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

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Gentle ping. I think this patch would make a nice addition to LIR, even if there aren't too many idioms of this type in the wild.

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