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WebKit Unifies JavaScript Compilation With LLVM Optimizer 170

Posted by Soulskill
from the like-peanut-butter-and-javascript dept.
An anonymous reader tips this post at Webkit.org: "Just a decade ago, JavaScript – the programming language used to drive web page interactions – was thought to be too slow for serious application development. But thanks to continuous optimization efforts, it's now possible to write sophisticated, high-performance applications – even graphics-intensive games – using portable standards-compliant JavaScript and HTML5. This post describes a new advancement in JavaScript optimization: the WebKit project has unified its existing JavaScript compilation infrastructure with the state-of-the-art LLVM optimizer. This will allow JavaScript programs to leverage sophisticated optimizations that were previously only available to native applications written in languages like C++ or Objective-C. ... I'm happy to report that our LLVM-based just-in-time (JIT) compiler, dubbed the FTL – short for Fourth Tier LLVM – has been enabled by default on the Mac and iOS ports. This post summarizes the FTL engineering that was undertaken over the past year. It first reviews how WebKit's JIT compilers worked prior to the FTL. Then it describes the FTL architecture along with how we solved some of the fundamental challenges of using LLVM as a dynamic language JIT. Finally, this post shows how the FTL enables a couple of JavaScript-specific optimizations."
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WebKit Unifies JavaScript Compilation With LLVM Optimizer

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  • by Hognoxious (631665) on Wednesday May 14, 2014 @04:41AM (#46997321) Homepage Journal

    Just a decade ago, JavaScript â" the programming language used to drive web page interactions â" was thought to be too slow for serious application development.

    Of course know we know better.

    It's just too shit.

  • Just a decade ago. (Score:5, Insightful)

    by serviscope_minor (664417) on Wednesday May 14, 2014 @05:29AM (#46997439) Journal

    "Just a decade ago, JavaScript â" the programming language used to drive web page interactions â" was thought to be too slow for serious application development. ... and now after 10 years of increases in CPU speed, increase in amounts of RAM and fevered development in optimizing it's now got to the stage where new Javascript kinds sorta competes with C++ on a ten year old machine.

    As before, people will still write screeds on how it's really as fast as C++ this time, honest.

    Interestingly, there's one language out there which regularly benchmarks better than C++, and it's called FORTRAN (suck it '95ers) and that's one of the few where you never see long articles on micro benchmarks claiming how *this* year it's as fast as C++.

    Anyway, yeah, in some inner loop micro benchmarks where there's really good information available to the compiler, the dynamic languages (including Java) benchmark similarly to the native ones.

    Basically it's all about aliasing and consistency. The more assumptions of independence the compiler can make about what doesn't alias, the better the optimizations it can make. This folds well into consistency: if you have an inner loop diddling a bunch of floats, then due to the aliasing rules this means that usually the loop bounds are fixed, allowing lots of nice optimizations.

    FORTRAN does that really, really, really, REALLY well. C++ does it pretty well. C99 does it a bit better than C++11, though in practice pretty much all C++ implementations support the C99ism as an extension. Everything else is much worse, which means that a much smaller range of things can be optimized well.

    And then on to memory. Firstly, garbage collected languages can only get with a factor of 2 for memory use (or so) before the computational cost of GC starts to dominate [citation needed]. Really, there are papers studying this. This has an impact on speed because it can make the cache coherency worse, and does also affect scaling on large datasets.

    There's also the thing that memory allocation in C++ (and languages with a similar machine model) is largely completely free: unless you hammer the free store, it's all done on the stack which means the memory allocation is pre-computed at compile time as part of the function prolog. Sure, some of the dynamic languages can approach such things with escape analysis, but they can never do as well for the same reason C++ doesn't do as well as FORTRAN. With C++ you promise to never let local variables escape and the compiler can fuck you if you lie. With the dynamicer languages, the compiler has to figure it out to be correct.

    Now interestingly, the things like the simple inner loops of something like naive matrix multiplication can be optimized quite well in other languages now, because compielrs are getting quite good at that. However, not much of my stuff is as simple as that. If you have bigger, more complicated inner loops like you often get in computer vision for example (my job), then C++ really shines.

    This is why I've never been much of a fan of the "do the logic in python and the inner loop in C" style of things. Unless your inner loop is really simple, you have to do complex things in a not very expressive language otherwise it's slow.

    These improvements sort of make that model obsolete: if you have a really simple inner loop, they can optimize as well as C++. It's everythin else where they can't.

    TL;DR

    Alisaing.

  • The real question. (Score:4, Insightful)

    by MouseTheLuckyDog (2752443) on Wednesday May 14, 2014 @10:34AM (#46999501)

    What idiot would want JavaScript for application development?

  • by jellomizer (103300) on Wednesday May 14, 2014 @10:36AM (#46999517)

    JavaScript has a lot of faults... However there isn't a good standard to replace it. The Core Browser Engines. Trident (IE), Mozilla (FireFox), and WebKit (Chrome/Safari) They all support Javascript. Others are plugins that may work in some but not all.

    Alternatives would be not using Web Pages for development. Which sounds good, until you get into problems to platform compatibility, deployment, upgrades. Or you got middle approaches such as Flash, Active X, and Java Applets, that have their own issues.

    Until we can get the three core Engines to support an other uniformed language. we will be stuck with Javascript.

We warn the reader in advance that the proof presented here depends on a clever but highly unmotivated trick. -- Howard Anton, "Elementary Linear Algebra"

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