[llvm] [SLP] Fix isCommutative to check uses of the original instruction instead of the converted instruction. (PR #143094)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

This patch seems to fix the problems I saw in https://github.com/llvm/llvm-project/issues/142347

I suggest mentioning the ticket number in the commit message.

https://github.com/llvm/llvm-project/pull/143094