parallel processing - Getting rid of data dependency -


i have code:

for(i=0; i<size; i++) {     d[i] = d[i-1] + v[i]; }

when parallel processing loop, have data dependency , initiation interval becomes 2 meaning have:

initiation interval:2

|load v[i-1]|load d[i-2]|    add    |store d[i-1]| |           |           |  load v[i]|load d[i-1] |     add    | store d[i] |

i not want stall in between.

initiation interval:1

|load v[i-1]|load d[i-2]|    add    |store d[i-1]| |           |load v[i]  |load d[i-1]|     add    | store d[i] |

this not possible since d[i-1] not stored yet.

how make initiation interval 1 changing code?

you cannot reduce gap.

also (loop unrolling) not efficient way of parallel processing kind of loop. loop looks prefix-sum operation. there fast parallel algorithms , implementations available prefix-sum. example, this question


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