tree-optimization/97897 - complex lowering on abnormal edges

tree-optimization/97897 - complex lowering on abnormal edges

This fixes complex lowering to not put constants into abnormal
edge PHI values by making sure abnormally used SSA names are
VARYING in its propagation lattice.

2020-11-19  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97897
	* tree-complex.c (complex_propagate::visit_stmt): Make sure
	abnormally used SSA names are VARYING.
	(complex_propagate::visit_phi): Likewise.
	* tree-ssa.c (verify_phi_args): Verify PHI arguments on abnormal
	edges are SSA names.

	* gcc.dg/pr97897.c: New testcase.