Lpc2000

Hello.

I use IAR C for ARM V4.20a, and I try write FIQ as:
__fiq __arm void my_fiq (void) 

When I open listing, I see this prologue code:

00000000 04E04EE2 SUB LR,LR,#+0x4 
00000004 0F5F2DE9 STMDB SP!,{R0-R3,R8-R12,LR} 

But fiq has own shadow registers r8-r15. 
Why compiler saves this registers in stack?
I think, that this is not necessary and make undesirable overhead.
Can I avoid this somehow?