https://bugs.freedesktop.org/show_bug.cgi?id=111077
--- Comment #31 from Matt Turner mattst88@gmail.com --- (In reply to roland@rptd.ch from comment #30)
How I best test this? Just check out the branch and build it or apply it somehow to the mesa branch I have here from bisecting?
wget 'https://gitlab.freedesktop.org/mesa/mesa/merge_requests/1852.patch' and store it in /etc/portage/patches/media-libs/mesa/
Then just rebuild (with portage) a version of Mesa that is known to have the bug.