intel,nir: Lower TXD with min_lod when the sampler index is not < 16

When we have a larger sampler index, we get into the "high sampler"
scenario and need an instruction header.  Even in SIMD8, this pushes the
instruction over the sampler message size maximum of 11 registers.
Instead, we have to lower TXD to TXL.

Fixes: cb98e0755f "intel/fs: Support min_lod parameters on texture..."
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/nir/nir.h

@@ -3179,6 +3179,12 @@ typedef struct nir_lower_tex_options {
     */
    bool lower_txd_offset_clamp;
 
+   /**
+    * If true, lower nir_texop_txd with min_lod to a nir_texop_txl if the
+    * sampler index is not statically determinable to be less than 16.
+    */
+   bool lower_txd_clamp_if_sampler_index_not_lt_16;
+
    /**
     * If true, apply a .bagr swizzle on tg4 results to handle Broadcom's
     * mixed-up tg4 locations.

src/compiler/nir/nir_lower_tex.c

@@ -905,6 +905,25 @@ lower_tex_packing(nir_builder *b, nir_tex_instr *tex,
                                   color->parent_instr);
 }
 
+static bool
+sampler_index_lt(nir_tex_instr *tex, unsigned max)
+{
+   assert(nir_tex_instr_src_index(tex, nir_tex_src_sampler_deref) == -1);
+
+   unsigned sampler_index = tex->sampler_index;
+
+   int sampler_offset_idx =
+      nir_tex_instr_src_index(tex, nir_tex_src_sampler_offset);
+   if (sampler_offset_idx >= 0) {
+      if (!nir_src_is_const(tex->src[sampler_offset_idx].src))
+         return false;
+
+      sampler_index += nir_src_as_uint(tex->src[sampler_offset_idx].src);
+   }
+
+   return sampler_index < max;
+}
+
 static bool
 nir_lower_tex_block(nir_block *block, nir_builder *b,
                     const nir_lower_tex_options *options)
@@ -1026,6 +1045,8 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
            (options->lower_txd_shadow && tex->is_shadow) ||
            (options->lower_txd_shadow_clamp && tex->is_shadow && has_min_lod) ||
            (options->lower_txd_offset_clamp && has_offset && has_min_lod) ||
+           (options->lower_txd_clamp_if_sampler_index_not_lt_16 &&
+            has_min_lod && !sampler_index_lt(tex, 16)) ||
            (options->lower_txd_cube_map &&
             tex->sampler_dim == GLSL_SAMPLER_DIM_CUBE) ||
            (options->lower_txd_3d &&

src/intel/compiler/brw_nir.c

@@ -904,7 +904,9 @@ brw_nir_apply_sampler_key(nir_shader *nir,
                           bool is_scalar)
 {
    const struct gen_device_info *devinfo = compiler->devinfo;
-   nir_lower_tex_options tex_options = { 0 };
+   nir_lower_tex_options tex_options = {
+      .lower_txd_clamp_if_sampler_index_not_lt_16 = true,
+   };
 
    /* Iron Lake and prior require lowering of all rectangle textures */
    if (devinfo->gen < 6)