nir: support lowering nir_intrinsic_image_samples to a constant load

This can be used by multiple drivers that do not support ms images

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Rob Clark <robclark@freedesktop.org>
Reviewer-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Signed-off-by: Amber Amber <amber@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20813>

src/compiler/nir/nir.h

@@ -5328,6 +5328,12 @@ typedef struct nir_lower_image_options {
     * Lower multi sample image load and samples_identical to use fragment_mask_load.
     */
    bool lower_to_fragment_mask_load_amd;
+
+  /**
+   * Lower image_samples to a constant in case the driver doesn't support multisampled
+   * images.
+   */
+  bool lower_image_samples_to_one;
 } nir_lower_image_options;
 
 bool nir_lower_image(nir_shader *nir,

src/compiler/nir/nir_lower_image.c

@@ -182,6 +182,15 @@ lower_image_instr(nir_builder *b, nir_instr *instr, void *state)
       }
       return false;
 
+   case nir_intrinsic_image_samples: {
+      if (options->lower_image_samples_to_one) {
+         b->cursor = nir_after_instr(&intrin->instr);
+         nir_ssa_def *samples = nir_imm_intN_t(b, 1, nir_dest_bit_size(intrin->dest));
+         nir_ssa_def_rewrite_uses(&intrin->dest.ssa, samples);
+         return true;
+      }
+      return false;
+   }
    default:
       return false;
    }