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CS433ug: Computer System Organization
Quiz 4
Show all of your work. If you believe a problem is incorrectly or incompletely specified, make a reasonable assumption and solve the problem. The assumption should not result in a trivial solution. In all cases, clearly state any assumptions that you make in your answers.
1. [15 pts] Branch Prediction
a) [5 pts] The figure shows the state transition diagram of a branch predictor. Please draw a smallest state transition diagram (with the smallest number of states) that is equivalent to this figure.
Solution:
b) [10 pts] Write a loop which contains a branch that will be completely mis-predicted by a one-bit branch prediction scheme (i.e. the loop should contain an if statement which the one-bit predictor will always mis-predict).
Solution:
Here’s one example of such a loop: for (i=0; i<100; i++) { if ( (i % 2) ==0 ) { printf(“even \n”); } else { printf(“odd \n”)‘ } } The one-bit predictor predicts that the branch in the “if” statement will go the same direction it did the last time. By creating a statement which alternates between taken and not taken, we cause the one-bit predictor to mis-predict every time.
2 [15 pts] Tomasulo’s Algorithm
DIVD F1, F2, F
MULTD F1, F4, F
ADDD F4, F5, F
ADDD F5, F4, F
STORE F5, 8(R1)
a) [10 pts] List all the dependences in the code fragment and indicate what kind of dependences they are.
