[10/46] Temporarily make stmt_vec_info a class

[10/46] Temporarily make stmt_vec_info a class

This patch turns stmt_vec_info into an unspeakably bad wrapper class
and adds an implicit conversion to the associated gimple stmt.
Having this conversion makes the rest of the series easier to write,
but since the class goes away again at the end of the series, I've
not bothered adding any comments or tried to make it pretty.

2018-07-31  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (stmt_vec_info): Temporarily change from
	a typedef to a wrapper class.
	(NULL_STMT_VEC_INFO): New macro.
	(vec_info::stmt_infos): Change to vec<stmt_vec_info>.
	(stmt_vec_info::operator*): New function.
	(stmt_vec_info::operator gimple *): Likewise.
	(set_vinfo_for_stmt): Use NULL_STMT_VEC_INFO.
	(add_stmt_costs): Likewise.
	* tree-vect-loop-manip.c (iv_phi_p): Likewise.
	* tree-vect-loop.c (vect_compute_single_scalar_iteration_cost)
	(vect_get_known_peeling_cost): Likewise.
	(vect_estimate_min_profitable_iters): Likewise.
	* tree-vect-patterns.c (vect_init_pattern_stmt): Likewise.
	* tree-vect-slp.c (vect_remove_slp_scalar_calls): Likewise.
	* tree-vect-stmts.c (vect_build_gather_load_calls): Likewise.
	(vectorizable_store, free_stmt_vec_infos): Likewise.
	(new_stmt_vec_info): Change return type of xcalloc to
	_stmt_vec_info *.

From-SVN: r263125