absl/hash/hash_benchmark.cc - third_party/abseil-cpp - Git at Google

 // Copyright 2018 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
 //
 //      https://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.

 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
 #include <string>
 #include <tuple>
 #include <type_traits>
 #include <typeindex>
 #include <utility>
 #include <vector>

 #include "absl/base/attributes.h"
 #include "absl/container/flat_hash_set.h"
 #include "absl/hash/hash.h"
 #include "absl/random/random.h"
 #include "absl/strings/cord.h"
 #include "absl/strings/cord_test_helpers.h"
 #include "absl/strings/string_view.h"
 #include "benchmark/benchmark.h"

 namespace {

 using absl::Hash;

 template <template <typename> class H, typename T>
 void RunBenchmark(benchmark::State& state, T value) {
   H<T> h;
   for (auto _ : state) {
     benchmark::DoNotOptimize(value);
     benchmark::DoNotOptimize(h(value));
   }
 }

 }  // namespace

 template <typename T>
 using AbslHash = absl::Hash<T>;

 class TypeErasedInterface {
  public:
   virtual ~TypeErasedInterface() = default;

   template <typename H>
   friend H AbslHashValue(H state, const TypeErasedInterface& wrapper) {
     state = H::combine(std::move(state), std::type_index(typeid(wrapper)));
     wrapper.HashValue(absl::HashState::Create(&state));
     return state;
   }

  private:
   virtual void HashValue(absl::HashState state) const = 0;
 };

 template <typename T>
 struct TypeErasedAbslHash {
   class Wrapper : public TypeErasedInterface {
    public:
     explicit Wrapper(const T& value) : value_(value) {}

    private:
     void HashValue(absl::HashState state) const override {
       absl::HashState::combine(std::move(state), value_);
     }

     const T& value_;
   };

   size_t operator()(const T& value) {
     return absl::Hash<Wrapper>{}(Wrapper(value));
   }
 };

 absl::Cord FlatCord(size_t size) {
   absl::Cord result(std::string(size, 'a'));
   result.Flatten();
   return result;
 }

 absl::Cord FragmentedCord(size_t size) {
   const size_t orig_size = size;
   std::vector<std::string> chunks;
   size_t chunk_size = std::max<size_t>(1, size / 10);
   while (size > chunk_size) {
     chunks.push_back(std::string(chunk_size, 'a'));
     size -= chunk_size;
   }
   if (size > 0) {
     chunks.push_back(std::string(size, 'a'));
   }
   absl::Cord result = absl::MakeFragmentedCord(chunks);
   (void) orig_size;
   assert(result.size() == orig_size);
   return result;
 }

 template <typename T>
 std::vector<T> Vector(size_t count) {
   std::vector<T> result;
   for (size_t v = 0; v < count; ++v) {
     result.push_back(v);
   }
   return result;
 }

 // Bogus type that replicates an unorderd_set's bit mixing, but with
 // vector-speed iteration. This is intended to measure the overhead of unordered
 // hashing without counting the speed of unordered_set iteration.
 template <typename T>
 struct FastUnorderedSet {
   explicit FastUnorderedSet(size_t count) {
     for (size_t v = 0; v < count; ++v) {
       values.push_back(v);
     }
   }
   std::vector<T> values;

   template <typename H>
   friend H AbslHashValue(H h, const FastUnorderedSet& fus) {
     return H::combine(H::combine_unordered(std::move(h), fus.values.begin(),
                                            fus.values.end()),
                       fus.values.size());
   }
 };

 template <typename T>
 absl::flat_hash_set<T> FlatHashSet(size_t count) {
   absl::flat_hash_set<T> result;
   for (size_t v = 0; v < count; ++v) {
     result.insert(v);
   }
   return result;
 }

 // Generates a benchmark and a codegen method for the provided types.  The
 // codegen method provides a well known entrypoint for dumping assembly.
 #define MAKE_BENCHMARK(hash, name, ...)                          \
   namespace {                                                    \
   void BM_##hash##_##name(benchmark::State& state) {             \
     RunBenchmark<hash>(state, __VA_ARGS__);                      \
   }                                                              \
   BENCHMARK(BM_##hash##_##name);                                 \
   }                                                              \
   size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg);  \
   size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg) { \
     return hash<decltype(__VA_ARGS__)>{}(arg);                   \
   }                                                              \
   bool absl_hash_test_odr_use##hash##name =                      \
       (benchmark::DoNotOptimize(&Codegen##hash##name), false);

 MAKE_BENCHMARK(AbslHash, Int32, int32_t{});
 MAKE_BENCHMARK(AbslHash, Int64, int64_t{});
 MAKE_BENCHMARK(AbslHash, Double, 1.2);
 MAKE_BENCHMARK(AbslHash, DoubleZero, 0.0);
 MAKE_BENCHMARK(AbslHash, PairInt32Int32, std::pair<int32_t, int32_t>{});
 MAKE_BENCHMARK(AbslHash, PairInt64Int64, std::pair<int64_t, int64_t>{});
 MAKE_BENCHMARK(AbslHash, TupleInt32BoolInt64,
                std::tuple<int32_t, bool, int64_t>{});
 MAKE_BENCHMARK(AbslHash, String_0, std::string());
 MAKE_BENCHMARK(AbslHash, String_10, std::string(10, 'a'));
 MAKE_BENCHMARK(AbslHash, String_30, std::string(30, 'a'));
 MAKE_BENCHMARK(AbslHash, String_90, std::string(90, 'a'));
 MAKE_BENCHMARK(AbslHash, String_200, std::string(200, 'a'));
 MAKE_BENCHMARK(AbslHash, String_5000, std::string(5000, 'a'));
 MAKE_BENCHMARK(AbslHash, Cord_Flat_0, absl::Cord());
 MAKE_BENCHMARK(AbslHash, Cord_Flat_10, FlatCord(10));
 MAKE_BENCHMARK(AbslHash, Cord_Flat_30, FlatCord(30));
 MAKE_BENCHMARK(AbslHash, Cord_Flat_90, FlatCord(90));
 MAKE_BENCHMARK(AbslHash, Cord_Flat_200, FlatCord(200));
 MAKE_BENCHMARK(AbslHash, Cord_Flat_5000, FlatCord(5000));
 MAKE_BENCHMARK(AbslHash, Cord_Fragmented_200, FragmentedCord(200));
 MAKE_BENCHMARK(AbslHash, Cord_Fragmented_5000, FragmentedCord(5000));
 MAKE_BENCHMARK(AbslHash, VectorInt64_10, Vector<int64_t>(10));
 MAKE_BENCHMARK(AbslHash, VectorInt64_100, Vector<int64_t>(100));
 MAKE_BENCHMARK(AbslHash, VectorInt64_1000, Vector<int64_t>(1000));
 MAKE_BENCHMARK(AbslHash, VectorDouble_10, Vector<double>(10));
 MAKE_BENCHMARK(AbslHash, VectorDouble_100, Vector<double>(100));
 MAKE_BENCHMARK(AbslHash, VectorDouble_1000, Vector<double>(1000));
 MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_10, FlatHashSet<int64_t>(10));
 MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_100, FlatHashSet<int64_t>(100));
 MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_1000, FlatHashSet<int64_t>(1000));
 MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_10, FlatHashSet<double>(10));
 MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_100, FlatHashSet<double>(100));
 MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_1000, FlatHashSet<double>(1000));
 MAKE_BENCHMARK(AbslHash, FastUnorderedSetInt64_1000,
                FastUnorderedSet<int64_t>(1000));
 MAKE_BENCHMARK(AbslHash, FastUnorderedSetDouble_1000,
                FastUnorderedSet<double>(1000));
 MAKE_BENCHMARK(AbslHash, PairStringString_0,
                std::make_pair(std::string(), std::string()));
 MAKE_BENCHMARK(AbslHash, PairStringString_10,
                std::make_pair(std::string(10, 'a'), std::string(10, 'b')));
 MAKE_BENCHMARK(AbslHash, PairStringString_30,
                std::make_pair(std::string(30, 'a'), std::string(30, 'b')));
 MAKE_BENCHMARK(AbslHash, PairStringString_90,
                std::make_pair(std::string(90, 'a'), std::string(90, 'b')));
 MAKE_BENCHMARK(AbslHash, PairStringString_200,
                std::make_pair(std::string(200, 'a'), std::string(200, 'b')));
 MAKE_BENCHMARK(AbslHash, PairStringString_5000,
                std::make_pair(std::string(5000, 'a'), std::string(5000, 'b')));

 MAKE_BENCHMARK(TypeErasedAbslHash, Int32, int32_t{});
 MAKE_BENCHMARK(TypeErasedAbslHash, Int64, int64_t{});
 MAKE_BENCHMARK(TypeErasedAbslHash, PairInt32Int32,
                std::pair<int32_t, int32_t>{});
 MAKE_BENCHMARK(TypeErasedAbslHash, PairInt64Int64,
                std::pair<int64_t, int64_t>{});
 MAKE_BENCHMARK(TypeErasedAbslHash, TupleInt32BoolInt64,
                std::tuple<int32_t, bool, int64_t>{});
 MAKE_BENCHMARK(TypeErasedAbslHash, String_0, std::string());
 MAKE_BENCHMARK(TypeErasedAbslHash, String_10, std::string(10, 'a'));
 MAKE_BENCHMARK(TypeErasedAbslHash, String_30, std::string(30, 'a'));
 MAKE_BENCHMARK(TypeErasedAbslHash, String_90, std::string(90, 'a'));
 MAKE_BENCHMARK(TypeErasedAbslHash, String_200, std::string(200, 'a'));
 MAKE_BENCHMARK(TypeErasedAbslHash, String_5000, std::string(5000, 'a'));
 MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_10,
                std::vector<double>(10, 1.1));
 MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_100,
                std::vector<double>(100, 1.1));
 MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_1000,
                std::vector<double>(1000, 1.1));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_10,
                FlatHashSet<int64_t>(10));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_100,
                FlatHashSet<int64_t>(100));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_1000,
                FlatHashSet<int64_t>(1000));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_10,
                FlatHashSet<double>(10));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_100,
                FlatHashSet<double>(100));
 MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_1000,
                FlatHashSet<double>(1000));
 MAKE_BENCHMARK(TypeErasedAbslHash, FastUnorderedSetInt64_1000,
                FastUnorderedSet<int64_t>(1000));
 MAKE_BENCHMARK(TypeErasedAbslHash, FastUnorderedSetDouble_1000,
                FastUnorderedSet<double>(1000));

 // The latency benchmark attempts to model the speed of the hash function in
 // production. When a hash function is used for hashtable lookups it is rarely
 // used to hash N items in a tight loop nor on constant sized strings. Instead,
 // after hashing there is a potential equality test plus a (usually) large
 // amount of user code. To simulate this effectively we introduce a data
 // dependency between elements we hash by using the hash of the Nth element as
 // the selector of the N+1th element to hash. This isolates the hash function
 // code much like in production. As a bonus we use the hash to generate strings
 // of size [1,N] (instead of fixed N) to disable perfect branch predictions in
 // hash function implementations.
 namespace {
 // 16kb fits in L1 cache of most CPUs we care about. Keeping memory latency low
 // will allow us to attribute most time to CPU which means more accurate
 // measurements.
 static constexpr size_t kEntropySize = 16 << 10;
 static char entropy[kEntropySize + 1024];
 ABSL_ATTRIBUTE_UNUSED static const bool kInitialized = [] {
   absl::BitGen gen;
   static_assert(sizeof(entropy) % sizeof(uint64_t) == 0, "");
   for (int i = 0; i != sizeof(entropy); i += sizeof(uint64_t)) {
     auto rand = absl::Uniform<uint64_t>(gen);
     memcpy(&entropy[i], &rand, sizeof(uint64_t));
   }
   return true;
 }();
 }  // namespace

 template <class T>
 struct PodRand {
   static_assert(std::is_pod<T>::value, "");
   static_assert(kEntropySize + sizeof(T) < sizeof(entropy), "");

   T Get(size_t i) const {
     T v;
     memcpy(&v, &entropy[i % kEntropySize], sizeof(T));
     return v;
   }
 };

 template <size_t N>
 struct StringRand {
   static_assert(kEntropySize + N < sizeof(entropy), "");

   absl::string_view Get(size_t i) const {
     // This has a small bias towards small numbers. Because max N is ~200 this
     // is very small and prefer to be very fast instead of absolutely accurate.
     // Also we pass N = 2^K+1 so that mod reduces to a bitand.
     size_t s = (i % (N - 1)) + 1;
     return {&entropy[i % kEntropySize], s};
   }
 };

 #define MAKE_LATENCY_BENCHMARK(hash, name, ...)              \
   namespace {                                                \
   void BM_latency_##hash##_##name(benchmark::State& state) { \
     __VA_ARGS__ r;                                           \
     hash<decltype(r.Get(0))> h;                              \
     size_t i = 871401241;                                    \
     for (auto _ : state) {                                   \
       benchmark::DoNotOptimize(i = h(r.Get(i)));             \
     }                                                        \
   }                                                          \
   BENCHMARK(BM_latency_##hash##_##name);                     \
   }  // namespace

 MAKE_LATENCY_BENCHMARK(AbslHash, Int32, PodRand<int32_t>);
 MAKE_LATENCY_BENCHMARK(AbslHash, Int64, PodRand<int64_t>);
 MAKE_LATENCY_BENCHMARK(AbslHash, String9, StringRand<9>);
 MAKE_LATENCY_BENCHMARK(AbslHash, String33, StringRand<33>);
 MAKE_LATENCY_BENCHMARK(AbslHash, String65, StringRand<65>);
 MAKE_LATENCY_BENCHMARK(AbslHash, String257, StringRand<257>);
	// Copyright 2018 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
	//
	// https://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.

	#include <algorithm>
	#include <cassert>
	#include <cstddef>
	#include <cstdint>
	#include <cstring>
	#include <string>
	#include <tuple>
	#include <type_traits>
	#include <typeindex>
	#include <utility>
	#include <vector>

	#include "absl/base/attributes.h"
	#include "absl/container/flat_hash_set.h"
	#include "absl/hash/hash.h"
	#include "absl/random/random.h"
	#include "absl/strings/cord.h"
	#include "absl/strings/cord_test_helpers.h"
	#include "absl/strings/string_view.h"
	#include "benchmark/benchmark.h"

	namespace {

	using absl::Hash;

	template <template <typename> class H, typename T>
	void RunBenchmark(benchmark::State& state, T value) {
	H<T> h;
	for (auto _ : state) {
	benchmark::DoNotOptimize(value);
	benchmark::DoNotOptimize(h(value));
	}
	}

	} // namespace

	template <typename T>
	using AbslHash = absl::Hash<T>;

	class TypeErasedInterface {
	public:
	virtual ~TypeErasedInterface() = default;

	template <typename H>
	friend H AbslHashValue(H state, const TypeErasedInterface& wrapper) {
	state = H::combine(std::move(state), std::type_index(typeid(wrapper)));
	wrapper.HashValue(absl::HashState::Create(&state));
	return state;
	}

	private:
	virtual void HashValue(absl::HashState state) const = 0;
	};

	template <typename T>
	struct TypeErasedAbslHash {
	class Wrapper : public TypeErasedInterface {
	public:
	explicit Wrapper(const T& value) : value_(value) {}

	private:
	void HashValue(absl::HashState state) const override {
	absl::HashState::combine(std::move(state), value_);
	}

	const T& value_;
	};

	size_t operator()(const T& value) {
	return absl::Hash<Wrapper>{}(Wrapper(value));
	}
	};

	absl::Cord FlatCord(size_t size) {
	absl::Cord result(std::string(size, 'a'));
	result.Flatten();
	return result;
	}

	absl::Cord FragmentedCord(size_t size) {
	const size_t orig_size = size;
	std::vector<std::string> chunks;
	size_t chunk_size = std::max<size_t>(1, size / 10);
	while (size > chunk_size) {
	chunks.push_back(std::string(chunk_size, 'a'));
	size -= chunk_size;
	}
	if (size > 0) {
	chunks.push_back(std::string(size, 'a'));
	}
	absl::Cord result = absl::MakeFragmentedCord(chunks);
	(void) orig_size;
	assert(result.size() == orig_size);
	return result;
	}

	template <typename T>
	std::vector<T> Vector(size_t count) {
	std::vector<T> result;
	for (size_t v = 0; v < count; ++v) {
	result.push_back(v);
	}
	return result;
	}

	// Bogus type that replicates an unorderd_set's bit mixing, but with
	// vector-speed iteration. This is intended to measure the overhead of unordered
	// hashing without counting the speed of unordered_set iteration.
	template <typename T>
	struct FastUnorderedSet {
	explicit FastUnorderedSet(size_t count) {
	for (size_t v = 0; v < count; ++v) {
	values.push_back(v);
	}
	}
	std::vector<T> values;

	template <typename H>
	friend H AbslHashValue(H h, const FastUnorderedSet& fus) {
	return H::combine(H::combine_unordered(std::move(h), fus.values.begin(),
	fus.values.end()),
	fus.values.size());
	}
	};

	template <typename T>
	absl::flat_hash_set<T> FlatHashSet(size_t count) {
	absl::flat_hash_set<T> result;
	for (size_t v = 0; v < count; ++v) {
	result.insert(v);
	}
	return result;
	}

	// Generates a benchmark and a codegen method for the provided types. The
	// codegen method provides a well known entrypoint for dumping assembly.
	#define MAKE_BENCHMARK(hash, name, ...) \
	namespace { \
	void BM_##hash##_##name(benchmark::State& state) { \
	RunBenchmark<hash>(state, __VA_ARGS__); \
	} \
	BENCHMARK(BM_##hash##_##name); \
	} \
	size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg); \
	size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg) { \
	return hash<decltype(__VA_ARGS__)>{}(arg); \
	} \
	bool absl_hash_test_odr_use##hash##name = \
	(benchmark::DoNotOptimize(&Codegen##hash##name), false);

	MAKE_BENCHMARK(AbslHash, Int32, int32_t{});
	MAKE_BENCHMARK(AbslHash, Int64, int64_t{});
	MAKE_BENCHMARK(AbslHash, Double, 1.2);
	MAKE_BENCHMARK(AbslHash, DoubleZero, 0.0);
	MAKE_BENCHMARK(AbslHash, PairInt32Int32, std::pair<int32_t, int32_t>{});
	MAKE_BENCHMARK(AbslHash, PairInt64Int64, std::pair<int64_t, int64_t>{});
	MAKE_BENCHMARK(AbslHash, TupleInt32BoolInt64,
	std::tuple<int32_t, bool, int64_t>{});
	MAKE_BENCHMARK(AbslHash, String_0, std::string());
	MAKE_BENCHMARK(AbslHash, String_10, std::string(10, 'a'));
	MAKE_BENCHMARK(AbslHash, String_30, std::string(30, 'a'));
	MAKE_BENCHMARK(AbslHash, String_90, std::string(90, 'a'));
	MAKE_BENCHMARK(AbslHash, String_200, std::string(200, 'a'));
	MAKE_BENCHMARK(AbslHash, String_5000, std::string(5000, 'a'));
	MAKE_BENCHMARK(AbslHash, Cord_Flat_0, absl::Cord());
	MAKE_BENCHMARK(AbslHash, Cord_Flat_10, FlatCord(10));
	MAKE_BENCHMARK(AbslHash, Cord_Flat_30, FlatCord(30));
	MAKE_BENCHMARK(AbslHash, Cord_Flat_90, FlatCord(90));
	MAKE_BENCHMARK(AbslHash, Cord_Flat_200, FlatCord(200));
	MAKE_BENCHMARK(AbslHash, Cord_Flat_5000, FlatCord(5000));
	MAKE_BENCHMARK(AbslHash, Cord_Fragmented_200, FragmentedCord(200));
	MAKE_BENCHMARK(AbslHash, Cord_Fragmented_5000, FragmentedCord(5000));
	MAKE_BENCHMARK(AbslHash, VectorInt64_10, Vector<int64_t>(10));
	MAKE_BENCHMARK(AbslHash, VectorInt64_100, Vector<int64_t>(100));
	MAKE_BENCHMARK(AbslHash, VectorInt64_1000, Vector<int64_t>(1000));
	MAKE_BENCHMARK(AbslHash, VectorDouble_10, Vector<double>(10));
	MAKE_BENCHMARK(AbslHash, VectorDouble_100, Vector<double>(100));
	MAKE_BENCHMARK(AbslHash, VectorDouble_1000, Vector<double>(1000));
	MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_10, FlatHashSet<int64_t>(10));
	MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_100, FlatHashSet<int64_t>(100));
	MAKE_BENCHMARK(AbslHash, FlatHashSetInt64_1000, FlatHashSet<int64_t>(1000));
	MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_10, FlatHashSet<double>(10));
	MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_100, FlatHashSet<double>(100));
	MAKE_BENCHMARK(AbslHash, FlatHashSetDouble_1000, FlatHashSet<double>(1000));
	MAKE_BENCHMARK(AbslHash, FastUnorderedSetInt64_1000,
	FastUnorderedSet<int64_t>(1000));
	MAKE_BENCHMARK(AbslHash, FastUnorderedSetDouble_1000,
	FastUnorderedSet<double>(1000));
	MAKE_BENCHMARK(AbslHash, PairStringString_0,
	std::make_pair(std::string(), std::string()));
	MAKE_BENCHMARK(AbslHash, PairStringString_10,
	std::make_pair(std::string(10, 'a'), std::string(10, 'b')));
	MAKE_BENCHMARK(AbslHash, PairStringString_30,
	std::make_pair(std::string(30, 'a'), std::string(30, 'b')));
	MAKE_BENCHMARK(AbslHash, PairStringString_90,
	std::make_pair(std::string(90, 'a'), std::string(90, 'b')));
	MAKE_BENCHMARK(AbslHash, PairStringString_200,
	std::make_pair(std::string(200, 'a'), std::string(200, 'b')));
	MAKE_BENCHMARK(AbslHash, PairStringString_5000,
	std::make_pair(std::string(5000, 'a'), std::string(5000, 'b')));

	MAKE_BENCHMARK(TypeErasedAbslHash, Int32, int32_t{});
	MAKE_BENCHMARK(TypeErasedAbslHash, Int64, int64_t{});
	MAKE_BENCHMARK(TypeErasedAbslHash, PairInt32Int32,
	std::pair<int32_t, int32_t>{});
	MAKE_BENCHMARK(TypeErasedAbslHash, PairInt64Int64,
	std::pair<int64_t, int64_t>{});
	MAKE_BENCHMARK(TypeErasedAbslHash, TupleInt32BoolInt64,
	std::tuple<int32_t, bool, int64_t>{});
	MAKE_BENCHMARK(TypeErasedAbslHash, String_0, std::string());
	MAKE_BENCHMARK(TypeErasedAbslHash, String_10, std::string(10, 'a'));
	MAKE_BENCHMARK(TypeErasedAbslHash, String_30, std::string(30, 'a'));
	MAKE_BENCHMARK(TypeErasedAbslHash, String_90, std::string(90, 'a'));
	MAKE_BENCHMARK(TypeErasedAbslHash, String_200, std::string(200, 'a'));
	MAKE_BENCHMARK(TypeErasedAbslHash, String_5000, std::string(5000, 'a'));
	MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_10,
	std::vector<double>(10, 1.1));
	MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_100,
	std::vector<double>(100, 1.1));
	MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_1000,
	std::vector<double>(1000, 1.1));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_10,
	FlatHashSet<int64_t>(10));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_100,
	FlatHashSet<int64_t>(100));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetInt64_1000,
	FlatHashSet<int64_t>(1000));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_10,
	FlatHashSet<double>(10));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_100,
	FlatHashSet<double>(100));
	MAKE_BENCHMARK(TypeErasedAbslHash, FlatHashSetDouble_1000,
	FlatHashSet<double>(1000));
	MAKE_BENCHMARK(TypeErasedAbslHash, FastUnorderedSetInt64_1000,
	FastUnorderedSet<int64_t>(1000));
	MAKE_BENCHMARK(TypeErasedAbslHash, FastUnorderedSetDouble_1000,
	FastUnorderedSet<double>(1000));

	// The latency benchmark attempts to model the speed of the hash function in
	// production. When a hash function is used for hashtable lookups it is rarely
	// used to hash N items in a tight loop nor on constant sized strings. Instead,
	// after hashing there is a potential equality test plus a (usually) large
	// amount of user code. To simulate this effectively we introduce a data
	// dependency between elements we hash by using the hash of the Nth element as
	// the selector of the N+1th element to hash. This isolates the hash function
	// code much like in production. As a bonus we use the hash to generate strings
	// of size [1,N] (instead of fixed N) to disable perfect branch predictions in
	// hash function implementations.
	namespace {
	// 16kb fits in L1 cache of most CPUs we care about. Keeping memory latency low
	// will allow us to attribute most time to CPU which means more accurate
	// measurements.
	static constexpr size_t kEntropySize = 16 << 10;
	static char entropy[kEntropySize + 1024];
	ABSL_ATTRIBUTE_UNUSED static const bool kInitialized = [] {
	absl::BitGen gen;
	static_assert(sizeof(entropy) % sizeof(uint64_t) == 0, "");
	for (int i = 0; i != sizeof(entropy); i += sizeof(uint64_t)) {
	auto rand = absl::Uniform<uint64_t>(gen);
	memcpy(&entropy[i], &rand, sizeof(uint64_t));
	}
	return true;
	}();
	} // namespace

	template <class T>
	struct PodRand {
	static_assert(std::is_pod<T>::value, "");
	static_assert(kEntropySize + sizeof(T) < sizeof(entropy), "");

	T Get(size_t i) const {
	T v;
	memcpy(&v, &entropy[i % kEntropySize], sizeof(T));
	return v;
	}
	};

	template <size_t N>
	struct StringRand {
	static_assert(kEntropySize + N < sizeof(entropy), "");

	absl::string_view Get(size_t i) const {
	// This has a small bias towards small numbers. Because max N is ~200 this
	// is very small and prefer to be very fast instead of absolutely accurate.
	// Also we pass N = 2^K+1 so that mod reduces to a bitand.
	size_t s = (i % (N - 1)) + 1;
	return {&entropy[i % kEntropySize], s};
	}
	};

	#define MAKE_LATENCY_BENCHMARK(hash, name, ...) \
	namespace { \
	void BM_latency_##hash##_##name(benchmark::State& state) { \
	__VA_ARGS__ r; \
	hash<decltype(r.Get(0))> h; \
	size_t i = 871401241; \
	for (auto _ : state) { \
	benchmark::DoNotOptimize(i = h(r.Get(i))); \
	} \
	} \
	BENCHMARK(BM_latency_##hash##_##name); \
	} // namespace

	MAKE_LATENCY_BENCHMARK(AbslHash, Int32, PodRand<int32_t>);
	MAKE_LATENCY_BENCHMARK(AbslHash, Int64, PodRand<int64_t>);
	MAKE_LATENCY_BENCHMARK(AbslHash, String9, StringRand<9>);
	MAKE_LATENCY_BENCHMARK(AbslHash, String33, StringRand<33>);
	MAKE_LATENCY_BENCHMARK(AbslHash, String65, StringRand<65>);
	MAKE_LATENCY_BENCHMARK(AbslHash, String257, StringRand<257>);