CO-Grand Test 1-Q13

Question

Consider the following instruction sequence for a hypothetical RISC processor.

                                        

                                        

                                        

                                       

                                       

                                       

                                       

Which of the following is a possible legal execution order for this instruction on an out-of-order processor without register renaming?

 

Answer 1

(A)

    Here is a dependency between U and X so there must be 2 stall

    Here is a dependency between V and W so there must be 2 stall

(B)

    Here is a dependency between U and X so there must be 2 stall

   Dependency between V and W there is one stall

(C)

  Here is a dependency between V and U so 2 stalls

   Here is a dependency between U and X so 2 stalls 

  Here is a dependency between X and Y so 1 stall

(D)

   Dependency between T and Y so 1 stall

     

       

 

   

So from all of them, answer should be D because of less number of stalls        

Answer 2

Y is not there in test time.

Comments

Giving marks for all, for ranking, will put the right choice later

Answer 3

Answer is (A) because if we execute the above instructions in the orignal order and order which is given in the options we can clearly see in Option A the results of the registers after the complete execution of the sequence is equal to the result which would have been obtained if we have executed in the original order.

Registers------>	R1	R2	R3	R4	R5	R6	R7	R8	R9	R10	R11
Original sequence	R2+R3	R2	R3	R5+R6	R7+R8	R6	R7	R8	R2+R3+R5+R6	R5+R6+R2+R3	2*(R2+R3)+R5+R6
Option A	R2+R3	R2	R3	R5+R6	R7+R8	R6	R7	R8	R2+R3+R5+R6	R5+R6+R2+R3	2*(R2+R3)+R5+R6
Option B	R2+R3	R2	R3	R5+R6	R7+R8	R6	R7	R8	R2+R3+R7+R8	R5+R6+R2+R3	2*(R2+R3)+R5+R6
Option C	R2+R3	R2	R3	R6+R7+R8	R7+R8	R6	R7	R8	R2+R3+R6+R7+R8	R2+R3+R6+R7+R8	2*(R2+R3)+R6+R7+R8
Option D	R2+R3	R2	R3	R5+R6	R7+R8	R6	R7	R8	R2+R3+R5+R6	R2+R3+R5+R6	R2+R3+R10