2019-03-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/89789
	* tree-ssa-sccvn.c (set_ssa_val_to): Do not allow lattice
	changes from non-undefined back to undefined.

	* gcc.dg/torture/pr89789.c: New testcase.

From-SVN: r269917