[DAG] Reword comment for EnforceNodeIdInvariant and InvalidateNodeId. NFC.

[niravd]

LGTM modulo minor typo that was missed from before.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

1052–1060

While we're at it, "successor"*

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

1052–1060

comma after -1 I think.

1056

I think there should be a comma after "merged".

1057

Why did "property." get bumped off the previous line?

1062–1063

"reversable the original Id" -> "reversable to the original Id" maybe?

[madhur13490]

rebase + address comments

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

void NodeDeleted(SDNode *N, SDNode *E) override {
     if (ISelPosition == SelectionDAG::allnodes_iterator(N))
       ++ISelPosition;
   }
 };
 
 } // end anonymous namespace
 
 // This function is used to enforce the topological node id property
-// property leveraged during Instruction selection. Before selection all
-// nodes are given a non-negative id such that all nodes have a larger id than
+// leveraged during instruction selection. Before the selection process all
+// nodes are given a non-negative id such that all nodes have a greater id than
 // their operands. As this holds transitively we can prune checks that a node N
 // is a predecessor of M another by not recursively checking through M's
-// operands if N's ID is larger than M's ID. This is significantly improves
-// performance of for various legality checks (e.g. IsLegalToFold /
-// UpdateChains).
-
-// However, when we fuse multiple nodes into a single node
-// during selection we may induce a predecessor relationship between inputs and
-// outputs of distinct nodes being merged violating the topological property.
-// Should a fused node have a successor which has yet to be selected, our
-// legality checks would be incorrect. To avoid this we mark all unselected
-// sucessor nodes, i.e. id != -1 as invalid for pruning by bit-negating (x =>
+// operands if N's ID is larger than M's ID. This significantly improves
+// performance of various legality checks (e.g. IsLegalToFold / UpdateChains).
+
+// However, when we fuse multiple nodes into a single node during the
+// selection we may induce a predecessor relationship between inputs and
+// outputs of distinct nodes being merged, violating the topological property.
+// Should a fused node have a successor which has yet to be selected,
+// our legality checks would be incorrect. To avoid this we mark all unselected
+// successor nodes, i.e. id != -1, as invalid for pruning by bit-negating (x =>
 // (-(x+1))) the ids and modify our pruning check to ignore negative Ids of M.
 // We use bit-negation to more clearly enforce that node id -1 can only be
-// achieved by selected nodes). As the conversion is reversable the original Id,
-// topological pruning can still be leveraged when looking for unselected nodes.
-// This method is call internally in all ISel replacement calls.
+// achieved by selected nodes. As the conversion is reversable to the original
+// Id, topological pruning can still be leveraged when looking for unselected
+// nodes. This method is called internally in all ISel replacement related
+// functions.
 void SelectionDAGISel::EnforceNodeIdInvariant(SDNode *Node) {
   SmallVector<SDNode *, 4> Nodes;
   Nodes.push_back(Node);
 
   while (!Nodes.empty()) {
     SDNode *N = Nodes.pop_back_val();
     for (auto *U : N->uses()) {
       auto UId = U->getNodeId();
       if (UId > 0) {
         InvalidateNodeId(U);
         Nodes.push_back(U);
       }
     }
   }
 }
 
-// InvalidateNodeId - As discusses in EnforceNodeIdInvariant, mark a
+// InvalidateNodeId - As explained in EnforceNodeIdInvariant, mark a
 // NodeId with the equivalent node id which is invalid for topological
 // pruning.
 void SelectionDAGISel::InvalidateNodeId(SDNode *N) {
   int InvalidId = -(N->getNodeId() + 1);
   N->setNodeId(InvalidId);
 }
 
 // getUninvalidatedNodeId - get original uninvalidated node id.