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| author | Nikolas Klauser <nikolasklauser@berlin.de> | 2025-10-21 10:20:06 +0200 | 
|---|---|---|
| committer | GitHub <noreply@github.com> | 2025-10-21 10:20:06 +0200 | 
| commit | 253e43590842bffcc6950cc517a7f89cafe5ec69 (patch) | |
| tree | 4ecf172d5de7e0a75f6b751d9435bc7865fd623a /libcxx/include/__algorithm/sample.h | |
| parent | 1bf7ed27c1929152d876f9965895fd87ec8ccee4 (diff) | |
| download | llvm-253e43590842bffcc6950cc517a7f89cafe5ec69.zip llvm-253e43590842bffcc6950cc517a7f89cafe5ec69.tar.gz llvm-253e43590842bffcc6950cc517a7f89cafe5ec69.tar.bz2 | |
Reapply "[libc++] Optimize __hash_table::erase(iterator, iterator)" (#162850)
This reapplication fixes the use after free caused by not properly
updating the bucket list in one case.
Original commit message:
Instead of just calling the single element `erase` on every element of
the range, we can combine some of the operations in a custom
implementation. Specifically, we don't need to search for the previous
node or re-link the list every iteration. Removing this unnecessary work
results in some nice performance improvements:
```
-----------------------------------------------------------------------------------------------------------------------
Benchmark                                                                                             old           new
-----------------------------------------------------------------------------------------------------------------------
std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/0                    457 ns        459 ns
std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/32                   995 ns        626 ns
std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/1024               18196 ns       7995 ns
std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/8192              124722 ns      70125 ns
std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/0            456 ns        461 ns
std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/32          1183 ns        769 ns
std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/1024       27827 ns      18614 ns
std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/8192      266681 ns     226107 ns
std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/0               455 ns        462 ns
std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/32              996 ns        659 ns
std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/1024          15963 ns       8108 ns
std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/8192         136493 ns      71848 ns
std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/0               454 ns        455 ns
std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/32              985 ns        703 ns
std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/1024          16277 ns       9085 ns
std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/8192         125736 ns      82710 ns
std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/0          457 ns        454 ns
std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/32        1091 ns        646 ns
std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/1024     17784 ns       7664 ns
std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/8192    127098 ns      72806 ns
```
This reverts commit acc3a6234a91369b818fdd6482ded0ac32d8ffa6.
Diffstat (limited to 'libcxx/include/__algorithm/sample.h')
0 files changed, 0 insertions, 0 deletions
