https://bugs.freedesktop.org/show_bug.cgi?id=69062
--- Comment #7 from LRN lrn1986@gmail.com --- Upgraded kernel to b7a5ae97502e104371c7eb3b7b17ae959e50d6f5 No effect.
Tried to build and install older drm and mesa (git revs from ~Jan 2013, since i remember that things worked back then). Installed drm - no effect. Installed xf86-video-ati - no effect. Tried to build old mesa, got errors. Installed llvm-3.3, made it the default. Got some more errors. Tinkered a bit more. At some point i had to reboot. When the laptop booted again, gdm3 showed no corruption, and neither did gnome3.
Upgraded drm, xf86-video-ati and mesa back to git their respective git master HEADs. Rebooted. No corruption.
So, yeah. Weird. Maybe i was building xorg in a wrong order, and my git gyrations made it right...