Closed generator returns a completed object instead of throwing a error

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 674f64efe52b137e71210b2b9bad0553b2085798..eb0963d576626e796f0d33532884dd61cb25208b 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -2092,19 +2092,21 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
     Expression *value,
     JSGeneratorObject::ResumeMode resume_mode) {
   // The value stays in rax, and is ultimately read by the resumed generator, as
-  // if the CallRuntime(Runtime::kSuspendJSGeneratorObject) returned it.  rbx
-  // will hold the generator object until the activation has been resumed.
+  // if the CallRuntime(Runtime::kSuspendJSGeneratorObject) returned it. Or used
+  // to throw the value when the resumed generator is already closed. rbx will
+  // hold the generator object until the activation has been resumed.
   VisitForStackValue(generator);
   VisitForAccumulatorValue(value);
   __ pop(rbx);
 
   // Check generator state.
-  Label wrong_state, done;
-  STATIC_ASSERT(JSGeneratorObject::kGeneratorExecuting <= 0);
-  STATIC_ASSERT(JSGeneratorObject::kGeneratorClosed <= 0);
+  Label wrong_state, closed_state, done;
+  STATIC_ASSERT(JSGeneratorObject::kGeneratorExecuting < 0);
+  STATIC_ASSERT(JSGeneratorObject::kGeneratorClosed == 0);
   __ SmiCompare(FieldOperand(rbx, JSGeneratorObject::kContinuationOffset),
                 Smi::FromInt(0));
-  __ j(less_equal, &wrong_state);
+  __ j(equal, &closed_state);
+  __ j(less, &wrong_state);
 
   // Load suspended function and context.
   __ movq(rsi, FieldOperand(rbx, JSGeneratorObject::kContextOffset));
@@ -2175,6 +2177,20 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
   // Not reached: the runtime call returns elsewhere.
   __ Abort(kGeneratorFailedToResume);
 
+  // Reach here when generator is closed.
+  __ bind(&closed_state);
+  if (resume_mode == JSGeneratorObject::NEXT) {
+    // Return completed iterator result when generator is closed.
+    __ PushRoot(Heap::kUndefinedValueRootIndex);
+    // Pop value from top-of-stack slot; box result into result register.
+    EmitCreateIteratorResult(true);
+  } else {
+    // Throw the provided value.
+    __ push(rax);
+    __ CallRuntime(Runtime::kThrow, 1);
+  }
+  __ jmp(&done);
+
   // Throw error if we attempt to operate on a running generator.
   __ bind(&wrong_state);
   __ push(rbx);