Build LLVM

Recipes to download and build LLVM, Compiler front end and Compiler-RT from sources. The script builds the latest LLVM from release tarballs, which is currently version 7.0. The script also patches the LLVM 7.0 sources for PowerPC Issue 39704, Vector load/store builtins overstate alignment of pointers (see Review D54787).

Testing on Fedora, Ubuntu, CentOS and PowerPC reveals no LD_LIBRARY_PATH is needed to run an executable. LLVM fails to build on a old Apple PowerMac G5.

LLVM requires CMake 3.4.3 or above, and GCC 4.8.5 or above. Be sure you meet the prerequisites.

Variables

There are several variables of interest you can tune for the build. BS_ stands for BUILD_SCRIPT.

CMAKE - the tool to use for CMake. The default value is cmake.
BS_INSTALL_PREFIX - the installation directory. The default value is /opt/llvm.
BS_SOURCE_DIR - scratch directory to download an unpack the sources. The default value is $HOME/llvm_source. The scripts adds the llvm/ tail, so you should not add it.
BS_BUILD_DIR - scratch directory to build the the sources. Output artifacts are in this directory. The default value is $HOME/llvm_build.
BS_MAKE_JOBS - the number of concurrent make jobs. The default value is 4.
BS_TOOLS - controls compiler-rt. The default value is ON.
BS_LIBCXX - controls libcxx and libcxxabi. The default value is OFF because building libc++ mostly does not work.
BS_TESTS - controls the Test Suite. The Test Suite is a different download and more comprehensive than check. The default value is ON.

Building the sources

./build-llvm.sh is all that is required to download and build the LLVM sources. You will have to manually install Clang after you build it. The script honors alternate compilers, and you can pass them to CMake using:

# Attempt to build on PowerMac with MacPorts GCC
CC=/opt/local/bin/gcc-mp-5 CXX=/opt/local/bin/g++-mp-5 ./build-llvm.sh

And if you need an alternate CMake to satisfy LLVM requirements:

CMAKE=/opt/local/bin/cmake ./build-llvm.sh

And more options:

    CMAKE="$HOME/cmake/bin/cmake" \
    PREFIX="$HOME/llvm" \
    BS_LIBCXX="ON" \
    BS_TESTS="OFF" \
    BS_COMPILE_JOBS="8" \
./build-llvm.sh

Installing the toolchain

You have to manually install the LLVM toolchain after building it, if desired. Perform the following steps to install the toolchain:

# Defaults to $HOME/llvm_build
cd "$BS_BUILD_DIR"
sudo make install

You can also delete BS_SOURCE_DIR and BS_BUILD_DIR after installation. The defaults for BS_SOURCE_DIR and BS_BUILD_DIR and $HOME/llvm_build and $HOME/llvm_source, respectively.

libc++

The libcxx and libcxxabi recipes are mostly broken. There's a problem with a missing symbol called __thread_local_data(). We don't know how to work around it, and our LLVM mailing list questions have not been answered. Also see https://stackoverflow.com/q/53356172/608639 and https://stackoverflow.com/q/53459921/608639.

If you want to attempt to build libcxx and libcxxabi then set BS_LIBCXX=ON. On PowerPC and Solaris we unconditionally set BS_LIBCXX=OFF because we know it breaks us.

Building CMake

LLVM requires CMake 3.4.3 or higher. You can use build-cmake.sh to update CMake if needed. The script builds in the cmake_build directory and installs itself at $HOME/cmake. You can change the variables by editing the top of the script.

noloader / build-llvm