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ps6-sol

# ps6-sol - ECE 468 573 Problem Set 7 Dependence analysis 1...

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ECE 468 & 573 Problem Set 7: Dependence analysis 1. Draw the iteration space graph for the following loop: for (int i = 0; i < 5; i++) { for (int j = 0; j < 5; j++) { A[i][j - 1] = A[i - 1][j + 2] + A[i][j + 1]; } } Answer: Solid lines = flow dependences, dashed lines = anti dependences, dotted lines = output dependences. 2. Show the distance vector(s) for the loop from the previous problem. Answer: Flow dependence: (1, -3), Anti dependence (0, 2) 3. Show the direction vector(s) for the loop. Answer: Flow dependence: (+, -), Anti dependence (0, +) 4. Can the two loops be interchanged? Why or why not? Answer: No, because the flow dependence is a (+, -) dependence, and it will be broken by interchange. 5. Repeat the previous four steps for the following loop: 1

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for (int i = 0; i < 5; i++) { for (int j = 0; j < 5; j++) { A[i][j] = A[i + 1][j + 3]; } } Answer: Solid lines = flow dependences, dashed lines = anti dependences, dotted lines = output dependences. There is an anti dependence, with distance (1, 3), and direction (+, +). Thus, interchange is legal. 6. Give an example of a doubly-nested loop with a single statement in the loop body
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