699323 - Can parts of SetArrayElement be fast-pathed when we know we have a dense array with sufficient capacity?

Status: RESOLVED DUPLICATE of bug 1362753

(Core :: JavaScript Engine, defect)

Description

[Boris Zbarsky [:bzbarsky]]

SetArrayElement shows up high on slice() profiles.  At first glance, array_slice makes sure the result value is a dense array of sufficient size.  So a lot of the stuff SetArrayElement does (e.g. ensureDenseArrayCapacity) seems unnecessary.  If that's actually the case, can we fast-path it?

Comment 1

[André Bargull [:anba]]

The current slice() fast path [1] should work quite 


[1] https://searchfox.org/mozilla-central/rev/30ead7d1ae5bf95b8bc0fd67b950cd46ca05e32c/js/src/jsarray.cpp#3212-3221
[2] https://searchfox.org/mozilla-central/rev/30ead7d1ae5bf95b8bc0fd67b950cd46ca05e32c/js/src/jsarray.cpp#3241-3248

Comment 2

[André Bargull [:anba]]

Argh, hit enter while the focus was still in the duplicate-bug input box. What I meant to say:

The current slice() fast path [1] should work quite nice for dense arrays. Then there's an additional hook in [2] and bug  1362753 made the non-fast path a bit faster, too. Therefore marking as dup of bug 1362753.