[llvm] [GISel] funnel shift combiner port from SelectionDAG ISel to GlobalISel (PR #135132)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Thanks. The combine looks good - nice and clean - other than the points mentioned below.

We would not usually need to add combines that the midend can reliably perform unless they come up during lowering. I am not sure if that is expected in this case or not, from the legalization of higher sized types or from vectors.

https://github.com/llvm/llvm-project/pull/135132