[Bug rtl-optimization/101523] Huge number of combine attempts

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101523

--- Comment #61 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Sarah Julia Kriesch from comment #60)
> I have to agree with Richard. This problem has been serious for a long time
> but has been ignored by IBM based on distribution choices.

What?  What does IBM have to do with this?  Yes, they are my employer, but
what I decide is best for combine to do is not influenced by them *at all*
(except some times they want me to spend time doing paid work, distracting
me from things that really matter, like combine!)

> Anyway, we want to live within the open source community without any Linux
> distribution priorities (especially in upstream projects like here).

No idea what that means either.

> Segher, can you specify the failed test cases? Then, it should be possible
> to reproduce and improve that all. In such a collaborative way, we can also
> achieve a solution.

What failed test cases?  You completely lost me.

We used to do the wrong thing in combine.  Now that my fix was reverted, we
still do.  This should be undone soonish, so that I can commit an actual UNCSE
implementation, which fixes all "regressions" (quotes, because they are not!)
caused by my previous patch, and does a lot more too.  It also will allow us
to remove a bunch of other code from combine, speeding up things a lot more
(things that keep a copy of a set if the dest is used more than once).  There
has been talk of doing an UNCSE for over twenty years now, so annoying me
enough to get this done is a good result of this whole thing :-)