[Bug analyzer/124672] New: deref-before-check confused by macro with call

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124672

            Bug ID: 124672
           Summary: deref-before-check confused by macro with call
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: aoliva at gcc dot gnu.org
  Target Milestone: ---

deref-before-check-2.c fails on vxworks x86, because stderr is #defined to a
function call, and that causes deref_before_check::emit to return after:

    location_t check_loc = m_check_enode->get_point ().get_location ();
    if (linemap_location_from_macro_definition_p (line_table, check_loc))

That's odd because stderr isn't even part of the check stmt, it's part of the
deref stmt.

The following variant of the testcase triggers the problem on other targets:

#include <stdio.h>

struct st
{
  char *str;
  int i;
};

extern FILE *get_stream (void);
#define stream (get_stream ())

int test_1 (struct st *p)
{
  fprintf (stream, "str: %s\n", p->str); /* { dg-message "pointer 'p' is
dereferenced here" } */
  if (!p) /* { dg-warning "check of 'p' for NULL after already dereferencing
it" } */
    return -1;
  return p->i;  
}

Oddly, '#define stream stderr' does NOT trigger the problem.

I figure the presence of the unexpected unrelated call after the deref gimple
stmt gets things confused, but the fprintf call doesn't.

Assigning 'FILE *err = stream;' in the function and using err in the call is
enough to get the expected warning.