On 05/28/2015 11:33 AM, Borislav Petkov wrote:
> On Thu, May 28, 2015 at 09:57:15AM -0700, H. Peter Anvin wrote:
>> Why?!
>>
>> We are taking about 48 bytes run once per cpu. It isn't worth it to
>> optimize, in fact the extra code size hurts more.
>
> I wanted to save us the redundant copying of the exact same bytes.
> Because when there's no preceding whitespace, p and q point at the same
> thing so we end up doing *p = *p.
>
> OTOH, without the optimization, the code is even simpler.
>
> I can remove it if you wanna - I don't care all that much.
>
Yes, please. Actually, with a test inside the loop the way you have it,
the resulting code will almost certainly be slower -- a redundant write
to an already dirty cache line is way cheaper than a branch.
-hpa
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