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Bug 39129: Speeding up partition_point/lower_bound/upper_bound/ by using unsigned division by 2 when possible.

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Patch by Denis Yaroshevskiy (denis.yaroshevskij@gmail.com)

The rational and measurements can be found in the bug description: https://bugs.llvm.org/show_bug.cgi?id=39129

Reviewed as https://reviews.llvm.org/D52697


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345525 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2018-10-29 19:25:02 +00:00
parent 081dda5c16
commit 207b919735
3 changed files with 153 additions and 4 deletions
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64
benchmarks/algorithms.bench.cpp
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@@ -58,5 +58,69 @@ BENCHMARK_CAPTURE(BM_Sort, sorted_descending_strings,
BENCHMARK_CAPTURE(BM_Sort, single_element_strings,
getDuplicateStringInputs)->Arg(TestNumInputs);
template <typename GenInputs, typename Alg>
void do_binary_search_benchmark(benchmark::State& st, GenInputs gen, Alg alg)
{
using ValueType = typename decltype(gen(0))::value_type;
auto in = gen(st.range(0));
std::sort(in.begin(), in.end());
const auto every_10_percentile = [&]() -> std::vector<ValueType*> {
size_t step = in.size() / 10;
if (step == 0) {
st.SkipWithError("Input doesn't contain enough elements");
return {};
}
std::vector<ValueType*> res;
for (size_t i = 0; i < in.size(); i += step)
res.push_back(&in[i]);
return res;
}();
for (auto _ : st)
{
for (auto* test : every_10_percentile)
benchmark::DoNotOptimize(alg(in.begin(), in.end(), *test));
}
}
template <typename GenInputs>
void BM_LowerBound(benchmark::State& st, GenInputs gen)
{
do_binary_search_benchmark(st, gen, [](auto f, auto l, const auto& v) {
return std::lower_bound(f, l, v);
});
}
BENCHMARK_CAPTURE(BM_LowerBound, random_int32, getRandomIntegerInputs<int32_t>)
->Arg(TestNumInputs) // Small int32_t vector
->Arg(TestNumInputs * TestNumInputs); // Big int32_t vector
BENCHMARK_CAPTURE(BM_LowerBound, random_int64, getRandomIntegerInputs<int64_t>)
->Arg(TestNumInputs); // Small int64_t vector. Should also represent pointers.
BENCHMARK_CAPTURE(BM_LowerBound, random_strings, getRandomStringInputs)
->Arg(TestNumInputs); // Small string vector. What happens if the comparison is not very cheap.
template <typename GenInputs>
void BM_EqualRange(benchmark::State& st, GenInputs gen)
{
do_binary_search_benchmark(st, gen, [](auto f, auto l, const auto& v) {
return std::equal_range(f, l, v);
});
}
BENCHMARK_CAPTURE(BM_EqualRange, random_int32, getRandomIntegerInputs<int32_t>)
->Arg(TestNumInputs) // Small int32_t vector
->Arg(TestNumInputs * TestNumInputs); // Big int32_t vector
BENCHMARK_CAPTURE(BM_EqualRange, random_int64, getRandomIntegerInputs<int64_t>)
->Arg(TestNumInputs); // Small int64_t vector. Should also represent pointers.
BENCHMARK_CAPTURE(BM_EqualRange, random_strings, getRandomStringInputs)
->Arg(TestNumInputs); // Small string vector. What happens if the comparison is not very cheap.
BENCHMARK_MAIN();