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

Throwing and catching exceptions

Exception handling in LLVM IR is closely tied to the platform's support. Here, we will look at the most common type of exception handling using libunwind. Its full potential is used by C++, so we will look at an example in C++ first, where the bar() function can throw an int or a double value, as follows:

int bar(int x) {
  if (x == 1) throw 1;
  if (x == 2) throw 42.0;
  return x;

The foo() function calls bar(), but only handles a thrown int value. It also declares that it only throws int values, as follows:

int foo(int x) throw(int) {
  int y = 0;
  try {
    y = bar(x);
  catch (int e) {
    y = e;
  return y;

Throwing an exception requires two calls into the runtime library. First, memory for the exception is allocated with a call to __cxa_allocate_exception(). This function takes the number...