Clever memory tricks Written by me, proof-read by an LLM. Details at end. After exploring SIMD vectorisation over the last couple of days, let’s shift gears to look at another class of compiler cleverness: memory access patterns. String comparisons seem straightforward enough - check the length,…

Switching it up a bit Written by me, proof-read by an LLM. Details at end. The standard wisdom is that switch statements compile to jump tables. And they do - when the compiler can’t find something cleverer to do instead. Let’s start with a really simple example: Here the compiler has spotted the…

How SQLite Is Tested Table Of Contents 1. Introduction The reliability and robustness of SQLite is achieved in part by thorough and careful testing. As of version 3.42.0 (2023-05-16), the SQLite library consists of approximately 155.8 KSLOC of C code. (KSLOC means thousands of "Source Lines Of Code"…

As readers of the premium newsletter know, I have been playing some more go recently. In particular, thanks to the release of the book Mastering Mini Go, I have discovered how exciting go on a 9×9 board is. I feel like this faster-paced, smaller game has taught me a lot, because it is so rich in…

Don't Panic!Your ram is fine! What's going on? Like all modern operating systems, Linux is borrowing unused memory for disk caching. This makes it look like you are low on "free" memory, but you are not! Everything is fine! Why is it doing this? Disk caching makes the system much faster and more…

SIMD City: Auto-vectorisation Written by me, proof-read by an LLM. Details at end. It’s time to look at one of the most sophisticated optimisations compilers can do: autovectorisation. Most “big data” style problems boil down to “do this maths to huge arrays”, and the limiting factor isn’t the maths…

Partial inlining Written by me, proof-read by an LLM. Details at end. We’ve learned how important inlining is to optimisation, but also that it might sometimes cause code bloat. Inlining doesn’t have to be all-or-nothing! Let’s look at a simple function that has a fast path and slow path; and then…

Lately libc++ has been adding the C++17 [[nodiscard]] attribute aggressively to every header. (I’m not sure why this month, but my guess is that libc++ just dropped support for some old compiler such that all their supported compilers now permit the attribute even in C++11 mode.) libc++ is following…

Chasing your tail Written by me, proof-read by an LLM. Details at end. Inlining is fantastic, as we’ve seen recently. There’s a place it surely can’t help though: recursion! If we call our own function, then surely we can’t inline… Let’s see what the compiler does with the classic recursive…

Inlining - the ultimate optimisation Written by me, proof-read by an LLM. Details at end. Sixteen days in, and I’ve been dancing around what many consider the fundamental compiler optimisation: inlining. Not because it’s complicated - quite the opposite! - but because inlining is less interesting…

I have recently come across a (click-bait) post on X claiming that multiplying two 1000×1000 matrices in Python was several times faster than in C++ or other languages. So how do you multiply matrices in C++? Let’s see. First of all, how do you multiply matrices? It’s pretty simple: Here, c11 is…

Reading time: 8 minutes In this section, we’ll compare hotpath with established sampling profilers such as perf, flamegraph, and samply. We’ll walk through three common scenarios - CPU-bound code, blocking I/O, and async I/O - to show how the output of sampling profilers differs from hotpath…

Positional Memoization via Proc Macros in a Rust UI Framework Before diving in, I want to introduce what Tessera is. Tessera is a declarative, immediate-mode UI framework for Rust that emphasizes a friendly development experience through functional components while striving for extensibility and…

As a beginner, you might wonder where to start with Embedded Rust. I have been in the same place, and I have seen many others recently asking the same question. So I decided to write this blog post to help. In this guide, I will explain how to get started, what to focus on first, and share a list of…

Aliasing Written by me, proof-read by an LLM. Details at end. Yesterday we ended on a bit of a downer: aliasing stopped optimisations dead in their tracks. I know this is supposed to be the Advent of Compiler Optimisations, not the Advent of Compiler Giving Up! Knowing why your compiler can’t…