Function dr_read_saved_reg 

pub unsafe extern "C" fn dr_read_saved_reg(
    drcontext: *mut c_void,
    slot: dr_spill_slot_t,
) -> reg_t

Can be used from a clean call or a restore_state_event (see dr_register_restore_state_event()) to see the value saved in spill slot \p slot by dr_save_reg().