From: Ian Lance Taylor <iant@google.com>
To: gcc@gcc.gnu.org
Subject: Re: New no-undefined-overflow branch
Date: Fri, 06 Mar 2009 19:53:00 -0000 [thread overview]
Message-ID: <m3eixacuzn.fsf@google.com> (raw)
In-Reply-To: <1236364579.1654.5.camel@pc960.cambridge.arm.com> (Richard Earnshaw's message of "Fri\, 06 Mar 2009 18\:36\:19 +0000")
Richard Earnshaw <rearnsha@arm.com> writes:
> On Fri, 2009-03-06 at 16:09 +0100, Paolo Bonzini wrote:
>> If this does not work, on ARM you can also hope for something like this:
>>
>> ADD R0, R1, R2
>> XORS R0, R2, R3
>> XORSMI R1, R2, R3
>> SWIMI #trap
>
> On ARM you can just check for overflow directly...
>
> ADDS R0, R1, R2
> SWIVS #trap
This point should not be missed. Some processors (MIPS) have trapping
arithmetic instructions, but many processors have an overflow flag which
can be tested. Any useful design for -ftrapv needs to make it possible
to use that overflow flag in the generated code. It will always be more
efficient than using arithmetic to check for overflow.
Ian
next prev parent reply other threads:[~2009-03-06 19:28 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-26 11:05 Richard Guenther
2009-02-26 11:28 ` Manuel López-Ibáñez
2009-02-26 12:02 ` Richard Guenther
2009-02-26 13:07 ` Joseph S. Myers
2009-02-26 13:22 ` Richard Guenther
2009-02-26 14:16 ` Dave Korn
2009-02-26 23:08 ` Zdenek Dvorak
2009-02-27 10:16 ` Richard Guenther
2009-02-27 12:07 ` Dave Korn
2009-02-27 13:17 ` Richard Guenther
2009-02-27 13:35 ` Dave Korn
2009-02-27 13:45 ` Richard Guenther
2009-02-27 18:07 ` Zdenek Dvorak
2009-02-27 17:58 ` Zdenek Dvorak
2009-02-27 18:17 ` Richard Guenther
2009-02-27 23:07 ` Diego Novillo
2009-02-28 0:04 ` Joseph S. Myers
2009-02-28 10:29 ` Richard Guenther
2009-03-05 17:24 ` Geert Bosch
2009-03-06 12:28 ` Richard Guenther
2009-03-06 13:54 ` Joseph S. Myers
2009-03-06 14:10 ` Richard Guenther
2009-03-06 14:29 ` Joseph S. Myers
2009-03-06 17:17 ` Geert Bosch
2009-03-06 17:42 ` Joseph S. Myers
2009-03-06 14:44 ` Paolo Bonzini
2009-03-06 15:10 ` Richard Guenther
2009-03-06 15:23 ` Paolo Bonzini
2009-03-06 15:39 ` Paolo Bonzini
2009-03-06 16:19 ` Richard Guenther
2009-03-06 17:23 ` Joseph S. Myers
2009-03-06 18:54 ` Richard Earnshaw
2009-03-06 19:53 ` Ian Lance Taylor [this message]
2009-03-06 20:42 ` Robert Dewar
[not found] ` <1236364189.1654.2.camel@pc960.cambridge.arm.com>
2009-03-06 19:34 ` Paolo Bonzini
2009-03-06 15:58 ` Ian Lance Taylor
2009-03-06 17:25 ` Joseph S. Myers
2009-03-06 17:52 ` Paolo Bonzini
2009-03-06 18:36 ` Joseph S. Myers
2009-03-27 13:11 ` Eus
2009-03-27 18:07 ` Paolo Bonzini
2009-03-31 4:55 ` Eus
2009-03-06 17:21 ` Geert Bosch
2009-03-06 17:38 ` Joseph S. Myers
2009-03-06 18:47 ` Paolo Bonzini
2009-03-07 3:00 ` Joseph S. Myers
2009-03-06 22:46 ` Geert Bosch
2009-03-07 1:21 ` Richard Guenther
2009-02-28 10:25 ` Richard Guenther
2009-02-27 19:58 Jay Foad
2009-02-27 22:41 ` Richard Guenther
2009-02-27 23:00 ` Ian Lance Taylor
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