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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - STP TypedArray.subarray 5x slowdown compared to 9.1"
href="https://bugs.webkit.org/show_bug.cgi?id=156404#c4">Comment # 4</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - STP TypedArray.subarray 5x slowdown compared to 9.1"
href="https://bugs.webkit.org/show_bug.cgi?id=156404">bug 156404</a>
from <span class="vcard"><a class="email" href="mailto:keith_miller@apple.com" title="Keith Miller <keith_miller@apple.com>"> <span class="fn">Keith Miller</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=156404#c3">comment #3</a>)
<span class="quote">> (In reply to <a href="show_bug.cgi?id=156404#c2">comment #2</a>)
> > (In reply to <a href="show_bug.cgi?id=156404#c1">comment #1</a>)
> > > 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.</span >
I agree, unsurprising was the wrong word choice. I think the a JS wrapper would work. I just didn't bother implementing it as I was unsure how popular the subarray function was in practice. If the subarray function is popular then creating a wrapper is something we should consider doing.</pre>
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