[llvm] [LoopIdiomRecognizer] Implement CRC recognition (PR #79295)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

@joe-img I went through the code and just from looking this seems to work correctly. However, I still stand by my suggestions in this comment: https://github.com/llvm/llvm-project/pull/79295#issuecomment-1962269129 

I agree that the interpreter approach is better than trying to recognize all variations of the pattern in the source code.

I don't insist that you follow my suggestions and I am OK with someone else approving this as long as this is not enabled by default. This way we can merge your work and maybe improve on it gradually.

https://github.com/llvm/llvm-project/pull/79295