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https://github.com/llvm-mirror/libcxx.git
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66bdfe223e
Summary:
`std::move` and `std::forward` were not marked constexpr in C++11. This can be very damaging because it makes otherwise constant expressions non-constant. For example:
```
#include <utility>
template <class T>
struct Foo {
constexpr Foo(T&& tx) : t(std::move(tx)) {}
T t;
};
[[clang::require_constant_initialization]] Foo<int> f(42); // Foo should be constant initialized but C++11 move is not constexpr. As a result `f` is an unsafe global.
```
This patch applies `constexpr` to `move` and `forward` as an extension in C++11. Normally the library is not allowed to add `constexpr` because it may be observable to the user. In particular adding constexpr may cause valid code to stop compiling. However these problems only happen in more complex situations, like making `__invoke(...)` constexpr. `forward` and `move` are simply enough that applying `constexpr` is safe.
Note that libstdc++ has offered this extension since at least 4.8.1.
Most of the changes in this patch are simply test cleanups or additions. The main changes in the tests are:
* Fold all `forward_N.fail.cpp` tests into a single `forward.fail.cpp` test using -verify.
* Delete most `move_only_N.fail.cpp` tests because they weren't actually testing anything.
* Fold `move_copy.pass.cpp` and `move_only.pass.cpp` into a single `move.pass.cpp` test.
* Add return type and noexcept tests for `forward` and `move`.
Reviewers: rsmith, mclow.lists, EricWF
Subscribers: K-ballo, loladiro
Differential Revision: https://reviews.llvm.org/D24637
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@282439 91177308-0d34-0410-b5e6-96231b3b80d8
92 lines
3.1 KiB
C++
92 lines
3.1 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++98, c++03
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// test forward
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#include <utility>
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#include <type_traits>
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#include <cassert>
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#include "test_macros.h"
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struct A
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{
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};
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A source() noexcept {return A();}
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const A csource() noexcept {return A();}
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constexpr bool test_constexpr_forward() {
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#if TEST_STD_VER > 11
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int x = 42;
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const int cx = 101;
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return std::forward<int&>(x) == 42
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&& std::forward<int>(x) == 42
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&& std::forward<const int&>(x) == 42
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&& std::forward<const int>(x) == 42
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&& std::forward<int&&>(x) == 42
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&& std::forward<const int&&>(x) == 42
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&& std::forward<const int&>(cx) == 101
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&& std::forward<const int>(cx) == 101;
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#else
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return true;
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#endif
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}
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int main()
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{
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A a;
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const A ca = A();
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((void)a); // Prevent unused warning
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((void)ca); // Prevent unused warning
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static_assert(std::is_same<decltype(std::forward<A&>(a)), A&>::value, "");
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static_assert(std::is_same<decltype(std::forward<A>(a)), A&&>::value, "");
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static_assert(std::is_same<decltype(std::forward<A>(source())), A&&>::value, "");
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static_assert(noexcept(std::forward<A&>(a)), "");
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static_assert(noexcept(std::forward<A>(a)), "");
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static_assert(noexcept(std::forward<A>(source())), "");
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static_assert(std::is_same<decltype(std::forward<const A&>(a)), const A&>::value, "");
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static_assert(std::is_same<decltype(std::forward<const A>(a)), const A&&>::value, "");
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static_assert(std::is_same<decltype(std::forward<const A>(source())), const A&&>::value, "");
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static_assert(noexcept(std::forward<const A&>(a)), "");
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static_assert(noexcept(std::forward<const A>(a)), "");
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static_assert(noexcept(std::forward<const A>(source())), "");
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static_assert(std::is_same<decltype(std::forward<const A&>(ca)), const A&>::value, "");
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static_assert(std::is_same<decltype(std::forward<const A>(ca)), const A&&>::value, "");
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static_assert(std::is_same<decltype(std::forward<const A>(csource())), const A&&>::value, "");
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static_assert(noexcept(std::forward<const A&>(ca)), "");
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static_assert(noexcept(std::forward<const A>(ca)), "");
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static_assert(noexcept(std::forward<const A>(csource())), "");
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#if TEST_STD_VER > 11
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{
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constexpr int i2 = std::forward<int>(42);
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static_assert(std::forward<int>(42) == 42, "");
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static_assert(std::forward<const int&>(i2) == 42, "");
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static_assert(test_constexpr_forward(), "");
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}
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#endif
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#if TEST_STD_VER == 11 && defined(_LIBCPP_VERSION)
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// Test that std::forward is constexpr in C++11. This is an extension
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// provided by both libc++ and libstdc++.
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{
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constexpr int i2 = std::forward<int>(42);
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static_assert(std::forward<int>(42) == 42, "" );
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static_assert(std::forward<const int&>(i2) == 42, "");
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}
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#endif
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}
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