radv: gather MRTs that are written by the fragment shader

This will be used to filter color attachments without exports.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5786>

src/amd/vulkan/radv_shader.h

@@ -329,6 +329,7 @@ struct radv_shader_info {
       bool allow_flat_shading;
       bool has_epilog;
       unsigned spi_ps_input;
+      unsigned colors_written;
    } ps;
    struct {
       bool uses_grid_size;

src/amd/vulkan/radv_shader_info.c

@@ -77,6 +77,10 @@ gather_intrinsic_store_output_info(const nir_shader *nir, const nir_intrinsic_in
    case MESA_SHADER_GEOMETRY:
       output_usage_mask = info->gs.output_usage_mask;
       break;
+   case MESA_SHADER_FRAGMENT:
+      if (idx >= FRAG_RESULT_DATA0)
+         info->ps.colors_written |= 0xf << (4 * (idx - FRAG_RESULT_DATA0));
+      break;
    default:
       break;
    }