Moving Used_tables_and_const_chache from Item_func to Item_func_or_sum

and thus reusing Used_tables_and_const_cache for Item_sum instead of
declaring the same members inside Item_sum.

Author: Alexander Barkov

sql/item.h

@@ -3663,7 +3663,9 @@ class Used_tables_and_const_cache
   An abstract class representing common features of
   regular functions and aggregate functions.
 */
-class Item_func_or_sum: public Item_result_field, public Item_args
+class Item_func_or_sum: public Item_result_field,
+                        public Item_args,
+                        public Used_tables_and_const_cache
 {
   bool agg_item_collations(DTCollation &c, const char *name,
                            Item **items, uint nitems,
@@ -3794,7 +3796,8 @@ class Item_func_or_sum: public Item_result_field, public Item_args
   Item_func_or_sum(THD *thd, Item *a, Item *b, Item *c, Item *d, Item *e):
     Item_result_field(thd), Item_args(a, b, c, d, e) { }
   Item_func_or_sum(THD *thd, Item_func_or_sum *item):
-    Item_result_field(thd, item), Item_args(thd, item) { }
+    Item_result_field(thd, item), Item_args(thd, item),
+    Used_tables_and_const_cache(item) { }
   Item_func_or_sum(THD *thd, List<Item> &list):
     Item_result_field(thd), Item_args(thd, list) { }
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
@@ -3821,6 +3824,8 @@ class Item_func_or_sum: public Item_result_field, public Item_args
   */
   virtual const char *func_name() const= 0;
   virtual void fix_length_and_dec()= 0;
+  bool const_item() const { return const_item_cache; }
+  table_map used_tables() const { return used_tables_cache; }
 };
 
 

sql/item_func.cc

@@ -441,12 +441,6 @@ void Item_func::split_sum_func(THD *thd, Item **ref_pointer_array,
 }
 
 
-table_map Item_func::used_tables() const
-{
-  return used_tables_cache;
-}
-
-
 table_map Item_func::not_null_tables() const
 {
   return not_null_tables_cache;

sql/item_func.h

@@ -31,7 +31,7 @@ extern "C"				/* Bug in BSDI include file */
 #endif
 
 
-class Item_func :public Item_func_or_sum, public Used_tables_and_const_cache
+class Item_func :public Item_func_or_sum
 {
   void sync_with_sum_func_and_with_field(List<Item> &list);
 protected:
@@ -106,8 +106,8 @@ class Item_func :public Item_func_or_sum, public Used_tables_and_const_cache
     set_arguments(thd, list);
   }
   // Constructor used for Item_cond_and/or (see Item comment)
-  Item_func(THD *thd, Item_func *item)
-   :Item_func_or_sum(thd, item), Used_tables_and_const_cache(item),
+  Item_func(THD *thd, Item_func *item):
+    Item_func_or_sum(thd, item),
     allowed_arg_cols(item->allowed_arg_cols),
     not_null_tables_cache(item->not_null_tables_cache)
   {
@@ -120,7 +120,6 @@ class Item_func :public Item_func_or_sum, public Used_tables_and_const_cache
   }
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   void quick_fix_field();
-  table_map used_tables() const;
   table_map not_null_tables() const;
   void update_used_tables()
   {
@@ -137,7 +136,6 @@ class Item_func :public Item_func_or_sum, public Used_tables_and_const_cache
   }
   bool eq(const Item *item, bool binary_cmp) const;
   virtual Item *key_item() const { return args[0]; }
-  virtual bool const_item() const { return const_item_cache; }
   void set_arguments(THD *thd, List<Item> &list)
   {
     allowed_arg_cols= 1;

sql/item_sum.cc

@@ -401,8 +401,7 @@ bool Item_sum::collect_outer_ref_processor(uchar *param)
 }
 
 
-Item_sum::Item_sum(THD *thd, List<Item> &list): Item_func_or_sum(thd, list),
-  forced_const(FALSE)
+Item_sum::Item_sum(THD *thd, List<Item> &list): Item_func_or_sum(thd, list)
 {
   if (!(orig_args= (Item **) thd->alloc(sizeof(Item *) * arg_count)))
   {
@@ -423,9 +422,7 @@ Item_sum::Item_sum(THD *thd, Item_sum *item):
   aggr_sel(item->aggr_sel),
   nest_level(item->nest_level), aggr_level(item->aggr_level),
   quick_group(item->quick_group),
-  orig_args(NULL),
-  used_tables_cache(item->used_tables_cache),
-  forced_const(item->forced_const) 
+  orig_args(NULL)
 {
   if (arg_count <= 2)
   {
@@ -449,6 +446,7 @@ void Item_sum::mark_as_sum_func()
   SELECT_LEX *cur_select= current_thd->lex->current_select;
   cur_select->n_sum_items++;
   cur_select->with_sum_func= 1;
+  const_item_cache= false;
   with_sum_func= 1;
   with_field= 0;
 }
@@ -538,7 +536,7 @@ Field *Item_sum::create_tmp_field(bool group, TABLE *table,
 
 void Item_sum::update_used_tables ()
 {
-  if (!forced_const)
+  if (!Item_sum::const_item())
   {
     used_tables_cache= 0;
     for (uint i=0 ; i < arg_count ; i++)
@@ -610,7 +608,7 @@ void Item_sum::cleanup()
     aggr= NULL;
   }
   Item_result_field::cleanup();
-  forced_const= FALSE; 
+  const_item_cache= false;
 }
 
 Item *Item_sum::result_item(THD *thd, Field *field)
@@ -2073,7 +2071,6 @@ void Item_sum_hybrid::cleanup()
 {
   DBUG_ENTER("Item_sum_hybrid::cleanup");
   Item_sum::cleanup();
-  forced_const= FALSE;
   if (cmp)
     delete cmp;
   cmp= 0;

sql/item_sum.h

@@ -302,7 +302,13 @@ class st_select_lex;
   We assume that the nesting level of subquries does not exceed 127.
   TODO: to catch queries where the limit is exceeded to make the
   code clean here.  
-    
+
+  @note
+  The implementation takes into account the used strategy:
+  - Items resolved at optimization phase return 0 from Item_sum::used_tables().
+  - Items that depend on the number of join output records, but not columns of
+  any particular table (like COUNT(*)), returm 0 from Item_sum::used_tables(),
+  but still return false from Item_sum::const_item().
 */
 
 class Item_sum :public Item_func_or_sum
@@ -368,32 +374,25 @@ class Item_sum :public Item_func_or_sum
     the current argument list can be altered by usage of temporary tables.
   */
   Item **orig_args, *tmp_orig_args[2];
-  table_map used_tables_cache;
 
-  /*
-    TRUE <=> We've managed to calculate the value of this Item in
-    opt_sum_query(), hence it can be considered constant at all subsequent
-    steps.
-  */
-  bool forced_const;
   static ulonglong ram_limitation(THD *thd);
 
 public:  
 
   void mark_as_sum_func();
-  Item_sum(THD *thd): Item_func_or_sum(thd), quick_group(1), forced_const(FALSE)
+  Item_sum(THD *thd): Item_func_or_sum(thd), quick_group(1)
   {
     mark_as_sum_func();
     init_aggregator();
   }
   Item_sum(THD *thd, Item *a): Item_func_or_sum(thd, a), quick_group(1),
-    orig_args(tmp_orig_args), forced_const(FALSE)
+    orig_args(tmp_orig_args)
   {
     mark_as_sum_func();
     init_aggregator();
   }
   Item_sum(THD *thd, Item *a, Item *b): Item_func_or_sum(thd, a, b),
-    quick_group(1), orig_args(tmp_orig_args), forced_const(FALSE)
+    quick_group(1), orig_args(tmp_orig_args)
   {
     mark_as_sum_func();
     init_aggregator();
@@ -433,16 +432,6 @@ class Item_sum :public Item_func_or_sum
   virtual void fix_length_and_dec() { maybe_null=1; null_value=1; }
   virtual Item *result_item(THD *thd, Field *field);
 
-  /*
-    Return bitmap of tables that are needed to evaluate the item.
-
-    The implementation takes into account the used strategy: items resolved
-    at optimization phase will report 0.
-    Items that depend on the number of join output records, but not columns
-    of any particular table (like COUNT(*)) will report 0 from used_tables(),
-    but will still return false from const_item().
-  */
-  table_map used_tables() const { return used_tables_cache; }
   void update_used_tables ();
   COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                           bool link_item_fields,
@@ -458,12 +447,17 @@ class Item_sum :public Item_func_or_sum
                                    cond_equal_ref);
   }
   bool is_null() { return null_value; }
+  /**
+    make_const()
+    Called if we've managed to calculate the value of this Item in
+    opt_sum_query(), hence it can be considered constant at all subsequent
+    steps.
+  */
   void make_const () 
   { 
     used_tables_cache= 0; 
-    forced_const= TRUE; 
+    const_item_cache= true;
   }
-  virtual bool const_item() const { return forced_const; }
   virtual bool const_during_execution() const { return false; }
   virtual void print(String *str, enum_query_type query_type);
   void fix_num_length_and_dec();