MDEV-7950 Item_func::type() takes 0.26% in OLTP RO

Step#5: changing the function remove_eq_conds() into a virtual method in Item.
It removes 6 virtual calls for Item_func::type(), and adds only 2
virtual calls for Item***::remove_eq_conds().

sql/item.h

@@ -1135,6 +1135,8 @@ class Item: public Type_std_attributes
     DBUG_ASSERT(!cond_equal_ref || !cond_equal_ref[0]);
     return this;
   }
+  virtual COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
+                                bool top_level);
   /*
     Checks whether the item is:
     - a simple equality (field=field_item or field=constant_item), or

sql/item_cmpfunc.h

@@ -409,6 +409,8 @@ class Item_bool_func2 :public Item_bool_func
     Item_bool_func::cleanup();
     cmp.cleanup();
   }
+  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
+                        bool top_level);
 
   friend class  Arg_comparator;
 };
@@ -1467,6 +1469,8 @@ class Item_func_isnull :public Item_func_null_predicate
       const_item_cache= args[0]->const_item();
     }
   }
+  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
+                        bool top_level);
   table_map not_null_tables() const { return 0; }
   Item *neg_transformer(THD *thd);
 };
@@ -1775,6 +1779,8 @@ class Item_cond :public Item_bool_func
   COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                           bool link_item_fields,
                           COND_EQUAL **cond_equal_ref);
+  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
+                        bool top_level);
   virtual void print(String *str, enum_query_type query_type);
   void split_sum_func(THD *thd, Item **ref_pointer_array, List<Item> &fields);
   friend int setup_conds(THD *thd, TABLE_LIST *tables, TABLE_LIST *leaves,

sql/sql_delete.cc

@@ -372,7 +372,7 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   if (conds)
   {
     Item::cond_result result;
-    conds= remove_eq_conds(thd, conds, &result);
+    conds= conds->remove_eq_conds(thd, &result, true);
     if (result == Item::COND_FALSE)             // Impossible where
     {
       limit= 0;

sql/sql_select.h

@@ -1803,7 +1803,6 @@ bool cp_buffer_from_ref(THD *thd, TABLE *table, TABLE_REF *ref);
 bool error_if_full_join(JOIN *join);
 int report_error(TABLE *table, int error);
 int safe_index_read(JOIN_TAB *tab);
-COND *remove_eq_conds(THD *thd, COND *cond, Item::cond_result *cond_value);
 int get_quick_record(SQL_SELECT *select);
 SORT_FIELD * make_unireg_sortorder(THD *thd, ORDER *order, uint *length,
                                   SORT_FIELD *sortorder);

sql/sql_update.cc

@@ -377,7 +377,7 @@ int mysql_update(THD *thd,
   if (conds)
   {
     Item::cond_result cond_value;
-    conds= remove_eq_conds(thd, conds, &cond_value);
+    conds= conds->remove_eq_conds(thd, &cond_value, true);
     if (cond_value == Item::COND_FALSE)
     {
       limit= 0;                                   // Impossible WHERE