https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108860
Bug ID: 108860
Summary: New (since gcc 12) false positive null-dereference in
vector.resize
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dezi_0_1 at yahoo dot de
Target Milestone: ---
The following code produces a warning with gcc 12.1 (tested with godbolt) and
12.2 (tested with godbolt and the version on ubuntu 22.10), but not with gcc
11.3 (tested with godbolt):
❯ cat test.cpp
#include <vector>
void test(std::size_t val1, std::size_t val2) {
std::vector<int> data;
if(val2 > 0)
data.resize(val1 / val2);
}
❯ g++ -O2 -Wnull-dereference test.cpp
In file included from /usr/include/c++/12/vector:62,
from test.cpp:1:
In function ‘void std::_Construct(_Tp*, _Args&& ...) [with _Tp = int; _Args =
{}]’,
inlined from ‘static _ForwardIterator
std::__uninitialized_default_n_1<true>::__uninit_default_n(_ForwardIterator,
_Size) [with _ForwardIterator = int*; _Size = long unsigned int]’ at
/usr/include/c++/12/bits/stl_uninitialized.h:661:23,
inlined from ‘static _ForwardIterator
std::__uninitialized_default_n_1<true>::__uninit_default_n(_ForwardIterator,
_Size) [with _ForwardIterator = int*; _Size = long unsigned int]’ at
/usr/include/c++/12/bits/stl_uninitialized.h:655:9,
inlined from ‘_ForwardIterator
std::__uninitialized_default_n(_ForwardIterator, _Size) [with _ForwardIterator
= int*; _Size = long unsigned int]’ at
/usr/include/c++/12/bits/stl_uninitialized.h:701:20,
inlined from ‘_ForwardIterator
std::__uninitialized_default_n_a(_ForwardIterator, _Size, allocator<_Tp>&)
[with _ForwardIterator = int*; _Size = long unsigned int; _Tp = int]’ at
/usr/include/c++/12/bits/stl_uninitialized.h:766:44,
inlined from ‘void std::vector<_Tp, _Alloc>::_M_default_append(size_type)
[with _Tp = int; _Alloc = std::allocator<int>]’ at
/usr/include/c++/12/bits/vector.tcc:655:41,
inlined from ‘void std::vector<_Tp, _Alloc>::resize(size_type) [with _Tp =
int; _Alloc = std::allocator<int>]’ at
/usr/include/c++/12/bits/stl_vector.h:1011:21,
inlined from ‘void test(std::size_t, std::size_t)’ at test.cpp:6:20:
/usr/include/c++/12/bits/stl_construct.h:119:7: warning: null pointer
dereference [-Wnull-dereference]
119 | ::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `if(val2 > 0)` is not necessary to produce the warning but I wanted to make
sure that this isn't due to a possible division by zero.
The warning is also output with -O3 but not with -O1 or -O0.
