Add support for irreducible CFG #2007

Job	Run time
Boogie CI (Debug, batch_mode=True)	5m 14s
Boogie CI (Debug, batch_mode=False)	5m 13s
Boogie CI (Release, batch_mode=True)	4m 55s
Boogie CI (Release, batch_mode=False)	5m 2s
	20m 24s

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