gcc/testsuite/gcc.dg/uninit-31-gimple.c

/* { dg-do compile } */
/* { dg-options "-fgimple -O -Wmaybe-uninitialized" } */

unsigned int __GIMPLE (ssa,startwith("uninit1"))
foo (unsigned int v)
{
  /* If v == 2, then undef is used w/o being initialized.  */
  unsigned int undef;        /* { dg-warning "may be used uninitialized" } */
  unsigned int _2;
  unsigned int _9;
  unsigned int _10;
  unsigned int pred2;
  unsigned int pred1;

  __BB(2):
  pred2 = v_4(D) & 5u;
  if (pred2 != 0u)
    goto __BB3;
  else
    goto __BB4;

  /* 'undef' is defined conditionally (under 'v & 5' predicate).  */
  __BB(3):
  undef_8 = 8u;
  goto __BB4;

  /* An undef value flows into a phi.  */
  __BB(4):
  undef_1 = __PHI (__BB2: undef_5(D), __BB3: undef_8);
  pred1 = v_4(D) & 3u;
  if (pred1 != 0u)
    goto __BB5;
  else
    goto __BB6;

  /* The phi value is used here (under 'v & 3' predicate).  */
  __BB(5):
  _9 = undef_1;
  goto __BB7;

  __BB(6):
  _10 = v_4(D);
  goto __BB7;

  __BB(7):
  _2 = __PHI (__BB5: _9, __BB6: _10);
  return _2;
}