tree-optimization/96043 - BB vectorization costing improvement

tree-optimization/96043 - BB vectorization costing improvement

This makes the BB vectorizer cost independent SLP subgraphs
separately.  While on pristine trunk and for x86_64 I failed to
distill a testcase where the vectorizer would think _any_
basic-block vectorization opportunity is not profitable I do
have pending work that would make the cost savings of a
profitable opportunity make another independently not
profitable opportunity vectorized.

2020-09-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/96043
	* tree-vectorizer.h (_slp_instance::cost_vec): New.
	(_slp_instance::subgraph_entries): Likewise.
	(BB_VINFO_TARGET_COST_DATA): Remove.
	* tree-vect-slp.c (vect_free_slp_instance): Free
	cost_vec and subgraph_entries.
	(vect_analyze_slp_instance): Initialize them.
	(vect_slp_analyze_operations): Defer passing costs to
	the target, instead record them in the SLP graph entry.
	(get_ultimate_leader): New helper for graph partitioning.
	(vect_bb_partition_graph_r): Likewise.
	(vect_bb_partition_graph): New function to partition the
	SLP graph into independently costable parts.
	(vect_bb_vectorization_profitable_p): Adjust to work on
	a subgraph.
	(vect_bb_vectorization_profitable_p): New wrapper,
	discarding non-profitable vectorization of subgraphs.
	(vect_slp_analyze_bb_1): Call vect_bb_partition_graph before
	costing.

	* gcc.dg/vect/costmodel/x86_64/costmodel-pr69297.c: Adjust.