[Mesa-dev] [PATCH 3/3] i965: Stop splitting fma() prior to optimization

[Jason Ekstrand]

On Thu, May 5, 2016 at 6:22 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:

>
> On May 5, 2016 6:13 PM, "Ilia Mirkin" <imirkin at alum.mit.edu> wrote:
> >
> > On Thu, May 5, 2016 at 8:51 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> > > According to the GLSL spec, if the user uses fma directly and you have
> it
> > > in your hardware, you shouldn't split it.  For a while now, we've been
> > > splitting all fma's up-front and then planned to fuse them later.  The
> only
> > > reason why this possibly helped before was for ARB programs which is
> > > handled by the previous commit. This fixes rendering corruptions in
> Tomb
> > > Raider.
> > >
> > > Shader-db results on Haswell:
> > >
> > >    total instructions in shared programs: 7560300 -> 7561510 (0.02%)
> > >    instructions in affected programs: 56265 -> 57475 (2.15%)
> > >    helped: 86
> > >    HURT: 291
> > >
> > > The only shaders in the database that are affected are from Shadow of
> > > Mordor which is the first app in our database to use fma().
> > >
> > > Reported-by: Kenneth Graunke <kenneth at whitecape.org>
> > > ---
> > >  src/mesa/drivers/dri/i965/brw_compiler.c | 1 -
> > >  1 file changed, 1 deletion(-)
> > >
> > > diff --git a/src/mesa/drivers/dri/i965/brw_compiler.c
> b/src/mesa/drivers/dri/i965/brw_compiler.c
> > > index 0ea5e8b..7969543 100644
> > > --- a/src/mesa/drivers/dri/i965/brw_compiler.c
> > > +++ b/src/mesa/drivers/dri/i965/brw_compiler.c
> > > @@ -72,7 +72,6 @@ shader_perf_log_mesa(void *data, const char *fmt,
> ...)
> > >      * split all ffma instructions during opt_algebraic and we then
> re-combine \
> > >      * them as a later step.
>          \
> > >      */
>         \
> > > -   .lower_ffma = true,
>         \
> >
> > Looks like maybe there's a comment above in need of updating?
>
> Good call. :-)
>

Fixed locally.

> >     .lower_sub = true,
>        \
> > >     .lower_fdiv = true,
>         \
> > >     .lower_scmp = true,
>         \
> > > --
> > > 2.5.0.400.gff86faf
> > >
> > > _______________________________________________
> > > mesa-dev mailing list
> > > mesa-dev at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20160505/7149410f/attachment.html>