tree-ssa-loop-prefetch.c (determine_unroll_factor): Bound the unroll factor by the estimated number of iterations.

	* tree-ssa-loop-prefetch.c (determine_unroll_factor):  Bound the unroll
	factor by the estimated number of iterations.
	(loop_prefetch_arrays): Do not prefetch in loops that iterate less than
	prefetch latency.

	* gcc.dg/tree-ssa/prefetch-4.c: New test.

From-SVN: r122435