How to speed up the Rust compiler in December 2025
It has been more than six months since my last post on the Rust compiler’s performance. In that time I lost one job and gained another. I have less time to work directly on the Rust compiler than I used to, but I am still doing some stuff, while also working on other interesting things. Compiler improvements #142095: The compiler has a data structure called VecCache which is a key-value store used with keys that are densely-numbered IDs, such as CrateNum or LocalDefId. It’s a segmented vector with increasingly large buckets added as it grows. In this PR Josh Triplett optimized the common case when the key is in the first segment, which holds 4096 entries. This gave icount reductions across many benchmark runs, beyond 4% in the best cases. #148040: In this PR Ben Kimock added a fast…
