Make one-character strings into symbols more agressively.

src/heap.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 3605 matching lines @@
   object->set_map(constructor->initial_map());
 
   // Reinitialize the object from the constructor map.
   InitializeJSObjectFromMap(object, FixedArray::cast(properties), map);
   return object;
 }
 
 
 MaybeObject* Heap::AllocateStringFromAscii(Vector<const char> string,
                                            PretenureFlag pretenure) {
+  if (string.length() == 1) {
+    return Heap::LookupSingleCharacterStringFromCode(string[0]);
+  }
   Object* result;
   { MaybeObject* maybe_result =
         AllocateRawAsciiString(string.length(), pretenure);
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
   // Copy the characters into the new object.
   SeqAsciiString* string_result = SeqAsciiString::cast(result);
   for (int i = 0; i < string.length(); i++) {
     string_result->SeqAsciiStringSet(i, string[i]);
@@ skipping 2587 matching lines @@
 }
 
 
 void ExternalStringTable::TearDown() {
   new_space_strings_.Free();
   old_space_strings_.Free();
 }
 
 
 } }  // namespace v8::internal