llvm-project

LLVM is the compiler infrastructure that most of the modern toolchain runs on, whether you realize it or not. Clang (C/C++), Flang (Fortran), LLDB (debugger), LLD (linker), libc++, and more, all in one monorepo. Apple, Google, and most major tech companies depend on it. The entire thing is free under Apache 2.0.

Self-hosting LLVM is not really the right framing because this is not a service. You build it from source or use your OS package manager. The real question is whether you should use Clang over GCC. For most C/C++ work, Clang gives you better error messages, faster compile times, and tighter integration with modern tooling (LSP, sanitizers, static analysis). GCC still wins in some edge cases around Fortran and certain embedded targets.

Solo developers and small teams should just use whatever Clang version ships with their OS. Large teams doing compiler work or building language tooling will want to build from source and target specific LLVM passes. If you are writing a new programming language, LLVM as a backend saves you years of work.

The catch: the codebase is massive. Building from source takes serious hardware and time. Contributing requires deep compiler knowledge, and the learning curve is one of the steepest in open source.