# GAP Message (Diagnostic ID 30519)

## Message

Insert a "%s parallel" statement right before the loop at line %d to parallelize the loop.

## Advice

Add "#pragma parallel" before the specified loop. This pragma enables the parallelization of the loop at the specified line by ignoring assumed cross-iteration data dependencies.

## Example

Consider the following:

    void foo(float *a, int m, int n) {
      int i;
      for (i=0; i<n; i++) {
        a[i] = a[i+m]+1;
      }
      return;
    }

In this case, the compiler is unable to parallelize the loop without further information about m. For example, if m is negative, then each iteration will be dependent on the previous iteration. However, if m is known to be greater than n, you can parallelize the loop.

If you determine it is safe to do so, you can add the pragma as follows:

    void foo(float *a, int m, int n) {
      int i;
    #pragma parallel
      for (i=0; i<n; i++) {
        a[i] = a[i+m]+1;
      }
      return;
    }

## Verify

Confirm that any arrays in the loop do not have cross-iteration dependencies. A cross-iteration dependency exists if a memory location is modified in an iteration of the loop and accessed by a read or a write statement in another iteration of the loop.

Parent topic: Guided Auto Parallelism Messages