[async-iteration] add support for for-await-of loops in Async Functions

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index a21e978965ef0dcb8e1786d4004c213e39d656fb..5cbb300d7a32777972082dc8662ed1750d96e802 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -587,6 +587,8 @@ BytecodeGenerator::BytecodeGenerator(CompilationInfo* info)
       loop_depth_(0),
       home_object_symbol_(info->isolate()->factory()->home_object_symbol()),
       iterator_symbol_(info->isolate()->factory()->iterator_symbol()),
+      async_iterator_symbol_(
+          info->isolate()->factory()->async_iterator_symbol()),
       prototype_string_(info->isolate()->factory()->prototype_string()),
       empty_fixed_array_(info->isolate()->factory()->empty_fixed_array()),
       undefined_string_(
@@ -2932,8 +2934,8 @@ void BytecodeGenerator::VisitEmptyParentheses(EmptyParentheses* expr) {
 }
 
 void BytecodeGenerator::VisitGetIterator(GetIterator* expr) {
-  FeedbackVectorSlot load_slot = expr->IteratorPropertyFeedbackSlot();
-  FeedbackVectorSlot call_slot = expr->IteratorCallFeedbackSlot();
+  FeedbackVectorSlot load_iter_slot = expr->IteratorPropertyFeedbackSlot();
+  FeedbackVectorSlot call_iter_slot = expr->IteratorCallFeedbackSlot();
 
   RegisterList args = register_allocator()->NewRegisterList(1);
   Register method = register_allocator()->NewRegister();
@@ -2941,21 +2943,67 @@ void BytecodeGenerator::VisitGetIterator(GetIterator* expr) {
 
   VisitForAccumulatorValue(expr->iterable());
 
-  // Let method be GetMethod(obj, @@iterator).
-  builder()
-      ->StoreAccumulatorInRegister(obj)
-      .LoadNamedProperty(obj, iterator_symbol(), feedback_index(load_slot))
-      .StoreAccumulatorInRegister(method);
-
-  // Let iterator be Call(method, obj).
-  builder()->Call(method, args, feedback_index(call_slot),
-                  Call::NAMED_PROPERTY_CALL);
-
-  // If Type(iterator) is not Object, throw a TypeError exception.
-  BytecodeLabel no_type_error;
-  builder()->JumpIfJSReceiver(&no_type_error);
-  builder()->CallRuntime(Runtime::kThrowSymbolIteratorInvalid);
-  builder()->Bind(&no_type_error);
+  if (expr->hint() == GetIterator::Hint::kAsync) {
+    FeedbackVectorSlot load_async_iter_slot =
+        expr->AsyncIteratorPropertyFeedbackSlot();
+    FeedbackVectorSlot call_async_iter_slot =
+        expr->AsyncIteratorCallFeedbackSlot();
+
+    // Set method to GetMethod(obj, @@asyncIterator)
+    builder()->StoreAccumulatorInRegister(obj).LoadNamedProperty(
+        obj, async_iterator_symbol(), feedback_index(load_async_iter_slot));
+
+    BytecodeLabel async_iterator_undefined, async_iterator_null, done;
+    builder()->JumpIfUndefined(&async_iterator_undefined);
+    builder()->JumpIfNull(&async_iterator_null);
+
+    // Let iterator be Call(method, obj)
+    builder()->StoreAccumulatorInRegister(method).Call(
+        method, args, feedback_index(call_async_iter_slot),
+        Call::NAMED_PROPERTY_CALL);
+
+    // If Type(iterator) is not Object, throw a TypeError exception.
+    builder()->JumpIfJSReceiver(&done);
+    builder()->CallRuntime(Runtime::kThrowSymbolAsyncIteratorInvalid);
+
+    builder()->Bind(&async_iterator_undefined);
+    builder()->Bind(&async_iterator_null);
+    // If method is undefined,
+    //     Let syncMethod be GetMethod(obj, @@iterator)
+    builder()
+        ->LoadNamedProperty(obj, iterator_symbol(),
+                            feedback_index(load_iter_slot))
+        .StoreAccumulatorInRegister(method);
+
+    //     Let syncIterator be Call(syncMethod, obj)
+    builder()->Call(method, args, feedback_index(call_iter_slot),
+                    Call::NAMED_PROPERTY_CALL);
+
+    // Return CreateAsyncFromSyncIterator(syncIterator)
+    // alias `method` register as it's no longer used
+    Register sync_iter = method;
+    builder()->StoreAccumulatorInRegister(sync_iter).CallRuntime(
+        Runtime::kInlineCreateAsyncFromSyncIterator, sync_iter);
+
+    builder()->Bind(&done);
+  } else {
+    // Let method be GetMethod(obj, @@iterator).
+    builder()
+        ->StoreAccumulatorInRegister(obj)
+        .LoadNamedProperty(obj, iterator_symbol(),
+                           feedback_index(load_iter_slot))
+        .StoreAccumulatorInRegister(method);
+
+    // Let iterator be Call(method, obj).
+    builder()->Call(method, args, feedback_index(call_iter_slot),
+                    Call::NAMED_PROPERTY_CALL);
+
+    // If Type(iterator) is not Object, throw a TypeError exception.
+    BytecodeLabel no_type_error;
+    builder()->JumpIfJSReceiver(&no_type_error);
+    builder()->CallRuntime(Runtime::kThrowSymbolIteratorInvalid);
+    builder()->Bind(&no_type_error);
+  }
 }
 
 void BytecodeGenerator::VisitThisFunction(ThisFunction* expr) {