[llvm] InstCombine: extend select-equiv to support vectors (PR #111966)

[via llvm-commits]

goldsteinn wrote:

> Shufflevector is not the only lane-crossing operation, see
> 
> https://github.com/llvm/llvm-project/blob/80c15c48d1fbb53478c9400e598abcbdcae0d962/llvm/lib/Analysis/InstructionSimplify.cpp#L4347-L4351
> for a more accurate heuristic.

Might be nice to make this a helper

https://github.com/llvm/llvm-project/pull/111966