[libcxx] r349358 - [libcxx] Speeding up partition_point/lower_bound/upper_bound
Louis Dionne
ldionne at apple.com
Mon Dec 17 08:04:39 PST 2018
Author: ldionne
Date: Mon Dec 17 08:04:39 2018
New Revision: 349358
URL: http://llvm.org/viewvc/llvm-project?rev=349358&view=rev
Log:
[libcxx] Speeding up partition_point/lower_bound/upper_bound
This is a re-application of r345525, which had been reverted by fear of
a regression.
Reviewed as https://reviews.llvm.org/D53994.
Thanks to Denis Yaroshevskiy for the patch.
Added:
libcxx/trunk/benchmarks/algorithms.partition_point.bench.cpp
libcxx/trunk/test/libcxx/algorithms/half_positive.pass.cpp
Modified:
libcxx/trunk/include/algorithm
Added: libcxx/trunk/benchmarks/algorithms.partition_point.bench.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/benchmarks/algorithms.partition_point.bench.cpp?rev=349358&view=auto
==============================================================================
--- libcxx/trunk/benchmarks/algorithms.partition_point.bench.cpp (added)
+++ libcxx/trunk/benchmarks/algorithms.partition_point.bench.cpp Mon Dec 17 08:04:39 2018
@@ -0,0 +1,124 @@
+#include <array>
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <tuple>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+
+#include "CartesianBenchmarks.hpp"
+#include "GenerateInput.hpp"
+
+namespace {
+
+template <typename I, typename N>
+std::array<I, 10> every_10th_percentile_N(I first, N n) {
+ N step = n / 10;
+ std::array<I, 10> res;
+
+ for (size_t i = 0; i < 10; ++i) {
+ res[i] = first;
+ std::advance(first, step);
+ }
+
+ return res;
+}
+
+template <class IntT>
+struct TestIntBase {
+ static std::vector<IntT> generateInput(size_t size) {
+ std::vector<IntT> Res(size);
+ std::generate(Res.begin(), Res.end(),
+ [] { return getRandomInteger<IntT>(); });
+ return Res;
+ }
+};
+
+struct TestInt32 : TestIntBase<std::int32_t> {
+ static constexpr const char* Name = "TestInt32";
+};
+
+struct TestInt64 : TestIntBase<std::int64_t> {
+ static constexpr const char* Name = "TestInt64";
+};
+
+struct TestUint32 : TestIntBase<std::uint32_t> {
+ static constexpr const char* Name = "TestUint32";
+};
+
+struct TestMediumString {
+ static constexpr const char* Name = "TestMediumString";
+ static constexpr size_t StringSize = 32;
+
+ static std::vector<std::string> generateInput(size_t size) {
+ std::vector<std::string> Res(size);
+ std::generate(Res.begin(), Res.end(), [] { return getRandomString(StringSize); });
+ return Res;
+ }
+};
+
+using AllTestTypes = std::tuple<TestInt32, TestInt64, TestUint32, TestMediumString>;
+
+struct LowerBoundAlg {
+ template <class I, class V>
+ I operator()(I first, I last, const V& value) const {
+ return std::lower_bound(first, last, value);
+ }
+
+ static constexpr const char* Name = "LowerBoundAlg";
+};
+
+struct UpperBoundAlg {
+ template <class I, class V>
+ I operator()(I first, I last, const V& value) const {
+ return std::upper_bound(first, last, value);
+ }
+
+ static constexpr const char* Name = "UpperBoundAlg";
+};
+
+struct EqualRangeAlg {
+ template <class I, class V>
+ std::pair<I, I> operator()(I first, I last, const V& value) const {
+ return std::equal_range(first, last, value);
+ }
+
+ static constexpr const char* Name = "EqualRangeAlg";
+};
+
+using AllAlgs = std::tuple<LowerBoundAlg, UpperBoundAlg, EqualRangeAlg>;
+
+template <class Alg, class TestType>
+struct PartitionPointBench {
+ size_t Quantity;
+
+ std::string name() const {
+ return std::string("PartitionPointBench_") + Alg::Name + "_" +
+ TestType::Name + '/' + std::to_string(Quantity);
+ }
+
+ void run(benchmark::State& state) const {
+ auto Data = TestType::generateInput(Quantity);
+ std::sort(Data.begin(), Data.end());
+ auto Every10Percentile = every_10th_percentile_N(Data.begin(), Data.size());
+
+ for (auto _ : state) {
+ for (auto Test : Every10Percentile)
+ benchmark::DoNotOptimize(Alg{}(Data.begin(), Data.end(), *Test));
+ }
+ }
+};
+
+} // namespace
+
+int main(int argc, char** argv) {
+ benchmark::Initialize(&argc, argv);
+ if (benchmark::ReportUnrecognizedArguments(argc, argv))
+ return 1;
+
+ const std::vector<size_t> Quantities = {1 << 8, 1 << 10, 1 << 20};
+ makeCartesianProductBenchmark<PartitionPointBench, AllAlgs, AllTestTypes>(
+ Quantities);
+ benchmark::RunSpecifiedBenchmarks();
+}
Modified: libcxx/trunk/include/algorithm
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/algorithm?rev=349358&r1=349357&r2=349358&view=diff
==============================================================================
--- libcxx/trunk/include/algorithm (original)
+++ libcxx/trunk/include/algorithm Mon Dec 17 08:04:39 2018
@@ -750,6 +750,32 @@ public:
bool operator()(const _T1& __x, const _T2& __y) {return __p_(__y, __x);}
};
+// Perform division by two quickly for positive integers (llvm.org/PR39129)
+
+template <typename _Integral>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+typename enable_if
+<
+ is_integral<_Integral>::value,
+ _Integral
+>::type
+__half_positive(_Integral __value)
+{
+ return static_cast<_Integral>(static_cast<typename make_unsigned<_Integral>::type>(__value) / 2);
+}
+
+template <typename _Tp>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+typename enable_if
+<
+ !is_integral<_Tp>::value,
+ _Tp
+>::type
+__half_positive(_Tp __value)
+{
+ return __value / 2;
+}
+
#ifdef _LIBCPP_DEBUG
template <class _Compare>
@@ -3202,7 +3228,7 @@ partition_point(_ForwardIterator __first
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
- difference_type __l2 = __len / 2;
+ difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__pred(*__m))
@@ -4070,7 +4096,7 @@ __lower_bound(_ForwardIterator __first,
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
- difference_type __l2 = __len / 2;
+ difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))
@@ -4112,7 +4138,7 @@ __upper_bound(_ForwardIterator __first,
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
- difference_type __l2 = __len / 2;
+ difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(__value_, *__m))
@@ -4154,7 +4180,7 @@ __equal_range(_ForwardIterator __first,
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
- difference_type __l2 = __len / 2;
+ difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))
Added: libcxx/trunk/test/libcxx/algorithms/half_positive.pass.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/libcxx/algorithms/half_positive.pass.cpp?rev=349358&view=auto
==============================================================================
--- libcxx/trunk/test/libcxx/algorithms/half_positive.pass.cpp (added)
+++ libcxx/trunk/test/libcxx/algorithms/half_positive.pass.cpp Mon Dec 17 08:04:39 2018
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// __half_positive divides an integer number by 2 as unsigned number for known types.
+// It can be an important optimization for lower bound, for example.
+
+#include <algorithm>
+#include <cassert>
+#include <limits>
+#include <type_traits>
+
+#include "test_macros.h"
+#include "user_defined_integral.hpp"
+
+namespace {
+
+template <class IntType, class UnderlyingType = IntType>
+TEST_CONSTEXPR bool test(IntType max_v = IntType(std::numeric_limits<UnderlyingType>::max())) {
+ return std::__half_positive(max_v) == max_v / 2;
+}
+
+} // namespace
+
+int main()
+{
+ {
+ assert(test<char>());
+ assert(test<int>());
+ assert(test<long>());
+ assert((test<UserDefinedIntegral<int>, int>()));
+ assert(test<size_t>());
+#if !defined(_LIBCPP_HAS_NO_INT128)
+ assert(test<__int128_t>());
+#endif // !defined(_LIBCPP_HAS_NO_INT128)
+ }
+
+#if TEST_STD_VER >= 11
+ {
+ static_assert(test<char>(), "");
+ static_assert(test<int>(), "");
+ static_assert(test<long>(), "");
+ static_assert(test<size_t>(), "");
+#if !defined(_LIBCPP_HAS_NO_INT128)
+ static_assert(test<__int128_t>(), "");
+#endif // !defined(_LIBCPP_HAS_NO_INT128)
+ }
+#endif // TEST_STD_VER >= 11
+}
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