Friday, 12 December 2025

LLVM Concepts - Optimizable IL from SSA Approach

What is LLVM?

LLVM ("Low Level Virtual Machine") is a collection of modular and reusable compiler and toolchain technologies (you could call it a "compiler infrastructure framework" or a "framework of reusable components to build compilers"). 

LLVM was born from research work at the University of Illinois.

How does LLVM tackle the compilation problem?

LLVM analyses a program and renders it into intermediate language.

The intermediate language (IL) is constrained by static single assignment (or SSA), where variables are assigned only once - enabling aggressive optimization. 

The IL is an abstract RISC-like instruction set with additional information - a major feature being type information.  A detailed guide can be found here.  It is designed to be human-readable. Note that LLVM documentation does not refer tot the language as an IL but rather an IR, or intermediate representation.

A Core Tenent of LLVM - "Lifelong" Program Analysis and Transformation

One of the stated goals of LLVM is to make "lifelong program analysis and transformation available for arbitrary software".

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