Compiler Design

• Input to Code Generator: Must ensure correctness and exact form of the IR.
• Memory Management: Mapping names to specific runtime addresses and managing stack frames.
• Instruction Selection: Choosing the most efficient machine instructions.
• Register Allocation: Making optimal use of limited fast registers.
• Evaluation Order: The order of operations heavily affects register requirements.
• Cost Model: Accurately measuring the performance cost of instruction sequences to guide optimization choices.

A basic code generator processes three-address statements and maintains two important descriptors:

• Register Descriptor: Tracks what variable is currently held in each register.
• Address Descriptor: Tracks where (in a register or in memory) the current value of each variable is.

The getReg() Function

For an instruction x = y op z, the generator decides which registers to use:

• If y is already in a register, use it; else load y.
• If z is already in a register, use it; else load z.
• If x has a register allocated, use it; else find a free register or spill one to memory.