Created attachment 140780 [details]
Screenshot showing the issue

In a certain scene during the Unigine Valley benchmark, render artifacts
briefly flash on the screen multiple times. This does not occur with the same
card in another machine running Windows 10 -- neither with the DirectX 11 nor
with the OpenGL renderer -- and it does also not occur on this machine when
using a NVIDIA GeForce GTX 660 instead of the RX 580.
When I tried to get an apitrace, the benchmark slows down a lot during the
scene, skipping parts of it and not showing the artifacts. Additionally, the
replay is stuck on the loading screen and major shader compiler errors are
thrown.

I am using Gentoo with kernel 4.17.9 (with the gentoo patchset) and mesa git
(commit d0ee0a0a5d5fb658c87fed82cbcf9b48437abb2c).