With mesa from today's git the corruptions appear on the whole screen, like in
the attached image (see full_screen_corruptions.png).

After quick bisecting, it looks like commit "radeonsi: Use dma_copy when
possible for si_blit." (5d5c20920e0e570742a497aa047e99a2fa3c04f2) is
responsible for that. When reverted, the full screen corruptions disappear, but
window menu corruptions still persist.