cost invariant nodes from vect_slp_analyze_node_operations SLP walk

cost invariant nodes from vect_slp_analyze_node_operations SLP walk

2020-05-19  Richard Biener  <rguenther@suse.de>

	* tree-vectorizer.h (_slp_tree::vectype): Add field.
	(SLP_TREE_VECTYPE): New.
	* tree-vect-slp.c (vect_create_new_slp_node): Initialize
	SLP_TREE_VECTYPE.
	(vect_create_new_slp_node): Likewise.
	(vect_prologue_cost_for_slp): Move here from tree-vect-stmts.c
	and simplify.
	(vect_slp_analyze_node_operations): Walk nodes children for
	invariant costing.
	(vect_get_constant_vectors): Use local scope op variable.
	* tree-vect-stmts.c (vect_prologue_cost_for_slp_op): Remove here.
	(vect_model_simple_cost): Adjust.
	(vect_model_store_cost): Likewise.
	(vectorizable_store): Likewise.