DeVault: Announcing the Hare programming language [LWN.net]

DeVault: Announcing the Hare programming language

Posted May 4, 2022 18:28 UTC (Wed) by mathstuf (subscriber, #69389)
In reply to: DeVault: Announcing the Hare programming language by Vipketsh
Parent article: DeVault: Announcing the Hare programming language

There are certainly individuals at C++'s standards committee. I don't know that much about C since I haven't been there though. I don't think that "preserving the entrenchment" is at all how I'd describe it. There are certainly different pressures on things, but there is *not* a unified one anywhere other than "improve the language overall" (and not everyone agrees about every step taken). I've seen long-standing members get told "no, that idea doesn't work" about as much as I've seen new members get "oh, yeah, that's neat" (in rough proportion to their prevalence at least). Implementors have their hobby horses, library designers have theirs, and users are there too to express their views on things. "Unified" is not how I would describe it in relation to any single feature-in-progress.

FWIW, I go because I work on CMake and would like to ensure that modules are buildable (as would my employer). But I go to other presentations that I am personally interested in (when not a schedule conflict with what I'm there to do) and participate.

With the pandemic making face-to-face less tenable, I expect it to be easier than ever for folks to attend committee meetings.

> I think it was yourself who mentioned in some thread from a while ago that LLVM is doing all sorts of optimisations based on pointer provenance when there is exactly no mention of them in any standard.

That was me I believe. My understanding is that without provenance, pointers are extremely hard to actually reason about and make any kind of sensible optimizations around (this includes aliasing, thread safety, etc.). It was something that was encountered when implementing the language that turned out to be underlying a lot of things but was never spelled out. There is work to figure out what these rules actually are and how to put them into standard-ese ("pointer zap" is the search term to use for the paper titles).

DeVault: Announcing the Hare programming language

Posted May 4, 2022 19:06 UTC (Wed) by khim (subscriber, #9252) [Link] (2 responses)

> That was me I believe.

That was different discussion.

> There is work to figure out what these rules actually are and how to put them into standard-ese ("pointer zap" is the search term to use for the paper titles).

This would have been great if, while these rules are not finalized, compilers produced working programs by default.

Instead clang not just breaks programs by default, it even refuses to provide -fno-provenance switch which may be used to stop miscompiling them!

And it's not as if rules were actually designed, presented to C/C++ committee (like happend with DR 236) then rejected because of typical committee politics. At least then you can say “yes, changes to the standard are not accepted yet, but you can read about our rules here”.

Instead, for two decades compilers silently miscompiled valid programs and their developers offered no rules which software developers can follow to develop programs which wouldn't be miscompiled!

That's an act of deliberate sabotage. And, worst of all, it have only gained prominence because of Rust: since Rust developers actually care about program correctness (and because LLVM miscompiled programs which they believed to be correct) they tried to find the actual list of rules that govern provenance in C/C++… and found nothing.

Yes, this provenance fiasco is awful blow against C/C++ compiler developers. You couldn't say “standard is a treaty, you have to follow it” and then turn around and add “oh, but it's too hard for me to follow it, thus I would violate it whenever it would suit me”. That's not a treaty anymore, it's a joke.

But even then: the way forward is not to ignore the rules, but an attempt to patch them. Ideally new compilers should be written which would actually obey some rules, but that's too big of an endeavor, I don't think it'll happen.

DeVault: Announcing the Hare programming language

Posted May 4, 2022 19:36 UTC (Wed) by mathstuf (subscriber, #69389) [Link] (1 responses)

> Ideally new compilers should be written which would actually obey some rules, but that's too big of an endeavor, I don't think it'll happen.

There may be hope. Some docs: https://lightningcreations.github.io/lccc/xlang/pointer (though no mention of provenance yet(?)).

https://github.com/LightningCreations/lccc

DeVault: Announcing the Hare programming language

Posted May 5, 2022 9:59 UTC (Thu) by khim (subscriber, #9252) [Link]

I mean something which was done for safe Rust: formal mathematical model which may prove that transformation which are done during optimizations are sound.

Things like <a href="https://www.ralfj.de/blog/2020/12/14/provenance.html">that</a> should be impossible.

Today optimizations in compilers are dark art: not only they produce suboptimal code sometimes (that's probably something which we would never be able to fix), we discover, from time to time, that they are just simply invalid (as in: they turn perfectly valid programs into invalid).

Ideally we should ensure that all optimizations leave valid programs still valid (even if, perhaps, not optimal).