runtime dispatch and other goodies from upstream

[sunnygleason]

One idea we should consider soonish is compiling everything for the target architecture regardless of CPU features and doing runtime detection & dispatch (as implemented in upstream, hopefully easier in Rust?).

There might be other goodies in upstream as well...

[Licenser]

I got no idea how that'd work in rust but that just means we got to learn something new :D

[CJP10]

I’ll have a go at this. @Licenser can you assign this to me 😄 ?

[Licenser]

Thanks @CJP10 go for it :)

[AndreKR]

I got no idea how that'd work in rust but that just means we got to learn something new :D

From what I understand you use something like is_x86_feature_detected!("ssse3") to detect whether a particular feature is available. Then you call a function optimized for that feature. You have to mark the function with #[target_feature(enable = "ssse3")] to force usage of that feature within the function.

Here an example and another one.

[CJP10]

@AndreKR upstream does something similar to ifunc.

[Licenser]

Ja, we probably want something resembling the upstream solution that does only once include a conditional and after that memorizes the choice.

[CJP10]

To add, we should also have a simd_json::init(). Which would be optional but perform the runtime selection outside of the hot path.

[Licenser]

Yes very good idea 👍 that way applications who want to make sure there is 0 overhead on the hot path can call it on startup :), good thinking!

[Count-Count]

Maybe take some inspiration from rust-memchr: ifunc-like macro for Rust