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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
54 lines
1.4 KiB
C++
54 lines
1.4 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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// test forward
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#include <utility>
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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() {return A();}
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const A csource() {return A();}
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int main()
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{
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#if TEST_STD_VER >= 11
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{
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std::forward<A&>(source()); // expected-note {{requested here}}
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// expected-error@type_traits:* 1 {{static_assert failed "can not forward an rvalue as an lvalue"}}
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}
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#else
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{
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std::forward<A&>(source()); // expected-error {{no matching function for call to 'forward'}}
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}
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#endif
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{
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const A ca = A();
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std::forward<A&>(ca); // expected-error {{no matching function for call to 'forward'}}
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}
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{
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std::forward<A&>(csource()); // expected-error {{no matching function for call to 'forward'}}
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}
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{
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const A ca = A();
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std::forward<A>(ca); // expected-error {{no matching function for call to 'forward'}}
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}
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{
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std::forward<A>(csource()); // expected-error {{no matching function for call to 'forward'}}
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}
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{
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A a;
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std::forward(a); // expected-error {{no matching function for call to 'forward'}}
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}
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}
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