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"LuaJIT's interpreter () beats V8's JIT compiler" - Mike Pall (lambda-the-ultimate.org)
55 points by petermichaux on March 12, 2010 | hide | past | favorite | 17 comments

One question i have regarding these is how fair are the tests, a very quick look at the tests shows for "pidigits" the lua code has the line:

require"c-gmp"(g, aux)

Implying that it is using the GNU Multiprecision Library for it's big integer support, whereas the JS code has:


Which is apparently a big integer library implemented in javascript http://www-cs-students.stanford.edu/~tjw/jsbn/

In other words, in at least one of the tests a comparison is being made between javascript and C/C++, not javascript and Lua.

Actually reading the Lua mailing list post http://lua-users.org/lists/lua-l/2010-03/msg00305.html, referenced in the linked text might help:

> For pidigits I'm comparing the pure JS and Lua programs, not the GMP bindings.

I'm comparing these two:



Both are written in pure Lua and JavaScript and do not use a C binding.

The numbers you point to make use of http://shootout.alioth.debian.org/u32/program.php?test=pidig...

Which is using GMP, so maybe that particular link needs to be updated?

I have looked at a few of the other tests and nothing obviously pops out as being bogus, so it's likely just this pidigits test which has an unfair advantage

V8 is implemented in C++, so should you count it as just a really bad C++ benchmark?

The Lua benchmark uses features Lua can use. JavaScript does not have that feature.


If you're claiming that your interpreter is faster than someone elses you can't make your test depend on a native library for the bulk of the work. That may be a valid argument for "my language is better" but it isn't an argument for my interpreter is faster than yours.

Language Shootout, not Interpreter Shootout. You're playing directly into the Turing tarpit.

This is not an apples to apples comparison, the implemented Languages are fundamentally different. I do think this is an inspiring factoid that shows what is possible with a well done JIT.

Go Rubinius!

how are they very different? Syntax aside, Lua and Javascript are actually pretty similar. I would say they actually are close cousins.

One of the big issues is that any JS function can technically walks its own call stack, which makes inlining very difficult, and for many of these tests the ability to inline is actually a fairly substantial advantage.

The basic problem faced by a JS engine is that if it wants to be able to inline a function it has to be able to either:

* Prove that it knows everything that the function may do -- in effect this means you can't inline any functions that themselves call functions, or any functions that interact with any values you can't consider constant, or identify before you enter the inlined code; or

* Have the ability to at any point in time reconstruct the call stack, and all arguments correctly.

One of these choices is exceedingly limiting in what you can do, and the other is vastly complex.

As Mike Pall said: "None of the benchmarks make use of JavaScript's weird corners. And all of them can (or could) be reduced to simple constructs. So I wouldn't blame it on the language differences alone (maybe on the implementation)."

Only the use of such a feature should trip the "do it the safe but slow way" switch. Maybe that's not possible here though, I don't know that much about compiler optimization.

edit: I'm not implying it's easy either, but if it's possible the V8 team has the skills to implement it.

But 99.9% of JS code doesn't do that, so it should be optimized for that case.

LuaJIT keeps enough info around to go back to the interpreter at the moment anything goes different than previously traced -- I see no reason JS couldn't do the same.

Indeed, they are strikingly similar, one of the key differences being Lua's minimal/extensible dispatch. A function call, by default, involves no searching through superclasses/prototypes. This is likely a big advantage in benchmarks.

Which subclasses do you want to search through in JavaScript?

That said to me lua seems a little bit like JavaScript's sane cousin.

JavaScript has multiple critical blunders in its specification that offer no advantage to the programmer, but are very difficult to optimize.

They really are quite different. Here's one example: http://lambda-the-ultimate.org/node/3851#comment-57751

Define "quite different".

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