$ cat t.c
#include <string.h>
#include <stdio.h>

char b;
int x;
char a;

int main(int c, char *v[]) {
  char *p;
  printf("c:%d\n", c);
  if (c & 2) p = &a; else p = 0;
  memcpy(p, &b, c & 1);
  if (p) x=1; else x=0;
  printf("x:%d meaning p is %snull\np:%p\n", x, x?"non-":"", p);
}

$ /home/julien/prefix/gcc/fd7c447/bin/gcc -O2 -std=c11 t.c
$ ./a.out 2 3 4
c:4
x:1 meaning p is non-null
p:(nil)

$ /home/julien/prefix/gcc/fd7c447/bin/gcc -v
…
gcc version 4.9.2 20140818 (prerelease) (fd7c4470c415022ad8e98818a0b7ed6ce5044715)