[llvm] [SLP] Match poison as instruction with the same opcode (PR #115946)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> Thanks! In case it's useful, creduce just finished with a smaller repro here: https://crbug.com/380805017#comment6

Hmm, tried both reproducers (the original and reduced), unable to reproduce using top trunk. Can you recheck, please?

https://github.com/llvm/llvm-project/pull/115946