spirv: Handle the SubgroupSize execution mode

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12959>

src/compiler/shader_info.h

@@ -431,6 +431,11 @@ typedef struct shader_info {
           */
          enum gl_derivative_group derivative_group:2;
 
+         /**
+          * Explicit subgroup size if set by the shader, otherwise 0.
+          */
+         unsigned subgroup_size;
+
          /**
           * pointer size is:
           *   AddressingModelLogical:    0    (default)

src/compiler/spirv/spirv_to_nir.c

@@ -5137,6 +5137,11 @@ vtn_handle_execution_mode(struct vtn_builder *b, struct vtn_value *entry_point,
       /* Handled later by vtn_handle_execution_mode_id(). */
       break;
 
+   case SpvExecutionModeSubgroupSize:
+      vtn_assert(b->shader->info.stage == MESA_SHADER_KERNEL);
+      b->shader->info.cs.subgroup_size = mode->operands[0];
+      break;
+
    case SpvExecutionModeSubgroupUniformControlFlowKHR:
       /* There's no corresponding SPIR-V capability, so check here. */
       vtn_fail_if(!b->options->caps.subgroup_uniform_control_flow,