Optimize Sql_alloc

- Remove 'dummy_for_valgrind' overrun marker as this doesn't help much.
  The element also distorts the sizes of objects a bit, which makes it
  harder to calculate gain in object sizes when doing size optimizations.
- Replace usage of thd_get_current_thd() with _current_thd()
- Avoid one extra call indirection when using thd_get_current_thd(), which
  is used by Sql_alloc, by replacing it with _current_thd()

include/thread_pool_priv.h

@@ -44,7 +44,6 @@ void thd_clear_errors(THD *thd);
 void thd_set_thread_stack(THD *thd, char *stack_start);
 void thd_lock_thread_count(THD *thd);
 void thd_close_connection(THD *thd);
-THD *thd_get_current_thd();
 void thd_lock_data(THD *thd);
 void thd_unlock_data(THD *thd);
 bool thd_is_transaction_active(THD *thd);

sql/item.cc

@@ -447,10 +447,10 @@ Item::Item():
   name(null_clex_str), orig_name(0), is_expensive_cache(-1)
 {
   DBUG_ASSERT(my_progname == NULL); // before main()
+  common_flags= IS_AUTO_GENERATED_NAME;
   marker= 0;
   maybe_null= with_window_func= with_field= in_rollup= with_param= 0;
   fixed= 1;
-  null_value= 0;
   join_tab_idx= MAX_TABLES;
 }
 

sql/mysqld.cc

@@ -663,6 +663,12 @@ static std::atomic<char*> shutdown_user;
 
 static thread_local THD *THR_THD;
 
+/**
+  Get current THD object from thread local data
+
+  @retval     The THD object for the thread, NULL if not connection thread
+*/
+
 MYSQL_THD _current_thd() { return THR_THD; }
 void set_current_thd(THD *thd) { THR_THD= thd; }
 

sql/sql_alloc.h

@@ -18,20 +18,18 @@
 
 #include <my_sys.h>                    /* alloc_root, MEM_ROOT, TRASH */
 
-THD *thd_get_current_thd();
+/* MariaDB standard class memory allocator */
-
-/* mysql standard class memory allocator */
 
 class Sql_alloc
 {
 public:
   static void *operator new(size_t size) throw ()
   {
-    return thd_alloc(thd_get_current_thd(), size);
+    return thd_alloc(_current_thd(), size);
   }
   static void *operator new[](size_t size) throw ()
   {
-    return thd_alloc(thd_get_current_thd(), size);
+    return thd_alloc(_current_thd(), size);
   }
   static void *operator new[](size_t size, MEM_ROOT *mem_root) throw ()
   { return alloc_root(mem_root, size); }
@@ -42,9 +40,5 @@ public:
   static void operator delete[](void *, MEM_ROOT *)
   { /* never called */ }
   static void operator delete[](void *ptr, size_t size) { TRASH_FREE(ptr, size); }
-#ifdef HAVE_valgrind
-  bool dummy_for_valgrind;
-  inline Sql_alloc() :dummy_for_valgrind(0) {}
-#endif
 };
 #endif /* SQL_ALLOC_INCLUDED */

sql/sql_class.cc

@@ -325,17 +325,6 @@ bool Foreign_key::validate(List<Create_field> &table_fields)
 ** Thread specific functions
 ****************************************************************************/
 
-/**
-  Get current THD object from thread local data
-
-  @retval     The THD object for the thread, NULL if not connection thread
-*/
-THD *thd_get_current_thd()
-{
-  return current_thd;
-}
-
-
 extern "C" unsigned long long thd_query_id(const MYSQL_THD thd)
 {
   return((unsigned long long)thd->query_id);

storage/rocksdb/ha_rocksdb.cc

@@ -7812,7 +7812,7 @@ int ha_rocksdb::create(const char *const name, TABLE *const table_arg,
   }
 
   // FOREIGN KEY isn't supported yet
-  THD *const thd = my_core::thd_get_current_thd();
+  THD *const thd = _current_thd();
   if (contains_foreign_key(thd)) {
     my_error(ER_NOT_SUPPORTED_YET, MYF(0),
              "FOREIGN KEY for the RocksDB storage engine");