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Date: Wed, 15 Jun 2005 16:34:59 +0100 (BST)
From: "Maciej W. Rozycki" <macro@linux-mips.org>
To: cutaway@bellsouth.net
Cc: linux-kernel@vger.kernel.org
Subject: Re: .../asm-i386/bitops.h  performance improvements
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On Wed, 15 Jun 2005 cutaway@bellsouth.net wrote:

> In find_first_bit() there exists this the sequence:
> 
> shll $3,%%edi
> addl %%edi,%%eax
> 
> LEA knows how to multiply by small powers of 2 and add all in one shot very
> efficiently:
> 
> leal (%%eax,%%edi,8),%%eax

 Be careful about model-specific penalties from using certain address 
modes and AGIs when using "lea" for such calculations.

  Maciej