rust-playground VS compiler-explorer

If you have an object that's !Unpin, then Miri will not apply uniqueness rules to anything containing it [0], including boxes and &mut references. (In the example code, replacing the PhantomPinned with a () will make Miri complain again.) This is considered a temporary (if long-lived) measure to allow async executors to manipulate pinned futures without invalidating all their references and whatnot. Thus, it might be seen as undetected UB, in lieu of a permanent solution.

[0] https://play.rust-lang.org/?version=stable&mode=debug&editio...

That would be true if you used `Vec::clear` too, it doesn't allocate a new vector. My point was that you still end up running Drop implementations with RepeatedField, just not all at once. See https://play.rust-lang.org/?version=stable&mode=debug&editio...

That's a valid Unix path, but rust's quoting does nothing to stop it: https://play.rust-lang.org/?version=stable&mode=debug&editio...

Self-referential structs work fine in Rust and always have.

https://play.rust-lang.org/?version=stable&mode=debug&editio...

The compiler will correctly prevent you from moving the value.

The other way to have a struct that starts out as non-self-referential and then becomes self-referential can be achieved with `unsafe` and `Pin::new_unchecked`, which is how `async {}` is handled.

In rust as currently stands: https://play.rust-lang.org/?version=stable&mode=debug&editio...

On the other hand, both this wrapper and yours are counterproductive if the element size is dynamic (e.g. perhaps you're dealing with some nonsense like:)

    struct ITableColumn {

Overflow checks turn into two's compliments' wrapping, but that's only considered acceptable because bounds checks are not turned off.

https://play.rust-lang.org/?version=stable&mode=release&edit...

I have no idea what you're talking about, but it sounds unnecessarily complicated and why I don't use Rust for any serious work.

This demonstrates the ABA problem in safe Rust: https://play.rust-lang.org/?version=stable&mode=debug&editio...

Substitute the sleep with a combination of doing computation/work and the OS thread scheduler, and you can see how the bug surfaces.

You can also try Rust online using the Rust playground: https://play.rust-lang.org/

(Click ... beside build to get assembly) https://play.rust-lang.org/?version=stable&mode=release&edit...

Unfortunately the go playground doesn't seem to support emitting assembly?

At least on android arm64, looks like a `dmb ishst` is emitted after the constructor, which allows future loads to not need an explicit barrier. Removing `final` from the field causes that barrier to not be emitted.

https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename...

You said You won't get "extreme performance" from C++ because it is buried under the weight of decades of compatibility hacks.

Now your whole comment is about vector behavior. You haven't talked about what 'decades of compatibility hacks' are holding back performance. Whatever behavior you want from a vector is not a language limitation.

You could write your own vector and be done with it, although I'm still not sure what you mean, since once you reserve capacity a vector still doubles capacity when you overrun it. The reason this is never a performance obstacle is that if you're going to use more memory anyway, you reserve more up front. This is what any normal programmer does and they move on.

Show what you mean here:

https://godbolt.org/

I've never used ISPC. It's somewhat interesting although since it's Intel focused of course it's not actually portable.

I guess now the goal posts are shifting. First it was that "C++ as a language has performance limitations" now it's "rust has a vector that has a function I want and also I want SIMD stuff that doesn't exist. It does exist? not like that!"

Try to stay on track. You said there were "decades of compatibility hacks" holding back C++ performance then you went down a rabbit hole that has nothing to do with supporting that.

C++ Insights is available online at https://cppinsights.io/

It is also available at a touch of a button within the most excellent https://godbolt.org/

along side the button that takes your code sample to https://quick-bench.com/

Those sites and https://cppreference.com/ are what I'm using constantly while coding.

I recently discovered https://whitebox.systems/ It's a local app with a $69 one-time charge. And, it only really works with "C With Classes" style functions. But, it looks promising as another productivity boost.

[P&H RISC] https://www.google.com/books/edition/_/e8DvDwAAQBAJ

Compiler Explorer by Matt Godbolt [Godbolt] can help better understand what code a compiler generates under different circumstances.

[Godbolt] https://godbolt.org

The official CPU architecture manuals from CPU vendors are surprisingly readable and information-rich. I only read the fragments that I need or that I am interested in and move on. Here is the Intel’s one [Intel]. I use the Combined Volume Set, which is a huge PDF comprising all the ten volumes. It is easier to search in when it’s all in one file. I can open several copies on different pages to make navigation easier.

Intel also has a whole optimization reference manual [Intel] (scroll down, it’s all on the same page). The manual helps understand what exactly the CPU is doing.

[Intel] https://www.intel.com/content/www/us/en/developer/articles/t...

Personally, I believe in automated benchmarks that measure end-to-end what is actually important and notify you when a change impacts performance for the worse.

Let's compile it with https://godbolt.org/, turn on some optimisations and inspect the IR (-O2 -emit-llvm). Copying out the part that corresponds to the while loop:

  4:

resources were extra useful when building deeper intuitions about GPU performance for ML models at work and in graduate school.

- CMU's "Deep Learning Systems" Course is hosted online and has YouTube lectures online. While not generally relevant to software performance, it is especially useful for engineers interested in building strong fundamentals that will serve them well when taking ML models into production environments: https://dlsyscourse.org/

- Compiler Explorer is a tool that allows you easily input some code in and check how the assembly output maps to the source. I think this is exceptionally useful for beginner/intermediate programmers who are familiar with one compiled high-level language and have not been exposed to reading lots of assembly. It is also great for testing how different compiler flags affect assembly output. Many people used to coding in C and C++ probably know about this, but I still run into people who haven't so I share it whenever performance comes up: https://godbolt.org/

To really understand what's going on here we can look at the compiled assembly code. I'm working on a Mac and can do this using the objdump tool. Compiler Explorer is also a handy tool but doesn't seem to support Arm assembly which is what Rust will use when compiling on Apple Silicon.

Play around with it in godbolt if you're really curious: https://godbolt.org/