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
15676       These options are defined for AArch64 implementations:
15677
15678       -mabi=name
15679           Generate code for the specified data model.  Permissible values are
15680           ilp32 for SysV-like data model where int, long int and pointers are
15681           32 bits, and lp64 for SysV-like data model where int is 32 bits,
15682           but long int and pointers are 64 bits.
15683
15684           The default depends on the specific target configuration.  Note
15685           that the LP64 and ILP32 ABIs are not link-compatible; you must
15686           compile your entire program with the same ABI, and link with a
15687           compatible set of libraries.
15688
15689       -mbig-endian
15690           Generate big-endian code.  This is the default when GCC is
15691           configured for an aarch64_be-*-* target.
15692
15693       -mgeneral-regs-only
15694           Generate code which uses only the general-purpose registers.  This
15695           will prevent the compiler from using floating-point and Advanced
15696           SIMD registers but will not impose any restrictions on the
15697           assembler.
15698
15699       -mlittle-endian
15700           Generate little-endian code.  This is the default when GCC is
15701           configured for an aarch64-*-* but not an aarch64_be-*-* target.
15702
15703       -mcmodel=tiny
15704           Generate code for the tiny code model.  The program and its
15705           statically defined symbols must be within 1MB of each other.
15706           Programs can be statically or dynamically linked.
15707
15708       -mcmodel=small
15709           Generate code for the small code model.  The program and its
15710           statically defined symbols must be within 4GB of each other.
15711           Programs can be statically or dynamically linked.  This is the
15712           default code model.
15713
15714       -mcmodel=large
15715           Generate code for the large code model.  This makes no assumptions
15716           about addresses and sizes of sections.  Programs can be statically
15717           linked only.  The -mcmodel=large option is incompatible with
15718           -mabi=ilp32, -fpic and -fPIC.
15719
15720       -mstrict-align
15721       -mno-strict-align
15722           Avoid or allow generating memory accesses that may not be aligned
15723           on a natural object boundary as described in the architecture
15724           specification.
15725
15726       -momit-leaf-frame-pointer
15727       -mno-omit-leaf-frame-pointer
15728           Omit or keep the frame pointer in leaf functions.  The former
15729           behavior is the default.
15730
15731       -mstack-protector-guard=guard
15732       -mstack-protector-guard-reg=reg
15733       -mstack-protector-guard-offset=offset
15734           Generate stack protection code using canary at guard.  Supported
15735           locations are global for a global canary or sysreg for a canary in
15736           an appropriate system register.
15737
15738           With the latter choice the options -mstack-protector-guard-reg=reg
15739           and -mstack-protector-guard-offset=offset furthermore specify which
15740           system register to use as base register for reading the canary, and
15741           from what offset from that base register. There is no default
15742           register or offset as this is entirely for use within the Linux
15743           kernel.
15744
15745       -mtls-dialect=desc
15746           Use TLS descriptors as the thread-local storage mechanism for
15747           dynamic accesses of TLS variables.  This is the default.
15748
15749       -mtls-dialect=traditional
15750           Use traditional TLS as the thread-local storage mechanism for
15751           dynamic accesses of TLS variables.
15752
15753       -mtls-size=size
15754           Specify bit size of immediate TLS offsets.  Valid values are 12,
15755           24, 32, 48.  This option requires binutils 2.26 or newer.
15756
15757       -mfix-cortex-a53-835769
15758       -mno-fix-cortex-a53-835769
15759           Enable or disable the workaround for the ARM Cortex-A53 erratum
15760           number 835769.  This involves inserting a NOP instruction between
15761           memory instructions and 64-bit integer multiply-accumulate
15762           instructions.
15763
15764       -mfix-cortex-a53-843419
15765       -mno-fix-cortex-a53-843419
15766           Enable or disable the workaround for the ARM Cortex-A53 erratum
15767           number 843419.  This erratum workaround is made at link time and
15768           this will only pass the corresponding flag to the linker.
15769
15770       -mlow-precision-recip-sqrt
15771       -mno-low-precision-recip-sqrt
15772           Enable or disable the reciprocal square root approximation.  This
15773           option only has an effect if -ffast-math or
15774           -funsafe-math-optimizations is used as well.  Enabling this reduces
15775           precision of reciprocal square root results to about 16 bits for
15776           single precision and to 32 bits for double precision.
15777
15778       -mlow-precision-sqrt
15779       -mno-low-precision-sqrt
15780           Enable or disable the square root approximation.  This option only
15781           has an effect if -ffast-math or -funsafe-math-optimizations is used
15782           as well.  Enabling this reduces precision of square root results to
15783           about 16 bits for single precision and to 32 bits for double
15784           precision.  If enabled, it implies -mlow-precision-recip-sqrt.
15785
15786       -mlow-precision-div
15787       -mno-low-precision-div
15788           Enable or disable the division approximation.  This option only has
15789           an effect if -ffast-math or -funsafe-math-optimizations is used as
15790           well.  Enabling this reduces precision of division results to about
15791           16 bits for single precision and to 32 bits for double precision.
15792
15793       -mtrack-speculation
15794       -mno-track-speculation
15795           Enable or disable generation of additional code to track
15796           speculative execution through conditional branches.  The tracking
15797           state can then be used by the compiler when expanding calls to
15798           "__builtin_speculation_safe_copy" to permit a more efficient code
15799           sequence to be generated.
15800
15801       -moutline-atomics
15802       -mno-outline-atomics
15803           Enable or disable calls to out-of-line helpers to implement atomic
15804           operations.  These helpers will, at runtime, determine if the LSE
15805           instructions from ARMv8.1-A can be used; if not, they will use the
15806           load/store-exclusive instructions that are present in the base
15807           ARMv8.0 ISA.
15808
15809           This option is only applicable when compiling for the base ARMv8.0
15810           instruction set.  If using a later revision, e.g. -march=armv8.1-a
15811           or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be
15812           used directly.  The same applies when using -mcpu= when the
15813           selected cpu supports the lse feature.  This option is on by
15814           default.
15815
15816       -march=name
15817           Specify the name of the target architecture and, optionally, one or
15818           more feature modifiers.  This option has the form
15819           -march=arch{+[no]feature}*.
15820
15821           The table below summarizes the permissible values for arch and the
15822           features that they enable by default:
15823
15824           arch value : Architecture : Includes by default
15825           armv8-a : Armv8-A : +fp, +simd
15826           armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
15827           armv8.2-a : Armv8.2-A : armv8.1-a
15828           armv8.3-a : Armv8.3-A : armv8.2-a, +pauth
15829           armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod
15830           armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres
15831           armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm
15832           armv8-r : Armv8-R : armv8-r
15833
15834           The value native is available on native AArch64 GNU/Linux and
15835           causes the compiler to pick the architecture of the host system.
15836           This option has no effect if the compiler is unable to recognize
15837           the architecture of the host system,
15838
15839           The permissible values for feature are listed in the sub-section on
15840           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
15841           Where conflicting feature modifiers are specified, the right-most
15842           feature is used.
15843
15844           GCC uses name to determine what kind of instructions it can emit
15845           when generating assembly code.  If -march is specified without
15846           either of -mtune or -mcpu also being specified, the code is tuned
15847           to perform well across a range of target processors implementing
15848           the target architecture.
15849
15850       -mtune=name
15851           Specify the name of the target processor for which GCC should tune
15852           the performance of the code.  Permissible values for this option
15853           are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
15854           cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae,
15855           cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, cortex-a78,
15856           cortex-a78ae, cortex-a78c, ares, exynos-m1, emag, falkor,
15857           neoverse-e1, neoverse-n1, neoverse-n2, neoverse-v1, qdf24xx,
15858           saphira, phecda, xgene1, vulcan, octeontx, octeontx81,  octeontx83,
15859           octeontx2, octeontx2t98, octeontx2t96 octeontx2t93, octeontx2f95,
15860           octeontx2f95n, octeontx2f95mm, a64fx, thunderx, thunderxt88,
15861           thunderxt88p1, thunderxt81, tsv110, thunderxt83, thunderx2t99,
15862           thunderx3t110, zeus, cortex-a57.cortex-a53, cortex-a72.cortex-a53,
15863           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
15864           cortex-a75.cortex-a55, cortex-a76.cortex-a55, cortex-r82,
15865           cortex-x1, native.
15866
15867           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
15868           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
15869           cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC
15870           should tune for a big.LITTLE system.
15871
15872           Additionally on native AArch64 GNU/Linux systems the value native
15873           tunes performance to the host system.  This option has no effect if
15874           the compiler is unable to recognize the processor of the host
15875           system.
15876
15877           Where none of -mtune=, -mcpu= or -march= are specified, the code is
15878           tuned to perform well across a range of target processors.
15879
15880           This option cannot be suffixed by feature modifiers.
15881
15882       -mcpu=name
15883           Specify the name of the target processor, optionally suffixed by
15884           one or more feature modifiers.  This option has the form
15885           -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
15886           the same as those available for -mtune.  The permissible values for
15887           feature are documented in the sub-section on
15888           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
15889           Where conflicting feature modifiers are specified, the right-most
15890           feature is used.
15891
15892           GCC uses name to determine what kind of instructions it can emit
15893           when generating assembly code (as if by -march) and to determine
15894           the target processor for which to tune for performance (as if by
15895           -mtune).  Where this option is used in conjunction with -march or
15896           -mtune, those options take precedence over the appropriate part of
15897           this option.
15898
15899       -moverride=string
15900           Override tuning decisions made by the back-end in response to a
15901           -mtune= switch.  The syntax, semantics, and accepted values for
15902           string in this option are not guaranteed to be consistent across
15903           releases.
15904
15905           This option is only intended to be useful when developing GCC.
15906
15907       -mverbose-cost-dump
15908           Enable verbose cost model dumping in the debug dump files.  This
15909           option is provided for use in debugging the compiler.
15910
15911       -mpc-relative-literal-loads
15912       -mno-pc-relative-literal-loads
15913           Enable or disable PC-relative literal loads.  With this option
15914           literal pools are accessed using a single instruction and emitted
15915           after each function.  This limits the maximum size of functions to
15916           1MB.  This is enabled by default for -mcmodel=tiny.
15917
15918       -msign-return-address=scope
15919           Select the function scope on which return address signing will be
15920           applied.  Permissible values are none, which disables return
15921           address signing, non-leaf, which enables pointer signing for
15922           functions which are not leaf functions, and all, which enables
15923           pointer signing for all functions.  The default value is none. This
15924           option has been deprecated by -mbranch-protection.
15925
15926       -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti
15927           Select the branch protection features to use.  none is the default
15928           and turns off all types of branch protection.  standard turns on
15929           all types of branch protection features.  If a feature has
15930           additional tuning options, then standard sets it to its standard
15931           level.  pac-ret[+leaf] turns on return address signing to its
15932           standard level: signing functions that save the return address to
15933           memory (non-leaf functions will practically always do this) using
15934           the a-key.  The optional argument leaf can be used to extend the
15935           signing to include leaf functions.  The optional argument b-key can
15936           be used to sign the functions with the B-key instead of the A-key.
15937           bti turns on branch target identification mechanism.
15938
15939       -mharden-sls=opts
15940           Enable compiler hardening against straight line speculation (SLS).
15941           opts is a comma-separated list of the following options:
15942
15943           retbr
15944           blr
15945
15946           In addition, -mharden-sls=all enables all SLS hardening while
15947           -mharden-sls=none disables all SLS hardening.
15948
15949       -msve-vector-bits=bits
15950           Specify the number of bits in an SVE vector register.  This option
15951           only has an effect when SVE is enabled.
15952
15953           GCC supports two forms of SVE code generation: "vector-length
15954           agnostic" output that works with any size of vector register and
15955           "vector-length specific" output that allows GCC to make assumptions
15956           about the vector length when it is useful for optimization reasons.
15957           The possible values of bits are: scalable, 128, 256, 512, 1024 and
15958           2048.  Specifying scalable selects vector-length agnostic output.
15959           At present -msve-vector-bits=128 also generates vector-length
15960           agnostic output for big-endian targets.  All other values generate
15961           vector-length specific code.  The behavior of these values may
15962           change in future releases and no value except scalable should be
15963           relied on for producing code that is portable across different
15964           hardware SVE vector lengths.
15965
15966           The default is -msve-vector-bits=scalable, which produces vector-
15967           length agnostic code.
15968
15969       -march and -mcpu Feature Modifiers
15970
15971       Feature modifiers used with -march and -mcpu can be any of the
15972       following and their inverses nofeature:
15973
15974       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.
15975
15976       crypto
15977           Enable Crypto extension.  This also enables Advanced SIMD and
15978           floating-point instructions.
15979
15980       fp  Enable floating-point instructions.  This is on by default for all
15981           possible values for options -march and -mcpu.
15982
15983       simd
15984           Enable Advanced SIMD instructions.  This also enables floating-
15985           point instructions.  This is on by default for all possible values
15986           for options -march and -mcpu.
15987
15988       sve Enable Scalable Vector Extension instructions.  This also enables
15989           Advanced SIMD and floating-point instructions.
15990
15991       lse Enable Large System Extension instructions.  This is on by default
15992           for -march=armv8.1-a.
15993
15994       rdma
15995           Enable Round Double Multiply Accumulate instructions.  This is on
15996           by default for -march=armv8.1-a.
15997
15998       fp16
15999           Enable FP16 extension.  This also enables floating-point
16000           instructions.
16001
16002       fp16fml
16003           Enable FP16 fmla extension.  This also enables FP16 extensions and
16004           floating-point instructions. This option is enabled by default for
16005           -march=armv8.4-a. Use of this option with architectures prior to
16006           Armv8.2-A is not supported.
16007
16008       rcpc
16009           Enable the RcPc extension.  This does not change code generation
16010           from GCC, but is passed on to the assembler, enabling inline asm
16011           statements to use instructions from the RcPc extension.
16012
16013       dotprod
16014           Enable the Dot Product extension.  This also enables Advanced SIMD
16015           instructions.
16016
16017       aes Enable the Armv8-a aes and pmull crypto extension.  This also
16018           enables Advanced SIMD instructions.
16019
16020       sha2
16021           Enable the Armv8-a sha2 crypto extension.  This also enables
16022           Advanced SIMD instructions.
16023
16024       sha3
16025           Enable the sha512 and sha3 crypto extension.  This also enables
16026           Advanced SIMD instructions. Use of this option with architectures
16027           prior to Armv8.2-A is not supported.
16028
16029       sm4 Enable the sm3 and sm4 crypto extension.  This also enables
16030           Advanced SIMD instructions.  Use of this option with architectures
16031           prior to Armv8.2-A is not supported.
16032
16033       profile
16034           Enable the Statistical Profiling extension.  This option is only to
16035           enable the extension at the assembler level and does not affect
16036           code generation.
16037
16038       rng Enable the Armv8.5-a Random Number instructions.  This option is
16039           only to enable the extension at the assembler level and does not
16040           affect code generation.
16041
16042       memtag
16043           Enable the Armv8.5-a Memory Tagging Extensions.  Use of this option
16044           with architectures prior to Armv8.5-A is not supported.
16045
16046       sb  Enable the Armv8-a Speculation Barrier instruction.  This option is
16047           only to enable the extension at the assembler level and does not
16048           affect code generation.  This option is enabled by default for
16049           -march=armv8.5-a.
16050
16051       ssbs
16052           Enable the Armv8-a Speculative Store Bypass Safe instruction.  This
16053           option is only to enable the extension at the assembler level and
16054           does not affect code generation.  This option is enabled by default
16055           for -march=armv8.5-a.
16056
16057       predres
16058           Enable the Armv8-a Execution and Data Prediction Restriction
16059           instructions.  This option is only to enable the extension at the
16060           assembler level and does not affect code generation.  This option
16061           is enabled by default for -march=armv8.5-a.
16062
16063       sve2
16064           Enable the Armv8-a Scalable Vector Extension 2.  This also enables
16065           SVE instructions.
16066
16067       sve2-bitperm
16068           Enable SVE2 bitperm instructions.  This also enables SVE2
16069           instructions.
16070
16071       sve2-sm4
16072           Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.
16073
16074       sve2-aes
16075           Enable SVE2 aes instructions.  This also enables SVE2 instructions.
16076
16077       sve2-sha3
16078           Enable SVE2 sha3 instructions.  This also enables SVE2
16079           instructions.
16080
16081       tme Enable the Transactional Memory Extension.
16082
16083       i8mm
16084           Enable 8-bit Integer Matrix Multiply instructions.  This also
16085           enables Advanced SIMD and floating-point instructions.  This option
16086           is enabled by default for -march=armv8.6-a.  Use of this option
16087           with architectures prior to Armv8.2-A is not supported.
16088
16089       f32mm
16090           Enable 32-bit Floating point Matrix Multiply instructions.  This
16091           also enables SVE instructions.  Use of this option with
16092           architectures prior to Armv8.2-A is not supported.
16093
16094       f64mm
16095           Enable 64-bit Floating point Matrix Multiply instructions.  This
16096           also enables SVE instructions.  Use of this option with
16097           architectures prior to Armv8.2-A is not supported.
16098
16099       bf16
16100           Enable brain half-precision floating-point instructions.  This also
16101           enables Advanced SIMD and floating-point instructions.  This option
16102           is enabled by default for -march=armv8.6-a.  Use of this option
16103           with architectures prior to Armv8.2-A is not supported.
16104
16105       flagm
16106           Enable the Flag Manipulation instructions Extension.
16107
16108       pauth
16109           Enable the Pointer Authentication Extension.
16110
16111       Feature crypto implies aes, sha2, and simd, which implies fp.
16112       Conversely, nofp implies nosimd, which implies nocrypto, noaes and
16113       nosha2.
16114
16115       Adapteva Epiphany Options
16116
16117       These -m options are defined for Adapteva Epiphany:
16118
16119       -mhalf-reg-file
16120           Don't allocate any register in the range "r32"..."r63".  That
16121           allows code to run on hardware variants that lack these registers.
16122
16123       -mprefer-short-insn-regs
16124           Preferentially allocate registers that allow short instruction
16125           generation.  This can result in increased instruction count, so
16126           this may either reduce or increase overall code size.
16127
16128       -mbranch-cost=num
16129           Set the cost of branches to roughly num "simple" instructions.
16130           This cost is only a heuristic and is not guaranteed to produce
16131           consistent results across releases.
16132
16133       -mcmove
16134           Enable the generation of conditional moves.
16135
16136       -mnops=num
16137           Emit num NOPs before every other generated instruction.
16138
16139       -mno-soft-cmpsf
16140           For single-precision floating-point comparisons, emit an "fsub"
16141           instruction and test the flags.  This is faster than a software
16142           comparison, but can get incorrect results in the presence of NaNs,
16143           or when two different small numbers are compared such that their
16144           difference is calculated as zero.  The default is -msoft-cmpsf,
16145           which uses slower, but IEEE-compliant, software comparisons.
16146
16147       -mstack-offset=num
16148           Set the offset between the top of the stack and the stack pointer.
16149           E.g., a value of 8 means that the eight bytes in the range
16150           "sp+0...sp+7" can be used by leaf functions without stack
16151           allocation.  Values other than 8 or 16 are untested and unlikely to
16152           work.  Note also that this option changes the ABI; compiling a
16153           program with a different stack offset than the libraries have been
16154           compiled with generally does not work.  This option can be useful
16155           if you want to evaluate if a different stack offset would give you
16156           better code, but to actually use a different stack offset to build
16157           working programs, it is recommended to configure the toolchain with
16158           the appropriate --with-stack-offset=num option.
16159
16160       -mno-round-nearest
16161           Make the scheduler assume that the rounding mode has been set to
16162           truncating.  The default is -mround-nearest.
16163
16164       -mlong-calls
16165           If not otherwise specified by an attribute, assume all calls might
16166           be beyond the offset range of the "b" / "bl" instructions, and
16167           therefore load the function address into a register before
16168           performing a (otherwise direct) call.  This is the default.
16169
16170       -mshort-calls
16171           If not otherwise specified by an attribute, assume all direct calls
16172           are in the range of the "b" / "bl" instructions, so use these
16173           instructions for direct calls.  The default is -mlong-calls.
16174
16175       -msmall16
16176           Assume addresses can be loaded as 16-bit unsigned values.  This
16177           does not apply to function addresses for which -mlong-calls
16178           semantics are in effect.
16179
16180       -mfp-mode=mode
16181           Set the prevailing mode of the floating-point unit.  This
16182           determines the floating-point mode that is provided and expected at
16183           function call and return time.  Making this mode match the mode you
16184           predominantly need at function start can make your programs smaller
16185           and faster by avoiding unnecessary mode switches.
16186
16187           mode can be set to one the following values:
16188
16189           caller
16190               Any mode at function entry is valid, and retained or restored
16191               when the function returns, and when it calls other functions.
16192               This mode is useful for compiling libraries or other
16193               compilation units you might want to incorporate into different
16194               programs with different prevailing FPU modes, and the
16195               convenience of being able to use a single object file outweighs
16196               the size and speed overhead for any extra mode switching that
16197               might be needed, compared with what would be needed with a more
16198               specific choice of prevailing FPU mode.
16199
16200           truncate
16201               This is the mode used for floating-point calculations with
16202               truncating (i.e. round towards zero) rounding mode.  That
16203               includes conversion from floating point to integer.
16204
16205           round-nearest
16206               This is the mode used for floating-point calculations with
16207               round-to-nearest-or-even rounding mode.
16208
16209           int This is the mode used to perform integer calculations in the
16210               FPU, e.g.  integer multiply, or integer multiply-and-
16211               accumulate.
16212
16213           The default is -mfp-mode=caller
16214
16215       -mno-split-lohi
16216       -mno-postinc
16217       -mno-postmodify
16218           Code generation tweaks that disable, respectively, splitting of
16219           32-bit loads, generation of post-increment addresses, and
16220           generation of post-modify addresses.  The defaults are msplit-lohi,
16221           -mpost-inc, and -mpost-modify.
16222
16223       -mnovect-double
16224           Change the preferred SIMD mode to SImode.  The default is
16225           -mvect-double, which uses DImode as preferred SIMD mode.
16226
16227       -max-vect-align=num
16228           The maximum alignment for SIMD vector mode types.  num may be 4 or
16229           8.  The default is 8.  Note that this is an ABI change, even though
16230           many library function interfaces are unaffected if they don't use
16231           SIMD vector modes in places that affect size and/or alignment of
16232           relevant types.
16233
16234       -msplit-vecmove-early
16235           Split vector moves into single word moves before reload.  In theory
16236           this can give better register allocation, but so far the reverse
16237           seems to be generally the case.
16238
16239       -m1reg-reg
16240           Specify a register to hold the constant -1, which makes loading
16241           small negative constants and certain bitmasks faster.  Allowable
16242           values for reg are r43 and r63, which specify use of that register
16243           as a fixed register, and none, which means that no register is used
16244           for this purpose.  The default is -m1reg-none.
16245
16246       AMD GCN Options
16247
16248       These options are defined specifically for the AMD GCN port.
16249
16250       -march=gpu
16251       -mtune=gpu
16252           Set architecture type or tuning for gpu. Supported values for gpu
16253           are
16254
16255           fiji
16256               Compile for GCN3 Fiji devices (gfx803).
16257
16258           gfx900
16259               Compile for GCN5 Vega 10 devices (gfx900).
16260
16261           gfx906
16262               Compile for GCN5 Vega 20 devices (gfx906).
16263
16264       -mstack-size=bytes
16265           Specify how many bytes of stack space will be requested for each
16266           GPU thread (wave-front).  Beware that there may be many threads and
16267           limited memory available.  The size of the stack allocation may
16268           also have an impact on run-time performance.  The default is 32KB
16269           when using OpenACC or OpenMP, and 1MB otherwise.
16270
16271       ARC Options
16272
16273       The following options control the architecture variant for which code
16274       is being compiled:
16275
16276       -mbarrel-shifter
16277           Generate instructions supported by barrel shifter.  This is the
16278           default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.
16279
16280       -mjli-always
16281           Force to call a function using jli_s instruction.  This option is
16282           valid only for ARCv2 architecture.
16283
16284       -mcpu=cpu
16285           Set architecture type, register usage, and instruction scheduling
16286           parameters for cpu.  There are also shortcut alias options
16287           available for backward compatibility and convenience.  Supported
16288           values for cpu are
16289
16290           arc600
16291               Compile for ARC600.  Aliases: -mA6, -mARC600.
16292
16293           arc601
16294               Compile for ARC601.  Alias: -mARC601.
16295
16296           arc700
16297               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the
16298               default when configured with --with-cpu=arc700.
16299
16300           arcem
16301               Compile for ARC EM.
16302
16303           archs
16304               Compile for ARC HS.
16305
16306           em  Compile for ARC EM CPU with no hardware extensions.
16307
16308           em4 Compile for ARC EM4 CPU.
16309
16310           em4_dmips
16311               Compile for ARC EM4 DMIPS CPU.
16312
16313           em4_fpus
16314               Compile for ARC EM4 DMIPS CPU with the single-precision
16315               floating-point extension.
16316
16317           em4_fpuda
16318               Compile for ARC EM4 DMIPS CPU with single-precision floating-
16319               point and double assist instructions.
16320
16321           hs  Compile for ARC HS CPU with no hardware extensions except the
16322               atomic instructions.
16323
16324           hs34
16325               Compile for ARC HS34 CPU.
16326
16327           hs38
16328               Compile for ARC HS38 CPU.
16329
16330           hs38_linux
16331               Compile for ARC HS38 CPU with all hardware extensions on.
16332
16333           arc600_norm
16334               Compile for ARC 600 CPU with "norm" instructions enabled.
16335
16336           arc600_mul32x16
16337               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
16338               instructions enabled.
16339
16340           arc600_mul64
16341               Compile for ARC 600 CPU with "norm" and "mul64"-family
16342               instructions enabled.
16343
16344           arc601_norm
16345               Compile for ARC 601 CPU with "norm" instructions enabled.
16346
16347           arc601_mul32x16
16348               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
16349               instructions enabled.
16350
16351           arc601_mul64
16352               Compile for ARC 601 CPU with "norm" and "mul64"-family
16353               instructions enabled.
16354
16355           nps400
16356               Compile for ARC 700 on NPS400 chip.
16357
16358           em_mini
16359               Compile for ARC EM minimalist configuration featuring reduced
16360               register set.
16361
16362       -mdpfp
16363       -mdpfp-compact
16364           Generate double-precision FPX instructions, tuned for the compact
16365           implementation.
16366
16367       -mdpfp-fast
16368           Generate double-precision FPX instructions, tuned for the fast
16369           implementation.
16370
16371       -mno-dpfp-lrsr
16372           Disable "lr" and "sr" instructions from using FPX extension aux
16373           registers.
16374
16375       -mea
16376           Generate extended arithmetic instructions.  Currently only "divaw",
16377           "adds", "subs", and "sat16" are supported.  Only valid for
16378           -mcpu=ARC700.
16379
16380       -mno-mpy
16381           Do not generate "mpy"-family instructions for ARC700.  This option
16382           is deprecated.
16383
16384       -mmul32x16
16385           Generate 32x16-bit multiply and multiply-accumulate instructions.
16386
16387       -mmul64
16388           Generate "mul64" and "mulu64" instructions.  Only valid for
16389           -mcpu=ARC600.
16390
16391       -mnorm
16392           Generate "norm" instructions.  This is the default if -mcpu=ARC700
16393           is in effect.
16394
16395       -mspfp
16396       -mspfp-compact
16397           Generate single-precision FPX instructions, tuned for the compact
16398           implementation.
16399
16400       -mspfp-fast
16401           Generate single-precision FPX instructions, tuned for the fast
16402           implementation.
16403
16404       -msimd
16405           Enable generation of ARC SIMD instructions via target-specific
16406           builtins.  Only valid for -mcpu=ARC700.
16407
16408       -msoft-float
16409           This option ignored; it is provided for compatibility purposes
16410           only.  Software floating-point code is emitted by default, and this
16411           default can overridden by FPX options; -mspfp, -mspfp-compact, or
16412           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
16413           -mdpfp-fast for double precision.
16414
16415       -mswap
16416           Generate "swap" instructions.
16417
16418       -matomic
16419           This enables use of the locked load/store conditional extension to
16420           implement atomic memory built-in functions.  Not available for ARC
16421           6xx or ARC EM cores.
16422
16423       -mdiv-rem
16424           Enable "div" and "rem" instructions for ARCv2 cores.
16425
16426       -mcode-density
16427           Enable code density instructions for ARC EM.  This option is on by
16428           default for ARC HS.
16429
16430       -mll64
16431           Enable double load/store operations for ARC HS cores.
16432
16433       -mtp-regno=regno
16434           Specify thread pointer register number.
16435
16436       -mmpy-option=multo
16437           Compile ARCv2 code with a multiplier design option.  You can
16438           specify the option using either a string or numeric value for
16439           multo.  wlh1 is the default value.  The recognized values are:
16440
16441           0
16442           none
16443               No multiplier available.
16444
16445           1
16446           w   16x16 multiplier, fully pipelined.  The following instructions
16447               are enabled: "mpyw" and "mpyuw".
16448
16449           2
16450           wlh1
16451               32x32 multiplier, fully pipelined (1 stage).  The following
16452               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16453               "mpymu", and "mpy_s".
16454
16455           3
16456           wlh2
16457               32x32 multiplier, fully pipelined (2 stages).  The following
16458               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16459               "mpymu", and "mpy_s".
16460
16461           4
16462           wlh3
16463               Two 16x16 multipliers, blocking, sequential.  The following
16464               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16465               "mpymu", and "mpy_s".
16466
16467           5
16468           wlh4
16469               One 16x16 multiplier, blocking, sequential.  The following
16470               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16471               "mpymu", and "mpy_s".
16472
16473           6
16474           wlh5
16475               One 32x4 multiplier, blocking, sequential.  The following
16476               instructions are additionally enabled: "mpy", "mpyu", "mpym",
16477               "mpymu", and "mpy_s".
16478
16479           7
16480           plus_dmpy
16481               ARC HS SIMD support.
16482
16483           8
16484           plus_macd
16485               ARC HS SIMD support.
16486
16487           9
16488           plus_qmacw
16489               ARC HS SIMD support.
16490
16491           This option is only available for ARCv2 cores.
16492
16493       -mfpu=fpu
16494           Enables support for specific floating-point hardware extensions for
16495           ARCv2 cores.  Supported values for fpu are:
16496
16497           fpus
16498               Enables support for single-precision floating-point hardware
16499               extensions.
16500
16501           fpud
16502               Enables support for double-precision floating-point hardware
16503               extensions.  The single-precision floating-point extension is
16504               also enabled.  Not available for ARC EM.
16505
16506           fpuda
16507               Enables support for double-precision floating-point hardware
16508               extensions using double-precision assist instructions.  The
16509               single-precision floating-point extension is also enabled.
16510               This option is only available for ARC EM.
16511
16512           fpuda_div
16513               Enables support for double-precision floating-point hardware
16514               extensions using double-precision assist instructions.  The
16515               single-precision floating-point, square-root, and divide
16516               extensions are also enabled.  This option is only available for
16517               ARC EM.
16518
16519           fpuda_fma
16520               Enables support for double-precision floating-point hardware
16521               extensions using double-precision assist instructions.  The
16522               single-precision floating-point and fused multiply and add
16523               hardware extensions are also enabled.  This option is only
16524               available for ARC EM.
16525
16526           fpuda_all
16527               Enables support for double-precision floating-point hardware
16528               extensions using double-precision assist instructions.  All
16529               single-precision floating-point hardware extensions are also
16530               enabled.  This option is only available for ARC EM.
16531
16532           fpus_div
16533               Enables support for single-precision floating-point, square-
16534               root and divide hardware extensions.
16535
16536           fpud_div
16537               Enables support for double-precision floating-point, square-
16538               root and divide hardware extensions.  This option includes
16539               option fpus_div. Not available for ARC EM.
16540
16541           fpus_fma
16542               Enables support for single-precision floating-point and fused
16543               multiply and add hardware extensions.
16544
16545           fpud_fma
16546               Enables support for double-precision floating-point and fused
16547               multiply and add hardware extensions.  This option includes
16548               option fpus_fma.  Not available for ARC EM.
16549
16550           fpus_all
16551               Enables support for all single-precision floating-point
16552               hardware extensions.
16553
16554           fpud_all
16555               Enables support for all single- and double-precision floating-
16556               point hardware extensions.  Not available for ARC EM.
16557
16558       -mirq-ctrl-saved=register-range, blink, lp_count
16559           Specifies general-purposes registers that the processor
16560           automatically saves/restores on interrupt entry and exit.
16561           register-range is specified as two registers separated by a dash.
16562           The register range always starts with "r0", the upper limit is "fp"
16563           register.  blink and lp_count are optional.  This option is only
16564           valid for ARC EM and ARC HS cores.
16565
16566       -mrgf-banked-regs=number
16567           Specifies the number of registers replicated in second register
16568           bank on entry to fast interrupt.  Fast interrupts are interrupts
16569           with the highest priority level P0.  These interrupts save only PC
16570           and STATUS32 registers to avoid memory transactions during
16571           interrupt entry and exit sequences.  Use this option when you are
16572           using fast interrupts in an ARC V2 family processor.  Permitted
16573           values are 4, 8, 16, and 32.
16574
16575       -mlpc-width=width
16576           Specify the width of the "lp_count" register.  Valid values for
16577           width are 8, 16, 20, 24, 28 and 32 bits.  The default width is
16578           fixed to 32 bits.  If the width is less than 32, the compiler does
16579           not attempt to transform loops in your program to use the zero-
16580           delay loop mechanism unless it is known that the "lp_count"
16581           register can hold the required loop-counter value.  Depending on
16582           the width specified, the compiler and run-time library might
16583           continue to use the loop mechanism for various needs.  This option
16584           defines macro "__ARC_LPC_WIDTH__" with the value of width.
16585
16586       -mrf16
16587           This option instructs the compiler to generate code for a 16-entry
16588           register file.  This option defines the "__ARC_RF16__" preprocessor
16589           macro.
16590
16591       -mbranch-index
16592           Enable use of "bi" or "bih" instructions to implement jump tables.
16593
16594       The following options are passed through to the assembler, and also
16595       define preprocessor macro symbols.
16596
16597       -mdsp-packa
16598           Passed down to the assembler to enable the DSP Pack A extensions.
16599           Also sets the preprocessor symbol "__Xdsp_packa".  This option is
16600           deprecated.
16601
16602       -mdvbf
16603           Passed down to the assembler to enable the dual Viterbi butterfly
16604           extension.  Also sets the preprocessor symbol "__Xdvbf".  This
16605           option is deprecated.
16606
16607       -mlock
16608           Passed down to the assembler to enable the locked load/store
16609           conditional extension.  Also sets the preprocessor symbol
16610           "__Xlock".
16611
16612       -mmac-d16
16613           Passed down to the assembler.  Also sets the preprocessor symbol
16614           "__Xxmac_d16".  This option is deprecated.
16615
16616       -mmac-24
16617           Passed down to the assembler.  Also sets the preprocessor symbol
16618           "__Xxmac_24".  This option is deprecated.
16619
16620       -mrtsc
16621           Passed down to the assembler to enable the 64-bit time-stamp
16622           counter extension instruction.  Also sets the preprocessor symbol
16623           "__Xrtsc".  This option is deprecated.
16624
16625       -mswape
16626           Passed down to the assembler to enable the swap byte ordering
16627           extension instruction.  Also sets the preprocessor symbol
16628           "__Xswape".
16629
16630       -mtelephony
16631           Passed down to the assembler to enable dual- and single-operand
16632           instructions for telephony.  Also sets the preprocessor symbol
16633           "__Xtelephony".  This option is deprecated.
16634
16635       -mxy
16636           Passed down to the assembler to enable the XY memory extension.
16637           Also sets the preprocessor symbol "__Xxy".
16638
16639       The following options control how the assembly code is annotated:
16640
16641       -misize
16642           Annotate assembler instructions with estimated addresses.
16643
16644       -mannotate-align
16645           Explain what alignment considerations lead to the decision to make
16646           an instruction short or long.
16647
16648       The following options are passed through to the linker:
16649
16650       -marclinux
16651           Passed through to the linker, to specify use of the "arclinux"
16652           emulation.  This option is enabled by default in tool chains built
16653           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
16654           profiling is not requested.
16655
16656       -marclinux_prof
16657           Passed through to the linker, to specify use of the "arclinux_prof"
16658           emulation.  This option is enabled by default in tool chains built
16659           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
16660           profiling is requested.
16661
16662       The following options control the semantics of generated code:
16663
16664       -mlong-calls
16665           Generate calls as register indirect calls, thus providing access to
16666           the full 32-bit address range.
16667
16668       -mmedium-calls
16669           Don't use less than 25-bit addressing range for calls, which is the
16670           offset available for an unconditional branch-and-link instruction.
16671           Conditional execution of function calls is suppressed, to allow use
16672           of the 25-bit range, rather than the 21-bit range with conditional
16673           branch-and-link.  This is the default for tool chains built for
16674           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.
16675
16676       -G num
16677           Put definitions of externally-visible data in a small data section
16678           if that data is no bigger than num bytes.  The default value of num
16679           is 4 for any ARC configuration, or 8 when we have double load/store
16680           operations.
16681
16682       -mno-sdata
16683           Do not generate sdata references.  This is the default for tool
16684           chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
16685           targets.
16686
16687       -mvolatile-cache
16688           Use ordinarily cached memory accesses for volatile references.
16689           This is the default.
16690
16691       -mno-volatile-cache
16692           Enable cache bypass for volatile references.
16693
16694       The following options fine tune code generation:
16695
16696       -malign-call
16697           Do alignment optimizations for call instructions.
16698
16699       -mauto-modify-reg
16700           Enable the use of pre/post modify with register displacement.
16701
16702       -mbbit-peephole
16703           Enable bbit peephole2.
16704
16705       -mno-brcc
16706           This option disables a target-specific pass in arc_reorg to
16707           generate compare-and-branch ("brcc") instructions.  It has no
16708           effect on generation of these instructions driven by the combiner
16709           pass.
16710
16711       -mcase-vector-pcrel
16712           Use PC-relative switch case tables to enable case table shortening.
16713           This is the default for -Os.
16714
16715       -mcompact-casesi
16716           Enable compact "casesi" pattern.  This is the default for -Os, and
16717           only available for ARCv1 cores.  This option is deprecated.
16718
16719       -mno-cond-exec
16720           Disable the ARCompact-specific pass to generate conditional
16721           execution instructions.
16722
16723           Due to delay slot scheduling and interactions between operand
16724           numbers, literal sizes, instruction lengths, and the support for
16725           conditional execution, the target-independent pass to generate
16726           conditional execution is often lacking, so the ARC port has kept a
16727           special pass around that tries to find more conditional execution
16728           generation opportunities after register allocation, branch
16729           shortening, and delay slot scheduling have been done.  This pass
16730           generally, but not always, improves performance and code size, at
16731           the cost of extra compilation time, which is why there is an option
16732           to switch it off.  If you have a problem with call instructions
16733           exceeding their allowable offset range because they are
16734           conditionalized, you should consider using -mmedium-calls instead.
16735
16736       -mearly-cbranchsi
16737           Enable pre-reload use of the "cbranchsi" pattern.
16738
16739       -mexpand-adddi
16740           Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
16741           "adc" etc.  This option is deprecated.
16742
16743       -mindexed-loads
16744           Enable the use of indexed loads.  This can be problematic because
16745           some optimizers then assume that indexed stores exist, which is not
16746           the case.
16747
16748       -mlra
16749           Enable Local Register Allocation.  This is still experimental for
16750           ARC, so by default the compiler uses standard reload (i.e.
16751           -mno-lra).
16752
16753       -mlra-priority-none
16754           Don't indicate any priority for target registers.
16755
16756       -mlra-priority-compact
16757           Indicate target register priority for r0..r3 / r12..r15.
16758
16759       -mlra-priority-noncompact
16760           Reduce target register priority for r0..r3 / r12..r15.
16761
16762       -mmillicode
16763           When optimizing for size (using -Os), prologues and epilogues that
16764           have to save or restore a large number of registers are often
16765           shortened by using call to a special function in libgcc; this is
16766           referred to as a millicode call.  As these calls can pose
16767           performance issues, and/or cause linking issues when linking in a
16768           nonstandard way, this option is provided to turn on or off
16769           millicode call generation.
16770
16771       -mcode-density-frame
16772           This option enable the compiler to emit "enter" and "leave"
16773           instructions.  These instructions are only valid for CPUs with
16774           code-density feature.
16775
16776       -mmixed-code
16777           Tweak register allocation to help 16-bit instruction generation.
16778           This generally has the effect of decreasing the average instruction
16779           size while increasing the instruction count.
16780
16781       -mq-class
16782           Ths option is deprecated.  Enable q instruction alternatives.  This
16783           is the default for -Os.
16784
16785       -mRcq
16786           Enable Rcq constraint handling.  Most short code generation depends
16787           on this.  This is the default.
16788
16789       -mRcw
16790           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends
16791           on this.  This is the default.
16792
16793       -msize-level=level
16794           Fine-tune size optimization with regards to instruction lengths and
16795           alignment.  The recognized values for level are:
16796
16797           0   No size optimization.  This level is deprecated and treated
16798               like 1.
16799
16800           1   Short instructions are used opportunistically.
16801
16802           2   In addition, alignment of loops and of code after barriers are
16803               dropped.
16804
16805           3   In addition, optional data alignment is dropped, and the option
16806               Os is enabled.
16807
16808           This defaults to 3 when -Os is in effect.  Otherwise, the behavior
16809           when this is not set is equivalent to level 1.
16810
16811       -mtune=cpu
16812           Set instruction scheduling parameters for cpu, overriding any
16813           implied by -mcpu=.
16814
16815           Supported values for cpu are
16816
16817           ARC600
16818               Tune for ARC600 CPU.
16819
16820           ARC601
16821               Tune for ARC601 CPU.
16822
16823           ARC700
16824               Tune for ARC700 CPU with standard multiplier block.
16825
16826           ARC700-xmac
16827               Tune for ARC700 CPU with XMAC block.
16828
16829           ARC725D
16830               Tune for ARC725D CPU.
16831
16832           ARC750D
16833               Tune for ARC750D CPU.
16834
16835       -mmultcost=num
16836           Cost to assume for a multiply instruction, with 4 being equal to a
16837           normal instruction.
16838
16839       -munalign-prob-threshold=probability
16840           Set probability threshold for unaligning branches.  When tuning for
16841           ARC700 and optimizing for speed, branches without filled delay slot
16842           are preferably emitted unaligned and long, unless profiling
16843           indicates that the probability for the branch to be taken is below
16844           probability.  The default is (REG_BR_PROB_BASE/2), i.e. 5000.
16845
16846       The following options are maintained for backward compatibility, but
16847       are now deprecated and will be removed in a future release:
16848
16849       -margonaut
16850           Obsolete FPX.
16851
16852       -mbig-endian
16853       -EB Compile code for big-endian targets.  Use of these options is now
16854           deprecated.  Big-endian code is supported by configuring GCC to
16855           build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
16856           endian is the default.
16857
16858       -mlittle-endian
16859       -EL Compile code for little-endian targets.  Use of these options is
16860           now deprecated.  Little-endian code is supported by configuring GCC
16861           to build "arc-elf32" and "arc-linux-uclibc" targets, for which
16862           little endian is the default.
16863
16864       -mbarrel_shifter
16865           Replaced by -mbarrel-shifter.
16866
16867       -mdpfp_compact
16868           Replaced by -mdpfp-compact.
16869
16870       -mdpfp_fast
16871           Replaced by -mdpfp-fast.
16872
16873       -mdsp_packa
16874           Replaced by -mdsp-packa.
16875
16876       -mEA
16877           Replaced by -mea.
16878
16879       -mmac_24
16880           Replaced by -mmac-24.
16881
16882       -mmac_d16
16883           Replaced by -mmac-d16.
16884
16885       -mspfp_compact
16886           Replaced by -mspfp-compact.
16887
16888       -mspfp_fast
16889           Replaced by -mspfp-fast.
16890
16891       -mtune=cpu
16892           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
16893           by ARC600, ARC601, ARC700 and ARC700-xmac respectively.
16894
16895       -multcost=num
16896           Replaced by -mmultcost.
16897
16898       ARM Options
16899
16900       These -m options are defined for the ARM port:
16901
16902       -mabi=name
16903           Generate code for the specified ABI.  Permissible values are: apcs-
16904           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
16905
16906       -mapcs-frame
16907           Generate a stack frame that is compliant with the ARM Procedure
16908           Call Standard for all functions, even if this is not strictly
16909           necessary for correct execution of the code.  Specifying
16910           -fomit-frame-pointer with this option causes the stack frames not
16911           to be generated for leaf functions.  The default is
16912           -mno-apcs-frame.  This option is deprecated.
16913
16914       -mapcs
16915           This is a synonym for -mapcs-frame and is deprecated.
16916
16917       -mthumb-interwork
16918           Generate code that supports calling between the ARM and Thumb
16919           instruction sets.  Without this option, on pre-v5 architectures,
16920           the two instruction sets cannot be reliably used inside one
16921           program.  The default is -mno-thumb-interwork, since slightly
16922           larger code is generated when -mthumb-interwork is specified.  In
16923           AAPCS configurations this option is meaningless.
16924
16925       -mno-sched-prolog
16926           Prevent the reordering of instructions in the function prologue, or
16927           the merging of those instruction with the instructions in the
16928           function's body.  This means that all functions start with a
16929           recognizable set of instructions (or in fact one of a choice from a
16930           small set of different function prologues), and this information
16931           can be used to locate the start of functions inside an executable
16932           piece of code.  The default is -msched-prolog.
16933
16934       -mfloat-abi=name
16935           Specifies which floating-point ABI to use.  Permissible values are:
16936           soft, softfp and hard.
16937
16938           Specifying soft causes GCC to generate output containing library
16939           calls for floating-point operations.  softfp allows the generation
16940           of code using hardware floating-point instructions, but still uses
16941           the soft-float calling conventions.  hard allows generation of
16942           floating-point instructions and uses FPU-specific calling
16943           conventions.
16944
16945           The default depends on the specific target configuration.  Note
16946           that the hard-float and soft-float ABIs are not link-compatible;
16947           you must compile your entire program with the same ABI, and link
16948           with a compatible set of libraries.
16949
16950       -mgeneral-regs-only
16951           Generate code which uses only the general-purpose registers.  This
16952           will prevent the compiler from using floating-point and Advanced
16953           SIMD registers but will not impose any restrictions on the
16954           assembler.
16955
16956       -mlittle-endian
16957           Generate code for a processor running in little-endian mode.  This
16958           is the default for all standard configurations.
16959
16960       -mbig-endian
16961           Generate code for a processor running in big-endian mode; the
16962           default is to compile code for a little-endian processor.
16963
16964       -mbe8
16965       -mbe32
16966           When linking a big-endian image select between BE8 and BE32
16967           formats.  The option has no effect for little-endian images and is
16968           ignored.  The default is dependent on the selected target
16969           architecture.  For ARMv6 and later architectures the default is
16970           BE8, for older architectures the default is BE32.  BE32 format has
16971           been deprecated by ARM.
16972
16973       -march=name[+extension...]
16974           This specifies the name of the target ARM architecture.  GCC uses
16975           this name to determine what kind of instructions it can emit when
16976           generating assembly code.  This option can be used in conjunction
16977           with or instead of the -mcpu= option.
16978
16979           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
16980           armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
16981           armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
16982           armv8.6-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m,
16983           armv8-m.base, armv8-m.main, armv8.1-m.main, iwmmxt and iwmmxt2.
16984
16985           Additionally, the following architectures, which lack support for
16986           the Thumb execution state, are recognized but support is
16987           deprecated: armv4.
16988
16989           Many of the architectures support extensions.  These can be added
16990           by appending +extension to the architecture name.  Extension
16991           options are processed in order and capabilities accumulate.  An
16992           extension will also enable any necessary base extensions upon which
16993           it depends.  For example, the +crypto extension will always enable
16994           the +simd extension.  The exception to the additive construction is
16995           for extensions that are prefixed with +no...: these extensions
16996           disable the specified option and any other extensions that may
16997           depend on the presence of that extension.
16998
16999           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
17000           writing -march=armv7-a+vfpv4 since the +simd option is entirely
17001           disabled by the +nofp option that follows it.
17002
17003           Most extension names are generically named, but have an effect that
17004           is dependent upon the architecture to which it is applied.  For
17005           example, the +simd option can be applied to both armv7-a and
17006           armv8-a architectures, but will enable the original ARMv7-A
17007           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
17008           for armv8-a.
17009
17010           The table below lists the supported extensions for each
17011           architecture.  Architectures not mentioned do not support any
17012           extensions.
17013
17014           armv5te
17015           armv6
17016           armv6j
17017           armv6k
17018           armv6kz
17019           armv6t2
17020           armv6z
17021           armv6zk
17022               +fp The VFPv2 floating-point instructions.  The extension
17023                   +vfpv2 can be used as an alias for this extension.
17024
17025               +nofp
17026                   Disable the floating-point instructions.
17027
17028           armv7
17029               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
17030               architectures.
17031
17032               +fp The VFPv3 floating-point instructions, with 16 double-
17033                   precision registers.  The extension +vfpv3-d16 can be used
17034                   as an alias for this extension.  Note that floating-point
17035                   is not supported by the base ARMv7-M architecture, but is
17036                   compatible with both the ARMv7-A and ARMv7-R architectures.
17037
17038               +nofp
17039                   Disable the floating-point instructions.
17040
17041           armv7-a
17042               +mp The multiprocessing extension.
17043
17044               +sec
17045                   The security extension.
17046
17047               +fp The VFPv3 floating-point instructions, with 16 double-
17048                   precision registers.  The extension +vfpv3-d16 can be used
17049                   as an alias for this extension.
17050
17051               +simd
17052                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17053                   instructions.  The extensions +neon and +neon-vfpv3 can be
17054                   used as aliases for this extension.
17055
17056               +vfpv3
17057                   The VFPv3 floating-point instructions, with 32 double-
17058                   precision registers.
17059
17060               +vfpv3-d16-fp16
17061                   The VFPv3 floating-point instructions, with 16 double-
17062                   precision registers and the half-precision floating-point
17063                   conversion operations.
17064
17065               +vfpv3-fp16
17066                   The VFPv3 floating-point instructions, with 32 double-
17067                   precision registers and the half-precision floating-point
17068                   conversion operations.
17069
17070               +vfpv4-d16
17071                   The VFPv4 floating-point instructions, with 16 double-
17072                   precision registers.
17073
17074               +vfpv4
17075                   The VFPv4 floating-point instructions, with 32 double-
17076                   precision registers.
17077
17078               +neon-fp16
17079                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17080                   instructions, with the half-precision floating-point
17081                   conversion operations.
17082
17083               +neon-vfpv4
17084                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17085                   instructions.
17086
17087               +nosimd
17088                   Disable the Advanced SIMD instructions (does not disable
17089                   floating point).
17090
17091               +nofp
17092                   Disable the floating-point and Advanced SIMD instructions.
17093
17094           armv7ve
17095               The extended version of the ARMv7-A architecture with support
17096               for virtualization.
17097
17098               +fp The VFPv4 floating-point instructions, with 16 double-
17099                   precision registers.  The extension +vfpv4-d16 can be used
17100                   as an alias for this extension.
17101
17102               +simd
17103                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
17104                   instructions.  The extension +neon-vfpv4 can be used as an
17105                   alias for this extension.
17106
17107               +vfpv3-d16
17108                   The VFPv3 floating-point instructions, with 16 double-
17109                   precision registers.
17110
17111               +vfpv3
17112                   The VFPv3 floating-point instructions, with 32 double-
17113                   precision registers.
17114
17115               +vfpv3-d16-fp16
17116                   The VFPv3 floating-point instructions, with 16 double-
17117                   precision registers and the half-precision floating-point
17118                   conversion operations.
17119
17120               +vfpv3-fp16
17121                   The VFPv3 floating-point instructions, with 32 double-
17122                   precision registers and the half-precision floating-point
17123                   conversion operations.
17124
17125               +vfpv4-d16
17126                   The VFPv4 floating-point instructions, with 16 double-
17127                   precision registers.
17128
17129               +vfpv4
17130                   The VFPv4 floating-point instructions, with 32 double-
17131                   precision registers.
17132
17133               +neon
17134                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17135                   instructions.  The extension +neon-vfpv3 can be used as an
17136                   alias for this extension.
17137
17138               +neon-fp16
17139                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
17140                   instructions, with the half-precision floating-point
17141                   conversion operations.
17142
17143               +nosimd
17144                   Disable the Advanced SIMD instructions (does not disable
17145                   floating point).
17146
17147               +nofp
17148                   Disable the floating-point and Advanced SIMD instructions.
17149
17150           armv8-a
17151               +crc
17152                   The Cyclic Redundancy Check (CRC) instructions.
17153
17154               +simd
17155                   The ARMv8-A Advanced SIMD and floating-point instructions.
17156
17157               +crypto
17158                   The cryptographic instructions.
17159
17160               +nocrypto
17161                   Disable the cryptographic instructions.
17162
17163               +nofp
17164                   Disable the floating-point, Advanced SIMD and cryptographic
17165                   instructions.
17166
17167               +sb Speculation Barrier Instruction.
17168
17169               +predres
17170                   Execution and Data Prediction Restriction Instructions.
17171
17172           armv8.1-a
17173               +simd
17174                   The ARMv8.1-A Advanced SIMD and floating-point
17175                   instructions.
17176
17177               +crypto
17178                   The cryptographic instructions.  This also enables the
17179                   Advanced SIMD and floating-point instructions.
17180
17181               +nocrypto
17182                   Disable the cryptographic instructions.
17183
17184               +nofp
17185                   Disable the floating-point, Advanced SIMD and cryptographic
17186                   instructions.
17187
17188               +sb Speculation Barrier Instruction.
17189
17190               +predres
17191                   Execution and Data Prediction Restriction Instructions.
17192
17193           armv8.2-a
17194           armv8.3-a
17195               +fp16
17196                   The half-precision floating-point data processing
17197                   instructions.  This also enables the Advanced SIMD and
17198                   floating-point instructions.
17199
17200               +fp16fml
17201                   The half-precision floating-point fmla extension.  This
17202                   also enables the half-precision floating-point extension
17203                   and Advanced SIMD and floating-point instructions.
17204
17205               +simd
17206                   The ARMv8.1-A Advanced SIMD and floating-point
17207                   instructions.
17208
17209               +crypto
17210                   The cryptographic instructions.  This also enables the
17211                   Advanced SIMD and floating-point instructions.
17212
17213               +dotprod
17214                   Enable the Dot Product extension.  This also enables
17215                   Advanced SIMD instructions.
17216
17217               +nocrypto
17218                   Disable the cryptographic extension.
17219
17220               +nofp
17221                   Disable the floating-point, Advanced SIMD and cryptographic
17222                   instructions.
17223
17224               +sb Speculation Barrier Instruction.
17225
17226               +predres
17227                   Execution and Data Prediction Restriction Instructions.
17228
17229               +i8mm
17230                   8-bit Integer Matrix Multiply instructions.  This also
17231                   enables Advanced SIMD and floating-point instructions.
17232
17233               +bf16
17234                   Brain half-precision floating-point instructions.  This
17235                   also enables Advanced SIMD and floating-point instructions.
17236
17237           armv8.4-a
17238               +fp16
17239                   The half-precision floating-point data processing
17240                   instructions.  This also enables the Advanced SIMD and
17241                   floating-point instructions as well as the Dot Product
17242                   extension and the half-precision floating-point fmla
17243                   extension.
17244
17245               +simd
17246                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17247                   as well as the Dot Product extension.
17248
17249               +crypto
17250                   The cryptographic instructions.  This also enables the
17251                   Advanced SIMD and floating-point instructions as well as
17252                   the Dot Product extension.
17253
17254               +nocrypto
17255                   Disable the cryptographic extension.
17256
17257               +nofp
17258                   Disable the floating-point, Advanced SIMD and cryptographic
17259                   instructions.
17260
17261               +sb Speculation Barrier Instruction.
17262
17263               +predres
17264                   Execution and Data Prediction Restriction Instructions.
17265
17266               +i8mm
17267                   8-bit Integer Matrix Multiply instructions.  This also
17268                   enables Advanced SIMD and floating-point instructions.
17269
17270               +bf16
17271                   Brain half-precision floating-point instructions.  This
17272                   also enables Advanced SIMD and floating-point instructions.
17273
17274           armv8.5-a
17275               +fp16
17276                   The half-precision floating-point data processing
17277                   instructions.  This also enables the Advanced SIMD and
17278                   floating-point instructions as well as the Dot Product
17279                   extension and the half-precision floating-point fmla
17280                   extension.
17281
17282               +simd
17283                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17284                   as well as the Dot Product extension.
17285
17286               +crypto
17287                   The cryptographic instructions.  This also enables the
17288                   Advanced SIMD and floating-point instructions as well as
17289                   the Dot Product extension.
17290
17291               +nocrypto
17292                   Disable the cryptographic extension.
17293
17294               +nofp
17295                   Disable the floating-point, Advanced SIMD and cryptographic
17296                   instructions.
17297
17298               +i8mm
17299                   8-bit Integer Matrix Multiply instructions.  This also
17300                   enables Advanced SIMD and floating-point instructions.
17301
17302               +bf16
17303                   Brain half-precision floating-point instructions.  This
17304                   also enables Advanced SIMD and floating-point instructions.
17305
17306           armv8.6-a
17307               +fp16
17308                   The half-precision floating-point data processing
17309                   instructions.  This also enables the Advanced SIMD and
17310                   floating-point instructions as well as the Dot Product
17311                   extension and the half-precision floating-point fmla
17312                   extension.
17313
17314               +simd
17315                   The ARMv8.3-A Advanced SIMD and floating-point instructions
17316                   as well as the Dot Product extension.
17317
17318               +crypto
17319                   The cryptographic instructions.  This also enables the
17320                   Advanced SIMD and floating-point instructions as well as
17321                   the Dot Product extension.
17322
17323               +nocrypto
17324                   Disable the cryptographic extension.
17325
17326               +nofp
17327                   Disable the floating-point, Advanced SIMD and cryptographic
17328                   instructions.
17329
17330               +i8mm
17331                   8-bit Integer Matrix Multiply instructions.  This also
17332                   enables Advanced SIMD and floating-point instructions.
17333
17334               +bf16
17335                   Brain half-precision floating-point instructions.  This
17336                   also enables Advanced SIMD and floating-point instructions.
17337
17338           armv7-r
17339               +fp.sp
17340                   The single-precision VFPv3 floating-point instructions.
17341                   The extension +vfpv3xd can be used as an alias for this
17342                   extension.
17343
17344               +fp The VFPv3 floating-point instructions with 16 double-
17345                   precision registers.  The extension +vfpv3-d16 can be used
17346                   as an alias for this extension.
17347
17348               +vfpv3xd-d16-fp16
17349                   The single-precision VFPv3 floating-point instructions with
17350                   16 double-precision registers and the half-precision
17351                   floating-point conversion operations.
17352
17353               +vfpv3-d16-fp16
17354                   The VFPv3 floating-point instructions with 16 double-
17355                   precision registers and the half-precision floating-point
17356                   conversion operations.
17357
17358               +nofp
17359                   Disable the floating-point extension.
17360
17361               +idiv
17362                   The ARM-state integer division instructions.
17363
17364               +noidiv
17365                   Disable the ARM-state integer division extension.
17366
17367           armv7e-m
17368               +fp The single-precision VFPv4 floating-point instructions.
17369
17370               +fpv5
17371                   The single-precision FPv5 floating-point instructions.
17372
17373               +fp.dp
17374                   The single- and double-precision FPv5 floating-point
17375                   instructions.
17376
17377               +nofp
17378                   Disable the floating-point extensions.
17379
17380           armv8.1-m.main
17381               +dsp
17382                   The DSP instructions.
17383
17384               +mve
17385                   The M-Profile Vector Extension (MVE) integer instructions.
17386
17387               +mve.fp
17388                   The M-Profile Vector Extension (MVE) integer and single
17389                   precision floating-point instructions.
17390
17391               +fp The single-precision floating-point instructions.
17392
17393               +fp.dp
17394                   The single- and double-precision floating-point
17395                   instructions.
17396
17397               +nofp
17398                   Disable the floating-point extension.
17399
17400               +cdecp0, +cdecp1, ... , +cdecp7
17401                   Enable the Custom Datapath Extension (CDE) on selected
17402                   coprocessors according to the numbers given in the options
17403                   in the range 0 to 7.
17404
17405           armv8-m.main
17406               +dsp
17407                   The DSP instructions.
17408
17409               +nodsp
17410                   Disable the DSP extension.
17411
17412               +fp The single-precision floating-point instructions.
17413
17414               +fp.dp
17415                   The single- and double-precision floating-point
17416                   instructions.
17417
17418               +nofp
17419                   Disable the floating-point extension.
17420
17421               +cdecp0, +cdecp1, ... , +cdecp7
17422                   Enable the Custom Datapath Extension (CDE) on selected
17423                   coprocessors according to the numbers given in the options
17424                   in the range 0 to 7.
17425
17426           armv8-r
17427               +crc
17428                   The Cyclic Redundancy Check (CRC) instructions.
17429
17430               +fp.sp
17431                   The single-precision FPv5 floating-point instructions.
17432
17433               +simd
17434                   The ARMv8-A Advanced SIMD and floating-point instructions.
17435
17436               +crypto
17437                   The cryptographic instructions.
17438
17439               +nocrypto
17440                   Disable the cryptographic instructions.
17441
17442               +nofp
17443                   Disable the floating-point, Advanced SIMD and cryptographic
17444                   instructions.
17445
17446           -march=native causes the compiler to auto-detect the architecture
17447           of the build computer.  At present, this feature is only supported
17448           on GNU/Linux, and not all architectures are recognized.  If the
17449           auto-detect is unsuccessful the option has no effect.
17450
17451       -mtune=name
17452           This option specifies the name of the target ARM processor for
17453           which GCC should tune the performance of the code.  For some ARM
17454           implementations better performance can be obtained by using this
17455           option.  Permissible names are: arm7tdmi, arm7tdmi-s, arm710t,
17456           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
17457           0strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t,
17458           arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t,
17459           arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e,
17460           arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp,
17461           arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s,
17462           generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9,
17463           cortex-a12, cortex-a15, cortex-a17, cortex-a32, cortex-a35,
17464           cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73,
17465           cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a78,
17466           cortex-a78ae, cortex-a78c, ares, cortex-r4, cortex-r4f, cortex-r5,
17467           cortex-r7, cortex-r8, cortex-r52, cortex-m0, cortex-m0plus,
17468           cortex-m1, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33,
17469           cortex-m35p, cortex-m55, cortex-x1, cortex-m1.small-multiply,
17470           cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1,
17471           marvell-pj4, neoverse-n1, neoverse-n2, neoverse-v1, xscale, iwmmxt,
17472           iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te,
17473           xgene1.
17474
17475           Additionally, this option can specify that GCC should tune the
17476           performance of the code for a big.LITTLE system.  Permissible names
17477           are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
17478           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
17479           cortex-a72.cortex-a35, cortex-a73.cortex-a53,
17480           cortex-a75.cortex-a55, cortex-a76.cortex-a55.
17481
17482           -mtune=generic-arch specifies that GCC should tune the performance
17483           for a blend of processors within architecture arch.  The aim is to
17484           generate code that run well on the current most popular processors,
17485           balancing between optimizations that benefit some CPUs in the
17486           range, and avoiding performance pitfalls of other CPUs.  The
17487           effects of this option may change in future GCC versions as CPU
17488           models come and go.
17489
17490           -mtune permits the same extension options as -mcpu, but the
17491           extension options do not affect the tuning of the generated code.
17492
17493           -mtune=native causes the compiler to auto-detect the CPU of the
17494           build computer.  At present, this feature is only supported on
17495           GNU/Linux, and not all architectures are recognized.  If the auto-
17496           detect is unsuccessful the option has no effect.
17497
17498       -mcpu=name[+extension...]
17499           This specifies the name of the target ARM processor.  GCC uses this
17500           name to derive the name of the target ARM architecture (as if
17501           specified by -march) and the ARM processor type for which to tune
17502           for performance (as if specified by -mtune).  Where this option is
17503           used in conjunction with -march or -mtune, those options take
17504           precedence over the appropriate part of this option.
17505
17506           Many of the supported CPUs implement optional architectural
17507           extensions.  Where this is so the architectural extensions are
17508           normally enabled by default.  If implementations that lack the
17509           extension exist, then the extension syntax can be used to disable
17510           those extensions that have been omitted.  For floating-point and
17511           Advanced SIMD (Neon) instructions, the settings of the options
17512           -mfloat-abi and -mfpu must also be considered: floating-point and
17513           Advanced SIMD instructions will only be used if -mfloat-abi is not
17514           set to soft; and any setting of -mfpu other than auto will override
17515           the available floating-point and SIMD extension instructions.
17516
17517           For example, cortex-a9 can be found in three major configurations:
17518           integer only, with just a floating-point unit or with floating-
17519           point and Advanced SIMD.  The default is to enable all the
17520           instructions, but the extensions +nosimd and +nofp can be used to
17521           disable just the SIMD or both the SIMD and floating-point
17522           instructions respectively.
17523
17524           Permissible names for this option are the same as those for -mtune.
17525
17526           The following extension options are common to the listed CPUs:
17527
17528           +nodsp
17529               Disable the DSP instructions on cortex-m33, cortex-m35p.
17530
17531           +nofp
17532               Disables the floating-point instructions on arm9e, arm946e-s,
17533               arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
17534               arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
17535               cortex-m7, cortex-m33 and cortex-m35p.  Disables the floating-
17536               point and SIMD instructions on generic-armv7-a, cortex-a5,
17537               cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
17538               cortex-a17, cortex-a15.cortex-a7, cortex-a17.cortex-a7,
17539               cortex-a32, cortex-a35, cortex-a53 and cortex-a55.
17540
17541           +nofp.dp
17542               Disables the double-precision component of the floating-point
17543               instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52 and
17544               cortex-m7.
17545
17546           +nosimd
17547               Disables the SIMD (but not floating-point) instructions on
17548               generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.
17549
17550           +crypto
17551               Enables the cryptographic instructions on cortex-a32,
17552               cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
17553               cortex-a73, cortex-a75, exynos-m1, xgene1,
17554               cortex-a57.cortex-a53, cortex-a72.cortex-a53,
17555               cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
17556               cortex-a75.cortex-a55.
17557
17558           Additionally the generic-armv7-a pseudo target defaults to VFPv3
17559           with 16 double-precision registers.  It supports the following
17560           extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16,
17561           vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
17562           neon-vfpv4.  The meanings are the same as for the extensions to
17563           -march=armv7-a.
17564
17565           -mcpu=generic-arch is also permissible, and is equivalent to
17566           -march=arch -mtune=generic-arch.  See -mtune for more information.
17567
17568           -mcpu=native causes the compiler to auto-detect the CPU of the
17569           build computer.  At present, this feature is only supported on
17570           GNU/Linux, and not all architectures are recognized.  If the auto-
17571           detect is unsuccessful the option has no effect.
17572
17573       -mfpu=name
17574           This specifies what floating-point hardware (or hardware emulation)
17575           is available on the target.  Permissible names are: auto, vfpv2,
17576           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
17577           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
17578           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
17579           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
17580           and vfp is an alias for vfpv2.
17581
17582           The setting auto is the default and is special.  It causes the
17583           compiler to select the floating-point and Advanced SIMD
17584           instructions based on the settings of -mcpu and -march.
17585
17586           If the selected floating-point hardware includes the NEON extension
17587           (e.g. -mfpu=neon), note that floating-point operations are not
17588           generated by GCC's auto-vectorization pass unless
17589           -funsafe-math-optimizations is also specified.  This is because
17590           NEON hardware does not fully implement the IEEE 754 standard for
17591           floating-point arithmetic (in particular denormal values are
17592           treated as zero), so the use of NEON instructions may lead to a
17593           loss of precision.
17594
17595           You can also set the fpu name at function level by using the
17596           "target("fpu=")" function attributes or pragmas.
17597
17598       -mfp16-format=name
17599           Specify the format of the "__fp16" half-precision floating-point
17600           type.  Permissible names are none, ieee, and alternative; the
17601           default is none, in which case the "__fp16" type is not defined.
17602
17603       -mstructure-size-boundary=n
17604           The sizes of all structures and unions are rounded up to a multiple
17605           of the number of bits set by this option.  Permissible values are
17606           8, 32 and 64.  The default value varies for different toolchains.
17607           For the COFF targeted toolchain the default value is 8.  A value of
17608           64 is only allowed if the underlying ABI supports it.
17609
17610           Specifying a larger number can produce faster, more efficient code,
17611           but can also increase the size of the program.  Different values
17612           are potentially incompatible.  Code compiled with one value cannot
17613           necessarily expect to work with code or libraries compiled with
17614           another value, if they exchange information using structures or
17615           unions.
17616
17617           This option is deprecated.
17618
17619       -mabort-on-noreturn
17620           Generate a call to the function "abort" at the end of a "noreturn"
17621           function.  It is executed if the function tries to return.
17622
17623       -mlong-calls
17624       -mno-long-calls
17625           Tells the compiler to perform function calls by first loading the
17626           address of the function into a register and then performing a
17627           subroutine call on this register.  This switch is needed if the
17628           target function lies outside of the 64-megabyte addressing range of
17629           the offset-based version of subroutine call instruction.
17630
17631           Even if this switch is enabled, not all function calls are turned
17632           into long calls.  The heuristic is that static functions, functions
17633           that have the "short_call" attribute, functions that are inside the
17634           scope of a "#pragma no_long_calls" directive, and functions whose
17635           definitions have already been compiled within the current
17636           compilation unit are not turned into long calls.  The exceptions to
17637           this rule are that weak function definitions, functions with the
17638           "long_call" attribute or the "section" attribute, and functions
17639           that are within the scope of a "#pragma long_calls" directive are
17640           always turned into long calls.
17641
17642           This feature is not enabled by default.  Specifying -mno-long-calls
17643           restores the default behavior, as does placing the function calls
17644           within the scope of a "#pragma long_calls_off" directive.  Note
17645           these switches have no effect on how the compiler generates code to
17646           handle function calls via function pointers.
17647
17648       -msingle-pic-base
17649           Treat the register used for PIC addressing as read-only, rather
17650           than loading it in the prologue for each function.  The runtime
17651           system is responsible for initializing this register with an
17652           appropriate value before execution begins.
17653
17654       -mpic-register=reg
17655           Specify the register to be used for PIC addressing.  For standard
17656           PIC base case, the default is any suitable register determined by
17657           compiler.  For single PIC base case, the default is R9 if target is
17658           EABI based or stack-checking is enabled, otherwise the default is
17659           R10.
17660
17661       -mpic-data-is-text-relative
17662           Assume that the displacement between the text and data segments is
17663           fixed at static link time.  This permits using PC-relative
17664           addressing operations to access data known to be in the data
17665           segment.  For non-VxWorks RTP targets, this option is enabled by
17666           default.  When disabled on such targets, it will enable
17667           -msingle-pic-base by default.
17668
17669       -mpoke-function-name
17670           Write the name of each function into the text section, directly
17671           preceding the function prologue.  The generated code is similar to
17672           this:
17673
17674                        t0
17675                            .ascii "arm_poke_function_name", 0
17676                            .align
17677                        t1
17678                            .word 0xff000000 + (t1 - t0)
17679                        arm_poke_function_name
17680                            mov     ip, sp
17681                            stmfd   sp!, {fp, ip, lr, pc}
17682                            sub     fp, ip, #4
17683
17684           When performing a stack backtrace, code can inspect the value of
17685           "pc" stored at "fp + 0".  If the trace function then looks at
17686           location "pc - 12" and the top 8 bits are set, then we know that
17687           there is a function name embedded immediately preceding this
17688           location and has length "((pc[-3]) & 0xff000000)".
17689
17690       -mthumb
17691       -marm
17692           Select between generating code that executes in ARM and Thumb
17693           states.  The default for most configurations is to generate code
17694           that executes in ARM state, but the default can be changed by
17695           configuring GCC with the --with-mode=state configure option.
17696
17697           You can also override the ARM and Thumb mode for each function by
17698           using the "target("thumb")" and "target("arm")" function attributes
17699           or pragmas.
17700
17701       -mflip-thumb
17702           Switch ARM/Thumb modes on alternating functions.  This option is
17703           provided for regression testing of mixed Thumb/ARM code generation,
17704           and is not intended for ordinary use in compiling code.
17705
17706       -mtpcs-frame
17707           Generate a stack frame that is compliant with the Thumb Procedure
17708           Call Standard for all non-leaf functions.  (A leaf function is one
17709           that does not call any other functions.)  The default is
17710           -mno-tpcs-frame.
17711
17712       -mtpcs-leaf-frame
17713           Generate a stack frame that is compliant with the Thumb Procedure
17714           Call Standard for all leaf functions.  (A leaf function is one that
17715           does not call any other functions.)  The default is
17716           -mno-apcs-leaf-frame.
17717
17718       -mcallee-super-interworking
17719           Gives all externally visible functions in the file being compiled
17720           an ARM instruction set header which switches to Thumb mode before
17721           executing the rest of the function.  This allows these functions to
17722           be called from non-interworking code.  This option is not valid in
17723           AAPCS configurations because interworking is enabled by default.
17724
17725       -mcaller-super-interworking
17726           Allows calls via function pointers (including virtual functions) to
17727           execute correctly regardless of whether the target code has been
17728           compiled for interworking or not.  There is a small overhead in the
17729           cost of executing a function pointer if this option is enabled.
17730           This option is not valid in AAPCS configurations because
17731           interworking is enabled by default.
17732
17733       -mtp=name
17734           Specify the access model for the thread local storage pointer.  The
17735           valid models are soft, which generates calls to "__aeabi_read_tp",
17736           cp15, which fetches the thread pointer from "cp15" directly
17737           (supported in the arm6k architecture), and auto, which uses the
17738           best available method for the selected processor.  The default
17739           setting is auto.
17740
17741       -mtls-dialect=dialect
17742           Specify the dialect to use for accessing thread local storage.  Two
17743           dialects are supported---gnu and gnu2.  The gnu dialect selects the
17744           original GNU scheme for supporting local and global dynamic TLS
17745           models.  The gnu2 dialect selects the GNU descriptor scheme, which
17746           provides better performance for shared libraries.  The GNU
17747           descriptor scheme is compatible with the original scheme, but does
17748           require new assembler, linker and library support.  Initial and
17749           local exec TLS models are unaffected by this option and always use
17750           the original scheme.
17751
17752       -mword-relocations
17753           Only generate absolute relocations on word-sized values (i.e.
17754           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
17755           SymbianOS) where the runtime loader imposes this restriction, and
17756           when -fpic or -fPIC is specified. This option conflicts with
17757           -mslow-flash-data.
17758
17759       -mfix-cortex-m3-ldrd
17760           Some Cortex-M3 cores can cause data corruption when "ldrd"
17761           instructions with overlapping destination and base registers are
17762           used.  This option avoids generating these instructions.  This
17763           option is enabled by default when -mcpu=cortex-m3 is specified.
17764
17765       -munaligned-access
17766       -mno-unaligned-access
17767           Enables (or disables) reading and writing of 16- and 32- bit values
17768           from addresses that are not 16- or 32- bit aligned.  By default
17769           unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
17770           ARMv8-M Baseline architectures, and enabled for all other
17771           architectures.  If unaligned access is not enabled then words in
17772           packed data structures are accessed a byte at a time.
17773
17774           The ARM attribute "Tag_CPU_unaligned_access" is set in the
17775           generated object file to either true or false, depending upon the
17776           setting of this option.  If unaligned access is enabled then the
17777           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.
17778
17779       -mneon-for-64bits
17780           This option is deprecated and has no effect.
17781
17782       -mslow-flash-data
17783           Assume loading data from flash is slower than fetching instruction.
17784           Therefore literal load is minimized for better performance.  This
17785           option is only supported when compiling for ARMv7 M-profile and off
17786           by default. It conflicts with -mword-relocations.
17787
17788       -masm-syntax-unified
17789           Assume inline assembler is using unified asm syntax.  The default
17790           is currently off which implies divided syntax.  This option has no
17791           impact on Thumb2. However, this may change in future releases of
17792           GCC.  Divided syntax should be considered deprecated.
17793
17794       -mrestrict-it
17795           Restricts generation of IT blocks to conform to the rules of
17796           ARMv8-A.  IT blocks can only contain a single 16-bit instruction
17797           from a select set of instructions. This option is on by default for
17798           ARMv8-A Thumb mode.
17799
17800       -mprint-tune-info
17801           Print CPU tuning information as comment in assembler file.  This is
17802           an option used only for regression testing of the compiler and not
17803           intended for ordinary use in compiling code.  This option is
17804           disabled by default.
17805
17806       -mverbose-cost-dump
17807           Enable verbose cost model dumping in the debug dump files.  This
17808           option is provided for use in debugging the compiler.
17809
17810       -mpure-code
17811           Do not allow constant data to be placed in code sections.
17812           Additionally, when compiling for ELF object format give all text
17813           sections the ELF processor-specific section attribute
17814           "SHF_ARM_PURECODE".  This option is only available when generating
17815           non-pic code for M-profile targets.
17816
17817       -mcmse
17818           Generate secure code as per the "ARMv8-M Security Extensions:
17819           Requirements on Development Tools Engineering Specification", which
17820           can be found on
17821           <https://developer.arm.com/documentation/ecm0359818/latest/>.
17822
17823       -mfdpic
17824       -mno-fdpic
17825           Select the FDPIC ABI, which uses 64-bit function descriptors to
17826           represent pointers to functions.  When the compiler is configured
17827           for "arm-*-uclinuxfdpiceabi" targets, this option is on by default
17828           and implies -fPIE if none of the PIC/PIE-related options is
17829           provided.  On other targets, it only enables the FDPIC-specific
17830           code generation features, and the user should explicitly provide
17831           the PIC/PIE-related options as needed.
17832
17833           Note that static linking is not supported because it would still
17834           involve the dynamic linker when the program self-relocates.  If
17835           such behavior is acceptable, use -static and -Wl,-dynamic-linker
17836           options.
17837
17838           The opposite -mno-fdpic option is useful (and required) to build
17839           the Linux kernel using the same ("arm-*-uclinuxfdpiceabi")
17840           toolchain as the one used to build the userland programs.
17841
17842       AVR Options
17843
17844       These options are defined for AVR implementations:
17845
17846       -mmcu=mcu
17847           Specify Atmel AVR instruction set architectures (ISA) or MCU type.
17848
17849           The default for this option is avr2.
17850
17851           GCC supports the following AVR devices and ISAs:
17852
17853           "avr2"
17854               "Classic" devices with up to 8 KiB of program memory.  mcu =
17855               "attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333",
17856               "at90s2343", "at90s4414", "at90s4433", "at90s4434",
17857               "at90c8534", "at90s8515", "at90s8535".
17858
17859           "avr25"
17860               "Classic" devices with up to 8 KiB of program memory and with
17861               the "MOVW" instruction.  mcu = "attiny13", "attiny13a",
17862               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
17863               "attiny2313", "attiny2313a", "attiny43u", "attiny44",
17864               "attiny44a", "attiny45", "attiny48", "attiny441", "attiny461",
17865               "attiny461a", "attiny4313", "attiny84", "attiny84a",
17866               "attiny85", "attiny87", "attiny88", "attiny828", "attiny841",
17867               "attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401".
17868
17869           "avr3"
17870               "Classic" devices with 16 KiB up to 64 KiB of program memory.
17871               mcu = "at76c711", "at43usb355".
17872
17873           "avr31"
17874               "Classic" devices with 128 KiB of program memory.  mcu =
17875               "atmega103", "at43usb320".
17876
17877           "avr35"
17878               "Classic" devices with 16 KiB up to 64 KiB of program memory
17879               and with the "MOVW" instruction.  mcu = "attiny167",
17880               "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2",
17881               "ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162".
17882
17883           "avr4"
17884               "Enhanced" devices with up to 8 KiB of program memory.  mcu =
17885               "atmega48", "atmega48a", "atmega48p", "atmega48pa",
17886               "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88",
17887               "atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
17888               "atmega8515", "atmega8535", "ata6285", "ata6286", "ata6289",
17889               "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3",
17890               "at90pwm3b", "at90pwm81".
17891
17892           "avr5"
17893               "Enhanced" devices with 16 KiB up to 64 KiB of program memory.
17894               mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
17895               "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
17896               "atmega161", "atmega162", "atmega163", "atmega164a",
17897               "atmega164p", "atmega164pa", "atmega165", "atmega165a",
17898               "atmega165p", "atmega165pa", "atmega168", "atmega168a",
17899               "atmega168p", "atmega168pa", "atmega168pb", "atmega169",
17900               "atmega169a", "atmega169p", "atmega169pa", "atmega32",
17901               "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
17902               "atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
17903               "atmega324a", "atmega324p", "atmega324pa", "atmega325",
17904               "atmega325a", "atmega325p", "atmega325pa", "atmega328",
17905               "atmega328p", "atmega328pb", "atmega329", "atmega329a",
17906               "atmega329p", "atmega329pa", "atmega3250", "atmega3250a",
17907               "atmega3250p", "atmega3250pa", "atmega3290", "atmega3290a",
17908               "atmega3290p", "atmega3290pa", "atmega406", "atmega64",
17909               "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2",
17910               "atmega64m1", "atmega64rfr2", "atmega640", "atmega644",
17911               "atmega644a", "atmega644p", "atmega644pa", "atmega644rfr2",
17912               "atmega645", "atmega645a", "atmega645p", "atmega649",
17913               "atmega649a", "atmega649p", "atmega6450", "atmega6450a",
17914               "atmega6450p", "atmega6490", "atmega6490a", "atmega6490p",
17915               "ata5795", "ata5790", "ata5790n", "ata5791", "ata6613c",
17916               "ata6614q", "ata5782", "ata5831", "ata8210", "ata8510",
17917               "ata5702m322", "at90pwm161", "at90pwm216", "at90pwm316",
17918               "at90can32", "at90can64", "at90scr100", "at90usb646",
17919               "at90usb647", "at94k", "m3000".
17920
17921           "avr51"
17922               "Enhanced" devices with 128 KiB of program memory.  mcu =
17923               "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2",
17924               "atmega1280", "atmega1281", "atmega1284", "atmega1284p",
17925               "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".
17926
17927           "avr6"
17928               "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
17929               of program memory.  mcu = "atmega256rfr2", "atmega2560",
17930               "atmega2561", "atmega2564rfr2".
17931
17932           "avrxmega2"
17933               "XMEGA" devices with more than 8 KiB and up to 64 KiB of
17934               program memory.  mcu = "atxmega8e5", "atxmega16a4",
17935               "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5",
17936               "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
17937               "atxmega32d3", "atxmega32d4", "atxmega32e5".
17938
17939           "avrxmega3"
17940               "XMEGA" devices with up to 64 KiB of combined program memory
17941               and RAM, and with program memory visible in the RAM address
17942               space.  mcu = "attiny202", "attiny204", "attiny212",
17943               "attiny214", "attiny402", "attiny404", "attiny406",
17944               "attiny412", "attiny414", "attiny416", "attiny417",
17945               "attiny804", "attiny806", "attiny807", "attiny814",
17946               "attiny816", "attiny817", "attiny1604", "attiny1606",
17947               "attiny1607", "attiny1614", "attiny1616", "attiny1617",
17948               "attiny3214", "attiny3216", "attiny3217", "atmega808",
17949               "atmega809", "atmega1608", "atmega1609", "atmega3208",
17950               "atmega3209", "atmega4808", "atmega4809".
17951
17952           "avrxmega4"
17953               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
17954               program memory.  mcu = "atxmega64a3", "atxmega64a3u",
17955               "atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3",
17956               "atxmega64d3", "atxmega64d4".
17957
17958           "avrxmega5"
17959               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
17960               program memory and more than 64 KiB of RAM.  mcu =
17961               "atxmega64a1", "atxmega64a1u".
17962
17963           "avrxmega6"
17964               "XMEGA" devices with more than 128 KiB of program memory.  mcu
17965               = "atxmega128a3", "atxmega128a3u", "atxmega128b1",
17966               "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
17967               "atxmega192a3", "atxmega192a3u", "atxmega192c3",
17968               "atxmega192d3", "atxmega256a3", "atxmega256a3b",
17969               "atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
17970               "atxmega256d3", "atxmega384c3", "atxmega384d3".
17971
17972           "avrxmega7"
17973               "XMEGA" devices with more than 128 KiB of program memory and
17974               more than 64 KiB of RAM.  mcu = "atxmega128a1",
17975               "atxmega128a1u", "atxmega128a4u".
17976
17977           "avrtiny"
17978               "TINY" Tiny core devices with 512 B up to 4 KiB of program
17979               memory.  mcu = "attiny4", "attiny5", "attiny9", "attiny10",
17980               "attiny20", "attiny40".
17981
17982           "avr1"
17983               This ISA is implemented by the minimal AVR core and supported
17984               for assembler only.  mcu = "attiny11", "attiny12", "attiny15",
17985               "attiny28", "at90s1200".
17986
17987       -mabsdata
17988           Assume that all data in static storage can be accessed by LDS / STS
17989           instructions.  This option has only an effect on reduced Tiny
17990           devices like ATtiny40.  See also the "absdata" AVR Variable
17991           Attributes,variable attribute.
17992
17993       -maccumulate-args
17994           Accumulate outgoing function arguments and acquire/release the
17995           needed stack space for outgoing function arguments once in function
17996           prologue/epilogue.  Without this option, outgoing arguments are
17997           pushed before calling a function and popped afterwards.
17998
17999           Popping the arguments after the function call can be expensive on
18000           AVR so that accumulating the stack space might lead to smaller
18001           executables because arguments need not be removed from the stack
18002           after such a function call.
18003
18004           This option can lead to reduced code size for functions that
18005           perform several calls to functions that get their arguments on the
18006           stack like calls to printf-like functions.
18007
18008       -mbranch-cost=cost
18009           Set the branch costs for conditional branch instructions to cost.
18010           Reasonable values for cost are small, non-negative integers. The
18011           default branch cost is 0.
18012
18013       -mcall-prologues
18014           Functions prologues/epilogues are expanded as calls to appropriate
18015           subroutines.  Code size is smaller.
18016
18017       -mdouble=bits
18018       -mlong-double=bits
18019           Set the size (in bits) of the "double" or "long double" type,
18020           respectively.  Possible values for bits are 32 and 64.  Whether or
18021           not a specific value for bits is allowed depends on the
18022           "--with-double=" and "--with-long-double=" configure options
18023           ("https://gcc.gnu.org/install/configure.html#avr"), and the same
18024           applies for the default values of the options.
18025
18026       -mgas-isr-prologues
18027           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo
18028           instruction supported by GNU Binutils.  If this option is on, the
18029           feature can still be disabled for individual ISRs by means of the
18030           AVR Function Attributes,,"no_gccisr" function attribute.  This
18031           feature is activated per default if optimization is on (but not
18032           with -Og, @pxref{Optimize Options}), and if GNU Binutils support
18033           PR21683 ("https://sourceware.org/PR21683").
18034
18035       -mint8
18036           Assume "int" to be 8-bit integer.  This affects the sizes of all
18037           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
18038           and "long long" is 4 bytes.  Please note that this option does not
18039           conform to the C standards, but it results in smaller code size.
18040
18041       -mmain-is-OS_task
18042           Do not save registers in "main".  The effect is the same like
18043           attaching attribute AVR Function Attributes,,"OS_task" to "main".
18044           It is activated per default if optimization is on.
18045
18046       -mn-flash=num
18047           Assume that the flash memory has a size of num times 64 KiB.
18048
18049       -mno-interrupts
18050           Generated code is not compatible with hardware interrupts.  Code
18051           size is smaller.
18052
18053       -mrelax
18054           Try to replace "CALL" resp. "JMP" instruction by the shorter
18055           "RCALL" resp. "RJMP" instruction if applicable.  Setting -mrelax
18056           just adds the --mlink-relax option to the assembler's command line
18057           and the --relax option to the linker's command line.
18058
18059           Jump relaxing is performed by the linker because jump offsets are
18060           not known before code is located. Therefore, the assembler code
18061           generated by the compiler is the same, but the instructions in the
18062           executable may differ from instructions in the assembler code.
18063
18064           Relaxing must be turned on if linker stubs are needed, see the
18065           section on "EIND" and linker stubs below.
18066
18067       -mrmw
18068           Assume that the device supports the Read-Modify-Write instructions
18069           "XCH", "LAC", "LAS" and "LAT".
18070
18071       -mshort-calls
18072           Assume that "RJMP" and "RCALL" can target the whole program memory.
18073
18074           This option is used internally for multilib selection.  It is not
18075           an optimization option, and you don't need to set it by hand.
18076
18077       -msp8
18078           Treat the stack pointer register as an 8-bit register, i.e. assume
18079           the high byte of the stack pointer is zero.  In general, you don't
18080           need to set this option by hand.
18081
18082           This option is used internally by the compiler to select and build
18083           multilibs for architectures "avr2" and "avr25".  These
18084           architectures mix devices with and without "SPH".  For any setting
18085           other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or
18086           removes this option from the compiler proper's command line,
18087           because the compiler then knows if the device or architecture has
18088           an 8-bit stack pointer and thus no "SPH" register or not.
18089
18090       -mstrict-X
18091           Use address register "X" in a way proposed by the hardware.  This
18092           means that "X" is only used in indirect, post-increment or pre-
18093           decrement addressing.
18094
18095           Without this option, the "X" register may be used in the same way
18096           as "Y" or "Z" which then is emulated by additional instructions.
18097           For example, loading a value with "X+const" addressing with a small
18098           non-negative "const < 64" to a register Rn is performed as
18099
18100                   adiw r26, const   ; X += const
18101                   ld   <Rn>, X        ; <Rn> = *X
18102                   sbiw r26, const   ; X -= const
18103
18104       -mtiny-stack
18105           Only change the lower 8 bits of the stack pointer.
18106
18107       -mfract-convert-truncate
18108           Allow to use truncation instead of rounding towards zero for
18109           fractional fixed-point types.
18110
18111       -nodevicelib
18112           Don't link against AVR-LibC's device specific library "lib<mcu>.a".
18113
18114       -nodevicespecs
18115           Don't add -specs=device-specs/specs-mcu to the compiler driver's
18116           command line.  The user takes responsibility for supplying the sub-
18117           processes like compiler proper, assembler and linker with
18118           appropriate command line options.  This means that the user has to
18119           supply her private device specs file by means of -specs=path-to-
18120           specs-file.  There is no more need for option -mmcu=mcu.
18121
18122           This option can also serve as a replacement for the older way of
18123           specifying custom device-specs files that needed -B some-path to
18124           point to a directory which contains a folder named "device-specs"
18125           which contains a specs file named "specs-mcu", where mcu was
18126           specified by -mmcu=mcu.
18127
18128       -Waddr-space-convert
18129           Warn about conversions between address spaces in the case where the
18130           resulting address space is not contained in the incoming address
18131           space.
18132
18133       -Wmisspelled-isr
18134           Warn if the ISR is misspelled, i.e. without __vector prefix.
18135           Enabled by default.
18136
18137       "EIND" and Devices with More Than 128 Ki Bytes of Flash
18138
18139       Pointers in the implementation are 16 bits wide.  The address of a
18140       function or label is represented as word address so that indirect jumps
18141       and calls can target any code address in the range of 64 Ki words.
18142
18143       In order to facilitate indirect jump on devices with more than 128 Ki
18144       bytes of program memory space, there is a special function register
18145       called "EIND" that serves as most significant part of the target
18146       address when "EICALL" or "EIJMP" instructions are used.
18147
18148       Indirect jumps and calls on these devices are handled as follows by the
18149       compiler and are subject to some limitations:
18150
18151       *   The compiler never sets "EIND".
18152
18153       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
18154           instructions or might read "EIND" directly in order to emulate an
18155           indirect call/jump by means of a "RET" instruction.
18156
18157       *   The compiler assumes that "EIND" never changes during the startup
18158           code or during the application. In particular, "EIND" is not
18159           saved/restored in function or interrupt service routine
18160           prologue/epilogue.
18161
18162       *   For indirect calls to functions and computed goto, the linker
18163           generates stubs. Stubs are jump pads sometimes also called
18164           trampolines. Thus, the indirect call/jump jumps to such a stub.
18165           The stub contains a direct jump to the desired address.
18166
18167       *   Linker relaxation must be turned on so that the linker generates
18168           the stubs correctly in all situations. See the compiler option
18169           -mrelax and the linker option --relax.  There are corner cases
18170           where the linker is supposed to generate stubs but aborts without
18171           relaxation and without a helpful error message.
18172
18173       *   The default linker script is arranged for code with "EIND = 0".  If
18174           code is supposed to work for a setup with "EIND != 0", a custom
18175           linker script has to be used in order to place the sections whose
18176           name start with ".trampolines" into the segment where "EIND" points
18177           to.
18178
18179       *   The startup code from libgcc never sets "EIND".  Notice that
18180           startup code is a blend of code from libgcc and AVR-LibC.  For the
18181           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
18182           ("http://nongnu.org/avr-libc/user-manual/").
18183
18184       *   It is legitimate for user-specific startup code to set up "EIND"
18185           early, for example by means of initialization code located in
18186           section ".init3". Such code runs prior to general startup code that
18187           initializes RAM and calls constructors, but after the bit of
18188           startup code from AVR-LibC that sets "EIND" to the segment where
18189           the vector table is located.
18190
18191                   #include <avr/io.h>
18192
18193                   static void
18194                   __attribute__((section(".init3"),naked,used,no_instrument_function))
18195                   init3_set_eind (void)
18196                   {
18197                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
18198                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
18199                   }
18200
18201           The "__trampolines_start" symbol is defined in the linker script.
18202
18203       *   Stubs are generated automatically by the linker if the following
18204           two conditions are met:
18205
18206           -<The address of a label is taken by means of the "gs" modifier>
18207               (short for generate stubs) like so:
18208
18209                       LDI r24, lo8(gs(<func>))
18210                       LDI r25, hi8(gs(<func>))
18211
18212           -<The final location of that label is in a code segment>
18213               outside the segment where the stubs are located.
18214
18215       *   The compiler emits such "gs" modifiers for code labels in the
18216           following situations:
18217
18218           -<Taking address of a function or code label.>
18219           -<Computed goto.>
18220           -<If prologue-save function is used, see -mcall-prologues>
18221               command-line option.
18222
18223           -<Switch/case dispatch tables. If you do not want such dispatch>
18224               tables you can specify the -fno-jump-tables command-line
18225               option.
18226
18227           -<C and C++ constructors/destructors called during
18228           startup/shutdown.>
18229           -<If the tools hit a "gs()" modifier explained above.>
18230       *   Jumping to non-symbolic addresses like so is not supported:
18231
18232                   int main (void)
18233                   {
18234                       /* Call function at word address 0x2 */
18235                       return ((int(*)(void)) 0x2)();
18236                   }
18237
18238           Instead, a stub has to be set up, i.e. the function has to be
18239           called through a symbol ("func_4" in the example):
18240
18241                   int main (void)
18242                   {
18243                       extern int func_4 (void);
18244
18245                       /* Call function at byte address 0x4 */
18246                       return func_4();
18247                   }
18248
18249           and the application be linked with -Wl,--defsym,func_4=0x4.
18250           Alternatively, "func_4" can be defined in the linker script.
18251
18252       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
18253       Registers
18254
18255       Some AVR devices support memories larger than the 64 KiB range that can
18256       be accessed with 16-bit pointers.  To access memory locations outside
18257       this 64 KiB range, the content of a "RAMP" register is used as high
18258       part of the address: The "X", "Y", "Z" address register is concatenated
18259       with the "RAMPX", "RAMPY", "RAMPZ" special function register,
18260       respectively, to get a wide address. Similarly, "RAMPD" is used
18261       together with direct addressing.
18262
18263       *   The startup code initializes the "RAMP" special function registers
18264           with zero.
18265
18266       *   If a AVR Named Address Spaces,named address space other than
18267           generic or "__flash" is used, then "RAMPZ" is set as needed before
18268           the operation.
18269
18270       *   If the device supports RAM larger than 64 KiB and the compiler
18271           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
18272           reset to zero after the operation.
18273
18274       *   If the device comes with a specific "RAMP" register, the ISR
18275           prologue/epilogue saves/restores that SFR and initializes it with
18276           zero in case the ISR code might (implicitly) use it.
18277
18278       *   RAM larger than 64 KiB is not supported by GCC for AVR targets.  If
18279           you use inline assembler to read from locations outside the 16-bit
18280           address range and change one of the "RAMP" registers, you must
18281           reset it to zero after the access.
18282
18283       AVR Built-in Macros
18284
18285       GCC defines several built-in macros so that the user code can test for
18286       the presence or absence of features.  Almost any of the following
18287       built-in macros are deduced from device capabilities and thus triggered
18288       by the -mmcu= command-line option.
18289
18290       For even more AVR-specific built-in macros see AVR Named Address Spaces
18291       and AVR Built-in Functions.
18292
18293       "__AVR_ARCH__"
18294           Build-in macro that resolves to a decimal number that identifies
18295           the architecture and depends on the -mmcu=mcu option.  Possible
18296           values are:
18297
18298           2, 25, 3, 31, 35, 4, 5, 51, 6
18299
18300           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
18301           "avr51", "avr6",
18302
18303           respectively and
18304
18305           100, 102, 103, 104, 105, 106, 107
18306
18307           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
18308           "avrxmega5", "avrxmega6", "avrxmega7", respectively.  If mcu
18309           specifies a device, this built-in macro is set accordingly. For
18310           example, with -mmcu=atmega8 the macro is defined to 4.
18311
18312       "__AVR_Device__"
18313           Setting -mmcu=device defines this built-in macro which reflects the
18314           device's name. For example, -mmcu=atmega8 defines the built-in
18315           macro "__AVR_ATmega8__", -mmcu=attiny261a defines
18316           "__AVR_ATtiny261A__", etc.
18317
18318           The built-in macros' names follow the scheme "__AVR_Device__" where
18319           Device is the device name as from the AVR user manual. The
18320           difference between Device in the built-in macro and device in
18321           -mmcu=device is that the latter is always lowercase.
18322
18323           If device is not a device but only a core architecture like avr51,
18324           this macro is not defined.
18325
18326       "__AVR_DEVICE_NAME__"
18327           Setting -mmcu=device defines this built-in macro to the device's
18328           name. For example, with -mmcu=atmega8 the macro is defined to
18329           "atmega8".
18330
18331           If device is not a device but only a core architecture like avr51,
18332           this macro is not defined.
18333
18334       "__AVR_XMEGA__"
18335           The device / architecture belongs to the XMEGA family of devices.
18336
18337       "__AVR_HAVE_ELPM__"
18338           The device has the "ELPM" instruction.
18339
18340       "__AVR_HAVE_ELPMX__"
18341           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.
18342
18343       "__AVR_HAVE_MOVW__"
18344           The device has the "MOVW" instruction to perform 16-bit register-
18345           register moves.
18346
18347       "__AVR_HAVE_LPMX__"
18348           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.
18349
18350       "__AVR_HAVE_MUL__"
18351           The device has a hardware multiplier.
18352
18353       "__AVR_HAVE_JMP_CALL__"
18354           The device has the "JMP" and "CALL" instructions.  This is the case
18355           for devices with more than 8 KiB of program memory.
18356
18357       "__AVR_HAVE_EIJMP_EICALL__"
18358       "__AVR_3_BYTE_PC__"
18359           The device has the "EIJMP" and "EICALL" instructions.  This is the
18360           case for devices with more than 128 KiB of program memory.  This
18361           also means that the program counter (PC) is 3 bytes wide.
18362
18363       "__AVR_2_BYTE_PC__"
18364           The program counter (PC) is 2 bytes wide. This is the case for
18365           devices with up to 128 KiB of program memory.
18366
18367       "__AVR_HAVE_8BIT_SP__"
18368       "__AVR_HAVE_16BIT_SP__"
18369           The stack pointer (SP) register is treated as 8-bit respectively
18370           16-bit register by the compiler.  The definition of these macros is
18371           affected by -mtiny-stack.
18372
18373       "__AVR_HAVE_SPH__"
18374       "__AVR_SP8__"
18375           The device has the SPH (high part of stack pointer) special
18376           function register or has an 8-bit stack pointer, respectively.  The
18377           definition of these macros is affected by -mmcu= and in the cases
18378           of -mmcu=avr2 and -mmcu=avr25 also by -msp8.
18379
18380       "__AVR_HAVE_RAMPD__"
18381       "__AVR_HAVE_RAMPX__"
18382       "__AVR_HAVE_RAMPY__"
18383       "__AVR_HAVE_RAMPZ__"
18384           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
18385           function register, respectively.
18386
18387       "__NO_INTERRUPTS__"
18388           This macro reflects the -mno-interrupts command-line option.
18389
18390       "__AVR_ERRATA_SKIP__"
18391       "__AVR_ERRATA_SKIP_JMP_CALL__"
18392           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
18393           instructions because of a hardware erratum.  Skip instructions are
18394           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
18395           only defined if "__AVR_HAVE_JMP_CALL__" is also set.
18396
18397       "__AVR_ISA_RMW__"
18398           The device has Read-Modify-Write instructions (XCH, LAC, LAS and
18399           LAT).
18400
18401       "__AVR_SFR_OFFSET__=offset"
18402           Instructions that can address I/O special function registers
18403           directly like "IN", "OUT", "SBI", etc. may use a different address
18404           as if addressed by an instruction to access RAM like "LD" or "STS".
18405           This offset depends on the device architecture and has to be
18406           subtracted from the RAM address in order to get the respective I/O
18407           address.
18408
18409       "__AVR_SHORT_CALLS__"
18410           The -mshort-calls command line option is set.
18411
18412       "__AVR_PM_BASE_ADDRESS__=addr"
18413           Some devices support reading from flash memory by means of "LD*"
18414           instructions.  The flash memory is seen in the data address space
18415           at an offset of "__AVR_PM_BASE_ADDRESS__".  If this macro is not
18416           defined, this feature is not available.  If defined, the address
18417           space is linear and there is no need to put ".rodata" into RAM.
18418           This is handled by the default linker description file, and is
18419           currently available for "avrtiny" and "avrxmega3".  Even more
18420           convenient, there is no need to use address spaces like "__flash"
18421           or features like attribute "progmem" and "pgm_read_*".
18422
18423       "__WITH_AVRLIBC__"
18424           The compiler is configured to be used together with AVR-Libc.  See
18425           the --with-avrlibc configure option.
18426
18427       "__HAVE_DOUBLE_MULTILIB__"
18428           Defined if -mdouble= acts as a multilib option.
18429
18430       "__HAVE_DOUBLE32__"
18431       "__HAVE_DOUBLE64__"
18432           Defined if the compiler supports 32-bit double resp. 64-bit double.
18433           The actual layout is specified by option -mdouble=.
18434
18435       "__DEFAULT_DOUBLE__"
18436           The size in bits of "double" if -mdouble= is not set.  To test the
18437           layout of "double" in a program, use the built-in macro
18438           "__SIZEOF_DOUBLE__".
18439
18440       "__HAVE_LONG_DOUBLE32__"
18441       "__HAVE_LONG_DOUBLE64__"
18442       "__HAVE_LONG_DOUBLE_MULTILIB__"
18443       "__DEFAULT_LONG_DOUBLE__"
18444           Same as above, but for "long double" instead of "double".
18445
18446       "__WITH_DOUBLE_COMPARISON__"
18447           Reflects the "--with-double-comparison={tristate|bool|libf7}"
18448           configure option ("https://gcc.gnu.org/install/configure.html#avr")
18449           and is defined to 2 or 3.
18450
18451       "__WITH_LIBF7_LIBGCC__"
18452       "__WITH_LIBF7_MATH__"
18453       "__WITH_LIBF7_MATH_SYMBOLS__"
18454           Reflects the "--with-libf7={libgcc|math|math-symbols}"
18455           configure option
18456           ("https://gcc.gnu.org/install/configure.html#avr").
18457
18458       Blackfin Options
18459
18460       -mcpu=cpu[-sirevision]
18461           Specifies the name of the target Blackfin processor.  Currently,
18462           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
18463           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
18464           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
18465           bf547m, bf548m, bf549m, bf561, bf592.
18466
18467           The optional sirevision specifies the silicon revision of the
18468           target Blackfin processor.  Any workarounds available for the
18469           targeted silicon revision are enabled.  If sirevision is none, no
18470           workarounds are enabled.  If sirevision is any, all workarounds for
18471           the targeted processor are enabled.  The "__SILICON_REVISION__"
18472           macro is defined to two hexadecimal digits representing the major
18473           and minor numbers in the silicon revision.  If sirevision is none,
18474           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
18475           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
18476           optional sirevision is not used, GCC assumes the latest known
18477           silicon revision of the targeted Blackfin processor.
18478
18479           GCC defines a preprocessor macro for the specified cpu.  For the
18480           bfin-elf toolchain, this option causes the hardware BSP provided by
18481           libgloss to be linked in if -msim is not given.
18482
18483           Without this option, bf532 is used as the processor by default.
18484
18485           Note that support for bf561 is incomplete.  For bf561, only the
18486           preprocessor macro is defined.
18487
18488       -msim
18489           Specifies that the program will be run on the simulator.  This
18490           causes the simulator BSP provided by libgloss to be linked in.
18491           This option has effect only for bfin-elf toolchain.  Certain other
18492           options, such as -mid-shared-library and -mfdpic, imply -msim.
18493
18494       -momit-leaf-frame-pointer
18495           Don't keep the frame pointer in a register for leaf functions.
18496           This avoids the instructions to save, set up and restore frame
18497           pointers and makes an extra register available in leaf functions.
18498
18499       -mspecld-anomaly
18500           When enabled, the compiler ensures that the generated code does not
18501           contain speculative loads after jump instructions. If this option
18502           is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.
18503
18504       -mno-specld-anomaly
18505           Don't generate extra code to prevent speculative loads from
18506           occurring.
18507
18508       -mcsync-anomaly
18509           When enabled, the compiler ensures that the generated code does not
18510           contain CSYNC or SSYNC instructions too soon after conditional
18511           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
18512           is defined.
18513
18514       -mno-csync-anomaly
18515           Don't generate extra code to prevent CSYNC or SSYNC instructions
18516           from occurring too soon after a conditional branch.
18517
18518       -mlow64k
18519           When enabled, the compiler is free to take advantage of the
18520           knowledge that the entire program fits into the low 64k of memory.
18521
18522       -mno-low64k
18523           Assume that the program is arbitrarily large.  This is the default.
18524
18525       -mstack-check-l1
18526           Do stack checking using information placed into L1 scratchpad
18527           memory by the uClinux kernel.
18528
18529       -mid-shared-library
18530           Generate code that supports shared libraries via the library ID
18531           method.  This allows for execute in place and shared libraries in
18532           an environment without virtual memory management.  This option
18533           implies -fPIC.  With a bfin-elf target, this option implies -msim.
18534
18535       -mno-id-shared-library
18536           Generate code that doesn't assume ID-based shared libraries are
18537           being used.  This is the default.
18538
18539       -mleaf-id-shared-library
18540           Generate code that supports shared libraries via the library ID
18541           method, but assumes that this library or executable won't link
18542           against any other ID shared libraries.  That allows the compiler to
18543           use faster code for jumps and calls.
18544
18545       -mno-leaf-id-shared-library
18546           Do not assume that the code being compiled won't link against any
18547           ID shared libraries.  Slower code is generated for jump and call
18548           insns.
18549
18550       -mshared-library-id=n
18551           Specifies the identification number of the ID-based shared library
18552           being compiled.  Specifying a value of 0 generates more compact
18553           code; specifying other values forces the allocation of that number
18554           to the current library but is no more space- or time-efficient than
18555           omitting this option.
18556
18557       -msep-data
18558           Generate code that allows the data segment to be located in a
18559           different area of memory from the text segment.  This allows for
18560           execute in place in an environment without virtual memory
18561           management by eliminating relocations against the text section.
18562
18563       -mno-sep-data
18564           Generate code that assumes that the data segment follows the text
18565           segment.  This is the default.
18566
18567       -mlong-calls
18568       -mno-long-calls
18569           Tells the compiler to perform function calls by first loading the
18570           address of the function into a register and then performing a
18571           subroutine call on this register.  This switch is needed if the
18572           target function lies outside of the 24-bit addressing range of the
18573           offset-based version of subroutine call instruction.
18574
18575           This feature is not enabled by default.  Specifying -mno-long-calls
18576           restores the default behavior.  Note these switches have no effect
18577           on how the compiler generates code to handle function calls via
18578           function pointers.
18579
18580       -mfast-fp
18581           Link with the fast floating-point library. This library relaxes
18582           some of the IEEE floating-point standard's rules for checking
18583           inputs against Not-a-Number (NAN), in the interest of performance.
18584
18585       -minline-plt
18586           Enable inlining of PLT entries in function calls to functions that
18587           are not known to bind locally.  It has no effect without -mfdpic.
18588
18589       -mmulticore
18590           Build a standalone application for multicore Blackfin processors.
18591           This option causes proper start files and link scripts supporting
18592           multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
18593           can only be used with -mcpu=bf561[-sirevision].
18594
18595           This option can be used with -mcorea or -mcoreb, which selects the
18596           one-application-per-core programming model.  Without -mcorea or
18597           -mcoreb, the single-application/dual-core programming model is
18598           used. In this model, the main function of Core B should be named as
18599           "coreb_main".
18600
18601           If this option is not used, the single-core application programming
18602           model is used.
18603
18604       -mcorea
18605           Build a standalone application for Core A of BF561 when using the
18606           one-application-per-core programming model. Proper start files and
18607           link scripts are used to support Core A, and the macro
18608           "__BFIN_COREA" is defined.  This option can only be used in
18609           conjunction with -mmulticore.
18610
18611       -mcoreb
18612           Build a standalone application for Core B of BF561 when using the
18613           one-application-per-core programming model. Proper start files and
18614           link scripts are used to support Core B, and the macro
18615           "__BFIN_COREB" is defined. When this option is used, "coreb_main"
18616           should be used instead of "main".  This option can only be used in
18617           conjunction with -mmulticore.
18618
18619       -msdram
18620           Build a standalone application for SDRAM. Proper start files and
18621           link scripts are used to put the application into SDRAM, and the
18622           macro "__BFIN_SDRAM" is defined.  The loader should initialize
18623           SDRAM before loading the application.
18624
18625       -micplb
18626           Assume that ICPLBs are enabled at run time.  This has an effect on
18627           certain anomaly workarounds.  For Linux targets, the default is to
18628           assume ICPLBs are enabled; for standalone applications the default
18629           is off.
18630
18631       C6X Options
18632
18633       -march=name
18634           This specifies the name of the target architecture.  GCC uses this
18635           name to determine what kind of instructions it can emit when
18636           generating assembly code.  Permissible names are: c62x, c64x,
18637           c64x+, c67x, c67x+, c674x.
18638
18639       -mbig-endian
18640           Generate code for a big-endian target.
18641
18642       -mlittle-endian
18643           Generate code for a little-endian target.  This is the default.
18644
18645       -msim
18646           Choose startup files and linker script suitable for the simulator.
18647
18648       -msdata=default
18649           Put small global and static data in the ".neardata" section, which
18650           is pointed to by register "B14".  Put small uninitialized global
18651           and static data in the ".bss" section, which is adjacent to the
18652           ".neardata" section.  Put small read-only data into the ".rodata"
18653           section.  The corresponding sections used for large pieces of data
18654           are ".fardata", ".far" and ".const".
18655
18656       -msdata=all
18657           Put all data, not just small objects, into the sections reserved
18658           for small data, and use addressing relative to the "B14" register
18659           to access them.
18660
18661       -msdata=none
18662           Make no use of the sections reserved for small data, and use
18663           absolute addresses to access all data.  Put all initialized global
18664           and static data in the ".fardata" section, and all uninitialized
18665           data in the ".far" section.  Put all constant data into the
18666           ".const" section.
18667
18668       CRIS Options
18669
18670       These options are defined specifically for the CRIS ports.
18671
18672       -march=architecture-type
18673       -mcpu=architecture-type
18674           Generate code for the specified architecture.  The choices for
18675           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
18676           ETRAX 100, and ETRAX 100 LX.  Default is v0 except for cris-axis-
18677           linux-gnu, where the default is v10.
18678
18679       -mtune=architecture-type
18680           Tune to architecture-type everything applicable about the generated
18681           code, except for the ABI and the set of available instructions.
18682           The choices for architecture-type are the same as for
18683           -march=architecture-type.
18684
18685       -mmax-stack-frame=n
18686           Warn when the stack frame of a function exceeds n bytes.
18687
18688       -metrax4
18689       -metrax100
18690           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
18691           -march=v8 respectively.
18692
18693       -mmul-bug-workaround
18694       -mno-mul-bug-workaround
18695           Work around a bug in the "muls" and "mulu" instructions for CPU
18696           models where it applies.  This option is active by default.
18697
18698       -mpdebug
18699           Enable CRIS-specific verbose debug-related information in the
18700           assembly code.  This option also has the effect of turning off the
18701           #NO_APP formatted-code indicator to the assembler at the beginning
18702           of the assembly file.
18703
18704       -mcc-init
18705           Do not use condition-code results from previous instruction; always
18706           emit compare and test instructions before use of condition codes.
18707
18708       -mno-side-effects
18709           Do not emit instructions with side effects in addressing modes
18710           other than post-increment.
18711
18712       -mstack-align
18713       -mno-stack-align
18714       -mdata-align
18715       -mno-data-align
18716       -mconst-align
18717       -mno-const-align
18718           These options (no- options) arrange (eliminate arrangements) for
18719           the stack frame, individual data and constants to be aligned for
18720           the maximum single data access size for the chosen CPU model.  The
18721           default is to arrange for 32-bit alignment.  ABI details such as
18722           structure layout are not affected by these options.
18723
18724       -m32-bit
18725       -m16-bit
18726       -m8-bit
18727           Similar to the stack- data- and const-align options above, these
18728           options arrange for stack frame, writable data and constants to all
18729           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
18730           alignment.
18731
18732       -mno-prologue-epilogue
18733       -mprologue-epilogue
18734           With -mno-prologue-epilogue, the normal function prologue and
18735           epilogue which set up the stack frame are omitted and no return
18736           instructions or return sequences are generated in the code.  Use
18737           this option only together with visual inspection of the compiled
18738           code: no warnings or errors are generated when call-saved registers
18739           must be saved, or storage for local variables needs to be
18740           allocated.
18741
18742       -mno-gotplt
18743       -mgotplt
18744           With -fpic and -fPIC, don't generate (do generate) instruction
18745           sequences that load addresses for functions from the PLT part of
18746           the GOT rather than (traditional on other architectures) calls to
18747           the PLT.  The default is -mgotplt.
18748
18749       -melf
18750           Legacy no-op option only recognized with the cris-axis-elf and
18751           cris-axis-linux-gnu targets.
18752
18753       -mlinux
18754           Legacy no-op option only recognized with the cris-axis-linux-gnu
18755           target.
18756
18757       -sim
18758           This option, recognized for the cris-axis-elf, arranges to link
18759           with input-output functions from a simulator library.  Code,
18760           initialized data and zero-initialized data are allocated
18761           consecutively.
18762
18763       -sim2
18764           Like -sim, but pass linker options to locate initialized data at
18765           0x40000000 and zero-initialized data at 0x80000000.
18766
18767       CR16 Options
18768
18769       These options are defined specifically for the CR16 ports.
18770
18771       -mmac
18772           Enable the use of multiply-accumulate instructions. Disabled by
18773           default.
18774
18775       -mcr16cplus
18776       -mcr16c
18777           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
18778           is default.
18779
18780       -msim
18781           Links the library libsim.a which is in compatible with simulator.
18782           Applicable to ELF compiler only.
18783
18784       -mint32
18785           Choose integer type as 32-bit wide.
18786
18787       -mbit-ops
18788           Generates "sbit"/"cbit" instructions for bit manipulations.
18789
18790       -mdata-model=model
18791           Choose a data model. The choices for model are near, far or medium.
18792           medium is default.  However, far is not valid with -mcr16c, as the
18793           CR16C architecture does not support the far data model.
18794
18795       C-SKY Options
18796
18797       GCC supports these options when compiling for C-SKY V2 processors.
18798
18799       -march=arch
18800           Specify the C-SKY target architecture.  Valid values for arch are:
18801           ck801, ck802, ck803, ck807, and ck810.  The default is ck810.
18802
18803       -mcpu=cpu
18804           Specify the C-SKY target processor.  Valid values for cpu are:
18805           ck801, ck801t, ck802, ck802t, ck802j, ck803, ck803h, ck803t,
18806           ck803ht, ck803f, ck803fh, ck803e, ck803eh, ck803et, ck803eht,
18807           ck803ef, ck803efh, ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1,
18808           ck803tr1, ck803htr1, ck803fr1, ck803fhr1, ck803er1, ck803ehr1,
18809           ck803etr1, ck803ehtr1, ck803efr1, ck803efhr1, ck803ftr1,
18810           ck803eftr1, ck803efhtr1, ck803s, ck803st, ck803se, ck803sf,
18811           ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f, ck810e,
18812           ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t, ck810fv,
18813           ck810tv, ck810ft, and ck810ftv.
18814
18815       -mbig-endian
18816       -EB
18817       -mlittle-endian
18818       -EL Select big- or little-endian code.  The default is little-endian.
18819
18820       -mfloat-abi=name
18821           Specifies which floating-point ABI to use.  Permissible values are:
18822           soft, softfp and hard.
18823
18824           Specifying soft causes GCC to generate output containing library
18825           calls for floating-point operations.  softfp allows the generation
18826           of code using hardware floating-point instructions, but still uses
18827           the soft-float calling conventions.  hard allows generation of
18828           floating-point instructions and uses FPU-specific calling
18829           conventions.
18830
18831           The default depends on the specific target configuration.  Note
18832           that the hard-float and soft-float ABIs are not link-compatible;
18833           you must compile your entire program with the same ABI, and link
18834           with a compatible set of libraries.
18835
18836       -mhard-float
18837       -msoft-float
18838           Select hardware or software floating-point implementations.  The
18839           default is soft float.
18840
18841       -mdouble-float
18842       -mno-double-float
18843           When -mhard-float is in effect, enable generation of double-
18844           precision float instructions.  This is the default except when
18845           compiling for CK803.
18846
18847       -mfdivdu
18848       -mno-fdivdu
18849           When -mhard-float is in effect, enable generation of "frecipd",
18850           "fsqrtd", and "fdivd" instructions.  This is the default except
18851           when compiling for CK803.
18852
18853       -mfpu=fpu
18854           Select the floating-point processor.  This option can only be used
18855           with -mhard-float.  Values for fpu are fpv2_sf (equivalent to
18856           -mno-double-float -mno-fdivdu), fpv2 (-mdouble-float -mno-divdu),
18857           and fpv2_divd (-mdouble-float -mdivdu).
18858
18859       -melrw
18860       -mno-elrw
18861           Enable the extended "lrw" instruction.  This option defaults to on
18862           for CK801 and off otherwise.
18863
18864       -mistack
18865       -mno-istack
18866           Enable interrupt stack instructions; the default is off.
18867
18868           The -mistack option is required to handle the "interrupt" and "isr"
18869           function attributes.
18870
18871       -mmp
18872           Enable multiprocessor instructions; the default is off.
18873
18874       -mcp
18875           Enable coprocessor instructions; the default is off.
18876
18877       -mcache
18878           Enable coprocessor instructions; the default is off.
18879
18880       -msecurity
18881           Enable C-SKY security instructions; the default is off.
18882
18883       -mtrust
18884           Enable C-SKY trust instructions; the default is off.
18885
18886       -mdsp
18887       -medsp
18888       -mvdsp
18889           Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions,
18890           respectively.  All of these options default to off.
18891
18892       -mdiv
18893       -mno-div
18894           Generate divide instructions.  Default is off.
18895
18896       -msmart
18897       -mno-smart
18898           Generate code for Smart Mode, using only registers numbered 0-7 to
18899           allow use of 16-bit instructions.  This option is ignored for CK801
18900           where this is the required behavior, and it defaults to on for
18901           CK802.  For other targets, the default is off.
18902
18903       -mhigh-registers
18904       -mno-high-registers
18905           Generate code using the high registers numbered 16-31.  This option
18906           is not supported on CK801, CK802, or CK803, and is enabled by
18907           default for other processors.
18908
18909       -manchor
18910       -mno-anchor
18911           Generate code using global anchor symbol addresses.
18912
18913       -mpushpop
18914       -mno-pushpop
18915           Generate code using "push" and "pop" instructions.  This option
18916           defaults to on.
18917
18918       -mmultiple-stld
18919       -mstm
18920       -mno-multiple-stld
18921       -mno-stm
18922           Generate code using "stm" and "ldm" instructions.  This option
18923           isn't supported on CK801 but is enabled by default on other
18924           processors.
18925
18926       -mconstpool
18927       -mno-constpool
18928           Create constant pools in the compiler instead of deferring it to
18929           the assembler.  This option is the default and required for correct
18930           code generation on CK801 and CK802, and is optional on other
18931           processors.
18932
18933       -mstack-size
18934       -mno-stack-size
18935           Emit ".stack_size" directives for each function in the assembly
18936           output.  This option defaults to off.
18937
18938       -mccrt
18939       -mno-ccrt
18940           Generate code for the C-SKY compiler runtime instead of libgcc.
18941           This option defaults to off.
18942
18943       -mbranch-cost=n
18944           Set the branch costs to roughly "n" instructions.  The default is
18945           1.
18946
18947       -msched-prolog
18948       -mno-sched-prolog
18949           Permit scheduling of function prologue and epilogue sequences.
18950           Using this option can result in code that is not compliant with the
18951           C-SKY V2 ABI prologue requirements and that cannot be debugged or
18952           backtraced.  It is disabled by default.
18953
18954       -msim
18955           Links the library libsemi.a which is in compatible with simulator.
18956           Applicable to ELF compiler only.
18957
18958       Darwin Options
18959
18960       These options are defined for all architectures running the Darwin
18961       operating system.
18962
18963       FSF GCC on Darwin does not create "fat" object files; it creates an
18964       object file for the single architecture that GCC was built to target.
18965       Apple's GCC on Darwin does create "fat" files if multiple -arch options
18966       are used; it does so by running the compiler or linker multiple times
18967       and joining the results together with lipo.
18968
18969       The subtype of the file created (like ppc7400 or ppc970 or i686) is
18970       determined by the flags that specify the ISA that GCC is targeting,
18971       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
18972       override this.
18973
18974       The Darwin tools vary in their behavior when presented with an ISA
18975       mismatch.  The assembler, as, only permits instructions to be used that
18976       are valid for the subtype of the file it is generating, so you cannot
18977       put 64-bit instructions in a ppc750 object file.  The linker for shared
18978       libraries, /usr/bin/libtool, fails and prints an error if asked to
18979       create a shared library with a less restrictive subtype than its input
18980       files (for instance, trying to put a ppc970 object file in a ppc7400
18981       library).  The linker for executables, ld, quietly gives the executable
18982       the most restrictive subtype of any of its input files.
18983
18984       -Fdir
18985           Add the framework directory dir to the head of the list of
18986           directories to be searched for header files.  These directories are
18987           interleaved with those specified by -I options and are scanned in a
18988           left-to-right order.
18989
18990           A framework directory is a directory with frameworks in it.  A
18991           framework is a directory with a Headers and/or PrivateHeaders
18992           directory contained directly in it that ends in .framework.  The
18993           name of a framework is the name of this directory excluding the
18994           .framework.  Headers associated with the framework are found in one
18995           of those two directories, with Headers being searched first.  A
18996           subframework is a framework directory that is in a framework's
18997           Frameworks directory.  Includes of subframework headers can only
18998           appear in a header of a framework that contains the subframework,
18999           or in a sibling subframework header.  Two subframeworks are
19000           siblings if they occur in the same framework.  A subframework
19001           should not have the same name as a framework; a warning is issued
19002           if this is violated.  Currently a subframework cannot have
19003           subframeworks; in the future, the mechanism may be extended to
19004           support this.  The standard frameworks can be found in
19005           /System/Library/Frameworks and /Library/Frameworks.  An example
19006           include looks like "#include <Framework/header.h>", where Framework
19007           denotes the name of the framework and header.h is found in the
19008           PrivateHeaders or Headers directory.
19009
19010       -iframeworkdir
19011           Like -F except the directory is a treated as a system directory.
19012           The main difference between this -iframework and -F is that with
19013           -iframework the compiler does not warn about constructs contained
19014           within header files found via dir.  This option is valid only for
19015           the C family of languages.
19016
19017       -gused
19018           Emit debugging information for symbols that are used.  For stabs
19019           debugging format, this enables -feliminate-unused-debug-symbols.
19020           This is by default ON.
19021
19022       -gfull
19023           Emit debugging information for all symbols and types.
19024
19025       -mmacosx-version-min=version
19026           The earliest version of MacOS X that this executable will run on is
19027           version.  Typical values of version include 10.1, 10.2, and 10.3.9.
19028
19029           If the compiler was built to use the system's headers by default,
19030           then the default for this option is the system version on which the
19031           compiler is running, otherwise the default is to make choices that
19032           are compatible with as many systems and code bases as possible.
19033
19034       -mkernel
19035           Enable kernel development mode.  The -mkernel option sets -static,
19036           -fno-common, -fno-use-cxa-atexit, -fno-exceptions,
19037           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
19038           where applicable.  This mode also sets -mno-altivec, -msoft-float,
19039           -fno-builtin and -mlong-branch for PowerPC targets.
19040
19041       -mone-byte-bool
19042           Override the defaults for "bool" so that "sizeof(bool)==1".  By
19043           default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1
19044           when compiling for Darwin/x86, so this option has no effect on x86.
19045
19046           Warning: The -mone-byte-bool switch causes GCC to generate code
19047           that is not binary compatible with code generated without that
19048           switch.  Using this switch may require recompiling all other
19049           modules in a program, including system libraries.  Use this switch
19050           to conform to a non-default data model.
19051
19052       -mfix-and-continue
19053       -ffix-and-continue
19054       -findirect-data
19055           Generate code suitable for fast turnaround development, such as to
19056           allow GDB to dynamically load .o files into already-running
19057           programs.  -findirect-data and -ffix-and-continue are provided for
19058           backwards compatibility.
19059
19060       -all_load
19061           Loads all members of static archive libraries.  See man ld(1) for
19062           more information.
19063
19064       -arch_errors_fatal
19065           Cause the errors having to do with files that have the wrong
19066           architecture to be fatal.
19067
19068       -bind_at_load
19069           Causes the output file to be marked such that the dynamic linker
19070           will bind all undefined references when the file is loaded or
19071           launched.
19072
19073       -bundle
19074           Produce a Mach-o bundle format file.  See man ld(1) for more
19075           information.
19076
19077       -bundle_loader executable
19078           This option specifies the executable that will load the build
19079           output file being linked.  See man ld(1) for more information.
19080
19081       -dynamiclib
19082           When passed this option, GCC produces a dynamic library instead of
19083           an executable when linking, using the Darwin libtool command.
19084
19085       -force_cpusubtype_ALL
19086           This causes GCC's output file to have the ALL subtype, instead of
19087           one controlled by the -mcpu or -march option.
19088
19089       -allowable_client  client_name
19090       -client_name
19091       -compatibility_version
19092       -current_version
19093       -dead_strip
19094       -dependency-file
19095       -dylib_file
19096       -dylinker_install_name
19097       -dynamic
19098       -exported_symbols_list
19099       -filelist
19100       -flat_namespace
19101       -force_flat_namespace
19102       -headerpad_max_install_names
19103       -image_base
19104       -init
19105       -install_name
19106       -keep_private_externs
19107       -multi_module
19108       -multiply_defined
19109       -multiply_defined_unused
19110       -noall_load
19111       -no_dead_strip_inits_and_terms
19112       -nofixprebinding
19113       -nomultidefs
19114       -noprebind
19115       -noseglinkedit
19116       -pagezero_size
19117       -prebind
19118       -prebind_all_twolevel_modules
19119       -private_bundle
19120       -read_only_relocs
19121       -sectalign
19122       -sectobjectsymbols
19123       -whyload
19124       -seg1addr
19125       -sectcreate
19126       -sectobjectsymbols
19127       -sectorder
19128       -segaddr
19129       -segs_read_only_addr
19130       -segs_read_write_addr
19131       -seg_addr_table
19132       -seg_addr_table_filename
19133       -seglinkedit
19134       -segprot
19135       -segs_read_only_addr
19136       -segs_read_write_addr
19137       -single_module
19138       -static
19139       -sub_library
19140       -sub_umbrella
19141       -twolevel_namespace
19142       -umbrella
19143       -undefined
19144       -unexported_symbols_list
19145       -weak_reference_mismatches
19146       -whatsloaded
19147           These options are passed to the Darwin linker.  The Darwin linker
19148           man page describes them in detail.
19149
19150       DEC Alpha Options
19151
19152       These -m options are defined for the DEC Alpha implementations:
19153
19154       -mno-soft-float
19155       -msoft-float
19156           Use (do not use) the hardware floating-point instructions for
19157           floating-point operations.  When -msoft-float is specified,
19158           functions in libgcc.a are used to perform floating-point
19159           operations.  Unless they are replaced by routines that emulate the
19160           floating-point operations, or compiled in such a way as to call
19161           such emulations routines, these routines issue floating-point
19162           operations.   If you are compiling for an Alpha without floating-
19163           point operations, you must ensure that the library is built so as
19164           not to call them.
19165
19166           Note that Alpha implementations without floating-point operations
19167           are required to have floating-point registers.
19168
19169       -mfp-reg
19170       -mno-fp-regs
19171           Generate code that uses (does not use) the floating-point register
19172           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
19173           register set is not used, floating-point operands are passed in
19174           integer registers as if they were integers and floating-point
19175           results are passed in $0 instead of $f0.  This is a non-standard
19176           calling sequence, so any function with a floating-point argument or
19177           return value called by code compiled with -mno-fp-regs must also be
19178           compiled with that option.
19179
19180           A typical use of this option is building a kernel that does not
19181           use, and hence need not save and restore, any floating-point
19182           registers.
19183
19184       -mieee
19185           The Alpha architecture implements floating-point hardware optimized
19186           for maximum performance.  It is mostly compliant with the IEEE
19187           floating-point standard.  However, for full compliance, software
19188           assistance is required.  This option generates code fully IEEE-
19189           compliant code except that the inexact-flag is not maintained (see
19190           below).  If this option is turned on, the preprocessor macro
19191           "_IEEE_FP" is defined during compilation.  The resulting code is
19192           less efficient but is able to correctly support denormalized
19193           numbers and exceptional IEEE values such as not-a-number and
19194           plus/minus infinity.  Other Alpha compilers call this option
19195           -ieee_with_no_inexact.
19196
19197       -mieee-with-inexact
19198           This is like -mieee except the generated code also maintains the
19199           IEEE inexact-flag.  Turning on this option causes the generated
19200           code to implement fully-compliant IEEE math.  In addition to
19201           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
19202           On some Alpha implementations the resulting code may execute
19203           significantly slower than the code generated by default.  Since
19204           there is very little code that depends on the inexact-flag, you
19205           should normally not specify this option.  Other Alpha compilers
19206           call this option -ieee_with_inexact.
19207
19208       -mfp-trap-mode=trap-mode
19209           This option controls what floating-point related traps are enabled.
19210           Other Alpha compilers call this option -fptm trap-mode.  The trap
19211           mode can be set to one of four values:
19212
19213           n   This is the default (normal) setting.  The only traps that are
19214               enabled are the ones that cannot be disabled in software (e.g.,
19215               division by zero trap).
19216
19217           u   In addition to the traps enabled by n, underflow traps are
19218               enabled as well.
19219
19220           su  Like u, but the instructions are marked to be safe for software
19221               completion (see Alpha architecture manual for details).
19222
19223           sui Like su, but inexact traps are enabled as well.
19224
19225       -mfp-rounding-mode=rounding-mode
19226           Selects the IEEE rounding mode.  Other Alpha compilers call this
19227           option -fprm rounding-mode.  The rounding-mode can be one of:
19228
19229           n   Normal IEEE rounding mode.  Floating-point numbers are rounded
19230               towards the nearest machine number or towards the even machine
19231               number in case of a tie.
19232
19233           m   Round towards minus infinity.
19234
19235           c   Chopped rounding mode.  Floating-point numbers are rounded
19236               towards zero.
19237
19238           d   Dynamic rounding mode.  A field in the floating-point control
19239               register (fpcr, see Alpha architecture reference manual)
19240               controls the rounding mode in effect.  The C library
19241               initializes this register for rounding towards plus infinity.
19242               Thus, unless your program modifies the fpcr, d corresponds to
19243               round towards plus infinity.
19244
19245       -mtrap-precision=trap-precision
19246           In the Alpha architecture, floating-point traps are imprecise.
19247           This means without software assistance it is impossible to recover
19248           from a floating trap and program execution normally needs to be
19249           terminated.  GCC can generate code that can assist operating system
19250           trap handlers in determining the exact location that caused a
19251           floating-point trap.  Depending on the requirements of an
19252           application, different levels of precisions can be selected:
19253
19254           p   Program precision.  This option is the default and means a trap
19255               handler can only identify which program caused a floating-point
19256               exception.
19257
19258           f   Function precision.  The trap handler can determine the
19259               function that caused a floating-point exception.
19260
19261           i   Instruction precision.  The trap handler can determine the
19262               exact instruction that caused a floating-point exception.
19263
19264           Other Alpha compilers provide the equivalent options called
19265           -scope_safe and -resumption_safe.
19266
19267       -mieee-conformant
19268           This option marks the generated code as IEEE conformant.  You must
19269           not use this option unless you also specify -mtrap-precision=i and
19270           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
19271           to emit the line .eflag 48 in the function prologue of the
19272           generated assembly file.
19273
19274       -mbuild-constants
19275           Normally GCC examines a 32- or 64-bit integer constant to see if it
19276           can construct it from smaller constants in two or three
19277           instructions.  If it cannot, it outputs the constant as a literal
19278           and generates code to load it from the data segment at run time.
19279
19280           Use this option to require GCC to construct all integer constants
19281           using code, even if it takes more instructions (the maximum is
19282           six).
19283
19284           You typically use this option to build a shared library dynamic
19285           loader.  Itself a shared library, it must relocate itself in memory
19286           before it can find the variables and constants in its own data
19287           segment.
19288
19289       -mbwx
19290       -mno-bwx
19291       -mcix
19292       -mno-cix
19293       -mfix
19294       -mno-fix
19295       -mmax
19296       -mno-max
19297           Indicate whether GCC should generate code to use the optional BWX,
19298           CIX, FIX and MAX instruction sets.  The default is to use the
19299           instruction sets supported by the CPU type specified via -mcpu=
19300           option or that of the CPU on which GCC was built if none is
19301           specified.
19302
19303       -mfloat-vax
19304       -mfloat-ieee
19305           Generate code that uses (does not use) VAX F and G floating-point
19306           arithmetic instead of IEEE single and double precision.
19307
19308       -mexplicit-relocs
19309       -mno-explicit-relocs
19310           Older Alpha assemblers provided no way to generate symbol
19311           relocations except via assembler macros.  Use of these macros does
19312           not allow optimal instruction scheduling.  GNU binutils as of
19313           version 2.12 supports a new syntax that allows the compiler to
19314           explicitly mark which relocations should apply to which
19315           instructions.  This option is mostly useful for debugging, as GCC
19316           detects the capabilities of the assembler when it is built and sets
19317           the default accordingly.
19318
19319       -msmall-data
19320       -mlarge-data
19321           When -mexplicit-relocs is in effect, static data is accessed via
19322           gp-relative relocations.  When -msmall-data is used, objects 8
19323           bytes long or smaller are placed in a small data area (the ".sdata"
19324           and ".sbss" sections) and are accessed via 16-bit relocations off
19325           of the $gp register.  This limits the size of the small data area
19326           to 64KB, but allows the variables to be directly accessed via a
19327           single instruction.
19328
19329           The default is -mlarge-data.  With this option the data area is
19330           limited to just below 2GB.  Programs that require more than 2GB of
19331           data must use "malloc" or "mmap" to allocate the data in the heap
19332           instead of in the program's data segment.
19333
19334           When generating code for shared libraries, -fpic implies
19335           -msmall-data and -fPIC implies -mlarge-data.
19336
19337       -msmall-text
19338       -mlarge-text
19339           When -msmall-text is used, the compiler assumes that the code of
19340           the entire program (or shared library) fits in 4MB, and is thus
19341           reachable with a branch instruction.  When -msmall-data is used,
19342           the compiler can assume that all local symbols share the same $gp
19343           value, and thus reduce the number of instructions required for a
19344           function call from 4 to 1.
19345
19346           The default is -mlarge-text.
19347
19348       -mcpu=cpu_type
19349           Set the instruction set and instruction scheduling parameters for
19350           machine type cpu_type.  You can specify either the EV style name or
19351           the corresponding chip number.  GCC supports scheduling parameters
19352           for the EV4, EV5 and EV6 family of processors and chooses the
19353           default values for the instruction set from the processor you
19354           specify.  If you do not specify a processor type, GCC defaults to
19355           the processor on which the compiler was built.
19356
19357           Supported values for cpu_type are
19358
19359           ev4
19360           ev45
19361           21064
19362               Schedules as an EV4 and has no instruction set extensions.
19363
19364           ev5
19365           21164
19366               Schedules as an EV5 and has no instruction set extensions.
19367
19368           ev56
19369           21164a
19370               Schedules as an EV5 and supports the BWX extension.
19371
19372           pca56
19373           21164pc
19374           21164PC
19375               Schedules as an EV5 and supports the BWX and MAX extensions.
19376
19377           ev6
19378           21264
19379               Schedules as an EV6 and supports the BWX, FIX, and MAX
19380               extensions.
19381
19382           ev67
19383           21264a
19384               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
19385               extensions.
19386
19387           Native toolchains also support the value native, which selects the
19388           best architecture option for the host processor.  -mcpu=native has
19389           no effect if GCC does not recognize the processor.
19390
19391       -mtune=cpu_type
19392           Set only the instruction scheduling parameters for machine type
19393           cpu_type.  The instruction set is not changed.
19394
19395           Native toolchains also support the value native, which selects the
19396           best architecture option for the host processor.  -mtune=native has
19397           no effect if GCC does not recognize the processor.
19398
19399       -mmemory-latency=time
19400           Sets the latency the scheduler should assume for typical memory
19401           references as seen by the application.  This number is highly
19402           dependent on the memory access patterns used by the application and
19403           the size of the external cache on the machine.
19404
19405           Valid options for time are
19406
19407           number
19408               A decimal number representing clock cycles.
19409
19410           L1
19411           L2
19412           L3
19413           main
19414               The compiler contains estimates of the number of clock cycles
19415               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
19416               (also called Dcache, Scache, and Bcache), as well as to main
19417               memory.  Note that L3 is only valid for EV5.
19418
19419       eBPF Options
19420
19421       -mframe-limit=bytes
19422           This specifies the hard limit for frame sizes, in bytes.
19423           Currently, the value that can be specified should be less than or
19424           equal to 32767.  Defaults to whatever limit is imposed by the
19425           version of the Linux kernel targeted.
19426
19427       -mkernel=version
19428           This specifies the minimum version of the kernel that will run the
19429           compiled program.  GCC uses this version to determine which
19430           instructions to use, what kernel helpers to allow, etc.  Currently,
19431           version can be one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8,
19432           4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19,
19433           4.20, 5.0, 5.1, 5.2, latest and native.
19434
19435       -mbig-endian
19436           Generate code for a big-endian target.
19437
19438       -mlittle-endian
19439           Generate code for a little-endian target.  This is the default.
19440
19441       -mxbpf
19442           Generate code for an expanded version of BPF, which relaxes some of
19443           the restrictions imposed by the BPF architecture:
19444
19445           -<Save and restore callee-saved registers at function entry and>
19446               exit, respectively.
19447
19448       FR30 Options
19449
19450       These options are defined specifically for the FR30 port.
19451
19452       -msmall-model
19453           Use the small address space model.  This can produce smaller code,
19454           but it does assume that all symbolic values and addresses fit into
19455           a 20-bit range.
19456
19457       -mno-lsim
19458           Assume that runtime support has been provided and so there is no
19459           need to include the simulator library (libsim.a) on the linker
19460           command line.
19461
19462       FT32 Options
19463
19464       These options are defined specifically for the FT32 port.
19465
19466       -msim
19467           Specifies that the program will be run on the simulator.  This
19468           causes an alternate runtime startup and library to be linked.  You
19469           must not use this option when generating programs that will run on
19470           real hardware; you must provide your own runtime library for
19471           whatever I/O functions are needed.
19472
19473       -mlra
19474           Enable Local Register Allocation.  This is still experimental for
19475           FT32, so by default the compiler uses standard reload.
19476
19477       -mnodiv
19478           Do not use div and mod instructions.
19479
19480       -mft32b
19481           Enable use of the extended instructions of the FT32B processor.
19482
19483       -mcompress
19484           Compress all code using the Ft32B code compression scheme.
19485
19486       -mnopm
19487           Do not generate code that reads program memory.
19488
19489       FRV Options
19490
19491       -mgpr-32
19492           Only use the first 32 general-purpose registers.
19493
19494       -mgpr-64
19495           Use all 64 general-purpose registers.
19496
19497       -mfpr-32
19498           Use only the first 32 floating-point registers.
19499
19500       -mfpr-64
19501           Use all 64 floating-point registers.
19502
19503       -mhard-float
19504           Use hardware instructions for floating-point operations.
19505
19506       -msoft-float
19507           Use library routines for floating-point operations.
19508
19509       -malloc-cc
19510           Dynamically allocate condition code registers.
19511
19512       -mfixed-cc
19513           Do not try to dynamically allocate condition code registers, only
19514           use "icc0" and "fcc0".
19515
19516       -mdword
19517           Change ABI to use double word insns.
19518
19519       -mno-dword
19520           Do not use double word instructions.
19521
19522       -mdouble
19523           Use floating-point double instructions.
19524
19525       -mno-double
19526           Do not use floating-point double instructions.
19527
19528       -mmedia
19529           Use media instructions.
19530
19531       -mno-media
19532           Do not use media instructions.
19533
19534       -mmuladd
19535           Use multiply and add/subtract instructions.
19536
19537       -mno-muladd
19538           Do not use multiply and add/subtract instructions.
19539
19540       -mfdpic
19541           Select the FDPIC ABI, which uses function descriptors to represent
19542           pointers to functions.  Without any PIC/PIE-related options, it
19543           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
19544           small data are within a 12-bit range from the GOT base address;
19545           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
19546           bfin-elf target, this option implies -msim.
19547
19548       -minline-plt
19549           Enable inlining of PLT entries in function calls to functions that
19550           are not known to bind locally.  It has no effect without -mfdpic.
19551           It's enabled by default if optimizing for speed and compiling for
19552           shared libraries (i.e., -fPIC or -fpic), or when an optimization
19553           option such as -O3 or above is present in the command line.
19554
19555       -mTLS
19556           Assume a large TLS segment when generating thread-local code.
19557
19558       -mtls
19559           Do not assume a large TLS segment when generating thread-local
19560           code.
19561
19562       -mgprel-ro
19563           Enable the use of "GPREL" relocations in the FDPIC ABI for data
19564           that is known to be in read-only sections.  It's enabled by
19565           default, except for -fpic or -fpie: even though it may help make
19566           the global offset table smaller, it trades 1 instruction for 4.
19567           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
19568           may be shared by multiple symbols, and it avoids the need for a GOT
19569           entry for the referenced symbol, so it's more likely to be a win.
19570           If it is not, -mno-gprel-ro can be used to disable it.
19571
19572       -multilib-library-pic
19573           Link with the (library, not FD) pic libraries.  It's implied by
19574           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
19575           should never have to use it explicitly.
19576
19577       -mlinked-fp
19578           Follow the EABI requirement of always creating a frame pointer
19579           whenever a stack frame is allocated.  This option is enabled by
19580           default and can be disabled with -mno-linked-fp.
19581
19582       -mlong-calls
19583           Use indirect addressing to call functions outside the current
19584           compilation unit.  This allows the functions to be placed anywhere
19585           within the 32-bit address space.
19586
19587       -malign-labels
19588           Try to align labels to an 8-byte boundary by inserting NOPs into
19589           the previous packet.  This option only has an effect when VLIW
19590           packing is enabled.  It doesn't create new packets; it merely adds
19591           NOPs to existing ones.
19592
19593       -mlibrary-pic
19594           Generate position-independent EABI code.
19595
19596       -macc-4
19597           Use only the first four media accumulator registers.
19598
19599       -macc-8
19600           Use all eight media accumulator registers.
19601
19602       -mpack
19603           Pack VLIW instructions.
19604
19605       -mno-pack
19606           Do not pack VLIW instructions.
19607
19608       -mno-eflags
19609           Do not mark ABI switches in e_flags.
19610
19611       -mcond-move
19612           Enable the use of conditional-move instructions (default).
19613
19614           This switch is mainly for debugging the compiler and will likely be
19615           removed in a future version.
19616
19617       -mno-cond-move
19618           Disable the use of conditional-move instructions.
19619
19620           This switch is mainly for debugging the compiler and will likely be
19621           removed in a future version.
19622
19623       -mscc
19624           Enable the use of conditional set instructions (default).
19625
19626           This switch is mainly for debugging the compiler and will likely be
19627           removed in a future version.
19628
19629       -mno-scc
19630           Disable the use of conditional set instructions.
19631
19632           This switch is mainly for debugging the compiler and will likely be
19633           removed in a future version.
19634
19635       -mcond-exec
19636           Enable the use of conditional execution (default).
19637
19638           This switch is mainly for debugging the compiler and will likely be
19639           removed in a future version.
19640
19641       -mno-cond-exec
19642           Disable the use of conditional execution.
19643
19644           This switch is mainly for debugging the compiler and will likely be
19645           removed in a future version.
19646
19647       -mvliw-branch
19648           Run a pass to pack branches into VLIW instructions (default).
19649
19650           This switch is mainly for debugging the compiler and will likely be
19651           removed in a future version.
19652
19653       -mno-vliw-branch
19654           Do not run a pass to pack branches into VLIW instructions.
19655
19656           This switch is mainly for debugging the compiler and will likely be
19657           removed in a future version.
19658
19659       -mmulti-cond-exec
19660           Enable optimization of "&&" and "||" in conditional execution
19661           (default).
19662
19663           This switch is mainly for debugging the compiler and will likely be
19664           removed in a future version.
19665
19666       -mno-multi-cond-exec
19667           Disable optimization of "&&" and "||" in conditional execution.
19668
19669           This switch is mainly for debugging the compiler and will likely be
19670           removed in a future version.
19671
19672       -mnested-cond-exec
19673           Enable nested conditional execution optimizations (default).
19674
19675           This switch is mainly for debugging the compiler and will likely be
19676           removed in a future version.
19677
19678       -mno-nested-cond-exec
19679           Disable nested conditional execution optimizations.
19680
19681           This switch is mainly for debugging the compiler and will likely be
19682           removed in a future version.
19683
19684       -moptimize-membar
19685           This switch removes redundant "membar" instructions from the
19686           compiler-generated code.  It is enabled by default.
19687
19688       -mno-optimize-membar
19689           This switch disables the automatic removal of redundant "membar"
19690           instructions from the generated code.
19691
19692       -mtomcat-stats
19693           Cause gas to print out tomcat statistics.
19694
19695       -mcpu=cpu
19696           Select the processor type for which to generate code.  Possible
19697           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
19698           and simple.
19699
19700       GNU/Linux Options
19701
19702       These -m options are defined for GNU/Linux targets:
19703
19704       -mglibc
19705           Use the GNU C library.  This is the default except on
19706           *-*-linux-*uclibc*, *-*-linux-*musl* and *-*-linux-*android*
19707           targets.
19708
19709       -muclibc
19710           Use uClibc C library.  This is the default on *-*-linux-*uclibc*
19711           targets.
19712
19713       -mmusl
19714           Use the musl C library.  This is the default on *-*-linux-*musl*
19715           targets.
19716
19717       -mbionic
19718           Use Bionic C library.  This is the default on *-*-linux-*android*
19719           targets.
19720
19721       -mandroid
19722           Compile code compatible with Android platform.  This is the default
19723           on *-*-linux-*android* targets.
19724
19725           When compiling, this option enables -mbionic, -fPIC,
19726           -fno-exceptions and -fno-rtti by default.  When linking, this
19727           option makes the GCC driver pass Android-specific options to the
19728           linker.  Finally, this option causes the preprocessor macro
19729           "__ANDROID__" to be defined.
19730
19731       -tno-android-cc
19732           Disable compilation effects of -mandroid, i.e., do not enable
19733           -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.
19734
19735       -tno-android-ld
19736           Disable linking effects of -mandroid, i.e., pass standard Linux
19737           linking options to the linker.
19738
19739       H8/300 Options
19740
19741       These -m options are defined for the H8/300 implementations:
19742
19743       -mrelax
19744           Shorten some address references at link time, when possible; uses
19745           the linker option -relax.
19746
19747       -mh Generate code for the H8/300H.
19748
19749       -ms Generate code for the H8S.
19750
19751       -mn Generate code for the H8S and H8/300H in the normal mode.  This
19752           switch must be used either with -mh or -ms.
19753
19754       -ms2600
19755           Generate code for the H8S/2600.  This switch must be used with -ms.
19756
19757       -mexr
19758           Extended registers are stored on stack before execution of function
19759           with monitor attribute. Default option is -mexr.  This option is
19760           valid only for H8S targets.
19761
19762       -mno-exr
19763           Extended registers are not stored on stack before execution of
19764           function with monitor attribute. Default option is -mno-exr.  This
19765           option is valid only for H8S targets.
19766
19767       -mint32
19768           Make "int" data 32 bits by default.
19769
19770       -malign-300
19771           On the H8/300H and H8S, use the same alignment rules as for the
19772           H8/300.  The default for the H8/300H and H8S is to align longs and
19773           floats on 4-byte boundaries.  -malign-300 causes them to be aligned
19774           on 2-byte boundaries.  This option has no effect on the H8/300.
19775
19776       HPPA Options
19777
19778       These -m options are defined for the HPPA family of computers:
19779
19780       -march=architecture-type
19781           Generate code for the specified architecture.  The choices for
19782           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
19783           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
19784           system to determine the proper architecture option for your
19785           machine.  Code compiled for lower numbered architectures runs on
19786           higher numbered architectures, but not the other way around.
19787
19788       -mpa-risc-1-0
19789       -mpa-risc-1-1
19790       -mpa-risc-2-0
19791           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
19792
19793       -mcaller-copies
19794           The caller copies function arguments passed by hidden reference.
19795           This option should be used with care as it is not compatible with
19796           the default 32-bit runtime.  However, only aggregates larger than
19797           eight bytes are passed by hidden reference and the option provides
19798           better compatibility with OpenMP.
19799
19800       -mjump-in-delay
19801           This option is ignored and provided for compatibility purposes
19802           only.
19803
19804       -mdisable-fpregs
19805           Prevent floating-point registers from being used in any manner.
19806           This is necessary for compiling kernels that perform lazy context
19807           switching of floating-point registers.  If you use this option and
19808           attempt to perform floating-point operations, the compiler aborts.
19809
19810       -mdisable-indexing
19811           Prevent the compiler from using indexing address modes.  This
19812           avoids some rather obscure problems when compiling MIG generated
19813           code under MACH.
19814
19815       -mno-space-regs
19816           Generate code that assumes the target has no space registers.  This
19817           allows GCC to generate faster indirect calls and use unscaled index
19818           address modes.
19819
19820           Such code is suitable for level 0 PA systems and kernels.
19821
19822       -mfast-indirect-calls
19823           Generate code that assumes calls never cross space boundaries.
19824           This allows GCC to emit code that performs faster indirect calls.
19825
19826           This option does not work in the presence of shared libraries or
19827           nested functions.
19828
19829       -mfixed-range=register-range
19830           Generate code treating the given register range as fixed registers.
19831           A fixed register is one that the register allocator cannot use.
19832           This is useful when compiling kernel code.  A register range is
19833           specified as two registers separated by a dash.  Multiple register
19834           ranges can be specified separated by a comma.
19835
19836       -mlong-load-store
19837           Generate 3-instruction load and store sequences as sometimes
19838           required by the HP-UX 10 linker.  This is equivalent to the +k
19839           option to the HP compilers.
19840
19841       -mportable-runtime
19842           Use the portable calling conventions proposed by HP for ELF
19843           systems.
19844
19845       -mgas
19846           Enable the use of assembler directives only GAS understands.
19847
19848       -mschedule=cpu-type
19849           Schedule code according to the constraints for the machine type
19850           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
19851           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
19852           to determine the proper scheduling option for your machine.  The
19853           default scheduling is 8000.
19854
19855       -mlinker-opt
19856           Enable the optimization pass in the HP-UX linker.  Note this makes
19857           symbolic debugging impossible.  It also triggers a bug in the HP-UX
19858           8 and HP-UX 9 linkers in which they give bogus error messages when
19859           linking some programs.
19860
19861       -msoft-float
19862           Generate output containing library calls for floating point.
19863           Warning: the requisite libraries are not available for all HPPA
19864           targets.  Normally the facilities of the machine's usual C compiler
19865           are used, but this cannot be done directly in cross-compilation.
19866           You must make your own arrangements to provide suitable library
19867           functions for cross-compilation.
19868
19869           -msoft-float changes the calling convention in the output file;
19870           therefore, it is only useful if you compile all of a program with
19871           this option.  In particular, you need to compile libgcc.a, the
19872           library that comes with GCC, with -msoft-float in order for this to
19873           work.
19874
19875       -msio
19876           Generate the predefine, "_SIO", for server IO.  The default is
19877           -mwsio.  This generates the predefines, "__hp9000s700",
19878           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
19879           are available under HP-UX and HI-UX.
19880
19881       -mgnu-ld
19882           Use options specific to GNU ld.  This passes -shared to ld when
19883           building a shared library.  It is the default when GCC is
19884           configured, explicitly or implicitly, with the GNU linker.  This
19885           option does not affect which ld is called; it only changes what
19886           parameters are passed to that ld.  The ld that is called is
19887           determined by the --with-ld configure option, GCC's program search
19888           path, and finally by the user's PATH.  The linker used by GCC can
19889           be printed using which `gcc -print-prog-name=ld`.  This option is
19890           only available on the 64-bit HP-UX GCC, i.e. configured with
19891           hppa*64*-*-hpux*.
19892
19893       -mhp-ld
19894           Use options specific to HP ld.  This passes -b to ld when building
19895           a shared library and passes +Accept TypeMismatch to ld on all
19896           links.  It is the default when GCC is configured, explicitly or
19897           implicitly, with the HP linker.  This option does not affect which
19898           ld is called; it only changes what parameters are passed to that
19899           ld.  The ld that is called is determined by the --with-ld configure
19900           option, GCC's program search path, and finally by the user's PATH.
19901           The linker used by GCC can be printed using which `gcc
19902           -print-prog-name=ld`.  This option is only available on the 64-bit
19903           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.
19904
19905       -mlong-calls
19906           Generate code that uses long call sequences.  This ensures that a
19907           call is always able to reach linker generated stubs.  The default
19908           is to generate long calls only when the distance from the call site
19909           to the beginning of the function or translation unit, as the case
19910           may be, exceeds a predefined limit set by the branch type being
19911           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
19912           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
19913           always limited at 240,000 bytes.
19914
19915           Distances are measured from the beginning of functions when using
19916           the -ffunction-sections option, or when using the -mgas and
19917           -mno-portable-runtime options together under HP-UX with the SOM
19918           linker.
19919
19920           It is normally not desirable to use this option as it degrades
19921           performance.  However, it may be useful in large applications,
19922           particularly when partial linking is used to build the application.
19923
19924           The types of long calls used depends on the capabilities of the
19925           assembler and linker, and the type of code being generated.  The
19926           impact on systems that support long absolute calls, and long pic
19927           symbol-difference or pc-relative calls should be relatively small.
19928           However, an indirect call is used on 32-bit ELF systems in pic code
19929           and it is quite long.
19930
19931       -munix=unix-std
19932           Generate compiler predefines and select a startfile for the
19933           specified UNIX standard.  The choices for unix-std are 93, 95 and
19934           98.  93 is supported on all HP-UX versions.  95 is available on HP-
19935           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
19936           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
19937           11.00, and 98 for HP-UX 11.11 and later.
19938
19939           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
19940           -munix=95 provides additional predefines for "XOPEN_UNIX" and
19941           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
19942           provides additional predefines for "_XOPEN_UNIX",
19943           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
19944           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.
19945
19946           It is important to note that this option changes the interfaces for
19947           various library routines.  It also affects the operational behavior
19948           of the C library.  Thus, extreme care is needed in using this
19949           option.
19950
19951           Library code that is intended to operate with more than one UNIX
19952           standard must test, set and restore the variable
19953           "__xpg4_extended_mask" as appropriate.  Most GNU software doesn't
19954           provide this capability.
19955
19956       -nolibdld
19957           Suppress the generation of link options to search libdld.sl when
19958           the -static option is specified on HP-UX 10 and later.
19959
19960       -static
19961           The HP-UX implementation of setlocale in libc has a dependency on
19962           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
19963           when the -static option is specified, special link options are
19964           needed to resolve this dependency.
19965
19966           On HP-UX 10 and later, the GCC driver adds the necessary options to
19967           link with libdld.sl when the -static option is specified.  This
19968           causes the resulting binary to be dynamic.  On the 64-bit port, the
19969           linkers generate dynamic binaries by default in any case.  The
19970           -nolibdld option can be used to prevent the GCC driver from adding
19971           these link options.
19972
19973       -threads
19974           Add support for multithreading with the dce thread library under
19975           HP-UX.  This option sets flags for both the preprocessor and
19976           linker.
19977
19978       IA-64 Options
19979
19980       These are the -m options defined for the Intel IA-64 architecture.
19981
19982       -mbig-endian
19983           Generate code for a big-endian target.  This is the default for HP-
19984           UX.
19985
19986       -mlittle-endian
19987           Generate code for a little-endian target.  This is the default for
19988           AIX5 and GNU/Linux.
19989
19990       -mgnu-as
19991       -mno-gnu-as
19992           Generate (or don't) code for the GNU assembler.  This is the
19993           default.
19994
19995       -mgnu-ld
19996       -mno-gnu-ld
19997           Generate (or don't) code for the GNU linker.  This is the default.
19998
19999       -mno-pic
20000           Generate code that does not use a global pointer register.  The
20001           result is not position independent code, and violates the IA-64
20002           ABI.
20003
20004       -mvolatile-asm-stop
20005       -mno-volatile-asm-stop
20006           Generate (or don't) a stop bit immediately before and after
20007           volatile asm statements.
20008
20009       -mregister-names
20010       -mno-register-names
20011           Generate (or don't) in, loc, and out register names for the stacked
20012           registers.  This may make assembler output more readable.
20013
20014       -mno-sdata
20015       -msdata
20016           Disable (or enable) optimizations that use the small data section.
20017           This may be useful for working around optimizer bugs.
20018
20019       -mconstant-gp
20020           Generate code that uses a single constant global pointer value.
20021           This is useful when compiling kernel code.
20022
20023       -mauto-pic
20024           Generate code that is self-relocatable.  This implies
20025           -mconstant-gp.  This is useful when compiling firmware code.
20026
20027       -minline-float-divide-min-latency
20028           Generate code for inline divides of floating-point values using the
20029           minimum latency algorithm.
20030
20031       -minline-float-divide-max-throughput
20032           Generate code for inline divides of floating-point values using the
20033           maximum throughput algorithm.
20034
20035       -mno-inline-float-divide
20036           Do not generate inline code for divides of floating-point values.
20037
20038       -minline-int-divide-min-latency
20039           Generate code for inline divides of integer values using the
20040           minimum latency algorithm.
20041
20042       -minline-int-divide-max-throughput
20043           Generate code for inline divides of integer values using the
20044           maximum throughput algorithm.
20045
20046       -mno-inline-int-divide
20047           Do not generate inline code for divides of integer values.
20048
20049       -minline-sqrt-min-latency
20050           Generate code for inline square roots using the minimum latency
20051           algorithm.
20052
20053       -minline-sqrt-max-throughput
20054           Generate code for inline square roots using the maximum throughput
20055           algorithm.
20056
20057       -mno-inline-sqrt
20058           Do not generate inline code for "sqrt".
20059
20060       -mfused-madd
20061       -mno-fused-madd
20062           Do (don't) generate code that uses the fused multiply/add or
20063           multiply/subtract instructions.  The default is to use these
20064           instructions.
20065
20066       -mno-dwarf2-asm
20067       -mdwarf2-asm
20068           Don't (or do) generate assembler code for the DWARF line number
20069           debugging info.  This may be useful when not using the GNU
20070           assembler.
20071
20072       -mearly-stop-bits
20073       -mno-early-stop-bits
20074           Allow stop bits to be placed earlier than immediately preceding the
20075           instruction that triggered the stop bit.  This can improve
20076           instruction scheduling, but does not always do so.
20077
20078       -mfixed-range=register-range
20079           Generate code treating the given register range as fixed registers.
20080           A fixed register is one that the register allocator cannot use.
20081           This is useful when compiling kernel code.  A register range is
20082           specified as two registers separated by a dash.  Multiple register
20083           ranges can be specified separated by a comma.
20084
20085       -mtls-size=tls-size
20086           Specify bit size of immediate TLS offsets.  Valid values are 14,
20087           22, and 64.
20088
20089       -mtune=cpu-type
20090           Tune the instruction scheduling for a particular CPU, Valid values
20091           are itanium, itanium1, merced, itanium2, and mckinley.
20092
20093       -milp32
20094       -mlp64
20095           Generate code for a 32-bit or 64-bit environment.  The 32-bit
20096           environment sets int, long and pointer to 32 bits.  The 64-bit
20097           environment sets int to 32 bits and long and pointer to 64 bits.
20098           These are HP-UX specific flags.
20099
20100       -mno-sched-br-data-spec
20101       -msched-br-data-spec
20102           (Dis/En)able data speculative scheduling before reload.  This
20103           results in generation of "ld.a" instructions and the corresponding
20104           check instructions ("ld.c" / "chk.a").  The default setting is
20105           disabled.
20106
20107       -msched-ar-data-spec
20108       -mno-sched-ar-data-spec
20109           (En/Dis)able data speculative scheduling after reload.  This
20110           results in generation of "ld.a" instructions and the corresponding
20111           check instructions ("ld.c" / "chk.a").  The default setting is
20112           enabled.
20113
20114       -mno-sched-control-spec
20115       -msched-control-spec
20116           (Dis/En)able control speculative scheduling.  This feature is
20117           available only during region scheduling (i.e. before reload).  This
20118           results in generation of the "ld.s" instructions and the
20119           corresponding check instructions "chk.s".  The default setting is
20120           disabled.
20121
20122       -msched-br-in-data-spec
20123       -mno-sched-br-in-data-spec
20124           (En/Dis)able speculative scheduling of the instructions that are
20125           dependent on the data speculative loads before reload.  This is
20126           effective only with -msched-br-data-spec enabled.  The default
20127           setting is enabled.
20128
20129       -msched-ar-in-data-spec
20130       -mno-sched-ar-in-data-spec
20131           (En/Dis)able speculative scheduling of the instructions that are
20132           dependent on the data speculative loads after reload.  This is
20133           effective only with -msched-ar-data-spec enabled.  The default
20134           setting is enabled.
20135
20136       -msched-in-control-spec
20137       -mno-sched-in-control-spec
20138           (En/Dis)able speculative scheduling of the instructions that are
20139           dependent on the control speculative loads.  This is effective only
20140           with -msched-control-spec enabled.  The default setting is enabled.
20141
20142       -mno-sched-prefer-non-data-spec-insns
20143       -msched-prefer-non-data-spec-insns
20144           If enabled, data-speculative instructions are chosen for schedule
20145           only if there are no other choices at the moment.  This makes the
20146           use of the data speculation much more conservative.  The default
20147           setting is disabled.
20148
20149       -mno-sched-prefer-non-control-spec-insns
20150       -msched-prefer-non-control-spec-insns
20151           If enabled, control-speculative instructions are chosen for
20152           schedule only if there are no other choices at the moment.  This
20153           makes the use of the control speculation much more conservative.
20154           The default setting is disabled.
20155
20156       -mno-sched-count-spec-in-critical-path
20157       -msched-count-spec-in-critical-path
20158           If enabled, speculative dependencies are considered during
20159           computation of the instructions priorities.  This makes the use of
20160           the speculation a bit more conservative.  The default setting is
20161           disabled.
20162
20163       -msched-spec-ldc
20164           Use a simple data speculation check.  This option is on by default.
20165
20166       -msched-control-spec-ldc
20167           Use a simple check for control speculation.  This option is on by
20168           default.
20169
20170       -msched-stop-bits-after-every-cycle
20171           Place a stop bit after every cycle when scheduling.  This option is
20172           on by default.
20173
20174       -msched-fp-mem-deps-zero-cost
20175           Assume that floating-point stores and loads are not likely to cause
20176           a conflict when placed into the same instruction group.  This
20177           option is disabled by default.
20178
20179       -msel-sched-dont-check-control-spec
20180           Generate checks for control speculation in selective scheduling.
20181           This flag is disabled by default.
20182
20183       -msched-max-memory-insns=max-insns
20184           Limit on the number of memory insns per instruction group, giving
20185           lower priority to subsequent memory insns attempting to schedule in
20186           the same instruction group. Frequently useful to prevent cache bank
20187           conflicts.  The default value is 1.
20188
20189       -msched-max-memory-insns-hard-limit
20190           Makes the limit specified by msched-max-memory-insns a hard limit,
20191           disallowing more than that number in an instruction group.
20192           Otherwise, the limit is "soft", meaning that non-memory operations
20193           are preferred when the limit is reached, but memory operations may
20194           still be scheduled.
20195
20196       LM32 Options
20197
20198       These -m options are defined for the LatticeMico32 architecture:
20199
20200       -mbarrel-shift-enabled
20201           Enable barrel-shift instructions.
20202
20203       -mdivide-enabled
20204           Enable divide and modulus instructions.
20205
20206       -mmultiply-enabled
20207           Enable multiply instructions.
20208
20209       -msign-extend-enabled
20210           Enable sign extend instructions.
20211
20212       -muser-enabled
20213           Enable user-defined instructions.
20214
20215       M32C Options
20216
20217       -mcpu=name
20218           Select the CPU for which code is generated.  name may be one of r8c
20219           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
20220           m32cm for the M16C/80 series, or m32c for the M32C/80 series.
20221
20222       -msim
20223           Specifies that the program will be run on the simulator.  This
20224           causes an alternate runtime library to be linked in which supports,
20225           for example, file I/O.  You must not use this option when
20226           generating programs that will run on real hardware; you must
20227           provide your own runtime library for whatever I/O functions are
20228           needed.
20229
20230       -memregs=number
20231           Specifies the number of memory-based pseudo-registers GCC uses
20232           during code generation.  These pseudo-registers are used like real
20233           registers, so there is a tradeoff between GCC's ability to fit the
20234           code into available registers, and the performance penalty of using
20235           memory instead of registers.  Note that all modules in a program
20236           must be compiled with the same value for this option.  Because of
20237           that, you must not use this option with GCC's default runtime
20238           libraries.
20239
20240       M32R/D Options
20241
20242       These -m options are defined for Renesas M32R/D architectures:
20243
20244       -m32r2
20245           Generate code for the M32R/2.
20246
20247       -m32rx
20248           Generate code for the M32R/X.
20249
20250       -m32r
20251           Generate code for the M32R.  This is the default.
20252
20253       -mmodel=small
20254           Assume all objects live in the lower 16MB of memory (so that their
20255           addresses can be loaded with the "ld24" instruction), and assume
20256           all subroutines are reachable with the "bl" instruction.  This is
20257           the default.
20258
20259           The addressability of a particular object can be set with the
20260           "model" attribute.
20261
20262       -mmodel=medium
20263           Assume objects may be anywhere in the 32-bit address space (the
20264           compiler generates "seth/add3" instructions to load their
20265           addresses), and assume all subroutines are reachable with the "bl"
20266           instruction.
20267
20268       -mmodel=large
20269           Assume objects may be anywhere in the 32-bit address space (the
20270           compiler generates "seth/add3" instructions to load their
20271           addresses), and assume subroutines may not be reachable with the
20272           "bl" instruction (the compiler generates the much slower
20273           "seth/add3/jl" instruction sequence).
20274
20275       -msdata=none
20276           Disable use of the small data area.  Variables are put into one of
20277           ".data", ".bss", or ".rodata" (unless the "section" attribute has
20278           been specified).  This is the default.
20279
20280           The small data area consists of sections ".sdata" and ".sbss".
20281           Objects may be explicitly put in the small data area with the
20282           "section" attribute using one of these sections.
20283
20284       -msdata=sdata
20285           Put small global and static data in the small data area, but do not
20286           generate special code to reference them.
20287
20288       -msdata=use
20289           Put small global and static data in the small data area, and
20290           generate special instructions to reference them.
20291
20292       -G num
20293           Put global and static objects less than or equal to num bytes into
20294           the small data or BSS sections instead of the normal data or BSS
20295           sections.  The default value of num is 8.  The -msdata option must
20296           be set to one of sdata or use for this option to have any effect.
20297
20298           All modules should be compiled with the same -G num value.
20299           Compiling with different values of num may or may not work; if it
20300           doesn't the linker gives an error message---incorrect code is not
20301           generated.
20302
20303       -mdebug
20304           Makes the M32R-specific code in the compiler display some
20305           statistics that might help in debugging programs.
20306
20307       -malign-loops
20308           Align all loops to a 32-byte boundary.
20309
20310       -mno-align-loops
20311           Do not enforce a 32-byte alignment for loops.  This is the default.
20312
20313       -missue-rate=number
20314           Issue number instructions per cycle.  number can only be 1 or 2.
20315
20316       -mbranch-cost=number
20317           number can only be 1 or 2.  If it is 1 then branches are preferred
20318           over conditional code, if it is 2, then the opposite applies.
20319
20320       -mflush-trap=number
20321           Specifies the trap number to use to flush the cache.  The default
20322           is 12.  Valid numbers are between 0 and 15 inclusive.
20323
20324       -mno-flush-trap
20325           Specifies that the cache cannot be flushed by using a trap.
20326
20327       -mflush-func=name
20328           Specifies the name of the operating system function to call to
20329           flush the cache.  The default is _flush_cache, but a function call
20330           is only used if a trap is not available.
20331
20332       -mno-flush-func
20333           Indicates that there is no OS function for flushing the cache.
20334
20335       M680x0 Options
20336
20337       These are the -m options defined for M680x0 and ColdFire processors.
20338       The default settings depend on which architecture was selected when the
20339       compiler was configured; the defaults for the most common choices are
20340       given below.
20341
20342       -march=arch
20343           Generate code for a specific M680x0 or ColdFire instruction set
20344           architecture.  Permissible values of arch for M680x0 architectures
20345           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
20346           architectures are selected according to Freescale's ISA
20347           classification and the permissible values are: isaa, isaaplus, isab
20348           and isac.
20349
20350           GCC defines a macro "__mcfarch__" whenever it is generating code
20351           for a ColdFire target.  The arch in this macro is one of the -march
20352           arguments given above.
20353
20354           When used together, -march and -mtune select code that runs on a
20355           family of similar processors but that is optimized for a particular
20356           microarchitecture.
20357
20358       -mcpu=cpu
20359           Generate code for a specific M680x0 or ColdFire processor.  The
20360           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
20361           68332 and cpu32.  The ColdFire cpus are given by the table below,
20362           which also classifies the CPUs into families:
20363
20364           Family : -mcpu arguments
20365           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
20366           5206 : 5202 5204 5206
20367           5206e : 5206e
20368           5208 : 5207 5208
20369           5211a : 5210a 5211a
20370           5213 : 5211 5212 5213
20371           5216 : 5214 5216
20372           52235 : 52230 52231 52232 52233 52234 52235
20373           5225 : 5224 5225
20374           52259 : 52252 52254 52255 52256 52258 52259
20375           5235 : 5232 5233 5234 5235 523x
20376           5249 : 5249
20377           5250 : 5250
20378           5271 : 5270 5271
20379           5272 : 5272
20380           5275 : 5274 5275
20381           5282 : 5280 5281 5282 528x
20382           53017 : 53011 53012 53013 53014 53015 53016 53017
20383           5307 : 5307
20384           5329 : 5327 5328 5329 532x
20385           5373 : 5372 5373 537x
20386           5407 : 5407
20387           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
20388           5485
20389
20390           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
20391           Other combinations of -mcpu and -march are rejected.
20392
20393           GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is
20394           selected.  It also defines "__mcf_family_family", where the value
20395           of family is given by the table above.
20396
20397       -mtune=tune
20398           Tune the code for a particular microarchitecture within the
20399           constraints set by -march and -mcpu.  The M680x0 microarchitectures
20400           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
20401           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
20402
20403           You can also use -mtune=68020-40 for code that needs to run
20404           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
20405           is similar but includes 68060 targets as well.  These two options
20406           select the same tuning decisions as -m68020-40 and -m68020-60
20407           respectively.
20408
20409           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for
20410           680x0 architecture arch.  It also defines "mcarch" unless either
20411           -ansi or a non-GNU -std option is used.  If GCC is tuning for a
20412           range of architectures, as selected by -mtune=68020-40 or
20413           -mtune=68020-60, it defines the macros for every architecture in
20414           the range.
20415
20416           GCC also defines the macro "__muarch__" when tuning for ColdFire
20417           microarchitecture uarch, where uarch is one of the arguments given
20418           above.
20419
20420       -m68000
20421       -mc68000
20422           Generate output for a 68000.  This is the default when the compiler
20423           is configured for 68000-based systems.  It is equivalent to
20424           -march=68000.
20425
20426           Use this option for microcontrollers with a 68000 or EC000 core,
20427           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
20428
20429       -m68010
20430           Generate output for a 68010.  This is the default when the compiler
20431           is configured for 68010-based systems.  It is equivalent to
20432           -march=68010.
20433
20434       -m68020
20435       -mc68020
20436           Generate output for a 68020.  This is the default when the compiler
20437           is configured for 68020-based systems.  It is equivalent to
20438           -march=68020.
20439
20440       -m68030
20441           Generate output for a 68030.  This is the default when the compiler
20442           is configured for 68030-based systems.  It is equivalent to
20443           -march=68030.
20444
20445       -m68040
20446           Generate output for a 68040.  This is the default when the compiler
20447           is configured for 68040-based systems.  It is equivalent to
20448           -march=68040.
20449
20450           This option inhibits the use of 68881/68882 instructions that have
20451           to be emulated by software on the 68040.  Use this option if your
20452           68040 does not have code to emulate those instructions.
20453
20454       -m68060
20455           Generate output for a 68060.  This is the default when the compiler
20456           is configured for 68060-based systems.  It is equivalent to
20457           -march=68060.
20458
20459           This option inhibits the use of 68020 and 68881/68882 instructions
20460           that have to be emulated by software on the 68060.  Use this option
20461           if your 68060 does not have code to emulate those instructions.
20462
20463       -mcpu32
20464           Generate output for a CPU32.  This is the default when the compiler
20465           is configured for CPU32-based systems.  It is equivalent to
20466           -march=cpu32.
20467
20468           Use this option for microcontrollers with a CPU32 or CPU32+ core,
20469           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
20470           68341, 68349 and 68360.
20471
20472       -m5200
20473           Generate output for a 520X ColdFire CPU.  This is the default when
20474           the compiler is configured for 520X-based systems.  It is
20475           equivalent to -mcpu=5206, and is now deprecated in favor of that
20476           option.
20477
20478           Use this option for microcontroller with a 5200 core, including the
20479           MCF5202, MCF5203, MCF5204 and MCF5206.
20480
20481       -m5206e
20482           Generate output for a 5206e ColdFire CPU.  The option is now
20483           deprecated in favor of the equivalent -mcpu=5206e.
20484
20485       -m528x
20486           Generate output for a member of the ColdFire 528X family.  The
20487           option is now deprecated in favor of the equivalent -mcpu=528x.
20488
20489       -m5307
20490           Generate output for a ColdFire 5307 CPU.  The option is now
20491           deprecated in favor of the equivalent -mcpu=5307.
20492
20493       -m5407
20494           Generate output for a ColdFire 5407 CPU.  The option is now
20495           deprecated in favor of the equivalent -mcpu=5407.
20496
20497       -mcfv4e
20498           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
20499           This includes use of hardware floating-point instructions.  The
20500           option is equivalent to -mcpu=547x, and is now deprecated in favor
20501           of that option.
20502
20503       -m68020-40
20504           Generate output for a 68040, without using any of the new
20505           instructions.  This results in code that can run relatively
20506           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
20507           generated code does use the 68881 instructions that are emulated on
20508           the 68040.
20509
20510           The option is equivalent to -march=68020 -mtune=68020-40.
20511
20512       -m68020-60
20513           Generate output for a 68060, without using any of the new
20514           instructions.  This results in code that can run relatively
20515           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
20516           generated code does use the 68881 instructions that are emulated on
20517           the 68060.
20518
20519           The option is equivalent to -march=68020 -mtune=68020-60.
20520
20521       -mhard-float
20522       -m68881
20523           Generate floating-point instructions.  This is the default for
20524           68020 and above, and for ColdFire devices that have an FPU.  It
20525           defines the macro "__HAVE_68881__" on M680x0 targets and
20526           "__mcffpu__" on ColdFire targets.
20527
20528       -msoft-float
20529           Do not generate floating-point instructions; use library calls
20530           instead.  This is the default for 68000, 68010, and 68832 targets.
20531           It is also the default for ColdFire devices that have no FPU.
20532
20533       -mdiv
20534       -mno-div
20535           Generate (do not generate) ColdFire hardware divide and remainder
20536           instructions.  If -march is used without -mcpu, the default is "on"
20537           for ColdFire architectures and "off" for M680x0 architectures.
20538           Otherwise, the default is taken from the target CPU (either the
20539           default CPU, or the one specified by -mcpu).  For example, the
20540           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.
20541
20542           GCC defines the macro "__mcfhwdiv__" when this option is enabled.
20543
20544       -mshort
20545           Consider type "int" to be 16 bits wide, like "short int".
20546           Additionally, parameters passed on the stack are also aligned to a
20547           16-bit boundary even on targets whose API mandates promotion to
20548           32-bit.
20549
20550       -mno-short
20551           Do not consider type "int" to be 16 bits wide.  This is the
20552           default.
20553
20554       -mnobitfield
20555       -mno-bitfield
20556           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
20557           -m5200 options imply -mnobitfield.
20558
20559       -mbitfield
20560           Do use the bit-field instructions.  The -m68020 option implies
20561           -mbitfield.  This is the default if you use a configuration
20562           designed for a 68020.
20563
20564       -mrtd
20565           Use a different function-calling convention, in which functions
20566           that take a fixed number of arguments return with the "rtd"
20567           instruction, which pops their arguments while returning.  This
20568           saves one instruction in the caller since there is no need to pop
20569           the arguments there.
20570
20571           This calling convention is incompatible with the one normally used
20572           on Unix, so you cannot use it if you need to call libraries
20573           compiled with the Unix compiler.
20574
20575           Also, you must provide function prototypes for all functions that
20576           take variable numbers of arguments (including "printf"); otherwise
20577           incorrect code is generated for calls to those functions.
20578
20579           In addition, seriously incorrect code results if you call a
20580           function with too many arguments.  (Normally, extra arguments are
20581           harmlessly ignored.)
20582
20583           The "rtd" instruction is supported by the 68010, 68020, 68030,
20584           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
20585
20586           The default is -mno-rtd.
20587
20588       -malign-int
20589       -mno-align-int
20590           Control whether GCC aligns "int", "long", "long long", "float",
20591           "double", and "long double" variables on a 32-bit boundary
20592           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
20593           variables on 32-bit boundaries produces code that runs somewhat
20594           faster on processors with 32-bit busses at the expense of more
20595           memory.
20596
20597           Warning: if you use the -malign-int switch, GCC aligns structures
20598           containing the above types differently than most published
20599           application binary interface specifications for the m68k.
20600
20601           Use the pc-relative addressing mode of the 68000 directly, instead
20602           of using a global offset table.  At present, this option implies
20603           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
20604           -fPIC is not presently supported with -mpcrel, though this could be
20605           supported for 68020 and higher processors.
20606
20607       -mno-strict-align
20608       -mstrict-align
20609           Do not (do) assume that unaligned memory references are handled by
20610           the system.
20611
20612       -msep-data
20613           Generate code that allows the data segment to be located in a
20614           different area of memory from the text segment.  This allows for
20615           execute-in-place in an environment without virtual memory
20616           management.  This option implies -fPIC.
20617
20618       -mno-sep-data
20619           Generate code that assumes that the data segment follows the text
20620           segment.  This is the default.
20621
20622       -mid-shared-library
20623           Generate code that supports shared libraries via the library ID
20624           method.  This allows for execute-in-place and shared libraries in
20625           an environment without virtual memory management.  This option
20626           implies -fPIC.
20627
20628       -mno-id-shared-library
20629           Generate code that doesn't assume ID-based shared libraries are
20630           being used.  This is the default.
20631
20632       -mshared-library-id=n
20633           Specifies the identification number of the ID-based shared library
20634           being compiled.  Specifying a value of 0 generates more compact
20635           code; specifying other values forces the allocation of that number
20636           to the current library, but is no more space- or time-efficient
20637           than omitting this option.
20638
20639       -mxgot
20640       -mno-xgot
20641           When generating position-independent code for ColdFire, generate
20642           code that works if the GOT has more than 8192 entries.  This code
20643           is larger and slower than code generated without this option.  On
20644           M680x0 processors, this option is not needed; -fPIC suffices.
20645
20646           GCC normally uses a single instruction to load values from the GOT.
20647           While this is relatively efficient, it only works if the GOT is
20648           smaller than about 64k.  Anything larger causes the linker to
20649           report an error such as:
20650
20651                   relocation truncated to fit: R_68K_GOT16O foobar
20652
20653           If this happens, you should recompile your code with -mxgot.  It
20654           should then work with very large GOTs.  However, code generated
20655           with -mxgot is less efficient, since it takes 4 instructions to
20656           fetch the value of a global symbol.
20657
20658           Note that some linkers, including newer versions of the GNU linker,
20659           can create multiple GOTs and sort GOT entries.  If you have such a
20660           linker, you should only need to use -mxgot when compiling a single
20661           object file that accesses more than 8192 GOT entries.  Very few do.
20662
20663           These options have no effect unless GCC is generating position-
20664           independent code.
20665
20666       -mlong-jump-table-offsets
20667           Use 32-bit offsets in "switch" tables.  The default is to use
20668           16-bit offsets.
20669
20670       MCore Options
20671
20672       These are the -m options defined for the Motorola M*Core processors.
20673
20674       -mhardlit
20675       -mno-hardlit
20676           Inline constants into the code stream if it can be done in two
20677           instructions or less.
20678
20679       -mdiv
20680       -mno-div
20681           Use the divide instruction.  (Enabled by default).
20682
20683       -mrelax-immediate
20684       -mno-relax-immediate
20685           Allow arbitrary-sized immediates in bit operations.
20686
20687       -mwide-bitfields
20688       -mno-wide-bitfields
20689           Always treat bit-fields as "int"-sized.
20690
20691       -m4byte-functions
20692       -mno-4byte-functions
20693           Force all functions to be aligned to a 4-byte boundary.
20694
20695       -mcallgraph-data
20696       -mno-callgraph-data
20697           Emit callgraph information.
20698
20699       -mslow-bytes
20700       -mno-slow-bytes
20701           Prefer word access when reading byte quantities.
20702
20703       -mlittle-endian
20704       -mbig-endian
20705           Generate code for a little-endian target.
20706
20707       -m210
20708       -m340
20709           Generate code for the 210 processor.
20710
20711       -mno-lsim
20712           Assume that runtime support has been provided and so omit the
20713           simulator library (libsim.a) from the linker command line.
20714
20715       -mstack-increment=size
20716           Set the maximum amount for a single stack increment operation.
20717           Large values can increase the speed of programs that contain
20718           functions that need a large amount of stack space, but they can
20719           also trigger a segmentation fault if the stack is extended too
20720           much.  The default value is 0x1000.
20721
20722       MeP Options
20723
20724       -mabsdiff
20725           Enables the "abs" instruction, which is the absolute difference
20726           between two registers.
20727
20728       -mall-opts
20729           Enables all the optional instructions---average, multiply, divide,
20730           bit operations, leading zero, absolute difference, min/max, clip,
20731           and saturation.
20732
20733       -maverage
20734           Enables the "ave" instruction, which computes the average of two
20735           registers.
20736
20737       -mbased=n
20738           Variables of size n bytes or smaller are placed in the ".based"
20739           section by default.  Based variables use the $tp register as a base
20740           register, and there is a 128-byte limit to the ".based" section.
20741
20742       -mbitops
20743           Enables the bit operation instructions---bit test ("btstm"), set
20744           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
20745           ("tas").
20746
20747       -mc=name
20748           Selects which section constant data is placed in.  name may be
20749           tiny, near, or far.
20750
20751       -mclip
20752           Enables the "clip" instruction.  Note that -mclip is not useful
20753           unless you also provide -mminmax.
20754
20755       -mconfig=name
20756           Selects one of the built-in core configurations.  Each MeP chip has
20757           one or more modules in it; each module has a core CPU and a variety
20758           of coprocessors, optional instructions, and peripherals.  The
20759           "MeP-Integrator" tool, not part of GCC, provides these
20760           configurations through this option; using this option is the same
20761           as using all the corresponding command-line options.  The default
20762           configuration is default.
20763
20764       -mcop
20765           Enables the coprocessor instructions.  By default, this is a 32-bit
20766           coprocessor.  Note that the coprocessor is normally enabled via the
20767           -mconfig= option.
20768
20769       -mcop32
20770           Enables the 32-bit coprocessor's instructions.
20771
20772       -mcop64
20773           Enables the 64-bit coprocessor's instructions.
20774
20775       -mivc2
20776           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
20777
20778       -mdc
20779           Causes constant variables to be placed in the ".near" section.
20780
20781       -mdiv
20782           Enables the "div" and "divu" instructions.
20783
20784       -meb
20785           Generate big-endian code.
20786
20787       -mel
20788           Generate little-endian code.
20789
20790       -mio-volatile
20791           Tells the compiler that any variable marked with the "io" attribute
20792           is to be considered volatile.
20793
20794       -ml Causes variables to be assigned to the ".far" section by default.
20795
20796       -mleadz
20797           Enables the "leadz" (leading zero) instruction.
20798
20799       -mm Causes variables to be assigned to the ".near" section by default.
20800
20801       -mminmax
20802           Enables the "min" and "max" instructions.
20803
20804       -mmult
20805           Enables the multiplication and multiply-accumulate instructions.
20806
20807       -mno-opts
20808           Disables all the optional instructions enabled by -mall-opts.
20809
20810       -mrepeat
20811           Enables the "repeat" and "erepeat" instructions, used for low-
20812           overhead looping.
20813
20814       -ms Causes all variables to default to the ".tiny" section.  Note that
20815           there is a 65536-byte limit to this section.  Accesses to these
20816           variables use the %gp base register.
20817
20818       -msatur
20819           Enables the saturation instructions.  Note that the compiler does
20820           not currently generate these itself, but this option is included
20821           for compatibility with other tools, like "as".
20822
20823       -msdram
20824           Link the SDRAM-based runtime instead of the default ROM-based
20825           runtime.
20826
20827       -msim
20828           Link the simulator run-time libraries.
20829
20830       -msimnovec
20831           Link the simulator runtime libraries, excluding built-in support
20832           for reset and exception vectors and tables.
20833
20834       -mtf
20835           Causes all functions to default to the ".far" section.  Without
20836           this option, functions default to the ".near" section.
20837
20838       -mtiny=n
20839           Variables that are n bytes or smaller are allocated to the ".tiny"
20840           section.  These variables use the $gp base register.  The default
20841           for this option is 4, but note that there's a 65536-byte limit to
20842           the ".tiny" section.
20843
20844       MicroBlaze Options
20845
20846       -msoft-float
20847           Use software emulation for floating point (default).
20848
20849       -mhard-float
20850           Use hardware floating-point instructions.
20851
20852       -mmemcpy
20853           Do not optimize block moves, use "memcpy".
20854
20855       -mno-clearbss
20856           This option is deprecated.  Use -fno-zero-initialized-in-bss
20857           instead.
20858
20859       -mcpu=cpu-type
20860           Use features of, and schedule code for, the given CPU.  Supported
20861           values are in the format vX.YY.Z, where X is a major version, YY is
20862           the minor version, and Z is compatibility code.  Example values are
20863           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.
20864
20865       -mxl-soft-mul
20866           Use software multiply emulation (default).
20867
20868       -mxl-soft-div
20869           Use software emulation for divides (default).
20870
20871       -mxl-barrel-shift
20872           Use the hardware barrel shifter.
20873
20874       -mxl-pattern-compare
20875           Use pattern compare instructions.
20876
20877       -msmall-divides
20878           Use table lookup optimization for small signed integer divisions.
20879
20880       -mxl-stack-check
20881           This option is deprecated.  Use -fstack-check instead.
20882
20883       -mxl-gp-opt
20884           Use GP-relative ".sdata"/".sbss" sections.
20885
20886       -mxl-multiply-high
20887           Use multiply high instructions for high part of 32x32 multiply.
20888
20889       -mxl-float-convert
20890           Use hardware floating-point conversion instructions.
20891
20892       -mxl-float-sqrt
20893           Use hardware floating-point square root instruction.
20894
20895       -mbig-endian
20896           Generate code for a big-endian target.
20897
20898       -mlittle-endian
20899           Generate code for a little-endian target.
20900
20901       -mxl-reorder
20902           Use reorder instructions (swap and byte reversed load/store).
20903
20904       -mxl-mode-app-model
20905           Select application model app-model.  Valid models are
20906
20907           executable
20908               normal executable (default), uses startup code crt0.o.
20909
20910           -mpic-data-is-text-relative
20911               Assume that the displacement between the text and data segments
20912               is fixed at static link time.  This allows data to be
20913               referenced by offset from start of text address instead of GOT
20914               since PC-relative addressing is not supported.
20915
20916           xmdstub
20917               for use with Xilinx Microprocessor Debugger (XMD) based
20918               software intrusive debug agent called xmdstub. This uses
20919               startup file crt1.o and sets the start address of the program
20920               to 0x800.
20921
20922           bootstrap
20923               for applications that are loaded using a bootloader.  This
20924               model uses startup file crt2.o which does not contain a
20925               processor reset vector handler. This is suitable for
20926               transferring control on a processor reset to the bootloader
20927               rather than the application.
20928
20929           novectors
20930               for applications that do not require any of the MicroBlaze
20931               vectors. This option may be useful for applications running
20932               within a monitoring application. This model uses crt3.o as a
20933               startup file.
20934
20935           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-
20936           model.
20937
20938       MIPS Options
20939
20940       -EB Generate big-endian code.
20941
20942       -EL Generate little-endian code.  This is the default for mips*el-*-*
20943           configurations.
20944
20945       -march=arch
20946           Generate code that runs on arch, which can be the name of a generic
20947           MIPS ISA, or the name of a particular processor.  The ISA names
20948           are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3,
20949           mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and
20950           mips64r6.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
20951           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
20952           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1,
20953           74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400, i6500,
20954           interaptiv, loongson2e, loongson2f, loongson3a, gs464, gs464e,
20955           gs264e, m4k, m14k, m14kc, m14ke, m14kec, m5100, m5101, octeon,
20956           octeon+, octeon2, octeon3, orion, p5600, p6600, r2000, r3000,
20957           r3900, r4000, r4400, r4600, r4650, r4700, r5900, r6000, r8000,
20958           rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000,
20959           vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr
20960           and xlp.  The special value from-abi selects the most compatible
20961           architecture for the selected ABI (that is, mips1 for 32-bit ABIs
20962           and mips3 for 64-bit ABIs).
20963
20964           The native Linux/GNU toolchain also supports the value native,
20965           which selects the best architecture option for the host processor.
20966           -march=native has no effect if GCC does not recognize the
20967           processor.
20968
20969           In processor names, a final 000 can be abbreviated as k (for
20970           example, -march=r2k).  Prefixes are optional, and vr may be written
20971           r.
20972
20973           Names of the form nf2_1 refer to processors with FPUs clocked at
20974           half the rate of the core, names of the form nf1_1 refer to
20975           processors with FPUs clocked at the same rate as the core, and
20976           names of the form nf3_2 refer to processors with FPUs clocked a
20977           ratio of 3:2 with respect to the core.  For compatibility reasons,
20978           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
20979           as synonyms for nf1_1.
20980
20981           GCC defines two macros based on the value of this option.  The
20982           first is "_MIPS_ARCH", which gives the name of target architecture,
20983           as a string.  The second has the form "_MIPS_ARCH_foo", where foo
20984           is the capitalized value of "_MIPS_ARCH".  For example,
20985           -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro
20986           "_MIPS_ARCH_R2000".
20987
20988           Note that the "_MIPS_ARCH" macro uses the processor names given
20989           above.  In other words, it has the full prefix and does not
20990           abbreviate 000 as k.  In the case of from-abi, the macro names the
20991           resolved architecture (either "mips1" or "mips3").  It names the
20992           default architecture when no -march option is given.
20993
20994       -mtune=arch
20995           Optimize for arch.  Among other things, this option controls the
20996           way instructions are scheduled, and the perceived cost of
20997           arithmetic operations.  The list of arch values is the same as for
20998           -march.
20999
21000           When this option is not used, GCC optimizes for the processor
21001           specified by -march.  By using -march and -mtune together, it is
21002           possible to generate code that runs on a family of processors, but
21003           optimize the code for one particular member of that family.
21004
21005           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which
21006           work in the same way as the -march ones described above.
21007
21008       -mips1
21009           Equivalent to -march=mips1.
21010
21011       -mips2
21012           Equivalent to -march=mips2.
21013
21014       -mips3
21015           Equivalent to -march=mips3.
21016
21017       -mips4
21018           Equivalent to -march=mips4.
21019
21020       -mips32
21021           Equivalent to -march=mips32.
21022
21023       -mips32r3
21024           Equivalent to -march=mips32r3.
21025
21026       -mips32r5
21027           Equivalent to -march=mips32r5.
21028
21029       -mips32r6
21030           Equivalent to -march=mips32r6.
21031
21032       -mips64
21033           Equivalent to -march=mips64.
21034
21035       -mips64r2
21036           Equivalent to -march=mips64r2.
21037
21038       -mips64r3
21039           Equivalent to -march=mips64r3.
21040
21041       -mips64r5
21042           Equivalent to -march=mips64r5.
21043
21044       -mips64r6
21045           Equivalent to -march=mips64r6.
21046
21047       -mips16
21048       -mno-mips16
21049           Generate (do not generate) MIPS16 code.  If GCC is targeting a
21050           MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.
21051
21052           MIPS16 code generation can also be controlled on a per-function
21053           basis by means of "mips16" and "nomips16" attributes.
21054
21055       -mflip-mips16
21056           Generate MIPS16 code on alternating functions.  This option is
21057           provided for regression testing of mixed MIPS16/non-MIPS16 code
21058           generation, and is not intended for ordinary use in compiling user
21059           code.
21060
21061       -minterlink-compressed
21062       -mno-interlink-compressed
21063           Require (do not require) that code using the standard
21064           (uncompressed) MIPS ISA be link-compatible with MIPS16 and
21065           microMIPS code, and vice versa.
21066
21067           For example, code using the standard ISA encoding cannot jump
21068           directly to MIPS16 or microMIPS code; it must either use a call or
21069           an indirect jump.  -minterlink-compressed therefore disables direct
21070           jumps unless GCC knows that the target of the jump is not
21071           compressed.
21072
21073       -minterlink-mips16
21074       -mno-interlink-mips16
21075           Aliases of -minterlink-compressed and -mno-interlink-compressed.
21076           These options predate the microMIPS ASE and are retained for
21077           backwards compatibility.
21078
21079       -mabi=32
21080       -mabi=o64
21081       -mabi=n32
21082       -mabi=64
21083       -mabi=eabi
21084           Generate code for the given ABI.
21085
21086           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
21087           generates 64-bit code when you select a 64-bit architecture, but
21088           you can use -mgp32 to get 32-bit code instead.
21089
21090           For information about the O64 ABI, see
21091           <http://gcc.gnu.org/projects/mipso64-abi.html>.
21092
21093           GCC supports a variant of the o32 ABI in which floating-point
21094           registers are 64 rather than 32 bits wide.  You can select this
21095           combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1"
21096           and "mfhc1" instructions and is therefore only supported for
21097           MIPS32R2, MIPS32R3 and MIPS32R5 processors.
21098
21099           The register assignments for arguments and return values remain the
21100           same, but each scalar value is passed in a single 64-bit register
21101           rather than a pair of 32-bit registers.  For example, scalar
21102           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
21103           The set of call-saved registers also remains the same in that the
21104           even-numbered double-precision registers are saved.
21105
21106           Two additional variants of the o32 ABI are supported to enable a
21107           transition from 32-bit to 64-bit registers.  These are FPXX
21108           (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).  The FPXX extension
21109           mandates that all code must execute correctly when run using 32-bit
21110           or 64-bit registers.  The code can be interlinked with either FP32
21111           or FP64, but not both.  The FP64A extension is similar to the FP64
21112           extension but forbids the use of odd-numbered single-precision
21113           registers.  This can be used in conjunction with the "FRE" mode of
21114           FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to
21115           interlink and run in the same process without changing FPU modes.
21116
21117       -mabicalls
21118       -mno-abicalls
21119           Generate (do not generate) code that is suitable for SVR4-style
21120           dynamic objects.  -mabicalls is the default for SVR4-based systems.
21121
21122       -mshared
21123       -mno-shared
21124           Generate (do not generate) code that is fully position-independent,
21125           and that can therefore be linked into shared libraries.  This
21126           option only affects -mabicalls.
21127
21128           All -mabicalls code has traditionally been position-independent,
21129           regardless of options like -fPIC and -fpic.  However, as an
21130           extension, the GNU toolchain allows executables to use absolute
21131           accesses for locally-binding symbols.  It can also use shorter GP
21132           initialization sequences and generate direct calls to locally-
21133           defined functions.  This mode is selected by -mno-shared.
21134
21135           -mno-shared depends on binutils 2.16 or higher and generates
21136           objects that can only be linked by the GNU linker.  However, the
21137           option does not affect the ABI of the final executable; it only
21138           affects the ABI of relocatable objects.  Using -mno-shared
21139           generally makes executables both smaller and quicker.
21140
21141           -mshared is the default.
21142
21143       -mplt
21144       -mno-plt
21145           Assume (do not assume) that the static and dynamic linkers support
21146           PLTs and copy relocations.  This option only affects -mno-shared
21147           -mabicalls.  For the n64 ABI, this option has no effect without
21148           -msym32.
21149
21150           You can make -mplt the default by configuring GCC with
21151           --with-mips-plt.  The default is -mno-plt otherwise.
21152
21153       -mxgot
21154       -mno-xgot
21155           Lift (do not lift) the usual restrictions on the size of the global
21156           offset table.
21157
21158           GCC normally uses a single instruction to load values from the GOT.
21159           While this is relatively efficient, it only works if the GOT is
21160           smaller than about 64k.  Anything larger causes the linker to
21161           report an error such as:
21162
21163                   relocation truncated to fit: R_MIPS_GOT16 foobar
21164
21165           If this happens, you should recompile your code with -mxgot.  This
21166           works with very large GOTs, although the code is also less
21167           efficient, since it takes three instructions to fetch the value of
21168           a global symbol.
21169
21170           Note that some linkers can create multiple GOTs.  If you have such
21171           a linker, you should only need to use -mxgot when a single object
21172           file accesses more than 64k's worth of GOT entries.  Very few do.
21173
21174           These options have no effect unless GCC is generating position
21175           independent code.
21176
21177       -mgp32
21178           Assume that general-purpose registers are 32 bits wide.
21179
21180       -mgp64
21181           Assume that general-purpose registers are 64 bits wide.
21182
21183       -mfp32
21184           Assume that floating-point registers are 32 bits wide.
21185
21186       -mfp64
21187           Assume that floating-point registers are 64 bits wide.
21188
21189       -mfpxx
21190           Do not assume the width of floating-point registers.
21191
21192       -mhard-float
21193           Use floating-point coprocessor instructions.
21194
21195       -msoft-float
21196           Do not use floating-point coprocessor instructions.  Implement
21197           floating-point calculations using library calls instead.
21198
21199       -mno-float
21200           Equivalent to -msoft-float, but additionally asserts that the
21201           program being compiled does not perform any floating-point
21202           operations.  This option is presently supported only by some bare-
21203           metal MIPS configurations, where it may select a special set of
21204           libraries that lack all floating-point support (including, for
21205           example, the floating-point "printf" formats).  If code compiled
21206           with -mno-float accidentally contains floating-point operations, it
21207           is likely to suffer a link-time or run-time failure.
21208
21209       -msingle-float
21210           Assume that the floating-point coprocessor only supports single-
21211           precision operations.
21212
21213       -mdouble-float
21214           Assume that the floating-point coprocessor supports double-
21215           precision operations.  This is the default.
21216
21217       -modd-spreg
21218       -mno-odd-spreg
21219           Enable the use of odd-numbered single-precision floating-point
21220           registers for the o32 ABI.  This is the default for processors that
21221           are known to support these registers.  When using the o32 FPXX ABI,
21222           -mno-odd-spreg is set by default.
21223
21224       -mabs=2008
21225       -mabs=legacy
21226           These options control the treatment of the special not-a-number
21227           (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt"
21228           machine instructions.
21229
21230           By default or when -mabs=legacy is used the legacy treatment is
21231           selected.  In this case these instructions are considered
21232           arithmetic and avoided where correct operation is required and the
21233           input operand might be a NaN.  A longer sequence of instructions
21234           that manipulate the sign bit of floating-point datum manually is
21235           used instead unless the -ffinite-math-only option has also been
21236           specified.
21237
21238           The -mabs=2008 option selects the IEEE 754-2008 treatment.  In this
21239           case these instructions are considered non-arithmetic and therefore
21240           operating correctly in all cases, including in particular where the
21241           input operand is a NaN.  These instructions are therefore always
21242           used for the respective operations.
21243
21244       -mnan=2008
21245       -mnan=legacy
21246           These options control the encoding of the special not-a-number
21247           (NaN) IEEE 754 floating-point data.
21248
21249           The -mnan=legacy option selects the legacy encoding.  In this case
21250           quiet NaNs (qNaNs) are denoted by the first bit of their trailing
21251           significand field being 0, whereas signaling NaNs (sNaNs) are
21252           denoted by the first bit of their trailing significand field being
21253           1.
21254
21255           The -mnan=2008 option selects the IEEE 754-2008 encoding.  In this
21256           case qNaNs are denoted by the first bit of their trailing
21257           significand field being 1, whereas sNaNs are denoted by the first
21258           bit of their trailing significand field being 0.
21259
21260           The default is -mnan=legacy unless GCC has been configured with
21261           --with-nan=2008.
21262
21263       -mllsc
21264       -mno-llsc
21265           Use (do not use) ll, sc, and sync instructions to implement atomic
21266           memory built-in functions.  When neither option is specified, GCC
21267           uses the instructions if the target architecture supports them.
21268
21269           -mllsc is useful if the runtime environment can emulate the
21270           instructions and -mno-llsc can be useful when compiling for
21271           nonstandard ISAs.  You can make either option the default by
21272           configuring GCC with --with-llsc and --without-llsc respectively.
21273           --with-llsc is the default for some configurations; see the
21274           installation documentation for details.
21275
21276       -mdsp
21277       -mno-dsp
21278           Use (do not use) revision 1 of the MIPS DSP ASE.
21279             This option defines the preprocessor macro "__mips_dsp".  It also
21280           defines "__mips_dsp_rev" to 1.
21281
21282       -mdspr2
21283       -mno-dspr2
21284           Use (do not use) revision 2 of the MIPS DSP ASE.
21285             This option defines the preprocessor macros "__mips_dsp" and
21286           "__mips_dspr2".  It also defines "__mips_dsp_rev" to 2.
21287
21288       -msmartmips
21289       -mno-smartmips
21290           Use (do not use) the MIPS SmartMIPS ASE.
21291
21292       -mpaired-single
21293       -mno-paired-single
21294           Use (do not use) paired-single floating-point instructions.
21295             This option requires hardware floating-point support to be
21296           enabled.
21297
21298       -mdmx
21299       -mno-mdmx
21300           Use (do not use) MIPS Digital Media Extension instructions.  This
21301           option can only be used when generating 64-bit code and requires
21302           hardware floating-point support to be enabled.
21303
21304       -mips3d
21305       -mno-mips3d
21306           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
21307           -mpaired-single.
21308
21309       -mmicromips
21310       -mno-micromips
21311           Generate (do not generate) microMIPS code.
21312
21313           MicroMIPS code generation can also be controlled on a per-function
21314           basis by means of "micromips" and "nomicromips" attributes.
21315
21316       -mmt
21317       -mno-mt
21318           Use (do not use) MT Multithreading instructions.
21319
21320       -mmcu
21321       -mno-mcu
21322           Use (do not use) the MIPS MCU ASE instructions.
21323
21324       -meva
21325       -mno-eva
21326           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
21327
21328       -mvirt
21329       -mno-virt
21330           Use (do not use) the MIPS Virtualization (VZ) instructions.
21331
21332       -mxpa
21333       -mno-xpa
21334           Use (do not use) the MIPS eXtended Physical Address (XPA)
21335           instructions.
21336
21337       -mcrc
21338       -mno-crc
21339           Use (do not use) the MIPS Cyclic Redundancy Check (CRC)
21340           instructions.
21341
21342       -mginv
21343       -mno-ginv
21344           Use (do not use) the MIPS Global INValidate (GINV) instructions.
21345
21346       -mloongson-mmi
21347       -mno-loongson-mmi
21348           Use (do not use) the MIPS Loongson MultiMedia extensions
21349           Instructions (MMI).
21350
21351       -mloongson-ext
21352       -mno-loongson-ext
21353           Use (do not use) the MIPS Loongson EXTensions (EXT) instructions.
21354
21355       -mloongson-ext2
21356       -mno-loongson-ext2
21357           Use (do not use) the MIPS Loongson EXTensions r2 (EXT2)
21358           instructions.
21359
21360       -mlong64
21361           Force "long" types to be 64 bits wide.  See -mlong32 for an
21362           explanation of the default and the way that the pointer size is
21363           determined.
21364
21365       -mlong32
21366           Force "long", "int", and pointer types to be 32 bits wide.
21367
21368           The default size of "int"s, "long"s and pointers depends on the
21369           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
21370           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
21371           "long"s.  Pointers are the same size as "long"s, or the same size
21372           as integer registers, whichever is smaller.
21373
21374       -msym32
21375       -mno-sym32
21376           Assume (do not assume) that all symbols have 32-bit values,
21377           regardless of the selected ABI.  This option is useful in
21378           combination with -mabi=64 and -mno-abicalls because it allows GCC
21379           to generate shorter and faster references to symbolic addresses.
21380
21381       -G num
21382           Put definitions of externally-visible data in a small data section
21383           if that data is no bigger than num bytes.  GCC can then generate
21384           more efficient accesses to the data; see -mgpopt for details.
21385
21386           The default -G option depends on the configuration.
21387
21388       -mlocal-sdata
21389       -mno-local-sdata
21390           Extend (do not extend) the -G behavior to local data too, such as
21391           to static variables in C.  -mlocal-sdata is the default for all
21392           configurations.
21393
21394           If the linker complains that an application is using too much small
21395           data, you might want to try rebuilding the less performance-
21396           critical parts with -mno-local-sdata.  You might also want to build
21397           large libraries with -mno-local-sdata, so that the libraries leave
21398           more room for the main program.
21399
21400       -mextern-sdata
21401       -mno-extern-sdata
21402           Assume (do not assume) that externally-defined data is in a small
21403           data section if the size of that data is within the -G limit.
21404           -mextern-sdata is the default for all configurations.
21405
21406           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
21407           Mod references a variable Var that is no bigger than num bytes, you
21408           must make sure that Var is placed in a small data section.  If Var
21409           is defined by another module, you must either compile that module
21410           with a high-enough -G setting or attach a "section" attribute to
21411           Var's definition.  If Var is common, you must link the application
21412           with a high-enough -G setting.
21413
21414           The easiest way of satisfying these restrictions is to compile and
21415           link every module with the same -G option.  However, you may wish
21416           to build a library that supports several different small data
21417           limits.  You can do this by compiling the library with the highest
21418           supported -G setting and additionally using -mno-extern-sdata to
21419           stop the library from making assumptions about externally-defined
21420           data.
21421
21422       -mgpopt
21423       -mno-gpopt
21424           Use (do not use) GP-relative accesses for symbols that are known to
21425           be in a small data section; see -G, -mlocal-sdata and
21426           -mextern-sdata.  -mgpopt is the default for all configurations.
21427
21428           -mno-gpopt is useful for cases where the $gp register might not
21429           hold the value of "_gp".  For example, if the code is part of a
21430           library that might be used in a boot monitor, programs that call
21431           boot monitor routines pass an unknown value in $gp.  (In such
21432           situations, the boot monitor itself is usually compiled with -G0.)
21433
21434           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
21435
21436       -membedded-data
21437       -mno-embedded-data
21438           Allocate variables to the read-only data section first if possible,
21439           then next in the small data section if possible, otherwise in data.
21440           This gives slightly slower code than the default, but reduces the
21441           amount of RAM required when executing, and thus may be preferred
21442           for some embedded systems.
21443
21444       -muninit-const-in-rodata
21445       -mno-uninit-const-in-rodata
21446           Put uninitialized "const" variables in the read-only data section.
21447           This option is only meaningful in conjunction with -membedded-data.
21448
21449       -mcode-readable=setting
21450           Specify whether GCC may generate code that reads from executable
21451           sections.  There are three possible settings:
21452
21453           -mcode-readable=yes
21454               Instructions may freely access executable sections.  This is
21455               the default setting.
21456
21457           -mcode-readable=pcrel
21458               MIPS16 PC-relative load instructions can access executable
21459               sections, but other instructions must not do so.  This option
21460               is useful on 4KSc and 4KSd processors when the code TLBs have
21461               the Read Inhibit bit set.  It is also useful on processors that
21462               can be configured to have a dual instruction/data SRAM
21463               interface and that, like the M4K, automatically redirect PC-
21464               relative loads to the instruction RAM.
21465
21466           -mcode-readable=no
21467               Instructions must not access executable sections.  This option
21468               can be useful on targets that are configured to have a dual
21469               instruction/data SRAM interface but that (unlike the M4K) do
21470               not automatically redirect PC-relative loads to the instruction
21471               RAM.
21472
21473       -msplit-addresses
21474       -mno-split-addresses
21475           Enable (disable) use of the "%hi()" and "%lo()" assembler
21476           relocation operators.  This option has been superseded by
21477           -mexplicit-relocs but is retained for backwards compatibility.
21478
21479       -mexplicit-relocs
21480       -mno-explicit-relocs
21481           Use (do not use) assembler relocation operators when dealing with
21482           symbolic addresses.  The alternative, selected by
21483           -mno-explicit-relocs, is to use assembler macros instead.
21484
21485           -mexplicit-relocs is the default if GCC was configured to use an
21486           assembler that supports relocation operators.
21487
21488       -mcheck-zero-division
21489       -mno-check-zero-division
21490           Trap (do not trap) on integer division by zero.
21491
21492           The default is -mcheck-zero-division.
21493
21494       -mdivide-traps
21495       -mdivide-breaks
21496           MIPS systems check for division by zero by generating either a
21497           conditional trap or a break instruction.  Using traps results in
21498           smaller code, but is only supported on MIPS II and later.  Also,
21499           some versions of the Linux kernel have a bug that prevents trap
21500           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
21501           to allow conditional traps on architectures that support them and
21502           -mdivide-breaks to force the use of breaks.
21503
21504           The default is usually -mdivide-traps, but this can be overridden
21505           at configure time using --with-divide=breaks.  Divide-by-zero
21506           checks can be completely disabled using -mno-check-zero-division.
21507
21508       -mload-store-pairs
21509       -mno-load-store-pairs
21510           Enable (disable) an optimization that pairs consecutive load or
21511           store instructions to enable load/store bonding.  This option is
21512           enabled by default but only takes effect when the selected
21513           architecture is known to support bonding.
21514
21515       -mmemcpy
21516       -mno-memcpy
21517           Force (do not force) the use of "memcpy" for non-trivial block
21518           moves.  The default is -mno-memcpy, which allows GCC to inline most
21519           constant-sized copies.
21520
21521       -mlong-calls
21522       -mno-long-calls
21523           Disable (do not disable) use of the "jal" instruction.  Calling
21524           functions using "jal" is more efficient but requires the caller and
21525           callee to be in the same 256 megabyte segment.
21526
21527           This option has no effect on abicalls code.  The default is
21528           -mno-long-calls.
21529
21530       -mmad
21531       -mno-mad
21532           Enable (disable) use of the "mad", "madu" and "mul" instructions,
21533           as provided by the R4650 ISA.
21534
21535       -mimadd
21536       -mno-imadd
21537           Enable (disable) use of the "madd" and "msub" integer instructions.
21538           The default is -mimadd on architectures that support "madd" and
21539           "msub" except for the 74k architecture where it was found to
21540           generate slower code.
21541
21542       -mfused-madd
21543       -mno-fused-madd
21544           Enable (disable) use of the floating-point multiply-accumulate
21545           instructions, when they are available.  The default is
21546           -mfused-madd.
21547
21548           On the R8000 CPU when multiply-accumulate instructions are used,
21549           the intermediate product is calculated to infinite precision and is
21550           not subject to the FCSR Flush to Zero bit.  This may be undesirable
21551           in some circumstances.  On other processors the result is
21552           numerically identical to the equivalent computation using separate
21553           multiply, add, subtract and negate instructions.
21554
21555       -nocpp
21556           Tell the MIPS assembler to not run its preprocessor over user
21557           assembler files (with a .s suffix) when assembling them.
21558
21559       -mfix-24k
21560       -mno-fix-24k
21561           Work around the 24K E48 (lost data on stores during refill) errata.
21562           The workarounds are implemented by the assembler rather than by
21563           GCC.
21564
21565       -mfix-r4000
21566       -mno-fix-r4000
21567           Work around certain R4000 CPU errata:
21568
21569           -   A double-word or a variable shift may give an incorrect result
21570               if executed immediately after starting an integer division.
21571
21572           -   A double-word or a variable shift may give an incorrect result
21573               if executed while an integer multiplication is in progress.
21574
21575           -   An integer division may give an incorrect result if started in
21576               a delay slot of a taken branch or a jump.
21577
21578       -mfix-r4400
21579       -mno-fix-r4400
21580           Work around certain R4400 CPU errata:
21581
21582           -   A double-word or a variable shift may give an incorrect result
21583               if executed immediately after starting an integer division.
21584
21585       -mfix-r10000
21586       -mno-fix-r10000
21587           Work around certain R10000 errata:
21588
21589           -   "ll"/"sc" sequences may not behave atomically on revisions
21590               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.
21591
21592           This option can only be used if the target architecture supports
21593           branch-likely instructions.  -mfix-r10000 is the default when
21594           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
21595
21596       -mfix-r5900
21597       -mno-fix-r5900
21598           Do not attempt to schedule the preceding instruction into the delay
21599           slot of a branch instruction placed at the end of a short loop of
21600           six instructions or fewer and always schedule a "nop" instruction
21601           there instead.  The short loop bug under certain conditions causes
21602           loops to execute only once or twice, due to a hardware bug in the
21603           R5900 chip.  The workaround is implemented by the assembler rather
21604           than by GCC.
21605
21606       -mfix-rm7000
21607       -mno-fix-rm7000
21608           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds
21609           are implemented by the assembler rather than by GCC.
21610
21611       -mfix-vr4120
21612       -mno-fix-vr4120
21613           Work around certain VR4120 errata:
21614
21615           -   "dmultu" does not always produce the correct result.
21616
21617           -   "div" and "ddiv" do not always produce the correct result if
21618               one of the operands is negative.
21619
21620           The workarounds for the division errata rely on special functions
21621           in libgcc.a.  At present, these functions are only provided by the
21622           "mips64vr*-elf" configurations.
21623
21624           Other VR4120 errata require a NOP to be inserted between certain
21625           pairs of instructions.  These errata are handled by the assembler,
21626           not by GCC itself.
21627
21628       -mfix-vr4130
21629           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
21630           implemented by the assembler rather than by GCC, although GCC
21631           avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
21632           "dmacc" and "dmacchi" instructions are available instead.
21633
21634       -mfix-sb1
21635       -mno-fix-sb1
21636           Work around certain SB-1 CPU core errata.  (This flag currently
21637           works around the SB-1 revision 2 "F1" and "F2" floating-point
21638           errata.)
21639
21640       -mr10k-cache-barrier=setting
21641           Specify whether GCC should insert cache barriers to avoid the side
21642           effects of speculation on R10K processors.
21643
21644           In common with many processors, the R10K tries to predict the
21645           outcome of a conditional branch and speculatively executes
21646           instructions from the "taken" branch.  It later aborts these
21647           instructions if the predicted outcome is wrong.  However, on the
21648           R10K, even aborted instructions can have side effects.
21649
21650           This problem only affects kernel stores and, depending on the
21651           system, kernel loads.  As an example, a speculatively-executed
21652           store may load the target memory into cache and mark the cache line
21653           as dirty, even if the store itself is later aborted.  If a DMA
21654           operation writes to the same area of memory before the "dirty" line
21655           is flushed, the cached data overwrites the DMA-ed data.  See the
21656           R10K processor manual for a full description, including other
21657           potential problems.
21658
21659           One workaround is to insert cache barrier instructions before every
21660           memory access that might be speculatively executed and that might
21661           have side effects even if aborted.  -mr10k-cache-barrier=setting
21662           controls GCC's implementation of this workaround.  It assumes that
21663           aborted accesses to any byte in the following regions does not have
21664           side effects:
21665
21666           1.  the memory occupied by the current function's stack frame;
21667
21668           2.  the memory occupied by an incoming stack argument;
21669
21670           3.  the memory occupied by an object with a link-time-constant
21671               address.
21672
21673           It is the kernel's responsibility to ensure that speculative
21674           accesses to these regions are indeed safe.
21675
21676           If the input program contains a function declaration such as:
21677
21678                   void foo (void);
21679
21680           then the implementation of "foo" must allow "j foo" and "jal foo"
21681           to be executed speculatively.  GCC honors this restriction for
21682           functions it compiles itself.  It expects non-GCC functions (such
21683           as hand-written assembly code) to do the same.
21684
21685           The option has three forms:
21686
21687           -mr10k-cache-barrier=load-store
21688               Insert a cache barrier before a load or store that might be
21689               speculatively executed and that might have side effects even if
21690               aborted.
21691
21692           -mr10k-cache-barrier=store
21693               Insert a cache barrier before a store that might be
21694               speculatively executed and that might have side effects even if
21695               aborted.
21696
21697           -mr10k-cache-barrier=none
21698               Disable the insertion of cache barriers.  This is the default
21699               setting.
21700
21701       -mflush-func=func
21702       -mno-flush-func
21703           Specifies the function to call to flush the I and D caches, or to
21704           not call any such function.  If called, the function must take the
21705           same arguments as the common "_flush_func", that is, the address of
21706           the memory range for which the cache is being flushed, the size of
21707           the memory range, and the number 3 (to flush both caches).  The
21708           default depends on the target GCC was configured for, but commonly
21709           is either "_flush_func" or "__cpu_flush".
21710
21711       mbranch-cost=num
21712           Set the cost of branches to roughly num "simple" instructions.
21713           This cost is only a heuristic and is not guaranteed to produce
21714           consistent results across releases.  A zero cost redundantly
21715           selects the default, which is based on the -mtune setting.
21716
21717       -mbranch-likely
21718       -mno-branch-likely
21719           Enable or disable use of Branch Likely instructions, regardless of
21720           the default for the selected architecture.  By default, Branch
21721           Likely instructions may be generated if they are supported by the
21722           selected architecture.  An exception is for the MIPS32 and MIPS64
21723           architectures and processors that implement those architectures;
21724           for those, Branch Likely instructions are not be generated by
21725           default because the MIPS32 and MIPS64 architectures specifically
21726           deprecate their use.
21727
21728       -mcompact-branches=never
21729       -mcompact-branches=optimal
21730       -mcompact-branches=always
21731           These options control which form of branches will be generated.
21732           The default is -mcompact-branches=optimal.
21733
21734           The -mcompact-branches=never option ensures that compact branch
21735           instructions will never be generated.
21736
21737           The -mcompact-branches=always option ensures that a compact branch
21738           instruction will be generated if available.  If a compact branch
21739           instruction is not available, a delay slot form of the branch will
21740           be used instead.
21741
21742           This option is supported from MIPS Release 6 onwards.
21743
21744           The -mcompact-branches=optimal option will cause a delay slot
21745           branch to be used if one is available in the current ISA and the
21746           delay slot is successfully filled.  If the delay slot is not
21747           filled, a compact branch will be chosen if one is available.
21748
21749       -mfp-exceptions
21750       -mno-fp-exceptions
21751           Specifies whether FP exceptions are enabled.  This affects how FP
21752           instructions are scheduled for some processors.  The default is
21753           that FP exceptions are enabled.
21754
21755           For instance, on the SB-1, if FP exceptions are disabled, and we
21756           are emitting 64-bit code, then we can use both FP pipes.
21757           Otherwise, we can only use one FP pipe.
21758
21759       -mvr4130-align
21760       -mno-vr4130-align
21761           The VR4130 pipeline is two-way superscalar, but can only issue two
21762           instructions together if the first one is 8-byte aligned.  When
21763           this option is enabled, GCC aligns pairs of instructions that it
21764           thinks should execute in parallel.
21765
21766           This option only has an effect when optimizing for the VR4130.  It
21767           normally makes code faster, but at the expense of making it bigger.
21768           It is enabled by default at optimization level -O3.
21769
21770       -msynci
21771       -mno-synci
21772           Enable (disable) generation of "synci" instructions on
21773           architectures that support it.  The "synci" instructions (if
21774           enabled) are generated when "__builtin___clear_cache" is compiled.
21775
21776           This option defaults to -mno-synci, but the default can be
21777           overridden by configuring GCC with --with-synci.
21778
21779           When compiling code for single processor systems, it is generally
21780           safe to use "synci".  However, on many multi-core (SMP) systems, it
21781           does not invalidate the instruction caches on all cores and may
21782           lead to undefined behavior.
21783
21784       -mrelax-pic-calls
21785       -mno-relax-pic-calls
21786           Try to turn PIC calls that are normally dispatched via register $25
21787           into direct calls.  This is only possible if the linker can resolve
21788           the destination at link time and if the destination is within range
21789           for a direct call.
21790
21791           -mrelax-pic-calls is the default if GCC was configured to use an
21792           assembler and a linker that support the ".reloc" assembly directive
21793           and -mexplicit-relocs is in effect.  With -mno-explicit-relocs,
21794           this optimization can be performed by the assembler and the linker
21795           alone without help from the compiler.
21796
21797       -mmcount-ra-address
21798       -mno-mcount-ra-address
21799           Emit (do not emit) code that allows "_mcount" to modify the calling
21800           function's return address.  When enabled, this option extends the
21801           usual "_mcount" interface with a new ra-address parameter, which
21802           has type "intptr_t *" and is passed in register $12.  "_mcount" can
21803           then modify the return address by doing both of the following:
21804
21805           *   Returning the new address in register $31.
21806
21807           *   Storing the new address in "*ra-address", if ra-address is
21808               nonnull.
21809
21810           The default is -mno-mcount-ra-address.
21811
21812       -mframe-header-opt
21813       -mno-frame-header-opt
21814           Enable (disable) frame header optimization in the o32 ABI.  When
21815           using the o32 ABI, calling functions will allocate 16 bytes on the
21816           stack for the called function to write out register arguments.
21817           When enabled, this optimization will suppress the allocation of the
21818           frame header if it can be determined that it is unused.
21819
21820           This optimization is off by default at all optimization levels.
21821
21822       -mlxc1-sxc1
21823       -mno-lxc1-sxc1
21824           When applicable, enable (disable) the generation of "lwxc1",
21825           "swxc1", "ldxc1", "sdxc1" instructions.  Enabled by default.
21826
21827       -mmadd4
21828       -mno-madd4
21829           When applicable, enable (disable) the generation of 4-operand
21830           "madd.s", "madd.d" and related instructions.  Enabled by default.
21831
21832       MMIX Options
21833
21834       These options are defined for the MMIX:
21835
21836       -mlibfuncs
21837       -mno-libfuncs
21838           Specify that intrinsic library functions are being compiled,
21839           passing all values in registers, no matter the size.
21840
21841       -mepsilon
21842       -mno-epsilon
21843           Generate floating-point comparison instructions that compare with
21844           respect to the "rE" epsilon register.
21845
21846       -mabi=mmixware
21847       -mabi=gnu
21848           Generate code that passes function parameters and return values
21849           that (in the called function) are seen as registers $0 and up, as
21850           opposed to the GNU ABI which uses global registers $231 and up.
21851
21852       -mzero-extend
21853       -mno-zero-extend
21854           When reading data from memory in sizes shorter than 64 bits, use
21855           (do not use) zero-extending load instructions by default, rather
21856           than sign-extending ones.
21857
21858       -mknuthdiv
21859       -mno-knuthdiv
21860           Make the result of a division yielding a remainder have the same
21861           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
21862           the remainder follows the sign of the dividend.  Both methods are
21863           arithmetically valid, the latter being almost exclusively used.
21864
21865       -mtoplevel-symbols
21866       -mno-toplevel-symbols
21867           Prepend (do not prepend) a : to all global symbols, so the assembly
21868           code can be used with the "PREFIX" assembly directive.
21869
21870       -melf
21871           Generate an executable in the ELF format, rather than the default
21872           mmo format used by the mmix simulator.
21873
21874       -mbranch-predict
21875       -mno-branch-predict
21876           Use (do not use) the probable-branch instructions, when static
21877           branch prediction indicates a probable branch.
21878
21879       -mbase-addresses
21880       -mno-base-addresses
21881           Generate (do not generate) code that uses base addresses.  Using a
21882           base address automatically generates a request (handled by the
21883           assembler and the linker) for a constant to be set up in a global
21884           register.  The register is used for one or more base address
21885           requests within the range 0 to 255 from the value held in the
21886           register.  The generally leads to short and fast code, but the
21887           number of different data items that can be addressed is limited.
21888           This means that a program that uses lots of static data may require
21889           -mno-base-addresses.
21890
21891       -msingle-exit
21892       -mno-single-exit
21893           Force (do not force) generated code to have a single exit point in
21894           each function.
21895
21896       MN10300 Options
21897
21898       These -m options are defined for Matsushita MN10300 architectures:
21899
21900       -mmult-bug
21901           Generate code to avoid bugs in the multiply instructions for the
21902           MN10300 processors.  This is the default.
21903
21904       -mno-mult-bug
21905           Do not generate code to avoid bugs in the multiply instructions for
21906           the MN10300 processors.
21907
21908       -mam33
21909           Generate code using features specific to the AM33 processor.
21910
21911       -mno-am33
21912           Do not generate code using features specific to the AM33 processor.
21913           This is the default.
21914
21915       -mam33-2
21916           Generate code using features specific to the AM33/2.0 processor.
21917
21918       -mam34
21919           Generate code using features specific to the AM34 processor.
21920
21921       -mtune=cpu-type
21922           Use the timing characteristics of the indicated CPU type when
21923           scheduling instructions.  This does not change the targeted
21924           processor type.  The CPU type must be one of mn10300, am33, am33-2
21925           or am34.
21926
21927       -mreturn-pointer-on-d0
21928           When generating a function that returns a pointer, return the
21929           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
21930           only in "a0", and attempts to call such functions without a
21931           prototype result in errors.  Note that this option is on by
21932           default; use -mno-return-pointer-on-d0 to disable it.
21933
21934       -mno-crt0
21935           Do not link in the C run-time initialization object file.
21936
21937       -mrelax
21938           Indicate to the linker that it should perform a relaxation
21939           optimization pass to shorten branches, calls and absolute memory
21940           addresses.  This option only has an effect when used on the command
21941           line for the final link step.
21942
21943           This option makes symbolic debugging impossible.
21944
21945       -mliw
21946           Allow the compiler to generate Long Instruction Word instructions
21947           if the target is the AM33 or later.  This is the default.  This
21948           option defines the preprocessor macro "__LIW__".
21949
21950       -mno-liw
21951           Do not allow the compiler to generate Long Instruction Word
21952           instructions.  This option defines the preprocessor macro
21953           "__NO_LIW__".
21954
21955       -msetlb
21956           Allow the compiler to generate the SETLB and Lcc instructions if
21957           the target is the AM33 or later.  This is the default.  This option
21958           defines the preprocessor macro "__SETLB__".
21959
21960       -mno-setlb
21961           Do not allow the compiler to generate SETLB or Lcc instructions.
21962           This option defines the preprocessor macro "__NO_SETLB__".
21963
21964       Moxie Options
21965
21966       -meb
21967           Generate big-endian code.  This is the default for moxie-*-*
21968           configurations.
21969
21970       -mel
21971           Generate little-endian code.
21972
21973       -mmul.x
21974           Generate mul.x and umul.x instructions.  This is the default for
21975           moxiebox-*-* configurations.
21976
21977       -mno-crt0
21978           Do not link in the C run-time initialization object file.
21979
21980       MSP430 Options
21981
21982       These options are defined for the MSP430:
21983
21984       -masm-hex
21985           Force assembly output to always use hex constants.  Normally such
21986           constants are signed decimals, but this option is available for
21987           testsuite and/or aesthetic purposes.
21988
21989       -mmcu=
21990           Select the MCU to target.  This is used to create a C preprocessor
21991           symbol based upon the MCU name, converted to upper case and pre-
21992           and post-fixed with __.  This in turn is used by the msp430.h
21993           header file to select an MCU-specific supplementary header file.
21994
21995           The option also sets the ISA to use.  If the MCU name is one that
21996           is known to only support the 430 ISA then that is selected,
21997           otherwise the 430X ISA is selected.  A generic MCU name of msp430
21998           can also be used to select the 430 ISA.  Similarly the generic
21999           msp430x MCU name selects the 430X ISA.
22000
22001           In addition an MCU-specific linker script is added to the linker
22002           command line.  The script's name is the name of the MCU with .ld
22003           appended.  Thus specifying -mmcu=xxx on the gcc command line
22004           defines the C preprocessor symbol "__XXX__" and cause the linker to
22005           search for a script called xxx.ld.
22006
22007           The ISA and hardware multiply supported for the different MCUs is
22008           hard-coded into GCC.  However, an external devices.csv file can be
22009           used to extend device support beyond those that have been hard-
22010           coded.
22011
22012           GCC searches for the devices.csv file using the following methods
22013           in the given precedence order, where the first method takes
22014           precendence over the second which takes precedence over the third.
22015
22016           Include path specified with "-I" and "-L"
22017               devices.csv will be searched for in each of the directories
22018               specified by include paths and linker library search paths.
22019
22020           Path specified by the environment variable MSP430_GCC_INCLUDE_DIR
22021               Define the value of the global environment variable
22022               MSP430_GCC_INCLUDE_DIR to the full path to the directory
22023               containing devices.csv, and GCC will search this directory for
22024               devices.csv.  If devices.csv is found, this directory will also
22025               be registered as an include path, and linker library path.
22026               Header files and linker scripts in this directory can therefore
22027               be used without manually specifying "-I" and "-L" on the
22028               command line.
22029
22030           The msp430-elf{,bare}/include/devices directory
22031               Finally, GCC will examine msp430-elf{,bare}/include/devices
22032               from the toolchain root directory.  This directory does not
22033               exist in a default installation, but if the user has created it
22034               and copied devices.csv there, then the MCU data will be read.
22035               As above, this directory will also be registered as an include
22036               path, and linker library path.
22037
22038           If none of the above search methods find devices.csv, then the
22039           hard-coded MCU data is used.
22040
22041       -mwarn-mcu
22042       -mno-warn-mcu
22043           This option enables or disables warnings about conflicts between
22044           the MCU name specified by the -mmcu option and the ISA set by the
22045           -mcpu option and/or the hardware multiply support set by the
22046           -mhwmult option.  It also toggles warnings about unrecognized MCU
22047           names.  This option is on by default.
22048
22049       -mcpu=
22050           Specifies the ISA to use.  Accepted values are msp430, msp430x and
22051           msp430xv2.  This option is deprecated.  The -mmcu= option should be
22052           used to select the ISA.
22053
22054       -msim
22055           Link to the simulator runtime libraries and linker script.
22056           Overrides any scripts that would be selected by the -mmcu= option.
22057
22058       -mlarge
22059           Use large-model addressing (20-bit pointers, 20-bit "size_t").
22060
22061       -msmall
22062           Use small-model addressing (16-bit pointers, 16-bit "size_t").
22063
22064       -mrelax
22065           This option is passed to the assembler and linker, and allows the
22066           linker to perform certain optimizations that cannot be done until
22067           the final link.
22068
22069       mhwmult=
22070           Describes the type of hardware multiply supported by the target.
22071           Accepted values are none for no hardware multiply, 16bit for the
22072           original 16-bit-only multiply supported by early MCUs.  32bit for
22073           the 16/32-bit multiply supported by later MCUs and f5series for the
22074           16/32-bit multiply supported by F5-series MCUs.  A value of auto
22075           can also be given.  This tells GCC to deduce the hardware multiply
22076           support based upon the MCU name provided by the -mmcu option.  If
22077           no -mmcu option is specified or if the MCU name is not recognized
22078           then no hardware multiply support is assumed.  "auto" is the
22079           default setting.
22080
22081           Hardware multiplies are normally performed by calling a library
22082           routine.  This saves space in the generated code.  When compiling
22083           at -O3 or higher however the hardware multiplier is invoked inline.
22084           This makes for bigger, but faster code.
22085
22086           The hardware multiply routines disable interrupts whilst running
22087           and restore the previous interrupt state when they finish.  This
22088           makes them safe to use inside interrupt handlers as well as in
22089           normal code.
22090
22091       -minrt
22092           Enable the use of a minimum runtime environment - no static
22093           initializers or constructors.  This is intended for memory-
22094           constrained devices.  The compiler includes special symbols in some
22095           objects that tell the linker and runtime which code fragments are
22096           required.
22097
22098       -mtiny-printf
22099           Enable reduced code size "printf" and "puts" library functions.
22100           The tiny implementations of these functions are not reentrant, so
22101           must be used with caution in multi-threaded applications.
22102
22103           Support for streams has been removed and the string to be printed
22104           will always be sent to stdout via the "write" syscall.  The string
22105           is not buffered before it is sent to write.
22106
22107           This option requires Newlib Nano IO, so GCC must be configured with
22108           --enable-newlib-nano-formatted-io.
22109
22110       -mmax-inline-shift=
22111           This option takes an integer between 0 and 64 inclusive, and sets
22112           the maximum number of inline shift instructions which should be
22113           emitted to perform a shift operation by a constant amount.  When
22114           this value needs to be exceeded, an mspabi helper function is used
22115           instead.  The default value is 4.
22116
22117           This only affects cases where a shift by multiple positions cannot
22118           be completed with a single instruction (e.g. all shifts >1 on the
22119           430 ISA).
22120
22121           Shifts of a 32-bit value are at least twice as costly, so the value
22122           passed for this option is divided by 2 and the resulting value used
22123           instead.
22124
22125       -mcode-region=
22126       -mdata-region=
22127           These options tell the compiler where to place functions and data
22128           that do not have one of the "lower", "upper", "either" or "section"
22129           attributes.  Possible values are "lower", "upper", "either" or
22130           "any".  The first three behave like the corresponding attribute.
22131           The fourth possible value - "any" - is the default.  It leaves
22132           placement entirely up to the linker script and how it assigns the
22133           standard sections (".text", ".data", etc) to the memory regions.
22134
22135       -msilicon-errata=
22136           This option passes on a request to assembler to enable the fixes
22137           for the named silicon errata.
22138
22139       -msilicon-errata-warn=
22140           This option passes on a request to the assembler to enable warning
22141           messages when a silicon errata might need to be applied.
22142
22143       -mwarn-devices-csv
22144       -mno-warn-devices-csv
22145           Warn if devices.csv is not found or there are problem parsing it
22146           (default: on).
22147
22148       NDS32 Options
22149
22150       These options are defined for NDS32 implementations:
22151
22152       -mbig-endian
22153           Generate code in big-endian mode.
22154
22155       -mlittle-endian
22156           Generate code in little-endian mode.
22157
22158       -mreduced-regs
22159           Use reduced-set registers for register allocation.
22160
22161       -mfull-regs
22162           Use full-set registers for register allocation.
22163
22164       -mcmov
22165           Generate conditional move instructions.
22166
22167       -mno-cmov
22168           Do not generate conditional move instructions.
22169
22170       -mext-perf
22171           Generate performance extension instructions.
22172
22173       -mno-ext-perf
22174           Do not generate performance extension instructions.
22175
22176       -mext-perf2
22177           Generate performance extension 2 instructions.
22178
22179       -mno-ext-perf2
22180           Do not generate performance extension 2 instructions.
22181
22182       -mext-string
22183           Generate string extension instructions.
22184
22185       -mno-ext-string
22186           Do not generate string extension instructions.
22187
22188       -mv3push
22189           Generate v3 push25/pop25 instructions.
22190
22191       -mno-v3push
22192           Do not generate v3 push25/pop25 instructions.
22193
22194       -m16-bit
22195           Generate 16-bit instructions.
22196
22197       -mno-16-bit
22198           Do not generate 16-bit instructions.
22199
22200       -misr-vector-size=num
22201           Specify the size of each interrupt vector, which must be 4 or 16.
22202
22203       -mcache-block-size=num
22204           Specify the size of each cache block, which must be a power of 2
22205           between 4 and 512.
22206
22207       -march=arch
22208           Specify the name of the target architecture.
22209
22210       -mcmodel=code-model
22211           Set the code model to one of
22212
22213           small
22214               All the data and read-only data segments must be within 512KB
22215               addressing space.  The text segment must be within 16MB
22216               addressing space.
22217
22218           medium
22219               The data segment must be within 512KB while the read-only data
22220               segment can be within 4GB addressing space.  The text segment
22221               should be still within 16MB addressing space.
22222
22223           large
22224               All the text and data segments can be within 4GB addressing
22225               space.
22226
22227       -mctor-dtor
22228           Enable constructor/destructor feature.
22229
22230       -mrelax
22231           Guide linker to relax instructions.
22232
22233       Nios II Options
22234
22235       These are the options defined for the Altera Nios II processor.
22236
22237       -G num
22238           Put global and static objects less than or equal to num bytes into
22239           the small data or BSS sections instead of the normal data or BSS
22240           sections.  The default value of num is 8.
22241
22242       -mgpopt=option
22243       -mgpopt
22244       -mno-gpopt
22245           Generate (do not generate) GP-relative accesses.  The following
22246           option names are recognized:
22247
22248           none
22249               Do not generate GP-relative accesses.
22250
22251           local
22252               Generate GP-relative accesses for small data objects that are
22253               not external, weak, or uninitialized common symbols.  Also use
22254               GP-relative addressing for objects that have been explicitly
22255               placed in a small data section via a "section" attribute.
22256
22257           global
22258               As for local, but also generate GP-relative accesses for small
22259               data objects that are external, weak, or common.  If you use
22260               this option, you must ensure that all parts of your program
22261               (including libraries) are compiled with the same -G setting.
22262
22263           data
22264               Generate GP-relative accesses for all data objects in the
22265               program.  If you use this option, the entire data and BSS
22266               segments of your program must fit in 64K of memory and you must
22267               use an appropriate linker script to allocate them within the
22268               addressable range of the global pointer.
22269
22270           all Generate GP-relative addresses for function pointers as well as
22271               data pointers.  If you use this option, the entire text, data,
22272               and BSS segments of your program must fit in 64K of memory and
22273               you must use an appropriate linker script to allocate them
22274               within the addressable range of the global pointer.
22275
22276           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is
22277           equivalent to -mgpopt=none.
22278
22279           The default is -mgpopt except when -fpic or -fPIC is specified to
22280           generate position-independent code.  Note that the Nios II ABI does
22281           not permit GP-relative accesses from shared libraries.
22282
22283           You may need to specify -mno-gpopt explicitly when building
22284           programs that include large amounts of small data, including large
22285           GOT data sections.  In this case, the 16-bit offset for GP-relative
22286           addressing may not be large enough to allow access to the entire
22287           small data section.
22288
22289       -mgprel-sec=regexp
22290           This option specifies additional section names that can be accessed
22291           via GP-relative addressing.  It is most useful in conjunction with
22292           "section" attributes on variable declarations and a custom linker
22293           script.  The regexp is a POSIX Extended Regular Expression.
22294
22295           This option does not affect the behavior of the -G option, and the
22296           specified sections are in addition to the standard ".sdata" and
22297           ".sbss" small-data sections that are recognized by -mgpopt.
22298
22299       -mr0rel-sec=regexp
22300           This option specifies names of sections that can be accessed via a
22301           16-bit offset from "r0"; that is, in the low 32K or high 32K of the
22302           32-bit address space.  It is most useful in conjunction with
22303           "section" attributes on variable declarations and a custom linker
22304           script.  The regexp is a POSIX Extended Regular Expression.
22305
22306           In contrast to the use of GP-relative addressing for small data,
22307           zero-based addressing is never generated by default and there are
22308           no conventional section names used in standard linker scripts for
22309           sections in the low or high areas of memory.
22310
22311       -mel
22312       -meb
22313           Generate little-endian (default) or big-endian (experimental) code,
22314           respectively.
22315
22316       -march=arch
22317           This specifies the name of the target Nios II architecture.  GCC
22318           uses this name to determine what kind of instructions it can emit
22319           when generating assembly code.  Permissible names are: r1, r2.
22320
22321           The preprocessor macro "__nios2_arch__" is available to programs,
22322           with value 1 or 2, indicating the targeted ISA level.
22323
22324       -mbypass-cache
22325       -mno-bypass-cache
22326           Force all load and store instructions to always bypass cache by
22327           using I/O variants of the instructions. The default is not to
22328           bypass the cache.
22329
22330       -mno-cache-volatile
22331       -mcache-volatile
22332           Volatile memory access bypass the cache using the I/O variants of
22333           the load and store instructions. The default is not to bypass the
22334           cache.
22335
22336       -mno-fast-sw-div
22337       -mfast-sw-div
22338           Do not use table-based fast divide for small numbers. The default
22339           is to use the fast divide at -O3 and above.
22340
22341       -mno-hw-mul
22342       -mhw-mul
22343       -mno-hw-mulx
22344       -mhw-mulx
22345       -mno-hw-div
22346       -mhw-div
22347           Enable or disable emitting "mul", "mulx" and "div" family of
22348           instructions by the compiler. The default is to emit "mul" and not
22349           emit "div" and "mulx".
22350
22351       -mbmx
22352       -mno-bmx
22353       -mcdx
22354       -mno-cdx
22355           Enable or disable generation of Nios II R2 BMX (bit manipulation)
22356           and CDX (code density) instructions.  Enabling these instructions
22357           also requires -march=r2.  Since these instructions are optional
22358           extensions to the R2 architecture, the default is not to emit them.
22359
22360       -mcustom-insn=N
22361       -mno-custom-insn
22362           Each -mcustom-insn=N option enables use of a custom instruction
22363           with encoding N when generating code that uses insn.  For example,
22364           -mcustom-fadds=253 generates custom instruction 253 for single-
22365           precision floating-point add operations instead of the default
22366           behavior of using a library call.
22367
22368           The following values of insn are supported.  Except as otherwise
22369           noted, floating-point operations are expected to be implemented
22370           with normal IEEE 754 semantics and correspond directly to the C
22371           operators or the equivalent GCC built-in functions.
22372
22373           Single-precision floating point:
22374
22375           fadds, fsubs, fdivs, fmuls
22376               Binary arithmetic operations.
22377
22378           fnegs
22379               Unary negation.
22380
22381           fabss
22382               Unary absolute value.
22383
22384           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
22385               Comparison operations.
22386
22387           fmins, fmaxs
22388               Floating-point minimum and maximum.  These instructions are
22389               only generated if -ffinite-math-only is specified.
22390
22391           fsqrts
22392               Unary square root operation.
22393
22394           fcoss, fsins, ftans, fatans, fexps, flogs
22395               Floating-point trigonometric and exponential functions.  These
22396               instructions are only generated if -funsafe-math-optimizations
22397               is also specified.
22398
22399           Double-precision floating point:
22400
22401           faddd, fsubd, fdivd, fmuld
22402               Binary arithmetic operations.
22403
22404           fnegd
22405               Unary negation.
22406
22407           fabsd
22408               Unary absolute value.
22409
22410           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
22411               Comparison operations.
22412
22413           fmind, fmaxd
22414               Double-precision minimum and maximum.  These instructions are
22415               only generated if -ffinite-math-only is specified.
22416
22417           fsqrtd
22418               Unary square root operation.
22419
22420           fcosd, fsind, ftand, fatand, fexpd, flogd
22421               Double-precision trigonometric and exponential functions.
22422               These instructions are only generated if
22423               -funsafe-math-optimizations is also specified.
22424
22425           Conversions:
22426
22427           fextsd
22428               Conversion from single precision to double precision.
22429
22430           ftruncds
22431               Conversion from double precision to single precision.
22432
22433           fixsi, fixsu, fixdi, fixdu
22434               Conversion from floating point to signed or unsigned integer
22435               types, with truncation towards zero.
22436
22437           round
22438               Conversion from single-precision floating point to signed
22439               integer, rounding to the nearest integer and ties away from
22440               zero.  This corresponds to the "__builtin_lroundf" function
22441               when -fno-math-errno is used.
22442
22443           floatis, floatus, floatid, floatud
22444               Conversion from signed or unsigned integer types to floating-
22445               point types.
22446
22447           In addition, all of the following transfer instructions for
22448           internal registers X and Y must be provided to use any of the
22449           double-precision floating-point instructions.  Custom instructions
22450           taking two double-precision source operands expect the first
22451           operand in the 64-bit register X.  The other operand (or only
22452           operand of a unary operation) is given to the custom arithmetic
22453           instruction with the least significant half in source register src1
22454           and the most significant half in src2.  A custom instruction that
22455           returns a double-precision result returns the most significant 32
22456           bits in the destination register and the other half in 32-bit
22457           register Y.  GCC automatically generates the necessary code
22458           sequences to write register X and/or read register Y when double-
22459           precision floating-point instructions are used.
22460
22461           fwrx
22462               Write src1 into the least significant half of X and src2 into
22463               the most significant half of X.
22464
22465           fwry
22466               Write src1 into Y.
22467
22468           frdxhi, frdxlo
22469               Read the most or least (respectively) significant half of X and
22470               store it in dest.
22471
22472           frdy
22473               Read the value of Y and store it into dest.
22474
22475           Note that you can gain more local control over generation of Nios
22476           II custom instructions by using the "target("custom-insn=N")" and
22477           "target("no-custom-insn")" function attributes or pragmas.
22478
22479       -mcustom-fpu-cfg=name
22480           This option enables a predefined, named set of custom instruction
22481           encodings (see -mcustom-insn above).  Currently, the following sets
22482           are defined:
22483
22484           -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252
22485           -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant
22486
22487           -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252
22488           -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255
22489           -fsingle-precision-constant
22490
22491           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243
22492           -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246
22493           -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251
22494           -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254
22495           -mcustom-fdivs=255 -fsingle-precision-constant
22496
22497           -mcustom-fpu-cfg=fph2 is equivalent to: -mcustom-fabss=224
22498           -mcustom-fnegs=225 -mcustom-fcmpnes=226 -mcustom-fcmpeqs=227
22499           -mcustom-fcmpges=228 -mcustom-fcmpgts=229 -mcustom-fcmples=230
22500           -mcustom-fcmplts=231 -mcustom-fmaxs=232 -mcustom-fmins=233
22501           -mcustom-round=248 -mcustom-fixsi=249 -mcustom-floatis=250
22502           -mcustom-fsqrts=251 -mcustom-fmuls=252 -mcustom-fadds=253
22503           -mcustom-fsubs=254 -mcustom-fdivs=255
22504
22505           Custom instruction assignments given by individual -mcustom-insn=
22506           options override those given by -mcustom-fpu-cfg=, regardless of
22507           the order of the options on the command line.
22508
22509           Note that you can gain more local control over selection of a FPU
22510           configuration by using the "target("custom-fpu-cfg=name")" function
22511           attribute or pragma.
22512
22513           The name fph2 is an abbreviation for Nios II Floating Point
22514           Hardware 2 Component.  Please note that the custom instructions
22515           enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are only
22516           generated if -ffinite-math-only is specified.  The custom
22517           instruction enabled by -mcustom-round=248 is only generated if
22518           -fno-math-errno is specified.  In contrast to the other
22519           configurations, -fsingle-precision-constant is not set.
22520
22521       These additional -m options are available for the Altera Nios II ELF
22522       (bare-metal) target:
22523
22524       -mhal
22525           Link with HAL BSP.  This suppresses linking with the GCC-provided C
22526           runtime startup and termination code, and is typically used in
22527           conjunction with -msys-crt0= to specify the location of the
22528           alternate startup code provided by the HAL BSP.
22529
22530       -msmallc
22531           Link with a limited version of the C library, -lsmallc, rather than
22532           Newlib.
22533
22534       -msys-crt0=startfile
22535           startfile is the file name of the startfile (crt0) to use when
22536           linking.  This option is only useful in conjunction with -mhal.
22537
22538       -msys-lib=systemlib
22539           systemlib is the library name of the library that provides low-
22540           level system calls required by the C library, e.g. "read" and
22541           "write".  This option is typically used to link with a library
22542           provided by a HAL BSP.
22543
22544       Nvidia PTX Options
22545
22546       These options are defined for Nvidia PTX:
22547
22548       -m64
22549           Ignored, but preserved for backward compatibility.  Only 64-bit ABI
22550           is supported.
22551
22552       -misa=ISA-string
22553           Generate code for given the specified PTX ISA (e.g. sm_35).  ISA
22554           strings must be lower-case.  Valid ISA strings include sm_30 and
22555           sm_35.  The default ISA is sm_35.
22556
22557       -mmainkernel
22558           Link in code for a __main kernel.  This is for stand-alone instead
22559           of offloading execution.
22560
22561       -moptimize
22562           Apply partitioned execution optimizations.  This is the default
22563           when any level of optimization is selected.
22564
22565       -msoft-stack
22566           Generate code that does not use ".local" memory directly for stack
22567           storage. Instead, a per-warp stack pointer is maintained
22568           explicitly. This enables variable-length stack allocation (with
22569           variable-length arrays or "alloca"), and when global memory is used
22570           for underlying storage, makes it possible to access automatic
22571           variables from other threads, or with atomic instructions. This
22572           code generation variant is used for OpenMP offloading, but the
22573           option is exposed on its own for the purpose of testing the
22574           compiler; to generate code suitable for linking into programs using
22575           OpenMP offloading, use option -mgomp.
22576
22577       -muniform-simt
22578           Switch to code generation variant that allows to execute all
22579           threads in each warp, while maintaining memory state and side
22580           effects as if only one thread in each warp was active outside of
22581           OpenMP SIMD regions.  All atomic operations and calls to runtime
22582           (malloc, free, vprintf) are conditionally executed (iff current
22583           lane index equals the master lane index), and the register being
22584           assigned is copied via a shuffle instruction from the master lane.
22585           Outside of SIMD regions lane 0 is the master; inside, each thread
22586           sees itself as the master.  Shared memory array "int __nvptx_uni[]"
22587           stores all-zeros or all-ones bitmasks for each warp, indicating
22588           current mode (0 outside of SIMD regions).  Each thread can bitwise-
22589           and the bitmask at position "tid.y" with current lane index to
22590           compute the master lane index.
22591
22592       -mgomp
22593           Generate code for use in OpenMP offloading: enables -msoft-stack
22594           and -muniform-simt options, and selects corresponding multilib
22595           variant.
22596
22597       OpenRISC Options
22598
22599       These options are defined for OpenRISC:
22600
22601       -mboard=name
22602           Configure a board specific runtime.  This will be passed to the
22603           linker for newlib board library linking.  The default is "or1ksim".
22604
22605       -mnewlib
22606           This option is ignored; it is for compatibility purposes only.
22607           This used to select linker and preprocessor options for use with
22608           newlib.
22609
22610       -msoft-div
22611       -mhard-div
22612           Select software or hardware divide ("l.div", "l.divu")
22613           instructions.  This default is hardware divide.
22614
22615       -msoft-mul
22616       -mhard-mul
22617           Select software or hardware multiply ("l.mul", "l.muli")
22618           instructions.  This default is hardware multiply.
22619
22620       -msoft-float
22621       -mhard-float
22622           Select software or hardware for floating point operations.  The
22623           default is software.
22624
22625       -mdouble-float
22626           When -mhard-float is selected, enables generation of double-
22627           precision floating point instructions.  By default functions from
22628           libgcc are used to perform double-precision floating point
22629           operations.
22630
22631       -munordered-float
22632           When -mhard-float is selected, enables generation of unordered
22633           floating point compare and set flag ("lf.sfun*") instructions.  By
22634           default functions from libgcc are used to perform unordered
22635           floating point compare and set flag operations.
22636
22637       -mcmov
22638           Enable generation of conditional move ("l.cmov") instructions.  By
22639           default the equivalent will be generated using set and branch.
22640
22641       -mror
22642           Enable generation of rotate right ("l.ror") instructions.  By
22643           default functions from libgcc are used to perform rotate right
22644           operations.
22645
22646       -mrori
22647           Enable generation of rotate right with immediate ("l.rori")
22648           instructions.  By default functions from libgcc are used to perform
22649           rotate right with immediate operations.
22650
22651       -msext
22652           Enable generation of sign extension ("l.ext*") instructions.  By
22653           default memory loads are used to perform sign extension.
22654
22655       -msfimm
22656           Enable generation of compare and set flag with immediate ("l.sf*i")
22657           instructions.  By default extra instructions will be generated to
22658           store the immediate to a register first.
22659
22660       -mshftimm
22661           Enable generation of shift with immediate ("l.srai", "l.srli",
22662           "l.slli") instructions.  By default extra instructions will be
22663           generated to store the immediate to a register first.
22664
22665       PDP-11 Options
22666
22667       These options are defined for the PDP-11:
22668
22669       -mfpu
22670           Use hardware FPP floating point.  This is the default.  (FIS
22671           floating point on the PDP-11/40 is not supported.)  Implies -m45.
22672
22673       -msoft-float
22674           Do not use hardware floating point.
22675
22676       -mac0
22677           Return floating-point results in ac0 (fr0 in Unix assembler
22678           syntax).
22679
22680       -mno-ac0
22681           Return floating-point results in memory.  This is the default.
22682
22683       -m40
22684           Generate code for a PDP-11/40.  Implies -msoft-float -mno-split.
22685
22686       -m45
22687           Generate code for a PDP-11/45.  This is the default.
22688
22689       -m10
22690           Generate code for a PDP-11/10.  Implies -msoft-float -mno-split.
22691
22692       -mint16
22693       -mno-int32
22694           Use 16-bit "int".  This is the default.
22695
22696       -mint32
22697       -mno-int16
22698           Use 32-bit "int".
22699
22700       -msplit
22701           Target has split instruction and data space.  Implies -m45.
22702
22703       -munix-asm
22704           Use Unix assembler syntax.
22705
22706       -mdec-asm
22707           Use DEC assembler syntax.
22708
22709       -mgnu-asm
22710           Use GNU assembler syntax.  This is the default.
22711
22712       -mlra
22713           Use the new LRA register allocator.  By default, the old "reload"
22714           allocator is used.
22715
22716       picoChip Options
22717
22718       These -m options are defined for picoChip implementations:
22719
22720       -mae=ae_type
22721           Set the instruction set, register set, and instruction scheduling
22722           parameters for array element type ae_type.  Supported values for
22723           ae_type are ANY, MUL, and MAC.
22724
22725           -mae=ANY selects a completely generic AE type.  Code generated with
22726           this option runs on any of the other AE types.  The code is not as
22727           efficient as it would be if compiled for a specific AE type, and
22728           some types of operation (e.g., multiplication) do not work properly
22729           on all types of AE.
22730
22731           -mae=MUL selects a MUL AE type.  This is the most useful AE type
22732           for compiled code, and is the default.
22733
22734           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
22735           option may suffer from poor performance of byte (char)
22736           manipulation, since the DSP AE does not provide hardware support
22737           for byte load/stores.
22738
22739       -msymbol-as-address
22740           Enable the compiler to directly use a symbol name as an address in
22741           a load/store instruction, without first loading it into a register.
22742           Typically, the use of this option generates larger programs, which
22743           run faster than when the option isn't used.  However, the results
22744           vary from program to program, so it is left as a user option,
22745           rather than being permanently enabled.
22746
22747       -mno-inefficient-warnings
22748           Disables warnings about the generation of inefficient code.  These
22749           warnings can be generated, for example, when compiling code that
22750           performs byte-level memory operations on the MAC AE type.  The MAC
22751           AE has no hardware support for byte-level memory operations, so all
22752           byte load/stores must be synthesized from word load/store
22753           operations.  This is inefficient and a warning is generated to
22754           indicate that you should rewrite the code to avoid byte operations,
22755           or to target an AE type that has the necessary hardware support.
22756           This option disables these warnings.
22757
22758       PowerPC Options
22759
22760       These are listed under
22761
22762       PRU Options
22763
22764       These command-line options are defined for PRU target:
22765
22766       -minrt
22767           Link with a minimum runtime environment, with no support for static
22768           initializers and constructors.  Using this option can significantly
22769           reduce the size of the final ELF binary.  Beware that the compiler
22770           could still generate code with static initializers and
22771           constructors.  It is up to the programmer to ensure that the source
22772           program will not use those features.
22773
22774       -mmcu=mcu
22775           Specify the PRU MCU variant to use.  Check Newlib for the exact
22776           list of supported MCUs.
22777
22778       -mno-relax
22779           Make GCC pass the --no-relax command-line option to the linker
22780           instead of the --relax option.
22781
22782       -mloop
22783           Allow (or do not allow) GCC to use the LOOP instruction.
22784
22785       -mabi=variant
22786           Specify the ABI variant to output code for.  -mabi=ti selects the
22787           unmodified TI ABI while -mabi=gnu selects a GNU variant that copes
22788           more naturally with certain GCC assumptions.  These are the
22789           differences:
22790
22791           Function Pointer Size
22792               TI ABI specifies that function (code) pointers are 16-bit,
22793               whereas GNU supports only 32-bit data and code pointers.
22794
22795           Optional Return Value Pointer
22796               Function return values larger than 64 bits are passed by using
22797               a hidden pointer as the first argument of the function.  TI
22798               ABI, though, mandates that the pointer can be NULL in case the
22799               caller is not using the returned value.  GNU always passes and
22800               expects a valid return value pointer.
22801
22802           The current -mabi=ti implementation simply raises a compile error
22803           when any of the above code constructs is detected.  As a
22804           consequence the standard C library cannot be built and it is
22805           omitted when linking with -mabi=ti.
22806
22807           Relaxation is a GNU feature and for safety reasons is disabled when
22808           using -mabi=ti.  The TI toolchain does not emit relocations for
22809           QBBx instructions, so the GNU linker cannot adjust them when
22810           shortening adjacent LDI32 pseudo instructions.
22811
22812       RISC-V Options
22813
22814       These command-line options are defined for RISC-V targets:
22815
22816       -mbranch-cost=n
22817           Set the cost of branches to roughly n instructions.
22818
22819       -mplt
22820       -mno-plt
22821           When generating PIC code, do or don't allow the use of PLTs.
22822           Ignored for non-PIC.  The default is -mplt.
22823
22824       -mabi=ABI-string
22825           Specify integer and floating-point calling convention.  ABI-string
22826           contains two parts: the size of integer types and the registers
22827           used for floating-point types.  For example -march=rv64ifd
22828           -mabi=lp64d means that long and pointers are 64-bit (implicitly
22829           defining int to be 32-bit), and that floating-point values up to 64
22830           bits wide are passed in F registers.  Contrast this with
22831           -march=rv64ifd -mabi=lp64f, which still allows the compiler to
22832           generate code that uses the F and D extensions but only allows
22833           floating-point values up to 32 bits long to be passed in registers;
22834           or -march=rv64ifd -mabi=lp64, in which no floating-point arguments
22835           will be passed in registers.
22836
22837           The default for this argument is system dependent, users who want a
22838           specific calling convention should specify one explicitly.  The
22839           valid calling conventions are: ilp32, ilp32f, ilp32d, lp64, lp64f,
22840           and lp64d.  Some calling conventions are impossible to implement on
22841           some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid
22842           because the ABI requires 64-bit values be passed in F registers,
22843           but F registers are only 32 bits wide.  There is also the ilp32e
22844           ABI that can only be used with the rv32e architecture.  This ABI is
22845           not well specified at present, and is subject to change.
22846
22847       -mfdiv
22848       -mno-fdiv
22849           Do or don't use hardware floating-point divide and square root
22850           instructions.  This requires the F or D extensions for floating-
22851           point registers.  The default is to use them if the specified
22852           architecture has these instructions.
22853
22854       -mdiv
22855       -mno-div
22856           Do or don't use hardware instructions for integer division.  This
22857           requires the M extension.  The default is to use them if the
22858           specified architecture has these instructions.
22859
22860       -march=ISA-string
22861           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must
22862           be lower-case.  Examples include rv64i, rv32g, rv32e, and rv32imaf.
22863
22864           When -march= is not specified, use the setting from -mcpu.
22865
22866           If both -march and -mcpu= are not specified, the default for this
22867           argument is system dependent, users who want a specific
22868           architecture extensions should specify one explicitly.
22869
22870       -mcpu=processor-string
22871           Use architecture of and optimize the output for the given
22872           processor, specified by particular CPU name.  Permissible values
22873           for this option are: sifive-e20, sifive-e21, sifive-e24,
22874           sifive-e31, sifive-e34, sifive-e76, sifive-s21, sifive-s51,
22875           sifive-s54, sifive-s76, sifive-u54, and sifive-u74.
22876
22877       -mtune=processor-string
22878           Optimize the output for the given processor, specified by
22879           microarchitecture or particular CPU name.  Permissible values for
22880           this option are: rocket, sifive-3-series, sifive-5-series,
22881           sifive-7-series, size, and all valid options for -mcpu=.
22882
22883           When -mtune= is not specified, use the setting from -mcpu, the
22884           default is rocket if both are not specified.
22885
22886           The size choice is not intended for use by end-users.  This is used
22887           when -Os is specified.  It overrides the instruction cost info
22888           provided by -mtune=, but does not override the pipeline info.  This
22889           helps reduce code size while still giving good performance.
22890
22891       -mpreferred-stack-boundary=num
22892           Attempt to keep the stack boundary aligned to a 2 raised to num
22893           byte boundary.  If -mpreferred-stack-boundary is not specified, the
22894           default is 4 (16 bytes or 128-bits).
22895
22896           Warning: If you use this switch, then you must build all modules
22897           with the same value, including any libraries.  This includes the
22898           system libraries and startup modules.
22899
22900       -msmall-data-limit=n
22901           Put global and static data smaller than n bytes into a special
22902           section (on some targets).
22903
22904       -msave-restore
22905       -mno-save-restore
22906           Do or don't use smaller but slower prologue and epilogue code that
22907           uses library function calls.  The default is to use fast inline
22908           prologues and epilogues.
22909
22910       -mshorten-memrefs
22911       -mno-shorten-memrefs
22912           Do or do not attempt to make more use of compressed load/store
22913           instructions by replacing a load/store of 'base register + large
22914           offset' with a new load/store of 'new base + small offset'.  If the
22915           new base gets stored in a compressed register, then the new
22916           load/store can be compressed.  Currently targets 32-bit integer
22917           load/stores only.
22918
22919       -mstrict-align
22920       -mno-strict-align
22921           Do not or do generate unaligned memory accesses.  The default is
22922           set depending on whether the processor we are optimizing for
22923           supports fast unaligned access or not.
22924
22925       -mcmodel=medlow
22926           Generate code for the medium-low code model. The program and its
22927           statically defined symbols must lie within a single 2 GiB address
22928           range and must lie between absolute addresses -2 GiB and +2 GiB.
22929           Programs can be statically or dynamically linked. This is the
22930           default code model.
22931
22932       -mcmodel=medany
22933           Generate code for the medium-any code model. The program and its
22934           statically defined symbols must be within any single 2 GiB address
22935           range. Programs can be statically or dynamically linked.
22936
22937       -mexplicit-relocs
22938       -mno-exlicit-relocs
22939           Use or do not use assembler relocation operators when dealing with
22940           symbolic addresses.  The alternative is to use assembler macros
22941           instead, which may limit optimization.
22942
22943       -mrelax
22944       -mno-relax
22945           Take advantage of linker relaxations to reduce the number of
22946           instructions required to materialize symbol addresses. The default
22947           is to take advantage of linker relaxations.
22948
22949       -memit-attribute
22950       -mno-emit-attribute
22951           Emit (do not emit) RISC-V attribute to record extra information
22952           into ELF objects.  This feature requires at least binutils 2.32.
22953
22954       -malign-data=type
22955           Control how GCC aligns variables and constants of array, structure,
22956           or union types.  Supported values for type are xlen which uses x
22957           register width as the alignment value, and natural which uses
22958           natural alignment.  xlen is the default.
22959
22960       -mbig-endian
22961           Generate big-endian code.  This is the default when GCC is
22962           configured for a riscv64be-*-* or riscv32be-*-* target.
22963
22964       -mlittle-endian
22965           Generate little-endian code.  This is the default when GCC is
22966           configured for a riscv64-*-* or riscv32-*-* but not a riscv64be-*-*
22967           or riscv32be-*-* target.
22968
22969       -mstack-protector-guard=guard
22970       -mstack-protector-guard-reg=reg
22971       -mstack-protector-guard-offset=offset
22972           Generate stack protection code using canary at guard.  Supported
22973           locations are global for a global canary or tls for per-thread
22974           canary in the TLS block.
22975
22976           With the latter choice the options -mstack-protector-guard-reg=reg
22977           and -mstack-protector-guard-offset=offset furthermore specify which
22978           register to use as base register for reading the canary, and from
22979           what offset from that base register. There is no default register
22980           or offset as this is entirely for use within the Linux kernel.
22981
22982       RL78 Options
22983
22984       -msim
22985           Links in additional target libraries to support operation within a
22986           simulator.
22987
22988       -mmul=none
22989       -mmul=g10
22990       -mmul=g13
22991       -mmul=g14
22992       -mmul=rl78
22993           Specifies the type of hardware multiplication and division support
22994           to be used.  The simplest is "none", which uses software for both
22995           multiplication and division.  This is the default.  The "g13" value
22996           is for the hardware multiply/divide peripheral found on the
22997           RL78/G13 (S2 core) targets.  The "g14" value selects the use of the
22998           multiplication and division instructions supported by the RL78/G14
22999           (S3 core) parts.  The value "rl78" is an alias for "g14" and the
23000           value "mg10" is an alias for "none".
23001
23002           In addition a C preprocessor macro is defined, based upon the
23003           setting of this option.  Possible values are: "__RL78_MUL_NONE__",
23004           "__RL78_MUL_G13__" or "__RL78_MUL_G14__".
23005
23006       -mcpu=g10
23007       -mcpu=g13
23008       -mcpu=g14
23009       -mcpu=rl78
23010           Specifies the RL78 core to target.  The default is the G14 core,
23011           also known as an S3 core or just RL78.  The G13 or S2 core does not
23012           have multiply or divide instructions, instead it uses a hardware
23013           peripheral for these operations.  The G10 or S1 core does not have
23014           register banks, so it uses a different calling convention.
23015
23016           If this option is set it also selects the type of hardware multiply
23017           support to use, unless this is overridden by an explicit -mmul=none
23018           option on the command line.  Thus specifying -mcpu=g13 enables the
23019           use of the G13 hardware multiply peripheral and specifying
23020           -mcpu=g10 disables the use of hardware multiplications altogether.
23021
23022           Note, although the RL78/G14 core is the default target, specifying
23023           -mcpu=g14 or -mcpu=rl78 on the command line does change the
23024           behavior of the toolchain since it also enables G14 hardware
23025           multiply support.  If these options are not specified on the
23026           command line then software multiplication routines will be used
23027           even though the code targets the RL78 core.  This is for backwards
23028           compatibility with older toolchains which did not have hardware
23029           multiply and divide support.
23030
23031           In addition a C preprocessor macro is defined, based upon the
23032           setting of this option.  Possible values are: "__RL78_G10__",
23033           "__RL78_G13__" or "__RL78_G14__".
23034
23035       -mg10
23036       -mg13
23037       -mg14
23038       -mrl78
23039           These are aliases for the corresponding -mcpu= option.  They are
23040           provided for backwards compatibility.
23041
23042       -mallregs
23043           Allow the compiler to use all of the available registers.  By
23044           default registers "r24..r31" are reserved for use in interrupt
23045           handlers.  With this option enabled these registers can be used in
23046           ordinary functions as well.
23047
23048       -m64bit-doubles
23049       -m32bit-doubles
23050           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
23051           (-m32bit-doubles) in size.  The default is -m32bit-doubles.
23052
23053       -msave-mduc-in-interrupts
23054       -mno-save-mduc-in-interrupts
23055           Specifies that interrupt handler functions should preserve the MDUC
23056           registers.  This is only necessary if normal code might use the
23057           MDUC registers, for example because it performs multiplication and
23058           division operations.  The default is to ignore the MDUC registers
23059           as this makes the interrupt handlers faster.  The target option
23060           -mg13 needs to be passed for this to work as this feature is only
23061           available on the G13 target (S2 core).  The MDUC registers will
23062           only be saved if the interrupt handler performs a multiplication or
23063           division operation or it calls another function.
23064
23065       IBM RS/6000 and PowerPC Options
23066
23067       These -m options are defined for the IBM RS/6000 and PowerPC:
23068
23069       -mpowerpc-gpopt
23070       -mno-powerpc-gpopt
23071       -mpowerpc-gfxopt
23072       -mno-powerpc-gfxopt
23073       -mpowerpc64
23074       -mno-powerpc64
23075       -mmfcrf
23076       -mno-mfcrf
23077       -mpopcntb
23078       -mno-popcntb
23079       -mpopcntd
23080       -mno-popcntd
23081       -mfprnd
23082       -mno-fprnd
23083       -mcmpb
23084       -mno-cmpb
23085       -mhard-dfp
23086       -mno-hard-dfp
23087           You use these options to specify which instructions are available
23088           on the processor you are using.  The default value of these options
23089           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
23090           overrides the specification of these options.  We recommend you use
23091           the -mcpu=cpu_type option rather than the options listed above.
23092
23093           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC
23094           architecture instructions in the General Purpose group, including
23095           floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
23096           to use the optional PowerPC architecture instructions in the
23097           Graphics group, including floating-point select.
23098
23099           The -mmfcrf option allows GCC to generate the move from condition
23100           register field instruction implemented on the POWER4 processor and
23101           other processors that support the PowerPC V2.01 architecture.  The
23102           -mpopcntb option allows GCC to generate the popcount and double-
23103           precision FP reciprocal estimate instruction implemented on the
23104           POWER5 processor and other processors that support the PowerPC
23105           V2.02 architecture.  The -mpopcntd option allows GCC to generate
23106           the popcount instruction implemented on the POWER7 processor and
23107           other processors that support the PowerPC V2.06 architecture.  The
23108           -mfprnd option allows GCC to generate the FP round to integer
23109           instructions implemented on the POWER5+ processor and other
23110           processors that support the PowerPC V2.03 architecture.  The -mcmpb
23111           option allows GCC to generate the compare bytes instruction
23112           implemented on the POWER6 processor and other processors that
23113           support the PowerPC V2.05 architecture.  The -mhard-dfp option
23114           allows GCC to generate the decimal floating-point instructions
23115           implemented on some POWER processors.
23116
23117           The -mpowerpc64 option allows GCC to generate the additional 64-bit
23118           instructions that are found in the full PowerPC64 architecture and
23119           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
23120           -mno-powerpc64.
23121
23122       -mcpu=cpu_type
23123           Set architecture type, register usage, and instruction scheduling
23124           parameters for machine type cpu_type.  Supported values for
23125           cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476,
23126           476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400,
23127           7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3,
23128           e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,
23129           power4, power5, power5+, power6, power6x, power7, power8, power9,
23130           future, powerpc, powerpc64, powerpc64le, rs64, and native.
23131
23132           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure
23133           32-bit PowerPC (either endian), 64-bit big endian PowerPC and
23134           64-bit little endian PowerPC architecture machine types, with an
23135           appropriate, generic processor model assumed for scheduling
23136           purposes.
23137
23138           Specifying native as cpu type detects and selects the architecture
23139           option that corresponds to the host processor of the system
23140           performing the compilation.  -mcpu=native has no effect if GCC does
23141           not recognize the processor.
23142
23143           The other options specify a specific processor.  Code generated
23144           under those options runs best on that processor, and may not run at
23145           all on others.
23146
23147           The -mcpu options automatically enable or disable the following
23148           options:
23149
23150           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb
23151           -mpopcntd  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt -mmulhw
23152           -mdlmzb  -mmfpgpr  -mvsx -mcrypto  -mhtm  -mpower8-fusion
23153           -mpower8-vector -mquad-memory  -mquad-memory-atomic  -mfloat128
23154           -mfloat128-hardware -mprefixed -mpcrel -mmma -mrop-protect
23155
23156           The particular options set for any particular CPU varies between
23157           compiler versions, depending on what setting seems to produce
23158           optimal code for that CPU; it doesn't necessarily reflect the
23159           actual hardware's capabilities.  If you wish to set an individual
23160           option to a particular value, you may specify it after the -mcpu
23161           option, like -mcpu=970 -mno-altivec.
23162
23163           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
23164           disabled by the -mcpu option at present because AIX does not have
23165           full support for these options.  You may still enable or disable
23166           them individually if you're sure it'll work in your environment.
23167
23168       -mtune=cpu_type
23169           Set the instruction scheduling parameters for machine type
23170           cpu_type, but do not set the architecture type or register usage,
23171           as -mcpu=cpu_type does.  The same values for cpu_type are used for
23172           -mtune as for -mcpu.  If both are specified, the code generated
23173           uses the architecture and registers set by -mcpu, but the
23174           scheduling parameters set by -mtune.
23175
23176       -mcmodel=small
23177           Generate PowerPC64 code for the small model: The TOC is limited to
23178           64k.
23179
23180       -mcmodel=medium
23181           Generate PowerPC64 code for the medium model: The TOC and other
23182           static data may be up to a total of 4G in size.  This is the
23183           default for 64-bit Linux.
23184
23185       -mcmodel=large
23186           Generate PowerPC64 code for the large model: The TOC may be up to
23187           4G in size.  Other data and code is only limited by the 64-bit
23188           address space.
23189
23190       -maltivec
23191       -mno-altivec
23192           Generate code that uses (does not use) AltiVec instructions, and
23193           also enable the use of built-in functions that allow more direct
23194           access to the AltiVec instruction set.  You may also need to set
23195           -mabi=altivec to adjust the current ABI with AltiVec ABI
23196           enhancements.
23197
23198           When -maltivec is used, the element order for AltiVec intrinsics
23199           such as "vec_splat", "vec_extract", and "vec_insert" match array
23200           element order corresponding to the endianness of the target.  That
23201           is, element zero identifies the leftmost element in a vector
23202           register when targeting a big-endian platform, and identifies the
23203           rightmost element in a vector register when targeting a little-
23204           endian platform.
23205
23206       -mvrsave
23207       -mno-vrsave
23208           Generate VRSAVE instructions when generating AltiVec code.
23209
23210       -msecure-plt
23211           Generate code that allows ld and ld.so to build executables and
23212           shared libraries with non-executable ".plt" and ".got" sections.
23213           This is a PowerPC 32-bit SYSV ABI option.
23214
23215       -mbss-plt
23216           Generate code that uses a BSS ".plt" section that ld.so fills in,
23217           and requires ".plt" and ".got" sections that are both writable and
23218           executable.  This is a PowerPC 32-bit SYSV ABI option.
23219
23220       -misel
23221       -mno-isel
23222           This switch enables or disables the generation of ISEL
23223           instructions.
23224
23225       -mvsx
23226       -mno-vsx
23227           Generate code that uses (does not use) vector/scalar (VSX)
23228           instructions, and also enable the use of built-in functions that
23229           allow more direct access to the VSX instruction set.
23230
23231       -mcrypto
23232       -mno-crypto
23233           Enable the use (disable) of the built-in functions that allow
23234           direct access to the cryptographic instructions that were added in
23235           version 2.07 of the PowerPC ISA.
23236
23237       -mhtm
23238       -mno-htm
23239           Enable (disable) the use of the built-in functions that allow
23240           direct access to the Hardware Transactional Memory (HTM)
23241           instructions that were added in version 2.07 of the PowerPC ISA.
23242
23243       -mpower8-fusion
23244       -mno-power8-fusion
23245           Generate code that keeps (does not keeps) some integer operations
23246           adjacent so that the instructions can be fused together on power8
23247           and later processors.
23248
23249       -mpower8-vector
23250       -mno-power8-vector
23251           Generate code that uses (does not use) the vector and scalar
23252           instructions that were added in version 2.07 of the PowerPC ISA.
23253           Also enable the use of built-in functions that allow more direct
23254           access to the vector instructions.
23255
23256       -mquad-memory
23257       -mno-quad-memory
23258           Generate code that uses (does not use) the non-atomic quad word
23259           memory instructions.  The -mquad-memory option requires use of
23260           64-bit mode.
23261
23262       -mquad-memory-atomic
23263       -mno-quad-memory-atomic
23264           Generate code that uses (does not use) the atomic quad word memory
23265           instructions.  The -mquad-memory-atomic option requires use of
23266           64-bit mode.
23267
23268       -mfloat128
23269       -mno-float128
23270           Enable/disable the __float128 keyword for IEEE 128-bit floating
23271           point and use either software emulation for IEEE 128-bit floating
23272           point or hardware instructions.
23273
23274           The VSX instruction set (-mvsx, -mcpu=power7, -mcpu=power8), or
23275           -mcpu=power9 must be enabled to use the IEEE 128-bit floating point
23276           support.  The IEEE 128-bit floating point support only works on
23277           PowerPC Linux systems.
23278
23279           The default for -mfloat128 is enabled on PowerPC Linux systems
23280           using the VSX instruction set, and disabled on other systems.
23281
23282           If you use the ISA 3.0 instruction set (-mpower9-vector or
23283           -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point
23284           support will also enable the generation of ISA 3.0 IEEE 128-bit
23285           floating point instructions.  Otherwise, if you do not specify to
23286           generate ISA 3.0 instructions or you are targeting a 32-bit big
23287           endian system, IEEE 128-bit floating point will be done with
23288           software emulation.
23289
23290       -mfloat128-hardware
23291       -mno-float128-hardware
23292           Enable/disable using ISA 3.0 hardware instructions to support the
23293           __float128 data type.
23294
23295           The default for -mfloat128-hardware is enabled on PowerPC Linux
23296           systems using the ISA 3.0 instruction set, and disabled on other
23297           systems.
23298
23299       -m32
23300       -m64
23301           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
23302           targets (including GNU/Linux).  The 32-bit environment sets int,
23303           long and pointer to 32 bits and generates code that runs on any
23304           PowerPC variant.  The 64-bit environment sets int to 32 bits and
23305           long and pointer to 64 bits, and generates code for PowerPC64, as
23306           for -mpowerpc64.
23307
23308       -mfull-toc
23309       -mno-fp-in-toc
23310       -mno-sum-in-toc
23311       -mminimal-toc
23312           Modify generation of the TOC (Table Of Contents), which is created
23313           for every executable file.  The -mfull-toc option is selected by
23314           default.  In that case, GCC allocates at least one TOC entry for
23315           each unique non-automatic variable reference in your program.  GCC
23316           also places floating-point constants in the TOC.  However, only
23317           16,384 entries are available in the TOC.
23318
23319           If you receive a linker error message that saying you have
23320           overflowed the available TOC space, you can reduce the amount of
23321           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
23322           -mno-fp-in-toc prevents GCC from putting floating-point constants
23323           in the TOC and -mno-sum-in-toc forces GCC to generate code to
23324           calculate the sum of an address and a constant at run time instead
23325           of putting that sum into the TOC.  You may specify one or both of
23326           these options.  Each causes GCC to produce very slightly slower and
23327           larger code at the expense of conserving TOC space.
23328
23329           If you still run out of space in the TOC even when you specify both
23330           of these options, specify -mminimal-toc instead.  This option
23331           causes GCC to make only one TOC entry for every file.  When you
23332           specify this option, GCC produces code that is slower and larger
23333           but which uses extremely little TOC space.  You may wish to use
23334           this option only on files that contain less frequently-executed
23335           code.
23336
23337       -maix64
23338       -maix32
23339           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
23340           64-bit "long" type, and the infrastructure needed to support them.
23341           Specifying -maix64 implies -mpowerpc64, while -maix32 disables the
23342           64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.
23343
23344       -mxl-compat
23345       -mno-xl-compat
23346           Produce code that conforms more closely to IBM XL compiler
23347           semantics when using AIX-compatible ABI.  Pass floating-point
23348           arguments to prototyped functions beyond the register save area
23349           (RSA) on the stack in addition to argument FPRs.  Do not assume
23350           that most significant double in 128-bit long double value is
23351           properly rounded when comparing values and converting to double.
23352           Use XL symbol names for long double support routines.
23353
23354           The AIX calling convention was extended but not initially
23355           documented to handle an obscure K&R C case of calling a function
23356           that takes the address of its arguments with fewer arguments than
23357           declared.  IBM XL compilers access floating-point arguments that do
23358           not fit in the RSA from the stack when a subroutine is compiled
23359           without optimization.  Because always storing floating-point
23360           arguments on the stack is inefficient and rarely needed, this
23361           option is not enabled by default and only is necessary when calling
23362           subroutines compiled by IBM XL compilers without optimization.
23363
23364       -mpe
23365           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
23366           application written to use message passing with special startup
23367           code to enable the application to run.  The system must have PE
23368           installed in the standard location (/usr/lpp/ppe.poe/), or the
23369           specs file must be overridden with the -specs= option to specify
23370           the appropriate directory location.  The Parallel Environment does
23371           not support threads, so the -mpe option and the -pthread option are
23372           incompatible.
23373
23374       -malign-natural
23375       -malign-power
23376           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
23377           -malign-natural overrides the ABI-defined alignment of larger
23378           types, such as floating-point doubles, on their natural size-based
23379           boundary.  The option -malign-power instructs GCC to follow the
23380           ABI-specified alignment rules.  GCC defaults to the standard
23381           alignment defined in the ABI.
23382
23383           On 64-bit Darwin, natural alignment is the default, and
23384           -malign-power is not supported.
23385
23386       -msoft-float
23387       -mhard-float
23388           Generate code that does not use (uses) the floating-point register
23389           set.  Software floating-point emulation is provided if you use the
23390           -msoft-float option, and pass the option to GCC when linking.
23391
23392       -mmultiple
23393       -mno-multiple
23394           Generate code that uses (does not use) the load multiple word
23395           instructions and the store multiple word instructions.  These
23396           instructions are generated by default on POWER systems, and not
23397           generated on PowerPC systems.  Do not use -mmultiple on little-
23398           endian PowerPC systems, since those instructions do not work when
23399           the processor is in little-endian mode.  The exceptions are PPC740
23400           and PPC750 which permit these instructions in little-endian mode.
23401
23402       -mupdate
23403       -mno-update
23404           Generate code that uses (does not use) the load or store
23405           instructions that update the base register to the address of the
23406           calculated memory location.  These instructions are generated by
23407           default.  If you use -mno-update, there is a small window between
23408           the time that the stack pointer is updated and the address of the
23409           previous frame is stored, which means code that walks the stack
23410           frame across interrupts or signals may get corrupted data.
23411
23412       -mavoid-indexed-addresses
23413       -mno-avoid-indexed-addresses
23414           Generate code that tries to avoid (not avoid) the use of indexed
23415           load or store instructions. These instructions can incur a
23416           performance penalty on Power6 processors in certain situations,
23417           such as when stepping through large arrays that cross a 16M
23418           boundary.  This option is enabled by default when targeting Power6
23419           and disabled otherwise.
23420
23421       -mfused-madd
23422       -mno-fused-madd
23423           Generate code that uses (does not use) the floating-point multiply
23424           and accumulate instructions.  These instructions are generated by
23425           default if hardware floating point is used.  The machine-dependent
23426           -mfused-madd option is now mapped to the machine-independent
23427           -ffp-contract=fast option, and -mno-fused-madd is mapped to
23428           -ffp-contract=off.
23429
23430       -mmulhw
23431       -mno-mulhw
23432           Generate code that uses (does not use) the half-word multiply and
23433           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
23434           processors.  These instructions are generated by default when
23435           targeting those processors.
23436
23437       -mdlmzb
23438       -mno-dlmzb
23439           Generate code that uses (does not use) the string-search dlmzb
23440           instruction on the IBM 405, 440, 464 and 476 processors.  This
23441           instruction is generated by default when targeting those
23442           processors.
23443
23444       -mno-bit-align
23445       -mbit-align
23446           On System V.4 and embedded PowerPC systems do not (do) force
23447           structures and unions that contain bit-fields to be aligned to the
23448           base type of the bit-field.
23449
23450           For example, by default a structure containing nothing but 8
23451           "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary
23452           and has a size of 4 bytes.  By using -mno-bit-align, the structure
23453           is aligned to a 1-byte boundary and is 1 byte in size.
23454
23455       -mno-strict-align
23456       -mstrict-align
23457           On System V.4 and embedded PowerPC systems do not (do) assume that
23458           unaligned memory references are handled by the system.
23459
23460       -mrelocatable
23461       -mno-relocatable
23462           Generate code that allows (does not allow) a static executable to
23463           be relocated to a different address at run time.  A simple embedded
23464           PowerPC system loader should relocate the entire contents of
23465           ".got2" and 4-byte locations listed in the ".fixup" section, a
23466           table of 32-bit addresses generated by this option.  For this to
23467           work, all objects linked together must be compiled with
23468           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
23469           stack to an 8-byte boundary.
23470
23471       -mrelocatable-lib
23472       -mno-relocatable-lib
23473           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
23474           to allow static executables to be relocated at run time, but
23475           -mrelocatable-lib does not use the smaller stack alignment of
23476           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
23477           linked with objects compiled with any combination of the
23478           -mrelocatable options.
23479
23480       -mno-toc
23481       -mtoc
23482           On System V.4 and embedded PowerPC systems do not (do) assume that
23483           register 2 contains a pointer to a global area pointing to the
23484           addresses used in the program.
23485
23486       -mlittle
23487       -mlittle-endian
23488           On System V.4 and embedded PowerPC systems compile code for the
23489           processor in little-endian mode.  The -mlittle-endian option is the
23490           same as -mlittle.
23491
23492       -mbig
23493       -mbig-endian
23494           On System V.4 and embedded PowerPC systems compile code for the
23495           processor in big-endian mode.  The -mbig-endian option is the same
23496           as -mbig.
23497
23498       -mdynamic-no-pic
23499           On Darwin and Mac OS X systems, compile code so that it is not
23500           relocatable, but that its external references are relocatable.  The
23501           resulting code is suitable for applications, but not shared
23502           libraries.
23503
23504       -msingle-pic-base
23505           Treat the register used for PIC addressing as read-only, rather
23506           than loading it in the prologue for each function.  The runtime
23507           system is responsible for initializing this register with an
23508           appropriate value before execution begins.
23509
23510       -mprioritize-restricted-insns=priority
23511           This option controls the priority that is assigned to dispatch-slot
23512           restricted instructions during the second scheduling pass.  The
23513           argument priority takes the value 0, 1, or 2 to assign no, highest,
23514           or second-highest (respectively) priority to dispatch-slot
23515           restricted instructions.
23516
23517       -msched-costly-dep=dependence_type
23518           This option controls which dependences are considered costly by the
23519           target during instruction scheduling.  The argument dependence_type
23520           takes one of the following values:
23521
23522           no  No dependence is costly.
23523
23524           all All dependences are costly.
23525
23526           true_store_to_load
23527               A true dependence from store to load is costly.
23528
23529           store_to_load
23530               Any dependence from store to load is costly.
23531
23532           number
23533               Any dependence for which the latency is greater than or equal
23534               to number is costly.
23535
23536       -minsert-sched-nops=scheme
23537           This option controls which NOP insertion scheme is used during the
23538           second scheduling pass.  The argument scheme takes one of the
23539           following values:
23540
23541           no  Don't insert NOPs.
23542
23543           pad Pad with NOPs any dispatch group that has vacant issue slots,
23544               according to the scheduler's grouping.
23545
23546           regroup_exact
23547               Insert NOPs to force costly dependent insns into separate
23548               groups.  Insert exactly as many NOPs as needed to force an insn
23549               to a new group, according to the estimated processor grouping.
23550
23551           number
23552               Insert NOPs to force costly dependent insns into separate
23553               groups.  Insert number NOPs to force an insn to a new group.
23554
23555       -mcall-sysv
23556           On System V.4 and embedded PowerPC systems compile code using
23557           calling conventions that adhere to the March 1995 draft of the
23558           System V Application Binary Interface, PowerPC processor
23559           supplement.  This is the default unless you configured GCC using
23560           powerpc-*-eabiaix.
23561
23562       -mcall-sysv-eabi
23563       -mcall-eabi
23564           Specify both -mcall-sysv and -meabi options.
23565
23566       -mcall-sysv-noeabi
23567           Specify both -mcall-sysv and -mno-eabi options.
23568
23569       -mcall-aixdesc
23570           On System V.4 and embedded PowerPC systems compile code for the AIX
23571           operating system.
23572
23573       -mcall-linux
23574           On System V.4 and embedded PowerPC systems compile code for the
23575           Linux-based GNU system.
23576
23577       -mcall-freebsd
23578           On System V.4 and embedded PowerPC systems compile code for the
23579           FreeBSD operating system.
23580
23581       -mcall-netbsd
23582           On System V.4 and embedded PowerPC systems compile code for the
23583           NetBSD operating system.
23584
23585       -mcall-openbsd
23586           On System V.4 and embedded PowerPC systems compile code for the
23587           OpenBSD operating system.
23588
23589       -mtraceback=traceback_type
23590           Select the type of traceback table. Valid values for traceback_type
23591           are full, part, and no.
23592
23593       -maix-struct-return
23594           Return all structures in memory (as specified by the AIX ABI).
23595
23596       -msvr4-struct-return
23597           Return structures smaller than 8 bytes in registers (as specified
23598           by the SVR4 ABI).
23599
23600       -mabi=abi-type
23601           Extend the current ABI with a particular extension, or remove such
23602           extension.  Valid values are: altivec, no-altivec, ibmlongdouble,
23603           ieeelongdouble, elfv1, elfv2, and for AIX: vec-extabi, vec-default.
23604
23605       -mabi=ibmlongdouble
23606           Change the current ABI to use IBM extended-precision long double.
23607           This is not likely to work if your system defaults to using IEEE
23608           extended-precision long double.  If you change the long double type
23609           from IEEE extended-precision, the compiler will issue a warning
23610           unless you use the -Wno-psabi option.  Requires -mlong-double-128
23611           to be enabled.
23612
23613       -mabi=ieeelongdouble
23614           Change the current ABI to use IEEE extended-precision long double.
23615           This is not likely to work if your system defaults to using IBM
23616           extended-precision long double.  If you change the long double type
23617           from IBM extended-precision, the compiler will issue a warning
23618           unless you use the -Wno-psabi option.  Requires -mlong-double-128
23619           to be enabled.
23620
23621       -mabi=elfv1
23622           Change the current ABI to use the ELFv1 ABI.  This is the default
23623           ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
23624           ABI requires special system support and is likely to fail in
23625           spectacular ways.
23626
23627       -mabi=elfv2
23628           Change the current ABI to use the ELFv2 ABI.  This is the default
23629           ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
23630           ABI requires special system support and is likely to fail in
23631           spectacular ways.
23632
23633       -mgnu-attribute
23634       -mno-gnu-attribute
23635           Emit .gnu_attribute assembly directives to set tag/value pairs in a
23636           .gnu.attributes section that specify ABI variations in function
23637           parameters or return values.
23638
23639       -mprototype
23640       -mno-prototype
23641           On System V.4 and embedded PowerPC systems assume that all calls to
23642           variable argument functions are properly prototyped.  Otherwise,
23643           the compiler must insert an instruction before every non-prototyped
23644           call to set or clear bit 6 of the condition code register ("CR") to
23645           indicate whether floating-point values are passed in the floating-
23646           point registers in case the function takes variable arguments.
23647           With -mprototype, only calls to prototyped variable argument
23648           functions set or clear the bit.
23649
23650       -msim
23651           On embedded PowerPC systems, assume that the startup module is
23652           called sim-crt0.o and that the standard C libraries are libsim.a
23653           and libc.a.  This is the default for powerpc-*-eabisim
23654           configurations.
23655
23656       -mmvme
23657           On embedded PowerPC systems, assume that the startup module is
23658           called crt0.o and the standard C libraries are libmvme.a and
23659           libc.a.
23660
23661       -mads
23662           On embedded PowerPC systems, assume that the startup module is
23663           called crt0.o and the standard C libraries are libads.a and libc.a.
23664
23665       -myellowknife
23666           On embedded PowerPC systems, assume that the startup module is
23667           called crt0.o and the standard C libraries are libyk.a and libc.a.
23668
23669       -mvxworks
23670           On System V.4 and embedded PowerPC systems, specify that you are
23671           compiling for a VxWorks system.
23672
23673       -memb
23674           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags
23675           header to indicate that eabi extended relocations are used.
23676
23677       -meabi
23678       -mno-eabi
23679           On System V.4 and embedded PowerPC systems do (do not) adhere to
23680           the Embedded Applications Binary Interface (EABI), which is a set
23681           of modifications to the System V.4 specifications.  Selecting
23682           -meabi means that the stack is aligned to an 8-byte boundary, a
23683           function "__eabi" is called from "main" to set up the EABI
23684           environment, and the -msdata option can use both "r2" and "r13" to
23685           point to two separate small data areas.  Selecting -mno-eabi means
23686           that the stack is aligned to a 16-byte boundary, no EABI
23687           initialization function is called from "main", and the -msdata
23688           option only uses "r13" to point to a single small data area.  The
23689           -meabi option is on by default if you configured GCC using one of
23690           the powerpc*-*-eabi* options.
23691
23692       -msdata=eabi
23693           On System V.4 and embedded PowerPC systems, put small initialized
23694           "const" global and static data in the ".sdata2" section, which is
23695           pointed to by register "r2".  Put small initialized non-"const"
23696           global and static data in the ".sdata" section, which is pointed to
23697           by register "r13".  Put small uninitialized global and static data
23698           in the ".sbss" section, which is adjacent to the ".sdata" section.
23699           The -msdata=eabi option is incompatible with the -mrelocatable
23700           option.  The -msdata=eabi option also sets the -memb option.
23701
23702       -msdata=sysv
23703           On System V.4 and embedded PowerPC systems, put small global and
23704           static data in the ".sdata" section, which is pointed to by
23705           register "r13".  Put small uninitialized global and static data in
23706           the ".sbss" section, which is adjacent to the ".sdata" section.
23707           The -msdata=sysv option is incompatible with the -mrelocatable
23708           option.
23709
23710       -msdata=default
23711       -msdata
23712           On System V.4 and embedded PowerPC systems, if -meabi is used,
23713           compile code the same as -msdata=eabi, otherwise compile code the
23714           same as -msdata=sysv.
23715
23716       -msdata=data
23717           On System V.4 and embedded PowerPC systems, put small global data
23718           in the ".sdata" section.  Put small uninitialized global data in
23719           the ".sbss" section.  Do not use register "r13" to address small
23720           data however.  This is the default behavior unless other -msdata
23721           options are used.
23722
23723       -msdata=none
23724       -mno-sdata
23725           On embedded PowerPC systems, put all initialized global and static
23726           data in the ".data" section, and all uninitialized data in the
23727           ".bss" section.
23728
23729       -mreadonly-in-sdata
23730           Put read-only objects in the ".sdata" section as well.  This is the
23731           default.
23732
23733       -mblock-move-inline-limit=num
23734           Inline all block moves (such as calls to "memcpy" or structure
23735           copies) less than or equal to num bytes.  The minimum value for num
23736           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
23737           default value is target-specific.
23738
23739       -mblock-compare-inline-limit=num
23740           Generate non-looping inline code for all block compares (such as
23741           calls to "memcmp" or structure compares) less than or equal to num
23742           bytes. If num is 0, all inline expansion (non-loop and loop) of
23743           block compare is disabled. The default value is target-specific.
23744
23745       -mblock-compare-inline-loop-limit=num
23746           Generate an inline expansion using loop code for all block compares
23747           that are less than or equal to num bytes, but greater than the
23748           limit for non-loop inline block compare expansion. If the block
23749           length is not constant, at most num bytes will be compared before
23750           "memcmp" is called to compare the remainder of the block. The
23751           default value is target-specific.
23752
23753       -mstring-compare-inline-limit=num
23754           Compare at most num string bytes with inline code.  If the
23755           difference or end of string is not found at the end of the inline
23756           compare a call to "strcmp" or "strncmp" will take care of the rest
23757           of the comparison. The default is 64 bytes.
23758
23759       -G num
23760           On embedded PowerPC systems, put global and static items less than
23761           or equal to num bytes into the small data or BSS sections instead
23762           of the normal data or BSS section.  By default, num is 8.  The -G
23763           num switch is also passed to the linker.  All modules should be
23764           compiled with the same -G num value.
23765
23766       -mregnames
23767       -mno-regnames
23768           On System V.4 and embedded PowerPC systems do (do not) emit
23769           register names in the assembly language output using symbolic
23770           forms.
23771
23772       -mlongcall
23773       -mno-longcall
23774           By default assume that all calls are far away so that a longer and
23775           more expensive calling sequence is required.  This is required for
23776           calls farther than 32 megabytes (33,554,432 bytes) from the current
23777           location.  A short call is generated if the compiler knows the call
23778           cannot be that far away.  This setting can be overridden by the
23779           "shortcall" function attribute, or by "#pragma longcall(0)".
23780
23781           Some linkers are capable of detecting out-of-range calls and
23782           generating glue code on the fly.  On these systems, long calls are
23783           unnecessary and generate slower code.  As of this writing, the AIX
23784           linker can do this, as can the GNU linker for PowerPC/64.  It is
23785           planned to add this feature to the GNU linker for 32-bit PowerPC
23786           systems as well.
23787
23788           On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU
23789           linkers, GCC can generate long calls using an inline PLT call
23790           sequence (see -mpltseq).  PowerPC with -mbss-plt and PowerPC64
23791           ELFv1 (big-endian) do not support inline PLT calls.
23792
23793           On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee,
23794           L42", plus a branch island (glue code).  The two target addresses
23795           represent the callee and the branch island.  The Darwin/PPC linker
23796           prefers the first address and generates a "bl callee" if the PPC
23797           "bl" instruction reaches the callee directly; otherwise, the linker
23798           generates "bl L42" to call the branch island.  The branch island is
23799           appended to the body of the calling function; it computes the full
23800           32-bit address of the callee and jumps to it.
23801
23802           On Mach-O (Darwin) systems, this option directs the compiler emit
23803           to the glue for every direct call, and the Darwin linker decides
23804           whether to use or discard it.
23805
23806           In the future, GCC may ignore all longcall specifications when the
23807           linker is known to generate glue.
23808
23809       -mpltseq
23810       -mno-pltseq
23811           Implement (do not implement) -fno-plt and long calls using an
23812           inline PLT call sequence that supports lazy linking and long calls
23813           to functions in dlopen'd shared libraries.  Inline PLT calls are
23814           only supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with
23815           newer GNU linkers, and are enabled by default if the support is
23816           detected when configuring GCC, and, in the case of 32-bit PowerPC,
23817           if GCC is configured with --enable-secureplt.  -mpltseq code and
23818           -mbss-plt 32-bit PowerPC relocatable objects may not be linked
23819           together.
23820
23821       -mtls-markers
23822       -mno-tls-markers
23823           Mark (do not mark) calls to "__tls_get_addr" with a relocation
23824           specifying the function argument.  The relocation allows the linker
23825           to reliably associate function call with argument setup
23826           instructions for TLS optimization, which in turn allows GCC to
23827           better schedule the sequence.
23828
23829       -mrecip
23830       -mno-recip
23831           This option enables use of the reciprocal estimate and reciprocal
23832           square root estimate instructions with additional Newton-Raphson
23833           steps to increase precision instead of doing a divide or square
23834           root and divide for floating-point arguments.  You should use the
23835           -ffast-math option when using -mrecip (or at least
23836           -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math
23837           and -fno-trapping-math).  Note that while the throughput of the
23838           sequence is generally higher than the throughput of the non-
23839           reciprocal instruction, the precision of the sequence can be
23840           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
23841           0.99999994) for reciprocal square roots.
23842
23843       -mrecip=opt
23844           This option controls which reciprocal estimate instructions may be
23845           used.  opt is a comma-separated list of options, which may be
23846           preceded by a "!" to invert the option:
23847
23848           all Enable all estimate instructions.
23849
23850           default
23851               Enable the default instructions, equivalent to -mrecip.
23852
23853           none
23854               Disable all estimate instructions, equivalent to -mno-recip.
23855
23856           div Enable the reciprocal approximation instructions for both
23857               single and double precision.
23858
23859           divf
23860               Enable the single-precision reciprocal approximation
23861               instructions.
23862
23863           divd
23864               Enable the double-precision reciprocal approximation
23865               instructions.
23866
23867           rsqrt
23868               Enable the reciprocal square root approximation instructions
23869               for both single and double precision.
23870
23871           rsqrtf
23872               Enable the single-precision reciprocal square root
23873               approximation instructions.
23874
23875           rsqrtd
23876               Enable the double-precision reciprocal square root
23877               approximation instructions.
23878
23879           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
23880           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
23881           "XVRSQRTEDP" instructions which handle the double-precision
23882           reciprocal square root calculations.
23883
23884       -mrecip-precision
23885       -mno-recip-precision
23886           Assume (do not assume) that the reciprocal estimate instructions
23887           provide higher-precision estimates than is mandated by the PowerPC
23888           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
23889           automatically selects -mrecip-precision.  The double-precision
23890           square root estimate instructions are not generated by default on
23891           low-precision machines, since they do not provide an estimate that
23892           converges after three steps.
23893
23894       -mveclibabi=type
23895           Specifies the ABI type to use for vectorizing intrinsics using an
23896           external library.  The only type supported at present is mass,
23897           which specifies to use IBM's Mathematical Acceleration Subsystem
23898           (MASS) libraries for vectorizing intrinsics using external
23899           libraries.  GCC currently emits calls to "acosd2", "acosf4",
23900           "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4",
23901           "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4",
23902           "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2",
23903           "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4",
23904           "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4",
23905           "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4",
23906           "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2",
23907           "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and
23908           "tanhf4" when generating code for power7.  Both -ftree-vectorize
23909           and -funsafe-math-optimizations must also be enabled.  The MASS
23910           libraries must be specified at link time.
23911
23912       -mfriz
23913       -mno-friz
23914           Generate (do not generate) the "friz" instruction when the
23915           -funsafe-math-optimizations option is used to optimize rounding of
23916           floating-point values to 64-bit integer and back to floating point.
23917           The "friz" instruction does not return the same value if the
23918           floating-point number is too large to fit in an integer.
23919
23920       -mpointers-to-nested-functions
23921       -mno-pointers-to-nested-functions
23922           Generate (do not generate) code to load up the static chain
23923           register ("r11") when calling through a pointer on AIX and 64-bit
23924           Linux systems where a function pointer points to a 3-word
23925           descriptor giving the function address, TOC value to be loaded in
23926           register "r2", and static chain value to be loaded in register
23927           "r11".  The -mpointers-to-nested-functions is on by default.  You
23928           cannot call through pointers to nested functions or pointers to
23929           functions compiled in other languages that use the static chain if
23930           you use -mno-pointers-to-nested-functions.
23931
23932       -msave-toc-indirect
23933       -mno-save-toc-indirect
23934           Generate (do not generate) code to save the TOC value in the
23935           reserved stack location in the function prologue if the function
23936           calls through a pointer on AIX and 64-bit Linux systems.  If the
23937           TOC value is not saved in the prologue, it is saved just before the
23938           call through the pointer.  The -mno-save-toc-indirect option is the
23939           default.
23940
23941       -mcompat-align-parm
23942       -mno-compat-align-parm
23943           Generate (do not generate) code to pass structure parameters with a
23944           maximum alignment of 64 bits, for compatibility with older versions
23945           of GCC.
23946
23947           Older versions of GCC (prior to 4.9.0) incorrectly did not align a
23948           structure parameter on a 128-bit boundary when that structure
23949           contained a member requiring 128-bit alignment.  This is corrected
23950           in more recent versions of GCC.  This option may be used to
23951           generate code that is compatible with functions compiled with older
23952           versions of GCC.
23953
23954           The -mno-compat-align-parm option is the default.
23955
23956       -mstack-protector-guard=guard
23957       -mstack-protector-guard-reg=reg
23958       -mstack-protector-guard-offset=offset
23959       -mstack-protector-guard-symbol=symbol
23960           Generate stack protection code using canary at guard.  Supported
23961           locations are global for global canary or tls for per-thread canary
23962           in the TLS block (the default with GNU libc version 2.4 or later).
23963
23964           With the latter choice the options -mstack-protector-guard-reg=reg
23965           and -mstack-protector-guard-offset=offset furthermore specify which
23966           register to use as base register for reading the canary, and from
23967           what offset from that base register. The default for those is as
23968           specified in the relevant ABI.
23969           -mstack-protector-guard-symbol=symbol overrides the offset with a
23970           symbol reference to a canary in the TLS block.
23971
23972       -mpcrel
23973       -mno-pcrel
23974           Generate (do not generate) pc-relative addressing when the option
23975           -mcpu=future is used.  The -mpcrel option requires that the medium
23976           code model (-mcmodel=medium) and prefixed addressing (-mprefixed)
23977           options are enabled.
23978
23979       -mprefixed
23980       -mno-prefixed
23981           Generate (do not generate) addressing modes using prefixed load and
23982           store instructions when the option -mcpu=future is used.
23983
23984       -mmma
23985       -mno-mma
23986           Generate (do not generate) the MMA instructions when the option
23987           -mcpu=future is used.
23988
23989       -mrop-protect
23990       -mno-rop-protect
23991           Generate (do not generate) ROP protection instructions when the
23992           target processor supports them.  Currently this option disables the
23993           shrink-wrap optimization (-fshrink-wrap).
23994
23995       -mprivileged
23996       -mno-privileged
23997           Generate (do not generate) code that will run in privileged state.
23998
23999       -mblock-ops-unaligned-vsx
24000       -mno-block-ops-unaligned-vsx
24001           Generate (do not generate) unaligned vsx loads and stores for
24002           inline expansion of "memcpy" and "memmove".
24003
24004       RX Options
24005
24006       These command-line options are defined for RX targets:
24007
24008       -m64bit-doubles
24009       -m32bit-doubles
24010           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
24011           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
24012           RX floating-point hardware only works on 32-bit values, which is
24013           why the default is -m32bit-doubles.
24014
24015       -fpu
24016       -nofpu
24017           Enables (-fpu) or disables (-nofpu) the use of RX floating-point
24018           hardware.  The default is enabled for the RX600 series and disabled
24019           for the RX200 series.
24020
24021           Floating-point instructions are only generated for 32-bit floating-
24022           point values, however, so the FPU hardware is not used for doubles
24023           if the -m64bit-doubles option is used.
24024
24025           Note If the -fpu option is enabled then -funsafe-math-optimizations
24026           is also enabled automatically.  This is because the RX FPU
24027           instructions are themselves unsafe.
24028
24029       -mcpu=name
24030           Selects the type of RX CPU to be targeted.  Currently three types
24031           are supported, the generic RX600 and RX200 series hardware and the
24032           specific RX610 CPU.  The default is RX600.
24033
24034           The only difference between RX600 and RX610 is that the RX610 does
24035           not support the "MVTIPL" instruction.
24036
24037           The RX200 series does not have a hardware floating-point unit and
24038           so -nofpu is enabled by default when this type is selected.
24039
24040       -mbig-endian-data
24041       -mlittle-endian-data
24042           Store data (but not code) in the big-endian format.  The default is
24043           -mlittle-endian-data, i.e. to store data in the little-endian
24044           format.
24045
24046       -msmall-data-limit=N
24047           Specifies the maximum size in bytes of global and static variables
24048           which can be placed into the small data area.  Using the small data
24049           area can lead to smaller and faster code, but the size of area is
24050           limited and it is up to the programmer to ensure that the area does
24051           not overflow.  Also when the small data area is used one of the
24052           RX's registers (usually "r13") is reserved for use pointing to this
24053           area, so it is no longer available for use by the compiler.  This
24054           could result in slower and/or larger code if variables are pushed
24055           onto the stack instead of being held in this register.
24056
24057           Note, common variables (variables that have not been initialized)
24058           and constants are not placed into the small data area as they are
24059           assigned to other sections in the output executable.
24060
24061           The default value is zero, which disables this feature.  Note, this
24062           feature is not enabled by default with higher optimization levels
24063           (-O2 etc) because of the potentially detrimental effects of
24064           reserving a register.  It is up to the programmer to experiment and
24065           discover whether this feature is of benefit to their program.  See
24066           the description of the -mpid option for a description of how the
24067           actual register to hold the small data area pointer is chosen.
24068
24069       -msim
24070       -mno-sim
24071           Use the simulator runtime.  The default is to use the libgloss
24072           board-specific runtime.
24073
24074       -mas100-syntax
24075       -mno-as100-syntax
24076           When generating assembler output use a syntax that is compatible
24077           with Renesas's AS100 assembler.  This syntax can also be handled by
24078           the GAS assembler, but it has some restrictions so it is not
24079           generated by default.
24080
24081       -mmax-constant-size=N
24082           Specifies the maximum size, in bytes, of a constant that can be
24083           used as an operand in a RX instruction.  Although the RX
24084           instruction set does allow constants of up to 4 bytes in length to
24085           be used in instructions, a longer value equates to a longer
24086           instruction.  Thus in some circumstances it can be beneficial to
24087           restrict the size of constants that are used in instructions.
24088           Constants that are too big are instead placed into a constant pool
24089           and referenced via register indirection.
24090
24091           The value N can be between 0 and 4.  A value of 0 (the default) or
24092           4 means that constants of any size are allowed.
24093
24094       -mrelax
24095           Enable linker relaxation.  Linker relaxation is a process whereby
24096           the linker attempts to reduce the size of a program by finding
24097           shorter versions of various instructions.  Disabled by default.
24098
24099       -mint-register=N
24100           Specify the number of registers to reserve for fast interrupt
24101           handler functions.  The value N can be between 0 and 4.  A value of
24102           1 means that register "r13" is reserved for the exclusive use of
24103           fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A
24104           value of 3 reserves "r13", "r12" and "r11", and a value of 4
24105           reserves "r13" through "r10".  A value of 0, the default, does not
24106           reserve any registers.
24107
24108       -msave-acc-in-interrupts
24109           Specifies that interrupt handler functions should preserve the
24110           accumulator register.  This is only necessary if normal code might
24111           use the accumulator register, for example because it performs
24112           64-bit multiplications.  The default is to ignore the accumulator
24113           as this makes the interrupt handlers faster.
24114
24115       -mpid
24116       -mno-pid
24117           Enables the generation of position independent data.  When enabled
24118           any access to constant data is done via an offset from a base
24119           address held in a register.  This allows the location of constant
24120           data to be determined at run time without requiring the executable
24121           to be relocated, which is a benefit to embedded applications with
24122           tight memory constraints.  Data that can be modified is not
24123           affected by this option.
24124
24125           Note, using this feature reserves a register, usually "r13", for
24126           the constant data base address.  This can result in slower and/or
24127           larger code, especially in complicated functions.
24128
24129           The actual register chosen to hold the constant data base address
24130           depends upon whether the -msmall-data-limit and/or the
24131           -mint-register command-line options are enabled.  Starting with
24132           register "r13" and proceeding downwards, registers are allocated
24133           first to satisfy the requirements of -mint-register, then -mpid and
24134           finally -msmall-data-limit.  Thus it is possible for the small data
24135           area register to be "r8" if both -mint-register=4 and -mpid are
24136           specified on the command line.
24137
24138           By default this feature is not enabled.  The default can be
24139           restored via the -mno-pid command-line option.
24140
24141       -mno-warn-multiple-fast-interrupts
24142       -mwarn-multiple-fast-interrupts
24143           Prevents GCC from issuing a warning message if it finds more than
24144           one fast interrupt handler when it is compiling a file.  The
24145           default is to issue a warning for each extra fast interrupt handler
24146           found, as the RX only supports one such interrupt.
24147
24148       -mallow-string-insns
24149       -mno-allow-string-insns
24150           Enables or disables the use of the string manipulation instructions
24151           "SMOVF", "SCMPU", "SMOVB", "SMOVU", "SUNTIL" "SWHILE" and also the
24152           "RMPA" instruction.  These instructions may prefetch data, which is
24153           not safe to do if accessing an I/O register.  (See section 12.2.7
24154           of the RX62N Group User's Manual for more information).
24155
24156           The default is to allow these instructions, but it is not possible
24157           for GCC to reliably detect all circumstances where a string
24158           instruction might be used to access an I/O register, so their use
24159           cannot be disabled automatically.  Instead it is reliant upon the
24160           programmer to use the -mno-allow-string-insns option if their
24161           program accesses I/O space.
24162
24163           When the instructions are enabled GCC defines the C preprocessor
24164           symbol "__RX_ALLOW_STRING_INSNS__", otherwise it defines the symbol
24165           "__RX_DISALLOW_STRING_INSNS__".
24166
24167       -mjsr
24168       -mno-jsr
24169           Use only (or not only) "JSR" instructions to access functions.
24170           This option can be used when code size exceeds the range of "BSR"
24171           instructions.  Note that -mno-jsr does not mean to not use "JSR"
24172           but instead means that any type of branch may be used.
24173
24174       Note: The generic GCC command-line option -ffixed-reg has special
24175       significance to the RX port when used with the "interrupt" function
24176       attribute.  This attribute indicates a function intended to process
24177       fast interrupts.  GCC ensures that it only uses the registers "r10",
24178       "r11", "r12" and/or "r13" and only provided that the normal use of the
24179       corresponding registers have been restricted via the -ffixed-reg or
24180       -mint-register command-line options.
24181
24182       S/390 and zSeries Options
24183
24184       These are the -m options defined for the S/390 and zSeries
24185       architecture.
24186
24187       -mhard-float
24188       -msoft-float
24189           Use (do not use) the hardware floating-point instructions and
24190           registers for floating-point operations.  When -msoft-float is
24191           specified, functions in libgcc.a are used to perform floating-point
24192           operations.  When -mhard-float is specified, the compiler generates
24193           IEEE floating-point instructions.  This is the default.
24194
24195       -mhard-dfp
24196       -mno-hard-dfp
24197           Use (do not use) the hardware decimal-floating-point instructions
24198           for decimal-floating-point operations.  When -mno-hard-dfp is
24199           specified, functions in libgcc.a are used to perform decimal-
24200           floating-point operations.  When -mhard-dfp is specified, the
24201           compiler generates decimal-floating-point hardware instructions.
24202           This is the default for -march=z9-ec or higher.
24203
24204       -mlong-double-64
24205       -mlong-double-128
24206           These switches control the size of "long double" type. A size of 64
24207           bits makes the "long double" type equivalent to the "double" type.
24208           This is the default.
24209
24210       -mbackchain
24211       -mno-backchain
24212           Store (do not store) the address of the caller's frame as backchain
24213           pointer into the callee's stack frame.  A backchain may be needed
24214           to allow debugging using tools that do not understand DWARF call
24215           frame information.  When -mno-packed-stack is in effect, the
24216           backchain pointer is stored at the bottom of the stack frame; when
24217           -mpacked-stack is in effect, the backchain is placed into the
24218           topmost word of the 96/160 byte register save area.
24219
24220           In general, code compiled with -mbackchain is call-compatible with
24221           code compiled with -mno-backchain; however, use of the backchain
24222           for debugging purposes usually requires that the whole binary is
24223           built with -mbackchain.  Note that the combination of -mbackchain,
24224           -mpacked-stack and -mhard-float is not supported.  In order to
24225           build a linux kernel use -msoft-float.
24226
24227           The default is to not maintain the backchain.
24228
24229       -mpacked-stack
24230       -mno-packed-stack
24231           Use (do not use) the packed stack layout.  When -mno-packed-stack
24232           is specified, the compiler uses the all fields of the 96/160 byte
24233           register save area only for their default purpose; unused fields
24234           still take up stack space.  When -mpacked-stack is specified,
24235           register save slots are densely packed at the top of the register
24236           save area; unused space is reused for other purposes, allowing for
24237           more efficient use of the available stack space.  However, when
24238           -mbackchain is also in effect, the topmost word of the save area is
24239           always used to store the backchain, and the return address register
24240           is always saved two words below the backchain.
24241
24242           As long as the stack frame backchain is not used, code generated
24243           with -mpacked-stack is call-compatible with code generated with
24244           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
24245           S/390 or zSeries generated code that uses the stack frame backchain
24246           at run time, not just for debugging purposes.  Such code is not
24247           call-compatible with code compiled with -mpacked-stack.  Also, note
24248           that the combination of -mbackchain, -mpacked-stack and
24249           -mhard-float is not supported.  In order to build a linux kernel
24250           use -msoft-float.
24251
24252           The default is to not use the packed stack layout.
24253
24254       -msmall-exec
24255       -mno-small-exec
24256           Generate (or do not generate) code using the "bras" instruction to
24257           do subroutine calls.  This only works reliably if the total
24258           executable size does not exceed 64k.  The default is to use the
24259           "basr" instruction instead, which does not have this limitation.
24260
24261       -m64
24262       -m31
24263           When -m31 is specified, generate code compliant to the GNU/Linux
24264           for S/390 ABI.  When -m64 is specified, generate code compliant to
24265           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
24266           generate 64-bit instructions.  For the s390 targets, the default is
24267           -m31, while the s390x targets default to -m64.
24268
24269       -mzarch
24270       -mesa
24271           When -mzarch is specified, generate code using the instructions
24272           available on z/Architecture.  When -mesa is specified, generate
24273           code using the instructions available on ESA/390.  Note that -mesa
24274           is not possible with -m64.  When generating code compliant to the
24275           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
24276           code compliant to the GNU/Linux for zSeries ABI, the default is
24277           -mzarch.
24278
24279       -mhtm
24280       -mno-htm
24281           The -mhtm option enables a set of builtins making use of
24282           instructions available with the transactional execution facility
24283           introduced with the IBM zEnterprise EC12 machine generation S/390
24284           System z Built-in Functions.  -mhtm is enabled by default when
24285           using -march=zEC12.
24286
24287       -mvx
24288       -mno-vx
24289           When -mvx is specified, generate code using the instructions
24290           available with the vector extension facility introduced with the
24291           IBM z13 machine generation.  This option changes the ABI for some
24292           vector type values with regard to alignment and calling
24293           conventions.  In case vector type values are being used in an ABI-
24294           relevant context a GAS .gnu_attribute command will be added to mark
24295           the resulting binary with the ABI used.  -mvx is enabled by default
24296           when using -march=z13.
24297
24298       -mzvector
24299       -mno-zvector
24300           The -mzvector option enables vector language extensions and
24301           builtins using instructions available with the vector extension
24302           facility introduced with the IBM z13 machine generation.  This
24303           option adds support for vector to be used as a keyword to define
24304           vector type variables and arguments.  vector is only available when
24305           GNU extensions are enabled.  It will not be expanded when
24306           requesting strict standard compliance e.g. with -std=c99.  In
24307           addition to the GCC low-level builtins -mzvector enables a set of
24308           builtins added for compatibility with AltiVec-style implementations
24309           like Power and Cell.  In order to make use of these builtins the
24310           header file vecintrin.h needs to be included.  -mzvector is
24311           disabled by default.
24312
24313       -mmvcle
24314       -mno-mvcle
24315           Generate (or do not generate) code using the "mvcle" instruction to
24316           perform block moves.  When -mno-mvcle is specified, use a "mvc"
24317           loop instead.  This is the default unless optimizing for size.
24318
24319       -mdebug
24320       -mno-debug
24321           Print (or do not print) additional debug information when
24322           compiling.  The default is to not print debug information.
24323
24324       -march=cpu-type
24325           Generate code that runs on cpu-type, which is the name of a system
24326           representing a certain processor type.  Possible values for cpu-
24327           type are z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8,
24328           z196/arch9, zEC12, z13/arch11, z14/arch12, z15/arch13, and native.
24329
24330           The default is -march=z900.
24331
24332           Specifying native as cpu type can be used to select the best
24333           architecture option for the host processor.  -march=native has no
24334           effect if GCC does not recognize the processor.
24335
24336       -mtune=cpu-type
24337           Tune to cpu-type everything applicable about the generated code,
24338           except for the ABI and the set of available instructions.  The list
24339           of cpu-type values is the same as for -march.  The default is the
24340           value used for -march.
24341
24342       -mtpf-trace
24343       -mno-tpf-trace
24344           Generate code that adds (does not add) in TPF OS specific branches
24345           to trace routines in the operating system.  This option is off by
24346           default, even when compiling for the TPF OS.
24347
24348       -mtpf-trace-skip
24349       -mno-tpf-trace-skip
24350           Generate code that changes (does not change) the default branch
24351           targets enabled by -mtpf-trace to point to specialized trace
24352           routines providing the ability of selectively skipping function
24353           trace entries for the TPF OS.  This option is off by default, even
24354           when compiling for the TPF OS and specifying -mtpf-trace.
24355
24356       -mfused-madd
24357       -mno-fused-madd
24358           Generate code that uses (does not use) the floating-point multiply
24359           and accumulate instructions.  These instructions are generated by
24360           default if hardware floating point is used.
24361
24362       -mwarn-framesize=framesize
24363           Emit a warning if the current function exceeds the given frame
24364           size.  Because this is a compile-time check it doesn't need to be a
24365           real problem when the program runs.  It is intended to identify
24366           functions that most probably cause a stack overflow.  It is useful
24367           to be used in an environment with limited stack size e.g. the linux
24368           kernel.
24369
24370       -mwarn-dynamicstack
24371           Emit a warning if the function calls "alloca" or uses dynamically-
24372           sized arrays.  This is generally a bad idea with a limited stack
24373           size.
24374
24375       -mstack-guard=stack-guard
24376       -mstack-size=stack-size
24377           If these options are provided the S/390 back end emits additional
24378           instructions in the function prologue that trigger a trap if the
24379           stack size is stack-guard bytes above the stack-size (remember that
24380           the stack on S/390 grows downward).  If the stack-guard option is
24381           omitted the smallest power of 2 larger than the frame size of the
24382           compiled function is chosen.  These options are intended to be used
24383           to help debugging stack overflow problems.  The additionally
24384           emitted code causes only little overhead and hence can also be used
24385           in production-like systems without greater performance degradation.
24386           The given values have to be exact powers of 2 and stack-size has to
24387           be greater than stack-guard without exceeding 64k.  In order to be
24388           efficient the extra code makes the assumption that the stack starts
24389           at an address aligned to the value given by stack-size.  The stack-
24390           guard option can only be used in conjunction with stack-size.
24391
24392       -mhotpatch=pre-halfwords,post-halfwords
24393           If the hotpatch option is enabled, a "hot-patching" function
24394           prologue is generated for all functions in the compilation unit.
24395           The funtion label is prepended with the given number of two-byte
24396           NOP instructions (pre-halfwords, maximum 1000000).  After the
24397           label, 2 * post-halfwords bytes are appended, using the largest NOP
24398           like instructions the architecture allows (maximum 1000000).
24399
24400           If both arguments are zero, hotpatching is disabled.
24401
24402           This option can be overridden for individual functions with the
24403           "hotpatch" attribute.
24404
24405       Score Options
24406
24407       These options are defined for Score implementations:
24408
24409       -meb
24410           Compile code for big-endian mode.  This is the default.
24411
24412       -mel
24413           Compile code for little-endian mode.
24414
24415       -mnhwloop
24416           Disable generation of "bcnz" instructions.
24417
24418       -muls
24419           Enable generation of unaligned load and store instructions.
24420
24421       -mmac
24422           Enable the use of multiply-accumulate instructions. Disabled by
24423           default.
24424
24425       -mscore5
24426           Specify the SCORE5 as the target architecture.
24427
24428       -mscore5u
24429           Specify the SCORE5U of the target architecture.
24430
24431       -mscore7
24432           Specify the SCORE7 as the target architecture. This is the default.
24433
24434       -mscore7d
24435           Specify the SCORE7D as the target architecture.
24436
24437       SH Options
24438
24439       These -m options are defined for the SH implementations:
24440
24441       -m1 Generate code for the SH1.
24442
24443       -m2 Generate code for the SH2.
24444
24445       -m2e
24446           Generate code for the SH2e.
24447
24448       -m2a-nofpu
24449           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
24450           way that the floating-point unit is not used.
24451
24452       -m2a-single-only
24453           Generate code for the SH2a-FPU, in such a way that no double-
24454           precision floating-point operations are used.
24455
24456       -m2a-single
24457           Generate code for the SH2a-FPU assuming the floating-point unit is
24458           in single-precision mode by default.
24459
24460       -m2a
24461           Generate code for the SH2a-FPU assuming the floating-point unit is
24462           in double-precision mode by default.
24463
24464       -m3 Generate code for the SH3.
24465
24466       -m3e
24467           Generate code for the SH3e.
24468
24469       -m4-nofpu
24470           Generate code for the SH4 without a floating-point unit.
24471
24472       -m4-single-only
24473           Generate code for the SH4 with a floating-point unit that only
24474           supports single-precision arithmetic.
24475
24476       -m4-single
24477           Generate code for the SH4 assuming the floating-point unit is in
24478           single-precision mode by default.
24479
24480       -m4 Generate code for the SH4.
24481
24482       -m4-100
24483           Generate code for SH4-100.
24484
24485       -m4-100-nofpu
24486           Generate code for SH4-100 in such a way that the floating-point
24487           unit is not used.
24488
24489       -m4-100-single
24490           Generate code for SH4-100 assuming the floating-point unit is in
24491           single-precision mode by default.
24492
24493       -m4-100-single-only
24494           Generate code for SH4-100 in such a way that no double-precision
24495           floating-point operations are used.
24496
24497       -m4-200
24498           Generate code for SH4-200.
24499
24500       -m4-200-nofpu
24501           Generate code for SH4-200 without in such a way that the floating-
24502           point unit is not used.
24503
24504       -m4-200-single
24505           Generate code for SH4-200 assuming the floating-point unit is in
24506           single-precision mode by default.
24507
24508       -m4-200-single-only
24509           Generate code for SH4-200 in such a way that no double-precision
24510           floating-point operations are used.
24511
24512       -m4-300
24513           Generate code for SH4-300.
24514
24515       -m4-300-nofpu
24516           Generate code for SH4-300 without in such a way that the floating-
24517           point unit is not used.
24518
24519       -m4-300-single
24520           Generate code for SH4-300 in such a way that no double-precision
24521           floating-point operations are used.
24522
24523       -m4-300-single-only
24524           Generate code for SH4-300 in such a way that no double-precision
24525           floating-point operations are used.
24526
24527       -m4-340
24528           Generate code for SH4-340 (no MMU, no FPU).
24529
24530       -m4-500
24531           Generate code for SH4-500 (no FPU).  Passes -isa=sh4-nofpu to the
24532           assembler.
24533
24534       -m4a-nofpu
24535           Generate code for the SH4al-dsp, or for a SH4a in such a way that
24536           the floating-point unit is not used.
24537
24538       -m4a-single-only
24539           Generate code for the SH4a, in such a way that no double-precision
24540           floating-point operations are used.
24541
24542       -m4a-single
24543           Generate code for the SH4a assuming the floating-point unit is in
24544           single-precision mode by default.
24545
24546       -m4a
24547           Generate code for the SH4a.
24548
24549       -m4al
24550           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
24551           assembler.  GCC doesn't generate any DSP instructions at the
24552           moment.
24553
24554       -mb Compile code for the processor in big-endian mode.
24555
24556       -ml Compile code for the processor in little-endian mode.
24557
24558       -mdalign
24559           Align doubles at 64-bit boundaries.  Note that this changes the
24560           calling conventions, and thus some functions from the standard C
24561           library do not work unless you recompile it first with -mdalign.
24562
24563       -mrelax
24564           Shorten some address references at link time, when possible; uses
24565           the linker option -relax.
24566
24567       -mbigtable
24568           Use 32-bit offsets in "switch" tables.  The default is to use
24569           16-bit offsets.
24570
24571       -mbitops
24572           Enable the use of bit manipulation instructions on SH2A.
24573
24574       -mfmovd
24575           Enable the use of the instruction "fmovd".  Check -mdalign for
24576           alignment constraints.
24577
24578       -mrenesas
24579           Comply with the calling conventions defined by Renesas.
24580
24581       -mno-renesas
24582           Comply with the calling conventions defined for GCC before the
24583           Renesas conventions were available.  This option is the default for
24584           all targets of the SH toolchain.
24585
24586       -mnomacsave
24587           Mark the "MAC" register as call-clobbered, even if -mrenesas is
24588           given.
24589
24590       -mieee
24591       -mno-ieee
24592           Control the IEEE compliance of floating-point comparisons, which
24593           affects the handling of cases where the result of a comparison is
24594           unordered.  By default -mieee is implicitly enabled.  If
24595           -ffinite-math-only is enabled -mno-ieee is implicitly set, which
24596           results in faster floating-point greater-equal and less-equal
24597           comparisons.  The implicit settings can be overridden by specifying
24598           either -mieee or -mno-ieee.
24599
24600       -minline-ic_invalidate
24601           Inline code to invalidate instruction cache entries after setting
24602           up nested function trampolines.  This option has no effect if
24603           -musermode is in effect and the selected code generation option
24604           (e.g. -m4) does not allow the use of the "icbi" instruction.  If
24605           the selected code generation option does not allow the use of the
24606           "icbi" instruction, and -musermode is not in effect, the inlined
24607           code manipulates the instruction cache address array directly with
24608           an associative write.  This not only requires privileged mode at
24609           run time, but it also fails if the cache line had been mapped via
24610           the TLB and has become unmapped.
24611
24612       -misize
24613           Dump instruction size and location in the assembly code.
24614
24615       -mpadstruct
24616           This option is deprecated.  It pads structures to multiple of 4
24617           bytes, which is incompatible with the SH ABI.
24618
24619       -matomic-model=model
24620           Sets the model of atomic operations and additional parameters as a
24621           comma separated list.  For details on the atomic built-in functions
24622           see __atomic Builtins.  The following models and parameters are
24623           supported:
24624
24625           none
24626               Disable compiler generated atomic sequences and emit library
24627               calls for atomic operations.  This is the default if the target
24628               is not "sh*-*-linux*".
24629
24630           soft-gusa
24631               Generate GNU/Linux compatible gUSA software atomic sequences
24632               for the atomic built-in functions.  The generated atomic
24633               sequences require additional support from the
24634               interrupt/exception handling code of the system and are only
24635               suitable for SH3* and SH4* single-core systems.  This option is
24636               enabled by default when the target is "sh*-*-linux*" and SH3*
24637               or SH4*.  When the target is SH4A, this option also partially
24638               utilizes the hardware atomic instructions "movli.l" and
24639               "movco.l" to create more efficient code, unless strict is
24640               specified.
24641
24642           soft-tcb
24643               Generate software atomic sequences that use a variable in the
24644               thread control block.  This is a variation of the gUSA
24645               sequences which can also be used on SH1* and SH2* targets.  The
24646               generated atomic sequences require additional support from the
24647               interrupt/exception handling code of the system and are only
24648               suitable for single-core systems.  When using this model, the
24649               gbr-offset= parameter has to be specified as well.
24650
24651           soft-imask
24652               Generate software atomic sequences that temporarily disable
24653               interrupts by setting "SR.IMASK = 1111".  This model works only
24654               when the program runs in privileged mode and is only suitable
24655               for single-core systems.  Additional support from the
24656               interrupt/exception handling code of the system is not
24657               required.  This model is enabled by default when the target is
24658               "sh*-*-linux*" and SH1* or SH2*.
24659
24660           hard-llcs
24661               Generate hardware atomic sequences using the "movli.l" and
24662               "movco.l" instructions only.  This is only available on SH4A
24663               and is suitable for multi-core systems.  Since the hardware
24664               instructions support only 32 bit atomic variables access to 8
24665               or 16 bit variables is emulated with 32 bit accesses.  Code
24666               compiled with this option is also compatible with other
24667               software atomic model interrupt/exception handling systems if
24668               executed on an SH4A system.  Additional support from the
24669               interrupt/exception handling code of the system is not required
24670               for this model.
24671
24672           gbr-offset=
24673               This parameter specifies the offset in bytes of the variable in
24674               the thread control block structure that should be used by the
24675               generated atomic sequences when the soft-tcb model has been
24676               selected.  For other models this parameter is ignored.  The
24677               specified value must be an integer multiple of four and in the
24678               range 0-1020.
24679
24680           strict
24681               This parameter prevents mixed usage of multiple atomic models,
24682               even if they are compatible, and makes the compiler generate
24683               atomic sequences of the specified model only.
24684
24685       -mtas
24686           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice
24687           that depending on the particular hardware and software
24688           configuration this can degrade overall performance due to the
24689           operand cache line flushes that are implied by the "tas.b"
24690           instruction.  On multi-core SH4A processors the "tas.b" instruction
24691           must be used with caution since it can result in data corruption
24692           for certain cache configurations.
24693
24694       -mprefergot
24695           When generating position-independent code, emit function calls
24696           using the Global Offset Table instead of the Procedure Linkage
24697           Table.
24698
24699       -musermode
24700       -mno-usermode
24701           Don't allow (allow) the compiler generating privileged mode code.
24702           Specifying -musermode also implies -mno-inline-ic_invalidate if the
24703           inlined code would not work in user mode.  -musermode is the
24704           default when the target is "sh*-*-linux*".  If the target is SH1*
24705           or SH2* -musermode has no effect, since there is no user mode.
24706
24707       -multcost=number
24708           Set the cost to assume for a multiply insn.
24709
24710       -mdiv=strategy
24711           Set the division strategy to be used for integer division
24712           operations.  strategy can be one of:
24713
24714           call-div1
24715               Calls a library function that uses the single-step division
24716               instruction "div1" to perform the operation.  Division by zero
24717               calculates an unspecified result and does not trap.  This is
24718               the default except for SH4, SH2A and SHcompact.
24719
24720           call-fp
24721               Calls a library function that performs the operation in double
24722               precision floating point.  Division by zero causes a floating-
24723               point exception.  This is the default for SHcompact with FPU.
24724               Specifying this for targets that do not have a double precision
24725               FPU defaults to "call-div1".
24726
24727           call-table
24728               Calls a library function that uses a lookup table for small
24729               divisors and the "div1" instruction with case distinction for
24730               larger divisors.  Division by zero calculates an unspecified
24731               result and does not trap.  This is the default for SH4.
24732               Specifying this for targets that do not have dynamic shift
24733               instructions defaults to "call-div1".
24734
24735           When a division strategy has not been specified the default
24736           strategy is selected based on the current target.  For SH2A the
24737           default strategy is to use the "divs" and "divu" instructions
24738           instead of library function calls.
24739
24740       -maccumulate-outgoing-args
24741           Reserve space once for outgoing arguments in the function prologue
24742           rather than around each call.  Generally beneficial for performance
24743           and size.  Also needed for unwinding to avoid changing the stack
24744           frame around conditional code.
24745
24746       -mdivsi3_libfunc=name
24747           Set the name of the library function used for 32-bit signed
24748           division to name.  This only affects the name used in the call
24749           division strategies, and the compiler still expects the same sets
24750           of input/output/clobbered registers as if this option were not
24751           present.
24752
24753       -mfixed-range=register-range
24754           Generate code treating the given register range as fixed registers.
24755           A fixed register is one that the register allocator cannot use.
24756           This is useful when compiling kernel code.  A register range is
24757           specified as two registers separated by a dash.  Multiple register
24758           ranges can be specified separated by a comma.
24759
24760       -mbranch-cost=num
24761           Assume num to be the cost for a branch instruction.  Higher numbers
24762           make the compiler try to generate more branch-free code if
24763           possible.  If not specified the value is selected depending on the
24764           processor type that is being compiled for.
24765
24766       -mzdcbranch
24767       -mno-zdcbranch
24768           Assume (do not assume) that zero displacement conditional branch
24769           instructions "bt" and "bf" are fast.  If -mzdcbranch is specified,
24770           the compiler prefers zero displacement branch code sequences.  This
24771           is enabled by default when generating code for SH4 and SH4A.  It
24772           can be explicitly disabled by specifying -mno-zdcbranch.
24773
24774       -mcbranch-force-delay-slot
24775           Force the usage of delay slots for conditional branches, which
24776           stuffs the delay slot with a "nop" if a suitable instruction cannot
24777           be found.  By default this option is disabled.  It can be enabled
24778           to work around hardware bugs as found in the original SH7055.
24779
24780       -mfused-madd
24781       -mno-fused-madd
24782           Generate code that uses (does not use) the floating-point multiply
24783           and accumulate instructions.  These instructions are generated by
24784           default if hardware floating point is used.  The machine-dependent
24785           -mfused-madd option is now mapped to the machine-independent
24786           -ffp-contract=fast option, and -mno-fused-madd is mapped to
24787           -ffp-contract=off.
24788
24789       -mfsca
24790       -mno-fsca
24791           Allow or disallow the compiler to emit the "fsca" instruction for
24792           sine and cosine approximations.  The option -mfsca must be used in
24793           combination with -funsafe-math-optimizations.  It is enabled by
24794           default when generating code for SH4A.  Using -mno-fsca disables
24795           sine and cosine approximations even if -funsafe-math-optimizations
24796           is in effect.
24797
24798       -mfsrra
24799       -mno-fsrra
24800           Allow or disallow the compiler to emit the "fsrra" instruction for
24801           reciprocal square root approximations.  The option -mfsrra must be
24802           used in combination with -funsafe-math-optimizations and
24803           -ffinite-math-only.  It is enabled by default when generating code
24804           for SH4A.  Using -mno-fsrra disables reciprocal square root
24805           approximations even if -funsafe-math-optimizations and
24806           -ffinite-math-only are in effect.
24807
24808       -mpretend-cmove
24809           Prefer zero-displacement conditional branches for conditional move
24810           instruction patterns.  This can result in faster code on the SH4
24811           processor.
24812
24813       -mfdpic
24814           Generate code using the FDPIC ABI.
24815
24816       Solaris 2 Options
24817
24818       These -m options are supported on Solaris 2:
24819
24820       -mclear-hwcap
24821           -mclear-hwcap tells the compiler to remove the hardware
24822           capabilities generated by the Solaris assembler.  This is only
24823           necessary when object files use ISA extensions not supported by the
24824           current machine, but check at runtime whether or not to use them.
24825
24826       -mimpure-text
24827           -mimpure-text, used in addition to -shared, tells the compiler to
24828           not pass -z text to the linker when linking a shared object.  Using
24829           this option, you can link position-dependent code into a shared
24830           object.
24831
24832           -mimpure-text suppresses the "relocations remain against
24833           allocatable but non-writable sections" linker error message.
24834           However, the necessary relocations trigger copy-on-write, and the
24835           shared object is not actually shared across processes.  Instead of
24836           using -mimpure-text, you should compile all source code with -fpic
24837           or -fPIC.
24838
24839       These switches are supported in addition to the above on Solaris 2:
24840
24841       -pthreads
24842           This is a synonym for -pthread.
24843
24844       SPARC Options
24845
24846       These -m options are supported on the SPARC:
24847
24848       -mno-app-regs
24849       -mapp-regs
24850           Specify -mapp-regs to generate output using the global registers 2
24851           through 4, which the SPARC SVR4 ABI reserves for applications.
24852           Like the global register 1, each global register 2 through 4 is
24853           then treated as an allocable register that is clobbered by function
24854           calls.  This is the default.
24855
24856           To be fully SVR4 ABI-compliant at the cost of some performance
24857           loss, specify -mno-app-regs.  You should compile libraries and
24858           system software with this option.
24859
24860       -mflat
24861       -mno-flat
24862           With -mflat, the compiler does not generate save/restore
24863           instructions and uses a "flat" or single register window model.
24864           This model is compatible with the regular register window model.
24865           The local registers and the input registers (0--5) are still
24866           treated as "call-saved" registers and are saved on the stack as
24867           needed.
24868
24869           With -mno-flat (the default), the compiler generates save/restore
24870           instructions (except for leaf functions).  This is the normal
24871           operating mode.
24872
24873       -mfpu
24874       -mhard-float
24875           Generate output containing floating-point instructions.  This is
24876           the default.
24877
24878       -mno-fpu
24879       -msoft-float
24880           Generate output containing library calls for floating point.
24881           Warning: the requisite libraries are not available for all SPARC
24882           targets.  Normally the facilities of the machine's usual C compiler
24883           are used, but this cannot be done directly in cross-compilation.
24884           You must make your own arrangements to provide suitable library
24885           functions for cross-compilation.  The embedded targets sparc-*-aout
24886           and sparclite-*-* do provide software floating-point support.
24887
24888           -msoft-float changes the calling convention in the output file;
24889           therefore, it is only useful if you compile all of a program with
24890           this option.  In particular, you need to compile libgcc.a, the
24891           library that comes with GCC, with -msoft-float in order for this to
24892           work.
24893
24894       -mhard-quad-float
24895           Generate output containing quad-word (long double) floating-point
24896           instructions.
24897
24898       -msoft-quad-float
24899           Generate output containing library calls for quad-word (long
24900           double) floating-point instructions.  The functions called are
24901           those specified in the SPARC ABI.  This is the default.
24902
24903           As of this writing, there are no SPARC implementations that have
24904           hardware support for the quad-word floating-point instructions.
24905           They all invoke a trap handler for one of these instructions, and
24906           then the trap handler emulates the effect of the instruction.
24907           Because of the trap handler overhead, this is much slower than
24908           calling the ABI library routines.  Thus the -msoft-quad-float
24909           option is the default.
24910
24911       -mno-unaligned-doubles
24912       -munaligned-doubles
24913           Assume that doubles have 8-byte alignment.  This is the default.
24914
24915           With -munaligned-doubles, GCC assumes that doubles have 8-byte
24916           alignment only if they are contained in another type, or if they
24917           have an absolute address.  Otherwise, it assumes they have 4-byte
24918           alignment.  Specifying this option avoids some rare compatibility
24919           problems with code generated by other compilers.  It is not the
24920           default because it results in a performance loss, especially for
24921           floating-point code.
24922
24923       -muser-mode
24924       -mno-user-mode
24925           Do not generate code that can only run in supervisor mode.  This is
24926           relevant only for the "casa" instruction emitted for the LEON3
24927           processor.  This is the default.
24928
24929       -mfaster-structs
24930       -mno-faster-structs
24931           With -mfaster-structs, the compiler assumes that structures should
24932           have 8-byte alignment.  This enables the use of pairs of "ldd" and
24933           "std" instructions for copies in structure assignment, in place of
24934           twice as many "ld" and "st" pairs.  However, the use of this
24935           changed alignment directly violates the SPARC ABI.  Thus, it's
24936           intended only for use on targets where the developer acknowledges
24937           that their resulting code is not directly in line with the rules of
24938           the ABI.
24939
24940       -mstd-struct-return
24941       -mno-std-struct-return
24942           With -mstd-struct-return, the compiler generates checking code in
24943           functions returning structures or unions to detect size mismatches
24944           between the two sides of function calls, as per the 32-bit ABI.
24945
24946           The default is -mno-std-struct-return.  This option has no effect
24947           in 64-bit mode.
24948
24949       -mlra
24950       -mno-lra
24951           Enable Local Register Allocation.  This is the default for SPARC
24952           since GCC 7 so -mno-lra needs to be passed to get old Reload.
24953
24954       -mcpu=cpu_type
24955           Set the instruction set, register set, and instruction scheduling
24956           parameters for machine type cpu_type.  Supported values for
24957           cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3,
24958           leon3v7, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9,
24959           ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
24960           niagara7 and m8.
24961
24962           Native Solaris and GNU/Linux toolchains also support the value
24963           native, which selects the best architecture option for the host
24964           processor.  -mcpu=native has no effect if GCC does not recognize
24965           the processor.
24966
24967           Default instruction scheduling parameters are used for values that
24968           select an architecture and not an implementation.  These are v7,
24969           v8, sparclite, sparclet, v9.
24970
24971           Here is a list of each supported architecture and their supported
24972           implementations.
24973
24974           v7  cypress, leon3v7
24975
24976           v8  supersparc, hypersparc, leon, leon3
24977
24978           sparclite
24979               f930, f934, sparclite86x
24980
24981           sparclet
24982               tsc701
24983
24984           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
24985               niagara7, m8
24986
24987           By default (unless configured otherwise), GCC generates code for
24988           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
24989           compiler additionally optimizes it for the Cypress CY7C602 chip, as
24990           used in the SPARCStation/SPARCServer 3xx series.  This is also
24991           appropriate for the older SPARCStation 1, 2, IPX etc.
24992
24993           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
24994           architecture.  The only difference from V7 code is that the
24995           compiler emits the integer multiply and integer divide instructions
24996           which exist in SPARC-V8 but not in SPARC-V7.  With
24997           -mcpu=supersparc, the compiler additionally optimizes it for the
24998           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
24999           series.
25000
25001           With -mcpu=sparclite, GCC generates code for the SPARClite variant
25002           of the SPARC architecture.  This adds the integer multiply, integer
25003           divide step and scan ("ffs") instructions which exist in SPARClite
25004           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
25005           optimizes it for the Fujitsu MB86930 chip, which is the original
25006           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
25007           optimizes it for the Fujitsu MB86934 chip, which is the more recent
25008           SPARClite with FPU.
25009
25010           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
25011           the SPARC architecture.  This adds the integer multiply,
25012           multiply/accumulate, integer divide step and scan ("ffs")
25013           instructions which exist in SPARClet but not in SPARC-V7.  With
25014           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
25015           SPARClet chip.
25016
25017           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
25018           architecture.  This adds 64-bit integer and floating-point move
25019           instructions, 3 additional floating-point condition code registers
25020           and conditional move instructions.  With -mcpu=ultrasparc, the
25021           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
25022           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
25023           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
25024           -mcpu=niagara, the compiler additionally optimizes it for Sun
25025           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
25026           additionally optimizes it for Sun UltraSPARC T2 chips. With
25027           -mcpu=niagara3, the compiler additionally optimizes it for Sun
25028           UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler
25029           additionally optimizes it for Sun UltraSPARC T4 chips.  With
25030           -mcpu=niagara7, the compiler additionally optimizes it for Oracle
25031           SPARC M7 chips.  With -mcpu=m8, the compiler additionally optimizes
25032           it for Oracle M8 chips.
25033
25034       -mtune=cpu_type
25035           Set the instruction scheduling parameters for machine type
25036           cpu_type, but do not set the instruction set or register set that
25037           the option -mcpu=cpu_type does.
25038
25039           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
25040           but the only useful values are those that select a particular CPU
25041           implementation.  Those are cypress, supersparc, hypersparc, leon,
25042           leon3, leon3v7, f930, f934, sparclite86x, tsc701, ultrasparc,
25043           ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7 and
25044           m8.  With native Solaris and GNU/Linux toolchains, native can also
25045           be used.
25046
25047       -mv8plus
25048       -mno-v8plus
25049           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
25050           difference from the V8 ABI is that the global and out registers are
25051           considered 64 bits wide.  This is enabled by default on Solaris in
25052           32-bit mode for all SPARC-V9 processors.
25053
25054       -mvis
25055       -mno-vis
25056           With -mvis, GCC generates code that takes advantage of the
25057           UltraSPARC Visual Instruction Set extensions.  The default is
25058           -mno-vis.
25059
25060       -mvis2
25061       -mno-vis2
25062           With -mvis2, GCC generates code that takes advantage of version 2.0
25063           of the UltraSPARC Visual Instruction Set extensions.  The default
25064           is -mvis2 when targeting a cpu that supports such instructions,
25065           such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.
25066
25067       -mvis3
25068       -mno-vis3
25069           With -mvis3, GCC generates code that takes advantage of version 3.0
25070           of the UltraSPARC Visual Instruction Set extensions.  The default
25071           is -mvis3 when targeting a cpu that supports such instructions,
25072           such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and
25073           -mvis.
25074
25075       -mvis4
25076       -mno-vis4
25077           With -mvis4, GCC generates code that takes advantage of version 4.0
25078           of the UltraSPARC Visual Instruction Set extensions.  The default
25079           is -mvis4 when targeting a cpu that supports such instructions,
25080           such as niagara-7 and later.  Setting -mvis4 also sets -mvis3,
25081           -mvis2 and -mvis.
25082
25083       -mvis4b
25084       -mno-vis4b
25085           With -mvis4b, GCC generates code that takes advantage of version
25086           4.0 of the UltraSPARC Visual Instruction Set extensions, plus the
25087           additional VIS instructions introduced in the Oracle SPARC
25088           Architecture 2017.  The default is -mvis4b when targeting a cpu
25089           that supports such instructions, such as m8 and later.  Setting
25090           -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis.
25091
25092       -mcbcond
25093       -mno-cbcond
25094           With -mcbcond, GCC generates code that takes advantage of the
25095           UltraSPARC Compare-and-Branch-on-Condition instructions.  The
25096           default is -mcbcond when targeting a CPU that supports such
25097           instructions, such as Niagara-4 and later.
25098
25099       -mfmaf
25100       -mno-fmaf
25101           With -mfmaf, GCC generates code that takes advantage of the
25102           UltraSPARC Fused Multiply-Add Floating-point instructions.  The
25103           default is -mfmaf when targeting a CPU that supports such
25104           instructions, such as Niagara-3 and later.
25105
25106       -mfsmuld
25107       -mno-fsmuld
25108           With -mfsmuld, GCC generates code that takes advantage of the
25109           Floating-point Multiply Single to Double (FsMULd) instruction.  The
25110           default is -mfsmuld when targeting a CPU supporting the
25111           architecture versions V8 or V9 with FPU except -mcpu=leon.
25112
25113       -mpopc
25114       -mno-popc
25115           With -mpopc, GCC generates code that takes advantage of the
25116           UltraSPARC Population Count instruction.  The default is -mpopc
25117           when targeting a CPU that supports such an instruction, such as
25118           Niagara-2 and later.
25119
25120       -msubxc
25121       -mno-subxc
25122           With -msubxc, GCC generates code that takes advantage of the
25123           UltraSPARC Subtract-Extended-with-Carry instruction.  The default
25124           is -msubxc when targeting a CPU that supports such an instruction,
25125           such as Niagara-7 and later.
25126
25127       -mfix-at697f
25128           Enable the documented workaround for the single erratum of the
25129           Atmel AT697F processor (which corresponds to erratum #13 of the
25130           AT697E processor).
25131
25132       -mfix-ut699
25133           Enable the documented workarounds for the floating-point errata and
25134           the data cache nullify errata of the UT699 processor.
25135
25136       -mfix-ut700
25137           Enable the documented workaround for the back-to-back store errata
25138           of the UT699E/UT700 processor.
25139
25140       -mfix-gr712rc
25141           Enable the documented workaround for the back-to-back store errata
25142           of the GR712RC processor.
25143
25144       These -m options are supported in addition to the above on SPARC-V9
25145       processors in 64-bit environments:
25146
25147       -m32
25148       -m64
25149           Generate code for a 32-bit or 64-bit environment.  The 32-bit
25150           environment sets int, long and pointer to 32 bits.  The 64-bit
25151           environment sets int to 32 bits and long and pointer to 64 bits.
25152
25153       -mcmodel=which
25154           Set the code model to one of
25155
25156           medlow
25157               The Medium/Low code model: 64-bit addresses, programs must be
25158               linked in the low 32 bits of memory.  Programs can be
25159               statically or dynamically linked.
25160
25161           medmid
25162               The Medium/Middle code model: 64-bit addresses, programs must
25163               be linked in the low 44 bits of memory, the text and data
25164               segments must be less than 2GB in size and the data segment
25165               must be located within 2GB of the text segment.
25166
25167           medany
25168               The Medium/Anywhere code model: 64-bit addresses, programs may
25169               be linked anywhere in memory, the text and data segments must
25170               be less than 2GB in size and the data segment must be located
25171               within 2GB of the text segment.
25172
25173           embmedany
25174               The Medium/Anywhere code model for embedded systems: 64-bit
25175               addresses, the text and data segments must be less than 2GB in
25176               size, both starting anywhere in memory (determined at link
25177               time).  The global register %g4 points to the base of the data
25178               segment.  Programs are statically linked and PIC is not
25179               supported.
25180
25181       -mmemory-model=mem-model
25182           Set the memory model in force on the processor to one of
25183
25184           default
25185               The default memory model for the processor and operating
25186               system.
25187
25188           rmo Relaxed Memory Order
25189
25190           pso Partial Store Order
25191
25192           tso Total Store Order
25193
25194           sc  Sequential Consistency
25195
25196           These memory models are formally defined in Appendix D of the
25197           SPARC-V9 architecture manual, as set in the processor's "PSTATE.MM"
25198           field.
25199
25200       -mstack-bias
25201       -mno-stack-bias
25202           With -mstack-bias, GCC assumes that the stack pointer, and frame
25203           pointer if present, are offset by -2047 which must be added back
25204           when making stack frame references.  This is the default in 64-bit
25205           mode.  Otherwise, assume no such offset is present.
25206
25207       Options for System V
25208
25209       These additional options are available on System V Release 4 for
25210       compatibility with other compilers on those systems:
25211
25212       -G  Create a shared object.  It is recommended that -symbolic or
25213           -shared be used instead.
25214
25215       -Qy Identify the versions of each tool used by the compiler, in a
25216           ".ident" assembler directive in the output.
25217
25218       -Qn Refrain from adding ".ident" directives to the output file (this is
25219           the default).
25220
25221       -YP,dirs
25222           Search the directories dirs, and no others, for libraries specified
25223           with -l.
25224
25225       -Ym,dir
25226           Look in the directory dir to find the M4 preprocessor.  The
25227           assembler uses this option.
25228
25229       TILE-Gx Options
25230
25231       These -m options are supported on the TILE-Gx:
25232
25233       -mcmodel=small
25234           Generate code for the small model.  The distance for direct calls
25235           is limited to 500M in either direction.  PC-relative addresses are
25236           32 bits.  Absolute addresses support the full address range.
25237
25238       -mcmodel=large
25239           Generate code for the large model.  There is no limitation on call
25240           distance, pc-relative addresses, or absolute addresses.
25241
25242       -mcpu=name
25243           Selects the type of CPU to be targeted.  Currently the only
25244           supported type is tilegx.
25245
25246       -m32
25247       -m64
25248           Generate code for a 32-bit or 64-bit environment.  The 32-bit
25249           environment sets int, long, and pointer to 32 bits.  The 64-bit
25250           environment sets int to 32 bits and long and pointer to 64 bits.
25251
25252       -mbig-endian
25253       -mlittle-endian
25254           Generate code in big/little endian mode, respectively.
25255
25256       TILEPro Options
25257
25258       These -m options are supported on the TILEPro:
25259
25260       -mcpu=name
25261           Selects the type of CPU to be targeted.  Currently the only
25262           supported type is tilepro.
25263
25264       -m32
25265           Generate code for a 32-bit environment, which sets int, long, and
25266           pointer to 32 bits.  This is the only supported behavior so the
25267           flag is essentially ignored.
25268
25269       V850 Options
25270
25271       These -m options are defined for V850 implementations:
25272
25273       -mlong-calls
25274       -mno-long-calls
25275           Treat all calls as being far away (near).  If calls are assumed to
25276           be far away, the compiler always loads the function's address into
25277           a register, and calls indirect through the pointer.
25278
25279       -mno-ep
25280       -mep
25281           Do not optimize (do optimize) basic blocks that use the same index
25282           pointer 4 or more times to copy pointer into the "ep" register, and
25283           use the shorter "sld" and "sst" instructions.  The -mep option is
25284           on by default if you optimize.
25285
25286       -mno-prolog-function
25287       -mprolog-function
25288           Do not use (do use) external functions to save and restore
25289           registers at the prologue and epilogue of a function.  The external
25290           functions are slower, but use less code space if more than one
25291           function saves the same number of registers.  The -mprolog-function
25292           option is on by default if you optimize.
25293
25294       -mspace
25295           Try to make the code as small as possible.  At present, this just
25296           turns on the -mep and -mprolog-function options.
25297
25298       -mtda=n
25299           Put static or global variables whose size is n bytes or less into
25300           the tiny data area that register "ep" points to.  The tiny data
25301           area can hold up to 256 bytes in total (128 bytes for byte
25302           references).
25303
25304       -msda=n
25305           Put static or global variables whose size is n bytes or less into
25306           the small data area that register "gp" points to.  The small data
25307           area can hold up to 64 kilobytes.
25308
25309       -mzda=n
25310           Put static or global variables whose size is n bytes or less into
25311           the first 32 kilobytes of memory.
25312
25313       -mv850
25314           Specify that the target processor is the V850.
25315
25316       -mv850e3v5
25317           Specify that the target processor is the V850E3V5.  The
25318           preprocessor constant "__v850e3v5__" is defined if this option is
25319           used.
25320
25321       -mv850e2v4
25322           Specify that the target processor is the V850E3V5.  This is an
25323           alias for the -mv850e3v5 option.
25324
25325       -mv850e2v3
25326           Specify that the target processor is the V850E2V3.  The
25327           preprocessor constant "__v850e2v3__" is defined if this option is
25328           used.
25329
25330       -mv850e2
25331           Specify that the target processor is the V850E2.  The preprocessor
25332           constant "__v850e2__" is defined if this option is used.
25333
25334       -mv850e1
25335           Specify that the target processor is the V850E1.  The preprocessor
25336           constants "__v850e1__" and "__v850e__" are defined if this option
25337           is used.
25338
25339       -mv850es
25340           Specify that the target processor is the V850ES.  This is an alias
25341           for the -mv850e1 option.
25342
25343       -mv850e
25344           Specify that the target processor is the V850E.  The preprocessor
25345           constant "__v850e__" is defined if this option is used.
25346
25347           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor
25348           -mv850e2v3 nor -mv850e3v5 are defined then a default target
25349           processor is chosen and the relevant __v850*__ preprocessor
25350           constant is defined.
25351
25352           The preprocessor constants "__v850" and "__v851__" are always
25353           defined, regardless of which processor variant is the target.
25354
25355       -mdisable-callt
25356       -mno-disable-callt
25357           This option suppresses generation of the "CALLT" instruction for
25358           the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
25359           v850 architecture.
25360
25361           This option is enabled by default when the RH850 ABI is in use (see
25362           -mrh850-abi), and disabled by default when the GCC ABI is in use.
25363           If "CALLT" instructions are being generated then the C preprocessor
25364           symbol "__V850_CALLT__" is defined.
25365
25366       -mrelax
25367       -mno-relax
25368           Pass on (or do not pass on) the -mrelax command-line option to the
25369           assembler.
25370
25371       -mlong-jumps
25372       -mno-long-jumps
25373           Disable (or re-enable) the generation of PC-relative jump
25374           instructions.
25375
25376       -msoft-float
25377       -mhard-float
25378           Disable (or re-enable) the generation of hardware floating point
25379           instructions.  This option is only significant when the target
25380           architecture is V850E2V3 or higher.  If hardware floating point
25381           instructions are being generated then the C preprocessor symbol
25382           "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is
25383           defined.
25384
25385       -mloop
25386           Enables the use of the e3v5 LOOP instruction.  The use of this
25387           instruction is not enabled by default when the e3v5 architecture is
25388           selected because its use is still experimental.
25389
25390       -mrh850-abi
25391       -mghs
25392           Enables support for the RH850 version of the V850 ABI.  This is the
25393           default.  With this version of the ABI the following rules apply:
25394
25395           *   Integer sized structures and unions are returned via a memory
25396               pointer rather than a register.
25397
25398           *   Large structures and unions (more than 8 bytes in size) are
25399               passed by value.
25400
25401           *   Functions are aligned to 16-bit boundaries.
25402
25403           *   The -m8byte-align command-line option is supported.
25404
25405           *   The -mdisable-callt command-line option is enabled by default.
25406               The -mno-disable-callt command-line option is not supported.
25407
25408           When this version of the ABI is enabled the C preprocessor symbol
25409           "__V850_RH850_ABI__" is defined.
25410
25411       -mgcc-abi
25412           Enables support for the old GCC version of the V850 ABI.  With this
25413           version of the ABI the following rules apply:
25414
25415           *   Integer sized structures and unions are returned in register
25416               "r10".
25417
25418           *   Large structures and unions (more than 8 bytes in size) are
25419               passed by reference.
25420
25421           *   Functions are aligned to 32-bit boundaries, unless optimizing
25422               for size.
25423
25424           *   The -m8byte-align command-line option is not supported.
25425
25426           *   The -mdisable-callt command-line option is supported but not
25427               enabled by default.
25428
25429           When this version of the ABI is enabled the C preprocessor symbol
25430           "__V850_GCC_ABI__" is defined.
25431
25432       -m8byte-align
25433       -mno-8byte-align
25434           Enables support for "double" and "long long" types to be aligned on
25435           8-byte boundaries.  The default is to restrict the alignment of all
25436           objects to at most 4-bytes.  When -m8byte-align is in effect the C
25437           preprocessor symbol "__V850_8BYTE_ALIGN__" is defined.
25438
25439       -mbig-switch
25440           Generate code suitable for big switch tables.  Use this option only
25441           if the assembler/linker complain about out of range branches within
25442           a switch table.
25443
25444       -mapp-regs
25445           This option causes r2 and r5 to be used in the code generated by
25446           the compiler.  This setting is the default.
25447
25448       -mno-app-regs
25449           This option causes r2 and r5 to be treated as fixed registers.
25450
25451       VAX Options
25452
25453       These -m options are defined for the VAX:
25454
25455       -munix
25456           Do not output certain jump instructions ("aobleq" and so on) that
25457           the Unix assembler for the VAX cannot handle across long ranges.
25458
25459       -mgnu
25460           Do output those jump instructions, on the assumption that the GNU
25461           assembler is being used.
25462
25463       -mg Output code for G-format floating-point numbers instead of
25464           D-format.
25465
25466       Visium Options
25467
25468       -mdebug
25469           A program which performs file I/O and is destined to run on an MCM
25470           target should be linked with this option.  It causes the libraries
25471           libc.a and libdebug.a to be linked.  The program should be run on
25472           the target under the control of the GDB remote debugging stub.
25473
25474       -msim
25475           A program which performs file I/O and is destined to run on the
25476           simulator should be linked with option.  This causes libraries
25477           libc.a and libsim.a to be linked.
25478
25479       -mfpu
25480       -mhard-float
25481           Generate code containing floating-point instructions.  This is the
25482           default.
25483
25484       -mno-fpu
25485       -msoft-float
25486           Generate code containing library calls for floating-point.
25487
25488           -msoft-float changes the calling convention in the output file;
25489           therefore, it is only useful if you compile all of a program with
25490           this option.  In particular, you need to compile libgcc.a, the
25491           library that comes with GCC, with -msoft-float in order for this to
25492           work.
25493
25494       -mcpu=cpu_type
25495           Set the instruction set, register set, and instruction scheduling
25496           parameters for machine type cpu_type.  Supported values for
25497           cpu_type are mcm, gr5 and gr6.
25498
25499           mcm is a synonym of gr5 present for backward compatibility.
25500
25501           By default (unless configured otherwise), GCC generates code for
25502           the GR5 variant of the Visium architecture.
25503
25504           With -mcpu=gr6, GCC generates code for the GR6 variant of the
25505           Visium architecture.  The only difference from GR5 code is that the
25506           compiler will generate block move instructions.
25507
25508       -mtune=cpu_type
25509           Set the instruction scheduling parameters for machine type
25510           cpu_type, but do not set the instruction set or register set that
25511           the option -mcpu=cpu_type would.
25512
25513       -msv-mode
25514           Generate code for the supervisor mode, where there are no
25515           restrictions on the access to general registers.  This is the
25516           default.
25517
25518       -muser-mode
25519           Generate code for the user mode, where the access to some general
25520           registers is forbidden: on the GR5, registers r24 to r31 cannot be
25521           accessed in this mode; on the GR6, only registers r29 to r31 are
25522           affected.
25523
25524       VMS Options
25525
25526       These -m options are defined for the VMS implementations:
25527
25528       -mvms-return-codes
25529           Return VMS condition codes from "main". The default is to return
25530           POSIX-style condition (e.g. error) codes.
25531
25532       -mdebug-main=prefix
25533           Flag the first routine whose name starts with prefix as the main
25534           routine for the debugger.
25535
25536       -mmalloc64
25537           Default to 64-bit memory allocation routines.
25538
25539       -mpointer-size=size
25540           Set the default size of pointers. Possible options for size are 32
25541           or short for 32 bit pointers, 64 or long for 64 bit pointers, and
25542           no for supporting only 32 bit pointers.  The later option disables
25543           "pragma pointer_size".
25544
25545       VxWorks Options
25546
25547       The options in this section are defined for all VxWorks targets.
25548       Options specific to the target hardware are listed with the other
25549       options for that target.
25550
25551       -mrtp
25552           GCC can generate code for both VxWorks kernels and real time
25553           processes (RTPs).  This option switches from the former to the
25554           latter.  It also defines the preprocessor macro "__RTP__".
25555
25556       -non-static
25557           Link an RTP executable against shared libraries rather than static
25558           libraries.  The options -static and -shared can also be used for
25559           RTPs; -static is the default.
25560
25561       -Bstatic
25562       -Bdynamic
25563           These options are passed down to the linker.  They are defined for
25564           compatibility with Diab.
25565
25566       -Xbind-lazy
25567           Enable lazy binding of function calls.  This option is equivalent
25568           to -Wl,-z,now and is defined for compatibility with Diab.
25569
25570       -Xbind-now
25571           Disable lazy binding of function calls.  This option is the default
25572           and is defined for compatibility with Diab.
25573
25574       x86 Options
25575
25576       These -m options are defined for the x86 family of computers.
25577
25578       -march=cpu-type
25579           Generate instructions for the machine type cpu-type.  In contrast
25580           to -mtune=cpu-type, which merely tunes the generated code for the
25581           specified cpu-type, -march=cpu-type allows GCC to generate code
25582           that may not run at all on processors other than the one indicated.
25583           Specifying -march=cpu-type implies -mtune=cpu-type, except where
25584           noted otherwise.
25585
25586           The choices for cpu-type are:
25587
25588           native
25589               This selects the CPU to generate code for at compilation time
25590               by determining the processor type of the compiling machine.
25591               Using -march=native enables all instruction subsets supported
25592               by the local machine (hence the result might not run on
25593               different machines).  Using -mtune=native produces code
25594               optimized for the local machine under the constraints of the
25595               selected instruction set.
25596
25597           x86-64
25598               A generic CPU with 64-bit extensions.
25599
25600           x86-64-v2
25601           x86-64-v3
25602           x86-64-v4
25603               These choices for cpu-type select the corresponding micro-
25604               architecture level from the x86-64 psABI.  On ABIs other than
25605               the x86-64 psABI they select the same CPU features as the
25606               x86-64 psABI documents for the particular micro-architecture
25607               level.
25608
25609               Since these cpu-type values do not have a corresponding -mtune
25610               setting, using -march with these values enables generic tuning.
25611               Specific tuning can be enabled using the -mtune=other-cpu-type
25612               option with an appropriate other-cpu-type value.
25613
25614           i386
25615               Original Intel i386 CPU.
25616
25617           i486
25618               Intel i486 CPU.  (No scheduling is implemented for this chip.)
25619
25620           i586
25621           pentium
25622               Intel Pentium CPU with no MMX support.
25623
25624           lakemont
25625               Intel Lakemont MCU, based on Intel Pentium CPU.
25626
25627           pentium-mmx
25628               Intel Pentium MMX CPU, based on Pentium core with MMX
25629               instruction set support.
25630
25631           pentiumpro
25632               Intel Pentium Pro CPU.
25633
25634           i686
25635               When used with -march, the Pentium Pro instruction set is used,
25636               so the code runs on all i686 family chips.  When used with
25637               -mtune, it has the same meaning as generic.
25638
25639           pentium2
25640               Intel Pentium II CPU, based on Pentium Pro core with MMX
25641               instruction set support.
25642
25643           pentium3
25644           pentium3m
25645               Intel Pentium III CPU, based on Pentium Pro core with MMX and
25646               SSE instruction set support.
25647
25648           pentium-m
25649               Intel Pentium M; low-power version of Intel Pentium III CPU
25650               with MMX, SSE and SSE2 instruction set support.  Used by
25651               Centrino notebooks.
25652
25653           pentium4
25654           pentium4m
25655               Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set
25656               support.
25657
25658           prescott
25659               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and
25660               SSE3 instruction set support.
25661
25662           nocona
25663               Improved version of Intel Pentium 4 CPU with 64-bit extensions,
25664               MMX, SSE, SSE2 and SSE3 instruction set support.
25665
25666           core2
25667               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
25668               and SSSE3 instruction set support.
25669
25670           nehalem
25671               Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
25672               SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support.
25673
25674           westmere
25675               Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
25676               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction
25677               set support.
25678
25679           sandybridge
25680               Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
25681               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL
25682               instruction set support.
25683
25684           ivybridge
25685               Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
25686               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL,
25687               FSGSBASE, RDRND and F16C instruction set support.
25688
25689           haswell
25690               Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25691               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25692               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction
25693               set support.
25694
25695           broadwell
25696               Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25697               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25698               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED ADCX and
25699               PREFETCHW instruction set support.
25700
25701           skylake
25702               Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25703               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25704               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25705               PREFETCHW, CLFLUSHOPT, XSAVEC and XSAVES instruction set
25706               support.
25707
25708           bonnell
25709               Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
25710               SSE2, SSE3 and SSSE3 instruction set support.
25711
25712           silvermont
25713               Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25714               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25715               PCLMUL and RDRND instruction set support.
25716
25717           goldmont
25718               Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25719               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25720               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT and FSGSBASE
25721               instruction set support.
25722
25723           goldmont-plus
25724               Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX,
25725               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25726               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25727               PTWRITE, RDPID, SGX and UMIP instruction set support.
25728
25729           tremont
25730               Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE,
25731               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25732               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25733               PTWRITE, RDPID, SGX, UMIP, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
25734               CLDEMOTE and WAITPKG instruction set support.
25735
25736           knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX,
25737               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25738               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25739               PREFETCHW, PREFETCHWT1, AVX512F, AVX512PF, AVX512ER and
25740               AVX512CD instruction set support.
25741
25742           knm Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE,
25743               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
25744               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25745               PREFETCHW, PREFETCHWT1, AVX512F, AVX512PF, AVX512ER, AVX512CD,
25746               AVX5124VNNIW, AVX5124FMAPS and AVX512VPOPCNTDQ instruction set
25747               support.
25748
25749           skylake-avx512
25750               Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
25751               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25752               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25753               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,
25754               AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set
25755               support.
25756
25757           cannonlake
25758               Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX,
25759               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25760               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25761               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25762               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA and
25763               UMIP instruction set support.
25764
25765           icelake-client
25766               Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
25767               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25768               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25769               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25770               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25771               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25772               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set
25773               support.
25774
25775           icelake-server
25776               Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
25777               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25778               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25779               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25780               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25781               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25782               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG and
25783               WBNOINVD instruction set support.
25784
25785           cascadelake
25786               Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25787               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25788               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25789               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL,
25790               AVX512BW, AVX512DQ, AVX512CD and AVX512VNNI instruction set
25791               support.
25792
25793           cooperlake
25794               Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25795               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25796               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25797               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL,
25798               AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI and AVX512BF16
25799               instruction set support.
25800
25801           tigerlake
25802               Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25803               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25804               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25805               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25806               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25807               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25808               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG, WBNOINVD,
25809               MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT and KEYLOCKER
25810               instruction set support.
25811
25812           sapphirerapids
25813               Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX,
25814               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
25815               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
25816               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,
25817               AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VNNI, AVX512BF16,
25818               MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE,
25819               PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-
25820               TILE, AMX-INT8 and AVX-VNNI instruction set support.
25821
25822           alderlake
25823               Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25824               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW,
25825               PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE,
25826               PTWRITE, RDPID, SGX, UMIP, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B,
25827               CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA,
25828               LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL,
25829               WIDEKL and AVX-VNNI instruction set support.
25830
25831           rocketlake
25832               Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE,
25833               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES,
25834               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
25835               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
25836               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
25837               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
25838               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set
25839               support.
25840
25841           k6  AMD K6 CPU with MMX instruction set support.
25842
25843           k6-2
25844           k6-3
25845               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
25846               set support.
25847
25848           athlon
25849           athlon-tbird
25850               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
25851               prefetch instructions support.
25852
25853           athlon-4
25854           athlon-xp
25855           athlon-mp
25856               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
25857               full SSE instruction set support.
25858
25859           k8
25860           opteron
25861           athlon64
25862           athlon-fx
25863               Processors based on the AMD K8 core with x86-64 instruction set
25864               support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
25865               processors.  (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
25866               3DNow! and 64-bit instruction set extensions.)
25867
25868           k8-sse3
25869           opteron-sse3
25870           athlon64-sse3
25871               Improved versions of AMD K8 cores with SSE3 instruction set
25872               support.
25873
25874           amdfam10
25875           barcelona
25876               CPUs based on AMD Family 10h cores with x86-64 instruction set
25877               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
25878               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
25879
25880           bdver1
25881               CPUs based on AMD Family 15h cores with x86-64 instruction set
25882               support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCLMUL,
25883               CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
25884               and 64-bit instruction set extensions.)
25885
25886           bdver2
25887               AMD Family 15h core based CPUs with x86-64 instruction set
25888               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
25889               LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
25890               SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
25891
25892           bdver3
25893               AMD Family 15h core based CPUs with x86-64 instruction set
25894               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE,
25895               AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
25896               SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
25897               extensions.)
25898
25899           bdver4
25900               AMD Family 15h core based CPUs with x86-64 instruction set
25901               support.  (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
25902               FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE, MMX,
25903               SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit
25904               instruction set extensions.)
25905
25906           znver1
25907               AMD Family 17h core based CPUs with x86-64 instruction set
25908               support.  (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX,
25909               AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16,
25910               MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM,
25911               XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit instruction set
25912               extensions.)
25913
25914           znver2
25915               AMD Family 17h core based CPUs with x86-64 instruction set
25916               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
25917               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
25918               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
25919               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
25920               WBNOINVD, and 64-bit instruction set extensions.)
25921
25922           znver3
25923               AMD Family 19h core based CPUs with x86-64 instruction set
25924               support. (This supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE,
25925               AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL,
25926               CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
25927               SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID,
25928               WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set
25929               extensions.)
25930
25931           btver1
25932               CPUs based on AMD Family 14h cores with x86-64 instruction set
25933               support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
25934               CX16, ABM and 64-bit instruction set extensions.)
25935
25936           btver2
25937               CPUs based on AMD Family 16h cores with x86-64 instruction set
25938               support. This includes MOVBE, F16C, BMI, AVX, PCLMUL, AES,
25939               SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
25940               and 64-bit instruction set extensions.
25941
25942           winchip-c6
25943               IDT WinChip C6 CPU, dealt in same way as i486 with additional
25944               MMX instruction set support.
25945
25946           winchip2
25947               IDT WinChip 2 CPU, dealt in same way as i486 with additional
25948               MMX and 3DNow!  instruction set support.
25949
25950           c3  VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
25951               scheduling is implemented for this chip.)
25952
25953           c3-2
25954               VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
25955               support.  (No scheduling is implemented for this chip.)
25956
25957           c7  VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
25958               set support.  (No scheduling is implemented for this chip.)
25959
25960           samuel-2
25961               VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
25962               support.  (No scheduling is implemented for this chip.)
25963
25964           nehemiah
25965               VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
25966               (No scheduling is implemented for this chip.)
25967
25968           esther
25969               VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction
25970               set support.  (No scheduling is implemented for this chip.)
25971
25972           eden-x2
25973               VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3
25974               instruction set support.  (No scheduling is implemented for
25975               this chip.)
25976
25977           eden-x4
25978               VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
25979               SSE4.1, SSE4.2, AVX and AVX2 instruction set support.  (No
25980               scheduling is implemented for this chip.)
25981
25982           nano
25983               Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
25984               SSSE3 instruction set support.  (No scheduling is implemented
25985               for this chip.)
25986
25987           nano-1000
25988               VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
25989               instruction set support.  (No scheduling is implemented for
25990               this chip.)
25991
25992           nano-2000
25993               VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
25994               instruction set support.  (No scheduling is implemented for
25995               this chip.)
25996
25997           nano-3000
25998               VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and
25999               SSE4.1 instruction set support.  (No scheduling is implemented
26000               for this chip.)
26001
26002           nano-x2
26003               VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
26004               and SSE4.1 instruction set support.  (No scheduling is
26005               implemented for this chip.)
26006
26007           nano-x4
26008               VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
26009               and SSE4.1 instruction set support.  (No scheduling is
26010               implemented for this chip.)
26011
26012           geode
26013               AMD Geode embedded processor with MMX and 3DNow! instruction
26014               set support.
26015
26016       -mtune=cpu-type
26017           Tune to cpu-type everything applicable about the generated code,
26018           except for the ABI and the set of available instructions.  While
26019           picking a specific cpu-type schedules things appropriately for that
26020           particular chip, the compiler does not generate any code that
26021           cannot run on the default machine type unless you use a -march=cpu-
26022           type option.  For example, if GCC is configured for
26023           i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned
26024           for Pentium 4 but still runs on i686 machines.
26025
26026           The choices for cpu-type are the same as for -march.  In addition,
26027           -mtune supports 2 extra choices for cpu-type:
26028
26029           generic
26030               Produce code optimized for the most common IA32/AMD64/EM64T
26031               processors.  If you know the CPU on which your code will run,
26032               then you should use the corresponding -mtune or -march option
26033               instead of -mtune=generic.  But, if you do not know exactly
26034               what CPU users of your application will have, then you should
26035               use this option.
26036
26037               As new processors are deployed in the marketplace, the behavior
26038               of this option will change.  Therefore, if you upgrade to a
26039               newer version of GCC, code generation controlled by this option
26040               will change to reflect the processors that are most common at
26041               the time that version of GCC is released.
26042
26043               There is no -march=generic option because -march indicates the
26044               instruction set the compiler can use, and there is no generic
26045               instruction set applicable to all processors.  In contrast,
26046               -mtune indicates the processor (or, in this case, collection of
26047               processors) for which the code is optimized.
26048
26049           intel
26050               Produce code optimized for the most current Intel processors,
26051               which are Haswell and Silvermont for this version of GCC.  If
26052               you know the CPU on which your code will run, then you should
26053               use the corresponding -mtune or -march option instead of
26054               -mtune=intel.  But, if you want your application performs
26055               better on both Haswell and Silvermont, then you should use this
26056               option.
26057
26058               As new Intel processors are deployed in the marketplace, the
26059               behavior of this option will change.  Therefore, if you upgrade
26060               to a newer version of GCC, code generation controlled by this
26061               option will change to reflect the most current Intel processors
26062               at the time that version of GCC is released.
26063
26064               There is no -march=intel option because -march indicates the
26065               instruction set the compiler can use, and there is no common
26066               instruction set applicable to all processors.  In contrast,
26067               -mtune indicates the processor (or, in this case, collection of
26068               processors) for which the code is optimized.
26069
26070       -mcpu=cpu-type
26071           A deprecated synonym for -mtune.
26072
26073       -mfpmath=unit
26074           Generate floating-point arithmetic for selected unit unit.  The
26075           choices for unit are:
26076
26077           387 Use the standard 387 floating-point coprocessor present on the
26078               majority of chips and emulated otherwise.  Code compiled with
26079               this option runs almost everywhere.  The temporary results are
26080               computed in 80-bit precision instead of the precision specified
26081               by the type, resulting in slightly different results compared
26082               to most of other chips.  See -ffloat-store for more detailed
26083               description.
26084
26085               This is the default choice for non-Darwin x86-32 targets.
26086
26087           sse Use scalar floating-point instructions present in the SSE
26088               instruction set.  This instruction set is supported by Pentium
26089               III and newer chips, and in the AMD line by Athlon-4, Athlon XP
26090               and Athlon MP chips.  The earlier version of the SSE
26091               instruction set supports only single-precision arithmetic, thus
26092               the double and extended-precision arithmetic are still done
26093               using 387.  A later version, present only in Pentium 4 and AMD
26094               x86-64 chips, supports double-precision arithmetic too.
26095
26096               For the x86-32 compiler, you must use -march=cpu-type, -msse or
26097               -msse2 switches to enable SSE extensions and make this option
26098               effective.  For the x86-64 compiler, these extensions are
26099               enabled by default.
26100
26101               The resulting code should be considerably faster in the
26102               majority of cases and avoid the numerical instability problems
26103               of 387 code, but may break some existing code that expects
26104               temporaries to be 80 bits.
26105
26106               This is the default choice for the x86-64 compiler, Darwin
26107               x86-32 targets, and the default choice for x86-32 targets with
26108               the SSE2 instruction set when -ffast-math is enabled.
26109
26110           sse,387
26111           sse+387
26112           both
26113               Attempt to utilize both instruction sets at once.  This
26114               effectively doubles the amount of available registers, and on
26115               chips with separate execution units for 387 and SSE the
26116               execution resources too.  Use this option with care, as it is
26117               still experimental, because the GCC register allocator does not
26118               model separate functional units well, resulting in unstable
26119               performance.
26120
26121       -masm=dialect
26122           Output assembly instructions using selected dialect.  Also affects
26123           which dialect is used for basic "asm" and extended "asm". Supported
26124           choices (in dialect order) are att or intel. The default is att.
26125           Darwin does not support intel.
26126
26127       -mieee-fp
26128       -mno-ieee-fp
26129           Control whether or not the compiler uses IEEE floating-point
26130           comparisons.  These correctly handle the case where the result of a
26131           comparison is unordered.
26132
26133       -m80387
26134       -mhard-float
26135           Generate output containing 80387 instructions for floating point.
26136
26137       -mno-80387
26138       -msoft-float
26139           Generate output containing library calls for floating point.
26140
26141           Warning: the requisite libraries are not part of GCC.  Normally the
26142           facilities of the machine's usual C compiler are used, but this
26143           cannot be done directly in cross-compilation.  You must make your
26144           own arrangements to provide suitable library functions for cross-
26145           compilation.
26146
26147           On machines where a function returns floating-point results in the
26148           80387 register stack, some floating-point opcodes may be emitted
26149           even if -msoft-float is used.
26150
26151       -mno-fp-ret-in-387
26152           Do not use the FPU registers for return values of functions.
26153
26154           The usual calling convention has functions return values of types
26155           "float" and "double" in an FPU register, even if there is no FPU.
26156           The idea is that the operating system should emulate an FPU.
26157
26158           The option -mno-fp-ret-in-387 causes such values to be returned in
26159           ordinary CPU registers instead.
26160
26161       -mno-fancy-math-387
26162           Some 387 emulators do not support the "sin", "cos" and "sqrt"
26163           instructions for the 387.  Specify this option to avoid generating
26164           those instructions.  This option is overridden when -march
26165           indicates that the target CPU always has an FPU and so the
26166           instruction does not need emulation.  These instructions are not
26167           generated unless you also use the -funsafe-math-optimizations
26168           switch.
26169
26170       -malign-double
26171       -mno-align-double
26172           Control whether GCC aligns "double", "long double", and "long long"
26173           variables on a two-word boundary or a one-word boundary.  Aligning
26174           "double" variables on a two-word boundary produces code that runs
26175           somewhat faster on a Pentium at the expense of more memory.
26176
26177           On x86-64, -malign-double is enabled by default.
26178
26179           Warning: if you use the -malign-double switch, structures
26180           containing the above types are aligned differently than the
26181           published application binary interface specifications for the
26182           x86-32 and are not binary compatible with structures in code
26183           compiled without that switch.
26184
26185       -m96bit-long-double
26186       -m128bit-long-double
26187           These switches control the size of "long double" type.  The x86-32
26188           application binary interface specifies the size to be 96 bits, so
26189           -m96bit-long-double is the default in 32-bit mode.
26190
26191           Modern architectures (Pentium and newer) prefer "long double" to be
26192           aligned to an 8- or 16-byte boundary.  In arrays or structures
26193           conforming to the ABI, this is not possible.  So specifying
26194           -m128bit-long-double aligns "long double" to a 16-byte boundary by
26195           padding the "long double" with an additional 32-bit zero.
26196
26197           In the x86-64 compiler, -m128bit-long-double is the default choice
26198           as its ABI specifies that "long double" is aligned on 16-byte
26199           boundary.
26200
26201           Notice that neither of these options enable any extra precision
26202           over the x87 standard of 80 bits for a "long double".
26203
26204           Warning: if you override the default value for your target ABI,
26205           this changes the size of structures and arrays containing "long
26206           double" variables, as well as modifying the function calling
26207           convention for functions taking "long double".  Hence they are not
26208           binary-compatible with code compiled without that switch.
26209
26210       -mlong-double-64
26211       -mlong-double-80
26212       -mlong-double-128
26213           These switches control the size of "long double" type. A size of 64
26214           bits makes the "long double" type equivalent to the "double" type.
26215           This is the default for 32-bit Bionic C library.  A size of 128
26216           bits makes the "long double" type equivalent to the "__float128"
26217           type. This is the default for 64-bit Bionic C library.
26218
26219           Warning: if you override the default value for your target ABI,
26220           this changes the size of structures and arrays containing "long
26221           double" variables, as well as modifying the function calling
26222           convention for functions taking "long double".  Hence they are not
26223           binary-compatible with code compiled without that switch.
26224
26225       -malign-data=type
26226           Control how GCC aligns variables.  Supported values for type are
26227           compat uses increased alignment value compatible uses GCC 4.8 and
26228           earlier, abi uses alignment value as specified by the psABI, and
26229           cacheline uses increased alignment value to match the cache line
26230           size.  compat is the default.
26231
26232       -mlarge-data-threshold=threshold
26233           When -mcmodel=medium is specified, data objects larger than
26234           threshold are placed in the large data section.  This value must be
26235           the same across all objects linked into the binary, and defaults to
26236           65535.
26237
26238       -mrtd
26239           Use a different function-calling convention, in which functions
26240           that take a fixed number of arguments return with the "ret num"
26241           instruction, which pops their arguments while returning.  This
26242           saves one instruction in the caller since there is no need to pop
26243           the arguments there.
26244
26245           You can specify that an individual function is called with this
26246           calling sequence with the function attribute "stdcall".  You can
26247           also override the -mrtd option by using the function attribute
26248           "cdecl".
26249
26250           Warning: this calling convention is incompatible with the one
26251           normally used on Unix, so you cannot use it if you need to call
26252           libraries compiled with the Unix compiler.
26253
26254           Also, you must provide function prototypes for all functions that
26255           take variable numbers of arguments (including "printf"); otherwise
26256           incorrect code is generated for calls to those functions.
26257
26258           In addition, seriously incorrect code results if you call a
26259           function with too many arguments.  (Normally, extra arguments are
26260           harmlessly ignored.)
26261
26262       -mregparm=num
26263           Control how many registers are used to pass integer arguments.  By
26264           default, no registers are used to pass arguments, and at most 3
26265           registers can be used.  You can control this behavior for a
26266           specific function by using the function attribute "regparm".
26267
26268           Warning: if you use this switch, and num is nonzero, then you must
26269           build all modules with the same value, including any libraries.
26270           This includes the system libraries and startup modules.
26271
26272       -msseregparm
26273           Use SSE register passing conventions for float and double arguments
26274           and return values.  You can control this behavior for a specific
26275           function by using the function attribute "sseregparm".
26276
26277           Warning: if you use this switch then you must build all modules
26278           with the same value, including any libraries.  This includes the
26279           system libraries and startup modules.
26280
26281       -mvect8-ret-in-mem
26282           Return 8-byte vectors in memory instead of MMX registers.  This is
26283           the default on VxWorks to match the ABI of the Sun Studio compilers
26284           until version 12.  Only use this option if you need to remain
26285           compatible with existing code produced by those previous compiler
26286           versions or older versions of GCC.
26287
26288       -mpc32
26289       -mpc64
26290       -mpc80
26291           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
26292           -mpc32 is specified, the significands of results of floating-point
26293           operations are rounded to 24 bits (single precision); -mpc64 rounds
26294           the significands of results of floating-point operations to 53 bits
26295           (double precision) and -mpc80 rounds the significands of results of
26296           floating-point operations to 64 bits (extended double precision),
26297           which is the default.  When this option is used, floating-point
26298           operations in higher precisions are not available to the programmer
26299           without setting the FPU control word explicitly.
26300
26301           Setting the rounding of floating-point operations to less than the
26302           default 80 bits can speed some programs by 2% or more.  Note that
26303           some mathematical libraries assume that extended-precision (80-bit)
26304           floating-point operations are enabled by default; routines in such
26305           libraries could suffer significant loss of accuracy, typically
26306           through so-called "catastrophic cancellation", when this option is
26307           used to set the precision to less than extended precision.
26308
26309       -mstackrealign
26310           Realign the stack at entry.  On the x86, the -mstackrealign option
26311           generates an alternate prologue and epilogue that realigns the run-
26312           time stack if necessary.  This supports mixing legacy codes that
26313           keep 4-byte stack alignment with modern codes that keep 16-byte
26314           stack alignment for SSE compatibility.  See also the attribute
26315           "force_align_arg_pointer", applicable to individual functions.
26316
26317       -mpreferred-stack-boundary=num
26318           Attempt to keep the stack boundary aligned to a 2 raised to num
26319           byte boundary.  If -mpreferred-stack-boundary is not specified, the
26320           default is 4 (16 bytes or 128 bits).
26321
26322           Warning: When generating code for the x86-64 architecture with SSE
26323           extensions disabled, -mpreferred-stack-boundary=3 can be used to
26324           keep the stack boundary aligned to 8 byte boundary.  Since x86-64
26325           ABI require 16 byte stack alignment, this is ABI incompatible and
26326           intended to be used in controlled environment where stack space is
26327           important limitation.  This option leads to wrong code when
26328           functions compiled with 16 byte stack alignment (such as functions
26329           from a standard library) are called with misaligned stack.  In this
26330           case, SSE instructions may lead to misaligned memory access traps.
26331           In addition, variable arguments are handled incorrectly for 16 byte
26332           aligned objects (including x87 long double and __int128), leading
26333           to wrong results.  You must build all modules with
26334           -mpreferred-stack-boundary=3, including any libraries.  This
26335           includes the system libraries and startup modules.
26336
26337       -mincoming-stack-boundary=num
26338           Assume the incoming stack is aligned to a 2 raised to num byte
26339           boundary.  If -mincoming-stack-boundary is not specified, the one
26340           specified by -mpreferred-stack-boundary is used.
26341
26342           On Pentium and Pentium Pro, "double" and "long double" values
26343           should be aligned to an 8-byte boundary (see -malign-double) or
26344           suffer significant run time performance penalties.  On Pentium III,
26345           the Streaming SIMD Extension (SSE) data type "__m128" may not work
26346           properly if it is not 16-byte aligned.
26347
26348           To ensure proper alignment of this values on the stack, the stack
26349           boundary must be as aligned as that required by any value stored on
26350           the stack.  Further, every function must be generated such that it
26351           keeps the stack aligned.  Thus calling a function compiled with a
26352           higher preferred stack boundary from a function compiled with a
26353           lower preferred stack boundary most likely misaligns the stack.  It
26354           is recommended that libraries that use callbacks always use the
26355           default setting.
26356
26357           This extra alignment does consume extra stack space, and generally
26358           increases code size.  Code that is sensitive to stack space usage,
26359           such as embedded systems and operating system kernels, may want to
26360           reduce the preferred alignment to -mpreferred-stack-boundary=2.
26361
26362       -mmmx
26363       -msse
26364       -msse2
26365       -msse3
26366       -mssse3
26367       -msse4
26368       -msse4a
26369       -msse4.1
26370       -msse4.2
26371       -mavx
26372       -mavx2
26373       -mavx512f
26374       -mavx512pf
26375       -mavx512er
26376       -mavx512cd
26377       -mavx512vl
26378       -mavx512bw
26379       -mavx512dq
26380       -mavx512ifma
26381       -mavx512vbmi
26382       -msha
26383       -maes
26384       -mpclmul
26385       -mclflushopt
26386       -mclwb
26387       -mfsgsbase
26388       -mptwrite
26389       -mrdrnd
26390       -mf16c
26391       -mfma
26392       -mpconfig
26393       -mwbnoinvd
26394       -mfma4
26395       -mprfchw
26396       -mrdpid
26397       -mprefetchwt1
26398       -mrdseed
26399       -msgx
26400       -mxop
26401       -mlwp
26402       -m3dnow
26403       -m3dnowa
26404       -mpopcnt
26405       -mabm
26406       -madx
26407       -mbmi
26408       -mbmi2
26409       -mlzcnt
26410       -mfxsr
26411       -mxsave
26412       -mxsaveopt
26413       -mxsavec
26414       -mxsaves
26415       -mrtm
26416       -mhle
26417       -mtbm
26418       -mmwaitx
26419       -mclzero
26420       -mpku
26421       -mavx512vbmi2
26422       -mavx512bf16
26423       -mgfni
26424       -mvaes
26425       -mwaitpkg
26426       -mvpclmulqdq
26427       -mavx512bitalg
26428       -mmovdiri
26429       -mmovdir64b
26430       -menqcmd
26431       -muintr
26432       -mtsxldtrk
26433       -mavx512vpopcntdq
26434       -mavx512vp2intersect
26435       -mavx5124fmaps
26436       -mavx512vnni
26437       -mavxvnni
26438       -mavx5124vnniw
26439       -mcldemote
26440       -mserialize
26441       -mamx-tile
26442       -mamx-int8
26443       -mamx-bf16
26444       -mhreset
26445       -mkl
26446       -mwidekl
26447           These switches enable the use of instructions in the MMX, SSE,
26448           SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F,
26449           AVX512PF, AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ,
26450           AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB,
26451           FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, WBNOINVD, FMA4,
26452           PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, 3DNow!,
26453           enhanced 3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE,
26454           XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU,
26455           AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG,
26456           MOVDIRI, MOVDIR64B, AVX512BF16, ENQCMD, AVX512VPOPCNTDQ,
26457           AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, UINTR, HRESET,
26458           AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI or CLDEMOTE extended
26459           instruction sets. Each has a corresponding -mno- option to disable
26460           use of these instructions.
26461
26462           These extensions are also available as built-in functions: see x86
26463           Built-in Functions, for details of the functions enabled and
26464           disabled by these switches.
26465
26466           To generate SSE/SSE2 instructions automatically from floating-point
26467           code (as opposed to 387 instructions), see -mfpmath=sse.
26468
26469           GCC depresses SSEx instructions when -mavx is used. Instead, it
26470           generates new AVX instructions or AVX equivalence for all SSEx
26471           instructions when needed.
26472
26473           These options enable GCC to use these extended instructions in
26474           generated code, even without -mfpmath=sse.  Applications that
26475           perform run-time CPU detection must compile separate files for each
26476           supported architecture, using the appropriate flags.  In
26477           particular, the file containing the CPU detection code should be
26478           compiled without these options.
26479
26480       -mdump-tune-features
26481           This option instructs GCC to dump the names of the x86 performance
26482           tuning features and default settings. The names can be used in
26483           -mtune-ctrl=feature-list.
26484
26485       -mtune-ctrl=feature-list
26486           This option is used to do fine grain control of x86 code generation
26487           features.  feature-list is a comma separated list of feature names.
26488           See also -mdump-tune-features. When specified, the feature is
26489           turned on if it is not preceded with ^, otherwise, it is turned
26490           off.  -mtune-ctrl=feature-list is intended to be used by GCC
26491           developers. Using it may lead to code paths not covered by testing
26492           and can potentially result in compiler ICEs or runtime errors.
26493
26494       -mno-default
26495           This option instructs GCC to turn off all tunable features. See
26496           also -mtune-ctrl=feature-list and -mdump-tune-features.
26497
26498       -mcld
26499           This option instructs GCC to emit a "cld" instruction in the
26500           prologue of functions that use string instructions.  String
26501           instructions depend on the DF flag to select between autoincrement
26502           or autodecrement mode.  While the ABI specifies the DF flag to be
26503           cleared on function entry, some operating systems violate this
26504           specification by not clearing the DF flag in their exception
26505           dispatchers.  The exception handler can be invoked with the DF flag
26506           set, which leads to wrong direction mode when string instructions
26507           are used.  This option can be enabled by default on 32-bit x86
26508           targets by configuring GCC with the --enable-cld configure option.
26509           Generation of "cld" instructions can be suppressed with the
26510           -mno-cld compiler option in this case.
26511
26512       -mvzeroupper
26513           This option instructs GCC to emit a "vzeroupper" instruction before
26514           a transfer of control flow out of the function to minimize the AVX
26515           to SSE transition penalty as well as remove unnecessary "zeroupper"
26516           intrinsics.
26517
26518       -mprefer-avx128
26519           This option instructs GCC to use 128-bit AVX instructions instead
26520           of 256-bit AVX instructions in the auto-vectorizer.
26521
26522       -mprefer-vector-width=opt
26523           This option instructs GCC to use opt-bit vector width in
26524           instructions instead of default on the selected platform.
26525
26526           none
26527               No extra limitations applied to GCC other than defined by the
26528               selected platform.
26529
26530           128 Prefer 128-bit vector width for instructions.
26531
26532           256 Prefer 256-bit vector width for instructions.
26533
26534           512 Prefer 512-bit vector width for instructions.
26535
26536       -mcx16
26537           This option enables GCC to generate "CMPXCHG16B" instructions in
26538           64-bit code to implement compare-and-exchange operations on 16-byte
26539           aligned 128-bit objects.  This is useful for atomic updates of data
26540           structures exceeding one machine word in size.  The compiler uses
26541           this instruction to implement __sync Builtins.  However, for
26542           __atomic Builtins operating on 128-bit integers, a library call is
26543           always used.
26544
26545       -msahf
26546           This option enables generation of "SAHF" instructions in 64-bit
26547           code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
26548           the introduction of Pentium 4 G1 step in December 2005, lacked the
26549           "LAHF" and "SAHF" instructions which are supported by AMD64.  These
26550           are load and store instructions, respectively, for certain status
26551           flags.  In 64-bit mode, the "SAHF" instruction is used to optimize
26552           "fmod", "drem", and "remainder" built-in functions; see Other
26553           Builtins for details.
26554
26555       -mmovbe
26556           This option enables use of the "movbe" instruction to implement
26557           "__builtin_bswap32" and "__builtin_bswap64".
26558
26559       -mshstk
26560           The -mshstk option enables shadow stack built-in functions from x86
26561           Control-flow Enforcement Technology (CET).
26562
26563       -mcrc32
26564           This option enables built-in functions "__builtin_ia32_crc32qi",
26565           "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and
26566           "__builtin_ia32_crc32di" to generate the "crc32" machine
26567           instruction.
26568
26569       -mrecip
26570           This option enables use of "RCPSS" and "RSQRTSS" instructions (and
26571           their vectorized variants "RCPPS" and "RSQRTPS") with an additional
26572           Newton-Raphson step to increase precision instead of "DIVSS" and
26573           "SQRTSS" (and their vectorized variants) for single-precision
26574           floating-point arguments.  These instructions are generated only
26575           when -funsafe-math-optimizations is enabled together with
26576           -ffinite-math-only and -fno-trapping-math.  Note that while the
26577           throughput of the sequence is higher than the throughput of the
26578           non-reciprocal instruction, the precision of the sequence can be
26579           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
26580           0.99999994).
26581
26582           Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or
26583           "RSQRTPS") already with -ffast-math (or the above option
26584           combination), and doesn't need -mrecip.
26585
26586           Also note that GCC emits the above sequence with additional Newton-
26587           Raphson step for vectorized single-float division and vectorized
26588           "sqrtf(x)" already with -ffast-math (or the above option
26589           combination), and doesn't need -mrecip.
26590
26591       -mrecip=opt
26592           This option controls which reciprocal estimate instructions may be
26593           used.  opt is a comma-separated list of options, which may be
26594           preceded by a ! to invert the option:
26595
26596           all Enable all estimate instructions.
26597
26598           default
26599               Enable the default instructions, equivalent to -mrecip.
26600
26601           none
26602               Disable all estimate instructions, equivalent to -mno-recip.
26603
26604           div Enable the approximation for scalar division.
26605
26606           vec-div
26607               Enable the approximation for vectorized division.
26608
26609           sqrt
26610               Enable the approximation for scalar square root.
26611
26612           vec-sqrt
26613               Enable the approximation for vectorized square root.
26614
26615           So, for example, -mrecip=all,!sqrt enables all of the reciprocal
26616           approximations, except for square root.
26617
26618       -mveclibabi=type
26619           Specifies the ABI type to use for vectorizing intrinsics using an
26620           external library.  Supported values for type are svml for the Intel
26621           short vector math library and acml for the AMD math core library.
26622           To use this option, both -ftree-vectorize and
26623           -funsafe-math-optimizations have to be enabled, and an SVML or ACML
26624           ABI-compatible library must be specified at link time.
26625
26626           GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102",
26627           "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2",
26628           "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2", "vmldAsin2",
26629           "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4",
26630           "vmlsLn4", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4",
26631           "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4",
26632           "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4"
26633           and "vmlsAcos4" for corresponding function type when
26634           -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos",
26635           "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10",
26636           "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf",
26637           "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the
26638           corresponding function type when -mveclibabi=acml is used.
26639
26640       -mabi=name
26641           Generate code for the specified calling convention.  Permissible
26642           values are sysv for the ABI used on GNU/Linux and other systems,
26643           and ms for the Microsoft ABI.  The default is to use the Microsoft
26644           ABI when targeting Microsoft Windows and the SysV ABI on all other
26645           systems.  You can control this behavior for specific functions by
26646           using the function attributes "ms_abi" and "sysv_abi".
26647
26648       -mforce-indirect-call
26649           Force all calls to functions to be indirect. This is useful when
26650           using Intel Processor Trace where it generates more precise timing
26651           information for function calls.
26652
26653       -mmanual-endbr
26654           Insert ENDBR instruction at function entry only via the "cf_check"
26655           function attribute. This is useful when used with the option
26656           -fcf-protection=branch to control ENDBR insertion at the function
26657           entry.
26658
26659       -mcall-ms2sysv-xlogues
26660           Due to differences in 64-bit ABIs, any Microsoft ABI function that
26661           calls a System V ABI function must consider RSI, RDI and XMM6-15 as
26662           clobbered.  By default, the code for saving and restoring these
26663           registers is emitted inline, resulting in fairly lengthy prologues
26664           and epilogues.  Using -mcall-ms2sysv-xlogues emits prologues and
26665           epilogues that use stubs in the static portion of libgcc to perform
26666           these saves and restores, thus reducing function size at the cost
26667           of a few extra instructions.
26668
26669       -mtls-dialect=type
26670           Generate code to access thread-local storage using the gnu or gnu2
26671           conventions.  gnu is the conservative default; gnu2 is more
26672           efficient, but it may add compile- and run-time requirements that
26673           cannot be satisfied on all systems.
26674
26675       -mpush-args
26676       -mno-push-args
26677           Use PUSH operations to store outgoing parameters.  This method is
26678           shorter and usually equally fast as method using SUB/MOV operations
26679           and is enabled by default.  In some cases disabling it may improve
26680           performance because of improved scheduling and reduced
26681           dependencies.
26682
26683       -maccumulate-outgoing-args
26684           If enabled, the maximum amount of space required for outgoing
26685           arguments is computed in the function prologue.  This is faster on
26686           most modern CPUs because of reduced dependencies, improved
26687           scheduling and reduced stack usage when the preferred stack
26688           boundary is not equal to 2.  The drawback is a notable increase in
26689           code size.  This switch implies -mno-push-args.
26690
26691       -mthreads
26692           Support thread-safe exception handling on MinGW.  Programs that
26693           rely on thread-safe exception handling must compile and link all
26694           code with the -mthreads option.  When compiling, -mthreads defines
26695           -D_MT; when linking, it links in a special thread helper library
26696           -lmingwthrd which cleans up per-thread exception-handling data.
26697
26698       -mms-bitfields
26699       -mno-ms-bitfields
26700           Enable/disable bit-field layout compatible with the native
26701           Microsoft Windows compiler.
26702
26703           If "packed" is used on a structure, or if bit-fields are used, it
26704           may be that the Microsoft ABI lays out the structure differently
26705           than the way GCC normally does.  Particularly when moving packed
26706           data between functions compiled with GCC and the native Microsoft
26707           compiler (either via function call or as data in a file), it may be
26708           necessary to access either format.
26709
26710           This option is enabled by default for Microsoft Windows targets.
26711           This behavior can also be controlled locally by use of variable or
26712           type attributes.  For more information, see x86 Variable Attributes
26713           and x86 Type Attributes.
26714
26715           The Microsoft structure layout algorithm is fairly simple with the
26716           exception of the bit-field packing.  The padding and alignment of
26717           members of structures and whether a bit-field can straddle a
26718           storage-unit boundary are determine by these rules:
26719
26720           1. Structure members are stored sequentially in the order in which
26721           they are
26722               declared: the first member has the lowest memory address and
26723               the last member the highest.
26724
26725           2. Every data object has an alignment requirement.  The alignment
26726           requirement
26727               for all data except structures, unions, and arrays is either
26728               the size of the object or the current packing size (specified
26729               with either the "aligned" attribute or the "pack" pragma),
26730               whichever is less.  For structures, unions, and arrays, the
26731               alignment requirement is the largest alignment requirement of
26732               its members.  Every object is allocated an offset so that:
26733
26734                       offset % alignment_requirement == 0
26735
26736           3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte
26737           allocation
26738               unit if the integral types are the same size and if the next
26739               bit-field fits into the current allocation unit without
26740               crossing the boundary imposed by the common alignment
26741               requirements of the bit-fields.
26742
26743           MSVC interprets zero-length bit-fields in the following ways:
26744
26745           1. If a zero-length bit-field is inserted between two bit-fields
26746           that
26747               are normally coalesced, the bit-fields are not coalesced.
26748
26749               For example:
26750
26751                       struct
26752                        {
26753                          unsigned long bf_1 : 12;
26754                          unsigned long : 0;
26755                          unsigned long bf_2 : 12;
26756                        } t1;
26757
26758               The size of "t1" is 8 bytes with the zero-length bit-field.  If
26759               the zero-length bit-field were removed, "t1"'s size would be 4
26760               bytes.
26761
26762           2. If a zero-length bit-field is inserted after a bit-field, "foo",
26763           and the
26764               alignment of the zero-length bit-field is greater than the
26765               member that follows it, "bar", "bar" is aligned as the type of
26766               the zero-length bit-field.
26767
26768               For example:
26769
26770                       struct
26771                        {
26772                          char foo : 4;
26773                          short : 0;
26774                          char bar;
26775                        } t2;
26776
26777                       struct
26778                        {
26779                          char foo : 4;
26780                          short : 0;
26781                          double bar;
26782                        } t3;
26783
26784               For "t2", "bar" is placed at offset 2, rather than offset 1.
26785               Accordingly, the size of "t2" is 4.  For "t3", the zero-length
26786               bit-field does not affect the alignment of "bar" or, as a
26787               result, the size of the structure.
26788
26789               Taking this into account, it is important to note the
26790               following:
26791
26792               1. If a zero-length bit-field follows a normal bit-field, the
26793               type of the
26794                   zero-length bit-field may affect the alignment of the
26795                   structure as whole. For example, "t2" has a size of 4
26796                   bytes, since the zero-length bit-field follows a normal
26797                   bit-field, and is of type short.
26798
26799               2. Even if a zero-length bit-field is not followed by a normal
26800               bit-field, it may
26801                   still affect the alignment of the structure:
26802
26803                           struct
26804                            {
26805                              char foo : 6;
26806                              long : 0;
26807                            } t4;
26808
26809                   Here, "t4" takes up 4 bytes.
26810
26811           3. Zero-length bit-fields following non-bit-field members are
26812           ignored:
26813                       struct
26814                        {
26815                          char foo;
26816                          long : 0;
26817                          char bar;
26818                        } t5;
26819
26820               Here, "t5" takes up 2 bytes.
26821
26822       -mno-align-stringops
26823           Do not align the destination of inlined string operations.  This
26824           switch reduces code size and improves performance in case the
26825           destination is already aligned, but GCC doesn't know about it.
26826
26827       -minline-all-stringops
26828           By default GCC inlines string operations only when the destination
26829           is known to be aligned to least a 4-byte boundary.  This enables
26830           more inlining and increases code size, but may improve performance
26831           of code that depends on fast "memcpy" and "memset" for short
26832           lengths.  The option enables inline expansion of "strlen" for all
26833           pointer alignments.
26834
26835       -minline-stringops-dynamically
26836           For string operations of unknown size, use run-time checks with
26837           inline code for small blocks and a library call for large blocks.
26838
26839       -mstringop-strategy=alg
26840           Override the internal decision heuristic for the particular
26841           algorithm to use for inlining string operations.  The allowed
26842           values for alg are:
26843
26844           rep_byte
26845           rep_4byte
26846           rep_8byte
26847               Expand using i386 "rep" prefix of the specified size.
26848
26849           byte_loop
26850           loop
26851           unrolled_loop
26852               Expand into an inline loop.
26853
26854           libcall
26855               Always use a library call.
26856
26857       -mmemcpy-strategy=strategy
26858           Override the internal decision heuristic to decide if
26859           "__builtin_memcpy" should be inlined and what inline algorithm to
26860           use when the expected size of the copy operation is known. strategy
26861           is a comma-separated list of alg:max_size:dest_align triplets.  alg
26862           is specified in -mstringop-strategy, max_size specifies the max
26863           byte size with which inline algorithm alg is allowed.  For the last
26864           triplet, the max_size must be "-1". The max_size of the triplets in
26865           the list must be specified in increasing order.  The minimal byte
26866           size for alg is 0 for the first triplet and "max_size + 1" of the
26867           preceding range.
26868
26869       -mmemset-strategy=strategy
26870           The option is similar to -mmemcpy-strategy= except that it is to
26871           control "__builtin_memset" expansion.
26872
26873       -momit-leaf-frame-pointer
26874           Don't keep the frame pointer in a register for leaf functions.
26875           This avoids the instructions to save, set up, and restore frame
26876           pointers and makes an extra register available in leaf functions.
26877           The option -fomit-leaf-frame-pointer removes the frame pointer for
26878           leaf functions, which might make debugging harder.
26879
26880       -mtls-direct-seg-refs
26881       -mno-tls-direct-seg-refs
26882           Controls whether TLS variables may be accessed with offsets from
26883           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
26884           whether the thread base pointer must be added.  Whether or not this
26885           is valid depends on the operating system, and whether it maps the
26886           segment to cover the entire TLS area.
26887
26888           For systems that use the GNU C Library, the default is on.
26889
26890       -msse2avx
26891       -mno-sse2avx
26892           Specify that the assembler should encode SSE instructions with VEX
26893           prefix.  The option -mavx turns this on by default.
26894
26895       -mfentry
26896       -mno-fentry
26897           If profiling is active (-pg), put the profiling counter call before
26898           the prologue.  Note: On x86 architectures the attribute
26899           "ms_hook_prologue" isn't possible at the moment for -mfentry and
26900           -pg.
26901
26902       -mrecord-mcount
26903       -mno-record-mcount
26904           If profiling is active (-pg), generate a __mcount_loc section that
26905           contains pointers to each profiling call. This is useful for
26906           automatically patching and out calls.
26907
26908       -mnop-mcount
26909       -mno-nop-mcount
26910           If profiling is active (-pg), generate the calls to the profiling
26911           functions as NOPs. This is useful when they should be patched in
26912           later dynamically. This is likely only useful together with
26913           -mrecord-mcount.
26914
26915       -minstrument-return=type
26916           Instrument function exit in -pg -mfentry instrumented functions
26917           with call to specified function. This only instruments true returns
26918           ending with ret, but not sibling calls ending with jump. Valid
26919           types are none to not instrument, call to generate a call to
26920           __return__, or nop5 to generate a 5 byte nop.
26921
26922       -mrecord-return
26923       -mno-record-return
26924           Generate a __return_loc section pointing to all return
26925           instrumentation code.
26926
26927       -mfentry-name=name
26928           Set name of __fentry__ symbol called at function entry for -pg
26929           -mfentry functions.
26930
26931       -mfentry-section=name
26932           Set name of section to record -mrecord-mcount calls (default
26933           __mcount_loc).
26934
26935       -mskip-rax-setup
26936       -mno-skip-rax-setup
26937           When generating code for the x86-64 architecture with SSE
26938           extensions disabled, -mskip-rax-setup can be used to skip setting
26939           up RAX register when there are no variable arguments passed in
26940           vector registers.
26941
26942           Warning: Since RAX register is used to avoid unnecessarily saving
26943           vector registers on stack when passing variable arguments, the
26944           impacts of this option are callees may waste some stack space,
26945           misbehave or jump to a random location.  GCC 4.4 or newer don't
26946           have those issues, regardless the RAX register value.
26947
26948       -m8bit-idiv
26949       -mno-8bit-idiv
26950           On some processors, like Intel Atom, 8-bit unsigned integer divide
26951           is much faster than 32-bit/64-bit integer divide.  This option
26952           generates a run-time check.  If both dividend and divisor are
26953           within range of 0 to 255, 8-bit unsigned integer divide is used
26954           instead of 32-bit/64-bit integer divide.
26955
26956       -mavx256-split-unaligned-load
26957       -mavx256-split-unaligned-store
26958           Split 32-byte AVX unaligned load and store.
26959
26960       -mstack-protector-guard=guard
26961       -mstack-protector-guard-reg=reg
26962       -mstack-protector-guard-offset=offset
26963           Generate stack protection code using canary at guard.  Supported
26964           locations are global for global canary or tls for per-thread canary
26965           in the TLS block (the default).  This option has effect only when
26966           -fstack-protector or -fstack-protector-all is specified.
26967
26968           With the latter choice the options -mstack-protector-guard-reg=reg
26969           and -mstack-protector-guard-offset=offset furthermore specify which
26970           segment register (%fs or %gs) to use as base register for reading
26971           the canary, and from what offset from that base register.  The
26972           default for those is as specified in the relevant ABI.
26973
26974       -mgeneral-regs-only
26975           Generate code that uses only the general-purpose registers.  This
26976           prevents the compiler from using floating-point, vector, mask and
26977           bound registers.
26978
26979       -mindirect-branch=choice
26980           Convert indirect call and jump with choice.  The default is keep,
26981           which keeps indirect call and jump unmodified.  thunk converts
26982           indirect call and jump to call and return thunk.  thunk-inline
26983           converts indirect call and jump to inlined call and return thunk.
26984           thunk-extern converts indirect call and jump to external call and
26985           return thunk provided in a separate object file.  You can control
26986           this behavior for a specific function by using the function
26987           attribute "indirect_branch".
26988
26989           Note that -mcmodel=large is incompatible with
26990           -mindirect-branch=thunk and -mindirect-branch=thunk-extern since
26991           the thunk function may not be reachable in the large code model.
26992
26993           Note that -mindirect-branch=thunk-extern is compatible with
26994           -fcf-protection=branch since the external thunk can be made to
26995           enable control-flow check.
26996
26997       -mfunction-return=choice
26998           Convert function return with choice.  The default is keep, which
26999           keeps function return unmodified.  thunk converts function return
27000           to call and return thunk.  thunk-inline converts function return to
27001           inlined call and return thunk.  thunk-extern converts function
27002           return to external call and return thunk provided in a separate
27003           object file.  You can control this behavior for a specific function
27004           by using the function attribute "function_return".
27005
27006           Note that -mindirect-return=thunk-extern is compatible with
27007           -fcf-protection=branch since the external thunk can be made to
27008           enable control-flow check.
27009
27010           Note that -mcmodel=large is incompatible with
27011           -mfunction-return=thunk and -mfunction-return=thunk-extern since
27012           the thunk function may not be reachable in the large code model.
27013
27014       -mindirect-branch-register
27015           Force indirect call and jump via register.
27016
27017       These -m switches are supported in addition to the above on x86-64
27018       processors in 64-bit environments.
27019
27020       -m32
27021       -m64
27022       -mx32
27023       -m16
27024       -miamcu
27025           Generate code for a 16-bit, 32-bit or 64-bit environment.  The -m32
27026           option sets "int", "long", and pointer types to 32 bits, and
27027           generates code that runs on any i386 system.
27028
27029           The -m64 option sets "int" to 32 bits and "long" and pointer types
27030           to 64 bits, and generates code for the x86-64 architecture.  For
27031           Darwin only the -m64 option also turns off the -fno-pic and
27032           -mdynamic-no-pic options.
27033
27034           The -mx32 option sets "int", "long", and pointer types to 32 bits,
27035           and generates code for the x86-64 architecture.
27036
27037           The -m16 option is the same as -m32, except for that it outputs the
27038           ".code16gcc" assembly directive at the beginning of the assembly
27039           output so that the binary can run in 16-bit mode.
27040
27041           The -miamcu option generates code which conforms to Intel MCU
27042           psABI.  It requires the -m32 option to be turned on.
27043
27044       -mno-red-zone
27045           Do not use a so-called "red zone" for x86-64 code.  The red zone is
27046           mandated by the x86-64 ABI; it is a 128-byte area beyond the
27047           location of the stack pointer that is not modified by signal or
27048           interrupt handlers and therefore can be used for temporary data
27049           without adjusting the stack pointer.  The flag -mno-red-zone
27050           disables this red zone.
27051
27052       -mcmodel=small
27053           Generate code for the small code model: the program and its symbols
27054           must be linked in the lower 2 GB of the address space.  Pointers
27055           are 64 bits.  Programs can be statically or dynamically linked.
27056           This is the default code model.
27057
27058       -mcmodel=kernel
27059           Generate code for the kernel code model.  The kernel runs in the
27060           negative 2 GB of the address space.  This model has to be used for
27061           Linux kernel code.
27062
27063       -mcmodel=medium
27064           Generate code for the medium model: the program is linked in the
27065           lower 2 GB of the address space.  Small symbols are also placed
27066           there.  Symbols with sizes larger than -mlarge-data-threshold are
27067           put into large data or BSS sections and can be located above 2GB.
27068           Programs can be statically or dynamically linked.
27069
27070       -mcmodel=large
27071           Generate code for the large model.  This model makes no assumptions
27072           about addresses and sizes of sections.
27073
27074       -maddress-mode=long
27075           Generate code for long address mode.  This is only supported for
27076           64-bit and x32 environments.  It is the default address mode for
27077           64-bit environments.
27078
27079       -maddress-mode=short
27080           Generate code for short address mode.  This is only supported for
27081           32-bit and x32 environments.  It is the default address mode for
27082           32-bit and x32 environments.
27083
27084       -mneeded
27085       -mno-needed
27086           Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to
27087           indicate the micro-architecture ISA level required to execute the
27088           binary.
27089
27090       x86 Windows Options
27091
27092       These additional options are available for Microsoft Windows targets:
27093
27094       -mconsole
27095           This option specifies that a console application is to be
27096           generated, by instructing the linker to set the PE header subsystem
27097           type required for console applications.  This option is available
27098           for Cygwin and MinGW targets and is enabled by default on those
27099           targets.
27100
27101       -mdll
27102           This option is available for Cygwin and MinGW targets.  It
27103           specifies that a DLL---a dynamic link library---is to be generated,
27104           enabling the selection of the required runtime startup object and
27105           entry point.
27106
27107       -mnop-fun-dllimport
27108           This option is available for Cygwin and MinGW targets.  It
27109           specifies that the "dllimport" attribute should be ignored.
27110
27111       -mthread
27112           This option is available for MinGW targets. It specifies that
27113           MinGW-specific thread support is to be used.
27114
27115       -municode
27116           This option is available for MinGW-w64 targets.  It causes the
27117           "UNICODE" preprocessor macro to be predefined, and chooses Unicode-
27118           capable runtime startup code.
27119
27120       -mwin32
27121           This option is available for Cygwin and MinGW targets.  It
27122           specifies that the typical Microsoft Windows predefined macros are
27123           to be set in the pre-processor, but does not influence the choice
27124           of runtime library/startup code.
27125
27126       -mwindows
27127           This option is available for Cygwin and MinGW targets.  It
27128           specifies that a GUI application is to be generated by instructing
27129           the linker to set the PE header subsystem type appropriately.
27130
27131       -fno-set-stack-executable
27132           This option is available for MinGW targets. It specifies that the
27133           executable flag for the stack used by nested functions isn't set.
27134           This is necessary for binaries running in kernel mode of Microsoft
27135           Windows, as there the User32 API, which is used to set executable
27136           privileges, isn't available.
27137
27138       -fwritable-relocated-rdata
27139           This option is available for MinGW and Cygwin targets.  It
27140           specifies that relocated-data in read-only section is put into the
27141           ".data" section.  This is a necessary for older runtimes not
27142           supporting modification of ".rdata" sections for pseudo-relocation.
27143
27144       -mpe-aligned-commons
27145           This option is available for Cygwin and MinGW targets.  It
27146           specifies that the GNU extension to the PE file format that permits
27147           the correct alignment of COMMON variables should be used when
27148           generating code.  It is enabled by default if GCC detects that the
27149           target assembler found during configuration supports the feature.
27150
27151       See also under x86 Options for standard options.
27152
27153       Xstormy16 Options
27154
27155       These options are defined for Xstormy16:
27156
27157       -msim
27158           Choose startup files and linker script suitable for the simulator.
27159
27160       Xtensa Options
27161
27162       These options are supported for Xtensa targets:
27163
27164       -mconst16
27165       -mno-const16
27166           Enable or disable use of "CONST16" instructions for loading
27167           constant values.  The "CONST16" instruction is currently not a
27168           standard option from Tensilica.  When enabled, "CONST16"
27169           instructions are always used in place of the standard "L32R"
27170           instructions.  The use of "CONST16" is enabled by default only if
27171           the "L32R" instruction is not available.
27172
27173       -mfused-madd
27174       -mno-fused-madd
27175           Enable or disable use of fused multiply/add and multiply/subtract
27176           instructions in the floating-point option.  This has no effect if
27177           the floating-point option is not also enabled.  Disabling fused
27178           multiply/add and multiply/subtract instructions forces the compiler
27179           to use separate instructions for the multiply and add/subtract
27180           operations.  This may be desirable in some cases where strict IEEE
27181           754-compliant results are required: the fused multiply add/subtract
27182           instructions do not round the intermediate result, thereby
27183           producing results with more bits of precision than specified by the
27184           IEEE standard.  Disabling fused multiply add/subtract instructions
27185           also ensures that the program output is not sensitive to the
27186           compiler's ability to combine multiply and add/subtract operations.
27187
27188       -mserialize-volatile
27189       -mno-serialize-volatile
27190           When this option is enabled, GCC inserts "MEMW" instructions before
27191           "volatile" memory references to guarantee sequential consistency.
27192           The default is -mserialize-volatile.  Use -mno-serialize-volatile
27193           to omit the "MEMW" instructions.
27194
27195       -mforce-no-pic
27196           For targets, like GNU/Linux, where all user-mode Xtensa code must
27197           be position-independent code (PIC), this option disables PIC for
27198           compiling kernel code.
27199
27200       -mtext-section-literals
27201       -mno-text-section-literals
27202           These options control the treatment of literal pools.  The default
27203           is -mno-text-section-literals, which places literals in a separate
27204           section in the output file.  This allows the literal pool to be
27205           placed in a data RAM/ROM, and it also allows the linker to combine
27206           literal pools from separate object files to remove redundant
27207           literals and improve code size.  With -mtext-section-literals, the
27208           literals are interspersed in the text section in order to keep them
27209           as close as possible to their references.  This may be necessary
27210           for large assembly files.  Literals for each function are placed
27211           right before that function.
27212
27213       -mauto-litpools
27214       -mno-auto-litpools
27215           These options control the treatment of literal pools.  The default
27216           is -mno-auto-litpools, which places literals in a separate section
27217           in the output file unless -mtext-section-literals is used.  With
27218           -mauto-litpools the literals are interspersed in the text section
27219           by the assembler.  Compiler does not produce explicit ".literal"
27220           directives and loads literals into registers with "MOVI"
27221           instructions instead of "L32R" to let the assembler do relaxation
27222           and place literals as necessary.  This option allows assembler to
27223           create several literal pools per function and assemble very big
27224           functions, which may not be possible with -mtext-section-literals.
27225
27226       -mtarget-align
27227       -mno-target-align
27228           When this option is enabled, GCC instructs the assembler to
27229           automatically align instructions to reduce branch penalties at the
27230           expense of some code density.  The assembler attempts to widen
27231           density instructions to align branch targets and the instructions
27232           following call instructions.  If there are not enough preceding
27233           safe density instructions to align a target, no widening is
27234           performed.  The default is -mtarget-align.  These options do not
27235           affect the treatment of auto-aligned instructions like "LOOP",
27236           which the assembler always aligns, either by widening density
27237           instructions or by inserting NOP instructions.
27238
27239       -mlongcalls
27240       -mno-longcalls
27241           When this option is enabled, GCC instructs the assembler to
27242           translate direct calls to indirect calls unless it can determine
27243           that the target of a direct call is in the range allowed by the
27244           call instruction.  This translation typically occurs for calls to
27245           functions in other source files.  Specifically, the assembler
27246           translates a direct "CALL" instruction into an "L32R" followed by a
27247           "CALLX" instruction.  The default is -mno-longcalls.  This option
27248           should be used in programs where the call target can potentially be
27249           out of range.  This option is implemented in the assembler, not the
27250           compiler, so the assembly code generated by GCC still shows direct
27251           call instructions---look at the disassembled object code to see the
27252           actual instructions.  Note that the assembler uses an indirect call
27253           for every cross-file call, not just those that really are out of
27254           range.
27255
27256       -mabi=name
27257           Generate code for the specified ABI.  Permissible values are:
27258           call0, windowed.  Default ABI is chosen by the Xtensa core
27259           configuration.
27260
27261       -mabi=call0
27262           When this option is enabled function parameters are passed in
27263           registers "a2" through "a7", registers "a12" through "a15" are
27264           caller-saved, and register "a15" may be used as a frame pointer.
27265           When this version of the ABI is enabled the C preprocessor symbol
27266           "__XTENSA_CALL0_ABI__" is defined.
27267
27268       -mabi=windowed
27269           When this option is enabled function parameters are passed in
27270           registers "a10" through "a15", and called function rotates register
27271           window by 8 registers on entry so that its arguments are found in
27272           registers "a2" through "a7".  Register "a7" may be used as a frame
27273           pointer.  Register window is rotated 8 registers back upon return.
27274           When this version of the ABI is enabled the C preprocessor symbol
27275           "__XTENSA_WINDOWED_ABI__" is defined.
27276
27277       zSeries Options
27278
27279       These are listed under
27280

ENVIRONMENT

27282       This section describes several environment variables that affect how
27283       GCC operates.  Some of them work by specifying directories or prefixes
27284       to use when searching for various kinds of files.  Some are used to
27285       specify other aspects of the compilation environment.
27286
27287       Note that you can also specify places to search using options such as
27288       -B, -I and -L.  These take precedence over places specified using
27289       environment variables, which in turn take precedence over those
27290       specified by the configuration of GCC.
27291
27292       LANG
27293       LC_CTYPE
27294       LC_MESSAGES
27295       LC_ALL
27296           These environment variables control the way that GCC uses
27297           localization information which allows GCC to work with different
27298           national conventions.  GCC inspects the locale categories LC_CTYPE
27299           and LC_MESSAGES if it has been configured to do so.  These locale
27300           categories can be set to any value supported by your installation.
27301           A typical value is en_GB.UTF-8 for English in the United Kingdom
27302           encoded in UTF-8.
27303
27304           The LC_CTYPE environment variable specifies character
27305           classification.  GCC uses it to determine the character boundaries
27306           in a string; this is needed for some multibyte encodings that
27307           contain quote and escape characters that are otherwise interpreted
27308           as a string end or escape.
27309
27310           The LC_MESSAGES environment variable specifies the language to use
27311           in diagnostic messages.
27312
27313           If the LC_ALL environment variable is set, it overrides the value
27314           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
27315           default to the value of the LANG environment variable.  If none of
27316           these variables are set, GCC defaults to traditional C English
27317           behavior.
27318
27319       TMPDIR
27320           If TMPDIR is set, it specifies the directory to use for temporary
27321           files.  GCC uses temporary files to hold the output of one stage of
27322           compilation which is to be used as input to the next stage: for
27323           example, the output of the preprocessor, which is the input to the
27324           compiler proper.
27325
27326       GCC_COMPARE_DEBUG
27327           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing
27328           -fcompare-debug to the compiler driver.  See the documentation of
27329           this option for more details.
27330
27331       GCC_EXEC_PREFIX
27332           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
27333           names of the subprograms executed by the compiler.  No slash is
27334           added when this prefix is combined with the name of a subprogram,
27335           but you can specify a prefix that ends with a slash if you wish.
27336
27337           If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an
27338           appropriate prefix to use based on the pathname it is invoked with.
27339
27340           If GCC cannot find the subprogram using the specified prefix, it
27341           tries looking in the usual places for the subprogram.
27342
27343           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
27344           prefix is the prefix to the installed compiler. In many cases
27345           prefix is the value of "prefix" when you ran the configure script.
27346
27347           Other prefixes specified with -B take precedence over this prefix.
27348
27349           This prefix is also used for finding files such as crt0.o that are
27350           used for linking.
27351
27352           In addition, the prefix is used in an unusual way in finding the
27353           directories to search for header files.  For each of the standard
27354           directories whose name normally begins with /usr/local/lib/gcc
27355           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
27356           replacing that beginning with the specified prefix to produce an
27357           alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar
27358           just before it searches the standard directory /usr/local/lib/bar.
27359           If a standard directory begins with the configured prefix then the
27360           value of prefix is replaced by GCC_EXEC_PREFIX when looking for
27361           header files.
27362
27363       COMPILER_PATH
27364           The value of COMPILER_PATH is a colon-separated list of
27365           directories, much like PATH.  GCC tries the directories thus
27366           specified when searching for subprograms, if it cannot find the
27367           subprograms using GCC_EXEC_PREFIX.
27368
27369       LIBRARY_PATH
27370           The value of LIBRARY_PATH is a colon-separated list of directories,
27371           much like PATH.  When configured as a native compiler, GCC tries
27372           the directories thus specified when searching for special linker
27373           files, if it cannot find them using GCC_EXEC_PREFIX.  Linking using
27374           GCC also uses these directories when searching for ordinary
27375           libraries for the -l option (but directories specified with -L come
27376           first).
27377
27378       LANG
27379           This variable is used to pass locale information to the compiler.
27380           One way in which this information is used is to determine the
27381           character set to be used when character literals, string literals
27382           and comments are parsed in C and C++.  When the compiler is
27383           configured to allow multibyte characters, the following values for
27384           LANG are recognized:
27385
27386           C-JIS
27387               Recognize JIS characters.
27388
27389           C-SJIS
27390               Recognize SJIS characters.
27391
27392           C-EUCJP
27393               Recognize EUCJP characters.
27394
27395           If LANG is not defined, or if it has some other value, then the
27396           compiler uses "mblen" and "mbtowc" as defined by the default locale
27397           to recognize and translate multibyte characters.
27398
27399       GCC_EXTRA_DIAGNOSTIC_OUTPUT
27400           If GCC_EXTRA_DIAGNOSTIC_OUTPUT is set to one of the following
27401           values, then additional text will be emitted to stderr when fix-it
27402           hints are emitted.  -fdiagnostics-parseable-fixits and
27403           -fno-diagnostics-parseable-fixits take precedence over this
27404           environment variable.
27405
27406           fixits-v1
27407               Emit parseable fix-it hints, equivalent to
27408               -fdiagnostics-parseable-fixits.  In particular, columns are
27409               expressed as a count of bytes, starting at byte 1 for the
27410               initial column.
27411
27412           fixits-v2
27413               As "fixits-v1", but columns are expressed as display columns,
27414               as per -fdiagnostics-column-unit=display.
27415
27416       Some additional environment variables affect the behavior of the
27417       preprocessor.
27418
27419       CPATH
27420       C_INCLUDE_PATH
27421       CPLUS_INCLUDE_PATH
27422       OBJC_INCLUDE_PATH
27423           Each variable's value is a list of directories separated by a
27424           special character, much like PATH, in which to look for header
27425           files.  The special character, "PATH_SEPARATOR", is target-
27426           dependent and determined at GCC build time.  For Microsoft Windows-
27427           based targets it is a semicolon, and for almost all other targets
27428           it is a colon.
27429
27430           CPATH specifies a list of directories to be searched as if
27431           specified with -I, but after any paths given with -I options on the
27432           command line.  This environment variable is used regardless of
27433           which language is being preprocessed.
27434
27435           The remaining environment variables apply only when preprocessing
27436           the particular language indicated.  Each specifies a list of
27437           directories to be searched as if specified with -isystem, but after
27438           any paths given with -isystem options on the command line.
27439
27440           In all these variables, an empty element instructs the compiler to
27441           search its current working directory.  Empty elements can appear at
27442           the beginning or end of a path.  For instance, if the value of
27443           CPATH is ":/special/include", that has the same effect as
27444           -I. -I/special/include.
27445
27446       DEPENDENCIES_OUTPUT
27447           If this variable is set, its value specifies how to output
27448           dependencies for Make based on the non-system header files
27449           processed by the compiler.  System header files are ignored in the
27450           dependency output.
27451
27452           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
27453           case the Make rules are written to that file, guessing the target
27454           name from the source file name.  Or the value can have the form
27455           file target, in which case the rules are written to file file using
27456           target as the target name.
27457
27458           In other words, this environment variable is equivalent to
27459           combining the options -MM and -MF, with an optional -MT switch too.
27460
27461       SUNPRO_DEPENDENCIES
27462           This variable is the same as DEPENDENCIES_OUTPUT (see above),
27463           except that system header files are not ignored, so it implies -M
27464           rather than -MM.  However, the dependence on the main input file is
27465           omitted.
27466
27467       SOURCE_DATE_EPOCH
27468           If this variable is set, its value specifies a UNIX timestamp to be
27469           used in replacement of the current date and time in the "__DATE__"
27470           and "__TIME__" macros, so that the embedded timestamps become
27471           reproducible.
27472
27473           The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
27474           the number of seconds (excluding leap seconds) since 01 Jan 1970
27475           00:00:00 represented in ASCII; identical to the output of "date
27476           +%s" on GNU/Linux and other systems that support the %s extension
27477           in the "date" command.
27478
27479           The value should be a known timestamp such as the last modification
27480           time of the source or package and it should be set by the build
27481           process.
27482

BUGS

27484       For instructions on reporting bugs, see <https://bugzilla.redhat.com/>.
27485

FOOTNOTES

27487       1.  On some systems, gcc -shared needs to build supplementary stub code
27488           for constructors to work.  On multi-libbed systems, gcc -shared
27489           must select the correct support libraries to link against.  Failing
27490           to supply the correct flags may lead to subtle defects.  Supplying
27491           them in cases where they are not necessary is innocuous.
27492

SEE ALSO

27494       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
27495       dbx(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb.
27496

AUTHOR

27498       See the Info entry for gcc, or
27499       <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors
27500       to GCC.
27501
27503       Copyright (c) 1988-2021 Free Software Foundation, Inc.
27504
27505       Permission is granted to copy, distribute and/or modify this document
27506       under the terms of the GNU Free Documentation License, Version 1.3 or
27507       any later version published by the Free Software Foundation; with the
27508       Invariant Sections being "GNU General Public License" and "Funding Free
27509       Software", the Front-Cover texts being (a) (see below), and with the
27510       Back-Cover Texts being (b) (see below).  A copy of the license is
27511       included in the gfdl(7) man page.
27512
27513       (a) The FSF's Front-Cover Text is:
27514
27515            A GNU Manual
27516
27517       (b) The FSF's Back-Cover Text is:
27518
27519            You have freedom to copy and modify this GNU Manual, like GNU
27520            software.  Copies published by the Free Software Foundation raise
27521            funds for GNU development.
27522
27523
27524
27525gcc-11.2.0                        2021-07-28                            GCC(1)
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