Overview — LLVM 5 documentation

# Overview

The LLVM compiler infrastructure supports a wide range of projects, from industrial strength compilers to specialized JIT applications to small research projects.

Similarly, documentation is broken down into several high-level groupings targeted at different audiences:

# LLVM Design & Overview

Several introductory papers and presentations.

LLVM Language Reference Manual
  Defines the LLVM intermediate representation.
Introduction to the LLVM Compiler
  Presentation providing a users introduction to LLVM.
Intro to LLVM
  Book chapter providing a compiler hacker’s introduction to LLVM.
LLVM: A Compilation Framework for Lifelong Program Analysis & Transformation
  Design overview.
LLVM: An Infrastructure for Multi-Stage Optimization
  More details (quite old now).
Publications mentioning LLVM

# User Guides

For those new to the LLVM system.

NOTE: If you are a user who is only interested in using LLVM-based compilers, you should look into Clang or DragonEgg instead. The documentation here is intended for users who have a need to work with the intermediate LLVM representation.

Getting Started with the LLVM System
  Discusses how to get up and running quickly with the LLVM infrastructure. Everything from unpacking and compilation of the distribution to execution of some tools.
Building LLVM with CMake
  An addendum to the main Getting Started guide for those using the CMake build system.
How To Build On ARM
  Notes on building and testing LLVM/Clang on ARM.
How To Cross-Compile Clang/LLVM using Clang/LLVM
  Notes on cross-building and testing LLVM/Clang.
Getting Started with the LLVM System using Microsoft Visual Studio
  An addendum to the main Getting Started guide for those using Visual Studio on Windows.
LLVM Tutorial: Table of Contents
  Tutorials about using LLVM. Includes a tutorial about making a custom language with LLVM.
LLVM Command Guide
  A reference manual for the LLVM command line utilities (“man” pages for LLVM tools).
LLVM’s Analysis and Transform Passes
  A list of optimizations and analyses implemented in LLVM.
Frequently Asked Questions (FAQ)
  A list of common questions and problems and their solutions.
Release notes for the current release
  This describes new features, known bugs, and other limitations.
How to submit an LLVM bug report
  Instructions for properly submitting information about any bugs you run into in the LLVM system.
Sphinx Quickstart Template
  A template + tutorial for writing new Sphinx documentation. It is meant to be read in source form.
LLVM Testing Infrastructure Guide
  A reference manual for using the LLVM testing infrastructure.
How to build the C, C++, ObjC, and ObjC++ front end
  Instructions for building the clang front-end from source.
The LLVM Lexicon
  Definition of acronyms, terms and concepts used in LLVM.
How To Add Your Build Configuration To LLVM Buildbot Infrastructure
  Instructions for adding new builder to LLVM buildbot master.
YAML I/O
  A reference guide for using LLVM’s YAML I/O library.
The Often Misunderstood GEP Instruction
  Answers to some very frequent questions about LLVM’s most frequently misunderstood instruction.
Performance Tips for Frontend Authors
  A collection of tips for frontend authors on how to generate IR which LLVM is able to effectively optimize.
A guide to Dockerfiles for building LLVM
  A reference for using Dockerfiles provided with LLVM.

# Programming Documentation

For developers of applications which use LLVM as a library.

LLVM Language Reference Manual
  Defines the LLVM intermediate representation and the assembly form of the different nodes.
LLVM Atomic Instructions and Concurrency Guide
  Information about LLVM’s concurrency model.
LLVM Programmer’s Manual
  Introduction to the general layout of the LLVM sourcebase, important classes and APIs, and some tips & tricks.
LLVM Extensions
  LLVM-specific extensions to tools and formats LLVM seeks compatibility with.
CommandLine 2.0 Library Manual
  Provides information on using the command line parsing library.
LLVM Coding Standards
  Details the LLVM coding standards and provides useful information on writing efficient C++ code.
How to set up LLVM-style RTTI for your class hierarchy
  How to make `isa<>`, `dyn_cast<>`, etc. available for clients of your class hierarchy.
Extending LLVM: Adding instructions, intrinsics, types, etc.
  Look here to see how to add instructions and intrinsics to LLVM.
Doxygen generated documentation
  (classes) (tarball)

Documentation for Go bindings

ViewVC Repository Browser
Architecture & Platform Information for Compiler Writers
  A list of helpful links for compiler writers.
libFuzzer – a library for coverage-guided fuzz testing.
  A library for writing in-process guided fuzzers.
Scudo Hardened Allocator
  A library that implements a security-hardened malloc().
Using -opt-bisect-limit to debug optimization errors
  A command line option for debugging optimization-induced failures.

# Subsystem Documentation

For API clients and LLVM developers.

Writing an LLVM Pass
  Information on how to write LLVM transformations and analyses.
Writing an LLVM Backend
  Information on how to write LLVM backends for machine targets.
The LLVM Target-Independent Code Generator
  The design and implementation of the LLVM code generator. Useful if you are working on retargetting LLVM to a new architecture, designing a new codegen pass, or enhancing existing components.
Machine IR (MIR) Format Reference Manual
  A reference manual for the MIR serialization format, which is used to test LLVM’s code generation passes.
TableGen
  Describes the TableGen tool, which is used heavily by the LLVM code generator.
LLVM Alias Analysis Infrastructure
  Information on how to write a new alias analysis implementation or how to use existing analyses.
MemorySSA
  Information about the MemorySSA utility in LLVM, as well as how to use it.
Garbage Collection with LLVM
  The interfaces source-language compilers should use for compiling GC’d programs.
Source Level Debugging with LLVM
  This document describes the design and philosophy behind the LLVM source-level debugger.
Auto-Vectorization in LLVM
  This document describes the current status of vectorization in LLVM.
Exception Handling in LLVM
  This document describes the design and implementation of exception handling in LLVM.
LLVM bugpoint tool: design and usage
  Automatic bug finder and test-case reducer description and usage information.
LLVM Bitcode File Format
  This describes the file format and encoding used for LLVM “bc” files.
System Library
  This document describes the LLVM System Library (`lib/System`) and how to keep LLVM source code portable
LLVM Link Time Optimization: Design and Implementation
  This document describes the interface between LLVM intermodular optimizer and the linker and its design
The LLVM gold plugin
  How to build your programs with link-time optimization on Linux.
Debugging JIT-ed Code With GDB
  How to debug JITed code with GDB.
MCJIT Design and Implementation
  Describes the inner workings of MCJIT execution engine.
LLVM Branch Weight Metadata
  Provides information about Branch Prediction Information.
LLVM Block Frequency Terminology
  Provides information about terminology used in the `BlockFrequencyInfo` analysis pass.
Segmented Stacks in LLVM
  This document describes segmented stacks and how they are used in LLVM.
LLVM’s Optional Rich Disassembly Output
  This document describes the optional rich disassembly output syntax.
How To Use Attributes
  Answers some questions about the new Attributes infrastructure.
User Guide for NVPTX Back-end
  This document describes using the NVPTX backend to compile GPU kernels.
User Guide for AMDGPU Backend
  This document describes using the AMDGPU backend to compile GPU kernels.
Stack maps and patch points in LLVM
  LLVM support for mapping instruction addresses to the location of values and allowing code to be patched.
Using ARM NEON instructions in big endian mode
  LLVM’s support for generating NEON instructions on big endian ARM targets is somewhat nonintuitive. This document explains the implementation and rationale.
LLVM Code Coverage Mapping Format
  This describes the format and encoding used for LLVM’s code coverage mapping.
Garbage Collection Safepoints in LLVM
  This describes a set of experimental extensions for garbage collection support.
MergeFunctions pass, how it works
  Describes functions merging optimization.
Design and Usage of the InAlloca Attribute
  Description of the `inalloca` argument attribute.
FaultMaps and implicit checks
  LLVM support for folding control flow into faulting machine instructions.
Compiling CUDA with clang
  LLVM support for CUDA.
Coroutines in LLVM
  LLVM support for coroutines.
Global Instruction Selection
  This describes the prototype instruction selection replacement, GlobalISel.
XRay Instrumentation
  High-level documentation of how to use XRay in LLVM.
Debugging with XRay
  An example of how to debug an application with XRay.
The Microsoft PDB File Format
  A detailed description of the Microsoft PDB (Program Database) file format.

# Development Process Documentation

Information about LLVM’s development process.

LLVM Developer Policy
  The LLVM project’s policy towards developers and their contributions.
Creating an LLVM Project
  How-to guide and templates for new projects that use the LLVM infrastructure. The templates (directory organization, Makefiles, and test tree) allow the project code to be located outside (or inside) the `llvm/` tree, while using LLVM header files and libraries.
LLVMBuild Guide
  Describes the LLVMBuild organization and files used by LLVM to specify component descriptions.
How To Release LLVM To The Public
  This is a guide to preparing LLVM releases. Most developers can ignore it.
How To Validate a New Release
  This is a guide to validate a new release, during the release process. Most developers can ignore it.
Advice on Packaging LLVM
  Advice on packaging LLVM into a distribution.
Code Reviews with Phabricator
  Describes how to use the Phabricator code review tool hosted on http://reviews.llvm.org/ and its command line interface, Arcanist.

# Community

LLVM has a thriving community of friendly and helpful developers. The two primary communication mechanisms in the LLVM community are mailing lists and IRC.

## Mailing Lists

If you can’t find what you need in these docs, try consulting the mailing lists.

Developer’s List (llvm-dev)
  This list is for people who want to be included in technical discussions of LLVM. People post to this list when they have questions about writing code for or using the LLVM tools. It is relatively low volume.
Commits Archive (llvm-commits)
  This list contains all commit messages that are made when LLVM developers commit code changes to the repository. It also serves as a forum for patch review (i.e. send patches here). It is useful for those who want to stay on the bleeding edge of LLVM development. This list is very high volume.
Bugs & Patches Archive (llvm-bugs)
  This list gets emailed every time a bug is opened and closed. It is higher volume than the LLVM-dev list.
Test Results Archive (llvm-testresults)
  A message is automatically sent to this list by every active nightly tester when it completes. As such, this list gets email several times each day, making it a high volume list.
LLVM Announcements List (llvm-announce)
  This is a low volume list that provides important announcements regarding LLVM. It gets email about once a month.

## IRC

Users and developers of the LLVM project (including subprojects such as Clang) can be found in #llvm on irc.oftc.net.

This channel has several bots.

- Buildbot reporters
  - llvmbb - Bot for the main LLVM buildbot master. http://lab.llvm.org:8011/console
  - bb-chapuni - An individually run buildbot master. http://bb.pgr.jp/console
  - smooshlab - Apple’s internal buildbot master.
- robot - Bugzilla linker. %bug <number>
- clang-bot - A geordi instance running near-trunk clang instead of gcc.

## Community wide proposals

Proposals for massive changes in how the community behaves and how the work flow can be better.

LLVM Community Code of Conduct
  Proposal to adopt a code of conduct on the LLVM social spaces (lists, events, IRC, etc).
Moving LLVM Projects to GitHub
  Proposal to move from SVN/Git to GitHub.
Vectorization Plan
  Proposal to model the process and upgrade the infrastructure of LLVM’s Loop Vectorizer.

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