Imported Upstream version 6.10.0.49

Former-commit-id: 1d6753294b2993e1fbf92de9366bb9544db4189b

external/llvm-project/compiler-rt/test/tsan/mop1.c

@@ -0,0 +1,40 @@
+// RUN: %clang_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
+#include "test.h"
+
+// We want to establish the following sequence of accesses to X:
+// - main thread writes X
+// - thread2 reads X, this read happens-before the write in main thread
+// - thread1 reads X, this read is concurrent with the write in main thread
+// Write in main thread and read in thread1 should be detected as a race.
+// Previously tsan replaced write by main thread with read by thread1,
+// as the result the race was not detected.
+
+volatile long X, Y, Z;
+
+void *Thread1(void *x) {
+  barrier_wait(&barrier);
+  barrier_wait(&barrier);
+  Y = X;
+  return NULL;
+}
+
+void *Thread2(void *x) {
+  Z = X;
+  barrier_wait(&barrier);
+  return NULL;
+}
+
+int main() {
+  barrier_init(&barrier, 2);
+  pthread_t t[2];
+  pthread_create(&t[0], 0, Thread1, 0);
+  X = 42;
+  barrier_wait(&barrier);
+  pthread_create(&t[1], 0, Thread2, 0);
+  pthread_join(t[0], 0);
+  pthread_join(t[1], 0);
+  return 0;
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+