"=&m" (res) fails to compile with the following error:
[...] error: ‘&’ constraint used with no register class
The short code below highlights the problem. Instead of 10, the output is a
random value (I compiled it with
g++ -o tst -O3 -Wall -march=native -mtune=native tst.C). If you add "memory"
to the clobber list, you get correct output.
#include <iostream>
using namespace std;
struct int128 {
unsigned long long int lo;
unsigned long long int hi;
} __attribute__ ((aligned(16))) ;
int128 testFN(unsigned long long a) {
unsigned long long alo = (unsigned int) a;
unsigned long long ahi = (a >> 32);
int128 res;
asm __volatile__ (
// compute basic products (alo * alo, ahi * ahi, 2 * alo * ahi)
"movq (%0) , %%xmm7 \n\t" // xmm7 = (alo, 0)
"movhpd (%1) , %%xmm7 \n\t" // xmm7 = (alo, ahi)
"movdqa %%xmm7 , (%2) \n\t" // res.lo = alo, res.hi = ahi
: //"=&m" (res)
: "rV" (&alo), "rV" (&ahi), "rV" (&res)
: "%xmm7" //, "memory"
);
return res;
}
int main() {
int128 res;
res.lo = 1;
res.hi = 2;
cout << testFN(testFN(10).lo).lo << '\n';
return 0;
}
--
View this message in context: http://old.nabble.com/extended-asm---memory-constraint-tp28725485p28749465.html
Sent from the gcc - Help mailing list archive at Nabble.com.
