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diff --git a/test/tsan/mop1.c b/test/tsan/mop1.c
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+// 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
+