Code Generator

. consider each statement

. remember if operand is in a register

. Register descriptor

- Keep track of what is currently in each register.

- Initially all the registers are empty

. Address descriptor

- Keep track of location where current value of the name can be found at runtime

- The location might be a register, stack, memory address or a set of those

The code generator generates target code for a sequence of three-address statement. It considers each statement in turn, remembering if any of the operands of the statement are currently in registers, and taking advantage of that fact, if possible. The code-generation uses descriptors to keep track of register contents and addresses for names.

1. A register descriptor keeps track of what is currently in each register. It is consulted whenever a new register is needed. We assume that initially the register descriptor shows that all registers are empty. (If registers are assigned across blocks, this would not be the case). As the code generation for the block progresses, each register will hold the value of zero or more names at any given time.

2. An address descriptor keeps track of the location (or locations) where the current value of the name can be found at run time. The location might be a register, a stack location, a memory address, or some set of these, since when copied, a value also stays where it was. This information can be stored in the symbol table and is used to determine the accessing method for a name.