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

Author: zmodem

lib/Target/X86/X86ISelLowering.cpp

@@ -7898,8 +7898,9 @@ LowerBUILD_VECTORAsVariablePermute(SDValue V, SelectionDAG &DAG,
         DAG.getNode(ISD::INSERT_SUBVECTOR, SDLoc(SrcVec), VT, DAG.getUNDEF(VT),
                     SrcVec, DAG.getIntPtrConstant(0, SDLoc(SrcVec)));
   }
-  return DAG.getNode(VT == MVT::v16i8 ? X86ISD::PSHUFB : X86ISD::VPERMV,
-                     SDLoc(V), VT, IndicesVec, SrcVec);
+  if (VT == MVT::v16i8)
+    return DAG.getNode(X86ISD::PSHUFB, SDLoc(V), VT, SrcVec, IndicesVec);
+  return DAG.getNode(X86ISD::VPERMV, SDLoc(V), VT, IndicesVec, SrcVec);
 }
 
 SDValue

test/CodeGen/X86/var-permute-128.ll

@@ -207,13 +207,12 @@ define <8 x i16> @var_shuffle_v8i16(<8 x i16> %v, <8 x i16> %indices) nounwind {
 define <16 x i8> @var_shuffle_v16i8(<16 x i8> %v, <16 x i8> %indices) nounwind {
 ; SSSE3-LABEL: var_shuffle_v16i8:
 ; SSSE3:       # %bb.0:
-; SSSE3-NEXT:    pshufb %xmm0, %xmm1
-; SSSE3-NEXT:    movdqa %xmm1, %xmm0
+; SSSE3-NEXT:    pshufb %xmm1, %xmm0
 ; SSSE3-NEXT:    retq
 ;
 ; AVX-LABEL: var_shuffle_v16i8:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vpshufb %xmm0, %xmm1, %xmm0
+; AVX-NEXT:    vpshufb %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %index0 = extractelement <16 x i8> %indices, i32 0
   %index1 = extractelement <16 x i8> %indices, i32 1