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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/57632] Operator new overloads with stdc++11 enabled looses
 exception specifier (MacOsX)
Date: Fri, 07 Jan 2022 23:47:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D57632

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #5)
> I agree with comment 3 that the current diagnostic is poor:

Oh I missed that.

>=20
> #include <new>
> void* operator new(std::size_t mem) throw(std::bad_alloc);
> void* operator new(std::size_t mem) throw(std::bad_alloc);
>=20
>=20
> g++ -std=3Dc++11  -c new.cc -Wno-deprecated
> new.cc:3:7: error: declaration of =E2=80=98void* operator new(std::size_t=
) throw
> (std::bad_alloc)=E2=80=99 has a different exception specifier
>     3 | void* operator new(std::size_t mem) throw(std::bad_alloc);
>       |       ^~~~~~~~
> new.cc:2:7: note: from previous declaration =E2=80=98void* operator new(s=
td::size_t)=E2=80=99
>     2 | void* operator new(std::size_t mem) throw(std::bad_alloc);
>       |       ^~~~~~~~
>=20

Reduced testcase for that:
void f(void);
void f(void) throw(int);
void f(void) throw(int);

Noexcept has the same issue:
void g(void);
void g(void) noexcept;
void g(void) noexcept;

I suspect what happens is the following when we merge the two decls we chose
the new decl for the location but we remove the exception specifier/noexcept
(confirmed by swapping the first two decls and seeing the error again).=