Exercise $4\mathrm{.}9$

In this exercise, we examine how data dependences affect execution in the basic

$5-$stage pipeline described in Section $4\mathrm{.}5.$

Problems in this exercise refer to the following sequence of instructions:

or $,r1,r2,r3$

or $,r2,r1,r4$

or $r1,r1,r2$

$4\mathrm{.}9\mathrm{.}1$

There are three data dependences $B$ that may cause a data harzard:

read after write $($RAW$).($True dependency$)$

write after read $($WAR$)($Antidependency$)$

write after write $($WAW$)($Output dependency$)$

In the basic five$-$stage pipeline WAR and WAW dependences do not cause any

hazards.

Without forwarding, any RAW dependence between an instruction and the next

two instructions cause data hazards.

Indicate dependences and their type.

A

B

C

D

E

$($Cont$.)$ Exercise $4\mathrm{.}9$

In the basic five$-$stage pipeline, choose the data dependence$($s$)$ that cause the

hazards. $($Assuming no forwarding.$)$

A

B

C

D

E