https://bugs.freedesktop.org/show_bug.cgi?id=108317
--- Comment #8 from John Galt johngaltfirstrun@gmail.com --- I've found evidence of Polaris users without this issue on llvm 6 + mesa mild. However, my attempts at downgrading and building with llvm 6 and current mesa haven't gone well yet.
At least we know this is probably a regression in llvm 7+