[llvm] [PHIElimination] Account for PHI operands that appear more than once (PR #146806)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

You should probably mention in the commit message that this patch also solves a problem where debug info affected codegen.

I've verified that this path fixes the debug info problem I mentioned in https://github.com/llvm/llvm-project/pull/131837#discussion_r2182026713 but apart from checking that I really don't feel confident reviewing this change.



https://github.com/llvm/llvm-project/pull/146806