Named register failed compilation

Hello! Everybody!

Please help me.
I would like to use named register. R6 for example.
After a subroutine, which modify this register, the compiler doesnt recognize it, and
place a nop where I want to rewrite this register.
Here is my simple example:

register unsigned int akku __asm("r6");

unsigned char test1()
{ akku=1; return 12;
}

unsigned char test(void)
{ unsigned char x,y; akku=10; //it is ok x=test1(); //this subroutine modify the akku(R6) register to 1 akku=10; //here is the problem if (x==12) { y=akku; } return y;
} After the subroutine y=1. But the correct value is 10.

Here you can see the dissasembly window. The problem is the 0x8000CE6.
Why it is NOP???

41: { 42: unsigned char x,y;
0x08000CDC B500 PUSH {lr} 43: akku=10;
0x08000CDE 260A MOVS r6,#0x0A 44: x=test1();
0x08000CE0 F000F807 BL.W test1 (0x08000CF2)
0x08000CE4 4602 MOV r2,r0 45: akku=10;
0x08000CE6 BF00 NOP 46: if (x==12) 47: {
0x08000CE8 2A0C CMP r2,#0x0C
0x08000CEA D100 BNE 0x08000CEE 48: y=akku; 49: }
0x08000CEC B2F1 UXTB r1,r6 50: return y;
0x08000CEE 4608 MOV r0,r1 51: }

Thank you.