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

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > We're missing expansion in LegalizeVectorOps. That's where `Expand` is supposed to be handled for vector arithmetic operations.
> 
> SelectionDAGLegalize::ExpandNode directly calls the CLMUL expansion, and LegalizeVectorOps is never called?

Ah yes, the code would be called when we follow-up with scalar custom-lowering of CLMUL[RH], without vector custom-lowering. Thanks.

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