https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90992
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If we inline the relevant code it reveals that t here are actually additional
warning lines that are being suppressed in system headers:
using size_t = decltype(sizeof(0));
void* operator new(size_t, void* p) { return p; }
struct allocator
{
template<typename T, typename... Args>
void
construct(T* p, Args... args)
noexcept(noexcept(::new((void*)p) T(args...)))
{ ::new((void*)p) T(args...); }
template<typename T>
void
destroy(T* p)
noexcept(noexcept(p->~T()))
{ p->~T(); }
};
class NotNoexcept {
public:
NotNoexcept() noexcept(false) {}
~NotNoexcept() noexcept(false) {}
};
class Automatic {
public:
Automatic(int bla) noexcept(false) : Bla(bla) {};
private:
int Bla;
NotNoexcept Dummy;
};
int main() {
alignas(Automatic) unsigned char buf[sizeof(Automatic)];
allocator a;
a.construct((Automatic*)buf, 42);
a.destroy((Automatic*)buf);
}
90992.cc: In instantiation of 'void allocator::construct(T*, Args ...) [with T
= Automatic; Args = {int}]':
90992.cc:37:34: required from here
90992.cc:8:5: warning: noexcept-expression evaluates to 'false' because of a
call to 'void* operator new(size_t, void*)' [-Wnoexcept]
8 | construct(T* p, Args... args)
| ^~~~~~~~~
90992.cc:2:7: warning: but 'void* operator new(size_t, void*)' does not throw;
perhaps it should be declared 'noexcept' [-Wnoexcept]
2 | void* operator new(size_t, void* p) { return p; }
| ^~~~~~~~
90992.cc:14:5: warning: noexcept-expression evaluates to 'false' because of a
call to 'Automatic::~Automatic()' [-Wnoexcept]
14 | destroy(T* p)
| ^~~~~~~
90992.cc:25:7: warning: but 'Automatic::~Automatic()' does not throw; perhaps
it should be declared 'noexcept' [-Wnoexcept]
25 | class Automatic {
| ^~~~~~~~~
The first first line is being suppressed, but the second is not. This isn't a
front-end regression as it's always done this, but it gets triggered by new
changes in libstdc++ since GCC 9.1
