[llvm] [RFC][Transforms] Prefer unreachable insn over optimizaiton with undef (PR #131020)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

Both of the proposed transforms are incorrect. Please see https://llvm.org/docs/InstCombineContributorGuide.html#proofs to learn how you can prove the correctness of proposed transforms.

https://github.com/llvm/llvm-project/pull/131020