Author: spop Date: Fri Dec 30 12:01:36 2016 New Revision: 290761 URL: http://llvm.org/viewvc/llvm-project?rev=290761&view=rev Log: improve performance of string::find
string::find used to call the generic algorithm ::find. The patch special case string::find such that it ultimately gets converted to calls to memchr and memcmp. The patch improves the performance of the string::find routine by about 20x. Without the patch, the performance on an x86_64-linux 3400 MHz machine is: Benchmark Time CPU Iterations ----------------------------------------------------------------- BM_StringFindNoMatch/10 4 ns 4 ns 166421326 BM_StringFindNoMatch/64 37 ns 37 ns 18754392 BM_StringFindNoMatch/512 268 ns 268 ns 2586060 BM_StringFindNoMatch/4k 2143 ns 2144 ns 328342 BM_StringFindNoMatch/32k 16910 ns 16917 ns 40623 BM_StringFindNoMatch/128k 67577 ns 67602 ns 10138 BM_StringFindAllMatch/1 3 ns 3 ns 265163471 BM_StringFindAllMatch/8 6 ns 6 ns 112582467 BM_StringFindAllMatch/64 36 ns 36 ns 19566457 BM_StringFindAllMatch/512 209 ns 209 ns 3318893 BM_StringFindAllMatch/4k 1618 ns 1618 ns 432963 BM_StringFindAllMatch/32k 12909 ns 12914 ns 54317 BM_StringFindAllMatch/128k 48342 ns 48361 ns 13922 BM_StringFindMatch1/1 33777 ns 33790 ns 20698 BM_StringFindMatch1/8 33940 ns 33953 ns 20619 BM_StringFindMatch1/64 34038 ns 34051 ns 20571 BM_StringFindMatch1/512 34217 ns 34230 ns 20480 BM_StringFindMatch1/4k 35510 ns 35524 ns 19752 BM_StringFindMatch1/32k 46438 ns 46456 ns 15030 BM_StringFindMatch2/1 33839 ns 33852 ns 20648 BM_StringFindMatch2/8 33950 ns 33963 ns 20594 BM_StringFindMatch2/64 33846 ns 33859 ns 20668 BM_StringFindMatch2/512 34023 ns 34036 ns 20279 BM_StringFindMatch2/4k 35422 ns 35436 ns 19716 BM_StringFindMatch2/32k 46570 ns 46588 ns 15027 With the patch applied Benchmark Time CPU Iterations ----------------------------------------------------------------- BM_StringFindNoMatch/10 5 ns 5 ns 133724346 BM_StringFindNoMatch/64 6 ns 6 ns 119312184 BM_StringFindNoMatch/512 13 ns 13 ns 51539628 BM_StringFindNoMatch/4k 77 ns 77 ns 8935934 BM_StringFindNoMatch/32k 551 ns 551 ns 1222808 BM_StringFindNoMatch/128k 2684 ns 2685 ns 259957 BM_StringFindAllMatch/1 7 ns 7 ns 98017959 BM_StringFindAllMatch/8 7 ns 7 ns 91466911 BM_StringFindAllMatch/64 8 ns 8 ns 85707392 BM_StringFindAllMatch/512 20 ns 20 ns 34490895 BM_StringFindAllMatch/4k 93 ns 93 ns 7360375 BM_StringFindAllMatch/32k 827 ns 828 ns 829944 BM_StringFindAllMatch/128k 3593 ns 3594 ns 195815 BM_StringFindMatch1/1 1332 ns 1332 ns 516354 BM_StringFindMatch1/8 1336 ns 1336 ns 495876 BM_StringFindMatch1/64 1338 ns 1339 ns 516656 BM_StringFindMatch1/512 1357 ns 1357 ns 510717 BM_StringFindMatch1/4k 1485 ns 1486 ns 461228 BM_StringFindMatch1/32k 2235 ns 2236 ns 318253 BM_StringFindMatch2/1 1335 ns 1335 ns 517105 BM_StringFindMatch2/8 1336 ns 1337 ns 518004 BM_StringFindMatch2/64 1344 ns 1345 ns 511751 BM_StringFindMatch2/512 1361 ns 1361 ns 508150 BM_StringFindMatch2/4k 1611 ns 1611 ns 463388 BM_StringFindMatch2/32k 2187 ns 2187 ns 317532 Patch written by Aditya Kumar and Sebastian Pop. Differential Revision: https://reviews.llvm.org/D27068 Added: libcxx/trunk/benchmarks/string.bench.cpp Modified: libcxx/trunk/include/__string Added: libcxx/trunk/benchmarks/string.bench.cpp URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/benchmarks/string.bench.cpp?rev=290761&view=auto ============================================================================== --- libcxx/trunk/benchmarks/string.bench.cpp (added) +++ libcxx/trunk/benchmarks/string.bench.cpp Fri Dec 30 12:01:36 2016 @@ -0,0 +1,49 @@ +#include <unordered_set> +#include <vector> +#include <cstdint> + +#include "benchmark/benchmark_api.h" +#include "GenerateInput.hpp" + +constexpr std::size_t MAX_STRING_LEN = 8 << 14; + +// Benchmark when there is no match. +static void BM_StringFindNoMatch(benchmark::State &state) { + std::string s1(state.range(0), '-'); + std::string s2(8, '*'); + while (state.KeepRunning()) + benchmark::DoNotOptimize(s1.find(s2)); +} +BENCHMARK(BM_StringFindNoMatch)->Range(10, MAX_STRING_LEN); + +// Benchmark when the string matches first time. +static void BM_StringFindAllMatch(benchmark::State &state) { + std::string s1(MAX_STRING_LEN, '-'); + std::string s2(state.range(0), '-'); + while (state.KeepRunning()) + benchmark::DoNotOptimize(s1.find(s2)); +} +BENCHMARK(BM_StringFindAllMatch)->Range(1, MAX_STRING_LEN); + +// Benchmark when the string matches somewhere in the end. +static void BM_StringFindMatch1(benchmark::State &state) { + std::string s1(MAX_STRING_LEN / 2, '*'); + s1 += std::string(state.range(0), '-'); + std::string s2(state.range(0), '-'); + while (state.KeepRunning()) + benchmark::DoNotOptimize(s1.find(s2)); +} +BENCHMARK(BM_StringFindMatch1)->Range(1, MAX_STRING_LEN / 4); + +// Benchmark when the string matches somewhere from middle to the end. +static void BM_StringFindMatch2(benchmark::State &state) { + std::string s1(MAX_STRING_LEN / 2, '*'); + s1 += std::string(state.range(0), '-'); + s1 += std::string(state.range(0), '*'); + std::string s2(state.range(0), '-'); + while (state.KeepRunning()) + benchmark::DoNotOptimize(s1.find(s2)); +} +BENCHMARK(BM_StringFindMatch2)->Range(1, MAX_STRING_LEN / 4); + +BENCHMARK_MAIN() Modified: libcxx/trunk/include/__string URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__string?rev=290761&r1=290760&r2=290761&view=diff ============================================================================== --- libcxx/trunk/include/__string (original) +++ libcxx/trunk/include/__string Fri Dec 30 12:01:36 2016 @@ -538,19 +538,59 @@ __str_find(const _CharT *__p, _SizeT __s return static_cast<_SizeT>(__r - __p); } +template <class _CharT, class _Traits> +inline _LIBCPP_CONSTEXPR_AFTER_CXX11 const _CharT * +__search_substring(const _CharT *__first1, const _CharT *__last1, + const _CharT *__first2, const _CharT *__last2) { + // Take advantage of knowing source and pattern lengths. + // Stop short when source is smaller than pattern. + const ptrdiff_t __len2 = __last2 - __first2; + if (__len2 == 0) + return __first1; + + ptrdiff_t __len1 = __last1 - __first1; + if (__len1 < __len2) + return __last1; + + // First element of __first2 is loop invariant. + _CharT __f2 = *__first2; + while (true) { + __len1 = __last1 - __first1; + // Check whether __first1 still has at least __len2 bytes. + if (__len1 < __len2) + return __last1; + + // Find __f2 the first byte matching in __first1. + __first1 = _Traits::find(__first1, __len1 - __len2 + 1, __f2); + if (__first1 == 0) + return __last1; + + // It is faster to compare from the first byte of __first1 even if we + // already know that it matches the first byte of __first2: this is because + // __first2 is most likely aligned, as it is user's "pattern" string, and + // __first1 + 1 is most likely not aligned, as the match is in the middle of + // the string. + if (_Traits::compare(__first1, __first2, __len2) == 0) + return __first1; + + ++__first1; + } +} + template<class _CharT, class _SizeT, class _Traits, _SizeT __npos> inline _SizeT _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY __str_find(const _CharT *__p, _SizeT __sz, const _CharT* __s, _SizeT __pos, _SizeT __n) _NOEXCEPT { - if (__pos > __sz || __sz - __pos < __n) + if (__pos > __sz) return __npos; - if (__n == 0) + + if (__n == 0) // There is nothing to search, just return __pos. return __pos; - const _CharT* __r = - _VSTD::__search(__p + __pos, __p + __sz, - __s, __s + __n, _Traits::eq, - random_access_iterator_tag(), random_access_iterator_tag()).first; + + const _CharT *__r = __search_substring<_CharT, _Traits>( + __p + __pos, __p + __sz, __s, __s + __n); + if (__r == __p + __sz) return __npos; return static_cast<_SizeT>(__r - __p); _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits