(In reply to Tom Stellard from comment #12)
> 
> I think the best solution here would be to teach the backend how to do a
> scalar select based on value of vccz.

You are missing the point. The condition code (VCC) isn't the same across all
threads. The problem is that the conditional assignment is transformed into a
form that makes descriptor load addresses non-uniform (dependent on a VGPR).
There is nothing the AMDGPU backend can do about it. It's not a problem in the
backend.