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

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

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


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