Book Image

LLVM Techniques, Tips, and Best Practices Clang and Middle-End Libraries

By : Min-Yih Hsu
Book Image

LLVM Techniques, Tips, and Best Practices Clang and Middle-End Libraries

By: Min-Yih Hsu

Overview of this book

Every programmer or engineer, at some point in their career, works with compilers to optimize their applications. Compilers convert a high-level programming language into low-level machine-executable code. LLVM provides the infrastructure, reusable libraries, and tools needed for developers to build their own compilers. With LLVM’s extensive set of tooling, you can effectively generate code for different backends as well as optimize them. In this book, you’ll explore the LLVM compiler infrastructure and understand how to use it to solve different problems. You’ll start by looking at the structure and design philosophy of important components of LLVM and gradually move on to using Clang libraries to build tools that help you analyze high-level source code. As you advance, the book will show you how to process LLVM IR – a powerful way to transform and optimize the source program for various purposes. Equipped with this knowledge, you’ll be able to leverage LLVM and Clang to create a wide range of useful programming language tools, including compilers, interpreters, IDEs, and source code analyzers. By the end of this LLVM book, you’ll have developed the skills to create powerful tools using the LLVM framework to overcome different real-world challenges.
Table of Contents (18 chapters)
1
Section 1: Build System and LLVM-Specific Tooling
6
Section 2: Frontend Development
11
Section 3: "Middle-End" Development

Printing diagnostic messages

In software development, there are many ways to diagnose a bug—for instance, using a debugger, inserting a sanitizer into your program (to catch invalid memory access, for example), or simply using one of the simplest yet most effective ways: adding print statements. While the last option doesn't sound really smart, it is actually pretty useful in many cases where other options cannot unleash their full potential (for example, release mode binaries with poor debug information quality or multithread programs).

LLVM provides a small utility that not only helps you to print out debug messages but also filters which messages to show. Let's say we have an LLVM Pass, SimpleMulOpt, which replaces multiplication by power-of-two constants with left-shifting operations (which is what we did in the last section of the previous chapter, Processing LLVM IR). Here is part of its run method:

PreservedAnalyses
SimpleMulOpt::run(Function &F, FunctionAnalysisManager...