Re: [v3] atomics

[David Daney <ddaney at avtrex dot com>]

Lawrence Crowl wrote:
> On 4/18/08, David Daney <ddaney@avtrex.com> wrote:
> > David Daney wrote:
> >
> > > Jakub Jelinek wrote:
> > >
> > > > On Fri, Apr 18, 2008 at 10:51:33AM -0700, David Daney wrote:
> > > >
> > > > > At this point I don't really have an opinion as to how to fix the
> > problem.  One thought that comes to mind is to change the definition of
> > atomic_flag so that the size of the atomic variable is appropriate for the
> > target architecture (32 bits in the case of MIPS)
> > > > Best is to add support for the 8 and 16-bit sync builtins.
> > > > See e.g. sparc or s390 backends how it can be done using 32-bit
> > > > compare and swap instruction.
> > > Thanks Jakub,
> > >
> > > Would it make sense to handle this in a more generic manner where the
> > operations are expanded?
> >  Well, that's not likely to work...
> >
> >
> > > Or should each target just write patterns for 8 and 16 bit operations if
> > they don't natively support it?
> >  I will do this for MIPS.
>
> The intent was that either implementations expand the size of the atomics
> to the minimum supported size or implement the operation with a
> compare-and-swap on the word containing the atomic.

Thanks,

Which would you recommend for this case?

Changing the size of the atomics could cause increased memory usage, 
implementing the atomic operations on sub-words would increase code size.

Changing our minds later would change the ABI.

David Daney