Created attachment 145032 [details]
Monitor placement crash/working cutoff

There's an issue with certain desktop environments crashing on startup when the monitors of a multi-display system are in certain positions. In my case, I have two monitors, and my desktop environment crashes with the error 

cinnamon: ../src/gallium/drivers/radeonsi/si_state_viewport.c:239: si_emit_guardband: Assertion `left <= -1 && top <= -1 && right >= 1 && bottom >= 1' failed.

when my secondary monitor is positioned to the left of the primary monitor. An example placement can be seen in the attached image. This is roughly the cutoff; moving the secondary monitor, the Philips, any farther left and restarting the DE will result in a crash. Keeping it further right and restarting the DE results in no issues. The secondary monitor can be either above or below the primary monitor with the same results. This error also occurs if the secondary monitor is too far left when the DE starts on system startup. Switching which monitor is the primary and secondary results in the same issue, with a crash if the new secondary is too far left.

I'm using Linux Mint 19.2, Cinnamon 4.2.3, and kernel version 5.0.0-23-generic, though I've tried several different kernel versions. I'm using an RX480. The issue has been confirmed by others at https://github.com/linuxmint/cinnamon/issues/8754 and a very similar and likely linked issue at https://bugs.launchpad.net/ubuntu/+source/cinnamon/+bug/1837087 . glxinfo output can be found at https://pastebin.com/RGnAR320 and I'm happy to provide any other information needed, though I may need some pointers on something like recompiling Mesa in debug mode and getting a trace stack.