src/builtins/builtins-async-iterator-gen.cc - v8/v8.git - 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/builtins/builtins-async-gen.h"
 #include "src/builtins/builtins-utils-gen.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/frames-inl.h"

 namespace v8 {
 namespace internal {

 using compiler::Node;

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

   void ThrowIfNotAsyncFromSyncIterator(Node* const context, Node* const object,
                                        Label* if_exception,
                                        Variable* var_exception,
                                        const char* method_name);

   typedef std::function<void(Node* const context, Node* const promise,
                              Label* if_exception)>
       UndefinedMethodHandler;
   typedef std::function<Node*(Node*)> SyncIteratorNodeGenerator;
   void Generate_AsyncFromSyncIteratorMethod(
       Node* const context, Node* const iterator, Node* const sent_value,
       const SyncIteratorNodeGenerator& get_method,
       const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       Node* const initial_exception_value = nullptr);
   void Generate_AsyncFromSyncIteratorMethodOptimized(
       Node* const context, Node* const iterator, Node* const sent_value,
       const SyncIteratorNodeGenerator& get_method,
       const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       Node* const initial_exception_value = nullptr);

   void Generate_AsyncFromSyncIteratorMethod(
       Node* const context, Node* const iterator, Node* const sent_value,
       Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       Node* const initial_exception_value = nullptr) {
     auto get_method = [=](Node* const sync_iterator) {
       return GetProperty(context, sync_iterator, name);
     };
     return Generate_AsyncFromSyncIteratorMethod(
         context, iterator, sent_value, get_method, if_method_undefined,
         operation_name, reject_label_type, initial_exception_value);
   }
   void Generate_AsyncFromSyncIteratorMethodOptimized(
       Node* const context, Node* const iterator, Node* const sent_value,
       Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
       const char* operation_name,
       Label::Type reject_label_type = Label::kDeferred,
       Node* const initial_exception_value = nullptr) {
     auto get_method = [=](Node* const sync_iterator) {
       return GetProperty(context, sync_iterator, name);
     };
     return Generate_AsyncFromSyncIteratorMethodOptimized(
         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 te `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<Node*, Node*> LoadIteratorResult(Node* const context,
                                              Node* const native_context,
                                              Node* const iter_result,
                                              Label* if_exception,
                                              Variable* var_exception);
 };

 void AsyncFromSyncBuiltinsAssembler::ThrowIfNotAsyncFromSyncIterator(
     Node* const context, Node* const object, Label* if_exception,
     Variable* var_exception, const char* method_name) {
   Label if_receiverisincompatible(this, Label::kDeferred), done(this);

   GotoIf(TaggedIsSmi(object), &if_receiverisincompatible);
   Branch(HasInstanceType(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.
     Node* const error =
         MakeTypeError(MessageTemplate::kIncompatibleMethodReceiver, context,
                       StringConstant(method_name), object);

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

   BIND(&done);
 }

 void AsyncFromSyncBuiltinsAssembler::Generate_AsyncFromSyncIteratorMethod(
     Node* const context, Node* const iterator, Node* const sent_value,
     const SyncIteratorNodeGenerator& get_method,
     const UndefinedMethodHandler& if_method_undefined,
     const char* operation_name, Label::Type reject_label_type,
     Node* const initial_exception_value) {
   Node* const native_context = LoadNativeContext(context);
   Node* const promise = AllocateAndInitJSPromise(context);

   VARIABLE(var_exception, MachineRepresentation::kTagged,
            initial_exception_value == nullptr ? UndefinedConstant()
                                               : initial_exception_value);
   Label reject_promise(this, reject_label_type);

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

   Node* const sync_iterator =
       LoadObjectField(iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

   Node* const method = get_method(sync_iterator);

   if (if_method_undefined) {
     Label if_isnotundefined(this);

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

     BIND(&if_isnotundefined);
   }

   Node* const iter_result = CallJS(CodeFactory::Call(isolate()), context,
                                    method, sync_iterator, sent_value);
   GotoIfException(iter_result, &reject_promise, &var_exception);

   Node* value;
   Node* done;
   std::tie(value, done) = LoadIteratorResult(
       context, native_context, iter_result, &reject_promise, &var_exception);
   Node* const wrapper = AllocateAndInitJSPromise(context);

   // Perform ! Call(valueWrapperCapability.[[Resolve]], undefined, «
   // throwValue »).
   CallBuiltin(Builtins::kResolvePromise, context, wrapper, value);

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

   // Perform ! PerformPromiseThen(valueWrapperCapability.[[Promise]],
   //     onFulfilled, undefined, promiseCapability).
   Return(CallBuiltin(Builtins::kPerformPromiseThen, context, wrapper,
                      on_fulfilled, UndefinedConstant(), promise));

   BIND(&reject_promise);
   {
     Node* const exception = var_exception.value();
     CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
                 TrueConstant());
     Return(promise);
   }
 }

 void AsyncFromSyncBuiltinsAssembler::
     Generate_AsyncFromSyncIteratorMethodOptimized(
         Node* const context, Node* const iterator, Node* const sent_value,
         const SyncIteratorNodeGenerator& get_method,
         const UndefinedMethodHandler& if_method_undefined,
         const char* operation_name, Label::Type reject_label_type,
         Node* const initial_exception_value) {
   Node* const native_context = LoadNativeContext(context);
   Node* const promise = AllocateAndInitJSPromise(context);

   VARIABLE(var_exception, MachineRepresentation::kTagged,
            initial_exception_value == nullptr ? UndefinedConstant()
                                               : initial_exception_value);
   Label reject_promise(this, reject_label_type);

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

   Node* const sync_iterator =
       LoadObjectField(iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

   Node* const method = get_method(sync_iterator);

   if (if_method_undefined) {
     Label if_isnotundefined(this);

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

     BIND(&if_isnotundefined);
   }

   Node* const iter_result = CallJS(CodeFactory::Call(isolate()), context,
                                    method, sync_iterator, sent_value);
   GotoIfException(iter_result, &reject_promise, &var_exception);

   Node* value;
   Node* done;
   std::tie(value, done) = LoadIteratorResult(
       context, native_context, iter_result, &reject_promise, &var_exception);

   Node* const promise_fun =
       LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
   CSA_ASSERT(this, IsConstructor(promise_fun));

   // Let valueWrapper be ? PromiseResolve(« value »).
   Node* const valueWrapper = 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.
   Node* const on_fulfilled = CreateUnwrapClosure(native_context, done);

   // Perform ! PerformPromiseThen(valueWrapper,
   //     onFulfilled, undefined, promiseCapability).
   Return(CallBuiltin(Builtins::kPerformPromiseThen, context, valueWrapper,
                      on_fulfilled, UndefinedConstant(), promise));

   BIND(&reject_promise);
   {
     Node* const exception = var_exception.value();
     CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
                 TrueConstant());
     Return(promise);
   }
 }
 std::pair<Node*, Node*> AsyncFromSyncBuiltinsAssembler::LoadIteratorResult(
     Node* const context, Node* const native_context, Node* const iter_result,
     Label* if_exception, Variable* 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);

   Node* const iter_result_map = LoadMap(iter_result);
   GotoIfNot(IsJSReceiverMap(iter_result_map), &if_notanobject);

   Node* const fast_iter_result_map =
       LoadContextElement(native_context, Context::ITERATOR_RESULT_MAP_INDEX);

   VARIABLE(var_value, MachineRepresentation::kTagged);
   VARIABLE(var_done, MachineRepresentation::kTagged);
   Branch(WordEqual(iter_result_map, fast_iter_result_map), &if_fastpath,
          &if_slowpath);

   BIND(&if_fastpath);
   {
     var_done.Bind(LoadObjectField(iter_result, JSIteratorResult::kDoneOffset));
     var_value.Bind(
         LoadObjectField(iter_result, JSIteratorResult::kValueOffset));
     Goto(&merge);
   }

   BIND(&if_slowpath);
   {
     // Let nextDone be IteratorComplete(nextResult).
     // IfAbruptRejectPromise(nextDone, promiseCapability).
     Node* const done =
         GetProperty(context, iter_result, factory()->done_string());
     GotoIfException(done, if_exception, var_exception);

     // Let nextValue be IteratorValue(nextResult).
     // IfAbruptRejectPromise(nextValue, promiseCapability).
     Node* const value =
         GetProperty(context, iter_result, factory()->value_string());
     GotoIfException(value, if_exception, var_exception);

     var_value.Bind(value);
     var_done.Bind(done);
     Goto(&merge);
   }

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

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

   BIND(&to_boolean);
   {
     Node* const result =
         CallBuiltin(Builtins::kToBoolean, context, var_done.value());
     var_done.Bind(result);
     Goto(&done);
   }

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

 }  // namespace

 // https://tc39.github.io/proposal-async-iteration/
 // Section #sec-%asyncfromsynciteratorprototype%.next
 TF_BUILTIN(AsyncFromSyncIteratorPrototypeNext, AsyncFromSyncBuiltinsAssembler) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const value = Parameter(Descriptor::kValue);
   Node* const context = Parameter(Descriptor::kContext);

   auto get_method = [=](Node* const unused) {
     return LoadObjectField(iterator, JSAsyncFromSyncIterator::kNextOffset);
   };
   Generate_AsyncFromSyncIteratorMethod(
       context, iterator, value, get_method, UndefinedMethodHandler(),
       "[Async-from-Sync Iterator].prototype.next");
 }

 TF_BUILTIN(AsyncFromSyncIteratorPrototypeNextOptimized,
            AsyncFromSyncBuiltinsAssembler) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const value = Parameter(Descriptor::kValue);
   Node* const context = Parameter(Descriptor::kContext);

   auto get_method = [=](Node* const unused) {
     return LoadObjectField(iterator, JSAsyncFromSyncIterator::kNextOffset);
   };
   Generate_AsyncFromSyncIteratorMethodOptimized(
       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) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const value = Parameter(Descriptor::kValue);
   Node* const context = Parameter(Descriptor::kContext);

   auto if_return_undefined = [=](Node* const native_context,
                                  Node* const promise, Label* if_exception) {
     // If return is undefined, then
     // Let iterResult be ! CreateIterResultObject(value, true)
     Node* const 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);
     Return(promise);
   };

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

 TF_BUILTIN(AsyncFromSyncIteratorPrototypeReturnOptimized,
            AsyncFromSyncBuiltinsAssembler) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const value = Parameter(Descriptor::kValue);
   Node* const context = Parameter(Descriptor::kContext);

   auto if_return_undefined = [=](Node* const native_context,
                                  Node* const promise, Label* if_exception) {
     // If return is undefined, then
     // Let iterResult be ! CreateIterResultObject(value, true)
     Node* const 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);
     Return(promise);
   };

   Generate_AsyncFromSyncIteratorMethodOptimized(
       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) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const reason = Parameter(Descriptor::kReason);
   Node* const context = Parameter(Descriptor::kContext);

   auto if_throw_undefined = [=](Node* const native_context, Node* const promise,
                                 Label* if_exception) { Goto(if_exception); };

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

 TF_BUILTIN(AsyncFromSyncIteratorPrototypeThrowOptimized,
            AsyncFromSyncBuiltinsAssembler) {
   Node* const iterator = Parameter(Descriptor::kReceiver);
   Node* const reason = Parameter(Descriptor::kReason);
   Node* const context = Parameter(Descriptor::kContext);

   auto if_throw_undefined = [=](Node* const native_context, Node* const promise,
                                 Label* if_exception) { Goto(if_exception); };

   Generate_AsyncFromSyncIteratorMethodOptimized(
       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/builtins/builtins-async-gen.h"
	#include "src/builtins/builtins-utils-gen.h"
	#include "src/builtins/builtins.h"
	#include "src/code-factory.h"
	#include "src/code-stub-assembler.h"
	#include "src/frames-inl.h"

	namespace v8 {
	namespace internal {

	using compiler::Node;

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

	void ThrowIfNotAsyncFromSyncIterator(Node* const context, Node* const object,
	Label* if_exception,
	Variable* var_exception,
	const char* method_name);

	typedef std::function<void(Node* const context, Node* const promise,
	Label* if_exception)>
	UndefinedMethodHandler;
	typedef std::function<Node(Node)> SyncIteratorNodeGenerator;
	void Generate_AsyncFromSyncIteratorMethod(
	Node* const context, Node* const iterator, Node* const sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	Node* const initial_exception_value = nullptr);
	void Generate_AsyncFromSyncIteratorMethodOptimized(
	Node* const context, Node* const iterator, Node* const sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	Node* const initial_exception_value = nullptr);

	void Generate_AsyncFromSyncIteratorMethod(
	Node* const context, Node* const iterator, Node* const sent_value,
	Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	Node* const initial_exception_value = nullptr) {
	auto get_method = [=](Node* const sync_iterator) {
	return GetProperty(context, sync_iterator, name);
	};
	return Generate_AsyncFromSyncIteratorMethod(
	context, iterator, sent_value, get_method, if_method_undefined,
	operation_name, reject_label_type, initial_exception_value);
	}
	void Generate_AsyncFromSyncIteratorMethodOptimized(
	Node* const context, Node* const iterator, Node* const sent_value,
	Handle<String> name, const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name,
	Label::Type reject_label_type = Label::kDeferred,
	Node* const initial_exception_value = nullptr) {
	auto get_method = [=](Node* const sync_iterator) {
	return GetProperty(context, sync_iterator, name);
	};
	return Generate_AsyncFromSyncIteratorMethodOptimized(
	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 te `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<Node, Node> LoadIteratorResult(Node* const context,
	Node* const native_context,
	Node* const iter_result,
	Label* if_exception,
	Variable* var_exception);
	};

	void AsyncFromSyncBuiltinsAssembler::ThrowIfNotAsyncFromSyncIterator(
	Node* const context, Node* const object, Label* if_exception,
	Variable* var_exception, const char* method_name) {
	Label if_receiverisincompatible(this, Label::kDeferred), done(this);

	GotoIf(TaggedIsSmi(object), &if_receiverisincompatible);
	Branch(HasInstanceType(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.
	Node* const error =
	MakeTypeError(MessageTemplate::kIncompatibleMethodReceiver, context,
	StringConstant(method_name), object);

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

	BIND(&done);
	}

	void AsyncFromSyncBuiltinsAssembler::Generate_AsyncFromSyncIteratorMethod(
	Node* const context, Node* const iterator, Node* const sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name, Label::Type reject_label_type,
	Node* const initial_exception_value) {
	Node* const native_context = LoadNativeContext(context);
	Node* const promise = AllocateAndInitJSPromise(context);

	VARIABLE(var_exception, MachineRepresentation::kTagged,
	initial_exception_value == nullptr ? UndefinedConstant()
	: initial_exception_value);
	Label reject_promise(this, reject_label_type);

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

	Node* const sync_iterator =
	LoadObjectField(iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

	Node* const method = get_method(sync_iterator);

	if (if_method_undefined) {
	Label if_isnotundefined(this);

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

	BIND(&if_isnotundefined);
	}

	Node* const iter_result = CallJS(CodeFactory::Call(isolate()), context,
	method, sync_iterator, sent_value);
	GotoIfException(iter_result, &reject_promise, &var_exception);

	Node* value;
	Node* done;
	std::tie(value, done) = LoadIteratorResult(
	context, native_context, iter_result, &reject_promise, &var_exception);
	Node* const wrapper = AllocateAndInitJSPromise(context);

	// Perform ! Call(valueWrapperCapability.[[Resolve]], undefined, «
	// throwValue »).
	CallBuiltin(Builtins::kResolvePromise, context, wrapper, value);

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

	// Perform ! PerformPromiseThen(valueWrapperCapability.[[Promise]],
	// onFulfilled, undefined, promiseCapability).
	Return(CallBuiltin(Builtins::kPerformPromiseThen, context, wrapper,
	on_fulfilled, UndefinedConstant(), promise));

	BIND(&reject_promise);
	{
	Node* const exception = var_exception.value();
	CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
	TrueConstant());
	Return(promise);
	}
	}

	void AsyncFromSyncBuiltinsAssembler::
	Generate_AsyncFromSyncIteratorMethodOptimized(
	Node* const context, Node* const iterator, Node* const sent_value,
	const SyncIteratorNodeGenerator& get_method,
	const UndefinedMethodHandler& if_method_undefined,
	const char* operation_name, Label::Type reject_label_type,
	Node* const initial_exception_value) {
	Node* const native_context = LoadNativeContext(context);
	Node* const promise = AllocateAndInitJSPromise(context);

	VARIABLE(var_exception, MachineRepresentation::kTagged,
	initial_exception_value == nullptr ? UndefinedConstant()
	: initial_exception_value);
	Label reject_promise(this, reject_label_type);

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

	Node* const sync_iterator =
	LoadObjectField(iterator, JSAsyncFromSyncIterator::kSyncIteratorOffset);

	Node* const method = get_method(sync_iterator);

	if (if_method_undefined) {
	Label if_isnotundefined(this);

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

	BIND(&if_isnotundefined);
	}

	Node* const iter_result = CallJS(CodeFactory::Call(isolate()), context,
	method, sync_iterator, sent_value);
	GotoIfException(iter_result, &reject_promise, &var_exception);

	Node* value;
	Node* done;
	std::tie(value, done) = LoadIteratorResult(
	context, native_context, iter_result, &reject_promise, &var_exception);

	Node* const promise_fun =
	LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
	CSA_ASSERT(this, IsConstructor(promise_fun));

	// Let valueWrapper be ? PromiseResolve(« value »).
	Node* const valueWrapper = 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.
	Node* const on_fulfilled = CreateUnwrapClosure(native_context, done);

	// Perform ! PerformPromiseThen(valueWrapper,
	// onFulfilled, undefined, promiseCapability).
	Return(CallBuiltin(Builtins::kPerformPromiseThen, context, valueWrapper,
	on_fulfilled, UndefinedConstant(), promise));

	BIND(&reject_promise);
	{
	Node* const exception = var_exception.value();
	CallBuiltin(Builtins::kRejectPromise, context, promise, exception,
	TrueConstant());
	Return(promise);
	}
	}
	std::pair<Node, Node> AsyncFromSyncBuiltinsAssembler::LoadIteratorResult(
	Node* const context, Node* const native_context, Node* const iter_result,
	Label* if_exception, Variable* 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);

	Node* const iter_result_map = LoadMap(iter_result);
	GotoIfNot(IsJSReceiverMap(iter_result_map), &if_notanobject);

	Node* const fast_iter_result_map =
	LoadContextElement(native_context, Context::ITERATOR_RESULT_MAP_INDEX);

	VARIABLE(var_value, MachineRepresentation::kTagged);
	VARIABLE(var_done, MachineRepresentation::kTagged);
	Branch(WordEqual(iter_result_map, fast_iter_result_map), &if_fastpath,
	&if_slowpath);

	BIND(&if_fastpath);
	{
	var_done.Bind(LoadObjectField(iter_result, JSIteratorResult::kDoneOffset));
	var_value.Bind(
	LoadObjectField(iter_result, JSIteratorResult::kValueOffset));
	Goto(&merge);
	}

	BIND(&if_slowpath);
	{
	// Let nextDone be IteratorComplete(nextResult).
	// IfAbruptRejectPromise(nextDone, promiseCapability).
	Node* const done =
	GetProperty(context, iter_result, factory()->done_string());
	GotoIfException(done, if_exception, var_exception);

	// Let nextValue be IteratorValue(nextResult).
	// IfAbruptRejectPromise(nextValue, promiseCapability).
	Node* const value =
	GetProperty(context, iter_result, factory()->value_string());
	GotoIfException(value, if_exception, var_exception);

	var_value.Bind(value);
	var_done.Bind(done);
	Goto(&merge);
	}

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

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

	BIND(&to_boolean);
	{
	Node* const result =
	CallBuiltin(Builtins::kToBoolean, context, var_done.value());
	var_done.Bind(result);
	Goto(&done);
	}

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

	} // namespace

	// https://tc39.github.io/proposal-async-iteration/
	// Section #sec-%asyncfromsynciteratorprototype%.next
	TF_BUILTIN(AsyncFromSyncIteratorPrototypeNext, AsyncFromSyncBuiltinsAssembler) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const value = Parameter(Descriptor::kValue);
	Node* const context = Parameter(Descriptor::kContext);

	auto get_method = [=](Node* const unused) {
	return LoadObjectField(iterator, JSAsyncFromSyncIterator::kNextOffset);
	};
	Generate_AsyncFromSyncIteratorMethod(
	context, iterator, value, get_method, UndefinedMethodHandler(),
	"[Async-from-Sync Iterator].prototype.next");
	}

	TF_BUILTIN(AsyncFromSyncIteratorPrototypeNextOptimized,
	AsyncFromSyncBuiltinsAssembler) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const value = Parameter(Descriptor::kValue);
	Node* const context = Parameter(Descriptor::kContext);

	auto get_method = [=](Node* const unused) {
	return LoadObjectField(iterator, JSAsyncFromSyncIterator::kNextOffset);
	};
	Generate_AsyncFromSyncIteratorMethodOptimized(
	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) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const value = Parameter(Descriptor::kValue);
	Node* const context = Parameter(Descriptor::kContext);

	auto if_return_undefined = [=](Node* const native_context,
	Node* const promise, Label* if_exception) {
	// If return is undefined, then
	// Let iterResult be ! CreateIterResultObject(value, true)
	Node* const 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);
	Return(promise);
	};

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

	TF_BUILTIN(AsyncFromSyncIteratorPrototypeReturnOptimized,
	AsyncFromSyncBuiltinsAssembler) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const value = Parameter(Descriptor::kValue);
	Node* const context = Parameter(Descriptor::kContext);

	auto if_return_undefined = [=](Node* const native_context,
	Node* const promise, Label* if_exception) {
	// If return is undefined, then
	// Let iterResult be ! CreateIterResultObject(value, true)
	Node* const 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);
	Return(promise);
	};

	Generate_AsyncFromSyncIteratorMethodOptimized(
	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) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const reason = Parameter(Descriptor::kReason);
	Node* const context = Parameter(Descriptor::kContext);

	auto if_throw_undefined = [=](Node* const native_context, Node* const promise,
	Label* if_exception) { Goto(if_exception); };

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

	TF_BUILTIN(AsyncFromSyncIteratorPrototypeThrowOptimized,
	AsyncFromSyncBuiltinsAssembler) {
	Node* const iterator = Parameter(Descriptor::kReceiver);
	Node* const reason = Parameter(Descriptor::kReason);
	Node* const context = Parameter(Descriptor::kContext);

	auto if_throw_undefined = [=](Node* const native_context, Node* const promise,
	Label* if_exception) { Goto(if_exception); };

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

	} // namespace internal
	} // namespace v8