Message-ID: <47B99D64.3090103@tiscali.nl>
Date: Mon, 18 Feb 2008 15:59:48 +0100
From: Roel Kluin <12o3l@tiscali.nl>
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To: David Howells <dhowells@redhat.com>
CC: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>,
       Adrian Bunk <bunk@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
       cbe-oss-dev@ozlabs.org, linuxppc-dev@ozlabs.org,
       Willy Tarreau <w@1wt.eu>, Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH 1/3] Fix Unlikely(x) == y
References: <Pine.LNX.4.64.0802181500410.13406@vixen.sonytel.be> <47B70A61.9030306@tiscali.nl> <20080216092552.325e5726@laptopd505.fenrus.org> <20080216173315.GU8953@1wt.eu> <20080216094226.1e8eede1@laptopd505.fenrus.org> <47B72BFE.9060302@am.sony.com> <20080216103927.2a02352b@laptopd505.fenrus.org> <1203249003.6718.24.camel@concordia> <20080218135609.GD21080@cs181133002.pp.htv.fi> <12131.1203344830@redhat.com>
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David Howells wrote:
> Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com> wrote:
> 
>> Hence shouldn't we ask the gcc people what's the purpose of
>> __builtin_expect(), if it doesn't live up to its promise?
> 
> __builtin_expect() is useful on FRV where you _have_ to give each branch and
> conditional branch instruction a measure of probability whether the branch
> will be taken.
> 
> David

I was wondering whether some of the uses of likely illustrated below are
incorrect or not useful.

x = likely(X) || Y

for ( ... ; likely(...); ... )

while ( likely(X) )

if ( unlikely(X) &&/|| likely(Y) )

if ( X &&/|| unlikely(Y) ) 

return likely(X);

return likely(X) ? a : b;
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