[PATCH] D21510: [libc++] Check hash before calling __hash_table key_eq function

[Kwasi Mensah via cfe-commits]

Thanks. For future reference, do these benchmarking tests live some place
where I can run them myself in the future?

On Thu, Jun 30, 2016 at 2:15 AM, Eric Fiselier <eric at efcs.ca> wrote:

> EricWF accepted this revision.
> EricWF added a comment.
> This revision is now accepted and ready to land.
>
> LGTM. I benchmarked the change against different key types and:
>
> 1. The change doesn't have a large detrimental impact when the key
> equality is as expensive as hash equality. I benchmarked
> std::unordered_set<int>.find(...) at 27ns and 29ns before and after the
> change for a load factor >= 3.5, and 15ns vs 17 ns when the load factor is
> less than one.
>
> 2. The change has a large positive impact when the load factor is > 1 and
> where key equality is more expensive than hash equality. For strings of
> size 1024 that only differed in the last characters I noticed a change of
> 880ns to 650ns. for a load factor >= 3.5.
>
> 3. This change has a slight positive inpact when the load factor is < 1.
> For the same string inputs (mentioned above)  I  saw timings of 661ns and
> 623ns before and after.
>
>
>
>
> Repository:
>   rL LLVM
>
> http://reviews.llvm.org/D21510
>
>
>
>
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