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

Scalar evolution

By scalar evolution, we mean how the value of a scalar changes in a program with the execution of code. We look at a particular scalar value and see how it is getting derived, what all other elements it is dependent on, whether this is known at compile time or not, and what all operations are being performed. We need to look into a block of code rather than looking into individual instructions. A scalar value is build up from two elements, a variable and an operation of constant step. The variable element that builds up this scalar value is unknown at compile time and its value can be known at run time only. The other element is the constant part. These elements themselves may be recursively broken into other elements such as a constant, an unknown value or an arithmetic operation.

The main idea here is to look at complete scalar value containing the unknown part at compile time and see how this value will evolve during execution and try to use this for optimization. One...