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Iterators collect and extend Iterator::collect converts an iterator into a collection such as Vec, which typically requires an allocation. You should avoid calling collect if the collection is then only iterated over again. For this reason,...
Bounds Checks By default, accesses to container types such as slices and vectors involve bounds checks in Rust. These can affect performance, e.g. within hot loops, though less often than you might expect. There are several safe ways to cha...
I/O Locking Rust's print! and println! macros lock stdout on every call. If you have repeated calls to these macros it may be better to lock stdout manually. For example, change this code: # let lines = vec!["one", "two", "three"]; for line...
Logging and Debugging Sometimes logging code or debugging code can slow down a program significantly. Either the logging/debugging code itself is slow, or data collection code that feeds into logging/debugging code is slow. Make sure that n...
Wrapper Types Rust has a variety of "wrapper" types, such as RefCell and Mutex, that provide special behavior for values. Accessing these values can take a non-trivial amount of time. If multiple such values are typically accessed together,...
Machine Code When you have a small piece of very hot code it may be worth inspecting the generated machine code to see if it has any inefficiencies, such as removable bounds checks. The Compiler Explorer website is an excellent resource whe...
Parallelism Rust provides excellent support for safe parallel programming, which can lead to large performance improvements. There are a variety of ways to introduce parallelism into a program and the best way for any program will depend gr...
General Tips The previous sections of this book have discussed Rust-specific techniques. This section gives a brief overview of some general performance principles. As long as the obvious pitfalls are avoided (e.g. using non-release builds)...
Compile Times Although this book is primarily about improving the performance of Rust programs, this section is about reducing the compile times of Rust programs, because that is a related topic of interest to many people. The Minimizing Co...
It has been five months since my last general update on the Rust compiler’s performance. Let’s see what has happened in that time. Big wins Let’s start with some big improvements. The information about metrics at the top of this post still...
Update: see the follow-up post for responses and updated data sets. Are you good at data analysis techniques such as linear regression? Want to help speed up the Rust compiler? Back-end parallelism in rustc Two weeks ago I wrote about my re...
This post describes some performance work I have been doing recently on rustc. I spent several weeks on a particular problem with only a small amount of success. I hope a write-up will be interesting and educational, and may even lead to su...
It’s time to look at some of the progress on Rust compiler speed made since my last post in July. Metrics First, a note about metrics. The rustc benchmark suite uses several different time-related metrics, each of which has its pros and con...
Like most compilers, rustc (the Rust compiler) has a lexer that breaks source code into tokens, which are small units such as identifiers, literals, operators, and punctuation. The parser then checks that these tokens are present in an orde...
Let’s look at some of the progress on Rust compiler speed made since my last post. I will start with some important changes made by other people. Windows PGO Profile-guided optimization is a technique for producing faster programs. It has t...
In my last post I introduced the Compiler performance roadmap for 2022. Let’s see how things are progressing. Normally in these posts I mostly write about my own work, but there is enough interesting stuff going on that I will mention work...
Between 2016 and 2020 I wrote a series of blog posts called “How to speed up the Rust compiler”. These were mostly about my work on the Rust compiler, plus some updates on the progress on the Rust compiler’s speed in general. I am now back...
Valgrind is a very useful tool for working with Rust. This may surprise you. Why would a tool for detecting memory errors be useful with a memory safe language? Two reasons: Valgrind is much more than a tool for detecting memory errors, and...
Update (Dec 10, 2021): I have added some extra information worth reading at the bottom of this post. Update (Feb 25, 2022): And some more. The Rust compiler uses hash tables heavily, and the choice of hash function used for these hash table...
I worked on Rust part-time for several years at Mozilla. During that period I regularly summarized how the compiler’s performance had improved. For example: 2017-11-12 to 2019-07-24. The last comparison I did was in August 2020. I had a bre...
""I did not want to inflict memory management on my son" – @M_a_s_s_i"