re PR tree-optimization/43432 (Missed vectorization: "complicated access pattern" for increasing and decreasing data indexing)

	PR tree-optimization/43432
	* tree-vect-data-refs.c (vect_analyze_data_ref_access):
	Accept backwards consecutive accesses.
	(vect_create_data_ref_ptr): If step is negative generate
	decreasing IVs.
	* tree-vect-stmts.c (vectorizable_store): Reject negative steps.
	(perm_mask_for_reverse, reverse_vec_elements): New functions.
	(vectorizable_load): Handle loads with negative steps when easily
	possible.

testsuite/
	PR tree-optimization/43432
	* lib/target-supports.exp (check_effective_target_vect_perm_byte,
	check_effective_target_vect_perm_short): New predicates.
	(check_effective_target_vect_perm): Include x86_64.
	* gcc.dg/vect/pr43432.c: New test.
	* gcc.dg/vect/vect-114.c: Adjust.
	* gcc.dg/vect/vect-15.c: Ditto.
	* gcc.dg/vect/slp-perm-8.c: Use new predicate.
	* gcc.dg/vect/slp-perm-9.c: Ditto.

From-SVN: r164367