[llvm] [LoopVectorizer] Prune VFs based on plan register pressure (PR #132190)

[John Brawn via llvm-commits]

john-brawn-arm wrote:

I _think_ what's caused this is previously in LoopVectorizationCostModel::getMaximizedVFForTarget only VFs greater than MaxVectorElementCount could be discarded for excess register usage, but now any VF can be discarded.

https://github.com/llvm/llvm-project/pull/132190