Turn -0.0 - X -> fneg

llvm-svn: 21011

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 75352982034..052daa29c4e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -314,7 +314,7 @@ public:
   //
   void visitBinary(User &I, unsigned Opcode);
   void visitAdd(User &I) { visitBinary(I, ISD::ADD); }
-  void visitSub(User &I) { visitBinary(I, ISD::SUB); }
+  void visitSub(User &I);
   void visitMul(User &I) { visitBinary(I, ISD::MUL); }
   void visitDiv(User &I) {
     visitBinary(I, I.getType()->isUnsigned() ? ISD::UDIV : ISD::SDIV);
@@ -454,6 +454,18 @@ void SelectionDAGLowering::visitBr(BranchInst &I) {
   }
 }
 
+void SelectionDAGLowering::visitSub(User &I) {
+  // -0.0 - X --> fneg
+  if (ConstantFP *CFP = dyn_cast<ConstantFP>(I.getOperand(0)))
+    if (CFP->isExactlyValue(-0.0)) {
+      SDOperand Op2 = getValue(I.getOperand(1));
+      setValue(&I, DAG.getNode(ISD::FNEG, Op2.getValueType(), Op2));
+      return;
+    }
+
+  visitBinary(I, ISD::SUB);
+}
+
 void SelectionDAGLowering::visitBinary(User &I, unsigned Opcode) {
   SDOperand Op1 = getValue(I.getOperand(0));
   SDOperand Op2 = getValue(I.getOperand(1));