[pair] Mark constructors as conditionally noexcept

Summary:
std::tuple marks its constructors as noexcept when the corresponding
memberwise constructors are noexcept too -- this commit improves std::pair
so that it behaves the same.

This is a re-application of r348824, which broke the build in C++03 mode
because a test was marked as supported in C++03 when it shouldn't be.

Note:
I did not add support in the explicit and non-explicit `pair(_Tuple&& __p)`
constructors because those are non-standard extensions, and supporting them
properly is tedious (we have to copy the rvalue-referenceness of the deduced
_Tuple&& onto the result of tuple_element).

<rdar://problem/29537079>

Reviewers: mclow.lists, EricWF

Subscribers: christof, llvm-commits

Differential Revision: https://reviews.llvm.org/D48669

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@348847 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 1 deletions

diff --git a/include/utility b/include/utility
index ddfa27e22..fb7f44705 100644
--- a/include/utility
+++ b/include/utility
@@ -409,13 +409,17 @@ struct _LIBCPP_TEMPLATE_VIS pair
             _CheckArgsDep<_Dummy>::template __enable_default<_T1, _T2>()
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
-    pair() : first(), second() {}
+    pair() _NOEXCEPT_(is_nothrow_default_constructible<first_type>::value &&
+                      is_nothrow_default_constructible<second_type>::value)
+        : first(), second() {}
 
     template <bool _Dummy = true, _EnableB<
              _CheckArgsDep<_Dummy>::template __enable_explicit<_T1 const&, _T2 const&>()
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     explicit pair(_T1 const& __t1, _T2 const& __t2)
+        _NOEXCEPT_(is_nothrow_copy_constructible<first_type>::value &&
+                   is_nothrow_copy_constructible<second_type>::value)
         : first(__t1), second(__t2) {}
 
     template<bool _Dummy = true, _EnableB<
@@ -423,6 +427,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     pair(_T1 const& __t1, _T2 const& __t2)
+        _NOEXCEPT_(is_nothrow_copy_constructible<first_type>::value &&
+                   is_nothrow_copy_constructible<second_type>::value)
         : first(__t1), second(__t2) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -430,6 +436,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     explicit pair(_U1&& __u1, _U2&& __u2)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1>::value &&
+                    is_nothrow_constructible<second_type, _U2>::value))
         : first(_VSTD::forward<_U1>(__u1)), second(_VSTD::forward<_U2>(__u2)) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -437,6 +445,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     pair(_U1&& __u1, _U2&& __u2)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1>::value &&
+                    is_nothrow_constructible<second_type, _U2>::value))
         : first(_VSTD::forward<_U1>(__u1)), second(_VSTD::forward<_U2>(__u2)) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -444,6 +454,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     explicit pair(pair<_U1, _U2> const& __p)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1 const&>::value &&
+                    is_nothrow_constructible<second_type, _U2 const&>::value))
         : first(__p.first), second(__p.second) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -451,6 +463,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     pair(pair<_U1, _U2> const& __p)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1 const&>::value &&
+                    is_nothrow_constructible<second_type, _U2 const&>::value))
         : first(__p.first), second(__p.second) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -458,6 +472,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     explicit pair(pair<_U1, _U2>&&__p)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1&&>::value &&
+                    is_nothrow_constructible<second_type, _U2&&>::value))
         : first(_VSTD::forward<_U1>(__p.first)), second(_VSTD::forward<_U2>(__p.second)) {}
 
     template<class _U1, class _U2, _EnableB<
@@ -465,6 +481,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     > = false>
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
     pair(pair<_U1, _U2>&& __p)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _U1&&>::value &&
+                    is_nothrow_constructible<second_type, _U2&&>::value))
         : first(_VSTD::forward<_U1>(__p.first)), second(_VSTD::forward<_U2>(__p.second)) {}
 
     template<class _Tuple, _EnableB<
@@ -487,6 +505,8 @@ struct _LIBCPP_TEMPLATE_VIS pair
     _LIBCPP_INLINE_VISIBILITY
     pair(piecewise_construct_t __pc,
          tuple<_Args1...> __first_args, tuple<_Args2...> __second_args)
+        _NOEXCEPT_((is_nothrow_constructible<first_type, _Args1...>::value &&
+                    is_nothrow_constructible<second_type, _Args2...>::value))
         : pair(__pc, __first_args, __second_args,
                 typename __make_tuple_indices<sizeof...(_Args1)>::type(),
                 typename __make_tuple_indices<sizeof...(_Args2) >::type()) {}