PR/67682, break SLP groups up if only some elements match

PR/67682, break SLP groups up if only some elements match

gcc/:

	* tree-vect-slp.c (vect_split_slp_store_group): New.
	(vect_analyze_slp_instance): During basic block SLP, recurse on
	subgroups if vect_build_slp_tree fails after 1st vector.

gcc/testsuite/:

	* gcc.dg/vect/bb-slp-7.c (main1): Make subgroups non-isomorphic.
	* gcc.dg/vect/bb-slp-subgroups-1.c: New.
	* gcc.dg/vect/bb-slp-subgroups-2.c: New.
	* gcc.dg/vect/bb-slp-subgroups-3.c: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@230330 138bc75d-0d04-0410-961f-82ee72b054a4