target/3920: wrong register number for CTR in stabs

[Mattias Engdegård]

>Why do you think this is incorrect?  The assembler code generated by
>GCC 3.1 with -O2 -g -mregnames is:
[...]
>.L9:
>        add %r0,%r0,%r3
>        addi %r3,%r3,-1
>        bdnz .L9

You are right of course. Gcc 2.95 didn't use an integer register that
worked in parallel with CTR and would instead do a mfctr in the loop
(which is less efficient of course), so I was confused in my reporting.
Sorry about that.

A better example would be

int sum(int n)
{
        int i, j = 0, s = 0;
        for(i = n; i != 0; i--) {
		s += j;
		j *= 2;
	}
        return s;
}

the loop of which gcc 3.0.2 (I didn't have 3.1 handy) turns into the nice code

.L8:
        add %r3,%r3,%r0
        slwi %r0,%r0,1
        bdnz .L8

but where the stabs claim 'i' lives in register 66, which does not make sense
for CTR. The DWARF2 output (compiling with -gdwarf-2) seems to use the same
incorrect numbering.

I will check 3.1 as soon as I have built it.