[llvm] [MachineCombiner] Don't ignore PHI depths (PR #82025)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

> LGTM (although I don't know this code that well) - any other comments?

I guess I will commit this then if there is no other comment. Thanks for review.

@LuoYuanke @asi-sc @preames @uweigand

https://github.com/llvm/llvm-project/pull/82025