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

Writing into a memory location

LLVM uses the store instruction to write into a memory location. There are two arguments to the store instruction: a value to store and an address at which to store it. The store instruction has no return value. Let's say that we want to write a data to the second element of the vector of two integers. The store instruction looks like store i32 3, i32* %a1. To emit the store instruction, we can use the following API provided by LLVM:

void getStore(IRBuilder<> &Builder, Value *Address, Value *V) {
  Builder.CreateStore(V, Address);

For example, we will multiply the second element of the <2 x i32> vector by 16 and store it back at the same location.

Consider the following code:

#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Verifier.h"
#include <vector>
using namespace llvm;

static LLVMContext &Context = getGlobalContext();
static Module *ModuleOb = new Module("my compiler...