Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

[Chris Lattner]

On Mar 6, 2008, at 2:06 PM, Andi Kleen wrote:

> On Thu, Mar 06, 2008 at 12:56:16PM -0800, H. Peter Anvin wrote:
> > Richard Guenther wrote:
> > > A patched GCC IMHO makes only sense if it is always-on, yet  
> > > another option
> > > won't help in corner cases.  And corner cases is exactly what  
> > > people seem
> > > to care about.  For this reason that we have this single release,  
> > > 4.3.0,
> > > that
> > > behaves "bad" is already a problem.
> >
> > The option will help embedded vendors who can guarantee that it's  
> > not a
> > problem.
>
> For very very low values of "help".
>
> To be realistic it is very unlikely anybody will measure a difference
> from a few more or a few less clds in a program. It's not that they're
> expensive instructions

They aren't?  According to http://www.agner.org/optimize/instruction_tables.pdf 
, they have a latency of 52 cycles on at least one popular x86 chip.

-Chris
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