1381469 - Improve TypedArray iteration by avoid the detached buffer check when the current length is non-zero

Status: RESOLVED FIXED

(Core :: JavaScript: Standard Library, enhancement)

Description

[André Bargull [:anba]]

It's faster to call PossiblyWrappedTypedArrayLength (because it can be inlined), than to call PossiblyWrappedTypedArrayHasDetachedBuffer (which isn't inlined). So to speed up typed array iteration, we can avoid calling PossiblyWrappedTypedArrayHasDetachedBuffer when the current typed array length is non-zero (we currently reset the length to zero when the underlying array buffer was detached, so any typed array with a non-zero length can't have a detached array buffer).


Improves this µ-benchmark from 240ms to 50ms for me:

    var a = new Int32Array(100).map((v, k) => k + 1);
    var q = 0;
    var t = Date.now();
    for (var i = 0; i < 100000; ++i) {
        for (var x of a) q += x;
    }
    print(Date.now() - t, q);

Comment 1

[André Bargull [:anba]]

Attachment: bug1381469.patch

This avoids the slow PossiblyWrappedTypedArrayHasDetachedBuffer check when the typed array is definitely not detached.

Comment 2

[Till Schneidereit [:till]]

Comment on attachment 8887030 [details] [diff] [review]
bug1381469.patch

Review of attachment 8887030 [details] [diff] [review]:
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nice, r=me

Comment 3

[André Bargull [:anba]]

Try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=d929d586209513f21fe082c7d03f2e4e97c43e68

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/75e1e435c2b6
Only check for detached buffers when iterating over typed arrays when the current length is zero. r=till

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/75e1e435c2b6