You can specify the number of times loops are unrolled by using the /unroll option. You can control the number of times a specific loop is unrolled by using the cDEC$ UNROLL Directive to Control Loop Unrolling.
Although unrolling loops usually improves run-time performance, the size of the executable program may increase.
On ia64 systems, the /unroll: num option can also influence the run-time results of software pipelining optimizations performed when you specify /optimize:5 or /pipeline.
For more information:
On loop unrolling, see Loop Unrolling.