https://bugs.freedesktop.org/show_bug.cgi?id=90221
--- Comment #1 from Michel Dänzer michel@daenzer.net --- (In reply to Lucas from comment #0)
Some special effects trigger a visible artifact on triangle primitive boundaries, probably, see screenshot attached.
Looks like bug 88642, which is fixed in current LLVM.
Running with the following env var (otherwise the game is unplayable slow on current video settings): R600_DEBUG=sb
That environment variable has no effect with the radeonsi driver.