interrupt routine

I found that my interrupt routine has strange

source code is:

void t3Isr(void) interrupt 3 using 0 {
        tm_flg |= (tm_sts ++ ^ tm_sts) & 0x7;
}

the compiler give me:
5: void t3Isr(void) interrupt 3 using 0 {
C:0x0003 C0E0 PUSH ACC(0xE0)
C:0x0005 C0D0 PUSH PSW(0xD0)
C:0x0007 75D000 MOV PSW(0xD0),#0x00

6: tm_flg |= (tm_sts ++ ^ tm_sts) & 0x7;
C:0x000A AF08 MOV R7,tm_sts(0x08)
C:0x000C 0508 INC tm_sts(0x08)
C:0x000E E508 MOV A,tm_sts(0x08)
C:0x0010 6F XRL A,R7
C:0x0011 5407 ANL A,#0x07
C:0x0013 4209 ORL tm_flg(0x09),A

7: }

8:
C:0x0015 D0D0 POP PSW(0xD0)
C:0x0017 D0E0 POP ACC(0xE0)
C:0x0019 32 RETI

the question is how to save R7 that the compiler uses ?