[llvm] [LoopIdiom] Use HashRecognize to optimize CRC (PR #143208)

[Piotr Fusik via llvm-commits]

https://github.com/pfusik commented:

What if the input loop did other things aside from calculating the CRC (such as calling `extern` functions)? Will we abandon this transform or preserve the non-CRC operations? Do we have a test for that?

I think we want to skip this transform if optimizing for size.

https://github.com/llvm/llvm-project/pull/143208