What is LLVM? The power behind Swift, Rust, Clang, and more

New languages, and improvements on existing ones, are mushrooming throughout the develoment landscape. Mozilla’s Rust, Apple’s Swift, Jetbrains’s Kotlin, and many other languages provide developers with a new range of choices for speed, safety, convenience, portability, and power.

Why now? One big reason is new tools for building languages—specifically, compilers. And chief among them is LLVM (Low-Level Virtual Machine), an open source project originally developed by Swift language creator Chris Lattner as a research project at the University of Illinois.

LLVM makes it easier to not only create new languages, but to enhance the development of existing ones. It provides tools for automating many of the most thankless parts of the task of language creation: creating a compiler, porting the outputted code to multiple platforms and architectures, and writing code to handle common language metaphors like exceptions. Its liberal licensing means it can be freely reused as a software component or deployed as a service.

The roster of languages making use of LLVM has many familiar names. Apple’s Swift language uses LLVM as its compiler framework, and Rust uses LLVM as a core component of its tool chain. Also, many compilers have an LLVM edition, such as Clang, the C/C++ compiler (this the name, “C-lang”), itself a project closely allied with LLVM. And Kotlin, nominally a JVM language, is developing a version of the language called Kotlin Native that uses LLVM to compile to machine-native code.

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