[IR] Add a dedicated FNeg IR Instruction

The IEEE-754 Standard makes it clear that fneg(x) and
fsub(-0.0, x) are two different operations. The former is a bitwise
operation, while the latter is an arithmetic operation. This patch
creates a dedicated FNeg IR Instruction to model that behavior.

Differential Revision: https://reviews.llvm.org/D53877

llvm-svn: 346774

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 2351e7e..7368a4c 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1780,6 +1780,36 @@ Constant *ConstantExpr::getAddrSpaceCast(Constant *C, Type *DstTy,
   return getFoldedCast(Instruction::AddrSpaceCast, C, DstTy, OnlyIfReduced);
 }
 
+Constant *ConstantExpr::get(unsigned Opcode, Constant *C, unsigned Flags, 
+                            Type *OnlyIfReducedTy) {
+  // Check the operands for consistency first.
+  assert(Instruction::isUnaryOp(Opcode) &&
+         "Invalid opcode in unary constant expression");
+
+#ifndef NDEBUG
+  switch (Opcode) {
+  case Instruction::FNeg:
+    assert(C->getType()->isFPOrFPVectorTy() &&
+           "Tried to create a floating-point operation on a "
+           "non-floating-point type!");
+    break;
+  default:
+    break;
+  }
+#endif
+
+  // TODO: Try to constant fold operation.
+
+  if (OnlyIfReducedTy == C->getType())
+    return nullptr;
+
+  Constant *ArgVec[] = { C };
+  ConstantExprKeyType Key(Opcode, ArgVec, 0, Flags);
+
+  LLVMContextImpl *pImpl = C->getContext().pImpl;
+  return pImpl->ExprConstants.getOrCreate(C->getType(), Key);
+}
+
 Constant *ConstantExpr::get(unsigned Opcode, Constant *C1, Constant *C2,
                             unsigned Flags, Type *OnlyIfReducedTy) {
   // Check the operands for consistency first.