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

Generating IR from the AST

The LLVM code generator takes a module as described in IR as input and turns it into object code or assembly text. We need to transform the AST representation into IR. To implement an IR code generator, we will look at a simple example first and then develop the classes required for the code generator. The complete implementation will be divided into three classes: the CodeGenerator, the CGModule, and the CGProcedure classes. The CodeGenerator class is the general interface used by the compiler driver. The CGModule and the CGProcedure classes hold the state required for generating the IR code for a compilation unit and a single function.

We begin with a look at the clang-generated IR in the next section.

Understanding the IR code

Before generating the IR code, it's good to know the main elements of the IR language. In Chapter 3, The Structure of a Compiler, we already had a brief look at IR. An easy way to get more knowledge of IR is to study...