[llvm] VectorCombine: Fold chains of shuffles fed by length-changing shuffles (PR #168819)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

I believe I addressed all the review comments. Let me know if you want to take another look, I'll give it some time and then push it.

https://github.com/llvm/llvm-project/pull/168819