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

LLVM intrinsics

An intrinsic function is a function built in to the compiler. The compiler knows how to best implement the functionality in the most optimized way for these functions and replaces with a set of machine instruction for a particular backend. Often, the code for the function is inserted inline thus avoiding the overhead of function call (In many cases, we do call the library function. For example, for the functions listed in we make a call to libc). These are also called built-in functions for other compilers.

In LLVM these intrinsics are introduced during code optimization at IR level (Intrinsics written in program code can be emitted through frontend directly). These function names will start with a prefix "llvm.", which is a reserved word in LLVM. These functions are always external and a user cannot specify the body for these functions in his/her code. In our code, we can only call these intrinsic functions.