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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 10:38:44 -0400	[thread overview]
Message-ID: <20200403143844.GB639586@coredump.intra.peff.net> (raw)
In-Reply-To: <20200403140447.GA639586@coredump.intra.peff.net>

On Fri, Apr 03, 2020 at 10:04:47AM -0400, Jeff King wrote:

> 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.

I guess I should have been more clear since the -O1 and -Og locations
are different. -O1 complains in filter_refs().

By the way, that function's handling of filter->kind seems very sketchy
to me. It does:

  int ret = 0;
  if (!filter->kind)
                die("filter_refs: invalid type");
  else {
          /*
           * For common cases where we need only branches or remotes or tags,
           * we only iterate through those refs. If a mix of refs is needed,
           * we iterate over all refs and filter out required refs with the help
           * of filter_ref_kind().
           */
          if (filter->kind == FILTER_REFS_BRANCHES)
                  ret = for_each_fullref_in("refs/heads/", ...);
          else if (filter->kind == FILTER_REFS_REMOTES)
                  ret = for_each_fullref_in("refs/remotes/", ...);
          else if (filter->kind == FILTER_REFS_TAGS)
                  ret = for_each_fullref_in("refs/tags/", ...);
          else if (filter->kind & FILTER_REFS_ALL)
                  ret = for_each_fullref_in_pattern(filter, ...);
          if (!ret && (filter->kind & FILTER_REFS_DETACHED_HEAD))
                  head_ref(...);
  }

So filter->kind is sometimes treated like a bitfield and sometimes not.
I can set it to (ALL & DETACHED_HEAD) to get something useful, but not
(BRANCHES & HEAD). The up-front check tries to complain if you didn't
ask for anything, but there are other flags like INCLUDE_BROKEN that
would cause "!filter->kind" to be false, but still not produce any
output.

And shouldn't we be checking the return value of head_ref() like the
others?

All of this is outside the scope of our current discussion, and
untangling it might be messy (because it could touch the callers). I
just wanted to document my findings for now. :)

-Peff

  reply	other threads:[~2020-04-03 14:38 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-01  7:30 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
2020-04-03 14:38       ` Jeff King [this message]
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

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