https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98465
Bug ID: 98465
Summary: Bogus warning stringop-overread wuth -std=gnu++20 -O2
and std::string::insert
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: romain.geissler at amadeus dot com
Target Milestone: ---
Hi,
The following C++ code compiled with -std=gnu++20 -O2 -Werror=stringop-overread
emits a bogus warning/error with gcc trunk, while it works without problem when
using gnu++17 instead. Tested on compiler explorer on x64 Linux:
#include <string>
const char constantString[] = {42, 53};
void f(std::string& s)
{
s.insert(0, static_cast<const char*>(constantString), 2);
}
In file included from
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/string:40,
from <source>:1:
In static member function 'static constexpr std::char_traits<char>::char_type*
std::char_traits<char>::copy(std::char_traits<char>::char_type*, const
char_type*, std::size_t)',
inlined from 'static void std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_S_copy(_CharT*, const _CharT*, std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::size_type) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]' at
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:351:21,
inlined from 'static void std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_S_copy(_CharT*, const _CharT*, std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::size_type) [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]' at
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:346:7,
inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_replace(std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]' at
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.tcc:481:20,
inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::replace(std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]' at
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:1946:19,
inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::insert(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type,
const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type)
[with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]' at
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:1693:29,
inlined from 'void f(std::string&)' at <source>:7:60:
/opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/char_traits.h:402:56:
error: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' reading
2 bytes from a region of size 0 [-Werror=stringop-overread]
402 | return static_cast<char_type*>(__builtin_memcpy(__s1, __s2,
__n));
|
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
<source>: In function 'void f(std::string&)':
<source>:3:12: note: at offset 2 into source object 'constantString' of size 2
3 | const char constantString[] = {42, 53};
| ^~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
Compiler returned: 1
Note that gcc 10 doesn't issue any warning even with -Wall -Wextra with
gnu++20.
Cheers,
Romain
