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 9CA503858402; Fri,  5 Apr 2024 03:42:36 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9CA503858402
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1712288556;
	bh=zTBfxAgWQV42hCYuM0Gv2ZOAFY0ces1hrlyVpScoh5g=;
	h=From:To:Subject:Date:From;
	b=WoHFOZH39QpN94uzea1NGX9k16oh0nUbuoloaXXaRu90JGSx63qtbEJHXL4ig2r7I
	 XM/EKmCJuWoX4wp8ArpeEXEBUJkYrcF/mcHepirwuj8NBctsGLQu16YG5Ax3ihXTGw
	 ILPZjT47VT7siSEKsCbmopln3ZHxP0+Oc9FigPpk=
From: "141242068 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/114597] New: [GCC-14] Miscompilation of pointer assignment
 with inline assembly
Date: Fri, 05 Apr 2024 03:42:36 +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: 141242068 at smail dot nju.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-114597-4@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=3D114597

            Bug ID: 114597
           Summary: [GCC-14] Miscompilation of pointer assignment with
                    inline assembly
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 141242068 at smail dot nju.edu.cn
  Target Milestone: ---

Compiler Explorer: https://gcc.godbolt.org/z/Pn4EG3zzj

```
struct node { void *p; } n;
struct head { struct node *n; } h;

int main () {
  n.p =3D &h;
  asm("":"=3Dm"(n.p):"r"(n.p));
  if (n.p !=3D &h)
    __builtin_abort();
  return 0;
}
```

I sanitized this program with all sanitizers I know, they report nothing.
When compile this program with `gcc-14 -O2`, the compiled program aborts, w=
hile
`-O0` normally exits.

Any potential undefined behavior:
1. strict aliasing, I added option `-fno-strict-aliasing` to `-O2`, the abo=
rt
still exists.
2. If there is some other undefined behavior unknown to me cause this
compilation inconsistency, please let me know.

Regarding the inline assembly, it's important to note that even though `n.p=
` is
specified as an output operand with `=3Dm`, this doesn't necessarily imply =
that
`n.p` will be altered. The inline assembly might simply reassign the origin=
al
value to `n.p`, leaving it effectively unchanged.=