[Bug c/21474] New: missed optimizations when comparing address to NULL

["trt at acm dot org" <gcc-bugzilla at gcc dot gnu dot org>]

The program below gives some expressions which gcc could, but does not, evaluate
to true.  E.g. gcc considers &p->a true, even when a is the first element
of the struct (is this a bug?), but does not consider &p->b[3] to be true.

struct foo {int a, b[10];};
 
int subr(int i, struct foo *p)
{
    int x[10];
 
#if 0
    // gcc folds this
    if (&p->a) return 1;
#else
    // but not these
    if (&p->b[3]) return 1;
 
    if (&x[3] != 0) return 1;
    if (&x[i] != 0) return 1;  // not sure if this one is safe to fold
#endif
    return 0;
}

-- 
           Summary: missed optimizations when comparing address to NULL
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: trt at acm dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21474