[gcc r12-6302] [Ada] Avoid building malformed component constraints

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:5bad97d7445d679921e87bc0f94286c3ade02d27

commit r12-6302-g5bad97d7445d679921e87bc0f94286c3ade02d27
Author: Steve Baird <baird@adacore.com>
Date:   Mon Dec 6 13:42:51 2021 -0800

    [Ada] Avoid building malformed component constraints
    
    gcc/ada/
    
            * sem_util.adb (Build_Discriminant_Reference): In the unexpected
            case where we previously would fail an assertion, we instead
            revert to the old behavior.

Diff:
---
 gcc/ada/sem_util.adb | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index 2bc3c95dbeb..e07e48749d6 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -2107,11 +2107,7 @@ package body Sem_Util is
       --  Start of processing for Build_Discriminant_Reference
 
       begin
-         if Obj_Is_Good_Prefix then
-            return Make_Selected_Component (Loc,
-                     Prefix => Copy_And_Maybe_Dereference (Obj),
-                     Selector_Name => New_Occurrence_Of (Discrim, Loc));
-         else
+         if not Obj_Is_Good_Prefix then
             --  If the given discriminant is not a component of the given
             --  object, then try the enclosing object.
 
@@ -2128,10 +2124,15 @@ package body Sem_Util is
                         (Discrim_Name => Discrim_Name,
                          Obj          => Name (Parent (Entity (Obj))));
             else
-               pragma Assert (False);
-               raise Program_Error;
+               --  We are in some unexpected case here, so revert to the
+               --  old behavior (by falling through to it).
+               null;
             end if;
          end if;
+
+         return Make_Selected_Component (Loc,
+                  Prefix => Copy_And_Maybe_Dereference (Obj),
+                  Selector_Name => New_Occurrence_Of (Discrim, Loc));
       end Build_Discriminant_Reference;
 
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