Lower BUILD_VECTOR to SHUFFLE + INSERT_VECTOR_ELT for X86

- If INSERT_VECTOR_ELT is supported (above SSE2, either by custom
  sequence of legal insn), transform BUILD_VECTOR into SHUFFLE +
  INSERT_VECTOR_ELT if most of elements could be built from SHUFFLE with few
  (so far 1) elements being inserted.

llvm-svn: 166288

1 files changed, 79 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a205aef7427..2e77e64f2f2 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5176,6 +5176,80 @@ X86TargetLowering::LowerVectorBroadcast(SDValue Op, SelectionDAG &DAG) const {
 }
 
 SDValue
+X86TargetLowering::buildFromShuffleMostly(SDValue Op, SelectionDAG &DAG) const {
+  EVT VT = Op.getValueType();
+
+  // Skip if insert_vec_elt is not supported.
+  if (!isOperationLegalOrCustom(ISD::INSERT_VECTOR_ELT, VT))
+    return SDValue();
+
+  DebugLoc DL = Op.getDebugLoc();
+  unsigned NumElems = Op.getNumOperands();
+
+  SDValue VecIn1;
+  SDValue VecIn2;
+  SmallVector<unsigned, 4> InsertIndices;
+  SmallVector<int, 8> Mask(NumElems, -1);
+
+  for (unsigned i = 0; i != NumElems; ++i) {
+    unsigned Opc = Op.getOperand(i).getOpcode();
+
+    if (Opc == ISD::UNDEF)
+      continue;
+
+    if (Opc != ISD::EXTRACT_VECTOR_ELT) {
+      // Quit if more than 1 elements need inserting.
+      if (InsertIndices.size() > 1)
+        return SDValue();
+
+      InsertIndices.push_back(i);
+      continue;
+    }
+
+    SDValue ExtractedFromVec = Op.getOperand(i).getOperand(0);
+    SDValue ExtIdx = Op.getOperand(i).getOperand(1);
+
+    // Quit if extracted from vector of different type.
+    if (ExtractedFromVec.getValueType() != VT)
+      return SDValue();
+
+    // Quit if non-constant index.
+    if (!isa<ConstantSDNode>(ExtIdx))
+      return SDValue();
+
+    if (VecIn1.getNode() == 0)
+      VecIn1 = ExtractedFromVec;
+    else if (VecIn1 != ExtractedFromVec) {
+      if (VecIn2.getNode() == 0)
+        VecIn2 = ExtractedFromVec;
+      else if (VecIn2 != ExtractedFromVec)
+        // Quit if more than 2 vectors to shuffle
+        return SDValue();
+    }
+
+    unsigned Idx = cast<ConstantSDNode>(ExtIdx)->getZExtValue();
+
+    if (ExtractedFromVec == VecIn1)
+      Mask[i] = Idx;
+    else if (ExtractedFromVec == VecIn2)
+      Mask[i] = Idx + NumElems;
+  }
+
+  if (VecIn1.getNode() == 0)
+    return SDValue();
+
+  VecIn2 = VecIn2.getNode() ? VecIn2 : DAG.getUNDEF(VT);
+  SDValue NV = DAG.getVectorShuffle(VT, DL, VecIn1, VecIn2, &Mask[0]);
+  for (unsigned i = 0, e = InsertIndices.size(); i != e; ++i) {
+    unsigned Idx = InsertIndices[i];
+    NV = DAG.getNode(ISD::INSERT_VECTOR_ELT, DL, VT, NV, Op.getOperand(Idx),
+                     DAG.getIntPtrConstant(Idx));
+  }
+
+  return NV;
+}
+
+SDValue
 X86TargetLowering::LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const {
   DebugLoc dl = Op.getDebugLoc();
 
@@ -5451,6 +5525,11 @@ X86TargetLowering::LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const {
     if (LD.getNode())
       return LD;
 
+    // Check for a build vector from mostly shuffle plus few inserting.
+    SDValue Sh = buildFromShuffleMostly(Op, DAG);
+    if (Sh.getNode())
+      return Sh;
+
     // For SSE 4.1, use insertps to put the high elements into the low element.
     if (getSubtarget()->hasSSE41()) {
       SDValue Result;