[llvm] [SelectionDAG] Recurse through mask expression trees in WidenVSELECTMask (PR #188085)

[Craig Topper via llvm-commits]

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topperc wrote:

How can we reuse the same ShuffleMask? Don't we need to increase the index for any element that references the second source if the number of elements changed?

https://github.com/llvm/llvm-project/pull/188085