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Comment by klipklop | Hacker News Reader

A shame operating systems like iOS/iPadOS do not allow JIT. iPad Pro's have such fast CPU's that you cant even use fully because of decisions like this.

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Those operating systems allow it, but Apple does not. Agree that it is a total waste.

They allow, but Apple's policy is to lock down that ability pretty much just to Safari/WKWebView. If you could transpile/compile your program to JS or WASM and run it through one of these blessed options, it should get JIT'ted.

They do, technically, allow JIT. You need a very hard-to-obtain entitlement that lets you turn writable pages into executable read-only pages, and good luck getting that entitlement if (for some reason) your name isn’t “mobilesafari”, but the capability exists.

When you say it's "hard" to obtain--is it possible to obtain if you aren't Apple? Does Apple ever provide it to third party developers, or is there even a path to requesting it?

Yes.

Source? Is there any non-Apple app that has this entitlement?

If your app happens to be a browser that's only usable in the EU then:

https://developer.apple.com/documentation/browserenginekit/p...

I believe the Delta emulator has JIT support, but possibly only when installed as a developer.

As far as I can tell, you need to connect your phone to a PC running software which enables JIT by exploiting a feature intended for remote debugging. https://faq.altstore.io/altstore-classic/enabling-jit

What advantage does JIT compilation have over Swift or Obj-C?

It speeds up interpreted languages.

And emulation.

What is an architecture but a scripting language to interpret? ;)

I get that, but what interpreted language do you want to write iOS apps in when there's Swift and Obj-C right there, with bespoke support and tooling from Apple?

And if you care about performance, why aren't you writing that code in native to begin with?

Why would you care about faster cars when planes exist?

https://0x0.st/XJZT.jpg

...Javascript.

JIT compilation can be faster for compiled languages too, as it allows data driven inlining and devirtualization, as well as "effective constant" propogation and runtime architecture feature detection

It can be but it never is.

To re-optimize compiled code blocks isn't without effort. Google has publicly spoken about AutoFDO and Propeller [0], after Meta had open sourced BOLT [1] in 2021.

AutoFDO has since been ported to Android and adopted by Yandex [3].

[0] https://lwn.net/Articles/995397/

[1] https://news.ycombinator.com/item?id=40868224

[2] https://news.ycombinator.com/item?id=42896716

Especially after PGO (profiling guided optimization) gets most of the way there

But is that because of JIT compilation or other decisions for how the language should work (dynamic typing, GC, etc.)?

Hard disagree. Many newer game system emulators (32-bit and up) rely on JIT or "dynarecs" to get playable speeds, and they pretty much all use high performance compiled languages already. They often double the performance over their interpreter or more.

Is there a production JIT for a compiled language that is actually faster? I understand the theory, I don't think the practice backs it up.

Depends, what do you consider Java?

Java is certainly not the fastest language out there.

Sure, but the relevant comparison isn't between languages: it's between a state-of-the-art JIT implementation of one language and a likewise-state-of-the-art AOT implementation of the same language. Unfortunately there aren't many examples of this; most languages have a preferred implementation strategy that receives much more effort than the other one.

I believe HotSpot is usually faster than GCJ.

Of course they do - this is how javascript in any site works

> that you cant even use fully because of decisions like this.

Have no clue what this means - you can pre-compile for target platforms and therefore "fully" use whichever Apple device CPU.

You can't precompile your web page's Javascript for iOS, even if you're willing to have it signed and notarized and submitted for policy review.

Apart from the fact that its JS engine is really fast, Safari accepts WebAssembly. What else would you precompile it to?

Originally, iOS Safari handled WASM but only with JIT disabled.

However the EU decreed that it must allow for fair competition, leading to it claiming that it will enable JIT for authorized developers: https://developer.apple.com/support/alternative-browser-engi...

But I'm not sure that they have done so...

Mozilla: https://github.com/mozilla/platform-tilt/issues/3

Chrome: https://issues.chromium.org/issues/42203058

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