WIP [esnext] implement async iteration proposal

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index b76d3357a32e9f4c2fc3750895f75471d3fd5909..5518366739045750dd0fa116c324d7e851449a05 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -390,6 +390,7 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(PROMISE_REACTION_JOB_INFO_TYPE)                             \
   V(DEBUG_INFO_TYPE)                                            \
   V(BREAK_POINT_INFO_TYPE)                                      \
+  V(ASYNC_GENERATOR_REQUEST_TYPE)                               \
   V(PROTOTYPE_INFO_TYPE)                                        \
   V(TUPLE2_TYPE)                                                \
   V(TUPLE3_TYPE)                                                \
@@ -416,6 +417,8 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(JS_ARGUMENTS_TYPE)                                          \
   V(JS_CONTEXT_EXTENSION_OBJECT_TYPE)                           \
   V(JS_GENERATOR_OBJECT_TYPE)                                   \
+  V(JS_ASYNC_GENERATOR_OBJECT_TYPE)                             \
+  V(JS_ASYNC_FROM_SYNC_ITERATOR_TYPE)                           \
   V(JS_MODULE_NAMESPACE_TYPE)                                   \
   V(JS_ARRAY_TYPE)                                              \
   V(JS_ARRAY_BUFFER_TYPE)                                       \
@@ -565,7 +568,8 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(CONTEXT_EXTENSION, ContextExtension, context_extension)                  \
   V(CONSTANT_ELEMENTS_PAIR, ConstantElementsPair, constant_elements_pair)    \
   V(MODULE, Module, module)                                                  \
-  V(MODULE_INFO_ENTRY, ModuleInfoEntry, module_info_entry)
+  V(MODULE_INFO_ENTRY, ModuleInfoEntry, module_info_entry)                   \
+  V(ASYNC_GENERATOR_REQUEST, AsyncGeneratorRequest, async_generator_request)
 
 // We use the full 8 bits of the instance_type field to encode heap object
 // instance types.  The high-order bit (bit 7) is set if the object is not a
@@ -729,6 +733,7 @@ enum InstanceType {
   BOX_TYPE,
   PROMISE_RESOLVE_THENABLE_JOB_INFO_TYPE,
   PROMISE_REACTION_JOB_INFO_TYPE,
+  ASYNC_GENERATOR_REQUEST_TYPE,
   DEBUG_INFO_TYPE,
   BREAK_POINT_INFO_TYPE,
   PROTOTYPE_INFO_TYPE,
@@ -764,6 +769,8 @@ enum InstanceType {
   JS_ARGUMENTS_TYPE,
   JS_CONTEXT_EXTENSION_OBJECT_TYPE,
   JS_GENERATOR_OBJECT_TYPE,
+  JS_ASYNC_GENERATOR_OBJECT_TYPE,
+  JS_ASYNC_FROM_SYNC_ITERATOR_TYPE,
   JS_MODULE_NAMESPACE_TYPE,
   JS_ARRAY_TYPE,
   JS_ARRAY_BUFFER_TYPE,
@@ -1056,6 +1063,7 @@ template <class C> inline bool Is(Object* obj);
   V(JSArgumentsObject)           \
   V(JSContextExtensionObject)    \
   V(JSGeneratorObject)           \
+  V(JSAsyncGeneratorObject)      \
   V(JSModuleNamespace)           \
   V(Map)                         \
   V(DescriptorArray)             \
@@ -2763,6 +2771,22 @@ class JSIteratorResult: public JSObject {
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSIteratorResult);
 };
 
+class JSAsyncFromSyncIterator : public JSObject {
+ public:
+  // Async-from-Sync Iterator instances are ordinary objects that inherit
+  // properties from the %AsyncFromSyncIteratorPrototype% intrinsic object.
+  // Async-from-Sync Iterator instances are initially created with the internal
+  // slots listed in Table 4.
+  // (proposal-async-iteration/#table-async-from-sync-iterator-internal-slots)
+  DECL_ACCESSORS(sync_iterator, HeapObject)
+
+  // Offsets of object fields.
+  static const int kSyncIteratorOffset = JSObject::kHeaderSize;
+  static const int kSize = kSyncIteratorOffset + kPointerSize;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(JSAsyncFromSyncIterator);
+};
 
 // Common superclass for JSSloppyArgumentsObject and JSStrictArgumentsObject.
 class JSArgumentsObject: public JSObject {
@@ -6642,6 +6666,30 @@ class PromiseReactionJobInfo : public Struct {
   DISALLOW_IMPLICIT_CONSTRUCTORS(PromiseReactionJobInfo);
 };
 
+class AsyncGeneratorRequest : public Struct {
+ public:
+  // Holds an AsyncGeneratorRequest, or Undefined.
+  DECL_ACCESSORS(next, Object)
+  DECL_INT_ACCESSORS(resume_mode)
+  DECL_ACCESSORS(value, Object)
+  DECL_ACCESSORS(promise, Object)
+  DECL_ACCESSORS(awaited_promise, Object)
+
+  static const int kNextOffset = Struct::kHeaderSize;
+  static const int kResumeModeOffset = kNextOffset + kPointerSize;
+  static const int kValueOffset = kResumeModeOffset + kPointerSize;
+  static const int kPromiseOffset = kValueOffset + kPointerSize;
+  static const int kAwaitedPromiseOffset = kPromiseOffset + kPointerSize;
+  static const int kSize = kAwaitedPromiseOffset + kPointerSize;
+
+  DECLARE_CAST(AsyncGeneratorRequest)
+  DECLARE_PRINTER(AsyncGeneratorRequest)
+  DECLARE_VERIFIER(AsyncGeneratorRequest)
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(AsyncGeneratorRequest);
+};
+
 // A simple one-element struct, useful where smis need to be boxed.
 class Box : public Struct {
  public:
@@ -7886,9 +7934,10 @@ class JSGeneratorObject: public JSObject {
   // [input_or_debug_pos]
   // For executing generators: the most recent input value.
   // For suspended generators: debug information (bytecode offset).
-  // There is currently no need to remember the most recent input value for a
-  // suspended generator.
+  // If a generator has been suspended via Await(), then the previous input
+  // value is moved to the Await value register, and restored on resume.
   DECL_ACCESSORS(input_or_debug_pos, Object)
+  DECL_ACCESSORS(await_input, Object)
 
   // [resume_mode]: The most recent resume mode.
   enum ResumeMode { kNext, kReturn, kThrow };
@@ -7926,7 +7975,8 @@ class JSGeneratorObject: public JSObject {
   static const int kContextOffset = kFunctionOffset + kPointerSize;
   static const int kReceiverOffset = kContextOffset + kPointerSize;
   static const int kInputOrDebugPosOffset = kReceiverOffset + kPointerSize;
-  static const int kResumeModeOffset = kInputOrDebugPosOffset + kPointerSize;
+  static const int kAwaitInputOffset = kInputOrDebugPosOffset + kPointerSize;
+  static const int kResumeModeOffset = kAwaitInputOffset + kPointerSize;
   static const int kContinuationOffset = kResumeModeOffset + kPointerSize;
   static const int kRegisterFileOffset = kContinuationOffset + kPointerSize;
   static const int kSize = kRegisterFileOffset + kPointerSize;
@@ -7935,6 +7985,30 @@ class JSGeneratorObject: public JSObject {
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGeneratorObject);
 };
 
+class JSAsyncGeneratorObject : public JSGeneratorObject {
+ public:
+  DECLARE_CAST(JSAsyncGeneratorObject)
+
+  // Dispatched behavior.
+  DECLARE_VERIFIER(JSAsyncGeneratorObject)
+
+  // [queue]
+  // Pointer to the head of a singly linked list of AsyncGeneratorRequest, or
+  // undefined.
+  DECL_ACCESSORS(queue, HeapObject)
+
+  // [awaited_promise]
+  // A reference to the Promise of an AwaitExpression.
+  DECL_ACCESSORS(awaited_promise, HeapObject)
+
+  // Layout description.
+  static const int kQueueOffset = JSGeneratorObject::kSize;
+  static const int kSize = kQueueOffset + kPointerSize;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(JSAsyncGeneratorObject);
+};
+
 class ModuleInfoEntry : public Struct {
  public:
   DECLARE_CAST(ModuleInfoEntry)