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[Frama-c-discuss] While/if conditions and slicing

Hello,

Le ven. 13 mars 2020 à 00:04, Gilbert Pajela <gpajela at gradcenter.cuny.edu>
a écrit :

>
>
> $ cat while.c
> int f() {
>   int x = 1;
>   while (x > 0) {
>     x--;
>   }
>   return x;
> }
> $ frama-c while.c -main f -slice-return f -then-on 'Slicing export' -print
> ...
> /* Generated by Frama-C */
> int f(void)
> {
>   int x = 1;
>   while (x > 0) x --;
>   return x;
> }
>
>
I haven't checked in detail, hence the answer below should be taken with a
grain of salt, but I tend to think that this is due to the way loops are
represented internally by Frama-C. Namely, the Loop AST node does not
contain directly the test. Basically, Frama-C sees something like:

int f() {
  int x = 1;
  while(true) {
    if (! (x>0)) { break; } else { }
    x--;
  }
  return x;
}

The pretty printer recognizes this while(true) { if (...) break; ... }
pattern and presents you with a normal while loop, but the slicer sees the
if and the fact that both branches are taken (the else { } in the first
step and the { break; } in the second step of the loop). Thus, it does not
remove the test, and the code stays as is.

Best regards,
-- 
E tutto per oggi, a la prossima volta
Virgile
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