[gcc r13-1771] libstdc++: Fix std::common_iterator triviality [PR100823]

[Jonathan Wakely]

https://gcc.gnu.org/g:87a9bfe86d8a87d09de5d60e430d14bfa6c816f0

commit r13-1771-g87a9bfe86d8a87d09de5d60e430d14bfa6c816f0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jul 20 16:51:44 2022 +0100

    libstdc++: Fix std::common_iterator triviality [PR100823]
    
    This fixes the remaining problem reported in the PR, that the special
    members should be trivial.  This can be done by constraining the
    non-trivial versions and adding defaulted overloads that will be used
    when the union members are trivial.
    
    Making these members trivial alters the argument passing ABI and so
    isn't suitable for backporting to release branches.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100823
            * include/bits/stl_iterator.h (common_iterator): Define
            destructor, copy constructor and move constructor as trivial
            when the underlying types allow.
            * testsuite/24_iterators/common_iterator/100823.cc: Check
            triviality of special members.

Diff:
---
 libstdc++-v3/include/bits/stl_iterator.h                  | 15 +++++++++++++++
 .../testsuite/24_iterators/common_iterator/100823.cc      | 15 +++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index a913c04deaa..9cd262cd1d9 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1925,9 +1925,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
+    common_iterator(const common_iterator&) = default;
+
     constexpr
     common_iterator(const common_iterator& __x)
     noexcept(_S_noexcept<const _It&, const _Sent&>())
+    requires (!is_trivially_copyable_v<_It> || !is_trivially_copyable_v<_Sent>)
     : _M_valueless(), _M_index(__x._M_index)
     {
       if (_M_index == 0)
@@ -1946,9 +1949,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
     }
 
+    common_iterator(common_iterator&&) = default;
+
     constexpr
     common_iterator(common_iterator&& __x)
     noexcept(_S_noexcept<_It, _Sent>())
+    requires (!is_trivially_copyable_v<_It> || !is_trivially_copyable_v<_Sent>)
     : _M_valueless(), _M_index(__x._M_index)
     {
       if (_M_index == 0)
@@ -2017,8 +2023,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+#if __cpp_concepts >= 202002L // Constrained special member functions
+    ~common_iterator() = default;
+
     constexpr
     ~common_iterator()
+      requires (!is_trivially_destructible_v<_It>
+		  || !is_trivially_destructible_v<_Sent>)
+#else
+    constexpr
+    ~common_iterator()
+#endif
     {
       if (_M_index == 0)
 	_M_it.~_It();
diff --git a/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc b/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc
index 4f2b23de8cc..b42dd087ab2 100644
--- a/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc
+++ b/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc
@@ -4,6 +4,21 @@
 #include <testsuite_iterators.h>
 #include <testsuite_hooks.h>
 
+void
+test_triviality()
+{
+  using I = std::common_iterator<int*, const int*>;
+
+  // Cannot be trivial, because it has to initialize members.
+  static_assert( ! std::is_trivially_default_constructible_v<I> );
+
+  static_assert( std::is_trivially_destructible_v<I> );
+  static_assert( std::is_trivially_copy_constructible_v<I> );
+  static_assert( std::is_trivially_copy_assignable_v<I> );
+  static_assert( std::is_trivially_move_constructible_v<I> );
+  static_assert( std::is_trivially_move_assignable_v<I> );
+}
+
 void
 test_valueless_assignment()
 {