Fix MSVC 1920+ auto NTTP mangling for pointers to members (#97007)

Fixes https://github.com/llvm/llvm-project/issues/70899.

This is a continuation of
https://github.com/llvm/llvm-project/pull/92477 for pointers to member
data and pointers to member functions.

The mangled name must be prefixed with `$M <mangled-type>` for the
deduced type of the nttp parameter.

6 files changed, 204 insertions, 20 deletions

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f149684..36cf615a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -106,6 +106,13 @@ ABI Changes in This Version
   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 Microsoft name mangling for auto non-type template arguments of pointer
+  to member type 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.
+  (GH#70899).
+
 AST Dumping Potentially Breaking Changes
 ----------------------------------------
 
diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index 7f1e9ab..fac14ce 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -368,11 +368,15 @@ public:
   void mangleFunctionEncoding(GlobalDecl GD, bool ShouldMangle);
   void mangleVariableEncoding(const VarDecl *VD);
   void mangleMemberDataPointer(const CXXRecordDecl *RD, const ValueDecl *VD,
+                               const NonTypeTemplateParmDecl *PD,
+                               QualType TemplateArgType,
                                StringRef Prefix = "$");
   void mangleMemberDataPointerInClassNTTP(const CXXRecordDecl *,
                                           const ValueDecl *);
   void mangleMemberFunctionPointer(const CXXRecordDecl *RD,
                                    const CXXMethodDecl *MD,
+                                   const NonTypeTemplateParmDecl *PD,
+                                   QualType TemplateArgType,
                                    StringRef Prefix = "$");
   void mangleFunctionPointer(const FunctionDecl *FD,
                              const NonTypeTemplateParmDecl *PD,
@@ -673,12 +677,17 @@ void MicrosoftCXXNameMangler::mangleVariableEncoding(const VarDecl *VD) {
   }
 }
 
-void MicrosoftCXXNameMangler::mangleMemberDataPointer(const CXXRecordDecl *RD,
-                                                      const ValueDecl *VD,
-                                                      StringRef Prefix) {
+void MicrosoftCXXNameMangler::mangleMemberDataPointer(
+    const CXXRecordDecl *RD, const ValueDecl *VD,
+    const NonTypeTemplateParmDecl *PD, QualType TemplateArgType,
+    StringRef Prefix) {
   // <member-data-pointer> ::= <integer-literal>
   //                       ::= $F <number> <number>
   //                       ::= $G <number> <number> <number>
+  //
+  // <auto-nttp> ::= $ M <type> <integer-literal>
+  // <auto-nttp> ::= $ M <type> F <name> <number>
+  // <auto-nttp> ::= $ M <type> G <name> <number> <number>
 
   int64_t FieldOffset;
   int64_t VBTableOffset;
@@ -707,7 +716,18 @@ void MicrosoftCXXNameMangler::mangleMemberDataPointer(const CXXRecordDecl *RD,
   case MSInheritanceModel::Unspecified: Code = 'G'; break;
   }
 
-  Out << Prefix << Code;
+  Out << Prefix;
+
+  if (VD &&
+      getASTContext().getLangOpts().isCompatibleWithMSVC(
+          LangOptions::MSVC2019) &&
+      PD && PD->getType()->getTypeClass() == Type::Auto &&
+      !TemplateArgType.isNull()) {
+    Out << "M";
+    mangleType(TemplateArgType, SourceRange(), QMM_Drop);
+  }
+
+  Out << Code;
 
   mangleNumber(FieldOffset);
 
@@ -728,7 +748,7 @@ void MicrosoftCXXNameMangler::mangleMemberDataPointerInClassNTTP(
   //                                  ::= 8 <postfix> @ <unqualified-name> @
 
   if (IM != MSInheritanceModel::Single && IM != MSInheritanceModel::Multiple)
-    return mangleMemberDataPointer(RD, VD, "");
+    return mangleMemberDataPointer(RD, VD, nullptr, QualType(), "");
 
   if (!VD) {
     Out << 'N';
@@ -742,14 +762,19 @@ void MicrosoftCXXNameMangler::mangleMemberDataPointerInClassNTTP(
   Out << '@';
 }
 
-void
-MicrosoftCXXNameMangler::mangleMemberFunctionPointer(const CXXRecordDecl *RD,
-                                                     const CXXMethodDecl *MD,
-                                                     StringRef Prefix) {
+void MicrosoftCXXNameMangler::mangleMemberFunctionPointer(
+    const CXXRecordDecl *RD, const CXXMethodDecl *MD,
+    const NonTypeTemplateParmDecl *PD, QualType TemplateArgType,
+    StringRef Prefix) {
   // <member-function-pointer> ::= $1? <name>
   //                           ::= $H? <name> <number>
   //                           ::= $I? <name> <number> <number>
   //                           ::= $J? <name> <number> <number> <number>
+  //
+  // <auto-nttp> ::= $ M <type> 1? <name>
+  // <auto-nttp> ::= $ M <type> H? <name> <number>
+  // <auto-nttp> ::= $ M <type> I? <name> <number> <number>
+  // <auto-nttp> ::= $ M <type> J? <name> <number> <number> <number>
 
   MSInheritanceModel IM = RD->getMSInheritanceModel();
 
@@ -767,7 +792,17 @@ MicrosoftCXXNameMangler::mangleMemberFunctionPointer(const CXXRecordDecl *RD,
   uint64_t VBTableOffset = 0;
   uint64_t VBPtrOffset = 0;
   if (MD) {
-    Out << Prefix << Code << '?';
+    Out << Prefix;
+
+    if (getASTContext().getLangOpts().isCompatibleWithMSVC(
+            LangOptions::MSVC2019) &&
+        PD && PD->getType()->getTypeClass() == Type::Auto &&
+        !TemplateArgType.isNull()) {
+      Out << "M";
+      mangleType(TemplateArgType, SourceRange(), QMM_Drop);
+    }
+
+    Out << Code << '?';
     if (MD->isVirtual()) {
       MicrosoftVTableContext *VTContext =
           cast<MicrosoftVTableContext>(getASTContext().getVTableContext());
@@ -859,7 +894,7 @@ void MicrosoftCXXNameMangler::mangleMemberFunctionPointerInClassNTTP(
 
   if (!MD) {
     if (RD->getMSInheritanceModel() != MSInheritanceModel::Single)
-      return mangleMemberFunctionPointer(RD, MD, "");
+      return mangleMemberFunctionPointer(RD, MD, nullptr, QualType(), "");
 
     Out << 'N';
     return;
@@ -1732,12 +1767,15 @@ void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
     if (isa<FieldDecl>(ND) || isa<IndirectFieldDecl>(ND)) {
       mangleMemberDataPointer(cast<CXXRecordDecl>(ND->getDeclContext())
                                   ->getMostRecentNonInjectedDecl(),
-                              cast<ValueDecl>(ND));
+                              cast<ValueDecl>(ND),
+                              cast<NonTypeTemplateParmDecl>(Parm),
+                              TA.getParamTypeForDecl());
     } else if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(ND)) {
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
       if (MD && MD->isInstance()) {
         mangleMemberFunctionPointer(
-            MD->getParent()->getMostRecentNonInjectedDecl(), MD);
+            MD->getParent()->getMostRecentNonInjectedDecl(), MD,
+            cast<NonTypeTemplateParmDecl>(Parm), TA.getParamTypeForDecl());
       } else {
         mangleFunctionPointer(FD, cast<NonTypeTemplateParmDecl>(Parm),
                               TA.getParamTypeForDecl());
@@ -1767,12 +1805,12 @@ void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
       const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
       if (MPT->isMemberFunctionPointerType() &&
           !isa<FunctionTemplateDecl>(TD)) {
-        mangleMemberFunctionPointer(RD, nullptr);
+        mangleMemberFunctionPointer(RD, nullptr, nullptr, QualType());
         return;
       }
       if (MPT->isMemberDataPointer()) {
         if (!isa<FunctionTemplateDecl>(TD)) {
-          mangleMemberDataPointer(RD, nullptr);
+          mangleMemberDataPointer(RD, nullptr, nullptr, QualType());
           return;
         }
         // nullptr data pointers are always represented with a single field
@@ -1979,9 +2017,10 @@ void MicrosoftCXXNameMangler::mangleTemplateArgValue(QualType T,
                                                cast_or_null<CXXMethodDecl>(D));
     } else {
       if (T->isMemberDataPointerType())
-        mangleMemberDataPointer(RD, D, "");
+        mangleMemberDataPointer(RD, D, nullptr, QualType(), "");
       else
-        mangleMemberFunctionPointer(RD, cast_or_null<CXXMethodDecl>(D), "");
+        mangleMemberFunctionPointer(RD, cast_or_null<CXXMethodDecl>(D), nullptr,
+                                    QualType(), "");
     }
     return;
   }
diff --git a/clang/test/CodeGenCXX/mangle-ms-auto-templates-memptrs.cpp b/clang/test/CodeGenCXX/mangle-ms-auto-templates-memptrs.cpp
new file mode 100644
index 0000000..360ebde
--- /dev/null
+++ b/clang/test/CodeGenCXX/mangle-ms-auto-templates-memptrs.cpp
@@ -0,0 +1,71 @@
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility-version=19.20 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-windows-msvc | FileCheck --check-prefix=AFTER %s
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility-version=19.14 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-windows-msvc | FileCheck --check-prefix=BEFORE %s
+
+template <auto a>
+class AutoParmTemplate {
+public:
+    AutoParmTemplate() {}
+};
+
+template <auto a>
+auto AutoFunc() {
+    return a;
+}
+
+struct A {};
+struct B {};
+
+struct S             { int a; void f(); virtual void g(); };
+struct M : A, B      { int a; void f(); virtual void g(); };
+struct V : virtual A { int a; void f(); virtual void g(); };
+
+void template_mangling() {
+
+  AutoParmTemplate<&S::f> auto_method_single_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MP8S@@EAAXXZ1?f@1@QEAAXXZ@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$1?f@S@@QEAAXXZ@@QEAA@XZ"
+
+  AutoParmTemplate<&M::f> auto_method_multiple_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MP8M@@EAAXXZH?f@1@QEAAXXZA@@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$H?f@M@@QEAAXXZA@@@QEAA@XZ"
+
+  AutoParmTemplate<&V::f> auto_method_virtual_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MP8V@@EAAXXZI?f@1@QEAAXXZA@A@@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$I?f@V@@QEAAXXZA@A@@@QEAA@XZ"
+
+  AutoFunc<&S::f>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MP8S@@EAAXXZ1?f@1@QEAAXXZ@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$1?f@S@@QEAAXXZ@@YA?A?<auto>@@XZ"
+
+  AutoFunc<&M::f>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MP8M@@EAAXXZH?f@1@QEAAXXZA@@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$H?f@M@@QEAAXXZA@@@YA?A?<auto>@@XZ"
+
+  AutoFunc<&V::f>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MP8V@@EAAXXZI?f@1@QEAAXXZA@A@@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$I?f@V@@QEAAXXZA@A@@@YA?A?<auto>@@XZ"
+
+  AutoParmTemplate<&S::a> auto_data_single_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MPEQS@@H07@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$07@@QEAA@XZ"
+
+  AutoParmTemplate<&M::a> auto_data_multiple_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MPEQM@@H0M@@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$0M@@@QEAA@XZ"
+
+  AutoParmTemplate<&V::a> auto_data_virtual_inheritance;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$MPEQV@@HFBA@A@@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$FBA@A@@@QEAA@XZ"
+
+  AutoFunc<&S::a>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MPEQS@@H07@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$07@@YA?A?<auto>@@XZ"
+
+  AutoFunc<&M::a>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MPEQM@@H0M@@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$0M@@@YA?A?<auto>@@XZ"
+
+  AutoFunc<&V::a>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$MPEQV@@HFBA@A@@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$FBA@A@@@YA?A?<auto>@@XZ"
+}
diff --git a/clang/test/CodeGenCXX/mangle-ms-auto-templates-nullptr.cpp b/clang/test/CodeGenCXX/mangle-ms-auto-templates-nullptr.cpp
new file mode 100644
index 0000000..8f98c1e
--- /dev/null
+++ b/clang/test/CodeGenCXX/mangle-ms-auto-templates-nullptr.cpp
@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility-version=19.20 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-windows-msvc | FileCheck --check-prefix=AFTER %s
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility-version=19.14 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-windows-msvc | FileCheck --check-prefix=BEFORE %s
+
+template <auto a>
+class AutoParmTemplate {
+public:
+    AutoParmTemplate() {}
+};
+
+template <auto a>
+auto AutoFunc() {
+    return a;
+}
+
+void template_mangling() {
+
+  AutoParmTemplate<nullptr> auto_nullptr;
+  // AFTER: call {{.*}} @"??0?$AutoParmTemplate@$M$$T0A@@@QEAA@XZ"
+  // BEFORE: call {{.*}} @"??0?$AutoParmTemplate@$0A@@@QEAA@XZ"
+
+  AutoFunc<nullptr>();
+  // AFTER: call {{.*}} @"??$AutoFunc@$M$$T0A@@@YA?A?<auto>@@XZ"
+  // BEFORE: call {{.*}} @"??$AutoFunc@$0A@@@YA?A?<auto>@@XZ"
+}
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
index e18de9a..c5835e8 100644
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -2343,12 +2343,13 @@ Demangler::demangleTemplateParameterList(std::string_view &MangledName) {
       TP.N = TPRN = Arena.alloc<TemplateParameterReferenceNode>();
       TPRN->Symbol = parse(MangledName);
       TPRN->Affinity = PointerAffinity::Reference;
-    } else if (llvm::itanium_demangle::starts_with(MangledName, "$F") ||
-               llvm::itanium_demangle::starts_with(MangledName, "$G")) {
+    } else if (startsWith(MangledName, "$F", "F", !IsAutoNTTP) ||
+               startsWith(MangledName, "$G", "G", !IsAutoNTTP)) {
       TP.N = TPRN = Arena.alloc<TemplateParameterReferenceNode>();
 
       // Data member pointer.
-      MangledName.remove_prefix(1);
+      if (!IsAutoNTTP)
+        MangledName.remove_prefix(1); // Remove leading '$'
       char InheritanceSpecifier = MangledName.front();
       MangledName.remove_prefix(1);
 
diff --git a/llvm/test/Demangle/ms-auto-templates.test b/llvm/test/Demangle/ms-auto-templates.test
index a90ffb6..414885d 100644
--- a/llvm/test/Demangle/ms-auto-templates.test
+++ b/llvm/test/Demangle/ms-auto-templates.test
@@ -55,3 +55,45 @@
 
 ??0?$AutoNTTPClass@$MH0A@$M_N0A@$MD0GB@@@QEAA@XZ
 ; CHECK: public: __cdecl AutoNTTPClass<0, 0, 97>::AutoNTTPClass<0, 0, 97>(void)
+
+??0?$AutoNTTPClass@$M$$T0A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0>::AutoNTTPClass<0>(void)
+
+??0?$AutoNTTPClass@$0A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<0>::AutoNTTPClass<0>(void)
+
+??0?$AutoNTTPClass@$MP8S@@EAAXXZ1?f@1@QEAAXXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&public: void __cdecl S::f(void)>::AutoNTTPClass<&public: void __cdecl S::f(void)>(void)
+
+??0?$AutoNTTPClass@$1?f@S@@QEAAXXZ@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<&public: void __cdecl S::f(void)>::AutoNTTPClass<&public: void __cdecl S::f(void)>(void)
+
+??0?$AutoNTTPClass@$MP8M@@EAAXXZH?f@1@QEAAXXZA@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{public: void __cdecl M::f(void), 0}>::AutoNTTPClass<{public: void __cdecl M::f(void), 0}>(void)
+
+??0?$AutoNTTPClass@$H?f@M@@QEAAXXZA@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{public: void __cdecl M::f(void), 0}>::AutoNTTPClass<{public: void __cdecl M::f(void), 0}>(void)
+
+??0?$AutoNTTPClass@$MP8V@@EAAXXZI?f@1@QEAAXXZA@A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{public: void __cdecl V::f(void), 0, 0}>::AutoNTTPClass<{public: void __cdecl V::f(void), 0, 0}>(void)
+
+??0?$AutoNTTPClass@$I?f@V@@QEAAXXZA@A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{public: void __cdecl V::f(void), 0, 0}>::AutoNTTPClass<{public: void __cdecl V::f(void), 0, 0}>(void)
+
+??0?$AutoNTTPClass@$MPEQS@@H07@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<8>::AutoNTTPClass<8>(void)
+
+??0?$AutoNTTPClass@$07@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<8>::AutoNTTPClass<8>(void)
+
+??0?$AutoNTTPClass@$MPEQM@@H0M@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<12>::AutoNTTPClass<12>(void)
+
+??0?$AutoNTTPClass@$0M@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<12>::AutoNTTPClass<12>(void)
+
+??0?$AutoNTTPClass@$MPEQV@@HFBA@A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{16, 0}>::AutoNTTPClass<{16, 0}>(void)
+
+??0?$AutoNTTPClass@$FBA@A@@@QEAA@XZ
+; CHECK: public: __cdecl AutoNTTPClass<{16, 0}>::AutoNTTPClass<{16, 0}>(void)