Add some simple copysign folds

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26543 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1250,6 +1250,8 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
       case ISD::FREM :
         if (C2) return getConstantFP(fmod(C1, C2), VT);
         break;
+      case ISD::FCOPYSIGN:
+        return getConstantFP(copysign(C1, C2), VT);
       default: break;
       }
     } else {      // Cannonicalize constant to RHS if commutative