Improve speed of Utf8Write by always flattening the string first and

src/api.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 3616 matching lines @@
 
 
 int String::WriteUtf8(char* buffer,
                       int capacity,
                       int* nchars_ref,
                       int options) const {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   if (IsDeadCheck(isolate, "v8::String::WriteUtf8()")) return 0;
   LOG_API(isolate, "String::WriteUtf8");
   ENTER_V8(isolate);
+  i::Handle<i::String> str = Utils::OpenHandle(this);
+  if (str->IsAsciiRepresentation()) {
+    if (capacity == -1) capacity = str->length() + 1;
+    int len = i::Min(capacity, str->length());
+    i::String::WriteToFlat(*str, buffer, 0, len);
+    if (nchars_ref != NULL) *nchars_ref = len;
+    if (!(options & NO_NULL_TERMINATION) && capacity > len) {
+      buffer[len] = '\0';
+      return len + 1;
+    }
+    return len;
+  }
+
   i::StringInputBuffer& write_input_buffer = *isolate->write_input_buffer();
-  i::Handle<i::String> str = Utils::OpenHandle(this);
   isolate->string_tracker()->RecordWrite(str);
   if (options & HINT_MANY_WRITES_EXPECTED) {
     // Flatten the string for efficiency.  This applies whether we are
     // using StringInputBuffer or Get(i) to access the characters.
-    str->TryFlatten();
+    FlattenString(str);
   }
   write_input_buffer.Reset(0, *str);
   int len = str->length();
   // Encode the first K - 3 bytes directly into the buffer since we
   // know there's room for them.  If no capacity is given we copy all
   // of them here.
   int fast_end = capacity - (unibrow::Utf8::kMaxEncodedSize - 1);
   int i;
   int pos = 0;
   int nchars = 0;
@@ skipping 2420 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* scope_implementer =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   scope_implementer->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal