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Re: cgraph callees availability
On Fri, Jul 1, 2011 at 11:41 AM, Paulo J. Matos <pocmatos@gmail.com> wrote:
> On 01/07/11 10:31, Richard Guenther wrote:
>>
>> It is being done because the edges are not kept up-to-date. ?There is
>> no other way to find callees but to walk all statements. ?I also do not
>> see a good reason why you would want to use the number of callees
>> of a function to decide whether to emit sibcalls from it.
>>
>
> Thanks for the input Richard. Makes sense. One way which seems to work is to
> obviously add a pass to rebuild the cgraph edges before pass_expand and
> remove them afterwards.
>
> The reason why I need them is that I need know if a given register is live.
> I can check this when I expand_epilogue but not during expand (because RA
> has not been done). This special register is used for the return address of
> a function. So, if it is live it tells me that there was another function
> call besides the sibcall. If there was, it means I have to emit some extra
> instructions to do the sibcall. However, if I have to emit extra
> instructions then I don't actually want to do the sibcall cause I will be
> adding to the resulting size of the function which goes against our backend
> port policy.
>
> By checking if there is more than 1 callee (an extra function called besides
> the sibcall) then I will know if I will need extra instructions or not and
> if I do, I say the function is _not_ ok for sibcall.
>
> I guess if I don't want to add the extra passes before and after pass expand
> then I have to walk the statements. Sounds like it's the cleaner solution if
> I don't want to mess with the core.
You could add this logic to the tree-tailcall.c pass. I suppose what you
really want is no dominating call rather than only a single call in total.
Richard.
> Cheers,
> --
> PMatos
>
>