Editing Loop unrolling (section)

==Advantages==
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. If an optimizing compiler or assembler is able to pre-calculate offsets to each ''individually referenced'' array variable, these can be built into the [[machine code]] instructions directly, therefore requiring no additional arithmetic operations at run time.

* Significant gains can be realized if the reduction in executed instructions compensates for any performance reduction caused by any increase in the size of the program.
* [[Branch predictor|Branch penalty]] is minimized.<ref name="fog2012">{{cite web|url=http://www.agner.org/optimize/optimizing_assembly.pdf|quote=12.11 Loop unrolling |pages=100|title=Optimizing subroutines in assembly language|first=Agner|last=Fog|author-link=Agner Fog |date=2012-02-29 |access-date=2012-09-22| publisher=Copenhagen University College of Engineering}}</ref>
* If the statements in the loop are independent of each other (i.e. where statements that occur earlier in the loop do not affect statements that follow them), the statements can potentially be executed in [[Parallel computing|parallel]].
* Can be implemented dynamically if the number of array elements is unknown at compile time (as in [[Duff's device]]).

Optimizing compilers will sometimes perform the unrolling automatically, or upon request.