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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit tests for the variant template. The 'is' and 'IsEmpty' methods
+// of variant are not explicitly tested because they are used repeatedly
+// in building other tests. All other public variant methods should have
+// explicit tests.
+
+#include "absl/types/variant.h"
+
+#include <cstddef>
+#include <cstdlib>
+#include <string>
+#include <tuple>
+
+#include "benchmark/benchmark.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+inline namespace lts_2018_06_20 {
+namespace {
+
+template <std::size_t I>
+struct VariantAlternative {
+ char member;
+};
+
+template <class Indices>
+struct VariantOfAlternativesImpl;
+
+template <std::size_t... Indices>
+struct VariantOfAlternativesImpl<absl::index_sequence<Indices...>> {
+ using type = absl::variant<VariantAlternative<Indices>...>;
+};
+
+template <std::size_t NumAlternatives>
+using VariantOfAlternatives = typename VariantOfAlternativesImpl<
+ absl::make_index_sequence<NumAlternatives>>::type;
+
+struct Empty {};
+
+template <class... T>
+void Ignore(T...) noexcept {}
+
+template <class T>
+Empty DoNotOptimizeAndReturnEmpty(T&& arg) noexcept {
+ benchmark::DoNotOptimize(arg);
+ return {};
+}
+
+struct VisitorApplier {
+ struct Visitor {
+ template <class... T>
+ void operator()(T&&... args) const noexcept {
+ Ignore(DoNotOptimizeAndReturnEmpty(args)...);
+ }
+ };
+
+ template <class... Vars>
+ void operator()(const Vars&... vars) const noexcept {
+ absl::visit(Visitor(), vars...);
+ }
+};
+
+template <std::size_t NumIndices, std::size_t CurrIndex = NumIndices - 1>
+struct MakeWithIndex {
+ using Variant = VariantOfAlternatives<NumIndices>;
+
+ static Variant Run(std::size_t index) {
+ return index == CurrIndex
+ ? Variant(absl::in_place_index_t<CurrIndex>())
+ : MakeWithIndex<NumIndices, CurrIndex - 1>::Run(index);
+ }
+};
+
+template <std::size_t NumIndices>
+struct MakeWithIndex<NumIndices, 0> {
+ using Variant = VariantOfAlternatives<NumIndices>;
+
+ static Variant Run(std::size_t /*index*/) { return Variant(); }
+};
+
+template <std::size_t NumIndices, class Dimensions>
+struct MakeVariantTuple;
+
+template <class T, std::size_t /*I*/>
+using always_t = T;
+
+template <std::size_t NumIndices>
+VariantOfAlternatives<NumIndices> MakeVariant(std::size_t dimension,
+ std::size_t index) {
+ return dimension == 0
+ ? MakeWithIndex<NumIndices>::Run(index % NumIndices)
+ : MakeVariant<NumIndices>(dimension - 1, index / NumIndices);
+}
+
+template <std::size_t NumIndices, std::size_t... Dimensions>
+struct MakeVariantTuple<NumIndices, absl::index_sequence<Dimensions...>> {
+ using VariantTuple =
+ std::tuple<always_t<VariantOfAlternatives<NumIndices>, Dimensions>...>;
+
+ static VariantTuple Run(int index) {
+ return std::make_tuple(MakeVariant<NumIndices>(Dimensions, index)...);
+ }
+};
+
+constexpr std::size_t integral_pow(std::size_t base, std::size_t power) {
+ return power == 0 ? 1 : base * integral_pow(base, power - 1);
+}
+
+template <std::size_t End, std::size_t I = 0>
+struct VisitTestBody {
+ template <class Vars, class State>
+ static bool Run(Vars& vars, State& state) {
+ if (state.KeepRunning()) {
+ absl::apply(VisitorApplier(), vars[I]);
+ return VisitTestBody<End, I + 1>::Run(vars, state);
+ }
+ return false;
+ }
+};
+
+template <std::size_t End>
+struct VisitTestBody<End, End> {
+ template <class Vars, class State>
+ static bool Run(Vars& /*vars*/, State& /*state*/) {
+ return true;
+ }
+};
+
+// Visit operations where branch prediction is likely to give a boost.
+template <std::size_t NumIndices, std::size_t NumDimensions = 1>
+void BM_RedundantVisit(benchmark::State& state) {
+ auto vars =
+ MakeVariantTuple<NumIndices, absl::make_index_sequence<NumDimensions>>::
+ Run(static_cast<std::size_t>(state.range(0)));
+
+ for (auto _ : state) { // NOLINT
+ benchmark::DoNotOptimize(vars);
+ absl::apply(VisitorApplier(), vars);
+ }
+}
+
+// Visit operations where branch prediction is unlikely to give a boost.
+template <std::size_t NumIndices, std::size_t NumDimensions = 1>
+void BM_Visit(benchmark::State& state) {
+ constexpr std::size_t num_possibilities =
+ integral_pow(NumIndices, NumDimensions);
+
+ using VariantTupleMaker =
+ MakeVariantTuple<NumIndices, absl::make_index_sequence<NumDimensions>>;
+ using Tuple = typename VariantTupleMaker::VariantTuple;
+
+ Tuple vars[num_possibilities];
+ for (std::size_t i = 0; i < num_possibilities; ++i)
+ vars[i] = VariantTupleMaker::Run(i);
+
+ while (VisitTestBody<num_possibilities>::Run(vars, state)) {
+ }
+}
+
+// Visitation
+// Each visit is on a different variant with a different active alternative)
+
+// Unary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1);
+BENCHMARK_TEMPLATE(BM_Visit, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 4);
+BENCHMARK_TEMPLATE(BM_Visit, 5);
+BENCHMARK_TEMPLATE(BM_Visit, 6);
+BENCHMARK_TEMPLATE(BM_Visit, 7);
+BENCHMARK_TEMPLATE(BM_Visit, 8);
+BENCHMARK_TEMPLATE(BM_Visit, 16);
+BENCHMARK_TEMPLATE(BM_Visit, 32);
+BENCHMARK_TEMPLATE(BM_Visit, 64);
+
+// Binary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 3, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 4, 2);
+BENCHMARK_TEMPLATE(BM_Visit, 5, 2);
+
+// Ternary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 3);
+BENCHMARK_TEMPLATE(BM_Visit, 3, 3);
+
+// Quaternary visit
+BENCHMARK_TEMPLATE(BM_Visit, 1, 4);
+BENCHMARK_TEMPLATE(BM_Visit, 2, 4);
+
+// Redundant Visitation
+// Each visit consistently has the same alternative active
+
+// Unary visit
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 1)->Arg(0);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 2)->DenseRange(0, 1);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 8)->DenseRange(0, 7);
+
+// Binary visit
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 1, 2)->Arg(0);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 2, 2)
+ ->DenseRange(0, integral_pow(2, 2) - 1);
+BENCHMARK_TEMPLATE(BM_RedundantVisit, 4, 2)
+ ->DenseRange(0, integral_pow(4, 2) - 1);
+
+} // namespace
+} // inline namespace lts_2018_06_20
+} // namespace absl