def get_phi_variables(self, block_addr):
        """
        Get a dict of phi variables and their corresponding variables.

        :param int block_addr:  Address of the block.
        :return:                A dict of phi variables of an empty dict if there are no phi variables at the block.
        :rtype:                 dict
        """

        if block_addr not in self._phi_variables_by_block:
            return dict()
        variables = { }
        for phi in self._phi_variables_by_block[block_addr]:
            variables[phi] = self._phi_variables[phi]
        return variables