编译通得过，功能仿真出错

进行波形仿真后出现很多错误。
怎样修改，出现什么问题？求助啊
Error: Zero-time oscillation in node "|opt_square|high[0]~reg0" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|high[0]" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add1|addcore:adder|unreg_res_node[1]~7" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add1|addcore:adder|_~17" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add0|addcore:adder|unreg_res_node[0]~0" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add0|addcore:adder|_~0" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add1|addcore:adder|unreg_res_node[1]" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add1|addcore:adder|_~24" at time 180.0 ns. Check the design or vector source file for combinational loop.
Error: Zero-time oscillation in node "|opt_square|lpm_add_sub:Add0|addcore:adder|unreg_res_node[0]" at time 180.0 ns. Check the design or vector source file for combinational loop.

而且进行时序仿真的时候能出现波形，但是波形是错误的