LLVM is a set of compiler and toolchain technologies[4] that can be used to develop a frontend for any programming language and a backend for any instruction set architecture.

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The name LLVM originally stood for Low Level Virtual Machine, though the project has expanded and the name is no longer officially an initialism.

LLVM is written in C++ and is designed for compile-time, link-time, runtime, and "idle-time" optimization.

Originally implemented for C and C++, the language-agnostic design of LLVM has since spawned a wide variety of frontends:

languages with compilers that use LLVM (or which do not directly use LLVM but can generate compiled programs as LLVM IR) include ActionScript, Ada, C# for .NET,[6][7][8] Common Lisp, PicoLisp,

Crystal, CUDA, D, Delphi, Dylan, Forth,[9] Fortran, FreeBASIC, Free Pascal, Halide, Haskell, Java bytecode, Julia, Kotlin, LabVIEW's G language,[10][11] Lua, Objective-C, OpenCL,[12] PostgreSQL's SQL and PLpgSQL,[13] Ruby,[14] Rust,[15] Scala,[16][17] Swift, Xojo, and Zig.

 LLVM is designed around a language-independent intermediate representation (IR) that serves as a portable, high-level assembly language that can be optimized with a variety of transformations over multiple passes.