1. More than one exit point in the loop. A loop must have a single entry and a single exit point. Multiple exit points in a loop can cause this message.
2. An iteration count that is data dependent. The iteration count must be known at entry to the loop.
3. Loop contains a subroutine or function call that prevents vectorization.
4. Other complex control structures, for example, use of multiple GOTO statements.
Below are examples for the first three scenarios.