[Bug ipa/113665] [11/12/13/14 regression] Regular for Loop results in Endless Loop with -O2 since r11-4987-g602c6cfc79ce4a

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113665

--- Comment #8 from Jan Hubicka <hubicka at ucw dot cz> ---
> Honza - ICF seems to fixup points-to sets when merging variables, so there
> should be a way to kill off flow-sensitive info inside prevailing bodies
> as well.  But would that happen before inlining the body?  Can you work
> on that?  I think comparing ranges would weaken ICF unnecessarily?

AFAIK ICF does no changes to winning function body. It basically relies
on the fact that early optimizations are local and thus arrive to same
solutions for most of metadata. So only really easy fix is to make it
match value ranges, too.  I will check how much that fire in practice -
I can only think of split funtions to diverge, which is probably not
that bad in practice.

IPA-prop and IPA-PTA is only done after ICF.

We indeed discussed clearing possibility of merging alias sets which is
relatively important in practice (increasing TBAA precision on LTO
slowly degraded ICF effectivity significantly), but got into glory
details of inventing representation which would make inliner to pick
right body (without alias sets cleared). This was never made to fly
(Martin got scared by the details and I got it on my ever overflowing
TODO list).

Honza