Author: Julia Lawall <julia@diku.dk> vpage is checked not to be NULL just after it is initialized at the beginning of each loop iteration. A simplified version of the semantic patch that makes this change is as follows: (http://www.emn.fr/x-info/coccinelle/) // @r exists@ local idexpression x; expression E; position p1,p2; @@ if (x@p1 == NULL || …) …