[Bug c++/57979] New: G++ accepts constant expression defined using floating point glvalue

[jogojapan at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57979

            Bug ID: 57979
           Summary: G++ accepts constant expression defined using floating
                    point glvalue
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jogojapan at gmail dot com

The following code is accepted and compiled without error by G++:

int main()
{
  const float f1 = 0.0;

  constexpr float f2 = f1;

  return 0;
}

Note that the declaration of f2 as constexpr requires f1 to be a constant
expression, which it isn't, according to §5.19/2:

====(QUOTE)========
A condition-expression is a core constant expression unless it involves
[...] 
[..9th item..]
 - an lvalue-to-rvalue conversion (4.1) unless it is applied to [...] a glvalue
of integral or enumeration type that refers to a non-volatile const object with
a preceding initialization, initialized with a constant expresion, or
[...]
====(ENDQUOTE)====

So if f1 had been declared as const int, the code would be acceptable, but
there is no such exception for floating point (or any other non-integral or
non-enum type).


Tested with a 20130708 snapshot checkout from the master branch of the
git-mirror of the repository. (I'll test with a more recent version soon.)