Use the property load IC for accessing the array length.

src/ic.cc

 // 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 834 matching lines @@
         if (FLAG_trace_ic) PrintF("[LoadIC : +#length /string]\n");
 #endif
       }
       // Get the string if we have a string wrapper object.
       Handle<Object> string = object->IsJSValue()
           ? Handle<Object>(Handle<JSValue>::cast(object)->value())
           : object;
       return Smi::FromInt(String::cast(*string)->length());
     }
 
-    // Use specialized code for getting the length of arrays.
-    if (object->IsJSArray() &&
-        name->Equals(isolate()->heap()->length_symbol())) {
-      Handle<Code> stub;
-      if (state == UNINITIALIZED) {
-        stub = pre_monomorphic_stub();
-      } else if (state == PREMONOMORPHIC) {
-        stub = isolate()->builtins()->LoadIC_ArrayLength();
-      } else if (state != MEGAMORPHIC) {
-        stub = megamorphic_stub();
-      }
-      if (!stub.is_null()) {
-        set_target(*stub);
-#ifdef DEBUG
-        if (FLAG_trace_ic) PrintF("[LoadIC : +#length /array]\n");
-#endif
-      }
-      return JSArray::cast(*object)->length();
-    }
-
     // Use specialized code for getting prototype of functions.
     if (object->IsJSFunction() &&
         name->Equals(isolate()->heap()->prototype_symbol()) &&
         Handle<JSFunction>::cast(object)->should_have_prototype()) {
       Handle<Code> stub;
       if (state == UNINITIALIZED) {
         stub = pre_monomorphic_stub();
       } else if (state == PREMONOMORPHIC) {
         stub = isolate()->builtins()->LoadIC_FunctionPrototype();
       } else if (state != MEGAMORPHIC) {
@@ skipping 112 matching lines @@
           code = isolate()->stub_cache()->ComputeLoadCallback(
               name, receiver, holder, info);
         } else if (callback->IsAccessorPair()) {
           Handle<Object> getter(Handle<AccessorPair>::cast(callback)->getter());
           if (!getter->IsJSFunction()) return;
           if (holder->IsGlobalObject()) return;
           if (!holder->HasFastProperties()) return;
           code = isolate()->stub_cache()->ComputeLoadViaGetter(
               name, receiver, holder, Handle<JSFunction>::cast(getter));
         } else {
-          ASSERT(callback->IsForeign());
-          // No IC support for old-style native accessors.
-          return;
+          // we have IC support only for getting the array length property.

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

nit: capital W

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

Done.

+          if (holder->IsJSArray() &&

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

nit: You can avoid one level of indentation here by moving this up into a new
"else if" block, and keeping the original "else { ASSERT(...); return; }" after
that.

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

Done.

+              name->Equals(isolate()->heap()->length_symbol())) {
+            ASSERT(reinterpret_cast<AccessorDescriptor*>(
+                Handle<Foreign>::cast(callback)->foreign_address())
+                == &Accessors::ArrayLength);
+            // Note that the resulting code object is marked as "Code::FIELD"
+            // and not as "Code::CALLBACKS".
+            code = isolate()->stub_cache()->ComputeLoadField(
+                name, receiver, holder, JSArray::ArrayLengthIndex());
+          }
+          if (code.is_null()) return;
         }
         break;
       }
       case INTERCEPTOR:
         ASSERT(HasInterceptorGetter(*holder));
         code = isolate()->stub_cache()->ComputeLoadInterceptor(
             name, receiver, holder);
         break;
       default:
         return;
@@ skipping 1680 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal