How about if the x+1 was from an inlined function? a macro? perhaps even just a variable defined 10 lines up?

In a 7-character sequence it may seem pretty obvious that it's probably intended to mean something, but when joining together multiple independent things doing redundant operations it's much less trivial.

    int game_logic(int prev_score, int bonus) {
      if (bonus < 0) { // check for bad argument
        return -1;
      }
      int new_score = prev_score + bonus;
      // ...
      if (new_score < prev_score) { // sanity check
        abort();
      }
      return new_score;
    }
    // in the above the abort path can (and is) already optimized out, but an invocation of game_logic(x,1) becomes exactly x+1<x