Re: volatile qualifier hurts single-threaded optimized case

[Paolo Carlini <pcarlini at suse dot de>]

Benjamin Kosnik wrote:

> > >  static inline _Atomic_word
> > >  __attribute__ ((__unused__))
> > > -  __exchange_and_add_dispatch(volatile _Atomic_word* __mem, int __val)
> > > +  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
> > >
> > >
> > >      
> > Agreed, but doing this means that in the improvements to rope that 
> > Richard (and Hans) also want we have to call __exchange_and_add and 
> > __atomic_add directly,  because in that case the involved memory 
> > locations are volatile and have to remain like that per Hans desiderata, 
> > I gather. 
> >    
> I find this somewhat confusing, but am going to go ahead with this, as
> I have other fixes in the pipeline for this file.
>  
Agreed, agreed. I was just pointing out, for completeness, that we had a 
very long discussion thread, Hans also participating: in that thread 
Richard proposed to change rope to use the atomic functions and prepared 
a patch. Hans was very happy with that patch besides the delicate point 
that, because of races in some cases (i.e., accesses to the atomic 
memory *not* using the primitives for performance reasons) the involved 
memory had to remain volatile for now, to be more safe. Then, the 
dispatchers could not be used...

Paolo.