From: Jeff King <peff@peff.net>
To: Denton Liu <liu.denton@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH] Fix -Wmaybe-uninitialized warnings under -O0
Date: Fri, 3 Apr 2020 10:04:47 -0400 [thread overview]
Message-ID: <20200403140447.GA639586@coredump.intra.peff.net> (raw)
In-Reply-To: <20200401140643.GA880372@generichostname>
On Wed, Apr 01, 2020 at 10:06:43AM -0400, Denton Liu wrote:
> > So why does your version behave differently? And if this is a temporary
> > state for a buggy version of gcc (that may be fixed in the next point
> > release), is it worth changing our source code to appease it?
>
> A correction to the earlier message... It seems like I wasn't reporting
> the correct settings. I was actually compiling with -Og, not -O0
> (whoops!).
>
> I tested it with gcc-8 and it seems like it also reports the same
> problem. Also, -O1 reports warnings as well.
Ah, OK, I can reproduce easily with -Og (up through gcc-10). Most of
them don't trigger with -O1; just the one in ref-filter.c.
That one's interesting. We have:
int ret = 0;
...
if (...)
...
else
ret = for_each_fullref_in_pattern(...);
...
return ret;
So we'd either have 0 or an assigned return. But the bug is actually in
for_each_fullref_in_pattern(), which does this:
int ret; /* uninitialized! */
/* a bunch of early return conditionals */
if (...)
return ...;
for_each_string_list_item(...) {
ret = for_each_fullref_in(...);
}
return ret;
but that will return an uninitialized value when there are no patterns.
I doubt we have such a case, but that may explain why -O0 does not
complain (it assumes "in_pattern" will return a useful value) and -O2
does not (it is able to figure out that it always does), but -O1 only
inlines part of it.
Curiously, -Og _does_ find the correct function.
Your patch silences it, but is it doing the right thing? It sets "ret =
0", but we haven't actually iterated anything. Should it be an error
instead?
-Peff
next prev parent reply other threads:[~2020-04-03 14:04 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-01 7:30 [PATCH] Fix -Wmaybe-uninitialized warnings under -O0 Denton Liu
[not found] ` <CAPUEspgBkmxszgBee8C9hZnEwqztf-XKEj7LB_jWVFJaJCge0w@mail.gmail.com>
2020-04-01 9:05 ` Denton Liu
2020-04-01 9:52 ` Jeff King
2020-04-01 14:06 ` Denton Liu
2020-04-03 14:04 ` Jeff King [this message]
2020-04-03 14:38 ` Jeff King
2020-04-04 12:07 ` Denton Liu
2020-04-04 14:21 ` Jeff King
2021-05-05 8:40 ` [PATCH] trace2: refactor to avoid gcc warning under -O3 Ævar Arnfjörð Bjarmason
2021-05-05 9:47 ` Junio C Hamano
2021-05-05 13:34 ` Jeff King
2021-05-05 14:38 ` Johannes Schindelin
2021-05-06 1:26 ` Junio C Hamano
2021-05-06 20:29 ` Johannes Schindelin
2021-05-06 21:10 ` Junio C Hamano
2021-05-11 14:34 ` Johannes Schindelin
2021-05-11 18:00 ` Jeff King
2021-05-11 20:58 ` Junio C Hamano
2021-05-11 21:07 ` Jeff King
2021-05-11 21:33 ` Junio C Hamano
2021-05-11 7:03 ` Junio C Hamano
2021-05-11 13:04 ` [PATCH v2] " Ævar Arnfjörð Bjarmason
2021-05-11 16:40 ` Jeff Hostetler
2021-05-11 17:54 ` Jeff King
2021-05-11 18:08 ` Jeff King
2021-05-11 21:09 ` Junio C Hamano
2021-05-20 0:20 ` Junio C Hamano
2021-05-20 11:05 ` [PATCH v3] " Ævar Arnfjörð Bjarmason
2021-05-20 13:13 ` Jeff King
2021-05-20 22:08 ` Junio C Hamano
2021-05-21 9:34 ` Jeff King
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=20200403140447.GA639586@coredump.intra.peff.net \
--to=peff@peff.net \
--cc=git@vger.kernel.org \
--cc=liu.denton@gmail.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).