Fixed bug #25027.

Blocked evaluation of constant objects of the classes
Item_func_is_null and Item_is_not_null_test at the
prepare phase in the cases when the objects used subqueries. 


mysql-test/r/ps.result:
  Extended test case for bug #25027.
mysql-test/t/ps.test:
  Extended test case for bug #25027.
sql/sql_lex.cc:
  Returned back the assertion in st_select_lex_unit::set_limit,
  removed by the previous commit for this bug.

mysql-test/r/ps.result

@@ -1528,5 +1528,12 @@ a
 1
 2
 DEALLOCATE PREPARE stmt;
+PREPARE stmt FROM 'SELECT a FROM t1 WHERE (SELECT b FROM t2 limit ?) IS NULL';
+SET @arg=1;
+EXECUTE stmt USING @arg;
+a
+1
+2
+DEALLOCATE PREPARE stmt;
 DROP TABLE t1,t2;
 End of 5.0 tests.

mysql-test/t/ps.test

@@ -1577,8 +1577,13 @@ SELECT a FROM t1 WHERE (SELECT b FROM t2) IS NULL;
 PREPARE stmt FROM 'SELECT a FROM t1 WHERE (SELECT b FROM t2) IS NULL';
 
 EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
 
+PREPARE stmt FROM 'SELECT a FROM t1 WHERE (SELECT b FROM t2 limit ?) IS NULL';
+SET @arg=1;
+EXECUTE stmt USING @arg;
 DEALLOCATE PREPARE stmt;
+
 DROP TABLE t1,t2;
 
 --echo End of 5.0 tests.

sql/item_cmpfunc.cc

@@ -2990,7 +2990,7 @@ longlong Item_func_isnull::val_int()
     Handle optimization if the argument can't be null
     This has to be here because of the test in update_used_tables().
   */
-  if (!used_tables_cache)
+  if (!used_tables_cache && !with_subselect)
     return cached_value;
   return args[0]->is_null() ? 1: 0;
 }
@@ -2999,7 +2999,7 @@ longlong Item_is_not_null_test::val_int()
 {
   DBUG_ASSERT(fixed == 1);
   DBUG_ENTER("Item_is_not_null_test::val_int");
-  if (!used_tables_cache)
+  if (!used_tables_cache && !with_subselect)
   {
     owner->was_null|= (!cached_value);
     DBUG_PRINT("info", ("cached :%ld", (long) cached_value));
@@ -3026,7 +3026,7 @@ void Item_is_not_null_test::update_used_tables()
   else
   {
     args[0]->update_used_tables();
-    if (!(used_tables_cache=args[0]->used_tables()))
+    if (!(used_tables_cache=args[0]->used_tables()) && !with_subselect)
     {
       /* Remember if the value is always NULL or never NULL */
       cached_value= (longlong) !args[0]->is_null();

sql/item_cmpfunc.h

@@ -1028,7 +1028,8 @@ public:
     else
     {
       args[0]->update_used_tables();
-      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables())))
+      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables())) &&
+          !with_subselect)
       {
 	/* Remember if the value is always NULL or never NULL */
 	cached_value= (longlong) args[0]->is_null();

sql/sql_lex.cc

@@ -1903,6 +1903,7 @@ void st_select_lex_unit::set_limit(SELECT_LEX *sl)
 {
   ha_rows select_limit_val;
 
+  DBUG_ASSERT(! thd->stmt_arena->is_stmt_prepare());
   select_limit_val= (ha_rows)(sl->select_limit ? sl->select_limit->val_uint() :
                                                  HA_POS_ERROR);
   offset_limit_cnt= (ha_rows)(sl->offset_limit ? sl->offset_limit->val_uint() :