841621 - Add inline script hint for self-hosted functions

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Shu-yu Guo [:shu]]

It is useful to have the ability to mark self-hosted functions as 'inline' so that when jitting them we ignore the normal heuristics.

Comment 1

[Jeff Walden [:Waldo]]

I'm not sure this is a good thing to have.  We should beef up our normal heuristics to be more robust against patterns like our self-hosted scripts use, not add backdoors usable only by self-hosted things.

Comment 2

[Shu-yu Guo [:shu]]

(In reply to Jeff Walden [:Waldo] (remove +bmo to email) from comment #1)
> I'm not sure this is a good thing to have.  We should beef up our normal
> heuristics to be more robust against patterns like our self-hosted scripts
> use, not add backdoors usable only by self-hosted things.

Adding more aggressive inlining heuristics for ParallelArray code is also an option (perhaps more preferred), though I'm not quite seeing the problem with adding backdoors for self-hosted code. To me that's a nice freedom self-hosted code allows -- we already have unsafe backdoors for ParallelArrays, and what I'm proposing here is just a hint.

Comment 3

[Jeff Walden [:Waldo]]

I see "freedom" and read "backdoor that sites can't put to their own use".  :-)  If some function in self-hosted code is short enough or hot enough that it should be inlined, it shouldn't just be inlined because it existed in self-hosted code and someone recognized and annotated that particular instance.

Comment 4

[Niko Matsakis [:nmatsakis]]

My take on this is that Waldo is correct in principle, but in practice there isn't a "one-size-fits-all" heuristic that will always get the right answer, and there will always be a need for hints.

Comment 5

[Niko Matsakis [:nmatsakis]]

I asked dvander about this on IRC and he wrote:

[12:00:48] <dvander> nmatsakis, improving inline heuristics is also very twitchy and complicated
[12:01:20] <dvander> nmatsakis, we have hints in C++, it makes sense to have those hints for self-hosted code as well IMO. it doesn't have to be something we expose to the web

Comment 6

[Niko Matsakis [:nmatsakis]]

Attachment: Add inline hint.

Comment 7

[Niko Matsakis [:nmatsakis]]

Attachment: Add inline hint.

Carrying over r+ from dvander.

Comment 8

[Niko Matsakis [:nmatsakis]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/8ef0e9fa1f16

Comment 9

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/8ef0e9fa1f16