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From: johnscpg@googlemail.com
Newsgroups: comp.lang.ada
Subject: Re: Problem with optimizations
Date: Wed, 29 Apr 2009 03:45:37 -0700 (PDT)
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Date: 2009-04-29T03:45:37-07:00
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On Apr 28, 8:15=A0pm, Olivier Scalbert <olivier.scalb...@algosyn.com>
wrote:
> Albrecht K=E4fer wrote:
> > (see below) schrieb::
> >> There is no else part for the following if:
>
> >> =A0 =A0 =A0 =A0 =A0 =A0 if Is_Solved(Cube) then
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 New_Line;
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Put("Solved !"); New_Line;
>
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 for i in 1..depth-1 loop
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Ada.Integer_Text_IO.Put(Intege=
r(Moves(i)));
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 end loop;
> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Result :=3D True;
> >> =A0 =A0 =A0 =A0 =A0 =A0 end if;
>
> >> So the procedure can exit with Result undefined. Since the program is
> >> incorrect, varying optimisation, or implementation details, is likely =
to
> >> give varying results. Some may co-incidentally be the results you expe=
ct.
>
> > Shouldn't that, you know, create a warning or something?
>
> > Albrecht
>
> That is what I was thinking, but with:
>
> gnatmake -f -O3 -W -gnatp rubikmain
>
> it detects the bug (and also an other one in the same function)
>
> Shame on me !

I also learned this recently (using gfortran).   You have to have -O
to
get the -W to work when you are looking for uninitialized variables.
Exactly as you've shown, it flags variables that may or may not
be initialized in for loops, or if then else blocks.  Its usually
wrong,
(it speculates) but I like it.  In gfortan you can write -O -
Wuninitialized; probably
same with gnatmake (it accepts it anyway).

cheers,
jonathan