pan/compiler: Replace frag_coord_zw_pan with var_special_pan

Just a bit cleaner, and we can unify point size too.

Signed-off-by: Lorenzo Rossi <lorenzo.rossi@collabora.com>
Reviewed-by: Christoph Pillmayer <christoph.pillmayer@arm.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40677>

src/compiler/nir/nir_divergence_analysis.c

@@ -861,6 +861,7 @@ visit_intrinsic(nir_intrinsic_instr *instr, struct divergence_state *state)
    case nir_intrinsic_load_barycentric_coord_at_offset:
    case nir_intrinsic_load_var_pan:
    case nir_intrinsic_load_var_buf_pan:
+   case nir_intrinsic_load_var_special_pan:
    case nir_intrinsic_load_persp_center_rhw_ir3:
    case nir_intrinsic_load_input_attachment_coord:
    case nir_intrinsic_interp_deref_at_offset:
@@ -874,7 +875,6 @@ visit_intrinsic(nir_intrinsic_instr *instr, struct divergence_state *state)
    case nir_intrinsic_load_frag_coord:
    case nir_intrinsic_load_frag_coord_z:
    case nir_intrinsic_load_frag_coord_w:
-   case nir_intrinsic_load_frag_coord_zw_pan:
    case nir_intrinsic_load_frag_coord_unscaled_ir3:
    case nir_intrinsic_load_frag_coord_gmem_ir3:
    case nir_intrinsic_load_pixel_coord:

src/compiler/nir/nir_intrinsics.py

@@ -1671,6 +1671,13 @@ load("var_buf_pan", [1, 2], [SRC_TYPE, IO_SEMANTICS], [CAN_ELIMINATE, CAN_REORDE
 # src[] = { offset }
 load("var_buf_flat_pan", [1], [SRC_TYPE, IO_SEMANTICS], [CAN_ELIMINATE, CAN_REORDER])
 
+# Panfrost-specific intrinsic to load special varyings, can load point coords
+# and frag_[zw] at specific barycentric coordinates.
+# src[] = { barycoord }
+# FLAGS is enum bi_varying_name
+intrinsic("load_var_special_pan", src_comp=[2], dest_comp=0, bit_sizes=[32],
+          indices=[FLAGS], flags=[CAN_ELIMINATE, CAN_REORDER])
+
 # Panfrost-specific intrinsic to load the shader_output special-FAU value on 5th Gen.
 intrinsic("load_shader_output_pan", dest_comp=1, src_comp=[], bit_sizes=[32],
           indices=[], flags=[CAN_REORDER, CAN_ELIMINATE])
@@ -1705,11 +1712,6 @@ store("raw_output_pan", [], [IO_SEMANTICS, BASE])
 store("combined_output_pan", [1, 1, 1, 4], [IO_SEMANTICS, COMPONENT, SRC_TYPE, DEST_TYPE])
 load("raw_output_pan", [1], [IO_SEMANTICS], [CAN_ELIMINATE, CAN_REORDER])
 
-# Like the frag_coord_zw intrinsic, but takes a barycentric. This is needed for
-# noperspective lowering.
-# src[] = { barycoord }
-intrinsic("load_frag_coord_zw_pan", [2], dest_comp=1, indices=[COMPONENT], flags=[CAN_ELIMINATE, CAN_REORDER], bit_sizes=[32])
-
 # Loads the sampler paramaters <min_lod, max_lod, lod_bias>
 # src[] = { sampler_index }
 load("sampler_lod_parameters", [1], flags=[CAN_ELIMINATE, CAN_REORDER])

src/compiler/nir/nir_opt_sink.c

@@ -248,7 +248,7 @@ can_sink_instr(nir_instr *instr, nir_move_options options, bool *can_mov_out_of_
       case nir_intrinsic_load_frag_coord:
       case nir_intrinsic_load_frag_coord_z:
       case nir_intrinsic_load_frag_coord_w:
-      case nir_intrinsic_load_frag_coord_zw_pan:
+      case nir_intrinsic_load_var_special_pan:
       case nir_intrinsic_load_pixel_coord:
          *can_mov_out_of_loop = true;
          return options & nir_move_load_frag_coord;

src/gallium/drivers/panfrost/pan_shader.c

@@ -143,6 +143,8 @@ panfrost_shader_compile(struct panfrost_screen *screen, const nir_shader *ir,
          NIR_PASS(_, s, nir_lower_texcoord_replace_late,
                   key->fs.sprite_coord_enable,
                   true /* point coord is sysval */);
+         /* Lower load_point_coord if present */
+         NIR_PASS(_, s, pan_nir_lower_var_special_pan);
       }
 
       if (key->fs.clip_plane_enable) {

src/panfrost/compiler/bifrost/bifrost_compile.c

@@ -1729,23 +1729,28 @@ bi_emit_atomic_i32_to(bi_builder *b, bi_index dst, bi_index addr, bi_index arg,
 }
 
 static void
-bi_emit_load_frag_coord_zw_pan(bi_builder *b, nir_intrinsic_instr *instr)
+bi_emit_load_var_special_pan(bi_builder *b, nir_intrinsic_instr *instr)
 {
    bi_index dst = bi_def_index(&instr->def);
-   unsigned channel = nir_intrinsic_component(instr);
+   enum bi_varying_name var_name = nir_intrinsic_flags(instr);
    nir_intrinsic_instr *bary = nir_src_as_intrinsic(instr->src[0]);
 
    enum bi_sample sample = bi_interp_for_intrinsic(bary->intrinsic);
    bi_index src0 = bi_varying_src0_for_barycentric(b, bary);
+   unsigned nr = instr->num_components;
+   assert(instr->def.bit_size == 32);
+
 
    /* .explicit is not supported with frag_z */
-   if (channel == 2)
+   if (var_name == BI_VARYING_NAME_FRAG_Z)
       assert(sample != BI_SAMPLE_EXPLICIT);
 
+   /* TODO: v10 adds BI_UPDATE_NONE and v14 introduces store/retrieve updates
+    * and the barycentric coordinate special varying */
    bi_ld_var_special_to(
       b, dst, src0, BI_REGISTER_FORMAT_F32, sample, BI_UPDATE_CLOBBER,
-      (channel == 2) ? BI_VARYING_NAME_FRAG_Z : BI_VARYING_NAME_FRAG_W,
-      BI_VECSIZE_NONE);
+      (enum bi_varying_name) var_name, nr - 1);
+   bi_emit_cached_split_i32(b, dst, nr);
 }
 
 static void
@@ -2179,10 +2184,6 @@ bi_emit_intrinsic(bi_builder *b, nir_intrinsic_instr *instr)
       bi_mov_i32_to(b, dst, bi_preload(b, 59));
       break;
 
-   case nir_intrinsic_load_frag_coord_zw_pan:
-      bi_emit_load_frag_coord_zw_pan(b, instr);
-      break;
-
    case nir_intrinsic_load_texel_buf_conv_pan:
       assert(b->shader->arch >= 9 &&
              "conv desc is loaded with the texel_buf_addr on Bifrost");
@@ -2269,11 +2270,8 @@ bi_emit_intrinsic(bi_builder *b, nir_intrinsic_instr *instr)
       break;
    }
 
-   case nir_intrinsic_load_point_coord:
-      bi_ld_var_special_to(b, dst, bi_zero(), BI_REGISTER_FORMAT_F32,
-                           BI_SAMPLE_CENTER, BI_UPDATE_CLOBBER,
-                           BI_VARYING_NAME_POINT, BI_VECSIZE_V2);
-      bi_emit_cached_split_i32(b, dst, 2);
+   case nir_intrinsic_load_var_special_pan:
+      bi_emit_load_var_special_pan(b, instr);
       break;
 
    /* It appears vertex_id is zero-based with Bifrost geometry flows, but
@@ -6183,7 +6181,7 @@ bifrost_postprocess_nir(nir_shader *nir, unsigned gpu_id)
    NIR_PASS(_, nir, nir_lower_var_copies);
    NIR_PASS(_, nir, nir_lower_alu);
    NIR_PASS(_, nir, nir_lower_frag_coord_to_pixel_coord);
-   NIR_PASS(_, nir, pan_nir_lower_frag_coord_zw);
+   NIR_PASS(_, nir, pan_nir_lower_var_special_pan);
 }
 
 void bifrost_lower_texture_nir(nir_shader *nir, unsigned gpu_id)

src/panfrost/compiler/meson.build

@@ -6,7 +6,7 @@ libpanfrost_compiler_files = files(
   'pan_compiler.h',
   'pan_nir_collect_varyings.c',
   'pan_nir_lower_bool_to_bitsize.c',
-  'pan_nir_lower_frag_coord_zw.c',
+  'pan_nir_lower_var_special.c',
   'pan_nir_lower_framebuffer.c',
   'pan_nir_lower_fs_inputs.c',
   'pan_nir_lower_fs_outputs.c',

src/panfrost/compiler/pan_nir.h

@@ -51,7 +51,7 @@ bool pan_nir_lower_vertex_id(nir_shader *shader);
 
 bool pan_nir_lower_image_ms(nir_shader *shader);
 
-bool pan_nir_lower_frag_coord_zw(nir_shader *shader);
+bool pan_nir_lower_var_special_pan(nir_shader *shader);
 bool pan_nir_lower_noperspective_vs(nir_shader *shader);
 bool pan_nir_lower_noperspective_fs(nir_shader *shader);
 

src/panfrost/compiler/pan_nir_lower_frag_coord_zw.c

@@ -1,34 +0,0 @@
-/*
- * Copyright © 2024 Collabora Ltd.
- * SPDX-License-Identifier: MIT
- */
-
-#include "compiler/nir/nir_builder.h"
-#include "pan_nir.h"
-
-/* Lowers nir_load_frag_coord_zw to nir_load_frag_coord_zw_pan. */
-
-static bool
-lower_frag_coord_zw(nir_builder *b, nir_intrinsic_instr *intrin, void *data)
-{
-   if (intrin->intrinsic != nir_intrinsic_load_frag_coord_z && intrin->intrinsic != nir_intrinsic_load_frag_coord_w)
-      return false;
-
-   b->cursor = nir_before_instr(&intrin->instr);
-
-   nir_def *bary = nir_load_barycentric_pixel(b, 32,
-      .interp_mode = INTERP_MODE_NOPERSPECTIVE
-   );
-   unsigned component = intrin->intrinsic == nir_intrinsic_load_frag_coord_z ? 2 : 3;
-   nir_def *new = nir_load_frag_coord_zw_pan(b, bary, .component = component);
-   nir_def_replace(&intrin->def, new);
-
-   return true;
-}
-
-bool
-pan_nir_lower_frag_coord_zw(nir_shader *shader)
-{
-   return nir_shader_intrinsics_pass(shader, lower_frag_coord_zw,
-                                     nir_metadata_control_flow, NULL);
-}

src/panfrost/compiler/pan_nir_lower_noperspective.c

@@ -4,6 +4,7 @@
  */
 
 #include "compiler/nir/nir_builder.h"
+#include "bi_opcodes.h"
 #include "pan_nir.h"
 
 /* Mali only provides instructions to fetch varyings with either flat or
@@ -207,7 +208,8 @@ lower_noperspective_fs(nir_builder *b, nir_intrinsic_instr *intrin,
    b->cursor = nir_after_instr(&intrin->instr);
 
    nir_def *bary = intrin->src[0].ssa;
-   nir_def *fragcoord_w = nir_load_frag_coord_zw_pan(b, bary, .component = 3);
+   nir_def *fragcoord_w =
+      nir_load_var_special_pan(b, 1, bary, .flags = BI_VARYING_NAME_FRAG_W);
    if (intrin->def.bit_size == 16)
       fragcoord_w = nir_f2f16(b, fragcoord_w);
 

src/panfrost/compiler/pan_nir_lower_var_special.c

@@ -0,0 +1,48 @@
+/*
+ * Copyright © 2024,2026 Collabora Ltd.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "compiler/nir/nir_builder.h"
+#include "bi_opcodes.h"
+#include "pan_nir.h"
+
+/* Lowers nir_load_frag_coord_zw and point_coord to nir_load_var_special_pan */
+
+static bool
+lower_var_special_pan(nir_builder *b, nir_intrinsic_instr *intrin, void *data)
+{
+   enum bi_varying_name var_name;
+
+   switch (intrin->intrinsic) {
+   case nir_intrinsic_load_frag_coord_z:
+      var_name = BI_VARYING_NAME_FRAG_Z;
+      break;
+   case nir_intrinsic_load_frag_coord_w:
+      var_name = BI_VARYING_NAME_FRAG_W;
+      break;
+   case nir_intrinsic_load_point_coord:
+      var_name = BI_VARYING_NAME_POINT;
+      break;
+   default:
+      return false;
+   }
+   b->cursor = nir_before_instr(&intrin->instr);
+
+   nir_def *bary = nir_load_barycentric_pixel(b, 32,
+      .interp_mode = INTERP_MODE_NOPERSPECTIVE
+   );
+
+   nir_def *new = nir_load_var_special_pan(b, intrin->def.num_components, bary,
+                                           .flags = var_name);
+   nir_def_replace(&intrin->def, new);
+
+   return true;
+}
+
+bool
+pan_nir_lower_var_special_pan(nir_shader *shader)
+{
+   return nir_shader_intrinsics_pass(shader, lower_var_special_pan,
+                                     nir_metadata_control_flow, NULL);
+}