[llvm] [DAGCombiner] Attempt to fold 'add' nodes to funnel-shift or rotate (PR #125612)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon approved this pull request.

LGTM - I am still worried that we're possibly missing a corner case with the ADD nodes, but I can't see anything. I'd have still preferred we tried haveNoCommonBitsSet first tbh as although there's duplication, it's a lot more self contained.

https://github.com/llvm/llvm-project/pull/125612