2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
21 #include <folly/Portability.h>
27 extern void assume_check(bool cond);
32 * Inform the compiler that the argument can be assumed true. It is
33 * undefined behavior if the argument is not actually true, so use
36 * Implemented as a function instead of a macro because
37 * __builtin_assume does not evaluate its argument at runtime, so it
38 * cannot be used with expressions that have side-effects.
41 FOLLY_ALWAYS_INLINE void assume(bool cond) {
43 detail::assume_check(cond);
45 #if defined(__clang__) // Must go first because Clang also defines __GNUC__.
46 __builtin_assume(cond);
47 #elif defined(__GNUC__)
48 if (!cond) { __builtin_unreachable(); }
49 #elif defined(_MSC_VER)
57 [[noreturn]] FOLLY_ALWAYS_INLINE void assume_unreachable() {
59 // Do a bit more to get the compiler to understand
60 // that this function really will never return.
62 __builtin_unreachable();
63 #elif defined(_MSC_VER)
66 // Well, it's better than nothing.