74 lines
1.8 KiB
C++
74 lines
1.8 KiB
C++
/*
|
|
* 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
|