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 608 pages

Edition 1st Edition

Languages

C++

Tools

LLVM

Concepts

Programming Language

Author (1):

Quentin Colombet

View More author details

Table of Contents (29) Chapters

Preface

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. 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. Introduction to the Backend

14. Getting Started with the Backend

15. Getting Started with the Machine Code Layer

16. The Machine Pass Pipeline

17. 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. Final Lowering and Optimizations

23. Instruction Scheduling

24. Register Allocation

25. Lowering of the Stack Layout

26. Getting Started with the Assembler

27. Other Books You May Enjoy

28. Index

Textual versus binary format

As already mentioned at the beginning of this chapter, the LLVM IR supports two formats: textual or human-readable and binary, also known as bitcode.

Aside from being more compact, the bitcode format offers some backward properties, meaning that a bitcode file created with an older version of LLVM will work with a new version of LLVM. There is no such guarantee for the textual format. What this means is that in theory, the human-readable syntax of LLVM IR can change all the time and IR written in the past may not work with a parser from a newer LLVM. In practice, the textual format is relatively stable but still breaks from time to time. When this happens, you can leverage the backward properties of the bitcode format by doing the following:

Saving your textual IR to bitcode using opt from the old LLVM
Loading your bitcode file using opt from the new LLVM and saving the output in textual format

This process is illustrated...