You put your design through a multitude of tools for various transformations.
Going back to formal verification in between every change to rely on your simulation tools can be a rigorous approach, but wait... there is an easier way: Use equivalence checking, with Conformal® Equivalence Checker.
And that easier way is made even easier with these videos on how to do your equivalence checking, along with a few of the gotchas and tricks to make it more useful.
Check these videos out:
Conformal Equivalence Checker - Nonequivalences (Video Channel)
Conformal Equivalence Checker - Aborts (Video)
But, if you want a full training, try this course instead: Conformal Equivalence Checking (cadence.com)