[Mesa-dev] [PATCH 1/6] i965: Don't force a header for texture offsets of 0.

[Jason Ekstrand]

Reviewed-by Jason Ekstrand <jason at jlekstrand.net>

The rest of the patches look just as good to me now as when I wrote them,
but you can't very well call that a review. :-p
On Apr 23, 2016 4:39 PM, "Kenneth Graunke" <kenneth at whitecape.org> wrote:

> Calling textureOffset() with an offset of <0, 0, 0> is equivalent to
> calliing texture().  We don't actually need to set up an offset,
> which causes a message header to be created.
>
> A fairly common pattern is to sample at a point with a bunch of
> offsets, and average them.  It's natural to write all the lookups
> as textureOffset, but use <0, 0> for the center sample.
>
> shader-db results on Skylake:
>
> total instructions in shared programs: 9092095 -> 9092087 (-0.00%)
> instructions in affected programs: 2826 -> 2818 (-0.28%)
> helped: 12
> HURT: 2
>
> total cycles in shared programs: 70870166 -> 70870144 (-0.00%)
> cycles in affected programs: 15924 -> 15902 (-0.14%)
> helped: 2
> HURT: 0
>
> This also helps prevent code quality regressions in a future patch.
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 4 +++-
>  1 file changed, 3 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 7ef3062..725f5da 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> @@ -3132,7 +3132,9 @@ fs_visitor::nir_emit_texture(const fs_builder &bld,
> nir_tex_instr *instr)
>           nir_const_value *const_offset =
>              nir_src_as_const_value(instr->src[i].src);
>           if (const_offset) {
> -            tex_offset = brw_imm_ud(brw_texture_offset(const_offset->i32,
> 3));
> +            unsigned header_bits = brw_texture_offset(const_offset->i32,
> 3);
> +            if (header_bits != 0)
> +               tex_offset = brw_imm_ud(header_bits);
>           } else {
>              tex_offset = retype(src, BRW_REGISTER_TYPE_D);
>           }
> --
> 2.8.0
>
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