https://bugs.freedesktop.org/show_bug.cgi?id=53130
--- Comment #3 from Darren Salt bugspam@moreofthesa.me.uk --- I've rebuilt mesa with this re-enabled and I saw a lot of rendering glitches. I suspect that DISCARD_RANGE being re-enabled is the problem, although I've also built and installed an updated xf86-video-ati (cdf522f→20bfc65).
My current mesa build has 1eedebc reverted; I'll re-check with that undone later.