[PATCH] D134879: [InstSimplify] look through vector select (shuffle) in min/max fold

[Sanjay Patel via Phabricator via llvm-commits]

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This is an extension of the existing min/max+select fold (which already has a very large number of variations) to allow a vector shuffle because that's what we have in the motivating example from issue #42100 <https://github.com/llvm/llvm-project/issues/42100>.

A couple of Alive2 checks of variants (I don't know how to generalize these in Alive):
https://alive2.llvm.org/ce/z/jUFAqT

And verify the PR42100 test:
https://alive2.llvm.org/ce/z/3EcASf

It's possible there is some generalization of the fold or a VectorCombine/SLP answer for the motivating test, but I haven't found a better/smaller solution yet. 
We can also add even more variants here as follow-up patches. For example, we can have shuffle followed by min/max; we also don't have this canonicalization or the reverse:
https://alive2.llvm.org/ce/z/StHD9f


https://reviews.llvm.org/D134879

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/select-maxmin.ll
  llvm/test/Transforms/PhaseOrdering/vector-select.ll

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