[Mesa-dev] [PATCH] anv/pipeline: Disable FS dispatch for pointless fragment shaders

[Kenneth Graunke]

On Thursday, August 2, 2018 10:31:19 AM PDT Jason Ekstrand wrote:
> ---
>  src/intel/vulkan/anv_pipeline.c | 37 +++++++++++++++++++++++++++++----
>  1 file changed, 33 insertions(+), 4 deletions(-)
> 
> diff --git a/src/intel/vulkan/anv_pipeline.c b/src/intel/vulkan/anv_pipeline.c
> index 85f38da60ff..86e0211a29d 100644
> --- a/src/intel/vulkan/anv_pipeline.c
> +++ b/src/intel/vulkan/anv_pipeline.c
> @@ -831,9 +831,25 @@ anv_pipeline_compile_fs(const struct brw_compiler *compiler,
>     fs_stage->key.wm.input_slots_valid =
>        prev_stage->prog_data.vue.vue_map.slots_valid;
>  
> -   return brw_compile_fs(compiler, NULL, mem_ctx, &fs_stage->key.wm,
> -                         &fs_stage->prog_data.wm, fs_stage->nir,
> -                         NULL, -1, -1, -1, true, false, NULL, NULL);
> +   const unsigned *code =
> +      brw_compile_fs(compiler, NULL, mem_ctx, &fs_stage->key.wm,
> +                     &fs_stage->prog_data.wm, fs_stage->nir,
> +                     NULL, -1, -1, -1, true, false, NULL, NULL);
> +
> +   if (fs_stage->key.wm.nr_color_regions == 0 &&
> +       !fs_stage->prog_data.wm.has_side_effects &&
> +       !fs_stage->prog_data.wm.uses_kill &&
> +       fs_stage->prog_data.wm.computed_depth_mode == BRW_PSCDEPTH_OFF &&
> +       !fs_stage->prog_data.wm.computed_stencil) {
> +      /* This fragment shader has not outputs and no side effects.  Go ahead

no outputs

Looks good to me...
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

> +       * and return the code pointer so we don't accidentally think the
> +       * compile failed but zero out prog_data which will set program_size to
> +       * zero and disable the stage.
> +       */
> +      memset(&fs_stage->prog_data, 0, sizeof(fs_stage->prog_data));
> +   }
> +
> +   return code;
>  }
>  
>  static VkResult
> @@ -915,7 +931,7 @@ anv_pipeline_compile_graphics(struct anv_pipeline *pipeline,
>  
>     if (found == __builtin_popcount(pipeline->active_stages)) {
>        /* We found all our shaders in the cache.  We're done. */
> -      return VK_SUCCESS;
> +      goto done;
>     } else if (found > 0) {
>        /* We found some but not all of our shaders.  This shouldn't happen
>         * most of the time but it can if we have a partially populated
> @@ -1057,6 +1073,19 @@ anv_pipeline_compile_graphics(struct anv_pipeline *pipeline,
>  
>     ralloc_free(pipeline_ctx);
>  
> +done:
> +
> +   if (pipeline->shaders[MESA_SHADER_FRAGMENT] &&
> +       pipeline->shaders[MESA_SHADER_FRAGMENT]->prog_data->program_size == 0) {
> +      /* This can happen if we decided to implicitly disable the fragment
> +       * shader.  See anv_pipeline_compile_fs().
> +       */
> +      anv_shader_bin_unref(pipeline->device,
> +                           pipeline->shaders[MESA_SHADER_FRAGMENT]);
> +      pipeline->shaders[MESA_SHADER_FRAGMENT] = NULL;
> +      pipeline->active_stages &= ~VK_SHADER_STAGE_FRAGMENT_BIT;
> +   }
> +
>     return VK_SUCCESS;
>  
>  fail:
> 

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