Don't flatten every time we call CharCodeAt

src/runtime.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 2042 matching lines @@
   if (index->IsSmi()) {
     int value = Smi::cast(index)->value();
     if (value < 0) return isolate->heap()->nan_value();
     i = value;
   } else {
     ASSERT(index->IsHeapNumber());
     double value = HeapNumber::cast(index)->value();
     i = static_cast<uint32_t>(DoubleToInteger(value));
   }
 
-  // Flatten the string.  If someone wants to get a char at an index
-  // in a cons string, it is likely that more indices will be
-  // accessed.
-  Object* flat;
-  { MaybeObject* maybe_flat = subject->TryFlatten();
-    if (!maybe_flat->ToObject(&flat)) return maybe_flat;
-  }
-  subject = String::cast(flat);
-
   if (i >= static_cast<uint32_t>(subject->length())) {
     return isolate->heap()->nan_value();
   }
 
-  return Smi::FromInt(subject->Get(i));
+  return subject->GetMayFlatten(i);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_CharFromCode) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   return CharFromCode(isolate, args[0]);
 }
 
 
@@ skipping 1542 matching lines @@
       isolate->heap()->AllocateStringFromAscii(CStrVector(str));
   DeleteArray(str);
   return res;
 }
 
 
 // Returns a single character string where first character equals
 // string->Get(index).
 static Handle<Object> GetCharAt(Handle<String> string, uint32_t index) {
   if (index < static_cast<uint32_t>(string->length())) {
-    string->TryFlatten();
     return LookupSingleCharacterStringFromCode(
-        string->Get(index));
+        StringGetMayFlatten(string, index));
   }
   return Execution::CharAt(string, index);
 }
 
 
 MaybeObject* Runtime::GetElementOrCharAt(Isolate* isolate,
                                          Handle<Object> object,
                                          uint32_t index) {
   // Handle [] indexing on Strings
   if (object->IsString()) {
@@ skipping 8522 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal