tree-optimization/104064 - UBSAN issue in vect dataref analysis

tree-optimization/104064 - UBSAN issue in vect dataref analysis

Since we order DRs after DR_INIT we know the difference will be
positive and thus can avoid signed overflow issues by using
unsigned arithmetic to produce the known unsigned result.

2022-01-18  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/104064
	* tree-vect-data-refs.cc (vect_analyze_data_ref_accesses): Check
	DR_INIT fits in a signed HWI, represent the difference from the
	first DR in unsigned.