Chapter 1, Playing with LLVM, introduces you to the modular design of LLVM and LLVM Intermediate Representation. In this chapter, we also look into some of the tools that LLVM provides.

Chapter 2, Building LLVM IR, introduces you to some basic function calls provided by the LLVM infrastructure to build LLVM IR. This chapter demonstrates building of modules, functions, basic blocks, condition statements, and loops using LLVM APIs.

Chapter 3, Advanced LLVM IR, introduces you to some advanced IR paradigms. This chapter explains advanced IR to the readers and shows how LLVM function calls can be used to emit them in the IR.

Chapter 4, Basic IR Transformations, deals with basic transformation optimizations at the IR level using the LLVM optimizer tool opt and the LLVM Pass infrastructure. You will learn how to use the information of one pass in another and then look into Instruction Simplification and Instruction Combining Passes.

Chapter 5, Advanced IR Block Transformations, deals with optimizations at block level on IR. We will discuss various optimizations such as Loop Optimizations, Scalar Evolution, Vectorization, and so on, followed by the summary of this chapter.

Chapter 6, IR to Selection DAG phase, takes you on a journey through the abstract infrastructure of a target-independent code generator. We explore how LLVM IR is converted to Selection DAG and various phases thereafter. It also introduces you to instruction selection, scheduling, register allocation, and so on.

Chapter 7, Generating Code for Target Architecture, introduces the readers to the tablegen concept. It shows how target architecture specifications such as register sets, instruction sets, calling conventions, and so on can be represented using tablegen, and how the output of tablegen can be used to emit code for a given architecture. This chapter can be used by readers as a reference for bootstrapping a target machine code generator.

All you need to work through most of the examples covered in this book is a Linux machine, preferably Ubuntu. You will also need a simple text or code editor, Internet access, and a browser. We recommend installing the meld tool to compare two files; it works well on the Linux platform.

This book is intended for those who already know some of the concepts concerning compilers and want to quickly become familiar with LLVM's infrastructure and the rich set of libraries that it provides. Compiler programmers, who are familiar with concepts of compilers and want to indulge in understanding, exploring, and using the LLVM infrastructure in a meaningful way in their work, will find this book useful.

This book is also for programmers who are not directly involved in compiler projects but are often involved in development phases where they write thousands of lines of code. With knowledge of how compilers work, they will be able to code in an optimal way and improve performance with clean code.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "The LLVM Pass Manager uses the explicitly mentioned dependency information."

A block of code is set as follows:

int add(int a) {
return globvar + a;
}

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

  Value *StartVal = Builder.getInt32(1);
  Value *Res = createLoop(Builder, List, VL, StartVal, Arg2);

  Builder.CreateRet(Res);

Any command-line input or output is written as follows:

$ clang -emit-llvm -c -S add.c
$ cat add.ll

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Clicking the Next button moves you to the next screen."

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