https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94472
--- Comment #9 from Jan Hubicka <hubicka at ucw dot cz> --- > --- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> --- > Oh, and bugfixing requires to first understand the bug. Especially for > performance related issues understanding what goes wrong is important. > I see no analysis being performed to date. The problem here is that -O2 -fprofile-use is now using -O2 inliner limits while previously it used -O3 inliner limit (because -fprofile-use enables -finline-functions). I can see this on SPEC GCC, perl, Firefox, real GCC and clang. We now have performance diference between -O2+FDO and -O3+FDO. It is something I kind of missed in my testing, because I was testing -O2 and -O3 + FDO but not -O2+FDO. I realize that -O2+FDO is kind of important because we use it in our bootstrap. So i was collecting data over weekend for Clang, GCC and Firefox. It is question how agressive we want to be at -O2+FDO but the observation is that in all these programs the code size growth for -O3 style limits is quite small (bellow 2%) simply because thraining coverage is quite small in all those programs (sub 10%) and thus the code size growth for inlining hot calls is acceptable and thus I think the current defaults are really suboptimal. I think there are few ways to proceed 1) make inline limits with FDO to be -O3 ones 2) invent yet another set of parameters for FDO 3) increase importance of known_hot hint that is set of calls that are known to be hot (either by inlining or by hot attribute). 1 is easiest but bit non-sytematic. I am not really keen about 2 because if parameter explosion. However 3 looks like good alternative so I am running benchmarks with few settings of it, but they take some time. Honza
