Simple assembly question.

#include <stdio.h>

int main() {
    int a = 20;
    int b = 10;

    int r = a / b; (#)

    printf("%d\n", r);

    return 0;
}

If you disable the # part here, it is shown below.

int r = a / b;
    0x8000660 mov -0xc(%rbp),%eax
    0x8000663 cltd
    0x8000664 idivl -0x8(%rbp)
    0x8000667 mov %eax,-0x4(%rbp)

I understand everything else, but the command cltd is a little hard to understand. I looked it up on the Internet and it said that it is a command to expand the 4-byte long data type to the 8-byte double data type, but what variable is the data type in this code specifically?