[Bug ada/79710] New: Assert of a static fixed point expression incorrectly fails

[georggcc at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79710

            Bug ID: 79710
           Summary: Assert of a static fixed point expression incorrectly
                    fails
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: georggcc at googlemail dot com
  Target Milestone: ---

The program below triggers an unexpected Assert failure of a static
expression. The same static expression occurs identically in the same
region and is accepted there (see Test constant).  The Assert failure
can, however, be "prevented" by uncommenting another Assert of another
static expression before it that involves the same type and number. The
diagnostic messages change accordingly, too.

with Ada.Text_IO;
procedure Bug_FxP is

   Shoe_Ounce : constant := 2.54/64.0;
   type FxP is delta Shoe_Ounce range 0.00 .. 0.32
   with
     Size => 16,
     Small => 2.0**(-15);

   --
   -- Remove the comments to make the Assert _after_ this one not
   -- raise (and no other Assert raise either, as expected):
   --
   -- pragma Assert
   --   (3276 * FxP'Small = 0.0999755859375);

   pragma Assert
      -- Fails .IFF. the assertion aboved it stays commented out!
     (FxP'(0.1) = 0.0999755859375);

   Test : constant :=
     (case True is
         when False => 0,
         when FxP'(0.1) = 0.0999755859375 => 1);

   package FIO is new Ada.Text_IO.Fixed_IO (Fxp);
begin
   Ada.Text_IO.Put (Test'Img);
   FIO.Put (Fxp'(0.1), Aft => 20);
end;


$ gnatmake -gnata -gnatwa -gnatv -f bug_fxp.adb 
gcc -c -gnata -gnatwa -gnatv bug_fxp.adb

GNAT 7.0.0 20161104 (experimental) [trunk revision 241862]
Copyright 1992-2016, Free Software Foundation, Inc.

Compiling: bug_fxp.adb
Source file time stamp: 2017-02-25 11:53:54
Compiled at: 2017-02-25 12:54:01

    19.      (FxP'(0.1) = 0.0999755859375); 
              1    2
        >>> warning: assertion will fail at run time
        >>> warning: static fixed-point value is not a multiple of Small

    24.          when FxP'(0.1) = 0.0999755859375 => 1);
                           |
        >>> warning: static fixed-point value is not a multiple of Small

    29.    FIO.Put (Fxp'(0.1), Aft => 20);
                         |
        >>> warning: static fixed-point value is not a multiple of Small

 30 lines: No errors, 4 warnings
gnatbind -x bug_fxp.ali
gnatlink bug_fxp.ali
$ ./bug_fxp 

raised SYSTEM.ASSERTIONS.ASSERT_FAILURE : bug_fxp.adb:19
$

When I remove the comments from the first Assert on line 15,
the one before line 19, the program runs without failure:

$ ./bug_fxp 
 1 0.09997558593750000000
$