[Bug ada/16910] New: Incorrect code generated for certain variant record source

[jeff at thecreems dot com]

I believe there is a longstanding bug that has been present in GNAT since about
GNAT 3.13. The old intermetrics Xlib Ada bindings stopped working at that time
and it seemed to be related to the processing of the XEvent variant records. I
have created a very small test program that  think demonstrates the same failure
mode.

The problem appears to be that if a variable that is a variant record is
declared as aliased, some of the constraint checking logic fails in such a way
that it relies on the default value of the discriminant rather than the current
value.

This program demonstrates the problem both on Solaris and Windows XP
using gcc 3.4.1


with Text_Io;
procedure Aaa is 


  type Var (A : Integer:=0) is
  record
    case A is
      when 0 =>
        Ok : Integer;
      when 1 =>
        Bad : Integer;
      when others =>
        null;
    end case;
  end record;


  procedure See (
        X : in out Var ) is 

  begin
    --
    -- The following will blow up with a discriminant
    -- check error (contraint_error) when the actual parameter
    -- associated with X is declared aliased. Note that
    -- in this code I realize there is no good reason to
    -- declare it as aliased however this still effectively
    -- shows the problem.
    --
    X:= (
      A   => 1, 
      Bad => 2);

  end See;

begin
  declare
    I : aliased Var;  -- If you make this not aliased, everything works fine
    --I : Var;
  begin
    See(I);
    Text_Io.Put_Line(Integer'Image(I.Bad));
  end;
end Aaa;

-- 
           Summary: Incorrect code generated for certain variant record
                    source
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jeff at thecreems dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16910