Speed up charCodeAt on very large cons strings, by insisting on...

src/runtime.cc

 // Copyright 2006-2009 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 1256 matching lines @@
   return *target;
 }
 
 
 static Object* CharCodeAt(String* subject, Object* index) {
   uint32_t i = 0;
   if (!Array::IndexFromObject(index, &i)) return Heap::nan_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.
-  subject->TryFlattenIfNotFlat();
+  Object* flat = subject->TryFlatten();
+  if (flat->IsFailure()) return flat;
+  subject = String::cast(flat);
   if (i >= static_cast<uint32_t>(subject->length())) {
     return Heap::nan_value();
   }
   return Smi::FromInt(subject->Get(i));
 }
 
 
 static Object* Runtime_StringCharCodeAt(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 2);
@@ skipping 6614 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal