How to speed up the Rust compiler in September 2026
A recent report highlights significant improvements to the Rust compiler's performance over the past two months. The mean wall-time reduction was measured at 4.57%, with 555 out of 629 benchmark measurements showing improvement and only 74 regressing. Some benchmarks achieved double-digit percentage reductions. Noah Lev's optimizations to rustdoc were particularly noteworthy, with substantial speed gains.
Jakub Beránek enabled Profile-Guided Optimization (PGO) for Clippy, resulting in impressive wall-time improvements across most Clippy benchmarks. Nikita Popov upgraded the LLVM version used by the compiler to LLVM 23, which also delivered notable speedups. The new borrow checker, Polonius Alpha, was enabled on Nightly, providing more precise borrow checking but introducing some compile time regressions for certain crates like serde. Jack Huey made several PRs aimed at reducing these regressions, with varying success.
New features like the trait solver, Penelope Hammertime, and optimizations by contributor xmakro contributed to the overall performance improvements. These included optimizations in impl handling, incremental compilation, trait solver selection code, CFG traversal algorithm, and EverInitializedPlaces, among others. These changes collectively contributed to the "sea of green" effect, showcasing overall performance gains despite a few regressions.
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