Add additional benchmark functions to libcxx/benchmarks/string.bench

[mvels]

Summary

This change adds the following benchmarks:

• StringAssignStr

Assign a const basic::string& value

• StringAssignAsciiz

Assign a const char* asciiz value

StringAssignAsciizMix
Assign mixed long/short const char* asciiz values

• StringResizeDefaultInit

Resize default init benchmark

[EricWF]

libcxx/benchmarks/string.bench.cpp

238

Have you looked at the dissasembly for these benchmarks? They scare me a little bit. I think the compiler may be able to optimize large chunks of them away.

[mvels]

libcxx/benchmarks/string.bench.cpp

238

I did look at the assembly, the compiler does not optimize out branches for either the opaque or transparent call paths, which makes sense as the compiler would be hard pressed to proof the constantness of the strings array.

There is basically no difference here between transparent and opaque, as there is no 'inlined' memset, memcpy, or other optimizations that would deeply separate the 2 of them other than a predicted branch which does not change much timing wise for short strings.

Given that the main purpose for this bench is more on baseline for inlined resize (always fast) and long resize (now through __grow_by), we could make it an 'Opaque only' test as this is not something where the difference between compile time known input (length) should make much of a difference (if any)

[EricWF]

I think this is fine as is. So long as you've looked at it.

LGTM.

[EricWF]

Committed as 0c5102bd939131b27105b74e73fc25b90207ef36

libcxx/benchmarks/string.bench.cpp

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);
for (auto _ : state) {
       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 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) {
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<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);
   }
 }