Improve performance of Array.prototype.join and String.prototype.substring...

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 3896 matching lines @@
       int element_length = string->length();
       String::WriteToFlat(string, sink + position, 0, element_length);
       position += element_length;
     }
   }
 }
 
 
 static Object* Runtime_StringBuilderConcat(Arguments args) {
   NoHandleAllocation ha;
-  ASSERT(args.length() == 2);
+  ASSERT(args.length() == 3);
   CONVERT_CHECKED(JSArray, array, args[0]);
-  CONVERT_CHECKED(String, special, args[1]);
+  if (!args[1]->IsSmi()) {
+    Top::context()->mark_out_of_memory();
+    return Failure::OutOfMemoryException();
+  }
+  int array_length = Smi::cast(args[1])->value();
+  CONVERT_CHECKED(String, special, args[2]);
 
   // This assumption is used by the slice encoding in one or two smis.
   ASSERT(Smi::kMaxValue >= String::kMaxLength);
 
   int special_length = special->length();
-  Object* smi_array_length = array->length();
-  if (!smi_array_length->IsSmi()) {
-    Top::context()->mark_out_of_memory();
-    return Failure::OutOfMemoryException();
-  }
-  int array_length = Smi::cast(smi_array_length)->value();
   if (!array->HasFastElements()) {
     return Top::Throw(Heap::illegal_argument_symbol());
   }
   FixedArray* fixed_array = FixedArray::cast(array->elements());
   if (fixed_array->length() < array_length) {
     array_length = fixed_array->length();
   }
 
   if (array_length == 0) {
     return Heap::empty_string();
@@ skipping 4086 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