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by tialaramex 2 days ago
> Until Rust has equal meta-programming support to C++ it's always going to be "slower".

I don't think that makes a lot of sense even theoretically because of e.g. aliasing, but it doesn't matter because as I said, C++ chooses to be slower, Titus gives a number of examples where we know how to do X fast, and that's how Rust does X - in theory C++ could X the same way, but none of the three C++ compilers people actually use do it, because they picked wrong and then froze their ABI and won't thaw it.
1 comments
tick_tock_tick 2 days ago
No one writing anything that needs performance cares about some standard library ABI issues. Rust already has warts from bad API designs that constrains performance and they are unlikely to ever be fixed even with new editions. Rust will continue to pick up baggage as basically every language has done.

Aliasing has yet to provide any real benefit for Rust and a hell of a lot of issues. Maybe one day it will be a big win but realistically anyplace that aliasing matter c/c++ will just drop __restrict on it.

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josephg 1 day ago
> Rust already has warts from bad API designs that constrains performance and they are unlikely to ever be fixed even with new editions.

Like what?

> Aliasing has yet to provide any real benefit for Rust and a hell of a lot of issues.

Yeah, the performance wins so far are quite small. But rust's noalias-by-default did unearth a whole lot of latent bugs in LLVM. Even if you don't care about rust, its great that rust led LLVM to track down and fix these bugs. They affected C/C++ code too.

> realistically anyplace that aliasing matter c/c++ will just drop __restrict on it.

Is there a way to tell? When I'm writing C, I have no idea if using restrict will help other than staring at the assembly. (Or just trying it). I'm also leery of using restrict in C because its so hard to audit callers. How do you know when restrict is safe?

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1718627440 1 day ago
> When I'm writing C, I have no idea if using restrict will help other than staring at the assembly.

It's also a statement, whether you want callers to pass the same object to different parameters. If that doesn't make sense or you don't want that, write restrict.

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