-O3 optimization

Rodolfo Lima rodolfo at rodsoft.org
Wed Apr 9 04:52:28 PDT 2003


Why you guys don't use -O3 optimization throughout the building of packages?

>From gcc's man:

   -O2 Optimize even more.  GCC performs nearly all supported optimiza-
           tions that do not involve a space-speed tradeoff.  The compiler
           does not perform loop unrolling or function inlining when you
spec-
           ify -O2.  As compared to -O, this option increases both
compilation
           time and the performance of the generated code.

           -O2 turns on all optional optimizations except for loop
unrolling,
           function inlining, and register renaming.  It also turns on the
           -fforce-mem option on all machines and frame pointer elimination
on
           machines where doing so does not interfere with debugging.

           Please note the warning under -fgcse about invoking -O2 on
programs
           that use computed gotos.

   -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
           and also turns on the -finline-functions and -frename-registers
           options.

I think loop unrolling and inline functions can do a lot for performance...

[]'s
rod


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