gcc optimizer

I found that the following code causes segfault when compiled with -O2. Compiler:
gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)

#include <stdlib.h>

struct prime {
        struct prime *next;
};

int main(){
        struct prime primes = {.next=NULL};
        struct prime *p = ℙ

        while (p->next != NULL){
                p = p->next;
        }
        p->next = (struct prime*) malloc (sizeof(struct prime));
        return 0;
}