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

Andi Kleen
2008-03-06T22:04:50Z

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 and they normally don't happen in inner loops either.

"If you enable this option you will get an optimization that you cannot
measure" @)

-Andi