Fix PR tree-optimization/15555
	* tree-dfa.c (dump_variable): If the variable is a pointer
	SSA_NAME, also dump its points-to information.
	* tree-flow.h (struct ptr_info_def): Add field
	is_dereferenced.
	(dump_points_to_info_for): Declare.
	(debug_points_to_info_for): Declare.
	* tree-optimize.c (init_tree_optimization_passes): Add a
	second alias analysis pass after DOM2.
	Move pass_del_pta to a later spot.
	* tree-ssa-alias.c (compute_points_to_and_addr_escape): Do not
	create a name tags when we find a dereferenced pointer.  Just
	mark the pointer dereferenced.
	(collect_points_to_info_for): Move code to clear points-to
	information to create_name_tags.
	(create_name_tags): New function.
	(compute_flow_sensitive_aliasing): Call it.
	(setup_pointers_and_addressables): Mark type tags for renaming
	here instead of ...
	(create_memory_tag): ... here.
	(merge_pointed_to_info): Do not merge PT_MALLOC attributes.
	(dump_points_to_info_for): Declare extern.
	(debug_points_to_info_for): New function.

From-SVN: r84378