According to the warning message it falls back to the TGSI backend. I have seen the warning with Sauerbraten, Unigine Tropics, and Stalker: SoC with Wine (full dynamic lighting).
I see that testing is the first item on the r600todo list, and to see if there are any differences between the two shader compilers. Maybe this should be a prerequisite of that, because most of the shader-heavy applications hit this fallback. BTW I don't see any performance difference between the two compilers on my hd6850 apart from what I reported in bug 51787
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