622302 - Figure out a way to call WebIDL functions directly when argument types match

Status: REOPENED

(Core :: JavaScript Engine, enhancement)

Description

[Boris Zbarsky [:bzbarsky]]

That would significantly speed up DOM bindings, by reducing the need for type conversions.

Comment 1

[Till Schneidereit [:till]]

JM is gone

Comment 2

[Boris Zbarsky [:bzbarsky]]

We might want something like this for IM, though...

Comment 3

[Jan de Mooij [:jandem]]

(In reply to Boris Zbarsky (:bz) (reading mail, but on paternity leave) from comment #2)
> We might want something like this for IM, though...

Is this still worth it for DOM calls with the jitinfo stuff etc we have now?

Comment 4

[Boris Zbarsky [:bzbarsky]]

That's a good question.

The primary benefit of the traceable natives was that they avoided the need for argument and return value boxing/unboxing.  The jitinfo stuff does nothing to address this (though it helps with this-value unboxing, and helps speed up return value unboxing a bit by communicating the general kind of return value).

It's pretty easy to write testcases in which the boxing and unboxing is a significant fraction of the time; the question is whether these commonly matter in web code...

The main likely beneficiary would presumably be WebGL; roc has had some thoughts about it in the past.

Comment 5

[Luke Wagner [:luke]]

Ah, so IIUC, the idea would be to have, hanging off a DOM builtin's jitinfo, an array of argument/return-type-specialized overloads that could be called directly?  ISTR, that's what we did for traceable natives.

Comment 6

[Boris Zbarsky [:bzbarsky]]

Or something along those lines, yes.

Comment 7

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I thought for each WebIDL method we'd have one function whose signature matches the corresponding C++ method (with 'this' passed as an explicit parameter), which tail-calls the C++ method. Then we could have IM assemble direct calls to this function, under the right conditions (e.g., all parameter types known).

Currently I don't know of any benchmarks that definitely need this. The closest I know of is canvas. So let's leave this bug open but not work on it until we have a benchmark.

Comment 8

[Mayank Bansal]

TI is gone now, but I see that this bug was reopend.
:jandem, is this bug still relevant?

Comment 9

[Jan de Mooij [:jandem]]

TI is gone but the idea is still relevant so I'll rename this bug.

Now that we're thinking about exposing WebIDL more directly in SpiderMonkey, it might be more feasible to do this eventually.