Re: Is this the expected behavior?

["Mohamed Shafi" <shafitvm at gmail dot com>]

2008/7/15 Ramana Radhakrishnan <ramana.r@gmail.com>:
> Hi Mohamed,
>
>
>
> Why not ? Callee save registers are after all registers and the split
> is in the ABI's head (so to speak). So GCC is well within its right to
> use callee save registers. In fact if you were in a leaf function that
> did not make any function calls the first preference would be to
> allocate caller save registers and then to allocate callee save
> registers - Instead of spilling a caller save register , GCC could
> very well use a callee save register and the only extra cost would be
> saving and restoring context of the callee save register in the
> prologue and the epilogue respectively.
>

   I agree with you, but what about when there are still caller save
register are available and there are no register restrictions for any
instructions? In my case i find that GCC has used only the argument
registers, stack pointer and callee saved registers. So out of the 16
available registers ony 5+1+4 registers were used, even though there
was 6 caller save registers were available

>
> HTH.
>
>
> cheers
> Ramana
>
> On Tue, Jul 15, 2008 at 7:50 AM, Mohamed Shafi <shafitvm@gmail.com> wrote:
>>
>> Hello all,
>>
>> I am not sure if this the right mailing list.
>>
>> I am involved in the porting of gcc 4.1.2 for a 16 bit target.
>> In some cases i noticed that callee save registers were getting
>> allocated in the body even though there isn't any function call. I
>> believe that callee save registers will be allocated only if some
>> variable values are required across a function call. So if there is no
>> function call there shouldn't be any callee save registers used in a
>> function body. So my question is will GCC allocate callee save
>> registers for function even if the function doesn't call any other
>> function?
>> Or is this a gcc bug?
>>
>> Hope my question is clear.
>>
>> Regards,
>> Shafi
>
>
>
> --
> Ramana Radhakrishnan
>