poly_int: vect_no_alias_p

This patch replaces the two-state vect_no_alias_p with a three-state
vect_compile_time_alias that handles polynomial segment lengths.

2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vect-data-refs.c (vect_no_alias_p): Replace with...
	(vect_compile_time_alias): ...this new function.  Do the calculation
	on poly_ints rather than trees.
	(vect_prune_runtime_alias_test_list): Update call accordingly.

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

From-SVN: r256142