Add FNeg IR constant folding support

llvm-svn: 359982

1 files changed, 46 insertions, 0 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");