1 files changed, 27 insertions, 0 deletions
diff --git a/test/msan/mul_by_const.cc b/test/msan/mul_by_const.cc
new file mode 100644
index 0000000000000..a975bb92167ed
--- /dev/null
+++ b/test/msan/mul_by_const.cc
@@ -0,0 +1,27 @@
+// RUN: %clangxx_msan -m64 -O2 %s -o %t && %run %t
+
+#include <sanitizer/msan_interface.h>
+
+struct S {
+  S(int a0) : a(a0) {}
+  int a;
+  int b;
+};
+
+// Here S is passed to FooRun as a 64-bit integer.
+// This triggers an optimization where 10000 * s.a is transformed into
+// ((*(uint64_t *)&s) * (10000 * 2**32)) >> 32
+// Test that MSan understands that this kills the uninitialized high half of S
+// (i.e. S::b).
+void FooRun(S s) {
+  int64_t x = 10000 * s.a;
+  __msan_check_mem_is_initialized(&x, sizeof(x));
+}
+
+int main(void) {
+  S z(1);
+  // Take &z to ensure that it is built on stack.
+  S *volatile p = &z;
+  FooRun(z);
+  return 0;
+}