Not super closely related: the polytope model (to the degree I'm familiar with it) is used as a representation that facilitates optimization of loop nests. That's optimization in the sense of finding an efficient program.

DiscoGrad deals with (or provides gradients for) mathematical optimization. In our case, the goal is to minimize or maximize the program's numerical output by adjusting it's input parameters. Typically, your C++ program will run somewhat slower with DiscoGrad than without, but you can now use gradient descent to quickly find the best possible input parameters.