On Fri, Aug 5, 2011 at 12:32 AM, Richard Guenther <richard.guent...@gmail.com> wrote: > On Thu, Aug 4, 2011 at 8:42 PM, Jan Hubicka <j...@suse.de> wrote: >>>> Did you try using FDO with -Os? FDO should make hot code parts >>>> optimized similar to -O3 but leave other pieces optimized for size. >>>> Using FDO with -O3 gives you the opposite, cold portions optimized >>>> for size while the rest is optimized for speed. >> >> FDO with -Os still optimize for size, even in hot parts. > > I don't think so. Or at least that would be a bug. Shouldn't 'hot' > BBs/functions > be optimized for speed even at -Os? Hm, I see predict.c indeed returns > always false for optimize_size :(
That is function level query. At the BB/EDGE level, the condition is refined: The BB (or instruction expansion) will be optimized for size if the bb is not 'hot'. This logic here is probably not ideal. It means that without specifying -Os, only the hot BBs are optimized for speed --> the 'righter' way is 'without -Os, only cold BBs are optimize for size' -- i.e., the lukewarm bbs are also optimize for speed. This will match the function level logic. David > > I thought we had just the neither cold or hot parts optimized according > to optimize_size. > >> So to get resonale >> speedups you need -O3+FDO. -O3+FDO effectively defaults to -Os in cold >> portions of program. > > Well, but unless your training coverage is 100% all parts with no coverage > get optimized with -O3 instead of -Os. And I bet coverage for mozilla > isn't even close to 100%. Thus I think recommending -O3 for FDO is > usually a bad idea. > > So - did you try FDO with -O2? ;) > >> Still -Os+FDO should be somewhat faster than -Os alone, so a slowdown is >> bug. It is not very thoroughly since it is not really used in practice. >> >>>> Also do you get any warnings on profile mismatches? Perhaps something >>>> is wrong to the degree that the relevant part of profile gets >>>> misapplied. >>> >>> I don't get any warning on profile mismatches. I only get a "few" >>> missing gcda files warning, but that's expected. >> >> Perhaps you could compile one of less trivial files you are sure that are >> covered by train run and send me -fdump-tree-all-blocks -fdump-ipa-all dumps >> of the compilation so I can double check the profile seems sane. This could >> be good start to rule out something stupid. >> >> Honza >>> >>> Cheers, >>> >>> Mike >>> >> >> >> >
