[Bug tree-optimization/116823] phiprop should ignore clobbers

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116823

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
And yes this shows up in GCC itself.
>From fold-const.cc:
```
  if (lr_bitpos.2401_412 < rr_bitpos.2402_413)
    goto <bb 198>; [INV]
  else
    goto <bb 197>; [INV]

  <bb 197> :

  <bb 198> :
  # iftmp.2400_515 = PHI <&lr_bitpos(196), &rr_bitpos(197)>
  # DEBUG this => &D.192544
  # DEBUG cs#0 => iftmp.2400_515
  # DEBUG INLINE_ENTRY __ct
  # DEBUG this => &D.192544
  # DEBUG cs#0 => iftmp.2400_515
  # DEBUG INLINE_ENTRY __ct
  MEM[(struct poly_int *)&D.192544] ={v} {CLOBBER(bob)};
  _1060 = MEM[(const long int &)iftmp.2400_515];
```

I had a small bug where I would go too far back in the clobbers so I just
happened upon this.