tree-vect-loop.c (needs_fold_left_reduction_p): Export.

2019-10-17  Richard Biener  <rguenther@suse.de>

	* tree-vect-loop.c (needs_fold_left_reduction_p): Export.
	(vect_is_simple_reduction): Move all validity checks ...
	(vectorizable_reduction): ... here.  Compute whether we
	need a fold-left reduction here.
	* tree-vect-patterns.c (vect_reassociating_reduction_p): Merge
	both overloads, check needs_fold_left_reduction_p directly.
	* tree-vectorizer.h (needs_fold_left_reduction_p): Declare.

From-SVN: r277100