https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445
--- Comment #38 from Christophe Leroy <christophe.leroy at csgroup dot eu> --- (In reply to Jan Hubicka from comment #32) > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 > > > > --- Comment #31 from Segher Boessenkool <segher at gcc dot gnu.org> --- > > (In reply to Jan Hubicka from comment #27) > > > 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. > > > > Do the heuristics account for that not inlining a "static inline" results > > in multiple copies? > > It prevents inlining only when there are multiple calls in the unit > being compiled (there is no way to know that the same inline function is > duplicated in other units). > This is what happens here: there are multiple calls so inliner concludes > inlining would cost too much of code size and later they are optimized > away. > > get_order is a wrapper around ffs64. This can be implemented w/o asm > statement as follows: > int > my_fls64 (__u64 x) > { > if (!x) > return 0; > return 64 - __builtin_clzl (x); > } > > This results in longer assembly than the kernel asm implementation. If > that matters I would replace builtin_constnat_p part of get_order by this > implementation that is more transparent to the code size estimation and > things will get inlined. > But on powerpc that's already the case and it doesn't solve the issue. static inline int fls(unsigned int x) { return 32 - __builtin_clz(x); } static inline int fls64(__u64 x) { return 64 - __builtin_clzll(x); }
