src/builtins/builtins-async-iterator-gen.cc - v8/v8 - Git at Google

 // Copyright 2017 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/base/optional.h"
 #include "src/builtins/builtins-async-gen.h"
 #include "src/builtins/builtins-utils-gen.h"
 #include "src/builtins/builtins.h"
 #include "src/codegen/code-factory.h"
 #include "src/codegen/code-stub-assembler.h"
 #include "src/execution/frames-inl.h"

 namespace v8 {
 namespace internal {

 namespace {
 class AsyncFromSyncBuiltinsAssembler : public AsyncBuiltinsAssembler {
  public:
   // The 'next' and 'return' take an optional value parameter, and the 'throw'
   // method take an optional reason parameter.
   static const int kValueOrReasonArg = 0;

   explicit AsyncFromSyncBuiltinsAssembler(compiler::CodeAssemblerState* state)
       : AsyncBuiltinsAssembler(state) {}

   void ThrowIfNotAsyncFromSyncIterator(const TNode<Context> context,
                                        const TNode<Object> object,
                                        Label* if_exception,
                                        TVariable<Object>* var_exception,
                                        const char* method_name);

   using UndefinedMethodHandler =
       std::function<void(const TNode<NativeContext> native_context,
                          const TNode<JSPromise> promise, Label* if_exception)>;
   using SyncIteratorNodeGenerator =
       std::function<TNode<Object>(TNode<JSReceiver>)>;
   void Generate_AsyncFromSyncIteratorMethod(
       CodeStubArguments* args, const TNode<Context> context,
       const TNode<Object> iterator, const TNode<Object> sent_value,
       const SyncIteratorNodeGenerator& get_method,
       const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       base::Optional<TNode<Object>> initial_exception_value = base::nullopt);

   void Generate_AsyncFromSyncIteratorMethod(
       CodeStubArguments* args, const TNode<Context> context,
       const TNode<Object> iterator, const TNode<Object> sent_value,
       Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       base::Optional<TNode<Object>> initial_exception_value = base::nullopt) {
     auto get_method = [=](const TNode<JSReceiver> sync_iterator) {
       return GetProperty(context, sync_iterator, name);
     };
     return Generate_AsyncFromSyncIteratorMethod(
         args, context, iterator, sent_value, get_method, if_method_undefined,
         operation_name, reject_label_type, initial_exception_value);
   }

   // Load "value" and "done" from an iterator result object. If an exception
   // is thrown at any point, jumps to the `if_exception` label with exception
   // stored in `var_exception`.
   //
   // Returns a Pair of Nodes, whose first element is the value of the "value"
   // property, and whose second element is the value of the "done" property,
   // converted to a Boolean if needed.
   std::pair<TNode<Object>, TNode<Oddball>> LoadIteratorResult(
       const TNode<Context> context, const TNode<NativeContext> native_context,
       const TNode<Object> iter_result, Label* if_exception,
       TVariable<Object>* var_exception);
 };

 void AsyncFromSyncBuiltinsAssembler::ThrowIfNotAsyncFromSyncIterator(
     const TNode<Context> context, const TNode<Object> object,
     Label* if_exception, TVariable<Object>* var_exception,
     const char* method_name) {
   Label if_receiverisincompatible(this, Label::kDeferred), done(this);

   GotoIf(TaggedIsSmi(object), &if_receiverisincompatible);
   Branch(HasInstanceType(CAST(object), JS_ASYNC_FROM_SYNC_ITERATOR_TYPE), &done,
          &if_receiverisincompatible);

   BIND(&if_receiverisincompatible);
   {
     // If Type(O) is not Object, or if O does not have a [[SyncIterator]]
     // internal slot, then

     // Let badIteratorError be a new TypeError exception.
     TNode<HeapObject> error =
         MakeTypeError(MessageTemplate::kIncompatibleMethodReceiver, context,
                       StringConstant(method_name), object);

     // Perform ! Call(promiseCapability.[[Reject]], undefined,
     //                « badIteratorError »).
     *var_exception = error;
     Goto(if_exception);
   }

   BIND(&done);
 }

 void AsyncFromSyncBuiltinsAssembler::Generate_AsyncFromSyncIteratorMethod(
     CodeStubArguments* args, const TNode<Context> context,
     const TNode<Object> iterator, const TNode<Object> sent_value,
     const SyncIteratorNodeGenerator& get_method,
     const UndefinedMethodHandler& if_method_undefined,
     const char* operation_name, Label::Type reject_label_type,
     base::Optional<TNode<Object>> initial_exception_value) {
   const TNode<NativeContext> native_context = LoadNativeContext(context);
   const TNode<JSPromise> promise = NewJSPromise(context);

   TVARIABLE(
       Object, var_exception,
       initial_exception_value ? *initial_exception_value : UndefinedConstant());
   Label reject_promise(this, reject_label_type);

   ThrowIfNotAsyncFromSyncIterator(context, iterator, &reject_promise,
                                   &var_exception, operation_name);

   TNode<JSAsyncFromSyncIterator> async_iterator = CAST(iterator);
   const TNode<JSReceiver> sync_iterator = LoadObjectField<JSReceiver>(
       async_iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

   TNode<Object> method = get_method(sync_iterator);

   if (if_method_undefined) {
     Label if_isnotundefined(this);

     GotoIfNot(IsNullOrUndefined(method), &if_isnotundefined);
     if_method_undefined(native_context, promise, &reject_promise);

     BIND(&if_isnotundefined);
   }

   TVARIABLE(Object, iter_result);
   {
     Label has_sent_value(this), no_sent_value(this), merge(this);
     ScopedExceptionHandler handler(this, &reject_promise, &var_exception);
     Branch(
         IntPtrGreaterThan(args->GetLength(), IntPtrConstant(kValueOrReasonArg)),
         &has_sent_value, &no_sent_value);
     BIND(&has_sent_value);
     {
       iter_result = Call(context, method, sync_iterator, sent_value);
       Goto(&merge);
     }
     BIND(&no_sent_value);
     {
       iter_result = Call(context, method, sync_iterator);
       Goto(&merge);
     }
     BIND(&merge);
   }

   TNode<Object> value;
   TNode<Oddball> done;
   std::tie(value, done) =
       LoadIteratorResult(context, native_context, iter_result.value(),
                          &reject_promise, &var_exception);

   const TNode<JSFunction> promise_fun =
       CAST(LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX));
   CSA_ASSERT(this, IsConstructor(promise_fun));

   // Let valueWrapper be PromiseResolve(%Promise%, « value »).
   // IfAbruptRejectPromise(valueWrapper, promiseCapability).
   TNode<Object> value_wrapper;
   {
     ScopedExceptionHandler handler(this, &reject_promise, &var_exception);
     value_wrapper = CallBuiltin(Builtins::kPromiseResolve, native_context,
                                 promise_fun, value);
   }

   // Let onFulfilled be a new built-in function object as defined in
   // Async Iterator Value Unwrap Functions.
   // Set onFulfilled.[[Done]] to throwDone.
   const TNode<JSFunction> on_fulfilled =
       CreateUnwrapClosure(native_context, done);

   // Perform ! PerformPromiseThen(valueWrapper,
   //     onFulfilled, undefined, promiseCapability).
   args->PopAndReturn(CallBuiltin(Builtins::kPerformPromiseThen, context,
                                  value_wrapper, on_fulfilled,
                                  UndefinedConstant(), promise));

   BIND(&reject_promise);
   {
     const TNode<Object> exception = var_exception.value();
     CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
                 TrueConstant());
     args->PopAndReturn(promise);
   }
 }

 std::pair<TNode<Object>, TNode<Oddball>>
 AsyncFromSyncBuiltinsAssembler::LoadIteratorResult(
     const TNode<Context> context, const TNode<NativeContext> native_context,
     const TNode<Object> iter_result, Label* if_exception,
     TVariable<Object>* var_exception) {
   Label if_fastpath(this), if_slowpath(this), merge(this), to_boolean(this),
       done(this), if_notanobject(this, Label::kDeferred);
   GotoIf(TaggedIsSmi(iter_result), &if_notanobject);

   const TNode<Map> iter_result_map = LoadMap(CAST(iter_result));
   GotoIfNot(IsJSReceiverMap(iter_result_map), &if_notanobject);

   const TNode<Object> fast_iter_result_map =
       LoadContextElement(native_context, Context::ITERATOR_RESULT_MAP_INDEX);

   TVARIABLE(Object, var_value);
   TVARIABLE(Object, var_done);
   Branch(TaggedEqual(iter_result_map, fast_iter_result_map), &if_fastpath,
          &if_slowpath);

   BIND(&if_fastpath);
   {
     TNode<JSObject> fast_iter_result = CAST(iter_result);
     var_done = LoadObjectField(fast_iter_result, JSIteratorResult::kDoneOffset);
     var_value =
         LoadObjectField(fast_iter_result, JSIteratorResult::kValueOffset);
     Goto(&merge);
   }

   BIND(&if_slowpath);
   {
     ScopedExceptionHandler handler(this, if_exception, var_exception);

     // Let nextDone be IteratorComplete(nextResult).
     // IfAbruptRejectPromise(nextDone, promiseCapability).
     const TNode<Object> done =
         GetProperty(context, iter_result, factory()->done_string());

     // Let nextValue be IteratorValue(nextResult).
     // IfAbruptRejectPromise(nextValue, promiseCapability).
     const TNode<Object> value =
         GetProperty(context, iter_result, factory()->value_string());

     var_value = value;
     var_done = done;
     Goto(&merge);
   }

   BIND(&if_notanobject);
   {
     // Sync iterator result is not an object --- Produce a TypeError and jump
     // to the `if_exception` path.
     const TNode<Object> error = MakeTypeError(
         MessageTemplate::kIteratorResultNotAnObject, context, iter_result);
     *var_exception = error;
     Goto(if_exception);
   }

   BIND(&merge);
   // Ensure `iterResult.done` is a Boolean.
   GotoIf(TaggedIsSmi(var_done.value()), &to_boolean);
   Branch(IsBoolean(CAST(var_done.value())), &done, &to_boolean);

   BIND(&to_boolean);
   {
     const TNode<Object> result =
         CallBuiltin(Builtins::kToBoolean, context, var_done.value());
     var_done = result;
     Goto(&done);
   }

   BIND(&done);
   return std::make_pair(var_value.value(), CAST(var_done.value()));
 }

 }  // namespace

 // https://tc39.github.io/proposal-async-iteration/
 // Section #sec-%asyncfromsynciteratorprototype%.next
 TF_BUILTIN(AsyncFromSyncIteratorPrototypeNext, AsyncFromSyncBuiltinsAssembler) {
   TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
       UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
   CodeStubArguments args(this, argc);

   const TNode<Object> iterator = args.GetReceiver();
   const TNode<Object> value = args.GetOptionalArgumentValue(kValueOrReasonArg);
   const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

   auto get_method = [=](const TNode<JSReceiver> unused) {
     return LoadObjectField(CAST(iterator),
                            JSAsyncFromSyncIterator::kNextOffset);
   };
   Generate_AsyncFromSyncIteratorMethod(
       &args, context, iterator, value, get_method, UndefinedMethodHandler(),
       "[Async-from-Sync Iterator].prototype.next");
 }

 // https://tc39.github.io/proposal-async-iteration/
 // Section #sec-%asyncfromsynciteratorprototype%.return
 TF_BUILTIN(AsyncFromSyncIteratorPrototypeReturn,
            AsyncFromSyncBuiltinsAssembler) {
   TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
       UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
   CodeStubArguments args(this, argc);

   const TNode<Object> iterator = args.GetReceiver();
   const TNode<Object> value = args.GetOptionalArgumentValue(kValueOrReasonArg);
   const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

   auto if_return_undefined = [=, &args](
                                  const TNode<NativeContext> native_context,
                                  const TNode<JSPromise> promise,
                                  Label* if_exception) {
     // If return is undefined, then
     // Let iterResult be ! CreateIterResultObject(value, true)
     const TNode<Object> iter_result = CallBuiltin(
         Builtins::kCreateIterResultObject, context, value, TrueConstant());

     // Perform ! Call(promiseCapability.[[Resolve]], undefined, « iterResult »).
     // IfAbruptRejectPromise(nextDone, promiseCapability).
     // Return promiseCapability.[[Promise]].
     CallBuiltin(Builtins::kResolvePromise, context, promise, iter_result);
     args.PopAndReturn(promise);
   };

   Generate_AsyncFromSyncIteratorMethod(
       &args, context, iterator, value, factory()->return_string(),
       if_return_undefined, "[Async-from-Sync Iterator].prototype.return");
 }

 // https://tc39.github.io/proposal-async-iteration/
 // Section #sec-%asyncfromsynciteratorprototype%.throw
 TF_BUILTIN(AsyncFromSyncIteratorPrototypeThrow,
            AsyncFromSyncBuiltinsAssembler) {
   TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
       UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
   CodeStubArguments args(this, argc);

   const TNode<Object> iterator = args.GetReceiver();
   const TNode<Object> reason = args.GetOptionalArgumentValue(kValueOrReasonArg);
   const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

   auto if_throw_undefined = [=](const TNode<NativeContext> native_context,
                                 const TNode<JSPromise> promise,
                                 Label* if_exception) { Goto(if_exception); };

   Generate_AsyncFromSyncIteratorMethod(
       &args, context, iterator, reason, factory()->throw_string(),
       if_throw_undefined, "[Async-from-Sync Iterator].prototype.throw",
       Label::kNonDeferred, reason);
 }

 }  // namespace internal
 }  // namespace v8
	// Copyright 2017 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/base/optional.h"
	#include "src/builtins/builtins-async-gen.h"
	#include "src/builtins/builtins-utils-gen.h"
	#include "src/builtins/builtins.h"
	#include "src/codegen/code-factory.h"
	#include "src/codegen/code-stub-assembler.h"
	#include "src/execution/frames-inl.h"

	namespace v8 {
	namespace internal {

	namespace {
	class AsyncFromSyncBuiltinsAssembler : public AsyncBuiltinsAssembler {
	public:
	// The 'next' and 'return' take an optional value parameter, and the 'throw'
	// method take an optional reason parameter.
	static const int kValueOrReasonArg = 0;

	explicit AsyncFromSyncBuiltinsAssembler(compiler::CodeAssemblerState* state)
	: AsyncBuiltinsAssembler(state) {}

	void ThrowIfNotAsyncFromSyncIterator(const TNode<Context> context,
	const TNode<Object> object,
	Label* if_exception,
	TVariable<Object>* var_exception,
	const char* method_name);

	using UndefinedMethodHandler =
	std::function<void(const TNode<NativeContext> native_context,
	const TNode<JSPromise> promise, Label* if_exception)>;
	using SyncIteratorNodeGenerator =
	std::function<TNode<Object>(TNode<JSReceiver>)>;
	void Generate_AsyncFromSyncIteratorMethod(
	CodeStubArguments* args, const TNode<Context> context,
	const TNode<Object> iterator, const TNode<Object> sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	base::Optional<TNode<Object>> initial_exception_value = base::nullopt);

	void Generate_AsyncFromSyncIteratorMethod(
	CodeStubArguments* args, const TNode<Context> context,
	const TNode<Object> iterator, const TNode<Object> sent_value,
	Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	base::Optional<TNode<Object>> initial_exception_value = base::nullopt) {
	auto get_method = [=](const TNode<JSReceiver> sync_iterator) {
	return GetProperty(context, sync_iterator, name);
	};
	return Generate_AsyncFromSyncIteratorMethod(
	args, context, iterator, sent_value, get_method, if_method_undefined,
	operation_name, reject_label_type, initial_exception_value);
	}

	// Load "value" and "done" from an iterator result object. If an exception
	// is thrown at any point, jumps to the `if_exception` label with exception
	// stored in `var_exception`.
	//
	// Returns a Pair of Nodes, whose first element is the value of the "value"
	// property, and whose second element is the value of the "done" property,
	// converted to a Boolean if needed.
	std::pair<TNode<Object>, TNode<Oddball>> LoadIteratorResult(
	const TNode<Context> context, const TNode<NativeContext> native_context,
	const TNode<Object> iter_result, Label* if_exception,
	TVariable<Object>* var_exception);
	};

	void AsyncFromSyncBuiltinsAssembler::ThrowIfNotAsyncFromSyncIterator(
	const TNode<Context> context, const TNode<Object> object,
	Label* if_exception, TVariable<Object>* var_exception,
	const char* method_name) {
	Label if_receiverisincompatible(this, Label::kDeferred), done(this);

	GotoIf(TaggedIsSmi(object), &if_receiverisincompatible);
	Branch(HasInstanceType(CAST(object), JS_ASYNC_FROM_SYNC_ITERATOR_TYPE), &done,
	&if_receiverisincompatible);

	BIND(&if_receiverisincompatible);
	{
	// If Type(O) is not Object, or if O does not have a [[SyncIterator]]
	// internal slot, then

	// Let badIteratorError be a new TypeError exception.
	TNode<HeapObject> error =
	MakeTypeError(MessageTemplate::kIncompatibleMethodReceiver, context,
	StringConstant(method_name), object);

	// Perform ! Call(promiseCapability.[[Reject]], undefined,
	// « badIteratorError »).
	*var_exception = error;
	Goto(if_exception);
	}

	BIND(&done);
	}

	void AsyncFromSyncBuiltinsAssembler::Generate_AsyncFromSyncIteratorMethod(
	CodeStubArguments* args, const TNode<Context> context,
	const TNode<Object> iterator, const TNode<Object> sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name, Label::Type reject_label_type,
	base::Optional<TNode<Object>> initial_exception_value) {
	const TNode<NativeContext> native_context = LoadNativeContext(context);
	const TNode<JSPromise> promise = NewJSPromise(context);

	TVARIABLE(
	Object, var_exception,
	initial_exception_value ? *initial_exception_value : UndefinedConstant());
	Label reject_promise(this, reject_label_type);

	ThrowIfNotAsyncFromSyncIterator(context, iterator, &reject_promise,
	&var_exception, operation_name);

	TNode<JSAsyncFromSyncIterator> async_iterator = CAST(iterator);
	const TNode<JSReceiver> sync_iterator = LoadObjectField<JSReceiver>(
	async_iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

	TNode<Object> method = get_method(sync_iterator);

	if (if_method_undefined) {
	Label if_isnotundefined(this);

	GotoIfNot(IsNullOrUndefined(method), &if_isnotundefined);
	if_method_undefined(native_context, promise, &reject_promise);

	BIND(&if_isnotundefined);
	}

	TVARIABLE(Object, iter_result);
	{
	Label has_sent_value(this), no_sent_value(this), merge(this);
	ScopedExceptionHandler handler(this, &reject_promise, &var_exception);
	Branch(
	IntPtrGreaterThan(args->GetLength(), IntPtrConstant(kValueOrReasonArg)),
	&has_sent_value, &no_sent_value);
	BIND(&has_sent_value);
	{
	iter_result = Call(context, method, sync_iterator, sent_value);
	Goto(&merge);
	}
	BIND(&no_sent_value);
	{
	iter_result = Call(context, method, sync_iterator);
	Goto(&merge);
	}
	BIND(&merge);
	}

	TNode<Object> value;
	TNode<Oddball> done;
	std::tie(value, done) =
	LoadIteratorResult(context, native_context, iter_result.value(),
	&reject_promise, &var_exception);

	const TNode<JSFunction> promise_fun =
	CAST(LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX));
	CSA_ASSERT(this, IsConstructor(promise_fun));

	// Let valueWrapper be PromiseResolve(%Promise%, « value »).
	// IfAbruptRejectPromise(valueWrapper, promiseCapability).
	TNode<Object> value_wrapper;
	{
	ScopedExceptionHandler handler(this, &reject_promise, &var_exception);
	value_wrapper = CallBuiltin(Builtins::kPromiseResolve, native_context,
	promise_fun, value);
	}

	// Let onFulfilled be a new built-in function object as defined in
	// Async Iterator Value Unwrap Functions.
	// Set onFulfilled.[[Done]] to throwDone.
	const TNode<JSFunction> on_fulfilled =
	CreateUnwrapClosure(native_context, done);

	// Perform ! PerformPromiseThen(valueWrapper,
	// onFulfilled, undefined, promiseCapability).
	args->PopAndReturn(CallBuiltin(Builtins::kPerformPromiseThen, context,
	value_wrapper, on_fulfilled,
	UndefinedConstant(), promise));

	BIND(&reject_promise);
	{
	const TNode<Object> exception = var_exception.value();
	CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
	TrueConstant());
	args->PopAndReturn(promise);
	}
	}

	std::pair<TNode<Object>, TNode<Oddball>>
	AsyncFromSyncBuiltinsAssembler::LoadIteratorResult(
	const TNode<Context> context, const TNode<NativeContext> native_context,
	const TNode<Object> iter_result, Label* if_exception,
	TVariable<Object>* var_exception) {
	Label if_fastpath(this), if_slowpath(this), merge(this), to_boolean(this),
	done(this), if_notanobject(this, Label::kDeferred);
	GotoIf(TaggedIsSmi(iter_result), &if_notanobject);

	const TNode<Map> iter_result_map = LoadMap(CAST(iter_result));
	GotoIfNot(IsJSReceiverMap(iter_result_map), &if_notanobject);

	const TNode<Object> fast_iter_result_map =
	LoadContextElement(native_context, Context::ITERATOR_RESULT_MAP_INDEX);

	TVARIABLE(Object, var_value);
	TVARIABLE(Object, var_done);
	Branch(TaggedEqual(iter_result_map, fast_iter_result_map), &if_fastpath,
	&if_slowpath);

	BIND(&if_fastpath);
	{
	TNode<JSObject> fast_iter_result = CAST(iter_result);
	var_done = LoadObjectField(fast_iter_result, JSIteratorResult::kDoneOffset);
	var_value =
	LoadObjectField(fast_iter_result, JSIteratorResult::kValueOffset);
	Goto(&merge);
	}

	BIND(&if_slowpath);
	{
	ScopedExceptionHandler handler(this, if_exception, var_exception);

	// Let nextDone be IteratorComplete(nextResult).
	// IfAbruptRejectPromise(nextDone, promiseCapability).
	const TNode<Object> done =
	GetProperty(context, iter_result, factory()->done_string());

	// Let nextValue be IteratorValue(nextResult).
	// IfAbruptRejectPromise(nextValue, promiseCapability).
	const TNode<Object> value =
	GetProperty(context, iter_result, factory()->value_string());

	var_value = value;
	var_done = done;
	Goto(&merge);
	}

	BIND(&if_notanobject);
	{
	// Sync iterator result is not an object --- Produce a TypeError and jump
	// to the `if_exception` path.
	const TNode<Object> error = MakeTypeError(
	MessageTemplate::kIteratorResultNotAnObject, context, iter_result);
	*var_exception = error;
	Goto(if_exception);
	}

	BIND(&merge);
	// Ensure `iterResult.done` is a Boolean.
	GotoIf(TaggedIsSmi(var_done.value()), &to_boolean);
	Branch(IsBoolean(CAST(var_done.value())), &done, &to_boolean);

	BIND(&to_boolean);
	{
	const TNode<Object> result =
	CallBuiltin(Builtins::kToBoolean, context, var_done.value());
	var_done = result;
	Goto(&done);
	}

	BIND(&done);
	return std::make_pair(var_value.value(), CAST(var_done.value()));
	}

	} // namespace

	// https://tc39.github.io/proposal-async-iteration/
	// Section #sec-%asyncfromsynciteratorprototype%.next
	TF_BUILTIN(AsyncFromSyncIteratorPrototypeNext, AsyncFromSyncBuiltinsAssembler) {
	TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
	UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
	CodeStubArguments args(this, argc);

	const TNode<Object> iterator = args.GetReceiver();
	const TNode<Object> value = args.GetOptionalArgumentValue(kValueOrReasonArg);
	const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

	auto get_method = [=](const TNode<JSReceiver> unused) {
	return LoadObjectField(CAST(iterator),
	JSAsyncFromSyncIterator::kNextOffset);
	};
	Generate_AsyncFromSyncIteratorMethod(
	&args, context, iterator, value, get_method, UndefinedMethodHandler(),
	"[Async-from-Sync Iterator].prototype.next");
	}

	// https://tc39.github.io/proposal-async-iteration/
	// Section #sec-%asyncfromsynciteratorprototype%.return
	TF_BUILTIN(AsyncFromSyncIteratorPrototypeReturn,
	AsyncFromSyncBuiltinsAssembler) {
	TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
	UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
	CodeStubArguments args(this, argc);

	const TNode<Object> iterator = args.GetReceiver();
	const TNode<Object> value = args.GetOptionalArgumentValue(kValueOrReasonArg);
	const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

	auto if_return_undefined = [=, &args](
	const TNode<NativeContext> native_context,
	const TNode<JSPromise> promise,
	Label* if_exception) {
	// If return is undefined, then
	// Let iterResult be ! CreateIterResultObject(value, true)
	const TNode<Object> iter_result = CallBuiltin(
	Builtins::kCreateIterResultObject, context, value, TrueConstant());

	// Perform ! Call(promiseCapability.[[Resolve]], undefined, « iterResult »).
	// IfAbruptRejectPromise(nextDone, promiseCapability).
	// Return promiseCapability.[[Promise]].
	CallBuiltin(Builtins::kResolvePromise, context, promise, iter_result);
	args.PopAndReturn(promise);
	};

	Generate_AsyncFromSyncIteratorMethod(
	&args, context, iterator, value, factory()->return_string(),
	if_return_undefined, "[Async-from-Sync Iterator].prototype.return");
	}

	// https://tc39.github.io/proposal-async-iteration/
	// Section #sec-%asyncfromsynciteratorprototype%.throw
	TF_BUILTIN(AsyncFromSyncIteratorPrototypeThrow,
	AsyncFromSyncBuiltinsAssembler) {
	TNode<IntPtrT> argc = ChangeInt32ToIntPtr(
	UncheckedCast<Int32T>(Parameter(Descriptor::kJSActualArgumentsCount)));
	CodeStubArguments args(this, argc);

	const TNode<Object> iterator = args.GetReceiver();
	const TNode<Object> reason = args.GetOptionalArgumentValue(kValueOrReasonArg);
	const TNode<Context> context = CAST(Parameter(Descriptor::kContext));

	auto if_throw_undefined = [=](const TNode<NativeContext> native_context,
	const TNode<JSPromise> promise,
	Label* if_exception) { Goto(if_exception); };

	Generate_AsyncFromSyncIteratorMethod(
	&args, context, iterator, reason, factory()->throw_string(),
	if_throw_undefined, "[Async-from-Sync Iterator].prototype.throw",
	Label::kNonDeferred, reason);
	}

	} // namespace internal
	} // namespace v8