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.

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,[8][9][10] Common Lisp,[11] PicoLisp, Crystal, CUDA, D,[12] Delphi,[13] Dylan, Forth,[14] Fortran,[15] FreeBASIC, Free Pascal, Halide, Haskell, Idris,[16] Jai (only for optimized release builds), Java bytecode, Julia, Kotlin, LabVIEW's G language,[17][18] Objective-C, OpenCL,[19] PostgreSQL's SQL and PLpgSQL,[20] Ruby,[21] Rust,[22] Scala,[23][24] Standard ML,[25] Swift, Xojo, and Zig.

The LLVM project started in 2000 at the University of Illinois at Urbana–Champaign, under the direction of Vikram Adve and Chris Lattner.

[32] "For designing and implementing LLVM", the Association for Computing Machinery presented Vikram Adve, Chris Lattner, and Evan Cheng with the 2012 ACM Software System Award.

[38] Graphics code within the OpenGL stack can be left in intermediate representation and then compiled when run on the target machine.

On systems with high-end graphics processing units (GPUs), the resulting code remains quite thin, passing the instructions on to the GPU with minimal changes.

A similar system was developed under the Gallium3D LLVMpipe, and incorporated into the GNOME shell to allow it to run without a proper 3D hardware driver loaded.

The modifications generally involve a GIMPLE-to-LLVM IR step so that LLVM optimizers and codegen can be used instead of GCC's GIMPLE system.

supports compiling of Ada, C, C++, D, Delphi, Fortran, Haskell, Julia, Objective-C, Rust, and Swift using various frontends.

[citation needed] The core of LLVM is the intermediate representation (IR), a low-level programming language similar to assembly.

Examples of target dependence beyond what is explicitly mentioned in the documentation can be found in a 2011 proposal for "wordcode", a fully target-independent variant of LLVM IR intended for online distribution.

In the past, LLVM also supported other backends, fully or partially, including C backend, Cell SPU, mblaze (MicroBlaze),[57] AMD R600, DEC/Compaq Alpha (Alpha AXP)[58] and Nios2,[59] but that hardware is mostly obsolete, and LLVM developers decided the support and maintenance costs were no longer justified.

[citation needed] LLVM also supports WebAssembly as a target, enabling compiled programs to execute in WebAssembly-enabled environments such as Google Chrome / Chromium, Firefox, Microsoft Edge, Apple Safari or WAVM.

LLVM-compliant WebAssembly compilers typically support mostly unmodified source code written in C, C++, D, Rust, Nim, Kotlin and several other languages.

For some targets, including the various MIPS instruction sets, integrated assembly support is usable but still in the beta stage.

[citation needed] Unlike the GNU linkers, lld has built-in support for link-time optimization (LTO).

This allows for faster code generation as it bypasses the use of a linker plugin, but on the other hand prohibits interoperability with other flavors of LTO.

[64] llvm-libc is an incomplete, upcoming, ABI independent C standard library designed by and for the LLVM project.

This is officially recognized by LLVM's documentation, which suggests against using version numbers in feature checks for this reason.