[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #132887)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

> We see a Clang crash after [8122bb9](https://github.com/llvm/llvm-project/commit/8122bb9dbe39a1dde77eb4aad76bf1c0e70b2d89) and [6e66cfe](https://github.com/llvm/llvm-project/commit/6e66cfeeaec6f09a4454400e45d690457ecdd3de) (unfortunately, I don't know yet more precisely, which of the two is the culprit, but they were committed one after another). See [8122bb9#commitcomment-154471110](https://github.com/llvm/llvm-project/commit/8122bb9dbe39a1dde77eb4aad76bf1c0e70b2d89#commitcomment-154471110)

It's addressed by the revert a2e5932e8b5cc887ecf5c03a6a3281a04d4214d5.

https://github.com/llvm/llvm-project/pull/132887