[gcc r13-529] [Ada] Deal with derived record types in Has_Compatible_Representation

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

https://gcc.gnu.org/g:d678717ab233610588ae15fcddeb20b39ac7daf5

commit r13-529-gd678717ab233610588ae15fcddeb20b39ac7daf5
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Mon Mar 21 08:35:53 2022 +0100

    [Ada] Deal with derived record types in Has_Compatible_Representation
    
    More precisely, untagged record types, as tagged record types are already
    handled by the predicate.  If the derived type has not been given its own
    representation clause, then the representations are the same.
    
    gcc/ada/
    
            * sem_ch13.adb (Has_Compatible_Representation): Return true for
            derived untagged record types without representation clause.

Diff:
---
 gcc/ada/sem_ch13.adb | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
index 93f5e452bd4..ac94de7e84a 100644
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -13539,6 +13539,16 @@ package body Sem_Ch13 is
          if Is_Packed (T1) /= Is_Packed (T2) then
             return False;
 
+         --  If the operand type is derived from the target type and no clause
+         --  has been given after the derivation, then the representations are
+         --  the same since the derived type inherits that of the parent type.
+
+         elsif Is_Derived_Type (T2)
+           and then Etype (T2) = T1
+           and then not Has_Record_Rep_Clause (T2)
+         then
+            return True;
+
          --  Otherwise we must check components. Typ2 maybe a constrained
          --  subtype with fewer components, so we compare the components
          --  of the base types.