The "Delphi Upgrade Advisor wizard" for RAD Studio 13 is a new tools that enables developers to identify meaningful changes to project configuration and code, significantly improving compilation time and the overall code tooling experience. The wizard is available as a separate GetIt package.
You can read more details, based on a practical example at:
https://blogs.embarcadero.com/introducing-the-delphi-upgrade-advisor-wizard/
Notice that the code refers advice already made available, for example in this blog post:
https://blogs.embarcadero.com/some-suggestions-to-help-the-delphi-compiler/
If you have a large, old application, it's worth running the tool over it, and see what it suggests, including spotting nested circular unit references.