radv: make sure to export the viewport index if FS needs it

If FS reads gl_ViewportIndex but VS doesn't export it, it should
be zero to avoid reading garbage.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2818
Fixes: b424d49ac05 ("radv/llvm: fix exporting the viewport index if the fragment shader needs it")
Signed-off-by: Samuel Pitoiset <[email protected]>
Reviewed-by: Bas Nieuwenhuizen <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4687>

3 files changed, 35 insertions, 0 deletions

diff --git a/src/amd/vulkan/radv_pipeline.c b/src/amd/vulkan/radv_pipeline.c
index f470432d20b..448cbebf2ad 100644
--- a/src/amd/vulkan/radv_pipeline.c
+++ b/src/amd/vulkan/radv_pipeline.c
@@ -2578,12 +2578,16 @@ radv_fill_shader_info(struct radv_pipeline *pipeline,
 		        infos[MESA_SHADER_FRAGMENT].ps.layer_input;
 		keys[MESA_SHADER_VERTEX].vs_common_out.export_clip_dists =
 		        !!infos[MESA_SHADER_FRAGMENT].ps.num_input_clips_culls;
+		keys[MESA_SHADER_VERTEX].vs_common_out.export_viewport_index =
+		        infos[MESA_SHADER_FRAGMENT].ps.viewport_index_input;
 		keys[MESA_SHADER_TESS_EVAL].vs_common_out.export_prim_id =
 		        infos[MESA_SHADER_FRAGMENT].ps.prim_id_input;
 		keys[MESA_SHADER_TESS_EVAL].vs_common_out.export_layer_id =
 		        infos[MESA_SHADER_FRAGMENT].ps.layer_input;
 		keys[MESA_SHADER_TESS_EVAL].vs_common_out.export_clip_dists =
 		        !!infos[MESA_SHADER_FRAGMENT].ps.num_input_clips_culls;
+		keys[MESA_SHADER_TESS_EVAL].vs_common_out.export_viewport_index =
+		        infos[MESA_SHADER_FRAGMENT].ps.viewport_index_input;
 
 		/* NGG passthrough mode can't be enabled for vertex shaders
 		 * that export the primitive ID.
@@ -4351,6 +4355,15 @@ radv_pipeline_generate_ps_inputs(struct radeon_cmdbuf *ctx_cs,
 		++ps_offset;
 	}
 
+	if (ps->info.ps.viewport_index_input) {
+		unsigned vs_offset = outinfo->vs_output_param_offset[VARYING_SLOT_VIEWPORT];
+		if (vs_offset != AC_EXP_PARAM_UNDEFINED)
+			ps_input_cntl[ps_offset] = offset_to_ps_input(vs_offset, true, false, false);
+		else
+			ps_input_cntl[ps_offset] = offset_to_ps_input(AC_EXP_PARAM_DEFAULT_VAL_0000, true, false, false);
+		++ps_offset;
+	}
+
 	if (ps->info.ps.has_pcoord) {
 		unsigned val;
 		val = S_028644_PT_SPRITE_TEX(1) | S_028644_OFFSET(0x20);
diff --git a/src/amd/vulkan/radv_shader.h b/src/amd/vulkan/radv_shader.h
index 0bd33d3025f..23ff7ddcdcc 100644
--- a/src/amd/vulkan/radv_shader.h
+++ b/src/amd/vulkan/radv_shader.h
@@ -59,6 +59,7 @@ struct radv_vs_out_key {
 	uint32_t export_prim_id:1;
 	uint32_t export_layer_id:1;
 	uint32_t export_clip_dists:1;
+	uint32_t export_viewport_index:1;
 };
 
 struct radv_vs_variant_key {
@@ -294,6 +295,7 @@ struct radv_shader_info {
 		bool has_pcoord;
 		bool prim_id_input;
 		bool layer_input;
+		bool viewport_index_input;
 		uint8_t num_input_clips_culls;
 		uint32_t input_mask;
 		uint32_t flat_shaded_mask;
diff --git a/src/amd/vulkan/radv_shader_info.c b/src/amd/vulkan/radv_shader_info.c
index 80f93b1c0a7..dfccba5600c 100644
--- a/src/amd/vulkan/radv_shader_info.c
+++ b/src/amd/vulkan/radv_shader_info.c
@@ -458,6 +458,9 @@ gather_info_input_decl_ps(const nir_shader *nir, const nir_variable *var,
 	case VARYING_SLOT_CLIP_DIST1:
 		info->ps.num_input_clips_culls += attrib_count;
 		break;
+	case VARYING_SLOT_VIEWPORT:
+		info->ps.viewport_index_input = true;
+		break;
 	default:
 		break;
 	}
@@ -730,6 +733,23 @@ radv_nir_shader_info_pass(const struct nir_shader *nir,
 		}
 	}
 
+	/* Make sure to export the ViewportIndex if the fragment shader needs it. */
+	if (key->vs_common_out.export_viewport_index) {
+		switch (nir->info.stage) {
+		case MESA_SHADER_VERTEX:
+			info->vs.output_usage_mask[VARYING_SLOT_VIEWPORT] |= 0x1;
+			break;
+		case MESA_SHADER_TESS_EVAL:
+			info->tes.output_usage_mask[VARYING_SLOT_VIEWPORT] |= 0x1;
+			break;
+		case MESA_SHADER_GEOMETRY:
+			info->gs.output_usage_mask[VARYING_SLOT_VIEWPORT] |= 0x1;
+			break;
+		default:
+			break;
+		}
+	}
+
 	if (nir->info.stage == MESA_SHADER_FRAGMENT)
 		info->ps.num_interp = nir->num_inputs;