1636946 - Optimize slot/element loads + MUnbox

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, task, P3)

Description

[Jan de Mooij [:jandem]]

Warp MIR often loads an element or slot and then does a fallible unbox to some type. It's more efficient to combine the load + unbox in a single MIR/LIR instruction. Especially for LoadElement because we can eliminate the hole check.

We already have this optimization for fixed slot loads, but the implementation is a bit ad-hoc and I think we can do better if we move this out of MUnbox::foldsTo.

Comment 1

[Jan de Mooij [:jandem]]

I have a patch for this but there's some complexity in the neighborhood that I want to clean up...

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Bug 1636946 part 1 - Rename MLoadSlot/MStoreSlot to MLoadDynamicSlot/MStoreDynamicSlot. r?evilpie!

Some long overdue renaming.

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Bug 1636946 part 2 - Don't use ObjectPolicy for slots/elements operands. r?evilpie!

The ObjectPolicy was a no-op in this case. Change that to an assert and stop using
ObjectPolicy for slots/elements, it didn't really make sense.

Depends on D75262

Comment 4

[Jan de Mooij [:jandem]]

Attachment: Bug 1636946 part 3 - Move LoadFixedSlotAndUnbox codegen logic into a helper function. r?evilpie!

Depends on D75263

Comment 5

[Jan de Mooij [:jandem]]

Attachment: Bug 1636946 part 4 - Add MDefinition::maybeSingleDefUse method. r?evilpie!

Depends on D75264

Comment 6

[Jan de Mooij [:jandem]]

Attachment: Bug 1636946 part 5 - Replace load + unbox folding in MUnbox::foldsTo with a proper optimization pass. r?evilpie!

Also adds support for MLoadDynamicSlot and MLoadElement.

Depends on D75265

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6b265b68d408
part 1 - Rename MLoadSlot/MStoreSlot to MLoadDynamicSlot/MStoreDynamicSlot. r=evilpie
https://hg.mozilla.org/integration/autoland/rev/c2c904b194ca
part 2 - Don't use ObjectPolicy for slots/elements operands. r=evilpie
https://hg.mozilla.org/integration/autoland/rev/d2e95cb1d217
part 3 - Move LoadFixedSlotAndUnbox codegen logic into a helper function. r=evilpie

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/2b968efa9858
part 4 - Add MDefinition::maybeSingleDefUse method. r=evilpie
https://hg.mozilla.org/integration/autoland/rev/db07a336651e
part 5 - Replace load + unbox folding in MUnbox::foldsTo with a proper optimization pass. r=evilpie

Comment 9

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/6b265b68d408
https://hg.mozilla.org/mozilla-central/rev/c2c904b194ca
https://hg.mozilla.org/mozilla-central/rev/d2e95cb1d217
https://hg.mozilla.org/mozilla-central/rev/2b968efa9858
https://hg.mozilla.org/mozilla-central/rev/db07a336651e