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

src/heap.cc

 // 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 2989 matching lines @@
 
 
 MaybeObject* Heap::AllocateExternalStringFromAscii(
     const ExternalAsciiString::Resource* resource) {
   size_t length = resource->length();
   if (length > static_cast<size_t>(String::kMaxLength)) {
     isolate()->context()->mark_out_of_memory();
     return Failure::OutOfMemoryException();
   }
 
-  Map* map = external_ascii_string_map();
+  Map* map;
+  if (length < static_cast<size_t>(ExternalString::kMinBufferedStringLength)) {
+    map = external_ascii_string_map();
+  } else {
+    map = external_buffered_ascii_string_map();
+  }
   Object* result;
   { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
   ExternalAsciiString* external_string = ExternalAsciiString::cast(result);
   external_string->set_length(static_cast<int>(length));
   external_string->set_hash_field(String::kEmptyHashField);
   external_string->set_resource(resource);
-
+  if (external_string->IsBuffered()) {
+    external_string->set_buffer_index(ExternalString::kInvalidBufferIndex);
+  }
   return result;
 }
 
 
 MaybeObject* Heap::AllocateExternalStringFromTwoByte(
     const ExternalTwoByteString::Resource* resource) {
   size_t length = resource->length();
   if (length > static_cast<size_t>(String::kMaxLength)) {
     isolate()->context()->mark_out_of_memory();
     return Failure::OutOfMemoryException();
   }
 
   // For small strings we check whether the resource contains only
   // ASCII characters.  If yes, we use a different string map.
   static const size_t kAsciiCheckLengthLimit = 32;
   bool is_ascii = length <= kAsciiCheckLengthLimit &&
       String::IsAscii(resource->data(), static_cast<int>(length));
-  Map* map = is_ascii ?
-      external_string_with_ascii_data_map() : external_string_map();
+  Map* map;
+  if (length < static_cast<size_t>(ExternalString::kMinBufferedStringLength)) {
+    map = is_ascii ? external_string_with_ascii_data_map()
+                   : external_string_map();
+  } else {
+    map = is_ascii ? external_buffered_string_with_ascii_data_map()
+                   : external_buffered_string_map();
+  }
   Object* result;
   { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
   ExternalTwoByteString* external_string = ExternalTwoByteString::cast(result);
   external_string->set_length(static_cast<int>(length));
   external_string->set_hash_field(String::kEmptyHashField);
   external_string->set_resource(resource);
-
+  if (external_string->IsBuffered()) {
+    external_string->set_buffer_index(ExternalString::kInvalidBufferIndex);
+  }
   return result;
 }
 
 
 MaybeObject* Heap::LookupSingleCharacterStringFromCode(uint16_t code) {
   if (code <= String::kMaxAsciiCharCode) {
     Object* value = single_character_string_cache()->get(code);
     if (value != undefined_value()) return value;
 
     char buffer[1];
@@ skipping 3398 matching lines @@
   isolate_->heap()->store_buffer()->Compact();
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
 } }  // namespace v8::internal