[llvm] [AMDGPU] Vectorize more 16 bit shuffles (PR #90648)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> > > Alive2 complains about this patch:
> > 
> > 
> > This patch can't have broken this as it just changes the cost model, this must have just added test coverage that hits it
> 
> Or that, yes. Sorry, I meant there is a new test failing. The test didn't exist before.

Looks like something wrong in SLP vectorizer, I'll double check

https://github.com/llvm/llvm-project/pull/90648