--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if29.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,28 @@
+// PR c++/85827
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wunused-variable -Wunused-parameter" }
+
+template <int N> int f()
+{
+    constexpr bool _1 = N == 1;
+    constexpr bool _2 = N == 2;
+    constexpr bool _3 = N == 3;
+    
+    if constexpr (_1) {
+        return 5;
+    } else if constexpr (_2) {
+        return 1;
+    } else if constexpr (_3) {
+        return 7;
+    }
+}
+
+int a() {
+    return f<1>();
+}
+int b() {
+    return f<2>();
+}
+int c() {
+    return f<3>();
+}