Comment # 7 on bug 84977 from Tom Stellard

(In reply to David Heidelberger (okias) from comment #6)
> in function r300FPTranslateRGBSwizzle is return value of sd == 0 (for sure)

So it sounds like this might be a bug somewhere in
rc_reg_class_variable_get_class()

At the very bottom of this function, there is a call to find_class(), it would
be good to put a printf to check the value of can_change_writemask and also
class_index.