Added item.real_type() for easy access to the underlaying types for Item_ref and Item_cache_wrapper()

This allows us to simplify and speed up some tests and also remove get_cached_item()

sql/item.h:
  Added item.real_type()
  Removed get_cached_item()
sql/opt_range.cc:
  Simplify test
sql/sql_select.cc:
  Simplify test
sql/sql_show.cc:
  Simplify test

sql/item.h

@@ -609,6 +609,12 @@ public:
   virtual enum_field_types string_field_type() const;
   virtual enum_field_types field_type() const;
   virtual enum Type type() const =0;
+  /*
+    real_type() is the type of base item.  This is same as type() for
+    most items, except Item_ref() and Item_cache_wrapper() where it
+    shows the type for the underlaying item.
+  */
+  virtual enum Type real_type() const { return type(); }
   
   /*
     Return information about function monotonicity. See comment for
@@ -1185,7 +1191,6 @@ public:
   bool eq_by_collation(Item *item, bool binary_cmp, CHARSET_INFO *cs); 
 
   Item* set_expr_cache(THD *thd, List<Item*> &depends_on);
-  virtual Item *get_cached_item() { return NULL; }
 };
 
 
@@ -2437,6 +2442,8 @@ public:
   Item_ref(THD *thd, Item_ref *item)
     :Item_ident(thd, item), result_field(item->result_field), ref(item->ref) {}
   enum Type type() const		{ return REF_ITEM; }
+  enum Type real_type() const           { return ref ? (*ref)->type() :
+                                          REF_ITEM; }
   bool eq(const Item *item, bool binary_cmp) const
   { 
     Item *it= ((Item *) item)->real_item();
@@ -2628,7 +2635,7 @@ public:
 
   const char *func_name() const { return "<expr_cache>"; }
   enum Type type() const { return EXPR_CACHE_ITEM; }
-  virtual Item *get_cached_item() { return orig_item; }
+  enum Type real_type() const { return orig_item->type(); }
 
   bool set_cache(THD *thd, List<Item*> &depends_on);
 

sql/opt_range.cc

@@ -11707,9 +11707,7 @@ check_group_min_max_predicates(COND *cond, Item_field *min_max_arg_item,
     the MIN/MAX argument field, and disallow the optimization only if this is
     so.
   */
-  if (cond_type == Item::SUBSELECT_ITEM ||
+  if (cond->real_type() == Item::SUBSELECT_ITEM)
-      (cond->get_cached_item() &&
-       cond->get_cached_item()->type() == Item::SUBSELECT_ITEM))
     DBUG_RETURN(FALSE);
 
   /*

sql/sql_select.cc

@@ -12055,9 +12055,7 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
       {
         if (item->used_tables() & OUTER_REF_TABLE_BIT)
           item->update_used_tables();
-        if (type == Item::SUBSELECT_ITEM ||
+        if ((item->real_type() == Item::SUBSELECT_ITEM) ||
-            (item->get_cached_item() &&
-             item->get_cached_item()->type() == Item::SUBSELECT_ITEM ) ||
             (item->used_tables() & ~OUTER_REF_TABLE_BIT))
         {
 	  /*
@@ -17989,9 +17987,7 @@ setup_copy_fields(THD *thd, TMP_TABLE_PARAM *param,
       }
     }
     else if ((real_pos->type() == Item::FUNC_ITEM ||
-	      real_pos->type() == Item::SUBSELECT_ITEM ||
+	      real_pos->real_type() == Item::SUBSELECT_ITEM ||
-              (real_pos->get_cached_item() &&
-               real_pos->get_cached_item()->type() == Item::SUBSELECT_ITEM) ||
 	      real_pos->type() == Item::CACHE_ITEM ||
 	      real_pos->type() == Item::COND_ITEM) &&
 	     !real_pos->with_sum_func)

sql/sql_show.cc

@@ -3003,10 +3003,7 @@ bool uses_only_table_name_fields(Item *item, TABLE_LIST *table)
   else if (item->type() == Item::REF_ITEM)
     return uses_only_table_name_fields(item->real_item(), table);
 
-  if ((item->type() == Item::SUBSELECT_ITEM ||
+  if (item->real_type() == Item::SUBSELECT_ITEM && !item->const_item())
-      (item->get_cached_item() &&
-       item->get_cached_item()->type() == Item::SUBSELECT_ITEM))
-      && !item->const_item())
     return 0;
 
   return 1;