This rejects lattice changes from one constant to another.

2020-05-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/95049
	* tree-ssa-sccvn.c (set_ssa_val_to): Reject lattice transition
	between different constants.

	* gcc.dg/torture/pr95049.c: New testcase.