[llvm] [HashRecognize] Rewrite arePHIsIntertwined (PR #144878)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> Checking that the two phis are somehow xored, but not checking what the xor is used for might catch some negative cases, but is not useful in general. What if the xor result is only written to stdout or an array? I believe we should check that the xor is in the use-def chain of `ConditionalRecurrence.Step`'s condition.

Thanks a lot for thinking deeply about this! There was indeed a huge hole in the previous implementation: I've added a pre-commit test, and completely redone the patch. This is a huge improvement!

https://github.com/llvm/llvm-project/pull/144878