message: Skip unknown devices since we can't optimize for them
diff: @@ -340,8 +340,11 @@ Status GraphExecutionState::OptimizeGraph(
  std::unordered_map<string, DeviceProperties> device_map;
  Device* cpu_device = nullptr;
  for (const auto& device : device_set_->devices()) {
  - device_map[device->name()] =
  - grappler::GetDeviceInfo(device->parsed_name());
  + DeviceProperties props = grappler::GetDeviceInfo(device->parsed_name());
  + if (props.type() == "UNKNOWN") {
  + continue;
  + }
  + device_map[device->name()] = props;
  if (device->parsed_name().id == 0 &&
  StringPiece(device->parsed_name().type) == "CPU" &&
  device->GetAllocator(AllocatorAttributes()) != nullptr) {
  