ac/nir: Add a NIR port of ac_llvm_cull.

The algorithms were originally implemented by Marek Olšák,
hence the copyright to AMD.

This commit just ports the LLVM based implementation to NIR,
using the new intrinsics added earlier.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10525>

3 files changed, 168 insertions, 0 deletions

diff --git a/src/amd/common/ac_nir.h b/src/amd/common/ac_nir.h
index 89512b86d52..1ce615b859b 100644
--- a/src/amd/common/ac_nir.h
+++ b/src/amd/common/ac_nir.h
@@ -28,12 +28,17 @@
 
 #include "nir.h"
 #include "ac_shader_args.h"
+#include "ac_shader_util.h"
 #include "amd_family.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/* Forward declaration of nir_builder so we don't have to include nir_builder.h here */
+struct nir_builder;
+typedef struct nir_builder nir_builder;
+
 void
 ac_nir_lower_ls_outputs_to_mem(nir_shader *ls,
                                bool tcs_in_out_eq,
@@ -112,6 +117,11 @@ ac_nir_lower_ngg_gs(nir_shader *shader,
                     unsigned gs_total_out_vtx_bytes,
                     bool provoking_vtx_last);
 
+nir_ssa_def *
+ac_nir_cull_triangle(nir_builder *b,
+                     nir_ssa_def *initially_accepted,
+                     nir_ssa_def *pos[3][4]);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/amd/common/ac_nir_cull.c b/src/amd/common/ac_nir_cull.c
new file mode 100644
index 00000000000..a5adf2a4614
--- /dev/null
+++ b/src/amd/common/ac_nir_cull.c
@@ -0,0 +1,157 @@
+/*
+ * Copyright 2019 Advanced Micro Devices, Inc.
+ * Copyright 2021 Valve Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "ac_nir.h"
+#include "nir_builder.h"
+
+/* This code is adapted from ac_llvm_cull.c, hence the copyright to AMD. */
+
+typedef struct
+{
+   nir_ssa_def *w_reflection;
+   nir_ssa_def *w_accepted;
+   nir_ssa_def *all_w_positive;
+   nir_ssa_def *any_w_negative;
+} position_w_info;
+
+static void
+analyze_position_w(nir_builder *b, nir_ssa_def *pos[3][4], position_w_info *w_info)
+{
+   nir_ssa_def *all_w_negative = nir_imm_bool(b, true);
+
+   w_info->w_reflection = nir_imm_bool(b, false);
+   w_info->any_w_negative = nir_imm_bool(b, false);
+
+   for (unsigned i = 0; i < 3; ++i) {
+      nir_ssa_def *neg_w = nir_flt(b, pos[i][3], nir_imm_float(b, 0.0f));
+      w_info->w_reflection = nir_ixor(b, neg_w, w_info->w_reflection);
+      w_info->any_w_negative = nir_ior(b, neg_w, w_info->any_w_negative);
+      all_w_negative = nir_iand(b, neg_w, all_w_negative);
+   }
+
+   w_info->all_w_positive = nir_inot(b, w_info->any_w_negative);
+   w_info->w_accepted = nir_inot(b, all_w_negative);
+}
+
+static nir_ssa_def *
+cull_face(nir_builder *b, nir_ssa_def *pos[3][4], const position_w_info *w_info)
+{
+   nir_ssa_def *det_t0 = nir_fsub(b, pos[2][0], pos[0][0]);
+   nir_ssa_def *det_t1 = nir_fsub(b, pos[1][1], pos[0][1]);
+   nir_ssa_def *det_t2 = nir_fsub(b, pos[0][0], pos[1][0]);
+   nir_ssa_def *det_t3 = nir_fsub(b, pos[0][1], pos[2][1]);
+   nir_ssa_def *det_p0 = nir_fmul(b, det_t0, det_t1);
+   nir_ssa_def *det_p1 = nir_fmul(b, det_t2, det_t3);
+   nir_ssa_def *det = nir_fsub(b, det_p0, det_p1);
+
+   det = nir_bcsel(b, w_info->w_reflection, nir_fneg(b, det), det);
+
+   nir_ssa_def *front_facing_cw = nir_flt(b, det, nir_imm_float(b, 0.0f));
+   nir_ssa_def *front_facing_ccw = nir_flt(b, nir_imm_float(b, 0.0f), det);
+   nir_ssa_def *ccw = nir_build_load_cull_ccw_amd(b);
+   nir_ssa_def *front_facing = nir_bcsel(b, ccw, front_facing_ccw, front_facing_cw);
+   nir_ssa_def *cull_front = nir_build_load_cull_front_face_enabled_amd(b);
+   nir_ssa_def *cull_back = nir_build_load_cull_back_face_enabled_amd(b);
+
+   return nir_inot(b, nir_bcsel(b, front_facing, cull_front, cull_back));
+}
+
+static nir_ssa_def *
+cull_bbox(nir_builder *b, nir_ssa_def *pos[3][4], nir_ssa_def *accepted, const position_w_info *w_info)
+{
+   nir_ssa_def *bbox_accepted = NULL;
+   nir_ssa_def *try_cull_bbox = nir_iand(b, accepted, w_info->all_w_positive);
+
+   nir_if *if_cull_bbox = nir_push_if(b, try_cull_bbox);
+   {
+      nir_ssa_def *bbox_min[3] = {0}, *bbox_max[3] = {0};
+
+      for (unsigned chan = 0; chan < 2; ++chan) {
+         bbox_min[chan] = nir_fmin(b, pos[0][chan], nir_fmin(b, pos[1][chan], pos[2][chan]));
+         bbox_max[chan] = nir_fmax(b, pos[0][chan], nir_fmax(b, pos[1][chan], pos[2][chan]));
+      }
+
+      nir_ssa_def *vp_scale[2] = { nir_build_load_viewport_x_scale(b), nir_build_load_viewport_y_scale(b), };
+      nir_ssa_def *vp_translate[2] = { nir_build_load_viewport_x_offset(b), nir_build_load_viewport_y_offset(b), };
+      nir_ssa_def *prim_outside_view = nir_imm_false(b);
+
+      /* Frustrum culling - eliminate triangles that are fully outside the view. */
+      for (unsigned chan = 0; chan < 2; ++chan) {
+         prim_outside_view = nir_ior(b, prim_outside_view, nir_flt(b, bbox_max[chan], nir_imm_float(b, -1.0f)));
+         prim_outside_view = nir_ior(b, prim_outside_view, nir_flt(b, nir_imm_float(b, 1.0f), bbox_min[chan]));
+      }
+
+      nir_ssa_def *prim_is_small = NULL;
+      nir_ssa_def *prim_is_small_else = nir_imm_false(b);
+
+      /* Small primitive filter - eliminate triangles that are too small to affect a sample. */
+      nir_if *if_cull_small_prims = nir_push_if(b, nir_build_load_cull_small_primitives_enabled_amd(b));
+      {
+         nir_ssa_def *small_prim_precision = nir_build_load_cull_small_prim_precision_amd(b);
+         prim_is_small = nir_imm_false(b);
+
+         for (unsigned chan = 0; chan < 2; ++chan) {
+            /* Convert the position to screen-space coordinates. */
+            nir_ssa_def *min = nir_ffma(b, bbox_min[chan], vp_scale[chan], vp_translate[chan]);
+            nir_ssa_def *max = nir_ffma(b, bbox_max[chan], vp_scale[chan], vp_translate[chan]);
+
+            /* Scale the bounding box according to precision. */
+            min = nir_fsub(b, min, small_prim_precision);
+            max = nir_fadd(b, max, small_prim_precision);
+
+            /* Determine if the bbox intersects the sample point, by checking if the min and max round to the same int. */
+            min = nir_fround_even(b, min);
+            max = nir_fround_even(b, max);
+
+            nir_ssa_def *rounded_to_eq = nir_feq(b, min, max);
+            prim_is_small = nir_ior(b, prim_is_small, rounded_to_eq);
+         }
+      }
+      nir_pop_if(b, if_cull_small_prims);
+
+      prim_is_small = nir_if_phi(b, prim_is_small, prim_is_small_else);
+      nir_ssa_def *prim_invisible = nir_ior(b, prim_outside_view, prim_is_small);
+
+      bbox_accepted = nir_inot(b, prim_invisible);
+   }
+   nir_pop_if(b, if_cull_bbox);
+   return nir_if_phi(b, bbox_accepted, accepted);
+}
+
+nir_ssa_def *
+ac_nir_cull_triangle(nir_builder *b,
+                     nir_ssa_def *initially_accepted,
+                     nir_ssa_def *pos[3][4])
+{
+   position_w_info w_info = {0};
+   analyze_position_w(b, pos, &w_info);
+
+   nir_ssa_def *accepted = initially_accepted;
+   accepted = nir_iand(b, accepted, w_info.w_accepted);
+   accepted = nir_iand(b, accepted, cull_face(b, pos, &w_info));
+   accepted = nir_iand(b, accepted, cull_bbox(b, pos, accepted, &w_info));
+
+   return accepted;
+}
diff --git a/src/amd/common/meson.build b/src/amd/common/meson.build
index 8edd357c670..09a1ed19129 100644
--- a/src/amd/common/meson.build
+++ b/src/amd/common/meson.build
@@ -89,6 +89,7 @@ amd_common_files = files(
   'ac_rgp_elf_object_pack.c',
   'ac_nir.c',
   'ac_nir.h',
+  'ac_nir_cull.c',
   'ac_nir_lower_esgs_io_to_mem.c',
   'ac_nir_lower_tess_io_to_mem.c',
   'ac_nir_lower_ngg.c',