[llvm] [polly] [InstSimplify] Fix incorrect poison propagation when folding phi (PR #96631)

[Nikita Popov via llvm-commits]

nikic wrote:

Sorry, my initial analysis of https://github.com/llvm/llvm-project/issues/97702 wasn't right, and this wasn't the cause of that issue after all. So this one remains a theoretical problem only for now...

https://github.com/llvm/llvm-project/pull/96631