nir: Add nir_texop_lod_bias_agx

Add a new texture opcode that returns the LOD bias of the sampler. This will be
used on AGX to lower sampler LOD bias to txb and friends. This needs to be a
texture op (and not a new intrinsic) to handle both bindless and bindful
samplers across GL and Vulkan in a uniform way.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21276>

src/compiler/nir/nir.c

@@ -3239,6 +3239,7 @@ nir_tex_instr_result_size(const nir_tex_instr *instr)
    case nir_texop_query_levels:
    case nir_texop_samples_identical:
    case nir_texop_fragment_mask_fetch_amd:
+   case nir_texop_lod_bias_agx:
       return 1;
 
    case nir_texop_descriptor_amd:
@@ -3265,6 +3266,7 @@ nir_tex_instr_is_query(const nir_tex_instr *instr)
    case nir_texop_query_levels:
    case nir_texop_descriptor_amd:
    case nir_texop_sampler_descriptor_amd:
+   case nir_texop_lod_bias_agx:
       return true;
    case nir_texop_tex:
    case nir_texop_txb:

src/compiler/nir/nir.h

@@ -2200,6 +2200,7 @@ typedef enum {
    nir_texop_fragment_mask_fetch_amd, /**< Multisample fragment mask texture fetch */
    nir_texop_descriptor_amd,     /**< Returns a buffer or image descriptor. */
    nir_texop_sampler_descriptor_amd, /**< Returns a sampler descriptor. */
+   nir_texop_lod_bias_agx,       /**< Returns the sampler's LOD bias */
 } nir_texop;
 
 /** Represents a texture instruction */

src/compiler/nir/nir_print.c

@@ -1314,6 +1314,9 @@ print_tex_instr(nir_tex_instr *instr, print_state *state)
    case nir_texop_sampler_descriptor_amd:
       fprintf(fp, "sampler_descriptor_amd ");
       break;
+   case nir_texop_lod_bias_agx:
+      fprintf(fp, "lod_bias_agx ");
+      break;
    default:
       unreachable("Invalid texture operation");
       break;

src/compiler/nir/nir_validate.c

@@ -923,6 +923,7 @@ validate_tex_instr(nir_tex_instr *instr, validate_state *state)
          case nir_texop_sampler_descriptor_amd:
             break;
          case nir_texop_lod:
+         case nir_texop_lod_bias_agx:
             validate_assert(state, nir_alu_type_get_base_type(instr->dest_type) == nir_type_float);
             break;
          case nir_texop_samples_identical:

src/compiler/spirv/spirv_to_nir.c

@@ -2847,6 +2847,9 @@ vtn_handle_texture(struct vtn_builder *b, SpvOp opcode,
    case nir_texop_sampler_descriptor_amd:
       vtn_fail("unexpected nir_texop_*descriptor_amd");
       break;
+   case nir_texop_lod_bias_agx:
+      vtn_fail("unexpected nir_texop_lod_bias_agx");
+      break;
    }
 
    unsigned idx = 4;