BUG#24127: merge fixes: If subselect is a union, dont allocate several

identical pushed_cond_guards arrays. Allocate only one always.

mysql-test/r/subselect.result

@@ -1464,7 +1464,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index; Full scan on NULL key
 Warnings:
-Note	1003	select `test`.`t1`.`s1` AS `s1`,not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL having trigcond(<is_not_null_test>(`test`.`t2`.`s1`)))))) AS `s1 NOT IN (SELECT s1 FROM t2)` from `test`.`t1`
+Note	1003	select `test`.`t1`.`s1` AS `s1`,(not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL having trigcond(<is_not_null_test>(`test`.`t2`.`s1`))))))) AS `s1 NOT IN (SELECT s1 FROM t2)` from `test`.`t1`
 explain extended select s1, s1 = ANY (SELECT s1 FROM t2) from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
@@ -1476,13 +1476,13 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index; Full scan on NULL key
 Warnings:
-Note	1003	select `test`.`t1`.`s1` AS `s1`,not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL having trigcond(<is_not_null_test>(`test`.`t2`.`s1`)))))) AS `s1 <> ALL (SELECT s1 FROM t2)` from `test`.`t1`
+Note	1003	select `test`.`t1`.`s1` AS `s1`,(not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL having trigcond(<is_not_null_test>(`test`.`t2`.`s1`))))))) AS `s1 <> ALL (SELECT s1 FROM t2)` from `test`.`t1`
 explain extended select s1, s1 NOT IN (SELECT s1 FROM t2 WHERE s1 < 'a2') from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index; Using where; Full scan on NULL key
 Warnings:
-Note	1003	select `test`.`t1`.`s1` AS `s1`,not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL where (`test`.`t2`.`s1` < _latin1'a2') having trigcond(<is_not_null_test>(`test`.`t2`.`s1`)))))) AS `s1 NOT IN (SELECT s1 FROM t2 WHERE s1 < 'a2')` from `test`.`t1`
+Note	1003	select `test`.`t1`.`s1` AS `s1`,(not(<in_optimizer>(`test`.`t1`.`s1`,<exists>(<index_lookup>(<cache>(`test`.`t1`.`s1`) in t2 on s1 checking NULL where (`test`.`t2`.`s1` < _latin1'a2') having trigcond(<is_not_null_test>(`test`.`t2`.`s1`))))))) AS `s1 NOT IN (SELECT s1 FROM t2 WHERE s1 < 'a2')` from `test`.`t1`
 drop table t1,t2;
 create table t2 (a int, b int);
 create table t3 (a int);

mysql-test/t/subselect3.test

@@ -46,7 +46,6 @@ select a, oref, a in (select max(ie)
 explain extended
 select a, oref from t2 
 where a in (select max(ie) from t1 where oref=t2.oref group by grp);
-
 select a, oref, a in (
   select max(ie) from t1 where oref=t2.oref group by grp union
   select max(ie) from t1 where oref=t2.oref group by grp

sql/item_subselect.cc

@@ -948,7 +948,7 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 
     unit->uncacheable|= UNCACHEABLE_DEPENDENT;
   }
-  if (!abort_on_null && left_expr->maybe_null)
+  if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
   {
     if (!(pushed_cond_guards= (bool*)join->thd->alloc(sizeof(bool))))
       DBUG_RETURN(RES_ERROR);
@@ -1163,7 +1163,7 @@ Item_in_subselect::row_value_transformer(JOIN *join)
     thd->lex->current_select= current;
     unit->uncacheable|= UNCACHEABLE_DEPENDENT;
 
-    if (!abort_on_null && left_expr->maybe_null)
+    if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
     {
       if (!(pushed_cond_guards= (bool*)join->thd->alloc(sizeof(bool) *
                                                         left_expr->cols())))