/* Statement isomorphisms - replace explicit checks against NULL with a
 * shorter variant, which relies on C's downgrade-to-bool feature.
 * The expression metavariables should be declared as pointers, however,
 * that doesn't work well with complex expressions like:
 * if (UNIT(p)->default_dependencies != NULL)
 */

Statement
@@
expression X;
statement S;
@@
if (X == NULL) S => if (!X) S

Statement
@@
expression X;
statement S;
@@
if (X != NULL) S => if (X) S