(In reply to John Galt from comment #12)
> llvm 5.0.2 + mesa mild + http://sprunge.us/oPqhzd + polaris, still not past
> the regression: https://i.imgur.com/RAOwPtM.png

I had to do a google search to find out what "mesa mild" is. Please do not use
this, it seems that was a hack to workaround the fact that radeonsi did not
have compatibility profile support. The dev version of Mesa in git has had 4.5
support for a number of months now. As will the stable 18.3 release due out
very soon.

Can you check if this is still a problem in Mesa from git? There is no need to
use  "mesa mild" it's just forked version on Mesa from June. It seems the
original author deleted the project when we got compat support in master and
somebody has revived the repo. I really wish they had not done so.