Property reconfiguring implemented. Tests added.

test/cctest/test-migrations.cc

+// Copyright 2015 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 <utility>
+
+#include "src/v8.h"
+
+#include "src/compilation-cache.h"
+#include "src/execution.h"
+#include "src/factory.h"
+#include "src/global-handles.h"
+#include "src/ic/stub-cache.h"
+#include "src/macro-assembler.h"
+#include "src/smart-pointers.h"
+#include "test/cctest/cctest.h"
+
+using namespace v8::internal;
+
+
+// TODO(ishell): fix this once ReconfigureProperty supports
+// "non equivalent" transitions.
+const bool IS_NON_EQUIVALENT_TRANSITION_SUPPORTED = false;
+
+
+// TODO(ishell): fix this once TransitionToPrototype stops generalizing
+// all field representations (crbug/448711).
+const bool IS_CRBUG_448711_FIXED = false;
+
+
+// TODO(ishell): fix this once TransitionToAccessorProperty is able to always
+// keep map in fast mode.
+const bool IS_ACCESSOR_FIELD_SUPPORTED = false;
+
+
+//
+// Helper functions.
+//
+
+static Handle<String> MakeString(const char* str) {
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  return factory->InternalizeUtf8String(str);
+}
+
+
+static Handle<String> MakeName(const char* str, int suffix) {
+  EmbeddedVector<char, 128> buffer;
+  SNPrintF(buffer, "%s%d", str, suffix);
+  return MakeString(buffer.start());
+}
+
+
+static Handle<AccessorPair> CreateAccessorPair(bool with_getter,
+                                               bool with_setter) {
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<AccessorPair> pair = factory->NewAccessorPair();
+  if (with_getter) {
+    pair->set_getter(*factory->NewFunction(factory->empty_string()));
+  }
+  if (with_setter) {
+    pair->set_setter(*factory->NewFunction(factory->empty_string()));
+  }
+  return pair;
+}
+
+
+static bool EqualDetails(DescriptorArray* descriptors, int descriptor,
+                         PropertyType type, PropertyAttributes attributes,
+                         Representation representation, int field_index = -1) {
+  PropertyDetails details = descriptors->GetDetails(descriptor);
+  if (details.type() != type) return false;
+  if (details.attributes() != attributes) return false;
+  if (!details.representation().Equals(representation)) return false;
+  if (field_index >= 0 && details.field_index() != field_index) return false;
+  return true;
+}
+
+
+class Expectations {
+  static const int MAX_PROPERTIES = 64;
+  Isolate* isolate_;
+  PropertyType types_[MAX_PROPERTIES];
+  PropertyAttributes attributes_[MAX_PROPERTIES];
+  Representation representations_[MAX_PROPERTIES];
+  // HeapType for kField, value for DATA_CONSTANT and getter for
+  // ACCESSOR_CONSTANT.
+  Handle<Object> values_[MAX_PROPERTIES];
+  // Setter for ACCESSOR_CONSTANT.
+  Handle<Object> setter_values_[MAX_PROPERTIES];
+  int number_of_properties_;
+
+ public:
+  explicit Expectations(Isolate* isolate)
+      : isolate_(isolate), number_of_properties_(0) {}
+
+  void Init(int index, PropertyType type, PropertyAttributes attributes,
+            Representation representation, Handle<Object> value) {
+    DCHECK(index < MAX_PROPERTIES);
+    types_[index] = type;
+    attributes_[index] = attributes;
+    representations_[index] = representation;
+    values_[index] = value;
+  }
+
+  Handle<HeapType> GetFieldType(int index) {
+    CHECK(index < MAX_PROPERTIES);
+    CHECK(types_[index] == DATA || types_[index] == ACCESSOR);
+    return Handle<HeapType>::cast(values_[index]);
+  }
+
+  void SetDataField(int index, PropertyAttributes attrs,
+                    Representation representation, Handle<HeapType> value) {
+    Init(index, DATA, attrs, representation, value);
+  }
+
+  void SetDataField(int index, Representation representation,
+                    Handle<HeapType> value) {
+    SetDataField(index, attributes_[index], representation, value);
+  }
+
+  void SetAccessorField(int index, PropertyAttributes attrs) {
+    Init(index, ACCESSOR, attrs, Representation::Tagged(),
+         HeapType::Any(isolate_));
+  }
+
+  void SetAccessorField(int index) {
+    SetAccessorField(index, attributes_[index]);
+  }
+
+  void SetDataConstant(int index, PropertyAttributes attrs,
+                       Handle<JSFunction> value) {
+    Init(index, DATA_CONSTANT, attrs, Representation::HeapObject(), value);
+  }
+
+  void SetDataConstant(int index, Handle<JSFunction> value) {
+    SetDataConstant(index, attributes_[index], value);
+  }
+
+  void SetAccessorConstant(int index, PropertyAttributes attrs,
+                           Handle<Object> getter, Handle<Object> setter) {
+    Init(index, ACCESSOR_CONSTANT, attrs, Representation::Tagged(), getter);
+    setter_values_[index] = setter;
+  }
+
+  void SetAccessorConstantComponent(int index, PropertyAttributes attrs,
+                                    AccessorComponent component,
+                                    Handle<Object> accessor) {
+    CHECK_EQ(ACCESSOR_CONSTANT, types_[index]);
+    CHECK(index < number_of_properties_);
+    if (component == ACCESSOR_GETTER) {
+      values_[index] = accessor;
+    } else {
+      setter_values_[index] = accessor;
+    }
+  }
+
+  void SetAccessorConstant(int index, PropertyAttributes attrs,
+                           Handle<AccessorPair> pair) {
+    Handle<Object> getter = handle(pair->getter(), isolate_);
+    Handle<Object> setter = handle(pair->setter(), isolate_);
+    SetAccessorConstant(index, attrs, getter, setter);
+  }
+
+  void SetAccessorConstant(int index, Handle<Object> getter,
+                           Handle<Object> setter) {
+    SetAccessorConstant(index, attributes_[index], getter, setter);
+  }
+
+  void SetAccessorConstant(int index, Handle<AccessorPair> pair) {
+    Handle<Object> getter = handle(pair->getter(), isolate_);
+    Handle<Object> setter = handle(pair->setter(), isolate_);
+    SetAccessorConstant(index, getter, setter);
+  }
+
+  void GeneralizeRepresentation(int index) {
+    CHECK(index < number_of_properties_);
+    representations_[index] = Representation::Tagged();
+    if (types_[index] == DATA || types_[index] == ACCESSOR) {
+      values_[index] = HeapType::Any(isolate_);
+    }
+  }
+
+
+  bool Check(DescriptorArray* descriptors, int descriptor) {
+    PropertyType type = types_[descriptor];
+    if (!EqualDetails(descriptors, descriptor, type, attributes_[descriptor],
+                      representations_[descriptor])) {
+      return false;
+    }
+    Object* expected_value = *values_[descriptor];
+    Object* value = descriptors->GetValue(descriptor);
+    switch (type) {
+      case DATA:
+      case ACCESSOR:
+        return HeapType::cast(expected_value)->Equals(HeapType::cast(value));
+
+      case DATA_CONSTANT:
+        return value == expected_value;
+
+      case ACCESSOR_CONSTANT: {
+        if (value == expected_value) return true;
+        if (!value->IsAccessorPair()) return false;
+        AccessorPair* pair = AccessorPair::cast(value);
+        return pair->Equals(expected_value, *setter_values_[descriptor]);
+      }
+    }
+    UNREACHABLE();
+    return false;
+  }
+
+  bool Check(Map* map, int expected_nof) {
+    CHECK(number_of_properties_ <= MAX_PROPERTIES);
+    CHECK_EQ(expected_nof, map->NumberOfOwnDescriptors());
+    CHECK(!map->is_dictionary_map());
+
+    DescriptorArray* descriptors = map->instance_descriptors();
+    CHECK(expected_nof <= number_of_properties_);
+    for (int i = 0; i < expected_nof; i++) {
+      if (!Check(descriptors, i)) {
+        Check(descriptors, i);
+        return false;
+      }
+    }
+    return true;
+  }
+
+  bool Check(Map* map) { return Check(map, number_of_properties_); }
+
+
+  //
+  // Helper methods for initializing expectations and adding properties to
+  // given |map|.
+  //
+
+  Handle<Map> AddDataField(Handle<Map> map, PropertyAttributes attributes,
+                           Representation representation,
+                           Handle<HeapType> heap_type) {
+    CHECK_EQ(number_of_properties_, map->NumberOfOwnDescriptors());
+    int property_index = number_of_properties_++;
+    SetDataField(property_index, attributes, representation, heap_type);
+
+    Handle<String> name = MakeName("prop", property_index);
+    return Map::CopyWithField(map, name, heap_type, attributes, representation,
+                              INSERT_TRANSITION).ToHandleChecked();
+  }
+
+  Handle<Map> AddDataConstant(Handle<Map> map, PropertyAttributes attributes,
+                              Handle<JSFunction> value) {
+    CHECK_EQ(number_of_properties_, map->NumberOfOwnDescriptors());
+    int property_index = number_of_properties_++;
+    SetDataConstant(property_index, attributes, value);
+
+    Handle<String> name = MakeName("prop", property_index);
+    return Map::CopyWithConstant(map, name, value, attributes,
+                                 INSERT_TRANSITION).ToHandleChecked();
+  }
+
+  Handle<Map> FollowDataTransition(Handle<Map> map,
+                                   PropertyAttributes attributes,
+                                   Representation representation,
+                                   Handle<HeapType> heap_type) {
+    CHECK_EQ(number_of_properties_, map->NumberOfOwnDescriptors());
+    int property_index = number_of_properties_++;
+    SetDataField(property_index, attributes, representation, heap_type);
+
+    Handle<String> name = MakeName("prop", property_index);
+    int t = map->SearchTransition(kData, *name, attributes);
+    CHECK_NE(TransitionArray::kNotFound, t);
+    return handle(map->GetTransition(t));
+  }
+
+  Handle<Map> AddAccessorConstant(Handle<Map> map,
+                                  PropertyAttributes attributes,
+                                  Handle<AccessorPair> pair) {
+    CHECK_EQ(number_of_properties_, map->NumberOfOwnDescriptors());
+    int property_index = number_of_properties_++;
+    SetAccessorConstant(property_index, attributes, pair);
+
+    Handle<String> name = MakeName("prop", property_index);
+
+    AccessorConstantDescriptor new_desc(name, pair, attributes);
+    return Map::CopyInsertDescriptor(map, &new_desc, INSERT_TRANSITION);
+  }
+
+  Handle<Map> AddAccessorConstant(Handle<Map> map,
+                                  PropertyAttributes attributes,
+                                  Handle<Object> getter,
+                                  Handle<Object> setter) {
+    CHECK_EQ(number_of_properties_, map->NumberOfOwnDescriptors());
+    int property_index = number_of_properties_++;
+    SetAccessorConstant(property_index, attributes, getter, setter);
+
+    Handle<String> name = MakeName("prop", property_index);
+
+    CHECK(!getter->IsNull() || !setter->IsNull());
+    Factory* factory = isolate_->factory();
+
+    if (!getter->IsNull()) {
+      Handle<AccessorPair> pair = factory->NewAccessorPair();
+      pair->SetComponents(*getter, *factory->null_value());
+      AccessorConstantDescriptor new_desc(name, pair, attributes);
+      map = Map::CopyInsertDescriptor(map, &new_desc, INSERT_TRANSITION);
+    }
+    if (!setter->IsNull()) {
+      Handle<AccessorPair> pair = factory->NewAccessorPair();
+      pair->SetComponents(*getter, *setter);
+      AccessorConstantDescriptor new_desc(name, pair, attributes);
+      map = Map::CopyInsertDescriptor(map, &new_desc, INSERT_TRANSITION);
+    }
+    return map;
+  }
+};
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests for basic transitioning mechanics.
+//
+
+TEST(TransitionToDataFieldProperty) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 50;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  Handle<Map> intermediate_maps[kPropCount];
+  Representation representations[] = {
+      Representation::Smi(), Representation::Double(),
+      Representation::HeapObject(), Representation::Tagged()};
+  // values[i] must fit into representations[i].
+  Handle<Object> values[] = {
+      handle(Smi::FromInt(0), isolate), factory->NewHeapNumber(0),
+      factory->NewJSObjectFromMap(Map::Create(isolate, 0)),
+      factory->undefined_value()};
+  const int kValuesCount = arraysize(values);
+  CHECK_EQ(kValuesCount, arraysize(representations));
+
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    Representation r = representations[i % kValuesCount];
+    CHECK(values[i % kValuesCount]->FitsRepresentation(r));
+
+    map = expectations.AddDataField(map, attributes, r, any_type);
+    intermediate_maps[i] = map;
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK(expectations.Check(*intermediate_maps[i], i + 1));
+  }
+
+  // Try to follow same transitions from the |initial_map|.
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    Handle<String> name = MakeName("prop", i);
+    map2 = Map::TransitionToDataProperty(
+        map2, name, values[i % kValuesCount], attributes,
+        Object::CERTAINLY_NOT_STORE_FROM_KEYED);
+
+    CHECK(!map2->is_deprecated());
+    CHECK(!map2->is_dictionary_map());
+    CHECK_EQ(*intermediate_maps[i], *map2);
+    CHECK(expectations.Check(*map2, i + 1));
+  }
+}
+
+
+TEST(TransitionToDataConstantProperty) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+
+  const int kPropCount = 50;
+  Expectations expectations(isolate);
+
+  Handle<JSFunction> functions[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    functions[i] = factory->NewFunction(factory->empty_string());
+  }
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  Handle<Map> intermediate_maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    map = expectations.AddDataConstant(map, attributes, functions[i]);
+    intermediate_maps[i] = map;
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK(expectations.Check(*intermediate_maps[i], i + 1));
+  }
+
+  // Try to follow same transitions from the |initial_map|.
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    Handle<String> name = MakeName("prop", i);
+    map2 =
+        Map::TransitionToDataProperty(map2, name, functions[i], attributes,
+                                      Object::CERTAINLY_NOT_STORE_FROM_KEYED);
+
+    CHECK(!map2->is_deprecated());
+    CHECK(!map2->is_dictionary_map());
+    CHECK_EQ(*intermediate_maps[i], *map2);
+    CHECK(expectations.Check(*map2, i + 1));
+  }
+}
+
+
+TEST(TransitionToAccessorConstantProperty) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+
+  const int kPropCount = 50;
+  Expectations expectations(isolate);
+
+  Handle<AccessorPair> accessor_pairs[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    // Getter only accessors.
+    accessor_pairs[i] = CreateAccessorPair(true, false);
+  }
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  Handle<Map> intermediate_maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    map = expectations.AddAccessorConstant(
+        map, attributes, handle(accessor_pairs[i]->getter(), isolate),
+        handle(accessor_pairs[i]->setter(), isolate));
+    intermediate_maps[i] = map;
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK(expectations.Check(*intermediate_maps[i], i + 1));
+  }
+
+  // Try to follow same transitions from the |initial_map|.
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    PropertyAttributes attributes = static_cast<PropertyAttributes>(i % 8);
+    Handle<String> name = MakeName("prop", i);
+    Handle<Object> getter(accessor_pairs[i]->getter(), isolate);
+    Handle<Object> setter(accessor_pairs[i]->setter(), isolate);
+
+    map2 = Map::TransitionToAccessorProperty(map2, name, ACCESSOR_GETTER,
+                                             getter, attributes);
+    CHECK(!map2->is_deprecated());
+    CHECK(!map2->is_dictionary_map());
+
+    map2 = Map::TransitionToAccessorProperty(map2, name, ACCESSOR_SETTER,
+                                             setter, attributes);
+    CHECK(!map2->is_deprecated());
+    CHECK(!map2->is_dictionary_map());
+    CHECK_EQ(*intermediate_maps[i], *map2);
+    CHECK(expectations.Check(*map2, i + 1));
+  }
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests for representation generalization case.
+//
+
+TEST(GeneralizeRepresentationSmiToDouble) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to double.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Double(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Double(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(GeneralizeRepresentationSmiToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to heap
+  // object.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(GeneralizeRepresentationDoubleToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Double(),
+                                    any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to heap
+  // object.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(GeneralizeRepresentationHeapObjectToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to smi.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Smi(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}

[Toon Verwaest, 2015/01/30 13:02:53]

Seems like you could merge the few tests above into a single one that has arrays
of [[start_repr, new_repr]*]. If you add "deprecated" you can also handle
none->* cases.

+
+
+TEST(GeneralizeRepresentationHeapObjectToHeapObject) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create some value types.
+  static const int kAdditionalValueTypesCount = 4;
+  Handle<HeapType> value_types[kAdditionalValueTypesCount];
+  for (int i = 0; i < kAdditionalValueTypesCount; i++) {
+    Handle<Map> value_map = Map::Create(isolate, 0);
+    CHECK(value_map->is_stable());
+    value_types[i] = HeapType::Class(value_map, isolate);
+  }
+
+  Zone zone;
+
+  // Create new maps by generalizing representation of propX field to various
+  // HeapObject types with stable maps.
+  for (int val_index = 0; val_index < kAdditionalValueTypesCount; val_index++) {
+    Handle<Map> maps[kPropCount];
+    for (int i = 0; i < kPropCount; i++) {
+      Handle<Map> field_owner(map->FindFieldOwner(i), isolate);
+      CompilationInfo info(isolate, &zone);
+      CHECK(!info.HasAbortedDueToDependencyChange());
+
+      Map::AddDependentCompilationInfo(field_owner,
+                                       DependentCode::kFieldTypeGroup, &info);
+
+      Handle<Map> new_map = Map::ReconfigureProperty(
+          map, i, kData, NONE, Representation::HeapObject(),
+          value_types[val_index], FORCE_FIELD);
+      maps[i] = new_map;
+
+      expectations.SetDataField(
+          i, Representation::HeapObject(),
+          HeapType::Union(value_types[val_index], expectations.GetFieldType(i),
+                          isolate));
+
+      // Maps should stay the same but field type modification should trigger
+      // respective dependents to deoptimize.
+      CHECK_EQ(*map, *new_map);
+      CHECK(info.HasAbortedDueToDependencyChange());
+      info.RollbackDependencies();  // Properly cleanup compilation info.
+
+      CHECK(!new_map->is_deprecated());
+      CHECK(!new_map->is_dictionary_map());
+      CHECK(expectations.Check(*new_map));
+    }
+
+    Handle<Map> active_map = maps[kPropCount - 1];
+    CHECK(!active_map->is_deprecated());
+
+    // Update all deprecated maps and check that they are now the same.
+    CHECK_EQ(*active_map, *Map::Update(map));
+    for (int i = 0; i < kPropCount; i++) {
+      CHECK_EQ(*active_map, *Map::Update(maps[i]));
+    }
+  }
+}
+
+
+TEST(GeneralizeRepresentationNoneToSmi) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> none_type = HeapType::None(isolate);
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map =
+        expectations.AddDataField(map, NONE, Representation::None(), none_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to smi.
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Smi(), any_type, FORCE_FIELD);
+
+    expectations.SetDataField(i, Representation::Smi(), any_type);
+
+    CHECK_EQ(*map, *new_map);  // None -> Smi change is trivial.
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  CHECK_EQ(*map, *Map::Update(map));
+}
+
+
+TEST(GeneralizeRepresentationNoneToDouble) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> none_type = HeapType::None(isolate);
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map =
+        expectations.AddDataField(map, NONE, Representation::None(), none_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to heap
+  // object.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Double(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Double(), any_type);
+
+    CHECK(map->is_deprecated());  // None -> Double change is NOT trivial.
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(GeneralizeRepresentationNoneToHeapObject) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> none_type = HeapType::None(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map =
+        expectations.AddDataField(map, NONE, Representation::None(), none_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to heap
+  // object.
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type, FORCE_FIELD);
+
+    expectations.SetDataField(i, Representation::HeapObject(), value_type);
+
+    CHECK_EQ(*map, *new_map);  // None -> HeapObject change is trivial.
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  CHECK_EQ(*map, *Map::Update(map));
+}
+
+
+TEST(GeneralizeRepresentationNoneToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> none_type = HeapType::None(isolate);
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map =
+        expectations.AddDataField(map, NONE, Representation::None(), none_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to heap
+  // object.
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Tagged(), any_type, FORCE_FIELD);
+
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+
+    CHECK_EQ(*map, *new_map);  // None -> Tagged change is trivial.
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  CHECK_EQ(*map, *Map::Update(map));
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests for representation generalization case with kAccessor
+// properties.
+//
+
+TEST(GeneralizeRepresentationWithAccessorProperties) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<AccessorPair> pair = CreateAccessorPair(true, true);
+
+  const int kPropCount = 5;
+  const int kAccessorProp = kPropCount / 2;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kAccessorProp) {
+      map = expectations.AddAccessorConstant(map, NONE, pair);
+    } else {
+      map =
+          expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+    }
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to double.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kAccessorProp) {
+      // Skip accessor property reconfiguration.
+      maps[i] = maps[i - 1];
+      continue;
+    }
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Double(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Double(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests for property location change case.
+//
+
+TEST(ReconfigureDataConstantToDataField) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<JSFunction> js_func = factory->NewFunction(factory->empty_string());
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataConstant(map, NONE, js_func);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by forcing propX to become a field.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::HeapObject(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(ReconfigureAccessorConstantToAccessorField) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<JSFunction> getter = factory->NewFunction(factory->empty_string());
+  Handle<JSFunction> setter = factory->NewFunction(factory->empty_string());
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  Handle<AccessorPair> accessor_pairs[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    // Getter only accessors.
+    accessor_pairs[i] = CreateAccessorPair(true, false);
+  }
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  Handle<Map> intermediate_maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddAccessorConstant(
+        map, NONE, handle(accessor_pairs[i]->getter(), isolate),
+        handle(accessor_pairs[i]->setter(), isolate));
+    intermediate_maps[i] = map;
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK(expectations.Check(*intermediate_maps[i], i + 1));
+  }
+
+  // Try to follow same transitions from the |initial_map|.
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<String> name = MakeName("prop", i);
+    map2 = Map::TransitionToAccessorProperty(map2, name, ACCESSOR_GETTER,
+                                             getter, NONE);
+    if (IS_ACCESSOR_FIELD_SUPPORTED) {
+      CHECK(!map2->is_dictionary_map());
+    } else {
+      CHECK(map2->is_dictionary_map());
+    }
+
+    map2 = Map::TransitionToAccessorProperty(map2, name, ACCESSOR_SETTER,
+                                             setter, NONE);
+    if (IS_ACCESSOR_FIELD_SUPPORTED) {
+      CHECK(!map2->is_dictionary_map());
+      CHECK(expectations.Check(*map2, i + 1));
+    } else {
+      CHECK(map2->is_dictionary_map());
+    }
+  }
+
+  if (!IS_ACCESSOR_FIELD_SUPPORTED) {
+    CHECK(map2->is_dictionary_map());
+  }
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests for attribute reconfiguration case.
+//
+
+TEST(ReconfigureDataFieldAttribute_GeneralizeRepresentationSmiToDouble) {

[Toon Verwaest, 2015/01/30 13:02:53]

Same here?

+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = kPropCount / 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY, Representation::Double(),
+                                    any_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    map2 = expectations2.AddDataField(map2, NONE, Representation::Double(),
+                                      any_type);
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  for (int i = kSplitProp; i < kPropCount; i++) {
+    expectations.SetDataField(i, Representation::Double(), any_type);
+  }
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_GeneralizeRepresentationSmiToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = kPropCount / 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    map2 = expectations2.AddDataField(map2, NONE, Representation::HeapObject(),
+                                      value_type);
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  for (int i = kSplitProp; i < kPropCount; i++) {
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+  }
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_GeneralizeRepresentationDoubleToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Double(),
+                                    any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = kPropCount / 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(
+        map2, NONE, Representation::Double(), any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    map2 = expectations2.AddDataField(map2, NONE, Representation::HeapObject(),
+                                      value_type);
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  for (int i = kSplitProp; i < kPropCount; i++) {
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+  }
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_GeneralizeRepresentationHeapObjectToTagged) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = kPropCount / 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(
+        map2, NONE, Representation::HeapObject(), value_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY, Representation::Smi(),
+                                    any_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    map2 =
+        expectations2.AddDataField(map2, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  for (int i = kSplitProp; i < kPropCount; i++) {
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+  }
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_SameDataConstantAfterTargetMap) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<JSFunction> js_func = factory->NewFunction(factory->empty_string());
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 7;
+  const int kConstantPropIndex = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map = expectations.AddDataConstant(map, NONE, js_func);
+
+    } else {
+      map =
+          expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+    }
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map2 = expectations2.AddDataConstant(map2, NONE, js_func);
+
+    } else {
+      map2 = expectations2.AddDataField(map2, NONE, Representation::Smi(),
+                                        any_type);
+    }
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  expectations.SetDataField(kSplitProp, Representation::Tagged(), any_type);
+
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_DataConstantToDataFieldAfterTargetMap) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<JSFunction> js_func = factory->NewFunction(factory->empty_string());
+  Handle<JSFunction> js_func2 = factory->NewFunction(factory->empty_string());
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 7;
+  const int kConstantPropIndex = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map = expectations.AddDataConstant(map, NONE, js_func);
+
+    } else {
+      map =
+          expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+    }
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map2 = expectations2.AddDataConstant(map2, NONE, js_func2);
+
+    } else {
+      map2 = expectations2.AddDataField(map2, NONE, Representation::Smi(),
+                                        any_type);
+    }
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  expectations.SetDataField(kSplitProp, Representation::Tagged(), any_type);
+  expectations.SetDataField(kConstantPropIndex, Representation::HeapObject(),
+                            any_type);
+
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_SameAccessorConstantAfterTargetMap) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<AccessorPair> pair = CreateAccessorPair(true, true);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 7;
+  const int kConstantPropIndex = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map = expectations.AddAccessorConstant(map, NONE, pair);
+
+    } else {
+      map =
+          expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+    }
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map2 = expectations2.AddAccessorConstant(map2, NONE, pair);
+
+    } else {
+      map2 = expectations2.AddDataField(map2, NONE, Representation::Smi(),
+                                        any_type);
+    }
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  expectations.SetDataField(kSplitProp, Representation::Tagged(), any_type);
+
+  CHECK(map->is_deprecated());
+  CHECK_NE(*map, *new_map);
+
+  CHECK(!new_map->is_deprecated());
+  CHECK(!new_map->is_dictionary_map());
+  CHECK(expectations.Check(*new_map));
+
+  // Update deprecated |map|, it should become |new_map|.
+  CHECK_EQ(*new_map, *Map::Update(map));
+}
+
+
+TEST(ReconfigureDataFieldAttribute_AccConstantToAccFieldAfterTargetMap) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<AccessorPair> pair = CreateAccessorPair(true, true);
+  Handle<AccessorPair> pair2 = CreateAccessorPair(true, true);
+  Handle<HeapType> value_type =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 7;
+  const int kConstantPropIndex = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map = expectations.AddAccessorConstant(map, NONE, pair);
+
+    } else {
+      map =
+          expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+    }
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create another branch in transition tree (property at index |kSplitProp|
+  // has different attributes), initialize expectations.
+  const int kSplitProp = 2;
+  Expectations expectations2(isolate);
+
+  Handle<Map> map2 = initial_map;
+  for (int i = 0; i < kSplitProp; i++) {
+    map2 = expectations2.FollowDataTransition(map2, NONE, Representation::Smi(),
+                                              any_type);
+  }
+  map2 = expectations2.AddDataField(map2, READ_ONLY,
+                                    Representation::HeapObject(), value_type);
+
+  for (int i = kSplitProp + 1; i < kPropCount; i++) {
+    if (i == kConstantPropIndex) {
+      map2 = expectations2.AddAccessorConstant(map2, NONE, pair2);
+
+    } else {
+      map2 = expectations2.AddDataField(map2, NONE, Representation::Smi(),
+                                        any_type);
+    }
+  }
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations2.Check(*map2));
+
+
+  // Reconfigure attributes of property |kSplitProp| of |map2| to NONE, which
+  // should generalize representations in |map1|.
+  Handle<Map> new_map =
+      Map::ReconfigureExistingProperty(map2, kSplitProp, kData, NONE);
+
+  // |map2| should be left unchanged.
+  CHECK(!map2->is_deprecated());
+  CHECK_NE(*map2, *new_map);
+  CHECK(expectations2.Check(*map2));
+
+  // |map| should be deprecated and |new_map| should match new expectations.
+  if (IS_ACCESSOR_FIELD_SUPPORTED) {
+    expectations.SetDataField(kSplitProp, Representation::Tagged(), any_type);
+    expectations.SetAccessorField(kConstantPropIndex);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    // Update deprecated |map|, it should become |new_map|.
+    CHECK_EQ(*new_map, *Map::Update(map));
+  } else {
+    // Currently we have a copy-generalize all representations case.
+    CHECK(new_map->GetBackPointer()->IsUndefined());
+    for (int i = 0; i < kPropCount; i++) {
+      if (i == kConstantPropIndex) {
+        expectations.SetAccessorConstant(i, pair2);
+
+      } else {
+        expectations.SetDataField(i, Representation::Tagged(), any_type);
+      }
+    }
+    CHECK(!map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+  }
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests checking split map deprecation.
+//
+
+TEST(ReconfigurePropertySplitMapTransitionsOverflow) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+
+  // Generalize representation of property at index |kSplitProp|.
+  const int kSplitProp = kPropCount / 2;
+  Handle<Map> split_map;
+  Handle<Map> map2 = initial_map;
+  {
+    for (int i = 0; i < kSplitProp + 1; i++) {
+      if (i == kSplitProp) {
+        split_map = map2;
+      }
+
+      Handle<String> name = MakeName("prop", i);
+      int t = map2->SearchTransition(kData, *name, NONE);
+      CHECK_NE(TransitionArray::kNotFound, t);
+      map2 = handle(map2->GetTransition(t));
+    }
+
+    map2 = Map::ReconfigureProperty(map2, kSplitProp, kData, NONE,
+                                    Representation::Double(), any_type,
+                                    FORCE_FIELD);
+    expectations.SetDataField(kSplitProp, Representation::Double(), any_type);
+
+    CHECK(expectations.Check(*split_map, kSplitProp));
+    CHECK(expectations.Check(*map2, kSplitProp + 1));
+  }
+
+  // At this point |map| should be deprecated and disconnected from the
+  // transition tree.
+  CHECK(map->is_deprecated());
+  CHECK(!split_map->is_deprecated());
+  CHECK(!map2->is_deprecated());
+
+  // Fill in transition tree of |map2| so that it can't have more transitions.
+  for (int i = 0; i < TransitionArray::kMaxNumberOfTransitions; i++) {
+    CHECK(map2->CanHaveMoreTransitions());
+    Handle<String> name = MakeName("foo", i);
+    Map::CopyWithField(map2, name, any_type, NONE, Representation::Smi(),
+                       INSERT_TRANSITION).ToHandleChecked();
+  }
+  CHECK(!map2->CanHaveMoreTransitions());
+
+  // Try to update |map|, since there is no place for propX transition at |map2|
+  // |map| should become "copy-generalized".
+  Handle<Map> updated_map = Map::Update(map);
+  CHECK(updated_map->GetBackPointer()->IsUndefined());
+
+  for (int i = 0; i < kPropCount; i++) {
+    expectations.SetDataField(i, Representation::Tagged(), any_type);
+  }
+  CHECK(expectations.Check(*updated_map));
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+// A set of tests involving special transitions.
+//
+
+TEST(ElementsKindTransitionFromMapOwningDescriptor) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> value_type1 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+  Handle<HeapType> value_type2 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type1);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  CHECK(map->owns_descriptors());
+
+  // Create an elements kind transition, it should always match |expectations|.
+  Handle<Map> map2 =
+      Map::CopyAsElementsKind(map, DICTIONARY_ELEMENTS, INSERT_TRANSITION);
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations.Check(*map2));
+
+  // |map1| should still match expectations.
+  CHECK(!map->is_deprecated());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to various
+  // HeapObject types with stable maps.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type2, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(
+        i, Representation::HeapObject(),
+        HeapType::Union(value_type2, expectations.GetFieldType(i), isolate));
+
+    // Maps should stay the same but field type modification should trigger
+    // respective dependents to deoptimize.
+    CHECK_EQ(*map, *new_map);
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      Handle<Map> new_map2 = Map::Update(map2);
+      CHECK(!new_map2->is_deprecated());
+      CHECK(!new_map2->is_dictionary_map());
+      CHECK(expectations.Check(*new_map2));
+    }
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(ElementsKindTransitionFromMapNotOwningDescriptor) {
+  if (!IS_CRBUG_448711_FIXED) return;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type1 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+  Handle<HeapType> value_type2 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type1);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Add one more transition to |map| in order to prevent descriptors ownership.
+  CHECK(map->owns_descriptors());
+  Map::CopyWithField(map, MakeString("foo"), any_type, NONE,
+                     Representation::Smi(),
+                     INSERT_TRANSITION).ToHandleChecked();
+  CHECK(!map->owns_descriptors());
+
+  // Create an elements kind transition, it should always match |expectations|.
+  Handle<Map> map2 =
+      Map::CopyAsElementsKind(map, DICTIONARY_ELEMENTS, INSERT_TRANSITION);
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations.Check(*map2));
+
+  // |map1| should still match expectations.
+  CHECK(!map->is_deprecated());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to various
+  // HeapObject types with stable maps.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type2, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(
+        i, Representation::HeapObject(),
+        HeapType::Union(value_type2, expectations.GetFieldType(i), isolate));
+
+    // Maps should stay the same but field type modification should trigger
+    // respective dependents to deoptimize.
+    CHECK_EQ(*map, *new_map);
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      Handle<Map> new_map2 = Map::Update(map2);
+      CHECK(!new_map2->is_deprecated());
+      CHECK(!new_map2->is_dictionary_map());
+      CHECK(expectations.Check(*new_map2));
+    }
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(ForObservedTransitionFromMapOwningDescriptor) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> value_type1 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+  Handle<HeapType> value_type2 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type1);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  CHECK(map->owns_descriptors());
+
+  // Create "for-observed" transition, it should always match |expectations|.
+  Handle<Map> map2 = Map::CopyForObserved(map);
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations.Check(*map2));
+
+  // |map1| should still match expectations.
+  CHECK(!map->is_deprecated());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to various
+  // HeapObject types with stable maps.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type2, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(
+        i, Representation::HeapObject(),
+        HeapType::Union(value_type2, expectations.GetFieldType(i), isolate));
+
+    // Maps should stay the same but field type modification should trigger
+    // respective dependents to deoptimize.
+    CHECK_EQ(*map, *new_map);
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      Handle<Map> new_map2 = Map::Update(map2);
+      CHECK(!new_map2->is_deprecated());
+      CHECK(!new_map2->is_dictionary_map());
+      CHECK(expectations.Check(*new_map2));
+    }
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(ForObservedTransitionFromMapNotOwningDescriptor) {
+  if (!IS_CRBUG_448711_FIXED) return;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<HeapType> value_type1 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+  Handle<HeapType> value_type2 =
+      HeapType::Class(Map::Create(isolate, 0), isolate);
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::HeapObject(),
+                                    value_type1);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Add one more transition to |map| in order to prevent descriptors ownership.
+  CHECK(map->owns_descriptors());
+  Map::CopyWithField(map, MakeString("foo"), any_type, NONE,
+                     Representation::Smi(),
+                     INSERT_TRANSITION).ToHandleChecked();
+  CHECK(!map->owns_descriptors());
+
+  // Create "for-observed" transition, it should always match |expectations|.
+  Handle<Map> map2 = Map::CopyForObserved(map);
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  CHECK(expectations.Check(*map2));
+
+  // |map1| should still match expectations.
+  CHECK(!map->is_deprecated());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to various
+  // HeapObject types with stable maps.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(map, i, kData, NONE,
+                                                   Representation::HeapObject(),
+                                                   value_type2, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(
+        i, Representation::HeapObject(),
+        HeapType::Union(value_type2, expectations.GetFieldType(i), isolate));
+
+    // Maps should stay the same but field type modification should trigger
+    // respective dependents to deoptimize.
+    CHECK_EQ(*map, *new_map);
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      Handle<Map> new_map2 = Map::Update(map2);
+      CHECK(!new_map2->is_deprecated());
+      CHECK(!new_map2->is_dictionary_map());
+      CHECK(expectations.Check(*new_map2));
+    }
+  }
+
+  Handle<Map> active_map = maps[kPropCount - 1];
+  CHECK(!active_map->is_deprecated());
+
+  // Update all deprecated maps and check that they are now the same.
+  CHECK_EQ(*active_map, *Map::Update(map));
+  for (int i = 0; i < kPropCount; i++) {
+    CHECK_EQ(*active_map, *Map::Update(maps[i]));
+  }
+}
+
+
+TEST(PrototypeTransitionFromMapOwningDescriptor) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<JSObject> prototype =
+      factory->NewJSObjectFromMap(Map::Create(isolate, 0));
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  for (int i = 0; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  CHECK(map->owns_descriptors());
+
+  // Create prototype transition, it should always match |expectations|.
+  Handle<Map> map2 =
+      Map::TransitionToPrototype(map, prototype, REGULAR_PROTOTYPE);
+
+  CHECK(!map2->is_deprecated());
+  CHECK(map2->is_stable());
+  if (IS_CRBUG_448711_FIXED) {
+    CHECK(expectations.Check(*map2));
+  }
+
+  // |map1| should still match expectations.
+  CHECK(!map->is_deprecated());
+  CHECK(expectations.Check(*map));
+
+  CHECK_EQ(*map2,
+           *Map::TransitionToPrototype(map, prototype, REGULAR_PROTOTYPE));
+
+  // Create new maps by generalizing representation of propX field to double.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Double(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    expectations.SetDataField(i, Representation::Double(), any_type);
+
+    CHECK(map->is_deprecated());
+    CHECK_NE(*map, *new_map);
+    CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+    CHECK(!new_map->is_deprecated());
+    CHECK(!new_map->is_dictionary_map());
+    CHECK(expectations.Check(*new_map));
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      Handle<Map> new_map2 = Map::Update(map2);
+      CHECK(!new_map2->is_deprecated());
+      CHECK(!new_map2->is_dictionary_map());
+      CHECK(expectations.Check(*new_map2));
+    }
+  }
+}
+
+
+TEST(GeneralizeRepresentationWithPrototypeTransition) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<HeapType> any_type = HeapType::Any(isolate);
+  Handle<JSObject> prototype =
+      factory->NewJSObjectFromMap(Map::Create(isolate, 0));
+  Handle<JSFunction> js_func = factory->NewFunction(factory->empty_string());
+
+  const int kPropCount = 5;
+  Expectations expectations(isolate);
+
+  // Create a map, add required properties to it and initialize expectations.
+  Handle<Map> initial_map = Map::Create(isolate, 0);
+  Handle<Map> map = initial_map;
+  map = expectations.AddDataConstant(map, NONE, js_func);
+  map = Map::TransitionToPrototype(map, prototype, REGULAR_PROTOTYPE);
+  if (!IS_CRBUG_448711_FIXED) {
+    expectations.GeneralizeRepresentation(0);
+  }
+  for (int i = 1; i < kPropCount; i++) {
+    map = expectations.AddDataField(map, NONE, Representation::Smi(), any_type);
+  }
+  CHECK(!map->is_deprecated());
+  CHECK(map->is_stable());
+  CHECK(expectations.Check(*map));
+
+  // Create new maps by generalizing representation of propX field to double.
+  Handle<Map> maps[kPropCount];
+  for (int i = 0; i < kPropCount; i++) {
+    Handle<Map> new_map = Map::ReconfigureProperty(
+        map, i, kData, NONE, Representation::Double(), any_type, FORCE_FIELD);
+    maps[i] = new_map;
+
+    if (!IS_NON_EQUIVALENT_TRANSITION_SUPPORTED) {
+      // If we reconfigure the property that was added before prototype
+      // transition, we would get Gen
+      CHECK(i != 0 || new_map->GetBackPointer()->IsUndefined());
+    }
+
+    if (IS_NON_EQUIVALENT_TRANSITION_SUPPORTED && IS_CRBUG_448711_FIXED) {
+      expectations.SetDataField(i, Representation::Double(), any_type);
+
+      CHECK(map->is_deprecated());
+      CHECK_NE(*map, *new_map);
+      CHECK(i == 0 || maps[i - 1]->is_deprecated());
+
+      CHECK(!new_map->is_deprecated());
+      CHECK(!new_map->is_dictionary_map());
+      CHECK(expectations.Check(*new_map));
+    }
+  }
+}