[Mesa-dev] [PATCH 12/17] intel/compiler/fs: Implement ddy without using align16 for Gen11+

[Kenneth Graunke]

On Tuesday, February 20, 2018 9:15:19 PM PST Matt Turner wrote:
> Align16 is no more. We previously generated an align16 ADD instruction
> to calculate DDY:
> 
>    add(8) g11<1>F  -g10<4>.xyxyF  g10<4>.zwzwF  { align16 1Q };
> 
> Without align16, we now implement it as two align1 instructions:
> 
>    add(4) g11<2>F   -g10<4,2,0>F    g10.2<4,2,0>F  { align1 1N };
>    add(4) g11.1<2>F -g10.1<4,2,0>F  g10.3<4,2,0>F  { align1 1N };
> ---
>  src/intel/compiler/brw_fs_generator.cpp | 70 ++++++++++++++++++++++++++-------
>  1 file changed, 56 insertions(+), 14 deletions(-)
> 
> diff --git a/src/intel/compiler/brw_fs_generator.cpp b/src/intel/compiler/brw_fs_generator.cpp
> index 013d2c820a0..ffc46972420 100644
> --- a/src/intel/compiler/brw_fs_generator.cpp
> +++ b/src/intel/compiler/brw_fs_generator.cpp
> @@ -1192,23 +1192,65 @@ fs_generator::generate_ddy(const fs_inst *inst,
>  {
>     if (inst->opcode == FS_OPCODE_DDY_FINE) {
>        /* produce accurate derivatives */
> -      struct brw_reg src0 = src;
> -      struct brw_reg src1 = src;
> +      if (devinfo->gen >= 11) {
> +         struct brw_reg x = src;
> +         struct brw_reg y = src;
> +         struct brw_reg z = src;
> +         struct brw_reg w = src;
> +         struct brw_reg dst_e = dst;
> +         struct brw_reg dst_o = dst;

Maybe call these dst_even and dst_odd?
Or perhaps dst_e = dst /* even channels */?

> +
> +         x.vstride = BRW_VERTICAL_STRIDE_4;
> +         y.vstride = BRW_VERTICAL_STRIDE_4;
> +         z.vstride = BRW_VERTICAL_STRIDE_4;
> +         w.vstride = BRW_VERTICAL_STRIDE_4;
> +
> +         x.width = BRW_WIDTH_2;
> +         y.width = BRW_WIDTH_2;
> +         z.width = BRW_WIDTH_2;
> +         w.width = BRW_WIDTH_2;
> +
> +         x.hstride = BRW_HORIZONTAL_STRIDE_0;
> +         y.hstride = BRW_HORIZONTAL_STRIDE_0;
> +         z.hstride = BRW_HORIZONTAL_STRIDE_0;
> +         w.hstride = BRW_HORIZONTAL_STRIDE_0;

If you like, you could drop some wordiness by doing:

      struct brw_reg x = stride(src, 4, 2, 0);
      struct brw_reg y = stride(src, 4, 2, 0);
      struct brw_reg z = stride(src, 4, 2, 0);
      struct brw_reg w = stride(src, 4, 2, 0);

> +
> +         x.subnr = 0 * sizeof(float);
> +         y.subnr = 1 * sizeof(float);
> +         z.subnr = 2 * sizeof(float);
> +         w.subnr = 3 * sizeof(float);
> +

With or without any suggestions, this patch is:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
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