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Is Rust faster than C?

steveklabnik.com

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Re: Is Rust faster than C?

#81

Post by cogman10 »

embedding-shape wrote: post #11
bfrog wrote: post #9

One example where Rust enables better and faster abstractions is traits. C you can do this with some ugly methods like macros and such but in Rust it’s not the implementers choice it’s the callers choice whether to use dynamic dispatch (function pointer table in C) or static dispatch (direct function calls!) In c the caller isn’t choosing typically. The author of some library or api decides this for you. This turns o…

It's a tradeoff though, as I think traits makes the Rust build times grow really quickly. I don't know the exact characteristics of it, also I think they speed it up compared to how it used to be, but I do remember that you'll get noticeable build slowdowns the more you use traits, especially "complicated" ones.

AFAIK, it's not the traits that does it but rather the generics.

Rust does make it a lot easier to use generics which is likely why using more traits appears to be the cause of longer build times. I think it's just more that the more traits you have, the more likely you are to stumble over some generic code which ultimately generates more code.

Re: Is Rust faster than C?

#82

Post by quotemstr »

dana321 wrote: post #67
OskarS wrote: post #51

I think personally the answer is "basically no", Rust, C and C++ are all the same kind of low-level languages with the same kind of compiler backends and optimizations, any performance thing you could do in one you can basically do in the other two. However, in the spirit of the question: someone mentioned the stricter aliasing rules, that one does come to mind on Rust's side over C/C++. On the other hand, signed int…

Rust has linker optimizations that can make it faster in some cases

Huh? Both have LTO. There are linker optimizations available to Rust and not to C and C++. They all use the same God damn linker.

Re: Is Rust faster than C?

#83

Post by toodlemcnoodle »

OskarS wrote: post #51

I think personally the answer is "basically no", Rust, C and C++ are all the same kind of low-level languages with the same kind of compiler backends and optimizations, any performance thing you could do in one you can basically do in the other two. However, in the spirit of the question: someone mentioned the stricter aliasing rules, that one does come to mind on Rust's side over C/C++. On the other hand, signed int…

I agree with this whole-heartedly. Rust is a LANGUAGE and C is a LANGUAGE. They are used to describe behaviours. When you COMPILE and then RUN them you can measure speed, but that's dependent on two additional bits that are not intrinsically part of the languages themselves.

Now: the languages may expose patterns that a compiler can make use of to improve optimizations. That IS interesting, but it is not a question of speed. It is a question of expressability.

Re: Is Rust faster than C?

#84

Post by jryb »

This post might get the record for people responding to the title without reading the article. Jeez people, it takes five seconds to discover that it subverts expectations.

Re: Is Rust faster than C?

#85

Post by Tuna-Fish »

gignico wrote: post #2

The article does not mention the possible additional optimisation opportunities that arise in Rust code due to stricter aliasing rules of references. But I don’t have an example in mind. Does anyone know of an example of it happening in real code?

I believe this advantage is currently mostly theoretical, as the code ultimately gets compiled with LLVM which does not fully utilize all the additional optimization opportunities.

Re: Is Rust faster than C?

#86

Post by bell-cot »

voidUpdate wrote: post #7

Depends what you're doing with it... You can make any language you want slower than another language by using it badly

True, but also a tautology.

Instead, I'd say that Rust & C are close enough, speed-wise, that (1) which one is faster will depend on small details of the particular use case, or (2) the speed difference will matter less than other language considerations.

Re: Is Rust faster than C?

#87

Post by Measter »

steveklabnik wrote: post #28
gignico wrote: post #2

The article does not mention the possible additional optimisation opportunities that arise in Rust code due to stricter aliasing rules of references. But I don’t have an example in mind. Does anyone know of an example of it happening in real code?

In the spirit of the article... there's a few ways in which this could go :) The first is, we do have some amount of empirical evidence here: Rust had to turn its aliasing optimizations on and off again a few times due to bugs in LLVM. A comment from 2021: https://github.com/rust-lang/rust/issues/54878#issuecomment-... > When noalias annotations were first disabled in 2015 it resulted in between 0-5% increased runtim…

Another issue we have to consider here for the measurements taken then is that it was miscompiling, which, to me, calls into question how much we can trust that performance change.

Additionally, it was 10 years ago and LLVM has changed. It could be that LLVM does better now, or it could do worse. I would actually be interested in seeing some benchmarks with modern rustc.

Re: Is Rust faster than C?

#88

Post by OptionOfT »

pornel wrote: post #76

In short, the maximum possible speed is the same (+/- some nitpicks), but there can be significant differences in typical code, and it's hard to define what's a realistic typical example. The big one is multi-threading. In Rust, whether you use threads or not, all globals must be thread-safe, and the borrow checker requires memory access to be shared XOR mutable. When writing single-threaded code takes 90% of effort…

Apart from multi threading, there is more information in the Rust type system. Would that would allow more optimizations?

Re: Is Rust faster than C?

#89

Post by bjourne »

Haha, I'm touting my own ten year old horn: https://news.ycombinator.com/item?id=12749717 Also see steveklabnik's comments. They are relevant.

Back then the C implementation of the (i.e., "one") micro benchmark beat the Rust implementation. I could squeeze out more performance by precisely controlling the loop unrolling. Nowadays, I don't really care and operate under the assumption that "Python is faster than $X and if it is not, it is still fast enough!"

Re: Is Rust faster than C?

#90

Post by justin66 »

pron wrote: post #63
xnorswap wrote: post #56

Earlier quoted context omitted.

Do you think C# / .NET doesn't stack up in terms of budget, or not stack up in terms of runtime speed?

It's probably in the same ballpark. To me, the contenders for "the fastest language" include Java, C#, and Go and not many more.

Ah thanks. That clarifies things.
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