Question

Consider the following operations: A B- C The corresponding assembly code instruction list generated by a compiler are 1 load [%r0 +4], %r1 2 load [%r0 + 8], %r2 3 sub %r1, %r2,%r3 4 load [ZrO + 12], %r4 5 add %r3, %r4 , %r5 6 store %r3, [%r0 + 16] 7 store %r5, [%r0 + 20] a) Identify the potential pipeline hazards. (10 points) b) State if the found hazards can be eliminated and if so propose a scheme that eliminates hazards. (10 points) al

Answer 1

a)

Potential Hazards :-

RAW: Instructions 4 and 6. Register R0.
RAW: Instructions 5 and 6. Register R3.

b)

Hazards eleminated through stalling :-

10 12 13 MEM WB MEM MEM WB MEM ID EX WB t- (0) MEM WB ID ID EX MEM WB ID EX MEM WB

Through forwarding :- (if forwarding enabled then no hazard )

10 9 6 5 4 3 2 WB MEM EX IF IM多 MEM lix WB MEM ID WB 2 2 2 MEM WB MEM MEM ID MEM EX ID