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

Target-specific elements in LLVM IR

While the core of LLVM IR is target-agnostic, target-specific constraints leak in more or less subtle ways into the IR.

In this section, we will cover some of the elements that may make running an LLVM IR program difficult from one target to another.

This knowledge can help you to investigate issues across platforms and understand the limitations of such an approach.

Let us start this list with an obvious one, the intrinsic functions.

Intrinsic functions

Intrinsic functions, or intrinsics for short, are built-in functions that map to low-level constructs, and potentially target-specific instructions.

When writing a frontend, you should aim to target the regular LLVM IR as much as possible. However, some constructs may be difficult to express, or it may be difficult to preserve the developer’s intent with only regular instructions. This is when intrinsics come in handy because they allow you to cross the frontend-backend...