15 / 18 Pipelining & Execution

WAR and WAW Hazards

Which of these represents a WAR (write-after-read) hazard?

; Sequence A
ADD R1, R2, R3    ; 
SUB R2, R4, R5    ; 

; Sequence B
ADD R1, R2, R3    ;
SUB R4, R1, R5    ;
A

Neither: WAR hazards only exist in multi-core systems

B

Sequence A: SUB writes R2 before ADD finishes reading it

C

Sequence B: SUB reads R1 before ADD finishes writing it

D

Both are WAR hazards