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Re: [patch][RFC] 160-bits bitmap_element
On Fri, Aug 17, 2012 at 02:04:50PM +0200, Steven Bosscher wrote:
> On Fri, Aug 17, 2012 at 1:54 PM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
> > Well, another effect of reducing the size of BITMAP_WORD is that
> > operations are not performed in a mode optimally using CPU regs
> > (did you check code generation differences on a 64bit host?).
>
> I did, on x86_64 and on powerpc64. The effect is not dramatic, most of
> these machines can perform 32 bits operations just fine (I think the
> only exception would be alpha, maybe?).
One this is testing a bit in a bitmap or setting it, except for old alpha I
guess it shouldn't be noticeable. But then there are functions that iterate
over the bitmap, where using larger type should be noticeable (I mean stuff
like bitmap copying, logical operations on whole bitmap, etc.).
Jakub