Fixed bug mdev-4336.

When iterating over a list of conditions using List_iterator
the function remove_eq_conds should skip all predicates that
replace a condition from the list. Otherwise it can come to
an infinite recursion. 

mysql-test/r/join_outer.result

@@ -1822,4 +1822,18 @@ b	c	d
 5	8	88
 5	8	81
 DROP TABLE t1,t2;
+#
+# Bug mdev-4336: LEFT JOIN with disjunctive 
+#                <non-nullable datetime field> IS NULL in WHERE 
+#                causes a hang and eventual crash   
+#
+CREATE TABLE t1 (
+id int(11) NOT NULL,
+modified datetime NOT NULL,
+PRIMARY KEY (id)
+);
+SELECT a.* FROM t1 a LEFT JOIN t1 b ON a.id = b.id 
+WHERE a.modified > b.modified or b.modified IS NULL;
+id	modified
+DROP TABLE t1;
 SET optimizer_switch=@save_optimizer_switch;

mysql-test/r/join_outer_jcl6.result

@@ -1833,6 +1833,20 @@ b	c	d
 5	8	88
 5	8	81
 DROP TABLE t1,t2;
+#
+# Bug mdev-4336: LEFT JOIN with disjunctive 
+#                <non-nullable datetime field> IS NULL in WHERE 
+#                causes a hang and eventual crash   
+#
+CREATE TABLE t1 (
+id int(11) NOT NULL,
+modified datetime NOT NULL,
+PRIMARY KEY (id)
+);
+SELECT a.* FROM t1 a LEFT JOIN t1 b ON a.id = b.id 
+WHERE a.modified > b.modified or b.modified IS NULL;
+id	modified
+DROP TABLE t1;
 SET optimizer_switch=@save_optimizer_switch;
 set join_cache_level=default;
 show variables like 'join_cache_level';

mysql-test/t/join_outer.test

@@ -1359,4 +1359,21 @@ ORDER BY t1.b;
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # Bug mdev-4336: LEFT JOIN with disjunctive 
+--echo #                <non-nullable datetime field> IS NULL in WHERE 
+--echo #                causes a hang and eventual crash   
+--echo #
+
+CREATE TABLE t1 (
+  id int(11) NOT NULL,
+  modified datetime NOT NULL,
+  PRIMARY KEY (id)
+);
+
+SELECT a.* FROM t1 a LEFT JOIN t1 b ON a.id = b.id 
+  WHERE a.modified > b.modified or b.modified IS NULL;
+
+DROP TABLE t1;
+
 SET optimizer_switch=@save_optimizer_switch;

sql/sql_select.cc

@@ -13197,7 +13197,8 @@ remove_eq_conds(THD *thd, COND *cond, Item::cond_result *cond_value)
             else
 	    {
               Item *list_item;
-              Item *new_list_item;      
+              Item *new_list_item; 
+              uint cnt= new_item_and_list->elements;     
               List_iterator<Item> it(*new_item_and_list);
               while ((list_item= it++))
 	      {
@@ -13211,7 +13212,9 @@ remove_eq_conds(THD *thd, COND *cond, Item::cond_result *cond_value)
                   it.replace(new_list_item);
                 new_list_item->update_used_tables();
               }              
-              li.replace(*new_item_and_list);  
+              li.replace(*new_item_and_list);
+              for (cnt--; cnt; cnt--)
+                item= li++;  
             }
             cond_and_list->concat((List<Item>*) cond_equal_items); 
           }
@@ -13232,7 +13235,13 @@ remove_eq_conds(THD *thd, COND *cond, Item::cond_result *cond_value)
           if (new_item->type() == Item::COND_ITEM &&
               ((Item_cond*) new_item)->functype() == 
               ((Item_cond*) cond)->functype())
-            li.replace(*((Item_cond*) new_item)->argument_list());
+	  {
+            List<Item> *arg_list= ((Item_cond*) new_item)->argument_list();
+            uint cnt= arg_list->elements;
+            li.replace(*arg_list);
+            for ( cnt--; cnt; cnt--)
+              item= li++;
+          }
 	  else
             li.replace(new_item);
         }