i965: Use SIMD16 instead of SIMD8 on Gen4 when possible.
Gen5+ systems allow you to specify multiple shader programs - both SIMD8 and SIMD16 - and the hardware will automatically dispatch to the most appropriate one, given the number of subspans to be processed. However, that is not the case on Gen4. Instead, you program a single shader. If you enable multiple dispatch modes (SIMD8 and SIMD16), the shader is supposed to contain a series of jump instructions at the beginning. The hardware will launch the shader at a small offset, hitting one of the jumps. We've always thought that sounds like a pain, and weren't clear how it affected performance - is it worth having multiple shader types? So, we never bothered with SIMD16 until now. This patch takes a simpler approach: try and compile a SIMD16 shader. If possible, set the no_8 flag, telling the hardware to just use the SIMD16 variant all the time. Signed-off-by:Kenneth Graunke <kenneth@whitecape.org> Reviewed-by:
Jordan Justen <jordan.l.justen@intel.com>