re PR target/69264 (ICE building spidermonkey -mcpu=970 -maltivec -O3: rs6000_builtin_vectorization_cost, at config/rs6000/rs6000.c:4350)

2017-01-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/69264
	* target.def (vector_alignment_reachable): Improve documentation.
	* doc/tm.texi: Regenerate.
	* targhooks.c (default_builtin_vector_alignment_reachable): Simplify
	and add a comment.
	* tree-vect-data-refs.c (vect_supportable_dr_alignment): Revert
	earlier changes with respect to TYPE_USER_ALIGN.
	(vector_alignment_reachable_p): Likewise.  Improve dumping.

	* g++.dg/torture/pr69264.C: New testcase.

From-SVN: r244897