streamline TARGET_MEM_REF dumping

streamline TARGET_MEM_REF dumping

The following streamlines TARGET_MEM_REF dumping building
on what we do for MEM_REF and thus dumping things like
access type, TBAA type and base/clique.  I've changed it
to do semantic dumping aka base + offset + step * index
rather than the odd base: A, step: way.

2020-08-27  Richard Biener  <rguenther@suse.de>

	* tree-pretty-print.c (dump_mem_ref): Handle TARGET_MEM_REFs.
	(dump_generic_node): Use dump_mem_ref also for TARGET_MEM_REF.

	* gcc.dg/tree-ssa/loop-19.c: Adjust.
	* gcc.dg/tree-ssa/loop-2.c: Likewise.
	* gcc.dg/tree-ssa/loop-3.c: Likewise.