From: Jeff King <peff@peff.net>
To: Ramsay Jones <ramsay@ramsayjones.plus.com>
Cc: Junio C Hamano <gitster@pobox.com>,
Johannes Schindelin <Johannes.Schindelin@gmx.de>,
GIT Mailing-list <git@vger.kernel.org>
Subject: Re: [PATCH 0/2] -Wuninitialized
Date: Tue, 20 Mar 2018 00:32:25 -0400 [thread overview]
Message-ID: <20180320043225.GB13302@sigill.intra.peff.net> (raw)
In-Reply-To: <8f6d8e2e-aba4-128c-f17c-6c1b9c12436c@ramsayjones.plus.com>
On Mon, Mar 19, 2018 at 05:53:09PM +0000, Ramsay Jones wrote:
> This series removes all 'self-initialised' variables (ie. <type> var = var;).
> This construct has been used to silence gcc '-W[maybe-]uninitialized' warnings
> in the past [1]. Unfortunately, this construct causes warnings to be issued by
> MSVC [2], along with clang static analysis complaining about an 'Assigned value
> is garbage or undefined'. The number of these constructs has dropped over the
> years (eg. see [3] and [4]), so there are currently only 6 remaining in the
> current codebase. As demonstrated below, 5 of these no longer cause gcc to
> issue warnings.
Great. I'm happy to see these going away, and thanks for all the careful
digging.
> If we now add a patch to remove all self-initialization, which would be the
> first patch plus the obvious change to 'saved_namelen' in read-cache.c, then
> note the warnings issued by various compilers at various optimization levels
> on several different platforms [5]:
>
> O0 O1 O2 O3 Os Og
> 1) gcc 4.8.3 | - 1,20 1 1,18-19 1-4,21-23 1,5-17
> 2) gcc 4.8.4 | - 1,20 1 1 1-4,21-23 1,5-8,10-13,15-16
> 3) clang 3.4 | - - - - - n/a
> 4) gcc 5.4.0 | - 1 1 1 1,3-4,21 1,5-8,10-13,16-16
> 5) clang 3.8.0 | - - - - - n/a
> 6) gcc 5.4.0 | - 1 1 1 1-4 1,5-17
> 7) clang 3.8.0 | - - - - - n/a
> 8) gcc 6.4.0 | - 1 1 1,18-19 1,4 1,5-17
> 9) clang 5.0.1 | - - - - - -
> 10) gcc 7.2.1 | - 1 1 1 1,4 1,5-17
So I guess this could create headaches for people using DEVELOPER=1 on
as ancient a compiler as 4.8.4, but most other people should be OK. I
think I can live with that as a cutoff, and the Travis builds should
work there.
(And if we do the detect-compiler stuff from the other nearby thread,
somebody who cares can even loosen the warnings for those old gcc
versions).
I'm neglecting anybody doing -O3 or -Os here, but IMHO those are
sufficiently rare that the builder can tweak their own settings.
I wonder if people use -Og, though? I don't (I usually do -O0 for my
edit-compile-debug cycle).
-Peff
next prev parent reply other threads:[~2018-03-20 4:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-19 17:53 [PATCH 0/2] -Wuninitialized Ramsay Jones
2018-03-20 4:32 ` Jeff King [this message]
2018-03-20 22:41 ` Ramsay Jones
2018-03-20 14:46 ` Johannes Schindelin
2018-03-20 23:02 ` Ramsay Jones
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180320043225.GB13302@sigill.intra.peff.net \
--to=peff@peff.net \
--cc=Johannes.Schindelin@gmx.de \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=ramsay@ramsayjones.plus.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).