How Rust 1.64 Became 10-20% Faster On Windows?

Tom Smykowski
5 min readOct 17, 2022

If you are a Rust developer you have most likely celebrated the news that the version 1.64 released on 22/09/2022 is 10-20% faster on Windows.

It is one of the most important changes in that release aside of stabilization of some APIs.

But how one merge request made it possible to account to such a performance improvement?

The person behind the merge request is Rémy Rakic aka lqd (pronounced liquid), a French software engineer regularly contributing changes to the Rust compiler.

On 12/05/2022 he submitted a new merge request illustrated with these performance test results:

As a proof he was able to improve performance consistently across all kinds of tests up to 18.92%. On hundreds of tests, all showed a significant improvement, while only two showed a slight decrease:

Such results are a Holy Grail of every performance hunter.

On 11/07/2022 Jakub Beránek announced the good news after two months of heavy work done by lqd to pass tests and fine tune the merge request.

Another two months was needed to make it to the release.

It only proves how much effort it required to provide the result. But what was it about?

Profile-guided…

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Tom Smykowski

Software Engineer & Tech Editor. Top 2% on StackOverflow, 3mil views on Quora, reached 23rd floor in Shuttered Pixel Dungeon