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

OPTIONS

60   Option Summary
61       Here is a summary of all the options, grouped by type.  Explanations
62       are in the following sections.
63
64       Overall Options
65           -c  -S  -E  -o file  -x language -v  -###  --help[=class[,...]]
66           --target-help  --version -pass-exit-codes  -pipe  -specs=file
67           -wrapper @file  -ffile-prefix-map=old=new -fplugin=file
68           -fplugin-arg-name=arg -fdump-ada-spec[-slim]
69           -fada-spec-parent=unit  -fdump-go-spec=file
70
71       C Language Options
72           -ansi  -std=standard  -fgnu89-inline
73           -fpermitted-flt-eval-methods=standard -aux-info filename
74           -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
75           -fno-builtin-function  -fgimple -fhosted  -ffreestanding  -fopenacc
76           -fopenmp  -fopenmp-simd -fms-extensions  -fplan9-extensions
77           -fsso-struct=endianness -fallow-single-precision  -fcond-mismatch
78           -flax-vector-conversions -fsigned-bitfields  -fsigned-char
79           -funsigned-bitfields  -funsigned-char
80
81       C++ Language Options
82           -fabi-version=n  -fno-access-control -faligned-new=n
83           -fargs-in-order=n  -fcheck-new -fconstexpr-depth=n
84           -fconstexpr-loop-limit=n -ffriend-injection -fno-elide-constructors
85           -fno-enforce-eh-specs -ffor-scope  -fno-for-scope
86           -fno-gnu-keywords -fno-implicit-templates
87           -fno-implicit-inline-templates -fno-implement-inlines
88           -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching
89           -fno-nonansi-builtins  -fnothrow-opt  -fno-operator-names
90           -fno-optional-diags  -fpermissive -fno-pretty-templates -frepo
91           -fno-rtti  -fsized-deallocation -ftemplate-backtrace-limit=n
92           -ftemplate-depth=n -fno-threadsafe-statics  -fuse-cxa-atexit
93           -fno-weak  -nostdinc++ -fvisibility-inlines-hidden
94           -fvisibility-ms-compat -fext-numeric-literals -Wabi=n  -Wabi-tag
95           -Wconversion-null  -Wctor-dtor-privacy -Wdelete-non-virtual-dtor
96           -Wliteral-suffix  -Wmultiple-inheritance -Wnamespaces  -Wnarrowing
97           -Wnoexcept  -Wnoexcept-type  -Wclass-memaccess -Wnon-virtual-dtor
98           -Wreorder  -Wregister -Weffc++  -Wstrict-null-sentinel  -Wtemplates
99           -Wno-non-template-friend  -Wold-style-cast -Woverloaded-virtual
100           -Wno-pmf-conversions -Wsign-promo  -Wvirtual-inheritance
101
102       Objective-C and Objective-C++ Language Options
103           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
104           -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors
105           -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck
106           -fobjc-std=objc1 -fno-local-ivars
107           -fivar-visibility=[public|protected|private|package]
108           -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept
109           -Wno-protocol  -Wselector -Wstrict-selector-match
110           -Wundeclared-selector
111
112       Diagnostic Message Formatting Options
113           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
114           -fdiagnostics-color=[auto|never|always]
115           -fno-diagnostics-show-option  -fno-diagnostics-show-caret
116           -fdiagnostics-parseable-fixits  -fdiagnostics-generate-patch
117           -fdiagnostics-show-template-tree -fno-elide-type -fno-show-column
118
119       Warning Options
120           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
121           -Wextra  -Wall  -Waddress  -Waggregate-return  -Waligned-new
122           -Walloc-zero  -Walloc-size-larger-than=n -Walloca
123           -Walloca-larger-than=n -Wno-aggressive-loop-optimizations
124           -Warray-bounds  -Warray-bounds=n -Wno-attributes  -Wbool-compare
125           -Wbool-operation -Wno-builtin-declaration-mismatch
126           -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat
127           -Wc++-compat  -Wc++11-compat  -Wc++14-compat -Wcast-align
128           -Wcast-align=strict  -Wcast-function-type  -Wcast-qual
129           -Wchar-subscripts  -Wchkp  -Wcatch-value  -Wcatch-value=n
130           -Wclobbered  -Wcomment  -Wconditionally-supported -Wconversion
131           -Wcoverage-mismatch  -Wno-cpp  -Wdangling-else  -Wdate-time
132           -Wdelete-incomplete -Wno-deprecated  -Wno-deprecated-declarations
133           -Wno-designated-init -Wdisabled-optimization
134           -Wno-discarded-qualifiers  -Wno-discarded-array-qualifiers
135           -Wno-div-by-zero  -Wdouble-promotion -Wduplicated-branches
136           -Wduplicated-cond -Wempty-body  -Wenum-compare  -Wno-endif-labels
137           -Wexpansion-to-defined -Werror  -Werror=*  -Wextra-semi
138           -Wfatal-errors -Wfloat-equal  -Wformat  -Wformat=2
139           -Wno-format-contains-nul  -Wno-format-extra-args
140           -Wformat-nonliteral -Wformat-overflow=n -Wformat-security
141           -Wformat-signedness  -Wformat-truncation=n -Wformat-y2k
142           -Wframe-address -Wframe-larger-than=len  -Wno-free-nonheap-object
143           -Wjump-misses-init -Wif-not-aligned -Wignored-qualifiers
144           -Wignored-attributes  -Wincompatible-pointer-types -Wimplicit
145           -Wimplicit-fallthrough  -Wimplicit-fallthrough=n
146           -Wimplicit-function-declaration  -Wimplicit-int -Winit-self
147           -Winline  -Wno-int-conversion  -Wint-in-bool-context
148           -Wno-int-to-pointer-cast  -Winvalid-memory-model
149           -Wno-invalid-offsetof -Winvalid-pch  -Wlarger-than=len -Wlogical-op
150           -Wlogical-not-parentheses  -Wlong-long -Wmain
151           -Wmaybe-uninitialized  -Wmemset-elt-size  -Wmemset-transposed-args
152           -Wmisleading-indentation  -Wmissing-attributes -Wmissing-braces
153           -Wmissing-field-initializers  -Wmissing-include-dirs -Wno-multichar
154           -Wmultistatement-macros  -Wnonnull  -Wnonnull-compare
155           -Wnormalized=[none|id|nfc|nfkc] -Wnull-dereference  -Wodr
156           -Wno-overflow  -Wopenmp-simd -Woverride-init-side-effects
157           -Woverlength-strings -Wpacked  -Wpacked-bitfield-compat
158           -Wpacked-not-aligned -Wpadded -Wparentheses
159           -Wno-pedantic-ms-format -Wplacement-new  -Wplacement-new=n
160           -Wpointer-arith  -Wpointer-compare  -Wno-pointer-to-int-cast
161           -Wno-pragmas  -Wredundant-decls  -Wrestrict  -Wno-return-local-addr
162           -Wreturn-type  -Wsequence-point  -Wshadow  -Wno-shadow-ivar
163           -Wshadow=global,  -Wshadow=local,  -Wshadow=compatible-local
164           -Wshift-overflow  -Wshift-overflow=n -Wshift-count-negative
165           -Wshift-count-overflow  -Wshift-negative-value -Wsign-compare
166           -Wsign-conversion  -Wfloat-conversion -Wno-scalar-storage-order
167           -Wsizeof-pointer-div -Wsizeof-pointer-memaccess
168           -Wsizeof-array-argument -Wstack-protector  -Wstack-usage=len
169           -Wstrict-aliasing -Wstrict-aliasing=n  -Wstrict-overflow
170           -Wstrict-overflow=n -Wstringop-overflow=n -Wstringop-truncation
171           -Wsuggest-attribute=[pure|const|noreturn|format|malloc]
172           -Wsuggest-final-types   -Wsuggest-final-methods  -Wsuggest-override
173           -Wmissing-format-attribute  -Wsubobject-linkage -Wswitch
174           -Wswitch-bool  -Wswitch-default  -Wswitch-enum -Wswitch-unreachable
175           -Wsync-nand -Wsystem-headers  -Wtautological-compare  -Wtrampolines
176           -Wtrigraphs -Wtype-limits  -Wundef -Wuninitialized
177           -Wunknown-pragmas -Wunsuffixed-float-constants  -Wunused
178           -Wunused-function -Wunused-label  -Wunused-local-typedefs
179           -Wunused-macros -Wunused-parameter  -Wno-unused-result
180           -Wunused-value  -Wunused-variable -Wunused-const-variable
181           -Wunused-const-variable=n -Wunused-but-set-parameter
182           -Wunused-but-set-variable -Wuseless-cast  -Wvariadic-macros
183           -Wvector-operation-performance -Wvla  -Wvla-larger-than=n
184           -Wvolatile-register-var  -Wwrite-strings
185           -Wzero-as-null-pointer-constant  -Whsa
186
187       C and Objective-C-only Warning Options
188           -Wbad-function-cast  -Wmissing-declarations
189           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
190           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
191           -Wtraditional  -Wtraditional-conversion
192           -Wdeclaration-after-statement  -Wpointer-sign
193
194       Debugging Options
195           -g  -glevel  -gdwarf  -gdwarf-version -ggdb  -grecord-gcc-switches
196           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf
197           -gno-strict-dwarf -gas-loc-support  -gno-as-loc-support
198           -gas-locview-support  -gno-as-locview-support -gcolumn-info
199           -gno-column-info -gstatement-frontiers  -gno-statement-frontiers
200           -gvariable-location-views  -gno-variable-location-views
201           -ginternal-reset-location-views  -gno-internal-reset-location-views
202           -ginline-points  -gno-inline-points -gvms  -gxcoff  -gxcoff+
203           -gz[=type] -fdebug-prefix-map=old=new  -fdebug-types-section
204           -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly
205           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-
206           list] -feliminate-unused-debug-symbols  -femit-class-debug-always
207           -fno-merge-debug-strings  -fno-dwarf2-cfi-asm -fvar-tracking
208           -fvar-tracking-assignments
209
210       Optimization Options
211           -faggressive-loop-optimizations  -falign-functions[=n]
212           -falign-jumps[=n] -falign-labels[=n]  -falign-loops[=n]
213           -fassociative-math  -fauto-profile  -fauto-profile[=path]
214           -fauto-inc-dec  -fbranch-probabilities
215           -fbranch-target-load-optimize  -fbranch-target-load-optimize2
216           -fbtr-bb-exclusive  -fcaller-saves -fcombine-stack-adjustments
217           -fconserve-stack -fcompare-elim  -fcprop-registers  -fcrossjumping
218           -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
219           -fcx-limited-range -fdata-sections  -fdce  -fdelayed-branch
220           -fdelete-null-pointer-checks  -fdevirtualize
221           -fdevirtualize-speculatively -fdevirtualize-at-ltrans  -fdse
222           -fearly-inlining  -fipa-sra  -fexpensive-optimizations
223           -ffat-lto-objects -ffast-math  -ffinite-math-only  -ffloat-store
224           -fexcess-precision=style -fforward-propagate  -ffp-contract=style
225           -ffunction-sections -fgcse  -fgcse-after-reload  -fgcse-las
226           -fgcse-lm  -fgraphite-identity -fgcse-sm  -fhoist-adjacent-loads
227           -fif-conversion -fif-conversion2  -findirect-inlining
228           -finline-functions  -finline-functions-called-once
229           -finline-limit=n -finline-small-functions  -fipa-cp  -fipa-cp-clone
230           -fipa-bit-cp -fipa-vrp -fipa-pta  -fipa-profile  -fipa-pure-const
231           -fipa-reference  -fipa-icf -fira-algorithm=algorithm
232           -fira-region=region  -fira-hoist-pressure -fira-loop-pressure
233           -fno-ira-share-save-slots -fno-ira-share-spill-slots
234           -fisolate-erroneous-paths-dereference
235           -fisolate-erroneous-paths-attribute -fivopts
236           -fkeep-inline-functions  -fkeep-static-functions
237           -fkeep-static-consts  -flimit-function-alignment
238           -flive-range-shrinkage -floop-block  -floop-interchange
239           -floop-strip-mine -floop-unroll-and-jam  -floop-nest-optimize
240           -floop-parallelize-all  -flra-remat  -flto  -flto-compression-level
241           -flto-partition=alg  -fmerge-all-constants -fmerge-constants
242           -fmodulo-sched  -fmodulo-sched-allow-regmoves
243           -fmove-loop-invariants  -fno-branch-count-reg -fno-defer-pop
244           -fno-fp-int-builtin-inexact  -fno-function-cse
245           -fno-guess-branch-probability  -fno-inline  -fno-math-errno
246           -fno-peephole -fno-peephole2  -fno-printf-return-value
247           -fno-sched-interblock -fno-sched-spec  -fno-signed-zeros
248           -fno-toplevel-reorder  -fno-trapping-math
249           -fno-zero-initialized-in-bss -fomit-frame-pointer
250           -foptimize-sibling-calls -fpartial-inlining  -fpeel-loops
251           -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction
252           -fprofile-use  -fprofile-use=path  -fprofile-values
253           -fprofile-reorder-functions -freciprocal-math  -free
254           -frename-registers  -freorder-blocks
255           -freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition
256           -freorder-functions -frerun-cse-after-loop
257           -freschedule-modulo-scheduled-loops -frounding-math
258           -fsched2-use-superblocks  -fsched-pressure -fsched-spec-load
259           -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n]
260           -fsched-stalled-insns[=n] -fsched-group-heuristic
261           -fsched-critical-path-heuristic -fsched-spec-insn-heuristic
262           -fsched-rank-heuristic -fsched-last-insn-heuristic
263           -fsched-dep-count-heuristic -fschedule-fusion -fschedule-insns
264           -fschedule-insns2  -fsection-anchors -fselective-scheduling
265           -fselective-scheduling2 -fsel-sched-pipelining
266           -fsel-sched-pipelining-outer-loops -fsemantic-interposition
267           -fshrink-wrap  -fshrink-wrap-separate -fsignaling-nans
268           -fsingle-precision-constant  -fsplit-ivs-in-unroller  -fsplit-loops
269           -fsplit-paths -fsplit-wide-types  -fssa-backprop  -fssa-phiopt
270           -fstdarg-opt  -fstore-merging  -fstrict-aliasing -fthread-jumps
271           -ftracer  -ftree-bit-ccp -ftree-builtin-call-dce  -ftree-ccp
272           -ftree-ch -ftree-coalesce-vars  -ftree-copy-prop  -ftree-dce
273           -ftree-dominator-opts -ftree-dse  -ftree-forwprop  -ftree-fre
274           -fcode-hoisting -ftree-loop-if-convert  -ftree-loop-im
275           -ftree-phiprop  -ftree-loop-distribution
276           -ftree-loop-distribute-patterns -ftree-loop-ivcanon
277           -ftree-loop-linear  -ftree-loop-optimize -ftree-loop-vectorize
278           -ftree-parallelize-loops=n  -ftree-pre  -ftree-partial-pre
279           -ftree-pta -ftree-reassoc  -ftree-sink  -ftree-slsr  -ftree-sra
280           -ftree-switch-conversion  -ftree-tail-merge -ftree-ter
281           -ftree-vectorize  -ftree-vrp  -funconstrained-commons
282           -funit-at-a-time  -funroll-all-loops  -funroll-loops
283           -funsafe-math-optimizations  -funswitch-loops -fipa-ra
284           -fvariable-expansion-in-unroller  -fvect-cost-model  -fvpt -fweb
285           -fwhole-program  -fwpa  -fuse-linker-plugin --param name=value -O
286           -O0  -O1  -O2  -O3  -Os  -Ofast  -Og
287
288       Program Instrumentation Options
289           -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage
290           -fprofile-abs-path -fprofile-dir=path  -fprofile-generate
291           -fprofile-generate=path -fsanitize=style  -fsanitize-recover
292           -fsanitize-recover=style -fasan-shadow-offset=number
293           -fsanitize-sections=s1,s2,...  -fsanitize-undefined-trap-on-error
294           -fbounds-check -fcheck-pointer-bounds  -fchkp-check-incomplete-type
295           -fchkp-first-field-has-own-bounds  -fchkp-narrow-bounds
296           -fchkp-narrow-to-innermost-array  -fchkp-optimize
297           -fchkp-use-fast-string-functions  -fchkp-use-nochk-string-functions
298           -fchkp-use-static-bounds  -fchkp-use-static-const-bounds
299           -fchkp-treat-zero-dynamic-size-as-infinite  -fchkp-check-read
300           -fchkp-check-read  -fchkp-check-write  -fchkp-store-bounds
301           -fchkp-instrument-calls  -fchkp-instrument-marked-only
302           -fchkp-use-wrappers  -fchkp-flexible-struct-trailing-arrays
303           -fcf-protection=[full|branch|return|none] -fstack-protector
304           -fstack-protector-all  -fstack-protector-strong
305           -fstack-protector-explicit  -fstack-check
306           -fstack-limit-register=reg  -fstack-limit-symbol=sym
307           -fno-stack-limit  -fsplit-stack -fvtable-verify=[std|preinit|none]
308           -fvtv-counts  -fvtv-debug -finstrument-functions
309           -finstrument-functions-exclude-function-list=sym,sym,...
310           -finstrument-functions-exclude-file-list=file,file,...
311
312       Preprocessor Options
313           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD
314           -dI  -dM  -dN  -dU -fdebug-cpp  -fdirectives-only
315           -fdollars-in-identifiers -fexec-charset=charset
316           -fextended-identifiers -finput-charset=charset
317           -fmacro-prefix-map=old=new -fno-canonical-system-headers
318           -fpch-deps  -fpch-preprocess -fpreprocessed -ftabstop=width
319           -ftrack-macro-expansion -fwide-exec-charset=charset
320           -fworking-directory -H  -imacros file  -include file -M  -MD  -MF
321           -MG  -MM  -MMD  -MP  -MQ  -MT -no-integrated-cpp  -P  -pthread
322           -remap -traditional  -traditional-cpp  -trigraphs -Umacro  -undef
323           -Wp,option  -Xpreprocessor option
324
325       Assembler Options
326           -Wa,option  -Xassembler option
327
328       Linker Options
329           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles
330           -nodefaultlibs  -nostdlib  -pie  -pthread  -rdynamic -s  -static
331           -static-pie -static-libgcc  -static-libstdc++ -static-libasan
332           -static-libtsan  -static-liblsan  -static-libubsan -static-libmpx
333           -static-libmpxwrappers -shared  -shared-libgcc  -symbolic -T script
334           -Wl,option  -Xlinker option -u symbol  -z keyword
335
336       Directory Options
337           -Bprefix  -Idir  -I- -idirafter dir -imacros file  -imultilib dir
338           -iplugindir=dir  -iprefix file -iquote dir  -isysroot dir  -isystem
339           dir -iwithprefix dir  -iwithprefixbefore dir -Ldir
340           -no-canonical-prefixes  --no-sysroot-suffix -nostdinc  -nostdinc++
341           --sysroot=dir
342
343       Code Generation Options
344           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
345           -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
346           -fasynchronous-unwind-tables -fno-gnu-unique
347           -finhibit-size-directive  -fno-common  -fno-ident
348           -fpcc-struct-return  -fpic  -fPIC  -fpie  -fPIE  -fno-plt
349           -fno-jump-tables -frecord-gcc-switches -freg-struct-return
350           -fshort-enums  -fshort-wchar -fverbose-asm  -fpack-struct[=n]
351           -fleading-underscore  -ftls-model=model -fstack-reuse=reuse_level
352           -ftrampolines  -ftrapv  -fwrapv
353           -fvisibility=[default|internal|hidden|protected]
354           -fstrict-volatile-bitfields  -fsync-libcalls
355
356       Developer Options
357           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion
358           -fchecking  -fchecking=n  -fdbg-cnt-list -fdbg-cnt=counter-value-
359           list -fdisable-ipa-pass_name -fdisable-rtl-pass_name
360           -fdisable-rtl-pass-name=range-list -fdisable-tree-pass_name
361           -fdisable-tree-pass-name=range-list -fdump-noaddr
362           -fdump-unnumbered  -fdump-unnumbered-links
363           -fdump-class-hierarchy[-n] -fdump-final-insns[=file] -fdump-ipa-all
364           -fdump-ipa-cgraph  -fdump-ipa-inline -fdump-lang-all
365           -fdump-lang-switch -fdump-lang-switch-options
366           -fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass
367           -fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all
368           -fdump-tree-switch -fdump-tree-switch-options
369           -fdump-tree-switch-options=filename -fcompare-debug[=opts]
370           -fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range-
371           list -fira-verbose=n -flto-report  -flto-report-wpa
372           -fmem-report-wpa -fmem-report  -fpre-ipa-mem-report
373           -fpost-ipa-mem-report -fopt-info  -fopt-info-options[=file]
374           -fprofile-report -frandom-seed=string  -fsched-verbose=n
375           -fsel-sched-verbose  -fsel-sched-dump-cfg
376           -fsel-sched-pipelining-verbose -fstats  -fstack-usage
377           -ftime-report  -ftime-report-details
378           -fvar-tracking-assignments-toggle  -gtoggle
379           -print-file-name=library  -print-libgcc-file-name
380           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
381           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
382           -print-sysroot-headers-suffix -save-temps  -save-temps=cwd
383           -save-temps=obj  -time[=file]
384
385       Machine-Dependent Options
386           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian
387           -mgeneral-regs-only -mcmodel=tiny  -mcmodel=small  -mcmodel=large
388           -mstrict-align -momit-leaf-frame-pointer -mtls-dialect=desc
389           -mtls-dialect=traditional -mtls-size=size -mfix-cortex-a53-835769
390           -mfix-cortex-a53-843419 -mlow-precision-recip-sqrt
391           -mlow-precision-sqrt  -mlow-precision-div
392           -mpc-relative-literal-loads -msign-return-address=scope -march=name
393           -mcpu=name  -mtune=name -moverride=string  -mverbose-cost-dump
394
395           Adapteva Epiphany Options -mhalf-reg-file  -mprefer-short-insn-regs
396           -mbranch-cost=num  -mcmove  -mnops=num  -msoft-cmpsf -msplit-lohi
397           -mpost-inc  -mpost-modify  -mstack-offset=num -mround-nearest
398           -mlong-calls  -mshort-calls  -msmall16 -mfp-mode=mode
399           -mvect-double  -max-vect-align=num -msplit-vecmove-early
400           -m1reg-reg
401
402           ARC Options -mbarrel-shifter -mjli-always -mcpu=cpu  -mA6  -mARC600
403           -mA7  -mARC700 -mdpfp  -mdpfp-compact  -mdpfp-fast  -mno-dpfp-lrsr
404           -mea  -mno-mpy  -mmul32x16  -mmul64  -matomic -mnorm  -mspfp
405           -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap -mcrc
406           -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc  -mswape
407           -mtelephony  -mxy  -misize  -mannotate-align  -marclinux
408           -marclinux_prof -mlong-calls  -mmedium-calls  -msdata
409           -mirq-ctrl-saved -mrgf-banked-regs -mlpc-width=width -G num
410           -mvolatile-cache  -mtp-regno=regno -malign-call  -mauto-modify-reg
411           -mbbit-peephole  -mno-brcc -mcase-vector-pcrel  -mcompact-casesi
412           -mno-cond-exec  -mearly-cbranchsi -mexpand-adddi  -mindexed-loads
413           -mlra  -mlra-priority-none -mlra-priority-compact mlra-priority-
414           noncompact  -mno-millicode -mmixed-code  -mq-class  -mRcq  -mRcw
415           -msize-level=level -mtune=cpu  -mmultcost=num
416           -munalign-prob-threshold=probability  -mmpy-option=multo -mdiv-rem
417           -mcode-density  -mll64  -mfpu=fpu -mrf16
418
419           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
420           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-reentrant
421           -mno-apcs-reentrant -msched-prolog  -mno-sched-prolog
422           -mlittle-endian  -mbig-endian -mbe8 -mbe32 -mfloat-abi=name
423           -mfp16-format=name -mthumb-interwork  -mno-thumb-interwork
424           -mcpu=name  -march=name  -mfpu=name -mtune=name  -mprint-tune-info
425           -mstructure-size-boundary=n -mabort-on-noreturn -mlong-calls
426           -mno-long-calls -msingle-pic-base  -mno-single-pic-base
427           -mpic-register=reg -mnop-fun-dllimport -mpoke-function-name -mthumb
428           -marm  -mflip-thumb -mtpcs-frame  -mtpcs-leaf-frame
429           -mcaller-super-interworking  -mcallee-super-interworking -mtp=name
430           -mtls-dialect=dialect -mword-relocations -mfix-cortex-m3-ldrd
431           -munaligned-access -mneon-for-64bits -mslow-flash-data
432           -masm-syntax-unified -mrestrict-it -mverbose-cost-dump -mpure-code
433           -mcmse
434
435           AVR Options -mmcu=mcu  -mabsdata  -maccumulate-args
436           -mbranch-cost=cost -mcall-prologues  -mgas-isr-prologues  -mint8
437           -mn_flash=size  -mno-interrupts -mmain-is-OS_task -mrelax  -mrmw
438           -mstrict-X  -mtiny-stack -mfract-convert-truncate -mshort-calls
439           -nodevicelib -Waddr-space-convert  -Wmisspelled-isr
440
441           Blackfin Options -mcpu=cpu[-sirevision] -msim
442           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
443           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
444           -mno-csync-anomaly -mlow-64k  -mno-low64k  -mstack-check-l1
445           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
446           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
447           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp
448           -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram -micplb
449
450           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim
451           -msdata=sdata-type
452
453           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
454           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init
455           -mno-side-effects -mstack-align  -mdata-align  -mconst-align
456           -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
457           -melf  -maout  -melinux  -mlinux  -sim  -sim2 -mmul-bug-workaround
458           -mno-mul-bug-workaround
459
460           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops
461           -mdata-model=model
462
463           Darwin Options -all_load  -allowable_client  -arch
464           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
465           -bundle_loader -client_name  -compatibility_version
466           -current_version -dead_strip -dependency-file  -dylib_file
467           -dylinker_install_name -dynamic  -dynamiclib
468           -exported_symbols_list -filelist  -flat_namespace
469           -force_cpusubtype_ALL -force_flat_namespace
470           -headerpad_max_install_names -iframework -image_base  -init
471           -install_name  -keep_private_externs -multi_module
472           -multiply_defined  -multiply_defined_unused -noall_load
473           -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs
474           -noprebind  -noseglinkedit -pagezero_size  -prebind
475           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
476           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
477           -sectobjectsymbols  -sectorder -segaddr  -segs_read_only_addr
478           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
479           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
480           -single_module  -static  -sub_library  -sub_umbrella
481           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
482           -weak_reference_mismatches -whatsloaded  -F  -gused  -gfull
483           -mmacosx-version-min=version -mkernel  -mone-byte-bool
484
485           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee
486           -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
487           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
488           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
489           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
490           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time
491
492           FR30 Options -msmall-model  -mno-lsim
493
494           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm
495
496           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
497           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
498           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
499           -minline-plt  -mgprel-ro  -multilib-library-pic -mlinked-fp
500           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
501           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
502           -moptimize-membar  -mno-optimize-membar -mscc  -mno-scc
503           -mcond-exec  -mno-cond-exec -mvliw-branch  -mno-vliw-branch
504           -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
505           -mno-nested-cond-exec  -mtomcat-stats -mTLS  -mtls -mcpu=cpu
506
507           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid
508           -tno-android-cc  -tno-android-ld
509
510           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32
511           -malign-300
512
513           HPPA Options -march=architecture-type -mcaller-copies
514           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
515           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
516           -mlinker-opt  -mlong-calls -mlong-load-store  -mno-disable-fpregs
517           -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
518           -mno-jump-in-delay  -mno-long-load-store -mno-portable-runtime
519           -mno-soft-float -mno-space-regs  -msoft-float  -mpa-risc-1-0
520           -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime -mschedule=cpu-
521           type  -mspace-regs  -msio  -mwsio -munix=unix-std  -nolibdld
522           -static  -threads
523
524           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
525           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata
526           -mconstant-gp  -mauto-pic  -mfused-madd
527           -minline-float-divide-min-latency
528           -minline-float-divide-max-throughput -mno-inline-float-divide
529           -minline-int-divide-min-latency -minline-int-divide-max-throughput
530           -mno-inline-int-divide -minline-sqrt-min-latency
531           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
532           -mearly-stop-bits -mfixed-range=register-range  -mtls-size=tls-size
533           -mtune=cpu-type  -milp32  -mlp64 -msched-br-data-spec
534           -msched-ar-data-spec  -msched-control-spec -msched-br-in-data-spec
535           -msched-ar-in-data-spec  -msched-in-control-spec -msched-spec-ldc
536           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
537           -msched-prefer-non-control-spec-insns
538           -msched-stop-bits-after-every-cycle
539           -msched-count-spec-in-critical-path
540           -msel-sched-dont-check-control-spec  -msched-fp-mem-deps-zero-cost
541           -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=max-
542           insns
543
544           LM32 Options -mbarrel-shift-enabled  -mdivide-enabled
545           -mmultiply-enabled -msign-extend-enabled  -muser-enabled
546
547           M32R/D Options -m32r2  -m32rx  -m32r -mdebug -malign-loops
548           -mno-align-loops -missue-rate=number -mbranch-cost=number
549           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
550           -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num
551
552           M32C Options -mcpu=cpu  -msim  -memregs=number
553
554           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
555           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
556           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
557           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
558           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
559           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
560           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
561           -mxgot  -mno-xgot  -mlong-jump-table-offsets
562
563           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
564           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
565           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
566           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
567           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
568           -mstack-increment
569
570           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops
571           -mc=n  -mclip  -mconfig=name  -mcop  -mcop32  -mcop64  -mivc2 -mdc
572           -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm  -mminmax
573           -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim
574           -msimnovec  -mtf -mtiny=n
575
576           MicroBlaze Options -msoft-float  -mhard-float  -msmall-divides
577           -mcpu=cpu -mmemcpy  -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift
578           -mxl-pattern-compare  -mxl-stack-check  -mxl-gp-opt  -mno-clearbss
579           -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
580           -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-app-model
581
582           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
583           -mips3  -mips4  -mips32  -mips32r2  -mips32r3  -mips32r5 -mips32r6
584           -mips64  -mips64r2  -mips64r3  -mips64r5  -mips64r6 -mips16
585           -mno-mips16  -mflip-mips16 -minterlink-compressed
586           -mno-interlink-compressed -minterlink-mips16  -mno-interlink-mips16
587           -mabi=abi  -mabicalls  -mno-abicalls -mshared  -mno-shared  -mplt
588           -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64
589           -mhard-float  -msoft-float -mno-float  -msingle-float
590           -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode
591           -mnan=encoding -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mmcu
592           -mmno-mcu -meva  -mno-eva -mvirt  -mno-virt -mxpa  -mno-xpa
593           -mmicromips  -mno-micromips -mmsa  -mno-msa -mfpu=fpu-type
594           -msmartmips  -mno-smartmips -mpaired-single  -mno-paired-single
595           -mdmx  -mno-mdmx -mips3d  -mno-mips3d  -mmt  -mno-mt  -mllsc
596           -mno-llsc -mlong64  -mlong32  -msym32  -mno-sym32 -Gnum
597           -mlocal-sdata  -mno-local-sdata -mextern-sdata  -mno-extern-sdata
598           -mgpopt  -mno-gopt -membedded-data  -mno-embedded-data
599           -muninit-const-in-rodata  -mno-uninit-const-in-rodata
600           -mcode-readable=setting -msplit-addresses  -mno-split-addresses
601           -mexplicit-relocs  -mno-explicit-relocs -mcheck-zero-division
602           -mno-check-zero-division -mdivide-traps  -mdivide-breaks
603           -mload-store-pairs  -mno-load-store-pairs -mmemcpy  -mno-memcpy
604           -mlong-calls  -mno-long-calls -mmad  -mno-mad  -mimadd  -mno-imadd
605           -mfused-madd  -mno-fused-madd  -nocpp -mfix-24k  -mno-fix-24k
606           -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
607           -mfix-r10000  -mno-fix-r10000  -mfix-rm7000  -mno-fix-rm7000
608           -mfix-vr4120  -mno-fix-vr4120 -mfix-vr4130  -mno-fix-vr4130
609           -mfix-sb1  -mno-fix-sb1 -mflush-func=func  -mno-flush-func
610           -mbranch-cost=num  -mbranch-likely  -mno-branch-likely
611           -mcompact-branches=policy -mfp-exceptions  -mno-fp-exceptions
612           -mvr4130-align  -mno-vr4130-align  -msynci  -mno-synci -mlxc1-sxc1
613           -mno-lxc1-sxc1 -mmadd4 -mno-madd4 -mrelax-pic-calls
614           -mno-relax-pic-calls  -mmcount-ra-address -mframe-header-opt
615           -mno-frame-header-opt
616
617           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
618           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
619           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
620           -mbase-addresses -mno-base-addresses  -msingle-exit
621           -mno-single-exit
622
623           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33  -mam33
624           -mam33-2  -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0
625           -mrelax  -mliw  -msetlb
626
627           Moxie Options -meb  -mel  -mmul.x  -mno-crt0
628
629           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall
630           -mrelax -mwarn-mcu -mcode-region=  -mdata-region= -msilicon-errata=
631           -msilicon-errata-warn= -mhwmult=  -minrt
632
633           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs
634           -mfull-regs -mcmov  -mno-cmov -mext-perf  -mno-ext-perf -mext-perf2
635           -mno-ext-perf2 -mext-string  -mno-ext-string -mv3push  -mno-v3push
636           -m16bit  -mno-16bit -misr-vector-size=num -mcache-block-size=num
637           -march=arch -mcmodel=code-model -mctor-dtor  -mrelax
638
639           Nios II Options -G num  -mgpopt=option  -mgpopt  -mno-gpopt
640           -mgprel-sec=regexp -mr0rel-sec=regexp -mel  -meb -mno-bypass-cache
641           -mbypass-cache -mno-cache-volatile  -mcache-volatile
642           -mno-fast-sw-div  -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx
643           -mno-hw-mulx  -mno-hw-div  -mhw-div -mcustom-insn=N
644           -mno-custom-insn -mcustom-fpu-cfg=name -mhal  -msmallc
645           -msys-crt0=name  -msys-lib=name -march=arch  -mbmx  -mno-bmx  -mcdx
646           -mno-cdx
647
648           Nvidia PTX Options -m32  -m64  -mmainkernel  -moptimize
649
650           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
651           -m10 -mbcopy  -mbcopy-builtin  -mint32  -mno-int16 -mint16
652           -mno-int32  -mfloat32  -mno-float64 -mfloat64  -mno-float32
653           -mabshi  -mno-abshi -mbranch-expensive  -mbranch-cheap -munix-asm
654           -mdec-asm
655
656           picoChip Options -mae=ae_type  -mvliw-lookahead=N
657           -msymbol-as-address  -mno-inefficient-warnings
658
659           PowerPC Options See RS/6000 and PowerPC Options.
660
661           PowerPC SPE Options -mcpu=cpu-type -mtune=cpu-type -mmfcrf
662           -mno-mfcrf  -mpopcntb  -mno-popcntb -mfull-toc   -mminimal-toc
663           -mno-fp-in-toc  -mno-sum-in-toc -m32  -mxl-compat  -mno-xl-compat
664           -malign-power  -malign-natural -msoft-float  -mhard-float
665           -mmultiple  -mno-multiple -msingle-float  -mdouble-float -mupdate
666           -mno-update -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
667           -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
668           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle
669           -mlittle-endian  -mbig  -mbig-endian -msingle-pic-base
670           -mprioritize-restricted-insns=priority
671           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
672           -mcall-sysv  -mcall-netbsd -maix-struct-return
673           -msvr4-struct-return -mabi=abi-type  -msecure-plt  -mbss-plt
674           -mblock-move-inline-limit=num -misel  -mno-isel -misel=yes
675           -misel=no -mspe  -mno-spe -mspe=yes  -mspe=no -mfloat-gprs=yes
676           -mfloat-gprs=no  -mfloat-gprs=single  -mfloat-gprs=double
677           -mprototype  -mno-prototype -msim  -mmvme  -mads  -myellowknife
678           -memb  -msdata -msdata=opt  -mvxworks  -G num -mrecip  -mrecip=opt
679           -mno-recip  -mrecip-precision -mno-recip-precision
680           -mpointers-to-nested-functions  -mno-pointers-to-nested-functions
681           -msave-toc-indirect  -mno-save-toc-indirect -mcompat-align-parm
682           -mno-compat-align-parm -mfloat128  -mno-float128 -mgnu-attribute
683           -mno-gnu-attribute -mstack-protector-guard=guard
684           -mstack-protector-guard-reg=reg
685           -mstack-protector-guard-offset=offset
686
687           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt
688           -mabi=ABI-string -mfdiv  -mno-fdiv -mdiv  -mno-div -march=ISA-
689           string -mtune=processor-string -mpreferred-stack-boundary=num
690           -msmall-data-limit=N-bytes -msave-restore  -mno-save-restore
691           -mstrict-align -mno-strict-align -mcmodel=medlow -mcmodel=medany
692           -mexplicit-relocs  -mno-explicit-relocs -mrelax -mno-relax
693
694           RL78 Options -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs
695           -mcpu=g10  -mcpu=g13  -mcpu=g14  -mg10  -mg13  -mg14
696           -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts
697
698           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type
699           -mcmodel=code-model -mpowerpc64 -maltivec  -mno-altivec
700           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
701           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
702           -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb
703           -mmfpgpr  -mno-mfpgpr  -mhard-dfp  -mno-hard-dfp -mfull-toc
704           -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32
705           -mxl-compat  -mno-xl-compat  -mpe -malign-power  -malign-natural
706           -msoft-float  -mhard-float  -mmultiple  -mno-multiple
707           -msingle-float  -mdouble-float  -msimple-fpu -mupdate  -mno-update
708           -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
709           -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
710           -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
711           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle
712           -mlittle-endian  -mbig  -mbig-endian -mdynamic-no-pic  -maltivec
713           -mswdiv  -msingle-pic-base -mprioritize-restricted-insns=priority
714           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
715           -mcall-aixdesc  -mcall-eabi  -mcall-freebsd -mcall-linux
716           -mcall-netbsd  -mcall-openbsd -mcall-sysv  -mcall-sysv-eabi
717           -mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return
718           -msvr4-struct-return -mabi=abi-type  -msecure-plt  -mbss-plt
719           -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
720           -mblock-compare-inline-loop-limit=num
721           -mstring-compare-inline-limit=num -misel  -mno-isel -misel=yes
722           -misel=no -mpaired -mvrsave  -mno-vrsave -mmulhw  -mno-mulhw
723           -mdlmzb  -mno-dlmzb -mprototype  -mno-prototype -msim  -mmvme
724           -mads  -myellowknife  -memb  -msdata -msdata=opt
725           -mreadonly-in-sdata  -mvxworks  -G num -mrecip  -mrecip=opt
726           -mno-recip  -mrecip-precision -mno-recip-precision -mveclibabi=type
727           -mfriz  -mno-friz -mpointers-to-nested-functions
728           -mno-pointers-to-nested-functions -msave-toc-indirect
729           -mno-save-toc-indirect -mpower8-fusion  -mno-mpower8-fusion
730           -mpower8-vector  -mno-power8-vector -mcrypto  -mno-crypto  -mhtm
731           -mno-htm -mquad-memory  -mno-quad-memory -mquad-memory-atomic
732           -mno-quad-memory-atomic -mcompat-align-parm  -mno-compat-align-parm
733           -mfloat128  -mno-float128  -mfloat128-hardware
734           -mno-float128-hardware -mgnu-attribute  -mno-gnu-attribute
735           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
736           -mstack-protector-guard-offset=offset
737
738           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
739           -mbig-endian-data  -mlittle-endian-data -msmall-data -msim
740           -mno-sim -mas100-syntax  -mno-as100-syntax -mrelax
741           -mmax-constant-size= -mint-register= -mpid -mallow-string-insns
742           -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
743           -msave-acc-in-interrupts
744
745           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
746           -mhard-float  -msoft-float  -mhard-dfp  -mno-hard-dfp
747           -mlong-double-64  -mlong-double-128 -mbackchain  -mno-backchain
748           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
749           -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
750           -mhtm  -mvx  -mzvector -mtpf-trace  -mno-tpf-trace  -mfused-madd
751           -mno-fused-madd -mwarn-framesize  -mwarn-dynamicstack  -mstack-size
752           -mstack-guard -mhotpatch=halfwords,halfwords
753
754           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u
755           -mscore7  -mscore7d
756
757           SH Options -m1  -m2  -m2e -m2a-nofpu  -m2a-single-only  -m2a-single
758           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
759           -m4a-nofpu  -m4a-single-only  -m4a-single  -m4a  -m4al -mb  -ml
760           -mdalign  -mrelax -mbigtable  -mfmovd  -mrenesas  -mno-renesas
761           -mnomacsave -mieee  -mno-ieee  -mbitops  -misize
762           -minline-ic_invalidate  -mpadstruct -mprefergot  -musermode
763           -multcost=number  -mdiv=strategy -mdivsi3_libfunc=name
764           -mfixed-range=register-range -maccumulate-outgoing-args
765           -matomic-model=atomic-model -mbranch-cost=num  -mzdcbranch
766           -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
767           -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra
768           -mpretend-cmove  -mtas
769
770           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text
771           -mno-impure-text -pthreads
772
773           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
774           -mmemory-model=mem-model -m32  -m64  -mapp-regs  -mno-app-regs
775           -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat -mfpu
776           -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
777           -msoft-quad-float -mstack-bias  -mno-stack-bias -mstd-struct-return
778           -mno-std-struct-return -munaligned-doubles  -mno-unaligned-doubles
779           -muser-mode  -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis
780           -mvis2  -mno-vis2  -mvis3  -mno-vis3 -mvis4 -mno-vis4 -mvis4b
781           -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld
782           -mno-fsmuld -mpopc  -mno-popc  -msubxc  -mno-subxc -mfix-at697f
783           -mfix-ut699  -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra
784
785           SPU Options -mwarn-reloc  -merror-reloc -msafe-dma  -munsafe-dma
786           -mbranch-hints -msmall-mem  -mlarge-mem  -mstdmain
787           -mfixed-range=register-range -mea32  -mea64
788           -maddress-space-conversion  -mno-address-space-conversion
789           -mcache-size=cache-size -matomic-updates  -mno-atomic-updates
790
791           System V Options -Qy  -Qn  -YP,paths  -Ym,dir
792
793           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian
794           -mlittle-endian -mcmodel=code-model
795
796           TILEPro Options -mcpu=cpu  -m32
797
798           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
799           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
800           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
801           -mno-disable-callt -mv850e2v3  -mv850e2  -mv850e1  -mv850es -mv850e
802           -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
803           -mhard-float -mgcc-abi -mrh850-abi -mbig-switch
804
805           VAX Options -mg  -mgnu  -munix
806
807           Visium Options -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float
808           -msoft-float -mcpu=cpu-type  -mtune=cpu-type  -msv-mode
809           -muser-mode
810
811           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64
812           -mpointer-size=size
813
814           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
815           -Xbind-now
816
817           x86 Options -mtune=cpu-type  -march=cpu-type -mtune-ctrl=feature-
818           list  -mdump-tune-features  -mno-default -mfpmath=unit
819           -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387  -m80387
820           -mhard-float  -msoft-float -mno-wide-multiply  -mrtd
821           -malign-double -mpreferred-stack-boundary=num
822           -mincoming-stack-boundary=num -mcld  -mcx16  -msahf  -mmovbe
823           -mcrc32 -mrecip  -mrecip=opt -mvzeroupper  -mprefer-avx128
824           -mprefer-vector-width=opt -mmmx  -msse  -msse2  -msse3  -mssse3
825           -msse4.1  -msse4.2  -msse4  -mavx -mavx2  -mavx512f  -mavx512pf
826           -mavx512er  -mavx512cd  -mavx512vl -mavx512bw  -mavx512dq
827           -mavx512ifma  -mavx512vbmi  -msha  -maes -mpclmul  -mfsgsbase
828           -mrdrnd  -mf16c  -mfma -mpconfig -mwbnoinvd -mprefetchwt1
829           -mclflushopt  -mxsavec  -mxsaves -msse4a  -m3dnow  -m3dnowa
830           -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop -mlzcnt  -mbmi2
831           -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mlwp  -mmpx -mmwaitx  -mclzero
832           -mpku  -mthreads -mgfni  -mvaes -mshstk -mforce-indirect-call
833           -mavx512vbmi2 -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b
834           -mavx512vpopcntdq -mms-bitfields  -mno-align-stringops
835           -minline-all-stringops -minline-stringops-dynamically
836           -mstringop-strategy=alg -mmemcpy-strategy=strategy
837           -mmemset-strategy=strategy -mpush-args  -maccumulate-outgoing-args
838           -m128bit-long-double -m96bit-long-double  -mlong-double-64
839           -mlong-double-80  -mlong-double-128 -mregparm=num  -msseregparm
840           -mveclibabi=type  -mvect8-ret-in-mem -mpc32  -mpc64  -mpc80
841           -mstackrealign -momit-leaf-frame-pointer  -mno-red-zone
842           -mno-tls-direct-seg-refs -mcmodel=code-model  -mabi=name
843           -maddress-mode=mode -m32  -m64  -mx32  -m16  -miamcu
844           -mlarge-data-threshold=num -msse2avx  -mfentry  -mrecord-mcount
845           -mnop-mcount  -m8bit-idiv -mavx256-split-unaligned-load
846           -mavx256-split-unaligned-store -malign-data=type
847           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
848           -mstack-protector-guard-offset=offset
849           -mstack-protector-guard-symbol=symbol -mmitigate-rop
850           -mgeneral-regs-only -mcall-ms2sysv-xlogues -mindirect-branch=choice
851           -mfunction-return=choice -mindirect-branch-register
852
853           x86 Windows Options -mconsole  -mcygwin  -mno-cygwin  -mdll
854           -mnop-fun-dllimport  -mthread -municode  -mwin32  -mwindows
855           -fno-set-stack-executable
856
857           Xstormy16 Options -msim
858
859           Xtensa Options -mconst16  -mno-const16 -mfused-madd
860           -mno-fused-madd -mforce-no-pic -mserialize-volatile
861           -mno-serialize-volatile -mtext-section-literals
862           -mno-text-section-literals -mauto-litpools  -mno-auto-litpools
863           -mtarget-align  -mno-target-align -mlongcalls  -mno-longcalls
864
865           zSeries Options See S/390 and zSeries Options.
866
867   Options Controlling the Kind of Output
868       Compilation can involve up to four stages: preprocessing, compilation
869       proper, assembly and linking, always in that order.  GCC is capable of
870       preprocessing and compiling several files either into several assembler
871       input files, or into one assembler input file; then each assembler
872       input file produces an object file, and linking combines all the object
873       files (those newly compiled, and those specified as input) into an
874       executable file.
875
876       For any given input file, the file name suffix determines what kind of
877       compilation is done:
878
879       file.c
880           C source code that must be preprocessed.
881
882       file.i
883           C source code that should not be preprocessed.
884
885       file.ii
886           C++ source code that should not be preprocessed.
887
888       file.m
889           Objective-C source code.  Note that you must link with the libobjc
890           library to make an Objective-C program work.
891
892       file.mi
893           Objective-C source code that should not be preprocessed.
894
895       file.mm
896       file.M
897           Objective-C++ source code.  Note that you must link with the
898           libobjc library to make an Objective-C++ program work.  Note that
899           .M refers to a literal capital M.
900
901       file.mii
902           Objective-C++ source code that should not be preprocessed.
903
904       file.h
905           C, C++, Objective-C or Objective-C++ header file to be turned into
906           a precompiled header (default), or C, C++ header file to be turned
907           into an Ada spec (via the -fdump-ada-spec switch).
908
909       file.cc
910       file.cp
911       file.cxx
912       file.cpp
913       file.CPP
914       file.c++
915       file.C
916           C++ source code that must be preprocessed.  Note that in .cxx, the
917           last two letters must both be literally x.  Likewise, .C refers to
918           a literal capital C.
919
920       file.mm
921       file.M
922           Objective-C++ source code that must be preprocessed.
923
924       file.mii
925           Objective-C++ source code that should not be preprocessed.
926
927       file.hh
928       file.H
929       file.hp
930       file.hxx
931       file.hpp
932       file.HPP
933       file.h++
934       file.tcc
935           C++ header file to be turned into a precompiled header or Ada spec.
936
937       file.f
938       file.for
939       file.ftn
940           Fixed form Fortran source code that should not be preprocessed.
941
942       file.F
943       file.FOR
944       file.fpp
945       file.FPP
946       file.FTN
947           Fixed form Fortran source code that must be preprocessed (with the
948           traditional preprocessor).
949
950       file.f90
951       file.f95
952       file.f03
953       file.f08
954           Free form Fortran source code that should not be preprocessed.
955
956       file.F90
957       file.F95
958       file.F03
959       file.F08
960           Free form Fortran source code that must be preprocessed (with the
961           traditional preprocessor).
962
963       file.go
964           Go source code.
965
966       file.brig
967           BRIG files (binary representation of HSAIL).
968
969       file.ads
970           Ada source code file that contains a library unit declaration (a
971           declaration of a package, subprogram, or generic, or a generic
972           instantiation), or a library unit renaming declaration (a package,
973           generic, or subprogram renaming declaration).  Such files are also
974           called specs.
975
976       file.adb
977           Ada source code file containing a library unit body (a subprogram
978           or package body).  Such files are also called bodies.
979
980       file.s
981           Assembler code.
982
983       file.S
984       file.sx
985           Assembler code that must be preprocessed.
986
987       other
988           An object file to be fed straight into linking.  Any file name with
989           no recognized suffix is treated this way.
990
991       You can specify the input language explicitly with the -x option:
992
993       -x language
994           Specify explicitly the language for the following input files
995           (rather than letting the compiler choose a default based on the
996           file name suffix).  This option applies to all following input
997           files until the next -x option.  Possible values for language are:
998
999                   c  c-header  cpp-output
1000                   c++  c++-header  c++-cpp-output
1001                   objective-c  objective-c-header  objective-c-cpp-output
1002                   objective-c++ objective-c++-header objective-c++-cpp-output
1003                   assembler  assembler-with-cpp
1004                   ada
1005                   f77  f77-cpp-input f95  f95-cpp-input
1006                   go
1007                   brig
1008
1009       -x none
1010           Turn off any specification of a language, so that subsequent files
1011           are handled according to their file name suffixes (as they are if
1012           -x has not been used at all).
1013
1014       If you only want some of the stages of compilation, you can use -x (or
1015       filename suffixes) to tell gcc where to start, and one of the options
1016       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
1017       (for example, -x cpp-output -E) instruct gcc to do nothing at all.
1018
1019       -c  Compile or assemble the source files, but do not link.  The linking
1020           stage simply is not done.  The ultimate output is in the form of an
1021           object file for each source file.
1022
1023           By default, the object file name for a source file is made by
1024           replacing the suffix .c, .i, .s, etc., with .o.
1025
1026           Unrecognized input files, not requiring compilation or assembly,
1027           are ignored.
1028
1029       -S  Stop after the stage of compilation proper; do not assemble.  The
1030           output is in the form of an assembler code file for each non-
1031           assembler input file specified.
1032
1033           By default, the assembler file name for a source file is made by
1034           replacing the suffix .c, .i, etc., with .s.
1035
1036           Input files that don't require compilation are ignored.
1037
1038       -E  Stop after the preprocessing stage; do not run the compiler proper.
1039           The output is in the form of preprocessed source code, which is
1040           sent to the standard output.
1041
1042           Input files that don't require preprocessing are ignored.
1043
1044       -o file
1045           Place output in file file.  This applies to whatever sort of output
1046           is being produced, whether it be an executable file, an object
1047           file, an assembler file or preprocessed C code.
1048
1049           If -o is not specified, the default is to put an executable file in
1050           a.out, the object file for source.suffix in source.o, its assembler
1051           file in source.s, a precompiled header file in source.suffix.gch,
1052           and all preprocessed C source on standard output.
1053
1054       -v  Print (on standard error output) the commands executed to run the
1055           stages of compilation.  Also print the version number of the
1056           compiler driver program and of the preprocessor and the compiler
1057           proper.
1058
1059       -###
1060           Like -v except the commands are not executed and arguments are
1061           quoted unless they contain only alphanumeric characters or "./-_".
1062           This is useful for shell scripts to capture the driver-generated
1063           command lines.
1064
1065       --help
1066           Print (on the standard output) a description of the command-line
1067           options understood by gcc.  If the -v option is also specified then
1068           --help is also passed on to the various processes invoked by gcc,
1069           so that they can display the command-line options they accept.  If
1070           the -Wextra option has also been specified (prior to the --help
1071           option), then command-line options that have no documentation
1072           associated with them are also displayed.
1073
1074       --target-help
1075           Print (on the standard output) a description of target-specific
1076           command-line options for each tool.  For some targets extra target-
1077           specific information may also be printed.
1078
1079       --help={class|[^]qualifier}[,...]
1080           Print (on the standard output) a description of the command-line
1081           options understood by the compiler that fit into all specified
1082           classes and qualifiers.  These are the supported classes:
1083
1084           optimizers
1085               Display all of the optimization options supported by the
1086               compiler.
1087
1088           warnings
1089               Display all of the options controlling warning messages
1090               produced by the compiler.
1091
1092           target
1093               Display target-specific options.  Unlike the --target-help
1094               option however, target-specific options of the linker and
1095               assembler are not displayed.  This is because those tools do
1096               not currently support the extended --help= syntax.
1097
1098           params
1099               Display the values recognized by the --param option.
1100
1101           language
1102               Display the options supported for language, where language is
1103               the name of one of the languages supported in this version of
1104               GCC.
1105
1106           common
1107               Display the options that are common to all languages.
1108
1109           These are the supported qualifiers:
1110
1111           undocumented
1112               Display only those options that are undocumented.
1113
1114           joined
1115               Display options taking an argument that appears after an equal
1116               sign in the same continuous piece of text, such as:
1117               --help=target.
1118
1119           separate
1120               Display options taking an argument that appears as a separate
1121               word following the original option, such as: -o output-file.
1122
1123           Thus for example to display all the undocumented target-specific
1124           switches supported by the compiler, use:
1125
1126                   --help=target,undocumented
1127
1128           The sense of a qualifier can be inverted by prefixing it with the ^
1129           character, so for example to display all binary warning options
1130           (i.e., ones that are either on or off and that do not take an
1131           argument) that have a description, use:
1132
1133                   --help=warnings,^joined,^undocumented
1134
1135           The argument to --help= should not consist solely of inverted
1136           qualifiers.
1137
1138           Combining several classes is possible, although this usually
1139           restricts the output so much that there is nothing to display.  One
1140           case where it does work, however, is when one of the classes is
1141           target.  For example, to display all the target-specific
1142           optimization options, use:
1143
1144                   --help=target,optimizers
1145
1146           The --help= option can be repeated on the command line.  Each
1147           successive use displays its requested class of options, skipping
1148           those that have already been displayed.
1149
1150           If the -Q option appears on the command line before the --help=
1151           option, then the descriptive text displayed by --help= is changed.
1152           Instead of describing the displayed options, an indication is given
1153           as to whether the option is enabled, disabled or set to a specific
1154           value (assuming that the compiler knows this at the point where the
1155           --help= option is used).
1156
1157           Here is a truncated example from the ARM port of gcc:
1158
1159                     % gcc -Q -mabi=2 --help=target -c
1160                     The following options are target specific:
1161                     -mabi=                                2
1162                     -mabort-on-noreturn                   [disabled]
1163                     -mapcs                                [disabled]
1164
1165           The output is sensitive to the effects of previous command-line
1166           options, so for example it is possible to find out which
1167           optimizations are enabled at -O2 by using:
1168
1169                   -Q -O2 --help=optimizers
1170
1171           Alternatively you can discover which binary optimizations are
1172           enabled by -O3 by using:
1173
1174                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1175                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1176                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1177
1178       --version
1179           Display the version number and copyrights of the invoked GCC.
1180
1181       -pass-exit-codes
1182           Normally the gcc program exits with the code of 1 if any phase of
1183           the compiler returns a non-success return code.  If you specify
1184           -pass-exit-codes, the gcc program instead returns with the
1185           numerically highest error produced by any phase returning an error
1186           indication.  The C, C++, and Fortran front ends return 4 if an
1187           internal compiler error is encountered.
1188
1189       -pipe
1190           Use pipes rather than temporary files for communication between the
1191           various stages of compilation.  This fails to work on some systems
1192           where the assembler is unable to read from a pipe; but the GNU
1193           assembler has no trouble.
1194
1195       -specs=file
1196           Process file after the compiler reads in the standard specs file,
1197           in order to override the defaults which the gcc driver program uses
1198           when determining what switches to pass to cc1, cc1plus, as, ld,
1199           etc.  More than one -specs=file can be specified on the command
1200           line, and they are processed in order, from left to right.
1201
1202       -wrapper
1203           Invoke all subcommands under a wrapper program.  The name of the
1204           wrapper program and its parameters are passed as a comma separated
1205           list.
1206
1207                   gcc -c t.c -wrapper gdb,--args
1208
1209           This invokes all subprograms of gcc under gdb --args, thus the
1210           invocation of cc1 is gdb --args cc1 ....
1211
1212       -ffile-prefix-map=old=new
1213           When compiling files residing in directory old, record any
1214           references to them in the result of the compilation as if the files
1215           resided in directory new instead.  Specifying this option is
1216           equivalent to specifying all the individual -f*-prefix-map options.
1217           This can be used to make reproducible builds that are location
1218           independent.  See also -fmacro-prefix-map and -fdebug-prefix-map.
1219
1220       -fplugin=name.so
1221           Load the plugin code in file name.so, assumed to be a shared object
1222           to be dlopen'd by the compiler.  The base name of the shared object
1223           file is used to identify the plugin for the purposes of argument
1224           parsing (See -fplugin-arg-name-key=value below).  Each plugin
1225           should define the callback functions specified in the Plugins API.
1226
1227       -fplugin-arg-name-key=value
1228           Define an argument called key with a value of value for the plugin
1229           called name.
1230
1231       -fdump-ada-spec[-slim]
1232           For C and C++ source and include files, generate corresponding Ada
1233           specs.
1234
1235       -fada-spec-parent=unit
1236           In conjunction with -fdump-ada-spec[-slim] above, generate Ada
1237           specs as child units of parent unit.
1238
1239       -fdump-go-spec=file
1240           For input files in any language, generate corresponding Go
1241           declarations in file.  This generates Go "const", "type", "var",
1242           and "func" declarations which may be a useful way to start writing
1243           a Go interface to code written in some other language.
1244
1245       @file
1246           Read command-line options from file.  The options read are inserted
1247           in place of the original @file option.  If file does not exist, or
1248           cannot be read, then the option will be treated literally, and not
1249           removed.
1250
1251           Options in file are separated by whitespace.  A whitespace
1252           character may be included in an option by surrounding the entire
1253           option in either single or double quotes.  Any character (including
1254           a backslash) may be included by prefixing the character to be
1255           included with a backslash.  The file may itself contain additional
1256           @file options; any such options will be processed recursively.
1257
1258   Compiling C++ Programs
1259       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
1260       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
1261       (for shared template code) .tcc; and preprocessed C++ files use the
1262       suffix .ii.  GCC recognizes files with these names and compiles them as
1263       C++ programs even if you call the compiler the same way as for
1264       compiling C programs (usually with the name gcc).
1265
1266       However, the use of gcc does not add the C++ library.  g++ is a program
1267       that calls GCC and automatically specifies linking against the C++
1268       library.  It treats .c, .h and .i files as C++ source files instead of
1269       C source files unless -x is used.  This program is also useful when
1270       precompiling a C header file with a .h extension for use in C++
1271       compilations.  On many systems, g++ is also installed with the name
1272       c++.
1273
1274       When you compile C++ programs, you may specify many of the same
1275       command-line options that you use for compiling programs in any
1276       language; or command-line options meaningful for C and related
1277       languages; or options that are meaningful only for C++ programs.
1278
1279   Options Controlling C Dialect
1280       The following options control the dialect of C (or languages derived
1281       from C, such as C++, Objective-C and Objective-C++) that the compiler
1282       accepts:
1283
1284       -ansi
1285           In C mode, this is equivalent to -std=c90. In C++ mode, it is
1286           equivalent to -std=c++98.
1287
1288           This turns off certain features of GCC that are incompatible with
1289           ISO C90 (when compiling C code), or of standard C++ (when compiling
1290           C++ code), such as the "asm" and "typeof" keywords, and predefined
1291           macros such as "unix" and "vax" that identify the type of system
1292           you are using.  It also enables the undesirable and rarely used ISO
1293           trigraph feature.  For the C compiler, it disables recognition of
1294           C++ style // comments as well as the "inline" keyword.
1295
1296           The alternate keywords "__asm__", "__extension__", "__inline__" and
1297           "__typeof__" continue to work despite -ansi.  You would not want to
1298           use them in an ISO C program, of course, but it is useful to put
1299           them in header files that might be included in compilations done
1300           with -ansi.  Alternate predefined macros such as "__unix__" and
1301           "__vax__" are also available, with or without -ansi.
1302
1303           The -ansi option does not cause non-ISO programs to be rejected
1304           gratuitously.  For that, -Wpedantic is required in addition to
1305           -ansi.
1306
1307           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
1308           used.  Some header files may notice this macro and refrain from
1309           declaring certain functions or defining certain macros that the ISO
1310           standard doesn't call for; this is to avoid interfering with any
1311           programs that might use these names for other things.
1312
1313           Functions that are normally built in but do not have semantics
1314           defined by ISO C (such as "alloca" and "ffs") are not built-in
1315           functions when -ansi is used.
1316
1317       -std=
1318           Determine the language standard.   This option is currently only
1319           supported when compiling C or C++.
1320
1321           The compiler can accept several base standards, such as c90 or
1322           c++98, and GNU dialects of those standards, such as gnu90 or
1323           gnu++98.  When a base standard is specified, the compiler accepts
1324           all programs following that standard plus those using GNU
1325           extensions that do not contradict it.  For example, -std=c90 turns
1326           off certain features of GCC that are incompatible with ISO C90,
1327           such as the "asm" and "typeof" keywords, but not other GNU
1328           extensions that do not have a meaning in ISO C90, such as omitting
1329           the middle term of a "?:" expression. On the other hand, when a GNU
1330           dialect of a standard is specified, all features supported by the
1331           compiler are enabled, even when those features change the meaning
1332           of the base standard.  As a result, some strict-conforming programs
1333           may be rejected.  The particular standard is used by -Wpedantic to
1334           identify which features are GNU extensions given that version of
1335           the standard. For example -std=gnu90 -Wpedantic warns about C++
1336           style // comments, while -std=gnu99 -Wpedantic does not.
1337
1338           A value for this option must be provided; possible values are
1339
1340           c90
1341           c89
1342           iso9899:1990
1343               Support all ISO C90 programs (certain GNU extensions that
1344               conflict with ISO C90 are disabled). Same as -ansi for C code.
1345
1346           iso9899:199409
1347               ISO C90 as modified in amendment 1.
1348
1349           c99
1350           c9x
1351           iso9899:1999
1352           iso9899:199x
1353               ISO C99.  This standard is substantially completely supported,
1354               modulo bugs and floating-point issues (mainly but not entirely
1355               relating to optional C99 features from Annexes F and G).  See
1356               <http://gcc.gnu.org/c99status.html> for more information.  The
1357               names c9x and iso9899:199x are deprecated.
1358
1359           c11
1360           c1x
1361           iso9899:2011
1362               ISO C11, the 2011 revision of the ISO C standard.  This
1363               standard is substantially completely supported, modulo bugs,
1364               floating-point issues (mainly but not entirely relating to
1365               optional C11 features from Annexes F and G) and the optional
1366               Annexes K (Bounds-checking interfaces) and L (Analyzability).
1367               The name c1x is deprecated.
1368
1369           c17
1370           c18
1371           iso9899:2017
1372           iso9899:2018
1373               ISO C17, the 2017 revision of the ISO C standard (expected to
1374               be published in 2018).  This standard is same as C11 except for
1375               corrections of defects (all of which are also applied with
1376               -std=c11) and a new value of "__STDC_VERSION__", and so is
1377               supported to the same extent as C11.
1378
1379           gnu90
1380           gnu89
1381               GNU dialect of ISO C90 (including some C99 features).
1382
1383           gnu99
1384           gnu9x
1385               GNU dialect of ISO C99.  The name gnu9x is deprecated.
1386
1387           gnu11
1388           gnu1x
1389               GNU dialect of ISO C11.  The name gnu1x is deprecated.
1390
1391           gnu17
1392           gnu18
1393               GNU dialect of ISO C17.  This is the default for C code.
1394
1395           c++98
1396           c++03
1397               The 1998 ISO C++ standard plus the 2003 technical corrigendum
1398               and some additional defect reports. Same as -ansi for C++ code.
1399
1400           gnu++98
1401           gnu++03
1402               GNU dialect of -std=c++98.
1403
1404           c++11
1405           c++0x
1406               The 2011 ISO C++ standard plus amendments.  The name c++0x is
1407               deprecated.
1408
1409           gnu++11
1410           gnu++0x
1411               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.
1412
1413           c++14
1414           c++1y
1415               The 2014 ISO C++ standard plus amendments.  The name c++1y is
1416               deprecated.
1417
1418           gnu++14
1419           gnu++1y
1420               GNU dialect of -std=c++14.  This is the default for C++ code.
1421               The name gnu++1y is deprecated.
1422
1423           c++17
1424           c++1z
1425               The 2017 ISO C++ standard plus amendments.  The name c++1z is
1426               deprecated.
1427
1428           gnu++17
1429           gnu++1z
1430               GNU dialect of -std=c++17.  The name gnu++1z is deprecated.
1431
1432           c++2a
1433               The next revision of the ISO C++ standard, tentatively planned
1434               for 2020.  Support is highly experimental, and will almost
1435               certainly change in incompatible ways in future releases.
1436
1437           gnu++2a
1438               GNU dialect of -std=c++2a.  Support is highly experimental, and
1439               will almost certainly change in incompatible ways in future
1440               releases.
1441
1442       -fgnu89-inline
1443           The option -fgnu89-inline tells GCC to use the traditional GNU
1444           semantics for "inline" functions when in C99 mode.
1445
1446           Using this option is roughly equivalent to adding the "gnu_inline"
1447           function attribute to all inline functions.
1448
1449           The option -fno-gnu89-inline explicitly tells GCC to use the C99
1450           semantics for "inline" when in C99 or gnu99 mode (i.e., it
1451           specifies the default behavior).  This option is not supported in
1452           -std=c90 or -std=gnu90 mode.
1453
1454           The preprocessor macros "__GNUC_GNU_INLINE__" and
1455           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
1456           effect for "inline" functions.
1457
1458       -fpermitted-flt-eval-methods=style
1459           ISO/IEC TS 18661-3 defines new permissible values for
1460           "FLT_EVAL_METHOD" that indicate that operations and constants with
1461           a semantic type that is an interchange or extended format should be
1462           evaluated to the precision and range of that type.  These new
1463           values are a superset of those permitted under C99/C11, which does
1464           not specify the meaning of other positive values of
1465           "FLT_EVAL_METHOD".  As such, code conforming to C11 may not have
1466           been written expecting the possibility of the new values.
1467
1468           -fpermitted-flt-eval-methods specifies whether the compiler should
1469           allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or
1470           the extended set of values specified in ISO/IEC TS 18661-3.
1471
1472           style is either "c11" or "ts-18661-3" as appropriate.
1473
1474           The default when in a standards compliant mode (-std=c11 or
1475           similar) is -fpermitted-flt-eval-methods=c11.  The default when in
1476           a GNU dialect (-std=gnu11 or similar) is
1477           -fpermitted-flt-eval-methods=ts-18661-3.
1478
1479       -aux-info filename
1480           Output to the given filename prototyped declarations for all
1481           functions declared and/or defined in a translation unit, including
1482           those in header files.  This option is silently ignored in any
1483           language other than C.
1484
1485           Besides declarations, the file indicates, in comments, the origin
1486           of each declaration (source file and line), whether the declaration
1487           was implicit, prototyped or unprototyped (I, N for new or O for
1488           old, respectively, in the first character after the line number and
1489           the colon), and whether it came from a declaration or a definition
1490           (C or F, respectively, in the following character).  In the case of
1491           function definitions, a K&R-style list of arguments followed by
1492           their declarations is also provided, inside comments, after the
1493           declaration.
1494
1495       -fallow-parameterless-variadic-functions
1496           Accept variadic functions without named parameters.
1497
1498           Although it is possible to define such a function, this is not very
1499           useful as it is not possible to read the arguments.  This is only
1500           supported for C as this construct is allowed by C++.
1501
1502       -fno-asm
1503           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
1504           code can use these words as identifiers.  You can use the keywords
1505           "__asm__", "__inline__" and "__typeof__" instead.  -ansi implies
1506           -fno-asm.
1507
1508           In C++, this switch only affects the "typeof" keyword, since "asm"
1509           and "inline" are standard keywords.  You may want to use the
1510           -fno-gnu-keywords flag instead, which has the same effect.  In C99
1511           mode (-std=c99 or -std=gnu99), this switch only affects the "asm"
1512           and "typeof" keywords, since "inline" is a standard keyword in ISO
1513           C99.
1514
1515       -fno-builtin
1516       -fno-builtin-function
1517           Don't recognize built-in functions that do not begin with
1518           __builtin_ as prefix.
1519
1520           GCC normally generates special code to handle certain built-in
1521           functions more efficiently; for instance, calls to "alloca" may
1522           become single instructions which adjust the stack directly, and
1523           calls to "memcpy" may become inline copy loops.  The resulting code
1524           is often both smaller and faster, but since the function calls no
1525           longer appear as such, you cannot set a breakpoint on those calls,
1526           nor can you change the behavior of the functions by linking with a
1527           different library.  In addition, when a function is recognized as a
1528           built-in function, GCC may use information about that function to
1529           warn about problems with calls to that function, or to generate
1530           more efficient code, even if the resulting code still contains
1531           calls to that function.  For example, warnings are given with
1532           -Wformat for bad calls to "printf" when "printf" is built in and
1533           "strlen" is known not to modify global memory.
1534
1535           With the -fno-builtin-function option only the built-in function
1536           function is disabled.  function must not begin with __builtin_.  If
1537           a function is named that is not built-in in this version of GCC,
1538           this option is ignored.  There is no corresponding
1539           -fbuiltin-function option; if you wish to enable built-in functions
1540           selectively when using -fno-builtin or -ffreestanding, you may
1541           define macros such as:
1542
1543                   #define abs(n)          __builtin_abs ((n))
1544                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))
1545
1546       -fgimple
1547           Enable parsing of function definitions marked with "__GIMPLE".
1548           This is an experimental feature that allows unit testing of GIMPLE
1549           passes.
1550
1551       -fhosted
1552           Assert that compilation targets a hosted environment.  This implies
1553           -fbuiltin.  A hosted environment is one in which the entire
1554           standard library is available, and in which "main" has a return
1555           type of "int".  Examples are nearly everything except a kernel.
1556           This is equivalent to -fno-freestanding.
1557
1558       -ffreestanding
1559           Assert that compilation targets a freestanding environment.  This
1560           implies -fno-builtin.  A freestanding environment is one in which
1561           the standard library may not exist, and program startup may not
1562           necessarily be at "main".  The most obvious example is an OS
1563           kernel.  This is equivalent to -fno-hosted.
1564
1565       -fopenacc
1566           Enable handling of OpenACC directives "#pragma acc" in C/C++ and
1567           "!$acc" in Fortran.  When -fopenacc is specified, the compiler
1568           generates accelerated code according to the OpenACC Application
1569           Programming Interface v2.0 <https://www.openacc.org>.  This option
1570           implies -pthread, and thus is only supported on targets that have
1571           support for -pthread.
1572
1573       -fopenacc-dim=geom
1574           Specify default compute dimensions for parallel offload regions
1575           that do not explicitly specify.  The geom value is a triple of
1576           ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A
1577           size can be omitted, to use a target-specific default value.
1578
1579       -fopenmp
1580           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
1581           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
1582           generates parallel code according to the OpenMP Application Program
1583           Interface v4.5 <http://www.openmp.org/>.  This option implies
1584           -pthread, and thus is only supported on targets that have support
1585           for -pthread. -fopenmp implies -fopenmp-simd.
1586
1587       -fopenmp-simd
1588           Enable handling of OpenMP's SIMD directives with "#pragma omp" in
1589           C/C++ and "!$omp" in Fortran. Other OpenMP directives are ignored.
1590
1591       -fgnu-tm
1592           When the option -fgnu-tm is specified, the compiler generates code
1593           for the Linux variant of Intel's current Transactional Memory ABI
1594           specification document (Revision 1.1, May 6 2009).  This is an
1595           experimental feature whose interface may change in future versions
1596           of GCC, as the official specification changes.  Please note that
1597           not all architectures are supported for this feature.
1598
1599           For more information on GCC's support for transactional memory,
1600
1601           Note that the transactional memory feature is not supported with
1602           non-call exceptions (-fnon-call-exceptions).
1603
1604       -fms-extensions
1605           Accept some non-standard constructs used in Microsoft header files.
1606
1607           In C++ code, this allows member names in structures to be similar
1608           to previous types declarations.
1609
1610                   typedef int UOW;
1611                   struct ABC {
1612                     UOW UOW;
1613                   };
1614
1615           Some cases of unnamed fields in structures and unions are only
1616           accepted with this option.
1617
1618           Note that this option is off for all targets but x86 targets using
1619           ms-abi.
1620
1621       -fplan9-extensions
1622           Accept some non-standard constructs used in Plan 9 code.
1623
1624           This enables -fms-extensions, permits passing pointers to
1625           structures with anonymous fields to functions that expect pointers
1626           to elements of the type of the field, and permits referring to
1627           anonymous fields declared using a typedef.    This is only
1628           supported for C, not C++.
1629
1630       -fcond-mismatch
1631           Allow conditional expressions with mismatched types in the second
1632           and third arguments.  The value of such an expression is void.
1633           This option is not supported for C++.
1634
1635       -flax-vector-conversions
1636           Allow implicit conversions between vectors with differing numbers
1637           of elements and/or incompatible element types.  This option should
1638           not be used for new code.
1639
1640       -funsigned-char
1641           Let the type "char" be unsigned, like "unsigned char".
1642
1643           Each kind of machine has a default for what "char" should be.  It
1644           is either like "unsigned char" by default or like "signed char" by
1645           default.
1646
1647           Ideally, a portable program should always use "signed char" or
1648           "unsigned char" when it depends on the signedness of an object.
1649           But many programs have been written to use plain "char" and expect
1650           it to be signed, or expect it to be unsigned, depending on the
1651           machines they were written for.  This option, and its inverse, let
1652           you make such a program work with the opposite default.
1653
1654           The type "char" is always a distinct type from each of "signed
1655           char" or "unsigned char", even though its behavior is always just
1656           like one of those two.
1657
1658       -fsigned-char
1659           Let the type "char" be signed, like "signed char".
1660
1661           Note that this is equivalent to -fno-unsigned-char, which is the
1662           negative form of -funsigned-char.  Likewise, the option
1663           -fno-signed-char is equivalent to -funsigned-char.
1664
1665       -fsigned-bitfields
1666       -funsigned-bitfields
1667       -fno-signed-bitfields
1668       -fno-unsigned-bitfields
1669           These options control whether a bit-field is signed or unsigned,
1670           when the declaration does not use either "signed" or "unsigned".
1671           By default, such a bit-field is signed, because this is consistent:
1672           the basic integer types such as "int" are signed types.
1673
1674       -fsso-struct=endianness
1675           Set the default scalar storage order of structures and unions to
1676           the specified endianness.  The accepted values are big-endian,
1677           little-endian and native for the native endianness of the target
1678           (the default).  This option is not supported for C++.
1679
1680           Warning: the -fsso-struct switch causes GCC to generate code that
1681           is not binary compatible with code generated without it if the
1682           specified endianness is not the native endianness of the target.
1683
1684   Options Controlling C++ Dialect
1685       This section describes the command-line options that are only
1686       meaningful for C++ programs.  You can also use most of the GNU compiler
1687       options regardless of what language your program is in.  For example,
1688       you might compile a file firstClass.C like this:
1689
1690               g++ -g -fstrict-enums -O -c firstClass.C
1691
1692       In this example, only -fstrict-enums is an option meant only for C++
1693       programs; you can use the other options with any language supported by
1694       GCC.
1695
1696       Some options for compiling C programs, such as -std, are also relevant
1697       for C++ programs.
1698
1699       Here is a list of options that are only for compiling C++ programs:
1700
1701       -fabi-version=n
1702           Use version n of the C++ ABI.  The default is version 0.
1703
1704           Version 0 refers to the version conforming most closely to the C++
1705           ABI specification.  Therefore, the ABI obtained using version 0
1706           will change in different versions of G++ as ABI bugs are fixed.
1707
1708           Version 1 is the version of the C++ ABI that first appeared in G++
1709           3.2.
1710
1711           Version 2 is the version of the C++ ABI that first appeared in G++
1712           3.4, and was the default through G++ 4.9.
1713
1714           Version 3 corrects an error in mangling a constant address as a
1715           template argument.
1716
1717           Version 4, which first appeared in G++ 4.5, implements a standard
1718           mangling for vector types.
1719
1720           Version 5, which first appeared in G++ 4.6, corrects the mangling
1721           of attribute const/volatile on function pointer types, decltype of
1722           a plain decl, and use of a function parameter in the declaration of
1723           another parameter.
1724
1725           Version 6, which first appeared in G++ 4.7, corrects the promotion
1726           behavior of C++11 scoped enums and the mangling of template
1727           argument packs, const/static_cast, prefix ++ and --, and a class
1728           scope function used as a template argument.
1729
1730           Version 7, which first appeared in G++ 4.8, that treats nullptr_t
1731           as a builtin type and corrects the mangling of lambdas in default
1732           argument scope.
1733
1734           Version 8, which first appeared in G++ 4.9, corrects the
1735           substitution behavior of function types with function-cv-
1736           qualifiers.
1737
1738           Version 9, which first appeared in G++ 5.2, corrects the alignment
1739           of "nullptr_t".
1740
1741           Version 10, which first appeared in G++ 6.1, adds mangling of
1742           attributes that affect type identity, such as ia32 calling
1743           convention attributes (e.g. stdcall).
1744
1745           Version 11, which first appeared in G++ 7, corrects the mangling of
1746           sizeof... expressions and operator names.  For multiple entities
1747           with the same name within a function, that are declared in
1748           different scopes, the mangling now changes starting with the
1749           twelfth occurrence.  It also implies -fnew-inheriting-ctors.
1750
1751           Version 12, which first appeared in G++ 8, corrects the calling
1752           conventions for empty classes on the x86_64 target and for classes
1753           with only deleted copy/move constructors.  It accidentally changes
1754           the calling convention for classes with a deleted copy constructor
1755           and a trivial move constructor.
1756
1757           Version 13, which first appeared in G++ 8.2, fixes the accidental
1758           change in version 12.
1759
1760           See also -Wabi.
1761
1762       -fabi-compat-version=n
1763           On targets that support strong aliases, G++ works around mangling
1764           changes by creating an alias with the correct mangled name when
1765           defining a symbol with an incorrect mangled name.  This switch
1766           specifies which ABI version to use for the alias.
1767
1768           With -fabi-version=0 (the default), this defaults to 11 (GCC 7
1769           compatibility).  If another ABI version is explicitly selected,
1770           this defaults to 0.  For compatibility with GCC versions 3.2
1771           through 4.9, use -fabi-compat-version=2.
1772
1773           If this option is not provided but -Wabi=n is, that version is used
1774           for compatibility aliases.  If this option is provided along with
1775           -Wabi (without the version), the version from this option is used
1776           for the warning.
1777
1778       -fno-access-control
1779           Turn off all access checking.  This switch is mainly useful for
1780           working around bugs in the access control code.
1781
1782       -faligned-new
1783           Enable support for C++17 "new" of types that require more alignment
1784           than "void* ::operator new(std::size_t)" provides.  A numeric
1785           argument such as "-faligned-new=32" can be used to specify how much
1786           alignment (in bytes) is provided by that function, but few users
1787           will need to override the default of "alignof(std::max_align_t)".
1788
1789           This flag is enabled by default for -std=c++17.
1790
1791       -fcheck-new
1792           Check that the pointer returned by "operator new" is non-null
1793           before attempting to modify the storage allocated.  This check is
1794           normally unnecessary because the C++ standard specifies that
1795           "operator new" only returns 0 if it is declared "throw()", in which
1796           case the compiler always checks the return value even without this
1797           option.  In all other cases, when "operator new" has a non-empty
1798           exception specification, memory exhaustion is signalled by throwing
1799           "std::bad_alloc".  See also new (nothrow).
1800
1801       -fconcepts
1802           Enable support for the C++ Extensions for Concepts Technical
1803           Specification, ISO 19217 (2015), which allows code like
1804
1805                   template <class T> concept bool Addable = requires (T t) { t + t; };
1806                   template <Addable T> T add (T a, T b) { return a + b; }
1807
1808       -fconstexpr-depth=n
1809           Set the maximum nested evaluation depth for C++11 constexpr
1810           functions to n.  A limit is needed to detect endless recursion
1811           during constant expression evaluation.  The minimum specified by
1812           the standard is 512.
1813
1814       -fconstexpr-loop-limit=n
1815           Set the maximum number of iterations for a loop in C++14 constexpr
1816           functions to n.  A limit is needed to detect infinite loops during
1817           constant expression evaluation.  The default is 262144 (1<<18).
1818
1819       -fdeduce-init-list
1820           Enable deduction of a template type parameter as
1821           "std::initializer_list" from a brace-enclosed initializer list,
1822           i.e.
1823
1824                   template <class T> auto forward(T t) -> decltype (realfn (t))
1825                   {
1826                     return realfn (t);
1827                   }
1828
1829                   void f()
1830                   {
1831                     forward({1,2}); // call forward<std::initializer_list<int>>
1832                   }
1833
1834           This deduction was implemented as a possible extension to the
1835           originally proposed semantics for the C++11 standard, but was not
1836           part of the final standard, so it is disabled by default.  This
1837           option is deprecated, and may be removed in a future version of
1838           G++.
1839
1840       -ffriend-injection
1841           Inject friend functions into the enclosing namespace, so that they
1842           are visible outside the scope of the class in which they are
1843           declared.  Friend functions were documented to work this way in the
1844           old Annotated C++ Reference Manual.  However, in ISO C++ a friend
1845           function that is not declared in an enclosing scope can only be
1846           found using argument dependent lookup.  GCC defaults to the
1847           standard behavior.
1848
1849           This option is deprecated and will be removed.
1850
1851       -fno-elide-constructors
1852           The C++ standard allows an implementation to omit creating a
1853           temporary that is only used to initialize another object of the
1854           same type.  Specifying this option disables that optimization, and
1855           forces G++ to call the copy constructor in all cases.  This option
1856           also causes G++ to call trivial member functions which otherwise
1857           would be expanded inline.
1858
1859           In C++17, the compiler is required to omit these temporaries, but
1860           this option still affects trivial member functions.
1861
1862       -fno-enforce-eh-specs
1863           Don't generate code to check for violation of exception
1864           specifications at run time.  This option violates the C++ standard,
1865           but may be useful for reducing code size in production builds, much
1866           like defining "NDEBUG".  This does not give user code permission to
1867           throw exceptions in violation of the exception specifications; the
1868           compiler still optimizes based on the specifications, so throwing
1869           an unexpected exception results in undefined behavior at run time.
1870
1871       -fextern-tls-init
1872       -fno-extern-tls-init
1873           The C++11 and OpenMP standards allow "thread_local" and
1874           "threadprivate" variables to have dynamic (runtime) initialization.
1875           To support this, any use of such a variable goes through a wrapper
1876           function that performs any necessary initialization.  When the use
1877           and definition of the variable are in the same translation unit,
1878           this overhead can be optimized away, but when the use is in a
1879           different translation unit there is significant overhead even if
1880           the variable doesn't actually need dynamic initialization.  If the
1881           programmer can be sure that no use of the variable in a non-
1882           defining TU needs to trigger dynamic initialization (either because
1883           the variable is statically initialized, or a use of the variable in
1884           the defining TU will be executed before any uses in another TU),
1885           they can avoid this overhead with the -fno-extern-tls-init option.
1886
1887           On targets that support symbol aliases, the default is
1888           -fextern-tls-init.  On targets that do not support symbol aliases,
1889           the default is -fno-extern-tls-init.
1890
1891       -ffor-scope
1892       -fno-for-scope
1893           If -ffor-scope is specified, the scope of variables declared in a
1894           for-init-statement is limited to the "for" loop itself, as
1895           specified by the C++ standard.  If -fno-for-scope is specified, the
1896           scope of variables declared in a for-init-statement extends to the
1897           end of the enclosing scope, as was the case in old versions of G++,
1898           and other (traditional) implementations of C++.
1899
1900           This option is deprecated and the associated non-standard
1901           functionality will be removed.
1902
1903       -fno-gnu-keywords
1904           Do not recognize "typeof" as a keyword, so that code can use this
1905           word as an identifier.  You can use the keyword "__typeof__"
1906           instead.  This option is implied by the strict ISO C++ dialects:
1907           -ansi, -std=c++98, -std=c++11, etc.
1908
1909       -fno-implicit-templates
1910           Never emit code for non-inline templates that are instantiated
1911           implicitly (i.e. by use); only emit code for explicit
1912           instantiations.
1913
1914       -fno-implicit-inline-templates
1915           Don't emit code for implicit instantiations of inline templates,
1916           either.  The default is to handle inlines differently so that
1917           compiles with and without optimization need the same set of
1918           explicit instantiations.
1919
1920       -fno-implement-inlines
1921           To save space, do not emit out-of-line copies of inline functions
1922           controlled by "#pragma implementation".  This causes linker errors
1923           if these functions are not inlined everywhere they are called.
1924
1925       -fms-extensions
1926           Disable Wpedantic warnings about constructs used in MFC, such as
1927           implicit int and getting a pointer to member function via non-
1928           standard syntax.
1929
1930       -fnew-inheriting-ctors
1931           Enable the P0136 adjustment to the semantics of C++11 constructor
1932           inheritance.  This is part of C++17 but also considered to be a
1933           Defect Report against C++11 and C++14.  This flag is enabled by
1934           default unless -fabi-version=10 or lower is specified.
1935
1936       -fnew-ttp-matching
1937           Enable the P0522 resolution to Core issue 150, template template
1938           parameters and default arguments: this allows a template with
1939           default template arguments as an argument for a template template
1940           parameter with fewer template parameters.  This flag is enabled by
1941           default for -std=c++17.
1942
1943       -fno-nonansi-builtins
1944           Disable built-in declarations of functions that are not mandated by
1945           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
1946           "bzero", "conjf", and other related functions.
1947
1948       -fnothrow-opt
1949           Treat a "throw()" exception specification as if it were a
1950           "noexcept" specification to reduce or eliminate the text size
1951           overhead relative to a function with no exception specification.
1952           If the function has local variables of types with non-trivial
1953           destructors, the exception specification actually makes the
1954           function smaller because the EH cleanups for those variables can be
1955           optimized away.  The semantic effect is that an exception thrown
1956           out of a function with such an exception specification results in a
1957           call to "terminate" rather than "unexpected".
1958
1959       -fno-operator-names
1960           Do not treat the operator name keywords "and", "bitand", "bitor",
1961           "compl", "not", "or" and "xor" as synonyms as keywords.
1962
1963       -fno-optional-diags
1964           Disable diagnostics that the standard says a compiler does not need
1965           to issue.  Currently, the only such diagnostic issued by G++ is the
1966           one for a name having multiple meanings within a class.
1967
1968       -fpermissive
1969           Downgrade some diagnostics about nonconformant code from errors to
1970           warnings.  Thus, using -fpermissive allows some nonconforming code
1971           to compile.
1972
1973       -fno-pretty-templates
1974           When an error message refers to a specialization of a function
1975           template, the compiler normally prints the signature of the
1976           template followed by the template arguments and any typedefs or
1977           typenames in the signature (e.g. "void f(T) [with T = int]" rather
1978           than "void f(int)") so that it's clear which template is involved.
1979           When an error message refers to a specialization of a class
1980           template, the compiler omits any template arguments that match the
1981           default template arguments for that template.  If either of these
1982           behaviors make it harder to understand the error message rather
1983           than easier, you can use -fno-pretty-templates to disable them.
1984
1985       -frepo
1986           Enable automatic template instantiation at link time.  This option
1987           also implies -fno-implicit-templates.
1988
1989       -fno-rtti
1990           Disable generation of information about every class with virtual
1991           functions for use by the C++ run-time type identification features
1992           ("dynamic_cast" and "typeid").  If you don't use those parts of the
1993           language, you can save some space by using this flag.  Note that
1994           exception handling uses the same information, but G++ generates it
1995           as needed. The "dynamic_cast" operator can still be used for casts
1996           that do not require run-time type information, i.e. casts to "void
1997           *" or to unambiguous base classes.
1998
1999       -fsized-deallocation
2000           Enable the built-in global declarations
2001
2002                   void operator delete (void *, std::size_t) noexcept;
2003                   void operator delete[] (void *, std::size_t) noexcept;
2004
2005           as introduced in C++14.  This is useful for user-defined
2006           replacement deallocation functions that, for example, use the size
2007           of the object to make deallocation faster.  Enabled by default
2008           under -std=c++14 and above.  The flag -Wsized-deallocation warns
2009           about places that might want to add a definition.
2010
2011       -fstrict-enums
2012           Allow the compiler to optimize using the assumption that a value of
2013           enumerated type can only be one of the values of the enumeration
2014           (as defined in the C++ standard; basically, a value that can be
2015           represented in the minimum number of bits needed to represent all
2016           the enumerators).  This assumption may not be valid if the program
2017           uses a cast to convert an arbitrary integer value to the enumerated
2018           type.
2019
2020       -fstrong-eval-order
2021           Evaluate member access, array subscripting, and shift expressions
2022           in left-to-right order, and evaluate assignment in right-to-left
2023           order, as adopted for C++17.  Enabled by default with -std=c++17.
2024           -fstrong-eval-order=some enables just the ordering of member access
2025           and shift expressions, and is the default without -std=c++17.
2026
2027       -ftemplate-backtrace-limit=n
2028           Set the maximum number of template instantiation notes for a single
2029           warning or error to n.  The default value is 10.
2030
2031       -ftemplate-depth=n
2032           Set the maximum instantiation depth for template classes to n.  A
2033           limit on the template instantiation depth is needed to detect
2034           endless recursions during template class instantiation.  ANSI/ISO
2035           C++ conforming programs must not rely on a maximum depth greater
2036           than 17 (changed to 1024 in C++11).  The default value is 900, as
2037           the compiler can run out of stack space before hitting 1024 in some
2038           situations.
2039
2040       -fno-threadsafe-statics
2041           Do not emit the extra code to use the routines specified in the C++
2042           ABI for thread-safe initialization of local statics.  You can use
2043           this option to reduce code size slightly in code that doesn't need
2044           to be thread-safe.
2045
2046       -fuse-cxa-atexit
2047           Register destructors for objects with static storage duration with
2048           the "__cxa_atexit" function rather than the "atexit" function.
2049           This option is required for fully standards-compliant handling of
2050           static destructors, but only works if your C library supports
2051           "__cxa_atexit".
2052
2053       -fno-use-cxa-get-exception-ptr
2054           Don't use the "__cxa_get_exception_ptr" runtime routine.  This
2055           causes "std::uncaught_exception" to be incorrect, but is necessary
2056           if the runtime routine is not available.
2057
2058       -fvisibility-inlines-hidden
2059           This switch declares that the user does not attempt to compare
2060           pointers to inline functions or methods where the addresses of the
2061           two functions are taken in different shared objects.
2062
2063           The effect of this is that GCC may, effectively, mark inline
2064           methods with "__attribute__ ((visibility ("hidden")))" so that they
2065           do not appear in the export table of a DSO and do not require a PLT
2066           indirection when used within the DSO.  Enabling this option can
2067           have a dramatic effect on load and link times of a DSO as it
2068           massively reduces the size of the dynamic export table when the
2069           library makes heavy use of templates.
2070
2071           The behavior of this switch is not quite the same as marking the
2072           methods as hidden directly, because it does not affect static
2073           variables local to the function or cause the compiler to deduce
2074           that the function is defined in only one shared object.
2075
2076           You may mark a method as having a visibility explicitly to negate
2077           the effect of the switch for that method.  For example, if you do
2078           want to compare pointers to a particular inline method, you might
2079           mark it as having default visibility.  Marking the enclosing class
2080           with explicit visibility has no effect.
2081
2082           Explicitly instantiated inline methods are unaffected by this
2083           option as their linkage might otherwise cross a shared library
2084           boundary.
2085
2086       -fvisibility-ms-compat
2087           This flag attempts to use visibility settings to make GCC's C++
2088           linkage model compatible with that of Microsoft Visual Studio.
2089
2090           The flag makes these changes to GCC's linkage model:
2091
2092           1.  It sets the default visibility to "hidden", like
2093               -fvisibility=hidden.
2094
2095           2.  Types, but not their members, are not hidden by default.
2096
2097           3.  The One Definition Rule is relaxed for types without explicit
2098               visibility specifications that are defined in more than one
2099               shared object: those declarations are permitted if they are
2100               permitted when this option is not used.
2101
2102           In new code it is better to use -fvisibility=hidden and export
2103           those classes that are intended to be externally visible.
2104           Unfortunately it is possible for code to rely, perhaps
2105           accidentally, on the Visual Studio behavior.
2106
2107           Among the consequences of these changes are that static data
2108           members of the same type with the same name but defined in
2109           different shared objects are different, so changing one does not
2110           change the other; and that pointers to function members defined in
2111           different shared objects may not compare equal.  When this flag is
2112           given, it is a violation of the ODR to define types with the same
2113           name differently.
2114
2115       -fno-weak
2116           Do not use weak symbol support, even if it is provided by the
2117           linker.  By default, G++ uses weak symbols if they are available.
2118           This option exists only for testing, and should not be used by end-
2119           users; it results in inferior code and has no benefits.  This
2120           option may be removed in a future release of G++.
2121
2122       -nostdinc++
2123           Do not search for header files in the standard directories specific
2124           to C++, but do still search the other standard directories.  (This
2125           option is used when building the C++ library.)
2126
2127       In addition, these optimization, warning, and code generation options
2128       have meanings only for C++ programs:
2129
2130       -Wabi (C, Objective-C, C++ and Objective-C++ only)
2131           Warn when G++ it generates code that is probably not compatible
2132           with the vendor-neutral C++ ABI.  Since G++ now defaults to
2133           updating the ABI with each major release, normally -Wabi will warn
2134           only if there is a check added later in a release series for an ABI
2135           issue discovered since the initial release.  -Wabi will warn about
2136           more things if an older ABI version is selected (with
2137           -fabi-version=n).
2138
2139           -Wabi can also be used with an explicit version number to warn
2140           about compatibility with a particular -fabi-version level, e.g.
2141           -Wabi=2 to warn about changes relative to -fabi-version=2.
2142
2143           If an explicit version number is provided and -fabi-compat-version
2144           is not specified, the version number from this option is used for
2145           compatibility aliases.  If no explicit version number is provided
2146           with this option, but -fabi-compat-version is specified, that
2147           version number is used for ABI warnings.
2148
2149           Although an effort has been made to warn about all such cases,
2150           there are probably some cases that are not warned about, even
2151           though G++ is generating incompatible code.  There may also be
2152           cases where warnings are emitted even though the code that is
2153           generated is compatible.
2154
2155           You should rewrite your code to avoid these warnings if you are
2156           concerned about the fact that code generated by G++ may not be
2157           binary compatible with code generated by other compilers.
2158
2159           Known incompatibilities in -fabi-version=2 (which was the default
2160           from GCC 3.4 to 4.9) include:
2161
2162           *   A template with a non-type template parameter of reference type
2163               was mangled incorrectly:
2164
2165                       extern int N;
2166                       template <int &> struct S {};
2167                       void n (S<N>) {2}
2168
2169               This was fixed in -fabi-version=3.
2170
2171           *   SIMD vector types declared using "__attribute ((vector_size))"
2172               were mangled in a non-standard way that does not allow for
2173               overloading of functions taking vectors of different sizes.
2174
2175               The mangling was changed in -fabi-version=4.
2176
2177           *   "__attribute ((const))" and "noreturn" were mangled as type
2178               qualifiers, and "decltype" of a plain declaration was folded
2179               away.
2180
2181               These mangling issues were fixed in -fabi-version=5.
2182
2183           *   Scoped enumerators passed as arguments to a variadic function
2184               are promoted like unscoped enumerators, causing "va_arg" to
2185               complain.  On most targets this does not actually affect the
2186               parameter passing ABI, as there is no way to pass an argument
2187               smaller than "int".
2188
2189               Also, the ABI changed the mangling of template argument packs,
2190               "const_cast", "static_cast", prefix increment/decrement, and a
2191               class scope function used as a template argument.
2192
2193               These issues were corrected in -fabi-version=6.
2194
2195           *   Lambdas in default argument scope were mangled incorrectly, and
2196               the ABI changed the mangling of "nullptr_t".
2197
2198               These issues were corrected in -fabi-version=7.
2199
2200           *   When mangling a function type with function-cv-qualifiers, the
2201               un-qualified function type was incorrectly treated as a
2202               substitution candidate.
2203
2204               This was fixed in -fabi-version=8, the default for GCC 5.1.
2205
2206           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading
2207               to unaligned accesses.  Note that this did not affect the ABI
2208               of a function with a "nullptr_t" parameter, as parameters have
2209               a minimum alignment.
2210
2211               This was fixed in -fabi-version=9, the default for GCC 5.2.
2212
2213           *   Target-specific attributes that affect the identity of a type,
2214               such as ia32 calling conventions on a function type (stdcall,
2215               regparm, etc.), did not affect the mangled name, leading to
2216               name collisions when function pointers were used as template
2217               arguments.
2218
2219               This was fixed in -fabi-version=10, the default for GCC 6.1.
2220
2221           It also warns about psABI-related changes.  The known psABI changes
2222           at this point include:
2223
2224           *   For SysV/x86-64, unions with "long double" members are passed
2225               in memory as specified in psABI.  For example:
2226
2227                       union U {
2228                         long double ld;
2229                         int i;
2230                       };
2231
2232               "union U" is always passed in memory.
2233
2234       -Wabi-tag (C++ and Objective-C++ only)
2235           Warn when a type with an ABI tag is used in a context that does not
2236           have that ABI tag.  See C++ Attributes for more information about
2237           ABI tags.
2238
2239       -Wctor-dtor-privacy (C++ and Objective-C++ only)
2240           Warn when a class seems unusable because all the constructors or
2241           destructors in that class are private, and it has neither friends
2242           nor public static member functions.  Also warn if there are no non-
2243           private methods, and there's at least one private member function
2244           that isn't a constructor or destructor.
2245
2246       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
2247           Warn when "delete" is used to destroy an instance of a class that
2248           has virtual functions and non-virtual destructor. It is unsafe to
2249           delete an instance of a derived class through a pointer to a base
2250           class if the base class does not have a virtual destructor.  This
2251           warning is enabled by -Wall.
2252
2253       -Wliteral-suffix (C++ and Objective-C++ only)
2254           Warn when a string or character literal is followed by a ud-suffix
2255           which does not begin with an underscore.  As a conforming
2256           extension, GCC treats such suffixes as separate preprocessing
2257           tokens in order to maintain backwards compatibility with code that
2258           uses formatting macros from "<inttypes.h>".  For example:
2259
2260                   #define __STDC_FORMAT_MACROS
2261                   #include <inttypes.h>
2262                   #include <stdio.h>
2263
2264                   int main() {
2265                     int64_t i64 = 123;
2266                     printf("My int64: %" PRId64"\n", i64);
2267                   }
2268
2269           In this case, "PRId64" is treated as a separate preprocessing
2270           token.
2271
2272           Additionally, warn when a user-defined literal operator is declared
2273           with a literal suffix identifier that doesn't begin with an
2274           underscore. Literal suffix identifiers that don't begin with an
2275           underscore are reserved for future standardization.
2276
2277           This warning is enabled by default.
2278
2279       -Wlto-type-mismatch
2280           During the link-time optimization warn about type mismatches in
2281           global declarations from different compilation units.  Requires
2282           -flto to be enabled.  Enabled by default.
2283
2284       -Wno-narrowing (C++ and Objective-C++ only)
2285           For C++11 and later standards, narrowing conversions are diagnosed
2286           by default, as required by the standard.  A narrowing conversion
2287           from a constant produces an error, and a narrowing conversion from
2288           a non-constant produces a warning, but -Wno-narrowing suppresses
2289           the diagnostic.  Note that this does not affect the meaning of
2290           well-formed code; narrowing conversions are still considered ill-
2291           formed in SFINAE contexts.
2292
2293           With -Wnarrowing in C++98, warn when a narrowing conversion
2294           prohibited by C++11 occurs within { }, e.g.
2295
2296                   int i = { 2.2 }; // error: narrowing from double to int
2297
2298           This flag is included in -Wall and -Wc++11-compat.
2299
2300       -Wnoexcept (C++ and Objective-C++ only)
2301           Warn when a noexcept-expression evaluates to false because of a
2302           call to a function that does not have a non-throwing exception
2303           specification (i.e. "throw()" or "noexcept") but is known by the
2304           compiler to never throw an exception.
2305
2306       -Wnoexcept-type (C++ and Objective-C++ only)
2307           Warn if the C++17 feature making "noexcept" part of a function type
2308           changes the mangled name of a symbol relative to C++14.  Enabled by
2309           -Wabi and -Wc++17-compat.
2310
2311           As an example:
2312
2313                   template <class T> void f(T t) { t(); };
2314                   void g() noexcept;
2315                   void h() { f(g); }
2316
2317           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls
2318           "f<void(*)()noexcept>".
2319
2320       -Wclass-memaccess (C++ and Objective-C++ only)
2321           Warn when the destination of a call to a raw memory function such
2322           as "memset" or "memcpy" is an object of class type, and when
2323           writing into such an object might bypass the class non-trivial or
2324           deleted constructor or copy assignment, violate const-correctness
2325           or encapsulation, or corrupt virtual table pointers.  Modifying the
2326           representation of such objects may violate invariants maintained by
2327           member functions of the class.  For example, the call to "memset"
2328           below is undefined because it modifies a non-trivial class object
2329           and is, therefore, diagnosed.  The safe way to either initialize or
2330           clear the storage of objects of such types is by using the
2331           appropriate constructor or assignment operator, if one is
2332           available.
2333
2334                   std::string str = "abc";
2335                   memset (&str, 0, sizeof str);
2336
2337           The -Wclass-memaccess option is enabled by -Wall.  Explicitly
2338           casting the pointer to the class object to "void *" or to a type
2339           that can be safely accessed by the raw memory function suppresses
2340           the warning.
2341
2342       -Wnon-virtual-dtor (C++ and Objective-C++ only)
2343           Warn when a class has virtual functions and an accessible non-
2344           virtual destructor itself or in an accessible polymorphic base
2345           class, in which case it is possible but unsafe to delete an
2346           instance of a derived class through a pointer to the class itself
2347           or base class.  This warning is automatically enabled if -Weffc++
2348           is specified.
2349
2350       -Wregister (C++ and Objective-C++ only)
2351           Warn on uses of the "register" storage class specifier, except when
2352           it is part of the GNU Explicit Register Variables extension.  The
2353           use of the "register" keyword as storage class specifier has been
2354           deprecated in C++11 and removed in C++17.  Enabled by default with
2355           -std=c++17.
2356
2357       -Wreorder (C++ and Objective-C++ only)
2358           Warn when the order of member initializers given in the code does
2359           not match the order in which they must be executed.  For instance:
2360
2361                   struct A {
2362                     int i;
2363                     int j;
2364                     A(): j (0), i (1) { }
2365                   };
2366
2367           The compiler rearranges the member initializers for "i" and "j" to
2368           match the declaration order of the members, emitting a warning to
2369           that effect.  This warning is enabled by -Wall.
2370
2371       -fext-numeric-literals (C++ and Objective-C++ only)
2372           Accept imaginary, fixed-point, or machine-defined literal number
2373           suffixes as GNU extensions.  When this option is turned off these
2374           suffixes are treated as C++11 user-defined literal numeric
2375           suffixes.  This is on by default for all pre-C++11 dialects and all
2376           GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14.
2377           This option is off by default for ISO C++11 onwards (-std=c++11,
2378           ...).
2379
2380       The following -W... options are not affected by -Wall.
2381
2382       -Weffc++ (C++ and Objective-C++ only)
2383           Warn about violations of the following style guidelines from Scott
2384           Meyers' Effective C++ series of books:
2385
2386           *   Define a copy constructor and an assignment operator for
2387               classes with dynamically-allocated memory.
2388
2389           *   Prefer initialization to assignment in constructors.
2390
2391           *   Have "operator=" return a reference to *this.
2392
2393           *   Don't try to return a reference when you must return an object.
2394
2395           *   Distinguish between prefix and postfix forms of increment and
2396               decrement operators.
2397
2398           *   Never overload "&&", "||", or ",".
2399
2400           This option also enables -Wnon-virtual-dtor, which is also one of
2401           the effective C++ recommendations.  However, the check is extended
2402           to warn about the lack of virtual destructor in accessible non-
2403           polymorphic bases classes too.
2404
2405           When selecting this option, be aware that the standard library
2406           headers do not obey all of these guidelines; use grep -v to filter
2407           out those warnings.
2408
2409       -Wstrict-null-sentinel (C++ and Objective-C++ only)
2410           Warn about the use of an uncasted "NULL" as sentinel.  When
2411           compiling only with GCC this is a valid sentinel, as "NULL" is
2412           defined to "__null".  Although it is a null pointer constant rather
2413           than a null pointer, it is guaranteed to be of the same size as a
2414           pointer.  But this use is not portable across different compilers.
2415
2416       -Wno-non-template-friend (C++ and Objective-C++ only)
2417           Disable warnings when non-template friend functions are declared
2418           within a template.  In very old versions of GCC that predate
2419           implementation of the ISO standard, declarations such as friend int
2420           foo(int), where the name of the friend is an unqualified-id, could
2421           be interpreted as a particular specialization of a template
2422           function; the warning exists to diagnose compatibility problems,
2423           and is enabled by default.
2424
2425       -Wold-style-cast (C++ and Objective-C++ only)
2426           Warn if an old-style (C-style) cast to a non-void type is used
2427           within a C++ program.  The new-style casts ("dynamic_cast",
2428           "static_cast", "reinterpret_cast", and "const_cast") are less
2429           vulnerable to unintended effects and much easier to search for.
2430
2431       -Woverloaded-virtual (C++ and Objective-C++ only)
2432           Warn when a function declaration hides virtual functions from a
2433           base class.  For example, in:
2434
2435                   struct A {
2436                     virtual void f();
2437                   };
2438
2439                   struct B: public A {
2440                     void f(int);
2441                   };
2442
2443           the "A" class version of "f" is hidden in "B", and code like:
2444
2445                   B* b;
2446                   b->f();
2447
2448           fails to compile.
2449
2450       -Wno-pmf-conversions (C++ and Objective-C++ only)
2451           Disable the diagnostic for converting a bound pointer to member
2452           function to a plain pointer.
2453
2454       -Wsign-promo (C++ and Objective-C++ only)
2455           Warn when overload resolution chooses a promotion from unsigned or
2456           enumerated type to a signed type, over a conversion to an unsigned
2457           type of the same size.  Previous versions of G++ tried to preserve
2458           unsignedness, but the standard mandates the current behavior.
2459
2460       -Wtemplates (C++ and Objective-C++ only)
2461           Warn when a primary template declaration is encountered.  Some
2462           coding rules disallow templates, and this may be used to enforce
2463           that rule.  The warning is inactive inside a system header file,
2464           such as the STL, so one can still use the STL.  One may also
2465           instantiate or specialize templates.
2466
2467       -Wmultiple-inheritance (C++ and Objective-C++ only)
2468           Warn when a class is defined with multiple direct base classes.
2469           Some coding rules disallow multiple inheritance, and this may be
2470           used to enforce that rule.  The warning is inactive inside a system
2471           header file, such as the STL, so one can still use the STL.  One
2472           may also define classes that indirectly use multiple inheritance.
2473
2474       -Wvirtual-inheritance
2475           Warn when a class is defined with a virtual direct base class.
2476           Some coding rules disallow multiple inheritance, and this may be
2477           used to enforce that rule.  The warning is inactive inside a system
2478           header file, such as the STL, so one can still use the STL.  One
2479           may also define classes that indirectly use virtual inheritance.
2480
2481       -Wnamespaces
2482           Warn when a namespace definition is opened.  Some coding rules
2483           disallow namespaces, and this may be used to enforce that rule.
2484           The warning is inactive inside a system header file, such as the
2485           STL, so one can still use the STL.  One may also use using
2486           directives and qualified names.
2487
2488       -Wno-terminate (C++ and Objective-C++ only)
2489           Disable the warning about a throw-expression that will immediately
2490           result in a call to "terminate".
2491
2492   Options Controlling Objective-C and Objective-C++ Dialects
2493       (NOTE: This manual does not describe the Objective-C and Objective-C++
2494       languages themselves.
2495
2496       This section describes the command-line options that are only
2497       meaningful for Objective-C and Objective-C++ programs.  You can also
2498       use most of the language-independent GNU compiler options.  For
2499       example, you might compile a file some_class.m like this:
2500
2501               gcc -g -fgnu-runtime -O -c some_class.m
2502
2503       In this example, -fgnu-runtime is an option meant only for Objective-C
2504       and Objective-C++ programs; you can use the other options with any
2505       language supported by GCC.
2506
2507       Note that since Objective-C is an extension of the C language,
2508       Objective-C compilations may also use options specific to the C front-
2509       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
2510       use C++-specific options (e.g., -Wabi).
2511
2512       Here is a list of options that are only for compiling Objective-C and
2513       Objective-C++ programs:
2514
2515       -fconstant-string-class=class-name
2516           Use class-name as the name of the class to instantiate for each
2517           literal string specified with the syntax "@"..."".  The default
2518           class name is "NXConstantString" if the GNU runtime is being used,
2519           and "NSConstantString" if the NeXT runtime is being used (see
2520           below).  The -fconstant-cfstrings option, if also present,
2521           overrides the -fconstant-string-class setting and cause "@"...""
2522           literals to be laid out as constant CoreFoundation strings.
2523
2524       -fgnu-runtime
2525           Generate object code compatible with the standard GNU Objective-C
2526           runtime.  This is the default for most types of systems.
2527
2528       -fnext-runtime
2529           Generate output compatible with the NeXT runtime.  This is the
2530           default for NeXT-based systems, including Darwin and Mac OS X.  The
2531           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
2532           is used.
2533
2534       -fno-nil-receivers
2535           Assume that all Objective-C message dispatches ("[receiver
2536           message:arg]") in this translation unit ensure that the receiver is
2537           not "nil".  This allows for more efficient entry points in the
2538           runtime to be used.  This option is only available in conjunction
2539           with the NeXT runtime and ABI version 0 or 1.
2540
2541       -fobjc-abi-version=n
2542           Use version n of the Objective-C ABI for the selected runtime.
2543           This option is currently supported only for the NeXT runtime.  In
2544           that case, Version 0 is the traditional (32-bit) ABI without
2545           support for properties and other Objective-C 2.0 additions.
2546           Version 1 is the traditional (32-bit) ABI with support for
2547           properties and other Objective-C 2.0 additions.  Version 2 is the
2548           modern (64-bit) ABI.  If nothing is specified, the default is
2549           Version 0 on 32-bit target machines, and Version 2 on 64-bit target
2550           machines.
2551
2552       -fobjc-call-cxx-cdtors
2553           For each Objective-C class, check if any of its instance variables
2554           is a C++ object with a non-trivial default constructor.  If so,
2555           synthesize a special "- (id) .cxx_construct" instance method which
2556           runs non-trivial default constructors on any such instance
2557           variables, in order, and then return "self".  Similarly, check if
2558           any instance variable is a C++ object with a non-trivial
2559           destructor, and if so, synthesize a special "- (void)
2560           .cxx_destruct" method which runs all such default destructors, in
2561           reverse order.
2562
2563           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods
2564           thusly generated only operate on instance variables declared in the
2565           current Objective-C class, and not those inherited from
2566           superclasses.  It is the responsibility of the Objective-C runtime
2567           to invoke all such methods in an object's inheritance hierarchy.
2568           The "- (id) .cxx_construct" methods are invoked by the runtime
2569           immediately after a new object instance is allocated; the "- (void)
2570           .cxx_destruct" methods are invoked immediately before the runtime
2571           deallocates an object instance.
2572
2573           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
2574           later has support for invoking the "- (id) .cxx_construct" and "-
2575           (void) .cxx_destruct" methods.
2576
2577       -fobjc-direct-dispatch
2578           Allow fast jumps to the message dispatcher.  On Darwin this is
2579           accomplished via the comm page.
2580
2581       -fobjc-exceptions
2582           Enable syntactic support for structured exception handling in
2583           Objective-C, similar to what is offered by C++.  This option is
2584           required to use the Objective-C keywords @try, @throw, @catch,
2585           @finally and @synchronized.  This option is available with both the
2586           GNU runtime and the NeXT runtime (but not available in conjunction
2587           with the NeXT runtime on Mac OS X 10.2 and earlier).
2588
2589       -fobjc-gc
2590           Enable garbage collection (GC) in Objective-C and Objective-C++
2591           programs.  This option is only available with the NeXT runtime; the
2592           GNU runtime has a different garbage collection implementation that
2593           does not require special compiler flags.
2594
2595       -fobjc-nilcheck
2596           For the NeXT runtime with version 2 of the ABI, check for a nil
2597           receiver in method invocations before doing the actual method call.
2598           This is the default and can be disabled using -fno-objc-nilcheck.
2599           Class methods and super calls are never checked for nil in this way
2600           no matter what this flag is set to.  Currently this flag does
2601           nothing when the GNU runtime, or an older version of the NeXT
2602           runtime ABI, is used.
2603
2604       -fobjc-std=objc1
2605           Conform to the language syntax of Objective-C 1.0, the language
2606           recognized by GCC 4.0.  This only affects the Objective-C additions
2607           to the C/C++ language; it does not affect conformance to C/C++
2608           standards, which is controlled by the separate C/C++ dialect option
2609           flags.  When this option is used with the Objective-C or
2610           Objective-C++ compiler, any Objective-C syntax that is not
2611           recognized by GCC 4.0 is rejected.  This is useful if you need to
2612           make sure that your Objective-C code can be compiled with older
2613           versions of GCC.
2614
2615       -freplace-objc-classes
2616           Emit a special marker instructing ld(1) not to statically link in
2617           the resulting object file, and allow dyld(1) to load it in at run
2618           time instead.  This is used in conjunction with the Fix-and-
2619           Continue debugging mode, where the object file in question may be
2620           recompiled and dynamically reloaded in the course of program
2621           execution, without the need to restart the program itself.
2622           Currently, Fix-and-Continue functionality is only available in
2623           conjunction with the NeXT runtime on Mac OS X 10.3 and later.
2624
2625       -fzero-link
2626           When compiling for the NeXT runtime, the compiler ordinarily
2627           replaces calls to "objc_getClass("...")" (when the name of the
2628           class is known at compile time) with static class references that
2629           get initialized at load time, which improves run-time performance.
2630           Specifying the -fzero-link flag suppresses this behavior and causes
2631           calls to "objc_getClass("...")"  to be retained.  This is useful in
2632           Zero-Link debugging mode, since it allows for individual class
2633           implementations to be modified during program execution.  The GNU
2634           runtime currently always retains calls to "objc_get_class("...")"
2635           regardless of command-line options.
2636
2637       -fno-local-ivars
2638           By default instance variables in Objective-C can be accessed as if
2639           they were local variables from within the methods of the class
2640           they're declared in.  This can lead to shadowing between instance
2641           variables and other variables declared either locally inside a
2642           class method or globally with the same name.  Specifying the
2643           -fno-local-ivars flag disables this behavior thus avoiding variable
2644           shadowing issues.
2645
2646       -fivar-visibility=[public|protected|private|package]
2647           Set the default instance variable visibility to the specified
2648           option so that instance variables declared outside the scope of any
2649           access modifier directives default to the specified visibility.
2650
2651       -gen-decls
2652           Dump interface declarations for all classes seen in the source file
2653           to a file named sourcename.decl.
2654
2655       -Wassign-intercept (Objective-C and Objective-C++ only)
2656           Warn whenever an Objective-C assignment is being intercepted by the
2657           garbage collector.
2658
2659       -Wno-protocol (Objective-C and Objective-C++ only)
2660           If a class is declared to implement a protocol, a warning is issued
2661           for every method in the protocol that is not implemented by the
2662           class.  The default behavior is to issue a warning for every method
2663           not explicitly implemented in the class, even if a method
2664           implementation is inherited from the superclass.  If you use the
2665           -Wno-protocol option, then methods inherited from the superclass
2666           are considered to be implemented, and no warning is issued for
2667           them.
2668
2669       -Wselector (Objective-C and Objective-C++ only)
2670           Warn if multiple methods of different types for the same selector
2671           are found during compilation.  The check is performed on the list
2672           of methods in the final stage of compilation.  Additionally, a
2673           check is performed for each selector appearing in a
2674           "@selector(...)"  expression, and a corresponding method for that
2675           selector has been found during compilation.  Because these checks
2676           scan the method table only at the end of compilation, these
2677           warnings are not produced if the final stage of compilation is not
2678           reached, for example because an error is found during compilation,
2679           or because the -fsyntax-only option is being used.
2680
2681       -Wstrict-selector-match (Objective-C and Objective-C++ only)
2682           Warn if multiple methods with differing argument and/or return
2683           types are found for a given selector when attempting to send a
2684           message using this selector to a receiver of type "id" or "Class".
2685           When this flag is off (which is the default behavior), the compiler
2686           omits such warnings if any differences found are confined to types
2687           that share the same size and alignment.
2688
2689       -Wundeclared-selector (Objective-C and Objective-C++ only)
2690           Warn if a "@selector(...)" expression referring to an undeclared
2691           selector is found.  A selector is considered undeclared if no
2692           method with that name has been declared before the "@selector(...)"
2693           expression, either explicitly in an @interface or @protocol
2694           declaration, or implicitly in an @implementation section.  This
2695           option always performs its checks as soon as a "@selector(...)"
2696           expression is found, while -Wselector only performs its checks in
2697           the final stage of compilation.  This also enforces the coding
2698           style convention that methods and selectors must be declared before
2699           being used.
2700
2701       -print-objc-runtime-info
2702           Generate C header describing the largest structure that is passed
2703           by value, if any.
2704
2705   Options to Control Diagnostic Messages Formatting
2706       Traditionally, diagnostic messages have been formatted irrespective of
2707       the output device's aspect (e.g. its width, ...).  You can use the
2708       options described below to control the formatting algorithm for
2709       diagnostic messages, e.g. how many characters per line, how often
2710       source location information should be reported.  Note that some
2711       language front ends may not honor these options.
2712
2713       -fmessage-length=n
2714           Try to format error messages so that they fit on lines of about n
2715           characters.  If n is zero, then no line-wrapping is done; each
2716           error message appears on a single line.  This is the default for
2717           all front ends.
2718
2719       -fdiagnostics-show-location=once
2720           Only meaningful in line-wrapping mode.  Instructs the diagnostic
2721           messages reporter to emit source location information once; that
2722           is, in case the message is too long to fit on a single physical
2723           line and has to be wrapped, the source location won't be emitted
2724           (as prefix) again, over and over, in subsequent continuation lines.
2725           This is the default behavior.
2726
2727       -fdiagnostics-show-location=every-line
2728           Only meaningful in line-wrapping mode.  Instructs the diagnostic
2729           messages reporter to emit the same source location information (as
2730           prefix) for physical lines that result from the process of breaking
2731           a message which is too long to fit on a single line.
2732
2733       -fdiagnostics-color[=WHEN]
2734       -fno-diagnostics-color
2735           Use color in diagnostics.  WHEN is never, always, or auto.  The
2736           default depends on how the compiler has been configured, it can be
2737           any of the above WHEN options or also never if GCC_COLORS
2738           environment variable isn't present in the environment, and auto
2739           otherwise.  auto means to use color only when the standard error is
2740           a terminal.  The forms -fdiagnostics-color and
2741           -fno-diagnostics-color are aliases for -fdiagnostics-color=always
2742           and -fdiagnostics-color=never, respectively.
2743
2744           The colors are defined by the environment variable GCC_COLORS.  Its
2745           value is a colon-separated list of capabilities and Select Graphic
2746           Rendition (SGR) substrings. SGR commands are interpreted by the
2747           terminal or terminal emulator.  (See the section in the
2748           documentation of your text terminal for permitted values and their
2749           meanings as character attributes.)  These substring values are
2750           integers in decimal representation and can be concatenated with
2751           semicolons.  Common values to concatenate include 1 for bold, 4 for
2752           underline, 5 for blink, 7 for inverse, 39 for default foreground
2753           color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode
2754           foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color
2755           modes foreground colors, 49 for default background color, 40 to 47
2756           for background colors, 100 to 107 for 16-color mode background
2757           colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
2758           background colors.
2759
2760           The default GCC_COLORS is
2761
2762                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
2763                   quote=01:fixit-insert=32:fixit-delete=31:\
2764                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
2765                   type-diff=01;32
2766
2767           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
2768           32 is green, 34 is blue, 01 is bold, and 31 is red.  Setting
2769           GCC_COLORS to the empty string disables colors.  Supported
2770           capabilities are as follows.
2771
2772           "error="
2773               SGR substring for error: markers.
2774
2775           "warning="
2776               SGR substring for warning: markers.
2777
2778           "note="
2779               SGR substring for note: markers.
2780
2781           "range1="
2782               SGR substring for first additional range.
2783
2784           "range2="
2785               SGR substring for second additional range.
2786
2787           "locus="
2788               SGR substring for location information, file:line or
2789               file:line:column etc.
2790
2791           "quote="
2792               SGR substring for information printed within quotes.
2793
2794           "fixit-insert="
2795               SGR substring for fix-it hints suggesting text to be inserted
2796               or replaced.
2797
2798           "fixit-delete="
2799               SGR substring for fix-it hints suggesting text to be deleted.
2800
2801           "diff-filename="
2802               SGR substring for filename headers within generated patches.
2803
2804           "diff-hunk="
2805               SGR substring for the starts of hunks within generated patches.
2806
2807           "diff-delete="
2808               SGR substring for deleted lines within generated patches.
2809
2810           "diff-insert="
2811               SGR substring for inserted lines within generated patches.
2812
2813           "type-diff="
2814               SGR substring for highlighting mismatching types within
2815               template arguments in the C++ frontend.
2816
2817       -fno-diagnostics-show-option
2818           By default, each diagnostic emitted includes text indicating the
2819           command-line option that directly controls the diagnostic (if such
2820           an option is known to the diagnostic machinery).  Specifying the
2821           -fno-diagnostics-show-option flag suppresses that behavior.
2822
2823       -fno-diagnostics-show-caret
2824           By default, each diagnostic emitted includes the original source
2825           line and a caret ^ indicating the column.  This option suppresses
2826           this information.  The source line is truncated to n characters, if
2827           the -fmessage-length=n option is given.  When the output is done to
2828           the terminal, the width is limited to the width given by the
2829           COLUMNS environment variable or, if not set, to the terminal width.
2830
2831       -fdiagnostics-parseable-fixits
2832           Emit fix-it hints in a machine-parseable format, suitable for
2833           consumption by IDEs.  For each fix-it, a line will be printed after
2834           the relevant diagnostic, starting with the string "fix-it:".  For
2835           example:
2836
2837                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"
2838
2839           The location is expressed as a half-open range, expressed as a
2840           count of bytes, starting at byte 1 for the initial column.  In the
2841           above example, bytes 3 through 20 of line 45 of "test.c" are to be
2842           replaced with the given string:
2843
2844                   00000000011111111112222222222
2845                   12345678901234567890123456789
2846                     gtk_widget_showall (dlg);
2847                     ^^^^^^^^^^^^^^^^^^
2848                     gtk_widget_show_all
2849
2850           The filename and replacement string escape backslash as "\\", tab
2851           as "\t", newline as "\n", double quotes as "\"", non-printable
2852           characters as octal (e.g. vertical tab as "\013").
2853
2854           An empty replacement string indicates that the given range is to be
2855           removed.  An empty range (e.g. "45:3-45:3") indicates that the
2856           string is to be inserted at the given position.
2857
2858       -fdiagnostics-generate-patch
2859           Print fix-it hints to stderr in unified diff format, after any
2860           diagnostics are printed.  For example:
2861
2862                   --- test.c
2863                   +++ test.c
2864                   @ -42,5 +42,5 @
2865
2866                    void show_cb(GtkDialog *dlg)
2867                    {
2868                   -  gtk_widget_showall(dlg);
2869                   +  gtk_widget_show_all(dlg);
2870                    }
2871
2872           The diff may or may not be colorized, following the same rules as
2873           for diagnostics (see -fdiagnostics-color).
2874
2875       -fdiagnostics-show-template-tree
2876           In the C++ frontend, when printing diagnostics showing mismatching
2877           template types, such as:
2878
2879                     could not convert 'std::map<int, std::vector<double> >()'
2880                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
2881
2882           the -fdiagnostics-show-template-tree flag enables printing a tree-
2883           like structure showing the common and differing parts of the types,
2884           such as:
2885
2886                     map<
2887                       [...],
2888                       vector<
2889                         [double != float]>>
2890
2891           The parts that differ are highlighted with color ("double" and
2892           "float" in this case).
2893
2894       -fno-elide-type
2895           By default when the C++ frontend prints diagnostics showing
2896           mismatching template types, common parts of the types are printed
2897           as "[...]" to simplify the error message.  For example:
2898
2899                     could not convert 'std::map<int, std::vector<double> >()'
2900                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
2901
2902           Specifying the -fno-elide-type flag suppresses that behavior.  This
2903           flag also affects the output of the
2904           -fdiagnostics-show-template-tree flag.
2905
2906       -fno-show-column
2907           Do not print column numbers in diagnostics.  This may be necessary
2908           if diagnostics are being scanned by a program that does not
2909           understand the column numbers, such as dejagnu.
2910
2911   Options to Request or Suppress Warnings
2912       Warnings are diagnostic messages that report constructions that are not
2913       inherently erroneous but that are risky or suggest there may have been
2914       an error.
2915
2916       The following language-independent options do not enable specific
2917       warnings but control the kinds of diagnostics produced by GCC.
2918
2919       -fsyntax-only
2920           Check the code for syntax errors, but don't do anything beyond
2921           that.
2922
2923       -fmax-errors=n
2924           Limits the maximum number of error messages to n, at which point
2925           GCC bails out rather than attempting to continue processing the
2926           source code.  If n is 0 (the default), there is no limit on the
2927           number of error messages produced.  If -Wfatal-errors is also
2928           specified, then -Wfatal-errors takes precedence over this option.
2929
2930       -w  Inhibit all warning messages.
2931
2932       -Werror
2933           Make all warnings into errors.
2934
2935       -Werror=
2936           Make the specified warning into an error.  The specifier for a
2937           warning is appended; for example -Werror=switch turns the warnings
2938           controlled by -Wswitch into errors.  This switch takes a negative
2939           form, to be used to negate -Werror for specific warnings; for
2940           example -Wno-error=switch makes -Wswitch warnings not be errors,
2941           even when -Werror is in effect.
2942
2943           The warning message for each controllable warning includes the
2944           option that controls the warning.  That option can then be used
2945           with -Werror= and -Wno-error= as described above.  (Printing of the
2946           option in the warning message can be disabled using the
2947           -fno-diagnostics-show-option flag.)
2948
2949           Note that specifying -Werror=foo automatically implies -Wfoo.
2950           However, -Wno-error=foo does not imply anything.
2951
2952       -Wfatal-errors
2953           This option causes the compiler to abort compilation on the first
2954           error occurred rather than trying to keep going and printing
2955           further error messages.
2956
2957       You can request many specific warnings with options beginning with -W,
2958       for example -Wimplicit to request warnings on implicit declarations.
2959       Each of these specific warning options also has a negative form
2960       beginning -Wno- to turn off warnings; for example, -Wno-implicit.  This
2961       manual lists only one of the two forms, whichever is not the default.
2962       For further language-specific options also refer to C++ Dialect Options
2963       and Objective-C and Objective-C++ Dialect Options.
2964
2965       Some options, such as -Wall and -Wextra, turn on other options, such as
2966       -Wunused, which may turn on further options, such as -Wunused-value.
2967       The combined effect of positive and negative forms is that more
2968       specific options have priority over less specific ones, independently
2969       of their position in the command-line. For options of the same
2970       specificity, the last one takes effect. Options enabled or disabled via
2971       pragmas take effect as if they appeared at the end of the command-line.
2972
2973       When an unrecognized warning option is requested (e.g.,
2974       -Wunknown-warning), GCC emits a diagnostic stating that the option is
2975       not recognized.  However, if the -Wno- form is used, the behavior is
2976       slightly different: no diagnostic is produced for -Wno-unknown-warning
2977       unless other diagnostics are being produced.  This allows the use of
2978       new -Wno- options with old compilers, but if something goes wrong, the
2979       compiler warns that an unrecognized option is present.
2980
2981       -Wpedantic
2982       -pedantic
2983           Issue all the warnings demanded by strict ISO C and ISO C++; reject
2984           all programs that use forbidden extensions, and some other programs
2985           that do not follow ISO C and ISO C++.  For ISO C, follows the
2986           version of the ISO C standard specified by any -std option used.
2987
2988           Valid ISO C and ISO C++ programs should compile properly with or
2989           without this option (though a rare few require -ansi or a -std
2990           option specifying the required version of ISO C).  However, without
2991           this option, certain GNU extensions and traditional C and C++
2992           features are supported as well.  With this option, they are
2993           rejected.
2994
2995           -Wpedantic does not cause warning messages for use of the alternate
2996           keywords whose names begin and end with __.  Pedantic warnings are
2997           also disabled in the expression that follows "__extension__".
2998           However, only system header files should use these escape routes;
2999           application programs should avoid them.
3000
3001           Some users try to use -Wpedantic to check programs for strict ISO C
3002           conformance.  They soon find that it does not do quite what they
3003           want: it finds some non-ISO practices, but not all---only those for
3004           which ISO C requires a diagnostic, and some others for which
3005           diagnostics have been added.
3006
3007           A feature to report any failure to conform to ISO C might be useful
3008           in some instances, but would require considerable additional work
3009           and would be quite different from -Wpedantic.  We don't have plans
3010           to support such a feature in the near future.
3011
3012           Where the standard specified with -std represents a GNU extended
3013           dialect of C, such as gnu90 or gnu99, there is a corresponding base
3014           standard, the version of ISO C on which the GNU extended dialect is
3015           based.  Warnings from -Wpedantic are given where they are required
3016           by the base standard.  (It does not make sense for such warnings to
3017           be given only for features not in the specified GNU C dialect,
3018           since by definition the GNU dialects of C include all features the
3019           compiler supports with the given option, and there would be nothing
3020           to warn about.)
3021
3022       -pedantic-errors
3023           Give an error whenever the base standard (see -Wpedantic) requires
3024           a diagnostic, in some cases where there is undefined behavior at
3025           compile-time and in some other cases that do not prevent
3026           compilation of programs that are valid according to the standard.
3027           This is not equivalent to -Werror=pedantic, since there are errors
3028           enabled by this option and not enabled by the latter and vice
3029           versa.
3030
3031       -Wall
3032           This enables all the warnings about constructions that some users
3033           consider questionable, and that are easy to avoid (or modify to
3034           prevent the warning), even in conjunction with macros.  This also
3035           enables some language-specific warnings described in C++ Dialect
3036           Options and Objective-C and Objective-C++ Dialect Options.
3037
3038           -Wall turns on the following warning flags:
3039
3040           -Waddress -Warray-bounds=1 (only with -O2) -Wbool-compare
3041           -Wbool-operation -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++
3042           and Objective-C++ only) -Wchar-subscripts -Wcomment
3043           -Wduplicate-decl-specifier (C and Objective-C only) -Wenum-compare
3044           (in C/ObjC; this is on by default in C++) -Wformat
3045           -Wint-in-bool-context -Wimplicit (C and Objective-C only)
3046           -Wimplicit-int (C and Objective-C only)
3047           -Wimplicit-function-declaration (C and Objective-C only)
3048           -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only
3049           for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized
3050           -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation
3051           (only for C/C++) -Wmissing-attributes -Wmissing-braces (only for
3052           C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++)
3053           -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses
3054           -Wpointer-sign -Wreorder -Wrestrict -Wreturn-type -Wsequence-point
3055           -Wsign-compare (only in C++) -Wsizeof-pointer-div
3056           -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1
3057           -Wstringop-truncation -Wswitch -Wtautological-compare -Wtrigraphs
3058           -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label
3059           -Wunused-value -Wunused-variable -Wvolatile-register-var
3060
3061           Note that some warning flags are not implied by -Wall.  Some of
3062           them warn about constructions that users generally do not consider
3063           questionable, but which occasionally you might wish to check for;
3064           others warn about constructions that are necessary or hard to avoid
3065           in some cases, and there is no simple way to modify the code to
3066           suppress the warning. Some of them are enabled by -Wextra but many
3067           of them must be enabled individually.
3068
3069       -Wextra
3070           This enables some extra warning flags that are not enabled by
3071           -Wall. (This option used to be called -W.  The older name is still
3072           supported, but the newer name is more descriptive.)
3073
3074           -Wclobbered -Wcast-function-type -Wempty-body -Wignored-qualifiers
3075           -Wimplicit-fallthrough=3 -Wmissing-field-initializers
3076           -Wmissing-parameter-type (C only) -Wold-style-declaration (C only)
3077           -Woverride-init -Wsign-compare (C only) -Wtype-limits
3078           -Wuninitialized -Wshift-negative-value (in C++03 and in C99 and
3079           newer) -Wunused-parameter (only with -Wunused or -Wall)
3080           -Wunused-but-set-parameter (only with -Wunused or -Wall)
3081
3082           The option -Wextra also prints warning messages for the following
3083           cases:
3084
3085           *   A pointer is compared against integer zero with "<", "<=", ">",
3086               or ">=".
3087
3088           *   (C++ only) An enumerator and a non-enumerator both appear in a
3089               conditional expression.
3090
3091           *   (C++ only) Ambiguous virtual bases.
3092
3093           *   (C++ only) Subscripting an array that has been declared
3094               "register".
3095
3096           *   (C++ only) Taking the address of a variable that has been
3097               declared "register".
3098
3099           *   (C++ only) A base class is not initialized in the copy
3100               constructor of a derived class.
3101
3102       -Wchar-subscripts
3103           Warn if an array subscript has type "char".  This is a common cause
3104           of error, as programmers often forget that this type is signed on
3105           some machines.  This warning is enabled by -Wall.
3106
3107       -Wchkp
3108           Warn about an invalid memory access that is found by Pointer Bounds
3109           Checker (-fcheck-pointer-bounds).
3110
3111       -Wno-coverage-mismatch
3112           Warn if feedback profiles do not match when using the -fprofile-use
3113           option.  If a source file is changed between compiling with
3114           -fprofile-gen and with -fprofile-use, the files with the profile
3115           feedback can fail to match the source file and GCC cannot use the
3116           profile feedback information.  By default, this warning is enabled
3117           and is treated as an error.  -Wno-coverage-mismatch can be used to
3118           disable the warning or -Wno-error=coverage-mismatch can be used to
3119           disable the error.  Disabling the error for this warning can result
3120           in poorly optimized code and is useful only in the case of very
3121           minor changes such as bug fixes to an existing code-base.
3122           Completely disabling the warning is not recommended.
3123
3124       -Wno-cpp
3125           (C, Objective-C, C++, Objective-C++ and Fortran only)
3126
3127           Suppress warning messages emitted by "#warning" directives.
3128
3129       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
3130           Give a warning when a value of type "float" is implicitly promoted
3131           to "double".  CPUs with a 32-bit "single-precision" floating-point
3132           unit implement "float" in hardware, but emulate "double" in
3133           software.  On such a machine, doing computations using "double"
3134           values is much more expensive because of the overhead required for
3135           software emulation.
3136
3137           It is easy to accidentally do computations with "double" because
3138           floating-point literals are implicitly of type "double".  For
3139           example, in:
3140
3141                   float area(float radius)
3142                   {
3143                      return 3.14159 * radius * radius;
3144                   }
3145
3146           the compiler performs the entire computation with "double" because
3147           the floating-point literal is a "double".
3148
3149       -Wduplicate-decl-specifier (C and Objective-C only)
3150           Warn if a declaration has duplicate "const", "volatile", "restrict"
3151           or "_Atomic" specifier.  This warning is enabled by -Wall.
3152
3153       -Wformat
3154       -Wformat=n
3155           Check calls to "printf" and "scanf", etc., to make sure that the
3156           arguments supplied have types appropriate to the format string
3157           specified, and that the conversions specified in the format string
3158           make sense.  This includes standard functions, and others specified
3159           by format attributes, in the "printf", "scanf", "strftime" and
3160           "strfmon" (an X/Open extension, not in the C standard) families (or
3161           other target-specific families).  Which functions are checked
3162           without format attributes having been specified depends on the
3163           standard version selected, and such checks of functions without the
3164           attribute specified are disabled by -ffreestanding or -fno-builtin.
3165
3166           The formats are checked against the format features supported by
3167           GNU libc version 2.2.  These include all ISO C90 and C99 features,
3168           as well as features from the Single Unix Specification and some BSD
3169           and GNU extensions.  Other library implementations may not support
3170           all these features; GCC does not support warning about features
3171           that go beyond a particular library's limitations.  However, if
3172           -Wpedantic is used with -Wformat, warnings are given about format
3173           features not in the selected standard version (but not for
3174           "strfmon" formats, since those are not in any version of the C
3175           standard).
3176
3177           -Wformat=1
3178           -Wformat
3179               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is
3180               equivalent to -Wformat=0.  Since -Wformat also checks for null
3181               format arguments for several functions, -Wformat also implies
3182               -Wnonnull.  Some aspects of this level of format checking can
3183               be disabled by the options: -Wno-format-contains-nul,
3184               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat
3185               is enabled by -Wall.
3186
3187           -Wno-format-contains-nul
3188               If -Wformat is specified, do not warn about format strings that
3189               contain NUL bytes.
3190
3191           -Wno-format-extra-args
3192               If -Wformat is specified, do not warn about excess arguments to
3193               a "printf" or "scanf" format function.  The C standard
3194               specifies that such arguments are ignored.
3195
3196               Where the unused arguments lie between used arguments that are
3197               specified with $ operand number specifications, normally
3198               warnings are still given, since the implementation could not
3199               know what type to pass to "va_arg" to skip the unused
3200               arguments.  However, in the case of "scanf" formats, this
3201               option suppresses the warning if the unused arguments are all
3202               pointers, since the Single Unix Specification says that such
3203               unused arguments are allowed.
3204
3205           -Wformat-overflow
3206           -Wformat-overflow=level
3207               Warn about calls to formatted input/output functions such as
3208               "sprintf" and "vsprintf" that might overflow the destination
3209               buffer.  When the exact number of bytes written by a format
3210               directive cannot be determined at compile-time it is estimated
3211               based on heuristics that depend on the level argument and on
3212               optimization.  While enabling optimization will in most cases
3213               improve the accuracy of the warning, it may also result in
3214               false positives.
3215
3216               -Wformat-overflow
3217               -Wformat-overflow=1
3218                   Level 1 of -Wformat-overflow enabled by -Wformat employs a
3219                   conservative approach that warns only about calls that most
3220                   likely overflow the buffer.  At this level, numeric
3221                   arguments to format directives with unknown values are
3222                   assumed to have the value of one, and strings of unknown
3223                   length to be empty.  Numeric arguments that are known to be
3224                   bounded to a subrange of their type, or string arguments
3225                   whose output is bounded either by their directive's
3226                   precision or by a finite set of string literals, are
3227                   assumed to take on the value within the range that results
3228                   in the most bytes on output.  For example, the call to
3229                   "sprintf" below is diagnosed because even with both a and b
3230                   equal to zero, the terminating NUL character ('\0')
3231                   appended by the function to the destination buffer will be
3232                   written past its end.  Increasing the size of the buffer by
3233                   a single byte is sufficient to avoid the warning, though it
3234                   may not be sufficient to avoid the overflow.
3235
3236                           void f (int a, int b)
3237                           {
3238                             char buf [13];
3239                             sprintf (buf, "a = %i, b = %i\n", a, b);
3240                           }
3241
3242               -Wformat-overflow=2
3243                   Level 2 warns also about calls that might overflow the
3244                   destination buffer given an argument of sufficient length
3245                   or magnitude.  At level 2, unknown numeric arguments are
3246                   assumed to have the minimum representable value for signed
3247                   types with a precision greater than 1, and the maximum
3248                   representable value otherwise.  Unknown string arguments
3249                   whose length cannot be assumed to be bounded either by the
3250                   directive's precision, or by a finite set of string
3251                   literals they may evaluate to, or the character array they
3252                   may point to, are assumed to be 1 character long.
3253
3254                   At level 2, the call in the example above is again
3255                   diagnosed, but this time because with a equal to a 32-bit
3256                   "INT_MIN" the first %i directive will write some of its
3257                   digits beyond the end of the destination buffer.  To make
3258                   the call safe regardless of the values of the two
3259                   variables, the size of the destination buffer must be
3260                   increased to at least 34 bytes.  GCC includes the minimum
3261                   size of the buffer in an informational note following the
3262                   warning.
3263
3264                   An alternative to increasing the size of the destination
3265                   buffer is to constrain the range of formatted values.  The
3266                   maximum length of string arguments can be bounded by
3267                   specifying the precision in the format directive.  When
3268                   numeric arguments of format directives can be assumed to be
3269                   bounded by less than the precision of their type, choosing
3270                   an appropriate length modifier to the format specifier will
3271                   reduce the required buffer size.  For example, if a and b
3272                   in the example above can be assumed to be within the
3273                   precision of the "short int" type then using either the %hi
3274                   format directive or casting the argument to "short" reduces
3275                   the maximum required size of the buffer to 24 bytes.
3276
3277                           void f (int a, int b)
3278                           {
3279                             char buf [23];
3280                             sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
3281                           }
3282
3283           -Wno-format-zero-length
3284               If -Wformat is specified, do not warn about zero-length
3285               formats.  The C standard specifies that zero-length formats are
3286               allowed.
3287
3288           -Wformat=2
3289               Enable -Wformat plus additional format checks.  Currently
3290               equivalent to -Wformat -Wformat-nonliteral -Wformat-security
3291               -Wformat-y2k.
3292
3293           -Wformat-nonliteral
3294               If -Wformat is specified, also warn if the format string is not
3295               a string literal and so cannot be checked, unless the format
3296               function takes its format arguments as a "va_list".
3297
3298           -Wformat-security
3299               If -Wformat is specified, also warn about uses of format
3300               functions that represent possible security problems.  At
3301               present, this warns about calls to "printf" and "scanf"
3302               functions where the format string is not a string literal and
3303               there are no format arguments, as in "printf (foo);".  This may
3304               be a security hole if the format string came from untrusted
3305               input and contains %n.  (This is currently a subset of what
3306               -Wformat-nonliteral warns about, but in future warnings may be
3307               added to -Wformat-security that are not included in
3308               -Wformat-nonliteral.)
3309
3310           -Wformat-signedness
3311               If -Wformat is specified, also warn if the format string
3312               requires an unsigned argument and the argument is signed and
3313               vice versa.
3314
3315           -Wformat-truncation
3316           -Wformat-truncation=level
3317               Warn about calls to formatted input/output functions such as
3318               "snprintf" and "vsnprintf" that might result in output
3319               truncation.  When the exact number of bytes written by a format
3320               directive cannot be determined at compile-time it is estimated
3321               based on heuristics that depend on the level argument and on
3322               optimization.  While enabling optimization will in most cases
3323               improve the accuracy of the warning, it may also result in
3324               false positives.  Except as noted otherwise, the option uses
3325               the same logic -Wformat-overflow.
3326
3327               -Wformat-truncation
3328               -Wformat-truncation=1
3329                   Level 1 of -Wformat-truncation enabled by -Wformat employs
3330                   a conservative approach that warns only about calls to
3331                   bounded functions whose return value is unused and that
3332                   will most likely result in output truncation.
3333
3334               -Wformat-truncation=2
3335                   Level 2 warns also about calls to bounded functions whose
3336                   return value is used and that might result in truncation
3337                   given an argument of sufficient length or magnitude.
3338
3339           -Wformat-y2k
3340               If -Wformat is specified, also warn about "strftime" formats
3341               that may yield only a two-digit year.
3342
3343       -Wnonnull
3344           Warn about passing a null pointer for arguments marked as requiring
3345           a non-null value by the "nonnull" function attribute.
3346
3347           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
3348           with the -Wno-nonnull option.
3349
3350       -Wnonnull-compare
3351           Warn when comparing an argument marked with the "nonnull" function
3352           attribute against null inside the function.
3353
3354           -Wnonnull-compare is included in -Wall.  It can be disabled with
3355           the -Wno-nonnull-compare option.
3356
3357       -Wnull-dereference
3358           Warn if the compiler detects paths that trigger erroneous or
3359           undefined behavior due to dereferencing a null pointer.  This
3360           option is only active when -fdelete-null-pointer-checks is active,
3361           which is enabled by optimizations in most targets.  The precision
3362           of the warnings depends on the optimization options used.
3363
3364       -Winit-self (C, C++, Objective-C and Objective-C++ only)
3365           Warn about uninitialized variables that are initialized with
3366           themselves.  Note this option can only be used with the
3367           -Wuninitialized option.
3368
3369           For example, GCC warns about "i" being uninitialized in the
3370           following snippet only when -Winit-self has been specified:
3371
3372                   int f()
3373                   {
3374                     int i = i;
3375                     return i;
3376                   }
3377
3378           This warning is enabled by -Wall in C++.
3379
3380       -Wimplicit-int (C and Objective-C only)
3381           Warn when a declaration does not specify a type.  This warning is
3382           enabled by -Wall.
3383
3384       -Wimplicit-function-declaration (C and Objective-C only)
3385           Give a warning whenever a function is used before being declared.
3386           In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by
3387           default and it is made into an error by -pedantic-errors. This
3388           warning is also enabled by -Wall.
3389
3390       -Wimplicit (C and Objective-C only)
3391           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
3392           warning is enabled by -Wall.
3393
3394       -Wimplicit-fallthrough
3395           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and
3396           -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0.
3397
3398       -Wimplicit-fallthrough=n
3399           Warn when a switch case falls through.  For example:
3400
3401                   switch (cond)
3402                     {
3403                     case 1:
3404                       a = 1;
3405                       break;
3406                     case 2:
3407                       a = 2;
3408                     case 3:
3409                       a = 3;
3410                       break;
3411                     }
3412
3413           This warning does not warn when the last statement of a case cannot
3414           fall through, e.g. when there is a return statement or a call to
3415           function declared with the noreturn attribute.
3416           -Wimplicit-fallthrough= also takes into account control flow
3417           statements, such as ifs, and only warns when appropriate.  E.g.
3418
3419                   switch (cond)
3420                     {
3421                     case 1:
3422                       if (i > 3) {
3423                         bar (5);
3424                         break;
3425                       } else if (i < 1) {
3426                         bar (0);
3427                       } else
3428                         return;
3429                     default:
3430                       ...
3431                     }
3432
3433           Since there are occasions where a switch case fall through is
3434           desirable, GCC provides an attribute, "__attribute__
3435           ((fallthrough))", that is to be used along with a null statement to
3436           suppress this warning that would normally occur:
3437
3438                   switch (cond)
3439                     {
3440                     case 1:
3441                       bar (0);
3442                       __attribute__ ((fallthrough));
3443                     default:
3444                       ...
3445                     }
3446
3447           C++17 provides a standard way to suppress the
3448           -Wimplicit-fallthrough warning using "[[fallthrough]];" instead of
3449           the GNU attribute.  In C++11 or C++14 users can use
3450           "[[gnu::fallthrough]];", which is a GNU extension.  Instead of
3451           these attributes, it is also possible to add a fallthrough comment
3452           to silence the warning.  The whole body of the C or C++ style
3453           comment should match the given regular expressions listed below.
3454           The option argument n specifies what kind of comments are accepted:
3455
3456           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
3457           *<-Wimplicit-fallthrough=1 matches ".*" regular>
3458               expression, any comment is used as fallthrough comment.
3459
3460           *<-Wimplicit-fallthrough=2 case insensitively matches>
3461               ".*falls?[ \t-]*thr(ough|u).*" regular expression.
3462
3463           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
3464               following regular expressions:
3465
3466               *<"-fallthrough">
3467               *<"@fallthrough@">
3468               *<"lint -fallthrough[ \t]*">
3469               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S |
3470               |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?">
3471               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s |
3472               |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?">
3473               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s |
3474               |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?">
3475           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
3476               following regular expressions:
3477
3478               *<"-fallthrough">
3479               *<"@fallthrough@">
3480               *<"lint -fallthrough[ \t]*">
3481               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
3482           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
3483               fallthrough comments, only attributes disable the warning.
3484
3485           The comment needs to be followed after optional whitespace and
3486           other comments by "case" or "default" keywords or by a user label
3487           that precedes some "case" or "default" label.
3488
3489                   switch (cond)
3490                     {
3491                     case 1:
3492                       bar (0);
3493                       /* FALLTHRU */
3494                     default:
3495                       ...
3496                     }
3497
3498           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.
3499
3500       -Wif-not-aligned (C, C++, Objective-C and Objective-C++ only)
3501           Control if warning triggered by the "warn_if_not_aligned" attribute
3502           should be issued.  This is enabled by default.  Use
3503           -Wno-if-not-aligned to disable it.
3504
3505       -Wignored-qualifiers (C and C++ only)
3506           Warn if the return type of a function has a type qualifier such as
3507           "const".  For ISO C such a type qualifier has no effect, since the
3508           value returned by a function is not an lvalue.  For C++, the
3509           warning is only emitted for scalar types or "void".  ISO C
3510           prohibits qualified "void" return types on function definitions, so
3511           such return types always receive a warning even without this
3512           option.
3513
3514           This warning is also enabled by -Wextra.
3515
3516       -Wignored-attributes (C and C++ only)
3517           Warn when an attribute is ignored.  This is different from the
3518           -Wattributes option in that it warns whenever the compiler decides
3519           to drop an attribute, not that the attribute is either unknown,
3520           used in a wrong place, etc.  This warning is enabled by default.
3521
3522       -Wmain
3523           Warn if the type of "main" is suspicious.  "main" should be a
3524           function with external linkage, returning int, taking either zero
3525           arguments, two, or three arguments of appropriate types.  This
3526           warning is enabled by default in C++ and is enabled by either -Wall
3527           or -Wpedantic.
3528
3529       -Wmisleading-indentation (C and C++ only)
3530           Warn when the indentation of the code does not reflect the block
3531           structure.  Specifically, a warning is issued for "if", "else",
3532           "while", and "for" clauses with a guarded statement that does not
3533           use braces, followed by an unguarded statement with the same
3534           indentation.
3535
3536           In the following example, the call to "bar" is misleadingly
3537           indented as if it were guarded by the "if" conditional.
3538
3539                     if (some_condition ())
3540                       foo ();
3541                       bar ();  /* Gotcha: this is not guarded by the "if".  */
3542
3543           In the case of mixed tabs and spaces, the warning uses the
3544           -ftabstop= option to determine if the statements line up
3545           (defaulting to 8).
3546
3547           The warning is not issued for code involving multiline preprocessor
3548           logic such as the following example.
3549
3550                     if (flagA)
3551                       foo (0);
3552                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
3553                     if (flagB)
3554                   #endif
3555                       foo (1);
3556
3557           The warning is not issued after a "#line" directive, since this
3558           typically indicates autogenerated code, and no assumptions can be
3559           made about the layout of the file that the directive references.
3560
3561           This warning is enabled by -Wall in C and C++.
3562
3563       -Wmissing-attributes
3564           Warn when a declaration of a function is missing one or more
3565           attributes that a related function is declared with and whose
3566           absence may adversely affect the correctness or efficiency of
3567           generated code.  For example, in C++, the warning is issued when an
3568           explicit specialization of a primary template declared with
3569           attribute "alloc_align", "alloc_size", "assume_aligned", "format",
3570           "format_arg", "malloc", or "nonnull" is declared without it.
3571           Attributes "deprecated", "error", and "warning" suppress the
3572           warning..
3573
3574           -Wmissing-attributes is enabled by -Wall.
3575
3576           For example, since the declaration of the primary function template
3577           below makes use of both attribute "malloc" and "alloc_size" the
3578           declaration of the explicit specialization of the template is
3579           diagnosed because it is missing one of the attributes.
3580
3581                   template <class T>
3582                   T* __attribute__ ((malloc, alloc_size (1)))
3583                   allocate (size_t);
3584
3585                   template <>
3586                   void* __attribute__ ((malloc))   // missing alloc_size
3587                   allocate<void> (size_t);
3588
3589       -Wmissing-braces
3590           Warn if an aggregate or union initializer is not fully bracketed.
3591           In the following example, the initializer for "a" is not fully
3592           bracketed, but that for "b" is fully bracketed.  This warning is
3593           enabled by -Wall in C.
3594
3595                   int a[2][2] = { 0, 1, 2, 3 };
3596                   int b[2][2] = { { 0, 1 }, { 2, 3 } };
3597
3598           This warning is enabled by -Wall.
3599
3600       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
3601           Warn if a user-supplied include directory does not exist.
3602
3603       -Wmultistatement-macros
3604           Warn about unsafe multiple statement macros that appear to be
3605           guarded by a clause such as "if", "else", "for", "switch", or
3606           "while", in which only the first statement is actually guarded
3607           after the macro is expanded.
3608
3609           For example:
3610
3611                   #define DOIT x++; y++
3612                   if (c)
3613                     DOIT;
3614
3615           will increment "y" unconditionally, not just when "c" holds.  The
3616           can usually be fixed by wrapping the macro in a do-while loop:
3617
3618                   #define DOIT do { x++; y++; } while (0)
3619                   if (c)
3620                     DOIT;
3621
3622           This warning is enabled by -Wall in C and C++.
3623
3624       -Wparentheses
3625           Warn if parentheses are omitted in certain contexts, such as when
3626           there is an assignment in a context where a truth value is
3627           expected, or when operators are nested whose precedence people
3628           often get confused about.
3629
3630           Also warn if a comparison like "x<=y<=z" appears; this is
3631           equivalent to "(x<=y ? 1 : 0) <= z", which is a different
3632           interpretation from that of ordinary mathematical notation.
3633
3634           Also warn for dangerous uses of the GNU extension to "?:" with
3635           omitted middle operand. When the condition in the "?": operator is
3636           a boolean expression, the omitted value is always 1.  Often
3637           programmers expect it to be a value computed inside the conditional
3638           expression instead.
3639
3640           For C++ this also warns for some cases of unnecessary parentheses
3641           in declarations, which can indicate an attempt at a function call
3642           instead of a declaration:
3643
3644                   {
3645                     // Declares a local variable called mymutex.
3646                     std::unique_lock<std::mutex> (mymutex);
3647                     // User meant std::unique_lock<std::mutex> lock (mymutex);
3648                   }
3649
3650           This warning is enabled by -Wall.
3651
3652       -Wsequence-point
3653           Warn about code that may have undefined semantics because of
3654           violations of sequence point rules in the C and C++ standards.
3655
3656           The C and C++ standards define the order in which expressions in a
3657           C/C++ program are evaluated in terms of sequence points, which
3658           represent a partial ordering between the execution of parts of the
3659           program: those executed before the sequence point, and those
3660           executed after it.  These occur after the evaluation of a full
3661           expression (one which is not part of a larger expression), after
3662           the evaluation of the first operand of a "&&", "||", "? :" or ","
3663           (comma) operator, before a function is called (but after the
3664           evaluation of its arguments and the expression denoting the called
3665           function), and in certain other places.  Other than as expressed by
3666           the sequence point rules, the order of evaluation of subexpressions
3667           of an expression is not specified.  All these rules describe only a
3668           partial order rather than a total order, since, for example, if two
3669           functions are called within one expression with no sequence point
3670           between them, the order in which the functions are called is not
3671           specified.  However, the standards committee have ruled that
3672           function calls do not overlap.
3673
3674           It is not specified when between sequence points modifications to
3675           the values of objects take effect.  Programs whose behavior depends
3676           on this have undefined behavior; the C and C++ standards specify
3677           that "Between the previous and next sequence point an object shall
3678           have its stored value modified at most once by the evaluation of an
3679           expression.  Furthermore, the prior value shall be read only to
3680           determine the value to be stored.".  If a program breaks these
3681           rules, the results on any particular implementation are entirely
3682           unpredictable.
3683
3684           Examples of code with undefined behavior are "a = a++;", "a[n] =
3685           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
3686           diagnosed by this option, and it may give an occasional false
3687           positive result, but in general it has been found fairly effective
3688           at detecting this sort of problem in programs.
3689
3690           The C++17 standard will define the order of evaluation of operands
3691           in more cases: in particular it requires that the right-hand side
3692           of an assignment be evaluated before the left-hand side, so the
3693           above examples are no longer undefined.  But this warning will
3694           still warn about them, to help people avoid writing code that is
3695           undefined in C and earlier revisions of C++.
3696
3697           The standard is worded confusingly, therefore there is some debate
3698           over the precise meaning of the sequence point rules in subtle
3699           cases.  Links to discussions of the problem, including proposed
3700           formal definitions, may be found on the GCC readings page, at
3701           <http://gcc.gnu.org/readings.html>.
3702
3703           This warning is enabled by -Wall for C and C++.
3704
3705       -Wno-return-local-addr
3706           Do not warn about returning a pointer (or in C++, a reference) to a
3707           variable that goes out of scope after the function returns.
3708
3709       -Wreturn-type
3710           Warn whenever a function is defined with a return type that
3711           defaults to "int".  Also warn about any "return" statement with no
3712           return value in a function whose return type is not "void" (falling
3713           off the end of the function body is considered returning without a
3714           value).
3715
3716           For C only, warn about a "return" statement with an expression in a
3717           function whose return type is "void", unless the expression type is
3718           also "void".  As a GNU extension, the latter case is accepted
3719           without a warning unless -Wpedantic is used.
3720
3721           For C++, a function without return type always produces a
3722           diagnostic message, even when -Wno-return-type is specified.  The
3723           only exceptions are "main" and functions defined in system headers.
3724
3725           This warning is enabled by default for C++ and is enabled by -Wall.
3726
3727       -Wshift-count-negative
3728           Warn if shift count is negative. This warning is enabled by
3729           default.
3730
3731       -Wshift-count-overflow
3732           Warn if shift count >= width of type. This warning is enabled by
3733           default.
3734
3735       -Wshift-negative-value
3736           Warn if left shifting a negative value.  This warning is enabled by
3737           -Wextra in C99 and C++11 modes (and newer).
3738
3739       -Wshift-overflow
3740       -Wshift-overflow=n
3741           Warn about left shift overflows.  This warning is enabled by
3742           default in C99 and C++11 modes (and newer).
3743
3744           -Wshift-overflow=1
3745               This is the warning level of -Wshift-overflow and is enabled by
3746               default in C99 and C++11 modes (and newer).  This warning level
3747               does not warn about left-shifting 1 into the sign bit.
3748               (However, in C, such an overflow is still rejected in contexts
3749               where an integer constant expression is required.)
3750
3751           -Wshift-overflow=2
3752               This warning level also warns about left-shifting 1 into the
3753               sign bit, unless C++14 mode is active.
3754
3755       -Wswitch
3756           Warn whenever a "switch" statement has an index of enumerated type
3757           and lacks a "case" for one or more of the named codes of that
3758           enumeration.  (The presence of a "default" label prevents this
3759           warning.)  "case" labels outside the enumeration range also provoke
3760           warnings when this option is used (even if there is a "default"
3761           label).  This warning is enabled by -Wall.
3762
3763       -Wswitch-default
3764           Warn whenever a "switch" statement does not have a "default" case.
3765
3766       -Wswitch-enum
3767           Warn whenever a "switch" statement has an index of enumerated type
3768           and lacks a "case" for one or more of the named codes of that
3769           enumeration.  "case" labels outside the enumeration range also
3770           provoke warnings when this option is used.  The only difference
3771           between -Wswitch and this option is that this option gives a
3772           warning about an omitted enumeration code even if there is a
3773           "default" label.
3774
3775       -Wswitch-bool
3776           Warn whenever a "switch" statement has an index of boolean type and
3777           the case values are outside the range of a boolean type.  It is
3778           possible to suppress this warning by casting the controlling
3779           expression to a type other than "bool".  For example:
3780
3781                   switch ((int) (a == 4))
3782                     {
3783                     ...
3784                     }
3785
3786           This warning is enabled by default for C and C++ programs.
3787
3788       -Wswitch-unreachable
3789           Warn whenever a "switch" statement contains statements between the
3790           controlling expression and the first case label, which will never
3791           be executed.  For example:
3792
3793                   switch (cond)
3794                     {
3795                      i = 15;
3796                     ...
3797                      case 5:
3798                     ...
3799                     }
3800
3801           -Wswitch-unreachable does not warn if the statement between the
3802           controlling expression and the first case label is just a
3803           declaration:
3804
3805                   switch (cond)
3806                     {
3807                      int i;
3808                     ...
3809                      case 5:
3810                      i = 5;
3811                     ...
3812                     }
3813
3814           This warning is enabled by default for C and C++ programs.
3815
3816       -Wsync-nand (C and C++ only)
3817           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
3818           built-in functions are used.  These functions changed semantics in
3819           GCC 4.4.
3820
3821       -Wunused-but-set-parameter
3822           Warn whenever a function parameter is assigned to, but otherwise
3823           unused (aside from its declaration).
3824
3825           To suppress this warning use the "unused" attribute.
3826
3827           This warning is also enabled by -Wunused together with -Wextra.
3828
3829       -Wunused-but-set-variable
3830           Warn whenever a local variable is assigned to, but otherwise unused
3831           (aside from its declaration).  This warning is enabled by -Wall.
3832
3833           To suppress this warning use the "unused" attribute.
3834
3835           This warning is also enabled by -Wunused, which is enabled by
3836           -Wall.
3837
3838       -Wunused-function
3839           Warn whenever a static function is declared but not defined or a
3840           non-inline static function is unused.  This warning is enabled by
3841           -Wall.
3842
3843       -Wunused-label
3844           Warn whenever a label is declared but not used.  This warning is
3845           enabled by -Wall.
3846
3847           To suppress this warning use the "unused" attribute.
3848
3849       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
3850           Warn when a typedef locally defined in a function is not used.
3851           This warning is enabled by -Wall.
3852
3853       -Wunused-parameter
3854           Warn whenever a function parameter is unused aside from its
3855           declaration.
3856
3857           To suppress this warning use the "unused" attribute.
3858
3859       -Wno-unused-result
3860           Do not warn if a caller of a function marked with attribute
3861           "warn_unused_result" does not use its return value. The default is
3862           -Wunused-result.
3863
3864       -Wunused-variable
3865           Warn whenever a local or static variable is unused aside from its
3866           declaration. This option implies -Wunused-const-variable=1 for C,
3867           but not for C++. This warning is enabled by -Wall.
3868
3869           To suppress this warning use the "unused" attribute.
3870
3871       -Wunused-const-variable
3872       -Wunused-const-variable=n
3873           Warn whenever a constant static variable is unused aside from its
3874           declaration.  -Wunused-const-variable=1 is enabled by
3875           -Wunused-variable for C, but not for C++. In C this declares
3876           variable storage, but in C++ this is not an error since const
3877           variables take the place of "#define"s.
3878
3879           To suppress this warning use the "unused" attribute.
3880
3881           -Wunused-const-variable=1
3882               This is the warning level that is enabled by -Wunused-variable
3883               for C.  It warns only about unused static const variables
3884               defined in the main compilation unit, but not about static
3885               const variables declared in any header included.
3886
3887           -Wunused-const-variable=2
3888               This warning level also warns for unused constant static
3889               variables in headers (excluding system headers).  This is the
3890               warning level of -Wunused-const-variable and must be explicitly
3891               requested since in C++ this isn't an error and in C it might be
3892               harder to clean up all headers included.
3893
3894       -Wunused-value
3895           Warn whenever a statement computes a result that is explicitly not
3896           used. To suppress this warning cast the unused expression to
3897           "void". This includes an expression-statement or the left-hand side
3898           of a comma expression that contains no side effects. For example,
3899           an expression such as "x[i,j]" causes a warning, while
3900           "x[(void)i,j]" does not.
3901
3902           This warning is enabled by -Wall.
3903
3904       -Wunused
3905           All the above -Wunused options combined.
3906
3907           In order to get a warning about an unused function parameter, you
3908           must either specify -Wextra -Wunused (note that -Wall implies
3909           -Wunused), or separately specify -Wunused-parameter.
3910
3911       -Wuninitialized
3912           Warn if an automatic variable is used without first being
3913           initialized or if a variable may be clobbered by a "setjmp" call.
3914           In C++, warn if a non-static reference or non-static "const" member
3915           appears in a class without constructors.
3916
3917           If you want to warn about code that uses the uninitialized value of
3918           the variable in its own initializer, use the -Winit-self option.
3919
3920           These warnings occur for individual uninitialized or clobbered
3921           elements of structure, union or array variables as well as for
3922           variables that are uninitialized or clobbered as a whole.  They do
3923           not occur for variables or elements declared "volatile".  Because
3924           these warnings depend on optimization, the exact variables or
3925           elements for which there are warnings depends on the precise
3926           optimization options and version of GCC used.
3927
3928           Note that there may be no warning about a variable that is used
3929           only to compute a value that itself is never used, because such
3930           computations may be deleted by data flow analysis before the
3931           warnings are printed.
3932
3933       -Winvalid-memory-model
3934           Warn for invocations of __atomic Builtins, __sync Builtins, and the
3935           C11 atomic generic functions with a memory consistency argument
3936           that is either invalid for the operation or outside the range of
3937           values of the "memory_order" enumeration.  For example, since the
3938           "__atomic_store" and "__atomic_store_n" built-ins are only defined
3939           for the relaxed, release, and sequentially consistent memory orders
3940           the following code is diagnosed:
3941
3942                   void store (int *i)
3943                   {
3944                     __atomic_store_n (i, 0, memory_order_consume);
3945                   }
3946
3947           -Winvalid-memory-model is enabled by default.
3948
3949       -Wmaybe-uninitialized
3950           For an automatic (i.e. local) variable, if there exists a path from
3951           the function entry to a use of the variable that is initialized,
3952           but there exist some other paths for which the variable is not
3953           initialized, the compiler emits a warning if it cannot prove the
3954           uninitialized paths are not executed at run time.
3955
3956           These warnings are only possible in optimizing compilation, because
3957           otherwise GCC does not keep track of the state of variables.
3958
3959           These warnings are made optional because GCC may not be able to
3960           determine when the code is correct in spite of appearing to have an
3961           error.  Here is one example of how this can happen:
3962
3963                   {
3964                     int x;
3965                     switch (y)
3966                       {
3967                       case 1: x = 1;
3968                         break;
3969                       case 2: x = 4;
3970                         break;
3971                       case 3: x = 5;
3972                       }
3973                     foo (x);
3974                   }
3975
3976           If the value of "y" is always 1, 2 or 3, then "x" is always
3977           initialized, but GCC doesn't know this. To suppress the warning,
3978           you need to provide a default case with assert(0) or similar code.
3979
3980           This option also warns when a non-volatile automatic variable might
3981           be changed by a call to "longjmp".  The compiler sees only the
3982           calls to "setjmp".  It cannot know where "longjmp" will be called;
3983           in fact, a signal handler could call it at any point in the code.
3984           As a result, you may get a warning even when there is in fact no
3985           problem because "longjmp" cannot in fact be called at the place
3986           that would cause a problem.
3987
3988           Some spurious warnings can be avoided if you declare all the
3989           functions you use that never return as "noreturn".
3990
3991           This warning is enabled by -Wall or -Wextra.
3992
3993       -Wunknown-pragmas
3994           Warn when a "#pragma" directive is encountered that is not
3995           understood by GCC.  If this command-line option is used, warnings
3996           are even issued for unknown pragmas in system header files.  This
3997           is not the case if the warnings are only enabled by the -Wall
3998           command-line option.
3999
4000       -Wno-pragmas
4001           Do not warn about misuses of pragmas, such as incorrect parameters,
4002           invalid syntax, or conflicts between pragmas.  See also
4003           -Wunknown-pragmas.
4004
4005       -Wstrict-aliasing
4006           This option is only active when -fstrict-aliasing is active.  It
4007           warns about code that might break the strict aliasing rules that
4008           the compiler is using for optimization.  The warning does not catch
4009           all cases, but does attempt to catch the more common pitfalls.  It
4010           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3
4011
4012       -Wstrict-aliasing=n
4013           This option is only active when -fstrict-aliasing is active.  It
4014           warns about code that might break the strict aliasing rules that
4015           the compiler is using for optimization.  Higher levels correspond
4016           to higher accuracy (fewer false positives).  Higher levels also
4017           correspond to more effort, similar to the way -O works.
4018           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.
4019
4020           Level 1: Most aggressive, quick, least accurate.  Possibly useful
4021           when higher levels do not warn but -fstrict-aliasing still breaks
4022           the code, as it has very few false negatives.  However, it has many
4023           false positives.  Warns for all pointer conversions between
4024           possibly incompatible types, even if never dereferenced.  Runs in
4025           the front end only.
4026
4027           Level 2: Aggressive, quick, not too precise.  May still have many
4028           false positives (not as many as level 1 though), and few false
4029           negatives (but possibly more than level 1).  Unlike level 1, it
4030           only warns when an address is taken.  Warns about incomplete types.
4031           Runs in the front end only.
4032
4033           Level 3 (default for -Wstrict-aliasing): Should have very few false
4034           positives and few false negatives.  Slightly slower than levels 1
4035           or 2 when optimization is enabled.  Takes care of the common
4036           pun+dereference pattern in the front end: "*(int*)&some_float".  If
4037           optimization is enabled, it also runs in the back end, where it
4038           deals with multiple statement cases using flow-sensitive points-to
4039           information.  Only warns when the converted pointer is
4040           dereferenced.  Does not warn about incomplete types.
4041
4042       -Wstrict-overflow
4043       -Wstrict-overflow=n
4044           This option is only active when signed overflow is undefined.  It
4045           warns about cases where the compiler optimizes based on the
4046           assumption that signed overflow does not occur.  Note that it does
4047           not warn about all cases where the code might overflow: it only
4048           warns about cases where the compiler implements some optimization.
4049           Thus this warning depends on the optimization level.
4050
4051           An optimization that assumes that signed overflow does not occur is
4052           perfectly safe if the values of the variables involved are such
4053           that overflow never does, in fact, occur.  Therefore this warning
4054           can easily give a false positive: a warning about code that is not
4055           actually a problem.  To help focus on important issues, several
4056           warning levels are defined.  No warnings are issued for the use of
4057           undefined signed overflow when estimating how many iterations a
4058           loop requires, in particular when determining whether a loop will
4059           be executed at all.
4060
4061           -Wstrict-overflow=1
4062               Warn about cases that are both questionable and easy to avoid.
4063               For example the compiler simplifies "x + 1 > x" to 1.  This
4064               level of -Wstrict-overflow is enabled by -Wall; higher levels
4065               are not, and must be explicitly requested.
4066
4067           -Wstrict-overflow=2
4068               Also warn about other cases where a comparison is simplified to
4069               a constant.  For example: "abs (x) >= 0".  This can only be
4070               simplified when signed integer overflow is undefined, because
4071               "abs (INT_MIN)" overflows to "INT_MIN", which is less than
4072               zero.  -Wstrict-overflow (with no level) is the same as
4073               -Wstrict-overflow=2.
4074
4075           -Wstrict-overflow=3
4076               Also warn about other cases where a comparison is simplified.
4077               For example: "x + 1 > 1" is simplified to "x > 0".
4078
4079           -Wstrict-overflow=4
4080               Also warn about other simplifications not covered by the above
4081               cases.  For example: "(x * 10) / 5" is simplified to "x * 2".
4082
4083           -Wstrict-overflow=5
4084               Also warn about cases where the compiler reduces the magnitude
4085               of a constant involved in a comparison.  For example: "x + 2 >
4086               y" is simplified to "x + 1 >= y".  This is reported only at the
4087               highest warning level because this simplification applies to
4088               many comparisons, so this warning level gives a very large
4089               number of false positives.
4090
4091       -Wstringop-overflow
4092       -Wstringop-overflow=type
4093           Warn for calls to string manipulation functions such as "memcpy"
4094           and "strcpy" that are determined to overflow the destination
4095           buffer.  The optional argument is one greater than the type of
4096           Object Size Checking to perform to determine the size of the
4097           destination.  The argument is meaningful only for functions that
4098           operate on character arrays but not for raw memory functions like
4099           "memcpy" which always make use of Object Size type-0.  The option
4100           also warns for calls that specify a size in excess of the largest
4101           possible object or at most "SIZE_MAX / 2" bytes.  The option
4102           produces the best results with optimization enabled but can detect
4103           a small subset of simple buffer overflows even without optimization
4104           in calls to the GCC built-in functions like "__builtin_memcpy" that
4105           correspond to the standard functions.  In any case, the option
4106           warns about just a subset of buffer overflows detected by the
4107           corresponding overflow checking built-ins.  For example, the option
4108           will issue a warning for the "strcpy" call below because it copies
4109           at least 5 characters (the string "blue" including the terminating
4110           NUL) into the buffer of size 4.
4111
4112                   enum Color { blue, purple, yellow };
4113                   const char* f (enum Color clr)
4114                   {
4115                     static char buf [4];
4116                     const char *str;
4117                     switch (clr)
4118                       {
4119                         case blue: str = "blue"; break;
4120                         case purple: str = "purple"; break;
4121                         case yellow: str = "yellow"; break;
4122                       }
4123
4124                     return strcpy (buf, str);   // warning here
4125                   }
4126
4127           Option -Wstringop-overflow=2 is enabled by default.
4128
4129           -Wstringop-overflow
4130           -Wstringop-overflow=1
4131               The -Wstringop-overflow=1 option uses type-zero Object Size
4132               Checking to determine the sizes of destination objects.  This
4133               is the default setting of the option.  At this setting the
4134               option will not warn for writes past the end of subobjects of
4135               larger objects accessed by pointers unless the size of the
4136               largest surrounding object is known.  When the destination may
4137               be one of several objects it is assumed to be the largest one
4138               of them.  On Linux systems, when optimization is enabled at
4139               this setting the option warns for the same code as when the
4140               "_FORTIFY_SOURCE" macro is defined to a non-zero value.
4141
4142           -Wstringop-overflow=2
4143               The -Wstringop-overflow=2 option uses type-one Object Size
4144               Checking to determine the sizes of destination objects.  At
4145               this setting the option will warn about overflows when writing
4146               to members of the largest complete objects whose exact size is
4147               known.  It will, however, not warn for excessive writes to the
4148               same members of unknown objects referenced by pointers since
4149               they may point to arrays containing unknown numbers of
4150               elements.
4151
4152           -Wstringop-overflow=3
4153               The -Wstringop-overflow=3 option uses type-two Object Size
4154               Checking to determine the sizes of destination objects.  At
4155               this setting the option warns about overflowing the smallest
4156               object or data member.  This is the most restrictive setting of
4157               the option that may result in warnings for safe code.
4158
4159           -Wstringop-overflow=4
4160               The -Wstringop-overflow=4 option uses type-three Object Size
4161               Checking to determine the sizes of destination objects.  At
4162               this setting the option will warn about overflowing any data
4163               members, and when the destination is one of several objects it
4164               uses the size of the largest of them to decide whether to issue
4165               a warning.  Similarly to -Wstringop-overflow=3 this setting of
4166               the option may result in warnings for benign code.
4167
4168       -Wstringop-truncation
4169           Warn for calls to bounded string manipulation functions such as
4170           "strncat", "strncpy", and "stpncpy" that may either truncate the
4171           copied string or leave the destination unchanged.
4172
4173           In the following example, the call to "strncat" specifies a bound
4174           that is less than the length of the source string.  As a result,
4175           the copy of the source will be truncated and so the call is
4176           diagnosed.  To avoid the warning use "bufsize - strlen (buf) - 1)"
4177           as the bound.
4178
4179                   void append (char *buf, size_t bufsize)
4180                   {
4181                     strncat (buf, ".txt", 3);
4182                   }
4183
4184           As another example, the following call to "strncpy" results in
4185           copying to "d" just the characters preceding the terminating NUL,
4186           without appending the NUL to the end.  Assuming the result of
4187           "strncpy" is necessarily a NUL-terminated string is a common
4188           mistake, and so the call is diagnosed.  To avoid the warning when
4189           the result is not expected to be NUL-terminated, call "memcpy"
4190           instead.
4191
4192                   void copy (char *d, const char *s)
4193                   {
4194                     strncpy (d, s, strlen (s));
4195                   }
4196
4197           In the following example, the call to "strncpy" specifies the size
4198           of the destination buffer as the bound.  If the length of the
4199           source string is equal to or greater than this size the result of
4200           the copy will not be NUL-terminated.  Therefore, the call is also
4201           diagnosed.  To avoid the warning, specify "sizeof buf - 1" as the
4202           bound and set the last element of the buffer to "NUL".
4203
4204                   void copy (const char *s)
4205                   {
4206                     char buf[80];
4207                     strncpy (buf, s, sizeof buf);
4208                     ...
4209                   }
4210
4211           In situations where a character array is intended to store a
4212           sequence of bytes with no terminating "NUL" such an array may be
4213           annotated with attribute "nonstring" to avoid this warning.  Such
4214           arrays, however, are not suitable arguments to functions that
4215           expect "NUL"-terminated strings.  To help detect accidental misuses
4216           of such arrays GCC issues warnings unless it can prove that the use
4217           is safe.
4218
4219           Option -Wstringop-truncation is enabled by -Wall.
4220
4221       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
4222           Warn for cases where adding an attribute may be beneficial. The
4223           attributes currently supported are listed below.
4224
4225           -Wsuggest-attribute=pure
4226           -Wsuggest-attribute=const
4227           -Wsuggest-attribute=noreturn
4228           -Wsuggest-attribute=malloc
4229               Warn about functions that might be candidates for attributes
4230               "pure", "const" or "noreturn" or "malloc". The compiler only
4231               warns for functions visible in other compilation units or (in
4232               the case of "pure" and "const") if it cannot prove that the
4233               function returns normally. A function returns normally if it
4234               doesn't contain an infinite loop or return abnormally by
4235               throwing, calling "abort" or trapping.  This analysis requires
4236               option -fipa-pure-const, which is enabled by default at -O and
4237               higher.  Higher optimization levels improve the accuracy of the
4238               analysis.
4239
4240           -Wsuggest-attribute=format
4241           -Wmissing-format-attribute
4242               Warn about function pointers that might be candidates for
4243               "format" attributes.  Note these are only possible candidates,
4244               not absolute ones.  GCC guesses that function pointers with
4245               "format" attributes that are used in assignment,
4246               initialization, parameter passing or return statements should
4247               have a corresponding "format" attribute in the resulting type.
4248               I.e. the left-hand side of the assignment or initialization,
4249               the type of the parameter variable, or the return type of the
4250               containing function respectively should also have a "format"
4251               attribute to avoid the warning.
4252
4253               GCC also warns about function definitions that might be
4254               candidates for "format" attributes.  Again, these are only
4255               possible candidates.  GCC guesses that "format" attributes
4256               might be appropriate for any function that calls a function
4257               like "vprintf" or "vscanf", but this might not always be the
4258               case, and some functions for which "format" attributes are
4259               appropriate may not be detected.
4260
4261           -Wsuggest-attribute=cold
4262               Warn about functions that might be candidates for "cold"
4263               attribute.  This is based on static detection and generally
4264               will only warn about functions which always leads to a call to
4265               another "cold" function such as wrappers of C++ "throw" or
4266               fatal error reporting functions leading to "abort".
4267
4268       -Wsuggest-final-types
4269           Warn about types with virtual methods where code quality would be
4270           improved if the type were declared with the C++11 "final"
4271           specifier, or, if possible, declared in an anonymous namespace.
4272           This allows GCC to more aggressively devirtualize the polymorphic
4273           calls. This warning is more effective with link time optimization,
4274           where the information about the class hierarchy graph is more
4275           complete.
4276
4277       -Wsuggest-final-methods
4278           Warn about virtual methods where code quality would be improved if
4279           the method were declared with the C++11 "final" specifier, or, if
4280           possible, its type were declared in an anonymous namespace or with
4281           the "final" specifier.  This warning is more effective with link-
4282           time optimization, where the information about the class hierarchy
4283           graph is more complete. It is recommended to first consider
4284           suggestions of -Wsuggest-final-types and then rebuild with new
4285           annotations.
4286
4287       -Wsuggest-override
4288           Warn about overriding virtual functions that are not marked with
4289           the override keyword.
4290
4291       -Walloc-zero
4292           Warn about calls to allocation functions decorated with attribute
4293           "alloc_size" that specify zero bytes, including those to the built-
4294           in forms of the functions "aligned_alloc", "alloca", "calloc",
4295           "malloc", and "realloc".  Because the behavior of these functions
4296           when called with a zero size differs among implementations (and in
4297           the case of "realloc" has been deprecated) relying on it may result
4298           in subtle portability bugs and should be avoided.
4299
4300       -Walloc-size-larger-than=n
4301           Warn about calls to functions decorated with attribute "alloc_size"
4302           that attempt to allocate objects larger than the specified number
4303           of bytes, or where the result of the size computation in an integer
4304           type with infinite precision would exceed "SIZE_MAX / 2".  The
4305           option argument n may end in one of the standard suffixes
4306           designating a multiple of bytes such as "kB" and "KiB" for kilobyte
4307           and kibibyte, respectively, "MB" and "MiB" for megabyte and
4308           mebibyte, and so on.  -Walloc-size-larger-than=PTRDIFF_MAX is
4309           enabled by default.  Warnings controlled by the option can be
4310           disabled by specifying n of SIZE_MAX or more.
4311
4312       -Walloca
4313           This option warns on all uses of "alloca" in the source.
4314
4315       -Walloca-larger-than=n
4316           This option warns on calls to "alloca" that are not bounded by a
4317           controlling predicate limiting its argument of integer type to at
4318           most n bytes, or calls to "alloca" where the bound is unknown.
4319           Arguments of non-integer types are considered unbounded even if
4320           they appear to be constrained to the expected range.
4321
4322           For example, a bounded case of "alloca" could be:
4323
4324                   void func (size_t n)
4325                   {
4326                     void *p;
4327                     if (n <= 1000)
4328                       p = alloca (n);
4329                     else
4330                       p = malloc (n);
4331                     f (p);
4332                   }
4333
4334           In the above example, passing "-Walloca-larger-than=1000" would not
4335           issue a warning because the call to "alloca" is known to be at most
4336           1000 bytes.  However, if "-Walloca-larger-than=500" were passed,
4337           the compiler would emit a warning.
4338
4339           Unbounded uses, on the other hand, are uses of "alloca" with no
4340           controlling predicate constraining its integer argument.  For
4341           example:
4342
4343                   void func ()
4344                   {
4345                     void *p = alloca (n);
4346                     f (p);
4347                   }
4348
4349           If "-Walloca-larger-than=500" were passed, the above would trigger
4350           a warning, but this time because of the lack of bounds checking.
4351
4352           Note, that even seemingly correct code involving signed integers
4353           could cause a warning:
4354
4355                   void func (signed int n)
4356                   {
4357                     if (n < 500)
4358                       {
4359                         p = alloca (n);
4360                         f (p);
4361                       }
4362                   }
4363
4364           In the above example, n could be negative, causing a larger than
4365           expected argument to be implicitly cast into the "alloca" call.
4366
4367           This option also warns when "alloca" is used in a loop.
4368
4369           This warning is not enabled by -Wall, and is only active when
4370           -ftree-vrp is active (default for -O2 and above).
4371
4372           See also -Wvla-larger-than=n.
4373
4374       -Warray-bounds
4375       -Warray-bounds=n
4376           This option is only active when -ftree-vrp is active (default for
4377           -O2 and above). It warns about subscripts to arrays that are always
4378           out of bounds. This warning is enabled by -Wall.
4379
4380           -Warray-bounds=1
4381               This is the warning level of -Warray-bounds and is enabled by
4382               -Wall; higher levels are not, and must be explicitly requested.
4383
4384           -Warray-bounds=2
4385               This warning level also warns about out of bounds access for
4386               arrays at the end of a struct and for arrays accessed through
4387               pointers. This warning level may give a larger number of false
4388               positives and is deactivated by default.
4389
4390       -Wattribute-alias
4391           Warn about declarations using the "alias" and similar attributes
4392           whose target is incompatible with the type of the alias.
4393
4394       -Wbool-compare
4395           Warn about boolean expression compared with an integer value
4396           different from "true"/"false".  For instance, the following
4397           comparison is always false:
4398
4399                   int n = 5;
4400                   ...
4401                   if ((n > 1) == 2) { ... }
4402
4403           This warning is enabled by -Wall.
4404
4405       -Wbool-operation
4406           Warn about suspicious operations on expressions of a boolean type.
4407           For instance, bitwise negation of a boolean is very likely a bug in
4408           the program.  For C, this warning also warns about incrementing or
4409           decrementing a boolean, which rarely makes sense.  (In C++,
4410           decrementing a boolean is always invalid.  Incrementing a boolean
4411           is invalid in C++17, and deprecated otherwise.)
4412
4413           This warning is enabled by -Wall.
4414
4415       -Wduplicated-branches
4416           Warn when an if-else has identical branches.  This warning detects
4417           cases like
4418
4419                   if (p != NULL)
4420                     return 0;
4421                   else
4422                     return 0;
4423
4424           It doesn't warn when both branches contain just a null statement.
4425           This warning also warn for conditional operators:
4426
4427                     int i = x ? *p : *p;
4428
4429       -Wduplicated-cond
4430           Warn about duplicated conditions in an if-else-if chain.  For
4431           instance, warn for the following code:
4432
4433                   if (p->q != NULL) { ... }
4434                   else if (p->q != NULL) { ... }
4435
4436       -Wframe-address
4437           Warn when the __builtin_frame_address or __builtin_return_address
4438           is called with an argument greater than 0.  Such calls may return
4439           indeterminate values or crash the program.  The warning is included
4440           in -Wall.
4441
4442       -Wno-discarded-qualifiers (C and Objective-C only)
4443           Do not warn if type qualifiers on pointers are being discarded.
4444           Typically, the compiler warns if a "const char *" variable is
4445           passed to a function that takes a "char *" parameter.  This option
4446           can be used to suppress such a warning.
4447
4448       -Wno-discarded-array-qualifiers (C and Objective-C only)
4449           Do not warn if type qualifiers on arrays which are pointer targets
4450           are being discarded. Typically, the compiler warns if a "const int
4451           (*)[]" variable is passed to a function that takes a "int (*)[]"
4452           parameter.  This option can be used to suppress such a warning.
4453
4454       -Wno-incompatible-pointer-types (C and Objective-C only)
4455           Do not warn when there is a conversion between pointers that have
4456           incompatible types.  This warning is for cases not covered by
4457           -Wno-pointer-sign, which warns for pointer argument passing or
4458           assignment with different signedness.
4459
4460       -Wno-int-conversion (C and Objective-C only)
4461           Do not warn about incompatible integer to pointer and pointer to
4462           integer conversions.  This warning is about implicit conversions;
4463           for explicit conversions the warnings -Wno-int-to-pointer-cast and
4464           -Wno-pointer-to-int-cast may be used.
4465
4466       -Wno-div-by-zero
4467           Do not warn about compile-time integer division by zero.  Floating-
4468           point division by zero is not warned about, as it can be a
4469           legitimate way of obtaining infinities and NaNs.
4470
4471       -Wsystem-headers
4472           Print warning messages for constructs found in system header files.
4473           Warnings from system headers are normally suppressed, on the
4474           assumption that they usually do not indicate real problems and
4475           would only make the compiler output harder to read.  Using this
4476           command-line option tells GCC to emit warnings from system headers
4477           as if they occurred in user code.  However, note that using -Wall
4478           in conjunction with this option does not warn about unknown pragmas
4479           in system headers---for that, -Wunknown-pragmas must also be used.
4480
4481       -Wtautological-compare
4482           Warn if a self-comparison always evaluates to true or false.  This
4483           warning detects various mistakes such as:
4484
4485                   int i = 1;
4486                   ...
4487                   if (i > i) { ... }
4488
4489           This warning also warns about bitwise comparisons that always
4490           evaluate to true or false, for instance:
4491
4492                   if ((a & 16) == 10) { ... }
4493
4494           will always be false.
4495
4496           This warning is enabled by -Wall.
4497
4498       -Wtrampolines
4499           Warn about trampolines generated for pointers to nested functions.
4500           A trampoline is a small piece of data or code that is created at
4501           run time on the stack when the address of a nested function is
4502           taken, and is used to call the nested function indirectly.  For
4503           some targets, it is made up of data only and thus requires no
4504           special treatment.  But, for most targets, it is made up of code
4505           and thus requires the stack to be made executable in order for the
4506           program to work properly.
4507
4508       -Wfloat-equal
4509           Warn if floating-point values are used in equality comparisons.
4510
4511           The idea behind this is that sometimes it is convenient (for the
4512           programmer) to consider floating-point values as approximations to
4513           infinitely precise real numbers.  If you are doing this, then you
4514           need to compute (by analyzing the code, or in some other way) the
4515           maximum or likely maximum error that the computation introduces,
4516           and allow for it when performing comparisons (and when producing
4517           output, but that's a different problem).  In particular, instead of
4518           testing for equality, you should check to see whether the two
4519           values have ranges that overlap; and this is done with the
4520           relational operators, so equality comparisons are probably
4521           mistaken.
4522
4523       -Wtraditional (C and Objective-C only)
4524           Warn about certain constructs that behave differently in
4525           traditional and ISO C.  Also warn about ISO C constructs that have
4526           no traditional C equivalent, and/or problematic constructs that
4527           should be avoided.
4528
4529           *   Macro parameters that appear within string literals in the
4530               macro body.  In traditional C macro replacement takes place
4531               within string literals, but in ISO C it does not.
4532
4533           *   In traditional C, some preprocessor directives did not exist.
4534               Traditional preprocessors only considered a line to be a
4535               directive if the # appeared in column 1 on the line.  Therefore
4536               -Wtraditional warns about directives that traditional C
4537               understands but ignores because the # does not appear as the
4538               first character on the line.  It also suggests you hide
4539               directives like "#pragma" not understood by traditional C by
4540               indenting them.  Some traditional implementations do not
4541               recognize "#elif", so this option suggests avoiding it
4542               altogether.
4543
4544           *   A function-like macro that appears without arguments.
4545
4546           *   The unary plus operator.
4547
4548           *   The U integer constant suffix, or the F or L floating-point
4549               constant suffixes.  (Traditional C does support the L suffix on
4550               integer constants.)  Note, these suffixes appear in macros
4551               defined in the system headers of most modern systems, e.g. the
4552               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
4553               code might normally lead to spurious warnings, however GCC's
4554               integrated preprocessor has enough context to avoid warning in
4555               these cases.
4556
4557           *   A function declared external in one block and then used after
4558               the end of the block.
4559
4560           *   A "switch" statement has an operand of type "long".
4561
4562           *   A non-"static" function declaration follows a "static" one.
4563               This construct is not accepted by some traditional C compilers.
4564
4565           *   The ISO type of an integer constant has a different width or
4566               signedness from its traditional type.  This warning is only
4567               issued if the base of the constant is ten.  I.e. hexadecimal or
4568               octal values, which typically represent bit patterns, are not
4569               warned about.
4570
4571           *   Usage of ISO string concatenation is detected.
4572
4573           *   Initialization of automatic aggregates.
4574
4575           *   Identifier conflicts with labels.  Traditional C lacks a
4576               separate namespace for labels.
4577
4578           *   Initialization of unions.  If the initializer is zero, the
4579               warning is omitted.  This is done under the assumption that the
4580               zero initializer in user code appears conditioned on e.g.
4581               "__STDC__" to avoid missing initializer warnings and relies on
4582               default initialization to zero in the traditional C case.
4583
4584           *   Conversions by prototypes between fixed/floating-point values
4585               and vice versa.  The absence of these prototypes when compiling
4586               with traditional C causes serious problems.  This is a subset
4587               of the possible conversion warnings; for the full set use
4588               -Wtraditional-conversion.
4589
4590           *   Use of ISO C style function definitions.  This warning
4591               intentionally is not issued for prototype declarations or
4592               variadic functions because these ISO C features appear in your
4593               code when using libiberty's traditional C compatibility macros,
4594               "PARAMS" and "VPARAMS".  This warning is also bypassed for
4595               nested functions because that feature is already a GCC
4596               extension and thus not relevant to traditional C compatibility.
4597
4598       -Wtraditional-conversion (C and Objective-C only)
4599           Warn if a prototype causes a type conversion that is different from
4600           what would happen to the same argument in the absence of a
4601           prototype.  This includes conversions of fixed point to floating
4602           and vice versa, and conversions changing the width or signedness of
4603           a fixed-point argument except when the same as the default
4604           promotion.
4605
4606       -Wdeclaration-after-statement (C and Objective-C only)
4607           Warn when a declaration is found after a statement in a block.
4608           This construct, known from C++, was introduced with ISO C99 and is
4609           by default allowed in GCC.  It is not supported by ISO C90.
4610
4611       -Wshadow
4612           Warn whenever a local variable or type declaration shadows another
4613           variable, parameter, type, class member (in C++), or instance
4614           variable (in Objective-C) or whenever a built-in function is
4615           shadowed. Note that in C++, the compiler warns if a local variable
4616           shadows an explicit typedef, but not if it shadows a
4617           struct/class/enum.  Same as -Wshadow=global.
4618
4619       -Wno-shadow-ivar (Objective-C only)
4620           Do not warn whenever a local variable shadows an instance variable
4621           in an Objective-C method.
4622
4623       -Wshadow=global
4624           The default for -Wshadow. Warns for any (global) shadowing.
4625
4626       -Wshadow=local
4627           Warn when a local variable shadows another local variable or
4628           parameter.  This warning is enabled by -Wshadow=global.
4629
4630       -Wshadow=compatible-local
4631           Warn when a local variable shadows another local variable or
4632           parameter whose type is compatible with that of the shadowing
4633           variable. In C++, type compatibility here means the type of the
4634           shadowing variable can be converted to that of the shadowed
4635           variable. The creation of this flag (in addition to -Wshadow=local)
4636           is based on the idea that when a local variable shadows another one
4637           of incompatible type, it is most likely intentional, not a bug or
4638           typo, as shown in the following example:
4639
4640                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
4641                   {
4642                     for (int i = 0; i < N; ++i)
4643                     {
4644                       ...
4645                     }
4646                     ...
4647                   }
4648
4649           Since the two variable "i" in the example above have incompatible
4650           types, enabling only -Wshadow=compatible-local will not emit a
4651           warning.  Because their types are incompatible, if a programmer
4652           accidentally uses one in place of the other, type checking will
4653           catch that and emit an error or warning. So not warning (about
4654           shadowing) in this case will not lead to undetected bugs. Use of
4655           this flag instead of -Wshadow=local can possibly reduce the number
4656           of warnings triggered by intentional shadowing.
4657
4658           This warning is enabled by -Wshadow=local.
4659
4660       -Wlarger-than=len
4661           Warn whenever an object of larger than len bytes is defined.
4662
4663       -Wframe-larger-than=len
4664           Warn if the size of a function frame is larger than len bytes.  The
4665           computation done to determine the stack frame size is approximate
4666           and not conservative.  The actual requirements may be somewhat
4667           greater than len even if you do not get a warning.  In addition,
4668           any space allocated via "alloca", variable-length arrays, or
4669           related constructs is not included by the compiler when determining
4670           whether or not to issue a warning.
4671
4672       -Wno-free-nonheap-object
4673           Do not warn when attempting to free an object that was not
4674           allocated on the heap.
4675
4676       -Wstack-usage=len
4677           Warn if the stack usage of a function might be larger than len
4678           bytes.  The computation done to determine the stack usage is
4679           conservative.  Any space allocated via "alloca", variable-length
4680           arrays, or related constructs is included by the compiler when
4681           determining whether or not to issue a warning.
4682
4683           The message is in keeping with the output of -fstack-usage.
4684
4685           *   If the stack usage is fully static but exceeds the specified
4686               amount, it's:
4687
4688                         warning: stack usage is 1120 bytes
4689
4690           *   If the stack usage is (partly) dynamic but bounded, it's:
4691
4692                         warning: stack usage might be 1648 bytes
4693
4694           *   If the stack usage is (partly) dynamic and not bounded, it's:
4695
4696                         warning: stack usage might be unbounded
4697
4698       -Wno-pedantic-ms-format (MinGW targets only)
4699           When used in combination with -Wformat and -pedantic without GNU
4700           extensions, this option disables the warnings about non-ISO
4701           "printf" / "scanf" format width specifiers "I32", "I64", and "I"
4702           used on Windows targets, which depend on the MS runtime.
4703
4704       -Waligned-new
4705           Warn about a new-expression of a type that requires greater
4706           alignment than the "alignof(std::max_align_t)" but uses an
4707           allocation function without an explicit alignment parameter. This
4708           option is enabled by -Wall.
4709
4710           Normally this only warns about global allocation functions, but
4711           -Waligned-new=all also warns about class member allocation
4712           functions.
4713
4714       -Wplacement-new
4715       -Wplacement-new=n
4716           Warn about placement new expressions with undefined behavior, such
4717           as constructing an object in a buffer that is smaller than the type
4718           of the object.  For example, the placement new expression below is
4719           diagnosed because it attempts to construct an array of 64 integers
4720           in a buffer only 64 bytes large.
4721
4722                   char buf [64];
4723                   new (buf) int[64];
4724
4725           This warning is enabled by default.
4726
4727           -Wplacement-new=1
4728               This is the default warning level of -Wplacement-new.  At this
4729               level the warning is not issued for some strictly undefined
4730               constructs that GCC allows as extensions for compatibility with
4731               legacy code.  For example, the following "new" expression is
4732               not diagnosed at this level even though it has undefined
4733               behavior according to the C++ standard because it writes past
4734               the end of the one-element array.
4735
4736                       struct S { int n, a[1]; };
4737                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
4738                       new (s->a)int [32]();
4739
4740           -Wplacement-new=2
4741               At this level, in addition to diagnosing all the same
4742               constructs as at level 1, a diagnostic is also issued for
4743               placement new expressions that construct an object in the last
4744               member of structure whose type is an array of a single element
4745               and whose size is less than the size of the object being
4746               constructed.  While the previous example would be diagnosed,
4747               the following construct makes use of the flexible member array
4748               extension to avoid the warning at level 2.
4749
4750                       struct S { int n, a[]; };
4751                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
4752                       new (s->a)int [32]();
4753
4754       -Wpointer-arith
4755           Warn about anything that depends on the "size of" a function type
4756           or of "void".  GNU C assigns these types a size of 1, for
4757           convenience in calculations with "void *" pointers and pointers to
4758           functions.  In C++, warn also when an arithmetic operation involves
4759           "NULL".  This warning is also enabled by -Wpedantic.
4760
4761       -Wpointer-compare
4762           Warn if a pointer is compared with a zero character constant.  This
4763           usually means that the pointer was meant to be dereferenced.  For
4764           example:
4765
4766                   const char *p = foo ();
4767                   if (p == '\0')
4768                     return 42;
4769
4770           Note that the code above is invalid in C++11.
4771
4772           This warning is enabled by default.
4773
4774       -Wtype-limits
4775           Warn if a comparison is always true or always false due to the
4776           limited range of the data type, but do not warn for constant
4777           expressions.  For example, warn if an unsigned variable is compared
4778           against zero with "<" or ">=".  This warning is also enabled by
4779           -Wextra.
4780
4781       -Wcomment
4782       -Wcomments
4783           Warn whenever a comment-start sequence /* appears in a /* comment,
4784           or whenever a backslash-newline appears in a // comment.  This
4785           warning is enabled by -Wall.
4786
4787       -Wtrigraphs
4788           Warn if any trigraphs are encountered that might change the meaning
4789           of the program.  Trigraphs within comments are not warned about,
4790           except those that would form escaped newlines.
4791
4792           This option is implied by -Wall.  If -Wall is not given, this
4793           option is still enabled unless trigraphs are enabled.  To get
4794           trigraph conversion without warnings, but get the other -Wall
4795           warnings, use -trigraphs -Wall -Wno-trigraphs.
4796
4797       -Wundef
4798           Warn if an undefined identifier is evaluated in an "#if" directive.
4799           Such identifiers are replaced with zero.
4800
4801       -Wexpansion-to-defined
4802           Warn whenever defined is encountered in the expansion of a macro
4803           (including the case where the macro is expanded by an #if
4804           directive).  Such usage is not portable.  This warning is also
4805           enabled by -Wpedantic and -Wextra.
4806
4807       -Wunused-macros
4808           Warn about macros defined in the main file that are unused.  A
4809           macro is used if it is expanded or tested for existence at least
4810           once.  The preprocessor also warns if the macro has not been used
4811           at the time it is redefined or undefined.
4812
4813           Built-in macros, macros defined on the command line, and macros
4814           defined in include files are not warned about.
4815
4816           Note: If a macro is actually used, but only used in skipped
4817           conditional blocks, then the preprocessor reports it as unused.  To
4818           avoid the warning in such a case, you might improve the scope of
4819           the macro's definition by, for example, moving it into the first
4820           skipped block.  Alternatively, you could provide a dummy use with
4821           something like:
4822
4823                   #if defined the_macro_causing_the_warning
4824                   #endif
4825
4826       -Wno-endif-labels
4827           Do not warn whenever an "#else" or an "#endif" are followed by
4828           text.  This sometimes happens in older programs with code of the
4829           form
4830
4831                   #if FOO
4832                   ...
4833                   #else FOO
4834                   ...
4835                   #endif FOO
4836
4837           The second and third "FOO" should be in comments.  This warning is
4838           on by default.
4839
4840       -Wbad-function-cast (C and Objective-C only)
4841           Warn when a function call is cast to a non-matching type.  For
4842           example, warn if a call to a function returning an integer type is
4843           cast to a pointer type.
4844
4845       -Wc90-c99-compat (C and Objective-C only)
4846           Warn about features not present in ISO C90, but present in ISO C99.
4847           For instance, warn about use of variable length arrays, "long long"
4848           type, "bool" type, compound literals, designated initializers, and
4849           so on.  This option is independent of the standards mode.  Warnings
4850           are disabled in the expression that follows "__extension__".
4851
4852       -Wc99-c11-compat (C and Objective-C only)
4853           Warn about features not present in ISO C99, but present in ISO C11.
4854           For instance, warn about use of anonymous structures and unions,
4855           "_Atomic" type qualifier, "_Thread_local" storage-class specifier,
4856           "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and
4857           so on.  This option is independent of the standards mode.  Warnings
4858           are disabled in the expression that follows "__extension__".
4859
4860       -Wc++-compat (C and Objective-C only)
4861           Warn about ISO C constructs that are outside of the common subset
4862           of ISO C and ISO C++, e.g. request for implicit conversion from
4863           "void *" to a pointer to non-"void" type.
4864
4865       -Wc++11-compat (C++ and Objective-C++ only)
4866           Warn about C++ constructs whose meaning differs between ISO C++
4867           1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
4868           keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and is
4869           enabled by -Wall.
4870
4871       -Wc++14-compat (C++ and Objective-C++ only)
4872           Warn about C++ constructs whose meaning differs between ISO C++
4873           2011 and ISO C++ 2014.  This warning is enabled by -Wall.
4874
4875       -Wc++17-compat (C++ and Objective-C++ only)
4876           Warn about C++ constructs whose meaning differs between ISO C++
4877           2014 and ISO C++ 2017.  This warning is enabled by -Wall.
4878
4879       -Wcast-qual
4880           Warn whenever a pointer is cast so as to remove a type qualifier
4881           from the target type.  For example, warn if a "const char *" is
4882           cast to an ordinary "char *".
4883
4884           Also warn when making a cast that introduces a type qualifier in an
4885           unsafe way.  For example, casting "char **" to "const char **" is
4886           unsafe, as in this example:
4887
4888                     /* p is char ** value.  */
4889                     const char **q = (const char **) p;
4890                     /* Assignment of readonly string to const char * is OK.  */
4891                     *q = "string";
4892                     /* Now char** pointer points to read-only memory.  */
4893                     **p = 'b';
4894
4895       -Wcast-align
4896           Warn whenever a pointer is cast such that the required alignment of
4897           the target is increased.  For example, warn if a "char *" is cast
4898           to an "int *" on machines where integers can only be accessed at
4899           two- or four-byte boundaries.
4900
4901       -Wcast-align=strict
4902           Warn whenever a pointer is cast such that the required alignment of
4903           the target is increased.  For example, warn if a "char *" is cast
4904           to an "int *" regardless of the target machine.
4905
4906       -Wcast-function-type
4907           Warn when a function pointer is cast to an incompatible function
4908           pointer.  In a cast involving function types with a variable
4909           argument list only the types of initial arguments that are provided
4910           are considered.  Any parameter of pointer-type matches any other
4911           pointer-type.  Any benign differences in integral types are
4912           ignored, like "int" vs. "long" on ILP32 targets.  Likewise type
4913           qualifiers are ignored.  The function type "void (*) (void)" is
4914           special and matches everything, which can be used to suppress this
4915           warning.  In a cast involving pointer to member types this warning
4916           warns whenever the type cast is changing the pointer to member
4917           type.  This warning is enabled by -Wextra.
4918
4919       -Wwrite-strings
4920           When compiling C, give string constants the type "const
4921           char[length]" so that copying the address of one into a non-"const"
4922           "char *" pointer produces a warning.  These warnings help you find
4923           at compile time code that can try to write into a string constant,
4924           but only if you have been very careful about using "const" in
4925           declarations and prototypes.  Otherwise, it is just a nuisance.
4926           This is why we did not make -Wall request these warnings.
4927
4928           When compiling C++, warn about the deprecated conversion from
4929           string literals to "char *".  This warning is enabled by default
4930           for C++ programs.
4931
4932       -Wcatch-value
4933       -Wcatch-value=n (C++ and Objective-C++ only)
4934           Warn about catch handlers that do not catch via reference.  With
4935           -Wcatch-value=1 (or -Wcatch-value for short) warn about polymorphic
4936           class types that are caught by value.  With -Wcatch-value=2 warn
4937           about all class types that are caught by value. With
4938           -Wcatch-value=3 warn about all types that are not caught by
4939           reference. -Wcatch-value is enabled by -Wall.
4940
4941       -Wclobbered
4942           Warn for variables that might be changed by "longjmp" or "vfork".
4943           This warning is also enabled by -Wextra.
4944
4945       -Wconditionally-supported (C++ and Objective-C++ only)
4946           Warn for conditionally-supported (C++11 [intro.defs]) constructs.
4947
4948       -Wconversion
4949           Warn for implicit conversions that may alter a value. This includes
4950           conversions between real and integer, like "abs (x)" when "x" is
4951           "double"; conversions between signed and unsigned, like "unsigned
4952           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
4953           not warn for explicit casts like "abs ((int) x)" and "ui =
4954           (unsigned) -1", or if the value is not changed by the conversion
4955           like in "abs (2.0)".  Warnings about conversions between signed and
4956           unsigned integers can be disabled by using -Wno-sign-conversion.
4957
4958           For C++, also warn for confusing overload resolution for user-
4959           defined conversions; and conversions that never use a type
4960           conversion operator: conversions to "void", the same type, a base
4961           class or a reference to them. Warnings about conversions between
4962           signed and unsigned integers are disabled by default in C++ unless
4963           -Wsign-conversion is explicitly enabled.
4964
4965       -Wno-conversion-null (C++ and Objective-C++ only)
4966           Do not warn for conversions between "NULL" and non-pointer types.
4967           -Wconversion-null is enabled by default.
4968
4969       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
4970           Warn when a literal 0 is used as null pointer constant.  This can
4971           be useful to facilitate the conversion to "nullptr" in C++11.
4972
4973       -Wsubobject-linkage (C++ and Objective-C++ only)
4974           Warn if a class type has a base or a field whose type uses the
4975           anonymous namespace or depends on a type with no linkage.  If a
4976           type A depends on a type B with no or internal linkage, defining it
4977           in multiple translation units would be an ODR violation because the
4978           meaning of B is different in each translation unit.  If A only
4979           appears in a single translation unit, the best way to silence the
4980           warning is to give it internal linkage by putting it in an
4981           anonymous namespace as well.  The compiler doesn't give this
4982           warning for types defined in the main .C file, as those are
4983           unlikely to have multiple definitions.  -Wsubobject-linkage is
4984           enabled by default.
4985
4986       -Wdangling-else
4987           Warn about constructions where there may be confusion to which "if"
4988           statement an "else" branch belongs.  Here is an example of such a
4989           case:
4990
4991                   {
4992                     if (a)
4993                       if (b)
4994                         foo ();
4995                     else
4996                       bar ();
4997                   }
4998
4999           In C/C++, every "else" branch belongs to the innermost possible
5000           "if" statement, which in this example is "if (b)".  This is often
5001           not what the programmer expected, as illustrated in the above
5002           example by indentation the programmer chose.  When there is the
5003           potential for this confusion, GCC issues a warning when this flag
5004           is specified.  To eliminate the warning, add explicit braces around
5005           the innermost "if" statement so there is no way the "else" can
5006           belong to the enclosing "if".  The resulting code looks like this:
5007
5008                   {
5009                     if (a)
5010                       {
5011                         if (b)
5012                           foo ();
5013                         else
5014                           bar ();
5015                       }
5016                   }
5017
5018           This warning is enabled by -Wparentheses.
5019
5020       -Wdate-time
5021           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are
5022           encountered as they might prevent bit-wise-identical reproducible
5023           compilations.
5024
5025       -Wdelete-incomplete (C++ and Objective-C++ only)
5026           Warn when deleting a pointer to incomplete type, which may cause
5027           undefined behavior at runtime.  This warning is enabled by default.
5028
5029       -Wuseless-cast (C++ and Objective-C++ only)
5030           Warn when an expression is casted to its own type.
5031
5032       -Wempty-body
5033           Warn if an empty body occurs in an "if", "else" or "do while"
5034           statement.  This warning is also enabled by -Wextra.
5035
5036       -Wenum-compare
5037           Warn about a comparison between values of different enumerated
5038           types.  In C++ enumerated type mismatches in conditional
5039           expressions are also diagnosed and the warning is enabled by
5040           default.  In C this warning is enabled by -Wall.
5041
5042       -Wextra-semi (C++, Objective-C++ only)
5043           Warn about redundant semicolon after in-class function definition.
5044
5045       -Wjump-misses-init (C, Objective-C only)
5046           Warn if a "goto" statement or a "switch" statement jumps forward
5047           across the initialization of a variable, or jumps backward to a
5048           label after the variable has been initialized.  This only warns
5049           about variables that are initialized when they are declared.  This
5050           warning is only supported for C and Objective-C; in C++ this sort
5051           of branch is an error in any case.
5052
5053           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
5054           with the -Wno-jump-misses-init option.
5055
5056       -Wsign-compare
5057           Warn when a comparison between signed and unsigned values could
5058           produce an incorrect result when the signed value is converted to
5059           unsigned.  In C++, this warning is also enabled by -Wall.  In C, it
5060           is also enabled by -Wextra.
5061
5062       -Wsign-conversion
5063           Warn for implicit conversions that may change the sign of an
5064           integer value, like assigning a signed integer expression to an
5065           unsigned integer variable. An explicit cast silences the warning.
5066           In C, this option is enabled also by -Wconversion.
5067
5068       -Wfloat-conversion
5069           Warn for implicit conversions that reduce the precision of a real
5070           value.  This includes conversions from real to integer, and from
5071           higher precision real to lower precision real values.  This option
5072           is also enabled by -Wconversion.
5073
5074       -Wno-scalar-storage-order
5075           Do not warn on suspicious constructs involving reverse scalar
5076           storage order.
5077
5078       -Wsized-deallocation (C++ and Objective-C++ only)
5079           Warn about a definition of an unsized deallocation function
5080
5081                   void operator delete (void *) noexcept;
5082                   void operator delete[] (void *) noexcept;
5083
5084           without a definition of the corresponding sized deallocation
5085           function
5086
5087                   void operator delete (void *, std::size_t) noexcept;
5088                   void operator delete[] (void *, std::size_t) noexcept;
5089
5090           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.
5091
5092       -Wsizeof-pointer-div
5093           Warn for suspicious divisions of two sizeof expressions that divide
5094           the pointer size by the element size, which is the usual way to
5095           compute the array size but won't work out correctly with pointers.
5096           This warning warns e.g. about "sizeof (ptr) / sizeof (ptr[0])" if
5097           "ptr" is not an array, but a pointer.  This warning is enabled by
5098           -Wall.
5099
5100       -Wsizeof-pointer-memaccess
5101           Warn for suspicious length parameters to certain string and memory
5102           built-in functions if the argument uses "sizeof".  This warning
5103           triggers for example for "memset (ptr, 0, sizeof (ptr));" if "ptr"
5104           is not an array, but a pointer, and suggests a possible fix, or
5105           about "memcpy (&foo, ptr, sizeof (&foo));".
5106           -Wsizeof-pointer-memaccess also warns about calls to bounded string
5107           copy functions like "strncat" or "strncpy" that specify as the
5108           bound a "sizeof" expression of the source array.  For example, in
5109           the following function the call to "strncat" specifies the size of
5110           the source string as the bound.  That is almost certainly a mistake
5111           and so the call is diagnosed.
5112
5113                   void make_file (const char *name)
5114                   {
5115                     char path[PATH_MAX];
5116                     strncpy (path, name, sizeof path - 1);
5117                     strncat (path, ".text", sizeof ".text");
5118                     ...
5119                   }
5120
5121           The -Wsizeof-pointer-memaccess option is enabled by -Wall.
5122
5123       -Wsizeof-array-argument
5124           Warn when the "sizeof" operator is applied to a parameter that is
5125           declared as an array in a function definition.  This warning is
5126           enabled by default for C and C++ programs.
5127
5128       -Wmemset-elt-size
5129           Warn for suspicious calls to the "memset" built-in function, if the
5130           first argument references an array, and the third argument is a
5131           number equal to the number of elements, but not equal to the size
5132           of the array in memory.  This indicates that the user has omitted a
5133           multiplication by the element size.  This warning is enabled by
5134           -Wall.
5135
5136       -Wmemset-transposed-args
5137           Warn for suspicious calls to the "memset" built-in function, if the
5138           second argument is not zero and the third argument is zero.  This
5139           warns e.g.@ about "memset (buf, sizeof buf, 0)" where most probably
5140           "memset (buf, 0, sizeof buf)" was meant instead.  The diagnostics
5141           is only emitted if the third argument is literal zero.  If it is
5142           some expression that is folded to zero, a cast of zero to some
5143           type, etc., it is far less likely that the user has mistakenly
5144           exchanged the arguments and no warning is emitted.  This warning is
5145           enabled by -Wall.
5146
5147       -Waddress
5148           Warn about suspicious uses of memory addresses. These include using
5149           the address of a function in a conditional expression, such as
5150           "void func(void); if (func)", and comparisons against the memory
5151           address of a string literal, such as "if (x == "abc")".  Such uses
5152           typically indicate a programmer error: the address of a function
5153           always evaluates to true, so their use in a conditional usually
5154           indicate that the programmer forgot the parentheses in a function
5155           call; and comparisons against string literals result in unspecified
5156           behavior and are not portable in C, so they usually indicate that
5157           the programmer intended to use "strcmp".  This warning is enabled
5158           by -Wall.
5159
5160       -Wlogical-op
5161           Warn about suspicious uses of logical operators in expressions.
5162           This includes using logical operators in contexts where a bit-wise
5163           operator is likely to be expected.  Also warns when the operands of
5164           a logical operator are the same:
5165
5166                   extern int a;
5167                   if (a < 0 && a < 0) { ... }
5168
5169       -Wlogical-not-parentheses
5170           Warn about logical not used on the left hand side operand of a
5171           comparison.  This option does not warn if the right operand is
5172           considered to be a boolean expression.  Its purpose is to detect
5173           suspicious code like the following:
5174
5175                   int a;
5176                   ...
5177                   if (!a > 1) { ... }
5178
5179           It is possible to suppress the warning by wrapping the LHS into
5180           parentheses:
5181
5182                   if ((!a) > 1) { ... }
5183
5184           This warning is enabled by -Wall.
5185
5186       -Waggregate-return
5187           Warn if any functions that return structures or unions are defined
5188           or called.  (In languages where you can return an array, this also
5189           elicits a warning.)
5190
5191       -Wno-aggressive-loop-optimizations
5192           Warn if in a loop with constant number of iterations the compiler
5193           detects undefined behavior in some statement during one or more of
5194           the iterations.
5195
5196       -Wno-attributes
5197           Do not warn if an unexpected "__attribute__" is used, such as
5198           unrecognized attributes, function attributes applied to variables,
5199           etc.  This does not stop errors for incorrect use of supported
5200           attributes.
5201
5202       -Wno-builtin-declaration-mismatch
5203           Warn if a built-in function is declared with the wrong signature or
5204           as non-function.  This warning is enabled by default.
5205
5206       -Wno-builtin-macro-redefined
5207           Do not warn if certain built-in macros are redefined.  This
5208           suppresses warnings for redefinition of "__TIMESTAMP__",
5209           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".
5210
5211       -Wstrict-prototypes (C and Objective-C only)
5212           Warn if a function is declared or defined without specifying the
5213           argument types.  (An old-style function definition is permitted
5214           without a warning if preceded by a declaration that specifies the
5215           argument types.)
5216
5217       -Wold-style-declaration (C and Objective-C only)
5218           Warn for obsolescent usages, according to the C Standard, in a
5219           declaration. For example, warn if storage-class specifiers like
5220           "static" are not the first things in a declaration.  This warning
5221           is also enabled by -Wextra.
5222
5223       -Wold-style-definition (C and Objective-C only)
5224           Warn if an old-style function definition is used.  A warning is
5225           given even if there is a previous prototype.
5226
5227       -Wmissing-parameter-type (C and Objective-C only)
5228           A function parameter is declared without a type specifier in
5229           K&R-style functions:
5230
5231                   void foo(bar) { }
5232
5233           This warning is also enabled by -Wextra.
5234
5235       -Wmissing-prototypes (C and Objective-C only)
5236           Warn if a global function is defined without a previous prototype
5237           declaration.  This warning is issued even if the definition itself
5238           provides a prototype.  Use this option to detect global functions
5239           that do not have a matching prototype declaration in a header file.
5240           This option is not valid for C++ because all function declarations
5241           provide prototypes and a non-matching declaration declares an
5242           overload rather than conflict with an earlier declaration.  Use
5243           -Wmissing-declarations to detect missing declarations in C++.
5244
5245       -Wmissing-declarations
5246           Warn if a global function is defined without a previous
5247           declaration.  Do so even if the definition itself provides a
5248           prototype.  Use this option to detect global functions that are not
5249           declared in header files.  In C, no warnings are issued for
5250           functions with previous non-prototype declarations; use
5251           -Wmissing-prototypes to detect missing prototypes.  In C++, no
5252           warnings are issued for function templates, or for inline
5253           functions, or for functions in anonymous namespaces.
5254
5255       -Wmissing-field-initializers
5256           Warn if a structure's initializer has some fields missing.  For
5257           example, the following code causes such a warning, because "x.h" is
5258           implicitly zero:
5259
5260                   struct s { int f, g, h; };
5261                   struct s x = { 3, 4 };
5262
5263           This option does not warn about designated initializers, so the
5264           following modification does not trigger a warning:
5265
5266                   struct s { int f, g, h; };
5267                   struct s x = { .f = 3, .g = 4 };
5268
5269           In C this option does not warn about the universal zero initializer
5270           { 0 }:
5271
5272                   struct s { int f, g, h; };
5273                   struct s x = { 0 };
5274
5275           Likewise, in C++ this option does not warn about the empty { }
5276           initializer, for example:
5277
5278                   struct s { int f, g, h; };
5279                   s x = { };
5280
5281           This warning is included in -Wextra.  To get other -Wextra warnings
5282           without this one, use -Wextra -Wno-missing-field-initializers.
5283
5284       -Wno-multichar
5285           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
5286           they indicate a typo in the user's code, as they have
5287           implementation-defined values, and should not be used in portable
5288           code.
5289
5290       -Wnormalized=[none|id|nfc|nfkc]
5291           In ISO C and ISO C++, two identifiers are different if they are
5292           different sequences of characters.  However, sometimes when
5293           characters outside the basic ASCII character set are used, you can
5294           have two different character sequences that look the same.  To
5295           avoid confusion, the ISO 10646 standard sets out some normalization
5296           rules which when applied ensure that two sequences that look the
5297           same are turned into the same sequence.  GCC can warn you if you
5298           are using identifiers that have not been normalized; this option
5299           controls that warning.
5300
5301           There are four levels of warning supported by GCC.  The default is
5302           -Wnormalized=nfc, which warns about any identifier that is not in
5303           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
5304           form for most uses.  It is equivalent to -Wnormalized.
5305
5306           Unfortunately, there are some characters allowed in identifiers by
5307           ISO C and ISO C++ that, when turned into NFC, are not allowed in
5308           identifiers.  That is, there's no way to use these symbols in
5309           portable ISO C or C++ and have all your identifiers in NFC.
5310           -Wnormalized=id suppresses the warning for these characters.  It is
5311           hoped that future versions of the standards involved will correct
5312           this, which is why this option is not the default.
5313
5314           You can switch the warning off for all characters by writing
5315           -Wnormalized=none or -Wno-normalized.  You should only do this if
5316           you are using some other normalization scheme (like "D"), because
5317           otherwise you can easily create bugs that are literally impossible
5318           to see.
5319
5320           Some characters in ISO 10646 have distinct meanings but look
5321           identical in some fonts or display methodologies, especially once
5322           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
5323           LATIN SMALL LETTER N", displays just like a regular "n" that has
5324           been placed in a superscript.  ISO 10646 defines the NFKC
5325           normalization scheme to convert all these into a standard form as
5326           well, and GCC warns if your code is not in NFKC if you use
5327           -Wnormalized=nfkc.  This warning is comparable to warning about
5328           every identifier that contains the letter O because it might be
5329           confused with the digit 0, and so is not the default, but may be
5330           useful as a local coding convention if the programming environment
5331           cannot be fixed to display these characters distinctly.
5332
5333       -Wno-deprecated
5334           Do not warn about usage of deprecated features.
5335
5336       -Wno-deprecated-declarations
5337           Do not warn about uses of functions, variables, and types marked as
5338           deprecated by using the "deprecated" attribute.
5339
5340       -Wno-overflow
5341           Do not warn about compile-time overflow in constant expressions.
5342
5343       -Wno-odr
5344           Warn about One Definition Rule violations during link-time
5345           optimization.  Requires -flto-odr-type-merging to be enabled.
5346           Enabled by default.
5347
5348       -Wopenmp-simd
5349           Warn if the vectorizer cost model overrides the OpenMP simd
5350           directive set by user.  The -fsimd-cost-model=unlimited option can
5351           be used to relax the cost model.
5352
5353       -Woverride-init (C and Objective-C only)
5354           Warn if an initialized field without side effects is overridden
5355           when using designated initializers.
5356
5357           This warning is included in -Wextra.  To get other -Wextra warnings
5358           without this one, use -Wextra -Wno-override-init.
5359
5360       -Woverride-init-side-effects (C and Objective-C only)
5361           Warn if an initialized field with side effects is overridden when
5362           using designated initializers.  This warning is enabled by default.
5363
5364       -Wpacked
5365           Warn if a structure is given the packed attribute, but the packed
5366           attribute has no effect on the layout or size of the structure.
5367           Such structures may be mis-aligned for little benefit.  For
5368           instance, in this code, the variable "f.x" in "struct bar" is
5369           misaligned even though "struct bar" does not itself have the packed
5370           attribute:
5371
5372                   struct foo {
5373                     int x;
5374                     char a, b, c, d;
5375                   } __attribute__((packed));
5376                   struct bar {
5377                     char z;
5378                     struct foo f;
5379                   };
5380
5381       -Wpacked-bitfield-compat
5382           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
5383           bit-fields of type "char".  This has been fixed in GCC 4.4 but the
5384           change can lead to differences in the structure layout.  GCC
5385           informs you when the offset of such a field has changed in GCC 4.4.
5386           For example there is no longer a 4-bit padding between field "a"
5387           and "b" in this structure:
5388
5389                   struct foo
5390                   {
5391                     char a:4;
5392                     char b:8;
5393                   } __attribute__ ((packed));
5394
5395           This warning is enabled by default.  Use
5396           -Wno-packed-bitfield-compat to disable this warning.
5397
5398       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
5399           Warn if a structure field with explicitly specified alignment in a
5400           packed struct or union is misaligned.  For example, a warning will
5401           be issued on "struct S", like, "warning: alignment 1 of 'struct S'
5402           is less than 8", in this code:
5403
5404                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
5405                   struct __attribute__ ((packed)) S {
5406                     struct S8 s8;
5407                   };
5408
5409           This warning is enabled by -Wall.
5410
5411       -Wpadded
5412           Warn if padding is included in a structure, either to align an
5413           element of the structure or to align the whole structure.
5414           Sometimes when this happens it is possible to rearrange the fields
5415           of the structure to reduce the padding and so make the structure
5416           smaller.
5417
5418       -Wredundant-decls
5419           Warn if anything is declared more than once in the same scope, even
5420           in cases where multiple declaration is valid and changes nothing.
5421
5422       -Wno-restrict
5423           Warn when an object referenced by a "restrict"-qualified parameter
5424           (or, in C++, a "__restrict"-qualified parameter) is aliased by
5425           another argument, or when copies between such objects overlap.  For
5426           example, the call to the "strcpy" function below attempts to
5427           truncate the string by replacing its initial characters with the
5428           last four.  However, because the call writes the terminating NUL
5429           into "a[4]", the copies overlap and the call is diagnosed.
5430
5431                   void foo (void)
5432                   {
5433                     char a[] = "abcd1234";
5434                     strcpy (a, a + 4);
5435                     ...
5436                   }
5437
5438           The -Wrestrict option detects some instances of simple overlap even
5439           without optimization but works best at -O2 and above.  It is
5440           included in -Wall.
5441
5442       -Wnested-externs (C and Objective-C only)
5443           Warn if an "extern" declaration is encountered within a function.
5444
5445       -Wno-inherited-variadic-ctor
5446           Suppress warnings about use of C++11 inheriting constructors when
5447           the base class inherited from has a C variadic constructor; the
5448           warning is on by default because the ellipsis is not inherited.
5449
5450       -Winline
5451           Warn if a function that is declared as inline cannot be inlined.
5452           Even with this option, the compiler does not warn about failures to
5453           inline functions declared in system headers.
5454
5455           The compiler uses a variety of heuristics to determine whether or
5456           not to inline a function.  For example, the compiler takes into
5457           account the size of the function being inlined and the amount of
5458           inlining that has already been done in the current function.
5459           Therefore, seemingly insignificant changes in the source program
5460           can cause the warnings produced by -Winline to appear or disappear.
5461
5462       -Wno-invalid-offsetof (C++ and Objective-C++ only)
5463           Suppress warnings from applying the "offsetof" macro to a non-POD
5464           type.  According to the 2014 ISO C++ standard, applying "offsetof"
5465           to a non-standard-layout type is undefined.  In existing C++
5466           implementations, however, "offsetof" typically gives meaningful
5467           results.  This flag is for users who are aware that they are
5468           writing nonportable code and who have deliberately chosen to ignore
5469           the warning about it.
5470
5471           The restrictions on "offsetof" may be relaxed in a future version
5472           of the C++ standard.
5473
5474       -Wint-in-bool-context
5475           Warn for suspicious use of integer values where boolean values are
5476           expected, such as conditional expressions (?:) using non-boolean
5477           integer constants in boolean context, like "if (a <= b ? 2 : 3)".
5478           Or left shifting of signed integers in boolean context, like "for
5479           (a = 0; 1 << a; a++);".  Likewise for all kinds of multiplications
5480           regardless of the data type.  This warning is enabled by -Wall.
5481
5482       -Wno-int-to-pointer-cast
5483           Suppress warnings from casts to pointer type of an integer of a
5484           different size. In C++, casting to a pointer type of smaller size
5485           is an error. Wint-to-pointer-cast is enabled by default.
5486
5487       -Wno-pointer-to-int-cast (C and Objective-C only)
5488           Suppress warnings from casts from a pointer to an integer type of a
5489           different size.
5490
5491       -Winvalid-pch
5492           Warn if a precompiled header is found in the search path but cannot
5493           be used.
5494
5495       -Wlong-long
5496           Warn if "long long" type is used.  This is enabled by either
5497           -Wpedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
5498           the warning messages, use -Wno-long-long.
5499
5500       -Wvariadic-macros
5501           Warn if variadic macros are used in ISO C90 mode, or if the GNU
5502           alternate syntax is used in ISO C99 mode.  This is enabled by
5503           either -Wpedantic or -Wtraditional.  To inhibit the warning
5504           messages, use -Wno-variadic-macros.
5505
5506       -Wvarargs
5507           Warn upon questionable usage of the macros used to handle variable
5508           arguments like "va_start".  This is default.  To inhibit the
5509           warning messages, use -Wno-varargs.
5510
5511       -Wvector-operation-performance
5512           Warn if vector operation is not implemented via SIMD capabilities
5513           of the architecture.  Mainly useful for the performance tuning.
5514           Vector operation can be implemented "piecewise", which means that
5515           the scalar operation is performed on every vector element; "in
5516           parallel", which means that the vector operation is implemented
5517           using scalars of wider type, which normally is more performance
5518           efficient; and "as a single scalar", which means that vector fits
5519           into a scalar type.
5520
5521       -Wno-virtual-move-assign
5522           Suppress warnings about inheriting from a virtual base with a non-
5523           trivial C++11 move assignment operator.  This is dangerous because
5524           if the virtual base is reachable along more than one path, it is
5525           moved multiple times, which can mean both objects end up in the
5526           moved-from state.  If the move assignment operator is written to
5527           avoid moving from a moved-from object, this warning can be
5528           disabled.
5529
5530       -Wvla
5531           Warn if a variable-length array is used in the code.  -Wno-vla
5532           prevents the -Wpedantic warning of the variable-length array.
5533
5534       -Wvla-larger-than=n
5535           If this option is used, the compiler will warn on uses of variable-
5536           length arrays where the size is either unbounded, or bounded by an
5537           argument that can be larger than n bytes.  This is similar to how
5538           -Walloca-larger-than=n works, but with variable-length arrays.
5539
5540           Note that GCC may optimize small variable-length arrays of a known
5541           value into plain arrays, so this warning may not get triggered for
5542           such arrays.
5543
5544           This warning is not enabled by -Wall, and is only active when
5545           -ftree-vrp is active (default for -O2 and above).
5546
5547           See also -Walloca-larger-than=n.
5548
5549       -Wvolatile-register-var
5550           Warn if a register variable is declared volatile.  The volatile
5551           modifier does not inhibit all optimizations that may eliminate
5552           reads and/or writes to register variables.  This warning is enabled
5553           by -Wall.
5554
5555       -Wdisabled-optimization
5556           Warn if a requested optimization pass is disabled.  This warning
5557           does not generally indicate that there is anything wrong with your
5558           code; it merely indicates that GCC's optimizers are unable to
5559           handle the code effectively.  Often, the problem is that your code
5560           is too big or too complex; GCC refuses to optimize programs when
5561           the optimization itself is likely to take inordinate amounts of
5562           time.
5563
5564       -Wpointer-sign (C and Objective-C only)
5565           Warn for pointer argument passing or assignment with different
5566           signedness.  This option is only supported for C and Objective-C.
5567           It is implied by -Wall and by -Wpedantic, which can be disabled
5568           with -Wno-pointer-sign.
5569
5570       -Wstack-protector
5571           This option is only active when -fstack-protector is active.  It
5572           warns about functions that are not protected against stack
5573           smashing.
5574
5575       -Woverlength-strings
5576           Warn about string constants that are longer than the "minimum
5577           maximum" length specified in the C standard.  Modern compilers
5578           generally allow string constants that are much longer than the
5579           standard's minimum limit, but very portable programs should avoid
5580           using longer strings.
5581
5582           The limit applies after string constant concatenation, and does not
5583           count the trailing NUL.  In C90, the limit was 509 characters; in
5584           C99, it was raised to 4095.  C++98 does not specify a normative
5585           minimum maximum, so we do not diagnose overlength strings in C++.
5586
5587           This option is implied by -Wpedantic, and can be disabled with
5588           -Wno-overlength-strings.
5589
5590       -Wunsuffixed-float-constants (C and Objective-C only)
5591           Issue a warning for any floating constant that does not have a
5592           suffix.  When used together with -Wsystem-headers it warns about
5593           such constants in system header files.  This can be useful when
5594           preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from
5595           the decimal floating-point extension to C99.
5596
5597       -Wno-designated-init (C and Objective-C only)
5598           Suppress warnings when a positional initializer is used to
5599           initialize a structure that has been marked with the
5600           "designated_init" attribute.
5601
5602       -Whsa
5603           Issue a warning when HSAIL cannot be emitted for the compiled
5604           function or OpenMP construct.
5605
5606   Options for Debugging Your Program
5607       To tell GCC to emit extra information for use by a debugger, in almost
5608       all cases you need only to add -g to your other options.
5609
5610       GCC allows you to use -g with -O.  The shortcuts taken by optimized
5611       code may occasionally be surprising: some variables you declared may
5612       not exist at all; flow of control may briefly move where you did not
5613       expect it; some statements may not be executed because they compute
5614       constant results or their values are already at hand; some statements
5615       may execute in different places because they have been moved out of
5616       loops.  Nevertheless it is possible to debug optimized output.  This
5617       makes it reasonable to use the optimizer for programs that might have
5618       bugs.
5619
5620       If you are not using some other optimization option, consider using -Og
5621       with -g.  With no -O option at all, some compiler passes that collect
5622       information useful for debugging do not run at all, so that -Og may
5623       result in a better debugging experience.
5624
5625       -g  Produce debugging information in the operating system's native
5626           format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
5627           debugging information.
5628
5629           On most systems that use stabs format, -g enables use of extra
5630           debugging information that only GDB can use; this extra information
5631           makes debugging work better in GDB but probably makes other
5632           debuggers crash or refuse to read the program.  If you want to
5633           control for certain whether to generate the extra information, use
5634           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
5635
5636       -ggdb
5637           Produce debugging information for use by GDB.  This means to use
5638           the most expressive format available (DWARF, stabs, or the native
5639           format if neither of those are supported), including GDB extensions
5640           if at all possible.
5641
5642       -gdwarf
5643       -gdwarf-version
5644           Produce debugging information in DWARF format (if that is
5645           supported).  The value of version may be either 2, 3, 4 or 5; the
5646           default version for most targets is 4.  DWARF Version 5 is only
5647           experimental.
5648
5649           Note that with DWARF Version 2, some ports require and always use
5650           some non-conflicting DWARF 3 extensions in the unwind tables.
5651
5652           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
5653           maximum benefit.
5654
5655           GCC no longer supports DWARF Version 1, which is substantially
5656           different than Version 2 and later.  For historical reasons, some
5657           other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a
5658           reference to DWARF Version 2 in their names, but apply to all
5659           currently-supported versions of DWARF.
5660
5661       -gstabs
5662           Produce debugging information in stabs format (if that is
5663           supported), without GDB extensions.  This is the format used by DBX
5664           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
5665           this option produces stabs debugging output that is not understood
5666           by DBX.  On System V Release 4 systems this option requires the GNU
5667           assembler.
5668
5669       -gstabs+
5670           Produce debugging information in stabs format (if that is
5671           supported), using GNU extensions understood only by the GNU
5672           debugger (GDB).  The use of these extensions is likely to make
5673           other debuggers crash or refuse to read the program.
5674
5675       -gxcoff
5676           Produce debugging information in XCOFF format (if that is
5677           supported).  This is the format used by the DBX debugger on IBM
5678           RS/6000 systems.
5679
5680       -gxcoff+
5681           Produce debugging information in XCOFF format (if that is
5682           supported), using GNU extensions understood only by the GNU
5683           debugger (GDB).  The use of these extensions is likely to make
5684           other debuggers crash or refuse to read the program, and may cause
5685           assemblers other than the GNU assembler (GAS) to fail with an
5686           error.
5687
5688       -gvms
5689           Produce debugging information in Alpha/VMS debug format (if that is
5690           supported).  This is the format used by DEBUG on Alpha/VMS systems.
5691
5692       -glevel
5693       -ggdblevel
5694       -gstabslevel
5695       -gxcofflevel
5696       -gvmslevel
5697           Request debugging information and also use level to specify how
5698           much information.  The default level is 2.
5699
5700           Level 0 produces no debug information at all.  Thus, -g0 negates
5701           -g.
5702
5703           Level 1 produces minimal information, enough for making backtraces
5704           in parts of the program that you don't plan to debug.  This
5705           includes descriptions of functions and external variables, and line
5706           number tables, but no information about local variables.
5707
5708           Level 3 includes extra information, such as all the macro
5709           definitions present in the program.  Some debuggers support macro
5710           expansion when you use -g3.
5711
5712           -gdwarf does not accept a concatenated debug level, to avoid
5713           confusion with -gdwarf-level.  Instead use an additional -glevel
5714           option to change the debug level for DWARF.
5715
5716       -feliminate-unused-debug-symbols
5717           Produce debugging information in stabs format (if that is
5718           supported), for only symbols that are actually used.
5719
5720       -femit-class-debug-always
5721           Instead of emitting debugging information for a C++ class in only
5722           one object file, emit it in all object files using the class.  This
5723           option should be used only with debuggers that are unable to handle
5724           the way GCC normally emits debugging information for classes
5725           because using this option increases the size of debugging
5726           information by as much as a factor of two.
5727
5728       -fno-merge-debug-strings
5729           Direct the linker to not merge together strings in the debugging
5730           information that are identical in different object files.  Merging
5731           is not supported by all assemblers or linkers.  Merging decreases
5732           the size of the debug information in the output file at the cost of
5733           increasing link processing time.  Merging is enabled by default.
5734
5735       -fdebug-prefix-map=old=new
5736           When compiling files residing in directory old, record debugging
5737           information describing them as if the files resided in directory
5738           new instead.  This can be used to replace a build-time path with an
5739           install-time path in the debug info.  It can also be used to change
5740           an absolute path to a relative path by using . for new.  This can
5741           give more reproducible builds, which are location independent, but
5742           may require an extra command to tell GDB where to find the source
5743           files. See also -ffile-prefix-map.
5744
5745       -fvar-tracking
5746           Run variable tracking pass.  It computes where variables are stored
5747           at each position in code.  Better debugging information is then
5748           generated (if the debugging information format supports this
5749           information).
5750
5751           It is enabled by default when compiling with optimization (-Os, -O,
5752           -O2, ...), debugging information (-g) and the debug info format
5753           supports it.
5754
5755       -fvar-tracking-assignments
5756           Annotate assignments to user variables early in the compilation and
5757           attempt to carry the annotations over throughout the compilation
5758           all the way to the end, in an attempt to improve debug information
5759           while optimizing.  Use of -gdwarf-4 is recommended along with it.
5760
5761           It can be enabled even if var-tracking is disabled, in which case
5762           annotations are created and maintained, but discarded at the end.
5763           By default, this flag is enabled together with -fvar-tracking,
5764           except when selective scheduling is enabled.
5765
5766       -gsplit-dwarf
5767           Separate as much DWARF debugging information as possible into a
5768           separate output file with the extension .dwo.  This option allows
5769           the build system to avoid linking files with debug information.  To
5770           be useful, this option requires a debugger capable of reading .dwo
5771           files.
5772
5773       -gpubnames
5774           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.
5775
5776       -ggnu-pubnames
5777           Generate ".debug_pubnames" and ".debug_pubtypes" sections in a
5778           format suitable for conversion into a GDB index.  This option is
5779           only useful with a linker that can produce GDB index version 7.
5780
5781       -fdebug-types-section
5782           When using DWARF Version 4 or higher, type DIEs can be put into
5783           their own ".debug_types" section instead of making them part of the
5784           ".debug_info" section.  It is more efficient to put them in a
5785           separate comdat sections since the linker can then remove
5786           duplicates.  But not all DWARF consumers support ".debug_types"
5787           sections yet and on some objects ".debug_types" produces larger
5788           instead of smaller debugging information.
5789
5790       -grecord-gcc-switches
5791       -gno-record-gcc-switches
5792           This switch causes the command-line options used to invoke the
5793           compiler that may affect code generation to be appended to the
5794           DW_AT_producer attribute in DWARF debugging information.  The
5795           options are concatenated with spaces separating them from each
5796           other and from the compiler version.  It is enabled by default.
5797           See also -frecord-gcc-switches for another way of storing compiler
5798           options into the object file.
5799
5800       -gstrict-dwarf
5801           Disallow using extensions of later DWARF standard version than
5802           selected with -gdwarf-version.  On most targets using non-
5803           conflicting DWARF extensions from later standard versions is
5804           allowed.
5805
5806       -gno-strict-dwarf
5807           Allow using extensions of later DWARF standard version than
5808           selected with -gdwarf-version.
5809
5810       -gas-loc-support
5811           Inform the compiler that the assembler supports ".loc" directives.
5812           It may then use them for the assembler to generate DWARF2+ line
5813           number tables.
5814
5815           This is generally desirable, because assembler-generated line-
5816           number tables are a lot more compact than those the compiler can
5817           generate itself.
5818
5819           This option will be enabled by default if, at GCC configure time,
5820           the assembler was found to support such directives.
5821
5822       -gno-as-loc-support
5823           Force GCC to generate DWARF2+ line number tables internally, if
5824           DWARF2+ line number tables are to be generated.
5825
5826       gas-locview-support
5827           Inform the compiler that the assembler supports "view" assignment
5828           and reset assertion checking in ".loc" directives.
5829
5830           This option will be enabled by default if, at GCC configure time,
5831           the assembler was found to support them.
5832
5833       gno-as-locview-support
5834           Force GCC to assign view numbers internally, if
5835           -gvariable-location-views are explicitly requested.
5836
5837       -gcolumn-info
5838       -gno-column-info
5839           Emit location column information into DWARF debugging information,
5840           rather than just file and line.  This option is enabled by default.
5841
5842       -gstatement-frontiers
5843       -gno-statement-frontiers
5844           This option causes GCC to create markers in the internal
5845           representation at the beginning of statements, and to keep them
5846           roughly in place throughout compilation, using them to guide the
5847           output of "is_stmt" markers in the line number table.  This is
5848           enabled by default when compiling with optimization (-Os, -O, -O2,
5849           ...), and outputting DWARF 2 debug information at the normal level.
5850
5851       -gvariable-location-views
5852       -gvariable-location-views=incompat5
5853       -gno-variable-location-views
5854           Augment variable location lists with progressive view numbers
5855           implied from the line number table.  This enables debug information
5856           consumers to inspect state at certain points of the program, even
5857           if no instructions associated with the corresponding source
5858           locations are present at that point.  If the assembler lacks
5859           support for view numbers in line number tables, this will cause the
5860           compiler to emit the line number table, which generally makes them
5861           somewhat less compact.  The augmented line number tables and
5862           location lists are fully backward-compatible, so they can be
5863           consumed by debug information consumers that are not aware of these
5864           augmentations, but they won't derive any benefit from them either.
5865
5866           This is enabled by default when outputting DWARF 2 debug
5867           information at the normal level, as long as there is assembler
5868           support, -fvar-tracking-assignments is enabled and -gstrict-dwarf
5869           is not.  When assembler support is not available, this may still be
5870           enabled, but it will force GCC to output internal line number
5871           tables, and if -ginternal-reset-location-views is not enabled, that
5872           will most certainly lead to silently mismatching location views.
5873
5874           There is a proposed representation for view numbers that is not
5875           backward compatible with the location list format introduced in
5876           DWARF 5, that can be enabled with
5877           -gvariable-location-views=incompat5.  This option may be removed in
5878           the future, is only provided as a reference implementation of the
5879           proposed representation.  Debug information consumers are not
5880           expected to support this extended format, and they would be
5881           rendered unable to decode location lists using it.
5882
5883       -ginternal-reset-location-views
5884       -gnointernal-reset-location-views
5885           Attempt to determine location views that can be omitted from
5886           location view lists.  This requires the compiler to have very
5887           accurate insn length estimates, which isn't always the case, and it
5888           may cause incorrect view lists to be generated silently when using
5889           an assembler that does not support location view lists.  The GNU
5890           assembler will flag any such error as a "view number mismatch".
5891           This is only enabled on ports that define a reliable estimation
5892           function.
5893
5894       -ginline-points
5895       -gno-inline-points
5896           Generate extended debug information for inlined functions.
5897           Location view tracking markers are inserted at inlined entry
5898           points, so that address and view numbers can be computed and output
5899           in debug information.  This can be enabled independently of
5900           location views, in which case the view numbers won't be output, but
5901           it can only be enabled along with statement frontiers, and it is
5902           only enabled by default if location views are enabled.
5903
5904       -gz[=type]
5905           Produce compressed debug sections in DWARF format, if that is
5906           supported.  If type is not given, the default type depends on the
5907           capabilities of the assembler and linker used.  type may be one of
5908           none (don't compress debug sections), zlib (use zlib compression in
5909           ELF gABI format), or zlib-gnu (use zlib compression in traditional
5910           GNU format).  If the linker doesn't support writing compressed
5911           debug sections, the option is rejected.  Otherwise, if the
5912           assembler does not support them, -gz is silently ignored when
5913           producing object files.
5914
5915       -femit-struct-debug-baseonly
5916           Emit debug information for struct-like types only when the base
5917           name of the compilation source file matches the base name of file
5918           in which the struct is defined.
5919
5920           This option substantially reduces the size of debugging
5921           information, but at significant potential loss in type information
5922           to the debugger.  See -femit-struct-debug-reduced for a less
5923           aggressive option.  See -femit-struct-debug-detailed for more
5924           detailed control.
5925
5926           This option works only with DWARF debug output.
5927
5928       -femit-struct-debug-reduced
5929           Emit debug information for struct-like types only when the base
5930           name of the compilation source file matches the base name of file
5931           in which the type is defined, unless the struct is a template or
5932           defined in a system header.
5933
5934           This option significantly reduces the size of debugging
5935           information, with some potential loss in type information to the
5936           debugger.  See -femit-struct-debug-baseonly for a more aggressive
5937           option.  See -femit-struct-debug-detailed for more detailed
5938           control.
5939
5940           This option works only with DWARF debug output.
5941
5942       -femit-struct-debug-detailed[=spec-list]
5943           Specify the struct-like types for which the compiler generates
5944           debug information.  The intent is to reduce duplicate struct debug
5945           information between different object files within the same program.
5946
5947           This option is a detailed version of -femit-struct-debug-reduced
5948           and -femit-struct-debug-baseonly, which serves for most needs.
5949
5950           A specification has the
5951           syntax[dir:|ind:][ord:|gen:](any|sys|base|none)
5952
5953           The optional first word limits the specification to structs that
5954           are used directly (dir:) or used indirectly (ind:).  A struct type
5955           is used directly when it is the type of a variable, member.
5956           Indirect uses arise through pointers to structs.  That is, when use
5957           of an incomplete struct is valid, the use is indirect.  An example
5958           is struct one direct; struct two * indirect;.
5959
5960           The optional second word limits the specification to ordinary
5961           structs (ord:) or generic structs (gen:).  Generic structs are a
5962           bit complicated to explain.  For C++, these are non-explicit
5963           specializations of template classes, or non-template classes within
5964           the above.  Other programming languages have generics, but
5965           -femit-struct-debug-detailed does not yet implement them.
5966
5967           The third word specifies the source files for those structs for
5968           which the compiler should emit debug information.  The values none
5969           and any have the normal meaning.  The value base means that the
5970           base of name of the file in which the type declaration appears must
5971           match the base of the name of the main compilation file.  In
5972           practice, this means that when compiling foo.c, debug information
5973           is generated for types declared in that file and foo.h, but not
5974           other header files.  The value sys means those types satisfying
5975           base or declared in system or compiler headers.
5976
5977           You may need to experiment to determine the best settings for your
5978           application.
5979
5980           The default is -femit-struct-debug-detailed=all.
5981
5982           This option works only with DWARF debug output.
5983
5984       -fno-dwarf2-cfi-asm
5985           Emit DWARF unwind info as compiler generated ".eh_frame" section
5986           instead of using GAS ".cfi_*" directives.
5987
5988       -fno-eliminate-unused-debug-types
5989           Normally, when producing DWARF output, GCC avoids producing debug
5990           symbol output for types that are nowhere used in the source file
5991           being compiled.  Sometimes it is useful to have GCC emit debugging
5992           information for all types declared in a compilation unit,
5993           regardless of whether or not they are actually used in that
5994           compilation unit, for example if, in the debugger, you want to cast
5995           a value to a type that is not actually used in your program (but is
5996           declared).  More often, however, this results in a significant
5997           amount of wasted space.
5998
5999   Options That Control Optimization
6000       These options control various sorts of optimizations.
6001
6002       Without any optimization option, the compiler's goal is to reduce the
6003       cost of compilation and to make debugging produce the expected results.
6004       Statements are independent: if you stop the program with a breakpoint
6005       between statements, you can then assign a new value to any variable or
6006       change the program counter to any other statement in the function and
6007       get exactly the results you expect from the source code.
6008
6009       Turning on optimization flags makes the compiler attempt to improve the
6010       performance and/or code size at the expense of compilation time and
6011       possibly the ability to debug the program.
6012
6013       The compiler performs optimization based on the knowledge it has of the
6014       program.  Compiling multiple files at once to a single output file mode
6015       allows the compiler to use information gained from all of the files
6016       when compiling each of them.
6017
6018       Not all optimizations are controlled directly by a flag.  Only
6019       optimizations that have a flag are listed in this section.
6020
6021       Most optimizations are only enabled if an -O level is set on the
6022       command line.  Otherwise they are disabled, even if individual
6023       optimization flags are specified.
6024
6025       Depending on the target and how GCC was configured, a slightly
6026       different set of optimizations may be enabled at each -O level than
6027       those listed here.  You can invoke GCC with -Q --help=optimizers to
6028       find out the exact set of optimizations that are enabled at each level.
6029
6030       -O
6031       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
6032           lot more memory for a large function.
6033
6034           With -O, the compiler tries to reduce code size and execution time,
6035           without performing any optimizations that take a great deal of
6036           compilation time.
6037
6038           -O turns on the following optimization flags:
6039
6040           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments
6041           -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch
6042           -fdse -fforward-propagate -fguess-branch-probability
6043           -fif-conversion2 -fif-conversion -finline-functions-called-once
6044           -fipa-pure-const -fipa-profile -fipa-reference -fmerge-constants
6045           -fmove-loop-invariants -fomit-frame-pointer -freorder-blocks
6046           -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types
6047           -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch
6048           -ftree-coalesce-vars -ftree-copy-prop -ftree-dce
6049           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
6050           -ftree-phiprop -ftree-sink -ftree-slsr -ftree-sra -ftree-pta
6051           -ftree-ter -funit-at-a-time
6052
6053       -O2 Optimize even more.  GCC performs nearly all supported
6054           optimizations that do not involve a space-speed tradeoff.  As
6055           compared to -O, this option increases both compilation time and the
6056           performance of the generated code.
6057
6058           -O2 turns on all optimization flags specified by -O.  It also turns
6059           on the following optimization flags: -fthread-jumps
6060           -falign-functions  -falign-jumps -falign-loops  -falign-labels
6061           -fcaller-saves -fcrossjumping -fcse-follow-jumps  -fcse-skip-blocks
6062           -fdelete-null-pointer-checks -fdevirtualize
6063           -fdevirtualize-speculatively -fexpensive-optimizations -fgcse
6064           -fgcse-lm -fhoist-adjacent-loads -finline-small-functions
6065           -findirect-inlining -fipa-cp -fipa-bit-cp -fipa-vrp -fipa-sra
6066           -fipa-icf -fisolate-erroneous-paths-dereference -flra-remat
6067           -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining
6068           -fpeephole2 -freorder-blocks-algorithm=stc
6069           -freorder-blocks-and-partition -freorder-functions
6070           -frerun-cse-after-loop -fsched-interblock  -fsched-spec
6071           -fschedule-insns  -fschedule-insns2 -fstore-merging
6072           -fstrict-aliasing -ftree-builtin-call-dce -ftree-switch-conversion
6073           -ftree-tail-merge -fcode-hoisting -ftree-pre -ftree-vrp -fipa-ra
6074
6075           Please note the warning under -fgcse about invoking -O2 on programs
6076           that use computed gotos.
6077
6078       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
6079           and also turns on the following optimization flags:
6080           -finline-functions -funswitch-loops -fpredictive-commoning
6081           -fgcse-after-reload -ftree-loop-vectorize -ftree-loop-distribution
6082           -ftree-loop-distribute-patterns -floop-interchange
6083           -floop-unroll-and-jam -fsplit-paths -ftree-slp-vectorize
6084           -fvect-cost-model -ftree-partial-pre -fpeel-loops -fipa-cp-clone
6085
6086       -O0 Reduce compilation time and make debugging produce the expected
6087           results.  This is the default.
6088
6089       -Os Optimize for size.  -Os enables all -O2 optimizations that do not
6090           typically increase code size.  It also performs further
6091           optimizations designed to reduce code size.
6092
6093           -Os disables the following optimization flags: -falign-functions
6094           -falign-jumps  -falign-loops -falign-labels  -freorder-blocks
6095           -freorder-blocks-algorithm=stc -freorder-blocks-and-partition
6096           -fprefetch-loop-arrays
6097
6098       -Ofast
6099           Disregard strict standards compliance.  -Ofast enables all -O3
6100           optimizations.  It also enables optimizations that are not valid
6101           for all standard-compliant programs.  It turns on -ffast-math and
6102           the Fortran-specific -fstack-arrays, unless -fmax-stack-var-size is
6103           specified, and -fno-protect-parens.
6104
6105       -Og Optimize debugging experience.  -Og enables optimizations that do
6106           not interfere with debugging. It should be the optimization level
6107           of choice for the standard edit-compile-debug cycle, offering a
6108           reasonable level of optimization while maintaining fast compilation
6109           and a good debugging experience.
6110
6111       If you use multiple -O options, with or without level numbers, the last
6112       such option is the one that is effective.
6113
6114       Options of the form -fflag specify machine-independent flags.  Most
6115       flags have both positive and negative forms; the negative form of -ffoo
6116       is -fno-foo.  In the table below, only one of the forms is listed---the
6117       one you typically use.  You can figure out the other form by either
6118       removing no- or adding it.
6119
6120       The following options control specific optimizations.  They are either
6121       activated by -O options or are related to ones that are.  You can use
6122       the following flags in the rare cases when "fine-tuning" of
6123       optimizations to be performed is desired.
6124
6125       -fno-defer-pop
6126           Always pop the arguments to each function call as soon as that
6127           function returns.  For machines that must pop arguments after a
6128           function call, the compiler normally lets arguments accumulate on
6129           the stack for several function calls and pops them all at once.
6130
6131           Disabled at levels -O, -O2, -O3, -Os.
6132
6133       -fforward-propagate
6134           Perform a forward propagation pass on RTL.  The pass tries to
6135           combine two instructions and checks if the result can be
6136           simplified.  If loop unrolling is active, two passes are performed
6137           and the second is scheduled after loop unrolling.
6138
6139           This option is enabled by default at optimization levels -O, -O2,
6140           -O3, -Os.
6141
6142       -ffp-contract=style
6143           -ffp-contract=off disables floating-point expression contraction.
6144           -ffp-contract=fast enables floating-point expression contraction
6145           such as forming of fused multiply-add operations if the target has
6146           native support for them.  -ffp-contract=on enables floating-point
6147           expression contraction if allowed by the language standard.  This
6148           is currently not implemented and treated equal to
6149           -ffp-contract=off.
6150
6151           The default is -ffp-contract=fast.
6152
6153       -fomit-frame-pointer
6154           Omit the frame pointer in functions that don't need one.  This
6155           avoids the instructions to save, set up and restore the frame
6156           pointer; on many targets it also makes an extra register available.
6157
6158           On some targets this flag has no effect because the standard
6159           calling sequence always uses a frame pointer, so it cannot be
6160           omitted.
6161
6162           Note that -fno-omit-frame-pointer doesn't guarantee the frame
6163           pointer is used in all functions.  Several targets always omit the
6164           frame pointer in leaf functions.
6165
6166           Enabled by default at -O and higher.
6167
6168       -foptimize-sibling-calls
6169           Optimize sibling and tail recursive calls.
6170
6171           Enabled at levels -O2, -O3, -Os.
6172
6173       -foptimize-strlen
6174           Optimize various standard C string functions (e.g. "strlen",
6175           "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into
6176           faster alternatives.
6177
6178           Enabled at levels -O2, -O3.
6179
6180       -fno-inline
6181           Do not expand any functions inline apart from those marked with the
6182           "always_inline" attribute.  This is the default when not
6183           optimizing.
6184
6185           Single functions can be exempted from inlining by marking them with
6186           the "noinline" attribute.
6187
6188       -finline-small-functions
6189           Integrate functions into their callers when their body is smaller
6190           than expected function call code (so overall size of program gets
6191           smaller).  The compiler heuristically decides which functions are
6192           simple enough to be worth integrating in this way.  This inlining
6193           applies to all functions, even those not declared inline.
6194
6195           Enabled at levels -O2, -O3, -Os.
6196
6197       -findirect-inlining
6198           Inline also indirect calls that are discovered to be known at
6199           compile time thanks to previous inlining.  This option has any
6200           effect only when inlining itself is turned on by the
6201           -finline-functions or -finline-small-functions options.
6202
6203           Enabled at levels -O2, -O3, -Os.
6204
6205       -finline-functions
6206           Consider all functions for inlining, even if they are not declared
6207           inline.  The compiler heuristically decides which functions are
6208           worth integrating in this way.
6209
6210           If all calls to a given function are integrated, and the function
6211           is declared "static", then the function is normally not output as
6212           assembler code in its own right.
6213
6214           Enabled at levels -O2, -O3, -Os.
6215
6216       -finline-functions-called-once
6217           Consider all "static" functions called once for inlining into their
6218           caller even if they are not marked "inline".  If a call to a given
6219           function is integrated, then the function is not output as
6220           assembler code in its own right.
6221
6222           Enabled at levels -O1, -O2, -O3 and -Os.
6223
6224       -fearly-inlining
6225           Inline functions marked by "always_inline" and functions whose body
6226           seems smaller than the function call overhead early before doing
6227           -fprofile-generate instrumentation and real inlining pass.  Doing
6228           so makes profiling significantly cheaper and usually inlining
6229           faster on programs having large chains of nested wrapper functions.
6230
6231           Enabled by default.
6232
6233       -fipa-sra
6234           Perform interprocedural scalar replacement of aggregates, removal
6235           of unused parameters and replacement of parameters passed by
6236           reference by parameters passed by value.
6237
6238           Enabled at levels -O2, -O3 and -Os.
6239
6240       -finline-limit=n
6241           By default, GCC limits the size of functions that can be inlined.
6242           This flag allows coarse control of this limit.  n is the size of
6243           functions that can be inlined in number of pseudo instructions.
6244
6245           Inlining is actually controlled by a number of parameters, which
6246           may be specified individually by using --param name=value.  The
6247           -finline-limit=n option sets some of these parameters as follows:
6248
6249           max-inline-insns-single
6250               is set to n/2.
6251
6252           max-inline-insns-auto
6253               is set to n/2.
6254
6255           See below for a documentation of the individual parameters
6256           controlling inlining and for the defaults of these parameters.
6257
6258           Note: there may be no value to -finline-limit that results in
6259           default behavior.
6260
6261           Note: pseudo instruction represents, in this particular context, an
6262           abstract measurement of function's size.  In no way does it
6263           represent a count of assembly instructions and as such its exact
6264           meaning might change from one release to an another.
6265
6266       -fno-keep-inline-dllexport
6267           This is a more fine-grained version of -fkeep-inline-functions,
6268           which applies only to functions that are declared using the
6269           "dllexport" attribute or declspec.
6270
6271       -fkeep-inline-functions
6272           In C, emit "static" functions that are declared "inline" into the
6273           object file, even if the function has been inlined into all of its
6274           callers.  This switch does not affect functions using the "extern
6275           inline" extension in GNU C90.  In C++, emit any and all inline
6276           functions into the object file.
6277
6278       -fkeep-static-functions
6279           Emit "static" functions into the object file, even if the function
6280           is never used.
6281
6282       -fkeep-static-consts
6283           Emit variables declared "static const" when optimization isn't
6284           turned on, even if the variables aren't referenced.
6285
6286           GCC enables this option by default.  If you want to force the
6287           compiler to check if a variable is referenced, regardless of
6288           whether or not optimization is turned on, use the
6289           -fno-keep-static-consts option.
6290
6291       -fmerge-constants
6292           Attempt to merge identical constants (string constants and
6293           floating-point constants) across compilation units.
6294
6295           This option is the default for optimized compilation if the
6296           assembler and linker support it.  Use -fno-merge-constants to
6297           inhibit this behavior.
6298
6299           Enabled at levels -O, -O2, -O3, -Os.
6300
6301       -fmerge-all-constants
6302           Attempt to merge identical constants and identical variables.
6303
6304           This option implies -fmerge-constants.  In addition to
6305           -fmerge-constants this considers e.g. even constant initialized
6306           arrays or initialized constant variables with integral or floating-
6307           point types.  Languages like C or C++ require each variable,
6308           including multiple instances of the same variable in recursive
6309           calls, to have distinct locations, so using this option results in
6310           non-conforming behavior.
6311
6312       -fmodulo-sched
6313           Perform swing modulo scheduling immediately before the first
6314           scheduling pass.  This pass looks at innermost loops and reorders
6315           their instructions by overlapping different iterations.
6316
6317       -fmodulo-sched-allow-regmoves
6318           Perform more aggressive SMS-based modulo scheduling with register
6319           moves allowed.  By setting this flag certain anti-dependences edges
6320           are deleted, which triggers the generation of reg-moves based on
6321           the life-range analysis.  This option is effective only with
6322           -fmodulo-sched enabled.
6323
6324       -fno-branch-count-reg
6325           Avoid running a pass scanning for opportunities to use "decrement
6326           and branch" instructions on a count register instead of generating
6327           sequences of instructions that decrement a register, compare it
6328           against zero, and then branch based upon the result.  This option
6329           is only meaningful on architectures that support such instructions,
6330           which include x86, PowerPC, IA-64 and S/390.  Note that the
6331           -fno-branch-count-reg option doesn't remove the decrement and
6332           branch instructions from the generated instruction stream
6333           introduced by other optimization passes.
6334
6335           Enabled by default at -O1 and higher.
6336
6337           The default is -fbranch-count-reg.
6338
6339       -fno-function-cse
6340           Do not put function addresses in registers; make each instruction
6341           that calls a constant function contain the function's address
6342           explicitly.
6343
6344           This option results in less efficient code, but some strange hacks
6345           that alter the assembler output may be confused by the
6346           optimizations performed when this option is not used.
6347
6348           The default is -ffunction-cse
6349
6350       -fno-zero-initialized-in-bss
6351           If the target supports a BSS section, GCC by default puts variables
6352           that are initialized to zero into BSS.  This can save space in the
6353           resulting code.
6354
6355           This option turns off this behavior because some programs
6356           explicitly rely on variables going to the data section---e.g., so
6357           that the resulting executable can find the beginning of that
6358           section and/or make assumptions based on that.
6359
6360           The default is -fzero-initialized-in-bss.
6361
6362       -fthread-jumps
6363           Perform optimizations that check to see if a jump branches to a
6364           location where another comparison subsumed by the first is found.
6365           If so, the first branch is redirected to either the destination of
6366           the second branch or a point immediately following it, depending on
6367           whether the condition is known to be true or false.
6368
6369           Enabled at levels -O2, -O3, -Os.
6370
6371       -fsplit-wide-types
6372           When using a type that occupies multiple registers, such as "long
6373           long" on a 32-bit system, split the registers apart and allocate
6374           them independently.  This normally generates better code for those
6375           types, but may make debugging more difficult.
6376
6377           Enabled at levels -O, -O2, -O3, -Os.
6378
6379       -fcse-follow-jumps
6380           In common subexpression elimination (CSE), scan through jump
6381           instructions when the target of the jump is not reached by any
6382           other path.  For example, when CSE encounters an "if" statement
6383           with an "else" clause, CSE follows the jump when the condition
6384           tested is false.
6385
6386           Enabled at levels -O2, -O3, -Os.
6387
6388       -fcse-skip-blocks
6389           This is similar to -fcse-follow-jumps, but causes CSE to follow
6390           jumps that conditionally skip over blocks.  When CSE encounters a
6391           simple "if" statement with no else clause, -fcse-skip-blocks causes
6392           CSE to follow the jump around the body of the "if".
6393
6394           Enabled at levels -O2, -O3, -Os.
6395
6396       -frerun-cse-after-loop
6397           Re-run common subexpression elimination after loop optimizations
6398           are performed.
6399
6400           Enabled at levels -O2, -O3, -Os.
6401
6402       -fgcse
6403           Perform a global common subexpression elimination pass.  This pass
6404           also performs global constant and copy propagation.
6405
6406           Note: When compiling a program using computed gotos, a GCC
6407           extension, you may get better run-time performance if you disable
6408           the global common subexpression elimination pass by adding
6409           -fno-gcse to the command line.
6410
6411           Enabled at levels -O2, -O3, -Os.
6412
6413       -fgcse-lm
6414           When -fgcse-lm is enabled, global common subexpression elimination
6415           attempts to move loads that are only killed by stores into
6416           themselves.  This allows a loop containing a load/store sequence to
6417           be changed to a load outside the loop, and a copy/store within the
6418           loop.
6419
6420           Enabled by default when -fgcse is enabled.
6421
6422       -fgcse-sm
6423           When -fgcse-sm is enabled, a store motion pass is run after global
6424           common subexpression elimination.  This pass attempts to move
6425           stores out of loops.  When used in conjunction with -fgcse-lm,
6426           loops containing a load/store sequence can be changed to a load
6427           before the loop and a store after the loop.
6428
6429           Not enabled at any optimization level.
6430
6431       -fgcse-las
6432           When -fgcse-las is enabled, the global common subexpression
6433           elimination pass eliminates redundant loads that come after stores
6434           to the same memory location (both partial and full redundancies).
6435
6436           Not enabled at any optimization level.
6437
6438       -fgcse-after-reload
6439           When -fgcse-after-reload is enabled, a redundant load elimination
6440           pass is performed after reload.  The purpose of this pass is to
6441           clean up redundant spilling.
6442
6443       -faggressive-loop-optimizations
6444           This option tells the loop optimizer to use language constraints to
6445           derive bounds for the number of iterations of a loop.  This assumes
6446           that loop code does not invoke undefined behavior by for example
6447           causing signed integer overflows or out-of-bound array accesses.
6448           The bounds for the number of iterations of a loop are used to guide
6449           loop unrolling and peeling and loop exit test optimizations.  This
6450           option is enabled by default.
6451
6452       -funconstrained-commons
6453           This option tells the compiler that variables declared in common
6454           blocks (e.g. Fortran) may later be overridden with longer trailing
6455           arrays. This prevents certain optimizations that depend on knowing
6456           the array bounds.
6457
6458       -fcrossjumping
6459           Perform cross-jumping transformation.  This transformation unifies
6460           equivalent code and saves code size.  The resulting code may or may
6461           not perform better than without cross-jumping.
6462
6463           Enabled at levels -O2, -O3, -Os.
6464
6465       -fauto-inc-dec
6466           Combine increments or decrements of addresses with memory accesses.
6467           This pass is always skipped on architectures that do not have
6468           instructions to support this.  Enabled by default at -O and higher
6469           on architectures that support this.
6470
6471       -fdce
6472           Perform dead code elimination (DCE) on RTL.  Enabled by default at
6473           -O and higher.
6474
6475       -fdse
6476           Perform dead store elimination (DSE) on RTL.  Enabled by default at
6477           -O and higher.
6478
6479       -fif-conversion
6480           Attempt to transform conditional jumps into branch-less
6481           equivalents.  This includes use of conditional moves, min, max, set
6482           flags and abs instructions, and some tricks doable by standard
6483           arithmetics.  The use of conditional execution on chips where it is
6484           available is controlled by -fif-conversion2.
6485
6486           Enabled at levels -O, -O2, -O3, -Os.
6487
6488       -fif-conversion2
6489           Use conditional execution (where available) to transform
6490           conditional jumps into branch-less equivalents.
6491
6492           Enabled at levels -O, -O2, -O3, -Os.
6493
6494       -fdeclone-ctor-dtor
6495           The C++ ABI requires multiple entry points for constructors and
6496           destructors: one for a base subobject, one for a complete object,
6497           and one for a virtual destructor that calls operator delete
6498           afterwards.  For a hierarchy with virtual bases, the base and
6499           complete variants are clones, which means two copies of the
6500           function.  With this option, the base and complete variants are
6501           changed to be thunks that call a common implementation.
6502
6503           Enabled by -Os.
6504
6505       -fdelete-null-pointer-checks
6506           Assume that programs cannot safely dereference null pointers, and
6507           that no code or data element resides at address zero.  This option
6508           enables simple constant folding optimizations at all optimization
6509           levels.  In addition, other optimization passes in GCC use this
6510           flag to control global dataflow analyses that eliminate useless
6511           checks for null pointers; these assume that a memory access to
6512           address zero always results in a trap, so that if a pointer is
6513           checked after it has already been dereferenced, it cannot be null.
6514
6515           Note however that in some environments this assumption is not true.
6516           Use -fno-delete-null-pointer-checks to disable this optimization
6517           for programs that depend on that behavior.
6518
6519           This option is enabled by default on most targets.  On Nios II ELF,
6520           it defaults to off.  On AVR, CR16, and MSP430, this option is
6521           completely disabled.
6522
6523           Passes that use the dataflow information are enabled independently
6524           at different optimization levels.
6525
6526       -fdevirtualize
6527           Attempt to convert calls to virtual functions to direct calls.
6528           This is done both within a procedure and interprocedurally as part
6529           of indirect inlining (-findirect-inlining) and interprocedural
6530           constant propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.
6531
6532       -fdevirtualize-speculatively
6533           Attempt to convert calls to virtual functions to speculative direct
6534           calls.  Based on the analysis of the type inheritance graph,
6535           determine for a given call the set of likely targets. If the set is
6536           small, preferably of size 1, change the call into a conditional
6537           deciding between direct and indirect calls.  The speculative calls
6538           enable more optimizations, such as inlining.  When they seem
6539           useless after further optimization, they are converted back into
6540           original form.
6541
6542       -fdevirtualize-at-ltrans
6543           Stream extra information needed for aggressive devirtualization
6544           when running the link-time optimizer in local transformation mode.
6545           This option enables more devirtualization but significantly
6546           increases the size of streamed data. For this reason it is disabled
6547           by default.
6548
6549       -fexpensive-optimizations
6550           Perform a number of minor optimizations that are relatively
6551           expensive.
6552
6553           Enabled at levels -O2, -O3, -Os.
6554
6555       -free
6556           Attempt to remove redundant extension instructions.  This is
6557           especially helpful for the x86-64 architecture, which implicitly
6558           zero-extends in 64-bit registers after writing to their lower
6559           32-bit half.
6560
6561           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.
6562
6563       -fno-lifetime-dse
6564           In C++ the value of an object is only affected by changes within
6565           its lifetime: when the constructor begins, the object has an
6566           indeterminate value, and any changes during the lifetime of the
6567           object are dead when the object is destroyed.  Normally dead store
6568           elimination will take advantage of this; if your code relies on the
6569           value of the object storage persisting beyond the lifetime of the
6570           object, you can use this flag to disable this optimization.  To
6571           preserve stores before the constructor starts (e.g. because your
6572           operator new clears the object storage) but still treat the object
6573           as dead after the destructor you, can use -flifetime-dse=1.  The
6574           default behavior can be explicitly selected with -flifetime-dse=2.
6575           -flifetime-dse=0 is equivalent to -fno-lifetime-dse.
6576
6577       -flive-range-shrinkage
6578           Attempt to decrease register pressure through register live range
6579           shrinkage.  This is helpful for fast processors with small or
6580           moderate size register sets.
6581
6582       -fira-algorithm=algorithm
6583           Use the specified coloring algorithm for the integrated register
6584           allocator.  The algorithm argument can be priority, which specifies
6585           Chow's priority coloring, or CB, which specifies Chaitin-Briggs
6586           coloring.  Chaitin-Briggs coloring is not implemented for all
6587           architectures, but for those targets that do support it, it is the
6588           default because it generates better code.
6589
6590       -fira-region=region
6591           Use specified regions for the integrated register allocator.  The
6592           region argument should be one of the following:
6593
6594           all Use all loops as register allocation regions.  This can give
6595               the best results for machines with a small and/or irregular
6596               register set.
6597
6598           mixed
6599               Use all loops except for loops with small register pressure as
6600               the regions.  This value usually gives the best results in most
6601               cases and for most architectures, and is enabled by default
6602               when compiling with optimization for speed (-O, -O2, ...).
6603
6604           one Use all functions as a single region.  This typically results
6605               in the smallest code size, and is enabled by default for -Os or
6606               -O0.
6607
6608       -fira-hoist-pressure
6609           Use IRA to evaluate register pressure in the code hoisting pass for
6610           decisions to hoist expressions.  This option usually results in
6611           smaller code, but it can slow the compiler down.
6612
6613           This option is enabled at level -Os for all targets.
6614
6615       -fira-loop-pressure
6616           Use IRA to evaluate register pressure in loops for decisions to
6617           move loop invariants.  This option usually results in generation of
6618           faster and smaller code on machines with large register files (>=
6619           32 registers), but it can slow the compiler down.
6620
6621           This option is enabled at level -O3 for some targets.
6622
6623       -fno-ira-share-save-slots
6624           Disable sharing of stack slots used for saving call-used hard
6625           registers living through a call.  Each hard register gets a
6626           separate stack slot, and as a result function stack frames are
6627           larger.
6628
6629       -fno-ira-share-spill-slots
6630           Disable sharing of stack slots allocated for pseudo-registers.
6631           Each pseudo-register that does not get a hard register gets a
6632           separate stack slot, and as a result function stack frames are
6633           larger.
6634
6635       -flra-remat
6636           Enable CFG-sensitive rematerialization in LRA.  Instead of loading
6637           values of spilled pseudos, LRA tries to rematerialize (recalculate)
6638           values if it is profitable.
6639
6640           Enabled at levels -O2, -O3, -Os.
6641
6642       -fdelayed-branch
6643           If supported for the target machine, attempt to reorder
6644           instructions to exploit instruction slots available after delayed
6645           branch instructions.
6646
6647           Enabled at levels -O, -O2, -O3, -Os.
6648
6649       -fschedule-insns
6650           If supported for the target machine, attempt to reorder
6651           instructions to eliminate execution stalls due to required data
6652           being unavailable.  This helps machines that have slow floating
6653           point or memory load instructions by allowing other instructions to
6654           be issued until the result of the load or floating-point
6655           instruction is required.
6656
6657           Enabled at levels -O2, -O3.
6658
6659       -fschedule-insns2
6660           Similar to -fschedule-insns, but requests an additional pass of
6661           instruction scheduling after register allocation has been done.
6662           This is especially useful on machines with a relatively small
6663           number of registers and where memory load instructions take more
6664           than one cycle.
6665
6666           Enabled at levels -O2, -O3, -Os.
6667
6668       -fno-sched-interblock
6669           Don't schedule instructions across basic blocks.  This is normally
6670           enabled by default when scheduling before register allocation, i.e.
6671           with -fschedule-insns or at -O2 or higher.
6672
6673       -fno-sched-spec
6674           Don't allow speculative motion of non-load instructions.  This is
6675           normally enabled by default when scheduling before register
6676           allocation, i.e.  with -fschedule-insns or at -O2 or higher.
6677
6678       -fsched-pressure
6679           Enable register pressure sensitive insn scheduling before register
6680           allocation.  This only makes sense when scheduling before register
6681           allocation is enabled, i.e. with -fschedule-insns or at -O2 or
6682           higher.  Usage of this option can improve the generated code and
6683           decrease its size by preventing register pressure increase above
6684           the number of available hard registers and subsequent spills in
6685           register allocation.
6686
6687       -fsched-spec-load
6688           Allow speculative motion of some load instructions.  This only
6689           makes sense when scheduling before register allocation, i.e. with
6690           -fschedule-insns or at -O2 or higher.
6691
6692       -fsched-spec-load-dangerous
6693           Allow speculative motion of more load instructions.  This only
6694           makes sense when scheduling before register allocation, i.e. with
6695           -fschedule-insns or at -O2 or higher.
6696
6697       -fsched-stalled-insns
6698       -fsched-stalled-insns=n
6699           Define how many insns (if any) can be moved prematurely from the
6700           queue of stalled insns into the ready list during the second
6701           scheduling pass.  -fno-sched-stalled-insns means that no insns are
6702           moved prematurely, -fsched-stalled-insns=0 means there is no limit
6703           on how many queued insns can be moved prematurely.
6704           -fsched-stalled-insns without a value is equivalent to
6705           -fsched-stalled-insns=1.
6706
6707       -fsched-stalled-insns-dep
6708       -fsched-stalled-insns-dep=n
6709           Define how many insn groups (cycles) are examined for a dependency
6710           on a stalled insn that is a candidate for premature removal from
6711           the queue of stalled insns.  This has an effect only during the
6712           second scheduling pass, and only if -fsched-stalled-insns is used.
6713           -fno-sched-stalled-insns-dep is equivalent to
6714           -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a
6715           value is equivalent to -fsched-stalled-insns-dep=1.
6716
6717       -fsched2-use-superblocks
6718           When scheduling after register allocation, use superblock
6719           scheduling.  This allows motion across basic block boundaries,
6720           resulting in faster schedules.  This option is experimental, as not
6721           all machine descriptions used by GCC model the CPU closely enough
6722           to avoid unreliable results from the algorithm.
6723
6724           This only makes sense when scheduling after register allocation,
6725           i.e. with -fschedule-insns2 or at -O2 or higher.
6726
6727       -fsched-group-heuristic
6728           Enable the group heuristic in the scheduler.  This heuristic favors
6729           the instruction that belongs to a schedule group.  This is enabled
6730           by default when scheduling is enabled, i.e. with -fschedule-insns
6731           or -fschedule-insns2 or at -O2 or higher.
6732
6733       -fsched-critical-path-heuristic
6734           Enable the critical-path heuristic in the scheduler.  This
6735           heuristic favors instructions on the critical path.  This is
6736           enabled by default when scheduling is enabled, i.e. with
6737           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
6738
6739       -fsched-spec-insn-heuristic
6740           Enable the speculative instruction heuristic in the scheduler.
6741           This heuristic favors speculative instructions with greater
6742           dependency weakness.  This is enabled by default when scheduling is
6743           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
6744           or higher.
6745
6746       -fsched-rank-heuristic
6747           Enable the rank heuristic in the scheduler.  This heuristic favors
6748           the instruction belonging to a basic block with greater size or
6749           frequency.  This is enabled by default when scheduling is enabled,
6750           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
6751           higher.
6752
6753       -fsched-last-insn-heuristic
6754           Enable the last-instruction heuristic in the scheduler.  This
6755           heuristic favors the instruction that is less dependent on the last
6756           instruction scheduled.  This is enabled by default when scheduling
6757           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
6758           -O2 or higher.
6759
6760       -fsched-dep-count-heuristic
6761           Enable the dependent-count heuristic in the scheduler.  This
6762           heuristic favors the instruction that has more instructions
6763           depending on it.  This is enabled by default when scheduling is
6764           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
6765           or higher.
6766
6767       -freschedule-modulo-scheduled-loops
6768           Modulo scheduling is performed before traditional scheduling.  If a
6769           loop is modulo scheduled, later scheduling passes may change its
6770           schedule.  Use this option to control that behavior.
6771
6772       -fselective-scheduling
6773           Schedule instructions using selective scheduling algorithm.
6774           Selective scheduling runs instead of the first scheduler pass.
6775
6776       -fselective-scheduling2
6777           Schedule instructions using selective scheduling algorithm.
6778           Selective scheduling runs instead of the second scheduler pass.
6779
6780       -fsel-sched-pipelining
6781           Enable software pipelining of innermost loops during selective
6782           scheduling.  This option has no effect unless one of
6783           -fselective-scheduling or -fselective-scheduling2 is turned on.
6784
6785       -fsel-sched-pipelining-outer-loops
6786           When pipelining loops during selective scheduling, also pipeline
6787           outer loops.  This option has no effect unless
6788           -fsel-sched-pipelining is turned on.
6789
6790       -fsemantic-interposition
6791           Some object formats, like ELF, allow interposing of symbols by the
6792           dynamic linker.  This means that for symbols exported from the DSO,
6793           the compiler cannot perform interprocedural propagation, inlining
6794           and other optimizations in anticipation that the function or
6795           variable in question may change. While this feature is useful, for
6796           example, to rewrite memory allocation functions by a debugging
6797           implementation, it is expensive in the terms of code quality.  With
6798           -fno-semantic-interposition the compiler assumes that if
6799           interposition happens for functions the overwriting function will
6800           have precisely the same semantics (and side effects).  Similarly if
6801           interposition happens for variables, the constructor of the
6802           variable will be the same. The flag has no effect for functions
6803           explicitly declared inline (where it is never allowed for
6804           interposition to change semantics) and for symbols explicitly
6805           declared weak.
6806
6807       -fshrink-wrap
6808           Emit function prologues only before parts of the function that need
6809           it, rather than at the top of the function.  This flag is enabled
6810           by default at -O and higher.
6811
6812       -fshrink-wrap-separate
6813           Shrink-wrap separate parts of the prologue and epilogue separately,
6814           so that those parts are only executed when needed.  This option is
6815           on by default, but has no effect unless -fshrink-wrap is also
6816           turned on and the target supports this.
6817
6818       -fcaller-saves
6819           Enable allocation of values to registers that are clobbered by
6820           function calls, by emitting extra instructions to save and restore
6821           the registers around such calls.  Such allocation is done only when
6822           it seems to result in better code.
6823
6824           This option is always enabled by default on certain machines,
6825           usually those which have no call-preserved registers to use
6826           instead.
6827
6828           Enabled at levels -O2, -O3, -Os.
6829
6830       -fcombine-stack-adjustments
6831           Tracks stack adjustments (pushes and pops) and stack memory
6832           references and then tries to find ways to combine them.
6833
6834           Enabled by default at -O1 and higher.
6835
6836       -fipa-ra
6837           Use caller save registers for allocation if those registers are not
6838           used by any called function.  In that case it is not necessary to
6839           save and restore them around calls.  This is only possible if
6840           called functions are part of same compilation unit as current
6841           function and they are compiled before it.
6842
6843           Enabled at levels -O2, -O3, -Os, however the option is disabled if
6844           generated code will be instrumented for profiling (-p, or -pg) or
6845           if callee's register usage cannot be known exactly (this happens on
6846           targets that do not expose prologues and epilogues in RTL).
6847
6848       -fconserve-stack
6849           Attempt to minimize stack usage.  The compiler attempts to use less
6850           stack space, even if that makes the program slower.  This option
6851           implies setting the large-stack-frame parameter to 100 and the
6852           large-stack-frame-growth parameter to 400.
6853
6854       -ftree-reassoc
6855           Perform reassociation on trees.  This flag is enabled by default at
6856           -O and higher.
6857
6858       -fcode-hoisting
6859           Perform code hoisting.  Code hoisting tries to move the evaluation
6860           of expressions executed on all paths to the function exit as early
6861           as possible.  This is especially useful as a code size
6862           optimization, but it often helps for code speed as well.  This flag
6863           is enabled by default at -O2 and higher.
6864
6865       -ftree-pre
6866           Perform partial redundancy elimination (PRE) on trees.  This flag
6867           is enabled by default at -O2 and -O3.
6868
6869       -ftree-partial-pre
6870           Make partial redundancy elimination (PRE) more aggressive.  This
6871           flag is enabled by default at -O3.
6872
6873       -ftree-forwprop
6874           Perform forward propagation on trees.  This flag is enabled by
6875           default at -O and higher.
6876
6877       -ftree-fre
6878           Perform full redundancy elimination (FRE) on trees.  The difference
6879           between FRE and PRE is that FRE only considers expressions that are
6880           computed on all paths leading to the redundant computation.  This
6881           analysis is faster than PRE, though it exposes fewer redundancies.
6882           This flag is enabled by default at -O and higher.
6883
6884       -ftree-phiprop
6885           Perform hoisting of loads from conditional pointers on trees.  This
6886           pass is enabled by default at -O and higher.
6887
6888       -fhoist-adjacent-loads
6889           Speculatively hoist loads from both branches of an if-then-else if
6890           the loads are from adjacent locations in the same structure and the
6891           target architecture has a conditional move instruction.  This flag
6892           is enabled by default at -O2 and higher.
6893
6894       -ftree-copy-prop
6895           Perform copy propagation on trees.  This pass eliminates
6896           unnecessary copy operations.  This flag is enabled by default at -O
6897           and higher.
6898
6899       -fipa-pure-const
6900           Discover which functions are pure or constant.  Enabled by default
6901           at -O and higher.
6902
6903       -fipa-reference
6904           Discover which static variables do not escape the compilation unit.
6905           Enabled by default at -O and higher.
6906
6907       -fipa-pta
6908           Perform interprocedural pointer analysis and interprocedural
6909           modification and reference analysis.  This option can cause
6910           excessive memory and compile-time usage on large compilation units.
6911           It is not enabled by default at any optimization level.
6912
6913       -fipa-profile
6914           Perform interprocedural profile propagation.  The functions called
6915           only from cold functions are marked as cold. Also functions
6916           executed once (such as "cold", "noreturn", static constructors or
6917           destructors) are identified. Cold functions and loop less parts of
6918           functions executed once are then optimized for size.  Enabled by
6919           default at -O and higher.
6920
6921       -fipa-cp
6922           Perform interprocedural constant propagation.  This optimization
6923           analyzes the program to determine when values passed to functions
6924           are constants and then optimizes accordingly.  This optimization
6925           can substantially increase performance if the application has
6926           constants passed to functions.  This flag is enabled by default at
6927           -O2, -Os and -O3.
6928
6929       -fipa-cp-clone
6930           Perform function cloning to make interprocedural constant
6931           propagation stronger.  When enabled, interprocedural constant
6932           propagation performs function cloning when externally visible
6933           function can be called with constant arguments.  Because this
6934           optimization can create multiple copies of functions, it may
6935           significantly increase code size (see --param
6936           ipcp-unit-growth=value).  This flag is enabled by default at -O3.
6937
6938       -fipa-bit-cp
6939           When enabled, perform interprocedural bitwise constant propagation.
6940           This flag is enabled by default at -O2. It requires that -fipa-cp
6941           is enabled.
6942
6943       -fipa-vrp
6944           When enabled, perform interprocedural propagation of value ranges.
6945           This flag is enabled by default at -O2. It requires that -fipa-cp
6946           is enabled.
6947
6948       -fipa-icf
6949           Perform Identical Code Folding for functions and read-only
6950           variables.  The optimization reduces code size and may disturb
6951           unwind stacks by replacing a function by equivalent one with a
6952           different name. The optimization works more effectively with link-
6953           time optimization enabled.
6954
6955           Nevertheless the behavior is similar to Gold Linker ICF
6956           optimization, GCC ICF works on different levels and thus the
6957           optimizations are not same - there are equivalences that are found
6958           only by GCC and equivalences found only by Gold.
6959
6960           This flag is enabled by default at -O2 and -Os.
6961
6962       -fisolate-erroneous-paths-dereference
6963           Detect paths that trigger erroneous or undefined behavior due to
6964           dereferencing a null pointer.  Isolate those paths from the main
6965           control flow and turn the statement with erroneous or undefined
6966           behavior into a trap.  This flag is enabled by default at -O2 and
6967           higher and depends on -fdelete-null-pointer-checks also being
6968           enabled.
6969
6970       -fisolate-erroneous-paths-attribute
6971           Detect paths that trigger erroneous or undefined behavior due to a
6972           null value being used in a way forbidden by a "returns_nonnull" or
6973           "nonnull" attribute.  Isolate those paths from the main control
6974           flow and turn the statement with erroneous or undefined behavior
6975           into a trap.  This is not currently enabled, but may be enabled by
6976           -O2 in the future.
6977
6978       -ftree-sink
6979           Perform forward store motion on trees.  This flag is enabled by
6980           default at -O and higher.
6981
6982       -ftree-bit-ccp
6983           Perform sparse conditional bit constant propagation on trees and
6984           propagate pointer alignment information.  This pass only operates
6985           on local scalar variables and is enabled by default at -O and
6986           higher.  It requires that -ftree-ccp is enabled.
6987
6988       -ftree-ccp
6989           Perform sparse conditional constant propagation (CCP) on trees.
6990           This pass only operates on local scalar variables and is enabled by
6991           default at -O and higher.
6992
6993       -fssa-backprop
6994           Propagate information about uses of a value up the definition chain
6995           in order to simplify the definitions.  For example, this pass
6996           strips sign operations if the sign of a value never matters.  The
6997           flag is enabled by default at -O and higher.
6998
6999       -fssa-phiopt
7000           Perform pattern matching on SSA PHI nodes to optimize conditional
7001           code.  This pass is enabled by default at -O and higher.
7002
7003       -ftree-switch-conversion
7004           Perform conversion of simple initializations in a switch to
7005           initializations from a scalar array.  This flag is enabled by
7006           default at -O2 and higher.
7007
7008       -ftree-tail-merge
7009           Look for identical code sequences.  When found, replace one with a
7010           jump to the other.  This optimization is known as tail merging or
7011           cross jumping.  This flag is enabled by default at -O2 and higher.
7012           The compilation time in this pass can be limited using max-tail-
7013           merge-comparisons parameter and max-tail-merge-iterations
7014           parameter.
7015
7016       -ftree-dce
7017           Perform dead code elimination (DCE) on trees.  This flag is enabled
7018           by default at -O and higher.
7019
7020       -ftree-builtin-call-dce
7021           Perform conditional dead code elimination (DCE) for calls to built-
7022           in functions that may set "errno" but are otherwise free of side
7023           effects.  This flag is enabled by default at -O2 and higher if -Os
7024           is not also specified.
7025
7026       -ftree-dominator-opts
7027           Perform a variety of simple scalar cleanups (constant/copy
7028           propagation, redundancy elimination, range propagation and
7029           expression simplification) based on a dominator tree traversal.
7030           This also performs jump threading (to reduce jumps to jumps). This
7031           flag is enabled by default at -O and higher.
7032
7033       -ftree-dse
7034           Perform dead store elimination (DSE) on trees.  A dead store is a
7035           store into a memory location that is later overwritten by another
7036           store without any intervening loads.  In this case the earlier
7037           store can be deleted.  This flag is enabled by default at -O and
7038           higher.
7039
7040       -ftree-ch
7041           Perform loop header copying on trees.  This is beneficial since it
7042           increases effectiveness of code motion optimizations.  It also
7043           saves one jump.  This flag is enabled by default at -O and higher.
7044           It is not enabled for -Os, since it usually increases code size.
7045
7046       -ftree-loop-optimize
7047           Perform loop optimizations on trees.  This flag is enabled by
7048           default at -O and higher.
7049
7050       -ftree-loop-linear
7051       -floop-strip-mine
7052       -floop-block
7053           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To
7054           use this code transformation, GCC has to be configured with
7055           --with-isl to enable the Graphite loop transformation
7056           infrastructure.
7057
7058       -fgraphite-identity
7059           Enable the identity transformation for graphite.  For every SCoP we
7060           generate the polyhedral representation and transform it back to
7061           gimple.  Using -fgraphite-identity we can check the costs or
7062           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
7063           minimal optimizations are also performed by the code generator isl,
7064           like index splitting and dead code elimination in loops.
7065
7066       -floop-nest-optimize
7067           Enable the isl based loop nest optimizer.  This is a generic loop
7068           nest optimizer based on the Pluto optimization algorithms.  It
7069           calculates a loop structure optimized for data-locality and
7070           parallelism.  This option is experimental.
7071
7072       -floop-parallelize-all
7073           Use the Graphite data dependence analysis to identify loops that
7074           can be parallelized.  Parallelize all the loops that can be
7075           analyzed to not contain loop carried dependences without checking
7076           that it is profitable to parallelize the loops.
7077
7078       -ftree-coalesce-vars
7079           While transforming the program out of the SSA representation,
7080           attempt to reduce copying by coalescing versions of different user-
7081           defined variables, instead of just compiler temporaries.  This may
7082           severely limit the ability to debug an optimized program compiled
7083           with -fno-var-tracking-assignments.  In the negated form, this flag
7084           prevents SSA coalescing of user variables.  This option is enabled
7085           by default if optimization is enabled, and it does very little
7086           otherwise.
7087
7088       -ftree-loop-if-convert
7089           Attempt to transform conditional jumps in the innermost loops to
7090           branch-less equivalents.  The intent is to remove control-flow from
7091           the innermost loops in order to improve the ability of the
7092           vectorization pass to handle these loops.  This is enabled by
7093           default if vectorization is enabled.
7094
7095       -ftree-loop-distribution
7096           Perform loop distribution.  This flag can improve cache performance
7097           on big loop bodies and allow further loop optimizations, like
7098           parallelization or vectorization, to take place.  For example, the
7099           loop
7100
7101                   DO I = 1, N
7102                     A(I) = B(I) + C
7103                     D(I) = E(I) * F
7104                   ENDDO
7105
7106           is transformed to
7107
7108                   DO I = 1, N
7109                      A(I) = B(I) + C
7110                   ENDDO
7111                   DO I = 1, N
7112                      D(I) = E(I) * F
7113                   ENDDO
7114
7115       -ftree-loop-distribute-patterns
7116           Perform loop distribution of patterns that can be code generated
7117           with calls to a library.  This flag is enabled by default at -O3.
7118
7119           This pass distributes the initialization loops and generates a call
7120           to memset zero.  For example, the loop
7121
7122                   DO I = 1, N
7123                     A(I) = 0
7124                     B(I) = A(I) + I
7125                   ENDDO
7126
7127           is transformed to
7128
7129                   DO I = 1, N
7130                      A(I) = 0
7131                   ENDDO
7132                   DO I = 1, N
7133                      B(I) = A(I) + I
7134                   ENDDO
7135
7136           and the initialization loop is transformed into a call to memset
7137           zero.
7138
7139       -floop-interchange
7140           Perform loop interchange outside of graphite.  This flag can
7141           improve cache performance on loop nest and allow further loop
7142           optimizations, like vectorization, to take place.  For example, the
7143           loop
7144
7145                   for (int i = 0; i < N; i++)
7146                     for (int j = 0; j < N; j++)
7147                       for (int k = 0; k < N; k++)
7148                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
7149
7150           is transformed to
7151
7152                   for (int i = 0; i < N; i++)
7153                     for (int k = 0; k < N; k++)
7154                       for (int j = 0; j < N; j++)
7155                         c[i][j] = c[i][j] + a[i][k]*b[k][j];
7156
7157           This flag is enabled by default at -O3.
7158
7159       -floop-unroll-and-jam
7160           Apply unroll and jam transformations on feasible loops.  In a loop
7161           nest this unrolls the outer loop by some factor and fuses the
7162           resulting multiple inner loops.  This flag is enabled by default at
7163           -O3.
7164
7165       -ftree-loop-im
7166           Perform loop invariant motion on trees.  This pass moves only
7167           invariants that are hard to handle at RTL level (function calls,
7168           operations that expand to nontrivial sequences of insns).  With
7169           -funswitch-loops it also moves operands of conditions that are
7170           invariant out of the loop, so that we can use just trivial
7171           invariantness analysis in loop unswitching.  The pass also includes
7172           store motion.
7173
7174       -ftree-loop-ivcanon
7175           Create a canonical counter for number of iterations in loops for
7176           which determining number of iterations requires complicated
7177           analysis.  Later optimizations then may determine the number
7178           easily.  Useful especially in connection with unrolling.
7179
7180       -fivopts
7181           Perform induction variable optimizations (strength reduction,
7182           induction variable merging and induction variable elimination) on
7183           trees.
7184
7185       -ftree-parallelize-loops=n
7186           Parallelize loops, i.e., split their iteration space to run in n
7187           threads.  This is only possible for loops whose iterations are
7188           independent and can be arbitrarily reordered.  The optimization is
7189           only profitable on multiprocessor machines, for loops that are CPU-
7190           intensive, rather than constrained e.g. by memory bandwidth.  This
7191           option implies -pthread, and thus is only supported on targets that
7192           have support for -pthread.
7193
7194       -ftree-pta
7195           Perform function-local points-to analysis on trees.  This flag is
7196           enabled by default at -O and higher.
7197
7198       -ftree-sra
7199           Perform scalar replacement of aggregates.  This pass replaces
7200           structure references with scalars to prevent committing structures
7201           to memory too early.  This flag is enabled by default at -O and
7202           higher.
7203
7204       -fstore-merging
7205           Perform merging of narrow stores to consecutive memory addresses.
7206           This pass merges contiguous stores of immediate values narrower
7207           than a word into fewer wider stores to reduce the number of
7208           instructions.  This is enabled by default at -O2 and higher as well
7209           as -Os.
7210
7211       -ftree-ter
7212           Perform temporary expression replacement during the SSA->normal
7213           phase.  Single use/single def temporaries are replaced at their use
7214           location with their defining expression.  This results in non-
7215           GIMPLE code, but gives the expanders much more complex trees to
7216           work on resulting in better RTL generation.  This is enabled by
7217           default at -O and higher.
7218
7219       -ftree-slsr
7220           Perform straight-line strength reduction on trees.  This recognizes
7221           related expressions involving multiplications and replaces them by
7222           less expensive calculations when possible.  This is enabled by
7223           default at -O and higher.
7224
7225       -ftree-vectorize
7226           Perform vectorization on trees. This flag enables
7227           -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly
7228           specified.
7229
7230       -ftree-loop-vectorize
7231           Perform loop vectorization on trees. This flag is enabled by
7232           default at -O3 and when -ftree-vectorize is enabled.
7233
7234       -ftree-slp-vectorize
7235           Perform basic block vectorization on trees. This flag is enabled by
7236           default at -O3 and when -ftree-vectorize is enabled.
7237
7238       -fvect-cost-model=model
7239           Alter the cost model used for vectorization.  The model argument
7240           should be one of unlimited, dynamic or cheap.  With the unlimited
7241           model the vectorized code-path is assumed to be profitable while
7242           with the dynamic model a runtime check guards the vectorized code-
7243           path to enable it only for iteration counts that will likely
7244           execute faster than when executing the original scalar loop.  The
7245           cheap model disables vectorization of loops where doing so would be
7246           cost prohibitive for example due to required runtime checks for
7247           data dependence or alignment but otherwise is equal to the dynamic
7248           model.  The default cost model depends on other optimization flags
7249           and is either dynamic or cheap.
7250
7251       -fsimd-cost-model=model
7252           Alter the cost model used for vectorization of loops marked with
7253           the OpenMP simd directive.  The model argument should be one of
7254           unlimited, dynamic, cheap.  All values of model have the same
7255           meaning as described in -fvect-cost-model and by default a cost
7256           model defined with -fvect-cost-model is used.
7257
7258       -ftree-vrp
7259           Perform Value Range Propagation on trees.  This is similar to the
7260           constant propagation pass, but instead of values, ranges of values
7261           are propagated.  This allows the optimizers to remove unnecessary
7262           range checks like array bound checks and null pointer checks.  This
7263           is enabled by default at -O2 and higher.  Null pointer check
7264           elimination is only done if -fdelete-null-pointer-checks is
7265           enabled.
7266
7267       -fsplit-paths
7268           Split paths leading to loop backedges.  This can improve dead code
7269           elimination and common subexpression elimination.  This is enabled
7270           by default at -O2 and above.
7271
7272       -fsplit-ivs-in-unroller
7273           Enables expression of values of induction variables in later
7274           iterations of the unrolled loop using the value in the first
7275           iteration.  This breaks long dependency chains, thus improving
7276           efficiency of the scheduling passes.
7277
7278           A combination of -fweb and CSE is often sufficient to obtain the
7279           same effect.  However, that is not reliable in cases where the loop
7280           body is more complicated than a single basic block.  It also does
7281           not work at all on some architectures due to restrictions in the
7282           CSE pass.
7283
7284           This optimization is enabled by default.
7285
7286       -fvariable-expansion-in-unroller
7287           With this option, the compiler creates multiple copies of some
7288           local variables when unrolling a loop, which can result in superior
7289           code.
7290
7291       -fpartial-inlining
7292           Inline parts of functions.  This option has any effect only when
7293           inlining itself is turned on by the -finline-functions or
7294           -finline-small-functions options.
7295
7296           Enabled at levels -O2, -O3, -Os.
7297
7298       -fpredictive-commoning
7299           Perform predictive commoning optimization, i.e., reusing
7300           computations (especially memory loads and stores) performed in
7301           previous iterations of loops.
7302
7303           This option is enabled at level -O3.
7304
7305       -fprefetch-loop-arrays
7306           If supported by the target machine, generate instructions to
7307           prefetch memory to improve the performance of loops that access
7308           large arrays.
7309
7310           This option may generate better or worse code; results are highly
7311           dependent on the structure of loops within the source code.
7312
7313           Disabled at level -Os.
7314
7315       -fno-printf-return-value
7316           Do not substitute constants for known return value of formatted
7317           output functions such as "sprintf", "snprintf", "vsprintf", and
7318           "vsnprintf" (but not "printf" of "fprintf").  This transformation
7319           allows GCC to optimize or even eliminate branches based on the
7320           known return value of these functions called with arguments that
7321           are either constant, or whose values are known to be in a range
7322           that makes determining the exact return value possible.  For
7323           example, when -fprintf-return-value is in effect, both the branch
7324           and the body of the "if" statement (but not the call to "snprint")
7325           can be optimized away when "i" is a 32-bit or smaller integer
7326           because the return value is guaranteed to be at most 8.
7327
7328                   char buf[9];
7329                   if (snprintf (buf, "%08x", i) >= sizeof buf)
7330                     ...
7331
7332           The -fprintf-return-value option relies on other optimizations and
7333           yields best results with -O2 and above.  It works in tandem with
7334           the -Wformat-overflow and -Wformat-truncation options.  The
7335           -fprintf-return-value option is enabled by default.
7336
7337       -fno-peephole
7338       -fno-peephole2
7339           Disable any machine-specific peephole optimizations.  The
7340           difference between -fno-peephole and -fno-peephole2 is in how they
7341           are implemented in the compiler; some targets use one, some use the
7342           other, a few use both.
7343
7344           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
7345           -O2, -O3, -Os.
7346
7347       -fno-guess-branch-probability
7348           Do not guess branch probabilities using heuristics.
7349
7350           GCC uses heuristics to guess branch probabilities if they are not
7351           provided by profiling feedback (-fprofile-arcs).  These heuristics
7352           are based on the control flow graph.  If some branch probabilities
7353           are specified by "__builtin_expect", then the heuristics are used
7354           to guess branch probabilities for the rest of the control flow
7355           graph, taking the "__builtin_expect" info into account.  The
7356           interactions between the heuristics and "__builtin_expect" can be
7357           complex, and in some cases, it may be useful to disable the
7358           heuristics so that the effects of "__builtin_expect" are easier to
7359           understand.
7360
7361           The default is -fguess-branch-probability at levels -O, -O2, -O3,
7362           -Os.
7363
7364       -freorder-blocks
7365           Reorder basic blocks in the compiled function in order to reduce
7366           number of taken branches and improve code locality.
7367
7368           Enabled at levels -O, -O2, -O3, -Os.
7369
7370       -freorder-blocks-algorithm=algorithm
7371           Use the specified algorithm for basic block reordering.  The
7372           algorithm argument can be simple, which does not increase code size
7373           (except sometimes due to secondary effects like alignment), or stc,
7374           the "software trace cache" algorithm, which tries to put all often
7375           executed code together, minimizing the number of branches executed
7376           by making extra copies of code.
7377
7378           The default is simple at levels -O, -Os, and stc at levels -O2,
7379           -O3.
7380
7381       -freorder-blocks-and-partition
7382           In addition to reordering basic blocks in the compiled function, in
7383           order to reduce number of taken branches, partitions hot and cold
7384           basic blocks into separate sections of the assembly and .o files,
7385           to improve paging and cache locality performance.
7386
7387           This optimization is automatically turned off in the presence of
7388           exception handling or unwind tables (on targets using
7389           setjump/longjump or target specific scheme), for linkonce sections,
7390           for functions with a user-defined section attribute and on any
7391           architecture that does not support named sections.  When
7392           -fsplit-stack is used this option is not enabled by default (to
7393           avoid linker errors), but may be enabled explicitly (if using a
7394           working linker).
7395
7396           Enabled for x86 at levels -O2, -O3, -Os.
7397
7398       -freorder-functions
7399           Reorder functions in the object file in order to improve code
7400           locality.  This is implemented by using special subsections
7401           ".text.hot" for most frequently executed functions and
7402           ".text.unlikely" for unlikely executed functions.  Reordering is
7403           done by the linker so object file format must support named
7404           sections and linker must place them in a reasonable way.
7405
7406           Also profile feedback must be available to make this option
7407           effective.  See -fprofile-arcs for details.
7408
7409           Enabled at levels -O2, -O3, -Os.
7410
7411       -fstrict-aliasing
7412           Allow the compiler to assume the strictest aliasing rules
7413           applicable to the language being compiled.  For C (and C++), this
7414           activates optimizations based on the type of expressions.  In
7415           particular, an object of one type is assumed never to reside at the
7416           same address as an object of a different type, unless the types are
7417           almost the same.  For example, an "unsigned int" can alias an
7418           "int", but not a "void*" or a "double".  A character type may alias
7419           any other type.
7420
7421           Pay special attention to code like this:
7422
7423                   union a_union {
7424                     int i;
7425                     double d;
7426                   };
7427
7428                   int f() {
7429                     union a_union t;
7430                     t.d = 3.0;
7431                     return t.i;
7432                   }
7433
7434           The practice of reading from a different union member than the one
7435           most recently written to (called "type-punning") is common.  Even
7436           with -fstrict-aliasing, type-punning is allowed, provided the
7437           memory is accessed through the union type.  So, the code above
7438           works as expected.    However, this code might not:
7439
7440                   int f() {
7441                     union a_union t;
7442                     int* ip;
7443                     t.d = 3.0;
7444                     ip = &t.i;
7445                     return *ip;
7446                   }
7447
7448           Similarly, access by taking the address, casting the resulting
7449           pointer and dereferencing the result has undefined behavior, even
7450           if the cast uses a union type, e.g.:
7451
7452                   int f() {
7453                     double d = 3.0;
7454                     return ((union a_union *) &d)->i;
7455                   }
7456
7457           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
7458
7459       -falign-functions
7460       -falign-functions=n
7461           Align the start of functions to the next power-of-two greater than
7462           n, skipping up to n bytes.  For instance, -falign-functions=32
7463           aligns functions to the next 32-byte boundary, but
7464           -falign-functions=24 aligns to the next 32-byte boundary only if
7465           this can be done by skipping 23 bytes or less.
7466
7467           -fno-align-functions and -falign-functions=1 are equivalent and
7468           mean that functions are not aligned.
7469
7470           Some assemblers only support this flag when n is a power of two; in
7471           that case, it is rounded up.
7472
7473           If n is not specified or is zero, use a machine-dependent default.
7474           The maximum allowed n option value is 65536.
7475
7476           Enabled at levels -O2, -O3.
7477
7478       -flimit-function-alignment
7479           If this option is enabled, the compiler tries to avoid
7480           unnecessarily overaligning functions. It attempts to instruct the
7481           assembler to align by the amount specified by -falign-functions,
7482           but not to skip more bytes than the size of the function.
7483
7484       -falign-labels
7485       -falign-labels=n
7486           Align all branch targets to a power-of-two boundary, skipping up to
7487           n bytes like -falign-functions.  This option can easily make code
7488           slower, because it must insert dummy operations for when the branch
7489           target is reached in the usual flow of the code.
7490
7491           -fno-align-labels and -falign-labels=1 are equivalent and mean that
7492           labels are not aligned.
7493
7494           If -falign-loops or -falign-jumps are applicable and are greater
7495           than this value, then their values are used instead.
7496
7497           If n is not specified or is zero, use a machine-dependent default
7498           which is very likely to be 1, meaning no alignment.  The maximum
7499           allowed n option value is 65536.
7500
7501           Enabled at levels -O2, -O3.
7502
7503       -falign-loops
7504       -falign-loops=n
7505           Align loops to a power-of-two boundary, skipping up to n bytes like
7506           -falign-functions.  If the loops are executed many times, this
7507           makes up for any execution of the dummy operations.
7508
7509           -fno-align-loops and -falign-loops=1 are equivalent and mean that
7510           loops are not aligned.  The maximum allowed n option value is
7511           65536.
7512
7513           If n is not specified or is zero, use a machine-dependent default.
7514
7515           Enabled at levels -O2, -O3.
7516
7517       -falign-jumps
7518       -falign-jumps=n
7519           Align branch targets to a power-of-two boundary, for branch targets
7520           where the targets can only be reached by jumping, skipping up to n
7521           bytes like -falign-functions.  In this case, no dummy operations
7522           need be executed.
7523
7524           -fno-align-jumps and -falign-jumps=1 are equivalent and mean that
7525           loops are not aligned.
7526
7527           If n is not specified or is zero, use a machine-dependent default.
7528           The maximum allowed n option value is 65536.
7529
7530           Enabled at levels -O2, -O3.
7531
7532       -funit-at-a-time
7533           This option is left for compatibility reasons. -funit-at-a-time has
7534           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
7535           and -fno-section-anchors.
7536
7537           Enabled by default.
7538
7539       -fno-toplevel-reorder
7540           Do not reorder top-level functions, variables, and "asm"
7541           statements.  Output them in the same order that they appear in the
7542           input file.  When this option is used, unreferenced static
7543           variables are not removed.  This option is intended to support
7544           existing code that relies on a particular ordering.  For new code,
7545           it is better to use attributes when possible.
7546
7547           Enabled at level -O0.  When disabled explicitly, it also implies
7548           -fno-section-anchors, which is otherwise enabled at -O0 on some
7549           targets.
7550
7551       -fweb
7552           Constructs webs as commonly used for register allocation purposes
7553           and assign each web individual pseudo register.  This allows the
7554           register allocation pass to operate on pseudos directly, but also
7555           strengthens several other optimization passes, such as CSE, loop
7556           optimizer and trivial dead code remover.  It can, however, make
7557           debugging impossible, since variables no longer stay in a "home
7558           register".
7559
7560           Enabled by default with -funroll-loops.
7561
7562       -fwhole-program
7563           Assume that the current compilation unit represents the whole
7564           program being compiled.  All public functions and variables with
7565           the exception of "main" and those merged by attribute
7566           "externally_visible" become static functions and in effect are
7567           optimized more aggressively by interprocedural optimizers.
7568
7569           This option should not be used in combination with -flto.  Instead
7570           relying on a linker plugin should provide safer and more precise
7571           information.
7572
7573       -flto[=n]
7574           This option runs the standard link-time optimizer.  When invoked
7575           with source code, it generates GIMPLE (one of GCC's internal
7576           representations) and writes it to special ELF sections in the
7577           object file.  When the object files are linked together, all the
7578           function bodies are read from these ELF sections and instantiated
7579           as if they had been part of the same translation unit.
7580
7581           To use the link-time optimizer, -flto and optimization options
7582           should be specified at compile time and during the final link.  It
7583           is recommended that you compile all the files participating in the
7584           same link with the same options and also specify those options at
7585           link time.  For example:
7586
7587                   gcc -c -O2 -flto foo.c
7588                   gcc -c -O2 -flto bar.c
7589                   gcc -o myprog -flto -O2 foo.o bar.o
7590
7591           The first two invocations to GCC save a bytecode representation of
7592           GIMPLE into special ELF sections inside foo.o and bar.o.  The final
7593           invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
7594           the two files into a single internal image, and compiles the result
7595           as usual.  Since both foo.o and bar.o are merged into a single
7596           image, this causes all the interprocedural analyses and
7597           optimizations in GCC to work across the two files as if they were a
7598           single one.  This means, for example, that the inliner is able to
7599           inline functions in bar.o into functions in foo.o and vice-versa.
7600
7601           Another (simpler) way to enable link-time optimization is:
7602
7603                   gcc -o myprog -flto -O2 foo.c bar.c
7604
7605           The above generates bytecode for foo.c and bar.c, merges them
7606           together into a single GIMPLE representation and optimizes them as
7607           usual to produce myprog.
7608
7609           The only important thing to keep in mind is that to enable link-
7610           time optimizations you need to use the GCC driver to perform the
7611           link step.  GCC then automatically performs link-time optimization
7612           if any of the objects involved were compiled with the -flto
7613           command-line option.  You generally should specify the optimization
7614           options to be used for link-time optimization though GCC tries to
7615           be clever at guessing an optimization level to use from the options
7616           used at compile time if you fail to specify one at link time.  You
7617           can always override the automatic decision to do link-time
7618           optimization by passing -fno-lto to the link command.
7619
7620           To make whole program optimization effective, it is necessary to
7621           make certain whole program assumptions.  The compiler needs to know
7622           what functions and variables can be accessed by libraries and
7623           runtime outside of the link-time optimized unit.  When supported by
7624           the linker, the linker plugin (see -fuse-linker-plugin) passes
7625           information to the compiler about used and externally visible
7626           symbols.  When the linker plugin is not available, -fwhole-program
7627           should be used to allow the compiler to make these assumptions,
7628           which leads to more aggressive optimization decisions.
7629
7630           When -fuse-linker-plugin is not enabled, when a file is compiled
7631           with -flto, the generated object file is larger than a regular
7632           object file because it contains GIMPLE bytecodes and the usual
7633           final code (see -ffat-lto-objects.  This means that object files
7634           with LTO information can be linked as normal object files; if
7635           -fno-lto is passed to the linker, no interprocedural optimizations
7636           are applied.  Note that when -fno-fat-lto-objects is enabled the
7637           compile stage is faster but you cannot perform a regular, non-LTO
7638           link on them.
7639
7640           Additionally, the optimization flags used to compile individual
7641           files are not necessarily related to those used at link time.  For
7642           instance,
7643
7644                   gcc -c -O0 -ffat-lto-objects -flto foo.c
7645                   gcc -c -O0 -ffat-lto-objects -flto bar.c
7646                   gcc -o myprog -O3 foo.o bar.o
7647
7648           This produces individual object files with unoptimized assembler
7649           code, but the resulting binary myprog is optimized at -O3.  If,
7650           instead, the final binary is generated with -fno-lto, then myprog
7651           is not optimized.
7652
7653           When producing the final binary, GCC only applies link-time
7654           optimizations to those files that contain bytecode.  Therefore, you
7655           can mix and match object files and libraries with GIMPLE bytecodes
7656           and final object code.  GCC automatically selects which files to
7657           optimize in LTO mode and which files to link without further
7658           processing.
7659
7660           There are some code generation flags preserved by GCC when
7661           generating bytecodes, as they need to be used during the final link
7662           stage.  Generally options specified at link time override those
7663           specified at compile time.
7664
7665           If you do not specify an optimization level option -O at link time,
7666           then GCC uses the highest optimization level used when compiling
7667           the object files.
7668
7669           Currently, the following options and their settings are taken from
7670           the first object file that explicitly specifies them: -fPIC, -fpic,
7671           -fpie, -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and
7672           all the -m target flags.
7673
7674           Certain ABI-changing flags are required to match in all compilation
7675           units, and trying to override this at link time with a conflicting
7676           value is ignored.  This includes options such as
7677           -freg-struct-return and -fpcc-struct-return.
7678
7679           Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv,
7680           -fno-trapv or -fno-strict-aliasing are passed through to the link
7681           stage and merged conservatively for conflicting translation units.
7682           Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take
7683           precedence; and for example -ffp-contract=off takes precedence over
7684           -ffp-contract=fast.  You can override them at link time.
7685
7686           If LTO encounters objects with C linkage declared with incompatible
7687           types in separate translation units to be linked together
7688           (undefined behavior according to ISO C99 6.2.7), a non-fatal
7689           diagnostic may be issued.  The behavior is still undefined at run
7690           time.  Similar diagnostics may be raised for other languages.
7691
7692           Another feature of LTO is that it is possible to apply
7693           interprocedural optimizations on files written in different
7694           languages:
7695
7696                   gcc -c -flto foo.c
7697                   g++ -c -flto bar.cc
7698                   gfortran -c -flto baz.f90
7699                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
7700
7701           Notice that the final link is done with g++ to get the C++ runtime
7702           libraries and -lgfortran is added to get the Fortran runtime
7703           libraries.  In general, when mixing languages in LTO mode, you
7704           should use the same link command options as when mixing languages
7705           in a regular (non-LTO) compilation.
7706
7707           If object files containing GIMPLE bytecode are stored in a library
7708           archive, say libfoo.a, it is possible to extract and use them in an
7709           LTO link if you are using a linker with plugin support.  To create
7710           static libraries suitable for LTO, use gcc-ar and gcc-ranlib
7711           instead of ar and ranlib; to show the symbols of object files with
7712           GIMPLE bytecode, use gcc-nm.  Those commands require that ar,
7713           ranlib and nm have been compiled with plugin support.  At link
7714           time, use the flag -fuse-linker-plugin to ensure that the library
7715           participates in the LTO optimization process:
7716
7717                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
7718
7719           With the linker plugin enabled, the linker extracts the needed
7720           GIMPLE files from libfoo.a and passes them on to the running GCC to
7721           make them part of the aggregated GIMPLE image to be optimized.
7722
7723           If you are not using a linker with plugin support and/or do not
7724           enable the linker plugin, then the objects inside libfoo.a are
7725           extracted and linked as usual, but they do not participate in the
7726           LTO optimization process.  In order to make a static library
7727           suitable for both LTO optimization and usual linkage, compile its
7728           object files with -flto -ffat-lto-objects.
7729
7730           Link-time optimizations do not require the presence of the whole
7731           program to operate.  If the program does not require any symbols to
7732           be exported, it is possible to combine -flto and -fwhole-program to
7733           allow the interprocedural optimizers to use more aggressive
7734           assumptions which may lead to improved optimization opportunities.
7735           Use of -fwhole-program is not needed when linker plugin is active
7736           (see -fuse-linker-plugin).
7737
7738           The current implementation of LTO makes no attempt to generate
7739           bytecode that is portable between different types of hosts.  The
7740           bytecode files are versioned and there is a strict version check,
7741           so bytecode files generated in one version of GCC do not work with
7742           an older or newer version of GCC.
7743
7744           Link-time optimization does not work well with generation of
7745           debugging information on systems other than those using a
7746           combination of ELF and DWARF.
7747
7748           If you specify the optional n, the optimization and code generation
7749           done at link time is executed in parallel using n parallel jobs by
7750           utilizing an installed make program.  The environment variable MAKE
7751           may be used to override the program used.  The default value for n
7752           is 1.
7753
7754           You can also specify -flto=jobserver to use GNU make's job server
7755           mode to determine the number of parallel jobs. This is useful when
7756           the Makefile calling GCC is already executing in parallel.  You
7757           must prepend a + to the command recipe in the parent Makefile for
7758           this to work.  This option likely only works if MAKE is GNU make.
7759
7760       -flto-partition=alg
7761           Specify the partitioning algorithm used by the link-time optimizer.
7762           The value is either 1to1 to specify a partitioning mirroring the
7763           original source files or balanced to specify partitioning into
7764           equally sized chunks (whenever possible) or max to create new
7765           partition for every symbol where possible.  Specifying none as an
7766           algorithm disables partitioning and streaming completely.  The
7767           default value is balanced. While 1to1 can be used as an workaround
7768           for various code ordering issues, the max partitioning is intended
7769           for internal testing only.  The value one specifies that exactly
7770           one partition should be used while the value none bypasses
7771           partitioning and executes the link-time optimization step directly
7772           from the WPA phase.
7773
7774       -flto-odr-type-merging
7775           Enable streaming of mangled types names of C++ types and their
7776           unification at link time.  This increases size of LTO object files,
7777           but enables diagnostics about One Definition Rule violations.
7778
7779       -flto-compression-level=n
7780           This option specifies the level of compression used for
7781           intermediate language written to LTO object files, and is only
7782           meaningful in conjunction with LTO mode (-flto).  Valid values are
7783           0 (no compression) to 9 (maximum compression).  Values outside this
7784           range are clamped to either 0 or 9.  If the option is not given, a
7785           default balanced compression setting is used.
7786
7787       -fuse-linker-plugin
7788           Enables the use of a linker plugin during link-time optimization.
7789           This option relies on plugin support in the linker, which is
7790           available in gold or in GNU ld 2.21 or newer.
7791
7792           This option enables the extraction of object files with GIMPLE
7793           bytecode out of library archives. This improves the quality of
7794           optimization by exposing more code to the link-time optimizer.
7795           This information specifies what symbols can be accessed externally
7796           (by non-LTO object or during dynamic linking).  Resulting code
7797           quality improvements on binaries (and shared libraries that use
7798           hidden visibility) are similar to -fwhole-program.  See -flto for a
7799           description of the effect of this flag and how to use it.
7800
7801           This option is enabled by default when LTO support in GCC is
7802           enabled and GCC was configured for use with a linker supporting
7803           plugins (GNU ld 2.21 or newer or gold).
7804
7805       -ffat-lto-objects
7806           Fat LTO objects are object files that contain both the intermediate
7807           language and the object code. This makes them usable for both LTO
7808           linking and normal linking. This option is effective only when
7809           compiling with -flto and is ignored at link time.
7810
7811           -fno-fat-lto-objects improves compilation time over plain LTO, but
7812           requires the complete toolchain to be aware of LTO. It requires a
7813           linker with linker plugin support for basic functionality.
7814           Additionally, nm, ar and ranlib need to support linker plugins to
7815           allow a full-featured build environment (capable of building static
7816           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib
7817           wrappers to pass the right options to these tools. With non fat LTO
7818           makefiles need to be modified to use them.
7819
7820           Note that modern binutils provide plugin auto-load mechanism.
7821           Installing the linker plugin into $libdir/bfd-plugins has the same
7822           effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-
7823           ranlib).
7824
7825           The default is -fno-fat-lto-objects on targets with linker plugin
7826           support.
7827
7828       -fcompare-elim
7829           After register allocation and post-register allocation instruction
7830           splitting, identify arithmetic instructions that compute processor
7831           flags similar to a comparison operation based on that arithmetic.
7832           If possible, eliminate the explicit comparison operation.
7833
7834           This pass only applies to certain targets that cannot explicitly
7835           represent the comparison operation before register allocation is
7836           complete.
7837
7838           Enabled at levels -O, -O2, -O3, -Os.
7839
7840       -fcprop-registers
7841           After register allocation and post-register allocation instruction
7842           splitting, perform a copy-propagation pass to try to reduce
7843           scheduling dependencies and occasionally eliminate the copy.
7844
7845           Enabled at levels -O, -O2, -O3, -Os.
7846
7847       -fprofile-correction
7848           Profiles collected using an instrumented binary for multi-threaded
7849           programs may be inconsistent due to missed counter updates. When
7850           this option is specified, GCC uses heuristics to correct or smooth
7851           out such inconsistencies. By default, GCC emits an error message
7852           when an inconsistent profile is detected.
7853
7854       -fprofile-use
7855       -fprofile-use=path
7856           Enable profile feedback-directed optimizations, and the following
7857           optimizations which are generally profitable only with profile
7858           feedback available: -fbranch-probabilities, -fvpt, -funroll-loops,
7859           -fpeel-loops, -ftracer, -ftree-vectorize, and ftree-loop-
7860           distribute-patterns.
7861
7862           Before you can use this option, you must first generate profiling
7863           information.
7864
7865           By default, GCC emits an error message if the feedback profiles do
7866           not match the source code.  This error can be turned into a warning
7867           by using -Wcoverage-mismatch.  Note this may result in poorly
7868           optimized code.
7869
7870           If path is specified, GCC looks at the path to find the profile
7871           feedback data files. See -fprofile-dir.
7872
7873       -fauto-profile
7874       -fauto-profile=path
7875           Enable sampling-based feedback-directed optimizations, and the
7876           following optimizations which are generally profitable only with
7877           profile feedback available: -fbranch-probabilities, -fvpt,
7878           -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize,
7879           -finline-functions, -fipa-cp, -fipa-cp-clone,
7880           -fpredictive-commoning, -funswitch-loops, -fgcse-after-reload, and
7881           -ftree-loop-distribute-patterns.
7882
7883           path is the name of a file containing AutoFDO profile information.
7884           If omitted, it defaults to fbdata.afdo in the current directory.
7885
7886           Producing an AutoFDO profile data file requires running your
7887           program with the perf utility on a supported GNU/Linux target
7888           system.  For more information, see <https://perf.wiki.kernel.org/>.
7889
7890           E.g.
7891
7892                   perf record -e br_inst_retired:near_taken -b -o perf.data \
7893                       -- your_program
7894
7895           Then use the create_gcov tool to convert the raw profile data to a
7896           format that can be used by GCC.  You must also supply the
7897           unstripped binary for your program to this tool.  See
7898           <https://github.com/google/autofdo>.
7899
7900           E.g.
7901
7902                   create_gcov --binary=your_program.unstripped --profile=perf.data \
7903                       --gcov=profile.afdo
7904
7905       The following options control compiler behavior regarding floating-
7906       point arithmetic.  These options trade off between speed and
7907       correctness.  All must be specifically enabled.
7908
7909       -ffloat-store
7910           Do not store floating-point variables in registers, and inhibit
7911           other options that might change whether a floating-point value is
7912           taken from a register or memory.
7913
7914           This option prevents undesirable excess precision on machines such
7915           as the 68000 where the floating registers (of the 68881) keep more
7916           precision than a "double" is supposed to have.  Similarly for the
7917           x86 architecture.  For most programs, the excess precision does
7918           only good, but a few programs rely on the precise definition of
7919           IEEE floating point.  Use -ffloat-store for such programs, after
7920           modifying them to store all pertinent intermediate computations
7921           into variables.
7922
7923       -fexcess-precision=style
7924           This option allows further control over excess precision on
7925           machines where floating-point operations occur in a format with
7926           more precision or range than the IEEE standard and interchange
7927           floating-point types.  By default, -fexcess-precision=fast is in
7928           effect; this means that operations may be carried out in a wider
7929           precision than the types specified in the source if that would
7930           result in faster code, and it is unpredictable when rounding to the
7931           types specified in the source code takes place.  When compiling C,
7932           if -fexcess-precision=standard is specified then excess precision
7933           follows the rules specified in ISO C99; in particular, both casts
7934           and assignments cause values to be rounded to their semantic types
7935           (whereas -ffloat-store only affects assignments).  This option is
7936           enabled by default for C if a strict conformance option such as
7937           -std=c99 is used.  -ffast-math enables -fexcess-precision=fast by
7938           default regardless of whether a strict conformance option is used.
7939
7940           -fexcess-precision=standard is not implemented for languages other
7941           than C.  On the x86, it has no effect if -mfpmath=sse or
7942           -mfpmath=sse+387 is specified; in the former case, IEEE semantics
7943           apply without excess precision, and in the latter, rounding is
7944           unpredictable.
7945
7946       -ffast-math
7947           Sets the options -fno-math-errno, -funsafe-math-optimizations,
7948           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans,
7949           -fcx-limited-range and -fexcess-precision=fast.
7950
7951           This option causes the preprocessor macro "__FAST_MATH__" to be
7952           defined.
7953
7954           This option is not turned on by any -O option besides -Ofast since
7955           it can result in incorrect output for programs that depend on an
7956           exact implementation of IEEE or ISO rules/specifications for math
7957           functions. It may, however, yield faster code for programs that do
7958           not require the guarantees of these specifications.
7959
7960       -fno-math-errno
7961           Do not set "errno" after calling math functions that are executed
7962           with a single instruction, e.g., "sqrt".  A program that relies on
7963           IEEE exceptions for math error handling may want to use this flag
7964           for speed while maintaining IEEE arithmetic compatibility.
7965
7966           This option is not turned on by any -O option since it can result
7967           in incorrect output for programs that depend on an exact
7968           implementation of IEEE or ISO rules/specifications for math
7969           functions. It may, however, yield faster code for programs that do
7970           not require the guarantees of these specifications.
7971
7972           The default is -fmath-errno.
7973
7974           On Darwin systems, the math library never sets "errno".  There is
7975           therefore no reason for the compiler to consider the possibility
7976           that it might, and -fno-math-errno is the default.
7977
7978       -funsafe-math-optimizations
7979           Allow optimizations for floating-point arithmetic that (a) assume
7980           that arguments and results are valid and (b) may violate IEEE or
7981           ANSI standards.  When used at link time, it may include libraries
7982           or startup files that change the default FPU control word or other
7983           similar optimizations.
7984
7985           This option is not turned on by any -O option since it can result
7986           in incorrect output for programs that depend on an exact
7987           implementation of IEEE or ISO rules/specifications for math
7988           functions. It may, however, yield faster code for programs that do
7989           not require the guarantees of these specifications.  Enables
7990           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
7991           -freciprocal-math.
7992
7993           The default is -fno-unsafe-math-optimizations.
7994
7995       -fassociative-math
7996           Allow re-association of operands in series of floating-point
7997           operations.  This violates the ISO C and C++ language standard by
7998           possibly changing computation result.  NOTE: re-ordering may change
7999           the sign of zero as well as ignore NaNs and inhibit or create
8000           underflow or overflow (and thus cannot be used on code that relies
8001           on rounding behavior like "(x + 2**52) - 2**52".  May also reorder
8002           floating-point comparisons and thus may not be used when ordered
8003           comparisons are required.  This option requires that both
8004           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
8005           it doesn't make much sense with -frounding-math. For Fortran the
8006           option is automatically enabled when both -fno-signed-zeros and
8007           -fno-trapping-math are in effect.
8008
8009           The default is -fno-associative-math.
8010
8011       -freciprocal-math
8012           Allow the reciprocal of a value to be used instead of dividing by
8013           the value if this enables optimizations.  For example "x / y" can
8014           be replaced with "x * (1/y)", which is useful if "(1/y)" is subject
8015           to common subexpression elimination.  Note that this loses
8016           precision and increases the number of flops operating on the value.
8017
8018           The default is -fno-reciprocal-math.
8019
8020       -ffinite-math-only
8021           Allow optimizations for floating-point arithmetic that assume that
8022           arguments and results are not NaNs or +-Infs.
8023
8024           This option is not turned on by any -O option since it can result
8025           in incorrect output for programs that depend on an exact
8026           implementation of IEEE or ISO rules/specifications for math
8027           functions. It may, however, yield faster code for programs that do
8028           not require the guarantees of these specifications.
8029
8030           The default is -fno-finite-math-only.
8031
8032       -fno-signed-zeros
8033           Allow optimizations for floating-point arithmetic that ignore the
8034           signedness of zero.  IEEE arithmetic specifies the behavior of
8035           distinct +0.0 and -0.0 values, which then prohibits simplification
8036           of expressions such as x+0.0 or 0.0*x (even with
8037           -ffinite-math-only).  This option implies that the sign of a zero
8038           result isn't significant.
8039
8040           The default is -fsigned-zeros.
8041
8042       -fno-trapping-math
8043           Compile code assuming that floating-point operations cannot
8044           generate user-visible traps.  These traps include division by zero,
8045           overflow, underflow, inexact result and invalid operation.  This
8046           option requires that -fno-signaling-nans be in effect.  Setting
8047           this option may allow faster code if one relies on "non-stop" IEEE
8048           arithmetic, for example.
8049
8050           This option should never be turned on by any -O option since it can
8051           result in incorrect output for programs that depend on an exact
8052           implementation of IEEE or ISO rules/specifications for math
8053           functions.
8054
8055           The default is -ftrapping-math.
8056
8057       -frounding-math
8058           Disable transformations and optimizations that assume default
8059           floating-point rounding behavior.  This is round-to-zero for all
8060           floating point to integer conversions, and round-to-nearest for all
8061           other arithmetic truncations.  This option should be specified for
8062           programs that change the FP rounding mode dynamically, or that may
8063           be executed with a non-default rounding mode.  This option disables
8064           constant folding of floating-point expressions at compile time
8065           (which may be affected by rounding mode) and arithmetic
8066           transformations that are unsafe in the presence of sign-dependent
8067           rounding modes.
8068
8069           The default is -fno-rounding-math.
8070
8071           This option is experimental and does not currently guarantee to
8072           disable all GCC optimizations that are affected by rounding mode.
8073           Future versions of GCC may provide finer control of this setting
8074           using C99's "FENV_ACCESS" pragma.  This command-line option will be
8075           used to specify the default state for "FENV_ACCESS".
8076
8077       -fsignaling-nans
8078           Compile code assuming that IEEE signaling NaNs may generate user-
8079           visible traps during floating-point operations.  Setting this
8080           option disables optimizations that may change the number of
8081           exceptions visible with signaling NaNs.  This option implies
8082           -ftrapping-math.
8083
8084           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
8085           defined.
8086
8087           The default is -fno-signaling-nans.
8088
8089           This option is experimental and does not currently guarantee to
8090           disable all GCC optimizations that affect signaling NaN behavior.
8091
8092       -fno-fp-int-builtin-inexact
8093           Do not allow the built-in functions "ceil", "floor", "round" and
8094           "trunc", and their "float" and "long double" variants, to generate
8095           code that raises the "inexact" floating-point exception for
8096           noninteger arguments.  ISO C99 and C11 allow these functions to
8097           raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
8098           bindings to IEEE 754-2008, does not allow these functions to do so.
8099
8100           The default is -ffp-int-builtin-inexact, allowing the exception to
8101           be raised.  This option does nothing unless -ftrapping-math is in
8102           effect.
8103
8104           Even if -fno-fp-int-builtin-inexact is used, if the functions
8105           generate a call to a library function then the "inexact" exception
8106           may be raised if the library implementation does not follow TS
8107           18661.
8108
8109       -fsingle-precision-constant
8110           Treat floating-point constants as single precision instead of
8111           implicitly converting them to double-precision constants.
8112
8113       -fcx-limited-range
8114           When enabled, this option states that a range reduction step is not
8115           needed when performing complex division.  Also, there is no
8116           checking whether the result of a complex multiplication or division
8117           is "NaN + I*NaN", with an attempt to rescue the situation in that
8118           case.  The default is -fno-cx-limited-range, but is enabled by
8119           -ffast-math.
8120
8121           This option controls the default setting of the ISO C99
8122           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
8123           languages.
8124
8125       -fcx-fortran-rules
8126           Complex multiplication and division follow Fortran rules.  Range
8127           reduction is done as part of complex division, but there is no
8128           checking whether the result of a complex multiplication or division
8129           is "NaN + I*NaN", with an attempt to rescue the situation in that
8130           case.
8131
8132           The default is -fno-cx-fortran-rules.
8133
8134       The following options control optimizations that may improve
8135       performance, but are not enabled by any -O options.  This section
8136       includes experimental options that may produce broken code.
8137
8138       -fbranch-probabilities
8139           After running a program compiled with -fprofile-arcs, you can
8140           compile it a second time using -fbranch-probabilities, to improve
8141           optimizations based on the number of times each branch was taken.
8142           When a program compiled with -fprofile-arcs exits, it saves arc
8143           execution counts to a file called sourcename.gcda for each source
8144           file.  The information in this data file is very dependent on the
8145           structure of the generated code, so you must use the same source
8146           code and the same optimization options for both compilations.
8147
8148           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
8149           JUMP_INSN and CALL_INSN.  These can be used to improve
8150           optimization.  Currently, they are only used in one place: in
8151           reorg.c, instead of guessing which path a branch is most likely to
8152           take, the REG_BR_PROB values are used to exactly determine which
8153           path is taken more often.
8154
8155       -fprofile-values
8156           If combined with -fprofile-arcs, it adds code so that some data
8157           about values of expressions in the program is gathered.
8158
8159           With -fbranch-probabilities, it reads back the data gathered from
8160           profiling values of expressions for usage in optimizations.
8161
8162           Enabled with -fprofile-generate and -fprofile-use.
8163
8164       -fprofile-reorder-functions
8165           Function reordering based on profile instrumentation collects first
8166           time of execution of a function and orders these functions in
8167           ascending order.
8168
8169           Enabled with -fprofile-use.
8170
8171       -fvpt
8172           If combined with -fprofile-arcs, this option instructs the compiler
8173           to add code to gather information about values of expressions.
8174
8175           With -fbranch-probabilities, it reads back the data gathered and
8176           actually performs the optimizations based on them.  Currently the
8177           optimizations include specialization of division operations using
8178           the knowledge about the value of the denominator.
8179
8180       -frename-registers
8181           Attempt to avoid false dependencies in scheduled code by making use
8182           of registers left over after register allocation.  This
8183           optimization most benefits processors with lots of registers.
8184           Depending on the debug information format adopted by the target,
8185           however, it can make debugging impossible, since variables no
8186           longer stay in a "home register".
8187
8188           Enabled by default with -funroll-loops.
8189
8190       -fschedule-fusion
8191           Performs a target dependent pass over the instruction stream to
8192           schedule instructions of same type together because target machine
8193           can execute them more efficiently if they are adjacent to each
8194           other in the instruction flow.
8195
8196           Enabled at levels -O2, -O3, -Os.
8197
8198       -ftracer
8199           Perform tail duplication to enlarge superblock size.  This
8200           transformation simplifies the control flow of the function allowing
8201           other optimizations to do a better job.
8202
8203           Enabled with -fprofile-use.
8204
8205       -funroll-loops
8206           Unroll loops whose number of iterations can be determined at
8207           compile time or upon entry to the loop.  -funroll-loops implies
8208           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
8209           turns on complete loop peeling (i.e. complete removal of loops with
8210           a small constant number of iterations).  This option makes code
8211           larger, and may or may not make it run faster.
8212
8213           Enabled with -fprofile-use.
8214
8215       -funroll-all-loops
8216           Unroll all loops, even if their number of iterations is uncertain
8217           when the loop is entered.  This usually makes programs run more
8218           slowly.  -funroll-all-loops implies the same options as
8219           -funroll-loops.
8220
8221       -fpeel-loops
8222           Peels loops for which there is enough information that they do not
8223           roll much (from profile feedback or static analysis).  It also
8224           turns on complete loop peeling (i.e. complete removal of loops with
8225           small constant number of iterations).
8226
8227           Enabled with -O3 and/or -fprofile-use.
8228
8229       -fmove-loop-invariants
8230           Enables the loop invariant motion pass in the RTL loop optimizer.
8231           Enabled at level -O1
8232
8233       -fsplit-loops
8234           Split a loop into two if it contains a condition that's always true
8235           for one side of the iteration space and false for the other.
8236
8237       -funswitch-loops
8238           Move branches with loop invariant conditions out of the loop, with
8239           duplicates of the loop on both branches (modified according to
8240           result of the condition).
8241
8242       -ffunction-sections
8243       -fdata-sections
8244           Place each function or data item into its own section in the output
8245           file if the target supports arbitrary sections.  The name of the
8246           function or the name of the data item determines the section's name
8247           in the output file.
8248
8249           Use these options on systems where the linker can perform
8250           optimizations to improve locality of reference in the instruction
8251           space.  Most systems using the ELF object format have linkers with
8252           such optimizations.  On AIX, the linker rearranges sections
8253           (CSECTs) based on the call graph.  The performance impact varies.
8254
8255           Together with a linker garbage collection (linker --gc-sections
8256           option) these options may lead to smaller statically-linked
8257           executables (after stripping).
8258
8259           On ELF/DWARF systems these options do not degenerate the quality of
8260           the debug information.  There could be issues with other object
8261           files/debug info formats.
8262
8263           Only use these options when there are significant benefits from
8264           doing so.  When you specify these options, the assembler and linker
8265           create larger object and executable files and are also slower.
8266           These options affect code generation.  They prevent optimizations
8267           by the compiler and assembler using relative locations inside a
8268           translation unit since the locations are unknown until link time.
8269           An example of such an optimization is relaxing calls to short call
8270           instructions.
8271
8272       -fbranch-target-load-optimize
8273           Perform branch target register load optimization before prologue /
8274           epilogue threading.  The use of target registers can typically be
8275           exposed only during reload, thus hoisting loads out of loops and
8276           doing inter-block scheduling needs a separate optimization pass.
8277
8278       -fbranch-target-load-optimize2
8279           Perform branch target register load optimization after prologue /
8280           epilogue threading.
8281
8282       -fbtr-bb-exclusive
8283           When performing branch target register load optimization, don't
8284           reuse branch target registers within any basic block.
8285
8286       -fstdarg-opt
8287           Optimize the prologue of variadic argument functions with respect
8288           to usage of those arguments.
8289
8290       -fsection-anchors
8291           Try to reduce the number of symbolic address calculations by using
8292           shared "anchor" symbols to address nearby objects.  This
8293           transformation can help to reduce the number of GOT entries and GOT
8294           accesses on some targets.
8295
8296           For example, the implementation of the following function "foo":
8297
8298                   static int a, b, c;
8299                   int foo (void) { return a + b + c; }
8300
8301           usually calculates the addresses of all three variables, but if you
8302           compile it with -fsection-anchors, it accesses the variables from a
8303           common anchor point instead.  The effect is similar to the
8304           following pseudocode (which isn't valid C):
8305
8306                   int foo (void)
8307                   {
8308                     register int *xr = &x;
8309                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
8310                   }
8311
8312           Not all targets support this option.
8313
8314       --param name=value
8315           In some places, GCC uses various constants to control the amount of
8316           optimization that is done.  For example, GCC does not inline
8317           functions that contain more than a certain number of instructions.
8318           You can control some of these constants on the command line using
8319           the --param option.
8320
8321           The names of specific parameters, and the meaning of the values,
8322           are tied to the internals of the compiler, and are subject to
8323           change without notice in future releases.
8324
8325           In each case, the value is an integer.  The allowable choices for
8326           name are:
8327
8328           predictable-branch-outcome
8329               When branch is predicted to be taken with probability lower
8330               than this threshold (in percent), then it is considered well
8331               predictable. The default is 10.
8332
8333           max-rtl-if-conversion-insns
8334               RTL if-conversion tries to remove conditional branches around a
8335               block and replace them with conditionally executed
8336               instructions.  This parameter gives the maximum number of
8337               instructions in a block which should be considered for if-
8338               conversion.  The default is 10, though the compiler will also
8339               use other heuristics to decide whether if-conversion is likely
8340               to be profitable.
8341
8342           max-rtl-if-conversion-predictable-cost
8343           max-rtl-if-conversion-unpredictable-cost
8344               RTL if-conversion will try to remove conditional branches
8345               around a block and replace them with conditionally executed
8346               instructions.  These parameters give the maximum permissible
8347               cost for the sequence that would be generated by if-conversion
8348               depending on whether the branch is statically determined to be
8349               predictable or not.  The units for this parameter are the same
8350               as those for the GCC internal seq_cost metric.  The compiler
8351               will try to provide a reasonable default for this parameter
8352               using the BRANCH_COST target macro.
8353
8354           max-crossjump-edges
8355               The maximum number of incoming edges to consider for cross-
8356               jumping.  The algorithm used by -fcrossjumping is O(N^2) in the
8357               number of edges incoming to each block.  Increasing values mean
8358               more aggressive optimization, making the compilation time
8359               increase with probably small improvement in executable size.
8360
8361           min-crossjump-insns
8362               The minimum number of instructions that must be matched at the
8363               end of two blocks before cross-jumping is performed on them.
8364               This value is ignored in the case where all instructions in the
8365               block being cross-jumped from are matched.  The default value
8366               is 5.
8367
8368           max-grow-copy-bb-insns
8369               The maximum code size expansion factor when copying basic
8370               blocks instead of jumping.  The expansion is relative to a jump
8371               instruction.  The default value is 8.
8372
8373           max-goto-duplication-insns
8374               The maximum number of instructions to duplicate to a block that
8375               jumps to a computed goto.  To avoid O(N^2) behavior in a number
8376               of passes, GCC factors computed gotos early in the compilation
8377               process, and unfactors them as late as possible.  Only computed
8378               jumps at the end of a basic blocks with no more than max-goto-
8379               duplication-insns are unfactored.  The default value is 8.
8380
8381           max-delay-slot-insn-search
8382               The maximum number of instructions to consider when looking for
8383               an instruction to fill a delay slot.  If more than this
8384               arbitrary number of instructions are searched, the time savings
8385               from filling the delay slot are minimal, so stop searching.
8386               Increasing values mean more aggressive optimization, making the
8387               compilation time increase with probably small improvement in
8388               execution time.
8389
8390           max-delay-slot-live-search
8391               When trying to fill delay slots, the maximum number of
8392               instructions to consider when searching for a block with valid
8393               live register information.  Increasing this arbitrarily chosen
8394               value means more aggressive optimization, increasing the
8395               compilation time.  This parameter should be removed when the
8396               delay slot code is rewritten to maintain the control-flow
8397               graph.
8398
8399           max-gcse-memory
8400               The approximate maximum amount of memory that can be allocated
8401               in order to perform the global common subexpression elimination
8402               optimization.  If more memory than specified is required, the
8403               optimization is not done.
8404
8405           max-gcse-insertion-ratio
8406               If the ratio of expression insertions to deletions is larger
8407               than this value for any expression, then RTL PRE inserts or
8408               removes the expression and thus leaves partially redundant
8409               computations in the instruction stream.  The default value is
8410               20.
8411
8412           max-pending-list-length
8413               The maximum number of pending dependencies scheduling allows
8414               before flushing the current state and starting over.  Large
8415               functions with few branches or calls can create excessively
8416               large lists which needlessly consume memory and resources.
8417
8418           max-modulo-backtrack-attempts
8419               The maximum number of backtrack attempts the scheduler should
8420               make when modulo scheduling a loop.  Larger values can
8421               exponentially increase compilation time.
8422
8423           max-inline-insns-single
8424               Several parameters control the tree inliner used in GCC.  This
8425               number sets the maximum number of instructions (counted in
8426               GCC's internal representation) in a single function that the
8427               tree inliner considers for inlining.  This only affects
8428               functions declared inline and methods implemented in a class
8429               declaration (C++).  The default value is 400.
8430
8431           max-inline-insns-auto
8432               When you use -finline-functions (included in -O3), a lot of
8433               functions that would otherwise not be considered for inlining
8434               by the compiler are investigated.  To those functions, a
8435               different (more restrictive) limit compared to functions
8436               declared inline can be applied.  The default value is 30.
8437
8438           inline-min-speedup
8439               When estimated performance improvement of caller + callee
8440               runtime exceeds this threshold (in percent), the function can
8441               be inlined regardless of the limit on --param max-inline-insns-
8442               single and --param max-inline-insns-auto.  The default value is
8443               15.
8444
8445           large-function-insns
8446               The limit specifying really large functions.  For functions
8447               larger than this limit after inlining, inlining is constrained
8448               by --param large-function-growth.  This parameter is useful
8449               primarily to avoid extreme compilation time caused by non-
8450               linear algorithms used by the back end.  The default value is
8451               2700.
8452
8453           large-function-growth
8454               Specifies maximal growth of large function caused by inlining
8455               in percents.  The default value is 100 which limits large
8456               function growth to 2.0 times the original size.
8457
8458           large-unit-insns
8459               The limit specifying large translation unit.  Growth caused by
8460               inlining of units larger than this limit is limited by --param
8461               inline-unit-growth.  For small units this might be too tight.
8462               For example, consider a unit consisting of function A that is
8463               inline and B that just calls A three times.  If B is small
8464               relative to A, the growth of unit is 300\% and yet such
8465               inlining is very sane.  For very large units consisting of
8466               small inlineable functions, however, the overall unit growth
8467               limit is needed to avoid exponential explosion of code size.
8468               Thus for smaller units, the size is increased to --param large-
8469               unit-insns before applying --param inline-unit-growth.  The
8470               default is 10000.
8471
8472           inline-unit-growth
8473               Specifies maximal overall growth of the compilation unit caused
8474               by inlining.  The default value is 20 which limits unit growth
8475               to 1.2 times the original size. Cold functions (either marked
8476               cold via an attribute or by profile feedback) are not accounted
8477               into the unit size.
8478
8479           ipcp-unit-growth
8480               Specifies maximal overall growth of the compilation unit caused
8481               by interprocedural constant propagation.  The default value is
8482               10 which limits unit growth to 1.1 times the original size.
8483
8484           large-stack-frame
8485               The limit specifying large stack frames.  While inlining the
8486               algorithm is trying to not grow past this limit too much.  The
8487               default value is 256 bytes.
8488
8489           large-stack-frame-growth
8490               Specifies maximal growth of large stack frames caused by
8491               inlining in percents.  The default value is 1000 which limits
8492               large stack frame growth to 11 times the original size.
8493
8494           max-inline-insns-recursive
8495           max-inline-insns-recursive-auto
8496               Specifies the maximum number of instructions an out-of-line
8497               copy of a self-recursive inline function can grow into by
8498               performing recursive inlining.
8499
8500               --param max-inline-insns-recursive applies to functions
8501               declared inline.  For functions not declared inline, recursive
8502               inlining happens only when -finline-functions (included in -O3)
8503               is enabled; --param max-inline-insns-recursive-auto applies
8504               instead.  The default value is 450.
8505
8506           max-inline-recursive-depth
8507           max-inline-recursive-depth-auto
8508               Specifies the maximum recursion depth used for recursive
8509               inlining.
8510
8511               --param max-inline-recursive-depth applies to functions
8512               declared inline.  For functions not declared inline, recursive
8513               inlining happens only when -finline-functions (included in -O3)
8514               is enabled; --param max-inline-recursive-depth-auto applies
8515               instead.  The default value is 8.
8516
8517           min-inline-recursive-probability
8518               Recursive inlining is profitable only for function having deep
8519               recursion in average and can hurt for function having little
8520               recursion depth by increasing the prologue size or complexity
8521               of function body to other optimizers.
8522
8523               When profile feedback is available (see -fprofile-generate) the
8524               actual recursion depth can be guessed from the probability that
8525               function recurses via a given call expression.  This parameter
8526               limits inlining only to call expressions whose probability
8527               exceeds the given threshold (in percents).  The default value
8528               is 10.
8529
8530           early-inlining-insns
8531               Specify growth that the early inliner can make.  In effect it
8532               increases the amount of inlining for code having a large
8533               abstraction penalty.  The default value is 14.
8534
8535           max-early-inliner-iterations
8536               Limit of iterations of the early inliner.  This basically
8537               bounds the number of nested indirect calls the early inliner
8538               can resolve.  Deeper chains are still handled by late inlining.
8539
8540           comdat-sharing-probability
8541               Probability (in percent) that C++ inline function with comdat
8542               visibility are shared across multiple compilation units.  The
8543               default value is 20.
8544
8545           profile-func-internal-id
8546               A parameter to control whether to use function internal id in
8547               profile database lookup. If the value is 0, the compiler uses
8548               an id that is based on function assembler name and filename,
8549               which makes old profile data more tolerant to source changes
8550               such as function reordering etc.  The default value is 0.
8551
8552           min-vect-loop-bound
8553               The minimum number of iterations under which loops are not
8554               vectorized when -ftree-vectorize is used.  The number of
8555               iterations after vectorization needs to be greater than the
8556               value specified by this option to allow vectorization.  The
8557               default value is 0.
8558
8559           gcse-cost-distance-ratio
8560               Scaling factor in calculation of maximum distance an expression
8561               can be moved by GCSE optimizations.  This is currently
8562               supported only in the code hoisting pass.  The bigger the
8563               ratio, the more aggressive code hoisting is with simple
8564               expressions, i.e., the expressions that have cost less than
8565               gcse-unrestricted-cost.  Specifying 0 disables hoisting of
8566               simple expressions.  The default value is 10.
8567
8568           gcse-unrestricted-cost
8569               Cost, roughly measured as the cost of a single typical machine
8570               instruction, at which GCSE optimizations do not constrain the
8571               distance an expression can travel.  This is currently supported
8572               only in the code hoisting pass.  The lesser the cost, the more
8573               aggressive code hoisting is.  Specifying 0 allows all
8574               expressions to travel unrestricted distances.  The default
8575               value is 3.
8576
8577           max-hoist-depth
8578               The depth of search in the dominator tree for expressions to
8579               hoist.  This is used to avoid quadratic behavior in hoisting
8580               algorithm.  The value of 0 does not limit on the search, but
8581               may slow down compilation of huge functions.  The default value
8582               is 30.
8583
8584           max-tail-merge-comparisons
8585               The maximum amount of similar bbs to compare a bb with.  This
8586               is used to avoid quadratic behavior in tree tail merging.  The
8587               default value is 10.
8588
8589           max-tail-merge-iterations
8590               The maximum amount of iterations of the pass over the function.
8591               This is used to limit compilation time in tree tail merging.
8592               The default value is 2.
8593
8594           store-merging-allow-unaligned
8595               Allow the store merging pass to introduce unaligned stores if
8596               it is legal to do so.  The default value is 1.
8597
8598           max-stores-to-merge
8599               The maximum number of stores to attempt to merge into wider
8600               stores in the store merging pass.  The minimum value is 2 and
8601               the default is 64.
8602
8603           max-unrolled-insns
8604               The maximum number of instructions that a loop may have to be
8605               unrolled.  If a loop is unrolled, this parameter also
8606               determines how many times the loop code is unrolled.
8607
8608           max-average-unrolled-insns
8609               The maximum number of instructions biased by probabilities of
8610               their execution that a loop may have to be unrolled.  If a loop
8611               is unrolled, this parameter also determines how many times the
8612               loop code is unrolled.
8613
8614           max-unroll-times
8615               The maximum number of unrollings of a single loop.
8616
8617           max-peeled-insns
8618               The maximum number of instructions that a loop may have to be
8619               peeled.  If a loop is peeled, this parameter also determines
8620               how many times the loop code is peeled.
8621
8622           max-peel-times
8623               The maximum number of peelings of a single loop.
8624
8625           max-peel-branches
8626               The maximum number of branches on the hot path through the
8627               peeled sequence.
8628
8629           max-completely-peeled-insns
8630               The maximum number of insns of a completely peeled loop.
8631
8632           max-completely-peel-times
8633               The maximum number of iterations of a loop to be suitable for
8634               complete peeling.
8635
8636           max-completely-peel-loop-nest-depth
8637               The maximum depth of a loop nest suitable for complete peeling.
8638
8639           max-unswitch-insns
8640               The maximum number of insns of an unswitched loop.
8641
8642           max-unswitch-level
8643               The maximum number of branches unswitched in a single loop.
8644
8645           max-loop-headers-insns
8646               The maximum number of insns in loop header duplicated by the
8647               copy loop headers pass.
8648
8649           lim-expensive
8650               The minimum cost of an expensive expression in the loop
8651               invariant motion.
8652
8653           iv-consider-all-candidates-bound
8654               Bound on number of candidates for induction variables, below
8655               which all candidates are considered for each use in induction
8656               variable optimizations.  If there are more candidates than
8657               this, only the most relevant ones are considered to avoid
8658               quadratic time complexity.
8659
8660           iv-max-considered-uses
8661               The induction variable optimizations give up on loops that
8662               contain more induction variable uses.
8663
8664           iv-always-prune-cand-set-bound
8665               If the number of candidates in the set is smaller than this
8666               value, always try to remove unnecessary ivs from the set when
8667               adding a new one.
8668
8669           avg-loop-niter
8670               Average number of iterations of a loop.
8671
8672           dse-max-object-size
8673               Maximum size (in bytes) of objects tracked bytewise by dead
8674               store elimination.  Larger values may result in larger
8675               compilation times.
8676
8677           scev-max-expr-size
8678               Bound on size of expressions used in the scalar evolutions
8679               analyzer.  Large expressions slow the analyzer.
8680
8681           scev-max-expr-complexity
8682               Bound on the complexity of the expressions in the scalar
8683               evolutions analyzer.  Complex expressions slow the analyzer.
8684
8685           max-tree-if-conversion-phi-args
8686               Maximum number of arguments in a PHI supported by TREE if
8687               conversion unless the loop is marked with simd pragma.
8688
8689           vect-max-version-for-alignment-checks
8690               The maximum number of run-time checks that can be performed
8691               when doing loop versioning for alignment in the vectorizer.
8692
8693           vect-max-version-for-alias-checks
8694               The maximum number of run-time checks that can be performed
8695               when doing loop versioning for alias in the vectorizer.
8696
8697           vect-max-peeling-for-alignment
8698               The maximum number of loop peels to enhance access alignment
8699               for vectorizer. Value -1 means no limit.
8700
8701           max-iterations-to-track
8702               The maximum number of iterations of a loop the brute-force
8703               algorithm for analysis of the number of iterations of the loop
8704               tries to evaluate.
8705
8706           hot-bb-count-ws-permille
8707               A basic block profile count is considered hot if it contributes
8708               to the given permillage (i.e. 0...1000) of the entire profiled
8709               execution.
8710
8711           hot-bb-frequency-fraction
8712               Select fraction of the entry block frequency of executions of
8713               basic block in function given basic block needs to have to be
8714               considered hot.
8715
8716           max-predicted-iterations
8717               The maximum number of loop iterations we predict statically.
8718               This is useful in cases where a function contains a single loop
8719               with known bound and another loop with unknown bound.  The
8720               known number of iterations is predicted correctly, while the
8721               unknown number of iterations average to roughly 10.  This means
8722               that the loop without bounds appears artificially cold relative
8723               to the other one.
8724
8725           builtin-expect-probability
8726               Control the probability of the expression having the specified
8727               value. This parameter takes a percentage (i.e. 0 ... 100) as
8728               input.  The default probability of 90 is obtained empirically.
8729
8730           align-threshold
8731               Select fraction of the maximal frequency of executions of a
8732               basic block in a function to align the basic block.
8733
8734           align-loop-iterations
8735               A loop expected to iterate at least the selected number of
8736               iterations is aligned.
8737
8738           tracer-dynamic-coverage
8739           tracer-dynamic-coverage-feedback
8740               This value is used to limit superblock formation once the given
8741               percentage of executed instructions is covered.  This limits
8742               unnecessary code size expansion.
8743
8744               The tracer-dynamic-coverage-feedback parameter is used only
8745               when profile feedback is available.  The real profiles (as
8746               opposed to statically estimated ones) are much less balanced
8747               allowing the threshold to be larger value.
8748
8749           tracer-max-code-growth
8750               Stop tail duplication once code growth has reached given
8751               percentage.  This is a rather artificial limit, as most of the
8752               duplicates are eliminated later in cross jumping, so it may be
8753               set to much higher values than is the desired code growth.
8754
8755           tracer-min-branch-ratio
8756               Stop reverse growth when the reverse probability of best edge
8757               is less than this threshold (in percent).
8758
8759           tracer-min-branch-probability
8760           tracer-min-branch-probability-feedback
8761               Stop forward growth if the best edge has probability lower than
8762               this threshold.
8763
8764               Similarly to tracer-dynamic-coverage two parameters are
8765               provided.  tracer-min-branch-probability-feedback is used for
8766               compilation with profile feedback and tracer-min-branch-
8767               probability compilation without.  The value for compilation
8768               with profile feedback needs to be more conservative (higher) in
8769               order to make tracer effective.
8770
8771           stack-clash-protection-guard-size
8772               Specify the size of the operating system provided stack guard
8773               as 2 raised to num bytes.  The default value is 12 (4096
8774               bytes).  Acceptable values are between 12 and 30.  Higher
8775               values may reduce the number of explicit probes, but a value
8776               larger than the operating system provided guard will leave code
8777               vulnerable to stack clash style attacks.
8778
8779           stack-clash-protection-probe-interval
8780               Stack clash protection involves probing stack space as it is
8781               allocated.  This param controls the maximum distance between
8782               probes into the stack as 2 raised to num bytes.  Acceptable
8783               values are between 10 and 16 and defaults to 12.  Higher values
8784               may reduce the number of explicit probes, but a value larger
8785               than the operating system provided guard will leave code
8786               vulnerable to stack clash style attacks.
8787
8788           max-cse-path-length
8789               The maximum number of basic blocks on path that CSE considers.
8790               The default is 10.
8791
8792           max-cse-insns
8793               The maximum number of instructions CSE processes before
8794               flushing.  The default is 1000.
8795
8796           ggc-min-expand
8797               GCC uses a garbage collector to manage its own memory
8798               allocation.  This parameter specifies the minimum percentage by
8799               which the garbage collector's heap should be allowed to expand
8800               between collections.  Tuning this may improve compilation
8801               speed; it has no effect on code generation.
8802
8803               The default is 30% + 70% * (RAM/1GB) with an upper bound of
8804               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
8805               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
8806               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
8807               particular platform, the lower bound of 30% is used.  Setting
8808               this parameter and ggc-min-heapsize to zero causes a full
8809               collection to occur at every opportunity.  This is extremely
8810               slow, but can be useful for debugging.
8811
8812           ggc-min-heapsize
8813               Minimum size of the garbage collector's heap before it begins
8814               bothering to collect garbage.  The first collection occurs
8815               after the heap expands by ggc-min-expand% beyond ggc-min-
8816               heapsize.  Again, tuning this may improve compilation speed,
8817               and has no effect on code generation.
8818
8819               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
8820               that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
8821               exceeded, but with a lower bound of 4096 (four megabytes) and
8822               an upper bound of 131072 (128 megabytes).  If GCC is not able
8823               to calculate RAM on a particular platform, the lower bound is
8824               used.  Setting this parameter very large effectively disables
8825               garbage collection.  Setting this parameter and ggc-min-expand
8826               to zero causes a full collection to occur at every opportunity.
8827
8828           max-reload-search-insns
8829               The maximum number of instruction reload should look backward
8830               for equivalent register.  Increasing values mean more
8831               aggressive optimization, making the compilation time increase
8832               with probably slightly better performance.  The default value
8833               is 100.
8834
8835           max-cselib-memory-locations
8836               The maximum number of memory locations cselib should take into
8837               account.  Increasing values mean more aggressive optimization,
8838               making the compilation time increase with probably slightly
8839               better performance.  The default value is 500.
8840
8841           max-sched-ready-insns
8842               The maximum number of instructions ready to be issued the
8843               scheduler should consider at any given time during the first
8844               scheduling pass.  Increasing values mean more thorough
8845               searches, making the compilation time increase with probably
8846               little benefit.  The default value is 100.
8847
8848           max-sched-region-blocks
8849               The maximum number of blocks in a region to be considered for
8850               interblock scheduling.  The default value is 10.
8851
8852           max-pipeline-region-blocks
8853               The maximum number of blocks in a region to be considered for
8854               pipelining in the selective scheduler.  The default value is
8855               15.
8856
8857           max-sched-region-insns
8858               The maximum number of insns in a region to be considered for
8859               interblock scheduling.  The default value is 100.
8860
8861           max-pipeline-region-insns
8862               The maximum number of insns in a region to be considered for
8863               pipelining in the selective scheduler.  The default value is
8864               200.
8865
8866           min-spec-prob
8867               The minimum probability (in percents) of reaching a source
8868               block for interblock speculative scheduling.  The default value
8869               is 40.
8870
8871           max-sched-extend-regions-iters
8872               The maximum number of iterations through CFG to extend regions.
8873               A value of 0 (the default) disables region extensions.
8874
8875           max-sched-insn-conflict-delay
8876               The maximum conflict delay for an insn to be considered for
8877               speculative motion.  The default value is 3.
8878
8879           sched-spec-prob-cutoff
8880               The minimal probability of speculation success (in percents),
8881               so that speculative insns are scheduled.  The default value is
8882               40.
8883
8884           sched-state-edge-prob-cutoff
8885               The minimum probability an edge must have for the scheduler to
8886               save its state across it.  The default value is 10.
8887
8888           sched-mem-true-dep-cost
8889               Minimal distance (in CPU cycles) between store and load
8890               targeting same memory locations.  The default value is 1.
8891
8892           selsched-max-lookahead
8893               The maximum size of the lookahead window of selective
8894               scheduling.  It is a depth of search for available
8895               instructions.  The default value is 50.
8896
8897           selsched-max-sched-times
8898               The maximum number of times that an instruction is scheduled
8899               during selective scheduling.  This is the limit on the number
8900               of iterations through which the instruction may be pipelined.
8901               The default value is 2.
8902
8903           selsched-insns-to-rename
8904               The maximum number of best instructions in the ready list that
8905               are considered for renaming in the selective scheduler.  The
8906               default value is 2.
8907
8908           sms-min-sc
8909               The minimum value of stage count that swing modulo scheduler
8910               generates.  The default value is 2.
8911
8912           max-last-value-rtl
8913               The maximum size measured as number of RTLs that can be
8914               recorded in an expression in combiner for a pseudo register as
8915               last known value of that register.  The default is 10000.
8916
8917           max-combine-insns
8918               The maximum number of instructions the RTL combiner tries to
8919               combine.  The default value is 2 at -Og and 4 otherwise.
8920
8921           integer-share-limit
8922               Small integer constants can use a shared data structure,
8923               reducing the compiler's memory usage and increasing its speed.
8924               This sets the maximum value of a shared integer constant.  The
8925               default value is 256.
8926
8927           ssp-buffer-size
8928               The minimum size of buffers (i.e. arrays) that receive stack
8929               smashing protection when -fstack-protection is used.
8930
8931           min-size-for-stack-sharing
8932               The minimum size of variables taking part in stack slot sharing
8933               when not optimizing. The default value is 32.
8934
8935           max-jump-thread-duplication-stmts
8936               Maximum number of statements allowed in a block that needs to
8937               be duplicated when threading jumps.
8938
8939           max-fields-for-field-sensitive
8940               Maximum number of fields in a structure treated in a field
8941               sensitive manner during pointer analysis.  The default is zero
8942               for -O0 and -O1, and 100 for -Os, -O2, and -O3.
8943
8944           prefetch-latency
8945               Estimate on average number of instructions that are executed
8946               before prefetch finishes.  The distance prefetched ahead is
8947               proportional to this constant.  Increasing this number may also
8948               lead to less streams being prefetched (see simultaneous-
8949               prefetches).
8950
8951           simultaneous-prefetches
8952               Maximum number of prefetches that can run at the same time.
8953
8954           l1-cache-line-size
8955               The size of cache line in L1 cache, in bytes.
8956
8957           l1-cache-size
8958               The size of L1 cache, in kilobytes.
8959
8960           l2-cache-size
8961               The size of L2 cache, in kilobytes.
8962
8963           loop-interchange-max-num-stmts
8964               The maximum number of stmts in a loop to be interchanged.
8965
8966           loop-interchange-stride-ratio
8967               The minimum ratio between stride of two loops for interchange
8968               to be profitable.
8969
8970           min-insn-to-prefetch-ratio
8971               The minimum ratio between the number of instructions and the
8972               number of prefetches to enable prefetching in a loop.
8973
8974           prefetch-min-insn-to-mem-ratio
8975               The minimum ratio between the number of instructions and the
8976               number of memory references to enable prefetching in a loop.
8977
8978           use-canonical-types
8979               Whether the compiler should use the "canonical" type system.
8980               By default, this should always be 1, which uses a more
8981               efficient internal mechanism for comparing types in C++ and
8982               Objective-C++.  However, if bugs in the canonical type system
8983               are causing compilation failures, set this value to 0 to
8984               disable canonical types.
8985
8986           switch-conversion-max-branch-ratio
8987               Switch initialization conversion refuses to create arrays that
8988               are bigger than switch-conversion-max-branch-ratio times the
8989               number of branches in the switch.
8990
8991           max-partial-antic-length
8992               Maximum length of the partial antic set computed during the
8993               tree partial redundancy elimination optimization (-ftree-pre)
8994               when optimizing at -O3 and above.  For some sorts of source
8995               code the enhanced partial redundancy elimination optimization
8996               can run away, consuming all of the memory available on the host
8997               machine.  This parameter sets a limit on the length of the sets
8998               that are computed, which prevents the runaway behavior.
8999               Setting a value of 0 for this parameter allows an unlimited set
9000               length.
9001
9002           sccvn-max-scc-size
9003               Maximum size of a strongly connected component (SCC) during
9004               SCCVN processing.  If this limit is hit, SCCVN processing for
9005               the whole function is not done and optimizations depending on
9006               it are disabled.  The default maximum SCC size is 10000.
9007
9008           sccvn-max-alias-queries-per-access
9009               Maximum number of alias-oracle queries we perform when looking
9010               for redundancies for loads and stores.  If this limit is hit
9011               the search is aborted and the load or store is not considered
9012               redundant.  The number of queries is algorithmically limited to
9013               the number of stores on all paths from the load to the function
9014               entry.  The default maximum number of queries is 1000.
9015
9016           ira-max-loops-num
9017               IRA uses regional register allocation by default.  If a
9018               function contains more loops than the number given by this
9019               parameter, only at most the given number of the most
9020               frequently-executed loops form regions for regional register
9021               allocation.  The default value of the parameter is 100.
9022
9023           ira-max-conflict-table-size
9024               Although IRA uses a sophisticated algorithm to compress the
9025               conflict table, the table can still require excessive amounts
9026               of memory for huge functions.  If the conflict table for a
9027               function could be more than the size in MB given by this
9028               parameter, the register allocator instead uses a faster,
9029               simpler, and lower-quality algorithm that does not require
9030               building a pseudo-register conflict table.  The default value
9031               of the parameter is 2000.
9032
9033           ira-loop-reserved-regs
9034               IRA can be used to evaluate more accurate register pressure in
9035               loops for decisions to move loop invariants (see -O3).  The
9036               number of available registers reserved for some other purposes
9037               is given by this parameter.  The default value of the parameter
9038               is 2, which is the minimal number of registers needed by
9039               typical instructions.  This value is the best found from
9040               numerous experiments.
9041
9042           lra-inheritance-ebb-probability-cutoff
9043               LRA tries to reuse values reloaded in registers in subsequent
9044               insns.  This optimization is called inheritance.  EBB is used
9045               as a region to do this optimization.  The parameter defines a
9046               minimal fall-through edge probability in percentage used to add
9047               BB to inheritance EBB in LRA.  The default value of the
9048               parameter is 40.  The value was chosen from numerous runs of
9049               SPEC2000 on x86-64.
9050
9051           loop-invariant-max-bbs-in-loop
9052               Loop invariant motion can be very expensive, both in
9053               compilation time and in amount of needed compile-time memory,
9054               with very large loops.  Loops with more basic blocks than this
9055               parameter won't have loop invariant motion optimization
9056               performed on them.  The default value of the parameter is 1000
9057               for -O1 and 10000 for -O2 and above.
9058
9059           loop-max-datarefs-for-datadeps
9060               Building data dependencies is expensive for very large loops.
9061               This parameter limits the number of data references in loops
9062               that are considered for data dependence analysis.  These large
9063               loops are no handled by the optimizations using loop data
9064               dependencies.  The default value is 1000.
9065
9066           max-vartrack-size
9067               Sets a maximum number of hash table slots to use during
9068               variable tracking dataflow analysis of any function.  If this
9069               limit is exceeded with variable tracking at assignments
9070               enabled, analysis for that function is retried without it,
9071               after removing all debug insns from the function.  If the limit
9072               is exceeded even without debug insns, var tracking analysis is
9073               completely disabled for the function.  Setting the parameter to
9074               zero makes it unlimited.
9075
9076           max-vartrack-expr-depth
9077               Sets a maximum number of recursion levels when attempting to
9078               map variable names or debug temporaries to value expressions.
9079               This trades compilation time for more complete debug
9080               information.  If this is set too low, value expressions that
9081               are available and could be represented in debug information may
9082               end up not being used; setting this higher may enable the
9083               compiler to find more complex debug expressions, but compile
9084               time and memory use may grow.  The default is 12.
9085
9086           max-debug-marker-count
9087               Sets a threshold on the number of debug markers (e.g. begin
9088               stmt markers) to avoid complexity explosion at inlining or
9089               expanding to RTL.  If a function has more such gimple stmts
9090               than the set limit, such stmts will be dropped from the inlined
9091               copy of a function, and from its RTL expansion.  The default is
9092               100000.
9093
9094           min-nondebug-insn-uid
9095               Use uids starting at this parameter for nondebug insns.  The
9096               range below the parameter is reserved exclusively for debug
9097               insns created by -fvar-tracking-assignments, but debug insns
9098               may get (non-overlapping) uids above it if the reserved range
9099               is exhausted.
9100
9101           ipa-sra-ptr-growth-factor
9102               IPA-SRA replaces a pointer to an aggregate with one or more new
9103               parameters only when their cumulative size is less or equal to
9104               ipa-sra-ptr-growth-factor times the size of the original
9105               pointer parameter.
9106
9107           sra-max-scalarization-size-Ospeed
9108           sra-max-scalarization-size-Osize
9109               The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA)
9110               aim to replace scalar parts of aggregates with uses of
9111               independent scalar variables.  These parameters control the
9112               maximum size, in storage units, of aggregate which is
9113               considered for replacement when compiling for speed (sra-max-
9114               scalarization-size-Ospeed) or size (sra-max-scalarization-size-
9115               Osize) respectively.
9116
9117           tm-max-aggregate-size
9118               When making copies of thread-local variables in a transaction,
9119               this parameter specifies the size in bytes after which
9120               variables are saved with the logging functions as opposed to
9121               save/restore code sequence pairs.  This option only applies
9122               when using -fgnu-tm.
9123
9124           graphite-max-nb-scop-params
9125               To avoid exponential effects in the Graphite loop transforms,
9126               the number of parameters in a Static Control Part (SCoP) is
9127               bounded.  The default value is 10 parameters, a value of zero
9128               can be used to lift the bound.  A variable whose value is
9129               unknown at compilation time and defined outside a SCoP is a
9130               parameter of the SCoP.
9131
9132           loop-block-tile-size
9133               Loop blocking or strip mining transforms, enabled with
9134               -floop-block or -floop-strip-mine, strip mine each loop in the
9135               loop nest by a given number of iterations.  The strip length
9136               can be changed using the loop-block-tile-size parameter.  The
9137               default value is 51 iterations.
9138
9139           loop-unroll-jam-size
9140               Specify the unroll factor for the -floop-unroll-and-jam option.
9141               The default value is 4.
9142
9143           loop-unroll-jam-depth
9144               Specify the dimension to be unrolled (counting from the most
9145               inner loop) for the  -floop-unroll-and-jam.  The default value
9146               is 2.
9147
9148           ipa-cp-value-list-size
9149               IPA-CP attempts to track all possible values and types passed
9150               to a function's parameter in order to propagate them and
9151               perform devirtualization.  ipa-cp-value-list-size is the
9152               maximum number of values and types it stores per one formal
9153               parameter of a function.
9154
9155           ipa-cp-eval-threshold
9156               IPA-CP calculates its own score of cloning profitability
9157               heuristics and performs those cloning opportunities with scores
9158               that exceed ipa-cp-eval-threshold.
9159
9160           ipa-cp-recursion-penalty
9161               Percentage penalty the recursive functions will receive when
9162               they are evaluated for cloning.
9163
9164           ipa-cp-single-call-penalty
9165               Percentage penalty functions containing a single call to
9166               another function will receive when they are evaluated for
9167               cloning.
9168
9169           ipa-max-agg-items
9170               IPA-CP is also capable to propagate a number of scalar values
9171               passed in an aggregate. ipa-max-agg-items controls the maximum
9172               number of such values per one parameter.
9173
9174           ipa-cp-loop-hint-bonus
9175               When IPA-CP determines that a cloning candidate would make the
9176               number of iterations of a loop known, it adds a bonus of ipa-
9177               cp-loop-hint-bonus to the profitability score of the candidate.
9178
9179           ipa-cp-array-index-hint-bonus
9180               When IPA-CP determines that a cloning candidate would make the
9181               index of an array access known, it adds a bonus of ipa-cp-
9182               array-index-hint-bonus to the profitability score of the
9183               candidate.
9184
9185           ipa-max-aa-steps
9186               During its analysis of function bodies, IPA-CP employs alias
9187               analysis in order to track values pointed to by function
9188               parameters.  In order not spend too much time analyzing huge
9189               functions, it gives up and consider all memory clobbered after
9190               examining ipa-max-aa-steps statements modifying memory.
9191
9192           lto-partitions
9193               Specify desired number of partitions produced during WHOPR
9194               compilation.  The number of partitions should exceed the number
9195               of CPUs used for compilation.  The default value is 32.
9196
9197           lto-min-partition
9198               Size of minimal partition for WHOPR (in estimated
9199               instructions).  This prevents expenses of splitting very small
9200               programs into too many partitions.
9201
9202           lto-max-partition
9203               Size of max partition for WHOPR (in estimated instructions).
9204               to provide an upper bound for individual size of partition.
9205               Meant to be used only with balanced partitioning.
9206
9207           cxx-max-namespaces-for-diagnostic-help
9208               The maximum number of namespaces to consult for suggestions
9209               when C++ name lookup fails for an identifier.  The default is
9210               1000.
9211
9212           sink-frequency-threshold
9213               The maximum relative execution frequency (in percents) of the
9214               target block relative to a statement's original block to allow
9215               statement sinking of a statement.  Larger numbers result in
9216               more aggressive statement sinking.  The default value is 75.  A
9217               small positive adjustment is applied for statements with memory
9218               operands as those are even more profitable so sink.
9219
9220           max-stores-to-sink
9221               The maximum number of conditional store pairs that can be sunk.
9222               Set to 0 if either vectorization (-ftree-vectorize) or if-
9223               conversion (-ftree-loop-if-convert) is disabled.  The default
9224               is 2.
9225
9226           allow-store-data-races
9227               Allow optimizers to introduce new data races on stores.  Set to
9228               1 to allow, otherwise to 0.  This option is enabled by default
9229               at optimization level -Ofast.
9230
9231           case-values-threshold
9232               The smallest number of different values for which it is best to
9233               use a jump-table instead of a tree of conditional branches.  If
9234               the value is 0, use the default for the machine.  The default
9235               is 0.
9236
9237           tree-reassoc-width
9238               Set the maximum number of instructions executed in parallel in
9239               reassociated tree. This parameter overrides target dependent
9240               heuristics used by default if has non zero value.
9241
9242           sched-pressure-algorithm
9243               Choose between the two available implementations of
9244               -fsched-pressure.  Algorithm 1 is the original implementation
9245               and is the more likely to prevent instructions from being
9246               reordered.  Algorithm 2 was designed to be a compromise between
9247               the relatively conservative approach taken by algorithm 1 and
9248               the rather aggressive approach taken by the default scheduler.
9249               It relies more heavily on having a regular register file and
9250               accurate register pressure classes.  See haifa-sched.c in the
9251               GCC sources for more details.
9252
9253               The default choice depends on the target.
9254
9255           max-slsr-cand-scan
9256               Set the maximum number of existing candidates that are
9257               considered when seeking a basis for a new straight-line
9258               strength reduction candidate.
9259
9260           asan-globals
9261               Enable buffer overflow detection for global objects.  This kind
9262               of protection is enabled by default if you are using
9263               -fsanitize=address option.  To disable global objects
9264               protection use --param asan-globals=0.
9265
9266           asan-stack
9267               Enable buffer overflow detection for stack objects.  This kind
9268               of protection is enabled by default when using
9269               -fsanitize=address.  To disable stack protection use --param
9270               asan-stack=0 option.
9271
9272           asan-instrument-reads
9273               Enable buffer overflow detection for memory reads.  This kind
9274               of protection is enabled by default when using
9275               -fsanitize=address.  To disable memory reads protection use
9276               --param asan-instrument-reads=0.
9277
9278           asan-instrument-writes
9279               Enable buffer overflow detection for memory writes.  This kind
9280               of protection is enabled by default when using
9281               -fsanitize=address.  To disable memory writes protection use
9282               --param asan-instrument-writes=0 option.
9283
9284           asan-memintrin
9285               Enable detection for built-in functions.  This kind of
9286               protection is enabled by default when using -fsanitize=address.
9287               To disable built-in functions protection use --param
9288               asan-memintrin=0.
9289
9290           asan-use-after-return
9291               Enable detection of use-after-return.  This kind of protection
9292               is enabled by default when using the -fsanitize=address option.
9293               To disable it use --param asan-use-after-return=0.
9294
9295               Note: By default the check is disabled at run time.  To enable
9296               it, add "detect_stack_use_after_return=1" to the environment
9297               variable ASAN_OPTIONS.
9298
9299           asan-instrumentation-with-call-threshold
9300               If number of memory accesses in function being instrumented is
9301               greater or equal to this number, use callbacks instead of
9302               inline checks.  E.g. to disable inline code use --param
9303               asan-instrumentation-with-call-threshold=0.
9304
9305           use-after-scope-direct-emission-threshold
9306               If the size of a local variable in bytes is smaller or equal to
9307               this number, directly poison (or unpoison) shadow memory
9308               instead of using run-time callbacks.  The default value is 256.
9309
9310           chkp-max-ctor-size
9311               Static constructors generated by Pointer Bounds Checker may
9312               become very large and significantly increase compile time at
9313               optimization level -O1 and higher.  This parameter is a maximum
9314               number of statements in a single generated constructor.
9315               Default value is 5000.
9316
9317           max-fsm-thread-path-insns
9318               Maximum number of instructions to copy when duplicating blocks
9319               on a finite state automaton jump thread path.  The default is
9320               100.
9321
9322           max-fsm-thread-length
9323               Maximum number of basic blocks on a finite state automaton jump
9324               thread path.  The default is 10.
9325
9326           max-fsm-thread-paths
9327               Maximum number of new jump thread paths to create for a finite
9328               state automaton.  The default is 50.
9329
9330           parloops-chunk-size
9331               Chunk size of omp schedule for loops parallelized by parloops.
9332               The default is 0.
9333
9334           parloops-schedule
9335               Schedule type of omp schedule for loops parallelized by
9336               parloops (static, dynamic, guided, auto, runtime).  The default
9337               is static.
9338
9339           parloops-min-per-thread
9340               The minimum number of iterations per thread of an innermost
9341               parallelized loop for which the parallelized variant is
9342               prefered over the single threaded one.  The default is 100.
9343               Note that for a parallelized loop nest the minimum number of
9344               iterations of the outermost loop per thread is two.
9345
9346           max-ssa-name-query-depth
9347               Maximum depth of recursion when querying properties of SSA
9348               names in things like fold routines.  One level of recursion
9349               corresponds to following a use-def chain.
9350
9351           hsa-gen-debug-stores
9352               Enable emission of special debug stores within HSA kernels
9353               which are then read and reported by libgomp plugin.  Generation
9354               of these stores is disabled by default, use --param
9355               hsa-gen-debug-stores=1 to enable it.
9356
9357           max-speculative-devirt-maydefs
9358               The maximum number of may-defs we analyze when looking for a
9359               must-def specifying the dynamic type of an object that invokes
9360               a virtual call we may be able to devirtualize speculatively.
9361
9362           max-vrp-switch-assertions
9363               The maximum number of assertions to add along the default edge
9364               of a switch statement during VRP.  The default is 10.
9365
9366           unroll-jam-min-percent
9367               The minimum percentage of memory references that must be
9368               optimized away for the unroll-and-jam transformation to be
9369               considered profitable.
9370
9371           unroll-jam-max-unroll
9372               The maximum number of times the outer loop should be unrolled
9373               by the unroll-and-jam transformation.
9374
9375   Program Instrumentation Options
9376       GCC supports a number of command-line options that control adding run-
9377       time instrumentation to the code it normally generates.  For example,
9378       one purpose of instrumentation is collect profiling statistics for use
9379       in finding program hot spots, code coverage analysis, or profile-guided
9380       optimizations.  Another class of program instrumentation is adding run-
9381       time checking to detect programming errors like invalid pointer
9382       dereferences or out-of-bounds array accesses, as well as deliberately
9383       hostile attacks such as stack smashing or C++ vtable hijacking.  There
9384       is also a general hook which can be used to implement other forms of
9385       tracing or function-level instrumentation for debug or program analysis
9386       purposes.
9387
9388       -p  Generate extra code to write profile information suitable for the
9389           analysis program prof.  You must use this option when compiling the
9390           source files you want data about, and you must also use it when
9391           linking.
9392
9393       -pg Generate extra code to write profile information suitable for the
9394           analysis program gprof.  You must use this option when compiling
9395           the source files you want data about, and you must also use it when
9396           linking.
9397
9398       -fprofile-arcs
9399           Add code so that program flow arcs are instrumented.  During
9400           execution the program records how many times each branch and call
9401           is executed and how many times it is taken or returns.  On targets
9402           that support constructors with priority support, profiling properly
9403           handles constructors, destructors and C++ constructors (and
9404           destructors) of classes which are used as a type of a global
9405           variable.
9406
9407           When the compiled program exits it saves this data to a file called
9408           auxname.gcda for each source file.  The data may be used for
9409           profile-directed optimizations (-fbranch-probabilities), or for
9410           test coverage analysis (-ftest-coverage).  Each object file's
9411           auxname is generated from the name of the output file, if
9412           explicitly specified and it is not the final executable, otherwise
9413           it is the basename of the source file.  In both cases any suffix is
9414           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
9415           for output file specified as -o dir/foo.o).
9416
9417       --coverage
9418           This option is used to compile and link code instrumented for
9419           coverage analysis.  The option is a synonym for -fprofile-arcs
9420           -ftest-coverage (when compiling) and -lgcov (when linking).  See
9421           the documentation for those options for more details.
9422
9423           *   Compile the source files with -fprofile-arcs plus optimization
9424               and code generation options.  For test coverage analysis, use
9425               the additional -ftest-coverage option.  You do not need to
9426               profile every source file in a program.
9427
9428           *   Compile the source files additionally with -fprofile-abs-path
9429               to create absolute path names in the .gcno files.  This allows
9430               gcov to find the correct sources in projects where compilations
9431               occur with different working directories.
9432
9433           *   Link your object files with -lgcov or -fprofile-arcs (the
9434               latter implies the former).
9435
9436           *   Run the program on a representative workload to generate the
9437               arc profile information.  This may be repeated any number of
9438               times.  You can run concurrent instances of your program, and
9439               provided that the file system supports locking, the data files
9440               will be correctly updated.  Unless a strict ISO C dialect
9441               option is in effect, "fork" calls are detected and correctly
9442               handled without double counting.
9443
9444           *   For profile-directed optimizations, compile the source files
9445               again with the same optimization and code generation options
9446               plus -fbranch-probabilities.
9447
9448           *   For test coverage analysis, use gcov to produce human readable
9449               information from the .gcno and .gcda files.  Refer to the gcov
9450               documentation for further information.
9451
9452           With -fprofile-arcs, for each function of your program GCC creates
9453           a program flow graph, then finds a spanning tree for the graph.
9454           Only arcs that are not on the spanning tree have to be
9455           instrumented: the compiler adds code to count the number of times
9456           that these arcs are executed.  When an arc is the only exit or only
9457           entrance to a block, the instrumentation code can be added to the
9458           block; otherwise, a new basic block must be created to hold the
9459           instrumentation code.
9460
9461       -ftest-coverage
9462           Produce a notes file that the gcov code-coverage utility can use to
9463           show program coverage.  Each source file's note file is called
9464           auxname.gcno.  Refer to the -fprofile-arcs option above for a
9465           description of auxname and instructions on how to generate test
9466           coverage data.  Coverage data matches the source files more closely
9467           if you do not optimize.
9468
9469       -fprofile-abs-path
9470           Automatically convert relative source file names to absolute path
9471           names in the .gcno files.  This allows gcov to find the correct
9472           sources in projects where compilations occur with different working
9473           directories.
9474
9475       -fprofile-dir=path
9476           Set the directory to search for the profile data files in to path.
9477           This option affects only the profile data generated by
9478           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
9479           -fprofile-use and -fbranch-probabilities and its related options.
9480           Both absolute and relative paths can be used.  By default, GCC uses
9481           the current directory as path, thus the profile data file appears
9482           in the same directory as the object file.
9483
9484       -fprofile-generate
9485       -fprofile-generate=path
9486           Enable options usually used for instrumenting application to
9487           produce profile useful for later recompilation with profile
9488           feedback based optimization.  You must use -fprofile-generate both
9489           when compiling and when linking your program.
9490
9491           The following options are enabled: -fprofile-arcs,
9492           -fprofile-values, -fvpt.
9493
9494           If path is specified, GCC looks at the path to find the profile
9495           feedback data files. See -fprofile-dir.
9496
9497           To optimize the program based on the collected profile information,
9498           use -fprofile-use.
9499
9500       -fprofile-update=method
9501           Alter the update method for an application instrumented for profile
9502           feedback based optimization.  The method argument should be one of
9503           single, atomic or prefer-atomic.  The first one is useful for
9504           single-threaded applications, while the second one prevents profile
9505           corruption by emitting thread-safe code.
9506
9507           Warning: When an application does not properly join all threads (or
9508           creates an detached thread), a profile file can be still corrupted.
9509
9510           Using prefer-atomic would be transformed either to atomic, when
9511           supported by a target, or to single otherwise.  The GCC driver
9512           automatically selects prefer-atomic when -pthread is present in the
9513           command line.
9514
9515       -fsanitize=address
9516           Enable AddressSanitizer, a fast memory error detector.  Memory
9517           access instructions are instrumented to detect out-of-bounds and
9518           use-after-free bugs.  The option enables
9519           -fsanitize-address-use-after-scope.  See
9520           <https://github.com/google/sanitizers/wiki/AddressSanitizer> for
9521           more details.  The run-time behavior can be influenced using the
9522           ASAN_OPTIONS environment variable.  When set to "help=1", the
9523           available options are shown at startup of the instrumented program.
9524           See
9525           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
9526           for a list of supported options.  The option cannot be combined
9527           with -fsanitize=thread and/or -fcheck-pointer-bounds.
9528
9529       -fsanitize=kernel-address
9530           Enable AddressSanitizer for Linux kernel.  See
9531           <https://github.com/google/kasan/wiki> for more details.  The
9532           option cannot be combined with -fcheck-pointer-bounds.
9533
9534       -fsanitize=pointer-compare
9535           Instrument comparison operation (<, <=, >, >=) with pointer
9536           operands.  The option must be combined with either
9537           -fsanitize=kernel-address or -fsanitize=address The option cannot
9538           be combined with -fsanitize=thread and/or -fcheck-pointer-bounds.
9539           Note: By default the check is disabled at run time.  To enable it,
9540           add "detect_invalid_pointer_pairs=2" to the environment variable
9541           ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
9542           invalid operation only when both pointers are non-null.
9543
9544       -fsanitize=pointer-subtract
9545           Instrument subtraction with pointer operands.  The option must be
9546           combined with either -fsanitize=kernel-address or
9547           -fsanitize=address The option cannot be combined with
9548           -fsanitize=thread and/or -fcheck-pointer-bounds.  Note: By default
9549           the check is disabled at run time.  To enable it, add
9550           "detect_invalid_pointer_pairs=2" to the environment variable
9551           ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
9552           invalid operation only when both pointers are non-null.
9553
9554       -fsanitize=thread
9555           Enable ThreadSanitizer, a fast data race detector.  Memory access
9556           instructions are instrumented to detect data race bugs.  See
9557           <https://github.com/google/sanitizers/wiki#threadsanitizer> for
9558           more details. The run-time behavior can be influenced using the
9559           TSAN_OPTIONS environment variable; see
9560           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
9561           for a list of supported options.  The option cannot be combined
9562           with -fsanitize=address, -fsanitize=leak and/or
9563           -fcheck-pointer-bounds.
9564
9565           Note that sanitized atomic builtins cannot throw exceptions when
9566           operating on invalid memory addresses with non-call exceptions
9567           (-fnon-call-exceptions).
9568
9569       -fsanitize=leak
9570           Enable LeakSanitizer, a memory leak detector.  This option only
9571           matters for linking of executables and the executable is linked
9572           against a library that overrides "malloc" and other allocator
9573           functions.  See
9574           <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
9575           for more details.  The run-time behavior can be influenced using
9576           the LSAN_OPTIONS environment variable.  The option cannot be
9577           combined with -fsanitize=thread.
9578
9579       -fsanitize=undefined
9580           Enable UndefinedBehaviorSanitizer, a fast undefined behavior
9581           detector.  Various computations are instrumented to detect
9582           undefined behavior at runtime.  Current suboptions are:
9583
9584           -fsanitize=shift
9585               This option enables checking that the result of a shift
9586               operation is not undefined.  Note that what exactly is
9587               considered undefined differs slightly between C and C++, as
9588               well as between ISO C90 and C99, etc.  This option has two
9589               suboptions, -fsanitize=shift-base and
9590               -fsanitize=shift-exponent.
9591
9592           -fsanitize=shift-exponent
9593               This option enables checking that the second argument of a
9594               shift operation is not negative and is smaller than the
9595               precision of the promoted first argument.
9596
9597           -fsanitize=shift-base
9598               If the second argument of a shift operation is within range,
9599               check that the result of a shift operation is not undefined.
9600               Note that what exactly is considered undefined differs slightly
9601               between C and C++, as well as between ISO C90 and C99, etc.
9602
9603           -fsanitize=integer-divide-by-zero
9604               Detect integer division by zero as well as "INT_MIN / -1"
9605               division.
9606
9607           -fsanitize=unreachable
9608               With this option, the compiler turns the
9609               "__builtin_unreachable" call into a diagnostics message call
9610               instead.  When reaching the "__builtin_unreachable" call, the
9611               behavior is undefined.
9612
9613           -fsanitize=vla-bound
9614               This option instructs the compiler to check that the size of a
9615               variable length array is positive.
9616
9617           -fsanitize=null
9618               This option enables pointer checking.  Particularly, the
9619               application built with this option turned on will issue an
9620               error message when it tries to dereference a NULL pointer, or
9621               if a reference (possibly an rvalue reference) is bound to a
9622               NULL pointer, or if a method is invoked on an object pointed by
9623               a NULL pointer.
9624
9625           -fsanitize=return
9626               This option enables return statement checking.  Programs built
9627               with this option turned on will issue an error message when the
9628               end of a non-void function is reached without actually
9629               returning a value.  This option works in C++ only.
9630
9631           -fsanitize=signed-integer-overflow
9632               This option enables signed integer overflow checking.  We check
9633               that the result of "+", "*", and both unary and binary "-" does
9634               not overflow in the signed arithmetics.  Note, integer
9635               promotion rules must be taken into account.  That is, the
9636               following is not an overflow:
9637
9638                       signed char a = SCHAR_MAX;
9639                       a++;
9640
9641           -fsanitize=bounds
9642               This option enables instrumentation of array bounds.  Various
9643               out of bounds accesses are detected.  Flexible array members,
9644               flexible array member-like arrays, and initializers of
9645               variables with static storage are not instrumented.  The option
9646               cannot be combined with -fcheck-pointer-bounds.
9647
9648           -fsanitize=bounds-strict
9649               This option enables strict instrumentation of array bounds.
9650               Most out of bounds accesses are detected, including flexible
9651               array members and flexible array member-like arrays.
9652               Initializers of variables with static storage are not
9653               instrumented.  The option cannot be combined with
9654               -fcheck-pointer-bounds.
9655
9656           -fsanitize=alignment
9657               This option enables checking of alignment of pointers when they
9658               are dereferenced, or when a reference is bound to
9659               insufficiently aligned target, or when a method or constructor
9660               is invoked on insufficiently aligned object.
9661
9662           -fsanitize=object-size
9663               This option enables instrumentation of memory references using
9664               the "__builtin_object_size" function.  Various out of bounds
9665               pointer accesses are detected.
9666
9667           -fsanitize=float-divide-by-zero
9668               Detect floating-point division by zero.  Unlike other similar
9669               options, -fsanitize=float-divide-by-zero is not enabled by
9670               -fsanitize=undefined, since floating-point division by zero can
9671               be a legitimate way of obtaining infinities and NaNs.
9672
9673           -fsanitize=float-cast-overflow
9674               This option enables floating-point type to integer conversion
9675               checking.  We check that the result of the conversion does not
9676               overflow.  Unlike other similar options,
9677               -fsanitize=float-cast-overflow is not enabled by
9678               -fsanitize=undefined.  This option does not work well with
9679               "FE_INVALID" exceptions enabled.
9680
9681           -fsanitize=nonnull-attribute
9682               This option enables instrumentation of calls, checking whether
9683               null values are not passed to arguments marked as requiring a
9684               non-null value by the "nonnull" function attribute.
9685
9686           -fsanitize=returns-nonnull-attribute
9687               This option enables instrumentation of return statements in
9688               functions marked with "returns_nonnull" function attribute, to
9689               detect returning of null values from such functions.
9690
9691           -fsanitize=bool
9692               This option enables instrumentation of loads from bool.  If a
9693               value other than 0/1 is loaded, a run-time error is issued.
9694
9695           -fsanitize=enum
9696               This option enables instrumentation of loads from an enum type.
9697               If a value outside the range of values for the enum type is
9698               loaded, a run-time error is issued.
9699
9700           -fsanitize=vptr
9701               This option enables instrumentation of C++ member function
9702               calls, member accesses and some conversions between pointers to
9703               base and derived classes, to verify the referenced object has
9704               the correct dynamic type.
9705
9706           -fsanitize=pointer-overflow
9707               This option enables instrumentation of pointer arithmetics.  If
9708               the pointer arithmetics overflows, a run-time error is issued.
9709
9710           -fsanitize=builtin
9711               This option enables instrumentation of arguments to selected
9712               builtin functions.  If an invalid value is passed to such
9713               arguments, a run-time error is issued.  E.g. passing 0 as the
9714               argument to "__builtin_ctz" or "__builtin_clz" invokes
9715               undefined behavior and is diagnosed by this option.
9716
9717           While -ftrapv causes traps for signed overflows to be emitted,
9718           -fsanitize=undefined gives a diagnostic message.  This currently
9719           works only for the C family of languages.
9720
9721       -fno-sanitize=all
9722           This option disables all previously enabled sanitizers.
9723           -fsanitize=all is not allowed, as some sanitizers cannot be used
9724           together.
9725
9726       -fasan-shadow-offset=number
9727           This option forces GCC to use custom shadow offset in
9728           AddressSanitizer checks.  It is useful for experimenting with
9729           different shadow memory layouts in Kernel AddressSanitizer.
9730
9731       -fsanitize-sections=s1,s2,...
9732           Sanitize global variables in selected user-defined sections.  si
9733           may contain wildcards.
9734
9735       -fsanitize-recover[=opts]
9736           -fsanitize-recover= controls error recovery mode for sanitizers
9737           mentioned in comma-separated list of opts.  Enabling this option
9738           for a sanitizer component causes it to attempt to continue running
9739           the program as if no error happened.  This means multiple runtime
9740           errors can be reported in a single program run, and the exit code
9741           of the program may indicate success even when errors have been
9742           reported.  The -fno-sanitize-recover= option can be used to alter
9743           this behavior: only the first detected error is reported and
9744           program then exits with a non-zero exit code.
9745
9746           Currently this feature only works for -fsanitize=undefined (and its
9747           suboptions except for -fsanitize=unreachable and
9748           -fsanitize=return), -fsanitize=float-cast-overflow,
9749           -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict,
9750           -fsanitize=kernel-address and -fsanitize=address.  For these
9751           sanitizers error recovery is turned on by default, except
9752           -fsanitize=address, for which this feature is experimental.
9753           -fsanitize-recover=all and -fno-sanitize-recover=all is also
9754           accepted, the former enables recovery for all sanitizers that
9755           support it, the latter disables recovery for all sanitizers that
9756           support it.
9757
9758           Even if a recovery mode is turned on the compiler side, it needs to
9759           be also enabled on the runtime library side, otherwise the failures
9760           are still fatal.  The runtime library defaults to "halt_on_error=0"
9761           for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
9762           value for AddressSanitizer is "halt_on_error=1". This can be
9763           overridden through setting the "halt_on_error" flag in the
9764           corresponding environment variable.
9765
9766           Syntax without an explicit opts parameter is deprecated.  It is
9767           equivalent to specifying an opts list of:
9768
9769                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
9770
9771       -fsanitize-address-use-after-scope
9772           Enable sanitization of local variables to detect use-after-scope
9773           bugs.  The option sets -fstack-reuse to none.
9774
9775       -fsanitize-undefined-trap-on-error
9776           The -fsanitize-undefined-trap-on-error option instructs the
9777           compiler to report undefined behavior using "__builtin_trap" rather
9778           than a "libubsan" library routine.  The advantage of this is that
9779           the "libubsan" library is not needed and is not linked in, so this
9780           is usable even in freestanding environments.
9781
9782       -fsanitize-coverage=trace-pc
9783           Enable coverage-guided fuzzing code instrumentation.  Inserts a
9784           call to "__sanitizer_cov_trace_pc" into every basic block.
9785
9786       -fsanitize-coverage=trace-cmp
9787           Enable dataflow guided fuzzing code instrumentation.  Inserts a
9788           call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
9789           "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for
9790           integral comparison with both operands variable or
9791           "__sanitizer_cov_trace_const_cmp1",
9792           "__sanitizer_cov_trace_const_cmp2",
9793           "__sanitizer_cov_trace_const_cmp4" or
9794           "__sanitizer_cov_trace_const_cmp8" for integral comparison with one
9795           operand constant, "__sanitizer_cov_trace_cmpf" or
9796           "__sanitizer_cov_trace_cmpd" for float or double comparisons and
9797           "__sanitizer_cov_trace_switch" for switch statements.
9798
9799       -fbounds-check
9800           For front ends that support it, generate additional code to check
9801           that indices used to access arrays are within the declared range.
9802           This is currently only supported by the Fortran front end, where
9803           this option defaults to false.
9804
9805       -fcheck-pointer-bounds
9806           Enable Pointer Bounds Checker instrumentation.  Each memory
9807           reference is instrumented with checks of the pointer used for
9808           memory access against bounds associated with that pointer.
9809
9810           Currently there is only an implementation for Intel MPX available,
9811           thus x86 GNU/Linux target and -mmpx are required to enable this
9812           feature.  MPX-based instrumentation requires a runtime library to
9813           enable MPX in hardware and handle bounds violation signals.  By
9814           default when -fcheck-pointer-bounds and -mmpx options are used to
9815           link a program, the GCC driver links against the libmpx and
9816           libmpxwrappers libraries.  Bounds checking on calls to dynamic
9817           libraries requires a linker with -z bndplt support; if GCC was
9818           configured with a linker without support for this option (including
9819           the Gold linker and older versions of ld), a warning is given if
9820           you link with -mmpx without also specifying -static, since the
9821           overall effectiveness of the bounds checking protection is reduced.
9822           See also -static-libmpxwrappers.
9823
9824           MPX-based instrumentation may be used for debugging and also may be
9825           included in production code to increase program security.
9826           Depending on usage, you may have different requirements for the
9827           runtime library.  The current version of the MPX runtime library is
9828           more oriented for use as a debugging tool.  MPX runtime library
9829           usage implies -lpthread.  See also -static-libmpx.  The runtime
9830           library  behavior can be influenced using various CHKP_RT_*
9831           environment variables.  See
9832           <https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler>
9833           for more details.
9834
9835           Generated instrumentation may be controlled by various -fchkp-*
9836           options and by the "bnd_variable_size" structure field attribute
9837           and "bnd_legacy", and "bnd_instrument" function attributes.  GCC
9838           also provides a number of built-in functions for controlling the
9839           Pointer Bounds Checker.
9840
9841       -fchkp-check-incomplete-type
9842           Generate pointer bounds checks for variables with incomplete type.
9843           Enabled by default.
9844
9845       -fchkp-narrow-bounds
9846           Controls bounds used by Pointer Bounds Checker for pointers to
9847           object fields.  If narrowing is enabled then field bounds are used.
9848           Otherwise object bounds are used.  See also
9849           -fchkp-narrow-to-innermost-array and
9850           -fchkp-first-field-has-own-bounds.  Enabled by default.
9851
9852       -fchkp-first-field-has-own-bounds
9853           Forces Pointer Bounds Checker to use narrowed bounds for the
9854           address of the first field in the structure.  By default a pointer
9855           to the first field has the same bounds as a pointer to the whole
9856           structure.
9857
9858       -fchkp-flexible-struct-trailing-arrays
9859           Forces Pointer Bounds Checker to treat all trailing arrays in
9860           structures as possibly flexible.  By default only array fields with
9861           zero length or that are marked with attribute bnd_variable_size are
9862           treated as flexible.
9863
9864       -fchkp-narrow-to-innermost-array
9865           Forces Pointer Bounds Checker to use bounds of the innermost arrays
9866           in case of nested static array access.  By default this option is
9867           disabled and bounds of the outermost array are used.
9868
9869       -fchkp-optimize
9870           Enables Pointer Bounds Checker optimizations.  Enabled by default
9871           at optimization levels -O, -O2, -O3.
9872
9873       -fchkp-use-fast-string-functions
9874           Enables use of *_nobnd versions of string functions (not copying
9875           bounds) by Pointer Bounds Checker.  Disabled by default.
9876
9877       -fchkp-use-nochk-string-functions
9878           Enables use of *_nochk versions of string functions (not checking
9879           bounds) by Pointer Bounds Checker.  Disabled by default.
9880
9881       -fchkp-use-static-bounds
9882           Allow Pointer Bounds Checker to generate static bounds holding
9883           bounds of static variables.  Enabled by default.
9884
9885       -fchkp-use-static-const-bounds
9886           Use statically-initialized bounds for constant bounds instead of
9887           generating them each time they are required.  By default enabled
9888           when -fchkp-use-static-bounds is enabled.
9889
9890       -fchkp-treat-zero-dynamic-size-as-infinite
9891           With this option, objects with incomplete type whose dynamically-
9892           obtained size is zero are treated as having infinite size instead
9893           by Pointer Bounds Checker.  This option may be helpful if a program
9894           is linked with a library missing size information for some symbols.
9895           Disabled by default.
9896
9897       -fchkp-check-read
9898           Instructs Pointer Bounds Checker to generate checks for all read
9899           accesses to memory.  Enabled by default.
9900
9901       -fchkp-check-write
9902           Instructs Pointer Bounds Checker to generate checks for all write
9903           accesses to memory.  Enabled by default.
9904
9905       -fchkp-store-bounds
9906           Instructs Pointer Bounds Checker to generate bounds stores for
9907           pointer writes.  Enabled by default.
9908
9909       -fchkp-instrument-calls
9910           Instructs Pointer Bounds Checker to pass pointer bounds to calls.
9911           Enabled by default.
9912
9913       -fchkp-instrument-marked-only
9914           Instructs Pointer Bounds Checker to instrument only functions
9915           marked with the "bnd_instrument" attribute.  Disabled by default.
9916
9917       -fchkp-use-wrappers
9918           Allows Pointer Bounds Checker to replace calls to built-in
9919           functions with calls to wrapper functions.  When
9920           -fchkp-use-wrappers is used to link a program, the GCC driver
9921           automatically links against libmpxwrappers.  See also
9922           -static-libmpxwrappers.  Enabled by default.
9923
9924       -fcf-protection=[full|branch|return|none]
9925           Enable code instrumentation of control-flow transfers to increase
9926           program security by checking that target addresses of control-flow
9927           transfer instructions (such as indirect function call, function
9928           return, indirect jump) are valid.  This prevents diverting the flow
9929           of control to an unexpected target.  This is intended to protect
9930           against such threats as Return-oriented Programming (ROP), and
9931           similarly call/jmp-oriented programming (COP/JOP).
9932
9933           The value "branch" tells the compiler to implement checking of
9934           validity of control-flow transfer at the point of indirect branch
9935           instructions, i.e. call/jmp instructions.  The value "return"
9936           implements checking of validity at the point of returning from a
9937           function.  The value "full" is an alias for specifying both
9938           "branch" and "return". The value "none" turns off instrumentation.
9939
9940           The macro "__CET__" is defined when -fcf-protection is used.  The
9941           first bit of "__CET__" is set to 1 for the value "branch" and the
9942           second bit of "__CET__" is set to 1 for the "return".
9943
9944           You can also use the "nocf_check" attribute to identify which
9945           functions and calls should be skipped from instrumentation.
9946
9947           Currently the x86 GNU/Linux target provides an implementation based
9948           on Intel Control-flow Enforcement Technology (CET).
9949
9950       -fstack-protector
9951           Emit extra code to check for buffer overflows, such as stack
9952           smashing attacks.  This is done by adding a guard variable to
9953           functions with vulnerable objects.  This includes functions that
9954           call "alloca", and functions with buffers larger than 8 bytes.  The
9955           guards are initialized when a function is entered and then checked
9956           when the function exits.  If a guard check fails, an error message
9957           is printed and the program exits.
9958
9959       -fstack-protector-all
9960           Like -fstack-protector except that all functions are protected.
9961
9962       -fstack-protector-strong
9963           Like -fstack-protector but includes additional functions to be
9964           protected --- those that have local array definitions, or have
9965           references to local frame addresses.
9966
9967       -fstack-protector-explicit
9968           Like -fstack-protector but only protects those functions which have
9969           the "stack_protect" attribute.
9970
9971       -fstack-check
9972           Generate code to verify that you do not go beyond the boundary of
9973           the stack.  You should specify this flag if you are running in an
9974           environment with multiple threads, but you only rarely need to
9975           specify it in a single-threaded environment since stack overflow is
9976           automatically detected on nearly all systems if there is only one
9977           stack.
9978
9979           Note that this switch does not actually cause checking to be done;
9980           the operating system or the language runtime must do that.  The
9981           switch causes generation of code to ensure that they see the stack
9982           being extended.
9983
9984           You can additionally specify a string parameter: no means no
9985           checking, generic means force the use of old-style checking,
9986           specific means use the best checking method and is equivalent to
9987           bare -fstack-check.
9988
9989           Old-style checking is a generic mechanism that requires no specific
9990           target support in the compiler but comes with the following
9991           drawbacks:
9992
9993           1.  Modified allocation strategy for large objects: they are always
9994               allocated dynamically if their size exceeds a fixed threshold.
9995               Note this may change the semantics of some code.
9996
9997           2.  Fixed limit on the size of the static frame of functions: when
9998               it is topped by a particular function, stack checking is not
9999               reliable and a warning is issued by the compiler.
10000
10001           3.  Inefficiency: because of both the modified allocation strategy
10002               and the generic implementation, code performance is hampered.
10003
10004           Note that old-style stack checking is also the fallback method for
10005           specific if no target support has been added in the compiler.
10006
10007           -fstack-check= is designed for Ada's needs to detect infinite
10008           recursion and stack overflows.  specific is an excellent choice
10009           when compiling Ada code.  It is not generally sufficient to protect
10010           against stack-clash attacks.  To protect against those you want
10011           -fstack-clash-protection.
10012
10013       -fstack-clash-protection
10014           Generate code to prevent stack clash style attacks.  When this
10015           option is enabled, the compiler will only allocate one page of
10016           stack space at a time and each page is accessed immediately after
10017           allocation.  Thus, it prevents allocations from jumping over any
10018           stack guard page provided by the operating system.
10019
10020           Most targets do not fully support stack clash protection.  However,
10021           on those targets -fstack-clash-protection will protect dynamic
10022           stack allocations.  -fstack-clash-protection may also provide
10023           limited protection for static stack allocations if the target
10024           supports -fstack-check=specific.
10025
10026       -fstack-limit-register=reg
10027       -fstack-limit-symbol=sym
10028       -fno-stack-limit
10029           Generate code to ensure that the stack does not grow beyond a
10030           certain value, either the value of a register or the address of a
10031           symbol.  If a larger stack is required, a signal is raised at run
10032           time.  For most targets, the signal is raised before the stack
10033           overruns the boundary, so it is possible to catch the signal
10034           without taking special precautions.
10035
10036           For instance, if the stack starts at absolute address 0x80000000
10037           and grows downwards, you can use the flags
10038           -fstack-limit-symbol=__stack_limit and
10039           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
10040           128KB.  Note that this may only work with the GNU linker.
10041
10042           You can locally override stack limit checking by using the
10043           "no_stack_limit" function attribute.
10044
10045       -fsplit-stack
10046           Generate code to automatically split the stack before it overflows.
10047           The resulting program has a discontiguous stack which can only
10048           overflow if the program is unable to allocate any more memory.
10049           This is most useful when running threaded programs, as it is no
10050           longer necessary to calculate a good stack size to use for each
10051           thread.  This is currently only implemented for the x86 targets
10052           running GNU/Linux.
10053
10054           When code compiled with -fsplit-stack calls code compiled without
10055           -fsplit-stack, there may not be much stack space available for the
10056           latter code to run.  If compiling all code, including library code,
10057           with -fsplit-stack is not an option, then the linker can fix up
10058           these calls so that the code compiled without -fsplit-stack always
10059           has a large stack.  Support for this is implemented in the gold
10060           linker in GNU binutils release 2.21 and later.
10061
10062       -fvtable-verify=[std|preinit|none]
10063           This option is only available when compiling C++ code.  It turns on
10064           (or off, if using -fvtable-verify=none) the security feature that
10065           verifies at run time, for every virtual call, that the vtable
10066           pointer through which the call is made is valid for the type of the
10067           object, and has not been corrupted or overwritten.  If an invalid
10068           vtable pointer is detected at run time, an error is reported and
10069           execution of the program is immediately halted.
10070
10071           This option causes run-time data structures to be built at program
10072           startup, which are used for verifying the vtable pointers.  The
10073           options std and preinit control the timing of when these data
10074           structures are built.  In both cases the data structures are built
10075           before execution reaches "main".  Using -fvtable-verify=std causes
10076           the data structures to be built after shared libraries have been
10077           loaded and initialized.  -fvtable-verify=preinit causes them to be
10078           built before shared libraries have been loaded and initialized.
10079
10080           If this option appears multiple times in the command line with
10081           different values specified, none takes highest priority over both
10082           std and preinit; preinit takes priority over std.
10083
10084       -fvtv-debug
10085           When used in conjunction with -fvtable-verify=std or
10086           -fvtable-verify=preinit, causes debug versions of the runtime
10087           functions for the vtable verification feature to be called.  This
10088           flag also causes the compiler to log information about which vtable
10089           pointers it finds for each class.  This information is written to a
10090           file named vtv_set_ptr_data.log in the directory named by the
10091           environment variable VTV_LOGS_DIR if that is defined or the current
10092           working directory otherwise.
10093
10094           Note:  This feature appends data to the log file. If you want a
10095           fresh log file, be sure to delete any existing one.
10096
10097       -fvtv-counts
10098           This is a debugging flag.  When used in conjunction with
10099           -fvtable-verify=std or -fvtable-verify=preinit, this causes the
10100           compiler to keep track of the total number of virtual calls it
10101           encounters and the number of verifications it inserts.  It also
10102           counts the number of calls to certain run-time library functions
10103           that it inserts and logs this information for each compilation
10104           unit.  The compiler writes this information to a file named
10105           vtv_count_data.log in the directory named by the environment
10106           variable VTV_LOGS_DIR if that is defined or the current working
10107           directory otherwise.  It also counts the size of the vtable pointer
10108           sets for each class, and writes this information to
10109           vtv_class_set_sizes.log in the same directory.
10110
10111           Note:  This feature appends data to the log files.  To get fresh
10112           log files, be sure to delete any existing ones.
10113
10114       -finstrument-functions
10115           Generate instrumentation calls for entry and exit to functions.
10116           Just after function entry and just before function exit, the
10117           following profiling functions are called with the address of the
10118           current function and its call site.  (On some platforms,
10119           "__builtin_return_address" does not work beyond the current
10120           function, so the call site information may not be available to the
10121           profiling functions otherwise.)
10122
10123                   void __cyg_profile_func_enter (void *this_fn,
10124                                                  void *call_site);
10125                   void __cyg_profile_func_exit  (void *this_fn,
10126                                                  void *call_site);
10127
10128           The first argument is the address of the start of the current
10129           function, which may be looked up exactly in the symbol table.
10130
10131           This instrumentation is also done for functions expanded inline in
10132           other functions.  The profiling calls indicate where, conceptually,
10133           the inline function is entered and exited.  This means that
10134           addressable versions of such functions must be available.  If all
10135           your uses of a function are expanded inline, this may mean an
10136           additional expansion of code size.  If you use "extern inline" in
10137           your C code, an addressable version of such functions must be
10138           provided.  (This is normally the case anyway, but if you get lucky
10139           and the optimizer always expands the functions inline, you might
10140           have gotten away without providing static copies.)
10141
10142           A function may be given the attribute "no_instrument_function", in
10143           which case this instrumentation is not done.  This can be used, for
10144           example, for the profiling functions listed above, high-priority
10145           interrupt routines, and any functions from which the profiling
10146           functions cannot safely be called (perhaps signal handlers, if the
10147           profiling routines generate output or allocate memory).
10148
10149       -finstrument-functions-exclude-file-list=file,file,...
10150           Set the list of functions that are excluded from instrumentation
10151           (see the description of -finstrument-functions).  If the file that
10152           contains a function definition matches with one of file, then that
10153           function is not instrumented.  The match is done on substrings: if
10154           the file parameter is a substring of the file name, it is
10155           considered to be a match.
10156
10157           For example:
10158
10159                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys
10160
10161           excludes any inline function defined in files whose pathnames
10162           contain /bits/stl or include/sys.
10163
10164           If, for some reason, you want to include letter , in one of sym,
10165           write ,. For example,
10166           -finstrument-functions-exclude-file-list=',,tmp' (note the single
10167           quote surrounding the option).
10168
10169       -finstrument-functions-exclude-function-list=sym,sym,...
10170           This is similar to -finstrument-functions-exclude-file-list, but
10171           this option sets the list of function names to be excluded from
10172           instrumentation.  The function name to be matched is its user-
10173           visible name, such as "vector<int> blah(const vector<int> &)", not
10174           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
10175           match is done on substrings: if the sym parameter is a substring of
10176           the function name, it is considered to be a match.  For C99 and C++
10177           extended identifiers, the function name must be given in UTF-8, not
10178           using universal character names.
10179
10180       -fpatchable-function-entry=N[,M]
10181           Generate N NOPs right at the beginning of each function, with the
10182           function entry point before the Mth NOP.  If M is omitted, it
10183           defaults to 0 so the function entry points to the address just at
10184           the first NOP.  The NOP instructions reserve extra space which can
10185           be used to patch in any desired instrumentation at run time,
10186           provided that the code segment is writable.  The amount of space is
10187           controllable indirectly via the number of NOPs; the NOP instruction
10188           used corresponds to the instruction emitted by the internal GCC
10189           back-end interface "gen_nop".  This behavior is target-specific and
10190           may also depend on the architecture variant and/or other
10191           compilation options.
10192
10193           For run-time identification, the starting addresses of these areas,
10194           which correspond to their respective function entries minus M, are
10195           additionally collected in the "__patchable_function_entries"
10196           section of the resulting binary.
10197
10198           Note that the value of "__attribute__ ((patchable_function_entry
10199           (N,M)))" takes precedence over command-line option
10200           -fpatchable-function-entry=N,M.  This can be used to increase the
10201           area size or to remove it completely on a single function.  If
10202           "N=0", no pad location is recorded.
10203
10204           The NOP instructions are inserted at---and maybe before, depending
10205           on M---the function entry address, even before the prologue.
10206
10207   Options Controlling the Preprocessor
10208       These options control the C preprocessor, which is run on each C source
10209       file before actual compilation.
10210
10211       If you use the -E option, nothing is done except preprocessing.  Some
10212       of these options make sense only together with -E because they cause
10213       the preprocessor output to be unsuitable for actual compilation.
10214
10215       In addition to the options listed here, there are a number of options
10216       to control search paths for include files documented in Directory
10217       Options.  Options to control preprocessor diagnostics are listed in
10218       Warning Options.
10219
10220       -D name
10221           Predefine name as a macro, with definition 1.
10222
10223       -D name=definition
10224           The contents of definition are tokenized and processed as if they
10225           appeared during translation phase three in a #define directive.  In
10226           particular, the definition is truncated by embedded newline
10227           characters.
10228
10229           If you are invoking the preprocessor from a shell or shell-like
10230           program you may need to use the shell's quoting syntax to protect
10231           characters such as spaces that have a meaning in the shell syntax.
10232
10233           If you wish to define a function-like macro on the command line,
10234           write its argument list with surrounding parentheses before the
10235           equals sign (if any).  Parentheses are meaningful to most shells,
10236           so you should quote the option.  With sh and csh,
10237           -D'name(args...)=definition' works.
10238
10239           -D and -U options are processed in the order they are given on the
10240           command line.  All -imacros file and -include file options are
10241           processed after all -D and -U options.
10242
10243       -U name
10244           Cancel any previous definition of name, either built in or provided
10245           with a -D option.
10246
10247       -include file
10248           Process file as if "#include "file"" appeared as the first line of
10249           the primary source file.  However, the first directory searched for
10250           file is the preprocessor's working directory instead of the
10251           directory containing the main source file.  If not found there, it
10252           is searched for in the remainder of the "#include "..."" search
10253           chain as normal.
10254
10255           If multiple -include options are given, the files are included in
10256           the order they appear on the command line.
10257
10258       -imacros file
10259           Exactly like -include, except that any output produced by scanning
10260           file is thrown away.  Macros it defines remain defined.  This
10261           allows you to acquire all the macros from a header without also
10262           processing its declarations.
10263
10264           All files specified by -imacros are processed before all files
10265           specified by -include.
10266
10267       -undef
10268           Do not predefine any system-specific or GCC-specific macros.  The
10269           standard predefined macros remain defined.
10270
10271       -pthread
10272           Define additional macros required for using the POSIX threads
10273           library.  You should use this option consistently for both
10274           compilation and linking.  This option is supported on GNU/Linux
10275           targets, most other Unix derivatives, and also on x86 Cygwin and
10276           MinGW targets.
10277
10278       -M  Instead of outputting the result of preprocessing, output a rule
10279           suitable for make describing the dependencies of the main source
10280           file.  The preprocessor outputs one make rule containing the object
10281           file name for that source file, a colon, and the names of all the
10282           included files, including those coming from -include or -imacros
10283           command-line options.
10284
10285           Unless specified explicitly (with -MT or -MQ), the object file name
10286           consists of the name of the source file with any suffix replaced
10287           with object file suffix and with any leading directory parts
10288           removed.  If there are many included files then the rule is split
10289           into several lines using \-newline.  The rule has no commands.
10290
10291           This option does not suppress the preprocessor's debug output, such
10292           as -dM.  To avoid mixing such debug output with the dependency
10293           rules you should explicitly specify the dependency output file with
10294           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
10295           Debug output is still sent to the regular output stream as normal.
10296
10297           Passing -M to the driver implies -E, and suppresses warnings with
10298           an implicit -w.
10299
10300       -MM Like -M but do not mention header files that are found in system
10301           header directories, nor header files that are included, directly or
10302           indirectly, from such a header.
10303
10304           This implies that the choice of angle brackets or double quotes in
10305           an #include directive does not in itself determine whether that
10306           header appears in -MM dependency output.
10307
10308       -MF file
10309           When used with -M or -MM, specifies a file to write the
10310           dependencies to.  If no -MF switch is given the preprocessor sends
10311           the rules to the same place it would send preprocessed output.
10312
10313           When used with the driver options -MD or -MMD, -MF overrides the
10314           default dependency output file.
10315
10316           If file is -, then the dependencies are written to stdout.
10317
10318       -MG In conjunction with an option such as -M requesting dependency
10319           generation, -MG assumes missing header files are generated files
10320           and adds them to the dependency list without raising an error.  The
10321           dependency filename is taken directly from the "#include" directive
10322           without prepending any path.  -MG also suppresses preprocessed
10323           output, as a missing header file renders this useless.
10324
10325           This feature is used in automatic updating of makefiles.
10326
10327       -MP This option instructs CPP to add a phony target for each dependency
10328           other than the main file, causing each to depend on nothing.  These
10329           dummy rules work around errors make gives if you remove header
10330           files without updating the Makefile to match.
10331
10332           This is typical output:
10333
10334                   test.o: test.c test.h
10335
10336                   test.h:
10337
10338       -MT target
10339           Change the target of the rule emitted by dependency generation.  By
10340           default CPP takes the name of the main input file, deletes any
10341           directory components and any file suffix such as .c, and appends
10342           the platform's usual object suffix.  The result is the target.
10343
10344           An -MT option sets the target to be exactly the string you specify.
10345           If you want multiple targets, you can specify them as a single
10346           argument to -MT, or use multiple -MT options.
10347
10348           For example, -MT '$(objpfx)foo.o' might give
10349
10350                   $(objpfx)foo.o: foo.c
10351
10352       -MQ target
10353           Same as -MT, but it quotes any characters which are special to
10354           Make.  -MQ '$(objpfx)foo.o' gives
10355
10356                   $$(objpfx)foo.o: foo.c
10357
10358           The default target is automatically quoted, as if it were given
10359           with -MQ.
10360
10361       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
10362           The driver determines file based on whether an -o option is given.
10363           If it is, the driver uses its argument but with a suffix of .d,
10364           otherwise it takes the name of the input file, removes any
10365           directory components and suffix, and applies a .d suffix.
10366
10367           If -MD is used in conjunction with -E, any -o switch is understood
10368           to specify the dependency output file, but if used without -E, each
10369           -o is understood to specify a target object file.
10370
10371           Since -E is not implied, -MD can be used to generate a dependency
10372           output file as a side effect of the compilation process.
10373
10374       -MMD
10375           Like -MD except mention only user header files, not system header
10376           files.
10377
10378       -fpreprocessed
10379           Indicate to the preprocessor that the input file has already been
10380           preprocessed.  This suppresses things like macro expansion,
10381           trigraph conversion, escaped newline splicing, and processing of
10382           most directives.  The preprocessor still recognizes and removes
10383           comments, so that you can pass a file preprocessed with -C to the
10384           compiler without problems.  In this mode the integrated
10385           preprocessor is little more than a tokenizer for the front ends.
10386
10387           -fpreprocessed is implicit if the input file has one of the
10388           extensions .i, .ii or .mi.  These are the extensions that GCC uses
10389           for preprocessed files created by -save-temps.
10390
10391       -fdirectives-only
10392           When preprocessing, handle directives, but do not expand macros.
10393
10394           The option's behavior depends on the -E and -fpreprocessed options.
10395
10396           With -E, preprocessing is limited to the handling of directives
10397           such as "#define", "#ifdef", and "#error".  Other preprocessor
10398           operations, such as macro expansion and trigraph conversion are not
10399           performed.  In addition, the -dD option is implicitly enabled.
10400
10401           With -fpreprocessed, predefinition of command line and most builtin
10402           macros is disabled.  Macros such as "__LINE__", which are
10403           contextually dependent, are handled normally.  This enables
10404           compilation of files previously preprocessed with "-E
10405           -fdirectives-only".
10406
10407           With both -E and -fpreprocessed, the rules for -fpreprocessed take
10408           precedence.  This enables full preprocessing of files previously
10409           preprocessed with "-E -fdirectives-only".
10410
10411       -fdollars-in-identifiers
10412           Accept $ in identifiers.
10413
10414       -fextended-identifiers
10415           Accept universal character names in identifiers.  This option is
10416           enabled by default for C99 (and later C standard versions) and C++.
10417
10418       -fno-canonical-system-headers
10419           When preprocessing, do not shorten system header paths with
10420           canonicalization.
10421
10422       -ftabstop=width
10423           Set the distance between tab stops.  This helps the preprocessor
10424           report correct column numbers in warnings or errors, even if tabs
10425           appear on the line.  If the value is less than 1 or greater than
10426           100, the option is ignored.  The default is 8.
10427
10428       -ftrack-macro-expansion[=level]
10429           Track locations of tokens across macro expansions. This allows the
10430           compiler to emit diagnostic about the current macro expansion stack
10431           when a compilation error occurs in a macro expansion. Using this
10432           option makes the preprocessor and the compiler consume more memory.
10433           The level parameter can be used to choose the level of precision of
10434           token location tracking thus decreasing the memory consumption if
10435           necessary. Value 0 of level de-activates this option. Value 1
10436           tracks tokens locations in a degraded mode for the sake of minimal
10437           memory overhead. In this mode all tokens resulting from the
10438           expansion of an argument of a function-like macro have the same
10439           location. Value 2 tracks tokens locations completely. This value is
10440           the most memory hungry.  When this option is given no argument, the
10441           default parameter value is 2.
10442
10443           Note that "-ftrack-macro-expansion=2" is activated by default.
10444
10445       -fmacro-prefix-map=old=new
10446           When preprocessing files residing in directory old, expand the
10447           "__FILE__" and "__BASE_FILE__" macros as if the files resided in
10448           directory new instead.  This can be used to change an absolute path
10449           to a relative path by using . for new which can result in more
10450           reproducible builds that are location independent.  This option
10451           also affects "__builtin_FILE()" during compilation.  See also
10452           -ffile-prefix-map.
10453
10454       -fexec-charset=charset
10455           Set the execution character set, used for string and character
10456           constants.  The default is UTF-8.  charset can be any encoding
10457           supported by the system's "iconv" library routine.
10458
10459       -fwide-exec-charset=charset
10460           Set the wide execution character set, used for wide string and
10461           character constants.  The default is UTF-32 or UTF-16, whichever
10462           corresponds to the width of "wchar_t".  As with -fexec-charset,
10463           charset can be any encoding supported by the system's "iconv"
10464           library routine; however, you will have problems with encodings
10465           that do not fit exactly in "wchar_t".
10466
10467       -finput-charset=charset
10468           Set the input character set, used for translation from the
10469           character set of the input file to the source character set used by
10470           GCC.  If the locale does not specify, or GCC cannot get this
10471           information from the locale, the default is UTF-8.  This can be
10472           overridden by either the locale or this command-line option.
10473           Currently the command-line option takes precedence if there's a
10474           conflict.  charset can be any encoding supported by the system's
10475           "iconv" library routine.
10476
10477       -fpch-deps
10478           When using precompiled headers, this flag causes the dependency-
10479           output flags to also list the files from the precompiled header's
10480           dependencies.  If not specified, only the precompiled header are
10481           listed and not the files that were used to create it, because those
10482           files are not consulted when a precompiled header is used.
10483
10484       -fpch-preprocess
10485           This option allows use of a precompiled header together with -E.
10486           It inserts a special "#pragma", "#pragma GCC pch_preprocess
10487           "filename"" in the output to mark the place where the precompiled
10488           header was found, and its filename.  When -fpreprocessed is in use,
10489           GCC recognizes this "#pragma" and loads the PCH.
10490
10491           This option is off by default, because the resulting preprocessed
10492           output is only really suitable as input to GCC.  It is switched on
10493           by -save-temps.
10494
10495           You should not write this "#pragma" in your own code, but it is
10496           safe to edit the filename if the PCH file is available in a
10497           different location.  The filename may be absolute or it may be
10498           relative to GCC's current directory.
10499
10500       -fworking-directory
10501           Enable generation of linemarkers in the preprocessor output that
10502           let the compiler know the current working directory at the time of
10503           preprocessing.  When this option is enabled, the preprocessor
10504           emits, after the initial linemarker, a second linemarker with the
10505           current working directory followed by two slashes.  GCC uses this
10506           directory, when it's present in the preprocessed input, as the
10507           directory emitted as the current working directory in some
10508           debugging information formats.  This option is implicitly enabled
10509           if debugging information is enabled, but this can be inhibited with
10510           the negated form -fno-working-directory.  If the -P flag is present
10511           in the command line, this option has no effect, since no "#line"
10512           directives are emitted whatsoever.
10513
10514       -A predicate=answer
10515           Make an assertion with the predicate predicate and answer answer.
10516           This form is preferred to the older form -A predicate(answer),
10517           which is still supported, because it does not use shell special
10518           characters.
10519
10520       -A -predicate=answer
10521           Cancel an assertion with the predicate predicate and answer answer.
10522
10523       -C  Do not discard comments.  All comments are passed through to the
10524           output file, except for comments in processed directives, which are
10525           deleted along with the directive.
10526
10527           You should be prepared for side effects when using -C; it causes
10528           the preprocessor to treat comments as tokens in their own right.
10529           For example, comments appearing at the start of what would be a
10530           directive line have the effect of turning that line into an
10531           ordinary source line, since the first token on the line is no
10532           longer a #.
10533
10534       -CC Do not discard comments, including during macro expansion.  This is
10535           like -C, except that comments contained within macros are also
10536           passed through to the output file where the macro is expanded.
10537
10538           In addition to the side effects of the -C option, the -CC option
10539           causes all C++-style comments inside a macro to be converted to
10540           C-style comments.  This is to prevent later use of that macro from
10541           inadvertently commenting out the remainder of the source line.
10542
10543           The -CC option is generally used to support lint comments.
10544
10545       -P  Inhibit generation of linemarkers in the output from the
10546           preprocessor.  This might be useful when running the preprocessor
10547           on something that is not C code, and will be sent to a program
10548           which might be confused by the linemarkers.
10549
10550       -traditional
10551       -traditional-cpp
10552           Try to imitate the behavior of pre-standard C preprocessors, as
10553           opposed to ISO C preprocessors.  See the GNU CPP manual for
10554           details.
10555
10556           Note that GCC does not otherwise attempt to emulate a pre-standard
10557           C compiler, and these options are only supported with the -E
10558           switch, or when invoking CPP explicitly.
10559
10560       -trigraphs
10561           Support ISO C trigraphs.  These are three-character sequences, all
10562           starting with ??, that are defined by ISO C to stand for single
10563           characters.  For example, ??/ stands for \, so '??/n' is a
10564           character constant for a newline.
10565
10566           The nine trigraphs and their replacements are
10567
10568                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
10569                   Replacement:      [    ]    {    }    #    \    ^    |    ~
10570
10571           By default, GCC ignores trigraphs, but in standard-conforming modes
10572           it converts them.  See the -std and -ansi options.
10573
10574       -remap
10575           Enable special code to work around file systems which only permit
10576           very short file names, such as MS-DOS.
10577
10578       -H  Print the name of each header file used, in addition to other
10579           normal activities.  Each name is indented to show how deep in the
10580           #include stack it is.  Precompiled header files are also printed,
10581           even if they are found to be invalid; an invalid precompiled header
10582           file is printed with ...x and a valid one with ...! .
10583
10584       -dletters
10585           Says to make debugging dumps during compilation as specified by
10586           letters.  The flags documented here are those relevant to the
10587           preprocessor.  Other letters are interpreted by the compiler
10588           proper, or reserved for future versions of GCC, and so are silently
10589           ignored.  If you specify letters whose behavior conflicts, the
10590           result is undefined.
10591
10592           -dM Instead of the normal output, generate a list of #define
10593               directives for all the macros defined during the execution of
10594               the preprocessor, including predefined macros.  This gives you
10595               a way of finding out what is predefined in your version of the
10596               preprocessor.  Assuming you have no file foo.h, the command
10597
10598                       touch foo.h; cpp -dM foo.h
10599
10600               shows all the predefined macros.
10601
10602               If you use -dM without the -E option, -dM is interpreted as a
10603               synonym for -fdump-rtl-mach.
10604
10605           -dD Like -dM except in two respects: it does not include the
10606               predefined macros, and it outputs both the #define directives
10607               and the result of preprocessing.  Both kinds of output go to
10608               the standard output file.
10609
10610           -dN Like -dD, but emit only the macro names, not their expansions.
10611
10612           -dI Output #include directives in addition to the result of
10613               preprocessing.
10614
10615           -dU Like -dD except that only macros that are expanded, or whose
10616               definedness is tested in preprocessor directives, are output;
10617               the output is delayed until the use or test of the macro; and
10618               #undef directives are also output for macros tested but
10619               undefined at the time.
10620
10621       -fdebug-cpp
10622           This option is only useful for debugging GCC.  When used from CPP
10623           or with -E, it dumps debugging information about location maps.
10624           Every token in the output is preceded by the dump of the map its
10625           location belongs to.
10626
10627           When used from GCC without -E, this option has no effect.
10628
10629       -Wp,option
10630           You can use -Wp,option to bypass the compiler driver and pass
10631           option directly through to the preprocessor.  If option contains
10632           commas, it is split into multiple options at the commas.  However,
10633           many options are modified, translated or interpreted by the
10634           compiler driver before being passed to the preprocessor, and -Wp
10635           forcibly bypasses this phase.  The preprocessor's direct interface
10636           is undocumented and subject to change, so whenever possible you
10637           should avoid using -Wp and let the driver handle the options
10638           instead.
10639
10640       -Xpreprocessor option
10641           Pass option as an option to the preprocessor.  You can use this to
10642           supply system-specific preprocessor options that GCC does not
10643           recognize.
10644
10645           If you want to pass an option that takes an argument, you must use
10646           -Xpreprocessor twice, once for the option and once for the
10647           argument.
10648
10649       -no-integrated-cpp
10650           Perform preprocessing as a separate pass before compilation.  By
10651           default, GCC performs preprocessing as an integrated part of input
10652           tokenization and parsing.  If this option is provided, the
10653           appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
10654           and Objective-C, respectively) is instead invoked twice, once for
10655           preprocessing only and once for actual compilation of the
10656           preprocessed input.  This option may be useful in conjunction with
10657           the -B or -wrapper options to specify an alternate preprocessor or
10658           perform additional processing of the program source between normal
10659           preprocessing and compilation.
10660
10661   Passing Options to the Assembler
10662       You can pass options to the assembler.
10663
10664       -Wa,option
10665           Pass option as an option to the assembler.  If option contains
10666           commas, it is split into multiple options at the commas.
10667
10668       -Xassembler option
10669           Pass option as an option to the assembler.  You can use this to
10670           supply system-specific assembler options that GCC does not
10671           recognize.
10672
10673           If you want to pass an option that takes an argument, you must use
10674           -Xassembler twice, once for the option and once for the argument.
10675
10676   Options for Linking
10677       These options come into play when the compiler links object files into
10678       an executable output file.  They are meaningless if the compiler is not
10679       doing a link step.
10680
10681       object-file-name
10682           A file name that does not end in a special recognized suffix is
10683           considered to name an object file or library.  (Object files are
10684           distinguished from libraries by the linker according to the file
10685           contents.)  If linking is done, these object files are used as
10686           input to the linker.
10687
10688       -c
10689       -S
10690       -E  If any of these options is used, then the linker is not run, and
10691           object file names should not be used as arguments.
10692
10693       -fuse-ld=bfd
10694           Use the bfd linker instead of the default linker.
10695
10696       -fuse-ld=gold
10697           Use the gold linker instead of the default linker.
10698
10699       -llibrary
10700       -l library
10701           Search the library named library when linking.  (The second
10702           alternative with the library as a separate argument is only for
10703           POSIX compliance and is not recommended.)
10704
10705           It makes a difference where in the command you write this option;
10706           the linker searches and processes libraries and object files in the
10707           order they are specified.  Thus, foo.o -lz bar.o searches library z
10708           after file foo.o but before bar.o.  If bar.o refers to functions in
10709           z, those functions may not be loaded.
10710
10711           The linker searches a standard list of directories for the library,
10712           which is actually a file named liblibrary.a.  The linker then uses
10713           this file as if it had been specified precisely by name.
10714
10715           The directories searched include several standard system
10716           directories plus any that you specify with -L.
10717
10718           Normally the files found this way are library files---archive files
10719           whose members are object files.  The linker handles an archive file
10720           by scanning through it for members which define symbols that have
10721           so far been referenced but not defined.  But if the file that is
10722           found is an ordinary object file, it is linked in the usual
10723           fashion.  The only difference between using an -l option and
10724           specifying a file name is that -l surrounds library with lib and .a
10725           and searches several directories.
10726
10727       -lobjc
10728           You need this special case of the -l option in order to link an
10729           Objective-C or Objective-C++ program.
10730
10731       -nostartfiles
10732           Do not use the standard system startup files when linking.  The
10733           standard system libraries are used normally, unless -nostdlib or
10734           -nodefaultlibs is used.
10735
10736       -nodefaultlibs
10737           Do not use the standard system libraries when linking.  Only the
10738           libraries you specify are passed to the linker, and options
10739           specifying linkage of the system libraries, such as -static-libgcc
10740           or -shared-libgcc, are ignored.  The standard startup files are
10741           used normally, unless -nostartfiles is used.
10742
10743           The compiler may generate calls to "memcmp", "memset", "memcpy" and
10744           "memmove".  These entries are usually resolved by entries in libc.
10745           These entry points should be supplied through some other mechanism
10746           when this option is specified.
10747
10748       -nostdlib
10749           Do not use the standard system startup files or libraries when
10750           linking.  No startup files and only the libraries you specify are
10751           passed to the linker, and options specifying linkage of the system
10752           libraries, such as -static-libgcc or -shared-libgcc, are ignored.
10753
10754           The compiler may generate calls to "memcmp", "memset", "memcpy" and
10755           "memmove".  These entries are usually resolved by entries in libc.
10756           These entry points should be supplied through some other mechanism
10757           when this option is specified.
10758
10759           One of the standard libraries bypassed by -nostdlib and
10760           -nodefaultlibs is libgcc.a, a library of internal subroutines which
10761           GCC uses to overcome shortcomings of particular machines, or
10762           special needs for some languages.
10763
10764           In most cases, you need libgcc.a even when you want to avoid other
10765           standard libraries.  In other words, when you specify -nostdlib or
10766           -nodefaultlibs you should usually specify -lgcc as well.  This
10767           ensures that you have no unresolved references to internal GCC
10768           library subroutines.  (An example of such an internal subroutine is
10769           "__main", used to ensure C++ constructors are called.)
10770
10771       -pie
10772           Produce a dynamically linked position independent executable on
10773           targets that support it.  For predictable results, you must also
10774           specify the same set of options used for compilation (-fpie, -fPIE,
10775           or model suboptions) when you specify this linker option.
10776
10777       -no-pie
10778           Don't produce a dynamically linked position independent executable.
10779
10780       -static-pie
10781           Produce a static position independent executable on targets that
10782           support it.  A static position independent executable is similar to
10783           a static executable, but can be loaded at any address without a
10784           dynamic linker.  For predictable results, you must also specify the
10785           same set of options used for compilation (-fpie, -fPIE, or model
10786           suboptions) when you specify this linker option.
10787
10788       -pthread
10789           Link with the POSIX threads library.  This option is supported on
10790           GNU/Linux targets, most other Unix derivatives, and also on x86
10791           Cygwin and MinGW targets.  On some targets this option also sets
10792           flags for the preprocessor, so it should be used consistently for
10793           both compilation and linking.
10794
10795       -rdynamic
10796           Pass the flag -export-dynamic to the ELF linker, on targets that
10797           support it. This instructs the linker to add all symbols, not only
10798           used ones, to the dynamic symbol table. This option is needed for
10799           some uses of "dlopen" or to allow obtaining backtraces from within
10800           a program.
10801
10802       -s  Remove all symbol table and relocation information from the
10803           executable.
10804
10805       -static
10806           On systems that support dynamic linking, this overrides -pie and
10807           prevents linking with the shared libraries.  On other systems, this
10808           option has no effect.
10809
10810       -shared
10811           Produce a shared object which can then be linked with other objects
10812           to form an executable.  Not all systems support this option.  For
10813           predictable results, you must also specify the same set of options
10814           used for compilation (-fpic, -fPIC, or model suboptions) when you
10815           specify this linker option.[1]
10816
10817       -shared-libgcc
10818       -static-libgcc
10819           On systems that provide libgcc as a shared library, these options
10820           force the use of either the shared or static version, respectively.
10821           If no shared version of libgcc was built when the compiler was
10822           configured, these options have no effect.
10823
10824           There are several situations in which an application should use the
10825           shared libgcc instead of the static version.  The most common of
10826           these is when the application wishes to throw and catch exceptions
10827           across different shared libraries.  In that case, each of the
10828           libraries as well as the application itself should use the shared
10829           libgcc.
10830
10831           Therefore, the G++ and driver automatically adds -shared-libgcc
10832            whenever you build a shared library or a main executable, because
10833           C++
10834            programs typically use exceptions, so this is the right thing to
10835           do.
10836
10837           If, instead, you use the GCC driver to create shared libraries, you
10838           may find that they are not always linked with the shared libgcc.
10839           If GCC finds, at its configuration time, that you have a non-GNU
10840           linker or a GNU linker that does not support option --eh-frame-hdr,
10841           it links the shared version of libgcc into shared libraries by
10842           default.  Otherwise, it takes advantage of the linker and optimizes
10843           away the linking with the shared version of libgcc, linking with
10844           the static version of libgcc by default.  This allows exceptions to
10845           propagate through such shared libraries, without incurring
10846           relocation costs at library load time.
10847
10848           However, if a library or main executable is supposed to throw or
10849           catch exceptions, you must link it using the G++ driver, as
10850           appropriate for the languages used in the program, or using the
10851           option -shared-libgcc, such that it is linked with the shared
10852           libgcc.
10853
10854       -static-libasan
10855           When the -fsanitize=address option is used to link a program, the
10856           GCC driver automatically links against libasan.  If libasan is
10857           available as a shared library, and the -static option is not used,
10858           then this links against the shared version of libasan.  The
10859           -static-libasan option directs the GCC driver to link libasan
10860           statically, without necessarily linking other libraries statically.
10861
10862       -static-libtsan
10863           When the -fsanitize=thread option is used to link a program, the
10864           GCC driver automatically links against libtsan.  If libtsan is
10865           available as a shared library, and the -static option is not used,
10866           then this links against the shared version of libtsan.  The
10867           -static-libtsan option directs the GCC driver to link libtsan
10868           statically, without necessarily linking other libraries statically.
10869
10870       -static-liblsan
10871           When the -fsanitize=leak option is used to link a program, the GCC
10872           driver automatically links against liblsan.  If liblsan is
10873           available as a shared library, and the -static option is not used,
10874           then this links against the shared version of liblsan.  The
10875           -static-liblsan option directs the GCC driver to link liblsan
10876           statically, without necessarily linking other libraries statically.
10877
10878       -static-libubsan
10879           When the -fsanitize=undefined option is used to link a program, the
10880           GCC driver automatically links against libubsan.  If libubsan is
10881           available as a shared library, and the -static option is not used,
10882           then this links against the shared version of libubsan.  The
10883           -static-libubsan option directs the GCC driver to link libubsan
10884           statically, without necessarily linking other libraries statically.
10885
10886       -static-libmpx
10887           When the -fcheck-pointer bounds and -mmpx options are used to link
10888           a program, the GCC driver automatically links against libmpx.  If
10889           libmpx is available as a shared library, and the -static option is
10890           not used, then this links against the shared version of libmpx.
10891           The -static-libmpx option directs the GCC driver to link libmpx
10892           statically, without necessarily linking other libraries statically.
10893
10894       -static-libmpxwrappers
10895           When the -fcheck-pointer bounds and -mmpx options are used to link
10896           a program without also using -fno-chkp-use-wrappers, the GCC driver
10897           automatically links against libmpxwrappers.  If libmpxwrappers is
10898           available as a shared library, and the -static option is not used,
10899           then this links against the shared version of libmpxwrappers.  The
10900           -static-libmpxwrappers option directs the GCC driver to link
10901           libmpxwrappers statically, without necessarily linking other
10902           libraries statically.
10903
10904       -static-libstdc++
10905           When the g++ program is used to link a C++ program, it normally
10906           automatically links against libstdc++.  If libstdc++ is available
10907           as a shared library, and the -static option is not used, then this
10908           links against the shared version of libstdc++.  That is normally
10909           fine.  However, it is sometimes useful to freeze the version of
10910           libstdc++ used by the program without going all the way to a fully
10911           static link.  The -static-libstdc++ option directs the g++ driver
10912           to link libstdc++ statically, without necessarily linking other
10913           libraries statically.
10914
10915       -symbolic
10916           Bind references to global symbols when building a shared object.
10917           Warn about any unresolved references (unless overridden by the link
10918           editor option -Xlinker -z -Xlinker defs).  Only a few systems
10919           support this option.
10920
10921       -T script
10922           Use script as the linker script.  This option is supported by most
10923           systems using the GNU linker.  On some targets, such as bare-board
10924           targets without an operating system, the -T option may be required
10925           when linking to avoid references to undefined symbols.
10926
10927       -Xlinker option
10928           Pass option as an option to the linker.  You can use this to supply
10929           system-specific linker options that GCC does not recognize.
10930
10931           If you want to pass an option that takes a separate argument, you
10932           must use -Xlinker twice, once for the option and once for the
10933           argument.  For example, to pass -assert definitions, you must write
10934           -Xlinker -assert -Xlinker definitions.  It does not work to write
10935           -Xlinker "-assert definitions", because this passes the entire
10936           string as a single argument, which is not what the linker expects.
10937
10938           When using the GNU linker, it is usually more convenient to pass
10939           arguments to linker options using the option=value syntax than as
10940           separate arguments.  For example, you can specify -Xlinker
10941           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
10942           Other linkers may not support this syntax for command-line options.
10943
10944       -Wl,option
10945           Pass option as an option to the linker.  If option contains commas,
10946           it is split into multiple options at the commas.  You can use this
10947           syntax to pass an argument to the option.  For example,
10948           -Wl,-Map,output.map passes -Map output.map to the linker.  When
10949           using the GNU linker, you can also get the same effect with
10950           -Wl,-Map=output.map.
10951
10952       -u symbol
10953           Pretend the symbol symbol is undefined, to force linking of library
10954           modules to define it.  You can use -u multiple times with different
10955           symbols to force loading of additional library modules.
10956
10957       -z keyword
10958           -z is passed directly on to the linker along with the keyword
10959           keyword. See the section in the documentation of your linker for
10960           permitted values and their meanings.
10961
10962   Options for Directory Search
10963       These options specify directories to search for header files, for
10964       libraries and for parts of the compiler:
10965
10966       -I dir
10967       -iquote dir
10968       -isystem dir
10969       -idirafter dir
10970           Add the directory dir to the list of directories to be searched for
10971           header files during preprocessing.  If dir begins with = or
10972           $SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix;
10973           see --sysroot and -isysroot.
10974
10975           Directories specified with -iquote apply only to the quote form of
10976           the directive, "#include "file"".  Directories specified with -I,
10977           -isystem, or -idirafter apply to lookup for both the
10978           "#include "file"" and "#include <file>" directives.
10979
10980           You can specify any number or combination of these options on the
10981           command line to search for header files in several directories.
10982           The lookup order is as follows:
10983
10984           1.  For the quote form of the include directive, the directory of
10985               the current file is searched first.
10986
10987           2.  For the quote form of the include directive, the directories
10988               specified by -iquote options are searched in left-to-right
10989               order, as they appear on the command line.
10990
10991           3.  Directories specified with -I options are scanned in left-to-
10992               right order.
10993
10994           4.  Directories specified with -isystem options are scanned in
10995               left-to-right order.
10996
10997           5.  Standard system directories are scanned.
10998
10999           6.  Directories specified with -idirafter options are scanned in
11000               left-to-right order.
11001
11002           You can use -I to override a system header file, substituting your
11003           own version, since these directories are searched before the
11004           standard system header file directories.  However, you should not
11005           use this option to add directories that contain vendor-supplied
11006           system header files; use -isystem for that.
11007
11008           The -isystem and -idirafter options also mark the directory as a
11009           system directory, so that it gets the same special treatment that
11010           is applied to the standard system directories.
11011
11012           If a standard system include directory, or a directory specified
11013           with -isystem, is also specified with -I, the -I option is ignored.
11014           The directory is still searched but as a system directory at its
11015           normal position in the system include chain.  This is to ensure
11016           that GCC's procedure to fix buggy system headers and the ordering
11017           for the "#include_next" directive are not inadvertently changed.
11018           If you really need to change the search order for system
11019           directories, use the -nostdinc and/or -isystem options.
11020
11021       -I- Split the include path.  This option has been deprecated.  Please
11022           use -iquote instead for -I directories before the -I- and remove
11023           the -I- option.
11024
11025           Any directories specified with -I options before -I- are searched
11026           only for headers requested with "#include "file""; they are not
11027           searched for "#include <file>".  If additional directories are
11028           specified with -I options after the -I-, those directories are
11029           searched for all #include directives.
11030
11031           In addition, -I- inhibits the use of the directory of the current
11032           file directory as the first search directory for "#include "file"".
11033           There is no way to override this effect of -I-.
11034
11035       -iprefix prefix
11036           Specify prefix as the prefix for subsequent -iwithprefix options.
11037           If the prefix represents a directory, you should include the final
11038           /.
11039
11040       -iwithprefix dir
11041       -iwithprefixbefore dir
11042           Append dir to the prefix specified previously with -iprefix, and
11043           add the resulting directory to the include search path.
11044           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
11045           puts it where -idirafter would.
11046
11047       -isysroot dir
11048           This option is like the --sysroot option, but applies only to
11049           header files (except for Darwin targets, where it applies to both
11050           header files and libraries).  See the --sysroot option for more
11051           information.
11052
11053       -imultilib dir
11054           Use dir as a subdirectory of the directory containing target-
11055           specific C++ headers.
11056
11057       -nostdinc
11058           Do not search the standard system directories for header files.
11059           Only the directories explicitly specified with -I, -iquote,
11060           -isystem, and/or -idirafter options (and the directory of the
11061           current file, if appropriate) are searched.
11062
11063       -nostdinc++
11064           Do not search for header files in the C++-specific standard
11065           directories, but do still search the other standard directories.
11066           (This option is used when building the C++ library.)
11067
11068       -iplugindir=dir
11069           Set the directory to search for plugins that are passed by
11070           -fplugin=name instead of -fplugin=path/name.so.  This option is not
11071           meant to be used by the user, but only passed by the driver.
11072
11073       -Ldir
11074           Add directory dir to the list of directories to be searched for -l.
11075
11076       -Bprefix
11077           This option specifies where to find the executables, libraries,
11078           include files, and data files of the compiler itself.
11079
11080           The compiler driver program runs one or more of the subprograms
11081           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
11082           it tries to run, both with and without machine/version/ for the
11083           corresponding target machine and compiler version.
11084
11085           For each subprogram to be run, the compiler driver first tries the
11086           -B prefix, if any.  If that name is not found, or if -B is not
11087           specified, the driver tries two standard prefixes, /usr/lib/gcc/
11088           and /usr/local/lib/gcc/.  If neither of those results in a file
11089           name that is found, the unmodified program name is searched for
11090           using the directories specified in your PATH environment variable.
11091
11092           The compiler checks to see if the path provided by -B refers to a
11093           directory, and if necessary it adds a directory separator character
11094           at the end of the path.
11095
11096           -B prefixes that effectively specify directory names also apply to
11097           libraries in the linker, because the compiler translates these
11098           options into -L options for the linker.  They also apply to include
11099           files in the preprocessor, because the compiler translates these
11100           options into -isystem options for the preprocessor.  In this case,
11101           the compiler appends include to the prefix.
11102
11103           The runtime support file libgcc.a can also be searched for using
11104           the -B prefix, if needed.  If it is not found there, the two
11105           standard prefixes above are tried, and that is all.  The file is
11106           left out of the link if it is not found by those means.
11107
11108           Another way to specify a prefix much like the -B prefix is to use
11109           the environment variable GCC_EXEC_PREFIX.
11110
11111           As a special kludge, if the path provided by -B is [dir/]stageN/,
11112           where N is a number in the range 0 to 9, then it is replaced by
11113           [dir/]include.  This is to help with boot-strapping the compiler.
11114
11115       -no-canonical-prefixes
11116           Do not expand any symbolic links, resolve references to /../ or
11117           /./, or make the path absolute when generating a relative prefix.
11118
11119       --sysroot=dir
11120           Use dir as the logical root directory for headers and libraries.
11121           For example, if the compiler normally searches for headers in
11122           /usr/include and libraries in /usr/lib, it instead searches
11123           dir/usr/include and dir/usr/lib.
11124
11125           If you use both this option and the -isysroot option, then the
11126           --sysroot option applies to libraries, but the -isysroot option
11127           applies to header files.
11128
11129           The GNU linker (beginning with version 2.16) has the necessary
11130           support for this option.  If your linker does not support this
11131           option, the header file aspect of --sysroot still works, but the
11132           library aspect does not.
11133
11134       --no-sysroot-suffix
11135           For some targets, a suffix is added to the root directory specified
11136           with --sysroot, depending on the other options used, so that
11137           headers may for example be found in dir/suffix/usr/include instead
11138           of dir/usr/include.  This option disables the addition of such a
11139           suffix.
11140
11141   Options for Code Generation Conventions
11142       These machine-independent options control the interface conventions
11143       used in code generation.
11144
11145       Most of them have both positive and negative forms; the negative form
11146       of -ffoo is -fno-foo.  In the table below, only one of the forms is
11147       listed---the one that is not the default.  You can figure out the other
11148       form by either removing no- or adding it.
11149
11150       -fstack-reuse=reuse-level
11151           This option controls stack space reuse for user declared local/auto
11152           variables and compiler generated temporaries.  reuse_level can be
11153           all, named_vars, or none. all enables stack reuse for all local
11154           variables and temporaries, named_vars enables the reuse only for
11155           user defined local variables with names, and none disables stack
11156           reuse completely. The default value is all. The option is needed
11157           when the program extends the lifetime of a scoped local variable or
11158           a compiler generated temporary beyond the end point defined by the
11159           language.  When a lifetime of a variable ends, and if the variable
11160           lives in memory, the optimizing compiler has the freedom to reuse
11161           its stack space with other temporaries or scoped local variables
11162           whose live range does not overlap with it. Legacy code extending
11163           local lifetime is likely to break with the stack reuse
11164           optimization.
11165
11166           For example,
11167
11168                      int *p;
11169                      {
11170                        int local1;
11171
11172                        p = &local1;
11173                        local1 = 10;
11174                        ....
11175                      }
11176                      {
11177                         int local2;
11178                         local2 = 20;
11179                         ...
11180                      }
11181
11182                      if (*p == 10)  // out of scope use of local1
11183                        {
11184
11185                        }
11186
11187           Another example:
11188
11189                      struct A
11190                      {
11191                          A(int k) : i(k), j(k) { }
11192                          int i;
11193                          int j;
11194                      };
11195
11196                      A *ap;
11197
11198                      void foo(const A& ar)
11199                      {
11200                         ap = &ar;
11201                      }
11202
11203                      void bar()
11204                      {
11205                         foo(A(10)); // temp object's lifetime ends when foo returns
11206
11207                         {
11208                           A a(20);
11209                           ....
11210                         }
11211                         ap->i+= 10;  // ap references out of scope temp whose space
11212                                      // is reused with a. What is the value of ap->i?
11213                      }
11214
11215           The lifetime of a compiler generated temporary is well defined by
11216           the C++ standard. When a lifetime of a temporary ends, and if the
11217           temporary lives in memory, the optimizing compiler has the freedom
11218           to reuse its stack space with other temporaries or scoped local
11219           variables whose live range does not overlap with it. However some
11220           of the legacy code relies on the behavior of older compilers in
11221           which temporaries' stack space is not reused, the aggressive stack
11222           reuse can lead to runtime errors. This option is used to control
11223           the temporary stack reuse optimization.
11224
11225       -ftrapv
11226           This option generates traps for signed overflow on addition,
11227           subtraction, multiplication operations.  The options -ftrapv and
11228           -fwrapv override each other, so using -ftrapv -fwrapv on the
11229           command-line results in -fwrapv being effective.  Note that only
11230           active options override, so using -ftrapv -fwrapv -fno-wrapv on the
11231           command-line results in -ftrapv being effective.
11232
11233       -fwrapv
11234           This option instructs the compiler to assume that signed arithmetic
11235           overflow of addition, subtraction and multiplication wraps around
11236           using twos-complement representation.  This flag enables some
11237           optimizations and disables others.  The options -ftrapv and -fwrapv
11238           override each other, so using -ftrapv -fwrapv on the command-line
11239           results in -fwrapv being effective.  Note that only active options
11240           override, so using -ftrapv -fwrapv -fno-wrapv on the command-line
11241           results in -ftrapv being effective.
11242
11243       -fwrapv-pointer
11244           This option instructs the compiler to assume that pointer
11245           arithmetic overflow on addition and subtraction wraps around using
11246           twos-complement representation.  This flag disables some
11247           optimizations which assume pointer overflow is invalid.
11248
11249       -fstrict-overflow
11250           This option implies -fno-wrapv -fno-wrapv-pointer and when negated
11251           implies -fwrapv -fwrapv-pointer.
11252
11253       -fexceptions
11254           Enable exception handling.  Generates extra code needed to
11255           propagate exceptions.  For some targets, this implies GCC generates
11256           frame unwind information for all functions, which can produce
11257           significant data size overhead, although it does not affect
11258           execution.  If you do not specify this option, GCC enables it by
11259           default for languages like C++ that normally require exception
11260           handling, and disables it for languages like C that do not normally
11261           require it.  However, you may need to enable this option when
11262           compiling C code that needs to interoperate properly with exception
11263           handlers written in C++.  You may also wish to disable this option
11264           if you are compiling older C++ programs that don't use exception
11265           handling.
11266
11267       -fnon-call-exceptions
11268           Generate code that allows trapping instructions to throw
11269           exceptions.  Note that this requires platform-specific runtime
11270           support that does not exist everywhere.  Moreover, it only allows
11271           trapping instructions to throw exceptions, i.e. memory references
11272           or floating-point instructions.  It does not allow exceptions to be
11273           thrown from arbitrary signal handlers such as "SIGALRM".
11274
11275       -fdelete-dead-exceptions
11276           Consider that instructions that may throw exceptions but don't
11277           otherwise contribute to the execution of the program can be
11278           optimized away.  This option is enabled by default for the Ada
11279           front end, as permitted by the Ada language specification.
11280           Optimization passes that cause dead exceptions to be removed are
11281           enabled independently at different optimization levels.
11282
11283       -funwind-tables
11284           Similar to -fexceptions, except that it just generates any needed
11285           static data, but does not affect the generated code in any other
11286           way.  You normally do not need to enable this option; instead, a
11287           language processor that needs this handling enables it on your
11288           behalf.
11289
11290       -fasynchronous-unwind-tables
11291           Generate unwind table in DWARF format, if supported by target
11292           machine.  The table is exact at each instruction boundary, so it
11293           can be used for stack unwinding from asynchronous events (such as
11294           debugger or garbage collector).
11295
11296       -fno-gnu-unique
11297           On systems with recent GNU assembler and C library, the C++
11298           compiler uses the "STB_GNU_UNIQUE" binding to make sure that
11299           definitions of template static data members and static local
11300           variables in inline functions are unique even in the presence of
11301           "RTLD_LOCAL"; this is necessary to avoid problems with a library
11302           used by two different "RTLD_LOCAL" plugins depending on a
11303           definition in one of them and therefore disagreeing with the other
11304           one about the binding of the symbol.  But this causes "dlclose" to
11305           be ignored for affected DSOs; if your program relies on
11306           reinitialization of a DSO via "dlclose" and "dlopen", you can use
11307           -fno-gnu-unique.
11308
11309       -fpcc-struct-return
11310           Return "short" "struct" and "union" values in memory like longer
11311           ones, rather than in registers.  This convention is less efficient,
11312           but it has the advantage of allowing intercallability between GCC-
11313           compiled files and files compiled with other compilers,
11314           particularly the Portable C Compiler (pcc).
11315
11316           The precise convention for returning structures in memory depends
11317           on the target configuration macros.
11318
11319           Short structures and unions are those whose size and alignment
11320           match that of some integer type.
11321
11322           Warning: code compiled with the -fpcc-struct-return switch is not
11323           binary compatible with code compiled with the -freg-struct-return
11324           switch.  Use it to conform to a non-default application binary
11325           interface.
11326
11327       -freg-struct-return
11328           Return "struct" and "union" values in registers when possible.
11329           This is more efficient for small structures than
11330           -fpcc-struct-return.
11331
11332           If you specify neither -fpcc-struct-return nor -freg-struct-return,
11333           GCC defaults to whichever convention is standard for the target.
11334           If there is no standard convention, GCC defaults to
11335           -fpcc-struct-return, except on targets where GCC is the principal
11336           compiler.  In those cases, we can choose the standard, and we chose
11337           the more efficient register return alternative.
11338
11339           Warning: code compiled with the -freg-struct-return switch is not
11340           binary compatible with code compiled with the -fpcc-struct-return
11341           switch.  Use it to conform to a non-default application binary
11342           interface.
11343
11344       -fshort-enums
11345           Allocate to an "enum" type only as many bytes as it needs for the
11346           declared range of possible values.  Specifically, the "enum" type
11347           is equivalent to the smallest integer type that has enough room.
11348
11349           Warning: the -fshort-enums switch causes GCC to generate code that
11350           is not binary compatible with code generated without that switch.
11351           Use it to conform to a non-default application binary interface.
11352
11353       -fshort-wchar
11354           Override the underlying type for "wchar_t" to be "short unsigned
11355           int" instead of the default for the target.  This option is useful
11356           for building programs to run under WINE.
11357
11358           Warning: the -fshort-wchar switch causes GCC to generate code that
11359           is not binary compatible with code generated without that switch.
11360           Use it to conform to a non-default application binary interface.
11361
11362       -fno-common
11363           In C code, this option controls the placement of global variables
11364           defined without an initializer, known as tentative definitions in
11365           the C standard.  Tentative definitions are distinct from
11366           declarations of a variable with the "extern" keyword, which do not
11367           allocate storage.
11368
11369           Unix C compilers have traditionally allocated storage for
11370           uninitialized global variables in a common block.  This allows the
11371           linker to resolve all tentative definitions of the same variable in
11372           different compilation units to the same object, or to a non-
11373           tentative definition.  This is the behavior specified by -fcommon,
11374           and is the default for GCC on most targets.  On the other hand,
11375           this behavior is not required by ISO C, and on some targets may
11376           carry a speed or code size penalty on variable references.
11377
11378           The -fno-common option specifies that the compiler should instead
11379           place uninitialized global variables in the data section of the
11380           object file.  This inhibits the merging of tentative definitions by
11381           the linker so you get a multiple-definition error if the same
11382           variable is defined in more than one compilation unit.  Compiling
11383           with -fno-common is useful on targets for which it provides better
11384           performance, or if you wish to verify that the program will work on
11385           other systems that always treat uninitialized variable definitions
11386           this way.
11387
11388       -fno-ident
11389           Ignore the "#ident" directive.
11390
11391       -finhibit-size-directive
11392           Don't output a ".size" assembler directive, or anything else that
11393           would cause trouble if the function is split in the middle, and the
11394           two halves are placed at locations far apart in memory.  This
11395           option is used when compiling crtstuff.c; you should not need to
11396           use it for anything else.
11397
11398       -fverbose-asm
11399           Put extra commentary information in the generated assembly code to
11400           make it more readable.  This option is generally only of use to
11401           those who actually need to read the generated assembly code
11402           (perhaps while debugging the compiler itself).
11403
11404           -fno-verbose-asm, the default, causes the extra information to be
11405           omitted and is useful when comparing two assembler files.
11406
11407           The added comments include:
11408
11409           *   information on the compiler version and command-line options,
11410
11411           *   the source code lines associated with the assembly
11412               instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,
11413
11414           *   hints on which high-level expressions correspond to the various
11415               assembly instruction operands.
11416
11417           For example, given this C source file:
11418
11419                   int test (int n)
11420                   {
11421                     int i;
11422                     int total = 0;
11423
11424                     for (i = 0; i < n; i++)
11425                       total += i * i;
11426
11427                     return total;
11428                   }
11429
11430           compiling to (x86_64) assembly via -S and emitting the result
11431           direct to stdout via -o -
11432
11433                   gcc -S test.c -fverbose-asm -Os -o -
11434
11435           gives output similar to this:
11436
11437                           .file   "test.c"
11438                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
11439                     [...snip...]
11440                   # options passed:
11441                     [...snip...]
11442
11443                           .text
11444                           .globl  test
11445                           .type   test, @function
11446                   test:
11447                   .LFB0:
11448                           .cfi_startproc
11449                   # test.c:4:   int total = 0;
11450                           xorl    %eax, %eax      # <retval>
11451                   # test.c:6:   for (i = 0; i < n; i++)
11452                           xorl    %edx, %edx      # i
11453                   .L2:
11454                   # test.c:6:   for (i = 0; i < n; i++)
11455                           cmpl    %edi, %edx      # n, i
11456                           jge     .L5     #,
11457                   # test.c:7:     total += i * i;
11458                           movl    %edx, %ecx      # i, tmp92
11459                           imull   %edx, %ecx      # i, tmp92
11460                   # test.c:6:   for (i = 0; i < n; i++)
11461                           incl    %edx    # i
11462                   # test.c:7:     total += i * i;
11463                           addl    %ecx, %eax      # tmp92, <retval>
11464                           jmp     .L2     #
11465                   .L5:
11466                   # test.c:10: }
11467                           ret
11468                           .cfi_endproc
11469                   .LFE0:
11470                           .size   test, .-test
11471                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
11472                           .section        .note.GNU-stack,"",@progbits
11473
11474           The comments are intended for humans rather than machines and hence
11475           the precise format of the comments is subject to change.
11476
11477       -frecord-gcc-switches
11478           This switch causes the command line used to invoke the compiler to
11479           be recorded into the object file that is being created.  This
11480           switch is only implemented on some targets and the exact format of
11481           the recording is target and binary file format dependent, but it
11482           usually takes the form of a section containing ASCII text.  This
11483           switch is related to the -fverbose-asm switch, but that switch only
11484           records information in the assembler output file as comments, so it
11485           never reaches the object file.  See also -grecord-gcc-switches for
11486           another way of storing compiler options into the object file.
11487
11488       -fpic
11489           Generate position-independent code (PIC) suitable for use in a
11490           shared library, if supported for the target machine.  Such code
11491           accesses all constant addresses through a global offset table
11492           (GOT).  The dynamic loader resolves the GOT entries when the
11493           program starts (the dynamic loader is not part of GCC; it is part
11494           of the operating system).  If the GOT size for the linked
11495           executable exceeds a machine-specific maximum size, you get an
11496           error message from the linker indicating that -fpic does not work;
11497           in that case, recompile with -fPIC instead.  (These maximums are 8k
11498           on the SPARC, 28k on AArch64 and 32k on the m68k and RS/6000.  The
11499           x86 has no such limit.)
11500
11501           Position-independent code requires special support, and therefore
11502           works only on certain machines.  For the x86, GCC supports PIC for
11503           System V but not for the Sun 386i.  Code generated for the IBM
11504           RS/6000 is always position-independent.
11505
11506           When this flag is set, the macros "__pic__" and "__PIC__" are
11507           defined to 1.
11508
11509       -fPIC
11510           If supported for the target machine, emit position-independent
11511           code, suitable for dynamic linking and avoiding any limit on the
11512           size of the global offset table.  This option makes a difference on
11513           AArch64, m68k, PowerPC and SPARC.
11514
11515           Position-independent code requires special support, and therefore
11516           works only on certain machines.
11517
11518           When this flag is set, the macros "__pic__" and "__PIC__" are
11519           defined to 2.
11520
11521       -fpie
11522       -fPIE
11523           These options are similar to -fpic and -fPIC, but generated
11524           position independent code can be only linked into executables.
11525           Usually these options are used when -pie GCC option is used during
11526           linking.
11527
11528           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
11529           The macros have the value 1 for -fpie and 2 for -fPIE.
11530
11531       -fno-plt
11532           Do not use the PLT for external function calls in position-
11533           independent code.  Instead, load the callee address at call sites
11534           from the GOT and branch to it.  This leads to more efficient code
11535           by eliminating PLT stubs and exposing GOT loads to optimizations.
11536           On architectures such as 32-bit x86 where PLT stubs expect the GOT
11537           pointer in a specific register, this gives more register allocation
11538           freedom to the compiler.  Lazy binding requires use of the PLT;
11539           with -fno-plt all external symbols are resolved at load time.
11540
11541           Alternatively, the function attribute "noplt" can be used to avoid
11542           calls through the PLT for specific external functions.
11543
11544           In position-dependent code, a few targets also convert calls to
11545           functions that are marked to not use the PLT to use the GOT
11546           instead.
11547
11548       -fno-jump-tables
11549           Do not use jump tables for switch statements even where it would be
11550           more efficient than other code generation strategies.  This option
11551           is of use in conjunction with -fpic or -fPIC for building code that
11552           forms part of a dynamic linker and cannot reference the address of
11553           a jump table.  On some targets, jump tables do not require a GOT
11554           and this option is not needed.
11555
11556       -ffixed-reg
11557           Treat the register named reg as a fixed register; generated code
11558           should never refer to it (except perhaps as a stack pointer, frame
11559           pointer or in some other fixed role).
11560
11561           reg must be the name of a register.  The register names accepted
11562           are machine-specific and are defined in the "REGISTER_NAMES" macro
11563           in the machine description macro file.
11564
11565           This flag does not have a negative form, because it specifies a
11566           three-way choice.
11567
11568       -fcall-used-reg
11569           Treat the register named reg as an allocable register that is
11570           clobbered by function calls.  It may be allocated for temporaries
11571           or variables that do not live across a call.  Functions compiled
11572           this way do not save and restore the register reg.
11573
11574           It is an error to use this flag with the frame pointer or stack
11575           pointer.  Use of this flag for other registers that have fixed
11576           pervasive roles in the machine's execution model produces
11577           disastrous results.
11578
11579           This flag does not have a negative form, because it specifies a
11580           three-way choice.
11581
11582       -fcall-saved-reg
11583           Treat the register named reg as an allocable register saved by
11584           functions.  It may be allocated even for temporaries or variables
11585           that live across a call.  Functions compiled this way save and
11586           restore the register reg if they use it.
11587
11588           It is an error to use this flag with the frame pointer or stack
11589           pointer.  Use of this flag for other registers that have fixed
11590           pervasive roles in the machine's execution model produces
11591           disastrous results.
11592
11593           A different sort of disaster results from the use of this flag for
11594           a register in which function values may be returned.
11595
11596           This flag does not have a negative form, because it specifies a
11597           three-way choice.
11598
11599       -fpack-struct[=n]
11600           Without a value specified, pack all structure members together
11601           without holes.  When a value is specified (which must be a small
11602           power of two), pack structure members according to this value,
11603           representing the maximum alignment (that is, objects with default
11604           alignment requirements larger than this are output potentially
11605           unaligned at the next fitting location.
11606
11607           Warning: the -fpack-struct switch causes GCC to generate code that
11608           is not binary compatible with code generated without that switch.
11609           Additionally, it makes the code suboptimal.  Use it to conform to a
11610           non-default application binary interface.
11611
11612       -fleading-underscore
11613           This option and its counterpart, -fno-leading-underscore, forcibly
11614           change the way C symbols are represented in the object file.  One
11615           use is to help link with legacy assembly code.
11616
11617           Warning: the -fleading-underscore switch causes GCC to generate
11618           code that is not binary compatible with code generated without that
11619           switch.  Use it to conform to a non-default application binary
11620           interface.  Not all targets provide complete support for this
11621           switch.
11622
11623       -ftls-model=model
11624           Alter the thread-local storage model to be used.  The model
11625           argument should be one of global-dynamic, local-dynamic, initial-
11626           exec or local-exec.  Note that the choice is subject to
11627           optimization: the compiler may use a more efficient model for
11628           symbols not visible outside of the translation unit, or if -fpic is
11629           not given on the command line.
11630
11631           The default without -fpic is initial-exec; with -fpic the default
11632           is global-dynamic.
11633
11634       -ftrampolines
11635           For targets that normally need trampolines for nested functions,
11636           always generate them instead of using descriptors.  Otherwise, for
11637           targets that do not need them, like for example HP-PA or IA-64, do
11638           nothing.
11639
11640           A trampoline is a small piece of code that is created at run time
11641           on the stack when the address of a nested function is taken, and is
11642           used to call the nested function indirectly.  Therefore, it
11643           requires the stack to be made executable in order for the program
11644           to work properly.
11645
11646           -fno-trampolines is enabled by default on a language by language
11647           basis to let the compiler avoid generating them, if it computes
11648           that this is safe, and replace them with descriptors.  Descriptors
11649           are made up of data only, but the generated code must be prepared
11650           to deal with them.  As of this writing, -fno-trampolines is enabled
11651           by default only for Ada.
11652
11653           Moreover, code compiled with -ftrampolines and code compiled with
11654           -fno-trampolines are not binary compatible if nested functions are
11655           present.  This option must therefore be used on a program-wide
11656           basis and be manipulated with extreme care.
11657
11658       -fvisibility=[default|internal|hidden|protected]
11659           Set the default ELF image symbol visibility to the specified
11660           option---all symbols are marked with this unless overridden within
11661           the code.  Using this feature can very substantially improve
11662           linking and load times of shared object libraries, produce more
11663           optimized code, provide near-perfect API export and prevent symbol
11664           clashes.  It is strongly recommended that you use this in any
11665           shared objects you distribute.
11666
11667           Despite the nomenclature, default always means public; i.e.,
11668           available to be linked against from outside the shared object.
11669           protected and internal are pretty useless in real-world usage so
11670           the only other commonly used option is hidden.  The default if
11671           -fvisibility isn't specified is default, i.e., make every symbol
11672           public.
11673
11674           A good explanation of the benefits offered by ensuring ELF symbols
11675           have the correct visibility is given by "How To Write Shared
11676           Libraries" by Ulrich Drepper (which can be found at
11677           <https://www.akkadia.org/drepper/>)---however a superior solution
11678           made possible by this option to marking things hidden when the
11679           default is public is to make the default hidden and mark things
11680           public.  This is the norm with DLLs on Windows and with
11681           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
11682           instead of "__declspec(dllexport)" you get almost identical
11683           semantics with identical syntax.  This is a great boon to those
11684           working with cross-platform projects.
11685
11686           For those adding visibility support to existing code, you may find
11687           "#pragma GCC visibility" of use.  This works by you enclosing the
11688           declarations you wish to set visibility for with (for example)
11689           "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility
11690           pop".  Bear in mind that symbol visibility should be viewed as part
11691           of the API interface contract and thus all new code should always
11692           specify visibility when it is not the default; i.e., declarations
11693           only for use within the local DSO should always be marked
11694           explicitly as hidden as so to avoid PLT indirection
11695           overheads---making this abundantly clear also aids readability and
11696           self-documentation of the code.  Note that due to ISO C++
11697           specification requirements, "operator new" and "operator delete"
11698           must always be of default visibility.
11699
11700           Be aware that headers from outside your project, in particular
11701           system headers and headers from any other library you use, may not
11702           be expecting to be compiled with visibility other than the default.
11703           You may need to explicitly say "#pragma GCC visibility
11704           push(default)" before including any such headers.
11705
11706           "extern" declarations are not affected by -fvisibility, so a lot of
11707           code can be recompiled with -fvisibility=hidden with no
11708           modifications.  However, this means that calls to "extern"
11709           functions with no explicit visibility use the PLT, so it is more
11710           effective to use "__attribute ((visibility))" and/or "#pragma GCC
11711           visibility" to tell the compiler which "extern" declarations should
11712           be treated as hidden.
11713
11714           Note that -fvisibility does affect C++ vague linkage entities. This
11715           means that, for instance, an exception class that is be thrown
11716           between DSOs must be explicitly marked with default visibility so
11717           that the type_info nodes are unified between the DSOs.
11718
11719           An overview of these techniques, their benefits and how to use them
11720           is at <http://gcc.gnu.org/wiki/Visibility>.
11721
11722       -fstrict-volatile-bitfields
11723           This option should be used if accesses to volatile bit-fields (or
11724           other structure fields, although the compiler usually honors those
11725           types anyway) should use a single access of the width of the
11726           field's type, aligned to a natural alignment if possible.  For
11727           example, targets with memory-mapped peripheral registers might
11728           require all such accesses to be 16 bits wide; with this flag you
11729           can declare all peripheral bit-fields as "unsigned short" (assuming
11730           short is 16 bits on these targets) to force GCC to use 16-bit
11731           accesses instead of, perhaps, a more efficient 32-bit access.
11732
11733           If this option is disabled, the compiler uses the most efficient
11734           instruction.  In the previous example, that might be a 32-bit load
11735           instruction, even though that accesses bytes that do not contain
11736           any portion of the bit-field, or memory-mapped registers unrelated
11737           to the one being updated.
11738
11739           In some cases, such as when the "packed" attribute is applied to a
11740           structure field, it may not be possible to access the field with a
11741           single read or write that is correctly aligned for the target
11742           machine.  In this case GCC falls back to generating multiple
11743           accesses rather than code that will fault or truncate the result at
11744           run time.
11745
11746           Note:  Due to restrictions of the C/C++11 memory model, write
11747           accesses are not allowed to touch non bit-field members.  It is
11748           therefore recommended to define all bits of the field's type as
11749           bit-field members.
11750
11751           The default value of this option is determined by the application
11752           binary interface for the target processor.
11753
11754       -fsync-libcalls
11755           This option controls whether any out-of-line instance of the
11756           "__sync" family of functions may be used to implement the C++11
11757           "__atomic" family of functions.
11758
11759           The default value of this option is enabled, thus the only useful
11760           form of the option is -fno-sync-libcalls.  This option is used in
11761           the implementation of the libatomic runtime library.
11762
11763   GCC Developer Options
11764       This section describes command-line options that are primarily of
11765       interest to GCC developers, including options to support compiler
11766       testing and investigation of compiler bugs and compile-time performance
11767       problems.  This includes options that produce debug dumps at various
11768       points in the compilation; that print statistics such as memory use and
11769       execution time; and that print information about GCC's configuration,
11770       such as where it searches for libraries.  You should rarely need to use
11771       any of these options for ordinary compilation and linking tasks.
11772
11773       -dletters
11774       -fdump-rtl-pass
11775       -fdump-rtl-pass=filename
11776           Says to make debugging dumps during compilation at times specified
11777           by letters.  This is used for debugging the RTL-based passes of the
11778           compiler.  The file names for most of the dumps are made by
11779           appending a pass number and a word to the dumpname, and the files
11780           are created in the directory of the output file.  In case of
11781           =filename option, the dump is output on the given file instead of
11782           the pass numbered dump files.  Note that the pass number is
11783           assigned as passes are registered into the pass manager.  Most
11784           passes are registered in the order that they will execute and for
11785           these passes the number corresponds to the pass execution order.
11786           However, passes registered by plugins, passes specific to
11787           compilation targets, or passes that are otherwise registered after
11788           all the other passes are numbered higher than a pass named "final",
11789           even if they are executed earlier.  dumpname is generated from the
11790           name of the output file if explicitly specified and not an
11791           executable, otherwise it is the basename of the source file.
11792
11793           Some -dletters switches have different meaning when -E is used for
11794           preprocessing.
11795
11796           Debug dumps can be enabled with a -fdump-rtl switch or some -d
11797           option letters.  Here are the possible letters for use in pass and
11798           letters, and their meanings:
11799
11800           -fdump-rtl-alignments
11801               Dump after branch alignments have been computed.
11802
11803           -fdump-rtl-asmcons
11804               Dump after fixing rtl statements that have unsatisfied in/out
11805               constraints.
11806
11807           -fdump-rtl-auto_inc_dec
11808               Dump after auto-inc-dec discovery.  This pass is only run on
11809               architectures that have auto inc or auto dec instructions.
11810
11811           -fdump-rtl-barriers
11812               Dump after cleaning up the barrier instructions.
11813
11814           -fdump-rtl-bbpart
11815               Dump after partitioning hot and cold basic blocks.
11816
11817           -fdump-rtl-bbro
11818               Dump after block reordering.
11819
11820           -fdump-rtl-btl1
11821           -fdump-rtl-btl2
11822               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
11823               two branch target load optimization passes.
11824
11825           -fdump-rtl-bypass
11826               Dump after jump bypassing and control flow optimizations.
11827
11828           -fdump-rtl-combine
11829               Dump after the RTL instruction combination pass.
11830
11831           -fdump-rtl-compgotos
11832               Dump after duplicating the computed gotos.
11833
11834           -fdump-rtl-ce1
11835           -fdump-rtl-ce2
11836           -fdump-rtl-ce3
11837               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
11838               dumping after the three if conversion passes.
11839
11840           -fdump-rtl-cprop_hardreg
11841               Dump after hard register copy propagation.
11842
11843           -fdump-rtl-csa
11844               Dump after combining stack adjustments.
11845
11846           -fdump-rtl-cse1
11847           -fdump-rtl-cse2
11848               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
11849               two common subexpression elimination passes.
11850
11851           -fdump-rtl-dce
11852               Dump after the standalone dead code elimination passes.
11853
11854           -fdump-rtl-dbr
11855               Dump after delayed branch scheduling.
11856
11857           -fdump-rtl-dce1
11858           -fdump-rtl-dce2
11859               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
11860               two dead store elimination passes.
11861
11862           -fdump-rtl-eh
11863               Dump after finalization of EH handling code.
11864
11865           -fdump-rtl-eh_ranges
11866               Dump after conversion of EH handling range regions.
11867
11868           -fdump-rtl-expand
11869               Dump after RTL generation.
11870
11871           -fdump-rtl-fwprop1
11872           -fdump-rtl-fwprop2
11873               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
11874               the two forward propagation passes.
11875
11876           -fdump-rtl-gcse1
11877           -fdump-rtl-gcse2
11878               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
11879               global common subexpression elimination.
11880
11881           -fdump-rtl-init-regs
11882               Dump after the initialization of the registers.
11883
11884           -fdump-rtl-initvals
11885               Dump after the computation of the initial value sets.
11886
11887           -fdump-rtl-into_cfglayout
11888               Dump after converting to cfglayout mode.
11889
11890           -fdump-rtl-ira
11891               Dump after iterated register allocation.
11892
11893           -fdump-rtl-jump
11894               Dump after the second jump optimization.
11895
11896           -fdump-rtl-loop2
11897               -fdump-rtl-loop2 enables dumping after the rtl loop
11898               optimization passes.
11899
11900           -fdump-rtl-mach
11901               Dump after performing the machine dependent reorganization
11902               pass, if that pass exists.
11903
11904           -fdump-rtl-mode_sw
11905               Dump after removing redundant mode switches.
11906
11907           -fdump-rtl-rnreg
11908               Dump after register renumbering.
11909
11910           -fdump-rtl-outof_cfglayout
11911               Dump after converting from cfglayout mode.
11912
11913           -fdump-rtl-peephole2
11914               Dump after the peephole pass.
11915
11916           -fdump-rtl-postreload
11917               Dump after post-reload optimizations.
11918
11919           -fdump-rtl-pro_and_epilogue
11920               Dump after generating the function prologues and epilogues.
11921
11922           -fdump-rtl-sched1
11923           -fdump-rtl-sched2
11924               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
11925               the basic block scheduling passes.
11926
11927           -fdump-rtl-ree
11928               Dump after sign/zero extension elimination.
11929
11930           -fdump-rtl-seqabstr
11931               Dump after common sequence discovery.
11932
11933           -fdump-rtl-shorten
11934               Dump after shortening branches.
11935
11936           -fdump-rtl-sibling
11937               Dump after sibling call optimizations.
11938
11939           -fdump-rtl-split1
11940           -fdump-rtl-split2
11941           -fdump-rtl-split3
11942           -fdump-rtl-split4
11943           -fdump-rtl-split5
11944               These options enable dumping after five rounds of instruction
11945               splitting.
11946
11947           -fdump-rtl-sms
11948               Dump after modulo scheduling.  This pass is only run on some
11949               architectures.
11950
11951           -fdump-rtl-stack
11952               Dump after conversion from GCC's "flat register file" registers
11953               to the x87's stack-like registers.  This pass is only run on
11954               x86 variants.
11955
11956           -fdump-rtl-subreg1
11957           -fdump-rtl-subreg2
11958               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
11959               the two subreg expansion passes.
11960
11961           -fdump-rtl-unshare
11962               Dump after all rtl has been unshared.
11963
11964           -fdump-rtl-vartrack
11965               Dump after variable tracking.
11966
11967           -fdump-rtl-vregs
11968               Dump after converting virtual registers to hard registers.
11969
11970           -fdump-rtl-web
11971               Dump after live range splitting.
11972
11973           -fdump-rtl-regclass
11974           -fdump-rtl-subregs_of_mode_init
11975           -fdump-rtl-subregs_of_mode_finish
11976           -fdump-rtl-dfinit
11977           -fdump-rtl-dfinish
11978               These dumps are defined but always produce empty files.
11979
11980           -da
11981           -fdump-rtl-all
11982               Produce all the dumps listed above.
11983
11984           -dA Annotate the assembler output with miscellaneous debugging
11985               information.
11986
11987           -dD Dump all macro definitions, at the end of preprocessing, in
11988               addition to normal output.
11989
11990           -dH Produce a core dump whenever an error occurs.
11991
11992           -dp Annotate the assembler output with a comment indicating which
11993               pattern and alternative is used.  The length and cost of each
11994               instruction are also printed.
11995
11996           -dP Dump the RTL in the assembler output as a comment before each
11997               instruction.  Also turns on -dp annotation.
11998
11999           -dx Just generate RTL for a function instead of compiling it.
12000               Usually used with -fdump-rtl-expand.
12001
12002       -fdump-noaddr
12003           When doing debugging dumps, suppress address output.  This makes it
12004           more feasible to use diff on debugging dumps for compiler
12005           invocations with different compiler binaries and/or different text
12006           / bss / data / heap / stack / dso start locations.
12007
12008       -freport-bug
12009           Collect and dump debug information into a temporary file if an
12010           internal compiler error (ICE) occurs.
12011
12012       -fdump-unnumbered
12013           When doing debugging dumps, suppress instruction numbers and
12014           address output.  This makes it more feasible to use diff on
12015           debugging dumps for compiler invocations with different options, in
12016           particular with and without -g.
12017
12018       -fdump-unnumbered-links
12019           When doing debugging dumps (see -d option above), suppress
12020           instruction numbers for the links to the previous and next
12021           instructions in a sequence.
12022
12023       -fdump-ipa-switch
12024           Control the dumping at various stages of inter-procedural analysis
12025           language tree to a file.  The file name is generated by appending a
12026           switch specific suffix to the source file name, and the file is
12027           created in the same directory as the output file.  The following
12028           dumps are possible:
12029
12030           all Enables all inter-procedural analysis dumps.
12031
12032           cgraph
12033               Dumps information about call-graph optimization, unused
12034               function removal, and inlining decisions.
12035
12036           inline
12037               Dump after function inlining.
12038
12039       -fdump-lang-all
12040       -fdump-lang-switch
12041       -fdump-lang-switch-options
12042       -fdump-lang-switch-options=filename
12043           Control the dumping of language-specific information.  The options
12044           and filename portions behave as described in the -fdump-tree
12045           option.  The following switch values are accepted:
12046
12047           all Enable all language-specific dumps.
12048
12049           class
12050               Dump class hierarchy information.  Virtual table information is
12051               emitted unless 'slim' is specified.  This option is applicable
12052               to C++ only.
12053
12054           raw Dump the raw internal tree data.  This option is applicable to
12055               C++ only.
12056
12057       -fdump-passes
12058           Print on stderr the list of optimization passes that are turned on
12059           and off by the current command-line options.
12060
12061       -fdump-statistics-option
12062           Enable and control dumping of pass statistics in a separate file.
12063           The file name is generated by appending a suffix ending in
12064           .statistics to the source file name, and the file is created in the
12065           same directory as the output file.  If the -option form is used,
12066           -stats causes counters to be summed over the whole compilation unit
12067           while -details dumps every event as the passes generate them.  The
12068           default with no option is to sum counters for each function
12069           compiled.
12070
12071       -fdump-tree-all
12072       -fdump-tree-switch
12073       -fdump-tree-switch-options
12074       -fdump-tree-switch-options=filename
12075           Control the dumping at various stages of processing the
12076           intermediate language tree to a file.  The file name is generated
12077           by appending a switch-specific suffix to the source file name, and
12078           the file is created in the same directory as the output file. In
12079           case of =filename option, the dump is output on the given file
12080           instead of the auto named dump files.  If the -options form is
12081           used, options is a list of - separated options which control the
12082           details of the dump.  Not all options are applicable to all dumps;
12083           those that are not meaningful are ignored.  The following options
12084           are available
12085
12086           address
12087               Print the address of each node.  Usually this is not meaningful
12088               as it changes according to the environment and source file.
12089               Its primary use is for tying up a dump file with a debug
12090               environment.
12091
12092           asmname
12093               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
12094               that in the dump instead of "DECL_NAME".  Its primary use is
12095               ease of use working backward from mangled names in the assembly
12096               file.
12097
12098           slim
12099               When dumping front-end intermediate representations, inhibit
12100               dumping of members of a scope or body of a function merely
12101               because that scope has been reached.  Only dump such items when
12102               they are directly reachable by some other path.
12103
12104               When dumping pretty-printed trees, this option inhibits dumping
12105               the bodies of control structures.
12106
12107               When dumping RTL, print the RTL in slim (condensed) form
12108               instead of the default LISP-like representation.
12109
12110           raw Print a raw representation of the tree.  By default, trees are
12111               pretty-printed into a C-like representation.
12112
12113           details
12114               Enable more detailed dumps (not honored by every dump option).
12115               Also include information from the optimization passes.
12116
12117           stats
12118               Enable dumping various statistics about the pass (not honored
12119               by every dump option).
12120
12121           blocks
12122               Enable showing basic block boundaries (disabled in raw dumps).
12123
12124           graph
12125               For each of the other indicated dump files (-fdump-rtl-pass),
12126               dump a representation of the control flow graph suitable for
12127               viewing with GraphViz to file.passid.pass.dot.  Each function
12128               in the file is pretty-printed as a subgraph, so that GraphViz
12129               can render them all in a single plot.
12130
12131               This option currently only works for RTL dumps, and the RTL is
12132               always dumped in slim form.
12133
12134           vops
12135               Enable showing virtual operands for every statement.
12136
12137           lineno
12138               Enable showing line numbers for statements.
12139
12140           uid Enable showing the unique ID ("DECL_UID") for each variable.
12141
12142           verbose
12143               Enable showing the tree dump for each statement.
12144
12145           eh  Enable showing the EH region number holding each statement.
12146
12147           scev
12148               Enable showing scalar evolution analysis details.
12149
12150           optimized
12151               Enable showing optimization information (only available in
12152               certain passes).
12153
12154           missed
12155               Enable showing missed optimization information (only available
12156               in certain passes).
12157
12158           note
12159               Enable other detailed optimization information (only available
12160               in certain passes).
12161
12162           =filename
12163               Instead of an auto named dump file, output into the given file
12164               name. The file names stdout and stderr are treated specially
12165               and are considered already open standard streams. For example,
12166
12167                       gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
12168                            -fdump-tree-pre=/dev/stderr file.c
12169
12170               outputs vectorizer dump into foo.dump, while the PRE dump is
12171               output on to stderr. If two conflicting dump filenames are
12172               given for the same pass, then the latter option overrides the
12173               earlier one.
12174
12175           all Turn on all options, except raw, slim, verbose and lineno.
12176
12177           optall
12178               Turn on all optimization options, i.e., optimized, missed, and
12179               note.
12180
12181           To determine what tree dumps are available or find the dump for a
12182           pass of interest follow the steps below.
12183
12184           1.  Invoke GCC with -fdump-passes and in the stderr output look for
12185               a code that corresponds to the pass you are interested in.  For
12186               example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2"
12187               correspond to the three Value Range Propagation passes.  The
12188               number at the end distinguishes distinct invocations of the
12189               same pass.
12190
12191           2.  To enable the creation of the dump file, append the pass code
12192               to the -fdump- option prefix and invoke GCC with it.  For
12193               example, to enable the dump from the Early Value Range
12194               Propagation pass, invoke GCC with the -fdump-tree-evrp option.
12195               Optionally, you may specify the name of the dump file.  If you
12196               don't specify one, GCC creates as described below.
12197
12198           3.  Find the pass dump in a file whose name is composed of three
12199               components separated by a period: the name of the source file
12200               GCC was invoked to compile, a numeric suffix indicating the
12201               pass number followed by the letter t for tree passes (and the
12202               letter r for RTL passes), and finally the pass code.  For
12203               example, the Early VRP pass dump might be in a file named
12204               myfile.c.038t.evrp in the current working directory.  Note that
12205               the numeric codes are not stable and may change from one
12206               version of GCC to another.
12207
12208       -fopt-info
12209       -fopt-info-options
12210       -fopt-info-options=filename
12211           Controls optimization dumps from various optimization passes. If
12212           the -options form is used, options is a list of - separated option
12213           keywords to select the dump details and optimizations.
12214
12215           The options can be divided into two groups: options describing the
12216           verbosity of the dump, and options describing which optimizations
12217           should be included. The options from both the groups can be freely
12218           mixed as they are non-overlapping. However, in case of any
12219           conflicts, the later options override the earlier options on the
12220           command line.
12221
12222           The following options control the dump verbosity:
12223
12224           optimized
12225               Print information when an optimization is successfully applied.
12226               It is up to a pass to decide which information is relevant. For
12227               example, the vectorizer passes print the source location of
12228               loops which are successfully vectorized.
12229
12230           missed
12231               Print information about missed optimizations. Individual passes
12232               control which information to include in the output.
12233
12234           note
12235               Print verbose information about optimizations, such as certain
12236               transformations, more detailed messages about decisions etc.
12237
12238           all Print detailed optimization information. This includes
12239               optimized, missed, and note.
12240
12241           One or more of the following option keywords can be used to
12242           describe a group of optimizations:
12243
12244           ipa Enable dumps from all interprocedural optimizations.
12245
12246           loop
12247               Enable dumps from all loop optimizations.
12248
12249           inline
12250               Enable dumps from all inlining optimizations.
12251
12252           omp Enable dumps from all OMP (Offloading and Multi Processing)
12253               optimizations.
12254
12255           vec Enable dumps from all vectorization optimizations.
12256
12257           optall
12258               Enable dumps from all optimizations. This is a superset of the
12259               optimization groups listed above.
12260
12261           If options is omitted, it defaults to optimized-optall, which means
12262           to dump all info about successful optimizations from all the
12263           passes.
12264
12265           If the filename is provided, then the dumps from all the applicable
12266           optimizations are concatenated into the filename.  Otherwise the
12267           dump is output onto stderr. Though multiple -fopt-info options are
12268           accepted, only one of them can include a filename. If other
12269           filenames are provided then all but the first such option are
12270           ignored.
12271
12272           Note that the output filename is overwritten in case of multiple
12273           translation units. If a combined output from multiple translation
12274           units is desired, stderr should be used instead.
12275
12276           In the following example, the optimization info is output to
12277           stderr:
12278
12279                   gcc -O3 -fopt-info
12280
12281           This example:
12282
12283                   gcc -O3 -fopt-info-missed=missed.all
12284
12285           outputs missed optimization report from all the passes into
12286           missed.all, and this one:
12287
12288                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed
12289
12290           prints information about missed optimization opportunities from
12291           vectorization passes on stderr.  Note that -fopt-info-vec-missed is
12292           equivalent to -fopt-info-missed-vec.  The order of the optimization
12293           group names and message types listed after -fopt-info does not
12294           matter.
12295
12296           As another example,
12297
12298                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
12299
12300           outputs information about missed optimizations as well as optimized
12301           locations from all the inlining passes into inline.txt.
12302
12303           Finally, consider:
12304
12305                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
12306
12307           Here the two output filenames vec.miss and loop.opt are in conflict
12308           since only one output file is allowed. In this case, only the first
12309           option takes effect and the subsequent options are ignored. Thus
12310           only vec.miss is produced which contains dumps from the vectorizer
12311           about missed opportunities.
12312
12313       -fsched-verbose=n
12314           On targets that use instruction scheduling, this option controls
12315           the amount of debugging output the scheduler prints to the dump
12316           files.
12317
12318           For n greater than zero, -fsched-verbose outputs the same
12319           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
12320           greater than one, it also output basic block probabilities,
12321           detailed ready list information and unit/insn info.  For n greater
12322           than two, it includes RTL at abort point, control-flow and regions
12323           info.  And for n over four, -fsched-verbose also includes
12324           dependence info.
12325
12326       -fenable-kind-pass
12327       -fdisable-kind-pass=range-list
12328           This is a set of options that are used to explicitly disable/enable
12329           optimization passes.  These options are intended for use for
12330           debugging GCC.  Compiler users should use regular options for
12331           enabling/disabling passes instead.
12332
12333           -fdisable-ipa-pass
12334               Disable IPA pass pass. pass is the pass name.  If the same pass
12335               is statically invoked in the compiler multiple times, the pass
12336               name should be appended with a sequential number starting from
12337               1.
12338
12339           -fdisable-rtl-pass
12340           -fdisable-rtl-pass=range-list
12341               Disable RTL pass pass.  pass is the pass name.  If the same
12342               pass is statically invoked in the compiler multiple times, the
12343               pass name should be appended with a sequential number starting
12344               from 1.  range-list is a comma-separated list of function
12345               ranges or assembler names.  Each range is a number pair
12346               separated by a colon.  The range is inclusive in both ends.  If
12347               the range is trivial, the number pair can be simplified as a
12348               single number.  If the function's call graph node's uid falls
12349               within one of the specified ranges, the pass is disabled for
12350               that function.  The uid is shown in the function header of a
12351               dump file, and the pass names can be dumped by using option
12352               -fdump-passes.
12353
12354           -fdisable-tree-pass
12355           -fdisable-tree-pass=range-list
12356               Disable tree pass pass.  See -fdisable-rtl for the description
12357               of option arguments.
12358
12359           -fenable-ipa-pass
12360               Enable IPA pass pass.  pass is the pass name.  If the same pass
12361               is statically invoked in the compiler multiple times, the pass
12362               name should be appended with a sequential number starting from
12363               1.
12364
12365           -fenable-rtl-pass
12366           -fenable-rtl-pass=range-list
12367               Enable RTL pass pass.  See -fdisable-rtl for option argument
12368               description and examples.
12369
12370           -fenable-tree-pass
12371           -fenable-tree-pass=range-list
12372               Enable tree pass pass.  See -fdisable-rtl for the description
12373               of option arguments.
12374
12375           Here are some examples showing uses of these options.
12376
12377                   # disable ccp1 for all functions
12378                      -fdisable-tree-ccp1
12379                   # disable complete unroll for function whose cgraph node uid is 1
12380                      -fenable-tree-cunroll=1
12381                   # disable gcse2 for functions at the following ranges [1,1],
12382                   # [300,400], and [400,1000]
12383                   # disable gcse2 for functions foo and foo2
12384                      -fdisable-rtl-gcse2=foo,foo2
12385                   # disable early inlining
12386                      -fdisable-tree-einline
12387                   # disable ipa inlining
12388                      -fdisable-ipa-inline
12389                   # enable tree full unroll
12390                      -fenable-tree-unroll
12391
12392       -fchecking
12393       -fchecking=n
12394           Enable internal consistency checking.  The default depends on the
12395           compiler configuration.  -fchecking=2 enables further internal
12396           consistency checking that might affect code generation.
12397
12398       -frandom-seed=string
12399           This option provides a seed that GCC uses in place of random
12400           numbers in generating certain symbol names that have to be
12401           different in every compiled file.  It is also used to place unique
12402           stamps in coverage data files and the object files that produce
12403           them.  You can use the -frandom-seed option to produce reproducibly
12404           identical object files.
12405
12406           The string can either be a number (decimal, octal or hex) or an
12407           arbitrary string (in which case it's converted to a number by
12408           computing CRC32).
12409
12410           The string should be different for every file you compile.
12411
12412       -save-temps
12413       -save-temps=cwd
12414           Store the usual "temporary" intermediate files permanently; place
12415           them in the current directory and name them based on the source
12416           file.  Thus, compiling foo.c with -c -save-temps produces files
12417           foo.i and foo.s, as well as foo.o.  This creates a preprocessed
12418           foo.i output file even though the compiler now normally uses an
12419           integrated preprocessor.
12420
12421           When used in combination with the -x command-line option,
12422           -save-temps is sensible enough to avoid over writing an input
12423           source file with the same extension as an intermediate file.  The
12424           corresponding intermediate file may be obtained by renaming the
12425           source file before using -save-temps.
12426
12427           If you invoke GCC in parallel, compiling several different source
12428           files that share a common base name in different subdirectories or
12429           the same source file compiled for multiple output destinations, it
12430           is likely that the different parallel compilers will interfere with
12431           each other, and overwrite the temporary files.  For instance:
12432
12433                   gcc -save-temps -o outdir1/foo.o indir1/foo.c&
12434                   gcc -save-temps -o outdir2/foo.o indir2/foo.c&
12435
12436           may result in foo.i and foo.o being written to simultaneously by
12437           both compilers.
12438
12439       -save-temps=obj
12440           Store the usual "temporary" intermediate files permanently.  If the
12441           -o option is used, the temporary files are based on the object
12442           file.  If the -o option is not used, the -save-temps=obj switch
12443           behaves like -save-temps.
12444
12445           For example:
12446
12447                   gcc -save-temps=obj -c foo.c
12448                   gcc -save-temps=obj -c bar.c -o dir/xbar.o
12449                   gcc -save-temps=obj foobar.c -o dir2/yfoobar
12450
12451           creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i,
12452           dir2/yfoobar.s, and dir2/yfoobar.o.
12453
12454       -time[=file]
12455           Report the CPU time taken by each subprocess in the compilation
12456           sequence.  For C source files, this is the compiler proper and
12457           assembler (plus the linker if linking is done).
12458
12459           Without the specification of an output file, the output looks like
12460           this:
12461
12462                   # cc1 0.12 0.01
12463                   # as 0.00 0.01
12464
12465           The first number on each line is the "user time", that is time
12466           spent executing the program itself.  The second number is "system
12467           time", time spent executing operating system routines on behalf of
12468           the program.  Both numbers are in seconds.
12469
12470           With the specification of an output file, the output is appended to
12471           the named file, and it looks like this:
12472
12473                   0.12 0.01 cc1 <options>
12474                   0.00 0.01 as <options>
12475
12476           The "user time" and the "system time" are moved before the program
12477           name, and the options passed to the program are displayed, so that
12478           one can later tell what file was being compiled, and with which
12479           options.
12480
12481       -fdump-final-insns[=file]
12482           Dump the final internal representation (RTL) to file.  If the
12483           optional argument is omitted (or if file is "."), the name of the
12484           dump file is determined by appending ".gkd" to the compilation
12485           output file name.
12486
12487       -fcompare-debug[=opts]
12488           If no error occurs during compilation, run the compiler a second
12489           time, adding opts and -fcompare-debug-second to the arguments
12490           passed to the second compilation.  Dump the final internal
12491           representation in both compilations, and print an error if they
12492           differ.
12493
12494           If the equal sign is omitted, the default -gtoggle is used.
12495
12496           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
12497           and nonzero, implicitly enables -fcompare-debug.  If
12498           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
12499           it is used for opts, otherwise the default -gtoggle is used.
12500
12501           -fcompare-debug=, with the equal sign but without opts, is
12502           equivalent to -fno-compare-debug, which disables the dumping of the
12503           final representation and the second compilation, preventing even
12504           GCC_COMPARE_DEBUG from taking effect.
12505
12506           To verify full coverage during -fcompare-debug testing, set
12507           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
12508           rejects as an invalid option in any actual compilation (rather than
12509           preprocessing, assembly or linking).  To get just a warning,
12510           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
12511           will do.
12512
12513       -fcompare-debug-second
12514           This option is implicitly passed to the compiler for the second
12515           compilation requested by -fcompare-debug, along with options to
12516           silence warnings, and omitting other options that would cause the
12517           compiler to produce output to files or to standard output as a side
12518           effect.  Dump files and preserved temporary files are renamed so as
12519           to contain the ".gk" additional extension during the second
12520           compilation, to avoid overwriting those generated by the first.
12521
12522           When this option is passed to the compiler driver, it causes the
12523           first compilation to be skipped, which makes it useful for little
12524           other than debugging the compiler proper.
12525
12526       -gtoggle
12527           Turn off generation of debug info, if leaving out this option
12528           generates it, or turn it on at level 2 otherwise.  The position of
12529           this argument in the command line does not matter; it takes effect
12530           after all other options are processed, and it does so only once, no
12531           matter how many times it is given.  This is mainly intended to be
12532           used with -fcompare-debug.
12533
12534       -fvar-tracking-assignments-toggle
12535           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
12536           toggles -g.
12537
12538       -Q  Makes the compiler print out each function name as it is compiled,
12539           and print some statistics about each pass when it finishes.
12540
12541       -ftime-report
12542           Makes the compiler print some statistics about the time consumed by
12543           each pass when it finishes.
12544
12545       -ftime-report-details
12546           Record the time consumed by infrastructure parts separately for
12547           each pass.
12548
12549       -fira-verbose=n
12550           Control the verbosity of the dump file for the integrated register
12551           allocator.  The default value is 5.  If the value n is greater or
12552           equal to 10, the dump output is sent to stderr using the same
12553           format as n minus 10.
12554
12555       -flto-report
12556           Prints a report with internal details on the workings of the link-
12557           time optimizer.  The contents of this report vary from version to
12558           version.  It is meant to be useful to GCC developers when
12559           processing object files in LTO mode (via -flto).
12560
12561           Disabled by default.
12562
12563       -flto-report-wpa
12564           Like -flto-report, but only print for the WPA phase of Link Time
12565           Optimization.
12566
12567       -fmem-report
12568           Makes the compiler print some statistics about permanent memory
12569           allocation when it finishes.
12570
12571       -fmem-report-wpa
12572           Makes the compiler print some statistics about permanent memory
12573           allocation for the WPA phase only.
12574
12575       -fpre-ipa-mem-report
12576       -fpost-ipa-mem-report
12577           Makes the compiler print some statistics about permanent memory
12578           allocation before or after interprocedural optimization.
12579
12580       -fprofile-report
12581           Makes the compiler print some statistics about consistency of the
12582           (estimated) profile and effect of individual passes.
12583
12584       -fstack-usage
12585           Makes the compiler output stack usage information for the program,
12586           on a per-function basis.  The filename for the dump is made by
12587           appending .su to the auxname.  auxname is generated from the name
12588           of the output file, if explicitly specified and it is not an
12589           executable, otherwise it is the basename of the source file.  An
12590           entry is made up of three fields:
12591
12592           *   The name of the function.
12593
12594           *   A number of bytes.
12595
12596           *   One or more qualifiers: "static", "dynamic", "bounded".
12597
12598           The qualifier "static" means that the function manipulates the
12599           stack statically: a fixed number of bytes are allocated for the
12600           frame on function entry and released on function exit; no stack
12601           adjustments are otherwise made in the function.  The second field
12602           is this fixed number of bytes.
12603
12604           The qualifier "dynamic" means that the function manipulates the
12605           stack dynamically: in addition to the static allocation described
12606           above, stack adjustments are made in the body of the function, for
12607           example to push/pop arguments around function calls.  If the
12608           qualifier "bounded" is also present, the amount of these
12609           adjustments is bounded at compile time and the second field is an
12610           upper bound of the total amount of stack used by the function.  If
12611           it is not present, the amount of these adjustments is not bounded
12612           at compile time and the second field only represents the bounded
12613           part.
12614
12615       -fstats
12616           Emit statistics about front-end processing at the end of the
12617           compilation.  This option is supported only by the C++ front end,
12618           and the information is generally only useful to the G++ development
12619           team.
12620
12621       -fdbg-cnt-list
12622           Print the name and the counter upper bound for all debug counters.
12623
12624       -fdbg-cnt=counter-value-list
12625           Set the internal debug counter upper bound.  counter-value-list is
12626           a comma-separated list of name:value pairs which sets the upper
12627           bound of each debug counter name to value.  All debug counters have
12628           the initial upper bound of "UINT_MAX"; thus "dbg_cnt" returns true
12629           always unless the upper bound is set by this option.  For example,
12630           with -fdbg-cnt=dce:10,tail_call:0, "dbg_cnt(dce)" returns true only
12631           for first 10 invocations.
12632
12633       -print-file-name=library
12634           Print the full absolute name of the library file library that would
12635           be used when linking---and don't do anything else.  With this
12636           option, GCC does not compile or link anything; it just prints the
12637           file name.
12638
12639       -print-multi-directory
12640           Print the directory name corresponding to the multilib selected by
12641           any other switches present in the command line.  This directory is
12642           supposed to exist in GCC_EXEC_PREFIX.
12643
12644       -print-multi-lib
12645           Print the mapping from multilib directory names to compiler
12646           switches that enable them.  The directory name is separated from
12647           the switches by ;, and each switch starts with an @ instead of the
12648           -, without spaces between multiple switches.  This is supposed to
12649           ease shell processing.
12650
12651       -print-multi-os-directory
12652           Print the path to OS libraries for the selected multilib, relative
12653           to some lib subdirectory.  If OS libraries are present in the lib
12654           subdirectory and no multilibs are used, this is usually just ., if
12655           OS libraries are present in libsuffix sibling directories this
12656           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
12657           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
12658           or ev6.
12659
12660       -print-multiarch
12661           Print the path to OS libraries for the selected multiarch, relative
12662           to some lib subdirectory.
12663
12664       -print-prog-name=program
12665           Like -print-file-name, but searches for a program such as cpp.
12666
12667       -print-libgcc-file-name
12668           Same as -print-file-name=libgcc.a.
12669
12670           This is useful when you use -nostdlib or -nodefaultlibs but you do
12671           want to link with libgcc.a.  You can do:
12672
12673                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`
12674
12675       -print-search-dirs
12676           Print the name of the configured installation directory and a list
12677           of program and library directories gcc searches---and don't do
12678           anything else.
12679
12680           This is useful when gcc prints the error message installation
12681           problem, cannot exec cpp0: No such file or directory.  To resolve
12682           this you either need to put cpp0 and the other compiler components
12683           where gcc expects to find them, or you can set the environment
12684           variable GCC_EXEC_PREFIX to the directory where you installed them.
12685           Don't forget the trailing /.
12686
12687       -print-sysroot
12688           Print the target sysroot directory that is used during compilation.
12689           This is the target sysroot specified either at configure time or
12690           using the --sysroot option, possibly with an extra suffix that
12691           depends on compilation options.  If no target sysroot is specified,
12692           the option prints nothing.
12693
12694       -print-sysroot-headers-suffix
12695           Print the suffix added to the target sysroot when searching for
12696           headers, or give an error if the compiler is not configured with
12697           such a suffix---and don't do anything else.
12698
12699       -dumpmachine
12700           Print the compiler's target machine (for example,
12701           i686-pc-linux-gnu)---and don't do anything else.
12702
12703       -dumpversion
12704           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and
12705           don't do anything else.  This is the compiler version used in
12706           filesystem paths, specs, can be depending on how the compiler has
12707           been configured just a single number (major version), two numbers
12708           separated by dot (major and minor version) or three numbers
12709           separated by dots (major, minor and patchlevel version).
12710
12711       -dumpfullversion
12712           Print the full compiler version, always 3 numbers separated by
12713           dots, major, minor and patchlevel version.
12714
12715       -dumpspecs
12716           Print the compiler's built-in specs---and don't do anything else.
12717           (This is used when GCC itself is being built.)
12718
12719   Machine-Dependent Options
12720       Each target machine supported by GCC can have its own options---for
12721       example, to allow you to compile for a particular processor variant or
12722       ABI, or to control optimizations specific to that machine.  By
12723       convention, the names of machine-specific options start with -m.
12724
12725       Some configurations of the compiler also support additional target-
12726       specific options, usually for compatibility with other compilers on the
12727       same platform.
12728
12729   AArch64 Options
12730       These options are defined for AArch64 implementations:
12731
12732       -mabi=name
12733           Generate code for the specified data model.  Permissible values are
12734           ilp32 for SysV-like data model where int, long int and pointers are
12735           32 bits, and lp64 for SysV-like data model where int is 32 bits,
12736           but long int and pointers are 64 bits.
12737
12738           The default depends on the specific target configuration.  Note
12739           that the LP64 and ILP32 ABIs are not link-compatible; you must
12740           compile your entire program with the same ABI, and link with a
12741           compatible set of libraries.
12742
12743       -mbig-endian
12744           Generate big-endian code.  This is the default when GCC is
12745           configured for an aarch64_be-*-* target.
12746
12747       -mgeneral-regs-only
12748           Generate code which uses only the general-purpose registers.  This
12749           will prevent the compiler from using floating-point and Advanced
12750           SIMD registers but will not impose any restrictions on the
12751           assembler.
12752
12753       -mlittle-endian
12754           Generate little-endian code.  This is the default when GCC is
12755           configured for an aarch64-*-* but not an aarch64_be-*-* target.
12756
12757       -mcmodel=tiny
12758           Generate code for the tiny code model.  The program and its
12759           statically defined symbols must be within 1MB of each other.
12760           Programs can be statically or dynamically linked.
12761
12762       -mcmodel=small
12763           Generate code for the small code model.  The program and its
12764           statically defined symbols must be within 4GB of each other.
12765           Programs can be statically or dynamically linked.  This is the
12766           default code model.
12767
12768       -mcmodel=large
12769           Generate code for the large code model.  This makes no assumptions
12770           about addresses and sizes of sections.  Programs can be statically
12771           linked only.
12772
12773       -mstrict-align
12774           Avoid generating memory accesses that may not be aligned on a
12775           natural object boundary as described in the architecture
12776           specification.
12777
12778       -momit-leaf-frame-pointer
12779       -mno-omit-leaf-frame-pointer
12780           Omit or keep the frame pointer in leaf functions.  The former
12781           behavior is the default.
12782
12783       -mtls-dialect=desc
12784           Use TLS descriptors as the thread-local storage mechanism for
12785           dynamic accesses of TLS variables.  This is the default.
12786
12787       -mtls-dialect=traditional
12788           Use traditional TLS as the thread-local storage mechanism for
12789           dynamic accesses of TLS variables.
12790
12791       -mtls-size=size
12792           Specify bit size of immediate TLS offsets.  Valid values are 12,
12793           24, 32, 48.  This option requires binutils 2.26 or newer.
12794
12795       -mfix-cortex-a53-835769
12796       -mno-fix-cortex-a53-835769
12797           Enable or disable the workaround for the ARM Cortex-A53 erratum
12798           number 835769.  This involves inserting a NOP instruction between
12799           memory instructions and 64-bit integer multiply-accumulate
12800           instructions.
12801
12802       -mfix-cortex-a53-843419
12803       -mno-fix-cortex-a53-843419
12804           Enable or disable the workaround for the ARM Cortex-A53 erratum
12805           number 843419.  This erratum workaround is made at link time and
12806           this will only pass the corresponding flag to the linker.
12807
12808       -mlow-precision-recip-sqrt
12809       -mno-low-precision-recip-sqrt
12810           Enable or disable the reciprocal square root approximation.  This
12811           option only has an effect if -ffast-math or
12812           -funsafe-math-optimizations is used as well.  Enabling this reduces
12813           precision of reciprocal square root results to about 16 bits for
12814           single precision and to 32 bits for double precision.
12815
12816       -mlow-precision-sqrt
12817       -mno-low-precision-sqrt
12818           Enable or disable the square root approximation.  This option only
12819           has an effect if -ffast-math or -funsafe-math-optimizations is used
12820           as well.  Enabling this reduces precision of square root results to
12821           about 16 bits for single precision and to 32 bits for double
12822           precision.  If enabled, it implies -mlow-precision-recip-sqrt.
12823
12824       -mlow-precision-div
12825       -mno-low-precision-div
12826           Enable or disable the division approximation.  This option only has
12827           an effect if -ffast-math or -funsafe-math-optimizations is used as
12828           well.  Enabling this reduces precision of division results to about
12829           16 bits for single precision and to 32 bits for double precision.
12830
12831       -march=name
12832           Specify the name of the target architecture and, optionally, one or
12833           more feature modifiers.  This option has the form
12834           -march=arch{+[no]feature}*.
12835
12836           The permissible values for arch are armv8-a, armv8.1-a, armv8.2-a,
12837           armv8.3-a or armv8.4-a or native.
12838
12839           The value armv8.4-a implies armv8.3-a and enables compiler support
12840           for the ARMv8.4-A architecture extensions.
12841
12842           The value armv8.3-a implies armv8.2-a and enables compiler support
12843           for the ARMv8.3-A architecture extensions.
12844
12845           The value armv8.2-a implies armv8.1-a and enables compiler support
12846           for the ARMv8.2-A architecture extensions.
12847
12848           The value armv8.1-a implies armv8-a and enables compiler support
12849           for the ARMv8.1-A architecture extension.  In particular, it
12850           enables the +crc, +lse, and +rdma features.
12851
12852           The value native is available on native AArch64 GNU/Linux and
12853           causes the compiler to pick the architecture of the host system.
12854           This option has no effect if the compiler is unable to recognize
12855           the architecture of the host system,
12856
12857           The permissible values for feature are listed in the sub-section on
12858           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
12859           Where conflicting feature modifiers are specified, the right-most
12860           feature is used.
12861
12862           GCC uses name to determine what kind of instructions it can emit
12863           when generating assembly code.  If -march is specified without
12864           either of -mtune or -mcpu also being specified, the code is tuned
12865           to perform well across a range of target processors implementing
12866           the target architecture.
12867
12868       -mtune=name
12869           Specify the name of the target processor for which GCC should tune
12870           the performance of the code.  Permissible values for this option
12871           are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
12872           cortex-a72, cortex-a73, cortex-a75, exynos-m1, falkor, qdf24xx,
12873           saphira, xgene1, vulcan, thunderx, thunderxt88, thunderxt88p1,
12874           thunderxt81, thunderxt83, thunderx2t99, cortex-a57.cortex-a53,
12875           cortex-a72.cortex-a53, cortex-a73.cortex-a35,
12876           cortex-a73.cortex-a53, cortex-a75.cortex-a55, native.
12877
12878           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
12879           cortex-a73.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55
12880           specify that GCC should tune for a big.LITTLE system.
12881
12882           Additionally on native AArch64 GNU/Linux systems the value native
12883           tunes performance to the host system.  This option has no effect if
12884           the compiler is unable to recognize the processor of the host
12885           system.
12886
12887           Where none of -mtune=, -mcpu= or -march= are specified, the code is
12888           tuned to perform well across a range of target processors.
12889
12890           This option cannot be suffixed by feature modifiers.
12891
12892       -mcpu=name
12893           Specify the name of the target processor, optionally suffixed by
12894           one or more feature modifiers.  This option has the form
12895           -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
12896           the same as those available for -mtune.  The permissible values for
12897           feature are documented in the sub-section on
12898           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
12899           Where conflicting feature modifiers are specified, the right-most
12900           feature is used.
12901
12902           GCC uses name to determine what kind of instructions it can emit
12903           when generating assembly code (as if by -march) and to determine
12904           the target processor for which to tune for performance (as if by
12905           -mtune).  Where this option is used in conjunction with -march or
12906           -mtune, those options take precedence over the appropriate part of
12907           this option.
12908
12909       -moverride=string
12910           Override tuning decisions made by the back-end in response to a
12911           -mtune= switch.  The syntax, semantics, and accepted values for
12912           string in this option are not guaranteed to be consistent across
12913           releases.
12914
12915           This option is only intended to be useful when developing GCC.
12916
12917       -mverbose-cost-dump
12918           Enable verbose cost model dumping in the debug dump files.  This
12919           option is provided for use in debugging the compiler.
12920
12921       -mpc-relative-literal-loads
12922       -mno-pc-relative-literal-loads
12923           Enable or disable PC-relative literal loads.  With this option
12924           literal pools are accessed using a single instruction and emitted
12925           after each function.  This limits the maximum size of functions to
12926           1MB.  This is enabled by default for -mcmodel=tiny.
12927
12928       -msign-return-address=scope
12929           Select the function scope on which return address signing will be
12930           applied.  Permissible values are none, which disables return
12931           address signing, non-leaf, which enables pointer signing for
12932           functions which are not leaf functions, and all, which enables
12933           pointer signing for all functions.  The default value is none.
12934
12935       -msve-vector-bits=bits
12936           Specify the number of bits in an SVE vector register.  This option
12937           only has an effect when SVE is enabled.
12938
12939           GCC supports two forms of SVE code generation: "vector-length
12940           agnostic" output that works with any size of vector register and
12941           "vector-length specific" output that only works when the vector
12942           registers are a particular size.  Replacing bits with scalable
12943           selects vector-length agnostic output while replacing it with a
12944           number selects vector-length specific output.  The possible lengths
12945           in the latter case are: 128, 256, 512, 1024 and 2048.  scalable is
12946           the default.
12947
12948           At present, -msve-vector-bits=128 produces the same output as
12949           -msve-vector-bits=scalable.
12950
12951       -march and -mcpu Feature Modifiers
12952
12953       Feature modifiers used with -march and -mcpu can be any of the
12954       following and their inverses nofeature:
12955
12956       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.
12957
12958       crypto
12959           Enable Crypto extension.  This also enables Advanced SIMD and
12960           floating-point instructions.
12961
12962       fp  Enable floating-point instructions.  This is on by default for all
12963           possible values for options -march and -mcpu.
12964
12965       simd
12966           Enable Advanced SIMD instructions.  This also enables floating-
12967           point instructions.  This is on by default for all possible values
12968           for options -march and -mcpu.
12969
12970       sve Enable Scalable Vector Extension instructions.  This also enables
12971           Advanced SIMD and floating-point instructions.
12972
12973       lse Enable Large System Extension instructions.  This is on by default
12974           for -march=armv8.1-a.
12975
12976       rdma
12977           Enable Round Double Multiply Accumulate instructions.  This is on
12978           by default for -march=armv8.1-a.
12979
12980       fp16
12981           Enable FP16 extension.  This also enables floating-point
12982           instructions.
12983
12984       fp16fml
12985           Enable FP16 fmla extension.  This also enables FP16 extensions and
12986           floating-point instructions. This option is enabled by default for
12987           -march=armv8.4-a. Use of this option with architectures prior to
12988           Armv8.2-A is not supported.
12989
12990       rcpc
12991           Enable the RcPc extension.  This does not change code generation
12992           from GCC, but is passed on to the assembler, enabling inline asm
12993           statements to use instructions from the RcPc extension.
12994
12995       dotprod
12996           Enable the Dot Product extension.  This also enables Advanced SIMD
12997           instructions.
12998
12999       aes Enable the Armv8-a aes and pmull crypto extension.  This also
13000           enables Advanced SIMD instructions.
13001
13002       sha2
13003           Enable the Armv8-a sha2 crypto extension.  This also enables
13004           Advanced SIMD instructions.
13005
13006       sha3
13007           Enable the sha512 and sha3 crypto extension.  This also enables
13008           Advanced SIMD instructions. Use of this option with architectures
13009           prior to Armv8.2-A is not supported.
13010
13011       sm4 Enable the sm3 and sm4 crypto extension.  This also enables
13012           Advanced SIMD instructions.  Use of this option with architectures
13013           prior to Armv8.2-A is not supported.
13014
13015       Feature crypto implies aes, sha2, and simd, which implies fp.
13016       Conversely, nofp implies nosimd, which implies nocrypto, noaes and
13017       nosha2.
13018
13019   Adapteva Epiphany Options
13020       These -m options are defined for Adapteva Epiphany:
13021
13022       -mhalf-reg-file
13023           Don't allocate any register in the range "r32"..."r63".  That
13024           allows code to run on hardware variants that lack these registers.
13025
13026       -mprefer-short-insn-regs
13027           Preferentially allocate registers that allow short instruction
13028           generation.  This can result in increased instruction count, so
13029           this may either reduce or increase overall code size.
13030
13031       -mbranch-cost=num
13032           Set the cost of branches to roughly num "simple" instructions.
13033           This cost is only a heuristic and is not guaranteed to produce
13034           consistent results across releases.
13035
13036       -mcmove
13037           Enable the generation of conditional moves.
13038
13039       -mnops=num
13040           Emit num NOPs before every other generated instruction.
13041
13042       -mno-soft-cmpsf
13043           For single-precision floating-point comparisons, emit an "fsub"
13044           instruction and test the flags.  This is faster than a software
13045           comparison, but can get incorrect results in the presence of NaNs,
13046           or when two different small numbers are compared such that their
13047           difference is calculated as zero.  The default is -msoft-cmpsf,
13048           which uses slower, but IEEE-compliant, software comparisons.
13049
13050       -mstack-offset=num
13051           Set the offset between the top of the stack and the stack pointer.
13052           E.g., a value of 8 means that the eight bytes in the range
13053           "sp+0...sp+7" can be used by leaf functions without stack
13054           allocation.  Values other than 8 or 16 are untested and unlikely to
13055           work.  Note also that this option changes the ABI; compiling a
13056           program with a different stack offset than the libraries have been
13057           compiled with generally does not work.  This option can be useful
13058           if you want to evaluate if a different stack offset would give you
13059           better code, but to actually use a different stack offset to build
13060           working programs, it is recommended to configure the toolchain with
13061           the appropriate --with-stack-offset=num option.
13062
13063       -mno-round-nearest
13064           Make the scheduler assume that the rounding mode has been set to
13065           truncating.  The default is -mround-nearest.
13066
13067       -mlong-calls
13068           If not otherwise specified by an attribute, assume all calls might
13069           be beyond the offset range of the "b" / "bl" instructions, and
13070           therefore load the function address into a register before
13071           performing a (otherwise direct) call.  This is the default.
13072
13073       -mshort-calls
13074           If not otherwise specified by an attribute, assume all direct calls
13075           are in the range of the "b" / "bl" instructions, so use these
13076           instructions for direct calls.  The default is -mlong-calls.
13077
13078       -msmall16
13079           Assume addresses can be loaded as 16-bit unsigned values.  This
13080           does not apply to function addresses for which -mlong-calls
13081           semantics are in effect.
13082
13083       -mfp-mode=mode
13084           Set the prevailing mode of the floating-point unit.  This
13085           determines the floating-point mode that is provided and expected at
13086           function call and return time.  Making this mode match the mode you
13087           predominantly need at function start can make your programs smaller
13088           and faster by avoiding unnecessary mode switches.
13089
13090           mode can be set to one the following values:
13091
13092           caller
13093               Any mode at function entry is valid, and retained or restored
13094               when the function returns, and when it calls other functions.
13095               This mode is useful for compiling libraries or other
13096               compilation units you might want to incorporate into different
13097               programs with different prevailing FPU modes, and the
13098               convenience of being able to use a single object file outweighs
13099               the size and speed overhead for any extra mode switching that
13100               might be needed, compared with what would be needed with a more
13101               specific choice of prevailing FPU mode.
13102
13103           truncate
13104               This is the mode used for floating-point calculations with
13105               truncating (i.e. round towards zero) rounding mode.  That
13106               includes conversion from floating point to integer.
13107
13108           round-nearest
13109               This is the mode used for floating-point calculations with
13110               round-to-nearest-or-even rounding mode.
13111
13112           int This is the mode used to perform integer calculations in the
13113               FPU, e.g.  integer multiply, or integer multiply-and-
13114               accumulate.
13115
13116           The default is -mfp-mode=caller
13117
13118       -mnosplit-lohi
13119       -mno-postinc
13120       -mno-postmodify
13121           Code generation tweaks that disable, respectively, splitting of
13122           32-bit loads, generation of post-increment addresses, and
13123           generation of post-modify addresses.  The defaults are msplit-lohi,
13124           -mpost-inc, and -mpost-modify.
13125
13126       -mnovect-double
13127           Change the preferred SIMD mode to SImode.  The default is
13128           -mvect-double, which uses DImode as preferred SIMD mode.
13129
13130       -max-vect-align=num
13131           The maximum alignment for SIMD vector mode types.  num may be 4 or
13132           8.  The default is 8.  Note that this is an ABI change, even though
13133           many library function interfaces are unaffected if they don't use
13134           SIMD vector modes in places that affect size and/or alignment of
13135           relevant types.
13136
13137       -msplit-vecmove-early
13138           Split vector moves into single word moves before reload.  In theory
13139           this can give better register allocation, but so far the reverse
13140           seems to be generally the case.
13141
13142       -m1reg-reg
13143           Specify a register to hold the constant -1, which makes loading
13144           small negative constants and certain bitmasks faster.  Allowable
13145           values for reg are r43 and r63, which specify use of that register
13146           as a fixed register, and none, which means that no register is used
13147           for this purpose.  The default is -m1reg-none.
13148
13149   ARC Options
13150       The following options control the architecture variant for which code
13151       is being compiled:
13152
13153       -mbarrel-shifter
13154           Generate instructions supported by barrel shifter.  This is the
13155           default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.
13156
13157       -mjli-always
13158           Force to call a function using jli_s instruction.  This option is
13159           valid only for ARCv2 architecture.
13160
13161       -mcpu=cpu
13162           Set architecture type, register usage, and instruction scheduling
13163           parameters for cpu.  There are also shortcut alias options
13164           available for backward compatibility and convenience.  Supported
13165           values for cpu are
13166
13167           arc600
13168               Compile for ARC600.  Aliases: -mA6, -mARC600.
13169
13170           arc601
13171               Compile for ARC601.  Alias: -mARC601.
13172
13173           arc700
13174               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the
13175               default when configured with --with-cpu=arc700.
13176
13177           arcem
13178               Compile for ARC EM.
13179
13180           archs
13181               Compile for ARC HS.
13182
13183           em  Compile for ARC EM CPU with no hardware extensions.
13184
13185           em4 Compile for ARC EM4 CPU.
13186
13187           em4_dmips
13188               Compile for ARC EM4 DMIPS CPU.
13189
13190           em4_fpus
13191               Compile for ARC EM4 DMIPS CPU with the single-precision
13192               floating-point extension.
13193
13194           em4_fpuda
13195               Compile for ARC EM4 DMIPS CPU with single-precision floating-
13196               point and double assist instructions.
13197
13198           hs  Compile for ARC HS CPU with no hardware extensions except the
13199               atomic instructions.
13200
13201           hs34
13202               Compile for ARC HS34 CPU.
13203
13204           hs38
13205               Compile for ARC HS38 CPU.
13206
13207           hs38_linux
13208               Compile for ARC HS38 CPU with all hardware extensions on.
13209
13210           arc600_norm
13211               Compile for ARC 600 CPU with "norm" instructions enabled.
13212
13213           arc600_mul32x16
13214               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
13215               instructions enabled.
13216
13217           arc600_mul64
13218               Compile for ARC 600 CPU with "norm" and "mul64"-family
13219               instructions enabled.
13220
13221           arc601_norm
13222               Compile for ARC 601 CPU with "norm" instructions enabled.
13223
13224           arc601_mul32x16
13225               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
13226               instructions enabled.
13227
13228           arc601_mul64
13229               Compile for ARC 601 CPU with "norm" and "mul64"-family
13230               instructions enabled.
13231
13232           nps400
13233               Compile for ARC 700 on NPS400 chip.
13234
13235           em_mini
13236               Compile for ARC EM minimalist configuration featuring reduced
13237               register set.
13238
13239       -mdpfp
13240       -mdpfp-compact
13241           Generate double-precision FPX instructions, tuned for the compact
13242           implementation.
13243
13244       -mdpfp-fast
13245           Generate double-precision FPX instructions, tuned for the fast
13246           implementation.
13247
13248       -mno-dpfp-lrsr
13249           Disable "lr" and "sr" instructions from using FPX extension aux
13250           registers.
13251
13252       -mea
13253           Generate extended arithmetic instructions.  Currently only "divaw",
13254           "adds", "subs", and "sat16" are supported.  This is always enabled
13255           for -mcpu=ARC700.
13256
13257       -mno-mpy
13258           Do not generate "mpy"-family instructions for ARC700.  This option
13259           is deprecated.
13260
13261       -mmul32x16
13262           Generate 32x16-bit multiply and multiply-accumulate instructions.
13263
13264       -mmul64
13265           Generate "mul64" and "mulu64" instructions.  Only valid for
13266           -mcpu=ARC600.
13267
13268       -mnorm
13269           Generate "norm" instructions.  This is the default if -mcpu=ARC700
13270           is in effect.
13271
13272       -mspfp
13273       -mspfp-compact
13274           Generate single-precision FPX instructions, tuned for the compact
13275           implementation.
13276
13277       -mspfp-fast
13278           Generate single-precision FPX instructions, tuned for the fast
13279           implementation.
13280
13281       -msimd
13282           Enable generation of ARC SIMD instructions via target-specific
13283           builtins.  Only valid for -mcpu=ARC700.
13284
13285       -msoft-float
13286           This option ignored; it is provided for compatibility purposes
13287           only.  Software floating-point code is emitted by default, and this
13288           default can overridden by FPX options; -mspfp, -mspfp-compact, or
13289           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
13290           -mdpfp-fast for double precision.
13291
13292       -mswap
13293           Generate "swap" instructions.
13294
13295       -matomic
13296           This enables use of the locked load/store conditional extension to
13297           implement atomic memory built-in functions.  Not available for ARC
13298           6xx or ARC EM cores.
13299
13300       -mdiv-rem
13301           Enable "div" and "rem" instructions for ARCv2 cores.
13302
13303       -mcode-density
13304           Enable code density instructions for ARC EM.  This option is on by
13305           default for ARC HS.
13306
13307       -mll64
13308           Enable double load/store operations for ARC HS cores.
13309
13310       -mtp-regno=regno
13311           Specify thread pointer register number.
13312
13313       -mmpy-option=multo
13314           Compile ARCv2 code with a multiplier design option.  You can
13315           specify the option using either a string or numeric value for
13316           multo.  wlh1 is the default value.  The recognized values are:
13317
13318           0
13319           none
13320               No multiplier available.
13321
13322           1
13323           w   16x16 multiplier, fully pipelined.  The following instructions
13324               are enabled: "mpyw" and "mpyuw".
13325
13326           2
13327           wlh1
13328               32x32 multiplier, fully pipelined (1 stage).  The following
13329               instructions are additionally enabled: "mpy", "mpyu", "mpym",
13330               "mpymu", and "mpy_s".
13331
13332           3
13333           wlh2
13334               32x32 multiplier, fully pipelined (2 stages).  The following
13335               instructions are additionally enabled: "mpy", "mpyu", "mpym",
13336               "mpymu", and "mpy_s".
13337
13338           4
13339           wlh3
13340               Two 16x16 multipliers, blocking, sequential.  The following
13341               instructions are additionally enabled: "mpy", "mpyu", "mpym",
13342               "mpymu", and "mpy_s".
13343
13344           5
13345           wlh4
13346               One 16x16 multiplier, blocking, sequential.  The following
13347               instructions are additionally enabled: "mpy", "mpyu", "mpym",
13348               "mpymu", and "mpy_s".
13349
13350           6
13351           wlh5
13352               One 32x4 multiplier, blocking, sequential.  The following
13353               instructions are additionally enabled: "mpy", "mpyu", "mpym",
13354               "mpymu", and "mpy_s".
13355
13356           7
13357           plus_dmpy
13358               ARC HS SIMD support.
13359
13360           8
13361           plus_macd
13362               ARC HS SIMD support.
13363
13364           9
13365           plus_qmacw
13366               ARC HS SIMD support.
13367
13368           This option is only available for ARCv2 cores.
13369
13370       -mfpu=fpu
13371           Enables support for specific floating-point hardware extensions for
13372           ARCv2 cores.  Supported values for fpu are:
13373
13374           fpus
13375               Enables support for single-precision floating-point hardware
13376               extensions.
13377
13378           fpud
13379               Enables support for double-precision floating-point hardware
13380               extensions.  The single-precision floating-point extension is
13381               also enabled.  Not available for ARC EM.
13382
13383           fpuda
13384               Enables support for double-precision floating-point hardware
13385               extensions using double-precision assist instructions.  The
13386               single-precision floating-point extension is also enabled.
13387               This option is only available for ARC EM.
13388
13389           fpuda_div
13390               Enables support for double-precision floating-point hardware
13391               extensions using double-precision assist instructions.  The
13392               single-precision floating-point, square-root, and divide
13393               extensions are also enabled.  This option is only available for
13394               ARC EM.
13395
13396           fpuda_fma
13397               Enables support for double-precision floating-point hardware
13398               extensions using double-precision assist instructions.  The
13399               single-precision floating-point and fused multiply and add
13400               hardware extensions are also enabled.  This option is only
13401               available for ARC EM.
13402
13403           fpuda_all
13404               Enables support for double-precision floating-point hardware
13405               extensions using double-precision assist instructions.  All
13406               single-precision floating-point hardware extensions are also
13407               enabled.  This option is only available for ARC EM.
13408
13409           fpus_div
13410               Enables support for single-precision floating-point, square-
13411               root and divide hardware extensions.
13412
13413           fpud_div
13414               Enables support for double-precision floating-point, square-
13415               root and divide hardware extensions.  This option includes
13416               option fpus_div. Not available for ARC EM.
13417
13418           fpus_fma
13419               Enables support for single-precision floating-point and fused
13420               multiply and add hardware extensions.
13421
13422           fpud_fma
13423               Enables support for double-precision floating-point and fused
13424               multiply and add hardware extensions.  This option includes
13425               option fpus_fma.  Not available for ARC EM.
13426
13427           fpus_all
13428               Enables support for all single-precision floating-point
13429               hardware extensions.
13430
13431           fpud_all
13432               Enables support for all single- and double-precision floating-
13433               point hardware extensions.  Not available for ARC EM.
13434
13435       -mirq-ctrl-saved=register-range, blink, lp_count
13436           Specifies general-purposes registers that the processor
13437           automatically saves/restores on interrupt entry and exit.
13438           register-range is specified as two registers separated by a dash.
13439           The register range always starts with "r0", the upper limit is "fp"
13440           register.  blink and lp_count are optional.  This option is only
13441           valid for ARC EM and ARC HS cores.
13442
13443       -mrgf-banked-regs=number
13444           Specifies the number of registers replicated in second register
13445           bank on entry to fast interrupt.  Fast interrupts are interrupts
13446           with the highest priority level P0.  These interrupts save only PC
13447           and STATUS32 registers to avoid memory transactions during
13448           interrupt entry and exit sequences.  Use this option when you are
13449           using fast interrupts in an ARC V2 family processor.  Permitted
13450           values are 4, 8, 16, and 32.
13451
13452       -mlpc-width=width
13453           Specify the width of the "lp_count" register.  Valid values for
13454           width are 8, 16, 20, 24, 28 and 32 bits.  The default width is
13455           fixed to 32 bits.  If the width is less than 32, the compiler does
13456           not attempt to transform loops in your program to use the zero-
13457           delay loop mechanism unless it is known that the "lp_count"
13458           register can hold the required loop-counter value.  Depending on
13459           the width specified, the compiler and run-time library might
13460           continue to use the loop mechanism for various needs.  This option
13461           defines macro "__ARC_LPC_WIDTH__" with the value of width.
13462
13463       -mrf16
13464           This option instructs the compiler to generate code for a 16-entry
13465           register file.  This option defines the "__ARC_RF16__" preprocessor
13466           macro.
13467
13468       The following options are passed through to the assembler, and also
13469       define preprocessor macro symbols.
13470
13471       -mdsp-packa
13472           Passed down to the assembler to enable the DSP Pack A extensions.
13473           Also sets the preprocessor symbol "__Xdsp_packa".  This option is
13474           deprecated.
13475
13476       -mdvbf
13477           Passed down to the assembler to enable the dual Viterbi butterfly
13478           extension.  Also sets the preprocessor symbol "__Xdvbf".  This
13479           option is deprecated.
13480
13481       -mlock
13482           Passed down to the assembler to enable the locked load/store
13483           conditional extension.  Also sets the preprocessor symbol
13484           "__Xlock".
13485
13486       -mmac-d16
13487           Passed down to the assembler.  Also sets the preprocessor symbol
13488           "__Xxmac_d16".  This option is deprecated.
13489
13490       -mmac-24
13491           Passed down to the assembler.  Also sets the preprocessor symbol
13492           "__Xxmac_24".  This option is deprecated.
13493
13494       -mrtsc
13495           Passed down to the assembler to enable the 64-bit time-stamp
13496           counter extension instruction.  Also sets the preprocessor symbol
13497           "__Xrtsc".  This option is deprecated.
13498
13499       -mswape
13500           Passed down to the assembler to enable the swap byte ordering
13501           extension instruction.  Also sets the preprocessor symbol
13502           "__Xswape".
13503
13504       -mtelephony
13505           Passed down to the assembler to enable dual- and single-operand
13506           instructions for telephony.  Also sets the preprocessor symbol
13507           "__Xtelephony".  This option is deprecated.
13508
13509       -mxy
13510           Passed down to the assembler to enable the XY memory extension.
13511           Also sets the preprocessor symbol "__Xxy".
13512
13513       The following options control how the assembly code is annotated:
13514
13515       -misize
13516           Annotate assembler instructions with estimated addresses.
13517
13518       -mannotate-align
13519           Explain what alignment considerations lead to the decision to make
13520           an instruction short or long.
13521
13522       The following options are passed through to the linker:
13523
13524       -marclinux
13525           Passed through to the linker, to specify use of the "arclinux"
13526           emulation.  This option is enabled by default in tool chains built
13527           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
13528           profiling is not requested.
13529
13530       -marclinux_prof
13531           Passed through to the linker, to specify use of the "arclinux_prof"
13532           emulation.  This option is enabled by default in tool chains built
13533           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
13534           profiling is requested.
13535
13536       The following options control the semantics of generated code:
13537
13538       -mlong-calls
13539           Generate calls as register indirect calls, thus providing access to
13540           the full 32-bit address range.
13541
13542       -mmedium-calls
13543           Don't use less than 25-bit addressing range for calls, which is the
13544           offset available for an unconditional branch-and-link instruction.
13545           Conditional execution of function calls is suppressed, to allow use
13546           of the 25-bit range, rather than the 21-bit range with conditional
13547           branch-and-link.  This is the default for tool chains built for
13548           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.
13549
13550       -G num
13551           Put definitions of externally-visible data in a small data section
13552           if that data is no bigger than num bytes.  The default value of num
13553           is 4 for any ARC configuration, or 8 when we have double load/store
13554           operations.
13555
13556       -mno-sdata
13557           Do not generate sdata references.  This is the default for tool
13558           chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
13559           targets.
13560
13561       -mvolatile-cache
13562           Use ordinarily cached memory accesses for volatile references.
13563           This is the default.
13564
13565       -mno-volatile-cache
13566           Enable cache bypass for volatile references.
13567
13568       The following options fine tune code generation:
13569
13570       -malign-call
13571           Do alignment optimizations for call instructions.
13572
13573       -mauto-modify-reg
13574           Enable the use of pre/post modify with register displacement.
13575
13576       -mbbit-peephole
13577           Enable bbit peephole2.
13578
13579       -mno-brcc
13580           This option disables a target-specific pass in arc_reorg to
13581           generate compare-and-branch ("brcc") instructions.  It has no
13582           effect on generation of these instructions driven by the combiner
13583           pass.
13584
13585       -mcase-vector-pcrel
13586           Use PC-relative switch case tables to enable case table shortening.
13587           This is the default for -Os.
13588
13589       -mcompact-casesi
13590           Enable compact "casesi" pattern.  This is the default for -Os, and
13591           only available for ARCv1 cores.
13592
13593       -mno-cond-exec
13594           Disable the ARCompact-specific pass to generate conditional
13595           execution instructions.
13596
13597           Due to delay slot scheduling and interactions between operand
13598           numbers, literal sizes, instruction lengths, and the support for
13599           conditional execution, the target-independent pass to generate
13600           conditional execution is often lacking, so the ARC port has kept a
13601           special pass around that tries to find more conditional execution
13602           generation opportunities after register allocation, branch
13603           shortening, and delay slot scheduling have been done.  This pass
13604           generally, but not always, improves performance and code size, at
13605           the cost of extra compilation time, which is why there is an option
13606           to switch it off.  If you have a problem with call instructions
13607           exceeding their allowable offset range because they are
13608           conditionalized, you should consider using -mmedium-calls instead.
13609
13610       -mearly-cbranchsi
13611           Enable pre-reload use of the "cbranchsi" pattern.
13612
13613       -mexpand-adddi
13614           Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
13615           "adc" etc.  This option is deprecated.
13616
13617       -mindexed-loads
13618           Enable the use of indexed loads.  This can be problematic because
13619           some optimizers then assume that indexed stores exist, which is not
13620           the case.
13621
13622       -mlra
13623           Enable Local Register Allocation.  This is still experimental for
13624           ARC, so by default the compiler uses standard reload (i.e.
13625           -mno-lra).
13626
13627       -mlra-priority-none
13628           Don't indicate any priority for target registers.
13629
13630       -mlra-priority-compact
13631           Indicate target register priority for r0..r3 / r12..r15.
13632
13633       -mlra-priority-noncompact
13634           Reduce target register priority for r0..r3 / r12..r15.
13635
13636       -mno-millicode
13637           When optimizing for size (using -Os), prologues and epilogues that
13638           have to save or restore a large number of registers are often
13639           shortened by using call to a special function in libgcc; this is
13640           referred to as a millicode call.  As these calls can pose
13641           performance issues, and/or cause linking issues when linking in a
13642           nonstandard way, this option is provided to turn off millicode call
13643           generation.
13644
13645       -mmixed-code
13646           Tweak register allocation to help 16-bit instruction generation.
13647           This generally has the effect of decreasing the average instruction
13648           size while increasing the instruction count.
13649
13650       -mq-class
13651           Enable q instruction alternatives.  This is the default for -Os.
13652
13653       -mRcq
13654           Enable Rcq constraint handling.  Most short code generation depends
13655           on this.  This is the default.
13656
13657       -mRcw
13658           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends
13659           on this.  This is the default.
13660
13661       -msize-level=level
13662           Fine-tune size optimization with regards to instruction lengths and
13663           alignment.  The recognized values for level are:
13664
13665           0   No size optimization.  This level is deprecated and treated
13666               like 1.
13667
13668           1   Short instructions are used opportunistically.
13669
13670           2   In addition, alignment of loops and of code after barriers are
13671               dropped.
13672
13673           3   In addition, optional data alignment is dropped, and the option
13674               Os is enabled.
13675
13676           This defaults to 3 when -Os is in effect.  Otherwise, the behavior
13677           when this is not set is equivalent to level 1.
13678
13679       -mtune=cpu
13680           Set instruction scheduling parameters for cpu, overriding any
13681           implied by -mcpu=.
13682
13683           Supported values for cpu are
13684
13685           ARC600
13686               Tune for ARC600 CPU.
13687
13688           ARC601
13689               Tune for ARC601 CPU.
13690
13691           ARC700
13692               Tune for ARC700 CPU with standard multiplier block.
13693
13694           ARC700-xmac
13695               Tune for ARC700 CPU with XMAC block.
13696
13697           ARC725D
13698               Tune for ARC725D CPU.
13699
13700           ARC750D
13701               Tune for ARC750D CPU.
13702
13703       -mmultcost=num
13704           Cost to assume for a multiply instruction, with 4 being equal to a
13705           normal instruction.
13706
13707       -munalign-prob-threshold=probability
13708           Set probability threshold for unaligning branches.  When tuning for
13709           ARC700 and optimizing for speed, branches without filled delay slot
13710           are preferably emitted unaligned and long, unless profiling
13711           indicates that the probability for the branch to be taken is below
13712           probability.  The default is (REG_BR_PROB_BASE/2), i.e. 5000.
13713
13714       The following options are maintained for backward compatibility, but
13715       are now deprecated and will be removed in a future release:
13716
13717       -margonaut
13718           Obsolete FPX.
13719
13720       -mbig-endian
13721       -EB Compile code for big-endian targets.  Use of these options is now
13722           deprecated.  Big-endian code is supported by configuring GCC to
13723           build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
13724           endian is the default.
13725
13726       -mlittle-endian
13727       -EL Compile code for little-endian targets.  Use of these options is
13728           now deprecated.  Little-endian code is supported by configuring GCC
13729           to build "arc-elf32" and "arc-linux-uclibc" targets, for which
13730           little endian is the default.
13731
13732       -mbarrel_shifter
13733           Replaced by -mbarrel-shifter.
13734
13735       -mdpfp_compact
13736           Replaced by -mdpfp-compact.
13737
13738       -mdpfp_fast
13739           Replaced by -mdpfp-fast.
13740
13741       -mdsp_packa
13742           Replaced by -mdsp-packa.
13743
13744       -mEA
13745           Replaced by -mea.
13746
13747       -mmac_24
13748           Replaced by -mmac-24.
13749
13750       -mmac_d16
13751           Replaced by -mmac-d16.
13752
13753       -mspfp_compact
13754           Replaced by -mspfp-compact.
13755
13756       -mspfp_fast
13757           Replaced by -mspfp-fast.
13758
13759       -mtune=cpu
13760           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
13761           by ARC600, ARC601, ARC700 and ARC700-xmac respectively.
13762
13763       -multcost=num
13764           Replaced by -mmultcost.
13765
13766   ARM Options
13767       These -m options are defined for the ARM port:
13768
13769       -mabi=name
13770           Generate code for the specified ABI.  Permissible values are: apcs-
13771           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
13772
13773       -mapcs-frame
13774           Generate a stack frame that is compliant with the ARM Procedure
13775           Call Standard for all functions, even if this is not strictly
13776           necessary for correct execution of the code.  Specifying
13777           -fomit-frame-pointer with this option causes the stack frames not
13778           to be generated for leaf functions.  The default is
13779           -mno-apcs-frame.  This option is deprecated.
13780
13781       -mapcs
13782           This is a synonym for -mapcs-frame and is deprecated.
13783
13784       -mthumb-interwork
13785           Generate code that supports calling between the ARM and Thumb
13786           instruction sets.  Without this option, on pre-v5 architectures,
13787           the two instruction sets cannot be reliably used inside one
13788           program.  The default is -mno-thumb-interwork, since slightly
13789           larger code is generated when -mthumb-interwork is specified.  In
13790           AAPCS configurations this option is meaningless.
13791
13792       -mno-sched-prolog
13793           Prevent the reordering of instructions in the function prologue, or
13794           the merging of those instruction with the instructions in the
13795           function's body.  This means that all functions start with a
13796           recognizable set of instructions (or in fact one of a choice from a
13797           small set of different function prologues), and this information
13798           can be used to locate the start of functions inside an executable
13799           piece of code.  The default is -msched-prolog.
13800
13801       -mfloat-abi=name
13802           Specifies which floating-point ABI to use.  Permissible values are:
13803           soft, softfp and hard.
13804
13805           Specifying soft causes GCC to generate output containing library
13806           calls for floating-point operations.  softfp allows the generation
13807           of code using hardware floating-point instructions, but still uses
13808           the soft-float calling conventions.  hard allows generation of
13809           floating-point instructions and uses FPU-specific calling
13810           conventions.
13811
13812           The default depends on the specific target configuration.  Note
13813           that the hard-float and soft-float ABIs are not link-compatible;
13814           you must compile your entire program with the same ABI, and link
13815           with a compatible set of libraries.
13816
13817       -mlittle-endian
13818           Generate code for a processor running in little-endian mode.  This
13819           is the default for all standard configurations.
13820
13821       -mbig-endian
13822           Generate code for a processor running in big-endian mode; the
13823           default is to compile code for a little-endian processor.
13824
13825       -mbe8
13826       -mbe32
13827           When linking a big-endian image select between BE8 and BE32
13828           formats.  The option has no effect for little-endian images and is
13829           ignored.  The default is dependent on the selected target
13830           architecture.  For ARMv6 and later architectures the default is
13831           BE8, for older architectures the default is BE32.  BE32 format has
13832           been deprecated by ARM.
13833
13834       -march=name[+extension...]
13835           This specifies the name of the target ARM architecture.  GCC uses
13836           this name to determine what kind of instructions it can emit when
13837           generating assembly code.  This option can be used in conjunction
13838           with or instead of the -mcpu= option.
13839
13840           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
13841           armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
13842           armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv7-r,
13843           armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m, armv8-m.base,
13844           armv8-m.main, iwmmxt and iwmmxt2.
13845
13846           Additionally, the following architectures, which lack support for
13847           the Thumb execution state, are recognized but support is
13848           deprecated: armv2, armv2a, armv3, armv3m, armv4, armv5 and armv5e.
13849
13850           Many of the architectures support extensions.  These can be added
13851           by appending +extension to the architecture name.  Extension
13852           options are processed in order and capabilities accumulate.  An
13853           extension will also enable any necessary base extensions upon which
13854           it depends.  For example, the +crypto extension will always enable
13855           the +simd extension.  The exception to the additive construction is
13856           for extensions that are prefixed with +no...: these extensions
13857           disable the specified option and any other extensions that may
13858           depend on the presence of that extension.
13859
13860           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
13861           writing -march=armv7-a+vfpv4 since the +simd option is entirely
13862           disabled by the +nofp option that follows it.
13863
13864           Most extension names are generically named, but have an effect that
13865           is dependent upon the architecture to which it is applied.  For
13866           example, the +simd option can be applied to both armv7-a and
13867           armv8-a architectures, but will enable the original ARMv7-A
13868           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
13869           for armv8-a.
13870
13871           The table below lists the supported extensions for each
13872           architecture.  Architectures not mentioned do not support any
13873           extensions.
13874
13875           armv5e
13876           armv5te
13877           armv6
13878           armv6j
13879           armv6k
13880           armv6kz
13881           armv6t2
13882           armv6z
13883           armv6zk
13884               +fp The VFPv2 floating-point instructions.  The extension
13885                   +vfpv2 can be used as an alias for this extension.
13886
13887               +nofp
13888                   Disable the floating-point instructions.
13889
13890           armv7
13891               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
13892               architectures.
13893
13894               +fp The VFPv3 floating-point instructions, with 16 double-
13895                   precision registers.  The extension +vfpv3-d16 can be used
13896                   as an alias for this extension.  Note that floating-point
13897                   is not supported by the base ARMv7-M architecture, but is
13898                   compatible with both the ARMv7-A and ARMv7-R architectures.
13899
13900               +nofp
13901                   Disable the floating-point instructions.
13902
13903           armv7-a
13904               +fp The VFPv3 floating-point instructions, with 16 double-
13905                   precision registers.  The extension +vfpv3-d16 can be used
13906                   as an alias for this extension.
13907
13908               +simd
13909                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
13910                   instructions.  The extensions +neon and +neon-vfpv3 can be
13911                   used as aliases for this extension.
13912
13913               +vfpv3
13914                   The VFPv3 floating-point instructions, with 32 double-
13915                   precision registers.
13916
13917               +vfpv3-d16-fp16
13918                   The VFPv3 floating-point instructions, with 16 double-
13919                   precision registers and the half-precision floating-point
13920                   conversion operations.
13921
13922               +vfpv3-fp16
13923                   The VFPv3 floating-point instructions, with 32 double-
13924                   precision registers and the half-precision floating-point
13925                   conversion operations.
13926
13927               +vfpv4-d16
13928                   The VFPv4 floating-point instructions, with 16 double-
13929                   precision registers.
13930
13931               +vfpv4
13932                   The VFPv4 floating-point instructions, with 32 double-
13933                   precision registers.
13934
13935               +neon-fp16
13936                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
13937                   instructions, with the half-precision floating-point
13938                   conversion operations.
13939
13940               +neon-vfpv4
13941                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
13942                   instructions.
13943
13944               +nosimd
13945                   Disable the Advanced SIMD instructions (does not disable
13946                   floating point).
13947
13948               +nofp
13949                   Disable the floating-point and Advanced SIMD instructions.
13950
13951           armv7ve
13952               The extended version of the ARMv7-A architecture with support
13953               for virtualization.
13954
13955               +fp The VFPv4 floating-point instructions, with 16 double-
13956                   precision registers.  The extension +vfpv4-d16 can be used
13957                   as an alias for this extension.
13958
13959               +simd
13960                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
13961                   instructions.  The extension +neon-vfpv4 can be used as an
13962                   alias for this extension.
13963
13964               +vfpv3-d16
13965                   The VFPv3 floating-point instructions, with 16 double-
13966                   precision registers.
13967
13968               +vfpv3
13969                   The VFPv3 floating-point instructions, with 32 double-
13970                   precision registers.
13971
13972               +vfpv3-d16-fp16
13973                   The VFPv3 floating-point instructions, with 16 double-
13974                   precision registers and the half-precision floating-point
13975                   conversion operations.
13976
13977               +vfpv3-fp16
13978                   The VFPv3 floating-point instructions, with 32 double-
13979                   precision registers and the half-precision floating-point
13980                   conversion operations.
13981
13982               +vfpv4-d16
13983                   The VFPv4 floating-point instructions, with 16 double-
13984                   precision registers.
13985
13986               +vfpv4
13987                   The VFPv4 floating-point instructions, with 32 double-
13988                   precision registers.
13989
13990               +neon
13991                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
13992                   instructions.  The extension +neon-vfpv3 can be used as an
13993                   alias for this extension.
13994
13995               +neon-fp16
13996                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
13997                   instructions, with the half-precision floating-point
13998                   conversion operations.
13999
14000               +nosimd
14001                   Disable the Advanced SIMD instructions (does not disable
14002                   floating point).
14003
14004               +nofp
14005                   Disable the floating-point and Advanced SIMD instructions.
14006
14007           armv8-a
14008               +crc
14009                   The Cyclic Redundancy Check (CRC) instructions.
14010
14011               +simd
14012                   The ARMv8-A Advanced SIMD and floating-point instructions.
14013
14014               +crypto
14015                   The cryptographic instructions.
14016
14017               +nocrypto
14018                   Disable the cryptographic instructions.
14019
14020               +nofp
14021                   Disable the floating-point, Advanced SIMD and cryptographic
14022                   instructions.
14023
14024           armv8.1-a
14025               +simd
14026                   The ARMv8.1-A Advanced SIMD and floating-point
14027                   instructions.
14028
14029               +crypto
14030                   The cryptographic instructions.  This also enables the
14031                   Advanced SIMD and floating-point instructions.
14032
14033               +nocrypto
14034                   Disable the cryptographic instructions.
14035
14036               +nofp
14037                   Disable the floating-point, Advanced SIMD and cryptographic
14038                   instructions.
14039
14040           armv8.2-a
14041           armv8.3-a
14042               +fp16
14043                   The half-precision floating-point data processing
14044                   instructions.  This also enables the Advanced SIMD and
14045                   floating-point instructions.
14046
14047               +fp16fml
14048                   The half-precision floating-point fmla extension.  This
14049                   also enables the half-precision floating-point extension
14050                   and Advanced SIMD and floating-point instructions.
14051
14052               +simd
14053                   The ARMv8.1-A Advanced SIMD and floating-point
14054                   instructions.
14055
14056               +crypto
14057                   The cryptographic instructions.  This also enables the
14058                   Advanced SIMD and floating-point instructions.
14059
14060               +dotprod
14061                   Enable the Dot Product extension.  This also enables
14062                   Advanced SIMD instructions.
14063
14064               +nocrypto
14065                   Disable the cryptographic extension.
14066
14067               +nofp
14068                   Disable the floating-point, Advanced SIMD and cryptographic
14069                   instructions.
14070
14071           armv8.4-a
14072               +fp16
14073                   The half-precision floating-point data processing
14074                   instructions.  This also enables the Advanced SIMD and
14075                   floating-point instructions as well as the Dot Product
14076                   extension and the half-precision floating-point fmla
14077                   extension.
14078
14079               +simd
14080                   The ARMv8.3-A Advanced SIMD and floating-point instructions
14081                   as well as the Dot Product extension.
14082
14083               +crypto
14084                   The cryptographic instructions.  This also enables the
14085                   Advanced SIMD and floating-point instructions as well as
14086                   the Dot Product extension.
14087
14088               +nocrypto
14089                   Disable the cryptographic extension.
14090
14091               +nofp
14092                   Disable the floating-point, Advanced SIMD and cryptographic
14093                   instructions.
14094
14095           armv7-r
14096               +fp.sp
14097                   The single-precision VFPv3 floating-point instructions.
14098                   The extension +vfpv3xd can be used as an alias for this
14099                   extension.
14100
14101               +fp The VFPv3 floating-point instructions with 16 double-
14102                   precision registers.  The extension +vfpv3-d16 can be used
14103                   as an alias for this extension.
14104
14105               +nofp
14106                   Disable the floating-point extension.
14107
14108               +idiv
14109                   The ARM-state integer division instructions.
14110
14111               +noidiv
14112                   Disable the ARM-state integer division extension.
14113
14114           armv7e-m
14115               +fp The single-precision VFPv4 floating-point instructions.
14116
14117               +fpv5
14118                   The single-precision FPv5 floating-point instructions.
14119
14120               +fp.dp
14121                   The single- and double-precision FPv5 floating-point
14122                   instructions.
14123
14124               +nofp
14125                   Disable the floating-point extensions.
14126
14127           armv8-m.main
14128               +dsp
14129                   The DSP instructions.
14130
14131               +nodsp
14132                   Disable the DSP extension.
14133
14134               +fp The single-precision floating-point instructions.
14135
14136               +fp.dp
14137                   The single- and double-precision floating-point
14138                   instructions.
14139
14140               +nofp
14141                   Disable the floating-point extension.
14142
14143           armv8-r
14144               +crc
14145                   The Cyclic Redundancy Check (CRC) instructions.
14146
14147               +fp.sp
14148                   The single-precision FPv5 floating-point instructions.
14149
14150               +simd
14151                   The ARMv8-A Advanced SIMD and floating-point instructions.
14152
14153               +crypto
14154                   The cryptographic instructions.
14155
14156               +nocrypto
14157                   Disable the cryptographic instructions.
14158
14159               +nofp
14160                   Disable the floating-point, Advanced SIMD and cryptographic
14161                   instructions.
14162
14163           -march=native causes the compiler to auto-detect the architecture
14164           of the build computer.  At present, this feature is only supported
14165           on GNU/Linux, and not all architectures are recognized.  If the
14166           auto-detect is unsuccessful the option has no effect.
14167
14168       -mtune=name
14169           This option specifies the name of the target ARM processor for
14170           which GCC should tune the performance of the code.  For some ARM
14171           implementations better performance can be obtained by using this
14172           option.  Permissible names are: arm2, arm250, arm3, arm6, arm60,
14173           arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di,
14174           arm7dmi, arm70, arm700, arm700i, arm710, arm710c, arm7100, arm720,
14175           arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t, arm720t,
14176           arm740t, strongarm, strongarm110, strongarm1100, strongarm1110,
14177           arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t, arm946e-s,
14178           arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi,
14179           arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e, arm1136j-s,
14180           arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s, arm1156t2f-s,
14181           arm1176jz-s, arm1176jzf-s, generic-armv7-a, cortex-a5, cortex-a7,
14182           cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17,
14183           cortex-a32, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
14184           cortex-a72, cortex-a73, cortex-a75, cortex-r4, cortex-r4f,
14185           cortex-r5, cortex-r7, cortex-r8, cortex-r52, cortex-m33,
14186           cortex-m23, cortex-m7, cortex-m4, cortex-m3, cortex-m1, cortex-m0,
14187           cortex-m0plus, cortex-m1.small-multiply, cortex-m0.small-multiply,
14188           cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, xscale,
14189           iwmmxt, iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626,
14190           fa726te, xgene1.
14191
14192           Additionally, this option can specify that GCC should tune the
14193           performance of the code for a big.LITTLE system.  Permissible names
14194           are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
14195           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
14196           cortex-a72.cortex-a35, cortex-a73.cortex-a53,
14197           cortex-a75.cortex-a55.
14198
14199           -mtune=generic-arch specifies that GCC should tune the performance
14200           for a blend of processors within architecture arch.  The aim is to
14201           generate code that run well on the current most popular processors,
14202           balancing between optimizations that benefit some CPUs in the
14203           range, and avoiding performance pitfalls of other CPUs.  The
14204           effects of this option may change in future GCC versions as CPU
14205           models come and go.
14206
14207           -mtune permits the same extension options as -mcpu, but the
14208           extension options do not affect the tuning of the generated code.
14209
14210           -mtune=native causes the compiler to auto-detect the CPU of the
14211           build computer.  At present, this feature is only supported on
14212           GNU/Linux, and not all architectures are recognized.  If the auto-
14213           detect is unsuccessful the option has no effect.
14214
14215       -mcpu=name[+extension...]
14216           This specifies the name of the target ARM processor.  GCC uses this
14217           name to derive the name of the target ARM architecture (as if
14218           specified by -march) and the ARM processor type for which to tune
14219           for performance (as if specified by -mtune).  Where this option is
14220           used in conjunction with -march or -mtune, those options take
14221           precedence over the appropriate part of this option.
14222
14223           Many of the supported CPUs implement optional architectural
14224           extensions.  Where this is so the architectural extensions are
14225           normally enabled by default.  If implementations that lack the
14226           extension exist, then the extension syntax can be used to disable
14227           those extensions that have been omitted.  For floating-point and
14228           Advanced SIMD (Neon) instructions, the settings of the options
14229           -mfloat-abi and -mfpu must also be considered: floating-point and
14230           Advanced SIMD instructions will only be used if -mfloat-abi is not
14231           set to soft; and any setting of -mfpu other than auto will override
14232           the available floating-point and SIMD extension instructions.
14233
14234           For example, cortex-a9 can be found in three major configurations:
14235           integer only, with just a floating-point unit or with floating-
14236           point and Advanced SIMD.  The default is to enable all the
14237           instructions, but the extensions +nosimd and +nofp can be used to
14238           disable just the SIMD or both the SIMD and floating-point
14239           instructions respectively.
14240
14241           Permissible names for this option are the same as those for -mtune.
14242
14243           The following extension options are common to the listed CPUs:
14244
14245           +nodsp
14246               Disable the DSP instructions on cortex-m33.
14247
14248           +nofp
14249               Disables the floating-point instructions on arm9e, arm946e-s,
14250               arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
14251               arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
14252               cortex-m7 and cortex-m33.  Disables the floating-point and SIMD
14253               instructions on generic-armv7-a, cortex-a5, cortex-a7,
14254               cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17,
14255               cortex-a15.cortex-a7, cortex-a17.cortex-a7, cortex-a32,
14256               cortex-a35, cortex-a53 and cortex-a55.
14257
14258           +nofp.dp
14259               Disables the double-precision component of the floating-point
14260               instructions on cortex-r5, cortex-r52 and cortex-m7.
14261
14262           +nosimd
14263               Disables the SIMD (but not floating-point) instructions on
14264               generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.
14265
14266           +crypto
14267               Enables the cryptographic instructions on cortex-a32,
14268               cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
14269               cortex-a73, cortex-a75, exynos-m1, xgene1,
14270               cortex-a57.cortex-a53, cortex-a72.cortex-a53,
14271               cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
14272               cortex-a75.cortex-a55.
14273
14274           Additionally the generic-armv7-a pseudo target defaults to VFPv3
14275           with 16 double-precision registers.  It supports the following
14276           extension options: vfpv3-d16, vfpv3, vfpv3-d16-fp16, vfpv3-fp16,
14277           vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16, neon-vfpv4.  The
14278           meanings are the same as for the extensions to -march=armv7-a.
14279
14280           -mcpu=generic-arch is also permissible, and is equivalent to
14281           -march=arch -mtune=generic-arch.  See -mtune for more information.
14282
14283           -mcpu=native causes the compiler to auto-detect the CPU of the
14284           build computer.  At present, this feature is only supported on
14285           GNU/Linux, and not all architectures are recognized.  If the auto-
14286           detect is unsuccessful the option has no effect.
14287
14288       -mfpu=name
14289           This specifies what floating-point hardware (or hardware emulation)
14290           is available on the target.  Permissible names are: auto, vfpv2,
14291           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
14292           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
14293           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
14294           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
14295           and vfp is an alias for vfpv2.
14296
14297           The setting auto is the default and is special.  It causes the
14298           compiler to select the floating-point and Advanced SIMD
14299           instructions based on the settings of -mcpu and -march.
14300
14301           If the selected floating-point hardware includes the NEON extension
14302           (e.g. -mfpu=neon), note that floating-point operations are not
14303           generated by GCC's auto-vectorization pass unless
14304           -funsafe-math-optimizations is also specified.  This is because
14305           NEON hardware does not fully implement the IEEE 754 standard for
14306           floating-point arithmetic (in particular denormal values are
14307           treated as zero), so the use of NEON instructions may lead to a
14308           loss of precision.
14309
14310           You can also set the fpu name at function level by using the
14311           "target("fpu=")" function attributes or pragmas.
14312
14313       -mfp16-format=name
14314           Specify the format of the "__fp16" half-precision floating-point
14315           type.  Permissible names are none, ieee, and alternative; the
14316           default is none, in which case the "__fp16" type is not defined.
14317
14318       -mstructure-size-boundary=n
14319           The sizes of all structures and unions are rounded up to a multiple
14320           of the number of bits set by this option.  Permissible values are
14321           8, 32 and 64.  The default value varies for different toolchains.
14322           For the COFF targeted toolchain the default value is 8.  A value of
14323           64 is only allowed if the underlying ABI supports it.
14324
14325           Specifying a larger number can produce faster, more efficient code,
14326           but can also increase the size of the program.  Different values
14327           are potentially incompatible.  Code compiled with one value cannot
14328           necessarily expect to work with code or libraries compiled with
14329           another value, if they exchange information using structures or
14330           unions.
14331
14332           This option is deprecated.
14333
14334       -mabort-on-noreturn
14335           Generate a call to the function "abort" at the end of a "noreturn"
14336           function.  It is executed if the function tries to return.
14337
14338       -mlong-calls
14339       -mno-long-calls
14340           Tells the compiler to perform function calls by first loading the
14341           address of the function into a register and then performing a
14342           subroutine call on this register.  This switch is needed if the
14343           target function lies outside of the 64-megabyte addressing range of
14344           the offset-based version of subroutine call instruction.
14345
14346           Even if this switch is enabled, not all function calls are turned
14347           into long calls.  The heuristic is that static functions, functions
14348           that have the "short_call" attribute, functions that are inside the
14349           scope of a "#pragma no_long_calls" directive, and functions whose
14350           definitions have already been compiled within the current
14351           compilation unit are not turned into long calls.  The exceptions to
14352           this rule are that weak function definitions, functions with the
14353           "long_call" attribute or the "section" attribute, and functions
14354           that are within the scope of a "#pragma long_calls" directive are
14355           always turned into long calls.
14356
14357           This feature is not enabled by default.  Specifying -mno-long-calls
14358           restores the default behavior, as does placing the function calls
14359           within the scope of a "#pragma long_calls_off" directive.  Note
14360           these switches have no effect on how the compiler generates code to
14361           handle function calls via function pointers.
14362
14363       -msingle-pic-base
14364           Treat the register used for PIC addressing as read-only, rather
14365           than loading it in the prologue for each function.  The runtime
14366           system is responsible for initializing this register with an
14367           appropriate value before execution begins.
14368
14369       -mpic-register=reg
14370           Specify the register to be used for PIC addressing.  For standard
14371           PIC base case, the default is any suitable register determined by
14372           compiler.  For single PIC base case, the default is R9 if target is
14373           EABI based or stack-checking is enabled, otherwise the default is
14374           R10.
14375
14376       -mpic-data-is-text-relative
14377           Assume that the displacement between the text and data segments is
14378           fixed at static link time.  This permits using PC-relative
14379           addressing operations to access data known to be in the data
14380           segment.  For non-VxWorks RTP targets, this option is enabled by
14381           default.  When disabled on such targets, it will enable
14382           -msingle-pic-base by default.
14383
14384       -mpoke-function-name
14385           Write the name of each function into the text section, directly
14386           preceding the function prologue.  The generated code is similar to
14387           this:
14388
14389                        t0
14390                            .ascii "arm_poke_function_name", 0
14391                            .align
14392                        t1
14393                            .word 0xff000000 + (t1 - t0)
14394                        arm_poke_function_name
14395                            mov     ip, sp
14396                            stmfd   sp!, {fp, ip, lr, pc}
14397                            sub     fp, ip, #4
14398
14399           When performing a stack backtrace, code can inspect the value of
14400           "pc" stored at "fp + 0".  If the trace function then looks at
14401           location "pc - 12" and the top 8 bits are set, then we know that
14402           there is a function name embedded immediately preceding this
14403           location and has length "((pc[-3]) & 0xff000000)".
14404
14405       -mthumb
14406       -marm
14407           Select between generating code that executes in ARM and Thumb
14408           states.  The default for most configurations is to generate code
14409           that executes in ARM state, but the default can be changed by
14410           configuring GCC with the --with-mode=state configure option.
14411
14412           You can also override the ARM and Thumb mode for each function by
14413           using the "target("thumb")" and "target("arm")" function attributes
14414           or pragmas.
14415
14416       -mflip-thumb
14417           Switch ARM/Thumb modes on alternating functions.  This option is
14418           provided for regression testing of mixed Thumb/ARM code generation,
14419           and is not intended for ordinary use in compiling code.
14420
14421       -mtpcs-frame
14422           Generate a stack frame that is compliant with the Thumb Procedure
14423           Call Standard for all non-leaf functions.  (A leaf function is one
14424           that does not call any other functions.)  The default is
14425           -mno-tpcs-frame.
14426
14427       -mtpcs-leaf-frame
14428           Generate a stack frame that is compliant with the Thumb Procedure
14429           Call Standard for all leaf functions.  (A leaf function is one that
14430           does not call any other functions.)  The default is
14431           -mno-apcs-leaf-frame.
14432
14433       -mcallee-super-interworking
14434           Gives all externally visible functions in the file being compiled
14435           an ARM instruction set header which switches to Thumb mode before
14436           executing the rest of the function.  This allows these functions to
14437           be called from non-interworking code.  This option is not valid in
14438           AAPCS configurations because interworking is enabled by default.
14439
14440       -mcaller-super-interworking
14441           Allows calls via function pointers (including virtual functions) to
14442           execute correctly regardless of whether the target code has been
14443           compiled for interworking or not.  There is a small overhead in the
14444           cost of executing a function pointer if this option is enabled.
14445           This option is not valid in AAPCS configurations because
14446           interworking is enabled by default.
14447
14448       -mtp=name
14449           Specify the access model for the thread local storage pointer.  The
14450           valid models are soft, which generates calls to "__aeabi_read_tp",
14451           cp15, which fetches the thread pointer from "cp15" directly
14452           (supported in the arm6k architecture), and auto, which uses the
14453           best available method for the selected processor.  The default
14454           setting is auto.
14455
14456       -mtls-dialect=dialect
14457           Specify the dialect to use for accessing thread local storage.  Two
14458           dialects are supported---gnu and gnu2.  The gnu dialect selects the
14459           original GNU scheme for supporting local and global dynamic TLS
14460           models.  The gnu2 dialect selects the GNU descriptor scheme, which
14461           provides better performance for shared libraries.  The GNU
14462           descriptor scheme is compatible with the original scheme, but does
14463           require new assembler, linker and library support.  Initial and
14464           local exec TLS models are unaffected by this option and always use
14465           the original scheme.
14466
14467       -mword-relocations
14468           Only generate absolute relocations on word-sized values (i.e.
14469           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
14470           SymbianOS) where the runtime loader imposes this restriction, and
14471           when -fpic or -fPIC is specified.
14472
14473       -mfix-cortex-m3-ldrd
14474           Some Cortex-M3 cores can cause data corruption when "ldrd"
14475           instructions with overlapping destination and base registers are
14476           used.  This option avoids generating these instructions.  This
14477           option is enabled by default when -mcpu=cortex-m3 is specified.
14478
14479       -munaligned-access
14480       -mno-unaligned-access
14481           Enables (or disables) reading and writing of 16- and 32- bit values
14482           from addresses that are not 16- or 32- bit aligned.  By default
14483           unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
14484           ARMv8-M Baseline architectures, and enabled for all other
14485           architectures.  If unaligned access is not enabled then words in
14486           packed data structures are accessed a byte at a time.
14487
14488           The ARM attribute "Tag_CPU_unaligned_access" is set in the
14489           generated object file to either true or false, depending upon the
14490           setting of this option.  If unaligned access is enabled then the
14491           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.
14492
14493       -mneon-for-64bits
14494           Enables using Neon to handle scalar 64-bits operations. This is
14495           disabled by default since the cost of moving data from core
14496           registers to Neon is high.
14497
14498       -mslow-flash-data
14499           Assume loading data from flash is slower than fetching instruction.
14500           Therefore literal load is minimized for better performance.  This
14501           option is only supported when compiling for ARMv7 M-profile and off
14502           by default.
14503
14504       -masm-syntax-unified
14505           Assume inline assembler is using unified asm syntax.  The default
14506           is currently off which implies divided syntax.  This option has no
14507           impact on Thumb2. However, this may change in future releases of
14508           GCC.  Divided syntax should be considered deprecated.
14509
14510       -mrestrict-it
14511           Restricts generation of IT blocks to conform to the rules of
14512           ARMv8-A.  IT blocks can only contain a single 16-bit instruction
14513           from a select set of instructions. This option is on by default for
14514           ARMv8-A Thumb mode.
14515
14516       -mprint-tune-info
14517           Print CPU tuning information as comment in assembler file.  This is
14518           an option used only for regression testing of the compiler and not
14519           intended for ordinary use in compiling code.  This option is
14520           disabled by default.
14521
14522       -mverbose-cost-dump
14523           Enable verbose cost model dumping in the debug dump files.  This
14524           option is provided for use in debugging the compiler.
14525
14526       -mpure-code
14527           Do not allow constant data to be placed in code sections.
14528           Additionally, when compiling for ELF object format give all text
14529           sections the ELF processor-specific section attribute
14530           "SHF_ARM_PURECODE".  This option is only available when generating
14531           non-pic code for M-profile targets with the MOVT instruction.
14532
14533       -mcmse
14534           Generate secure code as per the "ARMv8-M Security Extensions:
14535           Requirements on Development Tools Engineering Specification", which
14536           can be found on
14537           <http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf>.
14538
14539   AVR Options
14540       These options are defined for AVR implementations:
14541
14542       -mmcu=mcu
14543           Specify Atmel AVR instruction set architectures (ISA) or MCU type.
14544
14545           The default for this option is@tie{}avr2.
14546
14547           GCC supports the following AVR devices and ISAs:
14548
14549           "avr2"
14550               "Classic" devices with up to 8@tie{}KiB of program memory.
14551               mcu@tie{}= "attiny22", "attiny26", "at90c8534", "at90s2313",
14552               "at90s2323", "at90s2333", "at90s2343", "at90s4414",
14553               "at90s4433", "at90s4434", "at90s8515", "at90s8535".
14554
14555           "avr25"
14556               "Classic" devices with up to 8@tie{}KiB of program memory and
14557               with the "MOVW" instruction.  mcu@tie{}= "ata5272", "ata6616c",
14558               "attiny13", "attiny13a", "attiny2313", "attiny2313a",
14559               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
14560               "attiny43u", "attiny4313", "attiny44", "attiny44a",
14561               "attiny441", "attiny45", "attiny461", "attiny461a", "attiny48",
14562               "attiny828", "attiny84", "attiny84a", "attiny841", "attiny85",
14563               "attiny861", "attiny861a", "attiny87", "attiny88", "at86rf401".
14564
14565           "avr3"
14566               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of
14567               program memory.  mcu@tie{}= "at43usb355", "at76c711".
14568
14569           "avr31"
14570               "Classic" devices with 128@tie{}KiB of program memory.
14571               mcu@tie{}= "atmega103", "at43usb320".
14572
14573           "avr35"
14574               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of program
14575               memory and with the "MOVW" instruction.  mcu@tie{}= "ata5505",
14576               "ata6617c", "ata664251", "atmega16u2", "atmega32u2",
14577               "atmega8u2", "attiny1634", "attiny167", "at90usb162",
14578               "at90usb82".
14579
14580           "avr4"
14581               "Enhanced" devices with up to 8@tie{}KiB of program memory.
14582               mcu@tie{}= "ata6285", "ata6286", "ata6289", "ata6612c",
14583               "atmega48", "atmega48a", "atmega48p", "atmega48pa",
14584               "atmega48pb", "atmega8", "atmega8a", "atmega8hva",
14585               "atmega8515", "atmega8535", "atmega88", "atmega88a",
14586               "atmega88p", "atmega88pa", "atmega88pb", "at90pwm1",
14587               "at90pwm2", "at90pwm2b", "at90pwm3", "at90pwm3b", "at90pwm81".
14588
14589           "avr5"
14590               "Enhanced" devices with 16@tie{}KiB up to 64@tie{}KiB of
14591               program memory.  mcu@tie{}= "ata5702m322", "ata5782",
14592               "ata5790", "ata5790n", "ata5791", "ata5795", "ata5831",
14593               "ata6613c", "ata6614q", "ata8210", "ata8510", "atmega16",
14594               "atmega16a", "atmega16hva", "atmega16hva2", "atmega16hvb",
14595               "atmega16hvbrevb", "atmega16m1", "atmega16u4", "atmega161",
14596               "atmega162", "atmega163", "atmega164a", "atmega164p",
14597               "atmega164pa", "atmega165", "atmega165a", "atmega165p",
14598               "atmega165pa", "atmega168", "atmega168a", "atmega168p",
14599               "atmega168pa", "atmega168pb", "atmega169", "atmega169a",
14600               "atmega169p", "atmega169pa", "atmega32", "atmega32a",
14601               "atmega32c1", "atmega32hvb", "atmega32hvbrevb", "atmega32m1",
14602               "atmega32u4", "atmega32u6", "atmega323", "atmega324a",
14603               "atmega324p", "atmega324pa", "atmega325", "atmega325a",
14604               "atmega325p", "atmega325pa", "atmega3250", "atmega3250a",
14605               "atmega3250p", "atmega3250pa", "atmega328", "atmega328p",
14606               "atmega328pb", "atmega329", "atmega329a", "atmega329p",
14607               "atmega329pa", "atmega3290", "atmega3290a", "atmega3290p",
14608               "atmega3290pa", "atmega406", "atmega64", "atmega64a",
14609               "atmega64c1", "atmega64hve", "atmega64hve2", "atmega64m1",
14610               "atmega64rfr2", "atmega640", "atmega644", "atmega644a",
14611               "atmega644p", "atmega644pa", "atmega644rfr2", "atmega645",
14612               "atmega645a", "atmega645p", "atmega6450", "atmega6450a",
14613               "atmega6450p", "atmega649", "atmega649a", "atmega649p",
14614               "atmega6490", "atmega6490a", "atmega6490p", "at90can32",
14615               "at90can64", "at90pwm161", "at90pwm216", "at90pwm316",
14616               "at90scr100", "at90usb646", "at90usb647", "at94k", "m3000".
14617
14618           "avr51"
14619               "Enhanced" devices with 128@tie{}KiB of program memory.
14620               mcu@tie{}= "atmega128", "atmega128a", "atmega128rfa1",
14621               "atmega128rfr2", "atmega1280", "atmega1281", "atmega1284",
14622               "atmega1284p", "atmega1284rfr2", "at90can128", "at90usb1286",
14623               "at90usb1287".
14624
14625           "avr6"
14626               "Enhanced" devices with 3-byte PC, i.e. with more than
14627               128@tie{}KiB of program memory.  mcu@tie{}= "atmega256rfr2",
14628               "atmega2560", "atmega2561", "atmega2564rfr2".
14629
14630           "avrxmega2"
14631               "XMEGA" devices with more than 8@tie{}KiB and up to 64@tie{}KiB
14632               of program memory.  mcu@tie{}= "atxmega16a4", "atxmega16a4u",
14633               "atxmega16c4", "atxmega16d4", "atxmega16e5", "atxmega32a4",
14634               "atxmega32a4u", "atxmega32c3", "atxmega32c4", "atxmega32d3",
14635               "atxmega32d4", "atxmega32e5", "atxmega8e5".
14636
14637           "avrxmega3"
14638               "XMEGA" devices with up to 64@tie{}KiB of combined program
14639               memory and RAM, and with program memory visible in the RAM
14640               address space.  mcu@tie{}= "attiny1614", "attiny1616",
14641               "attiny1617", "attiny212", "attiny214", "attiny3214",
14642               "attiny3216", "attiny3217", "attiny412", "attiny414",
14643               "attiny416", "attiny417", "attiny814", "attiny816",
14644               "attiny817".
14645
14646           "avrxmega4"
14647               "XMEGA" devices with more than 64@tie{}KiB and up to
14648               128@tie{}KiB of program memory.  mcu@tie{}= "atxmega64a3",
14649               "atxmega64a3u", "atxmega64a4u", "atxmega64b1", "atxmega64b3",
14650               "atxmega64c3", "atxmega64d3", "atxmega64d4".
14651
14652           "avrxmega5"
14653               "XMEGA" devices with more than 64@tie{}KiB and up to
14654               128@tie{}KiB of program memory and more than 64@tie{}KiB of
14655               RAM.  mcu@tie{}= "atxmega64a1", "atxmega64a1u".
14656
14657           "avrxmega6"
14658               "XMEGA" devices with more than 128@tie{}KiB of program memory.
14659               mcu@tie{}= "atxmega128a3", "atxmega128a3u", "atxmega128b1",
14660               "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
14661               "atxmega192a3", "atxmega192a3u", "atxmega192c3",
14662               "atxmega192d3", "atxmega256a3", "atxmega256a3b",
14663               "atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
14664               "atxmega256d3", "atxmega384c3", "atxmega384d3".
14665
14666           "avrxmega7"
14667               "XMEGA" devices with more than 128@tie{}KiB of program memory
14668               and more than 64@tie{}KiB of RAM.  mcu@tie{}= "atxmega128a1",
14669               "atxmega128a1u", "atxmega128a4u".
14670
14671           "avrtiny"
14672               "TINY" Tiny core devices with 512@tie{}B up to 4@tie{}KiB of
14673               program memory.  mcu@tie{}= "attiny10", "attiny20", "attiny4",
14674               "attiny40", "attiny5", "attiny9".
14675
14676           "avr1"
14677               This ISA is implemented by the minimal AVR core and supported
14678               for assembler only.  mcu@tie{}= "attiny11", "attiny12",
14679               "attiny15", "attiny28", "at90s1200".
14680
14681       -mabsdata
14682           Assume that all data in static storage can be accessed by LDS / STS
14683           instructions.  This option has only an effect on reduced Tiny
14684           devices like ATtiny40.  See also the "absdata" AVR Variable
14685           Attributes,variable attribute.
14686
14687       -maccumulate-args
14688           Accumulate outgoing function arguments and acquire/release the
14689           needed stack space for outgoing function arguments once in function
14690           prologue/epilogue.  Without this option, outgoing arguments are
14691           pushed before calling a function and popped afterwards.
14692
14693           Popping the arguments after the function call can be expensive on
14694           AVR so that accumulating the stack space might lead to smaller
14695           executables because arguments need not be removed from the stack
14696           after such a function call.
14697
14698           This option can lead to reduced code size for functions that
14699           perform several calls to functions that get their arguments on the
14700           stack like calls to printf-like functions.
14701
14702       -mbranch-cost=cost
14703           Set the branch costs for conditional branch instructions to cost.
14704           Reasonable values for cost are small, non-negative integers. The
14705           default branch cost is 0.
14706
14707       -mcall-prologues
14708           Functions prologues/epilogues are expanded as calls to appropriate
14709           subroutines.  Code size is smaller.
14710
14711       -mgas-isr-prologues
14712           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo
14713           instruction supported by GNU Binutils.  If this option is on, the
14714           feature can still be disabled for individual ISRs by means of the
14715           AVR Function Attributes,,"no_gccisr" function attribute.  This
14716           feature is activated per default if optimization is on (but not
14717           with -Og, @pxref{Optimize Options}), and if GNU Binutils support
14718           PR21683 ("https://sourceware.org/PR21683").
14719
14720       -mint8
14721           Assume "int" to be 8-bit integer.  This affects the sizes of all
14722           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
14723           and "long long" is 4 bytes.  Please note that this option does not
14724           conform to the C standards, but it results in smaller code size.
14725
14726       -mmain-is-OS_task
14727           Do not save registers in "main".  The effect is the same like
14728           attaching attribute AVR Function Attributes,,"OS_task" to "main".
14729           It is activated per default if optimization is on.
14730
14731       -mn-flash=num
14732           Assume that the flash memory has a size of num times 64@tie{}KiB.
14733
14734       -mno-interrupts
14735           Generated code is not compatible with hardware interrupts.  Code
14736           size is smaller.
14737
14738       -mrelax
14739           Try to replace "CALL" resp. "JMP" instruction by the shorter
14740           "RCALL" resp. "RJMP" instruction if applicable.  Setting -mrelax
14741           just adds the --mlink-relax option to the assembler's command line
14742           and the --relax option to the linker's command line.
14743
14744           Jump relaxing is performed by the linker because jump offsets are
14745           not known before code is located. Therefore, the assembler code
14746           generated by the compiler is the same, but the instructions in the
14747           executable may differ from instructions in the assembler code.
14748
14749           Relaxing must be turned on if linker stubs are needed, see the
14750           section on "EIND" and linker stubs below.
14751
14752       -mrmw
14753           Assume that the device supports the Read-Modify-Write instructions
14754           "XCH", "LAC", "LAS" and "LAT".
14755
14756       -mshort-calls
14757           Assume that "RJMP" and "RCALL" can target the whole program memory.
14758
14759           This option is used internally for multilib selection.  It is not
14760           an optimization option, and you don't need to set it by hand.
14761
14762       -msp8
14763           Treat the stack pointer register as an 8-bit register, i.e. assume
14764           the high byte of the stack pointer is zero.  In general, you don't
14765           need to set this option by hand.
14766
14767           This option is used internally by the compiler to select and build
14768           multilibs for architectures "avr2" and "avr25".  These
14769           architectures mix devices with and without "SPH".  For any setting
14770           other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or
14771           removes this option from the compiler proper's command line,
14772           because the compiler then knows if the device or architecture has
14773           an 8-bit stack pointer and thus no "SPH" register or not.
14774
14775       -mstrict-X
14776           Use address register "X" in a way proposed by the hardware.  This
14777           means that "X" is only used in indirect, post-increment or pre-
14778           decrement addressing.
14779
14780           Without this option, the "X" register may be used in the same way
14781           as "Y" or "Z" which then is emulated by additional instructions.
14782           For example, loading a value with "X+const" addressing with a small
14783           non-negative "const < 64" to a register Rn is performed as
14784
14785                   adiw r26, const   ; X += const
14786                   ld   <Rn>, X        ; <Rn> = *X
14787                   sbiw r26, const   ; X -= const
14788
14789       -mtiny-stack
14790           Only change the lower 8@tie{}bits of the stack pointer.
14791
14792       -mfract-convert-truncate
14793           Allow to use truncation instead of rounding towards zero for
14794           fractional fixed-point types.
14795
14796       -nodevicelib
14797           Don't link against AVR-LibC's device specific library "lib<mcu>.a".
14798
14799       -Waddr-space-convert
14800           Warn about conversions between address spaces in the case where the
14801           resulting address space is not contained in the incoming address
14802           space.
14803
14804       -Wmisspelled-isr
14805           Warn if the ISR is misspelled, i.e. without __vector prefix.
14806           Enabled by default.
14807
14808       "EIND" and Devices with More Than 128 Ki Bytes of Flash
14809
14810       Pointers in the implementation are 16@tie{}bits wide.  The address of a
14811       function or label is represented as word address so that indirect jumps
14812       and calls can target any code address in the range of 64@tie{}Ki words.
14813
14814       In order to facilitate indirect jump on devices with more than
14815       128@tie{}Ki bytes of program memory space, there is a special function
14816       register called "EIND" that serves as most significant part of the
14817       target address when "EICALL" or "EIJMP" instructions are used.
14818
14819       Indirect jumps and calls on these devices are handled as follows by the
14820       compiler and are subject to some limitations:
14821
14822       *   The compiler never sets "EIND".
14823
14824       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
14825           instructions or might read "EIND" directly in order to emulate an
14826           indirect call/jump by means of a "RET" instruction.
14827
14828       *   The compiler assumes that "EIND" never changes during the startup
14829           code or during the application. In particular, "EIND" is not
14830           saved/restored in function or interrupt service routine
14831           prologue/epilogue.
14832
14833       *   For indirect calls to functions and computed goto, the linker
14834           generates stubs. Stubs are jump pads sometimes also called
14835           trampolines. Thus, the indirect call/jump jumps to such a stub.
14836           The stub contains a direct jump to the desired address.
14837
14838       *   Linker relaxation must be turned on so that the linker generates
14839           the stubs correctly in all situations. See the compiler option
14840           -mrelax and the linker option --relax.  There are corner cases
14841           where the linker is supposed to generate stubs but aborts without
14842           relaxation and without a helpful error message.
14843
14844       *   The default linker script is arranged for code with "EIND = 0".  If
14845           code is supposed to work for a setup with "EIND != 0", a custom
14846           linker script has to be used in order to place the sections whose
14847           name start with ".trampolines" into the segment where "EIND" points
14848           to.
14849
14850       *   The startup code from libgcc never sets "EIND".  Notice that
14851           startup code is a blend of code from libgcc and AVR-LibC.  For the
14852           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
14853           ("http://nongnu.org/avr-libc/user-manual/").
14854
14855       *   It is legitimate for user-specific startup code to set up "EIND"
14856           early, for example by means of initialization code located in
14857           section ".init3". Such code runs prior to general startup code that
14858           initializes RAM and calls constructors, but after the bit of
14859           startup code from AVR-LibC that sets "EIND" to the segment where
14860           the vector table is located.
14861
14862                   #include <avr/io.h>
14863
14864                   static void
14865                   __attribute__((section(".init3"),naked,used,no_instrument_function))
14866                   init3_set_eind (void)
14867                   {
14868                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
14869                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
14870                   }
14871
14872           The "__trampolines_start" symbol is defined in the linker script.
14873
14874       *   Stubs are generated automatically by the linker if the following
14875           two conditions are met:
14876
14877           -<The address of a label is taken by means of the "gs" modifier>
14878               (short for generate stubs) like so:
14879
14880                       LDI r24, lo8(gs(<func>))
14881                       LDI r25, hi8(gs(<func>))
14882
14883           -<The final location of that label is in a code segment>
14884               outside the segment where the stubs are located.
14885
14886       *   The compiler emits such "gs" modifiers for code labels in the
14887           following situations:
14888
14889           -<Taking address of a function or code label.>
14890           -<Computed goto.>
14891           -<If prologue-save function is used, see -mcall-prologues>
14892               command-line option.
14893
14894           -<Switch/case dispatch tables. If you do not want such dispatch>
14895               tables you can specify the -fno-jump-tables command-line
14896               option.
14897
14898           -<C and C++ constructors/destructors called during
14899           startup/shutdown.>
14900           -<If the tools hit a "gs()" modifier explained above.>
14901       *   Jumping to non-symbolic addresses like so is not supported:
14902
14903                   int main (void)
14904                   {
14905                       /* Call function at word address 0x2 */
14906                       return ((int(*)(void)) 0x2)();
14907                   }
14908
14909           Instead, a stub has to be set up, i.e. the function has to be
14910           called through a symbol ("func_4" in the example):
14911
14912                   int main (void)
14913                   {
14914                       extern int func_4 (void);
14915
14916                       /* Call function at byte address 0x4 */
14917                       return func_4();
14918                   }
14919
14920           and the application be linked with -Wl,--defsym,func_4=0x4.
14921           Alternatively, "func_4" can be defined in the linker script.
14922
14923       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
14924       Registers
14925
14926       Some AVR devices support memories larger than the 64@tie{}KiB range
14927       that can be accessed with 16-bit pointers.  To access memory locations
14928       outside this 64@tie{}KiB range, the content of a "RAMP" register is
14929       used as high part of the address: The "X", "Y", "Z" address register is
14930       concatenated with the "RAMPX", "RAMPY", "RAMPZ" special function
14931       register, respectively, to get a wide address. Similarly, "RAMPD" is
14932       used together with direct addressing.
14933
14934       *   The startup code initializes the "RAMP" special function registers
14935           with zero.
14936
14937       *   If a AVR Named Address Spaces,named address space other than
14938           generic or "__flash" is used, then "RAMPZ" is set as needed before
14939           the operation.
14940
14941       *   If the device supports RAM larger than 64@tie{}KiB and the compiler
14942           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
14943           reset to zero after the operation.
14944
14945       *   If the device comes with a specific "RAMP" register, the ISR
14946           prologue/epilogue saves/restores that SFR and initializes it with
14947           zero in case the ISR code might (implicitly) use it.
14948
14949       *   RAM larger than 64@tie{}KiB is not supported by GCC for AVR
14950           targets.  If you use inline assembler to read from locations
14951           outside the 16-bit address range and change one of the "RAMP"
14952           registers, you must reset it to zero after the access.
14953
14954       AVR Built-in Macros
14955
14956       GCC defines several built-in macros so that the user code can test for
14957       the presence or absence of features.  Almost any of the following
14958       built-in macros are deduced from device capabilities and thus triggered
14959       by the -mmcu= command-line option.
14960
14961       For even more AVR-specific built-in macros see AVR Named Address Spaces
14962       and AVR Built-in Functions.
14963
14964       "__AVR_ARCH__"
14965           Build-in macro that resolves to a decimal number that identifies
14966           the architecture and depends on the -mmcu=mcu option.  Possible
14967           values are:
14968
14969           2, 25, 3, 31, 35, 4, 5, 51, 6
14970
14971           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
14972           "avr51", "avr6",
14973
14974           respectively and
14975
14976           100, 102, 103, 104, 105, 106, 107
14977
14978           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
14979           "avrxmega5", "avrxmega6", "avrxmega7", respectively.  If mcu
14980           specifies a device, this built-in macro is set accordingly. For
14981           example, with -mmcu=atmega8 the macro is defined to 4.
14982
14983       "__AVR_Device__"
14984           Setting -mmcu=device defines this built-in macro which reflects the
14985           device's name. For example, -mmcu=atmega8 defines the built-in
14986           macro "__AVR_ATmega8__", -mmcu=attiny261a defines
14987           "__AVR_ATtiny261A__", etc.
14988
14989           The built-in macros' names follow the scheme "__AVR_Device__" where
14990           Device is the device name as from the AVR user manual. The
14991           difference between Device in the built-in macro and device in
14992           -mmcu=device is that the latter is always lowercase.
14993
14994           If device is not a device but only a core architecture like avr51,
14995           this macro is not defined.
14996
14997       "__AVR_DEVICE_NAME__"
14998           Setting -mmcu=device defines this built-in macro to the device's
14999           name. For example, with -mmcu=atmega8 the macro is defined to
15000           "atmega8".
15001
15002           If device is not a device but only a core architecture like avr51,
15003           this macro is not defined.
15004
15005       "__AVR_XMEGA__"
15006           The device / architecture belongs to the XMEGA family of devices.
15007
15008       "__AVR_HAVE_ELPM__"
15009           The device has the "ELPM" instruction.
15010
15011       "__AVR_HAVE_ELPMX__"
15012           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.
15013
15014       "__AVR_HAVE_MOVW__"
15015           The device has the "MOVW" instruction to perform 16-bit register-
15016           register moves.
15017
15018       "__AVR_HAVE_LPMX__"
15019           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.
15020
15021       "__AVR_HAVE_MUL__"
15022           The device has a hardware multiplier.
15023
15024       "__AVR_HAVE_JMP_CALL__"
15025           The device has the "JMP" and "CALL" instructions.  This is the case
15026           for devices with more than 8@tie{}KiB of program memory.
15027
15028       "__AVR_HAVE_EIJMP_EICALL__"
15029       "__AVR_3_BYTE_PC__"
15030           The device has the "EIJMP" and "EICALL" instructions.  This is the
15031           case for devices with more than 128@tie{}KiB of program memory.
15032           This also means that the program counter (PC) is 3@tie{}bytes wide.
15033
15034       "__AVR_2_BYTE_PC__"
15035           The program counter (PC) is 2@tie{}bytes wide. This is the case for
15036           devices with up to 128@tie{}KiB of program memory.
15037
15038       "__AVR_HAVE_8BIT_SP__"
15039       "__AVR_HAVE_16BIT_SP__"
15040           The stack pointer (SP) register is treated as 8-bit respectively
15041           16-bit register by the compiler.  The definition of these macros is
15042           affected by -mtiny-stack.
15043
15044       "__AVR_HAVE_SPH__"
15045       "__AVR_SP8__"
15046           The device has the SPH (high part of stack pointer) special
15047           function register or has an 8-bit stack pointer, respectively.  The
15048           definition of these macros is affected by -mmcu= and in the cases
15049           of -mmcu=avr2 and -mmcu=avr25 also by -msp8.
15050
15051       "__AVR_HAVE_RAMPD__"
15052       "__AVR_HAVE_RAMPX__"
15053       "__AVR_HAVE_RAMPY__"
15054       "__AVR_HAVE_RAMPZ__"
15055           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
15056           function register, respectively.
15057
15058       "__NO_INTERRUPTS__"
15059           This macro reflects the -mno-interrupts command-line option.
15060
15061       "__AVR_ERRATA_SKIP__"
15062       "__AVR_ERRATA_SKIP_JMP_CALL__"
15063           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
15064           instructions because of a hardware erratum.  Skip instructions are
15065           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
15066           only defined if "__AVR_HAVE_JMP_CALL__" is also set.
15067
15068       "__AVR_ISA_RMW__"
15069           The device has Read-Modify-Write instructions (XCH, LAC, LAS and
15070           LAT).
15071
15072       "__AVR_SFR_OFFSET__=offset"
15073           Instructions that can address I/O special function registers
15074           directly like "IN", "OUT", "SBI", etc. may use a different address
15075           as if addressed by an instruction to access RAM like "LD" or "STS".
15076           This offset depends on the device architecture and has to be
15077           subtracted from the RAM address in order to get the respective
15078           I/O@tie{}address.
15079
15080       "__AVR_SHORT_CALLS__"
15081           The -mshort-calls command line option is set.
15082
15083       "__AVR_PM_BASE_ADDRESS__=addr"
15084           Some devices support reading from flash memory by means of "LD*"
15085           instructions.  The flash memory is seen in the data address space
15086           at an offset of "__AVR_PM_BASE_ADDRESS__".  If this macro is not
15087           defined, this feature is not available.  If defined, the address
15088           space is linear and there is no need to put ".rodata" into RAM.
15089           This is handled by the default linker description file, and is
15090           currently available for "avrtiny" and "avrxmega3".  Even more
15091           convenient, there is no need to use address spaces like "__flash"
15092           or features like attribute "progmem" and "pgm_read_*".
15093
15094       "__WITH_AVRLIBC__"
15095           The compiler is configured to be used together with AVR-Libc.  See
15096           the --with-avrlibc configure option.
15097
15098   Blackfin Options
15099       -mcpu=cpu[-sirevision]
15100           Specifies the name of the target Blackfin processor.  Currently,
15101           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
15102           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
15103           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
15104           bf547m, bf548m, bf549m, bf561, bf592.
15105
15106           The optional sirevision specifies the silicon revision of the
15107           target Blackfin processor.  Any workarounds available for the
15108           targeted silicon revision are enabled.  If sirevision is none, no
15109           workarounds are enabled.  If sirevision is any, all workarounds for
15110           the targeted processor are enabled.  The "__SILICON_REVISION__"
15111           macro is defined to two hexadecimal digits representing the major
15112           and minor numbers in the silicon revision.  If sirevision is none,
15113           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
15114           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
15115           optional sirevision is not used, GCC assumes the latest known
15116           silicon revision of the targeted Blackfin processor.
15117
15118           GCC defines a preprocessor macro for the specified cpu.  For the
15119           bfin-elf toolchain, this option causes the hardware BSP provided by
15120           libgloss to be linked in if -msim is not given.
15121
15122           Without this option, bf532 is used as the processor by default.
15123
15124           Note that support for bf561 is incomplete.  For bf561, only the
15125           preprocessor macro is defined.
15126
15127       -msim
15128           Specifies that the program will be run on the simulator.  This
15129           causes the simulator BSP provided by libgloss to be linked in.
15130           This option has effect only for bfin-elf toolchain.  Certain other
15131           options, such as -mid-shared-library and -mfdpic, imply -msim.
15132
15133       -momit-leaf-frame-pointer
15134           Don't keep the frame pointer in a register for leaf functions.
15135           This avoids the instructions to save, set up and restore frame
15136           pointers and makes an extra register available in leaf functions.
15137
15138       -mspecld-anomaly
15139           When enabled, the compiler ensures that the generated code does not
15140           contain speculative loads after jump instructions. If this option
15141           is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.
15142
15143       -mno-specld-anomaly
15144           Don't generate extra code to prevent speculative loads from
15145           occurring.
15146
15147       -mcsync-anomaly
15148           When enabled, the compiler ensures that the generated code does not
15149           contain CSYNC or SSYNC instructions too soon after conditional
15150           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
15151           is defined.
15152
15153       -mno-csync-anomaly
15154           Don't generate extra code to prevent CSYNC or SSYNC instructions
15155           from occurring too soon after a conditional branch.
15156
15157       -mlow-64k
15158           When enabled, the compiler is free to take advantage of the
15159           knowledge that the entire program fits into the low 64k of memory.
15160
15161       -mno-low-64k
15162           Assume that the program is arbitrarily large.  This is the default.
15163
15164       -mstack-check-l1
15165           Do stack checking using information placed into L1 scratchpad
15166           memory by the uClinux kernel.
15167
15168       -mid-shared-library
15169           Generate code that supports shared libraries via the library ID
15170           method.  This allows for execute in place and shared libraries in
15171           an environment without virtual memory management.  This option
15172           implies -fPIC.  With a bfin-elf target, this option implies -msim.
15173
15174       -mno-id-shared-library
15175           Generate code that doesn't assume ID-based shared libraries are
15176           being used.  This is the default.
15177
15178       -mleaf-id-shared-library
15179           Generate code that supports shared libraries via the library ID
15180           method, but assumes that this library or executable won't link
15181           against any other ID shared libraries.  That allows the compiler to
15182           use faster code for jumps and calls.
15183
15184       -mno-leaf-id-shared-library
15185           Do not assume that the code being compiled won't link against any
15186           ID shared libraries.  Slower code is generated for jump and call
15187           insns.
15188
15189       -mshared-library-id=n
15190           Specifies the identification number of the ID-based shared library
15191           being compiled.  Specifying a value of 0 generates more compact
15192           code; specifying other values forces the allocation of that number
15193           to the current library but is no more space- or time-efficient than
15194           omitting this option.
15195
15196       -msep-data
15197           Generate code that allows the data segment to be located in a
15198           different area of memory from the text segment.  This allows for
15199           execute in place in an environment without virtual memory
15200           management by eliminating relocations against the text section.
15201
15202       -mno-sep-data
15203           Generate code that assumes that the data segment follows the text
15204           segment.  This is the default.
15205
15206       -mlong-calls
15207       -mno-long-calls
15208           Tells the compiler to perform function calls by first loading the
15209           address of the function into a register and then performing a
15210           subroutine call on this register.  This switch is needed if the
15211           target function lies outside of the 24-bit addressing range of the
15212           offset-based version of subroutine call instruction.
15213
15214           This feature is not enabled by default.  Specifying -mno-long-calls
15215           restores the default behavior.  Note these switches have no effect
15216           on how the compiler generates code to handle function calls via
15217           function pointers.
15218
15219       -mfast-fp
15220           Link with the fast floating-point library. This library relaxes
15221           some of the IEEE floating-point standard's rules for checking
15222           inputs against Not-a-Number (NAN), in the interest of performance.
15223
15224       -minline-plt
15225           Enable inlining of PLT entries in function calls to functions that
15226           are not known to bind locally.  It has no effect without -mfdpic.
15227
15228       -mmulticore
15229           Build a standalone application for multicore Blackfin processors.
15230           This option causes proper start files and link scripts supporting
15231           multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
15232           can only be used with -mcpu=bf561[-sirevision].
15233
15234           This option can be used with -mcorea or -mcoreb, which selects the
15235           one-application-per-core programming model.  Without -mcorea or
15236           -mcoreb, the single-application/dual-core programming model is
15237           used. In this model, the main function of Core B should be named as
15238           "coreb_main".
15239
15240           If this option is not used, the single-core application programming
15241           model is used.
15242
15243       -mcorea
15244           Build a standalone application for Core A of BF561 when using the
15245           one-application-per-core programming model. Proper start files and
15246           link scripts are used to support Core A, and the macro
15247           "__BFIN_COREA" is defined.  This option can only be used in
15248           conjunction with -mmulticore.
15249
15250       -mcoreb
15251           Build a standalone application for Core B of BF561 when using the
15252           one-application-per-core programming model. Proper start files and
15253           link scripts are used to support Core B, and the macro
15254           "__BFIN_COREB" is defined. When this option is used, "coreb_main"
15255           should be used instead of "main".  This option can only be used in
15256           conjunction with -mmulticore.
15257
15258       -msdram
15259           Build a standalone application for SDRAM. Proper start files and
15260           link scripts are used to put the application into SDRAM, and the
15261           macro "__BFIN_SDRAM" is defined.  The loader should initialize
15262           SDRAM before loading the application.
15263
15264       -micplb
15265           Assume that ICPLBs are enabled at run time.  This has an effect on
15266           certain anomaly workarounds.  For Linux targets, the default is to
15267           assume ICPLBs are enabled; for standalone applications the default
15268           is off.
15269
15270   C6X Options
15271       -march=name
15272           This specifies the name of the target architecture.  GCC uses this
15273           name to determine what kind of instructions it can emit when
15274           generating assembly code.  Permissible names are: c62x, c64x,
15275           c64x+, c67x, c67x+, c674x.
15276
15277       -mbig-endian
15278           Generate code for a big-endian target.
15279
15280       -mlittle-endian
15281           Generate code for a little-endian target.  This is the default.
15282
15283       -msim
15284           Choose startup files and linker script suitable for the simulator.
15285
15286       -msdata=default
15287           Put small global and static data in the ".neardata" section, which
15288           is pointed to by register "B14".  Put small uninitialized global
15289           and static data in the ".bss" section, which is adjacent to the
15290           ".neardata" section.  Put small read-only data into the ".rodata"
15291           section.  The corresponding sections used for large pieces of data
15292           are ".fardata", ".far" and ".const".
15293
15294       -msdata=all
15295           Put all data, not just small objects, into the sections reserved
15296           for small data, and use addressing relative to the "B14" register
15297           to access them.
15298
15299       -msdata=none
15300           Make no use of the sections reserved for small data, and use
15301           absolute addresses to access all data.  Put all initialized global
15302           and static data in the ".fardata" section, and all uninitialized
15303           data in the ".far" section.  Put all constant data into the
15304           ".const" section.
15305
15306   CRIS Options
15307       These options are defined specifically for the CRIS ports.
15308
15309       -march=architecture-type
15310       -mcpu=architecture-type
15311           Generate code for the specified architecture.  The choices for
15312           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
15313           ETRAX 100, and ETRAX 100 LX.  Default is v0 except for cris-axis-
15314           linux-gnu, where the default is v10.
15315
15316       -mtune=architecture-type
15317           Tune to architecture-type everything applicable about the generated
15318           code, except for the ABI and the set of available instructions.
15319           The choices for architecture-type are the same as for
15320           -march=architecture-type.
15321
15322       -mmax-stack-frame=n
15323           Warn when the stack frame of a function exceeds n bytes.
15324
15325       -metrax4
15326       -metrax100
15327           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
15328           -march=v8 respectively.
15329
15330       -mmul-bug-workaround
15331       -mno-mul-bug-workaround
15332           Work around a bug in the "muls" and "mulu" instructions for CPU
15333           models where it applies.  This option is active by default.
15334
15335       -mpdebug
15336           Enable CRIS-specific verbose debug-related information in the
15337           assembly code.  This option also has the effect of turning off the
15338           #NO_APP formatted-code indicator to the assembler at the beginning
15339           of the assembly file.
15340
15341       -mcc-init
15342           Do not use condition-code results from previous instruction; always
15343           emit compare and test instructions before use of condition codes.
15344
15345       -mno-side-effects
15346           Do not emit instructions with side effects in addressing modes
15347           other than post-increment.
15348
15349       -mstack-align
15350       -mno-stack-align
15351       -mdata-align
15352       -mno-data-align
15353       -mconst-align
15354       -mno-const-align
15355           These options (no- options) arrange (eliminate arrangements) for
15356           the stack frame, individual data and constants to be aligned for
15357           the maximum single data access size for the chosen CPU model.  The
15358           default is to arrange for 32-bit alignment.  ABI details such as
15359           structure layout are not affected by these options.
15360
15361       -m32-bit
15362       -m16-bit
15363       -m8-bit
15364           Similar to the stack- data- and const-align options above, these
15365           options arrange for stack frame, writable data and constants to all
15366           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
15367           alignment.
15368
15369       -mno-prologue-epilogue
15370       -mprologue-epilogue
15371           With -mno-prologue-epilogue, the normal function prologue and
15372           epilogue which set up the stack frame are omitted and no return
15373           instructions or return sequences are generated in the code.  Use
15374           this option only together with visual inspection of the compiled
15375           code: no warnings or errors are generated when call-saved registers
15376           must be saved, or storage for local variables needs to be
15377           allocated.
15378
15379       -mno-gotplt
15380       -mgotplt
15381           With -fpic and -fPIC, don't generate (do generate) instruction
15382           sequences that load addresses for functions from the PLT part of
15383           the GOT rather than (traditional on other architectures) calls to
15384           the PLT.  The default is -mgotplt.
15385
15386       -melf
15387           Legacy no-op option only recognized with the cris-axis-elf and
15388           cris-axis-linux-gnu targets.
15389
15390       -mlinux
15391           Legacy no-op option only recognized with the cris-axis-linux-gnu
15392           target.
15393
15394       -sim
15395           This option, recognized for the cris-axis-elf, arranges to link
15396           with input-output functions from a simulator library.  Code,
15397           initialized data and zero-initialized data are allocated
15398           consecutively.
15399
15400       -sim2
15401           Like -sim, but pass linker options to locate initialized data at
15402           0x40000000 and zero-initialized data at 0x80000000.
15403
15404   CR16 Options
15405       These options are defined specifically for the CR16 ports.
15406
15407       -mmac
15408           Enable the use of multiply-accumulate instructions. Disabled by
15409           default.
15410
15411       -mcr16cplus
15412       -mcr16c
15413           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
15414           is default.
15415
15416       -msim
15417           Links the library libsim.a which is in compatible with simulator.
15418           Applicable to ELF compiler only.
15419
15420       -mint32
15421           Choose integer type as 32-bit wide.
15422
15423       -mbit-ops
15424           Generates "sbit"/"cbit" instructions for bit manipulations.
15425
15426       -mdata-model=model
15427           Choose a data model. The choices for model are near, far or medium.
15428           medium is default.  However, far is not valid with -mcr16c, as the
15429           CR16C architecture does not support the far data model.
15430
15431   Darwin Options
15432       These options are defined for all architectures running the Darwin
15433       operating system.
15434
15435       FSF GCC on Darwin does not create "fat" object files; it creates an
15436       object file for the single architecture that GCC was built to target.
15437       Apple's GCC on Darwin does create "fat" files if multiple -arch options
15438       are used; it does so by running the compiler or linker multiple times
15439       and joining the results together with lipo.
15440
15441       The subtype of the file created (like ppc7400 or ppc970 or i686) is
15442       determined by the flags that specify the ISA that GCC is targeting,
15443       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
15444       override this.
15445
15446       The Darwin tools vary in their behavior when presented with an ISA
15447       mismatch.  The assembler, as, only permits instructions to be used that
15448       are valid for the subtype of the file it is generating, so you cannot
15449       put 64-bit instructions in a ppc750 object file.  The linker for shared
15450       libraries, /usr/bin/libtool, fails and prints an error if asked to
15451       create a shared library with a less restrictive subtype than its input
15452       files (for instance, trying to put a ppc970 object file in a ppc7400
15453       library).  The linker for executables, ld, quietly gives the executable
15454       the most restrictive subtype of any of its input files.
15455
15456       -Fdir
15457           Add the framework directory dir to the head of the list of
15458           directories to be searched for header files.  These directories are
15459           interleaved with those specified by -I options and are scanned in a
15460           left-to-right order.
15461
15462           A framework directory is a directory with frameworks in it.  A
15463           framework is a directory with a Headers and/or PrivateHeaders
15464           directory contained directly in it that ends in .framework.  The
15465           name of a framework is the name of this directory excluding the
15466           .framework.  Headers associated with the framework are found in one
15467           of those two directories, with Headers being searched first.  A
15468           subframework is a framework directory that is in a framework's
15469           Frameworks directory.  Includes of subframework headers can only
15470           appear in a header of a framework that contains the subframework,
15471           or in a sibling subframework header.  Two subframeworks are
15472           siblings if they occur in the same framework.  A subframework
15473           should not have the same name as a framework; a warning is issued
15474           if this is violated.  Currently a subframework cannot have
15475           subframeworks; in the future, the mechanism may be extended to
15476           support this.  The standard frameworks can be found in
15477           /System/Library/Frameworks and /Library/Frameworks.  An example
15478           include looks like "#include <Framework/header.h>", where Framework
15479           denotes the name of the framework and header.h is found in the
15480           PrivateHeaders or Headers directory.
15481
15482       -iframeworkdir
15483           Like -F except the directory is a treated as a system directory.
15484           The main difference between this -iframework and -F is that with
15485           -iframework the compiler does not warn about constructs contained
15486           within header files found via dir.  This option is valid only for
15487           the C family of languages.
15488
15489       -gused
15490           Emit debugging information for symbols that are used.  For stabs
15491           debugging format, this enables -feliminate-unused-debug-symbols.
15492           This is by default ON.
15493
15494       -gfull
15495           Emit debugging information for all symbols and types.
15496
15497       -mmacosx-version-min=version
15498           The earliest version of MacOS X that this executable will run on is
15499           version.  Typical values of version include 10.1, 10.2, and 10.3.9.
15500
15501           If the compiler was built to use the system's headers by default,
15502           then the default for this option is the system version on which the
15503           compiler is running, otherwise the default is to make choices that
15504           are compatible with as many systems and code bases as possible.
15505
15506       -mkernel
15507           Enable kernel development mode.  The -mkernel option sets -static,
15508           -fno-common, -fno-use-cxa-atexit, -fno-exceptions,
15509           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
15510           where applicable.  This mode also sets -mno-altivec, -msoft-float,
15511           -fno-builtin and -mlong-branch for PowerPC targets.
15512
15513       -mone-byte-bool
15514           Override the defaults for "bool" so that "sizeof(bool)==1".  By
15515           default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1
15516           when compiling for Darwin/x86, so this option has no effect on x86.
15517
15518           Warning: The -mone-byte-bool switch causes GCC to generate code
15519           that is not binary compatible with code generated without that
15520           switch.  Using this switch may require recompiling all other
15521           modules in a program, including system libraries.  Use this switch
15522           to conform to a non-default data model.
15523
15524       -mfix-and-continue
15525       -ffix-and-continue
15526       -findirect-data
15527           Generate code suitable for fast turnaround development, such as to
15528           allow GDB to dynamically load .o files into already-running
15529           programs.  -findirect-data and -ffix-and-continue are provided for
15530           backwards compatibility.
15531
15532       -all_load
15533           Loads all members of static archive libraries.  See man ld(1) for
15534           more information.
15535
15536       -arch_errors_fatal
15537           Cause the errors having to do with files that have the wrong
15538           architecture to be fatal.
15539
15540       -bind_at_load
15541           Causes the output file to be marked such that the dynamic linker
15542           will bind all undefined references when the file is loaded or
15543           launched.
15544
15545       -bundle
15546           Produce a Mach-o bundle format file.  See man ld(1) for more
15547           information.
15548
15549       -bundle_loader executable
15550           This option specifies the executable that will load the build
15551           output file being linked.  See man ld(1) for more information.
15552
15553       -dynamiclib
15554           When passed this option, GCC produces a dynamic library instead of
15555           an executable when linking, using the Darwin libtool command.
15556
15557       -force_cpusubtype_ALL
15558           This causes GCC's output file to have the ALL subtype, instead of
15559           one controlled by the -mcpu or -march option.
15560
15561       -allowable_client  client_name
15562       -client_name
15563       -compatibility_version
15564       -current_version
15565       -dead_strip
15566       -dependency-file
15567       -dylib_file
15568       -dylinker_install_name
15569       -dynamic
15570       -exported_symbols_list
15571       -filelist
15572       -flat_namespace
15573       -force_flat_namespace
15574       -headerpad_max_install_names
15575       -image_base
15576       -init
15577       -install_name
15578       -keep_private_externs
15579       -multi_module
15580       -multiply_defined
15581       -multiply_defined_unused
15582       -noall_load
15583       -no_dead_strip_inits_and_terms
15584       -nofixprebinding
15585       -nomultidefs
15586       -noprebind
15587       -noseglinkedit
15588       -pagezero_size
15589       -prebind
15590       -prebind_all_twolevel_modules
15591       -private_bundle
15592       -read_only_relocs
15593       -sectalign
15594       -sectobjectsymbols
15595       -whyload
15596       -seg1addr
15597       -sectcreate
15598       -sectobjectsymbols
15599       -sectorder
15600       -segaddr
15601       -segs_read_only_addr
15602       -segs_read_write_addr
15603       -seg_addr_table
15604       -seg_addr_table_filename
15605       -seglinkedit
15606       -segprot
15607       -segs_read_only_addr
15608       -segs_read_write_addr
15609       -single_module
15610       -static
15611       -sub_library
15612       -sub_umbrella
15613       -twolevel_namespace
15614       -umbrella
15615       -undefined
15616       -unexported_symbols_list
15617       -weak_reference_mismatches
15618       -whatsloaded
15619           These options are passed to the Darwin linker.  The Darwin linker
15620           man page describes them in detail.
15621
15622   DEC Alpha Options
15623       These -m options are defined for the DEC Alpha implementations:
15624
15625       -mno-soft-float
15626       -msoft-float
15627           Use (do not use) the hardware floating-point instructions for
15628           floating-point operations.  When -msoft-float is specified,
15629           functions in libgcc.a are used to perform floating-point
15630           operations.  Unless they are replaced by routines that emulate the
15631           floating-point operations, or compiled in such a way as to call
15632           such emulations routines, these routines issue floating-point
15633           operations.   If you are compiling for an Alpha without floating-
15634           point operations, you must ensure that the library is built so as
15635           not to call them.
15636
15637           Note that Alpha implementations without floating-point operations
15638           are required to have floating-point registers.
15639
15640       -mfp-reg
15641       -mno-fp-regs
15642           Generate code that uses (does not use) the floating-point register
15643           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
15644           register set is not used, floating-point operands are passed in
15645           integer registers as if they were integers and floating-point
15646           results are passed in $0 instead of $f0.  This is a non-standard
15647           calling sequence, so any function with a floating-point argument or
15648           return value called by code compiled with -mno-fp-regs must also be
15649           compiled with that option.
15650
15651           A typical use of this option is building a kernel that does not
15652           use, and hence need not save and restore, any floating-point
15653           registers.
15654
15655       -mieee
15656           The Alpha architecture implements floating-point hardware optimized
15657           for maximum performance.  It is mostly compliant with the IEEE
15658           floating-point standard.  However, for full compliance, software
15659           assistance is required.  This option generates code fully IEEE-
15660           compliant code except that the inexact-flag is not maintained (see
15661           below).  If this option is turned on, the preprocessor macro
15662           "_IEEE_FP" is defined during compilation.  The resulting code is
15663           less efficient but is able to correctly support denormalized
15664           numbers and exceptional IEEE values such as not-a-number and
15665           plus/minus infinity.  Other Alpha compilers call this option
15666           -ieee_with_no_inexact.
15667
15668       -mieee-with-inexact
15669           This is like -mieee except the generated code also maintains the
15670           IEEE inexact-flag.  Turning on this option causes the generated
15671           code to implement fully-compliant IEEE math.  In addition to
15672           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
15673           On some Alpha implementations the resulting code may execute
15674           significantly slower than the code generated by default.  Since
15675           there is very little code that depends on the inexact-flag, you
15676           should normally not specify this option.  Other Alpha compilers
15677           call this option -ieee_with_inexact.
15678
15679       -mfp-trap-mode=trap-mode
15680           This option controls what floating-point related traps are enabled.
15681           Other Alpha compilers call this option -fptm trap-mode.  The trap
15682           mode can be set to one of four values:
15683
15684           n   This is the default (normal) setting.  The only traps that are
15685               enabled are the ones that cannot be disabled in software (e.g.,
15686               division by zero trap).
15687
15688           u   In addition to the traps enabled by n, underflow traps are
15689               enabled as well.
15690
15691           su  Like u, but the instructions are marked to be safe for software
15692               completion (see Alpha architecture manual for details).
15693
15694           sui Like su, but inexact traps are enabled as well.
15695
15696       -mfp-rounding-mode=rounding-mode
15697           Selects the IEEE rounding mode.  Other Alpha compilers call this
15698           option -fprm rounding-mode.  The rounding-mode can be one of:
15699
15700           n   Normal IEEE rounding mode.  Floating-point numbers are rounded
15701               towards the nearest machine number or towards the even machine
15702               number in case of a tie.
15703
15704           m   Round towards minus infinity.
15705
15706           c   Chopped rounding mode.  Floating-point numbers are rounded
15707               towards zero.
15708
15709           d   Dynamic rounding mode.  A field in the floating-point control
15710               register (fpcr, see Alpha architecture reference manual)
15711               controls the rounding mode in effect.  The C library
15712               initializes this register for rounding towards plus infinity.
15713               Thus, unless your program modifies the fpcr, d corresponds to
15714               round towards plus infinity.
15715
15716       -mtrap-precision=trap-precision
15717           In the Alpha architecture, floating-point traps are imprecise.
15718           This means without software assistance it is impossible to recover
15719           from a floating trap and program execution normally needs to be
15720           terminated.  GCC can generate code that can assist operating system
15721           trap handlers in determining the exact location that caused a
15722           floating-point trap.  Depending on the requirements of an
15723           application, different levels of precisions can be selected:
15724
15725           p   Program precision.  This option is the default and means a trap
15726               handler can only identify which program caused a floating-point
15727               exception.
15728
15729           f   Function precision.  The trap handler can determine the
15730               function that caused a floating-point exception.
15731
15732           i   Instruction precision.  The trap handler can determine the
15733               exact instruction that caused a floating-point exception.
15734
15735           Other Alpha compilers provide the equivalent options called
15736           -scope_safe and -resumption_safe.
15737
15738       -mieee-conformant
15739           This option marks the generated code as IEEE conformant.  You must
15740           not use this option unless you also specify -mtrap-precision=i and
15741           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
15742           to emit the line .eflag 48 in the function prologue of the
15743           generated assembly file.
15744
15745       -mbuild-constants
15746           Normally GCC examines a 32- or 64-bit integer constant to see if it
15747           can construct it from smaller constants in two or three
15748           instructions.  If it cannot, it outputs the constant as a literal
15749           and generates code to load it from the data segment at run time.
15750
15751           Use this option to require GCC to construct all integer constants
15752           using code, even if it takes more instructions (the maximum is
15753           six).
15754
15755           You typically use this option to build a shared library dynamic
15756           loader.  Itself a shared library, it must relocate itself in memory
15757           before it can find the variables and constants in its own data
15758           segment.
15759
15760       -mbwx
15761       -mno-bwx
15762       -mcix
15763       -mno-cix
15764       -mfix
15765       -mno-fix
15766       -mmax
15767       -mno-max
15768           Indicate whether GCC should generate code to use the optional BWX,
15769           CIX, FIX and MAX instruction sets.  The default is to use the
15770           instruction sets supported by the CPU type specified via -mcpu=
15771           option or that of the CPU on which GCC was built if none is
15772           specified.
15773
15774       -mfloat-vax
15775       -mfloat-ieee
15776           Generate code that uses (does not use) VAX F and G floating-point
15777           arithmetic instead of IEEE single and double precision.
15778
15779       -mexplicit-relocs
15780       -mno-explicit-relocs
15781           Older Alpha assemblers provided no way to generate symbol
15782           relocations except via assembler macros.  Use of these macros does
15783           not allow optimal instruction scheduling.  GNU binutils as of
15784           version 2.12 supports a new syntax that allows the compiler to
15785           explicitly mark which relocations should apply to which
15786           instructions.  This option is mostly useful for debugging, as GCC
15787           detects the capabilities of the assembler when it is built and sets
15788           the default accordingly.
15789
15790       -msmall-data
15791       -mlarge-data
15792           When -mexplicit-relocs is in effect, static data is accessed via
15793           gp-relative relocations.  When -msmall-data is used, objects 8
15794           bytes long or smaller are placed in a small data area (the ".sdata"
15795           and ".sbss" sections) and are accessed via 16-bit relocations off
15796           of the $gp register.  This limits the size of the small data area
15797           to 64KB, but allows the variables to be directly accessed via a
15798           single instruction.
15799
15800           The default is -mlarge-data.  With this option the data area is
15801           limited to just below 2GB.  Programs that require more than 2GB of
15802           data must use "malloc" or "mmap" to allocate the data in the heap
15803           instead of in the program's data segment.
15804
15805           When generating code for shared libraries, -fpic implies
15806           -msmall-data and -fPIC implies -mlarge-data.
15807
15808       -msmall-text
15809       -mlarge-text
15810           When -msmall-text is used, the compiler assumes that the code of
15811           the entire program (or shared library) fits in 4MB, and is thus
15812           reachable with a branch instruction.  When -msmall-data is used,
15813           the compiler can assume that all local symbols share the same $gp
15814           value, and thus reduce the number of instructions required for a
15815           function call from 4 to 1.
15816
15817           The default is -mlarge-text.
15818
15819       -mcpu=cpu_type
15820           Set the instruction set and instruction scheduling parameters for
15821           machine type cpu_type.  You can specify either the EV style name or
15822           the corresponding chip number.  GCC supports scheduling parameters
15823           for the EV4, EV5 and EV6 family of processors and chooses the
15824           default values for the instruction set from the processor you
15825           specify.  If you do not specify a processor type, GCC defaults to
15826           the processor on which the compiler was built.
15827
15828           Supported values for cpu_type are
15829
15830           ev4
15831           ev45
15832           21064
15833               Schedules as an EV4 and has no instruction set extensions.
15834
15835           ev5
15836           21164
15837               Schedules as an EV5 and has no instruction set extensions.
15838
15839           ev56
15840           21164a
15841               Schedules as an EV5 and supports the BWX extension.
15842
15843           pca56
15844           21164pc
15845           21164PC
15846               Schedules as an EV5 and supports the BWX and MAX extensions.
15847
15848           ev6
15849           21264
15850               Schedules as an EV6 and supports the BWX, FIX, and MAX
15851               extensions.
15852
15853           ev67
15854           21264a
15855               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
15856               extensions.
15857
15858           Native toolchains also support the value native, which selects the
15859           best architecture option for the host processor.  -mcpu=native has
15860           no effect if GCC does not recognize the processor.
15861
15862       -mtune=cpu_type
15863           Set only the instruction scheduling parameters for machine type
15864           cpu_type.  The instruction set is not changed.
15865
15866           Native toolchains also support the value native, which selects the
15867           best architecture option for the host processor.  -mtune=native has
15868           no effect if GCC does not recognize the processor.
15869
15870       -mmemory-latency=time
15871           Sets the latency the scheduler should assume for typical memory
15872           references as seen by the application.  This number is highly
15873           dependent on the memory access patterns used by the application and
15874           the size of the external cache on the machine.
15875
15876           Valid options for time are
15877
15878           number
15879               A decimal number representing clock cycles.
15880
15881           L1
15882           L2
15883           L3
15884           main
15885               The compiler contains estimates of the number of clock cycles
15886               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
15887               (also called Dcache, Scache, and Bcache), as well as to main
15888               memory.  Note that L3 is only valid for EV5.
15889
15890   FR30 Options
15891       These options are defined specifically for the FR30 port.
15892
15893       -msmall-model
15894           Use the small address space model.  This can produce smaller code,
15895           but it does assume that all symbolic values and addresses fit into
15896           a 20-bit range.
15897
15898       -mno-lsim
15899           Assume that runtime support has been provided and so there is no
15900           need to include the simulator library (libsim.a) on the linker
15901           command line.
15902
15903   FT32 Options
15904       These options are defined specifically for the FT32 port.
15905
15906       -msim
15907           Specifies that the program will be run on the simulator.  This
15908           causes an alternate runtime startup and library to be linked.  You
15909           must not use this option when generating programs that will run on
15910           real hardware; you must provide your own runtime library for
15911           whatever I/O functions are needed.
15912
15913       -mlra
15914           Enable Local Register Allocation.  This is still experimental for
15915           FT32, so by default the compiler uses standard reload.
15916
15917       -mnodiv
15918           Do not use div and mod instructions.
15919
15920       -mft32b
15921           Enable use of the extended instructions of the FT32B processor.
15922
15923       -mcompress
15924           Compress all code using the Ft32B code compression scheme.
15925
15926       -mnopm
15927           Do not generate code that reads program memory.
15928
15929   FRV Options
15930       -mgpr-32
15931           Only use the first 32 general-purpose registers.
15932
15933       -mgpr-64
15934           Use all 64 general-purpose registers.
15935
15936       -mfpr-32
15937           Use only the first 32 floating-point registers.
15938
15939       -mfpr-64
15940           Use all 64 floating-point registers.
15941
15942       -mhard-float
15943           Use hardware instructions for floating-point operations.
15944
15945       -msoft-float
15946           Use library routines for floating-point operations.
15947
15948       -malloc-cc
15949           Dynamically allocate condition code registers.
15950
15951       -mfixed-cc
15952           Do not try to dynamically allocate condition code registers, only
15953           use "icc0" and "fcc0".
15954
15955       -mdword
15956           Change ABI to use double word insns.
15957
15958       -mno-dword
15959           Do not use double word instructions.
15960
15961       -mdouble
15962           Use floating-point double instructions.
15963
15964       -mno-double
15965           Do not use floating-point double instructions.
15966
15967       -mmedia
15968           Use media instructions.
15969
15970       -mno-media
15971           Do not use media instructions.
15972
15973       -mmuladd
15974           Use multiply and add/subtract instructions.
15975
15976       -mno-muladd
15977           Do not use multiply and add/subtract instructions.
15978
15979       -mfdpic
15980           Select the FDPIC ABI, which uses function descriptors to represent
15981           pointers to functions.  Without any PIC/PIE-related options, it
15982           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
15983           small data are within a 12-bit range from the GOT base address;
15984           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
15985           bfin-elf target, this option implies -msim.
15986
15987       -minline-plt
15988           Enable inlining of PLT entries in function calls to functions that
15989           are not known to bind locally.  It has no effect without -mfdpic.
15990           It's enabled by default if optimizing for speed and compiling for
15991           shared libraries (i.e., -fPIC or -fpic), or when an optimization
15992           option such as -O3 or above is present in the command line.
15993
15994       -mTLS
15995           Assume a large TLS segment when generating thread-local code.
15996
15997       -mtls
15998           Do not assume a large TLS segment when generating thread-local
15999           code.
16000
16001       -mgprel-ro
16002           Enable the use of "GPREL" relocations in the FDPIC ABI for data
16003           that is known to be in read-only sections.  It's enabled by
16004           default, except for -fpic or -fpie: even though it may help make
16005           the global offset table smaller, it trades 1 instruction for 4.
16006           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
16007           may be shared by multiple symbols, and it avoids the need for a GOT
16008           entry for the referenced symbol, so it's more likely to be a win.
16009           If it is not, -mno-gprel-ro can be used to disable it.
16010
16011       -multilib-library-pic
16012           Link with the (library, not FD) pic libraries.  It's implied by
16013           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
16014           should never have to use it explicitly.
16015
16016       -mlinked-fp
16017           Follow the EABI requirement of always creating a frame pointer
16018           whenever a stack frame is allocated.  This option is enabled by
16019           default and can be disabled with -mno-linked-fp.
16020
16021       -mlong-calls
16022           Use indirect addressing to call functions outside the current
16023           compilation unit.  This allows the functions to be placed anywhere
16024           within the 32-bit address space.
16025
16026       -malign-labels
16027           Try to align labels to an 8-byte boundary by inserting NOPs into
16028           the previous packet.  This option only has an effect when VLIW
16029           packing is enabled.  It doesn't create new packets; it merely adds
16030           NOPs to existing ones.
16031
16032       -mlibrary-pic
16033           Generate position-independent EABI code.
16034
16035       -macc-4
16036           Use only the first four media accumulator registers.
16037
16038       -macc-8
16039           Use all eight media accumulator registers.
16040
16041       -mpack
16042           Pack VLIW instructions.
16043
16044       -mno-pack
16045           Do not pack VLIW instructions.
16046
16047       -mno-eflags
16048           Do not mark ABI switches in e_flags.
16049
16050       -mcond-move
16051           Enable the use of conditional-move instructions (default).
16052
16053           This switch is mainly for debugging the compiler and will likely be
16054           removed in a future version.
16055
16056       -mno-cond-move
16057           Disable the use of conditional-move instructions.
16058
16059           This switch is mainly for debugging the compiler and will likely be
16060           removed in a future version.
16061
16062       -mscc
16063           Enable the use of conditional set instructions (default).
16064
16065           This switch is mainly for debugging the compiler and will likely be
16066           removed in a future version.
16067
16068       -mno-scc
16069           Disable the use of conditional set instructions.
16070
16071           This switch is mainly for debugging the compiler and will likely be
16072           removed in a future version.
16073
16074       -mcond-exec
16075           Enable the use of conditional execution (default).
16076
16077           This switch is mainly for debugging the compiler and will likely be
16078           removed in a future version.
16079
16080       -mno-cond-exec
16081           Disable the use of conditional execution.
16082
16083           This switch is mainly for debugging the compiler and will likely be
16084           removed in a future version.
16085
16086       -mvliw-branch
16087           Run a pass to pack branches into VLIW instructions (default).
16088
16089           This switch is mainly for debugging the compiler and will likely be
16090           removed in a future version.
16091
16092       -mno-vliw-branch
16093           Do not run a pass to pack branches into VLIW instructions.
16094
16095           This switch is mainly for debugging the compiler and will likely be
16096           removed in a future version.
16097
16098       -mmulti-cond-exec
16099           Enable optimization of "&&" and "||" in conditional execution
16100           (default).
16101
16102           This switch is mainly for debugging the compiler and will likely be
16103           removed in a future version.
16104
16105       -mno-multi-cond-exec
16106           Disable optimization of "&&" and "||" in conditional execution.
16107
16108           This switch is mainly for debugging the compiler and will likely be
16109           removed in a future version.
16110
16111       -mnested-cond-exec
16112           Enable nested conditional execution optimizations (default).
16113
16114           This switch is mainly for debugging the compiler and will likely be
16115           removed in a future version.
16116
16117       -mno-nested-cond-exec
16118           Disable nested conditional execution optimizations.
16119
16120           This switch is mainly for debugging the compiler and will likely be
16121           removed in a future version.
16122
16123       -moptimize-membar
16124           This switch removes redundant "membar" instructions from the
16125           compiler-generated code.  It is enabled by default.
16126
16127       -mno-optimize-membar
16128           This switch disables the automatic removal of redundant "membar"
16129           instructions from the generated code.
16130
16131       -mtomcat-stats
16132           Cause gas to print out tomcat statistics.
16133
16134       -mcpu=cpu
16135           Select the processor type for which to generate code.  Possible
16136           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
16137           and simple.
16138
16139   GNU/Linux Options
16140       These -m options are defined for GNU/Linux targets:
16141
16142       -mglibc
16143           Use the GNU C library.  This is the default except on
16144           *-*-linux-*uclibc*, *-*-linux-*musl* and *-*-linux-*android*
16145           targets.
16146
16147       -muclibc
16148           Use uClibc C library.  This is the default on *-*-linux-*uclibc*
16149           targets.
16150
16151       -mmusl
16152           Use the musl C library.  This is the default on *-*-linux-*musl*
16153           targets.
16154
16155       -mbionic
16156           Use Bionic C library.  This is the default on *-*-linux-*android*
16157           targets.
16158
16159       -mandroid
16160           Compile code compatible with Android platform.  This is the default
16161           on *-*-linux-*android* targets.
16162
16163           When compiling, this option enables -mbionic, -fPIC,
16164           -fno-exceptions and -fno-rtti by default.  When linking, this
16165           option makes the GCC driver pass Android-specific options to the
16166           linker.  Finally, this option causes the preprocessor macro
16167           "__ANDROID__" to be defined.
16168
16169       -tno-android-cc
16170           Disable compilation effects of -mandroid, i.e., do not enable
16171           -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.
16172
16173       -tno-android-ld
16174           Disable linking effects of -mandroid, i.e., pass standard Linux
16175           linking options to the linker.
16176
16177   H8/300 Options
16178       These -m options are defined for the H8/300 implementations:
16179
16180       -mrelax
16181           Shorten some address references at link time, when possible; uses
16182           the linker option -relax.
16183
16184       -mh Generate code for the H8/300H.
16185
16186       -ms Generate code for the H8S.
16187
16188       -mn Generate code for the H8S and H8/300H in the normal mode.  This
16189           switch must be used either with -mh or -ms.
16190
16191       -ms2600
16192           Generate code for the H8S/2600.  This switch must be used with -ms.
16193
16194       -mexr
16195           Extended registers are stored on stack before execution of function
16196           with monitor attribute. Default option is -mexr.  This option is
16197           valid only for H8S targets.
16198
16199       -mno-exr
16200           Extended registers are not stored on stack before execution of
16201           function with monitor attribute. Default option is -mno-exr.  This
16202           option is valid only for H8S targets.
16203
16204       -mint32
16205           Make "int" data 32 bits by default.
16206
16207       -malign-300
16208           On the H8/300H and H8S, use the same alignment rules as for the
16209           H8/300.  The default for the H8/300H and H8S is to align longs and
16210           floats on 4-byte boundaries.  -malign-300 causes them to be aligned
16211           on 2-byte boundaries.  This option has no effect on the H8/300.
16212
16213   HPPA Options
16214       These -m options are defined for the HPPA family of computers:
16215
16216       -march=architecture-type
16217           Generate code for the specified architecture.  The choices for
16218           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
16219           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
16220           system to determine the proper architecture option for your
16221           machine.  Code compiled for lower numbered architectures runs on
16222           higher numbered architectures, but not the other way around.
16223
16224       -mpa-risc-1-0
16225       -mpa-risc-1-1
16226       -mpa-risc-2-0
16227           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
16228
16229       -mcaller-copies
16230           The caller copies function arguments passed by hidden reference.
16231           This option should be used with care as it is not compatible with
16232           the default 32-bit runtime.  However, only aggregates larger than
16233           eight bytes are passed by hidden reference and the option provides
16234           better compatibility with OpenMP.
16235
16236       -mjump-in-delay
16237           This option is ignored and provided for compatibility purposes
16238           only.
16239
16240       -mdisable-fpregs
16241           Prevent floating-point registers from being used in any manner.
16242           This is necessary for compiling kernels that perform lazy context
16243           switching of floating-point registers.  If you use this option and
16244           attempt to perform floating-point operations, the compiler aborts.
16245
16246       -mdisable-indexing
16247           Prevent the compiler from using indexing address modes.  This
16248           avoids some rather obscure problems when compiling MIG generated
16249           code under MACH.
16250
16251       -mno-space-regs
16252           Generate code that assumes the target has no space registers.  This
16253           allows GCC to generate faster indirect calls and use unscaled index
16254           address modes.
16255
16256           Such code is suitable for level 0 PA systems and kernels.
16257
16258       -mfast-indirect-calls
16259           Generate code that assumes calls never cross space boundaries.
16260           This allows GCC to emit code that performs faster indirect calls.
16261
16262           This option does not work in the presence of shared libraries or
16263           nested functions.
16264
16265       -mfixed-range=register-range
16266           Generate code treating the given register range as fixed registers.
16267           A fixed register is one that the register allocator cannot use.
16268           This is useful when compiling kernel code.  A register range is
16269           specified as two registers separated by a dash.  Multiple register
16270           ranges can be specified separated by a comma.
16271
16272       -mlong-load-store
16273           Generate 3-instruction load and store sequences as sometimes
16274           required by the HP-UX 10 linker.  This is equivalent to the +k
16275           option to the HP compilers.
16276
16277       -mportable-runtime
16278           Use the portable calling conventions proposed by HP for ELF
16279           systems.
16280
16281       -mgas
16282           Enable the use of assembler directives only GAS understands.
16283
16284       -mschedule=cpu-type
16285           Schedule code according to the constraints for the machine type
16286           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
16287           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
16288           to determine the proper scheduling option for your machine.  The
16289           default scheduling is 8000.
16290
16291       -mlinker-opt
16292           Enable the optimization pass in the HP-UX linker.  Note this makes
16293           symbolic debugging impossible.  It also triggers a bug in the HP-UX
16294           8 and HP-UX 9 linkers in which they give bogus error messages when
16295           linking some programs.
16296
16297       -msoft-float
16298           Generate output containing library calls for floating point.
16299           Warning: the requisite libraries are not available for all HPPA
16300           targets.  Normally the facilities of the machine's usual C compiler
16301           are used, but this cannot be done directly in cross-compilation.
16302           You must make your own arrangements to provide suitable library
16303           functions for cross-compilation.
16304
16305           -msoft-float changes the calling convention in the output file;
16306           therefore, it is only useful if you compile all of a program with
16307           this option.  In particular, you need to compile libgcc.a, the
16308           library that comes with GCC, with -msoft-float in order for this to
16309           work.
16310
16311       -msio
16312           Generate the predefine, "_SIO", for server IO.  The default is
16313           -mwsio.  This generates the predefines, "__hp9000s700",
16314           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
16315           are available under HP-UX and HI-UX.
16316
16317       -mgnu-ld
16318           Use options specific to GNU ld.  This passes -shared to ld when
16319           building a shared library.  It is the default when GCC is
16320           configured, explicitly or implicitly, with the GNU linker.  This
16321           option does not affect which ld is called; it only changes what
16322           parameters are passed to that ld.  The ld that is called is
16323           determined by the --with-ld configure option, GCC's program search
16324           path, and finally by the user's PATH.  The linker used by GCC can
16325           be printed using which `gcc -print-prog-name=ld`.  This option is
16326           only available on the 64-bit HP-UX GCC, i.e. configured with
16327           hppa*64*-*-hpux*.
16328
16329       -mhp-ld
16330           Use options specific to HP ld.  This passes -b to ld when building
16331           a shared library and passes +Accept TypeMismatch to ld on all
16332           links.  It is the default when GCC is configured, explicitly or
16333           implicitly, with the HP linker.  This option does not affect which
16334           ld is called; it only changes what parameters are passed to that
16335           ld.  The ld that is called is determined by the --with-ld configure
16336           option, GCC's program search path, and finally by the user's PATH.
16337           The linker used by GCC can be printed using which `gcc
16338           -print-prog-name=ld`.  This option is only available on the 64-bit
16339           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.
16340
16341       -mlong-calls
16342           Generate code that uses long call sequences.  This ensures that a
16343           call is always able to reach linker generated stubs.  The default
16344           is to generate long calls only when the distance from the call site
16345           to the beginning of the function or translation unit, as the case
16346           may be, exceeds a predefined limit set by the branch type being
16347           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
16348           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
16349           always limited at 240,000 bytes.
16350
16351           Distances are measured from the beginning of functions when using
16352           the -ffunction-sections option, or when using the -mgas and
16353           -mno-portable-runtime options together under HP-UX with the SOM
16354           linker.
16355
16356           It is normally not desirable to use this option as it degrades
16357           performance.  However, it may be useful in large applications,
16358           particularly when partial linking is used to build the application.
16359
16360           The types of long calls used depends on the capabilities of the
16361           assembler and linker, and the type of code being generated.  The
16362           impact on systems that support long absolute calls, and long pic
16363           symbol-difference or pc-relative calls should be relatively small.
16364           However, an indirect call is used on 32-bit ELF systems in pic code
16365           and it is quite long.
16366
16367       -munix=unix-std
16368           Generate compiler predefines and select a startfile for the
16369           specified UNIX standard.  The choices for unix-std are 93, 95 and
16370           98.  93 is supported on all HP-UX versions.  95 is available on HP-
16371           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
16372           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
16373           11.00, and 98 for HP-UX 11.11 and later.
16374
16375           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
16376           -munix=95 provides additional predefines for "XOPEN_UNIX" and
16377           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
16378           provides additional predefines for "_XOPEN_UNIX",
16379           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
16380           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.
16381
16382           It is important to note that this option changes the interfaces for
16383           various library routines.  It also affects the operational behavior
16384           of the C library.  Thus, extreme care is needed in using this
16385           option.
16386
16387           Library code that is intended to operate with more than one UNIX
16388           standard must test, set and restore the variable
16389           "__xpg4_extended_mask" as appropriate.  Most GNU software doesn't
16390           provide this capability.
16391
16392       -nolibdld
16393           Suppress the generation of link options to search libdld.sl when
16394           the -static option is specified on HP-UX 10 and later.
16395
16396       -static
16397           The HP-UX implementation of setlocale in libc has a dependency on
16398           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
16399           when the -static option is specified, special link options are
16400           needed to resolve this dependency.
16401
16402           On HP-UX 10 and later, the GCC driver adds the necessary options to
16403           link with libdld.sl when the -static option is specified.  This
16404           causes the resulting binary to be dynamic.  On the 64-bit port, the
16405           linkers generate dynamic binaries by default in any case.  The
16406           -nolibdld option can be used to prevent the GCC driver from adding
16407           these link options.
16408
16409       -threads
16410           Add support for multithreading with the dce thread library under
16411           HP-UX.  This option sets flags for both the preprocessor and
16412           linker.
16413
16414   IA-64 Options
16415       These are the -m options defined for the Intel IA-64 architecture.
16416
16417       -mbig-endian
16418           Generate code for a big-endian target.  This is the default for HP-
16419           UX.
16420
16421       -mlittle-endian
16422           Generate code for a little-endian target.  This is the default for
16423           AIX5 and GNU/Linux.
16424
16425       -mgnu-as
16426       -mno-gnu-as
16427           Generate (or don't) code for the GNU assembler.  This is the
16428           default.
16429
16430       -mgnu-ld
16431       -mno-gnu-ld
16432           Generate (or don't) code for the GNU linker.  This is the default.
16433
16434       -mno-pic
16435           Generate code that does not use a global pointer register.  The
16436           result is not position independent code, and violates the IA-64
16437           ABI.
16438
16439       -mvolatile-asm-stop
16440       -mno-volatile-asm-stop
16441           Generate (or don't) a stop bit immediately before and after
16442           volatile asm statements.
16443
16444       -mregister-names
16445       -mno-register-names
16446           Generate (or don't) in, loc, and out register names for the stacked
16447           registers.  This may make assembler output more readable.
16448
16449       -mno-sdata
16450       -msdata
16451           Disable (or enable) optimizations that use the small data section.
16452           This may be useful for working around optimizer bugs.
16453
16454       -mconstant-gp
16455           Generate code that uses a single constant global pointer value.
16456           This is useful when compiling kernel code.
16457
16458       -mauto-pic
16459           Generate code that is self-relocatable.  This implies
16460           -mconstant-gp.  This is useful when compiling firmware code.
16461
16462       -minline-float-divide-min-latency
16463           Generate code for inline divides of floating-point values using the
16464           minimum latency algorithm.
16465
16466       -minline-float-divide-max-throughput
16467           Generate code for inline divides of floating-point values using the
16468           maximum throughput algorithm.
16469
16470       -mno-inline-float-divide
16471           Do not generate inline code for divides of floating-point values.
16472
16473       -minline-int-divide-min-latency
16474           Generate code for inline divides of integer values using the
16475           minimum latency algorithm.
16476
16477       -minline-int-divide-max-throughput
16478           Generate code for inline divides of integer values using the
16479           maximum throughput algorithm.
16480
16481       -mno-inline-int-divide
16482           Do not generate inline code for divides of integer values.
16483
16484       -minline-sqrt-min-latency
16485           Generate code for inline square roots using the minimum latency
16486           algorithm.
16487
16488       -minline-sqrt-max-throughput
16489           Generate code for inline square roots using the maximum throughput
16490           algorithm.
16491
16492       -mno-inline-sqrt
16493           Do not generate inline code for "sqrt".
16494
16495       -mfused-madd
16496       -mno-fused-madd
16497           Do (don't) generate code that uses the fused multiply/add or
16498           multiply/subtract instructions.  The default is to use these
16499           instructions.
16500
16501       -mno-dwarf2-asm
16502       -mdwarf2-asm
16503           Don't (or do) generate assembler code for the DWARF line number
16504           debugging info.  This may be useful when not using the GNU
16505           assembler.
16506
16507       -mearly-stop-bits
16508       -mno-early-stop-bits
16509           Allow stop bits to be placed earlier than immediately preceding the
16510           instruction that triggered the stop bit.  This can improve
16511           instruction scheduling, but does not always do so.
16512
16513       -mfixed-range=register-range
16514           Generate code treating the given register range as fixed registers.
16515           A fixed register is one that the register allocator cannot use.
16516           This is useful when compiling kernel code.  A register range is
16517           specified as two registers separated by a dash.  Multiple register
16518           ranges can be specified separated by a comma.
16519
16520       -mtls-size=tls-size
16521           Specify bit size of immediate TLS offsets.  Valid values are 14,
16522           22, and 64.
16523
16524       -mtune=cpu-type
16525           Tune the instruction scheduling for a particular CPU, Valid values
16526           are itanium, itanium1, merced, itanium2, and mckinley.
16527
16528       -milp32
16529       -mlp64
16530           Generate code for a 32-bit or 64-bit environment.  The 32-bit
16531           environment sets int, long and pointer to 32 bits.  The 64-bit
16532           environment sets int to 32 bits and long and pointer to 64 bits.
16533           These are HP-UX specific flags.
16534
16535       -mno-sched-br-data-spec
16536       -msched-br-data-spec
16537           (Dis/En)able data speculative scheduling before reload.  This
16538           results in generation of "ld.a" instructions and the corresponding
16539           check instructions ("ld.c" / "chk.a").  The default setting is
16540           disabled.
16541
16542       -msched-ar-data-spec
16543       -mno-sched-ar-data-spec
16544           (En/Dis)able data speculative scheduling after reload.  This
16545           results in generation of "ld.a" instructions and the corresponding
16546           check instructions ("ld.c" / "chk.a").  The default setting is
16547           enabled.
16548
16549       -mno-sched-control-spec
16550       -msched-control-spec
16551           (Dis/En)able control speculative scheduling.  This feature is
16552           available only during region scheduling (i.e. before reload).  This
16553           results in generation of the "ld.s" instructions and the
16554           corresponding check instructions "chk.s".  The default setting is
16555           disabled.
16556
16557       -msched-br-in-data-spec
16558       -mno-sched-br-in-data-spec
16559           (En/Dis)able speculative scheduling of the instructions that are
16560           dependent on the data speculative loads before reload.  This is
16561           effective only with -msched-br-data-spec enabled.  The default
16562           setting is enabled.
16563
16564       -msched-ar-in-data-spec
16565       -mno-sched-ar-in-data-spec
16566           (En/Dis)able speculative scheduling of the instructions that are
16567           dependent on the data speculative loads after reload.  This is
16568           effective only with -msched-ar-data-spec enabled.  The default
16569           setting is enabled.
16570
16571       -msched-in-control-spec
16572       -mno-sched-in-control-spec
16573           (En/Dis)able speculative scheduling of the instructions that are
16574           dependent on the control speculative loads.  This is effective only
16575           with -msched-control-spec enabled.  The default setting is enabled.
16576
16577       -mno-sched-prefer-non-data-spec-insns
16578       -msched-prefer-non-data-spec-insns
16579           If enabled, data-speculative instructions are chosen for schedule
16580           only if there are no other choices at the moment.  This makes the
16581           use of the data speculation much more conservative.  The default
16582           setting is disabled.
16583
16584       -mno-sched-prefer-non-control-spec-insns
16585       -msched-prefer-non-control-spec-insns
16586           If enabled, control-speculative instructions are chosen for
16587           schedule only if there are no other choices at the moment.  This
16588           makes the use of the control speculation much more conservative.
16589           The default setting is disabled.
16590
16591       -mno-sched-count-spec-in-critical-path
16592       -msched-count-spec-in-critical-path
16593           If enabled, speculative dependencies are considered during
16594           computation of the instructions priorities.  This makes the use of
16595           the speculation a bit more conservative.  The default setting is
16596           disabled.
16597
16598       -msched-spec-ldc
16599           Use a simple data speculation check.  This option is on by default.
16600
16601       -msched-control-spec-ldc
16602           Use a simple check for control speculation.  This option is on by
16603           default.
16604
16605       -msched-stop-bits-after-every-cycle
16606           Place a stop bit after every cycle when scheduling.  This option is
16607           on by default.
16608
16609       -msched-fp-mem-deps-zero-cost
16610           Assume that floating-point stores and loads are not likely to cause
16611           a conflict when placed into the same instruction group.  This
16612           option is disabled by default.
16613
16614       -msel-sched-dont-check-control-spec
16615           Generate checks for control speculation in selective scheduling.
16616           This flag is disabled by default.
16617
16618       -msched-max-memory-insns=max-insns
16619           Limit on the number of memory insns per instruction group, giving
16620           lower priority to subsequent memory insns attempting to schedule in
16621           the same instruction group. Frequently useful to prevent cache bank
16622           conflicts.  The default value is 1.
16623
16624       -msched-max-memory-insns-hard-limit
16625           Makes the limit specified by msched-max-memory-insns a hard limit,
16626           disallowing more than that number in an instruction group.
16627           Otherwise, the limit is "soft", meaning that non-memory operations
16628           are preferred when the limit is reached, but memory operations may
16629           still be scheduled.
16630
16631   LM32 Options
16632       These -m options are defined for the LatticeMico32 architecture:
16633
16634       -mbarrel-shift-enabled
16635           Enable barrel-shift instructions.
16636
16637       -mdivide-enabled
16638           Enable divide and modulus instructions.
16639
16640       -mmultiply-enabled
16641           Enable multiply instructions.
16642
16643       -msign-extend-enabled
16644           Enable sign extend instructions.
16645
16646       -muser-enabled
16647           Enable user-defined instructions.
16648
16649   M32C Options
16650       -mcpu=name
16651           Select the CPU for which code is generated.  name may be one of r8c
16652           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
16653           m32cm for the M16C/80 series, or m32c for the M32C/80 series.
16654
16655       -msim
16656           Specifies that the program will be run on the simulator.  This
16657           causes an alternate runtime library to be linked in which supports,
16658           for example, file I/O.  You must not use this option when
16659           generating programs that will run on real hardware; you must
16660           provide your own runtime library for whatever I/O functions are
16661           needed.
16662
16663       -memregs=number
16664           Specifies the number of memory-based pseudo-registers GCC uses
16665           during code generation.  These pseudo-registers are used like real
16666           registers, so there is a tradeoff between GCC's ability to fit the
16667           code into available registers, and the performance penalty of using
16668           memory instead of registers.  Note that all modules in a program
16669           must be compiled with the same value for this option.  Because of
16670           that, you must not use this option with GCC's default runtime
16671           libraries.
16672
16673   M32R/D Options
16674       These -m options are defined for Renesas M32R/D architectures:
16675
16676       -m32r2
16677           Generate code for the M32R/2.
16678
16679       -m32rx
16680           Generate code for the M32R/X.
16681
16682       -m32r
16683           Generate code for the M32R.  This is the default.
16684
16685       -mmodel=small
16686           Assume all objects live in the lower 16MB of memory (so that their
16687           addresses can be loaded with the "ld24" instruction), and assume
16688           all subroutines are reachable with the "bl" instruction.  This is
16689           the default.
16690
16691           The addressability of a particular object can be set with the
16692           "model" attribute.
16693
16694       -mmodel=medium
16695           Assume objects may be anywhere in the 32-bit address space (the
16696           compiler generates "seth/add3" instructions to load their
16697           addresses), and assume all subroutines are reachable with the "bl"
16698           instruction.
16699
16700       -mmodel=large
16701           Assume objects may be anywhere in the 32-bit address space (the
16702           compiler generates "seth/add3" instructions to load their
16703           addresses), and assume subroutines may not be reachable with the
16704           "bl" instruction (the compiler generates the much slower
16705           "seth/add3/jl" instruction sequence).
16706
16707       -msdata=none
16708           Disable use of the small data area.  Variables are put into one of
16709           ".data", ".bss", or ".rodata" (unless the "section" attribute has
16710           been specified).  This is the default.
16711
16712           The small data area consists of sections ".sdata" and ".sbss".
16713           Objects may be explicitly put in the small data area with the
16714           "section" attribute using one of these sections.
16715
16716       -msdata=sdata
16717           Put small global and static data in the small data area, but do not
16718           generate special code to reference them.
16719
16720       -msdata=use
16721           Put small global and static data in the small data area, and
16722           generate special instructions to reference them.
16723
16724       -G num
16725           Put global and static objects less than or equal to num bytes into
16726           the small data or BSS sections instead of the normal data or BSS
16727           sections.  The default value of num is 8.  The -msdata option must
16728           be set to one of sdata or use for this option to have any effect.
16729
16730           All modules should be compiled with the same -G num value.
16731           Compiling with different values of num may or may not work; if it
16732           doesn't the linker gives an error message---incorrect code is not
16733           generated.
16734
16735       -mdebug
16736           Makes the M32R-specific code in the compiler display some
16737           statistics that might help in debugging programs.
16738
16739       -malign-loops
16740           Align all loops to a 32-byte boundary.
16741
16742       -mno-align-loops
16743           Do not enforce a 32-byte alignment for loops.  This is the default.
16744
16745       -missue-rate=number
16746           Issue number instructions per cycle.  number can only be 1 or 2.
16747
16748       -mbranch-cost=number
16749           number can only be 1 or 2.  If it is 1 then branches are preferred
16750           over conditional code, if it is 2, then the opposite applies.
16751
16752       -mflush-trap=number
16753           Specifies the trap number to use to flush the cache.  The default
16754           is 12.  Valid numbers are between 0 and 15 inclusive.
16755
16756       -mno-flush-trap
16757           Specifies that the cache cannot be flushed by using a trap.
16758
16759       -mflush-func=name
16760           Specifies the name of the operating system function to call to
16761           flush the cache.  The default is _flush_cache, but a function call
16762           is only used if a trap is not available.
16763
16764       -mno-flush-func
16765           Indicates that there is no OS function for flushing the cache.
16766
16767   M680x0 Options
16768       These are the -m options defined for M680x0 and ColdFire processors.
16769       The default settings depend on which architecture was selected when the
16770       compiler was configured; the defaults for the most common choices are
16771       given below.
16772
16773       -march=arch
16774           Generate code for a specific M680x0 or ColdFire instruction set
16775           architecture.  Permissible values of arch for M680x0 architectures
16776           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
16777           architectures are selected according to Freescale's ISA
16778           classification and the permissible values are: isaa, isaaplus, isab
16779           and isac.
16780
16781           GCC defines a macro "__mcfarch__" whenever it is generating code
16782           for a ColdFire target.  The arch in this macro is one of the -march
16783           arguments given above.
16784
16785           When used together, -march and -mtune select code that runs on a
16786           family of similar processors but that is optimized for a particular
16787           microarchitecture.
16788
16789       -mcpu=cpu
16790           Generate code for a specific M680x0 or ColdFire processor.  The
16791           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
16792           68332 and cpu32.  The ColdFire cpus are given by the table below,
16793           which also classifies the CPUs into families:
16794
16795           Family : -mcpu arguments
16796           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
16797           5206 : 5202 5204 5206
16798           5206e : 5206e
16799           5208 : 5207 5208
16800           5211a : 5210a 5211a
16801           5213 : 5211 5212 5213
16802           5216 : 5214 5216
16803           52235 : 52230 52231 52232 52233 52234 52235
16804           5225 : 5224 5225
16805           52259 : 52252 52254 52255 52256 52258 52259
16806           5235 : 5232 5233 5234 5235 523x
16807           5249 : 5249
16808           5250 : 5250
16809           5271 : 5270 5271
16810           5272 : 5272
16811           5275 : 5274 5275
16812           5282 : 5280 5281 5282 528x
16813           53017 : 53011 53012 53013 53014 53015 53016 53017
16814           5307 : 5307
16815           5329 : 5327 5328 5329 532x
16816           5373 : 5372 5373 537x
16817           5407 : 5407
16818           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
16819           5485
16820
16821           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
16822           Other combinations of -mcpu and -march are rejected.
16823
16824           GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is
16825           selected.  It also defines "__mcf_family_family", where the value
16826           of family is given by the table above.
16827
16828       -mtune=tune
16829           Tune the code for a particular microarchitecture within the
16830           constraints set by -march and -mcpu.  The M680x0 microarchitectures
16831           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
16832           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
16833
16834           You can also use -mtune=68020-40 for code that needs to run
16835           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
16836           is similar but includes 68060 targets as well.  These two options
16837           select the same tuning decisions as -m68020-40 and -m68020-60
16838           respectively.
16839
16840           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for
16841           680x0 architecture arch.  It also defines "mcarch" unless either
16842           -ansi or a non-GNU -std option is used.  If GCC is tuning for a
16843           range of architectures, as selected by -mtune=68020-40 or
16844           -mtune=68020-60, it defines the macros for every architecture in
16845           the range.
16846
16847           GCC also defines the macro "__muarch__" when tuning for ColdFire
16848           microarchitecture uarch, where uarch is one of the arguments given
16849           above.
16850
16851       -m68000
16852       -mc68000
16853           Generate output for a 68000.  This is the default when the compiler
16854           is configured for 68000-based systems.  It is equivalent to
16855           -march=68000.
16856
16857           Use this option for microcontrollers with a 68000 or EC000 core,
16858           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
16859
16860       -m68010
16861           Generate output for a 68010.  This is the default when the compiler
16862           is configured for 68010-based systems.  It is equivalent to
16863           -march=68010.
16864
16865       -m68020
16866       -mc68020
16867           Generate output for a 68020.  This is the default when the compiler
16868           is configured for 68020-based systems.  It is equivalent to
16869           -march=68020.
16870
16871       -m68030
16872           Generate output for a 68030.  This is the default when the compiler
16873           is configured for 68030-based systems.  It is equivalent to
16874           -march=68030.
16875
16876       -m68040
16877           Generate output for a 68040.  This is the default when the compiler
16878           is configured for 68040-based systems.  It is equivalent to
16879           -march=68040.
16880
16881           This option inhibits the use of 68881/68882 instructions that have
16882           to be emulated by software on the 68040.  Use this option if your
16883           68040 does not have code to emulate those instructions.
16884
16885       -m68060
16886           Generate output for a 68060.  This is the default when the compiler
16887           is configured for 68060-based systems.  It is equivalent to
16888           -march=68060.
16889
16890           This option inhibits the use of 68020 and 68881/68882 instructions
16891           that have to be emulated by software on the 68060.  Use this option
16892           if your 68060 does not have code to emulate those instructions.
16893
16894       -mcpu32
16895           Generate output for a CPU32.  This is the default when the compiler
16896           is configured for CPU32-based systems.  It is equivalent to
16897           -march=cpu32.
16898
16899           Use this option for microcontrollers with a CPU32 or CPU32+ core,
16900           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
16901           68341, 68349 and 68360.
16902
16903       -m5200
16904           Generate output for a 520X ColdFire CPU.  This is the default when
16905           the compiler is configured for 520X-based systems.  It is
16906           equivalent to -mcpu=5206, and is now deprecated in favor of that
16907           option.
16908
16909           Use this option for microcontroller with a 5200 core, including the
16910           MCF5202, MCF5203, MCF5204 and MCF5206.
16911
16912       -m5206e
16913           Generate output for a 5206e ColdFire CPU.  The option is now
16914           deprecated in favor of the equivalent -mcpu=5206e.
16915
16916       -m528x
16917           Generate output for a member of the ColdFire 528X family.  The
16918           option is now deprecated in favor of the equivalent -mcpu=528x.
16919
16920       -m5307
16921           Generate output for a ColdFire 5307 CPU.  The option is now
16922           deprecated in favor of the equivalent -mcpu=5307.
16923
16924       -m5407
16925           Generate output for a ColdFire 5407 CPU.  The option is now
16926           deprecated in favor of the equivalent -mcpu=5407.
16927
16928       -mcfv4e
16929           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
16930           This includes use of hardware floating-point instructions.  The
16931           option is equivalent to -mcpu=547x, and is now deprecated in favor
16932           of that option.
16933
16934       -m68020-40
16935           Generate output for a 68040, without using any of the new
16936           instructions.  This results in code that can run relatively
16937           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
16938           generated code does use the 68881 instructions that are emulated on
16939           the 68040.
16940
16941           The option is equivalent to -march=68020 -mtune=68020-40.
16942
16943       -m68020-60
16944           Generate output for a 68060, without using any of the new
16945           instructions.  This results in code that can run relatively
16946           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
16947           generated code does use the 68881 instructions that are emulated on
16948           the 68060.
16949
16950           The option is equivalent to -march=68020 -mtune=68020-60.
16951
16952       -mhard-float
16953       -m68881
16954           Generate floating-point instructions.  This is the default for
16955           68020 and above, and for ColdFire devices that have an FPU.  It
16956           defines the macro "__HAVE_68881__" on M680x0 targets and
16957           "__mcffpu__" on ColdFire targets.
16958
16959       -msoft-float
16960           Do not generate floating-point instructions; use library calls
16961           instead.  This is the default for 68000, 68010, and 68832 targets.
16962           It is also the default for ColdFire devices that have no FPU.
16963
16964       -mdiv
16965       -mno-div
16966           Generate (do not generate) ColdFire hardware divide and remainder
16967           instructions.  If -march is used without -mcpu, the default is "on"
16968           for ColdFire architectures and "off" for M680x0 architectures.
16969           Otherwise, the default is taken from the target CPU (either the
16970           default CPU, or the one specified by -mcpu).  For example, the
16971           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.
16972
16973           GCC defines the macro "__mcfhwdiv__" when this option is enabled.
16974
16975       -mshort
16976           Consider type "int" to be 16 bits wide, like "short int".
16977           Additionally, parameters passed on the stack are also aligned to a
16978           16-bit boundary even on targets whose API mandates promotion to
16979           32-bit.
16980
16981       -mno-short
16982           Do not consider type "int" to be 16 bits wide.  This is the
16983           default.
16984
16985       -mnobitfield
16986       -mno-bitfield
16987           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
16988           -m5200 options imply -mnobitfield.
16989
16990       -mbitfield
16991           Do use the bit-field instructions.  The -m68020 option implies
16992           -mbitfield.  This is the default if you use a configuration
16993           designed for a 68020.
16994
16995       -mrtd
16996           Use a different function-calling convention, in which functions
16997           that take a fixed number of arguments return with the "rtd"
16998           instruction, which pops their arguments while returning.  This
16999           saves one instruction in the caller since there is no need to pop
17000           the arguments there.
17001
17002           This calling convention is incompatible with the one normally used
17003           on Unix, so you cannot use it if you need to call libraries
17004           compiled with the Unix compiler.
17005
17006           Also, you must provide function prototypes for all functions that
17007           take variable numbers of arguments (including "printf"); otherwise
17008           incorrect code is generated for calls to those functions.
17009
17010           In addition, seriously incorrect code results if you call a
17011           function with too many arguments.  (Normally, extra arguments are
17012           harmlessly ignored.)
17013
17014           The "rtd" instruction is supported by the 68010, 68020, 68030,
17015           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
17016
17017       -mno-rtd
17018           Do not use the calling conventions selected by -mrtd.  This is the
17019           default.
17020
17021       -malign-int
17022       -mno-align-int
17023           Control whether GCC aligns "int", "long", "long long", "float",
17024           "double", and "long double" variables on a 32-bit boundary
17025           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
17026           variables on 32-bit boundaries produces code that runs somewhat
17027           faster on processors with 32-bit busses at the expense of more
17028           memory.
17029
17030           Warning: if you use the -malign-int switch, GCC aligns structures
17031           containing the above types differently than most published
17032           application binary interface specifications for the m68k.
17033
17034       -mpcrel
17035           Use the pc-relative addressing mode of the 68000 directly, instead
17036           of using a global offset table.  At present, this option implies
17037           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
17038           -fPIC is not presently supported with -mpcrel, though this could be
17039           supported for 68020 and higher processors.
17040
17041       -mno-strict-align
17042       -mstrict-align
17043           Do not (do) assume that unaligned memory references are handled by
17044           the system.
17045
17046       -msep-data
17047           Generate code that allows the data segment to be located in a
17048           different area of memory from the text segment.  This allows for
17049           execute-in-place in an environment without virtual memory
17050           management.  This option implies -fPIC.
17051
17052       -mno-sep-data
17053           Generate code that assumes that the data segment follows the text
17054           segment.  This is the default.
17055
17056       -mid-shared-library
17057           Generate code that supports shared libraries via the library ID
17058           method.  This allows for execute-in-place and shared libraries in
17059           an environment without virtual memory management.  This option
17060           implies -fPIC.
17061
17062       -mno-id-shared-library
17063           Generate code that doesn't assume ID-based shared libraries are
17064           being used.  This is the default.
17065
17066       -mshared-library-id=n
17067           Specifies the identification number of the ID-based shared library
17068           being compiled.  Specifying a value of 0 generates more compact
17069           code; specifying other values forces the allocation of that number
17070           to the current library, but is no more space- or time-efficient
17071           than omitting this option.
17072
17073       -mxgot
17074       -mno-xgot
17075           When generating position-independent code for ColdFire, generate
17076           code that works if the GOT has more than 8192 entries.  This code
17077           is larger and slower than code generated without this option.  On
17078           M680x0 processors, this option is not needed; -fPIC suffices.
17079
17080           GCC normally uses a single instruction to load values from the GOT.
17081           While this is relatively efficient, it only works if the GOT is
17082           smaller than about 64k.  Anything larger causes the linker to
17083           report an error such as:
17084
17085                   relocation truncated to fit: R_68K_GOT16O foobar
17086
17087           If this happens, you should recompile your code with -mxgot.  It
17088           should then work with very large GOTs.  However, code generated
17089           with -mxgot is less efficient, since it takes 4 instructions to
17090           fetch the value of a global symbol.
17091
17092           Note that some linkers, including newer versions of the GNU linker,
17093           can create multiple GOTs and sort GOT entries.  If you have such a
17094           linker, you should only need to use -mxgot when compiling a single
17095           object file that accesses more than 8192 GOT entries.  Very few do.
17096
17097           These options have no effect unless GCC is generating position-
17098           independent code.
17099
17100       -mlong-jump-table-offsets
17101           Use 32-bit offsets in "switch" tables.  The default is to use
17102           16-bit offsets.
17103
17104   MCore Options
17105       These are the -m options defined for the Motorola M*Core processors.
17106
17107       -mhardlit
17108       -mno-hardlit
17109           Inline constants into the code stream if it can be done in two
17110           instructions or less.
17111
17112       -mdiv
17113       -mno-div
17114           Use the divide instruction.  (Enabled by default).
17115
17116       -mrelax-immediate
17117       -mno-relax-immediate
17118           Allow arbitrary-sized immediates in bit operations.
17119
17120       -mwide-bitfields
17121       -mno-wide-bitfields
17122           Always treat bit-fields as "int"-sized.
17123
17124       -m4byte-functions
17125       -mno-4byte-functions
17126           Force all functions to be aligned to a 4-byte boundary.
17127
17128       -mcallgraph-data
17129       -mno-callgraph-data
17130           Emit callgraph information.
17131
17132       -mslow-bytes
17133       -mno-slow-bytes
17134           Prefer word access when reading byte quantities.
17135
17136       -mlittle-endian
17137       -mbig-endian
17138           Generate code for a little-endian target.
17139
17140       -m210
17141       -m340
17142           Generate code for the 210 processor.
17143
17144       -mno-lsim
17145           Assume that runtime support has been provided and so omit the
17146           simulator library (libsim.a) from the linker command line.
17147
17148       -mstack-increment=size
17149           Set the maximum amount for a single stack increment operation.
17150           Large values can increase the speed of programs that contain
17151           functions that need a large amount of stack space, but they can
17152           also trigger a segmentation fault if the stack is extended too
17153           much.  The default value is 0x1000.
17154
17155   MeP Options
17156       -mabsdiff
17157           Enables the "abs" instruction, which is the absolute difference
17158           between two registers.
17159
17160       -mall-opts
17161           Enables all the optional instructions---average, multiply, divide,
17162           bit operations, leading zero, absolute difference, min/max, clip,
17163           and saturation.
17164
17165       -maverage
17166           Enables the "ave" instruction, which computes the average of two
17167           registers.
17168
17169       -mbased=n
17170           Variables of size n bytes or smaller are placed in the ".based"
17171           section by default.  Based variables use the $tp register as a base
17172           register, and there is a 128-byte limit to the ".based" section.
17173
17174       -mbitops
17175           Enables the bit operation instructions---bit test ("btstm"), set
17176           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
17177           ("tas").
17178
17179       -mc=name
17180           Selects which section constant data is placed in.  name may be
17181           tiny, near, or far.
17182
17183       -mclip
17184           Enables the "clip" instruction.  Note that -mclip is not useful
17185           unless you also provide -mminmax.
17186
17187       -mconfig=name
17188           Selects one of the built-in core configurations.  Each MeP chip has
17189           one or more modules in it; each module has a core CPU and a variety
17190           of coprocessors, optional instructions, and peripherals.  The
17191           "MeP-Integrator" tool, not part of GCC, provides these
17192           configurations through this option; using this option is the same
17193           as using all the corresponding command-line options.  The default
17194           configuration is default.
17195
17196       -mcop
17197           Enables the coprocessor instructions.  By default, this is a 32-bit
17198           coprocessor.  Note that the coprocessor is normally enabled via the
17199           -mconfig= option.
17200
17201       -mcop32
17202           Enables the 32-bit coprocessor's instructions.
17203
17204       -mcop64
17205           Enables the 64-bit coprocessor's instructions.
17206
17207       -mivc2
17208           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
17209
17210       -mdc
17211           Causes constant variables to be placed in the ".near" section.
17212
17213       -mdiv
17214           Enables the "div" and "divu" instructions.
17215
17216       -meb
17217           Generate big-endian code.
17218
17219       -mel
17220           Generate little-endian code.
17221
17222       -mio-volatile
17223           Tells the compiler that any variable marked with the "io" attribute
17224           is to be considered volatile.
17225
17226       -ml Causes variables to be assigned to the ".far" section by default.
17227
17228       -mleadz
17229           Enables the "leadz" (leading zero) instruction.
17230
17231       -mm Causes variables to be assigned to the ".near" section by default.
17232
17233       -mminmax
17234           Enables the "min" and "max" instructions.
17235
17236       -mmult
17237           Enables the multiplication and multiply-accumulate instructions.
17238
17239       -mno-opts
17240           Disables all the optional instructions enabled by -mall-opts.
17241
17242       -mrepeat
17243           Enables the "repeat" and "erepeat" instructions, used for low-
17244           overhead looping.
17245
17246       -ms Causes all variables to default to the ".tiny" section.  Note that
17247           there is a 65536-byte limit to this section.  Accesses to these
17248           variables use the %gp base register.
17249
17250       -msatur
17251           Enables the saturation instructions.  Note that the compiler does
17252           not currently generate these itself, but this option is included
17253           for compatibility with other tools, like "as".
17254
17255       -msdram
17256           Link the SDRAM-based runtime instead of the default ROM-based
17257           runtime.
17258
17259       -msim
17260           Link the simulator run-time libraries.
17261
17262       -msimnovec
17263           Link the simulator runtime libraries, excluding built-in support
17264           for reset and exception vectors and tables.
17265
17266       -mtf
17267           Causes all functions to default to the ".far" section.  Without
17268           this option, functions default to the ".near" section.
17269
17270       -mtiny=n
17271           Variables that are n bytes or smaller are allocated to the ".tiny"
17272           section.  These variables use the $gp base register.  The default
17273           for this option is 4, but note that there's a 65536-byte limit to
17274           the ".tiny" section.
17275
17276   MicroBlaze Options
17277       -msoft-float
17278           Use software emulation for floating point (default).
17279
17280       -mhard-float
17281           Use hardware floating-point instructions.
17282
17283       -mmemcpy
17284           Do not optimize block moves, use "memcpy".
17285
17286       -mno-clearbss
17287           This option is deprecated.  Use -fno-zero-initialized-in-bss
17288           instead.
17289
17290       -mcpu=cpu-type
17291           Use features of, and schedule code for, the given CPU.  Supported
17292           values are in the format vX.YY.Z, where X is a major version, YY is
17293           the minor version, and Z is compatibility code.  Example values are
17294           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.
17295
17296       -mxl-soft-mul
17297           Use software multiply emulation (default).
17298
17299       -mxl-soft-div
17300           Use software emulation for divides (default).
17301
17302       -mxl-barrel-shift
17303           Use the hardware barrel shifter.
17304
17305       -mxl-pattern-compare
17306           Use pattern compare instructions.
17307
17308       -msmall-divides
17309           Use table lookup optimization for small signed integer divisions.
17310
17311       -mxl-stack-check
17312           This option is deprecated.  Use -fstack-check instead.
17313
17314       -mxl-gp-opt
17315           Use GP-relative ".sdata"/".sbss" sections.
17316
17317       -mxl-multiply-high
17318           Use multiply high instructions for high part of 32x32 multiply.
17319
17320       -mxl-float-convert
17321           Use hardware floating-point conversion instructions.
17322
17323       -mxl-float-sqrt
17324           Use hardware floating-point square root instruction.
17325
17326       -mbig-endian
17327           Generate code for a big-endian target.
17328
17329       -mlittle-endian
17330           Generate code for a little-endian target.
17331
17332       -mxl-reorder
17333           Use reorder instructions (swap and byte reversed load/store).
17334
17335       -mxl-mode-app-model
17336           Select application model app-model.  Valid models are
17337
17338           executable
17339               normal executable (default), uses startup code crt0.o.
17340
17341           xmdstub
17342               for use with Xilinx Microprocessor Debugger (XMD) based
17343               software intrusive debug agent called xmdstub. This uses
17344               startup file crt1.o and sets the start address of the program
17345               to 0x800.
17346
17347           bootstrap
17348               for applications that are loaded using a bootloader.  This
17349               model uses startup file crt2.o which does not contain a
17350               processor reset vector handler. This is suitable for
17351               transferring control on a processor reset to the bootloader
17352               rather than the application.
17353
17354           novectors
17355               for applications that do not require any of the MicroBlaze
17356               vectors. This option may be useful for applications running
17357               within a monitoring application. This model uses crt3.o as a
17358               startup file.
17359
17360           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-
17361           model.
17362
17363   MIPS Options
17364       -EB Generate big-endian code.
17365
17366       -EL Generate little-endian code.  This is the default for mips*el-*-*
17367           configurations.
17368
17369       -march=arch
17370           Generate code that runs on arch, which can be the name of a generic
17371           MIPS ISA, or the name of a particular processor.  The ISA names
17372           are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3,
17373           mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and
17374           mips64r6.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
17375           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
17376           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1,
17377           74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400, interaptiv,
17378           loongson2e, loongson2f, loongson3a, m4k, m14k, m14kc, m14ke,
17379           m14kec, m5100, m5101, octeon, octeon+, octeon2, octeon3, orion,
17380           p5600, r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700,
17381           r6000, r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1,
17382           sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400,
17383           vr5500, xlr and xlp.  The special value from-abi selects the most
17384           compatible architecture for the selected ABI (that is, mips1 for
17385           32-bit ABIs and mips3 for 64-bit ABIs).
17386
17387           The native Linux/GNU toolchain also supports the value native,
17388           which selects the best architecture option for the host processor.
17389           -march=native has no effect if GCC does not recognize the
17390           processor.
17391
17392           In processor names, a final 000 can be abbreviated as k (for
17393           example, -march=r2k).  Prefixes are optional, and vr may be written
17394           r.
17395
17396           Names of the form nf2_1 refer to processors with FPUs clocked at
17397           half the rate of the core, names of the form nf1_1 refer to
17398           processors with FPUs clocked at the same rate as the core, and
17399           names of the form nf3_2 refer to processors with FPUs clocked a
17400           ratio of 3:2 with respect to the core.  For compatibility reasons,
17401           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
17402           as synonyms for nf1_1.
17403
17404           GCC defines two macros based on the value of this option.  The
17405           first is "_MIPS_ARCH", which gives the name of target architecture,
17406           as a string.  The second has the form "_MIPS_ARCH_foo", where foo
17407           is the capitalized value of "_MIPS_ARCH".  For example,
17408           -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro
17409           "_MIPS_ARCH_R2000".
17410
17411           Note that the "_MIPS_ARCH" macro uses the processor names given
17412           above.  In other words, it has the full prefix and does not
17413           abbreviate 000 as k.  In the case of from-abi, the macro names the
17414           resolved architecture (either "mips1" or "mips3").  It names the
17415           default architecture when no -march option is given.
17416
17417       -mtune=arch
17418           Optimize for arch.  Among other things, this option controls the
17419           way instructions are scheduled, and the perceived cost of
17420           arithmetic operations.  The list of arch values is the same as for
17421           -march.
17422
17423           When this option is not used, GCC optimizes for the processor
17424           specified by -march.  By using -march and -mtune together, it is
17425           possible to generate code that runs on a family of processors, but
17426           optimize the code for one particular member of that family.
17427
17428           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which
17429           work in the same way as the -march ones described above.
17430
17431       -mips1
17432           Equivalent to -march=mips1.
17433
17434       -mips2
17435           Equivalent to -march=mips2.
17436
17437       -mips3
17438           Equivalent to -march=mips3.
17439
17440       -mips4
17441           Equivalent to -march=mips4.
17442
17443       -mips32
17444           Equivalent to -march=mips32.
17445
17446       -mips32r3
17447           Equivalent to -march=mips32r3.
17448
17449       -mips32r5
17450           Equivalent to -march=mips32r5.
17451
17452       -mips32r6
17453           Equivalent to -march=mips32r6.
17454
17455       -mips64
17456           Equivalent to -march=mips64.
17457
17458       -mips64r2
17459           Equivalent to -march=mips64r2.
17460
17461       -mips64r3
17462           Equivalent to -march=mips64r3.
17463
17464       -mips64r5
17465           Equivalent to -march=mips64r5.
17466
17467       -mips64r6
17468           Equivalent to -march=mips64r6.
17469
17470       -mips16
17471       -mno-mips16
17472           Generate (do not generate) MIPS16 code.  If GCC is targeting a
17473           MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.
17474
17475           MIPS16 code generation can also be controlled on a per-function
17476           basis by means of "mips16" and "nomips16" attributes.
17477
17478       -mflip-mips16
17479           Generate MIPS16 code on alternating functions.  This option is
17480           provided for regression testing of mixed MIPS16/non-MIPS16 code
17481           generation, and is not intended for ordinary use in compiling user
17482           code.
17483
17484       -minterlink-compressed
17485       -mno-interlink-compressed
17486           Require (do not require) that code using the standard
17487           (uncompressed) MIPS ISA be link-compatible with MIPS16 and
17488           microMIPS code, and vice versa.
17489
17490           For example, code using the standard ISA encoding cannot jump
17491           directly to MIPS16 or microMIPS code; it must either use a call or
17492           an indirect jump.  -minterlink-compressed therefore disables direct
17493           jumps unless GCC knows that the target of the jump is not
17494           compressed.
17495
17496       -minterlink-mips16
17497       -mno-interlink-mips16
17498           Aliases of -minterlink-compressed and -mno-interlink-compressed.
17499           These options predate the microMIPS ASE and are retained for
17500           backwards compatibility.
17501
17502       -mabi=32
17503       -mabi=o64
17504       -mabi=n32
17505       -mabi=64
17506       -mabi=eabi
17507           Generate code for the given ABI.
17508
17509           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
17510           generates 64-bit code when you select a 64-bit architecture, but
17511           you can use -mgp32 to get 32-bit code instead.
17512
17513           For information about the O64 ABI, see
17514           <http://gcc.gnu.org/projects/mipso64-abi.html>.
17515
17516           GCC supports a variant of the o32 ABI in which floating-point
17517           registers are 64 rather than 32 bits wide.  You can select this
17518           combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1"
17519           and "mfhc1" instructions and is therefore only supported for
17520           MIPS32R2, MIPS32R3 and MIPS32R5 processors.
17521
17522           The register assignments for arguments and return values remain the
17523           same, but each scalar value is passed in a single 64-bit register
17524           rather than a pair of 32-bit registers.  For example, scalar
17525           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
17526           The set of call-saved registers also remains the same in that the
17527           even-numbered double-precision registers are saved.
17528
17529           Two additional variants of the o32 ABI are supported to enable a
17530           transition from 32-bit to 64-bit registers.  These are FPXX
17531           (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).  The FPXX extension
17532           mandates that all code must execute correctly when run using 32-bit
17533           or 64-bit registers.  The code can be interlinked with either FP32
17534           or FP64, but not both.  The FP64A extension is similar to the FP64
17535           extension but forbids the use of odd-numbered single-precision
17536           registers.  This can be used in conjunction with the "FRE" mode of
17537           FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to
17538           interlink and run in the same process without changing FPU modes.
17539
17540       -mabicalls
17541       -mno-abicalls
17542           Generate (do not generate) code that is suitable for SVR4-style
17543           dynamic objects.  -mabicalls is the default for SVR4-based systems.
17544
17545       -mshared
17546       -mno-shared
17547           Generate (do not generate) code that is fully position-independent,
17548           and that can therefore be linked into shared libraries.  This
17549           option only affects -mabicalls.
17550
17551           All -mabicalls code has traditionally been position-independent,
17552           regardless of options like -fPIC and -fpic.  However, as an
17553           extension, the GNU toolchain allows executables to use absolute
17554           accesses for locally-binding symbols.  It can also use shorter GP
17555           initialization sequences and generate direct calls to locally-
17556           defined functions.  This mode is selected by -mno-shared.
17557
17558           -mno-shared depends on binutils 2.16 or higher and generates
17559           objects that can only be linked by the GNU linker.  However, the
17560           option does not affect the ABI of the final executable; it only
17561           affects the ABI of relocatable objects.  Using -mno-shared
17562           generally makes executables both smaller and quicker.
17563
17564           -mshared is the default.
17565
17566       -mplt
17567       -mno-plt
17568           Assume (do not assume) that the static and dynamic linkers support
17569           PLTs and copy relocations.  This option only affects -mno-shared
17570           -mabicalls.  For the n64 ABI, this option has no effect without
17571           -msym32.
17572
17573           You can make -mplt the default by configuring GCC with
17574           --with-mips-plt.  The default is -mno-plt otherwise.
17575
17576       -mxgot
17577       -mno-xgot
17578           Lift (do not lift) the usual restrictions on the size of the global
17579           offset table.
17580
17581           GCC normally uses a single instruction to load values from the GOT.
17582           While this is relatively efficient, it only works if the GOT is
17583           smaller than about 64k.  Anything larger causes the linker to
17584           report an error such as:
17585
17586                   relocation truncated to fit: R_MIPS_GOT16 foobar
17587
17588           If this happens, you should recompile your code with -mxgot.  This
17589           works with very large GOTs, although the code is also less
17590           efficient, since it takes three instructions to fetch the value of
17591           a global symbol.
17592
17593           Note that some linkers can create multiple GOTs.  If you have such
17594           a linker, you should only need to use -mxgot when a single object
17595           file accesses more than 64k's worth of GOT entries.  Very few do.
17596
17597           These options have no effect unless GCC is generating position
17598           independent code.
17599
17600       -mgp32
17601           Assume that general-purpose registers are 32 bits wide.
17602
17603       -mgp64
17604           Assume that general-purpose registers are 64 bits wide.
17605
17606       -mfp32
17607           Assume that floating-point registers are 32 bits wide.
17608
17609       -mfp64
17610           Assume that floating-point registers are 64 bits wide.
17611
17612       -mfpxx
17613           Do not assume the width of floating-point registers.
17614
17615       -mhard-float
17616           Use floating-point coprocessor instructions.
17617
17618       -msoft-float
17619           Do not use floating-point coprocessor instructions.  Implement
17620           floating-point calculations using library calls instead.
17621
17622       -mno-float
17623           Equivalent to -msoft-float, but additionally asserts that the
17624           program being compiled does not perform any floating-point
17625           operations.  This option is presently supported only by some bare-
17626           metal MIPS configurations, where it may select a special set of
17627           libraries that lack all floating-point support (including, for
17628           example, the floating-point "printf" formats).  If code compiled
17629           with -mno-float accidentally contains floating-point operations, it
17630           is likely to suffer a link-time or run-time failure.
17631
17632       -msingle-float
17633           Assume that the floating-point coprocessor only supports single-
17634           precision operations.
17635
17636       -mdouble-float
17637           Assume that the floating-point coprocessor supports double-
17638           precision operations.  This is the default.
17639
17640       -modd-spreg
17641       -mno-odd-spreg
17642           Enable the use of odd-numbered single-precision floating-point
17643           registers for the o32 ABI.  This is the default for processors that
17644           are known to support these registers.  When using the o32 FPXX ABI,
17645           -mno-odd-spreg is set by default.
17646
17647       -mabs=2008
17648       -mabs=legacy
17649           These options control the treatment of the special not-a-number
17650           (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt"
17651           machine instructions.
17652
17653           By default or when -mabs=legacy is used the legacy treatment is
17654           selected.  In this case these instructions are considered
17655           arithmetic and avoided where correct operation is required and the
17656           input operand might be a NaN.  A longer sequence of instructions
17657           that manipulate the sign bit of floating-point datum manually is
17658           used instead unless the -ffinite-math-only option has also been
17659           specified.
17660
17661           The -mabs=2008 option selects the IEEE 754-2008 treatment.  In this
17662           case these instructions are considered non-arithmetic and therefore
17663           operating correctly in all cases, including in particular where the
17664           input operand is a NaN.  These instructions are therefore always
17665           used for the respective operations.
17666
17667       -mnan=2008
17668       -mnan=legacy
17669           These options control the encoding of the special not-a-number
17670           (NaN) IEEE 754 floating-point data.
17671
17672           The -mnan=legacy option selects the legacy encoding.  In this case
17673           quiet NaNs (qNaNs) are denoted by the first bit of their trailing
17674           significand field being 0, whereas signaling NaNs (sNaNs) are
17675           denoted by the first bit of their trailing significand field being
17676           1.
17677
17678           The -mnan=2008 option selects the IEEE 754-2008 encoding.  In this
17679           case qNaNs are denoted by the first bit of their trailing
17680           significand field being 1, whereas sNaNs are denoted by the first
17681           bit of their trailing significand field being 0.
17682
17683           The default is -mnan=legacy unless GCC has been configured with
17684           --with-nan=2008.
17685
17686       -mllsc
17687       -mno-llsc
17688           Use (do not use) ll, sc, and sync instructions to implement atomic
17689           memory built-in functions.  When neither option is specified, GCC
17690           uses the instructions if the target architecture supports them.
17691
17692           -mllsc is useful if the runtime environment can emulate the
17693           instructions and -mno-llsc can be useful when compiling for
17694           nonstandard ISAs.  You can make either option the default by
17695           configuring GCC with --with-llsc and --without-llsc respectively.
17696           --with-llsc is the default for some configurations; see the
17697           installation documentation for details.
17698
17699       -mdsp
17700       -mno-dsp
17701           Use (do not use) revision 1 of the MIPS DSP ASE.
17702             This option defines the preprocessor macro "__mips_dsp".  It also
17703           defines "__mips_dsp_rev" to 1.
17704
17705       -mdspr2
17706       -mno-dspr2
17707           Use (do not use) revision 2 of the MIPS DSP ASE.
17708             This option defines the preprocessor macros "__mips_dsp" and
17709           "__mips_dspr2".  It also defines "__mips_dsp_rev" to 2.
17710
17711       -msmartmips
17712       -mno-smartmips
17713           Use (do not use) the MIPS SmartMIPS ASE.
17714
17715       -mpaired-single
17716       -mno-paired-single
17717           Use (do not use) paired-single floating-point instructions.
17718             This option requires hardware floating-point support to be
17719           enabled.
17720
17721       -mdmx
17722       -mno-mdmx
17723           Use (do not use) MIPS Digital Media Extension instructions.  This
17724           option can only be used when generating 64-bit code and requires
17725           hardware floating-point support to be enabled.
17726
17727       -mips3d
17728       -mno-mips3d
17729           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
17730           -mpaired-single.
17731
17732       -mmicromips
17733       -mno-micromips
17734           Generate (do not generate) microMIPS code.
17735
17736           MicroMIPS code generation can also be controlled on a per-function
17737           basis by means of "micromips" and "nomicromips" attributes.
17738
17739       -mmt
17740       -mno-mt
17741           Use (do not use) MT Multithreading instructions.
17742
17743       -mmcu
17744       -mno-mcu
17745           Use (do not use) the MIPS MCU ASE instructions.
17746
17747       -meva
17748       -mno-eva
17749           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
17750
17751       -mvirt
17752       -mno-virt
17753           Use (do not use) the MIPS Virtualization (VZ) instructions.
17754
17755       -mxpa
17756       -mno-xpa
17757           Use (do not use) the MIPS eXtended Physical Address (XPA)
17758           instructions.
17759
17760       -mlong64
17761           Force "long" types to be 64 bits wide.  See -mlong32 for an
17762           explanation of the default and the way that the pointer size is
17763           determined.
17764
17765       -mlong32
17766           Force "long", "int", and pointer types to be 32 bits wide.
17767
17768           The default size of "int"s, "long"s and pointers depends on the
17769           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
17770           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
17771           "long"s.  Pointers are the same size as "long"s, or the same size
17772           as integer registers, whichever is smaller.
17773
17774       -msym32
17775       -mno-sym32
17776           Assume (do not assume) that all symbols have 32-bit values,
17777           regardless of the selected ABI.  This option is useful in
17778           combination with -mabi=64 and -mno-abicalls because it allows GCC
17779           to generate shorter and faster references to symbolic addresses.
17780
17781       -G num
17782           Put definitions of externally-visible data in a small data section
17783           if that data is no bigger than num bytes.  GCC can then generate
17784           more efficient accesses to the data; see -mgpopt for details.
17785
17786           The default -G option depends on the configuration.
17787
17788       -mlocal-sdata
17789       -mno-local-sdata
17790           Extend (do not extend) the -G behavior to local data too, such as
17791           to static variables in C.  -mlocal-sdata is the default for all
17792           configurations.
17793
17794           If the linker complains that an application is using too much small
17795           data, you might want to try rebuilding the less performance-
17796           critical parts with -mno-local-sdata.  You might also want to build
17797           large libraries with -mno-local-sdata, so that the libraries leave
17798           more room for the main program.
17799
17800       -mextern-sdata
17801       -mno-extern-sdata
17802           Assume (do not assume) that externally-defined data is in a small
17803           data section if the size of that data is within the -G limit.
17804           -mextern-sdata is the default for all configurations.
17805
17806           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
17807           Mod references a variable Var that is no bigger than num bytes, you
17808           must make sure that Var is placed in a small data section.  If Var
17809           is defined by another module, you must either compile that module
17810           with a high-enough -G setting or attach a "section" attribute to
17811           Var's definition.  If Var is common, you must link the application
17812           with a high-enough -G setting.
17813
17814           The easiest way of satisfying these restrictions is to compile and
17815           link every module with the same -G option.  However, you may wish
17816           to build a library that supports several different small data
17817           limits.  You can do this by compiling the library with the highest
17818           supported -G setting and additionally using -mno-extern-sdata to
17819           stop the library from making assumptions about externally-defined
17820           data.
17821
17822       -mgpopt
17823       -mno-gpopt
17824           Use (do not use) GP-relative accesses for symbols that are known to
17825           be in a small data section; see -G, -mlocal-sdata and
17826           -mextern-sdata.  -mgpopt is the default for all configurations.
17827
17828           -mno-gpopt is useful for cases where the $gp register might not
17829           hold the value of "_gp".  For example, if the code is part of a
17830           library that might be used in a boot monitor, programs that call
17831           boot monitor routines pass an unknown value in $gp.  (In such
17832           situations, the boot monitor itself is usually compiled with -G0.)
17833
17834           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
17835
17836       -membedded-data
17837       -mno-embedded-data
17838           Allocate variables to the read-only data section first if possible,
17839           then next in the small data section if possible, otherwise in data.
17840           This gives slightly slower code than the default, but reduces the
17841           amount of RAM required when executing, and thus may be preferred
17842           for some embedded systems.
17843
17844       -muninit-const-in-rodata
17845       -mno-uninit-const-in-rodata
17846           Put uninitialized "const" variables in the read-only data section.
17847           This option is only meaningful in conjunction with -membedded-data.
17848
17849       -mcode-readable=setting
17850           Specify whether GCC may generate code that reads from executable
17851           sections.  There are three possible settings:
17852
17853           -mcode-readable=yes
17854               Instructions may freely access executable sections.  This is
17855               the default setting.
17856
17857           -mcode-readable=pcrel
17858               MIPS16 PC-relative load instructions can access executable
17859               sections, but other instructions must not do so.  This option
17860               is useful on 4KSc and 4KSd processors when the code TLBs have
17861               the Read Inhibit bit set.  It is also useful on processors that
17862               can be configured to have a dual instruction/data SRAM
17863               interface and that, like the M4K, automatically redirect PC-
17864               relative loads to the instruction RAM.
17865
17866           -mcode-readable=no
17867               Instructions must not access executable sections.  This option
17868               can be useful on targets that are configured to have a dual
17869               instruction/data SRAM interface but that (unlike the M4K) do
17870               not automatically redirect PC-relative loads to the instruction
17871               RAM.
17872
17873       -msplit-addresses
17874       -mno-split-addresses
17875           Enable (disable) use of the "%hi()" and "%lo()" assembler
17876           relocation operators.  This option has been superseded by
17877           -mexplicit-relocs but is retained for backwards compatibility.
17878
17879       -mexplicit-relocs
17880       -mno-explicit-relocs
17881           Use (do not use) assembler relocation operators when dealing with
17882           symbolic addresses.  The alternative, selected by
17883           -mno-explicit-relocs, is to use assembler macros instead.
17884
17885           -mexplicit-relocs is the default if GCC was configured to use an
17886           assembler that supports relocation operators.
17887
17888       -mcheck-zero-division
17889       -mno-check-zero-division
17890           Trap (do not trap) on integer division by zero.
17891
17892           The default is -mcheck-zero-division.
17893
17894       -mdivide-traps
17895       -mdivide-breaks
17896           MIPS systems check for division by zero by generating either a
17897           conditional trap or a break instruction.  Using traps results in
17898           smaller code, but is only supported on MIPS II and later.  Also,
17899           some versions of the Linux kernel have a bug that prevents trap
17900           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
17901           to allow conditional traps on architectures that support them and
17902           -mdivide-breaks to force the use of breaks.
17903
17904           The default is usually -mdivide-traps, but this can be overridden
17905           at configure time using --with-divide=breaks.  Divide-by-zero
17906           checks can be completely disabled using -mno-check-zero-division.
17907
17908       -mload-store-pairs
17909       -mno-load-store-pairs
17910           Enable (disable) an optimization that pairs consecutive load or
17911           store instructions to enable load/store bonding.  This option is
17912           enabled by default but only takes effect when the selected
17913           architecture is known to support bonding.
17914
17915       -mmemcpy
17916       -mno-memcpy
17917           Force (do not force) the use of "memcpy" for non-trivial block
17918           moves.  The default is -mno-memcpy, which allows GCC to inline most
17919           constant-sized copies.
17920
17921       -mlong-calls
17922       -mno-long-calls
17923           Disable (do not disable) use of the "jal" instruction.  Calling
17924           functions using "jal" is more efficient but requires the caller and
17925           callee to be in the same 256 megabyte segment.
17926
17927           This option has no effect on abicalls code.  The default is
17928           -mno-long-calls.
17929
17930       -mmad
17931       -mno-mad
17932           Enable (disable) use of the "mad", "madu" and "mul" instructions,
17933           as provided by the R4650 ISA.
17934
17935       -mimadd
17936       -mno-imadd
17937           Enable (disable) use of the "madd" and "msub" integer instructions.
17938           The default is -mimadd on architectures that support "madd" and
17939           "msub" except for the 74k architecture where it was found to
17940           generate slower code.
17941
17942       -mfused-madd
17943       -mno-fused-madd
17944           Enable (disable) use of the floating-point multiply-accumulate
17945           instructions, when they are available.  The default is
17946           -mfused-madd.
17947
17948           On the R8000 CPU when multiply-accumulate instructions are used,
17949           the intermediate product is calculated to infinite precision and is
17950           not subject to the FCSR Flush to Zero bit.  This may be undesirable
17951           in some circumstances.  On other processors the result is
17952           numerically identical to the equivalent computation using separate
17953           multiply, add, subtract and negate instructions.
17954
17955       -nocpp
17956           Tell the MIPS assembler to not run its preprocessor over user
17957           assembler files (with a .s suffix) when assembling them.
17958
17959       -mfix-24k
17960       -mno-fix-24k
17961           Work around the 24K E48 (lost data on stores during refill) errata.
17962           The workarounds are implemented by the assembler rather than by
17963           GCC.
17964
17965       -mfix-r4000
17966       -mno-fix-r4000
17967           Work around certain R4000 CPU errata:
17968
17969           -   A double-word or a variable shift may give an incorrect result
17970               if executed immediately after starting an integer division.
17971
17972           -   A double-word or a variable shift may give an incorrect result
17973               if executed while an integer multiplication is in progress.
17974
17975           -   An integer division may give an incorrect result if started in
17976               a delay slot of a taken branch or a jump.
17977
17978       -mfix-r4400
17979       -mno-fix-r4400
17980           Work around certain R4400 CPU errata:
17981
17982           -   A double-word or a variable shift may give an incorrect result
17983               if executed immediately after starting an integer division.
17984
17985       -mfix-r10000
17986       -mno-fix-r10000
17987           Work around certain R10000 errata:
17988
17989           -   "ll"/"sc" sequences may not behave atomically on revisions
17990               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.
17991
17992           This option can only be used if the target architecture supports
17993           branch-likely instructions.  -mfix-r10000 is the default when
17994           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
17995
17996       -mfix-rm7000
17997       -mno-fix-rm7000
17998           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds
17999           are implemented by the assembler rather than by GCC.
18000
18001       -mfix-vr4120
18002       -mno-fix-vr4120
18003           Work around certain VR4120 errata:
18004
18005           -   "dmultu" does not always produce the correct result.
18006
18007           -   "div" and "ddiv" do not always produce the correct result if
18008               one of the operands is negative.
18009
18010           The workarounds for the division errata rely on special functions
18011           in libgcc.a.  At present, these functions are only provided by the
18012           "mips64vr*-elf" configurations.
18013
18014           Other VR4120 errata require a NOP to be inserted between certain
18015           pairs of instructions.  These errata are handled by the assembler,
18016           not by GCC itself.
18017
18018       -mfix-vr4130
18019           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
18020           implemented by the assembler rather than by GCC, although GCC
18021           avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
18022           "dmacc" and "dmacchi" instructions are available instead.
18023
18024       -mfix-sb1
18025       -mno-fix-sb1
18026           Work around certain SB-1 CPU core errata.  (This flag currently
18027           works around the SB-1 revision 2 "F1" and "F2" floating-point
18028           errata.)
18029
18030       -mr10k-cache-barrier=setting
18031           Specify whether GCC should insert cache barriers to avoid the side
18032           effects of speculation on R10K processors.
18033
18034           In common with many processors, the R10K tries to predict the
18035           outcome of a conditional branch and speculatively executes
18036           instructions from the "taken" branch.  It later aborts these
18037           instructions if the predicted outcome is wrong.  However, on the
18038           R10K, even aborted instructions can have side effects.
18039
18040           This problem only affects kernel stores and, depending on the
18041           system, kernel loads.  As an example, a speculatively-executed
18042           store may load the target memory into cache and mark the cache line
18043           as dirty, even if the store itself is later aborted.  If a DMA
18044           operation writes to the same area of memory before the "dirty" line
18045           is flushed, the cached data overwrites the DMA-ed data.  See the
18046           R10K processor manual for a full description, including other
18047           potential problems.
18048
18049           One workaround is to insert cache barrier instructions before every
18050           memory access that might be speculatively executed and that might
18051           have side effects even if aborted.  -mr10k-cache-barrier=setting
18052           controls GCC's implementation of this workaround.  It assumes that
18053           aborted accesses to any byte in the following regions does not have
18054           side effects:
18055
18056           1.  the memory occupied by the current function's stack frame;
18057
18058           2.  the memory occupied by an incoming stack argument;
18059
18060           3.  the memory occupied by an object with a link-time-constant
18061               address.
18062
18063           It is the kernel's responsibility to ensure that speculative
18064           accesses to these regions are indeed safe.
18065
18066           If the input program contains a function declaration such as:
18067
18068                   void foo (void);
18069
18070           then the implementation of "foo" must allow "j foo" and "jal foo"
18071           to be executed speculatively.  GCC honors this restriction for
18072           functions it compiles itself.  It expects non-GCC functions (such
18073           as hand-written assembly code) to do the same.
18074
18075           The option has three forms:
18076
18077           -mr10k-cache-barrier=load-store
18078               Insert a cache barrier before a load or store that might be
18079               speculatively executed and that might have side effects even if
18080               aborted.
18081
18082           -mr10k-cache-barrier=store
18083               Insert a cache barrier before a store that might be
18084               speculatively executed and that might have side effects even if
18085               aborted.
18086
18087           -mr10k-cache-barrier=none
18088               Disable the insertion of cache barriers.  This is the default
18089               setting.
18090
18091       -mflush-func=func
18092       -mno-flush-func
18093           Specifies the function to call to flush the I and D caches, or to
18094           not call any such function.  If called, the function must take the
18095           same arguments as the common "_flush_func", that is, the address of
18096           the memory range for which the cache is being flushed, the size of
18097           the memory range, and the number 3 (to flush both caches).  The
18098           default depends on the target GCC was configured for, but commonly
18099           is either "_flush_func" or "__cpu_flush".
18100
18101       mbranch-cost=num
18102           Set the cost of branches to roughly num "simple" instructions.
18103           This cost is only a heuristic and is not guaranteed to produce
18104           consistent results across releases.  A zero cost redundantly
18105           selects the default, which is based on the -mtune setting.
18106
18107       -mbranch-likely
18108       -mno-branch-likely
18109           Enable or disable use of Branch Likely instructions, regardless of
18110           the default for the selected architecture.  By default, Branch
18111           Likely instructions may be generated if they are supported by the
18112           selected architecture.  An exception is for the MIPS32 and MIPS64
18113           architectures and processors that implement those architectures;
18114           for those, Branch Likely instructions are not be generated by
18115           default because the MIPS32 and MIPS64 architectures specifically
18116           deprecate their use.
18117
18118       -mcompact-branches=never
18119       -mcompact-branches=optimal
18120       -mcompact-branches=always
18121           These options control which form of branches will be generated.
18122           The default is -mcompact-branches=optimal.
18123
18124           The -mcompact-branches=never option ensures that compact branch
18125           instructions will never be generated.
18126
18127           The -mcompact-branches=always option ensures that a compact branch
18128           instruction will be generated if available.  If a compact branch
18129           instruction is not available, a delay slot form of the branch will
18130           be used instead.
18131
18132           This option is supported from MIPS Release 6 onwards.
18133
18134           The -mcompact-branches=optimal option will cause a delay slot
18135           branch to be used if one is available in the current ISA and the
18136           delay slot is successfully filled.  If the delay slot is not
18137           filled, a compact branch will be chosen if one is available.
18138
18139       -mfp-exceptions
18140       -mno-fp-exceptions
18141           Specifies whether FP exceptions are enabled.  This affects how FP
18142           instructions are scheduled for some processors.  The default is
18143           that FP exceptions are enabled.
18144
18145           For instance, on the SB-1, if FP exceptions are disabled, and we
18146           are emitting 64-bit code, then we can use both FP pipes.
18147           Otherwise, we can only use one FP pipe.
18148
18149       -mvr4130-align
18150       -mno-vr4130-align
18151           The VR4130 pipeline is two-way superscalar, but can only issue two
18152           instructions together if the first one is 8-byte aligned.  When
18153           this option is enabled, GCC aligns pairs of instructions that it
18154           thinks should execute in parallel.
18155
18156           This option only has an effect when optimizing for the VR4130.  It
18157           normally makes code faster, but at the expense of making it bigger.
18158           It is enabled by default at optimization level -O3.
18159
18160       -msynci
18161       -mno-synci
18162           Enable (disable) generation of "synci" instructions on
18163           architectures that support it.  The "synci" instructions (if
18164           enabled) are generated when "__builtin___clear_cache" is compiled.
18165
18166           This option defaults to -mno-synci, but the default can be
18167           overridden by configuring GCC with --with-synci.
18168
18169           When compiling code for single processor systems, it is generally
18170           safe to use "synci".  However, on many multi-core (SMP) systems, it
18171           does not invalidate the instruction caches on all cores and may
18172           lead to undefined behavior.
18173
18174       -mrelax-pic-calls
18175       -mno-relax-pic-calls
18176           Try to turn PIC calls that are normally dispatched via register $25
18177           into direct calls.  This is only possible if the linker can resolve
18178           the destination at link time and if the destination is within range
18179           for a direct call.
18180
18181           -mrelax-pic-calls is the default if GCC was configured to use an
18182           assembler and a linker that support the ".reloc" assembly directive
18183           and -mexplicit-relocs is in effect.  With -mno-explicit-relocs,
18184           this optimization can be performed by the assembler and the linker
18185           alone without help from the compiler.
18186
18187       -mmcount-ra-address
18188       -mno-mcount-ra-address
18189           Emit (do not emit) code that allows "_mcount" to modify the calling
18190           function's return address.  When enabled, this option extends the
18191           usual "_mcount" interface with a new ra-address parameter, which
18192           has type "intptr_t *" and is passed in register $12.  "_mcount" can
18193           then modify the return address by doing both of the following:
18194
18195           *   Returning the new address in register $31.
18196
18197           *   Storing the new address in "*ra-address", if ra-address is
18198               nonnull.
18199
18200           The default is -mno-mcount-ra-address.
18201
18202       -mframe-header-opt
18203       -mno-frame-header-opt
18204           Enable (disable) frame header optimization in the o32 ABI.  When
18205           using the o32 ABI, calling functions will allocate 16 bytes on the
18206           stack for the called function to write out register arguments.
18207           When enabled, this optimization will suppress the allocation of the
18208           frame header if it can be determined that it is unused.
18209
18210           This optimization is off by default at all optimization levels.
18211
18212       -mlxc1-sxc1
18213       -mno-lxc1-sxc1
18214           When applicable, enable (disable) the generation of "lwxc1",
18215           "swxc1", "ldxc1", "sdxc1" instructions.  Enabled by default.
18216
18217       -mmadd4
18218       -mno-madd4
18219           When applicable, enable (disable) the generation of 4-operand
18220           "madd.s", "madd.d" and related instructions.  Enabled by default.
18221
18222   MMIX Options
18223       These options are defined for the MMIX:
18224
18225       -mlibfuncs
18226       -mno-libfuncs
18227           Specify that intrinsic library functions are being compiled,
18228           passing all values in registers, no matter the size.
18229
18230       -mepsilon
18231       -mno-epsilon
18232           Generate floating-point comparison instructions that compare with
18233           respect to the "rE" epsilon register.
18234
18235       -mabi=mmixware
18236       -mabi=gnu
18237           Generate code that passes function parameters and return values
18238           that (in the called function) are seen as registers $0 and up, as
18239           opposed to the GNU ABI which uses global registers $231 and up.
18240
18241       -mzero-extend
18242       -mno-zero-extend
18243           When reading data from memory in sizes shorter than 64 bits, use
18244           (do not use) zero-extending load instructions by default, rather
18245           than sign-extending ones.
18246
18247       -mknuthdiv
18248       -mno-knuthdiv
18249           Make the result of a division yielding a remainder have the same
18250           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
18251           the remainder follows the sign of the dividend.  Both methods are
18252           arithmetically valid, the latter being almost exclusively used.
18253
18254       -mtoplevel-symbols
18255       -mno-toplevel-symbols
18256           Prepend (do not prepend) a : to all global symbols, so the assembly
18257           code can be used with the "PREFIX" assembly directive.
18258
18259       -melf
18260           Generate an executable in the ELF format, rather than the default
18261           mmo format used by the mmix simulator.
18262
18263       -mbranch-predict
18264       -mno-branch-predict
18265           Use (do not use) the probable-branch instructions, when static
18266           branch prediction indicates a probable branch.
18267
18268       -mbase-addresses
18269       -mno-base-addresses
18270           Generate (do not generate) code that uses base addresses.  Using a
18271           base address automatically generates a request (handled by the
18272           assembler and the linker) for a constant to be set up in a global
18273           register.  The register is used for one or more base address
18274           requests within the range 0 to 255 from the value held in the
18275           register.  The generally leads to short and fast code, but the
18276           number of different data items that can be addressed is limited.
18277           This means that a program that uses lots of static data may require
18278           -mno-base-addresses.
18279
18280       -msingle-exit
18281       -mno-single-exit
18282           Force (do not force) generated code to have a single exit point in
18283           each function.
18284
18285   MN10300 Options
18286       These -m options are defined for Matsushita MN10300 architectures:
18287
18288       -mmult-bug
18289           Generate code to avoid bugs in the multiply instructions for the
18290           MN10300 processors.  This is the default.
18291
18292       -mno-mult-bug
18293           Do not generate code to avoid bugs in the multiply instructions for
18294           the MN10300 processors.
18295
18296       -mam33
18297           Generate code using features specific to the AM33 processor.
18298
18299       -mno-am33
18300           Do not generate code using features specific to the AM33 processor.
18301           This is the default.
18302
18303       -mam33-2
18304           Generate code using features specific to the AM33/2.0 processor.
18305
18306       -mam34
18307           Generate code using features specific to the AM34 processor.
18308
18309       -mtune=cpu-type
18310           Use the timing characteristics of the indicated CPU type when
18311           scheduling instructions.  This does not change the targeted
18312           processor type.  The CPU type must be one of mn10300, am33, am33-2
18313           or am34.
18314
18315       -mreturn-pointer-on-d0
18316           When generating a function that returns a pointer, return the
18317           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
18318           only in "a0", and attempts to call such functions without a
18319           prototype result in errors.  Note that this option is on by
18320           default; use -mno-return-pointer-on-d0 to disable it.
18321
18322       -mno-crt0
18323           Do not link in the C run-time initialization object file.
18324
18325       -mrelax
18326           Indicate to the linker that it should perform a relaxation
18327           optimization pass to shorten branches, calls and absolute memory
18328           addresses.  This option only has an effect when used on the command
18329           line for the final link step.
18330
18331           This option makes symbolic debugging impossible.
18332
18333       -mliw
18334           Allow the compiler to generate Long Instruction Word instructions
18335           if the target is the AM33 or later.  This is the default.  This
18336           option defines the preprocessor macro "__LIW__".
18337
18338       -mnoliw
18339           Do not allow the compiler to generate Long Instruction Word
18340           instructions.  This option defines the preprocessor macro
18341           "__NO_LIW__".
18342
18343       -msetlb
18344           Allow the compiler to generate the SETLB and Lcc instructions if
18345           the target is the AM33 or later.  This is the default.  This option
18346           defines the preprocessor macro "__SETLB__".
18347
18348       -mnosetlb
18349           Do not allow the compiler to generate SETLB or Lcc instructions.
18350           This option defines the preprocessor macro "__NO_SETLB__".
18351
18352   Moxie Options
18353       -meb
18354           Generate big-endian code.  This is the default for moxie-*-*
18355           configurations.
18356
18357       -mel
18358           Generate little-endian code.
18359
18360       -mmul.x
18361           Generate mul.x and umul.x instructions.  This is the default for
18362           moxiebox-*-* configurations.
18363
18364       -mno-crt0
18365           Do not link in the C run-time initialization object file.
18366
18367   MSP430 Options
18368       These options are defined for the MSP430:
18369
18370       -masm-hex
18371           Force assembly output to always use hex constants.  Normally such
18372           constants are signed decimals, but this option is available for
18373           testsuite and/or aesthetic purposes.
18374
18375       -mmcu=
18376           Select the MCU to target.  This is used to create a C preprocessor
18377           symbol based upon the MCU name, converted to upper case and pre-
18378           and post-fixed with __.  This in turn is used by the msp430.h
18379           header file to select an MCU-specific supplementary header file.
18380
18381           The option also sets the ISA to use.  If the MCU name is one that
18382           is known to only support the 430 ISA then that is selected,
18383           otherwise the 430X ISA is selected.  A generic MCU name of msp430
18384           can also be used to select the 430 ISA.  Similarly the generic
18385           msp430x MCU name selects the 430X ISA.
18386
18387           In addition an MCU-specific linker script is added to the linker
18388           command line.  The script's name is the name of the MCU with .ld
18389           appended.  Thus specifying -mmcu=xxx on the gcc command line
18390           defines the C preprocessor symbol "__XXX__" and cause the linker to
18391           search for a script called xxx.ld.
18392
18393           This option is also passed on to the assembler.
18394
18395       -mwarn-mcu
18396       -mno-warn-mcu
18397           This option enables or disables warnings about conflicts between
18398           the MCU name specified by the -mmcu option and the ISA set by the
18399           -mcpu option and/or the hardware multiply support set by the
18400           -mhwmult option.  It also toggles warnings about unrecognized MCU
18401           names.  This option is on by default.
18402
18403       -mcpu=
18404           Specifies the ISA to use.  Accepted values are msp430, msp430x and
18405           msp430xv2.  This option is deprecated.  The -mmcu= option should be
18406           used to select the ISA.
18407
18408       -msim
18409           Link to the simulator runtime libraries and linker script.
18410           Overrides any scripts that would be selected by the -mmcu= option.
18411
18412       -mlarge
18413           Use large-model addressing (20-bit pointers, 32-bit "size_t").
18414
18415       -msmall
18416           Use small-model addressing (16-bit pointers, 16-bit "size_t").
18417
18418       -mrelax
18419           This option is passed to the assembler and linker, and allows the
18420           linker to perform certain optimizations that cannot be done until
18421           the final link.
18422
18423       mhwmult=
18424           Describes the type of hardware multiply supported by the target.
18425           Accepted values are none for no hardware multiply, 16bit for the
18426           original 16-bit-only multiply supported by early MCUs.  32bit for
18427           the 16/32-bit multiply supported by later MCUs and f5series for the
18428           16/32-bit multiply supported by F5-series MCUs.  A value of auto
18429           can also be given.  This tells GCC to deduce the hardware multiply
18430           support based upon the MCU name provided by the -mmcu option.  If
18431           no -mmcu option is specified or if the MCU name is not recognized
18432           then no hardware multiply support is assumed.  "auto" is the
18433           default setting.
18434
18435           Hardware multiplies are normally performed by calling a library
18436           routine.  This saves space in the generated code.  When compiling
18437           at -O3 or higher however the hardware multiplier is invoked inline.
18438           This makes for bigger, but faster code.
18439
18440           The hardware multiply routines disable interrupts whilst running
18441           and restore the previous interrupt state when they finish.  This
18442           makes them safe to use inside interrupt handlers as well as in
18443           normal code.
18444
18445       -minrt
18446           Enable the use of a minimum runtime environment - no static
18447           initializers or constructors.  This is intended for memory-
18448           constrained devices.  The compiler includes special symbols in some
18449           objects that tell the linker and runtime which code fragments are
18450           required.
18451
18452       -mcode-region=
18453       -mdata-region=
18454           These options tell the compiler where to place functions and data
18455           that do not have one of the "lower", "upper", "either" or "section"
18456           attributes.  Possible values are "lower", "upper", "either" or
18457           "any".  The first three behave like the corresponding attribute.
18458           The fourth possible value - "any" - is the default.  It leaves
18459           placement entirely up to the linker script and how it assigns the
18460           standard sections (".text", ".data", etc) to the memory regions.
18461
18462       -msilicon-errata=
18463           This option passes on a request to assembler to enable the fixes
18464           for the named silicon errata.
18465
18466       -msilicon-errata-warn=
18467           This option passes on a request to the assembler to enable warning
18468           messages when a silicon errata might need to be applied.
18469
18470   NDS32 Options
18471       These options are defined for NDS32 implementations:
18472
18473       -mbig-endian
18474           Generate code in big-endian mode.
18475
18476       -mlittle-endian
18477           Generate code in little-endian mode.
18478
18479       -mreduced-regs
18480           Use reduced-set registers for register allocation.
18481
18482       -mfull-regs
18483           Use full-set registers for register allocation.
18484
18485       -mcmov
18486           Generate conditional move instructions.
18487
18488       -mno-cmov
18489           Do not generate conditional move instructions.
18490
18491       -mext-perf
18492           Generate performance extension instructions.
18493
18494       -mno-ext-perf
18495           Do not generate performance extension instructions.
18496
18497       -mext-perf2
18498           Generate performance extension 2 instructions.
18499
18500       -mno-ext-perf2
18501           Do not generate performance extension 2 instructions.
18502
18503       -mext-string
18504           Generate string extension instructions.
18505
18506       -mno-ext-string
18507           Do not generate string extension instructions.
18508
18509       -mv3push
18510           Generate v3 push25/pop25 instructions.
18511
18512       -mno-v3push
18513           Do not generate v3 push25/pop25 instructions.
18514
18515       -m16-bit
18516           Generate 16-bit instructions.
18517
18518       -mno-16-bit
18519           Do not generate 16-bit instructions.
18520
18521       -misr-vector-size=num
18522           Specify the size of each interrupt vector, which must be 4 or 16.
18523
18524       -mcache-block-size=num
18525           Specify the size of each cache block, which must be a power of 2
18526           between 4 and 512.
18527
18528       -march=arch
18529           Specify the name of the target architecture.
18530
18531       -mcmodel=code-model
18532           Set the code model to one of
18533
18534           small
18535               All the data and read-only data segments must be within 512KB
18536               addressing space.  The text segment must be within 16MB
18537               addressing space.
18538
18539           medium
18540               The data segment must be within 512KB while the read-only data
18541               segment can be within 4GB addressing space.  The text segment
18542               should be still within 16MB addressing space.
18543
18544           large
18545               All the text and data segments can be within 4GB addressing
18546               space.
18547
18548       -mctor-dtor
18549           Enable constructor/destructor feature.
18550
18551       -mrelax
18552           Guide linker to relax instructions.
18553
18554   Nios II Options
18555       These are the options defined for the Altera Nios II processor.
18556
18557       -G num
18558           Put global and static objects less than or equal to num bytes into
18559           the small data or BSS sections instead of the normal data or BSS
18560           sections.  The default value of num is 8.
18561
18562       -mgpopt=option
18563       -mgpopt
18564       -mno-gpopt
18565           Generate (do not generate) GP-relative accesses.  The following
18566           option names are recognized:
18567
18568           none
18569               Do not generate GP-relative accesses.
18570
18571           local
18572               Generate GP-relative accesses for small data objects that are
18573               not external, weak, or uninitialized common symbols.  Also use
18574               GP-relative addressing for objects that have been explicitly
18575               placed in a small data section via a "section" attribute.
18576
18577           global
18578               As for local, but also generate GP-relative accesses for small
18579               data objects that are external, weak, or common.  If you use
18580               this option, you must ensure that all parts of your program
18581               (including libraries) are compiled with the same -G setting.
18582
18583           data
18584               Generate GP-relative accesses for all data objects in the
18585               program.  If you use this option, the entire data and BSS
18586               segments of your program must fit in 64K of memory and you must
18587               use an appropriate linker script to allocate them within the
18588               addressable range of the global pointer.
18589
18590           all Generate GP-relative addresses for function pointers as well as
18591               data pointers.  If you use this option, the entire text, data,
18592               and BSS segments of your program must fit in 64K of memory and
18593               you must use an appropriate linker script to allocate them
18594               within the addressable range of the global pointer.
18595
18596           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is
18597           equivalent to -mgpopt=none.
18598
18599           The default is -mgpopt except when -fpic or -fPIC is specified to
18600           generate position-independent code.  Note that the Nios II ABI does
18601           not permit GP-relative accesses from shared libraries.
18602
18603           You may need to specify -mno-gpopt explicitly when building
18604           programs that include large amounts of small data, including large
18605           GOT data sections.  In this case, the 16-bit offset for GP-relative
18606           addressing may not be large enough to allow access to the entire
18607           small data section.
18608
18609       -mgprel-sec=regexp
18610           This option specifies additional section names that can be accessed
18611           via GP-relative addressing.  It is most useful in conjunction with
18612           "section" attributes on variable declarations and a custom linker
18613           script.  The regexp is a POSIX Extended Regular Expression.
18614
18615           This option does not affect the behavior of the -G option, and the
18616           specified sections are in addition to the standard ".sdata" and
18617           ".sbss" small-data sections that are recognized by -mgpopt.
18618
18619       -mr0rel-sec=regexp
18620           This option specifies names of sections that can be accessed via a
18621           16-bit offset from "r0"; that is, in the low 32K or high 32K of the
18622           32-bit address space.  It is most useful in conjunction with
18623           "section" attributes on variable declarations and a custom linker
18624           script.  The regexp is a POSIX Extended Regular Expression.
18625
18626           In contrast to the use of GP-relative addressing for small data,
18627           zero-based addressing is never generated by default and there are
18628           no conventional section names used in standard linker scripts for
18629           sections in the low or high areas of memory.
18630
18631       -mel
18632       -meb
18633           Generate little-endian (default) or big-endian (experimental) code,
18634           respectively.
18635
18636       -march=arch
18637           This specifies the name of the target Nios II architecture.  GCC
18638           uses this name to determine what kind of instructions it can emit
18639           when generating assembly code.  Permissible names are: r1, r2.
18640
18641           The preprocessor macro "__nios2_arch__" is available to programs,
18642           with value 1 or 2, indicating the targeted ISA level.
18643
18644       -mbypass-cache
18645       -mno-bypass-cache
18646           Force all load and store instructions to always bypass cache by
18647           using I/O variants of the instructions. The default is not to
18648           bypass the cache.
18649
18650       -mno-cache-volatile
18651       -mcache-volatile
18652           Volatile memory access bypass the cache using the I/O variants of
18653           the load and store instructions. The default is not to bypass the
18654           cache.
18655
18656       -mno-fast-sw-div
18657       -mfast-sw-div
18658           Do not use table-based fast divide for small numbers. The default
18659           is to use the fast divide at -O3 and above.
18660
18661       -mno-hw-mul
18662       -mhw-mul
18663       -mno-hw-mulx
18664       -mhw-mulx
18665       -mno-hw-div
18666       -mhw-div
18667           Enable or disable emitting "mul", "mulx" and "div" family of
18668           instructions by the compiler. The default is to emit "mul" and not
18669           emit "div" and "mulx".
18670
18671       -mbmx
18672       -mno-bmx
18673       -mcdx
18674       -mno-cdx
18675           Enable or disable generation of Nios II R2 BMX (bit manipulation)
18676           and CDX (code density) instructions.  Enabling these instructions
18677           also requires -march=r2.  Since these instructions are optional
18678           extensions to the R2 architecture, the default is not to emit them.
18679
18680       -mcustom-insn=N
18681       -mno-custom-insn
18682           Each -mcustom-insn=N option enables use of a custom instruction
18683           with encoding N when generating code that uses insn.  For example,
18684           -mcustom-fadds=253 generates custom instruction 253 for single-
18685           precision floating-point add operations instead of the default
18686           behavior of using a library call.
18687
18688           The following values of insn are supported.  Except as otherwise
18689           noted, floating-point operations are expected to be implemented
18690           with normal IEEE 754 semantics and correspond directly to the C
18691           operators or the equivalent GCC built-in functions.
18692
18693           Single-precision floating point:
18694
18695           fadds, fsubs, fdivs, fmuls
18696               Binary arithmetic operations.
18697
18698           fnegs
18699               Unary negation.
18700
18701           fabss
18702               Unary absolute value.
18703
18704           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
18705               Comparison operations.
18706
18707           fmins, fmaxs
18708               Floating-point minimum and maximum.  These instructions are
18709               only generated if -ffinite-math-only is specified.
18710
18711           fsqrts
18712               Unary square root operation.
18713
18714           fcoss, fsins, ftans, fatans, fexps, flogs
18715               Floating-point trigonometric and exponential functions.  These
18716               instructions are only generated if -funsafe-math-optimizations
18717               is also specified.
18718
18719           Double-precision floating point:
18720
18721           faddd, fsubd, fdivd, fmuld
18722               Binary arithmetic operations.
18723
18724           fnegd
18725               Unary negation.
18726
18727           fabsd
18728               Unary absolute value.
18729
18730           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
18731               Comparison operations.
18732
18733           fmind, fmaxd
18734               Double-precision minimum and maximum.  These instructions are
18735               only generated if -ffinite-math-only is specified.
18736
18737           fsqrtd
18738               Unary square root operation.
18739
18740           fcosd, fsind, ftand, fatand, fexpd, flogd
18741               Double-precision trigonometric and exponential functions.
18742               These instructions are only generated if
18743               -funsafe-math-optimizations is also specified.
18744
18745           Conversions:
18746
18747           fextsd
18748               Conversion from single precision to double precision.
18749
18750           ftruncds
18751               Conversion from double precision to single precision.
18752
18753           fixsi, fixsu, fixdi, fixdu
18754               Conversion from floating point to signed or unsigned integer
18755               types, with truncation towards zero.
18756
18757           round
18758               Conversion from single-precision floating point to signed
18759               integer, rounding to the nearest integer and ties away from
18760               zero.  This corresponds to the "__builtin_lroundf" function
18761               when -fno-math-errno is used.
18762
18763           floatis, floatus, floatid, floatud
18764               Conversion from signed or unsigned integer types to floating-
18765               point types.
18766
18767           In addition, all of the following transfer instructions for
18768           internal registers X and Y must be provided to use any of the
18769           double-precision floating-point instructions.  Custom instructions
18770           taking two double-precision source operands expect the first
18771           operand in the 64-bit register X.  The other operand (or only
18772           operand of a unary operation) is given to the custom arithmetic
18773           instruction with the least significant half in source register src1
18774           and the most significant half in src2.  A custom instruction that
18775           returns a double-precision result returns the most significant 32
18776           bits in the destination register and the other half in 32-bit
18777           register Y.  GCC automatically generates the necessary code
18778           sequences to write register X and/or read register Y when double-
18779           precision floating-point instructions are used.
18780
18781           fwrx
18782               Write src1 into the least significant half of X and src2 into
18783               the most significant half of X.
18784
18785           fwry
18786               Write src1 into Y.
18787
18788           frdxhi, frdxlo
18789               Read the most or least (respectively) significant half of X and
18790               store it in dest.
18791
18792           frdy
18793               Read the value of Y and store it into dest.
18794
18795           Note that you can gain more local control over generation of Nios
18796           II custom instructions by using the "target("custom-insn=N")" and
18797           "target("no-custom-insn")" function attributes or pragmas.
18798
18799       -mcustom-fpu-cfg=name
18800           This option enables a predefined, named set of custom instruction
18801           encodings (see -mcustom-insn above).  Currently, the following sets
18802           are defined:
18803
18804           -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252
18805           -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant
18806
18807           -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252
18808           -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255
18809           -fsingle-precision-constant
18810
18811           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243
18812           -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246
18813           -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251
18814           -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254
18815           -mcustom-fdivs=255 -fsingle-precision-constant
18816
18817           Custom instruction assignments given by individual -mcustom-insn=
18818           options override those given by -mcustom-fpu-cfg=, regardless of
18819           the order of the options on the command line.
18820
18821           Note that you can gain more local control over selection of a FPU
18822           configuration by using the "target("custom-fpu-cfg=name")" function
18823           attribute or pragma.
18824
18825       These additional -m options are available for the Altera Nios II ELF
18826       (bare-metal) target:
18827
18828       -mhal
18829           Link with HAL BSP.  This suppresses linking with the GCC-provided C
18830           runtime startup and termination code, and is typically used in
18831           conjunction with -msys-crt0= to specify the location of the
18832           alternate startup code provided by the HAL BSP.
18833
18834       -msmallc
18835           Link with a limited version of the C library, -lsmallc, rather than
18836           Newlib.
18837
18838       -msys-crt0=startfile
18839           startfile is the file name of the startfile (crt0) to use when
18840           linking.  This option is only useful in conjunction with -mhal.
18841
18842       -msys-lib=systemlib
18843           systemlib is the library name of the library that provides low-
18844           level system calls required by the C library, e.g. "read" and
18845           "write".  This option is typically used to link with a library
18846           provided by a HAL BSP.
18847
18848   Nvidia PTX Options
18849       These options are defined for Nvidia PTX:
18850
18851       -m32
18852       -m64
18853           Generate code for 32-bit or 64-bit ABI.
18854
18855       -mmainkernel
18856           Link in code for a __main kernel.  This is for stand-alone instead
18857           of offloading execution.
18858
18859       -moptimize
18860           Apply partitioned execution optimizations.  This is the default
18861           when any level of optimization is selected.
18862
18863       -msoft-stack
18864           Generate code that does not use ".local" memory directly for stack
18865           storage. Instead, a per-warp stack pointer is maintained
18866           explicitly. This enables variable-length stack allocation (with
18867           variable-length arrays or "alloca"), and when global memory is used
18868           for underlying storage, makes it possible to access automatic
18869           variables from other threads, or with atomic instructions. This
18870           code generation variant is used for OpenMP offloading, but the
18871           option is exposed on its own for the purpose of testing the
18872           compiler; to generate code suitable for linking into programs using
18873           OpenMP offloading, use option -mgomp.
18874
18875       -muniform-simt
18876           Switch to code generation variant that allows to execute all
18877           threads in each warp, while maintaining memory state and side
18878           effects as if only one thread in each warp was active outside of
18879           OpenMP SIMD regions.  All atomic operations and calls to runtime
18880           (malloc, free, vprintf) are conditionally executed (iff current
18881           lane index equals the master lane index), and the register being
18882           assigned is copied via a shuffle instruction from the master lane.
18883           Outside of SIMD regions lane 0 is the master; inside, each thread
18884           sees itself as the master.  Shared memory array "int __nvptx_uni[]"
18885           stores all-zeros or all-ones bitmasks for each warp, indicating
18886           current mode (0 outside of SIMD regions).  Each thread can bitwise-
18887           and the bitmask at position "tid.y" with current lane index to
18888           compute the master lane index.
18889
18890       -mgomp
18891           Generate code for use in OpenMP offloading: enables -msoft-stack
18892           and -muniform-simt options, and selects corresponding multilib
18893           variant.
18894
18895   PDP-11 Options
18896       These options are defined for the PDP-11:
18897
18898       -mfpu
18899           Use hardware FPP floating point.  This is the default.  (FIS
18900           floating point on the PDP-11/40 is not supported.)
18901
18902       -msoft-float
18903           Do not use hardware floating point.
18904
18905       -mac0
18906           Return floating-point results in ac0 (fr0 in Unix assembler
18907           syntax).
18908
18909       -mno-ac0
18910           Return floating-point results in memory.  This is the default.
18911
18912       -m40
18913           Generate code for a PDP-11/40.
18914
18915       -m45
18916           Generate code for a PDP-11/45.  This is the default.
18917
18918       -m10
18919           Generate code for a PDP-11/10.
18920
18921       -mbcopy-builtin
18922           Use inline "movmemhi" patterns for copying memory.  This is the
18923           default.
18924
18925       -mbcopy
18926           Do not use inline "movmemhi" patterns for copying memory.
18927
18928       -mint16
18929       -mno-int32
18930           Use 16-bit "int".  This is the default.
18931
18932       -mint32
18933       -mno-int16
18934           Use 32-bit "int".
18935
18936       -mfloat64
18937       -mno-float32
18938           Use 64-bit "float".  This is the default.
18939
18940       -mfloat32
18941       -mno-float64
18942           Use 32-bit "float".
18943
18944       -mabshi
18945           Use "abshi2" pattern.  This is the default.
18946
18947       -mno-abshi
18948           Do not use "abshi2" pattern.
18949
18950       -mbranch-expensive
18951           Pretend that branches are expensive.  This is for experimenting
18952           with code generation only.
18953
18954       -mbranch-cheap
18955           Do not pretend that branches are expensive.  This is the default.
18956
18957       -munix-asm
18958           Use Unix assembler syntax.  This is the default when configured for
18959           pdp11-*-bsd.
18960
18961       -mdec-asm
18962           Use DEC assembler syntax.  This is the default when configured for
18963           any PDP-11 target other than pdp11-*-bsd.
18964
18965   picoChip Options
18966       These -m options are defined for picoChip implementations:
18967
18968       -mae=ae_type
18969           Set the instruction set, register set, and instruction scheduling
18970           parameters for array element type ae_type.  Supported values for
18971           ae_type are ANY, MUL, and MAC.
18972
18973           -mae=ANY selects a completely generic AE type.  Code generated with
18974           this option runs on any of the other AE types.  The code is not as
18975           efficient as it would be if compiled for a specific AE type, and
18976           some types of operation (e.g., multiplication) do not work properly
18977           on all types of AE.
18978
18979           -mae=MUL selects a MUL AE type.  This is the most useful AE type
18980           for compiled code, and is the default.
18981
18982           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
18983           option may suffer from poor performance of byte (char)
18984           manipulation, since the DSP AE does not provide hardware support
18985           for byte load/stores.
18986
18987       -msymbol-as-address
18988           Enable the compiler to directly use a symbol name as an address in
18989           a load/store instruction, without first loading it into a register.
18990           Typically, the use of this option generates larger programs, which
18991           run faster than when the option isn't used.  However, the results
18992           vary from program to program, so it is left as a user option,
18993           rather than being permanently enabled.
18994
18995       -mno-inefficient-warnings
18996           Disables warnings about the generation of inefficient code.  These
18997           warnings can be generated, for example, when compiling code that
18998           performs byte-level memory operations on the MAC AE type.  The MAC
18999           AE has no hardware support for byte-level memory operations, so all
19000           byte load/stores must be synthesized from word load/store
19001           operations.  This is inefficient and a warning is generated to
19002           indicate that you should rewrite the code to avoid byte operations,
19003           or to target an AE type that has the necessary hardware support.
19004           This option disables these warnings.
19005
19006   PowerPC Options
19007       These are listed under
19008
19009   PowerPC SPE Options
19010       These -m options are defined for PowerPC SPE:
19011
19012       -mmfcrf
19013       -mno-mfcrf
19014       -mpopcntb
19015       -mno-popcntb
19016           You use these options to specify which instructions are available
19017           on the processor you are using.  The default value of these options
19018           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
19019           overrides the specification of these options.  We recommend you use
19020           the -mcpu=cpu_type option rather than the options listed above.
19021
19022           The -mmfcrf option allows GCC to generate the move from condition
19023           register field instruction implemented on the POWER4 processor and
19024           other processors that support the PowerPC V2.01 architecture.  The
19025           -mpopcntb option allows GCC to generate the popcount and double-
19026           precision FP reciprocal estimate instruction implemented on the
19027           POWER5 processor and other processors that support the PowerPC
19028           V2.02 architecture.
19029
19030       -mcpu=cpu_type
19031           Set architecture type, register usage, and instruction scheduling
19032           parameters for machine type cpu_type.  Supported values for
19033           cpu_type are 8540, 8548, and native.
19034
19035           -mcpu=powerpc specifies pure 32-bit PowerPC (either endian), with
19036           an appropriate, generic processor model assumed for scheduling
19037           purposes.
19038
19039           Specifying native as cpu type detects and selects the architecture
19040           option that corresponds to the host processor of the system
19041           performing the compilation.  -mcpu=native has no effect if GCC does
19042           not recognize the processor.
19043
19044           The other options specify a specific processor.  Code generated
19045           under those options runs best on that processor, and may not run at
19046           all on others.
19047
19048           The -mcpu options automatically enable or disable the following
19049           options:
19050
19051           -mhard-float  -mmfcrf  -mmultiple -mpopcntb -mpopcntd
19052           -msingle-float -mdouble-float -mfloat128
19053
19054           The particular options set for any particular CPU varies between
19055           compiler versions, depending on what setting seems to produce
19056           optimal code for that CPU; it doesn't necessarily reflect the
19057           actual hardware's capabilities.  If you wish to set an individual
19058           option to a particular value, you may specify it after the -mcpu
19059           option, like -mcpu=8548.
19060
19061       -mtune=cpu_type
19062           Set the instruction scheduling parameters for machine type
19063           cpu_type, but do not set the architecture type or register usage,
19064           as -mcpu=cpu_type does.  The same values for cpu_type are used for
19065           -mtune as for -mcpu.  If both are specified, the code generated
19066           uses the architecture and registers set by -mcpu, but the
19067           scheduling parameters set by -mtune.
19068
19069       -msecure-plt
19070           Generate code that allows ld and ld.so to build executables and
19071           shared libraries with non-executable ".plt" and ".got" sections.
19072           This is a PowerPC 32-bit SYSV ABI option.
19073
19074       -mbss-plt
19075           Generate code that uses a BSS ".plt" section that ld.so fills in,
19076           and requires ".plt" and ".got" sections that are both writable and
19077           executable.  This is a PowerPC 32-bit SYSV ABI option.
19078
19079       -misel
19080       -mno-isel
19081           This switch enables or disables the generation of ISEL
19082           instructions.
19083
19084       -misel=yes/no
19085           This switch has been deprecated.  Use -misel and -mno-isel instead.
19086
19087       -mspe
19088       -mno-spe
19089           This switch enables or disables the generation of SPE simd
19090           instructions.
19091
19092       -mspe=yes/no
19093           This option has been deprecated.  Use -mspe and -mno-spe instead.
19094
19095       -mfloat128
19096       -mno-float128
19097           Enable/disable the __float128 keyword for IEEE 128-bit floating
19098           point and use either software emulation for IEEE 128-bit floating
19099           point or hardware instructions.
19100
19101       -mfloat-gprs=yes/single/double/no
19102       -mfloat-gprs
19103           This switch enables or disables the generation of floating-point
19104           operations on the general-purpose registers for architectures that
19105           support it.
19106
19107           The argument yes or single enables the use of single-precision
19108           floating-point operations.
19109
19110           The argument double enables the use of single and double-precision
19111           floating-point operations.
19112
19113           The argument no disables floating-point operations on the general-
19114           purpose registers.
19115
19116           This option is currently only available on the MPC854x.
19117
19118       -mfull-toc
19119       -mno-fp-in-toc
19120       -mno-sum-in-toc
19121       -mminimal-toc
19122           Modify generation of the TOC (Table Of Contents), which is created
19123           for every executable file.  The -mfull-toc option is selected by
19124           default.  In that case, GCC allocates at least one TOC entry for
19125           each unique non-automatic variable reference in your program.  GCC
19126           also places floating-point constants in the TOC.  However, only
19127           16,384 entries are available in the TOC.
19128
19129           If you receive a linker error message that saying you have
19130           overflowed the available TOC space, you can reduce the amount of
19131           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
19132           -mno-fp-in-toc prevents GCC from putting floating-point constants
19133           in the TOC and -mno-sum-in-toc forces GCC to generate code to
19134           calculate the sum of an address and a constant at run time instead
19135           of putting that sum into the TOC.  You may specify one or both of
19136           these options.  Each causes GCC to produce very slightly slower and
19137           larger code at the expense of conserving TOC space.
19138
19139           If you still run out of space in the TOC even when you specify both
19140           of these options, specify -mminimal-toc instead.  This option
19141           causes GCC to make only one TOC entry for every file.  When you
19142           specify this option, GCC produces code that is slower and larger
19143           but which uses extremely little TOC space.  You may wish to use
19144           this option only on files that contain less frequently-executed
19145           code.
19146
19147       -maix32
19148           Disables the 64-bit ABI.  GCC defaults to -maix32.
19149
19150       -mxl-compat
19151       -mno-xl-compat
19152           Produce code that conforms more closely to IBM XL compiler
19153           semantics when using AIX-compatible ABI.  Pass floating-point
19154           arguments to prototyped functions beyond the register save area
19155           (RSA) on the stack in addition to argument FPRs.  Do not assume
19156           that most significant double in 128-bit long double value is
19157           properly rounded when comparing values and converting to double.
19158           Use XL symbol names for long double support routines.
19159
19160           The AIX calling convention was extended but not initially
19161           documented to handle an obscure K&R C case of calling a function
19162           that takes the address of its arguments with fewer arguments than
19163           declared.  IBM XL compilers access floating-point arguments that do
19164           not fit in the RSA from the stack when a subroutine is compiled
19165           without optimization.  Because always storing floating-point
19166           arguments on the stack is inefficient and rarely needed, this
19167           option is not enabled by default and only is necessary when calling
19168           subroutines compiled by IBM XL compilers without optimization.
19169
19170       -malign-natural
19171       -malign-power
19172           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
19173           -malign-natural overrides the ABI-defined alignment of larger
19174           types, such as floating-point doubles, on their natural size-based
19175           boundary.  The option -malign-power instructs GCC to follow the
19176           ABI-specified alignment rules.  GCC defaults to the standard
19177           alignment defined in the ABI.
19178
19179           On 64-bit Darwin, natural alignment is the default, and
19180           -malign-power is not supported.
19181
19182       -msoft-float
19183       -mhard-float
19184           Generate code that does not use (uses) the floating-point register
19185           set.  Software floating-point emulation is provided if you use the
19186           -msoft-float option, and pass the option to GCC when linking.
19187
19188       -msingle-float
19189       -mdouble-float
19190           Generate code for single- or double-precision floating-point
19191           operations.  -mdouble-float implies -msingle-float.
19192
19193       -mmultiple
19194       -mno-multiple
19195           Generate code that uses (does not use) the load multiple word
19196           instructions and the store multiple word instructions.  These
19197           instructions are generated by default on POWER systems, and not
19198           generated on PowerPC systems.  Do not use -mmultiple on little-
19199           endian PowerPC systems, since those instructions do not work when
19200           the processor is in little-endian mode.  The exceptions are PPC740
19201           and PPC750 which permit these instructions in little-endian mode.
19202
19203       -mupdate
19204       -mno-update
19205           Generate code that uses (does not use) the load or store
19206           instructions that update the base register to the address of the
19207           calculated memory location.  These instructions are generated by
19208           default.  If you use -mno-update, there is a small window between
19209           the time that the stack pointer is updated and the address of the
19210           previous frame is stored, which means code that walks the stack
19211           frame across interrupts or signals may get corrupted data.
19212
19213       -mavoid-indexed-addresses
19214       -mno-avoid-indexed-addresses
19215           Generate code that tries to avoid (not avoid) the use of indexed
19216           load or store instructions. These instructions can incur a
19217           performance penalty on Power6 processors in certain situations,
19218           such as when stepping through large arrays that cross a 16M
19219           boundary.  This option is enabled by default when targeting Power6
19220           and disabled otherwise.
19221
19222       -mfused-madd
19223       -mno-fused-madd
19224           Generate code that uses (does not use) the floating-point multiply
19225           and accumulate instructions.  These instructions are generated by
19226           default if hardware floating point is used.  The machine-dependent
19227           -mfused-madd option is now mapped to the machine-independent
19228           -ffp-contract=fast option, and -mno-fused-madd is mapped to
19229           -ffp-contract=off.
19230
19231       -mno-strict-align
19232       -mstrict-align
19233           On System V.4 and embedded PowerPC systems do not (do) assume that
19234           unaligned memory references are handled by the system.
19235
19236       -mrelocatable
19237       -mno-relocatable
19238           Generate code that allows (does not allow) a static executable to
19239           be relocated to a different address at run time.  A simple embedded
19240           PowerPC system loader should relocate the entire contents of
19241           ".got2" and 4-byte locations listed in the ".fixup" section, a
19242           table of 32-bit addresses generated by this option.  For this to
19243           work, all objects linked together must be compiled with
19244           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
19245           stack to an 8-byte boundary.
19246
19247       -mrelocatable-lib
19248       -mno-relocatable-lib
19249           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
19250           to allow static executables to be relocated at run time, but
19251           -mrelocatable-lib does not use the smaller stack alignment of
19252           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
19253           linked with objects compiled with any combination of the
19254           -mrelocatable options.
19255
19256       -mno-toc
19257       -mtoc
19258           On System V.4 and embedded PowerPC systems do not (do) assume that
19259           register 2 contains a pointer to a global area pointing to the
19260           addresses used in the program.
19261
19262       -mlittle
19263       -mlittle-endian
19264           On System V.4 and embedded PowerPC systems compile code for the
19265           processor in little-endian mode.  The -mlittle-endian option is the
19266           same as -mlittle.
19267
19268       -mbig
19269       -mbig-endian
19270           On System V.4 and embedded PowerPC systems compile code for the
19271           processor in big-endian mode.  The -mbig-endian option is the same
19272           as -mbig.
19273
19274       -mdynamic-no-pic
19275           On Darwin and Mac OS X systems, compile code so that it is not
19276           relocatable, but that its external references are relocatable.  The
19277           resulting code is suitable for applications, but not shared
19278           libraries.
19279
19280       -msingle-pic-base
19281           Treat the register used for PIC addressing as read-only, rather
19282           than loading it in the prologue for each function.  The runtime
19283           system is responsible for initializing this register with an
19284           appropriate value before execution begins.
19285
19286       -mprioritize-restricted-insns=priority
19287           This option controls the priority that is assigned to dispatch-slot
19288           restricted instructions during the second scheduling pass.  The
19289           argument priority takes the value 0, 1, or 2 to assign no, highest,
19290           or second-highest (respectively) priority to dispatch-slot
19291           restricted instructions.
19292
19293       -msched-costly-dep=dependence_type
19294           This option controls which dependences are considered costly by the
19295           target during instruction scheduling.  The argument dependence_type
19296           takes one of the following values:
19297
19298           no  No dependence is costly.
19299
19300           all All dependences are costly.
19301
19302           true_store_to_load
19303               A true dependence from store to load is costly.
19304
19305           store_to_load
19306               Any dependence from store to load is costly.
19307
19308           number
19309               Any dependence for which the latency is greater than or equal
19310               to number is costly.
19311
19312       -minsert-sched-nops=scheme
19313           This option controls which NOP insertion scheme is used during the
19314           second scheduling pass.  The argument scheme takes one of the
19315           following values:
19316
19317           no  Don't insert NOPs.
19318
19319           pad Pad with NOPs any dispatch group that has vacant issue slots,
19320               according to the scheduler's grouping.
19321
19322           regroup_exact
19323               Insert NOPs to force costly dependent insns into separate
19324               groups.  Insert exactly as many NOPs as needed to force an insn
19325               to a new group, according to the estimated processor grouping.
19326
19327           number
19328               Insert NOPs to force costly dependent insns into separate
19329               groups.  Insert number NOPs to force an insn to a new group.
19330
19331       -mcall-sysv
19332           On System V.4 and embedded PowerPC systems compile code using
19333           calling conventions that adhere to the March 1995 draft of the
19334           System V Application Binary Interface, PowerPC processor
19335           supplement.  This is the default unless you configured GCC using
19336           powerpc-*-eabiaix.
19337
19338       -mcall-sysv-eabi
19339       -mcall-eabi
19340           Specify both -mcall-sysv and -meabi options.
19341
19342       -mcall-sysv-noeabi
19343           Specify both -mcall-sysv and -mno-eabi options.
19344
19345       -mcall-aixdesc
19346           On System V.4 and embedded PowerPC systems compile code for the AIX
19347           operating system.
19348
19349       -mcall-linux
19350           On System V.4 and embedded PowerPC systems compile code for the
19351           Linux-based GNU system.
19352
19353       -mcall-freebsd
19354           On System V.4 and embedded PowerPC systems compile code for the
19355           FreeBSD operating system.
19356
19357       -mcall-netbsd
19358           On System V.4 and embedded PowerPC systems compile code for the
19359           NetBSD operating system.
19360
19361       -mcall-openbsd
19362           On System V.4 and embedded PowerPC systems compile code for the
19363           OpenBSD operating system.
19364
19365       -maix-struct-return
19366           Return all structures in memory (as specified by the AIX ABI).
19367
19368       -msvr4-struct-return
19369           Return structures smaller than 8 bytes in registers (as specified
19370           by the SVR4 ABI).
19371
19372       -mabi=abi-type
19373           Extend the current ABI with a particular extension, or remove such
19374           extension.  Valid values are altivec, no-altivec, spe, no-spe,
19375           ibmlongdouble, ieeelongdouble, elfv1, elfv2.
19376
19377       -mabi=spe
19378           Extend the current ABI with SPE ABI extensions.  This does not
19379           change the default ABI, instead it adds the SPE ABI extensions to
19380           the current ABI.
19381
19382       -mabi=no-spe
19383           Disable Book-E SPE ABI extensions for the current ABI.
19384
19385       -mabi=ibmlongdouble
19386           Change the current ABI to use IBM extended-precision long double.
19387           This is not likely to work if your system defaults to using IEEE
19388           extended-precision long double.  If you change the long double type
19389           from IEEE extended-precision, the compiler will issue a warning
19390           unless you use the -Wno-psabi option.
19391
19392       -mabi=ieeelongdouble
19393           Change the current ABI to use IEEE extended-precision long double.
19394           This is not likely to work if your system defaults to using IBM
19395           extended-precision long double.  If you change the long double type
19396           from IBM extended-precision, the compiler will issue a warning
19397           unless you use the -Wno-psabi option.
19398
19399       -mabi=elfv1
19400           Change the current ABI to use the ELFv1 ABI.  This is the default
19401           ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
19402           ABI requires special system support and is likely to fail in
19403           spectacular ways.
19404
19405       -mabi=elfv2
19406           Change the current ABI to use the ELFv2 ABI.  This is the default
19407           ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
19408           ABI requires special system support and is likely to fail in
19409           spectacular ways.
19410
19411       -mgnu-attribute
19412       -mno-gnu-attribute
19413           Emit .gnu_attribute assembly directives to set tag/value pairs in a
19414           .gnu.attributes section that specify ABI variations in function
19415           parameters or return values.
19416
19417       -mprototype
19418       -mno-prototype
19419           On System V.4 and embedded PowerPC systems assume that all calls to
19420           variable argument functions are properly prototyped.  Otherwise,
19421           the compiler must insert an instruction before every non-prototyped
19422           call to set or clear bit 6 of the condition code register ("CR") to
19423           indicate whether floating-point values are passed in the floating-
19424           point registers in case the function takes variable arguments.
19425           With -mprototype, only calls to prototyped variable argument
19426           functions set or clear the bit.
19427
19428       -msim
19429           On embedded PowerPC systems, assume that the startup module is
19430           called sim-crt0.o and that the standard C libraries are libsim.a
19431           and libc.a.  This is the default for powerpc-*-eabisim
19432           configurations.
19433
19434       -mmvme
19435           On embedded PowerPC systems, assume that the startup module is
19436           called crt0.o and the standard C libraries are libmvme.a and
19437           libc.a.
19438
19439       -mads
19440           On embedded PowerPC systems, assume that the startup module is
19441           called crt0.o and the standard C libraries are libads.a and libc.a.
19442
19443       -myellowknife
19444           On embedded PowerPC systems, assume that the startup module is
19445           called crt0.o and the standard C libraries are libyk.a and libc.a.
19446
19447       -mvxworks
19448           On System V.4 and embedded PowerPC systems, specify that you are
19449           compiling for a VxWorks system.
19450
19451       -memb
19452           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags
19453           header to indicate that eabi extended relocations are used.
19454
19455       -meabi
19456       -mno-eabi
19457           On System V.4 and embedded PowerPC systems do (do not) adhere to
19458           the Embedded Applications Binary Interface (EABI), which is a set
19459           of modifications to the System V.4 specifications.  Selecting
19460           -meabi means that the stack is aligned to an 8-byte boundary, a
19461           function "__eabi" is called from "main" to set up the EABI
19462           environment, and the -msdata option can use both "r2" and "r13" to
19463           point to two separate small data areas.  Selecting -mno-eabi means
19464           that the stack is aligned to a 16-byte boundary, no EABI
19465           initialization function is called from "main", and the -msdata
19466           option only uses "r13" to point to a single small data area.  The
19467           -meabi option is on by default if you configured GCC using one of
19468           the powerpc*-*-eabi* options.
19469
19470       -msdata=eabi
19471           On System V.4 and embedded PowerPC systems, put small initialized
19472           "const" global and static data in the ".sdata2" section, which is
19473           pointed to by register "r2".  Put small initialized non-"const"
19474           global and static data in the ".sdata" section, which is pointed to
19475           by register "r13".  Put small uninitialized global and static data
19476           in the ".sbss" section, which is adjacent to the ".sdata" section.
19477           The -msdata=eabi option is incompatible with the -mrelocatable
19478           option.  The -msdata=eabi option also sets the -memb option.
19479
19480       -msdata=sysv
19481           On System V.4 and embedded PowerPC systems, put small global and
19482           static data in the ".sdata" section, which is pointed to by
19483           register "r13".  Put small uninitialized global and static data in
19484           the ".sbss" section, which is adjacent to the ".sdata" section.
19485           The -msdata=sysv option is incompatible with the -mrelocatable
19486           option.
19487
19488       -msdata=default
19489       -msdata
19490           On System V.4 and embedded PowerPC systems, if -meabi is used,
19491           compile code the same as -msdata=eabi, otherwise compile code the
19492           same as -msdata=sysv.
19493
19494       -msdata=data
19495           On System V.4 and embedded PowerPC systems, put small global data
19496           in the ".sdata" section.  Put small uninitialized global data in
19497           the ".sbss" section.  Do not use register "r13" to address small
19498           data however.  This is the default behavior unless other -msdata
19499           options are used.
19500
19501       -msdata=none
19502       -mno-sdata
19503           On embedded PowerPC systems, put all initialized global and static
19504           data in the ".data" section, and all uninitialized data in the
19505           ".bss" section.
19506
19507       -mblock-move-inline-limit=num
19508           Inline all block moves (such as calls to "memcpy" or structure
19509           copies) less than or equal to num bytes.  The minimum value for num
19510           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
19511           default value is target-specific.
19512
19513       -G num
19514           On embedded PowerPC systems, put global and static items less than
19515           or equal to num bytes into the small data or BSS sections instead
19516           of the normal data or BSS section.  By default, num is 8.  The -G
19517           num switch is also passed to the linker.  All modules should be
19518           compiled with the same -G num value.
19519
19520       -mregnames
19521       -mno-regnames
19522           On System V.4 and embedded PowerPC systems do (do not) emit
19523           register names in the assembly language output using symbolic
19524           forms.
19525
19526       -mlongcall
19527       -mno-longcall
19528           By default assume that all calls are far away so that a longer and
19529           more expensive calling sequence is required.  This is required for
19530           calls farther than 32 megabytes (33,554,432 bytes) from the current
19531           location.  A short call is generated if the compiler knows the call
19532           cannot be that far away.  This setting can be overridden by the
19533           "shortcall" function attribute, or by "#pragma longcall(0)".
19534
19535           Some linkers are capable of detecting out-of-range calls and
19536           generating glue code on the fly.  On these systems, long calls are
19537           unnecessary and generate slower code.  As of this writing, the AIX
19538           linker can do this, as can the GNU linker for PowerPC/64.  It is
19539           planned to add this feature to the GNU linker for 32-bit PowerPC
19540           systems as well.
19541
19542           In the future, GCC may ignore all longcall specifications when the
19543           linker is known to generate glue.
19544
19545       -mtls-markers
19546       -mno-tls-markers
19547           Mark (do not mark) calls to "__tls_get_addr" with a relocation
19548           specifying the function argument.  The relocation allows the linker
19549           to reliably associate function call with argument setup
19550           instructions for TLS optimization, which in turn allows GCC to
19551           better schedule the sequence.
19552
19553       -mrecip
19554       -mno-recip
19555           This option enables use of the reciprocal estimate and reciprocal
19556           square root estimate instructions with additional Newton-Raphson
19557           steps to increase precision instead of doing a divide or square
19558           root and divide for floating-point arguments.  You should use the
19559           -ffast-math option when using -mrecip (or at least
19560           -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math
19561           and -fno-trapping-math).  Note that while the throughput of the
19562           sequence is generally higher than the throughput of the non-
19563           reciprocal instruction, the precision of the sequence can be
19564           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
19565           0.99999994) for reciprocal square roots.
19566
19567       -mrecip=opt
19568           This option controls which reciprocal estimate instructions may be
19569           used.  opt is a comma-separated list of options, which may be
19570           preceded by a "!" to invert the option:
19571
19572           all Enable all estimate instructions.
19573
19574           default
19575               Enable the default instructions, equivalent to -mrecip.
19576
19577           none
19578               Disable all estimate instructions, equivalent to -mno-recip.
19579
19580           div Enable the reciprocal approximation instructions for both
19581               single and double precision.
19582
19583           divf
19584               Enable the single-precision reciprocal approximation
19585               instructions.
19586
19587           divd
19588               Enable the double-precision reciprocal approximation
19589               instructions.
19590
19591           rsqrt
19592               Enable the reciprocal square root approximation instructions
19593               for both single and double precision.
19594
19595           rsqrtf
19596               Enable the single-precision reciprocal square root
19597               approximation instructions.
19598
19599           rsqrtd
19600               Enable the double-precision reciprocal square root
19601               approximation instructions.
19602
19603           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
19604           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
19605           "XVRSQRTEDP" instructions which handle the double-precision
19606           reciprocal square root calculations.
19607
19608       -mrecip-precision
19609       -mno-recip-precision
19610           Assume (do not assume) that the reciprocal estimate instructions
19611           provide higher-precision estimates than is mandated by the PowerPC
19612           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
19613           automatically selects -mrecip-precision.  The double-precision
19614           square root estimate instructions are not generated by default on
19615           low-precision machines, since they do not provide an estimate that
19616           converges after three steps.
19617
19618       -mpointers-to-nested-functions
19619       -mno-pointers-to-nested-functions
19620           Generate (do not generate) code to load up the static chain
19621           register ("r11") when calling through a pointer on AIX and 64-bit
19622           Linux systems where a function pointer points to a 3-word
19623           descriptor giving the function address, TOC value to be loaded in
19624           register "r2", and static chain value to be loaded in register
19625           "r11".  The -mpointers-to-nested-functions is on by default.  You
19626           cannot call through pointers to nested functions or pointers to
19627           functions compiled in other languages that use the static chain if
19628           you use -mno-pointers-to-nested-functions.
19629
19630       -msave-toc-indirect
19631       -mno-save-toc-indirect
19632           Generate (do not generate) code to save the TOC value in the
19633           reserved stack location in the function prologue if the function
19634           calls through a pointer on AIX and 64-bit Linux systems.  If the
19635           TOC value is not saved in the prologue, it is saved just before the
19636           call through the pointer.  The -mno-save-toc-indirect option is the
19637           default.
19638
19639       -mcompat-align-parm
19640       -mno-compat-align-parm
19641           Generate (do not generate) code to pass structure parameters with a
19642           maximum alignment of 64 bits, for compatibility with older versions
19643           of GCC.
19644
19645           Older versions of GCC (prior to 4.9.0) incorrectly did not align a
19646           structure parameter on a 128-bit boundary when that structure
19647           contained a member requiring 128-bit alignment.  This is corrected
19648           in more recent versions of GCC.  This option may be used to
19649           generate code that is compatible with functions compiled with older
19650           versions of GCC.
19651
19652           The -mno-compat-align-parm option is the default.
19653
19654       -mstack-protector-guard=guard
19655       -mstack-protector-guard-reg=reg
19656       -mstack-protector-guard-offset=offset
19657       -mstack-protector-guard-symbol=symbol
19658           Generate stack protection code using canary at guard.  Supported
19659           locations are global for global canary or tls for per-thread canary
19660           in the TLS block (the default with GNU libc version 2.4 or later).
19661
19662           With the latter choice the options -mstack-protector-guard-reg=reg
19663           and -mstack-protector-guard-offset=offset furthermore specify which
19664           register to use as base register for reading the canary, and from
19665           what offset from that base register. The default for those is as
19666           specified in the relevant ABI.
19667           -mstack-protector-guard-symbol=symbol overrides the offset with a
19668           symbol reference to a canary in the TLS block.
19669
19670   RISC-V Options
19671       These command-line options are defined for RISC-V targets:
19672
19673       -mbranch-cost=n
19674           Set the cost of branches to roughly n instructions.
19675
19676       -mplt
19677       -mno-plt
19678           When generating PIC code, do or don't allow the use of PLTs.
19679           Ignored for non-PIC.  The default is -mplt.
19680
19681       -mabi=ABI-string
19682           Specify integer and floating-point calling convention.  ABI-string
19683           contains two parts: the size of integer types and the registers
19684           used for floating-point types.  For example -march=rv64ifd
19685           -mabi=lp64d means that long and pointers are 64-bit (implicitly
19686           defining int to be 32-bit), and that floating-point values up to 64
19687           bits wide are passed in F registers.  Contrast this with
19688           -march=rv64ifd -mabi=lp64f, which still allows the compiler to
19689           generate code that uses the F and D extensions but only allows
19690           floating-point values up to 32 bits long to be passed in registers;
19691           or -march=rv64ifd -mabi=lp64, in which no floating-point arguments
19692           will be passed in registers.
19693
19694           The default for this argument is system dependent, users who want a
19695           specific calling convention should specify one explicitly.  The
19696           valid calling conventions are: ilp32, ilp32f, ilp32d, lp64, lp64f,
19697           and lp64d.  Some calling conventions are impossible to implement on
19698           some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid
19699           because the ABI requires 64-bit values be passed in F registers,
19700           but F registers are only 32 bits wide.
19701
19702       -mfdiv
19703       -mno-fdiv
19704           Do or don't use hardware floating-point divide and square root
19705           instructions.  This requires the F or D extensions for floating-
19706           point registers.  The default is to use them if the specified
19707           architecture has these instructions.
19708
19709       -mdiv
19710       -mno-div
19711           Do or don't use hardware instructions for integer division.  This
19712           requires the M extension.  The default is to use them if the
19713           specified architecture has these instructions.
19714
19715       -march=ISA-string
19716           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must
19717           be lower-case.  Examples include rv64i, rv32g, and rv32imaf.
19718
19719       -mtune=processor-string
19720           Optimize the output for the given processor, specified by
19721           microarchitecture name.
19722
19723       -mpreferred-stack-boundary=num
19724           Attempt to keep the stack boundary aligned to a 2 raised to num
19725           byte boundary.  If -mpreferred-stack-boundary is not specified, the
19726           default is 4 (16 bytes or 128-bits).
19727
19728           Warning: If you use this switch, then you must build all modules
19729           with the same value, including any libraries.  This includes the
19730           system libraries and startup modules.
19731
19732       -msmall-data-limit=n
19733           Put global and static data smaller than n bytes into a special
19734           section (on some targets).
19735
19736       -msave-restore
19737       -mno-save-restore
19738           Do or don't use smaller but slower prologue and epilogue code that
19739           uses library function calls.  The default is to use fast inline
19740           prologues and epilogues.
19741
19742       -mstrict-align
19743       -mno-strict-align
19744           Do not or do generate unaligned memory accesses.  The default is
19745           set depending on whether the processor we are optimizing for
19746           supports fast unaligned access or not.
19747
19748       -mcmodel=medlow
19749           Generate code for the medium-low code model. The program and its
19750           statically defined symbols must lie within a single 2 GiB address
19751           range and must lie between absolute addresses -2 GiB and +2 GiB.
19752           Programs can be statically or dynamically linked. This is the
19753           default code model.
19754
19755       -mcmodel=medany
19756           Generate code for the medium-any code model. The program and its
19757           statically defined symbols must be within any single 2 GiB address
19758           range. Programs can be statically or dynamically linked.
19759
19760       -mexplicit-relocs
19761       -mno-exlicit-relocs
19762           Use or do not use assembler relocation operators when dealing with
19763           symbolic addresses.  The alternative is to use assembler macros
19764           instead, which may limit optimization.
19765
19766       -mrelax
19767       -mno-relax
19768           Take advantage of linker relaxations to reduce the number of
19769           instructions required to materialize symbol addresses. The default
19770           is to take advantage of linker relaxations.
19771
19772   RL78 Options
19773       -msim
19774           Links in additional target libraries to support operation within a
19775           simulator.
19776
19777       -mmul=none
19778       -mmul=g10
19779       -mmul=g13
19780       -mmul=g14
19781       -mmul=rl78
19782           Specifies the type of hardware multiplication and division support
19783           to be used.  The simplest is "none", which uses software for both
19784           multiplication and division.  This is the default.  The "g13" value
19785           is for the hardware multiply/divide peripheral found on the
19786           RL78/G13 (S2 core) targets.  The "g14" value selects the use of the
19787           multiplication and division instructions supported by the RL78/G14
19788           (S3 core) parts.  The value "rl78" is an alias for "g14" and the
19789           value "mg10" is an alias for "none".
19790
19791           In addition a C preprocessor macro is defined, based upon the
19792           setting of this option.  Possible values are: "__RL78_MUL_NONE__",
19793           "__RL78_MUL_G13__" or "__RL78_MUL_G14__".
19794
19795       -mcpu=g10
19796       -mcpu=g13
19797       -mcpu=g14
19798       -mcpu=rl78
19799           Specifies the RL78 core to target.  The default is the G14 core,
19800           also known as an S3 core or just RL78.  The G13 or S2 core does not
19801           have multiply or divide instructions, instead it uses a hardware
19802           peripheral for these operations.  The G10 or S1 core does not have
19803           register banks, so it uses a different calling convention.
19804
19805           If this option is set it also selects the type of hardware multiply
19806           support to use, unless this is overridden by an explicit -mmul=none
19807           option on the command line.  Thus specifying -mcpu=g13 enables the
19808           use of the G13 hardware multiply peripheral and specifying
19809           -mcpu=g10 disables the use of hardware multiplications altogether.
19810
19811           Note, although the RL78/G14 core is the default target, specifying
19812           -mcpu=g14 or -mcpu=rl78 on the command line does change the
19813           behavior of the toolchain since it also enables G14 hardware
19814           multiply support.  If these options are not specified on the
19815           command line then software multiplication routines will be used
19816           even though the code targets the RL78 core.  This is for backwards
19817           compatibility with older toolchains which did not have hardware
19818           multiply and divide support.
19819
19820           In addition a C preprocessor macro is defined, based upon the
19821           setting of this option.  Possible values are: "__RL78_G10__",
19822           "__RL78_G13__" or "__RL78_G14__".
19823
19824       -mg10
19825       -mg13
19826       -mg14
19827       -mrl78
19828           These are aliases for the corresponding -mcpu= option.  They are
19829           provided for backwards compatibility.
19830
19831       -mallregs
19832           Allow the compiler to use all of the available registers.  By
19833           default registers "r24..r31" are reserved for use in interrupt
19834           handlers.  With this option enabled these registers can be used in
19835           ordinary functions as well.
19836
19837       -m64bit-doubles
19838       -m32bit-doubles
19839           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
19840           (-m32bit-doubles) in size.  The default is -m32bit-doubles.
19841
19842       -msave-mduc-in-interrupts
19843       -mno-save-mduc-in-interrupts
19844           Specifies that interrupt handler functions should preserve the MDUC
19845           registers.  This is only necessary if normal code might use the
19846           MDUC registers, for example because it performs multiplication and
19847           division operations.  The default is to ignore the MDUC registers
19848           as this makes the interrupt handlers faster.  The target option
19849           -mg13 needs to be passed for this to work as this feature is only
19850           available on the G13 target (S2 core).  The MDUC registers will
19851           only be saved if the interrupt handler performs a multiplication or
19852           division operation or it calls another function.
19853
19854   IBM RS/6000 and PowerPC Options
19855       These -m options are defined for the IBM RS/6000 and PowerPC:
19856
19857       -mpowerpc-gpopt
19858       -mno-powerpc-gpopt
19859       -mpowerpc-gfxopt
19860       -mno-powerpc-gfxopt
19861       -mpowerpc64
19862       -mno-powerpc64
19863       -mmfcrf
19864       -mno-mfcrf
19865       -mpopcntb
19866       -mno-popcntb
19867       -mpopcntd
19868       -mno-popcntd
19869       -mfprnd
19870       -mno-fprnd
19871       -mcmpb
19872       -mno-cmpb
19873       -mmfpgpr
19874       -mno-mfpgpr
19875       -mhard-dfp
19876       -mno-hard-dfp
19877           You use these options to specify which instructions are available
19878           on the processor you are using.  The default value of these options
19879           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
19880           overrides the specification of these options.  We recommend you use
19881           the -mcpu=cpu_type option rather than the options listed above.
19882
19883           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC
19884           architecture instructions in the General Purpose group, including
19885           floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
19886           to use the optional PowerPC architecture instructions in the
19887           Graphics group, including floating-point select.
19888
19889           The -mmfcrf option allows GCC to generate the move from condition
19890           register field instruction implemented on the POWER4 processor and
19891           other processors that support the PowerPC V2.01 architecture.  The
19892           -mpopcntb option allows GCC to generate the popcount and double-
19893           precision FP reciprocal estimate instruction implemented on the
19894           POWER5 processor and other processors that support the PowerPC
19895           V2.02 architecture.  The -mpopcntd option allows GCC to generate
19896           the popcount instruction implemented on the POWER7 processor and
19897           other processors that support the PowerPC V2.06 architecture.  The
19898           -mfprnd option allows GCC to generate the FP round to integer
19899           instructions implemented on the POWER5+ processor and other
19900           processors that support the PowerPC V2.03 architecture.  The -mcmpb
19901           option allows GCC to generate the compare bytes instruction
19902           implemented on the POWER6 processor and other processors that
19903           support the PowerPC V2.05 architecture.  The -mmfpgpr option allows
19904           GCC to generate the FP move to/from general-purpose register
19905           instructions implemented on the POWER6X processor and other
19906           processors that support the extended PowerPC V2.05 architecture.
19907           The -mhard-dfp option allows GCC to generate the decimal floating-
19908           point instructions implemented on some POWER processors.
19909
19910           The -mpowerpc64 option allows GCC to generate the additional 64-bit
19911           instructions that are found in the full PowerPC64 architecture and
19912           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
19913           -mno-powerpc64.
19914
19915       -mcpu=cpu_type
19916           Set architecture type, register usage, and instruction scheduling
19917           parameters for machine type cpu_type.  Supported values for
19918           cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476,
19919           476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400,
19920           7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3,
19921           e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,
19922           power4, power5, power5+, power6, power6x, power7, power8, power9,
19923           powerpc, powerpc64, powerpc64le, rs64, and native.
19924
19925           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure
19926           32-bit PowerPC (either endian), 64-bit big endian PowerPC and
19927           64-bit little endian PowerPC architecture machine types, with an
19928           appropriate, generic processor model assumed for scheduling
19929           purposes.
19930
19931           Specifying native as cpu type detects and selects the architecture
19932           option that corresponds to the host processor of the system
19933           performing the compilation.  -mcpu=native has no effect if GCC does
19934           not recognize the processor.
19935
19936           The other options specify a specific processor.  Code generated
19937           under those options runs best on that processor, and may not run at
19938           all on others.
19939
19940           The -mcpu options automatically enable or disable the following
19941           options:
19942
19943           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb
19944           -mpopcntd  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt
19945           -msingle-float -mdouble-float -msimple-fpu  -mmulhw  -mdlmzb
19946           -mmfpgpr -mvsx -mcrypto -mhtm -mpower8-fusion -mpower8-vector
19947           -mquad-memory -mquad-memory-atomic -mfloat128 -mfloat128-hardware
19948
19949           The particular options set for any particular CPU varies between
19950           compiler versions, depending on what setting seems to produce
19951           optimal code for that CPU; it doesn't necessarily reflect the
19952           actual hardware's capabilities.  If you wish to set an individual
19953           option to a particular value, you may specify it after the -mcpu
19954           option, like -mcpu=970 -mno-altivec.
19955
19956           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
19957           disabled by the -mcpu option at present because AIX does not have
19958           full support for these options.  You may still enable or disable
19959           them individually if you're sure it'll work in your environment.
19960
19961       -mtune=cpu_type
19962           Set the instruction scheduling parameters for machine type
19963           cpu_type, but do not set the architecture type or register usage,
19964           as -mcpu=cpu_type does.  The same values for cpu_type are used for
19965           -mtune as for -mcpu.  If both are specified, the code generated
19966           uses the architecture and registers set by -mcpu, but the
19967           scheduling parameters set by -mtune.
19968
19969       -mcmodel=small
19970           Generate PowerPC64 code for the small model: The TOC is limited to
19971           64k.
19972
19973       -mcmodel=medium
19974           Generate PowerPC64 code for the medium model: The TOC and other
19975           static data may be up to a total of 4G in size.  This is the
19976           default for 64-bit Linux.
19977
19978       -mcmodel=large
19979           Generate PowerPC64 code for the large model: The TOC may be up to
19980           4G in size.  Other data and code is only limited by the 64-bit
19981           address space.
19982
19983       -maltivec
19984       -mno-altivec
19985           Generate code that uses (does not use) AltiVec instructions, and
19986           also enable the use of built-in functions that allow more direct
19987           access to the AltiVec instruction set.  You may also need to set
19988           -mabi=altivec to adjust the current ABI with AltiVec ABI
19989           enhancements.
19990
19991           When -maltivec is used, rather than -maltivec=le or -maltivec=be,
19992           the element order for AltiVec intrinsics such as "vec_splat",
19993           "vec_extract", and "vec_insert" match array element order
19994           corresponding to the endianness of the target.  That is, element
19995           zero identifies the leftmost element in a vector register when
19996           targeting a big-endian platform, and identifies the rightmost
19997           element in a vector register when targeting a little-endian
19998           platform.
19999
20000       -maltivec=be
20001           Generate AltiVec instructions using big-endian element order,
20002           regardless of whether the target is big- or little-endian.  This is
20003           the default when targeting a big-endian platform.  Using this
20004           option is currently deprecated.  Support for this feature will be
20005           removed in GCC 9.
20006
20007           The element order is used to interpret element numbers in AltiVec
20008           intrinsics such as "vec_splat", "vec_extract", and "vec_insert".
20009           By default, these match array element order corresponding to the
20010           endianness for the target.
20011
20012       -maltivec=le
20013           Generate AltiVec instructions using little-endian element order,
20014           regardless of whether the target is big- or little-endian.  This is
20015           the default when targeting a little-endian platform.  This option
20016           is currently ignored when targeting a big-endian platform.
20017
20018           The element order is used to interpret element numbers in AltiVec
20019           intrinsics such as "vec_splat", "vec_extract", and "vec_insert".
20020           By default, these match array element order corresponding to the
20021           endianness for the target.
20022
20023       -mvrsave
20024       -mno-vrsave
20025           Generate VRSAVE instructions when generating AltiVec code.
20026
20027       -msecure-plt
20028           Generate code that allows ld and ld.so to build executables and
20029           shared libraries with non-executable ".plt" and ".got" sections.
20030           This is a PowerPC 32-bit SYSV ABI option.
20031
20032       -mbss-plt
20033           Generate code that uses a BSS ".plt" section that ld.so fills in,
20034           and requires ".plt" and ".got" sections that are both writable and
20035           executable.  This is a PowerPC 32-bit SYSV ABI option.
20036
20037       -misel
20038       -mno-isel
20039           This switch enables or disables the generation of ISEL
20040           instructions.
20041
20042       -misel=yes/no
20043           This switch has been deprecated.  Use -misel and -mno-isel instead.
20044
20045       -mpaired
20046       -mno-paired
20047           This switch enables or disables the generation of PAIRED simd
20048           instructions.
20049
20050       -mvsx
20051       -mno-vsx
20052           Generate code that uses (does not use) vector/scalar (VSX)
20053           instructions, and also enable the use of built-in functions that
20054           allow more direct access to the VSX instruction set.
20055
20056       -mcrypto
20057       -mno-crypto
20058           Enable the use (disable) of the built-in functions that allow
20059           direct access to the cryptographic instructions that were added in
20060           version 2.07 of the PowerPC ISA.
20061
20062       -mhtm
20063       -mno-htm
20064           Enable (disable) the use of the built-in functions that allow
20065           direct access to the Hardware Transactional Memory (HTM)
20066           instructions that were added in version 2.07 of the PowerPC ISA.
20067
20068       -mpower8-fusion
20069       -mno-power8-fusion
20070           Generate code that keeps (does not keeps) some integer operations
20071           adjacent so that the instructions can be fused together on power8
20072           and later processors.
20073
20074       -mpower8-vector
20075       -mno-power8-vector
20076           Generate code that uses (does not use) the vector and scalar
20077           instructions that were added in version 2.07 of the PowerPC ISA.
20078           Also enable the use of built-in functions that allow more direct
20079           access to the vector instructions.
20080
20081       -mquad-memory
20082       -mno-quad-memory
20083           Generate code that uses (does not use) the non-atomic quad word
20084           memory instructions.  The -mquad-memory option requires use of
20085           64-bit mode.
20086
20087       -mquad-memory-atomic
20088       -mno-quad-memory-atomic
20089           Generate code that uses (does not use) the atomic quad word memory
20090           instructions.  The -mquad-memory-atomic option requires use of
20091           64-bit mode.
20092
20093       -mfloat128
20094       -mno-float128
20095           Enable/disable the __float128 keyword for IEEE 128-bit floating
20096           point and use either software emulation for IEEE 128-bit floating
20097           point or hardware instructions.
20098
20099           The VSX instruction set (-mvsx, -mcpu=power7, -mcpu=power8), or
20100           -mcpu=power9 must be enabled to use the IEEE 128-bit floating point
20101           support.  The IEEE 128-bit floating point support only works on
20102           PowerPC Linux systems.
20103
20104           The default for -mfloat128 is enabled on PowerPC Linux systems
20105           using the VSX instruction set, and disabled on other systems.
20106
20107           If you use the ISA 3.0 instruction set (-mpower9-vector or
20108           -mcpu=power9) on a 64-bit system, the IEEE 128-bit floating point
20109           support will also enable the generation of ISA 3.0 IEEE 128-bit
20110           floating point instructions.  Otherwise, if you do not specify to
20111           generate ISA 3.0 instructions or you are targeting a 32-bit big
20112           endian system, IEEE 128-bit floating point will be done with
20113           software emulation.
20114
20115       -mfloat128-hardware
20116       -mno-float128-hardware
20117           Enable/disable using ISA 3.0 hardware instructions to support the
20118           __float128 data type.
20119
20120           The default for -mfloat128-hardware is enabled on PowerPC Linux
20121           systems using the ISA 3.0 instruction set, and disabled on other
20122           systems.
20123
20124       -m32
20125       -m64
20126           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
20127           targets (including GNU/Linux).  The 32-bit environment sets int,
20128           long and pointer to 32 bits and generates code that runs on any
20129           PowerPC variant.  The 64-bit environment sets int to 32 bits and
20130           long and pointer to 64 bits, and generates code for PowerPC64, as
20131           for -mpowerpc64.
20132
20133       -mfull-toc
20134       -mno-fp-in-toc
20135       -mno-sum-in-toc
20136       -mminimal-toc
20137           Modify generation of the TOC (Table Of Contents), which is created
20138           for every executable file.  The -mfull-toc option is selected by
20139           default.  In that case, GCC allocates at least one TOC entry for
20140           each unique non-automatic variable reference in your program.  GCC
20141           also places floating-point constants in the TOC.  However, only
20142           16,384 entries are available in the TOC.
20143
20144           If you receive a linker error message that saying you have
20145           overflowed the available TOC space, you can reduce the amount of
20146           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
20147           -mno-fp-in-toc prevents GCC from putting floating-point constants
20148           in the TOC and -mno-sum-in-toc forces GCC to generate code to
20149           calculate the sum of an address and a constant at run time instead
20150           of putting that sum into the TOC.  You may specify one or both of
20151           these options.  Each causes GCC to produce very slightly slower and
20152           larger code at the expense of conserving TOC space.
20153
20154           If you still run out of space in the TOC even when you specify both
20155           of these options, specify -mminimal-toc instead.  This option
20156           causes GCC to make only one TOC entry for every file.  When you
20157           specify this option, GCC produces code that is slower and larger
20158           but which uses extremely little TOC space.  You may wish to use
20159           this option only on files that contain less frequently-executed
20160           code.
20161
20162       -maix64
20163       -maix32
20164           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
20165           64-bit "long" type, and the infrastructure needed to support them.
20166           Specifying -maix64 implies -mpowerpc64, while -maix32 disables the
20167           64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.
20168
20169       -mxl-compat
20170       -mno-xl-compat
20171           Produce code that conforms more closely to IBM XL compiler
20172           semantics when using AIX-compatible ABI.  Pass floating-point
20173           arguments to prototyped functions beyond the register save area
20174           (RSA) on the stack in addition to argument FPRs.  Do not assume
20175           that most significant double in 128-bit long double value is
20176           properly rounded when comparing values and converting to double.
20177           Use XL symbol names for long double support routines.
20178
20179           The AIX calling convention was extended but not initially
20180           documented to handle an obscure K&R C case of calling a function
20181           that takes the address of its arguments with fewer arguments than
20182           declared.  IBM XL compilers access floating-point arguments that do
20183           not fit in the RSA from the stack when a subroutine is compiled
20184           without optimization.  Because always storing floating-point
20185           arguments on the stack is inefficient and rarely needed, this
20186           option is not enabled by default and only is necessary when calling
20187           subroutines compiled by IBM XL compilers without optimization.
20188
20189       -mpe
20190           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
20191           application written to use message passing with special startup
20192           code to enable the application to run.  The system must have PE
20193           installed in the standard location (/usr/lpp/ppe.poe/), or the
20194           specs file must be overridden with the -specs= option to specify
20195           the appropriate directory location.  The Parallel Environment does
20196           not support threads, so the -mpe option and the -pthread option are
20197           incompatible.
20198
20199       -malign-natural
20200       -malign-power
20201           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
20202           -malign-natural overrides the ABI-defined alignment of larger
20203           types, such as floating-point doubles, on their natural size-based
20204           boundary.  The option -malign-power instructs GCC to follow the
20205           ABI-specified alignment rules.  GCC defaults to the standard
20206           alignment defined in the ABI.
20207
20208           On 64-bit Darwin, natural alignment is the default, and
20209           -malign-power is not supported.
20210
20211       -msoft-float
20212       -mhard-float
20213           Generate code that does not use (uses) the floating-point register
20214           set.  Software floating-point emulation is provided if you use the
20215           -msoft-float option, and pass the option to GCC when linking.
20216
20217       -msingle-float
20218       -mdouble-float
20219           Generate code for single- or double-precision floating-point
20220           operations.  -mdouble-float implies -msingle-float.
20221
20222       -msimple-fpu
20223           Do not generate "sqrt" and "div" instructions for hardware
20224           floating-point unit.
20225
20226       -mfpu=name
20227           Specify type of floating-point unit.  Valid values for name are
20228           sp_lite (equivalent to -msingle-float -msimple-fpu), dp_lite
20229           (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent to
20230           -msingle-float), and dp_full (equivalent to -mdouble-float).
20231
20232       -mxilinx-fpu
20233           Perform optimizations for the floating-point unit on Xilinx PPC
20234           405/440.
20235
20236       -mmultiple
20237       -mno-multiple
20238           Generate code that uses (does not use) the load multiple word
20239           instructions and the store multiple word instructions.  These
20240           instructions are generated by default on POWER systems, and not
20241           generated on PowerPC systems.  Do not use -mmultiple on little-
20242           endian PowerPC systems, since those instructions do not work when
20243           the processor is in little-endian mode.  The exceptions are PPC740
20244           and PPC750 which permit these instructions in little-endian mode.
20245
20246       -mupdate
20247       -mno-update
20248           Generate code that uses (does not use) the load or store
20249           instructions that update the base register to the address of the
20250           calculated memory location.  These instructions are generated by
20251           default.  If you use -mno-update, there is a small window between
20252           the time that the stack pointer is updated and the address of the
20253           previous frame is stored, which means code that walks the stack
20254           frame across interrupts or signals may get corrupted data.
20255
20256       -mavoid-indexed-addresses
20257       -mno-avoid-indexed-addresses
20258           Generate code that tries to avoid (not avoid) the use of indexed
20259           load or store instructions. These instructions can incur a
20260           performance penalty on Power6 processors in certain situations,
20261           such as when stepping through large arrays that cross a 16M
20262           boundary.  This option is enabled by default when targeting Power6
20263           and disabled otherwise.
20264
20265       -mfused-madd
20266       -mno-fused-madd
20267           Generate code that uses (does not use) the floating-point multiply
20268           and accumulate instructions.  These instructions are generated by
20269           default if hardware floating point is used.  The machine-dependent
20270           -mfused-madd option is now mapped to the machine-independent
20271           -ffp-contract=fast option, and -mno-fused-madd is mapped to
20272           -ffp-contract=off.
20273
20274       -mmulhw
20275       -mno-mulhw
20276           Generate code that uses (does not use) the half-word multiply and
20277           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
20278           processors.  These instructions are generated by default when
20279           targeting those processors.
20280
20281       -mdlmzb
20282       -mno-dlmzb
20283           Generate code that uses (does not use) the string-search dlmzb
20284           instruction on the IBM 405, 440, 464 and 476 processors.  This
20285           instruction is generated by default when targeting those
20286           processors.
20287
20288       -mno-bit-align
20289       -mbit-align
20290           On System V.4 and embedded PowerPC systems do not (do) force
20291           structures and unions that contain bit-fields to be aligned to the
20292           base type of the bit-field.
20293
20294           For example, by default a structure containing nothing but 8
20295           "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary
20296           and has a size of 4 bytes.  By using -mno-bit-align, the structure
20297           is aligned to a 1-byte boundary and is 1 byte in size.
20298
20299       -mno-strict-align
20300       -mstrict-align
20301           On System V.4 and embedded PowerPC systems do not (do) assume that
20302           unaligned memory references are handled by the system.
20303
20304       -mrelocatable
20305       -mno-relocatable
20306           Generate code that allows (does not allow) a static executable to
20307           be relocated to a different address at run time.  A simple embedded
20308           PowerPC system loader should relocate the entire contents of
20309           ".got2" and 4-byte locations listed in the ".fixup" section, a
20310           table of 32-bit addresses generated by this option.  For this to
20311           work, all objects linked together must be compiled with
20312           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
20313           stack to an 8-byte boundary.
20314
20315       -mrelocatable-lib
20316       -mno-relocatable-lib
20317           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
20318           to allow static executables to be relocated at run time, but
20319           -mrelocatable-lib does not use the smaller stack alignment of
20320           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
20321           linked with objects compiled with any combination of the
20322           -mrelocatable options.
20323
20324       -mno-toc
20325       -mtoc
20326           On System V.4 and embedded PowerPC systems do not (do) assume that
20327           register 2 contains a pointer to a global area pointing to the
20328           addresses used in the program.
20329
20330       -mlittle
20331       -mlittle-endian
20332           On System V.4 and embedded PowerPC systems compile code for the
20333           processor in little-endian mode.  The -mlittle-endian option is the
20334           same as -mlittle.
20335
20336       -mbig
20337       -mbig-endian
20338           On System V.4 and embedded PowerPC systems compile code for the
20339           processor in big-endian mode.  The -mbig-endian option is the same
20340           as -mbig.
20341
20342       -mdynamic-no-pic
20343           On Darwin and Mac OS X systems, compile code so that it is not
20344           relocatable, but that its external references are relocatable.  The
20345           resulting code is suitable for applications, but not shared
20346           libraries.
20347
20348       -msingle-pic-base
20349           Treat the register used for PIC addressing as read-only, rather
20350           than loading it in the prologue for each function.  The runtime
20351           system is responsible for initializing this register with an
20352           appropriate value before execution begins.
20353
20354       -mprioritize-restricted-insns=priority
20355           This option controls the priority that is assigned to dispatch-slot
20356           restricted instructions during the second scheduling pass.  The
20357           argument priority takes the value 0, 1, or 2 to assign no, highest,
20358           or second-highest (respectively) priority to dispatch-slot
20359           restricted instructions.
20360
20361       -msched-costly-dep=dependence_type
20362           This option controls which dependences are considered costly by the
20363           target during instruction scheduling.  The argument dependence_type
20364           takes one of the following values:
20365
20366           no  No dependence is costly.
20367
20368           all All dependences are costly.
20369
20370           true_store_to_load
20371               A true dependence from store to load is costly.
20372
20373           store_to_load
20374               Any dependence from store to load is costly.
20375
20376           number
20377               Any dependence for which the latency is greater than or equal
20378               to number is costly.
20379
20380       -minsert-sched-nops=scheme
20381           This option controls which NOP insertion scheme is used during the
20382           second scheduling pass.  The argument scheme takes one of the
20383           following values:
20384
20385           no  Don't insert NOPs.
20386
20387           pad Pad with NOPs any dispatch group that has vacant issue slots,
20388               according to the scheduler's grouping.
20389
20390           regroup_exact
20391               Insert NOPs to force costly dependent insns into separate
20392               groups.  Insert exactly as many NOPs as needed to force an insn
20393               to a new group, according to the estimated processor grouping.
20394
20395           number
20396               Insert NOPs to force costly dependent insns into separate
20397               groups.  Insert number NOPs to force an insn to a new group.
20398
20399       -mcall-sysv
20400           On System V.4 and embedded PowerPC systems compile code using
20401           calling conventions that adhere to the March 1995 draft of the
20402           System V Application Binary Interface, PowerPC processor
20403           supplement.  This is the default unless you configured GCC using
20404           powerpc-*-eabiaix.
20405
20406       -mcall-sysv-eabi
20407       -mcall-eabi
20408           Specify both -mcall-sysv and -meabi options.
20409
20410       -mcall-sysv-noeabi
20411           Specify both -mcall-sysv and -mno-eabi options.
20412
20413       -mcall-aixdesc
20414           On System V.4 and embedded PowerPC systems compile code for the AIX
20415           operating system.
20416
20417       -mcall-linux
20418           On System V.4 and embedded PowerPC systems compile code for the
20419           Linux-based GNU system.
20420
20421       -mcall-freebsd
20422           On System V.4 and embedded PowerPC systems compile code for the
20423           FreeBSD operating system.
20424
20425       -mcall-netbsd
20426           On System V.4 and embedded PowerPC systems compile code for the
20427           NetBSD operating system.
20428
20429       -mcall-openbsd
20430           On System V.4 and embedded PowerPC systems compile code for the
20431           OpenBSD operating system.
20432
20433       -mtraceback=traceback_type
20434           Select the type of traceback table. Valid values for traceback_type
20435           are full, part, and no.
20436
20437       -maix-struct-return
20438           Return all structures in memory (as specified by the AIX ABI).
20439
20440       -msvr4-struct-return
20441           Return structures smaller than 8 bytes in registers (as specified
20442           by the SVR4 ABI).
20443
20444       -mabi=abi-type
20445           Extend the current ABI with a particular extension, or remove such
20446           extension.  Valid values are altivec, no-altivec, spe, no-spe,
20447           ibmlongdouble, ieeelongdouble, elfv1, elfv2.
20448
20449       -mabi=ibmlongdouble
20450           Change the current ABI to use IBM extended-precision long double.
20451           This is not likely to work if your system defaults to using IEEE
20452           extended-precision long double.  If you change the long double type
20453           from IEEE extended-precision, the compiler will issue a warning
20454           unless you use the -Wno-psabi option.
20455
20456       -mabi=ieeelongdouble
20457           Change the current ABI to use IEEE extended-precision long double.
20458           This is not likely to work if your system defaults to using IBM
20459           extended-precision long double.  If you change the long double type
20460           from IBM extended-precision, the compiler will issue a warning
20461           unless you use the -Wno-psabi option.
20462
20463       -mabi=elfv1
20464           Change the current ABI to use the ELFv1 ABI.  This is the default
20465           ABI for big-endian PowerPC 64-bit Linux.  Overriding the default
20466           ABI requires special system support and is likely to fail in
20467           spectacular ways.
20468
20469       -mabi=elfv2
20470           Change the current ABI to use the ELFv2 ABI.  This is the default
20471           ABI for little-endian PowerPC 64-bit Linux.  Overriding the default
20472           ABI requires special system support and is likely to fail in
20473           spectacular ways.
20474
20475       -mgnu-attribute
20476       -mno-gnu-attribute
20477           Emit .gnu_attribute assembly directives to set tag/value pairs in a
20478           .gnu.attributes section that specify ABI variations in function
20479           parameters or return values.
20480
20481       -mprototype
20482       -mno-prototype
20483           On System V.4 and embedded PowerPC systems assume that all calls to
20484           variable argument functions are properly prototyped.  Otherwise,
20485           the compiler must insert an instruction before every non-prototyped
20486           call to set or clear bit 6 of the condition code register ("CR") to
20487           indicate whether floating-point values are passed in the floating-
20488           point registers in case the function takes variable arguments.
20489           With -mprototype, only calls to prototyped variable argument
20490           functions set or clear the bit.
20491
20492       -msim
20493           On embedded PowerPC systems, assume that the startup module is
20494           called sim-crt0.o and that the standard C libraries are libsim.a
20495           and libc.a.  This is the default for powerpc-*-eabisim
20496           configurations.
20497
20498       -mmvme
20499           On embedded PowerPC systems, assume that the startup module is
20500           called crt0.o and the standard C libraries are libmvme.a and
20501           libc.a.
20502
20503       -mads
20504           On embedded PowerPC systems, assume that the startup module is
20505           called crt0.o and the standard C libraries are libads.a and libc.a.
20506
20507       -myellowknife
20508           On embedded PowerPC systems, assume that the startup module is
20509           called crt0.o and the standard C libraries are libyk.a and libc.a.
20510
20511       -mvxworks
20512           On System V.4 and embedded PowerPC systems, specify that you are
20513           compiling for a VxWorks system.
20514
20515       -memb
20516           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags
20517           header to indicate that eabi extended relocations are used.
20518
20519       -meabi
20520       -mno-eabi
20521           On System V.4 and embedded PowerPC systems do (do not) adhere to
20522           the Embedded Applications Binary Interface (EABI), which is a set
20523           of modifications to the System V.4 specifications.  Selecting
20524           -meabi means that the stack is aligned to an 8-byte boundary, a
20525           function "__eabi" is called from "main" to set up the EABI
20526           environment, and the -msdata option can use both "r2" and "r13" to
20527           point to two separate small data areas.  Selecting -mno-eabi means
20528           that the stack is aligned to a 16-byte boundary, no EABI
20529           initialization function is called from "main", and the -msdata
20530           option only uses "r13" to point to a single small data area.  The
20531           -meabi option is on by default if you configured GCC using one of
20532           the powerpc*-*-eabi* options.
20533
20534       -msdata=eabi
20535           On System V.4 and embedded PowerPC systems, put small initialized
20536           "const" global and static data in the ".sdata2" section, which is
20537           pointed to by register "r2".  Put small initialized non-"const"
20538           global and static data in the ".sdata" section, which is pointed to
20539           by register "r13".  Put small uninitialized global and static data
20540           in the ".sbss" section, which is adjacent to the ".sdata" section.
20541           The -msdata=eabi option is incompatible with the -mrelocatable
20542           option.  The -msdata=eabi option also sets the -memb option.
20543
20544       -msdata=sysv
20545           On System V.4 and embedded PowerPC systems, put small global and
20546           static data in the ".sdata" section, which is pointed to by
20547           register "r13".  Put small uninitialized global and static data in
20548           the ".sbss" section, which is adjacent to the ".sdata" section.
20549           The -msdata=sysv option is incompatible with the -mrelocatable
20550           option.
20551
20552       -msdata=default
20553       -msdata
20554           On System V.4 and embedded PowerPC systems, if -meabi is used,
20555           compile code the same as -msdata=eabi, otherwise compile code the
20556           same as -msdata=sysv.
20557
20558       -msdata=data
20559           On System V.4 and embedded PowerPC systems, put small global data
20560           in the ".sdata" section.  Put small uninitialized global data in
20561           the ".sbss" section.  Do not use register "r13" to address small
20562           data however.  This is the default behavior unless other -msdata
20563           options are used.
20564
20565       -msdata=none
20566       -mno-sdata
20567           On embedded PowerPC systems, put all initialized global and static
20568           data in the ".data" section, and all uninitialized data in the
20569           ".bss" section.
20570
20571       -mreadonly-in-sdata
20572       -mreadonly-in-sdata
20573           Put read-only objects in the ".sdata" section as well.  This is the
20574           default.
20575
20576       -mblock-move-inline-limit=num
20577           Inline all block moves (such as calls to "memcpy" or structure
20578           copies) less than or equal to num bytes.  The minimum value for num
20579           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
20580           default value is target-specific.
20581
20582       -mblock-compare-inline-limit=num
20583           Generate non-looping inline code for all block compares (such as
20584           calls to "memcmp" or structure compares) less than or equal to num
20585           bytes. If num is 0, all inline expansion (non-loop and loop) of
20586           block compare is disabled. The default value is target-specific.
20587
20588       -mblock-compare-inline-loop-limit=num
20589           Generate an inline expansion using loop code for all block compares
20590           that are less than or equal to num bytes, but greater than the
20591           limit for non-loop inline block compare expansion. If the block
20592           length is not constant, at most num bytes will be compared before
20593           "memcmp" is called to compare the remainder of the block. The
20594           default value is target-specific.
20595
20596       -mstring-compare-inline-limit=num
20597           Compare at most num string bytes with inline code.  If the
20598           difference or end of string is not found at the end of the inline
20599           compare a call to "strcmp" or "strncmp" will take care of the rest
20600           of the comparison. The default is 64 bytes.
20601
20602       -G num
20603           On embedded PowerPC systems, put global and static items less than
20604           or equal to num bytes into the small data or BSS sections instead
20605           of the normal data or BSS section.  By default, num is 8.  The -G
20606           num switch is also passed to the linker.  All modules should be
20607           compiled with the same -G num value.
20608
20609       -mregnames
20610       -mno-regnames
20611           On System V.4 and embedded PowerPC systems do (do not) emit
20612           register names in the assembly language output using symbolic
20613           forms.
20614
20615       -mlongcall
20616       -mno-longcall
20617           By default assume that all calls are far away so that a longer and
20618           more expensive calling sequence is required.  This is required for
20619           calls farther than 32 megabytes (33,554,432 bytes) from the current
20620           location.  A short call is generated if the compiler knows the call
20621           cannot be that far away.  This setting can be overridden by the
20622           "shortcall" function attribute, or by "#pragma longcall(0)".
20623
20624           Some linkers are capable of detecting out-of-range calls and
20625           generating glue code on the fly.  On these systems, long calls are
20626           unnecessary and generate slower code.  As of this writing, the AIX
20627           linker can do this, as can the GNU linker for PowerPC/64.  It is
20628           planned to add this feature to the GNU linker for 32-bit PowerPC
20629           systems as well.
20630
20631           On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee,
20632           L42", plus a branch island (glue code).  The two target addresses
20633           represent the callee and the branch island.  The Darwin/PPC linker
20634           prefers the first address and generates a "bl callee" if the PPC
20635           "bl" instruction reaches the callee directly; otherwise, the linker
20636           generates "bl L42" to call the branch island.  The branch island is
20637           appended to the body of the calling function; it computes the full
20638           32-bit address of the callee and jumps to it.
20639
20640           On Mach-O (Darwin) systems, this option directs the compiler emit
20641           to the glue for every direct call, and the Darwin linker decides
20642           whether to use or discard it.
20643
20644           In the future, GCC may ignore all longcall specifications when the
20645           linker is known to generate glue.
20646
20647       -mtls-markers
20648       -mno-tls-markers
20649           Mark (do not mark) calls to "__tls_get_addr" with a relocation
20650           specifying the function argument.  The relocation allows the linker
20651           to reliably associate function call with argument setup
20652           instructions for TLS optimization, which in turn allows GCC to
20653           better schedule the sequence.
20654
20655       -mrecip
20656       -mno-recip
20657           This option enables use of the reciprocal estimate and reciprocal
20658           square root estimate instructions with additional Newton-Raphson
20659           steps to increase precision instead of doing a divide or square
20660           root and divide for floating-point arguments.  You should use the
20661           -ffast-math option when using -mrecip (or at least
20662           -funsafe-math-optimizations, -ffinite-math-only, -freciprocal-math
20663           and -fno-trapping-math).  Note that while the throughput of the
20664           sequence is generally higher than the throughput of the non-
20665           reciprocal instruction, the precision of the sequence can be
20666           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
20667           0.99999994) for reciprocal square roots.
20668
20669       -mrecip=opt
20670           This option controls which reciprocal estimate instructions may be
20671           used.  opt is a comma-separated list of options, which may be
20672           preceded by a "!" to invert the option:
20673
20674           all Enable all estimate instructions.
20675
20676           default
20677               Enable the default instructions, equivalent to -mrecip.
20678
20679           none
20680               Disable all estimate instructions, equivalent to -mno-recip.
20681
20682           div Enable the reciprocal approximation instructions for both
20683               single and double precision.
20684
20685           divf
20686               Enable the single-precision reciprocal approximation
20687               instructions.
20688
20689           divd
20690               Enable the double-precision reciprocal approximation
20691               instructions.
20692
20693           rsqrt
20694               Enable the reciprocal square root approximation instructions
20695               for both single and double precision.
20696
20697           rsqrtf
20698               Enable the single-precision reciprocal square root
20699               approximation instructions.
20700
20701           rsqrtd
20702               Enable the double-precision reciprocal square root
20703               approximation instructions.
20704
20705           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
20706           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
20707           "XVRSQRTEDP" instructions which handle the double-precision
20708           reciprocal square root calculations.
20709
20710       -mrecip-precision
20711       -mno-recip-precision
20712           Assume (do not assume) that the reciprocal estimate instructions
20713           provide higher-precision estimates than is mandated by the PowerPC
20714           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
20715           automatically selects -mrecip-precision.  The double-precision
20716           square root estimate instructions are not generated by default on
20717           low-precision machines, since they do not provide an estimate that
20718           converges after three steps.
20719
20720       -mveclibabi=type
20721           Specifies the ABI type to use for vectorizing intrinsics using an
20722           external library.  The only type supported at present is mass,
20723           which specifies to use IBM's Mathematical Acceleration Subsystem
20724           (MASS) libraries for vectorizing intrinsics using external
20725           libraries.  GCC currently emits calls to "acosd2", "acosf4",
20726           "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4",
20727           "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4",
20728           "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2",
20729           "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4",
20730           "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4",
20731           "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4",
20732           "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2",
20733           "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and
20734           "tanhf4" when generating code for power7.  Both -ftree-vectorize
20735           and -funsafe-math-optimizations must also be enabled.  The MASS
20736           libraries must be specified at link time.
20737
20738       -mfriz
20739       -mno-friz
20740           Generate (do not generate) the "friz" instruction when the
20741           -funsafe-math-optimizations option is used to optimize rounding of
20742           floating-point values to 64-bit integer and back to floating point.
20743           The "friz" instruction does not return the same value if the
20744           floating-point number is too large to fit in an integer.
20745
20746       -mpointers-to-nested-functions
20747       -mno-pointers-to-nested-functions
20748           Generate (do not generate) code to load up the static chain
20749           register ("r11") when calling through a pointer on AIX and 64-bit
20750           Linux systems where a function pointer points to a 3-word
20751           descriptor giving the function address, TOC value to be loaded in
20752           register "r2", and static chain value to be loaded in register
20753           "r11".  The -mpointers-to-nested-functions is on by default.  You
20754           cannot call through pointers to nested functions or pointers to
20755           functions compiled in other languages that use the static chain if
20756           you use -mno-pointers-to-nested-functions.
20757
20758       -msave-toc-indirect
20759       -mno-save-toc-indirect
20760           Generate (do not generate) code to save the TOC value in the
20761           reserved stack location in the function prologue if the function
20762           calls through a pointer on AIX and 64-bit Linux systems.  If the
20763           TOC value is not saved in the prologue, it is saved just before the
20764           call through the pointer.  The -mno-save-toc-indirect option is the
20765           default.
20766
20767       -mcompat-align-parm
20768       -mno-compat-align-parm
20769           Generate (do not generate) code to pass structure parameters with a
20770           maximum alignment of 64 bits, for compatibility with older versions
20771           of GCC.
20772
20773           Older versions of GCC (prior to 4.9.0) incorrectly did not align a
20774           structure parameter on a 128-bit boundary when that structure
20775           contained a member requiring 128-bit alignment.  This is corrected
20776           in more recent versions of GCC.  This option may be used to
20777           generate code that is compatible with functions compiled with older
20778           versions of GCC.
20779
20780           The -mno-compat-align-parm option is the default.
20781
20782       -mstack-protector-guard=guard
20783       -mstack-protector-guard-reg=reg
20784       -mstack-protector-guard-offset=offset
20785       -mstack-protector-guard-symbol=symbol
20786           Generate stack protection code using canary at guard.  Supported
20787           locations are global for global canary or tls for per-thread canary
20788           in the TLS block (the default with GNU libc version 2.4 or later).
20789
20790           With the latter choice the options -mstack-protector-guard-reg=reg
20791           and -mstack-protector-guard-offset=offset furthermore specify which
20792           register to use as base register for reading the canary, and from
20793           what offset from that base register. The default for those is as
20794           specified in the relevant ABI.
20795           -mstack-protector-guard-symbol=symbol overrides the offset with a
20796           symbol reference to a canary in the TLS block.
20797
20798   RX Options
20799       These command-line options are defined for RX targets:
20800
20801       -m64bit-doubles
20802       -m32bit-doubles
20803           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
20804           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
20805           RX floating-point hardware only works on 32-bit values, which is
20806           why the default is -m32bit-doubles.
20807
20808       -fpu
20809       -nofpu
20810           Enables (-fpu) or disables (-nofpu) the use of RX floating-point
20811           hardware.  The default is enabled for the RX600 series and disabled
20812           for the RX200 series.
20813
20814           Floating-point instructions are only generated for 32-bit floating-
20815           point values, however, so the FPU hardware is not used for doubles
20816           if the -m64bit-doubles option is used.
20817
20818           Note If the -fpu option is enabled then -funsafe-math-optimizations
20819           is also enabled automatically.  This is because the RX FPU
20820           instructions are themselves unsafe.
20821
20822       -mcpu=name
20823           Selects the type of RX CPU to be targeted.  Currently three types
20824           are supported, the generic RX600 and RX200 series hardware and the
20825           specific RX610 CPU.  The default is RX600.
20826
20827           The only difference between RX600 and RX610 is that the RX610 does
20828           not support the "MVTIPL" instruction.
20829
20830           The RX200 series does not have a hardware floating-point unit and
20831           so -nofpu is enabled by default when this type is selected.
20832
20833       -mbig-endian-data
20834       -mlittle-endian-data
20835           Store data (but not code) in the big-endian format.  The default is
20836           -mlittle-endian-data, i.e. to store data in the little-endian
20837           format.
20838
20839       -msmall-data-limit=N
20840           Specifies the maximum size in bytes of global and static variables
20841           which can be placed into the small data area.  Using the small data
20842           area can lead to smaller and faster code, but the size of area is
20843           limited and it is up to the programmer to ensure that the area does
20844           not overflow.  Also when the small data area is used one of the
20845           RX's registers (usually "r13") is reserved for use pointing to this
20846           area, so it is no longer available for use by the compiler.  This
20847           could result in slower and/or larger code if variables are pushed
20848           onto the stack instead of being held in this register.
20849
20850           Note, common variables (variables that have not been initialized)
20851           and constants are not placed into the small data area as they are
20852           assigned to other sections in the output executable.
20853
20854           The default value is zero, which disables this feature.  Note, this
20855           feature is not enabled by default with higher optimization levels
20856           (-O2 etc) because of the potentially detrimental effects of
20857           reserving a register.  It is up to the programmer to experiment and
20858           discover whether this feature is of benefit to their program.  See
20859           the description of the -mpid option for a description of how the
20860           actual register to hold the small data area pointer is chosen.
20861
20862       -msim
20863       -mno-sim
20864           Use the simulator runtime.  The default is to use the libgloss
20865           board-specific runtime.
20866
20867       -mas100-syntax
20868       -mno-as100-syntax
20869           When generating assembler output use a syntax that is compatible
20870           with Renesas's AS100 assembler.  This syntax can also be handled by
20871           the GAS assembler, but it has some restrictions so it is not
20872           generated by default.
20873
20874       -mmax-constant-size=N
20875           Specifies the maximum size, in bytes, of a constant that can be
20876           used as an operand in a RX instruction.  Although the RX
20877           instruction set does allow constants of up to 4 bytes in length to
20878           be used in instructions, a longer value equates to a longer
20879           instruction.  Thus in some circumstances it can be beneficial to
20880           restrict the size of constants that are used in instructions.
20881           Constants that are too big are instead placed into a constant pool
20882           and referenced via register indirection.
20883
20884           The value N can be between 0 and 4.  A value of 0 (the default) or
20885           4 means that constants of any size are allowed.
20886
20887       -mrelax
20888           Enable linker relaxation.  Linker relaxation is a process whereby
20889           the linker attempts to reduce the size of a program by finding
20890           shorter versions of various instructions.  Disabled by default.
20891
20892       -mint-register=N
20893           Specify the number of registers to reserve for fast interrupt
20894           handler functions.  The value N can be between 0 and 4.  A value of
20895           1 means that register "r13" is reserved for the exclusive use of
20896           fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A
20897           value of 3 reserves "r13", "r12" and "r11", and a value of 4
20898           reserves "r13" through "r10".  A value of 0, the default, does not
20899           reserve any registers.
20900
20901       -msave-acc-in-interrupts
20902           Specifies that interrupt handler functions should preserve the
20903           accumulator register.  This is only necessary if normal code might
20904           use the accumulator register, for example because it performs
20905           64-bit multiplications.  The default is to ignore the accumulator
20906           as this makes the interrupt handlers faster.
20907
20908       -mpid
20909       -mno-pid
20910           Enables the generation of position independent data.  When enabled
20911           any access to constant data is done via an offset from a base
20912           address held in a register.  This allows the location of constant
20913           data to be determined at run time without requiring the executable
20914           to be relocated, which is a benefit to embedded applications with
20915           tight memory constraints.  Data that can be modified is not
20916           affected by this option.
20917
20918           Note, using this feature reserves a register, usually "r13", for
20919           the constant data base address.  This can result in slower and/or
20920           larger code, especially in complicated functions.
20921
20922           The actual register chosen to hold the constant data base address
20923           depends upon whether the -msmall-data-limit and/or the
20924           -mint-register command-line options are enabled.  Starting with
20925           register "r13" and proceeding downwards, registers are allocated
20926           first to satisfy the requirements of -mint-register, then -mpid and
20927           finally -msmall-data-limit.  Thus it is possible for the small data
20928           area register to be "r8" if both -mint-register=4 and -mpid are
20929           specified on the command line.
20930
20931           By default this feature is not enabled.  The default can be
20932           restored via the -mno-pid command-line option.
20933
20934       -mno-warn-multiple-fast-interrupts
20935       -mwarn-multiple-fast-interrupts
20936           Prevents GCC from issuing a warning message if it finds more than
20937           one fast interrupt handler when it is compiling a file.  The
20938           default is to issue a warning for each extra fast interrupt handler
20939           found, as the RX only supports one such interrupt.
20940
20941       -mallow-string-insns
20942       -mno-allow-string-insns
20943           Enables or disables the use of the string manipulation instructions
20944           "SMOVF", "SCMPU", "SMOVB", "SMOVU", "SUNTIL" "SWHILE" and also the
20945           "RMPA" instruction.  These instructions may prefetch data, which is
20946           not safe to do if accessing an I/O register.  (See section 12.2.7
20947           of the RX62N Group User's Manual for more information).
20948
20949           The default is to allow these instructions, but it is not possible
20950           for GCC to reliably detect all circumstances where a string
20951           instruction might be used to access an I/O register, so their use
20952           cannot be disabled automatically.  Instead it is reliant upon the
20953           programmer to use the -mno-allow-string-insns option if their
20954           program accesses I/O space.
20955
20956           When the instructions are enabled GCC defines the C preprocessor
20957           symbol "__RX_ALLOW_STRING_INSNS__", otherwise it defines the symbol
20958           "__RX_DISALLOW_STRING_INSNS__".
20959
20960       -mjsr
20961       -mno-jsr
20962           Use only (or not only) "JSR" instructions to access functions.
20963           This option can be used when code size exceeds the range of "BSR"
20964           instructions.  Note that -mno-jsr does not mean to not use "JSR"
20965           but instead means that any type of branch may be used.
20966
20967       Note: The generic GCC command-line option -ffixed-reg has special
20968       significance to the RX port when used with the "interrupt" function
20969       attribute.  This attribute indicates a function intended to process
20970       fast interrupts.  GCC ensures that it only uses the registers "r10",
20971       "r11", "r12" and/or "r13" and only provided that the normal use of the
20972       corresponding registers have been restricted via the -ffixed-reg or
20973       -mint-register command-line options.
20974
20975   S/390 and zSeries Options
20976       These are the -m options defined for the S/390 and zSeries
20977       architecture.
20978
20979       -mhard-float
20980       -msoft-float
20981           Use (do not use) the hardware floating-point instructions and
20982           registers for floating-point operations.  When -msoft-float is
20983           specified, functions in libgcc.a are used to perform floating-point
20984           operations.  When -mhard-float is specified, the compiler generates
20985           IEEE floating-point instructions.  This is the default.
20986
20987       -mhard-dfp
20988       -mno-hard-dfp
20989           Use (do not use) the hardware decimal-floating-point instructions
20990           for decimal-floating-point operations.  When -mno-hard-dfp is
20991           specified, functions in libgcc.a are used to perform decimal-
20992           floating-point operations.  When -mhard-dfp is specified, the
20993           compiler generates decimal-floating-point hardware instructions.
20994           This is the default for -march=z9-ec or higher.
20995
20996       -mlong-double-64
20997       -mlong-double-128
20998           These switches control the size of "long double" type. A size of 64
20999           bits makes the "long double" type equivalent to the "double" type.
21000           This is the default.
21001
21002       -mbackchain
21003       -mno-backchain
21004           Store (do not store) the address of the caller's frame as backchain
21005           pointer into the callee's stack frame.  A backchain may be needed
21006           to allow debugging using tools that do not understand DWARF call
21007           frame information.  When -mno-packed-stack is in effect, the
21008           backchain pointer is stored at the bottom of the stack frame; when
21009           -mpacked-stack is in effect, the backchain is placed into the
21010           topmost word of the 96/160 byte register save area.
21011
21012           In general, code compiled with -mbackchain is call-compatible with
21013           code compiled with -mmo-backchain; however, use of the backchain
21014           for debugging purposes usually requires that the whole binary is
21015           built with -mbackchain.  Note that the combination of -mbackchain,
21016           -mpacked-stack and -mhard-float is not supported.  In order to
21017           build a linux kernel use -msoft-float.
21018
21019           The default is to not maintain the backchain.
21020
21021       -mpacked-stack
21022       -mno-packed-stack
21023           Use (do not use) the packed stack layout.  When -mno-packed-stack
21024           is specified, the compiler uses the all fields of the 96/160 byte
21025           register save area only for their default purpose; unused fields
21026           still take up stack space.  When -mpacked-stack is specified,
21027           register save slots are densely packed at the top of the register
21028           save area; unused space is reused for other purposes, allowing for
21029           more efficient use of the available stack space.  However, when
21030           -mbackchain is also in effect, the topmost word of the save area is
21031           always used to store the backchain, and the return address register
21032           is always saved two words below the backchain.
21033
21034           As long as the stack frame backchain is not used, code generated
21035           with -mpacked-stack is call-compatible with code generated with
21036           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
21037           S/390 or zSeries generated code that uses the stack frame backchain
21038           at run time, not just for debugging purposes.  Such code is not
21039           call-compatible with code compiled with -mpacked-stack.  Also, note
21040           that the combination of -mbackchain, -mpacked-stack and
21041           -mhard-float is not supported.  In order to build a linux kernel
21042           use -msoft-float.
21043
21044           The default is to not use the packed stack layout.
21045
21046       -msmall-exec
21047       -mno-small-exec
21048           Generate (or do not generate) code using the "bras" instruction to
21049           do subroutine calls.  This only works reliably if the total
21050           executable size does not exceed 64k.  The default is to use the
21051           "basr" instruction instead, which does not have this limitation.
21052
21053       -m64
21054       -m31
21055           When -m31 is specified, generate code compliant to the GNU/Linux
21056           for S/390 ABI.  When -m64 is specified, generate code compliant to
21057           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
21058           generate 64-bit instructions.  For the s390 targets, the default is
21059           -m31, while the s390x targets default to -m64.
21060
21061       -mzarch
21062       -mesa
21063           When -mzarch is specified, generate code using the instructions
21064           available on z/Architecture.  When -mesa is specified, generate
21065           code using the instructions available on ESA/390.  Note that -mesa
21066           is not possible with -m64.  When generating code compliant to the
21067           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
21068           code compliant to the GNU/Linux for zSeries ABI, the default is
21069           -mzarch.
21070
21071       -mhtm
21072       -mno-htm
21073           The -mhtm option enables a set of builtins making use of
21074           instructions available with the transactional execution facility
21075           introduced with the IBM zEnterprise EC12 machine generation S/390
21076           System z Built-in Functions.  -mhtm is enabled by default when
21077           using -march=zEC12.
21078
21079       -mvx
21080       -mno-vx
21081           When -mvx is specified, generate code using the instructions
21082           available with the vector extension facility introduced with the
21083           IBM z13 machine generation.  This option changes the ABI for some
21084           vector type values with regard to alignment and calling
21085           conventions.  In case vector type values are being used in an ABI-
21086           relevant context a GAS .gnu_attribute command will be added to mark
21087           the resulting binary with the ABI used.  -mvx is enabled by default
21088           when using -march=z13.
21089
21090       -mzvector
21091       -mno-zvector
21092           The -mzvector option enables vector language extensions and
21093           builtins using instructions available with the vector extension
21094           facility introduced with the IBM z13 machine generation.  This
21095           option adds support for vector to be used as a keyword to define
21096           vector type variables and arguments.  vector is only available when
21097           GNU extensions are enabled.  It will not be expanded when
21098           requesting strict standard compliance e.g. with -std=c99.  In
21099           addition to the GCC low-level builtins -mzvector enables a set of
21100           builtins added for compatibility with AltiVec-style implementations
21101           like Power and Cell.  In order to make use of these builtins the
21102           header file vecintrin.h needs to be included.  -mzvector is
21103           disabled by default.
21104
21105       -mmvcle
21106       -mno-mvcle
21107           Generate (or do not generate) code using the "mvcle" instruction to
21108           perform block moves.  When -mno-mvcle is specified, use a "mvc"
21109           loop instead.  This is the default unless optimizing for size.
21110
21111       -mdebug
21112       -mno-debug
21113           Print (or do not print) additional debug information when
21114           compiling.  The default is to not print debug information.
21115
21116       -march=cpu-type
21117           Generate code that runs on cpu-type, which is the name of a system
21118           representing a certain processor type.  Possible values for cpu-
21119           type are z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8,
21120           z196/arch9, zEC12, z13/arch11, and native.
21121
21122           The default is -march=z900.  g5/arch3 and g6 are deprecated and
21123           will be removed with future releases.
21124
21125           Specifying native as cpu type can be used to select the best
21126           architecture option for the host processor.  -march=native has no
21127           effect if GCC does not recognize the processor.
21128
21129       -mtune=cpu-type
21130           Tune to cpu-type everything applicable about the generated code,
21131           except for the ABI and the set of available instructions.  The list
21132           of cpu-type values is the same as for -march.  The default is the
21133           value used for -march.
21134
21135       -mtpf-trace
21136       -mno-tpf-trace
21137           Generate code that adds (does not add) in TPF OS specific branches
21138           to trace routines in the operating system.  This option is off by
21139           default, even when compiling for the TPF OS.
21140
21141       -mfused-madd
21142       -mno-fused-madd
21143           Generate code that uses (does not use) the floating-point multiply
21144           and accumulate instructions.  These instructions are generated by
21145           default if hardware floating point is used.
21146
21147       -mwarn-framesize=framesize
21148           Emit a warning if the current function exceeds the given frame
21149           size.  Because this is a compile-time check it doesn't need to be a
21150           real problem when the program runs.  It is intended to identify
21151           functions that most probably cause a stack overflow.  It is useful
21152           to be used in an environment with limited stack size e.g. the linux
21153           kernel.
21154
21155       -mwarn-dynamicstack
21156           Emit a warning if the function calls "alloca" or uses dynamically-
21157           sized arrays.  This is generally a bad idea with a limited stack
21158           size.
21159
21160       -mstack-guard=stack-guard
21161       -mstack-size=stack-size
21162           If these options are provided the S/390 back end emits additional
21163           instructions in the function prologue that trigger a trap if the
21164           stack size is stack-guard bytes above the stack-size (remember that
21165           the stack on S/390 grows downward).  If the stack-guard option is
21166           omitted the smallest power of 2 larger than the frame size of the
21167           compiled function is chosen.  These options are intended to be used
21168           to help debugging stack overflow problems.  The additionally
21169           emitted code causes only little overhead and hence can also be used
21170           in production-like systems without greater performance degradation.
21171           The given values have to be exact powers of 2 and stack-size has to
21172           be greater than stack-guard without exceeding 64k.  In order to be
21173           efficient the extra code makes the assumption that the stack starts
21174           at an address aligned to the value given by stack-size.  The stack-
21175           guard option can only be used in conjunction with stack-size.
21176
21177       -mhotpatch=pre-halfwords,post-halfwords
21178           If the hotpatch option is enabled, a "hot-patching" function
21179           prologue is generated for all functions in the compilation unit.
21180           The funtion label is prepended with the given number of two-byte
21181           NOP instructions (pre-halfwords, maximum 1000000).  After the
21182           label, 2 * post-halfwords bytes are appended, using the largest NOP
21183           like instructions the architecture allows (maximum 1000000).
21184
21185           If both arguments are zero, hotpatching is disabled.
21186
21187           This option can be overridden for individual functions with the
21188           "hotpatch" attribute.
21189
21190   Score Options
21191       These options are defined for Score implementations:
21192
21193       -meb
21194           Compile code for big-endian mode.  This is the default.
21195
21196       -mel
21197           Compile code for little-endian mode.
21198
21199       -mnhwloop
21200           Disable generation of "bcnz" instructions.
21201
21202       -muls
21203           Enable generation of unaligned load and store instructions.
21204
21205       -mmac
21206           Enable the use of multiply-accumulate instructions. Disabled by
21207           default.
21208
21209       -mscore5
21210           Specify the SCORE5 as the target architecture.
21211
21212       -mscore5u
21213           Specify the SCORE5U of the target architecture.
21214
21215       -mscore7
21216           Specify the SCORE7 as the target architecture. This is the default.
21217
21218       -mscore7d
21219           Specify the SCORE7D as the target architecture.
21220
21221   SH Options
21222       These -m options are defined for the SH implementations:
21223
21224       -m1 Generate code for the SH1.
21225
21226       -m2 Generate code for the SH2.
21227
21228       -m2e
21229           Generate code for the SH2e.
21230
21231       -m2a-nofpu
21232           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
21233           way that the floating-point unit is not used.
21234
21235       -m2a-single-only
21236           Generate code for the SH2a-FPU, in such a way that no double-
21237           precision floating-point operations are used.
21238
21239       -m2a-single
21240           Generate code for the SH2a-FPU assuming the floating-point unit is
21241           in single-precision mode by default.
21242
21243       -m2a
21244           Generate code for the SH2a-FPU assuming the floating-point unit is
21245           in double-precision mode by default.
21246
21247       -m3 Generate code for the SH3.
21248
21249       -m3e
21250           Generate code for the SH3e.
21251
21252       -m4-nofpu
21253           Generate code for the SH4 without a floating-point unit.
21254
21255       -m4-single-only
21256           Generate code for the SH4 with a floating-point unit that only
21257           supports single-precision arithmetic.
21258
21259       -m4-single
21260           Generate code for the SH4 assuming the floating-point unit is in
21261           single-precision mode by default.
21262
21263       -m4 Generate code for the SH4.
21264
21265       -m4-100
21266           Generate code for SH4-100.
21267
21268       -m4-100-nofpu
21269           Generate code for SH4-100 in such a way that the floating-point
21270           unit is not used.
21271
21272       -m4-100-single
21273           Generate code for SH4-100 assuming the floating-point unit is in
21274           single-precision mode by default.
21275
21276       -m4-100-single-only
21277           Generate code for SH4-100 in such a way that no double-precision
21278           floating-point operations are used.
21279
21280       -m4-200
21281           Generate code for SH4-200.
21282
21283       -m4-200-nofpu
21284           Generate code for SH4-200 without in such a way that the floating-
21285           point unit is not used.
21286
21287       -m4-200-single
21288           Generate code for SH4-200 assuming the floating-point unit is in
21289           single-precision mode by default.
21290
21291       -m4-200-single-only
21292           Generate code for SH4-200 in such a way that no double-precision
21293           floating-point operations are used.
21294
21295       -m4-300
21296           Generate code for SH4-300.
21297
21298       -m4-300-nofpu
21299           Generate code for SH4-300 without in such a way that the floating-
21300           point unit is not used.
21301
21302       -m4-300-single
21303           Generate code for SH4-300 in such a way that no double-precision
21304           floating-point operations are used.
21305
21306       -m4-300-single-only
21307           Generate code for SH4-300 in such a way that no double-precision
21308           floating-point operations are used.
21309
21310       -m4-340
21311           Generate code for SH4-340 (no MMU, no FPU).
21312
21313       -m4-500
21314           Generate code for SH4-500 (no FPU).  Passes -isa=sh4-nofpu to the
21315           assembler.
21316
21317       -m4a-nofpu
21318           Generate code for the SH4al-dsp, or for a SH4a in such a way that
21319           the floating-point unit is not used.
21320
21321       -m4a-single-only
21322           Generate code for the SH4a, in such a way that no double-precision
21323           floating-point operations are used.
21324
21325       -m4a-single
21326           Generate code for the SH4a assuming the floating-point unit is in
21327           single-precision mode by default.
21328
21329       -m4a
21330           Generate code for the SH4a.
21331
21332       -m4al
21333           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
21334           assembler.  GCC doesn't generate any DSP instructions at the
21335           moment.
21336
21337       -mb Compile code for the processor in big-endian mode.
21338
21339       -ml Compile code for the processor in little-endian mode.
21340
21341       -mdalign
21342           Align doubles at 64-bit boundaries.  Note that this changes the
21343           calling conventions, and thus some functions from the standard C
21344           library do not work unless you recompile it first with -mdalign.
21345
21346       -mrelax
21347           Shorten some address references at link time, when possible; uses
21348           the linker option -relax.
21349
21350       -mbigtable
21351           Use 32-bit offsets in "switch" tables.  The default is to use
21352           16-bit offsets.
21353
21354       -mbitops
21355           Enable the use of bit manipulation instructions on SH2A.
21356
21357       -mfmovd
21358           Enable the use of the instruction "fmovd".  Check -mdalign for
21359           alignment constraints.
21360
21361       -mrenesas
21362           Comply with the calling conventions defined by Renesas.
21363
21364       -mno-renesas
21365           Comply with the calling conventions defined for GCC before the
21366           Renesas conventions were available.  This option is the default for
21367           all targets of the SH toolchain.
21368
21369       -mnomacsave
21370           Mark the "MAC" register as call-clobbered, even if -mrenesas is
21371           given.
21372
21373       -mieee
21374       -mno-ieee
21375           Control the IEEE compliance of floating-point comparisons, which
21376           affects the handling of cases where the result of a comparison is
21377           unordered.  By default -mieee is implicitly enabled.  If
21378           -ffinite-math-only is enabled -mno-ieee is implicitly set, which
21379           results in faster floating-point greater-equal and less-equal
21380           comparisons.  The implicit settings can be overridden by specifying
21381           either -mieee or -mno-ieee.
21382
21383       -minline-ic_invalidate
21384           Inline code to invalidate instruction cache entries after setting
21385           up nested function trampolines.  This option has no effect if
21386           -musermode is in effect and the selected code generation option
21387           (e.g. -m4) does not allow the use of the "icbi" instruction.  If
21388           the selected code generation option does not allow the use of the
21389           "icbi" instruction, and -musermode is not in effect, the inlined
21390           code manipulates the instruction cache address array directly with
21391           an associative write.  This not only requires privileged mode at
21392           run time, but it also fails if the cache line had been mapped via
21393           the TLB and has become unmapped.
21394
21395       -misize
21396           Dump instruction size and location in the assembly code.
21397
21398       -mpadstruct
21399           This option is deprecated.  It pads structures to multiple of 4
21400           bytes, which is incompatible with the SH ABI.
21401
21402       -matomic-model=model
21403           Sets the model of atomic operations and additional parameters as a
21404           comma separated list.  For details on the atomic built-in functions
21405           see __atomic Builtins.  The following models and parameters are
21406           supported:
21407
21408           none
21409               Disable compiler generated atomic sequences and emit library
21410               calls for atomic operations.  This is the default if the target
21411               is not "sh*-*-linux*".
21412
21413           soft-gusa
21414               Generate GNU/Linux compatible gUSA software atomic sequences
21415               for the atomic built-in functions.  The generated atomic
21416               sequences require additional support from the
21417               interrupt/exception handling code of the system and are only
21418               suitable for SH3* and SH4* single-core systems.  This option is
21419               enabled by default when the target is "sh*-*-linux*" and SH3*
21420               or SH4*.  When the target is SH4A, this option also partially
21421               utilizes the hardware atomic instructions "movli.l" and
21422               "movco.l" to create more efficient code, unless strict is
21423               specified.
21424
21425           soft-tcb
21426               Generate software atomic sequences that use a variable in the
21427               thread control block.  This is a variation of the gUSA
21428               sequences which can also be used on SH1* and SH2* targets.  The
21429               generated atomic sequences require additional support from the
21430               interrupt/exception handling code of the system and are only
21431               suitable for single-core systems.  When using this model, the
21432               gbr-offset= parameter has to be specified as well.
21433
21434           soft-imask
21435               Generate software atomic sequences that temporarily disable
21436               interrupts by setting "SR.IMASK = 1111".  This model works only
21437               when the program runs in privileged mode and is only suitable
21438               for single-core systems.  Additional support from the
21439               interrupt/exception handling code of the system is not
21440               required.  This model is enabled by default when the target is
21441               "sh*-*-linux*" and SH1* or SH2*.
21442
21443           hard-llcs
21444               Generate hardware atomic sequences using the "movli.l" and
21445               "movco.l" instructions only.  This is only available on SH4A
21446               and is suitable for multi-core systems.  Since the hardware
21447               instructions support only 32 bit atomic variables access to 8
21448               or 16 bit variables is emulated with 32 bit accesses.  Code
21449               compiled with this option is also compatible with other
21450               software atomic model interrupt/exception handling systems if
21451               executed on an SH4A system.  Additional support from the
21452               interrupt/exception handling code of the system is not required
21453               for this model.
21454
21455           gbr-offset=
21456               This parameter specifies the offset in bytes of the variable in
21457               the thread control block structure that should be used by the
21458               generated atomic sequences when the soft-tcb model has been
21459               selected.  For other models this parameter is ignored.  The
21460               specified value must be an integer multiple of four and in the
21461               range 0-1020.
21462
21463           strict
21464               This parameter prevents mixed usage of multiple atomic models,
21465               even if they are compatible, and makes the compiler generate
21466               atomic sequences of the specified model only.
21467
21468       -mtas
21469           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice
21470           that depending on the particular hardware and software
21471           configuration this can degrade overall performance due to the
21472           operand cache line flushes that are implied by the "tas.b"
21473           instruction.  On multi-core SH4A processors the "tas.b" instruction
21474           must be used with caution since it can result in data corruption
21475           for certain cache configurations.
21476
21477       -mprefergot
21478           When generating position-independent code, emit function calls
21479           using the Global Offset Table instead of the Procedure Linkage
21480           Table.
21481
21482       -musermode
21483       -mno-usermode
21484           Don't allow (allow) the compiler generating privileged mode code.
21485           Specifying -musermode also implies -mno-inline-ic_invalidate if the
21486           inlined code would not work in user mode.  -musermode is the
21487           default when the target is "sh*-*-linux*".  If the target is SH1*
21488           or SH2* -musermode has no effect, since there is no user mode.
21489
21490       -multcost=number
21491           Set the cost to assume for a multiply insn.
21492
21493       -mdiv=strategy
21494           Set the division strategy to be used for integer division
21495           operations.  strategy can be one of:
21496
21497           call-div1
21498               Calls a library function that uses the single-step division
21499               instruction "div1" to perform the operation.  Division by zero
21500               calculates an unspecified result and does not trap.  This is
21501               the default except for SH4, SH2A and SHcompact.
21502
21503           call-fp
21504               Calls a library function that performs the operation in double
21505               precision floating point.  Division by zero causes a floating-
21506               point exception.  This is the default for SHcompact with FPU.
21507               Specifying this for targets that do not have a double precision
21508               FPU defaults to "call-div1".
21509
21510           call-table
21511               Calls a library function that uses a lookup table for small
21512               divisors and the "div1" instruction with case distinction for
21513               larger divisors.  Division by zero calculates an unspecified
21514               result and does not trap.  This is the default for SH4.
21515               Specifying this for targets that do not have dynamic shift
21516               instructions defaults to "call-div1".
21517
21518           When a division strategy has not been specified the default
21519           strategy is selected based on the current target.  For SH2A the
21520           default strategy is to use the "divs" and "divu" instructions
21521           instead of library function calls.
21522
21523       -maccumulate-outgoing-args
21524           Reserve space once for outgoing arguments in the function prologue
21525           rather than around each call.  Generally beneficial for performance
21526           and size.  Also needed for unwinding to avoid changing the stack
21527           frame around conditional code.
21528
21529       -mdivsi3_libfunc=name
21530           Set the name of the library function used for 32-bit signed
21531           division to name.  This only affects the name used in the call
21532           division strategies, and the compiler still expects the same sets
21533           of input/output/clobbered registers as if this option were not
21534           present.
21535
21536       -mfixed-range=register-range
21537           Generate code treating the given register range as fixed registers.
21538           A fixed register is one that the register allocator can not use.
21539           This is useful when compiling kernel code.  A register range is
21540           specified as two registers separated by a dash.  Multiple register
21541           ranges can be specified separated by a comma.
21542
21543       -mbranch-cost=num
21544           Assume num to be the cost for a branch instruction.  Higher numbers
21545           make the compiler try to generate more branch-free code if
21546           possible.  If not specified the value is selected depending on the
21547           processor type that is being compiled for.
21548
21549       -mzdcbranch
21550       -mno-zdcbranch
21551           Assume (do not assume) that zero displacement conditional branch
21552           instructions "bt" and "bf" are fast.  If -mzdcbranch is specified,
21553           the compiler prefers zero displacement branch code sequences.  This
21554           is enabled by default when generating code for SH4 and SH4A.  It
21555           can be explicitly disabled by specifying -mno-zdcbranch.
21556
21557       -mcbranch-force-delay-slot
21558           Force the usage of delay slots for conditional branches, which
21559           stuffs the delay slot with a "nop" if a suitable instruction cannot
21560           be found.  By default this option is disabled.  It can be enabled
21561           to work around hardware bugs as found in the original SH7055.
21562
21563       -mfused-madd
21564       -mno-fused-madd
21565           Generate code that uses (does not use) the floating-point multiply
21566           and accumulate instructions.  These instructions are generated by
21567           default if hardware floating point is used.  The machine-dependent
21568           -mfused-madd option is now mapped to the machine-independent
21569           -ffp-contract=fast option, and -mno-fused-madd is mapped to
21570           -ffp-contract=off.
21571
21572       -mfsca
21573       -mno-fsca
21574           Allow or disallow the compiler to emit the "fsca" instruction for
21575           sine and cosine approximations.  The option -mfsca must be used in
21576           combination with -funsafe-math-optimizations.  It is enabled by
21577           default when generating code for SH4A.  Using -mno-fsca disables
21578           sine and cosine approximations even if -funsafe-math-optimizations
21579           is in effect.
21580
21581       -mfsrra
21582       -mno-fsrra
21583           Allow or disallow the compiler to emit the "fsrra" instruction for
21584           reciprocal square root approximations.  The option -mfsrra must be
21585           used in combination with -funsafe-math-optimizations and
21586           -ffinite-math-only.  It is enabled by default when generating code
21587           for SH4A.  Using -mno-fsrra disables reciprocal square root
21588           approximations even if -funsafe-math-optimizations and
21589           -ffinite-math-only are in effect.
21590
21591       -mpretend-cmove
21592           Prefer zero-displacement conditional branches for conditional move
21593           instruction patterns.  This can result in faster code on the SH4
21594           processor.
21595
21596       -mfdpic
21597           Generate code using the FDPIC ABI.
21598
21599   Solaris 2 Options
21600       These -m options are supported on Solaris 2:
21601
21602       -mclear-hwcap
21603           -mclear-hwcap tells the compiler to remove the hardware
21604           capabilities generated by the Solaris assembler.  This is only
21605           necessary when object files use ISA extensions not supported by the
21606           current machine, but check at runtime whether or not to use them.
21607
21608       -mimpure-text
21609           -mimpure-text, used in addition to -shared, tells the compiler to
21610           not pass -z text to the linker when linking a shared object.  Using
21611           this option, you can link position-dependent code into a shared
21612           object.
21613
21614           -mimpure-text suppresses the "relocations remain against
21615           allocatable but non-writable sections" linker error message.
21616           However, the necessary relocations trigger copy-on-write, and the
21617           shared object is not actually shared across processes.  Instead of
21618           using -mimpure-text, you should compile all source code with -fpic
21619           or -fPIC.
21620
21621       These switches are supported in addition to the above on Solaris 2:
21622
21623       -pthreads
21624           This is a synonym for -pthread.
21625
21626   SPARC Options
21627       These -m options are supported on the SPARC:
21628
21629       -mno-app-regs
21630       -mapp-regs
21631           Specify -mapp-regs to generate output using the global registers 2
21632           through 4, which the SPARC SVR4 ABI reserves for applications.
21633           Like the global register 1, each global register 2 through 4 is
21634           then treated as an allocable register that is clobbered by function
21635           calls.  This is the default.
21636
21637           To be fully SVR4 ABI-compliant at the cost of some performance
21638           loss, specify -mno-app-regs.  You should compile libraries and
21639           system software with this option.
21640
21641       -mflat
21642       -mno-flat
21643           With -mflat, the compiler does not generate save/restore
21644           instructions and uses a "flat" or single register window model.
21645           This model is compatible with the regular register window model.
21646           The local registers and the input registers (0--5) are still
21647           treated as "call-saved" registers and are saved on the stack as
21648           needed.
21649
21650           With -mno-flat (the default), the compiler generates save/restore
21651           instructions (except for leaf functions).  This is the normal
21652           operating mode.
21653
21654       -mfpu
21655       -mhard-float
21656           Generate output containing floating-point instructions.  This is
21657           the default.
21658
21659       -mno-fpu
21660       -msoft-float
21661           Generate output containing library calls for floating point.
21662           Warning: the requisite libraries are not available for all SPARC
21663           targets.  Normally the facilities of the machine's usual C compiler
21664           are used, but this cannot be done directly in cross-compilation.
21665           You must make your own arrangements to provide suitable library
21666           functions for cross-compilation.  The embedded targets sparc-*-aout
21667           and sparclite-*-* do provide software floating-point support.
21668
21669           -msoft-float changes the calling convention in the output file;
21670           therefore, it is only useful if you compile all of a program with
21671           this option.  In particular, you need to compile libgcc.a, the
21672           library that comes with GCC, with -msoft-float in order for this to
21673           work.
21674
21675       -mhard-quad-float
21676           Generate output containing quad-word (long double) floating-point
21677           instructions.
21678
21679       -msoft-quad-float
21680           Generate output containing library calls for quad-word (long
21681           double) floating-point instructions.  The functions called are
21682           those specified in the SPARC ABI.  This is the default.
21683
21684           As of this writing, there are no SPARC implementations that have
21685           hardware support for the quad-word floating-point instructions.
21686           They all invoke a trap handler for one of these instructions, and
21687           then the trap handler emulates the effect of the instruction.
21688           Because of the trap handler overhead, this is much slower than
21689           calling the ABI library routines.  Thus the -msoft-quad-float
21690           option is the default.
21691
21692       -mno-unaligned-doubles
21693       -munaligned-doubles
21694           Assume that doubles have 8-byte alignment.  This is the default.
21695
21696           With -munaligned-doubles, GCC assumes that doubles have 8-byte
21697           alignment only if they are contained in another type, or if they
21698           have an absolute address.  Otherwise, it assumes they have 4-byte
21699           alignment.  Specifying this option avoids some rare compatibility
21700           problems with code generated by other compilers.  It is not the
21701           default because it results in a performance loss, especially for
21702           floating-point code.
21703
21704       -muser-mode
21705       -mno-user-mode
21706           Do not generate code that can only run in supervisor mode.  This is
21707           relevant only for the "casa" instruction emitted for the LEON3
21708           processor.  This is the default.
21709
21710       -mfaster-structs
21711       -mno-faster-structs
21712           With -mfaster-structs, the compiler assumes that structures should
21713           have 8-byte alignment.  This enables the use of pairs of "ldd" and
21714           "std" instructions for copies in structure assignment, in place of
21715           twice as many "ld" and "st" pairs.  However, the use of this
21716           changed alignment directly violates the SPARC ABI.  Thus, it's
21717           intended only for use on targets where the developer acknowledges
21718           that their resulting code is not directly in line with the rules of
21719           the ABI.
21720
21721       -mstd-struct-return
21722       -mno-std-struct-return
21723           With -mstd-struct-return, the compiler generates checking code in
21724           functions returning structures or unions to detect size mismatches
21725           between the two sides of function calls, as per the 32-bit ABI.
21726
21727           The default is -mno-std-struct-return.  This option has no effect
21728           in 64-bit mode.
21729
21730       -mlra
21731       -mno-lra
21732           Enable Local Register Allocation.  This is the default for SPARC
21733           since GCC 7 so -mno-lra needs to be passed to get old Reload.
21734
21735       -mcpu=cpu_type
21736           Set the instruction set, register set, and instruction scheduling
21737           parameters for machine type cpu_type.  Supported values for
21738           cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3,
21739           leon3v7, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9,
21740           ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
21741           niagara7 and m8.
21742
21743           Native Solaris and GNU/Linux toolchains also support the value
21744           native, which selects the best architecture option for the host
21745           processor.  -mcpu=native has no effect if GCC does not recognize
21746           the processor.
21747
21748           Default instruction scheduling parameters are used for values that
21749           select an architecture and not an implementation.  These are v7,
21750           v8, sparclite, sparclet, v9.
21751
21752           Here is a list of each supported architecture and their supported
21753           implementations.
21754
21755           v7  cypress, leon3v7
21756
21757           v8  supersparc, hypersparc, leon, leon3
21758
21759           sparclite
21760               f930, f934, sparclite86x
21761
21762           sparclet
21763               tsc701
21764
21765           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
21766               niagara7, m8
21767
21768           By default (unless configured otherwise), GCC generates code for
21769           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
21770           compiler additionally optimizes it for the Cypress CY7C602 chip, as
21771           used in the SPARCStation/SPARCServer 3xx series.  This is also
21772           appropriate for the older SPARCStation 1, 2, IPX etc.
21773
21774           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
21775           architecture.  The only difference from V7 code is that the
21776           compiler emits the integer multiply and integer divide instructions
21777           which exist in SPARC-V8 but not in SPARC-V7.  With
21778           -mcpu=supersparc, the compiler additionally optimizes it for the
21779           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
21780           series.
21781
21782           With -mcpu=sparclite, GCC generates code for the SPARClite variant
21783           of the SPARC architecture.  This adds the integer multiply, integer
21784           divide step and scan ("ffs") instructions which exist in SPARClite
21785           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
21786           optimizes it for the Fujitsu MB86930 chip, which is the original
21787           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
21788           optimizes it for the Fujitsu MB86934 chip, which is the more recent
21789           SPARClite with FPU.
21790
21791           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
21792           the SPARC architecture.  This adds the integer multiply,
21793           multiply/accumulate, integer divide step and scan ("ffs")
21794           instructions which exist in SPARClet but not in SPARC-V7.  With
21795           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
21796           SPARClet chip.
21797
21798           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
21799           architecture.  This adds 64-bit integer and floating-point move
21800           instructions, 3 additional floating-point condition code registers
21801           and conditional move instructions.  With -mcpu=ultrasparc, the
21802           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
21803           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
21804           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
21805           -mcpu=niagara, the compiler additionally optimizes it for Sun
21806           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
21807           additionally optimizes it for Sun UltraSPARC T2 chips. With
21808           -mcpu=niagara3, the compiler additionally optimizes it for Sun
21809           UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler
21810           additionally optimizes it for Sun UltraSPARC T4 chips.  With
21811           -mcpu=niagara7, the compiler additionally optimizes it for Oracle
21812           SPARC M7 chips.  With -mcpu=m8, the compiler additionally optimizes
21813           it for Oracle M8 chips.
21814
21815       -mtune=cpu_type
21816           Set the instruction scheduling parameters for machine type
21817           cpu_type, but do not set the instruction set or register set that
21818           the option -mcpu=cpu_type does.
21819
21820           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
21821           but the only useful values are those that select a particular CPU
21822           implementation.  Those are cypress, supersparc, hypersparc, leon,
21823           leon3, leon3v7, f930, f934, sparclite86x, tsc701, ultrasparc,
21824           ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7 and
21825           m8.  With native Solaris and GNU/Linux toolchains, native can also
21826           be used.
21827
21828       -mv8plus
21829       -mno-v8plus
21830           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
21831           difference from the V8 ABI is that the global and out registers are
21832           considered 64 bits wide.  This is enabled by default on Solaris in
21833           32-bit mode for all SPARC-V9 processors.
21834
21835       -mvis
21836       -mno-vis
21837           With -mvis, GCC generates code that takes advantage of the
21838           UltraSPARC Visual Instruction Set extensions.  The default is
21839           -mno-vis.
21840
21841       -mvis2
21842       -mno-vis2
21843           With -mvis2, GCC generates code that takes advantage of version 2.0
21844           of the UltraSPARC Visual Instruction Set extensions.  The default
21845           is -mvis2 when targeting a cpu that supports such instructions,
21846           such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.
21847
21848       -mvis3
21849       -mno-vis3
21850           With -mvis3, GCC generates code that takes advantage of version 3.0
21851           of the UltraSPARC Visual Instruction Set extensions.  The default
21852           is -mvis3 when targeting a cpu that supports such instructions,
21853           such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and
21854           -mvis.
21855
21856       -mvis4
21857       -mno-vis4
21858           With -mvis4, GCC generates code that takes advantage of version 4.0
21859           of the UltraSPARC Visual Instruction Set extensions.  The default
21860           is -mvis4 when targeting a cpu that supports such instructions,
21861           such as niagara-7 and later.  Setting -mvis4 also sets -mvis3,
21862           -mvis2 and -mvis.
21863
21864       -mvis4b
21865       -mno-vis4b
21866           With -mvis4b, GCC generates code that takes advantage of version
21867           4.0 of the UltraSPARC Visual Instruction Set extensions, plus the
21868           additional VIS instructions introduced in the Oracle SPARC
21869           Architecture 2017.  The default is -mvis4b when targeting a cpu
21870           that supports such instructions, such as m8 and later.  Setting
21871           -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis.
21872
21873       -mcbcond
21874       -mno-cbcond
21875           With -mcbcond, GCC generates code that takes advantage of the
21876           UltraSPARC Compare-and-Branch-on-Condition instructions.  The
21877           default is -mcbcond when targeting a CPU that supports such
21878           instructions, such as Niagara-4 and later.
21879
21880       -mfmaf
21881       -mno-fmaf
21882           With -mfmaf, GCC generates code that takes advantage of the
21883           UltraSPARC Fused Multiply-Add Floating-point instructions.  The
21884           default is -mfmaf when targeting a CPU that supports such
21885           instructions, such as Niagara-3 and later.
21886
21887       -mfsmuld
21888       -mno-fsmuld
21889           With -mfsmuld, GCC generates code that takes advantage of the
21890           Floating-point Multiply Single to Double (FsMULd) instruction.  The
21891           default is -mfsmuld when targeting a CPU supporting the
21892           architecture versions V8 or V9 with FPU except -mcpu=leon.
21893
21894       -mpopc
21895       -mno-popc
21896           With -mpopc, GCC generates code that takes advantage of the
21897           UltraSPARC Population Count instruction.  The default is -mpopc
21898           when targeting a CPU that supports such an instruction, such as
21899           Niagara-2 and later.
21900
21901       -msubxc
21902       -mno-subxc
21903           With -msubxc, GCC generates code that takes advantage of the
21904           UltraSPARC Subtract-Extended-with-Carry instruction.  The default
21905           is -msubxc when targeting a CPU that supports such an instruction,
21906           such as Niagara-7 and later.
21907
21908       -mfix-at697f
21909           Enable the documented workaround for the single erratum of the
21910           Atmel AT697F processor (which corresponds to erratum #13 of the
21911           AT697E processor).
21912
21913       -mfix-ut699
21914           Enable the documented workarounds for the floating-point errata and
21915           the data cache nullify errata of the UT699 processor.
21916
21917       -mfix-ut700
21918           Enable the documented workaround for the back-to-back store errata
21919           of the UT699E/UT700 processor.
21920
21921       -mfix-gr712rc
21922           Enable the documented workaround for the back-to-back store errata
21923           of the GR712RC processor.
21924
21925       These -m options are supported in addition to the above on SPARC-V9
21926       processors in 64-bit environments:
21927
21928       -m32
21929       -m64
21930           Generate code for a 32-bit or 64-bit environment.  The 32-bit
21931           environment sets int, long and pointer to 32 bits.  The 64-bit
21932           environment sets int to 32 bits and long and pointer to 64 bits.
21933
21934       -mcmodel=which
21935           Set the code model to one of
21936
21937           medlow
21938               The Medium/Low code model: 64-bit addresses, programs must be
21939               linked in the low 32 bits of memory.  Programs can be
21940               statically or dynamically linked.
21941
21942           medmid
21943               The Medium/Middle code model: 64-bit addresses, programs must
21944               be linked in the low 44 bits of memory, the text and data
21945               segments must be less than 2GB in size and the data segment
21946               must be located within 2GB of the text segment.
21947
21948           medany
21949               The Medium/Anywhere code model: 64-bit addresses, programs may
21950               be linked anywhere in memory, the text and data segments must
21951               be less than 2GB in size and the data segment must be located
21952               within 2GB of the text segment.
21953
21954           embmedany
21955               The Medium/Anywhere code model for embedded systems: 64-bit
21956               addresses, the text and data segments must be less than 2GB in
21957               size, both starting anywhere in memory (determined at link
21958               time).  The global register %g4 points to the base of the data
21959               segment.  Programs are statically linked and PIC is not
21960               supported.
21961
21962       -mmemory-model=mem-model
21963           Set the memory model in force on the processor to one of
21964
21965           default
21966               The default memory model for the processor and operating
21967               system.
21968
21969           rmo Relaxed Memory Order
21970
21971           pso Partial Store Order
21972
21973           tso Total Store Order
21974
21975           sc  Sequential Consistency
21976
21977           These memory models are formally defined in Appendix D of the
21978           SPARC-V9 architecture manual, as set in the processor's "PSTATE.MM"
21979           field.
21980
21981       -mstack-bias
21982       -mno-stack-bias
21983           With -mstack-bias, GCC assumes that the stack pointer, and frame
21984           pointer if present, are offset by -2047 which must be added back
21985           when making stack frame references.  This is the default in 64-bit
21986           mode.  Otherwise, assume no such offset is present.
21987
21988   SPU Options
21989       These -m options are supported on the SPU:
21990
21991       -mwarn-reloc
21992       -merror-reloc
21993           The loader for SPU does not handle dynamic relocations.  By
21994           default, GCC gives an error when it generates code that requires a
21995           dynamic relocation.  -mno-error-reloc disables the error,
21996           -mwarn-reloc generates a warning instead.
21997
21998       -msafe-dma
21999       -munsafe-dma
22000           Instructions that initiate or test completion of DMA must not be
22001           reordered with respect to loads and stores of the memory that is
22002           being accessed.  With -munsafe-dma you must use the "volatile"
22003           keyword to protect memory accesses, but that can lead to
22004           inefficient code in places where the memory is known to not change.
22005           Rather than mark the memory as volatile, you can use -msafe-dma to
22006           tell the compiler to treat the DMA instructions as potentially
22007           affecting all memory.
22008
22009       -mbranch-hints
22010           By default, GCC generates a branch hint instruction to avoid
22011           pipeline stalls for always-taken or probably-taken branches.  A
22012           hint is not generated closer than 8 instructions away from its
22013           branch.  There is little reason to disable them, except for
22014           debugging purposes, or to make an object a little bit smaller.
22015
22016       -msmall-mem
22017       -mlarge-mem
22018           By default, GCC generates code assuming that addresses are never
22019           larger than 18 bits.  With -mlarge-mem code is generated that
22020           assumes a full 32-bit address.
22021
22022       -mstdmain
22023           By default, GCC links against startup code that assumes the SPU-
22024           style main function interface (which has an unconventional
22025           parameter list).  With -mstdmain, GCC links your program against
22026           startup code that assumes a C99-style interface to "main",
22027           including a local copy of "argv" strings.
22028
22029       -mfixed-range=register-range
22030           Generate code treating the given register range as fixed registers.
22031           A fixed register is one that the register allocator cannot use.
22032           This is useful when compiling kernel code.  A register range is
22033           specified as two registers separated by a dash.  Multiple register
22034           ranges can be specified separated by a comma.
22035
22036       -mea32
22037       -mea64
22038           Compile code assuming that pointers to the PPU address space
22039           accessed via the "__ea" named address space qualifier are either 32
22040           or 64 bits wide.  The default is 32 bits.  As this is an ABI-
22041           changing option, all object code in an executable must be compiled
22042           with the same setting.
22043
22044       -maddress-space-conversion
22045       -mno-address-space-conversion
22046           Allow/disallow treating the "__ea" address space as superset of the
22047           generic address space.  This enables explicit type casts between
22048           "__ea" and generic pointer as well as implicit conversions of
22049           generic pointers to "__ea" pointers.  The default is to allow
22050           address space pointer conversions.
22051
22052       -mcache-size=cache-size
22053           This option controls the version of libgcc that the compiler links
22054           to an executable and selects a software-managed cache for accessing
22055           variables in the "__ea" address space with a particular cache size.
22056           Possible options for cache-size are 8, 16, 32, 64 and 128.  The
22057           default cache size is 64KB.
22058
22059       -matomic-updates
22060       -mno-atomic-updates
22061           This option controls the version of libgcc that the compiler links
22062           to an executable and selects whether atomic updates to the
22063           software-managed cache of PPU-side variables are used.  If you use
22064           atomic updates, changes to a PPU variable from SPU code using the
22065           "__ea" named address space qualifier do not interfere with changes
22066           to other PPU variables residing in the same cache line from PPU
22067           code.  If you do not use atomic updates, such interference may
22068           occur; however, writing back cache lines is more efficient.  The
22069           default behavior is to use atomic updates.
22070
22071       -mdual-nops
22072       -mdual-nops=n
22073           By default, GCC inserts NOPs to increase dual issue when it expects
22074           it to increase performance.  n can be a value from 0 to 10.  A
22075           smaller n inserts fewer NOPs.  10 is the default, 0 is the same as
22076           -mno-dual-nops.  Disabled with -Os.
22077
22078       -mhint-max-nops=n
22079           Maximum number of NOPs to insert for a branch hint.  A branch hint
22080           must be at least 8 instructions away from the branch it is
22081           affecting.  GCC inserts up to n NOPs to enforce this, otherwise it
22082           does not generate the branch hint.
22083
22084       -mhint-max-distance=n
22085           The encoding of the branch hint instruction limits the hint to be
22086           within 256 instructions of the branch it is affecting.  By default,
22087           GCC makes sure it is within 125.
22088
22089       -msafe-hints
22090           Work around a hardware bug that causes the SPU to stall
22091           indefinitely.  By default, GCC inserts the "hbrp" instruction to
22092           make sure this stall won't happen.
22093
22094   Options for System V
22095       These additional options are available on System V Release 4 for
22096       compatibility with other compilers on those systems:
22097
22098       -G  Create a shared object.  It is recommended that -symbolic or
22099           -shared be used instead.
22100
22101       -Qy Identify the versions of each tool used by the compiler, in a
22102           ".ident" assembler directive in the output.
22103
22104       -Qn Refrain from adding ".ident" directives to the output file (this is
22105           the default).
22106
22107       -YP,dirs
22108           Search the directories dirs, and no others, for libraries specified
22109           with -l.
22110
22111       -Ym,dir
22112           Look in the directory dir to find the M4 preprocessor.  The
22113           assembler uses this option.
22114
22115   TILE-Gx Options
22116       These -m options are supported on the TILE-Gx:
22117
22118       -mcmodel=small
22119           Generate code for the small model.  The distance for direct calls
22120           is limited to 500M in either direction.  PC-relative addresses are
22121           32 bits.  Absolute addresses support the full address range.
22122
22123       -mcmodel=large
22124           Generate code for the large model.  There is no limitation on call
22125           distance, pc-relative addresses, or absolute addresses.
22126
22127       -mcpu=name
22128           Selects the type of CPU to be targeted.  Currently the only
22129           supported type is tilegx.
22130
22131       -m32
22132       -m64
22133           Generate code for a 32-bit or 64-bit environment.  The 32-bit
22134           environment sets int, long, and pointer to 32 bits.  The 64-bit
22135           environment sets int to 32 bits and long and pointer to 64 bits.
22136
22137       -mbig-endian
22138       -mlittle-endian
22139           Generate code in big/little endian mode, respectively.
22140
22141   TILEPro Options
22142       These -m options are supported on the TILEPro:
22143
22144       -mcpu=name
22145           Selects the type of CPU to be targeted.  Currently the only
22146           supported type is tilepro.
22147
22148       -m32
22149           Generate code for a 32-bit environment, which sets int, long, and
22150           pointer to 32 bits.  This is the only supported behavior so the
22151           flag is essentially ignored.
22152
22153   V850 Options
22154       These -m options are defined for V850 implementations:
22155
22156       -mlong-calls
22157       -mno-long-calls
22158           Treat all calls as being far away (near).  If calls are assumed to
22159           be far away, the compiler always loads the function's address into
22160           a register, and calls indirect through the pointer.
22161
22162       -mno-ep
22163       -mep
22164           Do not optimize (do optimize) basic blocks that use the same index
22165           pointer 4 or more times to copy pointer into the "ep" register, and
22166           use the shorter "sld" and "sst" instructions.  The -mep option is
22167           on by default if you optimize.
22168
22169       -mno-prolog-function
22170       -mprolog-function
22171           Do not use (do use) external functions to save and restore
22172           registers at the prologue and epilogue of a function.  The external
22173           functions are slower, but use less code space if more than one
22174           function saves the same number of registers.  The -mprolog-function
22175           option is on by default if you optimize.
22176
22177       -mspace
22178           Try to make the code as small as possible.  At present, this just
22179           turns on the -mep and -mprolog-function options.
22180
22181       -mtda=n
22182           Put static or global variables whose size is n bytes or less into
22183           the tiny data area that register "ep" points to.  The tiny data
22184           area can hold up to 256 bytes in total (128 bytes for byte
22185           references).
22186
22187       -msda=n
22188           Put static or global variables whose size is n bytes or less into
22189           the small data area that register "gp" points to.  The small data
22190           area can hold up to 64 kilobytes.
22191
22192       -mzda=n
22193           Put static or global variables whose size is n bytes or less into
22194           the first 32 kilobytes of memory.
22195
22196       -mv850
22197           Specify that the target processor is the V850.
22198
22199       -mv850e3v5
22200           Specify that the target processor is the V850E3V5.  The
22201           preprocessor constant "__v850e3v5__" is defined if this option is
22202           used.
22203
22204       -mv850e2v4
22205           Specify that the target processor is the V850E3V5.  This is an
22206           alias for the -mv850e3v5 option.
22207
22208       -mv850e2v3
22209           Specify that the target processor is the V850E2V3.  The
22210           preprocessor constant "__v850e2v3__" is defined if this option is
22211           used.
22212
22213       -mv850e2
22214           Specify that the target processor is the V850E2.  The preprocessor
22215           constant "__v850e2__" is defined if this option is used.
22216
22217       -mv850e1
22218           Specify that the target processor is the V850E1.  The preprocessor
22219           constants "__v850e1__" and "__v850e__" are defined if this option
22220           is used.
22221
22222       -mv850es
22223           Specify that the target processor is the V850ES.  This is an alias
22224           for the -mv850e1 option.
22225
22226       -mv850e
22227           Specify that the target processor is the V850E.  The preprocessor
22228           constant "__v850e__" is defined if this option is used.
22229
22230           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor
22231           -mv850e2v3 nor -mv850e3v5 are defined then a default target
22232           processor is chosen and the relevant __v850*__ preprocessor
22233           constant is defined.
22234
22235           The preprocessor constants "__v850" and "__v851__" are always
22236           defined, regardless of which processor variant is the target.
22237
22238       -mdisable-callt
22239       -mno-disable-callt
22240           This option suppresses generation of the "CALLT" instruction for
22241           the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
22242           v850 architecture.
22243
22244           This option is enabled by default when the RH850 ABI is in use (see
22245           -mrh850-abi), and disabled by default when the GCC ABI is in use.
22246           If "CALLT" instructions are being generated then the C preprocessor
22247           symbol "__V850_CALLT__" is defined.
22248
22249       -mrelax
22250       -mno-relax
22251           Pass on (or do not pass on) the -mrelax command-line option to the
22252           assembler.
22253
22254       -mlong-jumps
22255       -mno-long-jumps
22256           Disable (or re-enable) the generation of PC-relative jump
22257           instructions.
22258
22259       -msoft-float
22260       -mhard-float
22261           Disable (or re-enable) the generation of hardware floating point
22262           instructions.  This option is only significant when the target
22263           architecture is V850E2V3 or higher.  If hardware floating point
22264           instructions are being generated then the C preprocessor symbol
22265           "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is
22266           defined.
22267
22268       -mloop
22269           Enables the use of the e3v5 LOOP instruction.  The use of this
22270           instruction is not enabled by default when the e3v5 architecture is
22271           selected because its use is still experimental.
22272
22273       -mrh850-abi
22274       -mghs
22275           Enables support for the RH850 version of the V850 ABI.  This is the
22276           default.  With this version of the ABI the following rules apply:
22277
22278           *   Integer sized structures and unions are returned via a memory
22279               pointer rather than a register.
22280
22281           *   Large structures and unions (more than 8 bytes in size) are
22282               passed by value.
22283
22284           *   Functions are aligned to 16-bit boundaries.
22285
22286           *   The -m8byte-align command-line option is supported.
22287
22288           *   The -mdisable-callt command-line option is enabled by default.
22289               The -mno-disable-callt command-line option is not supported.
22290
22291           When this version of the ABI is enabled the C preprocessor symbol
22292           "__V850_RH850_ABI__" is defined.
22293
22294       -mgcc-abi
22295           Enables support for the old GCC version of the V850 ABI.  With this
22296           version of the ABI the following rules apply:
22297
22298           *   Integer sized structures and unions are returned in register
22299               "r10".
22300
22301           *   Large structures and unions (more than 8 bytes in size) are
22302               passed by reference.
22303
22304           *   Functions are aligned to 32-bit boundaries, unless optimizing
22305               for size.
22306
22307           *   The -m8byte-align command-line option is not supported.
22308
22309           *   The -mdisable-callt command-line option is supported but not
22310               enabled by default.
22311
22312           When this version of the ABI is enabled the C preprocessor symbol
22313           "__V850_GCC_ABI__" is defined.
22314
22315       -m8byte-align
22316       -mno-8byte-align
22317           Enables support for "double" and "long long" types to be aligned on
22318           8-byte boundaries.  The default is to restrict the alignment of all
22319           objects to at most 4-bytes.  When -m8byte-align is in effect the C
22320           preprocessor symbol "__V850_8BYTE_ALIGN__" is defined.
22321
22322       -mbig-switch
22323           Generate code suitable for big switch tables.  Use this option only
22324           if the assembler/linker complain about out of range branches within
22325           a switch table.
22326
22327       -mapp-regs
22328           This option causes r2 and r5 to be used in the code generated by
22329           the compiler.  This setting is the default.
22330
22331       -mno-app-regs
22332           This option causes r2 and r5 to be treated as fixed registers.
22333
22334   VAX Options
22335       These -m options are defined for the VAX:
22336
22337       -munix
22338           Do not output certain jump instructions ("aobleq" and so on) that
22339           the Unix assembler for the VAX cannot handle across long ranges.
22340
22341       -mgnu
22342           Do output those jump instructions, on the assumption that the GNU
22343           assembler is being used.
22344
22345       -mg Output code for G-format floating-point numbers instead of
22346           D-format.
22347
22348   Visium Options
22349       -mdebug
22350           A program which performs file I/O and is destined to run on an MCM
22351           target should be linked with this option.  It causes the libraries
22352           libc.a and libdebug.a to be linked.  The program should be run on
22353           the target under the control of the GDB remote debugging stub.
22354
22355       -msim
22356           A program which performs file I/O and is destined to run on the
22357           simulator should be linked with option.  This causes libraries
22358           libc.a and libsim.a to be linked.
22359
22360       -mfpu
22361       -mhard-float
22362           Generate code containing floating-point instructions.  This is the
22363           default.
22364
22365       -mno-fpu
22366       -msoft-float
22367           Generate code containing library calls for floating-point.
22368
22369           -msoft-float changes the calling convention in the output file;
22370           therefore, it is only useful if you compile all of a program with
22371           this option.  In particular, you need to compile libgcc.a, the
22372           library that comes with GCC, with -msoft-float in order for this to
22373           work.
22374
22375       -mcpu=cpu_type
22376           Set the instruction set, register set, and instruction scheduling
22377           parameters for machine type cpu_type.  Supported values for
22378           cpu_type are mcm, gr5 and gr6.
22379
22380           mcm is a synonym of gr5 present for backward compatibility.
22381
22382           By default (unless configured otherwise), GCC generates code for
22383           the GR5 variant of the Visium architecture.
22384
22385           With -mcpu=gr6, GCC generates code for the GR6 variant of the
22386           Visium architecture.  The only difference from GR5 code is that the
22387           compiler will generate block move instructions.
22388
22389       -mtune=cpu_type
22390           Set the instruction scheduling parameters for machine type
22391           cpu_type, but do not set the instruction set or register set that
22392           the option -mcpu=cpu_type would.
22393
22394       -msv-mode
22395           Generate code for the supervisor mode, where there are no
22396           restrictions on the access to general registers.  This is the
22397           default.
22398
22399       -muser-mode
22400           Generate code for the user mode, where the access to some general
22401           registers is forbidden: on the GR5, registers r24 to r31 cannot be
22402           accessed in this mode; on the GR6, only registers r29 to r31 are
22403           affected.
22404
22405   VMS Options
22406       These -m options are defined for the VMS implementations:
22407
22408       -mvms-return-codes
22409           Return VMS condition codes from "main". The default is to return
22410           POSIX-style condition (e.g. error) codes.
22411
22412       -mdebug-main=prefix
22413           Flag the first routine whose name starts with prefix as the main
22414           routine for the debugger.
22415
22416       -mmalloc64
22417           Default to 64-bit memory allocation routines.
22418
22419       -mpointer-size=size
22420           Set the default size of pointers. Possible options for size are 32
22421           or short for 32 bit pointers, 64 or long for 64 bit pointers, and
22422           no for supporting only 32 bit pointers.  The later option disables
22423           "pragma pointer_size".
22424
22425   VxWorks Options
22426       The options in this section are defined for all VxWorks targets.
22427       Options specific to the target hardware are listed with the other
22428       options for that target.
22429
22430       -mrtp
22431           GCC can generate code for both VxWorks kernels and real time
22432           processes (RTPs).  This option switches from the former to the
22433           latter.  It also defines the preprocessor macro "__RTP__".
22434
22435       -non-static
22436           Link an RTP executable against shared libraries rather than static
22437           libraries.  The options -static and -shared can also be used for
22438           RTPs; -static is the default.
22439
22440       -Bstatic
22441       -Bdynamic
22442           These options are passed down to the linker.  They are defined for
22443           compatibility with Diab.
22444
22445       -Xbind-lazy
22446           Enable lazy binding of function calls.  This option is equivalent
22447           to -Wl,-z,now and is defined for compatibility with Diab.
22448
22449       -Xbind-now
22450           Disable lazy binding of function calls.  This option is the default
22451           and is defined for compatibility with Diab.
22452
22453   x86 Options
22454       These -m options are defined for the x86 family of computers.
22455
22456       -march=cpu-type
22457           Generate instructions for the machine type cpu-type.  In contrast
22458           to -mtune=cpu-type, which merely tunes the generated code for the
22459           specified cpu-type, -march=cpu-type allows GCC to generate code
22460           that may not run at all on processors other than the one indicated.
22461           Specifying -march=cpu-type implies -mtune=cpu-type.
22462
22463           The choices for cpu-type are:
22464
22465           native
22466               This selects the CPU to generate code for at compilation time
22467               by determining the processor type of the compiling machine.
22468               Using -march=native enables all instruction subsets supported
22469               by the local machine (hence the result might not run on
22470               different machines).  Using -mtune=native produces code
22471               optimized for the local machine under the constraints of the
22472               selected instruction set.
22473
22474           x86-64
22475               A generic CPU with 64-bit extensions.
22476
22477           i386
22478               Original Intel i386 CPU.
22479
22480           i486
22481               Intel i486 CPU.  (No scheduling is implemented for this chip.)
22482
22483           i586
22484           pentium
22485               Intel Pentium CPU with no MMX support.
22486
22487           lakemont
22488               Intel Lakemont MCU, based on Intel Pentium CPU.
22489
22490           pentium-mmx
22491               Intel Pentium MMX CPU, based on Pentium core with MMX
22492               instruction set support.
22493
22494           pentiumpro
22495               Intel Pentium Pro CPU.
22496
22497           i686
22498               When used with -march, the Pentium Pro instruction set is used,
22499               so the code runs on all i686 family chips.  When used with
22500               -mtune, it has the same meaning as generic.
22501
22502           pentium2
22503               Intel Pentium II CPU, based on Pentium Pro core with MMX
22504               instruction set support.
22505
22506           pentium3
22507           pentium3m
22508               Intel Pentium III CPU, based on Pentium Pro core with MMX and
22509               SSE instruction set support.
22510
22511           pentium-m
22512               Intel Pentium M; low-power version of Intel Pentium III CPU
22513               with MMX, SSE and SSE2 instruction set support.  Used by
22514               Centrino notebooks.
22515
22516           pentium4
22517           pentium4m
22518               Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set
22519               support.
22520
22521           prescott
22522               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and
22523               SSE3 instruction set support.
22524
22525           nocona
22526               Improved version of Intel Pentium 4 CPU with 64-bit extensions,
22527               MMX, SSE, SSE2 and SSE3 instruction set support.
22528
22529           core2
22530               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
22531               and SSSE3 instruction set support.
22532
22533           nehalem
22534               Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
22535               SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support.
22536
22537           westmere
22538               Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2,
22539               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction
22540               set support.
22541
22542           sandybridge
22543               Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
22544               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL
22545               instruction set support.
22546
22547           ivybridge
22548               Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2,
22549               SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL,
22550               FSGSBASE, RDRND and F16C instruction set support.
22551
22552           haswell
22553               Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE,
22554               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
22555               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction
22556               set support.
22557
22558           broadwell
22559               Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE,
22560               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
22561               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX and
22562               PREFETCHW instruction set support.
22563
22564           skylake
22565               Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE,
22566               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
22567               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
22568               PREFETCHW, CLFLUSHOPT, XSAVEC and XSAVES instruction set
22569               support.
22570
22571           bonnell
22572               Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE,
22573               SSE2, SSE3 and SSSE3 instruction set support.
22574
22575           silvermont
22576               Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE,
22577               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and
22578               RDRND instruction set support.
22579
22580           knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX,
22581               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
22582               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
22583               PREFETCHW, AVX512F, AVX512PF, AVX512ER and AVX512CD instruction
22584               set support.
22585
22586           knm Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE,
22587               SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES,
22588               PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
22589               PREFETCHW, AVX512F, AVX512PF, AVX512ER, AVX512CD, AVX5124VNNIW,
22590               AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support.
22591
22592           skylake-avx512
22593               Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,
22594               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
22595               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
22596               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,
22597               AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set
22598               support.
22599
22600           cannonlake
22601               Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX,
22602               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
22603               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
22604               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
22605               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA and
22606               UMIP instruction set support.
22607
22608           icelake-client
22609               Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,
22610               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
22611               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
22612               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
22613               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
22614               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
22615               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set
22616               support.
22617
22618           icelake-server
22619               Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,
22620               SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2,
22621               AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED,
22622               ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL,
22623               AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI, AVX512IFMA, SHA,
22624               CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
22625               AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG and
22626               WBNOINVD instruction set support.
22627
22628           k6  AMD K6 CPU with MMX instruction set support.
22629
22630           k6-2
22631           k6-3
22632               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
22633               set support.
22634
22635           athlon
22636           athlon-tbird
22637               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
22638               prefetch instructions support.
22639
22640           athlon-4
22641           athlon-xp
22642           athlon-mp
22643               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
22644               full SSE instruction set support.
22645
22646           k8
22647           opteron
22648           athlon64
22649           athlon-fx
22650               Processors based on the AMD K8 core with x86-64 instruction set
22651               support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
22652               processors.  (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
22653               3DNow! and 64-bit instruction set extensions.)
22654
22655           k8-sse3
22656           opteron-sse3
22657           athlon64-sse3
22658               Improved versions of AMD K8 cores with SSE3 instruction set
22659               support.
22660
22661           amdfam10
22662           barcelona
22663               CPUs based on AMD Family 10h cores with x86-64 instruction set
22664               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
22665               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
22666
22667           bdver1
22668               CPUs based on AMD Family 15h cores with x86-64 instruction set
22669               support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL,
22670               CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
22671               and 64-bit instruction set extensions.)
22672
22673           bdver2
22674               AMD Family 15h core based CPUs with x86-64 instruction set
22675               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP,
22676               LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
22677               SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
22678
22679           bdver3
22680               AMD Family 15h core based CPUs with x86-64 instruction set
22681               support.  (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE,
22682               AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
22683               SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
22684               extensions.
22685
22686           bdver4
22687               AMD Family 15h core based CPUs with x86-64 instruction set
22688               support.  (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4,
22689               FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCL_MUL, CX16, MOVBE, MMX,
22690               SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit
22691               instruction set extensions.
22692
22693           znver1
22694               AMD Family 17h core based CPUs with x86-64 instruction set
22695               support.  (This supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX,
22696               AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCL_MUL, CX16,
22697               MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM,
22698               XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit instruction set
22699               extensions.
22700
22701           btver1
22702               CPUs based on AMD Family 14h cores with x86-64 instruction set
22703               support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
22704               CX16, ABM and 64-bit instruction set extensions.)
22705
22706           btver2
22707               CPUs based on AMD Family 16h cores with x86-64 instruction set
22708               support. This includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES,
22709               SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
22710               and 64-bit instruction set extensions.
22711
22712           winchip-c6
22713               IDT WinChip C6 CPU, dealt in same way as i486 with additional
22714               MMX instruction set support.
22715
22716           winchip2
22717               IDT WinChip 2 CPU, dealt in same way as i486 with additional
22718               MMX and 3DNow!  instruction set support.
22719
22720           c3  VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
22721               scheduling is implemented for this chip.)
22722
22723           c3-2
22724               VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
22725               support.  (No scheduling is implemented for this chip.)
22726
22727           c7  VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction
22728               set support.  (No scheduling is implemented for this chip.)
22729
22730           samuel-2
22731               VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set
22732               support.  (No scheduling is implemented for this chip.)
22733
22734           nehemiah
22735               VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
22736               (No scheduling is implemented for this chip.)
22737
22738           esther
22739               VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction
22740               set support.  (No scheduling is implemented for this chip.)
22741
22742           eden-x2
22743               VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3
22744               instruction set support.  (No scheduling is implemented for
22745               this chip.)
22746
22747           eden-x4
22748               VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3,
22749               SSE4.1, SSE4.2, AVX and AVX2 instruction set support.  (No
22750               scheduling is implemented for this chip.)
22751
22752           nano
22753               Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and
22754               SSSE3 instruction set support.  (No scheduling is implemented
22755               for this chip.)
22756
22757           nano-1000
22758               VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
22759               instruction set support.  (No scheduling is implemented for
22760               this chip.)
22761
22762           nano-2000
22763               VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
22764               instruction set support.  (No scheduling is implemented for
22765               this chip.)
22766
22767           nano-3000
22768               VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and
22769               SSE4.1 instruction set support.  (No scheduling is implemented
22770               for this chip.)
22771
22772           nano-x2
22773               VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
22774               and SSE4.1 instruction set support.  (No scheduling is
22775               implemented for this chip.)
22776
22777           nano-x4
22778               VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3
22779               and SSE4.1 instruction set support.  (No scheduling is
22780               implemented for this chip.)
22781
22782           geode
22783               AMD Geode embedded processor with MMX and 3DNow! instruction
22784               set support.
22785
22786       -mtune=cpu-type
22787           Tune to cpu-type everything applicable about the generated code,
22788           except for the ABI and the set of available instructions.  While
22789           picking a specific cpu-type schedules things appropriately for that
22790           particular chip, the compiler does not generate any code that
22791           cannot run on the default machine type unless you use a -march=cpu-
22792           type option.  For example, if GCC is configured for
22793           i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned
22794           for Pentium 4 but still runs on i686 machines.
22795
22796           The choices for cpu-type are the same as for -march.  In addition,
22797           -mtune supports 2 extra choices for cpu-type:
22798
22799           generic
22800               Produce code optimized for the most common IA32/AMD64/EM64T
22801               processors.  If you know the CPU on which your code will run,
22802               then you should use the corresponding -mtune or -march option
22803               instead of -mtune=generic.  But, if you do not know exactly
22804               what CPU users of your application will have, then you should
22805               use this option.
22806
22807               As new processors are deployed in the marketplace, the behavior
22808               of this option will change.  Therefore, if you upgrade to a
22809               newer version of GCC, code generation controlled by this option
22810               will change to reflect the processors that are most common at
22811               the time that version of GCC is released.
22812
22813               There is no -march=generic option because -march indicates the
22814               instruction set the compiler can use, and there is no generic
22815               instruction set applicable to all processors.  In contrast,
22816               -mtune indicates the processor (or, in this case, collection of
22817               processors) for which the code is optimized.
22818
22819           intel
22820               Produce code optimized for the most current Intel processors,
22821               which are Haswell and Silvermont for this version of GCC.  If
22822               you know the CPU on which your code will run, then you should
22823               use the corresponding -mtune or -march option instead of
22824               -mtune=intel.  But, if you want your application performs
22825               better on both Haswell and Silvermont, then you should use this
22826               option.
22827
22828               As new Intel processors are deployed in the marketplace, the
22829               behavior of this option will change.  Therefore, if you upgrade
22830               to a newer version of GCC, code generation controlled by this
22831               option will change to reflect the most current Intel processors
22832               at the time that version of GCC is released.
22833
22834               There is no -march=intel option because -march indicates the
22835               instruction set the compiler can use, and there is no common
22836               instruction set applicable to all processors.  In contrast,
22837               -mtune indicates the processor (or, in this case, collection of
22838               processors) for which the code is optimized.
22839
22840       -mcpu=cpu-type
22841           A deprecated synonym for -mtune.
22842
22843       -mfpmath=unit
22844           Generate floating-point arithmetic for selected unit unit.  The
22845           choices for unit are:
22846
22847           387 Use the standard 387 floating-point coprocessor present on the
22848               majority of chips and emulated otherwise.  Code compiled with
22849               this option runs almost everywhere.  The temporary results are
22850               computed in 80-bit precision instead of the precision specified
22851               by the type, resulting in slightly different results compared
22852               to most of other chips.  See -ffloat-store for more detailed
22853               description.
22854
22855               This is the default choice for non-Darwin x86-32 targets.
22856
22857           sse Use scalar floating-point instructions present in the SSE
22858               instruction set.  This instruction set is supported by Pentium
22859               III and newer chips, and in the AMD line by Athlon-4, Athlon XP
22860               and Athlon MP chips.  The earlier version of the SSE
22861               instruction set supports only single-precision arithmetic, thus
22862               the double and extended-precision arithmetic are still done
22863               using 387.  A later version, present only in Pentium 4 and AMD
22864               x86-64 chips, supports double-precision arithmetic too.
22865
22866               For the x86-32 compiler, you must use -march=cpu-type, -msse or
22867               -msse2 switches to enable SSE extensions and make this option
22868               effective.  For the x86-64 compiler, these extensions are
22869               enabled by default.
22870
22871               The resulting code should be considerably faster in the
22872               majority of cases and avoid the numerical instability problems
22873               of 387 code, but may break some existing code that expects
22874               temporaries to be 80 bits.
22875
22876               This is the default choice for the x86-64 compiler, Darwin
22877               x86-32 targets, and the default choice for x86-32 targets with
22878               the SSE2 instruction set when -ffast-math is enabled.
22879
22880           sse,387
22881           sse+387
22882           both
22883               Attempt to utilize both instruction sets at once.  This
22884               effectively doubles the amount of available registers, and on
22885               chips with separate execution units for 387 and SSE the
22886               execution resources too.  Use this option with care, as it is
22887               still experimental, because the GCC register allocator does not
22888               model separate functional units well, resulting in unstable
22889               performance.
22890
22891       -masm=dialect
22892           Output assembly instructions using selected dialect.  Also affects
22893           which dialect is used for basic "asm" and extended "asm". Supported
22894           choices (in dialect order) are att or intel. The default is att.
22895           Darwin does not support intel.
22896
22897       -mieee-fp
22898       -mno-ieee-fp
22899           Control whether or not the compiler uses IEEE floating-point
22900           comparisons.  These correctly handle the case where the result of a
22901           comparison is unordered.
22902
22903       -m80387
22904       -mhard-float
22905           Generate output containing 80387 instructions for floating point.
22906
22907       -mno-80387
22908       -msoft-float
22909           Generate output containing library calls for floating point.
22910
22911           Warning: the requisite libraries are not part of GCC.  Normally the
22912           facilities of the machine's usual C compiler are used, but this
22913           cannot be done directly in cross-compilation.  You must make your
22914           own arrangements to provide suitable library functions for cross-
22915           compilation.
22916
22917           On machines where a function returns floating-point results in the
22918           80387 register stack, some floating-point opcodes may be emitted
22919           even if -msoft-float is used.
22920
22921       -mno-fp-ret-in-387
22922           Do not use the FPU registers for return values of functions.
22923
22924           The usual calling convention has functions return values of types
22925           "float" and "double" in an FPU register, even if there is no FPU.
22926           The idea is that the operating system should emulate an FPU.
22927
22928           The option -mno-fp-ret-in-387 causes such values to be returned in
22929           ordinary CPU registers instead.
22930
22931       -mno-fancy-math-387
22932           Some 387 emulators do not support the "sin", "cos" and "sqrt"
22933           instructions for the 387.  Specify this option to avoid generating
22934           those instructions.  This option is the default on OpenBSD and
22935           NetBSD.  This option is overridden when -march indicates that the
22936           target CPU always has an FPU and so the instruction does not need
22937           emulation.  These instructions are not generated unless you also
22938           use the -funsafe-math-optimizations switch.
22939
22940       -malign-double
22941       -mno-align-double
22942           Control whether GCC aligns "double", "long double", and "long long"
22943           variables on a two-word boundary or a one-word boundary.  Aligning
22944           "double" variables on a two-word boundary produces code that runs
22945           somewhat faster on a Pentium at the expense of more memory.
22946
22947           On x86-64, -malign-double is enabled by default.
22948
22949           Warning: if you use the -malign-double switch, structures
22950           containing the above types are aligned differently than the
22951           published application binary interface specifications for the
22952           x86-32 and are not binary compatible with structures in code
22953           compiled without that switch.
22954
22955       -m96bit-long-double
22956       -m128bit-long-double
22957           These switches control the size of "long double" type.  The x86-32
22958           application binary interface specifies the size to be 96 bits, so
22959           -m96bit-long-double is the default in 32-bit mode.
22960
22961           Modern architectures (Pentium and newer) prefer "long double" to be
22962           aligned to an 8- or 16-byte boundary.  In arrays or structures
22963           conforming to the ABI, this is not possible.  So specifying
22964           -m128bit-long-double aligns "long double" to a 16-byte boundary by
22965           padding the "long double" with an additional 32-bit zero.
22966
22967           In the x86-64 compiler, -m128bit-long-double is the default choice
22968           as its ABI specifies that "long double" is aligned on 16-byte
22969           boundary.
22970
22971           Notice that neither of these options enable any extra precision
22972           over the x87 standard of 80 bits for a "long double".
22973
22974           Warning: if you override the default value for your target ABI,
22975           this changes the size of structures and arrays containing "long
22976           double" variables, as well as modifying the function calling
22977           convention for functions taking "long double".  Hence they are not
22978           binary-compatible with code compiled without that switch.
22979
22980       -mlong-double-64
22981       -mlong-double-80
22982       -mlong-double-128
22983           These switches control the size of "long double" type. A size of 64
22984           bits makes the "long double" type equivalent to the "double" type.
22985           This is the default for 32-bit Bionic C library.  A size of 128
22986           bits makes the "long double" type equivalent to the "__float128"
22987           type. This is the default for 64-bit Bionic C library.
22988
22989           Warning: if you override the default value for your target ABI,
22990           this changes the size of structures and arrays containing "long
22991           double" variables, as well as modifying the function calling
22992           convention for functions taking "long double".  Hence they are not
22993           binary-compatible with code compiled without that switch.
22994
22995       -malign-data=type
22996           Control how GCC aligns variables.  Supported values for type are
22997           compat uses increased alignment value compatible uses GCC 4.8 and
22998           earlier, abi uses alignment value as specified by the psABI, and
22999           cacheline uses increased alignment value to match the cache line
23000           size.  compat is the default.
23001
23002       -mlarge-data-threshold=threshold
23003           When -mcmodel=medium is specified, data objects larger than
23004           threshold are placed in the large data section.  This value must be
23005           the same across all objects linked into the binary, and defaults to
23006           65535.
23007
23008       -mrtd
23009           Use a different function-calling convention, in which functions
23010           that take a fixed number of arguments return with the "ret num"
23011           instruction, which pops their arguments while returning.  This
23012           saves one instruction in the caller since there is no need to pop
23013           the arguments there.
23014
23015           You can specify that an individual function is called with this
23016           calling sequence with the function attribute "stdcall".  You can
23017           also override the -mrtd option by using the function attribute
23018           "cdecl".
23019
23020           Warning: this calling convention is incompatible with the one
23021           normally used on Unix, so you cannot use it if you need to call
23022           libraries compiled with the Unix compiler.
23023
23024           Also, you must provide function prototypes for all functions that
23025           take variable numbers of arguments (including "printf"); otherwise
23026           incorrect code is generated for calls to those functions.
23027
23028           In addition, seriously incorrect code results if you call a
23029           function with too many arguments.  (Normally, extra arguments are
23030           harmlessly ignored.)
23031
23032       -mregparm=num
23033           Control how many registers are used to pass integer arguments.  By
23034           default, no registers are used to pass arguments, and at most 3
23035           registers can be used.  You can control this behavior for a
23036           specific function by using the function attribute "regparm".
23037
23038           Warning: if you use this switch, and num is nonzero, then you must
23039           build all modules with the same value, including any libraries.
23040           This includes the system libraries and startup modules.
23041
23042       -msseregparm
23043           Use SSE register passing conventions for float and double arguments
23044           and return values.  You can control this behavior for a specific
23045           function by using the function attribute "sseregparm".
23046
23047           Warning: if you use this switch then you must build all modules
23048           with the same value, including any libraries.  This includes the
23049           system libraries and startup modules.
23050
23051       -mvect8-ret-in-mem
23052           Return 8-byte vectors in memory instead of MMX registers.  This is
23053           the default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of
23054           the Sun Studio compilers until version 12.  Later compiler versions
23055           (starting with Studio 12 Update@tie{}1) follow the ABI used by
23056           other x86 targets, which is the default on Solaris@tie{}10 and
23057           later.  Only use this option if you need to remain compatible with
23058           existing code produced by those previous compiler versions or older
23059           versions of GCC.
23060
23061       -mpc32
23062       -mpc64
23063       -mpc80
23064           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
23065           -mpc32 is specified, the significands of results of floating-point
23066           operations are rounded to 24 bits (single precision); -mpc64 rounds
23067           the significands of results of floating-point operations to 53 bits
23068           (double precision) and -mpc80 rounds the significands of results of
23069           floating-point operations to 64 bits (extended double precision),
23070           which is the default.  When this option is used, floating-point
23071           operations in higher precisions are not available to the programmer
23072           without setting the FPU control word explicitly.
23073
23074           Setting the rounding of floating-point operations to less than the
23075           default 80 bits can speed some programs by 2% or more.  Note that
23076           some mathematical libraries assume that extended-precision (80-bit)
23077           floating-point operations are enabled by default; routines in such
23078           libraries could suffer significant loss of accuracy, typically
23079           through so-called "catastrophic cancellation", when this option is
23080           used to set the precision to less than extended precision.
23081
23082       -mstackrealign
23083           Realign the stack at entry.  On the x86, the -mstackrealign option
23084           generates an alternate prologue and epilogue that realigns the run-
23085           time stack if necessary.  This supports mixing legacy codes that
23086           keep 4-byte stack alignment with modern codes that keep 16-byte
23087           stack alignment for SSE compatibility.  See also the attribute
23088           "force_align_arg_pointer", applicable to individual functions.
23089
23090       -mpreferred-stack-boundary=num
23091           Attempt to keep the stack boundary aligned to a 2 raised to num
23092           byte boundary.  If -mpreferred-stack-boundary is not specified, the
23093           default is 4 (16 bytes or 128 bits).
23094
23095           Warning: When generating code for the x86-64 architecture with SSE
23096           extensions disabled, -mpreferred-stack-boundary=3 can be used to
23097           keep the stack boundary aligned to 8 byte boundary.  Since x86-64
23098           ABI require 16 byte stack alignment, this is ABI incompatible and
23099           intended to be used in controlled environment where stack space is
23100           important limitation.  This option leads to wrong code when
23101           functions compiled with 16 byte stack alignment (such as functions
23102           from a standard library) are called with misaligned stack.  In this
23103           case, SSE instructions may lead to misaligned memory access traps.
23104           In addition, variable arguments are handled incorrectly for 16 byte
23105           aligned objects (including x87 long double and __int128), leading
23106           to wrong results.  You must build all modules with
23107           -mpreferred-stack-boundary=3, including any libraries.  This
23108           includes the system libraries and startup modules.
23109
23110       -mincoming-stack-boundary=num
23111           Assume the incoming stack is aligned to a 2 raised to num byte
23112           boundary.  If -mincoming-stack-boundary is not specified, the one
23113           specified by -mpreferred-stack-boundary is used.
23114
23115           On Pentium and Pentium Pro, "double" and "long double" values
23116           should be aligned to an 8-byte boundary (see -malign-double) or
23117           suffer significant run time performance penalties.  On Pentium III,
23118           the Streaming SIMD Extension (SSE) data type "__m128" may not work
23119           properly if it is not 16-byte aligned.
23120
23121           To ensure proper alignment of this values on the stack, the stack
23122           boundary must be as aligned as that required by any value stored on
23123           the stack.  Further, every function must be generated such that it
23124           keeps the stack aligned.  Thus calling a function compiled with a
23125           higher preferred stack boundary from a function compiled with a
23126           lower preferred stack boundary most likely misaligns the stack.  It
23127           is recommended that libraries that use callbacks always use the
23128           default setting.
23129
23130           This extra alignment does consume extra stack space, and generally
23131           increases code size.  Code that is sensitive to stack space usage,
23132           such as embedded systems and operating system kernels, may want to
23133           reduce the preferred alignment to -mpreferred-stack-boundary=2.
23134
23135       -mmmx
23136       -msse
23137       -msse2
23138       -msse3
23139       -mssse3
23140       -msse4
23141       -msse4a
23142       -msse4.1
23143       -msse4.2
23144       -mavx
23145       -mavx2
23146       -mavx512f
23147       -mavx512pf
23148       -mavx512er
23149       -mavx512cd
23150       -mavx512vl
23151       -mavx512bw
23152       -mavx512dq
23153       -mavx512ifma
23154       -mavx512vbmi
23155       -msha
23156       -maes
23157       -mpclmul
23158       -mclflushopt
23159       -mfsgsbase
23160       -mrdrnd
23161       -mf16c
23162       -mfma
23163       -mpconfig
23164       -mwbnoinvd
23165       -mfma4
23166       -mprefetchwt1
23167       -mxop
23168       -mlwp
23169       -m3dnow
23170       -m3dnowa
23171       -mpopcnt
23172       -mabm
23173       -mbmi
23174       -mbmi2
23175       -mlzcnt
23176       -mfxsr
23177       -mxsave
23178       -mxsaveopt
23179       -mxsavec
23180       -mxsaves
23181       -mrtm
23182       -mtbm
23183       -mmpx
23184       -mmwaitx
23185       -mclzero
23186       -mpku
23187       -mavx512vbmi2
23188       -mgfni
23189       -mvaes
23190       -mvpclmulqdq
23191       -mavx512bitalg
23192       -mmovdiri
23193       -mmovdir64b
23194       -mavx512vpopcntdq
23195           These switches enable the use of instructions in the MMX, SSE,
23196           SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER,
23197           AVX512CD, SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A,
23198           FMA4, XOP, LWP, ABM, AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA,
23199           AVX512VBMI, BMI, BMI2, VAES, FXSR, XSAVE, XSAVEOPT, LZCNT, RTM,
23200           MPX, MWAITX, PKU, IBT, SHSTK, AVX512VBMI2, GFNI, VPCLMULQDQ,
23201           AVX512BITALG, MOVDIRI, MOVDIR64B, AVX512VPOPCNTDQ3DNow! or enhanced
23202           3DNow! extended instruction sets.  Each has a corresponding -mno-
23203           option to disable use of these instructions.
23204
23205           These extensions are also available as built-in functions: see x86
23206           Built-in Functions, for details of the functions enabled and
23207           disabled by these switches.
23208
23209           To generate SSE/SSE2 instructions automatically from floating-point
23210           code (as opposed to 387 instructions), see -mfpmath=sse.
23211
23212           GCC depresses SSEx instructions when -mavx is used. Instead, it
23213           generates new AVX instructions or AVX equivalence for all SSEx
23214           instructions when needed.
23215
23216           These options enable GCC to use these extended instructions in
23217           generated code, even without -mfpmath=sse.  Applications that
23218           perform run-time CPU detection must compile separate files for each
23219           supported architecture, using the appropriate flags.  In
23220           particular, the file containing the CPU detection code should be
23221           compiled without these options.
23222
23223       -mdump-tune-features
23224           This option instructs GCC to dump the names of the x86 performance
23225           tuning features and default settings. The names can be used in
23226           -mtune-ctrl=feature-list.
23227
23228       -mtune-ctrl=feature-list
23229           This option is used to do fine grain control of x86 code generation
23230           features.  feature-list is a comma separated list of feature names.
23231           See also -mdump-tune-features. When specified, the feature is
23232           turned on if it is not preceded with ^, otherwise, it is turned
23233           off.  -mtune-ctrl=feature-list is intended to be used by GCC
23234           developers. Using it may lead to code paths not covered by testing
23235           and can potentially result in compiler ICEs or runtime errors.
23236
23237       -mno-default
23238           This option instructs GCC to turn off all tunable features. See
23239           also -mtune-ctrl=feature-list and -mdump-tune-features.
23240
23241       -mcld
23242           This option instructs GCC to emit a "cld" instruction in the
23243           prologue of functions that use string instructions.  String
23244           instructions depend on the DF flag to select between autoincrement
23245           or autodecrement mode.  While the ABI specifies the DF flag to be
23246           cleared on function entry, some operating systems violate this
23247           specification by not clearing the DF flag in their exception
23248           dispatchers.  The exception handler can be invoked with the DF flag
23249           set, which leads to wrong direction mode when string instructions
23250           are used.  This option can be enabled by default on 32-bit x86
23251           targets by configuring GCC with the --enable-cld configure option.
23252           Generation of "cld" instructions can be suppressed with the
23253           -mno-cld compiler option in this case.
23254
23255       -mvzeroupper
23256           This option instructs GCC to emit a "vzeroupper" instruction before
23257           a transfer of control flow out of the function to minimize the AVX
23258           to SSE transition penalty as well as remove unnecessary "zeroupper"
23259           intrinsics.
23260
23261       -mprefer-avx128
23262           This option instructs GCC to use 128-bit AVX instructions instead
23263           of 256-bit AVX instructions in the auto-vectorizer.
23264
23265       -mprefer-vector-width=opt
23266           This option instructs GCC to use opt-bit vector width in
23267           instructions instead of default on the selected platform.
23268
23269           none
23270               No extra limitations applied to GCC other than defined by the
23271               selected platform.
23272
23273           128 Prefer 128-bit vector width for instructions.
23274
23275           256 Prefer 256-bit vector width for instructions.
23276
23277           512 Prefer 512-bit vector width for instructions.
23278
23279       -mcx16
23280           This option enables GCC to generate "CMPXCHG16B" instructions in
23281           64-bit code to implement compare-and-exchange operations on 16-byte
23282           aligned 128-bit objects.  This is useful for atomic updates of data
23283           structures exceeding one machine word in size.  The compiler uses
23284           this instruction to implement __sync Builtins.  However, for
23285           __atomic Builtins operating on 128-bit integers, a library call is
23286           always used.
23287
23288       -msahf
23289           This option enables generation of "SAHF" instructions in 64-bit
23290           code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
23291           the introduction of Pentium 4 G1 step in December 2005, lacked the
23292           "LAHF" and "SAHF" instructions which are supported by AMD64.  These
23293           are load and store instructions, respectively, for certain status
23294           flags.  In 64-bit mode, the "SAHF" instruction is used to optimize
23295           "fmod", "drem", and "remainder" built-in functions; see Other
23296           Builtins for details.
23297
23298       -mmovbe
23299           This option enables use of the "movbe" instruction to implement
23300           "__builtin_bswap32" and "__builtin_bswap64".
23301
23302       -mshstk
23303           The -mshstk option enables shadow stack built-in functions from x86
23304           Control-flow Enforcement Technology (CET).
23305
23306       -mcrc32
23307           This option enables built-in functions "__builtin_ia32_crc32qi",
23308           "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and
23309           "__builtin_ia32_crc32di" to generate the "crc32" machine
23310           instruction.
23311
23312       -mrecip
23313           This option enables use of "RCPSS" and "RSQRTSS" instructions (and
23314           their vectorized variants "RCPPS" and "RSQRTPS") with an additional
23315           Newton-Raphson step to increase precision instead of "DIVSS" and
23316           "SQRTSS" (and their vectorized variants) for single-precision
23317           floating-point arguments.  These instructions are generated only
23318           when -funsafe-math-optimizations is enabled together with
23319           -ffinite-math-only and -fno-trapping-math.  Note that while the
23320           throughput of the sequence is higher than the throughput of the
23321           non-reciprocal instruction, the precision of the sequence can be
23322           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
23323           0.99999994).
23324
23325           Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or
23326           "RSQRTPS") already with -ffast-math (or the above option
23327           combination), and doesn't need -mrecip.
23328
23329           Also note that GCC emits the above sequence with additional Newton-
23330           Raphson step for vectorized single-float division and vectorized
23331           "sqrtf(x)" already with -ffast-math (or the above option
23332           combination), and doesn't need -mrecip.
23333
23334       -mrecip=opt
23335           This option controls which reciprocal estimate instructions may be
23336           used.  opt is a comma-separated list of options, which may be
23337           preceded by a ! to invert the option:
23338
23339           all Enable all estimate instructions.
23340
23341           default
23342               Enable the default instructions, equivalent to -mrecip.
23343
23344           none
23345               Disable all estimate instructions, equivalent to -mno-recip.
23346
23347           div Enable the approximation for scalar division.
23348
23349           vec-div
23350               Enable the approximation for vectorized division.
23351
23352           sqrt
23353               Enable the approximation for scalar square root.
23354
23355           vec-sqrt
23356               Enable the approximation for vectorized square root.
23357
23358           So, for example, -mrecip=all,!sqrt enables all of the reciprocal
23359           approximations, except for square root.
23360
23361       -mveclibabi=type
23362           Specifies the ABI type to use for vectorizing intrinsics using an
23363           external library.  Supported values for type are svml for the Intel
23364           short vector math library and acml for the AMD math core library.
23365           To use this option, both -ftree-vectorize and
23366           -funsafe-math-optimizations have to be enabled, and an SVML or ACML
23367           ABI-compatible library must be specified at link time.
23368
23369           GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102",
23370           "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2",
23371           "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2", "vmldAsin2",
23372           "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4",
23373           "vmlsLn4", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4",
23374           "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4",
23375           "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4"
23376           and "vmlsAcos4" for corresponding function type when
23377           -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos",
23378           "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10",
23379           "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf",
23380           "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the
23381           corresponding function type when -mveclibabi=acml is used.
23382
23383       -mabi=name
23384           Generate code for the specified calling convention.  Permissible
23385           values are sysv for the ABI used on GNU/Linux and other systems,
23386           and ms for the Microsoft ABI.  The default is to use the Microsoft
23387           ABI when targeting Microsoft Windows and the SysV ABI on all other
23388           systems.  You can control this behavior for specific functions by
23389           using the function attributes "ms_abi" and "sysv_abi".
23390
23391       -mforce-indirect-call
23392           Force all calls to functions to be indirect. This is useful when
23393           using Intel Processor Trace where it generates more precise timing
23394           information for function calls.
23395
23396       -mcall-ms2sysv-xlogues
23397           Due to differences in 64-bit ABIs, any Microsoft ABI function that
23398           calls a System V ABI function must consider RSI, RDI and XMM6-15 as
23399           clobbered.  By default, the code for saving and restoring these
23400           registers is emitted inline, resulting in fairly lengthy prologues
23401           and epilogues.  Using -mcall-ms2sysv-xlogues emits prologues and
23402           epilogues that use stubs in the static portion of libgcc to perform
23403           these saves and restores, thus reducing function size at the cost
23404           of a few extra instructions.
23405
23406       -mtls-dialect=type
23407           Generate code to access thread-local storage using the gnu or gnu2
23408           conventions.  gnu is the conservative default; gnu2 is more
23409           efficient, but it may add compile- and run-time requirements that
23410           cannot be satisfied on all systems.
23411
23412       -mpush-args
23413       -mno-push-args
23414           Use PUSH operations to store outgoing parameters.  This method is
23415           shorter and usually equally fast as method using SUB/MOV operations
23416           and is enabled by default.  In some cases disabling it may improve
23417           performance because of improved scheduling and reduced
23418           dependencies.
23419
23420       -maccumulate-outgoing-args
23421           If enabled, the maximum amount of space required for outgoing
23422           arguments is computed in the function prologue.  This is faster on
23423           most modern CPUs because of reduced dependencies, improved
23424           scheduling and reduced stack usage when the preferred stack
23425           boundary is not equal to 2.  The drawback is a notable increase in
23426           code size.  This switch implies -mno-push-args.
23427
23428       -mthreads
23429           Support thread-safe exception handling on MinGW.  Programs that
23430           rely on thread-safe exception handling must compile and link all
23431           code with the -mthreads option.  When compiling, -mthreads defines
23432           -D_MT; when linking, it links in a special thread helper library
23433           -lmingwthrd which cleans up per-thread exception-handling data.
23434
23435       -mms-bitfields
23436       -mno-ms-bitfields
23437           Enable/disable bit-field layout compatible with the native
23438           Microsoft Windows compiler.
23439
23440           If "packed" is used on a structure, or if bit-fields are used, it
23441           may be that the Microsoft ABI lays out the structure differently
23442           than the way GCC normally does.  Particularly when moving packed
23443           data between functions compiled with GCC and the native Microsoft
23444           compiler (either via function call or as data in a file), it may be
23445           necessary to access either format.
23446
23447           This option is enabled by default for Microsoft Windows targets.
23448           This behavior can also be controlled locally by use of variable or
23449           type attributes.  For more information, see x86 Variable Attributes
23450           and x86 Type Attributes.
23451
23452           The Microsoft structure layout algorithm is fairly simple with the
23453           exception of the bit-field packing.  The padding and alignment of
23454           members of structures and whether a bit-field can straddle a
23455           storage-unit boundary are determine by these rules:
23456
23457           1. Structure members are stored sequentially in the order in which
23458           they are
23459               declared: the first member has the lowest memory address and
23460               the last member the highest.
23461
23462           2. Every data object has an alignment requirement.  The alignment
23463           requirement
23464               for all data except structures, unions, and arrays is either
23465               the size of the object or the current packing size (specified
23466               with either the "aligned" attribute or the "pack" pragma),
23467               whichever is less.  For structures, unions, and arrays, the
23468               alignment requirement is the largest alignment requirement of
23469               its members.  Every object is allocated an offset so that:
23470
23471                       offset % alignment_requirement == 0
23472
23473           3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte
23474           allocation
23475               unit if the integral types are the same size and if the next
23476               bit-field fits into the current allocation unit without
23477               crossing the boundary imposed by the common alignment
23478               requirements of the bit-fields.
23479
23480           MSVC interprets zero-length bit-fields in the following ways:
23481
23482           1. If a zero-length bit-field is inserted between two bit-fields
23483           that
23484               are normally coalesced, the bit-fields are not coalesced.
23485
23486               For example:
23487
23488                       struct
23489                        {
23490                          unsigned long bf_1 : 12;
23491                          unsigned long : 0;
23492                          unsigned long bf_2 : 12;
23493                        } t1;
23494
23495               The size of "t1" is 8 bytes with the zero-length bit-field.  If
23496               the zero-length bit-field were removed, "t1"'s size would be 4
23497               bytes.
23498
23499           2. If a zero-length bit-field is inserted after a bit-field, "foo",
23500           and the
23501               alignment of the zero-length bit-field is greater than the
23502               member that follows it, "bar", "bar" is aligned as the type of
23503               the zero-length bit-field.
23504
23505               For example:
23506
23507                       struct
23508                        {
23509                          char foo : 4;
23510                          short : 0;
23511                          char bar;
23512                        } t2;
23513
23514                       struct
23515                        {
23516                          char foo : 4;
23517                          short : 0;
23518                          double bar;
23519                        } t3;
23520
23521               For "t2", "bar" is placed at offset 2, rather than offset 1.
23522               Accordingly, the size of "t2" is 4.  For "t3", the zero-length
23523               bit-field does not affect the alignment of "bar" or, as a
23524               result, the size of the structure.
23525
23526               Taking this into account, it is important to note the
23527               following:
23528
23529               1. If a zero-length bit-field follows a normal bit-field, the
23530               type of the
23531                   zero-length bit-field may affect the alignment of the
23532                   structure as whole. For example, "t2" has a size of 4
23533                   bytes, since the zero-length bit-field follows a normal
23534                   bit-field, and is of type short.
23535
23536               2. Even if a zero-length bit-field is not followed by a normal
23537               bit-field, it may
23538                   still affect the alignment of the structure:
23539
23540                           struct
23541                            {
23542                              char foo : 6;
23543                              long : 0;
23544                            } t4;
23545
23546                   Here, "t4" takes up 4 bytes.
23547
23548           3. Zero-length bit-fields following non-bit-field members are
23549           ignored:
23550                       struct
23551                        {
23552                          char foo;
23553                          long : 0;
23554                          char bar;
23555                        } t5;
23556
23557               Here, "t5" takes up 2 bytes.
23558
23559       -mno-align-stringops
23560           Do not align the destination of inlined string operations.  This
23561           switch reduces code size and improves performance in case the
23562           destination is already aligned, but GCC doesn't know about it.
23563
23564       -minline-all-stringops
23565           By default GCC inlines string operations only when the destination
23566           is known to be aligned to least a 4-byte boundary.  This enables
23567           more inlining and increases code size, but may improve performance
23568           of code that depends on fast "memcpy", "strlen", and "memset" for
23569           short lengths.
23570
23571       -minline-stringops-dynamically
23572           For string operations of unknown size, use run-time checks with
23573           inline code for small blocks and a library call for large blocks.
23574
23575       -mstringop-strategy=alg
23576           Override the internal decision heuristic for the particular
23577           algorithm to use for inlining string operations.  The allowed
23578           values for alg are:
23579
23580           rep_byte
23581           rep_4byte
23582           rep_8byte
23583               Expand using i386 "rep" prefix of the specified size.
23584
23585           byte_loop
23586           loop
23587           unrolled_loop
23588               Expand into an inline loop.
23589
23590           libcall
23591               Always use a library call.
23592
23593       -mmemcpy-strategy=strategy
23594           Override the internal decision heuristic to decide if
23595           "__builtin_memcpy" should be inlined and what inline algorithm to
23596           use when the expected size of the copy operation is known. strategy
23597           is a comma-separated list of alg:max_size:dest_align triplets.  alg
23598           is specified in -mstringop-strategy, max_size specifies the max
23599           byte size with which inline algorithm alg is allowed.  For the last
23600           triplet, the max_size must be "-1". The max_size of the triplets in
23601           the list must be specified in increasing order.  The minimal byte
23602           size for alg is 0 for the first triplet and "max_size + 1" of the
23603           preceding range.
23604
23605       -mmemset-strategy=strategy
23606           The option is similar to -mmemcpy-strategy= except that it is to
23607           control "__builtin_memset" expansion.
23608
23609       -momit-leaf-frame-pointer
23610           Don't keep the frame pointer in a register for leaf functions.
23611           This avoids the instructions to save, set up, and restore frame
23612           pointers and makes an extra register available in leaf functions.
23613           The option -fomit-leaf-frame-pointer removes the frame pointer for
23614           leaf functions, which might make debugging harder.
23615
23616       -mtls-direct-seg-refs
23617       -mno-tls-direct-seg-refs
23618           Controls whether TLS variables may be accessed with offsets from
23619           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
23620           whether the thread base pointer must be added.  Whether or not this
23621           is valid depends on the operating system, and whether it maps the
23622           segment to cover the entire TLS area.
23623
23624           For systems that use the GNU C Library, the default is on.
23625
23626       -msse2avx
23627       -mno-sse2avx
23628           Specify that the assembler should encode SSE instructions with VEX
23629           prefix.  The option -mavx turns this on by default.
23630
23631       -mfentry
23632       -mno-fentry
23633           If profiling is active (-pg), put the profiling counter call before
23634           the prologue.  Note: On x86 architectures the attribute
23635           "ms_hook_prologue" isn't possible at the moment for -mfentry and
23636           -pg.
23637
23638       -mrecord-mcount
23639       -mno-record-mcount
23640           If profiling is active (-pg), generate a __mcount_loc section that
23641           contains pointers to each profiling call. This is useful for
23642           automatically patching and out calls.
23643
23644       -mnop-mcount
23645       -mno-nop-mcount
23646           If profiling is active (-pg), generate the calls to the profiling
23647           functions as NOPs. This is useful when they should be patched in
23648           later dynamically. This is likely only useful together with
23649           -mrecord-mcount.
23650
23651       -mskip-rax-setup
23652       -mno-skip-rax-setup
23653           When generating code for the x86-64 architecture with SSE
23654           extensions disabled, -mskip-rax-setup can be used to skip setting
23655           up RAX register when there are no variable arguments passed in
23656           vector registers.
23657
23658           Warning: Since RAX register is used to avoid unnecessarily saving
23659           vector registers on stack when passing variable arguments, the
23660           impacts of this option are callees may waste some stack space,
23661           misbehave or jump to a random location.  GCC 4.4 or newer don't
23662           have those issues, regardless the RAX register value.
23663
23664       -m8bit-idiv
23665       -mno-8bit-idiv
23666           On some processors, like Intel Atom, 8-bit unsigned integer divide
23667           is much faster than 32-bit/64-bit integer divide.  This option
23668           generates a run-time check.  If both dividend and divisor are
23669           within range of 0 to 255, 8-bit unsigned integer divide is used
23670           instead of 32-bit/64-bit integer divide.
23671
23672       -mavx256-split-unaligned-load
23673       -mavx256-split-unaligned-store
23674           Split 32-byte AVX unaligned load and store.
23675
23676       -mstack-protector-guard=guard
23677       -mstack-protector-guard-reg=reg
23678       -mstack-protector-guard-offset=offset
23679           Generate stack protection code using canary at guard.  Supported
23680           locations are global for global canary or tls for per-thread canary
23681           in the TLS block (the default).  This option has effect only when
23682           -fstack-protector or -fstack-protector-all is specified.
23683
23684           With the latter choice the options -mstack-protector-guard-reg=reg
23685           and -mstack-protector-guard-offset=offset furthermore specify which
23686           segment register (%fs or %gs) to use as base register for reading
23687           the canary, and from what offset from that base register.  The
23688           default for those is as specified in the relevant ABI.
23689
23690       -mmitigate-rop
23691           Try to avoid generating code sequences that contain unintended
23692           return opcodes, to mitigate against certain forms of attack. At the
23693           moment, this option is limited in what it can do and should not be
23694           relied on to provide serious protection.
23695
23696       -mgeneral-regs-only
23697           Generate code that uses only the general-purpose registers.  This
23698           prevents the compiler from using floating-point, vector, mask and
23699           bound registers.
23700
23701       -mindirect-branch=choice
23702           Convert indirect call and jump with choice.  The default is keep,
23703           which keeps indirect call and jump unmodified.  thunk converts
23704           indirect call and jump to call and return thunk.  thunk-inline
23705           converts indirect call and jump to inlined call and return thunk.
23706           thunk-extern converts indirect call and jump to external call and
23707           return thunk provided in a separate object file.  You can control
23708           this behavior for a specific function by using the function
23709           attribute "indirect_branch".
23710
23711           Note that -mcmodel=large is incompatible with
23712           -mindirect-branch=thunk and -mindirect-branch=thunk-extern since
23713           the thunk function may not be reachable in the large code model.
23714
23715           Note that -mindirect-branch=thunk-extern is incompatible with
23716           -fcf-protection=branch and -fcheck-pointer-bounds since the
23717           external thunk can not be modified to disable control-flow check.
23718
23719       -mfunction-return=choice
23720           Convert function return with choice.  The default is keep, which
23721           keeps function return unmodified.  thunk converts function return
23722           to call and return thunk.  thunk-inline converts function return to
23723           inlined call and return thunk.  thunk-extern converts function
23724           return to external call and return thunk provided in a separate
23725           object file.  You can control this behavior for a specific function
23726           by using the function attribute "function_return".
23727
23728           Note that -mcmodel=large is incompatible with
23729           -mfunction-return=thunk and -mfunction-return=thunk-extern since
23730           the thunk function may not be reachable in the large code model.
23731
23732       -mindirect-branch-register
23733           Force indirect call and jump via register.
23734
23735       These -m switches are supported in addition to the above on x86-64
23736       processors in 64-bit environments.
23737
23738       -m32
23739       -m64
23740       -mx32
23741       -m16
23742       -miamcu
23743           Generate code for a 16-bit, 32-bit or 64-bit environment.  The -m32
23744           option sets "int", "long", and pointer types to 32 bits, and
23745           generates code that runs on any i386 system.
23746
23747           The -m64 option sets "int" to 32 bits and "long" and pointer types
23748           to 64 bits, and generates code for the x86-64 architecture.  For
23749           Darwin only the -m64 option also turns off the -fno-pic and
23750           -mdynamic-no-pic options.
23751
23752           The -mx32 option sets "int", "long", and pointer types to 32 bits,
23753           and generates code for the x86-64 architecture.
23754
23755           The -m16 option is the same as -m32, except for that it outputs the
23756           ".code16gcc" assembly directive at the beginning of the assembly
23757           output so that the binary can run in 16-bit mode.
23758
23759           The -miamcu option generates code which conforms to Intel MCU
23760           psABI.  It requires the -m32 option to be turned on.
23761
23762       -mno-red-zone
23763           Do not use a so-called "red zone" for x86-64 code.  The red zone is
23764           mandated by the x86-64 ABI; it is a 128-byte area beyond the
23765           location of the stack pointer that is not modified by signal or
23766           interrupt handlers and therefore can be used for temporary data
23767           without adjusting the stack pointer.  The flag -mno-red-zone
23768           disables this red zone.
23769
23770       -mcmodel=small
23771           Generate code for the small code model: the program and its symbols
23772           must be linked in the lower 2 GB of the address space.  Pointers
23773           are 64 bits.  Programs can be statically or dynamically linked.
23774           This is the default code model.
23775
23776       -mcmodel=kernel
23777           Generate code for the kernel code model.  The kernel runs in the
23778           negative 2 GB of the address space.  This model has to be used for
23779           Linux kernel code.
23780
23781       -mcmodel=medium
23782           Generate code for the medium model: the program is linked in the
23783           lower 2 GB of the address space.  Small symbols are also placed
23784           there.  Symbols with sizes larger than -mlarge-data-threshold are
23785           put into large data or BSS sections and can be located above 2GB.
23786           Programs can be statically or dynamically linked.
23787
23788       -mcmodel=large
23789           Generate code for the large model.  This model makes no assumptions
23790           about addresses and sizes of sections.
23791
23792       -maddress-mode=long
23793           Generate code for long address mode.  This is only supported for
23794           64-bit and x32 environments.  It is the default address mode for
23795           64-bit environments.
23796
23797       -maddress-mode=short
23798           Generate code for short address mode.  This is only supported for
23799           32-bit and x32 environments.  It is the default address mode for
23800           32-bit and x32 environments.
23801
23802   x86 Windows Options
23803       These additional options are available for Microsoft Windows targets:
23804
23805       -mconsole
23806           This option specifies that a console application is to be
23807           generated, by instructing the linker to set the PE header subsystem
23808           type required for console applications.  This option is available
23809           for Cygwin and MinGW targets and is enabled by default on those
23810           targets.
23811
23812       -mdll
23813           This option is available for Cygwin and MinGW targets.  It
23814           specifies that a DLL---a dynamic link library---is to be generated,
23815           enabling the selection of the required runtime startup object and
23816           entry point.
23817
23818       -mnop-fun-dllimport
23819           This option is available for Cygwin and MinGW targets.  It
23820           specifies that the "dllimport" attribute should be ignored.
23821
23822       -mthread
23823           This option is available for MinGW targets. It specifies that
23824           MinGW-specific thread support is to be used.
23825
23826       -municode
23827           This option is available for MinGW-w64 targets.  It causes the
23828           "UNICODE" preprocessor macro to be predefined, and chooses Unicode-
23829           capable runtime startup code.
23830
23831       -mwin32
23832           This option is available for Cygwin and MinGW targets.  It
23833           specifies that the typical Microsoft Windows predefined macros are
23834           to be set in the pre-processor, but does not influence the choice
23835           of runtime library/startup code.
23836
23837       -mwindows
23838           This option is available for Cygwin and MinGW targets.  It
23839           specifies that a GUI application is to be generated by instructing
23840           the linker to set the PE header subsystem type appropriately.
23841
23842       -fno-set-stack-executable
23843           This option is available for MinGW targets. It specifies that the
23844           executable flag for the stack used by nested functions isn't set.
23845           This is necessary for binaries running in kernel mode of Microsoft
23846           Windows, as there the User32 API, which is used to set executable
23847           privileges, isn't available.
23848
23849       -fwritable-relocated-rdata
23850           This option is available for MinGW and Cygwin targets.  It
23851           specifies that relocated-data in read-only section is put into the
23852           ".data" section.  This is a necessary for older runtimes not
23853           supporting modification of ".rdata" sections for pseudo-relocation.
23854
23855       -mpe-aligned-commons
23856           This option is available for Cygwin and MinGW targets.  It
23857           specifies that the GNU extension to the PE file format that permits
23858           the correct alignment of COMMON variables should be used when
23859           generating code.  It is enabled by default if GCC detects that the
23860           target assembler found during configuration supports the feature.
23861
23862       See also under x86 Options for standard options.
23863
23864   Xstormy16 Options
23865       These options are defined for Xstormy16:
23866
23867       -msim
23868           Choose startup files and linker script suitable for the simulator.
23869
23870   Xtensa Options
23871       These options are supported for Xtensa targets:
23872
23873       -mconst16
23874       -mno-const16
23875           Enable or disable use of "CONST16" instructions for loading
23876           constant values.  The "CONST16" instruction is currently not a
23877           standard option from Tensilica.  When enabled, "CONST16"
23878           instructions are always used in place of the standard "L32R"
23879           instructions.  The use of "CONST16" is enabled by default only if
23880           the "L32R" instruction is not available.
23881
23882       -mfused-madd
23883       -mno-fused-madd
23884           Enable or disable use of fused multiply/add and multiply/subtract
23885           instructions in the floating-point option.  This has no effect if
23886           the floating-point option is not also enabled.  Disabling fused
23887           multiply/add and multiply/subtract instructions forces the compiler
23888           to use separate instructions for the multiply and add/subtract
23889           operations.  This may be desirable in some cases where strict IEEE
23890           754-compliant results are required: the fused multiply add/subtract
23891           instructions do not round the intermediate result, thereby
23892           producing results with more bits of precision than specified by the
23893           IEEE standard.  Disabling fused multiply add/subtract instructions
23894           also ensures that the program output is not sensitive to the
23895           compiler's ability to combine multiply and add/subtract operations.
23896
23897       -mserialize-volatile
23898       -mno-serialize-volatile
23899           When this option is enabled, GCC inserts "MEMW" instructions before
23900           "volatile" memory references to guarantee sequential consistency.
23901           The default is -mserialize-volatile.  Use -mno-serialize-volatile
23902           to omit the "MEMW" instructions.
23903
23904       -mforce-no-pic
23905           For targets, like GNU/Linux, where all user-mode Xtensa code must
23906           be position-independent code (PIC), this option disables PIC for
23907           compiling kernel code.
23908
23909       -mtext-section-literals
23910       -mno-text-section-literals
23911           These options control the treatment of literal pools.  The default
23912           is -mno-text-section-literals, which places literals in a separate
23913           section in the output file.  This allows the literal pool to be
23914           placed in a data RAM/ROM, and it also allows the linker to combine
23915           literal pools from separate object files to remove redundant
23916           literals and improve code size.  With -mtext-section-literals, the
23917           literals are interspersed in the text section in order to keep them
23918           as close as possible to their references.  This may be necessary
23919           for large assembly files.  Literals for each function are placed
23920           right before that function.
23921
23922       -mauto-litpools
23923       -mno-auto-litpools
23924           These options control the treatment of literal pools.  The default
23925           is -mno-auto-litpools, which places literals in a separate section
23926           in the output file unless -mtext-section-literals is used.  With
23927           -mauto-litpools the literals are interspersed in the text section
23928           by the assembler.  Compiler does not produce explicit ".literal"
23929           directives and loads literals into registers with "MOVI"
23930           instructions instead of "L32R" to let the assembler do relaxation
23931           and place literals as necessary.  This option allows assembler to
23932           create several literal pools per function and assemble very big
23933           functions, which may not be possible with -mtext-section-literals.
23934
23935       -mtarget-align
23936       -mno-target-align
23937           When this option is enabled, GCC instructs the assembler to
23938           automatically align instructions to reduce branch penalties at the
23939           expense of some code density.  The assembler attempts to widen
23940           density instructions to align branch targets and the instructions
23941           following call instructions.  If there are not enough preceding
23942           safe density instructions to align a target, no widening is
23943           performed.  The default is -mtarget-align.  These options do not
23944           affect the treatment of auto-aligned instructions like "LOOP",
23945           which the assembler always aligns, either by widening density
23946           instructions or by inserting NOP instructions.
23947
23948       -mlongcalls
23949       -mno-longcalls
23950           When this option is enabled, GCC instructs the assembler to
23951           translate direct calls to indirect calls unless it can determine
23952           that the target of a direct call is in the range allowed by the
23953           call instruction.  This translation typically occurs for calls to
23954           functions in other source files.  Specifically, the assembler
23955           translates a direct "CALL" instruction into an "L32R" followed by a
23956           "CALLX" instruction.  The default is -mno-longcalls.  This option
23957           should be used in programs where the call target can potentially be
23958           out of range.  This option is implemented in the assembler, not the
23959           compiler, so the assembly code generated by GCC still shows direct
23960           call instructions---look at the disassembled object code to see the
23961           actual instructions.  Note that the assembler uses an indirect call
23962           for every cross-file call, not just those that really are out of
23963           range.
23964
23965   zSeries Options
23966       These are listed under
23967

ENVIRONMENT

23969       This section describes several environment variables that affect how
23970       GCC operates.  Some of them work by specifying directories or prefixes
23971       to use when searching for various kinds of files.  Some are used to
23972       specify other aspects of the compilation environment.
23973
23974       Note that you can also specify places to search using options such as
23975       -B, -I and -L.  These take precedence over places specified using
23976       environment variables, which in turn take precedence over those
23977       specified by the configuration of GCC.
23978
23979       LANG
23980       LC_CTYPE
23981       LC_MESSAGES
23982       LC_ALL
23983           These environment variables control the way that GCC uses
23984           localization information which allows GCC to work with different
23985           national conventions.  GCC inspects the locale categories LC_CTYPE
23986           and LC_MESSAGES if it has been configured to do so.  These locale
23987           categories can be set to any value supported by your installation.
23988           A typical value is en_GB.UTF-8 for English in the United Kingdom
23989           encoded in UTF-8.
23990
23991           The LC_CTYPE environment variable specifies character
23992           classification.  GCC uses it to determine the character boundaries
23993           in a string; this is needed for some multibyte encodings that
23994           contain quote and escape characters that are otherwise interpreted
23995           as a string end or escape.
23996
23997           The LC_MESSAGES environment variable specifies the language to use
23998           in diagnostic messages.
23999
24000           If the LC_ALL environment variable is set, it overrides the value
24001           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
24002           default to the value of the LANG environment variable.  If none of
24003           these variables are set, GCC defaults to traditional C English
24004           behavior.
24005
24006       TMPDIR
24007           If TMPDIR is set, it specifies the directory to use for temporary
24008           files.  GCC uses temporary files to hold the output of one stage of
24009           compilation which is to be used as input to the next stage: for
24010           example, the output of the preprocessor, which is the input to the
24011           compiler proper.
24012
24013       GCC_COMPARE_DEBUG
24014           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing
24015           -fcompare-debug to the compiler driver.  See the documentation of
24016           this option for more details.
24017
24018       GCC_EXEC_PREFIX
24019           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
24020           names of the subprograms executed by the compiler.  No slash is
24021           added when this prefix is combined with the name of a subprogram,
24022           but you can specify a prefix that ends with a slash if you wish.
24023
24024           If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an
24025           appropriate prefix to use based on the pathname it is invoked with.
24026
24027           If GCC cannot find the subprogram using the specified prefix, it
24028           tries looking in the usual places for the subprogram.
24029
24030           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
24031           prefix is the prefix to the installed compiler. In many cases
24032           prefix is the value of "prefix" when you ran the configure script.
24033
24034           Other prefixes specified with -B take precedence over this prefix.
24035
24036           This prefix is also used for finding files such as crt0.o that are
24037           used for linking.
24038
24039           In addition, the prefix is used in an unusual way in finding the
24040           directories to search for header files.  For each of the standard
24041           directories whose name normally begins with /usr/local/lib/gcc
24042           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
24043           replacing that beginning with the specified prefix to produce an
24044           alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar
24045           just before it searches the standard directory /usr/local/lib/bar.
24046           If a standard directory begins with the configured prefix then the
24047           value of prefix is replaced by GCC_EXEC_PREFIX when looking for
24048           header files.
24049
24050       COMPILER_PATH
24051           The value of COMPILER_PATH is a colon-separated list of
24052           directories, much like PATH.  GCC tries the directories thus
24053           specified when searching for subprograms, if it cannot find the
24054           subprograms using GCC_EXEC_PREFIX.
24055
24056       LIBRARY_PATH
24057           The value of LIBRARY_PATH is a colon-separated list of directories,
24058           much like PATH.  When configured as a native compiler, GCC tries
24059           the directories thus specified when searching for special linker
24060           files, if it cannot find them using GCC_EXEC_PREFIX.  Linking using
24061           GCC also uses these directories when searching for ordinary
24062           libraries for the -l option (but directories specified with -L come
24063           first).
24064
24065       LANG
24066           This variable is used to pass locale information to the compiler.
24067           One way in which this information is used is to determine the
24068           character set to be used when character literals, string literals
24069           and comments are parsed in C and C++.  When the compiler is
24070           configured to allow multibyte characters, the following values for
24071           LANG are recognized:
24072
24073           C-JIS
24074               Recognize JIS characters.
24075
24076           C-SJIS
24077               Recognize SJIS characters.
24078
24079           C-EUCJP
24080               Recognize EUCJP characters.
24081
24082           If LANG is not defined, or if it has some other value, then the
24083           compiler uses "mblen" and "mbtowc" as defined by the default locale
24084           to recognize and translate multibyte characters.
24085
24086       Some additional environment variables affect the behavior of the
24087       preprocessor.
24088
24089       CPATH
24090       C_INCLUDE_PATH
24091       CPLUS_INCLUDE_PATH
24092       OBJC_INCLUDE_PATH
24093           Each variable's value is a list of directories separated by a
24094           special character, much like PATH, in which to look for header
24095           files.  The special character, "PATH_SEPARATOR", is target-
24096           dependent and determined at GCC build time.  For Microsoft Windows-
24097           based targets it is a semicolon, and for almost all other targets
24098           it is a colon.
24099
24100           CPATH specifies a list of directories to be searched as if
24101           specified with -I, but after any paths given with -I options on the
24102           command line.  This environment variable is used regardless of
24103           which language is being preprocessed.
24104
24105           The remaining environment variables apply only when preprocessing
24106           the particular language indicated.  Each specifies a list of
24107           directories to be searched as if specified with -isystem, but after
24108           any paths given with -isystem options on the command line.
24109
24110           In all these variables, an empty element instructs the compiler to
24111           search its current working directory.  Empty elements can appear at
24112           the beginning or end of a path.  For instance, if the value of
24113           CPATH is ":/special/include", that has the same effect as
24114           -I. -I/special/include.
24115
24116       DEPENDENCIES_OUTPUT
24117           If this variable is set, its value specifies how to output
24118           dependencies for Make based on the non-system header files
24119           processed by the compiler.  System header files are ignored in the
24120           dependency output.
24121
24122           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
24123           case the Make rules are written to that file, guessing the target
24124           name from the source file name.  Or the value can have the form
24125           file target, in which case the rules are written to file file using
24126           target as the target name.
24127
24128           In other words, this environment variable is equivalent to
24129           combining the options -MM and -MF, with an optional -MT switch too.
24130
24131       SUNPRO_DEPENDENCIES
24132           This variable is the same as DEPENDENCIES_OUTPUT (see above),
24133           except that system header files are not ignored, so it implies -M
24134           rather than -MM.  However, the dependence on the main input file is
24135           omitted.
24136
24137       SOURCE_DATE_EPOCH
24138           If this variable is set, its value specifies a UNIX timestamp to be
24139           used in replacement of the current date and time in the "__DATE__"
24140           and "__TIME__" macros, so that the embedded timestamps become
24141           reproducible.
24142
24143           The value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as
24144           the number of seconds (excluding leap seconds) since 01 Jan 1970
24145           00:00:00 represented in ASCII; identical to the output of
24146           @command{date +%s} on GNU/Linux and other systems that support the
24147           %s extension in the "date" command.
24148
24149           The value should be a known timestamp such as the last modification
24150           time of the source or package and it should be set by the build
24151           process.
24152

BUGS

24154       For instructions on reporting bugs, see
24155       <http://bugzilla.redhat.com/bugzilla>.
24156

FOOTNOTES

24158       1.  On some systems, gcc -shared needs to build supplementary stub code
24159           for constructors to work.  On multi-libbed systems, gcc -shared
24160           must select the correct support libraries to link against.  Failing
24161           to supply the correct flags may lead to subtle defects.  Supplying
24162           them in cases where they are not necessary is innocuous.
24163

SEE ALSO

24165       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
24166       dbx(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb.
24167

AUTHOR

24169       See the Info entry for gcc, or
24170       <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors
24171       to GCC.
24172
24174       Copyright (c) 1988-2018 Free Software Foundation, Inc.
24175
24176       Permission is granted to copy, distribute and/or modify this document
24177       under the terms of the GNU Free Documentation License, Version 1.3 or
24178       any later version published by the Free Software Foundation; with the
24179       Invariant Sections being "GNU General Public License" and "Funding Free
24180       Software", the Front-Cover texts being (a) (see below), and with the
24181       Back-Cover Texts being (b) (see below).  A copy of the license is
24182       included in the gfdl(7) man page.
24183
24184       (a) The FSF's Front-Cover Text is:
24185
24186            A GNU Manual
24187
24188       (b) The FSF's Back-Cover Text is:
24189
24190            You have freedom to copy and modify this GNU Manual, like GNU
24191            software.  Copies published by the Free Software Foundation raise
24192            funds for GNU development.
24193
24194
24195
24196gcc-8                             2018-09-05                            GCC(1)
Impressum