https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100070
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is a partial solution:
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -654,6 +654,19 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
const allocator_type& __a = allocator_type())
: _Base(__a)
{
+#if __cpp_lib_concepts
+ if constexpr (forward_iterator<_InputIterator>)
+ {
+ size_type __n;
+ if constexpr (random_access_iterator<_InputIterator>)
+ __n = __last - __first;
+ else
+ __n = std::distance(__first, __last);
+ _M_range_initialize_n(__first, __last, __n);
+ return;
+ }
+ else
+#endif
_M_range_initialize(__first, __last,
std::__iterator_category(__first));
}
@@ -1577,7 +1590,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
std::forward_iterator_tag)
{
- const size_type __n = std::distance(__first, __last);
+ _M_range_initialize_n(__first, __last,
+ std::distance(__first, __last));
+ }
+
+ template<typename _InputIterator>
+ void
+ _M_range_initialize_n(_InputIterator __first, _InputIterator __last,
+ size_type __n)
+ {
this->_M_impl._M_start
= this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
this->_M_impl._M_end_of_storage = this->_M_impl._M_start + __n;
This doubles the speed of the vector construction, but it's still slow because
it uses std::copy to copy the range elements into the vector, and std::copy
also dispatches on the iterator_category.
