[Webkit-unassigned] [Bug 150137] IdentifierRepHash has a mismatch between hash() and equal()

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=150137

--- Comment #5 from Yusuke Suzuki <utatane.tea at gmail.com> ---
(In reply to comment #3)
> Do you recommend measuring distribution directly, or do you think it's OK to
> just see how performance is affected overall?

I was thinking about HashTable::dumpStats.
DUMP_HASHTABLE_STATS can dump the statistics including collisions.

> We may encounter a trade-off between a fast to compute hash function that
> gives worse distribution and a slow to compute hash function that gives
> better distribution.  I don't have a philosophical preference between the
> two, but I just suspect that unless the distribution is really bad, the
> faster-to-compute hash function will give better overall performance.  Maybe
> the best thing to do is just to look at end-to-end performance.  Probably,
> it doesn't matter at all.  In that case, PtrHash is nicer because it's the
> less surprising choice.

Agreed. If the change does not pose any performance regression & there are enough tests, I think it indirectly indicates the distribution of PtrHash is not so bad.

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