[Bug c++/96507] New: Feature request: improve "-Waddress" (or equivalent) for function references inside structs

[Bug c++/96507] New: Feature request: improve "-Waddress" (or equivalent) for function references inside structs

[federico.kircheis at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96507

            Bug ID: 96507
           Summary: Feature request: improve "-Waddress" (or equivalent)
                    for function references inside structs
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: federico.kircheis at gmail dot com
  Target Milestone: ---

This is a feature request.


I'm compiling the code with "-Wall -Wextra -pedantic"

----
#include <utility>

void foo(){}

int main(){
    void(&f)() = foo;
    static_assert(!std::is_pointer<decltype(f)>::value, "should not be a
pointer");
    return f != 0;
}
----

gcc correctly triggers the warning "warning: the address of 'void foo()' will
never be NULL [-Waddress]" (nitpick nullptr in the error message would be
better than NULL).

Also for following example gcc emits the desired diagnostic

----
#include <utility>

void foo(){}

using fun = void();

fun& get_fun();

int main(){
    fun& f = get_fun();
    static_assert(!std::is_pointer<decltype(f)>::value, "should not be a
pointer");
    return f != 0;
}
----

But if the function reference is inside a struct:

----
#include <utility>

void foo(){}

using fun = void();

struct s{
    fun& f;
};

s get_fun();

int main(){
    s ss = get_fun();
    static_assert(!std::is_pointer<decltype(ss.f)>::value, "should not be a
pointer");
    return ss.f != 0;
}
----


then gcc does not emit any diagnostic (notice: it does if it can inline
get_fun()), even if "knows" that it cannot be null, as the static_assert does
not fire.

As reference: https://godbolt.org/z/vqohqM

[Bug c++/96507] missing -Waddress for member references

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
            Summary|Feature request: improve    |missing -Waddress for
                   |"-Waddress" (or equivalent) |member references
                   |for function references     |
                   |inside structs              |
                 CC|                            |msebor at gcc dot gnu.org
   Last reconfirmed|                            |2021-11-22

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with GCC 12.  Since the warning is issued for non-member references
(the first case below) but not for members (the second case) I would consider
this a bug rather than an enhancement request.

$ cat pr96507.C && gcc -S -Wall pr96507.C
typedef void F ();

extern F &fr;
extern int &ir;

bool gfun ()
{
  return &fr != 0;   // -Waddress (expected)
}

bool gvar ()
{
  return &ir != 0;   // -Waddress (expected)
}


struct S
{
  F &fr;
  int &ir;
};

extern S s;

bool hfun ()
{
  return &s.fr != 0; // missing warning
}

bool hvar ()
{
  return &s.ir != 0; // missing warning
}

pr96507.C: In function ‘bool gfun()’:
pr96507.C:8:14: warning: the compiler can assume that the address of ‘fr’ will
never be NULL [-Waddress]
    8 |   return &fr != 0;   // -Waddress (expected)
      |          ~~~~^~~~
pr96507.C:3:11: note: ‘fr’ declared here
    3 | extern F &fr;
      |           ^~
pr96507.C: In function ‘bool gvar()’:
pr96507.C:13:14: warning: the compiler can assume that the address of ‘ir’ will
never be NULL [-Waddress]
   13 |   return &ir != 0;   // -Waddress (expected)
      |          ~~~~^~~~
pr96507.C:4:13: note: ‘ir’ declared here
    4 | extern int &ir;
      |             ^~

[Bug c++/96507] missing -Waddress for member references

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot gnu.org
             Status|NEW                         |ASSIGNED
           Keywords|                            |patch

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-November/585178.html

[Bug c++/96507] missing -Waddress for member references

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96507

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:2dd56aed3e4e1938a9020ab2fe6a410e1a1c2eb3

commit r12-5484-g2dd56aed3e4e1938a9020ab2fe6a410e1a1c2eb3
Author: Martin Sebor <msebor@redhat.com>
Date:   Tue Nov 23 15:35:31 2021 -0700

    Issue -Waddress also for reference members [PR96507].

    Resolves:
    PR c++/96507 - missing -Waddress for member references

    gcc/cp/ChangeLog:

            PR c++/96507
            * typeck.c (warn_for_null_address): Handle reference members.

    gcc/testsuite/ChangeLog:

            PR c++/96507
            * g++.dg/warn/Waddress-8.C: New test.

[Bug c++/96507] missing -Waddress for member references

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed in GCC 12.