re PR tree-optimization/71866 (gcc locks up after fix for PR70159)

re PR tree-optimization/71866 (gcc locks up after fix for PR70159)

2016-07-14  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/71866
	* tree-ssa-pre.c (get_constant_for_value_id): Remove.
	(do_hoist_insertion): Avoid endless recursion when we
	didn't insert anything because we managed to simplify
	things down to a constant or SSA name.
	(fully_constant_expression): Re-write in terms of ...
	* tree-ssa-sccvn.h (vn_nary_simplify): ... this.  Declare.
	* tree-ssa-sccvn.c (vn_nary_simplify): New wrapper around
	vn_nary_build_or_lookup_1.
	(vn_nary_build_or_lookup_1): Added flag and renamed from ...
	(vn_nary_build_or_lookup): ... this which now wraps it.

	* gcc.dg/torture/pr71866.c: New testcase.

From-SVN: r238334