[clang] Fix computeTypeLinkageInfo for non-record member pointers

MemberPointerType can point to records, functions, or types from
template parameters. computeTypeLinkageInfo used to expect only
records, and crash for anything else. It seems that the compiler never
executed this code path before patch llvm#136128 where the issue was
reported.

Function member (test74):

    MemberPointerType 'type-parameter-0-0 (type-parameter-0-1::*)(void)' dependent
    |-TemplateTypeParmType 'type-parameter-0-1' dependent depth 0 index 1
    `-FunctionProtoType 'type-parameter-0-0 (void)' dependent cdecl
      `-TemplateTypeParmType 'type-parameter-0-0' dependent depth 0 index 0

Template parameter (test75):

    MemberPointerType 'type-parameter-0-1 type-parameter-0-0::*' dependent
    |-TemplateTypeParmType 'type-parameter-0-0' dependent depth 0 index 0
    `-TemplateTypeParmType 'type-parameter-0-1' dependent depth 0 index 1

For non-record types, it should be enough to look at a pointee type to
determine linkage and visibility.

LIT tests 74 and 75 are reduced from Chromium and LLVM libc test
harness as reported in llvm#136128.

Author: asavonic

clang/lib/AST/Type.cpp

@@ -4787,8 +4787,10 @@ LinkageInfo LinkageComputer::computeTypeLinkageInfo(const Type *T) {
     return computeTypeLinkageInfo(cast<ReferenceType>(T)->getPointeeType());
   case Type::MemberPointer: {
     const auto *MPT = cast<MemberPointerType>(T);
-    LinkageInfo LV =
-        getDeclLinkageAndVisibility(MPT->getMostRecentCXXRecordDecl());
+    LinkageInfo LV;
+    if (auto *D = MPT->getMostRecentCXXRecordDecl()) {
+      LV.merge(getDeclLinkageAndVisibility(D));
+    }
     LV.merge(computeTypeLinkageInfo(MPT->getPointeeType()));
     return LV;
   }

clang/test/CodeGenCXX/visibility.cpp

@@ -1463,3 +1463,40 @@ namespace test71 {
   // CHECK-HIDDEN-LABEL: define linkonce_odr hidden noundef i64 @_ZN6test713fooIlE3zedEv(
   // CHECK-HIDDEN-LABEL: define linkonce_odr hidden noundef i32 @_ZN6test713fooIlE3barIiEET_v(
 }
+
+namespace test74 {
+  template <typename> struct T;
+  template <typename R>
+  struct T<void (R::*)()> {
+    template <typename M>
+    static __attribute__((__visibility__("hidden"))) void Invoke(M) {
+    }
+  };
+
+  struct C;
+  void (C::*MM)();
+
+  void Fun() {
+    T<decltype(MM)>::Invoke(0);
+  }
+  // CHECK-LABEL: define linkonce_odr void @_ZN6test741TIMNS_1CEFvvEE6InvokeIiEEvT_(
+  // CHECK-HIDDEN-LABEL: define linkonce_odr hidden void @_ZN6test741TIMNS_1CEFvvEE6InvokeIiEEvT_(
+}
+
+namespace test75 {
+  template <class> struct T;
+  template <class C, class Ret>
+  struct T<Ret C::*> {
+    template <class M>
+    static __attribute__((__visibility__("hidden")))
+    void Invoke(M) {
+    }
+  };
+
+  struct A;
+  void Fun() {
+    T<void (A::*)()>::Invoke(0);
+  }
+  // CHECK-LABEL: define linkonce_odr void @_ZN6test751TIMNS_1AEFvvEE6InvokeIiEEvT_(
+  // CHECK-HIDDEN-LABEL: define linkonce_odr hidden void @_ZN6test751TIMNS_1AEFvvEE6InvokeIiEEvT_(
+}