[turbofan] Add support for advanced reducers.

src/compiler/graph-reducer.h

Index: src/compiler/graph-reducer.h
diff --git a/src/compiler/graph-reducer.h b/src/compiler/graph-reducer.h
index a6cc1f2d94b0b14974907cd37b83ac7d8d81a448..eb3256d0624980d69d21f76dd2c1f0432f3a2696 100644
--- a/src/compiler/graph-reducer.h
+++ b/src/compiler/graph-reducer.h
@@ -20,10 +20,10 @@ 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_;
@@ -37,26 +37,66 @@ class Reduction final {
 // 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_; }
 
@@ -79,15 +119,26 @@ class GraphReducer final {
   // 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;
+
+  // 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* graph_;
+  Graph* const graph_;
   NodeMarker<State> state_;
   ZoneVector<Reducer*> reducers_;
   ZoneStack<Node*> revisit_;