LLVM Essentials

Suyog Sarda, Mayur Pandey

• Publisher: Packt Publishing
• Year: 2015
• eBook ISBN: 9781785280801
• Edition: 1
• Topic: Computer Science
• Subtopic: Open Source Programming
• Index: Computer Science

Become familiar with the LLVM infrastructure and start using LLVM libraries to design a compiler

About This Book

• Learn to use the LLVM libraries to emit intermediate representation (IR) from high-level language
• Build your own optimization pass for better code generation
• Understand AST generation and use it in a meaningful way

Who This Book Is For

This book is intended for those who already know some of the concepts of compilers and want to quickly get familiar with the LLVM infrastructure and the rich set of libraries that it provides.

What You Will Learn

• Get an introduction to LLVM modular design and LLVM tools
• Convert frontend code to LLVM IR
• Implement advanced LLVM IR paradigms
• Understand the LLVM IR Optimization Pass Manager infrastructure and write an optimization pass
• Absorb LLVM IR transformations
• Understand the steps involved in converting LLVM IR to Selection DAG
• Implement a custom target using the LLVM infrastructure
• Get a grasp of C's frontend clang, an AST dump, and static analysis

In Detail

LLVM is currently the point of interest for many firms, and has a very active open source community. It provides us with a compiler infrastructure that can be used to write a compiler for a language. It provides us with a set of reusable libraries that can be used to optimize code, and a target-independent code generator to generate code for different backends. It also provides us with a lot of other utility tools that can be easily integrated into compiler projects.

This book details how you can use the LLVM compiler infrastructure libraries effectively, and will enable you to design your own custom compiler with LLVM in a snap.

We start with the basics, where you'll get to know all about LLVM. We then cover how you can use LLVM library calls to emit intermediate representation (IR) of simple and complex high-level language paradigms. Moving on, we show you how to implement optimizations at different levels, write an optimization pass, generate code that is independent of a target, and then map the code generated to a backend. The book also walks you through CLANG, IR to IR transformations, advanced IR block transformations, and target machines.

By the end of this book, you'll be able to easily utilize the LLVM libraries in your own projects.

Style and approach

This book deals with topics sequentially, increasing the difficulty level in a step-by-step approach. Each topic is explained with a detailed example, and screenshots are included to help you understand the examples.

LLVM Essentials

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Table of Contents

LLVM Essentials

Credits

About the Authors

About the Reviewer

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Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Playing with LLVM

Modular design and collection of libraries

Getting familiar with LLVM IR

LLVM tools and using them in the command line

Summary

2. Building LLVM IR

Creating an LLVM module

Emitting a function in a module

Adding a block to a function

Emitting a global variable

Emitting a return statement

Emitting function arguments

Emitting a simple arithmetic statement in a basic block

Emitting if-else condition IR

Emitting LLVM IR for loop

Summary

3. Advanced LLVM IR

Memory access operations

Getting the address of an element

Reading from the memory

Writing into a memory location

Inserting a scalar into a vector

Extracting a scalar from a vector

Summary

4. Basic IR Transformations

Opt Tool

Pass and Pass Manager

Using other Pass info in current Pass

AnalysisUsage::addRequired<> method

AnalysisUsage:addRequiredTransitive<> method

AnalysisUsage::addPreserved<> method

Instruction simplification example

Instruction Combining

Summary

5. Advanced IR Block Transformations

Loop processing

Scalar evolution

LLVM intrinsics

Vectorization

Summary

6. IR to Selection DAG phase

Converting IR to selectionDAG

Legalizing SelectionDAG

Optimizing SelectionDAG

Instruction Selection

Scheduling and emitting machine instructions

Register allocation

Code Emission

Summary

7. Generating Code for Target Architecture

Sample backend

Defining registers and register sets

Defining the calling convention

Defining the instruction set

Implementing frame lowering

Lowering instructions

Printing an instruction

Summary

Index

LLVM Essentials

Copyright © 2015 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: December 2015

Production reference: 1021215

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham B3 2PB, UK.

ISBN 978-1-78528-080-1

www.packtpub.com

Credits

Authors

Suyog Sarda

Mayur Pandey

Reviewer

Renato Golin

Commissioning Editor

Nadeem Bagban

Acquisition Editor

Harsha Bharwani

Content Development Editor

Priyanka Mehta

Technical Editor

Ryan Kochery

Copy Editor

Imon Biswas

Project Coordinator

Izzat Contractor

Proofreader

Safis Editing

Indexer

Tejal Daruwale Soni

Production Coordinator

Aparna Bhagat

Cover Work

Aparna Bhagat

About the Authors

Suyog Sarda is a professional software engineer and an open source enthusiast. He focuses on compiler development and compiler tools. He is an active contributor to the LLVM open source community. Suyog was also involved in code performance improvements for the ARM and X86 architectures. He has been a part of the compiler team for the Tizen project. His interest in compiler development lies more in code optimization and vectorization.

Previously, he has authored a book on LLVM, titled LLVM Cookbook by Packt Publishing.

Apart from compilers, Suyog is also interested in Linux Kernel Development. He has published a technical paper titled Secure Co-resident Virtualization in Multicore Systems by VM Pinning and Page Coloring at the IEEE Proceedings of the 2012 International Conference on Cloud Computing, Technologies, Applications, and Management at the Birla Institute of Technology, Dubai. He has earned a bachelor's degree in computer technology from the College of Engineering, Pune, India.

I would like to thank my family and friends for encouraging me to write this book. I am thankful to my co-author and reviewers who did a tremendous job of refining the contents. I would also like to thank the LLVM open source community for always being helpful. It has been a great experience to interact with the community. It is amazing to see how fast LLVM has evolved.

Mayur Pandey is a professional software engineer and open source enthusiast focused on compiler development and tools. He is an active contributor to the LLVM open source community. He has been a part of the compiler team for the Tizen project and has hands-on experience of other proprietary compilers.

He has earned a bachelor's degree in Information Technology from Motilal Nehru National Institute of Technology, Allahabad, India. Currently, he lives in Bengaluru, India.

I would like to thank my family and friends who made it possible for me to complete the book by taking care of my other commitments, and who have always being encouraging.

About the Reviewer

Renato Golin has worked with toolchains since 2008, developing debuggers and compilers for multiple languages and platforms, and has also been LLVM Tech Lead at ARM and Linaro, focusing on code generation, correctness, performance, and providing a complete toolchain solution based on LLVM for the diverse ARM platforms.

Before that, he spent a decade moving between web back-ends, databases, distributed systems, big data and bioinformatics, always working on and with open source projects.

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Table of contents

• LLVM Essentials