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

Emitting a simple arithmetic statement in a basic block

A basic block consists of a list of instructions. For example, an instruction can be a simple statement performing tasks based on some simple arithmetic instruction. We will see how the LLVM API can be used to emit arithmetic instructions.

For example, if we want to multiply first argument a with integer value 16, we will create a constant integer value 16 with the following API:

Value *constant = Builder.getInt32(16);

We already have a from the function argument list:

Value *Arg1 = fooFunc->arg_begin();

LLVM provides a rich list of API's to create binary operations. You can go through the include/llvm/IR/IRBuild.h file for more details on the APIs.

Value *createArith(IRBuilder<> &Builder, Value *L, Value *R) {
  return Builder.CreateMul(L, R, "multmp");


Note that for demo purposes, the preceding function returns multiplication. We leave it to the readers to make this function more flexible to return any binary operations...