Merging r323190:

Merging r323190:
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r323190 | rksimon | 2018-01-23 12:39:06 +0100 (Tue, 23 Jan 2018) | 5 lines

[X86][SSE] LowerBUILD_VECTORAsVariablePermute - fix PSHUFB source/index operand ordering

As detailed in rL317463, PSHUFB (like most variable shuffle instructions) uses Op[0] for the source vector and Op[1] for the shuffle index vector, VPERMV works in reverse which is probably where the confusion comes from.

Differential Revision: https://reviews.llvm.org/D42380
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@323335 91177308-0d34-0410-b5e6-96231b3b80d8