Add support for irreducible CFG #2010

Job	Run time
Boogie CI (Release, batch_mode=False)	5m 11s
Boogie CI (Debug, batch_mode=True)	5m 3s
Boogie CI (Debug, batch_mode=False)	5m 16s
Boogie CI (Release, batch_mode=True)	4m 50s
	20m 20s

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