Table elimination is not used for tables inside semi-join

create table ten(a int);

insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);

create table one_k(a int);

insert into one_k select A.a + B.a* 10 + C.a * 100 from ten A, ten B, ten C;

create table t0 (a int, b int, c int);

insert into t0 select a,a,a from ten;

create table t1 (a int, b int, c int);

insert into t1 select a,a,a from ten;

create table t2 (pk int, b int, c int, primary key(pk));

insert into t2 select a,a,a from one_k;

create table t3 (pk int, b int, c int, primary key(pk));

insert into t3 select a,a,a from one_k;

explain select * from t0 

where t0.a in (

  select t1.a 

  from t1 

   left join t2 on t2.pk=t1.b

   left join t3 on t3.pk=t1.b

  );

+------+-------------+-------+--------+---------------+---------+---------+----------+------+------------------------------------------------------------------+

| id   | select_type | table | type   | possible_keys | key     | key_len | ref      | rows | Extra                                                            |

+------+-------------+-------+--------+---------------+---------+---------+----------+------+------------------------------------------------------------------+

|    1 | PRIMARY     | t0    | ALL    | NULL          | NULL    | NULL    | NULL     |   10 |                                                                  |

|    1 | PRIMARY     | t1    | ALL    | NULL          | NULL    | NULL    | NULL     |   10 | Using where; Start temporary; Using join buffer (flat, BNL join) |

|    1 | PRIMARY     | t2    | eq_ref | PRIMARY       | PRIMARY | 4       | j22.t1.b |    1 | Using where; Using index                                         |

|    1 | PRIMARY     | t3    | eq_ref | PRIMARY       | PRIMARY | 4       | j22.t1.b |    1 | Using where; Using index; End temporary                          |

+------+-------------+-------+--------+---------------+---------+---------+----------+------+------------------------------------------------------------------+

set optimizer_switch='semijoin=off';

explain ...

+------+--------------------+-------+------+---------------+------+---------+------+------+-------------+

| id   | select_type        | table | type | possible_keys | key  | key_len | ref  | rows | Extra       |

+------+--------------------+-------+------+---------------+------+---------+------+------+-------------+

|    1 | PRIMARY            | t0    | ALL  | NULL          | NULL | NULL    | NULL |   10 | Using where |

|    2 | DEPENDENT SUBQUERY | t1    | ALL  | NULL          | NULL | NULL    | NULL |   10 | Using where |

+------+--------------------+-------+------+---------------+------+---------+------+------+-------------+