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 81F7F3858D39; Wed, 15 Nov 2023 16:48:10 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 81F7F3858D39
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1700066890;
	bh=4ArqJguLM0H+cAy5i0OfltnrFQV4HtlL8sGe+T49l8o=;
	h=From:To:Subject:Date:From;
	b=hDYfn9w2eAF27Luvt+vmik9g6Cvr28pKINLzVFYOEmpo1cL4Tx+nKtyJxK0q4D99P
	 ZdDc9ggTwQltmF0v1N1jeBd8/DmJfD1y1X5fmQjIMVxh/13OnkDk6yeThIbqC3vWxk
	 WpatbQtdCfekfXFVvMQfnUY4P7w3Tor+0DAH59WA=
From: "dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/112550] New: Difference in output from -O0 to -01 ?
Date: Wed, 15 Nov 2023 16:48:10 +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: dcb314 at hotmail dot com
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
 attachments.created
Message-ID: <bug-112550-4@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=3D112550

            Bug ID: 112550
           Summary: Difference in output from -O0 to -01 ?
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

Created attachment 56594
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56594&action=3Dedit
C source code

For the attached C code, with this bash script:

$ cat qwe.sh
CC=3D"/home/dcb38/gcc/results/bin/gcc"
FLAGS=3D"-w -ftrivial-auto-var-init=3Dzero -fno-strict-aliasing"

echo bug 981
$CC -O0 $FLAGS bug981.c -o 1.exe
$CC -O1 $FLAGS bug981.c -o 2.exe
./1.exe 1 > 1.out
./2.exe 1 > 2.out
diff 1.out 2.out | head -5

$ source ./qwe.sh
bug 981
38c38
< ...checksum after hashing g_130[i][j] : 19463610
---
> ...checksum after hashing g_130[i][j] : 65FD073B
40c40
$ /home/dcb38/gcc/results/bin/gcc -v 2>&1 | grep exp
gcc version 14.0.0 20231115 (experimental) (081fddbbcf979022)=20
$=20

I don't understand why such a trivial change from -O0 to -O1 would cause
such a difference.

Is there perhaps another -f flag I should use to get no difference ?=