On 11/5/05, Giovanni Bajo <[EMAIL PROTECTED]> wrote: > Richard Guenther <[EMAIL PROTECTED]> wrote: > > >>>> I guess the issue is what does "huge" mean, it is hard to discuss based > >>>> on loaded adjectives taking the place of data :-) > >>> > >>> Huge here means 15-20% on x86* hosts. > >> > >> I don't consider this huge for -O3. I think -O3 can be slower if it > >> achieves better code, and -funroll-loops makes it do just that. > > > > First of all, this is too late for 4.1, second, we enable loop-unrolling > > with FDO. And without FDO, -funroll-loops is not necessarily an > > improvement. > > What is FDO?
Feedback Directed Optimization, i.e. -fprofile-generate/-fprofile-use. > My feeling is that -funroll-loops is almost always an improvement. It might > be false sometimes, but this can be said of many optimization passes. Can you back up this feeling with numbers? SPEC -O2 vs. -O2 -funroll-loops and/or -O3 vs. -O3 -funroll-loops would do it. Richard.
