[gcc/devel/autopar_devel] [Ada] Implement AI12-0032 fixes for 'Old attribute accessibility

[Giuliano Belinassi <giulianob@gcc.gnu.org>]

https://gcc.gnu.org/g:2a47240d1fbee5ea0b2f0e5faab782c998516c05

commit 2a47240d1fbee5ea0b2f0e5faab782c998516c05
Author: Steve Baird <baird@adacore.com>
Date:   Thu Apr 23 14:39:55 2020 -0700

    [Ada] Implement AI12-0032 fixes for 'Old attribute accessibility
    
    2020-06-18  Steve Baird  <baird@adacore.com>
    
    gcc/ada/
    
            * sem_util.adb (Object_Access_Level): Treat a 'Old attribute
            reference like an aggregate in determining its static
            accessibility level; after the evaluation of the relevant
            post-condition, the implicitly declared constant associated with
            an Old attribute reference ceases to exist. Similarly for
            Loop_Entry attribute.
            * exp_ch6.adb (Expand_Call_Helper): For an attribute reference
            that is expanded into a reference to an implicitly declared
            constant (e.g., a 'Old or 'Loop_Entry attribute), compute the
            dynamic accessibility level of that constant by looking at the
            declaration of the constant (as opposed to looking at the
            attribute reference).

Diff:
---
 gcc/ada/exp_ch6.adb  | 15 +++++++++++++++
 gcc/ada/sem_util.adb | 12 ++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/gcc/ada/exp_ch6.adb b/gcc/ada/exp_ch6.adb
index 9a32f7ed702..00a0aef0631 100644
--- a/gcc/ada/exp_ch6.adb
+++ b/gcc/ada/exp_ch6.adb
@@ -3617,6 +3617,21 @@ package body Exp_Ch6 is
             then
                Prev_Orig := Prev;
 
+            --  If the actual is an attribute reference that was expanded
+            --  into a reference to an entity, then get accessibility level
+            --  from that entity. AARM 6.1.1(27.d) says "... the implicit
+            --  constant declaration defines the accessibility level of X'Old".
+
+            elsif Nkind (Prev_Orig) = N_Attribute_Reference
+              and then Nam_In (Attribute_Name (Prev_Orig),
+                               Name_Old,
+                               Name_Loop_Entry)
+              and then Is_Entity_Name (Prev)
+              and then Present (Entity (Prev))
+              and then Is_Object (Entity (Prev))
+            then
+               Prev_Orig := Prev;
+
             elsif Nkind (Prev_Orig) = N_Type_Conversion then
                Prev_Orig := Expression (Prev_Orig);
             end if;
diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index 756162e4a2f..40f34fd7b8a 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -24237,6 +24237,18 @@ package body Sem_Util is
       elsif Nkind (Orig_Obj) = N_Aggregate then
          return Object_Access_Level (Current_Scope);
 
+      --  Treat an Old/Loop_Entry attribute reference like an aggregate.
+      --  AARM 6.1.1(27.d) says "... the implicit constant declaration
+      --  defines the accessibility level of X'Old", so that is what
+      --  we are trying to implement here.
+
+      elsif Nkind (Orig_Obj) = N_Attribute_Reference
+        and then Nam_In (Attribute_Name (Orig_Obj),
+                         Name_Old,
+                         Name_Loop_Entry)
+      then
+         return Object_Access_Level (Current_Scope);
+
       --  Otherwise return the scope level of Standard. (If there are cases
       --  that fall through to this point they will be treated as having
       --  global accessibility for now. ???)