000056afaa
This tweak makes possible to directly skip depgraph generation if the root node (the dependency to check, last node of the toposorted queue) is already up-to-date (wrt to stable: yes, for example). This is what Portage does internally (using backupenv) and may break in future releases without notice. So, keep the settings["ACCEPT_KEYWORDS"] setup as a guard, to ensure the safety property.