You may see this warning when compiling a Qsys based design containing an IRQ_Bridge in the Quartus® II software.
This warning can be safely ignored.
Other similar warnings that can safely be ignored are:
Warning (12251): <instance name>.sender1_irq: Cannot connect reset for irq_synchronizer_001.receiver
Warning (12251): <instance name>.sender2_irq: Cannot connect reset for irq_synchronizer_002.receiver
Warning (12251): <instance name>.sender3_irq: Cannot connect reset for irq_synchronizer_003.receiver
Warning (12251): <instance name>.sender4_irq: Cannot connect reset for irq_synchronizer_004.receiver
Warning (12251): <instance name>.sender5_irq: Cannot connect reset for irq_synchronizer_005.receiver