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

Implementing a Pass using the new Pass manager

A Pass can perform arbitrary complex transformations on the LLVM IR. To illustrate the mechanics of adding a new Pass, our new Pass only counts the number of IR instructions and basic blocks. We name the Pass countir. Adding the Pass to the LLVM source tree or as a standalone Pass differs slightly, so we will do both in the following sections. Let's begin by adding a new Pass to the LLVM source tree.

Adding a Pass to the LLVM source tree

Let's start by adding the new Pass to the LLVM source. This is the right approach if we later want to publish the new Pass in the LLVM tree.

The source of Passes that perform transformations on the LLVM IR is located in the llvm-project/llvm/lib/Transforms folder, and the header files are in the llvm-project/llvm/include/llvm/Transforms folder. Because there are so many Passes, they are sorted into subfolders after the category they fit in.

For our new Pass, we create a new folder...