What is the function of a reorder buffer in a dynamically scheduled processor?

The function of a reorder buffer in a dynamically scheduled processor is to hold results until it is safe to store them. This is crucial in out-of-order execution, where instructions may complete in a different order than they were issued, allowing the CPU to utilize its resources more efficiently.

When an instruction is executed and produces a result, that result must not be immediately written back to the architectural state (the registers or memory) until it is guaranteed to be the correct order of operations. The reorder buffer allows the processor to keep track of the completion status of instructions and ensures that they are committed to the architectural state in the precise order that they were issued.

This mechanism helps to maintain the integrity of the program’s execution order and avoids potential hazards that can occur when instructions are executed out of order. By holding results temporarily, the reorder buffer contributes to achieving both high performance and correctness in executing instructions.