Use the property load IC for accessing the array length.

src/objects.h

 // Copyright 2012 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 8335 matching lines @@
 
   static const int kForeignAddressOffset = HeapObject::kHeaderSize;
   static const int kSize = kForeignAddressOffset + kPointerSize;
 
   STATIC_CHECK(kForeignAddressOffset == Internals::kForeignAddressOffset);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Foreign);
 };
 
-
+class PropertyIndex;

[Jakob Kummerow, 2012/11/16 12:57:10]

nit: two empty lines between top-level definitions (i.e. two before "class
PropertyIndex" and two after).

[Massi, 2012/11/19 12:26:15]

Done.

 // The JSArray describes JavaScript Arrays
 //  Such an array can be in one of two modes:
 //    - fast, backing storage is a FixedArray and length <= elements.length();
 //       Please note: push and pop can be used to grow and shrink the array.
 //    - slow, backing storage is a HashTable with numbers as keys.
 class JSArray: public JSObject {
  public:
   // [length]: The length property.
   DECL_ACCESSORS(length, Object)
 
@@ skipping 32 matching lines @@
 #endif
   DECLARE_VERIFIER(JSArray)
 
   // Number of element slots to pre-allocate for an empty array.
   static const int kPreallocatedArrayElements = 4;
 
   // Layout description.
   static const int kLengthOffset = JSObject::kHeaderSize;
   static const int kSize = kLengthOffset + kPointerSize;
 
+  static inline PropertyIndex ArrayLengthIndex();
+  STATIC_ASSERT(kLengthOffset % kPointerSize == 0);
+
  private:
   // Expand the fixed array backing of a fast-case JSArray to at least
   // the requested size.
   void Expand(int minimum_size_of_backing_fixed_array);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSArray);
 };
 
 
 // JSRegExpResult is just a JSArray with a specific initial map.
@@ skipping 614 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_