re PR debug/89463 (debug information for iterator of an empty loop is gone (at -O3))

re PR debug/89463 (debug information for iterator of an empty loop is gone (at -O3))

2019-03-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/89463
	* tree-ssa-dce.c (remove_dead_stmt): Take output vector to
	queue edges to remove.
	(eliminate_unnecessary_stmts): Remove dead PHIs alongside
	dead stmts.  Delay edge removal until PHIs are removed to
	make debug-stmt creation not confused by seemingly degenerate
	PHIs.

	* gcc.dg/guality/pr89463.c: New testcase.

From-SVN: r269961