[Mesa-dev] [PATCH 16/28] glsl: don't pack tessellation stages like we do other stages

[Ilia Mirkin]

On Tue, Dec 29, 2015 at 12:00 AM, Timothy Arceri
<timothy.arceri at collabora.com> wrote:
> Tessellation shaders treat varyings as shared memory and invocations
> can access each others varyings therefore we can't use the existing
> method to lower them.

That's not strictly true... this is only true of tess control outputs
(which can be written by the current invocation, but also read in by
other invocations, effectively acting as a shared memory -- both true
of per-invocation outputs as well as per-patch outputs). Does that
information change this patch at all?

>
> This adds a check for these stages as following patches will
> allow explicit locations to be lowered even when the driver and existing
> tesselation checks ask for it to be disabled, we do this to enable support
> for the component layout qualifier.
> ---
>  src/glsl/lower_packed_varyings.cpp | 62 +++++++++++++++++++++-----------------
>  1 file changed, 34 insertions(+), 28 deletions(-)
>
> diff --git a/src/glsl/lower_packed_varyings.cpp b/src/glsl/lower_packed_varyings.cpp
> index 2899846..e4e9a35 100644
> --- a/src/glsl/lower_packed_varyings.cpp
> +++ b/src/glsl/lower_packed_varyings.cpp
> @@ -737,40 +737,46 @@ lower_packed_varyings(void *mem_ctx, unsigned locations_used,
>                        ir_variable_mode mode, unsigned gs_input_vertices,
>                        gl_shader *shader, bool disable_varying_packing)
>  {
> -   exec_list *instructions = shader->ir;
>     ir_function *main_func = shader->symbols->get_function("main");
>     exec_list void_parameters;
>     ir_function_signature *main_func_sig
>        = main_func->matching_signature(NULL, &void_parameters, false);
> -   exec_list new_instructions, new_variables;
> -   lower_packed_varyings_visitor visitor(mem_ctx, locations_used, mode,
> -                                         gs_input_vertices,
> -                                         &new_instructions,
> -                                         &new_variables,
> -                                         disable_varying_packing);
> -   visitor.run(shader);
> -   if (mode == ir_var_shader_out) {
> -      if (shader->Stage == MESA_SHADER_GEOMETRY) {
> -         /* For geometry shaders, outputs need to be lowered before each call
> -          * to EmitVertex()
> -          */
> -         lower_packed_varyings_gs_splicer splicer(mem_ctx, &new_instructions);
> -
> -         /* Add all the variables in first. */
> -         main_func_sig->body.head->insert_before(&new_variables);
>
> -         /* Now update all the EmitVertex instances */
> -         splicer.run(instructions);
> +   if (!(shader->Stage == MESA_SHADER_TESS_CTRL ||
> +         shader->Stage == MESA_SHADER_TESS_EVAL)) {
> +      exec_list *instructions = shader->ir;
> +      exec_list new_instructions, new_variables;
> +
> +      lower_packed_varyings_visitor visitor(mem_ctx, locations_used, mode,
> +                                            gs_input_vertices,
> +                                            &new_instructions,
> +                                            &new_variables,
> +                                            disable_varying_packing);
> +      visitor.run(shader);
> +      if (mode == ir_var_shader_out) {
> +         if (shader->Stage == MESA_SHADER_GEOMETRY) {
> +            /* For geometry shaders, outputs need to be lowered before each
> +             * call to EmitVertex()
> +             */
> +            lower_packed_varyings_gs_splicer splicer(mem_ctx,
> +                                                     &new_instructions);
> +
> +            /* Add all the variables in first. */
> +            main_func_sig->body.head->insert_before(&new_variables);
> +
> +            /* Now update all the EmitVertex instances */
> +            splicer.run(instructions);
> +         } else {
> +            /* For other shader types, outputs need to be lowered at the end
> +             * of main()
> +             */
> +            main_func_sig->body.append_list(&new_variables);
> +            main_func_sig->body.append_list(&new_instructions);
> +         }
>        } else {
> -         /* For other shader types, outputs need to be lowered at the end of
> -          * main()
> -          */
> -         main_func_sig->body.append_list(&new_variables);
> -         main_func_sig->body.append_list(&new_instructions);
> +         /* Shader inputs need to be lowered at the beginning of main() */
> +         main_func_sig->body.head->insert_before(&new_instructions);
> +         main_func_sig->body.head->insert_before(&new_variables);
>        }
> -   } else {
> -      /* Shader inputs need to be lowered at the beginning of main() */
> -      main_func_sig->body.head->insert_before(&new_instructions);
> -      main_func_sig->body.head->insert_before(&new_variables);
>     }
>  }
> --
> 2.4.3
>
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