From: Andrew Haley <aph@redhat.com>
To: Allan Sandfeld Jensen <linux@carewolf.com>, gcc@gcc.gnu.org
Cc: Jakub Jelinek <jakub@redhat.com>
Subject: Re: GCC turns &~ into | due to undefined bit-shift without warning
Date: Fri, 22 Mar 2019 13:38:00 -0000 [thread overview]
Message-ID: <e2c37a42-5daa-1e6b-502e-767ffc14b332@redhat.com> (raw)
In-Reply-To: <6941168.EvYhyI6sBW@twilight>
On 3/22/19 10:20 AM, Allan Sandfeld Jensen wrote:
> On Freitag, 22. März 2019 11:02:39 CET Andrew Haley wrote:
>> On 3/21/19 10:19 PM, Allan Sandfeld Jensen wrote:
>>> From having fixed UBSAN warnings, I have seen many cases where undefined
>>> behavior was performed, but where the code was aware of it and the final
>>> result of the expression was well defined nonetheless.
>>
>> Is this belief about undefined behaviour commonplace among C programmers?
>> There's nothing in the standard to justify it: any expression which contains
>> UB is undefined.
>
> Yes, even GCC uses undefined behavior when it is considered defined for
> specific architecture,
If it's defined for a specific architecture it's not undefined. Any compiler
is entitled to do anything with UB, and "anything" includes extending the
language to make it well defined.
--
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
next prev parent reply other threads:[~2019-03-22 13:38 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-11 8:49 Moritz Strübe
2019-03-11 9:14 ` Jakub Jelinek
2019-03-11 11:06 ` Moritz Strübe
2019-03-11 11:17 ` Jakub Jelinek
2019-03-20 14:08 ` Moritz Strübe
2019-03-20 14:26 ` Christophe Lyon
2019-03-20 15:39 ` Moritz Strübe
2019-03-20 15:49 ` Jakub Jelinek
2019-03-20 17:36 ` Andrew Haley
2019-03-21 8:17 ` Richard Biener
2019-03-21 8:25 ` Alexander Monakov
2019-03-21 8:35 ` Richard Biener
2019-03-21 8:54 ` Moritz Strübe
2019-03-21 9:52 ` Andrew Haley
2019-03-11 11:24 ` Vincent Lefevre
2019-03-11 12:51 ` David Brown
2019-03-12 15:40 ` Vincent Lefevre
2019-03-12 20:57 ` David Brown
2019-03-13 2:25 ` Vincent Lefevre
2019-03-13 10:18 ` David Brown
2019-03-26 22:51 ` Vincent Lefevre
2019-03-21 22:20 ` Allan Sandfeld Jensen
2019-03-21 22:31 ` Jakub Jelinek
2019-03-22 9:27 ` Allan Sandfeld Jensen
2019-03-22 9:50 ` Jakub Jelinek
2019-03-22 10:02 ` Andrew Haley
2019-03-22 10:20 ` Allan Sandfeld Jensen
2019-03-22 12:28 ` David Brown
2019-03-22 12:40 ` Jakub Jelinek
2019-03-22 13:38 ` Andrew Haley [this message]
2019-03-22 14:35 ` Allan Sandfeld Jensen
2019-03-22 22:08 ` Andrew Pinski
2019-03-22 22:38 ` Andrew Pinski
2019-03-22 23:42 ` Joseph Myers
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