GCC 4.6 performance regressions

[Jonathan Wakely]

On 9 February 2011 08:34, Sebastian Pop wrote:
>
> For example x264 defines CFLAGS="-O4 -ffast-math $CFLAGS", and so
> building this benchmark with CFLAGS="-O2" would have no effect.

Why not?

Ignoring the fact -O3 is the highest level for GCC, the manual says:
"If you use multiple -O options, with or without level numbers, the
last such option is the one that is effective."
http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

And CFLAGS="-fno-fast-math -O2" would cancel the effects of -ffast-math too.