[libc++] Optimize __tree::find and __tree::__erase_unique (#152370)
This patch changes `__tree::find` to return when it has found any equal
element instead of the lower bound of the equal elements. For `map` and
`set` there is no observable difference, since the keys are unique.
However for their `multi` versions this can mean a change in behaviour
since it's not longer guaranteed that `find` will return the first
element.
```
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Benchmark old new
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std::map<int, int>::erase(key) (existent)/0 24.4 ns 24.9 ns
std::map<int, int>::erase(key) (existent)/32 39.8 ns 32.1 ns
std::map<int, int>::erase(key) (existent)/1024 83.8 ns 52.5 ns
std::map<int, int>::erase(key) (existent)/8192 91.4 ns 66.4 ns
std::map<int, int>::erase(key) (non-existent)/0 0.511 ns 0.328 ns
std::map<int, int>::erase(key) (non-existent)/32 9.12 ns 5.62 ns
std::map<int, int>::erase(key) (non-existent)/1024 26.6 ns 11.3 ns
std::map<int, int>::erase(key) (non-existent)/8192 37.0 ns 16.9 ns
std::map<int, int>::find(key) (existent)/0 0.007 ns 0.007 ns
std::map<int, int>::find(key) (existent)/32 6.02 ns 4.32 ns
std::map<int, int>::find(key) (existent)/1024 13.6 ns 8.35 ns
std::map<int, int>::find(key) (existent)/8192 30.3 ns 12.8 ns
std::map<int, int>::find(key) (non-existent)/0 0.299 ns 0.545 ns
std::map<int, int>::find(key) (non-existent)/32 8.78 ns 4.60 ns
std::map<int, int>::find(key) (non-existent)/1024 26.1 ns 21.8 ns
std::map<int, int>::find(key) (non-existent)/8192 36.2 ns 27.9 ns
std::map<std::string, int>::erase(key) (existent)/0 74.1 ns 76.7 ns
std::map<std::string, int>::erase(key) (existent)/32 161 ns 114 ns
std::map<std::string, int>::erase(key) (existent)/1024 196 ns 126 ns
std::map<std::string, int>::erase(key) (existent)/8192 207 ns 160 ns
std::map<std::string, int>::erase(key) (non-existent)/0 0.754 ns 0.328 ns
std::map<std::string, int>::erase(key) (non-existent)/32 47.3 ns 40.7 ns
std::map<std::string, int>::erase(key) (non-existent)/1024 122 ns 96.1 ns
std::map<std::string, int>::erase(key) (non-existent)/8192 168 ns 123 ns
std::map<std::string, int>::find(key) (existent)/0 0.059 ns 0.058 ns
std::map<std::string, int>::find(key) (existent)/32 54.3 ns 34.6 ns
std::map<std::string, int>::find(key) (existent)/1024 125 ns 64.5 ns
std::map<std::string, int>::find(key) (existent)/8192 159 ns 79.2 ns
std::map<std::string, int>::find(key) (non-existent)/0 0.311 ns 0.299 ns
std::map<std::string, int>::find(key) (non-existent)/32 44.0 ns 42.7 ns
std::map<std::string, int>::find(key) (non-existent)/1024 120 ns 92.6 ns
std::map<std::string, int>::find(key) (non-existent)/8192 189 ns 124 ns
std::set<int>::erase(key) (existent)/0 25.1 ns 25.1 ns
std::set<int>::erase(key) (existent)/32 42.1 ns 33.1 ns
std::set<int>::erase(key) (existent)/1024 73.8 ns 55.5 ns
std::set<int>::erase(key) (existent)/8192 101 ns 68.8 ns
std::set<int>::erase(key) (non-existent)/0 0.511 ns 0.328 ns
std::set<int>::erase(key) (non-existent)/32 9.60 ns 4.67 ns
std::set<int>::erase(key) (non-existent)/1024 26.5 ns 11.2 ns
std::set<int>::erase(key) (non-existent)/8192 46.2 ns 16.8 ns
std::set<int>::find(key) (existent)/0 0.008 ns 0.007 ns
std::set<int>::find(key) (existent)/32 5.87 ns 4.51 ns
std::set<int>::find(key) (existent)/1024 14.3 ns 8.69 ns
std::set<int>::find(key) (existent)/8192 30.2 ns 12.8 ns
std::set<int>::find(key) (non-existent)/0 0.531 ns 0.530 ns
std::set<int>::find(key) (non-existent)/32 8.77 ns 4.64 ns
std::set<int>::find(key) (non-existent)/1024 26.1 ns 21.7 ns
std::set<int>::find(key) (non-existent)/8192 36.3 ns 27.8 ns
std::set<std::string>::erase(key) (existent)/0 93.2 ns 70.2 ns
std::set<std::string>::erase(key) (existent)/32 164 ns 116 ns
std::set<std::string>::erase(key) (existent)/1024 161 ns 136 ns
std::set<std::string>::erase(key) (existent)/8192 231 ns 140 ns
std::set<std::string>::erase(key) (non-existent)/0 0.532 ns 0.326 ns
std::set<std::string>::erase(key) (non-existent)/32 43.4 ns 40.1 ns
std::set<std::string>::erase(key) (non-existent)/1024 122 ns 99.5 ns
std::set<std::string>::erase(key) (non-existent)/8192 168 ns 125 ns
std::set<std::string>::find(key) (existent)/0 0.059 ns 0.059 ns
std::set<std::string>::find(key) (existent)/32 53.1 ns 35.5 ns
std::set<std::string>::find(key) (existent)/1024 124 ns 61.2 ns
std::set<std::string>::find(key) (existent)/8192 154 ns 73.9 ns
std::set<std::string>::find(key) (non-existent)/0 0.532 ns 0.301 ns
std::set<std::string>::find(key) (non-existent)/32 44.4 ns 39.5 ns
std::set<std::string>::find(key) (non-existent)/1024 120 ns 95.5 ns
std::set<std::string>::find(key) (non-existent)/8192 193 ns 119 ns
std::multimap<int, int>::erase(key) (existent)/0 26.5 ns 26.6 ns
std::multimap<int, int>::erase(key) (existent)/32 33.5 ns 32.9 ns
std::multimap<int, int>::erase(key) (existent)/1024 55.5 ns 58.0 ns
std::multimap<int, int>::erase(key) (existent)/8192 67.4 ns 70.0 ns
std::multimap<int, int>::erase(key) (non-existent)/0 0.523 ns 0.532 ns
std::multimap<int, int>::erase(key) (non-existent)/32 5.08 ns 5.09 ns
std::multimap<int, int>::erase(key) (non-existent)/1024 13.0 ns 12.9 ns
std::multimap<int, int>::erase(key) (non-existent)/8192 19.6 ns 19.8 ns
std::multimap<int, int>::find(key) (existent)/0 0.015 ns 0.037 ns
std::multimap<int, int>::find(key) (existent)/32 7.07 ns 3.85 ns
std::multimap<int, int>::find(key) (existent)/1024 22.0 ns 7.44 ns
std::multimap<int, int>::find(key) (existent)/8192 37.6 ns 12.0 ns
std::multimap<int, int>::find(key) (non-existent)/0 0.297 ns 0.305 ns
std::multimap<int, int>::find(key) (non-existent)/32 8.79 ns 4.59 ns
std::multimap<int, int>::find(key) (non-existent)/1024 26.0 ns 11.2 ns
std::multimap<int, int>::find(key) (non-existent)/8192 36.4 ns 16.8 ns
std::multimap<std::string, int>::erase(key) (existent)/0 93.4 ns 84.5 ns
std::multimap<std::string, int>::erase(key) (existent)/32 101 ns 101 ns
std::multimap<std::string, int>::erase(key) (existent)/1024 118 ns 126 ns
std::multimap<std::string, int>::erase(key) (existent)/8192 108 ns 124 ns
std::multimap<std::string, int>::erase(key) (non-existent)/0 2.39 ns 2.43 ns
std::multimap<std::string, int>::erase(key) (non-existent)/32 44.4 ns 49.7 ns
std::multimap<std::string, int>::erase(key) (non-existent)/1024 108 ns 103 ns
std::multimap<std::string, int>::erase(key) (non-existent)/8192 140 ns 125 ns
std::multimap<std::string, int>::find(key) (existent)/0 0.059 ns 0.058 ns
std::multimap<std::string, int>::find(key) (existent)/32 52.3 ns 32.6 ns
std::multimap<std::string, int>::find(key) (existent)/1024 122 ns 58.9 ns
std::multimap<std::string, int>::find(key) (existent)/8192 160 ns 72.7 ns
std::multimap<std::string, int>::find(key) (non-existent)/0 0.524 ns 0.494 ns
std::multimap<std::string, int>::find(key) (non-existent)/32 43.8 ns 38.9 ns
std::multimap<std::string, int>::find(key) (non-existent)/1024 123 ns 90.8 ns
std::multimap<std::string, int>::find(key) (non-existent)/8192 190 ns 126 ns
std::multiset<int>::erase(key) (existent)/0 27.1 ns 26.8 ns
std::multiset<int>::erase(key) (existent)/32 33.3 ns 34.1 ns
std::multiset<int>::erase(key) (existent)/1024 58.5 ns 58.8 ns
std::multiset<int>::erase(key) (existent)/8192 66.7 ns 64.1 ns
std::multiset<int>::erase(key) (non-existent)/0 0.318 ns 0.325 ns
std::multiset<int>::erase(key) (non-existent)/32 5.15 ns 5.25 ns
std::multiset<int>::erase(key) (non-existent)/1024 12.9 ns 12.7 ns
std::multiset<int>::erase(key) (non-existent)/8192 20.3 ns 20.3 ns
std::multiset<int>::find(key) (existent)/0 0.043 ns 0.015 ns
std::multiset<int>::find(key) (existent)/32 6.94 ns 4.22 ns
std::multiset<int>::find(key) (existent)/1024 21.4 ns 8.23 ns
std::multiset<int>::find(key) (existent)/8192 37.4 ns 12.6 ns
std::multiset<int>::find(key) (non-existent)/0 0.515 ns 0.300 ns
std::multiset<int>::find(key) (non-existent)/32 8.52 ns 4.62 ns
std::multiset<int>::find(key) (non-existent)/1024 25.5 ns 11.3 ns
std::multiset<int>::find(key) (non-existent)/8192 36.5 ns 27.0 ns
std::multiset<std::string>::erase(key) (existent)/0 81.9 ns 77.5 ns
std::multiset<std::string>::erase(key) (existent)/32 113 ns 129 ns
std::multiset<std::string>::erase(key) (existent)/1024 132 ns 148 ns
std::multiset<std::string>::erase(key) (existent)/8192 114 ns 165 ns
std::multiset<std::string>::erase(key) (non-existent)/0 2.33 ns 2.32 ns
std::multiset<std::string>::erase(key) (non-existent)/32 44.4 ns 42.0 ns
std::multiset<std::string>::erase(key) (non-existent)/1024 97.3 ns 95.1 ns
std::multiset<std::string>::erase(key) (non-existent)/8192 132 ns 123 ns
std::multiset<std::string>::find(key) (existent)/0 0.058 ns 0.059 ns
std::multiset<std::string>::find(key) (existent)/32 48.3 ns 34.4 ns
std::multiset<std::string>::find(key) (existent)/1024 121 ns 61.9 ns
std::multiset<std::string>::find(key) (existent)/8192 155 ns 77.7 ns
std::multiset<std::string>::find(key) (non-existent)/0 0.524 ns 0.306 ns
std::multiset<std::string>::find(key) (non-existent)/32 44.1 ns 40.4 ns
std::multiset<std::string>::find(key) (non-existent)/1024 121 ns 96.3 ns
std::multiset<std::string>::find(key) (non-existent)/8192 193 ns 121 ns
```
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