How to speed up the Rust compiler in September 2026
- ID
- 30940
- Status
- summarized
- Published
- 01 Oct 2026, 8:44 PM
- Fetched
- 02 Oct 2026, 4:44 AM
- Provider
- Hacker News
- Category
- dev-community
- Original URL
- https://nnethercote.github.io/2026/09/30/how-to-speed-up-the-rust-compiler-in-september-2026.html
- Source URL
- https://hnrss.org/best
Summary
- Score
- 6.5
- Created
- 02 Oct 2026, 4:45 AM
- Tags
- Audience
- developers
What happened
Nicholas Nethercote's September 2026 roundup measures a 4.57% mean wall-time reduction for the Rust compiler over 2026-07-29 to 2026-09-28, with 555 of 629 benchmarks improving and only 74 regressing. Standout single changes include PGO for Clippy (PR #159642, up to 18% faster on the best benchmark), the LLVM 23 upgrade (PR #158734, mean 1.2%), and Jack Huey's lazy liveness work (PR #161938) cutting serde instruction counts 3-5%. Two large nightly features landed: the Polonius Alpha borrow checker and the new trait solver 'Penelope Hammertime', both more capable but measurably slower in a minority of cases, including the popular serde crate.
Why it matters
If you build on stable Rust, the 4.57% mean gain and the LLVM 23 speedup reach you without code changes, but Polonius Alpha and the new trait solver do not: they are Nightly-only, and both are slower on some crates, with serde specifically called out as a regression case. So the decision is whether to try Nightly now for Polonius's more permissive borrow checking, and to budget for compile-time regressions in your own crates rather than assuming the nightly switch is free. Clippy's PGO win (up to 18%) is also a reason not to skip Clippy in CI on time grounds.
Discussion angle
Polonius Alpha and the new trait solver trade precision for compile time, with serde as the named regression example. Ask the room: would you accept slower builds on Nightly to get a borrow checker that accepts programs the old one rejects, and what compile-time budget would you actually tolerate?