On Sun, Dec 08, 2024 at 04:53:58AM +0000, Sam James wrote: > I fear this sort of assumes we won't switch to monobuild any time soon. > > I keep thinking [0] about how sustainable our current setup is: > * Fedora moved away from it for >=18 [1]. > * As we saw with offload, it broke a few times in just a week. So it's > only Gentoo who cares about this configuration AFAIK. > * It's not working great if we're already not able to easily package > mlir, flang, or polly. > > Violet attempted working on a merge before [2].
Hey! Thanks for bringing up my work on this. I've also been continuing this work in an overlay which I use myself on some of my machines: https://codeberg.org/vimproved/llvm-overlay. > IIRC, Violet ended up running into issues with getting the CMake to > properly handle both shared and static libraries to install with the > monobuild, so maybe LLVM's CMake is just broken in both directions and > we just have to pick whichever one is least-worst for us (which might be > the standalone builds as we do now)? LLVM's CMake is definitely just rather broken in many ways, yeah. The biggest issue I experienced when working on this was with LLD libraries. Currently, sys-devel/lld is built with -DBUILD_SHARED_LIBS=ON, which builds some LLD libraries used by e.g. zig as shared libraries. However, there's no way to do this in monobuild since passing -DBUILD_SHARED_LIBS=ON is not desirable. The solution I settled on was splitting a sys-libs/lld-libs package which builds LLD with -DBUILD_SHARED_LIBS=ON and then only installs the shared libraries. As for sys-libs/llvm-libs, this package is a result of me trying to figure out a way to have a statically linked system clang (for performance purposes) while still having LLVM functional as a library. After a lot of sifting through CMake spaghetti I settled on splitting the LLVM monobuild into two packages: sys-devel/llvm and sys-libs/llvm-libs. sys-devel/llvm installs the toolchain parts of LLVM (statically linked), and sys-libs/llvm-libs installs the library and CMake parts of LLVM. This overlay is just for my personal use, and I don't think the above package split would be viable for ::gentoo however. One more thing that wasn't mentioned here, LLVM monobuild would also potentially unblock PGO/BOLT optimizations for clang, so overall it could have some pretty good speed improvements for system LLVM toolchain users. - Violet
