Re: [tip:core/locking] locking, x86: Slightly shorten __ticket_spin_trylock()

[Avi Kivity]

On 12/02/2009 04:06 PM, Jan Beulich wrote:
> > > > Ingo Molnar<mingo@xxxxxxx>  02.12.09 14:29>>>
> > > >          
> > at first quick sight, this bit looks odd:
> >
> > +       union { int i; bool b; } new;
> >
> > +       return new.b;
> >
> > shouldnt that be short based, to work correctly in the 0-255 CPUs case?
> >      
> No, I can't see why. In both instances, we're using (and had been
> using previously, just with the added movzbl) the outcome of a
> setCC instruction, which produces valid bool (single byte) values.
> It is precisely that reason why I needed to introduce these unions,
> since the upper bytes of the register aren't valid (and shouldn't be
> looked at by the caller).
>
>    

Wouldn't 'u8 ret', as an additional argument be sufficient? gcc still 
ought to be able to use the same register for new and ret if we remove 
the early clobber.

--
error compiling committee.c: too many arguments to function

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