Check in LLVM r95781.
diff --git a/test/Preprocessor/cxx_true.cpp b/test/Preprocessor/cxx_true.cpp
new file mode 100644
index 0000000..b123e0c
--- /dev/null
+++ b/test/Preprocessor/cxx_true.cpp
@@ -0,0 +1,13 @@
+/* RUN: %clang_cc1 -E %s -x c++ | grep block_1
+   RUN: %clang_cc1 -E %s -x c++ | not grep block_2
+   RUN: %clang_cc1 -E %s -x c | not grep block
+*/
+
+#if true
+block_1
+#endif
+
+#if false
+block_2
+#endif
+