found bug in cf while reviewing the code

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
now marking back edges on CFG construction

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
correctly analyzing general acyclic in loops now

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
added test to make sure we can find acyclic regions headed by if statments

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
added test for iaote nested in if

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>