[X86] Combine vector anyext + and into a vector zext

Vector zext tends to get legalized into a vector anyext, represented as a vector shuffle with an undef vector + a bitcast, that gets ANDed with a mask that zeroes the undef elements.
Combine this into an explicit shuffle with a zero vector instead. This allows shuffle lowering to match it as a zext, instead of matching it as an anyext and emitting an explicit AND.
This combine only covers a subset of the cases, but it's a start.

Differential Revision: http://reviews.llvm.org/D7666

llvm-svn: 229480

1 files changed, 99 insertions, 9 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 92db12abfdf..1bdd6fead9d 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -24903,24 +24903,118 @@ static SDValue WidenMaskArithmetic(SDNode *N, SelectionDAG &DAG,
   }
 }
 
+static SDValue VectorZextCombine(SDNode *N, SelectionDAG &DAG,
+                                 TargetLowering::DAGCombinerInfo &DCI,
+                                 const X86Subtarget *Subtarget) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  SDLoc DL(N);
+
+  // A vector zext_in_reg may be represented as a shuffle,
+  // feeding into a bitcast (this represents anyext) feeding into
+  // an and with a mask.
+  // We'd like to try to combine that into a shuffle with zero
+  // plus a bitcast, removing the and.
+  if (N0.getOpcode() != ISD::BITCAST || 
+      N0.getOperand(0).getOpcode() != ISD::VECTOR_SHUFFLE)
+    return SDValue();
+
+  // The other side of the AND should be a splat of 2^C, where C
+  // is the number of bits in the source type.
+  if (N1.getOpcode() == ISD::BITCAST)
+    N1 = N1.getOperand(0);
+  if (N1.getOpcode() != ISD::BUILD_VECTOR)
+    return SDValue();
+  BuildVectorSDNode *Vector = cast<BuildVectorSDNode>(N1);
+
+  ShuffleVectorSDNode *Shuffle = cast<ShuffleVectorSDNode>(N0.getOperand(0));
+  EVT SrcType = Shuffle->getValueType(0);
+
+  // We expect a single-source shuffle
+  if (Shuffle->getOperand(1)->getOpcode() != ISD::UNDEF)
+    return SDValue();
+
+  unsigned SrcSize = SrcType.getScalarSizeInBits();
+
+  APInt SplatValue, SplatUndef;
+  unsigned SplatBitSize;
+  bool HasAnyUndefs;
+  if (!Vector->isConstantSplat(SplatValue, SplatUndef,
+                                SplatBitSize, HasAnyUndefs))
+    return SDValue();
+
+  unsigned ResSize = N1.getValueType().getScalarSizeInBits();
+  // Make sure the splat matches the mask we expect
+  if (SplatBitSize > ResSize || 
+      (SplatValue + 1).exactLogBase2() != SrcSize)
+    return SDValue();
+
+  // Make sure the input and output size make sense
+  if (SrcSize >= ResSize || ResSize % SrcSize)
+    return SDValue();
+
+  // We expect a shuffle of the form <0, u, u, u, 1, u, u, u...>
+  // The number of u's between each two values depends on the ratio between
+  // the source and dest type.
+  unsigned ZextRatio = ResSize / SrcSize;
+  bool IsZext = true;
+  for (unsigned i = 0; i < SrcType.getVectorNumElements(); ++i) {
+    if (i % ZextRatio) {
+      if (Shuffle->getMaskElt(i) > 0) {
+        // Expected undef
+        IsZext = false;
+        break;
+      }
+    } else {
+      if (Shuffle->getMaskElt(i) != (i / ZextRatio)) {
+        // Expected element number
+        IsZext = false;
+        break;
+      }
+    }
+  }
+
+  if (!IsZext)
+    return SDValue();
+
+  // Ok, perform the transformation - replace the shuffle with
+  // a shuffle of the form <0, k, k, k, 1, k, k, k> with zero
+  // (instead of undef) where the k elements come from the zero vector.
+  SmallVector<int, 8> Mask;
+  unsigned NumElems = SrcType.getVectorNumElements();
+  for (unsigned i = 0; i < NumElems; ++i)
+    if (i % ZextRatio)
+      Mask.push_back(NumElems);
+    else
+      Mask.push_back(i / ZextRatio);
+
+  SDValue NewShuffle = DAG.getVectorShuffle(Shuffle->getValueType(0), DL,
+    Shuffle->getOperand(0), DAG.getConstant(0, SrcType), Mask);
+  return DAG.getNode(ISD::BITCAST, DL,  N0.getValueType(), NewShuffle);
+}
+
 static SDValue PerformAndCombine(SDNode *N, SelectionDAG &DAG,
                                  TargetLowering::DAGCombinerInfo &DCI,
                                  const X86Subtarget *Subtarget) {
-  EVT VT = N->getValueType(0);
   if (DCI.isBeforeLegalizeOps())
     return SDValue();
 
+  SDValue Zext = VectorZextCombine(N, DAG, DCI, Subtarget);
+  if (Zext.getNode())
+    return Zext;
+
   SDValue R = CMPEQCombine(N, DAG, DCI, Subtarget);
   if (R.getNode())
     return R;
 
+  EVT VT = N->getValueType(0);
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  SDLoc DL(N);
+
   // Create BEXTR instructions
   // BEXTR is ((X >> imm) & (2**size-1))
   if (VT == MVT::i32 || VT == MVT::i64) {
-    SDValue N0 = N->getOperand(0);
-    SDValue N1 = N->getOperand(1);
-    SDLoc DL(N);
-
     // Check for BEXTR.
     if ((Subtarget->hasBMI() || Subtarget->hasTBM()) &&
         (N0.getOpcode() == ISD::SRA || N0.getOpcode() == ISD::SRL)) {
@@ -24948,10 +25042,6 @@ static SDValue PerformAndCombine(SDNode *N, SelectionDAG &DAG,
   if (VT != MVT::v2i64 && VT != MVT::v4i64)
     return SDValue();
 
-  SDValue N0 = N->getOperand(0);
-  SDValue N1 = N->getOperand(1);
-  SDLoc DL(N);
-
   // Check LHS for vnot
   if (N0.getOpcode() == ISD::XOR &&
       //ISD::isBuildVectorAllOnes(N0.getOperand(1).getNode()))