tree-optimization/101925 - fix VN with reverse storage order

tree-optimization/101925 - fix VN with reverse storage order

This fixes value-numbering breaking reverse storage order accesses
due to a missed check.  It adds a new overload for
reverse_storage_order_for_component_p and sets reversed on the
VN IL ops for component and array accesses accordingly.
It also compares the reversed reference ops flag on reference
lookup.

2021-08-16  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101925
	* tree-ssa-sccvn.c (copy_reference_ops_from_ref): Set
	reverse on COMPONENT_REF and ARRAY_REF according to
	what reverse_storage_order_for_component_p does.
	(vn_reference_eq): Compare reversed on reference ops.
	(reverse_storage_order_for_component_p): New overload.
	(vn_reference_lookup_3): Check reverse_storage_order_for_component_p
	on the reference looked up.

	* gcc.dg/sso-16.c: New testcase.

(cherry picked from commit 0215b3559e55f39f38e10984a804c53907f7491c)