[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, 9 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index bf24d7f7562..ebe172548e3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2801,6 +2801,15 @@ static bool isVectorReductionOp(const User *I) {
   return ReduxExtracted;
 }
 
+void SelectionDAGBuilder::visitUnary(const User &I, unsigned Opcode) {
+  SDNodeFlags Flags;
+
+  SDValue Op = getValue(I.getOperand(0));
+  SDValue UnNodeValue = DAG.getNode(Opcode, getCurSDLoc(), Op.getValueType(),
+                                    Op, Flags);
+  setValue(&I, UnNodeValue);
+}
+
 void SelectionDAGBuilder::visitBinary(const User &I, unsigned Opcode) {
   SDNodeFlags Flags;
   if (auto *OFBinOp = dyn_cast<OverflowingBinaryOperator>(&I)) {