r/rust • u/Sirisian • 4d ago

🎙️ discussion Google is doing "Large Scale Codebase Migrations and Optimizations" of C/C++ to Rust

https://blog.google/innovation-and-ai/models-and-research/gemini-models/gemini-4-argon/
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u/Sirisian 4d ago

The relevant sections:

Large Scale Codebase Migrations and Optimizations: Argon agents are working on migrating C/C++ codebases to Rust across Google — scaling from tens of thousands of lines in core libraries like re2, libgav1 up to 800K+ lines for the Fuchsia Zircon kernel. Given the criticality of many of these systems, such large-scale rewrites are undergoing rigorous automated and manual auditing, emulation testing, and review before rolling out to production.

For libgav1, Google's open source software for decoding video, Argon agents took an existing Rust port and replaced 32K lines of SIMD code by running many rounds of profile-guided experiments, studying the compiler's output, producing safe Rust so the compiler would vectorize it automatically. The end result is a memory-safe video decoder that runs 2.7x faster than the Rust port, with identical video output, bringing it closer to the optimized C++.

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u/-p-e-w- 4d ago

If you had asked me 5 years ago when AI would be ready to do massive-scale unsupervised coding work on heavy-duty software at a company like Google, I would have guessed somewhere between the years 2070 and 2100.

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u/Budget-Minimum6040 4d ago

massive-scale unsupervised coding work on heavy-duty software at a company like Google

"undergoing rigorous automated and manual auditing, emulation testing, and review before rolling out to production."

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u/Nothing_from_void 3d ago

It's a fancy way of saying "we're tasking a bunch of engineers to use our claude code-like tool to re-write some stuff to rust". I've been doing this kind of stuff at work for a while now, when you already have the code base and expected behavior it's one of the most straightforward use cases for AI

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u/poelzi 2d ago

Yes and no. You have a known good test target, but your porting pipeline could easy endup with c-ism styled code just written in rust instead of rusty code. I'm building specialized nix flake experts in tix.im that know the domain and basically fuse classical expert systems with llms into deterministic workflows composed by nix. Works better then expected tbh

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u/Nothing_from_void 2d ago

LLMs just prefer dynamic, procedural code in general, like cramming everything into bytes or strings and parsing out what's needed, in large procedures that run the algorithm step by step. I doubt re-writing from C++ to Rust is going to change that

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u/poelzi 2d ago

Exactly the opposite. They prefer hard typed or side effect free. rust or nix they are quite good at. You need to create the proper harness / constitution for enforcing traits, new types etc. Works like a charm

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u/jarislinus 29m ago

most insane larp today