Contributions to Rust and LLVM in 2025

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The Rust Programming Language

github.com/mozilla/rust

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2025

Rust: Merged 28 PRs, reviewed 24 PRs
LLVM: Merged 13 PRs

2024

Rust: Merged 40 PRs
LLVM: Merged 20 PRs

I have much less spare time this year because I have a baby :p. And I'm looking for a sustainable way to contribute.

I joined the Rust compiler team (in 2024! :3).

LLVM: A performance regression in LLVM that affected Ajla and Python

This regression has been discussed elsewhere; see lobste.rs/s/9paxz2/performance_python_3_14_tail_call.

I introduced the regression due to a limit for compile time in llvm#78582. Finally, I learned a resolve from GCC, and then I fixed the regression in llvm#114990 and llvm#132536.

Rust: Transforming “Clone” to “Copy”

To me, the most interesting issue is rust#128081.

The "Clone" method can be transformed to "Copy" in GVN. I have several PRs for this and am working on more.

The first key PR (rust#128299) exposed variant miscompilations. Camille Gillot identified the root cause in rust#147844:

We can reason with the value behind a reference because it is UB to directly assign to the underlying local while the reference is live. We allow creating new derefs, this means extending the liveness of references, so we are creating UB.

Rust: Debuginfo in MIR Basic Blocks

rust#129931 turns out that handling Debuginfo in MIR Basic Blocks is required. I implemented this in rust#142771.

This left some stuff:

Better remapping locals for debuginfos; see rust#147525.
A tracking issue: Figure out all debugging information representations of statements #147679.
Add documentation for the change in the Rust Compiler Development Guide.

Rust: 4 P-critical

I caused 4 P-critical issues. :(

The rust#124150 and rust#132353 are miscompilations in MIR opt. I'm investigating some translation validation tools, such as Miri, Alive2, and model checker, but I haven't made any progress. So far, I have only read Program Z3, and I have forgotten many things. Furthermore, I'm thinking about picking it up next year. :p

Other

While reviewing PRs can be exhausting, it's also a great learning opportunity. For instance, working through PRs like rust#142707, rust#143784, rust#136840, and rust#133832 taught me a great deal.

I realize that the knowledge of the LLVM backend is essential to me, since more and more issues happened in the LLVM backend. I'm not sure how to tackle these issues, but I have begun studying LLVM Code Generation: A deep dive into compiler backend development.

MIR optimizations are still important to me. I'd like to thank Camille Gillot for their help on MIR.

I'm trying to immerse myself in English, and I have stopped using LLM for Chinese-to-English translation anymore. :p

I'm also learning Japanese for fun. If you are interested in anime and manga, I recommend you read learnjapanese.moe.

家里没地方了 :(，卖掉我的 7950X 主机：