[llvm] [InstCombine] Simplify and/or of icmp eq with op replacement (PR #70335)

[Nikita Popov via llvm-commits]

nikic wrote:

> > I reverted this because I'm seeing segfaults in stage2 llvm-tblgen on a build server, but for some reason I can't reproduce this in local stage2 builds :/ Not sure what the difference is, my best guess is the libstdc++ version.
> 
> @nikic We saw miscompiles with this patch when testing our out-of-tree target. I don't have any reproducer to share at the moment but if you're struggling to reproduce yourself I can try to see if I might be able to extract something that shows the problem on trunk as well. Should I try?

If it's not too much effort, I'd really appreciate that!

https://github.com/llvm/llvm-project/pull/70335