GNU bug report logs - #23442
[PATCH] maint: avoid new warning from gcc (GCC) 7.0.0 20160503 (experimental)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: bug-coreutils <at> gnu.org
Subject: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0 20160503
 (experimental)
Date: Tue, 3 May 2016 20:59:32 -0700

[Message part 1 (text/plain, inline)]

coreutils failed to build when configured with --enable-gcc-warnings
and the latest gcc built from git.

Here's a patch to fix that:

[0001-maint-avoid-new-warning-from-gcc-GCC-7.0.0-20160503-.patch (text/x-patch, attachment)]

Message #8 received at 23442 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: 23442 <at> debbugs.gnu.org
Subject: Re: bug#23442: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0
 20160503 (experimental)
Date: Tue, 3 May 2016 21:23:59 -0700

On Tue, May 3, 2016 at 8:59 PM, Jim Meyering <jim <at> meyering.net> wrote:
> coreutils failed to build when configured with --enable-gcc-warnings
> and the latest gcc built from git.
>
> Here's a patch to fix that:

One nit in the commit log, fixed locally: s/U0/0U/

Message #11 received at 23442 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Jim Meyering <jim <at> meyering.net>, 23442 <at> debbugs.gnu.org
Subject: Re: bug#23442: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0
 20160503 (experimental)
Date: Wed, 4 May 2016 09:40:05 +0200

On 05/04/2016 05:59 AM, Jim Meyering wrote:
> -  bool default_format = (just_user + just_group + just_group_list
> +  bool default_format = (0U + just_user + just_group + just_group_list
>                           + just_context == 0);

These are all bool - wouldn't it be better to use boolean instead of
arithmetical operators?

Have a nice day,
Berny

Message #14 received at 23442 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 23442 <at> debbugs.gnu.org
Subject: Re: bug#23442: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0
 20160503 (experimental)
Date: Wed, 4 May 2016 08:08:21 -0700

[Message part 1 (text/plain, inline)]

On Wed, May 4, 2016 at 12:40 AM, Bernhard Voelker
<mail <at> bernhard-voelker.de> wrote:
> On 05/04/2016 05:59 AM, Jim Meyering wrote:
>> -  bool default_format = (just_user + just_group + just_group_list
>> +  bool default_format = (0U + just_user + just_group + just_group_list
>>                           + just_context == 0);
>
> These are all bool - wouldn't it be better to use boolean instead of
> arithmetical operators?

Thanks for the review. Indeed. Using "0U" there is a bit too much: a
hack upon the hack of using addition.

While using addition can be seen as slightly more readable (assuming
you know the idiom), or even better because the generated code is
jump-free, I would argue that this code should be readable, and that
whether there is a short-circuiting jump is irrelevant to the
performance of id.

While it is tempting to use "|" (the code generated by gcc-5.3 -O3 is
smaller and still jump-free: https://godbolt.org/g/zqMTtg), that still
feels dubious, especially when you remember that with gnulib, we may
still be simulating "bool" on some crufty systems.
So it seems best to use the bool-appropriate operators.

Here's the adjusted patch:

[0001-maint-avoid-new-warning-from-gcc-GCC-7.0.0-20160503-.patch (text/x-patch, attachment)]

Message #17 received at 23442 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Jim Meyering <jim <at> meyering.net>
Cc: 23442 <at> debbugs.gnu.org
Subject: Re: bug#23442: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0
 20160503 (experimental)
Date: Thu, 5 May 2016 10:54:57 +0200

On 05/04/2016 05:08 PM, Jim Meyering wrote:
> Subject: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0 20160503
>  (experimental)
> 
> * src/id.c (main): When configured with --enable-gcc-warnings and using
> the very latest gcc built from git, building would fail with this:
>   src/id.c:200:8: error: assuming signed overflow does not occur when \
>     simplifying conditional to constant [-Werror=strict-overflow]
>      bool default_format = (just_user + just_group + just_group_list
>           ^~~~~~~~~~~~~~
> Rewrite to use bool-appropriate operators.

Thanks, that looks much cleaner.

Have a nice day,
Berny

Message #22 received at 23442-done <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 23442-done <at> debbugs.gnu.org
Subject: Re: bug#23442: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0
 20160503 (experimental)
Date: Thu, 5 May 2016 08:17:18 -0700

On Thu, May 5, 2016 at 1:54 AM, Bernhard Voelker
<mail <at> bernhard-voelker.de> wrote:
> On 05/04/2016 05:08 PM, Jim Meyering wrote:
>> Subject: [PATCH] maint: avoid new warning from gcc (GCC) 7.0.0 20160503
>>  (experimental)
>>
>> * src/id.c (main): When configured with --enable-gcc-warnings and using
>> the very latest gcc built from git, building would fail with this:
>>   src/id.c:200:8: error: assuming signed overflow does not occur when \
>>     simplifying conditional to constant [-Werror=strict-overflow]
>>      bool default_format = (just_user + just_group + just_group_list
>>           ^~~~~~~~~~~~~~
>> Rewrite to use bool-appropriate operators.
>
> Thanks, that looks much cleaner.

Thanks again. Pushed and closed.

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