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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
122 lines
3.0 KiB
C++
122 lines
3.0 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 move
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// UNSUPPORTED: c++98, c++03
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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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class move_only
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{
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move_only(const move_only&);
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move_only& operator=(const move_only&);
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public:
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move_only(move_only&&) {}
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move_only& operator=(move_only&&) {return *this;}
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move_only() {}
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};
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move_only source() {return move_only();}
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const move_only csource() {return move_only();}
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void test(move_only) {}
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int x = 42;
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const int& cx = x;
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template <class QualInt>
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QualInt get() noexcept { return static_cast<QualInt>(x); }
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int copy_ctor = 0;
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int move_ctor = 0;
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struct A {
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A() {}
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A(const A&) {++copy_ctor;}
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A(A&&) {++move_ctor;}
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A& operator=(const A&) = delete;
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};
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constexpr bool test_constexpr_move() {
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#if TEST_STD_VER > 11
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int x = 42;
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const int cx = x;
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return std::move(x) == 42
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&& std::move(cx) == 42
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&& std::move(static_cast<int&&>(x)) == 42
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&& std::move(static_cast<int const&&>(x)) == 42;
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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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{ // Test return type and noexcept.
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static_assert(std::is_same<decltype(std::move(x)), int&&>::value, "");
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static_assert(noexcept(std::move(x)), "");
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static_assert(std::is_same<decltype(std::move(cx)), const int&&>::value, "");
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static_assert(noexcept(std::move(cx)), "");
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static_assert(std::is_same<decltype(std::move(42)), int&&>::value, "");
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static_assert(noexcept(std::move(42)), "");
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static_assert(std::is_same<decltype(std::move(get<const int&&>())), const int&&>::value, "");
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static_assert(noexcept(std::move(get<int const&&>())), "");
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}
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{ // test copy and move semantics
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A a;
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const A ca = A();
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assert(copy_ctor == 0);
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assert(move_ctor == 0);
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A a2 = a;
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assert(copy_ctor == 1);
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assert(move_ctor == 0);
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A a3 = std::move(a);
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assert(copy_ctor == 1);
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assert(move_ctor == 1);
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A a4 = ca;
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assert(copy_ctor == 2);
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assert(move_ctor == 1);
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A a5 = std::move(ca);
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assert(copy_ctor == 3);
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assert(move_ctor == 1);
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}
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{ // test on a move only type
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move_only mo;
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test(std::move(mo));
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test(source());
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}
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#if TEST_STD_VER > 11
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{
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constexpr int x = 42;
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static_assert(std::move(x) == 42, "");
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static_assert(test_constexpr_move(), "");
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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 x = 42;
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static_assert(std::move(x) == 42, "");
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}
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#endif
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}
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