I can confirm this issue, on a Radeon RX 580. BogDan.
- Bug#914267: mesa: [regression] with Mesa 18.2.5-2 the charac... Axel R.
- Bug#914267: mesa: [regression] with Mesa 18.2.5-2 the c... Bogdan Vatra
- Bug#914267: mesa: [regression] with Mesa 18.2.5-2 the c... GSR
- Bug#914267: mesa: [regression] with Mesa 18.2.5-2 the c... Michael Biebl
- Bug#914267: mesa: [regression] with Mesa 18.2.5-2 the c... Michael Biebl
- Bug#914316: Fixed in gcc-8 8.2.0-10 Michael Biebl