Chrome's v8 compiles JavaScript into machine code | Hacker News Reader

Chrome's v8 compiles JavaScript into machine code

code.google.com

46 pointsandreyf9 comments

Lars Bak (head of development for V8) has before made VM's for Self and SmallTalk. Other than that he was the technical lead for Java's HotSpot VM.

It's a very interesting approach they have taken, especially with class transitions and compilation. I hope Python / Ruby / Perl and other languages can learn and optimize with these ideas and code base.

Btw. Java was interpreted at first, JIT was first added with HotSpot and the speed improvement was around 20x.

"...hope Python/Ruby/Perl and other languages..." JITing code of these languages surely is possible (compare e.g. with psyco, exceptions might be eval'ed statements and the like...), however, all of these languages take the approach of a simple but fast compiler and having an interpreter as an execution engine (where more optimizations are easily possible), hence the ideas are not directly applicable (as far as python is concerned: their explicit goal is to have the utmost simplicity in their compiler/interpreter)

also, while the JITing part of the v8 surely is nice by itself, IMHO the real runtime performance seems to come from the inlining by what they call "fast property access" -- the papers cited are a very good reference; indepth details can be found via scholar.google.com, though not explicitly mentioned, i figure that PICS, polymorphic inlince caches, are relevant too...

besides that i find the source code very interesting, it seems that it's just a very small codebase (with "ugly" c++ coding standards--given my subjective taste of course; i liked ellemtel guidelines best...); actually, i found myself looking for the "rest" until it became obvious thats all...

Python and Ruby are just a bit more difficult for fast VM implementors because every Object is like a little dictionary. The ordering of the instance values in each Object's collection is dependent on runtime events. In languages where the instance variables are declared ahead of time, the VM implementor can just access each instance variable as an offset of the Object pointer. (Which is what happens in many Smalltalk and Java VMs.)

This is certainly not impossible to overcome. It's just an added difficulty.

Objects in JavaScript are also dictionaries.. hence the use of "object literals" for dictionaries. The hidden class system in v8 is the technique which allows offsets to be used instead of having to do dict lookups all the time.

For more info on the background of V8 -

http://news.ycombinator.com/item?id=293869

Is this the same strategy used in Ikarus Scheme?

http://www.cs.indiana.edu/~aghuloum/ikarus/#about

I don't see any comparisons to existing interpreter/compiler implementations in the V8 docs.

(edit: Oh. Strongtalk. So is that "incremental optimizing compilation" as well?)

Did anyone else read V8 as VB in the comic?

What cpu architectures are supported?

V8 implements ECMAScript as specified in ECMA-262, 3rd edition, and runs on Windows XP and Vista, Mac OS X 10.5 (Leopard), and Linux systems that use IA-32 or ARM processors.

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