[PATCH] [X86][AVX2] vpslldq/vpsrldq byte shifts for AVX2

[Simon Pilgrim]

The AVX1 splits fail because the x86 computeZeroableShuffleElements() call isn't recursive - so can't peek through nodes (mainly shuffles but concat / subvector etc, as well do crop up). I'm hoping to give that code an overhaul in the near future - plus there is nothing x86 specific about it and would be useful to provide for others targets, the DAGCombiner etc. to check for zeros/zeroables. If you want I can do that work first and then update this patch?


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http://reviews.llvm.org/D7596

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