From 87a9bfe86d8a87d09de5d60e430d14bfa6c816f0 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 20 Jul 2022 16:51:44 +0100
Subject: [PATCH] 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.
---
 libstdc++-v3/include/bits/stl_iterator.h          | 15 +++++++++++++++
 .../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()
 {
-- 
2.47.2