Replace vec_info::vector_size with vec_info::vector_mode

Replace vec_info::vector_size with vec_info::vector_mode

This patch replaces vec_info::vector_size with vec_info::vector_mode,
but for now continues to use it as a way of specifying a single
vector size.  This makes it easier for later patches to use
related_vector_mode instead.

2019-11-14  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vec_info::vector_size): Replace with...
	(vec_info::vector_mode): ...this new field.
	* tree-vect-loop.c (vect_update_vf_for_slp): Update accordingly.
	(vect_analyze_loop, vect_transform_loop): Likewise.
	* tree-vect-loop-manip.c (vect_do_peeling): Likewise.
	* tree-vect-slp.c (can_duplicate_and_interleave_p): Likewise.
	(vect_make_slp_decision, vect_slp_bb_region): Likewise.
	* tree-vect-stmts.c (get_vectype_for_scalar_type): Likewise.
	* tree-vectorizer.c (try_vectorize_loop_1): Likewise.

gcc/testsuite/
	* gcc.dg/vect/vect-tail-nomask-1.c: Update expected epilogue
	vectorization message.

From-SVN: r278237