We save/restore visibility by setting the Is_Immediately_Visible flag
and appending entities to / removing them from the tail of an element
list.
However, the Is_Immediately_Visible flag can be restored in any order,
while the element list is singly-linked and removal from the tail is
inefficient. This change removes a performance hot spot, which accounted
for up to 10% of compilation time of complex applications (e.g. QGen),
at least as measured on GNAT built with profiling support.
gcc/ada/
* sem_ch8.adb (Restore_Scope_Stack): Remove elements from the head
and not the tail of an element list.
-- we saved (we use Remove, since this list will not be used again).
loop
- Elmt := Last_Elmt (List);
+ Elmt := First_Elmt (List);
exit when Elmt = No_Elmt;
Set_Is_Immediately_Visible (Node (Elmt));
- Remove_Last_Elmt (List);
+ Remove_Elmt (List, Elmt);
end loop;
-- Restore use clauses