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From: "geoffreydgr at icloud dot com" <gcc-bugzilla@gcc.gnu.org>
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Date: Fri, 04 Nov 2022 15:11:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107526

            Bug ID: 107526
           Summary: - -Wanayzer-null-dereference false positive with
                    different behaviors when delete unrelated statement
                    =E2=80=9Cint *e =3D 0;=E2=80=9D
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: geoffreydgr at icloud dot com
  Target Milestone: ---

I encountered  a false positive when compiling the following MCVE program w=
ith
gcc (trunk) with -fanalyzer -O0 in https://godbolt.org/z/ojqa7PjPf

```
#include <stdio.h>
void f(short *g) {
  int a =3D0;
  int b =3D (0 !=3D g);

am:
  if (b) {=20
    int *c =3D &b;
    *c =3D printf("NPD_FLAG\n");
  }
  int *e =3D 0;  // (3) 'g' is NULL=20=20
  (*g)++;=20
  if (a)
    goto am;
}
int main() {=20
  short d=3D0;
  f(&d);=20
  return 0;
  }
```

Gcc static analyzer reports dereference of NULL 'g'  at line 4, which is a
false positive. while it gives wrong path note (3) 'g' is NULL  at line 12.
If I delete line 12 as the following code, gcc analyzer does not report NPD
warning anymore.The statement `int *e =3D 0; ` is unrelated to `g` , but gcc
analyzer has different behaviors before and after deleting the statement.

```
#include <stdio.h>
void f(short *g) {
  int a =3D0;
  int b =3D (0 !=3D g);

am:
  if (b) {=20
    int *c =3D &b;
    *c =3D printf("NPD_FLAG\n");
  }
  int *e =3D 0;  // (3) 'g' is NULL=20=20
  (*g)++;=20
  if (a)
    goto am;
}
int main() {=20
  short d=3D0;
  f(&d);=20
  return 0;
  }
```

Do you have any thoughts about this false positive?=