Negative array indices

gistfile1.c

#include <stdio.h>

int main() {
    struct {
      int scalar;
      int array[5];
    } some_struct;

    some_struct.scalar = 5;

    printf("%i\n", some_struct.array[-1]);

    return 0;
}

clang compiles this -- at any optimization level -- to:

leaq    L_.str(%rip), %rdi
movl    $5, %esi
xorb    %al, %al
callq   _printf