I get similar corruption in Chromium and Visual Studio Code with Mesa
19.1.0-rc3. There was no problem with 19.1.0-rc2.

This is on Archlinux, kernel 5.1.3, the card is an RX480. I tried compiling
Mesa with both LLVM 8 and 9 (r360929).

It's very visible in Chromium when Chromium is started with parameters that
enable its hardware acceleration:

chromium \
--ignore-gpu-blacklist \
--enable-gpu-rasterization \
--enable-native-gpu-memory-buffers \
--enable-zero-copy \
--disable-gpu-driver-bug-workarounds