[DAGCombiner] Remove extra bitcasts surrounding vector shuffles

Patch to remove extra bitcasts from shuffles, this is often a legacy of XformToShuffleWithZero being used to combine bitmaskings (of float vectors bitcast to integer vectors) into shuffles: bitcast(shuffle(bitcast(s0),bitcast(s1))) -> shuffle(s0,s1)

Differential Revision: http://reviews.llvm.org/D9097

llvm-svn: 235578

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -6934,6 +6934,51 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
       return CombineLD;
   }
 
+  // Remove double bitcasts from shuffles - this is often a legacy of
+  // XformToShuffleWithZero being used to combine bitmaskings (of
+  // float vectors bitcast to integer vectors) into shuffles.
+  // bitcast(shuffle(bitcast(s0),bitcast(s1))) -> shuffle(s0,s1)
+  if (Level < AfterLegalizeDAG && TLI.isTypeLegal(VT) && VT.isVector() &&
+      N0->getOpcode() == ISD::VECTOR_SHUFFLE &&
+      VT.getVectorNumElements() >= N0.getValueType().getVectorNumElements() &&
+      !(VT.getVectorNumElements() % N0.getValueType().getVectorNumElements())) {
+    ShuffleVectorSDNode *SVN = cast<ShuffleVectorSDNode>(N0);
+
+    // If operands are a bitcast, peek through if it casts the original VT.
+    // If operands are a UNDEF or constant, just bitcast back to original VT.
+    auto PeekThroughBitcast = [&](SDValue Op) {
+      if (Op.getOpcode() == ISD::BITCAST &&
+          Op.getOperand(0)->getValueType(0) == VT)
+        return SDValue(Op.getOperand(0));
+      if (ISD::isBuildVectorOfConstantSDNodes(Op.getNode()) ||
+          ISD::isBuildVectorOfConstantFPSDNodes(Op.getNode()))
+        return DAG.getNode(ISD::BITCAST, SDLoc(N), VT, Op);
+      return SDValue();
+    };
+
+    SDValue SV0 = PeekThroughBitcast(N0->getOperand(0));
+    SDValue SV1 = PeekThroughBitcast(N0->getOperand(1));
+    if (!(SV0 && SV1))
+      return SDValue();
+
+    int MaskScale =
+        VT.getVectorNumElements() / N0.getValueType().getVectorNumElements();
+    SmallVector<int, 8> NewMask;
+    for (int M : SVN->getMask())
+      for (int i = 0; i != MaskScale; ++i)
+        NewMask.push_back(M < 0 ? -1 : M * MaskScale + i);
+
+    bool LegalMask = TLI.isShuffleMaskLegal(NewMask, VT);
+    if (!LegalMask) {
+      std::swap(SV0, SV1);
+      ShuffleVectorSDNode::commuteMask(NewMask);
+      LegalMask = TLI.isShuffleMaskLegal(NewMask, VT);
+    }
+
+    if (LegalMask)
+      return DAG.getVectorShuffle(VT, SDLoc(N), SV0, SV1, NewMask);
+  }
+
   return SDValue();
 }
 

llvm/test/CodeGen/X86/combine-or.ll

@@ -277,6 +277,70 @@ define <2 x i64> @test21(<2 x i64> %a, <2 x i64> %b) {
   ret <2 x i64> %or
 }
 
+
+; Verify that the dag-combiner keeps the correct domain for float/double vectors
+; bitcast to use the mask-or blend combine.
+
+define <2 x double> @test22(<2 x double> %a0, <2 x double> %a1) {
+; CHECK-LABEL: test22:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    blendpd {{.*#+}} xmm0 = xmm1[0],xmm0[1]
+; CHECK-NEXT:    retq
+  %bc1 = bitcast <2 x double> %a0 to <2 x i64>
+  %bc2 = bitcast <2 x double> %a1 to <2 x i64>
+  %and1 = and <2 x i64> %bc1, <i64 0, i64 -1>
+  %and2 = and <2 x i64> %bc2, <i64 -1, i64 0>
+  %or = or <2 x i64> %and1, %and2
+  %bc3 = bitcast <2 x i64> %or to <2 x double>
+  ret <2 x double> %bc3
+}
+
+
+define <4 x float> @test23(<4 x float> %a0, <4 x float> %a1) {
+; CHECK-LABEL: test23:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    blendps {{.*#+}} xmm0 = xmm1[0],xmm0[1,2],xmm1[3]
+; CHECK-NEXT:    retq
+  %bc1 = bitcast <4 x float> %a0 to <4 x i32>
+  %bc2 = bitcast <4 x float> %a1 to <4 x i32>
+  %and1 = and <4 x i32> %bc1, <i32 0, i32 -1, i32 -1, i32 0>
+  %and2 = and <4 x i32> %bc2, <i32 -1, i32 0, i32 0, i32 -1>
+  %or = or <4 x i32> %and1, %and2
+  %bc3 = bitcast <4 x i32> %or to <4 x float>
+  ret <4 x float> %bc3
+}
+
+
+define <4 x float> @test24(<4 x float> %a0, <4 x float> %a1) {
+; CHECK-LABEL: test24:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    blendpd {{.*#+}} xmm0 = xmm1[0],xmm0[1]
+; CHECK-NEXT:    retq
+  %bc1 = bitcast <4 x float> %a0 to <2 x i64>
+  %bc2 = bitcast <4 x float> %a1 to <2 x i64>
+  %and1 = and <2 x i64> %bc1, <i64 0, i64 -1>
+  %and2 = and <2 x i64> %bc2, <i64 -1, i64 0>
+  %or = or <2 x i64> %and1, %and2
+  %bc3 = bitcast <2 x i64> %or to <4 x float>
+  ret <4 x float> %bc3
+}
+
+
+define <4 x float> @test25(<4 x float> %a0) {
+; CHECK-LABEL: test25:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    blendps {{.*#+}} xmm0 = mem[0],xmm0[1,2],mem[3]
+; CHECK-NEXT:    retq
+  %bc1 = bitcast <4 x float> %a0 to <4 x i32>
+  %bc2 = bitcast <4 x float> <float 1.0, float 1.0, float 1.0, float 1.0> to <4 x i32>
+  %and1 = and <4 x i32> %bc1, <i32 0, i32 -1, i32 -1, i32 0>
+  %and2 = and <4 x i32> %bc2, <i32 -1, i32 0, i32 0, i32 -1>
+  %or = or <4 x i32> %and1, %and2
+  %bc3 = bitcast <4 x i32> %or to <4 x float>
+  ret <4 x float> %bc3
+}
+
+
 ; Verify that the DAGCombiner doesn't crash in the attempt to check if a shuffle
 ; with illegal type has a legal mask. Method 'isShuffleMaskLegal' only knows how to
 ; handle legal vector value types.