string.bench.cpp

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

#include "CartesianBenchmarks.h"
#include "GenerateInput.h"
#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"};
};

static constexpr char SmallStringLiteral[] = "012345678";

TEST_ALWAYS_INLINE const char* getSmallString(DiffType D) {
  switch (D) {
  case DiffType::Control:
    return SmallStringLiteral;
  case DiffType::ChangeFirst:
    return "-12345678";
  case DiffType::ChangeMiddle:
    return "0123-5678";
  case DiffType::ChangeLast:
    return "01234567-";
  }
}

static constexpr char LargeStringLiteral[] = "012345678901234567890123456789012345678901234567890123456789012";

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 const char* getString(Length L, DiffType D = DiffType::Control) {
  switch (L) {
  case Length::Empty:
    return "";
  case Length::Small:
    return getSmallString(D);
  case Length::Large:
    return getLargeString(D);
  case Length::Huge:
    return getHugeString(D);
  }
}

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(); }
};

template <class Length, class Opaque>
struct StringResizeDefaultInit {
  static void run(benchmark::State& state) {
    constexpr bool opaque     = Opaque{} == Opacity::Opaque;
    constexpr int kNumStrings = 4 << 10;
    size_t length             = makeString(Length()).size();
    std::string strings[kNumStrings];
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        std::string().swap(strings[i]);
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i].__resize_default_init(maybeOpaque(length, opaque));
      }
    }
  }

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

template <class Length, class Opaque>
struct StringAssignStr {
  static void run(benchmark::State& state) {
    constexpr bool opaque     = Opaque{} == Opacity::Opaque;
    constexpr int kNumStrings = 4 << 10;
    std::string src           = makeString(Length());
    std::string strings[kNumStrings];
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        std::string().swap(strings[i]);
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i] = *maybeOpaque(&src, opaque);
      }
    }
  }

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

template <class Length, class Opaque>
struct StringAssignAsciiz {
  static void run(benchmark::State& state) {
    constexpr bool opaque     = Opaque{} == Opacity::Opaque;
    constexpr int kNumStrings = 4 << 10;
    std::string strings[kNumStrings];
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        std::string().swap(strings[i]);
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i] = maybeOpaque(getString(Length()), opaque);
      }
    }
  }

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

template <class Length, class Opaque>
struct StringEraseToEnd {
  static void run(benchmark::State& state) {
    constexpr bool opaque     = Opaque{} == Opacity::Opaque;
    constexpr int kNumStrings = 4 << 10;
    std::string strings[kNumStrings];
    const int mid = makeString(Length()).size() / 2;
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i] = makeString(Length());
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i].erase(maybeOpaque(mid, opaque), maybeOpaque(std::string::npos, opaque));
      }
    }
  }

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

template <class Length, class Opaque>
struct StringEraseWithMove {
  static void run(benchmark::State& state) {
    constexpr bool opaque     = Opaque{} == Opacity::Opaque;
    constexpr int kNumStrings = 4 << 10;
    std::string strings[kNumStrings];
    const int n   = makeString(Length()).size() / 2;
    const int pos = n / 2;
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i] = makeString(Length());
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        strings[i].erase(maybeOpaque(pos, opaque), maybeOpaque(n, opaque));
      }
    }
  }

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

template <class Opaque>
struct StringAssignAsciizMix {
  static void run(benchmark::State& state) {
    constexpr auto O          = Opaque{};
    constexpr auto D          = DiffType::Control;
    constexpr int kNumStrings = 4 << 10;
    std::string strings[kNumStrings];
    while (state.KeepRunningBatch(kNumStrings)) {
      state.PauseTiming();
      for (int i = 0; i < kNumStrings; ++i) {
        std::string().swap(strings[i]);
      }
      benchmark::DoNotOptimize(strings);
      state.ResumeTiming();
      for (int i = 0; i < kNumStrings - 7; i += 8) {
        strings[i + 0] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
        strings[i + 1] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
        strings[i + 2] = maybeOpaque(getLargeString(D), O == Opacity::Opaque);
        strings[i + 3] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
        strings[i + 4] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
        strings[i + 5] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
        strings[i + 6] = maybeOpaque(getLargeString(D), O == Opacity::Opaque);
        strings[i + 7] = maybeOpaque(getSmallString(D), O == Opacity::Opaque);
      }
    }
  }

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

template <class Rel, class LHLength, class RHLength, class DiffType>
struct StringRelationalLiteral {
  static void run(benchmark::State& state) {
    auto Lhs = makeString(LHLength(), DiffType());
    for (auto _ : state) {
      benchmark::DoNotOptimize(Lhs);
      constexpr const char* Literal =
          RHLength::value == Length::Empty ? ""
          : RHLength::value == Length::Small
              ? SmallStringLiteral
              : LargeStringLiteral;
      switch (Rel()) {
      case Relation::Eq:
        benchmark::DoNotOptimize(Lhs == Literal);
        break;
      case Relation::Less:
        benchmark::DoNotOptimize(Lhs < Literal);
        break;
      case Relation::Compare:
        benchmark::DoNotOptimize(Lhs.compare(Literal));
        break;
      }
    }
  }

  static bool skip() {
    // Doesn't matter how they differ if they have different size.
    if (LHLength() != RHLength() && DiffType() != ::DiffType::Control)
      return true;
    // We don't need huge. Doensn't give anything different than Large.
    if (LHLength() == Length::Huge || RHLength() == Length::Huge)
      return true;
    return false;
  }

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

// Some small codegen thunks to easily see generated code.
bool StringEqString(const std::string& a, const std::string& b) { return a == b; }
bool StringEqCStr(const std::string& a, const char* b) { return a == b; }
bool CStrEqString(const char* a, const std::string& b) { return a == b; }
bool StringEqCStrLiteralEmpty(const std::string& a) { return a == ""; }
bool StringEqCStrLiteralSmall(const std::string& a) { return a == SmallStringLiteral; }
bool StringEqCStrLiteralLarge(const std::string& a) { return a == LargeStringLiteral; }

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

  sanityCheckGeneratedStrings();

  makeCartesianProductBenchmark<StringConstructDestroyCStr, AllLengths, AllOpacity>();

  makeCartesianProductBenchmark<StringAssignStr, AllLengths, AllOpacity>();
  makeCartesianProductBenchmark<StringAssignAsciiz, AllLengths, AllOpacity>();
  makeCartesianProductBenchmark<StringAssignAsciizMix, AllOpacity>();

  makeCartesianProductBenchmark<StringCopy, AllLengths>();
  makeCartesianProductBenchmark<StringMove, AllLengths>();
  makeCartesianProductBenchmark<StringDestroy, AllLengths>();
  makeCartesianProductBenchmark<StringResizeDefaultInit, AllLengths, AllOpacity>();
  makeCartesianProductBenchmark<StringEraseToEnd, AllLengths, AllOpacity>();
  makeCartesianProductBenchmark<StringEraseWithMove, AllLengths, AllOpacity>();
  makeCartesianProductBenchmark<StringRelational, AllRelations, AllLengths, AllLengths, AllDiffTypes>();
  makeCartesianProductBenchmark<StringRelationalLiteral, AllRelations, AllLengths, AllLengths, AllDiffTypes>();
  makeCartesianProductBenchmark<StringRead, AllTemperatures, AllDepths, AllLengths>();
  benchmark::RunSpecifiedBenchmarks();

  if (argc < 0) {
    // ODR-use the functions to force them being generated in the binary.
    auto functions = std::make_tuple(
        StringEqString,
        StringEqCStr,
        CStrEqString,
        StringEqCStrLiteralEmpty,
        StringEqCStrLiteralSmall,
        StringEqCStrLiteralLarge);
    printf("%p", &functions);
  }
}