def list_vars(self):
        """list variables used (read/written) in this parfor by
        traversing the body and combining block uses.
        """
        all_uses = []
        for l, b in self.loop_body.items():
            for stmt in b.body:
                all_uses += stmt.list_vars()

        for loop in self.loop_nests:
            all_uses += loop.list_vars()

        for stmt in self.init_block.body:
            all_uses += stmt.list_vars()

        return all_uses
list variables used (read/written) in this parfor by
        traversing the body and combining block uses.
        
numba/parfors/parfor.py