[Bug c++/102378] missing -Waddress in template code at definition time rather than instantiation

["msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102378

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-09-16
   Target Milestone|---                         |12.0
     Ever confirmed|0                           |1

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> (In reply to Andrew Pinski from comment #1)
> > GCC warns only at instantiation time.
> 
> And it has been that way since at least 4.4.0.

Not quite.  It depends on where a warning is implemented.  As the test case
below shows, G++ does diagnose some problems in uninstantiated templates but
not others.  Jason's suggestion in the review I pointed to is to try to do
better and the purpose of this bug is to capture that limitation and
improvement for the work I'm doing.

$ cat t.C && gcc -S -Wall -Wredundant-tags t.C
struct A { A (); ~A (); };

template <class T>
void f ()
{
  volatile struct A a;            // -Wredundant-tags (good)
  register int n = sizeof a;      // -Wregister (good)
  __builtin_memset (&a, 0, n);    // missing -Wclass-memaccess and volatile A*
to A* conversion warning
}

t.C: In function ‘void f()’:
t.C:6:12: warning: redundant class-key ‘struct’ in reference to ‘struct A’
[-Wredundant-tags]
    6 |   volatile struct A a;            // -Wredundant-tags (good)
      |            ^~~~~~
      |            ------
t.C:7:16: warning: ISO C++17 does not allow ‘register’ storage class specifier
[-Wregister]
    7 |   register int n = sizeof a;      // -Wregister (good)
      |                ^