[Mesa-dev] [PATCH 5/9] i965/nir: Emit MUL + ADD for MAD on GEN <= 5

[Kenneth Graunke]

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.

Patches 3-6 are:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: This is a digitally signed message part.
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20150318/9be6b58f/attachment.sig>