On Mon, Jun 19, 2006 at 11:20:20AM -0700, Bill Studenmund wrote:
> On Thu, Jun 15, 2006 at 02:38:24PM -0700, Garrett D'Amore wrote:
> > 
> > I'm not sure how good gcc's optimizer is at detecting that:
> > 
> >     struct {
> >        bus_space_handle_t h;
> >        bus_space_tag_t   t;
> >     } s;
> > 
> >     bus_space_write_1(s->t, s->h, OFFSET1, VAL1);
> >     /* possibly insert code that doesn't modify s */
> >     bus_space_write_1(s->t, s->h, OFFSET2, VAL2);
> > 
> > both values of s->t and s->h are really the same and could be cached in
> > registers without having to dereference thru s for each
> > bus_space_write_1 call.
> 
> It probably can't assume that if there's a function call in there
> somewhere. Assign them to local variables & be explicit that they can be
> cached. :-)

I thought I already mentioned this, but maybe not.

If you use accessor functions, and mark them "pure", GCC should do CSE
on the calls.  This is sort of gross, but it would give the effect
you're looking for.