Comment # 38 on bug 66067 from Roland Scheidegger

(In reply to Nicholas Miell from comment #37)
> You could look for "# cgc version" near the beginning of the program source
> (almost certainly the second line), but that assumes the shaders weren't
> post-processed to strip out all the comments.
> 
> Alternately, you could just disable it entirely by default and include a
> driconf option.

Actually I suppose in theory it would be possible to do this in the state
tracker with relatively little overhead. You'd just have to validate the shadow
targets the first time you draw for arb_fp shaders iff they have shadow sampler
dcls and change them to non-shadow if the samplers don't have compare mode set
(it would have to be conditional on a driconf variable though that way, because
if you only validate the first time it would break conformant apps which happen
to have the samplers wrong the first time they draw which could for instance
happen if they try to force early compilation). Afterwards no further
validation should be required.
Not sure it's all that feasible though, for instance shader validation happens
before texture/sampler validation so you'd need to be careful, probably would
make the code somewhat ugly just for fixing broken shaders...