The code generator transforms the intermediate representation into object code using rules which denote the semantics of the source language. These rules are define a translation semantics.

The code generator’s task is to translate the intermediate representation to the native code of the target machine. The native code may be an actual executable binary, assembly code or another high-level language. Producing low-level code requires familiarity with such machine level issues such as

· data handling

· machine instruction syntax

· variable allocation

· program layout

· registers

· instruction set

The code generator may be integrated with the parser.

As the source program is processed, it is converted to an internal form. The internal representation in the example is that of an implicit parse tree. Other internal forms may be used which resemble assembly code. The internal form is translated by the code generator into object code. Typically, the object code is a program for a virtual machine. The virtual machine chosen for Simp consists of three segments. A data segment, a code segment and an expression stack.

The data segment contains the values associated with the variables. Each variable is assigned to a location which holds the associated value. Thus, part of the activity of code generation is to associate an address with each variable. The code segment consists of a sequence of operations. Program constants are incorporated in the code segment since their values do not change. The expression stack is a stack which is used to hold intermediate values in the evaluation of expressions. The presence of the expression stack indicates that the virtual machine for Simp is a “stack machine'’.