1420961 - Clean up iterator code

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement)

Description

[Jan de Mooij [:jandem]]

With for-each gone we can remove a bunch of stuff: JSOP_ITER flags operand, JSITER_ENUMERATE, and some checks in code that's pretty hot.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Part 1 - Make NativeIteratorNext infallible

It doesn't use its cx argument and always returns true.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Part 2 - Remove if-statement in js::GetIterator

In js::GetIterator we return early if the object is a PropertyIteratorObject. I don't see how this is possible since PropertyIteratorObject shouldn't escape to JS. This patch just turns it into an assert.

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Part 3 - Remove JSITER_ENUMERATE and flags arguments

Comment 4

[Tom S [:evilpie]]

I thought there was some other reason we didn't want to set the enumerate flags when calling from the Proxy::enumerate hook. Something to do with not putting the iterator object in the iterator list? I will look into that tomorrow.

Comment 5

[Jan de Mooij [:jandem]]

Attachment: Part 4 - Add missing markId call

Part 3 failed browser tests on Try. It turns out the Reify function was never called because in Wrapper::enumerate we would create an iterator with flags = 0 and then in CanReify check for flags & JSITER_ENUMERATE. I think this is a regression from bug 783829.

This patch adds a markId call to Reify and adds a shell test.

Having Reify work again makes some cross-compartment for-in micro-benchmarks > 20% faster.

Comment 6

[Jon Coppeard (:jonco)]

Comment on attachment 8932468 [details] [diff] [review]
Part 4 - Add missing markId call

Review of attachment 8932468 [details] [diff] [review]:
-----------------------------------------------------------------

Ah, nice.

It's a shame it's so easy to miss marking atoms.

Comment 7

[Jan de Mooij [:jandem]]

(In reply to Tom Schuster [:evilpie] from comment #4)
> I thought there was some other reason we didn't want to set the enumerate
> flags when calling from the Proxy::enumerate hook. Something to do with not
> putting the iterator object in the iterator list? I will look into that
> tomorrow.

FWIW I can't think of any issues here. If we wrap an iterator it will be in the enumerator list (of the wrappee's compartment). JSOP_ITEREND may not remove it from that list but that's okay - the enumerator list is a doubly linked list and is swept on GC - it's not a stack that has to stay balanced. Also, when the Reify optimization kicks in we won't use a wrapped iterator but we just copy it and then close the original.

Comment 8

[Tom S [:evilpie]]

Comment on attachment 8932139 [details] [diff] [review]
Part 3 - Remove JSITER_ENUMERATE and flags arguments

Review of attachment 8932139 [details] [diff] [review]:
-----------------------------------------------------------------

Sounds right, thanks Jan. It's great to have that flag removed.

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/6133d185ba8b
part 1 - Make NativeIteratorNext infallible. r=evilpie
https://hg.mozilla.org/integration/mozilla-inbound/rev/3f9a32b603db
part 2 - Replace if-statement with an assert in js::GetIterator. r=evilpie
https://hg.mozilla.org/integration/mozilla-inbound/rev/bb14fe85b1a9
part 3 - Remove JSITER_ENUMERATE and flags arguments. r=evilpie
https://hg.mozilla.org/integration/mozilla-inbound/rev/649756a338c8
part 4 - Add missing markId call to Reify function. r=jonco

Comment 10

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/6133d185ba8b
https://hg.mozilla.org/mozilla-central/rev/3f9a32b603db
https://hg.mozilla.org/mozilla-central/rev/bb14fe85b1a9
https://hg.mozilla.org/mozilla-central/rev/649756a338c8