Memory spill in my kernel

Hi ,

I have a question related to the compiler generated information.

I have compiled the kernel and see the following information.I am working on Gen9 GT2 system.

1> Maximum work-group size: 256

1> Compiler work-group size: (0, 0, 0)

1> Local memory size: 0

1> Preferred multiple of work-group size: 8

1> Minimum amount of private memory: 768

1> Amount of spill memory used by the kernel: 1024

I assume that private memory is mapped to the registers by the compiler. My workgroup size is "1". each EU thread has 128 GRFs and each GRF size is 256-bits . the total memory size of the private space is 4096 bytes. I see my kernel requires only 768 bytes of the GRF space which is much less than 4096 bytes , but compiler is generating a spill code of 1024 bytes. 

could you please explain me why this is happening?

Best Regards,

Rajesh