Auto merge of #118273 - AngelicosPhosphoros:dedup_2_loops_version_77772_2, r=the8472

Split `Vec::dedup_by` into 2 cycles

First cycle runs until we found 2 same elements, second runs after if there any found in the first one. This allows to avoid any memory writes until we found an item which we want to remove.

This leads to significant performance gains if all `Vec` items are kept: -40% on my benchmark with unique integers.

Results of benchmarks before implementation (including new benchmark where nothing needs to be removed):
 *   vec::bench_dedup_all_100                 74.00ns/iter  +/- 13.00ns
 *   vec::bench_dedup_all_1000               572.00ns/iter +/- 272.00ns
 *   vec::bench_dedup_all_100000              64.42µs/iter  +/- 19.47µs
 *   __vec::bench_dedup_none_100                67.00ns/iter  +/- 17.00ns__
 *   __vec::bench_dedup_none_1000              662.00ns/iter  +/- 86.00ns__
 *   __vec::bench_dedup_none_10000               9.16µs/iter   +/- 2.71µs__
 *   __vec::bench_dedup_none_100000             91.25µs/iter   +/- 1.82µs__
 *   vec::bench_dedup_random_100             105.00ns/iter  +/- 11.00ns
 *   vec::bench_dedup_random_1000            781.00ns/iter  +/- 10.00ns
 *   vec::bench_dedup_random_10000             9.00µs/iter   +/- 5.62µs
 *   vec::bench_dedup_random_100000          449.81µs/iter  +/- 74.99µs
 *   vec::bench_dedup_slice_truncate_100     105.00ns/iter  +/- 16.00ns
 *   vec::bench_dedup_slice_truncate_1000      2.65µs/iter +/- 481.00ns
 *   vec::bench_dedup_slice_truncate_10000    18.33µs/iter   +/- 5.23µs
 *   vec::bench_dedup_slice_truncate_100000  501.12µs/iter  +/- 46.97µs

Results after implementation:
 *   vec::bench_dedup_all_100                 75.00ns/iter   +/- 9.00ns
 *   vec::bench_dedup_all_1000               494.00ns/iter +/- 117.00ns
 *   vec::bench_dedup_all_100000              58.13µs/iter   +/- 8.78µs
 *   __vec::bench_dedup_none_100                52.00ns/iter  +/- 22.00ns__
 *   __vec::bench_dedup_none_1000              417.00ns/iter +/- 116.00ns__
 *   __vec::bench_dedup_none_10000               4.11µs/iter +/- 546.00ns__
 *   __vec::bench_dedup_none_100000             40.47µs/iter   +/- 5.36µs__
 *   vec::bench_dedup_random_100              77.00ns/iter  +/- 15.00ns
 *   vec::bench_dedup_random_1000            681.00ns/iter  +/- 86.00ns
 *   vec::bench_dedup_random_10000            11.66µs/iter   +/- 2.22µs
 *   vec::bench_dedup_random_100000          469.35µs/iter  +/- 20.53µs
 *   vec::bench_dedup_slice_truncate_100     100.00ns/iter   +/- 5.00ns
 *   vec::bench_dedup_slice_truncate_1000      2.55µs/iter +/- 224.00ns
 *   vec::bench_dedup_slice_truncate_10000    18.95µs/iter   +/- 2.59µs
 *   vec::bench_dedup_slice_truncate_100000  492.85µs/iter  +/- 72.84µs

Resolves #77772

P.S. Note that this is same PR as #92104 I just missed review then forgot about it.
Also, I cannot reopen that pull request so I am creating a new one.
I responded to remaining questions directly by adding commentaries to my code.
This commit is contained in:
bors 2023-12-05 21:40:02 +00:00
commit 499c191371

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