Index: llvm/lib/Transforms/Scalar/SCCP.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/SCCP.cpp
+++ llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -613,6 +613,7 @@
 
   void visitCastInst(CastInst &I);
   void visitSelectInst(SelectInst &I);
+  void visitUnaryOperator(Instruction &I);
   void visitBinaryOperator(Instruction &I);
   void visitCmpInst(CmpInst &I);
   void visitExtractValueInst(ExtractValueInst &EVI);
@@ -969,6 +970,29 @@
   markOverdefined(&I);
 }
 
+// Handle Unary Operators.
+void SCCPSolver::visitUnaryOperator(Instruction &I) {
+  LatticeVal V0State = getValueState(I.getOperand(0));
+
+  LatticeVal &IV = ValueState[&I];
+  if (IV.isOverdefined()) return;
+
+  if (V0State.isConstant()) {
+    Constant *C = ConstantExpr::get(I.getOpcode(), V0State.getConstant());
+
+    // op Y -> undef.
+    if (isa<UndefValue>(C))
+      return;
+    return (void)markConstant(IV, &I, C);
+  }
+
+  // If something is undef, wait for it to resolve.
+  if (!V0State.isOverdefined())
+    return;
+
+  markOverdefined(&I);
+}
+
 // Handle Binary Operators.
 void SCCPSolver::visitBinaryOperator(Instruction &I) {
   LatticeVal V1State = getValueState(I.getOperand(0));
@@ -1484,6 +1508,8 @@
         else
           markOverdefined(&I);
         return true;
+      case Instruction::FNeg:
+        break; // fneg undef -> undef
       case Instruction::ZExt:
       case Instruction::SExt:
       case Instruction::FPToUI:
Index: llvm/test/Transforms/SCCP/apfloat-basictest.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SCCP/apfloat-basictest.ll
@@ -0,0 +1,33 @@
+; This is a basic sanity check for constant propagation. The fneg instruction
+; should be eliminated.
+
+; RUN: opt < %s -sccp -S | not grep fneg
+
+define double @test(i1 %B) {
+	br i1 %B, label %BB1, label %BB2
+BB1:
+	%Val = fneg double 42.0
+	br label %BB3
+BB2:
+	br label %BB3
+BB3:
+	%Ret = phi double [%Val, %BB1], [1.0, %BB2]
+	ret double %Ret
+; CHECK-LABEL: @test(
+; CHECK: [[PHI:%.*]] = phi double [ -4.200000e+01, %BB1 ], [ 1.000000e+00, %BB2 ]i
+}
+
+define double @test1(i1 %B) {
+        br i1 %B, label %BB1, label %BB2
+BB1:    
+        %Div = fdiv double 1.0, 1.0        
+        %Val = fneg double %Div
+        br label %BB3
+BB2:
+        br label %BB3
+BB3:
+        %Ret = phi double [%Val, %BB1], [1.0, %BB2]
+        ret double %Ret
+; CHECK-LABEL: @test1(
+; CHECK: [[PHI:%.*]] = phi double [ -1.000000e+00, %BB1 ], [ 1.000000e+00, %BB2 ]
+}
Index: llvm/test/Transforms/SCCP/undef-resolve.ll
===================================================================
--- llvm/test/Transforms/SCCP/undef-resolve.ll
+++ llvm/test/Transforms/SCCP/undef-resolve.ll
@@ -180,3 +180,11 @@
 ; CHECK-LABEL: @test11(
 ; CHECK: ret i32 0
 }
+
+; Test unary ops
+define double @test12(double %x) {
+  %t = fneg double undef
+  ret double %t
+; CHECK-LABEL: @test12(
+; CHECK: double undef
+}