[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #127450)

[Han-Kuan Chen via llvm-commits]

HanKuanChen wrote:

> What about compile time?

https://llvm-compile-time-tracker.com/compare.php?from=d77ef140e66dda44a40ac2f316d3b8a42fb7bf07&to=4dfe0132270ecd71dcef0f9a9616104b72d2207e&stat=instructions:u

https://github.com/llvm/llvm-project/pull/127450