RADV Re-Enables NGG Geometry Shader Support

On top of the last minute Radeon Vulkan "RADV" improvements landing on Wednesday for Mesa 20.0, another big ticket item landed... Well, re-enabled.

Back in July shortly after the Radeon RX 5700 series unveil, RADV added NGG geometry shader support for Navi/GFX10. NGG is the Next-Gen Geometry engines found with Navi but as shown by the RADV driver work and RadeonSI OpenGL driver changes, it can be difficult/buggy to target.

The NGG geometry shader support was ultimately disabled over bugs but on Wednesday Valve's Samuel Pitoiset went ahead and re-enabled NGG GS. It is believed the NGG geometry shader support is good enough to enable by default now, but can still be toggled using RADV_DEBUG=nongg if wanting to confirm any bugs/differences in the code path.

Unless any major issues are uncovered, this geometry shader support and the other NGG improvements to RadeonSI and RADV from this cycle will come with Mesa 20.0 stable around the end of February. Fresh Mesa 20.0-devel benchmarks of AMD Radeon RX 5000 series hardware will come after the release candidates get underway.