Nilay Vaish 7f287390d7 [libc++] Add introsort to avoid O(n^2) behavior ... This commit adds a benchmark that tests std::sort on an adversarial inputs, and uses introsort in std::sort to avoid O(n^2) behavior on adversarial inputs. Inputs where partitions are unbalanced even after 2 log(n) pivots have been selected, the algorithm switches to heap sort to avoid the possibility of spending O(n^2) time on sorting the input. Benchmark results show that the intro sort implementation does significantly better. Benchmarking results before this change. Time represents the sorting time required per element: ---------------------------------------------------------------------------------------------------------- Benchmark Time CPU Iterations ---------------------------------------------------------------------------------------------------------- BM_Sort_uint32_QuickSortAdversary_1 3.75 ns 3.74 ns 187432960 BM_Sort_uint32_QuickSortAdversary_4 3.05 ns 3.05 ns 231211008 BM_Sort_uint32_QuickSortAdversary_16 2.45 ns 2.45 ns 288096256 BM_Sort_uint32_QuickSortAdversary_64 32.8 ns 32.8 ns 21495808 BM_Sort_uint32_QuickSortAdversary_256 132 ns 132 ns 5505024 BM_Sort_uint32_QuickSortAdversary_1024 498 ns 497 ns 1572864 BM_Sort_uint32_QuickSortAdversary_16384 3846 ns 3845 ns 262144 BM_Sort_uint32_QuickSortAdversary_262144 61431 ns 61400 ns 262144 BM_Sort_uint64_QuickSortAdversary_1 3.93 ns 3.92 ns 181141504 BM_Sort_uint64_QuickSortAdversary_4 3.10 ns 3.09 ns 222560256 BM_Sort_uint64_QuickSortAdversary_16 2.50 ns 2.50 ns 283639808 BM_Sort_uint64_QuickSortAdversary_64 33.2 ns 33.2 ns 21757952 BM_Sort_uint64_QuickSortAdversary_256 132 ns 132 ns 5505024 BM_Sort_uint64_QuickSortAdversary_1024 478 ns 477 ns 1572864 BM_Sort_uint64_QuickSortAdversary_16384 3932 ns 3930 ns 262144 BM_Sort_uint64_QuickSortAdversary_262144 61646 ns 61615 ns 262144 Benchmarking results after this change: ---------------------------------------------------------------------------------------------------------- Benchmark Time CPU Iterations ---------------------------------------------------------------------------------------------------------- BM_Sort_uint32_QuickSortAdversary_1 6.31 ns 6.30 ns 107741184 BM_Sort_uint32_QuickSortAdversary_4 4.51 ns 4.50 ns 158859264 BM_Sort_uint32_QuickSortAdversary_16 3.00 ns 3.00 ns 223608832 BM_Sort_uint32_QuickSortAdversary_64 44.8 ns 44.8 ns 15990784 BM_Sort_uint32_QuickSortAdversary_256 69.0 ns 68.9 ns 9961472 BM_Sort_uint32_QuickSortAdversary_1024 118 ns 118 ns 6029312 BM_Sort_uint32_QuickSortAdversary_16384 175 ns 175 ns 4194304 BM_Sort_uint32_QuickSortAdversary_262144 210 ns 210 ns 3407872 BM_Sort_uint64_QuickSortAdversary_1 6.75 ns 6.73 ns 103809024 BM_Sort_uint64_QuickSortAdversary_4 4.53 ns 4.53 ns 160432128 BM_Sort_uint64_QuickSortAdversary_16 2.98 ns 2.97 ns 234356736 BM_Sort_uint64_QuickSortAdversary_64 44.3 ns 44.3 ns 15990784 BM_Sort_uint64_QuickSortAdversary_256 69.2 ns 69.2 ns 10223616 BM_Sort_uint64_QuickSortAdversary_1024 119 ns 119 ns 6029312 BM_Sort_uint64_QuickSortAdversary_16384 173 ns 173 ns 4194304 BM_Sort_uint64_QuickSortAdversary_262144 212 ns 212 ns 3407872 Differential Revision: https://reviews.llvm.org/D113413		2021-11-16 11:38:46 -05:00
..
alg.binary.search	…
alg.clamp	[libc++] Remove the c++98 Lit feature from the test suite	2020-06-03 09:37:22 -04:00
alg.heap.operations	[libc++] [P0879] constexpr heap and partial_sort algorithms	2021-01-27 10:26:06 -05:00
alg.lex.comparison	[libcxx][nfc] prefixes test type `input_iterator` with `cpp17_`	2021-05-02 05:02:59 +00:00
alg.merge	[libc++] Remove test-suite annotations for unsupported Clang versions	2021-08-20 15:05:13 -04:00
alg.min.max	[libc++] Remove Lit annotations for unsupported GCC versions from the test suite	2021-08-12 13:30:47 -04:00
alg.nth.element	Revert "Revert "[libc++] [P0879] constexpr std::nth_element, and rewrite its tests.""	2021-02-05 12:02:43 -05:00
alg.permutation.generators	[libc++] [P0879] constexpr std::reverse, partition, *_permutation.	2021-01-25 13:09:30 -05:00
alg.set.operations	[libc++] Remove test-suite annotations for unsupported Clang versions	2021-08-20 15:05:13 -04:00
alg.sort	[libc++] Add introsort to avoid O(n^2) behavior	2021-11-16 11:38:46 -05:00
sortable_helpers.h	[libc++] NFC: Normalize `#endif //` comment indentation	2021-04-20 12:03:32 -04:00