diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 74468e8..2ea1e7d 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -999,7 +999,9 @@
                                        const TargetLibraryInfo *TLI) {
   Type *DestTy = InstOrCE->getType();
 
-  // Handle easy binops first.
+  if (Instruction::isUnaryOp(Opcode))
+    return ConstantFoldUnaryOpOperand(Opcode, Ops[0], DL);
+
   if (Instruction::isBinaryOp(Opcode))
     return ConstantFoldBinaryOpOperands(Opcode, Ops[0], Ops[1], DL);
 
@@ -1262,6 +1264,13 @@
   return ConstantExpr::getCompare(Predicate, Ops0, Ops1);
 }
 
+Constant *llvm::ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op,
+                                           const DataLayout &DL) {
+  assert(Instruction::isUnaryOp(Opcode));
+
+  return ConstantExpr::get(Opcode, Op);
+}
+
 Constant *llvm::ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS,
                                              Constant *RHS,
                                              const DataLayout &DL) {
diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 1dfd528..835fbb3 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -918,6 +918,52 @@
   return ConstantVector::get(Result);
 }
 
+Constant *llvm::ConstantFoldUnaryInstruction(unsigned Opcode, Constant *C) {
+  assert(Instruction::isUnaryOp(Opcode) && "Non-unary instruction detected");
+
+  // Handle scalar UndefValue. Vectors are always evaluated per element.
+  bool HasScalarUndef = !C->getType()->isVectorTy() && isa<UndefValue>(C);
+
+  if (HasScalarUndef) {
+    switch (static_cast<Instruction::UnaryOps>(Opcode)) {
+    case Instruction::FNeg:
+      return C; // -undef -> undef
+    case Instruction::UnaryOpsEnd:
+      llvm_unreachable("Invalid UnaryOp");
+    }
+  }
+
+  // Constant should not be UndefValue, unless these are vector constants.
+  assert(!HasScalarUndef && "Unexpected UndefValue");
+  // We only have FP UnaryOps right now.
+  assert(!isa<ConstantInt>(C) && "Unexpected Integer UnaryOp");
+
+  if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
+    const APFloat &CV = CFP->getValueAPF();
+    switch (Opcode) {
+    default:
+      break;
+    case Instruction::FNeg:
+      return ConstantFP::get(C->getContext(), neg(CV));
+    }
+  } else if (VectorType *VTy = dyn_cast<VectorType>(C->getType())) {
+    // Fold each element and create a vector constant from those constants.
+    SmallVector<Constant*, 16> Result;
+    Type *Ty = IntegerType::get(VTy->getContext(), 32);
+    for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
+      Constant *ExtractIdx = ConstantInt::get(Ty, i);
+      Constant *Elt = ConstantExpr::getExtractElement(C, ExtractIdx);
+
+      Result.push_back(ConstantExpr::get(Opcode, Elt));
+    }
+
+    return ConstantVector::get(Result);
+  }
+
+  // We don't know how to fold this.
+  return nullptr;
+}
+
 Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
                                               Constant *C2) {
   assert(Instruction::isBinaryOp(Opcode) && "Non-binary instruction detected");
diff --git a/llvm/lib/IR/ConstantFold.h b/llvm/lib/IR/ConstantFold.h
index b57153b..9ad6e14 100644
--- a/llvm/lib/IR/ConstantFold.h
+++ b/llvm/lib/IR/ConstantFold.h
@@ -43,6 +43,7 @@
                                                 ArrayRef<unsigned> Idxs);
   Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val,
                                                ArrayRef<unsigned> Idxs);
+  Constant *ConstantFoldUnaryInstruction(unsigned Opcode, Constant *V);
   Constant *ConstantFoldBinaryInstruction(unsigned Opcode, Constant *V1,
                                           Constant *V2);
   Constant *ConstantFoldCompareInstruction(unsigned short predicate,
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 00c7226..5545eb4 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1830,7 +1830,8 @@
   }
 #endif
 
-  // TODO: Try to constant fold operation.
+  if (Constant *FC = ConstantFoldUnaryInstruction(Opcode, C))
+    return FC;
 
   if (OnlyIfReducedTy == C->getType())
     return nullptr;
@@ -1909,7 +1910,7 @@
 #endif
 
   if (Constant *FC = ConstantFoldBinaryInstruction(Opcode, C1, C2))
-    return FC;          // Fold a few common cases.
+    return FC;
 
   if (OnlyIfReducedTy == C1->getType())
     return nullptr;
@@ -2235,7 +2236,7 @@
 Constant *ConstantExpr::getFNeg(Constant *C) {
   assert(C->getType()->isFPOrFPVectorTy() &&
          "Cannot FNEG a non-floating-point value!");
-  return getFSub(ConstantFP::getZeroValueForNegation(C->getType()), C);
+  return get(Instruction::FNeg, C);
 }
 
 Constant *ConstantExpr::getNot(Constant *C) {
@@ -3024,7 +3025,8 @@
   case Instruction::FCmp:
     return CmpInst::Create((Instruction::OtherOps)getOpcode(),
                            (CmpInst::Predicate)getPredicate(), Ops[0], Ops[1]);
-
+  case Instruction::FNeg:
+    return UnaryOperator::Create((Instruction::UnaryOps)getOpcode(), Ops[0]);
   default:
     assert(getNumOperands() == 2 && "Must be binary operator?");
     BinaryOperator *BO =