[llvm] [InstSimplify] fold exact non zero right shifts on undefs to poison (PR #212943)

[Karol Zwolak via llvm-commits]

karolzwolak wrote:

> What is the motivation?

Nothing in particular, I just saw the TODO and decided to implement it.

> As undef value is about to be deprecated, we only fix real-world miscompilations/significant performance regressions related to undef.

Ah I didn't know, we can close this then.

https://github.com/llvm/llvm-project/pull/212943