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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > 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?

Yes

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