func_test.result, item_cmpfunc.cc:

  Fixed bug #6187: a wrong initial setting for const_item_cache
  in Item_cond::fix_fields.

mysql-test/r/func_test.result

@@ -77,9 +77,9 @@ select * from t1 where 1 xor 1;
 a
 explain extended select * from t1 where 1 xor 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where (1 xor 1)
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1`
 select - a from t1;
 - a
 -1

sql/item_cmpfunc.cc

@@ -1956,7 +1956,7 @@ Item_cond::fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
   char buff[sizeof(char*)];			// Max local vars in function
 #endif
   not_null_tables_cache= used_tables_cache= 0;
-  const_item_cache= 0;
+  const_item_cache= 1;
   /*
     and_table_cache is the value that Item_cond_or() returns for
     not_null_tables()
@@ -2013,7 +2013,7 @@ void Item_cond::split_sum_func(Item **ref_pointer_array, List<Item> &fields)
   List_iterator<Item> li(list);
   Item *item;
   used_tables_cache=0;
-  const_item_cache=0;
+  const_item_cache=1;
   while ((item=li++))
   {
     if (item->with_sum_func && item->type() != SUM_FUNC_ITEM)