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

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

Legalization in SDISel

The legalization phase in SDISel adds another dimension: the concept of legal types. The core idea behind this is that you describe to the framework all the types that you natively support and SDISel will figure out how illegal types will be emulated on the legal ones.

Reminder

The concept of legalization does not exist in FastISel since you must handle the translation from the LLVM IR to the Machine IR in one go in this sub-framework. In other words, when selecting instruction through the FastISel sub-framework, you cannot leverage any of the legalization infrastructure that SDISel provides.

This concept of legal type has a side effect: as soon as you tell SDISel that a type is legal, all the operations on this type are assumed to be legal as well. For instance, imagine that your target can do 64-bit integer additions but not 64-bit integer multiplications. If you mark the 64-bit integer type legal, you must let SDISel know that all...