From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 66E653858D37; Thu, 25 May 2023 14:15:54 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 66E653858D37
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1685024154;
	bh=x7G6ZDMjeDZweGPxWJVPuVYTOWiJlDClIA+UHosomD0=;
	h=From:To:Subject:Date:From;
	b=M1omPAT4EXyQLiJZYIpk9nNWDvDC1s42nCZFWtRieoLu865rgYLlZEv8yEcZ5sUdu
	 tENaKCeqWpNNlDkK7Tn1DScyzUCATthcLBnsw31Fx5l4bIOn+yEidjOzssJD3CU4Iy
	 cPlxumLRBIPcTYAV5OrM1laOkB3X6EMyebHPI2rY=
From: "shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/109967] New: Wrong code at -O2 on x86_64-linux-gnu
Date: Thu, 25 May 2023 14:15:54 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: shaohua.li at inf dot ethz.ch
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-109967-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109967

            Bug ID: 109967
           Summary: Wrong code at -O2 on x86_64-linux-gnu
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
  Target Milestone: ---

For the following code, gcc trunk at -O2 emits the wrong code. This seems t=
o be
a long latent bug since GCC-7 (I tried gcc-7.4 on compiler explorer, which
still emits the wrong result.)

Compiler explorer: https://godbolt.org/z/YGeWedWq7

$ cat a.c
int printf(const char *, ...);
int a, c;
int main() {
  long f[2];
  int e =3D 0;
  for (; e < 2; e++) {
    {
      char g[20];
      char *b =3D g;
      int d =3D 48, e =3D 0;
      while (d && e < 5)
        b[e++] =3D d /=3D 10;
      c =3D e;
    }
    f[c - 2 + e] =3D 1;
  }
  a =3D f[0];
  printf("%d\n", a);
}
$
$ gcc-tk -O0 a.c && ./a.out
1
$ gcc-tk -O2 a.c && ./a.out
4
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=3Dgcc-tk
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f0=
50dabbf6dd3b992c3b46661848dbcf30d9e/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/=
lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=3Dc,c++
--prefix=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f050dabbf6dd3=
b992c3b46661848dbcf30d9e
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230523 (experimental) (GCC)=20
$=