Since a few weeks I'm using Lord Heavys https://wiki.archlinux.org/index.php/unofficial_user_repositories#mesa-git repo, to be able to play Dying Light on Arch.
As of November 30th, the repo broke my DE (Cinnamon). SDDM worked, although the user icon was missing. After login cinnamon is stuck in a restart loop. Downgrading mesa-git, llvm-libs-svn and llvm-svn fixed the problem.
Affected versions on my side are
cinnamon-session: WARNING: t+30,89171s: Application 'cinnamon.desktop' failed to register before timeout
cinnamon-session: CRITICAL: t+30,89191s: We failed, but the fail whale is dead. Sorry....
dbus-daemon: [system] Activating via systemd: service name='org.freedesktop.Accounts' unit='accounts-daemon.service' requested by ':1.101' (uid=1000 pid=3071 comm="/usr/lib/cinnamon-settings-daemon/csd-background ")
/cinnamon-killer-daemon: Bound Cinnamon restart to <Control><Alt>Escape.
This is my first bug report for mesa, so I don't know what other information you might need. The few lines before are from the journal, that I thought might be of importance. I'm not even sure whether I chose the right driver. (It might also be radeonsi? Thought that was deprecated.) Let me know if you need some more information.
AMD 8320e / 990X
Machine: Type: Desktop System: Gigabyte product: N/A v: N/A serial: <root required> Mobo: Gigabyte model: 990XA-UD3 v: x.x serial: <root required> UEFI: American Megatrends v: FD date: 02/04/2013