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>
22 #include <glog/logging.h>
27 * Inform the compiler that the argument can be assumed true. It is
28 * undefined behavior if the argument is not actually true, so use
31 * Implemented as a function instead of a macro because
32 * __builtin_assume does not evaluate its argument at runtime, so it
33 * cannot be used with expressions that have side-effects.
36 FOLLY_ALWAYS_INLINE void assume(bool cond) {
39 #elif defined(__clang__) // Must go first because Clang also defines __GNUC__.
40 __builtin_assume(cond);
41 #elif defined(__GNUC__)
42 if (!cond) { __builtin_unreachable(); }
43 #elif defined(_MSC_VER)
50 [[noreturn]] FOLLY_ALWAYS_INLINE void assume_unreachable() {
52 // Do a bit more to get the compiler to understand
53 // that this function really will never return.
55 __builtin_unreachable();
56 #elif defined(_MSC_VER)
59 // Well, it's better than nothing.