[Webkit-unassigned] [Bug 156404] STP TypedArray.subarray 5x slowdown compared to 9.1

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=156404

--- Comment #3 from Geoffrey Garen <ggaren at apple.com> ---
(In reply to comment #2)
> (In reply to comment #1)
> > Fascinating.  That's a pretty serious regression.  Keith, do you remember
> > what we've done with subarray?
> > 
> 
> This regression is not particularly surprising. The ES6 spec changes the
> behavior of the subarray function substantially. I expect that issue here is
> that the subarray function now uses species constructors, which require
> several property lookups. Namely, the constructor and the Symbol.species
> properties. Since the subarray function is in C++ (where we don't cache the
> property lookups) and the subarrays you are making are very small (4
> elements). The cost of the species construction will dominate the cost of
> the element copying.

Why not perform the property accesses in JavaScript and then call a helper function to do the allocation?

I don't think we want to consider a 5X regression unsurprising.

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