https://bugs.freedesktop.org/show_bug.cgi?id=90370
--- Comment #15 from Sylvain BERTRAND sylvain.bertrand@gmail.com --- Ok, I nailed down the choppyness: source engine games do compile a lot of shaders live... then a "safe" llvm won't do and will cripple performance. You must maximize shader compilation performance with threading and aggressive compilation options for llvm. Vulkan spir-v will be more than welcome. One down. One to go. Those graphical glitches are also into portal2, but less visible and more rare.