From: Frederic Weisbecker <fweisbec@gmail.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] perf tools: Prevent from BITS_PER_LONG redefinition
Date: Sat, 2 Jan 2010 18:01:54 +0100 [thread overview]
Message-ID: <20100102170151.GB5076@nowhere> (raw)
In-Reply-To: <4B3C8677.3030606@goop.org>
On Thu, Dec 31, 2009 at 10:09:43PM +1100, Jeremy Fitzhardinge wrote:
> On 12/31/2009 08:45 AM, Frederic Weisbecker wrote:
>>> You can use if() with a constant expression instead of #if.
>>>
>>
>>
>> I did not write this code. But yes you're right, although I
>> think CPP is more suitable here because fls() can be called
>> from fastpath and this conditional build makes one check less
>> and lesser i-cache footprint.
>>
>
> Constant if()s are removed at compile time, so there should be no
> runtime overhead. Constant if()s are generally preferable to #if
> because the compile will statically check the other code branch, even if
> it never gets executed, which helps prevent it from rotting.
Good point! I did not think about compile time optimizations.
I'll try that then. Thanks!
prev parent reply other threads:[~2010-01-02 17:02 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-18 22:05 [PATCH] perf tools: Prevent from BITS_PER_LONG redefinition Frederic Weisbecker
2009-12-19 9:26 ` Peter Zijlstra
2009-12-19 14:34 ` Frederic Weisbecker
2009-12-20 5:11 ` Jeremy Fitzhardinge
2009-12-30 21:45 ` Frederic Weisbecker
2009-12-31 11:09 ` Jeremy Fitzhardinge
2010-01-02 17:01 ` Frederic Weisbecker [this message]
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