[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #133888)

[Gaëtan Bossu via llvm-commits]

https://github.com/gbossu commented:

I brushed through the code, looks sensible. But I don't know too much about the SLPVectorizer yet, so do what you want with my comments 😉 

https://github.com/llvm/llvm-project/pull/133888