[llvm] [ISel] Introduce llvm.clmul intrinsic (PR #168731)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Is it not better to remove ISD::CLMULR and ISD::CLMULH from this patch? They seem to be complicating things and it might be better to just concentrate on clmul to begin with.

https://github.com/llvm/llvm-project/pull/168731