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- /*
- * Copyright 2015-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 <cstdlib>
- #include <folly/Portability.h>
- namespace folly {
- namespace detail {
- extern void assume_check(bool cond);
- } // namespace detail
- /**
- * Inform the compiler that the argument can be assumed true. It is
- * undefined behavior if the argument is not actually true, so use
- * with care.
- *
- * Implemented as a function instead of a macro because
- * __builtin_assume does not evaluate its argument at runtime, so it
- * cannot be used with expressions that have side-effects.
- */
- FOLLY_ALWAYS_INLINE void assume(bool cond) {
- if (kIsDebug) {
- detail::assume_check(cond);
- } else {
- #if defined(__clang__) // Must go first because Clang also defines __GNUC__.
- __builtin_assume(cond);
- #elif defined(__GNUC__)
- if (!cond) {
- __builtin_unreachable();
- }
- #elif defined(_MSC_VER)
- __assume(cond);
- #else
- // Do nothing.
- #endif
- }
- }
- [[noreturn]] FOLLY_ALWAYS_INLINE void assume_unreachable() {
- assume(false);
- // Do a bit more to get the compiler to understand
- // that this function really will never return.
- #if defined(__GNUC__)
- __builtin_unreachable();
- #elif defined(_MSC_VER)
- __assume(0);
- #else
- // Well, it's better than nothing.
- std::abort();
- #endif
- }
- } // namespace folly
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