The following program behaves differently
between gcc and clang. Overloaded function
foo(...) gets resolved differently depending
on which compiler is used. It outputs
3 different kinds of outputs depending on
which compiler or compiler version is used:

$ cat foo.cpp

#include <cstdio>
#include <cstdint>

struct Foo
{
  Foo(std::int64_t)
  {
  }
};

void foo(const char*)
{
  std::puts("In foo(const char*)");
}

void foo(const Foo&)
{
  std::puts("In foo(const Foo&)");
}

int main()
{
  foo((int)0);
  foo((unsigned)0);
  foo((short)0);
  foo((unsigned short)0);
  foo((std::int64_t)0);
  foo((std::uint64_t)0);
  foo(0);
  foo(NULL);
  foo(nullptr);
}


With g++-8 (Ubuntu 8.1.0-5ubuntu1~16.04) 8.1.0
or   g++-7 (Ubuntu 7.4.0-1ubuntu1~16.04~ppa1) 7.4.0
or   g++-6 (Ubuntu 6.5.0-2ubuntu1~16.04) 6.5.0 20181026

$ g++-8 -std=c++11 foo.cpp
$ ./a.out 
In foo(const Foo&)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)

With g++-5 (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609:

$ g++-5 -std=c++11 foo.cpp
$ ./a.out
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)
In foo(const char*)

Notice that the first call results in a different overload being called.


With clang version 7.0.0-svn338141-1~exp1+0~20180727181251.1677~1.gbpcccb1b (trunk)
or clang version 6.0.1-svn334776-1~exp1~20181018153226.114 (branches/release_60)
or clang version 5.0.2 (tags/RELEASE_502/final)
or clang version 4.0.0-1ubuntu1~16.04.2 (tags/RELEASE_400/rc1)
or clang version 3.9.1-4ubuntu3~16.04.2 (tags/RELEASE_391/rc2)

$ clang++-7 -std=c++11 foo.cpp
$ ./a.out
In foo(const Foo&)
In foo(const Foo&)
In foo(const Foo&)
In foo(const Foo&)
In foo(const Foo&)
In foo(const Foo&)
In foo(const char*)
In foo(const char*)
In foo(const char*)

Notice that clang resolve overload completely differently
than any version of gcc!?

I initially reported this as a clang bug in
https://bugs.llvm.org/show_bug.cgi?id=40193
albeit with a different program, which I decided
to simplify here to avoid a boost dependency.
According to comments in the clang ticket, it's
a gcc bug. Hence this bug report.