[PATCH] D31960: [InstSimplify] fold identity shuffles (recursing if needed)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added a subscriber: mcrosier.

Please have a hard look to make sure I haven't botched the shuffle mask logic...
This patch simplifies the examples from https://reviews.llvm.org/D31509 and https://reviews.llvm.org/D31927 (PR30630) and catches the basic identity shuffle tests that Zvi recently added.

I'm not sure if we have something like this in DAGCombiner, but we should?

It's worth noting that "MaxRecurse / RecursionLimit" is only 3 on entry at the moment. We might want to bump that up if there are longer shuffle chains like this in the wild.


https://reviews.llvm.org/D31960

Files:
  lib/Analysis/InstructionSimplify.cpp
  test/Transforms/InstSimplify/shufflevector.ll

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