diff mbox series

Fix some _Hashtable implementation inconsistencies

Message ID 33139fa4-bc8b-4adb-97c1-9da3a377f56c@gmail.com
State New
Headers show
Series Fix some _Hashtable implementation inconsistencies | expand

Commit Message

François Dumont Nov. 15, 2023, 5:55 a.m. UTC
Following several remarks on a previous patch of _Hashtable I considered 
clarifying its implementation.

     libstdc++: [_Hashtable] Fix some implementation inconsistencies

     Get rid of the different usages of the mutable keyword. For
     _Prime_rehash_policy methods are exported from the library, we need to
     keep their const qualifier, so adapt implementation to update 
previously
     mutable member.

     Remove useless noexcept qualification on _Hashtable _M_bucket_index 
overload.
     Fix comment to explain that we need the computation of bucket index 
to be
     noexcept to be able to rehash the container when needed. For Standard
     instantiations through std::unordered_xxx containers we already force
     usage of hash code cache when hash functor is not noexcep so it is 
guarantied.
     The static_assert purpose in _Hashtable on _M_bucket_index is thus 
limited
     to usages of _Hashtable with exotic _Hashtable_traits.

     libstdc++-v3/ChangeLog:

             * include/bits/hashtable_policy.h 
(_NodeBuilder<>::_S_build): Remove
             const qualification on _NodeGenerator instance.
(_ReuseOrAllocNode<>::operator()(_Args&&...)): Remove const qualification.
             (_ReuseOrAllocNode<>::_M_nodes): Remove mutable.
             (_Prime_rehash_policy::max_load_factor()): Remove noexcept.
             (_Prime_rehash_policy::_M_reset()): Remove noexcept.
             (_Prime_rehash_policy::_M_next_resize): Remove mutable.
             (_Power2_rehash_policy::_M_next_bkt(size_t)): Remove noexcept.
             (_Power2_rehash_policy::_M_bkt_for_elements(size_t)): 
Remove noexcept.
             (_Power2_rehash_policy::_M_neeed_rehash): Remove noexcept.
             (_Power2_rehash_policy::_M_reset): Remove noexcept.
             (_Insert_base<>::_M_insert_range): Remove _NodeGetter const 
qualification.
             (_Hash_code_base<>::_M_bucket_index(const 
_Hash_node_value<>&, size_t)):
             Simplify noexcept declaration, we already static_assert 
that _RangeHash functor
             is noexcept.
             * include/bits/hashtable.h: Rework comments. Remove const 
qualifier on
             _NodeGenerator& arguments.
             (_Hashtable<>::_M_bucket_index(const __node_value_type&)): 
Remove useless
             noexcept qualification.
             * src/c++11/hashtable_c++0x.cc (_Prime_rehash_policy): 
Workaround
             _M_next_resize not being mutable anymore.

Tested under Linux x86_64,

ok to commit ?

François
diff mbox series

Patch

diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index 89132430f3e..8d462ce7bd5 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -51,7 +51,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     using __cache_default
       =  __not_<__and_<// Do not cache for fast hasher.
 		       __is_fast_hash<_Hash>,
-		       // Mandatory to have erase not throwing.
+		       // Mandatory for the rehash process.
 		       __is_nothrow_invocable<const _Hash&, const _Tp&>>>;
 
   // Helper to conditionally delete the default constructor.
@@ -480,7 +480,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Ht, typename _NodeGenerator>
 	void
-	_M_assign(_Ht&&, const _NodeGenerator&);
+	_M_assign(_Ht&&, _NodeGenerator&);
 
       void
       _M_move_assign(_Hashtable&&, true_type);
@@ -795,7 +795,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     private:
       // Bucket index computation helpers.
       size_type
-      _M_bucket_index(const __node_value_type& __n) const noexcept
+      _M_bucket_index(const __node_value_type& __n) const
       { return __hash_code_base::_M_bucket_index(__n, _M_bucket_count); }
 
       size_type
@@ -923,7 +923,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert_unique(_Kt&&, _Arg&&, const _NodeGenerator&);
+	_M_insert_unique(_Kt&&, _Arg&&, _NodeGenerator&);
 
       template<typename _Kt>
 	static __conditional_t<
@@ -943,7 +943,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert_unique_aux(_Arg&& __arg, const _NodeGenerator& __node_gen)
+	_M_insert_unique_aux(_Arg&& __arg, _NodeGenerator& __node_gen)
 	{
 	  return _M_insert_unique(
 	    _S_forward_key(_ExtractKey{}(std::forward<_Arg>(__arg))),
@@ -952,7 +952,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert(_Arg&& __arg, const _NodeGenerator& __node_gen,
+	_M_insert(_Arg&& __arg, _NodeGenerator& __node_gen,
 		  true_type /* __uks */)
 	{
 	  using __to_value
@@ -963,7 +963,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	iterator
-	_M_insert(_Arg&& __arg, const _NodeGenerator& __node_gen,
+	_M_insert(_Arg&& __arg, _NodeGenerator& __node_gen,
 		  false_type __uks)
 	{
 	  using __to_value
@@ -976,7 +976,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Arg, typename _NodeGenerator>
 	iterator
 	_M_insert(const_iterator, _Arg&& __arg,
-		  const _NodeGenerator& __node_gen, true_type __uks)
+		  _NodeGenerator& __node_gen, true_type __uks)
 	{
 	  return
 	    _M_insert(std::forward<_Arg>(__arg), __node_gen, __uks).first;
@@ -986,7 +986,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Arg, typename _NodeGenerator>
 	iterator
 	_M_insert(const_iterator, _Arg&&,
-		  const _NodeGenerator&, false_type __uks);
+		  _NodeGenerator&, false_type __uks);
 
       size_type
       _M_erase(true_type __uks, const key_type&);
@@ -1381,7 +1381,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       void
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
-      _M_assign(_Ht&& __ht, const _NodeGenerator& __node_gen)
+      _M_assign(_Ht&& __ht, _NodeGenerator& __node_gen)
       {
 	__buckets_ptr __buckets = nullptr;
 	if (!_M_buckets)
@@ -1623,8 +1623,10 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ~_Hashtable() noexcept
     {
       // Getting a bucket index from a node shall not throw because it is used
-      // in methods (erase, swap...) that shall not throw. Need a complete
-      // type to check this, so do it in the destructor not at class scope.
+      // during the rehash process. This static_assert purpose is limited to usage
+      // of _Hashtable with _Hashtable_traits requesting non-cached hash code.
+      // Need a complete type to check this, so do it in the destructor not at
+      // class scope.
       static_assert(noexcept(declval<const __hash_code_base_access&>()
 			._M_bucket_index(declval<const __node_value_type&>(),
 					 (std::size_t)0)),
@@ -2225,7 +2227,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
       _M_insert_unique(_Kt&& __k, _Arg&& __v,
-		       const _NodeGenerator& __node_gen)
+		       _NodeGenerator& __node_gen)
       -> pair<iterator, bool>
       {
 	if (size() <= __small_size_threshold())
@@ -2262,7 +2264,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
       _M_insert(const_iterator __hint, _Arg&& __v,
-		const _NodeGenerator& __node_gen,
+		_NodeGenerator& __node_gen,
 		false_type /* __uks */)
       -> iterator
       {
diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index c67eebd3b2b..5c40be2cb72 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -155,7 +155,7 @@  namespace __detail
     {
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	static auto
-	_S_build(_Kt&& __k, _Arg&& __arg, const _NodeGenerator& __node_gen)
+	_S_build(_Kt&& __k, _Arg&& __arg, _NodeGenerator& __node_gen)
 	-> typename _NodeGenerator::__node_ptr
 	{
 	  return __node_gen(std::forward<_Kt>(__k),
@@ -168,7 +168,7 @@  namespace __detail
     {
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	static auto
-	_S_build(_Kt&& __k, _Arg&&, const _NodeGenerator& __node_gen)
+	_S_build(_Kt&& __k, _Arg&&, _NodeGenerator& __node_gen)
 	-> typename _NodeGenerator::__node_ptr
 	{ return __node_gen(std::forward<_Kt>(__k)); }
     };
@@ -212,7 +212,7 @@  namespace __detail
 
       template<typename... _Args>
 	__node_ptr
-	operator()(_Args&&... __args) const
+	operator()(_Args&&... __args)
 	{
 	  if (!_M_nodes)
 	    return _M_h._M_allocate_node(std::forward<_Args>(__args)...);
@@ -230,7 +230,7 @@  namespace __detail
 	}
 
     private:
-      mutable __node_ptr _M_nodes;
+      __node_ptr _M_nodes;
       __hashtable_alloc& _M_h;
     };
 
@@ -551,10 +551,11 @@  namespace __detail
     : _M_max_load_factor(__z), _M_next_resize(0) { }
 
     float
-    max_load_factor() const noexcept
+    max_load_factor() const
     { return _M_max_load_factor; }
 
     // Return a bucket size no smaller than n.
+    // TODO: 'const' qualifier is kept for abi compatibility reason.
     std::size_t
     _M_next_bkt(std::size_t __n) const;
 
@@ -567,6 +568,7 @@  namespace __detail
     // and __n_ins is number of elements to be inserted.  Do we need to
     // increase bucket count?  If so, return make_pair(true, n), where n
     // is the new bucket count.  If not, return make_pair(false, 0).
+    // TODO: 'const' qualifier is kept for abi compatibility reason.
     std::pair<bool, std::size_t>
     _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
 		   std::size_t __n_ins) const;
@@ -578,7 +580,7 @@  namespace __detail
     { return _M_next_resize; }
 
     void
-    _M_reset() noexcept
+    _M_reset()
     { _M_next_resize = 0; }
 
     void
@@ -588,7 +590,7 @@  namespace __detail
     static const std::size_t _S_growth_factor = 2;
 
     float		_M_max_load_factor;
-    mutable std::size_t	_M_next_resize;
+    std::size_t		_M_next_resize;
   };
 
   /// Range hashing function assuming that second arg is a power of 2.
@@ -629,13 +631,13 @@  namespace __detail
     : _M_max_load_factor(__z), _M_next_resize(0) { }
 
     float
-    max_load_factor() const noexcept
+    max_load_factor() const
     { return _M_max_load_factor; }
 
     // Return a bucket size no smaller than n (as long as n is not above the
     // highest power of 2).
     std::size_t
-    _M_next_bkt(std::size_t __n) noexcept
+    _M_next_bkt(std::size_t __n)
     {
       if (__n == 0)
 	// Special case on container 1st initialization with 0 bucket count
@@ -669,7 +671,7 @@  namespace __detail
 
     // Return a bucket count appropriate for n elements
     std::size_t
-    _M_bkt_for_elements(std::size_t __n) const noexcept
+    _M_bkt_for_elements(std::size_t __n) const
     { return __builtin_ceil(__n / (double)_M_max_load_factor); }
 
     // __n_bkt is current bucket count, __n_elt is current element count,
@@ -678,7 +680,7 @@  namespace __detail
     // is the new bucket count.  If not, return make_pair(false, 0).
     std::pair<bool, std::size_t>
     _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
-		   std::size_t __n_ins) noexcept
+		   std::size_t __n_ins)
     {
       if (__n_elt + __n_ins > _M_next_resize)
 	{
@@ -708,11 +710,11 @@  namespace __detail
     { return _M_next_resize; }
 
     void
-    _M_reset() noexcept
+    _M_reset()
     { _M_next_resize = 0; }
 
     void
-    _M_reset(_State __state) noexcept
+    _M_reset(_State __state)
     { _M_next_resize = __state; }
 
     static const std::size_t _S_growth_factor = 2;
@@ -931,12 +933,12 @@  namespace __detail
       template<typename _InputIterator, typename _NodeGetter>
 	void
 	_M_insert_range(_InputIterator __first, _InputIterator __last,
-			const _NodeGetter&, true_type __uks);
+			_NodeGetter&, true_type __uks);
 
       template<typename _InputIterator, typename _NodeGetter>
 	void
 	_M_insert_range(_InputIterator __first, _InputIterator __last,
-			const _NodeGetter&, false_type __uks);
+			_NodeGetter&, false_type __uks);
 
     public:
       using iterator = _Node_iterator<_Value, __constant_iterators::value,
@@ -1012,7 +1014,7 @@  namespace __detail
 		   _Hash, _RangeHash, _Unused,
 		   _RehashPolicy, _Traits>::
       _M_insert_range(_InputIterator __first, _InputIterator __last,
-		      const _NodeGetter& __node_gen, true_type __uks)
+		      _NodeGetter& __node_gen, true_type __uks)
       {
 	__hashtable& __h = _M_conjure_hashtable();
 	for (; __first != __last; ++__first)
@@ -1029,7 +1031,7 @@  namespace __detail
 		   _Hash, _RangeHash, _Unused,
 		   _RehashPolicy, _Traits>::
       _M_insert_range(_InputIterator __first, _InputIterator __last,
-		      const _NodeGetter& __node_gen, false_type __uks)
+		      _NodeGetter& __node_gen, false_type __uks)
       {
 	using __rehash_guard_t = typename __hashtable::__rehash_guard_t;
 	using __pair_type = std::pair<bool, std::size_t>;
@@ -1359,9 +1361,7 @@  namespace __detail
       std::size_t
       _M_bucket_index(const _Hash_node_value<_Value, false>& __n,
 		      std::size_t __bkt_count) const
-	noexcept( noexcept(declval<const _Hash&>()(declval<const _Key&>()))
-		  && noexcept(declval<const _RangeHash&>()((__hash_code)0,
-							   (std::size_t)0)) )
+      noexcept( noexcept(declval<const _Hash&>()(declval<const _Key&>())) )
       {
 	return _RangeHash{}(_M_hash_code(_ExtractKey{}(__n._M_v())),
 			    __bkt_count);
@@ -1369,9 +1369,7 @@  namespace __detail
 
       std::size_t
       _M_bucket_index(const _Hash_node_value<_Value, true>& __n,
-		      std::size_t __bkt_count) const
-	noexcept( noexcept(declval<const _RangeHash&>()((__hash_code)0,
-							(std::size_t)0)) )
+		      std::size_t __bkt_count) const noexcept
       { return _RangeHash{}(__n._M_hash_code, __bkt_count); }
 
       void
diff --git a/libstdc++-v3/src/c++11/hashtable_c++0x.cc b/libstdc++-v3/src/c++11/hashtable_c++0x.cc
index 9673d867402..e75b09a31bb 100644
--- a/libstdc++-v3/src/c++11/hashtable_c++0x.cc
+++ b/libstdc++-v3/src/c++11/hashtable_c++0x.cc
@@ -45,6 +45,7 @@  namespace __detail
   std::size_t
   _Prime_rehash_policy::_M_next_bkt(std::size_t __n) const
   {
+    auto __mutable_this = const_cast<_Prime_rehash_policy*>(this);
     // Optimize lookups involving the first elements of __prime_list.
     // (useful to speed-up, eg, constructors)
     static const unsigned char __fast_bkt[]
@@ -58,7 +59,7 @@  namespace __detail
 	  // want to add an element allocation will take place.
 	  return 1;
 
-	_M_next_resize =
+	__mutable_this->_M_next_resize =
 	  __builtin_floor(__fast_bkt[__n] * (double)_M_max_load_factor);
 	return __fast_bkt[__n];
       }
@@ -79,9 +80,9 @@  namespace __detail
       // Set next resize to the max value so that we never try to rehash again
       // as we already reach the biggest possible bucket number.
       // Note that it might result in max_load_factor not being respected.
-      _M_next_resize = size_t(-1);
+      __mutable_this->_M_next_resize = size_t(-1);
     else
-      _M_next_resize =
+      __mutable_this->_M_next_resize =
 	__builtin_floor(*__next_bkt * (double)_M_max_load_factor);
 
     return *__next_bkt;
@@ -101,6 +102,7 @@  namespace __detail
   _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
 		 std::size_t __n_ins) const
   {
+    auto __mutable_this = const_cast<_Prime_rehash_policy*>(this);
     if (__n_elt + __n_ins > _M_next_resize)
       {
 	// If _M_next_resize is 0 it means that we have nothing allocated so
@@ -114,7 +116,7 @@  namespace __detail
 	    _M_next_bkt(std::max<std::size_t>(__builtin_floor(__min_bkts) + 1,
 					      __n_bkt * _S_growth_factor)) };
 
-	_M_next_resize
+	__mutable_this->_M_next_resize
 	  = __builtin_floor(__n_bkt * (double)_M_max_load_factor);
 	return { false, 0 };
       }