Avoid computing ODR Hash duplicatly

Author: ChuanqiXu9

clang/lib/AST/ODRHash.cpp

@@ -803,16 +803,6 @@ void ODRHash::AddDecl(const Decl *D) {
 
   AddDeclarationName(ND->getDeclName());
 
-  const auto *Specialization =
-            dyn_cast<ClassTemplateSpecializationDecl>(D);
-  AddBoolean(Specialization);
-  if (Specialization) {
-    const TemplateArgumentList &List = Specialization->getTemplateArgs();
-    ID.AddInteger(List.size());
-    for (const TemplateArgument &TA : List.asArray())
-      AddTemplateArgument(TA);
-  }
-
   // If this was a specialization we should take into account its template
   // arguments. This helps to reduce collisions coming when visiting template
   // specialization types (eg. when processing type template arguments).

clang/test/Modules/recursive-instantiations.cppm

@@ -0,0 +1,40 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/type_traits.cppm -emit-module-interface -o %t/type_traits.pcm
+// RUN: %clang_cc1 -std=c++20 %t/test.cpp -fprebuilt-module-path=%t -verify
+
+//--- type_traits.cppm
+export module type_traits;
+
+export template <typename T>
+constexpr bool is_pod_v = __is_pod(T);
+
+//--- test.cpp
+// expected-no-diagnostics
+import type_traits;
+// Base is either void or wrapper<T>.
+template <class Base> struct wrapper : Base {};
+template <> struct wrapper<void> {};
+
+// wrap<0>::type<T> is wrapper<T>, wrap<1>::type<T> is wrapper<wrapper<T>>,
+// and so on.
+template <int N>
+struct wrap {
+  template <class Base>
+  using type = wrapper<typename wrap<N-1>::template type<Base>>;
+};
+
+template <>
+struct wrap<0> {
+  template <class Base>
+  using type = wrapper<Base>;
+};
+
+inline constexpr int kMaxRank = 40;
+template <int N, class Base = void>
+using rank = typename wrap<N>::template type<Base>;
+using rank_selector_t = rank<kMaxRank>;
+
+static_assert(is_pod_v<rank_selector_t>, "Must be POD");