2018-08-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87147
	* tree-ssa-sccvn.c (SSA_VISITED): New function.
	(visit_phi): When the degenerate result is from the backedge and
	we didn't visit its definition yet drop to VARYING.
	(do_rpo_vn): Properly mark blocks with incoming backedges as executable.

	* gcc.dg/torture/pr87147.c: New testcase.

From-SVN: r263980