1056260 - Improve performance of [...obj] and Array.from

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Boris Zbarsky [:bzbarsky]]

Attachment: Testcase

See attached testcase.  slice.call() is way faster than the more idiomatic things.

Two issues here:

1)  slice.call() does not need to do all the iterator jazz.
2)  slice has a fast path for nodelists where it only calls a single proxy hook
    and has it fill in the list.

It'd be nice if we could improve both of those for Array.from and destructuring...

Comment 1

[Jason Orendorff [:jorendorff]]

There may be relevant lessons in bug 904723, which was something of a slog.

The first step should be to measure improvement due to nbp's work on escape analysis and alias anlysis (see bug 927548 "scalar replacement").

Comment 2

[Guilherme Lima]

Firefox 53.0.3
Time to slice live nodelist: 0.411ms
Time to destructure live nodelist: 0.268ms
Time to Array.from live nodelist: 0.562ms

Time to slice static nodelist: 0.3955ms
Time to destructure static nodelist: 0.248ms
Time to Array.from static nodelist: 0.5525ms

Time to slice array: 0.0215ms
Time to destructure array: 0.107ms
Time to Array.from array: 0.3455ms


Nightly 55 (23-05-2017)
Time to slice live nodelist: 0.417ms
Time to destructure live nodelist: 0.216ms
Time to Array.from live nodelist: 0.214ms

Time to slice static nodelist: 0.38ms
Time to destructure static nodelist: 0.197ms
Time to Array.from static nodelist: 0.1835ms

Time to slice array: 0.021ms
Time to destructure array: 0.069ms
Time to Array.from array: 0.055ms

Improvement from bug 1366372?

Comment 3

[Mayank Bansal]

Nightly:

Time to slice live nodelist: 0.015ms
Time to destructure live nodelist: 0.0385ms
Time to Array.from live nodelist: 0.0375ms

Time to slice static nodelist: 0.013ms
Time to destructure static nodelist: 0.0365ms
Time to Array.from static nodelist: 0.0425ms

Time to slice array: 0.0005ms
Time to destructure array: 0.007ms
Time to Array.from array: 0.0065ms

Chrome:
Time to slice live nodelist: 0.106ms
Time to destructure live nodelist: 0.1345ms
Time to Array.from live nodelist: 0.133ms

Time to slice static nodelist: 0.1265ms
Time to destructure static nodelist: 0.127ms
Time to Array.from static nodelist: 0.124ms

Time to slice array: 0ms
Time to destructure array: 0.0005ms
Time to Array.from array: 0ms

We are faster in almost all the cases. Calling this fixed.