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

Structuring the lexer

As we know from the previous chapter, we need a Token class and a Lexer class. Additionally, a TokenKind enumeration is required to give each token class a unique number. Having an all-in-one header and an implementation file does not scale, so let's restructure things. The TokenKind enumeration can be used universally and is placed in the Basic component. The Token and Lexer classes belong to the Lexer component but are placed in different header and implementation files.

There are three different classes of tokens: keywords, punctuators, and the tokens representing sets of many values. Examples include the CONST keyword, the ; delimiter, and the ident token, which represent the identifiers in the source. Each token needs a member name for the enumeration. Keywords and punctuators have natural display names that can be used for messages.

Like in many programming languages, the keywords are a subset of the identifiers. To classify a token as a keyword...