[Mesa-dev] [PATCH 3/3] glsl: Mark gl_GlobalInvocationID dependencies as used

[Ilia Mirkin]

Why doesn't the lowering pass do that? Do you need to call it earlier?
Or does it rely on some information that only becomes available later?

On Thu, Aug 6, 2015 at 2:01 PM, Jordan Justen <jordan.l.justen at intel.com> wrote:
> gl_GlobalInvocationID =
>   gl_WorkGroupID * gl_WorkGroupSize + gl_LocalInvocationID
>
> Therefore, if gl_GlobalInvocationID is used, then we mark these other
> variables as being used. This prevents them from being considered dead
> variables and being removed.
>
> Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
> ---
>  src/glsl/glsl_parser_extras.cpp | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>
> diff --git a/src/glsl/glsl_parser_extras.cpp b/src/glsl/glsl_parser_extras.cpp
> index 46896d7..49fc12d 100644
> --- a/src/glsl/glsl_parser_extras.cpp
> +++ b/src/glsl/glsl_parser_extras.cpp
> @@ -1568,6 +1568,36 @@ set_shader_inout_layout(struct gl_shader *shader,
>     }
>  }
>
> +static void
> +set_cs_variable_deps_as_used(struct gl_shader *shader,
> +                             struct _mesa_glsl_parse_state *state)
> +{
> +   /* gl_GlobalInvocationID only exists in the compute shader.
> +    */
> +   if (shader->Stage != MESA_SHADER_COMPUTE)
> +      return;
> +
> +   ir_variable *gl_GlobalInvocationID =
> +      state->symbols->get_variable("gl_GlobalInvocationID");
> +   assert(gl_GlobalInvocationID);
> +
> +   if (!gl_GlobalInvocationID->data.used)
> +      return;
> +
> +   static const char *dep_var_names[] = {
> +      "gl_WorkGroupSize",
> +      "gl_WorkGroupID",
> +      "gl_LocalInvocationID"
> +   };
> +
> +   for (unsigned i = 0; i < ARRAY_SIZE(dep_var_names); i++) {
> +      ir_variable *var =
> +         state->symbols->get_variable(dep_var_names[i]);
> +      assert(var);
> +      var->data.used = true;
> +   }
> +}
> +
>  extern "C" {
>
>  void
> @@ -1618,6 +1648,9 @@ _mesa_glsl_compile_shader(struct gl_context *ctx, struct gl_shader *shader,
>           &ctx->Const.ShaderCompilerOptions[shader->Stage];
>
>        lower_subroutine(shader->ir, state);
> +
> +      set_cs_variable_deps_as_used(shader, state);
> +
>        /* Do some optimization at compile time to reduce shader IR size
>         * and reduce later work if the same shader is linked multiple times
>         */
> --
> 2.1.4
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev