Mesa (main): radv: Fix gs_vgpr_comp_cnt for NGG VS without passthrough mode.

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Module: Mesa
Branch: main
Commit: e02c71d6c53fda3fee295f93009c0e5f656e5f8b
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=e02c71d6c53fda3fee295f93009c0e5f656e5f8b

Author: Timur Kristóf <timur.kristof at gmail.com>
Date:   Sat Apr  9 22:00:10 2022 +0200

radv: Fix gs_vgpr_comp_cnt for NGG VS without passthrough mode.

When not in passthrough mode, the NGG shader needs to calculate the
primitive export value from the input primitive's vertex indices.

So, GS vertex offset 2 is needed when NGG has triangles
and isn't in passthrough mode.

Fixes: 7ad69e2f7ee10c0e7afc302b9324e7a320424dcb "radv: stop loading invocation ID for NGG vertex shaders"
Signed-off-by: Timur Kristóf <timur.kristof at gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15837>

---

 src/amd/vulkan/radv_shader.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/amd/vulkan/radv_shader.c b/src/amd/vulkan/radv_shader.c
index b1cdbb3d194..dc0a28160bc 100644
--- a/src/amd/vulkan/radv_shader.c
+++ b/src/amd/vulkan/radv_shader.c
@@ -1675,18 +1675,27 @@ radv_postprocess_config(const struct radv_device *device, const struct ac_shader
          unreachable("Unexpected ES shader stage");
       }
 
-      bool nggc = info->has_ngg_culling; /* Culling uses GS vertex offsets 0, 1, 2. */
-      bool tes_triangles =
-         stage == MESA_SHADER_TESS_EVAL && info->tes._primitive_mode != TESS_PRIMITIVE_ISOLINES;
+      /* GS vertex offsets in NGG:
+       * - in passthrough mode, they are all packed into VGPR0
+       * - in the default mode: VGPR0: offsets 0, 1; VGPR1: offsets 2, 3
+       *
+       * The vertex offset 2 is always needed when NGG isn't in passthrough mode
+       * and uses triangle input primitives, including with NGG culling.
+       */
+      bool need_gs_vtx_offset2 = !info->is_ngg_passthrough || info->gs.vertices_in >= 3;
+
+      if (stage == MESA_SHADER_TESS_EVAL)
+         need_gs_vtx_offset2 &= info->tes._primitive_mode != TESS_PRIMITIVE_ISOLINES;
+
       if (info->uses_invocation_id) {
          gs_vgpr_comp_cnt = 3; /* VGPR3 contains InvocationID. */
       } else if (info->uses_prim_id || (es_stage == MESA_SHADER_VERTEX &&
                                         info->vs.outinfo.export_prim_id)) {
          gs_vgpr_comp_cnt = 2; /* VGPR2 contains PrimitiveID. */
-      } else if (info->gs.vertices_in >= 3 || tes_triangles || nggc) {
+      } else if (need_gs_vtx_offset2) {
          gs_vgpr_comp_cnt = 1; /* VGPR1 contains offsets 2, 3 */
       } else {
-         gs_vgpr_comp_cnt = 0; /* VGPR0 contains offsets 0, 1 */
+         gs_vgpr_comp_cnt = 0; /* VGPR0 contains offsets 0, 1 (or passthrough prim) */
       }
 
       /* Disable the WGP mode on gfx10.3 because it can hang. (it