Red Hat ENTERPRISE LINUX 4 Manual page 62

54
-O
-O1
Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a
large function.
With , the compiler tries to reduce code size and execution time, without performing any
-O
optimizations that take a great deal of compilation time.
turns on the following optimization flags:
-O
-fdefer-pop
-fmerge-constants
-fthread-jumps
-floop-optimize
-fif-conversion
-fif-conversion2
-fdelayed-branch
-fguess-branch-probability
-fcprop-registers
also turns on
-O
debugging.
-O2
Optimize even more. GCC performs nearly all supported optimizations that do not involve a
space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when
you specify
-O2
mance of the generated code.
turns on all optimization flags specified by
-O2
flags:
-fforce-mem
-foptimize-sibling-calls
-fstrength-reduce
-fcse-follow-jumps
-frerun-cse-after-loop
-fgcse -fgcse-lm
-fdelete-null-pointer-checks
-fexpensive-optimizations
-fregmove
-fschedule-insns
-fsched-interblock
-fcaller-saves
-fpeephole2
-freorder-blocks
-fstrict-aliasing
-funit-at-a-time
-falign-functions
-falign-loops
-fcrossjumping
Please note the warning under
-O3
Optimize yet more.
-finline-functions
-O0
Do not optimize. This is the default.
-fomit-frame-pointer
. As compared to , this option increases both compilation time and the perfor-
-O
-fcse-skip-blocks
-frerun-loop-opt
-fgcse-sm
-fschedule-insns2
-fsched-spec
-freorder-functions
-falign-jumps
-falign-labels
-fgcse
turns on all optimizations specified by
-O3
, and
-fweb
Chapter 4. GCC Command Options
on machines where doing so does not interfere with
. It also turns on the following optimization
-O
-fgcse-las
about invoking
-O2
-frename-registers
on programs that use computed gotos.
and also turns on the
-O2
options.