[ItaniumMangle] Make sure class types are added to the dictionary of substitution candidates when compiling for older ABIs (#138947)

`mangleCXXRecordDecl` should add class types to the substitution
dictionary unless it is called by `mangleCXXCtorVTable` (see
#109970 for why that is
needed).

This fixes a mis-compile caused by
#132401, which started calling
`mangleCXXRecordDecl` in `CXXNameMangler::mangleType(const
MemberPointerType *T)`.

rdar://149307496

Author: ahatanak

clang/lib/AST/ItaniumMangle.cpp

@@ -455,7 +455,8 @@ class CXXNameMangler {
   void mangleSeqID(unsigned SeqID);
   void mangleName(GlobalDecl GD);
   void mangleType(QualType T);
-  void mangleCXXRecordDecl(const CXXRecordDecl *Record);
+  void mangleCXXRecordDecl(const CXXRecordDecl *Record,
+                           bool SuppressSubstitution = false);
   void mangleLambdaSig(const CXXRecordDecl *Lambda);
   void mangleModuleNamePrefix(StringRef Name, bool IsPartition = false);
   void mangleVendorQualifier(StringRef Name);
@@ -3103,11 +3104,12 @@ void CXXNameMangler::mangleType(QualType T) {
     addSubstitution(T);
 }
 
-void CXXNameMangler::mangleCXXRecordDecl(const CXXRecordDecl *Record) {
+void CXXNameMangler::mangleCXXRecordDecl(const CXXRecordDecl *Record,
+                                         bool SuppressSubstitution) {
   if (mangleSubstitution(Record))
     return;
   mangleName(Record);
-  if (isCompatibleWith(LangOptions::ClangABI::Ver19))
+  if (SuppressSubstitution)
     return;
   addSubstitution(Record);
 }
@@ -7557,7 +7559,12 @@ void ItaniumMangleContextImpl::mangleCXXCtorVTable(const CXXRecordDecl *RD,
   // <special-name> ::= TC <type> <offset number> _ <base type>
   CXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_ZTC";
-  Mangler.mangleCXXRecordDecl(RD);
+  // Older versions of clang did not add the record as a substitution candidate
+  // here.
+  bool SuppressSubstitution =
+      getASTContext().getLangOpts().getClangABICompat() <=
+      LangOptions::ClangABI::Ver19;
+  Mangler.mangleCXXRecordDecl(RD, SuppressSubstitution);
   Mangler.getStream() << Offset;
   Mangler.getStream() << '_';
   Mangler.mangleCXXRecordDecl(Type);

clang/test/CodeGenCXX/clang-abi-compat.cpp

@@ -160,3 +160,15 @@ template <typename T> void test10(typename T::Y::a, typename T::Y::b, float*, fl
 // PRE15: @_Z6test10I1XEvNT_1Y1aENS1_1Y1bEPfS4_
 // V15:   @_Z6test10I1XEvNT_1Y1aENS2_1bEPfS5_
 template void test10<X>(int, int, float*, float*);
+
+namespace test_substitution {
+struct S { int f(void *, void *); };
+
+typedef int (S::*s_func)(void *, void *);
+
+// clang used to incorrectly emit 'S0_' for the second 'void *' parameter type
+// when targeting older ABIs because of a bug in the mangler.
+
+// CHECK-LABEL: define dso_local void @_ZN17test_substitution4foo1EMNS_1SEFiPvS1_E(
+void foo1(s_func s) {}
+}

clang/test/CodeGenCXX/mangle-itanium-ptrauth.cpp

@@ -1,5 +1,19 @@
 // RUN: %clang_cc1 -std=c++11 -fptrauth-intrinsics -fptrauth-calls -emit-llvm -o - -triple=arm64-apple-ios %s | FileCheck %s
 // RUN: %clang_cc1 -std=c++11 -fptrauth-intrinsics -fptrauth-calls -emit-llvm -o - -triple=aarch64-linux-gnu %s | FileCheck %s
+// RUN: %clang_cc1 -std=c++11 -fptrauth-intrinsics -fptrauth-calls -emit-llvm -o - -triple=arm64-apple-ios -fclang-abi-compat=4 %s | FileCheck %s
+
+// clang previously emitted an incorrect discriminator for the member function
+// pointer because of a bug in the mangler.
+
+// CHECK: @_ZN17test_substitution5funcsE = global [1 x { i64, i64 }] [{ i64, i64 } { i64 ptrtoint (ptr ptrauth (ptr @_ZN17test_substitution1S1fEPvS1_, i32 0, i64 48995) to i64), i64 0 }], align 8
+namespace test_substitution {
+struct S { int f(void *, void *); };
+
+typedef int (S::*s_func)(void *, void *);
+
+s_func funcs[] = { (s_func)(&S::f) };
+}
+
 
 // CHECK: define {{.*}}void @_Z3fooPU9__ptrauthILj3ELb1ELj234EEPi(
 void foo(int * __ptrauth(3, 1, 234) *) {}