What is loop unrolling and how does it affect performance?

What is loop unrolling and how does it affect performance?

Loop unrolling is an optimization technique that reduces the overhead of loop control by increasing the number of operations performed in each iteration. This can lead to improved performance by decreasing the number of iterations and enhancing instruction-level parallelism.

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

Sure! Here's a simple example in C:

for (int i = 0; i < 8; i++) {
    sum += array[i];
}

This can be unrolled to:

sum += array[0];
sum += array[1];
sum += array[2];
sum += array[3];
sum += array[4];
sum += array[5];
sum += array[6];
sum += array[7];

This reduces the loop overhead.

What are the potential downsides of loop unrolling?

While loop unrolling can improve performance, it can also increase code size, which may lead to cache misses. Additionally, it can make the code less readable and harder to maintain.

Is loop unrolling always beneficial?

Not necessarily. The benefits of loop unrolling depend on the specific context, such as the size of the loop and the architecture of the CPU. It's important to profile the code to determine if unrolling is advantageous.