+
+/*
+ * Mark XFB varyings as always_active_io in the consumer so the linking opts
+ * don't touch them.
+ */
+void
+nir_link_xfb_varyings(nir_shader *producer, nir_shader *consumer)
+{
+ nir_variable *input_vars[MAX_VARYING] = { 0 };
+
+ nir_foreach_variable(var, &consumer->inputs) {
+ if (var->data.location >= VARYING_SLOT_VAR0 &&
+ var->data.location - VARYING_SLOT_VAR0 < MAX_VARYING) {
+
+ unsigned location = var->data.location - VARYING_SLOT_VAR0;
+ input_vars[location] = var;
+ }
+ }
+
+ nir_foreach_variable(var, &producer->outputs) {
+ if (var->data.location >= VARYING_SLOT_VAR0 &&
+ var->data.location - VARYING_SLOT_VAR0 < MAX_VARYING) {
+
+ if (!var->data.always_active_io)
+ continue;
+
+ unsigned location = var->data.location - VARYING_SLOT_VAR0;
+ if (input_vars[location]) {
+ input_vars[location]->data.always_active_io = true;
+ }
+ }
+ }
+}
+
+static bool
+does_varying_match(nir_variable *out_var, nir_variable *in_var)
+{
+ return in_var->data.location == out_var->data.location &&
+ in_var->data.location_frac == out_var->data.location_frac;
+}
+
+static nir_variable *
+get_matching_input_var(nir_shader *consumer, nir_variable *out_var)
+{
+ nir_foreach_variable(var, &consumer->inputs) {
+ if (does_varying_match(out_var, var))
+ return var;
+ }
+
+ return NULL;
+}
+
+static bool
+can_replace_varying(nir_variable *out_var)
+{
+ /* Skip types that require more complex handling.
+ * TODO: add support for these types.
+ */
+ if (glsl_type_is_array(out_var->type) ||
+ glsl_type_is_dual_slot(out_var->type) ||
+ glsl_type_is_matrix(out_var->type) ||
+ glsl_type_is_struct_or_ifc(out_var->type))
+ return false;
+
+ /* Limit this pass to scalars for now to keep things simple. Most varyings
+ * should have been lowered to scalars at this point anyway.
+ */
+ if (!glsl_type_is_scalar(out_var->type))
+ return false;
+
+ if (out_var->data.location < VARYING_SLOT_VAR0 ||
+ out_var->data.location - VARYING_SLOT_VAR0 >= MAX_VARYING)
+ return false;
+
+ return true;
+}
+
+static bool
+replace_constant_input(nir_shader *shader, nir_intrinsic_instr *store_intr)
+{
+ nir_function_impl *impl = nir_shader_get_entrypoint(shader);
+
+ nir_builder b;
+ nir_builder_init(&b, impl);
+
+ nir_variable *out_var =
+ nir_deref_instr_get_variable(nir_src_as_deref(store_intr->src[0]));
+
+ bool progress = false;
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+ if (intr->intrinsic != nir_intrinsic_load_deref)
+ continue;
+
+ nir_deref_instr *in_deref = nir_src_as_deref(intr->src[0]);
+ if (in_deref->mode != nir_var_shader_in)
+ continue;
+
+ nir_variable *in_var = nir_deref_instr_get_variable(in_deref);
+
+ if (!does_varying_match(out_var, in_var))
+ continue;
+
+ b.cursor = nir_before_instr(instr);
+
+ nir_load_const_instr *out_const =
+ nir_instr_as_load_const(store_intr->src[1].ssa->parent_instr);
+
+ /* Add new const to replace the input */
+ nir_ssa_def *nconst = nir_build_imm(&b, store_intr->num_components,
+ intr->dest.ssa.bit_size,
+ out_const->value);
+
+ nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(nconst));
+
+ progress = true;
+ }
+ }
+
+ return progress;
+}
+
+static bool
+replace_duplicate_input(nir_shader *shader, nir_variable *input_var,
+ nir_intrinsic_instr *dup_store_intr)
+{
+ assert(input_var);
+
+ nir_function_impl *impl = nir_shader_get_entrypoint(shader);
+
+ nir_builder b;
+ nir_builder_init(&b, impl);
+
+ nir_variable *dup_out_var =
+ nir_deref_instr_get_variable(nir_src_as_deref(dup_store_intr->src[0]));
+
+ bool progress = false;
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+ if (intr->intrinsic != nir_intrinsic_load_deref)
+ continue;
+
+ nir_deref_instr *in_deref = nir_src_as_deref(intr->src[0]);
+ if (in_deref->mode != nir_var_shader_in)
+ continue;
+
+ nir_variable *in_var = nir_deref_instr_get_variable(in_deref);
+
+ if (!does_varying_match(dup_out_var, in_var) ||
+ in_var->data.interpolation != input_var->data.interpolation ||
+ get_interp_loc(in_var) != get_interp_loc(input_var))
+ continue;
+
+ b.cursor = nir_before_instr(instr);
+
+ nir_ssa_def *load = nir_load_var(&b, input_var);
+ nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(load));
+
+ progress = true;
+ }
+ }
+
+ return progress;
+}
+
+bool
+nir_link_opt_varyings(nir_shader *producer, nir_shader *consumer)
+{
+ /* TODO: Add support for more shader stage combinations */
+ if (consumer->info.stage != MESA_SHADER_FRAGMENT ||
+ (producer->info.stage != MESA_SHADER_VERTEX &&
+ producer->info.stage != MESA_SHADER_TESS_EVAL))
+ return false;
+
+ bool progress = false;
+
+ nir_function_impl *impl = nir_shader_get_entrypoint(producer);
+
+ struct hash_table *varying_values = _mesa_pointer_hash_table_create(NULL);
+
+ /* If we find a store in the last block of the producer we can be sure this
+ * is the only possible value for this output.
+ */
+ nir_block *last_block = nir_impl_last_block(impl);
+ nir_foreach_instr_reverse(instr, last_block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+ if (intr->intrinsic != nir_intrinsic_store_deref)
+ continue;
+
+ nir_deref_instr *out_deref = nir_src_as_deref(intr->src[0]);
+ if (out_deref->mode != nir_var_shader_out)
+ continue;
+
+ nir_variable *out_var = nir_deref_instr_get_variable(out_deref);
+ if (!can_replace_varying(out_var))
+ continue;
+
+ if (intr->src[1].ssa->parent_instr->type == nir_instr_type_load_const) {
+ progress |= replace_constant_input(consumer, intr);
+ } else {
+ struct hash_entry *entry =
+ _mesa_hash_table_search(varying_values, intr->src[1].ssa);
+ if (entry) {
+ progress |= replace_duplicate_input(consumer,
+ (nir_variable *) entry->data,
+ intr);
+ } else {
+ nir_variable *in_var = get_matching_input_var(consumer, out_var);
+ if (in_var) {
+ _mesa_hash_table_insert(varying_values, intr->src[1].ssa,
+ in_var);
+ }
+ }
+ }
+ }
+
+ _mesa_hash_table_destroy(varying_values, NULL);
+
+ return progress;
+}