How to use the ailment.Expr.BasePointerOffset function in ailment

def _ail_handle_Add(self, expr):
        operand_0 = self._expr(expr.operands[0])
        operand_1 = self._expr(expr.operands[1])

        if isinstance(operand_0, Expr.Const) and isinstance(operand_1, Expr.Const):
            return Expr.Const(expr.idx, None, operand_0.value + operand_1.value, expr.bits)
        elif isinstance(operand_0, Expr.BasePointerOffset) and isinstance(operand_1, Expr.Const):
            r = operand_0.copy()
            r.offset += operand_1.value
            return r
        return Expr.BinaryOp(expr.idx, 'Add', [operand_0 if operand_0 is not None else expr.operands[0],
                                               operand_1 if operand_1 is not None else expr.operands[1]
                                               ])

self._link_variables_on_expr(variable_manager, block, stmt_idx, stmt, expr.operands[0])
                self._link_variables_on_expr(variable_manager, block, stmt_idx, stmt, expr.operands[1])

        elif type(expr) is ailment.Expr.UnaryOp:
            variables = variable_manager.find_variables_by_atom(block.addr, stmt_idx, expr)
            if len(variables) == 1:
                var, offset = next(iter(variables))
                expr.referenced_variable = var
                expr.offset = offset
            else:
                self._link_variables_on_expr(variable_manager, block, stmt_idx, stmt, expr.operands)

        elif type(expr) is ailment.Expr.Convert:
            self._link_variables_on_expr(variable_manager, block, stmt_idx, stmt, expr.operand)

        elif isinstance(expr, ailment.Expr.BasePointerOffset):
            variables = variable_manager.find_variables_by_atom(block.addr, stmt_idx, expr)
            if len(variables) == 1:
                var, offset = next(iter(variables))
                expr.referenced_variable = var
                expr.offset = offset