MDEV-14959: Moved calculation the number of items reserved for exists to in transformation

It is done now before call of select_lex->setup_ref_array()
in order to avoid allocation of SP/PS's memory on its second invocation.

sql/sql_select.cc

@@ -727,8 +727,7 @@ setup_without_group(THD *thd, Ref_ptr_array ref_pointer_array,
                               ORDER *group,
                               List<Window_spec> &win_specs,
 		              List<Item_window_func> &win_funcs,
-                              bool *hidden_group_fields,
-                              uint *reserved)
+                              bool *hidden_group_fields)
 {
   int res;
   enum_parsing_place save_place;
@@ -743,13 +742,6 @@ setup_without_group(THD *thd, Ref_ptr_array ref_pointer_array,
 
   thd->lex->allow_sum_func.clear_bit(select->nest_level);
   res= setup_conds(thd, tables, leaves, conds);
-  if (thd->lex->current_select->first_cond_optimization)
-  {
-    if (!res && *conds && ! thd->lex->current_select->merged_into)
-      (*reserved)= (*conds)->exists2in_reserved_items();
-    else
-      (*reserved)= 0;
-  }
 
   /* it's not wrong to have non-aggregated columns in a WHERE */
   select->set_non_agg_field_used(saved_non_agg_field_used);
@@ -1318,6 +1310,15 @@ JOIN::prepare(TABLE_LIST *tables_init,
   if (setup_wild(thd, tables_list, fields_list, &all_fields, wild_num,
                  &select_lex->hidden_bit_fields))
     DBUG_RETURN(-1);
+
+  if (thd->lex->current_select->first_cond_optimization)
+  {
+    if ( conds && ! thd->lex->current_select->merged_into)
+      select_lex->select_n_reserved= conds->exists2in_reserved_items();
+    else
+      select_lex->select_n_reserved= 0;
+  }
+
   if (select_lex->setup_ref_array(thd, real_og_num))
     DBUG_RETURN(-1);
 
@@ -1336,8 +1337,7 @@ JOIN::prepare(TABLE_LIST *tables_init,
                           all_fields, &conds, order, group_list,
                           select_lex->window_specs,
                           select_lex->window_funcs,
-                          &hidden_group_fields,
-                          &select_lex->select_n_reserved))
+                          &hidden_group_fields))
     DBUG_RETURN(-1);
 
   /*