[all-commits] [llvm/llvm-project] e85d2e: [InstCombine] prevent infinite loop from conflicti...

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: e85d2e4981b9db98798ce3e15078775eb50be854
      https://github.com/llvm/llvm-project/commit/e85d2e4981b9db98798ce3e15078775eb50be854
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2019-11-25 (Mon, 25 Nov 2019)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

  Log Message:
  -----------
  [InstCombine] prevent infinite loop from conflicting shuffle mask transforms

The pattern in question is currently not possible because we
aggressively (wrongly) transform mask elements to undef values
if they choose from an undef operand. That, however, would
change if we tighten our semantics for shuffles as discussed
in D70641. Adding this check gives us the flexibility to make
that change with minimal overhead for current definitions.