--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaCXX/compare-modules-cxx2a.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fcxx-exceptions -verify -std=c++2a -fmodules -I%S/Inputs %s -fno-modules-error-recovery
+
+#pragma clang module build compare
+module compare {
+  explicit module cmp {}
+  explicit module other {}
+}
+#pragma clang module contents
+#pragma clang module begin compare.cmp
+#include "std-compare.h"
+#pragma clang module end
+#pragma clang module endbuild
+
+struct CC { CC(...); };
+
+void a() { void(0 <=> 0); } // expected-error {{include <compare>}}
+
+struct A {
+  CC operator<=>(const A&) const = default; // expected-error {{include <compare>}}
+};
+auto va = A() <=> A(); // expected-note {{required here}}
+
+#pragma clang module import compare.other
+
+// expected-note@std-compare.h:* 2+{{previous definition}}
+
+void b() { void(0 <=> 0); } // expected-error 1+{{definition of 'strong_ordering' must be imported}}
+
+struct B {
+  CC operator<=>(const B&) const = default; // expected-error 1+{{definition of 'strong_ordering' must be imported}}
+};
+auto vb = B() <=> B(); // expected-note {{required here}}
+
+#pragma clang module import compare.cmp
+
+void c() { void(0 <=> 0); }
+
+struct C {
+  CC operator<=>(const C&) const = default;
+};
+auto vc = C() <=> C();
+
+
+#pragma clang module build compare2
+module compare2 {}
+#pragma clang module contents
+#pragma clang module begin compare2
+#include "std-compare.h"
+#pragma clang module end
+#pragma clang module endbuild
+
+#pragma clang module import compare2
+
+void g() { void(0.0 <=> 0.0); }