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

src/builtins/builtins-generator-gen.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins-utils-gen.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
 class GeneratorBuiltinsAssembler : public CodeStubAssembler {
  public:
   explicit GeneratorBuiltinsAssembler(compiler::CodeAssemblerState* state)
       : CodeStubAssembler(state) {}
 
  protected:
   void GeneratorPrototypeResume(Node* receiver, Node* value, Node* context,
                                 JSGeneratorObject::ResumeMode resume_mode,
                                 char const* const method_name);
 };
 
 void GeneratorBuiltinsAssembler::GeneratorPrototypeResume(
     Node* receiver, Node* value, Node* context,
     JSGeneratorObject::ResumeMode resume_mode, char const* const method_name) {
   Node* closed = SmiConstant(JSGeneratorObject::kGeneratorClosed);

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

Nit: move this down to where it's used.

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

Done.

 
   // Check if the {receiver} is actually a JSGeneratorObject.
   Label if_receiverisincompatible(this, Label::kDeferred);
   GotoIf(TaggedIsSmi(receiver), &if_receiverisincompatible);
   Node* receiver_instance_type = LoadInstanceType(receiver);
   GotoIfNot(Word32Equal(receiver_instance_type,
                         Int32Constant(JS_GENERATOR_OBJECT_TYPE)),
             &if_receiverisincompatible);
 
   // Check if the {receiver} is running or already closed.
   Node* receiver_continuation =
       LoadObjectField(receiver, JSGeneratorObject::kContinuationOffset);
   Label if_receiverisclosed(this, Label::kDeferred),
       if_receiverisrunning(this, Label::kDeferred);
   GotoIf(SmiEqual(receiver_continuation, closed), &if_receiverisclosed);
   DCHECK_LT(JSGeneratorObject::kGeneratorExecuting,
             JSGeneratorObject::kGeneratorClosed);
   GotoIf(SmiLessThan(receiver_continuation, closed), &if_receiverisrunning);
 
   // Resume the {receiver} using our trampoline.
   VARIABLE(var_exception, MachineRepresentation::kTagged, UndefinedConstant());
   Label if_exception(this, Label::kDeferred), if_final_return(this);
   Node* result =
       CallStub(CodeFactory::ResumeGenerator(isolate()), context, value,
                receiver, SmiConstant(resume_mode),
                SmiConstant(static_cast<int>(SuspendFlags::kGeneratorYield)));
   // 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()));
   }
 
   BIND(&if_receiverisincompatible);
   {
     // The {receiver} is not a valid JSGeneratorObject.
     CallRuntime(Runtime::kThrowIncompatibleMethodReceiver, context,
                 HeapConstant(
@@ skipping 60 matching lines @@
   Node* receiver = Parameter(Descriptor::kReceiver);
   Node* exception = Parameter(Descriptor::kException);
   Node* context = Parameter(Descriptor::kContext);
   GeneratorPrototypeResume(receiver, exception, context,
                            JSGeneratorObject::kThrow,
                            "[Generator].prototype.throw");
 }
 
 }  // namespace internal
 }  // namespace v8