libcxx/benchmarks/string.bench.cpp - rust-lang/llvm-project - Git at Google


 #include <cstdint>
 #include <new>
 #include <vector>

 #include "CartesianBenchmarks.hpp"
 #include "GenerateInput.hpp"
 #include "benchmark/benchmark.h"
 #include "test_macros.h"

 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, '*');
   for (auto _ : state)
     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), '-');
   for (auto _ : state)
     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), '-');
   for (auto _ : state)
     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), '-');
   for (auto _ : state)
     benchmark::DoNotOptimize(s1.find(s2));
 }
 BENCHMARK(BM_StringFindMatch2)->Range(1, MAX_STRING_LEN / 4);

 static void BM_StringCtorDefault(benchmark::State &state) {
   for (auto _ : state) {
     std::string Default;
     benchmark::DoNotOptimize(Default);
   }
 }
 BENCHMARK(BM_StringCtorDefault);

 enum class Length { Empty, Small, Large, Huge };
 struct AllLengths : EnumValuesAsTuple<AllLengths, Length, 4> {
   static constexpr const char* Names[] = {"Empty", "Small", "Large", "Huge"};
 };

 enum class Opacity { Opaque, Transparent };
 struct AllOpacity : EnumValuesAsTuple<AllOpacity, Opacity, 2> {
   static constexpr const char* Names[] = {"Opaque", "Transparent"};
 };

 enum class DiffType { Control, ChangeFirst, ChangeMiddle, ChangeLast };
 struct AllDiffTypes : EnumValuesAsTuple<AllDiffTypes, DiffType, 4> {
   static constexpr const char* Names[] = {"Control", "ChangeFirst",
                                           "ChangeMiddle", "ChangeLast"};
 };

 TEST_ALWAYS_INLINE const char* getSmallString(DiffType D) {
   switch (D) {
     case DiffType::Control:
       return "0123456";
     case DiffType::ChangeFirst:
       return "-123456";
     case DiffType::ChangeMiddle:
       return "012-456";
     case DiffType::ChangeLast:
       return "012345-";
   }
 }

 TEST_ALWAYS_INLINE const char* getLargeString(DiffType D) {
 #define LARGE_STRING_FIRST "123456789012345678901234567890"
 #define LARGE_STRING_SECOND "234567890123456789012345678901"
   switch (D) {
     case DiffType::Control:
       return "0" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "2";
     case DiffType::ChangeFirst:
       return "-" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "2";
     case DiffType::ChangeMiddle:
       return "0" LARGE_STRING_FIRST "-" LARGE_STRING_SECOND "2";
     case DiffType::ChangeLast:
       return "0" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "-";
   }
 }

 TEST_ALWAYS_INLINE const char* getHugeString(DiffType D) {
 #define HUGE_STRING0 "0123456789"
 #define HUGE_STRING1 HUGE_STRING0 HUGE_STRING0 HUGE_STRING0 HUGE_STRING0
 #define HUGE_STRING2 HUGE_STRING1 HUGE_STRING1 HUGE_STRING1 HUGE_STRING1
 #define HUGE_STRING3 HUGE_STRING2 HUGE_STRING2 HUGE_STRING2 HUGE_STRING2
 #define HUGE_STRING4 HUGE_STRING3 HUGE_STRING3 HUGE_STRING3 HUGE_STRING3
   switch (D) {
     case DiffType::Control:
       return "0123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "0123456789";
     case DiffType::ChangeFirst:
       return "-123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "0123456789";
     case DiffType::ChangeMiddle:
       return "0123456789" HUGE_STRING4 "01234-6789" HUGE_STRING4 "0123456789";
     case DiffType::ChangeLast:
       return "0123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "012345678-";
   }
 }

 TEST_ALWAYS_INLINE std::string makeString(Length L,
                                           DiffType D = DiffType::Control,
                                           Opacity O = Opacity::Transparent) {
   switch (L) {
   case Length::Empty:
     return maybeOpaque("", O == Opacity::Opaque);
   case Length::Small:
     return maybeOpaque(getSmallString(D), O == Opacity::Opaque);
   case Length::Large:
     return maybeOpaque(getLargeString(D), O == Opacity::Opaque);
   case Length::Huge:
     return maybeOpaque(getHugeString(D), O == Opacity::Opaque);
   }
 }

 template <class Length, class Opaque>
 struct StringConstructDestroyCStr {
   static void run(benchmark::State& state) {
     for (auto _ : state) {
       benchmark::DoNotOptimize(
           makeString(Length(), DiffType::Control, Opaque()));
     }
   }

   static std::string name() {
     return "BM_StringConstructDestroyCStr" + Length::name() + Opaque::name();
   }
 };

 template <class Length, bool MeasureCopy, bool MeasureDestroy>
 static void StringCopyAndDestroy(benchmark::State& state) {
   static constexpr size_t NumStrings = 1024;
   auto Orig = makeString(Length());
   std::aligned_storage<sizeof(std::string)>::type Storage[NumStrings];

   while (state.KeepRunningBatch(NumStrings)) {
     if (!MeasureCopy)
       state.PauseTiming();
     for (size_t I = 0; I < NumStrings; ++I) {
       ::new (static_cast<void*>(Storage + I)) std::string(Orig);
     }
     if (!MeasureCopy)
       state.ResumeTiming();
     if (!MeasureDestroy)
       state.PauseTiming();
     for (size_t I = 0; I < NumStrings; ++I) {
       using S = std::string;
       reinterpret_cast<S*>(Storage + I)->~S();
     }
     if (!MeasureDestroy)
       state.ResumeTiming();
   }
 }

 template <class Length>
 struct StringCopy {
   static void run(benchmark::State& state) {
     StringCopyAndDestroy<Length, true, false>(state);
   }

   static std::string name() { return "BM_StringCopy" + Length::name(); }
 };

 template <class Length>
 struct StringDestroy {
   static void run(benchmark::State& state) {
     StringCopyAndDestroy<Length, false, true>(state);
   }

   static std::string name() { return "BM_StringDestroy" + Length::name(); }
 };

 template <class Length>
 struct StringMove {
   static void run(benchmark::State& state) {
     // Keep two object locations and move construct back and forth.
     std::aligned_storage<sizeof(std::string), alignof(std::string)>::type Storage[2];
     using S = std::string;
     size_t I = 0;
     S *newS = new (static_cast<void*>(Storage)) std::string(makeString(Length()));
     for (auto _ : state) {
       // Switch locations.
       I ^= 1;
       benchmark::DoNotOptimize(Storage);
       // Move construct into the new location,
       S *tmpS = new (static_cast<void*>(Storage + I)) S(std::move(*newS));
       // then destroy the old one.
       newS->~S();
       newS = tmpS;
     }
     newS->~S();
   }

   static std::string name() { return "BM_StringMove" + Length::name(); }
 };

 enum class Relation { Eq, Less, Compare };
 struct AllRelations : EnumValuesAsTuple<AllRelations, Relation, 3> {
   static constexpr const char* Names[] = {"Eq", "Less", "Compare"};
 };

 template <class Rel, class LHLength, class RHLength, class DiffType>
 struct StringRelational {
   static void run(benchmark::State& state) {
     auto Lhs = makeString(RHLength());
     auto Rhs = makeString(LHLength(), DiffType());
     for (auto _ : state) {
       benchmark::DoNotOptimize(Lhs);
       benchmark::DoNotOptimize(Rhs);
       switch (Rel()) {
       case Relation::Eq:
         benchmark::DoNotOptimize(Lhs == Rhs);
         break;
       case Relation::Less:
         benchmark::DoNotOptimize(Lhs < Rhs);
         break;
       case Relation::Compare:
         benchmark::DoNotOptimize(Lhs.compare(Rhs));
         break;
       }
     }
   }

   static bool skip() {
     // Eq is commutative, so skip half the matrix.
     if (Rel() == Relation::Eq && LHLength() > RHLength())
       return true;
     // We only care about control when the lengths differ.
     if (LHLength() != RHLength() && DiffType() != ::DiffType::Control)
       return true;
     // For empty, only control matters.
     if (LHLength() == Length::Empty && DiffType() != ::DiffType::Control)
       return true;
     return false;
   }

   static std::string name() {
     return "BM_StringRelational" + Rel::name() + LHLength::name() +
            RHLength::name() + DiffType::name();
   }
 };

 enum class Depth { Shallow, Deep };
 struct AllDepths : EnumValuesAsTuple<AllDepths, Depth, 2> {
   static constexpr const char* Names[] = {"Shallow", "Deep"};
 };

 enum class Temperature { Hot, Cold };
 struct AllTemperatures : EnumValuesAsTuple<AllTemperatures, Temperature, 2> {
   static constexpr const char* Names[] = {"Hot", "Cold"};
 };

 template <class Temperature, class Depth, class Length>
 struct StringRead {
   void run(benchmark::State& state) const {
     static constexpr size_t NumStrings =
         Temperature() == ::Temperature::Hot
             ? 1 << 10
             : /* Enough strings to overflow the cache */ 1 << 20;
     static_assert((NumStrings & (NumStrings - 1)) == 0,
                   "NumStrings should be a power of two to reduce overhead.");

     std::vector<std::string> Values(NumStrings, makeString(Length()));
     size_t I = 0;
     for (auto _ : state) {
       // Jump long enough to defeat cache locality, and use a value that is
       // coprime with NumStrings to ensure we visit every element.
       I = (I + 17) % NumStrings;
       const auto& V = Values[I];

       // Read everything first. Escaping data() through DoNotOptimize might
       // cause the compiler to have to recalculate information about `V` due to
       // aliasing.
       const char* const Data = V.data();
       const size_t Size = V.size();
       benchmark::DoNotOptimize(Data);
       benchmark::DoNotOptimize(Size);
       if (Depth() == ::Depth::Deep) {
         // Read into the payload. This mainly shows the benefit of SSO when the
         // data is cold.
         benchmark::DoNotOptimize(*Data);
       }
     }
   }

   static bool skip() {
     // Huge does not give us anything that Large doesn't have. Skip it.
     if (Length() == ::Length::Huge) {
       return true;
     }
     return false;
   }

   std::string name() const {
     return "BM_StringRead" + Temperature::name() + Depth::name() +
            Length::name();
   }
 };

 void sanityCheckGeneratedStrings() {
   for (auto Lhs : {Length::Empty, Length::Small, Length::Large, Length::Huge}) {
     const auto LhsString = makeString(Lhs);
     for (auto Rhs :
          {Length::Empty, Length::Small, Length::Large, Length::Huge}) {
       if (Lhs > Rhs)
         continue;
       const auto RhsString = makeString(Rhs);

       // The smaller one must be a prefix of the larger one.
       if (RhsString.find(LhsString) != 0) {
         fprintf(stderr, "Invalid autogenerated strings for sizes (%d,%d).\n",
                 static_cast<int>(Lhs), static_cast<int>(Rhs));
         std::abort();
       }
     }
   }
   // Verify the autogenerated diffs
   for (auto L : {Length::Small, Length::Large, Length::Huge}) {
     const auto Control = makeString(L);
     const auto Verify = [&](std::string Exp, size_t Pos) {
       // Only change on the Pos char.
       if (Control[Pos] != Exp[Pos]) {
         Exp[Pos] = Control[Pos];
         if (Control == Exp)
           return;
       }
       fprintf(stderr, "Invalid autogenerated diff with size %d\n",
               static_cast<int>(L));
       std::abort();
     };
     Verify(makeString(L, DiffType::ChangeFirst), 0);
     Verify(makeString(L, DiffType::ChangeMiddle), Control.size() / 2);
     Verify(makeString(L, DiffType::ChangeLast), Control.size() - 1);
   }
 }

 int main(int argc, char** argv) {
   benchmark::Initialize(&argc, argv);
   if (benchmark::ReportUnrecognizedArguments(argc, argv))
     return 1;

   sanityCheckGeneratedStrings();

   makeCartesianProductBenchmark<StringConstructDestroyCStr, AllLengths,
                                 AllOpacity>();
   makeCartesianProductBenchmark<StringCopy, AllLengths>();
   makeCartesianProductBenchmark<StringMove, AllLengths>();
   makeCartesianProductBenchmark<StringDestroy, AllLengths>();
   makeCartesianProductBenchmark<StringRelational, AllRelations, AllLengths,
                                 AllLengths, AllDiffTypes>();
   makeCartesianProductBenchmark<StringRead, AllTemperatures, AllDepths,
                                 AllLengths>();
   benchmark::RunSpecifiedBenchmarks();
 }

	#include <cstdint>
	#include <new>
	#include <vector>

	#include "CartesianBenchmarks.hpp"
	#include "GenerateInput.hpp"
	#include "benchmark/benchmark.h"
	#include "test_macros.h"

	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, '*');
	for (auto _ : state)
	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), '-');
	for (auto _ : state)
	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), '-');
	for (auto _ : state)
	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), '-');
	for (auto _ : state)
	benchmark::DoNotOptimize(s1.find(s2));
	}
	BENCHMARK(BM_StringFindMatch2)->Range(1, MAX_STRING_LEN / 4);

	static void BM_StringCtorDefault(benchmark::State &state) {
	for (auto _ : state) {
	std::string Default;
	benchmark::DoNotOptimize(Default);
	}
	}
	BENCHMARK(BM_StringCtorDefault);

	enum class Length { Empty, Small, Large, Huge };
	struct AllLengths : EnumValuesAsTuple<AllLengths, Length, 4> {
	static constexpr const char* Names[] = {"Empty", "Small", "Large", "Huge"};
	};

	enum class Opacity { Opaque, Transparent };
	struct AllOpacity : EnumValuesAsTuple<AllOpacity, Opacity, 2> {
	static constexpr const char* Names[] = {"Opaque", "Transparent"};
	};

	enum class DiffType { Control, ChangeFirst, ChangeMiddle, ChangeLast };
	struct AllDiffTypes : EnumValuesAsTuple<AllDiffTypes, DiffType, 4> {
	static constexpr const char* Names[] = {"Control", "ChangeFirst",
	"ChangeMiddle", "ChangeLast"};
	};

	TEST_ALWAYS_INLINE const char* getSmallString(DiffType D) {
	switch (D) {
	case DiffType::Control:
	return "0123456";
	case DiffType::ChangeFirst:
	return "-123456";
	case DiffType::ChangeMiddle:
	return "012-456";
	case DiffType::ChangeLast:
	return "012345-";
	}
	}

	TEST_ALWAYS_INLINE const char* getLargeString(DiffType D) {
	#define LARGE_STRING_FIRST "123456789012345678901234567890"
	#define LARGE_STRING_SECOND "234567890123456789012345678901"
	switch (D) {
	case DiffType::Control:
	return "0" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "2";
	case DiffType::ChangeFirst:
	return "-" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "2";
	case DiffType::ChangeMiddle:
	return "0" LARGE_STRING_FIRST "-" LARGE_STRING_SECOND "2";
	case DiffType::ChangeLast:
	return "0" LARGE_STRING_FIRST "1" LARGE_STRING_SECOND "-";
	}
	}

	TEST_ALWAYS_INLINE const char* getHugeString(DiffType D) {
	#define HUGE_STRING0 "0123456789"
	#define HUGE_STRING1 HUGE_STRING0 HUGE_STRING0 HUGE_STRING0 HUGE_STRING0
	#define HUGE_STRING2 HUGE_STRING1 HUGE_STRING1 HUGE_STRING1 HUGE_STRING1
	#define HUGE_STRING3 HUGE_STRING2 HUGE_STRING2 HUGE_STRING2 HUGE_STRING2
	#define HUGE_STRING4 HUGE_STRING3 HUGE_STRING3 HUGE_STRING3 HUGE_STRING3
	switch (D) {
	case DiffType::Control:
	return "0123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "0123456789";
	case DiffType::ChangeFirst:
	return "-123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "0123456789";
	case DiffType::ChangeMiddle:
	return "0123456789" HUGE_STRING4 "01234-6789" HUGE_STRING4 "0123456789";
	case DiffType::ChangeLast:
	return "0123456789" HUGE_STRING4 "0123456789" HUGE_STRING4 "012345678-";
	}
	}

	TEST_ALWAYS_INLINE std::string makeString(Length L,
	DiffType D = DiffType::Control,
	Opacity O = Opacity::Transparent) {
	switch (L) {
	case Length::Empty:
	return maybeOpaque("", O == Opacity::Opaque);
	case Length::Small:
	return maybeOpaque(getSmallString(D), O == Opacity::Opaque);
	case Length::Large:
	return maybeOpaque(getLargeString(D), O == Opacity::Opaque);
	case Length::Huge:
	return maybeOpaque(getHugeString(D), O == Opacity::Opaque);
	}
	}

	template <class Length, class Opaque>
	struct StringConstructDestroyCStr {
	static void run(benchmark::State& state) {
	for (auto _ : state) {
	benchmark::DoNotOptimize(
	makeString(Length(), DiffType::Control, Opaque()));
	}
	}

	static std::string name() {
	return "BM_StringConstructDestroyCStr" + Length::name() + Opaque::name();
	}
	};

	template <class Length, bool MeasureCopy, bool MeasureDestroy>
	static void StringCopyAndDestroy(benchmark::State& state) {
	static constexpr size_t NumStrings = 1024;
	auto Orig = makeString(Length());
	std::aligned_storage<sizeof(std::string)>::type Storage[NumStrings];

	while (state.KeepRunningBatch(NumStrings)) {
	if (!MeasureCopy)
	state.PauseTiming();
	for (size_t I = 0; I < NumStrings; ++I) {
	::new (static_cast<void*>(Storage + I)) std::string(Orig);
	}
	if (!MeasureCopy)
	state.ResumeTiming();
	if (!MeasureDestroy)
	state.PauseTiming();
	for (size_t I = 0; I < NumStrings; ++I) {
	using S = std::string;
	reinterpret_cast<S*>(Storage + I)->~S();
	}
	if (!MeasureDestroy)
	state.ResumeTiming();
	}
	}

	template <class Length>
	struct StringCopy {
	static void run(benchmark::State& state) {
	StringCopyAndDestroy<Length, true, false>(state);
	}

	static std::string name() { return "BM_StringCopy" + Length::name(); }
	};

	template <class Length>
	struct StringDestroy {
	static void run(benchmark::State& state) {
	StringCopyAndDestroy<Length, false, true>(state);
	}

	static std::string name() { return "BM_StringDestroy" + Length::name(); }
	};

	template <class Length>
	struct StringMove {
	static void run(benchmark::State& state) {
	// Keep two object locations and move construct back and forth.
	std::aligned_storage<sizeof(std::string), alignof(std::string)>::type Storage[2];
	using S = std::string;
	size_t I = 0;
	S newS = new (static_cast<void>(Storage)) std::string(makeString(Length()));
	for (auto _ : state) {
	// Switch locations.
	I ^= 1;
	benchmark::DoNotOptimize(Storage);
	// Move construct into the new location,
	S tmpS = new (static_cast<void>(Storage + I)) S(std::move(*newS));
	// then destroy the old one.
	newS->~S();
	newS = tmpS;
	}
	newS->~S();
	}

	static std::string name() { return "BM_StringMove" + Length::name(); }
	};

	enum class Relation { Eq, Less, Compare };
	struct AllRelations : EnumValuesAsTuple<AllRelations, Relation, 3> {
	static constexpr const char* Names[] = {"Eq", "Less", "Compare"};
	};

	template <class Rel, class LHLength, class RHLength, class DiffType>
	struct StringRelational {
	static void run(benchmark::State& state) {
	auto Lhs = makeString(RHLength());
	auto Rhs = makeString(LHLength(), DiffType());
	for (auto _ : state) {
	benchmark::DoNotOptimize(Lhs);
	benchmark::DoNotOptimize(Rhs);
	switch (Rel()) {
	case Relation::Eq:
	benchmark::DoNotOptimize(Lhs == Rhs);
	break;
	case Relation::Less:
	benchmark::DoNotOptimize(Lhs < Rhs);
	break;
	case Relation::Compare:
	benchmark::DoNotOptimize(Lhs.compare(Rhs));
	break;
	}
	}
	}

	static bool skip() {
	// Eq is commutative, so skip half the matrix.
	if (Rel() == Relation::Eq && LHLength() > RHLength())
	return true;
	// We only care about control when the lengths differ.
	if (LHLength() != RHLength() && DiffType() != ::DiffType::Control)
	return true;
	// For empty, only control matters.
	if (LHLength() == Length::Empty && DiffType() != ::DiffType::Control)
	return true;
	return false;
	}

	static std::string name() {
	return "BM_StringRelational" + Rel::name() + LHLength::name() +
	RHLength::name() + DiffType::name();
	}
	};

	enum class Depth { Shallow, Deep };
	struct AllDepths : EnumValuesAsTuple<AllDepths, Depth, 2> {
	static constexpr const char* Names[] = {"Shallow", "Deep"};
	};

	enum class Temperature { Hot, Cold };
	struct AllTemperatures : EnumValuesAsTuple<AllTemperatures, Temperature, 2> {
	static constexpr const char* Names[] = {"Hot", "Cold"};
	};

	template <class Temperature, class Depth, class Length>
	struct StringRead {
	void run(benchmark::State& state) const {
	static constexpr size_t NumStrings =
	Temperature() == ::Temperature::Hot
	? 1 << 10
	: /* Enough strings to overflow the cache */ 1 << 20;
	static_assert((NumStrings & (NumStrings - 1)) == 0,
	"NumStrings should be a power of two to reduce overhead.");

	std::vector<std::string> Values(NumStrings, makeString(Length()));
	size_t I = 0;
	for (auto _ : state) {
	// Jump long enough to defeat cache locality, and use a value that is
	// coprime with NumStrings to ensure we visit every element.
	I = (I + 17) % NumStrings;
	const auto& V = Values[I];

	// Read everything first. Escaping data() through DoNotOptimize might
	// cause the compiler to have to recalculate information about `V` due to
	// aliasing.
	const char* const Data = V.data();
	const size_t Size = V.size();
	benchmark::DoNotOptimize(Data);
	benchmark::DoNotOptimize(Size);
	if (Depth() == ::Depth::Deep) {
	// Read into the payload. This mainly shows the benefit of SSO when the
	// data is cold.
	benchmark::DoNotOptimize(*Data);
	}
	}
	}

	static bool skip() {
	// Huge does not give us anything that Large doesn't have. Skip it.
	if (Length() == ::Length::Huge) {
	return true;
	}
	return false;
	}

	std::string name() const {
	return "BM_StringRead" + Temperature::name() + Depth::name() +
	Length::name();
	}
	};

	void sanityCheckGeneratedStrings() {
	for (auto Lhs : {Length::Empty, Length::Small, Length::Large, Length::Huge}) {
	const auto LhsString = makeString(Lhs);
	for (auto Rhs :
	{Length::Empty, Length::Small, Length::Large, Length::Huge}) {
	if (Lhs > Rhs)
	continue;
	const auto RhsString = makeString(Rhs);

	// The smaller one must be a prefix of the larger one.
	if (RhsString.find(LhsString) != 0) {
	fprintf(stderr, "Invalid autogenerated strings for sizes (%d,%d).\n",
	static_cast<int>(Lhs), static_cast<int>(Rhs));
	std::abort();
	}
	}
	}
	// Verify the autogenerated diffs
	for (auto L : {Length::Small, Length::Large, Length::Huge}) {
	const auto Control = makeString(L);
	const auto Verify = [&](std::string Exp, size_t Pos) {
	// Only change on the Pos char.
	if (Control[Pos] != Exp[Pos]) {
	Exp[Pos] = Control[Pos];
	if (Control == Exp)
	return;
	}
	fprintf(stderr, "Invalid autogenerated diff with size %d\n",
	static_cast<int>(L));
	std::abort();
	};
	Verify(makeString(L, DiffType::ChangeFirst), 0);
	Verify(makeString(L, DiffType::ChangeMiddle), Control.size() / 2);
	Verify(makeString(L, DiffType::ChangeLast), Control.size() - 1);
	}
	}

	int main(int argc, char** argv) {
	benchmark::Initialize(&argc, argv);
	if (benchmark::ReportUnrecognizedArguments(argc, argv))
	return 1;

	sanityCheckGeneratedStrings();

	makeCartesianProductBenchmark<StringConstructDestroyCStr, AllLengths,
	AllOpacity>();
	makeCartesianProductBenchmark<StringCopy, AllLengths>();
	makeCartesianProductBenchmark<StringMove, AllLengths>();
	makeCartesianProductBenchmark<StringDestroy, AllLengths>();
	makeCartesianProductBenchmark<StringRelational, AllRelations, AllLengths,
	AllLengths, AllDiffTypes>();
	makeCartesianProductBenchmark<StringRead, AllTemperatures, AllDepths,
	AllLengths>();
	benchmark::RunSpecifiedBenchmarks();
	}