fix: prevent optimizing out the benchmarks

Author: not-matthias

examples/google_benchmark_cmake/fixture_bench.hpp

@@ -16,10 +16,14 @@ class MyFixture : public benchmark::Fixture {
 };
 BENCHMARK_F(MyFixture, FooTest)(benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_DEFINE_F(MyFixture, BarTest)(benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_REGISTER_F(MyFixture, BarTest);
@@ -31,11 +35,15 @@ template <typename T>
 class MyTemplatedFixture : public benchmark::Fixture {};
 BENCHMARK_TEMPLATE_F(MyTemplatedFixture, IntTest, int)(benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_TEMPLATE_DEFINE_F(MyTemplatedFixture, DoubleTest, double)
 (benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_REGISTER_F(MyTemplatedFixture, DoubleTest);
@@ -47,6 +55,8 @@ template <typename T>
 class MyTemplate1 : public benchmark::Fixture {};
 BENCHMARK_TEMPLATE1_DEFINE_F(MyTemplate1, TestA, int)(benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_REGISTER_F(MyTemplate1, TestA);
@@ -59,6 +69,8 @@ class MyTemplate2 : public benchmark::Fixture {};
 BENCHMARK_TEMPLATE2_DEFINE_F(MyTemplate2, TestB, int, double)
 (benchmark::State &st) {
   for (auto _ : st) {
+    benchmark::DoNotOptimize(st);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_REGISTER_F(MyTemplate2, TestB);

examples/google_benchmark_cmake/main.cpp

@@ -9,8 +9,9 @@
 template <class... Args>
 void BM_Capture(benchmark::State &state, Args &&...args) {
   auto args_tuple = std::make_tuple(std::move(args)...);
-  (void)args_tuple;
   for (auto _ : state) {
+    benchmark::DoNotOptimize(args_tuple);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_CAPTURE(BM_Capture, int_string_test, 42, std::string("abc"));
@@ -21,6 +22,8 @@ static void BM_rand_vector(benchmark::State &state) {
   std::vector<int> v;
   for (auto _ : state) {
     std::string empty_string;
+    benchmark::DoNotOptimize(empty_string);
+    benchmark::ClobberMemory();
   }
 }
 // Register the function as a benchmark
@@ -31,6 +34,8 @@ static void BM_StringCopy(benchmark::State &state) {
   std::string x = "hello";
   for (auto _ : state) {
     std::string copy(x);
+    benchmark::DoNotOptimize(copy);
+    benchmark::ClobberMemory();
   }
 }
 // Register the function as a benchmark
@@ -40,7 +45,11 @@ static void BM_memcpy(benchmark::State &state) {
   char *src = new char[state.range(0)];
   char *dst = new char[state.range(0)];
   memset(src, 'x', state.range(0));
-  for (auto _ : state) memcpy(dst, src, state.range(0));
+  for (auto _ : state) {
+    memcpy(dst, src, state.range(0));
+    benchmark::DoNotOptimize(dst);
+    benchmark::ClobberMemory();
+  }
   delete[] src;
   delete[] dst;
 }

examples/google_benchmark_cmake/template_bench.hpp

@@ -12,6 +12,8 @@ void BM_Template(benchmark::State &state) {
   std::vector<T> v;
   for (auto _ : state) {
     v.push_back(T());
+    benchmark::DoNotOptimize(v);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_TEMPLATE(BM_Template, int);
@@ -50,6 +52,8 @@ template <typename T, class... ExtraArgs>
 void BM_Template1_Capture(benchmark::State &state, ExtraArgs &&...extra_args) {
   auto args_tuple = std::make_tuple(std::move(extra_args)...);
   for (auto _ : state) {
+    benchmark::DoNotOptimize(args_tuple);
+    benchmark::ClobberMemory();
   }
 }
 BENCHMARK_TEMPLATE1_CAPTURE(BM_Template1_Capture, void, int_string_test, 42,