Re-order buffer
A re-order buffer (ROB) is used in a Tomasulo algorithm for out-of-order instruction execution. It allows instructions to be committed in-order.
Normally, there are three stages of instructions: "Issue", "Execute", "Write Result". In Tomasulo algorithm, an additional stage called "commit" came up. In this stage, results of instructions will be stored in the register or memory. And in the "Write Result" stage, the results are just put in the re-order buffer. All contents in this buffer can be used when executing other instructions depending on these.
There are three fields in every entry of the buffer:
- Instruction type
- Destination
- Result
Additional benefits include allowing for precise exceptions and easy rollback control of target address mispredictions (branch or jump).
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