Asm.h

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/*
 * Copyright 2016-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <folly/Portability.h>

#include <chrono>
#include <cstdint>

#ifdef _MSC_VER
#include <intrin.h>
#endif

namespace folly {
inline void asm_volatile_memory() {
#if defined(__clang__) || defined(__GNUC__)
  asm volatile("" : : : "memory");
#elif defined(_MSC_VER)
  ::_ReadWriteBarrier();
#endif
}

inline void asm_volatile_pause() {
#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
  ::_mm_pause();
#elif defined(__i386__) || FOLLY_X64
  asm volatile("pause");
#elif FOLLY_AARCH64 || defined(__arm__)
  asm volatile("yield");
#elif FOLLY_PPC64
  asm volatile("or 27,27,27");
#endif
}

inline std::uint64_t asm_rdtsc() {
#if _MSC_VER
  return (uint64_t)__rdtsc();
#elif defined(__i386__) || FOLLY_X64
  // read the timestamp counter on x86
  auto hi = std::uint32_t{};
  auto lo = std::uint32_t{};
  asm volatile("rdtsc" : "=a"(lo), "=d"(hi));
  return (((std::uint64_t)lo) + (((std::uint64_t)hi) << 32));
#else
  // use steady_clock::now() as an approximation for the timestamp counter on
  // non-x86 systems
  return std::chrono::steady_clock::now().time_since_epoch().count();
#endif
}
} // namespace folly