[llvm] [VectorCombine] Align shrinkLoadForShuffles to register boundaries (PR #209775)

[Timur Golubovich via llvm-commits]

timurgol007 wrote:

The x86 regressions were introduced by this PR: https://github.com/llvm/llvm-project/pull/153138. @PeddleSpam, could you please take a look? The issue is that when the vector contains only a single element, the type is legalized to a scalar. As a result, DAGCombiner can no longer form a VectorShuffle, leading to the observed regressions.

https://github.com/llvm/llvm-project/pull/209775