[DAGCombine] Remove dead node when it is created by getNegatedExpression

We hit the compiling time reported by https://bugs.llvm.org/show_bug.cgi?id=46877
and the reason is the same as D77319. So we need to remove the dead node we created
to avoid increase the problem size of DAGCombiner.

Reviewed By: Spatel

Differential Revision: https://reviews.llvm.org/D86183

Author: QingShan Zhang

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -5737,6 +5737,11 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
       return SDValue();
   }
 
+  auto RemoveDeadNode = [&](SDValue N) {
+    if (N && N.getNode()->use_empty())
+      DAG.RemoveDeadNode(N.getNode());
+  };
+
   SDLoc DL(Op);
 
   switch (Opcode) {
@@ -5815,12 +5820,14 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
+      RemoveDeadNode(NegY);
       return DAG.getNode(ISD::FSUB, DL, VT, NegX, Y, Flags);
     }
 
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = CostY;
+      RemoveDeadNode(NegX);
       return DAG.getNode(ISD::FSUB, DL, VT, NegY, X, Flags);
     }
     break;
@@ -5858,6 +5865,7 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
+      RemoveDeadNode(NegY);
       return DAG.getNode(Opcode, DL, VT, NegX, Y, Flags);
     }
 
@@ -5869,6 +5877,7 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = CostY;
+      RemoveDeadNode(NegX);
       return DAG.getNode(Opcode, DL, VT, X, NegY, Flags);
     }
     break;
@@ -5898,12 +5907,14 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = std::min(CostX, CostZ);
+      RemoveDeadNode(NegY);
       return DAG.getNode(Opcode, DL, VT, NegX, Y, NegZ, Flags);
     }
 
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = std::min(CostY, CostZ);
+      RemoveDeadNode(NegX);
       return DAG.getNode(Opcode, DL, VT, X, NegY, NegZ, Flags);
     }
     break;