tree-optimization/102798 - avoid copying PTA info to old SSA names

tree-optimization/102798 - avoid copying PTA info to old SSA names

The vectorizer duplicates pointer-info to created pointer bases
but it has to avoid changing points-to info on existing SSA names
because there's now flow-sensitive info in there (pt->pt_null as
set from VRP).

2021-10-18  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/102798
	* tree-vect-data-refs.c (vect_create_addr_base_for_vector_ref):
	Only copy points-to info to newly generated SSA names.

	* gcc.dg/pr102798.c: New testcase.