[Bug ipa/94360] 6% run-time regression of 502.gcc_r against GCC 9 when compiled with -O2 and both PGO and LTO

["hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94360

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-01-18
     Ever confirmed|0                           |1

--- Comment #4 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
With -O2 -fprofile-use we now use -O2 inliner limits while previously we
switched to effectively -O3 inlining.
In a way it makes sense to have -O2 -fprofile-use to produce smaller and bit
slower code than -O3 -fprofile-use but it seems that current limits are way too
low.  I.e. the code size savings does not seem to justify the performance loss.

From maintenance perspective it kind of sucks to have 3 sets of values (-O2,
-O3 and -O2 + -fprofile-use) but maybe we can get cheaply out by simply making
"known hot" hint to be taken seriously with FDO.  FDO inlining is kind of easy
since hot calls are known well.

I will take a look.