From: Prarit Bhargava <prarit@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] x86, bitops, variable_test_bit should return 1 not -1 on a match
Date: Thu, 08 Oct 2015 07:48:34 -0400 [thread overview]
Message-ID: <56165812.6070101@redhat.com> (raw)
In-Reply-To: <E661604A-0C9E-4C4F-84C3-BDEAEE2E18F3@zytor.com>
On 08/21/2015 04:08 AM, H. Peter Anvin wrote:
> Wrong fix, though. Instead we should change it to use the set instruction, which would also make it easier to use the CC_SET/CC_OUT proposed macros to use assembly out in the future.
>
> The downside with set is that it only sets a single byte, the upside is that it always outputs 0 or 1, and apparently if the output variable is your bool gcc can use that for optimization.
>
hpa, I didn't realize your comment was suggesting a change. I've done a google
search on "gcc bool optimization" (and various incantations of that) and didn't
find anything that lead me in the direction of making a change. Could you
elaborate on what the issue is?
Thanks,
P.
next prev parent reply other threads:[~2015-10-08 11:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-19 17:18 [PATCH] x86, bitops, variable_test_bit should return 1 not -1 on a match Prarit Bhargava
2015-08-21 6:51 ` Ingo Molnar
2015-08-21 8:08 ` H. Peter Anvin
2015-08-21 11:53 ` Prarit Bhargava
2015-08-24 18:22 ` [PATCH v2] " Prarit Bhargava
2015-10-07 23:27 ` Prarit Bhargava
2015-10-08 8:51 ` Ingo Molnar
2015-10-08 11:48 ` Prarit Bhargava [this message]
2015-08-21 11:50 ` [PATCH] " Prarit Bhargava
2015-08-22 9:14 ` Ingo Molnar
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