[Bug analyzer/107526] New: - -Wanayzer-null-dereference false positive with different behaviors when delete unrelated statement “int *e = 0;”

[geoffreydgr at icloud dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107526

            Bug ID: 107526
           Summary: - -Wanayzer-null-dereference false positive with
                    different behaviors when delete unrelated statement
                    “int *e = 0;”
           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 with
gcc (trunk) with -fanalyzer -O0 in https://godbolt.org/z/ojqa7PjPf

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

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

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

Do you have any thoughts about this false positive?