poly_int: loop versioning threshold

poly_int: loop versioning threshold

This patch splits the loop versioning threshold out from the
cost model threshold so that the former can become a poly_uint64.
We still use a single test to enforce both limits where possible.

2017-12-21  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vectorizer.h (_loop_vec_info): Add a versioning_threshold
	field.
	(LOOP_VINFO_VERSIONING_THRESHOLD): New macro
	(vect_loop_versioning): Take the loop versioning threshold as a
	separate parameter.
	* tree-vect-loop-manip.c (vect_loop_versioning): Likewise.
	* tree-vect-loop.c (_loop_vec_info::_loop_vec_info): Initialize
	versioning_threshold.
	(vect_analyze_loop_2): Compute the loop versioning threshold
	whenever loop versioning is needed, and store it in the new
	field rather than combining it with the cost model threshold.
	(vect_transform_loop): Update call to vect_loop_versioning.
	Try to combine the loop versioning and cost thresholds here.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255934 138bc75d-0d04-0410-961f-82ee72b054a4