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

[Han-Kuan Chen via llvm-commits]

HanKuanChen wrote:

This is the compilation time result. https://llvm-compile-time-tracker.com/compare.php?from=a12ca57c1cb070be8e0048004c6b4e820029b6ee&to=b8c2e9e38d1e32cd2f23c928a50d83574b86c58f&stat=instructions:u

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