[X86][SSE] createVariablePermute - move index vector canonicalization to top of function. NFCI.

This is to make it easier to return early from the switch statement with custom lowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327140 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Simon Pilgrim

lib/Target/X86/X86ISelLowering.cpp

@@ -7914,9 +7914,19 @@ static SDValue materializeVectorConstant(SDValue Op, SelectionDAG &DAG,
 SDValue createVariablePermute(MVT VT, SDValue SrcVec, SDValue IndicesVec,
                               SDLoc &DL, SelectionDAG &DAG,
                               const X86Subtarget &Subtarget) {
-  unsigned Opcode = 0;
   MVT ShuffleVT = VT;
+  EVT IndicesVT = EVT(VT).changeVectorElementTypeToInteger();
+  unsigned NumElts = VT.getVectorNumElements();
 
+  // Adjust IndicesVec to match VT size.
+  assert(IndicesVec.getValueType().getVectorNumElements() >= NumElts &&
+         "Illegal variable permute mask size");
+  if (IndicesVec.getValueType().getVectorNumElements() > NumElts)
+    IndicesVec = extractSubVector(IndicesVec, 0, DAG, SDLoc(IndicesVec),
+                                  NumElts * VT.getScalarSizeInBits());
+  IndicesVec = DAG.getZExtOrTrunc(IndicesVec, SDLoc(IndicesVec), IndicesVT);
+
+  unsigned Opcode = 0;
   switch (VT.SimpleTy) {
   default:
     break;
@@ -7994,16 +8004,6 @@ SDValue createVariablePermute(MVT VT, SDValue SrcVec, SDValue IndicesVec,
          (VT.getScalarSizeInBits() % ShuffleVT.getScalarSizeInBits()) == 0 &&
          "Illegal variable permute shuffle type");
 
-  unsigned NumElts = VT.getVectorNumElements();
-  if (IndicesVec.getValueType().getVectorNumElements() < NumElts)
-    return SDValue();
-  else if (IndicesVec.getValueType().getVectorNumElements() > NumElts)
-    IndicesVec = extractSubVector(IndicesVec, 0, DAG, SDLoc(IndicesVec),
-                                  NumElts * VT.getScalarSizeInBits());
-
-  MVT IndicesVT = EVT(VT).changeVectorElementTypeToInteger().getSimpleVT();
-  IndicesVec = DAG.getZExtOrTrunc(IndicesVec, SDLoc(IndicesVec), IndicesVT);
-
   if (SrcVec.getValueSizeInBits() > VT.getSizeInBits())
     return SDValue();
   else if (SrcVec.getValueSizeInBits() < VT.getSizeInBits()) {