[PATCH] [X86, AVX] recognize shufflevector with zero input as a vperm2 (PR22984)

[Sanjay Patel]

Forgot to mention - the codegen difference looks like this:

  vxorps	        %ymm1, %ymm1, %ymm1
  vinsertf128	$1, %xmm0, %ymm1, %ymm0

becomes:

  vperm2f128      $40, %ymm0, %ymm0, %ymm0

Or this:

  vxorps	        %ymm1, %ymm1, %ymm1
  vperm2f128      $33, %ymm1, %ymm0, %ymm0

becomes:

  vperm2f128      $129, %ymm0, %ymm0, %ymm0

I didn't include negative test cases because I think those are thoroughly covered by existing tests for vinsertf128, vblend, and vperm2f128.


http://reviews.llvm.org/D8563

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