I know the focus of this site isn't neckbeardery, but this is the kind of stuff I'm interested in, and I'm sure it's going to be of interest to someone else too.

Since Mesa branched to 24.0.0 in git-master, the ACO shader compiler is now feature complete to use for RadeonSI OpenGL instead of the LLVM back end.

It may seem like a problem that didn't need solving, as OpenGL shaders aren't like Vulkan shaders, but newer OpenGL specs support more features now and I'd rather have a more efficient compiler.

This can be tested with the following environment variable (but defaults to that if built without LLVM)

AMD_DEBUG=useaco

However, what interests me more than that, is the ability to ditch the dependency on LLVM! It just burns my ass, that upgrading my LLVM toolchain breaks my graphics driver libraries. At the very least I have to have a mesa build ready to go, but it also needs caution because it's more than just a compiler suite, it's the back end for mesa. I don't wait for Arch to curate things either, they are often months behind my toolchain upgrades because of blocking issues with some stupid package.

So this frees me up.

It's not bad to do, but it does involve ditching some things in Mesa that I never use anyway. I long ago stopped building drivers I don't use (i.e. why build intel or nouveau... I'll be having those on the 21st of Never)

Firstly, these are the drivers that can be built like this:

-D gallium-drivers=radeonsi,swrast,zink
-D vulkan-drivers=amd

swrast for OpenGL can still be built, because it will fall back to legacy rather than llvmpipe if no LLVM.
swrast for Vulkan can't, because that uses lavapipe (llvmpipe)

OSMesa can still be built (off screen rendering), no need to disable that

-D gallium-nine=false

The gallium nine state tracker needs LLVM, so Nine can't be built. That's the old D3D9 support, I don't use WineD3D for anything anymore, I use DXVK (D9VK) now for DirectX 9 games.

-D gallium-omx=disabled

The OpenMax state tracker needs LLVM too, so OMX/Bellagio can't be built. I don't have any software that uses openmax, and to be honest I'd never even heard of it before I started compiling Mesa in Arch.

-D gallium-opencl=disabled

Gallium opencl (uses LLVM's libclc) can't be built. That might be a show stopper for some, but I don't use it. To me it's only ever been good for causing build failures, as it's super fussy on SPIRV headers and tools.

Finally, the business end of the change:

-D llvm=disabled

My Mesa is LLVM free :-)

I have tried every single OpenGL thing that I have and have not seen a single problem caused by this change. EGL in Firefox is fine too, no change to WebGL benchmark scores or anything (slightly better if anything, but didn't do enough repetitions to validate that). I've been using Mesa in this configuration since it branched on Oct. 26, anyway.

Last edited by Grogan on 2 November 2023 at 12:37 am UTC