This patch uses new, delete, constructors and desctructors to manage
vec_info.  This includes making ~vec_info free all the data shared
by bb_vec_info and loop_vec_info, whereas previously the code was
duplicated in destroy_bb_vec_info and destroy_loop_vec_info.  This
in turn meant changing the order of:

  FOR_EACH_VEC_ELT (slp_instances, i, instance)
    vect_free_slp_instance (instance);

and:

  gimple_set_uid (stmt, -1);

in destroy_bb_vec_info/~_bb_vec_info, so that now vect_free_slp_instance
could see a uid of -1 as well as 0.  The patch updates vinfo_for_stmt
so that it returns NULL for a uid of -1.

2017-08-04  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-vectorizer.h (vec_info): Add a constructor and destructor.
	Add an explicit name for the enum.  Use auto_vec for slp_instances
	and grouped_stores.
	(_loop_vec_info): Add a constructor and destructor.  Use auto_vec
	for all vectors.
	(_bb_vec_info): Add a constructor and destructor.
	(vinfo_for_stmt): Return NULL for uids of -1 as well.
	(destroy_loop_vec_info): Delete.
	(vect_destroy_datarefs): Likewise.
	* tree-vectorizer.c (vect_destroy_datarefs): Delete.
	(vec_info::vec_info): New function.
	(vec_info::~vec_info): Likewise.
	(vectorize_loops): Use delete instead of destroy_loop_vec_info.
	* tree-parloops.c (gather_scalar_reductions): Use delete instead of
	destroy_loop_vec_info.
	* tree-vect-loop.c (new_loop_vec_info): Replace with...
	(_loop_vec_info::_loop_vec_info): ...this.
	(destroy_loop_vec_info): Replace with...
	(_loop_vec_info::~_loop_vec_info): ...this.  Unconditionally delete
	the stmt_vec_infos.  Leave handling of vec_info information to its
	destructor.  Remove explicit vector releases.
	(vect_analyze_loop_form): Use new instead of new_loop_vec_info.
	(vect_analyze_loop): Use delete instead of destroy_loop_vec_info.
	* tree-vect-slp.c (new_bb_vec_info): Replace with...
	(_bb_vec_info::_bb_vec_info): ...this.  Don't reserve space in
	BB_VINFO_GROUPED_STORES or BB_VINFO_SLP_INSTANCES.
	(destroy_bb_vec_info): Replace with...
	(_bb_vec_info::~_bb_vec_info): ...this.  Leave handling of vec_info
	information to its destructor.
	(vect_slp_analyze_bb_1): Use new and delete instead of
	new_bb_vec_info and destroy_bb_vec_info.
	(vect_slp_bb): Replace 2 calls to destroy_bb_vec_info with a
	single delete.

From-SVN: r250869