--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/ext/constexpr-builtin1.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,37 @@
+// PR c++/80265
+// { dg-do compile { target c++14 } }
+
+constexpr bool compare() {
+  char s1[] = "foo";
+  char s2[] = "fxo";
+  if (!__builtin_memcmp(s1, s2, 3))
+    return false;
+  s2[1] = 'o';
+  if (__builtin_memcmp(s1, s2, 3))
+    return false;
+  if (__builtin_strcmp(s1, s2))
+    return false;
+  return true;
+}
+
+constexpr bool length() {
+  char s[] = "foo";
+  if (__builtin_strlen(s) != 3)
+    return false;
+  return true;
+}
+
+constexpr bool find() {
+  char s[] = "foo";
+  if (__builtin_memchr(s, 'f', 3) != s)
+    return false;
+  if (__builtin_strchr(s, 'o') != s+1)
+    return false;
+  if (__builtin_strstr(s, "oo") != s+1)
+    return false;
+  return true;
+}
+
+static_assert( compare(), "" );
+static_assert( length(), "" );
+static_assert( find(), "" );