2010-10-21  Richard Guenther  <rguenther@suse.de>
	Michael Matz  <matz@suse.de>

	PR tree-optimization/45764
	* tree-vect-data-refs.c (vect_compute_data_ref_alignment):
	Adjust initial misalignment for negative DR_STEP.
	(vect_find_same_alignment_drs): Two DRs with different DR_STEP
	do not have the same alignment over the whole iteration domain.

        * gcc.dg/torture/pr45764.c: New testcase.

Co-Authored-By: Michael Matz <matz@suse.de>

From-SVN: r165768