I found this in ppc32 3.3.3 (Debian), it also appears in 3.4.0 20040215.

If the loop count is large enough, it wont use the count register in the second
loop. eg:

#if 1
#define LOOPS 100000
#else
#define LOOPS 10
#endif
                                                                                
int main()
{
        unsigned long i;
                                                                                
        i = LOOPS;
        while (i--) {
                asm volatile("":::"memory");
        }
                                                                                
        i = LOOPS;
        while (i--) {
                asm volatile("":::"memory");
        }
}

produces the following code:

        lis 0,0x1
        ori 0,0,34464
        mtctr 0
.L13:
        bdnz .L13
        lis 0,0x1
        ori 0,0,34464
.L12:
        addic. 0,0,-1
        bne+ 0,.L12
        blr

If you reduce COUNT it will use the count register for both loops as expected