[gcc r17-1635] ada: Fix dangling reference with Bounded_Indefinite_Holders and Empty_Holder

[Marc Poulhies]

https://gcc.gnu.org/g:fb323d7f046139fc9ef31a51355fe83240a61cfb

commit r17-1635-gfb323d7f046139fc9ef31a51355fe83240a61cfb
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Fri May 29 08:34:39 2026 +0200

    ada: Fix dangling reference with Bounded_Indefinite_Holders and Empty_Holder
    
    The issue is that the finalization of an empty container does not deallocate
    its subpool, thus creating a dangling reference to it from the global pool.
    
    gcc/ada/ChangeLog:
    
            * libgnat/a-cbinho.adb (Clear): Deallocate the subpool even if the
            container is empty.

Diff:
---
 gcc/ada/libgnat/a-cbinho.adb | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/gcc/ada/libgnat/a-cbinho.adb b/gcc/ada/libgnat/a-cbinho.adb
index 5c5a8ed4139a..43a9f8b85280 100644
--- a/gcc/ada/libgnat/a-cbinho.adb
+++ b/gcc/ada/libgnat/a-cbinho.adb
@@ -75,13 +75,13 @@ package body Ada.Containers.Bounded_Indefinite_Holders is
 
    procedure Clear (Container : in out Holder) is
    begin
-      if Is_Empty (Container) then
-         return; -- nothing to do
-      end if;
-      if Container.Busy /= 0 then
-         raise Program_Error with "attempt to tamper with elements";
+      if not Is_Empty (Container) then
+         if Container.Busy /= 0 then
+            raise Program_Error with "attempt to tamper with elements";
+         end if;
+         Free (Container.Element); -- finalize element
       end if;
-      Free (Container.Element); -- finalize element
+      --  Unconditionally deallocate the subpool for Finalize, see below
       Ada.Unchecked_Deallocate_Subpool (Container.Handle);
    end Clear;