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

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Table of Contents (30) Chapters

Preface

1. Part 1: Getting Started with LLVM FREE CHAPTER

2. Building LLVM and Understanding the Directory Structure

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

Generic passes worth mentioning

Among the passes that the CodeGen library offers, we wanted to go over the CodeGenPrepare, PeepholeOptimizer, and MachineCombiner passes because they bring something that may not be obvious at first, are particularly useful, and require some backend work to leverage.

The last point is true for most CodeGen passes, but these are less useful than the other ones if you don’t put in some work.

Let’s start with the CodeGenPrepare pass.

The CodeGenPrepare pass

Despite being part of the CodeGen library, the CodeGenPrepare pass is an LLVM-IR-to-LLVM-IR pass. This pass is responsible for papering over some of the limitations of the legacy instruction selector called SelectionDAG. We’ll cover this in more detail in the next chapter, but at this point, the key takeaway is that you may have to perform some transformations at the LLVM IR level for this selector to produce the best possible code.

Among other things, the CodeGenPrepare...