https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118850
Bug ID: 118850
Summary: _Rb_tree emplace unique functions should avoid
allocating node when emplacing value_type
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
template<typename... _Args>
auto
_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::
_M_emplace_unique(_Args&&... __args)
-> pair<iterator, bool>
{
_Auto_node __z(*this, std::forward<_Args>(__args)...);
auto __res = _M_get_insert_unique_pos(__z._M_key());
if (__res.second)
return {__z._M_insert(__res), true};
return {iterator(__res.first), false};
}
We can avoid using an _Auto_node if sizeof...(_Args) == 1 and
remove_cvref_t<_Args> is value_type. We can get the key directly from the
value_type and decide whether we need to insert anything.
Similarly for _M_emplace_hint_unique
For std::map we could also optimize the case where sizeof...(_Args) == 2 and
the first arg is the key_type.
