[turbofan] Allow ReplaceWithValue to kill control.

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 bd732d5808938b4cc0c3bcd0589615b867ea6a89..21e0a84b99c86021556848e316a66f7c0e6d15c9 100644
--- a/src/compiler/graph-reducer.h
+++ b/src/compiler/graph-reducer.h
@@ -77,9 +77,8 @@ class AdvancedReducer : public Reducer {
     // Replace value uses of {node} with {value} and effect uses of {node} with
     // {effect}. If {effect == NULL}, then use the effect input to {node}. All
     // control uses will be relaxed assuming {node} cannot throw.
-    virtual void ReplaceWithValue(Node* node, Node* value,
-                                  Node* effect = nullptr,
-                                  Node* control = nullptr) = 0;
+    virtual void ReplaceWithValue(Node* node, Node* value, Node* effect,
+                                  Node* control) = 0;
   };
 
   explicit AdvancedReducer(Editor* editor) : editor_(editor) {}
@@ -107,15 +106,13 @@ class AdvancedReducer : public Reducer {
   // uses of {node} with the effect and control input to {node}.
   // TODO(turbofan): replace the effect input to {node} with {graph->start()}.
   void RelaxEffectsAndControls(Node* node) {
-    DCHECK_NOT_NULL(editor_);
-    editor_->ReplaceWithValue(node, node, nullptr, nullptr);
+    ReplaceWithValue(node, node, nullptr, nullptr);
   }
 
   // Relax the control uses of {node} by immediately replacing them with the
   // control input to {node}.
   void RelaxControls(Node* node) {
-    DCHECK_NOT_NULL(editor_);
-    editor_->ReplaceWithValue(node, node, node, nullptr);
+    ReplaceWithValue(node, node, node, nullptr);
   }
 
  private:
@@ -124,10 +121,11 @@ class AdvancedReducer : public Reducer {
 
 
 // Performs an iterative reduction of a node graph.
-class GraphReducer final : public AdvancedReducer::Editor {
+class GraphReducer : public AdvancedReducer::Editor {
  public:
-  GraphReducer(Graph* graph, Zone* zone);
-  ~GraphReducer() final;
+  GraphReducer(Zone* zone, Graph* graph, Node* dead_value = nullptr,
+               Node* dead_control = nullptr);
+  ~GraphReducer();
 
   Graph* graph() const { return graph_; }
 
@@ -156,8 +154,8 @@ class GraphReducer final : public AdvancedReducer::Editor {
   // Replace value uses of {node} with {value} and effect uses of {node} with
   // {effect}. If {effect == NULL}, then use the effect input to {node}. All
   // control uses will be relaxed assuming {node} cannot throw.
-  void ReplaceWithValue(Node* node, Node* value, Node* effect = nullptr,
-                        Node* control = nullptr) final;
+  void ReplaceWithValue(Node* node, Node* value, Node* effect,
+                        Node* control) final;
 
   // Replace all uses of {node} with {replacement} if the id of {replacement} is
   // less than or equal to {max_id}. Otherwise, replace all uses of {node} whose
@@ -173,6 +171,8 @@ class GraphReducer final : public AdvancedReducer::Editor {
   void Revisit(Node* node) final;
 
   Graph* const graph_;
+  Node* dead_value_;
+  Node* dead_control_;
   NodeMarker<State> state_;
   ZoneVector<Reducer*> reducers_;
   ZoneStack<Node*> revisit_;