[Mesa-dev] [PATCH 07/16] nir/lower_tex: Add support for lowering coordinate offsets

[Pohjolainen, Topi]

On Thu, Jul 21, 2016 at 09:21:53PM -0700, Jason Ekstrand wrote:
> On i965, we can't support coordinate offsets for texelFetch or rectangle
> textures.  Previously, we were doing this with a GLSL pass but we need to
> do it in NIR if we want those workarounds for SPIR-V.
> 
> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
> Cc: "12.0" <mesa-dev at lists.freedesktop.org>
> ---
>  src/compiler/nir/nir.h           | 10 ++++++++
>  src/compiler/nir/nir_lower_tex.c | 54 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index d0f52b0..45f758c 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2405,6 +2405,16 @@ typedef struct nir_lower_tex_options {
>     unsigned lower_txp;
>  
>     /**
> +    * If true, lower away nir_tex_src_offset for all texelfetch instructions.
> +    */
> +   bool lower_txf_offset;
> +
> +   /**
> +    * If true, lower away nir_tex_src_offset for all rect textures.
> +    */
> +   bool lower_rect_offset;
> +
> +   /**
>      * If true, lower rect textures to 2D, using txs to fetch the
>      * texture dimensions and dividing the texture coords by the
>      * texture dims to normalize.
> diff --git a/src/compiler/nir/nir_lower_tex.c b/src/compiler/nir/nir_lower_tex.c
> index 0cf1071..a1280e1 100644
> --- a/src/compiler/nir/nir_lower_tex.c
> +++ b/src/compiler/nir/nir_lower_tex.c
> @@ -128,6 +128,54 @@ project_src(nir_builder *b, nir_tex_instr *tex)
>     tex_instr_remove_src(tex, proj_index);
>  }
>  
> +static bool
> +lower_offset(nir_builder *b, nir_tex_instr *tex)
> +{
> +   int offset_index = tex_instr_find_src(tex, nir_tex_src_offset);

Could be 'const'.

> +   if (offset_index < 0)
> +      return false;
> +
> +   int coord_index = tex_instr_find_src(tex, nir_tex_src_coord);

Same here.

> +   assert(coord_index >= 0);
> +
> +   assert(tex->src[offset_index].src.is_ssa);
> +   assert(tex->src[coord_index].src.is_ssa);
> +   nir_ssa_def *offset = tex->src[offset_index].src.ssa;
> +   nir_ssa_def *coord = tex->src[coord_index].src.ssa;

In principle, it looks these could be declared constants as well:

      const nir_ssa_def * const offset = tex->src[offset_index].src.ssa;
      const nir_ssa_def * const coord = tex->src[coord_index].src.ssa;

But further digging tells me that they can be only:

      nir_ssa_def * const offset = tex->src[offset_index].src.ssa;
      nir_ssa_def * const coord = tex->src[coord_index].src.ssa;


Quite a few of the helpers in nir declare their inputs as read-write even
though they only read the contents...

> +
> +   b->cursor = nir_before_instr(&tex->instr);
> +
> +   nir_ssa_def *offset_coord;
> +   if (nir_tex_instr_src_type(tex, coord_index) == nir_type_float) {
> +      assert(tex->sampler_dim == GLSL_SAMPLER_DIM_RECT);
> +      offset_coord = nir_fadd(b, coord, nir_i2f(b, offset));
> +   } else {
> +      offset_coord = nir_iadd(b, coord, offset);
> +   }
> +
> +   if (tex->is_array) {
> +      /* The offset is not applied to the array index */
> +      if (tex->coord_components == 2) {
> +         offset_coord = nir_vec2(b, nir_channel(b, offset_coord, 0),
> +                                    nir_channel(b, coord, 1));
> +      } else if (tex->coord_components == 3) {
> +         offset_coord = nir_vec3(b, nir_channel(b, offset_coord, 0),
> +                                    nir_channel(b, offset_coord, 1),
> +                                    nir_channel(b, coord, 2));
> +      } else {
> +         unreachable("Invalid number of components");
> +      }
> +   }
> +
> +   nir_instr_rewrite_src(&tex->instr, &tex->src[coord_index].src,
> +                         nir_src_for_ssa(offset_coord));
> +
> +   tex_instr_remove_src(tex, offset_index);
> +
> +   return true;
> +}
> +
> +
>  static nir_ssa_def *
>  get_texture_size(nir_builder *b, nir_tex_instr *tex)
>  {
> @@ -458,6 +506,12 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
>           progress = true;
>        }
>  
> +      if ((tex->op == nir_texop_txf && options->lower_txf_offset) ||
> +          (tex->sampler_dim == GLSL_SAMPLER_DIM_RECT &&
> +           options->lower_rect_offset)) {
> +         progress = lower_offset(b, tex) || progress;
> +      }
> +
>        if ((tex->sampler_dim == GLSL_SAMPLER_DIM_RECT) && options->lower_rect) {
>           lower_rect(b, tex);
>           progress = true;
> -- 
> 2.5.0.400.gff86faf
> 
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