2017-04-24  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/79725
	* tree-ssa-sink.c (statement_sink_location): Return whether
	failure reason was zero uses.  Move that check later.
	(sink_code_in_bb): Deal with zero uses by removing the stmt
	if possible.

	* gcc.dg/tree-ssa/ssa-sink-15.c: New testcase.

From-SVN: r247091