tree-optimization/108522 Use COMPONENT_REF offset when available

tree-optimization/108522 Use COMPONENT_REF offset when available

Use the offset in TREE_OPERAND(component_ref, 2) when available instead
of DECL_FIELD_OFFSET when trying to compute offset for a COMPONENT_REF.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>
gcc/ChangeLog:

	PR tree-optimization/108522
	* tree-object-size.cc (compute_object_offset): Use
	TREE_OPERAND(ref, 2) for COMPONENT_REF when available.

gcc/testsuite/ChangeLog:

	PR tree-optimization/108522
	* gcc.dg/builtin-dynamic-object-size-0.c
	(test_dynarray_struct_member): New test.
	(main): Call it.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>