Re: large integer truncation in regex module

[Gianluigi Tiesi]

On 26/03/2012 7.33, Jim Meyering wrote:
> Gianluigi Tiesi wrote:
> > On 25/03/2012 6.58, Paul Eggert wrote:
> > > On 03/24/2012 09:28 PM, Gianluigi Tiesi wrote:
> > > > While compiling regex module one android I've discovered a problem
> > > > that on other 32bit compiler is only a warning
> > > >
> > > > ...
> > > > it's correct, but I think an ifdef may be used instead since
> > > > BITSET_WORD_BITS is a define
> > >
> > >
> > > Generally speaking we prefer 'if (xxx)' to '#if xxx' where either will
> > > do, because the former is easier to read and reason about. If the only
> > > problem with 'if (xxx)' is a bogus warning by some random compiler then
> > > it's probably better to leave it alone (and get the compiler fixed....).
> >
> > I don't think assigning a 64bit integer constant in a 32bit variable
> > type is a bogus warning,
>
> It is bogus in this case because your compiler is warning
> about what is called dead code: code that it can determine
> will never be executed.

hmm, if gcc is unable to detect dead code, this does not make legit 
everything in the dead code.

> > and some software using gnulib like parted
> > enable Werror by default
>
> Gnu parted does not enable -Werror by default.
> However, it is enabled if you configure with --enable-gcc-warnings.

gnu parted 2.4 enables by default -Werror, you can configure it with 
--enable-Werror=no, git version (3.1) removed at all the option and the 
flag. But I still don't understand why use dead code instead of ifdef if 
the compiler is unable to detect it. I've tested with gcc 4.4.3 (android 
ndk) and 4.6.2 (mingw), both warns.
I'm not really sure even if it warns that the code is compiled in the 
executable.

I've just tested the code:

#include <stdio.h>
#include <stdlib.h>
#define A 64
//#define A 32

int main(void)
{
    int a = 0;
    if (A == 32)
        a = ((unsigned long long) (-1));
    if (a)
        printf("%d\n", a);
    return 0;
}

it warns about an overflow, but if variable a is not initialized, it 
says it is used uninitialized (not maybe used)

a.c: In function 'main':
a.c:10:9: warning: overflow in implicit constant conversion [-Woverflow]
a.c:11:8: warning: 'a' is used uninitialized in this function 
[-Wuninitialized]

if you compile with -O2 and look at the asm the printf is removed,
but you still have a warn.

Ok I went a bit OT :) anyway it's uncommon for me to see if (DEFINE) 
else etc

Regards

--
Gianluigi Tiesi <address@hidden>
EDP Project Leader
Netfarm S.r.l. - http://www.netfarm.it/
Free Software: http://oss.netfarm.it/

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