tree-ssa-alias.c (get_continuation_for_phi): Improve looking for the last VUSE which def dominates the PHI.

2017-05-04  Richard Biener  <rguenther@suse.de>

	* tree-ssa-alias.c (get_continuation_for_phi): Improve looking
	for the last VUSE which def dominates the PHI.  Directly call
	maybe_skip_until.
	(get_continuation_for_phi_1): Remove.

	* gcc.dg/tree-ssa/ssa-fre-58.c: New testcase.

From-SVN: r247596