[Bug c++/67559] New: [C++] [regression] Passing non-trivially copyable objects through '...' doesn't generate warning or error

[Bug c++/67559] New: [C++] [regression] Passing non-trivially copyable objects through '...' doesn't generate warning or error

[bisqwit at iki dot fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67559

            Bug ID: 67559
           Summary: [C++] [regression] Passing non-trivially copyable
                    objects through '...' doesn't generate warning or
                    error
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bisqwit at iki dot fi
  Target Milestone: ---

In GCC 4.9, this code generates an error. In GCC 5.2, it generates no warning
or error, even on -Wall -Wextra -pedantic.

    struct test { test(){} ~test(){} };
    void a(int, ...) {}
    int main()
    {
        test object;
        a(5, object);
    }

Tried different standards modes: -std=c++98, -std=c++03, -std=c++11, -std=c++14

Tried also lambda functions with variadic args, same result.

The error message in GCC 4.9 (and earier down to 4.6) was:

    cannot pass objects of non-trivially-copyable type 'struct test' through
'...'

In GCC 5.2, no error or warning message is given in any of the standard modes.
In the standard version C++03, this behavior is undefined (§5.2.2/7). In C++11,
it is conditionally supported with implementation-defined semantics.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg540

--- Comment #4 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> If you had a sanitized version of libgfortran you could check them by yourself.

Could you please post the exact command line you are using for configure and
make and, if needed, the environment?

[Bug c++/67559] [C++] [regression] Passing non-trivially copyable objects through '...' doesn't generate warning or error

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67559

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
According the release notes of gcc 5 (https://gcc.gnu.org/gcc-5/changes.html)
this is by design:

"G++ now allows passing a non-trivially-copyable class via C varargs, which is
conditionally-supported with implementation-defined semantics in the standard.
This uses the same calling convention as a normal value parameter."

and as you already note this behaviour is supported by the C++11 standard.
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Subject: [Bug libstdc++/67566] New: <string> std::move is in global scope g++ 5.1 -std=c++14
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg566

            Bug ID: 67566
           Summary: <string> std::move is in global scope g++ 5.1
                    -std=c++14
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: forest_software at mail dot ru
  Target Milestone: ---

std::move is in global scope after #include <string>, conflict with boost::move

example:

main.cpp:

#include <string>
#include <boost/move/move.hpp>

using boost::move;

main()
{
  std::string a = "fff";
  std::string b = move(a);
}

Compile:

g++ main.cpp -std=c++14

[Bug c++/67559] [C++] [regression] Passing non-trivially copyable objects through '...' doesn't generate warning or error

[bisqwit at iki dot fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67559

--- Comment #2 from Joel Yliluoma <bisqwit at iki dot fi> ---
But when compiling for earlier standard versions that explicitly label this as
undefined behavior, it should at least give a warning.