spirv: handle ViewportMaskNV builtin/cap from SPV_NV_mesh_shader

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Acked-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14263>

src/compiler/shader_info.h

@@ -85,6 +85,7 @@ struct spirv_supported_capabilities {
    bool float_controls;
    bool shader_clock;
    bool shader_viewport_index_layer;
+   bool shader_viewport_mask_nv;
    bool sparse_residency;
    bool stencil_export;
    bool storage_8bit;

src/compiler/spirv/spirv_to_nir.c

@@ -4805,6 +4805,10 @@ vtn_handle_preamble_instruction(struct vtn_builder *b, SpvOp opcode,
          spv_check_supported(mesh_shading_nv, cap);
          break;
 
+      case SpvCapabilityShaderViewportMaskNV:
+         spv_check_supported(shader_viewport_mask_nv, cap);
+         break;
+
       default:
          vtn_fail("Unhandled capability: %s (%u)",
                   spirv_capability_to_string(cap), cap);

src/compiler/spirv/vtn_variables.c

@@ -864,6 +864,10 @@ vtn_get_builtin_location(struct vtn_builder *b,
       else
          vtn_fail("invalid stage for SpvBuiltInViewportIndex");
       break;
+   case SpvBuiltInViewportMaskNV:
+      *location = VARYING_SLOT_VIEWPORT_MASK;
+      *mode = nir_var_shader_out;
+      break;
    case SpvBuiltInTessLevelOuter:
       *location = VARYING_SLOT_TESS_LEVEL_OUTER;
       break;