[llvm] [AArch64][ISel] Add custom lowering for clmul nxv8i16 (PR #195893)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

> > I've only given this a passing glance so please take with a pinch of salt, but isn't this just `trn1(pmullb(a,b), pmullt(a,b)`?
> 
> Do you pmullb as size s or b?

Oh, I assumed pmullb H->S existed but I see that's not an option. I guess you could promote the operands and use the S->D variant.  That should be better than what we have today although presumably not as good as what you've already implemented?

https://github.com/llvm/llvm-project/pull/195893