[Bug ada/30740] Improper semantics in gnat's compilation of certain expressions involving modular arithmetic

["jaffem at erau dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #2 from jaffem at erau dot edu  2007-02-10 00:21 -------
Subject: Re:  Improper semantics in gnat's compilation of certain
 expressions involving modular arithmetic

For what it's worth (not much, I suspect ;-) I concur that this program, 
below, correctly demonstrates the same bug that I reported --- and does 
so a great deal more concisely than the demo program I sent in with the 
bug report.

ludovic at ludovic-brenta dot org wrote:
> ------- Comment #1 from ludovic at ludovic-brenta dot org  2007-02-09 14:34 -------
> Shorter test case that reproduces the problem.
>
> with Ada.Text_IO;
> procedure test1 is
>    type T1 is mod 9;
>    package T1_IO is new Ada.Text_IO.Modular_IO(T1);
>    X: T1 := 8;
>    J1: constant := 5;
> begin
>    for J2 in 5..5 loop
>       pragma assert(X*(2**J1) = X*(2**J2));
>       if X*(2**J1) /= X*(2**J2) then
>          Ada.Text_IO.Put_Line("Failed");
>          T1_IO.Put(X*(2**J1));
>          T1_IO.Put(X*(2**J2));
>          Ada.Text_IO.New_Line;
>       end if;
>    end loop;
> end test1;
>
> prints:
>
>    Failed
>     4 0
>
> To reproduce: gnatmake test1
>
> To reproduce with correct behaviour (no output): gnatmake -gnato test1
>
> Notice that when multiplying by 2**J1, the result is always correct because J2
> is a named number and the calculation is done at compile time with the correct
> semantics.  In contrast, J2 is non-static and exhibits the wrong semantics
> unless we add -gnato.
>
> Problem reproduced with GCC 4.1.1 but it's been there ever since 3.15p or even
> before.
>
>
>   


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30740