[Bug tree-optimization/69726] Bogus warnings with -O3 -Wuninitialized because of if-conversion

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69726

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, so forwprop fixes things up but nothing removes dead code before uninit
and it is confused by

  vect__ifc__525.36_152 = MEM[(int *)&temp + 224B];
  vect__ifc__523.38_154 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__525.36_152>;

where only _154 is dead.  That's forwprop not cleaning up after itself (it
is not expected to do that).