Book Image

Learn LLVM 12

By : Kai Nacke
Book Image

Learn LLVM 12

By: Kai Nacke

Overview of this book

LLVM was built to bridge the gap between compiler textbooks and actual compiler development. It provides a modular codebase and advanced tools which help developers to build compilers easily. This book provides a practical introduction to LLVM, gradually helping you navigate through complex scenarios with ease when it comes to building and working with compilers. You’ll start by configuring, building, and installing LLVM libraries, tools, and external projects. Next, the book will introduce you to LLVM design and how it works in practice during each LLVM compiler stage: frontend, optimizer, and backend. Using a subset of a real programming language as an example, you will then learn how to develop a frontend and generate LLVM IR, hand it over to the optimization pipeline, and generate machine code from it. Later chapters will show you how to extend LLVM with a new pass and how instruction selection in LLVM works. You’ll also focus on Just-in-Time compilation issues and the current state of JIT-compilation support that LLVM provides, before finally going on to understand how to develop a new backend for LLVM. By the end of this LLVM book, you will have gained real-world experience in working with the LLVM compiler development framework with the help of hands-on examples and source code snippets.
Table of Contents (17 chapters)
Section 1 – The Basics of Compiler Construction with LLVM
Section 2 – From Source to Machine Code Generation
Section 3 –Taking LLVM to the Next Level

Semantic analysis

The semantic analyzer walks the AST and checks for various semantic rules of the language; for example, a variable must be declared before use or types of variables must be compatible in an expression. The semantic analyzer can also print out warnings if it finds a situation that can be improved. For the example expression language, the sematic analyzer must check that each used variable is declared, because that is what the language requires. A possible extension (which will not be implemented here) is to print a warning message if a declared variable is not used.

The semantic analyzer is implemented in the Sema class, and semantic analysis is performed by the semantic() method. Here is the complete Sema.h header file:

#ifndef SEMA_H
#define SEMA_H
#include "AST.h"
#include "Lexer.h"
class Sema {
  bool semantic(AST *Tree);

The implementation is in the Sema.cpp file. The interesting part is the semantic analysis...