From: Alexander Monakov <amonakov@ispras.ru>
To: Joseph Myers <joseph@codesourcery.com>
Cc: Marek Polacek <polacek@redhat.com>,
Richard Biener <rguenther@suse.de>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Prevent extract_muldiv from introducing an overflow (PR sanitizer/80800)
Date: Fri, 19 May 2017 20:06:00 -0000 [thread overview]
Message-ID: <alpine.LNX.2.20.13.1705192231520.5721@monopod.intra.ispras.ru> (raw)
In-Reply-To: <alpine.DEB.2.20.1705191721030.11802@digraph.polyomino.org.uk>
On Fri, 19 May 2017, Joseph Myers wrote:
> On Fri, 19 May 2017, Alexander Monakov wrote:
> > (to be precise, if the multiplication is done in a signed type and the middle
> > constant factor was a negated power of two, the sign change needs to remain:
> >
> > a * -4 * b * 2
> >
> > needs to be transformed to
> >
> > a * -1 * b * 8 )
>
> Shouldn't that only be the case if the middle constant was -1 and the
> outer constant was 1? If a * -4 * b is INT_MIN, a * b won't overflow and
> so a * b * -8 should be a safe transformation.
Indeed, I should have considered the situation more carefully. Thank you for
the correction.
Alexander
next prev parent reply other threads:[~2017-05-19 19:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-19 7:21 Marek Polacek
2017-05-19 8:21 ` Richard Biener
2017-05-19 10:43 ` Marek Polacek
2017-05-19 10:57 ` Richard Biener
2017-05-19 10:59 ` Alexander Monakov
2017-05-19 15:36 ` Marek Polacek
2017-05-19 15:51 ` Alexander Monakov
2017-05-19 16:18 ` Richard Biener
2017-05-19 18:45 ` Joseph Myers
2017-05-19 20:06 ` Alexander Monakov [this message]
2017-05-24 8:11 ` Richard Biener
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