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 6354F3858018; Thu,  4 Jan 2024 12:01:25 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6354F3858018
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1704369685;
	bh=6b7uxHKo4qdcZEsa5yogMykOLbwm2eh8MsSCVuhAJQ4=;
	h=From:To:Subject:Date:From;
	b=SPMnxG4S+aBKt/PzywYTMSWwApXFsrZPZGbunQUzOwl3v41HmJaQpIItBtbSxMbcK
	 E/sW5XatXZmBrCpxG8lIa2ZHkrbyEEK7TBaIl8vufIBuFnf5gPi/9IqUg74MSVzenK
	 B3h1Pj5GUR6VMUINsHToxgHqAqVtEY3B0l+F1fN4=
From: "jwzeng at nuaa dot edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/113232] New: wrong code at -fpack-struct on
 x86_64-pc-linux-gnu
Date: Thu, 04 Jan 2024 12:01:24 +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: jwzeng at nuaa dot edu.cn
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-113232-4@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=3D113232

            Bug ID: 113232
           Summary: wrong code at -fpack-struct on x86_64-pc-linux-gnu
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jwzeng at nuaa dot edu.cn
  Target Milestone: ---

I compiled the following code with gcc at -fpack-struct, and it produces the
wrong code.=20

The correct output result should be 0, but 2048 was output under -fpack-str=
uct.=20

This bug seems to be a long-standing bug that exists on almost all gcc
versions.

Compiler explorer: https://godbolt.org/z/v4sq988P9

```c
$ cat test.c
int printf(const char *, ...);
struct a {
  char b;
  short c;
};
union {
  short b;
  struct a d;
} e;
int main() {
  e.b =3D 0;
  for (e.d.c =3D 0; e.d.c < 8; e.d.c++)
    ;=20=20
  printf("%d\n", e.b);
}
$
$ gcc-tk test.c -O0; ./test.c
0
$ gcc-tk test.c -fpack-struct; ./test.c
2048
$ ccomp test.c -O0; ./a.out
0
$
$ gcc-tk --version
gcc (GCC) 13.1.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$
$ ccomp --version
The CompCert C verified compiler, version 3.12
```=