Greetings Günther,
Sorry for taking so long to reply to you.
You are correct that Flow.merge() does indeed seem to be a deadcode, or at least it hasn't been called when we run the checker on the test suite or our case studies.
Unfortunately, Flow is the least documented code. And we are planning to rewrite it once the time permits. For the time-being, should you have any question or request for a sample code for anything, please shoot us an email.
I also recommend looking up the Gen-Kill program analysis (usually described in most compiler references).
Regards,
Mahmood