llvm-gcc-4.2/gcc/testsuite/gcc.dg/uninit-13.c

/* { dg-do compile } */
/* { dg-options "-O -Wuninitialized" } */

typedef _Complex float C;
C foo()
{
  C f;
  __imag__ f = 0;
  return f;		/* { dg-warning "" "uninit" { xfail *-*-* } } */
}