On Thu, Oct 10, 2013 at 03:23:30PM +0200, Andres Freund wrote:
> On 2013-10-10 08:59:47 -0400, Robert Haas wrote:
> > On Tue, Oct 8, 2013 at 6:24 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> > > Do you have a better alternative? Making the computation unconditionally
> > > 64bit will have a runtime overhead and adding a StaticAssert in the
> > > existing macro doesn't work because we use it in array sizes where gcc
> > > balks.
> > > We could try using inline functions, but that's not going to be pretty
> > > either.
> > >
> > > I don't really see that many further usecases that will align 64bit
> > > values on 32bit platforms, so I think we're ok for now.
> >
> > I'd be inclined to make the computation unconditionally 64-bit. I
> > doubt the speed penalty is enough to worry about, and I think we're
> > going to have more and more cases where optimizing for 32-bit
> > platforms is just not the right decision.
>
> MAXALIGN is used in several of PG's hottest functions in many
> scenarios. att_align_nominal is used in slot_deform_tuple,
> heap_deform_tuple, nocachegetattr, etc. So I don't think that's viable
> yet. At least not with much more benefit than this...
Agreed. Besides performance, aligning a wider-than-pointer value is an
unusual need; authors should think thrice before doing that. I might have
even defined the MAXALIGN64 macro in xlog.c rather than a core header.
Incidentally, why does MAXALIGN64 use unsigned math while MAXALIGN uses signed
math?
--
Noah Misch
EnterpriseDB http://www.enterprisedb.com
