Optimizations in C++ compilers

Compilers are a necessary technology to turn high-level, easier-to-write code into efficient machine code for computers to execute. Their sophistication at doing this is often overlooked. You may spend a lot of time carefully considering algorithms and fighting error messages but perhaps not enough time looking at what compilers are capable of doing. This article introduces some compiler and code generation concepts, and then shines a torch over a few of the very impressive feats of transformation your compilers are doing for you, with some practical demonstrations of my favorite optimizations. I hope you'll gain an appreciation for what kinds of optimizations you can expect your compiler to do for you, and how you might explore the subject further. Most of all, you may learn to love looking at the assembly output and may learn to respect the quality of the engineering in your compilers. The examples shown here are in C or C++, which are the languages I've had the most experience with, but many of these optimizations are also available in other compiled languages. Indeed, the advent of front-end-agnostic compiler toolkits such as LLVM3 means most of these optimizations work in the exact same way in languages such as Rust, Swift, and D. Copyright © 2019 held by owner/author. Publication rights licensed to ACM.