19 Facts About LLVM

LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture.

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

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

LLVM was originally developed as a research infrastructure to investigate dynamic compilation techniques for static and dynamic programming languages.

LLVM has been an integral part of Apple's Xcode development tools for macOS and iOS since Xcode 4.

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Name LLVM was originally an initialism for Low Level Virtual Machine.

However, the LLVM project evolved into an umbrella project that has little relationship to what most current developers think of as a virtual machine.

LLVM can provide the middle layers of a complete compiler system, taking intermediate representation code from a compiler and emitting an optimized IR.

LLVM can accept the IR from the GNU Compiler Collection toolchain, allowing it to be used with a wide array of existing compiler front-ends written for that project.

LLVM can generate relocatable machine code at compile-time or link-time or even binary machine code at run-time.

LLVM allows code to be compiled statically, as it is under the traditional GCC system, or left for late-compiling from the IR to machine code via just-in-time compilation, similar to Java.

On systems with low-end GPUs, LLVM will compile optional procedures that run on the local central processing unit that emulate instructions that the GPU cannot run internally.

LLVM improved performance on low-end machines using Intel GMA chipsets.

Newer results in 2013 indicate that LLVM has now caught up with GCC in this area, and is compiling binaries of approximately equal performance.

LLVM was originally written to be a replacement for the existing code generator in the GCC stack, and many of the GCC front ends have been modified to work with it, resulting in the now-defunct LLVM-GCC suite.

Widespread interest in LLVM has led to several efforts to develop new front ends for a variety of languages.

Core of LLVM is the intermediate representation, a low-level programming language similar to assembly.

LLVM project introduces another type of intermediate representation called MLIR which helps build reusable and extensible compiler infrastructure by employing a plugin architecture named Dialect.

Formerly, LLVM relied on the system assembler, or one provided by a toolchain, to translate assembly into machine code.