[llvm] Reduce shl64 to shl32 if shift range is [63-32] (PR #125574)

[via llvm-commits]

LU-JOHN wrote:





> > Should I generalize the reduction to include shl32 -> shl16?
> 
> I would prepare to generalize it, but do the reduction as a separate step

Then should we also add half-sized testing:

>I mean a 32-bit shift that is reducible to 16-bit. Everything just half sized. We should do that, but it's trickier because we don't > want to force vector usage in scalar contexts

in a separate step?

https://github.com/llvm/llvm-project/pull/125574