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

src/compiler/simplified-operator.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_SIMPLIFIED_OPERATOR_H_
 #define V8_COMPILER_SIMPLIFIED_OPERATOR_H_
 
 #include <iosfwd>
 
 #include "src/compiler/operator.h"
@@ skipping 130 matching lines @@
 std::ostream& operator<<(std::ostream&, CheckForMinusZeroMode);
 
 CheckForMinusZeroMode CheckMinusZeroModeOf(const Operator*) WARN_UNUSED_RESULT;
 
 // A descriptor for elements kind transitions.
 enum class ElementsTransition : uint8_t {
   kFastTransition,  // simple transition, just updating the map.
   kSlowTransition   // full transition, round-trip to the runtime.
 };
 
+size_t hash_value(ElementsTransition);
+
 std::ostream& operator<<(std::ostream&, ElementsTransition);
 
 ElementsTransition ElementsTransitionOf(const Operator* op) WARN_UNUSED_RESULT;
 
 BinaryOperationHints::Hint BinaryOperationHintOf(const Operator* op);
 
 CompareOperationHints::Hint CompareOperationHintOf(const Operator* op);
 
 // Interface for building simplified operators, which represent the
 // medium-level operations of V8, including adding numbers, allocating objects,
@@ skipping 143 matching lines @@
   const Operator* CheckFloat64Hole(CheckFloat64HoleMode);
   const Operator* CheckTaggedHole(CheckTaggedHoleMode);
 
   const Operator* ObjectIsCallable();
   const Operator* ObjectIsNumber();
   const Operator* ObjectIsReceiver();
   const Operator* ObjectIsSmi();
   const Operator* ObjectIsString();
   const Operator* ObjectIsUndetectable();
 
+  // ensure-writable-fast-elements object, elements
+  const Operator* EnsureWritableFastElements();
+
   // transition-elements-kind object, from-map, to-map
   const Operator* TransitionElementsKind(ElementsTransition transition);
 
   const Operator* Allocate(PretenureFlag pretenure = NOT_TENURED);
 
   const Operator* LoadField(FieldAccess const&);
   const Operator* StoreField(FieldAccess const&);
 
   // load-buffer buffer, offset, length
   const Operator* LoadBuffer(BufferAccess);
@@ skipping 20 matching lines @@
   Zone* const zone_;
 
   DISALLOW_COPY_AND_ASSIGN(SimplifiedOperatorBuilder);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_OPERATOR_H_