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Comment by bencyoung | Hacker News Reader

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

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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.

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