Befunge VS miri

1. C compilers don't do a good job, & thus even CPython, which has historically stuck to rather vanilla C, uses computed goto, as described in https://eli.thegreenplace.net/2012/07/12/computed-goto-for-e...

I resorted to similar techniques in optimizing Befunge: https://github.com/serprex/Befunge (See bejit.c & marsh.c/marsh.h)

2. Rust enums are not variable sized, think of them as tagged C unions, where the Rust compiler can sometimes apply tricks to make Option> the same size as Vec

3. match can specialize for straight forward cases, when in doubt use https://godbolt.org

I've found async to be straight forward anytime I've used it. Promise#then is equivalent to callbacks

async/await often requires very little changes compared to synchronous code, whereas reworking a program into callbacks is much more impactful. & the async/await compilation process tends to produce better performance in addition to this. My first async/await work was a few years ago to increase a data importer's performance by an order of magnitude compared to the blocking code

Here's an example where looping made for a callback that recursively called, using async/await I get to use a plain loop:

before: https://github.com/serprex/Befunge/blob/946ea0024c4d87a1b75d...

after: https://github.com/serprex/Befunge/blob/9677ddddb7a26b7a17dd...

I don't see why people find it so complicated to separate begin-compute & wait-on-compute

I've since rewritten a nodejs game server into rust, https://github.com/serprex/openEtG/tree/master/src/rs/server... handleget/handlews are quite straight forward

You'll also find them used in CPython's ceval.c

I use them in both my C befunge implementations:

https://github.com/serprex/Befunge/blob/c97c8e63a4eb262f3a60...

https://github.com/serprex/Befunge/blob/c97c8e63a4eb262f3a60...

>While we are many missing language features away from this being the case, the noalias case is also magic descended upon box itself, with no user code ever having access to it.

I'm not sure why the author thinks there's magic behind Box. Box is not a special case of `noalias`. Run this snippet with miri and you'll see the same issue: https://play.rust-lang.org/?version=stable&mode=debug&editio...

`Box` _does_ have an expectation that its inner pointer is not aliased to another Box (even if used for readonly operations). See: https://github.com/rust-lang/miri/issues/1800#issuecomment-8...)

Miri [0] is an interpreter for the mid-level intermediate representation (MIR) generated by the Rust compiler. MIR is input for more processing steps of the compiler. However miri also runs MIR directly. This means miri is a VM. Of course it's not a bytecode VM, because MIR is not a bytecode AFAIK. I still think that miri is a interesting example.

And why does miri exist?

It is a lot slower. However it can check for some undefined behavior.

[0]: https://github.com/rust-lang/miri

Provenance is a dynamic property of pointer values. The actual underlying rules that a program must follow, even when using raw pointers and `unsafe`, are written in terms of provenance. Miri (https://github.com/rust-lang/miri) represents provenance as an actual value stored alongside each pointer's address, so it can check for violations of these rules.

Lifetimes are a static approximation of provenance. They are erased after being validated by the borrow checker, and do not exist in Miri or have any impact on what transformations the optimizer may perform. In other words, the provenance rules allow a superset of what the borrow checker allows.

There has been discussion of doing this with MIRI, which would be easier than all of rustc.

This issue has been fixed: https://github.com/rust-lang/miri/issues/2964

Actually, I've done more advanced tests with MIRI (see https://github.com/rust-lang/miri/issues/2920 for example) which allowed me to fix some issues. I've also made the code compatible with loom, but I didn't found the time yet to write and execute loom tests. That's on the TODO-list, and I need to track it with an issue too.

He is one of the big brains behind Miri, which is a interpreter that runs on the MIR (compiler representation between human code and asm/machine code) and detects undefined behavior. Super useful tool for language safety, pretty interesting on its own.

I would also run your tests in Miri (https://github.com/rust-lang/miri) to try to cover more bases.