Codify the assumption that %GetArrayKeys can return only a single interval starting at zero

src/runtime.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 9677 matching lines @@
     int result = SeededNumberDictionary::cast(elements)->NumberOfElements();
     return Smi::FromInt(result);
   } else if (object->IsJSArray()) {
     return JSArray::cast(object)->length();
   } else {
     return Smi::FromInt(FixedArray::cast(elements)->length());
   }
 }
 
 
-static Handle<Object> NewSingleInterval(Isolate* isolate, uint32_t length) {
-  Handle<FixedArray> single_interval = isolate->factory()->NewFixedArray(2);
-  // -1 means start of array.
-  single_interval->set(0, Smi::FromInt(-1));
-  Handle<Object> number = isolate->factory()->NewNumberFromUint(length);
-  single_interval->set(1, *number);
-  return isolate->factory()->NewJSArrayWithElements(single_interval);
-}
-
-
 // Returns an array that tells you where in the [0, length) interval an array
-// might have elements.  Can either return keys (positive integers) or
-// intervals (pair of a negative integer (-start-1) followed by a
-// positive (length)) or undefined values.
+// might have elements.  Can either return an array of keys (positive integers
+// or undefined) or a number representing the positive length of an interval
+// starting at index 0.
 // Intervals can span over some keys that are not in the object.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_GetArrayKeys) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, array, 0);
   CONVERT_NUMBER_CHECKED(uint32_t, length, Uint32, args[1]);
   if (array->elements()->IsDictionary()) {
     Handle<FixedArray> keys = isolate->factory()->empty_fixed_array();
     for (Handle<Object> p = array;
          !p->IsNull();
          p = Handle<Object>(p->GetPrototype(isolate), isolate)) {
       if (p->IsJSProxy() || JSObject::cast(*p)->HasIndexedInterceptor()) {
         // Bail out if we find a proxy or interceptor, likely not worth
         // collecting keys in that case.
-        return *NewSingleInterval(isolate, length);
+        return *isolate->factory()->NewNumberFromUint(length);
       }
       Handle<JSObject> current = Handle<JSObject>::cast(p);
       Handle<FixedArray> current_keys =
           isolate->factory()->NewFixedArray(
               current->NumberOfLocalElements(NONE));
       current->GetLocalElementKeys(*current_keys, NONE);
       keys = UnionOfKeys(keys, current_keys);
     }
     // Erase any keys >= length.
     // TODO(adamk): Remove this step when the contract of %GetArrayKeys
     // is changed to let this happen on the JS side.
     for (int i = 0; i < keys->length(); i++) {
       if (NumberToUint32(keys->get(i)) >= length) keys->set_undefined(i);
     }
     return *isolate->factory()->NewJSArrayWithElements(keys);
   } else {
     ASSERT(array->HasFastSmiOrObjectElements() ||
            array->HasFastDoubleElements());
     uint32_t actual_length = static_cast<uint32_t>(array->elements()->length());
-    return *NewSingleInterval(isolate, Min(actual_length, length));
+    return *isolate->factory()->NewNumberFromUint(Min(actual_length, length));
   }
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_LookupAccessor) {
   NoHandleAllocation ha(isolate);
   ASSERT(args.length() == 3);
   CONVERT_ARG_CHECKED(JSReceiver, receiver, 0);
   CONVERT_ARG_CHECKED(Name, name, 1);
   CONVERT_SMI_ARG_CHECKED(flag, 2);
@@ skipping 3393 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal