Book Image

Learn LLVM 12

By : Kai Nacke
Book Image

Learn LLVM 12

By: Kai Nacke

Overview of this book

LLVM was built to bridge the gap between compiler textbooks and actual compiler development. It provides a modular codebase and advanced tools which help developers to build compilers easily. This book provides a practical introduction to LLVM, gradually helping you navigate through complex scenarios with ease when it comes to building and working with compilers. You’ll start by configuring, building, and installing LLVM libraries, tools, and external projects. Next, the book will introduce you to LLVM design and how it works in practice during each LLVM compiler stage: frontend, optimizer, and backend. Using a subset of a real programming language as an example, you will then learn how to develop a frontend and generate LLVM IR, hand it over to the optimization pipeline, and generate machine code from it. Later chapters will show you how to extend LLVM with a new pass and how instruction selection in LLVM works. You’ll also focus on Just-in-Time compilation issues and the current state of JIT-compilation support that LLVM provides, before finally going on to understand how to develop a new backend for LLVM. By the end of this LLVM book, you will have gained real-world experience in working with the LLVM compiler development framework with the help of hands-on examples and source code snippets.
Table of Contents (17 chapters)
Section 1 – The Basics of Compiler Construction with LLVM
Section 2 – From Source to Machine Code Generation
Section 3 –Taking LLVM to the Next Level

Creating your own Clang-based tool

The static analyzer is an impressive example of what you can do with the Clang infrastructure. It is also possible to extend Clang with plugins, so you are able to add your own functionality to Clang. The technique is very similar to adding a pass plugin to LLVM.

Let's explore the functionality with a simple plugin. The LLVM coding standard requires function names to begin with a lowercase letter. However, the coding standard has evolved over time, and there are many instances in which a function begins with an uppercase letter. A plugin that warns about a violation of the naming rule can help to fix the issue, so let's give it a try.

Because you want to run a user-defined action over the abstract syntax tree (AST), you need to define a subclass of the PluginASTAction class. If you write your own tool using the Clang libraries, then you define subclasses of the ASTFrontendAction class for your actions. The PluginASTAction class is...