Verifying Popcount

Popcount is the function that returns the number of set bits in its argument. Showing that a popcount implementation does what it claims to do has become one of my favorite examples to use when I need to quickly show students how we can reason about programs mathematically. Something like a selection sort is probably […]

How LLVM Optimizes a Function

An optimizing, ahead-of-time compiler is usually structured as: A frontend that converts source code into an intermediate representation (IR). A target-independent optimization pipeline: a sequence of passes that successively rewrite the IR to eliminate inefficiencies and forms that cannot be readily translated into machine code. Sometimes called the “middle end.” A target-dependent backend that generates […]

Trust Boundaries in Software Systems

One of the big things that has changed in computer science education over the last 20 years is that it is now mandatory to prepare students for writing software that lives in a hostile environment. This content can’t be limited to a computer security course, it has to be spread throughout the curriculum. My experience, […]

A Conversation about Teaching Software Engineering

For better or worse, my impressions of software engineering as a field were shaped by a course I took as an undergrad that I thought was mostly not very interesting or useful. We spent a lot of time on waterfalls and stuff, while not covering testing in any detail. For the final project in the […]