You're reading from LLVM Code Generation A deep dive into compiler backend development

Product type Paperback

Published in May 2025

Publisher Packt

ISBN-13 9781837637782

Length 620 pages

Edition 1st Edition

Languages

C++

Tools

LLVM

Concepts

Programming Language

Author (1):

Quentin Colombet

View More author details

Table of Contents (30) Chapters

Preface

1. Part 1: Getting Started with LLVM

2. Building LLVM and Understanding the Directory Structure FREE CHAPTER

3. Contributing to LLVM

4. Compiler Basics and How They Map to LLVM APIs

5. Writing Your First Optimization

6. Dealing with Pass Managers

7. TableGen – LLVM Swiss Army Knife for Modeling

8. Part 2: Middle-End: LLVM IR to LLVM IR

9. Understanding LLVM IR

10. Survey of the Existing Passes

11. Introducing Target-Specific Constructs

12. Hands-On Debugging LLVM IR Passes

13. Part 3: Introduction to the Backend

14. Getting Started with the Backend

15. Getting Started with the Machine Code Layer

16. The Machine Pass Pipeline

17. Part 4: LLVM IR to Machine IR

18. Getting Started with Instruction Selection

19. Instruction Selection: The IR Building Phase

20. Instruction Selection: The Legalization Phase

21. Instruction Selection: The Selection Phase and Beyond

22. Part 5: Final Lowering and Optimizations

23. Instruction Scheduling

24. Register Allocation

25. Lowering of the Stack Layout

26. Getting Started with the Assembler

27. Unlock Your Book’s Exclusive Benefits

28. Other Books You May Enjoy

29. Index

Tackling optimizations

A lot of the work of a backend compiler engineer is about improving the performance of the generated code – in other words, write optimizations.

Although you could write any optimization you want from scratch, the LLVM infrastructure provides many APIs to help you in this endeavor.

This section has two goals:

Teach you some of the basics of compiler optimizations
Show you how to leverage LLVM to do the heavy lifting

Let us start with our first concept: legality!

Legality

The concept of legality is prevalent in every aspect of the work of a compiler engineer. The question you should ask yourself when coming up with new optimization is: Is this legal? In other words, does this optimization preserve the semantics of the program?

If the answer is yes, great – you only have to worry about the profitability aspect described in the next section!

If the answer is no, think about what you need to prove to...