10.2.3.2 Inhibitors to Automatic Parallelization

Under automatic parallelization, the compilers do not parallelize a loop if:

• The DO loop is nested inside another DO loop that is parallelized

• Flow control allows jumping out of the DO loop

• A user-level subprogram is invoked inside the loop

• An I/O statement is in the loop

• Calculations within the loop change an aliased scalar variable