tree 7519f5483820ae89b8f48581dfeca25c5c81e55c
parent bfc32dd106f0fe191b8bcd9b76348a8875c30a60
parent 9f7b58f3c94708f344237f826b4f96a659b5fc82
author bors <bors@rust-lang.org> 1582882354 +0000
committer bors <bors@rust-lang.org> 1582882354 +0000

Auto merge of #68827 - ssomers:btree_navigation_revisited, r=Mark-Simulacrum

BTreeMap navigation done safer & faster

It turns out that there was a faster way to do the tree navigation code bundled in #67073, by moving from edge to KV and from KV to next edge separately. It extracts most of the code as safe functions, and contains the duplication of handles within the short wrapper functions.

This somehow hits a sweet spot in the compiler because it reports boosts all over the board:
```
>cargo benchcmp pre3.txt posz4.txt --threshold 5
 name                                           pre3.txt ns/iter  posz4.txt ns/iter  diff ns/iter   diff %  speedup
 btree::map::first_and_last_0                   40                37                           -3   -7.50%   x 1.08
 btree::map::first_and_last_100                 58                44                          -14  -24.14%   x 1.32
 btree::map::iter_1000                          8,920             3,419                    -5,501  -61.67%   x 2.61
 btree::map::iter_100000                        1,069,290         411,615                -657,675  -61.51%   x 2.60
 btree::map::iter_20                            169               58                         -111  -65.68%   x 2.91
 btree::map::iter_mut_1000                      8,701             3,303                    -5,398  -62.04%   x 2.63
 btree::map::iter_mut_100000                    1,034,560         405,975                -628,585  -60.76%   x 2.55
 btree::map::iter_mut_20                        165               58                         -107  -64.85%   x 2.84
 btree::set::clone_100                          1,831             1,562                      -269  -14.69%   x 1.17
 btree::set::clone_100_and_clear                1,831             1,565                      -266  -14.53%   x 1.17
 btree::set::clone_100_and_into_iter            1,917             1,541                      -376  -19.61%   x 1.24
 btree::set::clone_100_and_pop_all              2,609             2,441                      -168   -6.44%   x 1.07
 btree::set::clone_100_and_remove_all           4,598             3,927                      -671  -14.59%   x 1.17
 btree::set::clone_100_and_remove_half          2,765             2,551                      -214   -7.74%   x 1.08
 btree::set::clone_10k                          191,610           164,616                 -26,994  -14.09%   x 1.16
 btree::set::clone_10k_and_clear                192,003           164,616                 -27,387  -14.26%   x 1.17
 btree::set::clone_10k_and_into_iter            200,037           163,010                 -37,027  -18.51%   x 1.23
 btree::set::clone_10k_and_pop_all              267,023           250,913                 -16,110   -6.03%   x 1.06
 btree::set::clone_10k_and_remove_all           536,230           464,100                 -72,130  -13.45%   x 1.16
 btree::set::clone_10k_and_remove_half          453,350           430,545                 -22,805   -5.03%   x 1.05
 btree::set::difference_random_100_vs_100       1,787             801                        -986  -55.18%   x 2.23
 btree::set::difference_random_100_vs_10k       2,978             2,696                      -282   -9.47%   x 1.10
 btree::set::difference_random_10k_vs_100       111,075           54,734                  -56,341  -50.72%   x 2.03
 btree::set::difference_random_10k_vs_10k       246,380           175,980                 -70,400  -28.57%   x 1.40
 btree::set::difference_staggered_100_vs_100    1,789             951                        -838  -46.84%   x 1.88
 btree::set::difference_staggered_100_vs_10k    2,798             2,606                      -192   -6.86%   x 1.07
 btree::set::difference_staggered_10k_vs_10k    176,452           97,401                  -79,051  -44.80%   x 1.81
 btree::set::intersection_100_neg_vs_10k_pos    34                32                           -2   -5.88%   x 1.06
 btree::set::intersection_100_pos_vs_100_neg    30                27                           -3  -10.00%   x 1.11
 btree::set::intersection_random_100_vs_100     1,537             613                        -924  -60.12%   x 2.51
 btree::set::intersection_random_100_vs_10k     2,793             2,649                      -144   -5.16%   x 1.05
 btree::set::intersection_random_10k_vs_10k     222,127           147,166                 -74,961  -33.75%   x 1.51
 btree::set::intersection_staggered_100_vs_100  1,447             622                        -825  -57.01%   x 2.33
 btree::set::intersection_staggered_100_vs_10k  2,606             2,382                      -224   -8.60%   x 1.09
 btree::set::intersection_staggered_10k_vs_10k  143,620           58,790                  -84,830  -59.07%   x 2.44
 btree::set::is_subset_100_vs_100               1,349             488                        -861  -63.83%   x 2.76
 btree::set::is_subset_100_vs_10k               1,720             1,428                      -292  -16.98%   x 1.20
 btree::set::is_subset_10k_vs_10k               135,984           48,527                  -87,457  -64.31%   x 2.80
```
The `first_and_last` ones are noise (they don't do iteration), the others seem genuine.
As always, approved by Miri.

Also, a separate commit with some more benchmarks of mutable behaviour (which also benefit).

r? @cuviper