[Bug middle-end/80548] New: -Wmaybe-uninitialized false positive when an assignment is added

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80548

            Bug ID: 80548
           Summary: -Wmaybe-uninitialized false positive when an
                    assignment is added
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent-gcc at vinc17 dot net
  Target Milestone: ---

Consider:

int g (void);
void h (int, int);

void f (int b)
{
  int x, y;

  if (b)
    {
      x = g ();
      y = g ();
    }

  while (g ())
    if (b)
      {
        h (x, y);
        y = g ();
      }
}

Compiling this program with "-O -Wmaybe-uninitialized -c" yields:

tst.c: In function ‘f’:
tst.c:17:9: warning: ‘y’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
         h (x, y);
         ^~~~~~~~

Note that x and y play a symmetric role here, except that y has an additional
assignment, and this assignment makes GCC think that y may be used
uninitialized! Indeed, if one removes this assignment, the warning disappear.