Issue #3461860 by catch, smustgrave: More efficient route lookup caching

core/lib/Drupal/Core/Routing/RouteProvider.php

@@ -169,6 +169,9 @@ public function getRouteCollectionForRequest(Request $request) {
     if ($cached = $this->cache->get($cid)) {
       $this->currentPath->setPath($cached->data['path'], $request);
       $request->query->replace($cached->data['query']);
+      if ($cached->data['routes'] === FALSE) {
+        return new RouteCollection();
+      }
       return $cached->data['routes'];
     }
     else {
@@ -183,7 +186,7 @@ public function getRouteCollectionForRequest(Request $request) {
       $cache_value = [
         'path' => $path,
         'query' => $query_parameters,
-        'routes' => $routes,
+        'routes' => $routes->count() === 0 ? FALSE : $routes,
       ];
       $this->cache->set($cid, $cache_value, CacheBackendInterface::CACHE_PERMANENT, ['route_match']);
       return $routes;