[turbofan] Add support for copy-on-write element stores.

src/compiler/load-elimination.h

 // Copyright 2016 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_LOAD_ELIMINATION_H_
 #define V8_COMPILER_LOAD_ELIMINATION_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Foward declarations.
 struct FieldAccess;
+class JSGraph;
 
 class LoadElimination final : public AdvancedReducer {
  public:
-  LoadElimination(Editor* editor, Zone* zone)
-      : AdvancedReducer(editor), node_states_(zone) {}
+  LoadElimination(Editor* editor, JSGraph* jsgraph, Zone* zone)
+      : AdvancedReducer(editor), node_states_(zone), jsgraph_(jsgraph) {}
   ~LoadElimination() final {}
 
   Reduction Reduce(Node* node) final;
 
  private:
   static const size_t kMaxTrackedElements = 8;
 
   // Abstract state to approximate the current state of an element along the
   // effect paths through the graph.
   class AbstractElements final : public ZoneObject {
@@ skipping 112 matching lines @@
     AbstractState const* Get(Node* node) const;
     void Set(Node* node, AbstractState const* state);
 
     Zone* zone() const { return info_for_node_.get_allocator().zone(); }
 
    private:
     ZoneVector<AbstractState const*> info_for_node_;
   };
 
   Reduction ReduceCheckMaps(Node* node);
+  Reduction ReduceEnsureWritableFastElements(Node* node);
   Reduction ReduceTransitionElementsKind(Node* node);
   Reduction ReduceLoadField(Node* node);
   Reduction ReduceStoreField(Node* node);
   Reduction ReduceLoadElement(Node* node);
   Reduction ReduceStoreElement(Node* node);
   Reduction ReduceStoreTypedElement(Node* node);
   Reduction ReduceEffectPhi(Node* node);
   Reduction ReduceStart(Node* node);
   Reduction ReduceOtherNode(Node* node);
 
   Reduction UpdateState(Node* node, AbstractState const* state);
 
   AbstractState const* ComputeLoopState(Node* node,
                                         AbstractState const* state) const;
 
   static int FieldIndexOf(FieldAccess const& access);
 
   AbstractState const* empty_state() const { return &empty_state_; }
+  JSGraph* jsgraph() const { return jsgraph_; }
   Zone* zone() const { return node_states_.zone(); }
 
   AbstractState const empty_state_;
   AbstractStateForEffectNodes node_states_;
+  JSGraph* const jsgraph_;
 
   DISALLOW_COPY_AND_ASSIGN(LoadElimination);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOAD_ELIMINATION_H_