1437471 - Use singleton type only for big typed arrays created with an existing buffer

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

We have an optimization to give singleton type to TypedArrays with byteLength >= 10 MB. This was added to optimize asm.js/Mandreel type code better in Ion, but in practice this optimization can easily backfire because we quickly reach TypeSet limits when allocating many singleton arrays. mraleph ran into a SpiderMonkey perf cliff caused by this and I've seen it regress perf before.

One easy short-term fix is to only use this optimization for typed arrays created with an existing buffer, as that's the pattern used by Mandreel/asm.js code. That also makes it easier for people to opt-out of this optimization.

Longer term I think we should consider removing this optimization (because wasm) but as a first step restricting it seems reasonable.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Patch

Comment 2

[Brian Hackett [Laid off!]]

Comment on attachment 8950172 [details] [diff] [review]
Patch

Review of attachment 8950172 [details] [diff] [review]:
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It would be fine to remove this optimization entirely I think.

Comment 3

[Jan de Mooij [:jandem]]

(In reply to Brian Hackett (:bhackett) from comment #2)
> It would be fine to remove this optimization entirely I think.

This will regress Octane-mandreel a bit (~4000 points IIRC). Maybe we should take the hit and investigate but for now I'll just land this patch.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/e7519d21db96
Use singleton type only for big typed arrays created with an existing buffer. r=bhackett

Comment 5

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/e7519d21db96