Move folding logic from DAGCombiner to X86ISelLowering as it is specific to X86

Author: Rohit Aggarwal

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -14295,78 +14295,6 @@ static SDValue widenAbs(SDNode *Extend, SelectionDAG &DAG) {
   return DAG.getZExtOrTrunc(NewAbs, SDLoc(Extend), VT);
 }
 
-// Try to widen the build vector and bitcast it to the type of zext.
-// This is a special case for the 128-bit vector types. Intention is to remove
-// the zext and replace it with a bitcast the wider type. While lowering
-// the bitcast is removed and extra commutation due to zext is avoided.
-// For example:
-// zext v4i16 ( v4i8 build_vector (x, y, z, w)) -> bitcast v4i16 ( v8i8
-// build_vector (x, 0, y, 0, z, w, 0)
-static SDValue widenBuildVec(SDNode *Extend, SelectionDAG &DAG) {
-
-  assert(Extend->getOpcode() == ISD::ZERO_EXTEND && "Expected zero extend.");
-
-  EVT ExtendVT = Extend->getValueType(0);
-
-  SDValue BV = Extend->getOperand(0);
-  if (BV.getOpcode() != ISD::BUILD_VECTOR || !BV.hasOneUse())
-    return SDValue();
-
-  if (any_of(BV->op_values(), [](SDValue Op) { return Op.isUndef(); })) {
-    // If the build vector has undef elements, we cannot widen it.
-    // The widening would create a vector with more undef elements, which
-    // is not valid.
-    return SDValue();
-  }
-
-  if (!all_of(BV->op_values(),
-              [](SDValue Op) { return Op.getOpcode() == ISD::LOAD; })) {
-    // If the build vector any element other than \ISD::LOAD, we cannot widen
-    // it.
-    return SDValue();
-  }
-
-  SDLoc dl(BV);
-  EVT VT = BV.getValueType();
-  EVT EltVT = BV.getOperand(0).getValueType();
-  unsigned NumElts = VT.getVectorNumElements();
-
-  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-
-  if (TLI.getTypeAction(*DAG.getContext(), VT) !=
-      TargetLowering::TypeWidenVector)
-    return SDValue();
-
-  EVT WidenVT = TLI.getTypeToTransformTo(*DAG.getContext(), VT);
-  unsigned WidenNumElts = WidenVT.getVectorNumElements();
-
-  SmallVector<SDValue, 16> NewOps(BV->op_begin(), BV->op_end());
-  assert(WidenNumElts >= NumElts && "Shrinking vector instead of widening!");
-  // Fill the new elements with Zero.
-  NewOps.append(WidenNumElts - NumElts, DAG.getConstant(0, dl, EltVT));
-  // Compute the step to place the elements in the right place and control the
-  // iteration.
-  unsigned step = WidenNumElts / NumElts;
-  if (WidenVT.is128BitVector()) {
-    if (step > 1 && Extend->getValueSizeInBits(0) == WidenVT.getSizeInBits()) {
-      for (int i = NumElts - 1, j = WidenNumElts - step; i > 0;
-           i--, j -= step) {
-        SDValue temp = NewOps[i];
-        NewOps[i] = NewOps[j];
-        NewOps[j] = temp;
-      }
-      // Create new build vector with WidenVT and NewOps
-      SDValue NewBV = DAG.getBuildVector(WidenVT, dl, NewOps);
-      // Replace the old build vector with the new one. Bitcast the
-      // new build vector to the type of the zext.
-      SDValue NewBVBitcast = DAG.getBitcast(ExtendVT, NewBV);
-      DAG.ReplaceAllUsesOfValueWith(SDValue(Extend, 0), NewBVBitcast);
-      return NewBV;
-    }
-  }
-  return SDValue();
-}
-
 SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   EVT VT = N->getValueType(0);
@@ -14693,9 +14621,6 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
       return SDValue(CSENode, 0);
   }
 
-  if (SDValue V = widenBuildVec(N, DAG))
-    return V;
-
   return SDValue();
 }
 

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -55936,6 +55936,79 @@ static SDValue combineFMADDSUB(SDNode *N, SelectionDAG &DAG,
                      NegN2);
 }
 
+// Try to widen the build vector and bitcast it to the type of zext.
+// This is a special case for the 128-bit vector types. Intention is to remove
+// the zext and replace it with a bitcast the wider type. While lowering
+// the bitcast is removed and extra commutation due to zext is avoided.
+// For example:
+// zext v4i16 ( v4i8 build_vector (x, y, z, w)) -> bitcast v4i16 ( v8i8
+// build_vector (x, 0, y, 0, z, w, 0)
+static SDValue widenBuildVec(SDNode *Extend, SelectionDAG &DAG) {
+
+  if (Extend->getOpcode() != ISD::ZERO_EXTEND)
+    return SDValue();
+
+  EVT ExtendVT = Extend->getValueType(0);
+
+  SDValue BV = Extend->getOperand(0);
+  if (BV.getOpcode() != ISD::BUILD_VECTOR || !BV.hasOneUse())
+    return SDValue();
+
+  if (any_of(BV->op_values(), [](SDValue Op) { return Op.isUndef(); })) {
+    // If the build vector has undef elements, we cannot widen it.
+    // The widening would create a vector with more undef elements, which
+    // is not valid.
+    return SDValue();
+  }
+
+  if (!all_of(BV->op_values(),
+              [](SDValue Op) { return Op.getOpcode() == ISD::LOAD; })) {
+    // If the build vector any element other than \ISD::LOAD, we cannot widen
+    // it.
+    return SDValue();
+  }
+
+  SDLoc dl(BV);
+  EVT VT = BV.getValueType();
+  EVT EltVT = BV.getOperand(0).getValueType();
+  unsigned NumElts = VT.getVectorNumElements();
+
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+
+  if (TLI.getTypeAction(*DAG.getContext(), VT) !=
+      TargetLowering::TypeWidenVector)
+    return SDValue();
+
+  EVT WidenVT = TLI.getTypeToTransformTo(*DAG.getContext(), VT);
+  unsigned WidenNumElts = WidenVT.getVectorNumElements();
+
+  SmallVector<SDValue, 16> NewOps(BV->op_begin(), BV->op_end());
+  assert(WidenNumElts >= NumElts && "Shrinking vector instead of widening!");
+  // Fill the new elements with Zero.
+  NewOps.append(WidenNumElts - NumElts, DAG.getConstant(0, dl, EltVT));
+  // Compute the step to place the elements in the right place and control the
+  // iteration.
+  unsigned step = WidenNumElts / NumElts;
+  if (WidenVT.is128BitVector()) {
+    if (step > 1 && Extend->getValueSizeInBits(0) == WidenVT.getSizeInBits()) {
+      for (int i = NumElts - 1, j = WidenNumElts - step; i > 0;
+           i--, j -= step) {
+        SDValue temp = NewOps[i];
+        NewOps[i] = NewOps[j];
+        NewOps[j] = temp;
+      }
+      // Create new build vector with WidenVT and NewOps
+      SDValue NewBV = DAG.getBuildVector(WidenVT, dl, NewOps);
+      // Replace the old build vector with the new one. Bitcast the
+      // new build vector to the type of the zext.
+      SDValue NewBVBitcast = DAG.getBitcast(ExtendVT, NewBV);
+      DAG.ReplaceAllUsesOfValueWith(SDValue(Extend, 0), NewBVBitcast);
+      return NewBV;
+    }
+  }
+  return SDValue();
+}
+
 static SDValue combineZext(SDNode *N, SelectionDAG &DAG,
                            TargetLowering::DAGCombinerInfo &DCI,
                            const X86Subtarget &Subtarget) {
@@ -55995,6 +56068,9 @@ static SDValue combineZext(SDNode *N, SelectionDAG &DAG,
     }
   }
 
+  if (SDValue V = widenBuildVec(N, DAG))
+    return V;
+
   return SDValue();
 }