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

Introducing the LLVM Pass manager

The LLVM core libraries optimize the IR your compiler creates and turn it into object code. This giant task is broken down into separate steps, called Passes. These Passes need to be executed in the right order, which is the objective of the Pass manager.

But why not hardcode the order of the Passes? Well, the user of your compiler usually expects that your compiler provides a different level of optimization. Developers prefer a faster compilation speed over-optimization during development time. The final application should run as fast as possible, and your compiler should be able to perform sophisticated optimizations, with longer compilation times accepted. A different level of optimization means a different number of optimization Passes that need to be executed. And, as a compiler writer, you might want to provide your own Passes to take advantage of your knowledge of the source language. For example, you might want to replace well-known library...