MDEV-23001 Precreate static Item_bool() to simplify code

The following changes where done:
- Create global Item: Item_false and Item_true
- Replace all creation if 'FALSE' and 'TRUE' top level items used for
  WHERE/HAVING/ON clauses to use Item_false and Item_true.

The benefit are:
- Less and faster code
- No test needed if we where able to create the new item.
- Fixed possible errors if 'new' would have failed for the Item_bool's

fixup! 470277728d2e27fe057cf33a437a9e40e1a04b61

sql/item.cc

@@ -55,7 +55,8 @@ const char *item_empty_name="";
 const char *item_used_name= "\0";
 
 static int save_field_in_field(Field *, bool *, Field *, bool);
-
+const Item_bool_static Item_false("FALSE", 0);
+const Item_bool_static Item_true("TRUE", 1);
 
 /**
   Compare two Items for List<Item>::add_unique()
@@ -438,6 +439,21 @@ Item::Item(THD *thd):
   }
 }
 
+/*
+  This is only used for static const items
+*/
+
+Item::Item():
+  is_expensive_cache(-1), name(null_clex_str), orig_name(0)
+{
+  DBUG_ASSERT(my_progname == NULL); // before main()
+  marker= 0;
+  maybe_null= null_value= with_window_func= with_field= false;
+  in_rollup= 0;
+  with_param= 0;
+  join_tab_idx= MAX_TABLES;
+}
+
 
 const TABLE_SHARE *Item::field_table_or_null()
 {
@@ -3630,6 +3646,7 @@ String *Item_int::val_str(String *str)
   return str;
 }
 
+
 void Item_int::print(String *str, enum_query_type query_type)
 {
   StringBuffer<LONGLONG_BUFFER_SIZE+1> buf;

sql/item.h

@@ -963,6 +963,7 @@ public:
      optimisation changes in prepared statements
   */
   Item(THD *thd, Item *item);
+  Item();                                        /* For const item */
   virtual ~Item()
   {
 #ifdef EXTRA_DEBUG
@@ -1986,7 +1987,7 @@ public:
   virtual bool limit_index_condition_pushdown_processor(void *arg) { return 0; }
   virtual bool exists2in_processor(void *arg) { return 0; }
   virtual bool find_selective_predicates_list_processor(void *arg) { return 0; }
-  bool cleanup_is_expensive_cache_processor(void *arg)
+  virtual bool cleanup_is_expensive_cache_processor(void *arg)
   {
     is_expensive_cache= (int8)(-1);
     return 0;
@@ -2837,6 +2838,7 @@ protected:
     fix_charset_and_length(str.charset(), dv, Metadata(&str));
   }
   Item_basic_value(THD *thd): Item(thd) {}
+  Item_basic_value(): Item() {}
 public:
   Field *create_tmp_field_ex(MEM_ROOT *root,
                              TABLE *table, Tmp_field_src *src,
@@ -2866,6 +2868,7 @@ class Item_basic_constant :public Item_basic_value
 {
 public:
   Item_basic_constant(THD *thd): Item_basic_value(thd) {};
+  Item_basic_constant(): Item_basic_value() {};
   bool check_vcol_func_processor(void *arg) { return false; }
   const Item_const *get_item_const() const { return this; }
   virtual Item_basic_constant *make_string_literal_concat(THD *thd,
@@ -3247,10 +3250,14 @@ class Item_literal: public Item_basic_constant
 public:
   Item_literal(THD *thd): Item_basic_constant(thd)
   { }
+  Item_literal(): Item_basic_constant()
+  {}
   Type type() const override { return CONST_ITEM; }
-  bool check_partition_func_processor(void *) override { return false;}
+  bool check_partition_func_processor(void *int_arg) override { return false;}
   bool const_item() const override { return true; }
   bool basic_const_item() const override { return true; }
+  bool is_expensive() override { return false; }
+  bool cleanup_is_expensive_cache_processor(void *arg) override { return 0; }
 };
 
 
@@ -3258,6 +3265,7 @@ class Item_num: public Item_literal
 {
 public:
   Item_num(THD *thd): Item_literal(thd) { collation= DTCollation_numeric(); }
+  Item_num(): Item_literal() { collation= DTCollation_numeric(); }
   Item *safe_charset_converter(THD *thd, CHARSET_INFO *tocs) override;
   bool get_date(THD *thd, MYSQL_TIME *ltime, date_mode_t fuzzydate) override
   {
@@ -4236,6 +4244,13 @@ public:
       name.str= str_arg; name.length= safe_strlen(name.str);
       unsigned_flag= flag;
     }
+  Item_int(const char *str_arg,longlong i,size_t length):
+    Item_num(), value(i)
+    {
+      max_length=(uint32)length;
+      name.str= str_arg; name.length= safe_strlen(name.str);
+      unsigned_flag= 1;
+    }
   Item_int(THD *thd, const char *str_arg, size_t length=64);
   const Type_handler *type_handler() const override
   { return type_handler_long_or_longlong(); }
@@ -4270,6 +4285,8 @@ public:
   Item_bool(THD *thd, const char *str_arg, longlong i):
     Item_int(thd, str_arg, i, 1) {}
   Item_bool(THD *thd, bool i) :Item_int(thd, (longlong) i, 1) { }
+  Item_bool(const char *str_arg, longlong i):
+    Item_int(str_arg, i, 1) {}
   bool is_bool_literal() const override { return true; }
   Item *neg_transformer(THD *thd) override;
   const Type_handler *type_handler() const override
@@ -4286,6 +4303,18 @@ public:
 };
 
 
+class Item_bool_static :public Item_bool
+{
+public:
+  Item_bool_static(const char *str_arg, longlong i):
+    Item_bool(str_arg, i) {};
+
+  void set_join_tab_idx(uint join_tab_idx_arg) override
+  { DBUG_ASSERT(0); }
+};
+
+extern const Item_bool_static Item_false, Item_true;
+
 class Item_uint :public Item_int
 {
 public:

sql/item_xmlfunc.cc

@@ -1176,13 +1176,13 @@ my_xpath_keyword(MY_XPATH *x,
 
 static Item *create_func_true(MY_XPATH *xpath, Item **args, uint nargs)
 {
-  return new (xpath->thd->mem_root) Item_bool(xpath->thd, "xpath_bool", 1);
+  return (Item*) &Item_true;
 }
 
 
 static Item *create_func_false(MY_XPATH *xpath, Item **args, uint nargs)
 {
-  return new (xpath->thd->mem_root) Item_bool(xpath->thd, "xpath_bool", 0);
+  return (Item*) &Item_false;
 }
 
 

sql/opt_index_cond_pushdown.cc

@@ -185,8 +185,8 @@ bool uses_index_fields_only(Item *item, TABLE *tbl, uint keyno,
 static Item *make_cond_for_index(THD *thd, Item *cond, TABLE *table, uint keyno,
                                  bool other_tbls_ok)
 {
-  if (!cond)
+  if (!cond || cond->basic_const_item())
-    return NULL;
+    return cond;
   if (cond->type() == Item::COND_ITEM)
   {
     uint n_marked= 0;
@@ -218,7 +218,7 @@ static Item *make_cond_for_index(THD *thd, Item *cond, TABLE *table, uint keyno,
       case 0:
 	return (COND*) 0;
       case 1:
-        new_cond->used_tables_cache= used_tables;
+        /* remove AND level if there is only one argument */
 	return new_cond->argument_list()->head();
       default:
 	new_cond->quick_fix_field();

sql/sql_base.cc

@@ -7428,7 +7428,7 @@ store_top_level_join_columns(THD *thd, TABLE_LIST *table_ref,
     /* Add a TRUE condition to outer joins that have no common columns. */
     if (table_ref_2->outer_join &&
         !table_ref_1->on_expr && !table_ref_2->on_expr)
-      table_ref_2->on_expr= new (thd->mem_root) Item_int(thd, (longlong) 1, 1); // Always true.
+      table_ref_2->on_expr= (Item*) &Item_true;
 
     /* Change this table reference to become a leaf for name resolution. */
     if (left_neighbor)

sql/sql_select.cc

@@ -2444,7 +2444,7 @@ int JOIN::optimize_stage2()
   if (!conds && outer_join)
   {
     /* Handle the case where we have an OUTER JOIN without a WHERE */
-    conds= new (thd->mem_root) Item_bool(thd, true); // Always true
+    conds= (Item*) &Item_true;
   }
 
   if (impossible_where)
@@ -2615,7 +2615,7 @@ int JOIN::optimize_stage2()
   if (conds && const_table_map != found_const_table_map &&
       (select_options & SELECT_DESCRIBE))
   {
-    conds=new (thd->mem_root) Item_bool(thd, false); // Always false
+    conds= (Item*) &Item_false;
   }
 
   /* Cache constant expressions in WHERE, HAVING, ON clauses. */
@@ -2933,7 +2933,7 @@ int JOIN::optimize_stage2()
     having= having->remove_eq_conds(thd, &select_lex->having_value, true);
     if (select_lex->having_value == Item::COND_FALSE)
     {
-      having= new (thd->mem_root) Item_bool(thd, false);
+      having= (Item*) &Item_false;
       zero_result_cause= "Impossible HAVING noticed after reading const tables";
       error= 0;
       select_lex->mark_const_derived(zero_result_cause);
@@ -5513,7 +5513,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
     if (join->cond_value == Item::COND_FALSE)
     {
       join->impossible_where= true;
-      conds= new (join->thd->mem_root) Item_bool(join->thd, false);
+      conds= (Item*) &Item_false;
     }
 
     join->cond_equal= NULL;
@@ -11758,7 +11758,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
             below to check if we should use 'quick' instead.
           */
           DBUG_PRINT("info", ("Item_int"));
-          tmp= new (thd->mem_root) Item_bool(thd, true); // Always true
+          tmp= (Item*) &Item_true;
         }
 
       }
@@ -15318,7 +15318,7 @@ COND *Item_cond_and::build_equal_items(THD *thd,
   if (!cond_args->elements && 
       !cond_equal.current_level.elements && 
       !eq_list.elements)
-    return new (thd->mem_root) Item_bool(thd, true);
+    return (Item*) &Item_true;
 
   List_iterator_fast<Item_equal> it(cond_equal.current_level);
   while ((item_equal= it++))
@@ -15425,7 +15425,7 @@ COND *Item_func_eq::build_equal_items(THD *thd,
     Item_equal *item_equal;
     int n= cond_equal.current_level.elements + eq_list.elements;
     if (n == 0)
-      return new (thd->mem_root) Item_bool(thd, true);
+      return (Item*) &Item_true;
     else if (n == 1)
     {
       if ((item_equal= cond_equal.current_level.pop()))
@@ -15829,7 +15829,7 @@ Item *eliminate_item_equal(THD *thd, COND *cond, COND_EQUAL *upper_levels,
   List<Item> eq_list;
   Item_func_eq *eq_item= 0;
   if (((Item *) item_equal)->const_item() && !item_equal->val_int())
-    return new (thd->mem_root) Item_bool(thd, false);
+    return (Item*) &Item_false;
   Item *item_const= item_equal->get_const();
   Item_equal_fields_iterator it(*item_equal);
   Item *head;
@@ -15974,7 +15974,7 @@ Item *eliminate_item_equal(THD *thd, COND *cond, COND_EQUAL *upper_levels,
   switch (eq_list.elements)
   {
   case 0:
-    res= cond ? cond : new (thd->mem_root) Item_bool(thd, true);
+    res= cond ? cond : (Item*) &Item_true;
     break;
   case 1:
     if (!cond || cond->is_bool_literal())
@@ -17812,7 +17812,7 @@ Item_func_isnull::remove_eq_conds(THD *thd, Item::cond_result *cond_value,
 
       */
 
-      Item *item0= new(thd->mem_root) Item_bool(thd, false);
+      Item *item0= (Item*) &Item_false;
       Item *eq_cond= new(thd->mem_root) Item_func_eq(thd, args[0], item0);
       if (!eq_cond)
         return this;
@@ -22855,6 +22855,8 @@ make_cond_for_table_from_pred(THD *thd, Item *root_cond, Item *cond,
       return new_cond;
     }
   }
+  else if (cond->basic_const_item())
+    return cond;
 
   if (is_top_and_level && used_table == rand_table_bit &&
       (cond->used_tables() & ~OUTER_REF_TABLE_BIT) != rand_table_bit)
@@ -29431,18 +29433,14 @@ void JOIN::make_notnull_conds_for_range_scans()
 
   if (conds && build_notnull_conds_for_range_scans(this, conds,
                                                    conds->used_tables()))
-  {
-    Item *false_cond= new (thd->mem_root) Item_int(thd, (longlong) 0, 1);
-    if (false_cond)
   {
     /*
       Found a IS NULL conjunctive predicate for a null-rejected field
       in the WHERE clause
     */
-      conds= false_cond;
+    conds= (Item*) &Item_false;
     cond_equal= 0;
     impossible_where= true;
-    }
     DBUG_VOID_RETURN;
   }
 
@@ -29463,9 +29461,7 @@ void JOIN::make_notnull_conds_for_range_scans()
           Found a IS NULL conjunctive predicate for a null-rejected field
           of the inner table of an outer join with ON expression tbl->on_expr
         */
-        Item *false_cond= new (thd->mem_root) Item_int(thd, (longlong) 0, 1);
+        tbl->on_expr= (Item*) &Item_false;
-        if (false_cond)
-          tbl->on_expr= false_cond;
       }
     }
   }
@@ -29606,7 +29602,6 @@ void build_notnull_conds_for_inner_nest_of_outer_join(JOIN *join,
 {
   TABLE_LIST *tbl;
   table_map used_tables= 0;
-  THD *thd= join->thd;
   List_iterator<TABLE_LIST> li(nest_tbl->nested_join->join_list);
 
   while ((tbl= li++))
@@ -29617,9 +29612,7 @@ void build_notnull_conds_for_inner_nest_of_outer_join(JOIN *join,
   if (used_tables &&
       build_notnull_conds_for_range_scans(join, nest_tbl->on_expr, used_tables))
   {
-    Item *false_cond= new (thd->mem_root) Item_int(thd, (longlong) 0, 1);
+    nest_tbl->on_expr= (Item*) &Item_false;
-    if (false_cond)
-      nest_tbl->on_expr= false_cond;
   }
 
   li.rewind();
@@ -29633,11 +29626,7 @@ void build_notnull_conds_for_inner_nest_of_outer_join(JOIN *join,
       }
       else if (build_notnull_conds_for_range_scans(join, tbl->on_expr,
                                                    tbl->table->map))
-      {
+        tbl->on_expr= (Item*) &Item_false;
-        Item *false_cond= new (thd->mem_root) Item_int(thd, (longlong) 0, 1);
-        if (false_cond)
-          tbl->on_expr= false_cond;
-      }
     }
   }
 }