2018-09-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87263
	* tree-ssa-sccvn.c (visit_phi): Revert some earlier changes.
	(struct unwind_state): Add max_rpo field.
	(do_rpo_vn): Allow up-to-date loop state to be used when not iterating.
	Compute max_rpo, the max RPO number a block can be backwards reached
	from.  Re-write non-iterating mode to a RPO ordered worklist approach,
	separating it from the iterating mode.

	* gcc.dg/torture/pr87263.c: New testcase.
	* gcc.dg/torture/ssa-fre-2.c: Likewise.
	* gcc.dg/torture/ssa-fre-3.c: Likewise.
	* gcc.dg/torture/ssa-fre-4.c: Likewise.

From-SVN: r264273