Class descriptions are not only put into diagrams, they're interactive controls. Ten years ago, the model-driven development trends focused on making more and more of the code driveable by UI representations and code. People tried to model code using UML or UML-like representations, with two-way links. Tooling inferred models from existing code.

For more current approaches, see "Code Maps" in the VS 2015 release notes here - https://www.visualstudio.com/en-us/news/releasenotes/vs2015-...

Doing proper control flow is done less often for the reasons I explained. Profilers do it better. See e.g. the Call Graph in AQTime: https://support.smartbear.com/viewarticle/43205/ - it lets you drill through the callers and callees of each function as seen in practice. This means it can see through polymorphism, reflection, dynamic loading, function pointers - all the things that make static analysis infeasible.