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 2E0063870924; Wed,  5 Aug 2020 12:24:04 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 2E0063870924
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1596630244;
 bh=bfOdyRNBqtqAhbhBMsgnPHjcpQfe1i8zJ82airJeCCQ=;
 h=From:To:Subject:Date:In-Reply-To:References:From;
 b=dbYJ5bcWfZ201rh5xwzEEgVn0yPbd5RL0Dk1c0JxlW0TqSWi/B2uKhtws//1h5N/N
 239FcUpOdagL55X8zVeEX1bYBCNY18rE6C5b5ZbgMkG8KaiEzDExSUzew3Zbia5GfG
 BP1frXxhmxL4jwvzbokA2JUs0eBtSxdZT1k4Bdnw=
From: "matz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/96373] SVE miscompilation on vectorized division loop,
 leading to FP exception
Date: Wed, 05 Aug 2020 12:24:03 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 10.2.1
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: matz at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: rsandifo at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-96373-4-FyaPXTfqRP@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-96373-4@http.gcc.gnu.org/bugzilla/>
References: <bug-96373-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 05 Aug 2020 12:24:04 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96373

--- Comment #10 from Michael Matz <matz at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #5)
> > Just note that _all_ floating point operations, not just divisions, can=
 trap
> > (without fast-math).  You never know if the user enabled stops for any =
of
> > the FP exceptions (overflow, underflow, inexact, invalid op, div-by-zer=
o).=20
>=20
> You need #pragma STDC FENV_ACCESS ON for that, otherwise it's undefined
> behaviour.

Sure, that's for operations that occur due to normal abstract machine
evaluations.  The point here is that we introduce operations that aren't in=
 the
original
program (for the testcase on "array elements" after [10]), and if we do so
those
must be unobservable.  These pragmas don't give license to introduce additi=
onal
faults that can't possibly have happened in the abstract machine.  (To see
this, replace all arrays elements by 1.0, then the FP operations are all ex=
act,
we still get SIGFPE).=