Move closing of generators upon final return to the generator-resume builtin.

src/builtins/builtins-generator-gen.cc

Index: src/builtins/builtins-generator-gen.cc
diff --git a/src/builtins/builtins-generator-gen.cc b/src/builtins/builtins-generator-gen.cc
index 4fdb4addad91878d21ff5fba7d8648ebebbda8ab..aab01afd283b5c4110ca78b68eb02ca46dbf6636 100644
--- a/src/builtins/builtins-generator-gen.cc
+++ b/src/builtins/builtins-generator-gen.cc
@@ -56,18 +56,27 @@ void GeneratorBuiltinsAssembler::GeneratorPrototypeResume(
   // Make sure we close the generator if there was an exception.
   GotoIfException(result, &if_exception, &var_exception);
 
-  // If the generator is not suspended (i.e., it's state is 'closed'),
-  // wrap the return value in IteratorResult.
+  // If the generator is not suspended (i.e., it's state is 'executing'),

[neis, 2017/06/13 10:58:17]

s/it's/its/

[Jarin, 2017/06/13 11:05:56]

Done.

+  // close it and wrap the return value in IteratorResult.
   Node* result_continuation =
       LoadObjectField(receiver, JSGeneratorObject::kContinuationOffset);
-  GotoIf(SmiEqual(result_continuation, closed), &if_final_return);
+
+  // The generator function should not close the generator by itself, let's
+  // check it is indeed not closed yet.
+  CSA_ASSERT(this, SmiNotEqual(result_continuation, closed));
+
+  Node* executing = SmiConstant(JSGeneratorObject::kGeneratorExecuting);
+  GotoIf(SmiEqual(result_continuation, executing), &if_final_return);
+
   Return(result);

[neis, 2017/06/13 10:58:17]

Please add a comment saying that on suspend the generator function already
wrapped the result.

[Jarin, 2017/06/13 11:05:56]

Done.

 
   Callable create_iter_result_object =
       Builtins::CallableFor(isolate(), Builtins::kCreateIterResultObject);
-
   BIND(&if_final_return);
   {
+    // Close the generator.
+    StoreObjectFieldNoWriteBarrier(
+        receiver, JSGeneratorObject::kContinuationOffset, closed);
     // Return the wrapped result.
     Return(
         CallStub(create_iter_result_object, context, result, TrueConstant()));