Introduce {FAST,SLOW}_STRING_WRAPPER_ELEMENTS

src/elements-kind.h

 // Copyright 2012 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_ELEMENTS_KIND_H_
 #define V8_ELEMENTS_KIND_H_
 
 #include "src/base/macros.h"
 #include "src/checks.h"
 
@@ skipping 12 matching lines @@
   FAST_ELEMENTS,
   FAST_HOLEY_ELEMENTS,
 
   // The "fast" kind for unwrapped, non-tagged double values.
   FAST_DOUBLE_ELEMENTS,
   FAST_HOLEY_DOUBLE_ELEMENTS,
 
   // The "slow" kind.
   DICTIONARY_ELEMENTS,
 
+  // Elements kind of the "arguments" object (only in sloppy mode).
   FAST_SLOPPY_ARGUMENTS_ELEMENTS,
   SLOW_SLOPPY_ARGUMENTS_ELEMENTS,
 
-  // Fixed typed arrays
+  // For string wrapper objects ("new String('...')"), the string's characters
+  // are overlaid onto a regular elements backing store.
+  FAST_STRING_WRAPPER_ELEMENTS,
+  SLOW_STRING_WRAPPER_ELEMENTS,
+
+  // Fixed typed arrays.
   UINT8_ELEMENTS,
   INT8_ELEMENTS,
   UINT16_ELEMENTS,
   INT16_ELEMENTS,
   UINT32_ELEMENTS,
   INT32_ELEMENTS,
   FLOAT32_ELEMENTS,
   FLOAT64_ELEMENTS,
   UINT8_CLAMPED_ELEMENTS,
 
-  // Derived constants from ElementsKind
+  // Sentinel ElementsKind for objects with no elements.
+  NO_ELEMENTS,
+
+  // Derived constants from ElementsKind.
   FIRST_ELEMENTS_KIND = FAST_SMI_ELEMENTS,
   LAST_ELEMENTS_KIND = UINT8_CLAMPED_ELEMENTS,
   FIRST_FAST_ELEMENTS_KIND = FAST_SMI_ELEMENTS,
   LAST_FAST_ELEMENTS_KIND = FAST_HOLEY_DOUBLE_ELEMENTS,
   FIRST_FIXED_TYPED_ARRAY_ELEMENTS_KIND = UINT8_ELEMENTS,
   LAST_FIXED_TYPED_ARRAY_ELEMENTS_KIND = UINT8_CLAMPED_ELEMENTS,
   TERMINAL_FAST_ELEMENTS_KIND = FAST_HOLEY_ELEMENTS
 };
 
 const int kElementsKindCount = LAST_ELEMENTS_KIND - FIRST_ELEMENTS_KIND + 1;
@@ skipping 18 matching lines @@
 inline bool IsDictionaryElementsKind(ElementsKind kind) {
   return kind == DICTIONARY_ELEMENTS;
 }
 
 
 inline bool IsSloppyArgumentsElements(ElementsKind kind) {
   return kind == FAST_SLOPPY_ARGUMENTS_ELEMENTS ||
          kind == SLOW_SLOPPY_ARGUMENTS_ELEMENTS;
 }
 
+inline bool IsStringWrapperElementsKind(ElementsKind kind) {
+  return kind == FAST_STRING_WRAPPER_ELEMENTS ||
+         kind == SLOW_STRING_WRAPPER_ELEMENTS;
+}
 
 inline bool IsFixedTypedArrayElementsKind(ElementsKind kind) {
   return kind >= FIRST_FIXED_TYPED_ARRAY_ELEMENTS_KIND &&
          kind <= LAST_FIXED_TYPED_ARRAY_ELEMENTS_KIND;
 }
 
 
 inline bool IsTerminalElementsKind(ElementsKind kind) {
   return kind == TERMINAL_FAST_ELEMENTS_KIND ||
          IsFixedTypedArrayElementsKind(kind);
 }
 
 
 inline bool IsFastElementsKind(ElementsKind kind) {
   STATIC_ASSERT(FIRST_FAST_ELEMENTS_KIND == 0);
   return kind <= FAST_HOLEY_DOUBLE_ELEMENTS;
 }
 
 
 inline bool IsTransitionElementsKind(ElementsKind kind) {
   return IsFastElementsKind(kind) || IsFixedTypedArrayElementsKind(kind) ||
-         kind == FAST_SLOPPY_ARGUMENTS_ELEMENTS;
+         kind == FAST_SLOPPY_ARGUMENTS_ELEMENTS ||
+         kind == FAST_STRING_WRAPPER_ELEMENTS;
 }
 
 
 inline bool IsFastDoubleElementsKind(ElementsKind kind) {
   return kind == FAST_DOUBLE_ELEMENTS ||
       kind == FAST_HOLEY_DOUBLE_ELEMENTS;
 }
 
 
 inline bool IsFixedFloatElementsKind(ElementsKind kind) {
@@ skipping 105 matching lines @@
 inline bool IsTransitionableFastElementsKind(ElementsKind from_kind) {
   return IsFastElementsKind(from_kind) &&
       from_kind != TERMINAL_FAST_ELEMENTS_KIND;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ELEMENTS_KIND_H_