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title: How to speed up the Rust compiler in September 2026
description: A monthly progress report on Rust compiler performance covers a 4.57% mean wall-time reduction across 629 benchmarks over two months, driven by PGO for Clippy,...
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# How to speed up the Rust compiler in September 2026

**[Lobsters](https://daily.dev/sources/lobsters)** · 7 min read · 1 upvotes · 0 comments

## Summary

A monthly progress report on Rust compiler performance covers a 4.57% mean wall-time reduction across 629 benchmarks over two months, driven by PGO for Clippy, an LLVM 23 upgrade, optimizations from new contributor xmakro, dataflow analysis improvements, and work mitigating regressions from the newly Nightly-enabled Polonius Alpha borrow checker and new trait solver. The author also announces starting a new job at Hexcat focused on compiler performance optimization as a Rust project goal.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://nnethercote.github.io/2026/09/30/how-to-speed-up-the-rust-compiler-in-september-2026.html>

## Questions this post answers

### What LLVM version does the Rust compiler use after PR 158734?

The Rust compiler was upgraded to use LLVM 23 in pull request 158734, authored by Nikita Popov. This upgrade produced a mean wall-time reduction of 1.2% across all benchmarks, which is considered a large improvement for a single change to the compiler's backend.

_Developers tracking Rust compiler internals can follow LLVM version bumps and their performance impact on daily.dev._

### Does enabling Polonius Alpha borrow checker on Rust Nightly slow down compile times?

Yes, Polonius Alpha, the new borrow checker enabled on Nightly, does more work than the old borrow checker and measurably increases compile time in a minority of cases, including for the popular serde crate. Fixes such as making liveness computations lazy reduced instruction counts for serde by 3-5%, though further regressions remain to be addressed.

_Rust developers evaluating nightly borrow checker changes can keep tabs on Polonius Alpha's compile-time trade-offs via daily.dev._

### How much did the new CFG traversal algorithm in PR 160193 speed up compiling the cranelift-codegen crate?

Changing the CFG traversal algorithm used by dataflow analyses cut a check build of the cranelift-codegen crate's wall time by about 30%. The old algorithm needed 1.5 million calls to apply_effects_in_block to reach a fixpoint for the EverInitializedPlaces analysis used by the borrow checker, while the new algorithm needs only 90,000 calls.

_Compiler engineers debugging fixpoint analysis bottlenecks can compare such optimization techniques on daily.dev._

## Similar posts on daily.dev

- [Project goals update — December 2025](https://daily.dev/posts/project-goals-update-december-2025-lsuqsummh) · Rust · 20 upvotes · 9 comments

---

Tags: [#general-programming](https://daily.dev/tags/general-programming), [#rust](https://daily.dev/tags/rust)

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