Loop fission

In computer science, loop fission (or loop distribution) is a compiler optimization in which a loop is broken into multiple loops over the same index range with each taking only a part of the original loop's body. The goal is to break down a large loop body into smaller ones to achieve better utilization of locality of reference. This optimization is most efficient in multi-core processors that can split a task into multiple tasks for each processor. It is the opposite to loop fusion, which can also improve performance in other situations.

Example in C

 int i, a[100], b[100];
 for (i = 0; i < 100; i++) {
   a[i] = 1; 
   b[i] = 2;
 }

is equivalent to

 int i, a[100], b[100];
 for (i = 0; i < 100; i++) {
   a[i] = 1;                     
 }
 for (i = 0; i < 100; i++) {
   b[i] = 2;
 }

Further reading

Kennedy, Ken; & Allen, Randy. (2001). Optimizing Compilers for Modern Architectures: A Dependence-based Approach. Morgan Kaufmann. ISBN 1-55860-286-0.

See also

• Loop transformation
• Loop fusion

References

• Loop fission