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

The anatomy of a MachineInstr instance

While working in the backend, you’ll mainly be manipulating MachineInstr instances. As such, it’s important to have a good understanding of what they represent and how to make sure what you’re doing with them is legal since what you do preserves the semantics of the program.

At a high level, a MachineInstr object is a combination of three things:

An array of MachineOperand instances
Some flags that can be set or queried – for instance, the fast-math flags attached to this instruction, whether it’s an instruction used for setting up the call frame, and so on (see the MachineInstr::getFlag/setFlag family of methods).
Properties that allow the target independent passes to figure out the effects the instruction may have – for instance, the MachineInstr::mayLoad method returns true for instructions that can read from memory and the MachineInstr::isCommutable method returns true if...