[Bug c/105628] New: False positive with -Waddress

[Bug c/105628] New: False positive with -Waddress

[jochen447 at concept dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

            Bug ID: 105628
           Summary: False positive with -Waddress
           Product: gcc
           Version: 12.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jochen447 at concept dot de
  Target Milestone: ---

Created attachment 52986
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52986&action=edit
minified example program to show the false positive

Option -Wall also enables -Waddress, which causes a lot of false positives like
shown in my attached example problem (minimized and anonymized real world
example):

waddress.c: In function ‘comp_has_ExtraPtr’:
waddress.c:44:29: warning: the comparison will always evaluate as ‘true’ for
the pointer operand in ‘(struct Extra **)&comp->pin + 4’ must not be NULL
[-Waddress]
   44 |     return ExtraPtrOf(comp) ? 1 : 0;
      |                             ^

It only seems to be emitted when using the ?-operator.


# gcc -v
...
gcc version 12.1.1 20220507 (Red Hat 12.1.1-1) (GCC)


# uname -a
Linux fedora 5.17.6-300.fc36.x86_64 #1 SMP PREEMPT Mon May 9 15:47:11 UTC 2022
x86_64 x86_64 x86_64 GNU/Linux

[Bug c/105628] False positive with -Waddress

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The warning is correct but it should not be done.

Simpele testcase:
struct s{ int f; };
int g(struct s t){
  return (t.f?&t.f : 0)? 1 : 0;
}

The problem is gcc did some optimizations before the warning and pushed the
implicit != 0 into each arm of the ?; operator

[Bug c/105628] [12/13 Regression] False positive with -Waddress

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|False positive with         |[12/13 Regression] False
                   |-Waddress                   |positive with -Waddress
   Target Milestone|---                         |12.3
           Keywords|                            |needs-bisection

[Bug c/105628] [12/13 Regression] False positive with -Waddress

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org
           Priority|P3                          |P2

[Bug c/105628] [12/13/14 Regression] False positive with -Waddress

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.3                        |12.4

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.

[Bug c/105628] [12/13/14 Regression] False positive with -Waddress

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 114306 has been marked as a duplicate of this bug. ***

[Bug c/105628] [12/13/14 Regression] False positive with -Waddress

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105628

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So it turns out the change for ?: to warn for -Waddress was done on purpose.
See PR 102967  . PR 102967  is about the wrong location for the warning and
such but it was originally about the same type of expression.

*** This bug has been marked as a duplicate of bug 102967 ***