[turbofan] Avoid repeatedly revisiting inputs in GraphReducer.

src/compiler/graph-reducer.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_GRAPH_REDUCER_H_
 #define V8_COMPILER_GRAPH_REDUCER_H_
 
 #include "src/zone-containers.h"
 
 namespace v8 {
@@ skipping 50 matching lines @@
 
   void AddReducer(Reducer* reducer);
 
   // Reduce a single node.
   void ReduceNode(Node* const);
   // Reduce the whole graph.
   void ReduceGraph();
 
  private:
   enum class State : uint8_t;
+  struct NodeState {
+    Node* node;
+    int input_index;
+  };
 
   // Reduce a single node.
   Reduction Reduce(Node* const);
   // Reduce the node on top of the stack.
   void ReduceTop();
 
   // Node stack operations.
   void Pop();
   void Push(Node* const);
-  Node* Top() const;
 
   // Revisit queue operations.
   bool Recurse(Node* const);
   void Revisit(Node* const);
 
   Graph* graph_;
   ZoneVector<Reducer*> reducers_;
   ZoneStack<Node*> revisit_;
-  ZoneStack<Node*> stack_;
+  ZoneStack<NodeState> stack_;
   ZoneDeque<State> state_;
 
   DISALLOW_COPY_AND_ASSIGN(GraphReducer);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_REDUCER_H_