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

[via llvm-commits]

DianQK wrote:

> @nikic Can you provide some performance data on rust benchmarks before landing this patch?

Based on the known test set, this has no noticeable impact: https://github.com/rust-lang/rust/pull/127347#issuecomment-2210100734.








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