Kill previous defs. `addr_list` is a list of normalized addresses.

def _kill(self, live_defs, variable, code_loc):
        """
        Kill previous defs. `addr_list` is a list of normalized addresses.
        """

        # Case 1: address perfectly match, we kill
        # Case 2: a is a subset of the original address
        # Case 3: a is a superset of the original address

        live_defs[variable] = { code_loc }
        l.debug("XX CodeLoc %s kills variable %s", code_loc, variable)