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[Frama-c-discuss] Meaning of "FROM \nothing" for function calls in -deps analysis?

Hello David,

On Fri, Aug 28, 2015 at 3:55 PM, David MENTRE <dmentre at linux-france.org>
wrote:

>
> void main(int param)
> {
>   c = 3;
>
> [from] Function main:
>   b FROM \nothing
>   c FROM \nothing
>   e FROM \nothing
> """
>
> For main(), why -deps gives "b FROM \nothing" and "e FROM \nothing"? I
> would have expected "e FROM c" and "b FROM c" due to calls to loop_branch()
> and double_assign() and corresponding -deps analysis of those functions.
>

Option -deps show the dependencies, when the function under consideration
terminates, of the values of the variables when the function terminates
with respect to the values of variables when the function begins.

b FROM c for function main() would mean that b is computed from the value c
had when main() was entered. This is not the case because the first thing
does is to assign c, so as a consequence, b is really from “whatever c was
computed from when it was assigned at the beginning of main()”. The
assignment is in fact “c = 3;”, meaning that c is computed from nothing,
and this is why when the end of main() is reached, b has been computed from
nothing.
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