Attached code reports following warning:

unused.c: In function ‘main’:
unused.c:14: warning: ‘testvar.unusedval’ is used uninitialized in this function

Uncommenting "forget (testvar)" on line 15, this warning disappears, which is
even more strange.

The warning is invalid (should be "may be used uninitialized"), because gcc has
no knowledge about forget().

Related: http://bugzilla.gnome.org/show_bug.cgi?id=308923

gcc -c -O2 -Wall unused.c
------
struct testme {
    int testval;
    int unusedval;
};

extern void forget (struct testme forgotten);

int
main () {
    struct testme testarray[1];
    {
	struct testme testvar;
	testvar.testval = 0;
	testarray[0] = testvar;
/*	forget (testvar);*/
    }
    forget (testarray[0]);
    return 0;
}