middle-end: Move load/store-lanes check till late.

middle-end: Move load/store-lanes check till late.

This moves the code that checks for load/store lanes further in the pipeline and
places it after slp_optimize.  This would allow us to perform optimizations on
the SLP tree and only bail out if we really have a permute.

With this change it allows us to handle permutes such as {1,1,1,1} which should
be handled by a load and replicate.

This change however makes it all or nothing. Either all instances can be handled
or none at all.  This is why some of the test cases have been adjusted.

gcc/ChangeLog:

	* tree-vect-slp.c (vect_analyze_slp_instance): Moved load/store lanes
	check to ...
	* tree-vect-loop.c (vect_analyze_loop_2): ..Here

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/slp-11b.c: Update output scan.
	* gcc.dg/vect/slp-perm-6.c: Likewise.