Bug#42733: Type-punning warnings when compiling MySQL --

            strict aliasing violations.

One somewhat major source of strict-aliasing violations and
related warnings is the SQL_LIST structure. For example,
consider its member function `link_in_list` which takes
a pointer to pointer of type T (any type) as a pointer to
pointer to unsigned char. Dereferencing this pointer, which
is done to reset the next field, violates strict-aliasing
rules and might cause problems for surrounding code that
uses the next field of the object being added to the list.

The solution is to use templates to parametrize the SQL_LIST
structure in order to deference the pointers with compatible
types. As a side bonus, it becomes possible to remove quite
a few casts related to acessing data members of SQL_LIST.

1 files changed, 8 insertions, 9 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index f3fcbc4db68..b93ea6f241b 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -244,12 +244,12 @@ bool Item_subselect::walk(Item_processor processor, bool walk_subquery,
         if (item->walk(processor, walk_subquery, argument))
           return 1;
       }
-      for (order= (ORDER*) lex->order_list.first ; order; order= order->next)
+      for (order= lex->order_list.first ; order; order= order->next)
       {
         if ((*order->item)->walk(processor, walk_subquery, argument))
           return 1;
       }
-      for (order= (ORDER*) lex->group_list.first ; order; order= order->next)
+      for (order= lex->group_list.first ; order; order= order->next)
       {
         if ((*order->item)->walk(processor, walk_subquery, argument))
           return 1;
@@ -1781,15 +1781,15 @@ int subselect_single_select_engine::prepare()
   SELECT_LEX *save_select= thd->lex->current_select;
   thd->lex->current_select= select_lex;
   if (join->prepare(&select_lex->ref_pointer_array,
-		    (TABLE_LIST*) select_lex->table_list.first,
+		    select_lex->table_list.first,
 		    select_lex->with_wild,
 		    select_lex->where,
 		    select_lex->order_list.elements +
 		    select_lex->group_list.elements,
-		    (ORDER*) select_lex->order_list.first,
-		    (ORDER*) select_lex->group_list.first,
+		    select_lex->order_list.first,
+		    select_lex->group_list.first,
 		    select_lex->having,
-		    (ORDER*) 0, select_lex,
+		    NULL, select_lex,
 		    select_lex->master_unit()))
     return 1;
   thd->lex->current_select= save_select;
@@ -2450,14 +2450,13 @@ table_map subselect_engine::calc_const_tables(TABLE_LIST *table)
 
 table_map subselect_single_select_engine::upper_select_const_tables()
 {
-  return calc_const_tables((TABLE_LIST *) select_lex->outer_select()->
-			   leaf_tables);
+  return calc_const_tables(select_lex->outer_select()->leaf_tables);
 }
 
 
 table_map subselect_union_engine::upper_select_const_tables()
 {
-  return calc_const_tables((TABLE_LIST *) unit->outer_select()->leaf_tables);
+  return calc_const_tables(unit->outer_select()->leaf_tables);
 }