> For the complete documentation index, see [llms.txt](https://isubasinghe.gitbook.io/isithas-wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://isubasinghe.gitbook.io/isithas-wiki/software_engineering/frameworks/llvm/basics.md).

# LLVM Basics

## Basic idea

A toolkit of reusable compiler passes over a typed SSA IR. Front-ends emit LLVM IR; opt runs analysis/transform passes; llc lowers it to a target ISA. Decouples language design from back-end engineering.

## Key facts

* IR is SSA-form, statically typed, three-address.
* Pass kinds: analysis (read-only) and transform.
* Key tools: `clang`, `opt`, `llc`, `lld`, `lli`.
* Phi nodes select values at CFG join points.