[llvm] [SLPVectorizer][AMDGPU] Look-through vectorization of AMDGPU intrinsics (PR #175821)

[via llvm-commits]

xgxanq wrote:

> > @alexey-bataev The Look-through state is another sub-kind for target’s intrinsic call. The vectorized tree would otherwise be terminated by the target’s intrinsic call. Now the target’s intrinsic call is still the `NeedToGather` State, and `NeedToGather` of the target’s intrinsic call will be the root to try to build another vectorized tree.`NeedToGather` no longer marks the termination of the vectorized tree just because of the specific call. So do we need to consider introducing another state specifically for calls?
> 
> No, such nodes must serve as natural terminators of the trees and then as the roots of the new trees, they should not serve as the intermediate tree nodes

 In this PR  the `NeedToGather` of the target’s intrinsic call is already a kind of intermediate tree nodes,so what exactly are you arguing against?

https://github.com/llvm/llvm-project/pull/175821