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by steveklabnik 3662 days ago
There's two reasons Rust might not be ready here yet. First, while LLVM supports a wide number of platforms, some embedded devices literally only support the exact version of the C compiler they ship to you, sometimes, it's even got its own custom patches. Second, we sort of assume 32 bits at the lowest, though we have a patch in the queue that starts some work on 8/16 bit support. This means some tiny micros are out of reach at the moment.
3 comments
shepmaster 3662 days ago
> we have a patch in the queue

If you mean this one[1], it's merged. Still lots of work to do, and even more corners where things will shake out[2], but there's definitely progress.

[1]: https://github.com/rust-lang/rust/pull/33460 [2]: https://github.com/rust-lang/rust/pull/34174

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steveklabnik 3662 days ago
Ah nice! I was unsure if the first had gotten through bors yet or not, and I was pretty sure the second one hadn't.
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dv_dt 3662 days ago
A rust -> C compiler would be really nice for those custom/slow updating environments, but I can understand if that just too much of a distraction.
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steveklabnik 3662 days ago
Since I got two replies with basically the same thing at the same time, I'll pick one at random and it'll serve as a reply to both. You won the coin flip :)

This is feasible in a sense, but C is a fairly tricky target to compile to: you have to make sure that you don't accidentally include UB in the code you generate. I know pcwalton has lots of feels here...

The easiest way to do it would be if LLVM had a C backend; I know that it did, but it was removed a few years back, and I haven't heard anything about it coming back into tree yet. MIR might also in theory enable new backends, but then you'd have to re-implement all of the optimizations that we currently rely on LLVM supplying.

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ihnorton 3662 days ago
> I know that it did, but it was removed a few years back, and I haven't heard anything about it coming back into tree yet.

(out-of-tree) fork(s) have been kept alive by several groups. The most current one I'm aware of is: https://github.com/JuliaComputing/llvm-cbe

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ArkyBeagle 3662 days ago
I'll just say - I've generated A Great Deal of 'C' code. It's not hard to avoid UB at all. You only use a very concise subset of the language. YMMV.

This sounds more like generating 'C' is a distraction rather than a goal.

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steveklabnik 3662 days ago
It is certainly not impossible. I think it's just presented as a bit more trivial than it is. You can generate C, but is it easy to generate good C? That's what I was trying to get at with the LLVM comments. Rust relies a lot on a good optimizer; a straightforward transformation might be significantly slower.
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ArkyBeagle 3662 days ago
Agreed. I did not mean to minimize the effort involved.
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Bromskloss 3662 days ago
Is there any possibility of compiling Rust into C and then use that particular C compiler that works for the processor in question?
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