linux-kernel - Re: [PATCH 2/5] bitops: compile time optimization for hweight

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Message-ID: <20100218115155.GA20473@aftab>
Date:	Thu, 18 Feb 2010 12:51:55 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Michal Marek <mmarek@...e.cz>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Borislav Petkov <petkovbb@...glemail.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Thu, Feb 18, 2010 at 11:51:50AM +0100, Peter Zijlstra wrote:
> I guess one way to achieve that is to create a arch/x86/lib/hweight.c
> that includes lib/hweight.c and give the x86 one special compile flags
> and not build the lib on.

That's what I thought initially too but that won't fly because the
lib/hweight.c helpers have to be inlined into arch/x86/lib/hweight.c so
that gcc can take care of the clobbered registers. Otherwise, it just a
"call __sw_hweightXX" that gets issued into asm.


-- 
Regards/Gruss,
Boris.

-
Advanced Micro Devices, Inc.
Operating Systems Research Center
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