-foptimize-sibling-calls -fprefetch-loop-arrays @gol
-fprofile-generate -fprofile-use @gol
-freduce-all-givs -fregmove -frename-registers @gol
--freorder-blocks -freorder-functions @gol
+-freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
-frerun-cse-after-loop -frerun-loop-opt @gol
-frounding-math -fschedule-insns -fschedule-insns2 @gol
-fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
-mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
--mxgot -mno-xgot -membedded-pic -mno-embedded-pic @gol
--mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
--msingle-float -mdouble-float -mint64 -mlong64 -mlong32 @gol
+-mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
+-mhard-float -msoft-float -msingle-float -mdouble-float @gol
+-mint64 -mlong64 -mlong32 @gol
-G@var{num} -membedded-data -mno-embedded-data @gol
-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
-msplit-addresses -mno-split-addresses @gol
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
--mfix-vr4122-bugs -mno-fix-vr4122-bugs -mfix-sb1 -mno-fix-sb1 @gol
+-mfix-vr4120 -mno-fix-vr4120 -mfix-sb1 -mno-fix-sb1 @gol
-mflush-func=@var{func} -mno-flush-func @gol
--mbranch-likely -mno-branch-likely}
+-mbranch-likely -mno-branch-likely @gol
+-mfp-exceptions -mno-fp-exceptions}
@emph{i386 and x86-64 Options}
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
and possibly the ability to debug the program.
The compiler performs optimization based on the knowledge it has of
-the program. Using the @option{-funit-at-a-time} flag will allow the
-compiler to consider information gained from later functions in the
-file when compiling a function. Compiling multiple files at once to a
-single output file (and using @option{-funit-at-a-time}) will allow
+the program. Optimization levels @option{-O2} and above, in
+particular, enable @emph{unit-at-a-time} mode, which allows the
+compiler to consider information gained from later functions in
+the file when compiling a function. Compiling multiple files at
+once to a single output file in @emph{unit-at-a-time} mode allows
the compiler to use information gained from all of the files when
compiling each of them.
@option{-Os} disables the following optimization flags:
@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
--falign-labels -freorder-blocks -fprefetch-loop-arrays}
+-falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays}
If you use multiple @option{-O} options, with or without level numbers,
the last such option is the one that is effective.
Enabled at levels @option{-O2}, @option{-O3}.
+@item -freorder-blocks-and-partition
+@opindex freorder-blocks-and-partition
+In addition to reordering basic blocks in the compiled function, in order
+to reduce number of taken branches, partitions hot and cold basic blocks
+into separate sections of the assembly and .o files, to improve
+paging and cache locality performance.
+
@item -freorder-functions
@opindex freorder-functions
Reorder basic blocks in the compiled function in order to reduce number of
taken branches and improve code locality. This is implemented by using special
-subsections @code{text.hot} for most frequently executed functions and
-@code{text.unlikely} for unlikely executed functions. Reordering is done by
+subsections @code{.text.hot} for most frequently executed functions and
+@code{.text.unlikely} for unlikely executed functions. Reordering is done by
the linker so object file format must support named sections and linker must
place them in a reasonable way.
Enabled at levels @option{-O2}, @option{-O3}.
-@item -frename-registers
-@opindex frename-registers
-Attempt to avoid false dependencies in scheduled code by making use
-of registers left over after register allocation. This optimization
-will most benefit processors with lots of registers. It can, however,
-make debugging impossible, since variables will no longer stay in
-a ``home register''.
+@item -funit-at-a-time
+@opindex funit-at-a-time
+Parse the whole compilation unit before starting to produce code.
+This allows some extra optimizations to take place but consumes
+more memory (in general). There are some compatibility issues
+with @emph{unit-at-at-time} mode:
+@itemize @bullet
+@item
+enabling @emph{unit-at-a-time} mode may change the order
+in which functions, variables, and top-level @code{asm} statements
+are emitted, and will likely break code relying on some particular
+ordering. The majority of such top-level @code{asm} statements,
+though, can be replaced by @code{section} attributes.
+
+@item
+@emph{unit-at-a-time} mode removes unreferenced static variables
+and functions are removed. This may result in undefined references
+when an @code{asm} statement refers directly to variables or functions
+that are otherwise unused. In that case either the variable/function
+shall be listed as an operand of the @code{asm} statement operand or,
+in the case of top-level @code{asm} statements the attribute @code{used}
+shall be used on the declaration.
-Enabled at levels @option{-O3}.
+@item
+Static functions now can use non-standard passing conventions that
+may break @code{asm} statements calling functions directly. Again,
+attribute @code{used} will prevent this behavior.
+@end itemize
+
+As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
+but this scheme may not be supported by future releases of GCC.
+
+Enabled at levels @option{-O2}, @option{-O3}.
@item -fweb
@opindex fweb
however, make debugging impossible, since variables will no longer stay in a
``home register''.
-Enabled at levels @option{-O3}.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os},
+on targets where the default format for debugging information supports
+variable tracking.
@item -fno-cprop-registers
@opindex fno-cprop-registers
@item -fprofile-generate
@opindex fprofile-generate
-Enable options usually used for instrumenting application to produce profile usefull
-for later recompilation profile feedback based optimization.
-The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}
+Enable options usually used for instrumenting application to produce
+profile useful for later recompilation with profile feedback based
+optimization. You must use @code{-fprofile-generate} both when
+compiling and when linking your program.
+
+The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
@item -fprofile-use
@opindex fprofile-use
from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
notes to instructions for their later usage in optimizations.
-Enabled with @option{-profile-generate} and @option{-profile-use}.
+Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
@item -fvpt
@opindex fvpt
Currently the optimizations include specialization of division operation
using the knowledge about the value of the denominator.
-Enabled with @option{-profile-generate} and @option{-profile-use}.
+Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
+
+@item -frename-registers
+@opindex frename-registers
+Attempt to avoid false dependencies in scheduled code by making use
+of registers left over after register allocation. This optimization
+will most benefit processors with lots of registers. Depending on the
+debug information format adopted by the target, however, it can
+make debugging impossible, since variables will no longer stay in
+a ``home register''.
+
+Not enabled by default at any level because it has known bugs.
@item -fnew-ra
@opindex fnew-ra
simplifies the control flow of the function allowing other optimizations to do
better job.
-Enabled with @option{-profile-use}.
-
-@item -funit-at-a-time
-@opindex funit-at-a-time
-Parse the whole compilation unit before starting to produce code.
-This allows some extra optimizations to take place but consumes more
-memory.
-
-Enabled at levels @option{-O2}, @option{-O3}.
+Enabled with @option{-fprofile-use}.
@item -funroll-loops
@opindex funroll-loops
(i.e. complete removal of loops with small constant number of iterations).
This option makes code larger, and may or may not make it run faster.
-Enabled with @option{-profile-use}.
+Enabled with @option{-fprofile-use}.
@item -funroll-all-loops
@opindex funroll-all-loops
roll much (from profile feedback). It also turns on complete loop peeling
(i.e. complete removal of loops with small constant number of iterations).
-Enabled with @option{-profile-use}.
+Enabled with @option{-fprofile-use}.
@item -funswitch-loops
@opindex funswitch-loops
These options have no effect unless GCC is generating position
independent code.
-@item -membedded-pic
-@itemx -mno-embedded-pic
-@opindex membedded-pic
-@opindex mno-embedded-pic
-Generate (do not generate) position-independent code suitable for some
-embedded systems. All calls are made using PC relative addresses, and
-all data is addressed using the $gp register. No more than 65536
-bytes of global data may be used. This requires GNU as and GNU ld,
-which do most of the work.
-
@item -mgp32
@opindex mgp32
Assume that general-purpose registers are 32 bits wide.
immediately after starting an integer division.
@end itemize
-@item -mfix-vr4122-bugs
-@itemx -mno-fix-vr4122-bugs
-@opindex mfix-vr4122-bugs
-Work around certain VR4122 errata:
+@item -mfix-vr4120
+@itemx -mno-fix-vr4120
+@opindex mfix-vr4120
+Work around certain VR4120 errata:
@itemize @minus
@item
@code{dmultu} does not always produce the correct result.
@file{libgcc.a}. At present, these functions are only provided by
the @code{mips64vr*-elf} configurations.
-Other VR4122 errata require a nop to be inserted between certain pairs of
+Other VR4120 errata require a nop to be inserted between certain pairs of
instructions. These errata are handled by the assembler, not by GCC itself.
@item -mfix-sb1
and processors which implement those architectures; for those, Branch
Likely instructions will not be generated by default because the MIPS32
and MIPS64 architectures specifically deprecate their use.
+
+@item -mfp-exceptions
+@itemx -mno-fp-exceptions
+@opindex mfp-exceptions
+Specifies whether FP exceptions are enabled. This affects how we schedule
+FP instructions for some processors. The default is that FP exceptions are
+enabled.
+
+For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
+64-bit code, then we can use both FP pipes. Otherwise, we can only use one
+FP pipe.
@end table
@node i386 and x86-64 Options
OSDN Git Service
