[gcc r11-8062] libstdc++: Simplify noexcept-specifiers for move constructors

Jonathan Wakely redi@gcc.gnu.org
Thu Apr 8 16:50:09 GMT 2021


https://gcc.gnu.org/g:1cbba49e3417d9b0661e70301d6fb7a7f52fd360

commit r11-8062-g1cbba49e3417d9b0661e70301d6fb7a7f52fd360
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Apr 8 16:29:11 2021 +0100

    libstdc++: Simplify noexcept-specifiers for move constructors
    
    This puts the logic for the noexcept-specifier in one place, and then
    reuses it elsewhere. This means checking whether the move constructor
    can throw doesn't need to do overload resolution and then check whether
    some other constructor can throw, we just get the answer directly.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/hashtable.h (_Hashtable::_S_nothrow_move()):
            New function to determine noexcept-specifier for move
            constructors.
            (_Hashtable): Use _S_nothrow_move() on move constructors.
            * testsuite/23_containers/unordered_map/cons/noexcept_move_construct.cc:
            Correct static assertion message.
            * testsuite/23_containers/unordered_multimap/cons/noexcept_move_construct.cc:
            Likewise.
            * testsuite/23_containers/unordered_multiset/cons/noexcept_move_construct.cc:
            Likewise.
            * testsuite/23_containers/unordered_set/cons/noexcept_move_construct.cc:
            Likewise.

Diff:
---
 libstdc++-v3/include/bits/hashtable.h              | 26 ++++++++++++----------
 .../unordered_map/cons/noexcept_move_construct.cc  |  4 ++--
 .../cons/noexcept_move_construct.cc                |  4 ++--
 .../cons/noexcept_move_construct.cc                |  4 ++--
 .../unordered_set/cons/noexcept_move_construct.cc  |  4 ++--
 5 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index fa80675ad91..39872ce5342 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -472,10 +472,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	__hashtable_alloc(__node_alloc_type(__a))
       { }
 
+      template<bool _No_realloc = true>
+	static constexpr bool
+	_S_nothrow_move()
+	{
+	  if _GLIBCXX17_CONSTEXPR (_No_realloc)
+	    if _GLIBCXX17_CONSTEXPR (is_nothrow_copy_constructible<_Hash>())
+	      return is_nothrow_copy_constructible<_Equal>();
+	  return false;
+	}
+
       _Hashtable(_Hashtable&& __ht, __node_alloc_type&& __a,
 		 true_type /* alloc always equal */)
-	noexcept(std::is_nothrow_copy_constructible<_Hash>::value &&
-		 std::is_nothrow_copy_constructible<_Equal>::value);
+	noexcept(_S_nothrow_move());
 
       _Hashtable(_Hashtable&&, __node_alloc_type&&,
 		 false_type /* alloc always equal */);
@@ -508,19 +517,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // Use delegating constructors.
       _Hashtable(_Hashtable&& __ht)
-	noexcept( noexcept(
-	  _Hashtable(std::declval<_Hashtable>(),
-		     std::declval<__node_alloc_type>(),
-		     true_type{})) )
+	noexcept(_S_nothrow_move())
       : _Hashtable(std::move(__ht), std::move(__ht._M_node_allocator()),
 		   true_type{})
       { }
 
       _Hashtable(_Hashtable&& __ht, const allocator_type& __a)
-	noexcept( noexcept(
-	  _Hashtable(std::declval<_Hashtable>(),
-		     std::declval<__node_alloc_type>(),
-		     typename __node_alloc_traits::is_always_equal{})) )
+	noexcept(_S_nothrow_move<__node_alloc_traits::_S_always_equal()>())
       : _Hashtable(std::move(__ht), __node_alloc_type(__a),
 		   typename __node_alloc_traits::is_always_equal{})
       { }
@@ -1400,8 +1403,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	       _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
     _Hashtable(_Hashtable&& __ht, __node_alloc_type&& __a,
 	       true_type /* alloc always equal */)
-    noexcept(std::is_nothrow_copy_constructible<_Hash>::value &&
-	     std::is_nothrow_copy_constructible<_Equal>::value)
+    noexcept(_S_nothrow_move())
     : __hashtable_base(__ht),
       __map_base(__ht),
       __rehash_base(__ht),
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_map/cons/noexcept_move_construct.cc b/libstdc++-v3/testsuite/23_containers/unordered_map/cons/noexcept_move_construct.cc
index 96245aa4c88..015646adf23 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_map/cons/noexcept_move_construct.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_map/cons/noexcept_move_construct.cc
@@ -40,7 +40,7 @@ struct not_noexcept_copy_cons_hash
 using type2 = std::unordered_map<int, int, not_noexcept_copy_cons_hash>;
 
 static_assert( !std::is_nothrow_move_constructible<type2>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type2, type2&&,
 	       const typename type2::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
@@ -59,7 +59,7 @@ using type3 = std::unordered_map<int, int, std::hash<int>,
 				  not_noexcept_copy_cons_equal_to>;
 
 static_assert( !std::is_nothrow_move_constructible<type3>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type3, type3&&,
 	       const typename type3::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/noexcept_move_construct.cc b/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/noexcept_move_construct.cc
index efc8d337e7e..1e0b1059d7d 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/noexcept_move_construct.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/noexcept_move_construct.cc
@@ -40,7 +40,7 @@ struct not_noexcept_copy_cons_hash
 using type2 = std::unordered_multimap<int, int, not_noexcept_copy_cons_hash>;
 
 static_assert( !std::is_nothrow_move_constructible<type2>::value,
-	       "noexcept move constructor" );
+	       "not not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type2, type2&&,
 	       const typename type2::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
@@ -59,7 +59,7 @@ using type3 = std::unordered_multimap<int, int, std::hash<int>,
 				       not_noexcept_copy_cons_equal_to>;
 
 static_assert( !std::is_nothrow_move_constructible<type3>::value,
-	       "noexcept move constructor" );
+	       "not not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type3, type3&&,
 	       const typename type3::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_multiset/cons/noexcept_move_construct.cc b/libstdc++-v3/testsuite/23_containers/unordered_multiset/cons/noexcept_move_construct.cc
index cc2a8e31051..3e603802f13 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_multiset/cons/noexcept_move_construct.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multiset/cons/noexcept_move_construct.cc
@@ -40,7 +40,7 @@ struct not_noexcept_copy_cons_hash
 using type2 = std::unordered_multiset<int, not_noexcept_copy_cons_hash>;
 
 static_assert( !std::is_nothrow_move_constructible<type2>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type2, type2&&,
 	       const typename type2::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
@@ -59,7 +59,7 @@ using type3 = std::unordered_multiset<int, std::hash<int>,
 				      not_noexcept_copy_cons_equal_to>;
 
 static_assert( !std::is_nothrow_move_constructible<type3>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type3, type3&&,
 	       const typename type3::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/cons/noexcept_move_construct.cc b/libstdc++-v3/testsuite/23_containers/unordered_set/cons/noexcept_move_construct.cc
index f68095302d5..28cb539e9f5 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_set/cons/noexcept_move_construct.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/cons/noexcept_move_construct.cc
@@ -40,7 +40,7 @@ struct not_noexcept_copy_cons_hash
 using type2 = std::unordered_set<int, not_noexcept_copy_cons_hash>;
 
 static_assert( !std::is_nothrow_move_constructible<type2>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type2, type2&&,
 	       const typename type2::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );
@@ -59,7 +59,7 @@ using type3 = std::unordered_set<int, std::hash<int>,
 				  not_noexcept_copy_cons_equal_to>;
 
 static_assert( !std::is_nothrow_move_constructible<type3>::value,
-	       "noexcept move constructor" );
+	       "not noexcept move constructor" );
 static_assert( !std::is_nothrow_constructible<type3, type3&&,
 	       const typename type3::allocator_type&>::value,
 	       "not noexcept move constructor with allocator" );


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