[Ada] Fix PR ada/99095

[Eric Botcazou]

This is a regression present on the mainline and 10 branch, where we fail
to make the bounds explicit for the return value of a function returning
an unconstrained array of a limited record type.

Tested on x86-64/Linux, applied on mainline and 10 branch.


2021-03-02  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/99095
        * sem_ch8.adb (Check_Constrained_Object): Restrict again the special
        optimization for limited types to non-array types except in the case
        of an extended return statement.


2021-03-02  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/limited5.adb: New test.

-- 
Eric Botcazou
diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
index 4689ae4ba18..efff7145337 100644
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -830,11 +830,19 @@ package body Sem_Ch8 is
             --  that are used in iterators. This is an optimization, but it
             --  also prevents typing anomalies when the prefix is further
             --  expanded.
+
             --  Note that we cannot just use the Is_Limited_Record flag because
             --  it does not apply to records with limited components, for which
             --  this syntactic flag is not set, but whose size is also fixed.
 
-            elsif Is_Limited_Type (Typ) then
+            --  Note also that we need to build the constrained subtype for an
+            --  array in order to make the bounds explicit in most cases, but
+            --  not if the object comes from an extended return statement, as
+            --  this would create dangling references to them later on.
+
+            elsif Is_Limited_Type (Typ)
+              and then (not Is_Array_Type (Typ) or else Is_Return_Object (Id))
+            then
                null;
 
             else

--  { dg-do compile }

procedure Limited5 is

   type Command       is limited null record;
   type Command_Array is array (Positive range <>) of Command;
      
   function To_Commands return Command_Array is
   begin
      return Result : Command_Array (1 .. 2);
   end To_Commands;
   
   The_Commands : aliased Command_Array := To_Commands;

begin
   null;
end;