Category
Purpose
When optimization is enabled, breaks a stream contained in a for loop into multiple streams.
Parameters
- number
- A loop unrolling factor.
The value of number is a positive integral constant expression. 
The value of number is a positive scalar integer or
compile-time constant initialization expression.
An unroll factor of 1 disables unrolling.
If number is not specified, the optimizer determines an appropriate unrolling factor for each nested loop.
Usage
To enable stream unrolling, you must specify -qhot and -qstrict, or -qsmp, or use optimization level -O4 or higher. If -qstrict is in effect, no stream unrolling takes place.
For stream unrolling to occur, the #pragma stream_unroll directive must be the last pragma specified preceding a for loop. Specifying #pragma stream_unroll more than
once for the same for loop or combining it with other loop unrolling
pragmas (#pragma unroll, #pragma nounroll, #pragma unrollandfuse, #pragma
nounrollandfuse) results in a warning. The
compiler silently ignores all but the last of multiple loop unrolling pragmas
specified on the same for loop.
Examples
int i, m, n;
int a[1000][1000];
int b[1000][1000];
int c[1000][1000];
....
#pragma stream_unroll(4)
for (i=1; i<n; i++) {
a[i] = b[i] * c[i];
}
The unroll factor of 4 reduces the number of iterations from n to n/4, as follows:
for (i=1; i<n/4; i++) {
a[i] = b[i] + c[i];
a[i+m] = b[i+m] + c[i+m];
a[i+2*m] = b[i+2*m] + c[i+2*m];
a[i+3*m] = b[i+3*m] + c[i+3*m];
}