Fix inobject slack tracking for both subclassing and non-subclassing cases.

test/cctest/test-inobject-slack-tracking.cc

Index: test/cctest/test-inobject-slack-tracking.cc
diff --git a/test/cctest/test-inobject-slack-tracking.cc b/test/cctest/test-inobject-slack-tracking.cc
new file mode 100644
index 0000000000000000000000000000000000000000..79cb8335adbf6e1836541c8da3cc12c4ca506b6e
--- /dev/null
+++ b/test/cctest/test-inobject-slack-tracking.cc
@@ -0,0 +1,1098 @@
+// 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 <sstream>
+#include <utility>
+
+#include "src/api.h"
+#include "src/objects.h"
+#include "src/v8.h"
+
+#include "test/cctest/cctest.h"
+
+using namespace v8::base;
+using namespace v8::internal;
+
+
+static const int kMaxInobjectProperties =
+    (JSObject::kMaxInstanceSize - JSObject::kHeaderSize) >> kPointerSizeLog2;
+
+
+template <typename T>
+static Handle<T> OpenHandle(v8::Local<v8::Value> value) {
+  Handle<Object> obj = v8::Utils::OpenHandle(*value);
+  return Handle<T>::cast(obj);
+}
+
+
+static inline v8::Local<v8::Value> Run(v8::Local<v8::Script> script) {
+  v8::Local<v8::Value> result;
+  if (script->Run(v8::Isolate::GetCurrent()->GetCurrentContext())
+          .ToLocal(&result)) {
+    return result;
+  }
+  return v8::Local<v8::Value>();
+}
+
+
+template <typename T = Object>
+Handle<T> GetGlobal(const char* name) {
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+  Handle<String> str_name = factory->InternalizeUtf8String(name);
+
+  Handle<Object> value =
+      Object::GetProperty(isolate->global_object(), str_name).ToHandleChecked();
+  return Handle<T>::cast(value);
+}
+
+
+template <typename T = Object>
+Handle<T> GetLexical(const char* name) {
+  Isolate* isolate = CcTest::i_isolate();
+  Factory* factory = isolate->factory();
+
+  Handle<String> str_name = factory->InternalizeUtf8String(name);
+  Handle<ScriptContextTable> script_contexts(
+      isolate->native_context()->script_context_table());
+
+  ScriptContextTable::LookupResult lookup_result;
+  if (ScriptContextTable::Lookup(script_contexts, str_name, &lookup_result)) {
+    Handle<Object> result =
+        FixedArray::get(ScriptContextTable::GetContext(
+                            script_contexts, lookup_result.context_index),
+                        lookup_result.slot_index);
+    return Handle<T>::cast(result);
+  }
+  return Handle<T>();
+}
+
+
+template <typename T = Object>
+Handle<T> GetLexical(const std::string& name) {
+  return GetLexical<T>(name.c_str());
+}
+
+
+template <typename T>
+static inline Handle<T> Run(v8::Local<v8::Script> script) {
+  return OpenHandle<T>(Run(script));
+}
+
+
+template <typename T>
+static inline Handle<T> CompileRun(const char* script) {
+  return OpenHandle<T>(CompileRun(script));
+}
+
+
+static Object* GetFieldValue(JSObject* obj, int property_index) {
+  FieldIndex index = FieldIndex::ForPropertyIndex(obj->map(), property_index);
+  return obj->RawFastPropertyAt(index);
+}
+
+
+static double GetDoubleFieldValue(JSObject* obj, FieldIndex field_index) {
+  if (obj->IsUnboxedDoubleField(field_index)) {
+    return obj->RawFastDoublePropertyAt(field_index);
+  } else {
+    Object* value = obj->RawFastPropertyAt(field_index);
+    DCHECK(value->IsMutableHeapNumber());
+    return HeapNumber::cast(value)->value();
+  }
+}
+
+
+static double GetDoubleFieldValue(JSObject* obj, int property_index) {
+  FieldIndex index = FieldIndex::ForPropertyIndex(obj->map(), property_index);
+  return GetDoubleFieldValue(obj, index);
+}
+
+
+bool IsObjectShrinkable(JSObject* obj) {
+  Handle<Map> filler_map =
+      CcTest::i_isolate()->factory()->one_pointer_filler_map();
+
+  int inobject_properties = obj->map()->GetInObjectProperties();
+  int unused = obj->map()->unused_property_fields();
+  if (unused == 0) return false;
+
+  for (int i = inobject_properties - unused; i < inobject_properties; i++) {
+    if (*filler_map != GetFieldValue(obj, i)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
+TEST(JSObjectBasic) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  const char* source =
+      "function A() {"
+      "  this.a = 42;"
+      "  this.d = 4.2;"
+      "  this.o = this;"
+      "}";
+  CompileRun(source);
+
+  Handle<JSFunction> func = GetGlobal<JSFunction>("A");
+
+  // Zero instances were created so far.
+  CHECK(!func->has_initial_map());
+
+  v8::Local<v8::Script> new_A_script = v8_compile("new A();");
+
+  Handle<JSObject> obj = Run<JSObject>(new_A_script);
+
+  CHECK(func->has_initial_map());
+  Handle<Map> initial_map(func->initial_map());
+
+  // One instance created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+  CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+  // There must be at least some slack.
+  CHECK_LT(5, obj->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*obj, 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*obj, 1));
+  CHECK_EQ(*obj, GetFieldValue(*obj, 2));
+  CHECK(IsObjectShrinkable(*obj));
+
+  // Create several objects to complete the tracking.
+  for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_A_script);
+    CHECK_EQ(initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*obj));
+
+  // No slack left.
+  CHECK_EQ(3, obj->map()->GetInObjectProperties());
+}
+
+
+TEST(JSObjectBasicNoInlineNew) {
+  FLAG_inline_new = false;
+  TestJSObjectBasic();
+}
+
+
+TEST(JSObjectComplex) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  const char* source =
+      "function A(n) {"
+      "  if (n > 0) this.a = 42;"
+      "  if (n > 1) this.d = 4.2;"
+      "  if (n > 2) this.o1 = this;"
+      "  if (n > 3) this.o2 = this;"
+      "  if (n > 4) this.o3 = this;"
+      "  if (n > 5) this.o4 = this;"
+      "}";
+  CompileRun(source);
+
+  Handle<JSFunction> func = GetGlobal<JSFunction>("A");
+
+  // Zero instances were created so far.
+  CHECK(!func->has_initial_map());
+
+  Handle<JSObject> obj1 = CompileRun<JSObject>("new A(1);");
+  Handle<JSObject> obj3 = CompileRun<JSObject>("new A(3);");
+  Handle<JSObject> obj5 = CompileRun<JSObject>("new A(5);");
+
+  CHECK(func->has_initial_map());
+  Handle<Map> initial_map(func->initial_map());
+
+  // Three instances created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 3, initial_map->counter());
+  CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+  // There must be at least some slack.
+  CHECK_LT(5, obj3->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*obj3, 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*obj3, 1));
+  CHECK_EQ(*obj3, GetFieldValue(*obj3, 2));
+  CHECK(IsObjectShrinkable(*obj1));
+  CHECK(IsObjectShrinkable(*obj3));
+  CHECK(IsObjectShrinkable(*obj5));
+
+  // Create several objects to complete the tracking.
+  for (int i = 3; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+    CompileRun("new A(3);");
+  }
+  CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+
+  // obj1 and obj2 stays shrinkable because we don't clear unused fields.
+  CHECK(IsObjectShrinkable(*obj1));
+  CHECK(IsObjectShrinkable(*obj3));
+  CHECK(!IsObjectShrinkable(*obj5));
+
+  CHECK_EQ(5, obj1->map()->GetInObjectProperties());
+  CHECK_EQ(4, obj1->map()->unused_property_fields());
+
+  CHECK_EQ(5, obj3->map()->GetInObjectProperties());
+  CHECK_EQ(2, obj3->map()->unused_property_fields());
+
+  CHECK_EQ(5, obj5->map()->GetInObjectProperties());
+  CHECK_EQ(0, obj5->map()->unused_property_fields());
+
+  // Since slack tracking is complete, the new objects should not be shrinkable.
+  obj1 = CompileRun<JSObject>("new A(1);");
+  obj3 = CompileRun<JSObject>("new A(3);");
+  obj5 = CompileRun<JSObject>("new A(5);");
+
+  CHECK(!IsObjectShrinkable(*obj1));
+  CHECK(!IsObjectShrinkable(*obj3));
+  CHECK(!IsObjectShrinkable(*obj5));
+}
+
+
+TEST(JSObjectComplexNoInlineNew) {
+  FLAG_inline_new = false;
+  TestJSObjectComplex();
+}
+
+
+TEST(JSGeneratorObjectBasic) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  const char* source =
+      "function* A() {"
+      "  var i = 0;"
+      "  while(true) {"
+      "    yield i++;"
+      "  }"
+      "};"
+      "function CreateGenerator() {"
+      "  var o = A();"
+      "  o.a = 42;"
+      "  o.d = 4.2;"
+      "  o.o = o;"
+      "  return o;"
+      "}";
+  CompileRun(source);
+
+  Handle<JSFunction> func = GetGlobal<JSFunction>("A");
+
+  // Zero instances were created so far.
+  CHECK(!func->has_initial_map());
+
+  v8::Local<v8::Script> new_A_script = v8_compile("CreateGenerator();");
+
+  Handle<JSObject> obj = Run<JSObject>(new_A_script);
+
+  CHECK(func->has_initial_map());
+  Handle<Map> initial_map(func->initial_map());
+
+  // One instance created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+  CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+  // There must be at least some slack.
+  CHECK_LT(5, obj->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*obj, 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*obj, 1));
+  CHECK_EQ(*obj, GetFieldValue(*obj, 2));
+  CHECK(IsObjectShrinkable(*obj));
+
+  // Create several objects to complete the tracking.
+  for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_A_script);
+    CHECK_EQ(initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*obj));
+
+  // No slack left.
+  CHECK_EQ(3, obj->map()->GetInObjectProperties());
+}
+
+
+TEST(JSGeneratorObjectBasicNoInlineNew) {
+  FLAG_inline_new = false;
+  TestJSGeneratorObjectBasic();
+}
+
+
+TEST(SubclassBasicNoBaseClassInstances) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  // Check that base class' and subclass' slack tracking do not interfere with
+  // each other.
+  // In this test we never create base class instances.
+
+  const char* source =
+      "'use strict';"
+      "class A {"
+      "  constructor(...args) {"
+      "    this.aa = 42;"
+      "    this.ad = 4.2;"
+      "    this.ao = this;"
+      "  }"
+      "};"
+      "class B extends A {"
+      "  constructor(...args) {"
+      "    super(...args);"
+      "    this.ba = 142;"
+      "    this.bd = 14.2;"
+      "    this.bo = this;"
+      "  }"
+      "};";
+  CompileRun(source);
+
+  Handle<JSFunction> a_func = GetLexical<JSFunction>("A");
+  Handle<JSFunction> b_func = GetLexical<JSFunction>("B");
+
+  // Zero instances were created so far.
+  CHECK(!a_func->has_initial_map());
+  CHECK(!b_func->has_initial_map());
+
+  v8::Local<v8::Script> new_B_script = v8_compile("new B();");
+
+  Handle<JSObject> obj = Run<JSObject>(new_B_script);
+
+  CHECK(a_func->has_initial_map());
+  Handle<Map> a_initial_map(a_func->initial_map());
+
+  CHECK(b_func->has_initial_map());
+  Handle<Map> b_initial_map(b_func->initial_map());
+
+  // Zero instances of A created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart, a_initial_map->counter());
+  CHECK(a_initial_map->IsInobjectSlackTrackingInProgress());
+
+  // One instance of B created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, b_initial_map->counter());
+  CHECK(b_initial_map->IsInobjectSlackTrackingInProgress());
+
+  // There must be at least some slack.
+  CHECK_LT(10, obj->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*obj, 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*obj, 1));
+  CHECK_EQ(*obj, GetFieldValue(*obj, 2));
+  CHECK_EQ(Smi::FromInt(142), GetFieldValue(*obj, 3));
+  CHECK_EQ(14.2, GetDoubleFieldValue(*obj, 4));
+  CHECK_EQ(*obj, GetFieldValue(*obj, 5));
+  CHECK(IsObjectShrinkable(*obj));
+
+  // Create several subclass instances to complete the tracking.
+  for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(b_initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_B_script);
+    CHECK_EQ(b_initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!b_initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*obj));
+
+  // Zero instances of A created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart, a_initial_map->counter());
+  CHECK(a_initial_map->IsInobjectSlackTrackingInProgress());
+
+  // No slack left.
+  CHECK_EQ(6, obj->map()->GetInObjectProperties());
+}
+
+
+TEST(SubclassBasicNoBaseClassInstancesNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassBasicNoBaseClassInstances();
+}
+
+
+TEST(SubclassBasic) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  // Check that base class' and subclass' slack tracking do not interfere with
+  // each other.
+  // In this test we first create enough base class instances to complete
+  // the slack tracking and then proceed creating subclass instances.
+
+  const char* source =
+      "'use strict';"
+      "class A {"
+      "  constructor(...args) {"
+      "    this.aa = 42;"
+      "    this.ad = 4.2;"
+      "    this.ao = this;"
+      "  }"
+      "};"
+      "class B extends A {"
+      "  constructor(...args) {"
+      "    super(...args);"
+      "    this.ba = 142;"
+      "    this.bd = 14.2;"
+      "    this.bo = this;"
+      "  }"
+      "};";
+  CompileRun(source);
+
+  Handle<JSFunction> a_func = GetLexical<JSFunction>("A");
+  Handle<JSFunction> b_func = GetLexical<JSFunction>("B");
+
+  // Zero instances were created so far.
+  CHECK(!a_func->has_initial_map());
+  CHECK(!b_func->has_initial_map());
+
+  v8::Local<v8::Script> new_A_script = v8_compile("new A();");
+  v8::Local<v8::Script> new_B_script = v8_compile("new B();");
+
+  Handle<JSObject> a_obj = Run<JSObject>(new_A_script);
+  Handle<JSObject> b_obj = Run<JSObject>(new_B_script);
+
+  CHECK(a_func->has_initial_map());
+  Handle<Map> a_initial_map(a_func->initial_map());
+
+  CHECK(b_func->has_initial_map());
+  Handle<Map> b_initial_map(b_func->initial_map());
+
+  // One instance of a base class created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, a_initial_map->counter());
+  CHECK(a_initial_map->IsInobjectSlackTrackingInProgress());
+
+  // One instance of a subclass created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, b_initial_map->counter());
+  CHECK(b_initial_map->IsInobjectSlackTrackingInProgress());
+
+  // Create several base class instances to complete the tracking.
+  for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(a_initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_A_script);
+    CHECK_EQ(a_initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!a_initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*a_obj));
+
+  // No slack left.
+  CHECK_EQ(3, a_obj->map()->GetInObjectProperties());
+
+  // There must be at least some slack.
+  CHECK_LT(10, b_obj->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*b_obj, 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*b_obj, 1));
+  CHECK_EQ(*b_obj, GetFieldValue(*b_obj, 2));
+  CHECK_EQ(Smi::FromInt(142), GetFieldValue(*b_obj, 3));
+  CHECK_EQ(14.2, GetDoubleFieldValue(*b_obj, 4));
+  CHECK_EQ(*b_obj, GetFieldValue(*b_obj, 5));
+  CHECK(IsObjectShrinkable(*b_obj));
+
+  // Create several subclass instances to complete the tracking.
+  for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(b_initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_B_script);
+    CHECK_EQ(b_initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!b_initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*b_obj));
+
+  // No slack left.
+  CHECK_EQ(6, b_obj->map()->GetInObjectProperties());
+}
+
+
+TEST(SubclassBasicNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassBasic();
+}
+
+
+// Creates class hierachy of length matching the |hierarchy_desc| length and
+// with the number of fields at i'th level equal to |hierarchy_desc[i]|.
+static void CreateClassHierarchy(const std::vector<int>& hierarchy_desc) {
+  std::ostringstream os;
+  os << "'use strict';\n\n";
+
+  int n = static_cast<int>(hierarchy_desc.size());
+  for (int cur_class = 0; cur_class < n; cur_class++) {
+    os << "class A" << cur_class;
+    if (cur_class > 0) {
+      os << " extends A" << (cur_class - 1);
+    }
+    os << " {\n"
+          "  constructor(...args) {\n";
+    if (cur_class > 0) {
+      os << "    super(...args);\n";
+    }
+    int fields_count = hierarchy_desc[cur_class];
+    for (int k = 0; k < fields_count; k++) {
+      os << "    this.f" << cur_class << "_" << k << " = " << k << ";\n";
+    }
+    os << "  }\n"
+          "};\n\n";
+  }
+  CompileRun(os.str().c_str());
+}
+
+
+static std::string GetClassName(int class_index) {
+  std::ostringstream os;
+  os << "A" << class_index;
+  return os.str();
+}
+
+
+static v8::Local<v8::Script> GetNewObjectScript(const std::string& class_name) {
+  std::ostringstream os;
+  os << "new " << class_name << "();";
+  return v8_compile(os.str().c_str());
+}
+
+
+// Test that in-object slack tracking works as expected for first |n| classes
+// in the hierarchy.
+// This test works only for if the total property count is less than maximum
+// in-object properties count.
+static void TestClassHierarchy(const std::vector<int>& hierarchy_desc, int n) {
+  int fields_count = 0;
+  for (int cur_class = 0; cur_class < n; cur_class++) {
+    std::string class_name = GetClassName(cur_class);
+    int fields_count_at_current_level = hierarchy_desc[cur_class];
+    fields_count += fields_count_at_current_level;
+
+    // This test is not suitable for in-object properties count overflow case.
+    DCHECK_LT(fields_count, kMaxInobjectProperties);
+
+    // Create |class_name| objects and check slack tracking.
+    v8::Local<v8::Script> new_script = GetNewObjectScript(class_name);
+
+    Handle<JSFunction> func = GetLexical<JSFunction>(class_name);
+
+    Handle<JSObject> obj = Run<JSObject>(new_script);
+
+    CHECK(func->has_initial_map());
+    Handle<Map> initial_map(func->initial_map());
+
+    // There must be at least some slack.
+    CHECK_LT(fields_count, obj->map()->GetInObjectProperties());
+
+    // One instance was created.
+    CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+    // Create several instances to complete the tracking.
+    for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+      CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+      Handle<JSObject> tmp = Run<JSObject>(new_script);
+      CHECK_EQ(initial_map->IsInobjectSlackTrackingInProgress(),
+               IsObjectShrinkable(*tmp));
+    }
+    CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+    CHECK(!IsObjectShrinkable(*obj));
+
+    // No slack left.
+    CHECK_EQ(fields_count, obj->map()->GetInObjectProperties());
+  }
+}
+
+
+static void TestSubclassChain(const std::vector<int>& hierarchy_desc) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  CreateClassHierarchy(hierarchy_desc);
+  TestClassHierarchy(hierarchy_desc, static_cast<int>(hierarchy_desc.size()));
+}
+
+
+TEST(LongSubclassChain1) {
+  std::vector<int> hierarchy_desc;
+  for (int i = 0; i < 7; i++) {
+    hierarchy_desc.push_back(i * 10);
+  }
+  TestSubclassChain(hierarchy_desc);
+}
+
+
+TEST(LongSubclassChain2) {
+  std::vector<int> hierarchy_desc;
+  hierarchy_desc.push_back(10);
+  for (int i = 0; i < 42; i++) {
+    hierarchy_desc.push_back(0);
+  }
+  hierarchy_desc.push_back(230);
+  TestSubclassChain(hierarchy_desc);
+}
+
+
+TEST(LongSubclassChain3) {
+  std::vector<int> hierarchy_desc;
+  for (int i = 0; i < 42; i++) {
+    hierarchy_desc.push_back(5);
+  }
+  TestSubclassChain(hierarchy_desc);
+}
+
+
+TEST(InobjectPropetiesCountOverflowInSubclass) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  std::vector<int> hierarchy_desc;
+  const int kNoOverflowCount = 5;
+  for (int i = 0; i < kNoOverflowCount; i++) {
+    hierarchy_desc.push_back(50);
+  }
+  // In this class we are going to have properties in the backing store.
+  hierarchy_desc.push_back(100);
+
+  CreateClassHierarchy(hierarchy_desc);
+
+  // For the last class in the hierarchy we need different checks.
+  {
+    int cur_class = kNoOverflowCount;
+    std::string class_name = GetClassName(cur_class);
+
+    // Create |class_name| objects and check slack tracking.
+    v8::Local<v8::Script> new_script = GetNewObjectScript(class_name);
+
+    Handle<JSFunction> func = GetLexical<JSFunction>(class_name);
+
+    Handle<JSObject> obj = Run<JSObject>(new_script);
+
+    CHECK(func->has_initial_map());
+    Handle<Map> initial_map(func->initial_map());
+
+    // There must be no slack left.
+    CHECK_EQ(JSObject::kMaxInstanceSize, obj->map()->instance_size());
+    CHECK_EQ(kMaxInobjectProperties, obj->map()->GetInObjectProperties());
+
+    // One instance was created.
+    CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+    // Create several instances to complete the tracking.
+    for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+      CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+      Handle<JSObject> tmp = Run<JSObject>(new_script);
+      CHECK(!IsObjectShrinkable(*tmp));
+    }
+    CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+    CHECK(!IsObjectShrinkable(*obj));
+
+    // No slack left.
+    CHECK_EQ(kMaxInobjectProperties, obj->map()->GetInObjectProperties());
+  }
+
+  // The other classes in the hierarchy are not affected.
+  TestClassHierarchy(hierarchy_desc, kNoOverflowCount);
+}
+
+
+TEST(SlowModeSubclass) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  std::vector<int> hierarchy_desc;
+  const int kNoOverflowCount = 5;
+  for (int i = 0; i < kNoOverflowCount; i++) {
+    hierarchy_desc.push_back(50);
+  }
+  // This class should go dictionary mode.
+  hierarchy_desc.push_back(1000);
+
+  CreateClassHierarchy(hierarchy_desc);
+
+  // For the last class in the hierarchy we need different checks.
+  {
+    int cur_class = kNoOverflowCount;
+    std::string class_name = GetClassName(cur_class);
+
+    // Create |class_name| objects and check slack tracking.
+    v8::Local<v8::Script> new_script = GetNewObjectScript(class_name);
+
+    Handle<JSFunction> func = GetLexical<JSFunction>(class_name);
+
+    Handle<JSObject> obj = Run<JSObject>(new_script);
+
+    CHECK(func->has_initial_map());
+    Handle<Map> initial_map(func->initial_map());
+
+    // Object should go dictionary mode.
+    CHECK_EQ(JSObject::kHeaderSize, obj->map()->instance_size());
+    CHECK(obj->map()->is_dictionary_map());
+
+    // One instance was created.
+    CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+    // Create several instances to complete the tracking.
+    for (int i = 1; i < Map::kGenerousAllocationCount; i++) {
+      CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+      Handle<JSObject> tmp = Run<JSObject>(new_script);
+      CHECK(!IsObjectShrinkable(*tmp));
+    }
+    CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+    CHECK(!IsObjectShrinkable(*obj));
+
+    // Object should stay in dictionary mode.
+    CHECK_EQ(JSObject::kHeaderSize, obj->map()->instance_size());
+    CHECK(obj->map()->is_dictionary_map());
+  }
+
+  // The other classes in the hierarchy are not affected.
+  TestClassHierarchy(hierarchy_desc, kNoOverflowCount);
+}
+
+
+static void TestSubclassBuiltin(const char* subclass_name,
+                                InstanceType instance_type,
+                                const char* builtin_name,
+                                const char* ctor_arguments = "",
+                                int builtin_properties_count = 0) {
+  {
+    std::ostringstream os;
+    os << "'use strict';\n"
+          "class "
+       << subclass_name << " extends " << builtin_name
+       << " {\n"
+          "  constructor(...args) {\n"
+          "    super(...args);\n"
+          "    this.a = 42;\n"
+          "    this.d = 4.2;\n"
+          "    this.o = this;\n"
+          "  }\n"
+          "};\n";
+    CompileRun(os.str().c_str());
+  }
+
+  Handle<JSFunction> func = GetLexical<JSFunction>(subclass_name);
+
+  // Zero instances were created so far.
+  CHECK(!func->has_initial_map());
+
+  v8::Local<v8::Script> new_script;
+  {
+    std::ostringstream os;
+    os << "new " << subclass_name << "(" << ctor_arguments << ");";
+    new_script = v8_compile(os.str().c_str());
+  }
+
+  Run<JSObject>(new_script);
+
+  CHECK(func->has_initial_map());
+  Handle<Map> initial_map(func->initial_map());
+
+  CHECK_EQ(instance_type, initial_map->instance_type());
+
+  // One instance of a subclass created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 1, initial_map->counter());
+  CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+  // Create two instances in order to ensure that |obj|.o is a data field
+  // in case of Function subclassing.
+  Handle<JSObject> obj = Run<JSObject>(new_script);
+
+  // Two instances of a subclass created.
+  CHECK_EQ(Map::kSlackTrackingCounterStart - 2, initial_map->counter());
+  CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+
+  // There must be at least some slack.
+  CHECK_LT(builtin_properties_count + 5, obj->map()->GetInObjectProperties());
+  CHECK_EQ(Smi::FromInt(42), GetFieldValue(*obj, builtin_properties_count + 0));
+  CHECK_EQ(4.2, GetDoubleFieldValue(*obj, builtin_properties_count + 1));
+  CHECK_EQ(*obj, GetFieldValue(*obj, builtin_properties_count + 2));
+  CHECK(IsObjectShrinkable(*obj));
+
+  // Create several subclass instances to complete the tracking.
+  for (int i = 2; i < Map::kGenerousAllocationCount; i++) {
+    CHECK(initial_map->IsInobjectSlackTrackingInProgress());
+    Handle<JSObject> tmp = Run<JSObject>(new_script);
+    CHECK_EQ(initial_map->IsInobjectSlackTrackingInProgress(),
+             IsObjectShrinkable(*tmp));
+  }
+  CHECK(!initial_map->IsInobjectSlackTrackingInProgress());
+  CHECK(!IsObjectShrinkable(*obj));
+
+  // No slack left.
+  CHECK_EQ(builtin_properties_count + 3, obj->map()->GetInObjectProperties());
+
+  CHECK_EQ(instance_type, obj->map()->instance_type());
+}
+
+
+TEST(SubclassObjectBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_OBJECT_TYPE, "Object", "true");
+  TestSubclassBuiltin("A2", JS_OBJECT_TYPE, "Object", "42");
+  TestSubclassBuiltin("A3", JS_OBJECT_TYPE, "Object", "'some string'");
+}
+
+
+TEST(SubclassObjectBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassObjectBuiltin();
+}
+
+
+TEST(SubclassFunctionBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_FUNCTION_TYPE, "Function", "'return 153;'");
+  TestSubclassBuiltin("A2", JS_FUNCTION_TYPE, "Function", "'this.a = 44;'");
+}
+
+
+TEST(SubclassFunctionBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassFunctionBuiltin();
+}
+
+
+TEST(SubclassBooleanBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_VALUE_TYPE, "Boolean", "true");
+  TestSubclassBuiltin("A2", JS_VALUE_TYPE, "Boolean", "false");
+}
+
+
+TEST(SubclassBooleanBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassBooleanBuiltin();
+}
+
+
+TEST(SubclassErrorBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  const int first_field = 2;
+  TestSubclassBuiltin("A1", JS_OBJECT_TYPE, "Error", "'err'", first_field);
+  TestSubclassBuiltin("A2", JS_OBJECT_TYPE, "EvalError", "'err'", first_field);
+  TestSubclassBuiltin("A3", JS_OBJECT_TYPE, "RangeError", "'err'", first_field);
+  TestSubclassBuiltin("A4", JS_OBJECT_TYPE, "ReferenceError", "'err'",
+                      first_field);
+  TestSubclassBuiltin("A5", JS_OBJECT_TYPE, "SyntaxError", "'err'",
+                      first_field);
+  TestSubclassBuiltin("A6", JS_OBJECT_TYPE, "TypeError", "'err'", first_field);
+  TestSubclassBuiltin("A7", JS_OBJECT_TYPE, "URIError", "'err'", first_field);
+}
+
+
+TEST(SubclassErrorBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassErrorBuiltin();
+}
+
+
+TEST(SubclassNumberBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_VALUE_TYPE, "Number", "42");
+  TestSubclassBuiltin("A2", JS_VALUE_TYPE, "Number", "4.2");
+}
+
+
+TEST(SubclassNumberBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassNumberBuiltin();
+}
+
+
+TEST(SubclassDateBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_DATE_TYPE, "Date", "123456789");
+}
+
+
+TEST(SubclassDateBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassDateBuiltin();
+}
+
+
+TEST(SubclassStringBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_VALUE_TYPE, "String", "'some string'");
+  TestSubclassBuiltin("A2", JS_VALUE_TYPE, "String", "");
+}
+
+
+TEST(SubclassStringBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassStringBuiltin();
+}
+
+
+TEST(SubclassRegExpBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  const int first_field = 1;
+  TestSubclassBuiltin("A1", JS_REGEXP_TYPE, "RegExp", "'o(..)h', 'g'",
+                      first_field);
+}
+
+
+TEST(SubclassRegExpBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassRegExpBuiltin();
+}
+
+
+TEST(SubclassArrayBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_ARRAY_TYPE, "Array", "42");
+}
+
+
+TEST(SubclassArrayBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassArrayBuiltin();
+}
+
+
+TEST(SubclassTypedArrayBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+#define TYPED_ARRAY_TEST(Type, type, TYPE, elementType, size) \
+  TestSubclassBuiltin("A" #Type, JS_TYPED_ARRAY_TYPE, #Type "Array", "42");
+
+  TYPED_ARRAYS(TYPED_ARRAY_TEST)
+
+#undef TYPED_ARRAY_TEST
+}
+
+
+TEST(SubclassTypedArrayBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassTypedArrayBuiltin();
+}
+
+
+TEST(SubclassCollectionBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_SET_TYPE, "Set", "");
+  TestSubclassBuiltin("A2", JS_MAP_TYPE, "Map", "");
+  TestSubclassBuiltin("A3", JS_WEAK_SET_TYPE, "WeakSet", "");
+  TestSubclassBuiltin("A4", JS_WEAK_MAP_TYPE, "WeakMap", "");
+}
+
+
+TEST(SubclassCollectionBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassCollectionBuiltin();
+}
+
+
+TEST(SubclassArrayBufferBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  TestSubclassBuiltin("A1", JS_ARRAY_BUFFER_TYPE, "ArrayBuffer", "42");
+  TestSubclassBuiltin("A2", JS_DATA_VIEW_TYPE, "DataView",
+                      "new ArrayBuffer(42)");
+}
+
+
+TEST(SubclassArrayBufferBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassArrayBufferBuiltin();
+}
+
+
+TEST(SubclassPromiseBuiltin) {
+  // Avoid eventual completion of in-object slack tracking.
+  FLAG_inline_construct = false;
+  FLAG_always_opt = false;
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+
+  const int first_field = 4;
+  TestSubclassBuiltin("A1", JS_PROMISE_TYPE, "Promise",
+                      "function(resolve, reject) { resolve('ok'); }",
+                      first_field);
+}
+
+
+TEST(SubclassPromiseBuiltinNoInlineNew) {
+  FLAG_inline_new = false;
+  TestSubclassPromiseBuiltin();
+}