// evaluated.
  Scope grad_scope = scope.WithControlDependencies(grad);
  auto y = ConjugateHelper(grad_scope, op.output(0));
  grad_outputs->push_back(internal::SigmoidGrad(grad_scope, y, grad));
  return grad_scope.status();
}
REGISTER_GRADIENT_OP("Sigmoid", SigmoidGrad);

Status SignGrad(const Scope& scope, const Operation& op,
                const std::vector<Output>& grad_inputs,

            "ReciprocalGrad", "RsqrtGrad", "SqrtGrad", "TruncateDiv",
            "TruncateMod", "Equal", "NotEqual", "Greater", "GreaterEqual",
            "Less", "LessEqual", "SigmoidGrad", "SoftplusGrad", "SoftsignGrad",
            "TanhGrad", "Pow", "SquaredDifference", "ApproximateEqual",
            // Others
            "AddN", "Bitcast", "Cast", "ClipByValue", "Const", "Empty",