Faster handling of string indexing using [] with a SMI index....

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 2706 matching lines @@
   NoHandleAllocation ha;
   ASSERT(args.length() == 2);
 
   Handle<Object> object = args.at<Object>(0);
   Handle<Object> key = args.at<Object>(1);
 
   return Runtime::GetObjectProperty(object, key);
 }
 
 
-
 // KeyedStringGetProperty is called from KeyedLoadIC::GenerateGeneric.
 static Object* Runtime_KeyedGetProperty(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 2);
 
   // Fast cases for getting named properties of the receiver JSObject
   // itself.
   //
   // The global proxy objects has to be excluded since LocalLookup on
   // the global proxy object can return a valid result even though the
@@ skipping 31 matching lines @@
       int entry = dictionary->FindEntry(key);
       if ((entry != StringDictionary::kNotFound) &&
           (dictionary->DetailsAt(entry).type() == NORMAL)) {
         Object* value = dictionary->ValueAt(entry);
         if (!receiver->IsGlobalObject()) return value;
         value = JSGlobalPropertyCell::cast(value)->value();
         if (!value->IsTheHole()) return value;
         // If value is the hole do the general lookup.
       }
     }
+  } else if (args[0]->IsString() && args[1]->IsSmi()) {
+    // Fast case for string indexing using [] with a smi index.
+    HandleScope scope;
+    Handle<String> str = args.at<String>(0);
+    int index = Smi::cast(args[1])->value();
+    Handle<Object> result = GetCharAt(str, index);
+    return *result;
   }
 
   // Fall back to GetObjectProperty.
   return Runtime::GetObjectProperty(args.at<Object>(0),
                                     args.at<Object>(1));
 }
 
 
 Object* Runtime::SetObjectProperty(Handle<Object> object,
                                    Handle<Object> key,
@@ skipping 5253 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