--- /dev/null
+// RUN: %clangxx_tsan -O1 %s -o %t && %t 2>&1 | FileCheck %s --check-prefix=CHECK_O1
+// ---RUN: %clangxx_tsan -O2 %s -o %t && %t 2>&1 | FileCheck %s --check-prefix=CHECK_O2
+//
+// Check that load widening is not tsan-hostile.
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+
+struct {
+ int i;
+ char c1, c2, c3, c4;
+} S;
+
+int G;
+
+void *Thread1(void *x) {
+ G = S.c1 + S.c3;
+ return NULL;
+}
+
+void *Thread2(void *x) {
+ S.c2 = 1;
+ return NULL;
+}
+
+int main() {
+ pthread_t t[2];
+ memset(&S, 123, sizeof(S));
+ pthread_create(&t[0], NULL, Thread1, NULL);
+ pthread_create(&t[1], NULL, Thread2, NULL);
+ pthread_join(t[0], NULL);
+ pthread_join(t[1], NULL);
+ printf("PASS\n");
+}
+
+// FIXME: currently, this test fails at -O2 (reports false positive).
+// CHECK_O2: WARNING: ThreadSanitizer: data race
+
+// CHECK_O1: PASS
+// CHECK_O1-NOT: WARNING: ThreadSanitizer: data race