install-clang

This script installs self-contained standalone versions of clang, LLVM, libc++, and compiler-rt on Darwin and Linux, including linking clang and LLVM themselves against libc++ as well. The script keeps all of the installation within a given target prefix (e.g., /opt/llvm), and hence separate from any already installed compilers, libraries, and include files. In particular, you can later deinstall everything easily by just deleting, e.g., /opt/llvm. Furthermore, as long as the prefix path is writable, the installation doesn't need root privileges.

Usage

To see the available options, use -h:

> ./install-clang -h
Usage: install-clang [<options>] <install-prefix>

Available options:
    -a <abi>   ABI to use [libcxxrt or libcxxabi; default OS-specific]
    -j <n>     build with <n> threads in parallel [default: 1]
    -l         attempt to build LLDB (experimental)
    -m         use git/master instead of preconfigured versions
    -s <stage> begin build from <stage> [1, 2, 3]
    -c         skip cloning repositories, assume they are in place
    -u         update an existing build in <prefix> instead of installing new
    -h|-?      display this help

Environment variables:
    CC         path to the C compiler for bootstrapping
    CXX        path to the C++ compiler for bootstrapping

For example, to build Clang with libc++abi on a machine with multiple cores and install it in /opt/llvm, you can use:

> ./install-clang -a libcxxabi -j 16 /opt/llvm

Once finished, just prefix your PATH with <prefix>/bin and you're ready to use the new binaries:

> clang++ --std=c++11 --stdlib=libc++ test.cc -o a.out && ./a.out
Hello, Clang!

By default, install-clang currently installs the 3.4 release branches of the relevant llvm.org projects. Adding -m on the command line instructs the script to use the current git master versions instead. The script downloads all the sources from the corresponding git repositories and compiles the pieces as needed. Other OSs than Darwin and Linux are not currently supported.

The script also has an update option -u that allows for catching up with upstream repository changes without doing the complete compile/install-from-scratch cycle again. Note, however, that unless coupled with -m, this flag has no immediate effect since the git versions to use are hardcoded to the LLVM/clang release versions.

Details

Doing a self-contained clang/LLVM installation is a bit more messy than one would hope because the projects make assumptions about specific system-wide installation paths to use. The install-clang script captures some trial-and-error I went through to get an independent setup working. Specifically:

• It compiles clang/LLVM twice, once to boostrap with the system compiler and then again with itself linking against the new libraries. (By default, it indeed compiles LLVM a third time with assertions enabled and debug information included. In the end, the installed LLVM libraries have assertions enabled, while the clang binary has not. The 3rd stage can be disabled at the beginning of the script.)

• By default, it uses libabi++ on Darwin, and pathscale's libcxxrt on Linux, but also allows for manually specifiying an ABI via the -a switch.

• It patches some of the LLVM projects to incorporate the installation prefix into configuration and search paths, and to fix/tweak a few other things as well.