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.
