Closed generator returns a completed object instead of throwing a error

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2074 matching lines @@
       break;
     }
   }
 }
 
 
 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 it
+  // is read 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));
   __ movq(rdi, FieldOperand(rbx, JSGeneratorObject::kFunctionOffset));
 
   // Push receiver.
   __ push(FieldOperand(rbx, JSGeneratorObject::kReceiverOffset));
 
   // Push holes for arguments to generator function.
   __ movq(rdx, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
@@ skipping 50 matching lines @@
   __ push(rcx);
   __ jmp(&push_operand_holes);
   __ bind(&call_resume);
   __ push(rbx);
   __ push(result_register());
   __ Push(Smi::FromInt(resume_mode));
   __ CallRuntime(Runtime::kResumeJSGeneratorObject, 3);
   // 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);
   __ CallRuntime(Runtime::kThrowGeneratorStateError, 1);
 
   __ bind(&done);
   context()->Plug(result_register());
 }
 
 
@@ skipping 2695 matching lines @@
 
   ASSERT_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64