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There are several reasons. FACTOR (input INT) is the unrolling factor. This modification can make an important difference in performance. This page was last edited on 22 December 2022, at 15:49. The next example shows a loop with better prospects. Here is the code in C: The following is MIPS assembly code that will compute the dot product of two 100-entry vectors, A and B, before implementing loop unrolling. how to optimize this code with unrolling factor 3? The loop itself contributes nothing to the results desired, merely saving the programmer the tedium of replicating the code a hundred times which could have been done by a pre-processor generating the replications, or a text editor. As with loop interchange, the challenge is to retrieve as much data as possible with as few cache misses as possible. Look at the assembly language created by the compiler to see what its approach is at the highest level of optimization. This method called DHM (dynamic hardware multiplexing) is based upon the use of a hardwired controller dedicated to run-time task scheduling and automatic loop unrolling. Unblocked references to B zing off through memory, eating through cache and TLB entries. This usually requires "base plus offset" addressing, rather than indexed referencing. By the same token, if a particular loop is already fat, unrolling isnt going to help. See your article appearing on the GeeksforGeeks main page and help other Geeks. Depending on the construction of the loop nest, we may have some flexibility in the ordering of the loops. Processors on the market today can generally issue some combination of one to four operations per clock cycle. This is in contrast to dynamic unrolling which is accomplished by the compiler. Loop unrolling - Wikipedia I am trying to unroll a large loop completely. At the end of each iteration, the index value must be incremented, tested, and the control is branched back to the top of the loop if the loop has more iterations to process. The overhead in "tight" loops often consists of instructions to increment a pointer or index to the next element in an array (pointer arithmetic), as well as "end of loop" tests. Loop unrolling helps performance because it fattens up a loop with more calculations per iteration. Loop splitting takes a loop with multiple operations and creates a separate loop for each operation; loop fusion performs the opposite. determined without executing the loop. Predicting unroll factors using supervised classification | IEEE