It would not be possible to do it.
digitalRead, digitalWrite, analogWrite, analogRead, etc all do far more than just setting a bit, or reading a value.
They manipulate the port settings to ensure that it is in the right state to perform the operation. If you wanted it to reduce it down to single SFR manipulations, then the preprocessor would need to parse and understand the whole flow of all of your program to know what state the ports are in at any particular time. Given the nature of the Arduino, and the amount of external stimulus that the precompiler cannot ever know about, this is impossible to do.