From: Jeff Law <law@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>,
Mikael Morin <mikael.morin@sfr.fr>,
Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour
Date: Wed, 12 Aug 2015 18:07:00 -0000 [thread overview]
Message-ID: <55CB8B51.5080908@redhat.com> (raw)
In-Reply-To: <F89F5949-3938-4F58-9C31-8BC0B217533B@gmail.com>
On 08/12/2015 11:12 AM, Richard Biener wrote:
>
> Prec is almost never a constant and is heavily used from wide-int.
>
> We are not exploiting this undefined ness in C so I object to making this so much slower.
>
> Can we instead do what we do for abs_hwi and add a checking assert so we can move the tests to the callers that misbehave instead?
Given that ISO C++ is moving away from making shifting 1 into the sign
bit undefined behaviour, maybe we should make UBSan less strict in its
warning. That may eliminate the need for Mikael's patch.
jeff
next prev parent reply other threads:[~2015-08-12 18:07 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 [this message]
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
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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