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libstdc++: Refactor Hashtable erasure

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This reworks the internal member functions for erasure from
unordered containers, similarly to the earlier commit doing it for
insertion.

Instead of multiple overloads of _M_erase which are selected via tag
dispatching, the erase(const key_type&) member can use 'if constexpr' to
choose an appropriate implementation (returning after erasing a single
element for unique keys, or continuing to erase all equivalent elements
for non-unique keys).

libstdc++-v3/ChangeLog:

	* include/bits/hashtable.h (_Hashtable::_M_erase): Remove
	overloads for erasing by key, moving logic to ...
	(_Hashtable::erase): ... here.

Reviewed-by: François Dumont <fdumont@gcc.gnu.org>
This commit is contained in:
Jonathan Wakely 2024-10-31 19:53:55 +00:00 committed by Jonathan Wakely
parent ce2cf1f032
commit 73676cfb20
No known key found for this signature in database
1 changed files with 37 additions and 72 deletions
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109
libstdc++-v3/include/bits/hashtable.h
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@ -955,12 +955,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
iterator
_M_emplace_multi(const_iterator, _Args&&... __args);
size_type
_M_erase(true_type __uks, const key_type&);
size_type
_M_erase(false_type __uks, const key_type&);
iterator
_M_erase(size_type __bkt, __node_base_ptr __prev_n, __node_ptr __n);
@ -1002,8 +996,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ return erase(const_iterator(__it)); }
size_type
erase(const key_type& __k)
{ return _M_erase(__unique_keys{}, __k); }
erase(const key_type& __k);
iterator
erase(const_iterator, const_iterator);
@ -2372,6 +2365,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __result;
}
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
template<typename _Key, typename _Value, typename _Alloc,
typename _ExtractKey, typename _Equal,
typename _Hash, typename _RangeHash, typename _Unused,
@ -2379,7 +2374,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
auto
_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
_M_erase(true_type /* __uks */, const key_type& __k)
erase(const key_type& __k)
-> size_type
{
__node_base_ptr __prev_n;
@ -2409,77 +2404,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__n = static_cast<__node_ptr>(__prev_n->_M_nxt);
}
_M_erase(__bkt, __prev_n, __n);
return 1;
}
template<typename _Key, typename _Value, typename _Alloc,
typename _ExtractKey, typename _Equal,
typename _Hash, typename _RangeHash, typename _Unused,
typename _RehashPolicy, typename _Traits>
auto
_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
_M_erase(false_type /* __uks */, const key_type& __k)
-> size_type
{
std::size_t __bkt;
__node_base_ptr __prev_n;
__node_ptr __n;
if (size() <= __small_size_threshold())
if constexpr (__unique_keys::value)
{
__prev_n = _M_find_before_node(__k);
if (!__prev_n)
return 0;
// We found a matching node, erase it.
__n = static_cast<__node_ptr>(__prev_n->_M_nxt);
__bkt = _M_bucket_index(*__n);
_M_erase(__bkt, __prev_n, __n);
return 1;
}
else
{
__hash_code __code = this->_M_hash_code(__k);
__bkt = _M_bucket_index(__code);
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 526. Is it undefined if a function in the standard changes
// in parameters?
// We use one loop to find all matching nodes and another to
// deallocate them so that the key stays valid during the first loop.
// It might be invalidated indirectly when destroying nodes.
__node_ptr __n_last = __n->_M_next();
while (__n_last && this->_M_node_equals(*__n, *__n_last))
__n_last = __n_last->_M_next();
// Look for the node before the first matching node.
__prev_n = _M_find_before_node(__bkt, __k, __code);
if (!__prev_n)
return 0;
std::size_t __n_last_bkt
= __n_last ? _M_bucket_index(*__n_last) : __bkt;
__n = static_cast<__node_ptr>(__prev_n->_M_nxt);
// Deallocate nodes.
size_type __result = 0;
do
{
__node_ptr __p = __n->_M_next();
this->_M_deallocate_node(__n);
__n = __p;
++__result;
}
while (__n != __n_last);
_M_element_count -= __result;
if (__prev_n == _M_buckets[__bkt])
_M_remove_bucket_begin(__bkt, __n_last, __n_last_bkt);
else if (__n_last_bkt != __bkt)
_M_buckets[__n_last_bkt] = __prev_n;
__prev_n->_M_nxt = __n_last;
return __result;
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 526. Is it undefined if a function in the standard changes
// in parameters?
// We use one loop to find all matching nodes and another to deallocate
// them so that the key stays valid during the first loop. It might be
// invalidated indirectly when destroying nodes.
__node_ptr __n_last = __n->_M_next();
while (__n_last && this->_M_node_equals(*__n, *__n_last))
__n_last = __n_last->_M_next();
std::size_t __n_last_bkt = __n_last ? _M_bucket_index(*__n_last) : __bkt;
// Deallocate nodes.
size_type __result = 0;
do
{
__node_ptr __p = __n->_M_next();
this->_M_deallocate_node(__n);
__n = __p;
++__result;
}
while (__n != __n_last);
_M_element_count -= __result;
if (__prev_n == _M_buckets[__bkt])
_M_remove_bucket_begin(__bkt, __n_last, __n_last_bkt);
else if (__n_last_bkt != __bkt)
_M_buckets[__n_last_bkt] = __prev_n;
__prev_n->_M_nxt = __n_last;
return __result;
}
#pragma GCC diagnostic pop
template<typename _Key, typename _Value, typename _Alloc,
typename _ExtractKey, typename _Equal,