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Managing LLVM Versions

LLVM (Low-Level Virtual Machine) is a collection of modular and reusable compiler and toolchain technologies. Developers often need to manage multiple versions of LLVM for different projects or environments. In this guide, we will cover how to manage multiple LLVM versions and download the appropriate version for your needs.

Table of Contents​

Installing LLVM​

LLVM can be installed in different ways depending on your operating system.

macOS​

On macOS, you can use Homebrew to install LLVM:

brew install llvm

You can then access LLVM binaries (like clang, llvm-config, etc.) by adding the LLVM path to your PATH:

echo 'export PATH="/usr/local/opt/llvm/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc

Ubuntu​

On Ubuntu, LLVM can be installed using apt:

sudo apt install llvm

If you want a specific version of LLVM, you can add the LLVM repository:

sudo apt-add-repository "deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main"
sudo apt-get update
sudo apt-get install llvm-13

Replace `13` with the desired version.

Managing Multiple Versions​

If you need to manage different versions of LLVM for multiple projects, you can install them side by side. To make switching between versions easier, use the `update-alternatives` tool.

For example, to install both LLVM 12 and LLVM 13:

sudo apt install llvm-12 llvm-13

You can then configure `update-alternatives` to switch between versions:

sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-12 20
sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-13 10

To choose the version:

sudo update-alternatives --config clang

This will present a prompt to select the preferred version of LLVM.

Using llvm-config​

LLVM includes a tool called `llvm-config`, which provides information about the LLVM installation. It is especially useful when compiling programs with LLVM.

To get the version of LLVM:

llvm-config --version

To get information about LLVM components:

llvm-config --components

This tool can also help you set the correct include paths, libraries, and flags when compiling.

Switching LLVM Versions​

When you have multiple LLVM versions installed, it’s important to switch the version you want to use in your environment. Here’s how to change between them.

macOS​

If you installed LLVM via Homebrew, you can switch versions using the following commands:

brew switch llvm version

Replace `version` with the specific version number you want to switch to.

Ubuntu​

On Ubuntu, use the `update-alternatives` command to switch versions:

sudo update-alternatives --config clang

Similarly, you can configure `update-alternatives` for other tools like `clang++`, `lld`, `lldb`, etc.

You can download LLVM binaries directly from the official LLVM website or through package managers like Homebrew, `apt`, or `yum`.

For older versions of LLVM, refer to the LLVM Release Archive.

Conclusion​

Managing multiple LLVM versions is a common requirement for developers working with different compilers or toolchains. Using tools like update-alternatives or Homebrew makes switching between versions much easier. Ensure you always check the LLVM version using llvm-config to avoid mismatches when building your projects.