From: Marek Polacek <polacek@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>,
Mikael Morin <mikael.morin@sfr.fr>,
Jeff Law <law@redhat.com>,
gcc-patches <gcc-patches@gcc.gnu.org>,
Richard Sandiford <rdsandiford@googlemail.com>
Subject: Re: [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour
Date: Thu, 13 Aug 2015 13:48:00 -0000 [thread overview]
Message-ID: <20150813134032.GM3335@redhat.com> (raw)
In-Reply-To: <CAFiYyc0saOHRP8Z6J251eUmmxQK_58=CRhxh9p1s-2G4uU7AUw@mail.gmail.com>
On Thu, Aug 13, 2015 at 01:11:53PM +0200, Richard Biener wrote:
> Rather ubsan should not complain about implementation defined behavior (or
> should separate those cases out with a different switch compared to undefined
> behavior).
I think ubsan doesn't complain about implementation-defined behavior. It seems
to me that in this thread it only (rightfully) complained about left-shifting of
negative value.
Using __GCC__ conditional in a case where we rely on what gcc does when
right-shifting a negative value, i.e. that it sign-extends, seems fine
(ubsan certainly doesn't error on that).
Marek
next prev parent reply other threads:[~2015-08-13 13:40 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-06 10:26 Mikael Morin
2015-08-11 19:49 ` Jeff Law
2015-08-12 11:01 ` Richard Biener
2015-08-12 11:07 ` Markus Trippelsdorf
2015-08-12 11:09 ` Richard Biener
2015-08-12 13:34 ` Mikael Morin
2015-08-12 17:02 ` Jeff Law
2015-08-12 17:12 ` Richard Biener
2015-08-12 18:07 ` Jeff Law
2015-08-12 18:32 ` Richard Biener
2015-08-12 18:41 ` Jeff Law
2015-08-12 20:07 ` Richard Sandiford
2015-08-12 20:53 ` Mike Stump
2015-08-13 10:11 ` Richard Biener
2015-08-13 18:01 ` Mike Stump
2015-08-14 7:31 ` Richard Biener
2015-08-18 15:35 ` Mikael Morin
2015-08-18 17:51 ` Jeff Law
2015-08-13 11:03 ` Mikael Morin
2015-08-13 11:06 ` Mikael Morin
2015-08-13 11:09 ` Markus Trippelsdorf
2015-08-13 11:20 ` Richard Biener
2015-08-13 13:48 ` Marek Polacek [this message]
2015-08-13 13:55 ` Markus Trippelsdorf
2015-08-13 13:57 ` Marek Polacek
2015-08-12 19:20 ` Mike Stump
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