tree-optimization/98674 - improve dependence analysis

tree-optimization/98674 - improve dependence analysis

This improves dependence analysis on refs that access the same
array but with different typed but same sized accesses.  That's
obviously safe for the case of types that cannot have any
access function based off them.  For the testcase this is
signed short vs. unsigned short.

2021-01-14  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/98674
	* tree-data-ref.c (base_supports_access_fn_components_p): New.
	(initialize_data_dependence_relation): For two bases without
	possible access fns resort to type size equality when determining
	shape compatibility.

	* gcc.dg/vect/pr98674.c: New testcase.