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[Frama-c-discuss] unproven VC with newer why version

Hollas Boris (CR/AEY1) wrote:
>> Would it be useful to add automatically a clause "variant N-i;" for
>> loops having the simple syntactic structure "for (i = ... ; i < N ;
>> i++)"? This way proof obligations for such loops (which are quite
>> common) would be automatically discharged.
>>     
>
>   
>> Regards,
>> david
>>     
>
> In C, the loop variable can be modified in the body. Hence, The loop variant you propose may not hold. If a variant was added automatically, it wouldn't be possible to verify these loops. The same is true for loop invariants.
>   
Yes, that's why I'm reluctant to implement such an heuristic. the same 
for the heuristic loop inv 0 <= i <= N

But I think it would be possible to implement another plugin devoted to 
suggest simple annotations like this. Then running Jessie on the 
automatically annotated code could be done, and do a manual modification 
for wrong generated annotations.

In other words, I don't think it is a good idea to generate such an 
annotation without telling the user.

- Claude

> A solution is to use abstract interpretation to infer simple loop invariants and variants automatically.
>
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