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> One cannot expect a compiler to come up with such encoding.

One could, however, imagine a sufficiently expressive language that allows the developer to specify the encoding schema without resorting to raw 64-bit words.

by aa-jv2 hours ago|

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This breaks the language. Do you want safety or do you want expression?

by win311fwg14 hours ago|

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What is misleading about the title? A custom encoding scheme is exactly what it suggests. Maybe it has been edited since your comment was posted?

by dymk13 hours ago|

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It wasn’t replacing one rust enum, it was replacing what are effectively multiple enums

by dzaima13 hours ago|

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How so? It's replacing multiple enum variants, but just one enum, "enum Value".

(also; if anything, the title is implying the exact opposite of "Rust compiler was able to optimize ...", "Replacing a Rust [...] with [...]" is clearly moving away from Rust-magic to something else)

by Brian_K_White11 hours ago|

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Probably in the sense that you can remove the word rust and nothing changes. It's not about some failure of rust to be efficient at enums, but the title says it is.

by maxime_cb25 minutes ago|

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OP here: I think you're reading too much into the title. It's not about the failure of Rust. It's about where I stepped in with some custom optimizations for better performance. If you read the blog post, the solution implemented is very Rust-y as well. It uses a newtype with custom methods to try and make the code as nice and readable as possible.

FWIW this post was very well received on the Rust subreddit. They loved it and it got over 350 upvotes, so that community definitely didn't receive it as some sort of attack on Rust.

by win311fwg11 hours ago|

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'Enum' is ill-defined so the addition of Rust is significant as it indicates what one can expect with how data is structured. There is nothing in that speaks to the Rust compiler or Rust being inefficient or anything of the sort. It remains unclear where this idea is coming from. There is nothing in title that would send you there.

Unless, again, the title was edited at some point?

by benatkin9 hours ago|

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If you replaced it with Zig, the situation changes.

by gpm12 hours ago|

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I'd actually point at the other half of the title than the existing comment when being pedantic "Replacing [...] with a 64-Bit Word" isn't quite right, it was replaced with a manually packed 64-Bit Word and the occasional heap allocation.

I'm not sure being this pedantic is particularly useful in titles though...

by Dylan1680712 hours ago|

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It's worth calling out either way. It's not just an encoding scheme, it's a reasonably significant change in architecture.

by pbiggar13 hours ago|

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When I think of how a "compiler" could make these optimizations, I think the right place is an optimizing LLM (so, just a regular coding agent that you prompted to find optimizations like this one), making the changes in source at the request of the developer. That provides the dev with adequate input on whether they would like to opt-in to an unsafe optimization like this one. The compiler can continue to do deterministically-safe optimizations.

by gpm12 hours ago|

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What I'd like to enable this use of LLMs more recklessly is a compiler with formal methods that lets me guarantee equivalence between the opaque optimized code and something actually understandable.

by MobiusHorizons5 hours ago|

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Equivalence on what metrics? In theory what you are asking for makes sense, but I think it is very hard to actually specify what equivalent means in the context of an optimization process that needs to emit code with observably different behavior. Sometimes (although admittedly rarely) speeding up sections of code can even be undesirable for example branchless code for constant time algorithms that avoid timing or energy side channel leaks, or the much more mundane elimination of signed overflow checks or other undefined behavior quirks.

by trickypr13 hours ago|

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That seems like a horrible idea:

1. Do you really want the rust compiler to run at the speed of an llm?

2. Compiler optimisations are already extremely unpredictable with deterministic compilers[1], I hate to think how unpredictable your compiler would be.

3. What if someone else wants to build the software, do they have to decide on optimisations now? What if the optimisation depends on your features not available on old generations of CPU? (There is a reason we don’t compile with -march=native)

4. Compilers already have “unsafe” optimisations, but people rarely enable them (-ffast-math)

[1]: https://faultlore.com/blah/oops-that-was-important/

by jmalicki10 hours ago|

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> Do you really want the rust compiler to run at the speed of an llm?

That... might actually be an improvement?

by Quothling5 hours ago|

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What do you mean "might"? I can crank Fable or Sol up to max intelligence and they'll spend an hour reviewing my rust SDK for working with our ADLSgen2's, and it'll still be done before the rust compiler has compiled the same project.

by pbiggar13 hours ago|

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You misunderstand me. I'm saying that the developers can make these optimizations with LLMs, at the source level, and thus they don't need to be added to compilers.

Like just open Claude Code and ask it to find optimizations. That's the right place for this kind of optimization.

by aa-jv2 hours ago|

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We'll get there eventually whether we like it or not. Just as soon as the current crop of AI/ML engineers retire, or .. get replaced with bots.