bself: add a method to obtain paths of last k iterations of a loop

from slowbeast.symexe.statesset import intersection, union, complement

from slowbeast.symexe.symbolicexecution import SEStats

from slowbeast.symexe.annotations import AssertAnnotation

from slowbeast.kindse.annotatedcfa import AnnotatedCFAPath

from slowbeast.kindse.programstructure import ProgramStructure

from slowbeast.kindse.naive.naivekindse import Result

from slowbeast.kindse import KindSEOptions

            if yield_seq:

                yield seq

    def _last_k_iteration_paths(self, L, k = 0):

        """ Obtain the paths that correspond to the last k iterations of the loop """

        is_error_loc = L.cfa().is_err

        exits = [p for p in L.get_exit_paths() if not is_error_loc(p.last_loc())]

        if k == 0:

            return exits

        loop_paths = L.paths()

        paths = [e.edges() for e in exits]

        while k > 0:

            # we loose annotations if any -- but there should be none in this case

            paths = [l.edges() + s for l in loop_paths for s in paths]

            k -= 1

        return [AnnotatedCFAPath(p) for p in paths]

    def _initial_sets_from_exits(self, E, L: LoopInfo):

        """

        Strengthen the initial sequence through obtaining the

        last safe iteration of the loop.

        """

        is_error_loc = L.cfa().is_err

        create_set = self.create_set

        # execute the safe path that avoids error and then jumps out of the loop