intel/compiler: compactify locations of mesh outputs

Needed in support of anv code for Wa_14015590813.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17622>

src/intel/compiler/brw_nir.c

@@ -1095,6 +1095,78 @@ brw_nir_zero_inputs(nir_shader *shader, uint64_t *zero_inputs)
          nir_metadata_block_index | nir_metadata_dominance, zero_inputs);
 }
 
+/* Code for Wa_14015590813 may have created input/output variables beyond
+ * VARYING_SLOT_MAX and removed uses of variables below VARYING_SLOT_MAX.
+ * Clean it up, so they all stay below VARYING_SLOT_MAX.
+ */
+static void
+brw_mesh_compact_io(nir_shader *mesh, nir_shader *frag)
+{
+   gl_varying_slot mapping[VARYING_SLOT_MAX] = {0, };
+   gl_varying_slot cur = VARYING_SLOT_VAR0;
+   bool compact = false;
+
+   nir_foreach_shader_out_variable(var, mesh) {
+      gl_varying_slot location = var->data.location;
+      if (location < VARYING_SLOT_VAR0)
+         continue;
+      assert(location < ARRAY_SIZE(mapping));
+
+      const struct glsl_type *type = var->type;
+      if (nir_is_arrayed_io(var, MESA_SHADER_MESH) || var->data.per_view) {
+         assert(glsl_type_is_array(type));
+         type = glsl_get_array_element(type);
+      }
+
+      if (mapping[location])
+         continue;
+
+      unsigned num_slots = glsl_count_attribute_slots(type, false);
+
+      compact |= location + num_slots > VARYING_SLOT_MAX;
+
+      mapping[location] = cur;
+      cur += num_slots;
+   }
+
+   if (!compact)
+      return;
+
+   /* The rest of this function should be hit only for Wa_14015590813. */
+
+   nir_foreach_shader_out_variable(var, mesh) {
+      gl_varying_slot location = var->data.location;
+      if (location < VARYING_SLOT_VAR0)
+         continue;
+      location = mapping[location];
+      if (location == 0)
+         continue;
+      var->data.location = location;
+   }
+
+   nir_foreach_shader_in_variable(var, frag) {
+      gl_varying_slot location = var->data.location;
+      if (location < VARYING_SLOT_VAR0)
+         continue;
+      location = mapping[location];
+      if (location == 0)
+         continue;
+      var->data.location = location;
+   }
+
+   nir_shader_gather_info(mesh, nir_shader_get_entrypoint(mesh));
+   nir_shader_gather_info(frag, nir_shader_get_entrypoint(frag));
+
+   if (should_print_nir(mesh)) {
+      printf("%s\n", __func__);
+      nir_print_shader(mesh, stdout);
+   }
+   if (should_print_nir(frag)) {
+      printf("%s\n", __func__);
+      nir_print_shader(frag, stdout);
+   }
+}
+
 void
 brw_nir_link_shaders(const struct brw_compiler *compiler,
                      nir_shader *producer, nir_shader *consumer)
@@ -1177,6 +1249,11 @@ brw_nir_link_shaders(const struct brw_compiler *compiler,
 
       brw_nir_optimize(producer, compiler, p_is_scalar);
       brw_nir_optimize(consumer, compiler, c_is_scalar);
+
+      if (producer->info.stage == MESA_SHADER_MESH &&
+            consumer->info.stage == MESA_SHADER_FRAGMENT) {
+         brw_mesh_compact_io(producer, consumer);
+      }
    }
 
    NIR_PASS(_, producer, nir_lower_io_to_vector, nir_var_shader_out);