[turbofan] Add support for advanced reducers.

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/compiler/node-marker.h"
 #include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Forward declarations.
 class Graph;
 class Node;
 
 
 // Represents the result of trying to reduce a node in the graph.
 class Reduction final {
  public:
-  explicit Reduction(Node* replacement = NULL) : replacement_(replacement) {}
+  explicit Reduction(Node* replacement = nullptr) : replacement_(replacement) {}
 
   Node* replacement() const { return replacement_; }
-  bool Changed() const { return replacement() != NULL; }
+  bool Changed() const { return replacement() != nullptr; }
 
  private:
   Node* replacement_;
 };
 
 
 // A reducer can reduce or simplify a given node based on its operator and
 // inputs. This class functions as an extension point for the graph reducer for
 // language-specific reductions (e.g. reduction based on types or constant
 // folding of low-level operators) can be integrated into the graph reduction
 // phase.
 class Reducer {
  public:
-  Reducer() {}
   virtual ~Reducer() {}
 
   // Try to reduce a node if possible.
   virtual Reduction Reduce(Node* node) = 0;
 
+  // Ask this reducer to finish operation, returns {true} if the reducer is
+  // done, while {false} indicates that the graph might need to be reduced
+  // again.
+  // TODO(turbofan): Remove this once the dead node trimming is in the
+  // GraphReducer.
+  virtual bool Finish();
+
   // Helper functions for subclasses to produce reductions for a node.
   static Reduction NoChange() { return Reduction(); }
   static Reduction Replace(Node* node) { return Reduction(node); }
   static Reduction Changed(Node* node) { return Reduction(node); }
+};
+
+
+// An advanced reducer can also edit the graphs by changing and replacing nodes
+// other than the one currently being reduced.
+class AdvancedReducer : public Reducer {
+ public:
+  // Observe the actions of this reducer.
+  class Editor {
+   public:
+    virtual ~Editor() {}
+
+    // Replace {node} with {replacement}.
+    virtual void Replace(Node* node, Node* replacement) = 0;
+    // Revisit the {node} again later.
+    virtual void Revisit(Node* node) = 0;
+  };
+
+  explicit AdvancedReducer(Editor* editor) : editor_(editor) {}
+
+ protected:
+  // Helper functions for subclasses to produce reductions for a node.
+  static Reduction Replace(Node* node) { return Reducer::Replace(node); }
+
+  // Helper functions for subclasses to edit the graph.
+  void Replace(Node* node, Node* replacement) {
+    DCHECK_NOT_NULL(editor_);
+    editor_->Replace(node, replacement);
+  }
+  void Revisit(Node* node) {
+    DCHECK_NOT_NULL(editor_);
+    editor_->Revisit(node);
+  }
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(Reducer);
+  Editor* const editor_;
 };
 
 
 // Performs an iterative reduction of a node graph.
-class GraphReducer final {
+class GraphReducer final : public AdvancedReducer::Editor {
  public:
   GraphReducer(Graph* graph, Zone* zone);
+  ~GraphReducer() final;
 
   Graph* graph() const { return graph_; }
 
   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();
 
+  // Replace {node} with {replacement}.
+  void Replace(Node* node, Node* replacement) final;
+
   // Node stack operations.
   void Pop();
   void Push(Node* node);
 
   // Revisit queue operations.
   bool Recurse(Node* node);
-  void Revisit(Node* node);
+  void Revisit(Node* node) final;
 
-  Graph* graph_;
+  // Finish the graph reduction.
+  bool Finish() {

[titzer, 2015/05/06 09:22:08]

Why do we need this in the header?

[Benedikt Meurer, 2015/05/06 09:33:30]

Done.

+    for (Reducer* const reducer : reducers_) {
+      if (!reducer->Finish()) return false;
+    }
+    return true;
+  }
+
+  Graph* const graph_;
   NodeMarker<State> state_;
   ZoneVector<Reducer*> reducers_;
   ZoneStack<Node*> revisit_;
   ZoneStack<NodeState> stack_;
 
   DISALLOW_COPY_AND_ASSIGN(GraphReducer);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_REDUCER_H_