Pipeline hazards

Question

R1 <- R1+R2

R2 <- R3*R4

R3 <- R4-R1

R2 <- R3+R4

Can someone point out hazards. Thanks :)

Comments

raw hazard follow - inorder

war and waw  follow - out of order

try...

---

Ans is 2 RAW , 2 WAR and 1 WAW and didn't even show where hazards are -_-

I didn't get your point @Hradesh patel and which 2 RAW you pointed out? Probably @vishal chugh missed out that one. It would have been correct.

---

I found my mistake. There is RAW hazard in Instruction 3 for R1. So there are 2 RAW , 2 WAR and 1 WAW hazards.

Answer 1

RAW hazard in in I3 instruction.

RAW and WAW hazard takes place in I4 instruction.

Answer 2

RAW Dependency - 2

I-3 on I-1

I-4 on I-3

WAR Dependency - 2

I-3 on I-2

I-2 on I-1

I-4 on I-1

WAW Dependency - 1

I-4 on I-2

After seeing and solving lots of questions on this topic i would like to share what i found ,

RAW are only between adjecent instruction 

ex- R0← R1+R2

R0← R1+R0

R1← R0 + R2

here RAW is on only valid between I-3 and I-2 not in I-3 and I-1

whereas WAR are not only between adjacent instruction .

not sure about WAW for now i am taking WAW only between adjacent instruction

Comments

You forgot I4-I1 WAR hazard

---

thanx, i will correct it with some explanation