Avoid window iterations when no windows of desired class present

src/misc_gui.cpp

@@ -1352,6 +1352,7 @@ static WindowDesc _query_desc(
 
 static void RemoveExistingQueryWindow(Window *parent, QueryCallbackProc *callback)
 {
+	if (!HaveWindowByClass(WC_CONFIRM_POPUP_QUERY)) return;
 	for (Window *w : Window::IterateFromBack()) {
 		if (w->window_class != WC_CONFIRM_POPUP_QUERY) continue;
 

src/timetable_gui.cpp

@@ -1256,6 +1256,12 @@ void ShowTimetableWindow(const Vehicle *v)
 
 void SetTimetableWindowsDirty(const Vehicle *v, SetTimetableWindowsDirtyFlags flags)
 {
+	if (!(HaveWindowByClass(WC_VEHICLE_TIMETABLE) ||
+			((flags & STWDF_SCHEDULED_DISPATCH) && HaveWindowByClass(WC_SCHDISPATCH_SLOTS)) ||
+			((flags & STWDF_ORDERS) && HaveWindowByClass(WC_VEHICLE_ORDERS)))) {
+		return;
+	}
+
 	v = v->FirstShared();
 	for (Window *w : Window::Iterate()) {
 		if (w->window_class == WC_VEHICLE_TIMETABLE ||

src/vehicle_gui.cpp

@@ -2751,6 +2751,7 @@ void DirtyVehicleListWindowForVehicle(const Vehicle *v)
 {
 	WindowClass cls = static_cast<WindowClass>(WC_TRAINS_LIST + v->type);
 	WindowClass cls2 = (v->type == VEH_TRAIN) ? WC_TRACE_RESTRICT_SLOTS : cls;
+	if (!HaveWindowByClass(cls) && !HaveWindowByClass(cls2)) return;
 	for (Window *w : Window::Iterate()) {
 		if (w->window_class == cls || w->window_class == cls2) {
 			BaseVehicleListWindow *listwin = static_cast<BaseVehicleListWindow *>(w);

src/window.cpp

@@ -88,7 +88,7 @@ bool _mouse_hovering;      ///< The mouse is hovering over the same point.
 
 SpecialMouseMode _special_mouse_mode; ///< Mode of the mouse.
 
-static std::bitset<WC_END> _present_window_types;
+std::bitset<WC_END> _present_window_types;
 
 /**
  * List of all WindowDescs.
@@ -1105,6 +1105,8 @@ void Window::SetShaded(bool make_shaded)
  */
 static Window *FindChildWindow(const Window *w, WindowClass wc)
 {
+	if (wc < WC_END && !_present_window_types[wc]) return nullptr;
+
 	for (Window *v : Window::IterateFromBack()) {
 		if ((wc == WC_INVALID || wc == v->window_class) && v->parent == w) return v;
 	}

src/window_func.h

@@ -14,6 +14,8 @@
 #include "company_type.h"
 #include "core/geometry_type.hpp"
 
+#include <bitset>
+
 Window *FindWindowById(WindowClass cls, WindowNumber number);
 Window *FindWindowByClass(WindowClass cls);
 Window *GetMainWindow();
@@ -61,6 +63,12 @@ void CloseWindowByClass(WindowClass cls);
 
 bool FocusWindowById(WindowClass cls, WindowNumber number);
 
+inline bool HaveWindowByClass(WindowClass wc)
+{
+	extern std::bitset<WC_END> _present_window_types;
+	return wc < WC_END && _present_window_types[wc];
+}
+
 bool EditBoxInGlobalFocus();
 bool FocusedWindowIsConsole();
 Point GetCaretPosition();