This is used to fix wrong code generation of s_add_co_select_user in
s_addc_u32 s4, s6, 0 s_cselect_b64 vcc, 1, 0 <-- vcc set as 0x1 if SCC==1 v_mov_b32_e32 v1, s4 s_cmp_gt_u32 s6, 31 v_cndmask_b32_e32 v1, 0, v1, vcc
If the s_addc_u32 set SCC, then we will get value 0x1 in VCC.
The v_cndmask will do per thread selection with VCC as condition
register. As VCC only gets the first bit being set, only the first
thread/lane in destination register v1 can get correct result. Other
lanes will not get correct result. And if the whole piece of code was
placed inside control flow, the first lane may be even inactive.
Setting all bits of VCC will make the v_cndmask work correctly,
and the result VGPR will have the value broadcasted to all active lanes.
The idea here is we set -1 for uniform booleans holding in SGPR, this
would allow direct logical operation with divergent boolean or directly
be used by vector instruction like in above case.
The other tests changes introduced by this patch seems functionally
correct to me.