[llvm] LoopIdiomRecognize: add negative tests for powi idiom (PR #72648)

[Yueh-Ting Chen via llvm-commits]

eopXD wrote:

Do you mind providing a snippet through godbolt on the options that produce the bad vectorized code you have mentioned? Specifically what backend?


https://github.com/llvm/llvm-project/pull/72648