[Bug c/110694] New: False Positive -Werror=free-nonheap-object

[Bug c/110694] New: False Positive -Werror=free-nonheap-object

[biggs at biggs dot xyz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110694

            Bug ID: 110694
           Summary: False Positive -Werror=free-nonheap-object
           Product: gcc
           Version: 13.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: biggs at biggs dot xyz
  Target Milestone: ---

Created attachment 55559
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55559&action=edit
Source File

Observed on Trunk and 13.1.1
Consider:

```c
#include <stdlib.h>

typedef struct S S;

struct S {
    int* i;
};

static S* s_constructor(void) {
    S* s = malloc(sizeof(*s));
    if (s) s->i = calloc(1, sizeof(*(s->i)));
    return s;
}

static void s_destructor(S* s) {
    if (!s) return;
    free(s->i);
    free(s);
}

static void s_destructor2(S s[static 1]) {
    free(s->i);
    free(s);
}

int main(void) {
    S* s = s_constructor();
    s_destructor(s);

    s = s_constructor();
    if (s) s_destructor2(s);
    s = (void*) 0;

    return EXIT_SUCCESS;
}
```

Compiling with gcc -Wall -Werror produces the error:
<source>: In function 's_destructor2':
<source>:23:5: error: 'free' called on unallocated object 's'
[-Werror=free-nonheap-object]
   23 |     free(s);
      |     ^~~~~~~
<source>:21:29: note: declared here
   21 | static void s_destructor2(S s[static 1]) {
      |                           ~~^~~~~~~~~~~
cc1: all warnings being treated as errors

However, there is no error when compiled with -O1 or higher optimization flag.

I don't think s_destructor2(S s[static 1]) should emit an error in the first
place though. The function definition should be compatible with s_destructor(S*
s).

[Bug middle-end/110694] [11/12/13/14 Regression] False Positive -Werror=free-nonheap-object

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110694

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Target Milestone|---                         |11.5
      Known to fail|                            |11.1.0
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |10.5.0
   Last reconfirmed|                            |2023-07-17
            Summary|False Positive              |[11/12/13/14 Regression]
                   |-Werror=free-nonheap-object |False Positive
                   |                            |-Werror=free-nonheap-object

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug middle-end/110694] [11/12/13/14 Regression] False Positive -Werror=free-nonheap-object

[roman.zilka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110694

Roman Žilka <roman.zilka at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |roman.zilka at gmail dot com

--- Comment #2 from Roman Žilka <roman.zilka at gmail dot com> ---
I can see it on 13.2.1 20230826. The warning triggers even without any -W*
args. The manpage implies that shouldn't be the case.

[Bug middle-end/110694] [11/12/13/14 Regression] False Positive -Werror=free-nonheap-object

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110694

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

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