From: Jeff King <peff@peff.net>
To: Johannes Sixt <j.sixt@viscovery.net>
Cc: Junio C Hamano <gitster@pobox.com>, git@vger.kernel.org
Subject: Re: [PATCH 0/4] drop some "int x = x" hacks to silence gcc warnings
Date: Thu, 21 Mar 2013 07:55:45 -0400 [thread overview]
Message-ID: <20130321115545.GB21319@sigill.intra.peff.net> (raw)
In-Reply-To: <514AF2E1.7020409@viscovery.net>
On Thu, Mar 21, 2013 at 12:45:37PM +0100, Johannes Sixt wrote:
> Am 3/21/2013 12:03, schrieb Jeff King:
> > I was fooling around with clang and noticed that it complains about the
> > "int x = x" construct under -Wall. That is IMHO a deficiency in clang,
> > since the idiom has a well-defined use in silencing -Wuninitialized
> > warnings.
>
> IMO, that's a myth. The construct invokes undefined behavior at least
> since C99, and the compilers are right to complain about it.
While undefined behavior does leave the compiler free to do anything,
including nasal demons, it would be a very poor implementation that did
anything except leave random bytes in the value. And it also means that
gcc is free to take it as a hint to silence the warning; given that
clang tries to be compatible with gcc, I'd think it would want to do the
same. But I may be wrong that the behavior from gcc is intentional or
common (see below).
> But you might just say that standards are not worth the paper they are
> printed on, and you may possibly be right for practical reasons. But I
> still consider it a myth that "int x = x" is an idiom. I'm in the C
> business since more than 25 years, and the first time I saw the "idiom"
> was in git code. Is there any evidence that the construct is used
> elsewhere? Have I been in the wrong corner of the C world for such a long
> time?
Git code was my introduction to it, too, and I was led to believe it was
idiomatic, so I can't speak further on that. I think it was Junio who
introduced me to it, so maybe he can shed more light on the history.
-Peff
next prev parent reply other threads:[~2013-03-21 11:56 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-21 11:03 [PATCH 0/4] drop some "int x = x" hacks to silence gcc warnings Jeff King
2013-03-21 11:05 ` [PATCH 1/4] wt-status: fix possible use of uninitialized variable Jeff King
2013-03-21 19:49 ` Jonathan Nieder
2013-03-21 19:55 ` Junio C Hamano
2013-03-21 19:58 ` Jonathan Nieder
2013-03-22 16:15 ` Jeff King
2013-03-21 11:08 ` [PATCH 2/4] fast-import: use pointer-to-pointer to keep list tail Jeff King
2013-03-21 20:43 ` Jonathan Nieder
2013-03-21 11:10 ` [PATCH 3/4] drop some obsolete "x = x" compiler warning hacks Jeff King
2013-03-21 15:16 ` Erik Faye-Lund
2013-03-21 20:47 ` Jonathan Nieder
2013-03-24 7:17 ` Torsten Bögershausen
2013-03-21 11:13 ` [PATCH 4/4] transport: drop "int cmp = cmp" hack Jeff King
2013-03-21 20:59 ` Jonathan Nieder
2013-03-24 4:00 ` Junio C Hamano
2013-03-24 9:32 ` Jeff King
2013-03-24 14:54 ` Torsten Bögershausen
2013-03-25 19:50 ` Junio C Hamano
2013-03-25 21:06 ` Jeff King
2013-03-25 21:55 ` Junio C Hamano
2013-03-21 11:45 ` [PATCH 0/4] drop some "int x = x" hacks to silence gcc warnings Johannes Sixt
2013-03-21 11:55 ` Jeff King [this message]
2013-03-21 14:58 ` Junio C Hamano
2013-03-21 15:19 ` Junio C Hamano
2013-03-21 15:44 ` Jeff King
2013-03-21 15:44 ` [PATCH 5/4] fast-import: clarify "inline" logic in file_change_m Jeff King
2013-03-21 15:45 ` [PATCH 6/4] run-command: always set failed_errno in start_command Jeff King
2013-03-21 21:02 ` [PATCH 0/4] drop some "int x = x" hacks to silence gcc warnings Jonathan Nieder
2013-03-22 16:18 ` Jeff King
2013-03-22 16:19 ` [PATCH 7/4] submodule: clarify logic in show_submodule_summary Jeff King
2013-03-22 21:10 ` Junio C Hamano
2013-03-22 16:21 ` [PATCH 8/4] match-trees: drop "x = x" initializations Jeff King
2013-03-22 21:26 ` Junio C Hamano
2013-03-22 21:33 ` Junio C Hamano
2013-03-22 21:36 ` Jeff King
2013-03-23 18:57 ` René Scharfe
2013-03-24 4:55 ` Junio C Hamano
2013-03-24 10:01 ` Jeff King
2013-03-24 22:46 ` René Scharfe
2013-03-25 16:10 ` Junio C Hamano
2013-03-21 13:44 ` [PATCH 0/4] drop some "int x = x" hacks to silence gcc warnings Joachim Schmitz
2013-03-21 13:56 ` Joachim Schmitz
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