http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56613
Bug #: 56613
Summary: [4.8 Regression] map::operator[](key_type&&) fails
with custom allocator
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: r...@gcc.gnu.org
This program is valid in C++03 and C++11 but can't be compiled with trunk using
-std=c++11
#include <map>
template<typename T>
struct alloc
{
typedef T value_type;
typedef T* pointer;
typedef const T* const_pointer;
typedef T& reference;
typedef const T& const_reference;
typedef unsigned size_type;
typedef int difference_type;
template<typename U>
struct rebind {
typedef alloc<U> other;
};
alloc() { }
template<typename U>
alloc(const alloc<U>&) { }
pointer allocate(size_type n, const void* = 0) { return
std::allocator<T>().allocate(n); }
void deallocate(pointer p, size_type n) { std::allocator<T>().deallocate(p,
n); }
size_type max_size() const { return -1; }
void construct(pointer p, const T& t) { new ((void*) p) T(t); }
void destroy(pointer p) { p->~T(); }
};
template<typename T, typename U>
bool operator==(alloc<T>, alloc<U>) { return true; }
template<typename T, typename U>
bool operator!=(alloc<T>, alloc<U>) { return false; }
int main()
{
std::map<int, int, std::less<int>, alloc<int> > m;
m[1];
}
$ g++-4.8 -std=c++11 map.cc
In file included from /home/redi/gcc/4.x/include/c++/4.8.0/map:60:0,
from map.cc:1:
/home/redi/gcc/4.x/include/c++/4.8.0/bits/stl_tree.h: In instantiation of
'std::_Rb_tree_node<_Val>* std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_create_node(_Args&& ...) [with _Args = {const
std::piecewise_construct_t&, std::tuple<int&&>, std::tuple<>}; _Key = int; _Val
= std::pair<const int, int>; _KeyOfValue = std::_Select1st<std::pair<const int,
int> >; _Compare = std::less<int>; _Alloc = alloc<std::pair<const int, int> >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type =
std::_Rb_tree_node<std::pair<const int, int> >*]':
/home/redi/gcc/4.x/include/c++/4.8.0/bits/stl_tree.h:1662:64: required from
'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_emplace_hint_unique(std::_Rb_tree<_Key, _Val, _KeyOfValue,
_Compare, _Alloc>::const_iterator, _Args&& ...) [with _Args = {const
std::piecewise_construct_t&, std::tuple<int&&>, std::tuple<>}; _Key = int; _Val
= std::pair<const int, int>; _KeyOfValue = std::_Select1st<std::pair<const int,
int> >; _Compare = std::less<int>; _Alloc = alloc<std::pair<const int, int> >;
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator =
std::_Rb_tree_iterator<std::pair<const int, int> >; std::_Rb_tree<_Key, _Val,
_KeyOfValue, _Compare, _Alloc>::const_iterator =
std::_Rb_tree_const_iterator<std::pair<const int, int> >]'
/home/redi/gcc/4.x/include/c++/4.8.0/bits/stl_map.h:484:8: required from
'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp,
_Compare, _Alloc>::operator[](std::map<_Key, _Tp, _Compare,
_Alloc>::key_type&&) [with _Key = int; _Tp = int; _Compare = std::less<int>;
_Alloc = alloc<int>; std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = int;
std::map<_Key, _Tp, _Compare, _Alloc>::key_type = int]'
map.cc:41:8: required from here
/home/redi/gcc/4.x/include/c++/4.8.0/bits/stl_tree.h:403:8: error: no matching
function for call to 'alloc<std::_Rb_tree_node<std::pair<const int, int> >
>::construct(std::_Rb_tree_node<std::pair<const int, int> >*&, const
std::piecewise_construct_t&, std::tuple<int&&>, std::tuple<>)'
_M_get_Node_allocator().construct(__tmp,
^
/home/redi/gcc/4.x/include/c++/4.8.0/bits/stl_tree.h:403:8: note: candidate is:
map.cc:28:10: note: void alloc<T>::construct(alloc<T>::pointer, const T&) [with
T = std::_Rb_tree_node<std::pair<const int, int> >; alloc<T>::pointer =
std::_Rb_tree_node<std::pair<const int, int> >*]
void construct(pointer p, const T& t) { new ((void*) p) T(t); }
^
map.cc:28:10: note: candidate expects 2 arguments, 4 provided
The problem is that stl_map.h uses piecewise construction for the pair object,
which calls alloc::construct with four arguments, incorrectly assuming that all
allocators in C++11 have a variadic construct() member.
It's easily fixed by changing the C++11 version of _M_create_node to use
allocator_traits::construct:
std::allocator_traits<_Node_allocator>::
construct(_M_get_Node_allocator(), __tmp,
std::forward<_Args>(__args)...);
(For 4.9 I was going to make all the RB-trees allocator-aware, but this
regression needs to be fixed for 4.8 without the rest of the allocator changes)
