On Wednesday, March 18, 2015 11:27:19 PM Connor Abbott wrote:
> On Wed, Mar 18, 2015 at 11:24 PM, Kenneth Graunke <kenn...@whitecape.org>
> wrote:
> > On Tuesday, March 17, 2015 07:17:19 PM Jason Ekstrand wrote:
> >> ---
> >> src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 8 +++++++-
> >> 1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> >> b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> >> index 5da8423..41f9ae2 100644
> >> --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> >> +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> >> @@ -1234,7 +1234,13 @@ fs_visitor::nir_emit_alu(nir_alu_instr *instr)
> >> break;
> >>
> >> case nir_op_ffma:
> >> - inst = emit(MAD(result, op[2], op[1], op[0]));
> >> + if (brw->gen >= 6) {
> >> + inst = emit(MAD(result, op[2], op[1], op[0]));
> >> + } else {
> >> + fs_reg temp = vgrf(glsl_type::float_type);
> >> + emit(MUL(temp, op[0], op[1]));
> >> + inst = emit(ADD(result, temp, op[2]));
> >> + }
> >> inst->saturate = instr->dest.saturate;
> >> break;
> >>
> >>
> >
> > I think this is a reasonable plan for now - it's simple and works.
> > Connor is probably right that we can do better with nir_opt_algebraic,
> > but I think doing that as a follow-on patch justified by statistics
> > would be wise.
>
> Actually, it seems like we already have a lower_ffma option, so just
> setting that to true on gen < 6 should be even less code than this...You make a good point. Let's do that.
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