CO pipelining

Question

consider a 4-stage pipeline (IF, ID, EX, WB) used to execute the following code. All the instructions are spending 1 cycle in all the stags but MUL takes 4 cycles. Div takes 3 cycles in EX stages. The pipeline uses operand forwarding as an optimization

a- how many cycles are required to complete the program with optimization?

b- how many cycles are required to complete without optimization?

I1 : MUL  r0 , r1 , r2

I2 : DIV  r3 , r1 , r2

I3: SUB  r4, r3, r2

I4: ADD r5, r4, r1

Comments

check these gate question.

https://gateoverflow.in/1391/gate2005-68

https://gateoverflow.in/753/gate2001-12 you will understand better and one thing i forgot to mention that if you use split phase means writing in half cycle and reading in next cycle then only it will take 14 cycles. like this

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
I1	IF	ID	EX	EX	EX	EX	WB
I2		IF	ID				EX	EX	EX	WB
I3			IF							ID	EX	WB
I4												ID	EX	WB

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That is only when the ID phase includes register read as well, which is not mentioned in the given question..so i assume that should be given explicitly in the question.

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check this -

https://en.wikipedia.org/wiki/Classic_RISC_pipeline#Instruction_decode, Instruction decode phase includes decode the instruction and fetch the source operands.