> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 > > --- Comment #23 from Christophe Leroy <christophe.leroy at csgroup dot eu> --- > (In reply to Jan Hubicka from comment #19) > > > > It is always possible to always_inline functions that are intended to be > > always inlined. > > Honza > > Yes and I sent a patch for that to the Linux kernel, but what I would like to > understand is why does GCC 10 completely fails to inline that while GCC 9 was > doing things properly ?
It is because --param inline-insns-single was reduced for -O2 from 200 to 70. GCC 10 has newly different set of parameters for -O2 and -O3 and enables auto-inlining at -O2. Problem with inlininig funtions declared inline is that C++ codebases tends to abuse this keyword for things that are really too large (and get_order would be such example if it did not have builtin_constant_p check which inliner does not understand well). So having same limit at -O2 and -O3 turned out to be problematic with respect to code size and especially with respect to LTO, where a lot more inlining oppurtunities appear. I will implement the heuristics to push up inline limits of functions having builtin_constant_p of parameter which should help a bit in this case (but not very systematically: as dicussed in the PR log it is quite hard problem to get builtin_constant_p right in the code size metrics used by inliner before it knows exactly what is going to be constant and what is not). Honza
