WIP [esnext] implement async iteration proposal

src/interpreter/interpreter.cc

Index: src/interpreter/interpreter.cc
diff --git a/src/interpreter/interpreter.cc b/src/interpreter/interpreter.cc
index 81ee71caf3a6ee0a77bcf9303523357546a3f4af..da663c2d879f6d68edb21b1687dd0439a6906f59 100644
--- a/src/interpreter/interpreter.cc
+++ b/src/interpreter/interpreter.cc
@@ -3242,6 +3242,50 @@ void Interpreter::DoSuspendGenerator(InterpreterAssembler* assembler) {
   }
 }
 
+// AwaitGenerator <generator>
+//
+// Like SuspendGenerator, exports the register file and stores it into the
+// generator, along with current context, the continuation state. The current
+// bytecode offset is stored in the [await_input] field to prevent clobbering
+// the sent value.
+void Interpreter::DoAwaitGenerator(InterpreterAssembler* assembler) {
+  Node* generator_reg = __ BytecodeOperandReg(0);
+  Node* generator = __ LoadRegister(generator_reg);
+
+  Label if_stepping(assembler, Label::kDeferred), ok(assembler);
+  Node* step_action_address = __ ExternalConstant(
+      ExternalReference::debug_last_step_action_address(isolate_));
+  Node* step_action = __ Load(MachineType::Int8(), step_action_address);
+  STATIC_ASSERT(StepIn > StepNext);
+  STATIC_ASSERT(StepFrame > StepNext);
+  STATIC_ASSERT(LastStepAction == StepFrame);
+  Node* step_next = __ Int32Constant(StepNext);
+  __ Branch(__ Int32LessThanOrEqual(step_next, step_action), &if_stepping, &ok);
+  __ Bind(&ok);
+
+  Node* array =
+      __ LoadObjectField(generator, JSGeneratorObject::kRegisterFileOffset);
+  Node* context = __ GetContext();
+  Node* state = __ GetAccumulator();
+
+  __ ExportRegisterFile(array);
+  __ StoreObjectField(generator, JSGeneratorObject::kContextOffset, context);
+  __ StoreObjectField(generator, JSGeneratorObject::kContinuationOffset, state);
+
+  Node* offset = __ SmiTag(__ BytecodeOffset());
+  __ StoreObjectField(generator, JSAsyncGeneratorObject::kAwaitInputOffset,
+                      offset);
+
+  __ Dispatch();
+
+  __ Bind(&if_stepping);
+  {
+    Node* context = __ GetContext();
+    __ CallRuntime(Runtime::kDebugRecordGenerator, context, generator);
+    __ Goto(&ok);
+  }
+}
+
 // ResumeGenerator <generator>
 //
 // Imports the register file stored in the generator. Also loads the