Targeting Vulkan through Rusticl/Zink

[VarLad]

The mesa homebrew package links against an unsupported version of LLVM.
This makes it unusable to run OpenCL.jl on Macs.

This can be achieved by building a JLL for:

• Mesa (Zink + Rusticl)
• MoltenVK

Some points:

• We need a minimal build of Mesa with only Rusticl and Zink supported. I'm not sure if llvm is a required dependency here.
• MoltenVK doesn't seem to have a direct dependency on LLVM.

Building Mesa (Zink + Rusticl) also has the advantage to support many more GPUs than Apple like Qualcomm, Mediatek, Rockchip etc (anything with good enough Vulkan support)

[maleadt]

rusticl depends on LLVM, https://docs.mesa3d.org/rusticl.html, so this will be a tricky build. Furthermore, "Zink on macOS is experimental with very limited capabilities", so I wouldn't focus on macOS too much (it already has a perfectly functional Metal.jl). Targeting Vulkan in general seems like a much more interesting option, e.g., to target embedded platforms.

[VarLad]

@maleadt That makes sense! One thing egarding the diagnosis of MoltenVK+Zink+Rusticl not working on julia though. I passed all tests using RUSTICL_ENABLE=zink on my laptop using mesa-git. I'm not 100% sure, but I believe my distro (Fedora) dynamically links llvm too, and there it works. 🤔
Also, you've to use a recent commit from Mesa for this (provided by HEAD in brew I believe), I forgot to mention this.

[maleadt]

So on Linux we use symbol versioning, so it's likely that makes it work with a dynamically linked LLVM. Things are different on macOS -- it's supposed to work, but I also don't think it often happens that LLVM is used dynamically by macOS applications (it's a common occurrence on Linux as part of graphics drivers and because of distro's always wanting to link dynamically).