diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 47a1a2607..8b4f97ca8 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -1227,17 +1227,42 @@ namespace {
 
 size_t RTLIL::Design::gc_twines()
 {
-	// Mark phase: every live name and src_id on any AttrObject is a root.
+	// Mark phase: gather every TwineRef stored on a live object as a root.
+	// TwinePool::gc traces each root's concat/suffix children transitively.
 	pool<TwineRef> live;
+	auto root = [&](TwineRef ref) {
+		if (ref != Twine::Null)
+			live.insert(ref);
+	};
+
 	walk_attr_objects(this, [&](const RTLIL::AttrObject *obj) {
-		TwineRef src = obj->meta_->src;
-		if (src != Twine::Null)
-			live.insert(src);
-		TwineRef name = obj->meta_->name;
-		if (name != Twine::Null)
-			live.insert(name);
+		if (!obj->meta_)
+			return;
+		root(obj->meta_->src);
+		root(obj->meta_->name);
 	});
 
+	for (auto &[_, module] : modules_) {
+		for (auto &[_, wire] : module->wires_)
+			if (wire->known_driver())
+				root(wire->driverPort());
+		for (auto &[_, cell] : module->cells_) {
+			root(cell->type.ref());
+			for (auto &conn : cell->connections())
+				root(conn.first);
+		}
+	}
+
+	for (auto &[_, sel] : selection_vars) {
+		for (TwineRef m : sel.selected_modules)
+			root(m);
+		for (auto &[m, members] : sel.selected_members) {
+			root(m);
+			for (TwineRef member : members)
+				root(member);
+		}
+	}
+
 	// Sweep: backing refs are stable, so survivors need no remapping.
 	return twines.gc(live);
 }
@@ -5294,8 +5319,8 @@ void RTLIL::Cell::fixup_parameters(bool set_a_signed, bool set_b_signed)
 }
 
 bool RTLIL::Cell::has_keep_attr() const {
-	return get_bool_attribute(ID::keep) || (module && module->design && module->design->module(type) &&
-			module->design->module(type)->get_bool_attribute(ID::keep));
+	return get_bool_attribute(ID::keep) || (module && module->design && module->design->module(type_impl) &&
+			module->design->module(type_impl)->get_bool_attribute(ID::keep));
 }
 
 bool RTLIL::Cell::has_memid() const
diff --git a/kernel/twine.h b/kernel/twine.h
index 39c15b513..4a217efd8 100644
--- a/kernel/twine.h
+++ b/kernel/twine.h
@@ -169,12 +169,12 @@ struct TwinePool {
 	const Twine& operator[] (TwineRef ref) const {
 		ref = twine_untag(ref);
 		if (ref < STATIC_TWINE_END) {
-			if (yosys_xtrace)
-				std::cout << "#X# accessing " << (size_t)ref << " from globals\n";
+			// if (yosys_xtrace)
+			// 	std::cout << "#X# accessing " << (size_t)ref << " from globals\n";
 			return globals_[ref];
 		} else {
-			if (yosys_xtrace)
-				std::cout << "#X# accessing " << (size_t)ref << " from colony of size " << backing.size() << "\n";
+			// if (yosys_xtrace)
+			// 	std::cout << "#X# accessing " << (size_t)ref << " from colony of size " << backing.size() << "\n";
 			return backing[ref - STATIC_TWINE_END];
 		}
 	}