I am messing around in godbolt.org (compiler), and I tried to compile this code with -O2

unsigned int func(unsigned int x) {
    return x / 7;
}

Surprisingly, this is what I get

func:
        mov     eax, edi             # edi is argument (x). Move x to eax (register)
        imul    rax, rax, 613566757  # eax *= 613566757 (unsigned 64-bit multiplication, rax is 64-bit version of eax)
        shr     rax, 32              # eax >>= 32 (gets upper 32 bit of product)
        sub     edi, eax             # x -= eax
        shr     edi                  # x >>= 1
        add     eax, edi             # eax += x
        shr     eax, 2               # x >>= 2
        ret                          # return x

What is imul rax, rax, 613566757 doing? Where does the constant come from?

Also, this translated code works as intended:

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
        int i = 137;

        long long edi = i;
        long long eax = i;
        eax *= 613566757LL;
        eax >>= 32;
        edi -= eax;
        edi >>= 1;
        eax += edi;
        eax >>= 2;
        cout << i << " " << i / 7 << " " << eax << endl;
}

Thank you very much.

(Originally I had int instead of unsigned int, but it's more complicated)