All versions of GCC reject the following valid C++ 14 program.  (Clang and EDG accept it as expected.)

$ cat zzz.cpp && /home/msebor/build/gcc-6-branch/gcc/xgcc -B /home/msebor/build/gcc-6-branch/gcc -S -Wall -Wextra -Wpedantic zzz.cpp 
struct S { int a, b; };

constexpr S f ()
{
  int x = 0;
  S z = { 0, ++x }; 
  return z;
}

constexpr S s = f ();

static_assert (s.a + 1 == s.b, "");
zzz.cpp:12:1: error: non-constant condition for static assertion
 static_assert (s.a + 1 == s.b, "");
 ^~~~~~~~~~~~~
zzz.cpp:12:1: error: the value of ‘s’ is not usable in a constant expression
zzz.cpp:10:13: note: ‘s’ used in its own initializer
 constexpr S s = f ();
             ^