求助 帮忙解决warning问题

WARNING:Xst:1710 - FF/Latch  <idex_signimm_8> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_7> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_6> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_5> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_4> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_3> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_2> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_1> (without init value) has a constant value of 0 in block <mips/stage_ex>.
WARNING:Xst:1710 - FF/Latch  <idex_signimm_0> (without init value) has a constant value of 0 in block <mips/stage_ex>.

是什么情况啊
请各位前辈指教

源代码：
reg [31:0] idex_signimm;
always @(posedge clk) begin
       idex_signimm    <= id_signimm;
end

WARNING:Xst:1710 - FF/Latch  <idex_signimm_8> (without init value) has a constant value of 0 in block <mips/stage_ex>.
                                 -FF 锁存器 <idex_signimm_8>（没有初始值）有一个恒定值为0的块<mips/stage_ex>.