Link-time optimizations?

[AbigailBuccaneer]

Being able to optimize individual shaders is great, but it would be even better if a fragment and vertex shader could be optimized at the same time - this would allow, for example, removing vertex shader code that writes to a varying that's not read by the fragment shader.

I don't know if Mesa's shader compiler/linker does this at all, but if so it'd be great to have that functionality exposed in glsl-optimizer.