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

Introducing the live intervals

The liveness information is represented in LLVM through the concept of live intervals and the related LiveInterval class. Live intervals, at their core, are a set of ranges, described using the slot index representation, that model where a variable is alive in a function.

Table 19.1 shows an example of the live interval of a virtual register:

Machine IR

Live interval

0B bb.0
...
80B   %10:gpr32 = COPY $w0
...
208B   Bcc 1, %bb.2, ...
224B   B %bb.1
240B bb.1:
...
320B   %10:gpr32 = ... %10
368B bb.2:
400B   $w0 = COPY %10:gpr32

# Virtual register
%10
# Segments
[80r,320r:0)
[320r,368B:1)
[368B,400r:2)
# VNInfo
0@80r
1@320r
2@368B-phi

Table 19.1: An example of the live interval representation

The left column of Table 19.1 shows a snippet of a function...

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Table of Contents (30) Chapters

Introducing the live intervals

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Table of Contents (30) Chapters

Introducing the live intervals

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