Add more benchmarks for std::string.

[sbenza]

Summary

Added benchmarks for Construct, Copy, Move, Destroy, Relationals and
Read. On the ones that matter, the benchmarks tests hot and cold data,
and opaque and transparent inputs.

libcxx/trunk/benchmarks/string.bench.cpp

-#include <unordered_set>
-#include <vector>
+
 #include <cstdint>
+#include <new>
+#include <vector>
 
-#include "benchmark/benchmark.h"
+#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, '*');
-  while (state.KeepRunning())
+  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), '-');
-  while (state.KeepRunning())
+  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), '-');
-  while (state.KeepRunning())
+  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), '-');
-  while (state.KeepRunning())
+  for (auto _ : state)
     benchmark::DoNotOptimize(s1.find(s2));
 }
 BENCHMARK(BM_StringFindMatch2)->Range(1, MAX_STRING_LEN / 4);
 
 static void BM_StringCtorDefault(benchmark::State &state) {
-  while (state.KeepRunning()) {
-    for (unsigned I=0; I < 1000; ++I) {
-      std::string Default;
-      benchmark::DoNotOptimize(Default.c_str());
-    }
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(Default);
   }
 }
 BENCHMARK(BM_StringCtorDefault);
 
-static void BM_StringCtorCStr(benchmark::State &state) {
-  std::string Input = getRandomString(state.range(0));
-  const char *Str = Input.c_str();
-  benchmark::DoNotOptimize(Str);
-  while (state.KeepRunning()) {
-    std::string Tmp(Str);
-    benchmark::DoNotOptimize(Tmp.c_str());
+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)>::type Storage[2];
+    using S = std::string;
+    S* Data = reinterpret_cast<S*>(Storage);
+    size_t I = 0;
+    new (static_cast<void*>(Data)) std::string(makeString(Length()));
+    for (auto _ : state) {
+      // Switch locations.
+      I ^= 1;
+      benchmark::DoNotOptimize(Storage);
+      // Move construct into the new location,
+      new (static_cast<void*>(Storage + I)) S(std::move(Data[I ^ 1]));
+      // then destroy the old one.
+      Data[I ^ 1].~S();
+    }
+    Data[I].~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);
   }
-BENCHMARK(BM_StringCtorCStr)->Arg(1)->Arg(8)->Range(16, MAX_STRING_LEN / 4);
+}
+
+int main(int argc, char** argv) {
+  benchmark::Initialize(&argc, argv);
+  if (benchmark::ReportUnrecognizedArguments(argc, argv))
+    return 1;
 
-BENCHMARK_MAIN();
+  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();
+}