The PROB_ITERATE pragma specifies to the compiler certain properties of a loop. You assert that these properties are true in the common case. The PROB_ITERATE pragma aids the compiler in choosing the best loops and loop transformations (that is, software pipelining and nested loop transformations). PROB_ITERATE is useful only when the MUST_ITERATE pragma is not used or the PROB_ITERATE parameters are more constraining than the MUST_ITERATE parameters.
No statements are allowed between the PROB_ITERATE pragma and the for, while, or do-while loop to which it applies. However, other pragmas, such as UNROLL and MUST_ITERATE, may appear between the PROB_ITERATE pragma and the loop. The syntax of the pragma for C and C++ is:
| #pragma PROB_ITERATE(min, max) |
Where min and max are the minimum and maximum trip counts of the loop in the common case. The trip count is the number of times a loop iterates. Both arguments are optional.
For example, PROB_ITERATE could be applied to a loop that executes for eight iterations in the majority of cases (but sometimes may execute more or less than eight iterations):
#pragma PROB_ITERATE(8, 8)
If only the minimum expected trip count is known (say it is 5), the pragma would look like this:
#pragma PROB_ITERATE(5)
If only the maximum expected trip count is known (say it is 10), the pragma would look like this:
#pragma PROB_ITERATE(, 10) /* Note the blank field for min */