param modref-max-bases
10950               and --param modref-max-refs.
10951
10952           modref-max-depth
10953               Specifies the maximum depth of DFS walk used by modref escape
10954               analysis.  Setting to 0 disables the analysis completely.
10955
10956           modref-max-escape-points
10957               Specifies the maximum number of escape points tracked by modref
10958               per SSA-name.
10959
10960           profile-func-internal-id
10961               A parameter to control whether to use function internal id in
10962               profile database lookup. If the value is 0, the compiler uses
10963               an id that is based on function assembler name and filename,
10964               which makes old profile data more tolerant to source changes
10965               such as function reordering etc.
10966
10967           min-vect-loop-bound
10968               The minimum number of iterations under which loops are not
10969               vectorized when -ftree-vectorize is used.  The number of
10970               iterations after vectorization needs to be greater than the
10971               value specified by this option to allow vectorization.
10972
10973           gcse-cost-distance-ratio
10974               Scaling factor in calculation of maximum distance an expression
10975               can be moved by GCSE optimizations.  This is currently
10976               supported only in the code hoisting pass.  The bigger the
10977               ratio, the more aggressive code hoisting is with simple
10978               expressions, i.e., the expressions that have cost less than
10979               gcse-unrestricted-cost.  Specifying 0 disables hoisting of
10980               simple expressions.
10981
10982           gcse-unrestricted-cost
10983               Cost, roughly measured as the cost of a single typical machine
10984               instruction, at which GCSE optimizations do not constrain the
10985               distance an expression can travel.  This is currently supported
10986               only in the code hoisting pass.  The lesser the cost, the more
10987               aggressive code hoisting is.  Specifying 0 allows all
10988               expressions to travel unrestricted distances.
10989
10990           max-hoist-depth
10991               The depth of search in the dominator tree for expressions to
10992               hoist.  This is used to avoid quadratic behavior in hoisting
10993               algorithm.  The value of 0 does not limit on the search, but
10994               may slow down compilation of huge functions.
10995
10996           max-tail-merge-comparisons
10997               The maximum amount of similar bbs to compare a bb with.  This
10998               is used to avoid quadratic behavior in tree tail merging.
10999
11000           max-tail-merge-iterations
11001               The maximum amount of iterations of the pass over the function.
11002               This is used to limit compilation time in tree tail merging.
11003
11004           store-merging-allow-unaligned
11005               Allow the store merging pass to introduce unaligned stores if
11006               it is legal to do so.
11007
11008           max-stores-to-merge
11009               The maximum number of stores to attempt to merge into wider
11010               stores in the store merging pass.
11011
11012           max-store-chains-to-track
11013               The maximum number of store chains to track at the same time in
11014               the attempt to merge them into wider stores in the store
11015               merging pass.
11016
11017           max-stores-to-track
11018               The maximum number of stores to track at the same time in the
11019               attemt to to merge them into wider stores in the store merging
11020               pass.
11021
11022           max-unrolled-insns
11023               The maximum number of instructions that a loop may have to be
11024               unrolled.  If a loop is unrolled, this parameter also
11025               determines how many times the loop code is unrolled.
11026
11027           max-average-unrolled-insns
11028               The maximum number of instructions biased by probabilities of
11029               their execution that a loop may have to be unrolled.  If a loop
11030               is unrolled, this parameter also determines how many times the
11031               loop code is unrolled.
11032
11033           max-unroll-times
11034               The maximum number of unrollings of a single loop.
11035
11036           max-peeled-insns
11037               The maximum number of instructions that a loop may have to be
11038               peeled.  If a loop is peeled, this parameter also determines
11039               how many times the loop code is peeled.
11040
11041           max-peel-times
11042               The maximum number of peelings of a single loop.
11043
11044           max-peel-branches
11045               The maximum number of branches on the hot path through the
11046               peeled sequence.
11047
11048           max-completely-peeled-insns
11049               The maximum number of insns of a completely peeled loop.
11050
11051           max-completely-peel-times
11052               The maximum number of iterations of a loop to be suitable for
11053               complete peeling.
11054
11055           max-completely-peel-loop-nest-depth
11056               The maximum depth of a loop nest suitable for complete peeling.
11057
11058           max-unswitch-insns
11059               The maximum number of insns of an unswitched loop.
11060
11061           max-unswitch-level
11062               The maximum number of branches unswitched in a single loop.
11063
11064           lim-expensive
11065               The minimum cost of an expensive expression in the loop
11066               invariant motion.
11067
11068           min-loop-cond-split-prob
11069               When FDO profile information is available, min-loop-cond-split-
11070               prob specifies minimum threshold for probability of semi-
11071               invariant condition statement to trigger loop split.
11072
11073           iv-consider-all-candidates-bound
11074               Bound on number of candidates for induction variables, below
11075               which all candidates are considered for each use in induction
11076               variable optimizations.  If there are more candidates than
11077               this, only the most relevant ones are considered to avoid
11078               quadratic time complexity.
11079
11080           iv-max-considered-uses
11081               The induction variable optimizations give up on loops that
11082               contain more induction variable uses.
11083
11084           iv-always-prune-cand-set-bound
11085               If the number of candidates in the set is smaller than this
11086               value, always try to remove unnecessary ivs from the set when
11087               adding a new one.
11088
11089           avg-loop-niter
11090               Average number of iterations of a loop.
11091
11092           dse-max-object-size
11093               Maximum size (in bytes) of objects tracked bytewise by dead
11094               store elimination.  Larger values may result in larger
11095               compilation times.
11096
11097           dse-max-alias-queries-per-store
11098               Maximum number of queries into the alias oracle per store.
11099               Larger values result in larger compilation times and may result
11100               in more removed dead stores.
11101
11102           scev-max-expr-size
11103               Bound on size of expressions used in the scalar evolutions
11104               analyzer.  Large expressions slow the analyzer.
11105
11106           scev-max-expr-complexity
11107               Bound on the complexity of the expressions in the scalar
11108               evolutions analyzer.  Complex expressions slow the analyzer.
11109
11110           max-tree-if-conversion-phi-args
11111               Maximum number of arguments in a PHI supported by TREE if
11112               conversion unless the loop is marked with simd pragma.
11113
11114           vect-max-version-for-alignment-checks
11115               The maximum number of run-time checks that can be performed
11116               when doing loop versioning for alignment in the vectorizer.
11117
11118           vect-max-version-for-alias-checks
11119               The maximum number of run-time checks that can be performed
11120               when doing loop versioning for alias in the vectorizer.
11121
11122           vect-max-peeling-for-alignment
11123               The maximum number of loop peels to enhance access alignment
11124               for vectorizer. Value -1 means no limit.
11125
11126           max-iterations-to-track
11127               The maximum number of iterations of a loop the brute-force
11128               algorithm for analysis of the number of iterations of the loop
11129               tries to evaluate.
11130
11131           hot-bb-count-fraction
11132               The denominator n of fraction 1/n of the maximal execution
11133               count of a basic block in the entire program that a basic block
11134               needs to at least have in order to be considered hot.  The
11135               default is 10000, which means that a basic block is considered
11136               hot if its execution count is greater than 1/10000 of the
11137               maximal execution count.  0 means that it is never considered
11138               hot.  Used in non-LTO mode.
11139
11140           hot-bb-count-ws-permille
11141               The number of most executed permilles, ranging from 0 to 1000,
11142               of the profiled execution of the entire program to which the
11143               execution count of a basic block must be part of in order to be
11144               considered hot.  The default is 990, which means that a basic
11145               block is considered hot if its execution count contributes to
11146               the upper 990 permilles, or 99.0%, of the profiled execution of
11147               the entire program.  0 means that it is never considered hot.
11148               Used in LTO mode.
11149
11150           hot-bb-frequency-fraction
11151               The denominator n of fraction 1/n of the execution frequency of
11152               the entry block of a function that a basic block of this
11153               function needs to at least have in order to be considered hot.
11154               The default is 1000, which means that a basic block is
11155               considered hot in a function if it is executed more frequently
11156               than 1/1000 of the frequency of the entry block of the
11157               function.  0 means that it is never considered hot.
11158
11159           unlikely-bb-count-fraction
11160               The denominator n of fraction 1/n of the number of profiled
11161               runs of the entire program below which the execution count of a
11162               basic block must be in order for the basic block to be
11163               considered unlikely executed.  The default is 20, which means
11164               that a basic block is considered unlikely executed if it is
11165               executed in fewer than 1/20, or 5%, of the runs of the program.
11166               0 means that it is always considered unlikely executed.
11167
11168           max-predicted-iterations
11169               The maximum number of loop iterations we predict statically.
11170               This is useful in cases where a function contains a single loop
11171               with known bound and another loop with unknown bound.  The
11172               known number of iterations is predicted correctly, while the
11173               unknown number of iterations average to roughly 10.  This means
11174               that the loop without bounds appears artificially cold relative
11175               to the other one.
11176
11177           builtin-expect-probability
11178               Control the probability of the expression having the specified
11179               value. This parameter takes a percentage (i.e. 0 ... 100) as
11180               input.
11181
11182           builtin-string-cmp-inline-length
11183               The maximum length of a constant string for a builtin string
11184               cmp call eligible for inlining.
11185
11186           align-threshold
11187               Select fraction of the maximal frequency of executions of a
11188               basic block in a function to align the basic block.
11189
11190           align-loop-iterations
11191               A loop expected to iterate at least the selected number of
11192               iterations is aligned.
11193
11194           tracer-dynamic-coverage
11195           tracer-dynamic-coverage-feedback
11196               This value is used to limit superblock formation once the given
11197               percentage of executed instructions is covered.  This limits
11198               unnecessary code size expansion.
11199
11200               The tracer-dynamic-coverage-feedback parameter is used only
11201               when profile feedback is available.  The real profiles (as
11202               opposed to statically estimated ones) are much less balanced
11203               allowing the threshold to be larger value.
11204
11205           tracer-max-code-growth
11206               Stop tail duplication once code growth has reached given
11207               percentage.  This is a rather artificial limit, as most of the
11208               duplicates are eliminated later in cross jumping, so it may be
11209               set to much higher values than is the desired code growth.
11210
11211           tracer-min-branch-ratio
11212               Stop reverse growth when the reverse probability of best edge
11213               is less than this threshold (in percent).
11214
11215           tracer-min-branch-probability
11216           tracer-min-branch-probability-feedback
11217               Stop forward growth if the best edge has probability lower than
11218               this threshold.
11219
11220               Similarly to tracer-dynamic-coverage two parameters are
11221               provided.  tracer-min-branch-probability-feedback is used for
11222               compilation with profile feedback and tracer-min-branch-
11223               probability compilation without.  The value for compilation
11224               with profile feedback needs to be more conservative (higher) in
11225               order to make tracer effective.
11226
11227           stack-clash-protection-guard-size
11228               Specify the size of the operating system provided stack guard
11229               as 2 raised to num bytes.  Higher values may reduce the number
11230               of explicit probes, but a value larger than the operating
11231               system provided guard will leave code vulnerable to stack clash
11232               style attacks.
11233
11234           stack-clash-protection-probe-interval
11235               Stack clash protection involves probing stack space as it is
11236               allocated.  This param controls the maximum distance between
11237               probes into the stack as 2 raised to num bytes.  Higher values
11238               may reduce the number of explicit probes, but a value larger
11239               than the operating system provided guard will leave code
11240               vulnerable to stack clash style attacks.
11241
11242           max-cse-path-length
11243               The maximum number of basic blocks on path that CSE considers.
11244
11245           max-cse-insns
11246               The maximum number of instructions CSE processes before
11247               flushing.
11248
11249           ggc-min-expand
11250               GCC uses a garbage collector to manage its own memory
11251               allocation.  This parameter specifies the minimum percentage by
11252               which the garbage collector's heap should be allowed to expand
11253               between collections.  Tuning this may improve compilation
11254               speed; it has no effect on code generation.
11255
11256               The default is 30% + 70% * (RAM/1GB) with an upper bound of
11257               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
11258               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
11259               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
11260               particular platform, the lower bound of 30% is used.  Setting
11261               this parameter and ggc-min-heapsize to zero causes a full
11262               collection to occur at every opportunity.  This is extremely
11263               slow, but can be useful for debugging.
11264
11265           ggc-min-heapsize
11266               Minimum size of the garbage collector's heap before it begins
11267               bothering to collect garbage.  The first collection occurs
11268               after the heap expands by ggc-min-expand% beyond ggc-min-
11269               heapsize.  Again, tuning this may improve compilation speed,
11270               and has no effect on code generation.
11271
11272               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
11273               that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
11274               exceeded, but with a lower bound of 4096 (four megabytes) and
11275               an upper bound of 131072 (128 megabytes).  If GCC is not able
11276               to calculate RAM on a particular platform, the lower bound is
11277               used.  Setting this parameter very large effectively disables
11278               garbage collection.  Setting this parameter and ggc-min-expand
11279               to zero causes a full collection to occur at every opportunity.
11280
11281           max-reload-search-insns
11282               The maximum number of instruction reload should look backward
11283               for equivalent register.  Increasing values mean more
11284               aggressive optimization, making the compilation time increase
11285               with probably slightly better performance.
11286
11287           max-cselib-memory-locations
11288               The maximum number of memory locations cselib should take into
11289               account.  Increasing values mean more aggressive optimization,
11290               making the compilation time increase with probably slightly
11291               better performance.
11292
11293           max-sched-ready-insns
11294               The maximum number of instructions ready to be issued the
11295               scheduler should consider at any given time during the first
11296               scheduling pass.  Increasing values mean more thorough
11297               searches, making the compilation time increase with probably
11298               little benefit.
11299
11300           max-sched-region-blocks
11301               The maximum number of blocks in a region to be considered for
11302               interblock scheduling.
11303
11304           max-pipeline-region-blocks
11305               The maximum number of blocks in a region to be considered for
11306               pipelining in the selective scheduler.
11307
11308           max-sched-region-insns
11309               The maximum number of insns in a region to be considered for
11310               interblock scheduling.
11311
11312           max-pipeline-region-insns
11313               The maximum number of insns in a region to be considered for
11314               pipelining in the selective scheduler.
11315
11316           min-spec-prob
11317               The minimum probability (in percents) of reaching a source
11318               block for interblock speculative scheduling.
11319
11320           max-sched-extend-regions-iters
11321               The maximum number of iterations through CFG to extend regions.
11322               A value of 0 disables region extensions.
11323
11324           max-sched-insn-conflict-delay
11325               The maximum conflict delay for an insn to be considered for
11326               speculative motion.
11327
11328           sched-spec-prob-cutoff
11329               The minimal probability of speculation success (in percents),
11330               so that speculative insns are scheduled.
11331
11332           sched-state-edge-prob-cutoff
11333               The minimum probability an edge must have for the scheduler to
11334               save its state across it.
11335
11336           sched-mem-true-dep-cost
11337               Minimal distance (in CPU cycles) between store and load
11338               targeting same memory locations.
11339
11340           selsched-max-lookahead
11341               The maximum size of the lookahead window of selective
11342               scheduling.  It is a depth of search for available
11343               instructions.
11344
11345           selsched-max-sched-times
11346               The maximum number of times that an instruction is scheduled
11347               during selective scheduling.  This is the limit on the number
11348               of iterations through which the instruction may be pipelined.
11349
11350           selsched-insns-to-rename
11351               The maximum number of best instructions in the ready list that
11352               are considered for renaming in the selective scheduler.
11353
11354           sms-min-sc
11355               The minimum value of stage count that swing modulo scheduler
11356               generates.
11357
11358           max-last-value-rtl
11359               The maximum size measured as number of RTLs that can be
11360               recorded in an expression in combiner for a pseudo register as
11361               last known value of that register.
11362
11363           max-combine-insns
11364               The maximum number of instructions the RTL combiner tries to
11365               combine.
11366
11367           integer-share-limit
11368               Small integer constants can use a shared data structure,
11369               reducing the compiler's memory usage and increasing its speed.
11370               This sets the maximum value of a shared integer constant.
11371
11372           ssp-buffer-size
11373               The minimum size of buffers (i.e. arrays) that receive stack
11374               smashing protection when -fstack-protection is used.
11375
11376           min-size-for-stack-sharing
11377               The minimum size of variables taking part in stack slot sharing
11378               when not optimizing.
11379
11380           max-jump-thread-duplication-stmts
11381               Maximum number of statements allowed in a block that needs to
11382               be duplicated when threading jumps.
11383
11384           max-fields-for-field-sensitive
11385               Maximum number of fields in a structure treated in a field
11386               sensitive manner during pointer analysis.
11387
11388           prefetch-latency
11389               Estimate on average number of instructions that are executed
11390               before prefetch finishes.  The distance prefetched ahead is
11391               proportional to this constant.  Increasing this number may also
11392               lead to less streams being prefetched (see simultaneous-
11393               prefetches).
11394
11395           simultaneous-prefetches
11396               Maximum number of prefetches that can run at the same time.
11397
11398           l1-cache-line-size
11399               The size of cache line in L1 data cache, in bytes.
11400
11401           l1-cache-size
11402               The size of L1 data cache, in kilobytes.
11403
11404           l2-cache-size
11405               The size of L2 data cache, in kilobytes.
11406
11407           prefetch-dynamic-strides
11408               Whether the loop array prefetch pass should issue software
11409               prefetch hints for strides that are non-constant.  In some
11410               cases this may be beneficial, though the fact the stride is
11411               non-constant may make it hard to predict when there is clear
11412               benefit to issuing these hints.
11413
11414               Set to 1 if the prefetch hints should be issued for non-
11415               constant strides.  Set to 0 if prefetch hints should be issued
11416               only for strides that are known to be constant and below
11417               prefetch-minimum-stride.
11418
11419           prefetch-minimum-stride
11420               Minimum constant stride, in bytes, to start using prefetch
11421               hints for.  If the stride is less than this threshold, prefetch
11422               hints will not be issued.
11423
11424               This setting is useful for processors that have hardware
11425               prefetchers, in which case there may be conflicts between the
11426               hardware prefetchers and the software prefetchers.  If the
11427               hardware prefetchers have a maximum stride they can handle, it
11428               should be used here to improve the use of software prefetchers.
11429
11430               A value of -1 means we don't have a threshold and therefore
11431               prefetch hints can be issued for any constant stride.
11432
11433               This setting is only useful for strides that are known and
11434               constant.
11435
11436           loop-interchange-max-num-stmts
11437               The maximum number of stmts in a loop to be interchanged.
11438
11439           loop-interchange-stride-ratio
11440               The minimum ratio between stride of two loops for interchange
11441               to be profitable.
11442
11443           min-insn-to-prefetch-ratio
11444               The minimum ratio between the number of instructions and the
11445               number of prefetches to enable prefetching in a loop.
11446
11447           prefetch-min-insn-to-mem-ratio
11448               The minimum ratio between the number of instructions and the
11449               number of memory references to enable prefetching in a loop.
11450
11451           use-canonical-types
11452               Whether the compiler should use the "canonical" type system.
11453               Should always be 1, which uses a more efficient internal
11454               mechanism for comparing types in C++ and Objective-C++.
11455               However, if bugs in the canonical type system are causing
11456               compilation failures, set this value to 0 to disable canonical
11457               types.
11458
11459           switch-conversion-max-branch-ratio
11460               Switch initialization conversion refuses to create arrays that
11461               are bigger than switch-conversion-max-branch-ratio times the
11462               number of branches in the switch.
11463
11464           max-partial-antic-length
11465               Maximum length of the partial antic set computed during the
11466               tree partial redundancy elimination optimization (-ftree-pre)
11467               when optimizing at -O3 and above.  For some sorts of source
11468               code the enhanced partial redundancy elimination optimization
11469               can run away, consuming all of the memory available on the host
11470               machine.  This parameter sets a limit on the length of the sets
11471               that are computed, which prevents the runaway behavior.
11472               Setting a value of 0 for this parameter allows an unlimited set
11473               length.
11474
11475           rpo-vn-max-loop-depth
11476               Maximum loop depth that is value-numbered optimistically.  When
11477               the limit hits the innermost rpo-vn-max-loop-depth loops and
11478               the outermost loop in the loop nest are value-numbered
11479               optimistically and the remaining ones not.
11480
11481           sccvn-max-alias-queries-per-access
11482               Maximum number of alias-oracle queries we perform when looking
11483               for redundancies for loads and stores.  If this limit is hit
11484               the search is aborted and the load or store is not considered
11485               redundant.  The number of queries is algorithmically limited to
11486               the number of stores on all paths from the load to the function
11487               entry.
11488
11489           ira-max-loops-num
11490               IRA uses regional register allocation by default.  If a
11491               function contains more loops than the number given by this
11492               parameter, only at most the given number of the most
11493               frequently-executed loops form regions for regional register
11494               allocation.
11495
11496           ira-max-conflict-table-size
11497               Although IRA uses a sophisticated algorithm to compress the
11498               conflict table, the table can still require excessive amounts
11499               of memory for huge functions.  If the conflict table for a
11500               function could be more than the size in MB given by this
11501               parameter, the register allocator instead uses a faster,
11502               simpler, and lower-quality algorithm that does not require
11503               building a pseudo-register conflict table.
11504
11505           ira-loop-reserved-regs
11506               IRA can be used to evaluate more accurate register pressure in
11507               loops for decisions to move loop invariants (see -O3).  The
11508               number of available registers reserved for some other purposes
11509               is given by this parameter.  Default of the parameter is the
11510               best found from numerous experiments.
11511
11512           lra-inheritance-ebb-probability-cutoff
11513               LRA tries to reuse values reloaded in registers in subsequent
11514               insns.  This optimization is called inheritance.  EBB is used
11515               as a region to do this optimization.  The parameter defines a
11516               minimal fall-through edge probability in percentage used to add
11517               BB to inheritance EBB in LRA.  The default value was chosen
11518               from numerous runs of SPEC2000 on x86-64.
11519
11520           loop-invariant-max-bbs-in-loop
11521               Loop invariant motion can be very expensive, both in
11522               compilation time and in amount of needed compile-time memory,
11523               with very large loops.  Loops with more basic blocks than this
11524               parameter won't have loop invariant motion optimization
11525               performed on them.
11526
11527           loop-max-datarefs-for-datadeps
11528               Building data dependencies is expensive for very large loops.
11529               This parameter limits the number of data references in loops
11530               that are considered for data dependence analysis.  These large
11531               loops are no handled by the optimizations using loop data
11532               dependencies.
11533
11534           max-vartrack-size
11535               Sets a maximum number of hash table slots to use during
11536               variable tracking dataflow analysis of any function.  If this
11537               limit is exceeded with variable tracking at assignments
11538               enabled, analysis for that function is retried without it,
11539               after removing all debug insns from the function.  If the limit
11540               is exceeded even without debug insns, var tracking analysis is
11541               completely disabled for the function.  Setting the parameter to
11542               zero makes it unlimited.
11543
11544           max-vartrack-expr-depth
11545               Sets a maximum number of recursion levels when attempting to
11546               map variable names or debug temporaries to value expressions.
11547               This trades compilation time for more complete debug
11548               information.  If this is set too low, value expressions that
11549               are available and could be represented in debug information may
11550               end up not being used; setting this higher may enable the
11551               compiler to find more complex debug expressions, but compile
11552               time and memory use may grow.
11553
11554           max-debug-marker-count
11555               Sets a threshold on the number of debug markers (e.g. begin
11556               stmt markers) to avoid complexity explosion at inlining or
11557               expanding to RTL.  If a function has more such gimple stmts
11558               than the set limit, such stmts will be dropped from the inlined
11559               copy of a function, and from its RTL expansion.
11560
11561           min-nondebug-insn-uid
11562               Use uids starting at this parameter for nondebug insns.  The
11563               range below the parameter is reserved exclusively for debug
11564               insns created by -fvar-tracking-assignments, but debug insns
11565               may get (non-overlapping) uids above it if the reserved range
11566               is exhausted.
11567
11568           ipa-sra-ptr-growth-factor
11569               IPA-SRA replaces a pointer to an aggregate with one or more new
11570               parameters only when their cumulative size is less or equal to
11571               ipa-sra-ptr-growth-factor times the size of the original
11572               pointer parameter.
11573
11574           ipa-sra-max-replacements
11575               Maximum pieces of an aggregate that IPA-SRA tracks.  As a
11576               consequence, it is also the maximum number of replacements of a
11577               formal parameter.
11578
11579           sra-max-scalarization-size-Ospeed
11580           sra-max-scalarization-size-Osize
11581               The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA)
11582               aim to replace scalar parts of aggregates with uses of
11583               independent scalar variables.  These parameters control the
11584               maximum size, in storage units, of aggregate which is
11585               considered for replacement when compiling for speed (sra-max-
11586               scalarization-size-Ospeed) or size (sra-max-scalarization-size-
11587               Osize) respectively.
11588
11589           sra-max-propagations
11590               The maximum number of artificial accesses that Scalar
11591               Replacement of Aggregates (SRA) will track, per one local
11592               variable, in order to facilitate copy propagation.
11593
11594           tm-max-aggregate-size
11595               When making copies of thread-local variables in a transaction,
11596               this parameter specifies the size in bytes after which
11597               variables are saved with the logging functions as opposed to
11598               save/restore code sequence pairs.  This option only applies
11599               when using -fgnu-tm.
11600
11601           graphite-max-nb-scop-params
11602               To avoid exponential effects in the Graphite loop transforms,
11603               the number of parameters in a Static Control Part (SCoP) is
11604               bounded.  A value of zero can be used to lift the bound.  A
11605               variable whose value is unknown at compilation time and defined
11606               outside a SCoP is a parameter of the SCoP.
11607
11608           loop-block-tile-size
11609               Loop blocking or strip mining transforms, enabled with
11610               -floop-block or -floop-strip-mine, strip mine each loop in the
11611               loop nest by a given number of iterations.  The strip length
11612               can be changed using the loop-block-tile-size parameter.
11613
11614           ipa-jump-function-lookups
11615               Specifies number of statements visited during jump function
11616               offset discovery.
11617
11618           ipa-cp-value-list-size
11619               IPA-CP attempts to track all possible values and types passed
11620               to a function's parameter in order to propagate them and
11621               perform devirtualization.  ipa-cp-value-list-size is the
11622               maximum number of values and types it stores per one formal
11623               parameter of a function.
11624
11625           ipa-cp-eval-threshold
11626               IPA-CP calculates its own score of cloning profitability
11627               heuristics and performs those cloning opportunities with scores
11628               that exceed ipa-cp-eval-threshold.
11629
11630           ipa-cp-max-recursive-depth
11631               Maximum depth of recursive cloning for self-recursive function.
11632
11633           ipa-cp-min-recursive-probability
11634               Recursive cloning only when the probability of call being
11635               executed exceeds the parameter.
11636
11637           ipa-cp-recursion-penalty
11638               Percentage penalty the recursive functions will receive when
11639               they are evaluated for cloning.
11640
11641           ipa-cp-single-call-penalty
11642               Percentage penalty functions containing a single call to
11643               another function will receive when they are evaluated for
11644               cloning.
11645
11646           ipa-max-agg-items
11647               IPA-CP is also capable to propagate a number of scalar values
11648               passed in an aggregate. ipa-max-agg-items controls the maximum
11649               number of such values per one parameter.
11650
11651           ipa-cp-loop-hint-bonus
11652               When IPA-CP determines that a cloning candidate would make the
11653               number of iterations of a loop known, it adds a bonus of ipa-
11654               cp-loop-hint-bonus to the profitability score of the candidate.
11655
11656           ipa-max-loop-predicates
11657               The maximum number of different predicates IPA will use to
11658               describe when loops in a function have known properties.
11659
11660           ipa-max-aa-steps
11661               During its analysis of function bodies, IPA-CP employs alias
11662               analysis in order to track values pointed to by function
11663               parameters.  In order not spend too much time analyzing huge
11664               functions, it gives up and consider all memory clobbered after
11665               examining ipa-max-aa-steps statements modifying memory.
11666
11667           ipa-max-switch-predicate-bounds
11668               Maximal number of boundary endpoints of case ranges of switch
11669               statement.  For switch exceeding this limit, IPA-CP will not
11670               construct cloning cost predicate, which is used to estimate
11671               cloning benefit, for default case of the switch statement.
11672
11673           ipa-max-param-expr-ops
11674               IPA-CP will analyze conditional statement that references some
11675               function parameter to estimate benefit for cloning upon certain
11676               constant value.  But if number of operations in a parameter
11677               expression exceeds ipa-max-param-expr-ops, the expression is
11678               treated as complicated one, and is not handled by IPA analysis.
11679
11680           lto-partitions
11681               Specify desired number of partitions produced during WHOPR
11682               compilation.  The number of partitions should exceed the number
11683               of CPUs used for compilation.
11684
11685           lto-min-partition
11686               Size of minimal partition for WHOPR (in estimated
11687               instructions).  This prevents expenses of splitting very small
11688               programs into too many partitions.
11689
11690           lto-max-partition
11691               Size of max partition for WHOPR (in estimated instructions).
11692               to provide an upper bound for individual size of partition.
11693               Meant to be used only with balanced partitioning.
11694
11695           lto-max-streaming-parallelism
11696               Maximal number of parallel processes used for LTO streaming.
11697
11698           cxx-max-namespaces-for-diagnostic-help
11699               The maximum number of namespaces to consult for suggestions
11700               when C++ name lookup fails for an identifier.
11701
11702           sink-frequency-threshold
11703               The maximum relative execution frequency (in percents) of the
11704               target block relative to a statement's original block to allow
11705               statement sinking of a statement.  Larger numbers result in
11706               more aggressive statement sinking.  A small positive adjustment
11707               is applied for statements with memory operands as those are
11708               even more profitable so sink.
11709
11710           max-stores-to-sink
11711               The maximum number of conditional store pairs that can be sunk.
11712               Set to 0 if either vectorization (-ftree-vectorize) or if-
11713               conversion (-ftree-loop-if-convert) is disabled.
11714
11715           case-values-threshold
11716               The smallest number of different values for which it is best to
11717               use a jump-table instead of a tree of conditional branches.  If
11718               the value is 0, use the default for the machine.
11719
11720           jump-table-max-growth-ratio-for-size
11721               The maximum code size growth ratio when expanding into a jump
11722               table (in percent).  The parameter is used when optimizing for
11723               size.
11724
11725           jump-table-max-growth-ratio-for-speed
11726               The maximum code size growth ratio when expanding into a jump
11727               table (in percent).  The parameter is used when optimizing for
11728               speed.
11729
11730           tree-reassoc-width
11731               Set the maximum number of instructions executed in parallel in
11732               reassociated tree. This parameter overrides target dependent
11733               heuristics used by default if has non zero value.
11734
11735           sched-pressure-algorithm
11736               Choose between the two available implementations of
11737               -fsched-pressure.  Algorithm 1 is the original implementation
11738               and is the more likely to prevent instructions from being
11739               reordered.  Algorithm 2 was designed to be a compromise between
11740               the relatively conservative approach taken by algorithm 1 and
11741               the rather aggressive approach taken by the default scheduler.
11742               It relies more heavily on having a regular register file and
11743               accurate register pressure classes.  See haifa-sched.c in the
11744               GCC sources for more details.
11745
11746               The default choice depends on the target.
11747
11748           max-slsr-cand-scan
11749               Set the maximum number of existing candidates that are
11750               considered when seeking a basis for a new straight-line
11751               strength reduction candidate.
11752
11753           asan-globals
11754               Enable buffer overflow detection for global objects.  This kind
11755               of protection is enabled by default if you are using
11756               -fsanitize=address option.  To disable global objects
11757               protection use --param asan-globals=0.
11758
11759           asan-stack
11760               Enable buffer overflow detection for stack objects.  This kind
11761               of protection is enabled by default when using
11762               -fsanitize=address.  To disable stack protection use --param
11763               asan-stack=0 option.
11764
11765           asan-instrument-reads
11766               Enable buffer overflow detection for memory reads.  This kind
11767               of protection is enabled by default when using
11768               -fsanitize=address.  To disable memory reads protection use
11769               --param asan-instrument-reads=0.
11770
11771           asan-instrument-writes
11772               Enable buffer overflow detection for memory writes.  This kind
11773               of protection is enabled by default when using
11774               -fsanitize=address.  To disable memory writes protection use
11775               --param asan-instrument-writes=0 option.
11776
11777           asan-memintrin
11778               Enable detection for built-in functions.  This kind of
11779               protection is enabled by default when using -fsanitize=address.
11780               To disable built-in functions protection use --param
11781               asan-memintrin=0.
11782
11783           asan-use-after-return
11784               Enable detection of use-after-return.  This kind of protection
11785               is enabled by default when using the -fsanitize=address option.
11786               To disable it use --param asan-use-after-return=0.
11787
11788               Note: By default the check is disabled at run time.  To enable
11789               it, add "detect_stack_use_after_return=1" to the environment
11790               variable ASAN_OPTIONS.
11791
11792           asan-instrumentation-with-call-threshold
11793               If number of memory accesses in function being instrumented is
11794               greater or equal to this number, use callbacks instead of
11795               inline checks.  E.g. to disable inline code use --param
11796               asan-instrumentation-with-call-threshold=0.
11797
11798           hwasan-instrument-stack
11799               Enable hwasan instrumentation of statically sized stack-
11800               allocated variables.  This kind of instrumentation is enabled
11801               by default when using -fsanitize=hwaddress and disabled by
11802               default when using -fsanitize=kernel-hwaddress.  To disable
11803               stack instrumentation use --param hwasan-instrument-stack=0,
11804               and to enable it use --param hwasan-instrument-stack=1.
11805
11806           hwasan-random-frame-tag
11807               When using stack instrumentation, decide tags for stack
11808               variables using a deterministic sequence beginning at a random
11809               tag for each frame.  With this parameter unset tags are chosen
11810               using the same sequence but beginning from 1.  This is enabled
11811               by default for -fsanitize=hwaddress and unavailable for
11812               -fsanitize=kernel-hwaddress.  To disable it use --param
11813               hwasan-random-frame-tag=0.
11814
11815           hwasan-instrument-allocas
11816               Enable hwasan instrumentation of dynamically sized stack-
11817               allocated variables.  This kind of instrumentation is enabled
11818               by default when using -fsanitize=hwaddress and disabled by
11819               default when using -fsanitize=kernel-hwaddress.  To disable
11820               instrumentation of such variables use --param
11821               hwasan-instrument-allocas=0, and to enable it use --param
11822               hwasan-instrument-allocas=1.
11823
11824           hwasan-instrument-reads
11825               Enable hwasan checks on memory reads.  Instrumentation of reads
11826               is enabled by default for both -fsanitize=hwaddress and
11827               -fsanitize=kernel-hwaddress.  To disable checking memory reads
11828               use --param hwasan-instrument-reads=0.
11829
11830           hwasan-instrument-writes
11831               Enable hwasan checks on memory writes.  Instrumentation of
11832               writes is enabled by default for both -fsanitize=hwaddress and
11833               -fsanitize=kernel-hwaddress.  To disable checking memory writes
11834               use --param hwasan-instrument-writes=0.
11835
11836           hwasan-instrument-mem-intrinsics
11837               Enable hwasan instrumentation of builtin functions.
11838               Instrumentation of these builtin functions is enabled by
11839               default for both -fsanitize=hwaddress and
11840               -fsanitize=kernel-hwaddress.  To disable instrumentation of
11841               builtin functions use --param
11842               hwasan-instrument-mem-intrinsics=0.
11843
11844           use-after-scope-direct-emission-threshold
11845               If the size of a local variable in bytes is smaller or equal to
11846               this number, directly poison (or unpoison) shadow memory
11847               instead of using run-time callbacks.
11848
11849           tsan-distinguish-volatile
11850               Emit special instrumentation for accesses to volatiles.
11851
11852           tsan-instrument-func-entry-exit
11853               Emit instrumentation calls to __tsan_func_entry() and
11854               __tsan_func_exit().
11855
11856           max-fsm-thread-path-insns
11857               Maximum number of instructions to copy when duplicating blocks
11858               on a finite state automaton jump thread path.
11859
11860           max-fsm-thread-length
11861               Maximum number of basic blocks on a finite state automaton jump
11862               thread path.
11863
11864           max-fsm-thread-paths
11865               Maximum number of new jump thread paths to create for a finite
11866               state automaton.
11867
11868           parloops-chunk-size
11869               Chunk size of omp schedule for loops parallelized by parloops.
11870
11871           parloops-schedule
11872               Schedule type of omp schedule for loops parallelized by
11873               parloops (static, dynamic, guided, auto, runtime).
11874
11875           parloops-min-per-thread
11876               The minimum number of iterations per thread of an innermost
11877               parallelized loop for which the parallelized variant is
11878               preferred over the single threaded one.  Note that for a
11879               parallelized loop nest the minimum number of iterations of the
11880               outermost loop per thread is two.
11881
11882           max-ssa-name-query-depth
11883               Maximum depth of recursion when querying properties of SSA
11884               names in things like fold routines.  One level of recursion
11885               corresponds to following a use-def chain.
11886
11887           max-speculative-devirt-maydefs
11888               The maximum number of may-defs we analyze when looking for a
11889               must-def specifying the dynamic type of an object that invokes
11890               a virtual call we may be able to devirtualize speculatively.
11891
11892           max-vrp-switch-assertions
11893               The maximum number of assertions to add along the default edge
11894               of a switch statement during VRP.
11895
11896           evrp-mode
11897               Specifies the mode Early VRP should operate in.
11898
11899           unroll-jam-min-percent
11900               The minimum percentage of memory references that must be
11901               optimized away for the unroll-and-jam transformation to be
11902               considered profitable.
11903
11904           unroll-jam-max-unroll
11905               The maximum number of times the outer loop should be unrolled
11906               by the unroll-and-jam transformation.
11907
11908           max-rtl-if-conversion-unpredictable-cost
11909               Maximum permissible cost for the sequence that would be
11910               generated by the RTL if-conversion pass for a branch that is
11911               considered unpredictable.
11912
11913           max-variable-expansions-in-unroller
11914               If -fvariable-expansion-in-unroller is used, the maximum number
11915               of times that an individual variable will be expanded during
11916               loop unrolling.
11917
11918           tracer-min-branch-probability-feedback
11919               Stop forward growth if the probability of best edge is less
11920               than this threshold (in percent). Used when profile feedback is
11921               available.
11922
11923           partial-inlining-entry-probability
11924               Maximum probability of the entry BB of split region (in percent
11925               relative to entry BB of the function) to make partial inlining
11926               happen.
11927
11928           max-tracked-strlens
11929               Maximum number of strings for which strlen optimization pass
11930               will track string lengths.
11931
11932           gcse-after-reload-partial-fraction
11933               The threshold ratio for performing partial redundancy
11934               elimination after reload.
11935
11936           gcse-after-reload-critical-fraction
11937               The threshold ratio of critical edges execution count that
11938               permit performing redundancy elimination after reload.
11939
11940           max-loop-header-insns
11941               The maximum number of insns in loop header duplicated by the
11942               copy loop headers pass.
11943
11944           vect-epilogues-nomask
11945               Enable loop epilogue vectorization using smaller vector size.
11946
11947           vect-partial-vector-usage
11948               Controls when the loop vectorizer considers using partial
11949               vector loads and stores as an alternative to falling back to
11950               scalar code.  0 stops the vectorizer from ever using partial
11951               vector loads and stores.  1 allows partial vector loads and
11952               stores if vectorization removes the need for the code to
11953               iterate.  2 allows partial vector loads and stores in all
11954               loops.  The parameter only has an effect on targets that
11955               support partial vector loads and stores.
11956
11957           avoid-fma-max-bits
11958               Maximum number of bits for which we avoid creating FMAs.
11959
11960           sms-loop-average-count-threshold
11961               A threshold on the average loop count considered by the swing
11962               modulo scheduler.
11963
11964           sms-dfa-history
11965               The number of cycles the swing modulo scheduler considers when
11966               checking conflicts using DFA.
11967
11968           max-inline-insns-recursive-auto
11969               The maximum number of instructions non-inline function can grow
11970               to via recursive inlining.
11971
11972           graphite-allow-codegen-errors
11973               Whether codegen errors should be ICEs when -fchecking.
11974
11975           sms-max-ii-factor
11976               A factor for tuning the upper bound that swing modulo scheduler
11977               uses for scheduling a loop.
11978
11979           lra-max-considered-reload-pseudos
11980               The max number of reload pseudos which are considered during
11981               spilling a non-reload pseudo.
11982
11983           max-pow-sqrt-depth
11984               Maximum depth of sqrt chains to use when synthesizing
11985               exponentiation by a real constant.
11986
11987           max-dse-active-local-stores
11988               Maximum number of active local stores in RTL dead store
11989               elimination.
11990
11991           asan-instrument-allocas
11992               Enable asan allocas/VLAs protection.
11993
11994           max-iterations-computation-cost
11995               Bound on the cost of an expression to compute the number of
11996               iterations.
11997
11998           max-isl-operations
11999               Maximum number of isl operations, 0 means unlimited.
12000
12001           graphite-max-arrays-per-scop
12002               Maximum number of arrays per scop.
12003
12004           max-vartrack-reverse-op-size
12005               Max. size of loc list for which reverse ops should be added.
12006
12007           tracer-dynamic-coverage-feedback
12008               The percentage of function, weighted by execution frequency,
12009               that must be covered by trace formation.  Used when profile
12010               feedback is available.
12011
12012           max-inline-recursive-depth-auto
12013               The maximum depth of recursive inlining for non-inline
12014               functions.
12015
12016           fsm-scale-path-stmts
12017               Scale factor to apply to the number of statements in a
12018               threading path when comparing to the number of (scaled) blocks.
12019
12020           fsm-maximum-phi-arguments
12021               Maximum number of arguments a PHI may have before the FSM
12022               threader will not try to thread through its block.
12023
12024           uninit-control-dep-attempts
12025               Maximum number of nested calls to search for control
12026               dependencies during uninitialized variable analysis.
12027
12028           sra-max-scalarization-size-Osize
12029               Maximum size, in storage units, of an aggregate which should be
12030               considered for scalarization when compiling for size.
12031
12032           fsm-scale-path-blocks
12033               Scale factor to apply to the number of blocks in a threading
12034               path when comparing to the number of (scaled) statements.
12035
12036           sched-autopref-queue-depth
12037               Hardware autoprefetcher scheduler model control flag.  Number
12038               of lookahead cycles the model looks into; at ' ' only enable
12039               instruction sorting heuristic.
12040
12041           loop-versioning-max-inner-insns
12042               The maximum number of instructions that an inner loop can have
12043               before the loop versioning pass considers it too big to copy.
12044
12045           loop-versioning-max-outer-insns
12046               The maximum number of instructions that an outer loop can have
12047               before the loop versioning pass considers it too big to copy,
12048               discounting any instructions in inner loops that directly
12049               benefit from versioning.
12050
12051           ssa-name-def-chain-limit
12052               The maximum number of SSA_NAME assignments to follow in
12053               determining a property of a variable such as its value.  This
12054               limits the number of iterations or recursive calls GCC performs
12055               when optimizing certain statements or when determining their
12056               validity prior to issuing diagnostics.
12057
12058           store-merging-max-size
12059               Maximum size of a single store merging region in bytes.
12060
12061           hash-table-verification-limit
12062               The number of elements for which hash table verification is
12063               done for each searched element.
12064
12065           max-find-base-term-values
12066               Maximum number of VALUEs handled during a single find_base_term
12067               call.
12068
12069           analyzer-max-enodes-per-program-point
12070               The maximum number of exploded nodes per program point within
12071               the analyzer, before terminating analysis of that point.
12072
12073           analyzer-max-constraints
12074               The maximum number of constraints per state.
12075
12076           analyzer-min-snodes-for-call-summary
12077               The minimum number of supernodes within a function for the
12078               analyzer to consider summarizing its effects at call sites.
12079
12080           analyzer-max-enodes-for-full-dump
12081               The maximum depth of exploded nodes that should appear in a dot
12082               dump before switching to a less verbose format.
12083
12084           analyzer-max-recursion-depth
12085               The maximum number of times a callsite can appear in a call
12086               stack within the analyzer, before terminating analysis of a
12087               call that would recurse deeper.
12088
12089           analyzer-max-svalue-depth
12090               The maximum depth of a symbolic value, before approximating the
12091               value as unknown.
12092
12093           analyzer-max-infeasible-edges
12094               The maximum number of infeasible edges to reject before
12095               declaring a diagnostic as infeasible.
12096
12097           gimple-fe-computed-hot-bb-threshold
12098               The number of executions of a basic block which is considered
12099               hot.  The parameter is used only in GIMPLE FE.
12100
12101           analyzer-bb-explosion-factor
12102               The maximum number of 'after supernode' exploded nodes within
12103               the analyzer per supernode, before terminating analysis.
12104
12105           ranger-logical-depth
12106               Maximum depth of logical expression evaluation ranger will look
12107               through when evaluating outgoing edge ranges.
12108
12109           openacc-kernels
12110               Specify mode of OpenACC `kernels' constructs handling.  With
12111               --param=openacc-kernels=decompose, OpenACC `kernels' constructs
12112               are decomposed into parts, a sequence of compute constructs,
12113               each then handled individually.  This is work in progress.
12114               With --param=openacc-kernels=parloops, OpenACC `kernels'
12115               constructs are handled by the parloops pass, en bloc.  This is
12116               the current default.
12117
12118           The following choices of name are available on AArch64 targets:
12119
12120           aarch64-sve-compare-costs
12121               When vectorizing for SVE, consider using "unpacked" vectors for
12122               smaller elements and use the cost model to pick the cheapest
12123               approach.  Also use the cost model to choose between SVE and
12124               Advanced SIMD vectorization.
12125
12126               Using unpacked vectors includes storing smaller elements in
12127               larger containers and accessing elements with extending loads
12128               and truncating stores.
12129
12130           aarch64-float-recp-precision
12131               The number of Newton iterations for calculating the reciprocal
12132               for float type.  The precision of division is proportional to
12133               this param when division approximation is enabled.  The default
12134               value is 1.
12135
12136           aarch64-double-recp-precision
12137               The number of Newton iterations for calculating the reciprocal
12138               for double type.  The precision of division is propotional to
12139               this param when division approximation is enabled.  The default
12140               value is 2.
12141
12142           aarch64-autovec-preference
12143               Force an ISA selection strategy for auto-vectorization.
12144               Accepts values from 0 to 4, inclusive.
12145
12146               0   Use the default heuristics.
12147
12148               1   Use only Advanced SIMD for auto-vectorization.
12149
12150               2   Use only SVE for auto-vectorization.
12151
12152               3   Use both Advanced SIMD and SVE.  Prefer Advanced SIMD when
12153                   the costs are deemed equal.
12154
12155               4   Use both Advanced SIMD and SVE.  Prefer SVE when the costs
12156                   are deemed equal.
12157
12158               The default value is 0.
12159
12160           aarch64-loop-vect-issue-rate-niters
12161               The tuning for some AArch64 CPUs tries to take both latencies
12162               and issue rates into account when deciding whether a loop
12163               should be vectorized using SVE, vectorized using Advanced SIMD,
12164               or not vectorized at all.  If this parameter is set to n, GCC
12165               will not use this heuristic for loops that are known to execute
12166               in fewer than n Advanced SIMD iterations.
12167
12168   Program Instrumentation Options
12169       GCC supports a number of command-line options that control adding run-
12170       time instrumentation to the code it normally generates.  For example,
12171       one purpose of instrumentation is collect profiling statistics for use
12172       in finding program hot spots, code coverage analysis, or profile-guided
12173       optimizations.  Another class of program instrumentation is adding run-
12174       time checking to detect programming errors like invalid pointer
12175       dereferences or out-of-bounds array accesses, as well as deliberately
12176       hostile attacks such as stack smashing or C++ vtable hijacking.  There
12177       is also a general hook which can be used to implement other forms of
12178       tracing or function-level instrumentation for debug or program analysis
12179       purposes.
12180
12181       -p
12182       -pg Generate extra code to write profile information suitable for the
12183           analysis program prof (for -p) or gprof (for -pg).  You must use
12184           this option when compiling the source files you want data about,
12185           and you must also use it when linking.
12186
12187           You can use the function attribute "no_instrument_function" to
12188           suppress profiling of individual functions when compiling with
12189           these options.
12190
12191       -fprofile-arcs
12192           Add code so that program flow arcs are instrumented.  During
12193           execution the program records how many times each branch and call
12194           is executed and how many times it is taken or returns.  On targets
12195           that support constructors with priority support, profiling properly
12196           handles constructors, destructors and C++ constructors (and
12197           destructors) of classes which are used as a type of a global
12198           variable.
12199
12200           When the compiled program exits it saves this data to a file called
12201           auxname.gcda for each source file.  The data may be used for
12202           profile-directed optimizations (-fbranch-probabilities), or for
12203           test coverage analysis (-ftest-coverage).  Each object file's
12204           auxname is generated from the name of the output file, if
12205           explicitly specified and it is not the final executable, otherwise
12206           it is the basename of the source file.  In both cases any suffix is
12207           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
12208           for output file specified as -o dir/foo.o).
12209
12210       --coverage
12211           This option is used to compile and link code instrumented for
12212           coverage analysis.  The option is a synonym for -fprofile-arcs
12213           -ftest-coverage (when compiling) and -lgcov (when linking).  See
12214           the documentation for those options for more details.
12215
12216           *   Compile the source files with -fprofile-arcs plus optimization
12217               and code generation options.  For test coverage analysis, use
12218               the additional -ftest-coverage option.  You do not need to
12219               profile every source file in a program.
12220
12221           *   Compile the source files additionally with -fprofile-abs-path
12222               to create absolute path names in the .gcno files.  This allows
12223               gcov to find the correct sources in projects where compilations
12224               occur with different working directories.
12225
12226           *   Link your object files with -lgcov or -fprofile-arcs (the
12227               latter implies the former).
12228
12229           *   Run the program on a representative workload to generate the
12230               arc profile information.  This may be repeated any number of
12231               times.  You can run concurrent instances of your program, and
12232               provided that the file system supports locking, the data files
12233               will be correctly updated.  Unless a strict ISO C dialect
12234               option is in effect, "fork" calls are detected and correctly
12235               handled without double counting.
12236
12237           *   For profile-directed optimizations, compile the source files
12238               again with the same optimization and code generation options
12239               plus -fbranch-probabilities.
12240
12241           *   For test coverage analysis, use gcov to produce human readable
12242               information from the .gcno and .gcda files.  Refer to the gcov
12243               documentation for further information.
12244
12245           With -fprofile-arcs, for each function of your program GCC creates
12246           a program flow graph, then finds a spanning tree for the graph.
12247           Only arcs that are not on the spanning tree have to be
12248           instrumented: the compiler adds code to count the number of times
12249           that these arcs are executed.  When an arc is the only exit or only
12250           entrance to a block, the instrumentation code can be added to the
12251           block; otherwise, a new basic block must be created to hold the
12252           instrumentation code.
12253
12254       -ftest-coverage
12255           Produce a notes file that the gcov code-coverage utility can use to
12256           show program coverage.  Each source file's note file is called
12257           auxname.gcno.  Refer to the -fprofile-arcs option above for a
12258           description of auxname and instructions on how to generate test
12259           coverage data.  Coverage data matches the source files more closely
12260           if you do not optimize.
12261
12262       -fprofile-abs-path
12263           Automatically convert relative source file names to absolute path
12264           names in the .gcno files.  This allows gcov to find the correct
12265           sources in projects where compilations occur with different working
12266           directories.
12267
12268       -fprofile-dir=path
12269           Set the directory to search for the profile data files in to path.
12270           This option affects only the profile data generated by
12271           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
12272           -fprofile-use and -fbranch-probabilities and its related options.
12273           Both absolute and relative paths can be used.  By default, GCC uses
12274           the current directory as path, thus the profile data file appears
12275           in the same directory as the object file.  In order to prevent the
12276           file name clashing, if the object file name is not an absolute
12277           path, we mangle the absolute path of the sourcename.gcda file and
12278           use it as the file name of a .gcda file.  See similar option
12279           -fprofile-note.
12280
12281           When an executable is run in a massive parallel environment, it is
12282           recommended to save profile to different folders.  That can be done
12283           with variables in path that are exported during run-time:
12284
12285           %p  process ID.
12286
12287           %q{VAR}
12288               value of environment variable VAR
12289
12290       -fprofile-generate
12291       -fprofile-generate=path
12292           Enable options usually used for instrumenting application to
12293           produce profile useful for later recompilation with profile
12294           feedback based optimization.  You must use -fprofile-generate both
12295           when compiling and when linking your program.
12296
12297           The following options are enabled: -fprofile-arcs,
12298           -fprofile-values, -finline-functions, and -fipa-bit-cp.
12299
12300           If path is specified, GCC looks at the path to find the profile
12301           feedback data files. See -fprofile-dir.
12302
12303           To optimize the program based on the collected profile information,
12304           use -fprofile-use.
12305
12306       -fprofile-info-section
12307       -fprofile-info-section=name
12308           Register the profile information in the specified section instead
12309           of using a constructor/destructor.  The section name is name if it
12310           is specified, otherwise the section name defaults to ".gcov_info".
12311           A pointer to the profile information generated by -fprofile-arcs or
12312           -ftest-coverage is placed in the specified section for each
12313           translation unit.  This option disables the profile information
12314           registration through a constructor and it disables the profile
12315           information processing through a destructor.  This option is not
12316           intended to be used in hosted environments such as GNU/Linux.  It
12317           targets systems with limited resources which do not support
12318           constructors and destructors.  The linker could collect the input
12319           sections in a continuous memory block and define start and end
12320           symbols.  The runtime support could dump the profiling information
12321           registered in this linker set during program termination to a
12322           serial line for example.  A GNU linker script example which defines
12323           a linker output section follows:
12324
12325                     .gcov_info      :
12326                     {
12327                       PROVIDE (__gcov_info_start = .);
12328                       KEEP (*(.gcov_info))
12329                       PROVIDE (__gcov_info_end = .);
12330                     }
12331
12332       -fprofile-note=path
12333           If path is specified, GCC saves .gcno file into path location.  If
12334           you combine the option with multiple source files, the .gcno file
12335           will be overwritten.
12336
12337       -fprofile-prefix-path=path
12338           This option can be used in combination with
12339           profile-generate=profile_dir and profile-use=profile_dir to inform
12340           GCC where is the base directory of built source tree.  By default
12341           profile_dir will contain files with mangled absolute paths of all
12342           object files in the built project.  This is not desirable when
12343           directory used to build the instrumented binary differs from the
12344           directory used to build the binary optimized with profile feedback
12345           because the profile data will not be found during the optimized
12346           build.  In such setups -fprofile-prefix-path=path with path
12347           pointing to the base directory of the build can be used to strip
12348           the irrelevant part of the path and keep all file names relative to
12349           the main build directory.
12350
12351       -fprofile-update=method
12352           Alter the update method for an application instrumented for profile
12353           feedback based optimization.  The method argument should be one of
12354           single, atomic or prefer-atomic.  The first one is useful for
12355           single-threaded applications, while the second one prevents profile
12356           corruption by emitting thread-safe code.
12357
12358           Warning: When an application does not properly join all threads (or
12359           creates an detached thread), a profile file can be still corrupted.
12360
12361           Using prefer-atomic would be transformed either to atomic, when
12362           supported by a target, or to single otherwise.  The GCC driver
12363           automatically selects prefer-atomic when -pthread is present in the
12364           command line.
12365
12366       -fprofile-filter-files=regex
12367           Instrument only functions from files whose name matches any of the
12368           regular expressions (separated by semi-colons).
12369
12370           For example, -fprofile-filter-files=main\.c;module.*\.c will
12371           instrument only main.c and all C files starting with 'module'.
12372
12373       -fprofile-exclude-files=regex
12374           Instrument only functions from files whose name does not match any
12375           of the regular expressions (separated by semi-colons).
12376
12377           For example, -fprofile-exclude-files=/usr/.* will prevent
12378           instrumentation of all files that are located in the /usr/ folder.
12379
12380       -fprofile-reproducible=[multithreaded|parallel-runs|serial]
12381           Control level of reproducibility of profile gathered by
12382           "-fprofile-generate".  This makes it possible to rebuild program
12383           with same outcome which is useful, for example, for distribution
12384           packages.
12385
12386           With -fprofile-reproducible=serial the profile gathered by
12387           -fprofile-generate is reproducible provided the trained program
12388           behaves the same at each invocation of the train run, it is not
12389           multi-threaded and profile data streaming is always done in the
12390           same order.  Note that profile streaming happens at the end of
12391           program run but also before "fork" function is invoked.
12392
12393           Note that it is quite common that execution counts of some part of
12394           programs depends, for example, on length of temporary file names or
12395           memory space randomization (that may affect hash-table collision
12396           rate).  Such non-reproducible part of programs may be annotated by
12397           "no_instrument_function" function attribute. gcov-dump with -l can
12398           be used to dump gathered data and verify that they are indeed
12399           reproducible.
12400
12401           With -fprofile-reproducible=parallel-runs collected profile stays
12402           reproducible regardless the order of streaming of the data into
12403           gcda files.  This setting makes it possible to run multiple
12404           instances of instrumented program in parallel (such as with "make
12405           -j"). This reduces quality of gathered data, in particular of
12406           indirect call profiling.
12407
12408       -fsanitize=address
12409           Enable AddressSanitizer, a fast memory error detector.  Memory
12410           access instructions are instrumented to detect out-of-bounds and
12411           use-after-free bugs.  The option enables
12412           -fsanitize-address-use-after-scope.  See
12413           <https://github.com/google/sanitizers/wiki/AddressSanitizer> for
12414           more details.  The run-time behavior can be influenced using the
12415           ASAN_OPTIONS environment variable.  When set to "help=1", the
12416           available options are shown at startup of the instrumented program.
12417           See
12418           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
12419           for a list of supported options.  The option cannot be combined
12420           with -fsanitize=thread or -fsanitize=hwaddress.  Note that the only
12421           target -fsanitize=hwaddress is currently supported on is AArch64.
12422
12423       -fsanitize=kernel-address
12424           Enable AddressSanitizer for Linux kernel.  See
12425           <https://github.com/google/kasan> for more details.
12426
12427       -fsanitize=hwaddress
12428           Enable Hardware-assisted AddressSanitizer, which uses a hardware
12429           ability to ignore the top byte of a pointer to allow the detection
12430           of memory errors with a low memory overhead.  Memory access
12431           instructions are instrumented to detect out-of-bounds and use-
12432           after-free bugs.  The option enables
12433           -fsanitize-address-use-after-scope.  See
12434           <https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html>
12435           for more details.  The run-time behavior can be influenced using
12436           the HWASAN_OPTIONS environment variable.  When set to "help=1", the
12437           available options are shown at startup of the instrumented program.
12438           The option cannot be combined with -fsanitize=thread or
12439           -fsanitize=address, and is currently only available on AArch64.
12440
12441       -fsanitize=kernel-hwaddress
12442           Enable Hardware-assisted AddressSanitizer for compilation of the
12443           Linux kernel.  Similar to -fsanitize=kernel-address but using an
12444           alternate instrumentation method, and similar to
12445           -fsanitize=hwaddress but with instrumentation differences necessary
12446           for compiling the Linux kernel.  These differences are to avoid
12447           hwasan library initialization calls and to account for the stack
12448           pointer having a different value in its top byte.
12449
12450           Note: This option has different defaults to the
12451           -fsanitize=hwaddress.  Instrumenting the stack and alloca calls are
12452           not on by default but are still possible by specifying the command-
12453           line options --param hwasan-instrument-stack=1 and --param
12454           hwasan-instrument-allocas=1 respectively. Using a random frame tag
12455           is not implemented for kernel instrumentation.
12456
12457       -fsanitize=pointer-compare
12458           Instrument comparison operation (<, <=, >, >=) with pointer
12459           operands.  The option must be combined with either
12460           -fsanitize=kernel-address or -fsanitize=address The option cannot
12461           be combined with -fsanitize=thread.  Note: By default the check is
12462           disabled at run time.  To enable it, add
12463           "detect_invalid_pointer_pairs=2" to the environment variable
12464           ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
12465           invalid operation only when both pointers are non-null.
12466
12467       -fsanitize=pointer-subtract
12468           Instrument subtraction with pointer operands.  The option must be
12469           combined with either -fsanitize=kernel-address or
12470           -fsanitize=address The option cannot be combined with
12471           -fsanitize=thread.  Note: By default the check is disabled at run
12472           time.  To enable it, add "detect_invalid_pointer_pairs=2" to the
12473           environment variable ASAN_OPTIONS. Using
12474           "detect_invalid_pointer_pairs=1" detects invalid operation only
12475           when both pointers are non-null.
12476
12477       -fsanitize=thread
12478           Enable ThreadSanitizer, a fast data race detector.  Memory access
12479           instructions are instrumented to detect data race bugs.  See
12480           <https://github.com/google/sanitizers/wiki#threadsanitizer> for
12481           more details. The run-time behavior can be influenced using the
12482           TSAN_OPTIONS environment variable; see
12483           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
12484           for a list of supported options.  The option cannot be combined
12485           with -fsanitize=address, -fsanitize=leak.
12486
12487           Note that sanitized atomic builtins cannot throw exceptions when
12488           operating on invalid memory addresses with non-call exceptions
12489           (-fnon-call-exceptions).
12490
12491       -fsanitize=leak
12492           Enable LeakSanitizer, a memory leak detector.  This option only
12493           matters for linking of executables and the executable is linked
12494           against a library that overrides "malloc" and other allocator
12495           functions.  See
12496           <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
12497           for more details.  The run-time behavior can be influenced using
12498           the LSAN_OPTIONS environment variable.  The option cannot be
12499           combined with -fsanitize=thread.
12500
12501       -fsanitize=undefined
12502           Enable UndefinedBehaviorSanitizer, a fast undefined behavior
12503           detector.  Various computations are instrumented to detect
12504           undefined behavior at runtime.  Current suboptions are:
12505
12506           -fsanitize=shift
12507               This option enables checking that the result of a shift
12508               operation is not undefined.  Note that what exactly is
12509               considered undefined differs slightly between C and C++, as
12510               well as between ISO C90 and C99, etc.  This option has two
12511               suboptions, -fsanitize=shift-base and
12512               -fsanitize=shift-exponent.
12513
12514           -fsanitize=shift-exponent
12515               This option enables checking that the second argument of a
12516               shift operation is not negative and is smaller than the
12517               precision of the promoted first argument.
12518
12519           -fsanitize=shift-base
12520               If the second argument of a shift operation is within range,
12521               check that the result of a shift operation is not undefined.
12522               Note that what exactly is considered undefined differs slightly
12523               between C and C++, as well as between ISO C90 and C99, etc.
12524
12525           -fsanitize=integer-divide-by-zero
12526               Detect integer division by zero as well as "INT_MIN / -1"
12527               division.
12528
12529           -fsanitize=unreachable
12530               With this option, the compiler turns the
12531               "__builtin_unreachable" call into a diagnostics message call
12532               instead.  When reaching the "__builtin_unreachable" call, the
12533               behavior is undefined.
12534
12535           -fsanitize=vla-bound
12536               This option instructs the compiler to check that the size of a
12537               variable length array is positive.
12538
12539           -fsanitize=null
12540               This option enables pointer checking.  Particularly, the
12541               application built with this option turned on will issue an
12542               error message when it tries to dereference a NULL pointer, or
12543               if a reference (possibly an rvalue reference) is bound to a
12544               NULL pointer, or if a method is invoked on an object pointed by
12545               a NULL pointer.
12546
12547           -fsanitize=return
12548               This option enables return statement checking.  Programs built
12549               with this option turned on will issue an error message when the
12550               end of a non-void function is reached without actually
12551               returning a value.  This option works in C++ only.
12552
12553           -fsanitize=signed-integer-overflow
12554               This option enables signed integer overflow checking.  We check
12555               that the result of "+", "*", and both unary and binary "-" does
12556               not overflow in the signed arithmetics.  Note, integer
12557               promotion rules must be taken into account.  That is, the
12558               following is not an overflow:
12559
12560                       signed char a = SCHAR_MAX;
12561                       a++;
12562
12563           -fsanitize=bounds
12564               This option enables instrumentation of array bounds.  Various
12565               out of bounds accesses are detected.  Flexible array members,
12566               flexible array member-like arrays, and initializers of
12567               variables with static storage are not instrumented.
12568
12569           -fsanitize=bounds-strict
12570               This option enables strict instrumentation of array bounds.
12571               Most out of bounds accesses are detected, including flexible
12572               array members and flexible array member-like arrays.
12573               Initializers of variables with static storage are not
12574               instrumented.
12575
12576           -fsanitize=alignment
12577               This option enables checking of alignment of pointers when they
12578               are dereferenced, or when a reference is bound to
12579               insufficiently aligned target, or when a method or constructor
12580               is invoked on insufficiently aligned object.
12581
12582           -fsanitize=object-size
12583               This option enables instrumentation of memory references using
12584               the "__builtin_object_size" function.  Various out of bounds
12585               pointer accesses are detected.
12586
12587           -fsanitize=float-divide-by-zero
12588               Detect floating-point division by zero.  Unlike other similar
12589               options, -fsanitize=float-divide-by-zero is not enabled by
12590               -fsanitize=undefined, since floating-point division by zero can
12591               be a legitimate way of obtaining infinities and NaNs.
12592
12593           -fsanitize=float-cast-overflow
12594               This option enables floating-point type to integer conversion
12595               checking.  We check that the result of the conversion does not
12596               overflow.  Unlike other similar options,
12597               -fsanitize=float-cast-overflow is not enabled by
12598               -fsanitize=undefined.  This option does not work well with
12599               "FE_INVALID" exceptions enabled.
12600
12601           -fsanitize=nonnull-attribute
12602               This option enables instrumentation of calls, checking whether
12603               null values are not passed to arguments marked as requiring a
12604               non-null value by the "nonnull" function attribute.
12605
12606           -fsanitize=returns-nonnull-attribute
12607               This option enables instrumentation of return statements in
12608               functions marked with "returns_nonnull" function attribute, to
12609               detect returning of null values from such functions.
12610
12611           -fsanitize=bool
12612               This option enables instrumentation of loads from bool.  If a
12613               value other than 0/1 is loaded, a run-time error is issued.
12614
12615           -fsanitize=enum
12616               This option enables instrumentation of loads from an enum type.
12617               If a value outside the range of values for the enum type is
12618               loaded, a run-time error is issued.
12619
12620           -fsanitize=vptr
12621               This option enables instrumentation of C++ member function
12622               calls, member accesses and some conversions between pointers to
12623               base and derived classes, to verify the referenced object has
12624               the correct dynamic type.
12625
12626           -fsanitize=pointer-overflow
12627               This option enables instrumentation of pointer arithmetics.  If
12628               the pointer arithmetics overflows, a run-time error is issued.
12629
12630           -fsanitize=builtin
12631               This option enables instrumentation of arguments to selected
12632               builtin functions.  If an invalid value is passed to such
12633               arguments, a run-time error is issued.  E.g. passing 0 as the
12634               argument to "__builtin_ctz" or "__builtin_clz" invokes
12635               undefined behavior and is diagnosed by this option.
12636
12637           While -ftrapv causes traps for signed overflows to be emitted,
12638           -fsanitize=undefined gives a diagnostic message.  This currently
12639           works only for the C family of languages.
12640
12641       -fno-sanitize=all
12642           This option disables all previously enabled sanitizers.
12643           -fsanitize=all is not allowed, as some sanitizers cannot be used
12644           together.
12645
12646       -fasan-shadow-offset=number
12647           This option forces GCC to use custom shadow offset in
12648           AddressSanitizer checks.  It is useful for experimenting with
12649           different shadow memory layouts in Kernel AddressSanitizer.
12650
12651       -fsanitize-sections=s1,s2,...
12652           Sanitize global variables in selected user-defined sections.  si
12653           may contain wildcards.
12654
12655       -fsanitize-recover[=opts]
12656           -fsanitize-recover= controls error recovery mode for sanitizers
12657           mentioned in comma-separated list of opts.  Enabling this option
12658           for a sanitizer component causes it to attempt to continue running
12659           the program as if no error happened.  This means multiple runtime
12660           errors can be reported in a single program run, and the exit code
12661           of the program may indicate success even when errors have been
12662           reported.  The -fno-sanitize-recover= option can be used to alter
12663           this behavior: only the first detected error is reported and
12664           program then exits with a non-zero exit code.
12665
12666           Currently this feature only works for -fsanitize=undefined (and its
12667           suboptions except for -fsanitize=unreachable and
12668           -fsanitize=return), -fsanitize=float-cast-overflow,
12669           -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict,
12670           -fsanitize=kernel-address and -fsanitize=address.  For these
12671           sanitizers error recovery is turned on by default, except
12672           -fsanitize=address, for which this feature is experimental.
12673           -fsanitize-recover=all and -fno-sanitize-recover=all is also
12674           accepted, the former enables recovery for all sanitizers that
12675           support it, the latter disables recovery for all sanitizers that
12676           support it.
12677
12678           Even if a recovery mode is turned on the compiler side, it needs to
12679           be also enabled on the runtime library side, otherwise the failures
12680           are still fatal.  The runtime library defaults to "halt_on_error=0"
12681           for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
12682           value for AddressSanitizer is "halt_on_error=1". This can be
12683           overridden through setting the "halt_on_error" flag in the
12684           corresponding environment variable.
12685
12686           Syntax without an explicit opts parameter is deprecated.  It is
12687           equivalent to specifying an opts list of:
12688
12689                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
12690
12691       -fsanitize-address-use-after-scope
12692           Enable sanitization of local variables to detect use-after-scope
12693           bugs.  The option sets -fstack-reuse to none.
12694
12695       -fsanitize-undefined-trap-on-error
12696           The -fsanitize-undefined-trap-on-error option instructs the
12697           compiler to report undefined behavior using "__builtin_trap" rather
12698           than a "libubsan" library routine.  The advantage of this is that
12699           the "libubsan" library is not needed and is not linked in, so this
12700           is usable even in freestanding environments.
12701
12702       -fsanitize-coverage=trace-pc
12703           Enable coverage-guided fuzzing code instrumentation.  Inserts a
12704           call to "__sanitizer_cov_trace_pc" into every basic block.
12705
12706       -fsanitize-coverage=trace-cmp
12707           Enable dataflow guided fuzzing code instrumentation.  Inserts a
12708           call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
12709           "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for
12710           integral comparison with both operands variable or
12711           "__sanitizer_cov_trace_const_cmp1",
12712           "__sanitizer_cov_trace_const_cmp2",
12713           "__sanitizer_cov_trace_const_cmp4" or
12714           "__sanitizer_cov_trace_const_cmp8" for integral comparison with one
12715           operand constant, "__sanitizer_cov_trace_cmpf" or
12716           "__sanitizer_cov_trace_cmpd" for float or double comparisons and
12717           "__sanitizer_cov_trace_switch" for switch statements.
12718
12719       -fcf-protection=[full|branch|return|none|check]
12720           Enable code instrumentation of control-flow transfers to increase
12721           program security by checking that target addresses of control-flow
12722           transfer instructions (such as indirect function call, function
12723           return, indirect jump) are valid.  This prevents diverting the flow
12724           of control to an unexpected target.  This is intended to protect
12725           against such threats as Return-oriented Programming (ROP), and
12726           similarly call/jmp-oriented programming (COP/JOP).
12727
12728           The value "branch" tells the compiler to implement checking of
12729           validity of control-flow transfer at the point of indirect branch
12730           instructions, i.e. call/jmp instructions.  The value "return"
12731           implements checking of validity at the point of returning from a
12732           function.  The value "full" is an alias for specifying both
12733           "branch" and "return". The value "none" turns off instrumentation.
12734
12735           The value "check" is used for the final link with link-time
12736           optimization (LTO).  An error is issued if LTO object files are
12737           compiled with different -fcf-protection values.  The value "check"
12738           is ignored at the compile time.
12739
12740           The macro "__CET__" is defined when -fcf-protection is used.  The
12741           first bit of "__CET__" is set to 1 for the value "branch" and the
12742           second bit of "__CET__" is set to 1 for the "return".
12743
12744           You can also use the "nocf_check" attribute to identify which
12745           functions and calls should be skipped from instrumentation.
12746
12747           Currently the x86 GNU/Linux target provides an implementation based
12748           on Intel Control-flow Enforcement Technology (CET).
12749
12750       -fstack-protector
12751           Emit extra code to check for buffer overflows, such as stack
12752           smashing attacks.  This is done by adding a guard variable to
12753           functions with vulnerable objects.  This includes functions that
12754           call "alloca", and functions with buffers larger than or equal to 8
12755           bytes.  The guards are initialized when a function is entered and
12756           then checked when the function exits.  If a guard check fails, an
12757           error message is printed and the program exits.  Only variables
12758           that are actually allocated on the stack are considered, optimized
12759           away variables or variables allocated in registers don't count.
12760
12761       -fstack-protector-all
12762           Like -fstack-protector except that all functions are protected.
12763
12764       -fstack-protector-strong
12765           Like -fstack-protector but includes additional functions to be
12766           protected --- those that have local array definitions, or have
12767           references to local frame addresses.  Only variables that are
12768           actually allocated on the stack are considered, optimized away
12769           variables or variables allocated in registers don't count.
12770
12771       -fstack-protector-explicit
12772           Like -fstack-protector but only protects those functions which have
12773           the "stack_protect" attribute.
12774
12775       -fstack-check
12776           Generate code to verify that you do not go beyond the boundary of
12777           the stack.  You should specify this flag if you are running in an
12778           environment with multiple threads, but you only rarely need to
12779           specify it in a single-threaded environment since stack overflow is
12780           automatically detected on nearly all systems if there is only one
12781           stack.
12782
12783           Note that this switch does not actually cause checking to be done;
12784           the operating system or the language runtime must do that.  The
12785           switch causes generation of code to ensure that they see the stack
12786           being extended.
12787
12788           You can additionally specify a string parameter: no means no
12789           checking, generic means force the use of old-style checking,
12790           specific means use the best checking method and is equivalent to
12791           bare -fstack-check.
12792
12793           Old-style checking is a generic mechanism that requires no specific
12794           target support in the compiler but comes with the following
12795           drawbacks:
12796
12797           1.  Modified allocation strategy for large objects: they are always
12798               allocated dynamically if their size exceeds a fixed threshold.
12799               Note this may change the semantics of some code.
12800
12801           2.  Fixed limit on the size of the static frame of functions: when
12802               it is topped by a particular function, stack checking is not
12803               reliable and a warning is issued by the compiler.
12804
12805           3.  Inefficiency: because of both the modified allocation strategy
12806               and the generic implementation, code performance is hampered.
12807
12808           Note that old-style stack checking is also the fallback method for
12809           specific if no target support has been added in the compiler.
12810
12811           -fstack-check= is designed for Ada's needs to detect infinite
12812           recursion and stack overflows.  specific is an excellent choice
12813           when compiling Ada code.  It is not generally sufficient to protect
12814           against stack-clash attacks.  To protect against those you want
12815           -fstack-clash-protection.
12816
12817       -fstack-clash-protection
12818           Generate code to prevent stack clash style attacks.  When this
12819           option is enabled, the compiler will only allocate one page of
12820           stack space at a time and each page is accessed immediately after
12821           allocation.  Thus, it prevents allocations from jumping over any
12822           stack guard page provided by the operating system.
12823
12824           Most targets do not fully support stack clash protection.  However,
12825           on those targets -fstack-clash-protection will protect dynamic
12826           stack allocations.  -fstack-clash-protection may also provide
12827           limited protection for static stack allocations if the target
12828           supports -fstack-check=specific.
12829
12830       -fstack-limit-register=reg
12831       -fstack-limit-symbol=sym
12832       -fno-stack-limit
12833           Generate code to ensure that the stack does not grow beyond a
12834           certain value, either the value of a register or the address of a
12835           symbol.  If a larger stack is required, a signal is raised at run
12836           time.  For most targets, the signal is raised before the stack
12837           overruns the boundary, so it is possible to catch the signal
12838           without taking special precautions.
12839
12840           For instance, if the stack starts at absolute address 0x80000000
12841           and grows downwards, you can use the flags
12842           -fstack-limit-symbol=__stack_limit and
12843           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
12844           128KB.  Note that this may only work with the GNU linker.
12845
12846           You can locally override stack limit checking by using the
12847           "no_stack_limit" function attribute.
12848
12849       -fsplit-stack
12850           Generate code to automatically split the stack before it overflows.
12851           The resulting program has a discontiguous stack which can only
12852           overflow if the program is unable to allocate any more memory.
12853           This is most useful when running threaded programs, as it is no
12854           longer necessary to calculate a good stack size to use for each
12855           thread.  This is currently only implemented for the x86 targets
12856           running GNU/Linux.
12857
12858           When code compiled with -fsplit-stack calls code compiled without
12859           -fsplit-stack, there may not be much stack space available for the
12860           latter code to run.  If compiling all code, including library code,
12861           with -fsplit-stack is not an option, then the linker can fix up
12862           these calls so that the code compiled without -fsplit-stack always
12863           has a large stack.  Support for this is implemented in the gold
12864           linker in GNU binutils release 2.21 and later.
12865
12866       -fvtable-verify=[std|preinit|none]
12867           This option is only available when compiling C++ code.  It turns on
12868           (or off, if using -fvtable-verify=none) the security feature that
12869           verifies at run time, for every virtual call, that the vtable
12870           pointer through which the call is made is valid for the type of the
12871           object, and has not been corrupted or overwritten.  If an invalid
12872           vtable pointer is detected at run time, an error is reported and
12873           execution of the program is immediately halted.
12874
12875           This option causes run-time data structures to be built at program
12876           startup, which are used for verifying the vtable pointers.  The
12877           options std and preinit control the timing of when these data
12878           structures are built.  In both cases the data structures are built
12879           before execution reaches "main".  Using -fvtable-verify=std causes
12880           the data structures to be built after shared libraries have been
12881           loaded and initialized.  -fvtable-verify=preinit causes them to be
12882           built before shared libraries have been loaded and initialized.
12883
12884           If this option appears multiple times in the command line with
12885           different values specified, none takes highest priority over both
12886           std and preinit; preinit takes priority over std.
12887
12888       -fvtv-debug
12889           When used in conjunction with -fvtable-verify=std or
12890           -fvtable-verify=preinit, causes debug versions of the runtime
12891           functions for the vtable verification feature to be called.  This
12892           flag also causes the compiler to log information about which vtable
12893           pointers it finds for each class.  This information is written to a
12894           file named vtv_set_ptr_data.log in the directory named by the
12895           environment variable VTV_LOGS_DIR if that is defined or the current
12896           working directory otherwise.
12897
12898           Note:  This feature appends data to the log file. If you want a
12899           fresh log file, be sure to delete any existing one.
12900
12901       -fvtv-counts
12902           This is a debugging flag.  When used in conjunction with
12903           -fvtable-verify=std or -fvtable-verify=preinit, this causes the
12904           compiler to keep track of the total number of virtual calls it
12905           encounters and the number of verifications it inserts.  It also
12906           counts the number of calls to certain run-time library functions
12907           that it inserts and logs this information for each compilation
12908           unit.  The compiler writes this information to a file named
12909           vtv_count_data.log in the directory named by the environment
12910           variable VTV_LOGS_DIR if that is defined or the current working
12911           directory otherwise.  It also counts the size of the vtable pointer
12912           sets for each class, and writes this information to
12913           vtv_class_set_sizes.log in the same directory.
12914
12915           Note:  This feature appends data to the log files.  To get fresh
12916           log files, be sure to delete any existing ones.
12917
12918       -finstrument-functions
12919           Generate instrumentation calls for entry and exit to functions.
12920           Just after function entry and just before function exit, the
12921           following profiling functions are called with the address of the
12922           current function and its call site.  (On some platforms,
12923           "__builtin_return_address" does not work beyond the current
12924           function, so the call site information may not be available to the
12925           profiling functions otherwise.)
12926
12927                   void __cyg_profile_func_enter (void *this_fn,
12928                                                  void *call_site);
12929                   void __cyg_profile_func_exit  (void *this_fn,
12930                                                  void *call_site);
12931
12932           The first argument is the address of the start of the current
12933           function, which may be looked up exactly in the symbol table.
12934
12935           This instrumentation is also done for functions expanded inline in
12936           other functions.  The profiling calls indicate where, conceptually,
12937           the inline function is entered and exited.  This means that
12938           addressable versions of such functions must be available.  If all
12939           your uses of a function are expanded inline, this may mean an
12940           additional expansion of code size.  If you use "extern inline" in
12941           your C code, an addressable version of such functions must be
12942           provided.  (This is normally the case anyway, but if you get lucky
12943           and the optimizer always expands the functions inline, you might
12944           have gotten away without providing static copies.)
12945
12946           A function may be given the attribute "no_instrument_function", in
12947           which case this instrumentation is not done.  This can be used, for
12948           example, for the profiling functions listed above, high-priority
12949           interrupt routines, and any functions from which the profiling
12950           functions cannot safely be called (perhaps signal handlers, if the
12951           profiling routines generate output or allocate memory).
12952
12953       -finstrument-functions-exclude-file-list=file,file,...
12954           Set the list of functions that are excluded from instrumentation
12955           (see the description of -finstrument-functions).  If the file that
12956           contains a function definition matches with one of file, then that
12957           function is not instrumented.  The match is done on substrings: if
12958           the file parameter is a substring of the file name, it is
12959           considered to be a match.
12960
12961           For example:
12962
12963                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys
12964
12965           excludes any inline function defined in files whose pathnames
12966           contain /bits/stl or include/sys.
12967
12968           If, for some reason, you want to include letter , in one of sym,
12969           write ,. For example,
12970           -finstrument-functions-exclude-file-list=',,tmp' (note the single
12971           quote surrounding the option).
12972
12973       -finstrument-functions-exclude-function-list=sym,sym,...
12974           This is similar to -finstrument-functions-exclude-file-list, but
12975           this option sets the list of function names to be excluded from
12976           instrumentation.  The function name to be matched is its user-
12977           visible name, such as "vector<int> blah(const vector<int> &)", not
12978           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
12979           match is done on substrings: if the sym parameter is a substring of
12980           the function name, it is considered to be a match.  For C99 and C++
12981           extended identifiers, the function name must be given in UTF-8, not
12982           using universal character names.
12983
12984       -fpatchable-function-entry=N[,M]
12985           Generate N NOPs right at the beginning of each function, with the
12986           function entry point before the Mth NOP.  If M is omitted, it
12987           defaults to 0 so the function entry points to the address just at
12988           the first NOP.  The NOP instructions reserve extra space which can
12989           be used to patch in any desired instrumentation at run time,
12990           provided that the code segment is writable.  The amount of space is
12991           controllable indirectly via the number of NOPs; the NOP instruction
12992           used corresponds to the instruction emitted by the internal GCC
12993           back-end interface "gen_nop".  This behavior is target-specific and
12994           may also depend on the architecture variant and/or other
12995           compilation options.
12996
12997           For run-time identification, the starting addresses of these areas,
12998           which correspond to their respective function entries minus M, are
12999           additionally collected in the "__patchable_function_entries"
13000           section of the resulting binary.
13001
13002           Note that the value of "__attribute__ ((patchable_function_entry
13003           (N,M)))" takes precedence over command-line option
13004           -fpatchable-function-entry=N,M.  This can be used to increase the
13005           area size or to remove it completely on a single function.  If
13006           "N=0", no pad location is recorded.
13007
13008           The NOP instructions are inserted at---and maybe before, depending
13009           on M---the function entry address, even before the prologue.
13010
13011           The maximum value of N and M is 65535.
13012
13013   Options Controlling the Preprocessor
13014       These options control the C preprocessor, which is run on each C source
13015       file before actual compilation.
13016
13017       If you use the -E option, nothing is done except preprocessing.  Some
13018       of these options make sense only together with -E because they cause
13019       the preprocessor output to be unsuitable for actual compilation.
13020
13021       In addition to the options listed here, there are a number of options
13022       to control search paths for include files documented in Directory
13023       Options.  Options to control preprocessor diagnostics are listed in
13024       Warning Options.
13025
13026       -D name
13027           Predefine name as a macro, with definition 1.
13028
13029       -D name=definition
13030           The contents of definition are tokenized and processed as if they
13031           appeared during translation phase three in a #define directive.  In
13032           particular, the definition is truncated by embedded newline
13033           characters.
13034
13035           If you are invoking the preprocessor from a shell or shell-like
13036           program you may need to use the shell's quoting syntax to protect
13037           characters such as spaces that have a meaning in the shell syntax.
13038
13039           If you wish to define a function-like macro on the command line,
13040           write its argument list with surrounding parentheses before the
13041           equals sign (if any).  Parentheses are meaningful to most shells,
13042           so you should quote the option.  With sh and csh,
13043           -D'name(args...)=definition' works.
13044
13045           -D and -U options are processed in the order they are given on the
13046           command line.  All -imacros file and -include file options are
13047           processed after all -D and -U options.
13048
13049       -U name
13050           Cancel any previous definition of name, either built in or provided
13051           with a -D option.
13052
13053       -include file
13054           Process file as if "#include "file"" appeared as the first line of
13055           the primary source file.  However, the first directory searched for
13056           file is the preprocessor's working directory instead of the
13057           directory containing the main source file.  If not found there, it
13058           is searched for in the remainder of the "#include "..."" search
13059           chain as normal.
13060
13061           If multiple -include options are given, the files are included in
13062           the order they appear on the command line.
13063
13064       -imacros file
13065           Exactly like -include, except that any output produced by scanning
13066           file is thrown away.  Macros it defines remain defined.  This
13067           allows you to acquire all the macros from a header without also
13068           processing its declarations.
13069
13070           All files specified by -imacros are processed before all files
13071           specified by -include.
13072
13073       -undef
13074           Do not predefine any system-specific or GCC-specific macros.  The
13075           standard predefined macros remain defined.
13076
13077       -pthread
13078           Define additional macros required for using the POSIX threads
13079           library.  You should use this option consistently for both
13080           compilation and linking.  This option is supported on GNU/Linux
13081           targets, most other Unix derivatives, and also on x86 Cygwin and
13082           MinGW targets.
13083
13084       -M  Instead of outputting the result of preprocessing, output a rule
13085           suitable for make describing the dependencies of the main source
13086           file.  The preprocessor outputs one make rule containing the object
13087           file name for that source file, a colon, and the names of all the
13088           included files, including those coming from -include or -imacros
13089           command-line options.
13090
13091           Unless specified explicitly (with -MT or -MQ), the object file name
13092           consists of the name of the source file with any suffix replaced
13093           with object file suffix and with any leading directory parts
13094           removed.  If there are many included files then the rule is split
13095           into several lines using \-newline.  The rule has no commands.
13096
13097           This option does not suppress the preprocessor's debug output, such
13098           as -dM.  To avoid mixing such debug output with the dependency
13099           rules you should explicitly specify the dependency output file with
13100           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
13101           Debug output is still sent to the regular output stream as normal.
13102
13103           Passing -M to the driver implies -E, and suppresses warnings with
13104           an implicit -w.
13105
13106       -MM Like -M but do not mention header files that are found in system
13107           header directories, nor header files that are included, directly or
13108           indirectly, from such a header.
13109
13110           This implies that the choice of angle brackets or double quotes in
13111           an #include directive does not in itself determine whether that
13112           header appears in -MM dependency output.
13113
13114       -MF file
13115           When used with -M or -MM, specifies a file to write the
13116           dependencies to.  If no -MF switch is given the preprocessor sends
13117           the rules to the same place it would send preprocessed output.
13118
13119           When used with the driver options -MD or -MMD, -MF overrides the
13120           default dependency output file.
13121
13122           If file is -, then the dependencies are written to stdout.
13123
13124       -MG In conjunction with an option such as -M requesting dependency
13125           generation, -MG assumes missing header files are generated files
13126           and adds them to the dependency list without raising an error.  The
13127           dependency filename is taken directly from the "#include" directive
13128           without prepending any path.  -MG also suppresses preprocessed
13129           output, as a missing header file renders this useless.
13130
13131           This feature is used in automatic updating of makefiles.
13132
13133       -Mno-modules
13134           Disable dependency generation for compiled module interfaces.
13135
13136       -MP This option instructs CPP to add a phony target for each dependency
13137           other than the main file, causing each to depend on nothing.  These
13138           dummy rules work around errors make gives if you remove header
13139           files without updating the Makefile to match.
13140
13141           This is typical output:
13142
13143                   test.o: test.c test.h
13144
13145                   test.h:
13146
13147       -MT target
13148           Change the target of the rule emitted by dependency generation.  By
13149           default CPP takes the name of the main input file, deletes any
13150           directory components and any file suffix such as .c, and appends
13151           the platform's usual object suffix.  The result is the target.
13152
13153           An -MT option sets the target to be exactly the string you specify.
13154           If you want multiple targets, you can specify them as a single
13155           argument to -MT, or use multiple -MT options.
13156
13157           For example, -MT '$(objpfx)foo.o' might give
13158
13159                   $(objpfx)foo.o: foo.c
13160
13161       -MQ target
13162           Same as -MT, but it quotes any characters which are special to
13163           Make.  -MQ '$(objpfx)foo.o' gives
13164
13165                   $$(objpfx)foo.o: foo.c
13166
13167           The default target is automatically quoted, as if it were given
13168           with -MQ.
13169
13170       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
13171           The driver determines file based on whether an -o option is given.
13172           If it is, the driver uses its argument but with a suffix of .d,
13173           otherwise it takes the name of the input file, removes any
13174           directory components and suffix, and applies a .d suffix.
13175
13176           If -MD is used in conjunction with -E, any -o switch is understood
13177           to specify the dependency output file, but if used without -E, each
13178           -o is understood to specify a target object file.
13179
13180           Since -E is not implied, -MD can be used to generate a dependency
13181           output file as a side effect of the compilation process.
13182
13183       -MMD
13184           Like -MD except mention only user header files, not system header
13185           files.
13186
13187       -fpreprocessed
13188           Indicate to the preprocessor that the input file has already been
13189           preprocessed.  This suppresses things like macro expansion,
13190           trigraph conversion, escaped newline splicing, and processing of
13191           most directives.  The preprocessor still recognizes and removes
13192           comments, so that you can pass a file preprocessed with -C to the
13193           compiler without problems.  In this mode the integrated
13194           preprocessor is little more than a tokenizer for the front ends.
13195
13196           -fpreprocessed is implicit if the input file has one of the
13197           extensions .i, .ii or .mi.  These are the extensions that GCC uses
13198           for preprocessed files created by -save-temps.
13199
13200       -fdirectives-only
13201           When preprocessing, handle directives, but do not expand macros.
13202
13203           The option's behavior depends on the -E and -fpreprocessed options.
13204
13205           With -E, preprocessing is limited to the handling of directives
13206           such as "#define", "#ifdef", and "#error".  Other preprocessor
13207           operations, such as macro expansion and trigraph conversion are not
13208           performed.  In addition, the -dD option is implicitly enabled.
13209
13210           With -fpreprocessed, predefinition of command line and most builtin
13211           macros is disabled.  Macros such as "__LINE__", which are
13212           contextually dependent, are handled normally.  This enables
13213           compilation of files previously preprocessed with "-E
13214           -fdirectives-only".
13215
13216           With both -E and -fpreprocessed, the rules for -fpreprocessed take
13217           precedence.  This enables full preprocessing of files previously
13218           preprocessed with "-E -fdirectives-only".
13219
13220       -fdollars-in-identifiers
13221           Accept $ in identifiers.
13222
13223       -fextended-identifiers
13224           Accept universal character names and extended characters in
13225           identifiers.  This option is enabled by default for C99 (and later
13226           C standard versions) and C++.
13227
13228       -fno-canonical-system-headers
13229           When preprocessing, do not shorten system header paths with
13230           canonicalization.
13231
13232       -fmax-include-depth=depth
13233           Set the maximum depth of the nested #include. The default is 200.
13234
13235       -ftabstop=width
13236           Set the distance between tab stops.  This helps the preprocessor
13237           report correct column numbers in warnings or errors, even if tabs
13238           appear on the line.  If the value is less than 1 or greater than
13239           100, the option is ignored.  The default is 8.
13240
13241       -ftrack-macro-expansion[=level]
13242           Track locations of tokens across macro expansions. This allows the
13243           compiler to emit diagnostic about the current macro expansion stack
13244           when a compilation error occurs in a macro expansion. Using this
13245           option makes the preprocessor and the compiler consume more memory.
13246           The level parameter can be used to choose the level of precision of
13247           token location tracking thus decreasing the memory consumption if
13248           necessary. Value 0 of level de-activates this option. Value 1
13249           tracks tokens locations in a degraded mode for the sake of minimal
13250           memory overhead. In this mode all tokens resulting from the
13251           expansion of an argument of a function-like macro have the same
13252           location. Value 2 tracks tokens locations completely. This value is
13253           the most memory hungry.  When this option is given no argument, the
13254           default parameter value is 2.
13255
13256           Note that "-ftrack-macro-expansion=2" is activated by default.
13257
13258       -fmacro-prefix-map=old=new
13259           When preprocessing files residing in directory old, expand the
13260           "__FILE__" and "__BASE_FILE__" macros as if the files resided in
13261           directory new instead.  This can be used to change an absolute path
13262           to a relative path by using . for new which can result in more
13263           reproducible builds that are location independent.  This option
13264           also affects "__builtin_FILE()" during compilation.  See also
13265           -ffile-prefix-map.
13266
13267       -fexec-charset=charset
13268           Set the execution character set, used for string and character
13269           constants.  The default is UTF-8.  charset can be any encoding
13270           supported by the system's "iconv" library routine.
13271
13272       -fwide-exec-charset=charset
13273           Set the wide execution character set, used for wide string and
13274           character constants.  The default is UTF-32 or UTF-16, whichever
13275           corresponds to the width of "wchar_t".  As with -fexec-charset,
13276           charset can be any encoding supported by the system's "iconv"
13277           library routine; however, you will have problems with encodings
13278           that do not fit exactly in "wchar_t".
13279
13280       -finput-charset=charset
13281           Set the input character set, used for translation from the
13282           character set of the input file to the source character set used by
13283           GCC.  If the locale does not specify, or GCC cannot get this
13284           information from the locale, the default is UTF-8.  This can be
13285           overridden by either the locale or this command-line option.
13286           Currently the command-line option takes precedence if there's a
13287           conflict.  charset can be any encoding supported by the system's
13288           "iconv" library routine.
13289
13290       -fpch-deps
13291           When using precompiled headers, this flag causes the dependency-
13292           output flags to also list the files from the precompiled header's
13293           dependencies.  If not specified, only the precompiled header are
13294           listed and not the files that were used to create it, because those
13295           files are not consulted when a precompiled header is used.
13296
13297       -fpch-preprocess
13298           This option allows use of a precompiled header together with -E.
13299           It inserts a special "#pragma", "#pragma GCC pch_preprocess
13300           "filename"" in the output to mark the place where the precompiled
13301           header was found, and its filename.  When -fpreprocessed is in use,
13302           GCC recognizes this "#pragma" and loads the PCH.
13303
13304           This option is off by default, because the resulting preprocessed
13305           output is only really suitable as input to GCC.  It is switched on
13306           by -save-temps.
13307
13308           You should not write this "#pragma" in your own code, but it is
13309           safe to edit the filename if the PCH file is available in a
13310           different location.  The filename may be absolute or it may be
13311           relative to GCC's current directory.
13312
13313       -fworking-directory
13314           Enable generation of linemarkers in the preprocessor output that
13315           let the compiler know the current working directory at the time of
13316           preprocessing.  When this option is enabled, the preprocessor
13317           emits, after the initial linemarker, a second linemarker with the
13318           current working directory followed by two slashes.  GCC uses this
13319           directory, when it's present in the preprocessed input, as the
13320           directory emitted as the current working directory in some
13321           debugging information formats.  This option is implicitly enabled
13322           if debugging information is enabled, but this can be inhibited with
13323           the negated form -fno-working-directory.  If the -P flag is present
13324           in the command line, this option has no effect, since no "#line"
13325           directives are emitted whatsoever.
13326
13327       -A predicate=answer
13328           Make an assertion with the predicate predicate and answer answer.
13329           This form is preferred to the older form -A predicate(answer),
13330           which is still supported, because it does not use shell special
13331           characters.
13332
13333       -A -predicate=answer
13334           Cancel an assertion with the predicate predicate and answer answer.
13335
13336       -C  Do not discard comments.  All comments are passed through to the
13337           output file, except for comments in processed directives, which are
13338           deleted along with the directive.
13339
13340           You should be prepared for side effects when using -C; it causes
13341           the preprocessor to treat comments as tokens in their own right.
13342           For example, comments appearing at the start of what would be a
13343           directive line have the effect of turning that line into an
13344           ordinary source line, since the first token on the line is no
13345           longer a #.
13346
13347       -CC Do not discard comments, including during macro expansion.  This is
13348           like -C, except that comments contained within macros are also
13349           passed through to the output file where the macro is expanded.
13350
13351           In addition to the side effects of the -C option, the -CC option
13352           causes all C++-style comments inside a macro to be converted to
13353           C-style comments.  This is to prevent later use of that macro from
13354           inadvertently commenting out the remainder of the source line.
13355
13356           The -CC option is generally used to support lint comments.
13357
13358       -P  Inhibit generation of linemarkers in the output from the
13359           preprocessor.  This might be useful when running the preprocessor
13360           on something that is not C code, and will be sent to a program
13361           which might be confused by the linemarkers.
13362
13363       -traditional
13364       -traditional-cpp
13365           Try to imitate the behavior of pre-standard C preprocessors, as
13366           opposed to ISO C preprocessors.  See the GNU CPP manual for
13367           details.
13368
13369           Note that GCC does not otherwise attempt to emulate a pre-standard
13370           C compiler, and these options are only supported with the -E
13371           switch, or when invoking CPP explicitly.
13372
13373       -trigraphs
13374           Support ISO C trigraphs.  These are three-character sequences, all
13375           starting with ??, that are defined by ISO C to stand for single
13376           characters.  For example, ??/ stands for \, so '??/n' is a
13377           character constant for a newline.
13378
13379           The nine trigraphs and their replacements are
13380
13381                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
13382                   Replacement:      [    ]    {    }    #    \    ^    |    ~
13383
13384           By default, GCC ignores trigraphs, but in standard-conforming modes
13385           it converts them.  See the -std and -ansi options.
13386
13387       -remap
13388           Enable special code to work around file systems which only permit
13389           very short file names, such as MS-DOS.
13390
13391       -H  Print the name of each header file used, in addition to other
13392           normal activities.  Each name is indented to show how deep in the
13393           #include stack it is.  Precompiled header files are also printed,
13394           even if they are found to be invalid; an invalid precompiled header
13395           file is printed with ...x and a valid one with ...! .
13396
13397       -dletters
13398           Says to make debugging dumps during compilation as specified by
13399           letters.  The flags documented here are those relevant to the
13400           preprocessor.  Other letters are interpreted by the compiler
13401           proper, or reserved for future versions of GCC, and so are silently
13402           ignored.  If you specify letters whose behavior conflicts, the
13403           result is undefined.
13404
13405           -dM Instead of the normal output, generate a list of #define
13406               directives for all the macros defined during the execution of
13407               the preprocessor, including predefined macros.  This gives you
13408               a way of finding out what is predefined in your version of the
13409               preprocessor.  Assuming you have no file foo.h, the command
13410
13411                       touch foo.h; cpp -dM foo.h
13412
13413               shows all the predefined macros.
13414
13415               If you use -dM without the -E option, -dM is interpreted as a
13416               synonym for -fdump-rtl-mach.
13417
13418           -dD Like -dM except in two respects: it does not include the
13419               predefined macros, and it outputs both the #define directives
13420               and the result of preprocessing.  Both kinds of output go to
13421               the standard output file.
13422
13423           -dN Like -dD, but emit only the macro names, not their expansions.
13424
13425           -dI Output #include directives in addition to the result of
13426               preprocessing.
13427
13428           -dU Like -dD except that only macros that are expanded, or whose
13429               definedness is tested in preprocessor directives, are output;
13430               the output is delayed until the use or test of the macro; and
13431               #undef directives are also output for macros tested but
13432               undefined at the time.
13433
13434       -fdebug-cpp
13435           This option is only useful for debugging GCC.  When used from CPP
13436           or with -E, it dumps debugging information about location maps.
13437           Every token in the output is preceded by the dump of the map its
13438           location belongs to.
13439
13440           When used from GCC without -E, this option has no effect.
13441
13442       -Wp,option
13443           You can use -Wp,option to bypass the compiler driver and pass
13444           option directly through to the preprocessor.  If option contains
13445           commas, it is split into multiple options at the commas.  However,
13446           many options are modified, translated or interpreted by the
13447           compiler driver before being passed to the preprocessor, and -Wp
13448           forcibly bypasses this phase.  The preprocessor's direct interface
13449           is undocumented and subject to change, so whenever possible you
13450           should avoid using -Wp and let the driver handle the options
13451           instead.
13452
13453       -Xpreprocessor option
13454           Pass option as an option to the preprocessor.  You can use this to
13455           supply system-specific preprocessor options that GCC does not
13456           recognize.
13457
13458           If you want to pass an option that takes an argument, you must use
13459           -Xpreprocessor twice, once for the option and once for the
13460           argument.
13461
13462       -no-integrated-cpp
13463           Perform preprocessing as a separate pass before compilation.  By
13464           default, GCC performs preprocessing as an integrated part of input
13465           tokenization and parsing.  If this option is provided, the
13466           appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
13467           and Objective-C, respectively) is instead invoked twice, once for
13468           preprocessing only and once for actual compilation of the
13469           preprocessed input.  This option may be useful in conjunction with
13470           the -B or -wrapper options to specify an alternate preprocessor or
13471           perform additional processing of the program source between normal
13472           preprocessing and compilation.
13473
13474       -flarge-source-files
13475           Adjust GCC to expect large source files, at the expense of slower
13476           compilation and higher memory usage.
13477
13478           Specifically, GCC normally tracks both column numbers and line
13479           numbers within source files and it normally prints both of these
13480           numbers in diagnostics.  However, once it has processed a certain
13481           number of source lines, it stops tracking column numbers and only
13482           tracks line numbers.  This means that diagnostics for later lines
13483           do not include column numbers.  It also means that options like
13484           -Wmisleading-indentation cease to work at that point, although the
13485           compiler prints a note if this happens.  Passing
13486           -flarge-source-files significantly increases the number of source
13487           lines that GCC can process before it stops tracking columns.
13488
13489   Passing Options to the Assembler
13490       You can pass options to the assembler.
13491
13492       -Wa,option
13493           Pass option as an option to the assembler.  If option contains
13494           commas, it is split into multiple options at the commas.
13495
13496       -Xassembler option
13497           Pass option as an option to the assembler.  You can use this to
13498           supply system-specific assembler options that GCC does not
13499           recognize.
13500
13501           If you want to pass an option that takes an argument, you must use
13502           -Xassembler twice, once for the option and once for the argument.
13503
13504   Options for Linking
13505       These options come into play when the compiler links object files into
13506       an executable output file.  They are meaningless if the compiler is not
13507       doing a link step.
13508
13509       object-file-name
13510           A file name that does not end in a special recognized suffix is
13511           considered to name an object file or library.  (Object files are
13512           distinguished from libraries by the linker according to the file
13513           contents.)  If linking is done, these object files are used as
13514           input to the linker.
13515
13516       -c
13517       -S
13518       -E  If any of these options is used, then the linker is not run, and
13519           object file names should not be used as arguments.
13520
13521       -flinker-output=type
13522           This option controls code generation of the link-time optimizer.
13523           By default the linker output is automatically determined by the
13524           linker plugin.  For debugging the compiler and if incremental
13525           linking with a non-LTO object file is desired, it may be useful to
13526           control the type manually.
13527
13528           If type is exec, code generation produces a static binary. In this
13529           case -fpic and -fpie are both disabled.
13530
13531           If type is dyn, code generation produces a shared library.  In this
13532           case -fpic or -fPIC is preserved, but not enabled automatically.
13533           This allows to build shared libraries without position-independent
13534           code on architectures where this is possible, i.e. on x86.
13535
13536           If type is pie, code generation produces an -fpie executable. This
13537           results in similar optimizations as exec except that -fpie is not
13538           disabled if specified at compilation time.
13539
13540           If type is rel, the compiler assumes that incremental linking is
13541           done.  The sections containing intermediate code for link-time
13542           optimization are merged, pre-optimized, and output to the resulting
13543           object file. In addition, if -ffat-lto-objects is specified, binary
13544           code is produced for future non-LTO linking. The object file
13545           produced by incremental linking is smaller than a static library
13546           produced from the same object files.  At link time the result of
13547           incremental linking also loads faster than a static library
13548           assuming that the majority of objects in the library are used.
13549
13550           Finally nolto-rel configures the compiler for incremental linking
13551           where code generation is forced, a final binary is produced, and
13552           the intermediate code for later link-time optimization is stripped.
13553           When multiple object files are linked together the resulting code
13554           is better optimized than with link-time optimizations disabled (for
13555           example, cross-module inlining happens), but most of benefits of
13556           whole program optimizations are lost.
13557
13558           During the incremental link (by -r) the linker plugin defaults to
13559           rel. With current interfaces to GNU Binutils it is however not
13560           possible to incrementally link LTO objects and non-LTO objects into
13561           a single mixed object file.  If any of object files in incremental
13562           link cannot be used for link-time optimization, the linker plugin
13563           issues a warning and uses nolto-rel. To maintain whole program
13564           optimization, it is recommended to link such objects into static
13565           library instead. Alternatively it is possible to use H.J. Lu's
13566           binutils with support for mixed objects.
13567
13568       -fuse-ld=bfd
13569           Use the bfd linker instead of the default linker.
13570
13571       -fuse-ld=gold
13572           Use the gold linker instead of the default linker.
13573
13574       -fuse-ld=lld
13575           Use the LLVM lld linker instead of the default linker.
13576
13577       -llibrary
13578       -l library
13579           Search the library named library when linking.  (The second
13580           alternative with the library as a separate argument is only for
13581           POSIX compliance and is not recommended.)
13582
13583           The -l option is passed directly to the linker by GCC.  Refer to
13584           your linker documentation for exact details.  The general
13585           description below applies to the GNU linker.
13586
13587           The linker searches a standard list of directories for the library.
13588           The directories searched include several standard system
13589           directories plus any that you specify with -L.
13590
13591           Static libraries are archives of object files, and have file names
13592           like liblibrary.a.  Some targets also support shared libraries,
13593           which typically have names like liblibrary.so.  If both static and
13594           shared libraries are found, the linker gives preference to linking
13595           with the shared library unless the -static option is used.
13596
13597           It makes a difference where in the command you write this option;
13598           the linker searches and processes libraries and object files in the
13599           order they are specified.  Thus, foo.o -lz bar.o searches library z
13600           after file foo.o but before bar.o.  If bar.o refers to functions in
13601           z, those functions may not be loaded.
13602
13603       -lobjc
13604           You need this special case of the -l option in order to link an
13605           Objective-C or Objective-C++ program.
13606
13607       -nostartfiles
13608           Do not use the standard system startup files when linking.  The
13609           standard system libraries are used normally, unless -nostdlib,
13610           -nolibc, or -nodefaultlibs is used.
13611
13612       -nodefaultlibs
13613           Do not use the standard system libraries when linking.  Only the
13614           libraries you specify are passed to the linker, and options
13615           specifying linkage of the system libraries, such as -static-libgcc
13616           or -shared-libgcc, are ignored.  The standard startup files are
13617           used normally, unless -nostartfiles is used.
13618
13619           The compiler may generate calls to "memcmp", "memset", "memcpy" and
13620           "memmove".  These entries are usually resolved by entries in libc.
13621           These entry points should be supplied through some other mechanism
13622           when this option is specified.
13623
13624       -nolibc
13625           Do not use the C library or system libraries tightly coupled with
13626           it when linking.  Still link with the startup files, libgcc or
13627           toolchain provided language support libraries such as libgnat,
13628           libgfortran or libstdc++ unless options preventing their inclusion
13629           are used as well.  This typically removes -lc from the link command
13630           line, as well as system libraries that normally go with it and
13631           become meaningless when absence of a C library is assumed, for
13632           example -lpthread or -lm in some configurations.  This is intended
13633           for bare-board targets when there is indeed no C library available.
13634
13635       -nostdlib
13636           Do not use the standard system startup files or libraries when
13637           linking.  No startup files and only the libraries you specify are
13638           passed to the linker, and options specifying linkage of the system
13639           libraries, such as -static-libgcc or -shared-libgcc, are ignored.
13640
13641           The compiler may generate calls to "memcmp", "memset", "memcpy" and
13642           "memmove".  These entries are usually resolved by entries in libc.
13643           These entry points should be supplied through some other mechanism
13644           when this option is specified.
13645
13646           One of the standard libraries bypassed by -nostdlib and
13647           -nodefaultlibs is libgcc.a, a library of internal subroutines which
13648           GCC uses to overcome shortcomings of particular machines, or
13649           special needs for some languages.
13650
13651           In most cases, you need libgcc.a even when you want to avoid other
13652           standard libraries.  In other words, when you specify -nostdlib or
13653           -nodefaultlibs you should usually specify -lgcc as well.  This
13654           ensures that you have no unresolved references to internal GCC
13655           library subroutines.  (An example of such an internal subroutine is
13656           "__main", used to ensure C++ constructors are called.)
13657
13658       -e entry
13659       --entry=entry
13660           Specify that the program entry point is entry.  The argument is
13661           interpreted by the linker; the GNU linker accepts either a symbol
13662           name or an address.
13663
13664       -pie
13665           Produce a dynamically linked position independent executable on
13666           targets that support it.  For predictable results, you must also
13667           specify the same set of options used for compilation (-fpie, -fPIE,
13668           or model suboptions) when you specify this linker option.
13669
13670       -no-pie
13671           Don't produce a dynamically linked position independent executable.
13672
13673       -static-pie
13674           Produce a static position independent executable on targets that
13675           support it.  A static position independent executable is similar to
13676           a static executable, but can be loaded at any address without a
13677           dynamic linker.  For predictable results, you must also specify the
13678           same set of options used for compilation (-fpie, -fPIE, or model
13679           suboptions) when you specify this linker option.
13680
13681       -pthread
13682           Link with the POSIX threads library.  This option is supported on
13683           GNU/Linux targets, most other Unix derivatives, and also on x86
13684           Cygwin and MinGW targets.  On some targets this option also sets
13685           flags for the preprocessor, so it should be used consistently for
13686           both compilation and linking.
13687
13688       -r  Produce a relocatable object as output.  This is also known as
13689           partial linking.
13690
13691       -rdynamic
13692           Pass the flag -export-dynamic to the ELF linker, on targets that
13693           support it. This instructs the linker to add all symbols, not only
13694           used ones, to the dynamic symbol table. This option is needed for
13695           some uses of "dlopen" or to allow obtaining backtraces from within
13696           a program.
13697
13698       -s  Remove all symbol table and relocation information from the
13699           executable.
13700
13701       -static
13702           On systems that support dynamic linking, this overrides -pie and
13703           prevents linking with the shared libraries.  On other systems, this
13704           option has no effect.
13705
13706       -shared
13707           Produce a shared object which can then be linked with other objects
13708           to form an executable.  Not all systems support this option.  For
13709           predictable results, you must also specify the same set of options
13710           used for compilation (-fpic, -fPIC, or model suboptions) when you
13711           specify this linker option.[1]
13712
13713       -shared-libgcc
13714       -static-libgcc
13715           On systems that provide libgcc as a shared library, these options
13716           force the use of either the shared or static version, respectively.
13717           If no shared version of libgcc was built when the compiler was
13718           configured, these options have no effect.
13719
13720           There are several situations in which an application should use the
13721           shared libgcc instead of the static version.  The most common of
13722           these is when the application wishes to throw and catch exceptions
13723           across different shared libraries.  In that case, each of the
13724           libraries as well as the application itself should use the shared
13725           libgcc.
13726
13727           Therefore, the G++ driver automatically adds -shared-libgcc
13728           whenever you build a shared library or a main executable, because
13729           C++ programs typically use exceptions, so this is the right thing
13730           to do.
13731
13732           If, instead, you use the GCC driver to create shared libraries, you
13733           may find that they are not always linked with the shared libgcc.
13734           If GCC finds, at its configuration time, that you have a non-GNU
13735           linker or a GNU linker that does not support option --eh-frame-hdr,
13736           it links the shared version of libgcc into shared libraries by
13737           default.  Otherwise, it takes advantage of the linker and optimizes
13738           away the linking with the shared version of libgcc, linking with
13739           the static version of libgcc by default.  This allows exceptions to
13740           propagate through such shared libraries, without incurring
13741           relocation costs at library load time.
13742
13743           However, if a library or main executable is supposed to throw or
13744           catch exceptions, you must link it using the G++ driver, or using
13745           the option -shared-libgcc, such that it is linked with the shared
13746           libgcc.
13747
13748       -static-libasan
13749           When the -fsanitize=address option is used to link a program, the
13750           GCC driver automatically links against libasan.  If libasan is
13751           available as a shared library, and the -static option is not used,
13752           then this links against the shared version of libasan.  The
13753           -static-libasan option directs the GCC driver to link libasan
13754           statically, without necessarily linking other libraries statically.
13755
13756       -static-libtsan
13757           When the -fsanitize=thread option is used to link a program, the
13758           GCC driver automatically links against libtsan.  If libtsan is
13759           available as a shared library, and the -static option is not used,
13760           then this links against the shared version of libtsan.  The
13761           -static-libtsan option directs the GCC driver to link libtsan
13762           statically, without necessarily linking other libraries statically.
13763
13764       -static-liblsan
13765           When the -fsanitize=leak option is used to link a program, the GCC
13766           driver automatically links against liblsan.  If liblsan is
13767           available as a shared library, and the -static option is not used,
13768           then this links against the shared version of liblsan.  The
13769           -static-liblsan option directs the GCC driver to link liblsan
13770           statically, without necessarily linking other libraries statically.
13771
13772       -static-libubsan
13773           When the -fsanitize=undefined option is used to link a program, the
13774           GCC driver automatically links against libubsan.  If libubsan is
13775           available as a shared library, and the -static option is not used,
13776           then this links against the shared version of libubsan.  The
13777           -static-libubsan option directs the GCC driver to link libubsan
13778           statically, without necessarily linking other libraries statically.
13779
13780       -static-libstdc++
13781           When the g++ program is used to link a C++ program, it normally
13782           automatically links against libstdc++.  If libstdc++ is available
13783           as a shared library, and the -static option is not used, then this
13784           links against the shared version of libstdc++.  That is normally
13785           fine.  However, it is sometimes useful to freeze the version of
13786           libstdc++ used by the program without going all the way to a fully
13787           static link.  The -static-libstdc++ option directs the g++ driver
13788           to link libstdc++ statically, without necessarily linking other
13789           libraries statically.
13790
13791       -symbolic
13792           Bind references to global symbols when building a shared object.
13793           Warn about any unresolved references (unless overridden by the link
13794           editor option -Xlinker -z -Xlinker defs).  Only a few systems
13795           support this option.
13796
13797       -T script
13798           Use script as the linker script.  This option is supported by most
13799           systems using the GNU linker.  On some targets, such as bare-board
13800           targets without an operating system, the -T option may be required
13801           when linking to avoid references to undefined symbols.
13802
13803       -Xlinker option
13804           Pass option as an option to the linker.  You can use this to supply
13805           system-specific linker options that GCC does not recognize.
13806
13807           If you want to pass an option that takes a separate argument, you
13808           must use -Xlinker twice, once for the option and once for the
13809           argument.  For example, to pass -assert definitions, you must write
13810           -Xlinker -assert -Xlinker definitions.  It does not work to write
13811           -Xlinker "-assert definitions", because this passes the entire
13812           string as a single argument, which is not what the linker expects.
13813
13814           When using the GNU linker, it is usually more convenient to pass
13815           arguments to linker options using the option=value syntax than as
13816           separate arguments.  For example, you can specify -Xlinker
13817           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
13818           Other linkers may not support this syntax for command-line options.
13819
13820       -Wl,option
13821           Pass option as an option to the linker.  If option contains commas,
13822           it is split into multiple options at the commas.  You can use this
13823           syntax to pass an argument to the option.  For example,
13824           -Wl,-Map,output.map passes -Map output.map to the linker.  When
13825           using the GNU linker, you can also get the same effect with
13826           -Wl,-Map=output.map.
13827
13828       -u symbol
13829           Pretend the symbol symbol is undefined, to force linking of library
13830           modules to define it.  You can use -u multiple times with different
13831           symbols to force loading of additional library modules.
13832
13833       -z keyword
13834           -z is passed directly on to the linker along with the keyword
13835           keyword. See the section in the documentation of your linker for
13836           permitted values and their meanings.
13837
13838   Options for Directory Search
13839       These options specify directories to search for header files, for
13840       libraries and for parts of the compiler:
13841
13842       -I dir
13843       -iquote dir
13844       -isystem dir
13845       -idirafter dir
13846           Add the directory dir to the list of directories to be searched for
13847           header files during preprocessing.  If dir begins with = or
13848           $SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix;
13849           see --sysroot and -isysroot.
13850
13851           Directories specified with -iquote apply only to the quote form of
13852           the directive, "#include "file"".  Directories specified with -I,
13853           -isystem, or -idirafter apply to lookup for both the
13854           "#include "file"" and "#include <file>" directives.
13855
13856           You can specify any number or combination of these options on the
13857           command line to search for header files in several directories.
13858           The lookup order is as follows:
13859
13860           1.  For the quote form of the include directive, the directory of
13861               the current file is searched first.
13862
13863           2.  For the quote form of the include directive, the directories
13864               specified by -iquote options are searched in left-to-right
13865               order, as they appear on the command line.
13866
13867           3.  Directories specified with -I options are scanned in left-to-
13868               right order.
13869
13870           4.  Directories specified with -isystem options are scanned in
13871               left-to-right order.
13872
13873           5.  Standard system directories are scanned.
13874
13875           6.  Directories specified with -idirafter options are scanned in
13876               left-to-right order.
13877
13878           You can use -I to override a system header file, substituting your
13879           own version, since these directories are searched before the
13880           standard system header file directories.  However, you should not
13881           use this option to add directories that contain vendor-supplied
13882           system header files; use -isystem for that.
13883
13884           The -isystem and -idirafter options also mark the directory as a
13885           system directory, so that it gets the same special treatment that
13886           is applied to the standard system directories.
13887
13888           If a standard system include directory, or a directory specified
13889           with -isystem, is also specified with -I, the -I option is ignored.
13890           The directory is still searched but as a system directory at its
13891           normal position in the system include chain.  This is to ensure
13892           that GCC's procedure to fix buggy system headers and the ordering
13893           for the "#include_next" directive are not inadvertently changed.
13894           If you really need to change the search order for system
13895           directories, use the -nostdinc and/or -isystem options.
13896
13897       -I- Split the include path.  This option has been deprecated.  Please
13898           use -iquote instead for -I directories before the -I- and remove
13899           the -I- option.
13900
13901           Any directories specified with -I options before -I- are searched
13902           only for headers requested with "#include "file""; they are not
13903           searched for "#include <file>".  If additional directories are
13904           specified with -I options after the -I-, those directories are
13905           searched for all #include directives.
13906
13907           In addition, -I- inhibits the use of the directory of the current
13908           file directory as the first search directory for "#include "file"".
13909           There is no way to override this effect of -I-.
13910
13911       -iprefix prefix
13912           Specify prefix as the prefix for subsequent -iwithprefix options.
13913           If the prefix represents a directory, you should include the final
13914           /.
13915
13916       -iwithprefix dir
13917       -iwithprefixbefore dir
13918           Append dir to the prefix specified previously with -iprefix, and
13919           add the resulting directory to the include search path.
13920           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
13921           puts it where -idirafter would.
13922
13923       -isysroot dir
13924           This option is like the --sysroot option, but applies only to
13925           header files (except for Darwin targets, where it applies to both
13926           header files and libraries).  See the --sysroot option for more
13927           information.
13928
13929       -imultilib dir
13930           Use dir as a subdirectory of the directory containing target-
13931           specific C++ headers.
13932
13933       -nostdinc
13934           Do not search the standard system directories for header files.
13935           Only the directories explicitly specified with -I, -iquote,
13936           -isystem, and/or -idirafter options (and the directory of the
13937           current file, if appropriate) are searched.
13938
13939       -nostdinc++
13940           Do not search for header files in the C++-specific standard
13941           directories, but do still search the other standard directories.
13942           (This option is used when building the C++ library.)
13943
13944       -iplugindir=dir
13945           Set the directory to search for plugins that are passed by
13946           -fplugin=name instead of -fplugin=path/name.so.  This option is not
13947           meant to be used by the user, but only passed by the driver.
13948
13949       -Ldir
13950           Add directory dir to the list of directories to be searched for -l.
13951
13952       -Bprefix
13953           This option specifies where to find the executables, libraries,
13954           include files, and data files of the compiler itself.
13955
13956           The compiler driver program runs one or more of the subprograms
13957           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
13958           it tries to run, both with and without machine/version/ for the
13959           corresponding target machine and compiler version.
13960
13961           For each subprogram to be run, the compiler driver first tries the
13962           -B prefix, if any.  If that name is not found, or if -B is not
13963           specified, the driver tries two standard prefixes, /usr/lib/gcc/
13964           and /usr/local/lib/gcc/.  If neither of those results in a file
13965           name that is found, the unmodified program name is searched for
13966           using the directories specified in your PATH environment variable.
13967
13968           The compiler checks to see if the path provided by -B refers to a
13969           directory, and if necessary it adds a directory separator character
13970           at the end of the path.
13971
13972           -B prefixes that effectively specify directory names also apply to
13973           libraries in the linker, because the compiler translates these
13974           options into -L options for the linker.  They also apply to include
13975           files in the preprocessor, because the compiler translates these
13976           options into -isystem options for the preprocessor.  In this case,
13977           the compiler appends include to the prefix.
13978
13979           The runtime support file libgcc.a can also be searched for using
13980           the -B prefix, if needed.  If it is not found there, the two
13981           standard prefixes above are tried, and that is all.  The file is
13982           left out of the link if it is not found by those means.
13983
13984           Another way to specify a prefix much like the -B prefix is to use
13985           the environment variable GCC_EXEC_PREFIX.
13986
13987           As a special kludge, if the path provided by -B is [dir/]stageN/,
13988           where N is a number in the range 0 to 9, then it is replaced by
13989           [dir/]include.  This is to help with boot-strapping the compiler.
13990
13991       -no-canonical-prefixes
13992           Do not expand any symbolic links, resolve references to /../ or
13993           /./, or make the path absolute when generating a relative prefix.
13994
13995       --sysroot=dir
13996           Use dir as the logical root directory for headers and libraries.
13997           For example, if the compiler normally searches for headers in
13998           /usr/include and libraries in /usr/lib, it instead searches
13999           dir/usr/include and dir/usr/lib.
14000
14001           If you use both this option and the -isysroot option, then the
14002           --sysroot option applies to libraries, but the -isysroot option
14003           applies to header files.
14004
14005           The GNU linker (beginning with version 2.16) has the necessary
14006           support for this option.  If your linker does not support this
14007           option, the header file aspect of --sysroot still works, but the
14008           library aspect does not.
14009
14010       --no-sysroot-suffix
14011           For some targets, a suffix is added to the root directory specified
14012           with --sysroot, depending on the other options used, so that
14013           headers may for example be found in dir/suffix/usr/include instead
14014           of dir/usr/include.  This option disables the addition of such a
14015           suffix.
14016
14017   Options for Code Generation Conventions
14018       These machine-independent options control the interface conventions
14019       used in code generation.
14020
14021       Most of them have both positive and negative forms; the negative form
14022       of -ffoo is -fno-foo.  In the table below, only one of the forms is
14023       listed---the one that is not the default.  You can figure out the other
14024       form by either removing no- or adding it.
14025
14026       -fstack-reuse=reuse-level
14027           This option controls stack space reuse for user declared local/auto
14028           variables and compiler generated temporaries.  reuse_level can be
14029           all, named_vars, or none. all enables stack reuse for all local
14030           variables and temporaries, named_vars enables the reuse only for
14031           user defined local variables with names, and none disables stack
14032           reuse completely. The default value is all. The option is needed
14033           when the program extends the lifetime of a scoped local variable or
14034           a compiler generated temporary beyond the end point defined by the
14035           language.  When a lifetime of a variable ends, and if the variable
14036           lives in memory, the optimizing compiler has the freedom to reuse
14037           its stack space with other temporaries or scoped local variables
14038           whose live range does not overlap with it. Legacy code extending
14039           local lifetime is likely to break with the stack reuse
14040           optimization.
14041
14042           For example,
14043
14044                      int *p;
14045                      {
14046                        int local1;
14047
14048                        p = &local1;
14049                        local1 = 10;
14050                        ....
14051                      }
14052                      {
14053                         int local2;
14054                         local2 = 20;
14055                         ...
14056                      }
14057
14058                      if (*p == 10)  // out of scope use of local1
14059                        {
14060
14061                        }
14062
14063           Another example:
14064
14065                      struct A
14066                      {
14067                          A(int k) : i(k), j(k) { }
14068                          int i;
14069                          int j;
14070                      };
14071
14072                      A *ap;
14073
14074                      void foo(const A& ar)
14075                      {
14076                         ap = &ar;
14077                      }
14078
14079                      void bar()
14080                      {
14081                         foo(A(10)); // temp object's lifetime ends when foo returns
14082
14083                         {
14084                           A a(20);
14085                           ....
14086                         }
14087                         ap->i+= 10;  // ap references out of scope temp whose space
14088                                      // is reused with a. What is the value of ap->i?
14089                      }
14090
14091           The lifetime of a compiler generated temporary is well defined by
14092           the C++ standard. When a lifetime of a temporary ends, and if the
14093           temporary lives in memory, the optimizing compiler has the freedom
14094           to reuse its stack space with other temporaries or scoped local
14095           variables whose live range does not overlap with it. However some
14096           of the legacy code relies on the behavior of older compilers in
14097           which temporaries' stack space is not reused, the aggressive stack
14098           reuse can lead to runtime errors. This option is used to control
14099           the temporary stack reuse optimization.
14100
14101       -ftrapv
14102           This option generates traps for signed overflow on addition,
14103           subtraction, multiplication operations.  The options -ftrapv and
14104           -fwrapv override each other, so using -ftrapv -fwrapv on the
14105           command-line results in -fwrapv being effective.  Note that only
14106           active options override, so using -ftrapv -fwrapv -fno-wrapv on the
14107           command-line results in -ftrapv being effective.
14108
14109       -fwrapv
14110           This option instructs the compiler to assume that signed arithmetic
14111           overflow of addition, subtraction and multiplication wraps around
14112           using twos-complement representation.  This flag enables some
14113           optimizations and disables others.  The options -ftrapv and -fwrapv
14114           override each other, so using -ftrapv -fwrapv on the command-line
14115           results in -fwrapv being effective.  Note that only active options
14116           override, so using -ftrapv -fwrapv -fno-wrapv on the command-line
14117           results in -ftrapv being effective.
14118
14119       -fwrapv-pointer
14120           This option instructs the compiler to assume that pointer
14121           arithmetic overflow on addition and subtraction wraps around using
14122           twos-complement representation.  This flag disables some
14123           optimizations which assume pointer overflow is invalid.
14124
14125       -fstrict-overflow
14126           This option implies -fno-wrapv -fno-wrapv-pointer and when negated
14127           implies -fwrapv -fwrapv-pointer.
14128
14129       -fexceptions
14130           Enable exception handling.  Generates extra code needed to
14131           propagate exceptions.  For some targets, this implies GCC generates
14132           frame unwind information for all functions, which can produce
14133           significant data size overhead, although it does not affect
14134           execution.  If you do not specify this option, GCC enables it by
14135           default for languages like C++ that normally require exception
14136           handling, and disables it for languages like C that do not normally
14137           require it.  However, you may need to enable this option when
14138           compiling C code that needs to interoperate properly with exception
14139           handlers written in C++.  You may also wish to disable this option
14140           if you are compiling older C++ programs that don't use exception
14141           handling.
14142
14143       -fnon-call-exceptions
14144           Generate code that allows trapping instructions to throw
14145           exceptions.  Note that this requires platform-specific runtime
14146           support that does not exist everywhere.  Moreover, it only allows
14147           trapping instructions to throw exceptions, i.e. memory references
14148           or floating-point instructions.  It does not allow exceptions to be
14149           thrown from arbitrary signal handlers such as "SIGALRM".
14150
14151       -fdelete-dead-exceptions
14152           Consider that instructions that may throw exceptions but don't
14153           otherwise contribute to the execution of the program can be
14154           optimized away.  This option is enabled by default for the Ada
14155           compiler, as permitted by the Ada language specification.
14156           Optimization passes that cause dead exceptions to be removed are
14157           enabled independently at different optimization levels.
14158
14159       -funwind-tables
14160           Similar to -fexceptions, except that it just generates any needed
14161           static data, but does not affect the generated code in any other
14162           way.  You normally do not need to enable this option; instead, a
14163           language processor that needs this handling enables it on your
14164           behalf.
14165
14166       -fasynchronous-unwind-tables
14167           Generate unwind table in DWARF format, if supported by target
14168           machine.  The table is exact at each instruction boundary, so it
14169           can be used for stack unwinding from asynchronous events (such as
14170           debugger or garbage collector).
14171
14172       -fno-gnu-unique
14173           On systems with recent GNU assembler and C library, the C++
14174           compiler uses the "STB_GNU_UNIQUE" binding to make sure that
14175           definitions of template static data members and static local
14176           variables in inline functions are unique even in the presence of
14177           "RTLD_LOCAL"; this is necessary to avoid problems with a library
14178           used by two different "RTLD_LOCAL" plugins depending on a
14179           definition in one of them and therefore disagreeing with the other
14180           one about the binding of the symbol.  But this causes "dlclose" to
14181           be ignored for affected DSOs; if your program relies on
14182           reinitialization of a DSO via "dlclose" and "dlopen", you can use
14183           -fno-gnu-unique.
14184
14185       -fpcc-struct-return
14186           Return "short" "struct" and "union" values in memory like longer
14187           ones, rather than in registers.  This convention is less efficient,
14188           but it has the advantage of allowing intercallability between GCC-
14189           compiled files and files compiled with other compilers,
14190           particularly the Portable C Compiler (pcc).
14191
14192           The precise convention for returning structures in memory depends
14193           on the target configuration macros.
14194
14195           Short structures and unions are those whose size and alignment
14196           match that of some integer type.
14197
14198           Warning: code compiled with the -fpcc-struct-return switch is not
14199           binary compatible with code compiled with the -freg-struct-return
14200           switch.  Use it to conform to a non-default application binary
14201           interface.
14202
14203       -freg-struct-return
14204           Return "struct" and "union" values in registers when possible.
14205           This is more efficient for small structures than
14206           -fpcc-struct-return.
14207
14208           If you specify neither -fpcc-struct-return nor -freg-struct-return,
14209           GCC defaults to whichever convention is standard for the target.
14210           If there is no standard convention, GCC defaults to
14211           -fpcc-struct-return, except on targets where GCC is the principal
14212           compiler.  In those cases, we can choose the standard, and we chose
14213           the more efficient register return alternative.
14214
14215           Warning: code compiled with the -freg-struct-return switch is not
14216           binary compatible with code compiled with the -fpcc-struct-return
14217           switch.  Use it to conform to a non-default application binary
14218           interface.
14219
14220       -fshort-enums
14221           Allocate to an "enum" type only as many bytes as it needs for the
14222           declared range of possible values.  Specifically, the "enum" type
14223           is equivalent to the smallest integer type that has enough room.
14224
14225           Warning: the -fshort-enums switch causes GCC to generate code that
14226           is not binary compatible with code generated without that switch.
14227           Use it to conform to a non-default application binary interface.
14228
14229       -fshort-wchar
14230           Override the underlying type for "wchar_t" to be "short unsigned
14231           int" instead of the default for the target.  This option is useful
14232           for building programs to run under WINE.
14233
14234           Warning: the -fshort-wchar switch causes GCC to generate code that
14235           is not binary compatible with code generated without that switch.
14236           Use it to conform to a non-default application binary interface.
14237
14238       -fcommon
14239           In C code, this option controls the placement of global variables
14240           defined without an initializer, known as tentative definitions in
14241           the C standard.  Tentative definitions are distinct from
14242           declarations of a variable with the "extern" keyword, which do not
14243           allocate storage.
14244
14245           The default is -fno-common, which specifies that the compiler
14246           places uninitialized global variables in the BSS section of the
14247           object file.  This inhibits the merging of tentative definitions by
14248           the linker so you get a multiple-definition error if the same
14249           variable is accidentally defined in more than one compilation unit.
14250
14251           The -fcommon places uninitialized global variables in a common
14252           block.  This allows the linker to resolve all tentative definitions
14253           of the same variable in different compilation units to the same
14254           object, or to a non-tentative definition.  This behavior is
14255           inconsistent with C++, and on many targets implies a speed and code
14256           size penalty on global variable references.  It is mainly useful to
14257           enable legacy code to link without errors.
14258
14259       -fno-ident
14260           Ignore the "#ident" directive.
14261
14262       -finhibit-size-directive
14263           Don't output a ".size" assembler directive, or anything else that
14264           would cause trouble if the function is split in the middle, and the
14265           two halves are placed at locations far apart in memory.  This
14266           option is used when compiling crtstuff.c; you should not need to
14267           use it for anything else.
14268
14269       -fverbose-asm
14270           Put extra commentary information in the generated assembly code to
14271           make it more readable.  This option is generally only of use to
14272           those who actually need to read the generated assembly code
14273           (perhaps while debugging the compiler itself).
14274
14275           -fno-verbose-asm, the default, causes the extra information to be
14276           omitted and is useful when comparing two assembler files.
14277
14278           The added comments include:
14279
14280           *   information on the compiler version and command-line options,
14281
14282           *   the source code lines associated with the assembly
14283               instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,
14284
14285           *   hints on which high-level expressions correspond to the various
14286               assembly instruction operands.
14287
14288           For example, given this C source file:
14289
14290                   int test (int n)
14291                   {
14292                     int i;
14293                     int total = 0;
14294
14295                     for (i = 0; i < n; i++)
14296                       total += i * i;
14297
14298                     return total;
14299                   }
14300
14301           compiling to (x86_64) assembly via -S and emitting the result
14302           direct to stdout via -o -
14303
14304                   gcc -S test.c -fverbose-asm -Os -o -
14305
14306           gives output similar to this:
14307
14308                           .file   "test.c"
14309                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
14310                     [...snip...]
14311                   # options passed:
14312                     [...snip...]
14313
14314                           .text
14315                           .globl  test
14316                           .type   test, @function
14317                   test:
14318                   .LFB0:
14319                           .cfi_startproc
14320                   # test.c:4:   int total = 0;
14321                           xorl    %eax, %eax      # <retval>
14322                   # test.c:6:   for (i = 0; i < n; i++)
14323                           xorl    %edx, %edx      # i
14324                   .L2:
14325                   # test.c:6:   for (i = 0; i < n; i++)
14326                           cmpl    %edi, %edx      # n, i
14327                           jge     .L5     #,
14328                   # test.c:7:     total += i * i;
14329                           movl    %edx, %ecx      # i, tmp92
14330                           imull   %edx, %ecx      # i, tmp92
14331                   # test.c:6:   for (i = 0; i < n; i++)
14332                           incl    %edx    # i
14333                   # test.c:7:     total += i * i;
14334                           addl    %ecx, %eax      # tmp92, <retval>
14335                           jmp     .L2     #
14336                   .L5:
14337                   # test.c:10: }
14338                           ret
14339                           .cfi_endproc
14340                   .LFE0:
14341                           .size   test, .-test
14342                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
14343                           .section        .note.GNU-stack,"",@progbits
14344
14345           The comments are intended for humans rather than machines and hence
14346           the precise format of the comments is subject to change.
14347
14348       -frecord-gcc-switches
14349           This switch causes the command line used to invoke the compiler to
14350           be recorded into the object file that is being created.  This
14351           switch is only implemented on some targets and the exact format of
14352           the recording is target and binary file format dependent, but it
14353           usually takes the form of a section containing ASCII text.  This
14354           switch is related to the -fverbose-asm switch, but that switch only
14355           records information in the assembler output file as comments, so it
14356           never reaches the object file.  See also -grecord-gcc-switches for
14357           another way of storing compiler options into the object file.
14358
14359       -fpic
14360           Generate position-independent code (PIC) suitable for use in a
14361           shared library, if supported for the target machine.  Such code
14362           accesses all constant addresses through a global offset table
14363           (GOT).  The dynamic loader resolves the GOT entries when the
14364           program starts (the dynamic loader is not part of GCC; it is part
14365           of the operating system).  If the GOT size for the linked
14366           executable exceeds a machine-specific maximum size, you get an
14367           error message from the linker indicating that -fpic does not work;
14368           in that case, recompile with -fPIC instead.  (These maximums are 8k
14369           on the SPARC, 28k on AArch64 and 32k on the m68k and RS/6000.  The
14370           x86 has no such limit.)
14371
14372           Position-independent code requires special support, and therefore
14373           works only on certain machines.  For the x86, GCC supports PIC for
14374           System V but not for the Sun 386i.  Code generated for the IBM
14375           RS/6000 is always position-independent.
14376
14377           When this flag is set, the macros "__pic__" and "__PIC__" are
14378           defined to 1.
14379
14380       -fPIC
14381           If supported for the target machine, emit position-independent
14382           code, suitable for dynamic linking and avoiding any limit on the
14383           size of the global offset table.  This option makes a difference on
14384           AArch64, m68k, PowerPC and SPARC.
14385
14386           Position-independent code requires special support, and therefore
14387           works only on certain machines.
14388
14389           When this flag is set, the macros "__pic__" and "__PIC__" are
14390           defined to 2.
14391
14392       -fpie
14393       -fPIE
14394           These options are similar to -fpic and -fPIC, but the generated
14395           position-independent code can be only linked into executables.
14396           Usually these options are used to compile code that will be linked
14397           using the -pie GCC option.
14398
14399           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
14400           The macros have the value 1 for -fpie and 2 for -fPIE.
14401
14402       -fno-plt
14403           Do not use the PLT for external function calls in position-
14404           independent code.  Instead, load the callee address at call sites
14405           from the GOT and branch to it.  This leads to more efficient code
14406           by eliminating PLT stubs and exposing GOT loads to optimizations.
14407           On architectures such as 32-bit x86 where PLT stubs expect the GOT
14408           pointer in a specific register, this gives more register allocation
14409           freedom to the compiler.  Lazy binding requires use of the PLT;
14410           with -fno-plt all external symbols are resolved at load time.
14411
14412           Alternatively, the function attribute "noplt" can be used to avoid
14413           calls through the PLT for specific external functions.
14414
14415           In position-dependent code, a few targets also convert calls to
14416           functions that are marked to not use the PLT to use the GOT
14417           instead.
14418
14419       -fno-jump-tables
14420           Do not use jump tables for switch statements even where it would be
14421           more efficient than other code generation strategies.  This option
14422           is of use in conjunction with -fpic or -fPIC for building code that
14423           forms part of a dynamic linker and cannot reference the address of
14424           a jump table.  On some targets, jump tables do not require a GOT
14425           and this option is not needed.
14426
14427       -fno-bit-tests
14428           Do not use bit tests for switch statements even where it would be
14429           more efficient than other code generation strategies.
14430
14431       -ffixed-reg
14432           Treat the register named reg as a fixed register; generated code
14433           should never refer to it (except perhaps as a stack pointer, frame
14434           pointer or in some other fixed role).
14435
14436           reg must be the name of a register.  The register names accepted
14437           are machine-specific and are defined in the "REGISTER_NAMES" macro
14438           in the machine description macro file.
14439
14440           This flag does not have a negative form, because it specifies a
14441           three-way choice.
14442
14443       -fcall-used-reg
14444           Treat the register named reg as an allocable register that is
14445           clobbered by function calls.  It may be allocated for temporaries
14446           or variables that do not live across a call.  Functions compiled
14447           this way do not save and restore the register reg.
14448
14449           It is an error to use this flag with the frame pointer or stack
14450           pointer.  Use of this flag for other registers that have fixed
14451           pervasive roles in the machine's execution model produces
14452           disastrous results.
14453
14454           This flag does not have a negative form, because it specifies a
14455           three-way choice.
14456
14457       -fcall-saved-reg
14458           Treat the register named reg as an allocable register saved by
14459           functions.  It may be allocated even for temporaries or variables
14460           that live across a call.  Functions compiled this way save and
14461           restore the register reg if they use it.
14462
14463           It is an error to use this flag with the frame pointer or stack
14464           pointer.  Use of this flag for other registers that have fixed
14465           pervasive roles in the machine's execution model produces
14466           disastrous results.
14467
14468           A different sort of disaster results from the use of this flag for
14469           a register in which function values may be returned.
14470
14471           This flag does not have a negative form, because it specifies a
14472           three-way choice.
14473
14474       -fpack-struct[=n]
14475           Without a value specified, pack all structure members together
14476           without holes.  When a value is specified (which must be a small
14477           power of two), pack structure members according to this value,
14478           representing the maximum alignment (that is, objects with default
14479           alignment requirements larger than this are output potentially
14480           unaligned at the next fitting location.
14481
14482           Warning: the -fpack-struct switch causes GCC to generate code that
14483           is not binary compatible with code generated without that switch.
14484           Additionally, it makes the code suboptimal.  Use it to conform to a
14485           non-default application binary interface.
14486
14487       -fleading-underscore
14488           This option and its counterpart, -fno-leading-underscore, forcibly
14489           change the way C symbols are represented in the object file.  One
14490           use is to help link with legacy assembly code.
14491
14492           Warning: the -fleading-underscore switch causes GCC to generate
14493           code that is not binary compatible with code generated without that
14494           switch.  Use it to conform to a non-default application binary
14495           interface.  Not all targets provide complete support for this
14496           switch.
14497
14498       -ftls-model=model
14499           Alter the thread-local storage model to be used.  The model
14500           argument should be one of global-dynamic, local-dynamic, initial-
14501           exec or local-exec.  Note that the choice is subject to
14502           optimization: the compiler may use a more efficient model for
14503           symbols not visible outside of the translation unit, or if -fpic is
14504           not given on the command line.
14505
14506           The default without -fpic is initial-exec; with -fpic the default
14507           is global-dynamic.
14508
14509       -ftrampolines
14510           For targets that normally need trampolines for nested functions,
14511           always generate them instead of using descriptors.  Otherwise, for
14512           targets that do not need them, like for example HP-PA or IA-64, do
14513           nothing.
14514
14515           A trampoline is a small piece of code that is created at run time
14516           on the stack when the address of a nested function is taken, and is
14517           used to call the nested function indirectly.  Therefore, it
14518           requires the stack to be made executable in order for the program
14519           to work properly.
14520
14521           -fno-trampolines is enabled by default on a language by language
14522           basis to let the compiler avoid generating them, if it computes
14523           that this is safe, and replace them with descriptors.  Descriptors
14524           are made up of data only, but the generated code must be prepared
14525           to deal with them.  As of this writing, -fno-trampolines is enabled
14526           by default only for Ada.
14527
14528           Moreover, code compiled with -ftrampolines and code compiled with
14529           -fno-trampolines are not binary compatible if nested functions are
14530           present.  This option must therefore be used on a program-wide
14531           basis and be manipulated with extreme care.
14532
14533       -fvisibility=[default|internal|hidden|protected]
14534           Set the default ELF image symbol visibility to the specified
14535           option---all symbols are marked with this unless overridden within
14536           the code.  Using this feature can very substantially improve
14537           linking and load times of shared object libraries, produce more
14538           optimized code, provide near-perfect API export and prevent symbol
14539           clashes.  It is strongly recommended that you use this in any
14540           shared objects you distribute.
14541
14542           Despite the nomenclature, default always means public; i.e.,
14543           available to be linked against from outside the shared object.
14544           protected and internal are pretty useless in real-world usage so
14545           the only other commonly used option is hidden.  The default if
14546           -fvisibility isn't specified is default, i.e., make every symbol
14547           public.
14548
14549           A good explanation of the benefits offered by ensuring ELF symbols
14550           have the correct visibility is given by "How To Write Shared
14551           Libraries" by Ulrich Drepper (which can be found at
14552           <https://www.akkadia.org/drepper/>)---however a superior solution
14553           made possible by this option to marking things hidden when the
14554           default is public is to make the default hidden and mark things
14555           public.  This is the norm with DLLs on Windows and with
14556           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
14557           instead of "__declspec(dllexport)" you get almost identical
14558           semantics with identical syntax.  This is a great boon to those
14559           working with cross-platform projects.
14560
14561           For those adding visibility support to existing code, you may find
14562           "#pragma GCC visibility" of use.  This works by you enclosing the
14563           declarations you wish to set visibility for with (for example)
14564           "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility
14565           pop".  Bear in mind that symbol visibility should be viewed as part
14566           of the API interface contract and thus all new code should always
14567           specify visibility when it is not the default; i.e., declarations
14568           only for use within the local DSO should always be marked
14569           explicitly as hidden as so to avoid PLT indirection
14570           overheads---making this abundantly clear also aids readability and
14571           self-documentation of the code.  Note that due to ISO C++
14572           specification requirements, "operator new" and "operator delete"
14573           must always be of default visibility.
14574
14575           Be aware that headers from outside your project, in particular
14576           system headers and headers from any other library you use, may not
14577           be expecting to be compiled with visibility other than the default.
14578           You may need to explicitly say "#pragma GCC visibility
14579           push(default)" before including any such headers.
14580
14581           "extern" declarations are not affected by -fvisibility, so a lot of
14582           code can be recompiled with -fvisibility=hidden with no
14583           modifications.  However, this means that calls to "extern"
14584           functions with no explicit visibility use the PLT, so it is more
14585           effective to use "__attribute ((visibility))" and/or "#pragma GCC
14586           visibility" to tell the compiler which "extern" declarations should
14587           be treated as hidden.
14588
14589           Note that -fvisibility does affect C++ vague linkage entities. This
14590           means that, for instance, an exception class that is be thrown
14591           between DSOs must be explicitly marked with default visibility so
14592           that the type_info nodes are unified between the DSOs.
14593
14594           An overview of these techniques, their benefits and how to use them
14595           is at <http://gcc.gnu.org/wiki/Visibility>.
14596
14597       -fstrict-volatile-bitfields
14598           This option should be used if accesses to volatile bit-fields (or
14599           other structure fields, although the compiler usually honors those
14600           types anyway) should use a single access of the width of the
14601           field's type, aligned to a natural alignment if possible.  For
14602           example, targets with memory-mapped peripheral registers might
14603           require all such accesses to be 16 bits wide; with this flag you
14604           can declare all peripheral bit-fields as "unsigned short" (assuming
14605           short is 16 bits on these targets) to force GCC to use 16-bit
14606           accesses instead of, perhaps, a more efficient 32-bit access.
14607
14608           If this option is disabled, the compiler uses the most efficient
14609           instruction.  In the previous example, that might be a 32-bit load
14610           instruction, even though that accesses bytes that do not contain
14611           any portion of the bit-field, or memory-mapped registers unrelated
14612           to the one being updated.
14613
14614           In some cases, such as when the "packed" attribute is applied to a
14615           structure field, it may not be possible to access the field with a
14616           single read or write that is correctly aligned for the target
14617           machine.  In this case GCC falls back to generating multiple
14618           accesses rather than code that will fault or truncate the result at
14619           run time.
14620
14621           Note:  Due to restrictions of the C/C++11 memory model, write
14622           accesses are not allowed to touch non bit-field members.  It is
14623           therefore recommended to define all bits of the field's type as
14624           bit-field members.
14625
14626           The default value of this option is determined by the application
14627           binary interface for the target processor.
14628
14629       -fsync-libcalls
14630           This option controls whether any out-of-line instance of the
14631           "__sync" family of functions may be used to implement the C++11
14632           "__atomic" family of functions.
14633
14634           The default value of this option is enabled, thus the only useful
14635           form of the option is -fno-sync-libcalls.  This option is used in
14636           the implementation of the libatomic runtime library.
14637
14638   GCC Developer Options
14639       This section describes command-line options that are primarily of
14640       interest to GCC developers, including options to support compiler
14641       testing and investigation of compiler bugs and compile-time performance
14642       problems.  This includes options that produce debug dumps at various
14643       points in the compilation; that print statistics such as memory use and
14644       execution time; and that print information about GCC's configuration,
14645       such as where it searches for libraries.  You should rarely need to use
14646       any of these options for ordinary compilation and linking tasks.
14647
14648       Many developer options that cause GCC to dump output to a file take an
14649       optional =filename suffix. You can specify stdout or - to dump to
14650       standard output, and stderr for standard error.
14651
14652       If =filename is omitted, a default dump file name is constructed by
14653       concatenating the base dump file name, a pass number, phase letter, and
14654       pass name.  The base dump file name is the name of output file produced
14655       by the compiler if explicitly specified and not an executable;
14656       otherwise it is the source file name.  The pass number is determined by
14657       the order passes are registered with the compiler's pass manager.  This
14658       is generally the same as the order of execution, but passes registered
14659       by plugins, target-specific passes, or passes that are otherwise
14660       registered late are numbered higher than the pass named final, even if
14661       they are executed earlier.  The phase letter is one of i (inter-
14662       procedural analysis), l (language-specific), r (RTL), or t (tree).  The
14663       files are created in the directory of the output file.
14664
14665       -fcallgraph-info
14666       -fcallgraph-info=MARKERS
14667           Makes the compiler output callgraph information for the program, on
14668           a per-object-file basis.  The information is generated in the
14669           common VCG format.  It can be decorated with additional, per-node
14670           and/or per-edge information, if a list of comma-separated markers
14671           is additionally specified.  When the "su" marker is specified, the
14672           callgraph is decorated with stack usage information; it is
14673           equivalent to -fstack-usage.  When the "da" marker is specified,
14674           the callgraph is decorated with information about dynamically
14675           allocated objects.
14676
14677           When compiling with -flto, no callgraph information is output along
14678           with the object file.  At LTO link time, -fcallgraph-info may
14679           generate multiple callgraph information files next to intermediate
14680           LTO output files.
14681
14682       -dletters
14683       -fdump-rtl-pass
14684       -fdump-rtl-pass=filename
14685           Says to make debugging dumps during compilation at times specified
14686           by letters.  This is used for debugging the RTL-based passes of the
14687           compiler.
14688
14689           Some -dletters switches have different meaning when -E is used for
14690           preprocessing.
14691
14692           Debug dumps can be enabled with a -fdump-rtl switch or some -d
14693           option letters.  Here are the possible letters for use in pass and
14694           letters, and their meanings:
14695
14696           -fdump-rtl-alignments
14697               Dump after branch alignments have been computed.
14698
14699           -fdump-rtl-asmcons
14700               Dump after fixing rtl statements that have unsatisfied in/out
14701               constraints.
14702
14703           -fdump-rtl-auto_inc_dec
14704               Dump after auto-inc-dec discovery.  This pass is only run on
14705               architectures that have auto inc or auto dec instructions.
14706
14707           -fdump-rtl-barriers
14708               Dump after cleaning up the barrier instructions.
14709
14710           -fdump-rtl-bbpart
14711               Dump after partitioning hot and cold basic blocks.
14712
14713           -fdump-rtl-bbro
14714               Dump after block reordering.
14715
14716           -fdump-rtl-btl1
14717           -fdump-rtl-btl2
14718               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
14719               two branch target load optimization passes.
14720
14721           -fdump-rtl-bypass
14722               Dump after jump bypassing and control flow optimizations.
14723
14724           -fdump-rtl-combine
14725               Dump after the RTL instruction combination pass.
14726
14727           -fdump-rtl-compgotos
14728               Dump after duplicating the computed gotos.
14729
14730           -fdump-rtl-ce1
14731           -fdump-rtl-ce2
14732           -fdump-rtl-ce3
14733               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
14734               dumping after the three if conversion passes.
14735
14736           -fdump-rtl-cprop_hardreg
14737               Dump after hard register copy propagation.
14738
14739           -fdump-rtl-csa
14740               Dump after combining stack adjustments.
14741
14742           -fdump-rtl-cse1
14743           -fdump-rtl-cse2
14744               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
14745               two common subexpression elimination passes.
14746
14747           -fdump-rtl-dce
14748               Dump after the standalone dead code elimination passes.
14749
14750           -fdump-rtl-dbr
14751               Dump after delayed branch scheduling.
14752
14753           -fdump-rtl-dce1
14754           -fdump-rtl-dce2
14755               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
14756               two dead store elimination passes.
14757
14758           -fdump-rtl-eh
14759               Dump after finalization of EH handling code.
14760
14761           -fdump-rtl-eh_ranges
14762               Dump after conversion of EH handling range regions.
14763
14764           -fdump-rtl-expand
14765               Dump after RTL generation.
14766
14767           -fdump-rtl-fwprop1
14768           -fdump-rtl-fwprop2
14769               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
14770               the two forward propagation passes.
14771
14772           -fdump-rtl-gcse1
14773           -fdump-rtl-gcse2
14774               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
14775               global common subexpression elimination.
14776
14777           -fdump-rtl-init-regs
14778               Dump after the initialization of the registers.
14779
14780           -fdump-rtl-initvals
14781               Dump after the computation of the initial value sets.
14782
14783           -fdump-rtl-into_cfglayout
14784               Dump after converting to cfglayout mode.
14785
14786           -fdump-rtl-ira
14787               Dump after iterated register allocation.
14788
14789           -fdump-rtl-jump
14790               Dump after the second jump optimization.
14791
14792           -fdump-rtl-loop2
14793               -fdump-rtl-loop2 enables dumping after the rtl loop
14794               optimization passes.
14795
14796           -fdump-rtl-mach
14797               Dump after performing the machine dependent reorganization
14798               pass, if that pass exists.
14799
14800           -fdump-rtl-mode_sw
14801               Dump after removing redundant mode switches.
14802
14803           -fdump-rtl-rnreg
14804               Dump after register renumbering.
14805
14806           -fdump-rtl-outof_cfglayout
14807               Dump after converting from cfglayout mode.
14808
14809           -fdump-rtl-peephole2
14810               Dump after the peephole pass.
14811
14812           -fdump-rtl-postreload
14813               Dump after post-reload optimizations.
14814
14815           -fdump-rtl-pro_and_epilogue
14816               Dump after generating the function prologues and epilogues.
14817
14818           -fdump-rtl-sched1
14819           -fdump-rtl-sched2
14820               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
14821               the basic block scheduling passes.
14822
14823           -fdump-rtl-ree
14824               Dump after sign/zero extension elimination.
14825
14826           -fdump-rtl-seqabstr
14827               Dump after common sequence discovery.
14828
14829           -fdump-rtl-shorten
14830               Dump after shortening branches.
14831
14832           -fdump-rtl-sibling
14833               Dump after sibling call optimizations.
14834
14835           -fdump-rtl-split1
14836           -fdump-rtl-split2
14837           -fdump-rtl-split3
14838           -fdump-rtl-split4
14839           -fdump-rtl-split5
14840               These options enable dumping after five rounds of instruction
14841               splitting.
14842
14843           -fdump-rtl-sms
14844               Dump after modulo scheduling.  This pass is only run on some
14845               architectures.
14846
14847           -fdump-rtl-stack
14848               Dump after conversion from GCC's "flat register file" registers
14849               to the x87's stack-like registers.  This pass is only run on
14850               x86 variants.
14851
14852           -fdump-rtl-subreg1
14853           -fdump-rtl-subreg2
14854               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
14855               the two subreg expansion passes.
14856
14857           -fdump-rtl-unshare
14858               Dump after all rtl has been unshared.
14859
14860           -fdump-rtl-vartrack
14861               Dump after variable tracking.
14862
14863           -fdump-rtl-vregs
14864               Dump after converting virtual registers to hard registers.
14865
14866           -fdump-rtl-web
14867               Dump after live range splitting.
14868
14869           -fdump-rtl-regclass
14870           -fdump-rtl-subregs_of_mode_init
14871           -fdump-rtl-subregs_of_mode_finish
14872           -fdump-rtl-dfinit
14873           -fdump-rtl-dfinish
14874               These dumps are defined but always produce empty files.
14875
14876           -da
14877           -fdump-rtl-all
14878               Produce all the dumps listed above.
14879
14880           -dA Annotate the assembler output with miscellaneous debugging
14881               information.
14882
14883           -dD Dump all macro definitions, at the end of preprocessing, in
14884               addition to normal output.
14885
14886           -dH Produce a core dump whenever an error occurs.
14887
14888           -dp Annotate the assembler output with a comment indicating which
14889               pattern and alternative is used.  The length and cost of each
14890               instruction are also printed.
14891
14892           -dP Dump the RTL in the assembler output as a comment before each
14893               instruction.  Also turns on -dp annotation.
14894
14895           -dx Just generate RTL for a function instead of compiling it.
14896               Usually used with -fdump-rtl-expand.
14897
14898       -fdump-debug
14899           Dump debugging information generated during the debug generation
14900           phase.
14901
14902       -fdump-earlydebug
14903           Dump debugging information generated during the early debug
14904           generation phase.
14905
14906       -fdump-noaddr
14907           When doing debugging dumps, suppress address output.  This makes it
14908           more feasible to use diff on debugging dumps for compiler
14909           invocations with different compiler binaries and/or different text
14910           / bss / data / heap / stack / dso start locations.
14911
14912       -freport-bug
14913           Collect and dump debug information into a temporary file if an
14914           internal compiler error (ICE) occurs.
14915
14916       -fdump-unnumbered
14917           When doing debugging dumps, suppress instruction numbers and
14918           address output.  This makes it more feasible to use diff on
14919           debugging dumps for compiler invocations with different options, in
14920           particular with and without -g.
14921
14922       -fdump-unnumbered-links
14923           When doing debugging dumps (see -d option above), suppress
14924           instruction numbers for the links to the previous and next
14925           instructions in a sequence.
14926
14927       -fdump-ipa-switch
14928       -fdump-ipa-switch-options
14929           Control the dumping at various stages of inter-procedural analysis
14930           language tree to a file.  The file name is generated by appending a
14931           switch specific suffix to the source file name, and the file is
14932           created in the same directory as the output file.  The following
14933           dumps are possible:
14934
14935           all Enables all inter-procedural analysis dumps.
14936
14937           cgraph
14938               Dumps information about call-graph optimization, unused
14939               function removal, and inlining decisions.
14940
14941           inline
14942               Dump after function inlining.
14943
14944           Additionally, the options -optimized, -missed, -note, and -all can
14945           be provided, with the same meaning as for -fopt-info, defaulting to
14946           -optimized.
14947
14948           For example, -fdump-ipa-inline-optimized-missed will emit
14949           information on callsites that were inlined, along with callsites
14950           that were not inlined.
14951
14952           By default, the dump will contain messages about successful
14953           optimizations (equivalent to -optimized) together with low-level
14954           details about the analysis.
14955
14956       -fdump-lang
14957           Dump language-specific information.  The file name is made by
14958           appending .lang to the source file name.
14959
14960       -fdump-lang-all
14961       -fdump-lang-switch
14962       -fdump-lang-switch-options
14963       -fdump-lang-switch-options=filename
14964           Control the dumping of language-specific information.  The options
14965           and filename portions behave as described in the -fdump-tree
14966           option.  The following switch values are accepted:
14967
14968           all Enable all language-specific dumps.
14969
14970           class
14971               Dump class hierarchy information.  Virtual table information is
14972               emitted unless 'slim' is specified.  This option is applicable
14973               to C++ only.
14974
14975           module
14976               Dump module information.  Options lineno (locations), graph
14977               (reachability), blocks (clusters), uid (serialization), alias
14978               (mergeable), asmname (Elrond), eh (mapper) & vops (macros) may
14979               provide additional information.  This option is applicable to
14980               C++ only.
14981
14982           raw Dump the raw internal tree data.  This option is applicable to
14983               C++ only.
14984
14985       -fdump-passes
14986           Print on stderr the list of optimization passes that are turned on
14987           and off by the current command-line options.
14988
14989       -fdump-statistics-option
14990           Enable and control dumping of pass statistics in a separate file.
14991           The file name is generated by appending a suffix ending in
14992           .statistics to the source file name, and the file is created in the
14993           same directory as the output file.  If the -option form is used,
14994           -stats causes counters to be summed over the whole compilation unit
14995           while -details dumps every event as the passes generate them.  The
14996           default with no option is to sum counters for each function
14997           compiled.
14998
14999       -fdump-tree-all
15000       -fdump-tree-switch
15001       -fdump-tree-switch-options
15002       -fdump-tree-switch-options=filename
15003           Control the dumping at various stages of processing the
15004           intermediate language tree to a file.  If the -options form is
15005           used, options is a list of - separated options which control the
15006           details of the dump.  Not all options are applicable to all dumps;
15007           those that are not meaningful are ignored.  The following options
15008           are available
15009
15010           address
15011               Print the address of each node.  Usually this is not meaningful
15012               as it changes according to the environment and source file.
15013               Its primary use is for tying up a dump file with a debug
15014               environment.
15015
15016           asmname
15017               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
15018               that in the dump instead of "DECL_NAME".  Its primary use is
15019               ease of use working backward from mangled names in the assembly
15020               file.
15021
15022           slim
15023               When dumping front-end intermediate representations, inhibit
15024               dumping of members of a scope or body of a function merely
15025               because that scope has been reached.  Only dump such items when
15026               they are directly reachable by some other path.
15027
15028               When dumping pretty-printed trees, this option inhibits dumping
15029               the bodies of control structures.
15030
15031               When dumping RTL, print the RTL in slim (condensed) form
15032               instead of the default LISP-like representation.
15033
15034           raw Print a raw representation of the tree.  By default, trees are
15035               pretty-printed into a C-like representation.
15036
15037           details
15038               Enable more detailed dumps (not honored by every dump option).
15039               Also include information from the optimization passes.
15040
15041           stats
15042               Enable dumping various statistics about the pass (not honored
15043               by every dump option).
15044
15045           blocks
15046               Enable showing basic block boundaries (disabled in raw dumps).
15047
15048           graph
15049               For each of the other indicated dump files (-fdump-rtl-pass),
15050               dump a representation of the control flow graph suitable for
15051               viewing with GraphViz to file.passid.pass.dot.  Each function
15052               in the file is pretty-printed as a subgraph, so that GraphViz
15053               can render them all in a single plot.
15054
15055               This option currently only works for RTL dumps, and the RTL is
15056               always dumped in slim form.
15057
15058           vops
15059               Enable showing virtual operands for every statement.
15060
15061           lineno
15062               Enable showing line numbers for statements.
15063
15064           uid Enable showing the unique ID ("DECL_UID") for each variable.
15065
15066           verbose
15067               Enable showing the tree dump for each statement.
15068
15069           eh  Enable showing the EH region number holding each statement.
15070
15071           scev
15072               Enable showing scalar evolution analysis details.
15073
15074           optimized
15075               Enable showing optimization information (only available in
15076               certain passes).
15077
15078           missed
15079               Enable showing missed optimization information (only available
15080               in certain passes).
15081
15082           note
15083               Enable other detailed optimization information (only available
15084               in certain passes).
15085
15086           all Turn on all options, except raw, slim, verbose and lineno.
15087
15088           optall
15089               Turn on all optimization options, i.e., optimized, missed, and
15090               note.
15091
15092           To determine what tree dumps are available or find the dump for a
15093           pass of interest follow the steps below.
15094
15095           1.  Invoke GCC with -fdump-passes and in the stderr output look for
15096               a code that corresponds to the pass you are interested in.  For
15097               example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2"
15098               correspond to the three Value Range Propagation passes.  The
15099               number at the end distinguishes distinct invocations of the
15100               same pass.
15101
15102           2.  To enable the creation of the dump file, append the pass code
15103               to the -fdump- option prefix and invoke GCC with it.  For
15104               example, to enable the dump from the Early Value Range
15105               Propagation pass, invoke GCC with the -fdump-tree-evrp option.
15106               Optionally, you may specify the name of the dump file.  If you
15107               don't specify one, GCC creates as described below.
15108
15109           3.  Find the pass dump in a file whose name is composed of three
15110               components separated by a period: the name of the source file
15111               GCC was invoked to compile, a numeric suffix indicating the
15112               pass number followed by the letter t for tree passes (and the
15113               letter r for RTL passes), and finally the pass code.  For
15114               example, the Early VRP pass dump might be in a file named
15115               myfile.c.038t.evrp in the current working directory.  Note that
15116               the numeric codes are not stable and may change from one
15117               version of GCC to another.
15118
15119       -fopt-info
15120       -fopt-info-options
15121       -fopt-info-options=filename
15122           Controls optimization dumps from various optimization passes. If
15123           the -options form is used, options is a list of - separated option
15124           keywords to select the dump details and optimizations.
15125
15126           The options can be divided into three groups:
15127
15128           1.  options describing what kinds of messages should be emitted,
15129
15130           2.  options describing the verbosity of the dump, and
15131
15132           3.  options describing which optimizations should be included.
15133
15134           The options from each group can be freely mixed as they are non-
15135           overlapping. However, in case of any conflicts, the later options
15136           override the earlier options on the command line.
15137
15138           The following options control which kinds of messages should be
15139           emitted:
15140
15141           optimized
15142               Print information when an optimization is successfully applied.
15143               It is up to a pass to decide which information is relevant. For
15144               example, the vectorizer passes print the source location of
15145               loops which are successfully vectorized.
15146
15147           missed
15148               Print information about missed optimizations. Individual passes
15149               control which information to include in the output.
15150
15151           note
15152               Print verbose information about optimizations, such as certain
15153               transformations, more detailed messages about decisions etc.
15154
15155           all Print detailed optimization information. This includes
15156               optimized, missed, and note.
15157
15158           The following option controls the dump verbosity:
15159
15160           internals
15161               By default, only "high-level" messages are emitted. This option
15162               enables additional, more detailed, messages, which are likely
15163               to only be of interest to GCC developers.
15164
15165           One or more of the following option keywords can be used to
15166           describe a group of optimizations:
15167
15168           ipa Enable dumps from all interprocedural optimizations.
15169
15170           loop
15171               Enable dumps from all loop optimizations.
15172
15173           inline
15174               Enable dumps from all inlining optimizations.
15175
15176           omp Enable dumps from all OMP (Offloading and Multi Processing)
15177               optimizations.
15178
15179           vec Enable dumps from all vectorization optimizations.
15180
15181           optall
15182               Enable dumps from all optimizations. This is a superset of the
15183               optimization groups listed above.
15184
15185           If options is omitted, it defaults to optimized-optall, which means
15186           to dump messages about successful optimizations from all the
15187           passes, omitting messages that are treated as "internals".
15188
15189           If the filename is provided, then the dumps from all the applicable
15190           optimizations are concatenated into the filename.  Otherwise the
15191           dump is output onto stderr. Though multiple -fopt-info options are
15192           accepted, only one of them can include a filename. If other
15193           filenames are provided then all but the first such option are
15194           ignored.
15195
15196           Note that the output filename is overwritten in case of multiple
15197           translation units. If a combined output from multiple translation
15198           units is desired, stderr should be used instead.
15199
15200           In the following example, the optimization info is output to
15201           stderr:
15202
15203                   gcc -O3 -fopt-info
15204
15205           This example:
15206
15207                   gcc -O3 -fopt-info-missed=missed.all
15208
15209           outputs missed optimization report from all the passes into
15210           missed.all, and this one:
15211
15212                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed
15213
15214           prints information about missed optimization opportunities from
15215           vectorization passes on stderr.  Note that -fopt-info-vec-missed is
15216           equivalent to -fopt-info-missed-vec.  The order of the optimization
15217           group names and message types listed after -fopt-info does not
15218           matter.
15219
15220           As another example,
15221
15222                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
15223
15224           outputs information about missed optimizations as well as optimized
15225           locations from all the inlining passes into inline.txt.
15226
15227           Finally, consider:
15228
15229                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
15230
15231           Here the two output filenames vec.miss and loop.opt are in conflict
15232           since only one output file is allowed. In this case, only the first
15233           option takes effect and the subsequent options are ignored. Thus
15234           only vec.miss is produced which contains dumps from the vectorizer
15235           about missed opportunities.
15236
15237       -fsave-optimization-record
15238           Write a SRCFILE.opt-record.json.gz file detailing what
15239           optimizations were performed, for those optimizations that support
15240           -fopt-info.
15241
15242           This option is experimental and the format of the data within the
15243           compressed JSON file is subject to change.
15244
15245           It is roughly equivalent to a machine-readable version of
15246           -fopt-info-all, as a collection of messages with source file, line
15247           number and column number, with the following additional data for
15248           each message:
15249
15250           *   the execution count of the code being optimized, along with
15251               metadata about whether this was from actual profile data, or
15252               just an estimate, allowing consumers to prioritize messages by
15253               code hotness,
15254
15255           *   the function name of the code being optimized, where
15256               applicable,
15257
15258           *   the "inlining chain" for the code being optimized, so that when
15259               a function is inlined into several different places (which
15260               might themselves be inlined), the reader can distinguish
15261               between the copies,
15262
15263           *   objects identifying those parts of the message that refer to
15264               expressions, statements or symbol-table nodes, which of these
15265               categories they are, and, when available, their source code
15266               location,
15267
15268           *   the GCC pass that emitted the message, and
15269
15270           *   the location in GCC's own code from which the message was
15271               emitted
15272
15273           Additionally, some messages are logically nested within other
15274           messages, reflecting implementation details of the optimization
15275           passes.
15276
15277       -fsched-verbose=n
15278           On targets that use instruction scheduling, this option controls
15279           the amount of debugging output the scheduler prints to the dump
15280           files.
15281
15282           For n greater than zero, -fsched-verbose outputs the same
15283           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
15284           greater than one, it also output basic block probabilities,
15285           detailed ready list information and unit/insn info.  For n greater
15286           than two, it includes RTL at abort point, control-flow and regions
15287           info.  And for n over four, -fsched-verbose also includes
15288           dependence info.
15289
15290       -fenable-kind-pass
15291       -fdisable-kind-pass=range-list
15292           This is a set of options that are used to explicitly disable/enable
15293           optimization passes.  These options are intended for use for
15294           debugging GCC.  Compiler users should use regular options for
15295           enabling/disabling passes instead.
15296
15297           -fdisable-ipa-pass
15298               Disable IPA pass pass. pass is the pass name.  If the same pass
15299               is statically invoked in the compiler multiple times, the pass
15300               name should be appended with a sequential number starting from
15301               1.
15302
15303           -fdisable-rtl-pass
15304           -fdisable-rtl-pass=range-list
15305               Disable RTL pass pass.  pass is the pass name.  If the same
15306               pass is statically invoked in the compiler multiple times, the
15307               pass name should be appended with a sequential number starting
15308               from 1.  range-list is a comma-separated list of function
15309               ranges or assembler names.  Each range is a number pair
15310               separated by a colon.  The range is inclusive in both ends.  If
15311               the range is trivial, the number pair can be simplified as a
15312               single number.  If the function's call graph node's uid falls
15313               within one of the specified ranges, the pass is disabled for
15314               that function.  The uid is shown in the function header of a
15315               dump file, and the pass names can be dumped by using option
15316               -fdump-passes.
15317
15318           -fdisable-tree-pass
15319           -fdisable-tree-pass=range-list
15320               Disable tree pass pass.  See -fdisable-rtl for the description
15321               of option arguments.
15322
15323           -fenable-ipa-pass
15324               Enable IPA pass pass.  pass is the pass name.  If the same pass
15325               is statically invoked in the compiler multiple times, the pass
15326               name should be appended with a sequential number starting from
15327               1.
15328
15329           -fenable-rtl-pass
15330           -fenable-rtl-pass=range-list
15331               Enable RTL pass pass.  See -fdisable-rtl for option argument
15332               description and examples.
15333
15334           -fenable-tree-pass
15335           -fenable-tree-pass=range-list
15336               Enable tree pass pass.  See -fdisable-rtl for the description
15337               of option arguments.
15338
15339           Here are some examples showing uses of these options.
15340
15341                   # disable ccp1 for all functions
15342                      -fdisable-tree-ccp1
15343                   # disable complete unroll for function whose cgraph node uid is 1
15344                      -fenable-tree-cunroll=1
15345                   # disable gcse2 for functions at the following ranges [1,1],
15346                   # [300,400], and [400,1000]
15347                   # disable gcse2 for functions foo and foo2
15348                      -fdisable-rtl-gcse2=foo,foo2
15349                   # disable early inlining
15350                      -fdisable-tree-einline
15351                   # disable ipa inlining
15352                      -fdisable-ipa-inline
15353                   # enable tree full unroll
15354                      -fenable-tree-unroll
15355
15356       -fchecking
15357       -fchecking=n
15358           Enable internal consistency checking.  The default depends on the
15359           compiler configuration.  -fchecking=2 enables further internal
15360           consistency checking that might affect code generation.
15361
15362       -frandom-seed=string
15363           This option provides a seed that GCC uses in place of random
15364           numbers in generating certain symbol names that have to be
15365           different in every compiled file.  It is also used to place unique
15366           stamps in coverage data files and the object files that produce
15367           them.  You can use the -frandom-seed option to produce reproducibly
15368           identical object files.
15369
15370           The string can either be a number (decimal, octal or hex) or an
15371           arbitrary string (in which case it's converted to a number by
15372           computing CRC32).
15373
15374           The string should be different for every file you compile.
15375
15376       -save-temps
15377           Store the usual "temporary" intermediate files permanently; name
15378           them as auxiliary output files, as specified described under
15379           -dumpbase and -dumpdir.
15380
15381           When used in combination with the -x command-line option,
15382           -save-temps is sensible enough to avoid overwriting an input source
15383           file with the same extension as an intermediate file.  The
15384           corresponding intermediate file may be obtained by renaming the
15385           source file before using -save-temps.
15386
15387       -save-temps=cwd
15388           Equivalent to -save-temps -dumpdir ./.
15389
15390       -save-temps=obj
15391           Equivalent to -save-temps -dumpdir outdir/, where outdir/ is the
15392           directory of the output file specified after the -o option,
15393           including any directory separators.  If the -o option is not used,
15394           the -save-temps=obj switch behaves like -save-temps=cwd.
15395
15396       -time[=file]
15397           Report the CPU time taken by each subprocess in the compilation
15398           sequence.  For C source files, this is the compiler proper and
15399           assembler (plus the linker if linking is done).
15400
15401           Without the specification of an output file, the output looks like
15402           this:
15403
15404                   # cc1 0.12 0.01
15405                   # as 0.00 0.01
15406
15407           The first number on each line is the "user time", that is time
15408           spent executing the program itself.  The second number is "system
15409           time", time spent executing operating system routines on behalf of
15410           the program.  Both numbers are in seconds.
15411
15412           With the specification of an output file, the output is appended to
15413           the named file, and it looks like this:
15414
15415                   0.12 0.01 cc1 <options>
15416                   0.00 0.01 as <options>
15417
15418           The "user time" and the "system time" are moved before the program
15419           name, and the options passed to the program are displayed, so that
15420           one can later tell what file was being compiled, and with which
15421           options.
15422
15423       -fdump-final-insns[=file]
15424           Dump the final internal representation (RTL) to file.  If the
15425           optional argument is omitted (or if file is "."), the name of the
15426           dump file is determined by appending ".gkd" to the dump base name,
15427           see -dumpbase.
15428
15429       -fcompare-debug[=opts]
15430           If no error occurs during compilation, run the compiler a second
15431           time, adding opts and -fcompare-debug-second to the arguments
15432           passed to the second compilation.  Dump the final internal
15433           representation in both compilations, and print an error if they
15434           differ.
15435
15436           If the equal sign is omitted, the default -gtoggle is used.
15437
15438           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
15439           and nonzero, implicitly enables -fcompare-debug.  If
15440           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
15441           it is used for opts, otherwise the default -gtoggle is used.
15442
15443           -fcompare-debug=, with the equal sign but without opts, is
15444           equivalent to -fno-compare-debug, which disables the dumping of the
15445           final representation and the second compilation, preventing even
15446           GCC_COMPARE_DEBUG from taking effect.
15447
15448           To verify full coverage during -fcompare-debug testing, set
15449           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
15450           rejects as an invalid option in any actual compilation (rather than
15451           preprocessing, assembly or linking).  To get just a warning,
15452           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
15453           will do.
15454
15455       -fcompare-debug-second
15456           This option is implicitly passed to the compiler for the second
15457           compilation requested by -fcompare-debug, along with options to
15458           silence warnings, and omitting other options that would cause the
15459           compiler to produce output to files or to standard output as a side
15460           effect.  Dump files and preserved temporary files are renamed so as
15461           to contain the ".gk" additional extension during the second
15462           compilation, to avoid overwriting those generated by the first.
15463
15464           When this option is passed to the compiler driver, it causes the
15465           first compilation to be skipped, which makes it useful for little
15466           other than debugging the compiler proper.
15467
15468       -gtoggle
15469           Turn off generation of debug info, if leaving out this option
15470           generates it, or turn it on at level 2 otherwise.  The position of
15471           this argument in the command line does not matter; it takes effect
15472           after all other options are processed, and it does so only once, no
15473           matter how many times it is given.  This is mainly intended to be
15474           used with -fcompare-debug.
15475
15476       -fvar-tracking-assignments-toggle
15477           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
15478           toggles -g.
15479
15480       -Q  Makes the compiler print out each function name as it is compiled,
15481           and print some statistics about each pass when it finishes.
15482
15483       -ftime-report
15484           Makes the compiler print some statistics about the time consumed by
15485           each pass when it finishes.
15486
15487       -ftime-report-details
15488           Record the time consumed by infrastructure parts separately for
15489           each pass.
15490
15491       -fira-verbose=n
15492           Control the verbosity of the dump file for the integrated register
15493           allocator.  The default value is 5.  If the value n is greater or
15494           equal to 10, the dump output is sent to stderr using the same
15495           format as n minus 10.
15496
15497       -flto-report
15498           Prints a report with internal details on the workings of the link-
15499           time optimizer.  The contents of this report vary from version to
15500           version.  It is meant to be useful to GCC developers when
15501           processing object files in LTO mode (via -flto).
15502
15503           Disabled by default.
15504
15505       -flto-report-wpa
15506           Like -flto-report, but only print for the WPA phase of link-time
15507           optimization.
15508
15509       -fmem-report
15510           Makes the compiler print some statistics about permanent memory
15511           allocation when it finishes.
15512
15513       -fmem-report-wpa
15514           Makes the compiler print some statistics about permanent memory
15515           allocation for the WPA phase only.
15516
15517       -fpre-ipa-mem-report
15518       -fpost-ipa-mem-report
15519           Makes the compiler print some statistics about permanent memory
15520           allocation before or after interprocedural optimization.
15521
15522       -fprofile-report
15523           Makes the compiler print some statistics about consistency of the
15524           (estimated) profile and effect of individual passes.
15525
15526       -fstack-usage
15527           Makes the compiler output stack usage information for the program,
15528           on a per-function basis.  The filename for the dump is made by
15529           appending .su to the auxname.  auxname is generated from the name
15530           of the output file, if explicitly specified and it is not an
15531           executable, otherwise it is the basename of the source file.  An
15532           entry is made up of three fields:
15533
15534           *   The name of the function.
15535
15536           *   A number of bytes.
15537
15538           *   One or more qualifiers: "static", "dynamic", "bounded".
15539
15540           The qualifier "static" means that the function manipulates the
15541           stack statically: a fixed number of bytes are allocated for the
15542           frame on function entry and released on function exit; no stack
15543           adjustments are otherwise made in the function.  The second field
15544           is this fixed number of bytes.
15545
15546           The qualifier "dynamic" means that the function manipulates the
15547           stack dynamically: in addition to the static allocation described
15548           above, stack adjustments are made in the body of the function, for
15549           example to push/pop arguments around function calls.  If the
15550           qualifier "bounded" is also present, the amount of these
15551           adjustments is bounded at compile time and the second field is an
15552           upper bound of the total amount of stack used by the function.  If
15553           it is not present, the amount of these adjustments is not bounded
15554           at compile time and the second field only represents the bounded
15555           part.
15556
15557       -fstats
15558           Emit statistics about front-end processing at the end of the
15559           compilation.  This option is supported only by the C++ front end,
15560           and the information is generally only useful to the G++ development
15561           team.
15562
15563       -fdbg-cnt-list
15564           Print the name and the counter upper bound for all debug counters.
15565
15566       -fdbg-cnt=counter-value-list
15567           Set the internal debug counter lower and upper bound.  counter-
15568           value-list is a comma-separated list of
15569           name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...]
15570           tuples which sets the name of the counter and list of closed
15571           intervals.  The lower_bound is optional and is zero initialized if
15572           not set.  For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10,
15573           "dbg_cnt(dce)" returns true only for second, third, fourth, tenth
15574           and eleventh invocation.  For "dbg_cnt(tail_call)" true is returned
15575           for first 10 invocations.
15576
15577       -print-file-name=library
15578           Print the full absolute name of the library file library that would
15579           be used when linking---and don't do anything else.  With this
15580           option, GCC does not compile or link anything; it just prints the
15581           file name.
15582
15583       -print-multi-directory
15584           Print the directory name corresponding to the multilib selected by
15585           any other switches present in the command line.  This directory is
15586           supposed to exist in GCC_EXEC_PREFIX.
15587
15588       -print-multi-lib
15589           Print the mapping from multilib directory names to compiler
15590           switches that enable them.  The directory name is separated from
15591           the switches by ;, and each switch starts with an @ instead of the
15592           -, without spaces between multiple switches.  This is supposed to
15593           ease shell processing.
15594
15595       -print-multi-os-directory
15596           Print the path to OS libraries for the selected multilib, relative
15597           to some lib subdirectory.  If OS libraries are present in the lib
15598           subdirectory and no multilibs are used, this is usually just ., if
15599           OS libraries are present in libsuffix sibling directories this
15600           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
15601           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
15602           or ev6.
15603
15604       -print-multiarch
15605           Print the path to OS libraries for the selected multiarch, relative
15606           to some lib subdirectory.
15607
15608       -print-prog-name=program
15609           Like -print-file-name, but searches for a program such as cpp.
15610
15611       -print-libgcc-file-name
15612           Same as -print-file-name=libgcc.a.
15613
15614           This is useful when you use -nostdlib or -nodefaultlibs but you do
15615           want to link with libgcc.a.  You can do:
15616
15617                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`
15618
15619       -print-search-dirs
15620           Print the name of the configured installation directory and a list
15621           of program and library directories gcc searches---and don't do
15622           anything else.
15623
15624           This is useful when gcc prints the error message installation
15625           problem, cannot exec cpp0: No such file or directory.  To resolve
15626           this you either need to put cpp0 and the other compiler components
15627           where gcc expects to find them, or you can set the environment
15628           variable GCC_EXEC_PREFIX to the directory where you installed them.
15629           Don't forget the trailing /.
15630
15631       -print-sysroot
15632           Print the target sysroot directory that is used during compilation.
15633           This is the target sysroot specified either at configure time or
15634           using the --sysroot option, possibly with an extra suffix that
15635           depends on compilation options.  If no target sysroot is specified,
15636           the option prints nothing.
15637
15638       -print-sysroot-headers-suffix
15639           Print the suffix added to the target sysroot when searching for
15640           headers, or give an error if the compiler is not configured with
15641           such a suffix---and don't do anything else.
15642
15643       -dumpmachine
15644           Print the compiler's target machine (for example,
15645           i686-pc-linux-gnu)---and don't do anything else.
15646
15647       -dumpversion
15648           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and
15649           don't do anything else.  This is the compiler version used in
15650           filesystem paths and specs. Depending on how the compiler has been
15651           configured it can be just a single number (major version), two
15652           numbers separated by a dot (major and minor version) or three
15653           numbers separated by dots (major, minor and patchlevel version).
15654
15655       -dumpfullversion
15656           Print the full compiler version---and don't do anything else. The
15657           output is always three numbers separated by dots, major, minor and
15658           patchlevel version.
15659
15660       -dumpspecs
15661           Print the compiler's built-in specs---and don't do anything else.
15662           (This is used when GCC itself is being built.)
15663
15664   Machine-Dependent Options
15665       Each target machine supported by GCC can have its own options---for
15666       example, to allow you to compile for a particular processor variant or
15667       ABI, or to control optimizations specific to that machine.  By
15668       convention, the names of machine-specific options start with -m.
15669
15670       Some configurations of the compiler also support additional target-
15671       specific options, usually for compatibility with other compilers on the
15672       same platform.
15673
15674   AArch64 Options
15675       These options are defined for AArch64 implementations:
15676
15677       -mabi=name
15678           Generate code for the specified data model.  Permissible values are
15679           ilp32 for SysV-like data model where int, long int and pointers are
15680           32 bits, and lp64 for SysV-like data model where int is 32 bits,
15681           but long int and pointers are 64 bits.
15682
15683           The default depends on the specific target configuration.  Note
15684           that the LP64 and ILP32 ABIs are not link-compatible; you must
15685           compile your entire program with the same ABI, and link with a
15686           compatible set of libraries.
15687
15688       -mbig-endian
15689           Generate big-endian code.  This is the default when GCC is
15690           configured for an aarch64_be-*-* target.
15691
15692       -mgeneral-regs-only
15693           Generate code which uses only the general-purpose registers.  This
15694           will prevent the compiler from using floating-point and Advanced
15695           SIMD registers but will not impose any restrictions on the
15696           assembler.
15697
15698       -mlittle-endian
15699           Generate little-endian code.  This is the default when GCC is
15700           configured for an aarch64-*-* but not an aarch64_be-*-* target.
15701
15702       -mcmodel=tiny
15703           Generate code for the tiny code model.  The program and its
15704           statically defined symbols must be within 1MB of each other.
15705           Programs can be statically or dynamically linked.
15706
15707       -mcmodel=small
15708           Generate code for the small code model.  The program and its
15709           statically defined symbols must be within 4GB of each other.
15710           Programs can be statically or dynamically linked.  This is the
15711           default code model.
15712
15713       -mcmodel=large
15714           Generate code for the large code model.  This makes no assumptions
15715           about addresses and sizes of sections.  Programs can be statically
15716           linked only.  The -mcmodel=large option is incompatible with
15717           -mabi=ilp32, -fpic and -fPIC.
15718
15719       -mstrict-align
15720       -mno-strict-align
15721           Avoid or allow generating memory accesses that may not be aligned
15722           on a natural object boundary as described in the architecture
15723           specification.
15724
15725       -momit-leaf-frame-pointer
15726       -mno-omit-leaf-frame-pointer
15727           Omit or keep the frame pointer in leaf functions.  The former
15728           behavior is the default.
15729
15730       -mstack-protector-guard=guard
15731       -mstack-protector-guard-reg=reg
15732       -mstack-protector-guard-offset=offset
15733           Generate stack protection code using canary at guard.  Supported
15734           locations are global for a global canary or sysreg for a canary in
15735           an appropriate system register.
15736
15737           With the latter choice the options -mstack-protector-guard-reg=reg
15738           and -mstack-protector-guard-offset=offset furthermore specify which
15739           system register to use as base register for reading the canary, and
15740           from what offset from that base register. There is no default
15741           register or offset as this is entirely for use within the Linux
15742           kernel.
15743
15744       -mtls-dialect=desc
15745           Use TLS descriptors as the thread-local storage mechanism for
15746           dynamic accesses of TLS variables.  This is the default.
15747
15748       -mtls-dialect=traditional
15749           Use traditional TLS as the thread-local storage mechanism for
15750           dynamic accesses of TLS variables.
15751
15752       -mtls-size=size
15753           Specify bit size of immediate TLS offsets.  Valid values are 12,
15754           24, 32, 48.  This option requires binutils 2.26 or newer.
15755
15756       -mfix-cortex-a53-835769
15757       -mno-fix-cortex-a53-835769
15758           Enable or disable the workaround for the ARM Cortex-A53 erratum
15759           number 835769.  This involves inserting a NOP instruction between
15760           memory instructions and 64-bit integer multiply-accumulate
15761           instructions.
15762
15763       -mfix-cortex-a53-843419
15764       -mno-fix-cortex-a53-843419
15765           Enable or disable the workaround for the ARM Cortex-A53 erratum
15766           number 843419.  This erratum workaround is made at link time and
15767           this will only pass the corresponding flag to the linker.
15768
15769       -mlow-precision-recip-sqrt
15770       -mno-low-precision-recip-sqrt
15771           Enable or disable the reciprocal square root approximation.  This
15772           option only has an effect if -ffast-math or
15773           -funsafe-math-optimizations is used as well.  Enabling this reduces
15774           precision of reciprocal square root results to about 16 bits for
15775           single precision and to 32 bits for double precision.
15776
15777       -mlow-precision-sqrt
15778       -mno-low-precision-sqrt
15779           Enable or disable the square root approximation.  This option only
15780           has an effect if -ffast-math or -funsafe-math-optimizations is used
15781           as well.  Enabling this reduces precision of square root results to
15782           about 16 bits for single precision and to 32 bits for double
15783           precision.  If enabled, it implies -mlow-precision-recip-sqrt.
15784
15785       -mlow-precision-div
15786       -mno-low-precision-div
15787           Enable or disable the division approximation.  This option only has
15788           an effect if -ffast-math or -funsafe-math-optimizations is used as
15789           well.  Enabling this reduces precision of division results to about
15790           16 bits for single precision and to 32 bits for double precision.
15791
15792       -mtrack-speculation
15793       -mno-track-speculation
15794           Enable or disable generation of additional code to track
15795           speculative execution through conditional branches.  The tracking
15796           state can then be used by the compiler when expanding calls to
15797           "__builtin_speculation_safe_copy" to permit a more efficient code
15798           sequence to be generated.
15799
15800       -moutline-atomics
15801       -mno-outline-atomics
15802           Enable or disable calls to out-of-line helpers to implement atomic
15803           operations.  These helpers will, at runtime, determine if the LSE
15804           instructions from ARMv8.1-A can be used; if not, they will use the
15805           load/store-exclusive instructions that are present in the base
15806           ARMv8.0 ISA.
15807
15808           This option is only applicable when compiling for the base ARMv8.0
15809           instruction set.  If using a later revision, e.g. -march=armv8.1-a
15810           or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be
15811           used directly.  The same applies when using -mcpu= when the
15812           selected cpu supports the lse feature.  This option is on by
15813           default.
15814
15815       -march=name
15816           Specify the name of the target architecture and, optionally, one or
15817           more feature modifiers.  This option has the form
15818           -march=arch{+[no]feature}*.
15819
15820           The table below summarizes the permissible values for arch and the
15821           features that they enable by default:
15822
15823           arch value : Architecture : Includes by default
15824           armv8-a : Armv8-A : +fp, +simd
15825           armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
15826           armv8.2-a : Armv8.2-A : armv8.1-a
15827           armv8.3-a : Armv8.3-A : armv8.2-a, +pauth
15828           armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod
15829           armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres
15830           armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm
15831           armv8-r : Armv8-R : armv8-r
15832
15833           The value native is available on native AArch64 GNU/Linux and
15834           causes the compiler to pick the architecture of the host system.
15835           This option has no effect if the compiler is unable to recognize
15836           the architecture of the host system,
15837
15838           The permissible values for feature are listed in the sub-section on
15839           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
15840           Where conflicting feature modifiers are specified, the right-most
15841           feature is used.
15842
15843           GCC uses name to determine what kind of instructions it can emit
15844           when generating assembly code.  If -march is specified without
15845           either of -mtune or -mcpu also being specified, the code is tuned
15846           to perform well across a range of target processors implementing
15847           the target architecture.
15848
15849       -mtune=name
15850           Specify the name of the target processor for which GCC should tune
15851           the performance of the code.  Permissible values for this option
15852           are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
15853           cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae,
15854           cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, cortex-a78,
15855           cortex-a78ae, cortex-a78c, ares, exynos-m1, emag, falkor,
15856           neoverse-e1, neoverse-n1, neoverse-n2, neoverse-v1, qdf24xx,
15857           saphira, phecda, xgene1, vulcan, octeontx, octeontx81,  octeontx83,
15858           octeontx2, octeontx2t98, octeontx2t96 octeontx2t93, octeontx2f95,
15859           octeontx2f95n, octeontx2f95mm, a64fx, thunderx, thunderxt88,
15860           thunderxt88p1, thunderxt81, tsv110, thunderxt83, thunderx2t99,
15861           thunderx3t110, zeus, cortex-a57.cortex-a53, cortex-a72.cortex-a53,
15862           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
15863           cortex-a75.cortex-a55, cortex-a76.cortex-a55, cortex-r82,
15864           cortex-x1, native.
15865
15866           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
15867           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
15868           cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC
15869           should tune for a big.LITTLE system.
15870
15871           Additionally on native AArch64 GNU/Linux systems the value native
15872           tunes performance to the host system.  This option has no effect if
15873           the compiler is unable to recognize the processor of the host
15874           system.
15875
15876           Where none of -mtune=, -mcpu= or -march= are specified, the code is
15877           tuned to perform well across a range of target processors.
15878
15879           This option cannot be suffixed by feature modifiers.
15880
15881       -mcpu=name
15882           Specify the name of the target processor, optionally suffixed by
15883           one or more feature modifiers.  This option has the form
15884           -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
15885           the same as those available for -mtune.  The permissible values for
15886           feature are documented in the sub-section on
15887           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
15888           Where conflicting feature modifiers are specified, the right-most
15889           feature is used.
15890
15891           GCC uses name to determine what kind of instructions it can emit
15892           when generating assembly code (as if by -march) and to determine
15893           the target processor for which to tune for performance (as if by
15894           -mtune).  Where this option is used in conjunction with -march or
15895           -mtune, those options take precedence over the appropriate part of
15896           this option.
15897
15898       -moverride=string
15899           Override tuning decisions made by the back-end in response to a
15900           -mtune= switch.  The syntax, semantics, and accepted values for
15901           string in this option are not guaranteed to be consistent across
15902           releases.
15903
15904           This option is only intended to be useful when developing GCC.
15905
15906       -mverbose-cost-dump
15907           Enable verbose cost model dumping in the debug dump files.  This
15908           option is provided for use in debugging the compiler.
15909
15910       -mpc-relative-literal-loads
15911       -mno-pc-relative-literal-loads
15912           Enable or disable PC-relative literal loads.  With this option
15913           literal pools are accessed using a single instruction and emitted
15914           after each function.  This limits the maximum size of functions to
15915           1MB.  This is enabled by default for -mcmodel=tiny.
15916
15917       -msign-return-address=scope
15918           Select the function scope on which return address signing will be
15919           applied.  Permissible values are none, which disables return
15920           address signing, non-leaf, which enables pointer signing for
15921           functions which are not leaf functions, and all, which enables
15922           pointer signing for all functions.  The default value is none. This
15923           option has been deprecated by -mbranch-protection.
15924
15925       -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti
15926           Select the branch protection features to use.  none is the default
15927           and turns off all types of branch protection.  standard turns on
15928           all types of branch protection features.  If a feature has
15929           additional tuning options, then standard sets it to its standard
15930           level.  pac-ret[+leaf] turns on return address signing to its
15931           standard level: signing functions that save the return address to
15932           memory (non-leaf functions will practically always do this) using
15933           the a-key.  The optional argument leaf can be used to extend the
15934           signing to include leaf functions.  The optional argument b-key can
15935           be used to sign the functions with the B-key instead of the A-key.
15936           bti turns on branch target identification mechanism.
15937
15938       -mharden-sls=opts
15939           Enable compiler hardening against straight line speculation (SLS).
15940           opts is a comma-separated list of the following options:
15941
15942           retbr
15943           blr
15944
15945           In addition, -mharden-sls=all enables all SLS hardening while
15946           -mharden-sls=none disables all SLS hardening.
15947
15948       -msve-vector-bits=bits
15949           Specify the number of bits in an SVE vector register.  This option
15950           only has an effect when SVE is enabled.
15951
15952           GCC supports two forms of SVE code generation: "vector-length
15953           agnostic" output that works with any size of vector register and
15954           "vector-length specific" output that allows GCC to make assumptions
15955           about the vector length when it is useful for optimization reasons.
15956           The possible values of bits are: scalable, 128, 256, 512, 1024 and
15957           2048.  Specifying scalable selects vector-length agnostic output.
15958           At present -msve-vector-bits=128 also generates vector-length
15959           agnostic output for big-endian targets.  All other values generate
15960           vector-length specific code.  The behavior of these values may
15961           change in future releases and no value except scalable should be
15962           relied on for producing code that is portable across different
15963           hardware SVE vector lengths.
15964
15965           The default is -msve-vector-bits=scalable, which produces vector-
15966           length agnostic code.
15967
15968       -march and -mcpu Feature Modifiers
15969
15970       Feature modifiers used with -march and -mcpu can be any of the
15971       following and their inverses nofeature:
15972
15973       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.
15974
15975       crypto
15976           Enable Crypto extension.  This also enables Advanced SIMD and
15977           floating-point instructions.
15978
15979       fp  Enable floating-point instructions.  This is on by default for all
15980           possible values for options -march and -mcpu.
15981
15982       simd
15983           Enable Advanced SIMD instructions.  This also enables floating-
15984           point instructions.  This is on by default for all possible values
15985           for options -march and -mcpu.
15986
15987       sve Enable Scalable Vector Extension instructions.  This also enables
15988           Advanced SIMD and floating-point instructions.
15989
15990       lse Enable Large System Extension instructions.  This is on by default
15991           for -march=armv8.1-a.
15992
15993       rdma
15994           Enable Round Double Multiply Accumulate instructions.  This is on
15995           by default for -march=armv8.1-a.
15996
15997       fp16
15998           Enable FP16 extension.  This also enables floating-point
15999           instructions.
16000
16001       fp16fml
16002           Enable FP16 fmla extension.  This also enables FP16 extensions and
16003           floating-point instructions. This option is enabled by default for
16004           -march=armv8.4-a. Use of this option with architectures prior to
16005           Armv8.2-A is not supported.
16006
16007       rcpc
16008           Enable the RcPc extension.  This does not change code generation
16009           from GCC, but is passed on to the assembler, enabling inline asm
16010           statements to use instructions from the RcPc extension.
16011
16012       dotprod
16013           Enable the Dot Product extension.  This also enables Advanced SIMD
16014           instructions.
16015
16016       aes Enable the Armv8-a aes and pmull crypto extension.  This also
16017           enables Advanced SIMD instructions.
16018
16019       sha2
16020           Enable the Armv8-a sha2 crypto extension.  This also enables
16021           Advanced SIMD instructions.
16022
16023       sha3
16024           Enable the sha512 and sha3 crypto extension.  This also enables
16025           Advanced SIMD instructions. Use of this option with architectures
16026           prior to Armv8.2-A is not supported.
16027
16028       sm4 Enable the sm3 and sm4 crypto extension.  This also enables
16029           Advanced SIMD instructions.  Use of this option with architectures
16030           prior to Armv8.2-A is not supported.
16031
16032       profile
16033           Enable the Statistical Profiling extension.  This option is only to
16034           enable the extension at the assembler level and does not affect
16035           code generation.
16036
16037       rng Enable the Armv8.5-a Random Number instructions.  This option is
16038           only to enable the extension at the assembler level and does not
16039           affect code generation.
16040
16041       memtag
16042           Enable the Armv8.5-a Memory Tagging Extensions.  Use of this option
16043           with architectures prior to Armv8.5-A is not supported.
16044
16045       sb  Enable the Armv8-a Speculation Barrier instruction.  This option is
16046           only to enable the extension at the assembler level and does not
16047           affect code generation.  This option is enabled by default for
16048           -march=armv8.5-a.
16049
16050       ssbs
16051           Enable the Armv8-a Speculative Store Bypass Safe instruction.  This
16052           option is only to enable the extension at the assembler level and
16053           does not affect code generation.  This option is enabled by default
16054           for -march=armv8.5-a.
16055
16056       predres
16057           Enable the Armv8-a Execution and Data Prediction Restriction
16058           instructions.  This option is only to enable the extension at the
16059           assembler level and does not affect code generation.  This option
16060           is enabled by default for -march=armv8.5-a.
16061
16062       sve2
16063           Enable the Armv8-a Scalable Vector Extension 2.  This also enables
16064           SVE instructions.
16065
16066       sve2-bitperm
16067           Enable SVE2 bitperm instructions.  This also enables SVE2
16068           instructions.
16069
16070       sve2-sm4
16071           Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.
16072
16073       sve2-aes
16074           Enable SVE2 aes instructions.  This also enables SVE2 instructions.
16075
16076       sve2-sha3
16077           Enable SVE2 sha3 instructions.  This also enables SVE2
16078           instructions.
16079
16080       tme Enable the Transactional Memory Extension.
16081
16082       i8mm
16083           Enable 8-bit Integer Matrix Multiply instructions.  This also
16084           enables Advanced SIMD and floating-point instructions.  This option
16085           is enabled by default for -march=armv8.6-a.  Use of this option
16086           with architectures prior to Armv8.2-A is not supported.
16087
16088       f32mm
16089           Enable 32-bit Floating point Matrix Multiply instructions.  This
16090           also enables SVE instructions.  Use of this option with
16091           architectures prior to Armv8.2-A is not supported.
16092
16093       f64mm
16094           Enable 64-bit Floating point Matrix Multiply instructions.  This
16095           also enables SVE instructions.  Use of this option with
16096           architectures prior to Armv8.2-A is not supported.
16097
16098       bf16
16099           Enable brain half-precision floating-point instructions.  This also
16100           enables Advanced SIMD and floating-point instructions.  This option
16101           is enabled by default for -march=armv8.6-a.  Use of this option
16102           with architectures prior to Armv8.2-A is not supported.
16103
16104       flagm
16105           Enable the Flag Manipulation instructions Extension.
16106
16107       pauth
16108           Enable the Pointer Authentication Extension.
16109
16110       Feature crypto implies aes, sha2, and simd, which implies fp.
16111       Conversely, nofp implies nosimd, which implies nocrypto, noaes and
16112       nosha2.
16113
16114   Adapteva Epiphany Options
16115       These -m options are defined for Adapteva Epiphany:
16116
16117       -mhalf-reg-file
16118           Don't allocate any register in the range "r32"..."r63".  That
16119           allows code to run on hardware variants that lack these registers.
16120
16121       -mprefer-short-insn-regs
16122           Preferentially allocate registers that allow short instruction
16123           generation.  This can result in increased instruction count, so
16124           this may either reduce or increase overall code size.
16125
16126       -mbranch-cost=num
16127           Set the cost of branches to roughly num "simple" instructions.
16128           This cost is only a heuristic and is not guaranteed to produce
16129           consistent results across releases.
16130
16131       -mcmove
16132           Enable the generation of conditional moves.
16133
16134       -mnops=num
16135           Emit num NOPs before every other generated instruction.
16136
16137       -mno-soft-cmpsf
16138           For single-precision floating-point comparisons, emit an "fsub"
16139           instruction and test the flags.  This is faster than a software
16140           comparison, but can get incorrect results in the presence of NaNs,
16141           or when two different small numbers are compared such that their
16142           difference is calculated as zero.  The default is -msoft-cmpsf,
16143           which uses slower, but IEEE-compliant, software comparisons.
16144
16145       -mstack-offset=num
16146           Set the offset between the top of the stack and the stack pointer.
16147           E.g., a value of 8 means that the eight bytes in the range
16148           "sp+0...sp+7" can be used by leaf functions without stack
16149           allocation.  Values other than 8 or 16 are untested and unlikely to
16150           work.  Note also that this option changes the ABI; compiling a
16151           program with a different stack offset than the libraries have been
16152           compiled with generally does not work.  This option can be useful
16153           if you want to evaluate if a different stack offset would give you
16154           better code, but to actually use a different stack offset to build
16155           working programs, it is recommended to configure the toolchain with
16156           the appropriate --with-stack-offset=num option.
16157
16158       -mno-round-nearest
16159           Make the scheduler assume that the rounding mode has been set to
16160           truncating.  The default is -mround-nearest.
16161
16162       -mlong-calls
16163           If not otherwise specified by an attribute, assume all calls might
16164           be beyond the offset range of the "b" / "bl" instructions, and
16165           therefore load the function address into a register before
16166           performing a (otherwise direct) call.  This is the default.
16167
16168       -mshort-calls
16169           If not otherwise specified by an attribute, assume all direct calls
16170           are in the range of the "b" / "bl" instructions, so use these
16171           instructions for direct calls.  The default is -mlong-calls.
16172
16173       -msmall16
16174           Assume addresses can be loaded as 16-bit unsigned values.  This
16175           does not apply to function addresses for which -mlong-calls
16176           semantics are in effect.
16177
16178       -mfp-mode=mode
16179           Set the prevailing mode of the floating-point unit.  This
16180           determines the floating-point mode that is provided and expected at
16181           function call and return time.  Making this mode match the mode you
16182           predominantly need at function start can make your programs smaller
16183           and faster by avoiding unnecessary mode switches.
16184
16185           mode can be set to one the following values:
16186
16187           caller
16188               Any mode at function entry is valid, and retained or restored
16189               when the function returns, and when it calls other functions.
16190               This mode is useful for compiling libraries or other
16191               compilation units you might want to incorporate into different
16192               programs with different prevailing FPU modes, and the
16193               convenience of being able to use a single object file outweighs
16194               the size and speed overhead for any extra mode switching that
16195               might be needed, compared with what would be needed with a more
16196               specific choice of prevailing FPU mode.
16197
16198           truncate
16199               This is the mode used for floating-point calculations with
16200               truncating (i.e. round towards zero) rounding mode.  That
16201               includes conversion from floating point to integer.
16202
16203           round-nearest
16204               This is the mode used for floating-point calculations with
16205               round-to-nearest-or-even rounding mode.
16206
16207           int This is the mode used to perform integer calculations in the
16208               FPU, e.g.  integer multiply, or integer multiply-and-
16209               accumulate.
16210
16211           The default is -mfp-mode=caller
16212
16213       -mno-split-lohi
16214       -mno-postinc
16215       -mno-postmodify
16216           Code generation tweaks that disable, respectively, splitting of
16217           32-bit loads, generation of post-increment addresses, and
16218           generation of post-modify addresses.  The defaults are msplit-lohi,
16219           -mpost-inc, and -mpost-modify.
16220
16221       -mnovect-double
16222           Change the preferred SIMD mode to SImode.  The default is
16223           -mvect-double, which uses DImode as preferred SIMD mode.
16224
16225       -max-vect-align=num
16226           The maximum alignment for SIMD vector mode types.  num may be 4 or
16227           8.  The default is 8.  Note that this is an ABI change, even though
16228           many library function interfaces are unaffected if they don't use
16229           SIMD vector modes in places that affect size and/or alignment of
16230           relevant types.
16231
16232       -msplit-vecmove-early
16233           Split vector moves into single word moves before reload.  In theory
16234           this can give better register allocation, but so far the reverse
16235           seems to be generally the case.
16236
16237       -m1reg-reg
16238           Specify a register to hold the constant -1, which makes loading
16239           small negative constants and certain bitmasks faster.  Allowable
16240           values for reg are r43 and r63, which specify use of that register
16241           as a fixed register, and none, which means that no register is used
16242           for this purpose.  The default is -m1reg-none.
16243
16244   AMD GCN Options
16245       These options are defined specifically for the AMD GCN port.
16246
16247       -march=gpu
16248       -mtune=gpu
16249           Set architecture type or tuning for gpu. Supported values for gpu
16250           are
16251
16252           fiji
16253               Compile for GCN3 Fiji devices (gfx803).
16254
16255           gfx900
16256               Compile for GCN5 Vega 10 devices (gfx900).
16257
16258           gfx906
16259               Compile for GCN5 Vega 20 devices (gfx906).
16260
16261       -mstack-size=bytes
16262           Specify how many bytes of stack space will be requested for each
16263           GPU thread (wave-front).  Beware that there may be many threads and
16264           limited memory available.  The size of the stack allocation may
16265           also have an impact on run-time performance.  The default is 32KB
16266           when using OpenACC or OpenMP, and 1MB otherwise.
16267
16268   ARC Options
16269       The following options control the architecture variant for which code
16270       is being compiled:
16271
16272       -mbarrel-shifter
16273           Generate instructions supported by barrel shifter.  This is the
16274           default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.
16275
16276       -mjli-always
16277           Force to call a function using jli_s instruction.  This option is
16278           valid only for ARCv2 architecture.
16279
16280       -mcpu=cpu
16281           Set architecture type, register usage, and instruction scheduling
16282           parameters for cpu.  There are also shortcut alias options
16283           available for backward compatibility and convenience.  Supported
16284           values for cpu are
16285
16286           arc600
16287               Compile for ARC600.  Aliases: -mA6, -mARC600.
16288
16289           arc601
16290               Compile for ARC601.  Alias: -mARC601.
16291
16292           arc700
16293               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the
16294               default when configured with --with-cpu=arc700.
16295
16296           arcem
16297               Compile for ARC EM.
16298
16299           archs
16300               Compile for ARC HS.
16301
16302           em  Compile for ARC EM CPU with no hardware extensions.
16303
16304           em4 Compile for ARC EM4 CPU.
16305
16306           em4_dmips
16307               Compile for ARC EM4 DMIPS CPU.
16308
16309           em4_fpus
16310               Compile for ARC EM4 DMIPS CPU with the single-precision
16311               floating-point extension.
16312
16313           em4_fpuda
16314               Compile for ARC EM4 DMIPS CPU with single-precision floating-
16315               point and double assist instructions.
16316
16317           hs  Compile for ARC HS CPU with no hardware extensions except the
16318               atomic instructions.
16319
16320           hs34
16321               Compile for ARC HS34 CPU.
16322
16323           hs38
16324               Compile for ARC HS38 CPU.
16325
16326           hs38_linux
16327               Compile for ARC HS38 CPU with all hardware extensions on.
16328
16329           arc600_norm
16330               Compile for ARC 600 CPU with "norm" instructions enabled.
16331
16332           arc600_mul32x16
16333               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
16334               instructions enabled.
16335
16336           arc600_mul64
16337               Compile for ARC 600 CPU with "norm" and "mul64"-family
16338               instructions enabled.
16339
16340           arc601_norm
16341               Compile for ARC 601 CPU with "norm" instructions enabled.
16342
16343           arc601_mul32x16
16344               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
16345               instructions enabled.
16346
16347           arc601_mul64
16348               Compile for ARC 601 CPU with "norm" and "mul64"-family
16349               instructions enabled.
16350
16351           nps400
16352               Compile for ARC 700 on NPS400 chip.
16353
16354           em_mini
16355               Compile for ARC EM minimalist configuration featuring reduced
16356               register set.
16357
16358       -mdpfp
16359       -mdpfp-compact
16360           Generate double-precision FPX instructions, tuned for the compact
16361           implementation.
16362
16363       -mdpfp-fast
16364           Generate double-precision FPX instructions, tuned for the fast
16365           implementation.
16366
16367       -mno-dpfp-lrsr
16368           Disable "lr" and "sr" instructions from using FPX extension aux
16369           registers.
16370
16371       -mea
16372           Generate extended arithmetic instructions.  Currently only "divaw",
16373           "adds", "subs", and "sat16" are supported.  Only valid for
16374           -mcpu=ARC700.
16375
16376       -mno-mpy
16377           Do not generate "mpy"-family instructions for ARC700.  This option
16378           is deprecated.
16379
16380       -mmul32x16
16381           Generate 32x16-bit multiply and multiply-accumulate instructions.
16382
16383       -mmul64
16384           Generate "mul64" and "mulu64" instructions.  Only valid for
16385           -mcpu=ARC600.
16386
16387       -mnorm
16388           Generate "norm" instructions.  This is the default if -mcpu=ARC700
16389           is in effect.
16390
16391       -mspfp
16392       -mspfp-compact
16393           Generate single-precision FPX instructions, tuned for the compact
16394           implementation.
16395
16396       -mspfp-fast
16397           Generate single-precision FPX instructions, tuned for the fast
16398           implementation.
16399
16400       -msimd
16401           Enable generation of ARC SIMD instructions via target-specific
16402           builtins.  Only valid for -mcpu=ARC700.
16403
16404       -msoft-float
16405           This option ignored; it is provided for compatibility purposes
16406           only.  Software floating-point code is emitted by default, and this
16407           default can overridden by FPX options; -mspfp, -mspfp-compact, or
16408           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
16409           -mdpfp-fast for double precision.
16410
16411       -mswap
16412           Generate "swap" instructions.
16413
16414       -matomic
16415           This enables use of the locked load/store conditional extension to
16416           implement atomic memory built-in functions.  Not available for ARC
16417           6xx or ARC EM cores.
16418
16419       -mdiv-rem
16420           Enable "div" and "rem" instructions for ARCv2 cores.
16421
16422       -mcode-density
16423           Enable code density instructions for ARC EM.  This option is on by
16424           default for ARC HS.
16425
16426       -mll64
16427           Enable double load/store operations for ARC HS cores.
16428
16429       -mtp-regno=regno
16430           Specify thread pointer register number.
16431
16432       -mmpy-option=multo
16433           Compile ARCv2 code with a multiplier design option.  You can
16434           specify the option using either a string or numeric value for
16435           multo.  wlh1 is the default value.  The recognized values are:
16436
16437           0
16438           none
16439               No multiplier available.
16440
16441           1
16442           w   16x16 multiplier, fully pipelined.  The following instructions
16443               are enabled: "mpyw" and "mpyuw".
16444
16445           2
16446           wlh1
16447               32x32 multiplier, fully pipelined (1 stage).  The following
16448               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16449               "mpymu", and "mpy_s".
16450
16451           3
16452           wlh2
16453               32x32 multiplier, fully pipelined (2 stages).  The following
16454               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16455               "mpymu", and "mpy_s".
16456
16457           4
16458           wlh3
16459               Two 16x16 multipliers, blocking, sequential.  The following
16460               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16461               "mpymu", and "mpy_s".
16462
16463           5
16464           wlh4
16465               One 16x16 multiplier, blocking, sequential.  The following
16466               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16467               "mpymu", and "mpy_s".
16468
16469           6
16470           wlh5
16471               One 32x4 multiplier, blocking, sequential.  The following
16472               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16473               "mpymu", and "mpy_s".
16474
16475           7
16476           plus_dmpy
16477               ARC HS SIMD support.
16478
16479           8
16480           plus_macd
16481               ARC HS SIMD support.
16482
16483           9
16484           plus_qmacw
16485               ARC HS SIMD support.
16486
16487           This option is only available for ARCv2 cores.
16488
16489       -mfpu=fpu
16490           Enables support for specific floating-point hardware extensions for
16491           ARCv2 cores.  Supported values for fpu are:
16492
16493           fpus
16494               Enables support for single-precision floating-point hardware
16495               extensions.
16496
16497           fpud
16498               Enables support for double-precision floating-point hardware
16499               extensions.  The single-precision floating-point extension is
16500               also enabled.  Not available for ARC EM.
16501
16502           fpuda
16503               Enables support for double-precision floating-point hardware
16504               extensions using double-precision assist instructions.  The
16505               single-precision floating-point extension is also enabled.
16506               This option is only available for ARC EM.
16507
16508           fpuda_div
16509               Enables support for double-precision floating-point hardware
16510               extensions using double-precision assist instructions.  The
16511               single-precision floating-point, square-root, and divide
16512               extensions are also enabled.  This option is only available for
16513               ARC EM.
16514
16515           fpuda_fma
16516               Enables support for double-precision floating-point hardware
16517               extensions using double-precision assist instructions.  The
16518               single-precision floating-point and fused multiply and add
16519               hardware extensions are also enabled.  This option is only
16520               available for ARC EM.
16521
16522           fpuda_all
16523               Enables support for double-precision floating-point hardware
16524               extensions using double-precision assist instructions.  All
16525               single-precision floating-point hardware extensions are also
16526               enabled.  This option is only available for ARC EM.
16527
16528           fpus_div
16529               Enables support for single-precision floating-point, square-
16530               root and divide hardware extensions.
16531
16532           fpud_div
16533               Enables support for double-precision floating-point, square-
16534               root and divide hardware extensions.  This option includes
16535               option fpus_div. Not available for ARC EM.
16536
16537           fpus_fma
16538               Enables support for single-precision floating-point and fused
16539               multiply and add hardware extensions.
16540
16541           fpud_fma
16542               Enables support for double-precision floating-point and fused
16543               multiply and add hardware extensions.  This option includes
16544               option fpus_fma.  Not available for ARC EM.
16545
16546           fpus_all
16547               Enables support for all single-precision floating-point
16548               hardware extensions.
16549
16550           fpud_all
16551               Enables support for all single- and double-precision floating-
16552               point hardware extensions.  Not available for ARC EM.
16553
16554       -mirq-ctrl-saved=register-range, blink, lp_count
16555           Specifies general-purposes registers that the processor
16556           automatically saves/restores on interrupt entry and exit.
16557           register-range is specified as two registers separated by a dash.
16558           The register range always starts with "r0", the upper limit is "fp"
16559           register.  blink and lp_count are optional.  This option is only
16560           valid for ARC EM and ARC HS cores.
16561
16562       -mrgf-banked-regs=number
16563           Specifies the number of registers replicated in second register
16564           bank on entry to fast interrupt.  Fast interrupts are interrupts
16565           with the highest priority level P0.  These interrupts save only PC
16566           and STATUS32 registers to avoid memory transactions during
16567           interrupt entry and exit sequences.  Use this option when you are
16568           using fast interrupts in an ARC V2 family processor.  Permitted
16569           values are 4, 8, 16, and 32.
16570
16571       -mlpc-width=width
16572           Specify the width of the "lp_count" register.  Valid values for
16573           width are 8, 16, 20, 24, 28 and 32 bits.  The default width is
16574           fixed to 32 bits.  If the width is less than 32, the compiler does
16575           not attempt to transform loops in your program to use the zero-
16576           delay loop mechanism unless it is known that the "lp_count"
16577           register can hold the required loop-counter value.  Depending on
16578           the width specified, the compiler and run-time library might
16579           continue to use the loop mechanism for various needs.  This option
16580           defines macro "__ARC_LPC_WIDTH__" with the value of width.
16581
16582       -mrf16
16583           This option instructs the compiler to generate code for a 16-entry
16584           register file.  This option defines the "__ARC_RF16__" preprocessor
16585           macro.
16586
16587       -mbranch-index
16588           Enable use of "bi" or "bih" instructions to implement jump tables.
16589
16590       The following options are passed through to the assembler, and also
16591       define preprocessor macro symbols.
16592
16593       -mdsp-packa
16594           Passed down to the assembler to enable the DSP Pack A extensions.
16595           Also sets the preprocessor symbol "__Xdsp_packa".  This option is
16596           deprecated.
16597
16598       -mdvbf
16599           Passed down to the assembler to enable the dual Viterbi butterfly
16600           extension.  Also sets the preprocessor symbol "__Xdvbf".  This
16601           option is deprecated.
16602
16603       -mlock
16604           Passed down to the assembler to enable the locked load/store
16605           conditional extension.  Also sets the preprocessor symbol
16606           "__Xlock".
16607
16608       -mmac-d16
16609           Passed down to the assembler.  Also sets the preprocessor symbol
16610           "__Xxmac_d16".  This option is deprecated.
16611
16612       -mmac-24
16613           Passed down to the assembler.  Also sets the preprocessor symbol
16614           "__Xxmac_24".  This option is deprecated.
16615
16616       -mrtsc
16617           Passed down to the assembler to enable the 64-bit time-stamp
16618           counter extension instruction.  Also sets the preprocessor symbol
16619           "__Xrtsc".  This option is deprecated.
16620
16621       -mswape
16622           Passed down to the assembler to enable the swap byte ordering
16623           extension instruction.  Also sets the preprocessor symbol
16624           "__Xswape".
16625
16626       -mtelephony
16627           Passed down to the assembler to enable dual- and single-operand
16628           instructions for telephony.  Also sets the preprocessor symbol
16629           "__Xtelephony".  This option is deprecated.
16630
16631       -mxy
16632           Passed down to the assembler to enable the XY memory extension.
16633           Also sets the preprocessor symbol "__Xxy".
16634
16635       The following options control how the assembly code is annotated:
16636
16637       -misize
16638           Annotate assembler instructions with estimated addresses.
16639
16640       -mannotate-align
16641           Explain what alignment considerations lead to the decision to make
16642           an instruction short or long.
16643
16644       The following options are passed through to the linker:
16645
16646       -marclinux
16647           Passed through to the linker, to specify use of the "arclinux"
16648           emulation.  This option is enabled by default in tool chains built
16649           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
16650           profiling is not requested.
16651
16652       -marclinux_prof
16653           Passed through to the linker, to specify use of the "arclinux_prof"
16654           emulation.  This option is enabled by default in tool chains built
16655           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
16656           profiling is requested.
16657
16658       The following options control the semantics of generated code:
16659
16660       -mlong-calls
16661           Generate calls as register indirect calls, thus providing access to
16662           the full 32-bit address range.
16663
16664       -mmedium-calls
16665           Don't use less than 25-bit addressing range for calls, which is the
16666           offset available for an unconditional branch-and-link instruction.
16667           Conditional execution of function calls is suppressed, to allow use
16668           of the 25-bit range, rather than the 21-bit range with conditional
16669           branch-and-link.  This is the default for tool chains built for
16670           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.
16671
16672       -G num
16673           Put definitions of externally-visible data in a small data section
16674           if that data is no bigger than num bytes.  The default value of num
16675           is 4 for any ARC configuration, or 8 when we have double load/store
16676           operations.
16677
16678       -mno-sdata
16679           Do not generate sdata references.  This is the default for tool
16680           chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
16681           targets.
16682
16683       -mvolatile-cache
16684           Use ordinarily cached memory accesses for volatile references.
16685           This is the default.
16686
16687       -mno-volatile-cache
16688           Enable cache bypass for volatile references.
16689
16690       The following options fine tune code generation:
16691
16692       -malign-call
16693           Do alignment optimizations for call instructions.
16694
16695       -mauto-modify-reg
16696           Enable the use of pre/post modify with register displacement.
16697
16698       -mbbit-peephole
16699           Enable bbit peephole2.
16700
16701       -mno-brcc
16702           This option disables a target-specific pass in arc_reorg to
16703           generate compare-and-branch ("brcc") instructions.  It has no
16704           effect on generation of these instructions driven by the combiner
16705           pass.
16706
16707       -mcase-vector-pcrel
16708           Use PC-relative switch case tables to enable case table shortening.
16709           This is the default for -Os.
16710
16711       -mcompact-casesi
16712           Enable compact "casesi" pattern.  This is the default for -Os, and
16713           only available for ARCv1 cores.  This option is deprecated.
16714
16715       -mno-cond-exec
16716           Disable the ARCompact-specific pass to generate conditional
16717           execution instructions.
16718
16719           Due to delay slot scheduling and interactions between operand
16720           numbers, literal sizes, instruction lengths, and the support for
16721           conditional execution, the target-independent pass to generate
16722           conditional execution is often lacking, so the ARC port has kept a
16723           special pass around that tries to find more conditional execution
16724           generation opportunities after register allocation, branch
16725           shortening, and delay slot scheduling have been done.  This pass
16726           generally, but not always, improves performance and code size, at
16727           the cost of extra compilation time, which is why there is an option
16728           to switch it off.  If you have a problem with call instructions
16729           exceeding their allowable offset range because they are
16730           conditionalized, you should consider using -mmedium-calls instead.
16731
16732       -mearly-cbranchsi
16733           Enable pre-reload use of the "cbranchsi" pattern.
16734
16735       -mexpand-adddi
16736           Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
16737           "adc" etc.  This option is deprecated.
16738
16739       -mindexed-loads
16740           Enable the use of indexed loads.  This can be problematic because
16741           some optimizers then assume that indexed stores exist, which is not
16742           the case.
16743
16744       -mlra
16745           Enable Local Register Allocation.  This is still experimental for
16746           ARC, so by default the compiler uses standard reload (i.e.
16747           -mno-lra).
16748
16749       -mlra-priority-none
16750           Don't indicate any priority for target registers.
16751
16752       -mlra-priority-compact
16753           Indicate target register priority for r0..r3 / r12..r15.
16754
16755       -mlra-priority-noncompact
16756           Reduce target register priority for r0..r3 / r12..r15.
16757
16758       -mmillicode
16759           When optimizing for size (using -Os), prologues and epilogues that
16760           have to save or restore a large number of registers are often
16761           shortened by using call to a special function in libgcc; this is
16762           referred to as a millicode call.  As these calls can pose
16763           performance issues, and/or cause linking issues when linking in a
16764           nonstandard way, this option is provided to turn on or off
16765           millicode call generation.
16766
16767       -mcode-density-frame
16768           This option enable the compiler to emit "enter" and "leave"
16769           instructions.  These instructions are only valid for CPUs with
16770           code-density feature.
16771
16772       -mmixed-code
16773           Tweak register allocation to help 16-bit instruction generation.
16774           This generally has the effect of decreasing the average instruction
16775           size while increasing the instruction count.
16776
16777       -mq-class
16778           Ths option is deprecated.  Enable q instruction alternatives.  This
16779           is the default for -Os.
16780
16781       -mRcq
16782           Enable Rcq constraint handling.  Most short code generation depends
16783           on this.  This is the default.
16784
16785       -mRcw
16786           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends
16787           on this.  This is the default.
16788
16789       -msize-level=level
16790           Fine-tune size optimization with regards to instruction lengths and
16791           alignment.  The recognized values for level are:
16792
16793           0   No size optimization.  This level is deprecated and treated
16794               like 1.
16795
16796           1   Short instructions are used opportunistically.
16797
16798           2   In addition, alignment of loops and of code after barriers are
16799               dropped.
16800
16801           3   In addition, optional data alignment is dropped, and the option
16802               Os is enabled.
16803
16804           This defaults to 3 when -Os is in effect.  Otherwise, the behavior
16805           when this is not set is equivalent to level 1.
16806
16807       -mtune=cpu
16808           Set instruction scheduling parameters for cpu, overriding any
16809           implied by -mcpu=.
16810
16811           Supported values for cpu are
16812
16813           ARC600
16814               Tune for ARC600 CPU.
16815
16816           ARC601
16817               Tune for ARC601 CPU.
16818
16819           ARC700
16820               Tune for ARC700 CPU with standard multiplier block.
16821
16822           ARC700-xmac
16823               Tune for ARC700 CPU with XMAC block.
16824
16825           ARC725D
16826               Tune for ARC725D CPU.
16827
16828           ARC750D
16829               Tune for ARC750D CPU.
16830
16831       -mmultcost=num
16832           Cost to assume for a multiply instruction, with 4 being equal to a
16833           normal instruction.
16834
16835       -munalign-prob-threshold=probability
16836           Set probability threshold for unaligning branches.  When tuning for
16837           ARC700 and optimizing for speed, branches without filled delay slot
16838           are preferably emitted unaligned and long, unless profiling
16839           indicates that the probability for the branch to be taken is below
16840           probability.  The default is (REG_BR_PROB_BASE/2), i.e. 5000.
16841
16842       The following options are maintained for backward compatibility, but
16843       are now deprecated and will be removed in a future release:
16844
16845       -margonaut
16846           Obsolete FPX.
16847
16848       -mbig-endian
16849       -EB Compile code for big-endian targets.  Use of these options is now
16850           deprecated.  Big-endian code is supported by configuring GCC to
16851           build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
16852           endian is the default.
16853
16854       -mlittle-endian
16855       -EL Compile code for little-endian targets.  Use of these options is
16856           now deprecated.  Little-endian code is supported by configuring GCC
16857           to build "arc-elf32" and "arc-linux-uclibc" targets, for which
16858           little endian is the default.
16859
16860       -mbarrel_shifter
16861           Replaced by -mbarrel-shifter.
16862
16863       -mdpfp_compact
16864           Replaced by -mdpfp-compact.
16865
16866       -mdpfp_fast
16867           Replaced by -mdpfp-fast.
16868
16869       -mdsp_packa
16870           Replaced by -mdsp-packa.
16871
16872       -mEA
16873           Replaced by -mea.
16874
16875       -mmac_24
16876           Replaced by -mmac-24.
16877
16878       -mmac_d16
16879           Replaced by -mmac-d16.
16880
16881       -mspfp_compact
16882           Replaced by -mspfp-compact.
16883
16884       -mspfp_fast
16885           Replaced by -mspfp-fast.
16886
16887       -mtune=cpu
16888           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
16889           by ARC600, ARC601, ARC700 and ARC700-xmac respectively.
16890
16891       -multcost=num
16892           Replaced by -mmultcost.
16893
16894   ARM Options
16895       These -m options are defined for the ARM port:
16896
16897       -mabi=name
16898           Generate code for the specified ABI.  Permissible values are: apcs-
16899           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
16900
16901       -mapcs-frame
16902           Generate a stack frame that is compliant with the ARM Procedure
16903           Call Standard for all functions, even if this is not strictly
16904           necessary for correct execution of the code.  Specifying
16905           -fomit-frame-pointer with this option causes the stack frames not
16906           to be generated for leaf functions.  The default is
16907           -mno-apcs-frame.  This option is deprecated.
16908
16909       -mapcs
16910           This is a synonym for -mapcs-frame and is deprecated.
16911
16912       -mthumb-interwork
16913           Generate code that supports calling between the ARM and Thumb
16914           instruction sets.  Without this option, on pre-v5 architectures,
16915           the two instruction sets cannot be reliably used inside one
16916           program.  The default is -mno-thumb-interwork, since slightly
16917           larger code is generated when -mthumb-interwork is specified.  In
16918           AAPCS configurations this option is meaningless.
16919
16920       -mno-sched-prolog
16921           Prevent the reordering of instructions in the function prologue, or
16922           the merging of those instruction with the instructions in the
16923           function's body.  This means that all functions start with a
16924           recognizable set of instructions (or in fact one of a choice from a
16925           small set of different function prologues), and this information
16926           can be used to locate the start of functions inside an executable
16927           piece of code.  The default is -msched-prolog.
16928
16929       -mfloat-abi=name
16930           Specifies which floating-point ABI to use.  Permissible values are:
16931           soft, softfp and hard.
16932
16933           Specifying soft causes GCC to generate output containing library
16934           calls for floating-point operations.  softfp allows the generation
16935           of code using hardware floating-point instructions, but still uses
16936           the soft-float calling conventions.  hard allows generation of
16937           floating-point instructions and uses FPU-specific calling
16938           conventions.
16939
16940           The default depends on the specific target configuration.  Note
16941           that the hard-float and soft-float ABIs are not link-compatible;
16942           you must compile your entire program with the same ABI, and link
16943           with a compatible set of libraries.
16944
16945       -mgeneral-regs-only
16946           Generate code which uses only the general-purpose registers.  This
16947           will prevent the compiler from using floating-point and Advanced
16948           SIMD registers but will not impose any restrictions on the
16949           assembler.
16950
16951       -mlittle-endian
16952           Generate code for a processor running in little-endian mode.  This
16953           is the default for all standard configurations.
16954
16955       -mbig-endian
16956           Generate code for a processor running in big-endian mode; the
16957           default is to compile code for a little-endian processor.
16958
16959       -mbe8
16960       -mbe32
16961           When linking a big-endian image select between BE8 and BE32
16962           formats.  The option has no effect for little-endian images and is
16963           ignored.  The default is dependent on the selected target
16964           architecture.  For ARMv6 and later architectures the default is
16965           BE8, for older architectures the default is BE32.  BE32 format has
16966           been deprecated by ARM.
16967
16968       -march=name[+extension...]
16969           This specifies the name of the target ARM architecture.  GCC uses
16970           this name to determine what kind of instructions it can emit when
16971           generating assembly code.  This option can be used in conjunction
16972           with or instead of the -mcpu= option.
16973
16974           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
16975           armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
16976           armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
16977           armv8.6-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m,
16978           armv8-m.base, armv8-m.main, armv8.1-m.main, iwmmxt and iwmmxt2.
16979
16980           Additionally, the following architectures, which lack support for
16981           the Thumb execution state, are recognized but support is
16982           deprecated: armv4.
16983
16984           Many of the architectures support extensions.  These can be added
16985           by appending +extension to the architecture name.  Extension
16986           options are processed in order and capabilities accumulate.  An
16987           extension will also enable any necessary base extensions upon which
16988           it depends.  For example, the +crypto extension will always enable
16989           the +simd extension.  The exception to the additive construction is
16990           for extensions that are prefixed with +no...: these extensions
16991           disable the specified option and any other extensions that may
16992           depend on the presence of that extension.
16993
16994           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
16995           writing -march=armv7-a+vfpv4 since the +simd option is entirely
16996           disabled by the +nofp option that follows it.
16997
16998           Most extension names are generically named, but have an effect that
16999           is dependent upon the architecture to which it is applied.  For
17000           example, the +simd option can be applied to both armv7-a and
17001           armv8-a architectures, but will enable the original ARMv7-A
17002           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
17003           for armv8-a.
17004
17005           The table below lists the supported extensions for each
17006           architecture.  Architectures not mentioned do not support any
17007           extensions.
17008
17009           armv5te
17010           armv6
17011           armv6j
17012           armv6k
17013           armv6kz
17014           armv6t2
17015           armv6z
17016           armv6zk
17017               +fp The VFPv2 floating-point instructions.  The extension
17018                   +vfpv2 can be used as an alias for this extension.
17019
17020               +nofp
17021                   Disable the floating-point instructions.
17022
17023           armv7
17024               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
17025               architectures.
17026
17027               +fp The VFPv3 floating-point instructions, with 16 double-
17028                   precision registers.  The extension +vfpv3-d16 can be used
17029                   as an alias for this extension.  Note that floating-point
17030                   is not supported by the base ARMv7-M architecture, but is
17031                   compatible with both the ARMv7-A and ARMv7-R architectures.
17032
17033               +nofp
17034                   Disable the floating-point instructions.
17035
17036           armv7-a
17037               +mp The multiprocessing extension.
17038
17039               +sec
17040                   The security extension.
17041
17042               +fp The VFPv3 floating-point instructions, with 16 double-
17043                   precision registers.  The extension +vfpv3-d16 can be used
17044                   as an alias for this extension.
17045
17046               +simd
17047                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17048                   instructions.  The extensions +neon and +neon-vfpv3 can be
17049                   used as aliases for this extension.
17050
17051               +vfpv3
17052                   The VFPv3 floating-point instructions, with 32 double-
17053                   precision registers.
17054
17055               +vfpv3-d16-fp16
17056                   The VFPv3 floating-point instructions, with 16 double-
17057                   precision registers and the half-precision floating-point
17058                   conversion operations.
17059
17060               +vfpv3-fp16
17061                   The VFPv3 floating-point instructions, with 32 double-
17062                   precision registers and the half-precision floating-point
17063                   conversion operations.
17064
17065               +vfpv4-d16
17066                   The VFPv4 floating-point instructions, with 16 double-
17067                   precision registers.
17068
17069               +vfpv4
17070                   The VFPv4 floating-point instructions, with 32 double-
17071                   precision registers.
17072
17073               +neon-fp16
17074                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17075                   instructions, with the half-precision floating-point
17076                   conversion operations.
17077
17078               +neon-vfpv4
17079                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17080                   instructions.
17081
17082               +nosimd
17083                   Disable the Advanced SIMD instructions (does not disable
17084                   floating point).
17085
17086               +nofp
17087                   Disable the floating-point and Advanced SIMD instructions.
17088
17089           armv7ve
17090               The extended version of the ARMv7-A architecture with support
17091               for virtualization.
17092
17093               +fp The VFPv4 floating-point instructions, with 16 double-
17094                   precision registers.  The extension +vfpv4-d16 can be used
17095                   as an alias for this extension.
17096
17097               +simd
17098                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17099                   instructions.  The extension +neon-vfpv4 can be used as an
17100                   alias for this extension.
17101
17102               +vfpv3-d16
17103                   The VFPv3 floating-point instructions, with 16 double-
17104                   precision registers.
17105
17106               +vfpv3
17107                   The VFPv3 floating-point instructions, with 32 double-
17108                   precision registers.
17109
17110               +vfpv3-d16-fp16
17111                   The VFPv3 floating-point instructions, with 16 double-
17112                   precision registers and the half-precision floating-point
17113                   conversion operations.
17114
17115               +vfpv3-fp16
17116                   The VFPv3 floating-point instructions, with 32 double-
17117                   precision registers and the half-precision floating-point
17118                   conversion operations.
17119
17120               +vfpv4-d16
17121                   The VFPv4 floating-point instructions, with 16 double-
17122                   precision registers.
17123
17124               +vfpv4
17125                   The VFPv4 floating-point instructions, with 32 double-
17126                   precision registers.
17127
17128               +neon
17129                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17130                   instructions.  The extension +neon-vfpv3 can be used as an
17131                   alias for this extension.
17132
17133               +neon-fp16
17134                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17135                   instructions, with the half-precision floating-point
17136                   conversion operations.
17137
17138               +nosimd
17139                   Disable the Advanced SIMD instructions (does not disable
17140                   floating point).
17141
17142               +nofp
17143                   Disable the floating-point and Advanced SIMD instructions.
17144
17145           armv8-a
17146               +crc
17147                   The Cyclic Redundancy Check (CRC) instructions.
17148
17149               +simd
17150                   The ARMv8-A Advanced SIMD and floating-point instructions.
17151
17152               +crypto
17153                   The cryptographic instructions.
17154
17155               +nocrypto
17156                   Disable the cryptographic instructions.
17157
17158               +nofp
17159                   Disable the floating-point, Advanced SIMD and cryptographic
17160                   instructions.
17161
17162               +sb Speculation Barrier Instruction.
17163
17164               +predres
17165                   Execution and Data Prediction Restriction Instructions.
17166
17167           armv8.1-a
17168               +simd
17169                   The ARMv8.1-A Advanced SIMD and floating-point
17170                   instructions.
17171
17172               +crypto
17173                   The cryptographic instructions.  This also enables the
17174                   Advanced SIMD and floating-point instructions.
17175
17176               +nocrypto
17177                   Disable the cryptographic instructions.
17178
17179               +nofp
17180                   Disable the floating-point, Advanced SIMD and cryptographic
17181                   instructions.
17182
17183               +sb Speculation Barrier Instruction.
17184
17185               +predres
17186                   Execution and Data Prediction Restriction Instructions.
17187
17188           armv8.2-a
17189           armv8.3-a
17190               +fp16
17191                   The half-precision floating-point data processing
17192                   instructions.  This also enables the Advanced SIMD and
17193                   floating-point instructions.
17194
17195               +fp16fml
17196                   The half-precision floating-point fmla extension.  This
17197                   also enables the half-precision floating-point extension
17198                   and Advanced SIMD and floating-point instructions.
17199
17200               +simd
17201                   The ARMv8.1-A Advanced SIMD and floating-point
17202                   instructions.
17203
17204               +crypto
17205                   The cryptographic instructions.  This also enables the
17206                   Advanced SIMD and floating-point instructions.
17207
17208               +dotprod
17209                   Enable the Dot Product extension.  This also enables
17210                   Advanced SIMD instructions.
17211
17212               +nocrypto
17213                   Disable the cryptographic extension.
17214
17215               +nofp
17216                   Disable the floating-point, Advanced SIMD and cryptographic
17217                   instructions.
17218
17219               +sb Speculation Barrier Instruction.
17220
17221               +predres
17222                   Execution and Data Prediction Restriction Instructions.
17223
17224               +i8mm
17225                   8-bit Integer Matrix Multiply instructions.  This also
17226                   enables Advanced SIMD and floating-point instructions.
17227
17228               +bf16
17229                   Brain half-precision floating-point instructions.  This
17230                   also enables Advanced SIMD and floating-point instructions.
17231
17232           armv8.4-a
17233               +fp16
17234                   The half-precision floating-point data processing
17235                   instructions.  This also enables the Advanced SIMD and
17236                   floating-point instructions as well as the Dot Product
17237                   extension and the half-precision floating-point fmla
17238                   extension.
17239
17240               +simd
17241                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17242                   as well as the Dot Product extension.
17243
17244               +crypto
17245                   The cryptographic instructions.  This also enables the
17246                   Advanced SIMD and floating-point instructions as well as
17247                   the Dot Product extension.
17248
17249               +nocrypto
17250                   Disable the cryptographic extension.
17251
17252               +nofp
17253                   Disable the floating-point, Advanced SIMD and cryptographic
17254                   instructions.
17255
17256               +sb Speculation Barrier Instruction.
17257
17258               +predres
17259                   Execution and Data Prediction Restriction Instructions.
17260
17261               +i8mm
17262                   8-bit Integer Matrix Multiply instructions.  This also
17263                   enables Advanced SIMD and floating-point instructions.
17264
17265               +bf16
17266                   Brain half-precision floating-point instructions.  This
17267                   also enables Advanced SIMD and floating-point instructions.
17268
17269           armv8.5-a
17270               +fp16
17271                   The half-precision floating-point data processing
17272                   instructions.  This also enables the Advanced SIMD and
17273                   floating-point instructions as well as the Dot Product
17274                   extension and the half-precision floating-point fmla
17275                   extension.
17276
17277               +simd
17278                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17279                   as well as the Dot Product extension.
17280
17281               +crypto
17282                   The cryptographic instructions.  This also enables the
17283                   Advanced SIMD and floating-point instructions as well as
17284                   the Dot Product extension.
17285
17286               +nocrypto
17287                   Disable the cryptographic extension.
17288
17289               +nofp
17290                   Disable the floating-point, Advanced SIMD and cryptographic
17291                   instructions.
17292
17293               +i8mm
17294                   8-bit Integer Matrix Multiply instructions.  This also
17295                   enables Advanced SIMD and floating-point instructions.
17296
17297               +bf16
17298                   Brain half-precision floating-point instructions.  This
17299                   also enables Advanced SIMD and floating-point instructions.
17300
17301           armv8.6-a
17302               +fp16
17303                   The half-precision floating-point data processing
17304                   instructions.  This also enables the Advanced SIMD and
17305                   floating-point instructions as well as the Dot Product
17306                   extension and the half-precision floating-point fmla
17307                   extension.
17308
17309               +simd
17310                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17311                   as well as the Dot Product extension.
17312
17313               +crypto
17314                   The cryptographic instructions.  This also enables the
17315                   Advanced SIMD and floating-point instructions as well as
17316                   the Dot Product extension.
17317
17318               +nocrypto
17319                   Disable the cryptographic extension.
17320
17321               +nofp
17322                   Disable the floating-point, Advanced SIMD and cryptographic
17323                   instructions.
17324
17325               +i8mm
17326                   8-bit Integer Matrix Multiply instructions.  This also
17327                   enables Advanced SIMD and floating-point instructions.
17328
17329               +bf16
17330                   Brain half-precision floating-point instructions.  This
17331                   also enables Advanced SIMD and floating-point instructions.
17332
17333           armv7-r
17334               +fp.sp
17335                   The single-precision VFPv3 floating-point instructions.
17336                   The extension +vfpv3xd can be used as an alias for this
17337                   extension.
17338
17339               +fp The VFPv3 floating-point instructions with 16 double-
17340                   precision registers.  The extension +vfpv3-d16 can be used
17341                   as an alias for this extension.
17342
17343               +vfpv3xd-d16-fp16
17344                   The single-precision VFPv3 floating-point instructions with
17345                   16 double-precision registers and the half-precision
17346                   floating-point conversion operations.
17347
17348               +vfpv3-d16-fp16
17349                   The VFPv3 floating-point instructions with 16 double-
17350                   precision registers and the half-precision floating-point
17351                   conversion operations.
17352
17353               +nofp
17354                   Disable the floating-point extension.
17355
17356               +idiv
17357                   The ARM-state integer division instructions.
17358
17359               +noidiv
17360                   Disable the ARM-state integer division extension.
17361
17362           armv7e-m
17363               +fp The single-precision VFPv4 floating-point instructions.
17364
17365               +fpv5
17366                   The single-precision FPv5 floating-point instructions.
17367
17368               +fp.dp
17369                   The single- and double-precision FPv5 floating-point
17370                   instructions.
17371
17372               +nofp
17373                   Disable the floating-point extensions.
17374
17375           armv8.1-m.main
17376               +dsp
17377                   The DSP instructions.
17378
17379               +mve
17380                   The M-Profile Vector Extension (MVE) integer instructions.
17381
17382               +mve.fp
17383                   The M-Profile Vector Extension (MVE) integer and single
17384                   precision floating-point instructions.
17385
17386               +fp The single-precision floating-point instructions.
17387
17388               +fp.dp
17389                   The single- and double-precision floating-point
17390                   instructions.
17391
17392               +nofp
17393                   Disable the floating-point extension.
17394
17395               +cdecp0, +cdecp1, ... , +cdecp7
17396                   Enable the Custom Datapath Extension (CDE) on selected
17397                   coprocessors according to the numbers given in the options
17398                   in the range 0 to 7.
17399
17400           armv8-m.main
17401               +dsp
17402                   The DSP instructions.
17403
17404               +nodsp
17405                   Disable the DSP extension.
17406
17407               +fp The single-precision floating-point instructions.
17408
17409               +fp.dp
17410                   The single- and double-precision floating-point
17411                   instructions.
17412
17413               +nofp
17414                   Disable the floating-point extension.
17415
17416               +cdecp0, +cdecp1, ... , +cdecp7
17417                   Enable the Custom Datapath Extension (CDE) on selected
17418                   coprocessors according to the numbers given in the options
17419                   in the range 0 to 7.
17420
17421           armv8-r
17422               +crc
17423                   The Cyclic Redundancy Check (CRC) instructions.
17424
17425               +fp.sp
17426                   The single-precision FPv5 floating-point instructions.
17427
17428               +simd
17429                   The ARMv8-A Advanced SIMD and floating-point instructions.
17430
17431               +crypto
17432                   The cryptographic instructions.
17433
17434               +nocrypto
17435                   Disable the cryptographic instructions.
17436
17437               +nofp
17438                   Disable the floating-point, Advanced SIMD and cryptographic
17439                   instructions.
17440
17441           -march=native causes the compiler to auto-detect the architecture
17442           of the build computer.  At present, this feature is only supported
17443           on GNU/Linux, and not all architectures are recognized.  If the
17444           auto-detect is unsuccessful the option has no effect.
17445
17446       -mtune=name
17447           This option specifies the name of the target ARM processor for
17448           which GCC should tune the performance of the code.  For some ARM
17449           implementations better performance can be obtained by using this
17450           option.  Permissible names are: arm7tdmi, arm7tdmi-s, arm710t,
17451           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
17452           0strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t,
17453           arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t,
17454           arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e,
17455           arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp,
17456           arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s,
17457           generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9,
17458           cortex-a12, cortex-a15, cortex-a17, cortex-a32, cortex-a35,
17459           cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73,
17460           cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a78,
17461           cortex-a78ae, cortex-a78c, ares, cortex-r4, cortex-r4f, cortex-r5,
17462           cortex-r7, cortex-r8, cortex-r52, cortex-m0, cortex-m0plus,
17463           cortex-m1, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33,
17464           cortex-m35p, cortex-m55, cortex-x1, cortex-m1.small-multiply,
17465           cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1,
17466           marvell-pj4, neoverse-n1, neoverse-n2, neoverse-v1, xscale, iwmmxt,
17467           iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te,
17468           xgene1.
17469
17470           Additionally, this option can specify that GCC should tune the
17471           performance of the code for a big.LITTLE system.  Permissible names
17472           are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
17473           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
17474           cortex-a72.cortex-a35, cortex-a73.cortex-a53,
17475           cortex-a75.cortex-a55, cortex-a76.cortex-a55.
17476
17477           -mtune=generic-arch specifies that GCC should tune the performance
17478           for a blend of processors within architecture arch.  The aim is to
17479           generate code that run well on the current most popular processors,
17480           balancing between optimizations that benefit some CPUs in the
17481           range, and avoiding performance pitfalls of other CPUs.  The
17482           effects of this option may change in future GCC versions as CPU
17483           models come and go.
17484
17485           -mtune permits the same extension options as -mcpu, but the
17486           extension options do not affect the tuning of the generated code.
17487
17488           -mtune=native causes the compiler to auto-detect the CPU of the
17489           build computer.  At present, this feature is only supported on
17490           GNU/Linux, and not all architectures are recognized.  If the auto-
17491           detect is unsuccessful the option has no effect.
17492
17493       -mcpu=name[+extension...]
17494           This specifies the name of the target ARM processor.  GCC uses this
17495           name to derive the name of the target ARM architecture (as if
17496           specified by -march) and the ARM processor type for which to tune
17497           for performance (as if specified by -mtune).  Where this option is
17498           used in conjunction with -march or -mtune, those options take
17499           precedence over the appropriate part of this option.
17500
17501           Many of the supported CPUs implement optional architectural
17502           extensions.  Where this is so the architectural extensions are
17503           normally enabled by default.  If implementations that lack the
17504           extension exist, then the extension syntax can be used to disable
17505           those extensions that have been omitted.  For floating-point and
17506           Advanced SIMD (Neon) instructions, the settings of the options
17507           -mfloat-abi and -mfpu must also be considered: floating-point and
17508           Advanced SIMD instructions will only be used if -mfloat-abi is not
17509           set to soft; and any setting of -mfpu other than auto will override
17510           the available floating-point and SIMD extension instructions.
17511
17512           For example, cortex-a9 can be found in three major configurations:
17513           integer only, with just a floating-point unit or with floating-
17514           point and Advanced SIMD.  The default is to enable all the
17515           instructions, but the extensions +nosimd and +nofp can be used to
17516           disable just the SIMD or both the SIMD and floating-point
17517           instructions respectively.
17518
17519           Permissible names for this option are the same as those for -mtune.
17520
17521           The following extension options are common to the listed CPUs:
17522
17523           +nodsp
17524               Disable the DSP instructions on cortex-m33, cortex-m35p.
17525
17526           +nofp
17527               Disables the floating-point instructions on arm9e, arm946e-s,
17528               arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
17529               arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
17530               cortex-m7, cortex-m33 and cortex-m35p.  Disables the floating-
17531               point and SIMD instructions on generic-armv7-a, cortex-a5,
17532               cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
17533               cortex-a17, cortex-a15.cortex-a7, cortex-a17.cortex-a7,
17534               cortex-a32, cortex-a35, cortex-a53 and cortex-a55.
17535
17536           +nofp.dp
17537               Disables the double-precision component of the floating-point
17538               instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52 and
17539               cortex-m7.
17540
17541           +nosimd
17542               Disables the SIMD (but not floating-point) instructions on
17543               generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.
17544
17545           +crypto
17546               Enables the cryptographic instructions on cortex-a32,
17547               cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
17548               cortex-a73, cortex-a75, exynos-m1, xgene1,
17549               cortex-a57.cortex-a53, cortex-a72.cortex-a53,
17550               cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
17551               cortex-a75.cortex-a55.
17552
17553           Additionally the generic-armv7-a pseudo target defaults to VFPv3
17554           with 16 double-precision registers.  It supports the following
17555           extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16,
17556           vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
17557           neon-vfpv4.  The meanings are the same as for the extensions to
17558           -march=armv7-a.
17559
17560           -mcpu=generic-arch is also permissible, and is equivalent to
17561           -march=arch -mtune=generic-arch.  See -mtune for more information.
17562
17563           -mcpu=native causes the compiler to auto-detect the CPU of the
17564           build computer.  At present, this feature is only supported on
17565           GNU/Linux, and not all architectures are recognized.  If the auto-
17566           detect is unsuccessful the option has no effect.
17567
17568       -mfpu=name
17569           This specifies what floating-point hardware (or hardware emulation)
17570           is available on the target.  Permissible names are: auto, vfpv2,
17571           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
17572           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
17573           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
17574           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
17575           and vfp is an alias for vfpv2.
17576
17577           The setting auto is the default and is special.  It causes the
17578           compiler to select the floating-point and Advanced SIMD
17579           instructions based on the settings of -mcpu and -march.
17580
17581           If the selected floating-point hardware includes the NEON extension
17582           (e.g. -mfpu=neon), note that floating-point operations are not
17583           generated by GCC's auto-vectorization pass unless
17584           -funsafe-math-optimizations is also specified.  This is because
17585           NEON hardware does not fully implement the IEEE 754 standard for
17586           floating-point arithmetic (in particular denormal values are
17587           treated as zero), so the use of NEON instructions may lead to a
17588           loss of precision.
17589
17590           You can also set the fpu name at function level by using the
17591           "target("fpu=")" function attributes or pragmas.
17592
17593       -mfp16-format=name
17594           Specify the format of the "__fp16" half-precision floating-point
17595           type.  Permissible names are none, ieee, and alternative; the
17596           default is none, in which case the "__fp16" type is not defined.
17597
17598       -mstructure-size-boundary=n
17599           The sizes of all structures and unions are rounded up to a multiple
17600           of the number of bits set by this option.  Permissible values are
17601           8, 32 and 64.  The default value varies for different toolchains.
17602           For the COFF targeted toolchain the default value is 8.  A value of
17603           64 is only allowed if the underlying ABI supports it.
17604
17605           Specifying a larger number can produce faster, more efficient code,
17606           but can also increase the size of the program.  Different values
17607           are potentially incompatible.  Code compiled with one value cannot
17608           necessarily expect to work with code or libraries compiled with
17609           another value, if they exchange information using structures or
17610           unions.
17611
17612           This option is deprecated.
17613
17614       -mabort-on-noreturn
17615           Generate a call to the function "abort" at the end of a "noreturn"
17616           function.  It is executed if the function tries to return.
17617
17618       -mlong-calls
17619       -mno-long-calls
17620           Tells the compiler to perform function calls by first loading the
17621           address of the function into a register and then performing a
17622           subroutine call on this register.  This switch is needed if the
17623           target function lies outside of the 64-megabyte addressing range of
17624           the offset-based version of subroutine call instruction.
17625
17626           Even if this switch is enabled, not all function calls are turned
17627           into long calls.  The heuristic is that static functions, functions
17628           that have the "short_call" attribute, functions that are inside the
17629           scope of a "#pragma no_long_calls" directive, and functions whose
17630           definitions have already been compiled within the current
17631           compilation unit are not turned into long calls.  The exceptions to
17632           this rule are that weak function definitions, functions with the
17633           "long_call" attribute or the "section" attribute, and functions
17634           that are within the scope of a "#pragma long_calls" directive are
17635           always turned into long calls.
17636
17637           This feature is not enabled by default.  Specifying -mno-long-calls
17638           restores the default behavior, as does placing the function calls
17639           within the scope of a "#pragma long_calls_off" directive.  Note
17640           these switches have no effect on how the compiler generates code to
17641           handle function calls via function pointers.
17642
17643       -msingle-pic-base
17644           Treat the register used for PIC addressing as read-only, rather
17645           than loading it in the prologue for each function.  The runtime
17646           system is responsible for initializing this register with an
17647           appropriate value before execution begins.
17648
17649       -mpic-register=reg
17650           Specify the register to be used for PIC addressing.  For standard
17651           PIC base case, the default is any suitable register determined by
17652           compiler.  For single PIC base case, the default is R9 if target is
17653           EABI based or stack-checking is enabled, otherwise the default is
17654           R10.
17655
17656       -mpic-data-is-text-relative
17657           Assume that the displacement between the text and data segments is
17658           fixed at static link time.  This permits using PC-relative
17659           addressing operations to access data known to be in the data
17660           segment.  For non-VxWorks RTP targets, this option is enabled by
17661           default.  When disabled on such targets, it will enable
17662           -msingle-pic-base by default.
17663
17664       -mpoke-function-name
17665           Write the name of each function into the text section, directly
17666           preceding the function prologue.  The generated code is similar to
17667           this:
17668
17669                        t0
17670                            .ascii "arm_poke_function_name", 0
17671                            .align
17672                        t1
17673                            .word 0xff000000 + (t1 - t0)
17674                        arm_poke_function_name
17675                            mov     ip, sp
17676                            stmfd   sp!, {fp, ip, lr, pc}
17677                            sub     fp, ip, #4
17678
17679           When performing a stack backtrace, code can inspect the value of
17680           "pc" stored at "fp + 0".  If the trace function then looks at
17681           location "pc - 12" and the top 8 bits are set, then we know that
17682           there is a function name embedded immediately preceding this
17683           location and has length "((pc[-3]) & 0xff000000)".
17684
17685       -mthumb
17686       -marm
17687           Select between generating code that executes in ARM and Thumb
17688           states.  The default for most configurations is to generate code
17689           that executes in ARM state, but the default can be changed by
17690           configuring GCC with the --with-mode=state configure option.
17691
17692           You can also override the ARM and Thumb mode for each function by
17693           using the "target("thumb")" and "target("arm")" function attributes
17694           or pragmas.
17695
17696       -mflip-thumb
17697           Switch ARM/Thumb modes on alternating functions.  This option is
17698           provided for regression testing of mixed Thumb/ARM code generation,
17699           and is not intended for ordinary use in compiling code.
17700
17701       -mtpcs-frame
17702           Generate a stack frame that is compliant with the Thumb Procedure
17703           Call Standard for all non-leaf functions.  (A leaf function is one
17704           that does not call any other functions.)  The default is
17705           -mno-tpcs-frame.
17706
17707       -mtpcs-leaf-frame
17708           Generate a stack frame that is compliant with the Thumb Procedure
17709           Call Standard for all leaf functions.  (A leaf function is one that
17710           does not call any other functions.)  The default is
17711           -mno-apcs-leaf-frame.
17712
17713       -mcallee-super-interworking
17714           Gives all externally visible functions in the file being compiled
17715           an ARM instruction set header which switches to Thumb mode before
17716           executing the rest of the function.  This allows these functions to
17717           be called from non-interworking code.  This option is not valid in
17718           AAPCS configurations because interworking is enabled by default.
17719
17720       -mcaller-super-interworking
17721           Allows calls via function pointers (including virtual functions) to
17722           execute correctly regardless of whether the target code has been
17723           compiled for interworking or not.  There is a small overhead in the
17724           cost of executing a function pointer if this option is enabled.
17725           This option is not valid in AAPCS configurations because
17726           interworking is enabled by default.
17727
17728       -mtp=name
17729           Specify the access model for the thread local storage pointer.  The
17730           valid models are soft, which generates calls to "__aeabi_read_tp",
17731           cp15, which fetches the thread pointer from "cp15" directly
17732           (supported in the arm6k architecture), and auto, which uses the
17733           best available method for the selected processor.  The default
17734           setting is auto.
17735
17736       -mtls-dialect=dialect
17737           Specify the dialect to use for accessing thread local storage.  Two
17738           dialects are supported---gnu and gnu2.  The gnu dialect selects the
17739           original GNU scheme for supporting local and global dynamic TLS
17740           models.  The gnu2 dialect selects the GNU descriptor scheme, which
17741           provides better performance for shared libraries.  The GNU
17742           descriptor scheme is compatible with the original scheme, but does
17743           require new assembler, linker and library support.  Initial and
17744           local exec TLS models are unaffected by this option and always use
17745           the original scheme.
17746
17747       -mword-relocations
17748           Only generate absolute relocations on word-sized values (i.e.
17749           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
17750           SymbianOS) where the runtime loader imposes this restriction, and
17751           when -fpic or -fPIC is specified. This option conflicts with
17752           -mslow-flash-data.
17753
17754       -mfix-cortex-m3-ldrd
17755           Some Cortex-M3 cores can cause data corruption when "ldrd"
17756           instructions with overlapping destination and base registers are
17757           used.  This option avoids generating these instructions.  This
17758           option is enabled by default when -mcpu=cortex-m3 is specified.
17759
17760       -munaligned-access
17761       -mno-unaligned-access
17762           Enables (or disables) reading and writing of 16- and 32- bit values
17763           from addresses that are not 16- or 32- bit aligned.  By default
17764           unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
17765           ARMv8-M Baseline architectures, and enabled for all other
17766           architectures.  If unaligned access is not enabled then words in
17767           packed data structures are accessed a byte at a time.
17768
17769           The ARM attribute "Tag_CPU_unaligned_access" is set in the
17770           generated object file to either true or false, depending upon the
17771           setting of this option.  If unaligned access is enabled then the
17772           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.
17773
17774       -mneon-for-64bits
17775           This option is deprecated and has no effect.
17776
17777       -mslow-flash-data
17778           Assume loading data from flash is slower than fetching instruction.
17779           Therefore literal load is minimized for better performance.  This
17780           option is only supported when compiling for ARMv7 M-profile and off
17781           by default. It conflicts with -mword-relocations.
17782
17783       -masm-syntax-unified
17784           Assume inline assembler is using unified asm syntax.  The default
17785           is currently off which implies divided syntax.  This option has no
17786           impact on Thumb2. However, this may change in future releases of
17787           GCC.  Divided syntax should be considered deprecated.
17788
17789       -mrestrict-it
17790           Restricts generation of IT blocks to conform to the rules of
17791           ARMv8-A.  IT blocks can only contain a single 16-bit instruction
17792           from a select set of instructions. This option is on by default for
17793           ARMv8-A Thumb mode.
17794
17795       -mprint-tune-info
17796           Print CPU tuning information as comment in assembler file.  This is
17797           an option used only for regression testing of the compiler and not
17798           intended for ordinary use in compiling code.  This option is
17799           disabled by default.
17800
17801       -mverbose-cost-dump
17802           Enable verbose cost model dumping in the debug dump files.  This
17803           option is provided for use in debugging the compiler.
17804
17805       -mpure-code
17806           Do not allow constant data to be placed in code sections.
17807           Additionally, when compiling for ELF object format give all text
17808           sections the ELF processor-specific section attribute
17809           "SHF_ARM_PURECODE".  This option is only available when generating
17810           non-pic code for M-profile targets.
17811
17812       -mcmse
17813           Generate secure code as per the "ARMv8-M Security Extensions:
17814           Requirements on Development Tools Engineering Specification", which
17815           can be found on
17816           <https://developer.arm.com/documentation/ecm0359818/latest/>.
17817
17818       -mfdpic
17819       -mno-fdpic
17820           Select the FDPIC ABI, which uses 64-bit function descriptors to
17821           represent pointers to functions.  When the compiler is configured
17822           for "arm-*-uclinuxfdpiceabi" targets, this option is on by default
17823           and implies -fPIE if none of the PIC/PIE-related options is
17824           provided.  On other targets, it only enables the FDPIC-specific
17825           code generation features, and the user should explicitly provide
17826           the PIC/PIE-related options as needed.
17827
17828           Note that static linking is not supported because it would still
17829           involve the dynamic linker when the program self-relocates.  If
17830           such behavior is acceptable, use -static and -Wl,-dynamic-linker
17831           options.
17832
17833           The opposite -mno-fdpic option is useful (and required) to build
17834           the Linux kernel using the same ("arm-*-uclinuxfdpiceabi")
17835           toolchain as the one used to build the userland programs.
17836
17837   AVR Options
17838       These options are defined for AVR implementations:
17839
17840       -mmcu=mcu
17841           Specify Atmel AVR instruction set architectures (ISA) or MCU type.
17842
17843           The default for this option is avr2.
17844
17845           GCC supports the following AVR devices and ISAs:
17846
17847           "avr2"
17848               "Classic" devices with up to 8 KiB of program memory.  mcu =
17849               "attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333",
17850               "at90s2343", "at90s4414", "at90s4433", "at90s4434",
17851               "at90c8534", "at90s8515", "at90s8535".
17852
17853           "avr25"
17854               "Classic" devices with up to 8 KiB of program memory and with
17855               the "MOVW" instruction.  mcu = "attiny13", "attiny13a",
17856               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
17857               "attiny2313", "attiny2313a", "attiny43u", "attiny44",
17858               "attiny44a", "attiny45", "attiny48", "attiny441", "attiny461",
17859               "attiny461a", "attiny4313", "attiny84", "attiny84a",
17860               "attiny85", "attiny87", "attiny88", "attiny828", "attiny841",
17861               "attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401".
17862
17863           "avr3"
17864               "Classic" devices with 16 KiB up to 64 KiB of program memory.
17865               mcu = "at76c711", "at43usb355".
17866
17867           "avr31"
17868               "Classic" devices with 128 KiB of program memory.  mcu =
17869               "atmega103", "at43usb320".
17870
17871           "avr35"
17872               "Classic" devices with 16 KiB up to 64 KiB of program memory
17873               and with the "MOVW" instruction.  mcu = "attiny167",
17874               "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2",
17875               "ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162".
17876
17877           "avr4"
17878               "Enhanced" devices with up to 8 KiB of program memory.  mcu =
17879               "atmega48", "atmega48a", "atmega48p", "atmega48pa",
17880               "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88",
17881               "atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
17882               "atmega8515", "atmega8535", "ata6285", "ata6286", "ata6289",
17883               "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3",
17884               "at90pwm3b", "at90pwm81".
17885
17886           "avr5"
17887               "Enhanced" devices with 16 KiB up to 64 KiB of program memory.
17888               mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
17889               "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
17890               "atmega161", "atmega162", "atmega163", "atmega164a",
17891               "atmega164p", "atmega164pa", "atmega165", "atmega165a",
17892               "atmega165p", "atmega165pa", "atmega168", "atmega168a",
17893               "atmega168p", "atmega168pa", "atmega168pb", "atmega169",
17894               "atmega169a", "atmega169p", "atmega169pa", "atmega32",
17895               "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
17896               "atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
17897               "atmega324a", "atmega324p", "atmega324pa", "atmega325",
17898               "atmega325a", "atmega325p", "atmega325pa", "atmega328",
17899               "atmega328p", "atmega328pb", "atmega329", "atmega329a",
17900               "atmega329p", "atmega329pa", "atmega3250", "atmega3250a",
17901               "atmega3250p", "atmega3250pa", "atmega3290", "atmega3290a",
17902               "atmega3290p", "atmega3290pa", "atmega406", "atmega64",
17903               "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2",
17904               "atmega64m1", "atmega64rfr2", "atmega640", "atmega644",
17905               "atmega644a", "atmega644p", "atmega644pa", "atmega644rfr2",
17906               "atmega645", "atmega645a", "atmega645p", "atmega649",
17907               "atmega649a", "atmega649p", "atmega6450", "atmega6450a",
17908               "atmega6450p", "atmega6490", "atmega6490a", "atmega6490p",
17909               "ata5795", "ata5790", "ata5790n", "ata5791", "ata6613c",
17910               "ata6614q", "ata5782", "ata5831", "ata8210", "ata8510",
17911               "ata5702m322", "at90pwm161", "at90pwm216", "at90pwm316",
17912               "at90can32", "at90can64", "at90scr100", "at90usb646",
17913               "at90usb647", "at94k", "m3000".
17914
17915           "avr51"
17916               "Enhanced" devices with 128 KiB of program memory.  mcu =
17917               "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2",
17918               "atmega1280", "atmega1281", "atmega1284", "atmega1284p",
17919               "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".
17920
17921           "avr6"
17922               "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
17923               of program memory.  mcu = "atmega256rfr2", "atmega2560",
17924               "atmega2561", "atmega2564rfr2".
17925
17926           "avrxmega2"
17927               "XMEGA" devices with more than 8 KiB and up to 64 KiB of
17928               program memory.  mcu = "atxmega8e5", "atxmega16a4",
17929               "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5",
17930               "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
17931               "atxmega32d3", "atxmega32d4", "atxmega32e5".
17932
17933           "avrxmega3"
17934               "XMEGA" devices with up to 64 KiB of combined program memory
17935               and RAM, and with program memory visible in the RAM address
17936               space.  mcu = "attiny202", "attiny204", "attiny212",
17937               "attiny214", "attiny402", "attiny404", "attiny406",
17938               "attiny412", "attiny414", "attiny416", "attiny417",
17939               "attiny804", "attiny806", "attiny807", "attiny814",
17940               "attiny816", "attiny817", "attiny1604", "attiny1606",
17941               "attiny1607", "attiny1614", "attiny1616", "attiny1617",
17942               "attiny3214", "attiny3216", "attiny3217", "atmega808",
17943               "atmega809", "atmega1608", "atmega1609", "atmega3208",
17944               "atmega3209", "atmega4808", "atmega4809".
17945
17946           "avrxmega4"
17947               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
17948               program memory.  mcu = "atxmega64a3", "atxmega64a3u",
17949               "atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3",
17950               "atxmega64d3", "atxmega64d4".
17951
17952           "avrxmega5"
17953               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
17954               program memory and more than 64 KiB of RAM.  mcu =
17955               "atxmega64a1", "atxmega64a1u".
17956
17957           "avrxmega6"
17958               "XMEGA" devices with more than 128 KiB of program memory.  mcu
17959               = "atxmega128a3", "atxmega128a3u", "atxmega128b1",
17960               "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
17961               "atxmega192a3", "atxmega192a3u", "atxmega192c3",
17962               "atxmega192d3", "atxmega256a3", "atxmega256a3b",
17963               "atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
17964               "atxmega256d3", "atxmega384c3", "atxmega384d3".
17965
17966           "avrxmega7"
17967               "XMEGA" devices with more than 128 KiB of program memory and
17968               more than 64 KiB of RAM.  mcu = "atxmega128a1",
17969               "atxmega128a1u", "atxmega128a4u".
17970
17971           "avrtiny"
17972               "TINY" Tiny core devices with 512 B up to 4 KiB of program
17973               memory.  mcu = "attiny4", "attiny5", "attiny9", "attiny10",
17974               "attiny20", "attiny40".
17975
17976           "avr1"
17977               This ISA is implemented by the minimal AVR core and supported
17978               for assembler only.  mcu = "attiny11", "attiny12", "attiny15",
17979               "attiny28", "at90s1200".
17980
17981       -mabsdata
17982           Assume that all data in static storage can be accessed by LDS / STS
17983           instructions.  This option has only an effect on reduced Tiny
17984           devices like ATtiny40.  See also the "absdata" AVR Variable
17985           Attributes,variable attribute.
17986
17987       -maccumulate-args
17988           Accumulate outgoing function arguments and acquire/release the
17989           needed stack space for outgoing function arguments once in function
17990           prologue/epilogue.  Without this option, outgoing arguments are
17991           pushed before calling a function and popped afterwards.
17992
17993           Popping the arguments after the function call can be expensive on
17994           AVR so that accumulating the stack space might lead to smaller
17995           executables because arguments need not be removed from the stack
17996           after such a function call.
17997
17998           This option can lead to reduced code size for functions that
17999           perform several calls to functions that get their arguments on the
18000           stack like calls to printf-like functions.
18001
18002       -mbranch-cost=cost
18003           Set the branch costs for conditional branch instructions to cost.
18004           Reasonable values for cost are small, non-negative integers. The
18005           default branch cost is 0.
18006
18007       -mcall-prologues
18008           Functions prologues/epilogues are expanded as calls to appropriate
18009           subroutines.  Code size is smaller.
18010
18011       -mdouble=bits
18012       -mlong-double=bits
18013           Set the size (in bits) of the "double" or "long double" type,
18014           respectively.  Possible values for bits are 32 and 64.  Whether or
18015           not a specific value for bits is allowed depends on the
18016           "--with-double=" and "--with-long-double=" configure options
18017           ("https://gcc.gnu.org/install/configure.html#avr"), and the same
18018           applies for the default values of the options.
18019
18020       -mgas-isr-prologues
18021           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo
18022           instruction supported by GNU Binutils.  If this option is on, the
18023           feature can still be disabled for individual ISRs by means of the
18024           AVR Function Attributes,,"no_gccisr" function attribute.  This
18025           feature is activated per default if optimization is on (but not
18026           with -Og, @pxref{Optimize Options}), and if GNU Binutils support
18027           PR21683 ("https://sourceware.org/PR21683").
18028
18029       -mint8
18030           Assume "int" to be 8-bit integer.  This affects the sizes of all
18031           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
18032           and "long long" is 4 bytes.  Please note that this option does not
18033           conform to the C standards, but it results in smaller code size.
18034
18035       -mmain-is-OS_task
18036           Do not save registers in "main".  The effect is the same like
18037           attaching attribute AVR Function Attributes,,"OS_task" to "main".
18038           It is activated per default if optimization is on.
18039
18040       -mn-flash=num
18041           Assume that the flash memory has a size of num times 64 KiB.
18042
18043       -mno-interrupts
18044           Generated code is not compatible with hardware interrupts.  Code
18045           size is smaller.
18046
18047       -mrelax
18048           Try to replace "CALL" resp. "JMP" instruction by the shorter
18049           "RCALL" resp. "RJMP" instruction if applicable.  Setting -mrelax
18050           just adds the --mlink-relax option to the assembler's command line
18051           and the --relax option to the linker's command line.
18052
18053           Jump relaxing is performed by the linker because jump offsets are
18054           not known before code is located. Therefore, the assembler code
18055           generated by the compiler is the same, but the instructions in the
18056           executable may differ from instructions in the assembler code.
18057
18058           Relaxing must be turned on if linker stubs are needed, see the
18059           section on "EIND" and linker stubs below.
18060
18061       -mrmw
18062           Assume that the device supports the Read-Modify-Write instructions
18063           "XCH", "LAC", "LAS" and "LAT".
18064
18065       -mshort-calls
18066           Assume that "RJMP" and "RCALL" can target the whole program memory.
18067
18068           This option is used internally for multilib selection.  It is not
18069           an optimization option, and you don't need to set it by hand.
18070
18071       -msp8
18072           Treat the stack pointer register as an 8-bit register, i.e. assume
18073           the high byte of the stack pointer is zero.  In general, you don't
18074           need to set this option by hand.
18075
18076           This option is used internally by the compiler to select and build
18077           multilibs for architectures "avr2" and "avr25".  These
18078           architectures mix devices with and without "SPH".  For any setting
18079           other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or
18080           removes this option from the compiler proper's command line,
18081           because the compiler then knows if the device or architecture has
18082           an 8-bit stack pointer and thus no "SPH" register or not.
18083
18084       -mstrict-X
18085           Use address register "X" in a way proposed by the hardware.  This
18086           means that "X" is only used in indirect, post-increment or pre-
18087           decrement addressing.
18088
18089           Without this option, the "X" register may be used in the same way
18090           as "Y" or "Z" which then is emulated by additional instructions.
18091           For example, loading a value with "X+const" addressing with a small
18092           non-negative "const < 64" to a register Rn is performed as
18093
18094                   adiw r26, const   ; X += const
18095                   ld   <Rn>, X        ; <Rn> = *X
18096                   sbiw r26, const   ; X -= const
18097
18098       -mtiny-stack
18099           Only change the lower 8 bits of the stack pointer.
18100
18101       -mfract-convert-truncate
18102           Allow to use truncation instead of rounding towards zero for
18103           fractional fixed-point types.
18104
18105       -nodevicelib
18106           Don't link against AVR-LibC's device specific library "lib<mcu>.a".
18107
18108       -nodevicespecs
18109           Don't add -specs=device-specs/specs-mcu to the compiler driver's
18110           command line.  The user takes responsibility for supplying the sub-
18111           processes like compiler proper, assembler and linker with
18112           appropriate command line options.  This means that the user has to
18113           supply her private device specs file by means of -specs=path-to-
18114           specs-file.  There is no more need for option -mmcu=mcu.
18115
18116           This option can also serve as a replacement for the older way of
18117           specifying custom device-specs files that needed -B some-path to
18118           point to a directory which contains a folder named "device-specs"
18119           which contains a specs file named "specs-mcu", where mcu was
18120           specified by -mmcu=mcu.
18121
18122       -Waddr-space-convert
18123           Warn about conversions between address spaces in the case where the
18124           resulting address space is not contained in the incoming address
18125           space.
18126
18127       -Wmisspelled-isr
18128           Warn if the ISR is misspelled, i.e. without __vector prefix.
18129           Enabled by default.
18130
18131       "EIND" and Devices with More Than 128 Ki Bytes of Flash
18132
18133       Pointers in the implementation are 16 bits wide.  The address of a
18134       function or label is represented as word address so that indirect jumps
18135       and calls can target any code address in the range of 64 Ki words.
18136
18137       In order to facilitate indirect jump on devices with more than 128 Ki
18138       bytes of program memory space, there is a special function register
18139       called "EIND" that serves as most significant part of the target
18140       address when "EICALL" or "EIJMP" instructions are used.
18141
18142       Indirect jumps and calls on these devices are handled as follows by the
18143       compiler and are subject to some limitations:
18144
18145       *   The compiler never sets "EIND".
18146
18147       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
18148           instructions or might read "EIND" directly in order to emulate an
18149           indirect call/jump by means of a "RET" instruction.
18150
18151       *   The compiler assumes that "EIND" never changes during the startup
18152           code or during the application. In particular, "EIND" is not
18153           saved/restored in function or interrupt service routine
18154           prologue/epilogue.
18155
18156       *   For indirect calls to functions and computed goto, the linker
18157           generates stubs. Stubs are jump pads sometimes also called
18158           trampolines. Thus, the indirect call/jump jumps to such a stub.
18159           The stub contains a direct jump to the desired address.
18160
18161       *   Linker relaxation must be turned on so that the linker generates
18162           the stubs correctly in all situations. See the compiler option
18163           -mrelax and the linker option --relax.  There are corner cases
18164           where the linker is supposed to generate stubs but aborts without
18165           relaxation and without a helpful error message.
18166
18167       *   The default linker script is arranged for code with "EIND = 0".  If
18168           code is supposed to work for a setup with "EIND != 0", a custom
18169           linker script has to be used in order to place the sections whose
18170           name start with ".trampolines" into the segment where "EIND" points
18171           to.
18172
18173       *   The startup code from libgcc never sets "EIND".  Notice that
18174           startup code is a blend of code from libgcc and AVR-LibC.  For the
18175           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
18176           ("http://nongnu.org/avr-libc/user-manual/").
18177
18178       *   It is legitimate for user-specific startup code to set up "EIND"
18179           early, for example by means of initialization code located in
18180           section ".init3". Such code runs prior to general startup code that
18181           initializes RAM and calls constructors, but after the bit of
18182           startup code from AVR-LibC that sets "EIND" to the segment where
18183           the vector table is located.
18184
18185                   #include <avr/io.h>
18186
18187                   static void
18188                   __attribute__((section(".init3"),naked,used,no_instrument_function))
18189                   init3_set_eind (void)
18190                   {
18191                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
18192                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
18193                   }
18194
18195           The "__trampolines_start" symbol is defined in the linker script.
18196
18197       *   Stubs are generated automatically by the linker if the following
18198           two conditions are met:
18199
18200           -<The address of a label is taken by means of the "gs" modifier>
18201               (short for generate stubs) like so:
18202
18203                       LDI r24, lo8(gs(<func>))
18204                       LDI r25, hi8(gs(<func>))
18205
18206           -<The final location of that label is in a code segment>
18207               outside the segment where the stubs are located.
18208
18209       *   The compiler emits such "gs" modifiers for code labels in the
18210           following situations:
18211
18212           -<Taking address of a function or code label.>
18213           -<Computed goto.>
18214           -<If prologue-save function is used, see -mcall-prologues>
18215               command-line option.
18216
18217           -<Switch/case dispatch tables. If you do not want such dispatch>
18218               tables you can specify the -fno-jump-tables command-line
18219               option.
18220
18221           -<C and C++ constructors/destructors called during
18222           startup/shutdown.>
18223           -<If the tools hit a "gs()" modifier explained above.>
18224       *   Jumping to non-symbolic addresses like so is not supported:
18225
18226                   int main (void)
18227                   {
18228                       /* Call function at word address 0x2 */
18229                       return ((int(*)(void)) 0x2)();
18230                   }
18231
18232           Instead, a stub has to be set up, i.e. the function has to be
18233           called through a symbol ("func_4" in the example):
18234
18235                   int main (void)
18236                   {
18237                       extern int func_4 (void);
18238
18239                       /* Call function at byte address 0x4 */
18240                       return func_4();
18241                   }
18242
18243           and the application be linked with -Wl,--defsym,func_4=0x4.
18244           Alternatively, "func_4" can be defined in the linker script.
18245
18246       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
18247       Registers
18248
18249       Some AVR devices support memories larger than the 64 KiB range that can
18250       be accessed with 16-bit pointers.  To access memory locations outside
18251       this 64 KiB range, the content of a "RAMP" register is used as high
18252       part of the address: The "X", "Y", "Z" address register is concatenated
18253       with the "RAMPX", "RAMPY", "RAMPZ" special function register,
18254       respectively, to get a wide address. Similarly, "RAMPD" is used
18255       together with direct addressing.
18256
18257       *   The startup code initializes the "RAMP" special function registers
18258           with zero.
18259
18260       *   If a AVR Named Address Spaces,named address space other than
18261           generic or "__flash" is used, then "RAMPZ" is set as needed before
18262           the operation.
18263
18264       *   If the device supports RAM larger than 64 KiB and the compiler
18265           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
18266           reset to zero after the operation.
18267
18268       *   If the device comes with a specific "RAMP" register, the ISR
18269           prologue/epilogue saves/restores that SFR and initializes it with
18270           zero in case the ISR code might (implicitly) use it.
18271
18272       *   RAM larger than 64 KiB is not supported by GCC for AVR targets.  If
18273           you use inline assembler to read from locations outside the 16-bit
18274           address range and change one of the "RAMP" registers, you must
18275           reset it to zero after the access.
18276
18277       AVR Built-in Macros
18278
18279       GCC defines several built-in macros so that the user code can test for
18280       the presence or absence of features.  Almost any of the following
18281       built-in macros are deduced from device capabilities and thus triggered
18282       by the -mmcu= command-line option.
18283
18284       For even more AVR-specific built-in macros see AVR Named Address Spaces
18285       and AVR Built-in Functions.
18286
18287       "__AVR_ARCH__"
18288           Build-in macro that resolves to a decimal number that identifies
18289           the architecture and depends on the -mmcu=mcu option.  Possible
18290           values are:
18291
18292           2, 25, 3, 31, 35, 4, 5, 51, 6
18293
18294           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
18295           "avr51", "avr6",
18296
18297           respectively and
18298
18299           100, 102, 103, 104, 105, 106, 107
18300
18301           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
18302           "avrxmega5", "avrxmega6", "avrxmega7", respectively.  If mcu
18303           specifies a device, this built-in macro is set accordingly. For
18304           example, with -mmcu=atmega8 the macro is defined to 4.
18305
18306       "__AVR_Device__"
18307           Setting -mmcu=device defines this built-in macro which reflects the
18308           device's name. For example, -mmcu=atmega8 defines the built-in
18309           macro "__AVR_ATmega8__", -mmcu=attiny261a defines
18310           "__AVR_ATtiny261A__", etc.
18311
18312           The built-in macros' names follow the scheme "__AVR_Device__" where
18313           Device is the device name as from the AVR user manual. The
18314           difference between Device in the built-in macro and device in
18315           -mmcu=device is that the latter is always lowercase.
18316
18317           If device is not a device but only a core architecture like avr51,
18318           this macro is not defined.
18319
18320       "__AVR_DEVICE_NAME__"
18321           Setting -mmcu=device defines this built-in macro to the device's
18322           name. For example, with -mmcu=atmega8 the macro is defined to
18323           "atmega8".
18324
18325           If device is not a device but only a core architecture like avr51,
18326           this macro is not defined.
18327
18328       "__AVR_XMEGA__"
18329           The device / architecture belongs to the XMEGA family of devices.
18330
18331       "__AVR_HAVE_ELPM__"
18332           The device has the "ELPM" instruction.
18333
18334       "__AVR_HAVE_ELPMX__"
18335           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.
18336
18337       "__AVR_HAVE_MOVW__"
18338           The device has the "MOVW" instruction to perform 16-bit register-
18339           register moves.
18340
18341       "__AVR_HAVE_LPMX__"
18342           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.
18343
18344       "__AVR_HAVE_MUL__"
18345           The device has a hardware multiplier.
18346
18347       "__AVR_HAVE_JMP_CALL__"
18348           The device has the "JMP" and "CALL" instructions.  This is the case
18349           for devices with more than 8 KiB of program memory.
18350
18351       "__AVR_HAVE_EIJMP_EICALL__"
18352       "__AVR_3_BYTE_PC__"
18353           The device has the "EIJMP" and "EICALL" instructions.  This is the
18354           case for devices with more than 128 KiB of program memory.  This
18355           also means that the program counter (PC) is 3 bytes wide.
18356
18357       "__AVR_2_BYTE_PC__"
18358           The program counter (PC) is 2 bytes wide. This is the case for
18359           devices with up to 128 KiB of program memory.
18360
18361       "__AVR_HAVE_8BIT_SP__"
18362       "__AVR_HAVE_16BIT_SP__"
18363           The stack pointer (SP) register is treated as 8-bit respectively
18364           16-bit register by the compiler.  The definition of these macros is
18365           affected by -mtiny-stack.
18366
18367       "__AVR_HAVE_SPH__"
18368       "__AVR_SP8__"
18369           The device has the SPH (high part of stack pointer) special
18370           function register or has an 8-bit stack pointer, respectively.  The
18371           definition of these macros is affected by -mmcu= and in the cases
18372           of -mmcu=avr2 and -mmcu=avr25 also by -msp8.
18373
18374       "__AVR_HAVE_RAMPD__"
18375       "__AVR_HAVE_RAMPX__"
18376       "__AVR_HAVE_RAMPY__"
18377       "__AVR_HAVE_RAMPZ__"
18378           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
18379           function register, respectively.
18380
18381       "__NO_INTERRUPTS__"
18382           This macro reflects the -mno-interrupts command-line option.
18383
18384       "__AVR_ERRATA_SKIP__"
18385       "__AVR_ERRATA_SKIP_JMP_CALL__"
18386           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
18387           instructions because of a hardware erratum.  Skip instructions are
18388           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
18389           only defined if "__AVR_HAVE_JMP_CALL__" is also set.
18390
18391       "__AVR_ISA_RMW__"
18392           The device has Read-Modify-Write instructions (XCH, LAC, LAS and
18393           LAT).
18394
18395       "__AVR_SFR_OFFSET__=offset"
18396           Instructions that can address I/O special function registers
18397           directly like "IN", "OUT", "SBI", etc. may use a different address
18398           as if addressed by an instruction to access RAM like "LD" or "STS".
18399           This offset depends on the device architecture and has to be
18400           subtracted from the RAM address in order to get the respective I/O
18401           address.
18402
18403       "__AVR_SHORT_CALLS__"
18404           The -mshort-calls command line option is set.
18405
18406       "__AVR_PM_BASE_ADDRESS__=addr"
18407           Some devices support reading from flash memory by means of "LD*"
18408           instructions.  The flash memory is seen in the data address space
18409           at an offset of "__AVR_PM_BASE_ADDRESS__".  If this macro is not
18410           defined, this feature is not available.  If defined, the address
18411           space is linear and there is no need to put ".rodata" into RAM.
18412           This is handled by the default linker description file, and is
18413           currently available for "avrtiny" and "avrxmega3".  Even more
18414           convenient, there is no need to use address spaces like "__flash"
18415           or features like attribute "progmem" and "pgm_read_*".
18416
18417       "__WITH_AVRLIBC__"
18418           The compiler is configured to be used together with AVR-Libc.  See
18419           the --with-avrlibc configure option.
18420
18421       "__HAVE_DOUBLE_MULTILIB__"
18422           Defined if -mdouble= acts as a multilib option.
18423
18424       "__HAVE_DOUBLE32__"
18425       "__HAVE_DOUBLE64__"
18426           Defined if the compiler supports 32-bit double resp. 64-bit double.
18427           The actual layout is specified by option -mdouble=.
18428
18429       "__DEFAULT_DOUBLE__"
18430           The size in bits of "double" if -mdouble= is not set.  To test the
18431           layout of "double" in a program, use the built-in macro
18432           "__SIZEOF_DOUBLE__".
18433
18434       "__HAVE_LONG_DOUBLE32__"
18435       "__HAVE_LONG_DOUBLE64__"
18436       "__HAVE_LONG_DOUBLE_MULTILIB__"
18437       "__DEFAULT_LONG_DOUBLE__"
18438           Same as above, but for "long double" instead of "double".
18439
18440       "__WITH_DOUBLE_COMPARISON__"
18441           Reflects the "--with-double-comparison={tristate|bool|libf7}"
18442           configure option ("https://gcc.gnu.org/install/configure.html#avr")
18443           and is defined to 2 or 3.
18444
18445       "__WITH_LIBF7_LIBGCC__"
18446       "__WITH_LIBF7_MATH__"
18447       "__WITH_LIBF7_MATH_SYMBOLS__"
18448           Reflects the "--with-libf7={libgcc|math|math-symbols}"
18449           configure option
18450           ("https://gcc.gnu.org/install/configure.html#avr").
18451
18452   Blackfin Options
18453       -mcpu=cpu[-sirevision]
18454           Specifies the name of the target Blackfin processor.  Currently,
18455           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
18456           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
18457           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
18458           bf547m, bf548m, bf549m, bf561, bf592.
18459
18460           The optional sirevision specifies the silicon revision of the
18461           target Blackfin processor.  Any workarounds available for the
18462           targeted silicon revision are enabled.  If sirevision is none, no
18463           workarounds are enabled.  If sirevision is any, all workarounds for
18464           the targeted processor are enabled.  The "__SILICON_REVISION__"
18465           macro is defined to two hexadecimal digits representing the major
18466           and minor numbers in the silicon revision.  If sirevision is none,
18467           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
18468           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
18469           optional sirevision is not used, GCC assumes the latest known
18470           silicon revision of the targeted Blackfin processor.
18471
18472           GCC defines a preprocessor macro for the specified cpu.  For the
18473           bfin-elf toolchain, this option causes the hardware BSP provided by
18474           libgloss to be linked in if -msim is not given.
18475
18476           Without this option, bf532 is used as the processor by default.
18477
18478           Note that support for bf561 is incomplete.  For bf561, only the
18479           preprocessor macro is defined.
18480
18481       -msim
18482           Specifies that the program will be run on the simulator.  This
18483           causes the simulator BSP provided by libgloss to be linked in.
18484           This option has effect only for bfin-elf toolchain.  Certain other
18485           options, such as -mid-shared-library and -mfdpic, imply -msim.
18486
18487       -momit-leaf-frame-pointer
18488           Don't keep the frame pointer in a register for leaf functions.
18489           This avoids the instructions to save, set up and restore frame
18490           pointers and makes an extra register available in leaf functions.
18491
18492       -mspecld-anomaly
18493           When enabled, the compiler ensures that the generated code does not
18494           contain speculative loads after jump instructions. If this option
18495           is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.
18496
18497       -mno-specld-anomaly
18498           Don't generate extra code to prevent speculative loads from
18499           occurring.
18500
18501       -mcsync-anomaly
18502           When enabled, the compiler ensures that the generated code does not
18503           contain CSYNC or SSYNC instructions too soon after conditional
18504           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
18505           is defined.
18506
18507       -mno-csync-anomaly
18508           Don't generate extra code to prevent CSYNC or SSYNC instructions
18509           from occurring too soon after a conditional branch.
18510
18511       -mlow64k
18512           When enabled, the compiler is free to take advantage of the
18513           knowledge that the entire program fits into the low 64k of memory.
18514
18515       -mno-low64k
18516           Assume that the program is arbitrarily large.  This is the default.
18517
18518       -mstack-check-l1
18519           Do stack checking using information placed into L1 scratchpad
18520           memory by the uClinux kernel.
18521
18522       -mid-shared-library
18523           Generate code that supports shared libraries via the library ID
18524           method.  This allows for execute in place and shared libraries in
18525           an environment without virtual memory management.  This option
18526           implies -fPIC.  With a bfin-elf target, this option implies -msim.
18527
18528       -mno-id-shared-library
18529           Generate code that doesn't assume ID-based shared libraries are
18530           being used.  This is the default.
18531
18532       -mleaf-id-shared-library
18533           Generate code that supports shared libraries via the library ID
18534           method, but assumes that this library or executable won't link
18535           against any other ID shared libraries.  That allows the compiler to
18536           use faster code for jumps and calls.
18537
18538       -mno-leaf-id-shared-library
18539           Do not assume that the code being compiled won't link against any
18540           ID shared libraries.  Slower code is generated for jump and call
18541           insns.
18542
18543       -mshared-library-id=n
18544           Specifies the identification number of the ID-based shared library
18545           being compiled.  Specifying a value of 0 generates more compact
18546           code; specifying other values forces the allocation of that number
18547           to the current library but is no more space- or time-efficient than
18548           omitting this option.
18549
18550       -msep-data
18551           Generate code that allows the data segment to be located in a
18552           different area of memory from the text segment.  This allows for
18553           execute in place in an environment without virtual memory
18554           management by eliminating relocations against the text section.
18555
18556       -mno-sep-data
18557           Generate code that assumes that the data segment follows the text
18558           segment.  This is the default.
18559
18560       -mlong-calls
18561       -mno-long-calls
18562           Tells the compiler to perform function calls by first loading the
18563           address of the function into a register and then performing a
18564           subroutine call on this register.  This switch is needed if the
18565           target function lies outside of the 24-bit addressing range of the
18566           offset-based version of subroutine call instruction.
18567
18568           This feature is not enabled by default.  Specifying -mno-long-calls
18569           restores the default behavior.  Note these switches have no effect
18570           on how the compiler generates code to handle function calls via
18571           function pointers.
18572
18573       -mfast-fp
18574           Link with the fast floating-point library. This library relaxes
18575           some of the IEEE floating-point standard's rules for checking
18576           inputs against Not-a-Number (NAN), in the interest of performance.
18577
18578       -minline-plt
18579           Enable inlining of PLT entries in function calls to functions that
18580           are not known to bind locally.  It has no effect without -mfdpic.
18581
18582       -mmulticore
18583           Build a standalone application for multicore Blackfin processors.
18584           This option causes proper start files and link scripts supporting
18585           multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
18586           can only be used with -mcpu=bf561[-sirevision].
18587
18588           This option can be used with -mcorea or -mcoreb, which selects the
18589           one-application-per-core programming model.  Without -mcorea or
18590           -mcoreb, the single-application/dual-core programming model is
18591           used. In this model, the main function of Core B should be named as
18592           "coreb_main".
18593
18594           If this option is not used, the single-core application programming
18595           model is used.
18596
18597       -mcorea
18598           Build a standalone application for Core A of BF561 when using the
18599           one-application-per-core programming model. Proper start files and
18600           link scripts are used to support Core A, and the macro
18601           "__BFIN_COREA" is defined.  This option can only be used in
18602           conjunction with -mmulticore.
18603
18604       -mcoreb
18605           Build a standalone application for Core B of BF561 when using the
18606           one-application-per-core programming model. Proper start files and
18607           link scripts are used to support Core B, and the macro
18608           "__BFIN_COREB" is defined. When this option is used, "coreb_main"
18609           should be used instead of "main".  This option can only be used in
18610           conjunction with -mmulticore.
18611
18612       -msdram
18613           Build a standalone application for SDRAM. Proper start files and
18614           link scripts are used to put the application into SDRAM, and the
18615           macro "__BFIN_SDRAM" is defined.  The loader should initialize
18616           SDRAM before loading the application.
18617
18618       -micplb
18619           Assume that ICPLBs are enabled at run time.  This has an effect on
18620           certain anomaly workarounds.  For Linux targets, the default is to
18621           assume ICPLBs are enabled; for standalone applications the default
18622           is off.
18623
18624   C6X Options
18625       -march=name
18626           This specifies the name of the target architecture.  GCC uses this
18627           name to determine what kind of instructions it can emit when
18628           generating assembly code.  Permissible names are: c62x, c64x,
18629           c64x+, c67x, c67x+, c674x.
18630
18631       -mbig-endian
18632           Generate code for a big-endian target.
18633
18634       -mlittle-endian
18635           Generate code for a little-endian target.  This is the default.
18636
18637       -msim
18638           Choose startup files and linker script suitable for the simulator.
18639
18640       -msdata=default
18641           Put small global and static data in the ".neardata" section, which
18642           is pointed to by register "B14".  Put small uninitialized global
18643           and static data in the ".bss" section, which is adjacent to the
18644           ".neardata" section.  Put small read-only data into the ".rodata"
18645           section.  The corresponding sections used for large pieces of data
18646           are ".fardata", ".far" and ".const".
18647
18648       -msdata=all
18649           Put all data, not just small objects, into the sections reserved
18650           for small data, and use addressing relative to the "B14" register
18651           to access them.
18652
18653       -msdata=none
18654           Make no use of the sections reserved for small data, and use
18655           absolute addresses to access all data.  Put all initialized global
18656           and static data in the ".fardata" section, and all uninitialized
18657           data in the ".far" section.  Put all constant data into the
18658           ".const" section.
18659
18660   CRIS Options
18661       These options are defined specifically for the CRIS ports.
18662
18663       -march=architecture-type
18664       -mcpu=architecture-type
18665           Generate code for the specified architecture.  The choices for
18666           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
18667           ETRAX 100, and ETRAX 100 LX.  Default is v0 except for cris-axis-
18668           linux-gnu, where the default is v10.
18669
18670       -mtune=architecture-type
18671           Tune to architecture-type everything applicable about the generated
18672           code, except for the ABI and the set of available instructions.
18673           The choices for architecture-type are the same as for
18674           -march=architecture-type.
18675
18676       -mmax-stack-frame=n
18677           Warn when the stack frame of a function exceeds n bytes.
18678
18679       -metrax4
18680       -metrax100
18681           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
18682           -march=v8 respectively.
18683
18684       -mmul-bug-workaround
18685       -mno-mul-bug-workaround
18686           Work around a bug in the "muls" and "mulu" instructions for CPU
18687           models where it applies.  This option is active by default.
18688
18689       -mpdebug
18690           Enable CRIS-specific verbose debug-related information in the
18691           assembly code.  This option also has the effect of turning off the
18692           #NO_APP formatted-code indicator to the assembler at the beginning
18693           of the assembly file.
18694
18695       -mcc-init
18696           Do not use condition-code results from previous instruction; always
18697           emit compare and test instructions before use of condition codes.
18698
18699       -mno-side-effects
18700           Do not emit instructions with side effects in addressing modes
18701           other than post-increment.
18702
18703       -mstack-align
18704       -mno-stack-align
18705       -mdata-align
18706       -mno-data-align
18707       -mconst-align
18708       -mno-const-align
18709           These options (no- options) arrange (eliminate arrangements) for
18710           the stack frame, individual data and constants to be aligned for
18711           the maximum single data access size for the chosen CPU model.  The
18712           default is to arrange for 32-bit alignment.  ABI details such as
18713           structure layout are not affected by these options.
18714
18715       -m32-bit
18716       -m16-bit
18717       -m8-bit
18718           Similar to the stack- data- and const-align options above, these
18719           options arrange for stack frame, writable data and constants to all
18720           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
18721           alignment.
18722
18723       -mno-prologue-epilogue
18724       -mprologue-epilogue
18725           With -mno-prologue-epilogue, the normal function prologue and
18726           epilogue which set up the stack frame are omitted and no return
18727           instructions or return sequences are generated in the code.  Use
18728           this option only together with visual inspection of the compiled
18729           code: no warnings or errors are generated when call-saved registers
18730           must be saved, or storage for local variables needs to be
18731           allocated.
18732
18733       -mno-gotplt
18734       -mgotplt
18735           With -fpic and -fPIC, don't generate (do generate) instruction
18736           sequences that load addresses for functions from the PLT part of
18737           the GOT rather than (traditional on other architectures) calls to
18738           the PLT.  The default is -mgotplt.
18739
18740       -melf
18741           Legacy no-op option only recognized with the cris-axis-elf and
18742           cris-axis-linux-gnu targets.
18743
18744       -mlinux
18745           Legacy no-op option only recognized with the cris-axis-linux-gnu
18746           target.
18747
18748       -sim
18749           This option, recognized for the cris-axis-elf, arranges to link
18750           with input-output functions from a simulator library.  Code,
18751           initialized data and zero-initialized data are allocated
18752           consecutively.
18753
18754       -sim2
18755           Like -sim, but pass linker options to locate initialized data at
18756           0x40000000 and zero-initialized data at 0x80000000.
18757
18758   CR16 Options
18759       These options are defined specifically for the CR16 ports.
18760
18761       -mmac
18762           Enable the use of multiply-accumulate instructions. Disabled by
18763           default.
18764
18765       -mcr16cplus
18766       -mcr16c
18767           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
18768           is default.
18769
18770       -msim
18771           Links the library libsim.a which is in compatible with simulator.
18772           Applicable to ELF compiler only.
18773
18774       -mint32
18775           Choose integer type as 32-bit wide.
18776
18777       -mbit-ops
18778           Generates "sbit"/"cbit" instructions for bit manipulations.
18779
18780       -mdata-model=model
18781           Choose a data model. The choices for model are near, far or medium.
18782           medium is default.  However, far is not valid with -mcr16c, as the
18783           CR16C architecture does not support the far data model.
18784
18785   C-SKY Options
18786       GCC supports these options when compiling for C-SKY V2 processors.
18787
18788       -march=arch
18789           Specify the C-SKY target architecture.  Valid values for arch are:
18790           ck801, ck802, ck803, ck807, and ck810.  The default is ck810.
18791
18792       -mcpu=cpu
18793           Specify the C-SKY target processor.  Valid values for cpu are:
18794           ck801, ck801t, ck802, ck802t, ck802j, ck803, ck803h, ck803t,
18795           ck803ht, ck803f, ck803fh, ck803e, ck803eh, ck803et, ck803eht,
18796           ck803ef, ck803efh, ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1,
18797           ck803tr1, ck803htr1, ck803fr1, ck803fhr1, ck803er1, ck803ehr1,
18798           ck803etr1, ck803ehtr1, ck803efr1, ck803efhr1, ck803ftr1,
18799           ck803eftr1, ck803efhtr1, ck803s, ck803st, ck803se, ck803sf,
18800           ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f, ck810e,
18801           ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t, ck810fv,
18802           ck810tv, ck810ft, and ck810ftv.
18803
18804       -mbig-endian
18805       -EB
18806       -mlittle-endian
18807       -EL Select big- or little-endian code.  The default is little-endian.
18808
18809       -mfloat-abi=name
18810           Specifies which floating-point ABI to use.  Permissible values are:
18811           soft, softfp and hard.
18812
18813           Specifying soft causes GCC to generate output containing library
18814           calls for floating-point operations.  softfp allows the generation
18815           of code using hardware floating-point instructions, but still uses
18816           the soft-float calling conventions.  hard allows generation of
18817           floating-point instructions and uses FPU-specific calling
18818           conventions.
18819
18820           The default depends on the specific target configuration.  Note
18821           that the hard-float and soft-float ABIs are not link-compatible;
18822           you must compile your entire program with the same ABI, and link
18823           with a compatible set of libraries.
18824
18825       -mhard-float
18826       -msoft-float
18827           Select hardware or software floating-point implementations.  The
18828           default is soft float.
18829
18830       -mdouble-float
18831       -mno-double-float
18832           When -mhard-float is in effect, enable generation of double-
18833           precision float instructions.  This is the default except when
18834           compiling for CK803.
18835
18836       -mfdivdu
18837       -mno-fdivdu
18838           When -mhard-float is in effect, enable generation of "frecipd",
18839           "fsqrtd", and "fdivd" instructions.  This is the default except
18840           when compiling for CK803.
18841
18842       -mfpu=fpu
18843           Select the floating-point processor.  This option can only be used
18844           with -mhard-float.  Values for fpu are fpv2_sf (equivalent to
18845           -mno-double-float -mno-fdivdu), fpv2 (-mdouble-float -mno-divdu),
18846           and fpv2_divd (-mdouble-float -mdivdu).
18847
18848       -melrw
18849       -mno-elrw
18850           Enable the extended "lrw" instruction.  This option defaults to on
18851           for CK801 and off otherwise.
18852
18853       -mistack
18854       -mno-istack
18855           Enable interrupt stack instructions; the default is off.
18856
18857           The -mistack option is required to handle the "interrupt" and "isr"
18858           function attributes.
18859
18860       -mmp
18861           Enable multiprocessor instructions; the default is off.
18862
18863       -mcp
18864           Enable coprocessor instructions; the default is off.
18865
18866       -mcache
18867           Enable coprocessor instructions; the default is off.
18868
18869       -msecurity
18870           Enable C-SKY security instructions; the default is off.
18871
18872       -mtrust
18873           Enable C-SKY trust instructions; the default is off.
18874
18875       -mdsp
18876       -medsp
18877       -mvdsp
18878           Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions,
18879           respectively.  All of these options default to off.
18880
18881       -mdiv
18882       -mno-div
18883           Generate divide instructions.  Default is off.
18884
18885       -msmart
18886       -mno-smart
18887           Generate code for Smart Mode, using only registers numbered 0-7 to
18888           allow use of 16-bit instructions.  This option is ignored for CK801
18889           where this is the required behavior, and it defaults to on for
18890           CK802.  For other targets, the default is off.
18891
18892       -mhigh-registers
18893       -mno-high-registers
18894           Generate code using the high registers numbered 16-31.  This option
18895           is not supported on CK801, CK802, or CK803, and is enabled by
18896           default for other processors.
18897
18898       -manchor
18899       -mno-anchor
18900           Generate code using global anchor symbol addresses.
18901
18902       -mpushpop
18903       -mno-pushpop
18904           Generate code using "push" and "pop" instructions.  This option
18905           defaults to on.
18906
18907       -mmultiple-stld
18908       -mstm
18909       -mno-multiple-stld
18910       -mno-stm
18911           Generate code using "stm" and "ldm" instructions.  This option
18912           isn't supported on CK801 but is enabled by default on other
18913           processors.
18914
18915       -mconstpool
18916       -mno-constpool
18917           Create constant pools in the compiler instead of deferring it to
18918           the assembler.  This option is the default and required for correct
18919           code generation on CK801 and CK802, and is optional on other
18920           processors.
18921
18922       -mstack-size
18923       -mno-stack-size
18924           Emit ".stack_size" directives for each function in the assembly
18925           output.  This option defaults to off.
18926
18927       -mccrt
18928       -mno-ccrt
18929           Generate code for the C-SKY compiler runtime instead of libgcc.
18930           This option defaults to off.
18931
18932       -mbranch-cost=n
18933           Set the branch costs to roughly "n" instructions.  The default is
18934           1.
18935
18936       -msched-prolog
18937       -mno-sched-prolog
18938           Permit scheduling of function prologue and epilogue sequences.
18939           Using this option can result in code that is not compliant with the
18940           C-SKY V2 ABI prologue requirements and that cannot be debugged or
18941           backtraced.  It is disabled by default.
18942
18943       -msim
18944           Links the library libsemi.a which is in compatible with simulator.
18945           Applicable to ELF compiler only.
18946
18947   Darwin Options
18948       These options are defined for all architectures running the Darwin
18949       operating system.
18950
18951       FSF GCC on Darwin does not create "fat" object files; it creates an
18952       object file for the single architecture that GCC was built to target.
18953       Apple's GCC on Darwin does create "fat" files if multiple -arch options
18954       are used; it does so by running the compiler or linker multiple times
18955       and joining the results together with lipo.
18956
18957       The subtype of the file created (like ppc7400 or ppc970 or i686) is
18958       determined by the flags that specify the ISA that GCC is targeting,
18959       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
18960       override this.
18961
18962       The Darwin tools vary in their behavior when presented with an ISA
18963       mismatch.  The assembler, as, only permits instructions to be used that
18964       are valid for the subtype of the file it is generating, so you cannot
18965       put 64-bit instructions in a ppc750 object file.  The linker for shared
18966       libraries, /usr/bin/libtool, fails and prints an error if asked to
18967       create a shared library with a less restrictive subtype than its input
18968       files (for instance, trying to put a ppc970 object file in a ppc7400
18969       library).  The linker for executables, ld, quietly gives the executable
18970       the most restrictive subtype of any of its input files.
18971
18972       -Fdir
18973           Add the framework directory dir to the head of the list of
18974           directories to be searched for header files.  These directories are
18975           interleaved with those specified by -I options and are scanned in a
18976           left-to-right order.
18977
18978           A framework directory is a directory with frameworks in it.  A
18979           framework is a directory with a Headers and/or PrivateHeaders
18980           directory contained directly in it that ends in .framework.  The
18981           name of a framework is the name of this directory excluding the
18982           .framework.  Headers associated with the framework are found in one
18983           of those two directories, with Headers being searched first.  A
18984           subframework is a framework directory that is in a framework's
18985           Frameworks directory.  Includes of subframework headers can only
18986           appear in a header of a framework that contains the subframework,
18987           or in a sibling subframework header.  Two subframeworks are
18988           siblings if they occur in the same framework.  A subframework
18989           should not have the same name as a framework; a warning is issued
18990           if this is violated.  Currently a subframework cannot have
18991           subframeworks; in the future, the mechanism may be extended to
18992           support this.  The standard frameworks can be found in
18993           /System/Library/Frameworks and /Library/Frameworks.  An example
18994           include looks like "#include <Framework/header.h>", where Framework
18995           denotes the name of the framework and header.h is found in the
18996           PrivateHeaders or Headers directory.
18997
18998       -iframeworkdir
18999           Like -F except the directory is a treated as a system directory.
19000           The main difference between this -iframework and -F is that with
19001           -iframework the compiler does not warn about constructs contained
19002           within header files found via dir.  This option is valid only for
19003           the C family of languages.
19004
19005       -gused
19006           Emit debugging information for symbols that are used.  For stabs
19007           debugging format, this enables -feliminate-unused-debug-symbols.
19008           This is by default ON.
19009
19010       -gfull
19011           Emit debugging information for all symbols and types.
19012
19013       -mmacosx-version-min=version
19014           The earliest version of MacOS X that this executable will run on is
19015           version.  Typical values of version include 10.1, 10.2, and 10.3.9.
19016
19017           If the compiler was built to use the system's headers by default,
19018           then the default for this option is the system version on which the
19019           compiler is running, otherwise the default is to make choices that
19020           are compatible with as many systems and code bases as possible.
19021
19022       -mkernel
19023           Enable kernel development mode.  The -mkernel option sets -static,
19024           -fno-common, -fno-use-cxa-atexit, -fno-exceptions,
19025           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
19026           where applicable.  This mode also sets -mno-altivec, -msoft-float,
19027           -fno-builtin and -mlong-branch for PowerPC targets.
19028
19029       -mone-byte-bool
19030           Override the defaults for "bool" so that "sizeof(bool)==1".  By
19031           default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1
19032           when compiling for Darwin/x86, so this option has no effect on x86.
19033
19034           Warning: The -mone-byte-bool switch causes GCC to generate code
19035           that is not binary compatible with code generated without that
19036           switch.  Using this switch may require recompiling all other
19037           modules in a program, including system libraries.  Use this switch
19038           to conform to a non-default data model.
19039
19040       -mfix-and-continue
19041       -ffix-and-continue
19042       -findirect-data
19043           Generate code suitable for fast turnaround development, such as to
19044           allow GDB to dynamically load .o files into already-running
19045           programs.  -findirect-data and -ffix-and-continue are provided for
19046           backwards compatibility.
19047
19048       -all_load
19049           Loads all members of static archive libraries.  See man ld(1) for
19050           more information.
19051
19052       -arch_errors_fatal
19053           Cause the errors having to do with files that have the wrong
19054           architecture to be fatal.
19055
19056       -bind_at_load
19057           Causes the output file to be marked such that the dynamic linker
19058           will bind all undefined references when the file is loaded or
19059           launched.
19060
19061       -bundle
19062           Produce a Mach-o bundle format file.  See man ld(1) for more
19063           information.
19064
19065       -bundle_loader executable
19066           This option specifies the executable that will load the build
19067           output file being linked.  See man ld(1) for more information.
19068
19069       -dynamiclib
19070           When passed this option, GCC produces a dynamic library instead of
19071           an executable when linking, using the Darwin libtool command.
19072
19073       -force_cpusubtype_ALL
19074           This causes GCC's output file to have the ALL subtype, instead of
19075           one controlled by the -mcpu or -march option.
19076
19077       -allowable_client  client_name
19078       -client_name
19079       -compatibility_version
19080       -current_version
19081       -dead_strip
19082       -dependency-file
19083       -dylib_file
19084       -dylinker_install_name
19085       -dynamic
19086       -exported_symbols_list
19087       -filelist
19088       -flat_namespace
19089       -force_flat_namespace
19090       -headerpad_max_install_names
19091       -image_base
19092       -init
19093       -install_name
19094       -keep_private_externs
19095       -multi_module
19096       -multiply_defined
19097       -multiply_defined_unused
19098       -noall_load
19099       -no_dead_strip_inits_and_terms
19100       -nofixprebinding
19101       -nomultidefs
19102       -noprebind
19103       -noseglinkedit
19104       -pagezero_size
19105       -prebind
19106       -prebind_all_twolevel_modules
19107       -private_bundle
19108       -read_only_relocs
19109       -sectalign
19110       -sectobjectsymbols
19111       -whyload
19112       -seg1addr
19113       -sectcreate
19114       -sectobjectsymbols
19115       -sectorder
19116       -segaddr
19117       -segs_read_only_addr
19118       -segs_read_write_addr
19119       -seg_addr_table
19120       -seg_addr_table_filename
19121       -seglinkedit
19122       -segprot
19123       -segs_read_only_addr
19124       -segs_read_write_addr
19125       -single_module
19126       -static
19127       -sub_library
19128       -sub_umbrella
19129       -twolevel_namespace
19130       -umbrella
19131       -undefined
19132       -unexported_symbols_list
19133       -weak_reference_mismatches
19134       -whatsloaded
19135           These options are passed to the Darwin linker.  The Darwin linker
19136           man page describes them in detail.
19137
19138   DEC Alpha Options
19139       These -m options are defined for the DEC Alpha implementations:
19140
19141       -mno-soft-float
19142       -msoft-float
19143           Use (do not use) the hardware floating-point instructions for
19144           floating-point operations.  When -msoft-float is specified,
19145           functions in libgcc.a are used to perform floating-point
19146           operations.  Unless they are replaced by routines that emulate the
19147           floating-point operations, or compiled in such a way as to call
19148           such emulations routines, these routines issue floating-point
19149           operations.   If you are compiling for an Alpha without floating-
19150           point operations, you must ensure that the library is built so as
19151           not to call them.
19152
19153           Note that Alpha implementations without floating-point operations
19154           are required to have floating-point registers.
19155
19156       -mfp-reg
19157       -mno-fp-regs
19158           Generate code that uses (does not use) the floating-point register
19159           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
19160           register set is not used, floating-point operands are passed in
19161           integer registers as if they were integers and floating-point
19162           results are passed in $0 instead of $f0.  This is a non-standard
19163           calling sequence, so any function with a floating-point argument or
19164           return value called by code compiled with -mno-fp-regs must also be
19165           compiled with that option.
19166
19167           A typical use of this option is building a kernel that does not
19168           use, and hence need not save and restore, any floating-point
19169           registers.
19170
19171       -mieee
19172           The Alpha architecture implements floating-point hardware optimized
19173           for maximum performance.  It is mostly compliant with the IEEE
19174           floating-point standard.  However, for full compliance, software
19175           assistance is required.  This option generates code fully IEEE-
19176           compliant code except that the inexact-flag is not maintained (see
19177           below).  If this option is turned on, the preprocessor macro
19178           "_IEEE_FP" is defined during compilation.  The resulting code is
19179           less efficient but is able to correctly support denormalized
19180           numbers and exceptional IEEE values such as not-a-number and
19181           plus/minus infinity.  Other Alpha compilers call this option
19182           -ieee_with_no_inexact.
19183
19184       -mieee-with-inexact
19185           This is like -mieee except the generated code also maintains the
19186           IEEE inexact-flag.  Turning on this option causes the generated
19187           code to implement fully-compliant IEEE math.  In addition to
19188           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
19189           On some Alpha implementations the resulting code may execute
19190           significantly slower than the code generated by default.  Since
19191           there is very little code that depends on the inexact-flag, you
19192           should normally not specify this option.  Other Alpha compilers
19193           call this option -ieee_with_inexact.
19194
19195       -mfp-trap-mode=trap-mode
19196           This option controls what floating-point related traps are enabled.
19197           Other Alpha compilers call this option -fptm trap-mode.  The trap
19198           mode can be set to one of four values:
19199
19200           n   This is the default (normal) setting.  The only traps that are
19201               enabled are the ones that cannot be disabled in software (e.g.,
19202               division by zero trap).
19203
19204           u   In addition to the traps enabled by n, underflow traps are
19205               enabled as well.
19206
19207           su  Like u, but the instructions are marked to be safe for software
19208               completion (see Alpha architecture manual for details).
19209
19210           sui Like su, but inexact traps are enabled as well.
19211
19212       -mfp-rounding-mode=rounding-mode
19213           Selects the IEEE rounding mode.  Other Alpha compilers call this
19214           option -fprm rounding-mode.  The rounding-mode can be one of:
19215
19216           n   Normal IEEE rounding mode.  Floating-point numbers are rounded
19217               towards the nearest machine number or towards the even machine
19218               number in case of a tie.
19219
19220           m   Round towards minus infinity.
19221
19222           c   Chopped rounding mode.  Floating-point numbers are rounded
19223               towards zero.
19224
19225           d   Dynamic rounding mode.  A field in the floating-point control
19226               register (fpcr, see Alpha architecture reference manual)
19227               controls the rounding mode in effect.  The C library
19228               initializes this register for rounding towards plus infinity.
19229               Thus, unless your program modifies the fpcr, d corresponds to
19230               round towards plus infinity.
19231
19232       -mtrap-precision=trap-precision
19233           In the Alpha architecture, floating-point traps are imprecise.
19234           This means without software assistance it is impossible to recover
19235           from a floating trap and program execution normally needs to be
19236           terminated.  GCC can generate code that can assist operating system
19237           trap handlers in determining the exact location that caused a
19238           floating-point trap.  Depending on the requirements of an
19239           application, different levels of precisions can be selected:
19240
19241           p   Program precision.  This option is the default and means a trap
19242               handler can only identify which program caused a floating-point
19243               exception.
19244
19245           f   Function precision.  The trap handler can determine the
19246               function that caused a floating-point exception.
19247
19248           i   Instruction precision.  The trap handler can determine the
19249               exact instruction that caused a floating-point exception.
19250
19251           Other Alpha compilers provide the equivalent options called
19252           -scope_safe and -resumption_safe.
19253
19254       -mieee-conformant
19255           This option marks the generated code as IEEE conformant.  You must
19256           not use this option unless you also specify -mtrap-precision=i and
19257           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
19258           to emit the line .eflag 48 in the function prologue of the
19259           generated assembly file.
19260
19261       -mbuild-constants
19262           Normally GCC examines a 32- or 64-bit integer constant to see if it
19263           can construct it from smaller constants in two or three
19264           instructions.  If it cannot, it outputs the constant as a literal
19265           and generates code to load it from the data segment at run time.
19266
19267           Use this option to require GCC to construct all integer constants
19268           using code, even if it takes more instructions (the maximum is
19269           six).
19270
19271           You typically use this option to build a shared library dynamic
19272           loader.  Itself a shared library, it must relocate itself in memory
19273           before it can find the variables and constants in its own data
19274           segment.
19275
19276       -mbwx
19277       -mno-bwx
19278       -mcix
19279       -mno-cix
19280       -mfix
19281       -mno-fix
19282       -mmax
19283       -mno-max
19284           Indicate whether GCC should generate code to use the optional BWX,
19285           CIX, FIX and MAX instruction sets.  The default is to use the
19286           instruction sets supported by the CPU type specified via -mcpu=
19287           option or that of the CPU on which GCC was built if none is
19288           specified.
19289
19290       -mfloat-vax
19291       -mfloat-ieee
19292           Generate code that uses (does not use) VAX F and G floating-point
19293           arithmetic instead of IEEE single and double precision.
19294
19295       -mexplicit-relocs
19296       -mno-explicit-relocs
19297           Older Alpha assemblers provided no way to generate symbol
19298           relocations except via assembler macros.  Use of these macros does
19299           not allow optimal instruction scheduling.  GNU binutils as of
19300           version 2.12 supports a new syntax that allows the compiler to
19301           explicitly mark which relocations should apply to which
19302           instructions.  This option is mostly useful for debugging, as GCC
19303           detects the capabilities of the assembler when it is built and sets
19304           the default accordingly.
19305
19306       -msmall-data
19307       -mlarge-data
19308           When -mexplicit-relocs is in effect, static data is accessed via
19309           gp-relative relocations.  When -msmall-data is used, objects 8
19310           bytes long or smaller are placed in a small data area (the ".sdata"
19311           and ".sbss" sections) and are accessed via 16-bit relocations off
19312           of the $gp register.  This limits the size of the small data area
19313           to 64KB, but allows the variables to be directly accessed via a
19314           single instruction.
19315
19316           The default is -mlarge-data.  With this option the data area is
19317           limited to just below 2GB.  Programs that require more than 2GB of
19318           data must use "malloc" or "mmap" to allocate the data in the heap
19319           instead of in the program's data segment.
19320
19321           When generating code for shared libraries, -fpic implies
19322           -msmall-data and -fPIC implies -mlarge-data.
19323
19324       -msmall-text
19325       -mlarge-text
19326           When -msmall-text is used, the compiler assumes that the code of
19327           the entire program (or shared library) fits in 4MB, and is thus
19328           reachable with a branch instruction.  When -msmall-data is used,
19329           the compiler can assume that all local symbols share the same $gp
19330           value, and thus reduce the number of instructions required for a
19331           function call from 4 to 1.
19332
19333           The default is -mlarge-text.
19334
19335       -mcpu=cpu_type
19336           Set the instruction set and instruction scheduling parameters for
19337           machine type cpu_type.  You can specify either the EV style name or
19338           the corresponding chip number.  GCC supports scheduling parameters
19339           for the EV4, EV5 and EV6 family of processors and chooses the
19340           default values for the instruction set from the processor you
19341           specify.  If you do not specify a processor type, GCC defaults to
19342           the processor on which the compiler was built.
19343
19344           Supported values for cpu_type are
19345
19346           ev4
19347           ev45
19348           21064
19349               Schedules as an EV4 and has no instruction set extensions.
19350
19351           ev5
19352           21164
19353               Schedules as an EV5 and has no instruction set extensions.
19354
19355           ev56
19356           21164a
19357               Schedules as an EV5 and supports the BWX extension.
19358
19359           pca56
19360           21164pc
19361           21164PC
19362               Schedules as an EV5 and supports the BWX and MAX extensions.
19363
19364           ev6
19365           21264
19366               Schedules as an EV6 and supports the BWX, FIX, and MAX
19367               extensions.
19368
19369           ev67
19370           21264a
19371               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
19372               extensions.
19373
19374           Native toolchains also support the value native, which selects the
19375           best architecture option for the host processor.  -mcpu=native has
19376           no effect if GCC does not recognize the processor.
19377
19378       -mtune=cpu_type
19379           Set only the instruction scheduling parameters for machine type
19380           cpu_type.  The instruction set is not changed.
19381
19382           Native toolchains also support the value native, which selects the
19383           best architecture option for the host processor.  -mtune=native has
19384           no effect if GCC does not recognize the processor.
19385
19386       -mmemory-latency=time
19387           Sets the latency the scheduler should assume for typical memory
19388           references as seen by the application.  This number is highly
19389           dependent on the memory access patterns used by the application and
19390           the size of the external cache on the machine.
19391
19392           Valid options for time are
19393
19394           number
19395               A decimal number representing clock cycles.
19396
19397           L1
19398           L2
19399           L3
19400           main
19401               The compiler contains estimates of the number of clock cycles
19402               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
19403               (also called Dcache, Scache, and Bcache), as well as to main
19404               memory.  Note that L3 is only valid for EV5.
19405
19406   eBPF Options
19407       -mframe-limit=bytes
19408           This specifies the hard limit for frame sizes, in bytes.
19409           Currently, the value that can be specified should be less than or
19410           equal to 32767.  Defaults to whatever limit is imposed by the
19411           version of the Linux kernel targeted.
19412
19413       -mkernel=version
19414           This specifies the minimum version of the kernel that will run the
19415           compiled program.  GCC uses this version to determine which
19416           instructions to use, what kernel helpers to allow, etc.  Currently,
19417           version can be one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8,
19418           4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19,
19419           4.20, 5.0, 5.1, 5.2, latest and native.
19420
19421       -mbig-endian
19422           Generate code for a big-endian target.
19423
19424       -mlittle-endian
19425           Generate code for a little-endian target.  This is the default.
19426
19427       -mxbpf
19428           Generate code for an expanded version of BPF, which relaxes some of
19429           the restrictions imposed by the BPF architecture:
19430
19431           -<Save and restore callee-saved registers at function entry and>
19432               exit, respectively.
19433
19434   FR30 Options
19435       These options are defined specifically for the FR30 port.
19436
19437       -msmall-model
19438           Use the small address space model.  This can produce smaller code,
19439           but it does assume that all symbolic values and addresses fit into
19440           a 20-bit range.
19441
19442       -mno-lsim
19443           Assume that runtime support has been provided and so there is no
19444           need to include the simulator library (libsim.a) on the linker
19445           command line.
19446
19447   FT32 Options
19448       These options are defined specifically for the FT32 port.
19449
19450       -msim
19451           Specifies that the program will be run on the simulator.  This
19452           causes an alternate runtime startup and library to be linked.  You
19453           must not use this option when generating programs that will run on
19454           real hardware; you must provide your own runtime library for
19455           whatever I/O functions are needed.
19456
19457       -mlra
19458           Enable Local Register Allocation.  This is still experimental for
19459           FT32, so by default the compiler uses standard reload.
19460
19461       -mnodiv
19462           Do not use div and mod instructions.
19463
19464       -mft32b
19465           Enable use of the extended instructions of the FT32B processor.
19466
19467       -mcompress
19468           Compress all code using the Ft32B code compression scheme.
19469
19470       -mnopm
19471           Do not generate code that reads program memory.
19472
19473   FRV Options
19474       -mgpr-32
19475           Only use the first 32 general-purpose registers.
19476
19477       -mgpr-64
19478           Use all 64 general-purpose registers.
19479
19480       -mfpr-32
19481           Use only the first 32 floating-point registers.
19482
19483       -mfpr-64
19484           Use all 64 floating-point registers.
19485
19486       -mhard-float
19487           Use hardware instructions for floating-point operations.
19488
19489       -msoft-float
19490           Use library routines for floating-point operations.
19491
19492       -malloc-cc
19493           Dynamically allocate condition code registers.
19494
19495       -mfixed-cc
19496           Do not try to dynamically allocate condition code registers, only
19497           use "icc0" and "fcc0".
19498
19499       -mdword
19500           Change ABI to use double word insns.
19501
19502       -mno-dword
19503           Do not use double word instructions.
19504
19505       -mdouble
19506           Use floating-point double instructions.
19507
19508       -mno-double
19509           Do not use floating-point double instructions.
19510
19511       -mmedia
19512           Use media instructions.
19513
19514       -mno-media
19515           Do not use media instructions.
19516
19517       -mmuladd
19518           Use multiply and add/subtract instructions.
19519
19520       -mno-muladd
19521           Do not use multiply and add/subtract instructions.
19522
19523       -mfdpic
19524           Select the FDPIC ABI, which uses function descriptors to represent
19525           pointers to functions.  Without any PIC/PIE-related options, it
19526           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
19527           small data are within a 12-bit range from the GOT base address;
19528           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
19529           bfin-elf target, this option implies -msim.
19530
19531       -minline-plt
19532           Enable inlining of PLT entries in function calls to functions that
19533           are not known to bind locally.  It has no effect without -mfdpic.
19534           It's enabled by default if optimizing for speed and compiling for
19535           shared libraries (i.e., -fPIC or -fpic), or when an optimization
19536           option such as -O3 or above is present in the command line.
19537
19538       -mTLS
19539           Assume a large TLS segment when generating thread-local code.
19540
19541       -mtls
19542           Do not assume a large TLS segment when generating thread-local
19543           code.
19544
19545       -mgprel-ro
19546           Enable the use of "GPREL" relocations in the FDPIC ABI for data
19547           that is known to be in read-only sections.  It's enabled by
19548           default, except for -fpic or -fpie: even though it may help make
19549           the global offset table smaller, it trades 1 instruction for 4.
19550           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
19551           may be shared by multiple symbols, and it avoids the need for a GOT
19552           entry for the referenced symbol, so it's more likely to be a win.
19553           If it is not, -mno-gprel-ro can be used to disable it.
19554
19555       -multilib-library-pic
19556           Link with the (library, not FD) pic libraries.  It's implied by
19557           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
19558           should never have to use it explicitly.
19559
19560       -mlinked-fp
19561           Follow the EABI requirement of always creating a frame pointer
19562           whenever a stack frame is allocated.  This option is enabled by
19563           default and can be disabled with -mno-linked-fp.
19564
19565       -mlong-calls
19566           Use indirect addressing to call functions outside the current
19567           compilation unit.  This allows the functions to be placed anywhere
19568           within the 32-bit address space.
19569
19570       -malign-labels
19571           Try to align labels to an 8-byte boundary by inserting NOPs into
19572           the previous packet.  This option only has an effect when VLIW
19573           packing is enabled.  It doesn't create new packets; it merely adds
19574           NOPs to existing ones.
19575
19576       -mlibrary-pic
19577           Generate position-independent EABI code.
19578
19579       -macc-4
19580           Use only the first four media accumulator registers.
19581
19582       -macc-8
19583           Use all eight media accumulator registers.
19584
19585       -mpack
19586           Pack VLIW instructions.
19587
19588       -mno-pack
19589           Do not pack VLIW instructions.
19590
19591       -mno-eflags
19592           Do not mark ABI switches in e_flags.
19593
19594       -mcond-move
19595           Enable the use of conditional-move instructions (default).
19596
19597           This switch is mainly for debugging the compiler and will likely be
19598           removed in a future version.
19599
19600       -mno-cond-move
19601           Disable the use of conditional-move instructions.
19602
19603           This switch is mainly for debugging the compiler and will likely be
19604           removed in a future version.
19605
19606       -mscc
19607           Enable the use of conditional set instructions (default).
19608
19609           This switch is mainly for debugging the compiler and will likely be
19610           removed in a future version.
19611
19612       -mno-scc
19613           Disable the use of conditional set instructions.
19614
19615           This switch is mainly for debugging the compiler and will likely be
19616           removed in a future version.
19617
19618       -mcond-exec
19619           Enable the use of conditional execution (default).
19620
19621           This switch is mainly for debugging the compiler and will likely be
19622           removed in a future version.
19623
19624       -mno-cond-exec
19625           Disable the use of conditional execution.
19626
19627           This switch is mainly for debugging the compiler and will likely be
19628           removed in a future version.
19629
19630       -mvliw-branch
19631           Run a pass to pack branches into VLIW instructions (default).
19632
19633           This switch is mainly for debugging the compiler and will likely be
19634           removed in a future version.
19635
19636       -mno-vliw-branch
19637           Do not run a pass to pack branches into VLIW instructions.
19638
19639           This switch is mainly for debugging the compiler and will likely be
19640           removed in a future version.
19641
19642       -mmulti-cond-exec
19643           Enable optimization of "&&" and "||" in conditional execution
19644           (default).
19645
19646           This switch is mainly for debugging the compiler and will likely be
19647           removed in a future version.
19648
19649       -mno-multi-cond-exec
19650           Disable optimization of "&&" and "||" in conditional execution.
19651
19652           This switch is mainly for debugging the compiler and will likely be
19653           removed in a future version.
19654
19655       -mnested-cond-exec
19656           Enable nested conditional execution optimizations (default).
19657
19658           This switch is mainly for debugging the compiler and will likely be
19659           removed in a future version.
19660
19661       -mno-nested-cond-exec
19662           Disable nested conditional execution optimizations.
19663
19664           This switch is mainly for debugging the compiler and will likely be
19665           removed in a future version.
19666
19667       -moptimize-membar
19668           This switch removes redundant "membar" instructions from the
19669           compiler-generated code.  It is enabled by default.
19670
19671       -mno-optimize-membar
19672           This switch disables the automatic removal of redundant "membar"
19673           instructions from the generated code.
19674
19675       -mtomcat-stats
19676           Cause gas to print out tomcat statistics.
19677
19678       -mcpu=cpu
19679           Select the processor type for which to generate code.  Possible
19680           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
19681           and simple.
19682
19683   GNU/Linux Options
19684       These -m options are defined for GNU/Linux targets:
19685
19686       -mglibc
19687           Use the GNU C library.  This is the default except on
19688           *-*-linux-*uclibc*, *-*-linux-*musl* and *-*-linux-*android*
19689           targets.
19690
19691       -muclibc
19692           Use uClibc C library.  This is the default on *-*-linux-*uclibc*
19693           targets.
19694
19695       -mmusl
19696           Use the musl C library.  This is the default on *-*-linux-*musl*
19697           targets.
19698
19699       -mbionic
19700           Use Bionic C library.  This is the default on *-*-linux-*android*
19701           targets.
19702
19703       -mandroid
19704           Compile code compatible with Android platform.  This is the default
19705           on *-*-linux-*android* targets.
19706
19707           When compiling, this option enables -mbionic, -fPIC,
19708           -fno-exceptions and -fno-rtti by default.  When linking, this
19709           option makes the GCC driver pass Android-specific options to the
19710           linker.  Finally, this option causes the preprocessor macro
19711           "__ANDROID__" to be defined.
19712
19713       -tno-android-cc
19714           Disable compilation effects of -mandroid, i.e., do not enable
19715           -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.
19716
19717       -tno-android-ld
19718           Disable linking effects of -mandroid, i.e., pass standard Linux
19719           linking options to the linker.
19720
19721   H8/300 Options
19722       These -m options are defined for the H8/300 implementations:
19723
19724       -mrelax
19725           Shorten some address references at link time, when possible; uses
19726           the linker option -relax.
19727
19728       -mh Generate code for the H8/300H.
19729
19730       -ms Generate code for the H8S.
19731
19732       -mn Generate code for the H8S and H8/300H in the normal mode.  This
19733           switch must be used either with -mh or -ms.
19734
19735       -ms2600
19736           Generate code for the H8S/2600.  This switch must be used with -ms.
19737
19738       -mexr
19739           Extended registers are stored on stack before execution of function
19740           with monitor attribute. Default option is -mexr.  This option is
19741           valid only for H8S targets.
19742
19743       -mno-exr
19744           Extended registers are not stored on stack before execution of
19745           function with monitor attribute. Default option is -mno-exr.  This
19746           option is valid only for H8S targets.
19747
19748       -mint32
19749           Make "int" data 32 bits by default.
19750
19751       -malign-300
19752           On the H8/300H and H8S, use the same alignment rules as for the
19753           H8/300.  The default for the H8/300H and H8S is to align longs and
19754           floats on 4-byte boundaries.  -malign-300 causes them to be aligned
19755           on 2-byte boundaries.  This option has no effect on the H8/300.
19756
19757   HPPA Options
19758       These -m options are defined for the HPPA family of computers:
19759
19760       -march=architecture-type
19761           Generate code for the specified architecture.  The choices for
19762           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
19763           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
19764           system to determine the proper architecture option for your
19765           machine.  Code compiled for lower numbered architectures runs on
19766           higher numbered architectures, but not the other way around.
19767
19768       -mpa-risc-1-0
19769       -mpa-risc-1-1
19770       -mpa-risc-2-0
19771           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
19772
19773       -mcaller-copies
19774           The caller copies function arguments passed by hidden reference.
19775           This option should be used with care as it is not compatible with
19776           the default 32-bit runtime.  However, only aggregates larger than
19777           eight bytes are passed by hidden reference and the option provides
19778           better compatibility with OpenMP.
19779
19780       -mjump-in-delay
19781           This option is ignored and provided for compatibility purposes
19782           only.
19783
19784       -mdisable-fpregs
19785           Prevent floating-point registers from being used in any manner.
19786           This is necessary for compiling kernels that perform lazy context
19787           switching of floating-point registers.  If you use this option and
19788           attempt to perform floating-point operations, the compiler aborts.
19789
19790       -mdisable-indexing
19791           Prevent the compiler from using indexing address modes.  This
19792           avoids some rather obscure problems when compiling MIG generated
19793           code under MACH.
19794
19795       -mno-space-regs
19796           Generate code that assumes the target has no space registers.  This
19797           allows GCC to generate faster indirect calls and use unscaled index
19798           address modes.
19799
19800           Such code is suitable for level 0 PA systems and kernels.
19801
19802       -mfast-indirect-calls
19803           Generate code that assumes calls never cross space boundaries.
19804           This allows GCC to emit code that performs faster indirect calls.
19805
19806           This option does not work in the presence of shared libraries or
19807           nested functions.
19808
19809       -mfixed-range=register-range
19810           Generate code treating the given register range as fixed registers.
19811           A fixed register is one that the register allocator cannot use.
19812           This is useful when compiling kernel code.  A register range is
19813           specified as two registers separated by a dash.  Multiple register
19814           ranges can be specified separated by a comma.
19815
19816       -mlong-load-store
19817           Generate 3-instruction load and store sequences as sometimes
19818           required by the HP-UX 10 linker.  This is equivalent to the +k
19819           option to the HP compilers.
19820
19821       -mportable-runtime
19822           Use the portable calling conventions proposed by HP for ELF
19823           systems.
19824
19825       -mgas
19826           Enable the use of assembler directives only GAS understands.
19827
19828       -mschedule=cpu-type
19829           Schedule code according to the constraints for the machine type
19830           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
19831           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
19832           to determine the proper scheduling option for your machine.  The
19833           default scheduling is 8000.
19834
19835       -mlinker-opt
19836           Enable the optimization pass in the HP-UX linker.  Note this makes
19837           symbolic debugging impossible.  It also triggers a bug in the HP-UX
19838           8 and HP-UX 9 linkers in which they give bogus error messages when
19839           linking some programs.
19840
19841       -msoft-float
19842           Generate output containing library calls for floating point.
19843           Warning: the requisite libraries are not available for all HPPA
19844           targets.  Normally the facilities of the machine's usual C compiler
19845           are used, but this cannot be done directly in cross-compilation.
19846           You must make your own arrangements to provide suitable library
19847           functions for cross-compilation.
19848
19849           -msoft-float changes the calling convention in the output file;
19850           therefore, it is only useful if you compile all of a program with
19851           this option.  In particular, you need to compile libgcc.a, the
19852           library that comes with GCC, with -msoft-float in order for this to
19853           work.
19854
19855       -msio
19856           Generate the predefine, "_SIO", for server IO.  The default is
19857           -mwsio.  This generates the predefines, "__hp9000s700",
19858           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
19859           are available under HP-UX and HI-UX.
19860
19861       -mgnu-ld
19862           Use options specific to GNU ld.  This passes -shared to ld when
19863           building a shared library.  It is the default when GCC is
19864           configured, explicitly or implicitly, with the GNU linker.  This
19865           option does not affect which ld is called; it only changes what
19866           parameters are passed to that ld.  The ld that is called is
19867           determined by the --with-ld configure option, GCC's program search
19868           path, and finally by the user's PATH.  The linker used by GCC can
19869           be printed using which `gcc -print-prog-name=ld`.  This option is
19870           only available on the 64-bit HP-UX GCC, i.e. configured with
19871           hppa*64*-*-hpux*.
19872
19873       -mhp-ld
19874           Use options specific to HP ld.  This passes -b to ld when building
19875           a shared library and passes +Accept TypeMismatch to ld on all
19876           links.  It is the default when GCC is configured, explicitly or
19877           implicitly, with the HP linker.  This option does not affect which
19878           ld is called; it only changes what parameters are passed to that
19879           ld.  The ld that is called is determined by the --with-ld configure
19880           option, GCC's program search path, and finally by the user's PATH.
19881           The linker used by GCC can be printed using which `gcc
19882           -print-prog-name=ld`.  This option is only available on the 64-bit
19883           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.
19884
19885       -mlong-calls
19886           Generate code that uses long call sequences.  This ensures that a
19887           call is always able to reach linker generated stubs.  The default
19888           is to generate long calls only when the distance from the call site
19889           to the beginning of the function or translation unit, as the case
19890           may be, exceeds a predefined limit set by the branch type being
19891           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
19892           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
19893           always limited at 240,000 bytes.
19894
19895           Distances are measured from the beginning of functions when using
19896           the -ffunction-sections option, or when using the -mgas and
19897           -mno-portable-runtime options together under HP-UX with the SOM
19898           linker.
19899
19900           It is normally not desirable to use this option as it degrades
19901           performance.  However, it may be useful in large applications,
19902           particularly when partial linking is used to build the application.
19903
19904           The types of long calls used depends on the capabilities of the
19905           assembler and linker, and the type of code being generated.  The
19906           impact on systems that support long absolute calls, and long pic
19907           symbol-difference or pc-relative calls should be relatively small.
19908           However, an indirect call is used on 32-bit ELF systems in pic code
19909           and it is quite long.
19910
19911       -munix=unix-std
19912           Generate compiler predefines and select a startfile for the
19913           specified UNIX standard.  The choices for unix-std are 93, 95 and
19914           98.  93 is supported on all HP-UX versions.  95 is available on HP-
19915           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
19916           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
19917           11.00, and 98 for HP-UX 11.11 and later.
19918
19919           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
19920           -munix=95 provides additional predefines for "XOPEN_UNIX" and
19921           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
19922           provides additional predefines for "_XOPEN_UNIX",
19923           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
19924           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.
19925
19926           It is important to note that this option changes the interfaces for
19927           various library routines.  It also affects the operational behavior
19928           of the C library.  Thus, extreme care is needed in using this
19929           option.
19930
19931           Library code that is intended to operate with more than one UNIX
19932           standard must test, set and restore the variable
19933           "__xpg4_extended_mask" as appropriate.  Most GNU software doesn't
19934           provide this capability.
19935
19936       -nolibdld
19937           Suppress the generation of link options to search libdld.sl when
19938           the -static option is specified on HP-UX 10 and later.
19939
19940       -static
19941           The HP-UX implementation of setlocale in libc has a dependency on
19942           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
19943           when the -static option is specified, special link options are
19944           needed to resolve this dependency.
19945
19946           On HP-UX 10 and later, the GCC driver adds the necessary options to
19947           link with libdld.sl when the -static option is specified.  This
19948           causes the resulting binary to be dynamic.  On the 64-bit port, the
19949           linkers generate dynamic binaries by default in any case.  The
19950           -nolibdld option can be used to prevent the GCC driver from adding
19951           these link options.
19952
19953       -threads
19954           Add support for multithreading with the dce thread library under
19955           HP-UX.  This option sets flags for both the preprocessor and
19956           linker.
19957
19958   IA-64 Options
19959       These are the -m options defined for the Intel IA-64 architecture.
19960
19961       -mbig-endian
19962           Generate code for a big-endian target.  This is the default for HP-
19963           UX.
19964
19965       -mlittle-endian
19966           Generate code for a little-endian target.  This is the default for
19967           AIX5 and GNU/Linux.
19968
19969       -mgnu-as
19970       -mno-gnu-as
19971           Generate (or don't) code for the GNU assembler.  This is the
19972           default.
19973
19974       -mgnu-ld
19975       -mno-gnu-ld
19976           Generate (or don't) code for the GNU linker.  This is the default.
19977
19978       -mno-pic
19979           Generate code that does not use a global pointer register.  The
19980           result is not position independent code, and violates the IA-64
19981           ABI.
19982
19983       -mvolatile-asm-stop
19984       -mno-volatile-asm-stop
19985           Generate (or don't) a stop bit immediately before and after
19986           volatile asm statements.
19987
19988       -mregister-names
19989       -mno-register-names
19990           Generate (or don't) in, loc, and out register names for the stacked
19991           registers.  This may make assembler output more readable.
19992
19993       -mno-sdata
19994       -msdata
19995           Disable (or enable) optimizations that use the small data section.
19996           This may be useful for working around optimizer bugs.
19997
19998       -mconstant-gp
19999           Generate code that uses a single constant global pointer value.
20000           This is useful when compiling kernel code.
20001
20002       -mauto-pic
20003           Generate code that is self-relocatable.  This implies
20004           -mconstant-gp.  This is useful when compiling firmware code.
20005
20006       -minline-float-divide-min-latency
20007           Generate code for inline divides of floating-point values using the
20008           minimum latency algorithm.
20009
20010       -minline-float-divide-max-throughput
20011           Generate code for inline divides of floating-point values using the
20012           maximum throughput algorithm.
20013
20014       -mno-inline-float-divide
20015           Do not generate inline code for divides of floating-point values.
20016
20017       -minline-int-divide-min-latency
20018           Generate code for inline divides of integer values using the
20019           minimum latency algorithm.
20020
20021       -minline-int-divide-max-throughput
20022           Generate code for inline divides of integer values using the
20023           maximum throughput algorithm.
20024
20025       -mno-inline-int-divide
20026           Do not generate inline code for divides of integer values.
20027
20028       -minline-sqrt-min-latency
20029           Generate code for inline square roots using the minimum latency
20030           algorithm.
20031
20032       -minline-sqrt-max-throughput
20033           Generate code for inline square roots using the maximum throughput
20034           algorithm.
20035
20036       -mno-inline-sqrt
20037           Do not generate inline code for "sqrt".
20038
20039       -mfused-madd
20040       -mno-fused-madd
20041           Do (don't) generate code that uses the fused multiply/add or
20042           multiply/subtract instructions.  The default is to use these
20043           instructions.
20044
20045       -mno-dwarf2-asm
20046       -mdwarf2-asm
20047           Don't (or do) generate assembler code for the DWARF line number
20048           debugging info.  This may be useful when not using the GNU
20049           assembler.
20050
20051       -mearly-stop-bits
20052       -mno-early-stop-bits
20053           Allow stop bits to be placed earlier than immediately preceding the
20054           instruction that triggered the stop bit.  This can improve
20055           instruction scheduling, but does not always do so.
20056
20057       -mfixed-range=register-range
20058           Generate code treating the given register range as fixed registers.
20059           A fixed register is one that the register allocator cannot use.
20060           This is useful when compiling kernel code.  A register range is
20061           specified as two registers separated by a dash.  Multiple register
20062           ranges can be specified separated by a comma.
20063
20064       -mtls-size=tls-size
20065           Specify bit size of immediate TLS offsets.  Valid values are 14,
20066           22, and 64.
20067
20068       -mtune=cpu-type
20069           Tune the instruction scheduling for a particular CPU, Valid values
20070           are itanium, itanium1, merced, itanium2, and mckinley.
20071
20072       -milp32
20073       -mlp64
20074           Generate code for a 32-bit or 64-bit environment.  The 32-bit
20075           environment sets int, long and pointer to 32 bits.  The 64-bit
20076           environment sets int to 32 bits and long and pointer to 64 bits.
20077           These are HP-UX specific flags.
20078
20079       -mno-sched-br-data-spec
20080       -msched-br-data-spec
20081           (Dis/En)able data speculative scheduling before reload.  This
20082           results in generation of "ld.a" instructions and the corresponding
20083           check instructions ("ld.c" / "chk.a").  The default setting is
20084           disabled.
20085
20086       -msched-ar-data-spec
20087       -mno-sched-ar-data-spec
20088           (En/Dis)able data speculative scheduling after reload.  This
20089           results in generation of "ld.a" instructions and the corresponding
20090           check instructions ("ld.c" / "chk.a").  The default setting is
20091           enabled.
20092
20093       -mno-sched-control-spec
20094       -msched-control-spec
20095           (Dis/En)able control speculative scheduling.  This feature is
20096           available only during region scheduling (i.e. before reload).  This
20097           results in generation of the "ld.s" instructions and the
20098           corresponding check instructions "chk.s".  The default setting is
20099           disabled.
20100
20101       -msched-br-in-data-spec
20102       -mno-sched-br-in-data-spec
20103           (En/Dis)able speculative scheduling of the instructions that are
20104           dependent on the data speculative loads before reload.  This is
20105           effective only with -msched-br-data-spec enabled.  The default
20106           setting is enabled.
20107
20108       -msched-ar-in-data-spec
20109       -mno-sched-ar-in-data-spec
20110           (En/Dis)able speculative scheduling of the instructions that are
20111           dependent on the data speculative loads after reload.  This is
20112           effective only with -msched-ar-data-spec enabled.  The default
20113           setting is enabled.
20114
20115       -msched-in-control-spec
20116       -mno-sched-in-control-spec
20117           (En/Dis)able speculative scheduling of the instructions that are
20118           dependent on the control speculative loads.  This is effective only
20119           with -msched-control-spec enabled.  The default setting is enabled.
20120
20121       -mno-sched-prefer-non-data-spec-insns
20122       -msched-prefer-non-data-spec-insns
20123           If enabled, data-speculative instructions are chosen for schedule
20124           only if there are no other choices at the moment.  This makes the
20125           use of the data speculation much more conservative.  The default
20126           setting is disabled.
20127
20128       -mno-sched-prefer-non-control-spec-insns
20129       -msched-prefer-non-control-spec-insns
20130           If enabled, control-speculative instructions are chosen for
20131           schedule only if there are no other choices at the moment.  This
20132           makes the use of the control speculation much more conservative.
20133           The default setting is disabled.
20134
20135       -mno-sched-count-spec-in-critical-path
20136       -msched-count-spec-in-critical-path
20137           If enabled, speculative dependencies are considered during
20138           computation of the instructions priorities.  This makes the use of
20139           the speculation a bit more conservative.  The default setting is
20140           disabled.
20141
20142       -msched-spec-ldc
20143           Use a simple data speculation check.  This option is on by default.
20144
20145       -msched-control-spec-ldc
20146           Use a simple check for control speculation.  This option is on by
20147           default.
20148
20149       -msched-stop-bits-after-every-cycle
20150           Place a stop bit after every cycle when scheduling.  This option is
20151           on by default.
20152
20153       -msched-fp-mem-deps-zero-cost
20154           Assume that floating-point stores and loads are not likely to cause
20155           a conflict when placed into the same instruction group.  This
20156           option is disabled by default.
20157
20158       -msel-sched-dont-check-control-spec
20159           Generate checks for control speculation in selective scheduling.
20160           This flag is disabled by default.
20161
20162       -msched-max-memory-insns=max-insns
20163           Limit on the number of memory insns per instruction group, giving
20164           lower priority to subsequent memory insns attempting to schedule in
20165           the same instruction group. Frequently useful to prevent cache bank
20166           conflicts.  The default value is 1.
20167
20168       -msched-max-memory-insns-hard-limit
20169           Makes the limit specified by msched-max-memory-insns a hard limit,
20170           disallowing more than that number in an instruction group.
20171           Otherwise, the limit is "soft", meaning that non-memory operations
20172           are preferred when the limit is reached, but memory operations may
20173           still be scheduled.
20174
20175   LM32 Options
20176       These -m options are defined for the LatticeMico32 architecture:
20177
20178       -mbarrel-shift-enabled
20179           Enable barrel-shift instructions.
20180
20181       -mdivide-enabled
20182           Enable divide and modulus instructions.
20183
20184       -mmultiply-enabled
20185           Enable multiply instructions.
20186
20187       -msign-extend-enabled
20188           Enable sign extend instructions.
20189
20190       -muser-enabled
20191           Enable user-defined instructions.
20192
20193   M32C Options
20194       -mcpu=name
20195           Select the CPU for which code is generated.  name may be one of r8c
20196           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
20197           m32cm for the M16C/80 series, or m32c for the M32C/80 series.
20198
20199       -msim
20200           Specifies that the program will be run on the simulator.  This
20201           causes an alternate runtime library to be linked in which supports,
20202           for example, file I/O.  You must not use this option when
20203           generating programs that will run on real hardware; you must
20204           provide your own runtime library for whatever I/O functions are
20205           needed.
20206
20207       -memregs=number
20208           Specifies the number of memory-based pseudo-registers GCC uses
20209           during code generation.  These pseudo-registers are used like real
20210           registers, so there is a tradeoff between GCC's ability to fit the
20211           code into available registers, and the performance penalty of using
20212           memory instead of registers.  Note that all modules in a program
20213           must be compiled with the same value for this option.  Because of
20214           that, you must not use this option with GCC's default runtime
20215           libraries.
20216
20217   M32R/D Options
20218       These -m options are defined for Renesas M32R/D architectures:
20219
20220       -m32r2
20221           Generate code for the M32R/2.
20222
20223       -m32rx
20224           Generate code for the M32R/X.
20225
20226       -m32r
20227           Generate code for the M32R.  This is the default.
20228
20229       -mmodel=small
20230           Assume all objects live in the lower 16MB of memory (so that their
20231           addresses can be loaded with the "ld24" instruction), and assume
20232           all subroutines are reachable with the "bl" instruction.  This is
20233           the default.
20234
20235           The addressability of a particular object can be set with the
20236           "model" attribute.
20237
20238       -mmodel=medium
20239           Assume objects may be anywhere in the 32-bit address space (the
20240           compiler generates "seth/add3" instructions to load their
20241           addresses), and assume all subroutines are reachable with the "bl"
20242           instruction.
20243
20244       -mmodel=large
20245           Assume objects may be anywhere in the 32-bit address space (the
20246           compiler generates "seth/add3" instructions to load their
20247           addresses), and assume subroutines may not be reachable with the
20248           "bl" instruction (the compiler generates the much slower
20249           "seth/add3/jl" instruction sequence).
20250
20251       -msdata=none
20252           Disable use of the small data area.  Variables are put into one of
20253           ".data", ".bss", or ".rodata" (unless the "section" attribute has
20254           been specified).  This is the default.
20255
20256           The small data area consists of sections ".sdata" and ".sbss".
20257           Objects may be explicitly put in the small data area with the
20258           "section" attribute using one of these sections.
20259
20260       -msdata=sdata
20261           Put small global and static data in the small data area, but do not
20262           generate special code to reference them.
20263
20264       -msdata=use
20265           Put small global and static data in the small data area, and
20266           generate special instructions to reference them.
20267
20268       -G num
20269           Put global and static objects less than or equal to num bytes into
20270           the small data or BSS sections instead of the normal data or BSS
20271           sections.  The default value of num is 8.  The -msdata option must
20272           be set to one of sdata or use for this option to have any effect.
20273
20274           All modules should be compiled with the same -G num value.
20275           Compiling with different values of num may or may not work; if it
20276           doesn't the linker gives an error message---incorrect code is not
20277           generated.
20278
20279       -mdebug
20280           Makes the M32R-specific code in the compiler display some
20281           statistics that might help in debugging programs.
20282
20283       -malign-loops
20284           Align all loops to a 32-byte boundary.
20285
20286       -mno-align-loops
20287           Do not enforce a 32-byte alignment for loops.  This is the default.
20288
20289       -missue-rate=number
20290           Issue number instructions per cycle.  number can only be 1 or 2.
20291
20292       -mbranch-cost=number
20293           number can only be 1 or 2.  If it is 1 then branches are preferred
20294           over conditional code, if it is 2, then the opposite applies.
20295
20296       -mflush-trap=number
20297           Specifies the trap number to use to flush the cache.  The default
20298           is 12.  Valid numbers are between 0 and 15 inclusive.
20299
20300       -mno-flush-trap
20301           Specifies that the cache cannot be flushed by using a trap.
20302
20303       -mflush-func=name
20304           Specifies the name of the operating system function to call to
20305           flush the cache.  The default is _flush_cache, but a function call
20306           is only used if a trap is not available.
20307
20308       -mno-flush-func
20309           Indicates that there is no OS function for flushing the cache.
20310
20311   M680x0 Options
20312       These are the -m options defined for M680x0 and ColdFire processors.
20313       The default settings depend on which architecture was selected when the
20314       compiler was configured; the defaults for the most common choices are
20315       given below.
20316
20317       -march=arch
20318           Generate code for a specific M680x0 or ColdFire instruction set
20319           architecture.  Permissible values of arch for M680x0 architectures
20320           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
20321           architectures are selected according to Freescale's ISA
20322           classification and the permissible values are: isaa, isaaplus, isab
20323           and isac.
20324
20325           GCC defines a macro "__mcfarch__" whenever it is generating code
20326           for a ColdFire target.  The arch in this macro is one of the -march
20327           arguments given above.
20328
20329           When used together, -march and -mtune select code that runs on a
20330           family of similar processors but that is optimized for a particular
20331           microarchitecture.
20332
20333       -mcpu=cpu
20334           Generate code for a specific M680x0 or ColdFire processor.  The
20335           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
20336           68332 and cpu32.  The ColdFire cpus are given by the table below,
20337           which also classifies the CPUs into families:
20338
20339           Family : -mcpu arguments
20340           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
20341           5206 : 5202 5204 5206
20342           5206e : 5206e
20343           5208 : 5207 5208
20344           5211a : 5210a 5211a
20345           5213 : 5211 5212 5213
20346           5216 : 5214 5216
20347           52235 : 52230 52231 52232 52233 52234 52235
20348           5225 : 5224 5225
20349           52259 : 52252 52254 52255 52256 52258 52259
20350           5235 : 5232 5233 5234 5235 523x
20351           5249 : 5249
20352           5250 : 5250
20353           5271 : 5270 5271
20354           5272 : 5272
20355           5275 : 5274 5275
20356           5282 : 5280 5281 5282 528x
20357           53017 : 53011 53012 53013 53014 53015 53016 53017
20358           5307 : 5307
20359           5329 : 5327 5328 5329 532x
20360           5373 : 5372 5373 537x
20361           5407 : 5407
20362           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
20363           5485
20364
20365           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
20366           Other combinations of -mcpu and -march are rejected.
20367
20368           GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is
20369           selected.  It also defines "__mcf_family_family", where the value
20370           of family is given by the table above.
20371
20372       -mtune=tune
20373           Tune the code for a particular microarchitecture within the
20374           constraints set by -march and -mcpu.  The M680x0 microarchitectures
20375           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
20376           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
20377
20378           You can also use -mtune=68020-40 for code that needs to run
20379           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
20380           is similar but includes 68060 targets as well.  These two options
20381           select the same tuning decisions as -m68020-40 and -m68020-60
20382           respectively.
20383
20384           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for
20385           680x0 architecture arch.  It also defines "mcarch" unless either
20386           -ansi or a non-GNU -std option is used.  If GCC is tuning for a
20387           range of architectures, as selected by -mtune=68020-40 or
20388           -mtune=68020-60, it defines the macros for every architecture in
20389           the range.
20390
20391           GCC also defines the macro "__muarch__" when tuning for ColdFire
20392           microarchitecture uarch, where uarch is one of the arguments given
20393           above.
20394
20395       -m68000
20396       -mc68000
20397           Generate output for a 68000.  This is the default when the compiler
20398           is configured for 68000-based systems.  It is equivalent to
20399           -march=68000.
20400
20401           Use this option for microcontrollers with a 68000 or EC000 core,
20402           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
20403
20404       -m68010
20405           Generate output for a 68010.  This is the default when the compiler
20406           is configured for 68010-based systems.  It is equivalent to
20407           -march=68010.
20408
20409       -m68020
20410       -mc68020
20411           Generate output for a 68020.  This is the default when the compiler
20412           is configured for 68020-based systems.  It is equivalent to
20413           -march=68020.
20414
20415       -m68030
20416           Generate output for a 68030.  This is the default when the compiler
20417           is configured for 68030-based systems.  It is equivalent to
20418           -march=68030.
20419
20420       -m68040
20421           Generate output for a 68040.  This is the default when the compiler
20422           is configured for 68040-based systems.  It is equivalent to
20423           -march=68040.
20424
20425           This option inhibits the use of 68881/68882 instructions that have
20426           to be emulated by software on the 68040.  Use this option if your
20427           68040 does not have code to emulate those instructions.
20428
20429       -m68060
20430           Generate output for a 68060.  This is the default when the compiler
20431           is configured for 68060-based systems.  It is equivalent to
20432           -march=68060.
20433
20434           This option inhibits the use of 68020 and 68881/68882 instructions
20435           that have to be emulated by software on the 68060.  Use this option
20436           if your 68060 does not have code to emulate those instructions.
20437
20438       -mcpu32
20439           Generate output for a CPU32.  This is the default when the compiler
20440           is configured for CPU32-based systems.  It is equivalent to
20441           -march=cpu32.
20442
20443           Use this option for microcontrollers with a CPU32 or CPU32+ core,
20444           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
20445           68341, 68349 and 68360.
20446
20447       -m5200
20448           Generate output for a 520X ColdFire CPU.  This is the default when
20449           the compiler is configured for 520X-based systems.  It is
20450           equivalent to -mcpu=5206, and is now deprecated in favor of that
20451           option.
20452
20453           Use this option for microcontroller with a 5200 core, including the
20454           MCF5202, MCF5203, MCF5204 and MCF5206.
20455
20456       -m5206e
20457           Generate output for a 5206e ColdFire CPU.  The option is now
20458           deprecated in favor of the equivalent -mcpu=5206e.
20459
20460       -m528x
20461           Generate output for a member of the ColdFire 528X family.  The
20462           option is now deprecated in favor of the equivalent -mcpu=528x.
20463
20464       -m5307
20465           Generate output for a ColdFire 5307 CPU.  The option is now
20466           deprecated in favor of the equivalent -mcpu=5307.
20467
20468       -m5407
20469           Generate output for a ColdFire 5407 CPU.  The option is now
20470           deprecated in favor of the equivalent -mcpu=5407.
20471
20472       -mcfv4e
20473           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
20474           This includes use of hardware floating-point instructions.  The
20475           option is equivalent to -mcpu=547x, and is now deprecated in favor
20476           of that option.
20477
20478       -m68020-40
20479           Generate output for a 68040, without using any of the new
20480           instructions.  This results in code that can run relatively
20481           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
20482           generated code does use the 68881 instructions that are emulated on
20483           the 68040.
20484
20485           The option is equivalent to -march=68020 -mtune=68020-40.
20486
20487       -m68020-60
20488           Generate output for a 68060, without using any of the new
20489           instructions.  This results in code that can run relatively
20490           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
20491           generated code does use the 68881 instructions that are emulated on
20492           the 68060.
20493
20494           The option is equivalent to -march=68020 -mtune=68020-60.
20495
20496       -mhard-float
20497       -m68881
20498           Generate floating-point instructions.  This is the default for
20499           68020 and above, and for ColdFire devices that have an FPU.  It
20500           defines the macro "__HAVE_68881__" on M680x0 targets and
20501           "__mcffpu__" on ColdFire targets.
20502
20503       -msoft-float
20504           Do not generate floating-point instructions; use library calls
20505           instead.  This is the default for 68000, 68010, and 68832 targets.
20506           It is also the default for ColdFire devices that have no FPU.
20507
20508       -mdiv
20509       -mno-div
20510           Generate (do not generate) ColdFire hardware divide and remainder
20511           instructions.  If -march is used without -mcpu, the default is "on"
20512           for ColdFire architectures and "off" for M680x0 architectures.
20513           Otherwise, the default is taken from the target CPU (either the
20514           default CPU, or the one specified by -mcpu).  For example, the
20515           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.
20516
20517           GCC defines the macro "__mcfhwdiv__" when this option is enabled.
20518
20519       -mshort
20520           Consider type "int" to be 16 bits wide, like "short int".
20521           Additionally, parameters passed on the stack are also aligned to a
20522           16-bit boundary even on targets whose API mandates promotion to
20523           32-bit.
20524
20525       -mno-short
20526           Do not consider type "int" to be 16 bits wide.  This is the
20527           default.
20528
20529       -mnobitfield
20530       -mno-bitfield
20531           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
20532           -m5200 options imply -mnobitfield.
20533
20534       -mbitfield
20535           Do use the bit-field instructions.  The -m68020 option implies
20536           -mbitfield.  This is the default if you use a configuration
20537           designed for a 68020.
20538
20539       -mrtd
20540           Use a different function-calling convention, in which functions
20541           that take a fixed number of arguments return with the "rtd"
20542           instruction, which pops their arguments while returning.  This
20543           saves one instruction in the caller since there is no need to pop
20544           the arguments there.
20545
20546           This calling convention is incompatible with the one normally used
20547           on Unix, so you cannot use it if you need to call libraries
20548           compiled with the Unix compiler.
20549
20550           Also, you must provide function prototypes for all functions that
20551           take variable numbers of arguments (including "printf"); otherwise
20552           incorrect code is generated for calls to those functions.
20553
20554           In addition, seriously incorrect code results if you call a
20555           function with too many arguments.  (Normally, extra arguments are
20556           harmlessly ignored.)
20557
20558           The "rtd" instruction is supported by the 68010, 68020, 68030,
20559           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
20560
20561           The default is -mno-rtd.
20562
20563       -malign-int
20564       -mno-align-int
20565           Control whether GCC aligns "int", "long", "long long", "float",
20566           "double", and "long double" variables on a 32-bit boundary
20567           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
20568           variables on 32-bit boundaries produces code that runs somewhat
20569           faster on processors with 32-bit busses at the expense of more
20570           memory.
20571
20572           Warning: if you use the -malign-int switch, GCC aligns structures
20573           containing the above types differently than most published
20574           application binary interface specifications for the m68k.
20575
20576           Use the pc-relative addressing mode of the 68000 directly, instead
20577           of using a global offset table.  At present, this option implies
20578           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
20579           -fPIC is not presently supported with -mpcrel, though this could be
20580           supported for 68020 and higher processors.
20581
20582       -mno-strict-align
20583       -mstrict-align
20584           Do not (do) assume that unaligned memory references are handled by
20585           the system.
20586
20587       -msep-data
20588           Generate code that allows the data segment to be located in a
20589           different area of memory from the text segment.  This allows for
20590           execute-in-place in an environment without virtual memory
20591           management.  This option implies -fPIC.
20592
20593       -mno-sep-data
20594           Generate code that assumes that the data segment follows the text
20595           segment.  This is the default.
20596
20597       -mid-shared-library
20598           Generate code that supports shared libraries via the library ID
20599           method.  This allows for execute-in-place and shared libraries in
20600           an environment without virtual memory management.  This option
20601           implies -fPIC.
20602
20603       -mno-id-shared-library
20604           Generate code that doesn't assume ID-based shared libraries are
20605           being used.  This is the default.
20606
20607       -mshared-library-id=n
20608           Specifies the identification number of the ID-based shared library
20609           being compiled.  Specifying a value of 0 generates more compact
20610           code; specifying other values forces the allocation of that number
20611           to the current library, but is no more space- or time-efficient
20612           than omitting this option.
20613
20614       -mxgot
20615       -mno-xgot
20616           When generating position-independent code for ColdFire, generate
20617           code that works if the GOT has more than 8192 entries.  This code
20618           is larger and slower than code generated without this option.  On
20619           M680x0 processors, this option is not needed; -fPIC suffices.
20620
20621           GCC normally uses a single instruction to load values from the GOT.
20622           While this is relatively efficient, it only works if the GOT is
20623           smaller than about 64k.  Anything larger causes the linker to
20624           report an error such as:
20625
20626                   relocation truncated to fit: R_68K_GOT16O foobar
20627
20628           If this happens, you should recompile your code with -mxgot.  It
20629           should then work with very large GOTs.  However, code generated
20630           with -mxgot is less efficient, since it takes 4 instructions to
20631           fetch the value of a global symbol.
20632
20633           Note that some linkers, including newer versions of the GNU linker,
20634           can create multiple GOTs and sort GOT entries.  If you have such a
20635           linker, you should only need to use -mxgot when compiling a single
20636           object file that accesses more than 8192 GOT entries.  Very few do.
20637
20638           These options have no effect unless GCC is generating position-
20639           independent code.
20640
20641       -mlong-jump-table-offsets
20642           Use 32-bit offsets in "switch" tables.  The default is to use
20643           16-bit offsets.
20644
20645   MCore Options
20646       These are the -m options defined for the Motorola M*Core processors.
20647
20648       -mhardlit
20649       -mno-hardlit
20650           Inline constants into the code stream if it can be done in two
20651           instructions or less.
20652
20653       -mdiv
20654       -mno-div
20655           Use the divide instruction.  (Enabled by default).
20656
20657       -mrelax-immediate
20658       -mno-relax-immediate
20659           Allow arbitrary-sized immediates in bit operations.
20660
20661       -mwide-bitfields
20662       -mno-wide-bitfields
20663           Always treat bit-fields as "int"-sized.
20664
20665       -m4byte-functions
20666       -mno-4byte-functions
20667           Force all functions to be aligned to a 4-byte boundary.
20668
20669       -mcallgraph-data
20670       -mno-callgraph-data
20671           Emit callgraph information.
20672
20673       -mslow-bytes
20674       -mno-slow-bytes
20675           Prefer word access when reading byte quantities.
20676
20677       -mlittle-endian
20678       -mbig-endian
20679           Generate code for a little-endian target.
20680
20681       -m210
20682       -m340
20683           Generate code for the 210 processor.
20684
20685       -mno-lsim
20686           Assume that runtime support has been provided and so omit the
20687           simulator library (libsim.a) from the linker command line.
20688
20689       -mstack-increment=size
20690           Set the maximum amount for a single stack increment operation.
20691           Large values can increase the speed of programs that contain
20692           functions that need a large amount of stack space, but they can
20693           also trigger a segmentation fault if the stack is extended too
20694           much.  The default value is 0x1000.
20695
20696   MeP Options
20697       -mabsdiff
20698           Enables the "abs" instruction, which is the absolute difference
20699           between two registers.
20700
20701       -mall-opts
20702           Enables all the optional instructions---average, multiply, divide,
20703           bit operations, leading zero, absolute difference, min/max, clip,
20704           and saturation.
20705
20706       -maverage
20707           Enables the "ave" instruction, which computes the average of two
20708           registers.
20709
20710       -mbased=n
20711           Variables of size n bytes or smaller are placed in the ".based"
20712           section by default.  Based variables use the $tp register as a base
20713           register, and there is a 128-byte limit to the ".based" section.
20714
20715       -mbitops
20716           Enables the bit operation instructions---bit test ("btstm"), set
20717           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
20718           ("tas").
20719
20720       -mc=name
20721           Selects which section constant data is placed in.  name may be
20722           tiny, near, or far.
20723
20724       -mclip
20725           Enables the "clip" instruction.  Note that -mclip is not useful
20726           unless you also provide -mminmax.
20727
20728       -mconfig=name
20729           Selects one of the built-in core configurations.  Each MeP chip has
20730           one or more modules in it; each module has a core CPU and a variety
20731           of coprocessors, optional instructions, and peripherals.  The
20732           "MeP-Integrator" tool, not part of GCC, provides these
20733           configurations through this option; using this option is the same
20734           as using all the corresponding command-line options.  The default
20735           configuration is default.
20736
20737       -mcop
20738           Enables the coprocessor instructions.  By default, this is a 32-bit
20739           coprocessor.  Note that the coprocessor is normally enabled via the
20740           -mconfig= option.
20741
20742       -mcop32
20743           Enables the 32-bit coprocessor's instructions.
20744
20745       -mcop64
20746           Enables the 64-bit coprocessor's instructions.
20747
20748       -mivc2
20749           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
20750
20751       -mdc
20752           Causes constant variables to be placed in the ".near" section.
20753
20754       -mdiv
20755           Enables the "div" and "divu" instructions.
20756
20757       -meb
20758           Generate big-endian code.
20759
20760       -mel
20761           Generate little-endian code.
20762
20763       -mio-volatile
20764           Tells the compiler that any variable marked with the "io" attribute
20765           is to be considered volatile.
20766
20767       -ml Causes variables to be assigned to the ".far" section by default.
20768
20769       -mleadz
20770           Enables the "leadz" (leading zero) instruction.
20771
20772       -mm Causes variables to be assigned to the ".near" section by default.
20773
20774       -mminmax
20775           Enables the "min" and "max" instructions.
20776
20777       -mmult
20778           Enables the multiplication and multiply-accumulate instructions.
20779
20780       -mno-opts
20781           Disables all the optional instructions enabled by -mall-opts.
20782
20783       -mrepeat
20784           Enables the "repeat" and "erepeat" instructions, used for low-
20785           overhead looping.
20786
20787       -ms Causes all variables to default to the ".tiny" section.  Note that
20788           there is a 65536-byte limit to this section.  Accesses to these
20789           variables use the %gp base register.
20790
20791       -msatur
20792           Enables the saturation instructions.  Note that the compiler does
20793           not currently generate these itself, but this option is included
20794           for compatibility with other tools, like "as".
20795
20796       -msdram
20797           Link the SDRAM-based runtime instead of the default ROM-based
20798           runtime.
20799
20800       -msim
20801           Link the simulator run-time libraries.
20802
20803       -msimnovec
20804           Link the simulator runtime libraries, excluding built-in support
20805           for reset and exception vectors and tables.
20806
20807       -mtf
20808           Causes all functions to default to the ".far" section.  Without
20809           this option, functions default to the ".near" section.
20810
20811       -mtiny=n
20812           Variables that are n bytes or smaller are allocated to the ".tiny"
20813           section.  These variables use the $gp base register.  The default
20814           for this option is 4, but note that there's a 65536-byte limit to
20815           the ".tiny" section.
20816
20817   MicroBlaze Options
20818       -msoft-float
20819           Use software emulation for floating point (default).
20820
20821       -mhard-float
20822           Use hardware floating-point instructions.
20823
20824       -mmemcpy
20825           Do not optimize block moves, use "memcpy".
20826
20827       -mno-clearbss
20828           This option is deprecated.  Use -fno-zero-initialized-in-bss
20829           instead.
20830
20831       -mcpu=cpu-type
20832           Use features of, and schedule code for, the given CPU.  Supported
20833           values are in the format vX.YY.Z, where X is a major version, YY is
20834           the minor version, and Z is compatibility code.  Example values are
20835           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.
20836
20837       -mxl-soft-mul
20838           Use software multiply emulation (default).
20839
20840       -mxl-soft-div
20841           Use software emulation for divides (default).
20842
20843       -mxl-barrel-shift
20844           Use the hardware barrel shifter.
20845
20846       -mxl-pattern-compare
20847           Use pattern compare instructions.
20848
20849       -msmall-divides
20850           Use table lookup optimization for small signed integer divisions.
20851
20852       -mxl-stack-check
20853           This option is deprecated.  Use -fstack-check instead.
20854
20855       -mxl-gp-opt
20856           Use GP-relative ".sdata"/".sbss" sections.
20857
20858       -mxl-multiply-high
20859           Use multiply high instructions for high part of 32x32 multiply.
20860
20861       -mxl-float-convert
20862           Use hardware floating-point conversion instructions.
20863
20864       -mxl-float-sqrt
20865           Use hardware floating-point square root instruction.
20866
20867       -mbig-endian
20868           Generate code for a big-endian target.
20869
20870       -mlittle-endian
20871           Generate code for a little-endian target.
20872
20873       -mxl-reorder
20874           Use reorder instructions (swap and byte reversed load/store).
20875
20876       -mxl-mode-app-model
20877           Select application model app-model.  Valid models are
20878
20879           executable
20880               normal executable (default), uses startup code crt0.o.
20881
20882           -mpic-data-is-text-relative
20883               Assume that the displacement between the text and data segments
20884               is fixed at static link time.  This allows data to be
20885               referenced by offset from start of text address instead of GOT
20886               since PC-relative addressing is not supported.
20887
20888           xmdstub
20889               for use with Xilinx Microprocessor Debugger (XMD) based
20890               software intrusive debug agent called xmdstub. This uses
20891               startup file crt1.o and sets the start address of the program
20892               to 0x800.
20893
20894           bootstrap
20895               for applications that are loaded using a bootloader.  This
20896               model uses startup file crt2.o which does not contain a
20897               processor reset vector handler. This is suitable for
20898               transferring control on a processor reset to the bootloader
20899               rather than the application.
20900
20901           novectors
20902               for applications that do not require any of the MicroBlaze
20903               vectors. This option may be useful for applications running
20904               within a monitoring application. This model uses crt3.o as a
20905               startup file.
20906
20907           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-
20908           model.
20909
20910   MIPS Options
20911       -EB Generate big-endian code.
20912
20913       -EL Generate little-endian code.  This is the default for mips*el-*-*
20914           configurations.
20915
20916       -march=arch
20917           Generate code that runs on arch, which can be the name of a generic
20918           MIPS ISA, or the name of a particular processor.  The ISA names
20919           are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3,
20920           mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and
20921           mips64r6.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
20922           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
20923           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1,
20924           74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400, i6500,
20925           interaptiv, loongson2e, loongson2f, loongson3a, gs464, gs464e,
20926           gs264e, m4k, m14k, m14kc, m14ke, m14kec, m5100, m5101, octeon,
20927           octeon+, octeon2, octeon3, orion, p5600, p6600, r2000, r3000,
20928           r3900, r4000, r4400, r4600, r4650, r4700, r5900, r6000, r8000,
20929           rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000,
20930           vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr
20931           and xlp.  The special value from-abi selects the most compatible
20932           architecture for the selected ABI (that is, mips1 for 32-bit ABIs
20933           and mips3 for 64-bit ABIs).
20934
20935           The native Linux/GNU toolchain also supports the value native,
20936           which selects the best architecture option for the host processor.
20937           -march=native has no effect if GCC does not recognize the
20938           processor.
20939
20940           In processor names, a final 000 can be abbreviated as k (for
20941           example, -march=r2k).  Prefixes are optional, and vr may be written
20942           r.
20943
20944           Names of the form nf2_1 refer to processors with FPUs clocked at
20945           half the rate of the core, names of the form nf1_1 refer to
20946           processors with FPUs clocked at the same rate as the core, and
20947           names of the form nf3_2 refer to processors with FPUs clocked a
20948           ratio of 3:2 with respect to the core.  For compatibility reasons,
20949           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
20950           as synonyms for nf1_1.
20951
20952           GCC defines two macros based on the value of this option.  The
20953           first is "_MIPS_ARCH", which gives the name of target architecture,
20954           as a string.  The second has the form "_MIPS_ARCH_foo", where foo
20955           is the capitalized value of "_MIPS_ARCH".  For example,
20956           -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro
20957           "_MIPS_ARCH_R2000".
20958
20959           Note that the "_MIPS_ARCH" macro uses the processor names given
20960           above.  In other words, it has the full prefix and does not
20961           abbreviate 000 as k.  In the case of from-abi, the macro names the
20962           resolved architecture (either "mips1" or "mips3").  It names the
20963           default architecture when no -march option is given.
20964
20965       -mtune=arch
20966           Optimize for arch.  Among other things, this option controls the
20967           way instructions are scheduled, and the perceived cost of
20968           arithmetic operations.  The list of arch values is the same as for
20969           -march.
20970
20971           When this option is not used, GCC optimizes for the processor
20972           specified by -march.  By using -march and -mtune together, it is
20973           possible to generate code that runs on a family of processors, but
20974           optimize the code for one particular member of that family.
20975
20976           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which
20977           work in the same way as the -march ones described above.
20978
20979       -mips1
20980           Equivalent to -march=mips1.
20981
20982       -mips2
20983           Equivalent to -march=mips2.
20984
20985       -mips3
20986           Equivalent to -march=mips3.
20987
20988       -mips4
20989           Equivalent to -march=mips4.
20990
20991       -mips32
20992           Equivalent to -march=mips32.
20993
20994       -mips32r3
20995           Equivalent to -march=mips32r3.
20996
20997       -mips32r5
20998           Equivalent to -march=mips32r5.
20999
21000       -mips32r6
21001           Equivalent to -march=mips32r6.
21002
21003       -mips64
21004           Equivalent to -march=mips64.
21005
21006       -mips64r2
21007           Equivalent to -march=mips64r2.
21008
21009       -mips64r3
21010           Equivalent to -march=mips64r3.
21011
21012       -mips64r5
21013           Equivalent to -march=mips64r5.
21014
21015       -mips64r6
21016           Equivalent to -march=mips64r6.
21017
21018       -mips16
21019       -mno-mips16
21020           Generate (do not generate) MIPS16 code.  If GCC is targeting a
21021           MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.
21022
21023           MIPS16 code generation can also be controlled on a per-function
21024           basis by means of "mips16" and "nomips16" attributes.
21025
21026       -mflip-mips16
21027           Generate MIPS16 code on alternating functions.  This option is
21028           provided for regression testing of mixed MIPS16/non-MIPS16 code
21029           generation, and is not intended for ordinary use in compiling user
21030           code.
21031
21032       -minterlink-compressed
21033       -mno-interlink-compressed
21034           Require (do not require) that code using the standard
21035           (uncompressed) MIPS ISA be link-compatible with MIPS16 and
21036           microMIPS code, and vice versa.
21037
21038           For example, code using the standard ISA encoding cannot jump
21039           directly to MIPS16 or microMIPS code; it must either use a call or
21040           an indirect jump.  -minterlink-compressed therefore disables direct
21041           jumps unless GCC knows that the target of the jump is not
21042           compressed.
21043
21044       -minterlink-mips16
21045       -mno-interlink-mips16
21046           Aliases of -minterlink-compressed and -mno-interlink-compressed.
21047           These options predate the microMIPS ASE and are retained for
21048           backwards compatibility.
21049
21050       -mabi=32
21051       -mabi=o64
21052       -mabi=n32
21053       -mabi=64
21054       -mabi=eabi
21055           Generate code for the given ABI.
21056
21057           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
21058           generates 64-bit code when you select a 64-bit architecture, but
21059           you can use -mgp32 to get 32-bit code instead.
21060
21061           For information about the O64 ABI, see
21062           <http://gcc.gnu.org/projects/mipso64-abi.html>.
21063
21064           GCC supports a variant of the o32 ABI in which floating-point
21065           registers are 64 rather than 32 bits wide.  You can select this
21066           combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1"
21067           and "mfhc1" instructions and is therefore only supported for
21068           MIPS32R2, MIPS32R3 and MIPS32R5 processors.
21069
21070           The register assignments for arguments and return values remain the
21071           same, but each scalar value is passed in a single 64-bit register
21072           rather than a pair of 32-bit registers.  For example, scalar
21073           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
21074           The set of call-saved registers also remains the same in that the
21075           even-numbered double-precision registers are saved.
21076
21077           Two additional variants of the o32 ABI are supported to enable a
21078           transition from 32-bit to 64-bit registers.  These are FPXX
21079           (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).  The FPXX extension
21080           mandates that all code must execute correctly when run using 32-bit
21081           or 64-bit registers.  The code can be interlinked with either FP32
21082           or FP64, but not both.  The FP64A extension is similar to the FP64
21083           extension but forbids the use of odd-numbered single-precision
21084           registers.  This can be used in conjunction with the "FRE" mode of
21085           FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to
21086           interlink and run in the same process without changing FPU modes.
21087
21088       -mabicalls
21089       -mno-abicalls
21090           Generate (do not generate) code that is suitable for SVR4-style
21091           dynamic objects.  -mabicalls is the default for SVR4-based systems.
21092
21093       -mshared
21094       -mno-shared
21095           Generate (do not generate) code that is fully position-independent,
21096           and that can therefore be linked into shared libraries.  This
21097           option only affects -mabicalls.
21098
21099           All -mabicalls code has traditionally been position-independent,
21100           regardless of options like -fPIC and -fpic.  However, as an
21101           extension, the GNU toolchain allows executables to use absolute
21102           accesses for locally-binding symbols.  It can also use shorter GP
21103           initialization sequences and generate direct calls to locally-
21104           defined functions.  This mode is selected by -mno-shared.
21105
21106           -mno-shared depends on binutils 2.16 or higher and generates
21107           objects that can only be linked by the GNU linker.  However, the
21108           option does not affect the ABI of the final executable; it only
21109           affects the ABI of relocatable objects.  Using -mno-shared
21110           generally makes executables both smaller and quicker.
21111
21112           -mshared is the default.
21113
21114       -mplt
21115       -mno-plt
21116           Assume (do not assume) that the static and dynamic linkers support
21117           PLTs and copy relocations.  This option only affects -mno-shared
21118           -mabicalls.  For the n64 ABI, this option has no effect without
21119           -msym32.
21120
21121           You can make -mplt the default by configuring GCC with
21122           --with-mips-plt.  The default is -mno-plt otherwise.
21123
21124       -mxgot
21125       -mno-xgot
21126           Lift (do not lift) the usual restrictions on the size of the global
21127           offset table.
21128
21129           GCC normally uses a single instruction to load values from the GOT.
21130           While this is relatively efficient, it only works if the GOT is
21131           smaller than about 64k.  Anything larger causes the linker to
21132           report an error such as:
21133
21134                   relocation truncated to fit: R_MIPS_GOT16 foobar
21135
21136           If this happens, you should recompile your code with -mxgot.  This
21137           works with very large GOTs, although the code is also less
21138           efficient, since it takes three instructions to fetch the value of
21139           a global symbol.
21140
21141           Note that some linkers can create multiple GOTs.  If you have such
21142           a linker, you should only need to use -mxgot when a single object
21143           file accesses more than 64k's worth of GOT entries.  Very few do.
21144
21145           These options have no effect unless GCC is generating position
21146           independent code.
21147
21148       -mgp32
21149           Assume that general-purpose registers are 32 bits wide.
21150
21151       -mgp64
21152           Assume that general-purpose registers are 64 bits wide.
21153
21154       -mfp32
21155           Assume that floating-point registers are 32 bits wide.
21156
21157       -mfp64
21158           Assume that floating-point registers are 64 bits wide.
21159
21160       -mfpxx
21161           Do not assume the width of floating-point registers.
21162
21163       -mhard-float
21164           Use floating-point coprocessor instructions.
21165
21166       -msoft-float
21167           Do not use floating-point coprocessor instructions.  Implement
21168           floating-point calculations using library calls instead.
21169
21170       -mno-float
21171           Equivalent to -msoft-float, but additionally asserts that the
21172           program being compiled does not perform any floating-point
21173           operations.  This option is presently supported only by some bare-
21174           metal MIPS configurations, where it may select a special set of
21175           libraries that lack all floating-point support (including, for
21176           example, the floating-point "printf" formats).  If code compiled
21177           with -mno-float accidentally contains floating-point operations, it
21178           is likely to suffer a link-time or run-time failure.
21179
21180       -msingle-float
21181           Assume that the floating-point coprocessor only supports single-
21182           precision operations.
21183
21184       -mdouble-float
21185           Assume that the floating-point coprocessor supports double-
21186           precision operations.  This is the default.
21187
21188       -modd-spreg
21189       -mno-odd-spreg
21190           Enable the use of odd-numbered single-precision floating-point
21191           registers for the o32 ABI.  This is the default for processors that
21192           are known to support these registers.  When using the o32 FPXX ABI,
21193           -mno-odd-spreg is set by default.
21194
21195       -mabs=2008
21196       -mabs=legacy
21197           These options control the treatment of the special not-a-number
21198           (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt"
21199           machine instructions.
21200
21201           By default or when -mabs=legacy is used the legacy treatment is
21202           selected.  In this case these instructions are considered
21203           arithmetic and avoided where correct operation is required and the
21204           input operand might be a NaN.  A longer sequence of instructions
21205           that manipulate the sign bit of floating-point datum manually is
21206           used instead unless the -ffinite-math-only option has also been
21207           specified.
21208
21209           The -mabs=2008 option selects the IEEE 754-2008 treatment.  In this
21210           case these instructions are considered non-arithmetic and therefore
21211           operating correctly in all cases, including in particular where the
21212           input operand is a NaN.  These instructions are therefore always
21213           used for the respective operations.
21214
21215       -mnan=2008
21216       -mnan=legacy
21217           These options control the encoding of the special not-a-number
21218           (NaN) IEEE 754 floating-point data.
21219
21220           The -mnan=legacy option selects the legacy encoding.  In this case
21221           quiet NaNs (qNaNs) are denoted by the first bit of their trailing
21222           significand field being 0, whereas signaling NaNs (sNaNs) are
21223           denoted by the first bit of their trailing significand field being
21224           1.
21225
21226           The -mnan=2008 option selects the IEEE 754-2008 encoding.  In this
21227           case qNaNs are denoted by the first bit of their trailing
21228           significand field being 1, whereas sNaNs are denoted by the first
21229           bit of their trailing significand field being 0.
21230
21231           The default is -mnan=legacy unless GCC has been configured with
21232           --with-nan=2008.
21233
21234       -mllsc
21235       -mno-llsc
21236           Use (do not use) ll, sc, and sync instructions to implement atomic
21237           memory built-in functions.  When neither option is specified, GCC
21238           uses the instructions if the target architecture supports them.
21239
21240           -mllsc is useful if the runtime environment can emulate the
21241           instructions and -mno-llsc can be useful when compiling for
21242           nonstandard ISAs.  You can make either option the default by
21243           configuring GCC with --with-llsc and --without-llsc respectively.
21244           --with-llsc is the default for some configurations; see the
21245           installation documentation for details.
21246
21247       -mdsp
21248       -mno-dsp
21249           Use (do not use) revision 1 of the MIPS DSP ASE.
21250             This option defines the preprocessor macro "__mips_dsp".  It also
21251           defines "__mips_dsp_rev" to 1.
21252
21253       -mdspr2
21254       -mno-dspr2
21255           Use (do not use) revision 2 of the MIPS DSP ASE.
21256             This option defines the preprocessor macros "__mips_dsp" and
21257           "__mips_dspr2".  It also defines "__mips_dsp_rev" to 2.
21258
21259       -msmartmips
21260       -mno-smartmips
21261           Use (do not use) the MIPS SmartMIPS ASE.
21262
21263       -mpaired-single
21264       -mno-paired-single
21265           Use (do not use) paired-single floating-point instructions.
21266             This option requires hardware floating-point support to be
21267           enabled.
21268
21269       -mdmx
21270       -mno-mdmx
21271           Use (do not use) MIPS Digital Media Extension instructions.  This
21272           option can only be used when generating 64-bit code and requires
21273           hardware floating-point support to be enabled.
21274
21275       -mips3d
21276       -mno-mips3d
21277           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
21278           -mpaired-single.
21279
21280       -mmicromips
21281       -mno-micromips
21282           Generate (do not generate) microMIPS code.
21283
21284           MicroMIPS code generation can also be controlled on a per-function
21285           basis by means of "micromips" and "nomicromips" attributes.
21286
21287       -mmt
21288       -mno-mt
21289           Use (do not use) MT Multithreading instructions.
21290
21291       -mmcu
21292       -mno-mcu
21293           Use (do not use) the MIPS MCU ASE instructions.
21294
21295       -meva
21296       -mno-eva
21297           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
21298
21299       -mvirt
21300       -mno-virt
21301           Use (do not use) the MIPS Virtualization (VZ) instructions.
21302
21303       -mxpa
21304       -mno-xpa
21305           Use (do not use) the MIPS eXtended Physical Address (XPA)
21306           instructions.
21307
21308       -mcrc
21309       -mno-crc
21310           Use (do not use) the MIPS Cyclic Redundancy Check (CRC)
21311           instructions.
21312
21313       -mginv
21314       -mno-ginv
21315           Use (do not use) the MIPS Global INValidate (GINV) instructions.
21316
21317       -mloongson-mmi
21318       -mno-loongson-mmi
21319           Use (do not use) the MIPS Loongson MultiMedia extensions
21320           Instructions (MMI).
21321
21322       -mloongson-ext
21323       -mno-loongson-ext
21324           Use (do not use) the MIPS Loongson EXTensions (EXT) instructions.
21325
21326       -mloongson-ext2
21327       -mno-loongson-ext2
21328           Use (do not use) the MIPS Loongson EXTensions r2 (EXT2)
21329           instructions.
21330
21331       -mlong64
21332           Force "long" types to be 64 bits wide.  See -mlong32 for an
21333           explanation of the default and the way that the pointer size is
21334           determined.
21335
21336       -mlong32
21337           Force "long", "int", and pointer types to be 32 bits wide.
21338
21339           The default size of "int"s, "long"s and pointers depends on the
21340           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
21341           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
21342           "long"s.  Pointers are the same size as "long"s, or the same size
21343           as integer registers, whichever is smaller.
21344
21345       -msym32
21346       -mno-sym32
21347           Assume (do not assume) that all symbols have 32-bit values,
21348           regardless of the selected ABI.  This option is useful in
21349           combination with -mabi=64 and -mno-abicalls because it allows GCC
21350           to generate shorter and faster references to symbolic addresses.
21351
21352       -G num
21353           Put definitions of externally-visible data in a small data section
21354           if that data is no bigger than num bytes.  GCC can then generate
21355           more efficient accesses to the data; see -mgpopt for details.
21356
21357           The default -G option depends on the configuration.
21358
21359       -mlocal-sdata
21360       -mno-local-sdata
21361           Extend (do not extend) the -G behavior to local data too, such as
21362           to static variables in C.  -mlocal-sdata is the default for all
21363           configurations.
21364
21365           If the linker complains that an application is using too much small
21366           data, you might want to try rebuilding the less performance-
21367           critical parts with -mno-local-sdata.  You might also want to build
21368           large libraries with -mno-local-sdata, so that the libraries leave
21369           more room for the main program.
21370
21371       -mextern-sdata
21372       -mno-extern-sdata
21373           Assume (do not assume) that externally-defined data is in a small
21374           data section if the size of that data is within the -G limit.
21375           -mextern-sdata is the default for all configurations.
21376
21377           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
21378           Mod references a variable Var that is no bigger than num bytes, you
21379           must make sure that Var is placed in a small data section.  If Var
21380           is defined by another module, you must either compile that module
21381           with a high-enough -G setting or attach a "section" attribute to
21382           Var's definition.  If Var is common, you must link the application
21383           with a high-enough -G setting.
21384
21385           The easiest way of satisfying these restrictions is to compile and
21386           link every module with the same -G option.  However, you may wish
21387           to build a library that supports several different small data
21388           limits.  You can do this by compiling the library with the highest
21389           supported -G setting and additionally using -mno-extern-sdata to
21390           stop the library from making assumptions about externally-defined
21391           data.
21392
21393       -mgpopt
21394       -mno-gpopt
21395           Use (do not use) GP-relative accesses for symbols that are known to
21396           be in a small data section; see -G, -mlocal-sdata and
21397           -mextern-sdata.  -mgpopt is the default for all configurations.
21398
21399           -mno-gpopt is useful for cases where the $gp register might not
21400           hold the value of "_gp".  For example, if the code is part of a
21401           library that might be used in a boot monitor, programs that call
21402           boot monitor routines pass an unknown value in $gp.  (In such
21403           situations, the boot monitor itself is usually compiled with -G0.)
21404
21405           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
21406
21407       -membedded-data
21408       -mno-embedded-data
21409           Allocate variables to the read-only data section first if possible,
21410           then next in the small data section if possible, otherwise in data.
21411           This gives slightly slower code than the default, but reduces the
21412           amount of RAM required when executing, and thus may be preferred
21413           for some embedded systems.
21414
21415       -muninit-const-in-rodata
21416       -mno-uninit-const-in-rodata
21417           Put uninitialized "const" variables in the read-only data section.
21418           This option is only meaningful in conjunction with -membedded-data.
21419
21420       -mcode-readable=setting
21421           Specify whether GCC may generate code that reads from executable
21422           sections.  There are three possible settings:
21423
21424           -mcode-readable=yes
21425               Instructions may freely access executable sections.  This is
21426               the default setting.
21427
21428           -mcode-readable=pcrel
21429               MIPS16 PC-relative load instructions can access executable
21430               sections, but other instructions must not do so.  This option
21431               is useful on 4KSc and 4KSd processors when the code TLBs have
21432               the Read Inhibit bit set.  It is also useful on processors that
21433               can be configured to have a dual instruction/data SRAM
21434               interface and that, like the M4K, automatically redirect PC-
21435               relative loads to the instruction RAM.
21436
21437           -mcode-readable=no
21438               Instructions must not access executable sections.  This option
21439               can be useful on targets that are configured to have a dual
21440               instruction/data SRAM interface but that (unlike the M4K) do
21441               not automatically redirect PC-relative loads to the instruction
21442               RAM.
21443
21444       -msplit-addresses
21445       -mno-split-addresses
21446           Enable (disable) use of the "%hi()" and "%lo()" assembler
21447           relocation operators.  This option has been superseded by
21448           -mexplicit-relocs but is retained for backwards compatibility.
21449
21450       -mexplicit-relocs
21451       -mno-explicit-relocs
21452           Use (do not use) assembler relocation operators when dealing with
21453           symbolic addresses.  The alternative, selected by
21454           -mno-explicit-relocs, is to use assembler macros instead.
21455
21456           -mexplicit-relocs is the default if GCC was configured to use an
21457           assembler that supports relocation operators.
21458
21459       -mcheck-zero-division
21460       -mno-check-zero-division
21461           Trap (do not trap) on integer division by zero.
21462
21463           The default is -mcheck-zero-division.
21464
21465       -mdivide-traps
21466       -mdivide-breaks
21467           MIPS systems check for division by zero by generating either a
21468           conditional trap or a break instruction.  Using traps results in
21469           smaller code, but is only supported on MIPS II and later.  Also,
21470           some versions of the Linux kernel have a bug that prevents trap
21471           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
21472           to allow conditional traps on architectures that support them and
21473           -mdivide-breaks to force the use of breaks.
21474
21475           The default is usually -mdivide-traps, but this can be overridden
21476           at configure time using --with-divide=breaks.  Divide-by-zero
21477           checks can be completely disabled using -mno-check-zero-division.
21478
21479       -mload-store-pairs
21480       -mno-load-store-pairs
21481           Enable (disable) an optimization that pairs consecutive load or
21482           store instructions to enable load/store bonding.  This option is
21483           enabled by default but only takes effect when the selected
21484           architecture is known to support bonding.
21485
21486       -mmemcpy
21487       -mno-memcpy
21488           Force (do not force) the use of "memcpy" for non-trivial block
21489           moves.  The default is -mno-memcpy, which allows GCC to inline most
21490           constant-sized copies.
21491
21492       -mlong-calls
21493       -mno-long-calls
21494           Disable (do not disable) use of the "jal" instruction.  Calling
21495           functions using "jal" is more efficient but requires the caller and
21496           callee to be in the same 256 megabyte segment.
21497
21498           This option has no effect on abicalls code.  The default is
21499           -mno-long-calls.
21500
21501       -mmad
21502       -mno-mad
21503           Enable (disable) use of the "mad", "madu" and "mul" instructions,
21504           as provided by the R4650 ISA.
21505
21506       -mimadd
21507       -mno-imadd
21508           Enable (disable) use of the "madd" and "msub" integer instructions.
21509           The default is -mimadd on architectures that support "madd" and
21510           "msub" except for the 74k architecture where it was found to
21511           generate slower code.
21512
21513       -mfused-madd
21514       -mno-fused-madd
21515           Enable (disable) use of the floating-point multiply-accumulate
21516           instructions, when they are available.  The default is
21517           -mfused-madd.
21518
21519           On the R8000 CPU when multiply-accumulate instructions are used,
21520           the intermediate product is calculated to infinite precision and is
21521           not subject to the FCSR Flush to Zero bit.  This may be undesirable
21522           in some circumstances.  On other processors the result is
21523           numerically identical to the equivalent computation using separate
21524           multiply, add, subtract and negate instructions.
21525
21526       -nocpp
21527           Tell the MIPS assembler to not run its preprocessor over user
21528           assembler files (with a .s suffix) when assembling them.
21529
21530       -mfix-24k
21531       -mno-fix-24k
21532           Work around the 24K E48 (lost data on stores during refill) errata.
21533           The workarounds are implemented by the assembler rather than by
21534           GCC.
21535
21536       -mfix-r4000
21537       -mno-fix-r4000
21538           Work around certain R4000 CPU errata:
21539
21540           -   A double-word or a variable shift may give an incorrect result
21541               if executed immediately after starting an integer division.
21542
21543           -   A double-word or a variable shift may give an incorrect result
21544               if executed while an integer multiplication is in progress.
21545
21546           -   An integer division may give an incorrect result if started in
21547               a delay slot of a taken branch or a jump.
21548
21549       -mfix-r4400
21550       -mno-fix-r4400
21551           Work around certain R4400 CPU errata:
21552
21553           -   A double-word or a variable shift may give an incorrect result
21554               if executed immediately after starting an integer division.
21555
21556       -mfix-r10000
21557       -mno-fix-r10000
21558           Work around certain R10000 errata:
21559
21560           -   "ll"/"sc" sequences may not behave atomically on revisions
21561               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.
21562
21563           This option can only be used if the target architecture supports
21564           branch-likely instructions.  -mfix-r10000 is the default when
21565           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
21566
21567       -mfix-r5900
21568       -mno-fix-r5900
21569           Do not attempt to schedule the preceding instruction into the delay
21570           slot of a branch instruction placed at the end of a short loop of
21571           six instructions or fewer and always schedule a "nop" instruction
21572           there instead.  The short loop bug under certain conditions causes
21573           loops to execute only once or twice, due to a hardware bug in the
21574           R5900 chip.  The workaround is implemented by the assembler rather
21575           than by GCC.
21576
21577       -mfix-rm7000
21578       -mno-fix-rm7000
21579           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds
21580           are implemented by the assembler rather than by GCC.
21581
21582       -mfix-vr4120
21583       -mno-fix-vr4120
21584           Work around certain VR4120 errata:
21585
21586           -   "dmultu" does not always produce the correct result.
21587
21588           -   "div" and "ddiv" do not always produce the correct result if
21589               one of the operands is negative.
21590
21591           The workarounds for the division errata rely on special functions
21592           in libgcc.a.  At present, these functions are only provided by the
21593           "mips64vr*-elf" configurations.
21594
21595           Other VR4120 errata require a NOP to be inserted between certain
21596           pairs of instructions.  These errata are handled by the assembler,
21597           not by GCC itself.
21598
21599       -mfix-vr4130
21600           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
21601           implemented by the assembler rather than by GCC, although GCC
21602           avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
21603           "dmacc" and "dmacchi" instructions are available instead.
21604
21605       -mfix-sb1
21606       -mno-fix-sb1
21607           Work around certain SB-1 CPU core errata.  (This flag currently
21608           works around the SB-1 revision 2 "F1" and "F2" floating-point
21609           errata.)
21610
21611       -mr10k-cache-barrier=setting
21612           Specify whether GCC should insert cache barriers to avoid the side
21613           effects of speculation on R10K processors.
21614
21615           In common with many processors, the R10K tries to predict the
21616           outcome of a conditional branch and speculatively executes
21617           instructions from the "taken" branch.  It later aborts these
21618           instructions if the predicted outcome is wrong.  However, on the
21619           R10K, even aborted instructions can have side effects.
21620
21621           This problem only affects kernel stores and, depending on the
21622           system, kernel loads.  As an example, a speculatively-executed
21623           store may load the target memory into cache and mark the cache line
21624           as dirty, even if the store itself is later aborted.  If a DMA
21625           operation writes to the same area of memory before the "dirty" line
21626           is flushed, the cached data overwrites the DMA-ed data.  See the
21627           R10K processor manual for a full description, including other
21628           potential problems.
21629
21630           One workaround is to insert cache barrier instructions before every
21631           memory access that might be speculatively executed and that might
21632           have side effects even if aborted.  -mr10k-cache-barrier=setting
21633           controls GCC's implementation of this workaround.  It assumes that
21634           aborted accesses to any byte in the following regions does not have
21635           side effects:
21636
21637           1.  the memory occupied by the current function's stack frame;
21638
21639           2.  the memory occupied by an incoming stack argument;
21640
21641           3.  the memory occupied by an object with a link-time-constant
21642               address.
21643
21644           It is the kernel's responsibility to ensure that speculative
21645           accesses to these regions are indeed safe.
21646
21647           If the input program contains a function declaration such as:
21648
21649                   void foo (void);
21650
21651           then the implementation of "foo" must allow "j foo" and "jal foo"
21652           to be executed speculatively.  GCC honors this restriction for
21653           functions it compiles itself.  It expects non-GCC functions (such
21654           as hand-written assembly code) to do the same.
21655
21656           The option has three forms:
21657
21658           -mr10k-cache-barrier=load-store
21659               Insert a cache barrier before a load or store that might be
21660               speculatively executed and that might have side effects even if
21661               aborted.
21662
21663           -mr10k-cache-barrier=store
21664               Insert a cache barrier before a store that might be
21665               speculatively executed and that might have side effects even if
21666               aborted.
21667
21668           -mr10k-cache-barrier=none
21669               Disable the insertion of cache barriers.  This is the default
21670               setting.
21671
21672       -mflush-func=func
21673       -mno-flush-func
21674           Specifies the function to call to flush the I and D caches, or to
21675           not call any such function.  If called, the function must take the
21676           same arguments as the common "_flush_func", that is, the address of
21677           the memory range for which the cache is being flushed, the size of
21678           the memory range, and the number 3 (to flush both caches).  The
21679           default depends on the target GCC was configured for, but commonly
21680           is either "_flush_func" or "__cpu_flush".
21681
21682       mbranch-cost=num
21683           Set the cost of branches to roughly num "simple" instructions.
21684           This cost is only a heuristic and is not guaranteed to produce
21685           consistent results across releases.  A zero cost redundantly
21686           selects the default, which is based on the -mtune setting.
21687
21688       -mbranch-likely
21689       -mno-branch-likely
21690           Enable or disable use of Branch Likely instructions, regardless of
21691           the default for the selected architecture.  By default, Branch
21692           Likely instructions may be generated if they are supported by the
21693           selected architecture.  An exception is for the MIPS32 and MIPS64
21694           architectures and processors that implement those architectures;
21695           for those, Branch Likely instructions are not be generated by
21696           default because the MIPS32 and MIPS64 architectures specifically
21697           deprecate their use.
21698
21699       -mcompact-branches=never
21700       -mcompact-branches=optimal
21701       -mcompact-branches=always
21702           These options control which form of branches will be generated.
21703           The default is -mcompact-branches=optimal.
21704
21705           The -mcompact-branches=never option ensures that compact branch
21706           instructions will never be generated.
21707
21708           The -mcompact-branches=always option ensures that a compact branch
21709           instruction will be generated if available.  If a compact branch
21710           instruction is not available, a delay slot form of the branch will
21711           be used instead.
21712
21713           This option is supported from MIPS Release 6 onwards.
21714
21715           The -mcompact-branches=optimal option will cause a delay slot
21716           branch to be used if one is available in the current ISA and the
21717           delay slot is successfully filled.  If the delay slot is not
21718           filled, a compact branch will be chosen if one is available.
21719
21720       -mfp-exceptions
21721       -mno-fp-exceptions
21722           Specifies whether FP exceptions are enabled.  This affects how FP
21723           instructions are scheduled for some processors.  The default is
21724           that FP exceptions are enabled.
21725
21726           For instance, on the SB-1, if FP exceptions are disabled, and we
21727           are emitting 64-bit code, then we can use both FP pipes.
21728           Otherwise, we can only use one FP pipe.
21729
21730       -mvr4130-align
21731       -mno-vr4130-align
21732           The VR4130 pipeline is two-way superscalar, but can only issue two
21733           instructions together if the first one is 8-byte aligned.  When
21734           this option is enabled, GCC aligns pairs of instructions that it
21735           thinks should execute in parallel.
21736
21737           This option only has an effect when optimizing for the VR4130.  It
21738           normally makes code faster, but at the expense of making it bigger.
21739           It is enabled by default at optimization level -O3.
21740
21741       -msynci
21742       -mno-synci
21743           Enable (disable) generation of "synci" instructions on
21744           architectures that support it.  The "synci" instructions (if
21745           enabled) are generated when "__builtin___clear_cache" is compiled.
21746
21747           This option defaults to -mno-synci, but the default can be
21748           overridden by configuring GCC with --with-synci.
21749
21750           When compiling code for single processor systems, it is generally
21751           safe to use "synci".  However, on many multi-core (SMP) systems, it
21752           does not invalidate the instruction caches on all cores and may
21753           lead to undefined behavior.
21754
21755       -mrelax-pic-calls
21756       -mno-relax-pic-calls
21757           Try to turn PIC calls that are normally dispatched via register $25
21758           into direct calls.  This is only possible if the linker can resolve
21759           the destination at link time and if the destination is within range
21760           for a direct call.
21761
21762           -mrelax-pic-calls is the default if GCC was configured to use an
21763           assembler and a linker that support the ".reloc" assembly directive
21764           and -mexplicit-relocs is in effect.  With -mno-explicit-relocs,
21765           this optimization can be performed by the assembler and the linker
21766           alone without help from the compiler.
21767
21768       -mmcount-ra-address
21769       -mno-mcount-ra-address
21770           Emit (do not emit) code that allows "_mcount" to modify the calling
21771           function's return address.  When enabled, this option extends the
21772           usual "_mcount" interface with a new ra-address parameter, which
21773           has type "intptr_t *" and is passed in register $12.  "_mcount" can
21774           then modify the return address by doing both of the following:
21775
21776           *   Returning the new address in register $31.
21777
21778           *   Storing the new address in "*ra-address", if ra-address is
21779               nonnull.
21780
21781           The default is -mno-mcount-ra-address.
21782
21783       -mframe-header-opt
21784       -mno-frame-header-opt
21785           Enable (disable) frame header optimization in the o32 ABI.  When
21786           using the o32 ABI, calling functions will allocate 16 bytes on the
21787           stack for the called function to write out register arguments.
21788           When enabled, this optimization will suppress the allocation of the
21789           frame header if it can be determined that it is unused.
21790
21791           This optimization is off by default at all optimization levels.
21792
21793       -mlxc1-sxc1
21794       -mno-lxc1-sxc1
21795           When applicable, enable (disable) the generation of "lwxc1",
21796           "swxc1", "ldxc1", "sdxc1" instructions.  Enabled by default.
21797
21798       -mmadd4
21799       -mno-madd4
21800           When applicable, enable (disable) the generation of 4-operand
21801           "madd.s", "madd.d" and related instructions.  Enabled by default.
21802
21803   MMIX Options
21804       These options are defined for the MMIX:
21805
21806       -mlibfuncs
21807       -mno-libfuncs
21808           Specify that intrinsic library functions are being compiled,
21809           passing all values in registers, no matter the size.
21810
21811       -mepsilon
21812       -mno-epsilon
21813           Generate floating-point comparison instructions that compare with
21814           respect to the "rE" epsilon register.
21815
21816       -mabi=mmixware
21817       -mabi=gnu
21818           Generate code that passes function parameters and return values
21819           that (in the called function) are seen as registers $0 and up, as
21820           opposed to the GNU ABI which uses global registers $231 and up.
21821
21822       -mzero-extend
21823       -mno-zero-extend
21824           When reading data from memory in sizes shorter than 64 bits, use
21825           (do not use) zero-extending load instructions by default, rather
21826           than sign-extending ones.
21827
21828       -mknuthdiv
21829       -mno-knuthdiv
21830           Make the result of a division yielding a remainder have the same
21831           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
21832           the remainder follows the sign of the dividend.  Both methods are
21833           arithmetically valid, the latter being almost exclusively used.
21834
21835       -mtoplevel-symbols
21836       -mno-toplevel-symbols
21837           Prepend (do not prepend) a : to all global symbols, so the assembly
21838           code can be used with the "PREFIX" assembly directive.
21839
21840       -melf
21841           Generate an executable in the ELF format, rather than the default
21842           mmo format used by the mmix simulator.
21843
21844       -mbranch-predict
21845       -mno-branch-predict
21846           Use (do not use) the probable-branch instructions, when static
21847           branch prediction indicates a probable branch.
21848
21849       -mbase-addresses
21850       -mno-base-addresses
21851           Generate (do not generate) code that uses base addresses.  Using a
21852           base address automatically generates a request (handled by the
21853           assembler and the linker) for a constant to be set up in a global
21854           register.  The register is used for one or more base address
21855           requests within the range 0 to 255 from the value held in the
21856           register.  The generally leads to short and fast code, but the
21857           number of different data items that can be addressed is limited.
21858           This means that a program that uses lots of static data may require
21859           -mno-base-addresses.
21860
21861       -msingle-exit
21862       -mno-single-exit
21863           Force (do not force) generated code to have a single exit point in
21864           each function.
21865
21866   MN10300 Options
21867       These -m options are defined for Matsushita MN10300 architectures:
21868
21869       -mmult-bug
21870           Generate code to avoid bugs in the multiply instructions for the
21871           MN10300 processors.  This is the default.
21872
21873       -mno-mult-bug
21874           Do not generate code to avoid bugs in the multiply instructions for
21875           the MN10300 processors.
21876
21877       -mam33
21878           Generate code using features specific to the AM33 processor.
21879
21880       -mno-am33
21881           Do not generate code using features specific to the AM33 processor.
21882           This is the default.
21883
21884       -mam33-2
21885           Generate code using features specific to the AM33/2.0 processor.
21886
21887       -mam34
21888           Generate code using features specific to the AM34 processor.
21889
21890       -mtune=cpu-type
21891           Use the timing characteristics of the indicated CPU type when
21892           scheduling instructions.  This does not change the targeted
21893           processor type.  The CPU type must be one of mn10300, am33, am33-2
21894           or am34.
21895
21896       -mreturn-pointer-on-d0
21897           When generating a function that returns a pointer, return the
21898           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
21899           only in "a0", and attempts to call such functions without a
21900           prototype result in errors.  Note that this option is on by
21901           default; use -mno-return-pointer-on-d0 to disable it.
21902
21903       -mno-crt0
21904           Do not link in the C run-time initialization object file.
21905
21906       -mrelax
21907           Indicate to the linker that it should perform a relaxation
21908           optimization pass to shorten branches, calls and absolute memory
21909           addresses.  This option only has an effect when used on the command
21910           line for the final link step.
21911
21912           This option makes symbolic debugging impossible.
21913
21914       -mliw
21915           Allow the compiler to generate Long Instruction Word instructions
21916           if the target is the AM33 or later.  This is the default.  This
21917           option defines the preprocessor macro "__LIW__".
21918
21919       -mno-liw
21920           Do not allow the compiler to generate Long Instruction Word
21921           instructions.  This option defines the preprocessor macro
21922           "__NO_LIW__".
21923
21924       -msetlb
21925           Allow the compiler to generate the SETLB and Lcc instructions if
21926           the target is the AM33 or later.  This is the default.  This option
21927           defines the preprocessor macro "__SETLB__".
21928
21929       -mno-setlb
21930           Do not allow the compiler to generate SETLB or Lcc instructions.
21931           This option defines the preprocessor macro "__NO_SETLB__".
21932
21933   Moxie Options
21934       -meb
21935           Generate big-endian code.  This is the default for moxie-*-*
21936           configurations.
21937
21938       -mel
21939           Generate little-endian code.
21940
21941       -mmul.x
21942           Generate mul.x and umul.x instructions.  This is the default for
21943           moxiebox-*-* configurations.
21944
21945       -mno-crt0
21946           Do not link in the C run-time initialization object file.
21947
21948   MSP430 Options
21949       These options are defined for the MSP430:
21950
21951       -masm-hex
21952           Force assembly output to always use hex constants.  Normally such
21953           constants are signed decimals, but this option is available for
21954           testsuite and/or aesthetic purposes.
21955
21956       -mmcu=
21957           Select the MCU to target.  This is used to create a C preprocessor
21958           symbol based upon the MCU name, converted to upper case and pre-
21959           and post-fixed with __.  This in turn is used by the msp430.h
21960           header file to select an MCU-specific supplementary header file.
21961
21962           The option also sets the ISA to use.  If the MCU name is one that
21963           is known to only support the 430 ISA then that is selected,
21964           otherwise the 430X ISA is selected.  A generic MCU name of msp430
21965           can also be used to select the 430 ISA.  Similarly the generic
21966           msp430x MCU name selects the 430X ISA.
21967
21968           In addition an MCU-specific linker script is added to the linker
21969           command line.  The script's name is the name of the MCU with .ld
21970           appended.  Thus specifying -mmcu=xxx on the gcc command line
21971           defines the C preprocessor symbol "__XXX__" and cause the linker to
21972           search for a script called xxx.ld.
21973
21974           The ISA and hardware multiply supported for the different MCUs is
21975           hard-coded into GCC.  However, an external devices.csv file can be
21976           used to extend device support beyond those that have been hard-
21977           coded.
21978
21979           GCC searches for the devices.csv file using the following methods
21980           in the given precedence order, where the first method takes
21981           precendence over the second which takes precedence over the third.
21982
21983           Include path specified with "-I" and "-L"
21984               devices.csv will be searched for in each of the directories
21985               specified by include paths and linker library search paths.
21986
21987           Path specified by the environment variable MSP430_GCC_INCLUDE_DIR
21988               Define the value of the global environment variable
21989               MSP430_GCC_INCLUDE_DIR to the full path to the directory
21990               containing devices.csv, and GCC will search this directory for
21991               devices.csv.  If devices.csv is found, this directory will also
21992               be registered as an include path, and linker library path.
21993               Header files and linker scripts in this directory can therefore
21994               be used without manually specifying "-I" and "-L" on the
21995               command line.
21996
21997           The msp430-elf{,bare}/include/devices directory
21998               Finally, GCC will examine msp430-elf{,bare}/include/devices
21999               from the toolchain root directory.  This directory does not
22000               exist in a default installation, but if the user has created it
22001               and copied devices.csv there, then the MCU data will be read.
22002               As above, this directory will also be registered as an include
22003               path, and linker library path.
22004
22005           If none of the above search methods find devices.csv, then the
22006           hard-coded MCU data is used.
22007
22008       -mwarn-mcu
22009       -mno-warn-mcu
22010           This option enables or disables warnings about conflicts between
22011           the MCU name specified by the -mmcu option and the ISA set by the
22012           -mcpu option and/or the hardware multiply support set by the
22013           -mhwmult option.  It also toggles warnings about unrecognized MCU
22014           names.  This option is on by default.
22015
22016       -mcpu=
22017           Specifies the ISA to use.  Accepted values are msp430, msp430x and
22018           msp430xv2.  This option is deprecated.  The -mmcu= option should be
22019           used to select the ISA.
22020
22021       -msim
22022           Link to the simulator runtime libraries and linker script.
22023           Overrides any scripts that would be selected by the -mmcu= option.
22024
22025       -mlarge
22026           Use large-model addressing (20-bit pointers, 20-bit "size_t").
22027
22028       -msmall
22029           Use small-model addressing (16-bit pointers, 16-bit "size_t").
22030
22031       -mrelax
22032           This option is passed to the assembler and linker, and allows the
22033           linker to perform certain optimizations that cannot be done until
22034           the final link.
22035
22036       mhwmult=
22037           Describes the type of hardware multiply supported by the target.
22038           Accepted values are none for no hardware multiply, 16bit for the
22039           original 16-bit-only multiply supported by early MCUs.  32bit for
22040           the 16/32-bit multiply supported by later MCUs and f5series for the
22041           16/32-bit multiply supported by F5-series MCUs.  A value of auto
22042           can also be given.  This tells GCC to deduce the hardware multiply
22043           support based upon the MCU name provided by the -mmcu option.  If
22044           no -mmcu option is specified or if the MCU name is not recognized
22045           then no hardware multiply support is assumed.  "auto" is the
22046           default setting.
22047
22048           Hardware multiplies are normally performed by calling a library
22049           routine.  This saves space in the generated code.  When compiling
22050           at -O3 or higher however the hardware multiplier is invoked inline.
22051           This makes for bigger, but faster code.
22052
22053           The hardware multiply routines disable interrupts whilst running
22054           and restore the previous interrupt state when they finish.  This
22055           makes them safe to use inside interrupt handlers as well as in
22056           normal code.
22057
22058       -minrt
22059           Enable the use of a minimum runtime environment - no static
22060           initializers or constructors.  This is intended for memory-
22061           constrained devices.  The compiler includes special symbols in some
22062           objects that tell the linker and runtime which code fragments are
22063           required.
22064
22065       -mtiny-printf
22066           Enable reduced code size "printf" and "puts" library functions.
22067           The tiny implementations of these functions are not reentrant, so
22068           must be used with caution in multi-threaded applications.
22069
22070           Support for streams has been removed and the string to be printed
22071           will always be sent to stdout via the "write" syscall.  The string
22072           is not buffered before it is sent to write.
22073
22074           This option requires Newlib Nano IO, so GCC must be configured with
22075           --enable-newlib-nano-formatted-io.
22076
22077       -mmax-inline-shift=
22078           This option takes an integer between 0 and 64 inclusive, and sets
22079           the maximum number of inline shift instructions which should be
22080           emitted to perform a shift operation by a constant amount.  When
22081           this value needs to be exceeded, an mspabi helper function is used
22082           instead.  The default value is 4.
22083
22084           This only affects cases where a shift by multiple positions cannot
22085           be completed with a single instruction (e.g. all shifts >1 on the
22086           430 ISA).
22087
22088           Shifts of a 32-bit value are at least twice as costly, so the value
22089           passed for this option is divided by 2 and the resulting value used
22090           instead.
22091
22092       -mcode-region=
22093       -mdata-region=
22094           These options tell the compiler where to place functions and data
22095           that do not have one of the "lower", "upper", "either" or "section"
22096           attributes.  Possible values are "lower", "upper", "either" or
22097           "any".  The first three behave like the corresponding attribute.
22098           The fourth possible value - "any" - is the default.  It leaves
22099           placement entirely up to the linker script and how it assigns the
22100           standard sections (".text", ".data", etc) to the memory regions.
22101
22102       -msilicon-errata=
22103           This option passes on a request to assembler to enable the fixes
22104           for the named silicon errata.
22105
22106       -msilicon-errata-warn=
22107           This option passes on a request to the assembler to enable warning
22108           messages when a silicon errata might need to be applied.
22109
22110       -mwarn-devices-csv
22111       -mno-warn-devices-csv
22112           Warn if devices.csv is not found or there are problem parsing it
22113           (default: on).
22114
22115   NDS32 Options
22116       These options are defined for NDS32 implementations:
22117
22118       -mbig-endian
22119           Generate code in big-endian mode.
22120
22121       -mlittle-endian
22122           Generate code in little-endian mode.
22123
22124       -mreduced-regs
22125           Use reduced-set registers for register allocation.
22126
22127       -mfull-regs
22128           Use full-set registers for register allocation.
22129
22130       -mcmov
22131           Generate conditional move instructions.
22132
22133       -mno-cmov
22134           Do not generate conditional move instructions.
22135
22136       -mext-perf
22137           Generate performance extension instructions.
22138
22139       -mno-ext-perf
22140           Do not generate performance extension instructions.
22141
22142       -mext-perf2
22143           Generate performance extension 2 instructions.
22144
22145       -mno-ext-perf2
22146           Do not generate performance extension 2 instructions.
22147
22148       -mext-string
22149           Generate string extension instructions.
22150
22151       -mno-ext-string
22152           Do not generate string extension instructions.
22153
22154       -mv3push
22155           Generate v3 push25/pop25 instructions.
22156
22157       -mno-v3push
22158           Do not generate v3 push25/pop25 instructions.
22159
22160       -m16-bit
22161           Generate 16-bit instructions.
22162
22163       -mno-16-bit
22164           Do not generate 16-bit instructions.
22165
22166       -misr-vector-size=num
22167           Specify the size of each interrupt vector, which must be 4 or 16.
22168
22169       -mcache-block-size=num
22170           Specify the size of each cache block, which must be a power of 2
22171           between 4 and 512.
22172
22173       -march=arch
22174           Specify the name of the target architecture.
22175
22176       -mcmodel=code-model
22177           Set the code model to one of
22178
22179           small
22180               All the data and read-only data segments must be within 512KB
22181               addressing space.  The text segment must be within 16MB
22182               addressing space.
22183
22184           medium
22185               The data segment must be within 512KB while the read-only data
22186               segment can be within 4GB addressing space.  The text segment
22187               should be still within 16MB addressing space.
22188
22189           large
22190               All the text and data segments can be within 4GB addressing
22191               space.
22192
22193       -mctor-dtor
22194           Enable constructor/destructor feature.
22195
22196       -mrelax
22197           Guide linker to relax instructions.
22198
22199   Nios II Options
22200       These are the options defined for the Altera Nios II processor.
22201
22202       -G num
22203           Put global and static objects less than or equal to num bytes into
22204           the small data or BSS sections instead of the normal data or BSS
22205           sections.  The default value of num is 8.
22206
22207       -mgpopt=option
22208       -mgpopt
22209       -mno-gpopt
22210           Generate (do not generate) GP-relative accesses.  The following
22211           option names are recognized:
22212
22213           none
22214               Do not generate GP-relative accesses.
22215
22216           local
22217               Generate GP-relative accesses for small data objects that are
22218               not external, weak, or uninitialized common symbols.  Also use
22219               GP-relative addressing for objects that have been explicitly
22220               placed in a small data section via a "section" attribute.
22221
22222           global
22223               As for local, but also generate GP-relative accesses for small
22224               data objects that are external, weak, or common.  If you use
22225               this option, you must ensure that all parts of your program
22226               (including libraries) are compiled with the same -G setting.
22227
22228           data
22229               Generate GP-relative accesses for all data objects in the
22230               program.  If you use this option, the entire data and BSS
22231               segments of your program must fit in 64K of memory and you must
22232               use an appropriate linker script to allocate them within the
22233               addressable range of the global pointer.
22234
22235           all Generate GP-relative addresses for function pointers as well as
22236               data pointers.  If you use this option, the entire text, data,
22237               and BSS segments of your program must fit in 64K of memory and
22238               you must use an appropriate linker script to allocate them
22239               within the addressable range of the global pointer.
22240
22241           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is
22242           equivalent to -mgpopt=none.
22243
22244           The default is -mgpopt except when -fpic or -fPIC is specified to
22245           generate position-independent code.  Note that the Nios II ABI does
22246           not permit GP-relative accesses from shared libraries.
22247
22248           You may need to specify -mno-gpopt explicitly when building
22249           programs that include large amounts of small data, including large
22250           GOT data sections.  In this case, the 16-bit offset for GP-relative
22251           addressing may not be large enough to allow access to the entire
22252           small data section.
22253
22254       -mgprel-sec=regexp
22255           This option specifies additional section names that can be accessed
22256           via GP-relative addressing.  It is most useful in conjunction with
22257           "section" attributes on variable declarations and a custom linker
22258           script.  The regexp is a POSIX Extended Regular Expression.
22259
22260           This option does not affect the behavior of the -G option, and the
22261           specified sections are in addition to the standard ".sdata" and
22262           ".sbss" small-data sections that are recognized by -mgpopt.
22263
22264       -mr0rel-sec=regexp
22265           This option specifies names of sections that can be accessed via a
22266           16-bit offset from "r0"; that is, in the low 32K or high 32K of the
22267           32-bit address space.  It is most useful in conjunction with
22268           "section" attributes on variable declarations and a custom linker
22269           script.  The regexp is a POSIX Extended Regular Expression.
22270
22271           In contrast to the use of GP-relative addressing for small data,
22272           zero-based addressing is never generated by default and there are
22273           no conventional section names used in standard linker scripts for
22274           sections in the low or high areas of memory.
22275
22276       -mel
22277       -meb
22278           Generate little-endian (default) or big-endian (experimental) code,
22279           respectively.
22280
22281       -march=arch
22282           This specifies the name of the target Nios II architecture.  GCC
22283           uses this name to determine what kind of instructions it can emit
22284           when generating assembly code.  Permissible names are: r1, r2.
22285
22286           The preprocessor macro "__nios2_arch__" is available to programs,
22287           with value 1 or 2, indicating the targeted ISA level.
22288
22289       -mbypass-cache
22290       -mno-bypass-cache
22291           Force all load and store instructions to always bypass cache by
22292           using I/O variants of the instructions. The default is not to
22293           bypass the cache.
22294
22295       -mno-cache-volatile
22296       -mcache-volatile
22297           Volatile memory access bypass the cache using the I/O variants of
22298           the load and store instructions. The default is not to bypass the
22299           cache.
22300
22301       -mno-fast-sw-div
22302       -mfast-sw-div
22303           Do not use table-based fast divide for small numbers. The default
22304           is to use the fast divide at -O3 and above.
22305
22306       -mno-hw-mul
22307       -mhw-mul
22308       -mno-hw-mulx
22309       -mhw-mulx
22310       -mno-hw-div
22311       -mhw-div
22312           Enable or disable emitting "mul", "mulx" and "div" family of
22313           instructions by the compiler. The default is to emit "mul" and not
22314           emit "div" and "mulx".
22315
22316       -mbmx
22317       -mno-bmx
22318       -mcdx
22319       -mno-cdx
22320           Enable or disable generation of Nios II R2 BMX (bit manipulation)
22321           and CDX (code density) instructions.  Enabling these instructions
22322           also requires -march=r2.  Since these instructions are optional
22323           extensions to the R2 architecture, the default is not to emit them.
22324
22325       -mcustom-insn=N
22326       -mno-custom-insn
22327           Each -mcustom-insn=N option enables use of a custom instruction
22328           with encoding N when generating code that uses insn.  For example,
22329           -mcustom-fadds=253 generates custom instruction 253 for single-
22330           precision floating-point add operations instead of the default
22331           behavior of using a library call.
22332
22333           The following values of insn are supported.  Except as otherwise
22334           noted, floating-point operations are expected to be implemented
22335           with normal IEEE 754 semantics and correspond directly to the C
22336           operators or the equivalent GCC built-in functions.
22337
22338           Single-precision floating point:
22339
22340           fadds, fsubs, fdivs, fmuls
22341               Binary arithmetic operations.
22342
22343           fnegs
22344               Unary negation.
22345
22346           fabss
22347               Unary absolute value.
22348
22349           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
22350               Comparison operations.
22351
22352           fmins, fmaxs
22353               Floating-point minimum and maximum.  These instructions are
22354               only generated if -ffinite-math-only is specified.
22355
22356           fsqrts
22357               Unary square root operation.
22358
22359           fcoss, fsins, ftans, fatans, fexps, flogs
22360               Floating-point trigonometric and exponential functions.  These
22361               instructions are only generated if -funsafe-math-optimizations
22362               is also specified.
22363
22364           Double-precision floating point:
22365
22366           faddd, fsubd, fdivd, fmuld
22367               Binary arithmetic operations.
22368
22369           fnegd
22370               Unary negation.
22371
22372           fabsd
22373               Unary absolute value.
22374
22375           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
22376               Comparison operations.
22377
22378           fmind, fmaxd
22379               Double-precision minimum and maximum.  These instructions are
22380               only generated if -ffinite-math-only is specified.
22381
22382           fsqrtd
22383               Unary square root operation.
22384
22385           fcosd, fsind, ftand, fatand, fexpd, flogd
22386               Double-precision trigonometric and exponential functions.
22387               These instructions are only generated if
22388               -funsafe-math-optimizations is also specified.
22389
22390           Conversions:
22391
22392           fextsd
22393               Conversion from single precision to double precision.
22394
22395           ftruncds
22396               Conversion from double precision to single precision.
22397
22398           fixsi, fixsu, fixdi, fixdu
22399               Conversion from floating point to signed or unsigned integer
22400               types, with truncation towards zero.
22401
22402           round
22403               Conversion from single-precision floating point to signed
22404               integer, rounding to the nearest integer and ties away from
22405               zero.  This corresponds to the "__builtin_lroundf" function
22406               when -fno-math-errno is used.
22407
22408           floatis, floatus, floatid, floatud
22409               Conversion from signed or unsigned integer types to floating-
22410               point types.
22411
22412           In addition, all of the following transfer instructions for
22413           internal registers X and Y must be provided to use any of the
22414           double-precision floating-point instructions.  Custom instructions
22415           taking two double-precision source operands expect the first
22416           operand in the 64-bit register X.  The other operand (or only
22417           operand of a unary operation) is given to the custom arithmetic
22418           instruction with the least significant half in source register src1
22419           and the most significant half in src2.  A custom instruction that
22420           returns a double-precision result returns the most significant 32
22421           bits in the destination register and the other half in 32-bit
22422           register Y.  GCC automatically generates the necessary code
22423           sequences to write register X and/or read register Y when double-
22424           precision floating-point instructions are used.
22425
22426           fwrx
22427               Write src1 into the least significant half of X and src2 into
22428               the most significant half of X.
22429
22430           fwry
22431               Write src1 into Y.
22432
22433           frdxhi, frdxlo
22434               Read the most or least (respectively) significant half of X and
22435               store it in dest.
22436
22437           frdy
22438               Read the value of Y and store it into dest.
22439
22440           Note that you can gain more local control over generation of Nios
22441           II custom instructions by using the "target("custom-insn=N")" and
22442           "target("no-custom-insn")" function attributes or pragmas.
22443
22444       -mcustom-fpu-cfg=name
22445           This option enables a predefined, named set of custom instruction
22446           encodings (see -mcustom-insn above).  Currently, the following sets
22447           are defined:
22448
22449           -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252
22450           -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant
22451
22452           -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252
22453           -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255
22454           -fsingle-precision-constant
22455
22456           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243
22457           -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246
22458           -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251
22459           -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254
22460           -mcustom-fdivs=255 -fsingle-precision-constant
22461
22462           -mcustom-fpu-cfg=fph2 is equivalent to: -mcustom-fabss=224
22463           -mcustom-fnegs=225 -mcustom-fcmpnes=226 -mcustom-fcmpeqs=227
22464           -mcustom-fcmpges=228 -mcustom-fcmpgts=229 -mcustom-fcmples=230
22465           -mcustom-fcmplts=231 -mcustom-fmaxs=232 -mcustom-fmins=233
22466           -mcustom-round=248 -mcustom-fixsi=249 -mcustom-floatis=250
22467           -mcustom-fsqrts=251 -mcustom-fmuls=252 -mcustom-fadds=253
22468           -mcustom-fsubs=254 -mcustom-fdivs=255
22469
22470           Custom instruction assignments given by individual -mcustom-insn=
22471           options override those given by -mcustom-fpu-cfg=, regardless of
22472           the order of the options on the command line.
22473
22474           Note that you can gain more local control over selection of a FPU
22475           configuration by using the "target("custom-fpu-cfg=name")" function
22476           attribute or pragma.
22477
22478           The name fph2 is an abbreviation for Nios II Floating Point
22479           Hardware 2 Component.  Please note that the custom instructions
22480           enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are only
22481           generated if -ffinite-math-only is specified.  The custom
22482           instruction enabled by -mcustom-round=248 is only generated if
22483           -fno-math-errno is specified.  In contrast to the other
22484           configurations, -fsingle-precision-constant is not set.
22485
22486       These additional -m options are available for the Altera Nios II ELF
22487       (bare-metal) target:
22488
22489       -mhal
22490           Link with HAL BSP.  This suppresses linking with the GCC-provided C
22491           runtime startup and termination code, and is typically used in
22492           conjunction with -msys-crt0= to specify the location of the
22493           alternate startup code provided by the HAL BSP.
22494
22495       -msmallc
22496           Link with a limited version of the C library, -lsmallc, rather than
22497           Newlib.
22498
22499       -msys-crt0=startfile
22500           startfile is the file name of the startfile (crt0) to use when
22501           linking.  This option is only useful in conjunction with -mhal.
22502
22503       -msys-lib=systemlib
22504           systemlib is the library name of the library that provides low-
22505           level system calls required by the C library, e.g. "read" and
22506           "write".  This option is typically used to link with a library
22507           provided by a HAL BSP.
22508
22509   Nvidia PTX Options
22510       These options are defined for Nvidia PTX:
22511
22512       -m64
22513           Ignored, but preserved for backward compatibility.  Only 64-bit ABI
22514           is supported.
22515
22516       -misa=ISA-string
22517           Generate code for given the specified PTX ISA (e.g. sm_35).  ISA
22518           strings must be lower-case.  Valid ISA strings include sm_30 and
22519           sm_35.  The default ISA is sm_35.
22520
22521       -mmainkernel
22522           Link in code for a __main kernel.  This is for stand-alone instead
22523           of offloading execution.
22524
22525       -moptimize
22526           Apply partitioned execution optimizations.  This is the default
22527           when any level of optimization is selected.
22528
22529       -msoft-stack
22530           Generate code that does not use ".local" memory directly for stack
22531           storage. Instead, a per-warp stack pointer is maintained
22532           explicitly. This enables variable-length stack allocation (with
22533           variable-length arrays or "alloca"), and when global memory is used
22534           for underlying storage, makes it possible to access automatic
22535           variables from other threads, or with atomic instructions. This
22536           code generation variant is used for OpenMP offloading, but the
22537           option is exposed on its own for the purpose of testing the
22538           compiler; to generate code suitable for linking into programs using
22539           OpenMP offloading, use option -mgomp.
22540
22541       -muniform-simt
22542           Switch to code generation variant that allows to execute all
22543           threads in each warp, while maintaining memory state and side
22544           effects as if only one thread in each warp was active outside of
22545           OpenMP SIMD regions.  All atomic operations and calls to runtime
22546           (malloc, free, vprintf) are conditionally executed (iff current
22547           lane index equals the master lane index), and the register being
22548           assigned is copied via a shuffle instruction from the master lane.
22549           Outside of SIMD regions lane 0 is the master; inside, each thread
22550           sees itself as the master.  Shared memory array "int __nvptx_uni[]"
22551           stores all-zeros or all-ones bitmasks for each warp, indicating
22552           current mode (0 outside of SIMD regions).  Each thread can bitwise-
22553           and the bitmask at position "tid.y" with current lane index to
22554           compute the master lane index.
22555
22556       -mgomp
22557           Generate code for use in OpenMP offloading: enables -msoft-stack
22558           and -muniform-simt options, and selects corresponding multilib
22559           variant.
22560
22561   OpenRISC Options
22562       These options are defined for OpenRISC:
22563
22564       -mboard=name
22565           Configure a board specific runtime.  This will be passed to the
22566           linker for newlib board library linking.  The default is "or1ksim".
22567
22568       -mnewlib
22569           This option is ignored; it is for compatibility purposes only.
22570           This used to select linker and preprocessor options for use with
22571           newlib.
22572
22573       -msoft-div
22574       -mhard-div
22575           Select software or hardware divide ("l.div", "l.divu")
22576           instructions.  This default is hardware divide.
22577
22578       -msoft-mul
22579       -mhard-mul
22580           Select software or hardware multiply ("l.mul", "l.muli")
22581           instructions.  This default is hardware multiply.
22582
22583       -msoft-float
22584       -mhard-float
22585           Select software or hardware for floating point operations.  The
22586           default is software.
22587
22588       -mdouble-float
22589           When -mhard-float is selected, enables generation of double-
22590           precision floating point instructions.  By default functions from
22591           libgcc are used to perform double-precision floating point
22592           operations.
22593
22594       -munordered-float
22595           When -mhard-float is selected, enables generation of unordered
22596           floating point compare and set flag ("lf.sfun*") instructions.  By
22597           default functions from libgcc are used to perform unordered
22598           floating point compare and set flag operations.
22599
22600       -mcmov
22601           Enable generation of conditional move ("l.cmov") instructions.  By
22602           default the equivalent will be generated using set and branch.
22603
22604       -mror
22605           Enable generation of rotate right ("l.ror") instructions.  By
22606           default functions from libgcc are used to perform rotate right
22607           operations.
22608
22609       -mrori
22610           Enable generation of rotate right with immediate ("l.rori")
22611           instructions.  By default functions from libgcc are used to perform
22612           rotate right with immediate operations.
22613
22614       -msext
22615           Enable generation of sign extension ("l.ext*") instructions.  By
22616           default memory loads are used to perform sign extension.
22617
22618       -msfimm
22619           Enable generation of compare and set flag with immediate ("l.sf*i")
22620           instructions.  By default extra instructions will be generated to
22621           store the immediate to a register first.
22622
22623       -mshftimm
22624           Enable generation of shift with immediate ("l.srai", "l.srli",
22625           "l.slli") instructions.  By default extra instructions will be
22626           generated to store the immediate to a register first.
22627
22628   PDP-11 Options
22629       These options are defined for the PDP-11:
22630
22631       -mfpu
22632           Use hardware FPP floating point.  This is the default.  (FIS
22633           floating point on the PDP-11/40 is not supported.)  Implies -m45.
22634
22635       -msoft-float
22636           Do not use hardware floating point.
22637
22638       -mac0
22639           Return floating-point results in ac0 (fr0 in Unix assembler
22640           syntax).
22641
22642       -mno-ac0
22643           Return floating-point results in memory.  This is the default.
22644
22645       -m40
22646           Generate code for a PDP-11/40.  Implies -msoft-float -mno-split.
22647
22648       -m45
22649           Generate code for a PDP-11/45.  This is the default.
22650
22651       -m10
22652           Generate code for a PDP-11/10.  Implies -msoft-float -mno-split.
22653
22654       -mint16
22655       -mno-int32
22656           Use 16-bit "int".  This is the default.
22657
22658       -mint32
22659       -mno-int16
22660           Use 32-bit "int".
22661
22662       -msplit
22663           Target has split instruction and data space.  Implies -m45.
22664
22665       -munix-asm
22666           Use Unix assembler syntax.
22667
22668       -mdec-asm
22669           Use DEC assembler syntax.
22670
22671       -mgnu-asm
22672           Use GNU assembler syntax.  This is the default.
22673
22674       -mlra
22675           Use the new LRA register allocator.  By default, the old "reload"
22676           allocator is used.
22677
22678   picoChip Options
22679       These -m options are defined for picoChip implementations:
22680
22681       -mae=ae_type
22682           Set the instruction set, register set, and instruction scheduling
22683           parameters for array element type ae_type.  Supported values for
22684           ae_type are ANY, MUL, and MAC.
22685
22686           -mae=ANY selects a completely generic AE type.  Code generated with
22687           this option runs on any of the other AE types.  The code is not as
22688           efficient as it would be if compiled for a specific AE type, and
22689           some types of operation (e.g., multiplication) do not work properly
22690           on all types of AE.
22691
22692           -mae=MUL selects a MUL AE type.  This is the most useful AE type
22693           for compiled code, and is the default.
22694
22695           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
22696           option may suffer from poor performance of byte (char)
22697           manipulation, since the DSP AE does not provide hardware support
22698           for byte load/stores.
22699
22700       -msymbol-as-address
22701           Enable the compiler to directly use a symbol name as an address in
22702           a load/store instruction, without first loading it into a register.
22703           Typically, the use of this option generates larger programs, which
22704           run faster than when the option isn't used.  However, the results
22705           vary from program to program, so it is left as a user option,
22706           rather than being permanently enabled.
22707
22708       -mno-inefficient-warnings
22709           Disables warnings about the generation of inefficient code.  These
22710           warnings can be generated, for example, when compiling code that
22711           performs byte-level memory operations on the MAC AE type.  The MAC
22712           AE has no hardware support for byte-level memory operations, so all
22713           byte load/stores must be synthesized from word load/store
22714           operations.  This is inefficient and a warning is generated to
22715           indicate that you should rewrite the code to avoid byte operations,
22716           or to target an AE type that has the necessary hardware support.
22717           This option disables these warnings.
22718
22719   PowerPC Options
22720       These are listed under
22721
22722   PRU Options
22723       These command-line options are defined for PRU target:
22724
22725       -minrt
22726           Link with a minimum runtime environment, with no support for static
22727           initializers and constructors.  Using this option can significantly
22728           reduce the size of the final ELF binary.  Beware that the compiler
22729           could still generate code with static initializers and
22730           constructors.  It is up to the programmer to ensure that the source
22731           program will not use those features.
22732
22733       -mmcu=mcu
22734           Specify the PRU MCU variant to use.  Check Newlib for the exact
22735           list of supported MCUs.
22736
22737       -mno-relax
22738           Make GCC pass the --no-relax command-line option to the linker
22739           instead of the --relax option.
22740
22741       -mloop
22742           Allow (or do not allow) GCC to use the LOOP instruction.
22743
22744       -mabi=variant
22745           Specify the ABI variant to output code for.  -mabi=ti selects the
22746           unmodified TI ABI while -mabi=gnu selects a GNU variant that copes
22747           more naturally with certain GCC assumptions.  These are the
22748           differences:
22749
22750           Function Pointer Size
22751               TI ABI specifies that function (code) pointers are 16-bit,
22752               whereas GNU supports only 32-bit data and code pointers.
22753
22754           Optional Return Value Pointer
22755               Function return values larger than 64 bits are passed by using
22756               a hidden pointer as the first argument of the function.  TI
22757               ABI, though, mandates that the pointer can be NULL in case the
22758               caller is not using the returned value.  GNU always passes and
22759               expects a valid return value pointer.
22760
22761           The current -mabi=ti implementation simply raises a compile error
22762           when any of the above code constructs is detected.  As a
22763           consequence the standard C library cannot be built and it is
22764           omitted when linking with -mabi=ti.
22765
22766           Relaxation is a GNU feature and for safety reasons is disabled when
22767           using -mabi=ti.  The TI toolchain does not emit relocations for
22768           QBBx instructions, so the GNU linker cannot adjust them when
22769           shortening adjacent LDI32 pseudo instructions.
22770
22771   RISC-V Options
22772       These command-line options are defined for RISC-V targets:
22773
22774       -mbranch-cost=n
22775           Set the cost of branches to roughly n instructions.
22776
22777       -mplt
22778       -mno-plt
22779           When generating PIC code, do or don't allow the use of PLTs.
22780           Ignored for non-PIC.  The default is -mplt.
22781
22782       -mabi=ABI-string
22783           Specify integer and floating-point calling convention.  ABI-string
22784           contains two parts: the size of integer types and the registers
22785           used for floating-point types.  For example -march=rv64ifd
22786           -mabi=lp64d means that long and pointers are 64-bit (implicitly
22787           defining int to be 32-bit), and that floating-point values up to 64
22788           bits wide are passed in F registers.  Contrast this with
22789           -march=rv64ifd -mabi=lp64f, which still allows the compiler to
22790           generate code that uses the F and D extensions but only allows
22791           floating-point values up to 32 bits long to be passed in registers;
22792           or -march=rv64ifd -mabi=lp64, in which no floating-point arguments
22793           will be passed in registers.
22794
22795           The default for this argument is system dependent, users who want a
22796           specific calling convention should specify one explicitly.  The
22797           valid calling conventions are: ilp32, ilp32f, ilp32d, lp64, lp64f,
22798           and lp64d.  Some calling conventions are impossible to implement on
22799           some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid
22800           because the ABI requires 64-bit values be passed in F registers,
22801           but F registers are only 32 bits wide.  There is also the ilp32e
22802           ABI that can only be used with the rv32e architecture.  This ABI is
22803           not well specified at present, and is subject to change.
22804
22805       -mfdiv
22806       -mno-fdiv
22807           Do or don't use hardware floating-point divide and square root
22808           instructions.  This requires the F or D extensions for floating-
22809           point registers.  The default is to use them if the specified
22810           architecture has these instructions.
22811
22812       -mdiv
22813       -mno-div
22814           Do or don't use hardware instructions for integer division.  This
22815           requires the M extension.  The default is to use them if the
22816           specified architecture has these instructions.
22817
22818       -march=ISA-string
22819           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must
22820           be lower-case.  Examples include rv64i, rv32g, rv32e, and rv32imaf.
22821
22822           When -march= is not specified, use the setting from -mcpu.
22823
22824           If both -march and -mcpu= are not specified, the default for this
22825           argument is system dependent, users who want a specific
22826           architecture extensions should specify one explicitly.
22827
22828       -mcpu=processor-string
22829           Use architecture of and optimize the output for the given
22830           processor, specified by particular CPU name.  Permissible values
22831           for this option are: sifive-e20, sifive-e21, sifive-e24,
22832           sifive-e31, sifive-e34, sifive-e76, sifive-s21, sifive-s51,
22833           sifive-s54, sifive-s76, sifive-u54, and sifive-u74.
22834
22835       -mtune=processor-string
22836           Optimize the output for the given processor, specified by
22837           microarchitecture or particular CPU name.  Permissible values for
22838           this option are: rocket, sifive-3-series, sifive-5-series,
22839           sifive-7-series, size, and all valid options for -mcpu=.
22840
22841           When -mtune= is not specified, use the setting from -mcpu, the
22842           default is rocket if both are not specified.
22843
22844           The size choice is not intended for use by end-users.  This is used
22845           when -Os is specified.  It overrides the instruction cost info
22846           provided by -mtune=, but does not override the pipeline info.  This
22847           helps reduce code size while still giving good performance.
22848
22849       -mpreferred-stack-boundary=num
22850           Attempt to keep the stack boundary aligned to a 2 raised to num
22851           byte boundary.  If -mpreferred-stack-boundary is not specified, the
22852           default is 4 (16 bytes or 128-bits).
22853
22854           Warning: If you use this switch, then you must build all modules
22855           with the same value, including any libraries.  This includes the
22856           system libraries and startup modules.
22857
22858       -msmall-data-limit=n
22859           Put global and static data smaller than n bytes into a special
22860           section (on some targets).
22861
22862       -msave-restore
22863       -mno-save-restore
22864           Do or don't use smaller but slower prologue and epilogue code that
22865           uses library function calls.  The default is to use fast inline
22866           prologues and epilogues.
22867
22868       -mshorten-memrefs
22869       -mno-shorten-memrefs
22870           Do or do not attempt to make more use of compressed load/store
22871           instructions by replacing a load/store of 'base register + large
22872           offset' with a new load/store of 'new base + small offset'.  If the
22873           new base gets stored in a compressed register, then the new
22874           load/store can be compressed.  Currently targets 32-bit integer
22875           load/stores only.
22876
22877       -mstrict-align
22878       -mno-strict-align
22879           Do not or do generate unaligned memory accesses.  The default is
22880           set depending on whether the processor we are optimizing for
22881           supports fast unaligned access or not.
22882
22883       -mcmodel=medlow
22884           Generate code for the medium-low code model. The program and its
22885           statically defined symbols must lie within a single 2 GiB address
22886           range and must lie between absolute addresses -2 GiB and +2 GiB.
22887           Programs can be statically or dynamically linked. This is the
22888           default code model.
22889
22890       -mcmodel=medany
22891           Generate code for the medium-any code model. The program and its
22892           statically defined symbols must be within any single 2 GiB address
22893           range. Programs can be statically or dynamically linked.
22894
22895       -mexplicit-relocs
22896       -mno-exlicit-relocs
22897           Use or do not use assembler relocation operators when dealing with
22898           symbolic addresses.  The alternative is to use assembler macros
22899           instead, which may limit optimization.
22900
22901       -mrelax
22902       -mno-relax
22903           Take advantage of linker relaxations to reduce the number of
22904           instructions required to materialize symbol addresses. The default
22905           is to take advantage of linker relaxations.
22906
22907       -memit-attribute
22908       -mno-emit-attribute
22909           Emit (do not emit) RISC-V attribute to record extra information
22910           into ELF objects.  This feature requires at least binutils 2.32.
22911
22912       -malign-data=type
22913           Control how GCC aligns variables and constants of array, structure,
22914           or union types.  Supported values for type are xlen which uses x
22915           register width as the alignment value, and natural which uses
22916           natural alignment.  xlen is the default.
22917
22918       -mbig-endian
22919           Generate big-endian code.  This is the default when GCC is
22920           configured for a riscv64be-*-* or riscv32be-*-* target.
22921
22922       -mlittle-endian
22923           Generate little-endian code.  This is the default when GCC is
22924           configured for a riscv64-*-* or riscv32-*-* but not a riscv64be-*-*
22925           or riscv32be-*-* target.
22926
22927       -mstack-protector-guard=guard
22928       -mstack-protector-guard-reg=reg
22929       -mstack-protector-guard-offset=offset
22930           Generate stack protection code using canary at guard.  Supported
22931           locations are global for a global canary or tls for per-thread
22932           canary in the TLS block.
22933
22934           With the latter choice the options -mstack-protector-guard-reg=reg
22935           and -mstack-protector-guard-offset=offset furthermore specify which
22936           register to use as base register for reading the canary, and from
22937           what offset from that base register. There is no default register
22938           or offset as this is entirely for use within the Linux kernel.
22939
22940   RL78 Options
22941       -msim
22942           Links in additional target libraries to support operation within a
22943           simulator.
22944
22945       -mmul=none
22946       -mmul=g10
22947       -mmul=g13
22948       -mmul=g14
22949       -mmul=rl78
22950           Specifies the type of hardware multiplication and division support
22951           to be used.  The simplest is "none", which uses software for both
22952           multiplication and division.  This is the default.  The "g13" value
22953           is for the hardware multiply/divide peripheral found on the
22954           RL78/G13 (S2 core) targets.  The "g14" value selects the use of the
22955           multiplication and division instructions supported by the RL78/G14
22956           (S3 core) parts.  The value "rl78" is an alias for "g14" and the
22957           value "mg10" is an alias for "none".
22958
22959           In addition a C preprocessor macro is defined, based upon the
22960           setting of this option.  Possible values are: "__RL78_MUL_NONE__",
22961           "__RL78_MUL_G13__" or "__RL78_MUL_G14__".
22962
22963       -mcpu=g10
22964       -mcpu=g13
22965       -mcpu=g14
22966       -mcpu=rl78
22967           Specifies the RL78 core to target.  The default is the G14 core,
22968           also known as an S3 core or just RL78.  The G13 or S2 core does not
22969           have multiply or divide instructions, instead it uses a hardware
22970           peripheral for these operations.  The G10 or S1 core does not have
22971           register banks, so it uses a different calling convention.
22972
22973           If this option is set it also selects the type of hardware multiply
22974           support to use, unless this is overridden by an explicit -mmul=none
22975           option on the command line.  Thus specifying -mcpu=g13 enables the
22976           use of the G13 hardware multiply peripheral and specifying
22977           -mcpu=g10 disables the use of hardware multiplications altogether.
22978
22979           Note, although the RL78/G14 core is the default target, specifying
22980           -mcpu=g14 or -mcpu=rl78 on the command line does change the
22981           behavior of the toolchain since it also enables G14 hardware
22982           multiply support.  If these options are not specified on the
22983           command line then software multiplication routines will be used
22984           even though the code targets the RL78 core.  This is for backwards
22985           compatibility with older toolchains which did not have hardware
22986           multiply and divide support.
22987
22988           In addition a C preprocessor macro is defined, based upon the
22989           setting of this option.  Possible values are: "__RL78_G10__",
22990           "__RL78_G13__" or "__RL78_G14__".
22991
22992       -mg10
22993       -mg13
22994       -mg14
22995       -mrl78
22996           These are aliases for the corresponding -mcpu= option.  They are
22997           provided for backwards compatibility.
22998
22999       -mallregs
23000           Allow the compiler to use all of the available registers.  By
23001           default registers "r24..r31" are reserved for use in interrupt
23002           handlers.  With this option enabled these registers can be used in
23003           ordinary functions as well.
23004
23005       -m64bit-doubles
23006       -m32bit-doubles
23007           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
23008           (-m32bit-doubles) in size.  The default is -m32bit-doubles.
23009
23010       -msave-mduc-in-interrupts
23011       -mno-save-mduc-in-interrupts
23012           Specifies that interrupt handler functions should preserve the MDUC
23013           registers.  This is only necessary if normal code might use the
23014           MDUC registers, for example because it performs multiplication and
23015           division operations.  The default is to ignore the MDUC registers
23016           as this makes the interrupt handlers faster.  The target option
23017           -mg13 needs to be passed for this to work as this feature is only
23018           available on the G13 target (S2 core).  The MDUC registers will
23019           only be saved if the interrupt handler performs a multiplication or
23020           division operation or it calls another function.
23021
23022   IBM RS/6000 and PowerPC Options
23023       These -m options are defined for the IBM RS/6000 and PowerPC:
23024
23025       -mpowerpc-gpopt
23026       -mno-powerpc-gpopt
23027       -mpowerpc-gfxopt
23028       -mno-powerpc-gfxopt
23029       -mpowerpc64
23030       -mno-powerpc64
23031       -mmfcrf
23032       -mno-mfcrf
23033       -mpopcntb
23034       -mno-popcntb
23035       -mpopcntd
23036       -mno-popcntd
23037       -mfprnd
23038       -mno-fprnd
23039       -mcmpb
23040       -mno-cmpb
23041       -mhard-dfp
23042       -mno-hard-dfp
23043           You use these options to specify which instructions are available
23044           on the processor you are using.  The default value of these options
23045           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
23046           overrides the specification of these options.  We recommend you use
23047           the -mcpu=cpu_type option rather than the options listed above.
23048
23049           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC
23050           architecture instructions in the General Purpose group, including
23051           floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
23052           to use the optional PowerPC architecture instructions in the
23053           Graphics group, including floating-point select.
23054
23055           The -mmfcrf option allows GCC to generate the move from condition
23056           register field instruction implemented on the POWER4 processor and
23057           other processors that support the PowerPC V2.01 architecture.  The
23058           -mpopcntb option allows GCC to generate the popcount and double-
23059           precision FP reciprocal estimate instruction implemented on the
23060           POWER5 processor and other processors that support the PowerPC
23061           V2.02 architecture.  The -mpopcntd option allows GCC to generate
23062           the popcount instruction implemented on the POWER7 processor and
23063           other processors that support the PowerPC V2.06 architecture.  The
23064           -mfprnd option allows GCC to generate the FP round to integer
23065           instructions implemented on the POWER5+ processor and other
23066           processors that support the PowerPC V2.03 architecture.  The -mcmpb
23067           option allows GCC to generate the compare bytes instruction
23068           implemented on the POWER6 processor and other processors that
23069           support the PowerPC V2.05 architecture.  The -mhard-dfp option
23070           allows GCC to generate the decimal floating-point instructions
23071           implemented on some POWER processors.
23072
23073           The -mpowerpc64 option allows GCC to generate the additional 64-bit
23074           instructions that are found in the full PowerPC64 architecture and
23075           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
23076           -mno-powerpc64.
23077
23078       -mcpu=cpu_type
23079           Set architecture type, register usage, and instruction scheduling
23080           parameters for machine type cpu_type.  Supported values for
23081           cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476,
23082           476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400,
23083           7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3,
23084           e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,
23085           power4, power5, power5+, power6, power6x, power7, power8, power9,
23086           future, powerpc, powerpc64, powerpc64le, rs64, and native.
23087
23088           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure
23089           32-bit PowerPC (either endian), 64-bit big endian PowerPC and
23090           64-bit little endian PowerPC architecture machine types, with an
23091           appropriate, generic processor model assumed for scheduling
23092           purposes.
23093
23094           Specifying native as cpu type detects and selects the architecture
23095           option that corresponds to the host processor of the system
23096           performing the compilation.  -mcpu=native has no effect if GCC does
23097           not recognize the processor.
23098
23099           The other options specify a specific processor.  Code generated
23100           under those options runs best on that processor, and may not run at
23101           all on others.
23102
23103           The -mcpu options automatically enable or disable the following
23104           options:
23105
23106           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb
23107           -mpopcntd  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt -mmulhw
23108           -mdlmzb  -mmfpgpr  -mvsx -mcrypto  -mhtm  -mpower8-fusion
23109           -mpower8-vector -mquad-memory  -mquad-memory-atomic  -mfloat128
23110           -mfloat128-hardware -mprefixed -mpcrel -mmma -mrop-protect
23111
23112           The particular options set for any particular CPU varies between
23113           compiler versions, depending on what setting seems to produce
23114           optimal code for that CPU; it doesn't necessarily reflect the
23115           actual hardware's capabilities.  If you wish to set an individual
23116           option to a particular value, you may specify it after the -mcpu
23117           option, like -mcpu=970 -mno-altivec.
23118
23119           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
23120           disabled by the -mcpu option at present because AIX does not have
23121           full support for these options.  You may still enable or disable
23122           them individually if you're sure it'll work in your environment.
23123
23124       -mtune=cpu_type
23125           Set the instruction scheduling parameters for machine type
23126           cpu_type, but do not set the architecture type or register usage,
23127           as -mcpu=cpu_type does.  The same values for cpu_type are used for
23128           -mtune as for -mcpu.  If both are specified, the code generated
23129           uses the architecture and registers set by -mcpu, but the
23130           scheduling parameters set by -mtune.
23131
23132       -mcmodel=small
23133           Generate PowerPC64 code for the small model: The TOC is limited to
23134           64k.
23135
23136       -mcmodel=medium
23137           Generate PowerPC64 code for the medium model: The TOC and other
23138           static data may be up to a total of 4G in size.  This is the
23139           default for 64-bit Linux.
23140
23141       -mcmodel=large
23142           Generate PowerPC64 code for the large model: The TOC may be up to
23143           4G in size.  Other data and code is only limited by the 64-bit
23144           address space.
23145
23146       -maltivec
23147       -mno-altivec
23148           Generate code that uses (does not use) AltiVec instructions, and
23149           also enable the use of built-in functions that allow more direct
23150           access to the AltiVec instruction set.  You may also need to set
23151           -mabi=altivec to adjust the current ABI with AltiVec ABI
23152           enhancements.
23153
23154           When -maltivec is used, the element order for AltiVec intrinsics
23155           such as "vec_splat", "vec_extract", and "vec_insert" match array
23156           element order corresponding to the endianness of the target.  That
23157           is, element zero identifies the leftmost element in a vector
23158           register when targeting a big-endian platform, and identifies the
23159           rightmost element in a vector register when targeting a little-
23160           endian platform.
23161
23162       -mvrsave
23163       -mno-vrsave
23164           Generate VRSAVE instructions when generating AltiVec code.
23165
23166       -msecure-plt
23167           Generate code that allows ld and ld.so to build executables and
23168           shared libraries with non-executable ".plt" and ".got" sections.
23169           This is a PowerPC 32-bit SYSV ABI option.
23170
23171       -mbss-plt
23172           Generate code that uses a BSS ".plt" section that ld.so fills in,
23173           and requires ".plt" and ".got" sections that are both writable and
23174           executable.  This is a PowerPC 32-bit SYSV ABI option.
23175
23176       -misel
23177       -mno-isel
23178           This switch enables or disables the generation of ISEL
23179           instructions.
23180
23181       -mvsx
23182       -mno-vsx
23183           Generate code that uses (does not use) vector/scalar (VSX)
23184           instructions, and also enable the use of built-in functions that
23185           allow more direct access to the VSX instruction set.
23186
23187       -mcrypto
23188       -mno-crypto
23189           Enable the use (disable) of the built-in functions that allow
23190           direct access to the cryptographic instructions that were added in
23191           version 2.07 of the PowerPC ISA.
23192
23193       -mhtm
23194       -mno-htm
23195           Enable (disable) the use of the built-in functions that allow
23196           direct access to the Hardware Transactional Memory (HTM)
23197           instructions that were added in version 2.07 of the PowerPC ISA.
23198
23199       -mpower8-fusion
23200       -mno-power8-fusion
23201           Generate code that keeps (does not keeps) some integer operations
23202           adjacent so that the instructions can be fused together on power8
23203           and later processors.
23204
23205       -mpower8-vector
23206       -mno-power8-vector
23207           Generate code that uses (does not use) the vector and scalar
23208           instructions that were added in version 2.07 of the PowerPC ISA.
23209           Also enable the use of built-in functions that allow more direct
23210           access to the vector instructions.
23211
23212       -mquad-memory
23213       -mno-quad-memory
23214           Generate code that uses (does not use) the non-atomic quad word
23215           memory instructions.  The -mquad-memory option requires use of
23216           64-bit mode.
23217
23218       -mquad-memory-atomic
23219       -mno-quad-memory-atomic
23220           Generate code that uses (does not use) the atomic quad word memory
23221           instructions.  The -mquad-memory-atomic option requires use of
23222           64-bit mode.
23223
23224       -mfloat128
23225       -mno-float128
23226           Enable/disable the __float128 keyword for IEEE 128-bit floating
23227           point and use either software emulation for IEEE 128-bit floating
23228           point or hardware instructions.
23229
23230           The VSX instruction set (-mvsx, -mcpu=power7, -mcpu=power8), or
23231           -mcpu=power9 must be enabled to use the IEEE 128-bit floating point
23232           support.  The IEEE 128-bit floating point support only works on
23233           PowerPC Linux systems.
23234
23235           The default for -mfloat128 is enabled on PowerPC Linux systems
23236           using the VSX instruction set, and disabled on other systems.
23237
23238           If you use the ISA 3.0 instruction set (-mpower9-vector or
23239           -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point
23240           support will also enable the generation of ISA 3.0 IEEE 128-bit
23241           floating point instructions.  Otherwise, if you do not specify to
23242           generate ISA 3.0 instructions or you are targeting a 32-bit big
23243           endian system, IEEE 128-bit floating point will be done with
23244           software emulation.
23245
23246       -mfloat128-hardware
23247       -mno-float128-hardware
23248           Enable/disable using ISA 3.0 hardware instructions to support the
23249           __float128 data type.
23250
23251           The default for -mfloat128-hardware is enabled on PowerPC Linux
23252           systems using the ISA 3.0 instruction set, and disabled on other
23253           systems.
23254
23255       -m32
23256       -m64
23257           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
23258           targets (including GNU/Linux).  The 32-bit environment sets int,
23259           long and pointer to 32 bits and generates code that runs on any
23260           PowerPC variant.  The 64-bit environment sets int to 32 bits and
23261           long and pointer to 64 bits, and generates code for PowerPC64, as
23262           for -mpowerpc64.
23263
23264       -mfull-toc
23265       -mno-fp-in-toc
23266       -mno-sum-in-toc
23267       -mminimal-toc
23268           Modify generation of the TOC (Table Of Contents), which is created
23269           for every executable file.  The -mfull-toc option is selected by
23270           default.  In that case, GCC allocates at least one TOC entry for
23271           each unique non-automatic variable reference in your program.  GCC
23272           also places floating-point constants in the TOC.  However, only
23273           16,384 entries are available in the TOC.
23274
23275           If you receive a linker error message that saying you have
23276           overflowed the available TOC space, you can reduce the amount of
23277           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
23278           -mno-fp-in-toc prevents GCC from putting floating-point constants
23279           in the TOC and -mno-sum-in-toc forces GCC to generate code to
23280           calculate the sum of an address and a constant at run time instead
23281           of putting that sum into the TOC.  You may specify one or both of
23282           these options.  Each causes GCC to produce very slightly slower and
23283           larger code at the expense of conserving TOC space.
23284
23285           If you still run out of space in the TOC even when you specify both
23286           of these options, specify -mminimal-toc instead.  This option
23287           causes GCC to make only one TOC entry for every file.  When you
23288           specify this option, GCC produces code that is slower and larger
23289           but which uses extremely little TOC space.  You may wish to use
23290           this option only on files that contain less frequently-executed
23291           code.
23292
23293       -maix64
23294       -maix32
23295           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
23296           64-bit "long" type, and the infrastructure needed to support them.
23297           Specifying -maix64 implies -mpowerpc64, while -maix32 disables the
23298           64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.
23299
23300       -mxl-compat
23301       -mno-xl-compat
23302           Produce code that conforms more closely to IBM XL compiler
23303           semantics when using AIX-compatible ABI.  Pass floating-point
23304           arguments to prototyped functions beyond the register save area
23305           (RSA) on the stack in addition to argument FPRs.  Do not assume
23306           that most significant double in 128-bit long double value is
23307           properly rounded when comparing values and converting to double.
23308           Use XL symbol names for long double support routines.
23309
23310           The AIX calling convention was extended but not initially
23311           documented to handle an obscure K&R C case of calling a function
23312           that takes the address of its arguments with fewer arguments than
23313           declared.  IBM XL compilers access floating-point arguments that do
23314           not fit in the RSA from the stack when a subroutine is compiled
23315           without optimization.  Because always storing floating-point
23316           arguments on the stack is inefficient and rarely needed, this
23317           option is not enabled by default and only is necessary when calling
23318           subroutines compiled by IBM XL compilers without optimization.
23319
23320       -mpe
23321           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
23322           application written to use message passing with special startup
23323           code to enable the application to run.  The system must have PE
23324           installed in the standard location (/usr/lpp/ppe.poe/), or the
23325           specs file must be overridden with the -specs= option to specify
23326           the appropriate directory location.  The Parallel Environment does
23327           not support threads, so the -mpe option and the -pthread option are
23328           incompatible.
23329
23330       -malign-natural
23331       -malign-power
23332           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
23333           -malign-natural overrides the ABI-defined alignment of larger
23334           types, such as floating-point doubles, on their natural size-based
23335           boundary.  The option -malign-power instructs GCC to follow the
23336           ABI-specified alignment rules.  GCC defaults to the standard
23337           alignment defined in the ABI.
23338
23339           On 64-bit Darwin, natural alignment is the default, and
23340           -malign-power is not supported.
23341
23342       -msoft-float
23343       -mhard-float
23344           Generate code that does not use (uses) the floating-point register
23345           set.  Software floating-point emulation is provided if you use the
23346           -msoft-float option, and pass the option to GCC when linking.
23347
23348       -mmultiple
23349       -mno-multiple
23350           Generate code that uses (does not use) the load multiple word
23351           instructions and the store multiple word instructions.  These
23352           instructions are generated by default on POWER systems, and not
23353           generated on PowerPC systems.  Do not use -mmultiple on little-
23354           endian PowerPC systems, since those instructions do not work when
23355           the processor is in little-endian mode.  The exceptions are PPC740
23356           and PPC750 which permit these instructions in little-endian mode.
23357
23358       -mupdate
23359       -mno-update
23360           Generate code that uses (does not use) the load or store
23361           instructions that update the base register to the address of the
23362           calculated memory location.  These instructions are generated by
23363           default.  If you use -mno-update, there is a small window between
23364           the time that the stack pointer is updated and the address of the
23365           previous frame is stored, which means code that walks the stack
23366           frame across interrupts or signals may get corrupted data.
23367
23368       -mavoid-indexed-addresses
23369       -mno-avoid-indexed-addresses
23370           Generate code that tries to avoid (not avoid) the use of indexed
23371           load or store instructions. These instructions can incur a
23372           performance penalty on Power6 processors in certain situations,
23373           such as when stepping through large arrays that cross a 16M
23374           boundary.  This option is enabled by default when targeting Power6
23375           and disabled otherwise.
23376
23377       -mfused-madd
23378       -mno-fused-madd
23379           Generate code that uses (does not use) the floating-point multiply
23380           and accumulate instructions.  These instructions are generated by
23381           default if hardware floating point is used.  The machine-dependent
23382           -mfused-madd option is now mapped to the machine-independent
23383           -ffp-contract=fast option, and -mno-fused-madd is mapped to
23384           -ffp-contract=off.
23385
23386       -mmulhw
23387       -mno-mulhw
23388           Generate code that uses (does not use) the half-word multiply and
23389           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
23390           processors.  These instructions are generated by default when
23391           targeting those processors.
23392
23393       -mdlmzb
23394       -mno-dlmzb
23395           Generate code that uses (does not use) the string-search dlmzb
23396           instruction on the IBM 405, 440, 464 and 476 processors.  This
23397           instruction is generated by default when targeting those
23398           processors.
23399
23400       -mno-bit-align
23401       -mbit-align
23402           On System V.4 and embedded PowerPC systems do not (do) force
23403           structures and unions that contain bit-fields to be aligned to the
23404           base type of the bit-field.
23405
23406           For example, by default a structure containing nothing but 8
23407           "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary
23408           and has a size of 4 bytes.  By using -mno-bit-align, the structure
23409           is aligned to a 1-byte boundary and is 1 byte in size.
23410
23411       -mno-strict-align
23412       -mstrict-align
23413           On System V.4 and embedded PowerPC systems do not (do) assume that
23414           unaligned memory references are handled by the system.
23415
23416       -mrelocatable
23417       -mno-relocatable
23418           Generate code that allows (does not allow) a static executable to
23419           be relocated to a different address at run time.  A simple embedded
23420           PowerPC system loader should relocate the entire contents of
23421           ".got2" and 4-byte locations listed in the ".fixup" section, a
23422           table of 32-bit addresses generated by this option.  For this to
23423           work, all objects linked together must be compiled with
23424           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
23425           stack to an 8-byte boundary.
23426
23427       -mrelocatable-lib
23428       -mno-relocatable-lib
23429           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
23430           to allow static executables to be relocated at run time, but
23431           -mrelocatable-lib does not use the smaller stack alignment of
23432           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
23433           linked with objects compiled with any combination of the
23434           -mrelocatable options.
23435
23436       -mno-toc
23437       -mtoc
23438           On System V.4 and embedded PowerPC systems do not (do) assume that
23439           register 2 contains a pointer to a global area pointing to the
23440           addresses used in the program.
23441
23442       -mlittle
23443       -mlittle-endian
23444           On System V.4 and embedded PowerPC systems compile code for the
23445           processor in little-endian mode.  The -mlittle-endian option is the
23446           same as -mlittle.
23447
23448       -mbig
23449       -mbig-endian
23450           On System V.4 and embedded PowerPC systems compile code for the
23451           processor in big-endian mode.  The -mbig-endian option is the same
23452           as -mbig.
23453
23454       -mdynamic-no-pic
23455           On Darwin and Mac OS X systems, compile code so that it is not
23456           relocatable, but that its external references are relocatable.  The
23457           resulting code is suitable for applications, but not shared
23458           libraries.
23459
23460       -msingle-pic-base
23461           Treat the register used for PIC addressing as read-only, rather
23462           than loading it in the prologue for each function.  The runtime
23463           system is responsible for initializing this register with an
23464           appropriate value before execution begins.
23465
23466       -mprioritize-restricted-insns=priority
23467           This option controls the priority that is assigned to dispatch-slot
23468           restricted instructions during the second scheduling pass.  The
23469           argument priority takes the value 0, 1, or 2 to assign no, highest,
23470           or second-highest (respectively) priority to dispatch-slot
23471           restricted instructions.
23472
23473       -msched-costly-dep=dependence_type
23474           This option controls which dependences are considered costly by the
23475           target during instruction scheduling.  The argument dependence_type
23476           takes one of the following values:
23477
23478           no  No dependence is costly.
23479
23480           all All dependences are costly.
23481
23482           true_store_to_load
23483               A true dependence from store to load is costly.
23484
23485           store_to_load
23486               Any dependence from store to load is costly.
23487
23488           number
23489               Any dependence for which the latency is greater than or equal
23490               to number is costly.
23491
23492       -minsert-sched-nops=scheme
23493           This option controls which NOP insertion scheme is used during the
23494           second scheduling pass.  The argument scheme takes one of the
23495           following values:
23496
23497           no  Don't insert NOPs.
23498
23499           pad Pad with NOPs any dispatch group that has vacant issue slots,
23500               according to the scheduler's grouping.
23501
23502           regroup_exact
23503               Insert NOPs to force costly dependent insns into separate
23504               groups.  Insert exactly as many NOPs as needed to force an insn
23505               to a new group, according to the estimated processor grouping.
23506
23507           number
23508               Insert NOPs to force costly dependent insns into separate
23509               groups.  Insert number NOPs to force an insn to a new group.
23510
23511       -mcall-sysv
23512           On System V.4 and embedded PowerPC systems compile code using
23513           calling conventions that adhere to the March 1995 draft of the
23514           System V Application Binary Interface, PowerPC processor
23515           supplement.  This is the default unless you configured GCC using
23516           powerpc-*-eabiaix.
23517
23518       -mcall-sysv-eabi
23519       -mcall-eabi
23520           Specify both -mcall-sysv and -meabi options.
23521
23522       -mcall-sysv-noeabi
23523           Specify both -mcall-sysv and -mno-eabi options.
23524
23525       -mcall-aixdesc
23526           On System V.4 and embedded PowerPC systems compile code for the AIX
23527           operating system.
23528
23529       -mcall-linux
23530           On System V.4 and embedded PowerPC systems compile code for the
23531           Linux-based GNU system.
23532
23533       -mcall-freebsd
23534           On System V.4 and embedded PowerPC systems compile code for the
23535           FreeBSD operating system.
23536
23537       -mcall-netbsd
23538           On System V.4 and embedded PowerPC systems compile code for the
23539           NetBSD operating system.
23540
23541       -mcall-openbsd
23542           On System V.4 and embedded PowerPC systems compile code for the
23543           OpenBSD operating system.
23544
23545       -mtraceback=traceback_type
23546           Select the type of traceback table. Valid values for traceback_type
23547           are full, part, and no.
23548
23549       -maix-struct-return
23550           Return all structures in memory (as specified by the AIX ABI).
23551
23552       -msvr4-struct-return
23553           Return structures smaller than 8 bytes in registers (as specified
23554           by the SVR4 ABI).
23555
23556       -mabi=abi-type
23557           Extend the current ABI with a particular extension, or remove such
23558           extension.  Valid values are: altivec, no-altivec, ibmlongdouble,
23559           ieeelongdouble, elfv1, elfv2, and for AIX: vec-extabi, vec-default.
23560
23561       -mabi=ibmlongdouble
23562           Change the current ABI to use IBM extended-precision long double.
23563           This is not likely to work if your system defaults to using IEEE
23564           extended-precision long double.  If you change the long double type
23565           from IEEE extended-precision, the compiler will issue a warning
23566           unless you use the -Wno-psabi option.  Requires -mlong-double-128
23567           to be enabled.
23568
23569       -mabi=ieeelongdouble
23570           Change the current ABI to use IEEE extended-precision long double.
23571           This is not likely to work if your system defaults to using IBM
23572           extended-precision long double.  If you change the long double type
23573           from IBM extended-precision, the compiler will issue a warning
23574           unless you use the -Wno-psabi option.  Requires -mlong-double-128
23575           to be enabled.
23576
23577       -mabi=elfv1
23578           Change the current ABI to use the ELFv1 ABI.  This is the default
23579           ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
23580           ABI requires special system support and is likely to fail in
23581           spectacular ways.
23582
23583       -mabi=elfv2
23584           Change the current ABI to use the ELFv2 ABI.  This is the default
23585           ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
23586           ABI requires special system support and is likely to fail in
23587           spectacular ways.
23588
23589       -mgnu-attribute
23590       -mno-gnu-attribute
23591           Emit .gnu_attribute assembly directives to set tag/value pairs in a
23592           .gnu.attributes section that specify ABI variations in function
23593           parameters or return values.
23594
23595       -mprototype
23596       -mno-prototype
23597           On System V.4 and embedded PowerPC systems assume that all calls to
23598           variable argument functions are properly prototyped.  Otherwise,
23599           the compiler must insert an instruction before every non-prototyped
23600           call to set or clear bit 6 of the condition code register ("CR") to
23601           indicate whether floating-point values are passed in the floating-
23602           point registers in case the function takes variable arguments.
23603           With -mprototype, only calls to prototyped variable argument
23604           functions set or clear the bit.
23605
23606       -msim
23607           On embedded PowerPC systems, assume that the startup module is
23608           called sim-crt0.o and that the standard C libraries are libsim.a
23609           and libc.a.  This is the default for powerpc-*-eabisim
23610           configurations.
23611
23612       -mmvme
23613           On embedded PowerPC systems, assume that the startup module is
23614           called crt0.o and the standard C libraries are libmvme.a and
23615           libc.a.
23616
23617       -mads
23618           On embedded PowerPC systems, assume that the startup module is
23619           called crt0.o and the standard C libraries are libads.a and libc.a.
23620
23621       -myellowknife
23622           On embedded PowerPC systems, assume that the startup module is
23623           called crt0.o and the standard C libraries are libyk.a and libc.a.
23624
23625       -mvxworks
23626           On System V.4 and embedded PowerPC systems, specify that you are
23627           compiling for a VxWorks system.
23628
23629       -memb
23630           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags
23631           header to indicate that eabi extended relocations are used.
23632
23633       -meabi
23634       -mno-eabi
23635           On System V.4 and embedded PowerPC systems do (do not) adhere to
23636           the Embedded Applications Binary Interface (EABI), which is a set
23637           of modifications to the System V.4 specifications.  Selecting
23638           -meabi means that the stack is aligned to an 8-byte boundary, a
23639           function "__eabi" is called from "main" to set up the EABI
23640           environment, and the -msdata option can use both "r2" and "r13" to
23641           point to two separate small data areas.  Selecting -mno-eabi means
23642           that the stack is aligned to a 16-byte boundary, no EABI
23643           initialization function is called from "main", and the -msdata
23644           option only uses "r13" to point to a single small data area.  The
23645           -meabi option is on by default if you configured GCC using one of
23646           the powerpc*-*-eabi* options.
23647
23648       -msdata=eabi
23649           On System V.4 and embedded PowerPC systems, put small initialized
23650           "const" global and static data in the ".sdata2" section, which is
23651           pointed to by register "r2".  Put small initialized non-"const"
23652           global and static data in the ".sdata" section, which is pointed to
23653           by register "r13".  Put small uninitialized global and static data
23654           in the ".sbss" section, which is adjacent to the ".sdata" section.
23655           The -msdata=eabi option is incompatible with the -mrelocatable
23656           option.  The -msdata=eabi option also sets the -memb option.
23657
23658       -msdata=sysv
23659           On System V.4 and embedded PowerPC systems, put small global and
23660           static data in the ".sdata" section, which is pointed to by
23661           register "r13".  Put small uninitialized global and static data in
23662           the ".sbss" section, which is adjacent to the ".sdata" section.
23663           The -msdata=sysv option is incompatible with the -mrelocatable
23664           option.
23665
23666       -msdata=default
23667       -msdata
23668           On System V.4 and embedded PowerPC systems, if -meabi is used,
23669           compile code the same as -msdata=eabi, otherwise compile code the
23670           same as -msdata=sysv.
23671
23672       -msdata=data
23673           On System V.4 and embedded PowerPC systems, put small global data
23674           in the ".sdata" section.  Put small uninitialized global data in
23675           the ".sbss" section.  Do not use register "r13" to address small
23676           data however.  This is the default behavior unless other -msdata
23677           options are used.
23678
23679       -msdata=none
23680       -mno-sdata
23681           On embedded PowerPC systems, put all initialized global and static
23682           data in the ".data" section, and all uninitialized data in the
23683           ".bss" section.
23684
23685       -mreadonly-in-sdata
23686           Put read-only objects in the ".sdata" section as well.  This is the
23687           default.
23688
23689       -mblock-move-inline-limit=num
23690           Inline all block moves (such as calls to "memcpy" or structure
23691           copies) less than or equal to num bytes.  The minimum value for num
23692           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
23693           default value is target-specific.
23694
23695       -mblock-compare-inline-limit=num
23696           Generate non-looping inline code for all block compares (such as
23697           calls to "memcmp" or structure compares) less than or equal to num
23698           bytes. If num is 0, all inline expansion (non-loop and loop) of
23699           block compare is disabled. The default value is target-specific.
23700
23701       -mblock-compare-inline-loop-limit=num
23702           Generate an inline expansion using loop code for all block compares
23703           that are less than or equal to num bytes, but greater than the
23704           limit for non-loop inline block compare expansion. If the block
23705           length is not constant, at most num bytes will be compared before
23706           "memcmp" is called to compare the remainder of the block. The
23707           default value is target-specific.
23708
23709       -mstring-compare-inline-limit=num
23710           Compare at most num string bytes with inline code.  If the
23711           difference or end of string is not found at the end of the inline
23712           compare a call to "strcmp" or "strncmp" will take care of the rest
23713           of the comparison. The default is 64 bytes.
23714
23715       -G num
23716           On embedded PowerPC systems, put global and static items less than
23717           or equal to num bytes into the small data or BSS sections instead
23718           of the normal data or BSS section.  By default, num is 8.  The -G
23719           num switch is also passed to the linker.  All modules should be
23720           compiled with the same -G num value.
23721
23722       -mregnames
23723       -mno-regnames
23724           On System V.4 and embedded PowerPC systems do (do not) emit
23725           register names in the assembly language output using symbolic
23726           forms.
23727
23728       -mlongcall
23729       -mno-longcall
23730           By default assume that all calls are far away so that a longer and
23731           more expensive calling sequence is required.  This is required for
23732           calls farther than 32 megabytes (33,554,432 bytes) from the current
23733           location.  A short call is generated if the compiler knows the call
23734           cannot be that far away.  This setting can be overridden by the
23735           "shortcall" function attribute, or by "#pragma longcall(0)".
23736
23737           Some linkers are capable of detecting out-of-range calls and
23738           generating glue code on the fly.  On these systems, long calls are
23739           unnecessary and generate slower code.  As of this writing, the AIX
23740           linker can do this, as can the GNU linker for PowerPC/64.  It is
23741           planned to add this feature to the GNU linker for 32-bit PowerPC
23742           systems as well.
23743
23744           On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU
23745           linkers, GCC can generate long calls using an inline PLT call
23746           sequence (see -mpltseq).  PowerPC with -mbss-plt and PowerPC64
23747           ELFv1 (big-endian) do not support inline PLT calls.
23748
23749           On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee,
23750           L42", plus a branch island (glue code).  The two target addresses
23751           represent the callee and the branch island.  The Darwin/PPC linker
23752           prefers the first address and generates a "bl callee" if the PPC
23753           "bl" instruction reaches the callee directly; otherwise, the linker
23754           generates "bl L42" to call the branch island.  The branch island is
23755           appended to the body of the calling function; it computes the full
23756           32-bit address of the callee and jumps to it.
23757
23758           On Mach-O (Darwin) systems, this option directs the compiler emit
23759           to the glue for every direct call, and the Darwin linker decides
23760           whether to use or discard it.
23761
23762           In the future, GCC may ignore all longcall specifications when the
23763           linker is known to generate glue.
23764
23765       -mpltseq
23766       -mno-pltseq
23767           Implement (do not implement) -fno-plt and long calls using an
23768           inline PLT call sequence that supports lazy linking and long calls
23769           to functions in dlopen'd shared libraries.  Inline PLT calls are
23770           only supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with
23771           newer GNU linkers, and are enabled by default if the support is
23772           detected when configuring GCC, and, in the case of 32-bit PowerPC,
23773           if GCC is configured with --enable-secureplt.  -mpltseq code and
23774           -mbss-plt 32-bit PowerPC relocatable objects may not be linked
23775           together.
23776
23777       -mtls-markers
23778       -mno-tls-markers
23779           Mark (do not mark) calls to "__tls_get_addr" with a relocation
23780           specifying the function argument.  The relocation allows the linker
23781           to reliably associate function call with argument setup
23782           instructions for TLS optimization, which in turn allows GCC to
23783           better schedule the sequence.
23784
23785       -mrecip
23786       -mno-recip
23787           This option enables use of the reciprocal estimate and reciprocal
23788           square root estimate instructions with additional Newton-Raphson
23789           steps to increase precision instead of doing a divide or square
23790           root and divide for floating-point arguments.  You should use the
23791           -ffast-math option when using -mrecip (or at least
23792           -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math
23793           and -fno-trapping-math).  Note that while the throughput of the
23794           sequence is generally higher than the throughput of the non-
23795           reciprocal instruction, the precision of the sequence can be
23796           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
23797           0.99999994) for reciprocal square roots.
23798
23799       -mrecip=opt
23800           This option controls which reciprocal estimate instructions may be
23801           used.  opt is a comma-separated list of options, which may be
23802           preceded by a "!" to invert the option:
23803
23804           all Enable all estimate instructions.
23805
23806           default
23807               Enable the default instructions, equivalent to -mrecip.
23808
23809           none
23810               Disable all estimate instructions, equivalent to -mno-recip.
23811
23812           div Enable the reciprocal approximation instructions for both
23813               single and double precision.
23814
23815           divf
23816               Enable the single-precision reciprocal approximation
23817               instructions.
23818
23819           divd
23820               Enable the double-precision reciprocal approximation
23821               instructions.
23822
23823           rsqrt
23824               Enable the reciprocal square root approximation instructions
23825               for both single and double precision.
23826
23827           rsqrtf
23828               Enable the single-precision reciprocal square root
23829               approximation instructions.
23830
23831           rsqrtd
23832               Enable the double-precision reciprocal square root
23833               approximation instructions.
23834
23835           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
23836           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
23837           "XVRSQRTEDP" instructions which handle the double-precision
23838           reciprocal square root calculations.
23839
23840       -mrecip-precision
23841       -mno-recip-precision
23842           Assume (do not assume) that the reciprocal estimate instructions
23843           provide higher-precision estimates than is mandated by the PowerPC
23844           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
23845           automatically selects -mrecip-precision.  The double-precision
23846           square root estimate instructions are not generated by default on
23847           low-precision machines, since they do not provide an estimate that
23848           converges after three steps.
23849
23850       -mveclibabi=type
23851           Specifies the ABI type to use for vectorizing intrinsics using an
23852           external library.  The only type supported at present is mass,
23853           which specifies to use IBM's Mathematical Acceleration Subsystem
23854           (MASS) libraries for vectorizing intrinsics using external
23855           libraries.  GCC currently emits calls to "acosd2", "acosf4",
23856           "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4",
23857           "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4",
23858           "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2",
23859           "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4",
23860           "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4",
23861           "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4",
23862           "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2",
23863           "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and
23864           "tanhf4" when generating code for power7.  Both -ftree-vectorize
23865           and -funsafe-math-optimizations must also be enabled.  The MASS
23866           libraries must be specified at link time.
23867
23868       -mfriz
23869       -mno-friz
23870           Generate (do not generate) the "friz" instruction when the
23871           -funsafe-math-optimizations option is used to optimize rounding of
23872           floating-point values to 64-bit integer and back to floating point.
23873           The "friz" instruction does not return the same value if the
23874           floating-point number is too large to fit in an integer.
23875
23876       -mpointers-to-nested-functions
23877       -mno-pointers-to-nested-functions
23878           Generate (do not generate) code to load up the static chain
23879           register ("r11") when calling through a pointer on AIX and 64-bit
23880           Linux systems where a function pointer points to a 3-word
23881           descriptor giving the function address, TOC value to be loaded in
23882           register "r2", and static chain value to be loaded in register
23883           "r11".  The -mpointers-to-nested-functions is on by default.  You
23884           cannot call through pointers to nested functions or pointers to
23885           functions compiled in other languages that use the static chain if
23886           you use -mno-pointers-to-nested-functions.
23887
23888       -msave-toc-indirect
23889       -mno-save-toc-indirect
23890           Generate (do not generate) code to save the TOC value in the
23891           reserved stack location in the function prologue if the function
23892           calls through a pointer on AIX and 64-bit Linux systems.  If the
23893           TOC value is not saved in the prologue, it is saved just before the
23894           call through the pointer.  The -mno-save-toc-indirect option is the
23895           default.
23896
23897       -mcompat-align-parm
23898       -mno-compat-align-parm
23899           Generate (do not generate) code to pass structure parameters with a
23900           maximum alignment of 64 bits, for compatibility with older versions
23901           of GCC.
23902
23903           Older versions of GCC (prior to 4.9.0) incorrectly did not align a
23904           structure parameter on a 128-bit boundary when that structure
23905           contained a member requiring 128-bit alignment.  This is corrected
23906           in more recent versions of GCC.  This option may be used to
23907           generate code that is compatible with functions compiled with older
23908           versions of GCC.
23909
23910           The -mno-compat-align-parm option is the default.
23911
23912       -mstack-protector-guard=guard
23913       -mstack-protector-guard-reg=reg
23914       -mstack-protector-guard-offset=offset
23915       -mstack-protector-guard-symbol=symbol
23916           Generate stack protection code using canary at guard.  Supported
23917           locations are global for global canary or tls for per-thread canary
23918           in the TLS block (the default with GNU libc version 2.4 or later).
23919
23920           With the latter choice the options -mstack-protector-guard-reg=reg
23921           and -mstack-protector-guard-offset=offset furthermore specify which
23922           register to use as base register for reading the canary, and from
23923           what offset from that base register. The default for those is as
23924           specified in the relevant ABI.
23925           -mstack-protector-guard-symbol=symbol overrides the offset with a
23926           symbol reference to a canary in the TLS block.
23927
23928       -mpcrel
23929       -mno-pcrel
23930           Generate (do not generate) pc-relative addressing when the option
23931           -mcpu=future is used.  The -mpcrel option requires that the medium
23932           code model (-mcmodel=medium) and prefixed addressing (-mprefixed)
23933           options are enabled.
23934
23935       -mprefixed
23936       -mno-prefixed
23937           Generate (do not generate) addressing modes using prefixed load and
23938           store instructions when the option -mcpu=future is used.
23939
23940       -mmma
23941       -mno-mma
23942           Generate (do not generate) the MMA instructions when the option
23943           -mcpu=future is used.
23944
23945       -mrop-protect
23946       -mno-rop-protect
23947           Generate (do not generate) ROP protection instructions when the
23948           target processor supports them.  Currently this option disables the
23949           shrink-wrap optimization (-fshrink-wrap).
23950
23951       -mprivileged
23952       -mno-privileged
23953           Generate (do not generate) code that will run in privileged state.
23954
23955       -mblock-ops-unaligned-vsx
23956       -mno-block-ops-unaligned-vsx
23957           Generate (do not generate) unaligned vsx loads and stores for
23958           inline expansion of "memcpy" and "memmove".
23959
23960   RX Options
23961       These command-line options are defined for RX targets:
23962
23963       -m64bit-doubles
23964       -m32bit-doubles
23965           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
23966           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
23967           RX floating-point hardware only works on 32-bit values, which is
23968           why the default is -m32bit-doubles.
23969
23970       -fpu
23971       -nofpu
23972           Enables (-fpu) or disables (-nofpu) the use of RX floating-point
23973           hardware.  The default is enabled for the RX600 series and disabled
23974           for the RX200 series.
23975
23976           Floating-point instructions are only generated for 32-bit floating-
23977           point values, however, so the FPU hardware is not used for doubles
23978           if the -m64bit-doubles option is used.
23979
23980           Note If the -fpu option is enabled then -funsafe-math-optimizations
23981           is also enabled automatically.  This is because the RX FPU
23982           instructions are themselves unsafe.
23983
23984       -mcpu=name
23985           Selects the type of RX CPU to be targeted.  Currently three types
23986           are supported, the generic RX600 and RX200 series hardware and the
23987           specific RX610 CPU.  The default is RX600.
23988
23989           The only difference between RX600 and RX610 is that the RX610 does
23990           not support the "MVTIPL" instruction.
23991
23992           The RX200 series does not have a hardware floating-point unit and
23993           so -nofpu is enabled by default when this type is selected.
23994
23995       -mbig-endian-data
23996       -mlittle-endian-data
23997           Store data (but not code) in the big-endian format.  The default is
23998           -mlittle-endian-data, i.e. to store data in the little-endian
23999           format.
24000
24001       -msmall-data-limit=N
24002           Specifies the maximum size in bytes of global and static variables
24003           which can be placed into the small data area.  Using the small data
24004           area can lead to smaller and faster code, but the size of area is
24005           limited and it is up to the programmer to ensure that the area does
24006           not overflow.  Also when the small data area is used one of the
24007           RX's registers (usually "r13") is reserved for use pointing to this
24008           area, so it is no longer available for use by the compiler.  This
24009           could result in slower and/or larger code if variables are pushed
24010           onto the stack instead of being held in this register.
24011
24012           Note, common variables (variables that have not been initialized)
24013           and constants are not placed into the small data area as they are
24014           assigned to other sections in the output executable.
24015
24016           The default value is zero, which disables this feature.  Note, this
24017           feature is not enabled by default with higher optimization levels
24018           (-O2 etc) because of the potentially detrimental effects of
24019           reserving a register.  It is up to the programmer to experiment and
24020           discover whether this feature is of benefit to their program.  See
24021           the description of the -mpid option for a description of how the
24022           actual register to hold the small data area pointer is chosen.
24023
24024       -msim
24025       -mno-sim
24026           Use the simulator runtime.  The default is to use the libgloss
24027           board-specific runtime.
24028
24029       -mas100-syntax
24030       -mno-as100-syntax
24031           When generating assembler output use a syntax that is compatible
24032           with Renesas's AS100 assembler.  This syntax can also be handled by
24033           the GAS assembler, but it has some restrictions so it is not
24034           generated by default.
24035
24036       -mmax-constant-size=N
24037           Specifies the maximum size, in bytes, of a constant that can be
24038           used as an operand in a RX instruction.  Although the RX
24039           instruction set does allow constants of up to 4 bytes in length to
24040           be used in instructions, a longer value equates to a longer
24041           instruction.  Thus in some circumstances it can be beneficial to
24042           restrict the size of constants that are used in instructions.
24043           Constants that are too big are instead placed into a constant pool
24044           and referenced via register indirection.
24045
24046           The value N can be between 0 and 4.  A value of 0 (the default) or
24047           4 means that constants of any size are allowed.
24048
24049       -mrelax
24050           Enable linker relaxation.  Linker relaxation is a process whereby
24051           the linker attempts to reduce the size of a program by finding
24052           shorter versions of various instructions.  Disabled by default.
24053
24054       -mint-register=N
24055           Specify the number of registers to reserve for fast interrupt
24056           handler functions.  The value N can be between 0 and 4.  A value of
24057           1 means that register "r13" is reserved for the exclusive use of
24058           fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A
24059           value of 3 reserves "r13", "r12" and "r11", and a value of 4
24060           reserves "r13" through "r10".  A value of 0, the default, does not
24061           reserve any registers.
24062
24063       -msave-acc-in-interrupts
24064           Specifies that interrupt handler functions should preserve the
24065           accumulator register.  This is only necessary if normal code might
24066           use the accumulator register, for example because it performs
24067           64-bit multiplications.  The default is to ignore the accumulator
24068           as this makes the interrupt handlers faster.
24069
24070       -mpid
24071       -mno-pid
24072           Enables the generation of position independent data.  When enabled
24073           any access to constant data is done via an offset from a base
24074           address held in a register.  This allows the location of constant
24075           data to be determined at run time without requiring the executable
24076           to be relocated, which is a benefit to embedded applications with
24077           tight memory constraints.  Data that can be modified is not
24078           affected by this option.
24079
24080           Note, using this feature reserves a register, usually "r13", for
24081           the constant data base address.  This can result in slower and/or
24082           larger code, especially in complicated functions.
24083
24084           The actual register chosen to hold the constant data base address
24085           depends upon whether the -msmall-data-limit and/or the
24086           -mint-register command-line options are enabled.  Starting with
24087           register "r13" and proceeding downwards, registers are allocated
24088           first to satisfy the requirements of -mint-register, then -mpid and
24089           finally -msmall-data-limit.  Thus it is possible for the small data
24090           area register to be "r8" if both -mint-register=4 and -mpid are
24091           specified on the command line.
24092
24093           By default this feature is not enabled.  The default can be
24094           restored via the -mno-pid command-line option.
24095
24096       -mno-warn-multiple-fast-interrupts
24097       -mwarn-multiple-fast-interrupts
24098           Prevents GCC from issuing a warning message if it finds more than
24099           one fast interrupt handler when it is compiling a file.  The
24100           default is to issue a warning for each extra fast interrupt handler
24101           found, as the RX only supports one such interrupt.
24102
24103       -mallow-string-insns
24104       -mno-allow-string-insns
24105           Enables or disables the use of the string manipulation instructions
24106           "SMOVF", "SCMPU", "SMOVB", "SMOVU", "SUNTIL" "SWHILE" and also the
24107           "RMPA" instruction.  These instructions may prefetch data, which is
24108           not safe to do if accessing an I/O register.  (See section 12.2.7
24109           of the RX62N Group User's Manual for more information).
24110
24111           The default is to allow these instructions, but it is not possible
24112           for GCC to reliably detect all circumstances where a string
24113           instruction might be used to access an I/O register, so their use
24114           cannot be disabled automatically.  Instead it is reliant upon the
24115           programmer to use the -mno-allow-string-insns option if their
24116           program accesses I/O space.
24117
24118           When the instructions are enabled GCC defines the C preprocessor
24119           symbol "__RX_ALLOW_STRING_INSNS__", otherwise it defines the symbol
24120           "__RX_DISALLOW_STRING_INSNS__".
24121
24122       -mjsr
24123       -mno-jsr
24124           Use only (or not only) "JSR" instructions to access functions.
24125           This option can be used when code size exceeds the range of "BSR"
24126           instructions.  Note that -mno-jsr does not mean to not use "JSR"
24127           but instead means that any type of branch may be used.
24128
24129       Note: The generic GCC command-line option -ffixed-reg has special
24130       significance to the RX port when used with the "interrupt" function
24131       attribute.  This attribute indicates a function intended to process
24132       fast interrupts.  GCC ensures that it only uses the registers "r10",
24133       "r11", "r12" and/or "r13" and only provided that the normal use of the
24134       corresponding registers have been restricted via the -ffixed-reg or
24135       -mint-register command-line options.
24136
24137   S/390 and zSeries Options
24138       These are the -m options defined for the S/390 and zSeries
24139       architecture.
24140
24141       -mhard-float
24142       -msoft-float
24143           Use (do not use) the hardware floating-point instructions and
24144           registers for floating-point operations.  When -msoft-float is
24145           specified, functions in libgcc.a are used to perform floating-point
24146           operations.  When -mhard-float is specified, the compiler generates
24147           IEEE floating-point instructions.  This is the default.
24148
24149       -mhard-dfp
24150       -mno-hard-dfp
24151           Use (do not use) the hardware decimal-floating-point instructions
24152           for decimal-floating-point operations.  When -mno-hard-dfp is
24153           specified, functions in libgcc.a are used to perform decimal-
24154           floating-point operations.  When -mhard-dfp is specified, the
24155           compiler generates decimal-floating-point hardware instructions.
24156           This is the default for -march=z9-ec or higher.
24157
24158       -mlong-double-64
24159       -mlong-double-128
24160           These switches control the size of "long double" type. A size of 64
24161           bits makes the "long double" type equivalent to the "double" type.
24162           This is the default.
24163
24164       -mbackchain
24165       -mno-backchain
24166           Store (do not store) the address of the caller's frame as backchain
24167           pointer into the callee's stack frame.  A backchain may be needed
24168           to allow debugging using tools that do not understand DWARF call
24169           frame information.  When -mno-packed-stack is in effect, the
24170           backchain pointer is stored at the bottom of the stack frame; when
24171           -mpacked-stack is in effect, the backchain is placed into the
24172           topmost word of the 96/160 byte register save area.
24173
24174           In general, code compiled with -mbackchain is call-compatible with
24175           code compiled with -mno-backchain; however, use of the backchain
24176           for debugging purposes usually requires that the whole binary is
24177           built with -mbackchain.  Note that the combination of -mbackchain,
24178           -mpacked-stack and -mhard-float is not supported.  In order to
24179           build a linux kernel use -msoft-float.
24180
24181           The default is to not maintain the backchain.
24182
24183       -mpacked-stack
24184       -mno-packed-stack
24185           Use (do not use) the packed stack layout.  When -mno-packed-stack
24186           is specified, the compiler uses the all fields of the 96/160 byte
24187           register save area only for their default purpose; unused fields
24188           still take up stack space.  When -mpacked-stack is specified,
24189           register save slots are densely packed at the top of the register
24190           save area; unused space is reused for other purposes, allowing for
24191           more efficient use of the available stack space.  However, when
24192           -mbackchain is also in effect, the topmost word of the save area is
24193           always used to store the backchain, and the return address register
24194           is always saved two words below the backchain.
24195
24196           As long as the stack frame backchain is not used, code generated
24197           with -mpacked-stack is call-compatible with code generated with
24198           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
24199           S/390 or zSeries generated code that uses the stack frame backchain
24200           at run time, not just for debugging purposes.  Such code is not
24201           call-compatible with code compiled with -mpacked-stack.  Also, note
24202           that the combination of -mbackchain, -mpacked-stack and
24203           -mhard-float is not supported.  In order to build a linux kernel
24204           use -msoft-float.
24205
24206           The default is to not use the packed stack layout.
24207
24208       -msmall-exec
24209       -mno-small-exec
24210           Generate (or do not generate) code using the "bras" instruction to
24211           do subroutine calls.  This only works reliably if the total
24212           executable size does not exceed 64k.  The default is to use the
24213           "basr" instruction instead, which does not have this limitation.
24214
24215       -m64
24216       -m31
24217           When -m31 is specified, generate code compliant to the GNU/Linux
24218           for S/390 ABI.  When -m64 is specified, generate code compliant to
24219           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
24220           generate 64-bit instructions.  For the s390 targets, the default is
24221           -m31, while the s390x targets default to -m64.
24222
24223       -mzarch
24224       -mesa
24225           When -mzarch is specified, generate code using the instructions
24226           available on z/Architecture.  When -mesa is specified, generate
24227           code using the instructions available on ESA/390.  Note that -mesa
24228           is not possible with -m64.  When generating code compliant to the
24229           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
24230           code compliant to the GNU/Linux for zSeries ABI, the default is
24231           -mzarch.
24232
24233       -mhtm
24234       -mno-htm
24235           The -mhtm option enables a set of builtins making use of
24236           instructions available with the transactional execution facility
24237           introduced with the IBM zEnterprise EC12 machine generation S/390
24238           System z Built-in Functions.  -mhtm is enabled by default when
24239           using -march=zEC12.
24240
24241       -mvx
24242       -mno-vx
24243           When -mvx is specified, generate code using the instructions
24244           available with the vector extension facility introduced with the
24245           IBM z13 machine generation.  This option changes the ABI for some
24246           vector type values with regard to alignment and calling
24247           conventions.  In case vector type values are being used in an ABI-
24248           relevant context a GAS .gnu_attribute command will be added to mark
24249           the resulting binary with the ABI used.  -mvx is enabled by default
24250           when using -march=z13.
24251
24252       -mzvector
24253       -mno-zvector
24254           The -mzvector option enables vector language extensions and
24255           builtins using instructions available with the vector extension
24256           facility introduced with the IBM z13 machine generation.  This
24257           option adds support for vector to be used as a keyword to define
24258           vector type variables and arguments.  vector is only available when
24259           GNU extensions are enabled.  It will not be expanded when
24260           requesting strict standard compliance e.g. with -std=c99.  In
24261           addition to the GCC low-level builtins -mzvector enables a set of
24262           builtins added for compatibility with AltiVec-style implementations
24263           like Power and Cell.  In order to make use of these builtins the
24264           header file vecintrin.h needs to be included.  -mzvector is
24265           disabled by default.
24266
24267       -mmvcle
24268       -mno-mvcle
24269           Generate (or do not generate) code using the "mvcle" instruction to
24270           perform block moves.  When -mno-mvcle is specified, use a "mvc"
24271           loop instead.  This is the default unless optimizing for size.
24272
24273       -mdebug
24274       -mno-debug
24275           Print (or do not print) additional debug information when
24276           compiling.  The default is to not print debug information.
24277
24278       -march=cpu-type
24279           Generate code that runs on cpu-type, which is the name of a system
24280           representing a certain processor type.  Possible values for cpu-
24281           type are z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8,
24282           z196/arch9, zEC12, z13/arch11, z14/arch12, z15/arch13, and native.
24283
24284           The default is -march=z900.
24285
24286           Specifying native as cpu type can be used to select the best
24287           architecture option for the host processor.  -march=native has no
24288           effect if GCC does not recognize the processor.
24289
24290       -mtune=cpu-type
24291           Tune to cpu-type everything applicable about the generated code,
24292           except for the ABI and the set of available instructions.  The list
24293           of cpu-type values is the same as for -march.  The default is the
24294           value used for -march.
24295
24296       -mtpf-trace
24297       -mno-tpf-trace
24298           Generate code that adds (does not add) in TPF OS specific branches
24299           to trace routines in the operating system.  This option is off by
24300           default, even when compiling for the TPF OS.
24301
24302       -mtpf-trace-skip
24303       -mno-tpf-trace-skip
24304           Generate code that changes (does not change) the default branch
24305           targets enabled by -mtpf-trace to point to specialized trace
24306           routines providing the ability of selectively skipping function
24307           trace entries for the TPF OS.  This option is off by default, even
24308           when compiling for the TPF OS and specifying -mtpf-trace.
24309
24310       -mfused-madd
24311       -mno-fused-madd
24312           Generate code that uses (does not use) the floating-point multiply
24313           and accumulate instructions.  These instructions are generated by
24314           default if hardware floating point is used.
24315
24316       -mwarn-framesize=framesize
24317           Emit a warning if the current function exceeds the given frame
24318           size.  Because this is a compile-time check it doesn't need to be a
24319           real problem when the program runs.  It is intended to identify
24320           functions that most probably cause a stack overflow.  It is useful
24321           to be used in an environment with limited stack size e.g. the linux
24322           kernel.
24323
24324       -mwarn-dynamicstack
24325           Emit a warning if the function calls "alloca" or uses dynamically-
24326           sized arrays.  This is generally a bad idea with a limited stack
24327           size.
24328
24329       -mstack-guard=stack-guard
24330       -mstack-size=stack-size
24331           If these options are provided the S/390 back end emits additional
24332           instructions in the function prologue that trigger a trap if the
24333           stack size is stack-guard bytes above the stack-size (remember that
24334           the stack on S/390 grows downward).  If the stack-guard option is
24335           omitted the smallest power of 2 larger than the frame size of the
24336           compiled function is chosen.  These options are intended to be used
24337           to help debugging stack overflow problems.  The additionally
24338           emitted code causes only little overhead and hence can also be used
24339           in production-like systems without greater performance degradation.
24340           The given values have to be exact powers of 2 and stack-size has to
24341           be greater than stack-guard without exceeding 64k.  In order to be
24342           efficient the extra code makes the assumption that the stack starts
24343           at an address aligned to the value given by stack-size.  The stack-
24344           guard option can only be used in conjunction with stack-size.
24345
24346       -mhotpatch=pre-halfwords,post-halfwords
24347           If the hotpatch option is enabled, a "hot-patching" function
24348           prologue is generated for all functions in the compilation unit.
24349           The funtion label is prepended with the given number of two-byte
24350           NOP instructions (pre-halfwords, maximum 1000000).  After the
24351           label, 2 * post-halfwords bytes are appended, using the largest NOP
24352           like instructions the architecture allows (maximum 1000000).
24353
24354           If both arguments are zero, hotpatching is disabled.
24355
24356           This option can be overridden for individual functions with the
24357           "hotpatch" attribute.
24358
24359   Score Options
24360       These options are defined for Score implementations:
24361
24362       -meb
24363           Compile code for big-endian mode.  This is the default.
24364
24365       -mel
24366           Compile code for little-endian mode.
24367
24368       -mnhwloop
24369           Disable generation of "bcnz" instructions.
24370
24371       -muls
24372           Enable generation of unaligned load and store instructions.
24373
24374       -mmac
24375           Enable the use of multiply-accumulate instructions. Disabled by
24376           default.
24377
24378       -mscore5
24379           Specify the SCORE5 as the target architecture.
24380
24381       -mscore5u
24382           Specify the SCORE5U of the target architecture.
24383
24384       -mscore7
24385           Specify the SCORE7 as the target architecture. This is the default.
24386
24387       -mscore7d
24388           Specify the SCORE7D as the target architecture.
24389
24390   SH Options
24391       These -m options are defined for the SH implementations:
24392
24393       -m1 Generate code for the SH1.
24394
24395       -m2 Generate code for the SH2.
24396
24397       -m2e
24398           Generate code for the SH2e.
24399
24400       -m2a-nofpu
24401           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
24402           way that the floating-point unit is not used.
24403
24404       -m2a-single-only
24405           Generate code for the SH2a-FPU, in such a way that no double-
24406           precision floating-point operations are used.
24407
24408       -m2a-single
24409           Generate code for the SH2a-FPU assuming the floating-point unit is
24410           in single-precision mode by default.
24411
24412       -m2a
24413           Generate code for the SH2a-FPU assuming the floating-point unit is
24414           in double-precision mode by default.
24415
24416       -m3 Generate code for the SH3.
24417
24418       -m3e
24419           Generate code for the SH3e.
24420
24421       -m4-nofpu
24422           Generate code for the SH4 without a floating-point unit.
24423
24424       -m4-single-only
24425           Generate code for the SH4 with a floating-point unit that only
24426           supports single-precision arithmetic.
24427
24428       -m4-single
24429           Generate code for the SH4 assuming the floating-point unit is in
24430           single-precision mode by default.
24431
24432       -m4 Generate code for the SH4.
24433
24434       -m4-100
24435           Generate code for SH4-100.
24436
24437       -m4-100-nofpu
24438           Generate code for SH4-100 in such a way that the floating-point
24439           unit is not used.
24440
24441       -m4-100-single
24442           Generate code for SH4-100 assuming the floating-point unit is in
24443           single-precision mode by default.
24444
24445       -m4-100-single-only
24446           Generate code for SH4-100 in such a way that no double-precision
24447           floating-point operations are used.
24448
24449       -m4-200
24450           Generate code for SH4-200.
24451
24452       -m4-200-nofpu
24453           Generate code for SH4-200 without in such a way that the floating-
24454           point unit is not used.
24455
24456       -m4-200-single
24457           Generate code for SH4-200 assuming the floating-point unit is in
24458           single-precision mode by default.
24459
24460       -m4-200-single-only
24461           Generate code for SH4-200 in such a way that no double-precision
24462           floating-point operations are used.
24463
24464       -m4-300
24465           Generate code for SH4-300.
24466
24467       -m4-300-nofpu
24468           Generate code for SH4-300 without in such a way that the floating-
24469           point unit is not used.
24470
24471       -m4-300-single
24472           Generate code for SH4-300 in such a way that no double-precision
24473           floating-point operations are used.
24474
24475       -m4-300-single-only
24476           Generate code for SH4-300 in such a way that no double-precision
24477           floating-point operations are used.
24478
24479       -m4-340
24480           Generate code for SH4-340 (no MMU, no FPU).
24481
24482       -m4-500
24483           Generate code for SH4-500 (no FPU).  Passes -isa=sh4-nofpu to the
24484           assembler.
24485
24486       -m4a-nofpu
24487           Generate code for the SH4al-dsp, or for a SH4a in such a way that
24488           the floating-point unit is not used.
24489
24490       -m4a-single-only
24491           Generate code for the SH4a, in such a way that no double-precision
24492           floating-point operations are used.
24493
24494       -m4a-single
24495           Generate code for the SH4a assuming the floating-point unit is in
24496           single-precision mode by default.
24497
24498       -m4a
24499           Generate code for the SH4a.
24500
24501       -m4al
24502           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
24503           assembler.  GCC doesn't generate any DSP instructions at the
24504           moment.
24505
24506       -mb Compile code for the processor in big-endian mode.
24507
24508       -ml Compile code for the processor in little-endian mode.
24509
24510       -mdalign
24511           Align doubles at 64-bit boundaries.  Note that this changes the
24512           calling conventions, and thus some functions from the standard C
24513           library do not work unless you recompile it first with -mdalign.
24514
24515       -mrelax
24516           Shorten some address references at link time, when possible; uses
24517           the linker option -relax.
24518
24519       -mbigtable
24520           Use 32-bit offsets in "switch" tables.  The default is to use
24521           16-bit offsets.
24522
24523       -mbitops
24524           Enable the use of bit manipulation instructions on SH2A.
24525
24526       -mfmovd
24527           Enable the use of the instruction "fmovd".  Check -mdalign for
24528           alignment constraints.
24529
24530       -mrenesas
24531           Comply with the calling conventions defined by Renesas.
24532
24533       -mno-renesas
24534           Comply with the calling conventions defined for GCC before the
24535           Renesas conventions were available.  This option is the default for
24536           all targets of the SH toolchain.
24537
24538       -mnomacsave
24539           Mark the "MAC" register as call-clobbered, even if -mrenesas is
24540           given.
24541
24542       -mieee
24543       -mno-ieee
24544           Control the IEEE compliance of floating-point comparisons, which
24545           affects the handling of cases where the result of a comparison is
24546           unordered.  By default -mieee is implicitly enabled.  If
24547           -ffinite-math-only is enabled -mno-ieee is implicitly set, which
24548           results in faster floating-point greater-equal and less-equal
24549           comparisons.  The implicit settings can be overridden by specifying
24550           either -mieee or -mno-ieee.
24551
24552       -minline-ic_invalidate
24553           Inline code to invalidate instruction cache entries after setting
24554           up nested function trampolines.  This option has no effect if
24555           -musermode is in effect and the selected code generation option
24556           (e.g. -m4) does not allow the use of the "icbi" instruction.  If
24557           the selected code generation option does not allow the use of the
24558           "icbi" instruction, and -musermode is not in effect, the inlined
24559           code manipulates the instruction cache address array directly with
24560           an associative write.  This not only requires privileged mode at
24561           run time, but it also fails if the cache line had been mapped via
24562           the TLB and has become unmapped.
24563
24564       -misize
24565           Dump instruction size and location in the assembly code.
24566
24567       -mpadstruct
24568           This option is deprecated.  It pads structures to multiple of 4
24569           bytes, which is incompatible with the SH ABI.
24570
24571       -matomic-model=model
24572           Sets the model of atomic operations and additional parameters as a
24573           comma separated list.  For details on the atomic built-in functions
24574           see __atomic Builtins.  The following models and parameters are
24575           supported:
24576
24577           none
24578               Disable compiler generated atomic sequences and emit library
24579               calls for atomic operations.  This is the default if the target
24580               is not "sh*-*-linux*".
24581
24582           soft-gusa
24583               Generate GNU/Linux compatible gUSA software atomic sequences
24584               for the atomic built-in functions.  The generated atomic
24585               sequences require additional support from the
24586               interrupt/exception handling code of the system and are only
24587               suitable for SH3* and SH4* single-core systems.  This option is
24588               enabled by default when the target is "sh*-*-linux*" and SH3*
24589               or SH4*.  When the target is SH4A, this option also partially
24590               utilizes the hardware atomic instructions "movli.l" and
24591               "movco.l" to create more efficient code, unless strict is
24592               specified.
24593
24594           soft-tcb
24595               Generate software atomic sequences that use a variable in the
24596               thread control block.  This is a variation of the gUSA
24597               sequences which can also be used on SH1* and SH2* targets.  The
24598               generated atomic sequences require additional support from the
24599               interrupt/exception handling code of the system and are only
24600               suitable for single-core systems.  When using this model, the
24601               gbr-offset= parameter has to be specified as well.
24602
24603           soft-imask
24604               Generate software atomic sequences that temporarily disable
24605               interrupts by setting "SR.IMASK = 1111".  This model works only
24606               when the program runs in privileged mode and is only suitable
24607               for single-core systems.  Additional support from the
24608               interrupt/exception handling code of the system is not
24609               required.  This model is enabled by default when the target is
24610               "sh*-*-linux*" and SH1* or SH2*.
24611
24612           hard-llcs
24613               Generate hardware atomic sequences using the "movli.l" and
24614               "movco.l" instructions only.  This is only available on SH4A
24615               and is suitable for multi-core systems.  Since the hardware
24616               instructions support only 32 bit atomic variables access to 8
24617               or 16 bit variables is emulated with 32 bit accesses.  Code
24618               compiled with this option is also compatible with other
24619               software atomic model interrupt/exception handling systems if
24620               executed on an SH4A system.  Additional support from the
24621               interrupt/exception handling code of the system is not required
24622               for this model.
24623
24624           gbr-offset=
24625               This parameter specifies the offset in bytes of the variable in
24626               the thread control block structure that should be used by the
24627               generated atomic sequences when the soft-tcb model has been
24628               selected.  For other models this parameter is ignored.  The
24629               specified value must be an integer multiple of four and in the
24630               range 0-1020.
24631
24632           strict
24633               This parameter prevents mixed usage of multiple atomic models,
24634               even if they are compatible, and makes the compiler generate
24635               atomic sequences of the specified model only.
24636
24637       -mtas
24638           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice
24639           that depending on the particular hardware and software
24640           configuration this can degrade overall performance due to the
24641           operand cache line flushes that are implied by the "tas.b"
24642           instruction.  On multi-core SH4A processors the "tas.b" instruction
24643           must be used with caution since it can result in data corruption
24644           for certain cache configurations.
24645
24646       -mprefergot
24647           When generating position-independent code, emit function calls
24648           using the Global Offset Table instead of the Procedure Linkage
24649           Table.
24650
24651       -musermode
24652       -mno-usermode
24653           Don't allow (allow) the compiler generating privileged mode code.
24654           Specifying -musermode also implies -mno-inline-ic_invalidate if the
24655           inlined code would not work in user mode.  -musermode is the
24656           default when the target is "sh*-*-linux*".  If the target is SH1*
24657           or SH2* -musermode has no effect, since there is no user mode.
24658
24659       -multcost=number
24660           Set the cost to assume for a multiply insn.
24661
24662       -mdiv=strategy
24663           Set the division strategy to be used for integer division
24664           operations.  strategy can be one of:
24665
24666           call-div1
24667               Calls a library function that uses the single-step division
24668               instruction "div1" to perform the operation.  Division by zero
24669               calculates an unspecified result and does not trap.  This is
24670               the default except for SH4, SH2A and SHcompact.
24671
24672           call-fp
24673               Calls a library function that performs the operation in double
24674               precision floating point.  Division by zero causes a floating-
24675               point exception.  This is the default for SHcompact with FPU.
24676               Specifying this for targets that do not have a double precision
24677               FPU defaults to "call-div1".
24678
24679           call-table
24680               Calls a library function that uses a lookup table for small
24681               divisors and the "div1" instruction with case distinction for
24682               larger divisors.  Division by zero calculates an unspecified
24683               result and does not trap.  This is the default for SH4.
24684               Specifying this for targets that do not have dynamic shift
24685               instructions defaults to "call-div1".
24686
24687           When a division strategy has not been specified the default
24688           strategy is selected based on the current target.  For SH2A the
24689           default strategy is to use the "divs" and "divu" instructions
24690           instead of library function calls.
24691
24692       -maccumulate-outgoing-args
24693           Reserve space once for outgoing arguments in the function prologue
24694           rather than around each call.  Generally beneficial for performance
24695           and size.  Also needed for unwinding to avoid changing the stack
24696           frame around conditional code.
24697
24698       -mdivsi3_libfunc=name
24699           Set the name of the library function used for 32-bit signed
24700           division to name.  This only affects the name used in the call
24701           division strategies, and the compiler still expects the same sets
24702           of input/output/clobbered registers as if this option were not
24703           present.
24704
24705       -mfixed-range=register-range
24706           Generate code treating the given register range as fixed registers.
24707           A fixed register is one that the register allocator cannot use.
24708           This is useful when compiling kernel code.  A register range is
24709           specified as two registers separated by a dash.  Multiple register
24710           ranges can be specified separated by a comma.
24711
24712       -mbranch-cost=num
24713           Assume num to be the cost for a branch instruction.  Higher numbers
24714           make the compiler try to generate more branch-free code if
24715           possible.  If not specified the value is selected depending on the
24716           processor type that is being compiled for.
24717
24718       -mzdcbranch
24719       -mno-zdcbranch
24720           Assume (do not assume) that zero displacement conditional branch
24721           instructions "bt" and "bf" are fast.  If -mzdcbranch is specified,
24722           the compiler prefers zero displacement branch code sequences.  This
24723           is enabled by default when generating code for SH4 and SH4A.  It
24724           can be explicitly disabled by specifying -mno-zdcbranch.
24725
24726       -mcbranch-force-delay-slot
24727           Force the usage of delay slots for conditional branches, which
24728           stuffs the delay slot with a "nop" if a suitable instruction cannot
24729           be found.  By default this option is disabled.  It can be enabled
24730           to work around hardware bugs as found in the original SH7055.
24731
24732       -mfused-madd
24733       -mno-fused-madd
24734           Generate code that uses (does not use) the floating-point multiply
24735           and accumulate instructions.  These instructions are generated by
24736           default if hardware floating point is used.  The machine-dependent
24737           -mfused-madd option is now mapped to the machine-independent
24738           -ffp-contract=fast option, and -mno-fused-madd is mapped to
24739           -ffp-contract=off.
24740
24741       -mfsca
24742       -mno-fsca
24743           Allow or disallow the compiler to emit the "fsca" instruction for
24744           sine and cosine approximations.  The option -mfsca must be used in
24745           combination with -funsafe-math-optimizations.  It is enabled by
24746           default when generating code for SH4A.  Using -mno-fsca disables
24747           sine and cosine approximations even if -funsafe-math-optimizations
24748           is in effect.
24749
24750       -mfsrra
24751       -mno-fsrra
24752           Allow or disallow the compiler to emit the "fsrra" instruction for
24753           reciprocal square root approximations.  The option -mfsrra must be
24754           used in combination with -funsafe-math-optimizations and
24755           -ffinite-math-only.  It is enabled by default when generating code
24756           for SH4A.  Using -mno-fsrra disables reciprocal square root
24757           approximations even if -funsafe-math-optimizations and
24758           -ffinite-math-only are in effect.
24759
24760       -mpretend-cmove
24761           Prefer zero-displacement conditional branches for conditional move
24762           instruction patterns.  This can result in faster code on the SH4
24763           processor.
24764
24765       -mfdpic
24766           Generate code using the FDPIC ABI.
24767
24768   Solaris 2 Options
24769       These -m options are supported on Solaris 2:
24770
24771       -mclear-hwcap
24772           -mclear-hwcap tells the compiler to remove the hardware
24773           capabilities generated by the Solaris assembler.  This is only
24774           necessary when object files use ISA extensions not supported by the
24775           current machine, but check at runtime whether or not to use them.
24776
24777       -mimpure-text
24778           -mimpure-text, used in addition to -shared, tells the compiler to
24779           not pass -z text to the linker when linking a shared object.  Using
24780           this option, you can link position-dependent code into a shared
24781           object.
24782
24783           -mimpure-text suppresses the "relocations remain against
24784           allocatable but non-writable sections" linker error message.
24785           However, the necessary relocations trigger copy-on-write, and the
24786           shared object is not actually shared across processes.  Instead of
24787           using -mimpure-text, you should compile all source code with -fpic
24788           or -fPIC.
24789
24790       These switches are supported in addition to the above on Solaris 2:
24791
24792       -pthreads
24793           This is a synonym for -pthread.
24794
24795   SPARC Options
24796       These -m options are supported on the SPARC:
24797
24798       -mno-app-regs
24799       -mapp-regs
24800           Specify -mapp-regs to generate output using the global registers 2
24801           through 4, which the SPARC SVR4 ABI reserves for applications.
24802           Like the global register 1, each global register 2 through 4 is
24803           then treated as an allocable register that is clobbered by function
24804           calls.  This is the default.
24805
24806           To be fully SVR4 ABI-compliant at the cost of some performance
24807           loss, specify -mno-app-regs.  You should compile libraries and
24808           system software with this option.
24809
24810       -mflat
24811       -mno-flat
24812           With -mflat, the compiler does not generate save/restore
24813           instructions and uses a "flat" or single register window model.
24814           This model is compatible with the regular register window model.
24815           The local registers and the input registers (0--5) are still
24816           treated as "call-saved" registers and are saved on the stack as
24817           needed.
24818
24819           With -mno-flat (the default), the compiler generates save/restore
24820           instructions (except for leaf functions).  This is the normal
24821           operating mode.
24822
24823       -mfpu
24824       -mhard-float
24825           Generate output containing floating-point instructions.  This is
24826           the default.
24827
24828       -mno-fpu
24829       -msoft-float
24830           Generate output containing library calls for floating point.
24831           Warning: the requisite libraries are not available for all SPARC
24832           targets.  Normally the facilities of the machine's usual C compiler
24833           are used, but this cannot be done directly in cross-compilation.
24834           You must make your own arrangements to provide suitable library
24835           functions for cross-compilation.  The embedded targets sparc-*-aout
24836           and sparclite-*-* do provide software floating-point support.
24837
24838           -msoft-float changes the calling convention in the output file;
24839           therefore, it is only useful if you compile all of a program with
24840           this option.  In particular, you need to compile libgcc.a, the
24841           library that comes with GCC, with -msoft-float in order for this to
24842           work.
24843
24844       -mhard-quad-float
24845           Generate output containing quad-word (long double) floating-point
24846           instructions.
24847
24848       -msoft-quad-float
24849           Generate output containing library calls for quad-word (long
24850           double) floating-point instructions.  The functions called are
24851           those specified in the SPARC ABI.  This is the default.
24852
24853           As of this writing, there are no SPARC implementations that have
24854           hardware support for the quad-word floating-point instructions.
24855           They all invoke a trap handler for one of these instructions, and
24856           then the trap handler emulates the effect of the instruction.
24857           Because of the trap handler overhead, this is much slower than
24858           calling the ABI library routines.  Thus the -msoft-quad-float
24859           option is the default.
24860
24861       -mno-unaligned-doubles
24862       -munaligned-doubles
24863           Assume that doubles have 8-byte alignment.  This is the default.
24864
24865           With -munaligned-doubles, GCC assumes that doubles have 8-byte
24866           alignment only if they are contained in another type, or if they
24867           have an absolute address.  Otherwise, it assumes they have 4-byte
24868           alignment.  Specifying this option avoids some rare compatibility
24869           problems with code generated by other compilers.  It is not the
24870           default because it results in a performance loss, especially for
24871           floating-point code.
24872
24873       -muser-mode
24874       -mno-user-mode
24875           Do not generate code that can only run in supervisor mode.  This is
24876           relevant only for the "casa" instruction emitted for the LEON3
24877           processor.  This is the default.
24878
24879       -mfaster-structs
24880       -mno-faster-structs
24881           With -mfaster-structs, the compiler assumes that structures should
24882           have 8-byte alignment.  This enables the use of pairs of "ldd" and
24883           "std" instructions for copies in structure assignment, in place of
24884           twice as many "ld" and "st" pairs.  However, the use of this
24885           changed alignment directly violates the SPARC ABI.  Thus, it's
24886           intended only for use on targets where the developer acknowledges
24887           that their resulting code is not directly in line with the rules of
24888           the ABI.
24889
24890       -mstd-struct-return
24891       -mno-std-struct-return
24892           With -mstd-struct-return, the compiler generates checking code in
24893           functions returning structures or unions to detect size mismatches
24894           between the two sides of function calls, as per the 32-bit ABI.
24895
24896           The default is -mno-std-struct-return.  This option has no effect
24897           in 64-bit mode.
24898
24899       -mlra
24900       -mno-lra
24901           Enable Local Register Allocation.  This is the default for SPARC
24902           since GCC 7 so -mno-lra needs to be passed to get old Reload.
24903
24904       -mcpu=cpu_type
24905           Set the instruction set, register set, and instruction scheduling
24906           parameters for machine type cpu_type.  Supported values for
24907           cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3,
24908           leon3v7, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9,
24909           ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
24910           niagara7 and m8.
24911
24912           Native Solaris and GNU/Linux toolchains also support the value
24913           native, which selects the best architecture option for the host
24914           processor.  -mcpu=native has no effect if GCC does not recognize
24915           the processor.
24916
24917           Default instruction scheduling parameters are used for values that
24918           select an architecture and not an implementation.  These are v7,
24919           v8, sparclite, sparclet, v9.
24920
24921           Here is a list of each supported architecture and their supported
24922           implementations.
24923
24924           v7  cypress, leon3v7
24925
24926           v8  supersparc, hypersparc, leon, leon3
24927
24928           sparclite
24929               f930, f934, sparclite86x
24930
24931           sparclet
24932               tsc701
24933
24934           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
24935               niagara7, m8
24936
24937           By default (unless configured otherwise), GCC generates code for
24938           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
24939           compiler additionally optimizes it for the Cypress CY7C602 chip, as
24940           used in the SPARCStation/SPARCServer 3xx series.  This is also
24941           appropriate for the older SPARCStation 1, 2, IPX etc.
24942
24943           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
24944           architecture.  The only difference from V7 code is that the
24945           compiler emits the integer multiply and integer divide instructions
24946           which exist in SPARC-V8 but not in SPARC-V7.  With
24947           -mcpu=supersparc, the compiler additionally optimizes it for the
24948           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
24949           series.
24950
24951           With -mcpu=sparclite, GCC generates code for the SPARClite variant
24952           of the SPARC architecture.  This adds the integer multiply, integer
24953           divide step and scan ("ffs") instructions which exist in SPARClite
24954           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
24955           optimizes it for the Fujitsu MB86930 chip, which is the original
24956           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
24957           optimizes it for the Fujitsu MB86934 chip, which is the more recent
24958           SPARClite with FPU.
24959
24960           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
24961           the SPARC architecture.  This adds the integer multiply,
24962           multiply/accumulate, integer divide step and scan ("ffs")
24963           instructions which exist in SPARClet but not in SPARC-V7.  With
24964           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
24965           SPARClet chip.
24966
24967           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
24968           architecture.  This adds 64-bit integer and floating-point move
24969           instructions, 3 additional floating-point condition code registers
24970           and conditional move instructions.  With -mcpu=ultrasparc, the
24971           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
24972           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
24973           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
24974           -mcpu=niagara, the compiler additionally optimizes it for Sun
24975           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
24976           additionally optimizes it for Sun UltraSPARC T2 chips. With
24977           -mcpu=niagara3, the compiler additionally optimizes it for Sun
24978           UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler
24979           additionally optimizes it for Sun UltraSPARC T4 chips.  With
24980           -mcpu=niagara7, the compiler additionally optimizes it for Oracle
24981           SPARC M7 chips.  With -mcpu=m8, the compiler additionally optimizes
24982           it for Oracle M8 chips.
24983
24984       -mtune=cpu_type
24985           Set the instruction scheduling parameters for machine type
24986           cpu_type, but do not set the instruction set or register set that
24987           the option -mcpu=cpu_type does.
24988
24989           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
24990           but the only useful values are those that select a particular CPU
24991           implementation.  Those are cypress, supersparc, hypersparc, leon,
24992           leon3, leon3v7, f930, f934, sparclite86x, tsc701, ultrasparc,
24993           ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7 and
24994           m8.  With native Solaris and GNU/Linux toolchains, native can also
24995           be used.
24996
24997       -mv8plus
24998       -mno-v8plus
24999           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
25000           difference from the V8 ABI is that the global and out registers are
25001           considered 64 bits wide.  This is enabled by default on Solaris in
25002           32-bit mode for all SPARC-V9 processors.
25003
25004       -mvis
25005       -mno-vis
25006           With -mvis, GCC generates code that takes advantage of the
25007           UltraSPARC Visual Instruction Set extensions.  The default is
25008           -mno-vis.
25009
25010       -mvis2
25011       -mno-vis2
25012           With -mvis2, GCC generates code that takes advantage of version 2.0
25013           of the UltraSPARC Visual Instruction Set extensions.  The default
25014           is -mvis2 when targeting a cpu that supports such instructions,
25015           such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.
25016
25017       -mvis3
25018       -mno-vis3
25019           With -mvis3, GCC generates code that takes advantage of version 3.0
25020           of the UltraSPARC Visual Instruction Set extensions.  The default
25021           is -mvis3 when targeting a cpu that supports such instructions,
25022           such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and
25023           -mvis.
25024
25025       -mvis4
25026       -mno-vis4
25027           With -mvis4, GCC generates code that takes advantage of version 4.0
25028           of the UltraSPARC Visual Instruction Set extensions.  The default
25029           is -mvis4 when targeting a cpu that supports such instructions,
25030           such as niagara-7 and later.  Setting -mvis4 also sets -mvis3,
25031           -mvis2 and -mvis.
25032
25033       -mvis4b
25034       -mno-vis4b
25035           With -mvis4b, GCC generates code that takes advantage of version
25036           4.0 of the UltraSPARC Visual Instruction Set extensions, plus the
25037           additional VIS instructions introduced in the Oracle SPARC
25038           Architecture 2017.  The default is -mvis4b when targeting a cpu
25039           that supports such instructions, such as m8 and later.  Setting
25040           -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis.
25041
25042       -mcbcond
25043       -mno-cbcond
25044           With -mcbcond, GCC generates code that takes advantage of the
25045           UltraSPARC Compare-and-Branch-on-Condition instructions.  The
25046           default is -mcbcond when targeting a CPU that supports such
25047           instructions, such as Niagara-4 and later.
25048
25049       -mfmaf
25050       -mno-fmaf
25051           With -mfmaf, GCC generates code that takes advantage of the
25052           UltraSPARC Fused Multiply-Add Floating-point instructions.  The
25053           default is -mfmaf when targeting a CPU that supports such
25054           instructions, such as Niagara-3 and later.
25055
25056       -mfsmuld
25057       -mno-fsmuld
25058           With -mfsmuld, GCC generates code that takes advantage of the
25059           Floating-point Multiply Single to Double (FsMULd) instruction.  The
25060           default is -mfsmuld when targeting a CPU supporting the
25061           architecture versions V8 or V9 with FPU except -mcpu=leon.
25062
25063       -mpopc
25064       -mno-popc
25065           With -mpopc, GCC generates code that takes advantage of the
25066           UltraSPARC Population Count instruction.  The default is -mpopc
25067           when targeting a CPU that supports such an instruction, such as
25068           Niagara-2 and later.
25069
25070       -msubxc
25071       -mno-subxc
25072           With -msubxc, GCC generates code that takes advantage of the
25073           UltraSPARC Subtract-Extended-with-Carry instruction.  The default
25074           is -msubxc when targeting a CPU that supports such an instruction,
25075           such as Niagara-7 and later.
25076
25077       -mfix-at697f
25078           Enable the documented workaround for the single erratum of the
25079           Atmel AT697F processor (which corresponds to erratum #13 of the
25080           AT697E processor).
25081
25082       -mfix-ut699
25083           Enable the documented workarounds for the floating-point errata and
25084           the data cache nullify errata of the UT699 processor.
25085
25086       -mfix-ut700
25087           Enable the documented workaround for the back-to-back store errata
25088           of the UT699E/UT700 processor.
25089
25090       -mfix-gr712rc
25091           Enable the documented workaround for the back-to-back store errata
25092           of the GR712RC processor.
25093
25094       These -m options are supported in addition to the above on SPARC-V9
25095       processors in 64-bit environments:
25096
25097       -m32
25098       -m64
25099           Generate code for a 32-bit or 64-bit environment.  The 32-bit
25100           environment sets int, long and pointer to 32 bits.  The 64-bit
25101           environment sets int to 32 bits and long and pointer to 64 bits.
25102
25103       -mcmodel=which
25104           Set the code model to one of
25105
25106           medlow
25107               The Medium/Low code model: 64-bit addresses, programs must be
25108               linked in the low 32 bits of memory.  Programs can be
25109               statically or dynamically linked.
25110
25111           medmid
25112               The Medium/Middle code model: 64-bit addresses, programs must
25113               be linked in the low 44 bits of memory, the text and data
25114               segments must be less than 2GB in size and the data segment
25115               must be located within 2GB of the text segment.
25116
25117           medany
25118               The Medium/Anywhere code model: 64-bit addresses, programs may
25119               be linked anywhere in memory, the text and data segments must
25120               be less than 2GB in size and the data segment must be located
25121               within 2GB of the text segment.
25122
25123           embmedany
25124               The Medium/Anywhere code model for embedded systems: 64-bit
25125               addresses, the text and data segments must be less than 2GB in
25126               size, both starting anywhere in memory (determined at link
25127               time).  The global register %g4 points to the base of the data
25128               segment.  Programs are statically linked and PIC is not
25129               supported.
25130
25131       -mmemory-model=mem-model
25132           Set the memory model in force on the processor to one of
25133
25134           default
25135               The default memory model for the processor and operating
25136               system.
25137
25138           rmo Relaxed Memory Order
25139
25140           pso Partial Store Order
25141
25142           tso Total Store Order
25143
25144           sc  Sequential Consistency
25145
25146           These memory models are formally defined in Appendix D of the
25147           SPARC-V9 architecture manual, as set in the processor's "PSTATE.MM"
25148           field.
25149
25150       -mstack-bias
25151       -mno-stack-bias
25152           With -mstack-bias, GCC assumes that the stack pointer, and frame
25153           pointer if present, are offset by -2047 which must be added back
25154           when making stack frame references.  This is the default in 64-bit
25155           mode.  Otherwise, assume no such offset is present.
25156
25157   Options for System V
25158       These additional options are available on System V Release 4 for
25159       compatibility with other compilers on those systems:
25160
25161       -G  Create a shared object.  It is recommended that -symbolic or
25162           -shared be used instead.
25163
25164       -Qy Identify the versions of each tool used by the compiler, in a
25165           ".ident" assembler directive in the output.
25166
25167       -Qn Refrain from adding ".ident" directives to the output file (this is
25168           the default).
25169
25170       -YP,dirs
25171           Search the directories dirs, and no others, for libraries specified
25172           with -l.
25173
25174       -Ym,dir
25175           Look in the directory dir to find the M4 preprocessor.  The
25176           assembler uses this option.
25177
25178   TILE-Gx Options
25179       These -m options are supported on the TILE-Gx:
25180
25181       -mcmodel=small
25182           Generate code for the small model.  The distance for direct calls
25183           is limited to 500M in either direction.  PC-relative addresses are
25184           32 bits.  Absolute addresses support the full address range.
25185
25186       -mcmodel=large
25187           Generate code for the large model.  There is no limitation on call
25188           distance, pc-relative addresses, or absolute addresses.
25189
25190       -mcpu=name
25191           Selects the type of CPU to be targeted.  Currently the only
25192           supported type is tilegx.
25193
25194       -m32
25195       -m64
25196           Generate code for a 32-bit or 64-bit environment.  The 32-bit
25197           environment sets int, long, and pointer to 32 bits.  The 64-bit
25198           environment sets int to 32 bits and long and pointer to 64 bits.
25199
25200       -mbig-endian
25201       -mlittle-endian
25202           Generate code in big/little endian mode, respectively.
25203
25204   TILEPro Options
25205       These -m options are supported on the TILEPro:
25206
25207       -mcpu=name
25208           Selects the type of CPU to be targeted.  Currently the only
25209           supported type is tilepro.
25210
25211       -m32
25212           Generate code for a 32-bit environment, which sets int, long, and
25213           pointer to 32 bits.  This is the only supported behavior so the
25214           flag is essentially ignored.
25215
25216   V850 Options
25217       These -m options are defined for V850 implementations:
25218
25219       -mlong-calls
25220       -mno-long-calls
25221           Treat all calls as being far away (near).  If calls are assumed to
25222           be far away, the compiler always loads the function's address into
25223           a register, and calls indirect through the pointer.
25224
25225       -mno-ep
25226       -mep
25227           Do not optimize (do optimize) basic blocks that use the same index
25228           pointer 4 or more times to copy pointer into the "ep" register, and
25229           use the shorter "sld" and "sst" instructions.  The -mep option is
25230           on by default if you optimize.
25231
25232       -mno-prolog-function
25233       -mprolog-function
25234           Do not use (do use) external functions to save and restore
25235           registers at the prologue and epilogue of a function.  The external
25236           functions are slower, but use less code space if more than one
25237           function saves the same number of registers.  The -mprolog-function
25238           option is on by default if you optimize.
25239
25240       -mspace
25241           Try to make the code as small as possible.  At present, this just
25242           turns on the -mep and -mprolog-function options.
25243
25244       -mtda=n
25245           Put static or global variables whose size is n bytes or less into
25246           the tiny data area that register "ep" points to.  The tiny data
25247           area can hold up to 256 bytes in total (128 bytes for byte
25248           references).
25249
25250       -msda=n
25251           Put static or global variables whose size is n bytes or less into
25252           the small data area that register "gp" points to.  The small data
25253           area can hold up to 64 kilobytes.
25254
25255       -mzda=n
25256           Put static or global variables whose size is n bytes or less into
25257           the first 32 kilobytes of memory.
25258
25259       -mv850
25260           Specify that the target processor is the V850.
25261
25262       -mv850e3v5
25263           Specify that the target processor is the V850E3V5.  The
25264           preprocessor constant "__v850e3v5__" is defined if this option is
25265           used.
25266
25267       -mv850e2v4
25268           Specify that the target processor is the V850E3V5.  This is an
25269           alias for the -mv850e3v5 option.
25270
25271       -mv850e2v3
25272           Specify that the target processor is the V850E2V3.  The
25273           preprocessor constant "__v850e2v3__" is defined if this option is
25274           used.
25275
25276       -mv850e2
25277           Specify that the target processor is the V850E2.  The preprocessor
25278           constant "__v850e2__" is defined if this option is used.
25279
25280       -mv850e1
25281           Specify that the target processor is the V850E1.  The preprocessor
25282           constants "__v850e1__" and "__v850e__" are defined if this option
25283           is used.
25284
25285       -mv850es
25286           Specify that the target processor is the V850ES.  This is an alias
25287           for the -mv850e1 option.
25288
25289       -mv850e
25290           Specify that the target processor is the V850E.  The preprocessor
25291           constant "__v850e__" is defined if this option is used.
25292
25293           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor
25294           -mv850e2v3 nor -mv850e3v5 are defined then a default target
25295           processor is chosen and the relevant __v850*__ preprocessor
25296           constant is defined.
25297
25298           The preprocessor constants "__v850" and "__v851__" are always
25299           defined, regardless of which processor variant is the target.
25300
25301       -mdisable-callt
25302       -mno-disable-callt
25303           This option suppresses generation of the "CALLT" instruction for
25304           the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
25305           v850 architecture.
25306
25307           This option is enabled by default when the RH850 ABI is in use (see
25308           -mrh850-abi), and disabled by default when the GCC ABI is in use.
25309           If "CALLT" instructions are being generated then the C preprocessor
25310           symbol "__V850_CALLT__" is defined.
25311
25312       -mrelax
25313       -mno-relax
25314           Pass on (or do not pass on) the -mrelax command-line option to the
25315           assembler.
25316
25317       -mlong-jumps
25318       -mno-long-jumps
25319           Disable (or re-enable) the generation of PC-relative jump
25320           instructions.
25321
25322       -msoft-float
25323       -mhard-float
25324           Disable (or re-enable) the generation of hardware floating point
25325           instructions.  This option is only significant when the target
25326           architecture is V850E2V3 or higher.  If hardware floating point
25327           instructions are being generated then the C preprocessor symbol
25328           "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is
25329           defined.
25330
25331       -mloop
25332           Enables the use of the e3v5 LOOP instruction.  The use of this
25333           instruction is not enabled by default when the e3v5 architecture is
25334           selected because its use is still experimental.
25335
25336       -mrh850-abi
25337       -mghs
25338           Enables support for the RH850 version of the V850 ABI.  This is the
25339           default.  With this version of the ABI the following rules apply:
25340
25341           *   Integer sized structures and unions are returned via a memory
25342               pointer rather than a register.
25343
25344           *   Large structures and unions (more than 8 bytes in size) are
25345               passed by value.
25346
25347           *   Functions are aligned to 16-bit boundaries.
25348
25349           *   The -m8byte-align command-line option is supported.
25350
25351           *   The -mdisable-callt command-line option is enabled by default.
25352               The -mno-disable-callt command-line option is not supported.
25353
25354           When this version of the ABI is enabled the C preprocessor symbol
25355           "__V850_RH850_ABI__" is defined.
25356
25357       -mgcc-abi
25358           Enables support for the old GCC version of the V850 ABI.  With this
25359           version of the ABI the following rules apply:
25360
25361           *   Integer sized structures and unions are returned in register
25362               "r10".
25363
25364           *   Large structures and unions (more than 8 bytes in size) are
25365               passed by reference.
25366
25367           *   Functions are aligned to 32-bit boundaries, unless optimizing
25368               for size.
25369
25370           *   The -m8byte-align command-line option is not supported.
25371
25372           *   The -mdisable-callt command-line option is supported but not
25373               enabled by default.
25374
25375           When this version of the ABI is enabled the C preprocessor symbol
25376           "__V850_GCC_ABI__" is defined.
25377
25378       -m8byte-align
25379       -mno-8byte-align
25380           Enables support for "double" and "long long" types to be aligned on
25381           8-byte boundaries.  The default is to restrict the alignment of all
25382           objects to at most 4-bytes.  When -m8byte-align is in effect the C
25383           preprocessor symbol "__V850_8BYTE_ALIGN__" is defined.
25384
25385       -mbig-switch
25386           Generate code suitable for big switch tables.  Use this option only
25387           if the assembler/linker complain about out of range branches within
25388           a switch table.
25389
25390       -mapp-regs
25391           This option causes r2 and r5 to be used in the code generated by
25392           the compiler.  This setting is the default.
25393
25394       -mno-app-regs
25395           This option causes r2 and r5 to be treated as fixed registers.
25396
25397   VAX Options
25398       These -m options are defined for the VAX:
25399
25400       -munix
25401           Do not output certain jump instructions ("aobleq" and so on) that
25402           the Unix assembler for the VAX cannot handle across long ranges.
25403
25404       -mgnu
25405           Do output those jump instructions, on the assumption that the GNU
25406           assembler is being used.
25407
25408       -mg Output code for G-format floating-point numbers instead of
25409           D-format.
25410
25411   Visium Options
25412       -mdebug
25413           A program which performs file I/O and is destined to run on an MCM
25414           target should be linked with this option.  It causes the libraries
25415           libc.a and libdebug.a to be linked.  The program should be run on
25416           the target under the control of the GDB remote debugging stub.
25417
25418       -msim
25419           A program which performs file I/O and is destined to run on the
25420           simulator should be linked with option.  This causes libraries
25421           libc.a and libsim.a to be linked.
25422
25423       -mfpu
25424       -mhard-float
25425           Generate code containing floating-point instructions.  This is the
25426           default.
25427
25428       -mno-fpu
25429       -msoft-float
25430           Generate code containing library calls for floating-point.
25431
25432           -msoft-float changes the calling convention in the output file;
25433           therefore, it is only useful if you compile all of a program with
25434           this option.  In particular, you need to compile libgcc.a, the
25435           library that comes with GCC, with -msoft-float in order for this to
25436           work.
25437
25438       -mcpu=cpu_type
25439           Set the instruction set, register set, and instruction scheduling
25440           parameters for machine type cpu_type.  Supported values for
25441           cpu_type are mcm, gr5 and gr6.
25442
25443           mcm is a synonym of gr5 present for backward compatibility.
25444
25445           By default (unless configured otherwise), GCC generates code for
25446           the GR5 variant of the Visium architecture.
25447
25448           With -mcpu=gr6, GCC generates code for the GR6 variant of the
25449           Visium architecture.  The only difference from GR5 code is that the
25450           compiler will generate block move instructions.
25451
25452       -mtune=cpu_type
25453           Set the instruction scheduling parameters for machine type
25454           cpu_type, but do not set the instruction set or register set that
25455           the option -mcpu=cpu_type would.
25456
25457       -msv-mode
25458           Generate code for the supervisor mode, where there are no
25459           restrictions on the access to general registers.  This is the
25460           default.
25461
25462       -muser-mode
25463           Generate code for the user mode, where the access to some general
25464           registers is forbidden: on the GR5, registers r24 to r31 cannot be
25465           accessed in this mode; on the GR6, only registers r29 to r31 are
25466           affected.
25467
25468   VMS Options
25469       These -m options are defined for the VMS implementations:
25470
25471       -mvms-return-codes
25472           Return VMS condition codes from "main". The default is to return
25473           POSIX-style condition (e.g. error) codes.
25474
25475       -mdebug-main=prefix
25476           Flag the first routine whose name starts with prefix as the main
25477           routine for the debugger.
25478
25479       -mmalloc64
25480           Default to 64-bit memory allocation routines.
25481
25482       -mpointer-size=size
25483           Set the default size of pointers. Possible options for size are 32
25484           or short for 32 bit pointers, 64 or long for 64 bit pointers, and
25485           no for supporting only 32 bit pointers.  The later option disables
25486           "pragma pointer_size".
25487
25488   VxWorks Options
25489       The options in this section are defined for all VxWorks targets.
25490       Options specific to the target hardware are listed with the other
25491       options for that target.
25492
25493       -mrtp
25494           GCC can generate code for both VxWorks kernels and real time
25495           processes (RTPs).  This option switches from the former to the
25496           latter.  It also defines the preprocessor macro "__RTP__".
25497
25498       -non-static
25499           Link an RTP executable against shared libraries rather than static
25500           libraries.  The options -static and -shared can also be used for
25501           RTPs; -static is the default.
25502
25503       -Bstatic
25504       -Bdynamic
25505           These options are passed down to the linker.  They are defined for
25506           compatibility with Diab.
25507
25508       -Xbind-lazy
25509           Enable lazy binding of function calls.  This option is equivalent
25510           to -Wl,-z,now and is defined for compatibility with Diab.
25511
25512       -Xbind-now
25513           Disable lazy binding of function calls.  This option is the default
25514           and is defined for compatibility with Diab.
25515
25516   x86 Options
25517       These -m options are defined for the x86 family of computers.
25518
25519       -march=cpu-type
25520           Generate instructions for the machine type cpu-type.  In contrast
25521           to -mtune=cpu-type, which merely tunes the generated code for the
25522           specified cpu-type, -march=cpu-type allows GCC to generate code
25523           that may not run at all on processors other than the one indicated.
25524           Specifying -march=cpu-type implies -mtune=cpu-type, except where
25525           noted otherwise.
25526
25527           The choices for cpu-type are:
25528
25529           native
25530               This selects the CPU to generate code for at compilation time
25531               by determining the processor type of the compiling machine.
25532               Using -march=native enables all instruction subsets supported
25533               by the local machine (hence the result might not run on
25534               different machines).  Using -mtune=native produces code
25535               optimized for the local machine under the constraints of the
25536               selected instruction set.
25537
25538           x86-64
25539               A generic CPU with 64-bit extensions.
25540
25541           x86-64-v2
25542           x86-64-v3
25543           x86-64-v4
25544               These choices for cpu-type select the corresponding micro-
25545               architecture level from the x86-64 psABI.  On ABIs other than
25546               the x86-64 psABI they select the same CPU features as the
25547               x86-64 psABI documents for the particular micro-architecture
25548               level.
25549
25550               Since these cpu-type values do not have a corresponding -mtune
25551               setting, using -march with these values enables generic tuning.
25552               Specific tuning can be enabled using the -mtune=other-cpu-type
25553               option with an appropriate other-cpu-type value.
25554
25555           i386
25556               Original Intel i386 CPU.
25557
25558           i486
25559               Intel i486 CPU.  (No scheduling is implemented for this chip.)
25560
25561           i586
25562           pentium
25563               Intel Pentium CPU with no MMX support.
25564
25565           lakemont
25566               Intel Lakemont MCU, based on Intel Pentium CPU.
25567
25568           pentium-mmx
25569               Intel Pentium MMX CPU, based on Pentium core with MMX
25570               instruction set support.
25571
25572           pentiumpro
25573               Intel Pentium Pro CPU.
25574
25575           i686
25576               When used with -march, the Pentium Pro instruction set is used,
25577               so the code runs on all i686 family chips.  When used with
25578               -mtune, it has the same meaning as generic.
25579
25580           pentium2
25581               Intel Pentium II CPU, based on Pentium Pro core with MMX
25582               instruction set support.
25583
25584           pentium3
25585           pentium3m
25586               Intel Pentium III CPU, based on Pentium Pro core with MMX and
25587               SSE instruction set support.
25588
25589           pentium-m
25590               Intel Pentium M; low-power version of Intel Pentium III CPU
25591               with MMX, SSE and SSE2 instruction set support.  Used by
25592               Centrino notebooks.
25593
25594           pentium4
25595           pentium4m
25596               Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set
25597               support.
25598
25599           prescott
25600               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and
25601               SSE3 instruction set support.
25602
25603           nocona
25604               Improved version of Intel Pentium 4 CPU with 64-bit extensions,
25605               MMX, SSE, SSE2 and SSE3 instruction set support.
25606
25607           core2
25608               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
25609               and SSSE3 instruction set support.
25610
25611           nehalem
25612               Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
25613               SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support.
25614
25615           westmere
25616               Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
25617               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction
25618               set support.
25619
25620           sandybridge
25621               Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
25622               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL
25623               instruction set support.
25624
25625           ivybridge
25626               Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
25627               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL,
25628               FSGSBASE, RDRND and F16C instruction set support.
25629
25630           haswell
25631               Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25632               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25633               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction
25634               set support.
25635
25636           broadwell
25637               Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25638               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25639               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED ADCX and
25640               PREFETCHW instruction set support.
25641
25642           skylake
25643               Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25644               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25645               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25646               PREFETCHW, CLFLUSHOPT, XSAVEC and XSAVES instruction set
25647               support.
25648
25649           bonnell
25650               Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25651               SSE2, SSE3 and SSSE3 instruction set support.
25652
25653           silvermont
25654               Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25655               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25656               PCLMUL and RDRND instruction set support.
25657
25658           goldmont
25659               Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25660               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25661               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT and FSGSBASE
25662               instruction set support.
25663
25664           goldmont-plus
25665               Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX,
25666               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25667               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25668               PTWRITE, RDPID, SGX and UMIP instruction set support.
25669
25670           tremont
25671               Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25672               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25673               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25674               PTWRITE, RDPID, SGX, UMIP, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
25675               CLDEMOTE and WAITPKG instruction set support.
25676
25677           knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX,
25678               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25679               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25680               PREFETCHW, PREFETCHWT1, AVX512F, AVX512PF, AVX512ER and
25681               AVX512CD instruction set support.
25682
25683           knm Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE,
25684               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25685               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25686               PREFETCHW, PREFETCHWT1, AVX512F, AVX512PF, AVX512ER, AVX512CD,
25687               AVX5124VNNIW, AVX5124FMAPS and AVX512VPOPCNTDQ instruction set
25688               support.
25689
25690           skylake-avx512
25691               Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
25692               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25693               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25694               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,
25695               AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set
25696               support.
25697
25698           cannonlake
25699               Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX,
25700               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25701               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25702               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25703               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA and
25704               UMIP instruction set support.
25705
25706           icelake-client
25707               Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
25708               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25709               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25710               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25711               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25712               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25713               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set
25714               support.
25715
25716           icelake-server
25717               Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
25718               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25719               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25720               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25721               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25722               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25723               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG and
25724               WBNOINVD instruction set support.
25725
25726           cascadelake
25727               Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25728               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25729               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25730               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL,
25731               AVX512BW, AVX512DQ, AVX512CD and AVX512VNNI instruction set
25732               support.
25733
25734           cooperlake
25735               Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25736               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25737               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25738               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL,
25739               AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI and AVX512BF16
25740               instruction set support.
25741
25742           tigerlake
25743               Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25744               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25745               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25746               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25747               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25748               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25749               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG, WBNOINVD,
25750               MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT and KEYLOCKER
25751               instruction set support.
25752
25753           sapphirerapids
25754               Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX,
25755               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25756               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25757               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,
25758               AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI, AVX512BF16,
25759               MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE,
25760               PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-
25761               TILE, AMX-INT8 and AVX-VNNI instruction set support.
25762
25763           alderlake
25764               Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25765               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25766               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25767               PTWRITE, RDPID, SGX, UMIP, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
25768               CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA,
25769               LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL,
25770               WIDEKL and AVX-VNNI instruction set support.
25771
25772           rocketlake
25773               Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25774               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25775               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25776               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25777               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25778               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25779               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set
25780               support.
25781
25782           k6  AMD K6 CPU with MMX instruction set support.
25783
25784           k6-2
25785           k6-3
25786               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
25787               set support.
25788
25789           athlon
25790           athlon-tbird
25791               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
25792               prefetch instructions support.
25793
25794           athlon-4
25795           athlon-xp
25796           athlon-mp
25797               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
25798               full SSE instruction set support.
25799
25800           k8
25801           opteron
25802           athlon64
25803           athlon-fx
25804               Processors based on the AMD K8 core with x86-64 instruction set
25805               support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
25806               processors.  (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
25807               3DNow! and 64-bit instruction set extensions.)
25808
25809           k8-sse3
25810           opteron-sse3
25811           athlon64-sse3
25812               Improved versions of AMD K8 cores with SSE3 instruction set
25813               support.
25814
25815           amdfam10
25816           barcelona
25817               CPUs based on AMD Family 10h cores with x86-64 instruction set
25818               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
25819               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
25820
25821           bdver1
25822               CPUs based on AMD Family 15h cores with x86-64 instruction set
25823               support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCLMUL,
25824               CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
25825               and 64-bit instruction set extensions.)
25826
25827           bdver2
25828               AMD Family 15h core based CPUs with x86-64 instruction set
25829               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
25830               LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
25831               SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
25832
25833           bdver3
25834               AMD Family 15h core based CPUs with x86-64 instruction set
25835               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE,
25836               AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
25837               SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
25838               extensions.)
25839
25840           bdver4
25841               AMD Family 15h core based CPUs with x86-64 instruction set
25842               support.  (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
25843               FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE, MMX,
25844               SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit
25845               instruction set extensions.)
25846
25847           znver1
25848               AMD Family 17h core based CPUs with x86-64 instruction set
25849               support.  (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX,
25850               AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16,
25851               MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM,
25852               XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit instruction set
25853               extensions.)
25854
25855           znver2
25856               AMD Family 17h core based CPUs with x86-64 instruction set
25857               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
25858               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
25859               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
25860               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
25861               WBNOINVD, and 64-bit instruction set extensions.)
25862
25863           znver3
25864               AMD Family 19h core based CPUs with x86-64 instruction set
25865               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
25866               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
25867               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
25868               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
25869               WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set
25870               extensions.)
25871
25872           btver1
25873               CPUs based on AMD Family 14h cores with x86-64 instruction set
25874               support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
25875               CX16, ABM and 64-bit instruction set extensions.)
25876
25877           btver2
25878               CPUs based on AMD Family 16h cores with x86-64 instruction set
25879               support. This includes MOVBE, F16C, BMI, AVX, PCLMUL, AES,
25880               SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
25881               and 64-bit instruction set extensions.
25882
25883           winchip-c6
25884               IDT WinChip C6 CPU, dealt in same way as i486 with additional
25885               MMX instruction set support.
25886
25887           winchip2
25888               IDT WinChip 2 CPU, dealt in same way as i486 with additional
25889               MMX and 3DNow!  instruction set support.
25890
25891           c3  VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
25892               scheduling is implemented for this chip.)
25893
25894           c3-2
25895               VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
25896               support.  (No scheduling is implemented for this chip.)
25897
25898           c7  VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
25899               set support.  (No scheduling is implemented for this chip.)
25900
25901           samuel-2
25902               VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
25903               support.  (No scheduling is implemented for this chip.)
25904
25905           nehemiah
25906               VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
25907               (No scheduling is implemented for this chip.)
25908
25909           esther
25910               VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction
25911               set support.  (No scheduling is implemented for this chip.)
25912
25913           eden-x2
25914               VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3
25915               instruction set support.  (No scheduling is implemented for
25916               this chip.)
25917
25918           eden-x4
25919               VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
25920               SSE4.1, SSE4.2, AVX and AVX2 instruction set support.  (No
25921               scheduling is implemented for this chip.)
25922
25923           nano
25924               Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
25925               SSSE3 instruction set support.  (No scheduling is implemented
25926               for this chip.)
25927
25928           nano-1000
25929               VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
25930               instruction set support.  (No scheduling is implemented for
25931               this chip.)
25932
25933           nano-2000
25934               VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
25935               instruction set support.  (No scheduling is implemented for
25936               this chip.)
25937
25938           nano-3000
25939               VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and
25940               SSE4.1 instruction set support.  (No scheduling is implemented
25941               for this chip.)
25942
25943           nano-x2
25944               VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
25945               and SSE4.1 instruction set support.  (No scheduling is
25946               implemented for this chip.)
25947
25948           nano-x4
25949               VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
25950               and SSE4.1 instruction set support.  (No scheduling is
25951               implemented for this chip.)
25952
25953           geode
25954               AMD Geode embedded processor with MMX and 3DNow! instruction
25955               set support.
25956
25957       -mtune=cpu-type
25958           Tune to cpu-type everything applicable about the generated code,
25959           except for the ABI and the set of available instructions.  While
25960           picking a specific cpu-type schedules things appropriately for that
25961           particular chip, the compiler does not generate any code that
25962           cannot run on the default machine type unless you use a -march=cpu-
25963           type option.  For example, if GCC is configured for
25964           i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned
25965           for Pentium 4 but still runs on i686 machines.
25966
25967           The choices for cpu-type are the same as for -march.  In addition,
25968           -mtune supports 2 extra choices for cpu-type:
25969
25970           generic
25971               Produce code optimized for the most common IA32/AMD64/EM64T
25972               processors.  If you know the CPU on which your code will run,
25973               then you should use the corresponding -mtune or -march option
25974               instead of -mtune=generic.  But, if you do not know exactly
25975               what CPU users of your application will have, then you should
25976               use this option.
25977
25978               As new processors are deployed in the marketplace, the behavior
25979               of this option will change.  Therefore, if you upgrade to a
25980               newer version of GCC, code generation controlled by this option
25981               will change to reflect the processors that are most common at
25982               the time that version of GCC is released.
25983
25984               There is no -march=generic option because -march indicates the
25985               instruction set the compiler can use, and there is no generic
25986               instruction set applicable to all processors.  In contrast,
25987               -mtune indicates the processor (or, in this case, collection of
25988               processors) for which the code is optimized.
25989
25990           intel
25991               Produce code optimized for the most current Intel processors,
25992               which are Haswell and Silvermont for this version of GCC.  If
25993               you know the CPU on which your code will run, then you should
25994               use the corresponding -mtune or -march option instead of
25995               -mtune=intel.  But, if you want your application performs
25996               better on both Haswell and Silvermont, then you should use this
25997               option.
25998
25999               As new Intel processors are deployed in the marketplace, the
26000               behavior of this option will change.  Therefore, if you upgrade
26001               to a newer version of GCC, code generation controlled by this
26002               option will change to reflect the most current Intel processors
26003               at the time that version of GCC is released.
26004
26005               There is no -march=intel option because -march indicates the
26006               instruction set the compiler can use, and there is no common
26007               instruction set applicable to all processors.  In contrast,
26008               -mtune indicates the processor (or, in this case, collection of
26009               processors) for which the code is optimized.
26010
26011       -mcpu=cpu-type
26012           A deprecated synonym for -mtune.
26013
26014       -mfpmath=unit
26015           Generate floating-point arithmetic for selected unit unit.  The
26016           choices for unit are:
26017
26018           387 Use the standard 387 floating-point coprocessor present on the
26019               majority of chips and emulated otherwise.  Code compiled with
26020               this option runs almost everywhere.  The temporary results are
26021               computed in 80-bit precision instead of the precision specified
26022               by the type, resulting in slightly different results compared
26023               to most of other chips.  See -ffloat-store for more detailed
26024               description.
26025
26026               This is the default choice for non-Darwin x86-32 targets.
26027
26028           sse Use scalar floating-point instructions present in the SSE
26029               instruction set.  This instruction set is supported by Pentium
26030               III and newer chips, and in the AMD line by Athlon-4, Athlon XP
26031               and Athlon MP chips.  The earlier version of the SSE
26032               instruction set supports only single-precision arithmetic, thus
26033               the double and extended-precision arithmetic are still done
26034               using 387.  A later version, present only in Pentium 4 and AMD
26035               x86-64 chips, supports double-precision arithmetic too.
26036
26037               For the x86-32 compiler, you must use -march=cpu-type, -msse or
26038               -msse2 switches to enable SSE extensions and make this option
26039               effective.  For the x86-64 compiler, these extensions are
26040               enabled by default.
26041
26042               The resulting code should be considerably faster in the
26043               majority of cases and avoid the numerical instability problems
26044               of 387 code, but may break some existing code that expects
26045               temporaries to be 80 bits.
26046
26047               This is the default choice for the x86-64 compiler, Darwin
26048               x86-32 targets, and the default choice for x86-32 targets with
26049               the SSE2 instruction set when -ffast-math is enabled.
26050
26051           sse,387
26052           sse+387
26053           both
26054               Attempt to utilize both instruction sets at once.  This
26055               effectively doubles the amount of available registers, and on
26056               chips with separate execution units for 387 and SSE the
26057               execution resources too.  Use this option with care, as it is
26058               still experimental, because the GCC register allocator does not
26059               model separate functional units well, resulting in unstable
26060               performance.
26061
26062       -masm=dialect
26063           Output assembly instructions using selected dialect.  Also affects
26064           which dialect is used for basic "asm" and extended "asm". Supported
26065           choices (in dialect order) are att or intel. The default is att.
26066           Darwin does not support intel.
26067
26068       -mieee-fp
26069       -mno-ieee-fp
26070           Control whether or not the compiler uses IEEE floating-point
26071           comparisons.  These correctly handle the case where the result of a
26072           comparison is unordered.
26073
26074       -m80387
26075       -mhard-float
26076           Generate output containing 80387 instructions for floating point.
26077
26078       -mno-80387
26079       -msoft-float
26080           Generate output containing library calls for floating point.
26081
26082           Warning: the requisite libraries are not part of GCC.  Normally the
26083           facilities of the machine's usual C compiler are used, but this
26084           cannot be done directly in cross-compilation.  You must make your
26085           own arrangements to provide suitable library functions for cross-
26086           compilation.
26087
26088           On machines where a function returns floating-point results in the
26089           80387 register stack, some floating-point opcodes may be emitted
26090           even if -msoft-float is used.
26091
26092       -mno-fp-ret-in-387
26093           Do not use the FPU registers for return values of functions.
26094
26095           The usual calling convention has functions return values of types
26096           "float" and "double" in an FPU register, even if there is no FPU.
26097           The idea is that the operating system should emulate an FPU.
26098
26099           The option -mno-fp-ret-in-387 causes such values to be returned in
26100           ordinary CPU registers instead.
26101
26102       -mno-fancy-math-387
26103           Some 387 emulators do not support the "sin", "cos" and "sqrt"
26104           instructions for the 387.  Specify this option to avoid generating
26105           those instructions.  This option is overridden when -march
26106           indicates that the target CPU always has an FPU and so the
26107           instruction does not need emulation.  These instructions are not
26108           generated unless you also use the -funsafe-math-optimizations
26109           switch.
26110
26111       -malign-double
26112       -mno-align-double
26113           Control whether GCC aligns "double", "long double", and "long long"
26114           variables on a two-word boundary or a one-word boundary.  Aligning
26115           "double" variables on a two-word boundary produces code that runs
26116           somewhat faster on a Pentium at the expense of more memory.
26117
26118           On x86-64, -malign-double is enabled by default.
26119
26120           Warning: if you use the -malign-double switch, structures
26121           containing the above types are aligned differently than the
26122           published application binary interface specifications for the
26123           x86-32 and are not binary compatible with structures in code
26124           compiled without that switch.
26125
26126       -m96bit-long-double
26127       -m128bit-long-double
26128           These switches control the size of "long double" type.  The x86-32
26129           application binary interface specifies the size to be 96 bits, so
26130           -m96bit-long-double is the default in 32-bit mode.
26131
26132           Modern architectures (Pentium and newer) prefer "long double" to be
26133           aligned to an 8- or 16-byte boundary.  In arrays or structures
26134           conforming to the ABI, this is not possible.  So specifying
26135           -m128bit-long-double aligns "long double" to a 16-byte boundary by
26136           padding the "long double" with an additional 32-bit zero.
26137
26138           In the x86-64 compiler, -m128bit-long-double is the default choice
26139           as its ABI specifies that "long double" is aligned on 16-byte
26140           boundary.
26141
26142           Notice that neither of these options enable any extra precision
26143           over the x87 standard of 80 bits for a "long double".
26144
26145           Warning: if you override the default value for your target ABI,
26146           this changes the size of structures and arrays containing "long
26147           double" variables, as well as modifying the function calling
26148           convention for functions taking "long double".  Hence they are not
26149           binary-compatible with code compiled without that switch.
26150
26151       -mlong-double-64
26152       -mlong-double-80
26153       -mlong-double-128
26154           These switches control the size of "long double" type. A size of 64
26155           bits makes the "long double" type equivalent to the "double" type.
26156           This is the default for 32-bit Bionic C library.  A size of 128
26157           bits makes the "long double" type equivalent to the "__float128"
26158           type. This is the default for 64-bit Bionic C library.
26159
26160           Warning: if you override the default value for your target ABI,
26161           this changes the size of structures and arrays containing "long
26162           double" variables, as well as modifying the function calling
26163           convention for functions taking "long double".  Hence they are not
26164           binary-compatible with code compiled without that switch.
26165
26166       -malign-data=type
26167           Control how GCC aligns variables.  Supported values for type are
26168           compat uses increased alignment value compatible uses GCC 4.8 and
26169           earlier, abi uses alignment value as specified by the psABI, and
26170           cacheline uses increased alignment value to match the cache line
26171           size.  compat is the default.
26172
26173       -mlarge-data-threshold=threshold
26174           When -mcmodel=medium is specified, data objects larger than
26175           threshold are placed in the large data section.  This value must be
26176           the same across all objects linked into the binary, and defaults to
26177           65535.
26178
26179       -mrtd
26180           Use a different function-calling convention, in which functions
26181           that take a fixed number of arguments return with the "ret num"
26182           instruction, which pops their arguments while returning.  This
26183           saves one instruction in the caller since there is no need to pop
26184           the arguments there.
26185
26186           You can specify that an individual function is called with this
26187           calling sequence with the function attribute "stdcall".  You can
26188           also override the -mrtd option by using the function attribute
26189           "cdecl".
26190
26191           Warning: this calling convention is incompatible with the one
26192           normally used on Unix, so you cannot use it if you need to call
26193           libraries compiled with the Unix compiler.
26194
26195           Also, you must provide function prototypes for all functions that
26196           take variable numbers of arguments (including "printf"); otherwise
26197           incorrect code is generated for calls to those functions.
26198
26199           In addition, seriously incorrect code results if you call a
26200           function with too many arguments.  (Normally, extra arguments are
26201           harmlessly ignored.)
26202
26203       -mregparm=num
26204           Control how many registers are used to pass integer arguments.  By
26205           default, no registers are used to pass arguments, and at most 3
26206           registers can be used.  You can control this behavior for a
26207           specific function by using the function attribute "regparm".
26208
26209           Warning: if you use this switch, and num is nonzero, then you must
26210           build all modules with the same value, including any libraries.
26211           This includes the system libraries and startup modules.
26212
26213       -msseregparm
26214           Use SSE register passing conventions for float and double arguments
26215           and return values.  You can control this behavior for a specific
26216           function by using the function attribute "sseregparm".
26217
26218           Warning: if you use this switch then you must build all modules
26219           with the same value, including any libraries.  This includes the
26220           system libraries and startup modules.
26221
26222       -mvect8-ret-in-mem
26223           Return 8-byte vectors in memory instead of MMX registers.  This is
26224           the default on VxWorks to match the ABI of the Sun Studio compilers
26225           until version 12.  Only use this option if you need to remain
26226           compatible with existing code produced by those previous compiler
26227           versions or older versions of GCC.
26228
26229       -mpc32
26230       -mpc64
26231       -mpc80
26232           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
26233           -mpc32 is specified, the significands of results of floating-point
26234           operations are rounded to 24 bits (single precision); -mpc64 rounds
26235           the significands of results of floating-point operations to 53 bits
26236           (double precision) and -mpc80 rounds the significands of results of
26237           floating-point operations to 64 bits (extended double precision),
26238           which is the default.  When this option is used, floating-point
26239           operations in higher precisions are not available to the programmer
26240           without setting the FPU control word explicitly.
26241
26242           Setting the rounding of floating-point operations to less than the
26243           default 80 bits can speed some programs by 2% or more.  Note that
26244           some mathematical libraries assume that extended-precision (80-bit)
26245           floating-point operations are enabled by default; routines in such
26246           libraries could suffer significant loss of accuracy, typically
26247           through so-called "catastrophic cancellation", when this option is
26248           used to set the precision to less than extended precision.
26249
26250       -mstackrealign
26251           Realign the stack at entry.  On the x86, the -mstackrealign option
26252           generates an alternate prologue and epilogue that realigns the run-
26253           time stack if necessary.  This supports mixing legacy codes that
26254           keep 4-byte stack alignment with modern codes that keep 16-byte
26255           stack alignment for SSE compatibility.  See also the attribute
26256           "force_align_arg_pointer", applicable to individual functions.
26257
26258       -mpreferred-stack-boundary=num
26259           Attempt to keep the stack boundary aligned to a 2 raised to num
26260           byte boundary.  If -mpreferred-stack-boundary is not specified, the
26261           default is 4 (16 bytes or 128 bits).
26262
26263           Warning: When generating code for the x86-64 architecture with SSE
26264           extensions disabled, -mpreferred-stack-boundary=3 can be used to
26265           keep the stack boundary aligned to 8 byte boundary.  Since x86-64
26266           ABI require 16 byte stack alignment, this is ABI incompatible and
26267           intended to be used in controlled environment where stack space is
26268           important limitation.  This option leads to wrong code when
26269           functions compiled with 16 byte stack alignment (such as functions
26270           from a standard library) are called with misaligned stack.  In this
26271           case, SSE instructions may lead to misaligned memory access traps.
26272           In addition, variable arguments are handled incorrectly for 16 byte
26273           aligned objects (including x87 long double and __int128), leading
26274           to wrong results.  You must build all modules with
26275           -mpreferred-stack-boundary=3, including any libraries.  This
26276           includes the system libraries and startup modules.
26277
26278       -mincoming-stack-boundary=num
26279           Assume the incoming stack is aligned to a 2 raised to num byte
26280           boundary.  If -mincoming-stack-boundary is not specified, the one
26281           specified by -mpreferred-stack-boundary is used.
26282
26283           On Pentium and Pentium Pro, "double" and "long double" values
26284           should be aligned to an 8-byte boundary (see -malign-double) or
26285           suffer significant run time performance penalties.  On Pentium III,
26286           the Streaming SIMD Extension (SSE) data type "__m128" may not work
26287           properly if it is not 16-byte aligned.
26288
26289           To ensure proper alignment of this values on the stack, the stack
26290           boundary must be as aligned as that required by any value stored on
26291           the stack.  Further, every function must be generated such that it
26292           keeps the stack aligned.  Thus calling a function compiled with a
26293           higher preferred stack boundary from a function compiled with a
26294           lower preferred stack boundary most likely misaligns the stack.  It
26295           is recommended that libraries that use callbacks always use the
26296           default setting.
26297
26298           This extra alignment does consume extra stack space, and generally
26299           increases code size.  Code that is sensitive to stack space usage,
26300           such as embedded systems and operating system kernels, may want to
26301           reduce the preferred alignment to -mpreferred-stack-boundary=2.
26302
26303       -mmmx
26304       -msse
26305       -msse2
26306       -msse3
26307       -mssse3
26308       -msse4
26309       -msse4a
26310       -msse4.1
26311       -msse4.2
26312       -mavx
26313       -mavx2
26314       -mavx512f
26315       -mavx512pf
26316       -mavx512er
26317       -mavx512cd
26318       -mavx512vl
26319       -mavx512bw
26320       -mavx512dq
26321       -mavx512ifma
26322       -mavx512vbmi
26323       -msha
26324       -maes
26325       -mpclmul
26326       -mclflushopt
26327       -mclwb
26328       -mfsgsbase
26329       -mptwrite
26330       -mrdrnd
26331       -mf16c
26332       -mfma
26333       -mpconfig
26334       -mwbnoinvd
26335       -mfma4
26336       -mprfchw
26337       -mrdpid
26338       -mprefetchwt1
26339       -mrdseed
26340       -msgx
26341       -mxop
26342       -mlwp
26343       -m3dnow
26344       -m3dnowa
26345       -mpopcnt
26346       -mabm
26347       -madx
26348       -mbmi
26349       -mbmi2
26350       -mlzcnt
26351       -mfxsr
26352       -mxsave
26353       -mxsaveopt
26354       -mxsavec
26355       -mxsaves
26356       -mrtm
26357       -mhle
26358       -mtbm
26359       -mmwaitx
26360       -mclzero
26361       -mpku
26362       -mavx512vbmi2
26363       -mavx512bf16
26364       -mgfni
26365       -mvaes
26366       -mwaitpkg
26367       -mvpclmulqdq
26368       -mavx512bitalg
26369       -mmovdiri
26370       -mmovdir64b
26371       -menqcmd
26372       -muintr
26373       -mtsxldtrk
26374       -mavx512vpopcntdq
26375       -mavx512vp2intersect
26376       -mavx5124fmaps
26377       -mavx512vnni
26378       -mavxvnni
26379       -mavx5124vnniw
26380       -mcldemote
26381       -mserialize
26382       -mamx-tile
26383       -mamx-int8
26384       -mamx-bf16
26385       -mhreset
26386       -mkl
26387       -mwidekl
26388           These switches enable the use of instructions in the MMX, SSE,
26389           SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F,
26390           AVX512PF, AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ,
26391           AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB,
26392           FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, WBNOINVD, FMA4,
26393           PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, 3DNow!,
26394           enhanced 3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE,
26395           XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU,
26396           AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG,
26397           MOVDIRI, MOVDIR64B, AVX512BF16, ENQCMD, AVX512VPOPCNTDQ,
26398           AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, UINTR, HRESET,
26399           AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI or CLDEMOTE extended
26400           instruction sets. Each has a corresponding -mno- option to disable
26401           use of these instructions.
26402
26403           These extensions are also available as built-in functions: see x86
26404           Built-in Functions, for details of the functions enabled and
26405           disabled by these switches.
26406
26407           To generate SSE/SSE2 instructions automatically from floating-point
26408           code (as opposed to 387 instructions), see -mfpmath=sse.
26409
26410           GCC depresses SSEx instructions when -mavx is used. Instead, it
26411           generates new AVX instructions or AVX equivalence for all SSEx
26412           instructions when needed.
26413
26414           These options enable GCC to use these extended instructions in
26415           generated code, even without -mfpmath=sse.  Applications that
26416           perform run-time CPU detection must compile separate files for each
26417           supported architecture, using the appropriate flags.  In
26418           particular, the file containing the CPU detection code should be
26419           compiled without these options.
26420
26421       -mdump-tune-features
26422           This option instructs GCC to dump the names of the x86 performance
26423           tuning features and default settings. The names can be used in
26424           -mtune-ctrl=feature-list.
26425
26426       -mtune-ctrl=feature-list
26427           This option is used to do fine grain control of x86 code generation
26428           features.  feature-list is a comma separated list of feature names.
26429           See also -mdump-tune-features. When specified, the feature is
26430           turned on if it is not preceded with ^, otherwise, it is turned
26431           off.  -mtune-ctrl=feature-list is intended to be used by GCC
26432           developers. Using it may lead to code paths not covered by testing
26433           and can potentially result in compiler ICEs or runtime errors.
26434
26435       -mno-default
26436           This option instructs GCC to turn off all tunable features. See
26437           also -mtune-ctrl=feature-list and -mdump-tune-features.
26438
26439       -mcld
26440           This option instructs GCC to emit a "cld" instruction in the
26441           prologue of functions that use string instructions.  String
26442           instructions depend on the DF flag to select between autoincrement
26443           or autodecrement mode.  While the ABI specifies the DF flag to be
26444           cleared on function entry, some operating systems violate this
26445           specification by not clearing the DF flag in their exception
26446           dispatchers.  The exception handler can be invoked with the DF flag
26447           set, which leads to wrong direction mode when string instructions
26448           are used.  This option can be enabled by default on 32-bit x86
26449           targets by configuring GCC with the --enable-cld configure option.
26450           Generation of "cld" instructions can be suppressed with the
26451           -mno-cld compiler option in this case.
26452
26453       -mvzeroupper
26454           This option instructs GCC to emit a "vzeroupper" instruction before
26455           a transfer of control flow out of the function to minimize the AVX
26456           to SSE transition penalty as well as remove unnecessary "zeroupper"
26457           intrinsics.
26458
26459       -mprefer-avx128
26460           This option instructs GCC to use 128-bit AVX instructions instead
26461           of 256-bit AVX instructions in the auto-vectorizer.
26462
26463       -mprefer-vector-width=opt
26464           This option instructs GCC to use opt-bit vector width in
26465           instructions instead of default on the selected platform.
26466
26467           none
26468               No extra limitations applied to GCC other than defined by the
26469               selected platform.
26470
26471           128 Prefer 128-bit vector width for instructions.
26472
26473           256 Prefer 256-bit vector width for instructions.
26474
26475           512 Prefer 512-bit vector width for instructions.
26476
26477       -mcx16
26478           This option enables GCC to generate "CMPXCHG16B" instructions in
26479           64-bit code to implement compare-and-exchange operations on 16-byte
26480           aligned 128-bit objects.  This is useful for atomic updates of data
26481           structures exceeding one machine word in size.  The compiler uses
26482           this instruction to implement __sync Builtins.  However, for
26483           __atomic Builtins operating on 128-bit integers, a library call is
26484           always used.
26485
26486       -msahf
26487           This option enables generation of "SAHF" instructions in 64-bit
26488           code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
26489           the introduction of Pentium 4 G1 step in December 2005, lacked the
26490           "LAHF" and "SAHF" instructions which are supported by AMD64.  These
26491           are load and store instructions, respectively, for certain status
26492           flags.  In 64-bit mode, the "SAHF" instruction is used to optimize
26493           "fmod", "drem", and "remainder" built-in functions; see Other
26494           Builtins for details.
26495
26496       -mmovbe
26497           This option enables use of the "movbe" instruction to implement
26498           "__builtin_bswap32" and "__builtin_bswap64".
26499
26500       -mshstk
26501           The -mshstk option enables shadow stack built-in functions from x86
26502           Control-flow Enforcement Technology (CET).
26503
26504       -mcrc32
26505           This option enables built-in functions "__builtin_ia32_crc32qi",
26506           "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and
26507           "__builtin_ia32_crc32di" to generate the "crc32" machine
26508           instruction.
26509
26510       -mrecip
26511           This option enables use of "RCPSS" and "RSQRTSS" instructions (and
26512           their vectorized variants "RCPPS" and "RSQRTPS") with an additional
26513           Newton-Raphson step to increase precision instead of "DIVSS" and
26514           "SQRTSS" (and their vectorized variants) for single-precision
26515           floating-point arguments.  These instructions are generated only
26516           when -funsafe-math-optimizations is enabled together with
26517           -ffinite-math-only and -fno-trapping-math.  Note that while the
26518           throughput of the sequence is higher than the throughput of the
26519           non-reciprocal instruction, the precision of the sequence can be
26520           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
26521           0.99999994).
26522
26523           Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or
26524           "RSQRTPS") already with -ffast-math (or the above option
26525           combination), and doesn't need -mrecip.
26526
26527           Also note that GCC emits the above sequence with additional Newton-
26528           Raphson step for vectorized single-float division and vectorized
26529           "sqrtf(x)" already with -ffast-math (or the above option
26530           combination), and doesn't need -mrecip.
26531
26532       -mrecip=opt
26533           This option controls which reciprocal estimate instructions may be
26534           used.  opt is a comma-separated list of options, which may be
26535           preceded by a ! to invert the option:
26536
26537           all Enable all estimate instructions.
26538
26539           default
26540               Enable the default instructions, equivalent to -mrecip.
26541
26542           none
26543               Disable all estimate instructions, equivalent to -mno-recip.
26544
26545           div Enable the approximation for scalar division.
26546
26547           vec-div
26548               Enable the approximation for vectorized division.
26549
26550           sqrt
26551               Enable the approximation for scalar square root.
26552
26553           vec-sqrt
26554               Enable the approximation for vectorized square root.
26555
26556           So, for example, -mrecip=all,!sqrt enables all of the reciprocal
26557           approximations, except for square root.
26558
26559       -mveclibabi=type
26560           Specifies the ABI type to use for vectorizing intrinsics using an
26561           external library.  Supported values for type are svml for the Intel
26562           short vector math library and acml for the AMD math core library.
26563           To use this option, both -ftree-vectorize and
26564           -funsafe-math-optimizations have to be enabled, and an SVML or ACML
26565           ABI-compatible library must be specified at link time.
26566
26567           GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102",
26568           "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2",
26569           "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2", "vmldAsin2",
26570           "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4",
26571           "vmlsLn4", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4",
26572           "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4",
26573           "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4"
26574           and "vmlsAcos4" for corresponding function type when
26575           -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos",
26576           "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10",
26577           "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf",
26578           "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the
26579           corresponding function type when -mveclibabi=acml is used.
26580
26581       -mabi=name
26582           Generate code for the specified calling convention.  Permissible
26583           values are sysv for the ABI used on GNU/Linux and other systems,
26584           and ms for the Microsoft ABI.  The default is to use the Microsoft
26585           ABI when targeting Microsoft Windows and the SysV ABI on all other
26586           systems.  You can control this behavior for specific functions by
26587           using the function attributes "ms_abi" and "sysv_abi".
26588
26589       -mforce-indirect-call
26590           Force all calls to functions to be indirect. This is useful when
26591           using Intel Processor Trace where it generates more precise timing
26592           information for function calls.
26593
26594       -mmanual-endbr
26595           Insert ENDBR instruction at function entry only via the "cf_check"
26596           function attribute. This is useful when used with the option
26597           -fcf-protection=branch to control ENDBR insertion at the function
26598           entry.
26599
26600       -mcall-ms2sysv-xlogues
26601           Due to differences in 64-bit ABIs, any Microsoft ABI function that
26602           calls a System V ABI function must consider RSI, RDI and XMM6-15 as
26603           clobbered.  By default, the code for saving and restoring these
26604           registers is emitted inline, resulting in fairly lengthy prologues
26605           and epilogues.  Using -mcall-ms2sysv-xlogues emits prologues and
26606           epilogues that use stubs in the static portion of libgcc to perform
26607           these saves and restores, thus reducing function size at the cost
26608           of a few extra instructions.
26609
26610       -mtls-dialect=type
26611           Generate code to access thread-local storage using the gnu or gnu2
26612           conventions.  gnu is the conservative default; gnu2 is more
26613           efficient, but it may add compile- and run-time requirements that
26614           cannot be satisfied on all systems.
26615
26616       -mpush-args
26617       -mno-push-args
26618           Use PUSH operations to store outgoing parameters.  This method is
26619           shorter and usually equally fast as method using SUB/MOV operations
26620           and is enabled by default.  In some cases disabling it may improve
26621           performance because of improved scheduling and reduced
26622           dependencies.
26623
26624       -maccumulate-outgoing-args
26625           If enabled, the maximum amount of space required for outgoing
26626           arguments is computed in the function prologue.  This is faster on
26627           most modern CPUs because of reduced dependencies, improved
26628           scheduling and reduced stack usage when the preferred stack
26629           boundary is not equal to 2.  The drawback is a notable increase in
26630           code size.  This switch implies -mno-push-args.
26631
26632       -mthreads
26633           Support thread-safe exception handling on MinGW.  Programs that
26634           rely on thread-safe exception handling must compile and link all
26635           code with the -mthreads option.  When compiling, -mthreads defines
26636           -D_MT; when linking, it links in a special thread helper library
26637           -lmingwthrd which cleans up per-thread exception-handling data.
26638
26639       -mms-bitfields
26640       -mno-ms-bitfields
26641           Enable/disable bit-field layout compatible with the native
26642           Microsoft Windows compiler.
26643
26644           If "packed" is used on a structure, or if bit-fields are used, it
26645           may be that the Microsoft ABI lays out the structure differently
26646           than the way GCC normally does.  Particularly when moving packed
26647           data between functions compiled with GCC and the native Microsoft
26648           compiler (either via function call or as data in a file), it may be
26649           necessary to access either format.
26650
26651           This option is enabled by default for Microsoft Windows targets.
26652           This behavior can also be controlled locally by use of variable or
26653           type attributes.  For more information, see x86 Variable Attributes
26654           and x86 Type Attributes.
26655
26656           The Microsoft structure layout algorithm is fairly simple with the
26657           exception of the bit-field packing.  The padding and alignment of
26658           members of structures and whether a bit-field can straddle a
26659           storage-unit boundary are determine by these rules:
26660
26661           1. Structure members are stored sequentially in the order in which
26662           they are
26663               declared: the first member has the lowest memory address and
26664               the last member the highest.
26665
26666           2. Every data object has an alignment requirement.  The alignment
26667           requirement
26668               for all data except structures, unions, and arrays is either
26669               the size of the object or the current packing size (specified
26670               with either the "aligned" attribute or the "pack" pragma),
26671               whichever is less.  For structures, unions, and arrays, the
26672               alignment requirement is the largest alignment requirement of
26673               its members.  Every object is allocated an offset so that:
26674
26675                       offset % alignment_requirement == 0
26676
26677           3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte
26678           allocation
26679               unit if the integral types are the same size and if the next
26680               bit-field fits into the current allocation unit without
26681               crossing the boundary imposed by the common alignment
26682               requirements of the bit-fields.
26683
26684           MSVC interprets zero-length bit-fields in the following ways:
26685
26686           1. If a zero-length bit-field is inserted between two bit-fields
26687           that
26688               are normally coalesced, the bit-fields are not coalesced.
26689
26690               For example:
26691
26692                       struct
26693                        {
26694                          unsigned long bf_1 : 12;
26695                          unsigned long : 0;
26696                          unsigned long bf_2 : 12;
26697                        } t1;
26698
26699               The size of "t1" is 8 bytes with the zero-length bit-field.  If
26700               the zero-length bit-field were removed, "t1"'s size would be 4
26701               bytes.
26702
26703           2. If a zero-length bit-field is inserted after a bit-field, "foo",
26704           and the
26705               alignment of the zero-length bit-field is greater than the
26706               member that follows it, "bar", "bar" is aligned as the type of
26707               the zero-length bit-field.
26708
26709               For example:
26710
26711                       struct
26712                        {
26713                          char foo : 4;
26714                          short : 0;
26715                          char bar;
26716                        } t2;
26717
26718                       struct
26719                        {
26720                          char foo : 4;
26721                          short : 0;
26722                          double bar;
26723                        } t3;
26724
26725               For "t2", "bar" is placed at offset 2, rather than offset 1.
26726               Accordingly, the size of "t2" is 4.  For "t3", the zero-length
26727               bit-field does not affect the alignment of "bar" or, as a
26728               result, the size of the structure.
26729
26730               Taking this into account, it is important to note the
26731               following:
26732
26733               1. If a zero-length bit-field follows a normal bit-field, the
26734               type of the
26735                   zero-length bit-field may affect the alignment of the
26736                   structure as whole. For example, "t2" has a size of 4
26737                   bytes, since the zero-length bit-field follows a normal
26738                   bit-field, and is of type short.
26739
26740               2. Even if a zero-length bit-field is not followed by a normal
26741               bit-field, it may
26742                   still affect the alignment of the structure:
26743
26744                           struct
26745                            {
26746                              char foo : 6;
26747                              long : 0;
26748                            } t4;
26749
26750                   Here, "t4" takes up 4 bytes.
26751
26752           3. Zero-length bit-fields following non-bit-field members are
26753           ignored:
26754                       struct
26755                        {
26756                          char foo;
26757                          long : 0;
26758                          char bar;
26759                        } t5;
26760
26761               Here, "t5" takes up 2 bytes.
26762
26763       -mno-align-stringops
26764           Do not align the destination of inlined string operations.  This
26765           switch reduces code size and improves performance in case the
26766           destination is already aligned, but GCC doesn't know about it.
26767
26768       -minline-all-stringops
26769           By default GCC inlines string operations only when the destination
26770           is known to be aligned to least a 4-byte boundary.  This enables
26771           more inlining and increases code size, but may improve performance
26772           of code that depends on fast "memcpy" and "memset" for short
26773           lengths.  The option enables inline expansion of "strlen" for all
26774           pointer alignments.
26775
26776       -minline-stringops-dynamically
26777           For string operations of unknown size, use run-time checks with
26778           inline code for small blocks and a library call for large blocks.
26779
26780       -mstringop-strategy=alg
26781           Override the internal decision heuristic for the particular
26782           algorithm to use for inlining string operations.  The allowed
26783           values for alg are:
26784
26785           rep_byte
26786           rep_4byte
26787           rep_8byte
26788               Expand using i386 "rep" prefix of the specified size.
26789
26790           byte_loop
26791           loop
26792           unrolled_loop
26793               Expand into an inline loop.
26794
26795           libcall
26796               Always use a library call.
26797
26798       -mmemcpy-strategy=strategy
26799           Override the internal decision heuristic to decide if
26800           "__builtin_memcpy" should be inlined and what inline algorithm to
26801           use when the expected size of the copy operation is known. strategy
26802           is a comma-separated list of alg:max_size:dest_align triplets.  alg
26803           is specified in -mstringop-strategy, max_size specifies the max
26804           byte size with which inline algorithm alg is allowed.  For the last
26805           triplet, the max_size must be "-1". The max_size of the triplets in
26806           the list must be specified in increasing order.  The minimal byte
26807           size for alg is 0 for the first triplet and "max_size + 1" of the
26808           preceding range.
26809
26810       -mmemset-strategy=strategy
26811           The option is similar to -mmemcpy-strategy= except that it is to
26812           control "__builtin_memset" expansion.
26813
26814       -momit-leaf-frame-pointer
26815           Don't keep the frame pointer in a register for leaf functions.
26816           This avoids the instructions to save, set up, and restore frame
26817           pointers and makes an extra register available in leaf functions.
26818           The option -fomit-leaf-frame-pointer removes the frame pointer for
26819           leaf functions, which might make debugging harder.
26820
26821       -mtls-direct-seg-refs
26822       -mno-tls-direct-seg-refs
26823           Controls whether TLS variables may be accessed with offsets from
26824           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
26825           whether the thread base pointer must be added.  Whether or not this
26826           is valid depends on the operating system, and whether it maps the
26827           segment to cover the entire TLS area.
26828
26829           For systems that use the GNU C Library, the default is on.
26830
26831       -msse2avx
26832       -mno-sse2avx
26833           Specify that the assembler should encode SSE instructions with VEX
26834           prefix.  The option -mavx turns this on by default.
26835
26836       -mfentry
26837       -mno-fentry
26838           If profiling is active (-pg), put the profiling counter call before
26839           the prologue.  Note: On x86 architectures the attribute
26840           "ms_hook_prologue" isn't possible at the moment for -mfentry and
26841           -pg.
26842
26843       -mrecord-mcount
26844       -mno-record-mcount
26845           If profiling is active (-pg), generate a __mcount_loc section that
26846           contains pointers to each profiling call. This is useful for
26847           automatically patching and out calls.
26848
26849       -mnop-mcount
26850       -mno-nop-mcount
26851           If profiling is active (-pg), generate the calls to the profiling
26852           functions as NOPs. This is useful when they should be patched in
26853           later dynamically. This is likely only useful together with
26854           -mrecord-mcount.
26855
26856       -minstrument-return=type
26857           Instrument function exit in -pg -mfentry instrumented functions
26858           with call to specified function. This only instruments true returns
26859           ending with ret, but not sibling calls ending with jump. Valid
26860           types are none to not instrument, call to generate a call to
26861           __return__, or nop5 to generate a 5 byte nop.
26862
26863       -mrecord-return
26864       -mno-record-return
26865           Generate a __return_loc section pointing to all return
26866           instrumentation code.
26867
26868       -mfentry-name=name
26869           Set name of __fentry__ symbol called at function entry for -pg
26870           -mfentry functions.
26871
26872       -mfentry-section=name
26873           Set name of section to record -mrecord-mcount calls (default
26874           __mcount_loc).
26875
26876       -mskip-rax-setup
26877       -mno-skip-rax-setup
26878           When generating code for the x86-64 architecture with SSE
26879           extensions disabled, -mskip-rax-setup can be used to skip setting
26880           up RAX register when there are no variable arguments passed in
26881           vector registers.
26882
26883           Warning: Since RAX register is used to avoid unnecessarily saving
26884           vector registers on stack when passing variable arguments, the
26885           impacts of this option are callees may waste some stack space,
26886           misbehave or jump to a random location.  GCC 4.4 or newer don't
26887           have those issues, regardless the RAX register value.
26888
26889       -m8bit-idiv
26890       -mno-8bit-idiv
26891           On some processors, like Intel Atom, 8-bit unsigned integer divide
26892           is much faster than 32-bit/64-bit integer divide.  This option
26893           generates a run-time check.  If both dividend and divisor are
26894           within range of 0 to 255, 8-bit unsigned integer divide is used
26895           instead of 32-bit/64-bit integer divide.
26896
26897       -mavx256-split-unaligned-load
26898       -mavx256-split-unaligned-store
26899           Split 32-byte AVX unaligned load and store.
26900
26901       -mstack-protector-guard=guard
26902       -mstack-protector-guard-reg=reg
26903       -mstack-protector-guard-offset=offset
26904           Generate stack protection code using canary at guard.  Supported
26905           locations are global for global canary or tls for per-thread canary
26906           in the TLS block (the default).  This option has effect only when
26907           -fstack-protector or -fstack-protector-all is specified.
26908
26909           With the latter choice the options -mstack-protector-guard-reg=reg
26910           and -mstack-protector-guard-offset=offset furthermore specify which
26911           segment register (%fs or %gs) to use as base register for reading
26912           the canary, and from what offset from that base register.  The
26913           default for those is as specified in the relevant ABI.
26914
26915       -mgeneral-regs-only
26916           Generate code that uses only the general-purpose registers.  This
26917           prevents the compiler from using floating-point, vector, mask and
26918           bound registers.
26919
26920       -mindirect-branch=choice
26921           Convert indirect call and jump with choice.  The default is keep,
26922           which keeps indirect call and jump unmodified.  thunk converts
26923           indirect call and jump to call and return thunk.  thunk-inline
26924           converts indirect call and jump to inlined call and return thunk.
26925           thunk-extern converts indirect call and jump to external call and
26926           return thunk provided in a separate object file.  You can control
26927           this behavior for a specific function by using the function
26928           attribute "indirect_branch".
26929
26930           Note that -mcmodel=large is incompatible with
26931           -mindirect-branch=thunk and -mindirect-branch=thunk-extern since
26932           the thunk function may not be reachable in the large code model.
26933
26934           Note that -mindirect-branch=thunk-extern is compatible with
26935           -fcf-protection=branch since the external thunk can be made to
26936           enable control-flow check.
26937
26938       -mfunction-return=choice
26939           Convert function return with choice.  The default is keep, which
26940           keeps function return unmodified.  thunk converts function return
26941           to call and return thunk.  thunk-inline converts function return to
26942           inlined call and return thunk.  thunk-extern converts function
26943           return to external call and return thunk provided in a separate
26944           object file.  You can control this behavior for a specific function
26945           by using the function attribute "function_return".
26946
26947           Note that -mindirect-return=thunk-extern is compatible with
26948           -fcf-protection=branch since the external thunk can be made to
26949           enable control-flow check.
26950
26951           Note that -mcmodel=large is incompatible with
26952           -mfunction-return=thunk and -mfunction-return=thunk-extern since
26953           the thunk function may not be reachable in the large code model.
26954
26955       -mindirect-branch-register
26956           Force indirect call and jump via register.
26957
26958       These -m switches are supported in addition to the above on x86-64
26959       processors in 64-bit environments.
26960
26961       -m32
26962       -m64
26963       -mx32
26964       -m16
26965       -miamcu
26966           Generate code for a 16-bit, 32-bit or 64-bit environment.  The -m32
26967           option sets "int", "long", and pointer types to 32 bits, and
26968           generates code that runs on any i386 system.
26969
26970           The -m64 option sets "int" to 32 bits and "long" and pointer types
26971           to 64 bits, and generates code for the x86-64 architecture.  For
26972           Darwin only the -m64 option also turns off the -fno-pic and
26973           -mdynamic-no-pic options.
26974
26975           The -mx32 option sets "int", "long", and pointer types to 32 bits,
26976           and generates code for the x86-64 architecture.
26977
26978           The -m16 option is the same as -m32, except for that it outputs the
26979           ".code16gcc" assembly directive at the beginning of the assembly
26980           output so that the binary can run in 16-bit mode.
26981
26982           The -miamcu option generates code which conforms to Intel MCU
26983           psABI.  It requires the -m32 option to be turned on.
26984
26985       -mno-red-zone
26986           Do not use a so-called "red zone" for x86-64 code.  The red zone is
26987           mandated by the x86-64 ABI; it is a 128-byte area beyond the
26988           location of the stack pointer that is not modified by signal or
26989           interrupt handlers and therefore can be used for temporary data
26990           without adjusting the stack pointer.  The flag -mno-red-zone
26991           disables this red zone.
26992
26993       -mcmodel=small
26994           Generate code for the small code model: the program and its symbols
26995           must be linked in the lower 2 GB of the address space.  Pointers
26996           are 64 bits.  Programs can be statically or dynamically linked.
26997           This is the default code model.
26998
26999       -mcmodel=kernel
27000           Generate code for the kernel code model.  The kernel runs in the
27001           negative 2 GB of the address space.  This model has to be used for
27002           Linux kernel code.
27003
27004       -mcmodel=medium
27005           Generate code for the medium model: the program is linked in the
27006           lower 2 GB of the address space.  Small symbols are also placed
27007           there.  Symbols with sizes larger than -mlarge-data-threshold are
27008           put into large data or BSS sections and can be located above 2GB.
27009           Programs can be statically or dynamically linked.
27010
27011       -mcmodel=large
27012           Generate code for the large model.  This model makes no assumptions
27013           about addresses and sizes of sections.
27014
27015       -maddress-mode=long
27016           Generate code for long address mode.  This is only supported for
27017           64-bit and x32 environments.  It is the default address mode for
27018           64-bit environments.
27019
27020       -maddress-mode=short
27021           Generate code for short address mode.  This is only supported for
27022           32-bit and x32 environments.  It is the default address mode for
27023           32-bit and x32 environments.
27024
27025       -mneeded
27026       -mno-needed
27027           Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to
27028           indicate the micro-architecture ISA level required to execute the
27029           binary.
27030
27031   x86 Windows Options
27032       These additional options are available for Microsoft Windows targets:
27033
27034       -mconsole
27035           This option specifies that a console application is to be
27036           generated, by instructing the linker to set the PE header subsystem
27037           type required for console applications.  This option is available
27038           for Cygwin and MinGW targets and is enabled by default on those
27039           targets.
27040
27041       -mdll
27042           This option is available for Cygwin and MinGW targets.  It
27043           specifies that a DLL---a dynamic link library---is to be generated,
27044           enabling the selection of the required runtime startup object and
27045           entry point.
27046
27047       -mnop-fun-dllimport
27048           This option is available for Cygwin and MinGW targets.  It
27049           specifies that the "dllimport" attribute should be ignored.
27050
27051       -mthread
27052           This option is available for MinGW targets. It specifies that
27053           MinGW-specific thread support is to be used.
27054
27055       -municode
27056           This option is available for MinGW-w64 targets.  It causes the
27057           "UNICODE" preprocessor macro to be predefined, and chooses Unicode-
27058           capable runtime startup code.
27059
27060       -mwin32
27061           This option is available for Cygwin and MinGW targets.  It
27062           specifies that the typical Microsoft Windows predefined macros are
27063           to be set in the pre-processor, but does not influence the choice
27064           of runtime library/startup code.
27065
27066       -mwindows
27067           This option is available for Cygwin and MinGW targets.  It
27068           specifies that a GUI application is to be generated by instructing
27069           the linker to set the PE header subsystem type appropriately.
27070
27071       -fno-set-stack-executable
27072           This option is available for MinGW targets. It specifies that the
27073           executable flag for the stack used by nested functions isn't set.
27074           This is necessary for binaries running in kernel mode of Microsoft
27075           Windows, as there the User32 API, which is used to set executable
27076           privileges, isn't available.
27077
27078       -fwritable-relocated-rdata
27079           This option is available for MinGW and Cygwin targets.  It
27080           specifies that relocated-data in read-only section is put into the
27081           ".data" section.  This is a necessary for older runtimes not
27082           supporting modification of ".rdata" sections for pseudo-relocation.
27083
27084       -mpe-aligned-commons
27085           This option is available for Cygwin and MinGW targets.  It
27086           specifies that the GNU extension to the PE file format that permits
27087           the correct alignment of COMMON variables should be used when
27088           generating code.  It is enabled by default if GCC detects that the
27089           target assembler found during configuration supports the feature.
27090
27091       See also under x86 Options for standard options.
27092
27093   Xstormy16 Options
27094       These options are defined for Xstormy16:
27095
27096       -msim
27097           Choose startup files and linker script suitable for the simulator.
27098
27099   Xtensa Options
27100       These options are supported for Xtensa targets:
27101
27102       -mconst16
27103       -mno-const16
27104           Enable or disable use of "CONST16" instructions for loading
27105           constant values.  The "CONST16" instruction is currently not a
27106           standard option from Tensilica.  When enabled, "CONST16"
27107           instructions are always used in place of the standard "L32R"
27108           instructions.  The use of "CONST16" is enabled by default only if
27109           the "L32R" instruction is not available.
27110
27111       -mfused-madd
27112       -mno-fused-madd
27113           Enable or disable use of fused multiply/add and multiply/subtract
27114           instructions in the floating-point option.  This has no effect if
27115           the floating-point option is not also enabled.  Disabling fused
27116           multiply/add and multiply/subtract instructions forces the compiler
27117           to use separate instructions for the multiply and add/subtract
27118           operations.  This may be desirable in some cases where strict IEEE
27119           754-compliant results are required: the fused multiply add/subtract
27120           instructions do not round the intermediate result, thereby
27121           producing results with more bits of precision than specified by the
27122           IEEE standard.  Disabling fused multiply add/subtract instructions
27123           also ensures that the program output is not sensitive to the
27124           compiler's ability to combine multiply and add/subtract operations.
27125
27126       -mserialize-volatile
27127       -mno-serialize-volatile
27128           When this option is enabled, GCC inserts "MEMW" instructions before
27129           "volatile" memory references to guarantee sequential consistency.
27130           The default is -mserialize-volatile.  Use -mno-serialize-volatile
27131           to omit the "MEMW" instructions.
27132
27133       -mforce-no-pic
27134           For targets, like GNU/Linux, where all user-mode Xtensa code must
27135           be position-independent code (PIC), this option disables PIC for
27136           compiling kernel code.
27137
27138       -mtext-section-literals
27139       -mno-text-section-literals
27140           These options control the treatment of literal pools.  The default
27141           is -mno-text-section-literals, which places literals in a separate
27142           section in the output file.  This allows the literal pool to be
27143           placed in a data RAM/ROM, and it also allows the linker to combine
27144           literal pools from separate object files to remove redundant
27145           literals and improve code size.  With -mtext-section-literals, the
27146           literals are interspersed in the text section in order to keep them
27147           as close as possible to their references.  This may be necessary
27148           for large assembly files.  Literals for each function are placed
27149           right before that function.
27150
27151       -mauto-litpools
27152       -mno-auto-litpools
27153           These options control the treatment of literal pools.  The default
27154           is -mno-auto-litpools, which places literals in a separate section
27155           in the output file unless -mtext-section-literals is used.  With
27156           -mauto-litpools the literals are interspersed in the text section
27157           by the assembler.  Compiler does not produce explicit ".literal"
27158           directives and loads literals into registers with "MOVI"
27159           instructions instead of "L32R" to let the assembler do relaxation
27160           and place literals as necessary.  This option allows assembler to
27161           create several literal pools per function and assemble very big
27162           functions, which may not be possible with -mtext-section-literals.
27163
27164       -mtarget-align
27165       -mno-target-align
27166           When this option is enabled, GCC instructs the assembler to
27167           automatically align instructions to reduce branch penalties at the
27168           expense of some code density.  The assembler attempts to widen
27169           density instructions to align branch targets and the instructions
27170           following call instructions.  If there are not enough preceding
27171           safe density instructions to align a target, no widening is
27172           performed.  The default is -mtarget-align.  These options do not
27173           affect the treatment of auto-aligned instructions like "LOOP",
27174           which the assembler always aligns, either by widening density
27175           instructions or by inserting NOP instructions.
27176
27177       -mlongcalls
27178       -mno-longcalls
27179           When this option is enabled, GCC instructs the assembler to
27180           translate direct calls to indirect calls unless it can determine
27181           that the target of a direct call is in the range allowed by the
27182           call instruction.  This translation typically occurs for calls to
27183           functions in other source files.  Specifically, the assembler
27184           translates a direct "CALL" instruction into an "L32R" followed by a
27185           "CALLX" instruction.  The default is -mno-longcalls.  This option
27186           should be used in programs where the call target can potentially be
27187           out of range.  This option is implemented in the assembler, not the
27188           compiler, so the assembly code generated by GCC still shows direct
27189           call instructions---look at the disassembled object code to see the
27190           actual instructions.  Note that the assembler uses an indirect call
27191           for every cross-file call, not just those that really are out of
27192           range.
27193
27194       -mabi=name
27195           Generate code for the specified ABI.  Permissible values are:
27196           call0, windowed.  Default ABI is chosen by the Xtensa core
27197           configuration.
27198
27199       -mabi=call0
27200           When this option is enabled function parameters are passed in
27201           registers "a2" through "a7", registers "a12" through "a15" are
27202           caller-saved, and register "a15" may be used as a frame pointer.
27203           When this version of the ABI is enabled the C preprocessor symbol
27204           "__XTENSA_CALL0_ABI__" is defined.
27205
27206       -mabi=windowed
27207           When this option is enabled function parameters are passed in
27208           registers "a10" through "a15", and called function rotates register
27209           window by 8 registers on entry so that its arguments are found in
27210           registers "a2" through "a7".  Register "a7" may be used as a frame
27211           pointer.  Register window is rotated 8 registers back upon return.
27212           When this version of the ABI is enabled the C preprocessor symbol
27213           "__XTENSA_WINDOWED_ABI__" is defined.
27214
27215   zSeries Options
27216       These are listed under
27217

ENVIRONMENT

27219       This section describes several environment variables that affect how
27220       GCC operates.  Some of them work by specifying directories or prefixes
27221       to use when searching for various kinds of files.  Some are used to
27222       specify other aspects of the compilation environment.
27223
27224       Note that you can also specify places to search using options such as
27225       -B, -I and -L.  These take precedence over places specified using
27226       environment variables, which in turn take precedence over those
27227       specified by the configuration of GCC.
27228
27229       LANG
27230       LC_CTYPE
27231       LC_MESSAGES
27232       LC_ALL
27233           These environment variables control the way that GCC uses
27234           localization information which allows GCC to work with different
27235           national conventions.  GCC inspects the locale categories LC_CTYPE
27236           and LC_MESSAGES if it has been configured to do so.  These locale
27237           categories can be set to any value supported by your installation.
27238           A typical value is en_GB.UTF-8 for English in the United Kingdom
27239           encoded in UTF-8.
27240
27241           The LC_CTYPE environment variable specifies character
27242           classification.  GCC uses it to determine the character boundaries
27243           in a string; this is needed for some multibyte encodings that
27244           contain quote and escape characters that are otherwise interpreted
27245           as a string end or escape.
27246
27247           The LC_MESSAGES environment variable specifies the language to use
27248           in diagnostic messages.
27249
27250           If the LC_ALL environment variable is set, it overrides the value
27251           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
27252           default to the value of the LANG environment variable.  If none of
27253           these variables are set, GCC defaults to traditional C English
27254           behavior.
27255
27256       TMPDIR
27257           If TMPDIR is set, it specifies the directory to use for temporary
27258           files.  GCC uses temporary files to hold the output of one stage of
27259           compilation which is to be used as input to the next stage: for
27260           example, the output of the preprocessor, which is the input to the
27261           compiler proper.
27262
27263       GCC_COMPARE_DEBUG
27264           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing
27265           -fcompare-debug to the compiler driver.  See the documentation of
27266           this option for more details.
27267
27268       GCC_EXEC_PREFIX
27269           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
27270           names of the subprograms executed by the compiler.  No slash is
27271           added when this prefix is combined with the name of a subprogram,
27272           but you can specify a prefix that ends with a slash if you wish.
27273
27274           If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an
27275           appropriate prefix to use based on the pathname it is invoked with.
27276
27277           If GCC cannot find the subprogram using the specified prefix, it
27278           tries looking in the usual places for the subprogram.
27279
27280           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
27281           prefix is the prefix to the installed compiler. In many cases
27282           prefix is the value of "prefix" when you ran the configure script.
27283
27284           Other prefixes specified with -B take precedence over this prefix.
27285
27286           This prefix is also used for finding files such as crt0.o that are
27287           used for linking.
27288
27289           In addition, the prefix is used in an unusual way in finding the
27290           directories to search for header files.  For each of the standard
27291           directories whose name normally begins with /usr/local/lib/gcc
27292           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
27293           replacing that beginning with the specified prefix to produce an
27294           alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar
27295           just before it searches the standard directory /usr/local/lib/bar.
27296           If a standard directory begins with the configured prefix then the
27297           value of prefix is replaced by GCC_EXEC_PREFIX when looking for
27298           header files.
27299
27300       COMPILER_PATH
27301           The value of COMPILER_PATH is a colon-separated list of
27302           directories, much like PATH.  GCC tries the directories thus
27303           specified when searching for subprograms, if it cannot find the
27304           subprograms using GCC_EXEC_PREFIX.
27305
27306       LIBRARY_PATH
27307           The value of LIBRARY_PATH is a colon-separated list of directories,
27308           much like PATH.  When configured as a native compiler, GCC tries
27309           the directories thus specified when searching for special linker
27310           files, if it cannot find them using GCC_EXEC_PREFIX.  Linking using
27311           GCC also uses these directories when searching for ordinary
27312           libraries for the -l option (but directories specified with -L come
27313           first).
27314
27315       LANG
27316           This variable is used to pass locale information to the compiler.
27317           One way in which this information is used is to determine the
27318           character set to be used when character literals, string literals
27319           and comments are parsed in C and C++.  When the compiler is
27320           configured to allow multibyte characters, the following values for
27321           LANG are recognized:
27322
27323           C-JIS
27324               Recognize JIS characters.
27325
27326           C-SJIS
27327               Recognize SJIS characters.
27328
27329           C-EUCJP
27330               Recognize EUCJP characters.
27331
27332           If LANG is not defined, or if it has some other value, then the
27333           compiler uses "mblen" and "mbtowc" as defined by the default locale
27334           to recognize and translate multibyte characters.
27335
27336       GCC_EXTRA_DIAGNOSTIC_OUTPUT
27337           If GCC_EXTRA_DIAGNOSTIC_OUTPUT is set to one of the following
27338           values, then additional text will be emitted to stderr when fix-it
27339           hints are emitted.  -fdiagnostics-parseable-fixits and
27340           -fno-diagnostics-parseable-fixits take precedence over this
27341           environment variable.
27342
27343           fixits-v1
27344               Emit parseable fix-it hints, equivalent to
27345               -fdiagnostics-parseable-fixits.  In particular, columns are
27346               expressed as a count of bytes, starting at byte 1 for the
27347               initial column.
27348
27349           fixits-v2
27350               As "fixits-v1", but columns are expressed as display columns,
27351               as per -fdiagnostics-column-unit=display.
27352
27353       Some additional environment variables affect the behavior of the
27354       preprocessor.
27355
27356       CPATH
27357       C_INCLUDE_PATH
27358       CPLUS_INCLUDE_PATH
27359       OBJC_INCLUDE_PATH
27360           Each variable's value is a list of directories separated by a
27361           special character, much like PATH, in which to look for header
27362           files.  The special character, "PATH_SEPARATOR", is target-
27363           dependent and determined at GCC build time.  For Microsoft Windows-
27364           based targets it is a semicolon, and for almost all other targets
27365           it is a colon.
27366
27367           CPATH specifies a list of directories to be searched as if
27368           specified with -I, but after any paths given with -I options on the
27369           command line.  This environment variable is used regardless of
27370           which language is being preprocessed.
27371
27372           The remaining environment variables apply only when preprocessing
27373           the particular language indicated.  Each specifies a list of
27374           directories to be searched as if specified with -isystem, but after
27375           any paths given with -isystem options on the command line.
27376
27377           In all these variables, an empty element instructs the compiler to
27378           search its current working directory.  Empty elements can appear at
27379           the beginning or end of a path.  For instance, if the value of
27380           CPATH is ":/special/include", that has the same effect as
27381           -I. -I/special/include.
27382
27383       DEPENDENCIES_OUTPUT
27384           If this variable is set, its value specifies how to output
27385           dependencies for Make based on the non-system header files
27386           processed by the compiler.  System header files are ignored in the
27387           dependency output.
27388
27389           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
27390           case the Make rules are written to that file, guessing the target
27391           name from the source file name.  Or the value can have the form
27392           file target, in which case the rules are written to file file using
27393           target as the target name.
27394
27395           In other words, this environment variable is equivalent to
27396           combining the options -MM and -MF, with an optional -MT switch too.
27397
27398       SUNPRO_DEPENDENCIES
27399           This variable is the same as DEPENDENCIES_OUTPUT (see above),
27400           except that system header files are not ignored, so it implies -M
27401           rather than -MM.  However, the dependence on the main input file is
27402           omitted.
27403
27404       SOURCE_DATE_EPOCH
27405           If this variable is set, its value specifies a UNIX timestamp to be
27406           used in replacement of the current date and time in the "__DATE__"
27407           and "__TIME__" macros, so that the embedded timestamps become
27408           reproducible.
27409
27410           The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
27411           the number of seconds (excluding leap seconds) since 01 Jan 1970
27412           00:00:00 represented in ASCII; identical to the output of "date
27413           +%s" on GNU/Linux and other systems that support the %s extension
27414           in the "date" command.
27415
27416           The value should be a known timestamp such as the last modification
27417           time of the source or package and it should be set by the build
27418           process.
27419

BUGS

27421       For instructions on reporting bugs, see
27422       <http://bugzilla.redhat.com/bugzilla>.
27423

FOOTNOTES

27425       1.  On some systems, gcc -shared needs to build supplementary stub code
27426           for constructors to work.  On multi-libbed systems, gcc -shared
27427           must select the correct support libraries to link against.  Failing
27428           to supply the correct flags may lead to subtle defects.  Supplying
27429           them in cases where they are not necessary is innocuous.
27430

SEE ALSO

27432       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
27433       dbx(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb.
27434

AUTHOR

27436       See the Info entry for gcc, or
27437       <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors
27438       to GCC.
27439
27441       Copyright (c) 1988-2021 Free Software Foundation, Inc.
27442
27443       Permission is granted to copy, distribute and/or modify this document
27444       under the terms of the GNU Free Documentation License, Version 1.3 or
27445       any later version published by the Free Software Foundation; with the
27446       Invariant Sections being "GNU General Public License" and "Funding Free
27447       Software", the Front-Cover texts being (a) (see below), and with the
27448       Back-Cover Texts being (b) (see below).  A copy of the license is
27449       included in the gfdl(7) man page.
27450
27451       (a) The FSF's Front-Cover Text is:
27452
27453            A GNU Manual
27454
27455       (b) The FSF's Back-Cover Text is:
27456
27457            You have freedom to copy and modify this GNU Manual, like GNU
27458            software.  Copies published by the Free Software Foundation raise
27459            funds for GNU development.
27460
27461
27462
27463gcc-11                            2021-07-28                            GCC(1)
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