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


In this chapter, you learned how the backend of an LLVM target is structured. You used the MIR to examine the state after a pass and you used machine IR to run a single pass. With this knowledge, you can investigate problems in backend passes.

You learned how instruction selection with the help of the selection DAG is implemented in LLVM, and you also were introduced to alternative methods for instruction selection with FastISel and GlobalISel, which helps in deciding which algorithm to choose if your platform offers all of them.

You extended LLVM to support a new machine instruction in the assembler and in the instruction selection, helping you to add support for currently unsupported CPU features. To validate the extension, you developed automated test cases for it.

In the next chapter, we examine another unique feature of LLVM: generating and executing code in one step, also known as Just-In-Time (JIT) compilation.