asahi: make txf robust properly

KHR-NoContext.gl43.robust_buffer_access_behavior.texel_fetch

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26963>

src/asahi/compiler/agx_nir_lower_texture.c

@@ -26,6 +26,17 @@ texture_descriptor_ptr(nir_builder *b, nir_tex_instr *tex)
    return nir_load_from_texture_handle_agx(b, tex->src[handle_idx].src.ssa);
 }
 
+static bool
+has_nonzero_lod(nir_tex_instr *tex)
+{
+   int idx = nir_tex_instr_src_index(tex, nir_tex_src_lod);
+   if (idx < 0)
+      return false;
+
+   nir_src src = tex->src[idx].src;
+   return !(nir_src_is_const(src) && nir_src_as_uint(src) == 0);
+}
+
 static bool
 lower_tex_crawl(nir_builder *b, nir_instr *instr, UNUSED void *data)
 {
@@ -167,6 +178,21 @@ lower_regular_texture(nir_builder *b, nir_instr *instr, UNUSED void *data)
    nir_def *coord = nir_steal_tex_src(tex, nir_tex_src_coord);
    nir_def *ms_idx = nir_steal_tex_src(tex, nir_tex_src_ms_index);
 
+   /* Apply txf workaround, see libagx_lower_txf_robustness */
+   bool is_txf = ((tex->op == nir_texop_txf) || (tex->op == nir_texop_txf_ms));
+
+   if (is_txf && has_nonzero_lod(tex) &&
+       !(tex->backend_flags & AGX_TEXTURE_FLAG_NO_CLAMP)) {
+
+      int lod_idx = nir_tex_instr_src_index(tex, nir_tex_src_lod);
+
+      nir_def *replaced = libagx_lower_txf_robustness(
+         b, texture_descriptor_ptr(b, tex), tex->src[lod_idx].src.ssa,
+         nir_channel(b, coord, 0));
+
+      coord = nir_vector_insert_imm(b, coord, replaced, 0);
+   }
+
    /* The layer is always the last component of the NIR coordinate, split it off
     * because we'll need to swizzle.
     */
@@ -178,7 +204,7 @@ lower_regular_texture(nir_builder *b, nir_instr *instr, UNUSED void *data)
       coord = nir_trim_vector(b, coord, lidx);
 
       /* Round layer to nearest even */
-      if (tex->op != nir_texop_txf && tex->op != nir_texop_txf_ms)
+      if (!is_txf)
          unclamped_layer = nir_f2u32(b, nir_fround_even(b, unclamped_layer));
 
       /* For a cube array, the layer is zero-indexed component 3 of the
@@ -572,6 +598,11 @@ agx_nir_lower_texture(nir_shader *s)
             nir_metadata_block_index | nir_metadata_dominance, NULL);
    NIR_PASS(progress, s, nir_legalize_16bit_sampler_srcs, tex_constraints);
 
+   /* Fold constants after nir_legalize_16bit_sampler_srcs so we can detect 0 in
+    * lower_regular_texture. This is required for correctness.
+    */
+   NIR_PASS(progress, s, nir_opt_constant_folding);
+
    /* Lower texture sources after legalizing types (as the lowering depends on
     * 16-bit multisample indices) but before lowering queries (as the lowering
     * generates txs for array textures).
@@ -661,9 +692,16 @@ agx_nir_needs_texture_crawl(nir_instr *instr)
       case nir_texop_query_levels:
          return true;
 
-      /* Buffer textures need their format read */
+      /* Buffer textures need their format read and txf needs its LOD clamped.
+       * Buffer textures are only read through txf.
+       */
+      case nir_texop_txf:
+      case nir_texop_txf_ms:
+         return has_nonzero_lod(tex) ||
+                tex->sampler_dim == GLSL_SAMPLER_DIM_BUF;
+
       default:
-         return tex->sampler_dim == GLSL_SAMPLER_DIM_BUF;
+         return false;
       }
    }
 

src/asahi/lib/shaders/texture.cl

@@ -80,6 +80,27 @@ libagx_texture_levels(constant struct agx_texture_packed *ptr)
       return (d.last_level - d.first_level) + 1;
 }
 
+/*
+ * Fix robustness behaviour of txf with out-of-bounds LOD. The hardware
+ * returns the correct out-of-bounds colour for out-of-bounds coordinates,
+ * just not LODs. So translate out-of-bounds LOD into an out-of-bounds
+ * coordinate to get correct behaviour in 1 instruction.
+ *
+ * Returns the fixed X-coordinate.
+ *
+ * TODO: This looks like it might be an erratum workaround on G13 (Apple does
+ * it), maybe check if G15 is affected.
+ */
+uint
+libagx_lower_txf_robustness(constant struct agx_texture_packed *ptr, ushort lod,
+                            uint x)
+{
+   agx_unpack(NULL, ptr, TEXTURE, d);
+
+   bool oob = (lod > (d.last_level - d.first_level));
+   return oob ? 0xFFFF : x;
+}
+
 static uint32_t
 calculate_twiddled_coordinates(ushort2 coord, uint16_t tile_w_px,
                                uint16_t tile_h_px, uint32_t width_tl)