[Bug middle-end/104761] [12 Regression] False positive -Wdangling-pointer warning on NetworkManager since r12-6606

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104761

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Keywords|                            |diagnostic
             Blocks|                            |104077

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
That's right, the pass never calls mark_dfs_back_edges().  Thanks for the hint.

A slightly simplified test case:

$ cat pr104761.c && gcc -O1 -S -Wall -fdump-tree-waccess1=/dev/stdout
pr104761.c
typedef struct { int i; } S;

void f (S **); 

void g (int);

void test (int x)
{
  S s = { 0 };

  __attribute__((__cleanup__ (f))) S *p = 0;

  if (x) 
     {
       g (s.i);
       for ( ; ; );
         }
}

;; Function test (test, funcdef_no=0, decl_uid=1986, cgraph_uid=1,
symbol_order=0)

pr104761.c: In function ‘test’:
pr104761.c:15:8: warning: dangling pointer to ‘s’ may be used
[-Wdangling-pointer=]
   15 |        g (s.i);
      |        ^~~~~~~
pr104761.c:9:5: note: ‘s’ declared here
    9 |   S s = { 0 };
      |     ^

void test (int x)
{
  struct S * p;
  struct S s;
  int _1;

  <bb 2> :
  s.i = 0;
  p = 0B;
  if (x_5(D) != 0)
    goto <bb 3>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 3> :
  _1 = s.i;
  g (_1);

  <bb 4> :
  goto <bb 4>; [INV]

  <bb 5> :
  f (&p);
  s ={v} {CLOBBER(eol)};
  p ={v} {CLOBBER(eol)};
  return;

}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104077
[Bug 104077] bogus/missing -Wdangling-pointer