tree-dfa.c (get_ref_base_and_extent): Use range-info to refine results when processing array refs with variable index.

2018-05-18  Richard Biener  <rguenther@suse.de>

	* tree-dfa.c (get_ref_base_and_extent): Use range-info to refine
	results when processing array refs with variable index.

	* gcc.dg/tree-ssa/ssa-dse-35.c: New testcase.
	* gcc.dg/graphite/scop-10.c: Adjust to avoid dead code.
	* gcc.dg/graphite/scop-6.c: Likewise.
	* gcc.dg/graphite/scop-7.c: Likewise.
	* gcc.dg/graphite/scop-8.c: Likewise.
	* gcc.dg/graphite/scop-9.c: Likewise.

From-SVN: r260354