Improve SeqString::Truncate for latest allocated strings.

src/json-stringifier.h

 // Copyright 2012 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 304 matching lines @@
                                                     Handle<String> string,
                                                     Handle<String> result) {
   AssertNoAllocation no_allocation;
   int final_size = 0;
   StringType* dest = StringType::cast(*result);
   dest->Set(final_size++, '\"');
   final_size += SerializeStringUnchecked_(StringType::cast(*string)->GetChars(),
                                           dest->GetChars() + 1,
                                           string->length());
   dest->Set(final_size++, '\"');
-  if (isolate->heap()->InNewSpace(*result)) {
-    // In new space, simply lower the allocation top to fit the actual size.
-    isolate->heap()->new_space()->ShrinkStringAtAllocationBoundary<StringType>(
-        *result, final_size);
-    return *result;
-  } else {
-    // Not in new space, need to fill the wasted space with filler objects.
-    return SeqString::cast(*result)->Truncate(final_size);
-  }
+  SeqString::cast(*result)->Truncate(final_size);
+  return *result;
 }
 
 
 template <bool is_ascii, typename Char>
 void BasicJsonStringifier::Append_(Char c) {
   if (is_ascii) {
     SeqOneByteString::cast(*current_part_)->SeqOneByteStringSet(
         current_index_++, c);
   } else {
     SeqTwoByteString::cast(*current_part_)->SeqTwoByteStringSet(
@@ skipping 346 matching lines @@
 
   Append('}');
   StackPop();
   current_part_ = handle_scope.CloseAndEscape(current_part_);
   return SUCCESS;
 }
 
 
 void BasicJsonStringifier::ShrinkCurrentPart() {
   ASSERT(current_index_ < part_length_);
-  current_part_ = Handle<String>(
-      SeqString::cast(*current_part_)->Truncate(current_index_), isolate_);
+  if (current_index_ == 0) {

[Hannes Payer (out of office), 2013/03/21 12:48:30]

Again, Truncate() should do the right thing for you.

+    current_part_ = isolate_->factory()->empty_string();
+  } else {
+    SeqString::cast(*current_part_)->Truncate(current_index_);
+  }
 }
 
 
 void BasicJsonStringifier::Extend() {
   set_accumulator(factory_->NewConsString(accumulator(), current_part_));
   if (part_length_ <= kMaxPartLength / kPartLengthGrowthFactor) {
     part_length_ *= kPartLengthGrowthFactor;
   }
   if (is_ascii_) {
     current_part_ = factory_->NewRawOneByteString(part_length_);
@@ skipping 128 matching lines @@
       SerializeString_<false, uint8_t>(object);
     } else {
       SerializeString_<false, uc16>(object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_