[turbofan] Initial version of allocation folding and write barrier elimination.

src/compiler/change-lowering.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_CHANGE_LOWERING_H_
-#define V8_COMPILER_CHANGE_LOWERING_H_
-
-#include "src/compiler/graph-reducer.h"
-
-namespace v8 {
-namespace internal {
-namespace compiler {
-
-// Forward declarations.
-class CommonOperatorBuilder;
-struct ElementAccess;
-class JSGraph;
-class Linkage;
-class MachineOperatorBuilder;
-class Operator;
-
-class ChangeLowering final : public AdvancedReducer {
- public:
-  ChangeLowering(Editor* editor, JSGraph* jsgraph)
-      : AdvancedReducer(editor), jsgraph_(jsgraph) {}
-  ~ChangeLowering() final;
-
-  Reduction Reduce(Node* node) final;
-
- private:
-  Reduction ReduceLoadField(Node* node);
-  Reduction ReduceStoreField(Node* node);
-  Reduction ReduceLoadElement(Node* node);
-  Reduction ReduceStoreElement(Node* node);
-  Reduction ReduceAllocate(Node* node);
-
-  Node* ComputeIndex(const ElementAccess& access, Node* const key);
-  Graph* graph() const;
-  Isolate* isolate() const;
-  JSGraph* jsgraph() const { return jsgraph_; }
-  CommonOperatorBuilder* common() const;
-  MachineOperatorBuilder* machine() const;
-
-  JSGraph* const jsgraph_;
-  SetOncePointer<const Operator> allocate_operator_;
-};
-
-}  // namespace compiler
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_COMPILER_CHANGE_LOWERING_H_