3. The variable(s) "list" cause a data dependency in this loop

A variable inside the loop is affected by the value of a variable in a previous iteration of the loop. For example:

do 99 i=1,n
	do 99 j = 1,m
		a[i, j+1] = a[i,j] + a[i,j-1]
99 continue

This is a contrived example, since for such a simple loop the optimizer would simply swap the inner and outer loops, so that the inner loop could be parallelized. But this example demonstrates the concept of data dependency, often referred to as, "loop-carried data dependency."

The compiler can often tell you the names of the variables that cause the loop-carried data dependency. If you rearrange your program to remove (or minimize) such dependencies, then the compiler can perform more aggressive optimizations.