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From: "biggs at biggs dot xyz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/110694] New: False Positive -Werror=free-nonheap-object
Date: Mon, 17 Jul 2023 00:54:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110694

            Bug ID: 110694
           Summary: False Positive -Werror=3Dfree-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=3D55559&action=3Dedit
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 =3D malloc(sizeof(*s));
    if (s) s->i =3D 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 =3D s_constructor();
    s_destructor(s);

    s =3D s_constructor();
    if (s) s_destructor2(s);
    s =3D (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=3Dfree-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 fl=
ag.

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_destructo=
r(S*
s).=