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

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri Apr 8 11:53:45 PDT 2016


--- Comment #2 from Keith Miller <keith_miller at apple.com> ---
(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.

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