[esnext] prototype runtime implementation for async functions

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 8013f1078f459d7cb83d4786ad6913a48c926668..e3eabe451c8405768607d6df24a0ec115891c328 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -2331,9 +2331,11 @@ void Builtins::Generate_MathTrunc(CodeStubAssembler* assembler) {
 
 namespace {
 
+enum class ResumeType { Generator, Async };
+
 void Generate_GeneratorPrototypeResume(
     CodeStubAssembler* assembler, JSGeneratorObject::ResumeMode resume_mode,
-    char const* const method_name) {
+    char const* const method_name, ResumeType type) {
   typedef CodeStubAssembler::Label Label;
   typedef compiler::Node Node;
 
@@ -2345,24 +2347,29 @@ void Generate_GeneratorPrototypeResume(
 
   // Check if the {receiver} is actually a JSGeneratorObject.
   Label if_receiverisincompatible(assembler, Label::kDeferred);
-  assembler->GotoIf(assembler->WordIsSmi(receiver), &if_receiverisincompatible);
-  Node* receiver_instance_type = assembler->LoadInstanceType(receiver);
-  assembler->GotoUnless(assembler->Word32Equal(
-                            receiver_instance_type,
-                            assembler->Int32Constant(JS_GENERATOR_OBJECT_TYPE)),
-                        &if_receiverisincompatible);
+  if (type == ResumeType::Generator || FLAG_debug_code) {
+    assembler->GotoIf(assembler->WordIsSmi(receiver),
+                      &if_receiverisincompatible);
+    Node* receiver_instance_type = assembler->LoadInstanceType(receiver);
+    assembler->GotoUnless(assembler->Word32Equal(receiver_instance_type,
+                                                 assembler->Int32Constant(
+                                                     JS_GENERATOR_OBJECT_TYPE)),
+                          &if_receiverisincompatible);
+  }
 
   // Check if the {receiver} is running or already closed.
   Node* receiver_continuation = assembler->LoadObjectField(
       receiver, JSGeneratorObject::kContinuationOffset);
   Label if_receiverisclosed(assembler, Label::kDeferred),
       if_receiverisrunning(assembler, Label::kDeferred);
-  assembler->GotoIf(assembler->SmiEqual(receiver_continuation, closed),
-                    &if_receiverisclosed);
-  DCHECK_LT(JSGeneratorObject::kGeneratorExecuting,
-            JSGeneratorObject::kGeneratorClosed);
-  assembler->GotoIf(assembler->SmiLessThan(receiver_continuation, closed),
-                    &if_receiverisrunning);
+  if (type == ResumeType::Generator || FLAG_debug_code) {
+    assembler->GotoIf(assembler->SmiEqual(receiver_continuation, closed),
+                      &if_receiverisclosed);
+    DCHECK_LT(JSGeneratorObject::kGeneratorExecuting,
+              JSGeneratorObject::kGeneratorClosed);
+    assembler->GotoIf(assembler->SmiLessThan(receiver_continuation, closed),
+                      &if_receiverisrunning);
+  }
 
   // Resume the {receiver} using our trampoline.
   Node* result = assembler->CallStub(
@@ -2371,7 +2378,7 @@ void Generate_GeneratorPrototypeResume(
   assembler->Return(result);
 
   assembler->Bind(&if_receiverisincompatible);
-  {
+  if (type == ResumeType::Generator || FLAG_debug_code) {
     // The {receiver} is not a valid JSGeneratorObject.
     Node* result = assembler->CallRuntime(
         Runtime::kThrowIncompatibleMethodReceiver, context,
@@ -2381,8 +2388,8 @@ void Generate_GeneratorPrototypeResume(
     assembler->Return(result);  // Never reached.
   }
 
-  assembler->Bind(&if_receiverisclosed);
-  {
+  if (type == ResumeType::Generator || FLAG_debug_code) {
+    assembler->Bind(&if_receiverisclosed);
     // The {receiver} is closed already.
     Node* result = nullptr;
     switch (resume_mode) {
@@ -2403,8 +2410,8 @@ void Generate_GeneratorPrototypeResume(
     assembler->Return(result);
   }
 
-  assembler->Bind(&if_receiverisrunning);
-  {
+  if (type == ResumeType::Generator || FLAG_debug_code) {
+    assembler->Bind(&if_receiverisrunning);
     Node* result =
         assembler->CallRuntime(Runtime::kThrowGeneratorRunning, context);
     assembler->Return(result);  // Never reached.
@@ -2416,19 +2423,32 @@ void Generate_GeneratorPrototypeResume(
 // ES6 section 25.3.1.2 Generator.prototype.next ( value )
 void Builtins::Generate_GeneratorPrototypeNext(CodeStubAssembler* assembler) {
   Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kNext,
-                                    "[Generator].prototype.next");
+                                    "[Generator].prototype.next",
+                                    ResumeType::Generator);
 }
 
 // ES6 section 25.3.1.3 Generator.prototype.return ( value )
 void Builtins::Generate_GeneratorPrototypeReturn(CodeStubAssembler* assembler) {
   Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kReturn,
-                                    "[Generator].prototype.return");
+                                    "[Generator].prototype.return",
+                                    ResumeType::Generator);
 }
 
 // ES6 section 25.3.1.4 Generator.prototype.throw ( exception )
 void Builtins::Generate_GeneratorPrototypeThrow(CodeStubAssembler* assembler) {
   Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kThrow,
-                                    "[Generator].prototype.throw");
+                                    "[Generator].prototype.throw",
+                                    ResumeType::Generator);
+}
+
+void Builtins::Generate_AsyncFunctionNext(CodeStubAssembler* assembler) {
+  Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kNext,
+                                    "[AsyncFunction].next", ResumeType::Async);
+}
+
+void Builtins::Generate_AsyncFunctionThrow(CodeStubAssembler* assembler) {
+  Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kThrow,
+                                    "[AsyncFunction].throw", ResumeType::Async);
 }
 
 // -----------------------------------------------------------------------------