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

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

By : Min-Yih Hsu
5 (7)
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LLVM Techniques, Tips, and Best Practices Clang and Middle-End Libraries

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

5 (7)
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)
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1
Section 1: Build System and LLVM-Specific Tooling
6
Section 2: Frontend Development
11
Section 3: "Middle-End" Development

Writing an LLVM Pass for the new PassManager

A Pass in LLVM is the basic unit that is required to perform certain actions against LLVM IR. It is similar to a single production step in a factory, where the products that need to be processed are LLVM IR and the factory workers are the Passes. In the same way that a normal factory usually has multiple manufacturing steps, LLVM also consists of multiple Passes that are executed in sequential order, called the Pass pipeline. Figure 9.1 shows an example of the Pass pipeline:

Figure 9.1 – An example of the LLVM Pass pipeline and its intermediate results

In the preceding diagram, multiple Passes are arranged in a straight line. The LLVM IR for the foo function is processed by one Pass after another. Pass B, for instance, performs code optimization on foo and replaces an arithmetic multiplication (mul) by 2 with left shifting (shl) by 1, which is considered easier than multiplication in most hardware architectures...

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