* var-tracking.c (remove_cselib_value_chains): Define only for
	ENABLE_CHECKING.
	(dataflow_set_preserve_mem_locs, dataflow_set_remove_mem_locs,
	delete_slot_part, emit_notes_for_differences_1): Don't call
	remove_cselib_value_chains here.
	(set_slot_part, emit_notes_for_differences_2): Don't call
	add_cselib_value_chains here.
	(preserved_values): New vector.
	(preserve_value): New function.
	(add_uses, add_stores, vt_add_function_parameters): Use it
	instead of cselib_preserve_value.
	(changed_values_stack): New vector.
	(check_changed_vars_0): New function.
	(check_changed_vars_1, check_changed_vars_2): Use it.
	(emit_notes_for_changes): Call set_dv_changed (*, false) on all
	changed_values_stack VALUEs.
	(vt_emit_notes): For all preserved_values call
	add_cselib_value_chains.  If ENABLE_CHECKING call
	remove_cselib_value_chains before verifying value_chains is empty.
	Initialize and free changed_values_stack.
	(vt_initialize): Initialize preserved_values.
	(vt_finalize): Free preserved_values.

From-SVN: r157277