Improve array to string conversion.

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 585 matching lines @@
 }
 
 
 void BasicJsonStringifier::ShrinkCurrentPart() {
   ASSERT(current_index_ < part_length_);
   if (current_index_ == 0) {
     current_part_ = factory_->empty_string();
     return;
   }
 
-  int string_size, allocated_string_size;
-  if (is_ascii_) {
-    allocated_string_size = SeqOneByteString::SizeFor(part_length_);
-    string_size = SeqOneByteString::SizeFor(current_index_);
-  } else {
-    allocated_string_size = SeqTwoByteString::SizeFor(part_length_);
-    string_size = SeqTwoByteString::SizeFor(current_index_);
-  }
-
-  int delta = allocated_string_size - string_size;
-  current_part_->set_length(current_index_);
-
-  // String sizes are pointer size aligned, so that we can use filler objects
-  // that are a multiple of pointer size.
-  Address end_of_string = current_part_->address() + string_size;
-  isolate_->heap()->CreateFillerObjectAt(end_of_string, delta);
-  if (Marking::IsBlack(Marking::MarkBitFrom(*current_part_))) {
-    MemoryChunk::IncrementLiveBytesFromMutator(
-        current_part_->address(), -delta);
-  }
+  SeqString::cast(*current_part_)->Truncate(current_index_);

[Toon Verwaest, 2012/12/05 14:29:12]

Runtime_Truncate returns the resulting string; and does not support length == 0.
This function on the other hand does support length == 0; and relies on the
internal truncate that does not handle == 0. Can we just unify it all and
support length == 0 directly in the Truncate called here, and make it return the
new string? That way we can just support truncation to length == 0 in
Runtime_Truncate as well and don't need external checks. Then we can also remove
this utility function and just call truncate directly where you'd call
ShrinkCurrentPart.

 }
 
 
 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 125 matching lines @@
       SerializeString_<false, char>(flat.ToAsciiVector(), object);
     } else {
       SerializeString_<false, uc16>(flat.ToUC16Vector(), object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_