github-repos/benchmark
1
0
Fork 0
mirror of https://github.com/google/benchmark.git synced 2024-12-27 13:00:36 +08:00
Code Issues Packages Projects Releases Wiki Activity

Add 'benchmark::DoNotOptimize(...)' to help users prevent optimizations

Browse Source
This commit is contained in:
Eric Fiselier 2015-03-27 16:35:46 -04:00
parent 0a0bb8feb1
commit e428b9eec3
5 changed files with 50 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
README.md
View File

@ -160,6 +160,19 @@ static void BM_MultiThreaded(benchmark::State& state) {
}
}
BENCHMARK(BM_MultiThreaded)->Threads(2);
To prevent a value or expression from being optimized away by the compiler
the `benchmark::DoNotOptimize(...)` function can be used.
```c++
static void BM_test(benchmark::State& state) {
while (state.KeepRunning()) {
int x = 0;
for (int i=0; i < 64; ++i) {
benchmark::DoNotOptimize(x += i);
}
}
}
```

19
include/benchmark/benchmark_api.h
View File

@ -174,8 +174,27 @@ struct EnableIfString<T, typename Voider<typename T::basic_string>::type> {
typedef int type;
};
void UseCharPointer(char const volatile*);
} // end namespace internal
// The DoNotOptimize(...) function can be used to prevent a value or
// expression from being optimized away by the compiler. This function is
// intented to add little to no overhead.
// See: http://stackoverflow.com/questions/28287064
#if defined(__GNUC__)
template <class Tp>
inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp const& value) {
asm volatile("" : "+r" (const_cast<Tp&>(value)));
}
#else
template <class Tp>
inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp const& value) {
internal::UseCharPointer(&reinterpret_cast<char const volatile&>(value));
}
#endif
// State is passed to a running Benchmark and contains state for the
// benchmark to use.
class State {

2
src/benchmark.cc
View File

@ -73,6 +73,8 @@ namespace benchmark {
namespace internal {
void UseCharPointer(char const volatile*) {}
// NOTE: This is a dummy "mutex" type used to denote the actual mutex
// returned by GetBenchmarkLock(). This is only used to placate the thread
// safety warnings by giving the return of GetBenchmarkLock() a name.

33
test/basic_test.cc
View File

@ -8,8 +8,7 @@
void BM_empty(benchmark::State& state) {
while (state.KeepRunning()) {
volatile std::size_t x = state.iterations();
((void)x);
benchmark::DoNotOptimize(state.iterations());
}
}
BENCHMARK(BM_empty);
@ -18,8 +17,7 @@ BENCHMARK(BM_empty)->ThreadPerCpu();
void BM_spin_empty(benchmark::State& state) {
while (state.KeepRunning()) {
for (int x = 0; x < state.range_x(); ++x) {
volatile int dummy = x;
((void)dummy);
benchmark::DoNotOptimize(x);
}
}
}
@ -28,13 +26,11 @@ BASIC_BENCHMARK_TEST(BM_spin_empty)->ThreadPerCpu();
void BM_spin_pause_before(benchmark::State& state) {
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
while(state.KeepRunning()) {
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
}
@ -46,13 +42,11 @@ void BM_spin_pause_during(benchmark::State& state) {
while(state.KeepRunning()) {
state.PauseTiming();
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
state.ResumeTiming();
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
}
@ -81,13 +75,11 @@ BENCHMARK(BM_pause_during_realtime)->ThreadPerCpu();
void BM_spin_pause_after(benchmark::State& state) {
while(state.KeepRunning()) {
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
BASIC_BENCHMARK_TEST(BM_spin_pause_after);
@ -96,18 +88,15 @@ BASIC_BENCHMARK_TEST(BM_spin_pause_after)->ThreadPerCpu();
void BM_spin_pause_before_and_after(benchmark::State& state) {
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
while(state.KeepRunning()) {
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
for (int i = 0; i < state.range_x(); ++i) {
volatile int dummy = i;
((void)dummy);
benchmark::DoNotOptimize(i);
}
}
BASIC_BENCHMARK_TEST(BM_spin_pause_before_and_after);

14
test/benchmark_test.cc
View File

@ -84,9 +84,8 @@ BENCHMARK_RANGE(BM_CalculatePiRange, 1, 1024 * 1024);
static void BM_CalculatePi(benchmark::State& state) {
static const int depth = 1024;
double pi BENCHMARK_UNUSED = 0.0;
while (state.KeepRunning()) {
pi = CalculatePi(depth);
benchmark::DoNotOptimize(CalculatePi(depth));
}
}
BENCHMARK(BM_CalculatePi)->Threads(8);
@ -129,11 +128,8 @@ BENCHMARK_TEMPLATE(BM_Sequential, std::vector<int>, int)->Arg(512);
static void BM_StringCompare(benchmark::State& state) {
std::string s1(state.range_x(), '-');
std::string s2(state.range_x(), '-');
int r = 0;
while (state.KeepRunning())
r |= s1.compare(s2);
// Prevent compiler optimizations
assert(r != std::numeric_limits<int>::max());
benchmark::DoNotOptimize(s1.compare(s2));
}
BENCHMARK(BM_StringCompare)->Range(1, 1<<20);
@ -159,10 +155,10 @@ BENCHMARK(BM_SetupTeardown)->ThreadPerCpu();
static void BM_LongTest(benchmark::State& state) {
double tracker = 0.0;
while (state.KeepRunning())
while (state.KeepRunning()) {
for (int i = 0; i < state.range_x(); ++i)
tracker += i;
assert(tracker > 1.0);
benchmark::DoNotOptimize(tracker += i);
}
}
BENCHMARK(BM_LongTest)->Range(1<<16,1<<28);