text: // RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
  #include "test.h"
  
  // Test case https://github.com/google/sanitizers/issues/494
  // Tsan sees false HB edge on address pointed to by syncp variable.
  // It is false because when acquire is done syncp points to a var in one frame,
  // and during release it points to a var in a different frame.
  // The code is somewhat tricky because it prevents compiler from optimizing
  // our accesses away, structured to not introduce other data races and
  // not introduce other synchronization, and to arrange the vars in different
  // frames to occupy the same address.
  
  // The data race CHECK-NOT below actually must be CHECK, because the program
  // does contain the data race on global.
  
  // CHECK-NOT: WARNING: ThreadSanitizer: data race
  // CHECK: DONE
  
  long global;
  long *syncp;
  long *addr;
  long sink;
  
  void *Thread(void *x) {
    while (__atomic_load_n(&syncp, __ATOMIC_ACQUIRE) == 0)
      usleep(1000);  // spin wait
    global = 42;
    __atomic_store_n(syncp, 1, __ATOMIC_RELEASE);
    __atomic_store_n(&syncp, 0, __ATOMIC_RELAXED);
    return NULL;
  }
  
  void __attribute__((noinline)) foobar() {
    __attribute__((aligned(64))) long s;
  
    addr = &s;
    __atomic_store_n(&s, 0, __ATOMIC_RELAXED);
    __atomic_store_n(&syncp, &s, __ATOMIC_RELEASE);
    while (__atomic_load_n(&syncp, __ATOMIC_RELAXED) != 0)
      usleep(1000);  // spin wait
  }
  
  void __attribute__((noinline)) barfoo() {
    __attribute__((aligned(64))) long s;
  
    if (addr != &s) {
      printf("address mismatch addr=%p &s=%p\n", addr, &s);
      exit(1);
    }
    __atomic_store_n(&addr, &s, __ATOMIC_RELAXED);
    __atomic_store_n(&s, 0, __ATOMIC_RELAXED);
    sink = __atomic_load_n(&s, __ATOMIC_ACQUIRE);
    global = 43;
  }
  
  int main() {
    pthread_t t;
    pthread_create(&t, 0, Thread, 0);
    foobar();
    barfoo();
    pthread_join(t, 0);
    if (sink != 0)
      exit(1);
    fprintf(stderr, "DONE\n");
    return 0;
  }
  
  