Ada tag comparison causes compiler to crash

Question

I'm not sure if this is a bug in my version of gcc (4.8.5) or gprbuild (2.2.0) but when I try to compile a project there is a specific function whose body causes the compiler to crash with a STORAGE_ERROR. When I build with -cargs -v I see that gnatl -quiet ... is the command that is most recently output before the crash.

The function in question produces an informative string from a tag belonging to a particular type hierarchy. It looks something like:

function Tag_To_String (From : Ada.Tags.Tag) return String is (
    if From = A'Tag then "This is tag A"
    elsif From = B'Tag then "This is tag B"
    --  ...
    elsif From = Z'Tag then "This is tag Z"
    else "");

Whereas I can get it to successfully compile if I change that body to:

function Tag_To_String (From : Ada.Tags.Tag) return String is ("");

The error I get is exactly:

gcc -c -gnat12 sourcefile.adb

raised STORAGE_ERROR : stack overflow or erroneous memory access
gprbuild: *** compilation phase failed

Any idea why gcc can't seem to compile this particular function?

Answer 1

The following program works properly using the 2018 release of GNAT and GPS.

with Ada.text_IO; use Ada.Text_IO;
with Ada.Tags; use Ada.Tags;

procedure Tag_Main is
   package foo is
      type A is tagged private;
      type B is tagged private;
   private
      type A is tagged null record;
      type B is tagged null record;
   end foo;

   use Foo;

   function Tag_To_String(From : Ada.Tags.Tag) return String is(
      if From = A'Tag then
         "This is tag A"
      else
         "This is tag B"
      );

begin
   Put_Line(Tag_To_String(A'Tag));
   Put_Line(Tag_To_String(B'Tag));
end Tag_Main;

Note that I have edited the code to use a function expression. It still works on the GNAT/GPS 2018 release. This version was compiled with gprbuild -d -PD