vect: Factor out and rename some functions/macros

vect: Factor out and rename some functions/macros

Power supports vector memory access with length (in bytes) instructions.
Like existing fully masking for SVE, it is another approach to vectorize
the loop using partially-populated vectors.

As Richard Sandiford suggested, we should share the codes in approaches
with partial vectors if possible.  This patch is to:
  1) factor out two functions:
     - vect_min_prec_for_max_niters
     - vect_known_niters_smaller_than_vf.
  2) rename four functions:
     - vect_iv_limit_for_full_masking
     - check_load_store_masking
     - vect_set_loop_condition_masked
     - vect_set_loop_condition_unmasked
  3) rename macros LOOP_VINFO_MASK_COMPARE_TYPE and LOOP_VINFO_MASK_IV_TYPE.

Bootstrapped/regtested on aarch64-linux-gnu.

gcc/ChangeLog:

	* tree-vect-loop-manip.c (vect_set_loop_controls_directly): Rename
	LOOP_VINFO_MASK_COMPARE_TYPE to LOOP_VINFO_RGROUP_COMPARE_TYPE.  Rename
	LOOP_VINFO_MASK_IV_TYPE to LOOP_VINFO_RGROUP_IV_TYPE.
	(vect_set_loop_condition_masked): Renamed to ...
	(vect_set_loop_condition_partial_vectors): ... this.  Rename
	LOOP_VINFO_MASK_COMPARE_TYPE to LOOP_VINFO_RGROUP_COMPARE_TYPE.  Rename
	vect_iv_limit_for_full_masking to vect_iv_limit_for_partial_vectors.
	(vect_set_loop_condition_unmasked): Renamed to ...
	(vect_set_loop_condition_normal): ... this.
	(vect_set_loop_condition): Rename vect_set_loop_condition_unmasked to
	vect_set_loop_condition_normal.  Rename vect_set_loop_condition_masked
	to vect_set_loop_condition_partial_vectors.
	(vect_prepare_for_masked_peels): Rename LOOP_VINFO_MASK_COMPARE_TYPE
	to LOOP_VINFO_RGROUP_COMPARE_TYPE.
	* tree-vect-loop.c (vect_known_niters_smaller_than_vf): New, factored
	out from ...
	(vect_analyze_loop_costing): ... this.
	(_loop_vec_info::_loop_vec_info): Rename mask_compare_type to
	compare_type.
	(vect_min_prec_for_max_niters): New, factored out from ...
	(vect_verify_full_masking): ... this.  Rename
	vect_iv_limit_for_full_masking to vect_iv_limit_for_partial_vectors.
	Rename LOOP_VINFO_MASK_COMPARE_TYPE to LOOP_VINFO_RGROUP_COMPARE_TYPE.
	Rename LOOP_VINFO_MASK_IV_TYPE to LOOP_VINFO_RGROUP_IV_TYPE.
	(vectorizable_reduction): Update some dumpings with partial
	vectors instead of fully-masked.
	(vectorizable_live_operation): Likewise.
	(vect_iv_limit_for_full_masking): Renamed to ...
	(vect_iv_limit_for_partial_vectors): ... this.
	* tree-vect-stmts.c (check_load_store_masking): Renamed to ...
	(check_load_store_for_partial_vectors): ... this.  Update some
	dumpings with partial vectors instead of fully-masked.
	(vectorizable_store): Rename check_load_store_masking to
	check_load_store_for_partial_vectors.
	(vectorizable_load): Likewise.
	* tree-vectorizer.h (LOOP_VINFO_MASK_COMPARE_TYPE): Renamed to ...
	(LOOP_VINFO_RGROUP_COMPARE_TYPE): ... this.
	(LOOP_VINFO_MASK_IV_TYPE): Renamed to ...
	(LOOP_VINFO_RGROUP_IV_TYPE): ... this.
	(vect_iv_limit_for_full_masking): Renamed to ...
	(vect_iv_limit_for_partial_vectors): this.
	(_loop_vec_info): Rename mask_compare_type to rgroup_compare_type.
	Rename iv_type to rgroup_iv_type.