[Bug c/102103] New: missing warning for arrays

[Bug c/102103] New: missing warning for arrays

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

            Bug ID: 102103
           Summary: missing warning for arrays
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC issues -Waddress only for the equality test in f() but not those in g() or
h(), even though all three evaluate to false (and even though GCC folds all
three to false even with no optimization).  It would be helpful to diagnose all
three.

$ cat z.c && gcc -S -Wall -fdump-tree-optimized=/dev/stdout z.c
void f (void)
{ 
  int i;
  if (&i == 0)   // -Waddress (good)
    __builtin_abort ();
}

void g (void)
{
  int a[1];
  if (a == 0)   // missing warning
    __builtin_abort ();
}

void h (void)
{
  int a[1][2];
  if (a[0] == 0)   // missing warning
    __builtin_abort ();
}

z.c: In function ‘f’:
z.c:4:10: warning: the comparison will always evaluate as ‘false’ for the
address of ‘i’ will never be NULL [-Waddress]
    4 |   if (&i == 0)   // -Waddress (good)
      |          ^~

;; Function f (f, funcdef_no=0, decl_uid=1943, cgraph_uid=1, symbol_order=0)

void f ()
{
  int i;

  <bb 2> :
  i ={v} {CLOBBER};
  return;

}



;; Function g (g, funcdef_no=1, decl_uid=1947, cgraph_uid=2, symbol_order=1)

void g ()
{
  int a[1];

  <bb 2> :
  a ={v} {CLOBBER};
  return;

}



;; Function h (h, funcdef_no=2, decl_uid=1951, cgraph_uid=3, symbol_order=2)

void h ()
{
  int a[1][2];

  <bb 2> :
  a ={v} {CLOBBER};
  return;

}


Clang diagnoses both the one in f() and in g() (but not the one in h()).  GCC
4.4.7 does as well but the latter has been lost since GCC 4.5  (see
https://gcc.godbolt.org/z/8dbjxv89E) so technically this could be viewed as a
regression.

[Bug c/102103] missing warning for arrays

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=33925

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Related to PR 33925.

[Bug c/102103] missing warning comparing array address to null

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
            Summary|missing warning for arrays  |missing warning comparing
                   |                            |array address to null
   Last reconfirmed|                            |2021-08-30
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot gnu.org

[Bug c/102103] missing warning comparing array address to null

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-September/578546.html

[Bug c/102103] missing warning comparing array address to null

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

--- 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:4dc7ce6fb3917958d1a6036d8acf2953b9c1b868

commit r12-4059-g4dc7ce6fb3917958d1a6036d8acf2953b9c1b868
Author: Martin Sebor <msebor@redhat.com>
Date:   Fri Oct 1 11:50:25 2021 -0600

    Enhance -Waddress to detect more suspicious expressions [PR102103].

    Resolves:
    PR c/102103 - missing warning comparing array address to null

    gcc/ChangeLog:

            PR c/102103
            * doc/invoke.texi (-Waddress): Update.
            * gengtype.c (write_types): Avoid -Waddress.
            * poly-int.h (POLY_SET_COEFF): Avoid using null.

    gcc/c-family/ChangeLog:

            PR c/102103
            * c-common.c (decl_with_nonnull_addr_p): Handle members.
            Check and perform warning suppression.
            (c_common_truthvalue_conversion): Enhance warning suppression.

    gcc/c/ChangeLog:

            PR c/102103
            * c-typeck.c (maybe_warn_for_null_address): New function.
            (build_binary_op): Call it.

    gcc/cp/ChangeLog:

            PR c/102103
            * typeck.c (warn_for_null_address): Enhance.
            (cp_build_binary_op): Call it also for member pointers.

    gcc/fortran/ChangeLog:

            PR c/102103
            * array.c: Remove an unnecessary test.
            * trans-array.c: Same.

    gcc/testsuite/ChangeLog:

            PR c/102103
            * g++.dg/cpp0x/constexpr-array-ptr10.C: Suppress a valid warning.
            * g++.dg/warn/Wreturn-local-addr-6.C: Correct a cast.
            * gcc.dg/Waddress.c: Expect a warning.
            * c-c++-common/Waddress-3.c: New test.
            * c-c++-common/Waddress-4.c: New test.
            * g++.dg/warn/Waddress-5.C: New test.
            * g++.dg/warn/Waddress-6.C: New test.
            * g++.dg/warn/pr101219.C: Expect a warning.
            * gcc.dg/Waddress-3.c: New test.

[Bug c/102103] missing warning comparing array address to null

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

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

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

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

[Bug c/102103] missing warning comparing array address to null

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |egallager at gcc dot gnu.org

--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> ---
This should probably get a note in gcc-12/changes.html IMO