[llvm] [InstCombine] Support gep nuw in icmp folds (PR #118472)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

> > That's definitely not the only patch in this area. [e21ab4d16b555c28ded307571d138f594f33e325](https://github.com/llvm/llvm-project/commit/e21ab4d16b555c28ded307571d138f594f33e325) discovers more cases of pointer arithmetic-related UB.
> 
> FWIW, I'd be happy to just revert that one entirely. I don't have a specific use case for that one, and am concerned that it currently slips through all the sanitizers.

FWIW, most issues I mentioned in my previous comments are actually coming from e21ab4d16b555c28ded307571d138f594f33e325, not this one. They happened to be tested together and I kind of conflated them in my head, hence the somewhat misleading report above.

Given that we also discovered a bad interaction of that change with msan, reverting it would definitely help us. A test case is being worked on by a colleague, but I'm not quite sure how far they are with it.

https://github.com/llvm/llvm-project/pull/118472