// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/builtins.h"

#include "src/api.h"
#include "src/api-natives.h"
#include "src/arguments.h"
#include "src/base/once.h"
#include "src/bootstrapper.h"
#include "src/elements.h"
#include "src/frames-inl.h"
#include "src/gdb-jit.h"
#include "src/ic/handler-compiler.h"
#include "src/ic/ic.h"
#include "src/isolate-inl.h"
#include "src/messages.h"
#include "src/profiler/cpu-profiler.h"
#include "src/property-descriptor.h"
#include "src/prototype.h"
#include "src/vm-state-inl.h"

namespace v8 {
namespace internal {

namespace {

// Arguments object passed to C++ builtins.
template <BuiltinExtraArguments extra_args>
class BuiltinArguments : public Arguments {
 public:
  BuiltinArguments(int length, Object** arguments)
      : Arguments(length, arguments) {
    // Check we have at least the receiver.
    DCHECK_LE(1, this->length());
  }

  Object*& operator[] (int index) {
    DCHECK(index < length());
    return Arguments::operator[](index);
  }

  template <class S> Handle<S> at(int index) {
    DCHECK(index < length());
    return Arguments::at<S>(index);
  }

  Handle<Object> receiver() {
    return Arguments::at<Object>(0);
  }

  Handle<JSFunction> target();
  Handle<HeapObject> new_target();

  // Gets the total number of arguments including the receiver (but
  // excluding extra arguments).
  int length() const;
};


// Specialize BuiltinArguments for the extra arguments.

template <>
int BuiltinArguments<BuiltinExtraArguments::kNone>::length() const {
  return Arguments::length();
}

template <>
int BuiltinArguments<BuiltinExtraArguments::kTarget>::length() const {
  return Arguments::length() - 1;
}

template <>
Handle<JSFunction> BuiltinArguments<BuiltinExtraArguments::kTarget>::target() {
  return Arguments::at<JSFunction>(Arguments::length() - 1);
}

template <>
int BuiltinArguments<BuiltinExtraArguments::kNewTarget>::length() const {
  return Arguments::length() - 1;
}

template <>
Handle<HeapObject>
BuiltinArguments<BuiltinExtraArguments::kNewTarget>::new_target() {
  return Arguments::at<HeapObject>(Arguments::length() - 1);
}

template <>
int BuiltinArguments<BuiltinExtraArguments::kTargetAndNewTarget>::length()
    const {
  return Arguments::length() - 2;
}

template <>
Handle<JSFunction>
BuiltinArguments<BuiltinExtraArguments::kTargetAndNewTarget>::target() {
  return Arguments::at<JSFunction>(Arguments::length() - 2);
}

template <>
Handle<HeapObject>
BuiltinArguments<BuiltinExtraArguments::kTargetAndNewTarget>::new_target() {
  return Arguments::at<HeapObject>(Arguments::length() - 1);
}


#define DEF_ARG_TYPE(name, spec) \
  typedef BuiltinArguments<BuiltinExtraArguments::spec> name##ArgumentsType;
BUILTIN_LIST_C(DEF_ARG_TYPE)
#undef DEF_ARG_TYPE


// ----------------------------------------------------------------------------
// Support macro for defining builtins in C++.
// ----------------------------------------------------------------------------
//
// A builtin function is defined by writing:
//
//   BUILTIN(name) {
//     ...
//   }
//
// In the body of the builtin function the arguments can be accessed
// through the BuiltinArguments object args.

#define BUILTIN(name)                                            \
  MUST_USE_RESULT static Object* Builtin_Impl_##name(            \
      name##ArgumentsType args, Isolate* isolate);               \
  MUST_USE_RESULT static Object* Builtin_##name(                 \
      int args_length, Object** args_object, Isolate* isolate) { \
    name##ArgumentsType args(args_length, args_object);          \
    return Builtin_Impl_##name(args, isolate);                   \
  }                                                              \
  MUST_USE_RESULT static Object* Builtin_Impl_##name(            \
      name##ArgumentsType args, Isolate* isolate)


// ----------------------------------------------------------------------------


inline bool ClampedToInteger(Object* object, int* out) {
  // This is an extended version of ECMA-262 7.1.11 handling signed values
  // Try to convert object to a number and clamp values to [kMinInt, kMaxInt]
  if (object->IsSmi()) {
    *out = Smi::cast(object)->value();
    return true;
  } else if (object->IsHeapNumber()) {
    double value = HeapNumber::cast(object)->value();
    if (std::isnan(value)) {
      *out = 0;
    } else if (value > kMaxInt) {
      *out = kMaxInt;
    } else if (value < kMinInt) {
      *out = kMinInt;
    } else {
      *out = static_cast<int>(value);
    }
    return true;
  } else if (object->IsUndefined() || object->IsNull()) {
    *out = 0;
    return true;
  } else if (object->IsBoolean()) {
    *out = object->IsTrue();
    return true;
  }
  return false;
}


inline bool GetSloppyArgumentsLength(Isolate* isolate, Handle<JSObject> object,
                                     int* out) {
  Map* arguments_map = isolate->native_context()->sloppy_arguments_map();
  if (object->map() != arguments_map) return false;
  DCHECK(object->HasFastElements());
  Object* len_obj = object->InObjectPropertyAt(Heap::kArgumentsLengthIndex);
  if (!len_obj->IsSmi()) return false;
  *out = Max(0, Smi::cast(len_obj)->value());
  return *out <= object->elements()->length();
}


inline bool PrototypeHasNoElements(PrototypeIterator* iter) {
  DisallowHeapAllocation no_gc;
  for (; !iter->IsAtEnd(); iter->Advance()) {
    if (iter->GetCurrent()->IsJSProxy()) return false;
    JSObject* current = iter->GetCurrent<JSObject>();
    if (current->IsAccessCheckNeeded()) return false;
    if (current->HasIndexedInterceptor()) return false;
    if (current->elements()->length() != 0) return false;
  }
  return true;
}


inline bool IsJSArrayFastElementMovingAllowed(Isolate* isolate,
                                              JSArray* receiver) {
  DisallowHeapAllocation no_gc;
  // If the array prototype chain is intact (and free of elements), and if the
  // receiver's prototype is the array prototype, then we are done.
  Object* prototype = receiver->map()->prototype();
  if (prototype->IsJSArray() &&
      isolate->is_initial_array_prototype(JSArray::cast(prototype)) &&
      isolate->IsFastArrayConstructorPrototypeChainIntact()) {
    return true;
  }

  // Slow case.
  PrototypeIterator iter(isolate, receiver);
  return PrototypeHasNoElements(&iter);
}


// Returns empty handle if not applicable.
MUST_USE_RESULT
inline MaybeHandle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
    Isolate* isolate, Handle<Object> receiver, Arguments* args,
    int first_added_arg) {
  if (!receiver->IsJSArray()) return MaybeHandle<FixedArrayBase>();
  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  // If there may be elements accessors in the prototype chain, the fast path
  // cannot be used if there arguments to add to the array.
  Heap* heap = isolate->heap();
  if (args != NULL && !IsJSArrayFastElementMovingAllowed(isolate, *array)) {
    return MaybeHandle<FixedArrayBase>();
  }
  if (array->map()->is_observed()) return MaybeHandle<FixedArrayBase>();
  if (!array->map()->is_extensible()) return MaybeHandle<FixedArrayBase>();
  Handle<FixedArrayBase> elms(array->elements(), isolate);
  Map* map = elms->map();
  if (map == heap->fixed_array_map()) {
    if (args == NULL || array->HasFastObjectElements()) return elms;
  } else if (map == heap->fixed_cow_array_map()) {
    elms = JSObject::EnsureWritableFastElements(array);
    if (args == NULL || array->HasFastObjectElements()) return elms;
  } else if (map == heap->fixed_double_array_map()) {
    if (args == NULL) return elms;
  } else {
    return MaybeHandle<FixedArrayBase>();
  }

  // Adding elements to the array prototype would break code that makes sure
  // it has no elements. Handle that elsewhere.
  if (isolate->IsAnyInitialArrayPrototype(array)) {
    return MaybeHandle<FixedArrayBase>();
  }

  // Need to ensure that the arguments passed in args can be contained in
  // the array.
  int args_length = args->length();
  if (first_added_arg >= args_length) return handle(array->elements(), isolate);

  ElementsKind origin_kind = array->map()->elements_kind();
  DCHECK(!IsFastObjectElementsKind(origin_kind));
  ElementsKind target_kind = origin_kind;
  {
    DisallowHeapAllocation no_gc;
    int arg_count = args_length - first_added_arg;
    Object** arguments = args->arguments() - first_added_arg - (arg_count - 1);
    for (int i = 0; i < arg_count; i++) {
      Object* arg = arguments[i];
      if (arg->IsHeapObject()) {
        if (arg->IsHeapNumber()) {
          target_kind = FAST_DOUBLE_ELEMENTS;
        } else {
          target_kind = FAST_ELEMENTS;
          break;
        }
      }
    }
  }
  if (target_kind != origin_kind) {
    JSObject::TransitionElementsKind(array, target_kind);
    return handle(array->elements(), isolate);
  }
  return elms;
}


MUST_USE_RESULT static Object* CallJsIntrinsic(
    Isolate* isolate, Handle<JSFunction> function,
    BuiltinArguments<BuiltinExtraArguments::kNone> args) {
  HandleScope handleScope(isolate);
  int argc = args.length() - 1;
  ScopedVector<Handle<Object> > argv(argc);
  for (int i = 0; i < argc; ++i) {
    argv[i] = args.at<Object>(i + 1);
  }
  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
      isolate, result,
      Execution::Call(isolate,
                      function,
                      args.receiver(),
                      argc,
                      argv.start()));
  return *result;
}


}  // namespace


BUILTIN(Illegal) {
  UNREACHABLE();
  return isolate->heap()->undefined_value();  // Make compiler happy.
}


BUILTIN(EmptyFunction) { return isolate->heap()->undefined_value(); }


BUILTIN(ArrayPush) {
  HandleScope scope(isolate);
  Handle<Object> receiver = args.receiver();
  MaybeHandle<FixedArrayBase> maybe_elms_obj =
      EnsureJSArrayWithWritableFastElements(isolate, receiver, &args, 1);
  Handle<FixedArrayBase> elms_obj;
  if (!maybe_elms_obj.ToHandle(&elms_obj)) {
    return CallJsIntrinsic(isolate, isolate->array_push(), args);
  }
  // Fast Elements Path
  int push_size = args.length() - 1;
  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  int len = Smi::cast(array->length())->value();
  if (push_size == 0) {
    return Smi::FromInt(len);
  }
  if (push_size > 0 &&
      JSArray::WouldChangeReadOnlyLength(array, len + push_size)) {
    return CallJsIntrinsic(isolate, isolate->array_push(), args);
  }
  DCHECK(!array->map()->is_observed());
  ElementsAccessor* accessor = array->GetElementsAccessor();
  int new_length = accessor->Push(array, elms_obj, &args, push_size);
  return Smi::FromInt(new_length);
}


BUILTIN(ArrayPop) {
  HandleScope scope(isolate);
  Handle<Object> receiver = args.receiver();
  MaybeHandle<FixedArrayBase> maybe_elms_obj =
      EnsureJSArrayWithWritableFastElements(isolate, receiver, NULL, 0);
  Handle<FixedArrayBase> elms_obj;
  if (!maybe_elms_obj.ToHandle(&elms_obj)) {
    return CallJsIntrinsic(isolate, isolate->array_pop(), args);
  }

  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  DCHECK(!array->map()->is_observed());

  uint32_t len = static_cast<uint32_t>(Smi::cast(array->length())->value());
  if (len == 0) return isolate->heap()->undefined_value();

  if (JSArray::HasReadOnlyLength(array)) {
    return CallJsIntrinsic(isolate, isolate->array_pop(), args);
  }

  Handle<Object> result;
  if (IsJSArrayFastElementMovingAllowed(isolate, JSArray::cast(*receiver))) {
    // Fast Elements Path
    result = array->GetElementsAccessor()->Pop(array, elms_obj);
  } else {
    // Use Slow Lookup otherwise
    uint32_t new_length = len - 1;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        isolate, result, Object::GetElement(isolate, array, new_length));
    JSArray::SetLength(array, new_length);
  }
  return *result;
}


BUILTIN(ArrayShift) {
  HandleScope scope(isolate);
  Heap* heap = isolate->heap();
  Handle<Object> receiver = args.receiver();
  MaybeHandle<FixedArrayBase> maybe_elms_obj =
      EnsureJSArrayWithWritableFastElements(isolate, receiver, NULL, 0);
  Handle<FixedArrayBase> elms_obj;
  if (!maybe_elms_obj.ToHandle(&elms_obj) ||
      !IsJSArrayFastElementMovingAllowed(isolate, JSArray::cast(*receiver))) {
    return CallJsIntrinsic(isolate, isolate->array_shift(), args);
  }
  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  DCHECK(!array->map()->is_observed());

  int len = Smi::cast(array->length())->value();
  if (len == 0) return heap->undefined_value();

  if (JSArray::HasReadOnlyLength(array)) {
    return CallJsIntrinsic(isolate, isolate->array_shift(), args);
  }

  Handle<Object> first = array->GetElementsAccessor()->Shift(array, elms_obj);
  return *first;
}


BUILTIN(ArrayUnshift) {
  HandleScope scope(isolate);
  Handle<Object> receiver = args.receiver();
  MaybeHandle<FixedArrayBase> maybe_elms_obj =
      EnsureJSArrayWithWritableFastElements(isolate, receiver, &args, 1);
  Handle<FixedArrayBase> elms_obj;
  if (!maybe_elms_obj.ToHandle(&elms_obj)) {
    return CallJsIntrinsic(isolate, isolate->array_unshift(), args);
  }
  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  DCHECK(!array->map()->is_observed());
  int to_add = args.length() - 1;
  if (to_add == 0) {
    return array->length();
  }
  // Currently fixed arrays cannot grow too big, so
  // we should never hit this case.
  DCHECK(to_add <= (Smi::kMaxValue - Smi::cast(array->length())->value()));

  if (to_add > 0 && JSArray::HasReadOnlyLength(array)) {
    return CallJsIntrinsic(isolate, isolate->array_unshift(), args);
  }

  ElementsAccessor* accessor = array->GetElementsAccessor();
  int new_length = accessor->Unshift(array, elms_obj, &args, to_add);
  return Smi::FromInt(new_length);
}


BUILTIN(ArraySlice) {
  HandleScope scope(isolate);
  Handle<Object> receiver = args.receiver();
  Handle<JSObject> object;
  Handle<FixedArrayBase> elms_obj;
  int len = -1;
  int relative_start = 0;
  int relative_end = 0;
  bool is_sloppy_arguments = false;

  if (receiver->IsJSArray()) {
    DisallowHeapAllocation no_gc;
    JSArray* array = JSArray::cast(*receiver);
    if (!array->HasFastElements() ||
        !IsJSArrayFastElementMovingAllowed(isolate, array)) {
      AllowHeapAllocation allow_allocation;
      return CallJsIntrinsic(isolate, isolate->array_slice(), args);
    }
    len = Smi::cast(array->length())->value();
    object = Handle<JSObject>::cast(receiver);
    elms_obj = handle(array->elements(), isolate);
  } else if (receiver->IsJSObject() &&
             GetSloppyArgumentsLength(isolate, Handle<JSObject>::cast(receiver),
                                      &len)) {
    // Array.prototype.slice(arguments, ...) is quite a common idiom
    // (notably more than 50% of invocations in Web apps).
    // Treat it in C++ as well.
    is_sloppy_arguments = true;
    object = Handle<JSObject>::cast(receiver);
    elms_obj = handle(object->elements(), isolate);
  } else {
    AllowHeapAllocation allow_allocation;
    return CallJsIntrinsic(isolate, isolate->array_slice(), args);
  }
  DCHECK(len >= 0);
  int argument_count = args.length() - 1;
  // Note carefully chosen defaults---if argument is missing,
  // it's undefined which gets converted to 0 for relative_start
  // and to len for relative_end.
  relative_start = 0;
  relative_end = len;
  if (argument_count > 0) {
    DisallowHeapAllocation no_gc;
    if (!ClampedToInteger(args[1], &relative_start)) {
      AllowHeapAllocation allow_allocation;
      return CallJsIntrinsic(isolate, isolate->array_slice(), args);
    }
    if (argument_count > 1) {
      Object* end_arg = args[2];
      // slice handles the end_arg specially
      if (end_arg->IsUndefined()) {
        relative_end = len;
      } else if (!ClampedToInteger(end_arg, &relative_end)) {
        AllowHeapAllocation allow_allocation;
        return CallJsIntrinsic(isolate, isolate->array_slice(), args);
      }
    }
  }

  // ECMAScript 232, 3rd Edition, Section 15.4.4.10, step 6.
  uint32_t actual_start = (relative_start < 0) ? Max(len + relative_start, 0)
                                               : Min(relative_start, len);

  // ECMAScript 232, 3rd Edition, Section 15.4.4.10, step 8.
  uint32_t actual_end =
      (relative_end < 0) ? Max(len + relative_end, 0) : Min(relative_end, len);

  if (actual_end <= actual_start) {
    Handle<JSArray> result_array = isolate->factory()->NewJSArray(
        GetPackedElementsKind(object->GetElementsKind()), 0, 0);
    return *result_array;
  }

  ElementsAccessor* accessor = object->GetElementsAccessor();
  if (is_sloppy_arguments &&
      !accessor->IsPacked(object, elms_obj, actual_start, actual_end)) {
    // Don't deal with arguments with holes in C++
    AllowHeapAllocation allow_allocation;
    return CallJsIntrinsic(isolate, isolate->array_slice(), args);
  }
  Handle<JSArray> result_array =
      accessor->Slice(object, elms_obj, actual_start, actual_end);
  return *result_array;
}


BUILTIN(ArraySplice) {
  HandleScope scope(isolate);
  Handle<Object> receiver = args.receiver();
  MaybeHandle<FixedArrayBase> maybe_elms_obj =
      EnsureJSArrayWithWritableFastElements(isolate, receiver, &args, 3);
  Handle<FixedArrayBase> elms_obj;
  if (!maybe_elms_obj.ToHandle(&elms_obj)) {
    return CallJsIntrinsic(isolate, isolate->array_splice(), args);
  }
  Handle<JSArray> array = Handle<JSArray>::cast(receiver);
  DCHECK(!array->map()->is_observed());

  int argument_count = args.length() - 1;
  int relative_start = 0;
  if (argument_count > 0) {
    DisallowHeapAllocation no_gc;
    if (!ClampedToInteger(args[1], &relative_start)) {
      AllowHeapAllocation allow_allocation;
      return CallJsIntrinsic(isolate, isolate->array_splice(), args);
    }
  }
  int len = Smi::cast(array->length())->value();
  // clip relative start to [0, len]
  int actual_start = (relative_start < 0) ? Max(len + relative_start, 0)
                                          : Min(relative_start, len);

  int actual_delete_count;
  if (argument_count == 1) {
    // SpiderMonkey, TraceMonkey and JSC treat the case where no delete count is
    // given as a request to delete all the elements from the start.
    // And it differs from the case of undefined delete count.
    // This does not follow ECMA-262, but we do the same for compatibility.
    DCHECK(len - actual_start >= 0);
    actual_delete_count = len - actual_start;
  } else {
    int delete_count = 0;
    DisallowHeapAllocation no_gc;
    if (argument_count > 1) {
      if (!ClampedToInteger(args[2], &delete_count)) {
        AllowHeapAllocation allow_allocation;
        return CallJsIntrinsic(isolate, isolate->array_splice(), args);
      }
    }
    actual_delete_count = Min(Max(delete_count, 0), len - actual_start);
  }

  int add_count = (argument_count > 1) ? (argument_count - 2) : 0;
  int new_length = len - actual_delete_count + add_count;

  if (new_length != len && JSArray::HasReadOnlyLength(array)) {
    AllowHeapAllocation allow_allocation;
    return CallJsIntrinsic(isolate, isolate->array_splice(), args);
  }
  ElementsAccessor* accessor = array->GetElementsAccessor();
  Handle<JSArray> result_array = accessor->Splice(
      array, elms_obj, actual_start, actual_delete_count, &args, add_count);
  return *result_array;
}


// Array Concat -------------------------------------------------------------

namespace {

/**
 * A simple visitor visits every element of Array's.
 * The backend storage can be a fixed array for fast elements case,
 * or a dictionary for sparse array. Since Dictionary is a subtype
 * of FixedArray, the class can be used by both fast and slow cases.
 * The second parameter of the constructor, fast_elements, specifies
 * whether the storage is a FixedArray or Dictionary.
 *
 * An index limit is used to deal with the situation that a result array
 * length overflows 32-bit non-negative integer.
 */
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),
        bit_field_(FastElementsField::encode(fast_elements) |
                   ExceedsLimitField::encode(false)) {}

  ~ArrayConcatVisitor() { clear_storage(); }

  void visit(uint32_t i, Handle<Object> elm) {
    if (i >= JSObject::kMaxElementCount - index_offset_) {
      set_exceeds_array_limit(true);
      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();
      // Fall-through to dictionary mode.
    }
    DCHECK(!fast_elements());
    Handle<SeededNumberDictionary> dict(
        SeededNumberDictionary::cast(*storage_));
    // The object holding this backing store has just been allocated, so
    // it cannot yet be used as a prototype.
    Handle<SeededNumberDictionary> result =
        SeededNumberDictionary::AtNumberPut(dict, index, elm, false);
    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;
    }
    // If the initial length estimate was off (see special case in visit()),
    // but the array blowing the limit didn't contain elements beyond the
    // provided-for index range, go to dictionary mode now.
    if (fast_elements() &&
        index_offset_ >
            static_cast<uint32_t>(FixedArrayBase::cast(*storage_)->length())) {
      SetDictionaryMode();
    }
  }

  bool exceeds_array_limit() const {
    return ExceedsLimitField::decode(bit_field_);
  }

  Handle<JSArray> ToArray() {
    Handle<JSArray> array = isolate_->factory()->NewJSArray(0);
    Handle<Object> length =
        isolate_->factory()->NewNumber(static_cast<double>(index_offset_));
    Handle<Map> map = JSObject::GetElementsTransitionMap(
        array, fast_elements() ? FAST_HOLEY_ELEMENTS : DICTIONARY_ELEMENTS);
    array->set_map(*map);
    array->set_length(*length);
    array->set_elements(*storage_);
    return array;
  }

 private:
  // Convert storage to dictionary mode.
  void SetDictionaryMode() {
    DCHECK(fast_elements());
    Handle<FixedArray> current_storage(*storage_);
    Handle<SeededNumberDictionary> slow_storage(
        SeededNumberDictionary::New(isolate_, 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(isolate_);
      Handle<Object> element(current_storage->get(i), isolate_);
      if (!element->IsTheHole()) {
        // The object holding this backing store has just been allocated, so
        // it cannot yet be used as a prototype.
        Handle<SeededNumberDictionary> new_storage =
            SeededNumberDictionary::AtNumberPut(slow_storage, i, element,
                                                false);
        if (!new_storage.is_identical_to(slow_storage)) {
          slow_storage = loop_scope.CloseAndEscape(new_storage);
        }
      }
    }
    clear_storage();
    set_storage(*slow_storage);
    set_fast_elements(false);
  }

  inline void clear_storage() {
    GlobalHandles::Destroy(Handle<Object>::cast(storage_).location());
  }

  inline void set_storage(FixedArray* storage) {
    storage_ =
        Handle<FixedArray>::cast(isolate_->global_handles()->Create(storage));
  }

  class FastElementsField : public BitField<bool, 0, 1> {};
  class ExceedsLimitField : public BitField<bool, 1, 1> {};

  bool fast_elements() const { return FastElementsField::decode(bit_field_); }
  void set_fast_elements(bool fast) {
    bit_field_ = FastElementsField::update(bit_field_, fast);
  }
  void set_exceeds_array_limit(bool exceeds) {
    bit_field_ = ExceedsLimitField::update(bit_field_, exceeds);
  }

  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_;
  uint32_t bit_field_;
};


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.
      DCHECK(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: {
      // Fast elements can't have lengths that are not representable by
      // a 32-bit signed integer.
      DCHECK(static_cast<int32_t>(FixedDoubleArray::kMaxLength) >= 0);
      int fast_length = static_cast<int>(length);
      if (array->elements()->IsFixedArray()) {
        DCHECK(FixedArray::cast(array->elements())->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::cast(array->elements()));
      for (int i = 0; i < fast_length; i++) {
        if (!elements->is_the_hole(i)) element_count++;
      }
      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), array->GetIsolate());
        if (dictionary->IsKey(*key)) {
          element_count++;
        }
      }
      break;
    }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS:
#define TYPED_ARRAY_CASE(Type, type, TYPE, ctype, size) case TYPE##_ELEMENTS:

      TYPED_ARRAYS(TYPED_ARRAY_CASE)
#undef TYPED_ARRAY_CASE
      // 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>
void IterateTypedArrayElements(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());

  DCHECK(visitor != NULL);
  if (elements_are_ints) {
    if (elements_are_guaranteed_smis) {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope(isolate);
        Handle<Smi> e(Smi::FromInt(static_cast<int>(array->get_scalar(j))),
                      isolate);
        visitor->visit(j, e);
      }
    } else {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope(isolate);
        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)), isolate);
          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>.
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;
}


void CollectElementIndices(Handle<JSObject> object, uint32_t range,
                           List<uint32_t>* indices) {
  Isolate* isolate = object->GetIsolate();
  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: {
      if (object->elements()->IsFixedArray()) {
        DCHECK(object->elements()->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::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->is_the_hole(i)) {
          indices->Add(i);
        }
      }
      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(isolate);
        Handle<Object> k(dict->KeyAt(j), isolate);
        if (dict->IsKey(*k)) {
          DCHECK(k->IsNumber());
          uint32_t index = static_cast<uint32_t>(k->Number());
          if (index < range) {
            indices->Add(index);
          }
        }
      }
      break;
    }
#define TYPED_ARRAY_CASE(Type, type, TYPE, ctype, size) case TYPE##_ELEMENTS:

      TYPED_ARRAYS(TYPED_ARRAY_CASE)
#undef TYPED_ARRAY_CASE
      {
        uint32_t length = static_cast<uint32_t>(
            FixedArrayBase::cast(object->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;
      }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS: {
      ElementsAccessor* accessor = object->GetElementsAccessor();
      for (uint32_t i = 0; i < range; i++) {
        if (accessor->HasElement(object, i)) {
          indices->Add(i);
        }
      }
      break;
    }
  }

  PrototypeIterator iter(isolate, object);
  if (!iter.IsAtEnd()) {
    // The prototype will usually have no inherited element indices,
    // but we have to check.
    CollectElementIndices(PrototypeIterator::GetCurrent<JSObject>(iter), range,
                          indices);
  }
}


bool IterateElementsSlow(Isolate* isolate, Handle<JSObject> receiver,
                         uint32_t length, ArrayConcatVisitor* visitor) {
  for (uint32_t i = 0; i < length; ++i) {
    HandleScope loop_scope(isolate);
    Maybe<bool> maybe = JSReceiver::HasElement(receiver, i);
    if (!maybe.IsJust()) return false;
    if (maybe.FromJust()) {
      Handle<Object> element_value;
      ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, element_value,
                                       Object::GetElement(isolate, receiver, i),
                                       false);
      visitor->visit(i, element_value);
    }
  }
  visitor->increase_index_offset(length);
  return true;
}


/**
 * A helper function that visits elements of a JSObject in numerical
 * order.
 *
 * The visitor argument called for each existing element in the array
 * with the element index and the element's value.
 * Afterwards it increments the base-index of the visitor by the array
 * length.
 * Returns false if any access threw an exception, otherwise true.
 */
bool IterateElements(Isolate* isolate, Handle<JSObject> receiver,
                     ArrayConcatVisitor* visitor) {
  uint32_t length = 0;

  if (receiver->IsJSArray()) {
    Handle<JSArray> array = Handle<JSArray>::cast(receiver);
    length = static_cast<uint32_t>(array->length()->Number());
  } else {
    Handle<Object> val;
    Handle<Object> key = isolate->factory()->length_string();
    ASSIGN_RETURN_ON_EXCEPTION_VALUE(
        isolate, val, Runtime::GetObjectProperty(isolate, receiver, key),
        false);
    ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, val,
                                     Object::ToLength(isolate, val), false);
    // TODO(caitp): Support larger element indexes (up to 2^53-1).
    if (!val->ToUint32(&length)) {
      length = 0;
    }
  }

  if (!(receiver->IsJSArray() || receiver->IsJSTypedArray())) {
    // For classes which are not known to be safe to access via elements alone,
    // use the slow case.
    return IterateElementsSlow(isolate, receiver, length, visitor);
  }

  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);
      DCHECK(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 {
          Maybe<bool> maybe = JSReceiver::HasElement(receiver, j);
          if (!maybe.IsJust()) return false;
          if (maybe.FromJust()) {
            // Call GetElement on receiver, not its prototype, or getters won't
            // have the correct receiver.
            ASSIGN_RETURN_ON_EXCEPTION_VALUE(
                isolate, element_value,
                Object::GetElement(isolate, receiver, j), false);
            visitor->visit(j, element_value);
          }
        }
      }
      break;
    }
    case FAST_HOLEY_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS: {
      // Empty array is FixedArray but not FixedDoubleArray.
      if (length == 0) break;
      // Run through the elements FixedArray and use HasElement and GetElement
      // to check the prototype for missing elements.
      if (receiver->elements()->IsFixedArray()) {
        DCHECK(receiver->elements()->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::cast(receiver->elements()));
      int fast_length = static_cast<int>(length);
      DCHECK(fast_length <= elements->length());
      for (int j = 0; j < fast_length; j++) {
        HandleScope loop_scope(isolate);
        if (!elements->is_the_hole(j)) {
          double double_value = elements->get_scalar(j);
          Handle<Object> element_value =
              isolate->factory()->NewNumber(double_value);
          visitor->visit(j, element_value);
        } else {
          Maybe<bool> maybe = JSReceiver::HasElement(receiver, j);
          if (!maybe.IsJust()) return false;
          if (maybe.FromJust()) {
            // Call GetElement on receiver, not its prototype, or getters won't
            // have the correct receiver.
            Handle<Object> element_value;
            ASSIGN_RETURN_ON_EXCEPTION_VALUE(
                isolate, element_value,
                Object::GetElement(isolate, receiver, j), false);
            visitor->visit(j, element_value);
          }
        }
      }
      break;
    }
    case DICTIONARY_ELEMENTS: {
      // CollectElementIndices() can't be called when there's a JSProxy
      // on the prototype chain.
      for (PrototypeIterator iter(isolate, receiver); !iter.IsAtEnd();
           iter.Advance()) {
        if (PrototypeIterator::GetCurrent(iter)->IsJSProxy()) {
          return IterateElementsSlow(isolate, receiver, length, visitor);
        }
      }
      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(isolate);
        uint32_t index = indices[j];
        Handle<Object> element;
        ASSIGN_RETURN_ON_EXCEPTION_VALUE(
            isolate, element, Object::GetElement(isolate, receiver, index),
            false);
        visitor->visit(index, element);
        // Skip to next different index (i.e., omit duplicates).
        do {
          j++;
        } while (j < n && indices[j] == index);
      }
      break;
    }
    case UINT8_CLAMPED_ELEMENTS: {
      Handle<FixedUint8ClampedArray> pixels(
          FixedUint8ClampedArray::cast(receiver->elements()));
      for (uint32_t j = 0; j < length; j++) {
        Handle<Smi> e(Smi::FromInt(pixels->get_scalar(j)), isolate);
        visitor->visit(j, e);
      }
      break;
    }
    case INT8_ELEMENTS: {
      IterateTypedArrayElements<FixedInt8Array, int8_t>(isolate, receiver, true,
                                                        true, visitor);
      break;
    }
    case UINT8_ELEMENTS: {
      IterateTypedArrayElements<FixedUint8Array, uint8_t>(isolate, receiver,
                                                          true, true, visitor);
      break;
    }
    case INT16_ELEMENTS: {
      IterateTypedArrayElements<FixedInt16Array, int16_t>(isolate, receiver,
                                                          true, true, visitor);
      break;
    }
    case UINT16_ELEMENTS: {
      IterateTypedArrayElements<FixedUint16Array, uint16_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case INT32_ELEMENTS: {
      IterateTypedArrayElements<FixedInt32Array, int32_t>(isolate, receiver,
                                                          true, false, visitor);
      break;
    }
    case UINT32_ELEMENTS: {
      IterateTypedArrayElements<FixedUint32Array, uint32_t>(
          isolate, receiver, true, false, visitor);
      break;
    }
    case FLOAT32_ELEMENTS: {
      IterateTypedArrayElements<FixedFloat32Array, float>(
          isolate, receiver, false, false, visitor);
      break;
    }
    case FLOAT64_ELEMENTS: {
      IterateTypedArrayElements<FixedFloat64Array, double>(
          isolate, receiver, false, false, visitor);
      break;
    }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS: {
      for (uint32_t index = 0; index < length; index++) {
        HandleScope loop_scope(isolate);
        Handle<Object> element;
        ASSIGN_RETURN_ON_EXCEPTION_VALUE(
            isolate, element, Object::GetElement(isolate, receiver, index),
            false);
        visitor->visit(index, element);
      }
      break;
    }
  }
  visitor->increase_index_offset(length);
  return true;
}


bool HasConcatSpreadableModifier(Isolate* isolate, Handle<JSArray> obj) {
  if (!FLAG_harmony_concat_spreadable) return false;
  Handle<Symbol> key(isolate->factory()->is_concat_spreadable_symbol());
  Maybe<bool> maybe =
      JSReceiver::HasProperty(Handle<JSReceiver>::cast(obj), key);
  if (!maybe.IsJust()) return false;
  return maybe.FromJust();
}


bool IsConcatSpreadable(Isolate* isolate, Handle<Object> obj) {
  HandleScope handle_scope(isolate);
  if (!obj->IsJSReceiver()) return false;
  if (FLAG_harmony_concat_spreadable) {
    Handle<Symbol> key(isolate->factory()->is_concat_spreadable_symbol());
    Handle<Object> value;
    MaybeHandle<Object> maybeValue =
        i::Runtime::GetObjectProperty(isolate, obj, key);
    if (maybeValue.ToHandle(&value) && !value->IsUndefined()) {
      return value->BooleanValue();
    }
  }
  return obj->IsJSArray();
}


/**
 * Array::concat implementation.
 * See ECMAScript 262, 15.4.4.4.
 * TODO(581): Fix non-compliance for very large concatenations and update to
 * following the ECMAScript 5 specification.
 */
Object* Slow_ArrayConcat(Arguments* args, Isolate* isolate) {
  int argument_count = args->length();

  // 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.

  ElementsKind kind = FAST_SMI_ELEMENTS;

  uint32_t estimate_result_length = 0;
  uint32_t estimate_nof_elements = 0;
  for (int i = 0; i < argument_count; i++) {
    HandleScope loop_scope(isolate);
    Handle<Object> obj((*args)[i], isolate);
    uint32_t length_estimate;
    uint32_t element_estimate;
    if (obj->IsJSArray()) {
      Handle<JSArray> array(Handle<JSArray>::cast(obj));
      length_estimate = static_cast<uint32_t>(array->length()->Number());
      if (length_estimate != 0) {
        ElementsKind array_kind =
            GetPackedElementsKind(array->map()->elements_kind());
        kind = GetMoreGeneralElementsKind(kind, array_kind);
      }
      element_estimate = EstimateElementCount(array);
    } else {
      if (obj->IsHeapObject()) {
        if (obj->IsNumber()) {
          kind = GetMoreGeneralElementsKind(kind, FAST_DOUBLE_ELEMENTS);
        } else {
          kind = GetMoreGeneralElementsKind(kind, FAST_ELEMENTS);
        }
      }
      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;

  if (fast_case && kind == FAST_DOUBLE_ELEMENTS) {
    Handle<FixedArrayBase> storage =
        isolate->factory()->NewFixedDoubleArray(estimate_result_length);
    int j = 0;
    bool failure = false;
    if (estimate_result_length > 0) {
      Handle<FixedDoubleArray> double_storage =
          Handle<FixedDoubleArray>::cast(storage);
      for (int i = 0; i < argument_count; i++) {
        Handle<Object> obj((*args)[i], isolate);
        if (obj->IsSmi()) {
          double_storage->set(j, Smi::cast(*obj)->value());
          j++;
        } else if (obj->IsNumber()) {
          double_storage->set(j, obj->Number());
          j++;
        } else {
          JSArray* array = JSArray::cast(*obj);
          uint32_t length = static_cast<uint32_t>(array->length()->Number());
          switch (array->map()->elements_kind()) {
            case FAST_HOLEY_DOUBLE_ELEMENTS:
            case FAST_DOUBLE_ELEMENTS: {
              // Empty array is FixedArray but not FixedDoubleArray.
              if (length == 0) break;
              FixedDoubleArray* elements =
                  FixedDoubleArray::cast(array->elements());
              for (uint32_t i = 0; i < length; i++) {
                if (elements->is_the_hole(i)) {
                  // TODO(jkummerow/verwaest): We could be a bit more clever
                  // here: Check if there are no elements/getters on the
                  // prototype chain, and if so, allow creation of a holey
                  // result array.
                  // Same thing below (holey smi case).
                  failure = true;
                  break;
                }
                double double_value = elements->get_scalar(i);
                double_storage->set(j, double_value);
                j++;
              }
              break;
            }
            case FAST_HOLEY_SMI_ELEMENTS:
            case FAST_SMI_ELEMENTS: {
              FixedArray* elements(FixedArray::cast(array->elements()));
              for (uint32_t i = 0; i < length; i++) {
                Object* element = elements->get(i);
                if (element->IsTheHole()) {
                  failure = true;
                  break;
                }
                int32_t int_value = Smi::cast(element)->value();
                double_storage->set(j, int_value);
                j++;
              }
              break;
            }
            case FAST_HOLEY_ELEMENTS:
            case FAST_ELEMENTS:
            case DICTIONARY_ELEMENTS:
              DCHECK_EQ(0u, length);
              break;
            default:
              UNREACHABLE();
          }
        }
        if (failure) break;
      }
    }
    if (!failure) {
      Handle<JSArray> array = isolate->factory()->NewJSArray(0);
      Smi* length = Smi::FromInt(j);
      Handle<Map> map;
      map = JSObject::GetElementsTransitionMap(array, kind);
      array->set_map(*map);
      array->set_length(length);
      array->set_elements(*storage);
      return *array;
    }
    // In case of failure, fall through.
  }

  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(
        SeededNumberDictionary::New(isolate, at_least_space_for));
  }

  ArrayConcatVisitor visitor(isolate, storage, fast_case);

  for (int i = 0; i < argument_count; i++) {
    Handle<Object> obj((*args)[i], isolate);
    bool spreadable = IsConcatSpreadable(isolate, obj);
    if (isolate->has_pending_exception()) return isolate->heap()->exception();
    if (spreadable) {
      Handle<JSObject> object = Handle<JSObject>::cast(obj);
      if (!IterateElements(isolate, object, &visitor)) {
        return isolate->heap()->exception();
      }
    } else {
      visitor.visit(0, obj);
      visitor.increase_index_offset(1);
    }
  }

  if (visitor.exceeds_array_limit()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewRangeError(MessageTemplate::kInvalidArrayLength));
  }
  return *visitor.ToArray();
}


MaybeHandle<JSArray> Fast_ArrayConcat(Isolate* isolate, Arguments* args) {
  if (!isolate->IsFastArrayConstructorPrototypeChainIntact()) {
    return MaybeHandle<JSArray>();
  }
  int n_arguments = args->length();
  int result_len = 0;
  {
    DisallowHeapAllocation no_gc;
    Object* array_proto = isolate->array_function()->prototype();
    // Iterate through all the arguments performing checks
    // and calculating total length.
    for (int i = 0; i < n_arguments; i++) {
      Object* arg = (*args)[i];
      if (!arg->IsJSArray()) return MaybeHandle<JSArray>();
      Handle<JSArray> array(JSArray::cast(arg), isolate);
      if (!array->HasFastElements()) return MaybeHandle<JSArray>();
      PrototypeIterator iter(isolate, arg);
      if (iter.GetCurrent() != array_proto) return MaybeHandle<JSArray>();
      if (HasConcatSpreadableModifier(isolate, array)) {
        return MaybeHandle<JSArray>();
      }
      int len = Smi::cast(array->length())->value();

      // We shouldn't overflow when adding another len.
      const int kHalfOfMaxInt = 1 << (kBitsPerInt - 2);
      STATIC_ASSERT(FixedArray::kMaxLength < kHalfOfMaxInt);
      USE(kHalfOfMaxInt);
      result_len += len;
      DCHECK(result_len >= 0);
      // Throw an Error if we overflow the FixedArray limits
      if (FixedArray::kMaxLength < result_len) {
        THROW_NEW_ERROR(isolate,
                        NewRangeError(MessageTemplate::kInvalidArrayLength),
                        JSArray);
      }
    }
  }
  return ElementsAccessor::Concat(isolate, args, n_arguments);
}

}  // namespace

BUILTIN(ArrayConcat) {
  HandleScope scope(isolate);

  Handle<Object> receiver;
  if (!Object::ToObject(isolate, handle(args[0], isolate))
           .ToHandle(&receiver)) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNullOrUndefined,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Array.prototype.concat")));
  }
  args[0] = *receiver;

  Handle<JSArray> result_array;
  if (Fast_ArrayConcat(isolate, &args).ToHandle(&result_array)) {
    return *result_array;
  }
  if (isolate->has_pending_exception()) return isolate->heap()->exception();
  return Slow_ArrayConcat(&args, isolate);
}


// ES6 section 22.1.2.2 Array.isArray
BUILTIN(ArrayIsArray) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Object> object = args.at<Object>(1);
  Maybe<bool> result = Object::IsArray(object);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 19.1.2.1 Object.assign
BUILTIN(ObjectAssign) {
  HandleScope scope(isolate);
  Handle<Object> target =
      args.length() > 1
          ? args.at<Object>(1)
          : Handle<Object>::cast(isolate->factory()->undefined_value());

  // 1. Let to be ? ToObject(target).
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, target,
                                     Execution::ToObject(isolate, target));
  Handle<JSReceiver> to = Handle<JSReceiver>::cast(target);
  // 2. If only one argument was passed, return to.
  if (args.length() == 2) return *to;
  // 3. Let sources be the List of argument values starting with the
  //    second argument.
  // 4. For each element nextSource of sources, in ascending index order,
  for (int i = 2; i < args.length(); ++i) {
    Handle<Object> next_source = args.at<Object>(i);
    // 4a. If nextSource is undefined or null, let keys be an empty List.
    if (next_source->IsUndefined() || next_source->IsNull()) continue;
    // 4b. Else,
    // 4b i. Let from be ToObject(nextSource).
    Handle<JSReceiver> from =
        Object::ToObject(isolate, next_source).ToHandleChecked();
    // 4b ii. Let keys be ? from.[[OwnPropertyKeys]]().
    Handle<FixedArray> keys;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        isolate, keys, JSReceiver::GetKeys(from, JSReceiver::OWN_ONLY,
                                           ALL_PROPERTIES, KEEP_NUMBERS));
    // 4c. Repeat for each element nextKey of keys in List order,
    for (int j = 0; j < keys->length(); ++j) {
      Handle<Object> next_key(keys->get(j), isolate);
      // 4c i. Let desc be ? from.[[GetOwnProperty]](nextKey).
      PropertyDescriptor desc;
      Maybe<bool> found =
          JSReceiver::GetOwnPropertyDescriptor(isolate, from, next_key, &desc);
      if (found.IsNothing()) return isolate->heap()->exception();
      // 4c ii. If desc is not undefined and desc.[[Enumerable]] is true, then
      if (found.FromJust() && desc.enumerable()) {
        // 4c ii 1. Let propValue be ? Get(from, nextKey).
        Handle<Object> prop_value;
        ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
            isolate, prop_value,
            Runtime::GetObjectProperty(isolate, from, next_key, STRICT));
        // 4c ii 2. Let status be ? Set(to, nextKey, propValue, true).
        Handle<Object> status;
        ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
            isolate, status, Runtime::SetObjectProperty(isolate, to, next_key,
                                                        prop_value, STRICT));
      }
    }
  }
  // 5. Return to.
  return *to;
}


// ES6 section 26.1.3 Reflect.defineProperty
BUILTIN(ReflectDefineProperty) {
  HandleScope scope(isolate);
  DCHECK_EQ(4, args.length());
  Handle<Object> target = args.at<Object>(1);
  Handle<Object> key = args.at<Object>(2);
  Handle<Object> attributes = args.at<Object>(3);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.defineProperty")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  PropertyDescriptor desc;
  if (!PropertyDescriptor::ToPropertyDescriptor(isolate, attributes, &desc)) {
    return isolate->heap()->exception();
  }

  Maybe<bool> result =
      JSReceiver::DefineOwnProperty(isolate, Handle<JSReceiver>::cast(target),
                                    name, &desc, Object::DONT_THROW);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 26.1.4 Reflect.deleteProperty
BUILTIN(ReflectDeleteProperty) {
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<Object> target = args.at<Object>(1);
  Handle<Object> key = args.at<Object>(2);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.deleteProperty")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  Maybe<bool> result = JSReceiver::DeletePropertyOrElement(
      Handle<JSReceiver>::cast(target), name, SLOPPY);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 26.1.6 Reflect.get
BUILTIN(ReflectGet) {
  HandleScope scope(isolate);
  Handle<Object> undef = isolate->factory()->undefined_value();
  Handle<Object> target = args.length() > 1 ? args.at<Object>(1) : undef;
  Handle<Object> key = args.length() > 2 ? args.at<Object>(2) : undef;
  Handle<Object> receiver = args.length() > 3 ? args.at<Object>(3) : target;

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.get")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
      isolate, result, Object::GetPropertyOrElement(
          Handle<JSReceiver>::cast(target), name, receiver));

  return *result;
}


// ES6 section 26.1.7 Reflect.getOwnPropertyDescriptor
BUILTIN(ReflectGetOwnPropertyDescriptor) {
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<Object> target = args.at<Object>(1);
  Handle<Object> key = args.at<Object>(2);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.getOwnPropertyDescriptor")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  PropertyDescriptor desc;
  Maybe<bool> found = JSReceiver::GetOwnPropertyDescriptor(
      isolate, Handle<JSReceiver>::cast(target), name, &desc);
  MAYBE_RETURN(found, isolate->heap()->exception());
  if (!found.FromJust()) return isolate->heap()->undefined_value();
  return *desc.ToObject(isolate);
}


// ES6 section 26.1.8 Reflect.getPrototypeOf
BUILTIN(ReflectGetPrototypeOf) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Object> target = args.at<Object>(1);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.getPrototypeOf")));
  }
  Handle<Object> prototype;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, prototype,
                                     Object::GetPrototype(isolate, target));
  return *prototype;
}


// ES6 section 26.1.9 Reflect.has
BUILTIN(ReflectHas) {
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<Object> target = args.at<Object>(1);
  Handle<Object> key = args.at<Object>(2);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.has")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  Maybe<bool> result =
      JSReceiver::HasProperty(Handle<JSReceiver>::cast(target), name);
  return result.IsJust() ? *isolate->factory()->ToBoolean(result.FromJust())
                         : isolate->heap()->exception();
}


// ES6 section 26.1.10 Reflect.isExtensible
BUILTIN(ReflectIsExtensible) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Object> target = args.at<Object>(1);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.isExtensible")));
  }

  Maybe<bool> result =
      JSReceiver::IsExtensible(Handle<JSReceiver>::cast(target));
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 26.1.11 Reflect.ownKeys
BUILTIN(ReflectOwnKeys) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Object> target = args.at<Object>(1);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.ownKeys")));
  }

  Handle<FixedArray> keys;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
      isolate, keys, JSReceiver::GetKeys(Handle<JSReceiver>::cast(target),
                                         JSReceiver::OWN_ONLY, ALL_PROPERTIES,
                                         CONVERT_TO_STRING));
  return *isolate->factory()->NewJSArrayWithElements(keys);
}


// ES6 section 26.1.12 Reflect.preventExtensions
BUILTIN(ReflectPreventExtensions) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Object> target = args.at<Object>(1);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.preventExtensions")));
  }

  Maybe<bool> result = JSReceiver::PreventExtensions(
      Handle<JSReceiver>::cast(target), Object::DONT_THROW);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 26.1.13 Reflect.set
BUILTIN(ReflectSet) {
  HandleScope scope(isolate);
  Handle<Object> undef = isolate->factory()->undefined_value();
  Handle<Object> target = args.length() > 1 ? args.at<Object>(1) : undef;
  Handle<Object> key = args.length() > 2 ? args.at<Object>(2) : undef;
  Handle<Object> value = args.length() > 3 ? args.at<Object>(3) : undef;
  Handle<Object> receiver = args.length() > 4 ? args.at<Object>(4) : target;

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.set")));
  }

  Handle<Name> name;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
                                     Object::ToName(isolate, key));

  LookupIterator it = LookupIterator::PropertyOrElement(
      isolate, receiver, name, Handle<JSReceiver>::cast(target));
  Maybe<bool> result = Object::SetSuperProperty(
      &it, value, SLOPPY, Object::MAY_BE_STORE_FROM_KEYED);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 26.1.14 Reflect.setPrototypeOf
BUILTIN(ReflectSetPrototypeOf) {
  HandleScope scope(isolate);
  DCHECK_EQ(3, args.length());
  Handle<Object> target = args.at<Object>(1);
  Handle<Object> proto = args.at<Object>(2);

  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Reflect.setPrototypeOf")));
  }

  if (!proto->IsJSReceiver() && !proto->IsNull()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kProtoObjectOrNull, proto));
  }

  Maybe<bool> result = JSReceiver::SetPrototype(
      Handle<JSReceiver>::cast(target), proto, true, Object::DONT_THROW);
  MAYBE_RETURN(result, isolate->heap()->exception());
  return *isolate->factory()->ToBoolean(result.FromJust());
}


// ES6 section 20.3.4.45 Date.prototype [ @@toPrimitive ] ( hint )
BUILTIN(DateToPrimitive) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  if (!args.receiver()->IsJSReceiver()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,
                              isolate->factory()->NewStringFromAsciiChecked(
                                  "Date.prototype [ @@toPrimitive ]"),
                              args.receiver()));
  }
  Handle<JSReceiver> receiver = args.at<JSReceiver>(0);
  Handle<Object> hint = args.at<Object>(1);
  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                     JSDate::ToPrimitive(receiver, hint));
  return *result;
}


// ES6 section 19.4.1.1 Symbol ( [ description ] ) for the [[Call]] case.
BUILTIN(SymbolConstructor) {
  HandleScope scope(isolate);
  DCHECK_EQ(2, args.length());
  Handle<Symbol> result = isolate->factory()->NewSymbol();
  Handle<Object> description = args.at<Object>(1);
  if (!description->IsUndefined()) {
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, description,
                                       Object::ToString(isolate, description));
    result->set_name(*description);
  }
  return *result;
}


// ES6 section 19.4.1.1 Symbol ( [ description ] ) for the [[Construct]] case.
BUILTIN(SymbolConstructor_ConstructStub) {
  HandleScope scope(isolate);
  // The ConstructStub is executed in the context of the caller, so we need
  // to enter the callee context first before raising an exception.
  isolate->set_context(args.target()->context());
  THROW_NEW_ERROR_RETURN_FAILURE(
      isolate, NewTypeError(MessageTemplate::kNotConstructor,
                            isolate->factory()->Symbol_string()));
}


// ES6 19.1.3.6 Object.prototype.toString
BUILTIN(ObjectProtoToString) {
  HandleScope scope(isolate);
  Handle<Object> object = args.at<Object>(0);
  Handle<String> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
      isolate, result, JSObject::ObjectProtoToString(isolate, object));
  return *result;
}


namespace {

// ES6 section 9.5.15 ProxyCreate (target, handler)
MaybeHandle<JSProxy> ProxyCreate(Isolate* isolate, Handle<Object> target,
                                 Handle<Object> handler) {
  if (!target->IsJSReceiver()) {
    THROW_NEW_ERROR(
        isolate, NewTypeError(MessageTemplate::kProxyTargetNonObject), JSProxy);
  }
  if (target->IsJSProxy() && JSProxy::cast(*target)->IsRevoked()) {
    THROW_NEW_ERROR(isolate,
                    NewTypeError(MessageTemplate::kProxyHandlerOrTargetRevoked),
                    JSProxy);
  }
  if (!handler->IsJSReceiver()) {
    THROW_NEW_ERROR(isolate,
                    NewTypeError(MessageTemplate::kProxyHandlerNonObject),
                    JSProxy);
  }
  if (handler->IsJSProxy() && JSProxy::cast(*handler)->IsRevoked()) {
    THROW_NEW_ERROR(isolate,
                    NewTypeError(MessageTemplate::kProxyHandlerOrTargetRevoked),
                    JSProxy);
  }
  return isolate->factory()->NewJSProxy(Handle<JSReceiver>::cast(target),
                                        Handle<JSReceiver>::cast(handler));
}

}  // namespace


// ES6 section 26.2.1.1 Proxy ( target, handler ) for the [[Call]] case.
BUILTIN(ProxyConstructor) {
  HandleScope scope(isolate);
  THROW_NEW_ERROR_RETURN_FAILURE(
      isolate,
      NewTypeError(MessageTemplate::kConstructorNotFunction,
                   isolate->factory()->NewStringFromAsciiChecked("Proxy")));
}


// ES6 section 26.2.1.1 Proxy ( target, handler ) for the [[Construct]] case.
BUILTIN(ProxyConstructor_ConstructStub) {
  HandleScope scope(isolate);
  DCHECK(isolate->proxy_function()->IsConstructor());
  Handle<Object> target;
  if (args.length() < 2) {
    target = isolate->factory()->undefined_value();
  } else {
    target = args.at<Object>(1);
  }
  Handle<Object> handler;
  if (args.length() < 3) {
    handler = isolate->factory()->undefined_value();
  } else {
    handler = args.at<Object>(2);
  }
  // The ConstructStub is executed in the context of the caller, so we need
  // to enter the callee context first before raising an exception.
  isolate->set_context(args.target()->context());
  Handle<JSProxy> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                     ProxyCreate(isolate, target, handler));
  return *result;
}


// -----------------------------------------------------------------------------
// Throwers for restricted function properties and strict arguments object
// properties


BUILTIN(RestrictedFunctionPropertiesThrower) {
  HandleScope scope(isolate);
  THROW_NEW_ERROR_RETURN_FAILURE(
      isolate, NewTypeError(MessageTemplate::kRestrictedFunctionProperties));
}


BUILTIN(RestrictedStrictArgumentsPropertiesThrower) {
  HandleScope scope(isolate);
  THROW_NEW_ERROR_RETURN_FAILURE(
      isolate, NewTypeError(MessageTemplate::kStrictPoisonPill));
}


// -----------------------------------------------------------------------------
//


namespace {

template <bool is_construct>
MUST_USE_RESULT MaybeHandle<Object> HandleApiCallHelper(
    Isolate* isolate, BuiltinArguments<BuiltinExtraArguments::kTarget> args) {
  HandleScope scope(isolate);
  Handle<JSFunction> function = args.target();
  // TODO(ishell): turn this back to a DCHECK.
  CHECK(function->shared()->IsApiFunction());

  Handle<FunctionTemplateInfo> fun_data(
      function->shared()->get_api_func_data(), isolate);
  if (is_construct) {
    ASSIGN_RETURN_ON_EXCEPTION(
        isolate, fun_data,
        ApiNatives::ConfigureInstance(isolate, fun_data,
                                      Handle<JSObject>::cast(args.receiver())),
        Object);
  }

  DCHECK(!args[0]->IsNull());
  if (args[0]->IsUndefined()) args[0] = function->global_proxy();

  if (!is_construct && !fun_data->accept_any_receiver()) {
    Handle<Object> receiver(&args[0]);
    if (receiver->IsJSObject() && receiver->IsAccessCheckNeeded()) {
      Handle<JSObject> js_receiver = Handle<JSObject>::cast(receiver);
      if (!isolate->MayAccess(handle(isolate->context()), js_receiver)) {
        isolate->ReportFailedAccessCheck(js_receiver);
        RETURN_EXCEPTION_IF_SCHEDULED_EXCEPTION(isolate, Object);
      }
    }
  }

  Object* raw_holder = fun_data->GetCompatibleReceiver(isolate, args[0]);

  if (raw_holder->IsNull()) {
    // This function cannot be called with the given receiver.  Abort!
    THROW_NEW_ERROR(isolate, NewTypeError(MessageTemplate::kIllegalInvocation),
                    Object);
  }

  Object* raw_call_data = fun_data->call_code();
  if (!raw_call_data->IsUndefined()) {
    // TODO(ishell): remove this debugging code.
    CHECK(raw_call_data->IsCallHandlerInfo());
    CallHandlerInfo* call_data = CallHandlerInfo::cast(raw_call_data);
    Object* callback_obj = call_data->callback();
    v8::FunctionCallback callback =
        v8::ToCData<v8::FunctionCallback>(callback_obj);
    Object* data_obj = call_data->data();

    LOG(isolate, ApiObjectAccess("call", JSObject::cast(*args.receiver())));
    DCHECK(raw_holder->IsJSObject());

    FunctionCallbackArguments custom(isolate,
                                     data_obj,
                                     *function,
                                     raw_holder,
                                     &args[0] - 1,
                                     args.length() - 1,
                                     is_construct);

    v8::Local<v8::Value> value = custom.Call(callback);
    Handle<Object> result;
    if (value.IsEmpty()) {
      result = isolate->factory()->undefined_value();
    } else {
      result = v8::Utils::OpenHandle(*value);
      result->VerifyApiCallResultType();
    }

    RETURN_EXCEPTION_IF_SCHEDULED_EXCEPTION(isolate, Object);
    if (!is_construct || result->IsJSObject()) {
      return scope.CloseAndEscape(result);
    }
  }

  return scope.CloseAndEscape(args.receiver());
}

}  // namespace


BUILTIN(HandleApiCall) {
  HandleScope scope(isolate);
  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                     HandleApiCallHelper<false>(isolate, args));
  return *result;
}


BUILTIN(HandleApiCallConstruct) {
  HandleScope scope(isolate);
  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                     HandleApiCallHelper<true>(isolate, args));
  return *result;
}


Handle<Code> Builtins::CallFunction(ConvertReceiverMode mode) {
  switch (mode) {
    case ConvertReceiverMode::kNullOrUndefined:
      return CallFunction_ReceiverIsNullOrUndefined();
    case ConvertReceiverMode::kNotNullOrUndefined:
      return CallFunction_ReceiverIsNotNullOrUndefined();
    case ConvertReceiverMode::kAny:
      return CallFunction_ReceiverIsAny();
  }
  UNREACHABLE();
  return Handle<Code>::null();
}


Handle<Code> Builtins::Call(ConvertReceiverMode mode) {
  switch (mode) {
    case ConvertReceiverMode::kNullOrUndefined:
      return Call_ReceiverIsNullOrUndefined();
    case ConvertReceiverMode::kNotNullOrUndefined:
      return Call_ReceiverIsNotNullOrUndefined();
    case ConvertReceiverMode::kAny:
      return Call_ReceiverIsAny();
  }
  UNREACHABLE();
  return Handle<Code>::null();
}


namespace {

class RelocatableArguments
    : public BuiltinArguments<BuiltinExtraArguments::kTarget>,
      public Relocatable {
 public:
  RelocatableArguments(Isolate* isolate, int length, Object** arguments)
      : BuiltinArguments<BuiltinExtraArguments::kTarget>(length, arguments),
        Relocatable(isolate) {}

  virtual inline void IterateInstance(ObjectVisitor* v) {
    if (length() == 0) return;
    v->VisitPointers(lowest_address(), highest_address() + 1);
  }

 private:
  DISALLOW_COPY_AND_ASSIGN(RelocatableArguments);
};

}  // namespace


MaybeHandle<Object> Builtins::InvokeApiFunction(Handle<JSFunction> function,
                                                Handle<Object> receiver,
                                                int argc,
                                                Handle<Object> args[]) {
  // Construct BuiltinArguments object: function, arguments reversed, receiver.
  const int kBufferSize = 32;
  Object* small_argv[kBufferSize];
  Object** argv;
  if (argc + 2 <= kBufferSize) {
    argv = small_argv;
  } else {
    argv = new Object* [argc + 2];
  }
  argv[argc + 1] = *receiver;
  for (int i = 0; i < argc; ++i) {
    argv[argc - i] = *args[i];
  }
  argv[0] = *function;
  MaybeHandle<Object> result;
  {
    auto isolate = function->GetIsolate();
    RelocatableArguments arguments(isolate, argc + 2, &argv[argc + 1]);
    result = HandleApiCallHelper<false>(isolate, arguments);
  }
  if (argv != small_argv) {
    delete[] argv;
  }
  return result;
}


// Helper function to handle calls to non-function objects created through the
// API. The object can be called as either a constructor (using new) or just as
// a function (without new).
MUST_USE_RESULT static Object* HandleApiCallAsFunctionOrConstructor(
    Isolate* isolate, bool is_construct_call,
    BuiltinArguments<BuiltinExtraArguments::kNone> args) {
  Heap* heap = isolate->heap();

  Handle<Object> receiver = args.receiver();

  // Get the object called.
  JSObject* obj = JSObject::cast(*receiver);

  // Get the invocation callback from the function descriptor that was
  // used to create the called object.
  DCHECK(obj->map()->is_callable());
  JSFunction* constructor = JSFunction::cast(obj->map()->GetConstructor());
  // TODO(ishell): turn this back to a DCHECK.
  CHECK(constructor->shared()->IsApiFunction());
  Object* handler =
      constructor->shared()->get_api_func_data()->instance_call_handler();
  DCHECK(!handler->IsUndefined());
  // TODO(ishell): remove this debugging code.
  CHECK(handler->IsCallHandlerInfo());
  CallHandlerInfo* call_data = CallHandlerInfo::cast(handler);
  Object* callback_obj = call_data->callback();
  v8::FunctionCallback callback =
      v8::ToCData<v8::FunctionCallback>(callback_obj);

  // Get the data for the call and perform the callback.
  Object* result;
  {
    HandleScope scope(isolate);
    LOG(isolate, ApiObjectAccess("call non-function", obj));

    FunctionCallbackArguments custom(isolate,
                                     call_data->data(),
                                     constructor,
                                     obj,
                                     &args[0] - 1,
                                     args.length() - 1,
                                     is_construct_call);
    v8::Local<v8::Value> value = custom.Call(callback);
    if (value.IsEmpty()) {
      result = heap->undefined_value();
    } else {
      result = *reinterpret_cast<Object**>(*value);
      result->VerifyApiCallResultType();
    }
  }
  // Check for exceptions and return result.
  RETURN_FAILURE_IF_SCHEDULED_EXCEPTION(isolate);
  return result;
}


// Handle calls to non-function objects created through the API. This delegate
// function is used when the call is a normal function call.
BUILTIN(HandleApiCallAsFunction) {
  return HandleApiCallAsFunctionOrConstructor(isolate, false, args);
}


// Handle calls to non-function objects created through the API. This delegate
// function is used when the call is a construct call.
BUILTIN(HandleApiCallAsConstructor) {
  return HandleApiCallAsFunctionOrConstructor(isolate, true, args);
}


static void Generate_LoadIC_Miss(MacroAssembler* masm) {
  LoadIC::GenerateMiss(masm);
}


static void Generate_LoadIC_Normal(MacroAssembler* masm) {
  LoadIC::GenerateNormal(masm, SLOPPY);
}


static void Generate_LoadIC_Normal_Strong(MacroAssembler* masm) {
  LoadIC::GenerateNormal(masm, STRONG);
}


static void Generate_LoadIC_Getter_ForDeopt(MacroAssembler* masm) {
  NamedLoadHandlerCompiler::GenerateLoadViaGetterForDeopt(masm);
}


static void Generate_LoadIC_Slow(MacroAssembler* masm) {
  LoadIC::GenerateRuntimeGetProperty(masm, SLOPPY);
}


static void Generate_LoadIC_Slow_Strong(MacroAssembler* masm) {
  LoadIC::GenerateRuntimeGetProperty(masm, STRONG);
}


static void Generate_KeyedLoadIC_Slow(MacroAssembler* masm) {
  KeyedLoadIC::GenerateRuntimeGetProperty(masm, SLOPPY);
}


static void Generate_KeyedLoadIC_Slow_Strong(MacroAssembler* masm) {
  KeyedLoadIC::GenerateRuntimeGetProperty(masm, STRONG);
}


static void Generate_KeyedLoadIC_Miss(MacroAssembler* masm) {
  KeyedLoadIC::GenerateMiss(masm);
}


static void Generate_KeyedLoadIC_Megamorphic(MacroAssembler* masm) {
  KeyedLoadIC::GenerateMegamorphic(masm, SLOPPY);
}


static void Generate_KeyedLoadIC_Megamorphic_Strong(MacroAssembler* masm) {
  KeyedLoadIC::GenerateMegamorphic(masm, STRONG);
}


static void Generate_StoreIC_Miss(MacroAssembler* masm) {
  StoreIC::GenerateMiss(masm);
}


static void Generate_StoreIC_Normal(MacroAssembler* masm) {
  StoreIC::GenerateNormal(masm);
}


static void Generate_StoreIC_Slow(MacroAssembler* masm) {
  NamedStoreHandlerCompiler::GenerateSlow(masm);
}


static void Generate_KeyedStoreIC_Slow(MacroAssembler* masm) {
  ElementHandlerCompiler::GenerateStoreSlow(masm);
}


static void Generate_StoreIC_Setter_ForDeopt(MacroAssembler* masm) {
  NamedStoreHandlerCompiler::GenerateStoreViaSetterForDeopt(masm);
}


static void Generate_KeyedStoreIC_Megamorphic(MacroAssembler* masm) {
  KeyedStoreIC::GenerateMegamorphic(masm, SLOPPY);
}


static void Generate_KeyedStoreIC_Megamorphic_Strict(MacroAssembler* masm) {
  KeyedStoreIC::GenerateMegamorphic(masm, STRICT);
}


static void Generate_KeyedStoreIC_Miss(MacroAssembler* masm) {
  KeyedStoreIC::GenerateMiss(masm);
}


static void Generate_KeyedStoreIC_Initialize(MacroAssembler* masm) {
  KeyedStoreIC::GenerateInitialize(masm);
}


static void Generate_KeyedStoreIC_Initialize_Strict(MacroAssembler* masm) {
  KeyedStoreIC::GenerateInitialize(masm);
}


static void Generate_KeyedStoreIC_PreMonomorphic(MacroAssembler* masm) {
  KeyedStoreIC::GeneratePreMonomorphic(masm);
}


static void Generate_KeyedStoreIC_PreMonomorphic_Strict(MacroAssembler* masm) {
  KeyedStoreIC::GeneratePreMonomorphic(masm);
}


static void Generate_Return_DebugBreak(MacroAssembler* masm) {
  DebugCodegen::GenerateDebugBreakStub(masm,
                                       DebugCodegen::SAVE_RESULT_REGISTER);
}


static void Generate_Slot_DebugBreak(MacroAssembler* masm) {
  DebugCodegen::GenerateDebugBreakStub(masm,
                                       DebugCodegen::IGNORE_RESULT_REGISTER);
}


static void Generate_FrameDropper_LiveEdit(MacroAssembler* masm) {
  DebugCodegen::GenerateFrameDropperLiveEdit(masm);
}


Builtins::Builtins() : initialized_(false) {
  memset(builtins_, 0, sizeof(builtins_[0]) * builtin_count);
  memset(names_, 0, sizeof(names_[0]) * builtin_count);
}


Builtins::~Builtins() {
}


#define DEF_ENUM_C(name, ignore) FUNCTION_ADDR(Builtin_##name),
Address const Builtins::c_functions_[cfunction_count] = {
  BUILTIN_LIST_C(DEF_ENUM_C)
};
#undef DEF_ENUM_C


struct BuiltinDesc {
  byte* generator;
  byte* c_code;
  const char* s_name;  // name is only used for generating log information.
  int name;
  Code::Flags flags;
  BuiltinExtraArguments extra_args;
};

#define BUILTIN_FUNCTION_TABLE_INIT { V8_ONCE_INIT, {} }

class BuiltinFunctionTable {
 public:
  BuiltinDesc* functions() {
    base::CallOnce(&once_, &Builtins::InitBuiltinFunctionTable);
    return functions_;
  }

  base::OnceType once_;
  BuiltinDesc functions_[Builtins::builtin_count + 1];

  friend class Builtins;
};

static BuiltinFunctionTable builtin_function_table =
    BUILTIN_FUNCTION_TABLE_INIT;

// Define array of pointers to generators and C builtin functions.
// We do this in a sort of roundabout way so that we can do the initialization
// within the lexical scope of Builtins:: and within a context where
// Code::Flags names a non-abstract type.
void Builtins::InitBuiltinFunctionTable() {
  BuiltinDesc* functions = builtin_function_table.functions_;
  functions[builtin_count].generator = NULL;
  functions[builtin_count].c_code = NULL;
  functions[builtin_count].s_name = NULL;
  functions[builtin_count].name = builtin_count;
  functions[builtin_count].flags = static_cast<Code::Flags>(0);
  functions[builtin_count].extra_args = BuiltinExtraArguments::kNone;

#define DEF_FUNCTION_PTR_C(aname, aextra_args)                \
  functions->generator = FUNCTION_ADDR(Generate_Adaptor);     \
  functions->c_code = FUNCTION_ADDR(Builtin_##aname);         \
  functions->s_name = #aname;                                 \
  functions->name = c_##aname;                                \
  functions->flags = Code::ComputeFlags(Code::BUILTIN);       \
  functions->extra_args = BuiltinExtraArguments::aextra_args; \
  ++functions;

#define DEF_FUNCTION_PTR_A(aname, kind, state, extra)              \
  functions->generator = FUNCTION_ADDR(Generate_##aname);          \
  functions->c_code = NULL;                                        \
  functions->s_name = #aname;                                      \
  functions->name = k##aname;                                      \
  functions->flags = Code::ComputeFlags(Code::kind, state, extra); \
  functions->extra_args = BuiltinExtraArguments::kNone;            \
  ++functions;

#define DEF_FUNCTION_PTR_H(aname, kind)                     \
  functions->generator = FUNCTION_ADDR(Generate_##aname);   \
  functions->c_code = NULL;                                 \
  functions->s_name = #aname;                               \
  functions->name = k##aname;                               \
  functions->flags = Code::ComputeHandlerFlags(Code::kind); \
  functions->extra_args = BuiltinExtraArguments::kNone;     \
  ++functions;

  BUILTIN_LIST_C(DEF_FUNCTION_PTR_C)
  BUILTIN_LIST_A(DEF_FUNCTION_PTR_A)
  BUILTIN_LIST_H(DEF_FUNCTION_PTR_H)
  BUILTIN_LIST_DEBUG_A(DEF_FUNCTION_PTR_A)

#undef DEF_FUNCTION_PTR_C
#undef DEF_FUNCTION_PTR_A
}


void Builtins::SetUp(Isolate* isolate, bool create_heap_objects) {
  DCHECK(!initialized_);

  // Create a scope for the handles in the builtins.
  HandleScope scope(isolate);

  const BuiltinDesc* functions = builtin_function_table.functions();

  // For now we generate builtin adaptor code into a stack-allocated
  // buffer, before copying it into individual code objects. Be careful
  // with alignment, some platforms don't like unaligned code.
#ifdef DEBUG
  // We can generate a lot of debug code on Arm64.
  const size_t buffer_size = 32*KB;
#elif V8_TARGET_ARCH_PPC64
  // 8 KB is insufficient on PPC64 when FLAG_debug_code is on.
  const size_t buffer_size = 10 * KB;
#else
  const size_t buffer_size = 8*KB;
#endif
  union { int force_alignment; byte buffer[buffer_size]; } u;

  // Traverse the list of builtins and generate an adaptor in a
  // separate code object for each one.
  for (int i = 0; i < builtin_count; i++) {
    if (create_heap_objects) {
      MacroAssembler masm(isolate, u.buffer, sizeof u.buffer,
                          CodeObjectRequired::kYes);
      // Generate the code/adaptor.
      typedef void (*Generator)(MacroAssembler*, int, BuiltinExtraArguments);
      Generator g = FUNCTION_CAST<Generator>(functions[i].generator);
      // We pass all arguments to the generator, but it may not use all of
      // them.  This works because the first arguments are on top of the
      // stack.
      DCHECK(!masm.has_frame());
      g(&masm, functions[i].name, functions[i].extra_args);
      // Move the code into the object heap.
      CodeDesc desc;
      masm.GetCode(&desc);
      Code::Flags flags = functions[i].flags;
      Handle<Code> code =
          isolate->factory()->NewCode(desc, flags, masm.CodeObject());
      // Log the event and add the code to the builtins array.
      PROFILE(isolate,
              CodeCreateEvent(Logger::BUILTIN_TAG, *code, functions[i].s_name));
      builtins_[i] = *code;
      code->set_builtin_index(i);
#ifdef ENABLE_DISASSEMBLER
      if (FLAG_print_builtin_code) {
        CodeTracer::Scope trace_scope(isolate->GetCodeTracer());
        OFStream os(trace_scope.file());
        os << "Builtin: " << functions[i].s_name << "\n";
        code->Disassemble(functions[i].s_name, os);
        os << "\n";
      }
#endif
    } else {
      // Deserializing. The values will be filled in during IterateBuiltins.
      builtins_[i] = NULL;
    }
    names_[i] = functions[i].s_name;
  }

  // Mark as initialized.
  initialized_ = true;
}


void Builtins::TearDown() {
  initialized_ = false;
}


void Builtins::IterateBuiltins(ObjectVisitor* v) {
  v->VisitPointers(&builtins_[0], &builtins_[0] + builtin_count);
}


const char* Builtins::Lookup(byte* pc) {
  // may be called during initialization (disassembler!)
  if (initialized_) {
    for (int i = 0; i < builtin_count; i++) {
      Code* entry = Code::cast(builtins_[i]);
      if (entry->contains(pc)) {
        return names_[i];
      }
    }
  }
  return NULL;
}


void Builtins::Generate_InterruptCheck(MacroAssembler* masm) {
  masm->TailCallRuntime(Runtime::kInterrupt, 0, 1);
}


void Builtins::Generate_StackCheck(MacroAssembler* masm) {
  masm->TailCallRuntime(Runtime::kStackGuard, 0, 1);
}


#define DEFINE_BUILTIN_ACCESSOR_C(name, ignore)               \
Handle<Code> Builtins::name() {                               \
  Code** code_address =                                       \
      reinterpret_cast<Code**>(builtin_address(k##name));     \
  return Handle<Code>(code_address);                          \
}
#define DEFINE_BUILTIN_ACCESSOR_A(name, kind, state, extra) \
Handle<Code> Builtins::name() {                             \
  Code** code_address =                                     \
      reinterpret_cast<Code**>(builtin_address(k##name));   \
  return Handle<Code>(code_address);                        \
}
#define DEFINE_BUILTIN_ACCESSOR_H(name, kind)               \
Handle<Code> Builtins::name() {                             \
  Code** code_address =                                     \
      reinterpret_cast<Code**>(builtin_address(k##name));   \
  return Handle<Code>(code_address);                        \
}
BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
#undef DEFINE_BUILTIN_ACCESSOR_C
#undef DEFINE_BUILTIN_ACCESSOR_A


}  // namespace internal
}  // namespace v8