intel/compiler: add support for fragment shading rate variable

v2: Drop old register type initializers (Jason)
    Simplify instruction snippet (Jason)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7455>

src/intel/compiler/brw_fs_nir.cpp

@@ -254,6 +254,12 @@ emit_system_values_block(nir_block *block, fs_visitor *v)
          }
          break;
 
+      case nir_intrinsic_load_frag_shading_rate:
+         reg = &v->nir_system_values[SYSTEM_VALUE_FRAG_SHADING_RATE];
+         if (reg->file == BAD_FILE)
+            *reg = *v->emit_shading_rate_setup();
+         break;
+
       default:
          break;
       }
@@ -3320,7 +3326,8 @@ fs_visitor::nir_emit_fs_intrinsic(const fs_builder &bld,
 
    case nir_intrinsic_load_helper_invocation:
    case nir_intrinsic_load_sample_mask_in:
-   case nir_intrinsic_load_sample_id: {
+   case nir_intrinsic_load_sample_id:
+   case nir_intrinsic_load_frag_shading_rate: {
       gl_system_value sv = nir_system_value_from_intrinsic(instr->intrinsic);
       fs_reg val = nir_system_values[sv];
       assert(val.file != BAD_FILE);