[PATCH] Add noexcept to tuple<> and simplify tuple noexcept-specifiers

[Jonathan Wakely]

        * include/std/tuple (tuple<>): Add noexcept to allocator-extended
        constructors.
        (tuple<T1, T2>::__nothrow_default_constructible()): New helper
        function.
        (tuple<T1, T2>::tuple(), explicit tuple<T1, T2>::tuple()): Use helper.

Tested powerpc64le-linux, committed to trunk.


commit d099e922a9b5ca48bed5a1fa3fc5977dbdb0f070
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri May 31 11:52:47 2019 +0100

    Add noexcept to tuple<> and simplify tuple<T1,T2> noexcept-specifiers
    
            * include/std/tuple (tuple<>): Add noexcept to allocator-extended
            constructors.
            (tuple<T1, T2>::__nothrow_default_constructible()): New helper
            function.
            (tuple<T1, T2>::tuple(), explicit tuple<T1, T2>::tuple()): Use 
helper.

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index b81157c097b..64516b1dece 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -898,9 +898,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       tuple() = default;
       // No-op allocator constructors.
       template<typename _Alloc>
-       tuple(allocator_arg_t, const _Alloc&) { }
+       tuple(allocator_arg_t, const _Alloc&) noexcept { }
       template<typename _Alloc>
-       tuple(allocator_arg_t, const _Alloc&, const tuple&) { }
+       tuple(allocator_arg_t, const _Alloc&, const tuple&) noexcept { }
     };
 
   /// Partial specialization, 2-element tuple.
@@ -925,11 +925,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        }
 
       template<typename _U1, typename _U2>
-    static constexpr bool __nothrow_constructible()
-    {
-      return __and_<is_nothrow_constructible<_T1, _U1>,
-                       is_nothrow_constructible<_T2, _U2>>::value;
-    }
+       static constexpr bool __nothrow_constructible()
+       {
+         return __and_<is_nothrow_constructible<_T1, _U1>,
+                           is_nothrow_constructible<_T2, _U2>>::value;
+       }
+
+      static constexpr bool __nothrow_default_constructible()
+      {
+       return __and_<is_nothrow_default_constructible<_T1>,
+                     is_nothrow_default_constructible<_T2>>::value;
+      }
 
     public:
       template <typename _U1 = _T1,
@@ -939,8 +945,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                                      
__is_implicitly_default_constructible<_U2>>
                                    ::value, bool>::type = true>
        constexpr tuple()
-       noexcept(__and_<is_nothrow_default_constructible<_T1>,
-                       is_nothrow_default_constructible<_T2>>::value)
+       noexcept(__nothrow_default_constructible())
        : _Inherited() { }
 
       template <typename _U1 = _T1,
@@ -954,8 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                              __is_implicitly_default_constructible<_U2>>>>
                   ::value, bool>::type = false>
        explicit constexpr tuple()
-       noexcept(__and_<is_nothrow_default_constructible<_T1>,
-                       is_nothrow_default_constructible<_T2>>::value)
+       noexcept(__nothrow_default_constructible())
        : _Inherited() { }
 
       // Shortcut for the cases where constructors taking _T1, _T2
@@ -1108,7 +1112,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                  && _TCC<_Dummy>::template
                    _ImplicitlyConvertibleTuple<_T1, _T2>(),
                bool>::type=true>
-
        tuple(allocator_arg_t __tag, const _Alloc& __a,
              const _T1& __a1, const _T2& __a2)
        : _Inherited(__tag, __a, __a1, __a2) { }