PR rtl-optimization/12092
	* loop.c (emit_prefetch_instructions): Do nothing if PREFETCH_BLOCK
	is zero.

	* gcc.dg/pr12092-1.c: New test case.

Co-Authored-By: Andrew Pinski <pinskia@physics.uc.edu>
Co-Authored-By: James E Wilson <wilson@specifixinc.com>

From-SVN: r92794