[llvm] [InstCombine] Fold patterns which uses <2N x iM> type for comparisons on <N x i2M> vector types (PR #184328)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

I'd expect this to be profitable in the general case, but I can help move this to VectorCombine if there's resistance to it being in InstCombine

https://github.com/llvm/llvm-project/pull/184328