[gcc r15-185] ada: Fix wrong Finalization_Size for No_Heap_Finalization objects

[Marc Poulhi?s <dkm@gcc.gnu.org>]

https://gcc.gnu.org/g:3862106d3506293ad5af2fc04d2d21ef3a5e0edf

commit r15-185-g3862106d3506293ad5af2fc04d2d21ef3a5e0edf
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Sat Dec 16 11:34:48 2023 +0100

    ada: Fix wrong Finalization_Size for No_Heap_Finalization objects
    
    When an access type is subject to the No_Heap_Finalization pragma, no header
    is added in front of objects allocated through it, and the value returned by
    Finalization_Size is defined to be the size of this header.
    
    gcc/ada/
    
            * exp_attr.adb (Expand_N_Attribute_Reference) <Finalization_Size>:
            Return 0 if the prefix is a dereference of an access value subject
            to the No_Heap_Finalization pragma.

Diff:
---
 gcc/ada/exp_attr.adb | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/ada/exp_attr.adb b/gcc/ada/exp_attr.adb
index 614f1fbe14d..a8e06f0005e 100644
--- a/gcc/ada/exp_attr.adb
+++ b/gcc/ada/exp_attr.adb
@@ -3563,6 +3563,14 @@ package body Exp_Attr is
       --  Start of processing for Finalization_Size
 
       begin
+         --  If the prefix is the dereference of an access value subject to
+         --  pragma No_Heap_Finalization, then no header has been added.
+
+         if Nkind (Pref) = N_Explicit_Dereference
+           and then No_Heap_Finalization (Etype (Prefix (Pref)))
+         then
+            Rewrite (N, Make_Integer_Literal (Loc, 0));
+
          --  An object of a class-wide type first requires a runtime check to
          --  determine whether it is actually controlled or not. Depending on
          --  the outcome of this check, the Finalization_Size of the object
@@ -3578,7 +3586,7 @@ package body Exp_Attr is
          --
          --  and the attribute reference is replaced with a reference to Size.
 
-         if Is_Class_Wide_Type (Ptyp) then
+         elsif Is_Class_Wide_Type (Ptyp) then
             Size := Make_Temporary (Loc, 'S');
 
             Insert_Actions (N, New_List (