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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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