runtime.cc

Go to the documentation of this file.

// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include <stdlib.h>

#include "v8.h"

#include "accessors.h"
#include "api.h"
#include "arguments.h"
#include "bootstrapper.h"
#include "codegen.h"
#include "compilation-cache.h"
#include "compiler.h"
#include "cpu.h"
#include "dateparser-inl.h"
#include "debug.h"
#include "deoptimizer.h"
#include "date.h"
#include "execution.h"
#include "global-handles.h"
#include "isolate-inl.h"
#include "jsregexp.h"
#include "json-parser.h"
#include "liveedit.h"
#include "liveobjectlist-inl.h"
#include "misc-intrinsics.h"
#include "parser.h"
#include "platform.h"
#include "runtime-profiler.h"
#include "runtime.h"
#include "scopeinfo.h"
#include "smart-array-pointer.h"
#include "string-search.h"
#include "stub-cache.h"
#include "v8threads.h"
#include "vm-state-inl.h"

namespace v8 {
namespace internal {


#define RUNTIME_ASSERT(value) \
  if (!(value)) return isolate->ThrowIllegalOperation();

// Cast the given object to a value of the specified type and store
// it in a variable with the given name.  If the object is not of the
// expected type call IllegalOperation and return.
#define CONVERT_ARG_CHECKED(Type, name, index)                       \
  RUNTIME_ASSERT(args[index]->Is##Type());                           \
  Type* name = Type::cast(args[index]);

#define CONVERT_ARG_HANDLE_CHECKED(Type, name, index)                \
  RUNTIME_ASSERT(args[index]->Is##Type());                           \
  Handle<Type> name = args.at<Type>(index);

// Cast the given object to a boolean and store it in a variable with
// the given name.  If the object is not a boolean call IllegalOperation
// and return.
#define CONVERT_BOOLEAN_ARG_CHECKED(name, index)                     \
  RUNTIME_ASSERT(args[index]->IsBoolean());                          \
  bool name = args[index]->IsTrue();

// Cast the given argument to a Smi and store its value in an int variable
// with the given name.  If the argument is not a Smi call IllegalOperation
// and return.
#define CONVERT_SMI_ARG_CHECKED(name, index)                         \
  RUNTIME_ASSERT(args[index]->IsSmi());                              \
  int name = args.smi_at(index);

// Cast the given argument to a double and store it in a variable with
// the given name.  If the argument is not a number (as opposed to
// the number not-a-number) call IllegalOperation and return.
#define CONVERT_DOUBLE_ARG_CHECKED(name, index)                      \
  RUNTIME_ASSERT(args[index]->IsNumber());                           \
  double name = args.number_at(index);

// Call the specified converter on the object *comand store the result in
// a variable of the specified type with the given name.  If the
// object is not a Number call IllegalOperation and return.
#define CONVERT_NUMBER_CHECKED(type, name, Type, obj)                \
  RUNTIME_ASSERT(obj->IsNumber());                                   \
  type name = NumberTo##Type(obj);


// Cast the given argument to PropertyDetails and store its value in a
// variable with the given name.  If the argument is not a Smi call
// IllegalOperation and return.
#define CONVERT_PROPERTY_DETAILS_CHECKED(name, index)                \
  RUNTIME_ASSERT(args[index]->IsSmi());                              \
  PropertyDetails name = PropertyDetails(Smi::cast(args[index]));


// Assert that the given argument has a valid value for a StrictModeFlag
// and store it in a StrictModeFlag variable with the given name.
#define CONVERT_STRICT_MODE_ARG_CHECKED(name, index)                 \
  RUNTIME_ASSERT(args[index]->IsSmi());                              \
  RUNTIME_ASSERT(args.smi_at(index) == kStrictMode ||                \
                 args.smi_at(index) == kNonStrictMode);              \
  StrictModeFlag name =                                              \
      static_cast<StrictModeFlag>(args.smi_at(index));


// Assert that the given argument has a valid value for a LanguageMode
// and store it in a LanguageMode variable with the given name.
#define CONVERT_LANGUAGE_MODE_ARG(name, index)                       \
  ASSERT(args[index]->IsSmi());                                      \
  ASSERT(args.smi_at(index) == CLASSIC_MODE ||                       \
         args.smi_at(index) == STRICT_MODE ||                        \
         args.smi_at(index) == EXTENDED_MODE);                       \
  LanguageMode name =                                                \
      static_cast<LanguageMode>(args.smi_at(index));


MUST_USE_RESULT static MaybeObject* DeepCopyBoilerplate(Isolate* isolate,
                                                   JSObject* boilerplate) {
  StackLimitCheck check(isolate);
  if (check.HasOverflowed()) return isolate->StackOverflow();

  Heap* heap = isolate->heap();
  Object* result;
  { MaybeObject* maybe_result = heap->CopyJSObject(boilerplate);
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }
  JSObject* copy = JSObject::cast(result);

  // Deep copy local properties.
  if (copy->HasFastProperties()) {
    FixedArray* properties = copy->properties();
    for (int i = 0; i < properties->length(); i++) {
      Object* value = properties->get(i);
      if (value->IsJSObject()) {
        JSObject* js_object = JSObject::cast(value);
        { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate, js_object);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
        properties->set(i, result);
      }
    }
    int nof = copy->map()->inobject_properties();
    for (int i = 0; i < nof; i++) {
      Object* value = copy->InObjectPropertyAt(i);
      if (value->IsJSObject()) {
        JSObject* js_object = JSObject::cast(value);
        { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate, js_object);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
        copy->InObjectPropertyAtPut(i, result);
      }
    }
  } else {
    { MaybeObject* maybe_result =
          heap->AllocateFixedArray(copy->NumberOfLocalProperties());
      if (!maybe_result->ToObject(&result)) return maybe_result;
    }
    FixedArray* names = FixedArray::cast(result);
    copy->GetLocalPropertyNames(names, 0);
    for (int i = 0; i < names->length(); i++) {
      ASSERT(names->get(i)->IsString());
      String* key_string = String::cast(names->get(i));
      PropertyAttributes attributes =
          copy->GetLocalPropertyAttribute(key_string);
      // Only deep copy fields from the object literal expression.
      // In particular, don't try to copy the length attribute of
      // an array.
      if (attributes != NONE) continue;
      Object* value =
          copy->GetProperty(key_string, &attributes)->ToObjectUnchecked();
      if (value->IsJSObject()) {
        JSObject* js_object = JSObject::cast(value);
        { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate, js_object);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
        { MaybeObject* maybe_result =
              // Creating object copy for literals. No strict mode needed.
              copy->SetProperty(key_string, result, NONE, kNonStrictMode);
          if (!maybe_result->ToObject(&result)) return maybe_result;
        }
      }
    }
  }

  // Deep copy local elements.
  // Pixel elements cannot be created using an object literal.
  ASSERT(!copy->HasExternalArrayElements());
  switch (copy->GetElementsKind()) {
    case FAST_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      FixedArray* elements = FixedArray::cast(copy->elements());
      if (elements->map() == heap->fixed_cow_array_map()) {
        isolate->counters()->cow_arrays_created_runtime()->Increment();
#ifdef DEBUG
        for (int i = 0; i < elements->length(); i++) {
          ASSERT(!elements->get(i)->IsJSObject());
        }
#endif
      } else {
        for (int i = 0; i < elements->length(); i++) {
          Object* value = elements->get(i);
          ASSERT(value->IsSmi() ||
                 value->IsTheHole() ||
                 (IsFastObjectElementsKind(copy->GetElementsKind())));
          if (value->IsJSObject()) {
            JSObject* js_object = JSObject::cast(value);
            { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate,
                                                              js_object);
              if (!maybe_result->ToObject(&result)) return maybe_result;
            }
            elements->set(i, result);
          }
        }
      }
      break;
    }
    case DICTIONARY_ELEMENTS: {
      SeededNumberDictionary* element_dictionary = copy->element_dictionary();
      int capacity = element_dictionary->Capacity();
      for (int i = 0; i < capacity; i++) {
        Object* k = element_dictionary->KeyAt(i);
        if (element_dictionary->IsKey(k)) {
          Object* value = element_dictionary->ValueAt(i);
          if (value->IsJSObject()) {
            JSObject* js_object = JSObject::cast(value);
            { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate,
                                                              js_object);
              if (!maybe_result->ToObject(&result)) return maybe_result;
            }
            element_dictionary->ValueAtPut(i, result);
          }
        }
      }
      break;
    }
    case NON_STRICT_ARGUMENTS_ELEMENTS:
      UNIMPLEMENTED();
      break;
    case EXTERNAL_PIXEL_ELEMENTS:
    case EXTERNAL_BYTE_ELEMENTS:
    case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
    case EXTERNAL_SHORT_ELEMENTS:
    case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
    case EXTERNAL_INT_ELEMENTS:
    case EXTERNAL_UNSIGNED_INT_ELEMENTS:
    case EXTERNAL_FLOAT_ELEMENTS:
    case EXTERNAL_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS:
    case FAST_HOLEY_DOUBLE_ELEMENTS:
      // No contained objects, nothing to do.
      break;
  }
  return copy;
}


static Handle<Map> ComputeObjectLiteralMap(
    Handle<Context> context,
    Handle<FixedArray> constant_properties,
    bool* is_result_from_cache) {
  Isolate* isolate = context->GetIsolate();
  int properties_length = constant_properties->length();
  int number_of_properties = properties_length / 2;
  // Check that there are only symbols and array indices among keys.
  int number_of_symbol_keys = 0;
  for (int p = 0; p != properties_length; p += 2) {
    Object* key = constant_properties->get(p);
    uint32_t element_index = 0;
    if (key->IsSymbol()) {
      number_of_symbol_keys++;
    } else if (key->ToArrayIndex(&element_index)) {
      // An index key does not require space in the property backing store.
      number_of_properties--;
    } else {
      // Bail out as a non-symbol non-index key makes caching impossible.
      // ASSERT to make sure that the if condition after the loop is false.
      ASSERT(number_of_symbol_keys != number_of_properties);
      break;
    }
  }
  // If we only have symbols and array indices among keys then we can
  // use the map cache in the global context.
  const int kMaxKeys = 10;
  if ((number_of_symbol_keys == number_of_properties) &&
      (number_of_symbol_keys < kMaxKeys)) {
    // Create the fixed array with the key.
    Handle<FixedArray> keys =
        isolate->factory()->NewFixedArray(number_of_symbol_keys);
    if (number_of_symbol_keys > 0) {
      int index = 0;
      for (int p = 0; p < properties_length; p += 2) {
        Object* key = constant_properties->get(p);
        if (key->IsSymbol()) {
          keys->set(index++, key);
        }
      }
      ASSERT(index == number_of_symbol_keys);
    }
    *is_result_from_cache = true;
    return isolate->factory()->ObjectLiteralMapFromCache(context, keys);
  }
  *is_result_from_cache = false;
  return isolate->factory()->CopyMap(
      Handle<Map>(context->object_function()->initial_map()),
      number_of_properties);
}


static Handle<Object> CreateLiteralBoilerplate(
    Isolate* isolate,
    Handle<FixedArray> literals,
    Handle<FixedArray> constant_properties);


static Handle<Object> CreateObjectLiteralBoilerplate(
    Isolate* isolate,
    Handle<FixedArray> literals,
    Handle<FixedArray> constant_properties,
    bool should_have_fast_elements,
    bool has_function_literal) {
  // Get the global context from the literals array.  This is the
  // context in which the function was created and we use the object
  // function from this context to create the object literal.  We do
  // not use the object function from the current global context
  // because this might be the object function from another context
  // which we should not have access to.
  Handle<Context> context =
      Handle<Context>(JSFunction::GlobalContextFromLiterals(*literals));

  // In case we have function literals, we want the object to be in
  // slow properties mode for now. We don't go in the map cache because
  // maps with constant functions can't be shared if the functions are
  // not the same (which is the common case).
  bool is_result_from_cache = false;
  Handle<Map> map = has_function_literal
      ? Handle<Map>(context->object_function()->initial_map())
      : ComputeObjectLiteralMap(context,
                                constant_properties,
                                &is_result_from_cache);

  Handle<JSObject> boilerplate = isolate->factory()->NewJSObjectFromMap(map);

  // Normalize the elements of the boilerplate to save space if needed.
  if (!should_have_fast_elements) JSObject::NormalizeElements(boilerplate);

  // Add the constant properties to the boilerplate.
  int length = constant_properties->length();
  bool should_transform =
      !is_result_from_cache && boilerplate->HasFastProperties();
  if (should_transform || has_function_literal) {
    // Normalize the properties of object to avoid n^2 behavior
    // when extending the object multiple properties. Indicate the number of
    // properties to be added.
    JSObject::NormalizeProperties(
        boilerplate, KEEP_INOBJECT_PROPERTIES, length / 2);
  }

  for (int index = 0; index < length; index +=2) {
    Handle<Object> key(constant_properties->get(index+0), isolate);
    Handle<Object> value(constant_properties->get(index+1), isolate);
    if (value->IsFixedArray()) {
      // The value contains the constant_properties of a
      // simple object or array literal.
      Handle<FixedArray> array = Handle<FixedArray>::cast(value);
      value = CreateLiteralBoilerplate(isolate, literals, array);
      if (value.is_null()) return value;
    }
    Handle<Object> result;
    uint32_t element_index = 0;
    if (key->IsSymbol()) {
      if (Handle<String>::cast(key)->AsArrayIndex(&element_index)) {
        // Array index as string (uint32).
        result = JSObject::SetOwnElement(
            boilerplate, element_index, value, kNonStrictMode);
      } else {
        Handle<String> name(String::cast(*key));
        ASSERT(!name->AsArrayIndex(&element_index));
        result = JSObject::SetLocalPropertyIgnoreAttributes(
            boilerplate, name, value, NONE);
      }
    } else if (key->ToArrayIndex(&element_index)) {
      // Array index (uint32).
      result = JSObject::SetOwnElement(
          boilerplate, element_index, value, kNonStrictMode);
    } else {
      // Non-uint32 number.
      ASSERT(key->IsNumber());
      double num = key->Number();
      char arr[100];
      Vector<char> buffer(arr, ARRAY_SIZE(arr));
      const char* str = DoubleToCString(num, buffer);
      Handle<String> name =
          isolate->factory()->NewStringFromAscii(CStrVector(str));
      result = JSObject::SetLocalPropertyIgnoreAttributes(
          boilerplate, name, value, NONE);
    }
    // If setting the property on the boilerplate throws an
    // exception, the exception is converted to an empty handle in
    // the handle based operations.  In that case, we need to
    // convert back to an exception.
    if (result.is_null()) return result;
  }

  // Transform to fast properties if necessary. For object literals with
  // containing function literals we defer this operation until after all
  // computed properties have been assigned so that we can generate
  // constant function properties.
  if (should_transform && !has_function_literal) {
    JSObject::TransformToFastProperties(
        boilerplate, boilerplate->map()->unused_property_fields());
  }

  return boilerplate;
}


MaybeObject* TransitionElements(Handle<Object> object,
                                ElementsKind to_kind,
                                Isolate* isolate) {
  HandleScope scope(isolate);
  if (!object->IsJSObject()) return isolate->ThrowIllegalOperation();
  ElementsKind from_kind =
      Handle<JSObject>::cast(object)->map()->elements_kind();
  if (Map::IsValidElementsTransition(from_kind, to_kind)) {
    Handle<Object> result = JSObject::TransitionElementsKind(
        Handle<JSObject>::cast(object), to_kind);
    if (result.is_null()) return isolate->ThrowIllegalOperation();
    return *result;
  }
  return isolate->ThrowIllegalOperation();
}


static const int kSmiLiteralMinimumLength = 1024;


Handle<Object> Runtime::CreateArrayLiteralBoilerplate(
    Isolate* isolate,
    Handle<FixedArray> literals,
    Handle<FixedArray> elements) {
  // Create the JSArray.
  Handle<JSFunction> constructor(
      JSFunction::GlobalContextFromLiterals(*literals)->array_function());
  Handle<JSArray> object =
      Handle<JSArray>::cast(isolate->factory()->NewJSObject(constructor));

  ElementsKind constant_elements_kind =
      static_cast<ElementsKind>(Smi::cast(elements->get(0))->value());
  Handle<FixedArrayBase> constant_elements_values(
      FixedArrayBase::cast(elements->get(1)));

  ASSERT(IsFastElementsKind(constant_elements_kind));
  Context* global_context = isolate->context()->global_context();
  Object* maybe_maps_array = global_context->js_array_maps();
  ASSERT(!maybe_maps_array->IsUndefined());
  Object* maybe_map = FixedArray::cast(maybe_maps_array)->get(
      constant_elements_kind);
  ASSERT(maybe_map->IsMap());
  object->set_map(Map::cast(maybe_map));

  Handle<FixedArrayBase> copied_elements_values;
  if (IsFastDoubleElementsKind(constant_elements_kind)) {
    ASSERT(FLAG_smi_only_arrays);
    copied_elements_values = isolate->factory()->CopyFixedDoubleArray(
        Handle<FixedDoubleArray>::cast(constant_elements_values));
  } else {
    ASSERT(IsFastSmiOrObjectElementsKind(constant_elements_kind));
    const bool is_cow =
        (constant_elements_values->map() ==
         isolate->heap()->fixed_cow_array_map());
    if (is_cow) {
      copied_elements_values = constant_elements_values;
#if DEBUG
      Handle<FixedArray> fixed_array_values =
          Handle<FixedArray>::cast(copied_elements_values);
      for (int i = 0; i < fixed_array_values->length(); i++) {
        ASSERT(!fixed_array_values->get(i)->IsFixedArray());
      }
#endif
    } else {
      Handle<FixedArray> fixed_array_values =
          Handle<FixedArray>::cast(constant_elements_values);
      Handle<FixedArray> fixed_array_values_copy =
          isolate->factory()->CopyFixedArray(fixed_array_values);
      copied_elements_values = fixed_array_values_copy;
      for (int i = 0; i < fixed_array_values->length(); i++) {
        Object* current = fixed_array_values->get(i);
        if (current->IsFixedArray()) {
          // The value contains the constant_properties of a
          // simple object or array literal.
          Handle<FixedArray> fa(FixedArray::cast(fixed_array_values->get(i)));
          Handle<Object> result =
              CreateLiteralBoilerplate(isolate, literals, fa);
          if (result.is_null()) return result;
          fixed_array_values_copy->set(i, *result);
        }
      }
    }
  }
  object->set_elements(*copied_elements_values);
  object->set_length(Smi::FromInt(copied_elements_values->length()));

  //  Ensure that the boilerplate object has FAST_*_ELEMENTS, unless the flag is
  //  on or the object is larger than the threshold.
  if (!FLAG_smi_only_arrays &&
      constant_elements_values->length() < kSmiLiteralMinimumLength) {
    ElementsKind elements_kind = object->GetElementsKind();
    if (!IsFastObjectElementsKind(elements_kind)) {
      if (IsFastHoleyElementsKind(elements_kind)) {
        CHECK(!TransitionElements(object, FAST_HOLEY_ELEMENTS,
                                  isolate)->IsFailure());
      } else {
        CHECK(!TransitionElements(object, FAST_ELEMENTS, isolate)->IsFailure());
      }
    }
  }

  object->ValidateElements();
  return object;
}


static Handle<Object> CreateLiteralBoilerplate(
    Isolate* isolate,
    Handle<FixedArray> literals,
    Handle<FixedArray> array) {
  Handle<FixedArray> elements = CompileTimeValue::GetElements(array);
  const bool kHasNoFunctionLiteral = false;
  switch (CompileTimeValue::GetType(array)) {
    case CompileTimeValue::OBJECT_LITERAL_FAST_ELEMENTS:
      return CreateObjectLiteralBoilerplate(isolate,
                                            literals,
                                            elements,
                                            true,
                                            kHasNoFunctionLiteral);
    case CompileTimeValue::OBJECT_LITERAL_SLOW_ELEMENTS:
      return CreateObjectLiteralBoilerplate(isolate,
                                            literals,
                                            elements,
                                            false,
                                            kHasNoFunctionLiteral);
    case CompileTimeValue::ARRAY_LITERAL:
      return Runtime::CreateArrayLiteralBoilerplate(
          isolate, literals, elements);
    default:
      UNREACHABLE();
      return Handle<Object>::null();
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateObjectLiteral) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 0);
  CONVERT_SMI_ARG_CHECKED(literals_index, 1);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, constant_properties, 2);
  CONVERT_SMI_ARG_CHECKED(flags, 3);
  bool should_have_fast_elements = (flags & ObjectLiteral::kFastElements) != 0;
  bool has_function_literal = (flags & ObjectLiteral::kHasFunction) != 0;

  // Check if boilerplate exists. If not, create it first.
  Handle<Object> boilerplate(literals->get(literals_index), isolate);
  if (*boilerplate == isolate->heap()->undefined_value()) {
    boilerplate = CreateObjectLiteralBoilerplate(isolate,
                                                 literals,
                                                 constant_properties,
                                                 should_have_fast_elements,
                                                 has_function_literal);
    if (boilerplate.is_null()) return Failure::Exception();
    // Update the functions literal and return the boilerplate.
    literals->set(literals_index, *boilerplate);
  }
  return DeepCopyBoilerplate(isolate, JSObject::cast(*boilerplate));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateObjectLiteralShallow) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 0);
  CONVERT_SMI_ARG_CHECKED(literals_index, 1);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, constant_properties, 2);
  CONVERT_SMI_ARG_CHECKED(flags, 3);
  bool should_have_fast_elements = (flags & ObjectLiteral::kFastElements) != 0;
  bool has_function_literal = (flags & ObjectLiteral::kHasFunction) != 0;

  // Check if boilerplate exists. If not, create it first.
  Handle<Object> boilerplate(literals->get(literals_index), isolate);
  if (*boilerplate == isolate->heap()->undefined_value()) {
    boilerplate = CreateObjectLiteralBoilerplate(isolate,
                                                 literals,
                                                 constant_properties,
                                                 should_have_fast_elements,
                                                 has_function_literal);
    if (boilerplate.is_null()) return Failure::Exception();
    // Update the functions literal and return the boilerplate.
    literals->set(literals_index, *boilerplate);
  }
  return isolate->heap()->CopyJSObject(JSObject::cast(*boilerplate));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateArrayLiteral) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 0);
  CONVERT_SMI_ARG_CHECKED(literals_index, 1);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, elements, 2);

  // Check if boilerplate exists. If not, create it first.
  Handle<Object> boilerplate(literals->get(literals_index), isolate);
  if (*boilerplate == isolate->heap()->undefined_value()) {
    boilerplate =
        Runtime::CreateArrayLiteralBoilerplate(isolate, literals, elements);
    if (boilerplate.is_null()) return Failure::Exception();
    // Update the functions literal and return the boilerplate.
    literals->set(literals_index, *boilerplate);
  }
  return DeepCopyBoilerplate(isolate, JSObject::cast(*boilerplate));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateArrayLiteralShallow) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 0);
  CONVERT_SMI_ARG_CHECKED(literals_index, 1);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, elements, 2);

  // Check if boilerplate exists. If not, create it first.
  Handle<Object> boilerplate(literals->get(literals_index), isolate);
  if (*boilerplate == isolate->heap()->undefined_value()) {
    ASSERT(*elements != isolate->heap()->empty_fixed_array());
    boilerplate =
        Runtime::CreateArrayLiteralBoilerplate(isolate, literals, elements);
    if (boilerplate.is_null()) return Failure::Exception();
    // Update the functions literal and return the boilerplate.
    literals->set(literals_index, *boilerplate);
  }
  if (JSObject::cast(*boilerplate)->elements()->map() ==
      isolate->heap()->fixed_cow_array_map()) {
    isolate->counters()->cow_arrays_created_runtime()->Increment();
  }
  return isolate->heap()->CopyJSObject(JSObject::cast(*boilerplate));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateJSProxy) {
  ASSERT(args.length() == 2);
  Object* handler = args[0];
  Object* prototype = args[1];
  Object* used_prototype =
      prototype->IsJSReceiver() ? prototype : isolate->heap()->null_value();
  return isolate->heap()->AllocateJSProxy(handler, used_prototype);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateJSFunctionProxy) {
  ASSERT(args.length() == 4);
  Object* handler = args[0];
  Object* call_trap = args[1];
  Object* construct_trap = args[2];
  Object* prototype = args[3];
  Object* used_prototype =
      prototype->IsJSReceiver() ? prototype : isolate->heap()->null_value();
  return isolate->heap()->AllocateJSFunctionProxy(
      handler, call_trap, construct_trap, used_prototype);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsJSProxy) {
  ASSERT(args.length() == 1);
  Object* obj = args[0];
  return isolate->heap()->ToBoolean(obj->IsJSProxy());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsJSFunctionProxy) {
  ASSERT(args.length() == 1);
  Object* obj = args[0];
  return isolate->heap()->ToBoolean(obj->IsJSFunctionProxy());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetHandler) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSProxy, proxy, 0);
  return proxy->handler();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetCallTrap) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSFunctionProxy, proxy, 0);
  return proxy->call_trap();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetConstructTrap) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSFunctionProxy, proxy, 0);
  return proxy->construct_trap();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Fix) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSProxy, proxy, 0);
  proxy->Fix();
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetInitialize) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSSet, holder, 0);
  Handle<ObjectHashSet> table = isolate->factory()->NewObjectHashSet(0);
  holder->set_table(*table);
  return *holder;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetAdd) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSSet, holder, 0);
  Handle<Object> key(args[1]);
  Handle<ObjectHashSet> table(ObjectHashSet::cast(holder->table()));
  table = ObjectHashSetAdd(table, key);
  holder->set_table(*table);
  return isolate->heap()->undefined_symbol();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetHas) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSSet, holder, 0);
  Handle<Object> key(args[1]);
  Handle<ObjectHashSet> table(ObjectHashSet::cast(holder->table()));
  return isolate->heap()->ToBoolean(table->Contains(*key));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetDelete) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSSet, holder, 0);
  Handle<Object> key(args[1]);
  Handle<ObjectHashSet> table(ObjectHashSet::cast(holder->table()));
  table = ObjectHashSetRemove(table, key);
  holder->set_table(*table);
  return isolate->heap()->undefined_symbol();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MapInitialize) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSMap, holder, 0);
  Handle<ObjectHashTable> table = isolate->factory()->NewObjectHashTable(0);
  holder->set_table(*table);
  return *holder;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MapGet) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSMap, holder, 0);
  Handle<Object> key(args[1]);
  return ObjectHashTable::cast(holder->table())->Lookup(*key);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MapSet) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSMap, holder, 0);
  Handle<Object> key(args[1]);
  Handle<Object> value(args[2]);
  Handle<ObjectHashTable> table(ObjectHashTable::cast(holder->table()));
  Handle<ObjectHashTable> new_table = PutIntoObjectHashTable(table, key, value);
  holder->set_table(*new_table);
  return *value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_WeakMapInitialize) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSWeakMap, weakmap, 0);
  ASSERT(weakmap->map()->inobject_properties() == 0);
  Handle<ObjectHashTable> table = isolate->factory()->NewObjectHashTable(0);
  weakmap->set_table(*table);
  weakmap->set_next(Smi::FromInt(0));
  return *weakmap;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_WeakMapGet) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSWeakMap, weakmap, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, key, 1);
  return ObjectHashTable::cast(weakmap->table())->Lookup(*key);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_WeakMapSet) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSWeakMap, weakmap, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, key, 1);
  Handle<Object> value(args[2]);
  Handle<ObjectHashTable> table(ObjectHashTable::cast(weakmap->table()));
  Handle<ObjectHashTable> new_table = PutIntoObjectHashTable(table, key, value);
  weakmap->set_table(*new_table);
  return *value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ClassOf) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  Object* obj = args[0];
  if (!obj->IsJSObject()) return isolate->heap()->null_value();
  return JSObject::cast(obj)->class_name();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetPrototype) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSReceiver, input_obj, 0);
  Object* obj = input_obj;
  // We don't expect access checks to be needed on JSProxy objects.
  ASSERT(!obj->IsAccessCheckNeeded() || obj->IsJSObject());
  do {
    if (obj->IsAccessCheckNeeded() &&
        !isolate->MayNamedAccess(JSObject::cast(obj),
                                 isolate->heap()->Proto_symbol(),
                                 v8::ACCESS_GET)) {
      isolate->ReportFailedAccessCheck(JSObject::cast(obj), v8::ACCESS_GET);
      return isolate->heap()->undefined_value();
    }
    obj = obj->GetPrototype();
  } while (obj->IsJSObject() &&
           JSObject::cast(obj)->map()->is_hidden_prototype());
  return obj;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsInPrototypeChain) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  // See ECMA-262, section 15.3.5.3, page 88 (steps 5 - 8).
  Object* O = args[0];
  Object* V = args[1];
  while (true) {
    Object* prototype = V->GetPrototype();
    if (prototype->IsNull()) return isolate->heap()->false_value();
    if (O == prototype) return isolate->heap()->true_value();
    V = prototype;
  }
}


// Recursively traverses hidden prototypes if property is not found
static void GetOwnPropertyImplementation(JSObject* obj,
                                         String* name,
                                         LookupResult* result) {
  obj->LocalLookupRealNamedProperty(name, result);

  if (!result->IsProperty()) {
    Object* proto = obj->GetPrototype();
    if (proto->IsJSObject() &&
      JSObject::cast(proto)->map()->is_hidden_prototype())
      GetOwnPropertyImplementation(JSObject::cast(proto),
                                   name, result);
  }
}


static bool CheckAccessException(LookupResult* result,
                                 v8::AccessType access_type) {
  if (result->type() == CALLBACKS) {
    Object* callback = result->GetCallbackObject();
    if (callback->IsAccessorInfo()) {
      AccessorInfo* info = AccessorInfo::cast(callback);
      bool can_access =
          (access_type == v8::ACCESS_HAS &&
              (info->all_can_read() || info->all_can_write())) ||
          (access_type == v8::ACCESS_GET && info->all_can_read()) ||
          (access_type == v8::ACCESS_SET && info->all_can_write());
      return can_access;
    }
  }

  return false;
}


static bool CheckAccess(JSObject* obj,
                        String* name,
                        LookupResult* result,
                        v8::AccessType access_type) {
  ASSERT(result->IsProperty());

  JSObject* holder = result->holder();
  JSObject* current = obj;
  Isolate* isolate = obj->GetIsolate();
  while (true) {
    if (current->IsAccessCheckNeeded() &&
        !isolate->MayNamedAccess(current, name, access_type)) {
      // Access check callback denied the access, but some properties
      // can have a special permissions which override callbacks descision
      // (currently see v8::AccessControl).
      break;
    }

    if (current == holder) {
      return true;
    }

    current = JSObject::cast(current->GetPrototype());
  }

  // API callbacks can have per callback access exceptions.
  switch (result->type()) {
    case CALLBACKS: {
      if (CheckAccessException(result, access_type)) {
        return true;
      }
      break;
    }
    case INTERCEPTOR: {
      // If the object has an interceptor, try real named properties.
      // Overwrite the result to fetch the correct property later.
      holder->LookupRealNamedProperty(name, result);
      if (result->IsProperty()) {
        if (CheckAccessException(result, access_type)) {
          return true;
        }
      }
      break;
    }
    default:
      break;
  }

  isolate->ReportFailedAccessCheck(current, access_type);
  return false;
}


// TODO(1095): we should traverse hidden prototype hierachy as well.
static bool CheckElementAccess(JSObject* obj,
                               uint32_t index,
                               v8::AccessType access_type) {
  if (obj->IsAccessCheckNeeded() &&
      !obj->GetIsolate()->MayIndexedAccess(obj, index, access_type)) {
    return false;
  }

  return true;
}


// Enumerator used as indices into the array returned from GetOwnProperty
enum PropertyDescriptorIndices {
  IS_ACCESSOR_INDEX,
  VALUE_INDEX,
  GETTER_INDEX,
  SETTER_INDEX,
  WRITABLE_INDEX,
  ENUMERABLE_INDEX,
  CONFIGURABLE_INDEX,
  DESCRIPTOR_SIZE
};


static MaybeObject* GetOwnProperty(Isolate* isolate,
                                   Handle<JSObject> obj,
                                   Handle<String> name) {
  Heap* heap = isolate->heap();
  Handle<FixedArray> elms = isolate->factory()->NewFixedArray(DESCRIPTOR_SIZE);
  Handle<JSArray> desc = isolate->factory()->NewJSArrayWithElements(elms);
  LookupResult result(isolate);
  // This could be an element.
  uint32_t index;
  if (name->AsArrayIndex(&index)) {
    switch (obj->HasLocalElement(index)) {
      case JSObject::UNDEFINED_ELEMENT:
        return heap->undefined_value();

      case JSObject::STRING_CHARACTER_ELEMENT: {
        // Special handling of string objects according to ECMAScript 5
        // 15.5.5.2. Note that this might be a string object with elements
        // other than the actual string value. This is covered by the
        // subsequent cases.
        Handle<JSValue> js_value = Handle<JSValue>::cast(obj);
        Handle<String> str(String::cast(js_value->value()));
        Handle<String> substr = SubString(str, index, index + 1, NOT_TENURED);

        elms->set(IS_ACCESSOR_INDEX, heap->false_value());
        elms->set(VALUE_INDEX, *substr);
        elms->set(WRITABLE_INDEX, heap->false_value());
        elms->set(ENUMERABLE_INDEX,  heap->true_value());
        elms->set(CONFIGURABLE_INDEX, heap->false_value());
        return *desc;
      }

      case JSObject::INTERCEPTED_ELEMENT:
      case JSObject::FAST_ELEMENT: {
        elms->set(IS_ACCESSOR_INDEX, heap->false_value());
        Handle<Object> value = Object::GetElement(obj, index);
        RETURN_IF_EMPTY_HANDLE(isolate, value);
        elms->set(VALUE_INDEX, *value);
        elms->set(WRITABLE_INDEX, heap->true_value());
        elms->set(ENUMERABLE_INDEX,  heap->true_value());
        elms->set(CONFIGURABLE_INDEX, heap->true_value());
        return *desc;
      }

      case JSObject::DICTIONARY_ELEMENT: {
        Handle<JSObject> holder = obj;
        if (obj->IsJSGlobalProxy()) {
          Object* proto = obj->GetPrototype();
          if (proto->IsNull()) return heap->undefined_value();
          ASSERT(proto->IsJSGlobalObject());
          holder = Handle<JSObject>(JSObject::cast(proto));
        }
        FixedArray* elements = FixedArray::cast(holder->elements());
        SeededNumberDictionary* dictionary = NULL;
        if (elements->map() == heap->non_strict_arguments_elements_map()) {
          dictionary = SeededNumberDictionary::cast(elements->get(1));
        } else {
          dictionary = SeededNumberDictionary::cast(elements);
        }
        int entry = dictionary->FindEntry(index);
        ASSERT(entry != SeededNumberDictionary::kNotFound);
        PropertyDetails details = dictionary->DetailsAt(entry);
        switch (details.type()) {
          case CALLBACKS: {
            // This is an accessor property with getter and/or setter.
            AccessorPair* accessors =
                AccessorPair::cast(dictionary->ValueAt(entry));
            elms->set(IS_ACCESSOR_INDEX, heap->true_value());
            if (CheckElementAccess(*obj, index, v8::ACCESS_GET)) {
              elms->set(GETTER_INDEX, accessors->GetComponent(ACCESSOR_GETTER));
            }
            if (CheckElementAccess(*obj, index, v8::ACCESS_SET)) {
              elms->set(SETTER_INDEX, accessors->GetComponent(ACCESSOR_SETTER));
            }
            break;
          }
          case NORMAL: {
            // This is a data property.
            elms->set(IS_ACCESSOR_INDEX, heap->false_value());
            Handle<Object> value = Object::GetElement(obj, index);
            ASSERT(!value.is_null());
            elms->set(VALUE_INDEX, *value);
            elms->set(WRITABLE_INDEX, heap->ToBoolean(!details.IsReadOnly()));
            break;
          }
          default:
            UNREACHABLE();
            break;
        }
        elms->set(ENUMERABLE_INDEX, heap->ToBoolean(!details.IsDontEnum()));
        elms->set(CONFIGURABLE_INDEX, heap->ToBoolean(!details.IsDontDelete()));
        return *desc;
      }
    }
  }

  // Use recursive implementation to also traverse hidden prototypes
  GetOwnPropertyImplementation(*obj, *name, &result);

  if (!result.IsProperty()) {
    return heap->undefined_value();
  }

  if (!CheckAccess(*obj, *name, &result, v8::ACCESS_HAS)) {
    return heap->false_value();
  }

  elms->set(ENUMERABLE_INDEX, heap->ToBoolean(!result.IsDontEnum()));
  elms->set(CONFIGURABLE_INDEX, heap->ToBoolean(!result.IsDontDelete()));

  bool is_js_accessor = (result.type() == CALLBACKS) &&
                        (result.GetCallbackObject()->IsAccessorPair());

  if (is_js_accessor) {
    // __defineGetter__/__defineSetter__ callback.
    elms->set(IS_ACCESSOR_INDEX, heap->true_value());

    AccessorPair* accessors = AccessorPair::cast(result.GetCallbackObject());
    if (CheckAccess(*obj, *name, &result, v8::ACCESS_GET)) {
      elms->set(GETTER_INDEX, accessors->GetComponent(ACCESSOR_GETTER));
    }
    if (CheckAccess(*obj, *name, &result, v8::ACCESS_SET)) {
      elms->set(SETTER_INDEX, accessors->GetComponent(ACCESSOR_SETTER));
    }
  } else {
    elms->set(IS_ACCESSOR_INDEX, heap->false_value());
    elms->set(WRITABLE_INDEX, heap->ToBoolean(!result.IsReadOnly()));

    PropertyAttributes attrs;
    Object* value;
    // GetProperty will check access and report any violations.
    { MaybeObject* maybe_value = obj->GetProperty(*obj, &result, *name, &attrs);
      if (!maybe_value->ToObject(&value)) return maybe_value;
    }
    elms->set(VALUE_INDEX, value);
  }

  return *desc;
}


// Returns an array with the property description:
//  if args[1] is not a property on args[0]
//          returns undefined
//  if args[1] is a data property on args[0]
//         [false, value, Writeable, Enumerable, Configurable]
//  if args[1] is an accessor on args[0]
//         [true, GetFunction, SetFunction, Enumerable, Configurable]
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetOwnProperty) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);
  return GetOwnProperty(isolate, obj, name);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PreventExtensions) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSObject, obj, 0);
  return obj->PreventExtensions();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsExtensible) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSObject, obj, 0);
  if (obj->IsJSGlobalProxy()) {
    Object* proto = obj->GetPrototype();
    if (proto->IsNull()) return isolate->heap()->false_value();
    ASSERT(proto->IsJSGlobalObject());
    obj = JSObject::cast(proto);
  }
  return isolate->heap()->ToBoolean(obj->map()->is_extensible());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpCompile) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, re, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, pattern, 1);
  CONVERT_ARG_HANDLE_CHECKED(String, flags, 2);
  Handle<Object> result = RegExpImpl::Compile(re, pattern, flags);
  if (result.is_null()) return Failure::Exception();
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateApiFunction) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(FunctionTemplateInfo, data, 0);
  return *isolate->factory()->CreateApiFunction(data);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsTemplate) {
  ASSERT(args.length() == 1);
  Object* arg = args[0];
  bool result = arg->IsObjectTemplateInfo() || arg->IsFunctionTemplateInfo();
  return isolate->heap()->ToBoolean(result);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetTemplateField) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(HeapObject, templ, 0);
  CONVERT_SMI_ARG_CHECKED(index, 1)
  int offset = index * kPointerSize + HeapObject::kHeaderSize;
  InstanceType type = templ->map()->instance_type();
  RUNTIME_ASSERT(type ==  FUNCTION_TEMPLATE_INFO_TYPE ||
                 type ==  OBJECT_TEMPLATE_INFO_TYPE);
  RUNTIME_ASSERT(offset > 0);
  if (type == FUNCTION_TEMPLATE_INFO_TYPE) {
    RUNTIME_ASSERT(offset < FunctionTemplateInfo::kSize);
  } else {
    RUNTIME_ASSERT(offset < ObjectTemplateInfo::kSize);
  }
  return *HeapObject::RawField(templ, offset);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DisableAccessChecks) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(HeapObject, object, 0);
  Map* old_map = object->map();
  bool needs_access_checks = old_map->is_access_check_needed();
  if (needs_access_checks) {
    // Copy map so it won't interfere constructor's initial map.
    Object* new_map;
    { MaybeObject* maybe_new_map =
          old_map->CopyDropTransitions(DescriptorArray::MAY_BE_SHARED);
      if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
    }

    Map::cast(new_map)->set_is_access_check_needed(false);
    object->set_map(Map::cast(new_map));
  }
  return isolate->heap()->ToBoolean(needs_access_checks);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_EnableAccessChecks) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(HeapObject, object, 0);
  Map* old_map = object->map();
  if (!old_map->is_access_check_needed()) {
    // Copy map so it won't interfere constructor's initial map.
    Object* new_map;
    { MaybeObject* maybe_new_map =
          old_map->CopyDropTransitions(DescriptorArray::MAY_BE_SHARED);
      if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
    }

    Map::cast(new_map)->set_is_access_check_needed(true);
    object->set_map(Map::cast(new_map));
  }
  return isolate->heap()->undefined_value();
}


static Failure* ThrowRedeclarationError(Isolate* isolate,
                                        const char* type,
                                        Handle<String> name) {
  HandleScope scope(isolate);
  Handle<Object> type_handle =
      isolate->factory()->NewStringFromAscii(CStrVector(type));
  Handle<Object> args[2] = { type_handle, name };
  Handle<Object> error =
      isolate->factory()->NewTypeError("redeclaration", HandleVector(args, 2));
  return isolate->Throw(*error);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DeclareGlobals) {
  ASSERT(args.length() == 3);
  HandleScope scope(isolate);
  Handle<GlobalObject> global = Handle<GlobalObject>(
      isolate->context()->global());

  Handle<Context> context = args.at<Context>(0);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, pairs, 1);
  CONVERT_SMI_ARG_CHECKED(flags, 2);

  // Traverse the name/value pairs and set the properties.
  int length = pairs->length();
  for (int i = 0; i < length; i += 2) {
    HandleScope scope(isolate);
    Handle<String> name(String::cast(pairs->get(i)));
    Handle<Object> value(pairs->get(i + 1), isolate);

    // We have to declare a global const property. To capture we only
    // assign to it when evaluating the assignment for "const x =
    // <expr>" the initial value is the hole.
    bool is_var = value->IsUndefined();
    bool is_const = value->IsTheHole();
    bool is_function = value->IsSharedFunctionInfo();
    bool is_module = value->IsJSModule();
    ASSERT(is_var + is_const + is_function + is_module == 1);

    if (is_var || is_const) {
      // Lookup the property in the global object, and don't set the
      // value of the variable if the property is already there.
      // Do the lookup locally only, see ES5 errata.
      LookupResult lookup(isolate);
      if (FLAG_es52_globals)
        global->LocalLookup(*name, &lookup);
      else
        global->Lookup(*name, &lookup);
      if (lookup.IsProperty()) {
        // We found an existing property. Unless it was an interceptor
        // that claims the property is absent, skip this declaration.
        if (lookup.type() != INTERCEPTOR) continue;
        PropertyAttributes attributes = global->GetPropertyAttribute(*name);
        if (attributes != ABSENT) continue;
        // Fall-through and introduce the absent property by using
        // SetProperty.
      }
    } else if (is_function) {
      // Copy the function and update its context. Use it as value.
      Handle<SharedFunctionInfo> shared =
          Handle<SharedFunctionInfo>::cast(value);
      Handle<JSFunction> function =
          isolate->factory()->NewFunctionFromSharedFunctionInfo(
              shared, context, TENURED);
      value = function;
    }

    LookupResult lookup(isolate);
    global->LocalLookup(*name, &lookup);

    // Compute the property attributes. According to ECMA-262,
    // the property must be non-configurable except in eval.
    int attr = NONE;
    bool is_eval = DeclareGlobalsEvalFlag::decode(flags);
    if (!is_eval || is_module) {
      attr |= DONT_DELETE;
    }
    bool is_native = DeclareGlobalsNativeFlag::decode(flags);
    if (is_const || is_module || (is_native && is_function)) {
      attr |= READ_ONLY;
    }

    LanguageMode language_mode = DeclareGlobalsLanguageMode::decode(flags);

    if (!lookup.IsProperty() || is_function || is_module) {
      // If the local property exists, check that we can reconfigure it
      // as required for function declarations.
      if (lookup.IsProperty() && lookup.IsDontDelete()) {
        if (lookup.IsReadOnly() || lookup.IsDontEnum() ||
            lookup.type() == CALLBACKS) {
          return ThrowRedeclarationError(
              isolate, is_function ? "function" : "module", name);
        }
        // If the existing property is not configurable, keep its attributes.
        attr = lookup.GetAttributes();
      }
      // Define or redefine own property.
      RETURN_IF_EMPTY_HANDLE(isolate,
          JSObject::SetLocalPropertyIgnoreAttributes(
              global, name, value, static_cast<PropertyAttributes>(attr)));
    } else {
      // Do a [[Put]] on the existing (own) property.
      RETURN_IF_EMPTY_HANDLE(isolate,
          JSObject::SetProperty(
              global, name, value, static_cast<PropertyAttributes>(attr),
              language_mode == CLASSIC_MODE ? kNonStrictMode : kStrictMode));
    }
  }

  ASSERT(!isolate->has_pending_exception());
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DeclareContextSlot) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);

  // Declarations are always made in a function or global context.  In the
  // case of eval code, the context passed is the context of the caller,
  // which may be some nested context and not the declaration context.
  RUNTIME_ASSERT(args[0]->IsContext());
  Handle<Context> context(Context::cast(args[0])->declaration_context());

  Handle<String> name(String::cast(args[1]));
  PropertyAttributes mode = static_cast<PropertyAttributes>(args.smi_at(2));
  RUNTIME_ASSERT(mode == READ_ONLY || mode == NONE);
  Handle<Object> initial_value(args[3], isolate);

  int index;
  PropertyAttributes attributes;
  ContextLookupFlags flags = DONT_FOLLOW_CHAINS;
  BindingFlags binding_flags;
  Handle<Object> holder =
      context->Lookup(name, flags, &index, &attributes, &binding_flags);

  if (attributes != ABSENT) {
    // The name was declared before; check for conflicting re-declarations.
    // Note: this is actually inconsistent with what happens for globals (where
    // we silently ignore such declarations).
    if (((attributes & READ_ONLY) != 0) || (mode == READ_ONLY)) {
      // Functions are not read-only.
      ASSERT(mode != READ_ONLY || initial_value->IsTheHole());
      const char* type = ((attributes & READ_ONLY) != 0) ? "const" : "var";
      return ThrowRedeclarationError(isolate, type, name);
    }

    // Initialize it if necessary.
    if (*initial_value != NULL) {
      if (index >= 0) {
        ASSERT(holder.is_identical_to(context));
        if (((attributes & READ_ONLY) == 0) ||
            context->get(index)->IsTheHole()) {
          context->set(index, *initial_value);
        }
      } else {
        // Slow case: The property is in the context extension object of a
        // function context or the global object of a global context.
        Handle<JSObject> object = Handle<JSObject>::cast(holder);
        RETURN_IF_EMPTY_HANDLE(
            isolate,
            JSReceiver::SetProperty(object, name, initial_value, mode,
                                    kNonStrictMode));
      }
    }

  } else {
    // The property is not in the function context. It needs to be
    // "declared" in the function context's extension context or as a
    // property of the the global object.
    Handle<JSObject> object;
    if (context->has_extension()) {
      object = Handle<JSObject>(JSObject::cast(context->extension()));
    } else {
      // Context extension objects are allocated lazily.
      ASSERT(context->IsFunctionContext());
      object = isolate->factory()->NewJSObject(
          isolate->context_extension_function());
      context->set_extension(*object);
    }
    ASSERT(*object != NULL);

    // Declare the property by setting it to the initial value if provided,
    // or undefined, and use the correct mode (e.g. READ_ONLY attribute for
    // constant declarations).
    ASSERT(!object->HasLocalProperty(*name));
    Handle<Object> value(isolate->heap()->undefined_value(), isolate);
    if (*initial_value != NULL) value = initial_value;
    // Declaring a const context slot is a conflicting declaration if
    // there is a callback with that name in a prototype. It is
    // allowed to introduce const variables in
    // JSContextExtensionObjects. They are treated specially in
    // SetProperty and no setters are invoked for those since they are
    // not real JSObjects.
    if (initial_value->IsTheHole() &&
        !object->IsJSContextExtensionObject()) {
      LookupResult lookup(isolate);
      object->Lookup(*name, &lookup);
      if (lookup.IsFound() && (lookup.type() == CALLBACKS)) {
        return ThrowRedeclarationError(isolate, "const", name);
      }
    }
    if (object->IsJSGlobalObject()) {
      // Define own property on the global object.
      RETURN_IF_EMPTY_HANDLE(isolate,
         JSObject::SetLocalPropertyIgnoreAttributes(object, name, value, mode));
    } else {
      RETURN_IF_EMPTY_HANDLE(isolate,
         JSReceiver::SetProperty(object, name, value, mode, kNonStrictMode));
    }
  }

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_InitializeVarGlobal) {
  NoHandleAllocation nha;
  // args[0] == name
  // args[1] == language_mode
  // args[2] == value (optional)

  // Determine if we need to assign to the variable if it already
  // exists (based on the number of arguments).
  RUNTIME_ASSERT(args.length() == 2 || args.length() == 3);
  bool assign = args.length() == 3;

  CONVERT_ARG_HANDLE_CHECKED(String, name, 0);
  GlobalObject* global = isolate->context()->global();
  RUNTIME_ASSERT(args[1]->IsSmi());
  CONVERT_LANGUAGE_MODE_ARG(language_mode, 1);
  StrictModeFlag strict_mode_flag = (language_mode == CLASSIC_MODE)
      ? kNonStrictMode : kStrictMode;

  // According to ECMA-262, section 12.2, page 62, the property must
  // not be deletable.
  PropertyAttributes attributes = DONT_DELETE;

  // Lookup the property locally in the global object. If it isn't
  // there, there is a property with this name in the prototype chain.
  // We follow Safari and Firefox behavior and only set the property
  // locally if there is an explicit initialization value that we have
  // to assign to the property.
  // Note that objects can have hidden prototypes, so we need to traverse
  // the whole chain of hidden prototypes to do a 'local' lookup.
  Object* object = global;
  LookupResult lookup(isolate);
  while (object->IsJSObject() &&
         JSObject::cast(object)->map()->is_hidden_prototype()) {
    JSObject* raw_holder = JSObject::cast(object);
    raw_holder->LocalLookup(*name, &lookup);
    if (lookup.IsFound() && lookup.type() == INTERCEPTOR) {
      HandleScope handle_scope(isolate);
      Handle<JSObject> holder(raw_holder);
      PropertyAttributes intercepted = holder->GetPropertyAttribute(*name);
      // Update the raw pointer in case it's changed due to GC.
      raw_holder = *holder;
      if (intercepted != ABSENT && (intercepted & READ_ONLY) == 0) {
        // Found an interceptor that's not read only.
        if (assign) {
          return raw_holder->SetProperty(
              &lookup, *name, args[2], attributes, strict_mode_flag);
        } else {
          return isolate->heap()->undefined_value();
        }
      }
    }
    object = raw_holder->GetPrototype();
  }

  // Reload global in case the loop above performed a GC.
  global = isolate->context()->global();
  if (assign) {
    return global->SetProperty(*name, args[2], attributes, strict_mode_flag);
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_InitializeConstGlobal) {
  // All constants are declared with an initial value. The name
  // of the constant is the first argument and the initial value
  // is the second.
  RUNTIME_ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 0);
  Handle<Object> value = args.at<Object>(1);

  // Get the current global object from top.
  GlobalObject* global = isolate->context()->global();

  // According to ECMA-262, section 12.2, page 62, the property must
  // not be deletable. Since it's a const, it must be READ_ONLY too.
  PropertyAttributes attributes =
      static_cast<PropertyAttributes>(DONT_DELETE | READ_ONLY);

  // Lookup the property locally in the global object. If it isn't
  // there, we add the property and take special precautions to always
  // add it as a local property even in case of callbacks in the
  // prototype chain (this rules out using SetProperty).
  // We use SetLocalPropertyIgnoreAttributes instead
  LookupResult lookup(isolate);
  global->LocalLookup(*name, &lookup);
  if (!lookup.IsProperty()) {
    return global->SetLocalPropertyIgnoreAttributes(*name,
                                                    *value,
                                                    attributes);
  }

  if (!lookup.IsReadOnly()) {
    // Restore global object from context (in case of GC) and continue
    // with setting the value.
    HandleScope handle_scope(isolate);
    Handle<GlobalObject> global(isolate->context()->global());

    // BUG 1213575: Handle the case where we have to set a read-only
    // property through an interceptor and only do it if it's
    // uninitialized, e.g. the hole. Nirk...
    // Passing non-strict mode because the property is writable.
    RETURN_IF_EMPTY_HANDLE(
        isolate,
        JSReceiver::SetProperty(global, name, value, attributes,
                                kNonStrictMode));
    return *value;
  }

  // Set the value, but only if we're assigning the initial value to a
  // constant. For now, we determine this by checking if the
  // current value is the hole.
  // Strict mode handling not needed (const is disallowed in strict mode).
  PropertyType type = lookup.type();
  if (type == FIELD) {
    FixedArray* properties = global->properties();
    int index = lookup.GetFieldIndex();
    if (properties->get(index)->IsTheHole() || !lookup.IsReadOnly()) {
      properties->set(index, *value);
    }
  } else if (type == NORMAL) {
    if (global->GetNormalizedProperty(&lookup)->IsTheHole() ||
        !lookup.IsReadOnly()) {
      global->SetNormalizedProperty(&lookup, *value);
    }
  } else {
    // Ignore re-initialization of constants that have already been
    // assigned a function value.
    ASSERT(lookup.IsReadOnly() && type == CONSTANT_FUNCTION);
  }

  // Use the set value as the result of the operation.
  return *value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_InitializeConstContextSlot) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);

  Handle<Object> value(args[0], isolate);
  ASSERT(!value->IsTheHole());

  // Initializations are always done in a function or global context.
  RUNTIME_ASSERT(args[1]->IsContext());
  Handle<Context> context(Context::cast(args[1])->declaration_context());

  Handle<String> name(String::cast(args[2]));

  int index;
  PropertyAttributes attributes;
  ContextLookupFlags flags = FOLLOW_CHAINS;
  BindingFlags binding_flags;
  Handle<Object> holder =
      context->Lookup(name, flags, &index, &attributes, &binding_flags);

  if (index >= 0) {
    ASSERT(holder->IsContext());
    // Property was found in a context.  Perform the assignment if we
    // found some non-constant or an uninitialized constant.
    Handle<Context> context = Handle<Context>::cast(holder);
    if ((attributes & READ_ONLY) == 0 || context->get(index)->IsTheHole()) {
      context->set(index, *value);
    }
    return *value;
  }

  // The property could not be found, we introduce it as a property of the
  // global object.
  if (attributes == ABSENT) {
    Handle<JSObject> global = Handle<JSObject>(
        isolate->context()->global());
    // Strict mode not needed (const disallowed in strict mode).
    RETURN_IF_EMPTY_HANDLE(
        isolate,
        JSReceiver::SetProperty(global, name, value, NONE, kNonStrictMode));
    return *value;
  }

  // The property was present in some function's context extension object,
  // as a property on the subject of a with, or as a property of the global
  // object.
  //
  // In most situations, eval-introduced consts should still be present in
  // the context extension object.  However, because declaration and
  // initialization are separate, the property might have been deleted
  // before we reach the initialization point.
  //
  // Example:
  //
  //    function f() { eval("delete x; const x;"); }
  //
  // In that case, the initialization behaves like a normal assignment.
  Handle<JSObject> object = Handle<JSObject>::cast(holder);

  if (*object == context->extension()) {
    // This is the property that was introduced by the const declaration.
    // Set it if it hasn't been set before.  NOTE: We cannot use
    // GetProperty() to get the current value as it 'unholes' the value.
    LookupResult lookup(isolate);
    object->LocalLookupRealNamedProperty(*name, &lookup);
    ASSERT(lookup.IsFound());  // the property was declared
    ASSERT(lookup.IsReadOnly());  // and it was declared as read-only

    PropertyType type = lookup.type();
    if (type == FIELD) {
      FixedArray* properties = object->properties();
      int index = lookup.GetFieldIndex();
      if (properties->get(index)->IsTheHole()) {
        properties->set(index, *value);
      }
    } else if (type == NORMAL) {
      if (object->GetNormalizedProperty(&lookup)->IsTheHole()) {
        object->SetNormalizedProperty(&lookup, *value);
      }
    } else {
      // We should not reach here. Any real, named property should be
      // either a field or a dictionary slot.
      UNREACHABLE();
    }
  } else {
    // The property was found on some other object.  Set it if it is not a
    // read-only property.
    if ((attributes & READ_ONLY) == 0) {
      // Strict mode not needed (const disallowed in strict mode).
      RETURN_IF_EMPTY_HANDLE(
          isolate,
          JSReceiver::SetProperty(object, name, value, attributes,
                                  kNonStrictMode));
    }
  }

  return *value;
}


RUNTIME_FUNCTION(MaybeObject*,
                 Runtime_OptimizeObjectForAddingMultipleProperties) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
  CONVERT_SMI_ARG_CHECKED(properties, 1);
  if (object->HasFastProperties()) {
    JSObject::NormalizeProperties(object, KEEP_INOBJECT_PROPERTIES, properties);
  }
  return *object;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpExec) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
  // Due to the way the JS calls are constructed this must be less than the
  // length of a string, i.e. it is always a Smi.  We check anyway for security.
  CONVERT_SMI_ARG_CHECKED(index, 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 3);
  RUNTIME_ASSERT(last_match_info->HasFastObjectElements());
  RUNTIME_ASSERT(index >= 0);
  RUNTIME_ASSERT(index <= subject->length());
  isolate->counters()->regexp_entry_runtime()->Increment();
  Handle<Object> result = RegExpImpl::Exec(regexp,
                                           subject,
                                           index,
                                           last_match_info,
                                           isolate->zone());
  if (result.is_null()) return Failure::Exception();
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpConstructResult) {
  ASSERT(args.length() == 3);
  CONVERT_SMI_ARG_CHECKED(elements_count, 0);
  if (elements_count < 0 ||
      elements_count > FixedArray::kMaxLength ||
      !Smi::IsValid(elements_count)) {
    return isolate->ThrowIllegalOperation();
  }
  Object* new_object;
  { MaybeObject* maybe_new_object =
        isolate->heap()->AllocateFixedArrayWithHoles(elements_count);
    if (!maybe_new_object->ToObject(&new_object)) return maybe_new_object;
  }
  FixedArray* elements = FixedArray::cast(new_object);
  { MaybeObject* maybe_new_object = isolate->heap()->AllocateRaw(
      JSRegExpResult::kSize, NEW_SPACE, OLD_POINTER_SPACE);
    if (!maybe_new_object->ToObject(&new_object)) return maybe_new_object;
  }
  {
    AssertNoAllocation no_gc;
    HandleScope scope(isolate);
    reinterpret_cast<HeapObject*>(new_object)->
        set_map(isolate->global_context()->regexp_result_map());
  }
  JSArray* array = JSArray::cast(new_object);
  array->set_properties(isolate->heap()->empty_fixed_array());
  array->set_elements(elements);
  array->set_length(Smi::FromInt(elements_count));
  // Write in-object properties after the length of the array.
  array->InObjectPropertyAtPut(JSRegExpResult::kIndexIndex, args[1]);
  array->InObjectPropertyAtPut(JSRegExpResult::kInputIndex, args[2]);
  return array;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpInitializeObject) {
  AssertNoAllocation no_alloc;
  ASSERT(args.length() == 5);
  CONVERT_ARG_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_CHECKED(String, source, 1);
  // If source is the empty string we set it to "(?:)" instead as
  // suggested by ECMA-262, 5th, section 15.10.4.1.
  if (source->length() == 0) source = isolate->heap()->query_colon_symbol();

  Object* global = args[2];
  if (!global->IsTrue()) global = isolate->heap()->false_value();

  Object* ignoreCase = args[3];
  if (!ignoreCase->IsTrue()) ignoreCase = isolate->heap()->false_value();

  Object* multiline = args[4];
  if (!multiline->IsTrue()) multiline = isolate->heap()->false_value();

  Map* map = regexp->map();
  Object* constructor = map->constructor();
  if (constructor->IsJSFunction() &&
      JSFunction::cast(constructor)->initial_map() == map) {
    // If we still have the original map, set in-object properties directly.
    regexp->InObjectPropertyAtPut(JSRegExp::kSourceFieldIndex, source);
    // Both true and false are immovable immortal objects so no need for write
    // barrier.
    regexp->InObjectPropertyAtPut(
        JSRegExp::kGlobalFieldIndex, global, SKIP_WRITE_BARRIER);
    regexp->InObjectPropertyAtPut(
        JSRegExp::kIgnoreCaseFieldIndex, ignoreCase, SKIP_WRITE_BARRIER);
    regexp->InObjectPropertyAtPut(
        JSRegExp::kMultilineFieldIndex, multiline, SKIP_WRITE_BARRIER);
    regexp->InObjectPropertyAtPut(JSRegExp::kLastIndexFieldIndex,
                                  Smi::FromInt(0),
                                  SKIP_WRITE_BARRIER);  // It's a Smi.
    return regexp;
  }

  // Map has changed, so use generic, but slower, method.
  PropertyAttributes final =
      static_cast<PropertyAttributes>(READ_ONLY | DONT_ENUM | DONT_DELETE);
  PropertyAttributes writable =
      static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE);
  Heap* heap = isolate->heap();
  MaybeObject* result;
  result = regexp->SetLocalPropertyIgnoreAttributes(heap->source_symbol(),
                                                    source,
                                                    final);
  ASSERT(!result->IsFailure());
  result = regexp->SetLocalPropertyIgnoreAttributes(heap->global_symbol(),
                                                    global,
                                                    final);
  ASSERT(!result->IsFailure());
  result =
      regexp->SetLocalPropertyIgnoreAttributes(heap->ignore_case_symbol(),
                                               ignoreCase,
                                               final);
  ASSERT(!result->IsFailure());
  result = regexp->SetLocalPropertyIgnoreAttributes(heap->multiline_symbol(),
                                                    multiline,
                                                    final);
  ASSERT(!result->IsFailure());
  result =
      regexp->SetLocalPropertyIgnoreAttributes(heap->last_index_symbol(),
                                               Smi::FromInt(0),
                                               writable);
  ASSERT(!result->IsFailure());
  USE(result);
  return regexp;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FinishArrayPrototypeSetup) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, prototype, 0);
  // This is necessary to enable fast checks for absence of elements
  // on Array.prototype and below.
  prototype->set_elements(isolate->heap()->empty_fixed_array());
  return Smi::FromInt(0);
}


static Handle<JSFunction> InstallBuiltin(Isolate* isolate,
                                         Handle<JSObject> holder,
                                         const char* name,
                                         Builtins::Name builtin_name) {
  Handle<String> key = isolate->factory()->LookupAsciiSymbol(name);
  Handle<Code> code(isolate->builtins()->builtin(builtin_name));
  Handle<JSFunction> optimized =
      isolate->factory()->NewFunction(key,
                                      JS_OBJECT_TYPE,
                                      JSObject::kHeaderSize,
                                      code,
                                      false);
  optimized->shared()->DontAdaptArguments();
  JSReceiver::SetProperty(holder, key, optimized, NONE, kStrictMode);
  return optimized;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SpecialArrayFunctions) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, holder, 0);

  InstallBuiltin(isolate, holder, "pop", Builtins::kArrayPop);
  InstallBuiltin(isolate, holder, "push", Builtins::kArrayPush);
  InstallBuiltin(isolate, holder, "shift", Builtins::kArrayShift);
  InstallBuiltin(isolate, holder, "unshift", Builtins::kArrayUnshift);
  InstallBuiltin(isolate, holder, "slice", Builtins::kArraySlice);
  InstallBuiltin(isolate, holder, "splice", Builtins::kArraySplice);
  InstallBuiltin(isolate, holder, "concat", Builtins::kArrayConcat);

  return *holder;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetDefaultReceiver) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSReceiver, callable, 0);

  if (!callable->IsJSFunction()) {
    HandleScope scope(isolate);
    bool threw = false;
    Handle<Object> delegate =
        Execution::TryGetFunctionDelegate(Handle<JSReceiver>(callable), &threw);
    if (threw) return Failure::Exception();
    callable = JSFunction::cast(*delegate);
  }
  JSFunction* function = JSFunction::cast(callable);

  SharedFunctionInfo* shared = function->shared();
  if (shared->native() || !shared->is_classic_mode()) {
    return isolate->heap()->undefined_value();
  }
  // Returns undefined for strict or native functions, or
  // the associated global receiver for "normal" functions.

  Context* global_context =
      function->context()->global()->global_context();
  return global_context->global()->global_receiver();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MaterializeRegExpLiteral) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 0);
  int index = args.smi_at(1);
  Handle<String> pattern = args.at<String>(2);
  Handle<String> flags = args.at<String>(3);

  // Get the RegExp function from the context in the literals array.
  // This is the RegExp function from the context in which the
  // function was created.  We do not use the RegExp function from the
  // current global context because this might be the RegExp function
  // from another context which we should not have access to.
  Handle<JSFunction> constructor =
      Handle<JSFunction>(
          JSFunction::GlobalContextFromLiterals(*literals)->regexp_function());
  // Compute the regular expression literal.
  bool has_pending_exception;
  Handle<Object> regexp =
      RegExpImpl::CreateRegExpLiteral(constructor, pattern, flags,
                                      &has_pending_exception);
  if (has_pending_exception) {
    ASSERT(isolate->has_pending_exception());
    return Failure::Exception();
  }
  literals->set(index, *regexp);
  return *regexp;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetName) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  return f->shared()->name();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetName) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  CONVERT_ARG_CHECKED(String, name, 1);
  f->shared()->set_name(name);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionNameShouldPrintAsAnonymous) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  return isolate->heap()->ToBoolean(
      f->shared()->name_should_print_as_anonymous());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionMarkNameShouldPrintAsAnonymous) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  f->shared()->set_name_should_print_as_anonymous(true);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionRemovePrototype) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  Object* obj = f->RemovePrototype();
  if (obj->IsFailure()) return obj;

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetScript) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
  Handle<Object> script = Handle<Object>(fun->shared()->script(), isolate);
  if (!script->IsScript()) return isolate->heap()->undefined_value();

  return *GetScriptWrapper(Handle<Script>::cast(script));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetSourceCode) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  CONVERT_ARG_HANDLE_CHECKED(JSFunction, f, 0);
  Handle<SharedFunctionInfo> shared(f->shared());
  return *shared->GetSourceCode();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetScriptSourcePosition) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
  int pos = fun->shared()->start_position();
  return Smi::FromInt(pos);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetPositionForOffset) {
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(Code, code, 0);
  CONVERT_NUMBER_CHECKED(int, offset, Int32, args[1]);

  RUNTIME_ASSERT(0 <= offset && offset < code->Size());

  Address pc = code->address() + offset;
  return Smi::FromInt(code->SourcePosition(pc));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetInstanceClassName) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
  CONVERT_ARG_CHECKED(String, name, 1);
  fun->SetInstanceClassName(name);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetLength) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
  CONVERT_SMI_ARG_CHECKED(length, 1);
  fun->shared()->set_length(length);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetPrototype) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
  ASSERT(fun->should_have_prototype());
  Object* obj;
  { MaybeObject* maybe_obj =
        Accessors::FunctionSetPrototype(fun, args[1], NULL);
    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
  }
  return args[0];  // return TOS
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetReadOnlyPrototype) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSFunction, function, 0);

  MaybeObject* maybe_name =
      isolate->heap()->AllocateStringFromAscii(CStrVector("prototype"));
  String* name;
  if (!maybe_name->To(&name)) return maybe_name;

  if (function->HasFastProperties()) {
    // Construct a new field descriptor with updated attributes.
    DescriptorArray* instance_desc = function->map()->instance_descriptors();
    int index = instance_desc->Search(name);
    ASSERT(index != DescriptorArray::kNotFound);
    PropertyDetails details = instance_desc->GetDetails(index);
    CallbacksDescriptor new_desc(name,
        instance_desc->GetValue(index),
        static_cast<PropertyAttributes>(details.attributes() | READ_ONLY),
        details.index());
    // Construct a new field descriptors array containing the new descriptor.
    Object* descriptors_unchecked;
    { MaybeObject* maybe_descriptors_unchecked =
        instance_desc->CopyInsert(&new_desc, REMOVE_TRANSITIONS);
      if (!maybe_descriptors_unchecked->ToObject(&descriptors_unchecked)) {
        return maybe_descriptors_unchecked;
      }
    }
    DescriptorArray* new_descriptors =
        DescriptorArray::cast(descriptors_unchecked);
    // Create a new map featuring the new field descriptors array.
    Object* map_unchecked;
    { MaybeObject* maybe_map_unchecked = function->map()->CopyDropDescriptors();
      if (!maybe_map_unchecked->ToObject(&map_unchecked)) {
        return maybe_map_unchecked;
      }
    }
    Map* new_map = Map::cast(map_unchecked);
    new_map->set_instance_descriptors(new_descriptors);
    function->set_map(new_map);
  } else {  // Dictionary properties.
    // Directly manipulate the property details.
    int entry = function->property_dictionary()->FindEntry(name);
    ASSERT(entry != StringDictionary::kNotFound);
    PropertyDetails details = function->property_dictionary()->DetailsAt(entry);
    PropertyDetails new_details(
        static_cast<PropertyAttributes>(details.attributes() | READ_ONLY),
        details.type(),
        details.index());
    function->property_dictionary()->DetailsAtPut(entry, new_details);
  }
  return function;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionIsAPIFunction) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  return isolate->heap()->ToBoolean(f->shared()->IsApiFunction());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionIsBuiltin) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  return isolate->heap()->ToBoolean(f->IsBuiltin());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetCode) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(JSFunction, target, 0);
  Handle<Object> code = args.at<Object>(1);

  if (code->IsNull()) return *target;
  RUNTIME_ASSERT(code->IsJSFunction());
  Handle<JSFunction> source = Handle<JSFunction>::cast(code);
  Handle<SharedFunctionInfo> target_shared(target->shared());
  Handle<SharedFunctionInfo> source_shared(source->shared());

  if (!source->is_compiled() &&
      !JSFunction::CompileLazy(source, KEEP_EXCEPTION)) {
    return Failure::Exception();
  }

  // Set the code, scope info, formal parameter count, and the length
  // of the target shared function info.  Set the source code of the
  // target function to undefined.  SetCode is only used for built-in
  // constructors like String, Array, and Object, and some web code
  // doesn't like seeing source code for constructors.
  target_shared->set_code(source_shared->code());
  target_shared->set_scope_info(source_shared->scope_info());
  target_shared->set_length(source_shared->length());
  target_shared->set_formal_parameter_count(
      source_shared->formal_parameter_count());
  target_shared->set_script(isolate->heap()->undefined_value());

  // Since we don't store the source we should never optimize this.
  target_shared->code()->set_optimizable(false);

  // Clear the optimization hints related to the compiled code as these
  // are no longer valid when the code is overwritten.
  target_shared->ClearThisPropertyAssignmentsInfo();

  // Set the code of the target function.
  target->ReplaceCode(source_shared->code());

  // Make sure we get a fresh copy of the literal vector to avoid cross
  // context contamination.
  Handle<Context> context(source->context());
  int number_of_literals = source->NumberOfLiterals();
  Handle<FixedArray> literals =
      isolate->factory()->NewFixedArray(number_of_literals, TENURED);
  if (number_of_literals > 0) {
    literals->set(JSFunction::kLiteralGlobalContextIndex,
                  context->global_context());
  }
  target->set_context(*context);
  target->set_literals(*literals);
  target->set_next_function_link(isolate->heap()->undefined_value());

  if (isolate->logger()->is_logging() || CpuProfiler::is_profiling(isolate)) {
    isolate->logger()->LogExistingFunction(
        source_shared, Handle<Code>(source_shared->code()));
  }

  return *target;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetExpectedNumberOfProperties) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  CONVERT_SMI_ARG_CHECKED(num, 1);
  RUNTIME_ASSERT(num >= 0);
  SetExpectedNofProperties(function, num);
  return isolate->heap()->undefined_value();
}


MUST_USE_RESULT static MaybeObject* CharFromCode(Isolate* isolate,
                                                 Object* char_code) {
  uint32_t code;
  if (char_code->ToArrayIndex(&code)) {
    if (code <= 0xffff) {
      return isolate->heap()->LookupSingleCharacterStringFromCode(code);
    }
  }
  return isolate->heap()->empty_string();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringCharCodeAt) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(String, subject, 0);
  Object* index = args[1];
  RUNTIME_ASSERT(index->IsNumber());

  uint32_t i = 0;
  if (index->IsSmi()) {
    int value = Smi::cast(index)->value();
    if (value < 0) return isolate->heap()->nan_value();
    i = value;
  } else {
    ASSERT(index->IsHeapNumber());
    double value = HeapNumber::cast(index)->value();
    i = static_cast<uint32_t>(DoubleToInteger(value));
  }

  // Flatten the string.  If someone wants to get a char at an index
  // in a cons string, it is likely that more indices will be
  // accessed.
  Object* flat;
  { MaybeObject* maybe_flat = subject->TryFlatten();
    if (!maybe_flat->ToObject(&flat)) return maybe_flat;
  }
  subject = String::cast(flat);

  if (i >= static_cast<uint32_t>(subject->length())) {
    return isolate->heap()->nan_value();
  }

  return Smi::FromInt(subject->Get(i));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CharFromCode) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  return CharFromCode(isolate, args[0]);
}


class FixedArrayBuilder {
 public:
  explicit FixedArrayBuilder(Isolate* isolate, int initial_capacity)
      : array_(isolate->factory()->NewFixedArrayWithHoles(initial_capacity)),
        length_(0),
        has_non_smi_elements_(false) {
    // Require a non-zero initial size. Ensures that doubling the size to
    // extend the array will work.
    ASSERT(initial_capacity > 0);
  }

  explicit FixedArrayBuilder(Handle<FixedArray> backing_store)
      : array_(backing_store),
        length_(0),
        has_non_smi_elements_(false) {
    // Require a non-zero initial size. Ensures that doubling the size to
    // extend the array will work.
    ASSERT(backing_store->length() > 0);
  }

  bool HasCapacity(int elements) {
    int length = array_->length();
    int required_length = length_ + elements;
    return (length >= required_length);
  }

  void EnsureCapacity(int elements) {
    int length = array_->length();
    int required_length = length_ + elements;
    if (length < required_length) {
      int new_length = length;
      do {
        new_length *= 2;
      } while (new_length < required_length);
      Handle<FixedArray> extended_array =
          array_->GetIsolate()->factory()->NewFixedArrayWithHoles(new_length);
      array_->CopyTo(0, *extended_array, 0, length_);
      array_ = extended_array;
    }
  }

  void Add(Object* value) {
    ASSERT(!value->IsSmi());
    ASSERT(length_ < capacity());
    array_->set(length_, value);
    length_++;
    has_non_smi_elements_ = true;
  }

  void Add(Smi* value) {
    ASSERT(value->IsSmi());
    ASSERT(length_ < capacity());
    array_->set(length_, value);
    length_++;
  }

  Handle<FixedArray> array() {
    return array_;
  }

  int length() {
    return length_;
  }

  int capacity() {
    return array_->length();
  }

  Handle<JSArray> ToJSArray() {
    Handle<JSArray> result_array = FACTORY->NewJSArrayWithElements(array_);
    result_array->set_length(Smi::FromInt(length_));
    return result_array;
  }

  Handle<JSArray> ToJSArray(Handle<JSArray> target_array) {
    FACTORY->SetContent(target_array, array_);
    target_array->set_length(Smi::FromInt(length_));
    return target_array;
  }

 private:
  Handle<FixedArray> array_;
  int length_;
  bool has_non_smi_elements_;
};


// Forward declarations.
const int kStringBuilderConcatHelperLengthBits = 11;
const int kStringBuilderConcatHelperPositionBits = 19;

template <typename schar>
static inline void StringBuilderConcatHelper(String*,
                                             schar*,
                                             FixedArray*,
                                             int);

typedef BitField<int, 0, kStringBuilderConcatHelperLengthBits>
    StringBuilderSubstringLength;
typedef BitField<int,
                 kStringBuilderConcatHelperLengthBits,
                 kStringBuilderConcatHelperPositionBits>
    StringBuilderSubstringPosition;


class ReplacementStringBuilder {
 public:
  ReplacementStringBuilder(Heap* heap,
                           Handle<String> subject,
                           int estimated_part_count)
      : heap_(heap),
        array_builder_(heap->isolate(), estimated_part_count),
        subject_(subject),
        character_count_(0),
        is_ascii_(subject->IsAsciiRepresentation()) {
    // Require a non-zero initial size. Ensures that doubling the size to
    // extend the array will work.
    ASSERT(estimated_part_count > 0);
  }

  static inline void AddSubjectSlice(FixedArrayBuilder* builder,
                                     int from,
                                     int to) {
    ASSERT(from >= 0);
    int length = to - from;
    ASSERT(length > 0);
    if (StringBuilderSubstringLength::is_valid(length) &&
        StringBuilderSubstringPosition::is_valid(from)) {
      int encoded_slice = StringBuilderSubstringLength::encode(length) |
          StringBuilderSubstringPosition::encode(from);
      builder->Add(Smi::FromInt(encoded_slice));
    } else {
      // Otherwise encode as two smis.
      builder->Add(Smi::FromInt(-length));
      builder->Add(Smi::FromInt(from));
    }
  }


  void EnsureCapacity(int elements) {
    array_builder_.EnsureCapacity(elements);
  }


  void AddSubjectSlice(int from, int to) {
    AddSubjectSlice(&array_builder_, from, to);
    IncrementCharacterCount(to - from);
  }


  void AddString(Handle<String> string) {
    int length = string->length();
    ASSERT(length > 0);
    AddElement(*string);
    if (!string->IsAsciiRepresentation()) {
      is_ascii_ = false;
    }
    IncrementCharacterCount(length);
  }


  Handle<String> ToString() {
    if (array_builder_.length() == 0) {
      return heap_->isolate()->factory()->empty_string();
    }

    Handle<String> joined_string;
    if (is_ascii_) {
      Handle<SeqAsciiString> seq = NewRawAsciiString(character_count_);
      AssertNoAllocation no_alloc;
      char* char_buffer = seq->GetChars();
      StringBuilderConcatHelper(*subject_,
                                char_buffer,
                                *array_builder_.array(),
                                array_builder_.length());
      joined_string = Handle<String>::cast(seq);
    } else {
      // Non-ASCII.
      Handle<SeqTwoByteString> seq = NewRawTwoByteString(character_count_);
      AssertNoAllocation no_alloc;
      uc16* char_buffer = seq->GetChars();
      StringBuilderConcatHelper(*subject_,
                                char_buffer,
                                *array_builder_.array(),
                                array_builder_.length());
      joined_string = Handle<String>::cast(seq);
    }
    return joined_string;
  }


  void IncrementCharacterCount(int by) {
    if (character_count_ > String::kMaxLength - by) {
      V8::FatalProcessOutOfMemory("String.replace result too large.");
    }
    character_count_ += by;
  }

  Handle<JSArray> GetParts() {
    return array_builder_.ToJSArray();
  }

 private:
  Handle<SeqAsciiString> NewRawAsciiString(int length) {
    return heap_->isolate()->factory()->NewRawAsciiString(length);
  }


  Handle<SeqTwoByteString> NewRawTwoByteString(int length) {
    return heap_->isolate()->factory()->NewRawTwoByteString(length);
  }


  void AddElement(Object* element) {
    ASSERT(element->IsSmi() || element->IsString());
    ASSERT(array_builder_.capacity() > array_builder_.length());
    array_builder_.Add(element);
  }

  Heap* heap_;
  FixedArrayBuilder array_builder_;
  Handle<String> subject_;
  int character_count_;
  bool is_ascii_;
};


class CompiledReplacement {
 public:
  explicit CompiledReplacement(Zone* zone)
      : parts_(1, zone), replacement_substrings_(0, zone),
        simple_hint_(false),
        zone_(zone) {}

  void Compile(Handle<String> replacement,
               int capture_count,
               int subject_length);

  void Apply(ReplacementStringBuilder* builder,
             int match_from,
             int match_to,
             Handle<JSArray> last_match_info);

  // Number of distinct parts of the replacement pattern.
  int parts() {
    return parts_.length();
  }

  bool simple_hint() {
    return simple_hint_;
  }

  Zone* zone() const { return zone_; }

 private:
  enum PartType {
    SUBJECT_PREFIX = 1,
    SUBJECT_SUFFIX,
    SUBJECT_CAPTURE,
    REPLACEMENT_SUBSTRING,
    REPLACEMENT_STRING,

    NUMBER_OF_PART_TYPES
  };

  struct ReplacementPart {
    static inline ReplacementPart SubjectMatch() {
      return ReplacementPart(SUBJECT_CAPTURE, 0);
    }
    static inline ReplacementPart SubjectCapture(int capture_index) {
      return ReplacementPart(SUBJECT_CAPTURE, capture_index);
    }
    static inline ReplacementPart SubjectPrefix() {
      return ReplacementPart(SUBJECT_PREFIX, 0);
    }
    static inline ReplacementPart SubjectSuffix(int subject_length) {
      return ReplacementPart(SUBJECT_SUFFIX, subject_length);
    }
    static inline ReplacementPart ReplacementString() {
      return ReplacementPart(REPLACEMENT_STRING, 0);
    }
    static inline ReplacementPart ReplacementSubString(int from, int to) {
      ASSERT(from >= 0);
      ASSERT(to > from);
      return ReplacementPart(-from, to);
    }

    // If tag <= 0 then it is the negation of a start index of a substring of
    // the replacement pattern, otherwise it's a value from PartType.
    ReplacementPart(int tag, int data)
        : tag(tag), data(data) {
      // Must be non-positive or a PartType value.
      ASSERT(tag < NUMBER_OF_PART_TYPES);
    }
    // Either a value of PartType or a non-positive number that is
    // the negation of an index into the replacement string.
    int tag;
    // The data value's interpretation depends on the value of tag:
    // tag == SUBJECT_PREFIX ||
    // tag == SUBJECT_SUFFIX:  data is unused.
    // tag == SUBJECT_CAPTURE: data is the number of the capture.
    // tag == REPLACEMENT_SUBSTRING ||
    // tag == REPLACEMENT_STRING:    data is index into array of substrings
    //                               of the replacement string.
    // tag <= 0: Temporary representation of the substring of the replacement
    //           string ranging over -tag .. data.
    //           Is replaced by REPLACEMENT_{SUB,}STRING when we create the
    //           substring objects.
    int data;
  };

  template<typename Char>
  static bool ParseReplacementPattern(ZoneList<ReplacementPart>* parts,
                                      Vector<Char> characters,
                                      int capture_count,
                                      int subject_length,
                                      Zone* zone) {
    int length = characters.length();
    int last = 0;
    for (int i = 0; i < length; i++) {
      Char c = characters[i];
      if (c == '$') {
        int next_index = i + 1;
        if (next_index == length) {  // No next character!
          break;
        }
        Char c2 = characters[next_index];
        switch (c2) {
        case '$':
          if (i > last) {
            // There is a substring before. Include the first "$".
            parts->Add(ReplacementPart::ReplacementSubString(last, next_index),
                       zone);
            last = next_index + 1;  // Continue after the second "$".
          } else {
            // Let the next substring start with the second "$".
            last = next_index;
          }
          i = next_index;
          break;
        case '`':
          if (i > last) {
            parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
          }
          parts->Add(ReplacementPart::SubjectPrefix(), zone);
          i = next_index;
          last = i + 1;
          break;
        case '\'':
          if (i > last) {
            parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
          }
          parts->Add(ReplacementPart::SubjectSuffix(subject_length), zone);
          i = next_index;
          last = i + 1;
          break;
        case '&':
          if (i > last) {
            parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
          }
          parts->Add(ReplacementPart::SubjectMatch(), zone);
          i = next_index;
          last = i + 1;
          break;
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9': {
          int capture_ref = c2 - '0';
          if (capture_ref > capture_count) {
            i = next_index;
            continue;
          }
          int second_digit_index = next_index + 1;
          if (second_digit_index < length) {
            // Peek ahead to see if we have two digits.
            Char c3 = characters[second_digit_index];
            if ('0' <= c3 && c3 <= '9') {  // Double digits.
              int double_digit_ref = capture_ref * 10 + c3 - '0';
              if (double_digit_ref <= capture_count) {
                next_index = second_digit_index;
                capture_ref = double_digit_ref;
              }
            }
          }
          if (capture_ref > 0) {
            if (i > last) {
              parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
            }
            ASSERT(capture_ref <= capture_count);
            parts->Add(ReplacementPart::SubjectCapture(capture_ref), zone);
            last = next_index + 1;
          }
          i = next_index;
          break;
        }
        default:
          i = next_index;
          break;
        }
      }
    }
    if (length > last) {
      if (last == 0) {
        parts->Add(ReplacementPart::ReplacementString(), zone);
        return true;
      } else {
        parts->Add(ReplacementPart::ReplacementSubString(last, length), zone);
      }
    }
    return false;
  }

  ZoneList<ReplacementPart> parts_;
  ZoneList<Handle<String> > replacement_substrings_;
  bool simple_hint_;
  Zone* zone_;
};


void CompiledReplacement::Compile(Handle<String> replacement,
                                  int capture_count,
                                  int subject_length) {
  {
    AssertNoAllocation no_alloc;
    String::FlatContent content = replacement->GetFlatContent();
    ASSERT(content.IsFlat());
    if (content.IsAscii()) {
      simple_hint_ = ParseReplacementPattern(&parts_,
                                             content.ToAsciiVector(),
                                             capture_count,
                                             subject_length,
                                             zone());
    } else {
      ASSERT(content.IsTwoByte());
      simple_hint_ = ParseReplacementPattern(&parts_,
                                             content.ToUC16Vector(),
                                             capture_count,
                                             subject_length,
                                             zone());
    }
  }
  Isolate* isolate = replacement->GetIsolate();
  // Find substrings of replacement string and create them as String objects.
  int substring_index = 0;
  for (int i = 0, n = parts_.length(); i < n; i++) {
    int tag = parts_[i].tag;
    if (tag <= 0) {  // A replacement string slice.
      int from = -tag;
      int to = parts_[i].data;
      replacement_substrings_.Add(
          isolate->factory()->NewSubString(replacement, from, to), zone());
      parts_[i].tag = REPLACEMENT_SUBSTRING;
      parts_[i].data = substring_index;
      substring_index++;
    } else if (tag == REPLACEMENT_STRING) {
      replacement_substrings_.Add(replacement, zone());
      parts_[i].data = substring_index;
      substring_index++;
    }
  }
}


void CompiledReplacement::Apply(ReplacementStringBuilder* builder,
                                int match_from,
                                int match_to,
                                Handle<JSArray> last_match_info) {
  for (int i = 0, n = parts_.length(); i < n; i++) {
    ReplacementPart part = parts_[i];
    switch (part.tag) {
      case SUBJECT_PREFIX:
        if (match_from > 0) builder->AddSubjectSlice(0, match_from);
        break;
      case SUBJECT_SUFFIX: {
        int subject_length = part.data;
        if (match_to < subject_length) {
          builder->AddSubjectSlice(match_to, subject_length);
        }
        break;
      }
      case SUBJECT_CAPTURE: {
        int capture = part.data;
        FixedArray* match_info = FixedArray::cast(last_match_info->elements());
        int from = RegExpImpl::GetCapture(match_info, capture * 2);
        int to = RegExpImpl::GetCapture(match_info, capture * 2 + 1);
        if (from >= 0 && to > from) {
          builder->AddSubjectSlice(from, to);
        }
        break;
      }
      case REPLACEMENT_SUBSTRING:
      case REPLACEMENT_STRING:
        builder->AddString(replacement_substrings_[part.data]);
        break;
      default:
        UNREACHABLE();
    }
  }
}


void FindAsciiStringIndices(Vector<const char> subject,
                            char pattern,
                            ZoneList<int>* indices,
                            unsigned int limit,
                            Zone* zone) {
  ASSERT(limit > 0);
  // Collect indices of pattern in subject using memchr.
  // Stop after finding at most limit values.
  const char* subject_start = reinterpret_cast<const char*>(subject.start());
  const char* subject_end = subject_start + subject.length();
  const char* pos = subject_start;
  while (limit > 0) {
    pos = reinterpret_cast<const char*>(
        memchr(pos, pattern, subject_end - pos));
    if (pos == NULL) return;
    indices->Add(static_cast<int>(pos - subject_start), zone);
    pos++;
    limit--;
  }
}


template <typename SubjectChar, typename PatternChar>
void FindStringIndices(Isolate* isolate,
                       Vector<const SubjectChar> subject,
                       Vector<const PatternChar> pattern,
                       ZoneList<int>* indices,
                       unsigned int limit,
                       Zone* zone) {
  ASSERT(limit > 0);
  // Collect indices of pattern in subject.
  // Stop after finding at most limit values.
  int pattern_length = pattern.length();
  int index = 0;
  StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
  while (limit > 0) {
    index = search.Search(subject, index);
    if (index < 0) return;
    indices->Add(index, zone);
    index += pattern_length;
    limit--;
  }
}


void FindStringIndicesDispatch(Isolate* isolate,
                               String* subject,
                               String* pattern,
                               ZoneList<int>* indices,
                               unsigned int limit,
                               Zone* zone) {
  {
    AssertNoAllocation no_gc;
    String::FlatContent subject_content = subject->GetFlatContent();
    String::FlatContent pattern_content = pattern->GetFlatContent();
    ASSERT(subject_content.IsFlat());
    ASSERT(pattern_content.IsFlat());
    if (subject_content.IsAscii()) {
      Vector<const char> subject_vector = subject_content.ToAsciiVector();
      if (pattern_content.IsAscii()) {
        Vector<const char> pattern_vector = pattern_content.ToAsciiVector();
        if (pattern_vector.length() == 1) {
          FindAsciiStringIndices(subject_vector,
                                 pattern_vector[0],
                                 indices,
                                 limit,
                                 zone);
        } else {
          FindStringIndices(isolate,
                            subject_vector,
                            pattern_vector,
                            indices,
                            limit,
                            zone);
        }
      } else {
        FindStringIndices(isolate,
                          subject_vector,
                          pattern_content.ToUC16Vector(),
                          indices,
                          limit,
                          zone);
      }
    } else {
      Vector<const uc16> subject_vector = subject_content.ToUC16Vector();
      if (pattern_content.IsAscii()) {
        FindStringIndices(isolate,
                          subject_vector,
                          pattern_content.ToAsciiVector(),
                          indices,
                          limit,
                          zone);
      } else {
        FindStringIndices(isolate,
                          subject_vector,
                          pattern_content.ToUC16Vector(),
                          indices,
                          limit,
                          zone);
      }
    }
  }
}


// Two smis before and after the match, for very long strings.
const int kMaxBuilderEntriesPerRegExpMatch = 5;


static void SetLastMatchInfoNoCaptures(Handle<String> subject,
                                       Handle<JSArray> last_match_info,
                                       int match_start,
                                       int match_end) {
  // Fill last_match_info with a single capture.
  last_match_info->EnsureSize(2 + RegExpImpl::kLastMatchOverhead);
  AssertNoAllocation no_gc;
  FixedArray* elements = FixedArray::cast(last_match_info->elements());
  RegExpImpl::SetLastCaptureCount(elements, 2);
  RegExpImpl::SetLastInput(elements, *subject);
  RegExpImpl::SetLastSubject(elements, *subject);
  RegExpImpl::SetCapture(elements, 0, match_start);
  RegExpImpl::SetCapture(elements, 1, match_end);
}


template <typename SubjectChar, typename PatternChar>
static bool SearchStringMultiple(Isolate* isolate,
                                 Vector<const SubjectChar> subject,
                                 Vector<const PatternChar> pattern,
                                 String* pattern_string,
                                 FixedArrayBuilder* builder,
                                 int* match_pos) {
  int pos = *match_pos;
  int subject_length = subject.length();
  int pattern_length = pattern.length();
  int max_search_start = subject_length - pattern_length;
  StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
  while (pos <= max_search_start) {
    if (!builder->HasCapacity(kMaxBuilderEntriesPerRegExpMatch)) {
      *match_pos = pos;
      return false;
    }
    // Position of end of previous match.
    int match_end = pos + pattern_length;
    int new_pos = search.Search(subject, match_end);
    if (new_pos >= 0) {
      // A match.
      if (new_pos > match_end) {
        ReplacementStringBuilder::AddSubjectSlice(builder,
            match_end,
            new_pos);
      }
      pos = new_pos;
      builder->Add(pattern_string);
    } else {
      break;
    }
  }

  if (pos < max_search_start) {
    ReplacementStringBuilder::AddSubjectSlice(builder,
                                              pos + pattern_length,
                                              subject_length);
  }
  *match_pos = pos;
  return true;
}




template<typename ResultSeqString>
MUST_USE_RESULT static MaybeObject* StringReplaceAtomRegExpWithString(
    Isolate* isolate,
    Handle<String> subject,
    Handle<JSRegExp> pattern_regexp,
    Handle<String> replacement,
    Handle<JSArray> last_match_info,
    Zone* zone) {
  ASSERT(subject->IsFlat());
  ASSERT(replacement->IsFlat());

  ZoneScope zone_space(isolate, DELETE_ON_EXIT);
  ZoneList<int> indices(8, isolate->zone());
  ASSERT_EQ(JSRegExp::ATOM, pattern_regexp->TypeTag());
  String* pattern =
      String::cast(pattern_regexp->DataAt(JSRegExp::kAtomPatternIndex));
  int subject_len = subject->length();
  int pattern_len = pattern->length();
  int replacement_len = replacement->length();

  FindStringIndicesDispatch(isolate, *subject, pattern, &indices, 0xffffffff,
                            zone);

  int matches = indices.length();
  if (matches == 0) return *subject;

  // Detect integer overflow.
  int64_t result_len_64 =
      (static_cast<int64_t>(replacement_len) -
       static_cast<int64_t>(pattern_len)) *
      static_cast<int64_t>(matches) +
      static_cast<int64_t>(subject_len);
  if (result_len_64 > INT_MAX) return Failure::OutOfMemoryException();
  int result_len = static_cast<int>(result_len_64);

  int subject_pos = 0;
  int result_pos = 0;

  Handle<ResultSeqString> result;
  if (ResultSeqString::kHasAsciiEncoding) {
    result = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawAsciiString(result_len));
  } else {
    result = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawTwoByteString(result_len));
  }

  for (int i = 0; i < matches; i++) {
    // Copy non-matched subject content.
    if (subject_pos < indices.at(i)) {
      String::WriteToFlat(*subject,
                          result->GetChars() + result_pos,
                          subject_pos,
                          indices.at(i));
      result_pos += indices.at(i) - subject_pos;
    }

    // Replace match.
    if (replacement_len > 0) {
      String::WriteToFlat(*replacement,
                          result->GetChars() + result_pos,
                          0,
                          replacement_len);
      result_pos += replacement_len;
    }

    subject_pos = indices.at(i) + pattern_len;
  }
  // Add remaining subject content at the end.
  if (subject_pos < subject_len) {
    String::WriteToFlat(*subject,
                        result->GetChars() + result_pos,
                        subject_pos,
                        subject_len);
  }

  SetLastMatchInfoNoCaptures(subject,
                             last_match_info,
                             indices.at(matches - 1),
                             indices.at(matches - 1) + pattern_len);

  return *result;
}


MUST_USE_RESULT static MaybeObject* StringReplaceRegExpWithString(
    Isolate* isolate,
    String* subject,
    JSRegExp* regexp,
    String* replacement,
    JSArray* last_match_info,
    Zone* zone) {
  ASSERT(subject->IsFlat());
  ASSERT(replacement->IsFlat());

  HandleScope handles(isolate);

  int length = subject->length();
  Handle<String> subject_handle(subject);
  Handle<JSRegExp> regexp_handle(regexp);
  Handle<String> replacement_handle(replacement);
  Handle<JSArray> last_match_info_handle(last_match_info);
  Handle<Object> match = RegExpImpl::Exec(regexp_handle,
                                          subject_handle,
                                          0,
                                          last_match_info_handle,
                                          isolate->zone());
  if (match.is_null()) {
    return Failure::Exception();
  }
  if (match->IsNull()) {
    return *subject_handle;
  }

  int capture_count = regexp_handle->CaptureCount();

  // CompiledReplacement uses zone allocation.
  ZoneScope zonescope(isolate, DELETE_ON_EXIT);
  CompiledReplacement compiled_replacement(isolate->zone());
  compiled_replacement.Compile(replacement_handle,
                               capture_count,
                               length);

  bool is_global = regexp_handle->GetFlags().is_global();

  // Shortcut for simple non-regexp global replacements
  if (is_global &&
      regexp_handle->TypeTag() == JSRegExp::ATOM &&
      compiled_replacement.simple_hint()) {
    if (subject_handle->HasOnlyAsciiChars() &&
        replacement_handle->HasOnlyAsciiChars()) {
      return StringReplaceAtomRegExpWithString<SeqAsciiString>(
          isolate,
          subject_handle,
          regexp_handle,
          replacement_handle,
          last_match_info_handle,
          zone);
    } else {
      return StringReplaceAtomRegExpWithString<SeqTwoByteString>(
          isolate,
          subject_handle,
          regexp_handle,
          replacement_handle,
          last_match_info_handle,
          zone);
    }
  }

  // Guessing the number of parts that the final result string is built
  // from. Global regexps can match any number of times, so we guess
  // conservatively.
  int expected_parts =
      (compiled_replacement.parts() + 1) * (is_global ? 4 : 1) + 1;
  ReplacementStringBuilder builder(isolate->heap(),
                                   subject_handle,
                                   expected_parts);

  // Index of end of last match.
  int prev = 0;

  // Number of parts added by compiled replacement plus preceeding
  // string and possibly suffix after last match.  It is possible for
  // all components to use two elements when encoded as two smis.
  const int parts_added_per_loop = 2 * (compiled_replacement.parts() + 2);
  bool matched = true;
  do {
    ASSERT(last_match_info_handle->HasFastObjectElements());
    // Increase the capacity of the builder before entering local handle-scope,
    // so its internal buffer can safely allocate a new handle if it grows.
    builder.EnsureCapacity(parts_added_per_loop);

    HandleScope loop_scope(isolate);
    int start, end;
    {
      AssertNoAllocation match_info_array_is_not_in_a_handle;
      FixedArray* match_info_array =
          FixedArray::cast(last_match_info_handle->elements());

      ASSERT_EQ(capture_count * 2 + 2,
                RegExpImpl::GetLastCaptureCount(match_info_array));
      start = RegExpImpl::GetCapture(match_info_array, 0);
      end = RegExpImpl::GetCapture(match_info_array, 1);
    }

    if (prev < start) {
      builder.AddSubjectSlice(prev, start);
    }
    compiled_replacement.Apply(&builder,
                               start,
                               end,
                               last_match_info_handle);
    prev = end;

    // Only continue checking for global regexps.
    if (!is_global) break;

    // Continue from where the match ended, unless it was an empty match.
    int next = end;
    if (start == end) {
      next = end + 1;
      if (next > length) break;
    }

    match = RegExpImpl::Exec(regexp_handle,
                             subject_handle,
                             next,
                             last_match_info_handle,
                             isolate->zone());
    if (match.is_null()) {
      return Failure::Exception();
    }
    matched = !match->IsNull();
  } while (matched);

  if (prev < length) {
    builder.AddSubjectSlice(prev, length);
  }

  return *(builder.ToString());
}


template <typename ResultSeqString>
MUST_USE_RESULT static MaybeObject* StringReplaceRegExpWithEmptyString(
    Isolate* isolate,
    String* subject,
    JSRegExp* regexp,
    JSArray* last_match_info,
    Zone* zone) {
  ASSERT(subject->IsFlat());

  HandleScope handles(isolate);

  Handle<String> subject_handle(subject);
  Handle<JSRegExp> regexp_handle(regexp);
  Handle<JSArray> last_match_info_handle(last_match_info);

  // Shortcut for simple non-regexp global replacements
  if (regexp_handle->GetFlags().is_global() &&
      regexp_handle->TypeTag() == JSRegExp::ATOM) {
    Handle<String> empty_string_handle(HEAP->empty_string());
    if (subject_handle->HasOnlyAsciiChars()) {
      return StringReplaceAtomRegExpWithString<SeqAsciiString>(
          isolate,
          subject_handle,
          regexp_handle,
          empty_string_handle,
          last_match_info_handle,
          zone);
    } else {
      return StringReplaceAtomRegExpWithString<SeqTwoByteString>(
          isolate,
          subject_handle,
          regexp_handle,
          empty_string_handle,
          last_match_info_handle,
          zone);
    }
  }

  Handle<Object> match = RegExpImpl::Exec(regexp_handle,
                                          subject_handle,
                                          0,
                                          last_match_info_handle,
                                          isolate->zone());
  if (match.is_null()) return Failure::Exception();
  if (match->IsNull()) return *subject_handle;

  ASSERT(last_match_info_handle->HasFastObjectElements());

  int start, end;
  {
    AssertNoAllocation match_info_array_is_not_in_a_handle;
    FixedArray* match_info_array =
        FixedArray::cast(last_match_info_handle->elements());

    start = RegExpImpl::GetCapture(match_info_array, 0);
    end = RegExpImpl::GetCapture(match_info_array, 1);
  }

  bool global = regexp_handle->GetFlags().is_global();

  if (start == end && !global) return *subject_handle;

  int length = subject_handle->length();
  int new_length = length - (end - start);
  if (new_length == 0) {
    return isolate->heap()->empty_string();
  }
  Handle<ResultSeqString> answer;
  if (ResultSeqString::kHasAsciiEncoding) {
    answer = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawAsciiString(new_length));
  } else {
    answer = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawTwoByteString(new_length));
  }

  // If the regexp isn't global, only match once.
  if (!global) {
    if (start > 0) {
      String::WriteToFlat(*subject_handle,
                          answer->GetChars(),
                          0,
                          start);
    }
    if (end < length) {
      String::WriteToFlat(*subject_handle,
                          answer->GetChars() + start,
                          end,
                          length);
    }
    return *answer;
  }

  int prev = 0;  // Index of end of last match.
  int next = 0;  // Start of next search (prev unless last match was empty).
  int position = 0;

  do {
    if (prev < start) {
      // Add substring subject[prev;start] to answer string.
      String::WriteToFlat(*subject_handle,
                          answer->GetChars() + position,
                          prev,
                          start);
      position += start - prev;
    }
    prev = end;
    next = end;
    // Continue from where the match ended, unless it was an empty match.
    if (start == end) {
      next++;
      if (next > length) break;
    }
    match = RegExpImpl::Exec(regexp_handle,
                             subject_handle,
                             next,
                             last_match_info_handle,
                             isolate->zone());
    if (match.is_null()) return Failure::Exception();
    if (match->IsNull()) break;

    ASSERT(last_match_info_handle->HasFastObjectElements());
    HandleScope loop_scope(isolate);
    {
      AssertNoAllocation match_info_array_is_not_in_a_handle;
      FixedArray* match_info_array =
          FixedArray::cast(last_match_info_handle->elements());
      start = RegExpImpl::GetCapture(match_info_array, 0);
      end = RegExpImpl::GetCapture(match_info_array, 1);
    }
  } while (true);

  if (prev < length) {
    // Add substring subject[prev;length] to answer string.
    String::WriteToFlat(*subject_handle,
                        answer->GetChars() + position,
                        prev,
                        length);
    position += length - prev;
  }

  if (position == 0) {
    return isolate->heap()->empty_string();
  }

  // Shorten string and fill
  int string_size = ResultSeqString::SizeFor(position);
  int allocated_string_size = ResultSeqString::SizeFor(new_length);
  int delta = allocated_string_size - string_size;

  answer->set_length(position);
  if (delta == 0) return *answer;

  Address end_of_string = answer->address() + string_size;
  isolate->heap()->CreateFillerObjectAt(end_of_string, delta);
  if (Marking::IsBlack(Marking::MarkBitFrom(*answer))) {
    MemoryChunk::IncrementLiveBytesFromMutator(answer->address(), -delta);
  }

  return *answer;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringReplaceRegExpWithString) {
  ASSERT(args.length() == 4);

  CONVERT_ARG_CHECKED(String, subject, 0);
  if (!subject->IsFlat()) {
    Object* flat_subject;
    { MaybeObject* maybe_flat_subject = subject->TryFlatten();
      if (!maybe_flat_subject->ToObject(&flat_subject)) {
        return maybe_flat_subject;
      }
    }
    subject = String::cast(flat_subject);
  }

  CONVERT_ARG_CHECKED(String, replacement, 2);
  if (!replacement->IsFlat()) {
    Object* flat_replacement;
    { MaybeObject* maybe_flat_replacement = replacement->TryFlatten();
      if (!maybe_flat_replacement->ToObject(&flat_replacement)) {
        return maybe_flat_replacement;
      }
    }
    replacement = String::cast(flat_replacement);
  }

  CONVERT_ARG_CHECKED(JSRegExp, regexp, 1);
  CONVERT_ARG_CHECKED(JSArray, last_match_info, 3);

  ASSERT(last_match_info->HasFastObjectElements());

  Zone* zone = isolate->zone();
  if (replacement->length() == 0) {
    if (subject->HasOnlyAsciiChars()) {
      return StringReplaceRegExpWithEmptyString<SeqAsciiString>(
          isolate, subject, regexp, last_match_info, zone);
    } else {
      return StringReplaceRegExpWithEmptyString<SeqTwoByteString>(
          isolate, subject, regexp, last_match_info, zone);
    }
  }

  return StringReplaceRegExpWithString(isolate,
                                       subject,
                                       regexp,
                                       replacement,
                                       last_match_info,
                                       zone);
}


Handle<String> Runtime::StringReplaceOneCharWithString(Isolate* isolate,
                                                       Handle<String> subject,
                                                       Handle<String> search,
                                                       Handle<String> replace,
                                                       bool* found,
                                                       int recursion_limit) {
  if (recursion_limit == 0) return Handle<String>::null();
  if (subject->IsConsString()) {
    ConsString* cons = ConsString::cast(*subject);
    Handle<String> first = Handle<String>(cons->first());
    Handle<String> second = Handle<String>(cons->second());
    Handle<String> new_first =
        StringReplaceOneCharWithString(isolate,
                                       first,
                                       search,
                                       replace,
                                       found,
                                       recursion_limit - 1);
    if (*found) return isolate->factory()->NewConsString(new_first, second);
    if (new_first.is_null()) return new_first;

    Handle<String> new_second =
        StringReplaceOneCharWithString(isolate,
                                       second,
                                       search,
                                       replace,
                                       found,
                                       recursion_limit - 1);
    if (*found) return isolate->factory()->NewConsString(first, new_second);
    if (new_second.is_null()) return new_second;

    return subject;
  } else {
    int index = StringMatch(isolate, subject, search, 0);
    if (index == -1) return subject;
    *found = true;
    Handle<String> first = isolate->factory()->NewSubString(subject, 0, index);
    Handle<String> cons1 = isolate->factory()->NewConsString(first, replace);
    Handle<String> second =
        isolate->factory()->NewSubString(subject, index + 1, subject->length());
    return isolate->factory()->NewConsString(cons1, second);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringReplaceOneCharWithString) {
  ASSERT(args.length() == 3);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, search, 1);
  CONVERT_ARG_HANDLE_CHECKED(String, replace, 2);

  // If the cons string tree is too deep, we simply abort the recursion and
  // retry with a flattened subject string.
  const int kRecursionLimit = 0x1000;
  bool found = false;
  Handle<String> result =
      Runtime::StringReplaceOneCharWithString(isolate,
                                              subject,
                                              search,
                                              replace,
                                              &found,
                                              kRecursionLimit);
  if (!result.is_null()) return *result;
  return *Runtime::StringReplaceOneCharWithString(isolate,
                                                  FlattenGetString(subject),
                                                  search,
                                                  replace,
                                                  &found,
                                                  kRecursionLimit);
}


// Perform string match of pattern on subject, starting at start index.
// Caller must ensure that 0 <= start_index <= sub->length(),
// and should check that pat->length() + start_index <= sub->length().
int Runtime::StringMatch(Isolate* isolate,
                         Handle<String> sub,
                         Handle<String> pat,
                         int start_index) {
  ASSERT(0 <= start_index);
  ASSERT(start_index <= sub->length());

  int pattern_length = pat->length();
  if (pattern_length == 0) return start_index;

  int subject_length = sub->length();
  if (start_index + pattern_length > subject_length) return -1;

  if (!sub->IsFlat()) FlattenString(sub);
  if (!pat->IsFlat()) FlattenString(pat);

  AssertNoAllocation no_heap_allocation;  // ensure vectors stay valid
  // Extract flattened substrings of cons strings before determining asciiness.
  String::FlatContent seq_sub = sub->GetFlatContent();
  String::FlatContent seq_pat = pat->GetFlatContent();

  // dispatch on type of strings
  if (seq_pat.IsAscii()) {
    Vector<const char> pat_vector = seq_pat.ToAsciiVector();
    if (seq_sub.IsAscii()) {
      return SearchString(isolate,
                          seq_sub.ToAsciiVector(),
                          pat_vector,
                          start_index);
    }
    return SearchString(isolate,
                        seq_sub.ToUC16Vector(),
                        pat_vector,
                        start_index);
  }
  Vector<const uc16> pat_vector = seq_pat.ToUC16Vector();
  if (seq_sub.IsAscii()) {
    return SearchString(isolate,
                        seq_sub.ToAsciiVector(),
                        pat_vector,
                        start_index);
  }
  return SearchString(isolate,
                      seq_sub.ToUC16Vector(),
                      pat_vector,
                      start_index);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringIndexOf) {
  HandleScope scope(isolate);  // create a new handle scope
  ASSERT(args.length() == 3);

  CONVERT_ARG_HANDLE_CHECKED(String, sub, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, pat, 1);

  Object* index = args[2];
  uint32_t start_index;
  if (!index->ToArrayIndex(&start_index)) return Smi::FromInt(-1);

  RUNTIME_ASSERT(start_index <= static_cast<uint32_t>(sub->length()));
  int position =
      Runtime::StringMatch(isolate, sub, pat, start_index);
  return Smi::FromInt(position);
}


template <typename schar, typename pchar>
static int StringMatchBackwards(Vector<const schar> subject,
                                Vector<const pchar> pattern,
                                int idx) {
  int pattern_length = pattern.length();
  ASSERT(pattern_length >= 1);
  ASSERT(idx + pattern_length <= subject.length());

  if (sizeof(schar) == 1 && sizeof(pchar) > 1) {
    for (int i = 0; i < pattern_length; i++) {
      uc16 c = pattern[i];
      if (c > String::kMaxAsciiCharCode) {
        return -1;
      }
    }
  }

  pchar pattern_first_char = pattern[0];
  for (int i = idx; i >= 0; i--) {
    if (subject[i] != pattern_first_char) continue;
    int j = 1;
    while (j < pattern_length) {
      if (pattern[j] != subject[i+j]) {
        break;
      }
      j++;
    }
    if (j == pattern_length) {
      return i;
    }
  }
  return -1;
}

RUNTIME_FUNCTION(MaybeObject*, Runtime_StringLastIndexOf) {
  HandleScope scope(isolate);  // create a new handle scope
  ASSERT(args.length() == 3);

  CONVERT_ARG_HANDLE_CHECKED(String, sub, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, pat, 1);

  Object* index = args[2];
  uint32_t start_index;
  if (!index->ToArrayIndex(&start_index)) return Smi::FromInt(-1);

  uint32_t pat_length = pat->length();
  uint32_t sub_length = sub->length();

  if (start_index + pat_length > sub_length) {
    start_index = sub_length - pat_length;
  }

  if (pat_length == 0) {
    return Smi::FromInt(start_index);
  }

  if (!sub->IsFlat()) FlattenString(sub);
  if (!pat->IsFlat()) FlattenString(pat);

  int position = -1;
  AssertNoAllocation no_heap_allocation;  // ensure vectors stay valid

  String::FlatContent sub_content = sub->GetFlatContent();
  String::FlatContent pat_content = pat->GetFlatContent();

  if (pat_content.IsAscii()) {
    Vector<const char> pat_vector = pat_content.ToAsciiVector();
    if (sub_content.IsAscii()) {
      position = StringMatchBackwards(sub_content.ToAsciiVector(),
                                      pat_vector,
                                      start_index);
    } else {
      position = StringMatchBackwards(sub_content.ToUC16Vector(),
                                      pat_vector,
                                      start_index);
    }
  } else {
    Vector<const uc16> pat_vector = pat_content.ToUC16Vector();
    if (sub_content.IsAscii()) {
      position = StringMatchBackwards(sub_content.ToAsciiVector(),
                                      pat_vector,
                                      start_index);
    } else {
      position = StringMatchBackwards(sub_content.ToUC16Vector(),
                                      pat_vector,
                                      start_index);
    }
  }

  return Smi::FromInt(position);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringLocaleCompare) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(String, str1, 0);
  CONVERT_ARG_CHECKED(String, str2, 1);

  if (str1 == str2) return Smi::FromInt(0);  // Equal.
  int str1_length = str1->length();
  int str2_length = str2->length();

  // Decide trivial cases without flattening.
  if (str1_length == 0) {
    if (str2_length == 0) return Smi::FromInt(0);  // Equal.
    return Smi::FromInt(-str2_length);
  } else {
    if (str2_length == 0) return Smi::FromInt(str1_length);
  }

  int end = str1_length < str2_length ? str1_length : str2_length;

  // No need to flatten if we are going to find the answer on the first
  // character.  At this point we know there is at least one character
  // in each string, due to the trivial case handling above.
  int d = str1->Get(0) - str2->Get(0);
  if (d != 0) return Smi::FromInt(d);

  str1->TryFlatten();
  str2->TryFlatten();

  StringInputBuffer& buf1 =
      *isolate->runtime_state()->string_locale_compare_buf1();
  StringInputBuffer& buf2 =
      *isolate->runtime_state()->string_locale_compare_buf2();

  buf1.Reset(str1);
  buf2.Reset(str2);

  for (int i = 0; i < end; i++) {
    uint16_t char1 = buf1.GetNext();
    uint16_t char2 = buf2.GetNext();
    if (char1 != char2) return Smi::FromInt(char1 - char2);
  }

  return Smi::FromInt(str1_length - str2_length);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SubString) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);

  CONVERT_ARG_CHECKED(String, value, 0);
  int start, end;
  // We have a fast integer-only case here to avoid a conversion to double in
  // the common case where from and to are Smis.
  if (args[1]->IsSmi() && args[2]->IsSmi()) {
    CONVERT_SMI_ARG_CHECKED(from_number, 1);
    CONVERT_SMI_ARG_CHECKED(to_number, 2);
    start = from_number;
    end = to_number;
  } else {
    CONVERT_DOUBLE_ARG_CHECKED(from_number, 1);
    CONVERT_DOUBLE_ARG_CHECKED(to_number, 2);
    start = FastD2I(from_number);
    end = FastD2I(to_number);
  }
  RUNTIME_ASSERT(end >= start);
  RUNTIME_ASSERT(start >= 0);
  RUNTIME_ASSERT(end <= value->length());
  isolate->counters()->sub_string_runtime()->Increment();
  return value->SubString(start, end);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringMatch) {
  ASSERT_EQ(3, args.length());

  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, regexp_info, 2);
  HandleScope handles;

  Handle<Object> match = RegExpImpl::Exec(regexp, subject, 0, regexp_info,
                                          isolate->zone());

  if (match.is_null()) {
    return Failure::Exception();
  }
  if (match->IsNull()) {
    return isolate->heap()->null_value();
  }
  int length = subject->length();

  Zone* zone = isolate->zone();
  ZoneScope zone_space(isolate, DELETE_ON_EXIT);
  ZoneList<int> offsets(8, zone);
  int start;
  int end;
  do {
    {
      AssertNoAllocation no_alloc;
      FixedArray* elements = FixedArray::cast(regexp_info->elements());
      start = Smi::cast(elements->get(RegExpImpl::kFirstCapture))->value();
      end = Smi::cast(elements->get(RegExpImpl::kFirstCapture + 1))->value();
    }
    offsets.Add(start, zone);
    offsets.Add(end, zone);
    if (start == end) if (++end > length) break;
    match = RegExpImpl::Exec(regexp, subject, end, regexp_info,
                             isolate->zone());
    if (match.is_null()) {
      return Failure::Exception();
    }
  } while (!match->IsNull());
  int matches = offsets.length() / 2;
  Handle<FixedArray> elements = isolate->factory()->NewFixedArray(matches);
  Handle<String> substring = isolate->factory()->
    NewSubString(subject, offsets.at(0), offsets.at(1));
  elements->set(0, *substring);
  for (int i = 1; i < matches ; i++) {
    int from = offsets.at(i * 2);
    int to = offsets.at(i * 2 + 1);
    Handle<String> substring = isolate->factory()->
        NewProperSubString(subject, from, to);
    elements->set(i, *substring);
  }
  Handle<JSArray> result = isolate->factory()->NewJSArrayWithElements(elements);
  result->set_length(Smi::FromInt(matches));
  return *result;
}


static bool SearchStringMultiple(Isolate* isolate,
                                 Handle<String> subject,
                                 Handle<String> pattern,
                                 Handle<JSArray> last_match_info,
                                 FixedArrayBuilder* builder) {
  ASSERT(subject->IsFlat());
  ASSERT(pattern->IsFlat());

  // Treating as if a previous match was before first character.
  int match_pos = -pattern->length();

  for (;;) {  // Break when search complete.
    builder->EnsureCapacity(kMaxBuilderEntriesPerRegExpMatch);
    AssertNoAllocation no_gc;
    String::FlatContent subject_content = subject->GetFlatContent();
    String::FlatContent pattern_content = pattern->GetFlatContent();
    if (subject_content.IsAscii()) {
      Vector<const char> subject_vector = subject_content.ToAsciiVector();
      if (pattern_content.IsAscii()) {
        if (SearchStringMultiple(isolate,
                                 subject_vector,
                                 pattern_content.ToAsciiVector(),
                                 *pattern,
                                 builder,
                                 &match_pos)) break;
      } else {
        if (SearchStringMultiple(isolate,
                                 subject_vector,
                                 pattern_content.ToUC16Vector(),
                                 *pattern,
                                 builder,
                                 &match_pos)) break;
      }
    } else {
      Vector<const uc16> subject_vector = subject_content.ToUC16Vector();
      if (pattern_content.IsAscii()) {
        if (SearchStringMultiple(isolate,
                                 subject_vector,
                                 pattern_content.ToAsciiVector(),
                                 *pattern,
                                 builder,
                                 &match_pos)) break;
      } else {
        if (SearchStringMultiple(isolate,
                                 subject_vector,
                                 pattern_content.ToUC16Vector(),
                                 *pattern,
                                 builder,
                                 &match_pos)) break;
      }
    }
  }

  if (match_pos >= 0) {
    SetLastMatchInfoNoCaptures(subject,
                               last_match_info,
                               match_pos,
                               match_pos + pattern->length());
    return true;
  }
  return false;  // No matches at all.
}


static int SearchRegExpNoCaptureMultiple(
    Isolate* isolate,
    Handle<String> subject,
    Handle<JSRegExp> regexp,
    Handle<JSArray> last_match_array,
    FixedArrayBuilder* builder) {
  ASSERT(subject->IsFlat());
  ASSERT(regexp->CaptureCount() == 0);
  int match_start = -1;
  int match_end = 0;
  int pos = 0;
  int registers_per_match = RegExpImpl::IrregexpPrepare(regexp, subject,
                                                        isolate->zone());
  if (registers_per_match < 0) return RegExpImpl::RE_EXCEPTION;

  int max_matches;
  int num_registers = RegExpImpl::GlobalOffsetsVectorSize(regexp,
                                                          registers_per_match,
                                                          &max_matches);
  OffsetsVector registers(num_registers, isolate);
  Vector<int32_t> register_vector(registers.vector(), registers.length());
  int subject_length = subject->length();
  bool first = true;
  for (;;) {  // Break on failure, return on exception.
    int num_matches = RegExpImpl::IrregexpExecRaw(regexp,
                                                  subject,
                                                  pos,
                                                  register_vector,
                                                  isolate->zone());
    if (num_matches > 0) {
      for (int match_index = 0; match_index < num_matches; match_index++) {
        int32_t* current_match = &register_vector[match_index * 2];
        match_start = current_match[0];
        builder->EnsureCapacity(kMaxBuilderEntriesPerRegExpMatch);
        if (match_end < match_start) {
          ReplacementStringBuilder::AddSubjectSlice(builder,
                                                    match_end,
                                                    match_start);
        }
        match_end = current_match[1];
        HandleScope loop_scope(isolate);
        if (!first) {
          builder->Add(*isolate->factory()->NewProperSubString(subject,
                                                               match_start,
                                                               match_end));
        } else {
          builder->Add(*isolate->factory()->NewSubString(subject,
                                                         match_start,
                                                         match_end));
          first = false;
        }
      }

      // If we did not get the maximum number of matches, we can stop here
      // since there are no matches left.
      if (num_matches < max_matches) break;

      if (match_start != match_end) {
        pos = match_end;
      } else {
        pos = match_end + 1;
        if (pos > subject_length) break;
      }
    } else if (num_matches == 0) {
      break;
    } else {
      ASSERT_EQ(num_matches, RegExpImpl::RE_EXCEPTION);
      return RegExpImpl::RE_EXCEPTION;
    }
  }

  if (match_start >= 0) {
    if (match_end < subject_length) {
      ReplacementStringBuilder::AddSubjectSlice(builder,
                                                match_end,
                                                subject_length);
    }
    SetLastMatchInfoNoCaptures(subject,
                               last_match_array,
                               match_start,
                               match_end);
    return RegExpImpl::RE_SUCCESS;
  } else {
    return RegExpImpl::RE_FAILURE;  // No matches at all.
  }
}


// Only called from Runtime_RegExpExecMultiple so it doesn't need to maintain
// separate last match info.  See comment on that function.
static int SearchRegExpMultiple(
    Isolate* isolate,
    Handle<String> subject,
    Handle<JSRegExp> regexp,
    Handle<JSArray> last_match_array,
    FixedArrayBuilder* builder) {

  ASSERT(subject->IsFlat());
  int registers_per_match = RegExpImpl::IrregexpPrepare(regexp, subject,
                                                        isolate->zone());
  if (registers_per_match < 0) return RegExpImpl::RE_EXCEPTION;

  int max_matches;
  int num_registers = RegExpImpl::GlobalOffsetsVectorSize(regexp,
                                                          registers_per_match,
                                                          &max_matches);
  OffsetsVector registers(num_registers, isolate);
  Vector<int32_t> register_vector(registers.vector(), registers.length());

  int num_matches = RegExpImpl::IrregexpExecRaw(regexp,
                                                subject,
                                                0,
                                                register_vector,
                                                isolate->zone());

  int capture_count = regexp->CaptureCount();
  int subject_length = subject->length();

  // Position to search from.
  int pos = 0;
  // End of previous match. Differs from pos if match was empty.
  int match_end = 0;
  bool first = true;

  if (num_matches > 0) {
    do {
      int match_start = 0;
      for (int match_index = 0; match_index < num_matches; match_index++) {
        int32_t* current_match =
            &register_vector[match_index * registers_per_match];
        match_start = current_match[0];
        builder->EnsureCapacity(kMaxBuilderEntriesPerRegExpMatch);
        if (match_end < match_start) {
          ReplacementStringBuilder::AddSubjectSlice(builder,
                                                    match_end,
                                                    match_start);
        }
        match_end = current_match[1];

        {
          // Avoid accumulating new handles inside loop.
          HandleScope temp_scope(isolate);
          // Arguments array to replace function is match, captures, index and
          // subject, i.e., 3 + capture count in total.
          Handle<FixedArray> elements =
              isolate->factory()->NewFixedArray(3 + capture_count);
          Handle<String> match;
          if (!first) {
            match = isolate->factory()->NewProperSubString(subject,
                                                           match_start,
                                                           match_end);
          } else {
            match = isolate->factory()->NewSubString(subject,
                                                     match_start,
                                                     match_end);
          }
          elements->set(0, *match);
          for (int i = 1; i <= capture_count; i++) {
            int start = current_match[i * 2];
            if (start >= 0) {
              int end = current_match[i * 2 + 1];
              ASSERT(start <= end);
              Handle<String> substring;
              if (!first) {
                substring =
                    isolate->factory()->NewProperSubString(subject, start, end);
              } else {
                substring =
                    isolate->factory()->NewSubString(subject, start, end);
              }
              elements->set(i, *substring);
            } else {
              ASSERT(current_match[i * 2 + 1] < 0);
              elements->set(i, isolate->heap()->undefined_value());
            }
          }
          elements->set(capture_count + 1, Smi::FromInt(match_start));
          elements->set(capture_count + 2, *subject);
          builder->Add(*isolate->factory()->NewJSArrayWithElements(elements));
        }
        first = false;
      }

      // If we did not get the maximum number of matches, we can stop here
      // since there are no matches left.
      if (num_matches < max_matches) break;

      if (match_end > match_start) {
        pos = match_end;
      } else {
        pos = match_end + 1;
        if (pos > subject_length) {
          break;
        }
      }

      num_matches = RegExpImpl::IrregexpExecRaw(regexp,
                                                subject,
                                                pos,
                                                register_vector,
                                                isolate->zone());
    } while (num_matches > 0);

    if (num_matches != RegExpImpl::RE_EXCEPTION) {
      // Finished matching, with at least one match.
      if (match_end < subject_length) {
        ReplacementStringBuilder::AddSubjectSlice(builder,
                                                  match_end,
                                                  subject_length);
      }

      int last_match_capture_count = (capture_count + 1) * 2;
      int last_match_array_size =
          last_match_capture_count + RegExpImpl::kLastMatchOverhead;
      last_match_array->EnsureSize(last_match_array_size);
      AssertNoAllocation no_gc;
      FixedArray* elements = FixedArray::cast(last_match_array->elements());
      // We have to set this even though the rest of the last match array is
      // ignored.
      RegExpImpl::SetLastCaptureCount(elements, last_match_capture_count);
      // These are also read without consulting the override.
      RegExpImpl::SetLastSubject(elements, *subject);
      RegExpImpl::SetLastInput(elements, *subject);
      return RegExpImpl::RE_SUCCESS;
    }
  }
  // No matches at all, return failure or exception result directly.
  return num_matches;
}


// This is only called for StringReplaceGlobalRegExpWithFunction.  This sets
// lastMatchInfoOverride to maintain the last match info, so we don't need to
// set any other last match array info.
RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpExecMultiple) {
  ASSERT(args.length() == 4);
  HandleScope handles(isolate);

  CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
  if (!subject->IsFlat()) FlattenString(subject);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, result_array, 3);

  ASSERT(last_match_info->HasFastObjectElements());
  ASSERT(regexp->GetFlags().is_global());
  Handle<FixedArray> result_elements;
  if (result_array->HasFastObjectElements()) {
    result_elements =
        Handle<FixedArray>(FixedArray::cast(result_array->elements()));
  }
  if (result_elements.is_null() || result_elements->length() < 16) {
    result_elements = isolate->factory()->NewFixedArrayWithHoles(16);
  }
  FixedArrayBuilder builder(result_elements);

  if (regexp->TypeTag() == JSRegExp::ATOM) {
    Handle<String> pattern(
        String::cast(regexp->DataAt(JSRegExp::kAtomPatternIndex)));
    ASSERT(pattern->IsFlat());
    if (SearchStringMultiple(isolate, subject, pattern,
                             last_match_info, &builder)) {
      return *builder.ToJSArray(result_array);
    }
    return isolate->heap()->null_value();
  }

  ASSERT_EQ(regexp->TypeTag(), JSRegExp::IRREGEXP);

  int result;
  if (regexp->CaptureCount() == 0) {
    result = SearchRegExpNoCaptureMultiple(isolate,
                                           subject,
                                           regexp,
                                           last_match_info,
                                           &builder);
  } else {
    result = SearchRegExpMultiple(isolate,
                                  subject,
                                  regexp,
                                  last_match_info,
                                  &builder);
  }
  if (result == RegExpImpl::RE_SUCCESS) return *builder.ToJSArray(result_array);
  if (result == RegExpImpl::RE_FAILURE) return isolate->heap()->null_value();
  ASSERT_EQ(result, RegExpImpl::RE_EXCEPTION);
  return Failure::Exception();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToRadixString) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_SMI_ARG_CHECKED(radix, 1);
  RUNTIME_ASSERT(2 <= radix && radix <= 36);

  // Fast case where the result is a one character string.
  if (args[0]->IsSmi()) {
    int value = args.smi_at(0);
    if (value >= 0 && value < radix) {
      // Character array used for conversion.
      static const char kCharTable[] = "0123456789abcdefghijklmnopqrstuvwxyz";
      return isolate->heap()->
          LookupSingleCharacterStringFromCode(kCharTable[value]);
    }
  }

  // Slow case.
  CONVERT_DOUBLE_ARG_CHECKED(value, 0);
  if (isnan(value)) {
    return *isolate->factory()->nan_symbol();
  }
  if (isinf(value)) {
    if (value < 0) {
      return *isolate->factory()->minus_infinity_symbol();
    }
    return *isolate->factory()->infinity_symbol();
  }
  char* str = DoubleToRadixCString(value, radix);
  MaybeObject* result =
      isolate->heap()->AllocateStringFromAscii(CStrVector(str));
  DeleteArray(str);
  return result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToFixed) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(value, 0);
  if (isnan(value)) {
    return *isolate->factory()->nan_symbol();
  }
  if (isinf(value)) {
    if (value < 0) {
      return *isolate->factory()->minus_infinity_symbol();
    }
    return *isolate->factory()->infinity_symbol();
  }
  CONVERT_DOUBLE_ARG_CHECKED(f_number, 1);
  int f = FastD2I(f_number);
  RUNTIME_ASSERT(f >= 0);
  char* str = DoubleToFixedCString(value, f);
  MaybeObject* res =
      isolate->heap()->AllocateStringFromAscii(CStrVector(str));
  DeleteArray(str);
  return res;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToExponential) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(value, 0);
  if (isnan(value)) {
    return *isolate->factory()->nan_symbol();
  }
  if (isinf(value)) {
    if (value < 0) {
      return *isolate->factory()->minus_infinity_symbol();
    }
    return *isolate->factory()->infinity_symbol();
  }
  CONVERT_DOUBLE_ARG_CHECKED(f_number, 1);
  int f = FastD2I(f_number);
  RUNTIME_ASSERT(f >= -1 && f <= 20);
  char* str = DoubleToExponentialCString(value, f);
  MaybeObject* res =
      isolate->heap()->AllocateStringFromAscii(CStrVector(str));
  DeleteArray(str);
  return res;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToPrecision) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(value, 0);
  if (isnan(value)) {
    return *isolate->factory()->nan_symbol();
  }
  if (isinf(value)) {
    if (value < 0) {
      return *isolate->factory()->minus_infinity_symbol();
    }
    return *isolate->factory()->infinity_symbol();
  }
  CONVERT_DOUBLE_ARG_CHECKED(f_number, 1);
  int f = FastD2I(f_number);
  RUNTIME_ASSERT(f >= 1 && f <= 21);
  char* str = DoubleToPrecisionCString(value, f);
  MaybeObject* res =
      isolate->heap()->AllocateStringFromAscii(CStrVector(str));
  DeleteArray(str);
  return res;
}


// Returns a single character string where first character equals
// string->Get(index).
static Handle<Object> GetCharAt(Handle<String> string, uint32_t index) {
  if (index < static_cast<uint32_t>(string->length())) {
    string->TryFlatten();
    return LookupSingleCharacterStringFromCode(
        string->Get(index));
  }
  return Execution::CharAt(string, index);
}


MaybeObject* Runtime::GetElementOrCharAt(Isolate* isolate,
                                         Handle<Object> object,
                                         uint32_t index) {
  // Handle [] indexing on Strings
  if (object->IsString()) {
    Handle<Object> result = GetCharAt(Handle<String>::cast(object), index);
    if (!result->IsUndefined()) return *result;
  }

  // Handle [] indexing on String objects
  if (object->IsStringObjectWithCharacterAt(index)) {
    Handle<JSValue> js_value = Handle<JSValue>::cast(object);
    Handle<Object> result =
        GetCharAt(Handle<String>(String::cast(js_value->value())), index);
    if (!result->IsUndefined()) return *result;
  }

  if (object->IsString() || object->IsNumber() || object->IsBoolean()) {
    return object->GetPrototype()->GetElement(index);
  }

  return object->GetElement(index);
}


MaybeObject* Runtime::GetObjectProperty(Isolate* isolate,
                                        Handle<Object> object,
                                        Handle<Object> key) {
  HandleScope scope(isolate);

  if (object->IsUndefined() || object->IsNull()) {
    Handle<Object> args[2] = { key, object };
    Handle<Object> error =
        isolate->factory()->NewTypeError("non_object_property_load",
                                         HandleVector(args, 2));
    return isolate->Throw(*error);
  }

  // Check if the given key is an array index.
  uint32_t index;
  if (key->ToArrayIndex(&index)) {
    return GetElementOrCharAt(isolate, object, index);
  }

  // Convert the key to a string - possibly by calling back into JavaScript.
  Handle<String> name;
  if (key->IsString()) {
    name = Handle<String>::cast(key);
  } else {
    bool has_pending_exception = false;
    Handle<Object> converted =
        Execution::ToString(key, &has_pending_exception);
    if (has_pending_exception) return Failure::Exception();
    name = Handle<String>::cast(converted);
  }

  // Check if the name is trivially convertible to an index and get
  // the element if so.
  if (name->AsArrayIndex(&index)) {
    return GetElementOrCharAt(isolate, object, index);
  } else {
    return object->GetProperty(*name);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetProperty) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  Handle<Object> object = args.at<Object>(0);
  Handle<Object> key = args.at<Object>(1);

  return Runtime::GetObjectProperty(isolate, object, key);
}


// KeyedStringGetProperty is called from KeyedLoadIC::GenerateGeneric.
RUNTIME_FUNCTION(MaybeObject*, Runtime_KeyedGetProperty) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  // Fast cases for getting named properties of the receiver JSObject
  // itself.
  //
  // The global proxy objects has to be excluded since LocalLookup on
  // the global proxy object can return a valid result even though the
  // global proxy object never has properties.  This is the case
  // because the global proxy object forwards everything to its hidden
  // prototype including local lookups.
  //
  // Additionally, we need to make sure that we do not cache results
  // for objects that require access checks.
  if (args[0]->IsJSObject()) {
    if (!args[0]->IsJSGlobalProxy() &&
        !args[0]->IsAccessCheckNeeded() &&
        args[1]->IsString()) {
      JSObject* receiver = JSObject::cast(args[0]);
      String* key = String::cast(args[1]);
      if (receiver->HasFastProperties()) {
        // Attempt to use lookup cache.
        Map* receiver_map = receiver->map();
        KeyedLookupCache* keyed_lookup_cache = isolate->keyed_lookup_cache();
        int offset = keyed_lookup_cache->Lookup(receiver_map, key);
        if (offset != -1) {
          Object* value = receiver->FastPropertyAt(offset);
          return value->IsTheHole()
              ? isolate->heap()->undefined_value()
              : value;
        }
        // Lookup cache miss.  Perform lookup and update the cache if
        // appropriate.
        LookupResult result(isolate);
        receiver->LocalLookup(key, &result);
        if (result.IsFound() && result.type() == FIELD) {
          int offset = result.GetFieldIndex();
          keyed_lookup_cache->Update(receiver_map, key, offset);
          return receiver->FastPropertyAt(offset);
        }
      } else {
        // Attempt dictionary lookup.
        StringDictionary* dictionary = receiver->property_dictionary();
        int entry = dictionary->FindEntry(key);
        if ((entry != StringDictionary::kNotFound) &&
            (dictionary->DetailsAt(entry).type() == NORMAL)) {
          Object* value = dictionary->ValueAt(entry);
          if (!receiver->IsGlobalObject()) return value;
          value = JSGlobalPropertyCell::cast(value)->value();
          if (!value->IsTheHole()) return value;
          // If value is the hole do the general lookup.
        }
      }
    } else if (FLAG_smi_only_arrays && args.at<Object>(1)->IsSmi()) {
      // JSObject without a string key. If the key is a Smi, check for a
      // definite out-of-bounds access to elements, which is a strong indicator
      // that subsequent accesses will also call the runtime. Proactively
      // transition elements to FAST_*_ELEMENTS to avoid excessive boxing of
      // doubles for those future calls in the case that the elements would
      // become FAST_DOUBLE_ELEMENTS.
      Handle<JSObject> js_object(args.at<JSObject>(0));
      ElementsKind elements_kind = js_object->GetElementsKind();
      if (IsFastElementsKind(elements_kind) &&
          !IsFastObjectElementsKind(elements_kind)) {
        FixedArrayBase* elements = js_object->elements();
        if (args.at<Smi>(1)->value() >= elements->length()) {
          if (IsFastHoleyElementsKind(elements_kind)) {
            elements_kind = FAST_HOLEY_ELEMENTS;
          } else {
            elements_kind = FAST_ELEMENTS;
          }
          MaybeObject* maybe_object = TransitionElements(js_object,
                                                         elements_kind,
                                                         isolate);
          if (maybe_object->IsFailure()) return maybe_object;
        }
      }
    }
  } else if (args[0]->IsString() && args[1]->IsSmi()) {
    // Fast case for string indexing using [] with a smi index.
    HandleScope scope(isolate);
    Handle<String> str = args.at<String>(0);
    int index = args.smi_at(1);
    if (index >= 0 && index < str->length()) {
      Handle<Object> result = GetCharAt(str, index);
      return *result;
    }
  }

  // Fall back to GetObjectProperty.
  return Runtime::GetObjectProperty(isolate,
                                    args.at<Object>(0),
                                    args.at<Object>(1));
}


static bool IsValidAccessor(Handle<Object> obj) {
  return obj->IsUndefined() || obj->IsSpecFunction() || obj->IsNull();
}


// Implements part of 8.12.9 DefineOwnProperty.
// There are 3 cases that lead here:
// Step 4b - define a new accessor property.
// Steps 9c & 12 - replace an existing data property with an accessor property.
// Step 12 - update an existing accessor property with an accessor or generic
//           descriptor.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DefineOrRedefineAccessorProperty) {
  ASSERT(args.length() == 5);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  RUNTIME_ASSERT(!obj->IsNull());
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);
  CONVERT_ARG_HANDLE_CHECKED(Object, getter, 2);
  RUNTIME_ASSERT(IsValidAccessor(getter));
  CONVERT_ARG_HANDLE_CHECKED(Object, setter, 3);
  RUNTIME_ASSERT(IsValidAccessor(setter));
  CONVERT_SMI_ARG_CHECKED(unchecked, 4);
  RUNTIME_ASSERT((unchecked & ~(READ_ONLY | DONT_ENUM | DONT_DELETE)) == 0);
  PropertyAttributes attr = static_cast<PropertyAttributes>(unchecked);

  bool fast = obj->HasFastProperties();
  JSObject::DefineAccessor(obj, name, getter, setter, attr);
  if (fast) JSObject::TransformToFastProperties(obj, 0);
  return isolate->heap()->undefined_value();
}

// Implements part of 8.12.9 DefineOwnProperty.
// There are 3 cases that lead here:
// Step 4a - define a new data property.
// Steps 9b & 12 - replace an existing accessor property with a data property.
// Step 12 - update an existing data property with a data or generic
//           descriptor.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DefineOrRedefineDataProperty) {
  ASSERT(args.length() == 4);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, js_object, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);
  CONVERT_ARG_HANDLE_CHECKED(Object, obj_value, 2);
  CONVERT_SMI_ARG_CHECKED(unchecked, 3);
  RUNTIME_ASSERT((unchecked & ~(READ_ONLY | DONT_ENUM | DONT_DELETE)) == 0);
  PropertyAttributes attr = static_cast<PropertyAttributes>(unchecked);

  LookupResult result(isolate);
  js_object->LocalLookupRealNamedProperty(*name, &result);

  // Special case for callback properties.
  if (result.IsFound() && result.type() == CALLBACKS) {
    Object* callback = result.GetCallbackObject();
    // To be compatible with Safari we do not change the value on API objects
    // in Object.defineProperty(). Firefox disagrees here, and actually changes
    // the value.
    if (callback->IsAccessorInfo()) {
      return isolate->heap()->undefined_value();
    }
    // Avoid redefining foreign callback as data property, just use the stored
    // setter to update the value instead.
    // TODO(mstarzinger): So far this only works if property attributes don't
    // change, this should be fixed once we cleanup the underlying code.
    if (callback->IsForeign() && result.GetAttributes() == attr) {
      return js_object->SetPropertyWithCallback(callback,
                                                *name,
                                                *obj_value,
                                                result.holder(),
                                                kStrictMode);
    }
  }

  // Take special care when attributes are different and there is already
  // a property. For simplicity we normalize the property which enables us
  // to not worry about changing the instance_descriptor and creating a new
  // map. The current version of SetObjectProperty does not handle attributes
  // correctly in the case where a property is a field and is reset with
  // new attributes.
  if (result.IsProperty() &&
      (attr != result.GetAttributes() || result.type() == CALLBACKS)) {
    // New attributes - normalize to avoid writing to instance descriptor
    if (js_object->IsJSGlobalProxy()) {
      // Since the result is a property, the prototype will exist so
      // we don't have to check for null.
      js_object = Handle<JSObject>(JSObject::cast(js_object->GetPrototype()));
    }
    JSObject::NormalizeProperties(js_object, CLEAR_INOBJECT_PROPERTIES, 0);
    // Use IgnoreAttributes version since a readonly property may be
    // overridden and SetProperty does not allow this.
    return js_object->SetLocalPropertyIgnoreAttributes(*name,
                                                       *obj_value,
                                                       attr);
  }

  return Runtime::ForceSetObjectProperty(isolate,
                                         js_object,
                                         name,
                                         obj_value,
                                         attr);
}


MaybeObject* Runtime::SetObjectProperty(Isolate* isolate,
                                        Handle<Object> object,
                                        Handle<Object> key,
                                        Handle<Object> value,
                                        PropertyAttributes attr,
                                        StrictModeFlag strict_mode) {
  SetPropertyMode set_mode = attr == NONE ? SET_PROPERTY : DEFINE_PROPERTY;
  HandleScope scope(isolate);

  if (object->IsUndefined() || object->IsNull()) {
    Handle<Object> args[2] = { key, object };
    Handle<Object> error =
        isolate->factory()->NewTypeError("non_object_property_store",
                                         HandleVector(args, 2));
    return isolate->Throw(*error);
  }

  if (object->IsJSProxy()) {
    bool has_pending_exception = false;
    Handle<Object> name = Execution::ToString(key, &has_pending_exception);
    if (has_pending_exception) return Failure::Exception();
    return JSProxy::cast(*object)->SetProperty(
        String::cast(*name), *value, attr, strict_mode);
  }

  // If the object isn't a JavaScript object, we ignore the store.
  if (!object->IsJSObject()) return *value;

  Handle<JSObject> js_object = Handle<JSObject>::cast(object);

  // Check if the given key is an array index.
  uint32_t index;
  if (key->ToArrayIndex(&index)) {
    // In Firefox/SpiderMonkey, Safari and Opera you can access the characters
    // of a string using [] notation.  We need to support this too in
    // JavaScript.
    // In the case of a String object we just need to redirect the assignment to
    // the underlying string if the index is in range.  Since the underlying
    // string does nothing with the assignment then we can ignore such
    // assignments.
    if (js_object->IsStringObjectWithCharacterAt(index)) {
      return *value;
    }

    js_object->ValidateElements();
    Handle<Object> result = JSObject::SetElement(
        js_object, index, value, attr, strict_mode, set_mode);
    js_object->ValidateElements();
    if (result.is_null()) return Failure::Exception();
    return *value;
  }

  if (key->IsString()) {
    Handle<Object> result;
    if (Handle<String>::cast(key)->AsArrayIndex(&index)) {
      result = JSObject::SetElement(
          js_object, index, value, attr, strict_mode, set_mode);
    } else {
      Handle<String> key_string = Handle<String>::cast(key);
      key_string->TryFlatten();
      result = JSReceiver::SetProperty(
          js_object, key_string, value, attr, strict_mode);
    }
    if (result.is_null()) return Failure::Exception();
    return *value;
  }

  // Call-back into JavaScript to convert the key to a string.
  bool has_pending_exception = false;
  Handle<Object> converted = Execution::ToString(key, &has_pending_exception);
  if (has_pending_exception) return Failure::Exception();
  Handle<String> name = Handle<String>::cast(converted);

  if (name->AsArrayIndex(&index)) {
    return js_object->SetElement(
        index, *value, attr, strict_mode, true, set_mode);
  } else {
    return js_object->SetProperty(*name, *value, attr, strict_mode);
  }
}


MaybeObject* Runtime::ForceSetObjectProperty(Isolate* isolate,
                                             Handle<JSObject> js_object,
                                             Handle<Object> key,
                                             Handle<Object> value,
                                             PropertyAttributes attr) {
  HandleScope scope(isolate);

  // Check if the given key is an array index.
  uint32_t index;
  if (key->ToArrayIndex(&index)) {
    // In Firefox/SpiderMonkey, Safari and Opera you can access the characters
    // of a string using [] notation.  We need to support this too in
    // JavaScript.
    // In the case of a String object we just need to redirect the assignment to
    // the underlying string if the index is in range.  Since the underlying
    // string does nothing with the assignment then we can ignore such
    // assignments.
    if (js_object->IsStringObjectWithCharacterAt(index)) {
      return *value;
    }

    return js_object->SetElement(
        index, *value, attr, kNonStrictMode, false, DEFINE_PROPERTY);
  }

  if (key->IsString()) {
    if (Handle<String>::cast(key)->AsArrayIndex(&index)) {
      return js_object->SetElement(
          index, *value, attr, kNonStrictMode, false, DEFINE_PROPERTY);
    } else {
      Handle<String> key_string = Handle<String>::cast(key);
      key_string->TryFlatten();
      return js_object->SetLocalPropertyIgnoreAttributes(*key_string,
                                                         *value,
                                                         attr);
    }
  }

  // Call-back into JavaScript to convert the key to a string.
  bool has_pending_exception = false;
  Handle<Object> converted = Execution::ToString(key, &has_pending_exception);
  if (has_pending_exception) return Failure::Exception();
  Handle<String> name = Handle<String>::cast(converted);

  if (name->AsArrayIndex(&index)) {
    return js_object->SetElement(
        index, *value, attr, kNonStrictMode, false, DEFINE_PROPERTY);
  } else {
    return js_object->SetLocalPropertyIgnoreAttributes(*name, *value, attr);
  }
}


MaybeObject* Runtime::ForceDeleteObjectProperty(Isolate* isolate,
                                                Handle<JSReceiver> receiver,
                                                Handle<Object> key) {
  HandleScope scope(isolate);

  // Check if the given key is an array index.
  uint32_t index;
  if (key->ToArrayIndex(&index)) {
    // In Firefox/SpiderMonkey, Safari and Opera you can access the
    // characters of a string using [] notation.  In the case of a
    // String object we just need to redirect the deletion to the
    // underlying string if the index is in range.  Since the
    // underlying string does nothing with the deletion, we can ignore
    // such deletions.
    if (receiver->IsStringObjectWithCharacterAt(index)) {
      return isolate->heap()->true_value();
    }

    return receiver->DeleteElement(index, JSReceiver::FORCE_DELETION);
  }

  Handle<String> key_string;
  if (key->IsString()) {
    key_string = Handle<String>::cast(key);
  } else {
    // Call-back into JavaScript to convert the key to a string.
    bool has_pending_exception = false;
    Handle<Object> converted = Execution::ToString(key, &has_pending_exception);
    if (has_pending_exception) return Failure::Exception();
    key_string = Handle<String>::cast(converted);
  }

  key_string->TryFlatten();
  return receiver->DeleteProperty(*key_string, JSReceiver::FORCE_DELETION);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetProperty) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 4 || args.length() == 5);

  Handle<Object> object = args.at<Object>(0);
  Handle<Object> key = args.at<Object>(1);
  Handle<Object> value = args.at<Object>(2);
  CONVERT_SMI_ARG_CHECKED(unchecked_attributes, 3);
  RUNTIME_ASSERT(
      (unchecked_attributes & ~(READ_ONLY | DONT_ENUM | DONT_DELETE)) == 0);
  // Compute attributes.
  PropertyAttributes attributes =
      static_cast<PropertyAttributes>(unchecked_attributes);

  StrictModeFlag strict_mode = kNonStrictMode;
  if (args.length() == 5) {
    CONVERT_STRICT_MODE_ARG_CHECKED(strict_mode_flag, 4);
    strict_mode = strict_mode_flag;
  }

  return Runtime::SetObjectProperty(isolate,
                                    object,
                                    key,
                                    value,
                                    attributes,
                                    strict_mode);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsSmiToDouble) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 1);
  Handle<Object> object = args.at<Object>(0);
  if (object->IsJSObject()) {
    Handle<JSObject> js_object(Handle<JSObject>::cast(object));
    ElementsKind new_kind = js_object->HasFastHoleyElements()
        ? FAST_HOLEY_DOUBLE_ELEMENTS
        : FAST_DOUBLE_ELEMENTS;
    return TransitionElements(object, new_kind, isolate);
  } else {
    return *object;
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsDoubleToObject) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 1);
  Handle<Object> object = args.at<Object>(0);
  if (object->IsJSObject()) {
    Handle<JSObject> js_object(Handle<JSObject>::cast(object));
    ElementsKind new_kind = js_object->HasFastHoleyElements()
        ? FAST_HOLEY_ELEMENTS
        : FAST_ELEMENTS;
    return TransitionElements(object, new_kind, isolate);
  } else {
    return *object;
  }
}


// Set the native flag on the function.
// This is used to decide if we should transform null and undefined
// into the global object when doing call and apply.
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetNativeFlag) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 1);

  Handle<Object> object = args.at<Object>(0);

  if (object->IsJSFunction()) {
    JSFunction* func = JSFunction::cast(*object);
    func->shared()->set_native(true);
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StoreArrayLiteralElement) {
  RUNTIME_ASSERT(args.length() == 5);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
  CONVERT_SMI_ARG_CHECKED(store_index, 1);
  Handle<Object> value = args.at<Object>(2);
  CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 3);
  CONVERT_SMI_ARG_CHECKED(literal_index, 4);
  HandleScope scope;

  Object* raw_boilerplate_object = literals->get(literal_index);
  Handle<JSArray> boilerplate_object(JSArray::cast(raw_boilerplate_object));
  ElementsKind elements_kind = object->GetElementsKind();
  ASSERT(IsFastElementsKind(elements_kind));
  // Smis should never trigger transitions.
  ASSERT(!value->IsSmi());

  if (value->IsNumber()) {
    ASSERT(IsFastSmiElementsKind(elements_kind));
    ElementsKind transitioned_kind = IsFastHoleyElementsKind(elements_kind)
        ? FAST_HOLEY_DOUBLE_ELEMENTS
        : FAST_DOUBLE_ELEMENTS;
    if (IsMoreGeneralElementsKindTransition(
            boilerplate_object->GetElementsKind(),
            transitioned_kind)) {
      JSObject::TransitionElementsKind(boilerplate_object, transitioned_kind);
    }
    JSObject::TransitionElementsKind(object, transitioned_kind);
    ASSERT(IsFastDoubleElementsKind(object->GetElementsKind()));
    FixedDoubleArray* double_array = FixedDoubleArray::cast(object->elements());
    HeapNumber* number = HeapNumber::cast(*value);
    double_array->set(store_index, number->Number());
  } else {
    ASSERT(IsFastSmiElementsKind(elements_kind) ||
           IsFastDoubleElementsKind(elements_kind));
    ElementsKind transitioned_kind = IsFastHoleyElementsKind(elements_kind)
        ? FAST_HOLEY_ELEMENTS
        : FAST_ELEMENTS;
    JSObject::TransitionElementsKind(object, transitioned_kind);
    if (IsMoreGeneralElementsKindTransition(
            boilerplate_object->GetElementsKind(),
            transitioned_kind)) {
      JSObject::TransitionElementsKind(boilerplate_object, transitioned_kind);
    }
    FixedArray* object_array = FixedArray::cast(object->elements());
    object_array->set(store_index, *value);
  }
  return *object;
}


// Check whether debugger and is about to step into the callback that is passed
// to a built-in function such as Array.forEach.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugCallbackSupportsStepping) {
  if (!isolate->IsDebuggerActive()) return isolate->heap()->false_value();
  CONVERT_ARG_CHECKED(Object, callback, 0);
  // We do not step into the callback if it's a builtin or not even a function.
  if (!callback->IsJSFunction() || JSFunction::cast(callback)->IsBuiltin()) {
    return isolate->heap()->false_value();
  }
  return isolate->heap()->true_value();
}


// Set one shot breakpoints for the callback function that is passed to a
// built-in function such as Array.forEach to enable stepping into the callback.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPrepareStepInIfStepping) {
  Debug* debug = isolate->debug();
  if (!debug->IsStepping()) return NULL;
  CONVERT_ARG_CHECKED(Object, callback, 0);
  HandleScope scope(isolate);
  Handle<SharedFunctionInfo> shared_info(JSFunction::cast(callback)->shared());
  // When leaving the callback, step out has been activated, but not performed
  // if we do not leave the builtin.  To be able to step into the callback
  // again, we need to clear the step out at this point.
  debug->ClearStepOut();
  debug->FloodWithOneShot(shared_info);
  return NULL;
}


// Set a local property, even if it is READ_ONLY.  If the property does not
// exist, it will be added with attributes NONE.
RUNTIME_FUNCTION(MaybeObject*, Runtime_IgnoreAttributesAndSetProperty) {
  NoHandleAllocation ha;
  RUNTIME_ASSERT(args.length() == 3 || args.length() == 4);
  CONVERT_ARG_CHECKED(JSObject, object, 0);
  CONVERT_ARG_CHECKED(String, name, 1);
  // Compute attributes.
  PropertyAttributes attributes = NONE;
  if (args.length() == 4) {
    CONVERT_SMI_ARG_CHECKED(unchecked_value, 3);
    // Only attribute bits should be set.
    RUNTIME_ASSERT(
        (unchecked_value & ~(READ_ONLY | DONT_ENUM | DONT_DELETE)) == 0);
    attributes = static_cast<PropertyAttributes>(unchecked_value);
  }

  return object->
      SetLocalPropertyIgnoreAttributes(name, args[2], attributes);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DeleteProperty) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);

  CONVERT_ARG_CHECKED(JSReceiver, object, 0);
  CONVERT_ARG_CHECKED(String, key, 1);
  CONVERT_STRICT_MODE_ARG_CHECKED(strict_mode, 2);
  return object->DeleteProperty(key, (strict_mode == kStrictMode)
                                      ? JSReceiver::STRICT_DELETION
                                      : JSReceiver::NORMAL_DELETION);
}


static Object* HasLocalPropertyImplementation(Isolate* isolate,
                                              Handle<JSObject> object,
                                              Handle<String> key) {
  if (object->HasLocalProperty(*key)) return isolate->heap()->true_value();
  // Handle hidden prototypes.  If there's a hidden prototype above this thing
  // then we have to check it for properties, because they are supposed to
  // look like they are on this object.
  Handle<Object> proto(object->GetPrototype());
  if (proto->IsJSObject() &&
      Handle<JSObject>::cast(proto)->map()->is_hidden_prototype()) {
    return HasLocalPropertyImplementation(isolate,
                                          Handle<JSObject>::cast(proto),
                                          key);
  }
  return isolate->heap()->false_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_HasLocalProperty) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(String, key, 1);

  uint32_t index;
  const bool key_is_array_index = key->AsArrayIndex(&index);

  Object* obj = args[0];
  // Only JS objects can have properties.
  if (obj->IsJSObject()) {
    JSObject* object = JSObject::cast(obj);
    // Fast case: either the key is a real named property or it is not
    // an array index and there are no interceptors or hidden
    // prototypes.
    if (object->HasRealNamedProperty(key)) return isolate->heap()->true_value();
    Map* map = object->map();
    if (!key_is_array_index &&
        !map->has_named_interceptor() &&
        !HeapObject::cast(map->prototype())->map()->is_hidden_prototype()) {
      return isolate->heap()->false_value();
    }
    // Slow case.
    HandleScope scope(isolate);
    return HasLocalPropertyImplementation(isolate,
                                          Handle<JSObject>(object),
                                          Handle<String>(key));
  } else if (obj->IsString() && key_is_array_index) {
    // Well, there is one exception:  Handle [] on strings.
    String* string = String::cast(obj);
    if (index < static_cast<uint32_t>(string->length())) {
      return isolate->heap()->true_value();
    }
  }
  return isolate->heap()->false_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_HasProperty) {
  NoHandleAllocation na;
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSReceiver, receiver, 0);
  CONVERT_ARG_CHECKED(String, key, 1);

  bool result = receiver->HasProperty(key);
  if (isolate->has_pending_exception()) return Failure::Exception();
  return isolate->heap()->ToBoolean(result);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_HasElement) {
  NoHandleAllocation na;
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSReceiver, receiver, 0);
  CONVERT_SMI_ARG_CHECKED(index, 1);

  bool result = receiver->HasElement(index);
  if (isolate->has_pending_exception()) return Failure::Exception();
  return isolate->heap()->ToBoolean(result);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IsPropertyEnumerable) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(JSObject, object, 0);
  CONVERT_ARG_CHECKED(String, key, 1);

  uint32_t index;
  if (key->AsArrayIndex(&index)) {
    JSObject::LocalElementType type = object->HasLocalElement(index);
    switch (type) {
      case JSObject::UNDEFINED_ELEMENT:
      case JSObject::STRING_CHARACTER_ELEMENT:
        return isolate->heap()->false_value();
      case JSObject::INTERCEPTED_ELEMENT:
      case JSObject::FAST_ELEMENT:
        return isolate->heap()->true_value();
      case JSObject::DICTIONARY_ELEMENT: {
        if (object->IsJSGlobalProxy()) {
          Object* proto = object->GetPrototype();
          if (proto->IsNull()) {
            return isolate->heap()->false_value();
          }
          ASSERT(proto->IsJSGlobalObject());
          object = JSObject::cast(proto);
        }
        FixedArray* elements = FixedArray::cast(object->elements());
        SeededNumberDictionary* dictionary = NULL;
        if (elements->map() ==
            isolate->heap()->non_strict_arguments_elements_map()) {
          dictionary = SeededNumberDictionary::cast(elements->get(1));
        } else {
          dictionary = SeededNumberDictionary::cast(elements);
        }
        int entry = dictionary->FindEntry(index);
        ASSERT(entry != SeededNumberDictionary::kNotFound);
        PropertyDetails details = dictionary->DetailsAt(entry);
        return isolate->heap()->ToBoolean(!details.IsDontEnum());
      }
    }
  }

  PropertyAttributes att = object->GetLocalPropertyAttribute(key);
  return isolate->heap()->ToBoolean(att != ABSENT && (att & DONT_ENUM) == 0);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetPropertyNames) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, object, 0);
  bool threw = false;
  Handle<JSArray> result = GetKeysFor(object, &threw);
  if (threw) return Failure::Exception();
  return *result;
}


// Returns either a FixedArray as Runtime_GetPropertyNames,
// or, if the given object has an enum cache that contains
// all enumerable properties of the object and its prototypes
// have none, the map of the object. This is used to speed up
// the check for deletions during a for-in.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetPropertyNamesFast) {
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSReceiver, raw_object, 0);

  if (raw_object->IsSimpleEnum()) return raw_object->map();

  HandleScope scope(isolate);
  Handle<JSReceiver> object(raw_object);
  bool threw = false;
  Handle<FixedArray> content =
      GetKeysInFixedArrayFor(object, INCLUDE_PROTOS, &threw);
  if (threw) return Failure::Exception();

  // Test again, since cache may have been built by preceding call.
  if (object->IsSimpleEnum()) return object->map();

  return *content;
}


// Find the length of the prototype chain that is to to handled as one. If a
// prototype object is hidden it is to be viewed as part of the the object it
// is prototype for.
static int LocalPrototypeChainLength(JSObject* obj) {
  int count = 1;
  Object* proto = obj->GetPrototype();
  while (proto->IsJSObject() &&
         JSObject::cast(proto)->map()->is_hidden_prototype()) {
    count++;
    proto = JSObject::cast(proto)->GetPrototype();
  }
  return count;
}


// Return the names of the local named properties.
// args[0]: object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLocalPropertyNames) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  if (!args[0]->IsJSObject()) {
    return isolate->heap()->undefined_value();
  }
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);

  // Skip the global proxy as it has no properties and always delegates to the
  // real global object.
  if (obj->IsJSGlobalProxy()) {
    // Only collect names if access is permitted.
    if (obj->IsAccessCheckNeeded() &&
        !isolate->MayNamedAccess(*obj,
                                 isolate->heap()->undefined_value(),
                                 v8::ACCESS_KEYS)) {
      isolate->ReportFailedAccessCheck(*obj, v8::ACCESS_KEYS);
      return *isolate->factory()->NewJSArray(0);
    }
    obj = Handle<JSObject>(JSObject::cast(obj->GetPrototype()));
  }

  // Find the number of objects making up this.
  int length = LocalPrototypeChainLength(*obj);

  // Find the number of local properties for each of the objects.
  ScopedVector<int> local_property_count(length);
  int total_property_count = 0;
  Handle<JSObject> jsproto = obj;
  for (int i = 0; i < length; i++) {
    // Only collect names if access is permitted.
    if (jsproto->IsAccessCheckNeeded() &&
        !isolate->MayNamedAccess(*jsproto,
                                 isolate->heap()->undefined_value(),
                                 v8::ACCESS_KEYS)) {
      isolate->ReportFailedAccessCheck(*jsproto, v8::ACCESS_KEYS);
      return *isolate->factory()->NewJSArray(0);
    }
    int n;
    n = jsproto->NumberOfLocalProperties();
    local_property_count[i] = n;
    total_property_count += n;
    if (i < length - 1) {
      jsproto = Handle<JSObject>(JSObject::cast(jsproto->GetPrototype()));
    }
  }

  // Allocate an array with storage for all the property names.
  Handle<FixedArray> names =
      isolate->factory()->NewFixedArray(total_property_count);

  // Get the property names.
  jsproto = obj;
  int proto_with_hidden_properties = 0;
  int next_copy_index = 0;
  for (int i = 0; i < length; i++) {
    jsproto->GetLocalPropertyNames(*names, next_copy_index);
    next_copy_index += local_property_count[i];
    if (jsproto->HasHiddenProperties()) {
      proto_with_hidden_properties++;
    }
    if (i < length - 1) {
      jsproto = Handle<JSObject>(JSObject::cast(jsproto->GetPrototype()));
    }
  }

  // Filter out name of hidden propeties object.
  if (proto_with_hidden_properties > 0) {
    Handle<FixedArray> old_names = names;
    names = isolate->factory()->NewFixedArray(
        names->length() - proto_with_hidden_properties);
    int dest_pos = 0;
    for (int i = 0; i < total_property_count; i++) {
      Object* name = old_names->get(i);
      if (name == isolate->heap()->hidden_symbol()) {
        continue;
      }
      names->set(dest_pos++, name);
    }
  }

  return *isolate->factory()->NewJSArrayWithElements(names);
}


// Return the names of the local indexed properties.
// args[0]: object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLocalElementNames) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  if (!args[0]->IsJSObject()) {
    return isolate->heap()->undefined_value();
  }
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);

  int n = obj->NumberOfLocalElements(static_cast<PropertyAttributes>(NONE));
  Handle<FixedArray> names = isolate->factory()->NewFixedArray(n);
  obj->GetLocalElementKeys(*names, static_cast<PropertyAttributes>(NONE));
  return *isolate->factory()->NewJSArrayWithElements(names);
}


// Return information on whether an object has a named or indexed interceptor.
// args[0]: object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetInterceptorInfo) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  if (!args[0]->IsJSObject()) {
    return Smi::FromInt(0);
  }
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);

  int result = 0;
  if (obj->HasNamedInterceptor()) result |= 2;
  if (obj->HasIndexedInterceptor()) result |= 1;

  return Smi::FromInt(result);
}


// Return property names from named interceptor.
// args[0]: object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetNamedInterceptorPropertyNames) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);

  if (obj->HasNamedInterceptor()) {
    v8::Handle<v8::Array> result = GetKeysForNamedInterceptor(obj, obj);
    if (!result.IsEmpty()) return *v8::Utils::OpenHandle(*result);
  }
  return isolate->heap()->undefined_value();
}


// Return element names from indexed interceptor.
// args[0]: object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetIndexedInterceptorElementNames) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);

  if (obj->HasIndexedInterceptor()) {
    v8::Handle<v8::Array> result = GetKeysForIndexedInterceptor(obj, obj);
    if (!result.IsEmpty()) return *v8::Utils::OpenHandle(*result);
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_LocalKeys) {
  ASSERT_EQ(args.length(), 1);
  CONVERT_ARG_CHECKED(JSObject, raw_object, 0);
  HandleScope scope(isolate);
  Handle<JSObject> object(raw_object);

  if (object->IsJSGlobalProxy()) {
    // Do access checks before going to the global object.
    if (object->IsAccessCheckNeeded() &&
        !isolate->MayNamedAccess(*object, isolate->heap()->undefined_value(),
                             v8::ACCESS_KEYS)) {
      isolate->ReportFailedAccessCheck(*object, v8::ACCESS_KEYS);
      return *isolate->factory()->NewJSArray(0);
    }

    Handle<Object> proto(object->GetPrototype());
    // If proxy is detached we simply return an empty array.
    if (proto->IsNull()) return *isolate->factory()->NewJSArray(0);
    object = Handle<JSObject>::cast(proto);
  }

  bool threw = false;
  Handle<FixedArray> contents =
      GetKeysInFixedArrayFor(object, LOCAL_ONLY, &threw);
  if (threw) return Failure::Exception();

  // Some fast paths through GetKeysInFixedArrayFor reuse a cached
  // property array and since the result is mutable we have to create
  // a fresh clone on each invocation.
  int length = contents->length();
  Handle<FixedArray> copy = isolate->factory()->NewFixedArray(length);
  for (int i = 0; i < length; i++) {
    Object* entry = contents->get(i);
    if (entry->IsString()) {
      copy->set(i, entry);
    } else {
      ASSERT(entry->IsNumber());
      HandleScope scope(isolate);
      Handle<Object> entry_handle(entry, isolate);
      Handle<Object> entry_str =
          isolate->factory()->NumberToString(entry_handle);
      copy->set(i, *entry_str);
    }
  }
  return *isolate->factory()->NewJSArrayWithElements(copy);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetArgumentsProperty) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  // Compute the frame holding the arguments.
  JavaScriptFrameIterator it(isolate);
  it.AdvanceToArgumentsFrame();
  JavaScriptFrame* frame = it.frame();

  // Get the actual number of provided arguments.
  const uint32_t n = frame->ComputeParametersCount();

  // Try to convert the key to an index. If successful and within
  // index return the the argument from the frame.
  uint32_t index;
  if (args[0]->ToArrayIndex(&index) && index < n) {
    return frame->GetParameter(index);
  }

  // Convert the key to a string.
  HandleScope scope(isolate);
  bool exception = false;
  Handle<Object> converted =
      Execution::ToString(args.at<Object>(0), &exception);
  if (exception) return Failure::Exception();
  Handle<String> key = Handle<String>::cast(converted);

  // Try to convert the string key into an array index.
  if (key->AsArrayIndex(&index)) {
    if (index < n) {
      return frame->GetParameter(index);
    } else {
      return isolate->initial_object_prototype()->GetElement(index);
    }
  }

  // Handle special arguments properties.
  if (key->Equals(isolate->heap()->length_symbol())) return Smi::FromInt(n);
  if (key->Equals(isolate->heap()->callee_symbol())) {
    Object* function = frame->function();
    if (function->IsJSFunction() &&
        !JSFunction::cast(function)->shared()->is_classic_mode()) {
      return isolate->Throw(*isolate->factory()->NewTypeError(
          "strict_arguments_callee", HandleVector<Object>(NULL, 0)));
    }
    return function;
  }

  // Lookup in the initial Object.prototype object.
  return isolate->initial_object_prototype()->GetProperty(*key);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ToFastProperties) {
  ASSERT(args.length() == 1);
  Object* object = args[0];
  return (object->IsJSObject() && !object->IsGlobalObject())
      ? JSObject::cast(object)->TransformToFastProperties(0)
      : object;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ToSlowProperties) {
  ASSERT(args.length() == 1);
  Object* obj = args[0];
  return (obj->IsJSObject() && !obj->IsJSGlobalProxy())
      ? JSObject::cast(obj)->NormalizeProperties(CLEAR_INOBJECT_PROPERTIES, 0)
      : obj;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ToBool) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  return args[0]->ToBoolean();
}


// Returns the type string of a value; see ECMA-262, 11.4.3 (p 47).
// Possible optimizations: put the type string into the oddballs.
RUNTIME_FUNCTION(MaybeObject*, Runtime_Typeof) {
  NoHandleAllocation ha;

  Object* obj = args[0];
  if (obj->IsNumber()) return isolate->heap()->number_symbol();
  HeapObject* heap_obj = HeapObject::cast(obj);

  // typeof an undetectable object is 'undefined'
  if (heap_obj->map()->is_undetectable()) {
    return isolate->heap()->undefined_symbol();
  }

  InstanceType instance_type = heap_obj->map()->instance_type();
  if (instance_type < FIRST_NONSTRING_TYPE) {
    return isolate->heap()->string_symbol();
  }

  switch (instance_type) {
    case ODDBALL_TYPE:
      if (heap_obj->IsTrue() || heap_obj->IsFalse()) {
        return isolate->heap()->boolean_symbol();
      }
      if (heap_obj->IsNull()) {
        return FLAG_harmony_typeof
            ? isolate->heap()->null_symbol()
            : isolate->heap()->object_symbol();
      }
      ASSERT(heap_obj->IsUndefined());
      return isolate->heap()->undefined_symbol();
    case JS_FUNCTION_TYPE:
    case JS_FUNCTION_PROXY_TYPE:
      return isolate->heap()->function_symbol();
    default:
      // For any kind of object not handled above, the spec rule for
      // host objects gives that it is okay to return "object"
      return isolate->heap()->object_symbol();
  }
}


static bool AreDigits(const char*s, int from, int to) {
  for (int i = from; i < to; i++) {
    if (s[i] < '0' || s[i] > '9') return false;
  }

  return true;
}


static int ParseDecimalInteger(const char*s, int from, int to) {
  ASSERT(to - from < 10);  // Overflow is not possible.
  ASSERT(from < to);
  int d = s[from] - '0';

  for (int i = from + 1; i < to; i++) {
    d = 10 * d + (s[i] - '0');
  }

  return d;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringToNumber) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(String, subject, 0);
  subject->TryFlatten();

  // Fast case: short integer or some sorts of junk values.
  int len = subject->length();
  if (subject->IsSeqAsciiString()) {
    if (len == 0) return Smi::FromInt(0);

    char const* data = SeqAsciiString::cast(subject)->GetChars();
    bool minus = (data[0] == '-');
    int start_pos = (minus ? 1 : 0);

    if (start_pos == len) {
      return isolate->heap()->nan_value();
    } else if (data[start_pos] > '9') {
      // Fast check for a junk value. A valid string may start from a
      // whitespace, a sign ('+' or '-'), the decimal point, a decimal digit or
      // the 'I' character ('Infinity'). All of that have codes not greater than
      // '9' except 'I'.
      if (data[start_pos] != 'I') {
        return isolate->heap()->nan_value();
      }
    } else if (len - start_pos < 10 && AreDigits(data, start_pos, len)) {
      // The maximal/minimal smi has 10 digits. If the string has less digits we
      // know it will fit into the smi-data type.
      int d = ParseDecimalInteger(data, start_pos, len);
      if (minus) {
        if (d == 0) return isolate->heap()->minus_zero_value();
        d = -d;
      } else if (!subject->HasHashCode() &&
                 len <= String::kMaxArrayIndexSize &&
                 (len == 1 || data[0] != '0')) {
        // String hash is not calculated yet but all the data are present.
        // Update the hash field to speed up sequential convertions.
        uint32_t hash = StringHasher::MakeArrayIndexHash(d, len);
#ifdef DEBUG
        subject->Hash();  // Force hash calculation.
        ASSERT_EQ(static_cast<int>(subject->hash_field()),
                  static_cast<int>(hash));
#endif
        subject->set_hash_field(hash);
      }
      return Smi::FromInt(d);
    }
  }

  // Slower case.
  return isolate->heap()->NumberFromDouble(
      StringToDouble(isolate->unicode_cache(), subject, ALLOW_HEX));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringFromCharCodeArray) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSArray, codes, 0);
  int length = Smi::cast(codes->length())->value();

  // Check if the string can be ASCII.
  int i;
  for (i = 0; i < length; i++) {
    Object* element;
    { MaybeObject* maybe_element = codes->GetElement(i);
      // We probably can't get an exception here, but just in order to enforce
      // the checking of inputs in the runtime calls we check here.
      if (!maybe_element->ToObject(&element)) return maybe_element;
    }
    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
    if ((chr & 0xffff) > String::kMaxAsciiCharCode)
      break;
  }

  MaybeObject* maybe_object = NULL;
  if (i == length) {  // The string is ASCII.
    maybe_object = isolate->heap()->AllocateRawAsciiString(length);
  } else {  // The string is not ASCII.
    maybe_object = isolate->heap()->AllocateRawTwoByteString(length);
  }

  Object* object = NULL;
  if (!maybe_object->ToObject(&object)) return maybe_object;
  String* result = String::cast(object);
  for (int i = 0; i < length; i++) {
    Object* element;
    { MaybeObject* maybe_element = codes->GetElement(i);
      if (!maybe_element->ToObject(&element)) return maybe_element;
    }
    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
    result->Set(i, chr & 0xffff);
  }
  return result;
}


// kNotEscaped is generated by the following:
//
// #!/bin/perl
// for (my $i = 0; $i < 256; $i++) {
//   print "\n" if $i % 16 == 0;
//   my $c = chr($i);
//   my $escaped = 1;
//   $escaped = 0 if $c =~ m#[A-Za-z0-9@*_+./-]#;
//   print $escaped ? "0, " : "1, ";
// }


static bool IsNotEscaped(uint16_t character) {
  // Only for 8 bit characters, the rest are always escaped (in a different way)
  ASSERT(character < 256);
  static const char kNotEscaped[256] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  };
  return kNotEscaped[character] != 0;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_URIEscape) {
  const char hex_chars[] = "0123456789ABCDEF";
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(String, source, 0);

  source->TryFlatten();

  int escaped_length = 0;
  int length = source->length();
  {
    Access<StringInputBuffer> buffer(
        isolate->runtime_state()->string_input_buffer());
    buffer->Reset(source);
    while (buffer->has_more()) {
      uint16_t character = buffer->GetNext();
      if (character >= 256) {
        escaped_length += 6;
      } else if (IsNotEscaped(character)) {
        escaped_length++;
      } else {
        escaped_length += 3;
      }
      // We don't allow strings that are longer than a maximal length.
      ASSERT(String::kMaxLength < 0x7fffffff - 6);  // Cannot overflow.
      if (escaped_length > String::kMaxLength) {
        isolate->context()->mark_out_of_memory();
        return Failure::OutOfMemoryException();
      }
    }
  }
  // No length change implies no change.  Return original string if no change.
  if (escaped_length == length) {
    return source;
  }
  Object* o;
  { MaybeObject* maybe_o =
        isolate->heap()->AllocateRawAsciiString(escaped_length);
    if (!maybe_o->ToObject(&o)) return maybe_o;
  }
  String* destination = String::cast(o);
  int dest_position = 0;

  Access<StringInputBuffer> buffer(
      isolate->runtime_state()->string_input_buffer());
  buffer->Rewind();
  while (buffer->has_more()) {
    uint16_t chr = buffer->GetNext();
    if (chr >= 256) {
      destination->Set(dest_position, '%');
      destination->Set(dest_position+1, 'u');
      destination->Set(dest_position+2, hex_chars[chr >> 12]);
      destination->Set(dest_position+3, hex_chars[(chr >> 8) & 0xf]);
      destination->Set(dest_position+4, hex_chars[(chr >> 4) & 0xf]);
      destination->Set(dest_position+5, hex_chars[chr & 0xf]);
      dest_position += 6;
    } else if (IsNotEscaped(chr)) {
      destination->Set(dest_position, chr);
      dest_position++;
    } else {
      destination->Set(dest_position, '%');
      destination->Set(dest_position+1, hex_chars[chr >> 4]);
      destination->Set(dest_position+2, hex_chars[chr & 0xf]);
      dest_position += 3;
    }
  }
  return destination;
}


static inline int TwoDigitHex(uint16_t character1, uint16_t character2) {
  static const signed char kHexValue['g'] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    0,  1,  2,   3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15 };

  if (character1 > 'f') return -1;
  int hi = kHexValue[character1];
  if (hi == -1) return -1;
  if (character2 > 'f') return -1;
  int lo = kHexValue[character2];
  if (lo == -1) return -1;
  return (hi << 4) + lo;
}


static inline int Unescape(String* source,
                           int i,
                           int length,
                           int* step) {
  uint16_t character = source->Get(i);
  int32_t hi = 0;
  int32_t lo = 0;
  if (character == '%' &&
      i <= length - 6 &&
      source->Get(i + 1) == 'u' &&
      (hi = TwoDigitHex(source->Get(i + 2),
                        source->Get(i + 3))) != -1 &&
      (lo = TwoDigitHex(source->Get(i + 4),
                        source->Get(i + 5))) != -1) {
    *step = 6;
    return (hi << 8) + lo;
  } else if (character == '%' &&
      i <= length - 3 &&
      (lo = TwoDigitHex(source->Get(i + 1),
                        source->Get(i + 2))) != -1) {
    *step = 3;
    return lo;
  } else {
    *step = 1;
    return character;
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_URIUnescape) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(String, source, 0);

  source->TryFlatten();

  bool ascii = true;
  int length = source->length();

  int unescaped_length = 0;
  for (int i = 0; i < length; unescaped_length++) {
    int step;
    if (Unescape(source, i, length, &step) > String::kMaxAsciiCharCode) {
      ascii = false;
    }
    i += step;
  }

  // No length change implies no change.  Return original string if no change.
  if (unescaped_length == length)
    return source;

  Object* o;
  { MaybeObject* maybe_o =
        ascii ?
        isolate->heap()->AllocateRawAsciiString(unescaped_length) :
        isolate->heap()->AllocateRawTwoByteString(unescaped_length);
    if (!maybe_o->ToObject(&o)) return maybe_o;
  }
  String* destination = String::cast(o);

  int dest_position = 0;
  for (int i = 0; i < length; dest_position++) {
    int step;
    destination->Set(dest_position, Unescape(source, i, length, &step));
    i += step;
  }
  return destination;
}


static const unsigned int kQuoteTableLength = 128u;

static const int kJsonQuotesCharactersPerEntry = 8;
static const char* const JsonQuotes =
    "\\u0000  \\u0001  \\u0002  \\u0003  "
    "\\u0004  \\u0005  \\u0006  \\u0007  "
    "\\b      \\t      \\n      \\u000b  "
    "\\f      \\r      \\u000e  \\u000f  "
    "\\u0010  \\u0011  \\u0012  \\u0013  "
    "\\u0014  \\u0015  \\u0016  \\u0017  "
    "\\u0018  \\u0019  \\u001a  \\u001b  "
    "\\u001c  \\u001d  \\u001e  \\u001f  "
    "        !       \\\"      #       "
    "$       %       &       '       "
    "(       )       *       +       "
    ",       -       .       /       "
    "0       1       2       3       "
    "4       5       6       7       "
    "8       9       :       ;       "
    "<       =       >       ?       "
    "@       A       B       C       "
    "D       E       F       G       "
    "H       I       J       K       "
    "L       M       N       O       "
    "P       Q       R       S       "
    "T       U       V       W       "
    "X       Y       Z       [       "
    "\\\\      ]       ^       _       "
    "`       a       b       c       "
    "d       e       f       g       "
    "h       i       j       k       "
    "l       m       n       o       "
    "p       q       r       s       "
    "t       u       v       w       "
    "x       y       z       {       "
    "|       }       ~       \177       ";


// For a string that is less than 32k characters it should always be
// possible to allocate it in new space.
static const int kMaxGuaranteedNewSpaceString = 32 * 1024;


// Doing JSON quoting cannot make the string more than this many times larger.
static const int kJsonQuoteWorstCaseBlowup = 6;

static const int kSpaceForQuotesAndComma = 3;
static const int kSpaceForBrackets = 2;

// Covers the entire ASCII range (all other characters are unchanged by JSON
// quoting).
static const byte JsonQuoteLengths[kQuoteTableLength] = {
    6, 6, 6, 6, 6, 6, 6, 6,
    2, 2, 2, 6, 2, 2, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6,
    1, 1, 2, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 2, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
};


template <typename StringType>
MaybeObject* AllocateRawString(Isolate* isolate, int length);


template <>
MaybeObject* AllocateRawString<SeqTwoByteString>(Isolate* isolate, int length) {
  return isolate->heap()->AllocateRawTwoByteString(length);
}


template <>
MaybeObject* AllocateRawString<SeqAsciiString>(Isolate* isolate, int length) {
  return isolate->heap()->AllocateRawAsciiString(length);
}


template <typename Char, typename StringType, bool comma>
static MaybeObject* SlowQuoteJsonString(Isolate* isolate,
                                        Vector<const Char> characters) {
  int length = characters.length();
  const Char* read_cursor = characters.start();
  const Char* end = read_cursor + length;
  const int kSpaceForQuotes = 2 + (comma ? 1 :0);
  int quoted_length = kSpaceForQuotes;
  while (read_cursor < end) {
    Char c = *(read_cursor++);
    if (sizeof(Char) > 1u && static_cast<unsigned>(c) >= kQuoteTableLength) {
      quoted_length++;
    } else {
      quoted_length += JsonQuoteLengths[static_cast<unsigned>(c)];
    }
  }
  MaybeObject* new_alloc = AllocateRawString<StringType>(isolate,
                                                         quoted_length);
  Object* new_object;
  if (!new_alloc->ToObject(&new_object)) {
    return new_alloc;
  }
  StringType* new_string = StringType::cast(new_object);

  Char* write_cursor = reinterpret_cast<Char*>(
      new_string->address() + SeqString::kHeaderSize);
  if (comma) *(write_cursor++) = ',';
  *(write_cursor++) = '"';

  read_cursor = characters.start();
  while (read_cursor < end) {
    Char c = *(read_cursor++);
    if (sizeof(Char) > 1u && static_cast<unsigned>(c) >= kQuoteTableLength) {
      *(write_cursor++) = c;
    } else {
      int len = JsonQuoteLengths[static_cast<unsigned>(c)];
      const char* replacement = JsonQuotes +
          static_cast<unsigned>(c) * kJsonQuotesCharactersPerEntry;
      for (int i = 0; i < len; i++) {
        *write_cursor++ = *replacement++;
      }
    }
  }
  *(write_cursor++) = '"';
  return new_string;
}


template <typename SinkChar, typename SourceChar>
static inline SinkChar* WriteQuoteJsonString(
    Isolate* isolate,
    SinkChar* write_cursor,
    Vector<const SourceChar> characters) {
  // SinkChar is only char if SourceChar is guaranteed to be char.
  ASSERT(sizeof(SinkChar) >= sizeof(SourceChar));
  const SourceChar* read_cursor = characters.start();
  const SourceChar* end = read_cursor + characters.length();
  *(write_cursor++) = '"';
  while (read_cursor < end) {
    SourceChar c = *(read_cursor++);
    if (sizeof(SourceChar) > 1u &&
        static_cast<unsigned>(c) >= kQuoteTableLength) {
      *(write_cursor++) = static_cast<SinkChar>(c);
    } else {
      int len = JsonQuoteLengths[static_cast<unsigned>(c)];
      const char* replacement = JsonQuotes +
          static_cast<unsigned>(c) * kJsonQuotesCharactersPerEntry;
      write_cursor[0] = replacement[0];
      if (len > 1) {
        write_cursor[1] = replacement[1];
        if (len > 2) {
          ASSERT(len == 6);
          write_cursor[2] = replacement[2];
          write_cursor[3] = replacement[3];
          write_cursor[4] = replacement[4];
          write_cursor[5] = replacement[5];
        }
      }
      write_cursor += len;
    }
  }
  *(write_cursor++) = '"';
  return write_cursor;
}


template <typename Char, typename StringType, bool comma>
static MaybeObject* QuoteJsonString(Isolate* isolate,
                                    Vector<const Char> characters) {
  int length = characters.length();
  isolate->counters()->quote_json_char_count()->Increment(length);
  int worst_case_length =
        length * kJsonQuoteWorstCaseBlowup + kSpaceForQuotesAndComma;
  if (worst_case_length > kMaxGuaranteedNewSpaceString) {
    return SlowQuoteJsonString<Char, StringType, comma>(isolate, characters);
  }

  MaybeObject* new_alloc = AllocateRawString<StringType>(isolate,
                                                         worst_case_length);
  Object* new_object;
  if (!new_alloc->ToObject(&new_object)) {
    return new_alloc;
  }
  if (!isolate->heap()->new_space()->Contains(new_object)) {
    // Even if our string is small enough to fit in new space we still have to
    // handle it being allocated in old space as may happen in the third
    // attempt.  See CALL_AND_RETRY in heap-inl.h and similar code in
    // CEntryStub::GenerateCore.
    return SlowQuoteJsonString<Char, StringType, comma>(isolate, characters);
  }
  StringType* new_string = StringType::cast(new_object);
  ASSERT(isolate->heap()->new_space()->Contains(new_string));

  Char* write_cursor = reinterpret_cast<Char*>(
      new_string->address() + SeqString::kHeaderSize);
  if (comma) *(write_cursor++) = ',';
  write_cursor = WriteQuoteJsonString<Char, Char>(isolate,
                                                  write_cursor,
                                                  characters);
  int final_length = static_cast<int>(
      write_cursor - reinterpret_cast<Char*>(
          new_string->address() + SeqString::kHeaderSize));
  isolate->heap()->new_space()->
      template ShrinkStringAtAllocationBoundary<StringType>(
          new_string, final_length);
  return new_string;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_QuoteJSONString) {
  NoHandleAllocation ha;
  CONVERT_ARG_CHECKED(String, str, 0);
  if (!str->IsFlat()) {
    MaybeObject* try_flatten = str->TryFlatten();
    Object* flat;
    if (!try_flatten->ToObject(&flat)) {
      return try_flatten;
    }
    str = String::cast(flat);
    ASSERT(str->IsFlat());
  }
  String::FlatContent flat = str->GetFlatContent();
  ASSERT(flat.IsFlat());
  if (flat.IsTwoByte()) {
    return QuoteJsonString<uc16, SeqTwoByteString, false>(isolate,
                                                          flat.ToUC16Vector());
  } else {
    return QuoteJsonString<char, SeqAsciiString, false>(isolate,
                                                        flat.ToAsciiVector());
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_QuoteJSONStringComma) {
  NoHandleAllocation ha;
  CONVERT_ARG_CHECKED(String, str, 0);
  if (!str->IsFlat()) {
    MaybeObject* try_flatten = str->TryFlatten();
    Object* flat;
    if (!try_flatten->ToObject(&flat)) {
      return try_flatten;
    }
    str = String::cast(flat);
    ASSERT(str->IsFlat());
  }
  String::FlatContent flat = str->GetFlatContent();
  if (flat.IsTwoByte()) {
    return QuoteJsonString<uc16, SeqTwoByteString, true>(isolate,
                                                         flat.ToUC16Vector());
  } else {
    return QuoteJsonString<char, SeqAsciiString, true>(isolate,
                                                       flat.ToAsciiVector());
  }
}


template <typename Char, typename StringType>
static MaybeObject* QuoteJsonStringArray(Isolate* isolate,
                                         FixedArray* array,
                                         int worst_case_length) {
  int length = array->length();

  MaybeObject* new_alloc = AllocateRawString<StringType>(isolate,
                                                         worst_case_length);
  Object* new_object;
  if (!new_alloc->ToObject(&new_object)) {
    return new_alloc;
  }
  if (!isolate->heap()->new_space()->Contains(new_object)) {
    // Even if our string is small enough to fit in new space we still have to
    // handle it being allocated in old space as may happen in the third
    // attempt.  See CALL_AND_RETRY in heap-inl.h and similar code in
    // CEntryStub::GenerateCore.
    return isolate->heap()->undefined_value();
  }
  AssertNoAllocation no_gc;
  StringType* new_string = StringType::cast(new_object);
  ASSERT(isolate->heap()->new_space()->Contains(new_string));

  Char* write_cursor = reinterpret_cast<Char*>(
      new_string->address() + SeqString::kHeaderSize);
  *(write_cursor++) = '[';
  for (int i = 0; i < length; i++) {
    if (i != 0) *(write_cursor++) = ',';
    String* str = String::cast(array->get(i));
    String::FlatContent content = str->GetFlatContent();
    ASSERT(content.IsFlat());
    if (content.IsTwoByte()) {
      write_cursor = WriteQuoteJsonString<Char, uc16>(isolate,
                                                      write_cursor,
                                                      content.ToUC16Vector());
    } else {
      write_cursor = WriteQuoteJsonString<Char, char>(isolate,
                                                      write_cursor,
                                                      content.ToAsciiVector());
    }
  }
  *(write_cursor++) = ']';

  int final_length = static_cast<int>(
      write_cursor - reinterpret_cast<Char*>(
          new_string->address() + SeqString::kHeaderSize));
  isolate->heap()->new_space()->
      template ShrinkStringAtAllocationBoundary<StringType>(
          new_string, final_length);
  return new_string;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_QuoteJSONStringArray) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSArray, array, 0);

  if (!array->HasFastObjectElements()) {
    return isolate->heap()->undefined_value();
  }
  FixedArray* elements = FixedArray::cast(array->elements());
  int n = elements->length();
  bool ascii = true;
  int total_length = 0;

  for (int i = 0; i < n; i++) {
    Object* elt = elements->get(i);
    if (!elt->IsString()) return isolate->heap()->undefined_value();
    String* element = String::cast(elt);
    if (!element->IsFlat()) return isolate->heap()->undefined_value();
    total_length += element->length();
    if (ascii && element->IsTwoByteRepresentation()) {
      ascii = false;
    }
  }

  int worst_case_length =
      kSpaceForBrackets + n * kSpaceForQuotesAndComma
      + total_length * kJsonQuoteWorstCaseBlowup;

  if (worst_case_length > kMaxGuaranteedNewSpaceString) {
    return isolate->heap()->undefined_value();
  }

  if (ascii) {
    return QuoteJsonStringArray<char, SeqAsciiString>(isolate,
                                                      elements,
                                                      worst_case_length);
  } else {
    return QuoteJsonStringArray<uc16, SeqTwoByteString>(isolate,
                                                        elements,
                                                        worst_case_length);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringParseInt) {
  NoHandleAllocation ha;

  CONVERT_ARG_CHECKED(String, s, 0);
  CONVERT_SMI_ARG_CHECKED(radix, 1);

  s->TryFlatten();

  RUNTIME_ASSERT(radix == 0 || (2 <= radix && radix <= 36));
  double value = StringToInt(isolate->unicode_cache(), s, radix);
  return isolate->heap()->NumberFromDouble(value);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringParseFloat) {
  NoHandleAllocation ha;
  CONVERT_ARG_CHECKED(String, str, 0);

  // ECMA-262 section 15.1.2.3, empty string is NaN
  double value = StringToDouble(isolate->unicode_cache(),
                                str, ALLOW_TRAILING_JUNK, OS::nan_value());

  // Create a number object from the value.
  return isolate->heap()->NumberFromDouble(value);
}


template <class Converter>
MUST_USE_RESULT static MaybeObject* ConvertCaseHelper(
    Isolate* isolate,
    String* s,
    int length,
    int input_string_length,
    unibrow::Mapping<Converter, 128>* mapping) {
  // We try this twice, once with the assumption that the result is no longer
  // than the input and, if that assumption breaks, again with the exact
  // length.  This may not be pretty, but it is nicer than what was here before
  // and I hereby claim my vaffel-is.
  //
  // Allocate the resulting string.
  //
  // NOTE: This assumes that the upper/lower case of an ASCII
  // character is also ASCII.  This is currently the case, but it
  // might break in the future if we implement more context and locale
  // dependent upper/lower conversions.
  Object* o;
  { MaybeObject* maybe_o = s->IsAsciiRepresentation()
        ? isolate->heap()->AllocateRawAsciiString(length)
        : isolate->heap()->AllocateRawTwoByteString(length);
    if (!maybe_o->ToObject(&o)) return maybe_o;
  }
  String* result = String::cast(o);
  bool has_changed_character = false;

  // Convert all characters to upper case, assuming that they will fit
  // in the buffer
  Access<StringInputBuffer> buffer(
      isolate->runtime_state()->string_input_buffer());
  buffer->Reset(s);
  unibrow::uchar chars[Converter::kMaxWidth];
  // We can assume that the string is not empty
  uc32 current = buffer->GetNext();
  for (int i = 0; i < length;) {
    bool has_next = buffer->has_more();
    uc32 next = has_next ? buffer->GetNext() : 0;
    int char_length = mapping->get(current, next, chars);
    if (char_length == 0) {
      // The case conversion of this character is the character itself.
      result->Set(i, current);
      i++;
    } else if (char_length == 1) {
      // Common case: converting the letter resulted in one character.
      ASSERT(static_cast<uc32>(chars[0]) != current);
      result->Set(i, chars[0]);
      has_changed_character = true;
      i++;
    } else if (length == input_string_length) {
      // We've assumed that the result would be as long as the
      // input but here is a character that converts to several
      // characters.  No matter, we calculate the exact length
      // of the result and try the whole thing again.
      //
      // Note that this leaves room for optimization.  We could just
      // memcpy what we already have to the result string.  Also,
      // the result string is the last object allocated we could
      // "realloc" it and probably, in the vast majority of cases,
      // extend the existing string to be able to hold the full
      // result.
      int next_length = 0;
      if (has_next) {
        next_length = mapping->get(next, 0, chars);
        if (next_length == 0) next_length = 1;
      }
      int current_length = i + char_length + next_length;
      while (buffer->has_more()) {
        current = buffer->GetNext();
        // NOTE: we use 0 as the next character here because, while
        // the next character may affect what a character converts to,
        // it does not in any case affect the length of what it convert
        // to.
        int char_length = mapping->get(current, 0, chars);
        if (char_length == 0) char_length = 1;
        current_length += char_length;
        if (current_length > Smi::kMaxValue) {
          isolate->context()->mark_out_of_memory();
          return Failure::OutOfMemoryException();
        }
      }
      // Try again with the real length.
      return Smi::FromInt(current_length);
    } else {
      for (int j = 0; j < char_length; j++) {
        result->Set(i, chars[j]);
        i++;
      }
      has_changed_character = true;
    }
    current = next;
  }
  if (has_changed_character) {
    return result;
  } else {
    // If we didn't actually change anything in doing the conversion
    // we simple return the result and let the converted string
    // become garbage; there is no reason to keep two identical strings
    // alive.
    return s;
  }
}


namespace {

static const uintptr_t kOneInEveryByte = kUintptrAllBitsSet / 0xFF;


// Given a word and two range boundaries returns a word with high bit
// set in every byte iff the corresponding input byte was strictly in
// the range (m, n). All the other bits in the result are cleared.
// This function is only useful when it can be inlined and the
// boundaries are statically known.
// Requires: all bytes in the input word and the boundaries must be
// ASCII (less than 0x7F).
static inline uintptr_t AsciiRangeMask(uintptr_t w, char m, char n) {
  // Every byte in an ASCII string is less than or equal to 0x7F.
  ASSERT((w & (kOneInEveryByte * 0x7F)) == w);
  // Use strict inequalities since in edge cases the function could be
  // further simplified.
  ASSERT(0 < m && m < n && n < 0x7F);
  // Has high bit set in every w byte less than n.
  uintptr_t tmp1 = kOneInEveryByte * (0x7F + n) - w;
  // Has high bit set in every w byte greater than m.
  uintptr_t tmp2 = w + kOneInEveryByte * (0x7F - m);
  return (tmp1 & tmp2 & (kOneInEveryByte * 0x80));
}


enum AsciiCaseConversion {
  ASCII_TO_LOWER,
  ASCII_TO_UPPER
};


template <AsciiCaseConversion dir>
struct FastAsciiConverter {
  static bool Convert(char* dst, char* src, int length) {
#ifdef DEBUG
    char* saved_dst = dst;
    char* saved_src = src;
#endif
    // We rely on the distance between upper and lower case letters
    // being a known power of 2.
    ASSERT('a' - 'A' == (1 << 5));
    // Boundaries for the range of input characters than require conversion.
    const char lo = (dir == ASCII_TO_LOWER) ? 'A' - 1 : 'a' - 1;
    const char hi = (dir == ASCII_TO_LOWER) ? 'Z' + 1 : 'z' + 1;
    bool changed = false;
    char* const limit = src + length;
#ifdef V8_HOST_CAN_READ_UNALIGNED
    // Process the prefix of the input that requires no conversion one
    // (machine) word at a time.
    while (src <= limit - sizeof(uintptr_t)) {
      uintptr_t w = *reinterpret_cast<uintptr_t*>(src);
      if (AsciiRangeMask(w, lo, hi) != 0) {
        changed = true;
        break;
      }
      *reinterpret_cast<uintptr_t*>(dst) = w;
      src += sizeof(uintptr_t);
      dst += sizeof(uintptr_t);
    }
    // Process the remainder of the input performing conversion when
    // required one word at a time.
    while (src <= limit - sizeof(uintptr_t)) {
      uintptr_t w = *reinterpret_cast<uintptr_t*>(src);
      uintptr_t m = AsciiRangeMask(w, lo, hi);
      // The mask has high (7th) bit set in every byte that needs
      // conversion and we know that the distance between cases is
      // 1 << 5.
      *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
      src += sizeof(uintptr_t);
      dst += sizeof(uintptr_t);
    }
#endif
    // Process the last few bytes of the input (or the whole input if
    // unaligned access is not supported).
    while (src < limit) {
      char c = *src;
      if (lo < c && c < hi) {
        c ^= (1 << 5);
        changed = true;
      }
      *dst = c;
      ++src;
      ++dst;
    }
#ifdef DEBUG
    CheckConvert(saved_dst, saved_src, length, changed);
#endif
    return changed;
  }

#ifdef DEBUG
  static void CheckConvert(char* dst, char* src, int length, bool changed) {
    bool expected_changed = false;
    for (int i = 0; i < length; i++) {
      if (dst[i] == src[i]) continue;
      expected_changed = true;
      if (dir == ASCII_TO_LOWER) {
        ASSERT('A' <= src[i] && src[i] <= 'Z');
        ASSERT(dst[i] == src[i] + ('a' - 'A'));
      } else {
        ASSERT(dir == ASCII_TO_UPPER);
        ASSERT('a' <= src[i] && src[i] <= 'z');
        ASSERT(dst[i] == src[i] - ('a' - 'A'));
      }
    }
    ASSERT(expected_changed == changed);
  }
#endif
};


struct ToLowerTraits {
  typedef unibrow::ToLowercase UnibrowConverter;

  typedef FastAsciiConverter<ASCII_TO_LOWER> AsciiConverter;
};


struct ToUpperTraits {
  typedef unibrow::ToUppercase UnibrowConverter;

  typedef FastAsciiConverter<ASCII_TO_UPPER> AsciiConverter;
};

}  // namespace


template <typename ConvertTraits>
MUST_USE_RESULT static MaybeObject* ConvertCase(
    Arguments args,
    Isolate* isolate,
    unibrow::Mapping<typename ConvertTraits::UnibrowConverter, 128>* mapping) {
  NoHandleAllocation ha;
  CONVERT_ARG_CHECKED(String, s, 0);
  s = s->TryFlattenGetString();

  const int length = s->length();
  // Assume that the string is not empty; we need this assumption later
  if (length == 0) return s;

  // Simpler handling of ASCII strings.
  //
  // NOTE: This assumes that the upper/lower case of an ASCII
  // character is also ASCII.  This is currently the case, but it
  // might break in the future if we implement more context and locale
  // dependent upper/lower conversions.
  if (s->IsSeqAsciiString()) {
    Object* o;
    { MaybeObject* maybe_o = isolate->heap()->AllocateRawAsciiString(length);
      if (!maybe_o->ToObject(&o)) return maybe_o;
    }
    SeqAsciiString* result = SeqAsciiString::cast(o);
    bool has_changed_character = ConvertTraits::AsciiConverter::Convert(
        result->GetChars(), SeqAsciiString::cast(s)->GetChars(), length);
    return has_changed_character ? result : s;
  }

  Object* answer;
  { MaybeObject* maybe_answer =
        ConvertCaseHelper(isolate, s, length, length, mapping);
    if (!maybe_answer->ToObject(&answer)) return maybe_answer;
  }
  if (answer->IsSmi()) {
    // Retry with correct length.
    { MaybeObject* maybe_answer =
          ConvertCaseHelper(isolate,
                            s, Smi::cast(answer)->value(), length, mapping);
      if (!maybe_answer->ToObject(&answer)) return maybe_answer;
    }
  }
  return answer;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringToLowerCase) {
  return ConvertCase<ToLowerTraits>(
      args, isolate, isolate->runtime_state()->to_lower_mapping());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringToUpperCase) {
  return ConvertCase<ToUpperTraits>(
      args, isolate, isolate->runtime_state()->to_upper_mapping());
}


static inline bool IsTrimWhiteSpace(unibrow::uchar c) {
  return unibrow::WhiteSpace::Is(c) || c == 0x200b || c == 0xfeff;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringTrim) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);

  CONVERT_ARG_CHECKED(String, s, 0);
  CONVERT_BOOLEAN_ARG_CHECKED(trimLeft, 1);
  CONVERT_BOOLEAN_ARG_CHECKED(trimRight, 2);

  s->TryFlatten();
  int length = s->length();

  int left = 0;
  if (trimLeft) {
    while (left < length && IsTrimWhiteSpace(s->Get(left))) {
      left++;
    }
  }

  int right = length;
  if (trimRight) {
    while (right > left && IsTrimWhiteSpace(s->Get(right - 1))) {
      right--;
    }
  }
  return s->SubString(left, right);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringSplit) {
  ASSERT(args.length() == 3);
  HandleScope handle_scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, pattern, 1);
  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[2]);

  int subject_length = subject->length();
  int pattern_length = pattern->length();
  RUNTIME_ASSERT(pattern_length > 0);

  if (limit == 0xffffffffu) {
    Handle<Object> cached_answer(StringSplitCache::Lookup(
        isolate->heap()->string_split_cache(),
        *subject,
        *pattern));
    if (*cached_answer != Smi::FromInt(0)) {
      Handle<JSArray> result =
          isolate->factory()->NewJSArrayWithElements(
              Handle<FixedArray>::cast(cached_answer));
      return *result;
    }
  }

  // The limit can be very large (0xffffffffu), but since the pattern
  // isn't empty, we can never create more parts than ~half the length
  // of the subject.

  if (!subject->IsFlat()) FlattenString(subject);

  static const int kMaxInitialListCapacity = 16;

  Zone* zone = isolate->zone();
  ZoneScope scope(isolate, DELETE_ON_EXIT);

  // Find (up to limit) indices of separator and end-of-string in subject
  int initial_capacity = Min<uint32_t>(kMaxInitialListCapacity, limit);
  ZoneList<int> indices(initial_capacity, zone);
  if (!pattern->IsFlat()) FlattenString(pattern);

  FindStringIndicesDispatch(isolate, *subject, *pattern, &indices, limit, zone);

  if (static_cast<uint32_t>(indices.length()) < limit) {
    indices.Add(subject_length, zone);
  }

  // The list indices now contains the end of each part to create.

  // Create JSArray of substrings separated by separator.
  int part_count = indices.length();

  Handle<JSArray> result = isolate->factory()->NewJSArray(part_count);
  MaybeObject* maybe_result = result->EnsureCanContainHeapObjectElements();
  if (maybe_result->IsFailure()) return maybe_result;
  result->set_length(Smi::FromInt(part_count));

  ASSERT(result->HasFastObjectElements());

  if (part_count == 1 && indices.at(0) == subject_length) {
    FixedArray::cast(result->elements())->set(0, *subject);
    return *result;
  }

  Handle<FixedArray> elements(FixedArray::cast(result->elements()));
  int part_start = 0;
  for (int i = 0; i < part_count; i++) {
    HandleScope local_loop_handle;
    int part_end = indices.at(i);
    Handle<String> substring =
        isolate->factory()->NewProperSubString(subject, part_start, part_end);
    elements->set(i, *substring);
    part_start = part_end + pattern_length;
  }

  if (limit == 0xffffffffu) {
    if (result->HasFastObjectElements()) {
      StringSplitCache::Enter(isolate->heap(),
                              isolate->heap()->string_split_cache(),
                              *subject,
                              *pattern,
                              *elements);
    }
  }

  return *result;
}


// Copies ASCII characters to the given fixed array looking up
// one-char strings in the cache. Gives up on the first char that is
// not in the cache and fills the remainder with smi zeros. Returns
// the length of the successfully copied prefix.
static int CopyCachedAsciiCharsToArray(Heap* heap,
                                       const char* chars,
                                       FixedArray* elements,
                                       int length) {
  AssertNoAllocation no_gc;
  FixedArray* ascii_cache = heap->single_character_string_cache();
  Object* undefined = heap->undefined_value();
  int i;
  WriteBarrierMode mode = elements->GetWriteBarrierMode(no_gc);
  for (i = 0; i < length; ++i) {
    Object* value = ascii_cache->get(chars[i]);
    if (value == undefined) break;
    elements->set(i, value, mode);
  }
  if (i < length) {
    ASSERT(Smi::FromInt(0) == 0);
    memset(elements->data_start() + i, 0, kPointerSize * (length - i));
  }
#ifdef DEBUG
  for (int j = 0; j < length; ++j) {
    Object* element = elements->get(j);
    ASSERT(element == Smi::FromInt(0) ||
           (element->IsString() && String::cast(element)->LooksValid()));
  }
#endif
  return i;
}


// Converts a String to JSArray.
// For example, "foo" => ["f", "o", "o"].
RUNTIME_FUNCTION(MaybeObject*, Runtime_StringToArray) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);

  s = FlattenGetString(s);
  const int length = static_cast<int>(Min<uint32_t>(s->length(), limit));

  Handle<FixedArray> elements;
  int position = 0;
  if (s->IsFlat() && s->IsAsciiRepresentation()) {
    // Try using cached chars where possible.
    Object* obj;
    { MaybeObject* maybe_obj =
          isolate->heap()->AllocateUninitializedFixedArray(length);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }
    elements = Handle<FixedArray>(FixedArray::cast(obj), isolate);
    String::FlatContent content = s->GetFlatContent();
    if (content.IsAscii()) {
      Vector<const char> chars = content.ToAsciiVector();
      // Note, this will initialize all elements (not only the prefix)
      // to prevent GC from seeing partially initialized array.
      position = CopyCachedAsciiCharsToArray(isolate->heap(),
                                             chars.start(),
                                             *elements,
                                             length);
    } else {
      MemsetPointer(elements->data_start(),
                    isolate->heap()->undefined_value(),
                    length);
    }
  } else {
    elements = isolate->factory()->NewFixedArray(length);
  }
  for (int i = position; i < length; ++i) {
    Handle<Object> str = LookupSingleCharacterStringFromCode(s->Get(i));
    elements->set(i, *str);
  }

#ifdef DEBUG
  for (int i = 0; i < length; ++i) {
    ASSERT(String::cast(elements->get(i))->length() == 1);
  }
#endif

  return *isolate->factory()->NewJSArrayWithElements(elements);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewStringWrapper) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(String, value, 0);
  return value->ToObject();
}


bool Runtime::IsUpperCaseChar(RuntimeState* runtime_state, uint16_t ch) {
  unibrow::uchar chars[unibrow::ToUppercase::kMaxWidth];
  int char_length = runtime_state->to_upper_mapping()->get(ch, 0, chars);
  return char_length == 0;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToString) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  Object* number = args[0];
  RUNTIME_ASSERT(number->IsNumber());

  return isolate->heap()->NumberToString(number);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToStringSkipCache) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  Object* number = args[0];
  RUNTIME_ASSERT(number->IsNumber());

  return isolate->heap()->NumberToString(number, false);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToInteger) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(number, 0);

  // We do not include 0 so that we don't have to treat +0 / -0 cases.
  if (number > 0 && number <= Smi::kMaxValue) {
    return Smi::FromInt(static_cast<int>(number));
  }
  return isolate->heap()->NumberFromDouble(DoubleToInteger(number));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToIntegerMapMinusZero) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(number, 0);

  // We do not include 0 so that we don't have to treat +0 / -0 cases.
  if (number > 0 && number <= Smi::kMaxValue) {
    return Smi::FromInt(static_cast<int>(number));
  }

  double double_value = DoubleToInteger(number);
  // Map both -0 and +0 to +0.
  if (double_value == 0) double_value = 0;

  return isolate->heap()->NumberFromDouble(double_value);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToJSUint32) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_NUMBER_CHECKED(int32_t, number, Uint32, args[0]);
  return isolate->heap()->NumberFromUint32(number);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToJSInt32) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(number, 0);

  // We do not include 0 so that we don't have to treat +0 / -0 cases.
  if (number > 0 && number <= Smi::kMaxValue) {
    return Smi::FromInt(static_cast<int>(number));
  }
  return isolate->heap()->NumberFromInt32(DoubleToInt32(number));
}


// Converts a Number to a Smi, if possible. Returns NaN if the number is not
// a small integer.
RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToSmi) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  Object* obj = args[0];
  if (obj->IsSmi()) {
    return obj;
  }
  if (obj->IsHeapNumber()) {
    double value = HeapNumber::cast(obj)->value();
    int int_value = FastD2I(value);
    if (value == FastI2D(int_value) && Smi::IsValid(int_value)) {
      return Smi::FromInt(int_value);
    }
  }
  return isolate->heap()->nan_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_AllocateHeapNumber) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 0);
  return isolate->heap()->AllocateHeapNumber(0);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberAdd) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  return isolate->heap()->NumberFromDouble(x + y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberSub) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  return isolate->heap()->NumberFromDouble(x - y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberMul) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  return isolate->heap()->NumberFromDouble(x * y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberUnaryMinus) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->heap()->NumberFromDouble(-x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberAlloc) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 0);

  return isolate->heap()->NumberFromDouble(9876543210.0);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberDiv) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  return isolate->heap()->NumberFromDouble(x / y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberMod) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);

  x = modulo(x, y);
  // NumberFromDouble may return a Smi instead of a Number object
  return isolate->heap()->NumberFromDouble(x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringAdd) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(String, str1, 0);
  CONVERT_ARG_CHECKED(String, str2, 1);
  isolate->counters()->string_add_runtime()->Increment();
  return isolate->heap()->AllocateConsString(str1, str2);
}


template <typename sinkchar>
static inline void StringBuilderConcatHelper(String* special,
                                             sinkchar* sink,
                                             FixedArray* fixed_array,
                                             int array_length) {
  int position = 0;
  for (int i = 0; i < array_length; i++) {
    Object* element = fixed_array->get(i);
    if (element->IsSmi()) {
      // Smi encoding of position and length.
      int encoded_slice = Smi::cast(element)->value();
      int pos;
      int len;
      if (encoded_slice > 0) {
        // Position and length encoded in one smi.
        pos = StringBuilderSubstringPosition::decode(encoded_slice);
        len = StringBuilderSubstringLength::decode(encoded_slice);
      } else {
        // Position and length encoded in two smis.
        Object* obj = fixed_array->get(++i);
        ASSERT(obj->IsSmi());
        pos = Smi::cast(obj)->value();
        len = -encoded_slice;
      }
      String::WriteToFlat(special,
                          sink + position,
                          pos,
                          pos + len);
      position += len;
    } else {
      String* string = String::cast(element);
      int element_length = string->length();
      String::WriteToFlat(string, sink + position, 0, element_length);
      position += element_length;
    }
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringBuilderConcat) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);
  CONVERT_ARG_CHECKED(JSArray, array, 0);
  if (!args[1]->IsSmi()) {
    isolate->context()->mark_out_of_memory();
    return Failure::OutOfMemoryException();
  }
  int array_length = args.smi_at(1);
  CONVERT_ARG_CHECKED(String, special, 2);

  // This assumption is used by the slice encoding in one or two smis.
  ASSERT(Smi::kMaxValue >= String::kMaxLength);

  MaybeObject* maybe_result = array->EnsureCanContainHeapObjectElements();
  if (maybe_result->IsFailure()) return maybe_result;

  int special_length = special->length();
  if (!array->HasFastObjectElements()) {
    return isolate->Throw(isolate->heap()->illegal_argument_symbol());
  }
  FixedArray* fixed_array = FixedArray::cast(array->elements());
  if (fixed_array->length() < array_length) {
    array_length = fixed_array->length();
  }

  if (array_length == 0) {
    return isolate->heap()->empty_string();
  } else if (array_length == 1) {
    Object* first = fixed_array->get(0);
    if (first->IsString()) return first;
  }

  bool ascii = special->HasOnlyAsciiChars();
  int position = 0;
  for (int i = 0; i < array_length; i++) {
    int increment = 0;
    Object* elt = fixed_array->get(i);
    if (elt->IsSmi()) {
      // Smi encoding of position and length.
      int smi_value = Smi::cast(elt)->value();
      int pos;
      int len;
      if (smi_value > 0) {
        // Position and length encoded in one smi.
        pos = StringBuilderSubstringPosition::decode(smi_value);
        len = StringBuilderSubstringLength::decode(smi_value);
      } else {
        // Position and length encoded in two smis.
        len = -smi_value;
        // Get the position and check that it is a positive smi.
        i++;
        if (i >= array_length) {
          return isolate->Throw(isolate->heap()->illegal_argument_symbol());
        }
        Object* next_smi = fixed_array->get(i);
        if (!next_smi->IsSmi()) {
          return isolate->Throw(isolate->heap()->illegal_argument_symbol());
        }
        pos = Smi::cast(next_smi)->value();
        if (pos < 0) {
          return isolate->Throw(isolate->heap()->illegal_argument_symbol());
        }
      }
      ASSERT(pos >= 0);
      ASSERT(len >= 0);
      if (pos > special_length || len > special_length - pos) {
        return isolate->Throw(isolate->heap()->illegal_argument_symbol());
      }
      increment = len;
    } else if (elt->IsString()) {
      String* element = String::cast(elt);
      int element_length = element->length();
      increment = element_length;
      if (ascii && !element->HasOnlyAsciiChars()) {
        ascii = false;
      }
    } else {
      ASSERT(!elt->IsTheHole());
      return isolate->Throw(isolate->heap()->illegal_argument_symbol());
    }
    if (increment > String::kMaxLength - position) {
      isolate->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
    }
    position += increment;
  }

  int length = position;
  Object* object;

  if (ascii) {
    { MaybeObject* maybe_object =
          isolate->heap()->AllocateRawAsciiString(length);
      if (!maybe_object->ToObject(&object)) return maybe_object;
    }
    SeqAsciiString* answer = SeqAsciiString::cast(object);
    StringBuilderConcatHelper(special,
                              answer->GetChars(),
                              fixed_array,
                              array_length);
    return answer;
  } else {
    { MaybeObject* maybe_object =
          isolate->heap()->AllocateRawTwoByteString(length);
      if (!maybe_object->ToObject(&object)) return maybe_object;
    }
    SeqTwoByteString* answer = SeqTwoByteString::cast(object);
    StringBuilderConcatHelper(special,
                              answer->GetChars(),
                              fixed_array,
                              array_length);
    return answer;
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringBuilderJoin) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);
  CONVERT_ARG_CHECKED(JSArray, array, 0);
  if (!args[1]->IsSmi()) {
    isolate->context()->mark_out_of_memory();
    return Failure::OutOfMemoryException();
  }
  int array_length = args.smi_at(1);
  CONVERT_ARG_CHECKED(String, separator, 2);

  if (!array->HasFastObjectElements()) {
    return isolate->Throw(isolate->heap()->illegal_argument_symbol());
  }
  FixedArray* fixed_array = FixedArray::cast(array->elements());
  if (fixed_array->length() < array_length) {
    array_length = fixed_array->length();
  }

  if (array_length == 0) {
    return isolate->heap()->empty_string();
  } else if (array_length == 1) {
    Object* first = fixed_array->get(0);
    if (first->IsString()) return first;
  }

  int separator_length = separator->length();
  int max_nof_separators =
      (String::kMaxLength + separator_length - 1) / separator_length;
  if (max_nof_separators < (array_length - 1)) {
      isolate->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
  }
  int length = (array_length - 1) * separator_length;
  for (int i = 0; i < array_length; i++) {
    Object* element_obj = fixed_array->get(i);
    if (!element_obj->IsString()) {
      // TODO(1161): handle this case.
      return isolate->Throw(isolate->heap()->illegal_argument_symbol());
    }
    String* element = String::cast(element_obj);
    int increment = element->length();
    if (increment > String::kMaxLength - length) {
      isolate->context()->mark_out_of_memory();
      return Failure::OutOfMemoryException();
    }
    length += increment;
  }

  Object* object;
  { MaybeObject* maybe_object =
        isolate->heap()->AllocateRawTwoByteString(length);
    if (!maybe_object->ToObject(&object)) return maybe_object;
  }
  SeqTwoByteString* answer = SeqTwoByteString::cast(object);

  uc16* sink = answer->GetChars();
#ifdef DEBUG
  uc16* end = sink + length;
#endif

  String* first = String::cast(fixed_array->get(0));
  int first_length = first->length();
  String::WriteToFlat(first, sink, 0, first_length);
  sink += first_length;

  for (int i = 1; i < array_length; i++) {
    ASSERT(sink + separator_length <= end);
    String::WriteToFlat(separator, sink, 0, separator_length);
    sink += separator_length;

    String* element = String::cast(fixed_array->get(i));
    int element_length = element->length();
    ASSERT(sink + element_length <= end);
    String::WriteToFlat(element, sink, 0, element_length);
    sink += element_length;
  }
  ASSERT(sink == end);

  ASSERT(!answer->HasOnlyAsciiChars());  // Use %_FastAsciiArrayJoin instead.
  return answer;
}

template <typename Char>
static void JoinSparseArrayWithSeparator(FixedArray* elements,
                                         int elements_length,
                                         uint32_t array_length,
                                         String* separator,
                                         Vector<Char> buffer) {
  int previous_separator_position = 0;
  int separator_length = separator->length();
  int cursor = 0;
  for (int i = 0; i < elements_length; i += 2) {
    int position = NumberToInt32(elements->get(i));
    String* string = String::cast(elements->get(i + 1));
    int string_length = string->length();
    if (string->length() > 0) {
      while (previous_separator_position < position) {
        String::WriteToFlat<Char>(separator, &buffer[cursor],
                                  0, separator_length);
        cursor += separator_length;
        previous_separator_position++;
      }
      String::WriteToFlat<Char>(string, &buffer[cursor],
                                0, string_length);
      cursor += string->length();
    }
  }
  if (separator_length > 0) {
    // Array length must be representable as a signed 32-bit number,
    // otherwise the total string length would have been too large.
    ASSERT(array_length <= 0x7fffffff);  // Is int32_t.
    int last_array_index = static_cast<int>(array_length - 1);
    while (previous_separator_position < last_array_index) {
      String::WriteToFlat<Char>(separator, &buffer[cursor],
                                0, separator_length);
      cursor += separator_length;
      previous_separator_position++;
    }
  }
  ASSERT(cursor <= buffer.length());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SparseJoinWithSeparator) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);
  CONVERT_ARG_CHECKED(JSArray, elements_array, 0);
  RUNTIME_ASSERT(elements_array->HasFastSmiOrObjectElements());
  CONVERT_NUMBER_CHECKED(uint32_t, array_length, Uint32, args[1]);
  CONVERT_ARG_CHECKED(String, separator, 2);
  // elements_array is fast-mode JSarray of alternating positions
  // (increasing order) and strings.
  // array_length is length of original array (used to add separators);
  // separator is string to put between elements. Assumed to be non-empty.

  // Find total length of join result.
  int string_length = 0;
  bool is_ascii = separator->IsAsciiRepresentation();
  int max_string_length;
  if (is_ascii) {
    max_string_length = SeqAsciiString::kMaxLength;
  } else {
    max_string_length = SeqTwoByteString::kMaxLength;
  }
  bool overflow = false;
  CONVERT_NUMBER_CHECKED(int, elements_length,
                         Int32, elements_array->length());
  RUNTIME_ASSERT((elements_length & 1) == 0);  // Even length.
  FixedArray* elements = FixedArray::cast(elements_array->elements());
  for (int i = 0; i < elements_length; i += 2) {
    RUNTIME_ASSERT(elements->get(i)->IsNumber());
    RUNTIME_ASSERT(elements->get(i + 1)->IsString());
    String* string = String::cast(elements->get(i + 1));
    int length = string->length();
    if (is_ascii && !string->IsAsciiRepresentation()) {
      is_ascii = false;
      max_string_length = SeqTwoByteString::kMaxLength;
    }
    if (length > max_string_length ||
        max_string_length - length < string_length) {
      overflow = true;
      break;
    }
    string_length += length;
  }
  int separator_length = separator->length();
  if (!overflow && separator_length > 0) {
    if (array_length <= 0x7fffffffu) {
      int separator_count = static_cast<int>(array_length) - 1;
      int remaining_length = max_string_length - string_length;
      if ((remaining_length / separator_length) >= separator_count) {
        string_length += separator_length * (array_length - 1);
      } else {
        // Not room for the separators within the maximal string length.
        overflow = true;
      }
    } else {
      // Nonempty separator and at least 2^31-1 separators necessary
      // means that the string is too large to create.
      STATIC_ASSERT(String::kMaxLength < 0x7fffffff);
      overflow = true;
    }
  }
  if (overflow) {
    // Throw OutOfMemory exception for creating too large a string.
    V8::FatalProcessOutOfMemory("Array join result too large.");
  }

  if (is_ascii) {
    MaybeObject* result_allocation =
        isolate->heap()->AllocateRawAsciiString(string_length);
    if (result_allocation->IsFailure()) return result_allocation;
    SeqAsciiString* result_string =
        SeqAsciiString::cast(result_allocation->ToObjectUnchecked());
    JoinSparseArrayWithSeparator<char>(elements,
                                       elements_length,
                                       array_length,
                                       separator,
                                       Vector<char>(result_string->GetChars(),
                                                    string_length));
    return result_string;
  } else {
    MaybeObject* result_allocation =
        isolate->heap()->AllocateRawTwoByteString(string_length);
    if (result_allocation->IsFailure()) return result_allocation;
    SeqTwoByteString* result_string =
        SeqTwoByteString::cast(result_allocation->ToObjectUnchecked());
    JoinSparseArrayWithSeparator<uc16>(elements,
                                       elements_length,
                                       array_length,
                                       separator,
                                       Vector<uc16>(result_string->GetChars(),
                                                    string_length));
    return result_string;
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberOr) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromInt32(x | y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberAnd) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromInt32(x & y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberXor) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromInt32(x ^ y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberNot) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  return isolate->heap()->NumberFromInt32(~x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberShl) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromInt32(x << (y & 0x1f));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberShr) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(uint32_t, x, Uint32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromUint32(x >> (y & 0x1f));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberSar) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_NUMBER_CHECKED(int32_t, x, Int32, args[0]);
  CONVERT_NUMBER_CHECKED(int32_t, y, Int32, args[1]);
  return isolate->heap()->NumberFromInt32(ArithmeticShiftRight(x, y & 0x1f));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberEquals) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  if (isnan(x)) return Smi::FromInt(NOT_EQUAL);
  if (isnan(y)) return Smi::FromInt(NOT_EQUAL);
  if (x == y) return Smi::FromInt(EQUAL);
  Object* result;
  if ((fpclassify(x) == FP_ZERO) && (fpclassify(y) == FP_ZERO)) {
    result = Smi::FromInt(EQUAL);
  } else {
    result = Smi::FromInt(NOT_EQUAL);
  }
  return result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringEquals) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(String, x, 0);
  CONVERT_ARG_CHECKED(String, y, 1);

  bool not_equal = !x->Equals(y);
  // This is slightly convoluted because the value that signifies
  // equality is 0 and inequality is 1 so we have to negate the result
  // from String::Equals.
  ASSERT(not_equal == 0 || not_equal == 1);
  STATIC_CHECK(EQUAL == 0);
  STATIC_CHECK(NOT_EQUAL == 1);
  return Smi::FromInt(not_equal);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberCompare) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  if (isnan(x) || isnan(y)) return args[2];
  if (x == y) return Smi::FromInt(EQUAL);
  if (isless(x, y)) return Smi::FromInt(LESS);
  return Smi::FromInt(GREATER);
}


// Compare two Smis as if they were converted to strings and then
// compared lexicographically.
RUNTIME_FUNCTION(MaybeObject*, Runtime_SmiLexicographicCompare) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_SMI_ARG_CHECKED(x_value, 0);
  CONVERT_SMI_ARG_CHECKED(y_value, 1);

  // If the integers are equal so are the string representations.
  if (x_value == y_value) return Smi::FromInt(EQUAL);

  // If one of the integers is zero the normal integer order is the
  // same as the lexicographic order of the string representations.
  if (x_value == 0 || y_value == 0)
    return Smi::FromInt(x_value < y_value ? LESS : GREATER);

  // If only one of the integers is negative the negative number is
  // smallest because the char code of '-' is less than the char code
  // of any digit.  Otherwise, we make both values positive.

  // Use unsigned values otherwise the logic is incorrect for -MIN_INT on
  // architectures using 32-bit Smis.
  uint32_t x_scaled = x_value;
  uint32_t y_scaled = y_value;
  if (x_value < 0 || y_value < 0) {
    if (y_value >= 0) return Smi::FromInt(LESS);
    if (x_value >= 0) return Smi::FromInt(GREATER);
    x_scaled = -x_value;
    y_scaled = -y_value;
  }

  static const uint32_t kPowersOf10[] = {
    1, 10, 100, 1000, 10*1000, 100*1000,
    1000*1000, 10*1000*1000, 100*1000*1000,
    1000*1000*1000
  };

  // If the integers have the same number of decimal digits they can be
  // compared directly as the numeric order is the same as the
  // lexicographic order.  If one integer has fewer digits, it is scaled
  // by some power of 10 to have the same number of digits as the longer
  // integer.  If the scaled integers are equal it means the shorter
  // integer comes first in the lexicographic order.

  // From http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
  int x_log2 = IntegerLog2(x_scaled);
  int x_log10 = ((x_log2 + 1) * 1233) >> 12;
  x_log10 -= x_scaled < kPowersOf10[x_log10];

  int y_log2 = IntegerLog2(y_scaled);
  int y_log10 = ((y_log2 + 1) * 1233) >> 12;
  y_log10 -= y_scaled < kPowersOf10[y_log10];

  int tie = EQUAL;

  if (x_log10 < y_log10) {
    // X has fewer digits.  We would like to simply scale up X but that
    // might overflow, e.g when comparing 9 with 1_000_000_000, 9 would
    // be scaled up to 9_000_000_000. So we scale up by the next
    // smallest power and scale down Y to drop one digit. It is OK to
    // drop one digit from the longer integer since the final digit is
    // past the length of the shorter integer.
    x_scaled *= kPowersOf10[y_log10 - x_log10 - 1];
    y_scaled /= 10;
    tie = LESS;
  } else if (y_log10 < x_log10) {
    y_scaled *= kPowersOf10[x_log10 - y_log10 - 1];
    x_scaled /= 10;
    tie = GREATER;
  }

  if (x_scaled < y_scaled) return Smi::FromInt(LESS);
  if (x_scaled > y_scaled) return Smi::FromInt(GREATER);
  return Smi::FromInt(tie);
}


static Object* StringInputBufferCompare(RuntimeState* state,
                                        String* x,
                                        String* y) {
  StringInputBuffer& bufx = *state->string_input_buffer_compare_bufx();
  StringInputBuffer& bufy = *state->string_input_buffer_compare_bufy();
  bufx.Reset(x);
  bufy.Reset(y);
  while (bufx.has_more() && bufy.has_more()) {
    int d = bufx.GetNext() - bufy.GetNext();
    if (d < 0) return Smi::FromInt(LESS);
    else if (d > 0) return Smi::FromInt(GREATER);
  }

  // x is (non-trivial) prefix of y:
  if (bufy.has_more()) return Smi::FromInt(LESS);
  // y is prefix of x:
  return Smi::FromInt(bufx.has_more() ? GREATER : EQUAL);
}


static Object* FlatStringCompare(String* x, String* y) {
  ASSERT(x->IsFlat());
  ASSERT(y->IsFlat());
  Object* equal_prefix_result = Smi::FromInt(EQUAL);
  int prefix_length = x->length();
  if (y->length() < prefix_length) {
    prefix_length = y->length();
    equal_prefix_result = Smi::FromInt(GREATER);
  } else if (y->length() > prefix_length) {
    equal_prefix_result = Smi::FromInt(LESS);
  }
  int r;
  String::FlatContent x_content = x->GetFlatContent();
  String::FlatContent y_content = y->GetFlatContent();
  if (x_content.IsAscii()) {
    Vector<const char> x_chars = x_content.ToAsciiVector();
    if (y_content.IsAscii()) {
      Vector<const char> y_chars = y_content.ToAsciiVector();
      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
    } else {
      Vector<const uc16> y_chars = y_content.ToUC16Vector();
      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
    }
  } else {
    Vector<const uc16> x_chars = x_content.ToUC16Vector();
    if (y_content.IsAscii()) {
      Vector<const char> y_chars = y_content.ToAsciiVector();
      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
    } else {
      Vector<const uc16> y_chars = y_content.ToUC16Vector();
      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
    }
  }
  Object* result;
  if (r == 0) {
    result = equal_prefix_result;
  } else {
    result = (r < 0) ? Smi::FromInt(LESS) : Smi::FromInt(GREATER);
  }
  ASSERT(result ==
      StringInputBufferCompare(Isolate::Current()->runtime_state(), x, y));
  return result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StringCompare) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_ARG_CHECKED(String, x, 0);
  CONVERT_ARG_CHECKED(String, y, 1);

  isolate->counters()->string_compare_runtime()->Increment();

  // A few fast case tests before we flatten.
  if (x == y) return Smi::FromInt(EQUAL);
  if (y->length() == 0) {
    if (x->length() == 0) return Smi::FromInt(EQUAL);
    return Smi::FromInt(GREATER);
  } else if (x->length() == 0) {
    return Smi::FromInt(LESS);
  }

  int d = x->Get(0) - y->Get(0);
  if (d < 0) return Smi::FromInt(LESS);
  else if (d > 0) return Smi::FromInt(GREATER);

  Object* obj;
  { MaybeObject* maybe_obj = isolate->heap()->PrepareForCompare(x);
    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
  }
  { MaybeObject* maybe_obj = isolate->heap()->PrepareForCompare(y);
    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
  }

  return (x->IsFlat() && y->IsFlat()) ? FlatStringCompare(x, y)
      : StringInputBufferCompare(isolate->runtime_state(), x, y);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_acos) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_acos()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::ACOS, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_asin) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_asin()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::ASIN, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_atan) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_atan()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::ATAN, x);
}


static const double kPiDividedBy4 = 0.78539816339744830962;


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_atan2) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  isolate->counters()->math_atan2()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  double result;
  if (isinf(x) && isinf(y)) {
    // Make sure that the result in case of two infinite arguments
    // is a multiple of Pi / 4. The sign of the result is determined
    // by the first argument (x) and the sign of the second argument
    // determines the multiplier: one or three.
    int multiplier = (x < 0) ? -1 : 1;
    if (y < 0) multiplier *= 3;
    result = multiplier * kPiDividedBy4;
  } else {
    result = atan2(x, y);
  }
  return isolate->heap()->AllocateHeapNumber(result);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_ceil) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_ceil()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->heap()->NumberFromDouble(ceiling(x));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_cos) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_cos()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::COS, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_exp) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_exp()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::EXP, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_floor) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_floor()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->heap()->NumberFromDouble(floor(x));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_log) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_log()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::LOG, x);
}

// Slow version of Math.pow.  We check for fast paths for special cases.
// Used if SSE2/VFP3 is not available.
RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_pow) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  isolate->counters()->math_pow()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);

  // If the second argument is a smi, it is much faster to call the
  // custom powi() function than the generic pow().
  if (args[1]->IsSmi()) {
    int y = args.smi_at(1);
    return isolate->heap()->NumberFromDouble(power_double_int(x, y));
  }

  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  int y_int = static_cast<int>(y);
  double result;
  if (y == y_int) {
    result = power_double_int(x, y_int);  // Returns 1 if exponent is 0.
  } else  if (y == 0.5) {
    result = (isinf(x)) ? V8_INFINITY
                        : fast_sqrt(x + 0.0);  // Convert -0 to +0.
  } else if (y == -0.5) {
    result = (isinf(x)) ? 0
                        : 1.0 / fast_sqrt(x + 0.0);  // Convert -0 to +0.
  } else {
    result = power_double_double(x, y);
  }
  if (isnan(result)) return isolate->heap()->nan_value();
  return isolate->heap()->AllocateHeapNumber(result);
}

// Fast version of Math.pow if we know that y is not an integer and y is not
// -0.5 or 0.5.  Used as slow case from full codegen.
RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_pow_cfunction) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  isolate->counters()->math_pow()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  CONVERT_DOUBLE_ARG_CHECKED(y, 1);
  if (y == 0) {
    return Smi::FromInt(1);
  } else {
    double result = power_double_double(x, y);
    if (isnan(result)) return isolate->heap()->nan_value();
    return isolate->heap()->AllocateHeapNumber(result);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RoundNumber) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_round()->Increment();

  if (!args[0]->IsHeapNumber()) {
    // Must be smi. Return the argument unchanged for all the other types
    // to make fuzz-natives test happy.
    return args[0];
  }

  HeapNumber* number = reinterpret_cast<HeapNumber*>(args[0]);

  double value = number->value();
  int exponent = number->get_exponent();
  int sign = number->get_sign();

  if (exponent < -1) {
    // Number in range ]-0.5..0.5[. These always round to +/-zero.
    if (sign) return isolate->heap()->minus_zero_value();
    return Smi::FromInt(0);
  }

  // We compare with kSmiValueSize - 2 because (2^30 - 0.1) has exponent 29 and
  // should be rounded to 2^30, which is not smi (for 31-bit smis, similar
  // argument holds for 32-bit smis).
  if (!sign && exponent < kSmiValueSize - 2) {
    return Smi::FromInt(static_cast<int>(value + 0.5));
  }

  // If the magnitude is big enough, there's no place for fraction part. If we
  // try to add 0.5 to this number, 1.0 will be added instead.
  if (exponent >= 52) {
    return number;
  }

  if (sign && value >= -0.5) return isolate->heap()->minus_zero_value();

  // Do not call NumberFromDouble() to avoid extra checks.
  return isolate->heap()->AllocateHeapNumber(floor(value + 0.5));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_sin) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_sin()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::SIN, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_sqrt) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_sqrt()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->heap()->AllocateHeapNumber(fast_sqrt(x));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_tan) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);
  isolate->counters()->math_tan()->Increment();

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  return isolate->transcendental_cache()->Get(TranscendentalCache::TAN, x);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateMakeDay) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);

  CONVERT_SMI_ARG_CHECKED(year, 0);
  CONVERT_SMI_ARG_CHECKED(month, 1);

  return Smi::FromInt(isolate->date_cache()->DaysFromYearMonth(year, month));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateSetValue) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);

  CONVERT_ARG_HANDLE_CHECKED(JSDate, date, 0);
  CONVERT_DOUBLE_ARG_CHECKED(time, 1);
  CONVERT_SMI_ARG_CHECKED(is_utc, 2);

  DateCache* date_cache = isolate->date_cache();

  Object* value = NULL;
  bool is_value_nan = false;
  if (isnan(time)) {
    value = isolate->heap()->nan_value();
    is_value_nan = true;
  } else if (!is_utc &&
             (time < -DateCache::kMaxTimeBeforeUTCInMs ||
              time > DateCache::kMaxTimeBeforeUTCInMs)) {
    value = isolate->heap()->nan_value();
    is_value_nan = true;
  } else {
    time = is_utc ? time : date_cache->ToUTC(static_cast<int64_t>(time));
    if (time < -DateCache::kMaxTimeInMs ||
        time > DateCache::kMaxTimeInMs) {
      value = isolate->heap()->nan_value();
      is_value_nan = true;
    } else  {
      MaybeObject* maybe_result =
          isolate->heap()->AllocateHeapNumber(DoubleToInteger(time));
      if (!maybe_result->ToObject(&value)) return maybe_result;
    }
  }
  date->SetValue(value, is_value_nan);
  return value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewArgumentsFast) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);

  Handle<JSFunction> callee = args.at<JSFunction>(0);
  Object** parameters = reinterpret_cast<Object**>(args[1]);
  const int argument_count = Smi::cast(args[2])->value();

  Handle<JSObject> result =
      isolate->factory()->NewArgumentsObject(callee, argument_count);
  // Allocate the elements if needed.
  int parameter_count = callee->shared()->formal_parameter_count();
  if (argument_count > 0) {
    if (parameter_count > 0) {
      int mapped_count = Min(argument_count, parameter_count);
      Handle<FixedArray> parameter_map =
          isolate->factory()->NewFixedArray(mapped_count + 2, NOT_TENURED);
      parameter_map->set_map(
          isolate->heap()->non_strict_arguments_elements_map());

      Handle<Map> old_map(result->map());
      Handle<Map> new_map =
          isolate->factory()->CopyMapDropTransitions(old_map);
      new_map->set_elements_kind(NON_STRICT_ARGUMENTS_ELEMENTS);

      result->set_map(*new_map);
      result->set_elements(*parameter_map);

      // Store the context and the arguments array at the beginning of the
      // parameter map.
      Handle<Context> context(isolate->context());
      Handle<FixedArray> arguments =
          isolate->factory()->NewFixedArray(argument_count, NOT_TENURED);
      parameter_map->set(0, *context);
      parameter_map->set(1, *arguments);

      // Loop over the actual parameters backwards.
      int index = argument_count - 1;
      while (index >= mapped_count) {
        // These go directly in the arguments array and have no
        // corresponding slot in the parameter map.
        arguments->set(index, *(parameters - index - 1));
        --index;
      }

      Handle<ScopeInfo> scope_info(callee->shared()->scope_info());
      while (index >= 0) {
        // Detect duplicate names to the right in the parameter list.
        Handle<String> name(scope_info->ParameterName(index));
        int context_local_count = scope_info->ContextLocalCount();
        bool duplicate = false;
        for (int j = index + 1; j < parameter_count; ++j) {
          if (scope_info->ParameterName(j) == *name) {
            duplicate = true;
            break;
          }
        }

        if (duplicate) {
          // This goes directly in the arguments array with a hole in the
          // parameter map.
          arguments->set(index, *(parameters - index - 1));
          parameter_map->set_the_hole(index + 2);
        } else {
          // The context index goes in the parameter map with a hole in the
          // arguments array.
          int context_index = -1;
          for (int j = 0; j < context_local_count; ++j) {
            if (scope_info->ContextLocalName(j) == *name) {
              context_index = j;
              break;
            }
          }
          ASSERT(context_index >= 0);
          arguments->set_the_hole(index);
          parameter_map->set(index + 2, Smi::FromInt(
              Context::MIN_CONTEXT_SLOTS + context_index));
        }

        --index;
      }
    } else {
      // If there is no aliasing, the arguments object elements are not
      // special in any way.
      Handle<FixedArray> elements =
          isolate->factory()->NewFixedArray(argument_count, NOT_TENURED);
      result->set_elements(*elements);
      for (int i = 0; i < argument_count; ++i) {
        elements->set(i, *(parameters - i - 1));
      }
    }
  }
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewStrictArgumentsFast) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);

  JSFunction* callee = JSFunction::cast(args[0]);
  Object** parameters = reinterpret_cast<Object**>(args[1]);
  const int length = args.smi_at(2);

  Object* result;
  { MaybeObject* maybe_result =
        isolate->heap()->AllocateArgumentsObject(callee, length);
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }
  // Allocate the elements if needed.
  if (length > 0) {
    // Allocate the fixed array.
    Object* obj;
    { MaybeObject* maybe_obj = isolate->heap()->AllocateRawFixedArray(length);
      if (!maybe_obj->ToObject(&obj)) return maybe_obj;
    }

    AssertNoAllocation no_gc;
    FixedArray* array = reinterpret_cast<FixedArray*>(obj);
    array->set_map_no_write_barrier(isolate->heap()->fixed_array_map());
    array->set_length(length);

    WriteBarrierMode mode = array->GetWriteBarrierMode(no_gc);
    for (int i = 0; i < length; i++) {
      array->set(i, *--parameters, mode);
    }
    JSObject::cast(result)->set_elements(FixedArray::cast(obj));
  }
  return result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewClosure) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(Context, context, 0);
  CONVERT_ARG_HANDLE_CHECKED(SharedFunctionInfo, shared, 1);
  CONVERT_BOOLEAN_ARG_CHECKED(pretenure, 2);

  // The caller ensures that we pretenure closures that are assigned
  // directly to properties.
  PretenureFlag pretenure_flag = pretenure ? TENURED : NOT_TENURED;
  Handle<JSFunction> result =
      isolate->factory()->NewFunctionFromSharedFunctionInfo(shared,
                                                            context,
                                                            pretenure_flag);
  return *result;
}


// Find the arguments of the JavaScript function invocation that called
// into C++ code. Collect these in a newly allocated array of handles (possibly
// prefixed by a number of empty handles).
static SmartArrayPointer<Handle<Object> > GetCallerArguments(
    int prefix_argc,
    int* total_argc) {
  // Find frame containing arguments passed to the caller.
  JavaScriptFrameIterator it;
  JavaScriptFrame* frame = it.frame();
  List<JSFunction*> functions(2);
  frame->GetFunctions(&functions);
  if (functions.length() > 1) {
    int inlined_jsframe_index = functions.length() - 1;
    JSFunction* inlined_function = functions[inlined_jsframe_index];
    Vector<SlotRef> args_slots =
        SlotRef::ComputeSlotMappingForArguments(
            frame,
            inlined_jsframe_index,
            inlined_function->shared()->formal_parameter_count());

    int args_count = args_slots.length();

    *total_argc = prefix_argc + args_count;
    SmartArrayPointer<Handle<Object> > param_data(
        NewArray<Handle<Object> >(*total_argc));
    for (int i = 0; i < args_count; i++) {
      Handle<Object> val = args_slots[i].GetValue();
      param_data[prefix_argc + i] = val;
    }

    args_slots.Dispose();

    return param_data;
  } else {
    it.AdvanceToArgumentsFrame();
    frame = it.frame();
    int args_count = frame->ComputeParametersCount();

    *total_argc = prefix_argc + args_count;
    SmartArrayPointer<Handle<Object> > param_data(
        NewArray<Handle<Object> >(*total_argc));
    for (int i = 0; i < args_count; i++) {
      Handle<Object> val = Handle<Object>(frame->GetParameter(i));
      param_data[prefix_argc + i] = val;
    }
    return param_data;
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionBindArguments) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, bound_function, 0);
  RUNTIME_ASSERT(args[3]->IsNumber());
  Handle<Object> bindee = args.at<Object>(1);

  // TODO(lrn): Create bound function in C++ code from premade shared info.
  bound_function->shared()->set_bound(true);
  // Get all arguments of calling function (Function.prototype.bind).
  int argc = 0;
  SmartArrayPointer<Handle<Object> > arguments = GetCallerArguments(0, &argc);
  // Don't count the this-arg.
  if (argc > 0) {
    ASSERT(*arguments[0] == args[2]);
    argc--;
  } else {
    ASSERT(args[2]->IsUndefined());
  }
  // Initialize array of bindings (function, this, and any existing arguments
  // if the function was already bound).
  Handle<FixedArray> new_bindings;
  int i;
  if (bindee->IsJSFunction() && JSFunction::cast(*bindee)->shared()->bound()) {
    Handle<FixedArray> old_bindings(
        JSFunction::cast(*bindee)->function_bindings());
    new_bindings =
        isolate->factory()->NewFixedArray(old_bindings->length() + argc);
    bindee = Handle<Object>(old_bindings->get(JSFunction::kBoundFunctionIndex));
    i = 0;
    for (int n = old_bindings->length(); i < n; i++) {
      new_bindings->set(i, old_bindings->get(i));
    }
  } else {
    int array_size = JSFunction::kBoundArgumentsStartIndex + argc;
    new_bindings = isolate->factory()->NewFixedArray(array_size);
    new_bindings->set(JSFunction::kBoundFunctionIndex, *bindee);
    new_bindings->set(JSFunction::kBoundThisIndex, args[2]);
    i = 2;
  }
  // Copy arguments, skipping the first which is "this_arg".
  for (int j = 0; j < argc; j++, i++) {
    new_bindings->set(i, *arguments[j + 1]);
  }
  new_bindings->set_map_no_write_barrier(
      isolate->heap()->fixed_cow_array_map());
  bound_function->set_function_bindings(*new_bindings);

  // Update length.
  Handle<String> length_symbol = isolate->factory()->length_symbol();
  Handle<Object> new_length(args.at<Object>(3));
  PropertyAttributes attr =
      static_cast<PropertyAttributes>(DONT_DELETE | DONT_ENUM | READ_ONLY);
  ForceSetProperty(bound_function, length_symbol, new_length, attr);
  return *bound_function;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_BoundFunctionGetBindings) {
  HandleScope handles(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, callable, 0);
  if (callable->IsJSFunction()) {
    Handle<JSFunction> function = Handle<JSFunction>::cast(callable);
    if (function->shared()->bound()) {
      Handle<FixedArray> bindings(function->function_bindings());
      ASSERT(bindings->map() == isolate->heap()->fixed_cow_array_map());
      return *isolate->factory()->NewJSArrayWithElements(bindings);
    }
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewObjectFromBound) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  // First argument is a function to use as a constructor.
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  RUNTIME_ASSERT(function->shared()->bound());

  // The argument is a bound function. Extract its bound arguments
  // and callable.
  Handle<FixedArray> bound_args =
      Handle<FixedArray>(FixedArray::cast(function->function_bindings()));
  int bound_argc = bound_args->length() - JSFunction::kBoundArgumentsStartIndex;
  Handle<Object> bound_function(
      JSReceiver::cast(bound_args->get(JSFunction::kBoundFunctionIndex)));
  ASSERT(!bound_function->IsJSFunction() ||
         !Handle<JSFunction>::cast(bound_function)->shared()->bound());

  int total_argc = 0;
  SmartArrayPointer<Handle<Object> > param_data =
      GetCallerArguments(bound_argc, &total_argc);
  for (int i = 0; i < bound_argc; i++) {
    param_data[i] = Handle<Object>(bound_args->get(
        JSFunction::kBoundArgumentsStartIndex + i));
  }

  if (!bound_function->IsJSFunction()) {
    bool exception_thrown;
    bound_function = Execution::TryGetConstructorDelegate(bound_function,
                                                          &exception_thrown);
    if (exception_thrown) return Failure::Exception();
  }
  ASSERT(bound_function->IsJSFunction());

  bool exception = false;
  Handle<Object> result =
      Execution::New(Handle<JSFunction>::cast(bound_function),
                     total_argc, *param_data, &exception);
  if (exception) {
    return Failure::Exception();
  }
  ASSERT(!result.is_null());
  return *result;
}


static void TrySettingInlineConstructStub(Isolate* isolate,
                                          Handle<JSFunction> function) {
  Handle<Object> prototype = isolate->factory()->null_value();
  if (function->has_instance_prototype()) {
    prototype = Handle<Object>(function->instance_prototype(), isolate);
  }
  if (function->shared()->CanGenerateInlineConstructor(*prototype)) {
    ConstructStubCompiler compiler(isolate);
    Handle<Code> code = compiler.CompileConstructStub(function);
    function->shared()->set_construct_stub(*code);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewObject) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  Handle<Object> constructor = args.at<Object>(0);

  // If the constructor isn't a proper function we throw a type error.
  if (!constructor->IsJSFunction()) {
    Vector< Handle<Object> > arguments = HandleVector(&constructor, 1);
    Handle<Object> type_error =
        isolate->factory()->NewTypeError("not_constructor", arguments);
    return isolate->Throw(*type_error);
  }

  Handle<JSFunction> function = Handle<JSFunction>::cast(constructor);

  // If function should not have prototype, construction is not allowed. In this
  // case generated code bailouts here, since function has no initial_map.
  if (!function->should_have_prototype() && !function->shared()->bound()) {
    Vector< Handle<Object> > arguments = HandleVector(&constructor, 1);
    Handle<Object> type_error =
        isolate->factory()->NewTypeError("not_constructor", arguments);
    return isolate->Throw(*type_error);
  }

#ifdef ENABLE_DEBUGGER_SUPPORT
  Debug* debug = isolate->debug();
  // Handle stepping into constructors if step into is active.
  if (debug->StepInActive()) {
    debug->HandleStepIn(function, Handle<Object>::null(), 0, true);
  }
#endif

  if (function->has_initial_map()) {
    if (function->initial_map()->instance_type() == JS_FUNCTION_TYPE) {
      // The 'Function' function ignores the receiver object when
      // called using 'new' and creates a new JSFunction object that
      // is returned.  The receiver object is only used for error
      // reporting if an error occurs when constructing the new
      // JSFunction. FACTORY->NewJSObject() should not be used to
      // allocate JSFunctions since it does not properly initialize
      // the shared part of the function. Since the receiver is
      // ignored anyway, we use the global object as the receiver
      // instead of a new JSFunction object. This way, errors are
      // reported the same way whether or not 'Function' is called
      // using 'new'.
      return isolate->context()->global();
    }
  }

  // The function should be compiled for the optimization hints to be
  // available. We cannot use EnsureCompiled because that forces a
  // compilation through the shared function info which makes it
  // impossible for us to optimize.
  if (!function->is_compiled()) {
    JSFunction::CompileLazy(function, CLEAR_EXCEPTION);
  }

  Handle<SharedFunctionInfo> shared(function->shared(), isolate);
  if (!function->has_initial_map() &&
      shared->IsInobjectSlackTrackingInProgress()) {
    // The tracking is already in progress for another function. We can only
    // track one initial_map at a time, so we force the completion before the
    // function is called as a constructor for the first time.
    shared->CompleteInobjectSlackTracking();
  }

  bool first_allocation = !shared->live_objects_may_exist();
  Handle<JSObject> result = isolate->factory()->NewJSObject(function);
  RETURN_IF_EMPTY_HANDLE(isolate, result);
  // Delay setting the stub if inobject slack tracking is in progress.
  if (first_allocation && !shared->IsInobjectSlackTrackingInProgress()) {
    TrySettingInlineConstructStub(isolate, function);
  }

  isolate->counters()->constructed_objects()->Increment();
  isolate->counters()->constructed_objects_runtime()->Increment();

  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FinalizeInstanceSize) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  function->shared()->CompleteInobjectSlackTracking();
  TrySettingInlineConstructStub(isolate, function);

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_LazyCompile) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  Handle<JSFunction> function = args.at<JSFunction>(0);
#ifdef DEBUG
  if (FLAG_trace_lazy && !function->shared()->is_compiled()) {
    PrintF("[lazy: ");
    function->PrintName();
    PrintF("]\n");
  }
#endif

  // Compile the target function.
  ASSERT(!function->is_compiled());
  if (!JSFunction::CompileLazy(function, KEEP_EXCEPTION)) {
    return Failure::Exception();
  }

  // All done. Return the compiled code.
  ASSERT(function->is_compiled());
  return function->code();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_LazyRecompile) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  Handle<JSFunction> function = args.at<JSFunction>(0);

  // If the function is not compiled ignore the lazy
  // recompilation. This can happen if the debugger is activated and
  // the function is returned to the not compiled state.
  if (!function->shared()->is_compiled()) {
    function->ReplaceCode(function->shared()->code());
    return function->code();
  }

  // If the function is not optimizable or debugger is active continue using the
  // code from the full compiler.
  if (!function->shared()->code()->optimizable() ||
      isolate->DebuggerHasBreakPoints()) {
    if (FLAG_trace_opt) {
      PrintF("[failed to optimize ");
      function->PrintName();
      PrintF(": is code optimizable: %s, is debugger enabled: %s]\n",
          function->shared()->code()->optimizable() ? "T" : "F",
          isolate->DebuggerHasBreakPoints() ? "T" : "F");
    }
    function->ReplaceCode(function->shared()->code());
    return function->code();
  }
  function->shared()->code()->set_profiler_ticks(0);
  if (JSFunction::CompileOptimized(function,
                                   AstNode::kNoNumber,
                                   CLEAR_EXCEPTION)) {
    return function->code();
  }
  if (FLAG_trace_opt) {
    PrintF("[failed to optimize ");
    function->PrintName();
    PrintF(": optimized compilation failed]\n");
  }
  function->ReplaceCode(function->shared()->code());
  return function->code();
}


class ActivationsFinder : public ThreadVisitor {
 public:
  explicit ActivationsFinder(JSFunction* function)
      : function_(function), has_activations_(false) {}

  void VisitThread(Isolate* isolate, ThreadLocalTop* top) {
    if (has_activations_) return;

    for (JavaScriptFrameIterator it(isolate, top); !it.done(); it.Advance()) {
      JavaScriptFrame* frame = it.frame();
      if (frame->is_optimized() && frame->function() == function_) {
        has_activations_ = true;
        return;
      }
    }
  }

  bool has_activations() { return has_activations_; }

 private:
  JSFunction* function_;
  bool has_activations_;
};


static void MaterializeArgumentsObjectInFrame(Isolate* isolate,
                                              JavaScriptFrame* frame) {
  Handle<JSFunction> function(JSFunction::cast(frame->function()), isolate);
  Handle<Object> arguments;
  for (int i = frame->ComputeExpressionsCount() - 1; i >= 0; --i) {
    if (frame->GetExpression(i) == isolate->heap()->arguments_marker()) {
      if (arguments.is_null()) {
        // FunctionGetArguments can't throw an exception, so cast away the
        // doubt with an assert.
        arguments = Handle<Object>(
            Accessors::FunctionGetArguments(*function,
                                            NULL)->ToObjectUnchecked());
        ASSERT(*arguments != isolate->heap()->null_value());
        ASSERT(*arguments != isolate->heap()->undefined_value());
      }
      frame->SetExpression(i, *arguments);
      if (FLAG_trace_deopt) {
        PrintF("Materializing arguments object for frame %p - %p: %p ",
               reinterpret_cast<void*>(frame->sp()),
               reinterpret_cast<void*>(frame->fp()),
               reinterpret_cast<void*>(*arguments));
        arguments->ShortPrint();
        PrintF("\n");
      }
    }
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NotifyDeoptimized) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  RUNTIME_ASSERT(args[0]->IsSmi());
  Deoptimizer::BailoutType type =
      static_cast<Deoptimizer::BailoutType>(args.smi_at(0));
  Deoptimizer* deoptimizer = Deoptimizer::Grab(isolate);
  ASSERT(isolate->heap()->IsAllocationAllowed());
  int jsframes = deoptimizer->jsframe_count();

  deoptimizer->MaterializeHeapNumbers();
  delete deoptimizer;

  JavaScriptFrameIterator it(isolate);
  for (int i = 0; i < jsframes - 1; i++) {
    MaterializeArgumentsObjectInFrame(isolate, it.frame());
    it.Advance();
  }

  JavaScriptFrame* frame = it.frame();
  RUNTIME_ASSERT(frame->function()->IsJSFunction());
  Handle<JSFunction> function(JSFunction::cast(frame->function()), isolate);
  MaterializeArgumentsObjectInFrame(isolate, frame);

  if (type == Deoptimizer::EAGER) {
    RUNTIME_ASSERT(function->IsOptimized());
  }

  // Avoid doing too much work when running with --always-opt and keep
  // the optimized code around.
  if (FLAG_always_opt || type == Deoptimizer::LAZY) {
    return isolate->heap()->undefined_value();
  }

  // Find other optimized activations of the function.
  bool has_other_activations = false;
  while (!it.done()) {
    JavaScriptFrame* frame = it.frame();
    if (frame->is_optimized() && frame->function() == *function) {
      has_other_activations = true;
      break;
    }
    it.Advance();
  }

  if (!has_other_activations) {
    ActivationsFinder activations_finder(*function);
    isolate->thread_manager()->IterateArchivedThreads(&activations_finder);
    has_other_activations = activations_finder.has_activations();
  }

  if (!has_other_activations) {
    if (FLAG_trace_deopt) {
      PrintF("[removing optimized code for: ");
      function->PrintName();
      PrintF("]\n");
    }
    function->ReplaceCode(function->shared()->code());
  } else {
    Deoptimizer::DeoptimizeFunction(*function);
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NotifyOSR) {
  Deoptimizer* deoptimizer = Deoptimizer::Grab(isolate);
  delete deoptimizer;
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DeoptimizeFunction) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  if (!function->IsOptimized()) return isolate->heap()->undefined_value();

  Deoptimizer::DeoptimizeFunction(*function);

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ClearFunctionTypeFeedback) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  Code* unoptimized = function->shared()->code();
  if (unoptimized->kind() == Code::FUNCTION) {
    unoptimized->ClearInlineCaches();
    unoptimized->ClearTypeFeedbackCells(isolate->heap());
  }
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_RunningInSimulator) {
#if defined(USE_SIMULATOR)
  return isolate->heap()->true_value();
#else
  return isolate->heap()->false_value();
#endif
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_OptimizeFunctionOnNextCall) {
  HandleScope scope(isolate);
  RUNTIME_ASSERT(args.length() == 1 || args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);

  if (!function->IsOptimizable()) return isolate->heap()->undefined_value();
  function->MarkForLazyRecompilation();

  Code* unoptimized = function->shared()->code();
  if (args.length() == 2 &&
      unoptimized->kind() == Code::FUNCTION) {
    CONVERT_ARG_HANDLE_CHECKED(String, type, 1);
    CHECK(type->IsEqualTo(CStrVector("osr")));
    isolate->runtime_profiler()->AttemptOnStackReplacement(*function);
    unoptimized->set_allow_osr_at_loop_nesting_level(
        Code::kMaxLoopNestingMarker);
  }

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetOptimizationStatus) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  // The least significant bit (after untagging) indicates whether the
  // function is currently optimized, regardless of reason.
  if (!V8::UseCrankshaft()) {
    return Smi::FromInt(4);  // 4 == "never".
  }
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  if (FLAG_always_opt) {
    // We may have always opt, but that is more best-effort than a real
    // promise, so we still say "no" if it is not optimized.
    return function->IsOptimized() ? Smi::FromInt(3)   // 3 == "always".
                                   : Smi::FromInt(2);  // 2 == "no".
  }
  return function->IsOptimized() ? Smi::FromInt(1)   // 1 == "yes".
                                 : Smi::FromInt(2);  // 2 == "no".
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetOptimizationCount) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  return Smi::FromInt(function->shared()->opt_count());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CompileForOnStackReplacement) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);

  // We're not prepared to handle a function with arguments object.
  ASSERT(!function->shared()->uses_arguments());

  // We have hit a back edge in an unoptimized frame for a function that was
  // selected for on-stack replacement.  Find the unoptimized code object.
  Handle<Code> unoptimized(function->shared()->code(), isolate);
  // Keep track of whether we've succeeded in optimizing.
  bool succeeded = unoptimized->optimizable();
  if (succeeded) {
    // If we are trying to do OSR when there are already optimized
    // activations of the function, it means (a) the function is directly or
    // indirectly recursive and (b) an optimized invocation has been
    // deoptimized so that we are currently in an unoptimized activation.
    // Check for optimized activations of this function.
    JavaScriptFrameIterator it(isolate);
    while (succeeded && !it.done()) {
      JavaScriptFrame* frame = it.frame();
      succeeded = !frame->is_optimized() || frame->function() != *function;
      it.Advance();
    }
  }

  int ast_id = AstNode::kNoNumber;
  if (succeeded) {
    // The top JS function is this one, the PC is somewhere in the
    // unoptimized code.
    JavaScriptFrameIterator it(isolate);
    JavaScriptFrame* frame = it.frame();
    ASSERT(frame->function() == *function);
    ASSERT(frame->LookupCode() == *unoptimized);
    ASSERT(unoptimized->contains(frame->pc()));

    // Use linear search of the unoptimized code's stack check table to find
    // the AST id matching the PC.
    Address start = unoptimized->instruction_start();
    unsigned target_pc_offset = static_cast<unsigned>(frame->pc() - start);
    Address table_cursor = start + unoptimized->stack_check_table_offset();
    uint32_t table_length = Memory::uint32_at(table_cursor);
    table_cursor += kIntSize;
    for (unsigned i = 0; i < table_length; ++i) {
      // Table entries are (AST id, pc offset) pairs.
      uint32_t pc_offset = Memory::uint32_at(table_cursor + kIntSize);
      if (pc_offset == target_pc_offset) {
        ast_id = static_cast<int>(Memory::uint32_at(table_cursor));
        break;
      }
      table_cursor += 2 * kIntSize;
    }
    ASSERT(ast_id != AstNode::kNoNumber);
    if (FLAG_trace_osr) {
      PrintF("[replacing on-stack at AST id %d in ", ast_id);
      function->PrintName();
      PrintF("]\n");
    }

    // Try to compile the optimized code.  A true return value from
    // CompileOptimized means that compilation succeeded, not necessarily
    // that optimization succeeded.
    if (JSFunction::CompileOptimized(function, ast_id, CLEAR_EXCEPTION) &&
        function->IsOptimized()) {
      DeoptimizationInputData* data = DeoptimizationInputData::cast(
          function->code()->deoptimization_data());
      if (data->OsrPcOffset()->value() >= 0) {
        if (FLAG_trace_osr) {
          PrintF("[on-stack replacement offset %d in optimized code]\n",
               data->OsrPcOffset()->value());
        }
        ASSERT(data->OsrAstId()->value() == ast_id);
      } else {
        // We may never generate the desired OSR entry if we emit an
        // early deoptimize.
        succeeded = false;
      }
    } else {
      succeeded = false;
    }
  }

  // Revert to the original stack checks in the original unoptimized code.
  if (FLAG_trace_osr) {
    PrintF("[restoring original stack checks in ");
    function->PrintName();
    PrintF("]\n");
  }
  Handle<Code> check_code;
  if (FLAG_count_based_interrupts) {
    InterruptStub interrupt_stub;
    check_code = interrupt_stub.GetCode();
  } else  // NOLINT
  {  // NOLINT
    StackCheckStub check_stub;
    check_code = check_stub.GetCode();
  }
  Handle<Code> replacement_code = isolate->builtins()->OnStackReplacement();
  Deoptimizer::RevertStackCheckCode(*unoptimized,
                                    *check_code,
                                    *replacement_code);

  // Allow OSR only at nesting level zero again.
  unoptimized->set_allow_osr_at_loop_nesting_level(0);

  // If the optimization attempt succeeded, return the AST id tagged as a
  // smi. This tells the builtin that we need to translate the unoptimized
  // frame to an optimized one.
  if (succeeded) {
    ASSERT(function->code()->kind() == Code::OPTIMIZED_FUNCTION);
    return Smi::FromInt(ast_id);
  } else {
    if (function->IsMarkedForLazyRecompilation()) {
      function->ReplaceCode(function->shared()->code());
    }
    return Smi::FromInt(-1);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CheckIsBootstrapping) {
  RUNTIME_ASSERT(isolate->bootstrapper()->IsActive());
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetRootNaN) {
  RUNTIME_ASSERT(isolate->bootstrapper()->IsActive());
  return isolate->heap()->nan_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Call) {
  HandleScope scope(isolate);
  ASSERT(args.length() >= 2);
  int argc = args.length() - 2;
  CONVERT_ARG_CHECKED(JSReceiver, fun, argc + 1);
  Object* receiver = args[0];

  // If there are too many arguments, allocate argv via malloc.
  const int argv_small_size = 10;
  Handle<Object> argv_small_buffer[argv_small_size];
  SmartArrayPointer<Handle<Object> > argv_large_buffer;
  Handle<Object>* argv = argv_small_buffer;
  if (argc > argv_small_size) {
    argv = new Handle<Object>[argc];
    if (argv == NULL) return isolate->StackOverflow();
    argv_large_buffer = SmartArrayPointer<Handle<Object> >(argv);
  }

  for (int i = 0; i < argc; ++i) {
     MaybeObject* maybe = args[1 + i];
     Object* object;
     if (!maybe->To<Object>(&object)) return maybe;
     argv[i] = Handle<Object>(object);
  }

  bool threw;
  Handle<JSReceiver> hfun(fun);
  Handle<Object> hreceiver(receiver);
  Handle<Object> result =
      Execution::Call(hfun, hreceiver, argc, argv, &threw, true);

  if (threw) return Failure::Exception();
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Apply) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 5);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, fun, 0);
  Handle<Object> receiver = args.at<Object>(1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, arguments, 2);
  CONVERT_SMI_ARG_CHECKED(offset, 3);
  CONVERT_SMI_ARG_CHECKED(argc, 4);
  ASSERT(offset >= 0);
  ASSERT(argc >= 0);

  // If there are too many arguments, allocate argv via malloc.
  const int argv_small_size = 10;
  Handle<Object> argv_small_buffer[argv_small_size];
  SmartArrayPointer<Handle<Object> > argv_large_buffer;
  Handle<Object>* argv = argv_small_buffer;
  if (argc > argv_small_size) {
    argv = new Handle<Object>[argc];
    if (argv == NULL) return isolate->StackOverflow();
    argv_large_buffer = SmartArrayPointer<Handle<Object> >(argv);
  }

  for (int i = 0; i < argc; ++i) {
    argv[i] = Object::GetElement(arguments, offset + i);
  }

  bool threw;
  Handle<Object> result =
      Execution::Call(fun, receiver, argc, argv, &threw, true);

  if (threw) return Failure::Exception();
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFunctionDelegate) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  RUNTIME_ASSERT(!args[0]->IsJSFunction());
  return *Execution::GetFunctionDelegate(args.at<Object>(0));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetConstructorDelegate) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  RUNTIME_ASSERT(!args[0]->IsJSFunction());
  return *Execution::GetConstructorDelegate(args.at<Object>(0));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewFunctionContext) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, function, 0);
  int length = function->shared()->scope_info()->ContextLength();
  Object* result;
  { MaybeObject* maybe_result =
        isolate->heap()->AllocateFunctionContext(length, function);
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }

  isolate->set_context(Context::cast(result));

  return result;  // non-failure
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PushWithContext) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  JSObject* extension_object;
  if (args[0]->IsJSObject()) {
    extension_object = JSObject::cast(args[0]);
  } else {
    // Convert the object to a proper JavaScript object.
    MaybeObject* maybe_js_object = args[0]->ToObject();
    if (!maybe_js_object->To(&extension_object)) {
      if (Failure::cast(maybe_js_object)->IsInternalError()) {
        HandleScope scope(isolate);
        Handle<Object> handle = args.at<Object>(0);
        Handle<Object> result =
            isolate->factory()->NewTypeError("with_expression",
                                             HandleVector(&handle, 1));
        return isolate->Throw(*result);
      } else {
        return maybe_js_object;
      }
    }
  }

  JSFunction* function;
  if (args[1]->IsSmi()) {
    // A smi sentinel indicates a context nested inside global code rather
    // than some function.  There is a canonical empty function that can be
    // gotten from the global context.
    function = isolate->context()->global_context()->closure();
  } else {
    function = JSFunction::cast(args[1]);
  }

  Context* context;
  MaybeObject* maybe_context =
      isolate->heap()->AllocateWithContext(function,
                                           isolate->context(),
                                           extension_object);
  if (!maybe_context->To(&context)) return maybe_context;
  isolate->set_context(context);
  return context;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PushCatchContext) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 3);
  String* name = String::cast(args[0]);
  Object* thrown_object = args[1];
  JSFunction* function;
  if (args[2]->IsSmi()) {
    // A smi sentinel indicates a context nested inside global code rather
    // than some function.  There is a canonical empty function that can be
    // gotten from the global context.
    function = isolate->context()->global_context()->closure();
  } else {
    function = JSFunction::cast(args[2]);
  }
  Context* context;
  MaybeObject* maybe_context =
      isolate->heap()->AllocateCatchContext(function,
                                            isolate->context(),
                                            name,
                                            thrown_object);
  if (!maybe_context->To(&context)) return maybe_context;
  isolate->set_context(context);
  return context;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PushBlockContext) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  ScopeInfo* scope_info = ScopeInfo::cast(args[0]);
  JSFunction* function;
  if (args[1]->IsSmi()) {
    // A smi sentinel indicates a context nested inside global code rather
    // than some function.  There is a canonical empty function that can be
    // gotten from the global context.
    function = isolate->context()->global_context()->closure();
  } else {
    function = JSFunction::cast(args[1]);
  }
  Context* context;
  MaybeObject* maybe_context =
      isolate->heap()->AllocateBlockContext(function,
                                            isolate->context(),
                                            scope_info);
  if (!maybe_context->To(&context)) return maybe_context;
  isolate->set_context(context);
  return context;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PushModuleContext) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(ScopeInfo, scope_info, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSModule, instance, 1);

  Context* context;
  MaybeObject* maybe_context =
      isolate->heap()->AllocateModuleContext(isolate->context(),
                                             scope_info);
  if (!maybe_context->To(&context)) return maybe_context;
  // Also initialize the context slot of the instance object.
  instance->set_context(context);
  isolate->set_context(context);

  return context;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DeleteContextSlot) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(Context, context, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);

  int index;
  PropertyAttributes attributes;
  ContextLookupFlags flags = FOLLOW_CHAINS;
  BindingFlags binding_flags;
  Handle<Object> holder = context->Lookup(name,
                                          flags,
                                          &index,
                                          &attributes,
                                          &binding_flags);

  // If the slot was not found the result is true.
  if (holder.is_null()) {
    return isolate->heap()->true_value();
  }

  // If the slot was found in a context, it should be DONT_DELETE.
  if (holder->IsContext()) {
    return isolate->heap()->false_value();
  }

  // The slot was found in a JSObject, either a context extension object,
  // the global object, or the subject of a with.  Try to delete it
  // (respecting DONT_DELETE).
  Handle<JSObject> object = Handle<JSObject>::cast(holder);
  return object->DeleteProperty(*name, JSReceiver::NORMAL_DELETION);
}


// A mechanism to return a pair of Object pointers in registers (if possible).
// How this is achieved is calling convention-dependent.
// All currently supported x86 compiles uses calling conventions that are cdecl
// variants where a 64-bit value is returned in two 32-bit registers
// (edx:eax on ia32, r1:r0 on ARM).
// In AMD-64 calling convention a struct of two pointers is returned in rdx:rax.
// In Win64 calling convention, a struct of two pointers is returned in memory,
// allocated by the caller, and passed as a pointer in a hidden first parameter.
#ifdef V8_HOST_ARCH_64_BIT
struct ObjectPair {
  MaybeObject* x;
  MaybeObject* y;
};

static inline ObjectPair MakePair(MaybeObject* x, MaybeObject* y) {
  ObjectPair result = {x, y};
  // Pointers x and y returned in rax and rdx, in AMD-x64-abi.
  // In Win64 they are assigned to a hidden first argument.
  return result;
}
#else
typedef uint64_t ObjectPair;
static inline ObjectPair MakePair(MaybeObject* x, MaybeObject* y) {
  return reinterpret_cast<uint32_t>(x) |
      (reinterpret_cast<ObjectPair>(y) << 32);
}
#endif


static inline MaybeObject* Unhole(Heap* heap,
                                  MaybeObject* x,
                                  PropertyAttributes attributes) {
  ASSERT(!x->IsTheHole() || (attributes & READ_ONLY) != 0);
  USE(attributes);
  return x->IsTheHole() ? heap->undefined_value() : x;
}


static Object* ComputeReceiverForNonGlobal(Isolate* isolate,
                                           JSObject* holder) {
  ASSERT(!holder->IsGlobalObject());
  Context* top = isolate->context();
  // Get the context extension function.
  JSFunction* context_extension_function =
      top->global_context()->context_extension_function();
  // If the holder isn't a context extension object, we just return it
  // as the receiver. This allows arguments objects to be used as
  // receivers, but only if they are put in the context scope chain
  // explicitly via a with-statement.
  Object* constructor = holder->map()->constructor();
  if (constructor != context_extension_function) return holder;
  // Fall back to using the global object as the implicit receiver if
  // the property turns out to be a local variable allocated in a
  // context extension object - introduced via eval. Implicit global
  // receivers are indicated with the hole value.
  return isolate->heap()->the_hole_value();
}


static ObjectPair LoadContextSlotHelper(Arguments args,
                                        Isolate* isolate,
                                        bool throw_error) {
  HandleScope scope(isolate);
  ASSERT_EQ(2, args.length());

  if (!args[0]->IsContext() || !args[1]->IsString()) {
    return MakePair(isolate->ThrowIllegalOperation(), NULL);
  }
  Handle<Context> context = args.at<Context>(0);
  Handle<String> name = args.at<String>(1);

  int index;
  PropertyAttributes attributes;
  ContextLookupFlags flags = FOLLOW_CHAINS;
  BindingFlags binding_flags;
  Handle<Object> holder = context->Lookup(name,
                                          flags,
                                          &index,
                                          &attributes,
                                          &binding_flags);

  // If the index is non-negative, the slot has been found in a context.
  if (index >= 0) {
    ASSERT(holder->IsContext());
    // If the "property" we were looking for is a local variable, the
    // receiver is the global object; see ECMA-262, 3rd., 10.1.6 and 10.2.3.
    //
    // Use the hole as the receiver to signal that the receiver is implicit
    // and that the global receiver should be used (as distinguished from an
    // explicit receiver that happens to be a global object).
    Handle<Object> receiver = isolate->factory()->the_hole_value();
    Object* value = Context::cast(*holder)->get(index);
    // Check for uninitialized bindings.
    switch (binding_flags) {
      case MUTABLE_CHECK_INITIALIZED:
      case IMMUTABLE_CHECK_INITIALIZED_HARMONY:
        if (value->IsTheHole()) {
          Handle<Object> reference_error =
              isolate->factory()->NewReferenceError("not_defined",
                                                    HandleVector(&name, 1));
          return MakePair(isolate->Throw(*reference_error), NULL);
        }
        // FALLTHROUGH
      case MUTABLE_IS_INITIALIZED:
      case IMMUTABLE_IS_INITIALIZED:
      case IMMUTABLE_IS_INITIALIZED_HARMONY:
        ASSERT(!value->IsTheHole());
        return MakePair(value, *receiver);
      case IMMUTABLE_CHECK_INITIALIZED:
        return MakePair(Unhole(isolate->heap(), value, attributes), *receiver);
      case MISSING_BINDING:
        UNREACHABLE();
        return MakePair(NULL, NULL);
    }
  }

  // Otherwise, if the slot was found the holder is a context extension
  // object, subject of a with, or a global object.  We read the named
  // property from it.
  if (!holder.is_null()) {
    Handle<JSObject> object = Handle<JSObject>::cast(holder);
    ASSERT(object->HasProperty(*name));
    // GetProperty below can cause GC.
    Handle<Object> receiver_handle(object->IsGlobalObject()
        ? GlobalObject::cast(*object)->global_receiver()
        : ComputeReceiverForNonGlobal(isolate, *object));

    // No need to unhole the value here.  This is taken care of by the
    // GetProperty function.
    MaybeObject* value = object->GetProperty(*name);
    return MakePair(value, *receiver_handle);
  }

  if (throw_error) {
    // The property doesn't exist - throw exception.
    Handle<Object> reference_error =
        isolate->factory()->NewReferenceError("not_defined",
                                              HandleVector(&name, 1));
    return MakePair(isolate->Throw(*reference_error), NULL);
  } else {
    // The property doesn't exist - return undefined.
    return MakePair(isolate->heap()->undefined_value(),
                    isolate->heap()->undefined_value());
  }
}


RUNTIME_FUNCTION(ObjectPair, Runtime_LoadContextSlot) {
  return LoadContextSlotHelper(args, isolate, true);
}


RUNTIME_FUNCTION(ObjectPair, Runtime_LoadContextSlotNoReferenceError) {
  return LoadContextSlotHelper(args, isolate, false);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StoreContextSlot) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);

  Handle<Object> value(args[0], isolate);
  CONVERT_ARG_HANDLE_CHECKED(Context, context, 1);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 2);
  CONVERT_LANGUAGE_MODE_ARG(language_mode, 3);
  StrictModeFlag strict_mode = (language_mode == CLASSIC_MODE)
      ? kNonStrictMode : kStrictMode;

  int index;
  PropertyAttributes attributes;
  ContextLookupFlags flags = FOLLOW_CHAINS;
  BindingFlags binding_flags;
  Handle<Object> holder = context->Lookup(name,
                                          flags,
                                          &index,
                                          &attributes,
                                          &binding_flags);

  if (index >= 0) {
    // The property was found in a context slot.
    Handle<Context> context = Handle<Context>::cast(holder);
    if (binding_flags == MUTABLE_CHECK_INITIALIZED &&
        context->get(index)->IsTheHole()) {
      Handle<Object> error =
          isolate->factory()->NewReferenceError("not_defined",
                                                HandleVector(&name, 1));
      return isolate->Throw(*error);
    }
    // Ignore if read_only variable.
    if ((attributes & READ_ONLY) == 0) {
      // Context is a fixed array and set cannot fail.
      context->set(index, *value);
    } else if (strict_mode == kStrictMode) {
      // Setting read only property in strict mode.
      Handle<Object> error =
          isolate->factory()->NewTypeError("strict_cannot_assign",
                                           HandleVector(&name, 1));
      return isolate->Throw(*error);
    }
    return *value;
  }

  // Slow case: The property is not in a context slot.  It is either in a
  // context extension object, a property of the subject of a with, or a
  // property of the global object.
  Handle<JSObject> object;

  if (!holder.is_null()) {
    // The property exists on the holder.
    object = Handle<JSObject>::cast(holder);
  } else {
    // The property was not found.
    ASSERT(attributes == ABSENT);

    if (strict_mode == kStrictMode) {
      // Throw in strict mode (assignment to undefined variable).
      Handle<Object> error =
          isolate->factory()->NewReferenceError(
              "not_defined", HandleVector(&name, 1));
      return isolate->Throw(*error);
    }
    // In non-strict mode, the property is added to the global object.
    attributes = NONE;
    object = Handle<JSObject>(isolate->context()->global());
  }

  // Set the property if it's not read only or doesn't yet exist.
  if ((attributes & READ_ONLY) == 0 ||
      (object->GetLocalPropertyAttribute(*name) == ABSENT)) {
    RETURN_IF_EMPTY_HANDLE(
        isolate,
        JSReceiver::SetProperty(object, name, value, NONE, strict_mode));
  } else if (strict_mode == kStrictMode && (attributes & READ_ONLY) != 0) {
    // Setting read only property in strict mode.
    Handle<Object> error =
      isolate->factory()->NewTypeError(
          "strict_cannot_assign", HandleVector(&name, 1));
    return isolate->Throw(*error);
  }
  return *value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Throw) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  return isolate->Throw(args[0]);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ReThrow) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  return isolate->ReThrow(args[0]);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_PromoteScheduledException) {
  ASSERT_EQ(0, args.length());
  return isolate->PromoteScheduledException();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ThrowReferenceError) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  Handle<Object> name(args[0], isolate);
  Handle<Object> reference_error =
    isolate->factory()->NewReferenceError("not_defined",
                                          HandleVector(&name, 1));
  return isolate->Throw(*reference_error);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_StackGuard) {
  ASSERT(args.length() == 0);

  // First check if this is a real stack overflow.
  if (isolate->stack_guard()->IsStackOverflow()) {
    NoHandleAllocation na;
    return isolate->StackOverflow();
  }

  return Execution::HandleStackGuardInterrupt(isolate);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Interrupt) {
  ASSERT(args.length() == 0);
  return Execution::HandleStackGuardInterrupt(isolate);
}


static int StackSize() {
  int n = 0;
  for (JavaScriptFrameIterator it; !it.done(); it.Advance()) n++;
  return n;
}


static void PrintTransition(Object* result) {
  // indentation
  { const int nmax = 80;
    int n = StackSize();
    if (n <= nmax)
      PrintF("%4d:%*s", n, n, "");
    else
      PrintF("%4d:%*s", n, nmax, "...");
  }

  if (result == NULL) {
    JavaScriptFrame::PrintTop(stdout, true, false);
    PrintF(" {\n");
  } else {
    // function result
    PrintF("} -> ");
    result->ShortPrint();
    PrintF("\n");
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_TraceEnter) {
  ASSERT(args.length() == 0);
  NoHandleAllocation ha;
  PrintTransition(NULL);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_TraceExit) {
  NoHandleAllocation ha;
  PrintTransition(args[0]);
  return args[0];  // return TOS
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPrint) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

#ifdef DEBUG
  if (args[0]->IsString()) {
    // If we have a string, assume it's a code "marker"
    // and print some interesting cpu debugging info.
    JavaScriptFrameIterator it(isolate);
    JavaScriptFrame* frame = it.frame();
    PrintF("fp = %p, sp = %p, caller_sp = %p: ",
           frame->fp(), frame->sp(), frame->caller_sp());
  } else {
    PrintF("DebugPrint: ");
  }
  args[0]->Print();
  if (args[0]->IsHeapObject()) {
    PrintF("\n");
    HeapObject::cast(args[0])->map()->Print();
  }
#else
  // ShortPrint is available in release mode. Print is not.
  args[0]->ShortPrint();
#endif
  PrintF("\n");
  Flush();

  return args[0];  // return TOS
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugTrace) {
  ASSERT(args.length() == 0);
  NoHandleAllocation ha;
  isolate->PrintStack();
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateCurrentTime) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 0);

  // According to ECMA-262, section 15.9.1, page 117, the precision of
  // the number in a Date object representing a particular instant in
  // time is milliseconds. Therefore, we floor the result of getting
  // the OS time.
  double millis = floor(OS::TimeCurrentMillis());
  return isolate->heap()->NumberFromDouble(millis);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateParseString) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(String, str, 0);
  FlattenString(str);

  CONVERT_ARG_HANDLE_CHECKED(JSArray, output, 1);

  MaybeObject* maybe_result_array =
      output->EnsureCanContainHeapObjectElements();
  if (maybe_result_array->IsFailure()) return maybe_result_array;
  RUNTIME_ASSERT(output->HasFastObjectElements());

  AssertNoAllocation no_allocation;

  FixedArray* output_array = FixedArray::cast(output->elements());
  RUNTIME_ASSERT(output_array->length() >= DateParser::OUTPUT_SIZE);
  bool result;
  String::FlatContent str_content = str->GetFlatContent();
  if (str_content.IsAscii()) {
    result = DateParser::Parse(str_content.ToAsciiVector(),
                               output_array,
                               isolate->unicode_cache());
  } else {
    ASSERT(str_content.IsTwoByte());
    result = DateParser::Parse(str_content.ToUC16Vector(),
                               output_array,
                               isolate->unicode_cache());
  }

  if (result) {
    return *output;
  } else {
    return isolate->heap()->null_value();
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateLocalTimezone) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  int64_t time = isolate->date_cache()->EquivalentTime(static_cast<int64_t>(x));
  const char* zone = OS::LocalTimezone(static_cast<double>(time));
  return isolate->heap()->AllocateStringFromUtf8(CStrVector(zone));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DateToUTC) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
  int64_t time = isolate->date_cache()->ToUTC(static_cast<int64_t>(x));

  return isolate->heap()->NumberFromDouble(static_cast<double>(time));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GlobalReceiver) {
  ASSERT(args.length() == 1);
  Object* global = args[0];
  if (!global->IsJSGlobalObject()) return isolate->heap()->null_value();
  return JSGlobalObject::cast(global)->global_receiver();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ParseJson) {
  HandleScope scope(isolate);
  ASSERT_EQ(1, args.length());
  CONVERT_ARG_HANDLE_CHECKED(String, source, 0);

  Zone* zone = isolate->zone();
  source = Handle<String>(source->TryFlattenGetString());
  // Optimized fast case where we only have ASCII characters.
  Handle<Object> result;
  if (source->IsSeqAsciiString()) {
    result = JsonParser<true>::Parse(source, zone);
  } else {
    result = JsonParser<false>::Parse(source, zone);
  }
  if (result.is_null()) {
    // Syntax error or stack overflow in scanner.
    ASSERT(isolate->has_pending_exception());
    return Failure::Exception();
  }
  return *result;
}


bool CodeGenerationFromStringsAllowed(Isolate* isolate,
                                      Handle<Context> context) {
  ASSERT(context->allow_code_gen_from_strings()->IsFalse());
  // Check with callback if set.
  AllowCodeGenerationFromStringsCallback callback =
      isolate->allow_code_gen_callback();
  if (callback == NULL) {
    // No callback set and code generation disallowed.
    return false;
  } else {
    // Callback set. Let it decide if code generation is allowed.
    VMState state(isolate, EXTERNAL);
    return callback(v8::Utils::ToLocal(context));
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CompileString) {
  HandleScope scope(isolate);
  ASSERT_EQ(1, args.length());
  CONVERT_ARG_HANDLE_CHECKED(String, source, 0);

  // Extract global context.
  Handle<Context> context(isolate->context()->global_context());

  // Check if global context allows code generation from
  // strings. Throw an exception if it doesn't.
  if (context->allow_code_gen_from_strings()->IsFalse() &&
      !CodeGenerationFromStringsAllowed(isolate, context)) {
    return isolate->Throw(*isolate->factory()->NewError(
        "code_gen_from_strings", HandleVector<Object>(NULL, 0)));
  }

  // Compile source string in the global context.
  Handle<SharedFunctionInfo> shared = Compiler::CompileEval(
      source, context, true, CLASSIC_MODE, RelocInfo::kNoPosition);
  if (shared.is_null()) return Failure::Exception();
  Handle<JSFunction> fun =
      isolate->factory()->NewFunctionFromSharedFunctionInfo(shared,
                                                            context,
                                                            NOT_TENURED);
  return *fun;
}


static ObjectPair CompileGlobalEval(Isolate* isolate,
                                    Handle<String> source,
                                    Handle<Object> receiver,
                                    LanguageMode language_mode,
                                    int scope_position) {
  Handle<Context> context = Handle<Context>(isolate->context());
  Handle<Context> global_context = Handle<Context>(context->global_context());

  // Check if global context allows code generation from
  // strings. Throw an exception if it doesn't.
  if (global_context->allow_code_gen_from_strings()->IsFalse() &&
      !CodeGenerationFromStringsAllowed(isolate, global_context)) {
    isolate->Throw(*isolate->factory()->NewError(
        "code_gen_from_strings", HandleVector<Object>(NULL, 0)));
    return MakePair(Failure::Exception(), NULL);
  }

  // Deal with a normal eval call with a string argument. Compile it
  // and return the compiled function bound in the local context.
  Handle<SharedFunctionInfo> shared = Compiler::CompileEval(
      source,
      Handle<Context>(isolate->context()),
      context->IsGlobalContext(),
      language_mode,
      scope_position);
  if (shared.is_null()) return MakePair(Failure::Exception(), NULL);
  Handle<JSFunction> compiled =
      isolate->factory()->NewFunctionFromSharedFunctionInfo(
          shared, context, NOT_TENURED);
  return MakePair(*compiled, *receiver);
}


RUNTIME_FUNCTION(ObjectPair, Runtime_ResolvePossiblyDirectEval) {
  ASSERT(args.length() == 5);

  HandleScope scope(isolate);
  Handle<Object> callee = args.at<Object>(0);

  // If "eval" didn't refer to the original GlobalEval, it's not a
  // direct call to eval.
  // (And even if it is, but the first argument isn't a string, just let
  // execution default to an indirect call to eval, which will also return
  // the first argument without doing anything).
  if (*callee != isolate->global_context()->global_eval_fun() ||
      !args[1]->IsString()) {
    return MakePair(*callee, isolate->heap()->the_hole_value());
  }

  CONVERT_LANGUAGE_MODE_ARG(language_mode, 3);
  ASSERT(args[4]->IsSmi());
  return CompileGlobalEval(isolate,
                           args.at<String>(1),
                           args.at<Object>(2),
                           language_mode,
                           args.smi_at(4));
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SetNewFunctionAttributes) {
  // This utility adjusts the property attributes for newly created Function
  // object ("new Function(...)") by changing the map.
  // All it does is changing the prototype property to enumerable
  // as specified in ECMA262, 15.3.5.2.
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, func, 0);

  Handle<Map> map = func->shared()->is_classic_mode()
      ? isolate->function_instance_map()
      : isolate->strict_mode_function_instance_map();

  ASSERT(func->map()->instance_type() == map->instance_type());
  ASSERT(func->map()->instance_size() == map->instance_size());
  func->set_map(*map);
  return *func;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_AllocateInNewSpace) {
  // Allocate a block of memory in NewSpace (filled with a filler).
  // Use as fallback for allocation in generated code when NewSpace
  // is full.
  ASSERT(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(Smi, size_smi, 0);
  int size = size_smi->value();
  RUNTIME_ASSERT(IsAligned(size, kPointerSize));
  RUNTIME_ASSERT(size > 0);
  Heap* heap = isolate->heap();
  const int kMinFreeNewSpaceAfterGC = heap->InitialSemiSpaceSize() * 3/4;
  RUNTIME_ASSERT(size <= kMinFreeNewSpaceAfterGC);
  Object* allocation;
  { MaybeObject* maybe_allocation = heap->new_space()->AllocateRaw(size);
    if (maybe_allocation->ToObject(&allocation)) {
      heap->CreateFillerObjectAt(HeapObject::cast(allocation)->address(), size);
    }
    return maybe_allocation;
  }
}


// Push an object unto an array of objects if it is not already in the
// array.  Returns true if the element was pushed on the stack and
// false otherwise.
RUNTIME_FUNCTION(MaybeObject*, Runtime_PushIfAbsent) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSArray, array, 0);
  CONVERT_ARG_CHECKED(JSObject, element, 1);
  RUNTIME_ASSERT(array->HasFastSmiOrObjectElements());
  int length = Smi::cast(array->length())->value();
  FixedArray* elements = FixedArray::cast(array->elements());
  for (int i = 0; i < length; i++) {
    if (elements->get(i) == element) return isolate->heap()->false_value();
  }
  Object* obj;
  // Strict not needed. Used for cycle detection in Array join implementation.
  { MaybeObject* maybe_obj =
        array->SetFastElement(length, element, kNonStrictMode, true);
    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
  }
  return isolate->heap()->true_value();
}


class ArrayConcatVisitor {
 public:
  ArrayConcatVisitor(Isolate* isolate,
                     Handle<FixedArray> storage,
                     bool fast_elements) :
      isolate_(isolate),
      storage_(Handle<FixedArray>::cast(
          isolate->global_handles()->Create(*storage))),
      index_offset_(0u),
      fast_elements_(fast_elements) { }

  ~ArrayConcatVisitor() {
    clear_storage();
  }

  void visit(uint32_t i, Handle<Object> elm) {
    if (i >= JSObject::kMaxElementCount - index_offset_) return;
    uint32_t index = index_offset_ + i;

    if (fast_elements_) {
      if (index < static_cast<uint32_t>(storage_->length())) {
        storage_->set(index, *elm);
        return;
      }
      // Our initial estimate of length was foiled, possibly by
      // getters on the arrays increasing the length of later arrays
      // during iteration.
      // This shouldn't happen in anything but pathological cases.
      SetDictionaryMode(index);
      // Fall-through to dictionary mode.
    }
    ASSERT(!fast_elements_);
    Handle<SeededNumberDictionary> dict(
        SeededNumberDictionary::cast(*storage_));
    Handle<SeededNumberDictionary> result =
        isolate_->factory()->DictionaryAtNumberPut(dict, index, elm);
    if (!result.is_identical_to(dict)) {
      // Dictionary needed to grow.
      clear_storage();
      set_storage(*result);
    }
}

  void increase_index_offset(uint32_t delta) {
    if (JSObject::kMaxElementCount - index_offset_ < delta) {
      index_offset_ = JSObject::kMaxElementCount;
    } else {
      index_offset_ += delta;
    }
  }

  Handle<JSArray> ToArray() {
    Handle<JSArray> array = isolate_->factory()->NewJSArray(0);
    Handle<Object> length =
        isolate_->factory()->NewNumber(static_cast<double>(index_offset_));
    Handle<Map> map;
    if (fast_elements_) {
      map = isolate_->factory()->GetElementsTransitionMap(array,
                                                          FAST_HOLEY_ELEMENTS);
    } else {
      map = isolate_->factory()->GetElementsTransitionMap(array,
                                                          DICTIONARY_ELEMENTS);
    }
    array->set_map(*map);
    array->set_length(*length);
    array->set_elements(*storage_);
    return array;
  }

 private:
  // Convert storage to dictionary mode.
  void SetDictionaryMode(uint32_t index) {
    ASSERT(fast_elements_);
    Handle<FixedArray> current_storage(*storage_);
    Handle<SeededNumberDictionary> slow_storage(
        isolate_->factory()->NewSeededNumberDictionary(
            current_storage->length()));
    uint32_t current_length = static_cast<uint32_t>(current_storage->length());
    for (uint32_t i = 0; i < current_length; i++) {
      HandleScope loop_scope;
      Handle<Object> element(current_storage->get(i));
      if (!element->IsTheHole()) {
        Handle<SeededNumberDictionary> new_storage =
          isolate_->factory()->DictionaryAtNumberPut(slow_storage, i, element);
        if (!new_storage.is_identical_to(slow_storage)) {
          slow_storage = loop_scope.CloseAndEscape(new_storage);
        }
      }
    }
    clear_storage();
    set_storage(*slow_storage);
    fast_elements_ = false;
  }

  inline void clear_storage() {
    isolate_->global_handles()->Destroy(
        Handle<Object>::cast(storage_).location());
  }

  inline void set_storage(FixedArray* storage) {
    storage_ = Handle<FixedArray>::cast(
        isolate_->global_handles()->Create(storage));
  }

  Isolate* isolate_;
  Handle<FixedArray> storage_;  // Always a global handle.
  // Index after last seen index. Always less than or equal to
  // JSObject::kMaxElementCount.
  uint32_t index_offset_;
  bool fast_elements_;
};


static uint32_t EstimateElementCount(Handle<JSArray> array) {
  uint32_t length = static_cast<uint32_t>(array->length()->Number());
  int element_count = 0;
  switch (array->GetElementsKind()) {
    case FAST_SMI_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      // Fast elements can't have lengths that are not representable by
      // a 32-bit signed integer.
      ASSERT(static_cast<int32_t>(FixedArray::kMaxLength) >= 0);
      int fast_length = static_cast<int>(length);
      Handle<FixedArray> elements(FixedArray::cast(array->elements()));
      for (int i = 0; i < fast_length; i++) {
        if (!elements->get(i)->IsTheHole()) element_count++;
      }
      break;
    }
    case FAST_DOUBLE_ELEMENTS:
    case FAST_HOLEY_DOUBLE_ELEMENTS:
      // TODO(1810): Decide if it's worthwhile to implement this.
      UNREACHABLE();
      break;
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dictionary(
          SeededNumberDictionary::cast(array->elements()));
      int capacity = dictionary->Capacity();
      for (int i = 0; i < capacity; i++) {
        Handle<Object> key(dictionary->KeyAt(i));
        if (dictionary->IsKey(*key)) {
          element_count++;
        }
      }
      break;
    }
    case NON_STRICT_ARGUMENTS_ELEMENTS:
    case EXTERNAL_BYTE_ELEMENTS:
    case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
    case EXTERNAL_SHORT_ELEMENTS:
    case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
    case EXTERNAL_INT_ELEMENTS:
    case EXTERNAL_UNSIGNED_INT_ELEMENTS:
    case EXTERNAL_FLOAT_ELEMENTS:
    case EXTERNAL_DOUBLE_ELEMENTS:
    case EXTERNAL_PIXEL_ELEMENTS:
      // External arrays are always dense.
      return length;
  }
  // As an estimate, we assume that the prototype doesn't contain any
  // inherited elements.
  return element_count;
}



template<class ExternalArrayClass, class ElementType>
static void IterateExternalArrayElements(Isolate* isolate,
                                         Handle<JSObject> receiver,
                                         bool elements_are_ints,
                                         bool elements_are_guaranteed_smis,
                                         ArrayConcatVisitor* visitor) {
  Handle<ExternalArrayClass> array(
      ExternalArrayClass::cast(receiver->elements()));
  uint32_t len = static_cast<uint32_t>(array->length());

  ASSERT(visitor != NULL);
  if (elements_are_ints) {
    if (elements_are_guaranteed_smis) {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope;
        Handle<Smi> e(Smi::FromInt(static_cast<int>(array->get_scalar(j))));
        visitor->visit(j, e);
      }
    } else {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope;
        int64_t val = static_cast<int64_t>(array->get_scalar(j));
        if (Smi::IsValid(static_cast<intptr_t>(val))) {
          Handle<Smi> e(Smi::FromInt(static_cast<int>(val)));
          visitor->visit(j, e);
        } else {
          Handle<Object> e =
              isolate->factory()->NewNumber(static_cast<ElementType>(val));
          visitor->visit(j, e);
        }
      }
    }
  } else {
    for (uint32_t j = 0; j < len; j++) {
      HandleScope loop_scope(isolate);
      Handle<Object> e = isolate->factory()->NewNumber(array->get_scalar(j));
      visitor->visit(j, e);
    }
  }
}


// Used for sorting indices in a List<uint32_t>.
static int compareUInt32(const uint32_t* ap, const uint32_t* bp) {
  uint32_t a = *ap;
  uint32_t b = *bp;
  return (a == b) ? 0 : (a < b) ? -1 : 1;
}


static void CollectElementIndices(Handle<JSObject> object,
                                  uint32_t range,
                                  List<uint32_t>* indices) {
  ElementsKind kind = object->GetElementsKind();
  switch (kind) {
    case FAST_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      Handle<FixedArray> elements(FixedArray::cast(object->elements()));
      uint32_t length = static_cast<uint32_t>(elements->length());
      if (range < length) length = range;
      for (uint32_t i = 0; i < length; i++) {
        if (!elements->get(i)->IsTheHole()) {
          indices->Add(i);
        }
      }
      break;
    }
    case FAST_HOLEY_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS: {
      // TODO(1810): Decide if it's worthwhile to implement this.
      UNREACHABLE();
      break;
    }
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dict(
          SeededNumberDictionary::cast(object->elements()));
      uint32_t capacity = dict->Capacity();
      for (uint32_t j = 0; j < capacity; j++) {
        HandleScope loop_scope;
        Handle<Object> k(dict->KeyAt(j));
        if (dict->IsKey(*k)) {
          ASSERT(k->IsNumber());
          uint32_t index = static_cast<uint32_t>(k->Number());
          if (index < range) {
            indices->Add(index);
          }
        }
      }
      break;
    }
    default: {
      int dense_elements_length;
      switch (kind) {
        case EXTERNAL_PIXEL_ELEMENTS: {
          dense_elements_length =
              ExternalPixelArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_BYTE_ELEMENTS: {
          dense_elements_length =
              ExternalByteArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_UNSIGNED_BYTE_ELEMENTS: {
          dense_elements_length =
              ExternalUnsignedByteArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_SHORT_ELEMENTS: {
          dense_elements_length =
              ExternalShortArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_UNSIGNED_SHORT_ELEMENTS: {
          dense_elements_length =
              ExternalUnsignedShortArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_INT_ELEMENTS: {
          dense_elements_length =
              ExternalIntArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_UNSIGNED_INT_ELEMENTS: {
          dense_elements_length =
              ExternalUnsignedIntArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_FLOAT_ELEMENTS: {
          dense_elements_length =
              ExternalFloatArray::cast(object->elements())->length();
          break;
        }
        case EXTERNAL_DOUBLE_ELEMENTS: {
          dense_elements_length =
              ExternalDoubleArray::cast(object->elements())->length();
          break;
        }
        default:
          UNREACHABLE();
          dense_elements_length = 0;
          break;
      }
      uint32_t length = static_cast<uint32_t>(dense_elements_length);
      if (range <= length) {
        length = range;
        // We will add all indices, so we might as well clear it first
        // and avoid duplicates.
        indices->Clear();
      }
      for (uint32_t i = 0; i < length; i++) {
        indices->Add(i);
      }
      if (length == range) return;  // All indices accounted for already.
      break;
    }
  }

  Handle<Object> prototype(object->GetPrototype());
  if (prototype->IsJSObject()) {
    // The prototype will usually have no inherited element indices,
    // but we have to check.
    CollectElementIndices(Handle<JSObject>::cast(prototype), range, indices);
  }
}


static bool IterateElements(Isolate* isolate,
                            Handle<JSArray> receiver,
                            ArrayConcatVisitor* visitor) {
  uint32_t length = static_cast<uint32_t>(receiver->length()->Number());
  switch (receiver->GetElementsKind()) {
    case FAST_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      // Run through the elements FixedArray and use HasElement and GetElement
      // to check the prototype for missing elements.
      Handle<FixedArray> elements(FixedArray::cast(receiver->elements()));
      int fast_length = static_cast<int>(length);
      ASSERT(fast_length <= elements->length());
      for (int j = 0; j < fast_length; j++) {
        HandleScope loop_scope(isolate);
        Handle<Object> element_value(elements->get(j), isolate);
        if (!element_value->IsTheHole()) {
          visitor->visit(j, element_value);
        } else if (receiver->HasElement(j)) {
          // Call GetElement on receiver, not its prototype, or getters won't
          // have the correct receiver.
          element_value = Object::GetElement(receiver, j);
          RETURN_IF_EMPTY_HANDLE_VALUE(isolate, element_value, false);
          visitor->visit(j, element_value);
        }
      }
      break;
    }
    case FAST_HOLEY_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS: {
      // TODO(1810): Decide if it's worthwhile to implement this.
      UNREACHABLE();
      break;
    }
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dict(receiver->element_dictionary());
      List<uint32_t> indices(dict->Capacity() / 2);
      // Collect all indices in the object and the prototypes less
      // than length. This might introduce duplicates in the indices list.
      CollectElementIndices(receiver, length, &indices);
      indices.Sort(&compareUInt32);
      int j = 0;
      int n = indices.length();
      while (j < n) {
        HandleScope loop_scope;
        uint32_t index = indices[j];
        Handle<Object> element = Object::GetElement(receiver, index);
        RETURN_IF_EMPTY_HANDLE_VALUE(isolate, element, false);
        visitor->visit(index, element);
        // Skip to next different index (i.e., omit duplicates).
        do {
          j++;
        } while (j < n && indices[j] == index);
      }
      break;
    }
    case EXTERNAL_PIXEL_ELEMENTS: {
      Handle<ExternalPixelArray> pixels(ExternalPixelArray::cast(
          receiver->elements()));
      for (uint32_t j = 0; j < length; j++) {
        Handle<Smi> e(Smi::FromInt(pixels->get_scalar(j)));
        visitor->visit(j, e);
      }
      break;
    }
    case EXTERNAL_BYTE_ELEMENTS: {
      IterateExternalArrayElements<ExternalByteArray, int8_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_UNSIGNED_BYTE_ELEMENTS: {
      IterateExternalArrayElements<ExternalUnsignedByteArray, uint8_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_SHORT_ELEMENTS: {
      IterateExternalArrayElements<ExternalShortArray, int16_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_UNSIGNED_SHORT_ELEMENTS: {
      IterateExternalArrayElements<ExternalUnsignedShortArray, uint16_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_INT_ELEMENTS: {
      IterateExternalArrayElements<ExternalIntArray, int32_t>(
          isolate, receiver, true, false, visitor);
      break;
    }
    case EXTERNAL_UNSIGNED_INT_ELEMENTS: {
      IterateExternalArrayElements<ExternalUnsignedIntArray, uint32_t>(
          isolate, receiver, true, false, visitor);
      break;
    }
    case EXTERNAL_FLOAT_ELEMENTS: {
      IterateExternalArrayElements<ExternalFloatArray, float>(
          isolate, receiver, false, false, visitor);
      break;
    }
    case EXTERNAL_DOUBLE_ELEMENTS: {
      IterateExternalArrayElements<ExternalDoubleArray, double>(
          isolate, receiver, false, false, visitor);
      break;
    }
    default:
      UNREACHABLE();
      break;
  }
  visitor->increase_index_offset(length);
  return true;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ArrayConcat) {
  ASSERT(args.length() == 1);
  HandleScope handle_scope(isolate);

  CONVERT_ARG_HANDLE_CHECKED(JSArray, arguments, 0);
  int argument_count = static_cast<int>(arguments->length()->Number());
  RUNTIME_ASSERT(arguments->HasFastObjectElements());
  Handle<FixedArray> elements(FixedArray::cast(arguments->elements()));

  // Pass 1: estimate the length and number of elements of the result.
  // The actual length can be larger if any of the arguments have getters
  // that mutate other arguments (but will otherwise be precise).
  // The number of elements is precise if there are no inherited elements.

  uint32_t estimate_result_length = 0;
  uint32_t estimate_nof_elements = 0;
  {
    for (int i = 0; i < argument_count; i++) {
      HandleScope loop_scope;
      Handle<Object> obj(elements->get(i));
      uint32_t length_estimate;
      uint32_t element_estimate;
      if (obj->IsJSArray()) {
        Handle<JSArray> array(Handle<JSArray>::cast(obj));
        // TODO(1810): Find out if it's worthwhile to properly support
        // arbitrary ElementsKinds. For now, pessimistically transition to
        // FAST_*_ELEMENTS.
        if (array->HasFastDoubleElements()) {
          ElementsKind to_kind = FAST_ELEMENTS;
          if (array->HasFastHoleyElements()) {
            to_kind = FAST_HOLEY_ELEMENTS;
          }
          array = Handle<JSArray>::cast(
              JSObject::TransitionElementsKind(array, to_kind));
        }
        length_estimate =
            static_cast<uint32_t>(array->length()->Number());
        element_estimate =
            EstimateElementCount(array);
      } else {
        length_estimate = 1;
        element_estimate = 1;
      }
      // Avoid overflows by capping at kMaxElementCount.
      if (JSObject::kMaxElementCount - estimate_result_length <
          length_estimate) {
        estimate_result_length = JSObject::kMaxElementCount;
      } else {
        estimate_result_length += length_estimate;
      }
      if (JSObject::kMaxElementCount - estimate_nof_elements <
          element_estimate) {
        estimate_nof_elements = JSObject::kMaxElementCount;
      } else {
        estimate_nof_elements += element_estimate;
      }
    }
  }

  // If estimated number of elements is more than half of length, a
  // fixed array (fast case) is more time and space-efficient than a
  // dictionary.
  bool fast_case = (estimate_nof_elements * 2) >= estimate_result_length;

  Handle<FixedArray> storage;
  if (fast_case) {
    // The backing storage array must have non-existing elements to
    // preserve holes across concat operations.
    storage = isolate->factory()->NewFixedArrayWithHoles(
        estimate_result_length);
  } else {
    // TODO(126): move 25% pre-allocation logic into Dictionary::Allocate
    uint32_t at_least_space_for = estimate_nof_elements +
                                  (estimate_nof_elements >> 2);
    storage = Handle<FixedArray>::cast(
        isolate->factory()->NewSeededNumberDictionary(at_least_space_for));
  }

  ArrayConcatVisitor visitor(isolate, storage, fast_case);

  for (int i = 0; i < argument_count; i++) {
    Handle<Object> obj(elements->get(i));
    if (obj->IsJSArray()) {
      Handle<JSArray> array = Handle<JSArray>::cast(obj);
      if (!IterateElements(isolate, array, &visitor)) {
        return Failure::Exception();
      }
    } else {
      visitor.visit(0, obj);
      visitor.increase_index_offset(1);
    }
  }

  return *visitor.ToArray();
}


// This will not allocate (flatten the string), but it may run
// very slowly for very deeply nested ConsStrings.  For debugging use only.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GlobalPrint) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(String, string, 0);
  StringInputBuffer buffer(string);
  while (buffer.has_more()) {
    uint16_t character = buffer.GetNext();
    PrintF("%c", character);
  }
  return string;
}

// Moves all own elements of an object, that are below a limit, to positions
// starting at zero. All undefined values are placed after non-undefined values,
// and are followed by non-existing element. Does not change the length
// property.
// Returns the number of non-undefined elements collected.
RUNTIME_FUNCTION(MaybeObject*, Runtime_RemoveArrayHoles) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSObject, object, 0);
  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);
  return object->PrepareElementsForSort(limit);
}


// Move contents of argument 0 (an array) to argument 1 (an array)
RUNTIME_FUNCTION(MaybeObject*, Runtime_MoveArrayContents) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSArray, from, 0);
  CONVERT_ARG_CHECKED(JSArray, to, 1);
  from->ValidateElements();
  to->ValidateElements();
  FixedArrayBase* new_elements = from->elements();
  ElementsKind from_kind = from->GetElementsKind();
  MaybeObject* maybe_new_map;
  maybe_new_map = to->GetElementsTransitionMap(isolate, from_kind);
  Object* new_map;
  if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
  to->set_map_and_elements(Map::cast(new_map), new_elements);
  to->set_length(from->length());
  Object* obj;
  { MaybeObject* maybe_obj = from->ResetElements();
    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
  }
  from->set_length(Smi::FromInt(0));
  to->ValidateElements();
  return to;
}


// How many elements does this object/array have?
RUNTIME_FUNCTION(MaybeObject*, Runtime_EstimateNumberOfElements) {
  ASSERT(args.length() == 1);
  CONVERT_ARG_CHECKED(JSObject, object, 0);
  HeapObject* elements = object->elements();
  if (elements->IsDictionary()) {
    int result = SeededNumberDictionary::cast(elements)->NumberOfElements();
    return Smi::FromInt(result);
  } else if (object->IsJSArray()) {
    return JSArray::cast(object)->length();
  } else {
    return Smi::FromInt(FixedArray::cast(elements)->length());
  }
}


// Returns an array that tells you where in the [0, length) interval an array
// might have elements.  Can either return keys (positive integers) or
// intervals (pair of a negative integer (-start-1) followed by a
// positive (length)) or undefined values.
// Intervals can span over some keys that are not in the object.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetArrayKeys) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, array, 0);
  CONVERT_NUMBER_CHECKED(uint32_t, length, Uint32, args[1]);
  if (array->elements()->IsDictionary()) {
    // Create an array and get all the keys into it, then remove all the
    // keys that are not integers in the range 0 to length-1.
    bool threw = false;
    Handle<FixedArray> keys =
        GetKeysInFixedArrayFor(array, INCLUDE_PROTOS, &threw);
    if (threw) return Failure::Exception();

    int keys_length = keys->length();
    for (int i = 0; i < keys_length; i++) {
      Object* key = keys->get(i);
      uint32_t index = 0;
      if (!key->ToArrayIndex(&index) || index >= length) {
        // Zap invalid keys.
        keys->set_undefined(i);
      }
    }
    return *isolate->factory()->NewJSArrayWithElements(keys);
  } else {
    ASSERT(array->HasFastSmiOrObjectElements() ||
           array->HasFastDoubleElements());
    Handle<FixedArray> single_interval = isolate->factory()->NewFixedArray(2);
    // -1 means start of array.
    single_interval->set(0, Smi::FromInt(-1));
    FixedArrayBase* elements = FixedArrayBase::cast(array->elements());
    uint32_t actual_length =
        static_cast<uint32_t>(elements->length());
    uint32_t min_length = actual_length < length ? actual_length : length;
    Handle<Object> length_object =
        isolate->factory()->NewNumber(static_cast<double>(min_length));
    single_interval->set(1, *length_object);
    return *isolate->factory()->NewJSArrayWithElements(single_interval);
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_LookupAccessor) {
  ASSERT(args.length() == 3);
  CONVERT_ARG_CHECKED(JSObject, obj, 0);
  CONVERT_ARG_CHECKED(String, name, 1);
  CONVERT_SMI_ARG_CHECKED(flag, 2);
  AccessorComponent component = flag == 0 ? ACCESSOR_GETTER : ACCESSOR_SETTER;
  return obj->LookupAccessor(name, component);
}


#ifdef ENABLE_DEBUGGER_SUPPORT
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugBreak) {
  ASSERT(args.length() == 0);
  return Execution::DebugBreakHelper();
}


// Helper functions for wrapping and unwrapping stack frame ids.
static Smi* WrapFrameId(StackFrame::Id id) {
  ASSERT(IsAligned(OffsetFrom(id), static_cast<intptr_t>(4)));
  return Smi::FromInt(id >> 2);
}


static StackFrame::Id UnwrapFrameId(int wrapped) {
  return static_cast<StackFrame::Id>(wrapped << 2);
}


// Adds a JavaScript function as a debug event listener.
// args[0]: debug event listener function to set or null or undefined for
//          clearing the event listener function
// args[1]: object supplied during callback
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetDebugEventListener) {
  ASSERT(args.length() == 2);
  RUNTIME_ASSERT(args[0]->IsJSFunction() ||
                 args[0]->IsUndefined() ||
                 args[0]->IsNull());
  Handle<Object> callback = args.at<Object>(0);
  Handle<Object> data = args.at<Object>(1);
  isolate->debugger()->SetEventListener(callback, data);

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Break) {
  ASSERT(args.length() == 0);
  isolate->stack_guard()->DebugBreak();
  return isolate->heap()->undefined_value();
}


static MaybeObject* DebugLookupResultValue(Heap* heap,
                                           Object* receiver,
                                           String* name,
                                           LookupResult* result,
                                           bool* caught_exception) {
  Object* value;
  switch (result->type()) {
    case NORMAL:
      value = result->holder()->GetNormalizedProperty(result);
      if (value->IsTheHole()) {
        return heap->undefined_value();
      }
      return value;
    case FIELD:
      value =
          JSObject::cast(
              result->holder())->FastPropertyAt(result->GetFieldIndex());
      if (value->IsTheHole()) {
        return heap->undefined_value();
      }
      return value;
    case CONSTANT_FUNCTION:
      return result->GetConstantFunction();
    case CALLBACKS: {
      Object* structure = result->GetCallbackObject();
      if (structure->IsForeign() || structure->IsAccessorInfo()) {
        MaybeObject* maybe_value = result->holder()->GetPropertyWithCallback(
            receiver, structure, name);
        if (!maybe_value->ToObject(&value)) {
          if (maybe_value->IsRetryAfterGC()) return maybe_value;
          ASSERT(maybe_value->IsException());
          maybe_value = heap->isolate()->pending_exception();
          heap->isolate()->clear_pending_exception();
          if (caught_exception != NULL) {
            *caught_exception = true;
          }
          return maybe_value;
        }
        return value;
      } else {
        return heap->undefined_value();
      }
    }
    case INTERCEPTOR:
    case MAP_TRANSITION:
    case CONSTANT_TRANSITION:
    case NULL_DESCRIPTOR:
      return heap->undefined_value();
    case HANDLER:
      UNREACHABLE();
      return heap->undefined_value();
  }
  UNREACHABLE();  // keep the compiler happy
  return heap->undefined_value();
}


// Get debugger related details for an object property.
// args[0]: object holding property
// args[1]: name of the property
//
// The array returned contains the following information:
// 0: Property value
// 1: Property details
// 2: Property value is exception
// 3: Getter function if defined
// 4: Setter function if defined
// Items 2-4 are only filled if the property has either a getter or a setter
// defined through __defineGetter__ and/or __defineSetter__.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugGetPropertyDetails) {
  HandleScope scope(isolate);

  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);

  // Make sure to set the current context to the context before the debugger was
  // entered (if the debugger is entered). The reason for switching context here
  // is that for some property lookups (accessors and interceptors) callbacks
  // into the embedding application can occour, and the embedding application
  // could have the assumption that its own global context is the current
  // context and not some internal debugger context.
  SaveContext save(isolate);
  if (isolate->debug()->InDebugger()) {
    isolate->set_context(*isolate->debug()->debugger_entry()->GetContext());
  }

  // Skip the global proxy as it has no properties and always delegates to the
  // real global object.
  if (obj->IsJSGlobalProxy()) {
    obj = Handle<JSObject>(JSObject::cast(obj->GetPrototype()));
  }


  // Check if the name is trivially convertible to an index and get the element
  // if so.
  uint32_t index;
  if (name->AsArrayIndex(&index)) {
    Handle<FixedArray> details = isolate->factory()->NewFixedArray(2);
    Object* element_or_char;
    { MaybeObject* maybe_element_or_char =
          Runtime::GetElementOrCharAt(isolate, obj, index);
      if (!maybe_element_or_char->ToObject(&element_or_char)) {
        return maybe_element_or_char;
      }
    }
    details->set(0, element_or_char);
    details->set(1, PropertyDetails(NONE, NORMAL).AsSmi());
    return *isolate->factory()->NewJSArrayWithElements(details);
  }

  // Find the number of objects making up this.
  int length = LocalPrototypeChainLength(*obj);

  // Try local lookup on each of the objects.
  Handle<JSObject> jsproto = obj;
  for (int i = 0; i < length; i++) {
    LookupResult result(isolate);
    jsproto->LocalLookup(*name, &result);
    if (result.IsProperty()) {
      // LookupResult is not GC safe as it holds raw object pointers.
      // GC can happen later in this code so put the required fields into
      // local variables using handles when required for later use.
      PropertyType result_type = result.type();
      Handle<Object> result_callback_obj;
      if (result_type == CALLBACKS) {
        result_callback_obj = Handle<Object>(result.GetCallbackObject(),
                                             isolate);
      }
      Smi* property_details = result.GetPropertyDetails().AsSmi();
      // DebugLookupResultValue can cause GC so details from LookupResult needs
      // to be copied to handles before this.
      bool caught_exception = false;
      Object* raw_value;
      { MaybeObject* maybe_raw_value =
            DebugLookupResultValue(isolate->heap(), *obj, *name,
                                   &result, &caught_exception);
        if (!maybe_raw_value->ToObject(&raw_value)) return maybe_raw_value;
      }
      Handle<Object> value(raw_value, isolate);

      // If the callback object is a fixed array then it contains JavaScript
      // getter and/or setter.
      bool hasJavaScriptAccessors = result_type == CALLBACKS &&
                                    result_callback_obj->IsAccessorPair();
      Handle<FixedArray> details =
          isolate->factory()->NewFixedArray(hasJavaScriptAccessors ? 5 : 2);
      details->set(0, *value);
      details->set(1, property_details);
      if (hasJavaScriptAccessors) {
        AccessorPair* accessors = AccessorPair::cast(*result_callback_obj);
        details->set(2, isolate->heap()->ToBoolean(caught_exception));
        details->set(3, accessors->GetComponent(ACCESSOR_GETTER));
        details->set(4, accessors->GetComponent(ACCESSOR_SETTER));
      }

      return *isolate->factory()->NewJSArrayWithElements(details);
    }
    if (i < length - 1) {
      jsproto = Handle<JSObject>(JSObject::cast(jsproto->GetPrototype()));
    }
  }

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugGetProperty) {
  HandleScope scope(isolate);

  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);

  LookupResult result(isolate);
  obj->Lookup(*name, &result);
  if (result.IsProperty()) {
    return DebugLookupResultValue(isolate->heap(), *obj, *name, &result, NULL);
  }
  return isolate->heap()->undefined_value();
}


// Return the property type calculated from the property details.
// args[0]: smi with property details.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPropertyTypeFromDetails) {
  ASSERT(args.length() == 1);
  CONVERT_PROPERTY_DETAILS_CHECKED(details, 0);
  return Smi::FromInt(static_cast<int>(details.type()));
}


// Return the property attribute calculated from the property details.
// args[0]: smi with property details.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPropertyAttributesFromDetails) {
  ASSERT(args.length() == 1);
  CONVERT_PROPERTY_DETAILS_CHECKED(details, 0);
  return Smi::FromInt(static_cast<int>(details.attributes()));
}


// Return the property insertion index calculated from the property details.
// args[0]: smi with property details.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPropertyIndexFromDetails) {
  ASSERT(args.length() == 1);
  CONVERT_PROPERTY_DETAILS_CHECKED(details, 0);
  return Smi::FromInt(details.index());
}


// Return property value from named interceptor.
// args[0]: object
// args[1]: property name
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugNamedInterceptorPropertyValue) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  RUNTIME_ASSERT(obj->HasNamedInterceptor());
  CONVERT_ARG_HANDLE_CHECKED(String, name, 1);

  PropertyAttributes attributes;
  return obj->GetPropertyWithInterceptor(*obj, *name, &attributes);
}


// Return element value from indexed interceptor.
// args[0]: object
// args[1]: index
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugIndexedInterceptorElementValue) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
  RUNTIME_ASSERT(obj->HasIndexedInterceptor());
  CONVERT_NUMBER_CHECKED(uint32_t, index, Uint32, args[1]);

  return obj->GetElementWithInterceptor(*obj, index);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_CheckExecutionState) {
  ASSERT(args.length() >= 1);
  CONVERT_NUMBER_CHECKED(int, break_id, Int32, args[0]);
  // Check that the break id is valid.
  if (isolate->debug()->break_id() == 0 ||
      break_id != isolate->debug()->break_id()) {
    return isolate->Throw(
        isolate->heap()->illegal_execution_state_symbol());
  }

  return isolate->heap()->true_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFrameCount) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  // Check arguments.
  Object* result;
  { MaybeObject* maybe_result = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }

  // Count all frames which are relevant to debugging stack trace.
  int n = 0;
  StackFrame::Id id = isolate->debug()->break_frame_id();
  if (id == StackFrame::NO_ID) {
    // If there is no JavaScript stack frame count is 0.
    return Smi::FromInt(0);
  }

  for (JavaScriptFrameIterator it(isolate, id); !it.done(); it.Advance()) {
    n += it.frame()->GetInlineCount();
  }
  return Smi::FromInt(n);
}


class FrameInspector {
 public:
  FrameInspector(JavaScriptFrame* frame,
                 int inlined_jsframe_index,
                 Isolate* isolate)
      : frame_(frame), deoptimized_frame_(NULL), isolate_(isolate) {
    // Calculate the deoptimized frame.
    if (frame->is_optimized()) {
      deoptimized_frame_ = Deoptimizer::DebuggerInspectableFrame(
          frame, inlined_jsframe_index, isolate);
    }
    has_adapted_arguments_ = frame_->has_adapted_arguments();
    is_bottommost_ = inlined_jsframe_index == 0;
    is_optimized_ = frame_->is_optimized();
  }

  ~FrameInspector() {
    // Get rid of the calculated deoptimized frame if any.
    if (deoptimized_frame_ != NULL) {
      Deoptimizer::DeleteDebuggerInspectableFrame(deoptimized_frame_,
                                                  isolate_);
    }
  }

  int GetParametersCount() {
    return is_optimized_
        ? deoptimized_frame_->parameters_count()
        : frame_->ComputeParametersCount();
  }
  int expression_count() { return deoptimized_frame_->expression_count(); }
  Object* GetFunction() {
    return is_optimized_
        ? deoptimized_frame_->GetFunction()
        : frame_->function();
  }
  Object* GetParameter(int index) {
    return is_optimized_
        ? deoptimized_frame_->GetParameter(index)
        : frame_->GetParameter(index);
  }
  Object* GetExpression(int index) {
    return is_optimized_
        ? deoptimized_frame_->GetExpression(index)
        : frame_->GetExpression(index);
  }
  int GetSourcePosition() {
    return is_optimized_
        ? deoptimized_frame_->GetSourcePosition()
        : frame_->LookupCode()->SourcePosition(frame_->pc());
  }
  bool IsConstructor() {
    return is_optimized_ && !is_bottommost_
        ? deoptimized_frame_->HasConstructStub()
        : frame_->IsConstructor();
  }

  // To inspect all the provided arguments the frame might need to be
  // replaced with the arguments frame.
  void SetArgumentsFrame(JavaScriptFrame* frame) {
    ASSERT(has_adapted_arguments_);
    frame_ = frame;
    is_optimized_ = frame_->is_optimized();
    ASSERT(!is_optimized_);
  }

 private:
  JavaScriptFrame* frame_;
  DeoptimizedFrameInfo* deoptimized_frame_;
  Isolate* isolate_;
  bool is_optimized_;
  bool is_bottommost_;
  bool has_adapted_arguments_;

  DISALLOW_COPY_AND_ASSIGN(FrameInspector);
};


static const int kFrameDetailsFrameIdIndex = 0;
static const int kFrameDetailsReceiverIndex = 1;
static const int kFrameDetailsFunctionIndex = 2;
static const int kFrameDetailsArgumentCountIndex = 3;
static const int kFrameDetailsLocalCountIndex = 4;
static const int kFrameDetailsSourcePositionIndex = 5;
static const int kFrameDetailsConstructCallIndex = 6;
static const int kFrameDetailsAtReturnIndex = 7;
static const int kFrameDetailsFlagsIndex = 8;
static const int kFrameDetailsFirstDynamicIndex = 9;


static SaveContext* FindSavedContextForFrame(Isolate* isolate,
                                             JavaScriptFrame* frame) {
  SaveContext* save = isolate->save_context();
  while (save != NULL && !save->IsBelowFrame(frame)) {
    save = save->prev();
  }
  ASSERT(save != NULL);
  return save;
}


// Return an array with frame details
// args[0]: number: break id
// args[1]: number: frame index
//
// The array returned contains the following information:
// 0: Frame id
// 1: Receiver
// 2: Function
// 3: Argument count
// 4: Local count
// 5: Source position
// 6: Constructor call
// 7: Is at return
// 8: Flags
// Arguments name, value
// Locals name, value
// Return value if any
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFrameDetails) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  // Check arguments.
  Object* check;
  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check->ToObject(&check)) return maybe_check;
  }
  CONVERT_NUMBER_CHECKED(int, index, Int32, args[1]);
  Heap* heap = isolate->heap();

  // Find the relevant frame with the requested index.
  StackFrame::Id id = isolate->debug()->break_frame_id();
  if (id == StackFrame::NO_ID) {
    // If there are no JavaScript stack frames return undefined.
    return heap->undefined_value();
  }

  int count = 0;
  JavaScriptFrameIterator it(isolate, id);
  for (; !it.done(); it.Advance()) {
    if (index < count + it.frame()->GetInlineCount()) break;
    count += it.frame()->GetInlineCount();
  }
  if (it.done()) return heap->undefined_value();

  bool is_optimized = it.frame()->is_optimized();

  int inlined_jsframe_index = 0;  // Inlined frame index in optimized frame.
  if (is_optimized) {
    inlined_jsframe_index =
        it.frame()->GetInlineCount() - (index - count) - 1;
  }
  FrameInspector frame_inspector(it.frame(), inlined_jsframe_index, isolate);

  // Traverse the saved contexts chain to find the active context for the
  // selected frame.
  SaveContext* save = FindSavedContextForFrame(isolate, it.frame());

  // Get the frame id.
  Handle<Object> frame_id(WrapFrameId(it.frame()->id()), isolate);

  // Find source position in unoptimized code.
  int position = frame_inspector.GetSourcePosition();

  // Check for constructor frame.
  bool constructor = frame_inspector.IsConstructor();

  // Get scope info and read from it for local variable information.
  Handle<JSFunction> function(JSFunction::cast(frame_inspector.GetFunction()));
  Handle<SharedFunctionInfo> shared(function->shared());
  Handle<ScopeInfo> scope_info(shared->scope_info());
  ASSERT(*scope_info != ScopeInfo::Empty());

  // Get the locals names and values into a temporary array.
  //
  // TODO(1240907): Hide compiler-introduced stack variables
  // (e.g. .result)?  For users of the debugger, they will probably be
  // confusing.
  Handle<FixedArray> locals =
      isolate->factory()->NewFixedArray(scope_info->LocalCount() * 2);

  // Fill in the values of the locals.
  int i = 0;
  for (; i < scope_info->StackLocalCount(); ++i) {
    // Use the value from the stack.
    locals->set(i * 2, scope_info->LocalName(i));
    locals->set(i * 2 + 1, frame_inspector.GetExpression(i));
  }
  if (i < scope_info->LocalCount()) {
    // Get the context containing declarations.
    Handle<Context> context(
        Context::cast(it.frame()->context())->declaration_context());
    for (; i < scope_info->LocalCount(); ++i) {
      Handle<String> name(scope_info->LocalName(i));
      VariableMode mode;
      InitializationFlag init_flag;
      locals->set(i * 2, *name);
      locals->set(i * 2 + 1, context->get(
          scope_info->ContextSlotIndex(*name, &mode, &init_flag)));
    }
  }

  // Check whether this frame is positioned at return. If not top
  // frame or if the frame is optimized it cannot be at a return.
  bool at_return = false;
  if (!is_optimized && index == 0) {
    at_return = isolate->debug()->IsBreakAtReturn(it.frame());
  }

  // If positioned just before return find the value to be returned and add it
  // to the frame information.
  Handle<Object> return_value = isolate->factory()->undefined_value();
  if (at_return) {
    StackFrameIterator it2(isolate);
    Address internal_frame_sp = NULL;
    while (!it2.done()) {
      if (it2.frame()->is_internal()) {
        internal_frame_sp = it2.frame()->sp();
      } else {
        if (it2.frame()->is_java_script()) {
          if (it2.frame()->id() == it.frame()->id()) {
            // The internal frame just before the JavaScript frame contains the
            // value to return on top. A debug break at return will create an
            // internal frame to store the return value (eax/rax/r0) before
            // entering the debug break exit frame.
            if (internal_frame_sp != NULL) {
              return_value =
                  Handle<Object>(Memory::Object_at(internal_frame_sp),
                                 isolate);
              break;
            }
          }
        }

        // Indicate that the previous frame was not an internal frame.
        internal_frame_sp = NULL;
      }
      it2.Advance();
    }
  }

  // Now advance to the arguments adapter frame (if any). It contains all
  // the provided parameters whereas the function frame always have the number
  // of arguments matching the functions parameters. The rest of the
  // information (except for what is collected above) is the same.
  if ((inlined_jsframe_index == 0) && it.frame()->has_adapted_arguments()) {
    it.AdvanceToArgumentsFrame();
    frame_inspector.SetArgumentsFrame(it.frame());
  }

  // Find the number of arguments to fill. At least fill the number of
  // parameters for the function and fill more if more parameters are provided.
  int argument_count = scope_info->ParameterCount();
  if (argument_count < frame_inspector.GetParametersCount()) {
    argument_count = frame_inspector.GetParametersCount();
  }

  // Calculate the size of the result.
  int details_size = kFrameDetailsFirstDynamicIndex +
                     2 * (argument_count + scope_info->LocalCount()) +
                     (at_return ? 1 : 0);
  Handle<FixedArray> details = isolate->factory()->NewFixedArray(details_size);

  // Add the frame id.
  details->set(kFrameDetailsFrameIdIndex, *frame_id);

  // Add the function (same as in function frame).
  details->set(kFrameDetailsFunctionIndex, frame_inspector.GetFunction());

  // Add the arguments count.
  details->set(kFrameDetailsArgumentCountIndex, Smi::FromInt(argument_count));

  // Add the locals count
  details->set(kFrameDetailsLocalCountIndex,
               Smi::FromInt(scope_info->LocalCount()));

  // Add the source position.
  if (position != RelocInfo::kNoPosition) {
    details->set(kFrameDetailsSourcePositionIndex, Smi::FromInt(position));
  } else {
    details->set(kFrameDetailsSourcePositionIndex, heap->undefined_value());
  }

  // Add the constructor information.
  details->set(kFrameDetailsConstructCallIndex, heap->ToBoolean(constructor));

  // Add the at return information.
  details->set(kFrameDetailsAtReturnIndex, heap->ToBoolean(at_return));

  // Add flags to indicate information on whether this frame is
  //   bit 0: invoked in the debugger context.
  //   bit 1: optimized frame.
  //   bit 2: inlined in optimized frame
  int flags = 0;
  if (*save->context() == *isolate->debug()->debug_context()) {
    flags |= 1 << 0;
  }
  if (is_optimized) {
    flags |= 1 << 1;
    flags |= inlined_jsframe_index << 2;
  }
  details->set(kFrameDetailsFlagsIndex, Smi::FromInt(flags));

  // Fill the dynamic part.
  int details_index = kFrameDetailsFirstDynamicIndex;

  // Add arguments name and value.
  for (int i = 0; i < argument_count; i++) {
    // Name of the argument.
    if (i < scope_info->ParameterCount()) {
      details->set(details_index++, scope_info->ParameterName(i));
    } else {
      details->set(details_index++, heap->undefined_value());
    }

    // Parameter value.
    if (i < frame_inspector.GetParametersCount()) {
      // Get the value from the stack.
      details->set(details_index++, frame_inspector.GetParameter(i));
    } else {
      details->set(details_index++, heap->undefined_value());
    }
  }

  // Add locals name and value from the temporary copy from the function frame.
  for (int i = 0; i < scope_info->LocalCount() * 2; i++) {
    details->set(details_index++, locals->get(i));
  }

  // Add the value being returned.
  if (at_return) {
    details->set(details_index++, *return_value);
  }

  // Add the receiver (same as in function frame).
  // THIS MUST BE DONE LAST SINCE WE MIGHT ADVANCE
  // THE FRAME ITERATOR TO WRAP THE RECEIVER.
  Handle<Object> receiver(it.frame()->receiver(), isolate);
  if (!receiver->IsJSObject() &&
      shared->is_classic_mode() &&
      !shared->native()) {
    // If the receiver is not a JSObject and the function is not a
    // builtin or strict-mode we have hit an optimization where a
    // value object is not converted into a wrapped JS objects. To
    // hide this optimization from the debugger, we wrap the receiver
    // by creating correct wrapper object based on the calling frame's
    // global context.
    it.Advance();
    Handle<Context> calling_frames_global_context(
        Context::cast(Context::cast(it.frame()->context())->global_context()));
    receiver =
        isolate->factory()->ToObject(receiver, calling_frames_global_context);
  }
  details->set(kFrameDetailsReceiverIndex, *receiver);

  ASSERT_EQ(details_size, details_index);
  return *isolate->factory()->NewJSArrayWithElements(details);
}


// Copy all the context locals into an object used to materialize a scope.
static bool CopyContextLocalsToScopeObject(
    Isolate* isolate,
    Handle<ScopeInfo> scope_info,
    Handle<Context> context,
    Handle<JSObject> scope_object) {
  // Fill all context locals to the context extension.
  for (int i = 0; i < scope_info->ContextLocalCount(); i++) {
    VariableMode mode;
    InitializationFlag init_flag;
    int context_index = scope_info->ContextSlotIndex(
        scope_info->ContextLocalName(i), &mode, &init_flag);

    RETURN_IF_EMPTY_HANDLE_VALUE(
        isolate,
        SetProperty(scope_object,
                    Handle<String>(scope_info->ContextLocalName(i)),
                    Handle<Object>(context->get(context_index), isolate),
                    NONE,
                    kNonStrictMode),
        false);
  }

  return true;
}


// Create a plain JSObject which materializes the local scope for the specified
// frame.
static Handle<JSObject> MaterializeLocalScopeWithFrameInspector(
    Isolate* isolate,
    JavaScriptFrame* frame,
    FrameInspector* frame_inspector) {
  Handle<JSFunction> function(JSFunction::cast(frame_inspector->GetFunction()));
  Handle<SharedFunctionInfo> shared(function->shared());
  Handle<ScopeInfo> scope_info(shared->scope_info());

  // Allocate and initialize a JSObject with all the arguments, stack locals
  // heap locals and extension properties of the debugged function.
  Handle<JSObject> local_scope =
      isolate->factory()->NewJSObject(isolate->object_function());

  // First fill all parameters.
  for (int i = 0; i < scope_info->ParameterCount(); ++i) {
    Handle<Object> value(
        i < frame_inspector->GetParametersCount() ?
        frame_inspector->GetParameter(i) : isolate->heap()->undefined_value());

    RETURN_IF_EMPTY_HANDLE_VALUE(
        isolate,
        SetProperty(local_scope,
                    Handle<String>(scope_info->ParameterName(i)),
                    value,
                    NONE,
                    kNonStrictMode),
        Handle<JSObject>());
  }

  // Second fill all stack locals.
  for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
    RETURN_IF_EMPTY_HANDLE_VALUE(
        isolate,
        SetProperty(local_scope,
                    Handle<String>(scope_info->StackLocalName(i)),
                    Handle<Object>(frame_inspector->GetExpression(i)),
                    NONE,
                    kNonStrictMode),
        Handle<JSObject>());
  }

  if (scope_info->HasContext()) {
    // Third fill all context locals.
    Handle<Context> frame_context(Context::cast(frame->context()));
    Handle<Context> function_context(frame_context->declaration_context());
    if (!CopyContextLocalsToScopeObject(
            isolate, scope_info, function_context, local_scope)) {
      return Handle<JSObject>();
    }

    // Finally copy any properties from the function context extension.
    // These will be variables introduced by eval.
    if (function_context->closure() == *function) {
      if (function_context->has_extension() &&
          !function_context->IsGlobalContext()) {
        Handle<JSObject> ext(JSObject::cast(function_context->extension()));
        bool threw = false;
        Handle<FixedArray> keys =
            GetKeysInFixedArrayFor(ext, INCLUDE_PROTOS, &threw);
        if (threw) return Handle<JSObject>();

        for (int i = 0; i < keys->length(); i++) {
          // Names of variables introduced by eval are strings.
          ASSERT(keys->get(i)->IsString());
          Handle<String> key(String::cast(keys->get(i)));
          RETURN_IF_EMPTY_HANDLE_VALUE(
              isolate,
              SetProperty(local_scope,
                          key,
                          GetProperty(ext, key),
                          NONE,
                          kNonStrictMode),
              Handle<JSObject>());
        }
      }
    }
  }

  return local_scope;
}


static Handle<JSObject> MaterializeLocalScope(
    Isolate* isolate,
    JavaScriptFrame* frame,
    int inlined_jsframe_index) {
  FrameInspector frame_inspector(frame, inlined_jsframe_index, isolate);
  return MaterializeLocalScopeWithFrameInspector(isolate,
                                                 frame,
                                                 &frame_inspector);
}


// Create a plain JSObject which materializes the closure content for the
// context.
static Handle<JSObject> MaterializeClosure(Isolate* isolate,
                                           Handle<Context> context) {
  ASSERT(context->IsFunctionContext());

  Handle<SharedFunctionInfo> shared(context->closure()->shared());
  Handle<ScopeInfo> scope_info(shared->scope_info());

  // Allocate and initialize a JSObject with all the content of this function
  // closure.
  Handle<JSObject> closure_scope =
      isolate->factory()->NewJSObject(isolate->object_function());

  // Fill all context locals to the context extension.
  if (!CopyContextLocalsToScopeObject(
          isolate, scope_info, context, closure_scope)) {
    return Handle<JSObject>();
  }

  // Finally copy any properties from the function context extension. This will
  // be variables introduced by eval.
  if (context->has_extension()) {
    Handle<JSObject> ext(JSObject::cast(context->extension()));
    bool threw = false;
    Handle<FixedArray> keys =
        GetKeysInFixedArrayFor(ext, INCLUDE_PROTOS, &threw);
    if (threw) return Handle<JSObject>();

    for (int i = 0; i < keys->length(); i++) {
      // Names of variables introduced by eval are strings.
      ASSERT(keys->get(i)->IsString());
      Handle<String> key(String::cast(keys->get(i)));
       RETURN_IF_EMPTY_HANDLE_VALUE(
          isolate,
          SetProperty(closure_scope,
                      key,
                      GetProperty(ext, key),
                      NONE,
                      kNonStrictMode),
          Handle<JSObject>());
    }
  }

  return closure_scope;
}


// Create a plain JSObject which materializes the scope for the specified
// catch context.
static Handle<JSObject> MaterializeCatchScope(Isolate* isolate,
                                              Handle<Context> context) {
  ASSERT(context->IsCatchContext());
  Handle<String> name(String::cast(context->extension()));
  Handle<Object> thrown_object(context->get(Context::THROWN_OBJECT_INDEX));
  Handle<JSObject> catch_scope =
      isolate->factory()->NewJSObject(isolate->object_function());
  RETURN_IF_EMPTY_HANDLE_VALUE(
      isolate,
      SetProperty(catch_scope, name, thrown_object, NONE, kNonStrictMode),
      Handle<JSObject>());
  return catch_scope;
}


// Create a plain JSObject which materializes the block scope for the specified
// block context.
static Handle<JSObject> MaterializeBlockScope(
    Isolate* isolate,
    Handle<Context> context) {
  ASSERT(context->IsBlockContext());
  Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));

  // Allocate and initialize a JSObject with all the arguments, stack locals
  // heap locals and extension properties of the debugged function.
  Handle<JSObject> block_scope =
      isolate->factory()->NewJSObject(isolate->object_function());

  // Fill all context locals.
  if (!CopyContextLocalsToScopeObject(
          isolate, scope_info, context, block_scope)) {
    return Handle<JSObject>();
  }

  return block_scope;
}


// Create a plain JSObject which materializes the module scope for the specified
// module context.
static Handle<JSObject> MaterializeModuleScope(
    Isolate* isolate,
    Handle<Context> context) {
  ASSERT(context->IsModuleContext());
  Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));

  // Allocate and initialize a JSObject with all the members of the debugged
  // module.
  Handle<JSObject> module_scope =
      isolate->factory()->NewJSObject(isolate->object_function());

  // Fill all context locals.
  if (!CopyContextLocalsToScopeObject(
          isolate, scope_info, context, module_scope)) {
    return Handle<JSObject>();
  }

  return module_scope;
}


// Iterate over the actual scopes visible from a stack frame or from a closure.
// The iteration proceeds from the innermost visible nested scope outwards.
// All scopes are backed by an actual context except the local scope,
// which is inserted "artificially" in the context chain.
class ScopeIterator {
 public:
  enum ScopeType {
    ScopeTypeGlobal = 0,
    ScopeTypeLocal,
    ScopeTypeWith,
    ScopeTypeClosure,
    ScopeTypeCatch,
    ScopeTypeBlock,
    ScopeTypeModule
  };

  ScopeIterator(Isolate* isolate,
                JavaScriptFrame* frame,
                int inlined_jsframe_index)
    : isolate_(isolate),
      frame_(frame),
      inlined_jsframe_index_(inlined_jsframe_index),
      function_(JSFunction::cast(frame->function())),
      context_(Context::cast(frame->context())),
      nested_scope_chain_(4) {

    // Catch the case when the debugger stops in an internal function.
    Handle<SharedFunctionInfo> shared_info(function_->shared());
    Handle<ScopeInfo> scope_info(shared_info->scope_info());
    if (shared_info->script() == isolate->heap()->undefined_value()) {
      while (context_->closure() == *function_) {
        context_ = Handle<Context>(context_->previous(), isolate_);
      }
      return;
    }

    // Get the debug info (create it if it does not exist).
    if (!isolate->debug()->EnsureDebugInfo(shared_info)) {
      // Return if ensuring debug info failed.
      return;
    }
    Handle<DebugInfo> debug_info = Debug::GetDebugInfo(shared_info);

    // Find the break point where execution has stopped.
    BreakLocationIterator break_location_iterator(debug_info,
                                                  ALL_BREAK_LOCATIONS);
    break_location_iterator.FindBreakLocationFromAddress(frame->pc());
    if (break_location_iterator.IsExit()) {
      // We are within the return sequence. At the momemt it is not possible to
      // get a source position which is consistent with the current scope chain.
      // Thus all nested with, catch and block contexts are skipped and we only
      // provide the function scope.
      if (scope_info->HasContext()) {
        context_ = Handle<Context>(context_->declaration_context(), isolate_);
      } else {
        while (context_->closure() == *function_) {
          context_ = Handle<Context>(context_->previous(), isolate_);
        }
      }
      if (scope_info->Type() != EVAL_SCOPE) nested_scope_chain_.Add(scope_info);
    } else {
      // Reparse the code and analyze the scopes.
      ZoneScope zone_scope(isolate, DELETE_ON_EXIT);
      Handle<Script> script(Script::cast(shared_info->script()));
      Scope* scope = NULL;

      // Check whether we are in global, eval or function code.
      Handle<ScopeInfo> scope_info(shared_info->scope_info());
      if (scope_info->Type() != FUNCTION_SCOPE) {
        // Global or eval code.
        CompilationInfo info(script);
        if (scope_info->Type() == GLOBAL_SCOPE) {
          info.MarkAsGlobal();
        } else {
          ASSERT(scope_info->Type() == EVAL_SCOPE);
          info.MarkAsEval();
          info.SetCallingContext(Handle<Context>(function_->context()));
        }
        if (ParserApi::Parse(&info, kNoParsingFlags) && Scope::Analyze(&info)) {
          scope = info.function()->scope();
        }
      } else {
        // Function code
        CompilationInfo info(shared_info);
        if (ParserApi::Parse(&info, kNoParsingFlags) && Scope::Analyze(&info)) {
          scope = info.function()->scope();
        }
      }

      // Retrieve the scope chain for the current position.
      if (scope != NULL) {
        int source_position = shared_info->code()->SourcePosition(frame_->pc());
        scope->GetNestedScopeChain(&nested_scope_chain_, source_position);
      } else {
        // A failed reparse indicates that the preparser has diverged from the
        // parser or that the preparse data given to the initial parse has been
        // faulty. We fail in debug mode but in release mode we only provide the
        // information we get from the context chain but nothing about
        // completely stack allocated scopes or stack allocated locals.
        UNREACHABLE();
      }
    }
  }

  ScopeIterator(Isolate* isolate,
                Handle<JSFunction> function)
    : isolate_(isolate),
      frame_(NULL),
      inlined_jsframe_index_(0),
      function_(function),
      context_(function->context()) {
    if (function->IsBuiltin()) {
      context_ = Handle<Context>();
    }
  }

  // More scopes?
  bool Done() { return context_.is_null(); }

  // Move to the next scope.
  void Next() {
    ScopeType scope_type = Type();
    if (scope_type == ScopeTypeGlobal) {
      // The global scope is always the last in the chain.
      ASSERT(context_->IsGlobalContext());
      context_ = Handle<Context>();
      return;
    }
    if (nested_scope_chain_.is_empty()) {
      context_ = Handle<Context>(context_->previous(), isolate_);
    } else {
      if (nested_scope_chain_.last()->HasContext()) {
        ASSERT(context_->previous() != NULL);
        context_ = Handle<Context>(context_->previous(), isolate_);
      }
      nested_scope_chain_.RemoveLast();
    }
  }

  // Return the type of the current scope.
  ScopeType Type() {
    if (!nested_scope_chain_.is_empty()) {
      Handle<ScopeInfo> scope_info = nested_scope_chain_.last();
      switch (scope_info->Type()) {
        case FUNCTION_SCOPE:
          ASSERT(context_->IsFunctionContext() ||
                 !scope_info->HasContext());
          return ScopeTypeLocal;
        case MODULE_SCOPE:
          ASSERT(context_->IsModuleContext());
          return ScopeTypeModule;
        case GLOBAL_SCOPE:
          ASSERT(context_->IsGlobalContext());
          return ScopeTypeGlobal;
        case WITH_SCOPE:
          ASSERT(context_->IsWithContext());
          return ScopeTypeWith;
        case CATCH_SCOPE:
          ASSERT(context_->IsCatchContext());
          return ScopeTypeCatch;
        case BLOCK_SCOPE:
          ASSERT(!scope_info->HasContext() ||
                 context_->IsBlockContext());
          return ScopeTypeBlock;
        case EVAL_SCOPE:
          UNREACHABLE();
      }
    }
    if (context_->IsGlobalContext()) {
      ASSERT(context_->global()->IsGlobalObject());
      return ScopeTypeGlobal;
    }
    if (context_->IsFunctionContext()) {
      return ScopeTypeClosure;
    }
    if (context_->IsCatchContext()) {
      return ScopeTypeCatch;
    }
    if (context_->IsBlockContext()) {
      return ScopeTypeBlock;
    }
    if (context_->IsModuleContext()) {
      return ScopeTypeModule;
    }
    ASSERT(context_->IsWithContext());
    return ScopeTypeWith;
  }

  // Return the JavaScript object with the content of the current scope.
  Handle<JSObject> ScopeObject() {
    switch (Type()) {
      case ScopeIterator::ScopeTypeGlobal:
        return Handle<JSObject>(CurrentContext()->global());
      case ScopeIterator::ScopeTypeLocal:
        // Materialize the content of the local scope into a JSObject.
        ASSERT(nested_scope_chain_.length() == 1);
        return MaterializeLocalScope(isolate_, frame_, inlined_jsframe_index_);
      case ScopeIterator::ScopeTypeWith:
        // Return the with object.
        return Handle<JSObject>(JSObject::cast(CurrentContext()->extension()));
      case ScopeIterator::ScopeTypeCatch:
        return MaterializeCatchScope(isolate_, CurrentContext());
      case ScopeIterator::ScopeTypeClosure:
        // Materialize the content of the closure scope into a JSObject.
        return MaterializeClosure(isolate_, CurrentContext());
      case ScopeIterator::ScopeTypeBlock:
        return MaterializeBlockScope(isolate_, CurrentContext());
      case ScopeIterator::ScopeTypeModule:
        return MaterializeModuleScope(isolate_, CurrentContext());
    }
    UNREACHABLE();
    return Handle<JSObject>();
  }

  Handle<ScopeInfo> CurrentScopeInfo() {
    if (!nested_scope_chain_.is_empty()) {
      return nested_scope_chain_.last();
    } else if (context_->IsBlockContext()) {
      return Handle<ScopeInfo>(ScopeInfo::cast(context_->extension()));
    } else if (context_->IsFunctionContext()) {
      return Handle<ScopeInfo>(context_->closure()->shared()->scope_info());
    }
    return Handle<ScopeInfo>::null();
  }

  // Return the context for this scope. For the local context there might not
  // be an actual context.
  Handle<Context> CurrentContext() {
    if (Type() == ScopeTypeGlobal ||
        nested_scope_chain_.is_empty()) {
      return context_;
    } else if (nested_scope_chain_.last()->HasContext()) {
      return context_;
    } else {
      return Handle<Context>();
    }
  }

#ifdef DEBUG
  // Debug print of the content of the current scope.
  void DebugPrint() {
    switch (Type()) {
      case ScopeIterator::ScopeTypeGlobal:
        PrintF("Global:\n");
        CurrentContext()->Print();
        break;

      case ScopeIterator::ScopeTypeLocal: {
        PrintF("Local:\n");
        function_->shared()->scope_info()->Print();
        if (!CurrentContext().is_null()) {
          CurrentContext()->Print();
          if (CurrentContext()->has_extension()) {
            Handle<Object> extension(CurrentContext()->extension());
            if (extension->IsJSContextExtensionObject()) {
              extension->Print();
            }
          }
        }
        break;
      }

      case ScopeIterator::ScopeTypeWith:
        PrintF("With:\n");
        CurrentContext()->extension()->Print();
        break;

      case ScopeIterator::ScopeTypeCatch:
        PrintF("Catch:\n");
        CurrentContext()->extension()->Print();
        CurrentContext()->get(Context::THROWN_OBJECT_INDEX)->Print();
        break;

      case ScopeIterator::ScopeTypeClosure:
        PrintF("Closure:\n");
        CurrentContext()->Print();
        if (CurrentContext()->has_extension()) {
          Handle<Object> extension(CurrentContext()->extension());
          if (extension->IsJSContextExtensionObject()) {
            extension->Print();
          }
        }
        break;

      default:
        UNREACHABLE();
    }
    PrintF("\n");
  }
#endif

 private:
  Isolate* isolate_;
  JavaScriptFrame* frame_;
  int inlined_jsframe_index_;
  Handle<JSFunction> function_;
  Handle<Context> context_;
  List<Handle<ScopeInfo> > nested_scope_chain_;

  DISALLOW_IMPLICIT_CONSTRUCTORS(ScopeIterator);
};


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetScopeCount) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  // Check arguments.
  Object* check;
  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check->ToObject(&check)) return maybe_check;
  }
  CONVERT_SMI_ARG_CHECKED(wrapped_id, 1);

  // Get the frame where the debugging is performed.
  StackFrame::Id id = UnwrapFrameId(wrapped_id);
  JavaScriptFrameIterator it(isolate, id);
  JavaScriptFrame* frame = it.frame();

  // Count the visible scopes.
  int n = 0;
  for (ScopeIterator it(isolate, frame, 0);
       !it.Done();
       it.Next()) {
    n++;
  }

  return Smi::FromInt(n);
}


static const int kScopeDetailsTypeIndex = 0;
static const int kScopeDetailsObjectIndex = 1;
static const int kScopeDetailsSize = 2;


static MaybeObject* MaterializeScopeDetails(Isolate* isolate,
    ScopeIterator* it) {
  // Calculate the size of the result.
  int details_size = kScopeDetailsSize;
  Handle<FixedArray> details = isolate->factory()->NewFixedArray(details_size);

  // Fill in scope details.
  details->set(kScopeDetailsTypeIndex, Smi::FromInt(it->Type()));
  Handle<JSObject> scope_object = it->ScopeObject();
  RETURN_IF_EMPTY_HANDLE(isolate, scope_object);
  details->set(kScopeDetailsObjectIndex, *scope_object);

  return *isolate->factory()->NewJSArrayWithElements(details);
}

// Return an array with scope details
// args[0]: number: break id
// args[1]: number: frame index
// args[2]: number: inlined frame index
// args[3]: number: scope index
//
// The array returned contains the following information:
// 0: Scope type
// 1: Scope object
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetScopeDetails) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 4);

  // Check arguments.
  Object* check;
  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check->ToObject(&check)) return maybe_check;
  }
  CONVERT_SMI_ARG_CHECKED(wrapped_id, 1);
  CONVERT_NUMBER_CHECKED(int, inlined_jsframe_index, Int32, args[2]);
  CONVERT_NUMBER_CHECKED(int, index, Int32, args[3]);

  // Get the frame where the debugging is performed.
  StackFrame::Id id = UnwrapFrameId(wrapped_id);
  JavaScriptFrameIterator frame_it(isolate, id);
  JavaScriptFrame* frame = frame_it.frame();

  // Find the requested scope.
  int n = 0;
  ScopeIterator it(isolate, frame, inlined_jsframe_index);
  for (; !it.Done() && n < index; it.Next()) {
    n++;
  }
  if (it.Done()) {
    return isolate->heap()->undefined_value();
  }
  return MaterializeScopeDetails(isolate, &it);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFunctionScopeCount) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  // Check arguments.
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);

  // Count the visible scopes.
  int n = 0;
  for (ScopeIterator it(isolate, fun); !it.Done(); it.Next()) {
    n++;
  }

  return Smi::FromInt(n);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFunctionScopeDetails) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  // Check arguments.
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
  CONVERT_NUMBER_CHECKED(int, index, Int32, args[1]);

  // Find the requested scope.
  int n = 0;
  ScopeIterator it(isolate, fun);
  for (; !it.Done() && n < index; it.Next()) {
    n++;
  }
  if (it.Done()) {
    return isolate->heap()->undefined_value();
  }

  return MaterializeScopeDetails(isolate, &it);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugPrintScopes) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 0);

#ifdef DEBUG
  // Print the scopes for the top frame.
  StackFrameLocator locator;
  JavaScriptFrame* frame = locator.FindJavaScriptFrame(0);
  for (ScopeIterator it(isolate, frame, 0);
       !it.Done();
       it.Next()) {
    it.DebugPrint();
  }
#endif
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetThreadCount) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  // Check arguments.
  Object* result;
  { MaybeObject* maybe_result = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }

  // Count all archived V8 threads.
  int n = 0;
  for (ThreadState* thread =
          isolate->thread_manager()->FirstThreadStateInUse();
       thread != NULL;
       thread = thread->Next()) {
    n++;
  }

  // Total number of threads is current thread and archived threads.
  return Smi::FromInt(n + 1);
}


static const int kThreadDetailsCurrentThreadIndex = 0;
static const int kThreadDetailsThreadIdIndex = 1;
static const int kThreadDetailsSize = 2;

// Return an array with thread details
// args[0]: number: break id
// args[1]: number: thread index
//
// The array returned contains the following information:
// 0: Is current thread?
// 1: Thread id
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetThreadDetails) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  // Check arguments.
  Object* check;
  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check->ToObject(&check)) return maybe_check;
  }
  CONVERT_NUMBER_CHECKED(int, index, Int32, args[1]);

  // Allocate array for result.
  Handle<FixedArray> details =
      isolate->factory()->NewFixedArray(kThreadDetailsSize);

  // Thread index 0 is current thread.
  if (index == 0) {
    // Fill the details.
    details->set(kThreadDetailsCurrentThreadIndex,
                 isolate->heap()->true_value());
    details->set(kThreadDetailsThreadIdIndex,
                 Smi::FromInt(ThreadId::Current().ToInteger()));
  } else {
    // Find the thread with the requested index.
    int n = 1;
    ThreadState* thread =
        isolate->thread_manager()->FirstThreadStateInUse();
    while (index != n && thread != NULL) {
      thread = thread->Next();
      n++;
    }
    if (thread == NULL) {
      return isolate->heap()->undefined_value();
    }

    // Fill the details.
    details->set(kThreadDetailsCurrentThreadIndex,
                 isolate->heap()->false_value());
    details->set(kThreadDetailsThreadIdIndex,
                 Smi::FromInt(thread->id().ToInteger()));
  }

  // Convert to JS array and return.
  return *isolate->factory()->NewJSArrayWithElements(details);
}


// Sets the disable break state
// args[0]: disable break state
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetDisableBreak) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  CONVERT_BOOLEAN_ARG_CHECKED(disable_break, 0);
  isolate->debug()->set_disable_break(disable_break);
  return  isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetBreakLocations) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);

  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
  Handle<SharedFunctionInfo> shared(fun->shared());
  // Find the number of break points
  Handle<Object> break_locations = Debug::GetSourceBreakLocations(shared);
  if (break_locations->IsUndefined()) return isolate->heap()->undefined_value();
  // Return array as JS array
  return *isolate->factory()->NewJSArrayWithElements(
      Handle<FixedArray>::cast(break_locations));
}


// Set a break point in a function
// args[0]: function
// args[1]: number: break source position (within the function source)
// args[2]: number: break point object
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetFunctionBreakPoint) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
  Handle<SharedFunctionInfo> shared(fun->shared());
  CONVERT_NUMBER_CHECKED(int32_t, source_position, Int32, args[1]);
  RUNTIME_ASSERT(source_position >= 0);
  Handle<Object> break_point_object_arg = args.at<Object>(2);

  // Set break point.
  isolate->debug()->SetBreakPoint(shared, break_point_object_arg,
                                  &source_position);

  return Smi::FromInt(source_position);
}


Object* Runtime::FindSharedFunctionInfoInScript(Isolate* isolate,
                                                Handle<Script> script,
                                                int position) {
  // Iterate the heap looking for SharedFunctionInfo generated from the
  // script. The inner most SharedFunctionInfo containing the source position
  // for the requested break point is found.
  // NOTE: This might require several heap iterations. If the SharedFunctionInfo
  // which is found is not compiled it is compiled and the heap is iterated
  // again as the compilation might create inner functions from the newly
  // compiled function and the actual requested break point might be in one of
  // these functions.
  bool done = false;
  // The current candidate for the source position:
  int target_start_position = RelocInfo::kNoPosition;
  Handle<SharedFunctionInfo> target;
  while (!done) {
    { // Extra scope for iterator and no-allocation.
      isolate->heap()->EnsureHeapIsIterable();
      AssertNoAllocation no_alloc_during_heap_iteration;
      HeapIterator iterator;
      for (HeapObject* obj = iterator.next();
           obj != NULL; obj = iterator.next()) {
        if (obj->IsSharedFunctionInfo()) {
          Handle<SharedFunctionInfo> shared(SharedFunctionInfo::cast(obj));
          if (shared->script() == *script) {
            // If the SharedFunctionInfo found has the requested script data and
            // contains the source position it is a candidate.
            int start_position = shared->function_token_position();
            if (start_position == RelocInfo::kNoPosition) {
              start_position = shared->start_position();
            }
            if (start_position <= position &&
                position <= shared->end_position()) {
              // If there is no candidate or this function is within the current
              // candidate this is the new candidate.
              if (target.is_null()) {
                target_start_position = start_position;
                target = shared;
              } else {
                if (target_start_position == start_position &&
                    shared->end_position() == target->end_position()) {
                    // If a top-level function contain only one function
                    // declartion the source for the top-level and the
                    // function is the same. In that case prefer the non
                    // top-level function.
                  if (!shared->is_toplevel()) {
                    target_start_position = start_position;
                    target = shared;
                  }
                } else if (target_start_position <= start_position &&
                           shared->end_position() <= target->end_position()) {
                  // This containment check includes equality as a function
                  // inside a top-level function can share either start or end
                  // position with the top-level function.
                  target_start_position = start_position;
                  target = shared;
                }
              }
            }
          }
        }
      }  // End for loop.
    }  // End No allocation scope.

    if (target.is_null()) {
      return isolate->heap()->undefined_value();
    }

    // If the candidate found is compiled we are done. NOTE: when lazy
    // compilation of inner functions is introduced some additional checking
    // needs to be done here to compile inner functions.
    done = target->is_compiled();
    if (!done) {
      // If the candidate is not compiled compile it to reveal any inner
      // functions which might contain the requested source position.
      SharedFunctionInfo::CompileLazy(target, KEEP_EXCEPTION);
    }
  }  // End while loop.

  return *target;
}


// Changes the state of a break point in a script and returns source position
// where break point was set. NOTE: Regarding performance see the NOTE for
// GetScriptFromScriptData.
// args[0]: script to set break point in
// args[1]: number: break source position (within the script source)
// args[2]: number: break point object
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetScriptBreakPoint) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSValue, wrapper, 0);
  CONVERT_NUMBER_CHECKED(int32_t, source_position, Int32, args[1]);
  RUNTIME_ASSERT(source_position >= 0);
  Handle<Object> break_point_object_arg = args.at<Object>(2);

  // Get the script from the script wrapper.
  RUNTIME_ASSERT(wrapper->value()->IsScript());
  Handle<Script> script(Script::cast(wrapper->value()));

  Object* result = Runtime::FindSharedFunctionInfoInScript(
      isolate, script, source_position);
  if (!result->IsUndefined()) {
    Handle<SharedFunctionInfo> shared(SharedFunctionInfo::cast(result));
    // Find position within function. The script position might be before the
    // source position of the first function.
    int position;
    if (shared->start_position() > source_position) {
      position = 0;
    } else {
      position = source_position - shared->start_position();
    }
    isolate->debug()->SetBreakPoint(shared, break_point_object_arg, &position);
    position += shared->start_position();
    return Smi::FromInt(position);
  }
  return  isolate->heap()->undefined_value();
}


// Clear a break point
// args[0]: number: break point object
RUNTIME_FUNCTION(MaybeObject*, Runtime_ClearBreakPoint) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  Handle<Object> break_point_object_arg = args.at<Object>(0);

  // Clear break point.
  isolate->debug()->ClearBreakPoint(break_point_object_arg);

  return isolate->heap()->undefined_value();
}


// Change the state of break on exceptions.
// args[0]: Enum value indicating whether to affect caught/uncaught exceptions.
// args[1]: Boolean indicating on/off.
RUNTIME_FUNCTION(MaybeObject*, Runtime_ChangeBreakOnException) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);
  RUNTIME_ASSERT(args[0]->IsNumber());
  CONVERT_BOOLEAN_ARG_CHECKED(enable, 1);

  // If the number doesn't match an enum value, the ChangeBreakOnException
  // function will default to affecting caught exceptions.
  ExceptionBreakType type =
      static_cast<ExceptionBreakType>(NumberToUint32(args[0]));
  // Update break point state.
  isolate->debug()->ChangeBreakOnException(type, enable);
  return isolate->heap()->undefined_value();
}


// Returns the state of break on exceptions
// args[0]: boolean indicating uncaught exceptions
RUNTIME_FUNCTION(MaybeObject*, Runtime_IsBreakOnException) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  RUNTIME_ASSERT(args[0]->IsNumber());

  ExceptionBreakType type =
      static_cast<ExceptionBreakType>(NumberToUint32(args[0]));
  bool result = isolate->debug()->IsBreakOnException(type);
  return Smi::FromInt(result);
}


// Prepare for stepping
// args[0]: break id for checking execution state
// args[1]: step action from the enumeration StepAction
// args[2]: number of times to perform the step, for step out it is the number
//          of frames to step down.
RUNTIME_FUNCTION(MaybeObject*, Runtime_PrepareStep) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 3);
  // Check arguments.
  Object* check;
  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check->ToObject(&check)) return maybe_check;
  }
  if (!args[1]->IsNumber() || !args[2]->IsNumber()) {
    return isolate->Throw(isolate->heap()->illegal_argument_symbol());
  }

  // Get the step action and check validity.
  StepAction step_action = static_cast<StepAction>(NumberToInt32(args[1]));
  if (step_action != StepIn &&
      step_action != StepNext &&
      step_action != StepOut &&
      step_action != StepInMin &&
      step_action != StepMin) {
    return isolate->Throw(isolate->heap()->illegal_argument_symbol());
  }

  // Get the number of steps.
  int step_count = NumberToInt32(args[2]);
  if (step_count < 1) {
    return isolate->Throw(isolate->heap()->illegal_argument_symbol());
  }

  // Clear all current stepping setup.
  isolate->debug()->ClearStepping();

  // Prepare step.
  isolate->debug()->PrepareStep(static_cast<StepAction>(step_action),
                                step_count);
  return isolate->heap()->undefined_value();
}


// Clear all stepping set by PrepareStep.
RUNTIME_FUNCTION(MaybeObject*, Runtime_ClearStepping) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 0);
  isolate->debug()->ClearStepping();
  return isolate->heap()->undefined_value();
}


// Creates a copy of the with context chain. The copy of the context chain is
// is linked to the function context supplied.
static Handle<Context> CopyNestedScopeContextChain(Isolate* isolate,
                                                   Handle<JSFunction> function,
                                                   Handle<Context> base,
                                                   JavaScriptFrame* frame,
                                                   int inlined_jsframe_index) {
  HandleScope scope(isolate);
  List<Handle<ScopeInfo> > scope_chain;
  List<Handle<Context> > context_chain;

  ScopeIterator it(isolate, frame, inlined_jsframe_index);
  for (; it.Type() != ScopeIterator::ScopeTypeGlobal &&
         it.Type() != ScopeIterator::ScopeTypeLocal ; it.Next()) {
    ASSERT(!it.Done());
    scope_chain.Add(it.CurrentScopeInfo());
    context_chain.Add(it.CurrentContext());
  }

  // At the end of the chain. Return the base context to link to.
  Handle<Context> context = base;

  // Iteratively copy and or materialize the nested contexts.
  while (!scope_chain.is_empty()) {
    Handle<ScopeInfo> scope_info = scope_chain.RemoveLast();
    Handle<Context> current = context_chain.RemoveLast();
    ASSERT(!(scope_info->HasContext() & current.is_null()));

    if (scope_info->Type() == CATCH_SCOPE) {
      Handle<String> name(String::cast(current->extension()));
      Handle<Object> thrown_object(current->get(Context::THROWN_OBJECT_INDEX));
      context =
          isolate->factory()->NewCatchContext(function,
                                              context,
                                              name,
                                              thrown_object);
    } else if (scope_info->Type() == BLOCK_SCOPE) {
      // Materialize the contents of the block scope into a JSObject.
      Handle<JSObject> block_scope_object =
          MaterializeBlockScope(isolate, current);
      if (block_scope_object.is_null()) {
        return Handle<Context>::null();
      }
      // Allocate a new function context for the debug evaluation and set the
      // extension object.
      Handle<Context> new_context =
          isolate->factory()->NewFunctionContext(Context::MIN_CONTEXT_SLOTS,
                                                 function);
      new_context->set_extension(*block_scope_object);
      new_context->set_previous(*context);
      context = new_context;
    } else {
      ASSERT(scope_info->Type() == WITH_SCOPE);
      ASSERT(current->IsWithContext());
      Handle<JSObject> extension(JSObject::cast(current->extension()));
      context =
          isolate->factory()->NewWithContext(function, context, extension);
    }
  }

  return scope.CloseAndEscape(context);
}


// Helper function to find or create the arguments object for
// Runtime_DebugEvaluate.
static Handle<Object> GetArgumentsObject(Isolate* isolate,
                                         JavaScriptFrame* frame,
                                         FrameInspector* frame_inspector,
                                         Handle<ScopeInfo> scope_info,
                                         Handle<Context> function_context) {
  // Try to find the value of 'arguments' to pass as parameter. If it is not
  // found (that is the debugged function does not reference 'arguments' and
  // does not support eval) then create an 'arguments' object.
  int index;
  if (scope_info->StackLocalCount() > 0) {
    index = scope_info->StackSlotIndex(isolate->heap()->arguments_symbol());
    if (index != -1) {
      return Handle<Object>(frame->GetExpression(index), isolate);
    }
  }

  if (scope_info->HasHeapAllocatedLocals()) {
    VariableMode mode;
    InitializationFlag init_flag;
    index = scope_info->ContextSlotIndex(
        isolate->heap()->arguments_symbol(), &mode, &init_flag);
    if (index != -1) {
      return Handle<Object>(function_context->get(index), isolate);
    }
  }

  Handle<JSFunction> function(JSFunction::cast(frame_inspector->GetFunction()));
  int length = frame_inspector->GetParametersCount();
  Handle<JSObject> arguments =
      isolate->factory()->NewArgumentsObject(function, length);
  Handle<FixedArray> array = isolate->factory()->NewFixedArray(length);

  AssertNoAllocation no_gc;
  WriteBarrierMode mode = array->GetWriteBarrierMode(no_gc);
  for (int i = 0; i < length; i++) {
    array->set(i, frame_inspector->GetParameter(i), mode);
  }
  arguments->set_elements(*array);
  return arguments;
}


static const char kSourceStr[] =
    "(function(arguments,__source__){return eval(__source__);})";


// Evaluate a piece of JavaScript in the context of a stack frame for
// debugging. This is accomplished by creating a new context which in its
// extension part has all the parameters and locals of the function on the
// stack frame. A function which calls eval with the code to evaluate is then
// compiled in this context and called in this context. As this context
// replaces the context of the function on the stack frame a new (empty)
// function is created as well to be used as the closure for the context.
// This function and the context acts as replacements for the function on the
// stack frame presenting the same view of the values of parameters and
// local variables as if the piece of JavaScript was evaluated at the point
// where the function on the stack frame is currently stopped.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugEvaluate) {
  HandleScope scope(isolate);

  // Check the execution state and decode arguments frame and source to be
  // evaluated.
  ASSERT(args.length() == 6);
  Object* check_result;
  { MaybeObject* maybe_check_result = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check_result->ToObject(&check_result)) {
      return maybe_check_result;
    }
  }
  CONVERT_SMI_ARG_CHECKED(wrapped_id, 1);
  CONVERT_NUMBER_CHECKED(int, inlined_jsframe_index, Int32, args[2]);
  CONVERT_ARG_HANDLE_CHECKED(String, source, 3);
  CONVERT_BOOLEAN_ARG_CHECKED(disable_break, 4);
  Handle<Object> additional_context(args[5]);

  // Handle the processing of break.
  DisableBreak disable_break_save(disable_break);

  // Get the frame where the debugging is performed.
  StackFrame::Id id = UnwrapFrameId(wrapped_id);
  JavaScriptFrameIterator it(isolate, id);
  JavaScriptFrame* frame = it.frame();
  FrameInspector frame_inspector(frame, inlined_jsframe_index, isolate);
  Handle<JSFunction> function(JSFunction::cast(frame_inspector.GetFunction()));
  Handle<ScopeInfo> scope_info(function->shared()->scope_info());

  // Traverse the saved contexts chain to find the active context for the
  // selected frame.
  SaveContext* save = FindSavedContextForFrame(isolate, frame);

  SaveContext savex(isolate);
  isolate->set_context(*(save->context()));

  // Create the (empty) function replacing the function on the stack frame for
  // the purpose of evaluating in the context created below. It is important
  // that this function does not describe any parameters and local variables
  // in the context. If it does then this will cause problems with the lookup
  // in Context::Lookup, where context slots for parameters and local variables
  // are looked at before the extension object.
  Handle<JSFunction> go_between =
      isolate->factory()->NewFunction(isolate->factory()->empty_string(),
                                      isolate->factory()->undefined_value());
  go_between->set_context(function->context());
#ifdef DEBUG
  Handle<ScopeInfo> go_between_scope_info(go_between->shared()->scope_info());
  ASSERT(go_between_scope_info->ParameterCount() == 0);
  ASSERT(go_between_scope_info->ContextLocalCount() == 0);
#endif

  // Materialize the content of the local scope into a JSObject.
  Handle<JSObject> local_scope = MaterializeLocalScopeWithFrameInspector(
      isolate, frame, &frame_inspector);
  RETURN_IF_EMPTY_HANDLE(isolate, local_scope);

  // Allocate a new context for the debug evaluation and set the extension
  // object build.
  Handle<Context> context =
      isolate->factory()->NewFunctionContext(Context::MIN_CONTEXT_SLOTS,
                                             go_between);
  context->set_extension(*local_scope);
  // Copy any with contexts present and chain them in front of this context.
  Handle<Context> frame_context(Context::cast(frame->context()));
  Handle<Context> function_context;
  // Get the function's context if it has one.
  if (scope_info->HasContext()) {
    function_context = Handle<Context>(frame_context->declaration_context());
  }
  context = CopyNestedScopeContextChain(isolate,
                                        go_between,
                                        context,
                                        frame,
                                        inlined_jsframe_index);

  if (additional_context->IsJSObject()) {
    Handle<JSObject> extension = Handle<JSObject>::cast(additional_context);
    context =
        isolate->factory()->NewWithContext(go_between, context, extension);
  }

  // Wrap the evaluation statement in a new function compiled in the newly
  // created context. The function has one parameter which has to be called
  // 'arguments'. This it to have access to what would have been 'arguments' in
  // the function being debugged.
  // function(arguments,__source__) {return eval(__source__);}

  Handle<String> function_source =
      isolate->factory()->NewStringFromAscii(
          Vector<const char>(kSourceStr, sizeof(kSourceStr) - 1));

  // Currently, the eval code will be executed in non-strict mode,
  // even in the strict code context.
  Handle<SharedFunctionInfo> shared =
      Compiler::CompileEval(function_source,
                            context,
                            context->IsGlobalContext(),
                            CLASSIC_MODE,
                            RelocInfo::kNoPosition);
  if (shared.is_null()) return Failure::Exception();
  Handle<JSFunction> compiled_function =
      isolate->factory()->NewFunctionFromSharedFunctionInfo(shared, context);

  // Invoke the result of the compilation to get the evaluation function.
  bool has_pending_exception;
  Handle<Object> receiver(frame->receiver(), isolate);
  Handle<Object> evaluation_function =
      Execution::Call(compiled_function, receiver, 0, NULL,
                      &has_pending_exception);
  if (has_pending_exception) return Failure::Exception();

  Handle<Object> arguments = GetArgumentsObject(isolate,
                                                frame,
                                                &frame_inspector,
                                                scope_info,
                                                function_context);

  // Invoke the evaluation function and return the result.
  Handle<Object> argv[] = { arguments, source };
  Handle<Object> result =
      Execution::Call(Handle<JSFunction>::cast(evaluation_function),
                      receiver,
                      ARRAY_SIZE(argv),
                      argv,
                      &has_pending_exception);
  if (has_pending_exception) return Failure::Exception();

  // Skip the global proxy as it has no properties and always delegates to the
  // real global object.
  if (result->IsJSGlobalProxy()) {
    result = Handle<JSObject>(JSObject::cast(result->GetPrototype()));
  }

  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugEvaluateGlobal) {
  HandleScope scope(isolate);

  // Check the execution state and decode arguments frame and source to be
  // evaluated.
  ASSERT(args.length() == 4);
  Object* check_result;
  { MaybeObject* maybe_check_result = Runtime_CheckExecutionState(
      RUNTIME_ARGUMENTS(isolate, args));
    if (!maybe_check_result->ToObject(&check_result)) {
      return maybe_check_result;
    }
  }
  CONVERT_ARG_HANDLE_CHECKED(String, source, 1);
  CONVERT_BOOLEAN_ARG_CHECKED(disable_break, 2);
  Handle<Object> additional_context(args[3]);

  // Handle the processing of break.
  DisableBreak disable_break_save(disable_break);

  // Enter the top context from before the debugger was invoked.
  SaveContext save(isolate);
  SaveContext* top = &save;
  while (top != NULL && *top->context() == *isolate->debug()->debug_context()) {
    top = top->prev();
  }
  if (top != NULL) {
    isolate->set_context(*top->context());
  }

  // Get the global context now set to the top context from before the
  // debugger was invoked.
  Handle<Context> context = isolate->global_context();

  bool is_global = true;

  if (additional_context->IsJSObject()) {
    // Create a new with context with the additional context information between
    // the context of the debugged function and the eval code to be executed.
    context = isolate->factory()->NewWithContext(
        Handle<JSFunction>(context->closure()),
        context,
        Handle<JSObject>::cast(additional_context));
    is_global = false;
  }

  // Compile the source to be evaluated.
  // Currently, the eval code will be executed in non-strict mode,
  // even in the strict code context.
  Handle<SharedFunctionInfo> shared =
      Compiler::CompileEval(source,
                            context,
                            is_global,
                            CLASSIC_MODE,
                            RelocInfo::kNoPosition);
  if (shared.is_null()) return Failure::Exception();
  Handle<JSFunction> compiled_function =
      Handle<JSFunction>(
          isolate->factory()->NewFunctionFromSharedFunctionInfo(shared,
                                                                context));

  // Invoke the result of the compilation to get the evaluation function.
  bool has_pending_exception;
  Handle<Object> receiver = isolate->global();
  Handle<Object> result =
    Execution::Call(compiled_function, receiver, 0, NULL,
                    &has_pending_exception);
  // Clear the oneshot breakpoints so that the debugger does not step further.
  isolate->debug()->ClearStepping();
  if (has_pending_exception) return Failure::Exception();
  return *result;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugGetLoadedScripts) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 0);

  // Fill the script objects.
  Handle<FixedArray> instances = isolate->debug()->GetLoadedScripts();

  // Convert the script objects to proper JS objects.
  for (int i = 0; i < instances->length(); i++) {
    Handle<Script> script = Handle<Script>(Script::cast(instances->get(i)));
    // Get the script wrapper in a local handle before calling GetScriptWrapper,
    // because using
    //   instances->set(i, *GetScriptWrapper(script))
    // is unsafe as GetScriptWrapper might call GC and the C++ compiler might
    // already have dereferenced the instances handle.
    Handle<JSValue> wrapper = GetScriptWrapper(script);
    instances->set(i, *wrapper);
  }

  // Return result as a JS array.
  Handle<JSObject> result =
      isolate->factory()->NewJSObject(isolate->array_function());
  isolate->factory()->SetContent(Handle<JSArray>::cast(result), instances);
  return *result;
}


// Helper function used by Runtime_DebugReferencedBy below.
static int DebugReferencedBy(HeapIterator* iterator,
                             JSObject* target,
                             Object* instance_filter, int max_references,
                             FixedArray* instances, int instances_size,
                             JSFunction* arguments_function) {
  NoHandleAllocation ha;
  AssertNoAllocation no_alloc;

  // Iterate the heap.
  int count = 0;
  JSObject* last = NULL;
  HeapObject* heap_obj = NULL;
  while (((heap_obj = iterator->next()) != NULL) &&
         (max_references == 0 || count < max_references)) {
    // Only look at all JSObjects.
    if (heap_obj->IsJSObject()) {
      // Skip context extension objects and argument arrays as these are
      // checked in the context of functions using them.
      JSObject* obj = JSObject::cast(heap_obj);
      if (obj->IsJSContextExtensionObject() ||
          obj->map()->constructor() == arguments_function) {
        continue;
      }

      // Check if the JS object has a reference to the object looked for.
      if (obj->ReferencesObject(target)) {
        // Check instance filter if supplied. This is normally used to avoid
        // references from mirror objects (see Runtime_IsInPrototypeChain).
        if (!instance_filter->IsUndefined()) {
          Object* V = obj;
          while (true) {
            Object* prototype = V->GetPrototype();
            if (prototype->IsNull()) {
              break;
            }
            if (instance_filter == prototype) {
              obj = NULL;  // Don't add this object.
              break;
            }
            V = prototype;
          }
        }

        if (obj != NULL) {
          // Valid reference found add to instance array if supplied an update
          // count.
          if (instances != NULL && count < instances_size) {
            instances->set(count, obj);
          }
          last = obj;
          count++;
        }
      }
    }
  }

  // Check for circular reference only. This can happen when the object is only
  // referenced from mirrors and has a circular reference in which case the
  // object is not really alive and would have been garbage collected if not
  // referenced from the mirror.
  if (count == 1 && last == target) {
    count = 0;
  }

  // Return the number of referencing objects found.
  return count;
}


// Scan the heap for objects with direct references to an object
// args[0]: the object to find references to
// args[1]: constructor function for instances to exclude (Mirror)
// args[2]: the the maximum number of objects to return
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugReferencedBy) {
  ASSERT(args.length() == 3);

  // First perform a full GC in order to avoid references from dead objects.
  isolate->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                                     "%DebugReferencedBy");
  // The heap iterator reserves the right to do a GC to make the heap iterable.
  // Due to the GC above we know it won't need to do that, but it seems cleaner
  // to get the heap iterator constructed before we start having unprotected
  // Object* locals that are not protected by handles.

  // Check parameters.
  CONVERT_ARG_CHECKED(JSObject, target, 0);
  Object* instance_filter = args[1];
  RUNTIME_ASSERT(instance_filter->IsUndefined() ||
                 instance_filter->IsJSObject());
  CONVERT_NUMBER_CHECKED(int32_t, max_references, Int32, args[2]);
  RUNTIME_ASSERT(max_references >= 0);


  // Get the constructor function for context extension and arguments array.
  JSObject* arguments_boilerplate =
      isolate->context()->global_context()->arguments_boilerplate();
  JSFunction* arguments_function =
      JSFunction::cast(arguments_boilerplate->map()->constructor());

  // Get the number of referencing objects.
  int count;
  HeapIterator heap_iterator;
  count = DebugReferencedBy(&heap_iterator,
                            target, instance_filter, max_references,
                            NULL, 0, arguments_function);

  // Allocate an array to hold the result.
  Object* object;
  { MaybeObject* maybe_object = isolate->heap()->AllocateFixedArray(count);
    if (!maybe_object->ToObject(&object)) return maybe_object;
  }
  FixedArray* instances = FixedArray::cast(object);

  // Fill the referencing objects.
  // AllocateFixedArray above does not make the heap non-iterable.
  ASSERT(HEAP->IsHeapIterable());
  HeapIterator heap_iterator2;
  count = DebugReferencedBy(&heap_iterator2,
                            target, instance_filter, max_references,
                            instances, count, arguments_function);

  // Return result as JS array.
  Object* result;
  MaybeObject* maybe_result = isolate->heap()->AllocateJSObject(
      isolate->context()->global_context()->array_function());
  if (!maybe_result->ToObject(&result)) return maybe_result;
  return JSArray::cast(result)->SetContent(instances);
}


// Helper function used by Runtime_DebugConstructedBy below.
static int DebugConstructedBy(HeapIterator* iterator,
                              JSFunction* constructor,
                              int max_references,
                              FixedArray* instances,
                              int instances_size) {
  AssertNoAllocation no_alloc;

  // Iterate the heap.
  int count = 0;
  HeapObject* heap_obj = NULL;
  while (((heap_obj = iterator->next()) != NULL) &&
         (max_references == 0 || count < max_references)) {
    // Only look at all JSObjects.
    if (heap_obj->IsJSObject()) {
      JSObject* obj = JSObject::cast(heap_obj);
      if (obj->map()->constructor() == constructor) {
        // Valid reference found add to instance array if supplied an update
        // count.
        if (instances != NULL && count < instances_size) {
          instances->set(count, obj);
        }
        count++;
      }
    }
  }

  // Return the number of referencing objects found.
  return count;
}


// Scan the heap for objects constructed by a specific function.
// args[0]: the constructor to find instances of
// args[1]: the the maximum number of objects to return
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugConstructedBy) {
  ASSERT(args.length() == 2);

  // First perform a full GC in order to avoid dead objects.
  isolate->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                                     "%DebugConstructedBy");

  // Check parameters.
  CONVERT_ARG_CHECKED(JSFunction, constructor, 0);
  CONVERT_NUMBER_CHECKED(int32_t, max_references, Int32, args[1]);
  RUNTIME_ASSERT(max_references >= 0);

  // Get the number of referencing objects.
  int count;
  HeapIterator heap_iterator;
  count = DebugConstructedBy(&heap_iterator,
                             constructor,
                             max_references,
                             NULL,
                             0);

  // Allocate an array to hold the result.
  Object* object;
  { MaybeObject* maybe_object = isolate->heap()->AllocateFixedArray(count);
    if (!maybe_object->ToObject(&object)) return maybe_object;
  }
  FixedArray* instances = FixedArray::cast(object);

  ASSERT(HEAP->IsHeapIterable());
  // Fill the referencing objects.
  HeapIterator heap_iterator2;
  count = DebugConstructedBy(&heap_iterator2,
                             constructor,
                             max_references,
                             instances,
                             count);

  // Return result as JS array.
  Object* result;
  { MaybeObject* maybe_result = isolate->heap()->AllocateJSObject(
          isolate->context()->global_context()->array_function());
    if (!maybe_result->ToObject(&result)) return maybe_result;
  }
  return JSArray::cast(result)->SetContent(instances);
}


// Find the effective prototype object as returned by __proto__.
// args[0]: the object to find the prototype for.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugGetPrototype) {
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSObject, obj, 0);

  // Use the __proto__ accessor.
  return Accessors::ObjectPrototype.getter(obj, NULL);
}


// Patches script source (should be called upon BeforeCompile event).
RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugSetScriptSource) {
  HandleScope scope(isolate);
  ASSERT(args.length() == 2);

  CONVERT_ARG_HANDLE_CHECKED(JSValue, script_wrapper, 0);
  Handle<String> source(String::cast(args[1]));

  RUNTIME_ASSERT(script_wrapper->value()->IsScript());
  Handle<Script> script(Script::cast(script_wrapper->value()));

  int compilation_state = Smi::cast(script->compilation_state())->value();
  RUNTIME_ASSERT(compilation_state == Script::COMPILATION_STATE_INITIAL);
  script->set_source(*source);

  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_SystemBreak) {
  ASSERT(args.length() == 0);
  CPU::DebugBreak();
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugDisassembleFunction) {
#ifdef DEBUG
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  // Get the function and make sure it is compiled.
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, func, 0);
  if (!JSFunction::CompileLazy(func, KEEP_EXCEPTION)) {
    return Failure::Exception();
  }
  func->code()->PrintLn();
#endif  // DEBUG
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugDisassembleConstructor) {
#ifdef DEBUG
  HandleScope scope(isolate);
  ASSERT(args.length() == 1);
  // Get the function and make sure it is compiled.
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, func, 0);
  if (!JSFunction::CompileLazy(func, KEEP_EXCEPTION)) {
    return Failure::Exception();
  }
  func->shared()->construct_stub()->PrintLn();
#endif  // DEBUG
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionGetInferredName) {
  NoHandleAllocation ha;
  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(JSFunction, f, 0);
  return f->shared()->inferred_name();
}


static int FindSharedFunctionInfosForScript(HeapIterator* iterator,
                                            Script* script,
                                            FixedArray* buffer) {
  AssertNoAllocation no_allocations;
  int counter = 0;
  int buffer_size = buffer->length();
  for (HeapObject* obj = iterator->next();
       obj != NULL;
       obj = iterator->next()) {
    ASSERT(obj != NULL);
    if (!obj->IsSharedFunctionInfo()) {
      continue;
    }
    SharedFunctionInfo* shared = SharedFunctionInfo::cast(obj);
    if (shared->script() != script) {
      continue;
    }
    if (counter < buffer_size) {
      buffer->set(counter, shared);
    }
    counter++;
  }
  return counter;
}

// For a script finds all SharedFunctionInfo's in the heap that points
// to this script. Returns JSArray of SharedFunctionInfo wrapped
// in OpaqueReferences.
RUNTIME_FUNCTION(MaybeObject*,
                 Runtime_LiveEditFindSharedFunctionInfosForScript) {
  ASSERT(args.length() == 1);
  HandleScope scope(isolate);
  CONVERT_ARG_CHECKED(JSValue, script_value, 0);


  Handle<Script> script = Handle<Script>(Script::cast(script_value->value()));

  const int kBufferSize = 32;

  Handle<FixedArray> array;
  array = isolate->factory()->NewFixedArray(kBufferSize);
  int number;
  {
    isolate->heap()->EnsureHeapIsIterable();
    AssertNoAllocation no_allocations;
    HeapIterator heap_iterator;
    Script* scr = *script;
    FixedArray* arr = *array;
    number = FindSharedFunctionInfosForScript(&heap_iterator, scr, arr);
  }
  if (number > kBufferSize) {
    array = isolate->factory()->NewFixedArray(number);
    isolate->heap()->EnsureHeapIsIterable();
    AssertNoAllocation no_allocations;
    HeapIterator heap_iterator;
    Script* scr = *script;
    FixedArray* arr = *array;
    FindSharedFunctionInfosForScript(&heap_iterator, scr, arr);
  }

  Handle<JSArray> result = isolate->factory()->NewJSArrayWithElements(array);
  result->set_length(Smi::FromInt(number));

  LiveEdit::WrapSharedFunctionInfos(result);

  return *result;
}

// For a script calculates compilation information about all its functions.
// The script source is explicitly specified by the second argument.
// The source of the actual script is not used, however it is important that
// all generated code keeps references to this particular instance of script.
// Returns a JSArray of compilation infos. The array is ordered so that
// each function with all its descendant is always stored in a continues range
// with the function itself going first. The root function is a script function.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditGatherCompileInfo) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_CHECKED(JSValue, script, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, source, 1);
  Handle<Script> script_handle = Handle<Script>(Script::cast(script->value()));

  JSArray* result =  LiveEdit::GatherCompileInfo(script_handle, source);

  if (isolate->has_pending_exception()) {
    return Failure::Exception();
  }

  return result;
}

// Changes the source of the script to a new_source.
// If old_script_name is provided (i.e. is a String), also creates a copy of
// the script with its original source and sends notification to debugger.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditReplaceScript) {
  ASSERT(args.length() == 3);
  HandleScope scope(isolate);
  CONVERT_ARG_CHECKED(JSValue, original_script_value, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, new_source, 1);
  Handle<Object> old_script_name(args[2], isolate);

  RUNTIME_ASSERT(original_script_value->value()->IsScript());
  Handle<Script> original_script(Script::cast(original_script_value->value()));

  Object* old_script = LiveEdit::ChangeScriptSource(original_script,
                                                    new_source,
                                                    old_script_name);

  if (old_script->IsScript()) {
    Handle<Script> script_handle(Script::cast(old_script));
    return *(GetScriptWrapper(script_handle));
  } else {
    return isolate->heap()->null_value();
  }
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditFunctionSourceUpdated) {
  ASSERT(args.length() == 1);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, shared_info, 0);
  return LiveEdit::FunctionSourceUpdated(shared_info);
}


// Replaces code of SharedFunctionInfo with a new one.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditReplaceFunctionCode) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, new_compile_info, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, shared_info, 1);

  return LiveEdit::ReplaceFunctionCode(new_compile_info, shared_info);
}

// Connects SharedFunctionInfo to another script.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditFunctionSetScript) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  Handle<Object> function_object(args[0], isolate);
  Handle<Object> script_object(args[1], isolate);

  if (function_object->IsJSValue()) {
    Handle<JSValue> function_wrapper = Handle<JSValue>::cast(function_object);
    if (script_object->IsJSValue()) {
      RUNTIME_ASSERT(JSValue::cast(*script_object)->value()->IsScript());
      Script* script = Script::cast(JSValue::cast(*script_object)->value());
      script_object = Handle<Object>(script, isolate);
    }

    LiveEdit::SetFunctionScript(function_wrapper, script_object);
  } else {
    // Just ignore this. We may not have a SharedFunctionInfo for some functions
    // and we check it in this function.
  }

  return isolate->heap()->undefined_value();
}


// In a code of a parent function replaces original function as embedded object
// with a substitution one.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditReplaceRefToNestedFunction) {
  ASSERT(args.length() == 3);
  HandleScope scope(isolate);

  CONVERT_ARG_HANDLE_CHECKED(JSValue, parent_wrapper, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSValue, orig_wrapper, 1);
  CONVERT_ARG_HANDLE_CHECKED(JSValue, subst_wrapper, 2);

  LiveEdit::ReplaceRefToNestedFunction(parent_wrapper, orig_wrapper,
                                       subst_wrapper);

  return isolate->heap()->undefined_value();
}


// Updates positions of a shared function info (first parameter) according
// to script source change. Text change is described in second parameter as
// array of groups of 3 numbers:
// (change_begin, change_end, change_end_new_position).
// Each group describes a change in text; groups are sorted by change_begin.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditPatchFunctionPositions) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, shared_array, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, position_change_array, 1);

  return LiveEdit::PatchFunctionPositions(shared_array, position_change_array);
}


// For array of SharedFunctionInfo's (each wrapped in JSValue)
// checks that none of them have activations on stacks (of any thread).
// Returns array of the same length with corresponding results of
// LiveEdit::FunctionPatchabilityStatus type.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditCheckAndDropActivations) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, shared_array, 0);
  CONVERT_BOOLEAN_ARG_CHECKED(do_drop, 1);

  return *LiveEdit::CheckAndDropActivations(shared_array, do_drop,
                                            isolate->zone());
}

// Compares 2 strings line-by-line, then token-wise and returns diff in form
// of JSArray of triplets (pos1, pos1_end, pos2_end) describing list
// of diff chunks.
RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditCompareStrings) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(String, s1, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, s2, 1);

  return *LiveEdit::CompareStrings(s1, s2);
}


// A testing entry. Returns statement position which is the closest to
// source_position.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFunctionCodePositionFromSource) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  CONVERT_NUMBER_CHECKED(int32_t, source_position, Int32, args[1]);

  Handle<Code> code(function->code(), isolate);

  if (code->kind() != Code::FUNCTION &&
      code->kind() != Code::OPTIMIZED_FUNCTION) {
    return isolate->heap()->undefined_value();
  }

  RelocIterator it(*code, RelocInfo::ModeMask(RelocInfo::STATEMENT_POSITION));
  int closest_pc = 0;
  int distance = kMaxInt;
  while (!it.done()) {
    int statement_position = static_cast<int>(it.rinfo()->data());
    // Check if this break point is closer that what was previously found.
    if (source_position <= statement_position &&
        statement_position - source_position < distance) {
      closest_pc =
          static_cast<int>(it.rinfo()->pc() - code->instruction_start());
      distance = statement_position - source_position;
      // Check whether we can't get any closer.
      if (distance == 0) break;
    }
    it.next();
  }

  return Smi::FromInt(closest_pc);
}


// Calls specified function with or without entering the debugger.
// This is used in unit tests to run code as if debugger is entered or simply
// to have a stack with C++ frame in the middle.
RUNTIME_FUNCTION(MaybeObject*, Runtime_ExecuteInDebugContext) {
  ASSERT(args.length() == 2);
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
  CONVERT_BOOLEAN_ARG_CHECKED(without_debugger, 1);

  Handle<Object> result;
  bool pending_exception;
  {
    if (without_debugger) {
      result = Execution::Call(function, isolate->global(), 0, NULL,
                               &pending_exception);
    } else {
      EnterDebugger enter_debugger;
      result = Execution::Call(function, isolate->global(), 0, NULL,
                               &pending_exception);
    }
  }
  if (!pending_exception) {
    return *result;
  } else {
    return Failure::Exception();
  }
}


// Sets a v8 flag.
RUNTIME_FUNCTION(MaybeObject*, Runtime_SetFlags) {
  CONVERT_ARG_CHECKED(String, arg, 0);
  SmartArrayPointer<char> flags =
      arg->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL);
  FlagList::SetFlagsFromString(*flags, StrLength(*flags));
  return isolate->heap()->undefined_value();
}


// Performs a GC.
// Presently, it only does a full GC.
RUNTIME_FUNCTION(MaybeObject*, Runtime_CollectGarbage) {
  isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags, "%CollectGarbage");
  return isolate->heap()->undefined_value();
}


// Gets the current heap usage.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetHeapUsage) {
  int usage = static_cast<int>(isolate->heap()->SizeOfObjects());
  if (!Smi::IsValid(usage)) {
    return *isolate->factory()->NewNumberFromInt(usage);
  }
  return Smi::FromInt(usage);
}


// Captures a live object list from the present heap.
RUNTIME_FUNCTION(MaybeObject*, Runtime_HasLOLEnabled) {
#ifdef LIVE_OBJECT_LIST
  return isolate->heap()->true_value();
#else
  return isolate->heap()->false_value();
#endif
}


// Captures a live object list from the present heap.
RUNTIME_FUNCTION(MaybeObject*, Runtime_CaptureLOL) {
#ifdef LIVE_OBJECT_LIST
  return LiveObjectList::Capture();
#else
  return isolate->heap()->undefined_value();
#endif
}


// Deletes the specified live object list.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DeleteLOL) {
#ifdef LIVE_OBJECT_LIST
  CONVERT_SMI_ARG_CHECKED(id, 0);
  bool success = LiveObjectList::Delete(id);
  return isolate->heap()->ToBoolean(success);
#else
  return isolate->heap()->undefined_value();
#endif
}


// Generates the response to a debugger request for a dump of the objects
// contained in the difference between the captured live object lists
// specified by id1 and id2.
// If id1 is 0 (i.e. not a valid lol), then the whole of lol id2 will be
// dumped.
RUNTIME_FUNCTION(MaybeObject*, Runtime_DumpLOL) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_SMI_ARG_CHECKED(id1, 0);
  CONVERT_SMI_ARG_CHECKED(id2, 1);
  CONVERT_SMI_ARG_CHECKED(start, 2);
  CONVERT_SMI_ARG_CHECKED(count, 3);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, filter_obj, 4);
  EnterDebugger enter_debugger;
  return LiveObjectList::Dump(id1, id2, start, count, filter_obj);
#else
  return isolate->heap()->undefined_value();
#endif
}


// Gets the specified object as requested by the debugger.
// This is only used for obj ids shown in live object lists.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLOLObj) {
#ifdef LIVE_OBJECT_LIST
  CONVERT_SMI_ARG_CHECKED(obj_id, 0);
  Object* result = LiveObjectList::GetObj(obj_id);
  return result;
#else
  return isolate->heap()->undefined_value();
#endif
}


// Gets the obj id for the specified address if valid.
// This is only used for obj ids shown in live object lists.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLOLObjId) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_ARG_HANDLE_CHECKED(String, address, 0);
  Object* result = LiveObjectList::GetObjId(address);
  return result;
#else
  return isolate->heap()->undefined_value();
#endif
}


// Gets the retainers that references the specified object alive.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLOLObjRetainers) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_SMI_ARG_CHECKED(obj_id, 0);
  RUNTIME_ASSERT(args[1]->IsUndefined() || args[1]->IsJSObject());
  RUNTIME_ASSERT(args[2]->IsUndefined() || args[2]->IsBoolean());
  RUNTIME_ASSERT(args[3]->IsUndefined() || args[3]->IsSmi());
  RUNTIME_ASSERT(args[4]->IsUndefined() || args[4]->IsSmi());
  CONVERT_ARG_HANDLE_CHECKED(JSObject, filter_obj, 5);

  Handle<JSObject> instance_filter;
  if (args[1]->IsJSObject()) {
    instance_filter = args.at<JSObject>(1);
  }
  bool verbose = false;
  if (args[2]->IsBoolean()) {
    verbose = args[2]->IsTrue();
  }
  int start = 0;
  if (args[3]->IsSmi()) {
    start = args.smi_at(3);
  }
  int limit = Smi::kMaxValue;
  if (args[4]->IsSmi()) {
    limit = args.smi_at(4);
  }

  return LiveObjectList::GetObjRetainers(obj_id,
                                         instance_filter,
                                         verbose,
                                         start,
                                         limit,
                                         filter_obj);
#else
  return isolate->heap()->undefined_value();
#endif
}


// Gets the reference path between 2 objects.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetLOLPath) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_SMI_ARG_CHECKED(obj_id1, 0);
  CONVERT_SMI_ARG_CHECKED(obj_id2, 1);
  RUNTIME_ASSERT(args[2]->IsUndefined() || args[2]->IsJSObject());

  Handle<JSObject> instance_filter;
  if (args[2]->IsJSObject()) {
    instance_filter = args.at<JSObject>(2);
  }

  Object* result =
      LiveObjectList::GetPath(obj_id1, obj_id2, instance_filter);
  return result;
#else
  return isolate->heap()->undefined_value();
#endif
}


// Generates the response to a debugger request for a list of all
// previously captured live object lists.
RUNTIME_FUNCTION(MaybeObject*, Runtime_InfoLOL) {
#ifdef LIVE_OBJECT_LIST
  CONVERT_SMI_ARG_CHECKED(start, 0);
  CONVERT_SMI_ARG_CHECKED(count, 1);
  return LiveObjectList::Info(start, count);
#else
  return isolate->heap()->undefined_value();
#endif
}


// Gets a dump of the specified object as requested by the debugger.
// This is only used for obj ids shown in live object lists.
RUNTIME_FUNCTION(MaybeObject*, Runtime_PrintLOLObj) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_SMI_ARG_CHECKED(obj_id, 0);
  Object* result = LiveObjectList::PrintObj(obj_id);
  return result;
#else
  return isolate->heap()->undefined_value();
#endif
}


// Resets and releases all previously captured live object lists.
RUNTIME_FUNCTION(MaybeObject*, Runtime_ResetLOL) {
#ifdef LIVE_OBJECT_LIST
  LiveObjectList::Reset();
  return isolate->heap()->undefined_value();
#else
  return isolate->heap()->undefined_value();
#endif
}


// Generates the response to a debugger request for a summary of the types
// of objects in the difference between the captured live object lists
// specified by id1 and id2.
// If id1 is 0 (i.e. not a valid lol), then the whole of lol id2 will be
// summarized.
RUNTIME_FUNCTION(MaybeObject*, Runtime_SummarizeLOL) {
#ifdef LIVE_OBJECT_LIST
  HandleScope scope;
  CONVERT_SMI_ARG_CHECKED(id1, 0);
  CONVERT_SMI_ARG_CHECKED(id2, 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, filter_obj, 2);

  EnterDebugger enter_debugger;
  return LiveObjectList::Summarize(id1, id2, filter_obj);
#else
  return isolate->heap()->undefined_value();
#endif
}

#endif  // ENABLE_DEBUGGER_SUPPORT


RUNTIME_FUNCTION(MaybeObject*, Runtime_ProfilerResume) {
  NoHandleAllocation ha;
  v8::V8::ResumeProfiler();
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_ProfilerPause) {
  NoHandleAllocation ha;
  v8::V8::PauseProfiler();
  return isolate->heap()->undefined_value();
}


// Finds the script object from the script data. NOTE: This operation uses
// heap traversal to find the function generated for the source position
// for the requested break point. For lazily compiled functions several heap
// traversals might be required rendering this operation as a rather slow
// operation. However for setting break points which is normally done through
// some kind of user interaction the performance is not crucial.
static Handle<Object> Runtime_GetScriptFromScriptName(
    Handle<String> script_name) {
  // Scan the heap for Script objects to find the script with the requested
  // script data.
  Handle<Script> script;
  script_name->GetHeap()->EnsureHeapIsIterable();
  AssertNoAllocation no_allocation_during_heap_iteration;
  HeapIterator iterator;
  HeapObject* obj = NULL;
  while (script.is_null() && ((obj = iterator.next()) != NULL)) {
    // If a script is found check if it has the script data requested.
    if (obj->IsScript()) {
      if (Script::cast(obj)->name()->IsString()) {
        if (String::cast(Script::cast(obj)->name())->Equals(*script_name)) {
          script = Handle<Script>(Script::cast(obj));
        }
      }
    }
  }

  // If no script with the requested script data is found return undefined.
  if (script.is_null()) return FACTORY->undefined_value();

  // Return the script found.
  return GetScriptWrapper(script);
}


// Get the script object from script data. NOTE: Regarding performance
// see the NOTE for GetScriptFromScriptData.
// args[0]: script data for the script to find the source for
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetScript) {
  HandleScope scope(isolate);

  ASSERT(args.length() == 1);

  CONVERT_ARG_CHECKED(String, script_name, 0);

  // Find the requested script.
  Handle<Object> result =
      Runtime_GetScriptFromScriptName(Handle<String>(script_name));
  return *result;
}


// Determines whether the given stack frame should be displayed in
// a stack trace.  The caller is the error constructor that asked
// for the stack trace to be collected.  The first time a construct
// call to this function is encountered it is skipped.  The seen_caller
// in/out parameter is used to remember if the caller has been seen
// yet.
static bool ShowFrameInStackTrace(StackFrame* raw_frame,
                                  Object* caller,
                                  bool* seen_caller) {
  // Only display JS frames.
  if (!raw_frame->is_java_script()) {
    return false;
  }
  JavaScriptFrame* frame = JavaScriptFrame::cast(raw_frame);
  Object* raw_fun = frame->function();
  // Not sure when this can happen but skip it just in case.
  if (!raw_fun->IsJSFunction()) {
    return false;
  }
  if ((raw_fun == caller) && !(*seen_caller)) {
    *seen_caller = true;
    return false;
  }
  // Skip all frames until we've seen the caller.
  if (!(*seen_caller)) return false;
  // Also, skip non-visible built-in functions and any call with the builtins
  // object as receiver, so as to not reveal either the builtins object or
  // an internal function.
  // The --builtins-in-stack-traces command line flag allows including
  // internal call sites in the stack trace for debugging purposes.
  if (!FLAG_builtins_in_stack_traces) {
    JSFunction* fun = JSFunction::cast(raw_fun);
    if (frame->receiver()->IsJSBuiltinsObject() ||
        (fun->IsBuiltin() && !fun->shared()->native())) {
      return false;
    }
  }
  return true;
}


// Collect the raw data for a stack trace.  Returns an array of 4
// element segments each containing a receiver, function, code and
// native code offset.
RUNTIME_FUNCTION(MaybeObject*, Runtime_CollectStackTrace) {
  ASSERT_EQ(args.length(), 3);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, error_object, 0);
  Handle<Object> caller = args.at<Object>(1);
  CONVERT_NUMBER_CHECKED(int32_t, limit, Int32, args[2]);

  HandleScope scope(isolate);
  Factory* factory = isolate->factory();

  limit = Max(limit, 0);  // Ensure that limit is not negative.
  int initial_size = Min(limit, 10);
  Handle<FixedArray> elements =
      factory->NewFixedArrayWithHoles(initial_size * 4);

  StackFrameIterator iter(isolate);
  // If the caller parameter is a function we skip frames until we're
  // under it before starting to collect.
  bool seen_caller = !caller->IsJSFunction();
  int cursor = 0;
  int frames_seen = 0;
  while (!iter.done() && frames_seen < limit) {
    StackFrame* raw_frame = iter.frame();
    if (ShowFrameInStackTrace(raw_frame, *caller, &seen_caller)) {
      frames_seen++;
      JavaScriptFrame* frame = JavaScriptFrame::cast(raw_frame);
      // Set initial size to the maximum inlining level + 1 for the outermost
      // function.
      List<FrameSummary> frames(Compiler::kMaxInliningLevels + 1);
      frame->Summarize(&frames);
      for (int i = frames.length() - 1; i >= 0; i--) {
        if (cursor + 4 > elements->length()) {
          int new_capacity = JSObject::NewElementsCapacity(elements->length());
          Handle<FixedArray> new_elements =
              factory->NewFixedArrayWithHoles(new_capacity);
          for (int i = 0; i < cursor; i++) {
            new_elements->set(i, elements->get(i));
          }
          elements = new_elements;
        }
        ASSERT(cursor + 4 <= elements->length());

        Handle<Object> recv = frames[i].receiver();
        Handle<JSFunction> fun = frames[i].function();
        Handle<Code> code = frames[i].code();
        Handle<Smi> offset(Smi::FromInt(frames[i].offset()));
        elements->set(cursor++, *recv);
        elements->set(cursor++, *fun);
        elements->set(cursor++, *code);
        elements->set(cursor++, *offset);
      }
    }
    iter.Advance();
  }
  Handle<JSArray> result = factory->NewJSArrayWithElements(elements);
  // Capture and attach a more detailed stack trace if necessary.
  isolate->CaptureAndSetCurrentStackTraceFor(error_object);
  result->set_length(Smi::FromInt(cursor));
  return *result;
}


// Returns V8 version as a string.
RUNTIME_FUNCTION(MaybeObject*, Runtime_GetV8Version) {
  ASSERT_EQ(args.length(), 0);

  NoHandleAllocation ha;

  const char* version_string = v8::V8::GetVersion();

  return isolate->heap()->AllocateStringFromAscii(CStrVector(version_string),
                                                  NOT_TENURED);
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_Abort) {
  ASSERT(args.length() == 2);
  OS::PrintError("abort: %s\n",
                 reinterpret_cast<char*>(args[0]) + args.smi_at(1));
  isolate->PrintStack();
  OS::Abort();
  UNREACHABLE();
  return NULL;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFromCache) {
  // This is only called from codegen, so checks might be more lax.
  CONVERT_ARG_CHECKED(JSFunctionResultCache, cache, 0);
  Object* key = args[1];

  int finger_index = cache->finger_index();
  Object* o = cache->get(finger_index);
  if (o == key) {
    // The fastest case: hit the same place again.
    return cache->get(finger_index + 1);
  }

  for (int i = finger_index - 2;
       i >= JSFunctionResultCache::kEntriesIndex;
       i -= 2) {
    o = cache->get(i);
    if (o == key) {
      cache->set_finger_index(i);
      return cache->get(i + 1);
    }
  }

  int size = cache->size();
  ASSERT(size <= cache->length());

  for (int i = size - 2; i > finger_index; i -= 2) {
    o = cache->get(i);
    if (o == key) {
      cache->set_finger_index(i);
      return cache->get(i + 1);
    }
  }

  // There is no value in the cache.  Invoke the function and cache result.
  HandleScope scope(isolate);

  Handle<JSFunctionResultCache> cache_handle(cache);
  Handle<Object> key_handle(key);
  Handle<Object> value;
  {
    Handle<JSFunction> factory(JSFunction::cast(
          cache_handle->get(JSFunctionResultCache::kFactoryIndex)));
    // TODO(antonm): consider passing a receiver when constructing a cache.
    Handle<Object> receiver(isolate->global_context()->global());
    // This handle is nor shared, nor used later, so it's safe.
    Handle<Object> argv[] = { key_handle };
    bool pending_exception;
    value = Execution::Call(factory,
                            receiver,
                            ARRAY_SIZE(argv),
                            argv,
                            &pending_exception);
    if (pending_exception) return Failure::Exception();
  }

#ifdef DEBUG
  if (FLAG_verify_heap) {
    cache_handle->JSFunctionResultCacheVerify();
  }
#endif

  // Function invocation may have cleared the cache.  Reread all the data.
  finger_index = cache_handle->finger_index();
  size = cache_handle->size();

  // If we have spare room, put new data into it, otherwise evict post finger
  // entry which is likely to be the least recently used.
  int index = -1;
  if (size < cache_handle->length()) {
    cache_handle->set_size(size + JSFunctionResultCache::kEntrySize);
    index = size;
  } else {
    index = finger_index + JSFunctionResultCache::kEntrySize;
    if (index == cache_handle->length()) {
      index = JSFunctionResultCache::kEntriesIndex;
    }
  }

  ASSERT(index % 2 == 0);
  ASSERT(index >= JSFunctionResultCache::kEntriesIndex);
  ASSERT(index < cache_handle->length());

  cache_handle->set(index, *key_handle);
  cache_handle->set(index + 1, *value);
  cache_handle->set_finger_index(index);

#ifdef DEBUG
  if (FLAG_verify_heap) {
    cache_handle->JSFunctionResultCacheVerify();
  }
#endif

  return *value;
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_NewMessageObject) {
  HandleScope scope(isolate);
  CONVERT_ARG_HANDLE_CHECKED(String, type, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, arguments, 1);
  return *isolate->factory()->NewJSMessageObject(
      type,
      arguments,
      0,
      0,
      isolate->factory()->undefined_value(),
      isolate->factory()->undefined_value(),
      isolate->factory()->undefined_value());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MessageGetType) {
  CONVERT_ARG_CHECKED(JSMessageObject, message, 0);
  return message->type();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MessageGetArguments) {
  CONVERT_ARG_CHECKED(JSMessageObject, message, 0);
  return message->arguments();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MessageGetStartPosition) {
  CONVERT_ARG_CHECKED(JSMessageObject, message, 0);
  return Smi::FromInt(message->start_position());
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_MessageGetScript) {
  CONVERT_ARG_CHECKED(JSMessageObject, message, 0);
  return message->script();
}


#ifdef DEBUG
// ListNatives is ONLY used by the fuzz-natives.js in debug mode
// Exclude the code in release mode.
RUNTIME_FUNCTION(MaybeObject*, Runtime_ListNatives) {
  ASSERT(args.length() == 0);
  HandleScope scope;
#define COUNT_ENTRY(Name, argc, ressize) + 1
  int entry_count = 0
      RUNTIME_FUNCTION_LIST(COUNT_ENTRY)
      INLINE_FUNCTION_LIST(COUNT_ENTRY)
      INLINE_RUNTIME_FUNCTION_LIST(COUNT_ENTRY);
#undef COUNT_ENTRY
  Factory* factory = isolate->factory();
  Handle<FixedArray> elements = factory->NewFixedArray(entry_count);
  int index = 0;
  bool inline_runtime_functions = false;
#define ADD_ENTRY(Name, argc, ressize)                                       \
  {                                                                          \
    HandleScope inner;                                                       \
    Handle<String> name;                                                     \
    /* Inline runtime functions have an underscore in front of the name. */  \
    if (inline_runtime_functions) {                                          \
      name = factory->NewStringFromAscii(                                    \
          Vector<const char>("_" #Name, StrLength("_" #Name)));              \
    } else {                                                                 \
      name = factory->NewStringFromAscii(                                    \
          Vector<const char>(#Name, StrLength(#Name)));                      \
    }                                                                        \
    Handle<FixedArray> pair_elements = factory->NewFixedArray(2);            \
    pair_elements->set(0, *name);                                            \
    pair_elements->set(1, Smi::FromInt(argc));                               \
    Handle<JSArray> pair = factory->NewJSArrayWithElements(pair_elements);   \
    elements->set(index++, *pair);                                           \
  }
  inline_runtime_functions = false;
  RUNTIME_FUNCTION_LIST(ADD_ENTRY)
  inline_runtime_functions = true;
  INLINE_FUNCTION_LIST(ADD_ENTRY)
  INLINE_RUNTIME_FUNCTION_LIST(ADD_ENTRY)
#undef ADD_ENTRY
  ASSERT_EQ(index, entry_count);
  Handle<JSArray> result = factory->NewJSArrayWithElements(elements);
  return *result;
}
#endif


RUNTIME_FUNCTION(MaybeObject*, Runtime_Log) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(String, format, 0);
  CONVERT_ARG_CHECKED(JSArray, elms, 1);
  String::FlatContent format_content = format->GetFlatContent();
  RUNTIME_ASSERT(format_content.IsAscii());
  Vector<const char> chars = format_content.ToAsciiVector();
  LOGGER->LogRuntime(chars, elms);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(MaybeObject*, Runtime_IS_VAR) {
  UNREACHABLE();  // implemented as macro in the parser
  return NULL;
}


#define ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(Name)        \
  RUNTIME_FUNCTION(MaybeObject*, Runtime_Has##Name) {     \
    CONVERT_ARG_CHECKED(JSObject, obj, 0);              \
    return isolate->heap()->ToBoolean(obj->Has##Name());  \
  }

ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastSmiElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastObjectElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastSmiOrObjectElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastDoubleElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastHoleyElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(DictionaryElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalPixelElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalArrayElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalByteElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedByteElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalShortElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedShortElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalIntElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedIntElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalFloatElements)
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalDoubleElements)
// Properties test sitting with elements tests - not fooling anyone.
ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastProperties)

#undef ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION


RUNTIME_FUNCTION(MaybeObject*, Runtime_HaveSameMap) {
  ASSERT(args.length() == 2);
  CONVERT_ARG_CHECKED(JSObject, obj1, 0);
  CONVERT_ARG_CHECKED(JSObject, obj2, 1);
  return isolate->heap()->ToBoolean(obj1->map() == obj2->map());
}

// ----------------------------------------------------------------------------
// Implementation of Runtime

#define F(name, number_of_args, result_size)                             \
  { Runtime::k##name, Runtime::RUNTIME, #name,   \
    FUNCTION_ADDR(Runtime_##name), number_of_args, result_size },


#define I(name, number_of_args, result_size)                             \
  { Runtime::kInline##name, Runtime::INLINE,     \
    "_" #name, NULL, number_of_args, result_size },

static const Runtime::Function kIntrinsicFunctions[] = {
  RUNTIME_FUNCTION_LIST(F)
  INLINE_FUNCTION_LIST(I)
  INLINE_RUNTIME_FUNCTION_LIST(I)
};


MaybeObject* Runtime::InitializeIntrinsicFunctionNames(Heap* heap,
                                                       Object* dictionary) {
  ASSERT(Isolate::Current()->heap() == heap);
  ASSERT(dictionary != NULL);
  ASSERT(StringDictionary::cast(dictionary)->NumberOfElements() == 0);
  for (int i = 0; i < kNumFunctions; ++i) {
    Object* name_symbol;
    { MaybeObject* maybe_name_symbol =
          heap->LookupAsciiSymbol(kIntrinsicFunctions[i].name);
      if (!maybe_name_symbol->ToObject(&name_symbol)) return maybe_name_symbol;
    }
    StringDictionary* string_dictionary = StringDictionary::cast(dictionary);
    { MaybeObject* maybe_dictionary = string_dictionary->Add(
          String::cast(name_symbol),
          Smi::FromInt(i),
          PropertyDetails(NONE, NORMAL));
      if (!maybe_dictionary->ToObject(&dictionary)) {
        // Non-recoverable failure.  Calling code must restart heap
        // initialization.
        return maybe_dictionary;
      }
    }
  }
  return dictionary;
}


const Runtime::Function* Runtime::FunctionForSymbol(Handle<String> name) {
  Heap* heap = name->GetHeap();
  int entry = heap->intrinsic_function_names()->FindEntry(*name);
  if (entry != kNotFound) {
    Object* smi_index = heap->intrinsic_function_names()->ValueAt(entry);
    int function_index = Smi::cast(smi_index)->value();
    return &(kIntrinsicFunctions[function_index]);
  }
  return NULL;
}


const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
  return &(kIntrinsicFunctions[static_cast<int>(id)]);
}


void Runtime::PerformGC(Object* result) {
  Isolate* isolate = Isolate::Current();
  Failure* failure = Failure::cast(result);
  if (failure->IsRetryAfterGC()) {
    if (isolate->heap()->new_space()->AddFreshPage()) {
      return;
    }

    // Try to do a garbage collection; ignore it if it fails. The C
    // entry stub will throw an out-of-memory exception in that case.
    isolate->heap()->CollectGarbage(failure->allocation_space(),
                                    "Runtime::PerformGC");
  } else {
    // Handle last resort GC and make sure to allow future allocations
    // to grow the heap without causing GCs (if possible).
    isolate->counters()->gc_last_resort_from_js()->Increment();
    isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                       "Runtime::PerformGC");
  }
}


} }  // namespace v8::internal