Basic array capacity feedback via allocation sites.

src/runtime/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 90 matching lines @@
   CONVERT_ARG_HANDLE_CHECKED(Object, prototype, 1);
   DCHECK(!obj->IsAccessCheckNeeded());
   DCHECK(!obj->map()->is_observed());
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result, JSObject::SetPrototype(obj, prototype, false));
   return *result;
 }
 
 
+RUNTIME_FUNCTION(Runtime_GetElementsCapacity) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, obj, 0);
+  return Smi::FromInt(obj->elements()->length());
+}
+
+
 RUNTIME_FUNCTION(Runtime_SetPrototype) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, prototype, 1);
   if (obj->IsAccessCheckNeeded() &&
       !isolate->MayNamedAccess(obj, isolate->factory()->proto_string(),
                                v8::ACCESS_SET)) {
     isolate->ReportFailedAccessCheck(obj, v8::ACCESS_SET);
     RETURN_FAILURE_IF_SCHEDULED_EXCEPTION(isolate);
@@ skipping 3192 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 }
 }  // namespace v8::internal