128-bit inline assembly addition

[Marcel Keller <mks.keller@xxxxxxxxx>]

Hi,

I've found that the attached program, which supposedly adds 1 and 0 as 
128-bit numbers using inline assembly, outputs 2^64 + 1 instead when 
compiled with g++ 7 or 8 and at least -O1. Am I doing something wrong, 
or is this a compiler bug?

Best regards,
Marcel

#include <immintrin.h>
#include <iostream>
using namespace std;

int main()
{
    long res[2] = { 0, 0 };
    long x[2] = { 1, 0 };
    __asm__ volatile (
            "add %2, %0 \n"
            "adc %3, %1 \n"
            : "+r"(res[0]), "+r"(res[1])
            : "rm"(x[0]), "rm"(x[1])
            : "cc"
    );
    cout << "res " << hex << res[0] << " " << res[1] << endl;
}