3 files changed, 53 insertions, 4 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 1dfd5284a97..835fbb3443b 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -918,6 +918,52 @@ Constant *llvm::ConstantFoldInsertValueInstruction(Constant *Agg,
   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 b57153bf00b..9ad6e14e9e4 100644
--- a/llvm/lib/IR/ConstantFold.h
+++ b/llvm/lib/IR/ConstantFold.h
@@ -43,6 +43,7 @@ template <typename T> class ArrayRef;
                                                 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 00c722651ed..5545eb46686 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1830,7 +1830,8 @@ Constant *ConstantExpr::get(unsigned Opcode, Constant *C, unsigned Flags,
   }
 #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 @@ Constant *ConstantExpr::get(unsigned Opcode, Constant *C1, Constant *C2,
 #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::getNeg(Constant *C, bool HasNUW, bool HasNSW) {
 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 @@ Instruction *ConstantExpr::getAsInstruction() {
   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 =