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 an LLVM-based compiler, you should look into Clang 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 Build Clang and LLVM with Profile-Guided Optimizations: Notes on building LLVM/Clang with PGO.
How to Cross Compile Compiler-rt Builtins For Arm: Notes on cross-building and testing the compiler-rt builtins for 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.
test-suite Guide: Describes how to compile and run the test-suite benchmarks.
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.
Building a Distribution of LLVM: A best-practices guide for using LLVM’s CMake build system to package and distribute LLVM-based tools.
Remarks: A reference on the implementation of remarks in 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)

Documentation for Go bindings

Github Source 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.
Fuzzing LLVM libraries and tools: Information on writing and using Fuzzers to find bugs in LLVM.
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.
How To Add A Constrained Floating-Point Intrinsic: Gives the steps necessary when adding a new constrained math intrinsic to 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.
Support Library: This document describes the LLVM Support Library (lib/Support) 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.
ORC Design and Implementation: Describes the design and implementation of the ORC APIs, including some usage examples, and a guide for users transitioning from ORCv1 to ORCv2.
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.
Control Flow Verification Tool Design Document: A description of the verification tool for Control Flow Integrity.
Speculative Load Hardening: A description of the Speculative Load Hardening mitigation for Spectre v1.
Stack Safety Analysis: This document describes the design of the stack safety analysis of local variables.

Development Process Documentation¶

Information about LLVM’s development process.

Contributing to LLVM: An overview on how to contribute to LLVM.
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.
LLVM Bug Life Cycle: Describes how bugs are reported, triaged and closed.

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
- 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.
Test-Suite Extentions: Proposals for additional benchmarks/programs for llvm’s test-suite.
Variable Names Plan: Proposal to change the variable names coding standard.
Vectorization Plan: Proposal to model the process and upgrade the infrastructure of LLVM’s Loop Vectorizer.