Many big shaders that currently fail with
r600_shader_select - Failed to build shader variant (type=1) -12
r600_shader_from_tgsi - GPR limit exceeded - shader requires foo registers

would actually work if the GPR check was moved to after SB, as SB reduces the
GPR usage quite nicely.

Another thing is that 128 is the lowest common denominator, and many cards have
192 or 256, which could be checked with the radeon_info ioctl.