https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118285
Bug ID: 118285
Summary: GCC rejects some constexpr std::string usages
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dangelog at gmail dot com
Target Milestone: ---
Hi,
This is a spin-off of PR103924.
The following testcase is rejected by GCC rejected by GCC but accepted by Clang
(with libstdc++):
https://gcc.godbolt.org/z/63Wss3Ej8
#include <string>
constexpr void f(std::initializer_list<std::string>) {}
constexpr bool test()
{
f({"x"});
return true;
}
static_assert(test());
<source>:10:19: error: non-constant condition for static assertion
10 | static_assert(test());
| ~~~~^~
In file included from
/opt/compiler-explorer/gcc-14.2.0/include/c++/14.2.0/string:54,
from <source>:1:
<source>:10:19: in 'constexpr' expansion of 'test()'
<source>:6:6: in 'constexpr' expansion of
'((std::__cxx11::basic_string<char>*)<anonymous>)->std::__cxx11::basic_string<char>::~basic_string()'
/opt/compiler-explorer/gcc-14.2.0/include/c++/14.2.0/bits/basic_string.h:809:19:
in 'constexpr' expansion of
'((std::__cxx11::basic_string<char>*)this)->std::__cxx11::basic_string<char>::_M_dispose()'
/opt/compiler-explorer/gcc-14.2.0/include/c++/14.2.0/bits/basic_string.h:288:22:
error: accessing 'std::__cxx11::basic_string<char>::<unnamed
union>::_M_allocated_capacity' member instead of initialized
'std::__cxx11::basic_string<char>::<unnamed union>::_M_local_buf' member in
constant expression
288 | _M_destroy(_M_allocated_capacity);
| ^~~~~~~~~~~~~~~~~~~~~
Compiler returned: 1
I've been trying to minimize the testcase by removing clutter from
basic_string: https://gcc.godbolt.org/z/haxvvr1YK
The fun part is that if one deletes the copy constructor (which is actually
never called) the code is accepted by GCC.
That's what makes me think this is a compiler bug.
