diff mbox series

[committed] libstdc++: Simplify noexcept-specifiers for move constructors

Message ID YG80SsOS4033NG9f@redhat.com
State New
Headers show
Series [committed] libstdc++: Simplify noexcept-specifiers for move constructors | expand

Commit Message

Jonathan Wakely April 8, 2021, 4:50 p.m. UTC 
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.

Tested powerpc64le-linux. Committed to trunk.
commit 1cbba49e3417d9b0661e70301d6fb7a7f52fd360
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Apr 8 16:29:11 2021

    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.

Comments

Jonathan Wakely April 9, 2021, 12:06 p.m. UTC | #1 
On 08/04/21 17:50 +0100, Jonathan Wakely wrote:
>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.
>

I keep forgetting that a constexpr function in C++11 has to be a single
return statement.

I'm testing this patch now and will push to trunk and backport to the
branches where I already backported the breakage (facepalm).
diff mbox series

Patch

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" );