Properties of Real and Abstract Machines

In this chapter we shall discuss the target machine properties relevant for code generation, and the mapping of the language-oriented objects and operations onto objects and operations of the target machine. Systematic code generation must, of course, take account of the peculiarities and weaknesses of the target computer’s instruction set. It cannot, however, become bogged down in exploitation of these special idiosyncrasies; the payoff in code efficiency will not cover the implementation cost. Thus the compiler writer endeavors to derive a model of the target machine that is not distorted by exceptions, but is as uniform as possible, to serve as a base for code generator construction. To this end some properties of the hardware may be ignored, or gaps in the instruction set may be filled by subroutine invocations or inline sequences treated as elementary operations. In particular, the instruction set is extended by the operations of a run-time system that interfaces input/output and similar actions to the operating system, and attends to storage management.