Hardware interview practice
Preserve Correct State in a Five-Stage Pipeline
An in-order IF/ID/EX/MEM/WB core has full ALU forwarding, detects a load-use hazard in ID, resolves branches in EX, and can see a data-access fault in MEM. Architectural exceptions must be precise. Which control policy is correct?
Choose one
Answer choices
- A. Forward the load address as load data to avoid the stall, never flush on a taken branch, and repair any wrong-path writes after WB.
- B. Handle every dependency by flushing the complete pipeline and restarting at the consumer instruction; branch and exception age do not affect which writes are allowed.
- C. Stall the dependent instruction for a load-use gap, forward other available results, flush younger instructions when an EX branch is taken, and on a MEM fault allow older instructions to complete while suppressing the faulting instruction's writeback and flushing all younger state before entering the handler.
- D. On a MEM fault, immediately discard every older and younger instruction, including one already committed in WB, so the machine restarts from an empty pipeline.