cxa_demangle: make demangler's parsing functions overridable

[labath]

Summary

This uses CRTP (for performance reasons) to allow a user the override
demangler functions to implement custom parsing logic. The motivation
for this is LLDB, which needs to occasionaly modify the mangled names.
One such instance is already implemented via the TypeCallback member,
but this is very specific functionality which does not help with any
other use case. Currently we have a use case for modifying the
constructor flavours, which would require adding another callback. This
approach does not scale.

With CRTP, the user (LLDB) can override any function it needs without
any special support from the demangler library. After LLDB is ported to
use this instead of the TypeCallback mechanism, the callback can be
removed.

More context can be found in D50599.

[rsmith]

src/demangle/ItaniumDemangle.h

2140–2211 ↗

(On Diff #168679)

I'd like for us to be moving towards making this particular allocator implementation be libc++abi-specific (LLVM's use of the demangler code doesn't want it, for instance, and I suspect it's not really what LLDB wants either). This change seems to entrench the use of this allocator by giving Db it as a default argument, which seems like a step backwards. I also think this change is orthogonal to the rest of the patch; we don't need these classes to be in the header to convert Db to a CRTP base class, right?

2214 ↗

(On Diff #168679)

If you're going to do a mass rename on this class anyway, have you considered giving it a more reasonable name (maybe something like ManglingParser)?

[erik.pilkington]

Thanks for doing this!

src/demangle/ItaniumDemangle.h

2214 ↗

(On Diff #168679)

Yep, I agree. Db is a really horrible name for this.

2246 ↗

(On Diff #168679)

I think libcxxabi's clang-format moved all the pointers to the left. I just committed r344316, which overrides libcxxabi's behaviour for this directory. Can you re-run this through clang-format-diff?

[labath]

src/demangle/ItaniumDemangle.h

2140–2211 ↗

(On Diff #168679)

You're right, they are orthogonal. I needed an allocator since I wanted to write a test for this (in LLVM), and I didn't want to reimplement an allocator there. Later, I realised that I can just use allocator from LLVMSupport instead and that this will not cause a dependency cycle, since it's test-only, but i didn't get around to updating the test (AFK).

I'll revert this part in the next update.

2214 ↗

(On Diff #168679)

ManglingParser sounds good.

2246 ↗

(On Diff #168679)

Will do.

[labath]

• rename Db into (Abstract)ManglingParser
• revert Allocator changes
• re-clang-format

[erik.pilkington]

LGTM, thanks again! Are you planning on updating itaniumFindTypesInMangledName to use this too? (If not, I'll get around to it eventually!)

[labath]

Thanks for the review.

In D52992#1265866, @erik.pilkington wrote:

Are you planning on updating itaniumFindTypesInMangledName to use this too? (If not, I'll get around to it eventually!)

My plan was to implement the equivalent to itaniumFindTypesInMangledName within LLDB and then delete the LLVM copy together with the callback hook (this seems like a very specialized piece of functionality for such a low-level library). However, if you prefer keeping this in libDemangle, I can do that too.

libcxxabi/trunk/src/cxa_demangle.cpp

public:
   }
 };
 }  // unnamed namespace
 
 //===----------------------------------------------------------------------===//
 // Code beyond this point should not be synchronized with LLVM.
 //===----------------------------------------------------------------------===//
 
-using Demangler = itanium_demangle::Db<DefaultAllocator>;
+using Demangler = itanium_demangle::ManglingParser<DefaultAllocator>;
 
 namespace {
 enum : int {
   demangle_invalid_args = -3,
   demangle_invalid_mangled_name = -2,
   demangle_memory_alloc_failure = -1,
   demangle_success = 0,
 };

libcxxabi/trunk/src/demangle/ItaniumDemangle.h

public:
   void clear() { Last = First; }
 
   ~PODSmallVector() {
     if (!isInline())
       std::free(First);
   }
 };
 
-template <typename Alloc>
-struct Db {
+template <typename Derived, typename Alloc> struct AbstractManglingParser {
   const char *First;
   const char *Last;
 
   // Name stack, this is used by the parser to hold temporary names that were
   // parsed. The parser collapses multiple names into new nodes to construct
   // the AST. Once the parser is finished, names.size() == 1.
   PODSmallVector<Node *, 32> Names;
 
template <typename Derived, typename Alloc> struct AbstractManglingParser {
   void *TypeCallbackContext = nullptr;
 
   bool TryToParseTemplateArgs = true;
   bool PermitForwardTemplateReferences = false;
   bool ParsingLambdaParams = false;
 
   Alloc ASTAllocator;
 
-  Db(const char *First_, const char *Last_) : First(First_), Last(Last_) {}
+  AbstractManglingParser(const char *First_, const char *Last_)
+      : First(First_), Last(Last_) {}
+
+  Derived &getDerived() { return static_cast<Derived &>(*this); }
 
   void reset(const char *First_, const char *Last_) {
     First = First_;
     Last = Last_;
     Names.clear();
     Subs.clear();
     TemplateParams.clear();
     ParsingLambdaParams = false;
template <typename Derived, typename Alloc> struct AbstractManglingParser {
   /// information is only pertinent if the <name> refers to an <encoding>.
   struct NameState {
     bool CtorDtorConversion = false;
     bool EndsWithTemplateArgs = false;
     Qualifiers CVQualifiers = QualNone;
     FunctionRefQual ReferenceQualifier = FrefQualNone;
     size_t ForwardTemplateRefsBegin;
 
-    NameState(Db *Enclosing)
+    NameState(AbstractManglingParser *Enclosing)
         : ForwardTemplateRefsBegin(Enclosing->ForwardTemplateRefs.size()) {}
   };
 
   bool resolveForwardTemplateRefs(NameState &State) {
     size_t I = State.ForwardTemplateRefsBegin;
     size_t E = ForwardTemplateRefs.size();
     for (; I < E; ++I) {
       size_t Idx = ForwardTemplateRefs[I]->Index;

 
 // <name> ::= <nested-name> // N
 //        ::= <local-name> # See Scope Encoding below  // Z
 //        ::= <unscoped-template-name> <template-args>
 //        ::= <unscoped-name>
 //
 // <unscoped-template-name> ::= <unscoped-name>
 //                          ::= <substitution>
-template<typename Alloc> Node *Db<Alloc>::parseName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseName(NameState *State) {
   consumeIf('L'); // extension
 
   if (look() == 'N')
-    return parseNestedName(State);
+    return getDerived().parseNestedName(State);
   if (look() == 'Z')
-    return parseLocalName(State);
+    return getDerived().parseLocalName(State);
 
   //        ::= <unscoped-template-name> <template-args>
   if (look() == 'S' && look(1) != 't') {
-    Node *S = parseSubstitution();
+    Node *S = getDerived().parseSubstitution();
     if (S == nullptr)
       return nullptr;
     if (look() != 'I')
       return nullptr;
-    Node *TA = parseTemplateArgs(State != nullptr);
+    Node *TA = getDerived().parseTemplateArgs(State != nullptr);
     if (TA == nullptr)
       return nullptr;
     if (State) State->EndsWithTemplateArgs = true;
     return make<NameWithTemplateArgs>(S, TA);
   }
 
-  Node *N = parseUnscopedName(State);
+  Node *N = getDerived().parseUnscopedName(State);
   if (N == nullptr)
     return nullptr;
   //        ::= <unscoped-template-name> <template-args>
   if (look() == 'I') {
     Subs.push_back(N);
-    Node *TA = parseTemplateArgs(State != nullptr);
+    Node *TA = getDerived().parseTemplateArgs(State != nullptr);
     if (TA == nullptr)
       return nullptr;
     if (State) State->EndsWithTemplateArgs = true;
     return make<NameWithTemplateArgs>(N, TA);
   }
   //        ::= <unscoped-name>
   return N;
 }
 
 // <local-name> := Z <function encoding> E <entity name> [<discriminator>]
 //              := Z <function encoding> E s [<discriminator>]
 //              := Z <function encoding> Ed [ <parameter number> ] _ <entity name>
-template<typename Alloc> Node *Db<Alloc>::parseLocalName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseLocalName(NameState *State) {
   if (!consumeIf('Z'))
     return nullptr;
-  Node *Encoding = parseEncoding();
+  Node *Encoding = getDerived().parseEncoding();
   if (Encoding == nullptr || !consumeIf('E'))
     return nullptr;
 
   if (consumeIf('s')) {
     First = parse_discriminator(First, Last);
     auto *StringLitName = make<NameType>("string literal");
     if (!StringLitName)
       return nullptr;
     return make<LocalName>(Encoding, StringLitName);
   }
 
   if (consumeIf('d')) {
     parseNumber(true);
     if (!consumeIf('_'))
       return nullptr;
-    Node *N = parseName(State);
+    Node *N = getDerived().parseName(State);
     if (N == nullptr)
       return nullptr;
     return make<LocalName>(Encoding, N);
   }
 
-  Node *Entity = parseName(State);
+  Node *Entity = getDerived().parseName(State);
   if (Entity == nullptr)
     return nullptr;
   First = parse_discriminator(First, Last);
   return make<LocalName>(Encoding, Entity);
 }
 
 // <unscoped-name> ::= <unqualified-name>
 //                 ::= St <unqualified-name>   # ::std::
 // extension       ::= StL<unqualified-name>
-template<typename Alloc> Node *Db<Alloc>::parseUnscopedName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseUnscopedName(NameState *State) {
   if (consumeIf("StL") || consumeIf("St")) {
-   Node *R = parseUnqualifiedName(State);
+    Node *R = getDerived().parseUnqualifiedName(State);
     if (R == nullptr)
       return nullptr;
     return make<StdQualifiedName>(R);
   }
- return parseUnqualifiedName(State);
+  return getDerived().parseUnqualifiedName(State);
 }
 
 // <unqualified-name> ::= <operator-name> [abi-tags]
 //                    ::= <ctor-dtor-name>
 //                    ::= <source-name>
 //                    ::= <unnamed-type-name>
 //                    ::= DC <source-name>+ E      # structured binding declaration
-template<typename Alloc>
-Node *Db<Alloc>::parseUnqualifiedName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseUnqualifiedName(NameState *State) {
   // <ctor-dtor-name>s are special-cased in parseNestedName().
   Node *Result;
   if (look() == 'U')
-    Result = parseUnnamedTypeName(State);
+    Result = getDerived().parseUnnamedTypeName(State);
   else if (look() >= '1' && look() <= '9')
-    Result = parseSourceName(State);
+    Result = getDerived().parseSourceName(State);
   else if (consumeIf("DC")) {
     size_t BindingsBegin = Names.size();
     do {
-      Node *Binding = parseSourceName(State);
+      Node *Binding = getDerived().parseSourceName(State);
       if (Binding == nullptr)
         return nullptr;
       Names.push_back(Binding);
     } while (!consumeIf('E'));
     Result = make<StructuredBindingName>(popTrailingNodeArray(BindingsBegin));
   } else
-    Result = parseOperatorName(State);
+    Result = getDerived().parseOperatorName(State);
   if (Result != nullptr)
-    Result = parseAbiTags(Result);
+    Result = getDerived().parseAbiTags(Result);
   return Result;
 }
 
 // <unnamed-type-name> ::= Ut [<nonnegative number>] _
 //                     ::= <closure-type-name>
 //
 // <closure-type-name> ::= Ul <lambda-sig> E [ <nonnegative number> ] _
 //
 // <lambda-sig> ::= <parameter type>+  # Parameter types or "v" if the lambda has no parameters
-template<typename Alloc> Node *Db<Alloc>::parseUnnamedTypeName(NameState *) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseUnnamedTypeName(NameState *) {
   if (consumeIf("Ut")) {
     StringView Count = parseNumber();
     if (!consumeIf('_'))
       return nullptr;
     return make<UnnamedTypeName>(Count);
   }
   if (consumeIf("Ul")) {
     NodeArray Params;
     SwapAndRestore<bool> SwapParams(ParsingLambdaParams, true);
     if (!consumeIf("vE")) {
       size_t ParamsBegin = Names.size();
       do {
-        Node *P = parseType();
+        Node *P = getDerived().parseType();
         if (P == nullptr)
           return nullptr;
         Names.push_back(P);
       } while (!consumeIf('E'));
       Params = popTrailingNodeArray(ParamsBegin);
     }
     StringView Count = parseNumber();
     if (!consumeIf('_'))
       return nullptr;
     return make<ClosureTypeName>(Params, Count);
   }
   return nullptr;
 }
 
 // <source-name> ::= <positive length number> <identifier>
-template<typename Alloc> Node *Db<Alloc>::parseSourceName(NameState *) {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseSourceName(NameState *) {
   size_t Length = 0;
   if (parsePositiveInteger(&Length))
     return nullptr;
   if (numLeft() < Length || Length == 0)
     return nullptr;
   StringView Name(First, First + Length);
   First += Length;
   if (Name.startsWith("_GLOBAL__N"))

 //                   ::= pt    # ->
 //                   ::= qu    # ?
 //                   ::= rm    # %
 //                   ::= rM    # %=
 //                   ::= rs    # >>
 //                   ::= rS    # >>=
 //                   ::= ss    # <=> C++2a
 //                   ::= v <digit> <source-name>        # vendor extended operator
-template<typename Alloc> Node *Db<Alloc>::parseOperatorName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseOperatorName(NameState *State) {
   switch (look()) {
   case 'a':
     switch (look(1)) {
     case 'a':
       First += 2;
       return make<NameType>("operator&&");
     case 'd':
     case 'n':
case 'v': {
       First += 2;
       SwapAndRestore<bool> SaveTemplate(TryToParseTemplateArgs, false);
       // If we're parsing an encoding, State != nullptr and the conversion
       // operators' <type> could have a <template-param> that refers to some
       // <template-arg>s further ahead in the mangled name.
       SwapAndRestore<bool> SavePermit(PermitForwardTemplateReferences,
                                       PermitForwardTemplateReferences ||
                                           State != nullptr);
-      Node* Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       if (State) State->CtorDtorConversion = true;
       return make<ConversionOperatorType>(Ty);
     }
     }
     return nullptr;
   case 'd':
AbstractManglingParser<Derived, Alloc>::parseOperatorName(NameState *State) {
   case 'l':
     switch (look(1)) {
     case 'e':
       First += 2;
       return make<NameType>("operator<=");
     //                   ::= li <source-name>  # operator ""
     case 'i': {
       First += 2;
-      Node *SN = parseSourceName(State);
+      Node *SN = getDerived().parseSourceName(State);
       if (SN == nullptr)
         return nullptr;
       return make<LiteralOperator>(SN);
     }
     case 's':
       First += 2;
       return make<NameType>("operator<<");
     case 'S':
if (look(1) == 's') {
       First += 2;
       return make<NameType>("operator<=>");
     }
     return nullptr;
   // ::= v <digit> <source-name>        # vendor extended operator
   case 'v':
     if (std::isdigit(look(1))) {
       First += 2;
-      Node *SN = parseSourceName(State);
+      Node *SN = getDerived().parseSourceName(State);
       if (SN == nullptr)
         return nullptr;
       return make<ConversionOperatorType>(SN);
     }
     return nullptr;
   }
   return nullptr;
 }
 
 // <ctor-dtor-name> ::= C1  # complete object constructor
 //                  ::= C2  # base object constructor
 //                  ::= C3  # complete object allocating constructor
 //   extension      ::= C5    # ?
 //                  ::= D0  # deleting destructor
 //                  ::= D1  # complete object destructor
 //                  ::= D2  # base object destructor
 //   extension      ::= D5    # ?
-template<typename Alloc>
-Node *Db<Alloc>::parseCtorDtorName(Node *&SoFar, NameState *State) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseCtorDtorName(Node *&SoFar,
+                                                          NameState *State) {
   if (SoFar->getKind() == Node::KSpecialSubstitution) {
     auto SSK = static_cast<SpecialSubstitution *>(SoFar)->SSK;
     switch (SSK) {
     case SpecialSubKind::string:
     case SpecialSubKind::istream:
     case SpecialSubKind::ostream:
     case SpecialSubKind::iostream:
       SoFar = make<ExpandedSpecialSubstitution>(SSK);
       if (!SoFar)
         return nullptr;
     default:
       break;
     }
   }
 
   if (consumeIf('C')) {
     bool IsInherited = consumeIf('I');
     if (look() != '1' && look() != '2' && look() != '3' && look() != '5')
       return nullptr;
     int Variant = look() - '0';
     ++First;
     if (State) State->CtorDtorConversion = true;
     if (IsInherited) {
-      if (parseName(State) == nullptr)
+      if (getDerived().parseName(State) == nullptr)
         return nullptr;
     }
     return make<CtorDtorName>(SoFar, false, Variant);
   }
 
   if (look() == 'D' &&
       (look(1) == '0' || look(1) == '1' || look(1) == '2' || look(1) == '5')) {
     int Variant = look(1) - '0';

 //          ::= <prefix> <data-member-prefix>
 //  extension ::= L
 //
 // <data-member-prefix> := <member source-name> [<template-args>] M
 //
 // <template-prefix> ::= <prefix> <template unqualified-name>
 //                   ::= <template-param>
 //                   ::= <substitution>
-template<typename Alloc> Node *Db<Alloc>::parseNestedName(NameState *State) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseNestedName(NameState *State) {
   if (!consumeIf('N'))
     return nullptr;
 
   Qualifiers CVTmp = parseCVQualifiers();
   if (State) State->CVQualifiers = CVTmp;
 
   if (consumeIf('O')) {
     if (State) State->ReferenceQualifier = FrefQualRValue;
while (!consumeIf('E')) {
     if (consumeIf('M')) {
       if (SoFar == nullptr)
         return nullptr;
       continue;
     }
 
     //          ::= <template-param>
     if (look() == 'T') {
-      if (!PushComponent(parseTemplateParam()))
+      if (!PushComponent(getDerived().parseTemplateParam()))
         return nullptr;
       Subs.push_back(SoFar);
       continue;
     }
 
     //          ::= <template-prefix> <template-args>
     if (look() == 'I') {
-      Node *TA = parseTemplateArgs(State != nullptr);
+      Node *TA = getDerived().parseTemplateArgs(State != nullptr);
       if (TA == nullptr || SoFar == nullptr)
         return nullptr;
       SoFar = make<NameWithTemplateArgs>(SoFar, TA);
       if (!SoFar)
         return nullptr;
       if (State) State->EndsWithTemplateArgs = true;
       Subs.push_back(SoFar);
       continue;
     }
 
     //          ::= <decltype>
     if (look() == 'D' && (look(1) == 't' || look(1) == 'T')) {
-      if (!PushComponent(parseDecltype()))
+      if (!PushComponent(getDerived().parseDecltype()))
         return nullptr;
       Subs.push_back(SoFar);
       continue;
     }
 
     //          ::= <substitution>
     if (look() == 'S' && look(1) != 't') {
-      Node *S = parseSubstitution();
+      Node *S = getDerived().parseSubstitution();
       if (!PushComponent(S))
         return nullptr;
       if (SoFar != S)
         Subs.push_back(S);
       continue;
     }
 
     // Parse an <unqualified-name> thats actually a <ctor-dtor-name>.
     if (look() == 'C' || (look() == 'D' && look(1) != 'C')) {
       if (SoFar == nullptr)
         return nullptr;
-      if (!PushComponent(parseCtorDtorName(SoFar, State)))
+      if (!PushComponent(getDerived().parseCtorDtorName(SoFar, State)))
         return nullptr;
-      SoFar = parseAbiTags(SoFar);
+      SoFar = getDerived().parseAbiTags(SoFar);
       if (SoFar == nullptr)
         return nullptr;
       Subs.push_back(SoFar);
       continue;
     }
 
     //          ::= <prefix> <unqualified-name>
-    if (!PushComponent(parseUnqualifiedName(State)))
+    if (!PushComponent(getDerived().parseUnqualifiedName(State)))
       return nullptr;
     Subs.push_back(SoFar);
   }
 
   if (SoFar == nullptr || Subs.empty())
     return nullptr;
 
   Subs.pop_back();
   return SoFar;
 }
 
 // <simple-id> ::= <source-name> [ <template-args> ]
-template<typename Alloc> Node *Db<Alloc>::parseSimpleId() {
-  Node *SN = parseSourceName(/*NameState=*/nullptr);
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseSimpleId() {
+  Node *SN = getDerived().parseSourceName(/*NameState=*/nullptr);
   if (SN == nullptr)
     return nullptr;
   if (look() == 'I') {
-    Node *TA = parseTemplateArgs();
+    Node *TA = getDerived().parseTemplateArgs();
     if (TA == nullptr)
       return nullptr;
     return make<NameWithTemplateArgs>(SN, TA);
   }
   return SN;
 }
 
 // <destructor-name> ::= <unresolved-type>  # e.g., ~T or ~decltype(f())
 //                   ::= <simple-id>        # e.g., ~A<2*N>
-template<typename Alloc> Node *Db<Alloc>::parseDestructorName() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseDestructorName() {
   Node *Result;
   if (std::isdigit(look()))
-    Result = parseSimpleId();
+    Result = getDerived().parseSimpleId();
   else
-    Result = parseUnresolvedType();
+    Result = getDerived().parseUnresolvedType();
   if (Result == nullptr)
     return nullptr;
   return make<DtorName>(Result);
 }
 
 // <unresolved-type> ::= <template-param>
 //                   ::= <decltype>
 //                   ::= <substitution>
-template<typename Alloc> Node *Db<Alloc>::parseUnresolvedType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseUnresolvedType() {
   if (look() == 'T') {
-    Node *TP = parseTemplateParam();
+    Node *TP = getDerived().parseTemplateParam();
     if (TP == nullptr)
       return nullptr;
     Subs.push_back(TP);
     return TP;
   }
   if (look() == 'D') {
-    Node *DT = parseDecltype();
+    Node *DT = getDerived().parseDecltype();
     if (DT == nullptr)
       return nullptr;
     Subs.push_back(DT);
     return DT;
   }
-  return parseSubstitution();
+  return getDerived().parseSubstitution();
 }
 
 // <base-unresolved-name> ::= <simple-id>                                # unresolved name
 //          extension     ::= <operator-name>                            # unresolved operator-function-id
 //          extension     ::= <operator-name> <template-args>            # unresolved operator template-id
 //                        ::= on <operator-name>                         # unresolved operator-function-id
 //                        ::= on <operator-name> <template-args>         # unresolved operator template-id
 //                        ::= dn <destructor-name>                       # destructor or pseudo-destructor;
 //                                                                         # e.g. ~X or ~X<N-1>
-template<typename Alloc> Node *Db<Alloc>::parseBaseUnresolvedName() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseBaseUnresolvedName() {
   if (std::isdigit(look()))
-    return parseSimpleId();
+    return getDerived().parseSimpleId();
 
   if (consumeIf("dn"))
-    return parseDestructorName();
+    return getDerived().parseDestructorName();
 
   consumeIf("on");
 
-  Node *Oper = parseOperatorName(/*NameState=*/nullptr);
+  Node *Oper = getDerived().parseOperatorName(/*NameState=*/nullptr);
   if (Oper == nullptr)
     return nullptr;
   if (look() == 'I') {
-    Node *TA = parseTemplateArgs();
+    Node *TA = getDerived().parseTemplateArgs();
     if (TA == nullptr)
       return nullptr;
     return make<NameWithTemplateArgs>(Oper, TA);
   }
   return Oper;
 }
 
 // <unresolved-name>
 //  extension        ::= srN <unresolved-type> [<template-args>] <unresolved-qualifier-level>* E <base-unresolved-name>
 //                   ::= [gs] <base-unresolved-name>                     # x or (with "gs") ::x
 //                   ::= [gs] sr <unresolved-qualifier-level>+ E <base-unresolved-name>
 //                                                                       # A::x, N::y, A<T>::z; "gs" means leading "::"
 //                   ::= sr <unresolved-type> <base-unresolved-name>     # T::x / decltype(p)::x
 //  extension        ::= sr <unresolved-type> <template-args> <base-unresolved-name>
 //                                                                       # T::N::x /decltype(p)::N::x
 //  (ignored)        ::= srN <unresolved-type>  <unresolved-qualifier-level>+ E <base-unresolved-name>
 //
 // <unresolved-qualifier-level> ::= <simple-id>
-template<typename Alloc> Node *Db<Alloc>::parseUnresolvedName() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseUnresolvedName() {
   Node *SoFar = nullptr;
 
   // srN <unresolved-type> [<template-args>] <unresolved-qualifier-level>* E <base-unresolved-name>
   // srN <unresolved-type>                   <unresolved-qualifier-level>+ E <base-unresolved-name>
   if (consumeIf("srN")) {
-    SoFar = parseUnresolvedType();
+    SoFar = getDerived().parseUnresolvedType();
     if (SoFar == nullptr)
       return nullptr;
 
     if (look() == 'I') {
-      Node *TA = parseTemplateArgs();
+      Node *TA = getDerived().parseTemplateArgs();
       if (TA == nullptr)
         return nullptr;
       SoFar = make<NameWithTemplateArgs>(SoFar, TA);
       if (!SoFar)
         return nullptr;
     }
 
     while (!consumeIf('E')) {
-      Node *Qual = parseSimpleId();
+      Node *Qual = getDerived().parseSimpleId();
       if (Qual == nullptr)
         return nullptr;
       SoFar = make<QualifiedName>(SoFar, Qual);
       if (!SoFar)
         return nullptr;
     }
 
-    Node *Base = parseBaseUnresolvedName();
+    Node *Base = getDerived().parseBaseUnresolvedName();
     if (Base == nullptr)
       return nullptr;
     return make<QualifiedName>(SoFar, Base);
   }
 
   bool Global = consumeIf("gs");
 
   // [gs] <base-unresolved-name>                     # x or (with "gs") ::x
   if (!consumeIf("sr")) {
-    SoFar = parseBaseUnresolvedName();
+    SoFar = getDerived().parseBaseUnresolvedName();
     if (SoFar == nullptr)
       return nullptr;
     if (Global)
       SoFar = make<GlobalQualifiedName>(SoFar);
     return SoFar;
   }
 
   // [gs] sr <unresolved-qualifier-level>+ E   <base-unresolved-name>
   if (std::isdigit(look())) {
     do {
-      Node *Qual = parseSimpleId();
+      Node *Qual = getDerived().parseSimpleId();
       if (Qual == nullptr)
         return nullptr;
       if (SoFar)
         SoFar = make<QualifiedName>(SoFar, Qual);
       else if (Global)
         SoFar = make<GlobalQualifiedName>(Qual);
       else
         SoFar = Qual;
       if (!SoFar)
         return nullptr;
     } while (!consumeIf('E'));
   }
   //      sr <unresolved-type>                 <base-unresolved-name>
   //      sr <unresolved-type> <template-args> <base-unresolved-name>
   else {
-    SoFar = parseUnresolvedType();
+    SoFar = getDerived().parseUnresolvedType();
     if (SoFar == nullptr)
       return nullptr;
 
     if (look() == 'I') {
-      Node *TA = parseTemplateArgs();
+      Node *TA = getDerived().parseTemplateArgs();
       if (TA == nullptr)
         return nullptr;
       SoFar = make<NameWithTemplateArgs>(SoFar, TA);
       if (!SoFar)
         return nullptr;
     }
   }
 
   assert(SoFar != nullptr);
 
-  Node *Base = parseBaseUnresolvedName();
+  Node *Base = getDerived().parseBaseUnresolvedName();
   if (Base == nullptr)
     return nullptr;
   return make<QualifiedName>(SoFar, Base);
 }
 
 // <abi-tags> ::= <abi-tag> [<abi-tags>]
 // <abi-tag> ::= B <source-name>
-template<typename Alloc> Node *Db<Alloc>::parseAbiTags(Node *N) {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseAbiTags(Node *N) {
   while (consumeIf('B')) {
     StringView SN = parseBareSourceName();
     if (SN.empty())
       return nullptr;
     N = make<AbiTagAttr>(N, SN);
     if (!N)
       return nullptr;
   }
   return N;
 }
 
 // <number> ::= [n] <non-negative decimal integer>
-template<typename Alloc>
-StringView Db<Alloc>::parseNumber(bool AllowNegative) {
+template <typename Alloc, typename Derived>
+StringView
+AbstractManglingParser<Alloc, Derived>::parseNumber(bool AllowNegative) {
   const char *Tmp = First;
   if (AllowNegative)
     consumeIf('n');
   if (numLeft() == 0 || !std::isdigit(*First))
     return StringView();
   while (numLeft() != 0 && std::isdigit(*First))
     ++First;
   return StringView(Tmp, First);
 }
 
 // <positive length number> ::= [0-9]*
-template<typename Alloc> bool Db<Alloc>::parsePositiveInteger(size_t *Out) {
+template <typename Alloc, typename Derived>
+bool AbstractManglingParser<Alloc, Derived>::parsePositiveInteger(size_t *Out) {
   *Out = 0;
   if (look() < '0' || look() > '9')
     return true;
   while (look() >= '0' && look() <= '9') {
     *Out *= 10;
     *Out += static_cast<size_t>(consume() - '0');
   }
   return false;
 }
 
-template<typename Alloc> StringView Db<Alloc>::parseBareSourceName() {
+template <typename Alloc, typename Derived>
+StringView AbstractManglingParser<Alloc, Derived>::parseBareSourceName() {
   size_t Int = 0;
   if (parsePositiveInteger(&Int) || numLeft() < Int)
     return StringView();
   StringView R(First, First + Int);
   First += Int;
   return R;
 }
 
 // <function-type> ::= [<CV-qualifiers>] [<exception-spec>] [Dx] F [Y] <bare-function-type> [<ref-qualifier>] E
 //
 // <exception-spec> ::= Do                # non-throwing exception-specification (e.g., noexcept, throw())
 //                  ::= DO <expression> E # computed (instantiation-dependent) noexcept
 //                  ::= Dw <type>+ E      # dynamic exception specification with instantiation-dependent types
 //
 // <ref-qualifier> ::= R                   # & ref-qualifier
 // <ref-qualifier> ::= O                   # && ref-qualifier
-template<typename Alloc> Node *Db<Alloc>::parseFunctionType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseFunctionType() {
   Qualifiers CVQuals = parseCVQualifiers();
 
   Node *ExceptionSpec = nullptr;
   if (consumeIf("Do")) {
     ExceptionSpec = make<NameType>("noexcept");
     if (!ExceptionSpec)
       return nullptr;
   } else if (consumeIf("DO")) {
-    Node *E = parseExpr();
+    Node *E = getDerived().parseExpr();
     if (E == nullptr || !consumeIf('E'))
       return nullptr;
     ExceptionSpec = make<NoexceptSpec>(E);
     if (!ExceptionSpec)
       return nullptr;
   } else if (consumeIf("Dw")) {
     size_t SpecsBegin = Names.size();
     while (!consumeIf('E')) {
-      Node *T = parseType();
+      Node *T = getDerived().parseType();
       if (T == nullptr)
         return nullptr;
       Names.push_back(T);
     }
     ExceptionSpec =
       make<DynamicExceptionSpec>(popTrailingNodeArray(SpecsBegin));
     if (!ExceptionSpec)
       return nullptr;
   }
 
   consumeIf("Dx"); // transaction safe
 
   if (!consumeIf('F'))
     return nullptr;
   consumeIf('Y'); // extern "C"
-  Node *ReturnType = parseType();
+  Node *ReturnType = getDerived().parseType();
   if (ReturnType == nullptr)
     return nullptr;
 
   FunctionRefQual ReferenceQualifier = FrefQualNone;
   size_t ParamsBegin = Names.size();
   while (true) {
     if (consumeIf('E'))
       break;
     if (consumeIf('v'))
       continue;
     if (consumeIf("RE")) {
       ReferenceQualifier = FrefQualLValue;
       break;
     }
     if (consumeIf("OE")) {
       ReferenceQualifier = FrefQualRValue;
       break;
     }
-    Node *T = parseType();
+    Node *T = getDerived().parseType();
     if (T == nullptr)
       return nullptr;
     Names.push_back(T);
   }
 
   NodeArray Params = popTrailingNodeArray(ParamsBegin);
   return make<FunctionType>(ReturnType, Params, CVQuals,
                             ReferenceQualifier, ExceptionSpec);
 }
 
 // extension:
 // <vector-type>           ::= Dv <positive dimension number> _ <extended element type>
 //                         ::= Dv [<dimension expression>] _ <element type>
 // <extended element type> ::= <element type>
 //                         ::= p # AltiVec vector pixel
-template<typename Alloc> Node *Db<Alloc>::parseVectorType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseVectorType() {
   if (!consumeIf("Dv"))
     return nullptr;
   if (look() >= '1' && look() <= '9') {
     StringView DimensionNumber = parseNumber();
     if (!consumeIf('_'))
       return nullptr;
     if (consumeIf('p'))
       return make<PixelVectorType>(DimensionNumber);
-    Node *ElemType = parseType();
+    Node *ElemType = getDerived().parseType();
     if (ElemType == nullptr)
       return nullptr;
     return make<VectorType>(ElemType, DimensionNumber);
   }
 
   if (!consumeIf('_')) {
-    Node *DimExpr = parseExpr();
+    Node *DimExpr = getDerived().parseExpr();
     if (!DimExpr)
       return nullptr;
     if (!consumeIf('_'))
       return nullptr;
-    Node *ElemType = parseType();
+    Node *ElemType = getDerived().parseType();
     if (!ElemType)
       return nullptr;
     return make<VectorType>(ElemType, DimExpr);
   }
-  Node *ElemType = parseType();
+  Node *ElemType = getDerived().parseType();
   if (!ElemType)
     return nullptr;
   return make<VectorType>(ElemType, StringView());
 }
 
 // <decltype>  ::= Dt <expression> E  # decltype of an id-expression or class member access (C++0x)
 //             ::= DT <expression> E  # decltype of an expression (C++0x)
-template<typename Alloc> Node *Db<Alloc>::parseDecltype() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseDecltype() {
   if (!consumeIf('D'))
     return nullptr;
   if (!consumeIf('t') && !consumeIf('T'))
     return nullptr;
-  Node *E = parseExpr();
+  Node *E = getDerived().parseExpr();
   if (E == nullptr)
     return nullptr;
   if (!consumeIf('E'))
     return nullptr;
   return make<EnclosingExpr>("decltype(", E, ")");
 }
 
 // <array-type> ::= A <positive dimension number> _ <element type>
 //              ::= A [<dimension expression>] _ <element type>
-template<typename Alloc> Node *Db<Alloc>::parseArrayType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseArrayType() {
   if (!consumeIf('A'))
     return nullptr;
 
   NodeOrString Dimension;
 
   if (std::isdigit(look())) {
     Dimension = parseNumber();
     if (!consumeIf('_'))
       return nullptr;
   } else if (!consumeIf('_')) {
-    Node *DimExpr = parseExpr();
+    Node *DimExpr = getDerived().parseExpr();
     if (DimExpr == nullptr)
       return nullptr;
     if (!consumeIf('_'))
       return nullptr;
     Dimension = DimExpr;
   }
 
-  Node *Ty = parseType();
+  Node *Ty = getDerived().parseType();
   if (Ty == nullptr)
     return nullptr;
   return make<ArrayType>(Ty, Dimension);
 }
 
 // <pointer-to-member-type> ::= M <class type> <member type>
-template<typename Alloc> Node *Db<Alloc>::parsePointerToMemberType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parsePointerToMemberType() {
   if (!consumeIf('M'))
     return nullptr;
-  Node *ClassType = parseType();
+  Node *ClassType = getDerived().parseType();
   if (ClassType == nullptr)
     return nullptr;
-  Node *MemberType = parseType();
+  Node *MemberType = getDerived().parseType();
   if (MemberType == nullptr)
     return nullptr;
   return make<PointerToMemberType>(ClassType, MemberType);
 }
 
 // <class-enum-type> ::= <name>     # non-dependent type name, dependent type name, or dependent typename-specifier
 //                   ::= Ts <name>  # dependent elaborated type specifier using 'struct' or 'class'
 //                   ::= Tu <name>  # dependent elaborated type specifier using 'union'
 //                   ::= Te <name>  # dependent elaborated type specifier using 'enum'
-template<typename Alloc> Node *Db<Alloc>::parseClassEnumType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseClassEnumType() {
   StringView ElabSpef;
   if (consumeIf("Ts"))
     ElabSpef = "struct";
   else if (consumeIf("Tu"))
     ElabSpef = "union";
   else if (consumeIf("Te"))
     ElabSpef = "enum";
 
-  Node *Name = parseName();
+  Node *Name = getDerived().parseName();
   if (Name == nullptr)
     return nullptr;
 
   if (!ElabSpef.empty())
     return make<ElaboratedTypeSpefType>(ElabSpef, Name);
 
   return Name;
 }
 
 // <qualified-type>     ::= <qualifiers> <type>
 // <qualifiers> ::= <extended-qualifier>* <CV-qualifiers>
 // <extended-qualifier> ::= U <source-name> [<template-args>] # vendor extended type qualifier
-template<typename Alloc> Node *Db<Alloc>::parseQualifiedType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseQualifiedType() {
   if (consumeIf('U')) {
     StringView Qual = parseBareSourceName();
     if (Qual.empty())
       return nullptr;
 
     // FIXME parse the optional <template-args> here!
 
     // extension            ::= U <objc-name> <objc-type>  # objc-type<identifier>
     if (Qual.startsWith("objcproto")) {
       StringView ProtoSourceName = Qual.dropFront(std::strlen("objcproto"));
       StringView Proto;
       {
         SwapAndRestore<const char *> SaveFirst(First, ProtoSourceName.begin()),
                                      SaveLast(Last, ProtoSourceName.end());
         Proto = parseBareSourceName();
       }
       if (Proto.empty())
         return nullptr;
-      Node *Child = parseQualifiedType();
+      Node *Child = getDerived().parseQualifiedType();
       if (Child == nullptr)
         return nullptr;
       return make<ObjCProtoName>(Child, Proto);
     }
 
-    Node *Child = parseQualifiedType();
+    Node *Child = getDerived().parseQualifiedType();
     if (Child == nullptr)
       return nullptr;
     return make<VendorExtQualType>(Child, Qual);
   }
 
   Qualifiers Quals = parseCVQualifiers();
-  Node *Ty = parseType();
+  Node *Ty = getDerived().parseType();
   if (Ty == nullptr)
     return nullptr;
   if (Quals != QualNone)
     Ty = make<QualType>(Ty, Quals);
   return Ty;
 }
 
 // <type>      ::= <builtin-type>

 //             ::= C <type>        # complex pair (C99)
 //             ::= G <type>        # imaginary (C99)
 //             ::= <substitution>  # See Compression below
 // extension   ::= U <objc-name> <objc-type>  # objc-type<identifier>
 // extension   ::= <vector-type> # <vector-type> starts with Dv
 //
 // <objc-name> ::= <k0 number> objcproto <k1 number> <identifier>  # k0 = 9 + <number of digits in k1> + k1
 // <objc-type> ::= <source-name>  # PU<11+>objcproto 11objc_object<source-name> 11objc_object -> id<source-name>
-template<typename Alloc> Node *Db<Alloc>::parseType() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseType() {
   Node *Result = nullptr;
 
   if (TypeCallback != nullptr)
     TypeCallback(TypeCallbackContext, First);
 
   switch (look()) {
   //             ::= <qualified-type>
   case 'r':
   case 'V':
   case 'K': {
     unsigned AfterQuals = 0;
     if (look(AfterQuals) == 'r') ++AfterQuals;
     if (look(AfterQuals) == 'V') ++AfterQuals;
     if (look(AfterQuals) == 'K') ++AfterQuals;
 
     if (look(AfterQuals) == 'F' ||
         (look(AfterQuals) == 'D' &&
          (look(AfterQuals + 1) == 'o' || look(AfterQuals + 1) == 'O' ||
           look(AfterQuals + 1) == 'w' || look(AfterQuals + 1) == 'x'))) {
-      Result = parseFunctionType();
+      Result = getDerived().parseFunctionType();
       break;
     }
     _LIBCPP_FALLTHROUGH();
   }
   case 'U': {
-    Result = parseQualifiedType();
+    Result = getDerived().parseQualifiedType();
     break;
   }
   // <builtin-type> ::= v    # void
   case 'v':
     ++First;
     return make<NameType>("void");
   //                ::= w    # wchar_t
   case 'w':
case 'D':
     //                ::= Dn   # std::nullptr_t (i.e., decltype(nullptr))
     case 'n':
       First += 2;
       return make<NameType>("std::nullptr_t");
 
     //             ::= <decltype>
     case 't':
     case 'T': {
-      Result = parseDecltype();
+      Result = getDerived().parseDecltype();
       break;
     }
     // extension   ::= <vector-type> # <vector-type> starts with Dv
     case 'v': {
-      Result = parseVectorType();
+      Result = getDerived().parseVectorType();
       break;
     }
     //           ::= Dp <type>       # pack expansion (C++0x)
     case 'p': {
       First += 2;
-      Node *Child = parseType();
+      Node *Child = getDerived().parseType();
       if (!Child)
         return nullptr;
       Result = make<ParameterPackExpansion>(Child);
       break;
     }
     // Exception specifier on a function type.
     case 'o':
     case 'O':
     case 'w':
     // Transaction safe function type.
     case 'x':
-      Result = parseFunctionType();
+      Result = getDerived().parseFunctionType();
       break;
     }
     break;
   //             ::= <function-type>
   case 'F': {
-    Result = parseFunctionType();
+    Result = getDerived().parseFunctionType();
     break;
   }
   //             ::= <array-type>
   case 'A': {
-    Result = parseArrayType();
+    Result = getDerived().parseArrayType();
     break;
   }
   //             ::= <pointer-to-member-type>
   case 'M': {
-    Result = parsePointerToMemberType();
+    Result = getDerived().parsePointerToMemberType();
     break;
   }
   //             ::= <template-param>
   case 'T': {
     // This could be an elaborate type specifier on a <class-enum-type>.
     if (look(1) == 's' || look(1) == 'u' || look(1) == 'e') {
-      Result = parseClassEnumType();
+      Result = getDerived().parseClassEnumType();
       break;
     }
 
-    Result = parseTemplateParam();
+    Result = getDerived().parseTemplateParam();
     if (Result == nullptr)
       return nullptr;
 
     // Result could be either of:
     //   <type>        ::= <template-param>
     //   <type>        ::= <template-template-param> <template-args>
     //
     //   <template-template-param> ::= <template-param>
     //                             ::= <substitution>
     //
     // If this is followed by some <template-args>, and we're permitted to
     // parse them, take the second production.
 
     if (TryToParseTemplateArgs && look() == 'I') {
-      Node *TA = parseTemplateArgs();
+      Node *TA = getDerived().parseTemplateArgs();
       if (TA == nullptr)
         return nullptr;
       Result = make<NameWithTemplateArgs>(Result, TA);
     }
     break;
   }
   //             ::= P <type>        # pointer
   case 'P': {
     ++First;
-    Node *Ptr = parseType();
+    Node *Ptr = getDerived().parseType();
     if (Ptr == nullptr)
       return nullptr;
     Result = make<PointerType>(Ptr);
     break;
   }
   //             ::= R <type>        # l-value reference
   case 'R': {
     ++First;
-    Node *Ref = parseType();
+    Node *Ref = getDerived().parseType();
     if (Ref == nullptr)
       return nullptr;
     Result = make<ReferenceType>(Ref, ReferenceKind::LValue);
     break;
   }
   //             ::= O <type>        # r-value reference (C++11)
   case 'O': {
     ++First;
-    Node *Ref = parseType();
+    Node *Ref = getDerived().parseType();
     if (Ref == nullptr)
       return nullptr;
     Result = make<ReferenceType>(Ref, ReferenceKind::RValue);
     break;
   }
   //             ::= C <type>        # complex pair (C99)
   case 'C': {
     ++First;
-    Node *P = parseType();
+    Node *P = getDerived().parseType();
     if (P == nullptr)
       return nullptr;
     Result = make<PostfixQualifiedType>(P, " complex");
     break;
   }
   //             ::= G <type>        # imaginary (C99)
   case 'G': {
     ++First;
-    Node *P = parseType();
+    Node *P = getDerived().parseType();
     if (P == nullptr)
       return P;
     Result = make<PostfixQualifiedType>(P, " imaginary");
     break;
   }
   //             ::= <substitution>  # See Compression below
   case 'S': {
     if (look(1) && look(1) != 't') {
-      Node *Sub = parseSubstitution();
+      Node *Sub = getDerived().parseSubstitution();
       if (Sub == nullptr)
         return nullptr;
 
       // Sub could be either of:
       //   <type>        ::= <substitution>
       //   <type>        ::= <template-template-param> <template-args>
       //
       //   <template-template-param> ::= <template-param>
       //                             ::= <substitution>
       //
       // If this is followed by some <template-args>, and we're permitted to
       // parse them, take the second production.
 
       if (TryToParseTemplateArgs && look() == 'I') {
-        Node *TA = parseTemplateArgs();
+        Node *TA = getDerived().parseTemplateArgs();
         if (TA == nullptr)
           return nullptr;
         Result = make<NameWithTemplateArgs>(Sub, TA);
         break;
       }
 
       // If all we parsed was a substitution, don't re-insert into the
       // substitution table.
       return Sub;
     }
     _LIBCPP_FALLTHROUGH();
   }
   //        ::= <class-enum-type>
   default: {
-    Result = parseClassEnumType();
+    Result = getDerived().parseClassEnumType();
     break;
   }
   }
 
   // If we parsed a type, insert it into the substitution table. Note that all
   // <builtin-type>s and <substitution>s have already bailed out, because they
   // don't get substitutions.
   if (Result != nullptr)
     Subs.push_back(Result);
   return Result;
 }
 
-template<typename Alloc> Node *Db<Alloc>::parsePrefixExpr(StringView Kind) {
-  Node *E = parseExpr();
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parsePrefixExpr(StringView Kind) {
+  Node *E = getDerived().parseExpr();
   if (E == nullptr)
     return nullptr;
   return make<PrefixExpr>(Kind, E);
 }
 
-template<typename Alloc> Node *Db<Alloc>::parseBinaryExpr(StringView Kind) {
-  Node *LHS = parseExpr();
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseBinaryExpr(StringView Kind) {
+  Node *LHS = getDerived().parseExpr();
   if (LHS == nullptr)
     return nullptr;
-  Node *RHS = parseExpr();
+  Node *RHS = getDerived().parseExpr();
   if (RHS == nullptr)
     return nullptr;
   return make<BinaryExpr>(LHS, Kind, RHS);
 }
 
-template<typename Alloc> Node *Db<Alloc>::parseIntegerLiteral(StringView Lit) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseIntegerLiteral(StringView Lit) {
   StringView Tmp = parseNumber(true);
   if (!Tmp.empty() && consumeIf('E'))
     return make<IntegerLiteral>(Lit, Tmp);
   return nullptr;
 }
 
 // <CV-Qualifiers> ::= [r] [V] [K]
-template<typename Alloc> Qualifiers Db<Alloc>::parseCVQualifiers() {
+template <typename Alloc, typename Derived>
+Qualifiers AbstractManglingParser<Alloc, Derived>::parseCVQualifiers() {
   Qualifiers CVR = QualNone;
   if (consumeIf('r'))
     CVR |= QualRestrict;
   if (consumeIf('V'))
     CVR |= QualVolatile;
   if (consumeIf('K'))
     CVR |= QualConst;
   return CVR;
 }
 
 // <function-param> ::= fp <top-level CV-Qualifiers> _                                     # L == 0, first parameter
 //                  ::= fp <top-level CV-Qualifiers> <parameter-2 non-negative number> _   # L == 0, second and later parameters
 //                  ::= fL <L-1 non-negative number> p <top-level CV-Qualifiers> _         # L > 0, first parameter
 //                  ::= fL <L-1 non-negative number> p <top-level CV-Qualifiers> <parameter-2 non-negative number> _   # L > 0, second and later parameters
-template<typename Alloc> Node *Db<Alloc>::parseFunctionParam() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseFunctionParam() {
   if (consumeIf("fp")) {
     parseCVQualifiers();
     StringView Num = parseNumber();
     if (!consumeIf('_'))
       return nullptr;
     return make<FunctionParam>(Num);
   }
   if (consumeIf("fL")) {
Node *AbstractManglingParser<Derived, Alloc>::parseFunctionParam() {
   return nullptr;
 }
 
 // [gs] nw <expression>* _ <type> E                     # new (expr-list) type
 // [gs] nw <expression>* _ <type> <initializer>         # new (expr-list) type (init)
 // [gs] na <expression>* _ <type> E                     # new[] (expr-list) type
 // [gs] na <expression>* _ <type> <initializer>         # new[] (expr-list) type (init)
 // <initializer> ::= pi <expression>* E                 # parenthesized initialization
-template<typename Alloc> Node *Db<Alloc>::parseNewExpr() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseNewExpr() {
   bool Global = consumeIf("gs");
   bool IsArray = look(1) == 'a';
   if (!consumeIf("nw") && !consumeIf("na"))
     return nullptr;
   size_t Exprs = Names.size();
   while (!consumeIf('_')) {
-    Node *Ex = parseExpr();
+    Node *Ex = getDerived().parseExpr();
     if (Ex == nullptr)
       return nullptr;
     Names.push_back(Ex);
   }
   NodeArray ExprList = popTrailingNodeArray(Exprs);
-  Node *Ty = parseType();
+  Node *Ty = getDerived().parseType();
   if (Ty == nullptr)
     return Ty;
   if (consumeIf("pi")) {
     size_t InitsBegin = Names.size();
     while (!consumeIf('E')) {
-      Node *Init = parseExpr();
+      Node *Init = getDerived().parseExpr();
       if (Init == nullptr)
         return Init;
       Names.push_back(Init);
     }
     NodeArray Inits = popTrailingNodeArray(InitsBegin);
     return make<NewExpr>(ExprList, Ty, Inits, Global, IsArray);
   } else if (!consumeIf('E'))
     return nullptr;
   return make<NewExpr>(ExprList, Ty, NodeArray(), Global, IsArray);
 }
 
 // cv <type> <expression>                               # conversion with one argument
 // cv <type> _ <expression>* E                          # conversion with a different number of arguments
-template<typename Alloc> Node *Db<Alloc>::parseConversionExpr() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseConversionExpr() {
   if (!consumeIf("cv"))
     return nullptr;
   Node *Ty;
   {
     SwapAndRestore<bool> SaveTemp(TryToParseTemplateArgs, false);
-    Ty = parseType();
+    Ty = getDerived().parseType();
   }
 
   if (Ty == nullptr)
     return nullptr;
 
   if (consumeIf('_')) {
     size_t ExprsBegin = Names.size();
     while (!consumeIf('E')) {
-      Node *E = parseExpr();
+      Node *E = getDerived().parseExpr();
       if (E == nullptr)
         return E;
       Names.push_back(E);
     }
     NodeArray Exprs = popTrailingNodeArray(ExprsBegin);
     return make<ConversionExpr>(Ty, Exprs);
   }
 
-  Node *E[1] = {parseExpr()};
+  Node *E[1] = {getDerived().parseExpr()};
   if (E[0] == nullptr)
     return nullptr;
   return make<ConversionExpr>(Ty, makeNodeArray(E, E + 1));
 }
 
 // <expr-primary> ::= L <type> <value number> E                          # integer literal
 //                ::= L <type> <value float> E                           # floating literal
 //                ::= L <string type> E                                  # string literal
 //                ::= L <nullptr type> E                                 # nullptr literal (i.e., "LDnE")
 // FIXME:         ::= L <type> <real-part float> _ <imag-part float> E   # complex floating point literal (C 2000)
 //                ::= L <mangled-name> E                                 # external name
-template<typename Alloc> Node *Db<Alloc>::parseExprPrimary() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseExprPrimary() {
   if (!consumeIf('L'))
     return nullptr;
   switch (look()) {
   case 'w':
     ++First;
-    return parseIntegerLiteral("wchar_t");
+    return getDerived().parseIntegerLiteral("wchar_t");
   case 'b':
     if (consumeIf("b0E"))
       return make<BoolExpr>(0);
     if (consumeIf("b1E"))
       return make<BoolExpr>(1);
     return nullptr;
   case 'c':
     ++First;
-    return parseIntegerLiteral("char");
+    return getDerived().parseIntegerLiteral("char");
   case 'a':
     ++First;
-    return parseIntegerLiteral("signed char");
+    return getDerived().parseIntegerLiteral("signed char");
   case 'h':
     ++First;
-    return parseIntegerLiteral("unsigned char");
+    return getDerived().parseIntegerLiteral("unsigned char");
   case 's':
     ++First;
-    return parseIntegerLiteral("short");
+    return getDerived().parseIntegerLiteral("short");
   case 't':
     ++First;
-    return parseIntegerLiteral("unsigned short");
+    return getDerived().parseIntegerLiteral("unsigned short");
   case 'i':
     ++First;
-    return parseIntegerLiteral("");
+    return getDerived().parseIntegerLiteral("");
   case 'j':
     ++First;
-    return parseIntegerLiteral("u");
+    return getDerived().parseIntegerLiteral("u");
   case 'l':
     ++First;
-    return parseIntegerLiteral("l");
+    return getDerived().parseIntegerLiteral("l");
   case 'm':
     ++First;
-    return parseIntegerLiteral("ul");
+    return getDerived().parseIntegerLiteral("ul");
   case 'x':
     ++First;
-    return parseIntegerLiteral("ll");
+    return getDerived().parseIntegerLiteral("ll");
   case 'y':
     ++First;
-    return parseIntegerLiteral("ull");
+    return getDerived().parseIntegerLiteral("ull");
   case 'n':
     ++First;
-    return parseIntegerLiteral("__int128");
+    return getDerived().parseIntegerLiteral("__int128");
   case 'o':
     ++First;
-    return parseIntegerLiteral("unsigned __int128");
+    return getDerived().parseIntegerLiteral("unsigned __int128");
   case 'f':
     ++First;
-    return parseFloatingLiteral<float>();
+    return getDerived().template parseFloatingLiteral<float>();
   case 'd':
     ++First;
-    return parseFloatingLiteral<double>();
+    return getDerived().template parseFloatingLiteral<double>();
   case 'e':
     ++First;
-    return parseFloatingLiteral<long double>();
+    return getDerived().template parseFloatingLiteral<long double>();
   case '_':
     if (consumeIf("_Z")) {
-      Node *R = parseEncoding();
+      Node *R = getDerived().parseEncoding();
       if (R != nullptr && consumeIf('E'))
         return R;
     }
     return nullptr;
   case 'T':
     // Invalid mangled name per
     //   http://sourcerytools.com/pipermail/cxx-abi-dev/2011-August/002422.html
     return nullptr;
   default: {
     // might be named type
-    Node *T = parseType();
+    Node *T = getDerived().parseType();
     if (T == nullptr)
       return nullptr;
     StringView N = parseNumber();
     if (!N.empty()) {
       if (!consumeIf('E'))
         return nullptr;
       return make<IntegerCastExpr>(T, N);
     }
     if (consumeIf('E'))
       return T;
     return nullptr;
   }
   }
 }
 
 // <braced-expression> ::= <expression>
 //                     ::= di <field source-name> <braced-expression>    # .name = expr
 //                     ::= dx <index expression> <braced-expression>     # [expr] = expr
 //                     ::= dX <range begin expression> <range end expression> <braced-expression>
-template<typename Alloc> Node *Db<Alloc>::parseBracedExpr() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseBracedExpr() {
   if (look() == 'd') {
     switch (look(1)) {
     case 'i': {
       First += 2;
-      Node *Field = parseSourceName(/*NameState=*/nullptr);
+      Node *Field = getDerived().parseSourceName(/*NameState=*/nullptr);
       if (Field == nullptr)
         return nullptr;
-      Node *Init = parseBracedExpr();
+      Node *Init = getDerived().parseBracedExpr();
       if (Init == nullptr)
         return nullptr;
       return make<BracedExpr>(Field, Init, /*isArray=*/false);
     }
     case 'x': {
       First += 2;
-      Node *Index = parseExpr();
+      Node *Index = getDerived().parseExpr();
       if (Index == nullptr)
         return nullptr;
-      Node *Init = parseBracedExpr();
+      Node *Init = getDerived().parseBracedExpr();
       if (Init == nullptr)
         return nullptr;
       return make<BracedExpr>(Index, Init, /*isArray=*/true);
     }
     case 'X': {
       First += 2;
-      Node *RangeBegin = parseExpr();
+      Node *RangeBegin = getDerived().parseExpr();
       if (RangeBegin == nullptr)
         return nullptr;
-      Node *RangeEnd = parseExpr();
+      Node *RangeEnd = getDerived().parseExpr();
       if (RangeEnd == nullptr)
         return nullptr;
-      Node *Init = parseBracedExpr();
+      Node *Init = getDerived().parseBracedExpr();
       if (Init == nullptr)
         return nullptr;
       return make<BracedRangeExpr>(RangeBegin, RangeEnd, Init);
     }
     }
   }
-  return parseExpr();
+  return getDerived().parseExpr();
 }
 
 // (not yet in the spec)
 // <fold-expr> ::= fL <binary-operator-name> <expression> <expression>
 //             ::= fR <binary-operator-name> <expression> <expression>
 //             ::= fl <binary-operator-name> <expression>
 //             ::= fr <binary-operator-name> <expression>
-template<typename Alloc> Node *Db<Alloc>::parseFoldExpr() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseFoldExpr() {
   if (!consumeIf('f'))
     return nullptr;
 
   char FoldKind = look();
   bool IsLeftFold, HasInitializer;
   HasInitializer = FoldKind == 'L' || FoldKind == 'R';
   if (FoldKind == 'l' || FoldKind == 'L')
     IsLeftFold = true;
Node *AbstractManglingParser<Derived, Alloc>::parseFoldExpr() {
   else if (consumeIf("pl")) OperatorName = "+";
   else if (consumeIf("pL")) OperatorName = "+=";
   else if (consumeIf("rm")) OperatorName = "%";
   else if (consumeIf("rM")) OperatorName = "%=";
   else if (consumeIf("rs")) OperatorName = ">>";
   else if (consumeIf("rS")) OperatorName = ">>=";
   else return nullptr;
 
-  Node *Pack = parseExpr(), *Init = nullptr;
+  Node *Pack = getDerived().parseExpr(), *Init = nullptr;
   if (Pack == nullptr)
     return nullptr;
   if (HasInitializer) {
-    Init = parseExpr();
+    Init = getDerived().parseExpr();
     if (Init == nullptr)
       return nullptr;
   }
 
   if (IsLeftFold && Init)
     std::swap(Pack, Init);
 
   return make<FoldExpr>(IsLeftFold, OperatorName, Pack, Init);

 //              ::= <unresolved-name>                                    # f(p), N::f(p), ::f(p),
 //                                                                       # freestanding dependent name (e.g., T::x),
 //                                                                       # objectless nonstatic member reference
 //              ::= fL <binary-operator-name> <expression> <expression>
 //              ::= fR <binary-operator-name> <expression> <expression>
 //              ::= fl <binary-operator-name> <expression>
 //              ::= fr <binary-operator-name> <expression>
 //              ::= <expr-primary>
-template<typename Alloc> Node *Db<Alloc>::parseExpr() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseExpr() {
   bool Global = consumeIf("gs");
   if (numLeft() < 2)
     return nullptr;
 
   switch (*First) {
   case 'L':
-    return parseExprPrimary();
+    return getDerived().parseExprPrimary();
   case 'T':
-    return parseTemplateParam();
+    return getDerived().parseTemplateParam();
   case 'f': {
     // Disambiguate a fold expression from a <function-param>.
     if (look(1) == 'p' || (look(1) == 'L' && std::isdigit(look(2))))
-      return parseFunctionParam();
-    return parseFoldExpr();
+      return getDerived().parseFunctionParam();
+    return getDerived().parseFoldExpr();
   }
   case 'a':
     switch (First[1]) {
     case 'a':
       First += 2;
-      return parseBinaryExpr("&&");
+      return getDerived().parseBinaryExpr("&&");
     case 'd':
       First += 2;
-      return parsePrefixExpr("&");
+      return getDerived().parsePrefixExpr("&");
     case 'n':
       First += 2;
-      return parseBinaryExpr("&");
+      return getDerived().parseBinaryExpr("&");
     case 'N':
       First += 2;
-      return parseBinaryExpr("&=");
+      return getDerived().parseBinaryExpr("&=");
     case 'S':
       First += 2;
-      return parseBinaryExpr("=");
+      return getDerived().parseBinaryExpr("=");
     case 't': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       return make<EnclosingExpr>("alignof (", Ty, ")");
     }
     case 'z': {
       First += 2;
-      Node *Ty = parseExpr();
+      Node *Ty = getDerived().parseExpr();
       if (Ty == nullptr)
         return nullptr;
       return make<EnclosingExpr>("alignof (", Ty, ")");
     }
     }
     return nullptr;
   case 'c':
     switch (First[1]) {
     // cc <type> <expression>                               # const_cast<type>(expression)
     case 'c': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return Ty;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<CastExpr>("const_cast", Ty, Ex);
     }
     // cl <expression>+ E                                   # call
     case 'l': {
       First += 2;
-      Node *Callee = parseExpr();
+      Node *Callee = getDerived().parseExpr();
       if (Callee == nullptr)
         return Callee;
       size_t ExprsBegin = Names.size();
       while (!consumeIf('E')) {
-        Node *E = parseExpr();
+        Node *E = getDerived().parseExpr();
         if (E == nullptr)
           return E;
         Names.push_back(E);
       }
       return make<CallExpr>(Callee, popTrailingNodeArray(ExprsBegin));
     }
     case 'm':
       First += 2;
-      return parseBinaryExpr(",");
+      return getDerived().parseBinaryExpr(",");
     case 'o':
       First += 2;
-      return parsePrefixExpr("~");
+      return getDerived().parsePrefixExpr("~");
     case 'v':
-      return parseConversionExpr();
+      return getDerived().parseConversionExpr();
     }
     return nullptr;
   case 'd':
     switch (First[1]) {
     case 'a': {
       First += 2;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<DeleteExpr>(Ex, Global, /*is_array=*/true);
     }
     case 'c': {
       First += 2;
-      Node *T = parseType();
+      Node *T = getDerived().parseType();
       if (T == nullptr)
         return T;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<CastExpr>("dynamic_cast", T, Ex);
     }
     case 'e':
       First += 2;
-      return parsePrefixExpr("*");
+      return getDerived().parsePrefixExpr("*");
     case 'l': {
       First += 2;
-      Node *E = parseExpr();
+      Node *E = getDerived().parseExpr();
       if (E == nullptr)
         return E;
       return make<DeleteExpr>(E, Global, /*is_array=*/false);
     }
     case 'n':
-      return parseUnresolvedName();
+      return getDerived().parseUnresolvedName();
     case 's': {
       First += 2;
-      Node *LHS = parseExpr();
+      Node *LHS = getDerived().parseExpr();
       if (LHS == nullptr)
         return nullptr;
-      Node *RHS = parseExpr();
+      Node *RHS = getDerived().parseExpr();
       if (RHS == nullptr)
         return nullptr;
       return make<MemberExpr>(LHS, ".*", RHS);
     }
     case 't': {
       First += 2;
-      Node *LHS = parseExpr();
+      Node *LHS = getDerived().parseExpr();
       if (LHS == nullptr)
         return LHS;
-      Node *RHS = parseExpr();
+      Node *RHS = getDerived().parseExpr();
       if (RHS == nullptr)
         return nullptr;
       return make<MemberExpr>(LHS, ".", RHS);
     }
     case 'v':
       First += 2;
-      return parseBinaryExpr("/");
+      return getDerived().parseBinaryExpr("/");
     case 'V':
       First += 2;
-      return parseBinaryExpr("/=");
+      return getDerived().parseBinaryExpr("/=");
     }
     return nullptr;
   case 'e':
     switch (First[1]) {
     case 'o':
       First += 2;
-      return parseBinaryExpr("^");
+      return getDerived().parseBinaryExpr("^");
     case 'O':
       First += 2;
-      return parseBinaryExpr("^=");
+      return getDerived().parseBinaryExpr("^=");
     case 'q':
       First += 2;
-      return parseBinaryExpr("==");
+      return getDerived().parseBinaryExpr("==");
     }
     return nullptr;
   case 'g':
     switch (First[1]) {
     case 'e':
       First += 2;
-      return parseBinaryExpr(">=");
+      return getDerived().parseBinaryExpr(">=");
     case 't':
       First += 2;
-      return parseBinaryExpr(">");
+      return getDerived().parseBinaryExpr(">");
     }
     return nullptr;
   case 'i':
     switch (First[1]) {
     case 'x': {
       First += 2;
-      Node *Base = parseExpr();
+      Node *Base = getDerived().parseExpr();
       if (Base == nullptr)
         return nullptr;
-      Node *Index = parseExpr();
+      Node *Index = getDerived().parseExpr();
       if (Index == nullptr)
         return Index;
       return make<ArraySubscriptExpr>(Base, Index);
     }
     case 'l': {
       First += 2;
       size_t InitsBegin = Names.size();
       while (!consumeIf('E')) {
-        Node *E = parseBracedExpr();
+        Node *E = getDerived().parseBracedExpr();
         if (E == nullptr)
           return nullptr;
         Names.push_back(E);
       }
       return make<InitListExpr>(nullptr, popTrailingNodeArray(InitsBegin));
     }
     }
     return nullptr;
   case 'l':
     switch (First[1]) {
     case 'e':
       First += 2;
-      return parseBinaryExpr("<=");
+      return getDerived().parseBinaryExpr("<=");
     case 's':
       First += 2;
-      return parseBinaryExpr("<<");
+      return getDerived().parseBinaryExpr("<<");
     case 'S':
       First += 2;
-      return parseBinaryExpr("<<=");
+      return getDerived().parseBinaryExpr("<<=");
     case 't':
       First += 2;
-      return parseBinaryExpr("<");
+      return getDerived().parseBinaryExpr("<");
     }
     return nullptr;
   case 'm':
     switch (First[1]) {
     case 'i':
       First += 2;
-      return parseBinaryExpr("-");
+      return getDerived().parseBinaryExpr("-");
     case 'I':
       First += 2;
-      return parseBinaryExpr("-=");
+      return getDerived().parseBinaryExpr("-=");
     case 'l':
       First += 2;
-      return parseBinaryExpr("*");
+      return getDerived().parseBinaryExpr("*");
     case 'L':
       First += 2;
-      return parseBinaryExpr("*=");
+      return getDerived().parseBinaryExpr("*=");
     case 'm':
       First += 2;
       if (consumeIf('_'))
-        return parsePrefixExpr("--");
-      Node *Ex = parseExpr();
+        return getDerived().parsePrefixExpr("--");
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return nullptr;
       return make<PostfixExpr>(Ex, "--");
     }
     return nullptr;
   case 'n':
     switch (First[1]) {
     case 'a':
     case 'w':
-      return parseNewExpr();
+      return getDerived().parseNewExpr();
     case 'e':
       First += 2;
-      return parseBinaryExpr("!=");
+      return getDerived().parseBinaryExpr("!=");
     case 'g':
       First += 2;
-      return parsePrefixExpr("-");
+      return getDerived().parsePrefixExpr("-");
     case 't':
       First += 2;
-      return parsePrefixExpr("!");
+      return getDerived().parsePrefixExpr("!");
     case 'x':
       First += 2;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<EnclosingExpr>("noexcept (", Ex, ")");
     }
     return nullptr;
   case 'o':
     switch (First[1]) {
     case 'n':
-      return parseUnresolvedName();
+      return getDerived().parseUnresolvedName();
     case 'o':
       First += 2;
-      return parseBinaryExpr("||");
+      return getDerived().parseBinaryExpr("||");
     case 'r':
       First += 2;
-      return parseBinaryExpr("|");
+      return getDerived().parseBinaryExpr("|");
     case 'R':
       First += 2;
-      return parseBinaryExpr("|=");
+      return getDerived().parseBinaryExpr("|=");
     }
     return nullptr;
   case 'p':
     switch (First[1]) {
     case 'm':
       First += 2;
-      return parseBinaryExpr("->*");
+      return getDerived().parseBinaryExpr("->*");
     case 'l':
       First += 2;
-      return parseBinaryExpr("+");
+      return getDerived().parseBinaryExpr("+");
     case 'L':
       First += 2;
-      return parseBinaryExpr("+=");
+      return getDerived().parseBinaryExpr("+=");
     case 'p': {
       First += 2;
       if (consumeIf('_'))
-        return parsePrefixExpr("++");
-      Node *Ex = parseExpr();
+        return getDerived().parsePrefixExpr("++");
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<PostfixExpr>(Ex, "++");
     }
     case 's':
       First += 2;
-      return parsePrefixExpr("+");
+      return getDerived().parsePrefixExpr("+");
     case 't': {
       First += 2;
-      Node *L = parseExpr();
+      Node *L = getDerived().parseExpr();
       if (L == nullptr)
         return nullptr;
-      Node *R = parseExpr();
+      Node *R = getDerived().parseExpr();
       if (R == nullptr)
         return nullptr;
       return make<MemberExpr>(L, "->", R);
     }
     }
     return nullptr;
   case 'q':
     if (First[1] == 'u') {
       First += 2;
-      Node *Cond = parseExpr();
+      Node *Cond = getDerived().parseExpr();
       if (Cond == nullptr)
         return nullptr;
-      Node *LHS = parseExpr();
+      Node *LHS = getDerived().parseExpr();
       if (LHS == nullptr)
         return nullptr;
-      Node *RHS = parseExpr();
+      Node *RHS = getDerived().parseExpr();
       if (RHS == nullptr)
         return nullptr;
       return make<ConditionalExpr>(Cond, LHS, RHS);
     }
     return nullptr;
   case 'r':
     switch (First[1]) {
     case 'c': {
       First += 2;
-      Node *T = parseType();
+      Node *T = getDerived().parseType();
       if (T == nullptr)
         return T;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<CastExpr>("reinterpret_cast", T, Ex);
     }
     case 'm':
       First += 2;
-      return parseBinaryExpr("%");
+      return getDerived().parseBinaryExpr("%");
     case 'M':
       First += 2;
-      return parseBinaryExpr("%=");
+      return getDerived().parseBinaryExpr("%=");
     case 's':
       First += 2;
-      return parseBinaryExpr(">>");
+      return getDerived().parseBinaryExpr(">>");
     case 'S':
       First += 2;
-      return parseBinaryExpr(">>=");
+      return getDerived().parseBinaryExpr(">>=");
     }
     return nullptr;
   case 's':
     switch (First[1]) {
     case 'c': {
       First += 2;
-      Node *T = parseType();
+      Node *T = getDerived().parseType();
       if (T == nullptr)
         return T;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<CastExpr>("static_cast", T, Ex);
     }
     case 'p': {
       First += 2;
-      Node *Child = parseExpr();
+      Node *Child = getDerived().parseExpr();
       if (Child == nullptr)
         return nullptr;
       return make<ParameterPackExpansion>(Child);
     }
     case 'r':
-      return parseUnresolvedName();
+      return getDerived().parseUnresolvedName();
     case 't': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return Ty;
       return make<EnclosingExpr>("sizeof (", Ty, ")");
     }
     case 'z': {
       First += 2;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<EnclosingExpr>("sizeof (", Ex, ")");
     }
     case 'Z':
       First += 2;
       if (look() == 'T') {
-        Node *R = parseTemplateParam();
+        Node *R = getDerived().parseTemplateParam();
         if (R == nullptr)
           return nullptr;
         return make<SizeofParamPackExpr>(R);
       } else if (look() == 'f') {
-        Node *FP = parseFunctionParam();
+        Node *FP = getDerived().parseFunctionParam();
         if (FP == nullptr)
           return nullptr;
         return make<EnclosingExpr>("sizeof... (", FP, ")");
       }
       return nullptr;
     case 'P': {
       First += 2;
       size_t ArgsBegin = Names.size();
       while (!consumeIf('E')) {
-        Node *Arg = parseTemplateArg();
+        Node *Arg = getDerived().parseTemplateArg();
         if (Arg == nullptr)
           return nullptr;
         Names.push_back(Arg);
       }
       auto *Pack = make<NodeArrayNode>(popTrailingNodeArray(ArgsBegin));
       if (!Pack)
         return nullptr;
       return make<EnclosingExpr>("sizeof... (", Pack, ")");
     }
     }
     return nullptr;
   case 't':
     switch (First[1]) {
     case 'e': {
       First += 2;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return Ex;
       return make<EnclosingExpr>("typeid (", Ex, ")");
     }
     case 'i': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return Ty;
       return make<EnclosingExpr>("typeid (", Ty, ")");
     }
     case 'l': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       size_t InitsBegin = Names.size();
       while (!consumeIf('E')) {
-        Node *E = parseBracedExpr();
+        Node *E = getDerived().parseBracedExpr();
         if (E == nullptr)
           return nullptr;
         Names.push_back(E);
       }
       return make<InitListExpr>(Ty, popTrailingNodeArray(InitsBegin));
     }
     case 'r':
       First += 2;
       return make<NameType>("throw");
     case 'w': {
       First += 2;
-      Node *Ex = parseExpr();
+      Node *Ex = getDerived().parseExpr();
       if (Ex == nullptr)
         return nullptr;
       return make<ThrowExpr>(Ex);
     }
     }
     return nullptr;
   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':
   case '7':
   case '8':
   case '9':
-    return parseUnresolvedName();
+    return getDerived().parseUnresolvedName();
   }
   return nullptr;
 }
 
 // <call-offset> ::= h <nv-offset> _
 //               ::= v <v-offset> _
 //
 // <nv-offset> ::= <offset number>
 //               # non-virtual base override
 //
 // <v-offset>  ::= <offset number> _ <virtual offset number>
 //               # virtual base override, with vcall offset
-template<typename Alloc> bool Db<Alloc>::parseCallOffset() {
+template <typename Alloc, typename Derived>
+bool AbstractManglingParser<Alloc, Derived>::parseCallOffset() {
   // Just scan through the call offset, we never add this information into the
   // output.
   if (consumeIf('h'))
     return parseNumber(true).empty() || !consumeIf('_');
   if (consumeIf('v'))
     return parseNumber(true).empty() || !consumeIf('_') ||
            parseNumber(true).empty() || !consumeIf('_');
   return true;

 //                ::= GV <object name> # Guard variable for one-time initialization
 //                                     # No <type>
 //                ::= TW <object name> # Thread-local wrapper
 //                ::= TH <object name> # Thread-local initialization
 //                ::= GR <object name> _             # First temporary
 //                ::= GR <object name> <seq-id> _    # Subsequent temporaries
 //      extension ::= TC <first type> <number> _ <second type> # construction vtable for second-in-first
 //      extension ::= GR <object name> # reference temporary for object
-template<typename Alloc> Node *Db<Alloc>::parseSpecialName() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseSpecialName() {
   switch (look()) {
   case 'T':
     switch (look(1)) {
     // TV <type>    # virtual table
     case 'V': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       return make<SpecialName>("vtable for ", Ty);
     }
     // TT <type>    # VTT structure (construction vtable index)
     case 'T': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       return make<SpecialName>("VTT for ", Ty);
     }
     // TI <type>    # typeinfo structure
     case 'I': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       return make<SpecialName>("typeinfo for ", Ty);
     }
     // TS <type>    # typeinfo name (null-terminated byte string)
     case 'S': {
       First += 2;
-      Node *Ty = parseType();
+      Node *Ty = getDerived().parseType();
       if (Ty == nullptr)
         return nullptr;
       return make<SpecialName>("typeinfo name for ", Ty);
     }
     // Tc <call-offset> <call-offset> <base encoding>
     case 'c': {
       First += 2;
       if (parseCallOffset() || parseCallOffset())
         return nullptr;
-      Node *Encoding = parseEncoding();
+      Node *Encoding = getDerived().parseEncoding();
       if (Encoding == nullptr)
         return nullptr;
       return make<SpecialName>("covariant return thunk to ", Encoding);
     }
     // extension ::= TC <first type> <number> _ <second type>
     //               # construction vtable for second-in-first
     case 'C': {
       First += 2;
-      Node *FirstType = parseType();
+      Node *FirstType = getDerived().parseType();
       if (FirstType == nullptr)
         return nullptr;
       if (parseNumber(true).empty() || !consumeIf('_'))
         return nullptr;
-      Node *SecondType = parseType();
+      Node *SecondType = getDerived().parseType();
       if (SecondType == nullptr)
         return nullptr;
       return make<CtorVtableSpecialName>(SecondType, FirstType);
     }
     // TW <object name> # Thread-local wrapper
     case 'W': {
       First += 2;
-      Node *Name = parseName();
+      Node *Name = getDerived().parseName();
       if (Name == nullptr)
         return nullptr;
       return make<SpecialName>("thread-local wrapper routine for ", Name);
     }
     // TH <object name> # Thread-local initialization
     case 'H': {
       First += 2;
-      Node *Name = parseName();
+      Node *Name = getDerived().parseName();
       if (Name == nullptr)
         return nullptr;
       return make<SpecialName>("thread-local initialization routine for ", Name);
     }
     // T <call-offset> <base encoding>
     default: {
       ++First;
       bool IsVirt = look() == 'v';
       if (parseCallOffset())
         return nullptr;
-      Node *BaseEncoding = parseEncoding();
+      Node *BaseEncoding = getDerived().parseEncoding();
       if (BaseEncoding == nullptr)
         return nullptr;
       if (IsVirt)
         return make<SpecialName>("virtual thunk to ", BaseEncoding);
       else
         return make<SpecialName>("non-virtual thunk to ", BaseEncoding);
     }
     }
   case 'G':
     switch (look(1)) {
     // GV <object name> # Guard variable for one-time initialization
     case 'V': {
       First += 2;
-      Node *Name = parseName();
+      Node *Name = getDerived().parseName();
       if (Name == nullptr)
         return nullptr;
       return make<SpecialName>("guard variable for ", Name);
     }
     // GR <object name> # reference temporary for object
     // GR <object name> _             # First temporary
     // GR <object name> <seq-id> _    # Subsequent temporaries
     case 'R': {
       First += 2;
-      Node *Name = parseName();
+      Node *Name = getDerived().parseName();
       if (Name == nullptr)
         return nullptr;
       size_t Count;
       bool ParsedSeqId = !parseSeqId(&Count);
       if (!consumeIf('_') && ParsedSeqId)
         return nullptr;
       return make<SpecialName>("reference temporary for ", Name);
     }
     }
   }
   return nullptr;
 }
 
 // <encoding> ::= <function name> <bare-function-type>
 //            ::= <data name>
 //            ::= <special-name>
-template<typename Alloc> Node *Db<Alloc>::parseEncoding() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseEncoding() {
   if (look() == 'G' || look() == 'T')
-    return parseSpecialName();
+    return getDerived().parseSpecialName();
 
   auto IsEndOfEncoding = [&] {
     // The set of chars that can potentially follow an <encoding> (none of which
     // can start a <type>). Enumerating these allows us to avoid speculative
     // parsing.
     return numLeft() == 0 || look() == 'E' || look() == '.' || look() == '_';
   };
 
   NameState NameInfo(this);
-  Node *Name = parseName(&NameInfo);
+  Node *Name = getDerived().parseName(&NameInfo);
   if (Name == nullptr)
     return nullptr;
 
   if (resolveForwardTemplateRefs(NameInfo))
     return nullptr;
 
   if (IsEndOfEncoding())
     return Name;
 
   Node *Attrs = nullptr;
   if (consumeIf("Ua9enable_ifI")) {
     size_t BeforeArgs = Names.size();
     while (!consumeIf('E')) {
-      Node *Arg = parseTemplateArg();
+      Node *Arg = getDerived().parseTemplateArg();
       if (Arg == nullptr)
         return nullptr;
       Names.push_back(Arg);
     }
     Attrs = make<EnableIfAttr>(popTrailingNodeArray(BeforeArgs));
     if (!Attrs)
       return nullptr;
   }
 
   Node *ReturnType = nullptr;
   if (!NameInfo.CtorDtorConversion && NameInfo.EndsWithTemplateArgs) {
-    ReturnType = parseType();
+    ReturnType = getDerived().parseType();
     if (ReturnType == nullptr)
       return nullptr;
   }
 
   if (consumeIf('v'))
     return make<FunctionEncoding>(ReturnType, Name, NodeArray(),
                                   Attrs, NameInfo.CVQualifiers,
                                   NameInfo.ReferenceQualifier);
 
   size_t ParamsBegin = Names.size();
   do {
-    Node *Ty = parseType();
+    Node *Ty = getDerived().parseType();
     if (Ty == nullptr)
       return nullptr;
     Names.push_back(Ty);
   } while (!IsEndOfEncoding());
 
   return make<FunctionEncoding>(ReturnType, Name,
                                 popTrailingNodeArray(ParamsBegin),
                                 Attrs, NameInfo.CVQualifiers,
#elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;
 #else
     static const size_t mangled_size = 20;  // May need to be adjusted to 16 or 24 on other platforms
 #endif
     static const size_t max_demangled_size = 40;
     static constexpr const char *spec = "%LaL";
 };
 
-template<typename Alloc>
-template<class Float>
-Node *Db<Alloc>::parseFloatingLiteral() {
+template <typename Alloc, typename Derived>
+template <class Float>
+Node *AbstractManglingParser<Alloc, Derived>::parseFloatingLiteral() {
   const size_t N = FloatData<Float>::mangled_size;
   if (numLeft() <= N)
     return nullptr;
   StringView Data(First, First + N);
   for (char C : Data)
     if (!std::isxdigit(C))
       return nullptr;
   First += N;
   if (!consumeIf('E'))
     return nullptr;
   return make<FloatLiteralImpl<Float>>(Data);
 }
 
 // <seq-id> ::= <0-9A-Z>+
-template<typename Alloc> bool Db<Alloc>::parseSeqId(size_t *Out) {
+template <typename Alloc, typename Derived>
+bool AbstractManglingParser<Alloc, Derived>::parseSeqId(size_t *Out) {
   if (!(look() >= '0' && look() <= '9') &&
       !(look() >= 'A' && look() <= 'Z'))
     return true;
 
   size_t Id = 0;
   while (true) {
     if (look() >= '0' && look() <= '9') {
       Id *= 36;

 // <substitution> ::= Sa # ::std::allocator
 // <substitution> ::= Sb # ::std::basic_string
 // <substitution> ::= Ss # ::std::basic_string < char,
 //                                               ::std::char_traits<char>,
 //                                               ::std::allocator<char> >
 // <substitution> ::= Si # ::std::basic_istream<char,  std::char_traits<char> >
 // <substitution> ::= So # ::std::basic_ostream<char,  std::char_traits<char> >
 // <substitution> ::= Sd # ::std::basic_iostream<char, std::char_traits<char> >
-template<typename Alloc> Node *Db<Alloc>::parseSubstitution() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseSubstitution() {
   if (!consumeIf('S'))
     return nullptr;
 
   if (std::islower(look())) {
     Node *SpecialSub;
     switch (look()) {
     case 'a':
       ++First;
if (std::islower(look())) {
     default:
       return nullptr;
     }
     if (!SpecialSub)
       return nullptr;
     // Itanium C++ ABI 5.1.2: If a name that would use a built-in <substitution>
     // has ABI tags, the tags are appended to the substitution; the result is a
     // substitutable component.
-    Node *WithTags = parseAbiTags(SpecialSub);
+    Node *WithTags = getDerived().parseAbiTags(SpecialSub);
     if (WithTags != SpecialSub) {
       Subs.push_back(WithTags);
       SpecialSub = WithTags;
     }
     return SpecialSub;
   }
 
   //                ::= S_
Node *AbstractManglingParser<Derived, Alloc>::parseSubstitution() {
   ++Index;
   if (!consumeIf('_') || Index >= Subs.size())
     return nullptr;
   return Subs[Index];
 }
 
 // <template-param> ::= T_    # first template parameter
 //                  ::= T <parameter-2 non-negative number> _
-template<typename Alloc> Node *Db<Alloc>::parseTemplateParam() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParam() {
   if (!consumeIf('T'))
     return nullptr;
 
   size_t Index = 0;
   if (!consumeIf('_')) {
     if (parsePositiveInteger(&Index))
       return nullptr;
     ++Index;
Node *AbstractManglingParser<Derived, Alloc>::parseTemplateParam() {
   return TemplateParams[Index];
 }
 
 // <template-arg> ::= <type>                    # type or template
 //                ::= X <expression> E          # expression
 //                ::= <expr-primary>            # simple expressions
 //                ::= J <template-arg>* E       # argument pack
 //                ::= LZ <encoding> E           # extension
-template<typename Alloc> Node *Db<Alloc>::parseTemplateArg() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parseTemplateArg() {
   switch (look()) {
   case 'X': {
     ++First;
-    Node *Arg = parseExpr();
+    Node *Arg = getDerived().parseExpr();
     if (Arg == nullptr || !consumeIf('E'))
       return nullptr;
     return Arg;
   }
   case 'J': {
     ++First;
     size_t ArgsBegin = Names.size();
     while (!consumeIf('E')) {
-      Node *Arg = parseTemplateArg();
+      Node *Arg = getDerived().parseTemplateArg();
       if (Arg == nullptr)
         return nullptr;
       Names.push_back(Arg);
     }
     NodeArray Args = popTrailingNodeArray(ArgsBegin);
     return make<TemplateArgumentPack>(Args);
   }
   case 'L': {
     //                ::= LZ <encoding> E           # extension
     if (look(1) == 'Z') {
       First += 2;
-      Node *Arg = parseEncoding();
+      Node *Arg = getDerived().parseEncoding();
       if (Arg == nullptr || !consumeIf('E'))
         return nullptr;
       return Arg;
     }
     //                ::= <expr-primary>            # simple expressions
-    return parseExprPrimary();
+    return getDerived().parseExprPrimary();
   }
   default:
-    return parseType();
+    return getDerived().parseType();
   }
 }
 
 // <template-args> ::= I <template-arg>* E
 //     extension, the abi says <template-arg>+
-template <typename Alloc>
-Node *Db<Alloc>::parseTemplateArgs(bool TagTemplates) {
+template <typename Derived, typename Alloc>
+Node *
+AbstractManglingParser<Derived, Alloc>::parseTemplateArgs(bool TagTemplates) {
   if (!consumeIf('I'))
     return nullptr;
 
   // <template-params> refer to the innermost <template-args>. Clear out any
   // outer args that we may have inserted into TemplateParams.
   if (TagTemplates)
     TemplateParams.clear();
 
   size_t ArgsBegin = Names.size();
   while (!consumeIf('E')) {
     if (TagTemplates) {
       auto OldParams = std::move(TemplateParams);
-      Node *Arg = parseTemplateArg();
+      Node *Arg = getDerived().parseTemplateArg();
       TemplateParams = std::move(OldParams);
       if (Arg == nullptr)
         return nullptr;
       Names.push_back(Arg);
       Node *TableEntry = Arg;
       if (Arg->getKind() == Node::KTemplateArgumentPack) {
         TableEntry = make<ParameterPack>(
             static_cast<TemplateArgumentPack*>(TableEntry)->getElements());
         if (!TableEntry)
           return nullptr;
       }
       TemplateParams.push_back(TableEntry);
     } else {
-      Node *Arg = parseTemplateArg();
+      Node *Arg = getDerived().parseTemplateArg();
       if (Arg == nullptr)
         return nullptr;
       Names.push_back(Arg);
     }
   }
   return make<TemplateArgs>(popTrailingNodeArray(ArgsBegin));
 }
 
 // <mangled-name> ::= _Z <encoding>
 //                ::= <type>
 // extension      ::= ___Z <encoding> _block_invoke
 // extension      ::= ___Z <encoding> _block_invoke<decimal-digit>+
 // extension      ::= ___Z <encoding> _block_invoke_<decimal-digit>+
-template<typename Alloc> Node *Db<Alloc>::parse() {
+template <typename Derived, typename Alloc>
+Node *AbstractManglingParser<Derived, Alloc>::parse() {
   if (consumeIf("_Z")) {
-    Node *Encoding = parseEncoding();
+    Node *Encoding = getDerived().parseEncoding();
     if (Encoding == nullptr)
       return nullptr;
     if (look() == '.') {
       Encoding = make<DotSuffix>(Encoding, StringView(First, Last));
       First = Last;
     }
     if (numLeft() != 0)
       return nullptr;
     return Encoding;
   }
 
   if (consumeIf("___Z")) {
-    Node *Encoding = parseEncoding();
+    Node *Encoding = getDerived().parseEncoding();
     if (Encoding == nullptr || !consumeIf("_block_invoke"))
       return nullptr;
     bool RequireNumber = consumeIf('_');
     if (parseNumber().empty() && RequireNumber)
       return nullptr;
     if (look() == '.')
       First = Last;
     if (numLeft() != 0)
       return nullptr;
     return make<SpecialName>("invocation function for block in ", Encoding);
   }
 
-  Node *Ty = parseType();
+  Node *Ty = getDerived().parseType();
   if (numLeft() != 0)
     return nullptr;
   return Ty;
 }
 
+template <typename Alloc>
+struct ManglingParser : AbstractManglingParser<ManglingParser<Alloc>, Alloc> {
+  using AbstractManglingParser<ManglingParser<Alloc>,
+                               Alloc>::AbstractManglingParser;
+};
+
 }  // namespace itanium_demangle
 }  // namespace
 
 #endif // LIBCXX_DEMANGLE_ITANIUMDEMANGLE_H