[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
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f85582d..97043e1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6934,6 +6934,51 @@
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();
}