let merge ff1 ff2 =
let pdg1, fm1 = ff1.T.ff_marks in
let pdg2, fm2 = ff2.T.ff_marks in
assert (Db.Pdg.from_same_fun pdg1 pdg2) ;
let merge_marks m1 m2 = Marks.merge_marks [m1; m2] in
let merge_call_info _c1 _c2 = None in
let fm = FI.merge fm1 fm2 merge_marks merge_call_info in
(pdg1, fm)