2 * Copyright 2017-present 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.
19 #include <folly/CPortability.h>
20 #include <folly/Portability.h>
25 * Approximate backport from C++17 of std::launder. It should be `constexpr`
26 * but that can't be done without specific support from the compiler.
29 FOLLY_NODISCARD inline T* launder(T* in) noexcept {
30 #if FOLLY_HAS_BUILTIN(__builtin_launder) || __GNUC__ >= 7
31 // The builtin has no unwanted side-effects.
32 return __builtin_launder(in);
34 // This inline assembler block declares that `in` is an input and an output,
35 // so the compiler has to assume that it has been changed inside the block.
36 __asm__("" : "+r"(in));
40 false, "folly::launder is not implemented for this environment");
44 /* The standard explicitly forbids laundering these */
45 void launder(void*) = delete;
46 void launder(void const*) = delete;
47 void launder(void volatile*) = delete;
48 void launder(void const volatile*) = delete;
49 template <typename T, typename... Args>
50 void launder(T (*)(Args...)) = delete;