Merge in fix for PR9561.

  // Okay, we have stores to two completely different pointers.  Try to

  // decompose the pointer into a "base + constant_offset" form.  If the base

  // pointers are equal, then we can reason about the two stores.

  int64_t Off1 = 0, Off2 = 0;

  const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);

  const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);

  int64_t EarlierOff = 0, LaterOff = 0;

  const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);

  const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);

  // If the base pointers still differ, we have two completely different stores.

  if (BP1 != BP2)

    return false;

  // Otherwise, we might have a situation like:

  //  store i16 -> P + 1 Byte

  //  store i32 -> P

  // In this case, we see if the later store completely overlaps all bytes

  // stored by the previous store.

  if (Off1 < Off2 ||                       // Earlier starts before Later.

      Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.

    return false;

  // Otherwise, we have complete overlap.

  // The later store completely overlaps the earlier store if:

  // 

  // 1. Both start at the same offset and the later one's size is greater than

  //    or equal to the earlier one's, or

  //

  //      |--earlier--|

  //      |--   later   --|

  //      

  // 2. The earlier store has an offset greater than the later offset, but which

  //    still lies completely within the later store.

  //

  //        |--earlier--|

  //    |-----  later  ------|

  if (EarlierOff >= LaterOff &&

      EarlierOff + Earlier.Size <= LaterOff + Later.Size)

    return true;

  // Otherwise, they don't completely overlap.

  return false;

}

/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a