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From: "nickolay.merkin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/100825] function signature constraints are not a part of
 mangled name
Date: Wed, 09 Jun 2021 16:56:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100825

Nickolay Merkin <nickolay.merkin at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nickolay.merkin at gmail d=
ot com

--- Comment #8 from Nickolay Merkin <nickolay.merkin at gmail dot com> ---
(In reply to Jonathan Wakely from comment #3)
> Clang and EDG agree with GCC here.
>=20
> I think your code is ill-formed due to [temp.constr.atomic] p3:
>=20
> "If, at different points in the program, the satisfaction result is
> different for identical atomic constraints and template arguments, the
> program is ill-formed, no diagnostic required."

Of course the constraints are different! First constraint is empty, second =
is
always-true.
So, these are different overloads.

Okay, let's help the compiler giving different mangled names:

https://gcc.godbolt.org/z/K8d9vv8oT

namespace a {}
namespace b {}

using namespace a;
using namespace b;

namespace a {
template<class T> void f() { std::cout << __PRETTY_FUNCTION__ << std::endl;=
 }
}

void g() { f<int>(); }

namespace b {
template<class T> void f() requires true { std::cout << __PRETTY_FUNCTION__=
 <<
std::endl; }
}

void h() { f<int>(); }

g addresses to a::f, h addresses to b::f.

Is this still "ill-formed, no diagnostics required"?
Does it mean that a compiler may produce any corrupted binary code with any
undefined behavior? Just because we wrote same "f<int>()" both times?
I believe, not, it does not.

The program is well-formed.
Both overloads are valid. And both are different, - it is not an ODR violat=
ion.

So, the issue is on the compiler's side: wrong rules of mangling.=