In reply to cgales:
I strongly recommend cgales advice about use your tool’s coverage capabilities to collect toggle coverage.
Regardless of how you collect coverage, you would want to use an associate array to model a 2GB memory. They only allocate array elements that are explicitly written to. Any test that you could run would only have enough time to use a tiny fraction of the array, and that all you need to toggle a 32-bits of an address register.