Book Image

LLVM Essentials

By : Mayur Pandey, Suyog Sarda, David Farago
Book Image

LLVM Essentials

By: Mayur Pandey, Suyog Sarda, David Farago

Overview of this book

LLVM is currently the point of interest for many firms, and has a very active open source community. It provides us with a compiler infrastructure that can be used to write a compiler for a language. It provides us with a set of reusable libraries that can be used to optimize code, and a target-independent code generator to generate code for different backends. It also provides us with a lot of other utility tools that can be easily integrated into compiler projects. This book details how you can use the LLVM compiler infrastructure libraries effectively, and will enable you to design your own custom compiler with LLVM in a snap. We start with the basics, where you’ll get to know all about LLVM. We then cover how you can use LLVM library calls to emit intermediate representation (IR) of simple and complex high-level language paradigms. Moving on, we show you how to implement optimizations at different levels, write an optimization pass, generate code that is independent of a target, and then map the code generated to a backend. The book also walks you through CLANG, IR to IR transformations, advanced IR block transformations, and target machines. By the end of this book, you’ll be able to easily utilize the LLVM libraries in your own projects.
Table of Contents (14 chapters)
LLVM Essentials
About the Authors
About the Reviewer

Sample backend

To understand target code generation, we define a simple RISC-type architecture TOY machine with minimal registers, say r0-r3, a stack pointer SP, a link register, LR (for storing the return address); and a CPSR – current state program register. The calling convention of this toy backend is similar to the ARM thumb-like architecture—arguments passed to the function will be stored in register sets r0-r1, and the return value will be stored in r0.

Defining registers and register sets

Register sets are defined using the tablegen tool. Tablegen helps to maintain large number of records of domain specific information. It factors out the common features of these records. This helps in reducing duplication in the description and forms a structural way of representing domain information. Please visit to understand tablegen in detail. TableGen files are interpreted by the TableGen binary: llvm-tblgen.

We have described our sample backend in the preceding...