[Clang] [AST] Fix placeholder return type name mangling for MSVC 1920+ / VS2019+

clang/docs/ReleaseNotes.rst

@@ -46,6 +46,8 @@ C++ Specific Potentially Breaking Changes
 ABI Changes in This Version
 ---------------------------
 
+- Fixed Microsoft name mangling of placeholder, auto and decltype(auto), return types for MSVC 1920+. This change resolves incompatibilities with code compiled by MSVC 1920+ but will introduce incompatibilities with code compiled by earlier versions of Clang unless such code is built with the compiler option -fms-compatibility-version=19.14 to imitate the MSVC 1914 mangling behavior.
+
 AST Dumping Potentially Breaking Changes
 ----------------------------------------
 

clang/lib/AST/MicrosoftMangle.cpp

@@ -408,6 +408,8 @@ class MicrosoftCXXNameMangler {
   void mangleSourceName(StringRef Name);
   void mangleNestedName(GlobalDecl GD);
 
+  void mangleAutoReturnType(QualType T, QualifierMangleMode QMM);
+
 private:
   bool isStructorDecl(const NamedDecl *ND) const {
     return ND == Structor || getStructor(ND) == Structor;
@@ -477,6 +479,11 @@ class MicrosoftCXXNameMangler {
                           SourceRange Range);
   void mangleObjCKindOfType(const ObjCObjectType *T, Qualifiers Quals,
                             SourceRange Range);
+
+  void mangleAutoReturnType(const MemberPointerType *T, Qualifiers Quals);
+  void mangleAutoReturnType(const PointerType *T, Qualifiers Quals);
+  void mangleAutoReturnType(const LValueReferenceType *T, Qualifiers Quals);
+  void mangleAutoReturnType(const RValueReferenceType *T, Qualifiers Quals);
 };
 }
 
@@ -2494,6 +2501,57 @@ void MicrosoftCXXNameMangler::mangleAddressSpaceType(QualType T,
   mangleArtificialTagType(TagTypeKind::Struct, ASMangling, {"__clang"});
 }
 
+void MicrosoftCXXNameMangler::mangleAutoReturnType(QualType T,
+                                                   QualifierMangleMode QMM) {
+  assert(getASTContext().getLangOpts().isCompatibleWithMSVC(
+             LangOptions::MSVC2019) &&
+         "Cannot mangle MSVC 2017 auto return types!");
+
+  if (isa<AutoType>(T)) {
+    const auto *AT = T->getContainedAutoType();
+    Qualifiers Quals = T.getLocalQualifiers();
+
+    if (QMM == QMM_Result)
+      Out << '?';
+    if (QMM != QMM_Drop)
+      mangleQualifiers(Quals, false);
+    Out << (AT->isDecltypeAuto() ? "_T" : "_P");
+    return;
+  }
+
+  T = T.getDesugaredType(getASTContext());
+  Qualifiers Quals = T.getLocalQualifiers();
+
+  switch (QMM) {
+  case QMM_Drop:
+  case QMM_Result:
+    break;
+  case QMM_Mangle:
+    mangleQualifiers(Quals, false);
+    break;
+  default:
+    llvm_unreachable("QMM_Escape unexpected");
+  }
+
+  const Type *ty = T.getTypePtr();
+  switch (ty->getTypeClass()) {
+  case Type::MemberPointer:
+    mangleAutoReturnType(cast<MemberPointerType>(ty), Quals);
+    break;
+  case Type::Pointer:
+    mangleAutoReturnType(cast<PointerType>(ty), Quals);
+    break;
+  case Type::LValueReference:
+    mangleAutoReturnType(cast<LValueReferenceType>(ty), Quals);
+    break;
+  case Type::RValueReference:
+    mangleAutoReturnType(cast<RValueReferenceType>(ty), Quals);
+    break;
+  default:
+    llvm_unreachable("Invalid type expected");
+  }
+}
+
 void MicrosoftCXXNameMangler::mangleType(QualType T, SourceRange Range,
                                          QualifierMangleMode QMM) {
   // Don't use the canonical types.  MSVC includes things like 'const' on
@@ -2900,17 +2958,51 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
       // can differ by their calling convention and are typically deduced.  So
       // we make sure that this type gets mangled properly.
       mangleType(ResultType, Range, QMM_Result);
-    } else if (const auto *AT = dyn_cast_or_null<AutoType>(
-                   ResultType->getContainedAutoType())) {
-      Out << '?';
-      mangleQualifiers(ResultType.getLocalQualifiers(), /*IsMember=*/false);
-      Out << '?';
+    } else if (IsInLambda) {
+      if (const auto *AT = ResultType->getContainedAutoType()) {
+        assert(AT->getKeyword() == AutoTypeKeyword::Auto &&
+               "should only need to mangle auto!");
+        Out << '?';
+        mangleQualifiers(ResultType.getLocalQualifiers(), /*IsMember=*/false);
+        Out << '?';
+        mangleSourceName("<auto>");
+        Out << '@';
+      } else {
+        Out << '@';
+      }
+    } else if (const auto *AT = ResultType->getContainedAutoType()) {
       assert(AT->getKeyword() != AutoTypeKeyword::GNUAutoType &&
              "shouldn't need to mangle __auto_type!");
-      mangleSourceName(AT->isDecltypeAuto() ? "<decltype-auto>" : "<auto>");
-      Out << '@';
-    } else if (IsInLambda) {
-      Out << '@';
+
+      // If we have any pointer types with the clang address space extension
+      // then defer to the custom clang mangling to keep backwards
+      // compatibility. See `mangleType(const PointerType *T, Qualifiers Quals,
+      // SourceRange Range)` for details.
+      auto UseClangMangling = [](QualType ResultType) {
+        QualType T = ResultType;
+        while (const auto *PT = dyn_cast<PointerType>(T.getTypePtr())) {
+          T = T->getPointeeType();
+          if (T.getQualifiers().hasAddressSpace())
+            return true;
+        }
+        return false;
+      };
+
+      if (getASTContext().getLangOpts().isCompatibleWithMSVC(
+              LangOptions::MSVC2019) &&
+          !UseClangMangling(ResultType)) {
+        if (D && !D->getPrimaryTemplate()) {
+          Out << '@';
+        } else {
+          mangleAutoReturnType(ResultType, QMM_Result);
+        }
+      } else {
+        Out << '?';
+        mangleQualifiers(ResultType.getLocalQualifiers(), /*IsMember=*/false);
+        Out << '?';
+        mangleSourceName(AT->isDecltypeAuto() ? "<decltype-auto>" : "<auto>");
+        Out << '@';
+      }
     } else {
       if (ResultType->isVoidType())
         ResultType = ResultType.getUnqualifiedType();
@@ -4213,6 +4305,57 @@ void MicrosoftMangleContextImpl::mangleStringLiteral(const StringLiteral *SL,
   Mangler.getStream() << '@';
 }
 
+void MicrosoftCXXNameMangler::mangleAutoReturnType(const MemberPointerType *T,
+                                                   Qualifiers Quals) {
+  QualType PointeeType = T->getPointeeType();
+  manglePointerCVQualifiers(Quals);
+  manglePointerExtQualifiers(Quals, PointeeType);
+  if (const FunctionProtoType *FPT = PointeeType->getAs<FunctionProtoType>()) {
+    Out << '8';
+    mangleName(T->getClass()->castAs<RecordType>()->getDecl());
+    mangleFunctionType(FPT, nullptr, true);
+  } else {
+    mangleQualifiers(PointeeType.getQualifiers(), true);
+    mangleName(T->getClass()->castAs<RecordType>()->getDecl());
+    mangleAutoReturnType(PointeeType, QMM_Drop);
+  }
+}
+
+void MicrosoftCXXNameMangler::mangleAutoReturnType(const PointerType *T,
+                                                   Qualifiers Quals) {
+  QualType PointeeType = T->getPointeeType();
+  assert(!PointeeType.getQualifiers().hasAddressSpace() &&
+         "Unexpected address space mangling required");
+
+  manglePointerCVQualifiers(Quals);
+  manglePointerExtQualifiers(Quals, PointeeType);
+
+  if (const FunctionProtoType *FPT = PointeeType->getAs<FunctionProtoType>()) {
+    Out << '6';
+    mangleFunctionType(FPT);
+  } else {
+    mangleAutoReturnType(PointeeType, QMM_Mangle);
+  }
+}
+
+void MicrosoftCXXNameMangler::mangleAutoReturnType(const LValueReferenceType *T,
+                                                   Qualifiers Quals) {
+  QualType PointeeType = T->getPointeeType();
+  assert(!Quals.hasConst() && !Quals.hasVolatile() && "unexpected qualifier!");
+  Out << 'A';
+  manglePointerExtQualifiers(Quals, PointeeType);
+  mangleAutoReturnType(PointeeType, QMM_Mangle);
+}
+
+void MicrosoftCXXNameMangler::mangleAutoReturnType(const RValueReferenceType *T,
+                                                   Qualifiers Quals) {
+  QualType PointeeType = T->getPointeeType();
+  assert(!Quals.hasConst() && !Quals.hasVolatile() && "unexpected qualifier!");
+  Out << "$$Q";
+  manglePointerExtQualifiers(Quals, PointeeType);
+  mangleAutoReturnType(PointeeType, QMM_Mangle);
+}
+
 MicrosoftMangleContext *MicrosoftMangleContext::create(ASTContext &Context,
                                                        DiagnosticsEngine &Diags,
                                                        bool IsAux) {