create table t1 (a int, b int);

insert into t1

values (1,2), (4,6), (9,7), (1,1), (2,5), (7,8);

set @@in_predicate_conversion_threshold= 2;

prepare stmt from "select * from t1 where a in (1,2)";

execute stmt;

execute stmt;

  Type_holder *holders;

  ...

  if (!(holders= new (thd->stmt_arena->mem_root) Type_holder[cnt]) ||

      join_type_handlers_for_tvc(thd, li, holders, cnt) ||

      get_type_attributes_for_tvc(thd, li, holders,

                                                  lists_of_values.elements, cnt))