Book Image

Learn LLVM 17 - Second Edition

By : Kai Nacke, Amy Kwan
Book Image

Learn LLVM 17 - Second Edition

By: Kai Nacke, Amy Kwan

Overview of this book

LLVM was built to bridge the gap between the theoretical knowledge found in compiler textbooks and the practical demands of compiler development. With a modular codebase and advanced tools, LLVM empowers developers to build compilers with ease. This book serves as a practical introduction to LLVM, guiding you progressively through complex scenarios and ensuring that you navigate the challenges of building and working with compilers like a pro. The book starts by showing you how to configure, build, and install LLVM libraries, tools, and external projects. You’ll then be introduced to LLVM's design, unraveling its applications in each compiler stage: frontend, optimizer, and backend. Using a real programming language subset, you'll build a frontend, generate LLVM IR, optimize it through the pipeline, and generate machine code. Advanced chapters extend your expertise, covering topics such as extending LLVM with a new pass, using LLVM tools for debugging, and enhancing the quality of your code. You'll also focus on just-in-time compilation issues and the current state of JIT-compilation support with LLVM. Finally, you’ll develop a new backend for LLVM, gaining insights into target description and how instruction selection works. By the end of this book, you'll have hands-on experience with the LLVM compiler development framework through real-world examples and source code snippets.
Table of Contents (20 chapters)
1
Part 1: The Basics of Compiler Construction with LLVM
4
Part 2: From Source to Machine Code Generation
10
Part 3: Taking LLVM to the Next Level
14
Part 4: Roll Your Own Backend

Setting up the module and the driver

We collect all the functions and global variables of a compilation unit in an LLVM module. To ease the IR generation process, we can wrap all the functions from the previous sections into a code generator class. To get a working compiler, we also need to define the target architecture for which we want to generate code, and also add the passes that emit the code. We will implement this in this and the next few chapters, starting with the code generator.

Wrapping all in the code generator

The IR module is the brace around all elements we generate for a compilation unit. At the global level, we iterate through the declarations at the module level, create global variables, and call the code generation for procedures. A global variable in tinylang is mapped to an instance of the llvm::GobalValue class. This mapping is saved in Globals and made available to the code generation for procedures:

void CGModule::run(ModuleDeclaration *Mod) {
 ...