Open requested to merge jljusten/mesa:rt-channel-num into main
This seems simpler, and made the sim happy (albeit in a case that doesn't impact Mesa today).
As a tangent, the sim was also happy with the codegen after:
- ubld8.ADD(quarter(tmp, 1), quarter(tmp, 0), brw_imm_ud(8)); + ubld8.ADD(quarter(tmp, 1), quarter(tmp, 0), brw_imm_uw(8));
This more closely matches the code from 8f48d23e, which after 6132992c is used to build SYSTEM_VALUE_SUBGROUP_INVOCATION.
Tested in ci: https://mesa-ci.01.org/jljusten/builds/371/group/63a9f0ea7bb98050796b649e85481845
Cc: @llandwerlin, @gfxstrand