Closed generator returns a completed object instead of throwing a error

src/ia32/full-codegen-ia32.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 2056 matching lines @@
       break;
     }
   }
 }
 
 
 void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
     Expression *value,
     JSGeneratorObject::ResumeMode resume_mode) {
   // The value stays in eax, and is ultimately read by the resumed generator, as
-  // if the CallRuntime(Runtime::kSuspendJSGeneratorObject) returned it.  ebx
-  // 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.
+  // ebx will hold the generator object until the activation has been resumed.
   VisitForStackValue(generator);
   VisitForAccumulatorValue(value);
   __ pop(ebx);
 
   // 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);
   __ cmp(FieldOperand(ebx, JSGeneratorObject::kContinuationOffset),
          Immediate(Smi::FromInt(0)));
-  __ j(less_equal, &wrong_state);
+  __ j(equal, &closed_state);
+  __ j(less, &wrong_state);
 
   // Load suspended function and context.
   __ mov(esi, FieldOperand(ebx, JSGeneratorObject::kContextOffset));
   __ mov(edi, FieldOperand(ebx, JSGeneratorObject::kFunctionOffset));
 
   // Push receiver.
   __ push(FieldOperand(ebx, JSGeneratorObject::kReceiverOffset));
 
   // Push holes for arguments to generator function.
   __ mov(edx, FieldOperand(edi, JSFunction::kSharedFunctionInfoOffset));
@@ skipping 49 matching lines @@
   __ push(ecx);
   __ jmp(&push_operand_holes);
   __ bind(&call_resume);
   __ push(ebx);
   __ 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.
+    __ push(Immediate(isolate()->factory()->undefined_value()));
+    // Pop value from top-of-stack slot; box result into result register.
+    EmitCreateIteratorResult(true);
+  } else {
+    // Throw the provided value.
+    __ push(eax);
+    __ CallRuntime(Runtime::kThrow, 1);

[Michael Starzinger, 2014/01/14 13:17:44]

I am not sure if throwing directly from within here without first restoring all
stack handlers is generally correct. IMHO we should drop into the runtime at
this point similar to what we do for a general JSGeneratorObject::THROW. I think
this can be achieved by moving the "closed_state" block above the "slow_resume"
block and simply fall-through in the case of JSGeneratorObject::THROW. Please
correct me if I am missing something. I was thinking about a structure along the
lines of ...

// If we are sending a value and there is no operand stack, we can jump back
// in directly.
if (resume_mode == JSGeneratorObject::NEXT) {
  [...]
}

// Reach here when generator is closed.
__ bind(&closed_state);
if (resume_mode == JSGeneratorObject::NEXT) {
  [...]
}

// Otherwise, we push holes for the operand stack and call the runtime to fix
// up the stack and the handlers.
__ bind(&slow_resume);
[...]

+  }
+  __ jmp(&done);
+
   // Throw error if we attempt to operate on a running generator.
   __ bind(&wrong_state);
   __ push(ebx);
   __ CallRuntime(Runtime::kThrowGeneratorStateError, 1);
 
   __ bind(&done);
   context()->Plug(result_register());
 }
 
 
@@ skipping 2720 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_IA32