making heap verification more aggressive

src/objects-debug.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 "src/objects.h"
 
 #include "src/bootstrapper.h"
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/field-type.h"
@@ skipping 82 matching lines @@
 #undef VERIFY_TYPED_ARRAY
 
     case CODE_TYPE:
       Code::cast(this)->CodeVerify();
       break;
     case ODDBALL_TYPE:
       Oddball::cast(this)->OddballVerify();
       break;
     case JS_OBJECT_TYPE:
     case JS_ERROR_TYPE:
-    case JS_ARGUMENTS_TYPE:
     case JS_API_OBJECT_TYPE:
     case JS_SPECIAL_API_OBJECT_TYPE:
     case JS_CONTEXT_EXTENSION_OBJECT_TYPE:
     case JS_PROMISE_TYPE:
       JSObject::cast(this)->JSObjectVerify();
       break;
+    case JS_ARGUMENTS_TYPE:
+      JSArgumentsObject::cast(this)->JSArgumentsObjectVerify();
+      break;
     case JS_GENERATOR_OBJECT_TYPE:
       JSGeneratorObject::cast(this)->JSGeneratorObjectVerify();
       break;
     case JS_VALUE_TYPE:
       JSValue::cast(this)->JSValueVerify();
       break;
     case JS_DATE_TYPE:
       JSDate::cast(this)->JSDateVerify();
       break;
     case JS_BOUND_FUNCTION_TYPE:
@@ skipping 119 matching lines @@
 }
 
 
 void FreeSpace::FreeSpaceVerify() {
   CHECK(IsFreeSpace());
 }
 
 
 template <class Traits>
 void FixedTypedArray<Traits>::FixedTypedArrayVerify() {
-  CHECK(IsHeapObject() &&
-        HeapObject::cast(this)->map()->instance_type() ==
-            Traits::kInstanceType);
+  CHECK(IsHeapObject());
+  CHECK(HeapObject::cast(this)->map()->instance_type() ==
+        Traits::kInstanceType);
   if (base_pointer() == this) {
     CHECK(external_pointer() ==
           ExternalReference::fixed_typed_array_base_data_offset().address());
   } else {
     CHECK(base_pointer() == nullptr);
   }
 }
 
 
 bool JSObject::ElementsAreSafeToExamine() {
   // If a GC was caused while constructing this object, the elements
   // pointer may point to a one pointer filler map.
   return reinterpret_cast<Map*>(elements()) !=
       GetHeap()->one_pointer_filler_map();
 }
 
+namespace {
 
-void JSObject::JSObjectVerify() {
-  VerifyHeapPointer(properties());
-  VerifyHeapPointer(elements());
+void VerifyFastProperties(JSReceiver* receiver) {
+  // TODO(cbruni): JSProxy support for slow properties
+  if (!receiver->IsJSObject()) return;
+  Isolate* isolate = receiver->GetIsolate();
+  Map* map = receiver->map();
+  CHECK(!map->is_dictionary_map());
+  JSObject* obj = JSObject::cast(receiver);
+  int actual_unused_property_fields = map->GetInObjectProperties() +
+                                      obj->properties()->length() -
+                                      map->NextFreePropertyIndex();
+  if (map->unused_property_fields() != actual_unused_property_fields) {
+    // This could actually happen in the middle of StoreTransitionStub
+    // when the new extended backing store is already set into the object and
+    // the allocation of the MutableHeapNumber triggers GC (in this case map
+    // is not updated yet).
+    CHECK_EQ(map->unused_property_fields(),
+             actual_unused_property_fields - JSObject::kFieldsAdded);
+  }
+  DescriptorArray* descriptors = map->instance_descriptors();
+  for (int i = 0; i < map->NumberOfOwnDescriptors(); i++) {
+    if (descriptors->GetDetails(i).type() != DATA) continue;
+    Representation r = descriptors->GetDetails(i).representation();
+    FieldIndex index = FieldIndex::ForDescriptor(map, i);
+    if (obj->IsUnboxedDoubleField(index)) {
+      DCHECK(r.IsDouble());
+      continue;
+    }
+    Object* value = obj->RawFastPropertyAt(index);
+    if (r.IsDouble()) DCHECK(value->IsMutableHeapNumber());
+    if (value->IsUninitialized(isolate)) continue;
+    if (r.IsSmi()) DCHECK(value->IsSmi());
+    if (r.IsHeapObject()) DCHECK(value->IsHeapObject());
+    FieldType* field_type = descriptors->GetFieldType(i);
+    bool type_is_none = field_type->IsNone();
+    bool type_is_any = field_type->IsAny();
+    if (r.IsNone()) {
+      CHECK(type_is_none);
+    } else if (!type_is_any && !(type_is_none && r.IsHeapObject())) {
+      // If allocation folding is off then GC could happen during inner
+      // object literal creation and we will end up having and undefined
+      // value that does not match the field type.
+      CHECK(!field_type->NowStable() || field_type->NowContains(value) ||
+            (!FLAG_use_allocation_folding && value->IsUndefined(isolate)));
+    }
+  }
+}
 
-  if (HasSloppyArgumentsElements()) {
-    CHECK(this->elements()->IsFixedArray());
-    CHECK_GE(this->elements()->length(), 2);
+template <typename T>
+void VerifyDictionary(T* dict) {
+  CHECK(dict->IsFixedArray());
+  CHECK(dict->IsDictionary());
+  int capacity = dict->Capacity();
+  int nof = dict->NumberOfElements();
+  int nod = dict->NumberOfDeletedElements();
+  CHECK_LE(capacity, dict->length());
+  CHECK_LE(nof, capacity);
+  CHECK_LE(0, nof + nod);
+  CHECK_LE(nof + nod, capacity);
+}
+
+void VerifySlowProperties(JSReceiver* obj) {
+  Map* map = obj->map();
+  CHECK(map->is_dictionary_map());
+  CHECK_EQ(0, map->NumberOfOwnDescriptors());
+  CHECK_EQ(0, map->unused_property_fields());
+  CHECK_EQ(kInvalidEnumCacheSentinel, map->EnumLength());
+  CHECK(obj->properties()->IsDictionary());
+  // Kept in-object properties for sow-mode object need to be zapped:
+  int nof_in_object_properties = map->GetInObjectProperties();
+  if (nof_in_object_properties > 0) {
+    JSObject* js_object = JSObject::cast(obj);
+    Smi* zap_value = Smi::FromInt(0);
+    for (int i = 0; i < nof_in_object_properties; i++) {
+      FieldIndex index = FieldIndex::ForLoadByFieldIndex(map, i);
+      Object* field = js_object->RawFastPropertyAt(index);
+      CHECK_EQ(field, zap_value);
+    }
   }
+  if (obj->IsJSGlobalObject()) {
+    VerifyDictionary(JSObject::cast(obj)->global_dictionary());
+  } else {
+    VerifyDictionary(obj->property_dictionary());
+  }
+}
 
-  if (HasFastProperties()) {
-    int actual_unused_property_fields = map()->GetInObjectProperties() +
-                                        properties()->length() -
-                                        map()->NextFreePropertyIndex();
-    if (map()->unused_property_fields() != actual_unused_property_fields) {
-      // This could actually happen in the middle of StoreTransitionStub
-      // when the new extended backing store is already set into the object and
-      // the allocation of the MutableHeapNumber triggers GC (in this case map
-      // is not updated yet).
-      CHECK_EQ(map()->unused_property_fields(),
-               actual_unused_property_fields - JSObject::kFieldsAdded);
+void VerifyProperties(JSReceiver* obj) {
+  obj->VerifyHeapPointer(obj->properties());
+  if (obj->HasFastProperties()) {
+    VerifyFastProperties(obj);
+  } else {
+    VerifySlowProperties(obj);
+  }
+}
+
+void VerifyElements(JSObject* obj) {
+  obj->VerifyHeapPointer(obj->elements());
+  // If a GC was caused while constructing this object, the elements
+  // pointer may point to a one pointer filler map.
+  if (!obj->ElementsAreSafeToExamine()) return;
+  Map* map = obj->map();
+  Heap* heap = obj->GetHeap();
+  FixedArrayBase* elements = obj->elements();
+  CHECK_EQ((map->has_fast_smi_or_object_elements() ||
+            (elements == heap->empty_fixed_array()) ||
+            obj->HasFastStringWrapperElements()),
+           (elements->map() == heap->fixed_array_map() ||
+            elements->map() == heap->fixed_cow_array_map()));
+  CHECK_EQ(map->has_fast_object_elements(), obj->HasFastObjectElements());
+
+  ElementsKind kind = obj->GetElementsKind();
+  if (IsFastSmiOrObjectElementsKind(kind)) {
+    CHECK(elements->map() == heap->fixed_array_map() ||
+          elements->map() == heap->fixed_cow_array_map());
+  } else if (IsFastDoubleElementsKind(kind)) {
+    CHECK(elements->IsFixedDoubleArray() ||
+          elements == heap->empty_fixed_array());
+  } else if (kind == DICTIONARY_ELEMENTS) {
+    CHECK(elements->IsSeededNumberDictionary());
+    VerifyDictionary(SeededNumberDictionary::cast(elements));
+    return;
+  } else {
+    CHECK(kind > DICTIONARY_ELEMENTS);
+  }
+  CHECK(!IsSloppyArgumentsElements(kind) ||
+        (elements->IsFixedArray() && elements->length() >= 2));
+
+  if (IsFastPackedElementsKind(kind)) {
+    uint32_t length = elements->length();
+    if (obj->IsJSArray()) {
+      Object* number = JSArray::cast(obj)->length();
+      if (number->IsSmi()) {
+        length = Min(length, static_cast<uint32_t>(Smi::cast(number)->value()));
+      }
     }
-    DescriptorArray* descriptors = map()->instance_descriptors();
-    Isolate* isolate = GetIsolate();
-    for (int i = 0; i < map()->NumberOfOwnDescriptors(); i++) {
-      if (descriptors->GetDetails(i).type() == DATA) {
-        Representation r = descriptors->GetDetails(i).representation();
-        FieldIndex index = FieldIndex::ForDescriptor(map(), i);
-        if (IsUnboxedDoubleField(index)) {
-          DCHECK(r.IsDouble());
-          continue;
-        }
-        Object* value = RawFastPropertyAt(index);
-        if (r.IsDouble()) DCHECK(value->IsMutableHeapNumber());
-        if (value->IsUninitialized(isolate)) continue;
-        if (r.IsSmi()) DCHECK(value->IsSmi());
-        if (r.IsHeapObject()) DCHECK(value->IsHeapObject());
-        FieldType* field_type = descriptors->GetFieldType(i);
-        bool type_is_none = field_type->IsNone();
-        bool type_is_any = field_type->IsAny();
-        if (r.IsNone()) {
-          CHECK(type_is_none);
-        } else if (!type_is_any && !(type_is_none && r.IsHeapObject())) {
-          // If allocation folding is off then GC could happen during inner
-          // object literal creation and we will end up having and undefined
-          // value that does not match the field type.
-          CHECK(!field_type->NowStable() || field_type->NowContains(value) ||
-                (!FLAG_use_allocation_folding && value->IsUndefined(isolate)));
-        }
+    if (kind == FAST_DOUBLE_ELEMENTS) {
+      for (uint32_t i = 0; i < length; i++) {
+        CHECK(!FixedDoubleArray::cast(elements)->is_the_hole(i));
+      }
+    } else {
+      for (uint32_t i = 0; i < length; i++) {
+        CHECK_NE(FixedArray::cast(elements)->get(i), heap->the_hole_value());
       }
     }
   }
-
-  // If a GC was caused while constructing this object, the elements
-  // pointer may point to a one pointer filler map.
-  if (ElementsAreSafeToExamine()) {
-    CHECK_EQ((map()->has_fast_smi_or_object_elements() ||
-              (elements() == GetHeap()->empty_fixed_array()) ||
-              HasFastStringWrapperElements()),
-             (elements()->map() == GetHeap()->fixed_array_map() ||
-              elements()->map() == GetHeap()->fixed_cow_array_map()));
-    CHECK(map()->has_fast_object_elements() == HasFastObjectElements());
-  }
 }
 
+}  // namespace
+
+void JSObject::JSObjectVerify() {
+  VerifyProperties(this);
+  VerifyElements(this);
+}
 
 void Map::MapVerify() {
   Heap* heap = GetHeap();
   CHECK(!heap->InNewSpace(this));
-  CHECK(FIRST_TYPE <= instance_type() && instance_type() <= LAST_TYPE);
+  CHECK_LE(FIRST_TYPE, instance_type());
+  CHECK_LE(instance_type(), LAST_TYPE);
   CHECK(instance_size() == kVariableSizeSentinel ||
          (kPointerSize <= instance_size() &&
           instance_size() < heap->Capacity()));
   CHECK(GetBackPointer()->IsUndefined(heap->isolate()) ||
         !Map::cast(GetBackPointer())->is_stable());
   VerifyHeapPointer(prototype());
   VerifyHeapPointer(instance_descriptors());
   SLOW_DCHECK(instance_descriptors()->IsSortedNoDuplicates());
   SLOW_DCHECK(TransitionArray::IsSortedNoDuplicates(this));
   SLOW_DCHECK(TransitionArray::IsConsistentWithBackPointers(this));
   // TODO(ishell): turn it back to SLOW_DCHECK.
   CHECK(!FLAG_unbox_double_fields ||
         layout_descriptor()->IsConsistentWithMap(this));
 }
 
 
 void Map::DictionaryMapVerify() {
   MapVerify();
   CHECK(is_dictionary_map());
   CHECK(instance_descriptors()->IsEmpty());
   CHECK_EQ(0, unused_property_fields());
   CHECK_EQ(Heap::GetStaticVisitorIdForMap(this), visitor_id());
+  CHECK_EQ(kInvalidEnumCacheSentinel, EnumLength());
 }
 
 
 void Map::VerifyOmittedMapChecks() {
   if (!FLAG_omit_map_checks_for_leaf_maps) return;
   if (!is_stable() ||
       is_deprecated() ||
       is_dictionary_map()) {
     CHECK(dependent_code()->IsEmpty(DependentCode::kPrototypeCheckGroup));
   }
@@ skipping 49 matching lines @@
 
 void JSGeneratorObject::JSGeneratorObjectVerify() {
   // In an expression like "new g()", there can be a point where a generator
   // object is allocated but its fields are all undefined, as it hasn't yet been
   // initialized by the generator.  Hence these weak checks.
   VerifyObjectField(kFunctionOffset);
   VerifyObjectField(kContextOffset);
   VerifyObjectField(kReceiverOffset);
   VerifyObjectField(kOperandStackOffset);
   VerifyObjectField(kContinuationOffset);
+  JSObjectVerify();
+}
+
+namespace {
+
+void VerifyArgumentsParameterMap(FixedArray* elements) {
+  Isolate* isolate = elements->GetIsolate();
+  CHECK(elements->IsFixedArray());
+  CHECK_GE(elements->length(), 2);
+  HeapObject* context = HeapObject::cast(elements->get(0));
+  HeapObject* arguments = HeapObject::cast(elements->get(1));
+  // TODO(cbruni): fix arguments creation to be atomic.
+  CHECK(!(context->IsUndefined(isolate) && !arguments->IsUndefined(isolate)));

[Igor Sheludko, 2016/07/11 15:37:10]

CHECK_IMPLIES?

+  CHECK(context->IsUndefined(isolate) || context->IsContext());
+  CHECK(arguments->IsUndefined(isolate) || arguments->IsFixedArray());
+}
+
+}  // namespace
+
+void JSArgumentsObject::JSArgumentsObjectVerify() {
+  VerifyObjectField(kLengthOffset);
+  JSObjectVerify();
+  Isolate* isolate = GetIsolate();
+
+  if (isolate->bootstrapper()->IsActive()) return;
+  Context* context = isolate->context();
+  Object* constructor = map()->GetConstructor();
+  if (constructor->IsJSFunction()) {
+    context = JSFunction::cast(constructor)->context();
+  }
+  // TODO(cbruni): replace with NULL check once all hydrogren stubs manage to
+  // set up the contexts properly.
+  if (isolate->context()->IsSmi()) return;
+  Context* native_context = context->native_context();
+  if (map() == native_context->sloppy_arguments_map()) {
+    // Sloppy arguments without aliased arguments has a normal elements backing
+    // store which is already verified by JSObjectVerify() above.
+  } else if (map() == native_context->fast_aliased_arguments_map()) {
+    CHECK(HasFastArgumentsElements());
+    FixedArray* elements = FixedArray::cast(this->elements());
+    VerifyArgumentsParameterMap(FixedArray::cast(elements));
+    CHECK_EQ(elements->map(), isolate->heap()->sloppy_arguments_elements_map());
+  } else if (map() == native_context->slow_aliased_arguments_map()) {
+    CHECK(HasSlowArgumentsElements());
+    FixedArray* elements = FixedArray::cast(this->elements());
+    VerifyArgumentsParameterMap(elements);
+    VerifyDictionary(SeededNumberDictionary::cast(elements->get(1)));
+    CHECK_EQ(elements->map(), isolate->heap()->sloppy_arguments_elements_map());
+  } else if (map() == native_context->strict_arguments_map()) {
+    CHECK(HasFastElements());
+  } else {
+    // TODO(cbruni): follow up on normalized argument maps.
+  }
 }
 
 
 void JSValue::JSValueVerify() {
   Object* v = value();
   if (v->IsHeapObject()) {
     VerifyHeapPointer(v);
   }
+  JSObjectVerify();
 }
 
 
 void JSDate::JSDateVerify() {
   if (value()->IsHeapObject()) {
     VerifyHeapPointer(value());
   }

[Igor Sheludko, 2016/07/11 15:37:10]

Either add JSObjectVerify(); here or even replace the above code with
JSValueVerify();

   Isolate* isolate = GetIsolate();
   CHECK(value()->IsUndefined(isolate) || value()->IsSmi() ||
         value()->IsHeapNumber());
   CHECK(year()->IsUndefined(isolate) || year()->IsSmi() || year()->IsNaN());
   CHECK(month()->IsUndefined(isolate) || month()->IsSmi() || month()->IsNaN());
   CHECK(day()->IsUndefined(isolate) || day()->IsSmi() || day()->IsNaN());
   CHECK(weekday()->IsUndefined(isolate) || weekday()->IsSmi() ||
         weekday()->IsNaN());
   CHECK(hour()->IsUndefined(isolate) || hour()->IsSmi() || hour()->IsNaN());
   CHECK(min()->IsUndefined(isolate) || min()->IsSmi() || min()->IsNaN());
@@ skipping 31 matching lines @@
   }
 }
 
 
 void JSMessageObject::JSMessageObjectVerify() {
   CHECK(IsJSMessageObject());
   VerifyObjectField(kStartPositionOffset);
   VerifyObjectField(kEndPositionOffset);
   VerifyObjectField(kArgumentsOffset);
   VerifyObjectField(kScriptOffset);
   VerifyObjectField(kStackFramesOffset);

[Igor Sheludko, 2016/07/11 15:37:10]

JSObjectVerify();

 }
 
 
 void String::StringVerify() {
   CHECK(IsString());
   CHECK(length() >= 0 && length() <= Smi::kMaxValue);
   if (IsInternalizedString()) {
     CHECK(!GetHeap()->InNewSpace(this));
   }
   if (IsConsString()) {
@@ skipping 32 matching lines @@
   VerifyObjectField(kBoundTargetFunctionOffset);
   VerifyObjectField(kBoundArgumentsOffset);
   CHECK(bound_target_function()->IsCallable());
   CHECK(IsCallable());
   CHECK_EQ(IsConstructor(), bound_target_function()->IsConstructor());
 }
 
 
 void JSFunction::JSFunctionVerify() {
   CHECK(IsJSFunction());
+  JSObjectVerify();
   VerifyObjectField(kPrototypeOrInitialMapOffset);
   VerifyObjectField(kNextFunctionLinkOffset);
   CHECK(code()->IsCode());
   CHECK(next_function_link() == NULL ||
         next_function_link()->IsUndefined(GetIsolate()) ||
         next_function_link()->IsJSFunction());
   CHECK(map()->is_callable());
 }
 
 
@@ skipping 26 matching lines @@
 }
 
 
 void JSGlobalObject::JSGlobalObjectVerify() {
   CHECK(IsJSGlobalObject());
   // Do not check the dummy global object for the builtins.
   if (GlobalDictionary::cast(properties())->NumberOfElements() == 0 &&
       elements()->length() == 0) {
     return;
   }
+  CHECK(!HasFastProperties());
   JSObjectVerify();
 }
 
 
 void Oddball::OddballVerify() {
   CHECK(IsOddball());
   Heap* heap = GetHeap();
   VerifyHeapPointer(to_string());
   Object* number = to_number();
   if (number->IsHeapObject()) {
@@ skipping 83 matching lines @@
   for (RelocIterator it(this, mode_mask); !it.done(); it.next()) {
     Object* obj = it.rinfo()->target_object();
     if (IsWeakObject(obj)) {
       if (obj->IsMap()) {
         Map* map = Map::cast(obj);
         CHECK(map->dependent_code()->Contains(DependentCode::kWeakCodeGroup,
                                               cell));
       } else if (obj->IsJSObject()) {
         if (isolate->heap()->InNewSpace(obj)) {
           ArrayList* list =
-              GetIsolate()->heap()->weak_new_space_object_to_code_list();
+              isolate->heap()->weak_new_space_object_to_code_list();
           bool found = false;
           for (int i = 0; i < list->Length(); i += 2) {
             WeakCell* obj_cell = WeakCell::cast(list->Get(i));
             if (!obj_cell->cleared() && obj_cell->value() == obj &&
                 WeakCell::cast(list->Get(i + 1)) == cell) {
               found = true;
               break;
             }
           }
           CHECK(found);
         } else {
           Handle<HeapObject> key_obj(HeapObject::cast(obj), isolate);
           DependentCode* dep =
-              GetIsolate()->heap()->LookupWeakObjectToCodeDependency(key_obj);
+              isolate->heap()->LookupWeakObjectToCodeDependency(key_obj);
           dep->Contains(DependentCode::kWeakCodeGroup, cell);
         }
       }
     }
   }
 }
 
 
 void JSArray::JSArrayVerify() {
+  CHECK(IsJSArray());
   JSObjectVerify();
   Isolate* isolate = GetIsolate();
-  CHECK(length()->IsNumber() || length()->IsUndefined(isolate));
+  // Allow undefined for not fully initialized JSArrays
+  if (length()->IsUndefined(isolate)) {
+    CHECK_EQ(FixedArray::cast(elements()),
+             isolate->heap()->empty_fixed_array());
+    return;
+  }
+  CHECK(length()->IsNumber());
   // If a GC was caused while constructing this array, the elements
   // pointer may point to a one pointer filler map.
   if (ElementsAreSafeToExamine()) {
-    CHECK(elements()->IsUndefined(isolate) || elements()->IsFixedArray() ||
-          elements()->IsFixedDoubleArray());
+    CHECK(elements()->IsFixedArray() || elements()->IsFixedDoubleArray());
   }
 }
 
-
 void JSSet::JSSetVerify() {
   CHECK(IsJSSet());
   JSObjectVerify();
   VerifyHeapPointer(table());
   CHECK(table()->IsOrderedHashTable() || table()->IsUndefined(GetIsolate()));
   // TODO(arv): Verify OrderedHashTable too.
 }
 
 
 void JSMap::JSMapVerify() {
@@ skipping 546 matching lines @@
   if (isolate->bootstrapper()->IsActive()) return;
 
   static const int mask = RelocInfo::kCodeTargetMask;
   RelocIterator old_it(old_code, mask);
   RelocIterator new_it(new_code, mask);
   Code* stack_check = isolate->builtins()->builtin(Builtins::kStackCheck);
 
   while (!old_it.done()) {
     RelocInfo* rinfo = old_it.rinfo();
     Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
-    CHECK(!target->is_handler() && !target->is_inline_cache_stub());
+    CHECK(!target->is_handler());
+    CHECK(!target->is_inline_cache_stub());
     if (target == stack_check) break;
     old_it.next();
   }
 
   while (!new_it.done()) {
     RelocInfo* rinfo = new_it.rinfo();
     Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
-    CHECK(!target->is_handler() && !target->is_inline_cache_stub());
+    CHECK(!target->is_handler());
+    CHECK(!target->is_inline_cache_stub());
     if (target == stack_check) break;
     new_it.next();
   }
 
   // Either both are done because there is no stack check.
   // Or we are past the prologue for both.
   CHECK_EQ(new_it.done(), old_it.done());
 
   // After the prologue, each call in the old code has a corresponding call
   // in the new code.
@@ skipping 15 matching lines @@
 
   // Both are done at the same time.
   CHECK_EQ(new_it.done(), old_it.done());
 }
 
 
 #endif  // DEBUG
 
 }  // namespace internal
 }  // namespace v8