Removing Used_tables_and_const_cache from "class udf_handler".

It was used only temporary, during udf_handler::fix_fields() time,
and then copied to the owner Item_func_or_sum object.
Changing the code to use the Used_tables_and_const_cache part
of the owner Item_sum_or_func object directly.

Author: Alexander Barkov

sql/item.h

@@ -3617,10 +3617,6 @@ class Used_tables_and_const_cache
     used_tables_cache= 0;
     const_item_cache= true;
   }
-  void used_tables_and_const_cache_copy(const Used_tables_and_const_cache *c)
-  {
-    *this= *c;
-  }
   void used_tables_and_const_cache_join(const Item *item)
   {
     used_tables_cache|= item->used_tables();

sql/item_func.cc

@@ -3508,7 +3508,7 @@ udf_handler::fix_fields(THD *thd, Item_func_or_sum *func,
 
   /* Fix all arguments */
   func->maybe_null=0;
-  used_tables_and_const_cache_init();
+  func->used_tables_and_const_cache_init();
 
   if ((f_args.arg_count=arg_count))
   {
@@ -3550,7 +3550,7 @@ udf_handler::fix_fields(THD *thd, Item_func_or_sum *func,
       func->with_sum_func= func->with_sum_func || item->with_sum_func;
       func->with_field= func->with_field || item->with_field;
       func->with_subselect|= item->with_subselect;
-      used_tables_and_const_cache_join(item);
+      func->used_tables_and_const_cache_join(item);
       f_args.arg_type[i]=item->result_type();
     }
     //TODO: why all following memory is not allocated with 1 call of sql_alloc?
@@ -3572,7 +3572,7 @@ udf_handler::fix_fields(THD *thd, Item_func_or_sum *func,
   func->fix_length_and_dec();
   initid.max_length=func->max_length;
   initid.maybe_null=func->maybe_null;
-  initid.const_item=const_item_cache;
+  initid.const_item=func->const_item_cache;
   initid.decimals=func->decimals;
   initid.ptr=0;
 
@@ -3637,13 +3637,12 @@ udf_handler::fix_fields(THD *thd, Item_func_or_sum *func,
     }
     func->max_length=MY_MIN(initid.max_length,MAX_BLOB_WIDTH);
     func->maybe_null=initid.maybe_null;
-    const_item_cache=initid.const_item;
-    /* 
-      Keep used_tables_cache in sync with const_item_cache.
-      See the comment in Item_udf_func::update_used tables.
-    */  
-    if (!const_item_cache && !used_tables_cache)
-      used_tables_cache= RAND_TABLE_BIT;
+    /*
+      The above call for init() can reset initid.const_item to "false",
+      e.g. when the UDF function wants to be non-deterministic.
+      See sequence_init() in udf_example.cc.
+    */
+    func->const_item_cache= initid.const_item;
     func->decimals=MY_MIN(initid.decimals,NOT_FIXED_DEC);
   }
   initialized=1;

sql/item_func.h

@@ -1364,6 +1364,15 @@ class Item_func_sleep :public Item_int_func
 
 class Item_udf_func :public Item_func
 {
+  /**
+    Mark "this" as non-deterministic if it uses no tables
+    and is not a constant at the same time.
+  */
+  void set_non_deterministic_if_needed()
+  {
+    if (!const_item_cache && !used_tables_cache)
+      used_tables_cache= RAND_TABLE_BIT;
+  }
 protected:
   udf_handler udf;
   bool is_expensive_processor(uchar *arg) { return TRUE; }
@@ -1379,7 +1388,7 @@ class Item_udf_func :public Item_func
   {
     DBUG_ASSERT(fixed == 0);
     bool res= udf.fix_fields(thd, this, arg_count, args);
-    used_tables_and_const_cache_copy(&udf);
+    set_non_deterministic_if_needed();
     fixed= 1;
     return res;
   }
@@ -1430,8 +1439,7 @@ class Item_udf_func :public Item_func
         !(used_tables_cache & RAND_TABLE_BIT))
     {
       Item_func::update_used_tables();
-      if (!const_item_cache && !used_tables_cache)
-        used_tables_cache= RAND_TABLE_BIT;
+      set_non_deterministic_if_needed();
     }
   }
   void cleanup();

sql/item_sum.h

@@ -1209,9 +1209,27 @@ class Item_udf_sum : public Item_sum
       return TRUE;
 
     fixed= 1;
+    /*
+      We set const_item_cache to false in constructors.
+      It can be later changed to "true", in a Item_sum::make_const() call.
+      No make_const() calls should have happened so far.
+    */
+    DBUG_ASSERT(!const_item_cache);
     if (udf.fix_fields(thd, this, this->arg_count, this->args))
       return TRUE;
-
+    /**
+      The above call for udf.fix_fields() updates
+      the Used_tables_and_const_cache part of "this" as if it was a regular
+      non-aggregate UDF function and can change both const_item_cache and
+      used_tables_cache members.
+      - The used_tables_cache will be re-calculated in update_used_tables()
+        which is called from check_sum_func() below. So we don't care about
+        its current value.
+      - The const_item_cache must stay "false" until a Item_sum::make_const()
+        call happens, if ever. So we need to reset const_item_cache back to
+        "false" here.
+    */
+    const_item_cache= false;
     memcpy (orig_args, args, sizeof (Item *) * arg_count);
     return check_sum_func(thd, ref);
   }

sql/sql_udf.h

@@ -52,7 +52,7 @@ typedef struct st_udf_func
 
 class Item_result_field;
 
-class udf_handler :public Sql_alloc, public Used_tables_and_const_cache
+class udf_handler :public Sql_alloc
 {
  protected:
   udf_func *u_d;