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 BE13C3858CDB; Fri, 12 Apr 2024 10:12:54 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org BE13C3858CDB
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1712916774;
	bh=BCJcG9qNrqQbwh9AV82qdLDfF/bWuGY6R/6fF0XrjyU=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=OQNqTGkcgphmAszVArR09oS6leHdAIqAKNMmi7RW7NBhgfPhAX0vYXV0cEadTOLSW
	 79qpTYAHIMy3k9JHbDaNITy70sVZLrodV4wOaO4RY36gp4LxeNK2S6/7c/sas5JGgH
	 syNKO/AIi0z5gy+tVTXOyurQHld69Bi+1Qired04=
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114403] [14 regression] LLVM miscompiled with
 -O3 -march=znver2 -fno-vect-cost-model since r14-6822-g01f4251b8775c8
Date: Fri, 12 Apr 2024 10:12:51 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: tnfchris at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 14.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-114403-4-HmyckY7vpz@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-114403-4@http.gcc.gnu.org/bugzilla/>
References: <bug-114403-4@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=3D114403

--- Comment #23 from Richard Biener <rguenth at gcc dot gnu.org> ---
Maybe easier to understand testcase:

long x[9];
long a[20];
struct { long x; long b[40]; } b;
int __attribute__((noipa))
foo (int n)
{
  int i =3D 0;
  int k =3D 0;
  do
    {
      if (x[k++])  // early exit, loop upper bound is 8 because of this
        break;
      a[i] =3D b.b[2*i]; // the misaligned 2*i access causes peeling for ga=
ps
    }
  while (++i < n);
  return i;
}

int main()
{
  x[8] =3D 1;
  if (foo (20) !=3D 8)
    __builtin_abort ();
  return 0;
}

with -O3 -msse4.1 -fno-vect-cost-model we return 20 instead of 8.  Adding
-fdisable-tree-cunroll avoids the issue.  The upper bound we set on the
vector loop causes us to force taking the IV exit which continues
with i =3D=3D (niter - 1) / VF * VF, but 'niter' is 20 here.=