VLOG(1) << "Guaranteed const found: " << src_arg.first->DebugString();
      src_arg.second->AddAttr("_is_guaranteed_constant", true);
    }
  }
}

struct OutputInputTensorPairHasher {
  uint64 operator()(std::pair<OutputTensor, InputTensor> const& s) const {
    return Hash64Combine(OutputTensor::Hash()(s.first),
                         InputTensor::Hash()(s.second));
  }
};