falk@juist:/tmp% cat test.c
#ifdef __cplusplus
extern "C"
#endif
void abort(void);

__attribute__((noinline))
unsigned long f(const unsigned long x) {
    struct { unsigned long x : 1; } s;
    s.x = x;
    return s.x;
}

int main() {
    if (f(3) != 1)
        abort();
}
falk@juist:/tmp% gcc test.c && ./a.out   
falk@juist:/tmp% g++ test.c && ./a.out  
falk@juist:/tmp% g++ -O test.c && ./a.out 
zsh: abort (core dumped)  ./a.out

not a problem with 4.0 or earlier