Add a vect_get_num_copies helper routine

This patch adds a vectoriser helper routine to calculate how
many copies of a vector statement we need.  At present this
is always:

  LOOP_VINFO_VECT_FACTOR (loop_vinfo) / TYPE_VECTOR_SUBPARTS (vectype)

but later patches add other cases.  Another benefit of using
a helper routine is that it can assert that the division is
exact (which it must be).

2017-09-14  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vectorizer.h (vect_get_num_copies): New function.
	* tree-vect-data-refs.c (vect_get_data_access_cost): Use it.
	* tree-vect-loop.c (vectorizable_reduction): Likewise.
	(vectorizable_induction): Likewise.
	(vectorizable_live_operation): Likewise.
	* tree-vect-stmts.c (vectorizable_mask_load_store): Likewise.
	(vectorizable_bswap): Likewise.
	(vectorizable_call): Likewise.
	(vectorizable_conversion): Likewise.
	(vectorizable_assignment): Likewise.
	(vectorizable_shift): Likewise.
	(vectorizable_operation): Likewise.
	(vectorizable_store): Likewise.
	(vectorizable_load): Likewise.
	(vectorizable_condition): Likewise.
	(vectorizable_comparison): Likewise.
	(vect_analyze_stmt): Pass the slp node to vectorizable_live_operation.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r252764