ac/nir,radv: lower task payload to zeroes when the mesh shader has no task

The Vulkan spec allows this to be used in a mesh shader as long as
it's not accessed, so it can be eliminated.

This fixes dEQP-VK.mesh_shader.ext.misc.payload_not_accessed.

Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41828>

src/amd/common/nir/ac_nir.h

@@ -258,7 +258,7 @@ ac_nir_lower_task_outputs_to_mem(nir_shader *shader,
                                  bool has_query);
 
 bool
-ac_nir_lower_mesh_inputs_to_mem(nir_shader *shader);
+ac_nir_lower_mesh_inputs_to_mem(nir_shader *shader, bool has_task_shader);
 
 bool
 ac_nir_lower_global_access(nir_shader *shader);

src/amd/common/nir/ac_nir_lower_taskmesh_io_to_mem.c

@@ -18,6 +18,8 @@
 typedef struct {
    /* True if the lowering needs to insert shader query. */
    bool has_query;
+   /* True if the mesh shader is linked with a task shader. */
+   bool has_task_shader;
 } lower_tsms_io_state;
 
 static nir_def *
@@ -264,6 +266,13 @@ lower_taskmesh_payload_load(nir_builder *b,
    unsigned num_components = intrin->def.num_components;
    unsigned bit_size = intrin->def.bit_size;
 
+   /* Lower payload to zeroes when the mesh shader isn't linked with a task
+    * shader because isn't going to be accessed.
+    */
+   if (b->shader->info.stage == MESA_SHADER_MESH && !s->has_task_shader) {
+      return nir_imm_zero(b, num_components, bit_size);
+   }
+
    nir_def *ptr =
       b->shader->info.stage == MESA_SHADER_TASK ?
       task_ring_entry_index(b, s) :
@@ -361,10 +370,12 @@ lower_mesh_intrinsics(nir_builder *b,
 }
 
 bool
-ac_nir_lower_mesh_inputs_to_mem(nir_shader *shader)
+ac_nir_lower_mesh_inputs_to_mem(nir_shader *shader, bool has_task_shader)
 {
    lower_tsms_io_state state = {0};
 
+   state.has_task_shader = has_task_shader;
+
    return nir_shader_lower_instructions(shader,
                                         filter_mesh_input_load,
                                         lower_mesh_intrinsics,

src/amd/vulkan/nir/radv_nir_lower_io.c

@@ -130,7 +130,7 @@ radv_nir_lower_io_to_mem(const struct radv_compiler_info *compiler_info, struct
       ac_nir_lower_task_outputs_to_mem(nir, info->cs.has_query);
       return true;
    } else if (nir->info.stage == MESA_SHADER_MESH) {
-      ac_nir_lower_mesh_inputs_to_mem(nir);
+      ac_nir_lower_mesh_inputs_to_mem(nir, stage->info.ms.has_task);
       return true;
    }
 

src/gallium/drivers/radeonsi/gfx/si_shader.c

@@ -690,7 +690,7 @@ static void si_preprocess_nir(struct si_nir_shader_ctx *ctx)
    if (nir->info.stage == MESA_SHADER_TASK) {
       NIR_PASS(progress, nir, ac_nir_lower_task_outputs_to_mem, false);
    } else if (nir->info.stage == MESA_SHADER_MESH) {
-      NIR_PASS(progress, nir, ac_nir_lower_mesh_inputs_to_mem);
+      NIR_PASS(progress, nir, ac_nir_lower_mesh_inputs_to_mem, true);
    }
 
    if (mesa_shader_stage_is_compute(nir->info.stage)) {