[Bug ipa/106716] Identical Code Folding (-fipa-icf) confuses between functions with different [[likely]] attributes

[Bug ipa/106716] Identical Code Folding (-fipa-icf) confuses between functions with different [[likely]] attributes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106716

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |moncef.mechri at gmail dot com

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 111297 has been marked as a duplicate of this bug. ***

[Bug ipa/106716] Identical Code Folding (-fipa-icf) confuses between functions with different [[likely]] attributes

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106716

--- Comment #6 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
The reason why GIMPLE_PREDICT is ignored is that it is never used after ipa-icf
and gets removed at the very beggining of late optimizations.  

GIMPLE_PREDICT is consumed by profile_generate pass which is run before
ipa-icf.  The reason why GIMPLE_PREDICT statements are not stripped during ICF
is early inlining.  If we early inline, we throw away its profile and estimate
it again (in the context of function it was inlined to) and for that it is a
good idea to keep predicts.

There is no convenient place to remove them after early inlining was done and
before IPA passes and that is the only reason why they are around.  We may
revisit that since streaming them to LTO bytecode is probably more harmful then
adding extra pass after early opts to strip them.

ICF doesn't code to compare edge profiles and stmt histograms.  It knows how to
merge them (so resulting BB profile is consistent with merging) but I suppose
we may want to have some threshold on when we do not want to marge functions
with very different branch probabilities in the hot part of their bodies...