cycleclock.h | Explore in Territory

// ----------------------------------------------------------------------
// CycleClock
//    A CycleClock tells you the current time in Cycles.  The "time"
//    is actually time since power-on.  This is like time() but doesn't
//    involve a system call and is much more precise.
//
// NOTE: Not all cpu/platform/kernel combinations guarantee that this
// clock increments at a constant rate or is synchronized across all logical
// cpus in a system.
//
// If you need the above guarantees, please consider using a different
// API. There are efforts to provide an interface which provides a millisecond
// granularity and implemented as a memory read. A memory read is generally
// cheaper than the CycleClock for many architectures.
//
// Also, in some out of order CPU implementations, the CycleClock is not
// serializing. So if you're trying to count at cycles granularity, your
// data might be inaccurate due to out of order instruction execution.
// ----------------------------------------------------------------------

#ifndef BENCHMARK_CYCLECLOCK_H_
#define BENCHMARK_CYCLECLOCK_H_

#include <cstdint>

#include "benchmark/benchmark.h"
#include "internal_macros.h"

#if defined(BENCHMARK_OS_MACOSX)
#include <mach/mach_time.h>
#endif
// For MSVC, we want to use '_asm rdtsc' when possible (since it works
// with even ancient MSVC compilers), and when not possible the
// __rdtsc intrinsic, declared in <intrin.h>.  Unfortunately, in some
// environments, <windows.h> and <intrin.h> have conflicting
// declarations of some other intrinsics, breaking compilation.
// Therefore, we simply declare __rdtsc ourselves. See also
// http://connect.microsoft.com/VisualStudio/feedback/details/262047
#if defined(COMPILER_MSVC) && !defined(_M_IX86) && !defined(_M_ARM64) && \
    !defined(_M_ARM64EC)
extern "C" uint64_t __rdtsc();
#pragma intrinsic(__rdtsc)
#endif

#if !defined(BENCHMARK_OS_WINDOWS) || defined(BENCHMARK_OS_MINGW)
#include <sys/time.h>
#include <time.h>
#endif

#ifdef BENCHMARK_OS_EMSCRIPTEN
#include <emscripten.h>
#endif

namespace benchmark {
// NOTE: only i386 and x86_64 have been well tested.
// PPC, sparc, alpha, and ia64 are based on
//    http://peter.kuscsik.com/wordpress/?p=14
// with modifications by m3b.  See also
//    https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h
namespace cycleclock {
// This should return the number of cycles since power-on.  Thread-safe.
inline BENCHMARK_ALWAYS_INLINE int64_t Now() { … }
}  // end namespace cycleclock
}  // end namespace benchmark

#endif  // BENCHMARK_CYCLECLOCK_H_
llvm/third-party/benchmark/src/cycleclock.h
