auto x_1 = ConjugateHelper(scope, op.input(0));
  auto x_2 = ConjugateHelper(scope, op.input(1));
  // y = (x_1 - x_2)^2
  // dy/dx_1 = 2 * (x_1 - x_2)
  // dy/dx_2 = -2 * (x_1 - x_2)
  auto two = Cast(scope, Const(scope, 2), grad_inputs[0].type());
  auto gx_1 = Mul(scope, grad_inputs[0], Mul(scope, two, Sub(scope, x_1, x_2)));
  auto gx_2 = Neg(scope, gx_1);

"top" function is configurable.

For example, the code
  x.a()
  x.b()
  %c = y.c()
  x.d(%c)
would be transformed into something like
  call @x_1()
  %c = call @y_1()
  call @x_2(%c)
with @x_1, @x_2 and @y_1 filled in.
### `-tf-guarantee-all-funcs-one-use`

_Guarantee all FuncOp's have only a single use._

### `-tf-hoist-loop-invariant`