[ItaniumMangle] Add substitutions for record types when mangling vtables (#109970)

Fix #108015 

The `mangleNameOrStandardSubstitution` function does not add the RD type
into the substitution, which causes the mangling of the \<base type\> to
be incorrect.
Rename `mangleNameOrStandardSubstitution` to `mangleCXXRecordDecl` and add `Record` as a substitution

Author: tcwzxx

clang/docs/ReleaseNotes.rst

@@ -103,6 +103,7 @@ 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.
+- Fixed the Itanium mangling of the construction vtable name. This change will introduce incompatibilities with code compiled by Clang 19 and earlier versions, unless the -fclang-abi-compat=19 option is used. (#GH108015)
 
 AST Dumping Potentially Breaking Changes
 ----------------------------------------

clang/include/clang/Basic/LangOptions.h

@@ -239,6 +239,12 @@ class LangOptionsBase {
     /// in the initializers of members of local classes.
     Ver18,
 
+    /// Attempt to be ABI-compatible with code generated by Clang 19.0.x.
+    /// This causes clang to:
+    ///   - Incorrectly mangles the 'base type' substitutions of the CXX
+    ///   construction vtable because it hasn't added 'type' as a substitution.
+    Ver19,
+
     /// Conform to the underlying platform's C and C++ ABIs as closely
     /// as we can.
     Latest

clang/lib/AST/ItaniumMangle.cpp

@@ -464,7 +464,7 @@ class CXXNameMangler {
   void mangleSeqID(unsigned SeqID);
   void mangleName(GlobalDecl GD);
   void mangleType(QualType T);
-  void mangleNameOrStandardSubstitution(const NamedDecl *ND);
+  void mangleCXXRecordDecl(const CXXRecordDecl *Record);
   void mangleLambdaSig(const CXXRecordDecl *Lambda);
   void mangleModuleNamePrefix(StringRef Name, bool IsPartition = false);
   void mangleVendorQualifier(StringRef Name);
@@ -3029,9 +3029,13 @@ void CXXNameMangler::mangleType(QualType T) {
     addSubstitution(T);
 }
 
-void CXXNameMangler::mangleNameOrStandardSubstitution(const NamedDecl *ND) {
-  if (!mangleStandardSubstitution(ND))
-    mangleName(ND);
+void CXXNameMangler::mangleCXXRecordDecl(const CXXRecordDecl *Record) {
+  if (mangleSubstitution(Record))
+    return;
+  mangleName(Record);
+  if (isCompatibleWith(LangOptions::ClangABI::Ver19))
+    return;
+  addSubstitution(Record);
 }
 
 void CXXNameMangler::mangleType(const BuiltinType *T) {
@@ -7309,15 +7313,15 @@ void ItaniumMangleContextImpl::mangleCXXVTable(const CXXRecordDecl *RD,
   // <special-name> ::= TV <type>  # virtual table
   CXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_ZTV";
-  Mangler.mangleNameOrStandardSubstitution(RD);
+  Mangler.mangleCXXRecordDecl(RD);
 }
 
 void ItaniumMangleContextImpl::mangleCXXVTT(const CXXRecordDecl *RD,
                                             raw_ostream &Out) {
   // <special-name> ::= TT <type>  # VTT structure
   CXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_ZTT";
-  Mangler.mangleNameOrStandardSubstitution(RD);
+  Mangler.mangleCXXRecordDecl(RD);
 }
 
 void ItaniumMangleContextImpl::mangleCXXCtorVTable(const CXXRecordDecl *RD,
@@ -7327,10 +7331,10 @@ void ItaniumMangleContextImpl::mangleCXXCtorVTable(const CXXRecordDecl *RD,
   // <special-name> ::= TC <type> <offset number> _ <base type>
   CXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_ZTC";
-  Mangler.mangleNameOrStandardSubstitution(RD);
+  Mangler.mangleCXXRecordDecl(RD);
   Mangler.getStream() << Offset;
   Mangler.getStream() << '_';
-  Mangler.mangleNameOrStandardSubstitution(Type);
+  Mangler.mangleCXXRecordDecl(Type);
 }
 
 void ItaniumMangleContextImpl::mangleCXXRTTI(QualType Ty, raw_ostream &Out) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3830,6 +3830,9 @@ void CompilerInvocationBase::GenerateLangArgs(const LangOptions &Opts,
   case LangOptions::ClangABI::Ver18:
     GenerateArg(Consumer, OPT_fclang_abi_compat_EQ, "18.0");
     break;
+  case LangOptions::ClangABI::Ver19:
+    GenerateArg(Consumer, OPT_fclang_abi_compat_EQ, "19.0");
+    break;
   case LangOptions::ClangABI::Latest:
     break;
   }
@@ -4372,6 +4375,8 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
         Opts.setClangABICompat(LangOptions::ClangABI::Ver17);
       else if (Major <= 18)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver18);
+      else if (Major <= 19)
+        Opts.setClangABICompat(LangOptions::ClangABI::Ver19);
     } else if (Ver != "latest") {
       Diags.Report(diag::err_drv_invalid_value)
           << A->getAsString(Args) << A->getValue();

clang/test/CodeGenCXX/mangle-subst.cpp

@@ -1,4 +1,8 @@
 // RUN: %clang_cc1 -emit-llvm %s -o - -triple=x86_64-apple-darwin9 | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm %s -o - -triple=x86_64-apple-darwin9 -fclang-abi-compat=19 | FileCheck %s --check-prefix=CHECK-CLANG-19
+
+//CHECK: @_ZTCN16MangleCtorVTable4InstE0_NS_1A4ImplINS1_4WrapEEE
+//CHECK-CLANG-19: @_ZTCN16MangleCtorVTable4InstE0_NS_1A4ImplINS0_4WrapEEE
 
 struct X {};
 
@@ -96,3 +100,26 @@ typename X<T>::template Y<T>::type f(typename X<T>::template Y<T>::type2) { retu
 // CHECK: @_ZN12ManglePrefix1fIiEENS_1XIT_E1YIS2_E4typeENS5_5type2E
 template int f<int>(int);
 }
+
+namespace MangleCtorVTable {
+namespace A {
+
+class VBase {
+ public:
+  virtual ~VBase() {};
+};
+
+struct Wrap {};
+
+template <typename T>
+class Impl : public virtual VBase {
+ public:
+};
+
+}  // namespace A
+
+struct Inst : public A::Impl<A::Wrap> {};
+
+void Test() { Inst a; }
+
+}