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 VState = getValueState(I.getOperand(0));
+
+  LatticeVal &IV = ValueState[&I];
+  if (IV.isOverdefined()) return;
+
+  if (VState.isConstant()) {
+    Constant *C = ConstantExpr::get(I.getOpcode(), VState.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 (!VState.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/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
+}