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From: "kasper93 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106931] New: -Wstringop-overflow false
 positive
Date: Tue, 13 Sep 2022 18:34:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106931

            Bug ID: 106931
           Summary: -Wstringop-overflow false positive
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kasper93 at gmail dot com
  Target Milestone: ---

Created attachment 53572
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53572&action=3Dedit
minimal test case

Hello,

I noticed increased amount of -Wstringop-overflow warnings on FFmpeg build =
with
gcc 12.2.0, doesn't happen with gcc 11.3.0. At first glance most of them are
bogus and happen only when specific set of compiler flags are used.

I minimized one case, see attachment, it is pretty simple. I think gcc shou=
ld
handle this properly. Happens with this specific command
gcc -O3 -fno-tree-vectorize -Wstringop-overflow -c test.c

Attached case is minimized cbs_av1.c. For more cases which looks like gcc12
regression you can compile FFmpeg
./configure --enable-lto
make

Note that lto has to be enabled, without lto it doesn't produce those warni=
ngs.
I can minimize more cases, but frankly I don't want to spend time minimizin=
g it
only to see the same pattern at the end. So maybe let's work on this first.

Tested with FFmpeg 60d8c2019f

Thanks,
Kacper=