Introduce read buffer for external strings when using charAt (ia32).

src/objects-inl.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 238 matching lines @@
          String::cast(this)->IsAsciiRepresentation();
 }
 
 
 bool Object::IsExternalTwoByteString() {
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsExternal() &&
          String::cast(this)->IsTwoByteRepresentation();
 }
 
+
 bool Object::HasValidElements() {
   // Dictionary is covered under FixedArray.
   return IsFixedArray() || IsFixedDoubleArray() || IsExternalArray();
 }
 
+
 StringShape::StringShape(String* str)
   : type_(str->map()->instance_type()) {
   set_valid();
   ASSERT((type_ & kIsNotStringMask) == kStringTag);
 }
 
 
 StringShape::StringShape(Map* map)
   : type_(map->instance_type()) {
   set_valid();
@@ skipping 1862 matching lines @@
 
 
 String* String::TryFlattenGetString(PretenureFlag pretenure) {
   MaybeObject* flat = TryFlatten(pretenure);
   Object* successfully_flattened;
   if (!flat->ToObject(&successfully_flattened)) return this;
   return String::cast(successfully_flattened);
 }
 
 
-uint16_t String::Get(int index) {
+uint16_t String::Get(int index, ExternalStringBufferFlag flag) {
   ASSERT(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {
     case kSeqStringTag | kAsciiStringTag:
       return SeqAsciiString::cast(this)->SeqAsciiStringGet(index);
     case kSeqStringTag | kTwoByteStringTag:
       return SeqTwoByteString::cast(this)->SeqTwoByteStringGet(index);
     case kConsStringTag | kAsciiStringTag:
     case kConsStringTag | kTwoByteStringTag:
-      return ConsString::cast(this)->ConsStringGet(index);
+      return ConsString::cast(this)->ConsStringGet(index, flag);
     case kExternalStringTag | kAsciiStringTag:
-      return ExternalAsciiString::cast(this)->ExternalAsciiStringGet(index);
+      return ExternalAsciiString::cast(this)->ExternalAsciiStringGet(index,
+                                                                     flag);
     case kExternalStringTag | kTwoByteStringTag:
-      return ExternalTwoByteString::cast(this)->ExternalTwoByteStringGet(index);
+      return ExternalTwoByteString::cast(this)->ExternalTwoByteStringGet(index,
+                                                                         flag);
     case kSlicedStringTag | kAsciiStringTag:
     case kSlicedStringTag | kTwoByteStringTag:
-      return SlicedString::cast(this)->SlicedStringGet(index);
+      return SlicedString::cast(this)->SlicedStringGet(index, flag);
     default:
       break;
   }
 
   UNREACHABLE();
   return 0;
 }
 
 
 void String::Set(int index, uint16_t value) {
@@ skipping 117 matching lines @@
   return READ_FIELD(this, kSecondOffset);
 }
 
 
 void ConsString::set_second(String* value, WriteBarrierMode mode) {
   WRITE_FIELD(this, kSecondOffset, value);
   CONDITIONAL_WRITE_BARRIER(GetHeap(), this, kSecondOffset, value, mode);
 }
 
 
+bool ExternalString::IsBuffered() {
+  uint32_t type = map()->instance_type();
+  ASSERT(StringShape(this).IsExternal());
+  return (type & kBufferedStringMask) == kBufferedStringTag;
+}
+
+
+int ExternalString::buffer_index() {
+  ASSERT(IsBuffered());
+  Object* value = READ_FIELD(this, kBufferIndexOffset);
+  return Smi::cast(value)->value();
+}
+
+
+void ExternalString::set_buffer_index(int value) {
+  ASSERT(IsBuffered());
+  WRITE_FIELD(this, kBufferIndexOffset, Smi::FromInt(value));
+}
+
+
+Address ExternalString::buffer() {
+  return reinterpret_cast<Address>(
+      HeapObject::RawField(this, kBufferContentOffset));
+}
+
+
 const ExternalAsciiString::Resource* ExternalAsciiString::resource() {
   return *reinterpret_cast<Resource**>(FIELD_ADDR(this, kResourceOffset));
 }
 
 
 void ExternalAsciiString::set_resource(
     const ExternalAsciiString::Resource* resource) {
   *reinterpret_cast<const Resource**>(
       FIELD_ADDR(this, kResourceOffset)) = resource;
 }
@@ skipping 2318 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_