1eedebc65b02130ef7a27062a1ed67972a317a08 is the first bad commit
commit 1eedebc65b02130ef7a27062a1ed67972a317a08
Author: Marek Olšák <maraeo@gmail.com>
Date:   Thu Nov 1 02:00:37 2012 +0100

    r600g: re-enable handling of DISCARD_RANGE, improving performance

    It seems to work for me now. Even the graphics corruption is gone.

    This also boosts performance in Reaction Quake.

Reverting this commit on current master (e721a76) does fix the garbled UI
on my rv770.