tree-optimization/98137 - enhance split_constant_offset range handling

tree-optimization/98137 - enhance split_constant_offset range handling

split_constant_offset currently gives up looking at ranges when
dealing with possibly wrapping operations for looking through
conversions when the downstream analysis does not yield a SSA name.
That's overly conservative and we have a nice helper that can
deal with arbitrary expresssions.  Use that.  This helps data
reference group analysis so the testcase is fully SLP vectorized,
making use of the whole-function "BB" vectorization capabilities
we now have.

2020-12-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/98137
	* tree-data-ref.c (split_constant_offset_1): Use
	determine_value_range instead of get_range_info to handle
	arbitrary expressions.

	* gcc.dg/vect/bb-slp-pr98137.c: New testcase.