https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65467
--- Comment #21 from Jeff Hammond <jeff.science at gmail dot com> ---
Thanks. This is great. I built GCC master last night and can now compile both
the trivial test program and a more interesting one that encapsulates what I
actually need to work to make progress on OpenMP 5 and other activities.
/* trivial */
#include <stdatomic.h>
int main(void)
{
return 0;
}
/* nontrivial */
#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L) &&
!defined(__STDC_NO_ATOMICS__)
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdatomic.h>
#ifdef _OPENMP
# include <omp.h>
#else
# error No OpenMP support!
#endif
#ifdef SEQUENTIAL_CONSISTENCY
int load_model = memory_order_seq_cst;
int store_model = memory_order_seq_cst;
#else
int load_model = memory_order_acquire;
int store_model = memory_order_release;
#endif
int main(int argc, char * argv[])
{
int nt = omp_get_max_threads();
#if 1
if (nt != 2) omp_set_num_threads(2);
#else
if (nt < 2) omp_set_num_threads(2);
if (nt % 2 != 0) omp_set_num_threads(nt-1);
#endif
int iterations = (argc>1) ? atoi(argv[1]) : 100;
printf("thread ping-pong benchmark\n");
printf("num threads = %d\n", omp_get_max_threads());
printf("iterations = %d\n", iterations);
#ifdef SEQUENTIAL_CONSISTENCY
printf("memory model = %s\n", "seq_cst");
#else
printf("memory model = %s\n", "acq-rel");
#endif
fflush(stdout);
_Atomic int left_ready = -1;
_Atomic int right_ready = -1;
int left_payload = 0;
int right_payload = 0;
#pragma omp parallel
{
int me = omp_get_thread_num();
/// 0=left 1=right
bool parity = (me % 2 == 0);
int junk = 0;
/// START TIME
#pragma omp barrier
double t0 = omp_get_wtime();
for (int i=0; i<iterations; ++i) {
if (parity) {
/// send to left
left_payload = i;
atomic_store_explicit( &left_ready, i, store_model);
/// recv from right
while (i != atomic_load_explicit( &right_ready, load_model));
//printf("%d: left received %d\n", i, right_payload);
junk += right_payload;
} else {
/// recv from left
while (i != atomic_load_explicit( &left_ready, load_model));
//printf("%d: right received %d\n", i, left_payload);
junk += left_payload;
///send to right
right_payload = i;
atomic_store_explicit( &right_ready, i, store_model);
}
}
/// STOP TIME
#pragma omp barrier
double t1 = omp_get_wtime();
/// PRINT TIME
double dt = t1-t0;
#pragma omp critical
{
printf("total time elapsed = %e\n", dt);
printf("time per iteration = %e\n", dt/iterations);
printf("%d\n", junk);
}
}
return 0;
}
#else // C11
#error You need C11 atomics for this test!
#endif // C11
