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 DB8B83858C60; Thu,  8 Feb 2024 16:37:29 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DB8B83858C60
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1707410249;
	bh=3niYRHsuqYOety/aRfT5lxd4YBcbi9TjZr7r4dhm17Y=;
	h=From:To:Subject:Date:From;
	b=nAHUY4fIM3SIszASptscBD3wS9euGAc5I8u92Dl8olEalN4wqIwjZHBBuUeqDQA0U
	 BQAwPCrMxCn5EUewAPFDiQ2icVxKtNqxS+jOF6hdOPuLul1EDPiwcRYs9LBuX2u+U3
	 5/kkYeSHbrAoB351GlraO67sqeiE8cRfDTkFW1gc=
From: "jamborm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113833] New: 435.gromacs fails verification
 on with -Ofast -march={cascadelake,icelake-server} and PGO after
 r14-7272-g57f611604e8bab
Date: Thu, 08 Feb 2024 16:37:29 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jamborm at gcc dot gnu.org
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 cc blocked
 target_milestone cf_gcchost cf_gcctarget
Message-ID: <bug-113833-4@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=3D113833

            Bug ID: 113833
           Summary: 435.gromacs fails verification on with -Ofast
                    -march=3D{cascadelake,icelake-server} and PGO after
                    r14-7272-g57f611604e8bab
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
                CC: fxue at os dot amperecomputing.com
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

After r14-7272-g57f611604e8bab (Feng Xue: Do not count unused scalar
use when marking STMT_VINFO_LIVE_P [PR113091]), our runs of SPEC 2006
CPU benchmark 435.gromacs on Icelake-server CPU compiled with -Ofast
-march=3Dnative and PGO (with and without LTO) started failing with
miscompare error:

  0002:  3.07684e+02
         3.03476e+02
                   ^

I subsequently verified the failure on an Intel CascadeLake and
bisected it to the aforementioned commit.  We don't see it on our AMD
or Ampere testers (using -march=3Dnative).

I guess the miscomparison error may be well within what is expected
when using -Ofast but even in that case it would be nice to have it
documented here that that is indeed expected.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95=
)=