What is loop unrolling and why is it used?

What is loop unrolling and why is it used?

Loop unrolling is an optimization technique that reduces the overhead of loop control by increasing the number of operations within a single loop iteration.

Can you give me an example of loop unrolling in C?

Sure! Instead of writing a loop that increments an array element by one in each iteration, you can unroll it to process multiple elements at once, like this:

for (int i = 0; i < n; i += 4) {
    array[i] += 1;
    array[i + 1] += 1;
    array[i + 2] += 1;
    array[i + 3] += 1;
}

What are the benefits of using loop unrolling?

The benefits include reduced loop overhead, improved cache performance, and better utilization of CPU pipelines, leading to faster execution.

Are there any downsides to loop unrolling?

Yes, downsides include increased code size, potential register pressure, and reduced readability, which can complicate maintenance.