folly/folly/portability/Builtins.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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

#if defined(_WIN32) && !defined(__MINGW32__) && !defined(__clang__)
#include <assert.h>

#include <folly/Portability.h>

#include <intrin.h>
#include <stdint.h>

// MSVC had added support for __builtin_clz etc. in 16.3 (1923) but it will be
// removed in 16.8 (1928).
#if (_MSC_VER >= 1923) && (_MSC_VER < 1928)
#define FOLLY_DETAILFOLLY_DETAIL_MSC_BUILTIN_SUPPORT …
#else
#define FOLLY_DETAILFOLLY_DETAIL_MSC_BUILTIN_SUPPORT …
#endif

namespace folly {
namespace portability {
namespace detail {
void call_flush_instruction_cache_self_pid(void* begin, size_t size);
}
} // namespace portability
} // namespace folly

FOLLY_ALWAYS_INLINE void __builtin___clear_cache(char* begin, char* end) {
  if (folly::kIsArchAmd64) {
    // x86_64 doesn't require the instruction cache to be flushed after
    // modification.
  } else {
    // Default to flushing it for everything else, such as ARM.
    folly::portability::detail::call_flush_instruction_cache_self_pid(
        static_cast<void*>(begin), static_cast<size_t>(end - begin));
  }
}

#if !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)
FOLLY_ALWAYS_INLINE int __builtin_clz(unsigned int x) {
  unsigned long index;
  return int(_BitScanReverse(&index, (unsigned long)x) ? 31 - index : 32);
}

FOLLY_ALWAYS_INLINE int __builtin_clzl(unsigned long x) {
  return __builtin_clz((unsigned int)x);
}

#if defined(_M_IX86) || defined(_M_ARM) || defined(_M_ARM64)
FOLLY_ALWAYS_INLINE int __builtin_clzll(unsigned long long x) {
  if (x == 0) {
    return 64;
  }
  unsigned int msb = (unsigned int)(x >> 32);
  unsigned int lsb = (unsigned int)x;
  return (msb != 0) ? __builtin_clz(msb) : 32 + __builtin_clz(lsb);
}
#else
FOLLY_ALWAYS_INLINE int __builtin_clzll(unsigned long long x) {
  unsigned long index;
  return int(_BitScanReverse64(&index, x) ? 63 - index : 64);
}
#endif

FOLLY_ALWAYS_INLINE int __builtin_ctz(unsigned int x) {
  unsigned long index;
  return int(_BitScanForward(&index, (unsigned long)x) ? index : 32);
}

FOLLY_ALWAYS_INLINE int __builtin_ctzl(unsigned long x) {
  return __builtin_ctz((unsigned int)x);
}

#if defined(_M_IX86) || defined(_M_ARM) || defined(_M_ARM64)
FOLLY_ALWAYS_INLINE int __builtin_ctzll(unsigned long long x) {
  unsigned long index;
  unsigned int msb = (unsigned int)(x >> 32);
  unsigned int lsb = (unsigned int)x;
  if (lsb != 0) {
    return (int)(_BitScanForward(&index, lsb) ? index : 64);
  } else {
    return (int)(_BitScanForward(&index, msb) ? index + 32 : 64);
  }
}
#else
FOLLY_ALWAYS_INLINE int __builtin_ctzll(unsigned long long x) {
  unsigned long index;
  return int(_BitScanForward64(&index, x) ? index : 64);
}
#endif
#endif // !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)

FOLLY_ALWAYS_INLINE int __builtin_ffs(int x) {
  unsigned long index;
  return int(_BitScanForward(&index, (unsigned long)x) ? index + 1 : 0);
}

FOLLY_ALWAYS_INLINE int __builtin_ffsl(long x) {
  return __builtin_ffs(int(x));
}

#if defined(_M_IX86) || defined(_M_ARM) || defined(_M_ARM64)
FOLLY_ALWAYS_INLINE int __builtin_ffsll(long long x) {
  int ctzll = __builtin_ctzll((unsigned long long)x);
  return ctzll != 64 ? ctzll + 1 : 0;
}
#else
FOLLY_ALWAYS_INLINE int __builtin_ffsll(long long x) {
  unsigned long index;
  return int(_BitScanForward64(&index, (unsigned long long)x) ? index + 1 : 0);
}

FOLLY_ALWAYS_INLINE int __builtin_popcount(unsigned int x) {
  return int(__popcnt(x));
}

#if !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)
FOLLY_ALWAYS_INLINE int __builtin_popcountl(unsigned long x) {
  static_assert(sizeof(x) == 4, "");
  return int(__popcnt(x));
}
#endif // !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)
#endif

#if !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)
#if defined(_M_IX86)
FOLLY_ALWAYS_INLINE int __builtin_popcountll(unsigned long long x) {
  return int(__popcnt((unsigned int)(x >> 32))) +
      int(__popcnt((unsigned int)x));
}
#elif defined(_M_X64)
FOLLY_ALWAYS_INLINE int __builtin_popcountll(unsigned long long x) {
  return int(__popcnt64(x));
}
#endif
#endif // !defined(_MSC_VER) || !defined(FOLLY_DETAIL_MSC_BUILTIN_SUPPORT)

FOLLY_ALWAYS_INLINE void* __builtin_return_address(unsigned int frame) {
  // I really hope frame is zero...
  (void)frame;
  assert(frame == 0);
  return _ReturnAddress();
}
#endif

#undef FOLLY_DETAIL_MSC_BUILTIN_SUPPORT