[llvm] [InstCombine] Fold `(icmp pred (trunc nuw/nsw X), C)` -> `(icmp pred X, (zext/sext C))` (PR #87935)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> > This patch causing false MSAN reports. It's likely a bug in MSAN, but I didn't figured out the fix yet.
> 
> As in breaks MSAN, or MSAN now complains about LLVM?

Msan reports false bugs in users code.

> 
> > Would it be OK to revert the patch while I am investigating, to avoid false reports for us and other MSAN users?
> 
> I guess preferably not. Can you wait until there have some actual reports / an issue justifying.

I have multiple reports on our internal codebase, I just need to minimize them. Inconveniently, I am traveling this week.
Also as soon I have reduced reproducer I will likely have a msan patch. Usually it's just over aggressive handling of some instruction which need to be relaxed.

Also if we wait, it can be branched into clang RC, which will need cherry-picks, potentially with conflicts.

https://github.com/llvm/llvm-project/pull/87935