[llvm] LoopIdiomRecognize: detect and convert powi idiom (PR #72650)

[Joe Faulls via llvm-commits]

https://github.com/joe-img commented:

I don't know if this is out of the scope of this change, but all the loops in the unit tests get reduced to a select and the icmp 0. Would it better off eliminating the check all together? Seeing as we're calling the intrinsic and I think it can handle the 0 exponent.

https://github.com/llvm/llvm-project/pull/72650