[Bug c/88058] gcc fails to detect use of out of scope variable ?

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88058

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-11-16
     Ever confirmed|0                           |1
           Severity|normal                      |enhancement

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  There's nothing that can easily help - points-to analysis is
closest.  With it's help and the clobber present one could warn, but I fear
the false positive rate would be quite high.  Note that g() may not actually
touch *p2.  Note the path n>=0 may never be taken at runtime.

This may be something to sanitize instead?

f (int n, char * p1)
{
  int n_5(D) = n;
  # PT = nonlocal null
  char * p1_3(D) = p1;
  char buf[10];
  char * p2;

  <bb 2> :
  if (n_5(D) >= 0)
    goto <bb 3>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 3> :
  buf ={v} {CLOBBER};

  <bb 4> :
  # PT = nonlocal null { D.1967 } (escaped)
  # p2_1 = PHI <p1_3(D)(2), &buf(3)>
  # USE = nonlocal { D.1967 } (escaped)
  # CLB = nonlocal { D.1967 } (escaped)
  g (p2_1);