Saint's Log

Building LLVM on macOS

This is a trivial task but I figured I would document what happens if you step off the beaten path in simple ways. My goal was to build llvm/llvm-project at release/21.x (commit 2078da43e25a4623) on macOS (AArch64). I started with the command cmake ~/repos/llvm/llvm-project which I thought was what Building LLVM with CMake — LLVM 23.0.0git documentation suggested. cmake failed with this error:

saint@MacBookPro build_llvm_Aarch64 % pwd
/Users/saint/repos/llvm/llvm-project/build_llvm_Aarch64
saint@MacBookPro build_llvm_Aarch64 % cmake ~/repos/llvm/llvm-project 
CMake Warning:
  Ignoring extra path from command line:

   "/Users/saint/repos/llvm/llvm-project"


CMake Error: The source directory "/Users/saint/repos/llvm/llvm-project" does not appear to contain CMakeLists.txt.
Specify --help for usage, or press the help button on the CMake GUI.

This error was a good reminder of why we use the ../llvm argument (e.g. in Building LLVM for Windows ARM64 – Saint’s Log). The second attempt failed due to a missing release type:

saint@MacBookPro build_llvm_Aarch64 % cmake ~/repos/llvm/llvm-project/llvm
-- The C compiler identification is AppleClang 17.0.0.17000404
-- The CXX compiler identification is AppleClang 17.0.0.17000404
-- The ASM compiler identification is Clang with GNU-like command-line
-- Found assembler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:82 (message):
  

  No build type selected.  You need to pass -DCMAKE_BUILD_TYPE=<type> in
  order to configure LLVM.

  Available options are:

    * -DCMAKE_BUILD_TYPE=Release - For an optimized build with no assertions or debug info.
    * -DCMAKE_BUILD_TYPE=Debug - For an unoptimized build with assertions and debug info.
    * -DCMAKE_BUILD_TYPE=RelWithDebInfo - For an optimized build with no assertions but with debug info.
    * -DCMAKE_BUILD_TYPE=MinSizeRel - For a build optimized for size instead of speed.

  Learn more about these options in our documentation at
  https://llvm.org/docs/CMake.html#cmake-build-type



-- Configuring incomplete, errors occurred!
See also "/Users/saint/repos/llvm/llvm-project/build_llvm_Aarch64/CMakeFiles/CMakeOutput.log".
See also "/Users/saint/repos/llvm/llvm-project/build_llvm_Aarch64/CMakeFiles/CMakeError.log".

I don’t know why it wouldn’t just default to the release build. Providing that flag was sufficient for the configuration and build to succeed.

mkdir build
cd build

cmake ../llvm -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=install_local

cmake --build . --target install

My first successful build was via the cmake --build . command, which took over 3 hours on my M1. This was longer than I expected but it was a very simple process overall when compared to Windows AArch64 cross-compilation.