// all the gradients from the shape it fills.
  // We use ReduceSum to implement this, which needs an argument providing
  // the indices of all the dimensions of the incoming gradient.
  // grad(x) = reduce_sum(grad(y), [0..rank(grad(y))])
  auto all_dims = Range(scope, Const(scope, 0), Rank(scope, grad_inputs[0]),
                        Const(scope, 1));
  grad_outputs->push_back(ReduceSum(scope, grad_inputs[0], all_dims));
  return scope.status();

      scope, Slice1dHelper(scope, x_shape, bx_start, bx_end),
      Slice1dHelper(scope, y_shape, by_start, by_end));
  grad_x = Reshape(
      scope, ReduceSum(scope, grad_x, Add(scope, bx_start, args.r0)), x_shape);
  grad_y = Reshape(
      scope, ReduceSum(scope, grad_y, Add(scope, by_start, args.r1)), y_shape);
  grad_outputs->push_back(grad_x);
  grad_outputs->push_back(grad_y);
  return scope.status();
}