[llvm] [SLP]Vectorize unique scalars of splat gather nodes as separate subtrees (PR #218250)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> > I think it is unrelated issue, will fix it in another PR
> 
> My understanding is that it is caused by the newly added `SplatGatheredScalarsRoots` not being cleared when it gets trimmed.

Fixed

https://github.com/llvm/llvm-project/pull/218250