[gcc r13-346] [Ada] Fix remaining asymmetry in Specific_Type

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

https://gcc.gnu.org/g:b9cff88ca79664ade8bd1c870d01b56f8599afa4

commit r13-346-gb9cff88ca79664ade8bd1c870d01b56f8599afa4
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Sun Feb 6 15:54:25 2022 +0100

    [Ada] Fix remaining asymmetry in Specific_Type
    
    gcc/ada/
    
            * sem_type.adb (Specific_Type): Add swapped cases for interfaces.

Diff:
---
 gcc/ada/sem_type.adb | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/gcc/ada/sem_type.adb b/gcc/ada/sem_type.adb
index d5ee20b0c74..971b1a3183b 100644
--- a/gcc/ada/sem_type.adb
+++ b/gcc/ada/sem_type.adb
@@ -3354,13 +3354,8 @@ package body Sem_Type is
       elsif T2 = Raise_Type then
          return B1;
 
-      --  ----------------------------------------------------------
-      --  Special cases for equality operators (all other predefined
-      --  operators can never apply to tagged types)
-      --  ----------------------------------------------------------
-
       --  Ada 2005 (AI-251): T1 and T2 are class-wide types, and T2 is an
-      --  interface
+      --  interface, return T1, and vice versa.
 
       elsif Is_Class_Wide_Type (T1)
         and then Is_Class_Wide_Type (T2)
@@ -3368,8 +3363,14 @@ package body Sem_Type is
       then
          return T1;
 
+      elsif Is_Class_Wide_Type (T2)
+        and then Is_Class_Wide_Type (T1)
+        and then Is_Interface (Etype (T1))
+      then
+         return T2;
+
       --  Ada 2005 (AI-251): T1 is a concrete type that implements the
-      --  class-wide interface T2
+      --  class-wide interface T2, return T1, and vice versa.
 
       elsif Is_Tagged_Type (T1)
         and then Is_Class_Wide_Type (T2)
@@ -3379,6 +3380,14 @@ package body Sem_Type is
       then
          return T1;
 
+      elsif Is_Tagged_Type (T2)
+        and then Is_Class_Wide_Type (T1)
+        and then Is_Interface (Etype (T1))
+        and then Interface_Present_In_Ancestor (Typ   => T2,
+                                                Iface => Etype (T1))
+      then
+         return T2;
+
       elsif Is_Class_Wide_Type (T1)
         and then Is_Ancestor (Root_Type (T1), T2)
       then