Typical Advice

 advice #30003: Loop at line 8 cannot be scheduled efficiently, as it
contains complex conditional expression. Try to simplify
condition.

Why is the Compiler giving this Advice?

This Advice is issued to alert you to a complex conditional expression, generally a large "if" clause, within a loop. This will disable software-pipelining, which is critical for generating efficient code sequences.

What it means:

The C6000 compiler will optimize small if statements (if statements with if and else blocks that are short or empty). The compiler will not optimize large "if" statements, and such large if statements within the loop body will disqualify the loop for software pipelining. Software-pipelining is a key optimization; you will see reduced performance without software pipelining. In the simple examples below, Example 1 will pipeline, but Example 2 won't :

Example 1:

for (i=0; i < N; i++)
{
        if (!flag)
        {
           //statements
        }
        else
        {
          x[i] = y[i];
        }
}

Example 2:

for (i = 0; i < n; i++)
{
        if (!flag)
        {
           //statements
        }
        else
        {
           if (flag == 1) x[i] = y[i];
        }
}

for (i = 0; i < n; i++)
{
        if (!flag)
        {
           //statements
        }
        else
        {
           p = (flag == 1);
           x[i] = !p * x[i] + p * y[i] ;
        }
}

To see other examples of how "if" statements can be modified to allow software pipelining, refer to Hand Tuning Loops and Control Code on the TMS320C6000.

Risks, Severity

If this condition occurs, the compiler cannot perform the software pipelining loop optimization, which is crucial to getting good performance.

Suggested Action

Simplify complex conditional expression/"if" statements.

More Resources

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