1635185 - Consider storing an object's dynamic slot count directly in a header

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P3)

Description

[Jon Coppeard (:jonco)]

Jan suggested that we might store the number of dynamic slots in a header like we do for object elements.

Currently it's quite involved working this out (see NativeObject::numDynamicSlots, NativeObject::dynamicSlotsCount, NativeObject::slotSpan) and touches the class, the shape and possibly the base shape.

Comment 1

[Jan de Mooij [:jandem]]

I wonder if the new field could eventually replace BaseShape::slotSpan_, so the slot span would always be stored in obj->slots->slotSpan, for both dictionary and non-dictionary native objects... For that to work we'd need statically-allocated empty-dynamic-slots structs for slot span 0-16, similar to EmptyObjectElements.

Comment 2

[Jon Coppeard (:jonco)]

Attachment: Bug 1635185 - Part 1: Use a header for dynamic object slots and use it to store the capacity r?jandem

Comment 3

[Jon Coppeard (:jonco)]

Attachment: Bug 1635185 - Part 2: Use the stored capacity for NativeObject::numDynamicSlots() r?jandem

Depends on D87596

Comment 4

[Jon Coppeard (:jonco)]

Attachment: Bug 1635185 - Part 3: Store dictionary object slot span in the slots header r?jandem

As suggested, this uses special shared header objects if there are no dynamic slots.

Depends on D87597

Comment 5

[Jon Coppeard (:jonco)]

Attachment: Bug 1635185 - Part 4: Removed the unused slotSpan field from BaseShape r?jandem

This also shrinks BaseShape down to 16 bytes on 32 bit platforms.

Depends on D87888

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9eb95eed348c
Part 1: Use a header for dynamic object slots and use it to store the capacity r=jandem
https://hg.mozilla.org/integration/autoland/rev/d00c06a25def
Part 2: Use the stored capacity for NativeObject::numDynamicSlots() r=jandem
https://hg.mozilla.org/integration/autoland/rev/a1ede76c8e1c
Part 3: Store dictionary object slot span in the slots header r=jandem
https://hg.mozilla.org/integration/autoland/rev/1f3b9d75281c
Part 4: Removed the unused slotSpan field from BaseShape r=jandem

Comment 7

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/9eb95eed348c
https://hg.mozilla.org/mozilla-central/rev/d00c06a25def
https://hg.mozilla.org/mozilla-central/rev/a1ede76c8e1c
https://hg.mozilla.org/mozilla-central/rev/1f3b9d75281c