$($Loop unrolling and instruction reordering$)$ Given the code segment

shown below, assume we use a conventional $5-$stage pipeline. Load$-$use would

cause $1-$cycle pipeline stall, and branches are resolved at the instruction decode

stage. Registers St$0$ ~ St$9$ are for temporal use. Please answer the following

questions.

Loop: lw$.$ $to$,0($$s$1)$

addu $t$0,$ St$0,$ $s$2$

SW $t$0,0($$s$1)$

add $s$1,$ $s$1,-4$

bne $s$1,$ Szero, Loop

$($a$)(4$ pts$)$ Without loop unrolling and instruction reordering, how many

needed to execute four iterations?

$($b$)(16$ pts$)$ With loop unrolling that unrolls the loop four times and instruction

reordering, how many cycles are required to execute fous iterations?