add a simple xform
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21203 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index f33ecd7..7cf8914 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -892,6 +892,12 @@
return getNode(ISD::SUB, VT, N1, N2.getOperand(0));
if (N1.getOpcode() == ISD::FNEG) // ((-A)+B) -> B-A
return getNode(ISD::SUB, VT, N2, N1.getOperand(0));
+ if (N1.getOpcode() == ISD::SUB && isa<ConstantSDNode>(N1.getOperand(0)) &&
+ cast<ConstantSDNode>(N1.getOperand(0))->getValue() == 0)
+ return getNode(ISD::SUB, VT, N2, N1.getOperand(1)); // (0-A)+B -> B-A
+ if (N2.getOpcode() == ISD::SUB && isa<ConstantSDNode>(N2.getOperand(0)) &&
+ cast<ConstantSDNode>(N2.getOperand(0))->getValue() == 0)
+ return getNode(ISD::SUB, VT, N1, N2.getOperand(1)); // A+(0-B) -> A-B
break;
case ISD::SUB:
if (N1.getOpcode() == ISD::ADD) {