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Comment by mutagen | Hacker News Reader

Glorious indeed. At least three levels of abstraction, two JITs, and a host of supporting code. Can we add some more layers like an emulator or get recursive by getting something like Pyasm running inside it?

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Have you seen Gary Bernhardt's THE BIRTH & DEATH OF JAVASCRIPT?

https://www.destroyallsoftware.com/talks/the-birth-and-death...

I saw this a few months ago, and it never gets any less insane (in a good way) to watch. Just following Atwood's Law, I suppose.

Since PyPy is written in (R)Python, you can just run PyPy inside the resulting interpreter, for a 1000x slowdown.

But... Hardware is cheap, right? Hardware gets faster all the time, right? Sure, the end user rarely sees any noticeable improvement because we just use the speed increase as an excuse to write ever more inefficient code, but at least you get to use your favorite language in the browser.

http://en.wikipedia.org/wiki/Wirth%27s_law

I work on a machine that has two hypervisors, one third in plan, and more abstraction layers than a lasagna software.

It is still very very efficient.

It may be fast, but I doubt it's very efficient...

How can you have multiple hypervisors...? Do they both run in ring -1?

Heh, that could be a good trick against hypervisor malware. Just run inside your own hypervisor...

http://en.wikipedia.org/wiki/Virtualization#Nested_virtualiz...

This crashes my mobile (webview based) web browser.

Fast(ish) != efficient. Your setup is categorically inefficient. That may be fine for your use case, but let's not lie to ourselves.

Potentially just one JIT, right? asm.js is AOT compiled on Firefox.

No, because it's "AOT" compiled when it's downloaded or executed (since you have one JIT, you can't AOT compile what it produces). So you can think about it as "just" one JIT, but a very inefficient one

> since you have one JIT, you can't AOT compile what it produces

I'm not sure what this means, but if you mean that Firefox doesn't cache compiled asm.js code, that's not true. It does [1].

[1]: https://blog.mozilla.org/luke/2014/01/14/asm-js-aot-compilat...

So look. PyPy compiles bits and pieces of code generating assembler. This assembler then gets to be turned into Javascript (asm.js) which needs to be parsed and compiled. All of this happens at runtime and while you can technically call the second piece of it AOT, it's essentially a double JIT or at least you pay the cost of double jitting. The equivalent in C would be generating C at runtime and sending it through gcc/clang.

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