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Use C++11 atomic_signal_fence for ClobberMemory #1190

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Merged
merged 3 commits into from
Jun 28, 2021
Merged

Use C++11 atomic_signal_fence for ClobberMemory #1190

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5f3236a
Use C++11 atomic_signal_fence for ClobberMemory
mtrofin Jun 26, 2021
21b2765
include
mtrofin Jun 26, 2021
c894924
Conditionally using std::atomic_signal_fence when C++11 is available
mtrofin Jun 28, 2021
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Use C++11 atomic_signal_fence for ClobberMemory
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@mtrofin
mtrofin committed Jun 26, 2021
commit 5f3236ae92e3a8a6f352ec5faac0b543383f354a
14 changes: 7 additions & 7 deletions include/benchmark/benchmark.h
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Original file line number Diff line number Diff line change
Expand Up @@ -187,6 +187,7 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
#include <vector>

#if defined(BENCHMARK_HAS_CXX11)
#include <atomic>
#include <initializer_list>
#include <type_traits>
#include <utility>
Expand Down Expand Up @@ -327,6 +328,12 @@ BENCHMARK_UNUSED static int stream_init_anchor = InitializeStreams();
#define BENCHMARK_HAS_NO_INLINE_ASSEMBLY
#endif

// Force the compiler to flush pending writes to global memory. Acts as an
// effective read/write barrier
inline BENCHMARK_ALWAYS_INLINE void ClobberMemory() {
std::atomic_signal_fence(std::memory_order_acq_rel);
}

// The DoNotOptimize(...) function can be used to prevent a value or
// expression from being optimized away by the compiler. This function is
// intended to add little to no overhead.
Expand All @@ -346,25 +353,18 @@ inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp& value) {
#endif
}

// Force the compiler to flush pending writes to global memory. Acts as an
// effective read/write barrier
inline BENCHMARK_ALWAYS_INLINE void ClobberMemory() {
asm volatile("" : : : "memory");
}
#elif defined(_MSC_VER)
template <class Tp>
inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp const& value) {
internal::UseCharPointer(&reinterpret_cast<char const volatile&>(value));
_ReadWriteBarrier();
}

inline BENCHMARK_ALWAYS_INLINE void ClobberMemory() { _ReadWriteBarrier(); }
#else
template <class Tp>
inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp const& value) {
internal::UseCharPointer(&reinterpret_cast<char const volatile&>(value));
}
// FIXME Add ClobberMemory() for non-gnu and non-msvc compilers
#endif

// This class is used for user-defined counters.
Expand Down