GATE Papers >> CSE >> 2015 >> Question No 249

Question No. 249 CSE | GATE 2015

Consider the following code sequence having five instructions I1 to I5. Each of these instructions has the following format.
OP Ri, Rj, Rk
Where operation Op is performed on contents of registers Rj and Rk and the result is stored in register Ri.
I1: ADD R1, R2, R3
I2: MUL R7., R1, R3
I3: SUB R4, R1, R5
I4: ADD R3, R2, R4
I5: MUL R7, R8, R9

Consider the following three statements.

S1:There is an anti-dependence between instruction I2 and I5
S2:There is an anti-dependence between instructions I2 and I4
S3:Within an instruction pipeline an anti-dependence always creates one or more stalls

Which one of above statements is/are correct?

Answer : (B) only S2 is true

Solution of Question No 249 of GATE 2015 CSE Paper

S1 is false

S2 is true because there is an anti-dependence between intructions I2 and I4.

S3 is false because anti-dependence stalls may be avoided when register renaming is used.

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