LLVM Upgrade Process

This page documents how to update the Zig source code to a new LLVM version.

1. Update the version numbers in:
   1. README.md
   2. cmake/Findllvm.cmake
   3. cmake/Findclang.cmake
   4. cmake/Findlld.cmake
2. Do an git diff in LLVM's compiler-rt project to find out what has changed since the previous release. Apply the relevant changes to Zig.
3. Build LLVM, clang, and LLD in debug mode, applying Zig's outstanding patches to LLD.
4. Upgrade deps/lld and deps/lld-prebuilt to the new LLD code, and then reapply any outstanding patches that we have against upstream. You can find out about outstanding patches with git, since they are done in separate commits.
5. Update src/zig_clang_*.cpp to the new versions. Before updating, replace each file with the original file from the old LLVM version and do a git diff to see what patches have been applied by Zig. Then update each file to the versions from the new LLVM, and re-apply the patches as necessary.
   • src/zig_clang_driver.cpp corresponds to llvm-project/clang/tools/driver/driver.cpp
   • src/zig_clang_cc1_main.cpp corresponds to llvm-project/clang/tools/driver/cc1_main.cpp
   • src/zig_clang_cc1as_main.cpp corresponds to llvm-project/clang/tools/driver/cc1as_main.cpp
6. Update c_headers/ to the latest clang_release_XY/build-debug/lib/clang/X.Y.Z/include/. Then update CMakeLists.txt to have the new list of files.
7. Update the CI scripts to the new version
8. Update How to build LLVM, libclang, and liblld from source
9. Update Building Zig on Windows
10. Update the static asserts at the bottom of src/zig_llvm.cpp
11. Build zig in debug mode with the debug mode llvm, clang, patched lld, and run the full Zig test suite. This takes several hours.

master branch is always the latest LLVM release. The llvmX branch is kept up to date with the next LLVM release. The day that LLVM is released, we merge the llvmX branch into master, and start the next llvmX branch, following this upgrade process.